共查询到20条相似文献,搜索用时 31 毫秒
1.
P. Contucci M. Degli Esposti C. Giardinà S. Graffi 《Communications in Mathematical Physics》2003,236(1):55-63
Let {E Σ (N)} ΣΣN be a family of |Σ N |=2 N centered unit Gaussian random variables defined by the covariance matrix C N of elements c N (Σ,τ):=Av(E Σ (N)E τ (N)) and the corresponding random Hamiltonian. Then the quenched thermodynamical limit exists if, for every decomposition N=N 1 +N 2 , and all pairs (Σ,τ)Σ N ×Σ N :
where π k (Σ),k=1,2 are the projections of ΣΣ N into Σ Nk . The condition is explicitly verified for the Sherrington-Kirkpatrick, the even p-spin, the Derrida REM and the Derrida-Gardner GREM models. 相似文献
2.
N. A. Chumakova V. I. Pergushov A. Kh. Vorobiev A. I. Kokorin 《Applied magnetic resonance》2010,39(4):409-421
Rotational and translational movements of 1-oxyl-2,2,6,6-tetramethyl-4-oxypiperidine (TEMPOL) spin probe in the room temperature
ionic liquid (RTIL) 1-octyl-3-methylimidazolium tetrafluoroborate (omimBF4) and in two molecular solvents, 1-propanol and isopropyl benzene (cumene), have been studied by X-band electron paramagnetic
resonance (EPR) spectroscopy. Rotational correlation times τ
c of spin probes and the intermolecular spin exchange rate constants k
e were measured from EPR spectra at different temperatures and TEMPOL concentrations, and compared with the published data.
The τ
c values were calculated both by known equations and from the EPR spectra simulation. Rotation movements of TEMPOL in omimBF4 cannot be described by the model of the isotropic Brownian diffusion, which is valid for conventional solvents. The correct
modeling of EPR spectra in RTIL can be achieved with the assumption of different rotational mobility of the spin probe around
different molecular axes. The rotational, D
rot, and translational, D
tr, diffusion coefficients were calculated from τ
c and k
e values. The Debye–Stokes–Einstein law is valid in all three solvents while the dependence of D
tr on T/η is not linear in Stokes–Einstein coordinates. The effective activation energy E
rota of the rotational movements in omimBF4 is noticeably higher than the corresponding values for conventional solvents, while the effective activation energies E
tra of the translational movements are comparable in all solvents studied. 相似文献
3.
We demonstrate that all liquids in supercritical region may exist in two qualitatively different states: solid-like and gas-like.
Solid-like to gas-like crossover corresponds to the condition τ ≈ τ0, where τ is liquid relaxation time and τ0 is the minimum period of transverse waves. This condition corresponds to the loss of shear stiffness of a liquid at all frequencies
and defines a new narrow crossover zone on the phase diagram. We show that the intersection of this zone corresponds to the
disappearance of high-frequency sound, qualitative changes of diffusion and viscous flow, increase in particle thermal speed
to half of the speed of sound and reduction of the specific heat at constant volume to 2k
B per particle. The new crossover is universal: it separates two liquid states at arbitrarily high pressure and temperature,
and even exists in systems where liquid-gas transition and the critical point are absent overall. 相似文献
4.
Y. -S. Hong K. S. Hong J. -H. Cho V. I. Volkov C. -H. Lee 《Applied magnetic resonance》2009,35(2):261-270
The diffusion behavior of hydroxyl protons (OH) in quercetin in 100% DMSO-d6 (deuterium dimethylsulfoxide) and a 90% DMSO-d6 solution containing 10% H2O was investigated with 600 MHz 1H pulsed field gradient (PFG) nuclear magnetic resonance (NMR). Only resonances of the 5-hydroxyl protons (OH5) were well
resolved in NMR spectra of quercetin for all solutions under study. This phenomenon is explained by the intramolecular hydrogen
bonding between OH5 protons and the 4-carbonyl oxygen (CO4). During diffusion experiments, the OH5 protons showed a biexponential
diffusion decay, indicating an exchange process with water. As water content in the solvents increased, the lifetime (τ
q) of the OH5 protons decreased from 96.7±10.0 ms in 100% DMSO-d6 to 14.3±1.4 ms in the 90% DMSO-d6 solution containing 10% H2O, indicating an increase in the exchange rate (k
q = l/τ
q) of the OH5 protons. This study demonstrates that the diffusion approach with PFG-NMR is much faster and easier for estimating
the short lifetime or fast exchange rate of hydroxyl protons in quercetin. 相似文献
5.
J.W. Eerkens 《Applied physics. B, Lasers and optics》2001,72(7):885-892
An approximate closed-form expression is derived for the average wall-reaching rate kW or time τW=kW
-1 of laser-tagged molecules diluted in an inert carrier gas migrating to the wall of a long cylinder where they are removed
with sticking coefficient ηW. The exact equation for the sticky wall problem requires a trial-and-error solution of a transcendental relation with Bessel–functions.
With the aid of the Fermi–Amaldi albedo theory, an explicit “compromise” relation is derived which approximates the exact
diffusion curve of kW versus ηW rather well. The result is applied to obtain curves of kW versus ηW at different gas mix pressures for UF6 diluted in N2.
Received: 5 June 2000 / Revised version: 31 January 2001 / Published online: 27 April 2001 相似文献
6.
A number of laws have been established that govern the motion of a Brownian particle in a periodic potential profile for the
adiabatically fast (with the time τ0) and adiabatically slow variations in its shape. The average velocity of a particle has been calculated including a nonadiabatic
contribution depending on τ0 and the characteristic times of the system, which are determined by the characteristic features of the potential profile.
It has been shown that the nonadiabatic correction to the velocity is proportional to τ02 for a smooth potential profile and to τ0 for a hopping movement in a potential containing barriers and wells, and this correction limits the large values of the rectification
factor of motion for a high-performance motor operation mode. 相似文献
7.
V. V. Klochkov F. Kh. Karatayeva R. A. Shaikhutdinov B. I. Khairutdinov M. -A. Molins M. Pons 《Applied magnetic resonance》2002,22(3):431-438
Variable temperature two-dimensional nuclear Overhauser enhancement experiment (2-D NOESY) is used to extract the rate constants and cross-relaxation rates that contribute to the same cross-peaks in NOESY spectra. Rate constants (k AB) and cross-relaxation rates (R AB) for two-site spin systems are related to the ratio between the cross-peak and diagonal peak integrals (F) by the expression:R AB -k AB = (1/2τ m)ln[(1 -F)/(1 +F)], where τm is the mixing time. As a model, we investigated the exchange processes in a system of dimer calix[4]arenes of C4v symmetrical configuration with guest inclusion (benzene or benzene-d6), where the measurement of exchange processes is hindered by the presence of strong nuclear Overhauser enhancement between protons in adjacent aromatic rings in the cone conformation of the calix[4]arene. 相似文献
8.
Measurements have been made of the Hall coefficientR of some alloys of silver in palladium over the temperature range 1°K to 120°K. The alloys contain between ∼1 and ∼10 at.-%
silver. Values ofR were also obtained at room temperature and these were in good agreement with earlier published work. The values ofR are negative in all the alloys, and |R| increases both on reducing the temperature and increasing the silver concentration,c. Below ∼10°K, |R| becomes independent of temperature but shows a linear dependence onc, increasing by a factor of 2.5 over the concentration range measured.
This increase is too great to be accounted for in terms of band structure changes alone, so we have examined the effects of
anisotropic impurity scattering. To a first approximation it can be shown thatR is proportional to an anisotropy parameterA, defined asA=〈τ
2(k)〉/〈τ(k)〉2, whereτ(k) represents the relaxation time of an electron in a statek, and 〈〉 is an average over the Fermi surface. In palladium we assume that the majority of the current is carried by the s-electrons.
In the presence of silver impurities these electrons can be scattered into s-states or d-states with relaxation times given
byτ
ss
α1/c(1−c) andτ
sd
α1/c
2(1−c) respectively. FollowingPlate we have assumed thatτ
ss is isotropic and thatτ
sd is anisotropic, leading to an overall anisotropic relaxation time for impurity scattering. We then find the parameterA increases approximately linearly with silver content, in accordance with our experimental results. 相似文献
9.
We study a reaction-diffusion system of N equations with k nonzero and N − k zero diffusion coefficients. More exactly, the first k equations of the system contain the terms a
i
Δu
i
− f
j
(u, v), i = 1, …, k, with the diffusion coefficient a
i
> 0. The right-hand sides of the other N − k equations contain only nonlinear interaction functions −h
j
(u, v), j = k + 1, …, N, with zero diffusion. Here u = (u
1, …, u
k
) and v = (υ
k+1, …, υ
N
) are unknown concentration vectors. Under appropriate assumptions on the interaction functions f(·) and h(·), we construct the trajectory attractor of this reaction-diffusion system. We also find the trajectory attractors , δ = (δ
1, …, δ
k
), for the analogous reaction-diffusion systems having the terms δ
j
Δυ
j
− h
j
(u, v), j = k + 1, …, N, with small diffusion coefficients δ
j
⩾ 0 in the last N − k equations. We prove that the trajectory attractors converge to (in an appropriate topology) as δ → 0+.
Dedicated to the memory of Vladimir Borovikov
Partially supported by the Russian Foundation for Basic Research (projects nos. 08-01-00784 and 07-01-00500). 相似文献
10.
The magnetic structure of intermetallic compounds Ce2Fe17 − x
Mn
x
(0 ≤ x ≤ 3) was studied using neutron diffraction. The neutron diffraction patterns measured at 4.2 K contain satellites indicating
a modulated structure with the wave vector k = [0, 0, τ]. As the concentration x increases, the value of τ increases, while the average magnetic moment of Fe/Mn atoms decreases. A change in the magnitudes
of the average magnetic moment and wave vector k is explained by competition between exchange interactions at distances of nearest neighbor transition element atoms. 相似文献
11.
D. L. Budnitskii O. B. Koretskaya О. P. Тоlbanov А. V. Tyazhev 《Russian Physics Journal》2010,53(1):44-48
The electrophysical and photoelectrical properties of high-resistance GaAs produced by single crystal growth are studied and
analyzed. The electron (τ
n
) and hole (τ
p
) lifetimes are estimated. The charge-carrier lifetimes are compared in as-grown and diffusion high-resistance GaAs. The conclusion
is made that in high-resistance GaAs produced by chromium diffusion, the charge-carrier recombination mechanism qualitatively
differs from that in as-grown GaAs. The charge-carrier recombination in diffusion GaAs is determined by the occurrence of
recombination barriers due to chromium diffusion. 相似文献
12.
Vassiliki Katsika-Tsigourakou Efthimios S. Skordas 《Central European Journal of Physics》2010,8(6):900-904
Various experimental techniques have revealed that the predominant intrinsic point defects in BaF2 are anion Frenkel defects. Their formation, enthalpy and entropy, as well as the corresponding parameters for the fluorine
vacancy and fluorine interstitial motion have been determined. In addition, low temperature dielectric relaxation measurements
in BaF2doped with uranium leads to the parameters τ0, E in the Arrhenius relation τ = τ0 exp(E/k
B
T) for the relaxation time τ. For the relaxation peak associated with a single tetravalent uranium, the migration entropy deduced
from the pre-exponential factor τ0 is smaller than the anion Frenkel defect formation entropy by almost two orders of magnitude. We show that, despite their
great variation, the defect entropies and enthalpies are interconnected through a model based on anharmonic properties of
the bulk material which have been recently studied by employing density-functional theory and density-functional perturbation
theory. 相似文献
13.
Dr. M. C. Jones 《Zeitschrift für Physik B Condensed Matter》1969,9(1-2):98-103
Using the iterative solution to the Boltzmann equation for electrons in d.c. electric and magnetic fields, an expression for
the resistivity tensor can be obtained in the form of an infinite series. This series can be approximated by retaining only
the first two terms. In the cases where relaxation times exist — in the sense that the collision term in the Boltzmann equation
can be written asg(k)/τ(k), whereτ(k) is the relaxation time, andf (k) = f
E(ɛ k) + [∂f
E(εk)/∂ε]·g(k) the distribution function for electrons with wavevectork — this approximation is exact. For polyvalent metals in the one-OPW approximation, the complete galvanomagnetic tensor can
be obtained using this approximation and the result differs from that obtained by using a time of relaxation given by an expression
suggested byZiman. A calculation for a simple model Fermi surface, with screened Coulomb scattering, is carried out and the results compared
with those of the relaxation time approximation. 相似文献
14.
In this paper, two approaches of constructing entanglement witnesses for finite- or infinite-dimensional bipartite quantum
systems are presented. Let H
A
and H
B
be complex Hilbert spaces and {E
k
} and {F
k
} be sequences of self-adjoint Hilbert-Schmidt operators on H
A
and H
B
, respectively, such that Tr(EfkEl)=Tr(FfkFl)=dkl\mathrm{Tr}(E^{\dag}_{k}E_{l})=\mathrm{Tr}(F^{\dag}_{k}F_{l})=\delta_{kl}. Then W=I−∑
k
E
k
⊗F
k
is an entanglement witness on H
A
⊗H
B
if
W\not 3 0W\not\geq 0. If ρ is an entangled state and τ
0 is the nearest separable state to ρ under the Hilbert-Schmidt norm, then W=c
0
I+τ
0−ρ with c
0=Tr[τ
0(ρ−τ
0)] is an entanglement witness. 相似文献
15.
One-dimensional system of Brownian motions called Dyson’s model is the particle system with long-range repulsive forces acting
between any pair of particles, where the strength of force is β/2 times the inverse of particle distance. When β=2, it is realized as the Brownian motions in one dimension conditioned never to collide with each other. For any initial
configuration, it is proved that Dyson’s model with β=2 and N particles,
$\mbox {\boldmath $\mbox {\boldmath
, is determinantal in the sense that any multitime correlation function is given by a determinant with a continuous kernel.
The Airy function
(z){\rm Ai}(z)
is an entire function with zeros all located on the negative part of the real axis ℝ. We consider Dyson’s model with β=2 starting from the first N zeros of
Ai(z){\rm Ai}(z)
, 0>a
1>⋅⋅⋅>a
N
, N≥2. In order to properly control the effect of such initial confinement of particles in the negative region of ℝ, we put the
drift term to each Brownian motion, which increases in time as a parabolic function: Y
j
(t)=X
j
(t)+t
2/4+{d
1+∑
ℓ=1
N
(1/a
ℓ
)}t,1≤j≤N, where
d1=Ai¢(0)/Ai(0)d_{1}={\rm Ai}'(0)/{\rm Ai}(0)
. We show that, as the N→∞ limit of
$\mbox {\boldmath $\mbox {\boldmath
, we obtain an infinite particle system, which is the relaxation process from the configuration, in which every zero of
(z){\rm Ai}(z)
on the negative ℝ is occupied by one particle, to the stationary state
mAi\mu_{{\rm Ai}}
. The stationary state
mAi\mu_{{\rm Ai}}
is the determinantal point process with the Airy kernel, which is spatially inhomogeneous on ℝ and in which the Tracy-Widom
distribution describes the rightmost particle position. 相似文献
16.
V. I. Gaman 《Russian Physics Journal》2008,51(4):425-441
The most probable physical models of hydrogen sensors based on thin stannic oxide films, MOS-structures, and tunnel MOS-diodes
are discussed. The emphasis is on the mechanisms of formation of sensor response to hydrogen. The analytical equations describing
the dependence of the response on the hydrogen concentration nH2 are derived for all types of sensors. The relations describing the dependences of the SnO
2-sensor conductivity and response on the absolute humidity of a gas mixture are given. It is shown that the relaxation time
τrel of the response of SnO
2-and MOS-structure sensors is determined by the relaxation time τa of hydrogen atom adsorption on the SnO
2 and SiO
2 surfaces, respectively. For the MOS-diodes, τrel = τa at nH2 and τrel = τd at nH2≥7.5·103, where τd is the relaxation time of hydrogen atom diffusion through an SiO
2 layer.
__________
Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 84–98, April, 2008. 相似文献
17.
Parongama Sen 《Pramana》2008,71(2):313-317
We consider navigation or search schemes on networks which have a degree distribution of the form P(k) ∝ exp(−k
γ). In addition, the linking probability is taken to be dependent on social distances and is governed by a parameter λ. The searches are realistic in the sense that not all search chains can be completed. An estimate of μ = ρ/s
d, where ρ is the success rate and s
d the dynamic path length, shows that for a network of N nodes, μ ∝ N
−δ
in general. Dynamic small world effect, i.e., δ ≃ 0 is shown to exist in a restricted region of the λ−γ plane.
相似文献
18.
19.
A. Nersessian 《Czechoslovak Journal of Physics》2000,50(11):1309-1315
We propose the model ofD-dimensional massless particle whose Lagrangian is given by theN-th extrinsic curvature of world-line. The system hasN+1 gauge degrees of freedom constitutingW-like algebra; the classical trajectories of the model are space-like curves which obey the conditionsk
N+a=kN−a, k2N
=0,a=1, ...,N−1,N≤[(D−2)/2], while the firstN curvaturesk
i remain arbitrary. We show that the model admits consistent formulation on the anti-DeSitter space. The solutions of the system
are the massless irreducible representations of Poincaré group withN nonzero helicities, which are equal to each other.
Presented at the 9th Colloquium “Quantum Groups and Integrable Systems”, Prague, 22–24 June 2000. 相似文献
20.
Akselrod Z. Z. Filossofov D. V. Kochetov O. I. Korolev N. A. Lebedev N. A. Milanov M. Novgorodov A. F. Shirani E. N. Timkin V. V. Velichkov A. I. 《Hyperfine Interactions》2001,136(3-8):705-710
111Cd–PAC measurements have been made using the high specific activity of 111In in the methanol–water mixtures of various concentrations at the room temperature. These experiments revealed that the perturbation
factors 〈A
2
G
2〉 (integrated over two mean lives τN) do not follow the dependence of the macroscopic viscosity η. The observed dynamic character of the PAC spectra in ice is
explained by the mobility of orientational and ionic defects. The activation energy for the diffusion process was determined
to be E
a
=0.35(1) eV.
This revised version was published online in September 2006 with corrections to the Cover Date. 相似文献