Kohn anomalies in momentum dependence of magnetic susceptibility of some three-dimensional systems

We study a question of presence of Kohn points, yielding at low temperatures non-analytic momentum dependence of magnetic susceptibility near its maximum, in electronic spectum of some three-dimensional systems. In particular, we consider one-band model on face centered cubic lattice with hopping between nearest and next-nearest neighbors, which models some aspects of the dispersion of ZrZn$_2$, and the two-band model on body centered cubic lattice, modeling the dispersion of chromium. For the former model it is shown that Kohn points yielding maxima of susceptibility exist in a certain (sufficiently wide) region of electronic concentrations; the dependence of the wave vectors, corresponding to the maxima, on the chemical potential is investigated. For the two-band model we show existence of the lines of Kohn points, yielding maximum of the susceptibility, which position agrees with the results of band structure calculations and experimental data on the wave vector of antiferromagnetism of chromium.Comment: 13 pages, 9 figures. JETP, in press (2017

Modeling of dynamic stability of flexible ultrasonic waveguides

The article considers mathematical model intended for study of dynamic stability and parametric resonance of flexible ultrasonic waveguides for applications in technology and medicine. Considered problem is reduced to the well-known Mathieu equation applied in the theory of dynamic stability of elastic systems. Parameters of the Mathieu equation defining stability of the waveguide are determined by means of finite elements method using ANSYS software and APDL programming languag

Temporal Correlations of Local Network Losses

We introduce a continuum model describing data losses in a single node of a packet-switched network (like the Internet) which preserves the discrete nature of the data loss process. {\em By construction}, the model has critical behavior with a sharp transition from exponentially small to finite losses with increasing data arrival rate. We show that such a model exhibits strong fluctuations in the loss rate at the critical point and non-Markovian power-law correlations in time, in spite of the Markovian character of the data arrival process. The continuum model allows for rather general incoming data packet distributions and can be naturally generalized to consider the buffer server idleness statistics

Nonlinear effects related to vibrations of long elastic waveguides: formulation of nonlinear equations

A number of effects arising during vibrations of long elastic waveguides can not be explained in the context of the linear theory. One of these effects is redistribution of energy between the longitudinal and transverse vibration modes. Nonlinear equations describing such effects have been studied in momentless approximation with application to vibrations of strings and they account for tension of the string axis as a result of transverse vibrations. The authors have studied a possibility of generalization of these equations for the case of elastic waveguides taking into account internal moments and lateral forces arising during bending of the waveguid

The study of methods of preliminary cooling of fruits

The studies were aimed at scientific grounding of expedience of combination of preliminary cooling of apples, pears and plums and their processing by antioxidant compositions before the long storage and also at establishing of the optimal regimes and methods of this technological operation. The objects of studies were apple, pear and plums fruits of the different pomological species. As a result of studies was offered the combined method that provides preliminary cooling of apple fruits firstly by hydro-cooling in solutions of antioxidant compositions during 1 hour to the temperature in fruit center 8,5 °С, then additional cooling in AOC solutions during 1,5 hours to the temperature in fruit center 9 °С, additional cooling in chamber of intensive cooling during 50 minutes to the temperature in fruit center 1°С. For plum: hydro-cooling in AOC solutions during 40 minutes to the temperature in fruit center 9 °С, additional cooling in chamber of intensive cooling during 30 minutes to the temperature in fruit center 1°С. The use of such method of preliminary cooling provides the fast decrease of intensity of breath and thermal flux of fruits and essentially decreases the lost of their mass. It favors the prolongation of term of storage of fruit raw material with maximal preservation of quality and biological value. The received data and their scientific grounding give a possibility to recommend producers to use the offered method of preliminary cooling in production condition

The higher-order magnetic skyrmions in non-uniform magnetic fields

For 2D Hubbard model with spin-orbit Rashba coupling in external magnetic field the structure of effective spin interactions is studied in the regime of strong electron correlations and at half-filling. It is shown that in the third order of perturbation theory, the scalar and vector chiral spin-spin interactions of the same order arise. The emergence of the latter is due to orbital effects of magnetic field. It is shown that for nonuniform fields, scalar chiral interaction can lead to stabilization of axially symmetric skyrmion states with arbitrary topological charges. Taking into account the hierarchy of effective spin interactions, an analytical theory on the optimal sizes of such states -- the higher-order magnetic skyrmions -- is developed for axially symmetric magnetic fields of the form $h(r) \sim r^{\beta}$ with $\beta \in \mathbb{R}$.Comment: 20 pages, 10 figures, 75 reference

Universal Quantum Computation through Control of Spin-Orbit Coupling

We propose a method for quantum computation which uses control of spin-orbit coupling in a linear array of single electron quantum dots. Quantum gates are carried out by pulsing the exchange interaction between neighboring electron spins, including the anisotropic corrections due to spin-orbit coupling. Control over these corrections, even if limited, is sufficient for universal quantum computation over qubits encoded into pairs of electron spins. The number of voltage pulses required to carry out either single qubit rotations or controlled-Not gates scales as the inverse of a dimensionless measure of the degree of control of spin-orbit coupling.Comment: 4 pages, 3 figures (minor revision, references added

Spintronic single qubit gate based on a quantum ring with spin-orbit interaction

In a quantum ring connected with two external leads the spin properties of an incoming electron are modified by the spin-orbit interaction resulting in a transformation of the qubit state carried by the spin. The ring acts as a one qubit spintronic quantum gate whose properties can be varied by tuning the Rashba parameter of the spin-orbit interaction, by changing the relative position of the junctions, as well as by the size of the ring. We show that a large class of unitary transformations can be attained with already one ring -- or a few rings in series -- including the important cases of the Z, X, and Hadamard gates. By choosing appropriate parameters the spin transformations can be made unitary, which corresponds to lossless gates.Comment: 4 pages, 4 figure

Spin electric effects in molecular antiferromagnets

Molecular nanomagnets show clear signatures of coherent behavior and have a wide variety of effective low-energy spin Hamiltonians suitable for encoding qubits and implementing spin-based quantum information processing. At the nanoscale, the preferred mechanism for control of quantum systems is through application of electric fields, which are strong, can be locally applied, and rapidly switched. In this work, we provide the theoretical tools for the search for single molecule magnets suitable for electric control. By group-theoretical symmetry analysis we find that the spin-electric coupling in triangular molecules is governed by the modification of the exchange interaction, and is possible even in the absence of spin-orbit coupling. In pentagonal molecules the spin-electric coupling can exist only in the presence of spin-orbit interaction. This kind of coupling is allowed for both $s=1/2$ and $s=3/2$ spins at the magnetic centers. Within the Hubbard model, we find a relation between the spin-electric coupling and the properties of the chemical bonds in a molecule, suggesting that the best candidates for strong spin-electric coupling are molecules with nearly degenerate bond orbitals. We also investigate the possible experimental signatures of spin-electric coupling in nuclear magnetic resonance and electron spin resonance spectroscopy, as well as in the thermodynamic measurements of magnetization, electric polarization, and specific heat of the molecules.Comment: 31 pages, 24 figure

Study of the process of interaction between low-frequency ultrasound and biological tissue phantoms

This paper presents the results of a series of experimental studies on the impact of low-frequency ultrasound on biological tissue phantoms, acoustic pressure on the motion of particles in an acoustic field generated by annular waveguide. Experiments have demonstrated that when vibrations with a frequency corresponding to its natural frequency of bending vibrations are induced in the annular waveguide, micropowder particles form arranged bulk structures on the substrate. Analysis of results on the behavior of micropowder particles in the ring insonation area revealed that frequency variations of ultrasonic vibrations lead to variations in spatial distribution of acoustic pressure inside the ring. The thermal effect of low-frequency ultrasound from annular waveguide on biological tissue phantoms has been studied. It was established that the annular waveguide enables heating of fluid when it has no direct contact with the media, thereby demonstrating its applicability for non-contact treatment of tumors