1.
Anechoic chamber
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An anechoic chamber is a room designed to completely absorb reflections of either sound or electromagnetic waves. They are also isolated from waves entering from their surroundings. This combination means that a person or detector exclusively hears direct sounds, Anechoic chambers, a term coined by American acoustics expert Leo Beranek, were initially exclusively used to refer to acoustic anechoic chambers. Recently, the term has been extended to RF anechoic chambers, Anechoic chambers range from small compartments the size of household microwave ovens to ones as large as aircraft hangars. The size of the chamber depends on the size of the objects, Anechoic chambers are commonly used in acoustics to conduct experiments in nominally free field conditions, free-field meaning that there are no reflected signals. All sound energy will be traveling away from the source with almost none reflected back, common anechoic chamber experiments include measuring the transfer function of a loudspeaker or the directivity of noise radiation from industrial machinery. In general, the interior of a chamber is very quiet. In 2005, the best anechoic chamber measured at −9.4 dBA, in 2015, an anechoic chamber on the campus of Microsoft broke the world record with a measurement of −20.6 dBA. The human ear can detect sounds above 0 dBA, so a human in such a chamber would perceive the surroundings as devoid of sound. Anecdotally, some humans may not like such quietness and can become disoriented and this wall is composed of a series of wedges W with height H. After the impingement, the incident wave I is reflected as a series of waves R which in turn bounce up-and-down in the gap of air A between the wedges W, such bouncing may produce a standing wave pattern in A. During this process, the energy of the waves R gets dissipated via the airs molecular viscosity. In addition, with the use of materials to fabricate the wedges. As a result, the component of the reflected waves R along the direction of I that escapes the gaps A, even though this explanation is two-dimensional, it is representative and applicable to the actual three-dimensional wedge structures used in anechoic chambers. Full anechoic chambers aim to absorb energy in all directions and this floor is damped and floating on absorbent buffers to isolate it from outside vibration or electromagnetic signals. Uses for RF anechoic chambers include testing antennae, radars, and is used to house the equipment for performing measurements of antenna radiation patterns. Performance expectations constitute primary challenges in designing stand alone or embedded antennae, designs are becoming ever more complex with a single device incorporating multiple technologies such as cellular, WiFi, Bluetooth, LTE, MIMO, RFID and GPS. RAM is designed and shaped to absorb incident RF radiation as effectively as possible, the more effective the RAM, the lower the resulting level of reflected RF radiation
2.
Physics
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Physics is the natural science that involves the study of matter and its motion and behavior through space and time, along with related concepts such as energy and force. One of the most fundamental disciplines, the main goal of physics is to understand how the universe behaves. Physics is one of the oldest academic disciplines, perhaps the oldest through its inclusion of astronomy, Physics intersects with many interdisciplinary areas of research, such as biophysics and quantum chemistry, and the boundaries of physics are not rigidly defined. New ideas in physics often explain the mechanisms of other sciences while opening new avenues of research in areas such as mathematics. Physics also makes significant contributions through advances in new technologies that arise from theoretical breakthroughs, the United Nations named 2005 the World Year of Physics. Astronomy is the oldest of the natural sciences, the stars and planets were often a target of worship, believed to represent their gods. While the explanations for these phenomena were often unscientific and lacking in evidence, according to Asger Aaboe, the origins of Western astronomy can be found in Mesopotamia, and all Western efforts in the exact sciences are descended from late Babylonian astronomy. The most notable innovations were in the field of optics and vision, which came from the works of many scientists like Ibn Sahl, Al-Kindi, Ibn al-Haytham, Al-Farisi and Avicenna. The most notable work was The Book of Optics, written by Ibn Al-Haitham, in which he was not only the first to disprove the ancient Greek idea about vision, but also came up with a new theory. In the book, he was also the first to study the phenomenon of the pinhole camera, many later European scholars and fellow polymaths, from Robert Grosseteste and Leonardo da Vinci to René Descartes, Johannes Kepler and Isaac Newton, were in his debt. Indeed, the influence of Ibn al-Haythams Optics ranks alongside that of Newtons work of the same title, the translation of The Book of Optics had a huge impact on Europe. From it, later European scholars were able to build the devices as what Ibn al-Haytham did. From this, such important things as eyeglasses, magnifying glasses, telescopes, Physics became a separate science when early modern Europeans used experimental and quantitative methods to discover what are now considered to be the laws of physics. Newton also developed calculus, the study of change, which provided new mathematical methods for solving physical problems. The discovery of new laws in thermodynamics, chemistry, and electromagnetics resulted from greater research efforts during the Industrial Revolution as energy needs increased, however, inaccuracies in classical mechanics for very small objects and very high velocities led to the development of modern physics in the 20th century. Modern physics began in the early 20th century with the work of Max Planck in quantum theory, both of these theories came about due to inaccuracies in classical mechanics in certain situations. Quantum mechanics would come to be pioneered by Werner Heisenberg, Erwin Schrödinger, from this early work, and work in related fields, the Standard Model of particle physics was derived. Areas of mathematics in general are important to this field, such as the study of probabilities, in many ways, physics stems from ancient Greek philosophy
3.
Mechanical wave
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A mechanical wave is a wave that is an oscillation of matter, and therefore transfers energy through a medium. While waves can move long distances, the movement of the medium of transmission—the material—is limited. Therefore, oscillating material does not move far from its equilibrium position. This energy propagates in the direction as the wave. Any kind of wave has a certain energy, mechanical waves can be produced only in media which possess elasticity and inertia. A mechanical wave requires an energy input. Once this initial energy is added, the travels through the medium until all its energy is transferred. In contrast, electromagnetic waves require no medium, but can travel through one. One important property of waves is that their amplitudes are measured in an unusual way. When this gets comparable to unity, significant nonlinear effects such as harmonic generation may occur, for example, waves on the surface of a body of water break when this dimensionless amplitude exceeds 1, resulting in a foam on the surface and turbulent mixing. Some of the most common examples of mechanical waves are waves, sound waves. There are three types of waves, transverse waves, longitudinal waves, and surface waves. Transverse waves cause the medium to vibrate at an angle to the direction of the wave or energy being carried by the medium. Transverse waves have two parts—the crest and the trough, the crest is the highest point of the wave and the trough is the lowest. The distance between a crest and a trough is half of wavelength, the wavelength is the distance from crest to crest or from trough to trough. To see an example, move an end of a Slinky to the left-and-right of the Slinky, light also has properties of a transverse wave, although it is an electromagnetic wave. Longitudinal waves cause the medium to vibrate parallel to the direction of the wave and it consists of multiple compressions and rarefactions. The rarefaction is the farthest distance apart in the longitudinal wave, the speed of the longitudinal wave is increased in higher index of refraction, due to the closer proximity of the atoms in the medium that is being compressed
4.
Vibration
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Vibration is a mechanical phenomenon whereby oscillations occur about an equilibrium point. The word comes from Latin vibrationem, the oscillations may be periodic, such as the motion of a pendulum—or random, such as the movement of a tire on a gravel road. Vibration can be desirable, for example, the motion of a fork, the reed in a woodwind instrument or harmonica. In many cases, however, vibration is undesirable, wasting energy, for example, the vibrational motions of engines, electric motors, or any mechanical device in operation are typically unwanted. Such vibrations could be caused by imbalances in the parts, uneven friction. Careful designs usually minimize unwanted vibrations, the studies of sound and vibration are closely related. Sound, or pressure waves, are generated by vibrating structures, hence, attempts to reduce noise are often related to issues of vibration. Free vibration occurs when a system is set in motion with an initial input. Examples of this type of vibration are pulling a child back on a swing and letting go, or hitting a tuning fork, the mechanical system vibrates at one or more of its natural frequencies and damps down to motionlessness. Forced vibration is when a disturbance is applied to a mechanical system. The disturbance can be a periodic and steady-state input, a transient input, the periodic input can be a harmonic or a non-harmonic disturbance. Damped vibration, When the energy of a system is gradually dissipated by friction and other resistances. The vibrations gradually reduce or change in frequency or intensity or cease, Vibration testing is accomplished by introducing a forcing function into a structure, usually with some type of shaker. Alternately, a DUT is attached to the table of a shaker, Vibration testing is performed to examine the response of a device under test to a defined vibration environment. The measured response may be life, resonant frequencies or squeak. Squeak and rattle testing is performed with a type of quiet shaker that produces very low sound levels while under operation. For relatively low frequency forcing, servohydraulic shakers are used, for higher frequencies, electrodynamic shakers are used. Generally, one or more input or control points located on the DUT-side of a fixture is kept at a specified acceleration, other response points experience maximum vibration level or minimum vibration level
5.
Sound
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In physics, sound is a vibration that propagates as a typically audible mechanical wave of pressure and displacement, through a transmission medium such as air or water. In physiology and psychology, sound is the reception of such waves, humans can hear sound waves with frequencies between about 20 Hz and 20 kHz. Sound above 20 kHz is ultrasound and below 20 Hz is infrasound, other animals have different hearing ranges. Acoustics is the science that deals with the study of mechanical waves in gases, liquids, and solids including vibration, sound, ultrasound. A scientist who works in the field of acoustics is an acoustician, an audio engineer, on the other hand, is concerned with the recording, manipulation, mixing, and reproduction of sound. Auditory sensation evoked by the oscillation described in, sound can propagate through a medium such as air, water and solids as longitudinal waves and also as a transverse wave in solids. The sound waves are generated by a source, such as the vibrating diaphragm of a stereo speaker. The sound source creates vibrations in the surrounding medium, as the source continues to vibrate the medium, the vibrations propagate away from the source at the speed of sound, thus forming the sound wave. At a fixed distance from the source, the pressure, velocity, at an instant in time, the pressure, velocity, and displacement vary in space. Note that the particles of the medium do not travel with the sound wave and this is intuitively obvious for a solid, and the same is true for liquids and gases. During propagation, waves can be reflected, refracted, or attenuated by the medium, the behavior of sound propagation is generally affected by three things, A complex relationship between the density and pressure of the medium. This relationship, affected by temperature, determines the speed of sound within the medium, if the medium is moving, this movement may increase or decrease the absolute speed of the sound wave depending on the direction of the movement. For example, sound moving through wind will have its speed of propagation increased by the speed of the if the sound and wind are moving in the same direction. If the sound and wind are moving in opposite directions, the speed of the wave will be decreased by the speed of the wind. Medium viscosity determines the rate at which sound is attenuated, for many media, such as air or water, attenuation due to viscosity is negligible. When sound is moving through a medium that does not have constant physical properties, the mechanical vibrations that can be interpreted as sound can travel through all forms of matter, gases, liquids, solids, and plasmas. The matter that supports the sound is called the medium, sound cannot travel through a vacuum. Sound is transmitted through gases, plasma, and liquids as longitudinal waves and it requires a medium to propagate
6.
Ultrasound
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Ultrasound is sound waves with frequencies higher than the upper audible limit of human hearing. Ultrasound is no different from normal sound in its physical properties and this limit varies from person to person and is approximately 20 kilohertz in healthy, young adults. Ultrasound devices operate with frequencies from 20 kHz up to several gigahertz, Ultrasound is used in many different fields. Ultrasonic devices are used to detect objects and measure distances, Ultrasound imaging or sonography is often used in medicine. In the nondestructive testing of products and structures, ultrasound is used to detect invisible flaws, industrially, ultrasound is used for cleaning, mixing, and to accelerate chemical processes. Animals such as bats and porpoises use ultrasound for locating prey, scientist are also studying ultrasound using graphene diaphragms as a method of communication. Acoustics, the science of sound, starts as far back as Pythagoras in the 6th century BC, echolocation in bats was discovered by Lazzaro Spallanzani in 1794, when he demonstrated that bats hunted and navigated by inaudible sound and not vision. The first technological application of ultrasound was an attempt to detect submarines by Paul Langevin in 1917, the piezoelectric effect, discovered by Jacques and Pierre Curie in 1880, was useful in transducers to generate and detect ultrasonic waves in air and water. Ultrasound is defined by the American National Standards Institute as sound at frequencies greater than 20 kHz, in air at atmospheric pressure ultrasonic waves have wavelengths of 1.9 cm or less. The upper frequency limit in humans is due to limitations of the middle ear, auditory sensation can occur if high‐intensity ultrasound is fed directly into the human skull and reaches the cochlea through bone conduction, without passing through the middle ear. Children can hear some high-pitched sounds that older adults cannot hear, the Mosquito is an electronic device that uses a high pitched frequency to deter loitering by young people. Bats use a variety of ultrasonic ranging techniques to detect their prey and they can detect frequencies beyond 100 kHz, possibly up to 200 kHz. Many insects have good hearing and most of these are nocturnal insects listening for echolocating bats. This includes many groups of moths, beetles, praying mantids, upon hearing a bat, some insects will make evasive manoeuvres to escape being caught. Ultrasonic frequencies trigger an action in the noctuid moth that cause it to drop slightly in its flight to evade attack. Tiger moths also emit clicks which may disturb bats echolocation, dogs and cats hearing range extends into the ultrasound, the top end of a dogs hearing range is about 45 kHz, while a cats is 64 kHz. The wild ancestors of cats and dogs evolved this higher hearing range to hear sounds made by their preferred prey. A dog whistle is a whistle that emits ultrasound, used for training and calling dogs, porpoises have the highest known upper hearing limit, at around 160 kHz
7.
Infrasound
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Infrasound, sometimes referred to as low-frequency sound, is sound that is lower in frequency than 20 Hz or cycles per second, the normal limit of human hearing. Hearing becomes gradually less sensitive as frequency decreases, so for humans to perceive infrasound, the ear is the primary organ for sensing infrasound, but at higher intensities it is possible to feel infrasound vibrations in various parts of the body. The study of sound waves is sometimes referred to as infrasonics, covering sounds beneath 20 Hz down to 0. 1Hz. Infrasound is characterized by an ability to cover long distances and get around obstacles with little dissipation, subwoofers designed to produce infrasound are capable of sound reproduction an octave or more below that of most commercially available subwoofers, and are often about 10 times the size. Infrasound was used by the Allies of World War I to locate artillery, one of the pioneers in infrasonic research was French scientist Vladimir Gavreau. He concluded it was caused by a large fan and duct system. One of his experiments was a whistle, an oversized organ pipe. Infrasound is defined by the American National Standards Institute as sound at less than 20 Hz. Nonlinear ocean wave interactions in ocean storms produce pervasive infrasound vibrations around 0.2 Hz, in particular, the Sumatran Rhinoceros has been shown to produce sounds with frequencies as low as 3 Hz which have similarities with the song of the humpback whale. The roar of the tiger contains infrasound of 18 Hz and lower, and it has also been suggested that migrating birds use naturally generated infrasound, from sources such as turbulent airflow over mountain ranges, as a navigational aid. Infrasound also may be used for communication, especially well documented in baleen whales. The frequency of baleen whale sounds can range from 10 Hz to 31 kHz, elephants also produce infrasound waves that travel through solid ground and are sensed by other herds using their feet, although they may be separated by hundreds of kilometres. These calls may be used to coordinate the movement of herds, human singers, some vocalists, including Tim Storms, can produce notes in the infrasound range. Animals have been known to perceive the infrasonic waves going through the earth by natural disasters, a recent example of this is the 2004 Indian Ocean earthquake and tsunami. Animals were reported to flee the area hours before the tsunami hit the shores of Asia. It is not known for sure that this is the cause, some have suggested that it may have been the influence of waves, and not of infrasonic waves. Research in 2013 by Jon Hagstrum of the US Geological Survey suggests that pigeons use low-frequency infrasound to navigate. 20 Hz is considered the normal limit of human hearing
8.
Acoustical engineering
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Acoustical engineering is the branch of engineering dealing with sound and vibration. It is the application of acoustics, the science of sound and vibration, Acoustical engineers are typically concerned with the design, analysis and control of sound. One goal of engineering can be the reduction of unwanted noise. Unwanted noise can have significant impacts on animal and human health and well-being, reduce attainment by pupils in schools, acoustic engineers usually possess a bachelors degree or higher qualification in acoustics, physics or another engineering discipline. Practicing as an acoustic engineer usually requires a degree with significant scientific. Acoustic engineers might work in consultancy, specializing in particular fields, such as architectural acoustics. Acousticians are also involved in researching and understanding sound scientifically, some positions, such as faculty require a Doctor of Philosophy. In most countries, a degree in acoustics can represent the first step towards professional certification, after completing a certified degree program the engineer must satisfy a range of requirements before being certified. Once certified, the engineer is designated the title of Chartered Engineer, the listed subdisciplines are loosely based on the PACS coding used by the Acoustical Society of America. Aeroacoustics is concerned with how noise is generated by the movement of air, for instance via turbulence, aeroacoustics plays an important role in understanding how noise is generated by aircraft and wind turbines, as well as exploring how wind musical instruments work. Audio signal processing is the manipulation of audio signals using analog. Perceptual coding in MP3 and Opus, and to understand the content of the signal, audio engineers develop and use audio signal processing algorithms. Architectural acoustics is the science and engineering of achieving a good sound within a building, architectural acoustic design is usually done by acoustic consultants. Bioacoustics usually concerns the study of sound production and hearing in animals. This branch of acoustic engineering deals with the design of headphones, microphones, loudspeakers, sound systems, sound reproduction, environmental acoustics work is usually done by acoustic consultants or those working in environmental health. Recent research work has put an emphasis on soundscapes, the positive use of sound. Musical acoustics is concerned with researching and describing the physics of music, noise control is a set of strategies to reduce noise pollution by reducing noise at its source, by inhibiting sound propagation using noise barriers or similar, or by the use of ear protection. Control at the source is the most cost-effective way of providing noise control, noise control engineering applied to cars and trucks is known as noise, vibration, and harshness
9.
Noise control
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Noise control or noise mitigation is a set of strategies to reduce noise pollution or to reduce the impact of that noise, whether outdoors or indoors. The main areas of noise mitigation or abatement are, transportation noise control, architectural design, urban planning through zoning codes, roadway noise and aircraft noise are the most pervasive sources of environmental noise. Many of these techniques rely upon materials science applications of constructing sound baffles or using sound-absorbing liners for interior spaces, sound masking is the active addition of noise to reduce the annoyance of certain sounds, the opposite of soundproofing. Sound insulation, prevent the transmission of noise by the introduction of a mass barrier, common materials have high-density properties such as brick, thick glass, concrete, metal etc. Sound absorption, a material which acts as a ‘noise sponge’ by converting the sound energy into heat within the material. Common sound absorption materials include decoupled lead-based tiles, open cell foams and fiberglass Vibration damping, the damping mechanism works by extracting the vibration energy from the thin sheet and dissipating it as heat. A common material is sound deadened steel, Vibration isolation, prevents transmission of vibration energy from a source to a receiver by introducing a flexible element or a physical break. Common vibration isolators are springs, rubber mounts, cork etc, highway noise is today less affected by motor type, since the effects in higher speed are aerodynamic and tire noise related. The most fertile areas for roadway noise mitigation are in planning decisions, roadway design, noise barrier design, speed control, surface pavement selection. Speed control is effective since the lowest sound emissions arise from vehicles moving smoothly at 30 to 60 kilometres per hour, above that range, sound emissions double with each five miles per hour of speed. At the lowest speeds, braking and acceleration noise dominates, selection of road surface pavement can make a difference of a factor of two in sound levels, for the speed regime above 30 kilometres per hour. Surface friction and roadway safety are important considerations as well for pavement decisions, when designing new urban freeways or arterials, there are numerous design decisions regarding alignment and roadway geometrics. Use of a model to calculate sound levels has become standard practice since the early 1970s. In this way exposure of sensitive receptors to elevated sound levels can be minimized, an analogous process exists for urban mass transit systems and other rail transportation decisions. Noise barriers can be applicable for existing or planned surface transportation projects and they are probably the single most effective weapon in retrofitting an existing roadway, and commonly can reduce adjacent land use sound levels by up to ten decibels. A computer model is required to design the barrier since terrain, micrometeorology, for example, a roadway in cut or strong prevailing winds can produce a setting where atmospheric sound propagation is unfavorable to any noise barrier. As in the case of noise, little progress has been made in quelling aircraft noise at the source, other than elimination of loud engine designs from the 1960s. Because of its velocity and volume, jet engine exhaust noise defies reduction by any simple means
10.
Hearing
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Hearing, or auditory perception, is the ability to perceive sound by detecting vibrations, changes in the pressure of the surrounding medium through time, through an organ such as the ear. Sound may be heard through solid, liquid, or gaseous matter and it is one of the traditional five senses, partial or total inability to hear is called hearing loss. Like touch, audition requires sensitivity to the movement of molecules in the world outside the organism, both hearing and touch are types of mechanosensation. There are three components of the human ear, the outer ear, the middle ear. The outer ear includes the pinna, the part of the ear, as well as the ear canal which terminates at the eardrum. The pinna serves to focus sound waves through the ear canal toward the eardrum, because of the asymmetrical character of the outer ear of most mammals, sound is filtered differently on its way into the ear depending on what vertical location it is coming from. This gives these animals the ability to localize sound vertically, the eardrum is an airtight membrane, and when sound waves arrive there, they cause it to vibrate following the waveform of the sound. The middle ear consists of a small air-filled chamber that is located medial to the eardrum, within this chamber are the three smallest bones in the body, known collectively as the ossicles which include the malleus, incus and stapes. They aid in the transmission of the vibrations from the eardrum to the inner ear, the purpose of the middle ear ossicles is to overcome the impedance mismatch between air and water, by providing impedance matching. Also located in the ear are the stapedius and tensor tympani muscles which protect the hearing mechanism through a stiffening reflex. The stapes transmits sound waves to the ear through the oval window. The round window, another flexible membrane, allows for the displacement of the inner ear fluid caused by the entering sound waves. The inner ear consists of the cochlea, which is a spiral-shaped, fluid-filled tube and it is divided lengthwise by the organ of Corti, which is the main organ of mechanical to neural transduction. Inside the organ of Corti is the membrane, a structure that vibrates when waves from the middle ear propagate through the cochlear fluid – endolymph. The basilar membrane is tonotopic, so that frequency has a characteristic place of resonance along it. Characteristic frequencies are high at the entrance to the cochlea. Basilar membrane motion causes depolarization of the cells, specialized auditory receptors located within the organ of Corti. While the hair cells do not produce action potentials themselves, they release neurotransmitter at synapses with the fibers of the auditory nerve, which does produce action potentials
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Speech
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Speech is the vocalized form of communication based upon the syntactic combination of lexicals and names that are drawn from very large vocabularies. Each spoken word is created out of the combination of a limited set of vowel. These vocabularies, the syntax that structures them, and their sets of speech sound units differ, creating thousands of different. Most human speakers are able to communicate in two or more of them, hence being polyglots, the vocal abilities that enable humans to produce speech also enable them to sing. A gestural form of human communication exists for the deaf in the form of sign language, speech in some cultures has become the basis of a written language, often one that differs in its vocabulary, syntax and phonetics from its associated spoken one, a situation called diglossia. Speech is researched in terms of the production and speech perception of the sounds used in vocal language. Several academic disciplines study these, including acoustics, psychology, speech pathology, linguistics, cognitive science, communication studies, otolaryngology, another area of research is how the human brain in its different areas such as the Brocas area and Wernickes area underlies speech. It is controversial how far human speech is unique, in animals also communicate with vocalizations. The origins of speech are unknown and subject to much debate, in linguistics, manner of articulation describes how the tongue, lips, jaw, vocal cords, and other speech organs used to produce sounds, make contact with each other. Often the concept is used for the production of consonants. For any place of articulation, there may be several manners of articulation, normal human speech is produced with pressure from the lungs, which creates phonation in the glottis in the larynx, which is then modified by the vocal tract into different vowels and consonants. However humans can pronounce words without the use of the lungs and glottis in alaryngeal speech, speech perception refers to the processes by which humans can interpret and understand the sounds used in language. The study of perception is closely linked to the fields of phonetics and phonology in linguistics and cognitive psychology. Research in speech perception seeks to understand how human listeners recognize speech sounds, speech research has applications in building computer systems that can recognize speech, as well as improving speech recognition for hearing- and language-impaired listeners. Spoken vocalizations are quickly turned from sensory inputs into motor instructions needed for their immediate or delayed vocal imitation and this occurs independently of speech perception. This type of mapping plays a key role in enabling children to expand their spoken vocabulary, speech is a complex activity, as a result, errors are often made in speech. Speech errors have been analyzed by scientists to understand the nature of the involved in the production of speech. There are several organic and psychological factors that can affect speech, among these are, Diseases and disorders of the lungs or the vocal cords, including paralysis, respiratory infections, vocal fold nodules and cancers of the lungs and throat
12.
Ancient Greek
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Ancient Greek includes the forms of Greek used in ancient Greece and the ancient world from around the 9th century BC to the 6th century AD. It is often divided into the Archaic period, Classical period. It is antedated in the second millennium BC by Mycenaean Greek, the language of the Hellenistic phase is known as Koine. Koine is regarded as a historical stage of its own, although in its earliest form it closely resembled Attic Greek. Prior to the Koine period, Greek of the classic and earlier periods included several regional dialects, Ancient Greek was the language of Homer and of fifth-century Athenian historians, playwrights, and philosophers. It has contributed many words to English vocabulary and has been a subject of study in educational institutions of the Western world since the Renaissance. This article primarily contains information about the Epic and Classical phases of the language, Ancient Greek was a pluricentric language, divided into many dialects. The main dialect groups are Attic and Ionic, Aeolic, Arcadocypriot, some dialects are found in standardized literary forms used in literature, while others are attested only in inscriptions. There are also several historical forms, homeric Greek is a literary form of Archaic Greek used in the epic poems, the Iliad and Odyssey, and in later poems by other authors. Homeric Greek had significant differences in grammar and pronunciation from Classical Attic, the origins, early form and development of the Hellenic language family are not well understood because of a lack of contemporaneous evidence. Several theories exist about what Hellenic dialect groups may have existed between the divergence of early Greek-like speech from the common Proto-Indo-European language and the Classical period and they have the same general outline, but differ in some of the detail. The invasion would not be Dorian unless the invaders had some relationship to the historical Dorians. The invasion is known to have displaced population to the later Attic-Ionic regions, the Greeks of this period believed there were three major divisions of all Greek people—Dorians, Aeolians, and Ionians, each with their own defining and distinctive dialects. Often non-west is called East Greek, Arcadocypriot apparently descended more closely from the Mycenaean Greek of the Bronze Age. Boeotian had come under a strong Northwest Greek influence, and can in some respects be considered a transitional dialect, thessalian likewise had come under Northwest Greek influence, though to a lesser degree. Most of the dialect sub-groups listed above had further subdivisions, generally equivalent to a city-state and its surrounding territory, Doric notably had several intermediate divisions as well, into Island Doric, Southern Peloponnesus Doric, and Northern Peloponnesus Doric. The Lesbian dialect was Aeolic Greek and this dialect slowly replaced most of the older dialects, although Doric dialect has survived in the Tsakonian language, which is spoken in the region of modern Sparta. Doric has also passed down its aorist terminations into most verbs of Demotic Greek, by about the 6th century AD, the Koine had slowly metamorphosized into Medieval Greek
13.
Frequency
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Frequency is the number of occurrences of a repeating event per unit time. It is also referred to as frequency, which emphasizes the contrast to spatial frequency. The period is the duration of time of one cycle in a repeating event, for example, if a newborn babys heart beats at a frequency of 120 times a minute, its period—the time interval between beats—is half a second. Frequency is an important parameter used in science and engineering to specify the rate of oscillatory and vibratory phenomena, such as vibrations, audio signals, radio waves. For cyclical processes, such as rotation, oscillations, or waves, in physics and engineering disciplines, such as optics, acoustics, and radio, frequency is usually denoted by a Latin letter f or by the Greek letter ν or ν. For a simple motion, the relation between the frequency and the period T is given by f =1 T. The SI unit of frequency is the hertz, named after the German physicist Heinrich Hertz, a previous name for this unit was cycles per second. The SI unit for period is the second, a traditional unit of measure used with rotating mechanical devices is revolutions per minute, abbreviated r/min or rpm. As a matter of convenience, longer and slower waves, such as ocean surface waves, short and fast waves, like audio and radio, are usually described by their frequency instead of period. Spatial frequency is analogous to temporal frequency, but the axis is replaced by one or more spatial displacement axes. Y = sin = sin d θ d x = k Wavenumber, in the case of more than one spatial dimension, wavenumber is a vector quantity. For periodic waves in nondispersive media, frequency has a relationship to the wavelength. Even in dispersive media, the frequency f of a wave is equal to the phase velocity v of the wave divided by the wavelength λ of the wave. In the special case of electromagnetic waves moving through a vacuum, then v = c, where c is the speed of light in a vacuum, and this expression becomes, f = c λ. When waves from a monochrome source travel from one medium to another, their remains the same—only their wavelength. For example, if 71 events occur within 15 seconds the frequency is, the latter method introduces a random error into the count of between zero and one count, so on average half a count. This is called gating error and causes an error in the calculated frequency of Δf = 1/, or a fractional error of Δf / f = 1/ where Tm is the timing interval. This error decreases with frequency, so it is a problem at low frequencies where the number of counts N is small, an older method of measuring the frequency of rotating or vibrating objects is to use a stroboscope
14.
Infrasonic
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Infrasound, sometimes referred to as low-frequency sound, is sound that is lower in frequency than 20 Hz or cycles per second, the normal limit of human hearing. Hearing becomes gradually less sensitive as frequency decreases, so for humans to perceive infrasound, the ear is the primary organ for sensing infrasound, but at higher intensities it is possible to feel infrasound vibrations in various parts of the body. The study of sound waves is sometimes referred to as infrasonics, covering sounds beneath 20 Hz down to 0. 1Hz. Infrasound is characterized by an ability to cover long distances and get around obstacles with little dissipation, subwoofers designed to produce infrasound are capable of sound reproduction an octave or more below that of most commercially available subwoofers, and are often about 10 times the size. Infrasound was used by the Allies of World War I to locate artillery, one of the pioneers in infrasonic research was French scientist Vladimir Gavreau. He concluded it was caused by a large fan and duct system. One of his experiments was a whistle, an oversized organ pipe. Infrasound is defined by the American National Standards Institute as sound at less than 20 Hz. Nonlinear ocean wave interactions in ocean storms produce pervasive infrasound vibrations around 0.2 Hz, in particular, the Sumatran Rhinoceros has been shown to produce sounds with frequencies as low as 3 Hz which have similarities with the song of the humpback whale. The roar of the tiger contains infrasound of 18 Hz and lower, and it has also been suggested that migrating birds use naturally generated infrasound, from sources such as turbulent airflow over mountain ranges, as a navigational aid. Infrasound also may be used for communication, especially well documented in baleen whales. The frequency of baleen whale sounds can range from 10 Hz to 31 kHz, elephants also produce infrasound waves that travel through solid ground and are sensed by other herds using their feet, although they may be separated by hundreds of kilometres. These calls may be used to coordinate the movement of herds, human singers, some vocalists, including Tim Storms, can produce notes in the infrasound range. Animals have been known to perceive the infrasonic waves going through the earth by natural disasters, a recent example of this is the 2004 Indian Ocean earthquake and tsunami. Animals were reported to flee the area hours before the tsunami hit the shores of Asia. It is not known for sure that this is the cause, some have suggested that it may have been the influence of waves, and not of infrasonic waves. Research in 2013 by Jon Hagstrum of the US Geological Survey suggests that pigeons use low-frequency infrasound to navigate. 20 Hz is considered the normal limit of human hearing
15.
Fundamental frequency
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The fundamental frequency, often referred to simply as the fundamental, is defined as the lowest frequency of a periodic waveform. In music, the fundamental is the pitch of a note that is perceived as the lowest partial present. In terms of a superposition of sinusoids, the frequency is the lowest frequency sinusoidal in the sum. In some contexts, the fundamental is usually abbreviated as f0, in other contexts, it is more common to abbreviate it as f1, the first harmonic. All sinusoidal and many non-sinusoidal waveforms are periodic, which is to say they repeat exactly over time. The period of a waveform is the T for which the equation is true. This means that this equation and a definition of the values over any interval of length T is all that is required to describe the waveform completely. Every waveform may be described using any multiple of this period, there exists a smallest period over which the function may be described completely and this period is the fundamental period. The fundamental frequency is defined as its reciprocal, f 0 =1 T Since the period is measured in units of time, when the time units are seconds, the frequency is in s −1, also known as Hertz. For a tube of length L with one end closed and the end open the wavelength of the fundamental harmonic is 4 L. If the ends of the tube are now both closed or both opened as in the last two animations, the wavelength of the fundamental harmonic becomes 2 L. By the same method as above, the frequency is found to be f 0 = v 2 L. At 20 °C the speed of sound in air is 343 m/s and this speed is temperature dependent and does increase at a rate of 0.6 m/s for each degree Celsius increase in temperature. The fundamental may be created by vibration over the length of a string or air column. The fundamental is one of the harmonics, a harmonic is any member of the harmonic series, an ideal set of frequencies that are positive integer multiples of a common fundamental frequency. The reason a fundamental is also considered a harmonic is because it is 1 times itself, the fundamental is the frequency at which the entire wave vibrates. Overtones are other components present at frequencies above the fundamental. All of the components that make up the total waveform, including the fundamental
16.
Overtone
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An overtone is any frequency greater than the fundamental frequency of a sound. Using the model of Fourier analysis, the fundamental and the overtones together are called partials, harmonics, or more precisely, harmonic partials, are partials whose frequencies are integer multiples of the fundamental. These overlapping terms are used when discussing the acoustic behavior of musical instruments. The model of Fourier analysis provides for the inclusion of inharmonic partials, when a resonant system such as a blown pipe or plucked string is excited, a number of overtones may be produced along with the fundamental tone. In simple cases, such as for most musical instruments, the frequencies of these tones are the same as the harmonics. Examples of exceptions include the drum, – a timpani whose first overtone is about 1.6 times its fundamental resonance frequency, gongs and cymbals. The human vocal tract is able to produce highly variable amplitudes of the overtones, called formants, most oscillators, from a guitar string to a flute, will naturally vibrate at a series of distinct frequencies known as normal modes. The lowest normal mode frequency is known as the fundamental frequency, often, when an oscillator is excited by, for example, plucking a guitar string, it will oscillate at several of its modal frequencies at the same time. So when a note is played, this gives the sensation of hearing other frequencies above the lowest frequency, timbre is the quality that gives the listener the ability to distinguish between the sound of different instruments. The timbre of an instrument is determined by which overtones it emphasizes and that is to say, the relative volumes of these overtones to each other determines the specific flavor or color of sound of that family of instruments. The intensity of each of these overtones is rarely constant for the duration of a note, over time, different overtones may decay at different rates, causing the relative intensity of each overtone to rise or fall independent of the overall volume of the sound. A carefully trained ear can hear these changes even in a single note and this is why the timbre of a note may be perceived differently when played staccato or legato. A driven non-linear oscillator, such as the folds, a blown wind instrument, or a bowed violin string will oscillate in a periodic. This generates the impression of sound at integer multiple frequencies of the known as harmonics, or more precisely. Thus, in music, overtones are often called harmonics, depending upon how the string is plucked or bowed, different overtones can be emphasized. However, some overtones in some instruments may not be of an integer multiplication of the fundamental frequency. High quality instruments are built in such a manner that their individual notes do not create disharmonious overtones. This is illustrated by the following, Consider a guitar string and this dead length actually varies from string to string, being more pronounced with thicker and/or stiffer strings
17.
Pythagoras
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Pythagoras of Samos was an Ionian Greek philosopher, mathematician, and the putative founder of the movement called Pythagoreanism. Most of the information about Pythagoras was written centuries after he lived. He was born on the island of Samos, and travelled, visiting Egypt and Greece, around 530 BC, he moved to Croton, in Magna Graecia, and there established some kind of school or guild. In 520 BC, he returned to Samos, Pythagoras made influential contributions to philosophy and religion in the late 6th century BC. He is often revered as a mathematician and scientist and is best known for the Pythagorean theorem which bears his name. Many of the accomplishments credited to Pythagoras may actually have been accomplishments of his colleagues, some accounts mention that the philosophy associated with Pythagoras was related to mathematics and that numbers were important. It was said that he was the first man to himself a philosopher, or lover of wisdom, and Pythagorean ideas exercised a marked influence on Plato. Burkert states that Aristoxenus and Dicaearchus are the most important accounts, Aristotle had written a separate work On the Pythagoreans, which is no longer extant. However, the Protrepticus possibly contains parts of On the Pythagoreans and his disciples Dicaearchus, Aristoxenus, and Heraclides Ponticus had written on the same subject. These writers, late as they are, were among the best sources from whom Porphyry and Iamblichus drew, while adding some legendary accounts. Herodotus, Isocrates, and other writers agree that Pythagoras was the son of Mnesarchus and born on the Greek island of Samos. His father is said to have been a gem-engraver or a wealthy merchant, a late source gives his mothers name as Pythais. As to the date of his birth, Aristoxenus stated that Pythagoras left Samos in the reign of Polycrates, at the age of 40, around 530 BC he arrived in the Greek colony of Croton in what was then Magna Graecia. There he founded his own school the members of which he engaged to a disciplined. He furthermore aquired some political influence, on Greeks and non-Greeks of the region, following a conflict with the neighbouring colony of Sybaris, internal discord drove most of the Pythagoreans out of Croton. Pythagoras left the city before the outbreak of civil unrest and moved to Metapontum, after his death, his house was transformed into a sanctuary of Demeter, out of veneration for the philosopher, by the local population. In ancient sources there was disagreement and inconsistency about the late life of Pythagoras. His tomb was shown at Metapontum in the time of Cicero, according to Walter Burkert, Most obvious is the contradiction between Aristoxenus and Dicaearchus, regarding the catastrophe that overwhelmed the Pythagorean society
18.
Interval (music)
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In music theory, an interval is the difference between two pitches. In Western music, intervals are most commonly differences between notes of a diatonic scale, the smallest of these intervals is a semitone. Intervals smaller than a semitone are called microtones and they can be formed using the notes of various kinds of non-diatonic scales. Some of the very smallest ones are called commas, and describe small discrepancies, observed in some tuning systems, Intervals can be arbitrarily small, and even imperceptible to the human ear. In physical terms, an interval is the ratio between two sonic frequencies, for example, any two notes an octave apart have a frequency ratio of 2,1. This means that successive increments of pitch by the same result in an exponential increase of frequency. For this reason, intervals are often measured in cents, a derived from the logarithm of the frequency ratio. In Western music theory, the most common naming scheme for intervals describes two properties of the interval, the quality and number, examples include the minor third or perfect fifth. These names describe not only the difference in semitones between the upper and lower notes, but also how the interval is spelled, the importance of spelling stems from the historical practice of differentiating the frequency ratios of enharmonic intervals such as G–G♯ and G–A♭. The size of an interval can be represented using two alternative and equivalently valid methods, each appropriate to a different context, frequency ratios or cents, the size of an interval between two notes may be measured by the ratio of their frequencies. When a musical instrument is tuned using a just intonation tuning system, Intervals with small-integer ratios are often called just intervals, or pure intervals. Most commonly, however, musical instruments are tuned using a different tuning system. As a consequence, the size of most equal-tempered intervals cannot be expressed by small-integer ratios, for instance, an equal-tempered fifth has a frequency ratio of 2 7⁄12,1, approximately equal to 1.498,1, or 2.997,2. For a comparison between the size of intervals in different tuning systems, see section Size in different tuning systems, the standard system for comparing interval sizes is with cents. The cent is a unit of measurement. If frequency is expressed in a scale, and along that scale the distance between a given frequency and its double is divided into 1200 equal parts, each of these parts is one cent. In twelve-tone equal temperament, a system in which all semitones have the same size. Hence, in 12-TET the cent can be defined as one hundredth of a semitone
19.
Harmonic
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A harmonic is any member of the harmonic series, the divergent infinite series. Every term of the series after the first is the mean of the neighboring terms. The phrase harmonic mean likewise derives from music, the term is employed in various disciplines, including music, physics, acoustics, electronic power transmission, radio technology, and other fields. It is typically applied to repeating signals, such as sinusoidal waves, a harmonic of such a wave is a wave with a frequency that is a positive integer multiple of the frequency of the original wave, known as the fundamental frequency. The original wave is called the 1st harmonic, the following harmonics are known as higher harmonics. As all harmonics are periodic at the frequency, the sum of harmonics is also periodic at that frequency. On strings, harmonics that are bowed have a glassy, pure tone, harmonics may also be called overtones, partials or upper partials. In some music contexts, the harmonic, overtone and partial are used fairly interchangeably. Most acoustic instruments emit complex tones containing many individual partials, rather, a musical note is perceived as one sound, the quality or timbre of that sound being a result of the relative strengths of the individual partials. Oscillators that produce harmonic partials behave somewhat like one-dimensional resonators, and are long and thin. Wind instruments whose air column is open at one end, such as trumpets and clarinets. However they only produce partials matching the odd harmonics, at least in theory, the reality of acoustic instruments is such that none of them behaves as perfectly as the somewhat simplified theoretical models would predict. Partials whose frequencies are not integer multiples of the fundamental are referred to as inharmonic partials, antique singing bowls are known for producing multiple harmonic partials or multiphonics. An overtone is any partial higher than the lowest partial in a compound tone, the relative strengths and frequency relationships of the component partials determine the timbre of an instrument. This chart demonstrates how the three types of names are counted, In many musical instruments, it is possible to play the upper harmonics without the note being present. In a simple case this has the effect of making the note go up in pitch by an octave, in some cases it also changes the timbre of the note. This is part of the method of obtaining higher notes in wind instruments. The extended technique of playing multiphonics also produces harmonics, on string instruments it is possible to produce very pure sounding notes, called harmonics or flageolets by string players, which have an eerie quality, as well as being high in pitch
20.
Harmonic series (music)
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A harmonic series is the sequence of sounds where the base frequency of each sound is an integer multiple of the lowest base frequency. Pitched musical instruments are based on an approximate harmonic oscillator such as a string or a column of air. At these resonant frequencies, waves travel in both directions along the string or air column, reinforcing and canceling each other to form standing waves, interaction with the surrounding air causes audible sound waves, which travel away from the instrument. Because of the spacing of the resonances, these frequencies are mostly limited to integer multiples, or harmonics, of the lowest frequency. The musical timbre of a tone from such an instrument is determined by the relative strengths of each harmonic. A complex tone can be described as a combination of many simple periodic waves or partials, each with its own frequency of vibration, amplitude, a partial is any of the sine waves of which a complex tone is composed. A harmonic is any member of the series, an ideal set of frequencies that are positive integer multiples of a common fundamental frequency. The fundamental is also considered a harmonic because it is 1 times itself, a harmonic partial is any real partial component of a complex tone that matches an ideal harmonic. An inharmonic partial is any partial that does not match an ideal harmonic, Inharmonicity is a measure of the deviation of a partial from the closest ideal harmonic, typically measured in cents for each partial. Unpitched, or indefinite-pitched instruments, such as cymbals, gongs, or tam-tams make sounds that are rich in inharmonic partials, an overtone is any partial except the lowest partial. The term overtone does not imply harmonicity or inharmonicity and has no special meaning other than to exclude the fundamental. It is the relative strengths of the different overtones that gives an instrument its particular timbre, some electronic instruments, such as synthesizers, can play a pure frequency with no overtones. Synthesizers can also combine pure frequencies into more complex tones, such as to other instruments. Certain flutes and ocarinas are very nearly without overtones, in most pitched musical instruments, the fundamental is accompanied by other, higher-frequency harmonics. Thus shorter-wavelength, higher-frequency waves occur with varying prominence and give each instrument its characteristic tone quality, the fact that a string is fixed at each end means that the longest allowed wavelength on the string is twice the length of the string. Other allowed wavelengths are 1/2, 1/3, 1/4, 1/5, 1/6, theoretically, these shorter wavelengths correspond to vibrations at frequencies that are 2,3,4,5,6, etc. times the fundamental frequency. Physical characteristics of the vibrating medium and/or the resonator it vibrates against often alter these frequencies, the harmonic series is an arithmetic series. In terms of frequency, the difference between consecutive harmonics is therefore constant and equal to the fundamental, but because human ears respond to sound nonlinearly, higher harmonics are perceived as closer together than lower ones
21.
Musical tuning
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In music, there are two common meanings for tuning, Tuning practice, the act of tuning an instrument or voice. Tuning systems, the systems of pitches used to tune an instrument. Tuning is the process of adjusting the pitch of one or many tones from musical instruments to establish typical intervals between these tones, Tuning is usually based on a fixed reference, such as A =440 Hz. Out of tune refers to a pitch/tone that is too high or too low in relation to a given reference pitch. While an instrument might be in relative to its own range of notes. Some instruments become out of tune with damage or time and must be readjusted or repaired, different methods of sound production require different methods of adjustment, Tuning to a pitch with ones voice is called matching pitch and is the most basic skill learned in ear training. Turning pegs to increase or decrease the tension on strings so as to control the pitch, instruments such as the harp, piano, and harpsichord require a wrench to turn the tuning pegs, while others such as the violin can be tuned manually. Modifying the length or width of the tube of an instrument, brass instrument, pipe, bell. The sounds of instruments such as cymbals are inharmonic—they have irregular overtones not conforming to the harmonic series. Tuning may be done aurally by sounding two pitches and adjusting one of them to match or relate to the other, a tuning fork or electronic tuning device may be used as a reference pitch, though in ensemble rehearsals often a piano is used. Symphony orchestras and concert bands tend to tune to an A or a B♭, respectively, interference beats are used to objectively measure the accuracy of tuning. As the two approach a harmonic relationship, the frequency of beating decreases. When tuning a unison or octave it is desired to reduce the beating frequency until it cannot be detected, for other intervals, this is dependent on the tuning system being used. Harmonics may be used to facilitate tuning of strings that are not themselves tuned to the unison, for example, lightly touching the highest string of a cello at the middle while bowing produces the same pitch as doing the same a third of the way down its second-highest string. The resulting unison is more easily and quickly judged than the quality of the fifth between the fundamentals of the two strings. In music, the open string refers to the fundamental note of the unstopped. The strings of a guitar are tuned to fourths, as are the strings of the bass guitar. Violin, viola, and cello strings are tuned to fifths, however, non-standard tunings exist to change the sound of the instrument or create other playing options
22.
Aristotle
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Aristotle was an ancient Greek philosopher and scientist born in the city of Stagira, Chalkidice, on the northern periphery of Classical Greece. His father, Nicomachus, died when Aristotle was a child, at seventeen or eighteen years of age, he joined Platos Academy in Athens and remained there until the age of thirty-seven. Shortly after Plato died, Aristotle left Athens and, at the request of Philip II of Macedon, teaching Alexander the Great gave Aristotle many opportunities and an abundance of supplies. He established a library in the Lyceum which aided in the production of many of his hundreds of books and he believed all peoples concepts and all of their knowledge was ultimately based on perception. Aristotles views on natural sciences represent the groundwork underlying many of his works, Aristotles views on physical science profoundly shaped medieval scholarship. Their influence extended from Late Antiquity and the Early Middle Ages into the Renaissance, some of Aristotles zoological observations, such as on the hectocotyl arm of the octopus, were not confirmed or refuted until the 19th century. His works contain the earliest known study of logic, which was incorporated in the late 19th century into modern formal logic. Aristotle was well known among medieval Muslim intellectuals and revered as The First Teacher and his ethics, though always influential, gained renewed interest with the modern advent of virtue ethics. All aspects of Aristotles philosophy continue to be the object of academic study today. Though Aristotle wrote many elegant treatises and dialogues – Cicero described his style as a river of gold – it is thought that only around a third of his original output has survived. Aristotle, whose means the best purpose, was born in 384 BC in Stagira, Chalcidice. His father Nicomachus was the physician to King Amyntas of Macedon. Aristotle was orphaned at a young age, although there is little information on Aristotles childhood, he probably spent some time within the Macedonian palace, making his first connections with the Macedonian monarchy. At the age of seventeen or eighteen, Aristotle moved to Athens to continue his education at Platos Academy and he remained there for nearly twenty years before leaving Athens in 348/47 BC. Aristotle then accompanied Xenocrates to the court of his friend Hermias of Atarneus in Asia Minor, there, he traveled with Theophrastus to the island of Lesbos, where together they researched the botany and zoology of the island. Aristotle married Pythias, either Hermiass adoptive daughter or niece and she bore him a daughter, whom they also named Pythias. Soon after Hermias death, Aristotle was invited by Philip II of Macedon to become the tutor to his son Alexander in 343 BC, Aristotle was appointed as the head of the royal academy of Macedon. During that time he gave not only to Alexander
23.
Wave
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In physics, a wave is an oscillation accompanied by a transfer of energy that travels through a medium. Frequency refers to the addition of time, wave motion transfers energy from one point to another, which displace particles of the transmission medium–that is, with little or no associated mass transport. Waves consist, instead, of oscillations or vibrations, around almost fixed locations, there are two main types of waves. Mechanical waves propagate through a medium, and the substance of this medium is deformed, restoring forces then reverse the deformation. For example, sound waves propagate via air molecules colliding with their neighbors, when the molecules collide, they also bounce away from each other. This keeps the molecules from continuing to travel in the direction of the wave, the second main type, electromagnetic waves, do not require a medium. Instead, they consist of periodic oscillations of electrical and magnetic fields generated by charged particles. These types vary in wavelength, and include radio waves, microwaves, infrared radiation, visible light, ultraviolet radiation, X-rays, waves are described by a wave equation which sets out how the disturbance proceeds over time. The mathematical form of this varies depending on the type of wave. Further, the behavior of particles in quantum mechanics are described by waves, in addition, gravitational waves also travel through space, which are a result of a vibration or movement in gravitational fields. While mechanical waves can be transverse and longitudinal, all electromagnetic waves are transverse in free space. A single, all-encompassing definition for the wave is not straightforward. A vibration can be defined as a back-and-forth motion around a reference value, however, a vibration is not necessarily a wave. An attempt to define the necessary and sufficient characteristics that qualify a phenomenon as a results in a blurred line. The term wave is often understood as referring to a transport of spatial disturbances that are generally not accompanied by a motion of the medium occupying this space as a whole. In a wave, the energy of a vibration is moving away from the source in the form of a disturbance within the surrounding medium and it may appear that the description of waves is closely related to their physical origin for each specific instance of a wave process. For example, acoustics is distinguished from optics in that sound waves are related to a rather than an electromagnetic wave transfer caused by vibration. Concepts such as mass, momentum, inertia, or elasticity and this difference in origin introduces certain wave characteristics particular to the properties of the medium involved
24.
Vitruvius
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His discussion of perfect proportion in architecture and the human body, led to the famous Renaissance drawing by Da Vinci of Vitruvian Man. By his own description Vitruvius served as an artilleryman, the class of arms in the military offices. He probably served as a officer of artillery in charge of doctores ballistarum. Little is known about Vitruvius life, most inferences about him are extracted from his only surviving work De Architectura. Even his first name Marcus and his cognomen Pollio are uncertain. Cetius Faventinus writes of Vitruvius Polio aliique auctores, this can be read as Vitruvius Polio, and others or, less likely, as Vitruvius, Polio, Vitruvius was a military engineer, or a praefect architectus armamentarius of the apparitor status group. He is mentioned in Pliny the Elders table of contents for Naturalis Historia, frontinus refers to Vitruvius the architect in his late 1st-century work De aquaeductu. Likely born a free Roman citizen, by his own account, Vitruvius served the Roman army under Caesar with the otherwise poorly identified Marcus Aurelius, Publius Minidius and these names vary depending on the edition of De architectura. Publius Minidius is also written as Publius Numidicus and Publius Numidius, as an army engineer he specialized in the construction of ballista and scorpio artillery war machines for sieges. It is speculated that Vitruvius served with Caesars chief engineer Lucius Cornelius Balbus, the locations where he served can be reconstructed from, for example, descriptions of the building methods of various foreign tribes. Although he describes places throughout De Architectura, he not say he was present. His service likely included north Africa, Hispania, Gaul and Pontus, the position of the camp, the direction of the entrenchments, the inspection of the tents or huts of the soldiers and the baggage were comprehended in his province. His authority extended over the sick, and the physicians who had the care of them and he had the charge of providing carriages, bathhouses and the proper tools for sawing and cutting wood, digging trenches, raising parapets, sinking wells and bringing water into the camp. He likewise had the care of furnishing the troops with wood and straw, as well as the rams, onagri, balistae, at various locations described by Vitruvius, battles and sieges occurred. He is the source for the siege of Larignum in 56 BC. The broken siege at Gergovia in 52 BC, and the siege of Uxellodunum in 51 BC. These are all sieges of large Gallic oppida, a legion that fits the same sequence of locations is the Legio VI Ferrata, of which ballista would be an auxiliary unit. Mainly known for his writings, Vitruvius was himself an architect, frontinus mentions him in connection with the standard sizes of pipes
25.
Architectural acoustics
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Architectural acoustics is the science and engineering of achieving a good sound within a building and is a branch of acoustical engineering. Architectural acoustic design is usually done by acoustic consultants and this science analyzes noise transmission from building exterior envelope to interior and vice versa. The main noise paths are roofs, eaves, walls, windows, door, sufficient control ensures space functionality and is often required based on building use and local municipal codes. An example would be providing a design for a home which is to be constructed close to a high volume roadway, or under the flight path of a major airport. The science of limiting and/or controlling noise transmission from one building space to another to ensure space functionality, the typical sound paths are ceilings, room partitions, acoustic ceiling panels, doors, windows, flanking, ducting and other penetrations. Technical solutions depend on the source of the noise and the path of acoustic transmission, an example would be providing suitable party wall design in an apartment complex to minimize the mutual disturbance due to noise by residents in adjacent apartments. This is the science of controlling a rooms surfaces based on sound absorbing and reflecting properties, excessive reverberation time, which can be calculated, can lead to poor speech intelligibility. Sound reflections create standing waves that produce natural resonances that can be heard as a pleasant sensation or an annoying one, reflective surfaces can be angled and coordinated to provide good coverage of sound for a listener in a concert hall or music recital space. To illustrate this concept consider the difference between a large office meeting room or lecture theater and a traditional classroom with all hard surfaces. Interior building surfaces can be constructed of different materials and finishes. Ideal acoustical panels are those without a face or finish material that interferes with the acoustical infill or substrate, fabric covered panels are one way to heighten acoustical absorption. Perforated metal shows also sound absorbing qualities, finish material is used to cover over the acoustical substrate. Mineral fiber board, or Micore, is a commonly used acoustical substrate, finish materials often consist of fabric, wood or acoustical tile. Fabric can be wrapped around substrates to create what is referred to as a pre-fabricated panel, prefabricated panels are limited to the size of the substrate ranging from 2 by 4 feet to 4 by 10 feet. Fabric retained in a perimeter track system, is referred to as on-site acoustical wall panels. This is constructed by framing the perimeter track into shape, infilling the acoustical substrate, on-site wall panels can be constructed to accommodate door frames, baseboard, or any other intrusion. Large panels can be created on walls and ceilings with this method, wood finishes can consist of punched or routed slots and provide a natural look to the interior space, although acoustical absorption may not be great. There are three ways to improve workplace acoustics and solve workplace sound problems – the ABCs, inadequate control may lead to elevated sound levels within the space which can be annoying and reduce speech intelligibility
26.
De architectura
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It contains a variety of information on Greek and Roman buildings, as well as prescriptions for the planning and design of military camps, cities, and structures both large and small. Derived partially from Latin rhetoric, Vitruvian terms for order, arrangement, proportion, and fitness for intended purposes have guided architects for centuries, the Roman author also gave advice on the qualifications of an architect and on types of architectural drawing. The ten books or scrolls are organized as follows, De architectura – Ten Books on Architecture Roman architects were skilled in engineering, art, Vitruvius was very much of this type, a fact reflected in De architectura. He covered a variety of subjects he saw as touching on architecture. This included many aspects that may seem irrelevant to modern eyes, ranging from mathematics to astronomy, meteorology, in the Roman conception, architecture needed to take into account everything touching on the physical and intellectual life of man and his surroundings. Vitruvius, thus, deals with many issues concerning architecture. Book IX relates the abstract geometry of Plato to the work of the surveyor. Astrology is cited for its insights into the organisation of human life, likewise, Vitruvius cites Ctesibius of Alexandria and Archimedes for their inventions, Aristoxenus for music, Agatharchus for theatre, and Varro for architecture. Vitruvius sought to address the ethos of architecture, declaring that quality depends on the relevance of the artists work. Perhaps the most famous declaration from De architectura is one still quoted by architects, a modern interpretation of Wottons English might render it thus, The ideal building has three elements, it is sturdy, useful, and beautiful. Vitruvius also studied human proportions and his canones were later encoded in a famous drawing by Leonardo da Vinci. Vitruvius also described the construction of sundials and water clocks, numerous such massive structures occur across the former empire, a testament to the power of Roman engineering. Vitruvius description of Roman aqueduct construction is short, but mentions key details especially for the way they were surveyed, and his book would have been of assistance to Frontinus, a general who was appointed in the late 1st century AD to administer the many aqueducts of Rome. The Roman Empire went far in exploiting water power, as the set of no fewer than 16 water mills at Barbegal in France demonstrates, the mills ground grain in a very efficient operation, and many other mills are now known, such as the much later Hierapolis sawmill. Vitruvius described many different construction materials used for a variety of different structures. Cement, concrete, and lime received in-depth descriptions, the longevity of many Roman structures being mute testimony to their skill in building materials, Vitruvius advised that lead should not be used to conduct drinking water, clay pipes being preferred. He comes to conclusion in Book VIII of De architectura after empirical observation of the apparent laborer illnesses in the plumbum foundries of his time. In 1986, the United States banned the use of lead in plumbing due to lead poisonings neurological damage, however, much of the water used by Rome and many other cities was very hard, and coated the inner surfaces of the pipes, so lead poisoning was unlikely
27.
Roman theatre (structure)
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Roman theatres derive from and are part of the overall evolution of earlier Greek theatres. Indeed, much of the influence on the Romans came from the Greeks. However, Roman theatres have specific differences, such as generally being built upon their own instead of earthen works or a hillside. Roman theatres were built in all areas of the empire from Spain to the Middle East, because of the Romans ability to influence local architecture, we see numerous theatres around the world with uniquely Roman attributes. There exist similarities between the theatres and amphitheatres of ancient Rome/Italy and they were constructed out of the same material, Roman concrete, and provided a place for the public to go and see numerous events throughout the Empire. However, they are two different structures, with specific layouts that lend to the different events they held. Amphitheatres did not need superior acoustics, unlike those provided by the structure of a Roman theatre, while amphitheatres would feature races and gladiatorial events, theatres hosted events such as plays, pantomimes, choral events, and orations. Their design, with its form, enhances the natural acoustics. These buildings were semi-circular and possessed certain inherent architectural structures, with minor differences depending on the region in which they were constructed, the scaenae frons was a high back wall of the stage floor, supported by columns. The proscaenium was a wall that supported the front edge of the stage with ornately decorated niches off to the sides, the Hellenistic influence is seen through the use of the proscaenium. The Roman theatre also had a podium, which supported the columns of the scaenae frons. The theatre itself was divided into the stage and the seating section, vomitoria or entrances and exits were made available to the audience. The auditorium, the area in which people gathered, was constructed on a small hill or slope in which stacked seating could be easily made in the tradition of the Greek Theatres. The center of the auditorium was hollowed out of a hill or slope, while the outer radian seats required structural support and this was of course not always the case as Romans tended to build their theatres regardless of the availability of hillsides. All theatres built within the city of Rome were completely man-made without the use of earthworks, the auditorium was not roofed, rather, awnings could be pulled overhead to provide shelter from rain or sunlight. Some Roman theatres, constructed of wood, were torn down after the festival for which they were erected concluded. This practice was due to a moratorium on permanent theatre structures that lasted until 55 BC when the Theatre of Pompey was built with the addition of a temple to avoid the law, some Roman theatres show signs of never having been completed in the first place. Inside Rome, few theatres have survived the centuries following their construction, Theatre of ancient Greece Theatre of ancient Rome Amphitheatre Roman architecture
28.
Amman
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Amman is the capital and most populous city of Jordan, and the countrys economic, political and cultural centre. Situated in north-central Jordan, Amman is the centre of the Amman Governorate. The city has a population of 4,007,526, today, Amman is considered to be among the most liberal and westernized Arab cities. It is a major tourist destination in the region, particularly among Arab, the earliest evidence of settlement in the area is a Neolithic site known as Ain Ghazal. Its successor was known as Rabbath Ammon, which was the capital of the Ammonites, then as Philadelphia and it was initially built on seven hills but now spans over 19 hills combining 27 districts, which are administered by the Greater Amman Municipality headed by its mayor Aqel Biltaji. Areas of Amman have either gained their names from the hills or valleys they lie on, such as Jabal Lweibdeh, East Amman is predominantly filled with historic sites that frequently host cultural activities, while West Amman is more modern and serves as the economic center of the city. Approximately 2 million visitors arrived in Amman in 2014, which ranked it as the 93rd most visited city in the world, Amman has a relatively fast growing economy, and it is ranked Beta− on the global city index. Moreover, it was named one of the Middle East and North Africas best cities according to economic, labor, environmental, the city is among the most popular locations in the Arab world for multinational corporations to set up their regional offices, alongside Doha and only behind Dubai. It is expected that in the next 10 years these three cities will capture the largest share of multinational corporation activity in the region. Amman derives its name from the 13th century BC when the Ammonites named it Rabbath Ammon, over time, the term Rabbath was no longer used and the city became known as Ammon. The influence of new civilizations that conquered the city changed its name to Amman. In the Hebrew Bible, it is referred to as Rabbat ʿAmmon, however, Ptolemy II Philadelphus, the Macedonian ruler of the Ptolemaic Kingdom who reigned from 283 to 246 BC, renamed the city to Philadelphia after occupying it. The name was given as an adulation to his own nickname, in the outskirts of Amman, one of the largest known ancient settlements in the Near East was discovered. The site, known as Ain Ghazal which is situated on a valley-side, dates back to 7250 BC and it was a typical average sized aceramic Neolithic village that accommodated around 3,000 inhabitants. Its houses were rectangular mud-bricked buildings that included a main square living room, the site was discovered in 1974 as construction workers were working on a road crossing the area. By 1982 when the excavations started, around 600 meters of road ran through the site, despite the damage brought by urban expansion, the remains of Ain Ghazal provided a wealth of information. These statues are human figures made with white plaster, the figures have painted clothes, hair, and in some cases ornamental tattoos. Thirty-two figures were found in two caches, fifteen of them full figures, fifteen busts, and two fragmentary heads, three of the busts were two-headed, the significance of which is not clear
29.
Scientific revolution
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While its dates are debated, the publication in 1543 of Nicolaus Copernicuss De revolutionibus orbium coelestium is often cited as marking the beginning of the scientific revolution. By the end of the 18th century, the revolution had given way to the Age of Reflection. Great advances in science have been termed revolutions since the 18th century, in 1747, Clairaut wrote that Newton was said in his own lifetime to have created a revolution. The word was used in the preface to Lavoisiers 1789 work announcing the discovery of oxygen. Few revolutions in science have immediately excited so much general notice as the introduction of the theory of oxygen, lavoisier saw his theory accepted by all the most eminent men of his time, and established over a great part of Europe within a few years from its first promulgation. In the 19th century, William Whewell described the revolution in science itself -- the scientific method -- that had taken place in the 15th–16th century. This gave rise to the view of the scientific revolution today, A new view of nature emerged. Science became a discipline, distinct from both philosophy and technology and came to be regarded as having utilitarian goals. The scientific revolution is traditionally assumed to start with the Copernican Revolution, in the 20th century, Alexandre Koyré introduced the term scientific revolution, centering his analysis on Galileo. The term was popularized by Butterfield in his Origins of Modern Science, the scientific revolution led to the establishment of several modern sciences. In 1984, Joseph Ben-David wrote, Rapid accumulation of knowledge, the new kind of scientific activity emerged only in a few countries of Western Europe, and it was restricted to that small area for about two hundred years. Many contemporary writers and modern historians claim that there was a change in world view. Looms so large as the origin both of the modern world and of the modern mentality that our customary periodization of European history has become an anachronism. Some scholars have noted a direct tie between particular aspects of traditional Christianity and the rise of science, the Aristotelian tradition was still an important intellectual framework in the 17th century, although by that time natural philosophers had moved away from much of it. Key scientific ideas dating back to classical antiquity had changed drastically over the years, the ideas that remained, which were transformed fundamentally during the scientific revolution, include, Aristotles cosmology that placed the Earth at the center of a spherical hierarchic cosmos. The terrestrial and celestial regions were made up of different elements which had different kinds of natural movement, the terrestrial region, according to Aristotle, consisted of concentric spheres of the four elements—earth, water, air, and fire. All bodies naturally moved in straight lines until they reached the sphere appropriate to their elemental composition—their natural place, all other terrestrial motions were non-natural, or violent. The celestial region was made up of the element, aether
30.
Galileo Galilei
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Galileo Galilei was an Italian polymath, astronomer, physicist, engineer, philosopher, and mathematician. He played a role in the scientific revolution of the seventeenth century. Galileo also worked in applied science and technology, inventing an improved military compass, Galileos championing of heliocentrism and Copernicanism was controversial during his lifetime, when most subscribed to either geocentrism or the Tychonic system. He met with opposition from astronomers, who doubted heliocentrism because of the absence of a stellar parallax. He was tried by the Inquisition, found vehemently suspect of heresy and he spent the rest of his life under house arrest. He has been called the father of observational astronomy, the father of modern physics, the father of scientific method, and the father of science. Galileo was born in Pisa, Italy, on 15 February 1564, the first of six children of Vincenzo Galilei, a famous lutenist, composer, and music theorist, and Giulia, three of Galileos five siblings survived infancy. The youngest, Michelangelo, also became a noted lutenist and composer although he contributed to financial burdens during Galileos young adulthood, Michelangelo was unable to contribute his fair share of their fathers promised dowries to their brothers-in-law, who would later attempt to seek legal remedies for payments due. Michelangelo would also occasionally have to borrow funds from Galileo to support his musical endeavours and these financial burdens may have contributed to Galileos early fire to develop inventions that would bring him additional income. When Galileo Galilei was eight, his family moved to Florence and he then was educated in the Vallombrosa Abbey, about 30 km southeast of Florence. Galileo Bonaiuti was buried in the church, the Basilica of Santa Croce in Florence. It was common for mid-sixteenth century Tuscan families to name the eldest son after the parents surname, hence, Galileo Galilei was not necessarily named after his ancestor Galileo Bonaiuti. The Italian male given name Galileo derives from the Latin Galilaeus, meaning of Galilee, the biblical roots of Galileos name and surname were to become the subject of a famous pun. In 1614, during the Galileo affair, one of Galileos opponents, in it he made a point of quoting Acts 1,11, Ye men of Galilee, why stand ye gazing up into heaven. Despite being a genuinely pious Roman Catholic, Galileo fathered three children out of wedlock with Marina Gamba and they had two daughters, Virginia and Livia, and a son, Vincenzo. Their only worthy alternative was the religious life, both girls were accepted by the convent of San Matteo in Arcetri and remained there for the rest of their lives. Virginia took the name Maria Celeste upon entering the convent and she died on 2 April 1634, and is buried with Galileo at the Basilica of Santa Croce, Florence. Livia took the name Sister Arcangela and was ill for most of her life, Vincenzo was later legitimised as the legal heir of Galileo and married Sestilia Bocchineri
31.
Marin Mersenne
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Marin Mersenne, Marin Mersennus or le Père Mersenne was a French theologian, philosopher, mathematician and music theorist, often referred to as the father of acoustics. Mersenne, an ordained priest, had contacts in the scientific world and has been called the center of the world of science. Marin Mersenne was born of peasant parents near Oizé, Maine and he was educated at Le Mans and at the Jesuit College of La Flèche. On 17 July 1611, he joined the Minim Friars, and, after studying theology, between 1614 and 1618, he taught theology and philosophy at Nevers, but he returned to Paris and settled at the convent of LAnnonciade in 1620. There he studied mathematics and music and met with other kindred spirits such as René Descartes, Étienne Pascal, Pierre Petit, Gilles de Roberval and he corresponded with Giovanni Doni, Constantijn Huygens, Galileo Galilei, and other scholars in Italy, England and the Dutch Republic. He was a defender of Galileo, assisting him in translations of some of his mechanical works. For four years, Mersenne devoted himself entirely to philosophic and theological writing and it is sometimes incorrectly stated that he was a Jesuit. He was educated by Jesuits, but he never joined the Society of Jesus and he taught theology and philosophy at Nevers and Paris. He was not afraid to cause disputes among his friends in order to compare their views. In 1635 Mersenne met with Tommaso Campanella, but concluded that he could teach nothing in the sciences but still he has a good memory, Mersenne asked if René Descartes wanted Campanella to come to Holland to meet him, but Descartes declined. He visited Italy fifteen times, in 1640,1641 and 1645, in 1643–1644 Mersenne also corresponded with the German Socinian Marcin Ruar concerning the Copernican ideas of Pierre Gassendi, finding Ruar already a supporter of Gassendis position. Among his correspondents were Descartes, Galilei, Roberval, Pascal, Beeckman and he died September 1 through complications arising from a lung abscess. Some history scientists suggest he died for having drunk a huge quantity of water, along with Descartes. It was written as a commentary on the Book of Genesis, at first sight the book appears to be a collection of treatises on various miscellaneous topics. However Robert Lenoble has shown that the principle of unity in the work is a polemic against magical and divinatory arts, cabalism and he mentions Martin Del Rios Investigations into Magic and criticises Marsilio Ficino for claiming power for images and characters. He condemns astral magic and astrology and the anima mundi, a popular amongst Renaissance neo-platonists. Whilst allowing for an interpretation of the Cabala, he wholeheartedly condemned its magical application—particularly to angelology. He also criticises Pico della Mirandola, Cornelius Agrippa and Francesco Giorgio with Robert Fludd as his main target, Fludd responded with Sophia cum moria certamen, wherein Fludd admits his involvement with the Rosicrucians
32.
Mersenne's laws
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Mersennes laws are laws describing the frequency of oscillation of a stretched string or monochord, useful in musical tuning and musical instrument construction. The equation was first proposed by French mathematician and music theorist Marin Mersenne in his 1637 work Traité de lharmonie universelle. Mersennes laws govern the construction and operation of string instruments, pianos, harps, lower strings are thicker, thus having a greater mass per unit length. Higher-pitched strings typically are thinner, have higher tension, and may be shorter and this result does not differ substantially from Galileos, yet it is rightly known as Mersennes law, because Mersenne physically proved their truth through experiments. Mersenne investigated and refined these relationships by experiment but did not himself originate them, though his theories are correct, his measurements are not very exact, and his calculations where greatly improved by Joseph Sauveur through the use of acoustic beats and metronomes. These laws are derived from Mersennes equation 22, f 0 = ν λ =12 L F μ. The formula for the frequency is, f 0 =12 L F μ. Beat Cycloid Long-string instrument Mersenne conjectures Overtone Standing wave
33.
Speed of sound
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The speed of sound is the distance travelled per unit time by a sound wave as it propagates through an elastic medium. In dry air at 20 °C, the speed of sound is 343 metres per second, the speed of sound in an ideal gas depends only on its temperature and composition. The speed has a dependence on frequency and pressure in ordinary air. In common everyday speech, speed of sound refers to the speed of waves in air. However, the speed of sound varies from substance to substance, sound travels most slowly in gases, it travels faster in liquids, and faster still in solids. For example, sound travels at 343 m/s in air, it travels at 1,484 m/s in water, in an exceptionally stiff material such as diamond, sound travels at 12,000 m/s, which is around the maximum speed that sound will travel under normal conditions. Sound waves in solids are composed of waves, and a different type of sound wave called a shear wave. Shear waves in solids usually travel at different speeds, as exhibited in seismology, the speed of compression waves in solids is determined by the mediums compressibility, shear modulus and density. The speed of waves is determined only by the solid materials shear modulus. In fluid dynamics, the speed of sound in a medium is used as a relative measure for the speed of an object moving through the medium. The ratio of the speed of an object to the speed of sound in the fluid is called the objects Mach number, objects moving at speeds greater than Mach1 are said to be traveling at supersonic speeds. During the 17th century, there were attempts to measure the speed of sound accurately, including attempts by Marin Mersenne in 1630, Pierre Gassendi in 1635. In 1709, the Reverend William Derham, Rector of Upminster, published an accurate measure of the speed of sound. Measurements were made of gunshots from a number of local landmarks, the distance was known by triangulation, and thus the speed that the sound had travelled was calculated. The transmission of sound can be illustrated by using a model consisting of an array of balls interconnected by springs, for real material the balls represent molecules and the springs represent the bonds between them. Sound passes through the model by compressing and expanding the springs, transmitting energy to neighbouring balls, which transmit energy to their springs, the speed of sound through the model depends on the stiffness of the springs, and the mass of the balls. As long as the spacing of the balls remains constant, stiffer springs transmit energy more quickly, effects like dispersion and reflection can also be understood using this model. In a real material, the stiffness of the springs is called the modulus
34.
Hermann von Helmholtz
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Hermann Ludwig Ferdinand von Helmholtz was a German physician and physicist who made significant contributions in several scientific fields. The largest German association of institutions, the Helmholtz Association, is named after him. In physics, he is known for his theories on the conservation of energy, work in electrodynamics, chemical thermodynamics, Helmholtzs work is influenced by the philosophy of Johann Gottlieb Fichte and Immanuel Kant. He tried to trace their theories in empirical matters like physiology, as a young man, Helmholtz was interested in natural science, but his father wanted him to study medicine at the Charité because there was financial support for medical students. Trained primarily in physiology, Helmholtz wrote on other topics, ranging from theoretical physics, to the age of the Earth. Helmholtzs first academic position was as a teacher of Anatomy at the Academy of Arts in Berlin in 1848 and he then moved to take a post of associate professor of physiology at the Prussian University of Königsberg, where he was appointed in 1849. In 1855 he accepted a professorship of anatomy and physiology at the University of Bonn. He was not particularly happy in Bonn, however, and three later he transferred to the University of Heidelberg, in Baden, where he served as professor of physiology. In 1871 he accepted his final university position, as professor of physics at the University of Berlin and his first important scientific achievement, an 1847 treatise on the conservation of energy, was written in the context of his medical studies and philosophical background. He discovered the principle of conservation of energy while studying muscle metabolism and he tried to demonstrate that no energy is lost in muscle movement, motivated by the implication that there were no vital forces necessary to move a muscle. This was a rejection of the tradition of Naturphilosophie which was at that time a dominant philosophical paradigm in German physiology. He published his theories in his book Über die Erhaltung der Kraft, in the 1850s and 60s, building on the publications of William Thomson, Helmholtz and William Rankine popularized the idea of the heat death of the universe. In fluid dynamics, Helmholtz made several contributions, including Helmholtzs theorems for vortex dynamics in inviscid fluids, Helmholtz was a pioneer in the scientific study of human vision and audition. He coined the term psychophysics, to capture the distinction between the measurement of physical stimuli and their effect on human perception. The physical sound needs to be increased exponentially in order for equal steps to seem linear, Helmholtz paved the way in experimental studies on the relationship between the physical energy and its appreciation, with the goal in mind to develop psychophysical laws. The sensory physiology of Helmholtz was the basis of the work of Wilhelm Wundt, a student of Helmholtz and he, more explicitly than Helmholtz, described his research as a form of empirical philosophy and as a study of the mind as something separate. Helmholtz had, in his early repudiation of Naturphilosophie, stressed the importance of materialism, in 1851, Helmholtz revolutionized the field of ophthalmology with the invention of the ophthalmoscope, an instrument used to examine the inside of the human eye. Helmholtzs interests at that time were focused on the physiology of the senses
35.
John William Strutt, 3rd Baron Rayleigh
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John William Strutt, 3rd Baron Rayleigh OM PC PRS was a physicist who, with William Ramsay, discovered argon, an achievement for which he earned the Nobel Prize for Physics in 1904. He also discovered the now called Rayleigh scattering, which can be used to explain why the sky is blue. Rayleighs textbook, The Theory of Sound, is referred to by acoustic engineers today. John William Strutt, of Terling Place Essex, suffered from frailty and he attended Harrow School, before going on to the University of Cambridge in 1861 where he studied mathematics at Trinity College, Cambridge. He obtained a Bachelor of Arts degree in 1865, and a Master of Arts in 1868 and he was subsequently elected to a Fellowship of Trinity. He held the post until his marriage to Evelyn Balfour, daughter of James Maitland Balfour and he had three sons with her. In 1873, on the death of his father, John Strutt, 2nd Baron Rayleigh and he was the second Cavendish Professor of Physics at the University of Cambridge, from 1879 to 1884. He first described dynamic soaring by seabirds in 1883, in the British journal Nature, from 1887 to 1905 he was Professor of Natural Philosophy at the Royal Institution. Around the year 1900 Lord Rayleigh developed the theory of human sound localisation using two binaural cues, interaural phase difference and interaural level difference. The theory posits that we use two primary cues for sound lateralisation, using the difference in the phases of sinusoidal components of the sound, in 1919, Rayleigh served as President of the Society for Psychical Research. The rayl unit of acoustic impedance is named after him, as an advocate that simplicity and theory be part of the scientific method, Lord Rayleigh argued for the principle of similitude. Lord Rayleigh was elected Fellow of the Royal Society on 12 June 1873, from time to time Lord Rayleigh participated in the House of Lords, however, he spoke up only if politics attempted to become involved in science. He died on 30 June 1919, in Witham, Essex and he was succeeded, as the 4th Lord Rayleigh, by his son Robert John Strutt, another well-known physicist. Lord Rayleigh was buried in the graveyard of All Saints Church in Terling in Essex, though he did not write about the relationship of science and religion, he retained a personal interest in spiritual matters. The Secretary to the Press suggested with many apologies that the reader might suppose that I was the Lord, still, he kept his wish and the quotation was printed in the five-volume collection of scientific papers. What is more, I think that Christ and indeed other spiritually gifted men see further and truer than I do, Lord Rayleigh was the president of the SPR in 1919. He gave an address the year of his death but did not come to any definite conclusions. Craters on Mars and the Moon are named in his honour as well as a type of surface wave known as a Rayleigh wave, the asteroid 22740 Rayleigh was named in his honour on 1 June 2007
36.
Wallace Clement Sabine
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Wallace Clement Sabine was an American physicist who founded the field of architectural acoustics. He graduated from Ohio State University in 1886 at the age of 18 before joining Harvard University for graduate study, Sabine was architectural acoustician of Bostons Symphony Hall, widely considered one of the two or three best concert halls in the world for its acoustics. Sabines career is the story of the birth of the field of architectural acoustics. In 1895, acoustically improving the Fogg Lecture Hall, part of the recently constructed Fogg Art Museum, was considered a task by the senior staff of the physics department at Harvard. The assignment was passed down until it landed on the shoulders of a physics professor. Although considered a popular lecturer by the students, Sabine had never received his Ph. D. Sabine tackled the problem by trying to determine what made the Fogg Lecture Hall different from other, acoustically acceptable facilities. In particular, the Sanders Theater was considered acoustically excellent, for the next several years, Sabine and a group of assistants spent each night moving materials between the two lecture halls and testing the acoustics. On some nights they would borrow hundreds of seat cushions from the Sanders Theater, once the measurements were taken and before morning arrived, everything was quickly replaced in both lecture halls, in order to be ready for classes the next day. His formula, if all units are SI, is T = V A ⋅0.25 seconds, while optimal lecture hall acoustics featured reverberation times of slightly under 1 second. Regarding the Fogg Museum lecture room, Sabine noted that a word remained audible for about 5.5 seconds. Listeners thus contended with a high degree of resonance and echo. Using what he discovered, Sabine deployed sound absorbing materials throughout the Fogg Lecture Hall to cut its reverberation time and reduce the echo effect. This accomplishment cemented Wallace Sabines career, and led to his hiring as the consultant for Bostons Symphony Hall. His acoustic design was successful and Symphony Hall is generally considered one of the best symphony halls in the world, the unit of sound absorption, the sabin, was named in his honor. F. Sanders Theatre Wallace Clement Sabine at the Mathematics Genealogy Project
37.
Sound recording and reproduction
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Sound recording and reproduction is an electrical, mechanical, electronic, or digital inscription and re-creation of sound waves, such as spoken voice, singing, instrumental music, or sound effects. The two main classes of sound recording technology are analog recording and digital recording, prior to the development of analog recording, there were mechanical systems for reproducing instrumental music, such as wind-up music boxes and later, in the late 19th century, player pianos. Analog sound reproduction is the process, with a bigger loudspeaker diaphragm causing changes to atmospheric pressure to form acoustic sound waves. Digital recording and reproduction converts the sound signal picked up by the microphone to a digital form by the process of digitization. This lets the audio data be stored and transmitted by a variety of media. Whereas successive copies of an analog recording tend to degrade in quality, as noise is added. A digital audio signal must be reconverted to analog form during playback before it is amplified and connected to a loudspeaker to produce sound, long before sound was first recorded on cylinders or records, music was recorded—first by written music notation, then also by mechanical devices. Fowler, this. cylinder with raised pins on the surface remained the device to produce and reproduce music mechanically until the second half of the nineteenth century. The Banu Musa brothers also invented an automatic flute player, which appears to have been the first programmable machine, according to Fowler, the automata were a robot band that performed. more than fifty facial and body actions during each musical selection. In the 14th century, Flanders introduced a mechanical bell-ringer controlled by a rotating cylinder, similar designs appeared in barrel organs, musical clocks, barrel pianos, and musical boxes. A music box is a musical instrument that produces sounds by the use of a set of pins placed on a revolving cylinder or disc so as to pluck the tuned teeth of a steel comb. They were developed from musical snuff boxes of the 18th century, some of the more complex boxes also have a tiny drum and/or bells, in addition to the metal comb. The fairground organ, developed in 1892, used a system of accordion-folded punched cardboard books, the player piano, first demonstrated in 1876, used a punched paper scroll that could store an long piece of music. The most sophisticated of the rolls were hand-played, meaning that the roll represented the actual performance of an individual. This technology to record a live performance onto a piano roll was not developed until 1904, piano rolls were in continuous mass production from 1896 to 2008. A1908 U. S. Supreme Court copyright case noted that, in 1902 alone, the use of piano rolls began to decline in the 1920s although one type is still being made today. The first device that could record actual sounds as they passed through the air was the phonautograph, the earliest known recordings of the human voice are phonautograph recordings, called phonautograms, made in 1857. They consist of sheets of paper with sound-wave-modulated white lines created by a stylus that cut through a coating of soot as the paper was passed under it
38.
Jay Pritzker Pavilion
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Jay Pritzker Pavilion, also known as Pritzker Pavilion or Pritzker Music Pavilion, is a bandshell in Millennium Park in the Loop community area of Chicago in Cook County, Illinois, United States. It is located on the side of Randolph Street and east of the Chicago Landmark Historic Michigan Boulevard District. The pavilion was named after Jay Pritzker, whose family is known for owning Hyatt Hotels and it also hosts a wide range of music series and annual performing arts events. Performers ranging from rock bands to classical musicians and opera singers have appeared at the pavilion. All rehearsals at the pavilion are open to the public, trained guides are available for the music festival rehearsals, Millennium Park is part of the larger Grant Park. The pavilion, which has a capacity of 11,000, is Grant Parks small event outdoor performing venue, and complements Petrillo Music Shell. Pritzker Pavilion is built atop the Harris Theater for Music and Dance. Initially the pavilions lawn seats were free for all concerts, the construction of the pavilion created a legal controversy, given that there are historic limitations on the height of buildings in Grant Park. To avoid these restrictions, the city classifies the bandshell as a work of art rather than a building. With several design and assembly problems, the plans were revised over time, with features eliminated. In the end, the venue was designed with a large fixed seating area, a Great Lawn, a trellis network to support the sound system. It features a system with an acoustic design that replicates an indoor concert hall sound experience. The Jay Pritzker Pavilion is a home for the Grant Park Music Festival, lying between Lake Michigan to the east and the Loop to the west, Grant Park has been Chicagos front yard since the mid-19th century. In 2007, Millennium Park trailed only Navy Pier as a Chicago tourist attraction, when the city first determined that a new pavilion should be built, the commission was supposed to go to Skidmore, Owings and Merrill. The original pavilion design was more modest than the structure that was eventually built, with a smaller shell structure. However, two led to the cancellation of the original plans. First, the projects scope changed as a result of funds raised by John H. Bryan. The second factor was the intervention of the Pritzker family as potential donors, unimpressed with the pavilions original design, Cindy Pritzker mandated that Frank Gehry be involved in its re-design
39.
Sound reinforcement system
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In both cases, these systems reinforce sound to make it louder or distribute it to a wider audience. Some audio engineers and others in the audio industry disagree over whether these audio systems should be called sound reinforcement systems or PA systems. Distinguishing between the two terms by technology and capability is common, while others distinguish by intended use, in some regions or markets, the distinction between the two terms is important, though the terms are considered interchangeable in many professional circles. These primary parts involve varying amounts of components to achieve the desired goal of reinforcing and clarifying the sound to the audience, performers. These signal inputs are plugged into the input jacks of a thick multicore cable, the snake then routes the signals of all of the inputs to either one or two mixing consoles. In these cases, at least two audio engineers are required, one to do the FOH Main mix and one to do the Monitor mix, once the signal arrives at a channel on the mixing console, this signal can be adjusted in many ways by the sound engineer. A signal can be equalized, compressed, or panned before being routed to an output bus. The signal may also be routed into an effects processor, such as a reverb effect, which outputs a wet version of the signal. Many electronic effects units are used in sound reinforcement systems, including digital delay, some concerts use pitch correction effects, which electronically correct any out-of-tune singing. A group of signals may be routed through a bus before being sent to the main bus to allow the engineer to control the levels of several related signals at once. A bus can often be processed just like an input channel. The mix of all the different signals and channels to the master faders on the console. Mixing consoles also have additional sends, also referred to as auxes or aux sends, on each channel so that a different mix can be created. One usage for aux sends is to create a mix of the vocal, another use of an aux send is to select varying amounts of certain channels, and then route these signals to an effects processor. A common example of the use of aux sends is to send all of the vocal signals from a rock band through a reverb effect. While reverb is usually added to vocals in the mix, it is not usually added to electric bass. The next step in the path generally depends on the size of the system in place. In smaller systems, the outputs are often sent to an additional equalizer, or directly to a power amplifier
40.
Acoustic wave equation
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In physics, the acoustic wave equation governs the propagation of acoustic waves through a material medium. The form of the equation is a second order differential equation. The equation describes the evolution of acoustic pressure p or particle velocity u as a function of position x, a simplified form of the equation describes acoustic waves in only one spatial dimension, while a more general form describes waves in three dimensions. The acoustic wave equation was an important point of reference in the development of the wave equation in Kelvins master class at Johns Hopkins University. For lossy media, more intricate models need to be applied in order to take into account frequency-dependent attenuation, such models include acoustic wave equations that incorporate fractional derivative terms, see also the acoustic attenuation article or the survey paper. Provided that the c is a constant, not dependent on frequency. This may be pictured as the superposition of two waveforms of arbitrary profile, one travelling up the x-axis and the other down the x-axis at the speed c. The particular case of a wave travelling in one direction is obtained by choosing either f or g to be a sinusoid. Where ω is the frequency of the wave and k is its wave number. The wave equation can be developed from the linearized one-dimensional continuity equation, the linearized one-dimensional force equation and the equation of state. The equation of state P V = n R T In an adiabatic process, breaking the pressure and density into their mean and total components and noting that C = ∂ P ∂ ρ, P − P0 =. The adiabatic bulk modulus for a fluid is defined as B = ρ0 a d i a b a t i c which gives the result P − P0 = B ρ − ρ0 ρ0. Condensation, s, is defined as the change in density for an ambient fluid density. S = ρ − ρ0 ρ0 The linearized equation of state becomes p = B s where p is the acoustic pressure, the continuity equation in one dimension is ∂ ρ ∂ t + ∂ ∂ x =0. Where u is the velocity of the fluid. Again the equation must be linearized and the split into mean. Linearizing the variables, u + ∂ ∂ x =0, rearranging and neglecting small terms, the resultant equation becomes the linearized one-dimensional Euler Equation, ρ0 ∂ u ∂ t + ∂ p ∂ x =0. Multiplying the first by ρ0, subtracting the two, and substituting the linearized equation of state, − ρ0 B ∂2 p ∂ t 2 + ∂2 p ∂ x 2 =0
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Earthquake
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An earthquake is the shaking of the surface of the Earth, resulting from the sudden release of energy in the Earths lithosphere that creates seismic waves. Earthquakes can range in size from those that are so weak that they cannot be felt to those violent enough to people around. The seismicity or seismic activity of an area refers to the frequency, type, Earthquakes are measured using measurements from seismometers. The moment magnitude is the most common scale on which earthquakes larger than approximately 5 are reported for the entire globe and these two scales are numerically similar over their range of validity. Magnitude 3 or lower earthquakes are mostly imperceptible or weak and magnitude 7 and over potentially cause damage over larger areas. The largest earthquakes in historic times have been of magnitude slightly over 9, intensity of shaking is measured on the modified Mercalli scale. The shallower an earthquake, the damage to structures it causes. At the Earths surface, earthquakes manifest themselves by shaking and sometimes displacement of the ground, when the epicenter of a large earthquake is located offshore, the seabed may be displaced sufficiently to cause a tsunami. Earthquakes can also trigger landslides, and occasionally volcanic activity, in its most general sense, the word earthquake is used to describe any seismic event — whether natural or caused by humans — that generates seismic waves. Earthquakes are caused mostly by rupture of faults, but also by other events such as volcanic activity, landslides, mine blasts. An earthquakes point of rupture is called its focus or hypocenter. The epicenter is the point at ground level directly above the hypocenter, tectonic earthquakes occur anywhere in the earth where there is sufficient stored elastic strain energy to drive fracture propagation along a fault plane. The sides of a fault move past each other smoothly and aseismically only if there are no irregularities or asperities along the surface that increase the frictional resistance. Most fault surfaces do have such asperities and this leads to a form of stick-slip behavior, once the fault has locked, continued relative motion between the plates leads to increasing stress and therefore, stored strain energy in the volume around the fault surface. This continues until the stress has risen sufficiently to break through the asperity, suddenly allowing sliding over the portion of the fault. This energy is released as a combination of radiated elastic strain seismic waves, frictional heating of the fault surface and this process of gradual build-up of strain and stress punctuated by occasional sudden earthquake failure is referred to as the elastic-rebound theory. It is estimated that only 10 percent or less of a total energy is radiated as seismic energy. Most of the energy is used to power the earthquake fracture growth or is converted into heat generated by friction
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