共查询到20条相似文献,搜索用时 78 毫秒
1.
Let (A,α) be a C*-dynamical system. We introduce the notion of pressure P
α(H) of the automorphism α at a self-adjoint operator H∈A. Then we consider the class of AF-systems satisfying the following condition: there exists a dense α-invariant *-subalgebra
? of A such that for all pairs a,b∈? the C*-algebra they generate is finite dimensional, and there is p=p(a,b)∈ℕ such that [α
j
(a),b]= 0 for |j|≥p. For systems in this class we prove the variational principle, i.e. show that P
α(H) is the supremum of the quantities h
φ(α) −φ(H), where h
φ(α) is the Connes–Narnhofer–Thirring dynamical entropy of α with respect to the α-invariant state φ. If H∈A, and P
α(H) is finite, we show that any state on which the supremum is attained is a KMS-state with respect to a one-parameter automorphism
group naturally associated with H. In particular, Voiculescu's topological entropy is equal to the supremum of h
φ(α), and any state of finite maximal entropy is a trace.
Received: 19 April 2000 / Accepted: 14 June 2000 相似文献
2.
The effect of an electric field on the differential thermopower α(E) of a one-dimensional superlattice is investigated in the semiclassical approximation. A nonmonotonic temperature dependence
of α(0) is established for a degenerate electron gas. It is shown that, in principle, an electric field can be used to control
the thermoelectric properties of superlattices.
Fiz. Tverd. Tela (St. Petersburg) 41, 1314–1316 (July 1999) 相似文献
3.
The thermoelectric performance of a thermoelement is ideally defined in terms of the so-called figure-of-meritZ = α2σ/λ, where α,σ and λ refer respectively to the Seebeck coefficient, electrical conductivity and thermal conductivity of the thermoelement
material. However, there are other parameters which are fairly good indicators of a material’s thermoelectric ‘worth’. A simple
yet useful performance indicator is possible with only two parameters — energy gap and lattice thermal conductivity. This
indicator can outline all potentially useful thermoelectric materials. Thermal conductivity in place of lattice thermal conductivity
can provide some additional information about the temperature range of operation. Yet another performance indicator may be
based on the slope of α vs. ln σ plots. α plotted against ln σ shows a linear relationship in a simplified model, but shows
a variation with temperature and carrier concentration. Assuming that such a relationship is true for a narrow range of temperature
and carrier concentration, one can calculate the slope m of α vs. ln σ plots against temperature and carrier concentrations.
A comparison between the variation ofZT and slopem suggests that such plots may be useful to identify potential thermoelectric materials. 相似文献
4.
Z. P. Niu 《The European Physical Journal B - Condensed Matter and Complex Systems》2011,82(2):153-158
We investigate the thermoelectric effects in a double-dot Aharonov-Bohm
interferometer coupled to ferromagnetic leads held at different
temperatures. The interplay of Rashba spin-orbit interaction (RSOI) and
magnetic flux ϕ induces various interesting spin-dependent interference
phenomena. The thermoelectric transport oscillates with ϕ. The peak of
the thermopower S and figure of merit ZT splits into two new peaks and
its splitting increases with the Rashba induced phase factor φ
R
.
With increasing φ
R
S and ZT at ϕ = ± 2nπ
(n = 0,1,2,...) exhibit a conversion from a peak to a valley. In the
presence of the interplay of RSOI and ϕ by increasing spin polarization
the splitting peaks of S (ZT) become asymmetric and ZT is greatly
enhanced. The influence of the quantum dot levels on thermoelectric effects
is also analyzed. 相似文献
5.
M. Esen A. T. Tüzemen M. Ozdemir 《The European Physical Journal B - Condensed Matter and Complex Systems》2012,85(4):117
We study the equilibration of an initial surface of conic shape that consists of concentric circular monolayers by Kinetic
Monte Carlo (KMC) method. The kinetic processes of attachment and/or detachment of particles to/from steps, diffusion of particles
on the surface, along a step or cluster edges are considered. The difference between an up hill and down hill motion of a
particle at a step are taken into account through the Ehrlich-Schwoebel (ES) barrier. The height of the cone evolves as h(0) − h(t) ~ t
1/α
where h(0) is the initial height of the surface and α is approximately 2. The ES barrier slows down the equilibration of the surface but the time dependence remains as given above.
The exponent α depends neither on ES barrier nor on the temperature. The equilibration is found also to be independent of energy barrier
to the motion of particles along the step edges. The number of particles in each layer except the top two circular layers
is found to decrease as t
0.57. 相似文献
6.
Guy Jumarie 《Central European Journal of Physics》2008,6(3):737-753
In a first stage, the paper deals with the derivation and the solution of the equation of the probability density function
of a stochastic system driven simultaneously by a fractional Gaussian white noise and a fractional Poissonian white noise
both of the same order. The key is the Taylor’s series of fractional order f(x + h) = E
α(hαD
x
α)f(x) where E
α() denotes the Mittag-Leffler function, and D
x
α is the so-called modified Riemann-Liouville fractional derivative which removes the effects of the non-zero initial value
of the function under consideration. The corresponding fractional linear partial differential equation is solved by using
a suitable extension of the Lagrange’s technique involving an auxiliary set of fractional differential equations. As an example,
one considers a half-oscillator of fractional order driven by a fractional Poissonian noise.
相似文献
7.
采用熔体旋甩结合放电等离子烧结(MS-SPS)技术制备了单相n型四元(Bi0.85Sb0.15)2(Te1-xSex)3(x=0.15,0.17,0.19,0.21)化合物,并对所得样品的微结构和热电传输性能进行了系统研究.样品自由断裂面的场发射扫描电子显微镜及抛光面的背散射电子成分分析表明:块体材料晶粒细小,晶粒排列紧密,成分分布均匀且相结构单一,样品中存在大量10—100nm的层状结构.随着Se含量x的增加,样品的电导率和热导率逐渐增加,而Seebeck系数逐渐降低.相比商业应用的区熔材料,MS-SPS方法合成的高Se组成的样品均在425K后表现出更高的ZT值,其中(Bi0.85Sb0.15)2(Te0.83Se0.17)3样品具有最高的ZT值,在360K可达到0.96,并在320—500K均保持较高的ZT值,500K时其ZT值相比区熔材料提高了48%.此外,通过调节Se的含量,可以有效地调控材料的ZT峰值出现的温度段,这对多级或梯度热电器件的制备具有重要意义. 相似文献
8.
Viktor Bezák 《Czechoslovak Journal of Physics》1999,49(7):1017-1025
The time evolution of a random surfacez=h(r, t) (r=x, y) formed by a deposition process of the Edwards-Wilkinson type is discussed. The discussion is based on the author’s former
derivation of the autocorrelation functionA
h(|r − r′|,t, t′)=〈h(r,t)h(r′,t′)〉 of the height functionh(r,t) under the assumption of a stochastic initial condition [V. Bezák: Acta Physica Univ. Comenianae39 (1998) 135]. Under the assumption of a steady (non-zero) deposition rate, the varianceσ
h
2
(t)=〈[h(r,t)]2〉 increases logarithmically in time whilst the correlation lengthl
h(t) of the height functionh(r,t) increases as ∼t
1/2. Therefore, the ratioσ
h(t)/l
h
(t) tends to zero and the surfacez=h(r,t) does always tend towards a smoothened appearance.
This work has been supported by the Slovak Grant Agency VEGA under contract No. 1/4319/97. 相似文献
9.
The electronic phase transition in cerium occurring near 7 kbar pressure at room temperature which is attributed to the 4f–5d
electron promotion has been studied using thermoelectric power as a tool. The important results that have emerged out of this
work are: (a) the relatively large variation in the absolute thermoelectric power ofγ-cerium (normal fcc phase) with pressure prior to the phase transition (in contrast to the rather small resistivity change
with pressure in this region); (b) a sharp decrease in the thermoelectric power accompanying the iso-structuralγ-α phase transition; and (c) the continuous decrease in the thermoelectric power ofα-cerium (collapsed fcc phase) with pressure, ultimately changing sign at higher pressures. An explanation based on the “virtual
bound state” model is proposed to account for these results. 相似文献
10.
Osamu Yamashita Hirotaka Odahara Takahiro Ochi Jun-ichi Shigeto 《Applied Physics A: Materials Science & Processing》2009,97(1):133-141
The local Seebeck coefficient α
L
and the resultant Seebeck coefficient α
R
of M/Bi0.88Sb0.12/M (M = Cu and Ni) composites with different thicknesses t
Bi–Sb of Bi–Sb alloy were measured as functions of z and T, where T is the absolute temperature, z is the distance from a center of Bi–Sb alloy to the middle point of two probes and α
L
and α
R
were measured using two probes separated by s=1.0 mm and s=t
Bi−Sb+0.1 mm, respectively. As a result, α
L
was enhanced extremely at the position of 0.2–0.3 mm away from the interfaces, while the local temperature along a composite
varies linearly with changes in z within Bi–Sb alloy. The local maximum of α
R
at 344 K appeared at t
Bi−Sb≈0.9 mm, so that it is expected to increase up to −167 μV/K at t
Bi−Sb=0.87 mm from the expression fitted well to the experimental data, which is 2.1 times as large as the intrinsic α at 344 K of Bi–Sb alloy. Such a local enhancement in α
L
would probably be caused by a temperature gradient across the depletion layer formed at the interface. The thermoelectric
figure of merit ZT of a composite with an optimum t
Bi−Sb of 0.87 mm is expected to reach the large value of 0.98 at 344 K, which corresponds to 4.5 times as high a value as ZT=0.22 at 344 K of Bi–Sb alloy. It is thus considered that the increase in α
L
at the interface is available as a useful mean of further increase in ZT of thermoelectric devices. 相似文献
11.
Zhong Liu Yuhu Zhang Yingjun Ma Y. Sasaki K. Yamada H. Oshima H. Yokose M. Ishizuka T. Komatsubara K. Furuno 《中国科学G辑(英文版)》2003,46(4):390-397
Excited states of125Sb have been studied using in-beam γ spectroscopy techniques via the124Sn(7Li, α2n) reaction at a beam energy of 32 MeV. A high-spin level scheme including 21 new γ-transitions and 14 new excited states
have been established. Three isomers have been identified at 1970, 2110 and 2471 keV and the ranges of their half-lives have
been estimated from the delayed coincidence data. The level structure of125Sb is discussed in terms of particle-core excitation coupling. With the help of empirical shell model calculations the three
isomers are proposed to have three-quasiparticle πg7/2⊗v(h
11/2
s
1/2)5−, πg7/2⊗v(h
11/2
d
3/2)7− and πg7/2⊗v(h
112/2)10
+ configurations, respectively. 相似文献
12.
V. S. Rabinovich 《Russian Journal of Mathematical Physics》2009,16(2):300-308
We consider the class of matrix h-pseudodifferential operators Op h (a) with symbols a = (a ij ) i,j=1 N , where the coefficients a ij ∈ C ∞(? x n × ? ξ n ? C(0, 1] satisfy the estimates |? x β g6 ξ α α ij (x, ξ, h)| ? C αβ 〈ξ〉 m and 〈ξ〉 = (1 + |ξ|2)1/2 for every multi-indices α, β. We also assume that a ij (x, ξ) is analytically continued with respect to ξ to a tube domain ? n + i $ \mathcal{B} We consider the class of matrix h-pseudodifferential operators Op
h
(a) with symbols a = (a
ij
)
i,j=1N, where the coefficients a
ij
∈ C
∞(ℝ
x
n
× ℝ
ξ
n
⊗ C(0, 1] satisfy the estimates |ϖ
x
β
g6
ξ
α
α
ij
(x, ξ, h)| ⩽ C
αβ
〈ξ〉
m
and 〈ξ〉 = (1 + |ξ|2)1/2 for every multi-indices α, β. We also assume that a
ij
(x, ξ) is analytically continued with respect to ξ to a tube domain ℝ
n
+ i
, where is a bounded domain in ℝ
n
containing the origin. The main results of the paper are the local estimates for solutions of h-pseudodifferential equations.
Let H
h
s
(ℝ
n
, ℂ
N
) be the space of distributions with values in ℂ
N
which is equipped with the norm , let Ω ⊂ ℝ
n
be a bounded open set, let v ∈ C
∞(ℝ
n
), let ▿v(x) ∈ for any x ∈ Ω, and let . Let u
h
(∈ H
h
s
(ℝ
n
,‒
N
)) be a solution of the equation Op
h
(α)u = 0. In this case, for every ϕ ∈ C
0∞ (Ω) such that ϕ(x) = 1 on Supp v and for a sufficiently small h
0 > 0, there exists a constant C > 0 such that the following estimate holds for every h ∈ (0, h
0]:
We apply estimate (1) to local tunnel exponential estimates for the behavior as h → 0 of the eigenfunctions of matrix Schr?dinger, Dirac, and square-root Klein-Gordon operators.
To the memory of Professor V. A. Borovikov 相似文献
((1)) |
13.
Let G be a reductive Lie group, g its Lie algebra, and M a G-manifold. Suppose 𝔸
h
(M) is a 𝕌
h
(g)-equivariant quantization of the function algebra 𝔸(M) on M. We develop a method of building 𝕌
h
(g)-equivariant quantization on G-orbits in M as quotients of 𝔸
h
(M). We are concerned with those quantizations that may be simultaneously represented as subalgebras in 𝕌*
h
(g) and quotients of 𝔸
h
(M). It turns out that they are in one-to-one correspondence with characters of the algebra 𝔸
h
(M). We specialize our approach to the situation g=gl(n,ℂ), M=End(ℂ
n
), and 𝔸
h
(M) the so-called reflection equation algebra associated with the representation of 𝕌
h
(g) on ℂ
n
. For this particular case, we present in an explicit form all possible quantizations of this type; they cover symmetric and
bisymmetric orbits. We build a two-parameter deformation family and obtain, as a limit case, the 𝕌(g)-equivariant quantization of the Kirillov-Kostant-Souriau bracket on symmetric orbits.
Received: 28 April 2002 / Accepted: 3 October 2002 Published online: 24 January 2003
RID="*"
ID="*" This research is partially supported by the Israel Academy of Sciences grant no. 8007/99-01.
Communicated by L. Takhtajan 相似文献
14.
L. G. Moyano A. P. Majtey C. Tsallis 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,52(4):493-500
We introduce, and numerically study, a system of N symplectically and globally coupled
standard maps localized in a d=1 lattice array. The global coupling is modulated
through a factor r-α, being
r the distance between maps. Thus, interactions are long-range (nonintegrable) when
0≤α≤1, and short-range (integrable) when α>1.
We verify that the largest Lyapunov exponent λM scales as λM ∝
N-κ(α), where κ(α) is positive when interactions are
long-range, yielding weak chaos in the thermodynamic
limit N↦∞ (hence λM→0). In the short-range case,
κ(α) appears to vanish,
and the behaviour corresponds to strong chaos. We show that, for certain
values of the control parameters of the system, long-lasting metastable states
can be present. Their duration tc scales as tc ∝Nβ(α),
where β(α) appears to be numerically in agreement with the following
behavior: β>0 for 0 ≤α< 1, and zero for α≥1.
These results are consistent with features typically found in nonextensive statistical mechanics.
Moreover, they exhibit strong similarity between the present
discrete-time system, and the α-XY Hamiltonian ferromagnetic model. 相似文献
15.
N. A. Silant’ev 《Journal of Experimental and Theoretical Physics》1999,89(1):45-55
In this paper the procedure of large-scale averaging of the magnetic-field diffusion equation with the α-term curlα(r,t)B(r,t) is used to show that a nonuniform distribution of the turbulent helicity fluctuations (more precisely, the fluctuations
of the coefficient α) with a zero average value gives rise to large-scale amplification of the initial magnetic field. A detailed study is carried
out of the dependence of the resulting large-scale α effect on the characteristics of the correlator 〈〈α(r, t)α(r″,t″)〉〉 in a rotating medium with a nonuniform distribution of the angular velocity ω=ω(ρ,z) (ρ is the distance for the rotation axis z). The effect of helicity fluctuations and the diffusion coefficient on the turbulent diffusion process is also investigated.
Zh. éksp. Teor. Fiz. 116, 85–104 (July 1999) 相似文献
16.
A. Bahraminasab M. Sadegh Movahed S. D. Nasiri A. A. Masoudi Muhammad Sahimi 《Journal of statistical physics》2006,124(6):1471-1490
We carry out an exact analysis of the average frequency ν+
αxi
in the direction x
i
of positiveslope crossing of a given level α such that, h(x, t) − = α, of growing surfaces in spatial dimension d. Here, h(x, t) is the surface height at time t, and is its mean value. We analyze the problem when the surface growth dynamics is governed by the Kardar-Parisi-Zhang (KPZ) equation without surface tension, in the time regime prior to appearance of cusp singularities (sharp valleys), as well as in the random deposition (RD) model. The total number N
+ of such level-crossings with positive slope in all the directions is then shown to scale with time as t
d/2 for both the KPZ equation and the RD model.
PACS number(s): 52.75.Rx, 68.35.Ct 相似文献
17.
B. Cameron Reed 《Central European Journal of Physics》2005,3(1):1-7
The ground-state energy of neutral helium is estimated variationally with a trial wavefunction of the form ϕ≈e
−γ(rA/a
o)ne−γ(rB/a
o)n. This model represents a modification of traditional textbook examinations of this problem via inclusion of the power “n”
as a second nonlinear variational parameter in addition to the usual effective nuclear charge γ and leads to an upper-limit
on the ground state energy of −2.86107 E
h
(E
h
=1 hartree) in comparison with the traditional (n=1) result of −2.84766 E
h
. This result represents a reduction of the percentage overestimate from the true ground-state energy (−2.90373 E
h
) of from 1.93 to 1.47. In comparison with the maximum accuracy obtainable from an uncorrelated trial wavefunction, −2.86168
E
h
, the present trial wavefunction reduces the percentage overestimate from 0.49 (n=1) to 0.021. The optimum values of (n, γ)
are determined to be ≈(0.897, 1.825). 相似文献
18.
Bernard Derrida Giambattista Giacomin Hubert Lacoin Fabio Lucio Toninelli 《Communications in Mathematical Physics》2009,287(3):867-887
We study the critical point of directed pinning/wetting models with quenched disorder. The distribution K(·) of the location of the first contact of the (free) polymer with the defect line is assumed to be of the form K(n) = n
−α-1
L(n), with α ≥ 0 and L(·) slowly varying. The model undergoes a (de)-localization phase transition: the free energy (per unit length) is zero in
the delocalized phase and positive in the localized phase. For α < 1/2 disorder is irrelevant: quenched and annealed critical points coincide for small disorder, as well as quenched and
annealed critical exponents [3,28]. The same has been proven also for α = 1/2, but under the assumption that L(·) diverges sufficiently fast at infinity, a hypothesis that is not satisfied in the (1 + 1)-dimensional wetting model considered
in [12,17], where L(·) is asymptotically constant. Here we prove that, if 1/2 < α < 1 or α > 1, then quenched and annealed critical points differ whenever disorder is present, and we give the scaling form of their
difference for small disorder. In agreement with the so-called Harris criterion, disorder is therefore relevant in this case.
In the marginal case α = 1/2, under the assumption that L(·) vanishes sufficiently fast at infinity, we prove that the difference between quenched and annealed critical points, which
is smaller than any power of the disorder strength, is positive: disorder is marginally relevant. Again, the case considered in [12,17] is out of our analysis and remains open.
The results are achieved by setting the parameters of the model so that the annealed system is localized, but close to criticality,
and by first considering a quenched system of size that does not exceed the correlation length of the annealed model. In such
a regime we can show that the expectation of the partition function raised to a suitably chosen power is small. We then exploit such an information to prove that the expectation of the same fractional power of the partition
function goes to zero with the size of the system, a fact that immediately entails that the quenched system is delocalized. 相似文献
19.
A. I. Shtern 《Russian Journal of Mathematical Physics》2011,18(2):211-215
Let G be a topological group. For a function f: G → ℝ and h ∈ G, the difference function Δ
h
f is defined by the rule Δ
h
f(x) = f(xh) − f(x) (x ∈ G). A function H: G → ℝ is said to be additive if it satisfies the Cauchy functional equation H(x + y) = H(x) + H(y) for every x, y ∈ G. A class F of real-valued functions defined on G is said to have the difference property if, for every function f: G → ℝ satisfying Δ
h
f ∈ F for each h ∈ G, there is an additive function H such that f − H ∈ F. Erdős’ conjecture claiming that the class of continuous functions on ℝ has the difference property was proved by N. G. de
Bruijn; later on, F. W. Carroll and F. S. Koehl obtained a similar result for compact Abelian groups and, under the additional
assumption that the other one-sided difference function ∇
h
f defined by ∇
h
f(x) = f(xh) − f(x) (x ∈ G, h ∈ G) is measurable for any h ∈ G, also for noncommutative compact metric groups. In the present paper, we consider a narrower class of groups, namely, the
family of semisimple compact connected Lie groups. It turns out that these groups admit a significantly stronger difference
property. Namely, if a function f: G → ℝ on a semisimple compact connected Lie group has continuous difference functions Δ
h
f for any h ∈ G (without the additional assumption concerning the measurability of the functions of the form ∇
h
f), then f is automatically continuous, and no nontrivial additive function of the form H is needed. Some applications are indicated, including difference theorems for homogeneous spaces of compact connected Lie
groups. 相似文献
20.
G. van Dijk 《Russian Journal of Mathematical Physics》2008,15(4):548-551
Denote by G = GL(n + 1, ℝ) the group of invertible (n + 1) × (n + 1) matrices with real entries, acting on ℝ
n+1 in the usual way, and let H
1 = GL(n, ℝ) be the stabilizer of the first unit vector e
0. Let H
0 = GL(1, ℝ) and set H = H
0 × H
1. It is known that the pair (G,H) is a generalized Gelfand pair. Define a character χ of H by χ(h) = χ(h
0
h
1) = χ0(h
0) where χ0 is a unitary character of H
0 (h
0 ∈ H
0, h
1 ∈ H
1). Let σ be the anti-involution on G given by σ(g) =
t
g. In this note, we show that any distribution T on G satisfying T(h
1
gh
2) = χ(h
1
h
2) T(g) (g ∈ G; h
1, h
2 ∈ H) is invariant under the anti-involution σ. This result implies that (G,H
1) is a generalized Gelfand pair. 相似文献