The structure factor and correlation energy of a quantum wire of thickness b ? aB are studied in random phase approximation (RPA) and for the less investigated region rs < 1. Using the single-loop approximation, analytical expressions of the structure factor are obtained. The exact expressions for the exchange energy are also derived for a cylindrical and harmonic wire. The correlation energy in RPA is found to be represented by ?c(b, rs) = α(rs)/b + β(rs) ln(b) + η(rs), for small b and high densities. For a pragmatic width of the wire, the correlation energy is in agreement with the quantum Monte Carlo simulation data. 相似文献
Hamaker interaction energies and cutoff distances have been calculated for disordered carbon films, in contact with purely dispersive (diiodomethane) or polar (water) liquids, using their experimental dielectric functions ε (q, ω) obtained over a broad energy range. In contrast with previous works, a q-averaged <ε (q, ω) > q is derived from photoelectron energy-loss spectroscopy (XPS-PEELS) where the energy loss function (ELF) < Im[?1/ε (q, ω)] > q is a weighted average over allowed transferred wave vector values, q, given by the physics of bulk plasmon excitation. For microcrystalline diamond and amorphous carbon films with a wide range of (sp3/sp2 + sp3) hybridization, non-retarded Hamaker energies, A132 (L < 1 nm), were calculated in several configurations, and distance and wavenumber cutoff values were then calculated based on A132 and the dispersive work of adhesion obtained from contact angles. A geometric average approximation, H0?CVL?=?(H0?CVCH0?LVL)1/2, holds for the cutoff separation distances obtained for carbon-vacuum-liquid (CVL), carbon-vacuum-carbon (CVC) and liquid-vacuum-liquid (LVL) equilibrium configurations. The linear dependence found for ACVL, ACLC and ACLV values as a function of ACVC, for each liquid, allows predictive relationships for Hamaker energies (in any configuration) using experimental determination of the dispersive component of the surface tension, \( {\gamma}_{CV}^d \), and a guess value of the cutoff distance H0?CVC of the solid.
The spin-precession-induced current through ferromagnet/nanomagnet/superconductorjunctions is investigated by using the nonequilibrium Green’s function method. It is foundthat the charge current Ic for the spinprecession frequency ω less than the energy gap Δ onlyarises from the equal-spin Andreev reflection, which is independent of the spinpolarization p of the ferromagnetic lead, while that forω > Δ mainly originates from the quasiparticle’scontribution. Both equal-spin AR and quasiparticle scattering processes contribute to thespin current Is and the quasiparticlescattering process plays a dominant role. WhileIc forω < Δ can be enhanced by the spin polarizationp, Is decreases withp. These features may be of interest for ongoing experiments in thefield of molecular spintronics. 相似文献
We employed density-functional theory (DFT) within the generalized gradient approximation(GGA) to investigate the ZrTi2 alloy, and obtained its structural phase transition,mechanical behavior, Gibbs free energy as a function of pressure, P-V equation of state,electronic and Mulliken population analysis results. The lattice parameters andP-V EOS for α, β and ω phases revealed by ourcalculations are consistent with other experimental and computational values. The elasticconstants obtained suggest that ω-ZrTi2 and α-ZrTi2 are mechanically stable, and that β-ZrTi2 is mechanically unstableat 0 GPa, but becomes more stable with increasing pressure. Our calculated resultsindicate a phase transition sequence of α → ω → β forZrTi2. Both thebulk modulus B and shear modulus G increase linearly withincreasing pressure for three phases. The G/B values illustrated goodductility of ZrTi2alloy for three phases, with ω<α<β at0 GPa. The Mulliken population analysis showed that the increment of d electron occupancystabilized the β phase. A low value for B '0 is the feature of EOS for ZrTi2 and this softness in the EOS isrepresentative of pressure induced s-d electron transfer. 相似文献
An apparatus is described, with which, for the first time, the spectra of Augere-lectrons and of X-rays, produced by the impact of electrons, were measured simultaneously. The electron spectrometer was a magnetic 180°-spectrometer with a half-width of 0·5%. The X-ray spectrometer was a NaJ-crystal with a photomultiplier. The electron- and the X-rays were produced in metallic foils of a thickness of 50 Å by the impact of 55-keV-electrons. The knownK-fluorescence-yields of copper and selenium were used to determine the various yields for theL-shells of gold. TheL-fluorescence-yields areωL1=0·08±0·01;ωL2=0·26±0·03;ωL3=0·24±0·02. 相似文献
Photoionization of the Xe atom and Xe@C60 molecule have been studied usingthe random phase approximation with exchange (RPAE) method. The Xe atom was described byrelaxed orbitals including overlap integrals. The C60 fullerene has beenrepresented by an attractive short range spherical well with potentialV(r), given byV(r) = ?V0 forri < r < ro,otherwise V(r) = 0 whereri andro are respectively, the inner and outerradii of the spherical shell. The time independent Schrödinger equation was solved usingboth regular and irregular solutions and the continuous boundary conditions atri andro. The results demonstrate improvementto previous calculations for both the Xe atom and Xe@C60 molecule and comparevery well with the recent experimental data. 相似文献
Single crystal X-band electron paramagnetic resonance (EPR) studies on divalent copper ions embedded in dipotassium diaquabis(malonato-κ2O,O′) nickelate dihydrate have been performed at 300, 123 and 77 K to understand the nature of Jahn–Teller distortion in the paramagnetic host lattice. The angular variation of the EPR spectra reveals the presence of two sites, with one site not showing hyperfine resolution even at 77 K. The spin-Hamiltonian parameters of this six-coordinated Cu(II) ion, evaluated from EPR spectra at various temperatures, are:
respectively. The low value observed for A33 at 123 and 77 K has been explained by assuming a ground state \({\text{d}}_{{x^{2} - y^{2} }}\) wave function for Cu(II) ions, contaminated with the excited state \({\text{d}}_{{z^{2} }}\). From the temperature dependence of the EPR spectra, the Cu(II) ions can be considered as a static Jahn–Teller system, with contaminated ground state. The admixture coefficients and bonding parameters have also been calculated by combining EPR and optical data. The EPR spectrum of powder sample confirms single crystal data.
Polymer-derived SiCN ceramics, annealed (also referred to as pyrolyzed) at 1000, 1100, and 1285 °C, and doped with Fe(III) acetylacetonate, are investigated by electron paramagnetic resonance (EPR) from 4 to 120 K at X-band (9.425 GHz). In addition, the SiCN ceramic, annealed at 1100 °C, was studied by EPR at 300 K at W-band (93.96 GHz). There was observed a significant increase in EPR linewidth due to dangling bonds (g = 2.001) below 20 K at X-band. The low-field X-band FMR line (g ≈ 12) indicated the presence of ferromagnetic Fe5Si3 crystallites. There were found two EPR lines due to carbon-related dangling bonds: (1) those present as defects on the surface of the free-carbon phase (as sp2 carbon-related dangling bonds with g = 2.0011) and (2) those present within the bulk of carbon phase (as sp3 carbon-related dangling bonds with g = 2.0033). On the other hand, the intense low-field EPR signal observed at X-band was not observed at W-band. As well, there was observed splitting of the single broad EPR signal observed at g = 2.05 at X-band into two signals at W-band at g = 1.99 and g = 2.06, due to two different Fe-containing superparamagnetic nanocrystallites. Two new EPR signals, not observed at X-band, were observed at W-band, namely at g = 2.28 and g = 3.00, which are also due to g∥ of these superparamagnetic nanocrystallites. 相似文献
Based on the Heisenberg model including single-site uniaxial anisotropy and using aGreen’s function technique we studied the influence of size and composition effects on theCurie temperature TC, saturationmagnetization MS and coercivityHC of spherical nanoparticles with astructural formulaMe1?xZnxFe2O4,Me = Ni, Cu, Co, Mn. It is shown that for x = 0.4–0.5and d = 10–20 nm these nanoparticles have aTC = 315 K and are suitable for aself-controlled magnetic hyperthermia. 相似文献
The general class of problems we consider is the following: Let Ω1 be a bounded domain in \({\mathbb{R}^d}\) for d ≥ 2 and let u0 be a velocity field on all of \({\mathbb{R}^d}\) . Suppose that for all R ≥ 1 we have an operator \({\mathcal{T}_R}\) that projects u0 restricted to RΩ1 (Ω1 scaled by R) into a function space on RΩ1 for which the solution to some initial value problem is well-posed with \({\mathcal{T}_{R}u^0}\) as the initial velocity. Can we show that as R → ∞ the solution to the initial value problem on RΩ1 converges to a solution in the whole space? We answer this question when d = 2 for weak solutions to the Navier-Stokes and Euler equations. For the Navier-Stokes equations we assume the lowest regularity of u0 for which one can obtain adequate control on the pressure. For the Euler equations we assume the lowest feasible regularity of u0 for which uniqueness of solutions to the Euler equations is known (thus, we allow “slightly unbounded” vorticity). In both cases, we obtain strong convergence of the velocity and the vorticity as R → ∞ and, for the Euler equations, the flow. Our approach yields, in principle, a bound on the rates of convergence. 相似文献
The dielectric constant of a liquid metal is calculated with the temperature Green's functions technique in the frequency rangeωPΩ?ξ0 andΩξ0, whereξ0 is the resistivity relaxation frequency, andωP the plasma frequency. The electron scattering is described in the Born approximation using the empirical dynamical structure factor ofVan Hove and a screened electron-ion pseudopotential. At low frequencies (?Ω?F=Fermi energy) the result can be identified with Drude's classical formula introducing an effective number of electrons per ion. For?Ω~?F, however, the result differs in form. 相似文献
For a two-dimensional Schrödinger operator HαV = ?Δ ?αV with the radial potential V(x) = F(|x|), F(r) ≥ 0, we study the behavior of the number N?(HαV) of its negative eigenvalues, as the coupling parameter α tends to infinity. We obtain the necessary and sufficient conditions for the semi-classical growth N?(HαV) = O(α) and for the validity of the Weyl asymptotic law. 相似文献
Single-phase solid solutions of Sm2 ? xCexCuO4 + δ (0.05 ≤ x ≤ 0.20) with tetragonal structure are synthesized using acetate combustion followed by sintering at 1373 K for 10 h. X-ray powder diffraction and transmission electron microscopy studies confirmed the formation of solid solution in a single phase. Maximum conductivity (σ = 96.0 ± 0.5 S cm?1 at 973 K) giving composition Sm1.90Ce0.10CuO4 offers the minimum activation energy (Ea = 0.32 ± 0.004 eV) among all prepared compositions. Lowest cathode polarization resistance (Rp = 3.92 ± 0.07 Ω cm2 at 973 K) and activation energy (Ea = 1.12 ± 0.03 eV) values across the measured temperature range are obtained for Sm1.90Ce0.10CuO4. The impedance data fitted well to the Gerischer model indicates that a chemical-electrochemical-chemical-type reaction occurred at the mixed electronic-ionic conducting cathode. 相似文献
In this paper, we study the motion of photons around a Kehagias–Sfetsos (KS) black hole and obtain constraints on IR modified Ho?ava gravity without cosmological constant (~ΛW). An analytic formula for the light deflection angle is obtained. For a propagating photon, the deflection angle δφ increases with large values of the Ho?ava gravity parameter ω. Under the UV limit \({\omega \longrightarrow \infty}\), deflection angle reduces to the result of usual Schwarzschild case, 4GM/R. It is also found that with increasing scale of astronomical observation system the Ho?ava–Lifshitz gravity should satisfy |ωM2| > 1.1725 × 10?16 with 12% precision for Earth system, |ωM2| > 8.27649 × 10?17 with 17% precision for Jupiter system and |ωM2| > 8.27650 × 10?15 with 0.17% precision for solar system. 相似文献
The energy of the Dirac sea of interacting urfermions in a lattice space withZ3 points is calculated using Heisenberg's Hamiltonian and a two-particle approximation which is a variational calculation with the test function ¦?〉=eiη¦D0〉; ¦D0〉 is the Dirac sea without interaction,η=(ψ°ψ) a bilinear expression of the urfermion creation and annihilation operators. The same result is obtained by a BCS-calculation. Beyond that, we derive simple lower and upper bounds for the energy. Excited states are considered consisting of a particle-antiparticle pair with the energyE=2√ω2+M2. The massM and the interaction constantW are connected by the equation (4W)?1=Z?3∑(ω2+M2)?1/2. For usual masses 4W~√Z/1 (1 a nuclear length). Methods are discussed to improve the results. 相似文献
An exact definition of the group velocity vg is proposed for a wave process with arbitrary dispersion relation ω = ω′(k) + iω″(k). For the monochromatic approximation, a limit expression vg(k) is obtained. A condition under which vg(k) takes the form of the Kuzelev–Rukhadze expression [1] dω′(k)/dk is found. In the general case, it appears that vg(k) is defined not only by the dispersion relation ω(k), but also by other elements of the initial problem. As applied to the dissipative medium, it is shown that vg(k) defines the field energy transfer velocity, and this velocity does not exceed thee light speed in vacuum. An expression for the energy transfer velocity is also obtained for the case where the dispersion relation is given in the form k = k′(ω) + ik″(ω) which corresponds to the boundary problem. 相似文献
We link the Boundary Control Theory and the Titchmarsh-Weyl Theory. This provides a natural interpretation of the A?amplitude due to Simon and yields a new efficient method to evaluate the Titchmarsh-Weyl m?function associated with the Schrödinger operator H = ??x2 + q(x) on L2(0, ∞) with Dirichlet boundary condition at x = 0. 相似文献
We calculate the Komar energy E for a noncommutative inspired Schwarzschild black hole. A deformation from the conventional identity E = 2STH is found in the next to leading order computation in the noncommutative parameter θ (i.e. \({\mathcal{O}(\sqrt{\theta}e^{-M^2/\theta})}\)) which is also consistent with the fact that the area law now breaks down. This deformation yields a nonvanishing Komar energy at the extremal point TH = 0 of these black holes. We then work out the Smarr formula, clearly elaborating the differences from the standard result M = 2STH, where the mass (M) of the black hole is identified with the asymptotic limit of the Komar energy. Similar conclusions are also shown to hold for a deSitter–Schwarzschild geometry. 相似文献
In this paper we prove a sufficient condition, in terms of the behavior of a ground state of a symmetric critical operator P1, such that a nonzero subsolution of a symmetric nonnegative operator P0 is a ground state. Particularly, if Pj : = ?Δ + Vj, for j = 0,1, are two nonnegative Schrödinger operators defined on \(\Omega\subseteq \mathbb{R}^d\) such that P1 is critical in Ω with a ground state φ, the function \(\psi\nleq 0\) is a subsolution of the equation P0u = 0 in Ω and satisfies \(\psi_+\leq C\varphi\) in Ω, then P0 is critical in Ω and \(\psi\) is its ground state. In particular, \(\psi\) is (up to a multiplicative constant) the unique positive supersolution of the equation P0u = 0 in Ω. Similar results hold for general symmetric operators, and also on Riemannian manifolds. 相似文献
A polarization operator constructed in the random phase approximation is used to obtain zero-sound excitations in isospin asymmetric nuclear matter (ANM). Two families of the complex solutions ωsτ(k),τ= p,n are presented. The imaginary part of the solutions corresponds to the damping of the collective mode due to its overlapping with the particle-hole modes and the subsequent emission of a proton (ωsp(k)) or a neutron (ωsn(k)). The dependence of the solutions on the asymmetry parameter is studied. 相似文献