In-Situ and Real-Time Investigation of Columnar-to-Equiaxed Transition in Metallic Alloy

In this article, we present a review of observations during Al-3.5 wt pct Ni alloy solidi.cation experiments performed at the European Synchrotron Radiation Facility (ESRF) in Grenoble. These experiments provide direct access to dynamical phenomena during columnar growth (initial transient and breakdown of a planar solid-liquid interface), and for the first time to the transition from columnar-to-equiaxed microstructure (nucleation ahead of a columnar front and blocking of a columnar front by an equiaxed microstructure) and fully equiaxed growth (propagation of an effective front). Based on these experimental observations, critical parameters such as columnar growth velocity variation during the transition or equiaxed-grain diameter are measured and discussed. This article is based on a presentation made in the symposium entitled “Solidi.cation Modeling and Microstructure Formation: In Honor of Prof. John Hunt,” which occurred March 13–15, 2006, during the TMS Spring Meeting in San Antonio, Texas, under the auspices of the TMS Materials Processing and Manufacturing Division, Solidification Committee.     

The microscopy cell (MicCell), a versatile modular flowthrough system for cell biology, biomaterial research, and nanotechnology

We describe a novel microfluidic perfusion system for high-resolution microscopes. Its modular design allows pre-coating of the coverslip surface with reagents, biomolecules, or cells. A poly(dimethylsiloxane) (PDMS) layer is cast in a special molding station, using masters made by photolithography and dry etching of silicon or by photoresist patterning on glass or silicon. This channel system can be reused while the coverslip is exchanged between experiments. As normal fluidic connectors are used, the link to external, computer-programmable syringe pumps is standardized and various fluidic channel networks can be used in the same setup. The system can house hydrogel microvalves and microelectrodes close to the imaging area to control the influx of reaction partners. We present a range of applications, including single-molecule analysis by fluorescence correlation spectroscopy (FCS), manipulation of single molecules for nanostructuring by hydrodynamic flow fields or the action of motor proteins, generation of concentration gradients, trapping and stretching of live cells using optical fibers precisely mounted in the PDMS layer, and the integration of microelectrodes for actuation and sensing.     

Growth of GaAs on polycrystalline silicon-on-insulator

The growth of GaAs on polycrystalline silicon-on-insulator (SOI) substrates by metal organic vapor phase epitaxy using a two-step growth process was studied in this work. We have compared the variation of the growth temperature and the thickness of the initial GaAs epilayer in the structures grown on polycrystalline SOI to ones grown on SOI and epi-Si. Structural properties were studied using high-resolution X-ray diffraction (XRD). The growth temperature had a strong effect on the FWHM of the (0 0 4) XRD curve in structures grown on SOI and epi-Si. In the case of polycrystalline SOI the effect was not as strong. Optical properties of the samples in which the optically active layer consisted of self-organized In_0.5Ga_0.5As quantum dots were investigated by photoluminescence measurements. The photoluminescence intensity from structures grown on polycrystalline SOI was comparable to that from structures grown on SOI and epi-Si.     

Tunneling through Thin Oxides—New Insights from Microscopic Calculations

In this paper, we summarize our recent efforts to analyze transmission probabilities of extremely thin SiO₂ gate oxides using microscopic models of Si[100]-SiO₂-Si[100] heterojunctions. We predict energy-dependent tunneling masses and their influence on transmission coefficients, discuss tunneling probabilities and analyze effects arising from the violation of parallel momentum conservation. As an application of the present method, gate currents in short bulk MOSFETs are calculated, including elastic defect-assisted contributions.     

High-temperature,high-pressure thermophysical measurements on liquid zinc

Wire-shaped zinc samples were resistively volume heated as part of a fast-capacitor discharge circuit. Time-resolved measurements with submicrosecond resolution of the current through the specimen, the voltage drop across it, and the thermal expansion of the specimen as a function of time allow determination of the enthalpy, electrical resistivity, and density at different temperatures up to superheated liquid states of zinc far above the normal boiling point. High static pressures, up to 3800 bar of the ambient medium water, were used. An estimate of the critical pressure for zinc is given by investigations of the stability of the sample with a framing CCD camera, taking pictures of different samples varying the ambient static pressure. The critical volume and the critical temperature are obtained by means of an extrapolation of measured data at different pressures.Paper presented at the Fourth International Workshop on Subsecond Thermophysics, June 27–29, 1995, Köln, Germany.     

38. Generalversammlung von CENELEC

Ohne Zusammenfassung     

Ewald Hering und die Gegenfarbtheorie

Ewald Hering's color-opponent-theory is still considered one of the foundations of the visual sciences. Prior to Hering, Hermann v. Helmholtz introduced a theory of color appearance, which was based primarily on the physical aspects of the stimulus. In contrast to Helmholtz, Hering's theory strongly emphasized the subject's perception of color. As a consequence, Hering considered Helmholtz' theory inadequate. Contrary to some historical accounts, he did not object to Helmholtz's three-receptor explanation for color-mixture. Instead of Helmholtz' fundamental colors red, green, and blue, Hering suggested that the colors possess opponent character: blue-yellow; red-green; and, black-white. Helmholtz, on the other hand, refused to accept Hering's theory. Finally, a student with Helmholtz, Johannes v. Kries, developed the so-called “zone-theory”, which combines both, Young-Helmholtz's and Hering's theory at different stages of the visual information processing system.     

International collaboration: Will it be keeping alive East European research?

International scientific collaboration is very sensitive to political and economic changes in a country or a geopolitical region. Collaboration in research is reflected by the corresponding coauthorship of the published results which can be analysed with the help of bibliometric methods. Based on data from theScience Citation Index (SCI), the change of annual international coauthorship patterns ofBulgaria, Czechoslovakia, Hungary, Poland andRomania have been analysed for the periods 1981–1985 and 1984–1993, respectively. It is shown that international collaboration was not developing similarly in the countries under study. Whilst scientific communities of Hungary and Poland have already been opening in the early 80s, the international collaboration of the other East-European countries was still dominated by COMECON relations till 1989. As expected, since 1990 an increasing scientific collaboration with highly developed countries can be observed in all five countries. At the same time, scientific collaboration with the former communist countries shows a clear decline. The great share of international co-authorship links is some countries reflect various tendencies part of which are interpreted with the help of a cardiologic model.     

Assessment of Capillary Rise from Shallow Groundwater by the Simulation Model SIMWASER Using Either Estimated Pedotransfer Functions or Measured Hydraulic Parameters

The performance of the water balance and crop growth model SIMWASER to estimate the water supply of a lawn by capillary rise from shallow ground water was investigated by using lysimeter measurements with a sandy and a clayey soil. Moreover the robustness of the model was evaluated by running it either with measured hydraulic soil parameters or with estimated pedotransfer functions (PTFs) derived from texture and bulk density. Simulations were performed for the years 1996–1998 with input data from the lysimeter station Berlin-Dahlem (Germany) for lysimeters containing undisturbed sandy or clayey soil monoliths, with groundwater at 135 cm depth. Simulated evapotranspiration and percolation/capillary rise were in good agreement with the measured data for all variants, while simulated soil water storage was acceptable only for the variants using hydraulic soil data based on laboratory measurements or using PTFs derived from known soil class and bulk density. PTFs based on mean total pore volume of the respective soil classes yielded soil water storages which were evidently too high; therefore they should be used with care and must be avoided at all in simulating the soil water balance of arid sites with shallow groundwater.     

Scaled model measurements of embedding impedances for SIS waveguide mixers

Several scaled models have been used to determine the contributions of various waveguide mount parameters to the embedding impedance of a mm-wave SIS mixer. Measured effects of waveguide height, substrate orientation and width, junction location, lead inductance and RF-filter impedance are presented and discussed.