Luminescence is spontaneous emission of light by a substance not resulting from heat. It can be caused by electrical energy, subatomic motions or stress on a crystal; this distinguishes luminescence from incandescence, light emitted by a substance as a result of heating. Radioactivity was thought of as a form of "radio-luminescence", although it is today considered to be separate since it involves more than electromagnetic radiation; the dials, hands and signs of aviation and navigational instruments and markings are coated with luminescent materials in a process known as "luminising". The following are types of luminescence: Chemiluminescence, the emission of light as a result of a chemical reaction Bioluminescence, a result of biochemical reactions in a living organism Electrochemiluminescence, a result of an electrochemical reaction Lyoluminescence, a result of dissolving a solid in a liquid solvent Candoluminescence, is light emitted by certain materials at elevated temperatures, which differs from the blackbody emission expected at the temperature in question.
Crystalloluminescence, produced during crystallization Electroluminescence, a result of an electric current passed through a substance Cathodoluminescence, a result of a luminescent material being struck by electrons Mechanoluminescence, a result of a mechanical action on a solid Triboluminescence, generated when bonds in a material are broken when that material is scratched, crushed, or rubbed Fractoluminescence, generated when bonds in certain crystals are broken by fractures Piezoluminescence, produced by the action of pressure on certain solids Sonoluminescence, a result of imploding bubbles in a liquid when excited by sound Photoluminescence, a result of absorption of photons Fluorescence, photoluminescence as a result of singlet–singlet electronic relaxation Phosphorescence, photoluminescence as a result of triplet–singlet electronic relaxation Raman emission, photoluminescence as a result of inelastic light scattering, Radioluminescence, a result of bombardment by ionizing radiation Thermoluminescence, the re-emission of absorbed energy when a substance is heatedCryoluminescence, the emission of light when an object is cooled Light-emitting diodes emit light via electro-luminescence.
Phosphors, materials that emit light when irradiated by higher-energy electromagnetic radiation or particle radiation Phosphor thermometry, measuring temperature using phosphorescence Thermoluminescence dating Thermoluminescent dosimeter Non-disruptive observation of processes within a cell. Luminescence occurs in some minerals when they are exposed to low-powered sources of ultraviolet or infrared electromagnetic radiation, at atmospheric pressure and atmospheric temperatures; this property of these minerals can be used during the process of mineral identification at rock outcrops in the field, or in the laboratory. List of light sources Fluorophores.org A database of luminescent dyes
In physics, electromagnetic radiation refers to the waves of the electromagnetic field, propagating through space, carrying electromagnetic radiant energy. It includes radio waves, infrared, ultraviolet, X-rays, gamma rays. Classically, electromagnetic radiation consists of electromagnetic waves, which are synchronized oscillations of electric and magnetic fields that propagate at the speed of light, which, in a vacuum, is denoted c. In homogeneous, isotropic media, the oscillations of the two fields are perpendicular to each other and perpendicular to the direction of energy and wave propagation, forming a transverse wave; the wavefront of electromagnetic waves emitted from a point source is a sphere. The position of an electromagnetic wave within the electromagnetic spectrum can be characterized by either its frequency of oscillation or its wavelength. Electromagnetic waves of different frequency are called by different names since they have different sources and effects on matter. In order of increasing frequency and decreasing wavelength these are: radio waves, infrared radiation, visible light, ultraviolet radiation, X-rays and gamma rays.
Electromagnetic waves are emitted by electrically charged particles undergoing acceleration, these waves can subsequently interact with other charged particles, exerting force on them. EM waves carry energy and angular momentum away from their source particle and can impart those quantities to matter with which they interact. Electromagnetic radiation is associated with those EM waves that are free to propagate themselves without the continuing influence of the moving charges that produced them, because they have achieved sufficient distance from those charges. Thus, EMR is sometimes referred to as the far field. In this language, the near field refers to EM fields near the charges and current that directly produced them electromagnetic induction and electrostatic induction phenomena. In quantum mechanics, an alternate way of viewing EMR is that it consists of photons, uncharged elementary particles with zero rest mass which are the quanta of the electromagnetic force, responsible for all electromagnetic interactions.
Quantum electrodynamics is the theory of. Quantum effects provide additional sources of EMR, such as the transition of electrons to lower energy levels in an atom and black-body radiation; the energy of an individual photon is greater for photons of higher frequency. This relationship is given by Planck's equation E = hν, where E is the energy per photon, ν is the frequency of the photon, h is Planck's constant. A single gamma ray photon, for example, might carry ~100,000 times the energy of a single photon of visible light; the effects of EMR upon chemical compounds and biological organisms depend both upon the radiation's power and its frequency. EMR of visible or lower frequencies is called non-ionizing radiation, because its photons do not individually have enough energy to ionize atoms or molecules or break chemical bonds; the effects of these radiations on chemical systems and living tissue are caused by heating effects from the combined energy transfer of many photons. In contrast, high frequency ultraviolet, X-rays and gamma rays are called ionizing radiation, since individual photons of such high frequency have enough energy to ionize molecules or break chemical bonds.
These radiations have the ability to cause chemical reactions and damage living cells beyond that resulting from simple heating, can be a health hazard. James Clerk Maxwell derived a wave form of the electric and magnetic equations, thus uncovering the wave-like nature of electric and magnetic fields and their symmetry; because the speed of EM waves predicted by the wave equation coincided with the measured speed of light, Maxwell concluded that light itself is an EM wave. Maxwell's equations were confirmed by Heinrich Hertz through experiments with radio waves. According to Maxwell's equations, a spatially varying electric field is always associated with a magnetic field that changes over time. A spatially varying magnetic field is associated with specific changes over time in the electric field. In an electromagnetic wave, the changes in the electric field are always accompanied by a wave in the magnetic field in one direction, vice versa; this relationship between the two occurs without either type of field causing the other.
In fact, magnetic fields can be viewed as electric fields in another frame of reference, electric fields can be viewed as magnetic fields in another frame of reference, but they have equal significance as physics is the same in all frames of reference, so the close relationship between space and time changes here is more than an analogy. Together, these fields form a propagating electromagnetic wave, which moves out into space and need never again interact with the source; the distant EM field formed in this way by the acceleration of a charge carries energy with it that "radiates" away through space, hence the term. Maxwell's equations established that some charges and currents produce a local type of electromagnetic field near them that does not have the behaviour of EMR. Currents directly produce a magnetic field, but it is of a magnetic dipole type that dies out with distance from the current. In a similar manner, moving charges pushed apart in a conductor by a changing electrical potential produce an electric dipole type electric
Black-body radiation is the thermal electromagnetic radiation within or surrounding a body in thermodynamic equilibrium with its environment, or emitted by a black body. It has a specific spectrum and intensity that depends only on the body's temperature, assumed for the sake of calculations and theory to be uniform and constant; the thermal radiation spontaneously emitted by many ordinary objects can be approximated as black-body radiation. A insulated enclosure, in thermal equilibrium internally contains black-body radiation and will emit it through a hole made in its wall, provided the hole is small enough to have negligible effect upon the equilibrium. A black-body at room temperature appears black, as most of the energy it radiates is infra-red and cannot be perceived by the human eye; because the human eye cannot perceive light waves at lower frequencies, a black body, viewed in the dark at the lowest just faintly visible temperature, subjectively appears grey though its objective physical spectrum peak is in the infrared range.
When it becomes a little hotter, it appears dull red. As its temperature increases further it becomes yellow and blue-white. Although planets and stars are neither in thermal equilibrium with their surroundings nor perfect black bodies, black-body radiation is used as a first approximation for the energy they emit. Black holes are near-perfect black bodies, in the sense that they absorb all the radiation that falls on them, it has been proposed that they emit black-body radiation, with a temperature that depends on the mass of the black hole. The term black body was introduced by Gustav Kirchhoff in 1860. Black-body radiation is called thermal radiation, cavity radiation, complete radiation or temperature radiation. Black-body radiation has a characteristic, continuous frequency spectrum that depends only on the body's temperature, called the Planck spectrum or Planck's law; the spectrum is peaked at a characteristic frequency that shifts to higher frequencies with increasing temperature, at room temperature most of the emission is in the infrared region of the electromagnetic spectrum.
As the temperature increases past about 500 degrees Celsius, black bodies start to emit significant amounts of visible light. Viewed in the dark by the human eye, the first faint glow appears as a "ghostly" grey. With rising temperature, the glow becomes visible when there is some background surrounding light: first as a dull red yellow, a "dazzling bluish-white" as the temperature rises; when the body appears white, it is emitting a substantial fraction of its energy as ultraviolet radiation. The Sun, with an effective temperature of 5800 K, is an approximate black body with an emission spectrum peaked in the central, yellow-green part of the visible spectrum, but with significant power in the ultraviolet as well. Black-body radiation provides insight into the thermodynamic equilibrium state of cavity radiation. All normal matter emits electromagnetic radiation; the radiation represents a conversion of a body's internal energy into electromagnetic energy, is therefore called thermal radiation.
It is a spontaneous process of radiative distribution of entropy. Conversely all normal matter absorbs electromagnetic radiation to some degree. An object that absorbs all radiation falling on it, at all wavelengths, is called a black body; when a black body is at a uniform temperature, its emission has a characteristic frequency distribution that depends on the temperature. Its emission is called black-body radiation; the concept of the black body is an idealization. Graphite and lamp black, with emissivities greater than 0.95, are good approximations to a black material. Experimentally, black-body radiation may be established best as the stable steady state equilibrium radiation in a cavity in a rigid body, at a uniform temperature, opaque and is only reflective. A closed box of graphite walls at a constant temperature with a small hole on one side produces a good approximation to ideal black-body radiation emanating from the opening. Black-body radiation has the unique stable distribution of radiative intensity that can persist in thermodynamic equilibrium in a cavity.
In equilibrium, for each frequency the total intensity of radiation, emitted and reflected from a body is determined by the equilibrium temperature, does not depend upon the shape, material or structure of the body. For a black body there is no reflected radiation, so the spectral radiance is due to emission. In addition, a black body is a diffuse emitter. Black-body radiation may be viewed as the radiation from a black body at thermal equilibrium. Black-body radiation becomes a visible glow of light if the temperature of the object is high enough; the Draper point is the temperature at which all solids glow a dim red, about 798 K. At 1000 K, a small opening in the wall of a large uniformly heated opaque-walled cavity, viewed from outside, looks red. No matter how the oven is constructed, or of what material, as long as it is built so that all light entering is absorbed by its walls, it will contain a good approximation to black-body radiation; the spectrum, therefore color, of the light that comes out will be a function of
Pottery is the process of forming vessels and other objects with clay and other ceramic materials, which are fired to give them a hard, durable form. Major types include earthenware and porcelain; the place where such wares are made by a potter is called a pottery. The definition of pottery used by the American Society for Testing and Materials, is "all fired ceramic wares that contain clay when formed, except technical and refractory products." In archaeology of ancient and prehistoric periods, "pottery" means vessels only, figures etc. of the same material are called "terracottas". Clay as a part of the materials used is required by some definitions of pottery, but this is dubious. Pottery is one of the oldest human inventions, originating before the Neolithic period, with ceramic objects like the Gravettian culture Venus of Dolní Věstonice figurine discovered in the Czech Republic dating back to 29,000–25,000 BC, pottery vessels that were discovered in Jiangxi, which date back to 18,000 BC.
Early Neolithic pottery artefacts have been found in places such as Jōmon Japan, the Russian Far East, Sub-Saharan Africa and South America. Pottery is made by forming a ceramic body into objects of a desired shape and heating them to high temperatures in a kiln and induces reactions that lead to permanent changes including increasing the strength and solidity of the object's shape. Much pottery is purely utilitarian, but much can be regarded as ceramic art. A clay body can be decorated after firing. Clay-based pottery can divided in three main groups: earthenware and porcelain; these require more specific clay material, higher firing temperatures. All three are made for different purposes. All may be decorated by various techniques. In many examples the group a piece belongs to is visually apparent, but this is not always the case; the fritware of the Islamic world does not use clay, so technically falls outside these groups. Historic pottery of all these types is grouped as either "fine" wares expensive and well-made, following the aesthetic taste of the culture concerned, or alternatively "coarse", "popular" "folk" or "village" wares undecorated, or so, less well-made.
All the earliest forms of pottery were made from clays that were fired at low temperatures in pit-fires or in open bonfires. They were hand undecorated. Earthenware can be fired as low as 600°C, is fired below 1200°C; because unglazed biscuit earthenware is porous, it has limited utility for the storage of liquids, eating off. However, earthenware has a continuous history from the Neolithic period to today, it can be made from a wide variety of clays, some of which fire to a buff, brown or black colour, with iron in the constituent minerals resulting in a reddish-brown. Reddish coloured varieties are called terracotta when unglazed or used for sculpture; the development of ceramic glaze which makes it impermeable makes it a popular and practical form of pottery. The addition of decoration has evolved throughout its history. Stoneware is pottery, fired in a kiln at a high temperature, from about 1,100°C to 1,200°C, is stronger and non-porous to liquids; the Chinese, who developed stoneware early on, classify this together with porcelain as high-fired wares.
In contrast, stoneware could only be produced in Europe from the late Middle Ages, as European kilns were less efficient, the right sorts of clay less common. It remained a speciality of Germany until the Renaissance. Stoneware is tough and practical, much of it has always been utilitarian, for the kitchen or storage rather than the table, but "fine" stoneware has been important in China and the West, continues to be made. Many utilitarian types have come to be appreciated as art. Porcelain is made by heating materials including kaolin, in a kiln to temperatures between 1,200 and 1,400 °C; this is higher than used for the other types, achieving these temperatures was a long struggle, as well as realizing what materials were needed. The toughness and translucence of porcelain, relative to other types of pottery, arises from vitrification and the formation of the mineral mullite within the body at these high temperatures. Although porcelain was first made in China, the Chinese traditionally do not recognise it as a distinct category, grouping it with stoneware as "high-fired" ware, opposed to "low-fired" earthenware.
This confuses the issue of. A degree of translucency and whiteness was achieved by the Tang Dynasty, considerable quantities were being exported; the modern level of whiteness was not reached until much in the 14th century. Porcelain was made in Korea and in Japan from the end of the 16th century, after suitable kaolin was located in those countries, it was not made outside East Asia until the 18th century. Before being shaped, clay must be prepared. Kneading helps to ensure an moisture content throughout the body. Air trapped within the clay body needs to be removed; this is called de-airing and can be accomplished either by a machine called a vacuum pug or manually by wedging. Wedging can help produce an moisture content. Once a clay body has been kneaded and de-aired or wedged, it is shaped by a variety of techniques. After it has been shaped, it is dried and fired. Greenware refers to unfired objects. At sufficient moisture content, bodies at this stage are in their most plastic form (as they are soft and mal
Beach nourishment describes a process by which sediment sand, lost through longshore drift or erosion is replaced from other sources. A wider beach can reduce storm damage to coastal structures by dissipating energy across the surf zone, protecting upland structures and infrastructure from storm surges and unusually high tides. Beach nourishment is part of a larger coastal defense scheme. Nourishment is a repetitive process since it does not remove the physical forces that cause erosion but mitigates their effects; the first nourishment project in the United States was at Coney Island, New York in 1922 and 1923. It is now a common shore protection measure used by private entities. Nourishment is one of three accepted methods for protecting shorelines; the structural alternative involves constructing a seawall, groyne or breakwater. Alternatively, with managed retreat the shoreline is left to erode, while relocating buildings and infrastructure further inland. Nourishment gained popularity because it preserved beach resources and avoided the negative effects of hard structures.
Instead, nourishment creates a “soft” structure by creating a larger sand reservoir, pushing the shoreline seaward. Beaches can erode both and due to human impacts. Erosion is a natural response to storm activity. During storms, sand from the visible beach submerges to form sand bars. Submersion is only part of the cycle. During calm weather smaller waves return sand from bars to the visible beach surface in a process called accretion; some beaches do not have enough sand available to coastal processes to respond to storms. When not enough sand is available, the beach cannot recover following storms. Many areas of high erosion are due to human activities. Reasons can include: seawalls locking up sand dunes, coastal structures like ports and harbors that prevent longshore transport and other river management structures. Continuous, long-term renourishment efforts in cuspate-cape coastlines, can play a role in longshore transport inhibition and downdrift erosion; these activities interfere with the natural sediment flows either through dam construction or construction of littoral barriers such as jetties, or by deepening of inlets.
The proportion of total sand in a beach that lies below the waterline critically impacts beach nourishment. Two beaches with the same amount of visible sand may be much different below the surface. An eroded beach with substantial submerged sand surrounding it may recover without nourishment. Nourishing a beach that has little submerged sand requires understanding of the reason that the submerged sand is missing; the same forces that stripped the submerged sand once are to do so again. The amount of submerged sand eroded is much greater than the amount of missing sand on shore. Replacing only the visible sand is insufficient unless the submerged sand is replaced. Otherwise, the beach is unstable and the replenished sand erodes. If human activity is a major cause of the erosion, mitigating that activity may be more cost effective over both short and long term periods than direct nourishment. Sand fill must be compatible with native beach sand. Beach Profile Nourishment describes programs. In this instance, "profile" means the slope of the uneroded beach from above the water out to sea.
The Gold Coast profile nourishment program placed 75% of its total sand volume below low water level. Some coastal authorities overnourish the below water beach so that over time the natural beach increases in size; these approaches do not permanently protect beaches eroded by human activity, which requires that activity to be mitigated. The selection of suitable material for a particular project depends upon the design needs, environmental factors and transport costs, considering both short and long-term implications; the most important material characteristic is the sediment grain size, which must match the native material. Excess silt and clay fraction versus the natural turbidity in the nourishment area disqualifies some materials. Projects with unmatched grain sizes performed poorly. Nourishment sand, only smaller than native sand can result in narrower equilibrated dry beach widths compared to sand the same size as native sand. Evaluating material fit requires a sand survey that includes geophysical profiles and surface and core samples.
Some beaches were nourished using a finer sand than the original. Thermoluminescence monitoring reveals; this was observed at a Waikiki nourishment project in Hawaii. Advantages: Widens the beach. Protects structures behind beach. Disadvantages: Added sand may erode, because of storms or lack of up-drift sand sources. Expensive and requires repeated application. Restricted access during nourishment. Destroy/bury marine life. Difficulty finding sufficiently similar materials. Beach nourishment has significant impacts on local ecosystems. Nourishment may cause direct mortality to sessile organisms in the target area by burying them under the new sand. Seafloor habitat in both source and target areas are disrupted, e.g. when sand is deposited on coral reefs or when deposited sand hardens. Imported sand may differ in character from that of the target environment. Light availability may be reduced, affecting nearby reefs an