A 43Ca and 13C NMR study of the chemical interaction between poly(ethylene-vinyl acetate) and white cement during hydration

⁴³Ca and ¹³C NMR methods were used to study the chemical interaction of poly(ethylene–vinyl acetate) (PEVAc) admixture in commercial-grade white cement. From ⁴³Ca NMR it is shown both that PEVAc induces modest changes in the hydrated cement structure, and that hydrated commercial cement is significantly more complex than models that have been used for its structure in past work. The ¹³C NMR results show that the PEVAc hydrolysis occurs early in the cement hydration acceleration period, with a rate well-fit by an exponential decay using a time constant of 6±1 days.     

Operation of a Raman laser in bulk silicon

A Raman laser based on a bulk silicon single crystal with 1.127 μm emission wavelength is demonstrated. The Si crystal with 30 mm length was placed into an external cavity and pumped by a Q-switched Nd:YAG master oscillator power amplifier system. Strong defocusing of the pump and Raman laser beam by free carriers was compensated by an intracavity lens. Raman laser operation with a pulse duration of 2.5 ns was identified by a Raman laser threshold significantly lower than the single-pass stimulated Raman-scattering threshold. Linear absorption losses of the 1.06415 μm pump radiation are strongly reduced by cooling the Si crystal to a temperature of 10 K.     

Bonus or flat wage? An experiment into the principal-agent problem

We conduct a simple principal-agent experiment in order to find the effects of information asymmetry on compensation. Our aim is the analysis of the appropriate compensation and its impact on employee’s effort. Furthermore we want to compare the offered compensation and the supplied effort in the version without communication and we want to know whether the experimental observations are consistent with the theoretical considerations.The experimenters found out that compensations observed during the experiment were different from those suggested by the theory and although they were theoretically not enough to induce high effort, we could observe high performance supplied by the agents.     

Understanding the Buoy Effect of Surface-Enriched Pt Complexes in Ionic Liquids: A Combined ARXPS and Pendant Drop Study**

Recently, we demonstrated that Pt catalyst complexes dissolved in the ionic liquid (IL) [C₄C₁Im][PF₆] can be deliberately enriched at the IL surface by introducing perfluorinated substituents, which act like buoys dragging the metal complex towards the surface. Herein, we extend our previous angle-resolved X-ray photoelectron spectroscopy (ARXPS) studies at complex concentrations between 30 and 5 %_mol down to 1 %_mol and present complementary surface tension pendant drop (PD) measurements under ultraclean vacuum conditions. This combination allows for connecting the microscopic information on the IL/gas interface derived from ARXPS with the macroscopic property surface tension. The surface enrichment of the Pt complexes is found to be most pronounced at 1 %_mol. It also displays a strong temperature dependence, which was not observed for 5 %_mol and above, where the surface is already saturated with the complex. The surface enrichment deduced from ARXPS is also reflected by the pronounced decrease in surface tension with increasing concentration of the catalyst. We furthermore observe by ARXPS and PD a much stronger surface affinity of the buoy-complex as compared to the free ligands in solution. Our results are highly interesting for an optimum design of IL-based catalyst systems with large contact areas to the surrounding reactant/product phase, such as in supported IL phase (SILP) catalysis.     

Enantiocomplementary enzymes: classification, molecular basis for their enantiopreference, and prospects for mirror-image biotransformations

One often-cited weakness of biocatalysis is the lack of mirror-image enzymes for the formation of either enantiomer of a product in asymmetric synthesis. Enantiocomplementary enzymes exist as the solution to this problem in nature. These enzyme pairs, which catalyze the same reaction but favor opposite enantiomers, are not mirror-image molecules; however, they contain active sites that are functionally mirror images of one another. To create mirror-image active sites, nature can change the location of the binding site and/or the location of key catalytic groups. In this Minireview, X-ray crystal structures of enantiocomplementary enzymes are surveyed and classified into four groups according to how the mirror-image active sites are formed.     

Popular branchings and their dual certificates

Mathematical Programming - Let G be a digraph where every node has preferences over its incoming edges. The preferences of a node extend naturally to preferences over branchings, i.e., directed...     

Separation of phenylthiohydantoin amino acids by capillary electrochromatography

Capillary electrochromatography (CEC) was employed as a rapid and high-efficiency method for the isocratic separation of all 20 important phenylthiohydantoin (PTH) amino acids, the end products of Edman degradation during N-terminal protein sequencing. For this purpose, 75 microm ID fused-silica capillaries were packed with standard 3 microm Hypersil octadecyl silica (ODS) particles using a two-step column fabrication process, which represents a fast, reliable and efficient means of producing long-term stable columns. The influence of solvent composition, pH, type of buffer cation, buffer concentration, and temperature on retention behavior of PTH amino acids was investigated. Same-day and day-to-day reproducibility of the retention times (over a period of two months) were found to be better than 3%. When comparing this new technique with traditional reversed phase-high performance liquid chromatography (RP-HPLC) methods applied in automated protein sequenators, CEC shows essentially shorter separation times and superior resolution.