Generalized Kinetic Criterion of the Liquid–Glass Transition

Physics of the Solid State - Justification and generalization of the glass transition criterion of Schmelzer is proposed with the involvement of the model of delocalized atoms. Unlike the...     

Quantum–Chemical Studies on the Superposition of Absorption Bands in the Carbonyl Region of the IR Spectra of Acetylacetone

Using the MO LCAO SCF method in the PM3 approximation, we have investigated the influence of various internal motions of the enol molecule of acetylacetone on the harmonic vibrational frequencies of the C=O and C=C groups. The results of the investigation are discussed with reference to the available literature data on vibrational spectra of acetylacetone and its substituted derivatives. They suggest that the nature of the wide intense IR band 1620 cm^–1 in the spectra of acetylacetone vapors responsible for the absorption of its enol double bonds and its temperature dependence are determined by the tunnel mechanism of enol proton motion in the H–bond channel, the probability of whose realization is controlled by the internal rotation of methyl substituents.     

Trimer–Tetramer Interwoven States in the Scaling Limit

We report here some results we have obtained on the scale dependence of tetramer energies at the unitary limit, considering the number of tetramer energy levels appearing between the ground and the excited Efimov trimers. Our numerical investigation is done by solving a renormalized set of Faddeev–Yakubovsky equations for identical bosons with zero-range interaction, requiring a four-body scale, which in principle can be independent of the trimer properties. The ratio between the three- and four-body scales is introduced by considering the two lower trimer states and corresponding associated tetramers. We conclude that at least three tetramers are possible to exist between two Efimov states by varying the relation between such scales, and considering the relation between three-body Efimov states in the unitary limit. The results for the trimer–tetramer interwoven states are shown through a correlation between tetramers attached to consecutive Efimov trimer states.     

Exploration of Pseudospin Symmetry in the Resonant States

Taking ^120Sn as an example, we discuss the pseudospin symmetry in the single proton resonant states by examining the energies, widths and the wavefunctions. The information of the single proton resonant states in spherical nuclei are extracted from an analytic continuation in the coupling constant method within the framework of the self-consistent relativistic mean field theory under the relativistic boundary condition. We find small energy splitting in a pair of pseudospin partners in the resonant states. The lower components of the Dirac wavefunctions of a pseudospin doublet agree well in the region where nuclear potential dominates. It is concluded that the pseudospin symmetry is also well conserved for the resonant states in realistic nuclei.     

Variations in the Ozone Concentration in the Stratosphere over Moscow due to Dunamic Processes in the Cold Period of 2015–2016

New data on variations in vertical distribution of stratospheric ozone overMoscow in the cold half-year of 2015–2016 are presented. This period differed significantly from previous winters in a number of stratospheric parameters. The features of these ozone variations are considered and their relation to the stratospheric dynamics is studied. The most significant decrease in the ozone concentration in comparison with average values was observed at the beginning of March, 2016. The development of further significant ozone layer depletion similar to that occurred in spring 2011 was prevented by major sudden stratospheric warming in March 2016.     

Characteristic Features of Photoluminescence of the Opal–Tellurite Glass–Er3+ Nanocomposite

We carried out a comparative investigation of the photoluminescence of Er³⁺ ions in tellurite glasses on melted quartz substrates and when introduced into the matrices of artificial opal. We have discovered an increase in the photoluminescence of the opal–tellurite glass–Er³⁺ nanocomposite in comparison with the specimens of the same glass on melted quartz substrates.     

Possible Explanation of the Negative Values of m_ve~2Obtained from the β-Spectrum Shape Analyses

By comparing the results obtained using the same experimental data of CIAE but different theoretical formula fits it is pointed out that the negative value of mv2 is most likely stemmed from inaccuracy of the theoretical formula of the β-spectrum.     

New N2+Electronic States in the Region of 23–28 eV

Threshold photoelectron spectra of N₂⁺were measured between 23.4 and 27.6 eV with high resolution and high intensity by using the penetrating field technique and synchrotron radiation. Five vibrational progressions were observed. The first of these progressions was theC²Σ_u⁺state. The second progression was identified as the transition to the second state of²Π_gsymmetry found by P. Baltzer, M. Larsson, L. Karlsson, B. Wannberg, and M. Carlsson (1992.Phys. Rev. A46,5545). The third progression, which was discovered by F. Merkt and P. M. Guyon (1993.J. Chem. Phys.99,3400), can be designated as the²Σ_u⁻state by comparison with previous theoretical study (E. W. Thulstrup and A. Andersen, 1975.J. Phys. B8,965). The fourth and fifth progressions were designated as the²Δ_uand 2²Π_ustates by similar comparison with previous theories.     

Molecular Dynamics Simulation of Cage Effect in the Glass Transition of Argon

The glass transition process of argon is studied by molecular dynamics simulations with Lennard-Jones potential. The cage effect appears at about 24K. The Lindemann length of argon is found to be 0.55A. Two relaxation processes are clearly observed near the glass transition temperature, which is in agreement with the mode-coupling theory.     

Order-Parameter Temperature Dependences in Nanocomposites of Porous Glass–Sodium Nitrite

Temperature dependences of the order parameter in nanocomposites based on porous borosilicate glasses with mean pore diameters of 20 and 46 nm and filled with sodium nitrite are studied via the diffraction of synchrotron radiation. The mean diffraction sizes of NaNO₂ nanoparticles in the pores of these matrices and the temperatures of the transition of sodium nitrite to the ferroelectric state are determined. It is shown that the phase transition for these nanoparticles remains a first-order phase transition.     

Size Dependences of the Magnetic Properties of Superconducting Lead–Porous Glass Nanostructures

Superconducting structures Pb–PG formed by filling a porous glass matrix with the lead from melt under pressure have been investigated. Samples with characteristic pore structure diameters of d ≈ 7, 3, and 2 nm have been studied. It has been found that the critical temperature of the superconducting transition in the samples under study is similar to the corresponding value T_c ≈ 7.2 K for bulk lead. At the same time, it has been observed that the critical magnetic field of the nanocomposites, which attains H_c(T = 0 K) ≈ 165 kOe for Pb–PG (3 nm), exceeds several times the value H_c(0) = 803 Oe for bulk lead. The low-temperature magnetic- field dependences of magnetic moment M(H) contain quasi-periodic flux jumps, which vanish with a decrease in the lead nanostructure diameter. A qualitative model of the observed effects is considered.     

Quantum–Chemical Calculations of the Spatial Structure of Bilirubin Molecule Fragments

Using the semiempirical methods MINDO/3, MNDO, AM1, and PM3 and the molecular mechanics (MM) method, we have calculated the geometrical structure of eight bilirubin molecule–fragments. For a number of molecules, calculations have also been made by the ab initio method. Effects arising as a result of successive complication of the molecular structure have been analyzed. The electronic spectra of the investigated molecules have been calculated by the CNDO/S and INDO/S methods. It is shown that the semiempirical quantum–chemical methods underestimate the contribution of conjugation effects to the geometrical structure of molecules, whereas the MM method overestimates it. Wave–like instabilities towards nonplanar distortions have been revealed in the five–membered rings A and D of the investigated molecules.     

The role of the background in the extraction of resonance contributions from meson–baryon scattering

The separation of background and resonance contributions in pion–nucleon scattering is an often discussed issue. We investigate to what extent the background can be separated from the pole contribution. For illustration we use results from an analytic model for the meson–baryon interaction derived from meson exchange. We focus on the two distinct cases of an elastic and a highly inelastic resonance, namely the Δ(1232)$\Delta (1232)$ and the Δ^∗(1700)${\Delta }^{\ast }(1700)$. Our results are also relevant for studies of dynamically generated resonances and attempts to extract bare quantities from hadronic models to be compared to quark model results.     

In situ Raman Spectroscopic Study of the Kinetics of the Chemical Dissolution of Ytterbium Oxide in YbCl3–KCl Melt

Journal of Applied Spectroscopy - Using the Yb2O3–YbCl3–KCl oxide–chloride system as an example, an approach has been proposed and tested permitting a Raman spectral study of the...     

Periodic Ground States in the Neutral Falicov–Kimball Model in Two Dimensions

We consider the Falicov–Kimball model in two dimensions in the neutral case, i.e., the number of mobile electrons is equal to the number of ions. For rational densities between 1/3 and 2/5 we prove that the ground state is periodic if the strength of the attraction between the ions and electrons is large enough. The periodic ground state is given by taking the one dimensional periodic ground state found by Lemberger and then extending it into two dimensions in such a way that the configuration is constant along lines at a 45 degree angle to the lattice directions.     

Magnetic States of Fe2+ Ions in FexMn1 – xS Induced by Chemical Pressure

Physics of the Solid State - Influence of the chemical pressure (x) in single crystals of FexMn1 – xS (0.12 ≤ x ≤ 0.29) on the spin state of iron ions was...     

Analyses of Valid Range for the Linear Approximation in a Single-Mode Laser

Using the linear approximation method, we calculated the steady-state mean normalized intensity fluctuation for a loss-noise model of a single-mode laser driven by a pump noise and a quantum noise, whose real part and imaginary part are cross-correlated. We analyzed the valid range for the linear approximation method by studying the influences on the steady-state mean normalized intensity fluctuation by the cross-correlation coefficient, the intensities of the quantum and pump noise, the net gain, and the amplitude and frequency of the input signal, and we found that the valid range becomes wider when the cross-correlation between the real and imaginary part of quantum noise is weaker, the noise intensities of quantum and pump are weaker, the laser system is far from the threshold and the signal has smaller amplitude and higher frequency.     

Calculation of Quantum‐Chemical Characteristics of the Ground and Excited Electronic States of Porphin and Its Tetrapyrrole Isomers

Using the CNDO/S method, we have performed quantumchemical calculations of the ground and excited electronic states of porphin molecules (symmetry D _2h ) and a number of porphin isomers: porphycene (C_2h ), hemiporphycene, corphycene (C_2v ), isoporphycene, and three nonsynthesized structural isomers of the porphin skeleton by its bridge groups —(CH) _meso —. The results of the calculations are compared with the corresponding data for the freebase porphin molecule (H₂P). Near the boundary between the occupied and vacant orbitals the isomers form rows of singleelectron levels with similar energy characteristics. For the MOs of these isomers, the H₂P MOs closest in distribution on the comparable atomic centers are given. The weak (Q) and strong (B) transitions in the visible and near UV regions point to the porphyrin type of spectra of all the isomers. The calculation data on the excited electronic states of N, g, and ntype H₂P near and above the B states are given; the presence of such states in other isomers is shown. The calculation does not point to a difference in the position of the first singlet transitions in the first five isomers. The calculation data on the lower singlettriplet transitions are also reported.     

Limitations of the Quantification of Organic Carbon in Sediment from C–H Stretching Vibrations in DRIFT Spectra

Abstract

The limitations of quantifying organic carbon (OC) or various organic substances in sediment from the integration of infrared C–H stretching bands using diffuse reflectance infrared Fourier transform (DRIFT) spectra are pointed out, both from theoretical arguments and by presenting experimental data. Such determinations are inaccurate and imprecise because (i) the band at 2930 cm^?1 is not exclusively due to CH₂ groups; (ii) there is a spectral interference from CO₃ ^2? absorption; and (iii) the proportion of CH₂ groups in organic matter varies for different sediments. The measurement of aliphatic C–H stretching band areas only provides an approximate measurement of aliphatic carbon bonded to hydrogen, which turns out to be a factor of about 3 to 3.5 times smaller than the OC content for Hong Kong marine sediments, depending on their nature and origin.