Surface analysis of a glass leached with stable isotopes

The distribution of oxygen and other elements within the leached layer of a soda-lime glass after a short-time treatment (15–60 min) in pure H₂ ¹⁸O and D₂ ¹⁸O was investigated by means of neutral primary beam secondary ion mass spectrometry (NPB-SIMS). The¹⁸O^– profiles resulting from the penetration of an oxygen containing species are not disturbed by interference of the species H₂ ¹⁶O^–, originating from the residual gas in the vacuum chamber. In agreement with previous results, no isotope effect could be detected. Hydration of the glass leads to a pronounced matrix effect which impedes oxygen analysis in the negative secondary ion mode. The ratio of the maximum¹⁸O^– intensity in the leached layer to the¹⁶O^– intensity in the bulk was recorded as a function of time for one series of experiments. The result is in accordance with the time-dependence of the Na₂O concentration in the leached layer.     

Time-dependent thermal lensing and Kerr nonlinearity in CS2 with CO2-laser radiation

We report on optical limiting and z-scan in CS₂ as a function of the pulse duration of 10 µm TEA CO₂-laser radiation. We present a comprehensive and simple model for the shape of a laser pulse transmitted through this limiting device. For the first time, we propose the use of an optical limiting device for beam shaping.     

Study of the microstructure influence on the transport properties of Bi86.5Sb13.5 polycrystalline alloy

This study is focused on the investigation of the transport properties of Bi_86.5Sb_13.5 polycrystalline alloys. Bulk materials were prepared by cold pressing ultrafine powders of alloy and by annealing the resulting pellets. Special care was taken to avoid contamination of the powders. Starting with powders of average grain size of 0.06 μm bulk semi-conducting sample with mean grain size respectively of 0.1, 0.8, 2.5 and 200 μm were obtained. The influence of the grain size on both electrical resistivity, thermal conductivity, thermoelectric power, thermoelectric figure of merit is presented within the range 80-330 K. The thermoelectric properties are discussed and compared with those of single crystals presented in previous studies.     

Identification of Two New Phosphorylated Polyketides from a Brazilian Streptomyces sp. Through the Use of LC–SPE/NMR

Two new polyketide phosphate monoesters, phosdiecin A ( 1 ) and phosdiecin B ( 2 ), were isolated from a culture of the marine Streptomyces sp. SS99BA‐2 using the hyphenated technology LC–SPE/NMR. The compounds showed to be new representatives of an important class of antitumor antibiotic metabolites known as fostriecins. Their structures, including relative configuration attribution, were fully elucidated through extensive analyses of NMR and MALDI‐TOF/TOF HR‐MS data. Herein, the application of this system to isolate and identify the new compounds is described.     

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Basenkatalysierte Cyclisierungen von 2-(2-Propinyl)oxybenzamiden

Base Catalysed Cyclizations of 2-(2-Propynyl)oxy-benzamide Systems 2-(2-Propynyl)oxy-benzamides were cyclized under base catalysis to 6- or 7-membered ring compounds, depending on the reaction conditions. Treatment of 2-(2-propynyl)oxy-benzamide ( 10 ) with sodium methylsulfinylmethanide (NaMSM) in DMSO gave two isomeric oxazepinons 11 (34%) and 12 (7%), while the transformation with sodium-2-propanolate in 2-propanol afforded the oxazinone 13 (34%) and with lithium cyclohexyl-isopropylamide (Li-CHIP) in N-methylpyrrolidone 11 (48%) exclusively (Scheme 4). N-Methyl-2-(2-propynyl)-oxy-benzamide ( 14 ) behaved similarly. In the reaction of 14 with sodium 2-propanolate in 2-propanol yielding the benzoxazinone 16 , the allenyloxy-benzamide 17 could be isolated as an intermediate (Scheme 5). The N-phenyl-compounds 18 and 22 treated with NaMSM/DMSO were converted to 3-anilino-2-methyl-benzo- and naphtho-pyran-4-ones, respectively (Schemes 6 and 7). The mechanisms for these reactions are discussed (Schemes 8, 9 and 10).     

Ultrashort far-infrared superradiant emissions optically pumped by truncated hybrid 10 μm CO2 laster pulses

We investigate the generation of superradiant far-infrared 496 m CH₃F pulses and produce for the first time smooth and reproducible 373 m CH₃CN superradiant pulses by pumping with pulses from a hybrid 10 m CO₂ laser truncated within 10 ps by a plasma shutter of new design. Superradiance is confirmed by measurement of the pressure dependence of the intensity, the width and the delay versus the pump pulse. We observe pulse durations considerably under the limit of the inverse linewidth of the transition. Thus, we demonstrate for the first time that rapid truncation of the pump pulse is essential for reducing pulse duration of superradiant far-infrared emissions.     

The surface properties of the hydride forming alloy ErFe2 — Confirmation of a model

By means of photoelectron spectroscopy and measurements of the magnetic susceptibility we found that oxygen induced surface segregation occurs on ErFe₂. For small doses of O₂ metallic Fe precipitates are formed, which together with the ErFe₂ subsurface, catalyze the H₂ dissociation. The segregation tends to saturate at the O₂ exposure of ≈ 10 L.     

A specialized column generation approach for a vehicle routing problem with demand allocation

Motivated by logistical operations for a food bank, this paper addresses a class of vehicle routing problems with demand allocation considerations over a network of partner agencies locations and candidate delivery sites. Any delivery tour starts at a central depot operated by the food bank and selected delivery sites are sequentially visited in order to supply goods to a set of partner agencies who travel from their respective locations to their assigned delivery sites. The problem is modelled as a mixed-integer programme with the objective of minimizing a weighted average of the distances travelled by delivery vehicles and partner agencies, and is tackled via two heuristics. First, a relax-and-fix heuristic is presented for the proposed model and is computationally enhanced using two symmetry-defeating strategies. Second, the problem is reformulated as a set partitioning model with side packing constraints that prompts a specialized column generation approach. Computational experience is provided using realistic data instances to demonstrate the usefulness of the proposed heuristics and the importance of integrated solution techniques for this class of problems.