Time-resolved fluorescence study of the single tryptophan in thiocyanate and azide derivatives of horseradish peroxidase: Implication for a p H-induced conformational change in the heme cavity

Detailed pH-dependent steady state and picosecond time-resolved tryptophan fluorescence studies on thiocyanate and azide complexes of horseradish peroxidase have been carried out. The fluorescence decay of the single tryptophan in these species was fitted to a discrete three exponential model. Maximum entropy method analysis also gave three distinct regions of lifetime distributions. The fast subnanosecond lifetime component was found to have > 97% amplitude contribution while other two longer lifetime components have small contributions. Small contributions from the nanosecond lifetime components possibly arise from apoprotein impurity or some small amount of disordered heme conformer of the protein. pH dependence of the fast picosecond lifetime components was found to show a systematic behavior which has been interpreted in the light of obligatory conformation change associated with activation of the enzyme at low pH.     

X-ray induced fluorescence spectrometry at grazing incidence for quantitative surface and layer analysis

Summary Single layers and layer systems on diverse substrates were measured by Total Reflection X-Ray Fluorescence (TXRF) spectrometry. The angular dependence of the fluorescence intensities at grazing incidence allows the elemental composition, density and thickness of the layers to be evaluated using model calculations.     

Theoretical and experimental investigation of the linear optical response of YBa2Cu4O8 The relevance of LDA calculations

We report results of ellipsometric measurements of the dielectric tensor of YBa₂Cu₄O₈ as well as calculations employing density functional theory in the local density approximation (LDA). For the computation of the one-electron eigenvalues and states the linear-muffin-tin-orbital method (LMTO) was used. Measured and calculated results show good agreement. In particular, the calculation predicts different band structures for YBa₂Cu₃O₇ and YBa₂Cu₄O₈ in the vicinity of the Fermi energy which lead to significant differences in the optical spectra. One such difference is a region of small ε₂ in the near infrared which is a fingerprint of the high (relative to the top of the highest fully occupied band) Fermi energy as compared to the situation in YBa₂Cu₃O₇. Our experimental results confirm the theoretical findings.     

Microwave reflection properties of grooved metallic mirrors

Maxwell's equations are solved using finite difference equations to obtain the near and the far field distribution of electromagnetic waves in front of corrugated mirrors. We treat the case of perpendicular incidence to obtain both the phaseshift between TE- and TM-modes in polarisation twisters and mode converters as well as the amplitude of the electromagnetic field.     

The kinetics of the (5 × 20) → (1 × 1) structural transition for Au(100)

The kinetics of the anion-induced (5 × 20) → (1 × 1) surface structural transition of reconstructed Au(100) electrodes was studied in sulfate-containing solutions by current transients. It is shown that lifting of the reconstruction follows a nucleation-and-growth type behavior which can be described by the Avrami equation. Moreover, for high positive potentials, i.e., high anion coverages, the current-transient analysis reveals instantaneous nucleation, whereas for low transition overpotentials and long transition times a mechanism with constant transition rate prevails. Apparent activation energies, which depend strongly on the electrode potential, are derived from the temperature dependence of the Avrami plots.     

Rb(62D)原子与基态Rb原子,H2分子碰撞转移截面

本文用荧光法测量Rb(6²D)原子与基态Rb原子,H₂分子碰撞转移截面。结果表明:Rb(6²D)-Rb(5²s)转移截面为σ_fs=67×10^-14cm²,σ_tr=4.3×10^-14cm²,Rb(6²D)—H₂转移截面为σ_fs 关键词：     

自由电子激光振荡器的二维数值模拟

在柱二维坐标系中,用数值计算方法求解了摇摆器内电子模拟方程组、光场方程组和无源区(不含摇摆器区)经非自适应方法变换后的无源旁轴波动方程并设计了相应的程序R_2D。用该程序计算的数值结果表明,在有源条件下二维数值模拟结果与高斯光束近似下的数值模拟结果符合较好;取完全相同的计算条件R-2D程序与洛斯阿拉莫斯实验室(LANL)的FELEX程序的计算结果符合较好;初步认为LANL实验数据的物理图象合理,数值结果基本可信;最后给出北京自由电子激光器(BFEL)的一些物理数据。     

腔靶等离子体辐射温度空间分布测量

本文描述了用膜吸收法测量激光等离子体辐射温度空间分布的原理和方法给出了柱形缝靶轴向辐射温度随空间位置变化的特征,对测量结果进行了分析讨论。