用恒电流法研究Fe(Ⅲ)EDTA对银的氧化过程

本文采用银旋转圆盘电极,在氟离子、溴离子、碘离子以及其他照相辅加剂存在下对Fe(Ⅲ)EDTA氧化金属银的过程进行了研究,以恒电流法做为检测手段,初步探讨了Fe(Ⅲ)EDTA络合物对金属银漂白过程机理。实验揭示了各种卤离子在Fe(Ⅲ)EDTA对银的氧化过程中的行为。pH和Fe(Ⅲ)EDTA浓度对该氧化还原反应的影响,以及某些含有巯基的化合物对Fe(Ⅲ)EDTA氧化反应的加速作用机理。     

Convergence rates for the coupling of FEM and collocation BEM

We prove convergence of the coupling of finite and boundaryelements where Galerkin's methd is used for finite elementsand collocation for boundary elements. We consider linear ellipticboundary value problems in two dimensions, in particular problemsin elasticity. The mesh width k of the boundary elements andthe mesh width h of the finite elements are required to satisfykßh with suitable ß. Asymptotic error estimatesin the energy norm and in the L²-norm are derived. Numericalexamples are included.     

MECHANISTIC STUDIES OF THE PHOTOREACTION OF FLAVIN WITH N, N-DIMETHYLPROPARGYLAMINE

Abstract Both photoexcited free flavin and protein-bound flavin react with N, N-dimethylpropargyla-mine (DMPA) to yield dihydroflavin-adducts which are not reoxidizable by oxygen. The mechanism of the photoreaction was reinvestigated by flash photolysis and continuous illumination experiments. We suggest that a mechanism occurs in which a flavosemiquinone and a DMPA radical result in the first photoinduced reaction. The flavin-DMPA adducts are then formed by combinations of the two radicals.     

漂白过程的电化学研究——Ⅰ、Fe(Ⅲ)EDTA氧化金属银的反应动力学

在卤离子存在下,Fe(Ⅲ)络合物与金属银之间的氧化还原反应,可用氧化形成的卤化银的电化学还原时间τ进行测定。本工作用银旋转圆盘电极研究了在改变氧化时间,反应物浓度和电极旋转速度的情况下,Fe(Ⅲ)络合物与金属银之间反应动力学,并测定了形成溴化银的初始速率与pH的关系。 该氧化还原反应是扩散控制反应,对于Fe(Ⅲ)EDTA和卤离子来说均为一级反应。Fe(Ⅲ)EDTA在水溶液中的扩散系数可由极限电流与Fe(Ⅲ)EDTA的浓度和银旋转圆盘电极的旋转速度的平方根之间的关系求算出来。     

DOSE RESPONSE BEHAVIOUR FOR POLAROTROPISM OF THE CHLORONEMA OF THE FERN DRYOPTERIS FILIX-MAS (L.) SCHOTT

Abstract— The dose response behaviour for polarotropism of the chloronema of the fern Dryopteris filix-mas was studied in detail. By varying the two factors, time and intensity, dose response curves were obtained, which consisted of as many as two maxima and minima or no maxima and minima at all. Furthermore, the effects of red light and dark, given before polarotropic induction, were compared, and the influence of temperature on the dose response behaviour was examined. There are two main results: (1) Under all conditions tested, the dose response behaviour in far-red, red, blue, and near U.V. apparently is the same. (2) In this one system, the chloronema of Dryopteris , all types of dose response curves, which have been described previously for tropic responses mediated by light, could be obtained simply by varying the conditions. The variable and complex dose response behaviour is discussed in connection with other photoresponses in lower and higher plants.     

非晶Nd-Fe薄膜的磁性

在用闪蒸法制备的非晶Nd_xFe_1-x薄膜中Nd的原子磁矩呈散铁磁性排列,其有效磁矩随Nd含量增加而减小。磁有序温度T_c的值与外场和测量方法有关,表明了具有不同磁有序温度的磁性原子团的存在。交换交互作用,而不是自发磁化强度,明显地受制备条件的影响。 关键词：     

On Sparse Solvers in a Stiff Integrator of Extrapolation Type

We consider the use of software for the direct solution of sparselinear equations within a stiff integration package which usesextrapolation techniques. We discuss the effect of varying thefrequency of matrix decompositions and of altering the pivotingstrategy. We compare the use of two sparse matrix packages,NSPFAC (Sherman, 1978) and MA28 (Duff, 1977), within the chemicalkinetics package LARKIN (Deuflhard et al., 1983).     

31P and 13C chemical shielding tensors in the phosphoenolpyruvate moiety from rotary resonance recoupling 13C and 31P MAS and single crystal 31P NMR

A ³¹P and ¹³C NMR study of powder and single crystal samples of two phosphoenolpyruvate (PEP) compounds, the tris-ammonium salt monohydrate (NH₄)₃(PEP)·H₂O (1), and the mono-ammonium-salt (NH₄)(H₂PEP) (2) is presented. The P chemical shielding tensors in 1 are measured by ³¹P single crystal NMR on four minuscule samples and assigned without ambiguity by exploiting the orientation-dependent ³¹P-³¹p dipolar splittings of the resonance lines. The orientation of the ³¹P chemical shielding tensor is discussed in terms of the C_2v — and C₃-type distortions of the phosphate PO₄-coordination sphere. From ¹³C MAS NMR experiments with ³¹P rotary resonance recoupling on polycrystalline powder samples the orientations of the ³¹P chemical shielding tensors in 1 and 2 are obtained, for 1 in very good agreement with the ³¹P single crystal NMR results. Only some of the orientational parameters of the three ¹³C chemical shielding tensors in the PEP moiety of 1 could be derived from ¹³C MAS NMR experiments with ³¹P rotary resonance recoupling.     

Electric and magnetic properties of hexaethynylbenzene

Coupled Hartree—Fock theory is used to compute the magnetizability and nuclear shielding tensors of hexaethynylbenzene (HEB), and to map the electron current density induced by an external magnetic field. The electric quadrupole moment and polarizability are also computed, and compared with those of benzene and ethyne. The calculations of magnetic properties demonstrate the clear superiority of distributed-origin methods over the conventional common-origin method in which a single fixed origin of vector potential is used. It is shown that the CTOCD-PZ2 formulation provides an efficient and accurate method for the magnetic properties. The current-density maps of HEB show the characteristic π ring current associated with the delocalization of π electrons around the central ring of carbons and local circulations in the ethynyl groups. There is no evidence of a significant induced current linking the ethynyl groups, either through space or through bond. The experimental shielding constants of HEB are well reproduced by the CTOCD-PZ2 calculations, and an analysis of the computed shielding tensors is used to provide a detailed interpretation of the NMR spectrum.