Resonanzerscheinungen in der Ausgangsleistung eines He-Ne-Lasers im axialen Magnetfeld

Zeitschrift für Physik A Hadrons and nuclei - The output power of a He-Ne-laser (λ=633 nm) has been measured as a function of the strength of an axial magnetic field. This function has...     

Finite-Size Scaling in the p-State Mean-Field Potts Glass: A Monte Carlo Investigation

The p-state mean-field Potts glass with bimodal bond distribution (±J) is studied by Monte Carlo simulations, both for p = 3 and p = 6 states, for system sizes from N = 5 to N = 120 spins, considering particularly the finite-size scaling behavior at the exactly known glass transition temperature T _c. It is shown that for p = 3 the moments q ^(k) of the spin-glass order parameter satisfy a simple scaling behavior, being the appropriate scaling function and T the temperature. Also the specific heat maxima have a similar behavior, , while moments of the magnetization scale as . The approach of the positions T _max of these specific heat maxima to T _c as N is nonmonotonic. For p = 6 the results are compatible with a first-order transition, q ^(k) (q _jump)^k as N but since the order parameter q _jump at T _c is rather small, a behavior q ^(k) N ^-k/3 as N also is compatible with the data. Thus no firm conclusions on the finite-size behavior of the order parameter can be drawn. The specific heat maxima c _V ^max behave qualitatively in the same way as for p = 3, consistent with the prediction that there is no latent heat. A speculative phenomenological discussion of finite-size scaling for such transitions is given. For small N (N 15 for p = 3, N 12 for p = 6) the Monte Carlo data are compared to exact partition function calculations, and excellent agreement is found. We also discuss ratios , for various quantities X, to test the possible lack of self-averaging at T _c.     

Multi-stage stochastic linear programs for portfolio optimization

The paper demonstrates how multi-period portfolio optimization problems can be efficiently solved as multi-stage stochastic linear programs. A scheme based on a blending of classical Benders decomposition techniques and a special technique, called importance sampling, is used to solve this general class of multi-stochastic linear programs. We discuss the case where stochastic parameters are dependent within a period as well as between periods. Initial computational results are presented.Research and reproduction of this report were partially supported by the Office of Naval Research Contract N00014-89-J-1659; the National Science Foundation Grants ECS-8906260, DMS-8913089, the Electric Power Research Institute Contract RP-8010-09, CSA-4O05335, and the Austrian Science Foundation, Fonds zur Förderung der wissenschaftlichen Forschung, Grant J0323-Phy. Any opinions, findings, and conclusions or recommendations expressed in this publication are those of the authors and do NOT necessarily reflect the views of the above sponsors. The comments of anonymous referees are gratefully acknowledged.     

Rhenium trichloride,ReCl3, and its 5/3-hydrate synthesis,crystal structure,and thermal expansion

Single crystals of ReCl₃ were grown by vacuum sublimation and the crystal structure (trigonal, R3 m, a = 1020.62(5), c = 2035.3(2) pm, V_m = 61.430(8) cm³mol^?1) was refined to R = 0.049, R_w = 0.031. From hydrochloric acid solutions of ReCl₃ containing me₄NCl, the hydrete ReCl₃ · 5/3 H₂O is salted out: hexagonal, P6 2_c, a = 944.89(3), c = 1470.07(9) pm, V_m = 114.09(1) cm³ mol^?1. The crystal structure (R = 0.079, R_w = 0.051) contains hexagonally closest-packed [Re₃Cl₉(H₂O)₃] molecules held loosely together by two molecules of crystal water positioned between the clusters in the [00.1] direction thereby forming chains that are shifted against each other by 1/2c. Thermal expansion of ReCl₃, ReCl₃. 5/3 H₂O and RbReCl₄ has been recorded and is discussed in connection with the crystal structures.     

Hydrogen bonding of water confined in mesoporous silica MCM-41 and SBA-15 studied by 1H solid-state NMR

The adsorption of water in two mesoporous silica materials with cylindrical pores of uniform diameter, MCM-41 and SBA-15, was studied by 1H MAS (MAS=magic angle spinning) and static solid-state NMR spectroscopy. All observed hydrogen atoms are either surface -SiOH groups or hydrogen-bonded water molecules. Unlike MCM-41, some strongly bound water molecules exist at the inner surfaces of SBA-15 that are assigned to surface defects. At higher filling levels, a further difference between MCM-41 and SBA-15 is observed. Water molecules in MCM-41 exhibit a bimodal line distribution of chemical shifts, with one peak at the position of inner-bulk water, and the second peak at the position of water molecules in fast exchange with surface -SiOH groups. In SBA-15, a single line is observed that shifts continuously as the pore filling is increased. This result is attributed to a different pore-filling mechanism for the two silica materials. In MCM-41, due to its small pore diameter (3.3 nm), pore filling by pore condensation (axial-pore-filling mode) occurs at a low relative pressure, corresponding roughly to a single adsorbed monolayer. For SBA-15, owing to its larger pore diameter (8 nm), a gradual increase in the thickness of the adsorbed layer (radial-pore-filling mode) prevails until pore condensation takes place at a higher level of pore filling.     

Fluorescence monitoring of immobilzed microorganisms in cultures

An experimental reactor system for monitoring the fluorescence of suspended and immobilized cells is described. The growth of S. cerevisiae was monitored during batch fermentations by fluorescence of the culture. Thus, it was possible to use this intracellular parameter to study the influence of immobilization on cells. The fermentations were done under aerobic conditions with suspended and immobilized cells. A comparison of these two systems showed that the rate of ethanol consumption was significantly slower for the cells immobilized in calcium alginate. This reduced rate of oxidative decomposition may be due to mass-transfer limitations of oxygen. Pulse experiments with different substrates (glucose and ethanol) were made to monitor the changes in cell metabolism. The reactor system presented is also suitable as a “toxin guard system”, because substances toxic to cells, such as 2,4-dinitrophenol, cause clearly visible changes in the fluorescence of the immobilized cells.     

Modeling laboratory data from clinical trials

Laboratory data from clinical trials are considered precursors of potential organ dysfunctions. The routine analysis of these data focusses on the occurrence of extremely high or low values relative to normal ranges, the change of these incidences compared to baseline, or the worst values from each individual patient. However, only rarely is an attempt made to model the dynamics of the measurements over time. In this paper we propose to model laboratory measurements by stochastic processes, specifically by Ornstein-Uhlenbeck processes. The aim is to estimate parameters of these processes in order to characterize a potential effect of drugs or other medical treatments. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Polypropylene-Clay Nanocomposites: Comparison of Different Layered Silicates

In former studies of the preparation of polypropylene(PP)-clay nanocomposites, different types of layered silicates were used. However, the obtained results were not comparable due to different preparation conditions and types of silicates. The aim of this work was the investigation of the influence of different layered silicates on the properties of the resulting nanocomposites. FT-IR-spectra, SAXS, TEM micrographs, elemental analysis, mechanical properties and surface tension measurements were used for the comparison of the four different layered silicates under investigation.