共查询到20条相似文献,搜索用时 31 毫秒
1.
We give an analytical formula for the critical temperature of a superconductor taking into account the enhanced Coulomb repulsion which will be considered as frequency dependent. 相似文献
2.
A recent theoretical study of plane waves with orthogonal phase velocity is premised on incorrect assumptions. The conclusion reached therein – namely, that “a plane wave with orthogonal phase velocity cannot possess linear momentum” and therefore “cannot propagate at all” – is incorrect in general. 相似文献
3.
We compare the electronic structures of single FeSe layer films on SrTiO 3 substrate (FeSe/STO) and K x Fe 2-y Se 2 superconductors obtained from extensive LDA and LDA + DMFT calculations with the results of ARPES experiments. It is demonstrated that correlation effects on Fe-3d states are sufficient in principle to explain the formation of the shallow electron-like bands at the M(X)-point. However, in FeSe/STO these effects alone are apparently insufficient for the simultaneous elimination of the hole-like Fermi surface around the Γ-point which is not observed in ARPES experiments. Detailed comparison of ARPES detected and calculated quasiparticle bands shows reasonable agreement between theory and experiment. Analysis of the bands with respect to their origin and orbital composition shows, that for FeSe/STO system the experimentally observed “replica” quasiparticle band at the M-point (usually attributed to forward scattering interactions with optical phonons in SrTiO 3 substrate) can be reasonably understood just as the LDA calculated Fe-3d xy band, renormalized by electronic correlations. The only manifestation of the substrate reduces to lifting the degeneracy between Fe-3d xz and Fe-3d yz bands near M-point. For the case of K x Fe 2-y Se 2 most bands observed in ARPES can also be understood as correlation renormalized Fe-3d LDA calculated bands, with overall semi-quantitative agreement with LDA + DMFT calculations. 相似文献
5.
Complex structural and magnetic studies of polycrystalline samples of the Y 1 – xFe xBa 2Cu 3O y high- Tc superconductor ( x = 0, 0.02, 0.05) have been carried out in order to determine the effect of weak doping with a magnetic 3 d ion on structural changes and the critical current density Jc. An increase in the Fe content results in a significant change in Jc and its field dependence. The dependences Jc( H) become nonmonotonic and demonstrate a pronounced peak (peak effect); as a result, the Jc increases strongly in wide temperature and magnetic field regions. The analysis of the field dependences of the pinning force reveals a scaling behavior. The parameters of the scaling function correspond to the point magnetic defects under strong effects of a thermally activated flux flow. Thus, the weak Fe doping (several molar percent) is a promising way to significant improvement of transport properties of high- Tc superconducting materials based on 123-type compounds. 相似文献
6.
We study the possibility of the small-polaron creation in α-helix proteins, accounting for the self-trapping of the intramolecular
vibration energy quanta. The small-polaron concept of energy transfer in polypeptides has been revisited on the basis of these
results. It was found that traditional small-polaron theories cannot be directly applied to the vibrational quanta transfer
in these substances. In particular, true eigenstates of system should correspond to a partial dressed polarons rather than
to the fully dressed small polaron states. 相似文献
7.
Billiards corresponding to planar periodic Lorentz processes are considered in the usual (hard) sense and in the case when the hard core potential of the scatterers is replaced by some other circularly symmetric potential. A review on certain important aspects of the history of the subject is given and some new results on exponential decay of correlations are formulated. Both the results from the literature and those of our own mentioned are mathematically rigorous, nevertheless, proofs are only briefly sketched. For further details, see the preprint [Correlation decay in certain soft billiards, Commun. Math. Phys., in press]. 相似文献
8.
All known stationary black hole solutions in higher dimensions possess additional rotational symmetries in addition to the
stationary Killing field. Also, for all known stationary solutions, the event horizon is a Killing horizon, and the surface
gravity is constant. In the case of non-degenerate horizons (non-extremal black holes), a general theorem was previously established
[24] proving that these statements are in fact generally true under the assumption that the spacetime is analytic, and that
the metric satisfies Einstein’s equation. Here, we extend the analysis to the case of degenerate (extremal) black holes. It
is shown that the theorem still holds true if the vector of angular velocities of the horizon satisfies a certain “diophantine
condition,” which holds except for a set of measure zero. 相似文献
9.
ABSTRACTOlivine with chemical composition (Mg,Fe) 2SiO 4 is a silicate which is supposed to strongly constrain the flow of the Earth’s upper mantle under thermal convection. Its mechanical properties are thus of primary importance. Slip systems in olivine involve two types of dislocations with [100] and [001] Burgers vectors. In this study, we report atomistic modelling of screw dislocations with [100] Burgers vector and their intrinsic properties. We show that the [100] screw dislocation core exhibits several configurations corresponding to spreading in different planes and different relative stabilities. At low pressure, we identify a clear tendency for core spreading in (010). At higher pressure, relevant for the Earth’s mantle, we show that pressure promotes a change in core configuration with spreading into equivalent {021} planes. Based on the systematic investigation of the minimum energy path between the different configurations, we show that the variability of core structures allows complex glide paths which has been described at the macroscopic level as ‘pencil glide’. Our results suggest that the pencil glide is more efficient at high pressure. 相似文献
10.
‘Planetodiversity’ is a composite word from planetary diversity. This denomination wants to parallel the common use of the term biodiversity employed in biology but translated here to the context of planetary sciences due to the proliferating variety of planets discovered outside the Solar System and theoretically proposed to exist. There are two properties that allow us a classification of a body as a planet or more generally as a ‘planetary mass object’: the orbital configuration and the physical structure (mass, energy and chemical composition). This leads respectively to the concepts that we term the ‘orbital planetodiversity’ and the ‘physical planetodiversity’. We present in a comparative way the basic planetary types observed or expected to exist within the framework of these two concepts. 相似文献
11.
The use of the nephelauxetic ratio for the calculation of percent covalency is examined. Values of Fk and Ek obtained from four parameter fits (e.g. F 2, F 4, F 6 and ζ 4f) neglecting configuration interaction for Pr 3+ in various host lattices are compared to those of the free ion. By including the effects of 4f-ligand overlap one can account for the empirically obtained order of sensitivity to the environment for Fk : F 2 > F 4 > F 6 and for Ek : E 2 > E 3 > E 1. The results further indicate that by using the nephelauxetic effect and the relationship b = (1 - β)/2 one is likely to overestimate the degree of covalency of a complex. 相似文献
13.
Physicists have been interested in accelerated observers for quite some time. Since the advent of special relativity, many authors have tried to understand these observers in the framework of Minkowski spacetime. One of the most important issues related to these observers is the problematic definition of rigid motion. In this paper, I write the metric in terms of the Frenet–Serret curvatures and the proper coordinate system of a general accelerated observer. Then, I use this approach to create a systematic way to construct a rigid motion in Minkowski spacetime. Finally, I exemplify the benefits of this procedure by applying it to two well-known observers, namely, the Rindler and the rotating ones, and also by creating a set of observers that, perhaps, may be interpreted as a rigid cylinder which rotates while accelerating along the axis of rotation. 相似文献
14.
The Rayleigh–Schrödinger perturbation theory of high orders and the algebraic Padé–Hermite approximants are used to determine the singular points of a vibrational energy function of the formaldehyde molecule dependent on a complex perturbation parameter as on the argument. It is shown that the Fermi, Darling–Dennison, and other higher-order vibrational resonances are related to Katz’s points—common branch points on the complex plane of the energy of two vibrational states. Analysis of Katz’s points that connect different vibrational states allows one to reveal essential resonance perturbations, to introduce an additional classification for them, and to determine the polyad structure of an energy spectrum. 相似文献
15.
All pulsed electron-nuclear double resonance (ENDOR) techniques, and in particular the Mims and Davies sequences, suffer from detectability biases (‘blindspots’) that are directly correlated to the size of the hyperfine interactions of coupled nuclei. Our efforts at ENDOR ‘crystallography’ and ‘mechanism determination’ with these techniques have led our group to refine our simulations of pulsed ENDOR spectra to take into account these biases, and we here describe the process and illustrate it with several examples. We first focus on an issue whose major significance is not widely appreciated, the ‘hole in the middle’ of pulsed ENDOR spectra caused by the n = 0 suppression hole in Mims ENDOR and by the analogous A → 0 suppression in Davies ENDOR for I = ½ and for 2H ( I = 1). We then discuss the general treatment of suppression effects for I = 1, illustrating it with a treatment of Mims suppression for 14N. 相似文献
16.
We investigate a one-dimensional system of N particles, initially distributed with random positions and velocities, interacting through binary collisions. The collision rule is such that there is a time after which the N particles do not interact and become sorted according to their velocities. When the collisions are elastic, we derive asymptotic distributions for the final collision time of a single particle and the final collision time of the system as the number of particles approaches infinity, under different assumptions for the initial distributions of the particles’ positions and velocities. For comparison, a numerical investigation is carried out to determine how a non-elastic collision rule, which conserves neither momentum nor energy, affects the median collision time of a particle and the median final collision time of the system. 相似文献
17.
The properties of trapping centres in – as grown – Tl 4GaIn 3S 8 layered single crystals were investigated in the temperature range of 10–300 K using thermoluminescence (TL) measurements. TL curve was analysed to characterize the defects responsible for the observed peaks. Thermal activation energies of the trapping centres were determined using various methods: curve fitting, initial rise and peak shape methods. The results indicated that the peak observed in the low-temperature region composed of many overlapped peaks corresponding to distributed trapping centres in the crystal structure. The apparent thermal energies of the distributed traps were observed to be shifted from ~12 to ~125 meV by increasing the illumination temperature from 10 to 36 K. The analysis revealed that the first-order kinetics (slow retrapping) obeys for deeper level located at 292 meV. 相似文献
18.
Under the actions of different Hamiltonians on the different two-qubit input states by using the quantum Yang-Baxterization approach, we investigate the behaviors of the fidelity and the trace distance as measures of ‘closeness’ and distinguishability of two quantum states. The results show that the fidelity that is the main figure of merit for any communication and computing process can be kept to high values depending on the choice of the initial states and the Hamiltonians constructed by the Yang-Baxter equation. On the other hand, by choosing the initial states and Yang-Baxter systems which are the various extensions of the Yang-Baxter equations for several matrices, these quantifiers can be adjusted as desired to achieve many quantum computing and computational tasks. Furthermore, to quantify the performance of quantum teleportation we examine the teleportation fidelity for the outputs that correspond to the different two-qubit X-type states under the actions of the different Hamiltonians. It is possible to obtain high fidelity to use the quantum teleportation process. 相似文献
19.
Building on our earlier work (Misra and Shukla, Nucl. Phys. B 827:112, 2010; Phys. Lett. B 685:347–352, 2010), we show the possibility of generating “light” fermion mass scales of MeV–GeV range (possibly related to the first two generations of quarks/leptons) as well as eV (possibly related to first two generations of neutrinos) in type IIB string theory compactified on Swiss-Cheese orientifolds in the presence of a mobile space-time filling D3-brane restricted to (in principle) stacks of fluxed D7-branes wrapping the “big” divisor Σ B . This part of the paper is an expanded version of the latter half of Sect. 3 of a published short invited review (Misra, Mod. Phys. Lett. A 26:1, 2011) written by one of the authors [AM]. Further, we also show that there are no SUSY GUT-type dimension-five operators corresponding to proton decay, and we estimate the proton lifetime from a SUSY GUT-type four-fermion dimension-six operator to be 10 61 years. Based on GLSM calculations in (Misra and Shukla, Nucl. Phys. B 827:112, 2010) for obtaining the geometric K?hler potential for the “big divisor,” using further the Donaldson’s algorithm, we also briefly discuss in the first of the two appendices the metric for the Swiss-Cheese Calabi–Yau used, which we obtain and which becomes Ricci flat in the large-volume limit. 相似文献
20.
We correct a data processing error in the article “Construction of explicit and implicit dynamic finite difference schemes and application to the large-eddy simulation of the Taylor–Green vortex” by Dieter Fauconnier, Chris De Langhe and Erik Dick published in the Journal of Computational Physics 228 (2009), pp. 8053–8084. 相似文献
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