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p20

1. p20-ARC One of the subunits of ARP2/3. 2. p20-CGGBP (CGG-binding protein1) A protein that binds to the unmethylated form of the trinucleotide repeat ...

speed of sound

speed of sound  

Symbol c or cs. 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 ...
wind power

wind power  

The use of winds in the earth's atmosphere to drive machinery, especially to drive an electrical generator. Practical land-based wind generators ( aerogenerators) are probably capable of providing ...
oscillator

oscillator  

An electronic device that produces an alternating output of known frequency. If the output voltage or current has the form of a sine wave with respect to time, the device is called a sinusoidal (or ...
electronics

electronics  

The study and design of control, communication, and computing devices that rely on the movement of electrons in circuits containing semiconductors, thermionic valves, resistors, capacitors, and ...
mass

mass  

A measure of a body's inertia, i.e. its resistance to acceleration. According to Newton's laws of motion, if two unequal masses, m1 and m2, are allowed to collide, in the absence of any other forces ...
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...

americium

americium   Quick reference

A Dictionary of Physics (8 ed.)

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

...americium Symbol Am. A radioactive metallic transuranic element belonging to the actinoids; a.n. 95; mass number of most stable isotope 243 (half-life 7.95 × 10 3 years); r.d. 13.67 (20°C); m.p. 994 ± 4°C; b.p. 2607°C. Ten isotopes are known. The element was discovered by G. T. Seaborg and associates in 1945 , who obtained it by bombarding uranium–238 with alpha...

plutonium

plutonium   Quick reference

A Dictionary of Physics (8 ed.)

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

...transuranic element belonging to the actinoids; a.n. 94; mass number of most stable isotope 244 (half-life 7.6×10 7 years); r.d. 19.84; m.p. 641°C; b.p. 3232°C. Thirteen isotopes are known, by far the most important being plutonium–239 (half-life 2.44×10 4 years), which undergoes nuclear fission with slow neutrons and is therefore a vital power source for nuclear weapons and some nuclear reactors . About 20 tonnes of plutonium are produced annually by the world’s nuclear reactors, a detailed inventory of every gram of which is kept in order to...

radon

radon   Quick reference

A Dictionary of Physics (8 ed.)

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

...radon Symbol Rn. A colourless radioactive gaseous element belonging to group 18 of the periodic table (the noble gases); a.n. 86; r.a.m. 222; d. 9.73 g dm −3 ; m.p. −71°C; b.p. −61.8°C. At least 20 isotopes are known, the most stable being radon–222 (half-life 3.8 days). It is formed by decay of radium–226 and undergoes alpha decay. It is used in radiotherapy. Radon occurs naturally, particularly in areas underlain by granite, where it is thought to be a health hazard. As a noble gas, radon is practically inert, although a few compounds, e.g. radon...

wind power

wind power   Quick reference

A Dictionary of Physics (8 ed.)

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

...the earth’s atmosphere to drive machinery, especially to drive an electrical generator. Practical land-based wind generators ( aerogenerators ) are probably capable of providing some 10 20 J (10 14 kW h) of energy per year throughout the world and interest in this form of renewable energy is increasing. The power, P , available to drive a wind generator is given by P = kd 2 v 3 , where k is the air density, d is the diameter of the blades, and v is the average wind speed. Wind farms now exist in many parts of the world; California, for example, has...

astatine

astatine   Quick reference

A Dictionary of Physics (8 ed.)

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

...astatine Symbol At. A radioactive halogen element; a.n. 85; r.a.m. 211; m.p. 302°C; b.p. 337°C. It occurs naturally by radioactive decay from uranium and thorium isotopes. Astatine forms at least 20 isotopes, the most stable astatine–210 has a half-life of 8.3 hours. It can also be produced by alpha bombardment of bismuth–200. Astatine is stated to be more metallic than iodine; at least five oxidation states are known in aqueous solutions. It will form interhalogen compounds, such as AtI and AtCl. The existence of At 2 has not yet been established. The...

uranium

uranium   Quick reference

A Dictionary of Physics (8 ed.)

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

...uranium Symbol U. A white radioactive metallic element belonging to the actinoids; a.n. 92; r.a.m. 238.03; r.d. 19.05 (20°C); m.p. 1132±1°C; b.p. 3818°C. It occurs as uraninite, from which the metal is extracted by an ion-exchange process. Three isotopes are found in nature: uranium–238 (99.28%), uranium–235 (0.71%), and uranium–234 (0.006%). As uranium–235 undergoes nuclear fission with slow neutrons it is the fuel used in nuclear reactors and nuclear weapons . Uranium was discovered by Martin Heinrich Klaproth ( 1743–1817 ) in 1789 . See also ...

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...

relative density

relative density   Quick reference

A Dictionary of Physics (8 ed.)

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

...density ( r.d. ) The ratio of the density of a substance to the density of some reference substance. For liquids or solids it is the ratio of the density (usually at 20°C) to the density of water (at its maximum density). This quantity was formerly called specific gravity . Sometimes relative densities of gases are used; for example, relative to dry air, both gases being at s.t.p...

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

...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 specific heat capacities and p is the pressure of the...

deuterium

deuterium   Quick reference

A Dictionary of Physics (8 ed.)

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

...or fractional distillation. Its chemical behaviour is almost identical to hydrogen although deuterium compounds tend to react rather more slowly than the corresponding hydrogen compounds. Its physical properties are slightly different from those of hydrogen, e.g. b.p. 23.6 K (hydrogen 20.4...

quantum mechanics

quantum mechanics   Quick reference

A Dictionary of Physics (8 ed.)

Reference type:
Subject Reference
Current Version:
2019
Subject:
Science and technology, Physics
Length:
1,612 words
Illustration(s):
3

...transported by an electromagnetic wave at a rate W joules per unit area per second, the wave exerts a radiation pressure W/c , where c is the speed of light. Planck’s expression for the energy of photons therefore led to an equivalent expression for the momentum p of these photons: p = h / λ , where λ ‎ is the wavelength of the light. Experimental studies of the Compton effect produce results in good agreement with this expression. Both the photoelectric effect and the Compton effect imply that light imparts energy and momentum to matter in the form...

phon

phon   Quick reference

A Dictionary of Weights, Measures, and Units

Reference type:
Subject Reference
Current Version:
2004

...acoustics . Symbol P. A measure of loudness level, as agreed in 1937 at the first International Acoustical Conference, Nature 140, 370 (1937) the decibels of sound pressure above 20 μPa of a pure tone of 1 000 Hz subjectively judged by a group of listeners as equally loud as the sound being measured. ISO 131:1979 Acoustics – Expression of Physical and Subjective Magnitudes of Sound and Noise in Air (The reference pressure was 316 μPa earlier.) If p and s represent the loudness respectively in phons and sones, then p = 40 + 10 log 2 s...

alpha particle mass

alpha particle mass   Quick reference

A Dictionary of Weights, Measures, and Units

Reference type:
Subject Reference
Current Version:
2004

...particle mass sub-atomic physics . Symbol m α . 6.644 656 20(33) × 10 -27 kg = 7 294.299 536 5(31) m e with relative standard uncertainties 5.0 × 10 -8 and 4.2 × 10 -10 . Mohr P. J. , Taylor B. N. CODATA Recommended Values of the Fundamental Physical Constants: 2002 (to be published) Mohr P. J. , Taylor B. N. Rev. Mod. Phys. 72:351–495 (2000) Mohr P. Phys. Today 53:7, 11–16 (2000) For latest recommended values, see ...

poise

poise   Quick reference

A Dictionary of Weights, Measures, and Units

Reference type:
Subject Reference
Current Version:
2004

...[ J. L. M. Poiseuille ; France 1799–1869 ] dynamic viscosity . Symbol P. Metric-c.g.s. Identically dyne⋅second per square centimetre (dyn⋅s⋅cm -2 ) = 10 -1 N⋅s⋅m -2 = 10 -1 Pa⋅s(= cm -1 ⋅g⋅s -1 in c.g.s. base terms). Hence • P⋅(g⋅cm -3 ) -1 = stokes for kinematic viscosity. The poise is a large unit for most purposes, water at 20°C having a viscosity of 10.020∼ mP and most free-flowing liquids typically being similar; gases are around 1 μP. There is no equivalent special term in the...

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