Polarization fluctuations in vertical cavity surface emitting lasers: a key to the mechanism behind polarization stability

We investigate the effects of the electron-hole spin dynamics on the polarization fluctuations in the light emitted from a vertical cavity surface emitting laser (VCSEL). The Langevin equations are derived based on a rate equation model including birefringence, dichroism, and two carrier density pools seperately coupled to right and left circular polarization. The results show that the carrier dynamics phase lock the polarization fluctuations to the laser mode. This is clearly seen in the difference between fluctuations in ellipticity and fluctuations in polarization direction. Seperate measurements of the polarization fluctuations in ellipticity and in polarization direction can therefore provide quantitative information on the non-linear contribution of the carrier dynamics to polarization stability in VCSELs.Comment: 6 pages RevTex and 3 figures, to be published in Quantum and Semiclassical Optics, minor changes to the discussion of timescale

Short Adolescents Born Small for Gestational Age : Gonadal and thyroid function, bone mineral density, quality of life and adult height: The effects of growth hormone and additional postponement of puberty

From 1991, our research group and others have been investigating children with short stature who were born small for gestational age (SGA), both before and during treatment with biosynthetic growth hormone (GH). In 2005, GH treatment was licensed for short SGA children in the Netherlands. Many questions though remained unanswered, especially about the efficacy of GH treatment when started at an older age, just before or during puberty. This doctoral thesis describes studies evaluating short adolescents born SGA who were treated with GH, and additionally with postponement of puberty by gonadotropin-releasing hormone analogue (GnRHa)

Spectroscopic studies of hydrogen dopants in ZnO crystals

University of Technology, Sydney. Faculty of Science.ZnO is a semiconductor with a direct band gap of 3:37 eV and an exciton binding energy of 60meV at room temperature. These properties make it an attractive material for optoelectronic devices across a wide range of applications. Significant obstacles preventing the wide scale usage of ZnO include the lack of reliable p-type doping and high uncertainty surrounding the nature of its defects. Moreover, as-grown ZnO is intrinsically n-type and it is thought that hydrogen is the cause for the high n-type character. The aim of this thesis is therefore to elucidate the role of hydrogen with respect to the optical and electrical properties of ZnO as well as its interaction with native defects and impurities. During this work, hydrogen was introduced in ZnO single crystals through an RF plasma source. Hydrogen incorporation was confirmed by XPS measurements which showed an increase in hydrogenated oxygen states. Hydrogen also modified the near-surface region of the crystals only and not the bulk. Hydrogen doped ZnO showed significant increases in the carrier concentration as well as in the near band edge (NBE) luminescence. This is attributed to hydrogen introducing new shallow donors. The green luminescence, whose origin is attributed to VZn, was quenched after hydrogen incorporation, indicating formation of neutral VZn-H2 complexes. The yellow luminescence in the as-received crystal is identical to that in Li doped ZnO and was assigned to recombinations involving LiZn. Hydrogen doped ZnO also exhibits a negative thermal quenching (NTQ) of the NBE luminescence where the intensity of the luminescence increases with increasing temperature. Q-DLTS measurements detected new electronic states being created following hydrogen incorporation. A model involving the H-related state at 11meV releasing electrons to form free excitons is proposed to explain the NTQ behaviour. XANES studies of H-doped ZnO showed that hydrogen interacted with oxygen states only but not zinc. This suggests that most of the hydrogen dopants introduced by plasma sit at the oxygen anti-bonding site. The recombination kinetics of the various luminescence was investigated. While the kinetics of the NBE luminescence followed the expected behaviour for excitonic type recombination, the green and yellow luminescences showed high temperature dependencies and is explained in terms of different recombination mechanisms.a Finally, it was found that hydrogen is stable under normal SEM excitation conditions

Efficiency of aerosol collection on wires exposed in the stratosphere

The theory of inertial impaction is briefly presented. Stratospheric aerosol research experiments were performed duplicating Wong et al. experiments. The use of the curve of inertial parameters vs particle collection efficiency, derived from Wong et al., was found to be justified. The results show that stratospheric aerosol particles of all sizes are collectible by wire impaction technique. Curves and tables are presented and used to correct particle counts for collection efficiencies less than 100%

An integrated approach to the interpretation of Single Amino Acid Polymorphisms within the framework of CATH and Gene3D

Background: The phenotypic effects of sequence variations in protein-coding regions come about primarily via their effects on the resulting structures, for example by disrupting active sites or affecting structural stability. In order better to understand the mechanisms behind known mutant phenotypes, and predict the effects of novel variations, biologists need tools to gauge the impacts of DNA mutations in terms of their structural manifestation. Although many mutations occur within domains whose structure has been solved, many more occur within genes whose protein products have not been structurally characterized.Results: Here we present 3DSim (3D Structural Implication of Mutations), a database and web application facilitating the localization and visualization of single amino acid polymorphisms (SAAPs) mapped to protein structures even where the structure of the protein of interest is unknown. The server displays information on 6514 point mutations, 4865 of them known to be associated with disease. These polymorphisms are drawn from SAAPdb, which aggregates data from various sources including dbSNP and several pathogenic mutation databases. While the SAAPdb interface displays mutations on known structures, 3DSim projects mutations onto known sequence domains in Gene3D. This resource contains sequences annotated with domains predicted to belong to structural families in the CATH database. Mappings between domain sequences in Gene3D and known structures in CATH are obtained using a MUSCLE alignment. 1210 three-dimensional structures corresponding to CATH structural domains are currently included in 3DSim; these domains are distributed across 396 CATH superfamilies, and provide a comprehensive overview of the distribution of mutations in structural space.Conclusion: The server is publicly available at http://3DSim.bioinfo.cnio.es/. In addition, the database containing the mapping between SAAPdb, Gene3D and CATH is available on request and most of the functionality is available through programmatic web service access

Peleraian Buah Sawit dari Tandan Menggunakan Kaedah Kimia

A study was conducted on the effectiveness of a chemical substance, ethephon, on the 100 ening of oil palm fruit lets. Factors considered in the study were storage period, degree of ripeness, region and layer of spikelets within the oil palm bunch. Ethephon was poured into the stalk through a hole made using an electrical auger. The results obtained were analysed statistically using ANOVA and showed that the loosening of oil palm fruitlets was affected significantly by storage period, degree of ripeness and layer of spikelets within the bunch, but not by the region of spikelets

Results of Skylab medical experiment M171: Metabolic activity

The experiment was conducted to establish whether man's ability to perform mechanical work would be progressively altered as a result of exposure to the weightless environment of space flight. The Skylab crewmen exercised on a bicycle ergometer at workloads approximating 25, 50, and 75 percent of their maximum aerobic capacity. The physiological parameters monitored were respiratory gas exchange, blood pressure, and vectorcardiogram/heart rate. The results of these tests indicate that the crewmen had no significant decrement in their responses to exercise during their exposure to zero gravity. The results of the third manned Skylab mission (Skylab 4) are presented and a comparison is made of the overall results obtained from the three successively longer Skylab manned missions. The Skylab 4 crewmembers' 84-day in-flight responses to exercise were no worse and were probably better than the responses of the crewmen on the first two Skylab missions. Indications that exercise was an important contributing factor in maintaining this response are discussed

Characterization of pathogenic germline mutations in human Protein Kinases

Background: Protein Kinases are a superfamily of proteins involved in crucial cellular processes such as cell cycle regulation and signal transduction. Accordingly, they play an important role in cancer biology. To contribute to the study of the relation between kinases and disease we compared pathogenic mutations to neutral mutations as an extension to our previous analysis of cancer somatic mutations. First, we analyzed native and mutant proteins in terms of amino acid composition. Secondly, mutations were characterized according to their potential structural effects and finally, we assessed the location of the different classes of polymorphisms with respect to kinase-relevant positions in terms of subfamily specificity, conservation, accessibility and functional sites.Results: Pathogenic Protein Kinase mutations perturb essential aspects of protein function, including disruption of substrate binding and/or effector recognition at family-specific positions. Interestingly these mutations in Protein Kinases display a tendency to avoid structurally relevant positions, what represents a significant difference with respect to the average distribution of pathogenic mutations in other protein families.Conclusions: Disease-associated mutations display sound differences with respect to neutral mutations: several amino acids are specific of each mutation type, different structural properties characterize each class and the distribution of pathogenic mutations within the consensus structure of the Protein Kinase domain is substantially different to that for non-pathogenic mutations. This preferential distribution confirms previous observations about the functional and structural distribution of the controversial cancer driver and passenger somatic mutations and their use as a proxy for the study of the involvement of somatic mutations in cancer development. © 2011 Izarzugaza et al; licensee BioMed Central Ltd

Light-Dependent Translocation of Arrestin in the Absence of Rhodopsin Phosphorylation and Transducin Signaling

Visual arrestin plays a crucial role in the termination of the light response in vertebrate photoreceptors by binding selectively to light-activated, phosphorylated rhodopsin. Arrestin localizes predominantly to the inner segments and perinuclear region of dark-adapted rod photoreceptors, whereas light induces redistribution of arrestin to the rod outer segments. The mechanism by which arrestin redistributes in response to light is not known, but it is thought to be associated with the ability of arrestin to bind photolyzed, phosphorylated rhodopsin in the outer segment. In this study, we show that light-driven translocation of arrestin is unaffected in two different mouse models in which rhodopsin phosphorylation is lacking. We further show that arrestin movement is initiated by rhodopsin but does not require transducin signaling. These results exclude passive diffusion and point toward active transport as the mechanism for light-dependent arrestin movement in rod photoreceptor cells