Reaction of carboxylic acids on CeO2(111) and CeO2(100)

The reactions of HCOOH and CH₃COOH on CeO₂(111) and CeO₂(100) were studied using temperature programmed desorption (TPD) and high resolution electron energy loss spectroscopy (HREELS). The carboxylic acids were found to dissociate on both surfaces to form carboxylates. Adsorbed formates and acetates decomposed near 600 K to produce primarily the dehydration products CO and CH₂CO, respectively. This result is consistent with previous studies which have indicated that the ease of reduction of the oxide is the primary factor in determining the selectivity for dehydration versus dehydrogenation during carboxylate decomposition. In addition to CO and CO₂, small amounts of formaldehyde were produced during formate decomposition on both CeO₂(111) and CeO₂(100). In contrast, acetone was observed as a product during acetate decomposition only on the CeO₂(111) surface.     

International intercomparison of horn gain at X-band

An international intercomparison of horn gain and polarization measurements at X-band has previously been completed. There were seven participating laboratories with the National Institute of Standards and Technology serving as the pilot laboratory. Two X-band pyramidal standard gain horns with a nominal gain of 22 dB served as the traveling standards. Quantities measured included on-axis fixed frequency gain at 8, 10, and 12 GHz, swept frequency gain between 8-12 GHz and polarization characteristics at the three fixed frequencies. All laboratories performed the fixed frequency-gain measurements. The swept-frequency and polarization measurements were optional, with four laboratories performing swept-frequency measurements and three laboratories measuring polarization. The results of the gain measurements generally agreed within the reported uncertainties which were of the order of 0.1 dB or less     

Polyionic fusion peptides function as specific dimerization motifs

The de novo design of a molecular adapter for directed associationand covalent linkage of two polypeptides is presented. Usingpeptides containing charged amino acid residues and an additionalcysteine residue (AlaCysLys₈ and AlaCysGlu₈) we demonstratethat the electrostatic interaction promotes the associationof two synthetic peptides and, subsequently, disulfide bondformation. The reaction depends on both the redox potentialand on the ionic strength of the buffer. Varying the redox potential,the interaction of the peptides was quantified by a G^0' of 6.6± 0.2 kcal/mol. Heterodimerization of the peptides ishighly specific, a competition of association by other cysteinecontaining compounds could not be observed. Two proteins comprisingcysteine-containing polyionic fusion peptides, a modified Fabfragment and an -glucosidase fusion, could be specifically conjugatedby directed association and subsequent disulfide bond formation.Both proteins retain their functional characteristics withinthe bifunctional conjugate: enzymatic activity of the glucosidaseand antigen-binding capacity of the Fab fragment are equivalentto the non-conjugated components.     

Spontaneous emission study on 1.3 µm InAs/InGaAs/GaAs quantum dot lasers

True spontaneous emission (TSE) measurements on InAs/InGaAs/GaAs quantum dot (QD) lasers have been performed as a function of injection current and cavity length. For each laser, TSE from both the ground state (GS) transition and the excited state (ES) transition has been analyzed. It is found that Auger processes are the major nonradiative recombination (NR) processes for both the GS and ES transitions. In particular, for the first time, the existence of Auger like NR features in ES transitions has been experimentally demonstrated. In addition, obvious competition for carriers between the ES transition and the GS transition has been observed in TSE analysis. Furthermore, the QD laser's cavity length has a strong effect on the NR process in GS transitions, due to GS gain saturation. Therefore, when analyzing the NR processes in operating QD lasers, gain saturation due to cavity length limits should be properly considered.     

Effect of random errors in planar near-field measurement

Expressions that relate the signal-to-noise ratio in the near field to the signal-to-noise ratio in the far field are developed. The expressions are then used to predict errors in far-field patterns obtained from near-field data. A technique for measuring the noise in the calculated far-field pattern by calculating the spectrum in the evanescent region from a single-dimensional oversampled scan is also described     

Synthesis of pyrogallolestrogens (2,3,4-trihydroxy-1,3,5(10)-estratrienes) and their methyl ethers

The preparation of 2,4-dihydroxyestrone, 2,4-dihydroxyestradiol-17beta and their methyl ethers (14 compounds) is described. The structures were established by nuclear magnetic resonance, infrared and mass spectra as well as by elemental analyses, microchemical reactions, alternative synthetic routes and by their chromatographic properties.     

Foam-based cleaning of surfaces contaminated with mixtures of oil and soot

Liquid foams of intermediate stability have been shown to be very efficient in the cleaning of sensitive surfaces because of the synergy between imbibition and foam decay. While we quantified these mechanisms for contaminations with liquid oils in our previous work, we show here their extension to oils containing soot particles in an effort to simulate increasingly realistic contaminations. Using foams with a wide range of liquid fractions and with different stabilities, we show that the main cleaning mechanisms remain very similar, with the oil entraining the soot particles. However, we find much less efficient soot removal when the liquid channels of the foams are small enough to hinder efficient transport of the soot particles.     

Comparison of measured and calculated mutual coupling in the near field between microwave antennas

Measurements of near-field mutual coupling between two moderate sized microwave antennas were performed and compared to coupling calculated using recently developed computer programs. Required input data for the programs are the complex far-field radiation patterns of the antennas and various geometrical factors describing the relative positions and orientations of the two antennas. Measured and calculated coupling as a function of both transverse and radial displacement showed good agreement.     

The significance of the bacterial steroid degradation for the etiology of large bowel cancer. V. Transformation of chenodeoxycholic acid by saccharolytic bacteroides-species (author's transl)

We analysed a total of 36 strains of the obligately anaerobic Bacteroides species B. vulgatus, B. fragilis, B. thetaiotaomicron, and B. distasonis to test their faculties to metabolize chenodeoxycholate. For experiments with growing cultures, we used a synthetic medium with inorganic salts, glucose, citrate, amino acids, vitamins, and hemin. The same medium, but without amino acids and vitamins was used for experiments with resting cells, incubated aerobically. After preincubation in a medium containing bile and deoxycholate, we observed that 26 strains of 35 (74 per cent) could degrade this bile acid, when cultivated anaerobically, compared to 30 strains of 36 (83 per cent), when incubated aerobically. To sum up the number of active strains, there are 32, corresponding 89 per cent. With the exception of two strains, which formed two transformation products, all active strains formed one degradation product only. All strains but one, active when cultured anaerobically, belong to the species B. fragilis and B. thetaiotaomicron. As can be seen by the results of aerobic incubation most strains of the species B. vulgatus posses the degradative activity, found inactive, however, under anerobic conditions. We therefore suppose that its regulatory mechanism is different from the other species. Thin-layer, gas chromatography, and combined gas chromatography-mass spectrometry were used for the identification of transformation products. With these methods, we were able to demonstrate the bacteria to metabolize chenodeoxycholate to 3 alpha-hydroxy-7-oxo-5 beta-cholanoate, either if growing anaerobically or incubated aerobically. The second degradation products of two strains, found in traces or as by-product, could not be identified on account of minor amounts.