Atomic-Scale Structure and Chemistry of Segregation at Matrix/Precipitate Heterophase Interfaces

We study experimentally the local chemistry and atomic structure of heterophase interfaces on an atomic scale. In this work, the heterophase precipitate/matrix interfaces of small molybdenum nitride precipitates in an -iron matrix are investigated on a subnanometer scale by 1-dimensional atom-probe field-ion microscopy (1D-APFIM) and 3-dimensional atom-probe microscopy (3DAPM). Molybdenum nitride precipitates are generated by annealing Fe- 2 at.% Mo- X, where X = 0.4 at.% Sb or 0.5 at.% Sn, at 550°C, in an ammonia/hydrogen atmosphere. Internal nitridation at this temperature produces thin, coherent platelet-shaped molybdenum nitride precipitates. 1D-APFIM selected area analyses are efficient in determining the composition of the precipitates and it is found that a possible Sn or Sb segregation at coherent matrix/precipitate interfaces is either nonexistent or below the detection limit of 1D-APFIM. 3DAPM analyses, however, provide significantly better counting statistics and detect a small, but significant segregation of Sb at the matrix/precipitate interface with a Gibbsian interfacial excess of 0.30 ± 0.15 nm^–2. This is in distinct contrast to the segregation behavior of Sn or Sb at the interfaces of semicoherent coarse precipitates produced by internal nitridation at 600°C, for which much larger Gibbsian interfacial excesses of Sn or Sb, up to 7 ± 3 nm^–2, have been measured. In contrast, the thin platelets are either coherent or have significantly fewer misfit dislocations than is geometrically necessary for a full compensation of the lattice parameter misfit between precipitate and matrix. This demonstrates that Sn or Sb segregation with an appreciable Gibbsian interfacial excess is related to the presence of misfit dislocations at the interfaces of the coarse precipitates.     

A direct method for modifying certain phase-integral approximations of arbitrary order

The approximate solution of the differential equation $\text{d}{}^2\text{ψ}\text{dz}{}^2\text{+ Q}{}^2\text{(z)ψ = 0}$ by a general modification of certain phase-integral approximations of arbitrary order is considered. A consistent modification of these higher-order phase-integral approximations is derived on the assumption that one has found a function Q_mod²(z) which makes the modified first-order approximation good at certain singular points of Q²(z), where the unmodified approximation would break down.     

On the design of Dammann gratings

In recent years the design of Dammann gratings for the application as array illuminators has been widely discussed. Important progress has been made. However, some problems concerning the control of design algorithms remain to be solved. It is shown how design theory of diffractive elements can be used to avoid these difficulties and to formulate a straightforward design method to obtain Dammann gratings optimized in diffraction efficiency and uniformity.     

Doubly charged ions of bridged [4n] annulenes. An evaluation of diatropic ring current effects.

[4n]Annulenes are transformed into doubly charged ions (dianion, dication) and characterized NMR spectroscopically. The diatropic character of the ionic (4n+2)π-systems is studied as a function of the number of π-electrons.     

Solvent-dependent, kinetically controlled stereoselective synthesis of 3- and 4-thioglycosides

Facile approaches to prepare 3- and 4-thioglycosides of the galacto, gulo, and gluco type from the parent triflates are presented. The dependencies of the solvent and the protecting group pattern, as well as the configuration of the neighboring and leaving groups, have been studied for these reactions. The results clearly show that the efficient stereoselective synthesis of methyl 3-thio-galactoside depends highly on the solvent and the nucleophile concentration.     

Sugar separations on ion-exchange resins in mixture with celite

The Chromatographie separation of sugars in ethanol -water solutions by means of anion-excliange resins can be improved markedly by using extremely fine resin particles. To avoid an excessively high pressure drop in the column when crushed rosin particles are employed the resin can be used in mixture with Celite, Working at elevated température results in improved separations and a considerable saving of time.     

A physically important class of integrals expressed as a parameter derivative

The paper deals with a class of integrals, the integrands of which contain the square of a solution of a second-order linear, ordinary differential equation. Such integrals often arise in quantum mechanics as normalization integrals or expectation values. A generalized, unified procedure for rewriting such an integral, associated with a differential equation of the Sturm-Liouville type with unspecified boundary conditions, as a parameter derivative is presented. The formula thus obtained can be used for the evaluation of various integrals of physical interest. As an application we present a simplified derivation of a formula given by de Alfaro and Regge, in which the quantal normalization integral is expressed in terms of the Jost function. Other applications to integrals involving special functions and to integrals associated with the one-dimensional Schrödinger equation are also presented. Furthermore, it is explained why an approximate formula for expectation values is much more accurate than one can expect from the usual, crude derivation of it, and why certain attempts to improve that derivation have failed.     

Fluorimetric determinations by ion-pair extraction : Part V. Studies on ion-pair extraction with the fluorescent anion 9,10-dimethoxyanthracene-2-sulphonate

The fluorescent anion 9,10-dimethoxyanthracene-2-sulphonate has been studied in ion-pair extractions. Its ability to extract amines and quaternary ammonium compounds was investigated by fluorimetric determination of extraction and dissociation constants with methylene chloride as organic phase for two amines (amitriptyline and protriptyline) and two quaternary ammonium ions (tetrabutyl-and tetrapropylammonium). The optical properties of the anion and its ion pairs were characterized by quantum yield of fluorescence and a fluorescence sensitivity index. The determination of two of the ion pairs was studied, both after extraction to an organic phase and after a subsequent back-extraction of the anion component to an aqueous phase. Recoveries and standard deviations are given.     

Growth and production of buckwheat (Fagopyrum esculentum) treated with reduced, ambient, and enhanced UV-B radiation

The effect of enhanced UV-B radiation on buckwheat (Fagopyrum esculentum Moench. variety 'Darja'), an important high elevation crop, was studied in order to estimate its vulnerability in changing UV-B environment. Plants were grown in outdoor experiments from July to October under reduced and ambient UV-B levels, and an UV-B level simulating 17% ozone depletion in Ljubljana. During the development the following parameters were monitored: light saturated photosynthetic activity, transpiration, potential and effective photochemical efficiencies of photosystem II, the contents of photosynthetic pigments and methanol soluble UV-B absorbing compounds. At the end of the experiment, growth rate and production of seeds were estimated. In the following growth season the seeds collected from plants exposed to different UV-B treatments were tested for germination capacity. Total UV-B absorbing compounds during plant development were increased by UV-B radiation, photosynthetic pigments (chlorophyll a and b and carotenoids) decreased. Photosynthetic rate was lowered in an early stage of development. UV-B treatment resulted in the increase in the transpiration rate and consequently the decrease in water use efficiency (WUE). The disturbances in water economy and in photosynthesis affected the reproduction potential negatively; the production of seeds in plants cultivated under ambient and enhanced UV-B was 57 and 39% of the production of specimens treated with reduced UV-B, respectively. The germination of seeds collected from treated plants revealed on average about 95% success, independently of the treatment, but the time needed for germination was the shortest for seeds developed under enhanced UV-B level treatment. Enhanced UV-B radiation affected water relations and production of buckwheat, but not the potential of seeds for germination.