ZnO Nanowires,Nanotubes, and Complex Hierarchical Structures Obtained by Electrochemical Deposition

Increasing the aspect ratio of ZnO nanostructures is one possible strategy to improve their thermoelectric properties. ZnO nanostructures with one-dimensional (1D) and three-dimensional (3D) morphologies were obtained using electrochemical deposition. Adjusting various deposition parameters made it possible to obtain arrays of vertically aligned ZnO nanowires (NWs) with controlled dimensions, density, and electrical properties. The concentrations of zinc or chloride ions in the solution were found to be key parameters. ZnO NWs were transformed into ZnO nanotubes (NTs), with an increased aspect ratio compared with the NWs, by selectively dissolving the core of the ZnO NWs in a concentrated KCl solution. The aspect ratio was strongly increased when the ZnO NWs were hierarchically organized in a 3D morphology. The synthesis of thin films composed of ordered hollow urchin-like ZnO NW structures was performed by combining the electrochemical deposition and polystyrene sphere templating methods. The electronic properties of the urchin-like ZnO structures were investigated by means of photoluminescence and transmission measurements.     

Analysis of systematic errors in Mueller matrix ellipsometry as a function of the retardance of the dual rotating compensators

A dual rotating compensator ellipsometer based on the optical PC1SC2A configuration described by Collins [1, chap. 7.3] has been developed. The systematic errors for this configuration if the compensators are quarter-wave plates have been already studied [2, 3, 4]. Smith [5] has demonstrated that the optimum retardance of a dual-rotating-retarder (DRR) instrument must be equal to 127° compared to the quarter-wave (90°) retarders generally used. In this condition random errors are optimized. The aim of this work is to used such retarders and verify if the systematic errors due to uncertainties of the optical elements (i.e. analyzer, polarizer, first and second compensators) are improved too. For each optical element in different configurations like single or 4-zone average measurements, the systematic errors are given and compared according to the compensators. It is demonstrated that using a 127° instead of quarter-wave retarders coupled with 4-zone averaging measurement is the best configuration for this instrument. These results were confirmed by a statistical study.     

Single-photon emission from single InGaAs/GaAs quantum dots grown by droplet epitaxy at high substrate temperature

ABSTRACT: The authors report single-photon emission from InGaAs quantum dots grown by droplet epitaxy on (100) GaAs substrates using a solid-source molecular beam epitaxy system at elevated substrate temperatures above 400 [DEGREE SIGN]C without post-growth annealing. High-resolution micro-photoluminescence spectroscopy exhibits sharp excitonic emissions with lifetimes ranging from 0.7 to 1.1 ns. The coherence properties of the emitted photons are investigated by measuring the first-order field correlation function.     

Inhibited wood degradation of cement-coated beech Laminated Veneer Lumber (LVL) for temporary in-ground applications

This paper investigates the long-term tensile properties of laminated veneer lumber (LVL) beech sections coated with cement and exposed to fungal decay. A set of LVL coupon (dog-bone) samples was stored in compost, tested in tension after 6 and 12 months and compared to reference samples stored at 20 °C and 65% relative humidity. Results showed that after 26 weeks of compost exposure, a fungus of the Ascomycota genus was identified in cement-coated samples using a molecular biology polymerase chain reaction (PCR) technique, which analyses the internal transcribed spacer (ITS) region of the ribosomal DNA. However, no visual deterioration was noticed. Still in cement-covered samples and after 12 months of exposure, a common white rot fungus was determined by DNA chip technology, but no fungal wood decay was visible in areas where the applied coating had a thickness of at least 5 mm. Decay in uncoated LVL samples was significant with the samples having an average residual strength equal to 7%. This compares to the tensile strength of coated samples, which only decreased by 65% relative to the reference samples. Strength and stiffness of coated samples did not differ significantly between 6 and 12 months of exposure. Preliminary investigations tend to show that the strength reduction in cement-coated samples is due to an alkaline degradation of the wood. The observed influence of the coating thickness on the visual fungal decay can probably be ascribed to the protection mechanism due to a physical fungal barrier with a high pH.     

Studies addressing the importance of charge in the binding of fosmidomycin-like molecules to deoxyxylulosephosphate reductoisomerase

Fosmidomycin and its homologue FR900098 are inhibitors of 1-deoxy-D-xylulose-5-phosphate reductoisomerase, which is part of the mevalonate-independent isoprenoid biosynthetic pathway. Replacement of the phosphonate moiety by uncharged sulfone or sulfonamide partial structures resulted in complete loss of activity. Dropping one of the two negative charges resulted in a marked decrease in activity. Through occupation of a hydrophobic binding site, some activity could be regained, leading to compounds with micromolar activity against cultured malaria parasites.     

Degradation and possible carry over of feed DNA monitored in pigs and poultry

A possible carry over of foreign food DNA into the body after consumption was examined. After feeding pigs with conventional and recombinant (Bt-) maize, different body samples were investigated using DNA-extraction followed by PCR procedures to detect chloroplast genes of different length (199 bp and 532 bp), a maize-specific gene (zein) and a specific transgene present in Bt-maize (cryIa). Initially, a time-dependent degradation of feed DNA in the gastrointestinal tract of pigs was analysed within the juices from stomach and three parts of the small intestine (duodenum, jejunum, ileum). Subsequently, a possible transfer of residual chloroplast specific DNA as well as recombinant Bt-maize DNA fragments into different pig organs (blood, muscle, liver, spleen and lymph nodes) was examined. The suitability of the introduced DNA extraction procedure was verified through amplification of a universal gene (ubiquitin) demonstrating the successful PCR analysis within a range of 189-417 bp long DNA. Short chloroplast DNA fragments (199 bp) could be successfully amplified from the intestinal juices of pigs up to 12 h after the last feeding. In contrast, chloroplast-specific DNA was not found in any pig organ investigated so far. Specific gene fragments from the transgene maize (Bt-maize) were never detected in any pig sample. A field study examining supermarket poultry samples (leg, breast and wing muscle, stomach) led to frequent detections of the short chloroplast DNA fragment (199 bp). Furthermore, faint signals for the maize specific zein gene fragment were detected in these poultry tissues. Additional PCR examinations using unhatched chicken embryos provided the first indication that neither chloroplast nor maize genes are present endogenously within the wild-type poultry genome. Therefore, a transient transfer of short forage DNA into most poultry organs can be suspected.     

Prevalence of antibiotic-resistant enterobacteriaceae isolated from chicken and pork meat purchased at the slaughterhouse and at retail in Bavaria, Germany

The purpose of this study was to investigate chicken and pork meat sampled at the slaughterhouse and at retail for differences in the presence of antibiotic resistant Gram-negative bacteria. For this aim, Escherichia coli (n=677), Enterobacter spp. (n=167), Citrobacter spp. (n=83), Serratia spp. (n=116), Klebsiella spp. (n=125), and Salmonella spp. (n=89) were isolated from 500 chicken and 500 pork samples purchased at the slaughterhouse and at retail (in the same amounts) in Germany. Salmonella were present in 17% of the chicken, and in 0.4% of the pork meat samples. There was a clear shift in the spectrum of coliforms from slaughterhouse to retail: Enterobacter, Citrobacter and Klebsiella were the most frequently detected coliforms (other than E. coli) from slaughterhouse samples, whereas the prevalence of Serratia spp. was up to eight times higher in retail samples. The prevalence of E. coli was higher in slaughterhouse samples, whereas the prevalence of other coliforms and Salmonella spp. was higher in retail samples. E. coli strains were often resistant to penicillins, streptomycin, spectinomycin, doxycycline and sulfamethoxazole/trimethoprim. Resistance rates of the other coliforms were generally low. Resistant and multi-resistant isolates were significantly more common in chicken meat. Compared to samples from the slaughterhouse, the prevalence of resistant bacteria tended to be higher in retail samples, probably due to good conditions for resistant bacteria on the matrix meat and/or due to secondary contamination with resistant strains. Therefore, stringent hygiene measures should be observed to reduce the risk of transmission of resistant bacteria from food to humans.     

Measurement of the bending strength of vapor-liquid-solid grown silicon nanowires

The fracture strength of silicon nanowires grown on a [111] silicon substrate by the vapor-liquid-solid process was measured. The nanowires, with diameters between 100 and 200 nm and a typical length of 2 microm, were subjected to bending tests using an atomic force microscopy setup inside a scanning electron microscope. The average strength calculated from the maximum nanowire deflection before fracture was around 12 GPa, which is 6% of the Young's modulus of silicon along the nanowire direction. This value is close to the theoretical fracture strength, which indicates that surface or volume defects, if present, play only a minor role in fracture initiation.     

Tiefengestaffeltes Wasserprobennahmesystem zur spezifischen Beprobung der ungesättigten Zone, dem Kapillarsaum und der gesättigten Zone

Flow and transport processes in the transition area between the unsaturated and the saturated zone can influence the quality and properties of the groundwater. Special hydraulic properties have to be considered throughout the entire transition zone, which is a physically and bio-chemically highly active reaction chamber. Using the available measuring techniques, the present processes cannot be fully comprehended or, on the other hand, require significant effort. Thus, the influence of the transition zone is often neglected (Ronen and Sorek, The Unsaturated Zone—A Neglected Component of Nature. Water Quality Division, Israel Water Commision, Tel-Aviv, 2005). Utilizing laboratory experiments and numerical simulations, an innovative concept for a depth-specific measuring technique was evaluated. Results show that with some modifications of the actual design, the device is capable of sampling the entire transition zone between the unsaturated and the saturated zone, including the capillary fringe, with high temporal and spatial resolution.