On the null geodesics from the viewpoint of space-time singularities

We examined the complete form of the propagation equation of the expansion for null geodesies and we found some restrictions in integral form on the Ricci and Weyl tensors near a singularity.     

Reciprocal transformations of the space-time shifted nonlocal short pulse equations

Reciprocal transformations of the space-time shifted nonlocal short pulse equations are elaborated. Covariance of dependent and independent variables involved in the reciprocal transformations is investigated. Exact solutions of the space-time shifted nonlocal short pulse equations are given in terms of double Wronskians. Realness of independent variables involved in the reciprocal transformations is verified. Dynamics of some obtained solutions are illustrated.     

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.     

Electrophonon resonance in narrow band semiconductors

The theory of the electric current splashes on a current-voltage characteristic due to the phonon-induced-electron-transitions between Stark ladder levels is developed. Splitting and broadening of the current peaks because of an electric field vector deviation from the [ 111 ] direction is considered. The recent experimental results on current-voltage characteristic of the tellurium cluster superlattice in ceolite are accounted for by the electrophonon resonance studied in the present paper.     

Breakdown of the narrow width approximation for new physics

The narrow-width approximation is used in high-energy physics to reduce the complexity of scattering calculations. It is a fortunate accident that it works so well for the standard model, but in general it will fail in the context of new physics. We find numerous examples of significant corrections when the calculation is performed fully off shell including a finite width, notably from effects from the decay matrix elements, not just phase space. If not taken into account, attempts to reconstruct the Lagrangian of a new physics discovery from data would result in considerable inaccuracies and likely inconsistencies.     

Depth resolution and narrow nuclear resonance profiling

The basic stochastic theory of narrow nuclear resonance profiling is presented. We show that nm depth resolution is achievable in some cases. It is shown that the usual notions of depth resolution such as the full width at half maximum of the instrument function, adequate for instrument functions which vary only slowly over the depth range corresponding to the depth resolution, are unsatisfactory for narrow resonance profiling in the near surface region. Here, the system response to a delta function concentration profile varies very rapidly. However, the shape of the excitation curve is very sensitive to certain kinds of small changes in the concentration profile in the surface region. We discuss some first efforts to define a more general concept for depth resolution, consistent with the usually used definitions, intended to adequately express the perceived sensitivity of a measured excitation curve to variations in the underlying concentration profile.     

A nonuniform narrow band correlated-k approximation using the k-moment method

Narrow band k-moment (NBKM) formulations of the transmission function for nonuniform gaseous paths are developed. One of them, called the scaled variance (SV) approximation, is based on the assumption of correlated absorption coefficients. Theoretical derivations are properly detailed and several test cases taken from the literature are provided to assess the approximate modeling results against LBL reference calculations. In most cases representative of combustion configurations, it is shown that the scaled variance approximation is more accurate than the Curtis–Godson one for CO₂ but not for H₂O.     

A monopole-dipole resonance absorber in a narrow waveguide

A sound absorber in a narrow waveguide is considered. The absorber consists of one monopole and one dipole resonator placed in a narrow pipe. The optimum parameters of the resonators that provide for the maximum absorption of acoustic power are determined. Results of an experimental study of a two-resonator absorbing system are presented. A 95% absorption is achieved.     

Calculation of a narrow resonance with the LIT method

The possibility to resolve narrow structures in reaction cross sections in calculations with the Lorentz integral-transform (LIT) method is studied. To this end we consider a fictitious two-nucleon problem with a low-lying and narrow resonance in the ³ P ₁ nucleon-nucleon partial wave and calculate the corresponding “deuteron photoabsorption cross section”. In the LIT method the use of continuum wave functions is avoided and one works instead with a localized function $\widetilde{\Psi}$ . In this case study it is investigated how far into the asymptotic region $\widetilde{\Psi}$ has to be determined in order to obtain a precise resolution of the artificially introduced E1 resonance. Comparing with the results of a conventional calculation with explicit neutron-proton continuum wave functions it is shown that the LIT approach leads to an excellent reproduction of the cross section in the resonance region and of further finer cross-section details at higher energies. To this end, however, for $\widetilde{\Psi}$ one has to take into account two-nucleon distances up to at least 30?fm.     

Invariants,singularities, and source parameters of an electrovacuum generalization of a kerr space-time

The properties of the basis of Narlikar-Karmarkar invariants of a Newman-Couch-Chinnapared-Ikston-Prakash-Torrance space-time are analyzed. Their relationship with the singularities of the gravitational field potentials and the parameters of the source of this field is also analyzed.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 97–99, October, 1988.     

Dipole resonance muffler at the exit of a narrow pipe

Locking of sound by a dipole resonator installed at the exit of a narrow pipe is studied theoretically and experimentally. The efficiencies of locking by dipole and monopole resonators are compared, and the dipole resonator is found to be more efficient than the monopole one.     

Atom-dimer and dimer-dimer scattering in fermionic mixtures near a narrow Feshbach resonance

We develop a diagrammatic approach for solving few-body problems in heteronuclear fermionic mixtures near a narrow interspecies Feshbach resonance. We calculate s-, p-, and d-wave phaseshifts for the scattering of an atom by a weakly-bound dimer. The fermionic statistics of atoms and the composite nature of the dimer lead to a strong angular momentum dependence of the atom-dimer interaction, which manifests itself in a peculiar interference of the scattered s- and p-waves. This effect strengthens with the mass ratio and is remarkably pronounced in ⁴⁰K-(⁴⁰K-⁶Li) atom-dimer collisions. We calculate the scattering length for two dimers formed near a narrow interspecies resonance. Finally, we discuss the collisional relaxation of the dimers to deeply bound states and evaluate the corresponding rate constant as a function of the detuning and collision energy.     

一级近似下的双模激光随机共振

将周期信号输入双模激光,对激光光强方程中的乘法噪声项取一级近似,用线性化近似方法计算相关函数和功率谱,结果发现:信噪比随抽运噪声强度、量子噪声强度及信号频率的变化均出现随机共振.     

The approximation of confluence by resonance in inhomogeneous plasmas

The degree to which a Budden-type equation describes the behaviour of the long wavelength branches of the modes of a higher order differential equation such as governs confluence in a plasma at ion-ion and upper hybrid resonance frequencies and at cyclotron harmonics is examined.