Growth condition dependence of unintentional oxygen incorporation in epitaxial GaN

Growth conditions have a tremendous impact on the unintentional background impurity concentration in gallium nitride (GaN) synthesized by molecular beam epitaxy and its resulting chemical and physical properties. In particular for oxygen identified as the dominant background impurity we demonstrate that under optimized growth stoichiometry the growth temperature is the key parameter to control its incorporation and that an increase by 55?°C leads to an oxygen reduction by one order of magnitude. Quantitatively this reduction and the resulting optical and electrical properties are analyzed by secondary ion mass spectroscopy, photoluminescence, capacitance versus voltage measurements, low temperature magneto-transport and parasitic current paths in lateral transistor test structures based on two-dimensional electron gases. At a growth temperature of 665?°C the residual charge carrier concentration is decreased to below 10¹⁵ cm^?3, resulting in insulating behavior and thus making the material suitable for beyond state-of-the-art device applications.     

Surface Acoustic Wave (SAW) Biosensor for Rapid and Label-Free Detection of Penicillin G in Milk

Surface acoustic wave (SAW) biosensors were introduced for rapid and label-free detection of penicillin G in milk. This is the first time that the use of SAW biosensors for antibiotic detection is reported. Penicillin G belongs to the β-lactam antibiotics which are commonly used in human and veterinary medicine. Particularly because of the latter, the detection of antibiotics in foodstuffs of animal origin is essential. Current methods for specific antibiotic detection often require complex laboratory equipment and procedures. SAW biosensors, however, offer rapid detection of analyte concentrations with a minimum of experimental effort. They use label-free acoustic (gravimetric) detection. Owing to the small mass of antibiotics, detection via binding inhibition assay was preferred to direct detection in this work. Samples containing penicillin G were preincubated with the corresponding antibody, and SAW biosensor surfaces were coated with penicillin G epitopes. The antibody in the sample bound to the biosensor surface, unless it was inhibited by penicillin G. The assay allowed the detection of 2 ng/ml penicillin G in buffer and 2.2 ng/ml in low-fat milk. This is below the maximum residue limit of 4 ng/ml given by the European Commission for penicillin G and other β-lactam residues in food.     

Antimicrobial resistance profile of five major food-borne pathogens isolated from beef, pork and poultry

This study was performed to evaluate the resistance rate against antimicrobials of food isolates of the five major food-borne pathogens to compare these and to possibly distinguish a pattern. A total of 922 samples of the major meat species (pork, beef and poultry) were analysed for thermophilic Campylobacter, Salmonella, Yersinia enterocolitica, pathogenic Escherichia coli and Listeria monocytogenes. Isolates were subjected to antimicrobial resistance testing by the disc diffusion method. Roughly the same overall rate of resistance was identified for thermophilic Campylobacter, Salmonella and pathogenic E. coli. Resistance to quinolones and tetracycline was determined most frequently. In contrast, food isolates of Y. enterocolitica and L. monocytogenes were rarely tested resistant. The significance of our findings is that resistance rates in enteric bacteria seem to be much higher than in pathogens found in a variety of environments, closely associated to the host environment.     

Active masks and active inhibition: A comment on Lleras and Enns (2004) and on Verleger, Ja?kowski, Aydemir, van der Lubbe, and Groen (2004).

Verleger, Ja?kowski, Aydemir, van der Lubbe, and Groen (see record 2004-21166-002) and Lleras and Enns (see record 2004-21166-001) have argued that negative compatibility effects (NCEs) obtained with masked primes do not reflect self-inhibition processes in motor control. Instead, NCEs are assumed to reflect activation of the response opposite to the prime, triggered by the presence of prime/targetlike features in the mask. Thus, no NCEs should be elicited when masks do not contain such task-relevant features. In Experiments 1 and 3, the authors demonstrate that NCEs can be obtained when masks contain only irrelevant features. Experiment 2 demonstrates that positive compatibility effects (PCEs) will occur with such masks when masked primes are presented peripherally. These results are inconsistent with the mask-induced activation accounts but are in line with the self-inhibition hypothesis of the NCE. Although perceptual interactions and mask-induced motor activations may contribute to NCEs under certain conditions, they cannot provide a full explanation for these effects. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Volumetric hemodynamic parameters to guide fluid removal on hemodialysis in the intensive care unit

Estimation of removable excess body fluid is difficult in critically ill patients with renal failure. Volumetric hemodynamic parameters are increasingly being used to guide fluid therapy in the intensive care unit, but their suitability to monitor fluid removal with hemodialysis in critically ill patients is not known. Changes in the extravascular lung water index (EVLWI) and intrathoracic blood volume index (ITBVI) measured with transpulmonary thermodilution immediately before and after hemodialysis were analyzed from 39 hemodialysis sessions of 9 patients consecutively treated in the medical intensive care unit of a German University Hospital. Additional hemodynamic, ventilation, and oxygenation-related parameters were recorded at the same time. Online relative blood volume (RBV) monitoring was performed in 29 sessions. Comparisons of pre and postdialysis values showed a significant reduction of the EVLWI with fluid removal (p=0.009), with only a slight nonsignificant decrease in the ITBVI. The cardiac index (CI) also decreased significantly (p=0.010), whereas blood pressure remained stable. Oxygenation improved significantly (p=0.005), and the hematocrit increased significantly with dialysis (p=0.039). There was no correlation between hematocrit changes and RBV measurements. Significant correlations existed between ITBVI and CI changes (p<0.001), but not to EVLWI reduction. The removal of excess body fluid on hemodialysis is reflected by the EVLWI reduction, whereas the preservation of cardiac preload is shown by ITBVI stability. Volumetric hemodynamic parameters could be useful to guide fluid removal with hemodialysis in the intensive care unit.     

Biosynthesis of the Myxobacterial Antibiotic Corallopyronin A

Corallopyronin A is a myxobacterial compound with potent antibacterial activity. Feeding experiments with labelled precursors resulted in the deduction of all biosynthetic building blocks for corallopyronin A and revealed an unusual feature of this metabolite: its biosynthesis from two chains, one solely PKS‐derived and the other NRPS/PKS‐derived. The starter molecule is believed to be carbonic acid or its monomethyl ester. The putative corallopyronin A biosynthetic gene cluster is a trans‐AT‐type mixed PKS/NRPS gene cluster, containing a β‐branching cassette. Striking features of this gene cluster are a NRPS‐like adenylation domain that is part of a PKS‐type module and is believed to be responsible for glycine incorporation, as well as split modules with individual domains occurring on different genes. It is suggested that CorB is a trans‐acting ketosynthase and it is proposed that it catalyses the Claisen condensation responsible for the interconnection of the two chains. Additionally, the stereochemistry of corallopyronin A was deduced by a combination of a modified Mosher's method and ozonolysis with subsequent chiral GC analyses.     

Artist intermediaries in Berlin: cultural intermediation as an interscalar strategy of self-organizational survival

This paper argues that intermediation is both a valuable form of occupational self-organization for professional artists and a political act of embedding with socio-spatial ramifications at different local, urban, and global scales. A case study of events organized in Berlin by the interdisciplinary cultural centre Zentrum für Kunst und Urbanistik demonstrates how artists strategically practice intermediation as modes of autopoietic and dissipative self-organization and as an interscalar survival strategy. These artist intermediaries add improvisational flexibility to the state’s understanding of Verstetigung (sustainable anchoring that fosters a reliable relationship between urban policymakers and cultural producers) and challenge neoliberal urban development logics that instrumentalize creativity.