Environment potential in Hartree-Fock-Slater formalism

A new formulation of the environment potential approach (EPA) is developed within the Hartree-Fock-Slater framework. As the results of illustrative applications to C₅ cluster which is the smallest unit of diamond lattice, EPA is shown to annul efficiently the fictitious-surface effects which are inevitably brought into a finite-size-cluster model.     

A gap closing gap

<正>The intrinsic magnetic topological insulator MnBi₂Te₄ is believed to be a feasible pathway to high temperature quantum anomalous Hall(QAH) effect for its large magnetically induced energy gap(～50 meV) at its Dirac surface states predicted in theory [1]. The quantized anomalous Hall resistance has been achieved in its thin flakes [2] and films[3], though in most cases a magnetic field of several teslas is still required. The expected large surface state gap, however...     

Metallic bonds in clusters

It is stressed that the characters of interatomic bonds in metals change somewhat with the size and geometry of clusters. This change reacts directly on the equilibrium configurations. Specific effects related to electron correlations are less marked than for more electropositive elements.     

Stable bonds and unstable bonds in Y(Pr)-123 system

The Pr content dependence of the bond lengths of Y–Cu, Y–O, O–O, Cu–O, Ba–Cu and Ba–O in PrBa₂Cu₃O_y are analyzed and discussed in detail. The different valence bonds can be divided into two groups: stable bonds and unstable bonds. Since the bond lengths and angles between every two ions among O2, Cu2 and O3 are very stable, we conclude that the three ions form an unchangeable triangle when the Pr doping changes. The triangle is called “fixed triangle”. This “fixed triangle” can slightly rotate around the Cu2 ions. It is just this rotation that leads to the unstable bonds. As the increase of the Pr content, the bond lengths between the two Cu(2)–O planes becomes larger and larger, the Cu(2)–O planes bend towards the Ba–O plane. The bonds lengths between the Cu(2)–O and Ba–O planes vary oppositely from those of Cu(2)–O, and become shorter and shorter. These changes connected with the superconductivity are discussed.     

Hydrogen bonds in polymer folding

We studied the thermodynamics of a homopolymeric chain with both van der Waals and directed hydrogen bond interaction. The effect of hydrogen bonds is to reduce dramatically the entropy of low-lying states and to give rise to long-range order and to conformations displaying secondary structures. For compact polymers a transition is found between helix-rich states and low-entropy sheet-dominated states. The consequences of this transition for protein folding and, in particular, for the problem of prions are discussed.     

Coarse-graining stiff bonds

The method of constraints in molecular dynamics is useful because it avoids the resolution of high frequency motions with very small time steps. However, the price to pay is that both the dynamics and the statistics of a constrained system differ from those of the unconstrained one. Instead of using constraints, we propose to dispose of high frequency motions by a coarse-graining procedure in which fast variables are eliminated. These fast variables are thus modeled as friction and thermal fluctuations. We illustrate the methodology with a simple model case, a diatomic molecule in a monoatomic solvent, in which the bond between the atoms of a diatomic molecule is stiff. Although the example is very simple and does not display the interesting effects of “wrong” statistics of the constrained system (i.e. the well-known issue connected to the Fixman potential), it is well suited to give the proof of concept of the whole procedure.     

Application of Mathieu potential to photoemission calculations: the case of a strong potential

We have applied the Mathieu potential model to photoemission calculations from metals. The case of a strong potential is considered to describe the wavefunctions which is used for the evaluation of photocurrent from tungsten, molybdenum, copper and silicon.     

Mapping the double bonds in triglycerides

This study presents and validates a theoretical model for estimating the number of double bonds in triglyceride molecules using magnetic resonance imaging. The model enables reliable estimation of the number of double bonds from a small number of time points, as are typically acquired with chemical shift imaging. Prior knowledge from the US Department of Agriculture (USDA) is used to constrain the properties of triglyceride. Validation in oil phantoms shows agreement between the measured number of double bonds and USDA reference values (correlation 0.95, significance P=.0003, slope 0.95±0.31, intercept 0.08±1.24). Feasibility in a human subject was demonstrated using a long breath-hold (43 s) scan.     

Intramolecular hydrogen bonds in sulfur-containing aminophenols

IR Fourier spectroscopy methods have been adopted to study intramolecular interactions that occur in CCl₄ solutions of antiviral derivatives of aminophenol. Analysis of the IR spectra showed that intramolecular bonds O–H···N, O–H···O=C, N–H···O=S=O, and O–H···O=S=O can occur in these compounds depending on the substituent on the amino group. Not only the presence of intramolecular O–H···N, O–H···O=S=O, and N– H···O=S=O hydrogen bonds in 2-amino-4,6-di-tert-butylphenol derivatives containing a sulfonamide fragment but also conformational equilibrium among these types of intramolecular interactions are essential for the manifestation of high efficiency in suppressing HIV-infection in cell culture.     

Superconductivity in crystals with covalent bonds

Novel types of ground states associated with properties of heavy fermion systems are derived for crystals with covalent bonds generated by short-range exchange forces between valence electrons of atoms localized at lattice sites. It is shown that the short-range exchange forces can give rise to a narrow energy band in which electrons can exhibit an enormous effective mass. The same exchange forces provide the microscopic mechanism for spin-singlet pairing of electrons into Cooper pairs which are responsible for superconductivity in these systems. This superconductivity exhibits several different anisotropic superconducting states. The effective mass, Fermi energy, specific heat, Pauli susceptibility, critical temperatures and critical magnetic field of heavy fermion systems are calculated and compared with experimental data.The authors thank Dr. . Jano for discussions.     

Symmetric hydrogen bonds in ice X

Raman measurements on Ice VIII under pressures up to 50 GPa reveal strong line shifts, changes in isotope frequency ratio, intensity decreases, and the appearance of one new line around 38 GPa. These observations are consistent with the formation of symmetric hydrogen bonds and a new phase, Ice X, with cuprit structure.     

Variants of closing the nuclear fuel cycle

Influence of the nuclear energy structure, the conditions of fuel burnup, and accumulation of new fissile isotopes from the raw isotopes on the main parameters of a closed fuel cycle is considered. The effects of the breeding ratio, the cooling time of the spent fuel in the external fuel cycle, and the separation of the breeding area and the fissile isotope burning area on the parameters of the fuel cycle are analyzed.     

Analysis of car door closing sound quality

The perception of the noise coming from a car’s door closure has been analyzed, the focus being put on the image of the quality of the car that the listener can have in mind while hearing the sound. Different experiments have been realized: a free sorting experiment for reducing the number of stimuli without any loss of generality, paired comparisons with similarity and preference ratings and, finally, free verbalizations analysis. The results have agreed on the importance of two timbre parameters, the frequency balance of the sound and its cleanness (only one temporal event should be audible). In particular, even if loudness had appeared as the most important sound feature in previously published studies, it did not in this one; the reason is probably that previous studies had focused on annoyance creating by sounds.In a more general way, this study has proved the stability of the perceptual space derived from two different methods: a multi-dimensional analysis of similarity ratings and the analysis of free verbalizations.     

Multichannel closing switch for water energy stores

This paper describes a megavolt closing spark gap switch designed to switch water energy stores in pulse power generators. A peculiarity of the closing spark gap switch is the multichannel regime of the current flow in all discharge gaps that prolongs the lifetime of the switch, decreases its inductance and resistance, and finally, reduces the losses of the stored energy transfered to a load. Institute of High Current Electronics, Siberian Branch of the Russian Academy of Sciences. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 12, pp. 91–99, December, 1999.     

Intramolecular hydrogen bonds in the phenylazomethine biomolecules

The FTIR spectra of the solutions of biologically active molecules (screened phenylazomethines) in CCl₄ are studied. The role of the OH- and N=C groups in the formation of the intramolecular H bonds is analyzed. The analysis of the FTIR spectra shows that three types of H bonds (O-H…O-H, O-H…N=C, and O-H…O-H…N=C) are possible in the molecules under study. A correlation of the H-bond formation in the phenylazomethine molecules and the antivirus properties of such molecules is revealed. The antivirus activity is observed for molecules that exhibit intramolecular O-H…O-H…N=C bonds in the absence of free hydroxyls. The antivirus activity decreases when the molecule contains additional OH groups that are not involved in H bonds.