Surface morphology for ion-beam sputtered Al layer with varying sputtering conditions

We study the growth morphology of thin macrostructure films which is known to be largely affected by the deposition conditions as thin film nucleation and formation is dependent on the kinetic energy and chemical free energy of the atoms. The ion-beam sputtering technique used for depositing thin layers is due to the advantage over other techniques, e.g. the independent control of many process parameters, such as the pressure and/or the energy of the ion-beam and the substrate temperature. Therefore, the dependence of various sputtering parameters such as: (i) sputtering pressure and/or the rate of deposition and (ii) the effect of substrate temperature on the growth has been studied by depositing a single layer of Al. The variations show some interesting dependencies on the structural parameters for the Al layer deposited which has been understood in terms of thin film growth and nucleation theory.     

Molecular beams and model catalysis: activity and selectivity of specific reaction centers on supported nanoparticles.

Reaction kinetics on nanometer-scale particles are different from those on extended surfaces of bulk materials. This fact has been utilized for a long time to empirically maximize the performance of heterogeneous catalysts, but the understanding of the underlying effects is poor at the microscopic level. Modern molecular beam-based methods, however, allow us to derive very detailed kinetic information on catalytically active surfaces. In combination with structurally highly controlled model catalysts, microscopic insights into the activity and selectivity of specific reaction centers on catalyst nanoparticles can be obtained. This combined approach is illustrated through simple model reactions.     

Evidence for Pdx(CO)y compound formation on an alumina substrate

Although stable binary Pd carbonyls are unknown in the gas phase, we found strong evidence for a stable carbonyl-like Pd compound on an oxide surface: by in situ vapour deposition of Pd at a rate of 2 × 10¹³ atoms s⁻¹ cm⁻² onto an alumina substrate (90 K) at a pressure of 2 × 10⁻⁶ mbar CO, a binary compound of Pd and CO is formed which is stable up to 190 K. As substrate serves a well-ordered aluminium oxide film grown on a NiAl(110) single crystal surface. The system was characterized under UHV (ultrahigh vacuum) conditions by means of TDS, LEED, UPS and XPS in a coverage range between 1.4 × 10¹⁴ Pd atoms cm⁻² and 1.4 × 10¹⁶ Pd atoms cm⁻². The decomposition at 190 K results in the formation of metallic Pd particles and is accompanied by a sharp and dominant feature in the thermal desorption spectra.     

Mapping of possible prion protein self-interaction domains using peptide arrays

Background  

The common event in transmissible spongiform encephalopathies (TSEs) or prion diseases is the conversion of host-encoded protease sensitive cellular prion protein (PrP^C) into strain dependent isoforms of scrapie associated protease resistant isoform (PrP^Sc) of prion protein (PrP). These processes are determined by similarities as well as strain dependent variations in the PrP structure. Selective self-interaction between PrP molecules is the most probable basis for initiation of these processes, potentially influenced by chaperone molecules, however the mechanisms behind these processes are far from understood. We previously determined that polymorphisms do not affect initial PrP^C to PrP^Sc binding but rather modulate a subsequent step in the conversion process. Determining possible sites of self-interaction could elucidate which amino acid(s) or amino acid sequences contribute to binding and further conversion into other isoforms. To this end, ovine – and bovine PrP peptide-arrays consisting of 15-mer overlapping peptides were probed with recombinant sheep PrP^C fused to maltose binding protein (MBP-PrP).     

Arsinothioyl-sugars produced by in vitro incubation of seaweed extract with liver cytosol analysed by HPLC coupled simultaneously to ES-MS and ICP-MS

It has been shown, that in vitro incubation of Laminaria digitata extract (containing mainly As-sugar 1 (glycerol-arsenoribose) and As-sugar 3 (sulfonate-arsenoribose)) with liver cytosol, produced the same two arsenicals, as when L. digitata extract was treated with H(2)S. By parallel use of HPLC-ICP-MS and HPLC-ES-MS the compounds displayed mainly m/z 345 and m/z 409. A pure As-sugar 1 standard was obtained, and a standard of arsinothioyl-sugar 1 (m/z 345) was produced, by purging a solution of As-sugar 1 with gaseous H(2)S. The identity of arsinothioyl-sugar 1 was characterised by ES-MS, 1D and 2D NMR. Arsinothioyl-sugar 1 showed the same chromatographic behaviour and MS characteristics as one of the two arsenic-containing compounds (m/z 345) produced by incubation of L. digitata extracts with liver cytosol, and as the product of the incubation of As-sugar 1 with liver cytosol (HPLC-ICP-MS, HPLC-ES-MS). Assuming that As-sugar 3 reacts in a similar way to As-sugar 1 with H(2)S, it is most likely that the second unknown (m/z 409) is arsinothioyl-sugar 3. The degradation of As-sugar 1 in acidic solution (100 mM HCl) was followed by (1)H-NMR, and the relative slow degradation (t(1/2)= 17 h) suggests that arsenosugars are taken up from the stomach in their original chemical form, hence the study of arsenosugar incubation in tissue is highly relevant. The arsinothioyls are a new group of organoarsenicals, which have only recently been identified in nature. Here, arsinothioyl sugars are detected for the first time. The in vitro formation of arsinothioyl-sugars in liver cytosol suggests that arsinothioyls may be of large biochemical and toxicological importance.     

A continuum, O(N) Monte Carlo algorithm for charged particles

We introduce a Monte Carlo algorithm for the simulation of charged particles moving in the continuum. Electrostatic interactions are not instantaneous as in conventional approaches, but are mediated by a constrained, diffusing electric field on an interpolating lattice. We discuss the theoretical justifications of the algorithm and show that it efficiently equilibrates model electrolytes and polar fluids. In order to reduce lattice artifacts that arise from the interpolation of charges to the grid we implement a local, dynamic subtraction algorithm. This dynamic scheme is completely general and can also be used with other Coulomb codes, such as multigrid based methods.     

A molecular beam study of the NO + CO reaction on Pd(111) surfaces

Nitric oxide (NO) reduction with carbon monoxide (CO) on the Pd(111) surface was studied under isothermal conditions by molecular beam techniques as a function of temperature, NO:CO beam composition, and beam flux. Systematic experiments were performed under transient and steady state conditions. Displacement of adsorbed CO by NO in the transient state of the reaction was observed at temperatures between 375 and 475 K for all the NO:CO compositions studied. NO accumulation occurs on Pd(111) surface under steady state conditions, below 475 K, due to stronger chemisorption of NO. The steady state reaction rates attain a maximum at about 475 K, nearly independent of beam composition. N2 was found to be the major product of the reduction, along with a minor production of N2O. The production of N2 and N2O indicates molecular and dissociative adsorption of NO on Pd(111) at temperatures up to 525 K. Postreaction TPD measurements were performed in order to determine the nitrogen coverage under steady-state conditions. Finally, the results are discussed with respect to the rate-controlling character of the different elementary steps of the reaction system.     

Strongly Mixing Sequences of Measure Preserving Transformations

We call a sequence (T _n ) of measure preserving transformations strongly mixing if tends to P(A)P(B) for arbitrary measurable A, B. We investigate whether one can pass to a suitable subsequence such that almost surely for all (or "many") integrable f.     

Conformations of random polyampholytes

We study the size R(g) of random polyampholytes (i.e., polymers with randomly charged monomers) as a function of their length N. All results of our extensive Monte Carlo simulations can be rationalized in terms of the scaling theory we develop for the Kantor-Kardar necklace model, although this theory neglects the quenched disorder in the charge sequence along the chain. We find approximately N1/2. The elongated globule model, the initial predictions of both Higgs and Joanny ( approximately N1/3) and Kantor and Kardar ( approximately N), and previous numerical estimates are ruled out.