A study of a coadsorbate surface diffusion (Pb on C/W)

The influence of a coadsorbed submonolayer (carbon) on the diffusion of adatoms (lead) along a crystal surface (tungsten) is studied in a preliminary manner by a field electron microscope technique. Experiments show that the surface diffusion of lead is strongly affected by the coadsorption of carbon: (1) The diffusion of Pb which is easy around (110) and (111) and difficult around (100) on clean tungsten becomes easier around (100) than around (110) and (111). (2) The diffusion anisotropy on the stepped surface around (100) is changed by carbon adsorption. (3) C adatoms enhance the diffusion of Pb especially around (100). (4) The mean carbon coverage required to observe these effects is only a few hundredths of a monolayer. The dependence of the surface diffusion on such small impurity coverages is discussed.     

Decision Trees and the Second Law

Every system, left unto itself, tends towards disorder. Disorder frequently appears in the form of queues-machines, materials or customers waiting for service or waiting to be served. This article suggests a method of measuring disorder, and shows how this may be used in the analysis of complex decision type of systems.     

Laserspektroskopie

X-Ray spectra and chemical binding     

U(4) spin gauge theory over a Riemann-Cartan space-time

A spin gauge theory based on the groupU(4) is investigated in a general relativistic context including the possibility of nonzero torsion. The language of Clifford bundles over a space-time with metric and metric compatible torsion is used as a convenient tool for the study of fields defined on space-time possessing Clifford multiplication properties. A Dirac-type representation is investigated in detail and the geometric implications for spin gauge theory are pointed out.     

Eine Temperaturabhängigkeit der Feldelektronenemission bei sehr geringen Stromdichten

Low current density field electron emission between 1 and 10^?6 A/cm² was measured for clean tungsten as a function of temperature between 300 and 1350° K. A strong increase in temperature dependence was found with decreasing current density. Measurements are interpreted according to calculations ofMurphy, Good andMüller. Agreement is better if the work function temperature dependence is also considered.     

Efficient preparation of nitrosoarenes for the synthesis of azobenzenes

[reaction: see text] Reaction conditions are described for the oxidation of anilines furnishing nitrosoarenes and the synthesis of unsymmetrically substituted azobenzenes. In a comparative study, the catalytic oxidation of methyl 4-aminobenzoate by hydrogen peroxide was investigated, and SeO(2) proved to be superior or equal to methyl trioxorhenium (MTO) and Na(2)WO(4), respectively. Nevertheless, the application of the inexpensive, environmentally friendly, Oxone in a biphasic system proved to be more efficient, and a variety of useful nitrosoarenes for the synthesis of azo compounds were prepared in high yield and purity on a large scale.     

Crystallization behavior of supercooled smectic cholesteryl myristate nanoparticles containing phospholipids as stabilizers

Supercooled smectic nanoparticles based on physiological cholesterol esters are under investigation as a potential novel carrier system for lipophilic drugs. The present study investigates the very complex crystallization behavior of such nanoparticles stabilized with the aid of phospholipids. Phospholipid and phospholipid/bile salt stabilized cholesteryl myristate dispersions were prepared by high-pressure melt homogenization and characterized by particle size measurements, differential scanning calorimetry, X-ray diffraction and electron microscopy. To obtain fractions with very small smectic nanoparticles, selected dispersions were ultracentrifuged. A mixture of cholesteryl myristate and the phospholipid used for the stabilization of the dispersions was also investigated by light microscopy. The nanoparticles usually display a bimodal crystallization event which depends on the thermal treatment and cannot be attributed to crystalline polymorphism. The ratio of the particle fractions crystallizing in the two successive steps strongly depends on the particle size of the dispersions. The presence of larger particles leads to an increased fraction crystallizing at higher temperature and a higher recrystallization tendency upon storage. The observed peculiarities of the crystallization behavior seem to be mainly caused by the presence of particles with different shapes (cylindrical and spherical) as observed in electron microscopy. Alterations in the composition of the nanoparticles may also play a role.