E.S.R. study of the conformational kinetics of a biradical

Intramolecular motion in the biradical N,N'-bis(2,2,6,6-tetramethyl-1-oxyl-4-piperidinyl)ethylenediamine which contains two ionizable amine groups has been studied by E.S.R. spectroscopy. The line-shapes of the spectra as a function of pH and temperature were analysed by density matrix methods to give values for rates and free-energies of activation.     

The importance of gravitational self-field effects in binary systems with compact objects. I. The “static two-body problem” and the attraction law in a post-Newtonian approximation of general relativity

As a first step toward a proper treatment of compact objects in binary systems the attraction force of two massive bodies connected by a rod is calculated in a post-Newtonian expansion. Contrary to a calculation by Weyl und Bach we start without specializing the internal structure of the bodies. We consider general anisotropic pressures and do not require axial symmetry for the bodies. We calculate the attraction force first in a post-Newtonian approximation and then (in paper II) we shall be concerned with the post-post-Newtonian approximation. In both approximations we obtain Newton's attraction forceM _S1 M _S2/R ² plus terms of order 1/R ³ and higher, whereM _S1,M _S2 are the Schwarzschild masses of the bodies.     

On the thermodynamic limit of the B.C.S. state

We consider vector states in the Fock representation of the C.A.R. algebra, representing condensed pair states. We prove that in the thermodynamic limit these states give rise to a direct integral of gauge-dependent B.C.S. states.Partially supported by C.N.R.Equipe de Recherche associée au C.N.R.S. n^o 154.     

Decay of correlations. IV. Necessary and sufficient conditions for a rapid decay of correlations

We considerN-particle systems whose probability distributions obey the master equation. For these systems, we derive the necessary and sufficient conditions under which the reducedn-particle (n) probabilities also obey master equations and under which the Ursell functions decay to their equilibrium values faster than the probability distributions. These conditions impose restrictions on the form of the transition rate matrix and thus on the form of its eigenfunctions. We first consider systems in which the eigenfunctions of theN-particle transition rate matrix are completely factorized and demonstrate that for such systems, the reduced probabilities obey master equations and the Ursell functions decay rapidly if certain additional conditions are imposed. As an example of such a system, we discuss a random walk ofN pairwise interacting walkers. We then demonstrate that for systems whoseN-particle transition matrix can be written as a sum of one-particle, two-particle, etc. contributions, and for which the reduced probabilities obey master equations, the reduced master equations become, in the thermodynamic limit, those for independent particles, which have been discussed by us previously. As an example of suchN-particle systems, we discuss the relaxation of a gas of interacting harmonic oscillators.Supported in part (grants to D.B. and K.E.S.) by the Advanced Research Projects Agency of the Department of Defense as monitored by the U.S. Office of Naval Research under Contract N00014-69-A-0200-6018, and in part (grant to I.O.) by the National Science Foundation.     

An E.L.S., A.E.S. and L.E.E.D. study of the interaction of O2 with Pd(111) surface

The interaction of oxygen with a Palladium (111) single crystal has been studied using L.E.E.D., A.E.S., E.L.S. techniques at room temperature in the range 10^-7 to 1 torr. Various amounts of two types of chemisorbed oxygen (well-ordered and disordered) are detected. The characteristic energy losses are attributed to different electronic states : surface , volume and particular states induced by oxygen.     

Search for a dark matter annihilation signal from the galactic center halo with H.E.S.S

A search for a very-high-energy (VHE; ≥100 GeV) γ-ray signal from self-annihilating particle dark matter (DM) is performed towards a region of projected distance r～45-150 pc from the Galactic center. The background-subtracted γ-ray spectrum measured with the High Energy Stereoscopic System (H.E.S.S.) γ-ray instrument in the energy range between 300 GeV and 30 TeV shows no hint of a residual γ-ray flux. Assuming conventional Navarro-Frenk-White and Einasto density profiles, limits are derived on the velocity-weighted annihilation cross section (σv) as a function of the DM particle mass. These are among the best reported so far for this energy range and in particular differ only little between the chosen density profile parametrizations. In particular, for the DM particle mass of ～1 TeV, values for (σv) above 3×10(-25) cm(3)?s(-1) are excluded for the Einasto density profile.     

Minimum metallic conductivity in a thin crystal

Electrical conductivities of thin crystals of Bi₂(Te,S)₃ measured from 4.2°K to 300°K fall into four regions: 1) σ < 1.3×10^?5 S with positive temperature coefficient of conductivity; 2) 1.3×10^?5 S < σ < 1.4×10^?5 S with temperature independent conductivity; 3) 1.4×10^?5 S σ < 4×10^?5 S with negative temperature coefficient of conductivity, and 4) σ > 4×10^?5 S with hardly any temperature dependence. A disproportionately high fraction of samples falls into the second range; 1.3×10^?5 S < σ < 1.4×10^?5 S.     

Reflection of a focused light beam in a kerr medium II. Numerical solution of the wave equation

The problem of studying the self-effect of a light beam in a nonlinear medium, and its scattering and reflection by the collapse region has been reduced to solving a system of high-order differential equations. This enabled us to use the Runge-Kutta method which improves considerably the accuracy in solving self-effect problems as compared with the conventional phase screen method. The self-effect and reflection of a light beam from the collapse region where the beam diameter decreases to the light wavelength is investigated numerically. Calculations confirmed the main conclusions of the approximate solution of this problem which we obtained earlier in [1].Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 39, No. 8, pp. 1014–1025, August, 1996.The author is grateful to A. Consortini, J. C. Dainty, S. M. Flatte, R. F. Sharma, A. S. Gurvich, V. P. Kandidov, and V. I. Talanov for their help in this work and V. I. Tatarsky for the discussion and presentation of the results of this investigation at the Symposium on Progress in Electromagnetics Research (PIERS-95) in Seattle, USA.This work was supported in part by the International Foundation for Fundamental Research and by the Government of the Russian Federation (Project codes MR1000 and MR1300).     

E.S.R. spectra and hyperfine structure of symmetric trinuclear clusters

The E.S.R. spectrum hyperfine structure of trigonal trinuclear exchange clusters with half-integral spins is presented. In the case of antiferromagnetic exchange coupling, the ground state with the total spin S = ½ is four-fold degenerate. The Heisenberg-Dirac-Van Vleck model is shown to be incorrect for the problem of hyperfine interactions. The theory of E.S.R. hyperfine structure presented here arises from the group-theoretical analysis of exchange multiplets. By means of irreducible tensor methods the hyperfine interaction effective hamiltonian is constructed. The angular and field dependence of the hyperfine structure is investigated.     

Effective Hamiltonian of Bloch electrons in a homogeneous electrical field. Two-band approximation

The method proposed earlier [1] for determining the renormalized dispersion law _q ^F () from Bloch electrons in a homogeneous electrical field is developed in a two-band approximation. For a broadband semiconductor with a narrow forbidden band, a form of _q ^F () valid in arbitrary fields is determined. The electronic transition for a certain critical field intensity determined by the forbidden band width is predicted.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 80–85, July, 1984.The author is grateful to A. S. Kotosonov, V. L. Bonch-Bruevich, and the participants of his seminar, S. D. Beneslavskii and A. G. Mironov, for fruitful discussion of the results obtained.     

E.S.R. spectra of SiF3 radicals produced in a single crystal of SiF4

E.S.R. spectra of a γ-irradiated single crystal of SiF₄ were investigated. The spectra observed were attributed to SiF₃ radicals having ²⁸Si (I=0) and ²⁹Si (I=1/2) atoms. From the angular dependence of the spectral lines on rotation of the single crystal, hyperfine tensors were determined for three fluorine atoms and the ²⁹Si atom of the SiF₃ radical. The three fluorine atoms in the radical are equivalent, whereas the directions of their hyperfine tensors are different from one another owing to the pyramidal structure of the radical. In addition to the hyperfine analysis, the analysis of the superhyperfine structure due to neighbouring fluorine atoms gave information on the orientation of the radicals in the crystal and the mechanism of radical formation. The structure of the radical is discussed in comparison with that of the CF₃ radical.     

Synthesis of ZnO nanospheres with uniform nanopores by a hydrothermal process

ZnO nanospheres were successfully synthesized by a hydrothermal process (S1 sample) and a wet-chemical method (S2 sample). Following synthesis, calcination treatment at 450 °C was performed for the sample prepared by the wet-chemical method (S3 sample). All of the samples possessed a regular spherical shape. A polycrystalline wurtzite structure was confirmed in the S1 and S3 samples by X-ray diffraction and selected area electron diffraction, whereas a mixture of ZnO nanoparticles and amorphous materials was observed in the sample S2. The surface area and pore structure of the samples were investigated by nitrogen adsorption–desorption measurements. Uniform nanopores with a diameter of 4.07 nm were present in the S1 sample while a broad pore size distribution was obtained for the S2 and S3 samples. The highest surface area was obtained for the S1 sample and a possible formation mechanism was studied.     

Defect annealing in phosphorus implanted silicon: A D.L.T.S. study

Deep-level transient spectroscopy (D.L.T.S.) has been applied to the determination of defects in ion implanted silicon. Preliminary results concerning defects introduced by 130 KeV phosphorous ion implantation are described. Four electron traps are found: atE _c -0.21 eV,E _c -0.39 eV,E _c -0.52 eV andE _c -0.58 eV and their cross-sections estimated. The annealing behaviour in the range 450–800°C of these traps is described. Work supported in part by the Institute of Physics, Polish Academy of Science, Warsaw. Laboratoire associé au C.N.R.S.     

Breaking a chaotic secure communication scheme

The chaotic direct sequence spread spectrum (CD3S) has been extensively studied and accepted as an approach of chaotic secure communication. However, we find that CD3S is insecure and present the results of breaking CD3S. A modified unscented-Kalman-filter chaos fitting method is proposed. With the proposed method, an intruder can use a different chaotic system to fit the transmitter's chaotic system and break the CD3S scheme without any knowledge of the chaotic transmitter's structure, parameters or initial value, even under the following conditions: (A) the chaotic spreading sequence is complex and generated by two chaotic maps; (B) there exists noise in the CD3S signal; (C) the CD3S signal is constructed in frames. Simulation results verify the method.     

Motion of a particle in the field of a rotating body in the post-Newtonian approximation. Alternative solutions

The components of the gravitational field are compared in the post-Newtonian approximation in the geometric (Einstein tensor) and field (Maxwellian vector form) theories of gravitation. The fundamental difference of these fields in the motion of a test particle is shown. The feasibility of qualitative detection of the vortex component of the gravitational field is found experimentally. The scheme for an alternate experiment is given.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 15–18, May, 1990.The author thanks A. S. Lantsev for the experimental part of the article presented here.     

Growth of gallium arsenide in a GaAs-AsCl3-H2 gas-transport system. 2. Growth mechanism

Electron microscopy of platinum-shadowed carbon replicas has been used in examining the growth surfaces of autoepitaxial GaAs films produced at various initial supersaturations on substrates of (111)A, (111)B, (110), and (100) orientations. The changes in growth kinetics previously described are found to be accompanied by an alteration in the structure of the growing layer, together with the change in the nature of the centers responsible for producing the sinks (steps).Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 12, pp. 24–29, December, 1977.We are indebted to S. M. Dolgikh for performing various experiments on the production of the GaAs specimens.     

1，8-二羟基-2-萘甲醛激发态双质子转移反应的MS-CASPT2//CASSCF研究

激发态双质子转移反应长期困扰着理论和实验科学家并成为了一个悬而未决的热点问题. 本文利用完全活化空间自洽场方法及其二阶微扰理论(MS-CASPT2//CASSCF)系统地研究了典型体系1,8-二羟基-2-萘甲醛(DHNA)的激发态双质子转移反应以及相关的激发态弛豫过程. 在MS-CASPT2//CASSCF水平下,本文优化了三个能量相近但结构不同的S₁态互变异构体,即S1-ENOL、S1-KETO-1和S1-KETO-2,以及两个关键的S₁/S₀锥形交叉点结构,即S1S0-KETO-1和S1S0-KETO-2. 其中,两个极小点S1-KETO-1和S1-KETO-2与实验上观测到的双荧光发射现象密切相关. 本文还利用MS-CASPT2//CASSCF方法计算了双质子转移反应的二维势能面以及从极小点到交叉点结构的线性内插路径;相应计算结果证实了DHNA体系具有分步的激发态双质子转移机制. 具体来说,从S1-ENOL到S1-KETO-1的第一个质子转移过程是无能垒的,而从S1-KETO-1到S1-KETO-2的第二个质子转移过程则需要克服一个大约6.0 kcal/mol的能垒. 此外,由于从S1-KETO-1 (S1-KETO-2)到S1S0-KETO-1 (S1S0-KETO-2)的线性内插路径显示DHNA体系需要翻越一个约为12.0 kcal/mol的能垒,因此DHNA体系将在S₁态上停留一段时间并发生双荧光发射现象. 当然,S₁/S₀锥形交叉点也会促使DHNA体系从S₁态内转换到S₀态,而这会一定程度上降低DHNA体系发射荧光的效率. 可以通过限制C5-C8-C9-O10二面角旋转来降低体系的内转换效率,进而提高DHNA体系的发光效率. 本工作不仅有助于理解激发态双质子转移机制,还有助于设计具有优异发光性能的新型分子材料.     

Calculation of the E.S.R. spectrum of a dynamic biradical system with more than two conformations

The E.S.R. spectrum of a biradical with any number of conformations is calculated. It is shown that in some cases the interpretation of the E.S.R. spectra of such biradicals can be carried out in terms of groups of the conformations with fast exchange inside the groups. It is shown also that in the case of fast exchange the averaging of describing spectrum parameters is performed over concentrations of the exchanging conformations but not over their lifetimes, as it was suggested earlier. A detailed treatment of the spectra of biradicals with three conformations is carried out, and the possibilities of the analysis of experimental spectra of long-chain nitroxide biradicals are shown.     

A naturally occurring omega current in a Kv3 family potassium channel from a platyhelminth

Background  

Voltage-gated ion channels are membrane proteins containing a selective pore that allows permeable ions to transit the membrane in response to a change in the transmembrane voltage. The typical selectivity filter in potassium channels is formed by a tetrameric arrangement of the carbonyl groups of the conserved amino-acid sequence Gly-Tyr-Gly. This canonical pore is opened or closed by conformational changes that originate in the voltage sensor (S4), a transmembrane helix with a series of positively charged amino acids. This sensor moves through a gating pore formed by elements of the S1, S2 and S3 helices, across the plane of the membrane, without allowing ions to pass through the membrane at that site. Recently, synthetic mutagenesis studies in the Drosophila melanogaster Shaker channel and analysis of human disease-causing mutations in sodium channels have identified amino acid residues that are integral parts of the gating-pore; when these residues are mutated the proteins allow a non-specific cation current, known as the omega current, to pass through the gating-pore with relatively low selectivity.     

Extension of K.M.S. states with respect to some locally compact groups

Given a state ω on the C^*-system { , R×G, α} which is K.M.S. with respect to time on the sub-algebra of of fixed points under the action of some locally compact group G, we study its K.M.S.-extension to the whole algebra. In this work, we study more precisely the cases where G is a class of locally compact abelian groups (such that { , G, α|G} is almost periodic) or a product of these groups with a compact group.