A study of kinetic molecular exchange processes in the medium frequency range by surface SHG on an oscillating bubble

The dilatational properties of fluid surfaces and interfaces have been comprehensively investigated in recent years. For example, an improved oscillating bubble device provided experimental results that allow for critical testing of established surface models, such as the Lucassen/van den Tempel (LvdT) model. The comparison of the LvdT model with the oscillating bubble experiments demonstrates a mismatch between the model parameters. For example, near the CMC or the limit of solubility the calculated parameters of surfactant solutions become unrealistically large. The deviation can be explained by the introduction of more detailed surface models, in particular by the modification of the effective thickness of the surface layer, its internal structure and the molecular exchange processes between these structures. For the verification of such processes an experimental setup was realized which allows for an independent determination of the instantaneous adsorption state at the surface of an oscillating bubble inside a surfactant solution. The setup utilizes the Second Harmonic Generation (SHG)--effect at the air-solution interface generated by the light of a pulsed LASER. The set-up is described in detail, and the results of a first experimental series are presented and discussed in this paper. As system, aqueous solutions of the fluortenside F381 were used.     

Distributionen mit Werten in Topologischen Vektorräumen II

The research of [3] is continued. After some preparations on topological tensor products of algebras and modules, including a theorem for continuous bilinear operations on spaces of vector-valued distributions (cf. L. Schwartz [13]), we define the convolution for elements ofE(B) = L,(E(^N),B), where B denotes a complete locally pseudoconvex algebra with continuous multiplication. A Paley-Wiener-Schwartz theorem on the Fourier-Laplace transform (FLT) of vector-distributions enables us to reduce the convolution to a pointwise product of B-valued entire functions and to derive some properties of the convolution algebra (B), *).Those elements of a complete m-convex algebra, for which the analytic functional calculus can be continued to (E(B),*), are characterized by use of the FLT. In the last section, we look at representations of distributions in or with values in a complete topological vector space E by means of analytic E-valued functions.

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Während der Fertigstellung eines Teils dieser Arbeit Research Associate der University of Maryland, College Park, Md. 20742, USA.     

Über eine Störung bei Trennungen durch Verteilung zwischen zwei Flüssigkeiten

The diminution of the percentage extraction of metal complexes at extremely low concentrations is investigated for 4 different systems. In every case this effect is caused by incomplete formation of the extracted complex.     

Beitrag zur Multi-Elementanreicherung aus reinem Cadmium

Zusammenfassung Zur Analyse von Fein-Cadmium (99,99% Cd) werden Spurenverunreinigungen wie Ag, Bi, Cr, Cu, Fe, Ni und Pb an einem Mischkollektor aus CdS, MnO₂ und -Benzildioxim angereichert. Das Spurenkonzentrat wird nach Auflösen in Säure durch Flammen-Atomabsorptions-Spektrometrie (Injektionstechnik) analysiert. Es werden relative Standardabweichungen um 5% erzielt; die Nachweisgrenzen (3) liegen — je nach Element — zwischen 0, 1 und 2 g/g.Herrn Prof. Dr. Fritz Umland zum 60. Geburtstag gewidmet.     

Temperature dependence of upper critical fields for clean superconductors of the second kind. II

A numerical mistake made in a previous paper is corrected. For specular reflexion of electrons by the surface the result now agrees with a result obtained earlier byEbneth andTewordt. In order to facilitate a comparison with experimental data the calculation of the ratioH _c3(T)H_c2(T) is extended up to terms linear (T _c ?T)/T _c for arbitrary reflexion kernels.     

Temperature-dependent Fe Mössbauer spectroscopy and local structure of the mullite-type Bi2(FexGa1−x)4O9 (0.1≤x≤1) solid solution

The Bi₂(Fe_xGa_1−x)₄O₉ oxide solid solution possessing a mullite-type structure has been investigated by ⁵⁷Fe Mössbauer spectroscopy in dependence of composition (0.1≤x≤1) and temperature (293≤T/K≤1073). The spectra have been fitted with two doublets for tetrahedrally and octahedrally coordinated high-spin Fe³⁺ ions, respectively. The experimental areas of the subspectra were used to determine the distribution of iron on the two inequivalent structural sites. The fraction of iron cations occupying the octahedral site is found to increase with decreasing Fe content and the cation distribution is almost independent of temperature. The unusual temperature dependence of the quadrupolar splitting, QS, observed for the octahedral site with dQS/dT>0 is discussed in connexion with structural data for Bi₂Fe₄O₉. The temperature dependence of Mössbauer isomer shifts and signal intensities is examined in the context of local vibrational properties of iron on the two inequivalent sites of the mullite-type lattice structure.     

Defect chemistry, redox kinetics, and chemical diffusion of lithium deficient lithium niobate

High-temperature optical in situ spectroscopy was used to investigate the defect absorption, redox kinetics, and chemical diffusion of a lithium deficient (48.4 mol% Li(2)O) congruent melting lithium niobate single crystal (c-LN). Under reducing atmospheres of various oxygen activities, a(O(2)), UV-Vis-NIR spectra measured at 1000 °C are dominated by an absorption band due to free small polarons centered at about 0.93 eV. The polaron band intensity was found to follow a power law of the form a(O(2))(m) with m = -1/4. A chemical reduction model involving electrons localized on niobium ions on regular lattice sites can explain the observed defect absorption and its dependence on oxygen activity. The kinetics of reduction and oxidation processes upon oxygen activity jumps and the associated chemical diffusion coefficients are found in close agreement over a range from -0.70 to -14.70 in log a(O(2)), indicating a reversible redox process. Assuming coupled fluxes of lithium vacancies and free small polarons for the attainment of stoichiometry, the diffusion coefficients of lithium vacancies as well as of lithium ions in the lithium deficient c-LN have been determined at 1000 °C.     

Scission of C-C σ-bonds via electron transfer processes

Certain hydrocarbons, preferrable strained ones, can be cleaved via electron transfer processes whereby lithium dust or lithium 4,4′-di-tert-butylbiphenylide (LiDBB) have been used as electron transfer reagents. For the scission of a C-C σ-bond the presence of a π-system in the neighborhood (α or β) is an absolute prerequisite.