Search

Abstract: The review summarizes and analyzes literary data on the distribution and host-parasite relations of the tick Ixodes triangulicepsBirula, 1895 (Ixodidae) in Northwestern Russia and adjacent European countries. Factors influencing population density of ticks, including habitats and main and additional hosts, are discussed.

Nuclear charge radii globally scale with atomic mass number Aas A1∕3, and isotopes with an odd number of neutrons are usually slightly smaller in size than their even-neutron neighbours. This odd–even staggering, ubiquitous throughout the nuclear landscape1, varies with the number of protons and neutrons, and poses a substantial challenge for nuclear theory2–4. Here, we report measurements of the charge radii of short-lived copper isotopes up to the very exotic 78Cu (with proton number Z= 29 and neutron number N= 49), produced at only 20 ions s–1, using the collinear resonance ionization spectroscopy method at the Isotope Mass Separator On-Line Device facility (ISOLDE) at CERN. We observe an unexpected reduction in the odd–even staggering for isotopes approaching the N= 50 shell gap. To describe the data, we applied models based on nuclear density functional theory5,6and A-body valence-space in-medium similarity renormalization group theory7,8. Through these comparisons, we demonstrate a relation between the global behaviour of charge radii and the saturation density of nuclear matter, and show that the local charge radii variations, which reflect the many-body polarization effects, naturally emerge from A-body calculations fitted to properties of A≤ 4 nuclei.

In rare cases, the removal of a single proton (Z) or neutron (N) from an atomic nucleus leads to a dramatic shape change. These instances are crucial for understanding the components of the nuclear interactions that drive deformation. The mercury isotopes (Z = 80) are a striking example1,2: their close neighbours, the lead isotopes (Z = 82), are spherical and steadily shrink with decreasing N. The even-mass (A = N + Z) mercury isotopes follow this trend. The odd-mass mercury isotopes 181,183,185Hg, however, exhibit noticeably larger charge radii. Due to the experimental difficulties of probing extremely neutron-deficient systems, and the computational complexity of modelling such heavy nuclides, the microscopic origin of this unique shape staggering has remained unclear. Here, by applying resonance ionization spectroscopy, mass spectrometry and nuclear spectroscopy as far as 177Hg, we determine 181Hg as the shape-staggering endpoint. By combining our experimental measurements with Monte Carlo shell model calculations, we conclude that this phenomenon results from the interplay between monopole and quadrupole interactions driving a quantum phase transition, for which we identify the participating orbitals. Although shape staggering in the mercury isotopes is a unique and localized feature in the nuclear chart, it nicely illustrates the concurrence of single-particle and collective degrees of freedom at play in atomic nuclei.

The luminescence excitation spectra of localized excitons in GaSe0.85Te0.15solid solutions have been investigated at the temperature T= 2 K. It has been shown that the excitation spectra of excitons with the localization energy ε > 10 mV exhibit an additional maximum MElocated on the low-energy side of the maximum corresponding to the free exciton absorption band with n= 1. It has been found that the shift in the position of the maximum MEin the excitation spectrum with respect to the energy of detected photons increases as the energy of detected photons decreases, i.e., with an increase in the localization energy of excitons. Under the resonant excitation of localized excitons by a monochromatic light from the region of the exciton emission band, in the exciton luminescence spectrum on the low-energy side from the excitation line, there is also a maximum of the luminescence (ML). The energy distance between the position of the excitation line and the position of the maximum in the luminescence spectrum increases with a decrease in the frequency of the excitation light. The possible mechanisms of the formation of the described structure of the luminescence excitation and exciton luminescence spectra of GaSe0.85Te0.15have been considered. It has been concluded that the maximum MEin the excitation spectrum and the maximum MLin the luminescence spectrum are attributed to electronic–vibrational transitions with the creation and annihilation of localized excitons, respectively.

The capacity of uranium carbide target materials of different structure and density for production of neutron-rich and heavy neutron-deficient nuclides have been investigated. The yields of Cs and Fr produced by a 1 GeV proton beam of the PNPI synchrocyclotron and release properties of different targets have been measured. Yields and release efficiencies of Cs and Fr produced from a high density UC target material and from low density UCx prepared by the ISOLDE method at IRIS in the collaboration with PARRNe group from Orsay are compared. The yields from ISOLDE original target are presented for comparison as well.

The reactions of components of the catalytic systems (C5H5)4Zr–MAO and (C5H5)4Ti–MAO in the absence and in the presence of the monomer were studied in order to obtain information on the mechanism of polymerization and copolymerization of ethylene. It was shown that the reactions accompanied by a change in the coordination mode of the ligands in the metallocene complex, a change in the coordination number of the transition metal, and the reduction of the transition metal can occur in these systems. A mechanism for the interaction of components in the indicated catalytic systems was proposed on the basis of our results obtained by various physicochemical methods and literature data.

The time dependence of the Zeeman-sublevel anticrossing signal in triplet localized exciton emission in the GaSe0.87Te0.13semiconductor solid solution has been studied by the time-resolved spectroscopy method under conditions of unpolarized pumping. It has been shown that the anticrossing signal shape changes significantly for the lifetime t of localized excitons. At the time point t= 0, the anticrossing signal is not detected; as tincreases, a maximum is formed in the dependence of the exciton emission intensity on the magnetic field (at this stage, the anticrossing signal shape is identical to that observed under conditions of steady-state excitation), which is split into a doublet as tfurther increases. A theoretical interpretation of the observed time dependence of the Zeeman-sublevel anticrossing signal in localized exciton emission has been proposed. The fine structure parameters and lifetimes of the triplet localized excitons have been determined in different spin states by comparing theory and experiment.

Polarization of radiation of triplet localized excitons induced by an external magnetic field in uniaxial GaSe-GaTe solid solutions (Voigt geometry) has been investigated using the time-resolved spectroscopy method. The linear radiation polarization occurring in a magnetic field is caused by a different behavior of radiation components polarized with E‖ Band E⊥ B(π- and σ-components, respectively). Under steadystate conditions of excitation by unpolarized light, the π-component intensity increases in the field, whereas the σ-component intensity gradually decreases with increasing field. It has been shown that the dependences of the π- and σ-component intensities Iπ(B, t) and Iσ(B, t) on the magnetic field significantly change for the lifetime tof excited states. The different decay rates of π- and σ-components lead to the strong time dependence of the linear polarization of exciton radiation induced by a magnetic field. The degree of linear radiation polarization at the exciton luminescence band maximum in fields B≥ 0.4 T at long times tapproaches unity. A theoretical description of the observed dependences Iπ(B, t) and Iσ(B, t) has been proposed. The fine structure parameters and lifetimes of triplet excitons in different spin states have been determined by comparing the theory and experiment.

We examine a one-dimensional two-component fermionic system in a trap, assuming that all particles have the same mass and interact through a strong repulsive zero-range force. First we show how a simple system of three strongly interacting particles in a harmonic trap can be treated using the hyperspherical formalism. Next we discuss the behavior of the energy for the N-body system.

We investigate three-boson recombination of equal mass systems as function of (negative) scattering length, mass, finite energy, and finite temperature. An optical model with an imaginary potential at short distance reproduces experimental recombination data and allows us to provide a simple parametrization of the recombination rate as function of scattering length and energy. Using the two-body van der Waals length as unit we find that the imaginary potential range and also the potential depth agree to within 30% for lithium and cesium atoms. As opposed to recent studies suggesting universality of the threshold for bound-state formation, our results suggest that the recombination process itself could have universal features. [ABSTRACT FROM AUTHOR]

This paper describes methods of multiscale interpolation. Image-scaling methods with an integral factor based on a multichannel discrete wavelet transform are investigated. Algorithms are developed for constructing multichannel nonorthogonal wavelet filters based on B-splines and orthogonal wavelet filters. The proposed image-scaling algorithms are investigated. Estimates are obtained for the efficiency of the algorithms thus developed.

We calculate shallow three-body bound states in the universal regime, defined by Efimov, with inclusion of both scattering length and effective range parameters. We find corrections to the universal scaling laws for large binding energies. For narrow resonances we find a distinct nonmonotonic behavior of the threshold at which the lowest Efimov trimer merges with the three-body continuum. The origin of the three-body parameter is related to the two-body atom-atom interactions in a physically clear model. Our results demonstrate that experimental information from narrow Feshbach resonances and/or mixed systems are of vital importance to pin down the relation of two- and three-body physics in atomic systems. [ABSTRACT FROM AUTHOR]

Recording of elementary holographic gratings in polymer films and solutions coloured with organic dyes has been investigated. Possible mechanisms of modifying a recorded grating by an additional laser pulse are considered. A theoretical model is proposed to describe the processes of recording/relaxation and modification of gratings recorded on triplet states of photochrome molecules; the predictions of this model are found to be in good agreement with the experimental data.

Bound structures among dipolar molecules in multilayers are a topic of great interest in the light of recent experiments that have demonstrated the feasibility of the setup. While it is known that two molecules in two adjacent layers will always bind, larger complexes have only been scarcely addressed thus far. Here we prove rigorously that three- and four-body states will never be bound when the dipoles are oriented perpendicular to the layers. The technique employed is general and can be used for more molecules or layers and other geometries. Our analytical findings are supported by numerical calculations for both fermionic and bosonic molecules. Furthermore, we calculate the reduction in intralayer repulsion necessary to bind large complexes and estimate the influence of bound complexes in systems with many layers. [ABSTRACT FROM AUTHOR]

Abstract: The band structure, total and projected densities of states, and distributions of the valence and difference electron densities for copper and silver oxides are calculated in the framework of the density functional theory in the local approximation with ab initio norm-conserving pseudopotentials in the basis set of pseudoatomic orbitals. The results obtained are compared with the experimental data and calculations performed by other authors. The energy spectrum and spatial distribution of electrons in crystals are similar to each other. Metal ions are bonded to each other through charge density channels with a weakly pronounced maximum at the center of the empty tetrahedron.

Abstract: On the basis of the mean-field method (single-chain approximation), expressions were derived for the free energy of a chain with dipolar orientation-deformation interactions of Gaussian subchains with a fixed mean-square length. In terms of this approach, the systems experience a second-order phase transition from the isotropic state to an ordered state. The Curie point and the dipole and quadrupole order parameters were related to the thermodynamic chain bending rigidity. The types and characteristics of transitions in anisotropic lattice models with dipolar orientational interactions were compared with those in continuous models with quadrupole interactions in terms of the mean-field approximation (Maier-Saupe theory). The short-and long-range orientational order in single-chain models (mean molecular field) and the corresponding multichain models (with local intrachain interactions of subchains) were compared. A comparison of the orientational correlation functions in single-chain and multichain models composed of flexible segments of a fixed length and rigid elements showed their qualitative equivalence as applied to the description of the statistical properties of chains in polymer systems with dipolar orientational-deformational interchain interactions, especially in the case of high chain ordering. Owing to the long-range fluctuation instability in two-dimensional multichain systems, the results of the mean-field theory are applicable only to parts of systems with finite sizes (domains).

We investigate two-component boson systems consisting of atoms and binary bound molecules of the same atoms. We assume that a coherent superposition of atomic and molecular Bose–Einstein condensates is formed in a non-stationary state leading to oscillations between the two condensates. To facilitate the formulation, we first give analogies in neutrino oscillations applicable for two states of one particle. We then extend to many non-interacting particles in an external field treated in the mean-field approximation as for collective motion of finite systems. We then go beyond the mean field and provide a framework for interacting particles and correlated wavefunctions. The atom–molecule oscillation frequency is dominated by the molecular binding energy when the atom–atom scattering length is substantially smaller than the oscillator trap length. Comparable scattering lengths can completely change the oscillation frequency. The damping time of the oscillations decreases with atom number and scattering lengths, although a large increase can occur for special combinations of the different interactions.

Abstract: The transformation of electronic states in Ca(001) films in strong electrostatic fields is studied using electron density functional theory. It is shown that an excess film charge of either sign pins the Fermi level (with respect to the conduction band edge) in a wide range of fields. For positively charged films, the change in the density of states at the Fermi level is small but the energy derivative of the density of states changes sign with increasing excess charge of the film. For negatively charged Ca(001) films, the change in the density of states at the Fermi level plays the main role in stabilizing the width of the occupied part of the conduction band; this should be manifested in the electronic thermodynamic and transport properties of negatively charged Ca(001) films with quantum confinement.

There are different methods to produce low-alloyed iron-based powders. The properties of such powders depend on the method of alloying as well as on the characteristics of the basic grade of iron powder. A comparative experimental study to estimate the influence of the basic iron powders on low alloyed powder properties has been conducted. The method of co-reduction of powdered oxides that contain alloying elements and selected iron powder grades has been selected. Chemical and mass spectrometer analysis has shown satisfactory alloying element distribution. Tensile strength test of the sintered parts has shown that the best results are obtained for specimens produced from low alloyed powder of Indian “Blue Dus” concentrate as the basic iron powder grade.

We use the hyperspherical adiabatic expansion method to formulate the angular Faddeev-like equation for Nidentical bosons including effects of two-body correlations. Eigenvalues and eigenfunctions determine the effective potentials in the coupled set of radial equations. The zero-range approximation is implemented on the free solutions as a boundary condition obtained by using the effective-range expansion of the two-body phase shift. This results in a new angular eigenvalue equation expressed as a transcendental equation in the index of the Jacobi functions corresponding to solutions for non-interacting particles. The collapse for attractive potentials is avoided by including scattering length, effective range and shape-parameter terms in the effective-range expansion of the phase shift. Correspondingly the hyperradial dependence in the eigenvalue equation is either a polynomial of first, second, or fourth order. Two-body correlations are included. The arithmetic eigenvalue equation allows derivation of analytic properties such as for example simple scaling relations for the particle number dependence. Excellent agreement with finite-range numerical results is obtained. The couplings between adiabatic channels are discussed. Including only the lowest adiabatic potential is shown to be sufficient for most applications on dilute systems.

Abstract: The electron response of a Ca(001) face-centered cubic film to an external electrostatic field is calculated. The results of calculations are compared with the previously obtained data on the electron response of a Cu(001) film. The energy location of occupied and unoccupied excited surface states of the Ca(001) film is determined.

The different kinds of behaviour of three-body systems in the weak-binding limit are classified with specific attention to the transition from a true three-body system to an effective two-body system. For weakly bound Borromean systems approaching the limit of binding we show that the size-binding energy relation is an almost universal function of the three s-wave scattering lengths measured in units of a hyperradial scaling parameter defined as a mass weighted average of two-body equivalent square well radii. We explain why three-body halos follow this curve and why systems appearing above reveal two-body substructures. Three-body quantum halos 2-3 times larger than the limit set by zero hypermoment are possible.

A theoretical study of the methyl and ethyl derivatives of C, Si, Ge, Sn, and Pb has been conducted. All-electron basis sets have been used and the relativistic effects taken care with the relativistic elimination of small components (RESC) method, and electron correlation has been taken into account with density functional theory (DFT). A comprehensive set of fully optimized geometries and reaction energies are presented for both methyl and ethyl families. For the methyl derivatives, a more detailed study has been conducted and the following results are juxtaposed:  those obtained with two different functionals (BOP and B3LYP) and relativistic vs nonrelativistic. Second, for the methyl derivatives, we also present common thermodynamic quantities as a function of temperature, such as enthalpy, Gibbs' energy, and heat capacity, all of which have been obtained from computing Hessians and using harmonic oscillator and rigid rotor models. Good agreement with experiment is achieved, within a few picometers in optimized geometries and several kcal/mol for reaction energies.

Abstract: This paper reports on the results of investigations into the phase composition of HgI2 microcrystals formed in the bulk and on the surface of different nanocrystalline matrices: pressed, finely dispersed (with a specific surface of more than 210 m2/g) aluminum oxide powders; porous borosilicate glasses with pore radii ranging from 2 to 20 nm; and Al2O3-HgI2 and SiO2-HgI2 nanocrystalline composites. The results of spectroscopic analysis (diffuse reflection, absorption, and luminescence spectroscopy) are complemented by the data of atomic-force microscopy (AFM) and x-ray diffraction. The experimental results indicate that nonequilibrium modifications, namely, the high-temperature yellow phase and the orange phase metastable in bulk crystals at all temperatures, can be stabilized in HgI2 nanoparticles at room temperature.

Abstract.:  We use the adiabatic hyperspheric expansion and the Faddeev decomposition of the wave function with only s-waves. We derive for a fixed hyperradius an integro-differential equation for the angular eigenvalue and wave function. The correlations lower the interaction energy for N = 20 by about a factor of 5.

Abstract.:  We propose an extended contact interaction model (also referred to as zero-range potential) for three-body systems. The model utilizes the effective range and shape parameters in the boundary condition of the contact interaction. The Thomas collapse is removed. The proposed model is tested against atomic helium trimers and is shown to provide an adequate quantitative description of these systems.

Abstract:: Production yields and β-decay half-lives (T 1/2) of very neutron-rich indium isotopes were determined at CERN/ISOLDE using isobaric selectivity of a resonance-ionization laser ion-source. Beta-delayed neutron (βdn) multiscaling measurements have yielded improved T 1/2 for 206(6) ms 132In, 165(3) ms 133In and 141(5) ms 134In. With 92(10) ms 135In, a new r-process nuclide has been identified which acts as an important “waiting point” in the In isotopic chain for neutron densities in the range n n≃ 1024-1026 n/cm3, where the r-matter flow has already passed the A≃ 130 abundance peak region.

The dissociation energy curves of low-lying spin-mixed states for Group 4 hydrides, TiH, ZrH, and HfH, have been calculated using both effective core potential and all-electron approaches. A comprehensive set of theoretical results including the dissociation energies, equilibrium distances, harmonic frequencies, anharmonicities, rotational constants, and dipole moments are reported for these molecules. We present results for both ground and a few excited states, filling a considerable gap in available data for these molecules. Absorption spectra are also predicted on the basis of the results. The present study uses three methods, all based on the multiconfigurational self-consistent field (MCSCF) method, augmented by second-order configuration interaction (SOCI), with either an effective core potential basis set (SBKJC) or a double-ζ basis set (MIDI):  (i) MCSCF+SOCI/SBKJC(f,p) with a one-electron approximation using effective nuclear charges, (ii) MCSCF+SOCI/MIDI(3p,3p) with the full Breit−Pauli Hamiltonian, and (iii) MCSCF +SOCI/MIDI(3p,3p) with the relativistic elimination of the small component scheme and full Breit−Pauli Hamiltonian. The results are compared with previous theoretical studies and available experimental data reported previously. Good agreement is obtained between the results obtained when the first and third methods are used.

The spin−orbit splittings of low-lying states in third-row transition elements were calculated using both an effective core potential (ECP) method within the one-electron (Zeff) approximation and all-electron (AE) methods using three different approaches. The wave functions were obtained using the multiconfiguration self consistent field (MCSCF) method followed by second-order configuration interaction (SOCI) calculations. All calculated results, except for the ones on atomic Ir, are in reasonable agreement with the corresponding experimental observations. The unsatisfactory results for atomic Ir are attributed to the poor theoretical prediction of the adiabatic energy gap between the lowest two ⁴F states. This gap has an incorrect sign in AE calculations without scalar relativistic corrections, but the gap can be reproduced qualitatively if these corrections are added using the newly developed RESC (relativistic elimination of small components) scheme. As a result, the AE calculations with the RESC approximation give spin−orbit splittings similar to those obtained by the ECP calculations with the Zeff approximation.

Abstract: The response of the electrons of an fcc copper (001) film to an external electrostatic field is calculated. In order to determine the distribution of the screening charge, the equations of the electron density-functional theory are solved self-consistently by an original method. The position of the “image plane,” which is involved in a correct asymptotic expression for the exchange-correlation potential in the vacuum region, is first determined when performing a quantum-mechanical calculation for an anisotropic crystal film. The nonlinear electron response is characterized by the evolution of the “center of gravity” of the induced charge, which is also investigated. The calculations take into account the crystal structure of the film, and the results differ essentially from the predictions of the “jelly” model.

We investigate dissociation reactions of loosely bound and spatially extended three-body systems. We formulate a practical method for simultaneous treatment of long-range Coulomb and short-range nuclear interactions. We use 6He (n+n+?) and 11Li (n+n+9Li) as examples and study the two-neutron separation cross-sections as functions of target and beam energy. Individual Coulomb and nuclear as well as interference contributions are also extracted.

The triplet potential energy surface for the reaction of cobalt cation with propane has been studied along the two main reaction pathways leading to the formation of (i) hydrogen and propene and (ii) methane and ethene. Effective core potentials for all elements have been used for all calculations. The geometries have been optimized at the complete active space self-consistent field (CASSCF) level of theory, and the final energetics have been refined at the multireference second-order perturbation theory (MRMP2) level with polarization function augmented basis sets. Reasonable agreement with the experimental energetics has been obtained, and the predicted mechanism is consistent with the experimentally determined mechanism of Haynes, Fisher, and Armentrout (J. Phys. Chem. 1996, 100, 18300).

Abstract.:  The quantum-mechanical three-body problem is reformulated in two dimensions by use of hyperspherical coordinates and an adiabatic expansion of the Faddeev equations. The effective radial potentials are calculated and their large-distance asymptotic behavior is derived analytically for short-range two-body interactions. Energies and wave functions are computed numerically for various potentials. An infinite series of Efimov states does not exist in two dimensions. Borromean systems, i.e. bound three-body systems without bound binary subsystems, can only appear when a short-range repulsive barrier at finite distance is present in the two-body interaction. The corresponding Borromean state is never spatially extended. For a system of three weakly interacting identical bosons we find two bound states with both binding energies proportional to the two-body binding energy. In the limit of small binding these states are spatially located at the very large distances characterized by the scattering length. Their properties are universal and independent of the details of the potential. We compare throughout with the corresponding properties in three dimensions.

Abstract: Differential (wavelength-modulated) absorption of sulfoselenide solid-solution nanocrystals has been studied in a glassy fluorophosphate matrix near the fundamental absorption edge at 360–620 nm. The observed oscillations in the absorption are attributed to size quantization of electrons and holes under strong quantum-confinement conditions. The sulfur content in the mixed semiconductor has been refined from Raman scattering spectra in CdSxSe1−x samples with x=0.30, and the nanocrystal size (R≅30 ) has been derived from low-frequency Raman scattering spectra. These data were used to calculate the energies of electron-hole transitions in nanocrystals of mixed composition, and their subsequent comparison with experiment. The calculations were found to be in a good agreement with the observed experimental absorption spectrum for nanocrystals about 45 in size. The applicability of band-structure simulation for a nonspherical nanocrystal grown in a fluorophosphate glass matrix is discussed.

Abstract: An asymptotic approximation of multiple-scattering theory has been used to analyze the intensity of very-low-energy-electron diffraction (VLEED). An analytic expression relating the amplitudes of the Bloch waves excited in a crystal (and, hence, the VLEED intensities) to the critical zone points of an infinite crystal has been obtained. The possibilities of the new approach are compared with a calculation of partial electron-transmission coefficients made by the matching method employed conventionally in interpretation of VLEED data. While providing a comparable accuracy, the proposed approach is fairly simple and free of the instabilities inherent in matching-method calculations. The explicit connection of the quantities obtained by this method with the electron dispersion relation for an infinite crystal makes it promising for analysis of band-structure effects in VLEED and photoemission experiments.