Determination of sheath parameters by test particles upon local electrode bias and plasma switching

Equilibrating gravitation by electric forces, microparticles can be confined in the plasma sheath above suitably biased local electrodes. Their position depends on the detailed structure of the plasma sheath and on the charge that the particles acquire in the surrounding plasma, that is by the electron and ion currents towards it. Bias switching experiments reveal how the charge and equilibrium position of the microparticle change upon altered sheath conditions. Above a critical bias, the particle is subject to an additional downward acceleration that cannot be explained solely by gravity and ion drag. This acceleration can be attributed to a positive charging of the particle induced by extreme out-of-equilibrium conditions of the plasma sheath in its surroundings: locally the plasma sheath can be completely deprived of electrons by means of the bias. We observe similar particle behaviors also in the afterglow of the discharge for a persisting bias voltage on the electrode: damped oscillation into a new equilibrium or (accelerated) fall according to the bias. The observed particle dynamics in locally tailored plasma sheath environments directly monitors changes in electric field structures and plasma density profiles.     

Alkylation studies on 6-ethyl-2,3-dihydrothiazolo-[3,2-A] pyrimidine-5,7-diones

The title compound 7b undergoes alkylation with ethyl iodide or ethyl sulfate at the 7-position yielding the O-ethylated product 10 rather than 6,6-diethyl product 8 as reported previously. Reaction of 7b with mesyl chloride gives 13b which on reaction with potassium carbonate in absolute ethanol also gives 10. Treatment of 7b with phosphorus oxychloride gives 11b which on reaction with potassium carbonate or sodium ethoxide in ethanol produced a mixture from which no 10 was isolated. Authentic 8 was prepared by the reaction of 2-amino-thiazoline with ethyl diethylmalonyl chloride (20) in THF containing triethylamine or by the reaction of 5,5-diethyl-2-thiouracil (18) with excess 1,2-dibromoethane.     

Generalized ellipsometry for biaxial absorbing materials: determination of crystal orientation and optical constants of Sb(2)S(3)

We demonstrate generalized ellipsometry for precise measurement of the principal indices of refraction, the extinction coefficients, and the orientations of the crystal a, b, and c axes of orthorhombic absorbing materials. Stibnite (Sb(2)S(3)) single crystals cut approximately parallel to (100), (010), (001), and (313) are studied at a representative wavelength of 589 nm. The (313) surface is sufficient for retrieval of all optical constants. The expected effects of surface over-layer formation are removed numerically. We propose generalized ellipsometry as a powerful tool for measurement of anisotropic optical function spectra of biaxial materials.     

Determination of electron temperature in low pressure gas discharges by resonant laser light scattering

It is shown that the electron temperature in low pressure discharges can be estimated from the drift velocity of the ions towards the wall. Velocity measurements by resonant laser light scattering lead to electron temperatures consistent with such values obtained by probe measurements.     

A covariant representation of the Ball–Chiu vertex

In nonabelian gauge theory the three-gluon vertex function contains important structural information, in particular on infrared divergences, and is also an essential ingredient in the Schwinger–Dyson equations. Much effort has gone into analyzing its general structure, and at the one-loop level also a number of explicit computations have been done, using various approaches. Here we use the string-inspired formalism to unify the calculations of the scalar, spinor and gluon loop contributions to the one-loop vertex, leading to an extremely compact representation in all cases. The vertex is computed fully off-shell and in dimensionally continued form, so that it can be used as a building block for higher-loop calculations. We find that the Bern–Kosower loop replacement rules, originally derived for the on-shell case, hold off-shell as well. We explain the relation of the structure of this representation to the low-energy effective action, and establish the precise connection with the standard Ball–Chiu decomposition of the vertex. This allows us also to predict that the vanishing of the completely antisymmetric coefficient function S   of this decomposition is not a one-loop accident, but persists at higher-loop orders. The sum rule found by Binger and Brodsky, which leads to the vanishing of the one-loop vertex in N=4$N=4$ SYM theory, in the present approach relates to worldline supersymmetry.     

IR-device Grade (Hg,Cd)Te Crystals Grown by a Modified Bridgman Method

Electrical and photoelectrical properties of IR-devices manufactured on (Hg, Cd)Te-wafers cut from single crystals grown by modified Bridgman method are reported and compared to those of devices made on THM-(Hg, Cd)Te. MIS-structures and photodiodes were used in order to investigate the different materials. The influence of material parameters and device technology respectively is involved in our discussion of device properties. The quality of modified Bridgman-(Hg, Cd)Te was found to be comparable to that of the THM-(Hg, Cd)Te. At T = 80 K and FOV = 60° background limited detectivity of photodiodes with a cut-off wavelength of λ_co = 10.7 μm was achieved.     

Micelle and Vesicle Formation of Amphiphilic Nanoparticles

Nanoparticle brushes : Complex nanostructures can be formed by self assembly of amphiphilic CdSe/CdS core–shell nanoparticles that bear a brushlike layer of poly(ethylene oxide) chains. This route is based on controlling the volume fractions of hydrophilic and hydrophobic moieties within the particles and allows the formation of micellar, cylindrical, or vesicular nanoobjects (see picture).

     

Vortex motion in high-Tc films and a micropattern-induced phase transition

A micropattern-induced transition in the mechanism of vortex motion and vortex mobility is observed in high-T_c thin films. The competition between the anomalous Hall effect and the guidance of vortices by rows of microholes (antidots) lead to a sudden change in the direction of vortex motion that is accompanied by a change in the critical current density and microwave losses. The latter effect demonstrates the difference in vortex mobility in different phases of vortex motion in between and within the rows of antidots.     

Concepts and realization of microstructure heat exchangers for enhanced heat transfer

Microstructure heat exchangers have unique properties that make them useful for numerous scientific and industrial applications. The power transferred per unit volume is mainly a function of the distance between heat source and heat sink—the smaller this distance, the better the heat transfer. Another parameter governing for the heat transfer is the lateral characteristic dimension of the heat transfer structure; in the case of microchannels, this is the hydraulic diameter. Decreasing this characteristic dimension into the range of several 10s of micrometers leads to very high values for the heat transfer rate.

Another possible way of increasing the heat transfer rate of a heat exchanger is changing the flow regime. Microchannel devices usually operate within the laminar flow regime. By changing from microchannels to three dimensional structures, or to planar geometries with microcolumn arrays, a significant increase of the heat transfer rate can be achieved.

Microheat exchangers in the form of both microchannel devices (with different hydraulic diameters) and microcolumn array devices (with different microcolumn layouts) are presented and compared. Electrically heated microchannel devices are presented, and industrial applications are briefly described.