Monotone Dualization Problem and Its Generalizations: Asymptotic Estimates of the Number of Solutions

Computational Mathematics and Mathematical Physics - Issues related to the construction of efficient algorithms for intractable discrete problems are studied. Enumeration problems are considered....     

Admissible quivers

We describe admissible quivers in the class of weighted quivers.     

Coherent spin dynamics of different density high mobility two-dimensional electron gas in a GaAs quantum well

We have addressed the dependence of quasi-two-dimensional electron spin dephasing time on the electron gas density in a 17-nm GaAs quantum well using the time-resolved magneto-optical Kerr effect. A superlinear increase in the electron dephasing time with decreasing electron density has been found. The degree of electron spin relaxation anisotropy has been measured and the dependence of spin-orbit splitting on electron gas density has been determined.     

Structure and electronic properties of oxyanionic crystal surfaces

The atomic and electronic structures of the surfaces of alkali-metal nitrates, chlorates, and perchlorates are determined in the gradient approximation of density functional theory via the linear combination of atomic orbitals using the CRYSTAL09 program package. The geometric parameters, surface energies, densities of states, overlap populations, and atomic charges are calculated. It is established that the upper layer is formed by oxygen atoms for the most stable surfaces. For oxygen atoms of the upper layer, the intra-anionic bond length decreases with respect to that in the bulk, the overlap populations increase, and the charges decrease. Changes in the atomic and electronic structures of the surface decrease with respect to those of the bulk as the cation atomic number increases.     

A new shimmy model

Shimmy is a phenomenon of intense angular self-excited vibrations of the wheels of a carriage. Such self-excited vibrations present a serious threat to traffic safety, which accounts for the great interest of researchers in this phenomenon. The problem is of highest importance for the front wheels of aircraft. Usually, the deformation of pneumatic tires is considered to be the main factor responsible for shimmy. Without challenging this thesis, we nevertheless note that this is not the only factor. The shimmy phenomenon can be observed in everyday life in the case of various carriages that often have nothing to do with pneumatics if the wheels are rigid. Below we will show that the theory of polycomponent dry friction fully explains the shimmy phenomenon for absolutely rigid wheels and, hence, is at least one of the factors responsible for shimmy in the general case. The reason why researchers have not taken dry friction into account when explaining shimmy is that the theory of this kind of friction has not been well developed; at the same time one has failed to explain shimmy in the framework of other existing theories.     

Nuclear interaction dynamics in the 56Fe (α, xn) reaction

Neutron spectra and angular distributions in the ⁵⁶Fe (α, xn) reaction are measured at α-particle energies of 12.5, 16.3, 18.3, 26.8, and 45.2 MeV. The measurements are performed using time-of-flight fast neutron spectrometers on pulsed accelerators. The measured data are analyzed in the context of equilibrium, preequilibrium, and direct nuclear reaction mechanisms. The contributions from equilibrium, preequilibrium, and direct mechanisms of neutron emission are studied over a wide range of α-particle energies.     

Collapse of resonances in semiconductor heterostructures as a transition with symmetry breaking in an open quantum system

The collapse of resonances in resonant tunneling heterostructures, which is merging of two unit-transparency resonances into a single resonance with transparency less than unity has been theoretically analyzed. The electron density distribution becomes asymmetric at the collapse point in a geometrically symmetric system. The asymmetry parameter behaves as the order parameter in the second-order phase transition. The physical mechanism of the transition is associated with the broadening of the quasistationary levels of a quantum system due to the interaction with the continuum of delocalized states. The possibility of the existence of two qualitatively different types of low-energy resonances differing in the sign of the effective range of the potential has been demonstrated.     

Resonance parametric excitation of temperature oscillations in levitating aerosol droplets

The threshold conditions of excitation of temperature oscillations in high-Q water aerosol droplets have been studied under the conditions of slow evaporation. Selection rules have been obtained for interacting modes in a droplet. The threshold intensity of excitation of temperature oscillations has been analyzed in comparison with the threshold intensity of stimulated Brillouin and stimulated Raman scattering in a droplet. It is shown that, in the three-mode regime, the temperature oscillations can be excited at a rather low pumping level (about 10 W/cm²). A method is proposed for the remote measurement of the microphysical parameters of a droplet from the periodic temperature shift of eigenfrequencies of a droplet, the threshold intensity of excitation of temperature oscillations, and the thermal Raman frequency.     

Multidimensional Nonlinear Klein–Gordon Equations and Rivertons

Theoretical and Mathematical Physics - Based on solutions of a system of quasilinear first-order equations of a special kind (rivertons), we construct classes of exact solutions of multidimensional...     

Magnetic Suceptibility of Materials of the Dy–In–O System

Russian Physics Journal - Design of complex inorganic compounds of rare earth transition 3d-metals and their template-directed synthesis is a line of research intensively pursued in the present-day...