Heterogeneous hydride pyrolysis in a chemical beam epitaxy cracker cell and growth of high quality InP

The decomposition of phosphine and arsine in a chemical beam epitaxy cracker cell was investigated with a quadrupole mass spectrometer. We have determined the kinetical parameters for a unimolecular reaction of the first order, i.e. the activation energy and frequency factor, from the decomposition efficiency as a function of temperature. These results are compared with data from literature. We find the lowest activation energies ever reported for the hydride pyrolysis, namely 72 and 48 kJ/mol for phosphine and arsine, respectively. This is due to the heterogeneous decomposition on catalytic molybdenum baffles inside the cracker cell. Additionally, we have studied the impurity incorporation in epitaxially grown bulk InP layers in relation to the efficiency of this particular molybdenum containing cracker cell. Impurity levels were determined by fitting calculated Hall values to experimental data. The best quality is achieved for the cracker temperature at which the efficiency starts to saturate. At this cracker temperature, optimized mass flow rates resulted in InP layers with a maximum mobility of 186¿000 cm2/V¿s and impurity concentrations in the low 1014 cm-3 range

The Evolution of Functionally Redundant Species; Evidence from Beetles

While species fulfill many different roles in ecosystems, it has been suggested that numerous species might actually share the same function in a near neutral way. So-far, however, it is unclear whether such functional redundancy really exists. We scrutinize this question using extensive data on the world’s 4168 species of diving beetles. We show that across the globe these animals have evolved towards a small number of regularly-spaced body sizes, and that locally co-existing species are either very similar in size or differ by at least 35%. Surprisingly, intermediate size differences (10–20%) are rare. As body-size strongly reflects functional aspects such as the food that these generalist predators can eat, these beetles thus form relatively distinct groups of functional look-a-likes. The striking global regularity of these patterns support the idea that a self-organizing process drives such species-rich groups to self-organize evolutionary into clusters where functional redundancy ensures resilience through an insurance effect

Evolution of Blind Beetles in Isolated Aquifers: A Test of Alternative Modes of Speciation

Evidence is growing that not only allopatric but also sympatric speciation can be important in the evolution of species. Sympatric speciation has most convincingly been demonstrated in laboratory experiments with bacteria, but field-based evidence is limited to a few cases. The recently discovered plethora of subterranean diving beetle species in isolated aquifers in the arid interior of Australia offers a unique opportunity to evaluate alternative modes of speciation. This naturally replicated evolutionary experiment started 10-5 million years ago, when climate change forced the surface species to occupy geographically isolated subterranean aquifers. Using phylogenetic analysis, we determine the frequency of aquifers containing closely related sister species. By comparing observed frequencies with predictions from different statistical models, we show that it is very unlikely that the high number of sympatrically occurring sister species can be explained by a combination of allopatric evolution and repeated colonisations alone. Thus, diversification has occurred within the aquifers and likely involved sympatric, parapatric and/or microallopatric speciation

The Relationship between Dioxin-Like Polychlorobiphenyls and IGF-I Serum Levels in Healthy Adults: Evidence from a Cross-Sectional Study

OBJECTIVE: Insulin-like growth factor I (IGF-I) and dioxin-like polychlorobiphenyls (DL-PCBs) have been associated with the pathogenesis of several diseases like cancer, diabetes and growth disorders. Because it has been suggested that organohalogenated contaminants could influence IGF-I levels in adults, the potential relationship between DL-PCBs and IGF-I serum levels was studied in 456 healthy adults from a representative sample of the general population of the Canary Islands (Spain). DESIGN: Free circulating serum levels of IGF-I and IGFBP-3 were measured through an ELISA methodology, while the serum levels of the 12 DL-PCBs congeners (IUPAC numbers # 77, 81, 105, 114, 118, 123, 126, 156, 157, 167, 169, and 189) were measured by gas chromatography/mass spectrometry (GC-MS). RESULTS: DL-PCBs 156 and 167, Total DL-PCBs body burden (∑PCBs: sum over the 12 measured DL-PCBs), and Total toxic burden (in terms of toxic equivalence to dioxins: ∑TEQs) showed a trend of inverse association with IGF-I serum levels in the whole studied population. After adjusting for potential confounders, including gender, body mass index (BMI), age, and IGF-binding protein-3 (IGFBP-3), younger (18-45 years) women with lower BMI (<27 kg/m(2)) and detectable levels of DL-PCB-156 showed significantly lower IGF-I levels than those in the same age and BMI subgroup with non-detectable levels of DL-PCB-156 (p<0.001). Similarly, ∑PCBs and ∑TEQs showed a tendency to an inverse association with IGF-I levels in the same group of women (p=0.017 and p=0.019 respectively). CONCLUSIONS: These findings suggest that DL-PCBs could be involved in the regulation of the IGF-system in a way possibly influenced by gender, age and BMI. Although these results should be interpreted with caution, such circumstances could contribute to explain the development of diseases associated to the IGF system

Systematics and evolution of the Australian subterranean hydroporine diving beetles (Dytiscidae), with notes on Carabhydrus

© CSIRO 2008Calcrete aquifers of the Yilgarn area of Western Australia and the Ngalia Basin, Northern Territory, Australia are known to contain a rich invertebrate stygofauna, including the world’s most diverse assemblage of subterranean diving beetles. Here we determine the generic relationships of these subterranean diving beetle species in the tribe Hydroporini and assess their evolutionary origins. Phylogenetic analyses of 1642 base pairs of mitochondrial DNA (mtDNA), comprising segments of CO1, 16S rRNA, tRNAleu and ND1 genes, revealed that the subterranean species from the arid zone, previously classified under the genus Nirripirti Watts & Humphreys (Hydroporini), are all closely related to the genus Paroster Sharp. We synonymise the stygobitic genus Nirripirti with the genus Paroster. Factors that may have been important for the transitions to stygobitic life such as historical and contemporary species distributions, reproductive ecology and body size are discussed. We show that pre-adaptations such as preference for temporary, but seasonally reliable, water and preference to live among gravel and sand along running water would have favoured transitions from surface to stygobitic life, but that large body size may have restricted the likelihood of successful transitions.Remko Leys and Chris H. Watt

Notes on Australian Hyphydrus ILLIGER, including taxonomy, key to the species and sexual dimorphism (Coleoptera: Dytiscidae)

C.H.S. Watts & R. Ley

Effect of butt joint reflections on the performance of extended cavity lasers and phased array multi-wavelength lasers

We have fabricated two types of integrated optical amplifiers using a Selective Area Chemical Beam Epitaxy regrowth step. In the first type of amplifier, the Multi Quantum Well active layer is on top of a waveguiding film, and the transition from the active to the passive regions is characterized by a small residual reflection. In the second type, the active layer is in the center of the film, and the residual reflection is very low. We report on the influence of the residual inter-cavity butt joint reflections on the performance of Extended Cavity Lasers and Phased Array Multi-Wavelength Lasers