ISSN:0005-9021    

DOI:10.1002/bbpc.198800136

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1988

数据来源: WILEY

摘要:

AbstractThe photocapacitance (PC) technique allows the determination of deep‐level as well as surface states at semiconductor/electrolyte (SC/EL) contacts. Expressions of the PC signal, given in several peculiar cases, help in the understanding of the results obtained with GaAs in contact with an aqueous electrolyte. It is found that relevant experimental conditions of band bending and/or incident photon flux are required to detect transitions which have a small magnitude compared to the large response due to EL2 in GaAs. A quantitative interpretation of the spectrum is also give

ISSN:0005-9021    

DOI:10.1002/bbpc.198800137

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1988

数据来源: WILEY

摘要:

AbstractThe growth and dissolution of oxide layers on silicon has been studied under illumination and in the dark by analyzing current transients at different voltages in solutions of NH4F of various concentrations at pH values between 1 and 4.5. When the oxidation rate of the silicon at high enough anodic bias and, for n‐type specimens, high enough illumination intensity exceeds the rate of oxide dissolution in the fluoride, the film grows until it has reached a thickness where the dissolution is rate‐determining for the net process. At higher voltages the current begins to oscillate. The data give some insight into the composition of the oxide layers and their electronic and ionic propert

ISSN:0005-9021    

DOI:10.1002/bbpc.198800138

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1988

数据来源: WILEY

摘要:

AbstractMembrane transport processes involving diffusion and migration of redox‐ions are analyzed. Two‐electron redox‐systems of the type A+/B3+are considered. At equilibrium the transference number of the electroactive species in the membrane is assumed to be unity. At timet= 0 a potential step is applied to the coated electrode which leads to zero surface concentration of the electroactive species. Time‐dependent electric field, potential and concentration profiles of A and B across the coating are derived from the Nernst‐Planck and continuity equations with a digital simulation technique. The resulting current transients are shown to follow Cottrell's law, however, the observed “effective” diffusion coefficients differ significantly from the diffusion coefficients of the reacting redox ions. — By comparing values of the potential drop across the membrane with the corresponding currents, “effective membrane resistance,RM” values are derived.RMis shown to differ significantly between the forward and back reactions, and it is time dependent. This has important consequences for accurate analyses of cur

ISSN:0005-9021    

DOI:10.1002/bbpc.198800139

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1988

数据来源: WILEY

摘要:

AbstractThe behavior of three sialoglycolipids of different polarity (the gangliosides GM1, GD1a, GT1b) have been investigated at the Hg/electrolyte interface by means of ac polarography. In solution the gangliosides exist as micelles. We have determined the dependence of the differential capacity of the electrical double layer on the potential difference across this layer and on pH, temperature and addition of bivalent cations (Ca2+, Mg+). The structure of the double layer varies at different electrode potentials. At anodic potentials specific adsorption of ganglioside clusters with the charged head groups towards the electrode is observed. At about +0.2 V (NHE) a rearrangement, reversion of the molecules and strong adsorption of their nonpolar hydrocarbon chains between +0.1 V and −0.7 V is observed. At the stationary electrode (HMDE) at a potential of about −0.8 V condensation of the clusters to a monolayer is inferred which is destroyed at about −1.2 V, probably with desorption of the gangliosides from the electrode. Ca2+ions induce increased stability of the monolayer at the electrode, a specific Ca2+‐effect is verified by comparison with Mg2+. The relevance of these findings for biological membranes is di

ISSN:0005-9021    

DOI:10.1002/bbpc.198800140

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1988

数据来源: WILEY

摘要:

AbstractFor an AO — BO interdiffusion process a formal analysis is given. The conceptual difficulties in using either structural elements, building units or components in the framework of irreversible thermodynamics are discussed. The matrix of transport coefficients of a n‐component system is evaluated and is transformed into a matrix of diffusivities. The interdiffusion problem has been solved numerically, starting with a set of two coupled diffusion equations. Point defect relaxation during interdiffusion has been taken into account through a quasi‐homogeneous point defect relaxation term. The calculated supersaturation and undersaturation of point defects result in concentration profiles which cannot be normalized with √t. Experiments with the diffusion couple FeO — MnO demonstrate the theoretically predicted behavior and the influence of the cation vacancy relaxation at the sample surface on the concentration

ISSN:0005-9021    

DOI:10.1002/bbpc.198800141

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1988

数据来源: WILEY

摘要:

AbstractHydrostatic pressure in the range from 1 to 3400 bar induces the transition phenomenon in diluted solutions of polydiacetylenes. With respect to the influence of pressure on the absorption bands, the transition was studied by UV spectroscopy. The transition is shown to depend strongly on the hydrogen bonds between the sidegroups. In the case of P‐DDD which is free of H‐bonds, the temperature and pressure effect on the transition is first‐order‐like in that temperature range where no precipitation occurs. Transient processes, except those involving precipitated particles, occur below the experimental time scale of minutes. In P‐4BCMU, a polydiacetylene with H‐bonds between the sidegroups, the pressure‐induced isothermal transient phenomena are slowed down, and exhibit a nonexponential time law. The transition shows a hysteresis in temperature in such a way that the heating branch of the hysteresis loop is remarkably shifted by pressure to higher temperatures whilst the cooling branch remains nearly unshifted. Hydrostatic pressure is shown to give additional information concerning the molecular origin of the transiti

ISSN:0005-9021    

DOI:10.1002/bbpc.198800142

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1988

数据来源: WILEY

摘要:

AbstractThe excess molar Gibbs free energyGEhas been determined by mass spectrometric techniques for the solid phase of the system RbReO4— CsReO4at 790 K. The liquidus curve of theT—xphase diagram has been determined by thermal analysis. The solidus and the difference between the excess molar Gibbs free energies of the liquid and the solid phases have been calcula

ISSN:0005-9021    

DOI:10.1002/bbpc.198800143

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1988

数据来源: WILEY

摘要:

AbstractThe magnetic susceptibility χ and the1H‐Knight shiftKHof the b.c.c. system Ta1−xTixHy, (0 ≤x≤ 0.3, 0

ISSN:0005-9021    

DOI:10.1002/bbpc.198800144

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1988

数据来源: WILEY

摘要:

AbstractBetween 1 MHz and 40 GHz the complex (electric) permittivity of aqueous solutions of purine and 6‐methylpurine has been measured as a function of frequency for various solute concentrations. Different relaxation spectral functions are fitted to the measured spectra to yield the solvent contribution to the static permittivity, the dipole moment of solute, the principal dielectric relaxation time of the solvent water, the number of hydration water molecules per molecule of solute, the hydration water relaxation time, and the relaxation time of solute. Unexspectedly, no effect of self‐association of the purine bases is found in these paramet

ISSN:0005-9021    

DOI:10.1002/bbpc.198800145

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1988

数据来源: WILEY