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A20

A cytoplasmic zinc finger protein (790 aa) that inhibits NFκB activity and TNF-mediated programmed cell death. The expression of the A20 mRNA is upregulated by TNFα. It is a dual function ...

audibility

audibility   Quick reference

A Dictionary of Physics (8 ed.)

Reference type:
Subject Reference
Current Version:
2019
Subject:
Science and technology, Physics
Length:
33 words

...audibility The limits of audibility of the human ear are between about 20 hertz (a low rumble) and 20 000 hertz (a shrill whistle). With increased age the upper limit falls quite...

freezing mixture

freezing mixture   Quick reference

A Dictionary of Physics (8 ed.)

Reference type:
Subject Reference
Current Version:
2019
Subject:
Science and technology, Physics
Length:
25 words

...freezing mixture A mixture of components that produces a low temperature. For example, a mixture of ice and sodium chloride gives a temperature of −20...

cobalt steel

cobalt steel   Quick reference

A Dictionary of Physics (8 ed.)

Reference type:
Subject Reference
Current Version:
2019
Subject:
Science and technology, Physics
Length:
40 words

...cobalt steel Any of a group of alloy steels containing 5–12% of cobalt, 14–20% of tungsten, usually with 4% of chromium and 1–2% of vanadium. They are very hard but somewhat brittle. Their main use is in high-speed...

tennessine

tennessine   Quick reference

A Dictionary of Physics (8 ed.)

Reference type:
Subject Reference
Current Version:
2019
Subject:
Science and technology, Physics
Length:
60 words

...tennessine Symbol Ts. A radioactive transuranic element that is a p -block transactinide element ; a.n. 117; mass number of the most stable isotope 294, with a half-life of about 50 ms (there is one other main isotope). Tennessine was discovered in the first decade of the 21st century in a nuclear reaction between berkelium -249 and calcium-20...

loudspeaker

loudspeaker   Quick reference

A Dictionary of Physics (8 ed.)

Reference type:
Subject Reference
Current Version:
2019
Subject:
Science and technology, Physics
Length:
100 words

... A transducer for converting an electrical signal into an acoustic signal. Usually it is important to preserve as many characteristics of the electrical waveform as possible. The device must be capable of reproducing frequencies in the range 150–8000 hertz for speech and 2020 000 Hz for music. The most common loudspeaker consists of a moving-coil device. In this a cone-shaped diaphragm is attached to a coil of wire and made to vibrate in accordance with the electrical signal by the interaction between the current passing through the coil and a steady...

resistivity

resistivity   Quick reference

A Dictionary of Physics (8 ed.)

Reference type:
Subject Reference
Current Version:
2019
Subject:
Science and technology, Physics
Length:
83 words

...resistivity Symbol ρ ‎. A measure of a material’s ability to oppose the flow of an electric current. The resistivity of a material is given by RA / l , where R is the resistance of a uniform specimen of the material, having a length l and a cross-sectional area A . It is usually given at 0°C or 20°C and is measured in ohm metres. It was formerly known as specific resistance . http://www.kayelaby.npl.co.uk/general_physics/2_6/2_6_1.html Values of resistivity for a range of materials at the NPL...

sound

sound   Quick reference

A Dictionary of Physics (8 ed.)

Reference type:
Subject Reference
Current Version:
2019
Subject:
Science and technology, Physics
Length:
143 words

...sound A vibration in an elastic medium at a frequency and intensity that is capable of being heard by the human ear. The frequency of sounds lie in the range 2020 000 Hz, but the ability to hear sounds in the upper part of the frequency range declines with age ( see also pitch ). Vibrations that have a lower frequency than sound are called infrasounds and those with a higher frequency are called ultrasounds . Sound is propagated through an elastic fluid as a longitudinal sound wave , in which a region of high pressure travels through the fluid at...

ammonia clock

ammonia clock   Quick reference

A Dictionary of Physics (8 ed.)

Reference type:
Subject Reference
Current Version:
2019
Subject:
Science and technology, Physics
Length:
138 words

...ammonia clock A form of atomic clock in which the frequency of a quartz oscillator is controlled by the vibrations of excited ammonia molecules ( see excitation ). The ammonia molecule (NH 3 ) consists of a pyramid with a nitrogen atom at the apex and one hydrogen atom at each corner of the triangular base. When the molecule is excited, once every 20.9 microseconds the nitrogen atom passes through the base and forms a pyramid the other side: 20.9 microseconds later it returns to its original position. This vibration back and forth has a frequency of 23...

noise

noise   Quick reference

A Dictionary of Physics (8 ed.)

Reference type:
Subject Reference
Current Version:
2019
Subject:
Science and technology, Physics
Length:
85 words
Illustration(s):
1

...noise 1. Any undesired sound. It is measured on a decibel scale ranging from the threshold of hearing (0 dB) to the threshold of pain (130 dB). Between these limits a whisper registers about 20 dB, heavy urban traffic about 90 dB, and a heavy hammer on steel plate about 110 dB. A high noise level (industrial or from overamplified music, for example) can cause permanent hearing impairment. 2. Any unwanted disturbance within a useful frequency band in a communication channel. Noise. Decibel scale. ...

tomography

tomography   Quick reference

A Dictionary of Physics (8 ed.)

Reference type:
Subject Reference
Current Version:
2019
Subject:
Science and technology, Physics
Length:
87 words

...tomography The use of X-rays to photograph a selected plane of a human body with other planes eliminated. The CT ( computerized tomography ) scanner is a ring-shaped X-ray machine that rotates through 180° around the horizontal patient, making numerous X-ray measurements every few degrees. The vast amount of information acquired is built into a three-dimensional image of the tissues under examination by the scanner’s own computer. The patient is exposed to a dose of X-rays only some 20% of that used in a normal diagnostic...

nihonium

nihonium   Quick reference

A Dictionary of Physics (8 ed.)

Reference type:
Subject Reference
Current Version:
2019
Subject:
Science and technology, Physics
Length:
79 words

...nihonium Symbol Nh. A radioactive transuranic element that is a p -block transactinide element ; a.n. 113; mass number of the most stable isotope 286, with a half-life of about eight seconds. It has been predicted that the heavier isotope rihonium-287 might have a half-life of about 20 minutes, but this isotope has not been discovered yet. There are seven main isotopes of nihonium. Nihonium was discovered in the 1900s using a nuclear reaction between bismuth-209 and...

speed of sound

speed of sound   Quick reference

A Dictionary of Physics (8 ed.)

Reference type:
Subject Reference
Current Version:
2019
Subject:
Science and technology, Physics
Length:
217 words

...s . The speed at which sound waves are propagated through a material medium. In air at 20°C sound travels at 344 m s −1 , in water at 20°C it travels at 1461 m s −1 , and in steel at 20°C at 5000 m s −1 . The speed of sound in a medium depends on the medium’s modulus of elasticity ( E ) and its density ( ρ ‎) according to the relationship c =√( E / ρ ‎). For longitudinal waves in a narrow solid specimen, E is the Young modulus; for a liquid E is the bulk modulus ( see elastic modulus ); and for a gas E = γ ‎ p , where γ ‎ is the ratio of the principal...

nucleon emission

nucleon emission   Quick reference

A Dictionary of Physics (8 ed.)

Reference type:
Subject Reference
Current Version:
2019
Subject:
Science and technology, Physics
Length:
152 words

...nucleon emission A decay mechanism in which a particularly unstable nuclide regains some stability by the emission of a nucleon (i.e. a proton or neutron). Proton emitters have fewer neutrons than their stable isotopes. Proton emitters are therefore found below the Segrè plot stability line. For example, 17 Ne (neon–17) has three fewer neutrons than its most abundant stable isotope 20 Ne (neon–20). There are no naturally occurring proton emitters. Neutron emitters have many more neutrons than their stable isotopes. For this reason, emitters may be found...

binary prefixes

binary prefixes   Quick reference

A Dictionary of Physics (8 ed.)

Reference type:
Subject Reference
Current Version:
2019
Subject:
Science and technology, Physics
Length:
259 words

...is taken to be 2 20 (1 048 576) rather than 10 6 (1 000 000). However, there is a variation in usage depending on the context. In discussing memory capacities megabyte generally means 2 20 bytes, but in disk storage (and data transmission) megabyte is often taken to mean 10 6 bytes. (In some contexts, as in the capacity of a floppy disk, it has even been quoted as 1 024 000 bytes, i.e. 1000 times a (binary) kilobyte.) The IEC attempted to resolve this confusion by introducing binary prefixes, modelled on the normal decimal prefixes, as follows: kibi-...

sherardizing

sherardizing   Quick reference

A Dictionary of Physics (8 ed.)

Reference type:
Subject Reference
Current Version:
2019
Subject:
Science and technology, Physics
Length:
75 words

...sherardizing The process of coating iron or steel with a zinc corrosion-resistant layer by heating the iron or steel in contact with zinc dust to a temperature slightly below the melting point of zinc. At a temperature of about 371°C the two metals amalgamate to form internal layers of zinc–iron alloys and an external layer of pure zinc. The process was invented by Sherard Cowper-Coles ( 1867–1935 ) at the beginning of the 20th...

Planck, Max Karl Ernst Ludwig

Planck, Max Karl Ernst Ludwig (1858–1947)   Quick reference

A Dictionary of Physics (8 ed.)

Reference type:
Subject Reference
Current Version:
2019
Subject:
Science and technology, Physics
Length:
80 words

...Planck, Max Karl Ernst Ludwig ( 1858–1947 ) German physicist , who became a professor at Berlin University in 1892 . Here he formulated the quantum theory , which had its basis in a paper of 1900 . ( See also Planck constant ; Planck’s radiation law .) One of the most important scientific discoveries of the 20th century, this theory earned him the 1918 Nobel Prize for physics. He also made important contributions to thermodynamics and the special theory of relativity...

geocentric universe

geocentric universe   Quick reference

A Dictionary of Physics (8 ed.)

Reference type:
Subject Reference
Current Version:
2019
Subject:
Science and technology, Physics
Length:
89 words

...geocentric universe A view of the universe in which the earth is regarded as being at its centre. Galileo Galilei finally established that the earth revolves round the sun (not the other way round, as the church believed); during the 20th century it became clear from advances in observational astronomy that the earth is no more than one of a number of planets orbiting the sun, which is one of countless millions of similar stars, many of which undoubtedly possess planetary bodies on which life could have...

ultrasonics

ultrasonics   Quick reference

A Dictionary of Physics (8 ed.)

Reference type:
Subject Reference
Current Version:
2019
Subject:
Science and technology, Physics
Length:
97 words

...ultrasonics The study and use of pressure waves that have a frequency in excess of 20 000 Hz and are therefore inaudible to the human ear. Ultrasonic generators make use of the piezoelectric effect , ferroelectric materials , or magnetostriction to act as transducers in converting electrical energy into mechanical energy. Ultrasonics are used in medical diagnosis, particularly in conditions such as pregnancy, in which X-rays could have a harmful effect. Ultrasonic techniques are also used industrially to test for flaws in metals, to clean surfaces, to...

flerovium

flerovium   Quick reference

A Dictionary of Physics (8 ed.)

Reference type:
Subject Reference
Current Version:
2019
Subject:
Science and technology, Physics
Length:
85 words

...flerovium Symbol Fl. A radioactive transactinide element ; a.n. 114. It was first made in 1998 at Dubna, Russia, by bombarding plutonium–244 nuclei with calcium–20 nuclei and also occurs from the decay of even heavier elements. About 80 atoms of flerovium have been made. It is thought that the isotope flerovium–298 should be relatively long-lived since both the number of protons (114) and that of neutrons (184) are magic numbers . Flerovium is named after the Russian nuclear physicist Georgy Flerov...

cryogenic pump

cryogenic pump   Quick reference

A Dictionary of Physics (8 ed.)

Reference type:
Subject Reference
Current Version:
2019
Subject:
Science and technology, Physics
Length:
71 words

...cryogenic pump A vacuum pump in which pressure is reduced by condensing gases on surfaces maintained at about 20 K by means of liquid hydrogen or at 4 K by means of liquid helium. Pressures down to 10 −8 mmHg (10 −6 Pa) can be maintained; if they are used in conjunction with a diffusion pump , pressures as low as 10 −15 mmHg (10 −13 Pa) can be...

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