An electron paramagnetic resonance study of conformational substate distribution in high spin heme-proteins

The electron paramagnetic resonance spectra of high spin ferric horse myoglobin and human hemoglobin have been analyzed by computer simulation in terms of a distribution of the metal ion crystal field energies Δ₁ and Δ₂. The widths of these distributions have been put into relation 0 to the distribution of the conformational substates which may be sampled by the biomolecules during their physiological activity and become eventually arrested at low temperature. These distributions are found to be dependent upon both the solvent used and the cooling history to which the samples were submitted. The results are discussed in connection with the physical analogies displayed by these biomolecules and the glassy systems in general.     

Spatially Periodic Inhomogeneous States in a Nonlinear Crystal with a Nonlinear Defect

Spatially periodic inhomogeneous stationary states are shown to exist near a thin defect layer with nonlinear properties separating nonlinear Kerr-type crystals. The contacts of nonlinear self-focusing and defocusing crystals have been analyzed. The spatial field distribution obeys a time-independent nonlinear Schrödinger equation with a nonlinear (relative to the field) potential modeling the thin defect layer with nonlinear properties. Both symmetric and asymmetric states relative to the defect plane are shown to exist. It has been established that new states emerge in a self-focusing crystal, whose existence is attributable to the defect nonlinearity and which do not emerge in the case of a linear defect. The dispersion relations defining the energy of spatially periodic inhomogeneous stationary states have been derived. The expressions for the energies of such states have been derived in an explicit analytical form in special cases. The conditions for the existence of periodic states and their localization, depending on the defect and medium characteristics, have been determined.     

叶绿素C的光学性质

本文采用Hückel分子轨道(HMO)近似方法,定量计算了叶绿素C(Chlc)分子的能级、π-键级及π-电荷密度.分析了Chlc的电子光谱及Chlc与氧之间的敏化荧光.     

Quasi-stationary electron states in a multilayered structure in longitudinal electric and transverse magnetic fields

A theory of spectral parameters, dynamic conductivity, and relative integrated emission intensity has been proposed in the model of the open resonant-tunneling structure as a separate cascade of a quantum cascade laser in a transverse magnetic field. It has been shown that, according to the experiment by Blaser and colleagues, as the magnetic field strength increases to 8 T, the emission peak shifts to higher energies, while its relative integrated intensity in the strength range of 0–14 T decreases abruptly.     

Evolution from deep inelastic transfer to quasi-fission

Recoil techniques have been used to study the evolution of the features of four-charge transfer reactions in ¹⁴⁸Sm targets when the mass and energy of the projectile are varied. Beams of ⁶³Cu and ⁵⁶Fe were used, and their energies were chosen in order to be equal to 1.2B and 1.5B for both projectiles, B being the interaction barrier. The residual nuclei ^149gTb, ¹⁵⁰Dy and ¹⁵¹Dy were identified by their radioactive properties. This study has shown a continuous evolution of the characteristics of the c.m. angular distributions, especially the position of the maxima, from typical deep inelastic transfer to quasi-fission features, when the value of $\text{E}\text{B}$ decreases. For equal values of this ratio, no difference was observed between Fe and Cu induced reactions. The c.m, energies corresponding to the maximum cross section increases when the incident energy is increased, for a given projectile. At low incident energies (igE = 1.2B), the relative motion appears to be completely damped, and the distance of the two nuclei after separation is equal to about 5 fm. At higher incident energies, the c.m. energy is significantly higher. This may mean that the relative motion is not completely damped. Part of the effect may be explained by the differences in the angular momenta involved in the reaction.     

Comparative study of various stopping power formulations for heavy ions in solids

A comparative study of different energy loss formulations viz. Benton and Henke, Mukherjee and Nayak, Zieglar et al. and Hubert et al. has been done at lower energies (0.5 to 5 MeV/n) with the aim to identify their relative validity in this energy range. Calculated results using these formulations have been compared with experimental results available in literature.     

Complex and superlattice stacking faults in D019 Co3W

Planar defects present in annealed D0₁₉?Co₃W crystals have been investigated by conventional transmission electron microscopy. Although a predominance of superlattice stacking faults was observed, five antiphase boundaries and four complex stacking faults were identified. All planar defects were observed in locked configurations or ended at grain boundaries. A comparison of relative defect energies has been carried out with a geometrical model based on pairwise interaction energies. The results suggest that the relative number of defects is not directly related to their expected energy, but rather has origin in locked configurations adopted during crystal growth and annealing.     

Computer simulation of solute segregation to a Σ = 5 tilt boundary in Au,Cu and Ni

A Lattice Energy Function that combines a Mie type interatomic potential and a free electron gas volume dependence has been applied to the study of grain boundary energy and structure of a Σ = 5 tilt boundary in Au, Cu and Ni and of solute segregation to the same. Interatomic potentials and volume dependencies of the solvent and solute were adjusted to fit the relative partial molar enthalpy and volume at infinite dilution order to construct a AB type potential and volume dependence. This AB interaction is then applied to calculate the binding energies of solute to various grain boundary sites and the resulting change in grain boundary energy. A relationship between the binding energy and change in grain boundary is derived. The relative values of the grain boundary energy are in agreement with experimental values of the average grain boundary energies. The relative binding energies of the tested solvent-solute systems are in agreemnet with expectations that certain systems should have larger binding energies than others. The behavior of solute binding energies and local relaxations are in agreement with other studies of grain boundary segregation which use different Lattice Energy Functions and relaxation algorithms. The change in grain boundary energy is shown to be directly proportional to the binding energy.     

Energy and charge distribution of helium atoms reflected from a Cu surface under grazing incidence

The energy and charge distributions of helium ions and atoms reflected from a Cu surface at grazing incidence have been measured at the energies 250 and 300 keV. The dependence of the relative number of helium atoms in the scattered beam on the scattering angle at incidence angles less than 2° and scattered particle energies below 150 keV has been discovered. It is shown that, for a theoretical estimation of the charge fractions of particles reflected from the target surface, charge-exchange cross sections used in calculations must be corrected when solids are considered instead of gases.     

五种典型力场对气相中不同末端氨基酸的表现

选择了Amb-er99SB、CHARMM27、ENCADS、GROMOS-53A6和OPLSAA/L五种力场,并以BHandHLYP/6-311++G**优化后的气象氨基酸构型与能量作为参考标准. 研究了中性、质子化、去质子化和带帽氨基酸在不同力场下的表现. 比较了构型相对能量、顺反式结构能量差、氢键数目与强度和优化所得构型质量等代表性结果. AMBER99SB、CHARMM27和OPLSAA/L比较GROMOS53A6和ENCADS力场更为适用于气相氨基酸. 对一般性气象氨基酸和小肽分子,最推荐的力场是CHARMM27,其次为OPLSAA/L.     

INVESTIGATION OF THE EFFECT OF SLOW NEUTRON IRRADIATION ON HALOGEN-DOPED HIGH-Tc SUPERCONDUCTORS AND ITS MECHANISM

Irradiation effect of low-fluence (-10⁸ n/cm² ) slow neutrons on halogen-doped superconductors is presented in this paper. And the mechanism of the effect is also described from the viewpoint of nuclear physics for both fast and slow neutrons on high-temperature superconductors (HTSC). It is shown ex-perimentally and theoretically that slow neutrons of low fluence has a similar irradiation effect to that of fast neutron beams with an energy E_n>0.1 MeV and fluence 10¹⁶-10¹⁸ n/cm²-However,quite differ-ent mechanisms are involved in them: Fast neutrons transfer their energies through elastic scattering in HTSC, whereas slow neutrons give off their energies during the slow neutron capture (n,γ) reaction.     

Electron impact desorption of hydrogen on tungsten: II. Hydrogen in mixed adsorption layers

The electron impact desorption (EID) of H⁺ ions and of H₂ molecules from hydrogen coadsorbed with carbon monoxide or oxygen on tungsten has been investigated mass spectrometrically. It is shown that the high EID cross sections for hydrogen on tungsten reported in some earlier investigations must have been due to coadsorbed states. These states have been investigated in some detail with respect to their general adsorptive (relative coverages, sticking coefficients, isosteric heats, and desorption rates) and their EID properties (total and ionic cross sections, threshold energies). The results stress the high specificity of EID for certain (usually weakly bound) adsorption states and its applicability for the investigation of such states even in the presence of other states with much higher populations.     

Generation of X-ray radiation during planar channeling of relativistic electrons in crystals

A classical model of the emission of radiation by relativistic electrons in a crystal has been developed using the form of the potential maximally close to its actual form. The dynamics of electrons with energies 20–25 MeV performing channeling in crystals is simulated numerically. The generation of electromagnetic radiation that accompanies this motion has been considered. It has been shown that, in the given electron energy range, this radiation corresponds to the X-ray spectral band with characteristic photon energies of up to 40 keV. The radiation yield is estimated. The requirements to the electron beam parameters are formulated based on the results of the simulation. It has been shown that numerical simulation gives results that correlate with the analytic results obtained earlier and with the experimental data.     

Influence of the image charge effect on the hydrogen-like impurity-bound polaron in a spherical quantum dot in the presence of an electric field

We have investigated the influence of an external electric field on the binding energies and polaronic shifts of the ground and some first few excited states of a hydrogenic impurity in a spherical quantum dot by taking into account the image charge effect. By using Landau–Pekar variational method the general analytical expression is obtained for the impurity bound-polaron energies. It has been numerically identified the conditions (electric field, nominal radius of quantum dot, etc.) in which the bound-polaron states can be existence in GaAs quantum dot. We have shown that the polaronic shifts in the binding energy of 1s-like state are the same in cases with and without image charge effect while they for 2s-like state are not coincide and have different monotonic behavior versus confinement potential. Electron–phonon interaction lifts the degeneracy of the 2px-, 2py-, and 2pz-like states of a donor impurity and reduces their binding energies.     

Relaxation energies of oxygen auger transitions in some oxides

Relaxation effects are of major importance in the so-called chemical shifts observed in XPS and AES. These chemical shifts mainly arise from changes in the electrostatic environment due to the field of the neighbouring atoms in the initial neutral state and from electron redistribution in the surrounding electron cloud in order to screen the final state holes of the excited atom. Using a three-step model for the Auger process, we succeeded in deriving cross-relaxation energies from the KLL spectrum of oxygen in oxides, provided a careful calibration of experimental binding and Auger kinetic energies is achieved. It has been shown that the extra-atomic relaxation energy increases with ionicity for oxides of non-transition metals. In the case of transition metal oxides, it has been found that the cross-relaxation energies are larger than for the other oxides; it is believed that this is due to a more efficient screening effect of the d-electrons of the neighbouring metal atoms.     

Fluorescence spectra of cultured normal and malignant lung cells

Fluorescence Spectroscopy has emerged as a new modality to characterize physicochemical properties of biomolecules. The biomolecules have certain photophysical properties based on their molecular structure and these properties have been considered as useful parameters to monitor alterations in the functional, morphological and micro environmental changes in the cells and tissues. In this study the fluorescence emission spectra of normal and malignant lung cells were recorded for different excitation wavelengths: 230, 300, 340, and 450 nm, corresponding to the absorption of tyrosine, tryptophan, collagen or elastin, Nicotinamide adenine dinucleotide (NADH) and flavin adeno dinucleotide (FAD). Similarly excitation spectra were also recorded at 340 nm. The emission profiles showed considerable difference between the malignant and normal cells with the malignant cells having more fluorescence intensity than that of normal cells keeping emission at 340 nm. Our study had shown the discriminating features between normal and carcinoma cells lines because of higher concentration of tryptophan (1.5 times), NADH (3 times), and flavin (4 times) in carcinoma cell lines.     

Effect of X-rays on effective nonlinearity of crystals of the triglycine sulfate group

The effect of low irradiation doses on the threshold behavior of the effective permittivity of crystals of the triglycine sulfate group in an ac electric field has been studied. It has been shown that the effect of radiation-induced radicals on the domain structure of the studied crystals is not identical and is controlled by the nature of the previously introduced defects. Interaction energies of domain walls with defects have been calculated.     

氮的三原子化合物的从头算及密度泛函研究

在6－311＋G＊基组水平上,对氮的三原子化合物N3^-、N3、N3^+,用MP2及六种密度泛涵方法进行了研究。结果表明,对于已知结构的化合物和计算结果与实验测定值非常吻合,对实验上未知的化合物分子的稳定几何构型及其有关参数进行了新的探讨和补充,同时比较了N3^-、N3、N3^+间相对稳定性和几何性质,并讨论了几种不同方法对该化合物系列诸性质参数的影响,结合MO理论及成键能的计算结果进行了成键分析。