Issue 2, 2019

I. M. Belyaev$^1$, V. Yu. Egorychev$^1$, V. I. Matiunin$^1$, D. V. Savrina$^{1,2}$

The results of search for new decays of beauty baryons in the LHCb experiment are presented. In particular the new decays \mbox{$\Lambda_b^0\to\psi(2S)p\pi^-,$} \mbox{$\Lambda_b^0\to\Lambda_c^+p\overline{p}\pi^-,$} \mbox{$\Lambda_b^0\to pK^-\pi^+\pi^-,$} \mbox{$\Lambda_b^0\to pK^-K^+K^-,$} \mbox{$\Xi_b^0\to pK^-\pi^+\pi^-,$} \mbox{$\Xi_b^0\to pK^-\pi^+K^-$} are observed and ratios of branching fractions are measured. The results are based on the proton-proton collisions data collected by the LHCb experiment at the Large Hadron Collider.

S. S. Belyshev$^1$, B. S. Ishkhanov$^{1,2}$, D. E. Lanskoy$^1$, T. Yu. Tretyakova$^2$

A review of theoretical studies of the spectrum of the $^{44}$Ti nucleus is given. In this example, we demonstrate the diversity of nuclear degrees of freedom in complex nuclei and coexistence of excitations of different nature. The main attention is paid to the cluster model $^{40}$Ca$ + \alpha$ and the shell model. In the latter case, we present the results of our calculations and the detailed analysis of the role of nucleon pairing. Similarities and differences in the spectra obtained in these approaches are considered. Rotational states and states of the molecular type are also briefly discussed. It is shown that many properties of the spectrum can be reaonably described in various models, which, therefore, are not completely independent and express in some cases the same physical phenomena.

A. V. Gusev$^1$, V. N. Rudenko$^{1,2}$

The problem of optimal combining component of gravitational laser antennas is considered to improve the efficiency of registration and a better assessment of the parameters of the gravitational-wave astrophysical signals. As the signal selected quasiharmonical burst (chirp) that accompanies the merger of relativistic double stars at the end of its evolution. The form of such a signal is known with accuracy up to a set of parameters to be evaluated against the background of the many coherent and stochastic noises. In addition to the known method of filtering of coincident on time signals (output unification of network components) it examines the alternative possibility of coherent phase excitation of selected detectors ( input unification of network components ). Calculates the statistical characteristics of detection for both modes. Shows a significant increase in the effectiveness of the registration in the input the unification of network components

Novel fundaments to characterize and to assess the material quality for high photon beam filtration efficiency

M. Bencheikh, A. Maghnouj, J. Tajmouati, A. Didi

The photon beam attenuation was evaluated for primary photon fluence and secondary photon fluence for checking the dependence on energy; the beam softening was also evaluated based on beam attenuation coefficients. Based on the beam softening coefficients that were correlated by attenuation coefficients, the softening index was introduced as a new parameter to assess the material effects for high filtration system quality. These novel fundaments allow assessing the quality of a material for high photon beam filtration system quality

One dimensional nonlinear control of st fusion reactorwith D3He fuelusing back-stepping method

S. N. Hosseinimotlagh$^1$, m. rezaiee$^2$, a. gharati$^3$, s. mohammadi$^4$

Abstract-In this article a model for calculating energy and particles densities is presented in order to control burning plasma in the case of D3He fuel in spherical tokamak (ST). A spherical tokamak is a possible candidate for a D3He fusion reactor due to its high-beta value. In this model a one-dimensional approximation of the transport equation for energy as well as the density of deuterium-helium3 fuel ions and alpha particles is represented in cylindrical coordinates by a system of partial differential equation. By applying these simulation equations to control particles and energy densities profiles, the system is discretized in space using a finite difference method and a back-stepping design for D3He aneutronic fuel in tokamaks. Results obtained for boundary control conditions shows that initial values are approaching to equilibrium profiles and also the system achieves the stable equilibrium. It is also seen that with the controller modulation of the alpha particles, deuterium-helium3 and energy densities at the edge of the plasma, they are approaching to stable equilibrium points. The results of boundary control law show that the profiles can be successfully controlled with just one step of back-stepping.

S. A. Goncharov$^1$, R. V. Sukhorukov$^1$, A. A. Ogloblin$^2$, A. S. Demyanova$^2$, A. N. Danilov$^2$, S. V. S.V. Dmitriev$^2$, V. I. Staraststin$^2$

The analysis of elastic scattering of α + 9Be was carried out on the basis of the available experimental data in the energy range from 28 to 104 MeV, including recently measured at energies of 30, 40 and 90 MeV. The parameters of the semi-microscopic potential were obtained in the framework of the dispersion optical model, in which the exchange components of the average field potential were calculated using the previously proposed pseudo-oscillator approximation for the single-particle density matrix. The found potential was tested using the distorted wave method on the analysis of inelastic scattering in the considered energy region with excitation of the 5/2– (2.43 MeV) and 7/2– (6.38 MeV) levels of the ground-state rotational band. The output potential parameters were estimated using obtained dependence on energy. A satisfactory description of the angular distributions and the values of the deformation length were obtained.

M. B. Gromov$^1$, A. S. Kubankin$^{2,3}$, V. Yu. Ionidi$^1$, A. A. Kaplii$^2$, M. A. Kirsanov$^4$, A. A. Klenin$^2$, D. A. Kolesnikov$^{2,5}$, A. N. Oleinik$^6$, A. S. Chepurnov$^1$, A. V. Shchagin$^{2,5}$

The pyroelectric neutron generator is a compact source of fast neutrons with an energy of 2.45 MeV and an yield up to 10^4 n/s. The device is designed for calibrations of low-background neutrino and dark matter detectors, and it can also be applied as an alternative to traditional radioactive sources of fast neutrons in various studies and in a practicum on physics. For the correct calculation of the neutron yield in the full solid angle, and in any direction the numerical simulation of the angular distribution of neutron emission from the pyroelectric generator was performed in the case of the D(d,n)3He reaction inside the device. Anisotropy expressed in the increase of neutron yield along the direction of motion of the incident deuterium ions and reaching ~25% at the maximum energy of the incident particles of 28 keV was revealed during the radiation phase. It was found that anisotropy grew nonlinearly with increasing the ions energy, amounting to ~70% at 50 keV and a monoenergetic flux, but it is virtually absent at the energies below 10 keV. The obtained angular distribution is similar to the angular distribution of neutrons in case of the 15 keV monoenergetic flux of deuterium ions.

Anti-resonance in a laterally coupled triple-quantum-dot chain

M. Lu$^1$, Z. He$^1$, K. Chen$^2$, N. Liu$^1$

Employing the nonequilibrium Green’s function technique, electron transport characteristics through a laterally coupled triple-quantum-dot chain are investigated. The conductance versus electron energy is numerically calculated. Two anti-resonance points change into two anti-resonance bands with increasing the size of triple-quantum-dot chain. The widths of two anti-resonance bands are the same and can be regulated via adjusting the inter-dot tunneling coupling strength in the main chain or its attachment. Spin-polarized window emerges due to Zeeman splitting as an external magnetic flux is introduced. Our studies demonstrate that the system can be used as a quantum switch or an efficient spin filtering.

D. E. Presnov, S. A. Dagesyan, I. V. Bozhev, V. V. Shorokhov, A. S. Trifonov, A. A. Shemukhin, I. V. Sapkov, I. G. Prokhorova, O. V. Snigirev, V. A. Krupenin

Here we present CMOS compatible fabrication methods and the results of an experimental study of single-atom single-electron transistors made from silicon on insulator and based on various dopant atoms. Transistors with channels doped with arsenic (As), phosphorus (P), gold (Au) and potassium (K) atoms were fabricated and studied. Two methods for fabricating of experimental transistor structures are presented. The first method (As, P transistors) used a inhomogeneously doped in depth silicon layer and controlled reduction of the size of the transistor channel in several cycles of isotropic reactive-ion etching. The second method (Au and K transistors) used an undoped silicon layer and the subsequent implantation of dopant atoms into a preformed transistor channel. Dopant electron and hole levels of Au and K atoms in silicon are located near the middle of the silicon band gap, which provides a small effective size of the dopant charge center and, as a result, a high value of the charge energy and operating temperature of the transistor compared to the traditional dopants (P, As, Sb, B). The values of the charge energy of the Au and K transistors, which were estimated from the measurements ($Ec \geq 150$\,meV), are much higher than those of the As and P transistors ($Ec < 30$\,meV). Important advantages of the proposed methods are: controlled implantation of various impurities and possibility to combine etching and implantation cycles during sample preparation.

F. V. Grigoriev, V. B. Sulimov, A. V. Tikhonravov

Dependence of the thin films porosity on substrate temperature and deposition energy is studied using the classical atomistic simulation. It is revealed that pores sizes increase with the decrease of the energy of deposited atoms. For the case of the low-energy deposition up to several percent of cluster volume is available for atoms and small molecules having van der Waals radii less than 0.2 nm. Sizes of pores can achieve to several nanometers. The growth of substrate temperature from 300 K to 500 K results in the decrease of porosity. Structural properties of the deposited films vary insignificantly with the variation of energy distribution of deposited atoms if the averaged energy is kept fixed.

L. Enkhtor, V. M. Silonov

The diffuse scattering of X-rays was used to study the short-range order in a polycrystalline solid solution of Ni-14 at. % Pt. Its parameters are determined in the first six coordination spheres. It has been experimentally proved that there is a short-range order in type of L12. The ordering energies for the considered coordination spheres are estimated. The stabilizing role of short-range order in the formation of the crystal structure of Ni-14 at. % Pt alloy is revealed. The temperature of the order-disorder phase transition is estimated.

S. V. Pavlov

The classification of phenomenological models of phase transitions with a three-component order parameter and with a number of control parameters from 1 to 4 has been carried out using equivariant catastrophe theory. Analysis of the phase diagrams of the obtained models has shown that to describe all low symmetry phases, fewer terms in the power series expansion are required, than in the model constructed by the traditional method, taking into account all terms up to 2n-th power (n> 1). The theoretical temperature dependence of the heat capacity is compared with the experimental data in the GaV4S8 compound.

P. N. Nikolaev

In this work, the free energy and the equation of state of a system of solid spheres in narrow cylindrical pores are determined using the combined method of accelerated convergence of series. This method includes the Euler method and the method based on taking into account the behavior of the system at high densities near the dense packing and on the idea of the effective number of the nearest neighbors. The results obtained are compared with the data of a computer experiment for three different values of pore size, and in all cases good agreement between theory and experiment was obtained. They are much better than the results of virial expansion, and with an increase in the transverse pore sizes - and the results found on the basis of a series of pressure classes. The method used makes it possible to estimate the limits of applicability of the method of convergence acceleration, based on the transition from a series in density to a series in terms of pressure. To do this, the density with close packaging and the maximum allowable density found by the method of Euler is compared. If these densities are close, then only the Euler method can be used. In the case of a significant difference, a combined method of accelerated convergence is required.

D. V. Lukyanenko, V. T. Volkov, N. N. Nefedov, A. G. Agola

Asymptotic analysis of a singularly perturbed reaction-diffusion-advection equation, called on practics as equation of Burgers type, and having a solution with a sharp transition layer, was used to solve the coefficient inverse problem of indentification the coefficient of linear amplification from known information on the observed solution of the direct problem at the final instant of time. On series of model numerical experiments the efficiency of proposed approach is showed.

D. V. Pushkarev$^1$, A. A. Ushakov$^{1,3}$, E. V. Mitina$^1$, N. A. Panov$^{1,2}$, D. S. Uruypina$^1$, D. E. Shipilo$^1$, R. V. Volkov$^1$, P. A. Chizhov$^3$, A. P. Shkurinov$^{1,2}$, O. G. Kosareva$^{1,2}$, A. B. Savel'ev$^{1,2}$

Results of experimental studies on generation of terahertz radiation under filamentation in air of two-color radiation in loose focusing conditions with focal lengths F from 30 to 312 cm and beam diameter of 0.8 cm are presented. The two-color radiation was generated in a nonlinear BBO crystal mounted in a converging laser beam. Measurements showed that energy input to the mediem increases dramatically with decreasing focal length to 50 cm or less, and the energy of a terahertz pulse at F = 30 cm linearly depends on the laser pulse energy and increases significantly at F = 50 cm. At longer focal lengths, it was impossible to observe terahertz radiation, which is apparently due to space-time mismatch of the radiation of the first and second harmonics.

A. V. Tikhonravov, I. V. Kochikov, S. A. Sharapova

We consider the applicability of broad band optical monitoring to the production of gain flattening filters for telecommunication applications. Based on the simulation of filter deposition and on the rigorous mathematical analysis, we show that it is possible to achieve filter target characteristics due to the correlation of thickness errors and to the error self-compensation effect connected with this correlation. We also discuss the choice of a practically optimal spectral range of the monitoring procedure.

V. K. Milyukov$^1$, M. V. Sazhin$^1$, V. N. Sementsov$^1$, H. C. Yeh$^2$, C. .. Xue$^2$

The development of space technology opens new perspectives in creating high-resolution models of the Earth's gravitational field. The use of a precision laser interferometric system requires taking into account relativistic effects in measurements of the inter-satellite range in the space formation. The key quantity measured by the laser system is the phase shift of the laser beam during the passage of a double one-way range between the satellites.In this paper we obtain a solution for the relativistic phase, which in addition to the usual Shapiro term takes into account the contribution of the quadrupole term in the distribution of the Earth's mass, the Earth's spin and tidal gravitational fields due to the gravitational potentials of the outer bodies of the solar system. The evaluation of the relativistic reduction terms was made at an accuracy level of $\sim 1\,$nm, which fully satisfies the accuracy of precision measurements in the two-spacecraft formation. Next-generation gravitational multi-pair missions will need to take into account the relativistic effects of the next order of smallness.

M. P. Vinogradov, V. K. Milyukov, A. P. Mironov, A. V. Myasnikov

The Schlichter mode (1S1) is the longest period of the Earth's own oscillations. The period of this mode depends on the difference in density between the outer liquid and internal hard core, which makes its detection very important for the refinement of Earth models. Despite numerous attempts to detect the mode using a network of superconducting gravimeters, at the moment there is no confirmed experimental data on the observation of the Schlichter mode, which is due to its insignificant amplitude on the surface. In the paper, it is proposed to use the data of the laser interferometer-deformograph of the Baksan station of the SAI MSU (Northern Caucasus) with a measuring arm length of 75 m for the detection of the Schlichter mode. To this end, an asymptotically optimal algorithm was developed for analyzing data with their statistical properties, simulation on artificial data processing to estimate the magnitude of the possible observed effect and detection rates.