Isotopes are variants of a particular chemical element which differ in neutron number. All isotopes of an element have the same number of protons in each atom. The number of protons within the nucleus is called atomic number and is equal to the number of electrons in the neutral atom. Each atomic number identifies a specific element, but not the isotope, the number of nucleons in the nucleus is the atoms mass number, and each isotope of a given element has a different mass number. For example, carbon-12, carbon-13 and carbon-14 are three isotopes of the element carbon with mass numbers 12,13 and 14 respectively. The atomic number of carbon is 6, which means that carbon atom has 6 protons. Nuclide refers to a rather than to an atom. Identical nuclei belong to one nuclide, for each nucleus of the carbon-13 nuclide is composed of 6 protons and 7 neutrons. The nuclide concept emphasizes nuclear properties over chemical properties, whereas the isotope concept emphasizes chemical over nuclear, the neutron number has large effects on nuclear properties, but its effect on chemical properties is negligible for most elements.
Because isotope is the term, it is better known than nuclide. An isotope and/or nuclide is specified by the name of the particular element followed by a hyphen, when a chemical symbol is used, e. g. C for carbon, standard notation is to indicate the number with a superscript at the upper left of the chemical symbol. Because the atomic number is given by the element symbol, it is common to only the mass number in the superscript. The letter m is sometimes appended after the number to indicate a nuclear isomer. For example, 14C is a form of carbon, whereas 12C. There are about 339 naturally occurring nuclides on Earth, of which 286 are primordial nuclides, primordial nuclides include 32 nuclides with very long half-lives and 254 that are formally considered as stable nuclides, because they have not been observed to decay. In most cases, for reasons, if an element has stable isotopes. Theory predicts that many apparently stable isotopes/nuclides are radioactive, with extremely long half-lives, of the 254 nuclides never observed to decay, only 90 of these are theoretically stable to all known forms of decay
The cerebral cortex is the outer layer of neural tissue of the cerebrum of the brain, in humans and other mammals. It is separated into two cortices, by the fissure that divides the cerebrum into the left and right cerebral hemispheres. The two hemispheres are joined beneath the cortex by the corpus callosum, the cerebral cortex plays a key role in memory, perception, thought and consciousness. In large mammals, the cortex is folded, giving a much greater surface area in the confined volume of the skull. A fold or ridge in the cortex is termed a gyrus, in the human brain more than two-thirds of the cerebral cortex is buried in the sulci. The human cerebral cortex is 2 to 4 millimetres thick, the cerebral cortex is composed of gray matter, consisting mainly of cell bodies and capillaries. It contrasts with the white matter, consisting mainly of the white myelinated sheaths of neuronal axons. The most recent part of the cortex to develop in the evolutionary history of mammals is the neocortex.
Neurons in various layers connect vertically to form small microcircuits, called cortical columns, Different neocortical regions known as Brodmann areas are distinguished by variations in their cytoarchitectonics and functional roles in sensation and behavior. The different cortical layers each contain a distribution of neuronal cell types. There are direct connections between different cortical areas and indirect connections via the thalamus, for example, one of the clearest examples of cortical layering is the stria of Gennari in the primary visual cortex. This is a band of tissue that can be observed with the naked eye in the fundus of the calcarine sulcus of the occipital lobe. The Stria of Gennari is composed of axons bringing visual information from the thalamus into layer four of the visual cortex, during development Cajal-Retzius and subpial granular layer cells are present in this layer. Also, some spiny stellate cells can be found here, inputs to the apical tufts are thought to be crucial for the ‘‘feedback’’ interactions in the cerebral cortex involved in associative learning and attention.
Layer II, the granular layer, contains small pyramidal neurons. Layer V, the internal pyramidal layer, contains large pyramidal neurons which give rise to axons leaving the cortex and that is, layer VI neurons from one cortical column connect with thalamus neurons that provide input to the same cortical column. These connections are both excitatory and inhibitory, neurons send excitatory fibers to neurons in the thalamus and send collaterals to the thalamic reticular nucleus that inhibit these same thalamus neurons or ones adjacent to them. One theory is that because the output is reduced by cholinergic input to the cerebral cortex
The primary auditory cortex is the part of the temporal lobe that processes auditory information in humans and other vertebrates. It is a part of the system, performing basic. Unilateral destruction results in hearing loss, whereas bilateral destruction results in cortical deafness. The auditory cortex was previously subdivided into primary and secondary projection areas, the modern divisions of the auditory cortex are the core, the belt, and the parabelt. The belt is the area surrounding the core, the parabelt is adjacent to the lateral side of the belt. Besides receiving input from the ears via lower parts of the auditory system, data about the auditory cortex has been obtained through studies in rodents, cats and other animals. In humans, the structure and function of the cortex has been studied using functional magnetic resonance imaging, electroencephalography. Like many areas in the neocortex, the properties of the adult primary auditory cortex are highly dependent on the sounds encountered early in life.
This has been best studied using models, especially cats and rats. In the rat, exposure to a single frequency during postnatal day 11 to 13 can cause a 2-fold expansion in the representation of that frequency in A1. Importantly, the change is persistent, in that it lasts throughout the animals life, as with other primary sensory cortical areas, auditory sensations reach perception only if received and processed by a cortical area. Neurons in the cortex are organized according to the frequency of sound to which they respond best. Neurons at one end of the cortex respond best to low frequencies. There are multiple areas, which can be distinguished anatomically. The purpose of this map is unknown, and is likely to reflect the fact that the cochlea is arranged according to sound frequency. The auditory cortex is involved in such as identifying and segregating auditory objects. Human brain scans have indicated that a bit of this brain region is active when trying to identify musical pitch. Individual cells consistently get excited by sounds at frequencies, or multiples of that frequency
Supplementary motor area
The supplementary motor area is a part of the primate cerebral cortex that contributes to the control of movement. It is located on the surface of the hemisphere just in front of the primary motor cortex leg representation. In monkeys the SMA contains a map of the body. In humans the body map is not apparent, neurons in the SMA project directly to the spinal cord and may play a role in the direct control of movement. All of these functions remain hypotheses. The precise role of the SMA is not yet known and it may serve multiple roles, for the discovery of the SMA and its relationship to other motor cortical areas, see the main article on the motor cortex. At least six areas are now recognized within the region once defined as the SMA. These subdivisions have been studied most extensively in the monkey brain, the most anterior portion is now commonly termed pre-SMA. It has sparse or no connections to the cord or the primary motor cortex and has extensive connectivity with prefrontal areas. The supplementary eye field is an anterior portion of the SMA that.
The functions of the motor areas have not yet been systematically studied. SMA proper in monkeys has now been confined to a region on the crown of the hemisphere and extending partly onto the medial wall, SMA proper projects directly to the spinal cord and therefore is one of the primary output areas of the cortical motor system. Recently, Zhang et al. investigated the functional subdivisions of the medial SFC on the basis of whole-brain connectivity characterized from a large resting-state fMRI data set. Other than replicating the boundaries between SMA and preSMA, the current results support a functional difference between the posterior and anterior preSMA, in contrast to the posterior preSMA, the anterior preSMA is connected with most of the prefrontal but not somatomotor areas. Penfield and Welch in 1951 first described SMA in the monkey brain and colleagues in 1952 confirmed SMA in the monkey brain, describing it as a rough somatotopic map with the legs in a posterior location and the face in an anterior location.
The representations of different body parts were found to overlap extensively, stimulation of many sites evoked bilateral movements and sometimes movements of all four limbs. This overlapping somatotopic map in SMA was confirmed by many others, the data, tend not to support an exclusive role of SMA in any one of these functions. Indeed, SMA is demonstrably active during non-sequential, for human voluntary movement the role of the SMA has been elucidated, Its activity generates the early component of the Bereitschaftspotential or readiness potential BP1 or BPearly
The cerebellum is a major feature of the hindbrain of all vertebrates. Although usually smaller than the cerebrum, in animals such as the mormyrid fishes it may be as large as or even larger. Cerebellar damage produces disorders in fine movement, posture, the human cerebellum has the appearance of a separate structure attached to the bottom of the brain, tucked underneath the cerebral hemispheres. Its cortical surface is covered with finely spaced parallel grooves, in striking contrast to the broad irregular convolutions of the cerebral cortex and these parallel grooves conceal the fact that the cerebellar cortex is actually a continuous thin layer of tissue tightly folded in the style of an accordion. Within this thin layer are several types of neurons with a regular arrangement. In addition to its role in motor control, the cerebellum is necessary for several types of motor learning. Several theoretical models have developed to explain sensorimotor calibration in terms of synaptic plasticity within the cerebellum.
The basic concept of the Marr–Albus theory is that the climbing fiber serves as a teaching signal, observations of long-term depression in parallel fiber inputs have provided support for theories of this type, but their validity remains controversial. At the level of gross anatomy, the cerebellum consists of a tightly folded layer of cortex, with white matter underneath, four deep cerebellar nuclei are embedded in the white matter. Each part of the consists of the same small set of neuronal elements. At an intermediate level, the cerebellum and its structures can be separated into several hundred or thousand independently functioning modules called microzones or microcompartments. The cerebellum is located in the posterior cranial fossa, the fourth ventricle and medulla are in front of the cerebellum. It is separated from the overlying cerebrum by a layer of dura mater. Anatomists classify the cerebellum as part of the metencephalon, which includes the pons. Like the cerebral cortex, the cerebellum is divided into two hemispheres, it contains a narrow midline zone. A set of large folds is, by convention, used to divide the structure into 10 smaller lobules.
Because of its number of tiny granule cells, the cerebellum contains more neurons than the total from the rest of the brain. The number of neurons in the cerebellum is related to the number of neurons in the neocortex, there are about 3.6 times as many neurons in the cerebellum as in the neocortex, a ratio that is conserved across many different mammalian species
International Standard Book Number
The International Standard Book Number is a unique numeric commercial book identifier. An ISBN is assigned to each edition and variation of a book, for example, an e-book, a paperback and a hardcover edition of the same book would each have a different ISBN. The ISBN is 13 digits long if assigned on or after 1 January 2007, the method of assigning an ISBN is nation-based and varies from country to country, often depending on how large the publishing industry is within a country. The initial ISBN configuration of recognition was generated in 1967 based upon the 9-digit Standard Book Numbering created in 1966, the 10-digit ISBN format was developed by the International Organization for Standardization and was published in 1970 as international standard ISO2108. Occasionally, a book may appear without a printed ISBN if it is printed privately or the author does not follow the usual ISBN procedure, this can be rectified later. Another identifier, the International Standard Serial Number, identifies periodical publications such as magazines, the ISBN configuration of recognition was generated in 1967 in the United Kingdom by David Whitaker and in 1968 in the US by Emery Koltay.
The 10-digit ISBN format was developed by the International Organization for Standardization and was published in 1970 as international standard ISO2108, the United Kingdom continued to use the 9-digit SBN code until 1974. The ISO on-line facility only refers back to 1978, an SBN may be converted to an ISBN by prefixing the digit 0. For example, the edition of Mr. J. G. Reeder Returns, published by Hodder in 1965, has SBN340013818 -340 indicating the publisher,01381 their serial number. This can be converted to ISBN 0-340-01381-8, the check digit does not need to be re-calculated, since 1 January 2007, ISBNs have contained 13 digits, a format that is compatible with Bookland European Article Number EAN-13s. An ISBN is assigned to each edition and variation of a book, for example, an ebook, a paperback, and a hardcover edition of the same book would each have a different ISBN. The ISBN is 13 digits long if assigned on or after 1 January 2007, a 13-digit ISBN can be separated into its parts, and when this is done it is customary to separate the parts with hyphens or spaces.
Separating the parts of a 10-digit ISBN is done with either hyphens or spaces, figuring out how to correctly separate a given ISBN number is complicated, because most of the parts do not use a fixed number of digits. ISBN issuance is country-specific, in that ISBNs are issued by the ISBN registration agency that is responsible for country or territory regardless of the publication language. Some ISBN registration agencies are based in national libraries or within ministries of culture, in other cases, the ISBN registration service is provided by organisations such as bibliographic data providers that are not government funded. In Canada, ISBNs are issued at no cost with the purpose of encouraging Canadian culture. In the United Kingdom, United States, and some countries, where the service is provided by non-government-funded organisations. Australia, ISBNs are issued by the library services agency Thorpe-Bowker
Functional magnetic resonance imaging
Functional magnetic resonance imaging or functional MRI is a functional neuroimaging procedure using MRI technology that measures brain activity by detecting changes associated with blood flow. This technique relies on the fact that blood flow and neuronal activation are coupled. When an area of the brain is in use, blood flow to that increases. The primary form of fMRI uses the blood-oxygen-level dependent contrast, discovered by Seiji Ogawa and this measure is frequently corrupted by noise from various sources and hence statistical procedures are used to extract the underlying signal. The resulting brain activation can be presented graphically by color-coding the strength of activation across the brain or the specific region studied, the technique can localize activity to within millimeters but, using standard techniques, no better than within a window of a few seconds. Other methods of obtaining contrast are arterial spin labeling and diffusion MRI, the latter procedure is similar to BOLD fMRI but provides contrast based on the magnitude of diffusion of water molecules in the brain. FMRI is used both in the world, and to a lesser extent, in the clinical world.
It can be combined and complemented with other measures of brain physiology such as EEG, newer methods which improve both spatial and time resolution are being researched, and these largely use biomarkers other than the BOLD signal. Some companies have developed products such as lie detectors based on fMRI techniques. The fMRI concept builds on the earlier MRI scanning technology and the discovery of properties of oxygen-rich blood, MRI brain scans use a strong, static magnetic field to align nuclei in the brain region being studied. Another magnetic field, the gradient field, is applied to spatially locate different nuclei. Finally, a pulse is played to kick the nuclei to higher magnetization levels. When the RF field is removed, the nuclei go back to their states. MRI thus provides a static view of brain matter. The central thrust behind fMRI was to extend MRI to capture changes in the brain caused by neuronal activity. Differences in magnetic properties between arterial and venous blood provided this link, since the 1890s it has been known that changes in blood flow and blood oxygenation in the brain are closely linked to neural activity.
When neurons become active, local blood flow to those regions increases. This rises to a peak over 4–6 seconds, before falling back to the original level, oxygen is carried by the hemoglobin molecule in red blood cells
A metronome is a device that produces an audible beat—a click or other sound—at regular intervals that the user can set in beats per minute. Musicians use the device to practice playing to a regular pulse, metronomes typically include synchronized visual motion. A kind of metronome was among the inventions of Andalusian polymath Abbas ibn Firnas, in 1815 Johann Maelzel patented it as a tool for musicians, under the title Instrument/Machine for the Improvement of all Musical Performance, called Metronome. Musicians practice with metronomes to improve their timing, especially the ability to stick to a tempo, Metronome practice helps internalize a clear sense of timing and tempo. Composers often use a metronome as a standard tempo reference—and may play or sing their work to the metronome to derive beats per minute if they want to indicate that in a composition, when interpreting emotion and other qualities in music, performers seldom play exactly on every beat. Typically, every beat of an expressive performance doesnt align exactly with each click of a metronome.
This has led some musicians to use of a metronome. Some go as far as to suggest that musicians shouldnt use metronomes at all and those in favour of metronome use understand this as a criticism of metronome technique as commonly practiced by musicians, rather than criticism of the tool as such. Their response has been to better methods of metronome technique to address the various issues raised by the critics. These techniques however arent widely known by musicians generally, including critics of metronome use. Metronome technique has developed, but the body of published information is small—so some critics may think that metronome technique consists only of playing music along with the metronome. In his book, Metronome Techniques, Frederick Franz maintains that those who disparage metronomes as making you mechanical misunderstand their proper use, the word metronome first appeared in English c.1815 and is Greek in origin, metron measure and nomos regulating, law. According to Lynn Townsend White, Jr.
the Andalusian inventor, Abbas Ibn Firnas, galileo Galilei first studied and discovered concepts involving the pendulum in the late 16th and early 17th centuries. To get the pulse with this kind of visual devices. The more familiar mechanical musical chronometer was invented by Dietrich Nikolaus Winkel in Amsterdam in 1814, the original text of Maelzels patent in England can be downloaded. Ludwig van Beethoven was maybe the first notable composer to indicate specific metronome markings in his music, musicians practice playing to metronomes to develop and maintain a sense of timing and tempo. For example, a musician fighting a tendency to speed up play a phrase repeatedly while slightly slowing the BPM setting each time. Even pieces that do not require a constant tempo sometimes provide a BPM marking to indicate the general tempo
Pitch can be determined only in sounds that have a frequency that is clear and stable enough to distinguish from noise. Pitch is a major attribute of musical tones, along with duration, loudness. Pitch may be quantified as a frequency, but pitch is not a purely objective physical property, Pitch is an auditory sensation in which a listener assigns musical tones to relative positions on a musical scale based primarily on their perception of the frequency of vibration. Pitch is closely related to frequency, but the two are not equivalent, frequency is an objective, scientific attribute that can be measured. Pitch is each persons subjective perception of a wave, which cannot be directly measured. However, this not necessarily mean that most people wont agree on which notes are higher and lower. Sound waves themselves do not have pitch, but their oscillations can be measured to obtain a frequency and it takes a sentient mind to map the internal quality of pitch. However, pitches are usually associated with, and thus quantified as frequencies in cycles per second, or hertz, by comparing sounds with pure tones and aperiodic sound waves can often be assigned a pitch by this method.
According to the American National Standards Institute, pitch is the attribute of sound according to which sounds can be ordered on a scale from low to high. That is, high pitch means very rapid oscillation, and low pitch corresponds to slower oscillation, despite that, the idiom relating vertical height to sound pitch is shared by most languages. At least in English, it is just one of many deep conceptual metaphors that involve up/down, the exact etymological history of the musical sense of high and low pitch is still unclear. There is evidence that humans do actually perceive that the source of a sound is slightly higher or lower in vertical space when the frequency is increased or reduced. The pitch of tones can be ambiguous, meaning that two or more different pitches can be perceived, depending upon the observer. In a situation like this, the percept at 200 Hz is commonly referred to as the missing fundamental, Pitch depends to a lesser degree on the sound pressure level of the tone, especially at frequencies below 1,000 Hz and above 2,000 Hz.
The pitch of lower tones gets lower as sound pressure increases, for instance, a tone of 200 Hz that is very loud seems one semitone lower in pitch than if it is just barely audible. Above 2,000 Hz, the pitch gets higher as the sound gets louder, theories of pitch perception try to explain how the physical sound and specific physiology of the auditory system work together to yield the experience of pitch. In general, pitch perception theories can be divided into place coding, place theory holds that the perception of pitch is determined by the place of maximum excitation on the basilar membrane. However, a purely place-based theory cannot account for the accuracy of pitch perception in the low, temporal theories offer an alternative that appeals to the temporal structure of action potentials, mostly the phase-locking and mode-locking of action potentials to frequencies in a stimulus