Cylindrically symmetric distributions of matter taking into account pressure

A cylindrically symmetric distribution of matter under pressure which evolves with time is considered. A new class of non-steady-state solutions to the Einstein equations with cylindrical symmetry is found (for cases when the matter is under zero, constant, and time-dependent pressure). A homogeneous, anisotropic universe and an analog of the Schwarzschild solution are considered as particular cases.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 12, pp. 33–36, December, 1985.     

Optimization of pulse-width of passively Q-switched lasers by taking into account intracavity laser spatial distribution

The intracavity photon density and the initial population-inversion density in the diode-pumped passively Q-switched lasers are assumed to be Gaussian spatial distributions. The space-dependent rate equations are solved numerically. The key parameters of a passively Q-switched laser with the shortest pulse-width under Gaussian approximation are determined, and a group of general curves are generated for the first time. The curves clearly show the dependence of the optimal key parameters on the parameters of the gain medium, the saturable absorber, and the resonator. In addition, the importance including the space variation is also shown. The optimal calculations for a diode-pumped passively Nd:YVO₄ laser are presented to demonstrate the use of the curves and the related formulas.     

Optimization of peak power of passively Q-switched lasers by taking into account intracavity laser spatial distribution

The intracavity photon density and the initial population-inversion density in the diode-pumped passively Q-switched lasers are assumed to be Gaussian spatial distributions. The space-dependent rate equations are solved numerically. The key parameters of an optimally coupled passively Q-switched laser under Gaussian approximation are determined, and a group of general curves are generated for the first time. These key parameters include the optimal normalized coupling parameter and the optimal normalized saturable absorber parameter that maximize the peak power, and the corresponding normalized energy, normalized peak power, and normalized pulse width. The curves clearly show the dependence of the optimal key parameters on the parameters of the gain medium, the saturable absorber, and the resonator. In addition, the importance including the space variation is also shown. The optimal calculations for a diode-pumped passively Nd:YVO₄ laser are presented to demonstrate the use of the curves and the related formulas.     

Leontovich-Levin equation taking into account finite conductivity of a conductor

A generalization of the Leontovich-Levin equation for current in an ideally conducting linear vibrator to the case of a finite-conductivity conductor is considered. This generalization is valid for strong and weak skin effects, as well as for inhomogeneous conductors with an axisymmetric conductivity distribution (in particular, for carbon nanotubes, CNTs). The internal structure of the conductor is fully described by the internal impedance per unit length. A recurrent scheme is proposed for calculating such an impedance for layer-inhomogeneous conductors. A particular case of the impedance for metallic achiral CNTs is considered, and substantial differences between this case and the macroscopic model of a conductor with full skin effect are indicated.     

Modelling the length distribution of etched tracks taking into account fragmentation due to partial annealing

Fission track length measurements on apatite minerals are of great interest in thermo-chronology studies. RBS analyses on Durango apatites irradiated by Krypton ions have previously shown the progressive fragmentation of tracks by annealing. This study made for different irradiation energies corresponding to those of uranium fission fragments has been completed by TEM and AFM on etched tracks. In all cases, segmentation figures have been observed, that clearly necessitates to introduce fragmentation of latent tracks to model the length distribution of uranium etched fission tracks. This presentation concerns the case of a homogeneous population of tracks with partial amorphization. The next step will consist in considering multiple sub-populations with different segmentation rates. This algorithm is a new aspect to be included in our model, which already takes into account diffusion and crystallography in the track etching process.     

An improvement of the Peierls equation by taking into account the lattice effects

An improvement of the Peierls equation has been made by including the lattice effects. By using the non-trivially gluing mechanism for the simple cubic lattice, in which atoms interact with its first and second nearest neighbours through a central force, the dislocation equation has been derived rigorously for the isotropic case. In the slowly varying approximation, the Peierls equation with the improvement by including the lattice effects has been obtained explicitly. The new equation can be used to substitute for the old one in theoretical investigations of dislocations. The major change of the predicted dislocation structure is in the core region. The width of the dislocation given by using the new equation is about three times that given by the classical Peierls--Nabarro theory for the simple cubic lattice.     

Angular distribution of Cherenkov radiation from relativistic heavy ions taking into account deceleration in the radiator

Numerical methods are used to study the dependence of the structure and the width of the angular distribution of Vavilov-Cherenkov radiation with a fixed wavelength in the vicinity of the Cherenkov cone on the radiator parameters (thickness and refractive index), as well as on the parameters of the relativistic heavy ion beam (charge and initial energy). The deceleration of relativistic heavy ions in the radiator, which decreases the velocity of ions, modifies the condition of structural interference of the waves emitted from various segments of the trajectory; as a result, a complex distribution of Vavilov-Cherenkov radiation appears. The main quantity is the stopping power of a thin layer of the radiator (average loss of the ion energy), which is calculated by the Bethe-Bloch formula and using the SRIM code package. A simple formula is obtained to estimate the angular distribution width of Cherenkov radiation (with a fixed wavelength) from relativistic heavy ions taking into account the deceleration in the radiator. The measurement of this width can provide direct information on the charge of the ion that passes through the radiator, which extends the potentialities of Cherenkov detectors. The isotopic effect (dependence of the angular distribution of Vavilov-Cherenkov radiation on the ion mass) is also considered.     

Conditions for self-excitation of a gyrotron taking space charge into account

Institute of Applied Physics, Academy of Sciences of the USSR. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 32, No. 11, pp. 1408–1416, November, 1989.     

IR signature estimation of an object or a target by taking into account atmospheric effects

In this study, a reference infrared (IR) image of an object or a target was analyzed, and the IR signature was calculated. Background and atmospheric effects were decomposed so that the calculation errors were minimized. Depending on the reference IR image, the IR signature at any distance and any angle was estimated while considering atmospheric effects. Calculated results were obtained from IR images taken from the same distance and angle, and were compared with the estimated results. The comparison of the measured and calculated signatures demonstrated the accuracy of the proposed method of estimation.     

Current-voltage characteristic of a narrow-band semiconductor taking into account ionization of impurities

The current-voltage characteristic of a material with a narrow conduction band in a strong electric field is studied taking into account ionization of deeply lying impurities in the model, in which collisions of charge carriers are described in the Fokker-Planck approximation. The results are compared with analogous results obtained in the v approximation. It is shown that the results obtained earlier in the v approximation coincide with our results to within ∼ 5%. It is noted that the Fokker-Planck model additionally provides the temperature dependence of the current-voltage characteristic.     

Second-harmonic generation taking into account dispersion of nonlinear susceptibility

Second-harmonic generation in the field of an ultrashort pulse and the propagation of extremely short pulses in a medium with quadratic nonlinearity are analyzed. Second-harmonic generation is analyzed taking into account the effect of second-and third-order group velocity dispersion and dispersion of nonlinear susceptibility up to the second order. Corrections, whose order of smallness is determined by the parameter (ω_L t _p)^?1, where t _p is the pulse duration and ω_L is the carrier frequency of the pump wave, are obtained. For a large phase mismatch, two new solutions are found that describe the stationary evolution of solitary pump and second-harmonic waves in the regions of both anomalous and normal group velocity dispersions.     

Solution of polarization eigenvalue problems taking depolarization into account

The shape of the transmission band of an active interferometer, a resonator with amplification and absorption cells excited by an external signal, is studied. Upon tuning the external signal frequency, the narrow saturated absorption resonances can be observed in the transmission band of the interferometer. It is shown that, by varying the gain, the resonance absorption amplitude can be compensated for one order of smallness in pressure. The effect of amplitude and frequency noises of the external signal on the results obtained is studied.     

Probabilistic distribution and noise factor of solid state photomultiplier signals,taking into account cross-talk processes

Solid-state photomultipliers (SSPMs) are a new type of photodetectors based on avalanche breakdown of the semiconductor in the Geiger mode, limited by negative feedback. Under such conditions, the avalanche breakdown is characterized by high multiplication factors, 10⁴–10⁶, and low noise, which allows detection of single photons. However, in practice, each primary breakdown in the SSPM can be accompanied by secondary breakdowns due to cross-talk processes which change the probabilistic distribution of the signal and introduce excess noise. In this paper, the effect of cross-talk on signal and noise characteristics of SSPMs is considered based on the generalized Poisson distribution.     

Electromagnetic solitons in a system of quantum dots taking into account the Hubbard interaction

We consider the Maxwell equations for an electromagnetic field propagating in a solid with a three-dimensional superlattice of quantum dots linked by strong tunneling along one axis, where electrons with different spin projections are affected by the strong Coulomb repulsion at a single site. We obtain a phenomenological equation in the form of the classical 1+1-dimensional sine-Gordon equation. Electrons are considered within the framework of quantum formalism taking into account the changes in the dispersion law provided by the presence of Coulomb interactions. The phenomenological equation is solved numerically, and the influence of Coulomb repulsion and the degree of band population on the propagation of ultra-short optical pulses is analyzed.     

Equilibrium of a pending drop taking into account the flexural rigidity of the intermediate layer

A model of the equilibrium state of a drop pending from the horizontal plane is considered. We take into account the work necessary for the formation of the intermediate layer between the liquid and gas phases and its elastic properties. The theorem of existence of the equilibrium surface of the drop is proven using the variational principle taking into account the flexibility of the intermediate layer.     

Characteristics of the heating dynamics of a graphite conductor taking into account the skin effect

Calculations for a one-dimensional model of RF heating of a cylindrical graphite conductor have been carried out. The heating dynamics are analyzed in the general form. Conductor temperature profiles and the times for heating up to the graphite sublimation temperature as a function of current and frequency have been obtained. A model of conductor heating with partial return of the energy irradiated by the conductor surface has been considered. Frequency and current ranges have been determined to carry out this graphite sublimation method in a chamber with reflecting walls. The problem is associated with carbon vapor production and subsequent synthesis of fullerenes and other carbon structures.     

Gradient-norm-based histogram equalization taking account of HSV color space distribution

In the present paper, we propose an image contrast enhancement method that can enhance the contrast of a color image naturally by taking account of a color space shape. The proposed method realizes the natural enhancement based on two kinds of intensity histograms: a gradient-norm-based histogram and an ideal histogram derived from the shape of a color space. The former histogram is used to suppress over-enhancement in the flat regions of an image and the latter histogram is used to prevent the whole image from being darken. Concretely, the aforementioned intensity histograms are appropriately mixed into a histogram with a weight based on the average intensity of the input image. The contrast enhancement of the input image is realized using the cumulative histogram of the mixed histogram as an intensity transform function. To verify the validity of the proposed method, in experiments, the proposed method is applied to a variety of images and experimental results are evaluated qualitatively and quantitatively.