共查询到20条相似文献,搜索用时 62 毫秒
1.
V. Yu. Yushankhai 《Hyperfine Interactions》1989,50(1-4):775-779
On the basis of current theoretical views on the critical phenomena in isotropic Heisenberg ferromagnets the power temperature
behavior Λ=c(τ)λ0τ-w has been derived for the muon spin relaxation rate Λ as π-T
c
−1
(T-T
c
) → 0+. It is shown that the crossover from an exchange critical regime to a dipolar one is accompanied not only with the change
in the critical exponentw in the above law, but also with the reduction of the coefficientc(π). A comparison with the temperature behaviour of the inverse nuclear relaxation timet
R
−1
measured in the PAC experiment is carried out. 相似文献
2.
The temperature dependence of the hyperfine field of substitutional111Cd in antiferromagnetic CoO has been measured by means of the perturbed angular correlation technique. The Larmor frequency
ωL is found to obey a power law ωL(t=ω0
t
β) up tot
max=0.4 wheret=1−T/T
N is the reduced temperature withT
N=291.2(3) K and β=0.393 (5) the critical exponent. The results are discussed and compared with PAC experiments on111Cd in NiO and Ni and with results obtained by other methods. 相似文献
3.
I. M. Suslov 《Journal of Experimental and Theoretical Physics》2010,111(3):450-465
The previously-obtained analytical asymptotic expressions for the Gell-Mann-Low function β(g) and anomalous dimensions in the ϕ4 theory in the limit g → ∞ are based on the parametric representation of the form g = f(t), β(g) = f
1(t) (where t ∝ g
0−1/2 is the running parameter related to the bare charge g
0), which is simplified in the complex t plane near a zero of one of the functional integrals. In this work, it has been shown that the parametric representation
has a singularity at t → 0; for this reason, similar results can be obtained for real g
0 values. The problem of the correct transition to the strong-coupling regime is simultaneously solved; in particular, the
constancy of the bare or renormalized mass is not a correct condition of this transition. A partial proof has been given for
the theorem of the renormalizability in the strong-coupling region. 相似文献
4.
Hatem Zaag 《Communications in Mathematical Physics》2002,225(3):523-549
We consider u(x,t) a solution of u
t
=Δu+|u|
p
− 1
u that blows up at time T, where u:ℝ
N
×[0, T)→ℝ, p>1, (N−2)p<N+2 and either u(0)≥ 0 or (3N−4)p<3N+8. We are concerned with the behavior of the solution near a non isolated blow-up point, as T−t→ 0. Under a non-degeneracy condition and assuming that the blow-up set is locally continuous and N−1 dimensional, we escape logarithmic scales of the variable T−t and give a sharper expansion of the solution with the much smaller error term (T−t)1, 1/2−η for any η>0. In particular, if in addition p>3, then the solution is very close to a superposition of one dimensional solutions as functions of the distance to the blow-up
set. Finally, we prove that the mere hypothesis that the blow-up set is continuous implies that it is C
1, 1/2−η for any η>0.
Received: 20 June 2001 / Accepted: 6 October 2001 相似文献
5.
L. L. Jenkovszky 《Physics of Atomic Nuclei》2008,71(2):351-363
A model for generalized parton distributions (GPDs) in the form of ∼(x/g
0)(1−x)ᾶ(t), where ᾶ(t) = α(t) − α(0) is the nonlinear part of the Regge trajectory and g
0 is a parameter, g
0 > 1, is presented. For linear trajectories, it reduces to earlier proposals. We compare the calculated moments of these GPDs
with the experimental data on form factors and find that the effects from the nonlinearity of Regge trajectories are large.
By Fourier transforming the obtained GPDs, we access the spatial distribution of protons in the transverse plane. The relation
between dual amplitudes with Mandelstam analyticity and composite models in the infinite-momentum frame is discussed, the
integration variable in dual models being associated with the quark longitudinal-momentum fraction x in the nucleon.
The text was submitted by the authors in English. 相似文献
6.
V. Bezák 《Czechoslovak Journal of Physics》1998,48(5):529-535
The linear stochastic equation dx
β
/dt+[1+f
β
(t)]x
β
(t)=A sin (Ωt) is discussed. The functionƒ
β
(t) is defined as a Poissonian noise dependent on a parameterβ>0,ƒ
β
(t)=β Σ
j
[δ(t − t
j
+
) −δ (t − t
j
−
)]. The mean frequency of the delta-pulses is chosen asβ-dependent in the formλ(β)=2γ(β
−2 + 1) exp(−β) whereγ is a constant from the interval (0, 0.974). With the stochastic functionƒ
β
(t) defined in this way, attention is paid on the oscillational term of the averaged function 〈x(t)〉, 〈x(t)〉osc=Āsin(Ωt − α). It is found that the dependenceĀ=Ā(β) exhibits one maximum and one minimum. The occurrence of these extrema seems to affirm the presence of stochastic resonance.
This work has been supported by the Slovak Grant Agency VEGA under contract No. 1/4319/97. 相似文献
7.
V. P. Goncharov 《JETP Letters》2009,89(8):393-398
A Hamiltonian version has been formulated for the model of a potential jet stream of a homogeneous incompressible fluid with a free boundary. In the framework of this model, instability regimes have been analyzed. It has been shown that self-similar solutions with a compact support can be dominant structures. Analysis of the instability mechanism shows that two collapse scenarios are possible. The first scenario occurs without the deformation of the shape and leads to an intensification of the vortex sheet according to the law (t 0 ? t)?1, where t 0 is the collapse time. The second scenario leads to the formation of a singularity for the surface shape and to a decrease in the intensity of the vortex sheet according to the laws (t 0 ? t)?1/5 and (t 0 ? t)1/5, respectively. The integral collapse criterion has been found. 相似文献
8.
The rare t-quark decays t → cl
j
+
l
k
−
and t → cṽ
j
k
k
induced by scalar-leptoquark doublets are considered within the minimal model involving four-color quark-lepton symmetry
and the Higgs mechanism of quark and lepton mass splitting. The partial widths with respect to the decays being considered
and the total widths Γ(t → cl
+′l
−) = Σj,k Γ(t → cl
j
+
l
k
−
) and Γ(t → cl
+′l
−) = Σj,kΓ(t → cṽ
j
v
k
) with respect to, respectively, the charged leptonic and neutrino modes are calculated. It is shown that, at scalar-leptoquark
masses higher than the t-quark mass (m
S > m
t), the branching ratios for these modes are Br(t → cl
+′l
−) ≈ (3.5−0.4) × 10−5 and Br(t → cṽ′v) ≈ (7.1−0.8) × 10−5 at m
s
= 180–250 GeV and an appropriate value of the leptoquark-mixing angle (sin β ≈ 0.2) and can increase for m
S < m
t to Br(t → cl
+′l
−) ≈ 0.03−0.002 and Br(t → cl
+′l
−) ≈ 0.46−0.05 for the charged mode at m
S
= 150–170 GeV for sin β ≈ 1 and sin β ≈ 0.2, respectively. In the cases being considered, t-quark decays to pairs of charged leptons can be accessible to detection at LHC. In the last case, these decays could manifest
themselves (for example, in dilepton events) at the Tevatron as well.
Original Russian Text ? P.Yu. Popov, A.D. Smirnov, 2006, published in Yadernaya Fizika, 2006, Vol. 69, No. 6, pp. 1006–1016. 相似文献
9.
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
10.
The integral energy spectrum of primary cosmic rays has been obtained. In the energy range (2.4×103−1.1×105 GeV), the spectrum of all nuclei is consistent with a power law of indexγ=1.55±0.06 and the flux of all nuclei is:N(⩾E
0)⋍(5.1±1.8)×10−1×E
0
−1.55
particles/cm2 sterad. sec., whereE
0 is in GeV. The spectrum of primaryα-particles in the energy range (4.4×103−4.8×104) GeV is also consistent with a power law of indexγ=1.71±0.12 and the flux is:N(⩾E
0)=(4.2±1.4)×10−1×E
0
−1.71
, particles per cm2 sterad. sec, whereE
0 is in GeV. 相似文献
11.
L. R. Fontes R. H. Schonmann V. Sidoravicius 《Communications in Mathematical Physics》2002,228(3):495-518
We study a class of continuous time Markov processes, which describes ± 1 spin flip dynamics on the hypercubic latticeℤ
d
, d≥ 2, with initial spin configurations chosen according to the Bernoulli product measure with density p of spins + 1. During the evolution the spin at each site flips at rate c= 0, or 0 < α≤ 1, or 1, depending on whether, respectively, a majority of spins of nearest neighbors to this site exists and
agrees with the value of the spin at the given site, or does not exist (there is a tie), or exists and disagrees with the
value of the spin at the given site. These dynamics correspond to various stochastic Ising models at 0 temperature, for the
Hamiltonian with uniform ferromagnetic interaction between nearest neighbors. In case α= 1, the dynamics is also a threshold
voter model. We show that if p is sufficiently close to 1, then the system fixates in the sense that for almost every realization of the initial configuration
and dynamical evolution, each site flips only finitely many times, reaching eventually the state + 1. Moreover, we show that
in this case the probability q(t) that a given spin is in state − 1 at time t satisfies the bound: for arbitrary ɛ > 0, q(t) ≤ exp(−t
(1/
d
) −ɛ), for large t. In d= 2 we obtain the complementary bound: for arbitrary ɛ > 0, q(t) ≥ exp(−t
(1/2) +ɛ), for large t.
Received: 12 July 2001 / Accepted: 1 February 2002 相似文献
12.
Boikov Yu. A. Lil’enfors T. Olsson E. Klaeson T. Danilov V. A. 《Physics of the Solid State》2011,53(10):2168-2173
A significant (∼1.8%) positive unit between the parameters of the crystal lattice is the reason of tetragonal distortion (a
⊥/a
‖ ≈ 1.04) and reduction in the volume of the unit cell of La0.67Ca0.33MnO3 films (15 nm) quasicoherently grown on the (001) surface of a LaAlO3 substrate. The films consist of single-crystal blocks with the lateral size of 30–50 nm. The atomically smooth LaAlO3-La0.67Ca0.33MnO3 interphase boundary has no misfit dislocations. At T = 4.2 K, the transformation of nonferromagnetic phase inclusions into ferromagnetic ones in a constant magnetic field H is accompanied by a stable reduction in the electrical resistivity ρ of manganite films with time, so that the curve ρ(t) is well approximated by the relationship ρ(t) ∼ ρ1(t − t
0)1/2, (where t
0 is the time for establishment of the specified value (μ0
H = 5 T) of the magnetic field and ρ1 is a coefficient independent of H). The magnetocrystalline anisotropy due to the elastic deformation of films by the substrate and stratification of electronic
phases are the reasons of the distinct hysteresis in the dependences ρ(μ0
H, T < 100 K) obtained on μ0
H scanning in the sequence 5 T → 0 → −5 T → 0 → 5 T. At T = 50 K and μ0
H = 0.4 T, the magnetoresistance MR = 100% [ρ(μ0
H) − ρ(μ0
H = 0)]/ρ(μ0
H = 0) of LCMO films attains 150%. 相似文献
13.
Itzhak Goldman 《International Journal of Theoretical Physics》1982,21(8-9):665-672
Dirac’s large number hypothesis (LNH), in the formG/G
0=HH
0
−1
, is applied to the matter-dominated cosmological era, using the framework of the scale covariant theory (Canuto et al., 1977).
We obtain explicit expressions forR andβ
a
as functions ofR
E
, whereR andR
E
are the scale factors of the cosmological Robertson-Walker metric, expressed in atomic and gravitational units, respectively,
andβ
a
is the ratio between the rates of gravitational and atomic clocks. The parameters in these expressions are
, the deceleration parameter in gravitational units, and
(t
0)H
0
−1
where
(t
0) is the present epoch value of the derivative ofβ
a
with respect to atomic time. We find that a necessary condition for the LNH to be compatible with a Robertson-Walker model
is that
(t
0)H
0
−1
≥
2
1
. The only experimental values for
(t
0) available at present are those based on the lengthening of the Moon’s period of revolution around the Earth, suggesting
0.86≥
(t
0)H
0
−1
≥0.21; the more promising technique of radar ranging to the inner planets has not yet produced a value for
(t
0). Using the lunar data, it follows that 0≤
≲0.42 corresponding to an open universe (k=−1). Closed models (k=1,
>1/2) are not compatible with the LNH since the required values of
(t
0)H
0
−1
are more than an order of magnitude above the observational upper limit.
Presented at the Dirac Symposium, Loyola University, New Orleans, 1981. 相似文献
14.
We present the results of simultaneous analysis of the S-wave ππ spectra in the reactions π
−
p → (ππ)S
n at p
lab=38 GeV/c (GAMS) and π
−
p → (ππ)S
n at p
lab=18 GeV/c (E852 Collaboration) at moderate momenta transferred to the nucleon, |t| ≲ 1.5 (GeV/c)2. The t distributions are described by the Reggeized π and a
1 exchanges provided by the leading and daughter trajectories, while the M
ππ
spectra are determined by a set of scalar-isoscalar resonances. With M
ππ
distributions averaged over different t intervals, we have found several solutions given by different t-channel-exchange mechanisms at |t| ∼ (0.5–1.5) (GeV/c)2, with resonance parameters close to each other. We conclude that, despite a poor knowledge of the structure of the t exchange, the characteristics of resonances such as masses and widths can be reliably determined using the processes under
discussion. As to pole positions, we have found (1031±10)−i(35±6) MeV for f
0(980) and (1315±20)−i(150±30) MeV for f
0(1300).
From Yadernaya Fizika, Vol. 66, No. 5, 2003, pp. 960–972.
Original English Text Copyright ? 2003 by Anisovich, Sarantsev.
This article was submitted by the authors in English. 相似文献
15.
The present paper reports that triboluminescence (TBL) does not appear at the instant of impact of the load but a certain
time lag is required for its appearance which depends on the value of the stress applied to the crystal. Since TBL appears
in sugar crystals during the creation of new surfaces, the fracture-initiation time of the crystal has been taken to be the
delay time in observing TBL pulse after the application of stress. The dependence of fracture-initiation time,t
f
σ
, of crystals on the stress, σ, may be expressed ast
f
σ
=t
o exp (− ασ), wheret
o and α are constants. The values of the lattice energy, and the change in lattice energy per unit stress, of sugar crystals
have been calculated from TBL measurements and they have been found to be 21·2 kcal mole−1 and 0·41 × 10−8 kcal mole−1 dyne−1 cm2 respectively. 相似文献
16.
Alessandro Torcini Paolo Politi 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,25(4):519-529
Surface growth models may give rise to instabilities with mound formation whose typical linear size L increases with time (coarsening process). In one dimensional systems coarsening is generally driven by an attractive interaction
between domain walls or kinks. This picture applies to growth models for which the largest surface slope remains constant
in time (corresponding to model B of dynamics): coarsening is known to be logarithmic in the absence of noise ( L(t) ∼ ln t) and to follow a power law ( L(t) ∼t
1/3) when noise is present. If the surface slope increases indefinitely, the deterministic equation looks like a modified Cahn-Hilliard
equation: here we study the late stages of coarsening through a linear stability analysis of the stationary periodic configurations
and through a direct numerical integration. Analytical and numerical results agree with regard to the conclusion that steepening
of mounds makes deterministic coarsening faster : if α is the exponent describing the steepening of the maximal slope M of mounds ( M
α∼L) we find that L(t) ∼t
n: n is equal to for 1≤α≤2 and it decreases from to for α≥2, according to n = α/(5α - 2). On the other side, the numerical solution of the corresponding stochastic equation clearly shows that in the
presence of shot noise steepening of mounds makes coarsening slower than in model B: L(t) ∼t
1/4, irrespectively of α. Finally, the presence of a symmetry breaking term is shown not to modify the coarsening law of model
α = 1, both in the absence and in the presence of noise.
Received 28 September 2001 and Received in final form 21 November 2001 相似文献
17.
Using intensity autocorrelation of multiply scattered light, we show that the increase in interparticle interaction in dense,
binary colloidal fluid mixtures of particle diameters 0.115μm and 0.089μm results in freezing into a crystalline phase at volume fractionφ of 0.1 and into a glassy state atφ=0.2. The functional form of the field autocorrelation functiong
(1)(t) for the binary fluid phase is fitted to exp[−γ(6k
0
2
D
eff
t)1/2] wherek
0 is the magnitude of the incident light wavevector andγ is a parameter inversely proportional to the photon transport mean free pathl*. TheD
eff is thel* weighted average of the individual diffusion coefficients of the pure species. Thel* used in calculatingD
eff was computed using the Mie theory. In the solid (crystal or glass) phase, theg
(1)(t) is fitted (only with a moderate success) to exp[−γ(6k
0
2
W(t))1/2] where the mean-squared displacementW(t) is evaluated for a harmonically bound overdamped Brownian oscillator. It is found that the fitted parameterγ for both the binary and monodisperse suspensions decreases significantly with the increase of interparticle interactions.
This has been justified by showing that the calculated values ofl* in a monodisperse suspension using Mie theory increase very significantly with the interactions incorporated inl* via the static structure factor. 相似文献
18.
This paper is concerned with the asymptotic behavior solutions of stochastic differential equations dy
t
=dω
t
−∇Γ(y
t
) dt, y
0=0 and d=2. Γ is a 2 &\times; 2 skew-symmetric matrix associated to a shear flow characterized by an infinite number of spatial scales
Γ12=−Γ21=h(x
1), with h(x
1)=∑
n
=0
∞γ
n
h
n
(x
1/R
n
), where h
n
are smooth functions of period 1, h
n
(0)=0, γ
n
and
R
n
grow exponentially fast with n. We can show that y
t
has an anomalous fast behavior (?[|y
t
|2]∼t
1+ν with ν > 0) and obtain quantitative estimates on the anomaly using and developing the tools of homogenization.
Received: 1 June 2001 / Accepted: 11 January 2002 相似文献
19.
V. P. Ruban 《Journal of Experimental and Theoretical Physics》2010,111(5):776-785
We consider slow, compared to the speed of sound, motions of an ideal compressible fluid (gas) in a gravitational field in
the presence of two isentropic layers with a small specific-entropy difference between them. Assuming the flow to be potential
in each of the layers (v
1, 2 = ▿ϕ1, 2) and neglecting the acoustic degrees of freedom (div($
\bar \rho
$
\bar \rho
(z)▿ϕ1, 2) ≈ 0, where $
\bar \rho
$
\bar \rho
(z) is the average equilibrium density), we derive the equations of motion for the boundary in terms of the shape of the surface
z = η(x, y, t) itself and the difference between the boundary values of the two velocity field potentials: ψ(x, y, t) = ψ1 − ψ2. We prove the Hamilto nian structure of the derived equations specified by a Lagrangian of the form ℒ = ∫$
\bar \rho
$
\bar \rho
(η)η
t
ψdxdy − ℋ{η, ψ}. The system under consideration is the simplest theoretical model for studying internal waves in a sharply stratified
atmosphere in which the decrease in equilibrium gas density due to gas compressibility with increasing height is essentially
taken into account. For plane flows, we make a generalization to the case where each of the layers has its own constant potential
vorticity. We investigate a system with a model dependence $
\bar \rho
$
\bar \rho
(z) ∝ e
−2αz
with which the Hamiltonian ℋ{η, ψ} can be represented explicitly. We consider a long-wavelength dynamic regime with dispersion
corrections and derive an approximate nonlinear equation of the form u
t
+ auu
x
− b[−$
\hat \partial _x^2
$
\hat \partial _x^2
+ α2]1/2
u
x
= 0 (Smith’s equation) for the slow evolution of a traveling wave. 相似文献
20.
On the Energy Growth of Some Periodically Driven Quantum Systems with Shrinking Gaps in the Spectrum
We consider quantum Hamiltonians of the form H(t)=H+V(t) where the spectrum of H is semibounded and discrete, and the eigenvalues behave as E
n
∼n
α
, with 0<α<1. In particular, the gaps between successive eigenvalues decay as n
α−1. V(t) is supposed to be periodic, bounded, continuously differentiable in the strong sense and such that the matrix entries with
respect to the spectral decomposition of H obey the estimate ‖V(t)
m,n
‖≤ε|m−n|−p
max {m,n}−2γ
for m≠n, where ε>0, p≥1 and γ=(1−α)/2. We show that the energy diffusion exponent can be arbitrarily small provided p is sufficiently large and ε is small enough. More precisely, for any initial condition Ψ∈Dom(H
1/2), the diffusion of energy is bounded from above as 〈H〉
Ψ
(t)=O(t
σ
), where
. As an application we consider the Hamiltonian H(t)=|p|
α
+ε
v(θ,t) on L
2(S
1,dθ) which was discussed earlier in the literature by Howland. 相似文献