双参数分岔平面内胰腺β细胞的簇放电分析

胰岛分泌胰岛素的放电活动以动作电位的簇放电为主要特点.文章考虑具有代表性且较为简单的Vries-Sherman模型,通过其快子系统的双参数分岔分析确定了双参数平面内不同簇放电类型的存在区域,并应用快慢动力学分析研究了参数v_m取不同值时所产生的簇放电模式的拓扑类型以及它们之间相互转迁的动力学机理. 关键词： 簇放电 快慢动力学 余维-2分岔     

Dislocation spectroscopy of crystals

A new method of studying the energy characteristics of dislocations is proposed, which is based on the investigation of the interaction of moving dislocations with purposefully introduced electronic and hole centers. A study has been made of KCl, NaCl, KBr, LiF, and KI alkali halide crystals containing electronic F and hole V _K and Me ⁺⁺ (Cu⁺⁺, Ag⁺⁺, Tl⁺⁺, In⁺⁺) centers. Investigation of the temperature dependence of the dislocation interaction with the F centers permitted determination of the position of the dislocation-induced electronic band (DEB) in the band diagram of the crystal. In KCl, the DEB is separated by ≈2.2 eV from the conduction-band minimum. It is shown that dislocations transport holes from the centers lying below the dislocation-induced hole band (DHB) (X ⁺, In⁺⁺, Tl⁺⁺, V _K) to those above the DHB (the Cu⁺ and Ag⁺ centers). Such a process is temperature independent. The DHB position in the crystal band diagram has been determined; in KCl it is separated by ≈1.6 eV from the valence-band top. The effective radii of the dislocation interaction with the electronic F and hole X ⁺, V _K, and Tl⁺⁺ centers have been found. Fiz. Tverd. Tela (St. Petersburg) 41, 2139–2146 (December 1999)     

Production of V0 pairs in the hyperon experiment WA89

We present a comprehensive study of the inclusive production of V⁰V⁰ pairs (V⁰=Λ, Λ̄ or K_S ) by Σ^- and π^- of 340 GeV/c momentum and neutrons of 260 GeV/c mean momentum in copper and carbon targets. In particular, the dependence of the x_F spectra on the combination of beam-particle and produced V⁰V⁰ pair is investigated and compared to predictions obtained from PYTHIA and QSGM calculations. The data and these predictions differ in many details, the agreement can at best be termed as qualitative. A signal from decays of the tensor meson f’₂(1525) was observed in the K_S K_S mass distribution and inclusive production cross sections were measured. No signal was found from the double-strange H-dibaryon decaying to ΛΛ.     

Mechanistic studies of reactions catalysed by diamine oxidase using isotope effects

Diamine oxidase (DAO), the enzyme that is responsible for amine biodegradation in animals, plants and humans, catalyses the biotransformation of amines such as histamine (HA), putrescine, 1-phenylethylamine, tyrosine, tryptamine, serotonine and spermine. The kinetic and solvent isotope effects (SIEs) were applied to study the mechanism of the biotransformation using HA and its methylderivatives. The SIE for the biotransformation of HA, N^τ-methylhistamine and N^π-methylhistamine was found to be 3.58, 2.22 and 5.70 on V_max, and 1.58, 1.06 and 1.14 on V_max/K_M, respectively. On the other hand, the kinetic isotope effect for oxidation of stereospecifically deuterium-labelled [(α R)-²H]-N^τ-methylhistamine and [(α R)-²H]-N^π-methylhistamine was 0.69 and 0.62 on V_max, and 15.06 and 7.50 on V_max/K_M, respectively. These results demonstrate that DAO catalyses amine biotransformation by stereospecifically cleaving the αC\bond H bond in the pro-S position. Moreover, the oxidation of amine to aldehyde involves several transition states, including hybridisation change from sp³ (Schiff base) to sp² (imine), then back again to sp³ to give a final product with hybridisation sp² (aldehyde).     

Equation of state and thermal expansivity of LiF and NaF

The high-pressure and high-temperature behaviors of LiF and NaF have been studied up to 37 GPa and 1000 K. No phase transformations have been observed for LiF up to the maximum pressure reached. The B1 to B2 transition of NaF at room temperature was observed at ～28 GPa, this transition pressure decreases with temperature. Unit-cell volumes of LiF and NaF B1 phase measured at various pressures and temperatures were fitted using a P–V–T Birch–Murnaghan equation of state. For LiF, the determined parameters are: α₀ = 1.05 (3)×10^?4 K^?1, dK/dT = ?0.025 (2) GPa/K, V ₀ = 65.7 (1) Å³, K ₀ = 73 (2) GPa, and K′ = 3.9 (2). For NaF, α₀ = 1.34 (4)×10^?4 K^?1, dK/dT = ?0.020 (1) GPa/K, V ₀ = 100.2 (2) Å³, K ₀ = 46 (1) GPa, and K′ = 4.5 (1).     

First-principles study of structural,elastic, electronic and thermodynamic properties of topological insulator Bi2Se3 under pressure

The structural, elastic, electronic and thermodynamic properties of the rhombohedral topological insulator Bi₂Se₃ are investigated by the generalized gradient approximation (GGA) with the Wu–Cohen (WC) exchange-correlation functional. The calculated lattice constants agree well with the available experimental and other theoretical data. Our GGA calculations indicate that Bi₂Se₃ is a 3D topological insulator with a band gap of 0.287 eV, which are well consistent with the experimental value of 0.3 eV. The pressure dependence of the elastic constants C_ij, bulk modulus B, shear modulus G, Young’s modulus E, and Poisson’s ratio σ of Bi₂Se₃ are also obtained successfully. The bulk modulus obtained from elastic constants is 53.5 GPa, which agrees well with the experimental value of 53 GPa. We also investigate the shear sound velocity V_S, longitudinal sound velocity V_L, and Debye temperature Θ_E from our elastic constants, as well as the thermodynamic properties from quasi-harmonic Debye model. We obtain that the heat capacity C_v and the thermal expansion coefficient α at 0 GPa and 300 K are 120.78 J mol^?1 K^?1 and 4.70 × 10^?5 K^?1, respectively.     

The intermolecular potential of NH+ 4-Ar I. Calculations for the internal rotor structure of the v 3 band

The intermolecular potential energy surface of the electronic ground state of the ammonium-argon ionic dimer, NH⁺ ₄-Ar, is calculated by ab initio methods using different levels of theory (MP2, MP4) and basis sets (aug-cc-pVXZ, X = D/T/Q). The deformation of the ammonium ion in the complex is shown to be small and its geometry is therefore fixed in these calculations to the tetrahedral structure optimized for the bare ion. The global minimum of the potential corresponds to a proton-bound structure with C_3v symmetry (R_e ≈ 3.4 Å, D_e ≈ 950 cm^?1) and the barrier to internal rotation between the four equivalent minima is around 200 cm^?1. The three-dimensional potential is expanded in tetrahedral harmonics whose radially dependent coefficients, V_i (R), are compared for the considered levels of theory. The rotation-intermolecular vibration Hamiltonian is solved using a two-dimensional fixed-R representation of the calculated potentials, V_i , ≡ V_i (R ^eff), where the effective intermolecular separation, RR^eff, is determined from the experimental rotational constants of the complex. The accuracy of these parametrized potential energy surfaces is judged by their ability to reproduce the hindered rotor subband structure in the experimental v ₃(t ₂) infrared band of the complex. The simulations using the potentials calculated at the MP2/aug-cc-pVTZ or higher levels of theory reproduce the coarse structure of the experimental spectrum well. Further improvement could be achieved by least-squares fitting the potential parameters to the observed subband positions. The fitted V ₃ and V ₄ parameters remain in close agreement with those determined from the ab initio calculations but the anisotropy of the potential is significantly different from that in a previous least-squares fit of V ₃ alone.     

Theory of tensor invariants of integrable Hamiltonian systems. I. Incompatible Poisson structures

This paper develops a new theory of tensor invariants of a completely integrable non-degenerate Hamiltonian system on a smooth manifoldM ⁿ. The central objects in this theory are supplementary invariant Poisson structuresP _c which are incompatable with the original Poisson structureP ₁ for this Hamiltonian system. A complete classification of invariant Poisson structures is derived in a neighbourhood of an invariant toroidal domain. This classification resolves the well-known Inverse Problem that was brought into prominence by Magri's 1978 paper deveoted to the theory of compatible Poisson structures. Applications connected with the KAM theory, with the Kepler problem, with the basic integrable problem of celestial mechanics, and with the harmonic oscillator are pointed out. A cohomology is defined for dynamical systems on smooth manifolds. The physically motivated concepts of dynamical compatibility and strong dynamical compatibility of pairs of Poisson structures are introduced to study the diversity of pairs of Poisson structures incompatible in Magri's sense. It is proved that if a dynamical systemV preserves two strongly dynamically compatible Poisson structuresP ₁ andP ₂ in a general position then this system is completely integrable. Such a systemV generates a hierarchy of integrable dynamical systems which in general are not Hamiltonian neither with respect toP ₁ nor with respect toP ₂. Necessary conditions for dynamical compatibility and for strong dynamical compatibility are derived which connect these global properties with new local invariants of an arbitrary pair of incompatible Poisson structures.Supported by NSERC grant OGPIN 337.     

An in situ high-pressure X-ray diffraction experiment of hydroxyapophyllite

The compression behavior of a natural hydroxyapophyllite is investigated up to about 10.01 GPa at 300 K using in situ angle-dispersive X-ray diffraction and a diamond anvil cell at High Pressure Experiment Station, Beijing Synchrotron Radiation Facility (BSRF). Over this pressure range, no phase change or disproportionation is observed. The isothermal equation of state is determined for the first time. The values of zero-pressure volume V₀, isothermal bulk modulus K₀, and K₀' refined with a third-order Birch-Murnaghan equation of state are V₀=1276.3±0.9 ų, K₀=71±3 GPa, and K₀'=8±1. Furthermore, we confirm that the values of linear compressibility β along a and c directions of hydroxyapophyllite are elastically anisotropic.     

Structural phase transitions in Pd0.8 Si0.2 and Pd0.75 Si0.20 Ag0.05 alloys observed by pac

The phase transition in the alloys Pd_0.8 Si_0.2 and Pd_0.75 Si_0.20 Ag_0.05 have been investigated through the quadrupole interaction of¹¹¹Cd impurities. The quadrupole interactions were measured by means of the TDPAC technique from room temperature up to about 870 K. The variation of the quadrupole interaction with temperature in the alloy PdSiAg shows aT ^3/2 dependence below and above 629 K, with coefficientsB=5.43(25)·10⁻⁵ K^−3/2 andB=3.70(15)·10⁻⁵ K^−3/2, respectively. This demonstrates that the alloy undergoes a phase transition around 629 K. The existence of two electric field gradients observed in the alloy PdSi,V _zz (1)=3.47(54)·10¹⁷ V/cm² andV _zz (2)=2.29(36)·10¹⁷ V/cm², indicates that there are two different¹¹¹Cd sites. The corresponding fractionsf ₁ andf ₂ strongly depend on temperature. Below 520 K, most¹¹¹Cd nuclei are subject to the higher EFGV _zz (1) (f ₁≈70%), whereas above 520 Kf ₁ falls rapidly to zero andV _zz (2) becomes dominant. The temperature dependences of thef ₁ andf ₂ reveal a picture of the phase transition between the two crystal structures.     

A theorem on the order of levels in confining potentials

We prove that in a two-body, non-relativistic system interacting via a potential V = ?g²/r + V_c(r), where V_c is a confining potential non-singular at the origin, the 2S level is above the 2P level if V_c satisfies the following sufficient condition: This covers the well-known cases of linear potentials or harmonic oscillator potentials, which were considered in charmonium models, but also more generally, for instance, V_c(r) = r^α, α >0.     

Hole-electron mechanism of F-H pair generation in RbCl crystals with impurity electron traps

Production of F, Cl ₃ ⁻ , Ag⁰, and Tl⁰ centers in RbCl:Ag and RbCl:Tl crystals by photons having energies ranging from 5 to 10 eV has been studied at 295 and 180 K. It is shown that creation of near-impurity excitations is accompanied by formation of F centers localized in the vicinity of Ag⁺ and Tl⁺ ions. F centers are produced in direct optical generation of self-trapped excitons. In addition to the well-known mechanism of F-H pair production in nonradiative recombination of electrons with self-trapped holes, a hole-electron process has been revealed for the first time to operate in RbCl:Ag having deep electron traps. By this mechanism, F-H pairs appear in the following sequence of stages: thermally stimulated unfreezing of hopping diffusion of self-trapped holes (V _K centers), tunneling electron transfer from Ag⁰ to the approaching V _K centers, and subsequent nonradiative decay of triplet self-trapped excitons near Ag⁺ ions. Fiz. Tverd. Tela (St. Petersburg) 40, 1238–1245 (July 1998)     

On the <Emphasis Type="Italic">K</Emphasis><Superscript>+</Superscript><Emphasis Type="Italic">d</Emphasis> interaction at low energies

The Kd reactions are considered in the impulse approximationwithNN final-state interactions (FSI) taken into account. Realistic parameters for the KN phase shifts are used. The “quasi-elastic” energy region, in which the elementary KN interaction is predominantly elastic, is considered. The theoretical predictions are compared with the data on the K ⁺ d → K ⁺ pn, K ⁺ d → K⁰ pp, K ⁺ d → K ⁺ d, and K ⁺ d total cross sections. The NN FSI effect in the reaction K ⁺ d → K ⁺ pn has been found to be large. The predictions for the Kd cross sections are also given for slow kaons, produced from ϕ(1020) decays, as the functions of the isoscalar KN scattering length a ₀. These predictions can be used to extract the value of a ₀ from the data. The text was submitted by the authors in English.     

Activation volumes of hydrolyses of maltose and maltotriose over an immobilized glucoamylase catalyst

Abstract

Initial rates of hydrolysis of maltose and maltotriose over an immobilized glucoamylase have been measured up to 127 MPa at 25±0.1°C. The observed rates have been analyzed showing the reaction pathways of both hydrolyses to be E+S?ES*?ES7ast;E+P, where E, S, P, ES*, and ES denote the enzyme, the substrate, the product, a substrate-subsite complex, and a substrate-active site complex, respectively. The apparent maximum rate r^mand the apparent Michaelis constant K^m as well as their respective pressure dependences in terms of the apparent activation volume Δ V_app ^# and the apparent volume of reaction Δ V_app have been evaluated. Small absolute values of Δ V_app ^num; and Δ V_app for both reactions have been discussed on the basis of the reaction mechanism.     

Compatibility of field emitter studies of oscillating surface reactions with single crystal measurements: catalytic CO oxidation on Pt

Kinetic oscillations in catalytic CO oxidation on Pt have been studied on large (millimeter size) single crystal planes of Pt as well as on a Pt field emitter tip that exposes different crystal facets of nanometer size. In order to examine the compatibility of results from the two types of experiments, the regions of different dynamical behavior (bifurcation diagram) have been mapped out in p_CO,T-parameter space using a field electron microscope (FEM) and a field ion microscope (FIM). The comparison with the results of single crystal measurements shows that in the case of applied electrostatic fields less than 5 V nm⁻¹ (FEM), the field-induced effects are negligible, but they are significant for fields exceeding 12 V nm⁻¹ (FIM). The field-induced shift of the bifurcation diagram toward lower p_CO values, observed with FIM, is explained in terms of a field-modified interaction of CO and O₂ with Pt studied here with field ion appearance energy spectroscopy. With coadsorbed lithium (submonolayer coverage), the existence range for rate oscillations is shifted toward higher p_CO values. This shift is attributed to a redistribution of the electron density at the surface induced by alkali metal co-adsorption.     

Ionic liquid type dye-sensitized solar cells: increases in photovoltaic performances by adding a small amount of water

Increases in photovoltaic performances for dye-sensitized solar cells having ionic liquid type electrolytes are reported. These results are explained by diffusion coefficient for I₃⁻, charge transfer resistances on counter electrodes, flat band potentials of TiO₂, redox potentials for I⁻/I₃⁻, electron diffusion constants, electron life time, and diffusion length in TiO₂ layers. Methylpropylimidazolium iodide is selected because of the lowest viscosity and the highest conductivity. Increases in the photovoltaic performance are observed when a small amount of water was added into the ionic liquid consisting of both LiI and t-butylpyridine as the additives. These improvements are brought about by enhancements of all of J_sc, ff and V_oc. The increases in J_sc and ff are associated with the decrease in charge transfer resistances on counter electrodes and increases in ionic conductivities. V_oc may be explained by an increase in the difference between redox potentials of I⁻/I₃⁻ and Fermi level.     

The stochastic properties of a molecular-dynamical Lennard-Jones system in equilibrium and nonequilibrium states

The K-entropy and the t _m time of dynamical memory (the time of forgetting initial conditions during numerical integration) of a classical system of particles whose interactions are governed by the Lennard-Jones potential were calculated by the method of molecular dynamics. The K value was a characteristic of a system of many particles, and the t _m value proved to increase logarithmically as fluctuations of the total energy of the system decreased; that is, as the accuracy of numerical integration increased. Two different K-entropy values corresponding to the same total energy of the system were found to exist, namely, K _e for the equilibrium and K _n for the nonequilibrium state. The rate of kinetic energy relaxation (t _r ^?1 ) was shown to equal K _n, and the K _n value was found to be a more fundamental characteristic than (t _r ^? ). The density dependences of K _e (monotonic) and K _n (nonmonotonic) were calculated. The transition from dynamical (Newtonian) correlations to stochastic for the velocity autocorrelation function was considered. The reasons for the finiteness of dynamical memory in physical processes are discussed. The duration of dynamical correlations in real systems is limited by quantum uncertainty and is of the order of picoseconds.     

Influence of Vibrational Excitation of Triplet Molecules of Anthraquinone on the Photochemical Processes in Gas Mixtures with Amines

By the quenching of the delayed fluorescence (DF) of anthraquinone vapors by aliphatic amines (diethylamine, dibutylamine, cyclohexylamine) and pyridine the photoinduced processes proceeding with the participation of vibrationally excited triplet molecules of anthraquinone have been investigated. The DF quenchingrate constants K _q varying from 1·10⁶ sec^–1·torr^–1 in mixtures with diethylamine to 7·10³ sec^–1·torr^–1 in mixtures with pyridine have been estimated. A correlation between the values of K _q and the ionization potentials of foreign gases confirming the important role of interactions with charge transfer in the quenching of triplet molecules in the gas phase has been established. The influence of other relaxation processes on the DF quenching is considered. It is shown that the intermolecular vibrational relaxation in the T ₁ triplet state leading to the establishment of relaxation equilibrium at a vibrational temperature T _vib considerably increasing the medium temperature is the fastest process among the biomolecular processes (rate constants K _col ^V > 10⁶ sec^–1·torr^–1 > K _q). The values of T _vib and the vibrational energies E _vib of the triplet molecules after the energy exchange in the collisional complex have been estimated. It has been concluded that the photochemical reaction yield is determined by the intermolecular processes proceeding in the T ₁ state at a vibrational equilibrium characterized by high values of T _vib. The influence of E _vib of triplet molecules on the DF quenching rates at a photoinduced electron transfer is considered.     

Analytic approach to the problem of constructing effective nucleon-nucleon potentials in the region of low and intermediate energies

A new relativistic approach to the problem of constructing effective local hadron-hadron potentials is proposed on the basis of analytic S-matrix theory and Gelfand-Levitan-Marchenko-Martin methods for solving the inverse quantum scattering problem. An effective potential is defined as a local operator in a partial-wave equation of the quasipotential type such that it generates an on-shell relativistic (Feynman) scattering amplitude that has required discontinuities at dynamical cuts. The method is used to construct nucleon-nucleon potentials in the ¹ S ₀-and ³ S ₁-wave states. The dynamical discontinuities of partial-wave amplitudes for nucleon-nucleon scattering are calculated on the basis of the one-bosonexchange model that takes into account the exchanges of π, σ, ρ, ω, η, and α ₀ mesons. It is shown that the nonlinear relation between the discontinuities of partial-wave scattering amplitudes at dynamical cuts and interaction operators generates additional short-range repulsion not associated with omega-meson exchange. The experimental energy dependences of phase shifts in the channels of nucleon-nucleon scattering that are considered here are faithfully reproduced by the results of the calculations up to the projectile-nucleon kinetic energies in the range T = 1.5–2.0 GeV.