Classical Heisenberg antiferromagnet on a garnet lattice: a Monte Carlo simulation

We have studied a classical antiferromagnet on a garnet lattice by means of Monte Carlo simulations in an attempt to examine the role of geometrical frustration in Gadolinium Gallium Garnet, Gd3Ga5O12 (GGG). Low-temperature specific heat, magnetisation, susceptibility, the autocorrelation function A(t) and the neutron scattering function S(Q) have been calculated for several models including different types of magnetic interactions and with the presence of an external magnetic field applied along the principal symmetry axes. A model, which includes only nearest-neighbour exchange, J1, neither orders down to the lowest temperature nor does it show any tendency towards forming a short-range coplanar spin structure. This model, however, does demonstrate a magnetic field induced ordering below T ~ 0.01 J1. In order to reproduce the experimentally observed properties of GGG, the simulated model must include nearest neighbour exchange interactions and also dipolar forces. The presence of weak next-to-nearest exchange interactions is found to be insignificant. In zero field S(Q) exhibits diffuse magnetic scattering around positions in reciprocal space where antiferromagnetic Bragg peaks appear in an applied magnetic field.Comment: 8 pages, 8 figures, to appear in PRB (JAN 2001

Triangular Antiferromagnets

In this article we review the effects of magnetic frustation in the stacked triangular lattice. Frustration increases the degeneracy of the ground state, giving rise to different physics. In particular it leads to unique phase diagrams with multicritical points and novel critical phenomena. We describe the confrontation of theory and experiment for a number of systems with differing magnetic Hamiltonians; Heisenberg, Heisenberg with easy-axis anisotropy, Heisenberg with easy-plane anisotropy, Ising and singlet ground state. Interestingly each leads to different magnetic properties and phase diagrams. We also describe the effects of ferromagnetic, rather than antiferromagnetic, stacking and of small distortions of the triangular lattice.Comment: Review article, 36 pages, revtex, 19 figures in PS format, to appear in Can. J. Phy

The study of the extended Higgs boson sector within 2HDM model

Consideration of the latest experimental data on the searches for extended sector of Higgs bosons produced at the LHC at a center-of-mass energy of 13 TeV, allows for computer modeling of the properties of supersymmetric particles within 2HDM model. The experimental restrictions on model parameters accounted in FeynHiggs code that is implemented in SusHi program, gave us the possibility to calculate the cross sections and branching fractions for three mechanisms of production and decay of Higgs bosons: 1) pp$\rightarrow H\rightarrow\tau\tau$, 2) pp$\rightarrow A\rightarrow Zh\rightarrow llbb$, 3) pp$\rightarrow H\rightarrow hh\rightarrow bb\tau\tau$ at a center-of-mass energy of 14 TeV. The considered computer modelling make it possible to draw conclusions about the need to take into account the b-associated production process of Higgs bosons for fermionic decay channel at large values of tan$\beta$. Differential cross sections with respect to the Higgs transverse momentum $p_t$ and pseudorapidity $\eta$ are calculated and the peculiarities of the kinematics of the Higgs boson decay products are recognized.Comment: 18 pages, 14 figures, presented at XV Conference of High energy physics, Kharkov, 21-24 March, 201

On the Specification and Verification of Communication Protocols

The purpose of this paper is to consider the most complicated problem related to computer network design, and especially to the so-called "gateways": the definition and estimation of the logical correctness of protocols. While the simple terminal connection of a computer to a computer system necessitates only the emulation of the chosen terminal, the very complicated interconnection of several computer networks requires the definition and implementation of a whole hierarchy of protocols. Naturally, all the protocols of each level must be rigorously specified and carefully verified before being implemented into soft-, firm-, or hardware. In order to achieve this goal, a technique based on a top-down approach, involving stepwise refinement and verification of the protocol actions in various situations, is proposed in this paper. This technique requires the formalism of a special kind of Petri net: the Petri net with enabling predicates

Shape-dependence of transmission, reflection and absorption eigenvalue densities in disordered waveguides with dissipation

The universal bimodal distribution of transmission eigenvalues in lossless diffusive systems un- derpins such celebrated phenomena as universal conductance fluctuations, quantum shot noise in condensed matter physics and enhanced transmission in optics and acoustics. Here, we show that in the presence of absorption, density of the transmission eigenvalues depends on the confinement geometry of scattering media. Furthermore, in an asymmetric waveguide, densities of the reflection and absorption eigenvalues also depend of the side from which the waves are incident. With increas- ing absorpotion, the density of absorption eigenvalues transforms from single-peak to double-peak function. Our findings open a new avenue for coherent control of wave transmission, reflection and absorption in random media.Comment: 9 pages 8 figure

Investigation of the Heating Processes and Temperature Field of the Frequency-controlled Asynchronous Engine Based on Mathematical Models

The study of the temperature field of the engine for non-stationary modes is done. A numerical simulation of a non-stationary thermal process using dynamic EHD, the characteristic of the rate of rise of temperatures is done. An increase in the temperature of individual parts in the idle interval, when the power of heat release is significantly reduced, is established, and the reverse of the heat flow through the air gap is established. It is shown that the EHD method, in contrast to the FEM, is self-sufficient, which determines its practical value. In various parts of the speed control range in the implementation of various laws of regulation. At the same time, the main electrical, magnetic and additional losses associated with the fundamental voltage harmonics (FVH), and mechanical losses, as well as additional electrical and magnetic losses associated with the higher voltage harmonics, change. When using serial asynchronous engines as frequency-controlled. Permissible under the conditions of heating power is significantly reduced by the power of serial engines. Depending on the synchronous speed, the reduction is from 10 % to 20 %. Given the additional overheating due to higher voltage harmonics, as well as the deterioration of the cooling conditions when adjusting the rotational speed "down" from the nominal, it seems very relevant

The gastroprotective action of the oral gel “quertulin” on rats which received adrenalin at background dysbiosis

Aim: To determine gastroprotective effectiveness of the oral gel “Quertulin” on rats which received adrenalin at background dysbiosis.Methods: The mucoso-adgesive oral phytogel “Quertulin” (quercetin + inulin + calcium citrate) was used. The dysbiosis was reproduced by lincomycin introduction with water in dose of 60 mg/kg during 5 days. The oral application of adrenalin gel (0,18 mg/kg) made everyday during 10 days. The activities of elastase, urease, lysozyme, catalase and content of malonic dialdehide (MDA) were determined into gastric mucosa.Results: It was established lowering of levels of elastase and MDA, but raise of lysozyme by adrenalin action. The introduction of adrenalin background dysbiosis was raised elastase and urease activities. The oral application of quertulin normalized the levels of elastase, MDA, urease, lysozyme, but raised the activity of catalase.Conclusion: The oral applications of adrenalin has gastroprotective action at the expense of the activity of lysozyme and catalase rise. The oral applications of quertulin make gastroprotective action at introduction of adrenalin background dysbiosis at the expense rise level of antioxidant system and lowering the dysbiosis degree