Non-isothermal kinetics in mixtures of barium carbonate and titanium dioxide (anatase)

The complexes AgL (L = theobromine, 1,3,8-trimethylxanthine and 3,8-dimethylxanthine) Hg₂L·NO₃ (L = 3,8-dimethylxanthine and 1,3,8-trimethylxanthine) and Hg₂C₂(NO₃)₂ (C = caffeine), were prepared in aqueous and HNO₃ medium. These complexes were characterized by IR, ¹H-NMR, TG, DTG and DSC techniques.     

Synthesis and antioxidant capacity of 5-selenopyranose derivatives

Described is a convenient method for the syntheses of sulfur and selenium containing carbohydrate derivatives of L-gulodeoxynojirimycin and the corresponding C-5 epimer D-mannodeoxynojirimycin. The key step in the synthesis of the latter involves epimerisation of the C-5 hydroxyl group by an oxidation followed by stereo-selective reduction to obtain the desired D-sugar derivative. Both derivatives displayed a dose-dependent prevention of the oxidation of methionine residues on human plasma proteins induced by the inflammatory oxidant hypochlorous acid. The seleno-analogues were considerably more active than their thio-equivalents.     

Synthesis and cytotoxicity of pyridine and quinoline oxorhenium(V) complexes with tridentate (NS2, S3)/monodentate (s) coordination*

New oxorhenium complexes with tridentate 3-thia- and 3-methylazapentane-1,5-dithiolate and monodentate pyridine and quinoline derivatives have been synthesized. As a result of investigation of biological activity a high cytotoxicity was found for the synthesized complexes in relation to tumor cells. The specificity of the 2-pyridylthiolato[3-(N-methyl)azapentane-1,5-dithiolato]oxorhenium(V) cytotoxic action towards cells of mouse hepatoma MG-22A on a background of low acute toxicity was established.     

Dynamics of laser-cooled Ca+ ions in a Penning trap with a rotating wall

We have performed systematic measurements of the dynamics of laser-cooled ⁴⁰Ca⁺ ions confined in a Penning trap and driven by a rotating dipole field (‘rotating wall’). The trap used is a copy of the one used in the SPECTRAP experiment located at the HITRAP facility at GSI, Germany. The size and shape of the ion cloud has been monitored using a CCD camera to image the fluorescence light resulting from excitation by the cooling laser. We have varied the experimental conditions such as amplitude and frequency of the rotating wall drive as well as the trapping parameters. The rotating wall can be used for a radial compression of the ion cloud thus increasing the ion density in the trap. We have also observed plasma mode excitations in agreement with theoretical expectations. This work will allow us to define the optimum parameters for high compression of the ions as needed for precision spectroscopy of forbidden transitions.     

Automated antenna positioning algorithms for wireless fixed-access networks

This article addresses a real-life problem - obtaining communication links between multiple base station sites, by positioning a minimal set of fixed-access relay antenna sites on a given terrain. Reducing the number of relay antenna sites is considered critical due to substantial installation and maintenance costs. Despite the significant cost saved by eliminating even a single antenna site, an inefficient manual approach is employed due to the computational complexity of the problem. From the theoretical point of view we show that this problem is not only NP hard, but also does not have a constant approximation. In this paper we suggest several alternative automated heuristics, relying on terrain preprocessing to find educated potential points for positioning relay stations. A large-scale computer-based experiment consisting of approximately 7,000 different scenarios was conducted. The quality of alternative solutions was compared by isolating and displaying factors that were found to affect the standard deviation of the solutions supplied by the tested heuristics. The results of the simulation based experiments show that the saving potential increases when more base stations are needed to be interconnected. The designs of a human expert were compared to the automatically generated solutions for a small subset of the experiment scenarios. Our studies indicate that for small networks (e.g., connecting up to ten base stations), the results obtained by human experts are adequate although they rarely exceed the quality of automated alternatives. However, the process of obtaining these results in comparison to automated heuristics is longer. In addition, when more base station sites need to be interconnected, the human approach is easily outperformed by our heuristics, both in terms of better results (fewer antennas) and in significant shorter calculation times.     

Tunable bands of electronic image states in nanowire lattices

We demonstrate that suspended arrays of parallel nanowires support bound electron image states with rich band structures. Surprisingly, these Bloch states can be highly detached from the surfaces of the nanowires, similar to the single-tube wave functions. This is because an electron hovering in such a periodic lattice of nanowires is influenced by a Coulombic-like attraction and a centrifugal repulsion, which are both central symmetric around each wire. These novel states could be used in building of waveguides, mirrors, and storage places for Rydberg-like electrons.     

Strong shape theory and resolutions

It is shown that the strong shape theory of compact metrizable spaces extends to a theory for all topological spaces. The extension resembles the inverse systems approach to shape theory of Marde?i? and Segal. Fundamental roles are played by the Steenrod homotopy theory of Edwards and Hastings and the theory of ANR-resolutions due to Marde?i?.     

The interference of an electron beam with the surface reaction between oxygen and germanium

Electron beam assisted adsorption and desorption of oxygen was studied by Auger electron spectroscopy (AES). Beam assisted adsorption was observed on clean as well as on oxidized surfaces. After an oxygen exposure of 1000 × 10^?7 Torr min and continuous irradiation with beam voltage of 1.5 kV and beam current density 2 microA mm^?2, the oxygen 510 eV signal amplitude from the point of beam impact was 2.5 times greater than the signal from the non-irradiated region. The Ge 89 eV signal showed a corresponding decrease. Enhanced adsorption occurred at beam energies as low as 16.5 eV. After irradiation, the oxidized surface was not carbon contaminated. Following an oxygen exposure of 30 min at 0.1 Torr and 550°C and subsequent additional beam assisted exposure of 1000 × 10^?7 Torr min, the maximum oxide thickness was about 18 Å. Beam assisted desorption did not occur from thin oxygen layers (0–510 eV signal strength less than 5 units, calculated oxide thickness about 6 Å), but occurred from thick oxides and stopped after the signal amplitude had decreased to 5 units. Based on these results, a model for the structure of the oxygen layer covering the Ge(111) surface is proposed. Mechanisms for adsorption and desorption are discussed. The implications of beam assisted adsorption and desorption on electron beam operated surface measurements (LEED, AES, ELS, APS etc.) are stressed.