关于“滴状冷凝中液滴内外压强差及临界半径”的评注

从力学和热力学角度简要证明了滴状冷凝时壁面球冠形液滴内外压强差不同于冷凝器内部球 形液滴的内外压强差，并指出有关文献对壁面自由能增量的理解存在概念上的混乱。 关键词： 滴状冷凝 压差 自由能     

On the choice of initial approximation in the problem of parameter identification of direct-gap semiconductors by cathodoluminescence microscopy

The problem of the choice of initial approximation has been considered to identify the parameters of direct-gap semiconductors by cathodoluminescence microscopy using the dependence of monochromatic cathodoluminescence intensity on electron beam energy for the case of a low level of signal excitation. It has been shown that the realization of the confluent analysis method can lead to the problem of multidimensional numerical minimization of a quadratic functional, the solution of which depends significantly on the choice of initial approximation. On this basis, some conditions of correct processing of the experimental data have been determined to identify the required parameters for gallium arsenide.     

Exchange pressure and the Wigner-Seitz approximation

Working formulas are derived for numerically calculating the exchange part of the pressure in a metal in the spherical Wigner-Seitz cell approximation. The derivation is based on an equation obtained by Dmitriev in the Hartree-Fock approximation. An ARRIEP research report, 1964. Prepared for printing by M.F. Sarry.     

On the condensation of electron-hole droplets

The phase diagram at low temperature (T ? 1 K) of an electron-hole system, is drastically modified by life time effects: the system is made of multiexcitonic clusters of different sizes, the size distribution function having only one peak instead of two.     

On the effective mass approximation

A one dimensional model for impurities in crystals is solved exactly. The results are compared with the effective mass theory. It turns out that this approximation is applicable even to deep states. For a more detailed calculation of these corrections are suggested. The theory is applied to impurities in Germanium and Silicon.     

On generalized condensation in the free boson gas

We investigate the free boson gas with Dirichlet boundary conditions in d-dimensional Euclidean space. For d > 2 we find three types of condensation when the mean density ρ exceeds a critical value ρ_c, depending on how the bulk limit is taken.     

On pion condensation in finite nuclei

The critical pionic state leading to pion condensation is investigated for finite nuclear systems. The threshold density for light nuclei, including⁴He, is found to be close to that of nuclear matter. For¹⁶O and⁴⁰Ca, the angular momenta of the most critical states areL=0 andL=2.     

On localized tachyon condensation in and

We study some aspects of localized tachyon condensation on non-supersymmetric orbifolds of the form C²/Z_n and C³/Z_n. We discuss the gauged linear sigma models for these orbifolds. We show how several features of the decay of orbifolds of C³ can be realised in terms of orbifolds of C².     

On the approximation of invariant measures

Given a discrete dynamical system defined by the map :X X, the density of the absolutely continuous (a.c.) invariant measure (if it exists) is the fixed point of the Frobenius-Perron operator defined on L¹(X). Ulam proposed a numerical method for approximating such densities based on the computation of a fixed point of a matrix approximation of the operator. T. Y. Li proved the convergence of the scheme for expanding maps of the interval. G. Keller and M. Blank extended this result to piecewise expanding maps of the cube in ⁿ. We show convergence of a variation of Ulam's scheme for maps of the cube for which the Frobenius-Perron operator is quasicompact. We also give sufficient conditions on for the existence of a unique fixed point of the matrix approximation, and if the fixed point of the operator is a function of bounded variation, we estimate the convergence rate.     

On Bose-Einstein condensation in any dimension

A general property of an ideal Bose gas as temperature tends to zero and when conditions of degeneracy are satisfied is to have an arbitrarily large population in the groud state (or in its neighborhood); thus, condensation occurs in any dimension D but for D ≤ 2 there is no critical temperature. Some astrophysical consequences, as well as the temperature-dependent mass case, are discussed.     

On condensation of extended structures

Solitons and vortices may condense if the coupling is of order one.     

On the unitarization of the Born approximation

A new approximation for the elastic scattering transition matrix is suggested. This approximation satisfies the unitarity condition. A modified Born series is introduced which has this unitarized Born approximation as the leading term. The series is applied to the solvable case of scattering by a separable potential and is found to converge in a wider region of energies than that of the conventional Born series.     

On the Bose-Einstein condensation of an ideal gas

A mathematically precise treatment is given of the well-known Bose-Einstein condensation of an ideal gas in the grand canonical ensemble at fixed density. The method works equally well for any of the standard boundary conditions and it is shown that the finite volume activity converges and that in three dimensions condensation occurs for Dirichlet, Neumann, periodic, and repulsive walls.     

On the variable-charge Coulomb-projected Born approximation

Total cross-sections for electron impact excitation of 1¹ S – 2³ S transition in helium have been calculated using variable-charge Coulomb-projected Born approximation and also using a distorted wave model in which the prior form of theT-matrix is used. The comparison of the two sets of results enables us to make certain observations about the suitability of the variable-charge Coulomb-projected Born approximation.     

On the Fermi approximation in slow neutron scattering

In this paper a general connection between the scattering from a bound and a free nucleus is derived in terms of formal scattering theory. The basic idea is to eliminate the interaction Hamiltonian between neutron and nucleus. Then theT-operator for a bound nucleus can be expressed by that of the free nucleus and its binding potential. From this equation an expansion is given as a power series in the binding potential for the nucleus. For slow neutron scattering the first term of the series leads to Fermi's approximation. The second term is the first correction to Fermi's approximation which contains no divergences for point scatterers contrarily to theories of other authors. In particular the correction to Fermi's approximation of the scattering amplitude is calculated for an elastically bound proton in the limit of zero-energy neutron.     

Extended-ion approximation and pressure shifts inF-band energies

Pressure variation of maximumF-band absorption energies in the halides of lithium, sodium and potassium has been investigated employing the extended-ion approximation for the calculation of theF-electron energy eigenvalues and using values of local compressibility in the neighbourhood of theF-centres which include the effect of vacancy and pressure. The results obtained agree with the experimental results.     

On the eikonal approximation in the theory of transition radiation

The transition radiation of relativistic electrons in nonuniform media is considered. Based on the equivalent photon method and the eikonal approximation in wave mechanics, a method for describing this process is proposed. For the case in which the permittivity depends on several coordinates, equations for the spectral-angular density of transition radiation are obtained. The main results obtained in the Born and eikonal approximations of the theory of transition radiation are compared. The equations obtained are used to analyze the transition radiation process for a fiberlike target.     

On the validity of the narrow band approximation

The accuracy of the narrow band approximation is estimated. It is shown that, in order to assess the accuracy of the approximation, not only the form of the source function but also the form of the integrand is required. The accuracy is improved when the integrand is symmetric.     

On the post-Newtonian approximation of the Einstein-Cartan-Sciama-Kibble theory

The post-Newtonian approximation of the Einstein-Cartan-Sciama-Kibble or ECSK theory is developed. It is used to obtain a drastic reduction on the density of the source needed to detect the spin. It is also proved that if we know the structure of the source, up to order ¯v, the spin can be detected, and if we know it up to order ¯v² the theory can be verified.Supported by a scholarship from the Consejo Nacional de Investigaciones Cientificas y Tecnicas (CONICET).