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1.
The field dependence of the nuclear spin-lattice relaxation (SLR) of cold implanted 82Br (T ≤ 25 mK) in α-Fe single crystals was investigated with nuclear magnetic resonance of oriented nuclei (NMR/ON) at low temperatures
as experimental technique. The SLR at the lattice sites with the hyperfine fields found by earlier NMR/ON experiments was
measured as a function of the applied external magnetic field B
ext parallel to the three principle axes [100], [110] and [111] of the iron single crystal. The data were evaluated with the
full relaxation formalism in the single impurity limit and for comparison also with the often employed model of a single exponential function with an effective relaxation time
T
1′. With a phenomenological model the high field values of the relaxation rates r
∞, [100]′ = 6.6(2) · 10−15 T2sK−1, r
∞, [110] = 5.4(2) · 10−15 T2sK−1 and r
∞, [111] = 5.2(1) · 10−15 T2sK−1 were obtained. 相似文献
2.
Numerical and experimental investigations on the mach 2 pseudo-shock wave in a square duct 总被引:1,自引:0,他引:1
This paper describes numerical and experimental investigations for the multiple shock wave/turbulent boundary layer interaction in a Mach 2 supersonic square duct. The numerical simulation is carried out with the Harten-Yee second-order accuracy TVD scheme and the Baldwin-Lomax turbulence model. The flow conditions are a free-stream Mach number ofM ∞≈=2.0 and a Reynolds number ofRe ∞;=2.5×107 and the flow confinements are δ∞/h=0.15 (case A) and δ∞/h=0.25 (case B), respectively. The computational results for both cases show good agreement with the experimental results. Based on these agreements, the flow quantities, which are very difficult to obtain experimentally, are analyzed by numerical simulation. Moreover, the effect of flow confinement on the pseudo-shock wave characteristics is also presented. 相似文献
3.
The four-dimensional Ising model is simulated on the Creutz cellular automaton using finite-size lattices with linear dimension
4≤L≤8. The exponents in the finite-size scaling relations for the order parameter and the magnetic susceptibility at the finite-lattice
critical temperature are computed to be β=0.49(7), β=0.49(5), β=0.50(1) and γ=1.04(4), γ=1.03(4), γ=1.02(4) for 7, 14, and 21 independent simulations, respectively. As the number of independent simulations increases, the
obtained results are consistent with the renormalization group predictions of β=0.5 and γ=1. The values for the critical temperature of the infinite lattice T
c
(∞)=6.6788(65), T
c
(∞)=6.6798(69), T
c
(∞)=6.6802(70) are obtained from the straight-line fit of the magnetic susceptibility maxima using 4≤L≤8 for 7, 14, and 21 independent simulations, respectively. As the number of independent simulations increases, the obtained
results are in very good agreement with the series expansion results of T
c
(∞)=6.6817(15), T
c
(∞)=6.6802(2), the dynamic Monte Carlo result of T
c
(∞)=6.6803(1), the cluster Monte Carlo result of T
c
(∞)=6.680(1) and the Monte Carlo using Metropolis and Wolff-cluster algorithm result of T
c
(∞)=6.6802632±5×10−5. 相似文献
4.
Development of three-dimensional turbulent separation in the neighborhood of incident crossing shock waves 总被引:1,自引:1,他引:0
The results are presented for experimental investigation of the peculiarities of the development of three-dimensional turbulent
separated flows on a flat surface for the Mach number M∞ = 4 and the Reynolds number Re1 ∼ 55·106 m−1 under the conditions of the flow around two identical cylindrical bodies of revolution of diameter D = 50 mm and the body aspect ratio L
b/D = 5 with conical forebodies with semi-apex angles βc = 30, 20, 15, and 10° located above plate in parallel to one another and to the flow. The typical stages of the three-dimensional
separation development are considered under the reducing distance between the axes of the bodies within the range of Z = Δz/D = 1.06–3.0 at their fixed distance from the surface (Y = Δy/D = 0.96). The topology of limiting streamlines and the peculiarities of pressure fields on the surface as well as the gasdynamic
structure of separated flows arising at the interaction of crossing bow shocks propagating from the bodies and at the interaction
of secondary disturbances with the boundary layer are analysed. 相似文献
5.
B. Canals D.A. Garanin 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,26(4):439-447
Thermodynamic quantities and correlation functions (CFs) of the classical antiferromagnet on the checkerboard lattice are
studied for the exactly solvable infinite-component spin-vector model, D↦∞. In contrast to conventional two-dimensional magnets with continuous symmetry showing extended short-range order at distances
smaller than the correlation length, r
ξ
c∝ exp(T
*/T), correlations in the checkerboard-lattice model decay already at the scale of the lattice spacing due to the strong degeneracy
of the ground state characterized by a macroscopic number of strongly fluctuating local degrees of freedom. At low temperatures,
spin CFs decay as <
>∝ 1/r
2 in the range a
0≪r≪ξ
c∝T
-1/2, where a0 is the lattice spacing. Analytical results for the principal thermodynamic quantities in our model are very similar with
MC simulations, exact and analytical results for the classical Heisenberg model (D = 3) on the pyrochlore lattice. This shows that the ground state of the infinite-component spin vector model on the checkerboard
lattice is a classical spin liquid.
Received 16 November 2001 and Received in final form 12 February 2002 相似文献
6.
According to recent progresses in the finite size scaling theory of
disordered systems, thermodynamic observables are not self-averaging
at critical points when the disorder is relevant in the
Harris criterion sense. This lack of
self-averageness at criticality is directly related to the distribution
of pseudo-critical temperatures Tc(i,L) over the ensemble of
samples (i) of size L. In this paper, we apply this analysis to
disordered Poland-Scheraga models with different loop exponents c,
corresponding to marginal and relevant disorder. In all cases, we
numerically obtain a Gaussian
histogram of pseudo-critical temperatures Tc(i,L) with mean
Tcav(L) and width ΔTc(L).
For the marginal case c=1.5 corresponding to two-dimensional wetting,
both the width ΔTc(L) and the shift
[Tc(∞)-Tcav(L)] decay as L-1/2, so the exponent is
unchanged (νrandom=2=νpure) but disorder is relevant and
leads to non self-averaging at criticality.
For relevant disorder
c=1.75, the width ΔTc(L) and the shift
[Tc(∞)-Tcav(L)] decay with the same new exponent
L-1/νrandom (where νrandom ∼2.7 > 2 > νpure) and
there is again no self-averaging at criticality. Finally for the value
c=2.15, of interest in the context of DNA denaturation, the
transition is first-order in the pure case. In the presence of
disorder, the width ΔTc(L) ∼L-1/2
dominates over the shift [Tc(∞)-Tcav(L)] ∼L-1,
i.e. there are two correlation length exponents ν=2 and
that govern respectively the averaged/typical loop distribution. 相似文献
7.
S. I. Masharov 《Russian Physics Journal》1996,39(9):839-842
A general expression is obtained for the thermodiffusion coefficientD
T of a film, also for its dependence on temperature, film thickness and type of concentration distribution of the interstitials,
according to its profile. In neglecting interaction of interstitials with each other in a model of a film with single-plane
boundaries with the vacuum and the substrate, it is shown thatD
T>D
T
(∞) is possible, whereD
T
(∞) is the thermodiffusion coefficient of a bulk specimen.
Ural State Technical University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 43–46, September,
1996. 相似文献
8.
V. N. Gorev M. M. Katasonov V. V. Kozlov P. A. Motyrev 《Thermophysics and Aeromechanics》2009,16(4):539-547
Turbulence production processes in boundary layer at a high level of free-stream turbulence have been studied. The tests were
carried out in the MT-324 subsonic wind tunnel of ITAM, SB RAS, on models of straight and 45° swept wings at Reynolds numbers
Rec1 = 97000 and Rec2 = 137000, and also at low (Tu = 0.18 % U
∞) and high (Tu = 0.79 and 2.31 % U
∞) levels of free-stream turbulence. The longitudinal localized disturbances developing in the boundary layer under the action
of free-stream turbulence were artificially modeled using local air suction through a slot on the model surface. Wave packets,
or forerunners, produced in the boundary layer, in the region preceding the abrupt local change of flow velocity near the
localized-disturbance fronts, were examined. The high level of free-stream turbulence was found to accelerate the downstream
evolution of the wave packets and their transformation into turbulent spots. 相似文献
9.
Galina A. Vergunova Sergey Yu. Gus’kov Vladislav B. Rozanov Olga N. Rozmej 《Journal of Russian Laser Research》2010,31(5):509-518
We investigate theoretically the formation of a plasma in a plane layer of polymer foam (density ρ = 0.002 g/cm3 and thickness 800 μm) under the action of an external source of soft X-ray radiation under the conditions of PHELIX experiments. The incident
flux is assumed to have a Planck’s distribution over the spectrum with T
rad = 20–40 eV. In numerical calculations, the flux of incident X-ray radiation and the spectral constants of the target substance
are varied. The action of an external X-ray radiation source on a low-density foam substance with a density of 2 mg/cm3 causes a plasma to be formed with relatively homogeneous profiles of density and temperature T = 15–35 eV. Absorption of externalradiation energy is distributed in the volume. The plasma temperature increases with increase
in the external energy, and the energy passed through the plasma also increases. The results prove to be sensitive to the
values of optical constants used in numeral simulation. The spectral flux of external radiation passed through the plasma
is chosen as a criterion of correctness of the optical constants used in the calculations. In future experiments using the
PHELIX facility, we plan to investigate the slowing-down of an ion beam in a plasma formed as a result of indirect heating
of low-density polymer triacetate cellulose (TAC) foam with densities ρ = 0.001–0.01 g/cm3 under the action of a pulse of X-ray radiation, into which the laser radiation is preliminarily transformed. 相似文献
10.
G. M. Molchan 《Communications in Mathematical Physics》1999,205(1):97-111
Let b
γ (t), b
γ(0)= 0 be a fractional Brownian motion, i.e., a Gaussian process with the structure function , 0 < γ < 2. We study the logarithmic asymptotics of P
T
= P{b
γ (t) < 1,□t∈TΔ} as T→∞, where Δ is either the interval (0,1) or a bounded region that contains a vicinity of 0 for the case of multidimensional
time. It is shown that ln P
T
= - D ln T(1 + o(1)), where D is the dimension of zeroes of b
γ (t) in the former case and the dimension of time in the latter.
Received: 28 September 1998 / Accepted: 19 February 1999 相似文献
11.
T. V. Dudnikova 《Russian Journal of Mathematical Physics》2010,17(1):77-95
The Hamiltonian system formed by a Klein-Gordon vector field and a particle in ℝ3 is considered. The initial data of the system are given by a random function, with finite mean energy density, which also
satisfies a Rosenblatt- or Ibragimov-type mixing condition. Moreover, initial correlation functions are assumed to be translation
invariant. The distribution μ
t
of the solution at time t ∈ ℝ is studied. The main result is the convergence of μ
t
to a Gaussian measure as t → ∞, where μ∞ is translation invariant. 相似文献
12.
Katsumi Sugita Yoshiwo Okamoto Matsuo Sekine 《International Journal of Theoretical Physics》2008,47(11):2875-2881
In a previous paper, we proposed the infinite sub-layer quark model, in which the proton and the neutron are made up of an
infinite number of point-like (structure-less) quarks u
∞ and anti-quarks u
∞
CP
at an infinite sub-layer level. In this paper, we propose that the dark matter is also made of an infinite number of quarks
u
∞ and anti-quarks u
∞
CP
. A pair of the ultimate quarks u
∞ and anti-quarks u
∞
CP
would be produced in the first moments after the Big Bang and then remain as the dark matter for all time, stable against
decay and subject only to the weak interaction and gravity. It is then shown that CP is violated in the doublet of u
∞ and u
∞
CP
quarks to account for the asymmetry of the number of particles and anti-particles in the present universe. Furthermore, it
is shown that the Higgs bosons are composed of u
∞ and u
∞
CP
dark matter particles and give the masses to gauge bosons, quarks and leptons. 相似文献
13.
The method of molecular dynamics (the Bird system) has been used to mathematically model a planar, strongly underexpanded
supersonic jet that encounters a hypersonic flow of rarefied gas. Particular attention is paid to the structure and parameters
of the shock layer close to the plane of symmetry. The results of calculations are presented for currents of a monatomic gas,
simulating argon, with a Mach number of the external flow of M∞=5.48, a Mach number at the nozzle edge of Ma=1, a ratio of the density at the nozzle edge to the density of the unperturbed flow equal to 130, and various stagnation
temperatures of the external flow and of the jet. The evolution of the structure and the parameters of the shock layer as
the Knudsen number Kn∞ varies from 0.02 to 0.35 is considered. The results are compared with the data calculated for the shock layer when argon
flows around thermally insulated cylinders. The main features and regularities of the relaxation of the translational degrees
of freedom of the gas for external and jet flows are considered. Data are presented on the form of the distribution function
over velocities and its evolution as gas moves through the shock layers.
Zh. Tekh. Fiz. 68, 13–18 (July 1998) 相似文献
14.
Evgeni Korotyaev 《Communications in Mathematical Physics》2000,213(2):471-489
The spectral properties of the Schr?dinger operator T(t)=−d
2/dx
2+q(x,t) in L
2(ℝ) are studied, where the potential q is defined by q=p(x+t), x>0, and q=p(x), x<0; p is a 1-periodic potential and t∈ℝ is the dislocation parameter. For each t the absolutely continuous spectrum σ
ac
(T(t))=σ
ac
(T(0)) consists of intervals, which are separated by the gaps γ
n
(T(t))=γ
n
(T(0))=(α
n
−,α
n
+), n≥1. We prove: in each gap γ
n
≠?, n≥ 1 there exist two unique “states” (an eigenvalue and a resonance) λ
n
±(t) of the dislocation operator, such that λ
n
±(0)=α
n
± and the point λ
n
±(t) runs clockwise around the gap γ
n
changing the energy sheet whenever it hits α
n
±, making n/2 complete revolutions in unit time. On the first sheet λ
n
±(t) is an eigenvalue and on the second sheet λ
n
±(t) is a resonance. In general, these motions are not monotonic. There exists a unique state λ0(t) in the basic gap
γ0(T(t))=γ0(T(0))=(−∞ ,α0
+). The asymptotics of λ
n
±(t) as n→∞ is determined.
Received: 5 April 1999 / Accepted: 3 March 2000 相似文献
15.
Remco van der Hofstad Frank den Hollander Gordon Slade 《Communications in Mathematical Physics》2002,231(3):435-461
We construct the incipient infinite cluster measure (IIC) for sufficiently spread-out oriented percolation on ℤ
d
× ℤ+, for d +1 > 4+1. We consider two different constructions. For the first construction, we define ℙ
n
(E) by taking the probability of the intersection of an event E with the event that the origin is connected to (x,n) ℤ
d
× ℤ+, summing this probability over x ℤ
d
, and normalising the sum to get a probability measure. We let n → ∞ and prove existence of a limiting measure ℙ∞, the IIC. For the second construction, we condition the connected cluster of the origin in critical oriented percolation
to survive to time n, and let n → ∞. Under the assumption that the critical survival probability is asymptotic to a multiple of n
−1, we prove existence of a limiting measure ℚ∞, with ℚ∞ = ℙ∞. In addition, we study the asymptotic behaviour of the size of the level set of the cluster of the origin, and the dimension
of the cluster of the origin, under ℙ∞. Our methods involve minor extensions of the lace expansion methods used in a previous paper to relate critical oriented
percolation to super-Brownian motion, for d+1 > 4+1.
Received: 13 December 2001 / Accepted: 11 July 2002 Published online: 29 October 2002
RID="*"
ID="*" Present address: Department of Mathematics and Computer Science, Eindhoven University of Technology, P.O. Box 513,
5600 MB Eindhoven, The Netherlands. E-mail: rhofstad@win.tue.nl 相似文献
16.
We study the characteristic polynomials Z(U, θ) of matrices U in the Circular Unitary Ensemble (CUE) of Random Matrix Theory. Exact expressions for any matrix size N are derived for the moments of |Z| and Z/Z
*, and from these we obtain the asymptotics of the value distributions and cumulants of the real and imaginary parts of log
Z as N→∞. In the limit, we show that these two distributions are independent and Gaussian. Costin and Lebowitz [15] previously found
the Gaussian limit distribution for Im log Z using a different approach, and our result for the cumulants proves a conjecture made by them in this case. We also calculate
the leading order N→∞ asymptotics of the moments of |Z| and Z/Z
*. These CUE results are then compared with what is known about the Riemann zeta function ζ (s) on its critical line Re s= 1/2, assuming the Riemann hypothesis. Equating the mean density of the non-trivial zeros of the zeta function at a height
T up the critical line with the mean density of the matrix eigenvalues gives a connection between N and T. Invoking this connection, our CUE results coincide with a theorem of Selberg for the value distribution of log ζ(1/2+iT) in the limit T→∞. They are also in close agreement with numerical data computed by Odlyzko [29] for large but finite T. This leads us to a conjecture for the moments of |ζ(1/2+it) |. Finally, we generalize our random matrix results to the Circular Orthogonal (COE) and Circular Symplectic (CSE) Ensembles.
Received: 20 December 1999 / Accepted: 24 March 2000 相似文献
17.
E. -S. Zanoun 《Thermophysics and Aeromechanics》2010,17(1):21-38
Effects of the upstream conditions and the degree of the wall roughness on the mean velocity profiles and some integral flow
parameters in two dimensional zero-pressure-gradient boundary layer were characterized experimentally. The results were analyzed
utilizing conventional and recent scaling flow parameters for 245< Re
θ
≤ 11·103, where Re
θ
is the Reynolds number based on the free stream velocity (Ū
∞) and the momentum thickness (θ). Good correlation of the quantity ΔŪ
+ as a function of the roughness parameter k
+ was obtained for sand roughness of 1.7 < k
+ ≤ 172, revealing a universality of the roughness effect, where ΔŪ
+ = = (Ū
∞ − Ū)/u
τ and K
+ = ku
τ
/v.The mean flow structure of the outer flow was observed not to be influenced by the degree of the wall roughness, i. e., the
outer flow of either the smooth or the rough surfaces scales similarly with the various scaling parameters regardless the
degree of the wall roughness. However, it made flow confined to the wall region away from the classical universality, allowing
similarity hypothesis not to be identical in the wall region at least for the current range of the Reynolds number. 相似文献
18.
John A. Toth 《Communications in Mathematical Physics》2003,238(1-2):225-256
Let (M,g) be a C
∞
compact Riemann manifold with classical Hamiltonian, HC
∞
(T
*
M). Assume that the corresponding -quantization P
1
:=Op
(H) is quantum completely integrable. We establish an -microlocal Weyl law on short spectral intervals of size 2−ε;∀ε>0 for various families of operators P
1
u
;uI containing P
1
, both in the mean and pointwise a.e. for uI. The -microlocalization refers to a small tubular neighbourhood of a non-degenerate, stable periodic bicharacteristic γ⊂T
*
M−0.
Received: 10 December 2001 / Accepted: 23 January 2003
Published online: 2 April 2003
RID="⋆"
ID="⋆" Supported in part by an Alfred P. Sloan Research Fellowship and NSERC grant OGP01720280
Communicated by P. Sarnak 相似文献
19.
A. P. Gerashenko K. N. Mikhalev S. V. Verkhovskii T. V. D’yachkova A. P. Tyutyunnik V. G. Zubkov 《Applied magnetic resonance》2001,21(2):157-163
Nuclear magnetic resonance (NMR) spectra and nuclear spin-lattice relaxation rateT
1−1 of11B have been measured in superconducting polycrystalline MgB2 with 7cons = 39.5 K. It is shown that (T
1T−1 and the Knight shiftK
s are independent of temperature and nearly isotropic aboveT
c. Both of these quantities are decreased gradually in going to the superconducting state. According to NMR data the density
of states near the Fermi level is flat at the scale of about 500 K. Some conclusions on the orbital content of the density
of states at the Fermi level were drawn and compared with the results of the band structure calculations. 相似文献
20.
N. N. Pilyugin 《Technical Physics》1997,42(5):466-472
AbstractExperimental data on the change in the electron density in the wake of a ballistic object traveling at velocities
V
∞=3.4–4.9 km/s in argon at pressures p
∞=30–100 Torr are processed and analyzed. A reaction scheme is proposed which takes into account the recombination of charged
particles, processes of ionic conversion, and the excited states of the atom. The solution of the equations of a nonequilibrium
boundary layer for flow in the wake is used to formulate the inverse problem of determining the rate constants for dissociative
recombination Ar
2
+
+e→Ar+Ar and ternary recombination Ar++e+Ar→Ar+Ar. The “nearest-neighbor” approximation is used to obtain theoretically an expression for the ternary recombination
coefficient as a function of temperature and pressure. Numerous solutions of inverse problems and a comparison with experiments
demonstrates the validity of the expression obtained for the ternary recombination coefficient. It is shown that this expression
is valid for moderate pressures and complements the Pitaevskii result for low pressures and the Langevin result for high pressures.
Zh. Tekh. Fiz. 67, 12–18 (May 1997) 相似文献