The Radiation Transfer at a Layer of Magnetized Plasma With Random Irregularities

The problem of radio wave reflection from an optically thick plane monotonous layer of magnetized plasma is considered at present work. The plasma electron density irregularities are described by spatial spectrum of an arbitrary form. The small-angle scattering approximation in the invariant ray coordinates is suggested for analytical investigation of the radiation transfer equation. The approximated solution describing spatial-and-angular distribution of radiation reflected from a plasma layer has been obtained. The obtained solution has been investigated numerically for the case of the ionospheric radio wave propagation. Two effects are the consequence of multiple scattering: change of the reflected signal intensity and anomalous refraction.Comment: 22 pages, 4 figure

How exactly did the Universe become neutral?

We present a refined treatment of H, He I, and He II recombination in the early Universe. The difference from previous calculations is that we use multi-level atoms and evolve the population of each level with redshift by including all bound-bound and bound-free transitions. In this framework we follow several hundred atomic energy levels for H, He I, and He II combined. The main improvements of this method over previous recombination calculations are: (1) allowing excited atomic level populations to depart from an equilibrium distribution; (2) replacing the total recombination coefficient with recombination to and photoionization from each level directly at each redshift step; and (3) correct treatment of the He I atom, including the triplet and singlet states. We find that the ionization fraction x_e = n_e/n_H is approximately 10% smaller at redshifts <~800 than in previous calculations, due to the non-equilibrium of the excited states of H, which is caused by the strong but cool radiation field at those redshifts. In addition we find that He I recombination is delayed compared with previous calculations, and occurs only just before H recombination. These changes in turn can affect the predicted power spectrum of microwave anisotropies at the few percent level. Other improvements such as including molecular and ionic species of H, including complete heating and cooling terms for the evolution of the matter temperature, including collisional rates, and including feedback of the secondary spectral distortions on the radiation field, produce negligible change to x_e. The lower x_e at low z found in this work affects the abundances of H molecular and ionic species by 10-25%. However this difference is probably not larger than other uncertainties in the reaction rates.Comment: 24 pages, including 18 figures, using emulateapj.sty, to appear in ApJ, the code recfast can be obtained at http://www.astro.ubc.ca/people/scott/recfast.html (in FORTRAN) and http://cfa-www.harvard.edu/~sasselov/rec/ (in C

Non-linear metric perturbations and production of primordial black holes

We consider the simple inflationary model with peculiarity in the form of "plateau" in the inflaton potential. We use the formalism of coarse-grained field to describe the production of metric perturbations $h$ of an arbitrary amplitude and obtain non-Gaussian probability function for such metric perturbations. We associate the spatial regions having large perturbations $h\sim 1$ with the regions going to primordial black holes after inflation. We show that in our model the non-linear effects can lead to overproduction of the primordial black holes.Comment: 13 pages, 2 Postscript figures, submitted to Phys. Rev.

Models and Methods for Three External Ballistics Inverse Problems

We consider three problems of selecting optimal gun barrel direction (or those of selecting optimal semi-axis position) when ring an unguided artillery projectile on the assumption that the gun barrel semi-axis can move in a connected nonconvex cone having a non-smooth lateral surface and modelling visibility zone restrictions. In the rst problem, the target is in the true horizon plane of the gun, the second and the third problems deal with some region of 3D space. A distinctive feature of the models is that the objective functions areε-Lipschitz ones. We have constructed a unied numerical method to solve these problems based on the algorithm of projecting a point ontoε-Lipschitz level function set. A computer programme has been based on it. À series of numerical experiments on each problem has been carried out.Рассматриваются три математические модели задачи выбора оптимального направления ствола орудия при стрельбе неуправляемым снарядом в предположении, что полуось ствола может перемещаться в связном невыпуклом конусе, имеющем негладкую боковую поверхность и моделирующем ограничения на зону видимости. В первой задаче цель расположена в плоскости истинного горизонта орудия, во второй и третьей - в некоторой области пространства. Отличительной особенностью моделей является epsilon-липшицевость целевых функций. Построен единый численный метод решения поставленных задач, базирующийся на одном алгоритме проектирования точки на множество уровня epsilon-липшицевой функции. На его основе составлена программа для ЭВМ. По каждой из задач проведена серия вычислительных экспериментов