Moscow University Physics Bulletin最新文献

This paper studies the three phases of RDX using the first-principles, and calculates electronic properties of RDX. At the same time, the properties of the three phases near the phase transition pressure are calculated. Under normal pressure, the lattice parameters of (alpha)-RDX are in good agreement with the experimental values. The lattice parameters of (gamma)-RDX are in good agreement with the experimental values. The theoretical value of the unit cell volume of (beta)-RDX is smaller than the experimental value, because (beta)-RDX will expand in volume at high temperature. Under normal pressure and pressure of 2.8 GPa, there is no virtual frequency in phonon spectrum of (alpha)-RDX. The appearance of virtual frequency under the pressure of 4 GPa indicates that the structure is unstable under this pressure and phase transition has occurred. Under the action of pressure, the peak values of conduction band and valence band decrease slightly, which is more obvious near the Fermi level, indicating that the electrons around the Fermi level are more sensitive to pressure. According to the calculation of Gibbs free energy, under the pressure of 2.8 GPa, (alpha)-RDX will change into (gamma)-RDX, which is in good agreement with the experimental value. The result is consistent with the previous phonon spectrum calculation. At the same time, under this pressure,when the temperature rises to 467 K, (alpha)-RDX transforms into high-temperature phase (beta)-RDX. Finally, the phase transition temperature of (alpha)-RDX and (beta)-RDX at 2.7 GPa was calculated. And the phase transition temperatures of (gamma)-RDX and (beta)-RDX at 2.9 GPa determine the phase boundary of the three phase of RDX.

In this work, numerical simulations are used to study ambipolar organic field-effect phototransistors, in which a spatially localized photoelectric effect can take place. This effect consists in the fact that there is a small spatially localized photosensitive region in the transistor channel, the position of which can be controlled by changing the gate voltage. The purpose of this work is to analyze the relationship between the form of the field dependence of the bound electron-hole pairs ((e/h) pairs) dissociation probability and characteristics of the studied ambipolar phototransistors such as normalized photocurrent, spatial resolution, and response time. It is shown that the optimal form of the field dependence of (e/h) pairs dissociation probability is stepwise-like form, which can provide a high spatial resolution at high values of the normalized photocurrent without degrading the response time of the phototransistor. This shape can be achieved when the organic semiconductor has an extremely narrow distribution of (e/h) pairs by size, described by the delta function. Also, using the example of several distributions of various shapes, it is shown that a decrease in the width of the distribution leads to an increase in the spatial resolution. Approaches to the selection and modification of organic semiconductor materials that would provide the most pronounced spatially localized photoelectric effect in ambipolar field-effect transistors are discussed.

In the present work, for the first time, a generalized Guggenheim equation for a system of hard spheres has been obtained based on the use of Euler’s accelerated convergence method. This equation allows for the consideration of an arbitrary number of known virial coefficients. For the metastable region, this equation is generalized to account for the asymptotic behaviour of free energy at high densities. The obtained expression for the compressibility of the homogeneous phase of a hard sphere system describes the data of the numerical experiment within the limits of its accuracy.

Using an analytical description of the evolution of harmonic power in free-electron laser (FEL) undulators, the influence of electron beam parameters on the fundamental characteristics of FEL radiation is investigated: gain length, spectrum, and harmonic power. The possibility of suppressing even harmonics in the FEL as a light source for material and surface studies using second harmonic generation (SHG) nonlinear response analysis is explored. The main factors affecting the emission of even harmonics in FELs are identified; the influence of the beam cross-section and the spread of electron energies on their radiation is analyzed. The example of the FEL LEUTL with visible light emission, which is used in the studies of optical properties of materials and the chemical state of molecules on surfaces and at interfaces, is considered. In this context, the possibility of suppressing the second harmonic in FELs is analyzed.

Using methods of X-ray structural analysis, scanning electron microscopy, and Mössbauer spectroscopy, the features of the structure formation in powder systems Fe–Ti, Fe/Ti–diamond and Fe–Ti–C during mechanical alloying under the conditions of the planetary ball mill AGO-2 (energy intensity 7 W/g) were studied. It is shown that titanium and iron with limited mutual solubility under high-energy mechanical impact with a duration of 20 min interact to form an alloy of nanostructured iron and grain boundary phases of the type solid solutions Fe(Ti), Ti(Fe), and FeTi with a total 22–24(%) content. In the composition of Fe-20(%) Ti, titanium reaches an X-ray amorphous state, and at a titanium content above 20 wt (%), the crystalline phase (alpha)-Ti is preserved in the amount of 5–10 wt (%). During mechanical activation of the Fe/Ti–diamond mixture, composite particles are formed with a size in the range of 2–12 (mu)m, with a metal matrix structure with a diamond particle size of 0.3–1.5 (mu)m. It has been established that titanium accelerates the process of grain boundary and bulk interaction of iron with diamond and titanium carbide. In the studied powder compositions, a solid solution based on iron and TiC, Fe({}_{3})C compounds is formed with their total content: Fe/40(%), Ti–diamond up to 62(%); Fe/TiC up to 34(%). Under similar conditions in the diamond–iron mixture, grain boundary phases of the solid solution do not exceed 26(%). The formation of graphite has not been detected by X-ray diffraction.

Hadron therapy (HT) is a technique that uses accelerated ions, notably protons, and carbon ions, to destroy tumors. It has demonstrated high success rates in the treatment of certain cancers resistant to irradiation. In HT, the majority of the dose is delivered to the tumor volume by electromagnetic interactions with atomic electrons. However, it is important to note that the primary particles used in HT can induce nuclear reactions, generating undesirable secondary radiation, certainly neutrons. As a result, a significant portion of the patients’ body may be exposed to the secondary background radiation field. Thus, these unwanted secondary neutrons should be evaluated. The purpose of this research in first is to characterize the secondary neutron production (SNP) during the administration of Hadrons with energies 140 MeV proton, and 264 MeV/u carbon ions (({}^{12})C) in a soft tissue phantom. Second, comparing the neutron spectrum for different angles for protons and carbon ions for carbon targets to experimental data. Our results show that the neutron spectra (thick target neutron yields TTNYs ) at energies less than (thickapprox)20 MeV, using the INCL4.6/GEM models and JQMD/GEM across a wide range would be suitable for the Monte Carlo transport simulation.

An experimental study has been conducted on the effect of wind blowing on a wave induced by a wave generator in a direct channel. It is shown that with a small wave steepness (ak<0.1) and wind speed (W<2.3) m/s, a drift current is generated on the water surface due to the action of viscous forces. A formula for calculating its velocity is proposed. It has been found that the phase velocity of the wave increases with the emergence of drift current and can be calculated by the formula obtained for linear waves in a flow with a constant velocity shear. With an increase in wave steepness (ak>0.19) and wind speed (W>2.3) m/s, the formation of a vortex deforming the water surface over the wave crest was observed in the air flow over the wave crest. The vortex destroys the viscous layer, reducing the drift velocity. This also reduces the phase velocity and the length of the wave. A mechanism explaining this process has been proposed.

The paper presents a method for separating contributions of pair and single top quark production to tWb associated final state using a neural network. The proposed method makes it possible to calculate such processes in a gauge-invariant way, taking into account interference contributions and dividing the phase space into single-resonant and double-resonant regions. The optimized set of observables is used to separate single-resonant and double-resonant contributions to the overall process for neural network training. A usage of the method allows for avoiding the disadvantages that are inherent in the schemes used in collider physics for calculation of the tWb associated top quark production with the removal of Feynman diagrams, which leads to violation of gauge invariance, or the addition of a subtraction scheme, which leads to the appearance of negative weights for the part of simulated events. The proposed method can be used to increase the efficiency of the search for deviations from the predictions of the Standard Model in the interaction of the top quark with the W boson and b-quark.

In the oil and gas industry, there is growing interest in using the PC-SAFT equation of state for predicting the phase behaviour and physical properties of hydrocarbons. This article demonstrates how this equation of state can be used in combination with the direct energy minimisation algorithm of an isochoric-isothermal system for calculating vapour-liquid equilibrium parameters of hydrocarbons. The proposed approach is tested on four substances: methane, ethane, propane, and n-butane.

The boundary value problem for a singularly perturbed system of two second-order ordinary differential equations with different powers of a small parameter at the second derivatives is considered without requiring the right-hand sides to be quasimonotonic. The specific feature of the problem is that one of the two equations of the degenerate system has a double root. It is proven that for sufficiently small values of a small parameter, the problem has a boundary layer type solution. A condition has been obtained that replaces the quasimonotonicity condition and expands the class of problems to which the results of the work are applicable.