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1.
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
2.
We study the effect of quantum fluctuations in an Ising
spin system on a scale-free network of
degree exponent γ>5 using
a quantum Monte Carlo simulation technique. In our model,
one can adjust the magnitude of the magnetic field perpendicular
to the Ising spin direction and can therefore control the
strength of quantum fluctuations for
each spin. Our numerical analysis
shows that quantum fluctuations reduce the transition
temperature Tc of the ferromagnetic-paramagnetic phase
transition. However, the phase transition belongs to
the same mean-field type universality class both with
and without the quantum fluctuations.
We also study the role of hubs by turning on the
quantum fluctuations exclusively
at the nodes with the most links. When only a small number of hub
spins fluctuate quantum mechanically, Tc
decreases with increasing magnetic field
until it saturates at high fields. This effect
becomes stronger as the number of hub spins increases.
In contrast, quantum fluctuations at the same number of
“non-hub” spins do not affect Tc. This implies
that the hubs play an important role in
maintaining order in the whole network. 相似文献
3.
A one-dimensional diagonal tight binding electronic system with dichotomic correlated disorder in the presence of external
d.c field is investigated. It is found numerically that the conductance distribution obeys fairly well to log-normal distribution
in weak disorder strength in localized regime, which indicates validity of single parameter scaling theory in this limit.
Contrary to the universal cumulant relation C
1 = 2C
2 in the absence of d.c. field, we demonstrated numerically that C
1 ≫ 2C
2 in the presence of the field in localized regime. We interpret this result as suppression of the fluctuation effects by the
external field. In addition, it is obtained that the quantity NF
c
, here N is the system size and F
c
is the crossover field, decreases as the as the system energy E increases. Moreover, we find numerically a simple linear relation between the average logarithm of the conductance 〈ln(g)〉 and the field strength as 〈ln(g)〉 = C(N, λ)F, here C(N, λ) is a constant for particular values of N and λ, which is the Poisson parameter of the dichotomic process. 相似文献
4.
F. Calvo P. Poulain 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2009,51(1):15-23
Monte Carlo simulations of gas-phase polyalanine peptides have been carried out with the Amber ff96 force field. A low-temperature structural transition takes place between the α-helix stable conformation and β-sheet structures,
followed by the unfolding phase change. The transition state ensembles connecting the helix and sheet conformations are investigated
by sampling the energy landscape along specific geometric order parameters as putative reaction coordinates, namely the electric
dipole μ, the end-to-end distance d, and the gyration radius Rg. By performing series of shooting trajectories, the committor probabilities and their distributions are obtained, revealing
that only the electric dipole provides a satisfactory transition coordinate for the α↔β interconversion. The nucleus at the
transition is found to have a high helical content. 相似文献
5.
P. K. Raina A. Shukla S. Singh P. K. Rath J. G. Hirsch 《The European Physical Journal A - Hadrons and Nuclei》2006,28(1):27-36
Theoretical results for two neutrinos in the nuclei 96Ru, 102Pd, 106Cd and 108Cd are presented. The study employs the Hartree-Fock-Bogoliubov model to obtain the wave functions of the parent and daughter
nuclei, in conjunction with the summation method to estimate the double-beta decay nuclear matrix elements. The reliability
of the intrinsic wave functions of 96, 102Ru, 96Mo, 102, 106, 108Pd and 106, 108Cd nuclei is tested by comparing the theoretically calculated spectroscopic properties with the available experimental data.
The calculated half-lives T1/22ν of 96Ru, 102Pd, 106Cd and 108Cd nuclei for 2ν β+β+, 2ν β+EC and 2ν ECEC modes are presented. The effect of deformation on the nuclear transition matrix element M2ν is also studied. 相似文献
6.
B. I. Smirnov T. S. Orlova A. N. Kudymov M. T. Lanagan N. Chen K. C. Goretta 《Physics of the Solid State》1997,39(11):1759-1761
An experimental study is reported of the influence of temperature (T), electric field polarity (±E), as well as of changes in the electrode/insulator/superconductor (E/I/S) measuring system on the field effect in the ceramic (BiPb)2Sr2Ca2Cu3Ox. It has been established that at 77 K and for E⩾60 MV/m the critical current I
c and conductivity of the sample increase for I>I
c, irrespective of the field polarity. For lower fields and a negative electrode potential the conductivity in an electric
field may decrease. The field effect decreases with increasing temperature, to practically vanish near T
c where the sample is still in superconducting state. Experiments carried out with more complex systems E/I/M/I/S and E/I/M/S (M stands for a metallic foil) support the conclusion that it is the external electric field that is responsible for the observed
effects.
Fiz. Tverd. Tela (St. Petersburg) 39, 1967–1970 (December 1997) 相似文献
7.
The Bardeen-Cooper-Schrieffer (BCS) gap equation is solved analytically in one, two and three dimensions, for temperatures
close to zero andT
c. We work in the weak coupling limit, but allow the interaction widthν≡ħω
m/E
F to lie in the interval (0, ∞) Here,ħω
m is the maximum energy of a force-mediating boson, andE
F denotes the Fermi energy. We obtain expressions forT
c and ΔC, the jump in the electronic specific heat acrossT=T
c, in the limitsν≪1 (the usual phonon pairing) andν>1 (non-phononic pairing). This enables us to see howT
c scales with the mediating boson cut off. Our results predict a larger jump in the specific heat for the caseν>1, compared toν≪1. We also briefly touch upon the role of a van Hove singularity in the density of states. 相似文献
8.
G. Pratesi A. Bellosi F. Barocchi 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,18(2):283-287
The pressure and temperature dependences of the depolarized light scattering spectra of salol have been measured at isobaric
condition P = 1 bar for T between 328 and 393 K, and at isothermal condition T = 343 K for P between 1 and 625 bar, i.e. outside the metastable liquid region. The experimental results for both the α- and β-relaxations can be well described by
the Mode Coupling Theory. The independence of the power-law parameters a, and consequently b and γ, from the thermodynamic variables T and P is demonstrated.The critical temperature T
c at 1 bar and the critical pressure P
c at T = 343 K have been determined from the normal liquid state.
Received 2 May 2000 相似文献
9.
Magnetoplastic effect in irradiated NaCl and LiF crystals 总被引:2,自引:0,他引:2
V. I. Al’shitz E. V. Darinskaya O. L. Kazakova 《Journal of Experimental and Theoretical Physics》1997,84(2):338-344
The effect of low x-ray irradiation doses (≈102 rad) on the magnetoplastic effect — the detachment of dislocations from paramagnetic centers under the action of an external
magnetic field B — in alkali-halide crystals has been investigated. The measurements were performed on LiF crystals and three types of NaCl
crystals, differing in impurity content. The dependence of the mean free path l of the dislocations on the rotational frequency ν of a sample in a magnetic field was especially sensitive to low irradiation doses. In unirradiated crystals this dependence
is a single-step dependence and is characterized by a critical frequency ν
c ∝B
2 above which the magnetoplastic effect is not observed. The frequency ν
c depends only on the type of paramagnetic centers, and not on their density. Even the lowest irradiation dose employed (<100
rad) leads to a sharp restructuring of the dependence l(ν), converting it into a two-step dependence (for edge dislocations) with an additional critical frequency ν
c2, that is insensitive to the irradiation dose, and that corresponds to the appearance of magnetically sensitive stoppers
of a new type under irradiation. The initial critical frequency ν
c1, as a rule, also varies with the dose, reflecting the change in state of the impurity complexes (Ca in NaCl and Mg in LiF).
Specifically, it is shown for NaCl(Ca) crystals that as the irradiation dose increases, the frequency ν
c1 increases, gradually approaching the value ν
c2, so that by the time the dose is ≈300 rad, the dependence l(ν) once again becomes a single-step dependence, dropping sharply only for ν⩾ν
c2. It is shown that the addition of a small number of Ni atoms to a NaCl crystal makes the Ca complexes radiation resistant,
and the critical frequency ν
c1 corresponding to them initially equals ν
c2 for crystals with no Ni. The recombination kinetics of radiation defects in the case in which the samples are irradiated
under a tungsten lamp was investigated. A possible physical model of the observed dependences is discussed.
Zh. éksp. Teor. Fiz. 111, 615–626 (February 1997) 相似文献
10.
Frank F. Haas Katharina Vollmayr Kurt Binder 《Zeitschrift für Physik B Condensed Matter》1995,99(1):393-400
As a simple model of an anisotropic orientational glass with short range forces, the 3-state Potts model on the simple cubic
lattice with nearest neighbor interactions drawn from a Gaussian distribution is considered. With Monte Carlo methods we study
the response of the system to a uniform “field” which favors one of the states. This is motivated by experiments which apply
stress that favors one molecular orientation of the quadrupolar glass. The responsem to that fieldh=H/k
BT is analyzed in terms of an expansionm= χ1
h+χ1
h
2+χ1
h
3+..., where χ1 is the linear susceptibility, and χ2,χ13 are nonlinear susceptibilities. Unlike the case of spin glasses, where the spin inversion symmetry of the system in the absence
of fields implies χ2≡0,χ2 is nonzero here and diverges to −∞ at the zero temperature transition of the model, while χ3 diverges to +∞ as in spin glasses. At inifinite temperature, however, χ1=1/3, χ2=1/18 and χ3=-1/54, i.e. the nonlinear susceptibilities have a different sign as at low temperature. In contrast, a random field does
not induce a uniform order parameterm but only a glass order parameterq. The temperature dependence of this glass order parameterq(T) shows for intermediate field strength order parameterq(T) shows for intermediate field strength a maximum of the slopedq(T)/dT very similar to corresponding experiments. 相似文献
11.
M. Kajita A. V. Avdeenkov 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,41(3):499-504
The collisions between linear polar molecules, trapped in
a microwave field with circular polarization, are theoretically
analyzed. We demonstrate that the collisional dynamics is mostly
controlled by two ratios ν/B and x=μ0E0/ħ
B (ν is the microwave frequency, B is the molecular
rotational constant, μ0 is the dipole moment, and E0 is
the electric field amplitude). We discuss the dependence of collision
cross sections on these ratios in order to find an advantageous
condition for evaporative cooling. 相似文献
12.
We report on the lattice location of indium in and the magnetic ordering of manganese in its α- and β-phases, as seen by perturbed
angular correlation. Quadrupole interaction spectra show that indium prefers to replace Mn atoms of type I in α-Mn, but replaces
type II atoms in the β-Mn structure. The interaction strength equalseQV
zz
/h=3.6 (6) MHz in α-Mn and 172.3 (3) MHz with ν=0.13 (1) in β-Mn. No magnetic ordering down to 4.2 K was observed in β-Mn, while
belowT
N
=95 K in the α-Mn phase, a magnetic hyperfine interaction appears indicating two distinct magnetic probe environments. The
hyperfine field, when measured atT=4.2 K, equals for 70% of the probes 6.33 (1) T, while the remaining fraction senses a 3.10 (4) T field. The magnitudes of
the hyperfine fields are essentially unaffected by a variety of conditions in the sample preparation. The ordering temperature,
on the contrary, turns out to be rather sensitive to residual impurities especially any oxygen contamination. 相似文献
13.
H. Chamati 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,24(2):241-249
The finite-size critical properties of the (n) vector ϕ4 model, with long-range interaction decaying algebraically with the interparticle distance r like r
-d - σ, are investigated. The system is confined to a finite geometry subject to periodic boundary condition. Special attention
is paid to the finite-size correction to the bulk susceptibility above the critical temperature T
c. We show that this correction has a power-law nature in the case of pure long-range interaction i.e. 0 < σ < 2 and it turns out to be exponential in case of short-range interaction i.e.σ = 2. The results are valid for arbitrary dimension d, between the lower ( d
< = σ) and the upper ( d
> = 2σ) critical dimensions.
Received 2 July 2001 and Received in final form 4 Septembre 2001 相似文献
14.
The dynamic and static properties of a supercooled (non-entangled) polymer melt are investigated via molecular-dynamics (MD) simulations. The system is confined between two completely smooth and purely repulsive walls. The
wall-to-wall separation (film thickness), D, is varied from about 3 to about 14 times the bulk radius of gyration. Despite the geometric confinement, the supercooled
films exhibit many qualitative features which were also observed in the bulk and could be analyzed in terms of mode-coupling
theory (MCT). Examples are the two-step relaxation of the incoherent intermediate scattering function, the time-temperature
superposition property of the late time α-process and the space-time factorization of the scattering function on the intermediate
time scale of the MCT β-process. An analysis of the temperature dependence of the α-relaxation time suggests that the critical
temperature, T
c, of MCT decreases with D. If the confinement is not too strong ( D≥10monomer diameter), the static structure factor of the film coincides with that of the bulk when compared for the same distance,
T - T
c(D), to the critical temperature. This suggests that T - T
c(D) is an important temperature scale of our model both in the bulk and in the films.
Received 12 September 2001 相似文献
15.
M. Paasch M. Winterlich R. Böhmer R. Sonntag G. J. McIntyre A. Loidl 《Zeitschrift für Physik B Condensed Matter》1995,99(1):333-338
The χ,T phase diagram of (NH4I)x(KI)1−x has been determined using neutron diffraction experiments and dielectric spectroscopy. At low temperatures and with decreasing
χ, the sequence γ, β, ε and glass phase has been detected. The critical concentration χc≈0.55 separates the glassy phase with frozen-in orientational disorder from the ε phase which reveals long-range orientational
order. Close to χc our experiments reveal evidence for two subsequent glass transitions. 相似文献
16.
Kuljeet Singh Z. Naik R. Kumar J. Goswamy D. Mehta N. Singh C. R. Praharaj E. S. Paul K. P. Singh R. P. Singh S. Muralithar N. Madhavan J. J. Das S. Nath A. Jhingan P. Sugathan R. K. Bhowmik 《The European Physical Journal A - Hadrons and Nuclei》2005,25(3):345-354
High-spin states in 123Cs, populated via the 100Mo ( 28Si, p4n) fusion-evaporation reaction at E
lab = 130 MeV, have been investigated employing in-beam γ-ray spectroscopic techniques. Rotational bands, built on πg
7/2, πg
9/2 and the unique-parity πh
11/2 orbitals, have been extended and evolve into bands involving rotationally aligned ν(h
11/2)2 and π(h
11/2)2 quasiparticles. A three-quasiparticle band based on the high-K πh
11/2 ⊗ νg
7/2 ⊗ νh
11/2 configuration has also been observed. Total Routhian Surface (TRS) calculations have been used to predict the nuclear shape
parameters ( β2, β4, γ) for the various assigned configurations. The assigned configurations have been discussed in the framework of a microscopic
theory based on the deformed Hartree-Fock (HF) and angular-momentum projection techniques. 相似文献
17.
In Yb3Fe5O12, the exchange effective field can be expressed as Heff=−λ·MFe=−λχeff·He=−γ·He where γ is named as the exchange field parameter and He is the external magnetic field. Then, in this paper, by the discussions on the characteristics of the exchange field parameter γ, the properties of exchange interaction in ytterbium iron garnet (Yb3Fe5O12) are analyzed under extreme conditions (high magnetic fields and low temperatures). Our theory suggests that the exchange field parameter γ is the function of the temperatures under different external magnetic fields, and γ=a+b·T+c·T2, where the coefficients a, b, c are associated with the external magnetic fields and the magnetized directions. Thus, the temperature-dependence, field-dependence and anisotropic characteristics of the exchange interaction in Yb3Fe5O12 are revealed. Also, excellent fits to the available experiments are obtained. 相似文献
18.
L. S. Li W. Chen W. Dong X. S. Chen 《The European Physical Journal B - Condensed Matter and Complex Systems》2011,80(2):189-193
Using Monte Carlo simulations and finite-size scaling, we
investigate the critical behavior of two-dimensional magnetic
lattice gas at densities ρ = 0.90, 0.95, 1.0. There is a
ferromagnetic phase transition at each density. As expected, the
critical temperature T
c
depends on system density ρ.
Unexpectedly, there is a density dependence of the critical
exponent of correlation length ν. For densities
ρ = 0.90,0.95,1.0, we obtain the inverse of critical exponent
1/ν = 0.835(5), 0.905(5), 1.00(1) respectively. It is found that
the ratios of critical exponent β/ν and γ/ν of
magnetization and susceptibility are independent of density. 相似文献
19.
V. A. Kul’bachinskii R. A. Lunin E. V. Bogdanov V. G. Kytin A. P. Senichkin V. I. Kadushkin 《JETP Letters》1996,63(5):336-341
The conductivity of GaAs structures δ-doped with tin on the vicinal and singular faces was investigated in strong electric fields up to E=104 V/cm and temperatures in the range 4.2 K <T<300 K. The measurements were performed in the dark and under illumination with visible light. Long-time photoconductivity
of 2D electrons with threshold T
c
≈240 K was observed in samples which were δ-doped with tin on the vicinal face. A strong electric field not only quenches photoconductivity, but also increases the resistance
of the structures at temperatures T<T
c
by several orders of magnitude with respect to the dark resistance.
Pis’ma Zh. éksp. Teor. Fiz. 63, No. 5, 326–330 (10 March 1996) 相似文献
20.
Ju. M. Gavriljuk A. M. Gangapshev V. V. Kuzminov S. I. Panasenko S. S. Ratkevich 《Physics of Atomic Nuclei》2006,69(12):2129-2133
A search for 2β decay of 136Xe with two high-pressure copper proportional counters was carried out in the Baksan Neutrino Observatory. The experiment
is based on comparison of spectra measured with natural and enriched xenon. No evidence was found for 2β(2ν) and 2β(0ν) decay. The decay half-life limit based on data measured for 8000 h is T
1/2 ≥ 8.5 × 1021 yr for 2ν mode and T
1/2 ≥ 3.1 × 1023 yr for 0ν mode (90% C.L.).
The text was submitted by the authors in English. 相似文献