Quark matter or QCD matter refers to any of a number of theorized phases of matter whose degrees of freedom include quarks and gluons. These theoretical phases would occur at high temperatures and/or densities, billions of times higher than can be produced in equilibrium in laboratories. Under such extreme conditions, the familiar structure of matter, where the basic constituents are nuclei and electrons, is disrupted. In quark matter it is more appropriate to treat the quarks themselves as the basic degrees of freedom. In the standard model of particle physics, the strong force is described by the theory of QCD. At ordinary temperatures or densities this force just confines the quarks into composite particles of size around 10−15 m = 1 femtometer = 1 fm and its effects are not noticeable at longer distances. However, when the temperature reaches the QCD energy scale or the density rises to the point where the average inter-quark separation is less than 1 fm, the hadrons are melted into their constituent quarks, the strong interaction becomes the dominant feature of the physics.
Such phases are called QCD matter. The strength of the color force makes the properties of quark matter unlike gas or plasma, instead leading to a state of matter more reminiscent of a liquid. At high densities, quark matter is a Fermi liquid, but is predicted to exhibit color superconductivity at high densities and temperatures below 1012 K. According to the Big Bang theory, in the early universe at high temperatures when the universe was only a few tens of microseconds old, the phase of matter took the form of a hot phase of quark matter called the quark–gluon plasma. Compact stars. A neutron star is much cooler than 1012 K, but it has been compressed by the supernova creating it to such high densities, that it is reasonable to surmise that quark matter may exist in the core. Compact stars composed or of quark matter are called quark stars or strange stars, yet at this time no star with properties expected of these objects has been observed. Strangelets; these are theoretically postulated lumps of strange matter comprising nearly equal amounts of up, down and strange quarks.
Strangelets are supposed to be present in the galactic flux of high energy particles and should therefore theoretically be detectable in cosmic rays here on Earth, but no strangelet has been detected with certainty. Cosmic ray impacts. Cosmic rays comprise a lot of different particles, including accelerated atomic nuclei that of iron. Laboratory experiments suggests that the inevitable interaction with heavy noble gas nuclei in the upper atmosphere would lead to quark–gluon plasma formation. Though quark-gluon plasma can only occur under quite extreme conditions of temperature and/or pressure, it is being studied at particle colliders, such as the Large Hadron Collider LHC at CERN and the Relativistic Heavy Ion Collider RHIC at Brookhaven National Laboratory. In these collisions, the plasma only occurs for a short time before it spontaneously disintegrates, because the extreme conditions during the collision process cannot be upheld; the plasma's physical characteristics are studied by detecting the debris emanating from the collision region with large particle detectors Heavy-ion collisions at high energies can produce small short-lived regions of space whose energy density is comparable to that of the 20-micro-second-old universe.
This has been achieved by colliding heavy nuclei such as lead nuclei at high speeds, a first time claim of formation of quark–gluon plasma came from the SPS accelerator at CERN in February 2000. This work has been continued at more powerful accelerators, such as RHIC in the US, as of 2010 at the European LHC at CERN located in the border area of Switzerland and France. There is good evidence that the quark–gluon plasma has been produced at RHIC; the context for understanding the thermodynamics of quark matter is the standard model of particle physics, which contains six different flavors of quarks, as well as leptons like electrons and neutrinos. These interact via the strong interaction and the weak interaction which allows one flavor of quark to turn into another. Electromagnetic interactions occur between particles; the correct thermodynamic treatment of quark matter depends on the physical context. For large quantities that exist for long periods of time, we must take into account the fact that the only conserved charges in the standard model are quark number, electric charge, the eight color charges, lepton number.
Each of these can have an associated chemical potential. However, large volumes of matter must be electrically and color-neutral, which determines the electric and color charge chemical potentials; this leaves a three-dimensional phase space, parameterized by quark chemical potential, lepton chemical potential, temperature. In compact stars quark matter would occupy cubic kilometers and exist for millions of years, so the thermodynamic limit is appropriate. However, the neutrinos escape, violating lepton number, so the phase space for quark matter in compact stars only has two dimensions and quark number chemical potential μ. A strangelet is not in the thermodynamic limit of large volume, so it is like an exotic nucleus: it may carry electric charge. A heavy-ion collision is in neither the thermodynamic limit of large volumes nor lon
Latent heat is thermal energy released or absorbed, by a body or a thermodynamic system, during a constant-temperature process — a first-order phase transition. Latent heat can be understood as heat energy in hidden form, supplied or extracted to change the state of a substance without changing its temperature. Examples are latent heat of fusion and latent heat of vaporization involved in phase changes, i.e. a substance condensing or vaporizing at a specified temperature and pressure. The term was introduced around 1762 by British chemist Joseph Black, it is derived from the Latin latere. Black used the term in the context of calorimetry where a heat transfer caused a volume change in a body while its temperature was constant. In contrast to latent heat, sensible heat is a heat transfer that results in a temperature change in a body; the terms ″sensible heat″ and ″latent heat″ refer to types of heat transfer between a body and its surroundings. ″ Sensible heat ″ felt in a process as a change in the body's temperature.
″Latent heat″ is heat transferred in a process without change of the body's temperature, for example, in a phase change. Both sensible and latent heats are observed in many processes of transfer of energy in nature. Latent heat is associated with the change of phase of atmospheric or ocean water, condensation, freezing or melting, whereas sensible heat is energy transferred, evident in change of the temperature of the atmosphere or ocean, or ice, without those phase changes, though it is associated with changes of pressure and volume; the original usage of the term, as introduced by Black, was applied to systems that were intentionally held at constant temperature. Such usage referred to latent heat of expansion and several other related latent heats; these latent heats. When a body is heated at constant temperature by thermal radiation in a microwave field for example, it may expand by an amount described by its latent heat with respect to volume or latent heat of expansion, or increase its pressure by an amount described by its latent heat with respect to pressure.
Latent heat is energy released or absorbed, by a body or a thermodynamic system, during a constant-temperature process. Two common forms of latent heat are latent heat of latent heat of vaporization; these names describe the direction of energy flow when changing from one phase to the next: from solid to liquid, liquid to gas. In both cases the change is endothermic, meaning. For example, when water evaporates, energy is required for the water molecules to overcome the forces of attraction between them, the transition from water to vapor requires an input of energy. If the vapor condenses to a liquid on a surface the vapor's latent energy absorbed during evaporation is released as the liquid's sensible heat onto the surface; the large value of the enthalpy of condensation of water vapor is the reason that steam is a far more effective heating medium than boiling water, is more hazardous. In meteorology, latent heat flux is the flux of heat from the Earth's surface to the atmosphere, associated with evaporation or transpiration of water at the surface and subsequent condensation of water vapor in the troposphere.
It is an important component of Earth's surface energy budget. Latent heat flux has been measured with the Bowen ratio technique, or more since the mid-1900s by the Jonathan Beaver method; the English word latent comes from Latin latēns. The term latent heat was introduced into calorimetry around 1750 when Joseph Black, commissioned by producers of Scotch whisky in search of ideal quantities of fuel and water for their distilling process, to studying system changes, such as of volume and pressure, when the thermodynamic system was held at constant temperature in a thermal bath. James Prescott Joule characterised latent energy as the energy of interaction in a given configuration of particles, i.e. a form of potential energy, the sensible heat as an energy, indicated by the thermometer, relating the latter to thermal energy. A specific latent heat expresses the amount of energy in the form of heat required to effect a phase change of a unit of mass 1kg, of a substance as an intensive property: L = Q m.
Intensive properties are material characteristics and are not dependent on the size or extent of the sample. Quoted and tabulated in the literature are the specific latent heat of fusion and the specific latent heat of vaporization for many substances. From this definition, the latent heat for a given mass of a substance is calculated by Q = m L where: Q is the amount of energy released or absorbed during the change of phase of the substance, m is the mass of the substance, L is the specific latent heat for a particular substance, either Lf for fusion, or Lv for vaporization; the following table shows the specific latent heats and change of phase temperatures of some common fluids and gases. The specific latent heat of condensation of water in the temperature range from −25 °C to 40 °C is approximated by the following empirical cubic function: L water =
Deposition (phase transition)
Deposition is the phase transition in which gas transforms into solid without passing through the liquid phase. Deposition is a thermodynamic process; the reverse of deposition is sublimation and hence sometimes deposition is called desublimation. One example of deposition is the process by which, in sub-freezing air, water vapor changes directly to ice without first becoming a liquid; this is how hoar frost form on the ground or other surfaces. Another example is. For deposition to occur, thermal energy must be removed from a gas; when the air becomes cold enough, water vapor in the air surrounding the leaf loses enough thermal energy to change into a solid. Though the air temperature may be below the dew point, the water vapor may not be able to condense spontaneously if there is no way to remove the latent heat; when the leaf is introduced, the supercooled water vapor begins to condense, but by this point is past the freezing point. This causes the water vapor to change directly into a solid.
Another example is the soot, deposited on the walls of chimneys. Soot molecules rise from the fire in a gaseous state; when they come into contact with the walls they cool, change to the solid state, without formation of the liquid state. The process is made use of industrially in combustion chemical vapor deposition. There is an industrial coatings process, known as evaporative deposition, whereby a solid material is heated to the gaseous state in a low-pressure chamber, the gas molecules travel across the chamber space and condense to the solid state on a target surface, forming a smooth and thin layer on the target surface. Again, the molecules do not go through an intermediate liquid state when going from the gas to the solid. See physical vapor deposition, a class of processes used to deposit thin films of various materials onto various surfaces. Deposition is an exothermic phase change. Jacobson, Mark Z. Fundamentals of Atmospheric Modeling, Cambridge University Press, 2nd ed. 2005, p. 525 ISBN 978-0-521-83970-9 Moore, John W. et al.
Principles of Chemistry: The Molecular Science, Brooks Cole, 2009, p. 387 ISBN 978-0-495-39079-4 Whitten, Kenneth W. et al. Chemistry, Brooks-Cole, 9th ed. 2009, p. 7 ISBN 978-0-495-39163-0 Focus on Physical Science. Glencoe Science
In classical physics and general chemistry, matter is any substance that has mass and takes up space by having volume. All everyday objects that can be touched are composed of atoms, which are made up of interacting subatomic particles, in everyday as well as scientific usage, "matter" includes atoms and anything made up of them, any particles that act as if they have both rest mass and volume; however it does not include massless particles such as photons, or other energy phenomena or waves such as light or sound. Matter exists in various states; these include classical everyday phases such as solid and gas – for example water exists as ice, liquid water, gaseous steam – but other states are possible, including plasma, Bose–Einstein condensates, fermionic condensates, quark–gluon plasma. Atoms can be imagined as a nucleus of protons and neutrons, a surrounding "cloud" of orbiting electrons which "take up space"; however this is only somewhat correct, because subatomic particles and their properties are governed by their quantum nature, which means they do not act as everyday objects appear to act – they can act like waves as well as particles and they do not have well-defined sizes or positions.
In the Standard Model of particle physics, matter is not a fundamental concept because the elementary constituents of atoms are quantum entities which do not have an inherent "size" or "volume" in any everyday sense of the word. Due to the exclusion principle and other fundamental interactions, some "point particles" known as fermions, many composites and atoms, are forced to keep a distance from other particles under everyday conditions. For much of the history of the natural sciences people have contemplated the exact nature of matter; the idea that matter was built of discrete building blocks, the so-called particulate theory of matter, was first put forward by the Greek philosophers Leucippus and Democritus. Matter should not be confused with mass. Matter is a general term describing any'physical substance'. By contrast, mass is not a substance but rather a quantitative property of matter and other substances or systems. While there are different views on what should be considered matter, the mass of a substance has exact scientific definitions.
Another difference is that matter has an "opposite" called antimatter, but mass has no opposite—there is no such thing as "anti-mass" or negative mass, so far as is known, although scientists do discuss the concept. Antimatter has the same mass property as its normal matter counterpart. Different fields of science use the term matter in different, sometimes incompatible, ways; some of these ways are based on loose historical meanings, from a time when there was no reason to distinguish mass from a quantity of matter. As such, there is no single universally agreed scientific meaning of the word "matter". Scientifically, the term "mass" is well-defined. Sometimes in the field of physics "matter" is equated with particles that exhibit rest mass, such as quarks and leptons. However, in both physics and chemistry, matter exhibits both wave-like and particle-like properties, the so-called wave–particle duality. A definition of "matter" based on its physical and chemical structure is: matter is made up of atoms.
Such atomic matter is sometimes termed ordinary matter. As an example, deoxyribonucleic acid molecules are matter under this definition because they are made of atoms; this definition can be extended to include charged atoms and molecules, so as to include plasmas and electrolytes, which are not included in the atoms definition. Alternatively, one can adopt the protons and electrons definition. A definition of "matter" more fine-scale than the atoms and molecules definition is: matter is made up of what atoms and molecules are made of, meaning anything made of positively charged protons, neutral neutrons, negatively charged electrons; this definition goes beyond atoms and molecules, however, to include substances made from these building blocks that are not atoms or molecules, for example electron beams in an old cathode ray tube television, or white dwarf matter—typically and oxygen nuclei in a sea of degenerate electrons. At a microscopic level, the constituent "particles" of matter such as protons and electrons obey the laws of quantum mechanics and exhibit wave–particle duality.
At an deeper level and neutrons are made up of quarks and the force fields that bind them together, leading to the next definition. As seen in the above discussion, many early definitions of what can be called "ordinary matter" were based upon its structure or "building blocks". On the scale of elementary particles, a definition that follows this tradition can be stated as: "ordinary matter is everything, composed of quarks and leptons", or "ordinary matter is everything, composed of any elementary fermions except antiquarks and antileptons"; the connection between these formulations follows. Leptons, quarks combine to form atoms, which in turn form molecules; because atoms and molecules are said to be matter, it is natural to phrase the definition as: "ordinary matter is anything
Boiling is the rapid vaporization of a liquid, which occurs when a liquid is heated to its boiling point, the temperature at which the vapour pressure of the liquid is equal to the pressure exerted on the liquid by the surrounding atmosphere. There are two main types of boiling: nucleate boiling where small bubbles of vapour form at discrete points, critical heat flux boiling where the boiling surface is heated above a certain critical temperature and a film of vapor forms on the surface. Transition boiling is an unstable form of boiling with elements of both types; the boiling point of water is 100 °C or 212 °F but is lower with the decreased atmospheric pressure found at higher altitudes. Boiling water is used as a method of making it potable by killing microbes; the sensitivity of different micro-organisms to heat varies, but if water is held at 70 °C for ten minutes, many organisms are killed, but some are more resistant to heat and require one minute at the boiling point of water. Boiling is used in cooking.
Foods suitable for boiling include vegetables, starchy foods such as rice and potatoes, eggs, "meats", sauces and soups. As a cooking method, it is suitable for large-scale cookery. Tough meats or poultry can be given a long, slow cooking and a nutritious stock is produced. Disadvantages include loss of water-soluble minerals. Commercially prepared foodstuffs are sometimes packed in polythene sachets and sold as "boil-in-the-bag" products. Nucleate boiling is characterized by the growth of bubbles or pops on a heated surface, which rises from discrete points on a surface, whose temperature is only above the liquids. In general, the number of nucleation sites are increased by an increasing surface temperature. An irregular surface of the boiling vessel or additives to the fluid can create additional nucleation sites, while an exceptionally smooth surface, such as plastic, lends itself to superheating. Under these conditions, a heated liquid may show boiling delay and the temperature may go somewhat above the boiling point without boiling.
As the boiling surface is heated above a critical temperature, a film of vapor forms on the surface. Since this vapor film is much less capable of carrying heat away from the surface, the temperature rises rapidly beyond this point into the transition boiling regime; the point at which this occurs is dependent on the characteristics of boiling fluid and the heating surface in question. Transition boiling may be defined as the unstable boiling, which occurs at surface temperatures between the maximum attainable in nucleate and the minimum attainable in film boiling; the formation of bubbles in a heated liquid is a complex physical process which involves cavitation and acoustic effects, such as the broad-spectrum hiss one hears in a kettle not yet heated to the point where bubbles boil to the surface. If a surface heating the liquid is hotter than the liquid film boiling will occur, where a thin layer of vapor, which has low thermal conductivity, insulates the surface; this condition of a vapor film insulating the surface from the liquid characterizes film boiling.
As a method of disinfecting water, bringing it to its boiling point at 100 °C, is the oldest and most effective way since it does not affect the taste, it is effective despite contaminants or particles present in it, is a single step process which eliminates most microbes responsible for causing intestine related diseases. Water's boiling point rests at around 100.0 degrees Celsius, when at an elevation of 0. In places having a proper water purification system, it is recommended only as an emergency treatment method or for obtaining potable water in the wilderness or in rural areas, as it cannot remove chemical toxins or impurities; the elimination of micro-organisms by boiling follows first-order kinetics—at high temperatures, it is achieved in less time and at lower temperatures, in more time. The heat sensitivity of micro-organisms varies, at 70 °C, Giardia species can take ten minutes for complete inactivation, most intestine affecting microbes and E. coli take less than a minute. Boiling does not ensure the elimination of all micro-organisms.
Thus for human health, complete sterilization of water is not required. The traditional advice of boiling water for ten minutes is for additional safety, since microbes start getting eliminated at temperatures greater than 60 °C and bringing it to its boiling point is a useful indication that can be seen without the help of a thermometer, by this time, the water is disinfected. Though the boiling point decreases with increasing altitude, it is not enough to affect the disinfecting process. Boiling is the method of cooking food in boiling water or other water-based liquids such as stock or milk. Simmering is gentle boiling; the boiling point of water is considered to be 100 °C or 212 °F. Pressure and a change in the composition of the liquid may alter the boiling point of the liquid. For this reason, high elevation cooking takes longer since boiling point is a function of atmospheric pressure. In Denver, Colorado, USA, at an elevation of about one mile, water boils at 95 °C or 203 °F. Depending on the type of food and the elevation, the boiling water may not be hot enough to cook the food properly.
A time crystal or space-time crystal is a structure that repeats in time, as well as in space. Normal three-dimensional crystals have a repeating pattern in space, but remain unchanged as time passes. Time crystals repeat themselves in time as well, leading the crystal to change from moment to moment. A time crystal never reaches thermal equilibrium, as it is a type of non-equilibrium matter, a form of matter proposed in 2012, first observed in 2017; this state of matter cannot be isolated from its environment—it is an open system in non-equilibrium. The idea of a time crystal was first described by Nobel laureate Frank Wilczek in 2012. Work developed a more precise definition for time crystals, it was proven. In 2014 Krzysztof Sacha predicted the behaviour of discrete time crystals in a periodically-driven many-body system, and in 2016, Norman Yao et al. proposed a different way to create time crystals in spin systems. From there, Christopher Monroe and Mikhail Lukin independently confirmed this in their labs.
Both experiments were published in Nature in 2017. The idea of a space-time crystal was first put forward by Frank Wilczek, a professor at MIT and Nobel laureate, in 2012. In 2013, Xiang Zhang, a nanoengineer at University of California and his team proposed creating a time crystal in the form of a rotating ring of charged ions. In response to Wilczek and Zhang, Patrick Bruno, a theorist at the European Synchrotron Radiation Facility in Grenoble, published several papers in 2013 claiming to show that space-time crystals were impossible. Masaki Oshikawa from the University of Tokyo showed that time crystals would be impossible at their ground state. Subsequent work developed more precise definitions of time translation symmetry-breaking which led to a'no-go' proof that quantum time crystals in equilibrium are not possible. Several realizations of time crystals, which avoid the equilibrium no-go arguments, were proposed. Krzysztof Sacha at Jagiellonian University in Krakow predicted the behaviour of discrete time crystals in a periodically driven system of ultracold atoms.
Works suggested periodically driven quantum spin systems could show similar behaviour. Norman Yao at Berkeley studied a different model of time crystals, his blueprint was used by two teams: a group led by Harvard's Mikhail Lukin and a group led by Christopher Monroe at University of Maryland. Symmetries in nature lead directly to conservation laws, something, formulated by the Noether theorem; the basic idea of time-translation symmetry is that a translation in time has no effect on physical laws, i.e. that the laws of nature that apply today were the same in the past and will be the same in the future. This symmetry implies the conservation of energy. Normal crystals exhibit broken translation symmetry: they have repeated patterns in space, are not invariant under arbitrary translations or rotations; the laws of physics are unchanged by arbitrary rotations. However, if we hold fixed the atoms of a crystal, the dynamics of electrons or other particles in the crystal depends on how it moves relative to the crystal, particles' momentum can change by interacting with the atoms of a crystal — for example in Umklapp processes.
Quasimomentum, however, is conserved in a perfect crystal. Time crystals shows a broken symmetry analogous to a discrete space-translation symmetry breaking. For example, the molecules of a liquid freezing on the surface of a crystal can align with the molecules of the crystal, but with a pattern less symmetric than the crystal: it breaks the initial symmetry; this broken symmetry exhibits three important characteristics: the system has a lower symmetry than the underlying arrangement of the crystal the system exhibits spatial and temporal long-range order it is the result of interactions between the constituents of the system, which aligns themselves relative to each other Time crystals seem to break time-translation symmetry, have repeated patterns in time if the laws of the system are invariant by translation of time. Studied time crystals shows discrete time-translation symmetry breaking: they are periodically driven systems which oscillate at a fraction of the frequency of the driving force.
The initial symmetry is a discrete time-translation symmetry, not a continuous one. Many systems can show behaviors of spontaneous time translation symmetry breaking: convection cells, oscillating chemical reactions, aerodynamic flutter, subharmonic response to a periodic driving force such as the Faraday instability, NMR spin echos, parametric down-conversion, period-doubled nonlinear dynamical systems. However, Floquet time crystals are unique in that they follow a strict definition of discrete time-translation symmetry breaking: it is a broken symmetry: the system shows oscillations with a period longer than the driving force the system is in crypto-equilibrium: these oscillations generate no entropy, a time-dependant frame can be found in which the system is indistinguishable from an equilibrium when measured stroboscopically the system exhibits long-range order: the oscillations are in phase over arbitrarily long distances and timeMoreover, the broken symmetry in time crystals is the result of many-body interactions: the order
A supercritical fluid is any substance at a temperature and pressure above its critical point, where distinct liquid and gas phases do not exist. It can effuse through solids like a gas, dissolve materials like a liquid. In addition, close to the critical point, small changes in pressure or temperature result in large changes in density, allowing many properties of a supercritical fluid to be "fine-tuned". Supercritical fluids occur in the atmospheres of the gas giants Jupiter and Saturn, in those of the ice giants Uranus and Neptune. In a range of industrial and laboratory processes, they are used as a substitute for organic solvents. Carbon dioxide and water are the most used supercritical fluids, being used for decaffeination and power generation, respectively. In general terms, supercritical fluids have properties between those of a liquid. In Table 1, the critical properties are shown for some substances that are used as supercritical fluids. Table 2 shows density and viscosity for typical liquids and supercritical fluids.
In addition, there is no surface tension in a supercritical fluid, as there is no liquid/gas phase boundary. By changing the pressure and temperature of the fluid, the properties can be "tuned" to be more liquid-like or more gas-like. One of the most important properties is the solubility of material in the fluid. Solubility in a supercritical fluid tends to increase with density of the fluid. Since density increases with pressure, solubility tends to increase with pressure; the relationship with temperature is a little more complicated. At constant density, solubility will increase with temperature. However, close to the critical point, the density can drop with a slight increase in temperature. Therefore, close to the critical temperature, solubility drops with increasing temperature rises again. All supercritical fluids are miscible with each other so for a mixture a single phase can be guaranteed if the critical point of the mixture is exceeded; the critical point of a binary mixture can be estimated as the arithmetic mean of the critical temperatures and pressures of the two components, Tc = × TcA + × TcB.
For greater accuracy, the critical point can be calculated using equations of state, such as the Peng Robinson, or group contribution methods. Other properties, such as density, can be calculated using equations of state. Figures 1 and 2 show two-dimensional projections of a phase diagram. In the pressure-temperature phase diagram the boiling separates the gas and liquid region and ends in the critical point, where the liquid and gas phases disappear to become a single supercritical phase; the appearance of a single phase can be observed in the density-pressure phase diagram for carbon dioxide. At well below the critical temperature, e.g. 280 K, as the pressure increases, the gas compresses and condenses into a much denser liquid, resulting in the discontinuity in the line. The system consists of 2 phases in a dense liquid and a low density gas; as the critical temperature is approached, the density of the gas at equilibrium becomes higher, that of the liquid lower. At the critical point, there is no difference in density, the 2 phases become one fluid phase.
Thus, above the critical temperature a gas cannot be liquefied by pressure. At above the critical temperature, in the vicinity of the critical pressure, the line is vertical. A small increase in pressure causes a large increase in the density of the supercritical phase. Many other physical properties show large gradients with pressure near the critical point, e.g. viscosity, the relative permittivity and the solvent strength, which are all related to the density. At higher temperatures, the fluid starts to behave like a gas, as can be seen in Figure 2. For carbon dioxide at 400 K, the density increases linearly with pressure. Many pressurized gases are supercritical fluids. For example, nitrogen has a critical point of 3.4 MPa. Therefore, nitrogen in a gas cylinder above this pressure is a supercritical fluid; these are more known as permanent gases. At room temperature, they are well above their critical temperature, therefore behave as a gas, similar to CO2 at 400 K above. However, they can not be liquified by pressure.
In recent years, a significant effort has been devoted to investigation of various properties of supercritical fluids. This has been an exciting field with a long history since 1822 when Baron Charles Cagniard de la Tour discovered supercritical fluids while conducting experiments involving the discontinuities of the sound in a sealed cannon barrel filled with various fluids at high temperature. More supercritical fluids have found application in a variety of fields, ranging from the extraction of floral fragrance from flowers to applications in food science such as creating decaffeinated coffee, functional food ingredients, cosmetics, powders, bio- and functional materials, nano-systems, natural products, biotechnology and bio-fuels, microelectronics and environment. Much of the excitement and interest of the past decade is due to the enormous progress made in increasing the power of relevant experimental tools; the development of new experimental methods and improvement of existing ones continues to play an important role in this field, with recent research focusing on dynamic properties of fluids.
The Fisher-Widom line, the Widom line, or the Frenk