Matter-positronium interaction: An exact diagonalization study of the He atom - positronium system

The many-body system comprising a He nucleus, three electrons, and a positron has been studied using the exact diagonalization technique. The purpose has been to clarify to which extent the system can be considered as a distinguishable positronium (Ps) atom interacting with a He atom and, thereby, to pave the way to a practical atomistic modeling of Ps states and annihilation in matter. The maximum value of the distance between the positron and the nucleus is constrained and the Ps atom at different distances from the nucleus is identified from the electron and positron densities, as well as from the electron-positron distance and center-of-mass distributions. The polarization of the Ps atom increases as its distance from the nucleus decreases. A depletion of the He electron density, particularly large at low density values, has been observed. The ortho-Ps pick-off annihilation rate calculated as the overlap of the positron and the free He electron densities has to be corrected for the observed depletion, specially at large pores/voids.Comment: 18 pages, 8 figure

Langmuir wave linear evolution in inhomogeneous nonstationary anisotropic plasma

Equations describing the linear evolution of a non-dissipative Langmuir wave in inhomogeneous nonstationary anisotropic plasma without magnetic field are derived in the geometrical optics approximation. A continuity equation is obtained for the wave action density, and the conditions for the action conservation are formulated. In homogeneous plasma, the wave field E universally scales with the electron density N as E ~ N^{3/4}, whereas the wavevector evolution varies depending on the wave geometry

Влияние физической обработки на физико-химические и биологические свойства воды и водных растворов

Objectives. Changes to the properties of water caused by factors such as pressure or temperature, can only be explained by its structural changes. Scientists study changes to the properties of water due to various physical stimuli only without the addition of any substances. Examples of stimuli are acoustic exposure, thermal exposure, pressure variation, shaking, intensive vibration treatment followed by dilutions, vortexing, bubble generation, inter alia.The aim of the present review article is to summarize the available data on how the above processes affect the physicochemical and biological properties of water and aqueous solutions.Results. It has been shown that heating makes water less compressible and decreases air solubility in water, while cooling enhances its viscosity. Acoustic exposure makes the structure of water become coarse-grained, followed by an increase the number of large clusters, pH and temperature inside a cavitation bubble. High pressure enhances the viscosity, self-diffusion, and compressibility of water. For bubble processed water, there are changes in the spin-spin and spin-lattice relaxation times. Reactive oxygen species are formed, as well as increased solubility of gases in liquids and reduced friction. Vortex process technology causes an increase of electrical conductivity of water and reduced viscosity. Intensive vibration treatment and dilution processes result in changes in electrical conductivity of water, dissolved gas concentration, ultrasonic wave velocity, рН, surface tension, dielectric constant, and spectral response. There is also data to support the biological effects of different types of physical treatment of solutions.Conclusions. This review shows that physical treatment of water can induce changes both in physicochemical and biological properties of water and aqueous solutions.Цели. Изменения свойств воды, вызванные различными факторами, такими как давление или температура, могут объясняться только структурными изменениями воды. Ученые исследуют изменения свойств воды, происходящие исключительно из-за различных физических раздражителей и без добавления каких-либо веществ. Примерами таких раздражителей являются акустическое и тепловое воздействие, изменение давления, встряхивание, интенсивная вибрационная обработка с последующим разведением, вихревое перемешивание, образование пузырьков и т.д.Целью данного обзора является обобщение имеющихся данных о том, как вышеуказанные процессы влияют на физико-химические и биологические свойства воды и водных растворов.Результаты. Показано, что нагрев делает воду менее сжимаемой и снижает растворимость воздуха в воде, а охлаждение повышает ее вязкость. Акустическое воздействие приводит к тому, что структура воды становится крупнозернистой, что сопровождается увеличением количества крупных кластеров, рН и температуры внутри кавитационного пузыря. Высокое давление способствует увеличению таких физических свойств воды, как вязкость, самодиффузия и сжимаемость. Для воды, обработанной пузырьками, происходят изменения времен спин-спиновой и спин-решеточной релаксации, образуются активные формы кислорода, а также наблюдается повышенная растворимость газов в жидкостях наряду со снижением вязкости. Вихревой технологический процесс приводит к увеличению электропроводности воды и снижению вязкости. Интенсивная вибрационная обработка и процессы разбавления приводят к изменению некоторых характеристик воды, таких как электропроводность, концентрация растворенного газа, скорость ультразвуковой волны, рН, поверхностное натяжение, диэлектрическая проницаемость и спектральный отклик. В работе также представлены данные, подтверждающие биологические эффекты различных типов упомянутой физической обработки растворов.Выводы. Данный обзор показывает, что физическая обработка воды может вызывать изменения как физико-химических, так и биологических свойств воды и водных растворов

Macro- and micro-strain in GaN nanowires on Si(111)

We analyze the strain state of GaN nanowire ensembles by x-ray diffraction. The nanowires are grown by molecular beam epitaxy on a Si(111) substrate in a self-organized manner. On a macroscopic scale, the nanowires are found to be free of strain. However, coalescence of the nanowires results in micro-strain with a magnitude from +-0.015% to +-0.03%.This micro-strain contributes to the linewidth observed in low-temperature photoluminescence spectra

Logarithmic perturbation theory for radial Klein-Gordon equation with screened Coulomb potentials via ℏ\hbar expansions

The explicit semiclassical treatment of logarithmic perturbation theory for the bound-state problem within the framework of the radial Klein-Gordon equation with attractive real-analytic screened Coulomb potentials, contained time-component of a Lorentz four-vector and a Lorentz-scalar term, is developed. Based upon $\hbar$-expansions and suitable quantization conditions a new procedure for deriving perturbation expansions is offered. Avoiding disadvantages of the standard approach, new handy recursion formulae with the same simple form both for ground and excited states have been obtained. As an example, the perturbation expansions for the energy eigenvalues for the Hulth\'en potential containing the vector part as well as the scalar component are considered.Comment: 14 pages, to be submitted to Journal of Physics

Foam Metals High-Temperature Electrical Characteristics’ Investigation

In the work presented we have carried out experimental investigations of high- temperature electrophysical properties of foam metals. We have obtained data of foam nickel and foam copper resistivity and temperature coefficients of resistance (TCR) versus their plane deformation degree within the temperature range from 100 to 950 ºС

Structure and hardness of B2 ordered refractory AlNbTiVZr0.5 high entropy alloy after high-pressure torsion

High-pressure torsion (HPT) at room temperature was applied to an AlNbTiVZr0.5 refractory high entropy alloy. In the initial as-cast condition the alloy was composed of a coarse-grained B2 matrix phase and a continuous network of C14 Laves phase particles with the volume fraction of 19%. HPT resulted in the formation of a nanocrystalline structure in the B2 matrix with an average size of grains/subgrains of 25 nm after 5 revolution

The "Horizon-T" Experiment: Extensive Air Showers Detection

Horizon-T is an innovative detector system constructed to study Extensive Air Showers (EAS) in the energy range above 10^16 eV coming from a wide range of zenith angles (0 - 85 degrees). The system is located at Tien Shan high-altitude Science Station of Lebedev Physical Institute of the Russian Academy of Sciences at approximately 3340 meters above the sea level. It consists of eight charged particle detection points separated by the distance up to one kilometer as well as optical detector subsystem to view the Vavilov-Cerenkov light from the EAS. The time resolution of charged particles and Vavilov-Cerenkov light photons passage of the detector system is a few ns. This level of resolution allows conducting research of atmospheric development of individual EAS.Comment: Initial technical note for Horizon-T experiment, updated with recent detector upgrades, 11/2016. Updated 12/2017 with minor edits. Large upgrade will be in another articl