The Influence of Metallicity on Star Formation in Protogalaxies

In cold dark matter cosmological models, the first stars to form are believed to do so within small protogalaxies. We wish to understand how the evolution of these early protogalaxies changes once the gas forming them has been enriched with small quantities of heavy elements, which are produced and dispersed into the intergalactic medium by the first supernovae. Our initial conditions represent protogalaxies forming within a fossil H II region, a previously ionized region that has not yet had time to cool and recombine. We study the influence of low levels of metal enrichment on the cooling and collapse of ionized gas in small protogalactic halos using three-dimensional, smoothed particle hydrodynamics (SPH) simulations that incorporate the effects of the appropriate chemical and thermal processes. Our previous simulations demonstrated that for metallicities Z < 0.001 Z_sun, metal line cooling alters the density and temperature evolution of the gas by less than 1% compared to the metal-free case at densities below 1 cm-3) and temperatures above 2000 K. Here, we present the results of high-resolution simulations using particle splitting to improve resolution in regions of interest. These simulations allow us to address the question of whether there is a critical metallicity above which fine structure cooling from metals allows efficient fragmentation to occur, producing an initial mass function (IMF) resembling the local Salpeter IMF, rather than only high-mass stars.Comment: 3 pages, 2 figures, First Stars III conference proceeding

Strengthening Capacities of Communities for Sustainable Forest Management : The Case of Renk County, South Sudan

Peer reviewe

The Drosophila phosphatidylinositol transfer protein encoded by vibrator is essential to maintain cleavage-furrow ingression in cytokinesis

Cytokinesis requires the coordination of cytoskeletal and plasma membrane dynamics. A role for phosphatidylinositol lipids has been proposed for the successful completion of cytokinesis but this is still poorly characterised. Here, we show mutants of the gene vibrator, previously found to encode the Drosophila phosphatidylinositol transfer protein, produce multinucleate cells indicative of cytokinesis failure in male meiosis. Examination of fixed preparations of mutant spermatocytes showed contractile rings of anillin and actin that were of normal appearance at early stages but were larger and less well organised at later stages of cytokinesis than in wild-type cells. Time-lapse imaging revealed sequential defects in cytokinesis of vibrator spermatocytes. In cells that fail cytokinesis, central spindle formation occurred correctly, but furrow ingression was delayed and the central spindle did not become compressed to the extent seen in wild-type cells. Cells then stalled at this point before the apparent connection between the constricted cytoskeleton and the plasma membrane was lost; the furrow then underwent elastic regression. We discuss these defects in relation to multiple functions of phosphoinositol lipids in regulating actin dynamics and membrane synthesis

Survey on Consumption of Vegetables and Fruits in a Coastal District in Ghana

In 2000, The World Health Organisation reported that at least 254 million preschool children suffer from subclinical vitamin A deficiency (VAD) globally. Vitamin A deficiency adversely affects growth, reproduction and resistance to infection, which could have serious economic consequences for a nation in terms of increased medical cost and reduced workforce. Strategies to reduce VAD included periodic vitamin A supplementation of children, but this is donor-dependent and therefore not sustainable. Dietary diversification in low income groups using beta-carotene rich foods such as orange fleshed foods and green leafy vegetables is being advocated. For an effective nutrition promotion drive, however, it is important to study the foods consumed in a particular locality so as to design an appropriate intervention package for that community. The current work therefore surveyed the consumption of vegetables and fruits in a coastal district of Ghana so as to identify the potential vegetables that could be promoted in the district for improving their vitamin A status. The results showed that several fruits and vegetables are eaten in the district, but the potential beta-carotene rich ones that could be promoted on a sustainable basis are mangoes and drumstick leaves. Mangoes are abundant in the district during the two fruiting seasons and could be easily accessed by the inhabitants. Likewise, drumstick leaves are available all year round and these could be incorporated into selected recipes in the school feeding programme, and could also be used in making convenience foods for easy access. Keywords: Beta-carotene, vitamin A deficiency (VAD), green leafy vegetables, fruit

Dynkin games with heterogeneous beliefs

Copyright © 2017 Applied Probability Trust. We study zero-sum optimal stopping games (Dynkin games) between two players who disagree about the underlying model. In a Markovian setting, a verification result is established showing that if a pair of functions can be found that satisfies some natural conditions then a Nash equilibrium of stopping times is obtained, with the given functions as the corresponding value functions. In general, however, there is no uniqueness of Nash equilibria, and different equilibria give rise to different value functions. As an example, we provide a thorough study of the game version of the American call option under heterogeneous beliefs. Finally, we also study equilibria in randomized stopping times

Data management for JGOFS: Theory and design

The Joint Global Ocean Flux Study (JGOFS), currently being organized under the auspices of the Scientific Committee for Ocean Research (SCOR), is intended to be a decade long internationally coordinated program. The main goal of JGOFS is to determine and understand on a global scale the processes controlling the time-varying fluxes of carbon and associated biogenic elements in the ocean and to evaluate the related exchanges with the atmosphere, sea floor and continental boundaries. 'A long-term goal of JGOFS will be to establish strategies for observing, on long time scales, changes in ocean biogeochemical cycles in relation to climate change'. Participation from a large number of U.S. and foreign institutions is expected. JGOFS investigators have begun a set of time-series measurements and global surveys of a wide variety of biological, chemical and physical quantities, detailed process-oriented studies, satellite observations of ocean color and wind stress and modeling of the bio-geochemical processes. These experiments will generate data in amounts unprecedented in the biological and chemical communities; rapid and effortless exchange of these data will be important to the success of JGOFS

MULTI-PARENTAL MATING DESIGN ANALYSIS: MODEL EVALUATION AND APPLICATION IN SPRING WHEAT

Conventional quantitative genetics studies have mainly focused on bi-parental mating systems. However, genetic potential of selected individuals within a segregating population may be limited due to only two parents being used for each cross. Multiple-parental mating systems have been proposed that involve three or four diverse parents. This provides a higher potential of combining desirable genes. Due to complexity of the data structure of multi-parental mating systems, analysis of variance (ANOVA) methods are not applicable in analysis. The objective of this study is to validate and apply a mixed linear model approach, minimum norm quadratic unbiased estimation (MINQUE), to analyze a widely used additive-dominance (AD) genetic model. Various simulations were conducted to validate the use of this approach. Twelve different spring wheat genotypes were used to develop populations in the study. Phenotypic data containing parents and their F2 (second filial generation) on preharvest sprouting (PHS) resistance in spring wheat (Triticum aestivum L.) developed by multi-parental crosses were used as a demonstration. The simulation study showed that a modified AD model can be used to estimate variance components in an unbiased manner within this complex data structure. Actual data analysis revealed that both additive and dominance effects were responsible for PHS resistance. Several parents associated with desirable additive effects for PHS were identified. In addition, some crosses with desirable heterozygous dominance effects were also identified, which can be used for hybrid development. Results should help breeders to obtain useful genetic information by using the methods suggested in this study

The 190 kDa centrosome-associated protein of Drosophila melanogaster contains four zinc finger motifs and binds to specific sites on polytene chromosomes

Microinjection of a bacterially expressed, TRITC labelled fragment of the centrosome-associated protein CP190 of Drosophila melanogaster, into syncytial Drosophila embryos, shows it to associate with the centrosomes during mitosis, and to relocate to chromatin during interphase. Indirect immunofluorescence staining of salivary gland chromosomes of third instar Drosophila larvae, with antibodies specific to CP190, indicate that the protein is associated with a large number of loci on these interphase polytene chromosomes. The 190 kDa CP190 protein is encoded by a 4.1 kb transcript with a single, long open reading frame specifying a polypeptide of 1,096 amino acids, with a molecular mass of 120 kDa, and an isoelectric point of 4.5. The central region of the predicted amino acid sequence of the CP190 protein contains four CysX₂CysX₁₂HisX₄His zinc-finger motifs which are similar to those described for several well characterised DNA binding proteins. The data suggest that the function of CP190 involves cell cycle dependent associations with both the centrosome, and with specific chromosomal loci

The 190 kDa centrosome-associated protein of Drosophila melanogaster contains four zinc finger motifs and binds to specific sites on polytene chromosomes

Microinjection of a bacterially expressed, TRITC labelled fragment of the centrosome-associated protein CP190 of Drosophila melanogaster, into syncytial Drosophila embryos, shows it to associate with the centrosomes during mitosis, and to relocate to chromatin during interphase. Indirect immunofluorescence staining of salivary gland chromosomes of third instar Drosophila larvae, with antibodies specific to CP190, indicate that the protein is associated with a large number of loci on these interphase polytene chromosomes. The 190 kDa CP190 protein is encoded by a 4.1 kb transcript with a single, long open reading frame specifying a polypeptide of 1,096 amino acids, with a molecular mass of 120 kDa, and an isoelectric point of 4.5. The central region of the predicted amino acid sequence of the CP190 protein contains four CysX₂CysX₁₂HisX₄His zinc-finger motifs which are similar to those described for several well characterised DNA binding proteins. The data suggest that the function of CP190 involves cell cycle dependent associations with both the centrosome, and with specific chromosomal loci