Eduard A. Manykin

Collisional recombination coefficient in an ultracold plasma: Calculation by the molecular dynamics method

New results of the calculations of the distribution function and the electron diffusion coefficient in energy space are presented. We analyze all of the data obtained and calculate the temperature dependence of the recombination coefficient. This dependence coincides with the Gurevich-Pitaevsky analytical formula in the region of a weakly coupled plasma and begins to differ in the direction of a decline in the region of a strongly coupled plasma; the difference can reach several orders of magnitude.

Tunable Oscillatory Network for Visual Image Segmentation

Recurrent oscillatory network with tunable oscillator dynamics and nonlocal dynamical interaction has been designed. Two versions of the network model have been suggested: 3D oscillatory network of columnar architecture that reflects some image processing features inherent in the brain visual cortex, and 2D version of the model, obtained from the 3D network by proper reduction. The developed image segmentation algorithm is based on cluster synchronization of the reduced network that is controlled by means of interaction adaptation method. Our approach provides successive separation of synchronized clusters and final decomposition of the network into a set of mutually desynchronized clusters corresponding to image fragments with different levels of brightness. The algorithm demonstrates the ability of automatic gray-level image segmentation with accurate edge detection. It also demonstrates noise reduction ability.

Low-temperature spectroscopy of nonequivalent Pr3+ optical centers in a Y2SiO5 crystal

An analysis of the absorption and luminescence spectra of a Y2SiO5:Pr3+ crystal has revealed the existence of two Pr3+ optical centers associated with the presence of impurity ions at nonequivalent cation sites. It is found that energy is transported nonradiatively between the nonequivalent Pr3+ optical centers. and a preliminary analysis of the transport mechanism is carried out.

Adiabatic quantum pumping in graphene with magnetic barriers

AbstractWe study an adiabatic quantum pump effect in a two terminal graphene device with two oscillating square electric barriers and a stationary magnetic barrier using the scattering matrix approach. The model employs the low-energy Dirac approximation and incorporates the possible existence of a finite band gap in graphene spectrum. We show that in this case valley-polarized and pure valley currents can be pumped due to the valley symmetry breaking. For a δ-function magnetic barrier we present analytical expressions for bilinear total and valley pumping responses. These results are compared to numerical ones for a double δ-function, a square and a triple square magnetic barriers.

Rydberg matter—a long-lived excited state of matter

The theory of condensed excited matter, the so-called Rydberg matter (RM), is examined briefly. Explicit results are given for several physical quantities, notably, the work function and the resistivity, for which experimental results exist. The most important aspects of the experiments, which are fully described elsewhere, are discussed. Large densities of Rydberg species are formed in the experiments with cesium vapor in contact with carbon (graphite) surfaces. The resistivity of the RM formed is found to be 10−2–10−3 Ω·m under varying conditions, while theory gives the order of 10−3 Ω·m. The work function is experimentally found to be less than 0.7 eV, perhaps even less than 0.5 eV. Two different methods were used to extract this quantity from thermionic diode data. These work function values are much lower than reported for any known material, especially at the high temperatures, and they thus give strong support for the description of RM as a very dilute metal. Theory gives values ranging from 0.6 down to 0.2 eV, depending on the principal quantum number, which is estimated to be n=12–14 from the lifetime calculations and from the known pressure. Supporting evidence is found from spectroscopic studies of RM, from jellium calculations, and from recent confirming experiments. From the good agreement between theory and experiment we conclude that RM exists.

Distribution function and diffusion of electrons in the Rydberg energy space in a nonideal ultracold plasma

The distribution functions and diffusion coefficient of electrons in the Rydberg energy space in an ultracold plasma are obtained as functions of temperature by numerically solving a system of kinetic balance equations. As the initial conditions, the results obtained in previous papers by the molecular dynamics method are used. From calculation of Rydberg electron fluxes, the temperature dependence of the recombination coefficient is obtained, in good agreement with the recombination coefficient calculated previously by the molecular dynamics method.

The near infrared (0.8-2.6 mu m) absorption spectrum of a dense sodium vapor and possible mechanisms of the spectrum formation

The absorption coefficient of a dense sodium vapor (N0 ∼ 1017–1018 cm− 3) in the near infrared spectral range (0.8–2.6 µm) was measured in a homogeneously heated isolated cell. In the range of parameters studied, the sample exhibits significant absorption. Neither the observed spectral features nor the measured absorption coefficients can be explained using the existing notions of the possible absorption mechanisms (absorption due to a forbidden intercombination transition, collision-induced processes, the trimer vapor component, and many-particle effects) and the available data.

Thermodynamics and correlation functions of an ultracold nonideal Rydberg plasma

A pseudopotential model is suggested to describe the thermodynamics and correlation functions of an ultracold, strongly nonideal Rydberg plasma. The Monte Carlo method is used to determine the energy, pressure, and correlation functions in the ranges of temperatures T=0.1–10 K and densities n=10−2–1016 cm−3. For a weakly nonideal plasma, the results closely agree with the Debye asymptotic behavior. For a strongly nonideal plasma, many-particle clusters and a spatial order in the arrangement of plasma electrons and ions have been found to be formed.

Interaction of Pr3+ optical centers in the Y2SiO5 crystal

It is shown on the basis of studies of the optical spectra and luminescence decay of nonequivalent Pr3+ optical centers in the Y2SiO5 crystal that the occupation of the nonequivalent cation sites of the crystal lattice by the activator ions is irregular. For excitation in the region of the optical transitions 3H4→1D2in the temperature interval 6–80 K there is no transfer of electronic excitation energy between Pr3+ ions localized in different cation sites. The luminescence decay law of the Pr3+ optical centers is determined by the concentration of activator ions and has a complicated non-single-exponential character; the quenching of the luminescence of the Pr3+ ions is due to the formation of dimers of these ions.

Electron distribution function and recombination coefficient in ultracold plasma in a magnetic field

The electron distribution function and diffusion coefficient in energy space have been calculated for the first time for a weakly coupled ultracold plasma in a magnetic field in the range of magnetic fields B = 100−50000 G for various temperatures. The dependence of these characteristics on the magnetic field is analyzed and the distribution function is shown to depend on the electron energy shift in a magnetic field. The position of the “bottleneck” of the distribution function has been found to be shifted toward negative energies with increasing magnetic field. The electron velocity autocorrelators as a function of the magnetic field have been calculated; their behavior suggests that the frequency of collisions between charged particles decreases significantly with increasing magnetic field. The collisional recombination coefficient αB has been calculated in the diffusion approximation for a weakly coupled ultracold plasma in a magnetic field. An increase in magnetic field is shown to lead to a decrease in αB and this decrease can be several orders of magnitude.