Entdeckung der geringsten Spuren von Wasser in Alkohol

Ohne Zusammenfassung     

Monte Carlo simulation of quantum statistical lattice models

In this article we review recent developments in computational methods for quantum statistical lattice problems. We begin by giving the necessary mathematical basis, the generalized Trotter formula, and discuss the computational tools, exact summations and Monte Carlo simulation, that will be used to examine explicit examples. To illustrate the general strategy, the method is applied to an analytically solvable, non-trivial, model: the one-dimensional Ising model in a transverse field. Next it is shown how to generalized Trotter formula most naturally leads to different path-integral representations of the partition function by considering one-dimensional fermion lattice models. We show how to analyze the different representations and discuss Monte Carlo simulation results for one-dimensional fermions. Then Monte Carlo work on one- and two-dimensional spin-$\text{1}\text{2}$ models based upon the Trotter formula approach is reviewed and the more dedicated Handscomb Monte Carlo method is discussed. We consider electron-phonon models and discuss Monte Carlo simulation data on the Molecular Crystal Model in one, two and three dimensions and related one-dimensional polaron models. Exact numerical results are presented for free fermions and free bosons in the canonical ensemble. We address the main problem of Monte Carlo simulations of fermions in more than one dimension: the cancellation of large contributions. Free bosons on a lattice are compared with bosons in a box and the effects of finite size on Bose-Einstein condensation are discussed.     

Poloidal Structure of the Turbulence and the Turbulent Flux During Edge Plasma Biasing in the Castor Tokamak

The poloidal structure of the turbulence and the turbulent particle flux in the scrape-off layer (SOL) of the CASTOR tokamak are analysed by means of a poloidal ring of 124 probes distributed uniformly along the whole poloidal circumference. Fluctuation measurements are performed in standard ohmic regime as well as in discharges when a biased electrode is inserted either into the SOL or deeper into the confinement region. It is found that in both cases a strongly sheared radial electric field is created in the SOL, which de-correlates the density and radial velocity fluctuations and reduces their levels. Consequently, the turbulent flux is reduced. However, no phase shift is observed between density and radial velocity fluctuations. When the electrode is localized in the confinement region, all the above effects are less pronounced because of a smaller shear. In addition, the increase of the E × B velocity at biasing leads in both cases to the formation of oscillations in the temporal correlation function. These oscillations are specifically associated to the poloidal mode (m = q), which is created for a limited time and rotates poloidally. This mode does not modify the phase between density and radial velocity fluctuations and has no further effect on the turbulent flux.     

Capturing the Genesis of an Active Fischer–Tropsch Synthesis Catalyst with Operando X‐ray Nanospectroscopy

A state‐of‐the‐art operando spectroscopic technique is applied to Co/TiO₂ catalysts, which account for nearly half of the world's transportation fuels produced by Fischer–Tropsch catalysis. This allows determination of, at a spatial resolution of approximately 50 nm, the interdependence of formed hydrocarbon species in the inorganic catalyst. Observed trends show intra‐ and interparticular heterogeneities previously believed not to occur in particles under 200 μm. These heterogeneities are strongly dependent on changes in H₂/CO ratio, but also on changes thereby induced on the Co and Ti valence states. We have captured the genesis of an active FTS particle over its propagation to steady‐state operation, in which microgradients lead to the gradual saturation of the Co/TiO₂ catalyst surface with long chain hydrocarbons (i.e., organic film formation).     

Adjuvant antiproliferative and cytotoxic effect of aloin in irradiated HeLaS3 cells

Naturally occurring phytoanthracycline, aloin, was used to radiosensitize HeLaS3 human cervix carcinoma cells. The results indicated that the cytotoxic adjuvant effect of aloin was synergistic with gammaionizing radiation at all drug concentrations and comparable to the cytotoxicity of 5–10 Gy ionizing radiation alone. Radiosensitization of HeLaS3 cells was achieved by 60 μM aloin, which reduced the IC₅₀ dose of ionizing radiation from 3.4 to 2 Gy. Ionizing radiation and aloin alone or in combination are shown to cause perturbation of the HeLaS3 cell-cycle and increase the percentage of cells in the DNA synthesis (S) phase of the cell cycle. While either of the agents applied alone causes programmed cell death by apoptosis, the simultaneous cell damage by both agents through the altered redox balance compromised cell capacity to conduct this program and led to synergic cytotoxic cell death by necrosis. The text was submitted by the authors in English.     

Experimental and theoretical determination of nucleic acid magnetic susceptibility: importance for the study of dynamics by field-induced residual dipolar couplings

Magnetic susceptibility anisotropies (Deltachi) are determined for the nucleic acid bases on the basis of a combined NMR spectroscopic and DFT study. Magnetic field-induced residual dipolar couplings (RDC) measured for the Dickerson dodecamer allow for the determination of a precise value of Deltachi for this DNA. A tensor summation employing the results of DFT calculations of the individual base magnetic susceptibility tensors and the known structure of the dodecamer provides a value of Deltachi which is in excellent agreement with experiment. The DFT results are shown to provide superior agreement with experiment for the dodecamer and a protein-DNA complex when compared with other sets of values in common use in the literature. The marked discrepancy between our Deltachi values and existing sets of values has a direct and significant impact on the interpretation of field-induced anisotropic interactions in terms of biomolecular structure and dynamics.     

Automated development of analytical chemical methods : The determination of senun calcium by the cresolphthalein complexone method

The cresolphthalein complexone method for serum calcium determination was investigated by means of a modified Technicon Autoanalyzer II under computer control. Simplex optimization of reagent concentrations, followed by response-surface mapping in the region of the optimum produced a method yielding 8.5% greater calcium sensitivity and 15% lower baseline absorbance than the standard method, with comparable insensitivity to interferences, and only a very slight sacrifice in linearity; a comprehensive operational understanding of the chemical system was also obtained.     

Development and validation of a liquid chromatographic-electrospray tandem mass spectrometric multiresidue method for anthelmintics in milk

A liquid chromatographic-tandem mass spectrometric multiresidue method for the simultaneous quantitative determination of the tetrahydroimidazole, levamisole and the benzimidazoles thiabendazole, oxfendazole, oxibendazole, albendazole, fenbendazole, febantel and triclabendazole in milk has been developed and validated. The anthelmintic residues were extracted with ethyl acetate. The liquid chromatographic separation was performed on a reversed-phase C18 column with gradient elution. The analytes were detected by tandem quadrupole mass spectrometry after positive electrospray ionisation by multiple reaction monitoring. The confirmatory method is very sensitive and each component can be detected at a residue level lower than 1 microgram/l. The method is validated according to the revised European Union requirements and all parameters were found conform the criteria. The evaluated parameters were linearity, specificity, stability, recovery, precision (repeatability and within-laboratory reproducibility) and analytical limits (detection limit, decision limit and detection capability). This analytical method is applied in the Belgian monitoring programme for classical anthelmintic veterinary drugs in raw farm cow's milk.     

Oxygen reduction on electrode surfaces modified by foreign metal ad-atoms: Lead ad-atoms on gold

Oxygen reduction on gold is considerably catalysed by foreign metal ad-atoms. The catalytic effects of lead have been studied in more detail as most illustrative. The two-electron reduction of O₂ to HO₂^? on Au changes into a four-electron process on Au modified by lead. In the potential region where AuOH constitutes the surface, the interaction of Pb ions with AuOH causes catalytic effects. At more negative potentials, on bare Au surface, the underpotential deposition of Pb ad-atoms gives rise to the catalytic effects.At AuOH surface modified by Pb ions the O₂ reduction involves a “series” mechanism, with only minute quantities of HO₂^? leaving the electrode surface. The reduction of HO₂^? is considerably catalysed. The mechanism of this reaction is changed from the rate-determining chemical step into the charge-transfer rate-determining step. The rate-determining step for O₂ reduction involves the first charge transfer: O₂+e→O₂^?(ads)The mechanism of HO₂^? formation is uncertain, while its reduction most probably involves a direct process. There are indications that on Au surface with Pb ad-atoms a “parallel” mechanism may be operative.The catalytic effect originates in the interaction of Pb²⁺ with AuOH surface, which considerably reduces a partial negative charge on OH. Such a surfaces, as well as that of Au covered by Pb ad-atoms, are more suitable for adsorption of O₂, O₂^? and HO₂^? which considerably alters the free energy of adsorption of these species.