Добавил:

fench Опубликованный материал нарушает ваши авторские права? Сообщите нам.

Вуз:

Сумский государственный университет

Предмет:

Английский язык

Файл:

Dictionary of Geophysics, Astrophysic, and Astronomy.pdf

Скачиваний:

122

Добавлен:

10.08.2013

Размер:

5.66 Mб

Скачать

☆

►Содержание►

<<< < Предыдущая 56 57 58 59 60 61 62 63 64 65 66 6768 / 13068 69 70 71 72 73 74 75 76 77 78 79 80 > Следующая >>>

Kelvin (Thompson) circulation theorem

Kelvin (Thompson) circulation theorem In a perfect ﬂuid, the circulation of the velocity of a ﬂuid element is constant as the element moves along ﬂow lines.

Keplerian map In planetary dynamics, an approximate but fast method to solve for the orbital evolution of a small body such as a comet in the solar system under the inﬂuence of the planetary perturbations. One assumes that planetary perturbations become signiﬁcant only during the short duration around perihelion passage, and the orbit changes either by systematic, or in some cases approximately random, small jumps from one Keplerian orbit to another, as the small body passes perihelion.

Kepler shear The velocity difference between particles in adjacent Keplerian orbits about a central massive body.

Kepler’s laws Observations of the motion of planets due to Johannes Kepler.

1.All planets move in elliptical orbits, with the sun at one focus of the ellipse.

2.The line connecting the sun and the planet sweeps out equal areas in equal times.

3.The square of the period T of orbit of a planet is proportional to the cube semimajor axis

a of its orbit:

T 2 = ka3

where the proportionality factor k is the same for all planets.

Kepler’s supernova (SN1604, 3C358) A supernova that occurred in 1604 and was ﬁrst observed by Kepler on October 17 of that year. Kepler reported that the star was initially as bright as Mars, then brightened and surpassed Jupiter within a few days, suggesting a peak brightness of magnitude −2.25. It plateaued at this brightness as it was lost in twilight of November 1604. It reappeared in January 1605, and Kepler found it still brighter than Antares (m = 1). It remained visible until March 1606, a naked-eye visibility of 18 months. From its light curve, it was almost certainly type I supernova. A remnant is now found at Right Ascension: 17h27 42 and Declination: −21◦27 . It is now observable as a remnant of about 3 arcmin diameter, consisting of faint ﬁlaments in

the optical, but as a shell in the radio and in X-ray. The distance is approximately 4.4 kpc.

Kerr black hole (1963) A rotating black hole, i.e., a black hole with angular momentum associated to its spinning motion. The spin axis of the Kerr black hole breaks the spherical symmetry of a nonrotating (Schwarzschild) black hole, and identiﬁes a preferential orientation in the space-time. In the vicinity of the hole, below a limiting distance called the static radius, the rotation of the hole forces every observer to orbit the black hole in the same direction as the black hole rotates. Inside the static radius is the event horizon (the true surface of the black hole). These two surfaces delimit the ergosphere of the Kerr black hole, a region from which a particle can in principle escape, extracting some of the rotational kinetic energy of the black hole. On theoretical grounds it is expected that gravitational collapse of massive stars or star systems will create spinning Kerr black holes, and the escape of particles from the ergosphere, may play an important role as the power source and collimation mechanism of jets observed in radio galaxies and quasars. See quasar.

Kerr metric (1963) The metric
ds2 =		2a2 cos2 θ	du + a sin2		2
− 1 − r2				θdφ
		Mr
		+
+ 2	du + a sin2 θdφ dr + a sin2 θdφ
+ r2 + a2 cos2 θ dθ2 + sin2 θdφ2

discovered by R.P. Kerr and representing the gravitational ﬁeld of a rotating Kerr black hole of mass M and angular momentum aM, when the condition a2 ≤ M2 holds. When the condition is not met, the space-time singularity at r = 0 and θ = π2 is “naked”, giving rise to global causality violation. Uniqueness theorems have been proven that (at least with a topology of a two-sphere of the event horizon) there are no other stationary vacuum black hole metrics, assuming general relativity is the correct theory of gravity. See cosmic censorship.

Kerr–Newman metric The unique asymptotically ﬂat general relativistic metric describ-

Killing horizon

ing the gravitational ﬁeld outside a rotating axisymmetric, electrically charged source. When the electric charge is zero, the metric becomes the Kerr metric.

The line element in Boyer–Lindquist coordinates (t, r, θ, φ) is

ds2 = − ρ2 & dt2 '2

+ '2 dφ2 − 2 a M r dt 2 ρ2 '2

+ρ2 dr2 + ρ2 dθ2 ,

where ρ2 = r2 + a2 cos2 θ, & = (r − r+) (r − r−), and '2 = (r2 + a2)2 − a2 & sin2 θ. The

quantity M is the ADM mass of the source, a ≡ J/M its angular momentum per unit mass, and Q its electric charge. When Q = 0 one also has an electromagnetic ﬁeld given by

Q r2 − a2 cos2 θ

ρ4

Fφr

a sin2 θ Frt

Ftθ

a2 r sin 2θ

ρ4

θφ

r2 + a2

tθ

For M2 < a2 + Q2

the metric describes

0 and θ

π/2.

naked singularity at

For M

≥ a

+ Q

the metric

describes

a charged, spinning black hole. See also Reissner–Nordström metric, black hole, naked singularity.

Kerr–Schild space-times The collection of metrics

ds2 = λ-a-bdxadxb + ds02

where λ is the parameter and ds02 is the “seed” metric, often assumed to be the Minkowski metric. The vector - is null with respect to all metrics of the collection. Many space-times, e.g., the Kerr metric and the plane-fronted gravitational waves, are in the Kerr–Schild class.

Keulegan–Carpenter Number A dimensionless parameter used in the study of waveinduced forces on structures. The Keulegan– Carpenter Number is deﬁned as u¯maxT /D,

where u¯max is the maximum wave-induced velocity, averaged over the water depth, T is wave period, and D is structure diameter.

K-function Diffuse attenuation coefﬁcient.

Kibble mechanism Process by which defects (strings, monopoles, domain walls) are produced in phase transitions occurring in the matter. In the simplest cases there is a ﬁeld

φ(called the Higgs ﬁeld) whose lowest-energy state evolves smoothly from an expected value of zero at high temperatures to some nonzero

φat low temperatures which gives minimum energies, but there is more than one such minimum energy (vacuum) conﬁguration. Both thermal and quantum ﬂuctuations inﬂuence the new value taken by φ, leading to the existence of domains wherein φ is coherent and regions where it is not. The coherent regions have typical size ξ,

the coherence length. Thus, points separated by r ξ will belong to domains with, in principle, arbitrarily different orientations of the ﬁeld. It is the interfaces of these different regions (sheets, strings, points) which become the topological defects. In cosmology, this is viewed as occurring in the early universe. Because of the ﬁnite speed of light, ξ is bounded by the distance light

	−	1	where
can travel in one Hubble time: ξ < H

H is the Hubble constant expressed as an inverse length. In cosmology, the defects (cosmic domain walls, cosmic strings, etc.) can have an important effect on later formation of cosmic inhomogeneities.

Kibel, I.A. (1904–1970) Regarded by many as the founder of the Soviet school of modern dynamical meteorology. He made important contributions to the theory of gas dynamics, nonhomogeneous turbulence in a compressible ﬂuid, the atmospheric boundary layer, cloud dynamics, global climate, and mesoscale wind systems.

Killing horizon The set of points where a non-vanishing Killing vector becomes null, i.e., lightlike. Examples are given by the horizons in the Schwarzschild, Reissner–Nordström, and Kerr–Newman metric.

Killing tensor

Killing tensor A totally symmetric n-index tensor ﬁeld Ka1...an which satisﬁes the equation

(bKa1...an) = 0 .

(the round brackets denote symmetrization). A trivial Killing tensor is a product of lower-rank Killing tensors. See Killing vector.

Killing vector The vector generator ξ associated with an isometry. When the Killing vector exists it may be viewed as generating an inﬁnitesimal displacement of coordinates xµ → xµ + 3 ξµ (|3| 1), with the essential feature that this motion is an isometry of the metric and of any auxiliary geometrical objects (e.g., matter ﬁelds). Such a vector satisﬁes the Killing condition

Lξ , g = 0 .

the vanishing of the Lie derivative of the metric tensor. In coordinates this is equivalent to ξµ;ν + ξν;µ = 0 where ; denotes a covariant derivative with respect to the metric. Similarly, other geometrical objects, T , satisfy Lξ T = 0.

In a coordinate system adapted to the Killing vector, ξ = ∂x∂a , the metric and other ﬁelds do not depend on the coordinate xa. The Killing vectors of a given D-dimensional metric space form a vector space whose maximum possible dimension is D (D + 1)/2. Wilhelm Killing (1888). See isometry.

K index The K index is a 3-hourly quasilogarithmic local index of geomagnetic activity based on the range of variation in the observed magnetic ﬁeld measured relative to an assumed quiet-day curve for the recording site. The range of the index is from 0 to 9. The K index measures the deviation of the most disturbed of the two horizontal components of the Earth’s magnetic ﬁeld. See geomagnetic indices.

kinematical invariants The quantities associated with the ﬂow of a continuous medium: acceleration, expansion, rotation, and shear. In a generic ﬂow, they are nonzero simultaneously.

kinematics The study of motion of noninteracting objects, and relations among force, position, velocity, and acceleration.

kinematic viscosity Molecular viscosity divided by ﬂuid density, ν = µ/ρ, where ν = kinematic viscosity, µ = molecular (or dynamic or absolute) viscosity, and ρ = ﬂuid density. See eddy viscosity, dynamic viscosity.

kinetic energy The energy associated with moving mass; since it is an energy, it has the units of ergs or Joules in metric systems. In nonrelativistic systems, for a point mass, in which position is described in rectangular coordinates {xi i = 1 · · · N, where N = the dimension of the space, the kinetic energy T is

T =	1	vi2
	2 m

=1 mδij vi vj

δij	= 1 if i = j; δij = 0 otherwise. Since
δij	are the components of the metric tensor in

rectangular coordinates, it can be seen that T is m2 times the square of velocity v, computed as a vector T = m2 (v · v). This can be computed in any frame, and in terms of components involves the components gij of the metric tensor as

T = mgij vi vj ,

where vi are now the components of velocity expressed in the general non-rectangular frame.

In systems involving ﬂuids, one can assign a kinetic energy density. Thus, if ρ is the mass velocity, the kinetic energy density (Joules/m3) is t = ρvv.

For relativistic motion, the kinetic energy is the increase in the relativistic mass with motion.

We use E	=	γ mc2						of
	=			, where m is the rest mass 10
				1		=	×	10
the object, c is the speed of light, c 3								10
cm/sec, and γ						is the relativistic dila-

			= 1− c2
					v2

tion factor and T = E −mc2. If v is small compared to c, then Taylor expansion of γ around v = 0 gives

T = m2c 1 +	1 v2			3 v4				− mc2
			+				· · ·
	2	c2			8	c4

which agrees with the nonrelativistic deﬁnition of kinetic energy, and also exhibits the ﬁrst relativistic correction. Since v c in everyday experience, relativistic corrections are not usually

Kolmogorov scale (Kolmogorov microscale)

observed. However, these corrections are extremely important in many atomic and nuclear processes, and in large-scale astrophysical processes. See summation convention.

kinetic temperature A measure of the random kinetic energy associated with a velocity distribution of particles. Kinetic temperatures are often given for gases that are far from thermal equilibrium, and the kinetic temperature should not be confused with thermodynamic temperature, even though the two can be expressed in the same units. Kinetic temperatures are most often given in Kelvin, though they are sometimes expressed in electron volts or other energy units. If the velocity distribution is isotropic, the kinetic temperature T is related to the mean square velocity v2 by

3kT = m v2 ,

where m is the particle mass, k is Boltzmann’s constant, and the velocity is reckoned in a reference frame in which the mean velocity v = 0. In a gyrotropic plasma it is common to speak of kinetic temperatures transverse and parallel to the magnetic ﬁeld,

2kT = m v2 ,

and

kT = m v2 .

Note that electrons and the various ion species comprising a plasma will in general have differing kinetic temperatures. See plasma stress tensor.

kink In materials, abrupt changes in the dislocation line direction which lie in the glide plane. In cosmic strings, the discontinuity in cosmic string motion occurring when two cosmic strings intersect and intercommute because segments of different strings previously evolving independently (both in velocity and direction) suddenly become connected. Similar behavior is seen in ﬂux lines in superconductors and in vortex lines in superﬂuids. See cosmic string, intercommutation (cosmic string).

Kippenhahn–Schlüter conﬁguration

See

ﬁlament.

Kirchoff’s law In thermodynamical equilibrium, the ratio between emission coefﬁcient 3ν and absorption coefﬁcient κν is a universal function Bν (T ) which depends on frequency ν and temperature T :

3ν = κν · Bν (T ) .

Bν is also the source function in the equation of radiative transport. For a black-body, Bν (T ) is given by Planck’s black-body formula. See black-body radiation.

Kirkwood gaps Features (gaps) in the distribution of the asteroids discovered by Kirkwood in 1867. They are located at positions corresponding to orbital periods of the asteroid 4, 3, 5/2, 7/3, and 2 times the period of Jupiter. Because of the resonance with Jupiter such orbits are very rare, and this results in “gaps” in the asteroid distribution.

knoll In oceanographic geophysics, a coneshaped isolated swell with a height difference of less than 1000 m from its ambient ocean bottom. Believed to be of volcanic origin.

knot A nautical mile per hour, 1.1508 statute miles per hour, 1.852 km per hour.

Knudsen ﬂow The ﬂow of ﬂuids under conditions in which the ﬂuid mean free path is signiﬁcant, and the behavior has features of both molecular ﬂow and laminar viscous ﬂow.

Knudsen number In a ﬂuid, the ratio of the mean free path to a typical length scale in the problem, e.g., surface roughness scale. A large Knudsen number indicates a free-molecule regime; a small Knudsen number indicates ﬂuid ﬂow.

Kolmogorov scale (Kolmogorov microscale)

The length scale, at which viscous and inertial forces are of the same order of magnitude; the length scale at which turbulent velocity gradients in a ﬂuid are damped out by molecular viscous effects. Kolmogorov suggested that this length scale depends only on parameters that are relevant to the smallest turbulent eddies. Hence, from dimensional considerations,

<<< < Предыдущая 56 57 58 59 60 61 62 63 64 65 66 6768 / 13068 69 70 71 72 73 74 75 76 77 78 79 80 > Следующая >>>

Соседние файлы в предмете Английский язык

#
10.08.201313.07 Mб448Dictionary of Contemporary Slang, Third Edition; Tony Thorne (A & C Black, 2005).pdf
#
10.08.201313.14 Mб169Dictionary of Contemporary Slang.pdf
#
10.08.20132.5 Mб61Dictionary of DNA and Genome Technology.pdf
#
10.08.20135.81 Mб131Dictionary of Engineering, 2nd Edition.pdf
#
10.08.201310.44 Mб244Dictionary of Food Ingredients 4th Edition.pdf
#
10.08.20135.66 Mб122Dictionary of Geophysics, Astrophysic, and Astronomy.pdf
#
10.08.20133.03 Mб108Dictionary of Literary Influences.pdf
#
10.08.201314.56 Mб228Dictionary of Medical Terms 4th Ed..pdf
#
10.08.201310.83 Mб94Dictionary of Microbiology and Molecular Biology 3rd Ed.pdf
#
10.08.20137.45 Mб295Dictionary of Military Terms.pdf
#
10.08.201314.38 Mб64Dictionary of Mining, Mineral, & Related Terms.pdf

Kelvin (Thompson) circulation theorem

Kepler shear The velocity difference between particles in adjacent Keplerian orbits about a central massive body.

Kepler’s laws Observations of the motion of planets due to Johannes Kepler.

Kerr metric (1963) The metric

Killing horizon

Keulegan–Carpenter Number A dimensionless parameter used in the study of waveinduced forces on structures. The Keulegan– Carpenter Number is deﬁned as u¯maxT /D,

K-function Diffuse attenuation coefﬁcient.

Kibble mechanism Process by which defects (strings, monopoles, domain walls) are produced in phase transitions occurring in the matter. In the simplest cases there is a ﬁeld

Killing tensor

kinematical invariants The quantities associated with the ﬂow of a continuous medium: acceleration, expansion, rotation, and shear. In a generic ﬂow, they are nonzero simultaneously.

kinematics The study of motion of noninteracting objects, and relations among force, position, velocity, and acceleration.

kinematic viscosity Molecular viscosity divided by ﬂuid density, ν = µ/ρ, where ν = kinematic viscosity, µ = molecular (or dynamic or absolute) viscosity, and ρ = ﬂuid density. See eddy viscosity, dynamic viscosity.

In systems involving ﬂuids, one can assign a kinetic energy density. Thus, if ρ is the mass velocity, the kinetic energy density (Joules/m3) is t = ρvv.

Kolmogorov scale (Kolmogorov microscale)

Kirchoff’s law In thermodynamical equilibrium, the ratio between emission coefﬁcient 3ν and absorption coefﬁcient κν is a universal function Bν (T ) which depends on frequency ν and temperature T :

knoll In oceanographic geophysics, a coneshaped isolated swell with a height difference of less than 1000 m from its ambient ocean bottom. Believed to be of volcanic origin.

knot A nautical mile per hour, 1.1508 statute miles per hour, 1.852 km per hour.

Knudsen number In a ﬂuid, the ratio of the mean free path to a typical length scale in the problem, e.g., surface roughness scale. A large Knudsen number indicates a free-molecule regime; a small Knudsen number indicates ﬂuid ﬂow.