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In particle physics, a lepton is an elementary particle of half-integer spin (spin ​1⁄2) that does not undergo strong interactions.
Two main classes of leptons exist, charged leptons (also known as the electron-like leptons), and neutral leptons (better known as neutrinos).
Charged leptons can combine with other particles to form various composite particles such as atoms and positronium, while neutrinos rarely interact with anything, and are consequently rarely observed.
Positronium (Ps) is a system consisting of an electron and its anti-particle, a positron, bound together into an exotic atom, specifically an onium.
The best known of all leptons is the electron.
There are six types of leptons, known as flavours, grouped in three generations.
The first-generation leptons, also called electronic leptons, comprise the electron ( e− ) and the electron neutrino ( ν e);
the second are the muonic leptons, comprising the muon ( μ− ) and the muon neutrino ( ν μ);
and the third are the tauonic leptons, comprising the tau ( τ− ) and the tau neutrino ( ν τ)
Electrons have the least mass of all the charged leptons.
The heavier muons and taus will rapidly change into electrons and neutrinos through a process of particle decay: the transformation from a higher mass state to a lower mass state.
Thus electrons are stable and the most common charged lepton in the universe, whereas muons and taus can only be produced in high energy collisions (such as those involving cosmic rays and those carried out in particle accelerators).
The system is unstable: the two particles annihilate each other to predominantly produce two or three gamma-rays, depending on the relative spin states.
In quantum mechanics and particle physics, spin is an intrinsic form of angular momentum carried by elementary particles, composite particles (hadrons), and atomic nuclei.
a helium atom in the ground state has spin 0 and behaves like a boson, even though the quarks and electrons which make it up are all fermions.
Leptons have various intrinsic properties, including electric charge, spin, and mass.
Unlike quarks, however, leptons are not subject to the strong interaction, but they are subject to the other three fundamental interactions: gravitation, the weak interaction, and to electromagnetism ...
electromagnetism ... is proportional to charge, and is thus zero for the electrically neutral neutrinos.
For every lepton flavor, there is a corresponding type of antiparticle, known as an antilepton, that differs from the lepton only in that some of its properties have equal magnitude but opposite sign.
According to certain theories, neutrinos may be their own antiparticle. It is not currently known whether this is the case.
In particle physics, every type of particle is associated with [an] antiparticle with the same mass but with opposite physical charges (such as electric charge).
For example, the antiparticle of the electron is the antielectron (which is often referred to as positron).
While the electron has a negative electric charge, the positron has a positive electric charge, and is produced naturally in certain types of radioactive decay. The opposite is also true: the antiparticle of the positron is the electron.
In modern physics, antimatter is defined as matter which is composed of the antiparticles (or "partners") of the corresponding particles of 'ordinary' matter.
In theory, a particle and its anti-particle (for example, a proton and an antiproton) have the same mass, but opposite electric charge and other differences in quantum numbers. For example, a proton has positive charge while an antiproton has negative ...
The invariant mass of an electron is approximately 9.109×10−31 kilograms, or 5.489×10−4 atomic mass units. On the basis of Einstein's principle of mass–energy equivalence, this mass corresponds to a rest energy of 0.511 MeV.
Electrons have an electric charge of −1.602176634×10−19 coulombs, which is used as a standard unit of charge for subatomic particles, and is also called the elementary charge.
Within the limits of experimental accuracy, the electron charge is identical to the charge of a proton, but with the opposite sign.
As the symbol e is used for the elementary charge, the electron is commonly symbolized by e−, where the minus sign indicates the negative charge.
The positron is symbolized by e+ because it has the same properties as the electron but with a positive rather than negative charge.
Leptons are spin 1/2 particles. The spin-statistics theorem thus implies that they are fermions and thus that they are subject to the Pauli exclusion principle: No two leptons of the same species can be in the same state at the same time.
Furthermore, it means that a lepton can have only two possible spin states, namely up or down.
there are only two possible values for a spin-1/2 particle: sz = +1/2 and sz = -1/2. These correspond to quantum states in which the spin component is pointing in the +z or −z directions respectively, and are often referred to as "spin up" and "spin down"
sz is the spin projection quantum number along the z-axis.
The Pauli exclusion principle is the quantum mechanical principle which states that two or more identical fermions (particles with half-integer spin) cannot occupy the same quantum state within a quantum system simultaneously.
In particle physics, a fermion is a particle that follows Fermi–Dirac statistics and generally has half odd integer spin 1/2, 3/2 etc. These particles obey the Pauli exclusion principle.
Fermions include all quarks and leptons, as well as all composite particles made of an odd number of these, such as all baryons and many atoms and nuclei.
Fermions differ from bosons, which obey Bose–Einstein statistics.
Some fermions are elementary particles, such as the electrons, and some are composite particles, such as the protons.
According to the spin-statistics theorem in any reasonable relativistic quantum field theory, particles with integer spin are bosons, while particles with half-integer spin are fermions.
In particle physics, a baryon is a type of composite subatomic particle which contains an odd number of valence quarks (at least 3).
Baryons belong to the hadron family of particles, which are the quark-based particles.
They are also classified as fermions, i.e., they have half-integer spin.
The most familiar baryons are protons and neutrons, both of which contain three quarks, and for this reason these particles are sometimes described as triquarks.
The neutron ... is a spin-½ fermion.
Protons are spin-1/2 fermions and are composed of three valence quarks, making them baryons (a sub-type of hadrons).
Quarks are fermionic particles of spin 1/2 (S = 1/2).
Because spin projections vary in increments of 1 (that is 1 ħ), a single quark has a spin vector of length 1/2, and has two spin projections (Sz = +1/2 and Sz = −1/2).
Two quarks can have their spins aligned, in which case the two spin vectors add to make a vector of length S = 1 and three spin projections (Sz = +1, Sz = 0, and Sz = −1).
If two quarks have unaligned spins, the spin vectors add up to make a vector of length S = 0 and has only one spin projection (Sz = 0), etc.
Since baryons are made of three quarks [DISPUTED], their spin vectors can add to make a vector of length S = 3/2, which has four spin projections (Sz = +3/2, Sz = +1/2, Sz = −1/2, and Sz = −3/2), or a vector of length S = 1/2 with two spin projections ...
Exotic baryons containing five quarks (known as pentaquarks) have also been discovered and studied.
In particle physics, a hadron ... is a subatomic composite particle made of two or more quarks ...
The Δ baryons have ... a spin of ​3⁄2 ...
Four closely related Δ baryons exist: Δ++ (constituent quarks: uuu), Δ+ (uud), Δ0 (udd), and Δ− (ddd), which respectively carry an electric charge of +2 e, +1 e, 0 e, and −1 e.
In particle physics, mesons are hadronic subatomic particles composed of one quark and one antiquark, bound together by strong interactions.
All mesons are unstable, with the longest-lived lasting for only a few hundredths of a microsecond.
Charged mesons decay (sometimes through mediating particles) to form electrons and neutrinos.
Uncharged mesons may decay to photons.
Both of these decays imply that color is no longer a property of the byproducts.
Unlike leptons, quarks possess color charge, which causes them to engage in the strong interaction.
The resulting attraction between different quarks causes the formation of composite particles known as hadrons
A quark is a type of elementary particle and a fundamental constituent of matter.
Quarks combine to form composite particles called hadrons, the most stable of which are protons and neutrons, the components of atomic nuclei.
Due to a phenomenon known as color confinement, quarks are never found in isolation; they can be found only within hadrons, which include baryons (such as protons and neutrons) and mesons, or in quark–gluon plasmas.
Quarks have various intrinsic properties, including electric charge, mass, color charge, and spin.
Quarks ... are the only elementary particles in the Standard Model of particle physics to experience all four fundamental interactions, also known as fundamental forces (electromagnetism, gravitation, strong interaction, and weak interaction).
Quarks ... are the only known particles whose electric charges are not integer multiples of the elementary charge.
A neutrino (denoted by the Greek letter ν) is a fermion (an elementary particle with spin of 1/2) that interacts only via the weak subatomic force and gravity.
There are six types, known as flavors, of quarks: up, down, strange, charm, bottom, and top.
Up and down quarks have the lowest masses of all quarks.
The heavier quarks rapidly change into up and down quarks through a process of particle decay: the transformation from a higher mass state to a lower mass state.
Because of this, up and down quarks are generally stable and the most common in the universe, whereas strange, charm, bottom, and top quarks can only be produced in high energy collisions (such as those involving cosmic rays and in particle accelerators).
For every quark flavor there is a corresponding type of antiparticle, known as an antiquark, that differs from the quark only in that some of its properties (such as the electric charge) have equal magnitude but opposite sign.
The Standard Model is the theoretical framework describing all the currently known elementary particles. This model contains six flavors of quarks (q), named up (u), down (d), strange (s), charm (c), bottom (b), and top (t).
Antiparticles of quarks are called antiquarks, and are denoted by a bar over the symbol for the corresponding quark, such as ū for an up antiquark.
Elementary fermions are grouped into three generations, each comprising two leptons and two quarks. The first generation includes up and down quarks, the second strange and charm quarks, and the third bottom and top quarks.
Elementary fermions are grouped into three generations, each comprising two leptons and two quarks.
Hadrons contain, along with the valence quarks that contribute to their quantum numbers, virtual quark–antiquark pairs known as sea quarks.
The quarks that determine the quantum numbers of hadrons are called valence quarks; apart from these, any hadron may contain an indefinite number of virtual "sea" quarks, antiquarks, and gluons, which do not influence its quantum numbers.
A proton is a subatomic particle, symbol p or p+, with a positive electric charge of +1e elementary charge and a mass slightly less than that of a neutron.
The two up quarks and one down quark of a proton are held together by the strong force, mediated by gluons.
A modern perspective has a proton composed of the valence quarks (up, up, down), the gluons, and transitory pairs of sea quarks.
Protons and neutrons, each with masses of approximately one atomic mass unit, are collectively referred to as "nucleons" (particles present in atomic nuclei).
One or more protons are present in the nucleus of every atom; they are a necessary part of the nucleus.
The number of protons in the nucleus is the defining property of an element, and is referred to as the atomic number (represented by the symbol Z). Since each element has a unique number of protons, each element has its own unique atomic number.
Although protons were originally considered fundamental or elementary particles, in the modern Standard Model of particle physics, protons are classified as hadrons, like neutrons, the other nucleon.
Protons are composite particles composed of three valence quarks: two up quarks of charge + 2/3e and one down quark of charge –1/3e.
The rest masses of quarks contribute only about 1% of a proton's mass.
The remainder of a proton's mass is due to quantum chromodynamics binding energy, which includes the kinetic energy of the quarks and the energy of the gluon fields that bind the quarks together.
The neutron is a subatomic particle, symbol n or n0, with no electric charge and a mass slightly greater than that of a proton.
Protons and neutrons constitute the nuclei of atoms.
Since protons and neutrons behave similarly within the nucleus, and each has a mass of approximately one atomic mass unit, they are both referred to as nucleons.
A free neutron is unstable, decaying to a proton, electron and antineutrino with a mean lifetime of just under 15 minutes (881.5±1.5 s).
This radioactive decay, known as beta decay, is possible because the mass of the neutron is slightly greater than the proton.
The free proton is stable.
Neutrons or protons bound in a nucleus can be stable or unstable, however, depending on the nuclide.
Beta decay, in which neutrons decay to protons, or vice versa, is governed by the weak force, and it requires the emission or absorption of electrons and neutrinos, or their antiparticles.
The free neutron has a mass of 939,565,413.3 eV/c2, or 1.674927471×10−27 kg, or 1.00866491588 u.
The neutron has a mean square radius of about 0.8×10−15 m, or 0.8 fm, and it is a spin-½ fermion.
The neutron has no measurable electric charge. With its positive electric charge, the proton is directly influenced by electric fields, whereas the neutron is unaffected by electric fields.
The neutron has a magnetic moment, however, so the neutron is influenced by magnetic fields. The neutron's magnetic moment has a negative value, because its orientation is opposite to the neutron's spin.
The neutron is classified as a hadron, because it is a composite particle made of quarks. The neutron is also classified as a baryon, because it is composed of three valence quarks.
The finite size of the neutron and its magnetic moment both indicate that the neutron is a composite, rather than elementary, particle.
A neutron contains two down quarks with charge −​1⁄3 e and one up quark with charge +​2⁄3 e.
Protons and neutrons are both nucleons, which may be bound together by the nuclear force to form atomic nuclei.
The atomic number or proton number (symbol Z) of a chemical element is the number of protons found in the nucleus of every atom of that element.
A telescope is an optical instrument using lenses, curved mirrors [DISPUTED], or a combination of both to observe distant objects ...
The word telescope now refers to a wide range of instruments capable of detecting different regions of the electromagnetic spectrum, and in some cases other types of detectors.
The first known practical telescopes were refracting telescopes invented in the Netherlands at the beginning of the 17th century, by using glass lenses.
They were used for both terrestrial applications and astronomy.
All refracting telescopes use the same principles. The combination of an objective lens and some type of eyepiece is used to gather more light than the human eye is able to collect on its own, focus it, and present the viewer with a brighter, clearer, ...
An eyepiece, or ocular lens, is a type of lens that is attached to a variety of optical devices such as telescopes and microscopes. It is so named because it is usually the lens that is closest to the eye when someone looks through the device.
The reflecting telescope, which uses mirrors to collect and focus light, was invented within a few decades of the first refracting telescope.
In the 20th century, many new types of telescopes were invented, including radio telescopes in the 1930s and infrared telescopes in the 1960s.
A reflecting telescope (also called a reflector) is a telescope that uses a single or a combination of curved mirrors that reflect light and form an image.
Optical radiation is part of the electromagnetic spectrum. It is subdivided into ultraviolet radiation (UV), the spectrum of light visible for man (VIS) and infrared radiation (IR). It ranges between wavelengths of 100 nm to 1 mm [DISPUTED]
Infrared and optical astronomy are often practiced using the same telescopes, as the same mirrors or lenses are usually effective over a wavelength range that includes both visible and infrared light.
Infrared astronomy is the branch of astronomy and astrophysics that studies astronomical objects visible in infrared (IR) radiation.
The wavelength of infrared light ranges from 0.75 to 300 micrometers. Infrared falls in between visible radiation, which ranges from 380 to 750 nanometers, and submillimeter waves.
Radio frequency (RF) is the oscillation rate of an alternating electric current or voltage or of a magnetic, electric or electromagnetic field or mechanical system in the frequency range from around 20 kHz to around 300 GHz.
Ultraviolet (UV) is a form of electromagnetic radiation with wavelength from 10 nm (with a corresponding frequency of approximately 30 PHz) to 400 nm (750 THz), shorter than that of visible light but longer than X-rays.
There are no precisely defined boundaries between the bands of the electromagnetic spectrum; rather they fade into each other like the bands in a rainbow (which is the sub-spectrum of visible light).
Far infrared (FIR) is a region in the infrared spectrum of electromagnetic radiation. Far infrared is often defined as any radiation with a wavelength of 15 micrometers (μm) to 1 mm
Infrared radiation with wavelengths just longer than visible light, known as near-infrared, behaves in a very similar way to visible light, and can be detected using similar solid state devices ...
For this reason, the near infrared region of the spectrum is commonly incorporated as part of the "optical" spectrum, along with the near ultraviolet.
Many optical telescopes, such as those at Keck Observatory, operate effectively in the near infrared as well as at visible wavelengths.
Near Infrared: 2.0 to 2.4: Wavelength (micrometres): K band: Most major optical telescopes and most dedicated infrared telescopes
The value of c can ... be found by using the relation c = fλ.
The speed of light in vacuum, commonly denoted c, is a universal physical constant important in many areas of physics. Its exact value is defined as 299792458 metres per second (approximately 300000 km/s, or 186000 mi/s)
It is exact because, by international agreement, a metre is defined as the length of the path travelled by light in vacuum during a time interval of ​1⁄299792458 second.
Various sources define visible light as narrowly as 420–680 nm to as broadly as 380–800 nm.
Under ideal laboratory conditions, people can see infrared up to at least 1050 nm; children and young adults may perceive ultraviolet wavelengths down to about 310–313 nm.
An optical telescope is a telescope that gathers and focuses light, mainly from the visible part of the electromagnetic spectrum, to create a magnified image for direct view, or to make a photograph, or to collect data through electronic image sensors.
The basic scheme is that the primary light-gathering element, the objective (the convex lens or concave mirror used to gather the incoming light), focuses that light from the distant object to a focal plane where it forms a real image.
This image may be recorded or viewed through an eyepiece, which acts like a magnifying glass. The eye then sees an inverted [DISPUTED] magnified virtual image of the object.
Most telescope designs produce an inverted image at the focal plane; these are referred to as inverting telescopes.
There are telescope designs that do not present an inverted image such as the Galilean refractor and the Gregorian reflector. These are referred to as erecting telescopes.
A telescope's ability to resolve small detail is directly related to the diameter (or aperture) of its objective (the primary lens or mirror that collects and focuses the light), and its light gathering power is related to the area of the objective.
In some contexts, especially in photography and astronomy, aperture refers to the diameter of the aperture stop rather than the physical stop or the opening itself.
For example, in a telescope, the aperture stop is typically the edges of the objective lens or mirror (or of the mount that holds it). One then speaks of a telescope as having, for example, a 100-centimeter aperture.
In optical engineering, the objective is the optical element that gathers light from the object being observed and focuses the light rays to produce a real image.
Objectives can be a single lens or mirror, or combinations of several optical elements.
The objective lens or mirror collects light and brings it to focus creating an image.
The eyepiece is placed near the focal point of the objective to magnify this image. The amount of magnification depends on the focal length of the eyepiece.
In optics, an image is defined as the collection of focus points of light rays coming from an object.
A real image is the collection of focus points actually made by converging rays, while a virtual image is the collection of focus points made by extensions of diverging rays.
a virtual image is found by tracing real rays that emerge from an optical device (lens, mirror, or some combination) backward to perceived or apparent origins of ray divergences.
In diagrams of optical systems, virtual rays are conventionally represented by dotted lines.
Because the rays never really converge, a virtual image cannot be projected onto a screen. In contrast, a real image can be projected on the screen as it is formed by rays that converge on a real location.
A diverging lens (one that is thicker at the edges than the middle) or a convex mirror forms a virtual image. Such an image is reduced in size when compared to the original object.
A converging lens (one that is thicker in the middle than at the edges) or a concave mirror is also capable of producing a virtual image if the object is within the focal length. Such an image will be magnified.
A real image ... is an image which is located in the plane of convergence for the light rays that originate from a given object.
In ray diagrams ... real rays of light are always represented by full, solid lines; perceived or extrapolated rays of light are represented by dashed lines.
A real image occurs where rays converge, whereas a virtual image occurs where rays only appear to diverge.
In geometrical optics, a focus, also called an image point, is the point where light rays originating from a point on the object converge.
Although the focus is conceptually a point, physically the focus has a spatial extent, called the blur circle. This non-ideal focusing may be caused by aberrations of the imaging optics.
An object infinitely far from the optical system forms an image at the rear focal plane.
The front and rear (or back) focal planes are defined as the planes, perpendicular to the optic axis, which pass through the front and rear focal points.
If the medium surrounding the optical system has a refractive index of 1 (e.g., air or vacuum), then the distance from the principal planes to their corresponding focal points is just the focal length of the system.
A principal focus or focal point is a special focus: For a lens, or a spherical or parabolic mirror, it is a point onto which collimated light parallel to the axis is focused.
rays that enter the system parallel to the optical axis are focused such that they pass through the rear focal point
Schematic of a Keplerian refracting telescope. The arrow at (4) is a (notional) representation of the original image; the arrow at (5) is the inverted image at the focal plane; the arrow at (6) is the virtual image that forms in the viewer's visual sphere
This image may be ... viewed through an eyepiece, which acts like a magnifying glass. The eye then sees a ... magnified virtual image of the object.
This image may be ... viewed through an eyepiece, which acts like a magnifying glass. The eye then sees an inverted magnified virtual image of the object.
A curved primary mirror is the reflector telescope's basic optical element that creates an image at the focal plane [OF THE PRIMARY IF THERE IS NO SECONDARY]. The distance from the mirror to the focal plane is called the focal length.
Film or a digital sensor may be located here to record the image, or a secondary mirror may be added to modify the optical characteristics and/or redirect the light to film, digital sensors, or an eyepiece for visual observation.
The Gregorian telescope ... employs a concave secondary mirror that reflects the image back through a hole in the primary mirror. This produces an upright image
There are several large modern telescopes that use a Gregorian configuration such as the Vatican Advanced Technology Telescope, the Magellan telescopes, the Large Binocular Telescope, and the Giant Magellan Telescope.
The Newtonian telescope ... usually has a paraboloid primary mirror but at focal ratios of f/8 or longer a spherical primary mirror can be sufficient for high visual resolution.
A flat secondary mirror reflects the light to a focal plane at the side of the top of the telescope tube.
The cassegrain telescope (sometimes called the "Classic Cassegrain") ... has a parabolic primary mirror, and a hyperbolic secondary mirror that reflects the light back down through a hole in the primary.
The Ritchey–Chrétien telescope ... is a specialized Cassegrain reflector which has two hyperbolic mirrors (instead of a parabolic primary).
It is free of coma and spherical aberration at a nearly flat focal plane if the primary and secondary curvature are properly figured.
A segmented mirror is an array of smaller mirrors designed to act as segments of a single large curved mirror. ... They are used as objectives for large reflecting telescopes.
The Gregorian telescope consists of two concave mirrors; the primary mirror (a concave paraboloid) collects the light and brings it to a focus before the secondary mirror (a concave ellipsoid) where it is reflected back through a hole in the centre ...
In a prime focus design no secondary optics are used, the image is accessed at the focal point of the primary mirror.
Diagram of the lightpath through a Gregorian telescope.
The overall focal ratio of the complete telescope will be f/8 and the optical prescription is an aplanatic Gregorian telescope.
Light path in a Newtonian telescope.
Light path in a Cassegrain telescope.
In optics, the f-number of an optical system such as a camera lens is the ratio of the system's focal length to the diameter of the entrance pupil ("clear aperture"). It is also known as the focal ratio, f-ratio, or f-stop
Collapsible "truss tube" Dobsonians appeared in the amateur telescope making community as early as 1982 and allow the optical tube assembly, the largest component, to be broken down.
As the name implies, the "tube" of this design is actually composed of an upper 'cage assembly', which contains the secondary mirror, and focuser, held in place by several rigid poles over a ‘mirror box’ which contains the objective mirror.
In the Gregorian design, the primary mirror creates a real image before the secondary mirror. This allows for a field stop to be placed at this location, so that the light from outside the field of view does not reach the secondary mirror.
This is a major advantage for solar telescopes, where a field stop (Gregorian stop) can reduce the amount of heat reaching the secondary mirror and subsequent optical components.
In an imperfect lens L, all the rays do not pass through a focal point. The smallest circle that they pass through C is called the circle of least confusion.
Top: The formation of a real image using a convex lens. Bottom: The formation of a real image using a concave mirror. In both diagrams, f is the focal point, O is the object, and I is the image.
Top: The formation of a virtual image using a diverging lens. Bottom: The formation of a virtual image using a convex mirror. In both diagrams, f is the focal point, O is the object and I is the image, shown in grey ...
A trade study or trade-off study, also known as a figure of merit analysis or a factor of merit analysis, is the activity of a multidisciplinary team to identify the most balanced technical solutions among a set of proposed viable solutions (FAA 2006).
These viable solutions are judged by their satisfaction of a series of measures or cost functions. These measures describe the desirable characteristics of a solution. They may be conflicting or even mutually exclusive.
Trade studies are commonly used in the design of aerospace and automotive vehicles and the software selection process ... to find the configuration that best meets conflicting performance requirements.
In software engineering, dependency injection is a technique in which an object receives other objects that it depends on. These other objects are called dependencies.
In the typical "using" relationship the receiving object is called a client and the passed (that is, "injected") object is called a service. The code that passes the service to the client can be many kinds of things and is called the injector.
Instead of the client specifying which service it will use, the injector tells the client what service to use. The "injection" refers to the passing of a dependency (a service) into the object (a client) that would use it.
Validation can be expressed by the query "Are you building the right thing?" and verification by "Are you building it right?"
A sensor is a transducer that receives and responds to a signal or stimulus from a physical system. It produces a signal, which represents information about the system
An actuator is a device that is responsible for moving or controlling a mechanism or system. It is controlled by a signal from a control system or manual control.
René François Ghislain Magritte was a Belgian surrealist artist. He became well known for creating a number of witty and thought-provoking images.
Often depicting ordinary objects in an unusual context, his work is known for challenging observers' preconditioned perceptions of reality.
The famous pipe. How people reproached me for it! And yet, could you stuff my pipe? No, it's just a representation, is it not? So if I had written on my picture "This is a pipe", I'd have been lying!
In nonideal fluid dynamics, the Hagen–Poiseuille equation ... is a physical law that gives the pressure drop in an incompressible and Newtonian fluid in laminar flow flowing through a long cylindrical pipe of constant cross section.
Isobaric volumetric heat capacity C(P,v) J⋅cm−3⋅K−1 of liquid Water at 25 °C = 4.1796
Isobaric volumetric heat capacity C(P,v) J⋅cm−3⋅K−1 of liquid Water at 100 °C = 4.2160
The volumetric heat capacity of a material is the heat capacity of a sample of the substance divided by the volume of the sample.
Informally, it is the amount of energy that must be added, in the form of heat, to one unit of volume of the material in order to cause an increase of one unit in its temperature.
The SI unit of volumetric heat capacity is joule per kelvin per cubic meter, J/K/m3 or J/(K·m3).
The volumetric heat capacity can also be expressed as the specific heat capacity (heat capacity per unit of mass, in J/K/kg) times the density of the substance (in kg/L, or g/mL).
The enthalpy of vaporization (symbol ∆Hvap), also known as the (latent) heat of vaporization or heat of evaporation, is the amount of energy (enthalpy) that must be added to a liquid substance to transform a quantity of that substance into a gas.
The enthalpy of vaporization is a function of the pressure at which that transformation takes place.
The enthalpy of vaporization is often quoted for the normal boiling temperature of the substance.
The enthalpy of vaporization of Water at 100 deg C = 2257 (J/g)
The litre (British English spelling) or liter (American English spelling) (SI symbols L and l, other symbol used: ℓ) is a metric unit of volume. It is equal to 1 cubic decimetre (dm^3), 1000 cubic centimetres (cm^3) or 0.001 cubic metre (m^3).
Originally, the only symbol for the litre was l (lowercase letter L), following the SI convention that only those unit symbols that abbreviate the name of a person start with a capital letter.
Therefore, the digit "1" may easily be confused with the letter "l". In some computer typefaces, the two characters are barely distinguishable. As a result, L (uppercase letter L) was adopted by the CIPM as an alternative symbol for litre in 1979.
The United States National Institute of Standards and Technology now recommends the use of the uppercase letter L, a practice that is also widely followed in Canada and Australia.
In these countries, the symbol L is also used with prefixes, as in mL and μL, instead of the traditional ml and μl used in Europe.
In the UK and Ireland, as well as the rest of Europe, lowercase l is used with prefixes, though whole litres are often written in full (so, "750 ml" on a wine bottle, but often "1 litre" on a juice carton).
In 1990, the International Committee for Weights and Measures stated that it was too early to choose a single symbol for the litre.
In many English-speaking countries, however, the most common shape of a handwritten Arabic digit 1 is just a vertical stroke; that is, it lacks the upstroke added in many other cultures.
In thermodynamics, heat is energy in transfer to or from a thermodynamic system, by mechanisms other than thermodynamic work or transfer of matter.
"The quick brown fox jumps over the lazy dog" is an English-language pangram — a sentence that contains all of the letters of the English alphabet.
"The quick brown fox jumps over the lazy dog" ...
... an English-language pangram — a sentence that contains all of the letters of the English alphabet.
The modern English alphabet is a Latin alphabet consisting of 26 letters, each having an upper- and lower-case form.
The BFG (short for The Big Friendly Giant) is a 1982 children's book written by British novelist Roald Dahl and illustrated by Quentin Blake.
When he sets Sophie down, she begins to plead for her life, believing that the giant will eat her.
The giant laughs and explains that most giants do eat human beings (which he pronounces as "human beans") ..
The giant then says that he will not eat her as he is the Big Friendly Giant, or BFG for short.
The start of the book begins with an eight-year-old orphan girl named Sophie lying in bed ...
A semantic triple, or RDF triple or simply triple, is the atomic data entity in the Resource Description Framework (RDF) data model.
As its name indicates, a triple is a set of three entities that codifies a statement about semantic data in the form of subject–predicate–object expressions (e.g., "Bob is 35", or "Bob knows John").
Don't judge a book by its cover
JTAG (named after the Joint Test Action Group which codified it) is an industry standard for verifying designs and testing printed circuit boards after manufacture.
JTAG: The connector pins are: 1. TDI (Test Data In); 2. TDO (Test Data Out); 3. TCK (Test Clock); 4. TMS (Test Mode Select); 5. TRST (Test Reset) optional.
Precise measurements show that the boiling point of VSMOW water under one standard atmosphere of pressure is actually 373.1339 K (99.9839 °C) when adhering strictly to the two-point definition of thermodynamic temperature.
When calibrated to ITS-90, where one must interpolate between the defining points of gallium and indium, the boiling point of VSMOW water is about 10 mK less, about 99.974 °C.
In chemistry and in various industries, the reference pressure referred to in standard temperature and pressure (STP) was commonly 1 atm (101.325 kPa) but standards have since diverged;
In 1982, the International Union of Pure and Applied Chemistry (IUPAC) recommended that for the purposes of specifying the physical properties of substances, standard pressure should be precisely 100 kPa (1 bar).
As part of the 2019 redefinition of SI base units, the Boltzmann constant is one of the seven "defining constants" that have been given exact definitions. They are used in various combinations to define the seven SI base units.
The Boltzmann constant is defined to be exactly 1.380649×10^(−23) J⋅K^(−1)
A thermodynamic system does not contain heat. Nevertheless, the term is also often used to refer to the thermal energy contained in a system as a component of its internal energy and that is reflected in the temperature of the system.
Heat is energy in transfer to or from a thermodynamic system, by a mechanism that involves the microscopic atomic modes of motion or the corresponding macroscopic properties.
Defined quantitatively, the heat involved in a process is the difference in internal energy between the final and initial states of a system, and subtracting the work done in the process. This is the formulation of the first law of thermodynamics.
In thermodynamics, heat is defined as the form of energy crossing the boundary of a thermodynamic system by virtue of a temperature difference across the boundary
Heat released by a system into its surroundings is by convention a negative quantity (Q < 0); when a system absorbs heat from its surroundings, it is positive (Q > 0).
In physics, a vapor or vapour is a substance in the gas phase at a temperature which means that the vapor can be condensed to a liquid by increasing the pressure on it without reducing the temperature of the vapor.
Vapor refers to a gas phase at a temperature where the same substance can also exist in the liquid or solid state, below the critical temperature of the substance.
"Don't repeat yourself" (DRY) is a principle of software development aimed at reducing repetition of information which is likely to change, replacing it with abstractions that are less likely to change, or using data normalization which avoids redundancy.
The DRY principle is stated as "Every piece of knowledge must have a single, unambiguous, authoritative representation within a system". The principle has been formulated by Andy Hunt and Dave Thomas in their book The Pragmatic Programmer.
When the DRY principle is applied successfully, a modification of any single element of a system does not require a change in other logically unrelated elements. Additionally, elements that are logically related all change predictably and uniformly, ...
WET: The opposing view to DRY is called WET, a backronym commonly taken to stand for write everything twice (alternatively write every time, we enjoy typing or waste everyone's time).
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