Hydrogen in Type Ic Supernovae?

By definition, a Type Ic supernova (SN Ic) does not have conspicuous lines of hydrogen or helium in its optical spectrum. SNe Ic usually are modelled in terms of the gravitational collapse of bare carbon-oxygen cores. We consider the possibility that the spectra of ordinary (SN 1994I-like) SNe Ic have been misinterpreted, and that SNe Ic eject hydrogen. An absorption feature usually attributed to a blend of Si II 6355 and C II 6580 may be produced by H-alpha. If SN 1994I-like SNe Ic eject hydrogen, the possibility that hypernova (SN 1998bw-like) SNe Ic, some of which are associated with gamma-ray bursts, also eject hydrogen should be considered. The implications of hydrogen for SN Ic progenitors and explosion models are briefly discussed.Comment: Accepted by PASP. Several significant changes including one additional figur

Neon and CNO Abundances for Extreme Helium Stars -- A Non-LTE Analysis

A non-LTE (NLTE) abundance analysis was carried out for three extreme helium stars (EHes): BD+10 2179, BD-9 4395, and LS IV+6 002, from their optical spectra with NLTE model atmospheres. NLTE TLUSTY model atmospheres were computed with H, He, C, N, O, and Ne treated in NLTE. Model atmosphere parameters were chosen from consideration of fits to observed He I line profiles and ionization equilibria of C and N ions. The program SYNSPEC was then used to determine the NLTE abundances for Ne as well as H, He, C, N, and O. LTE neon abundances from Ne I lines in the EHes: LSE 78, V1920 Cyg, HD 124448, and PV Tel, are derived from published models and an estimate of the NLTE correction applied to obtain the NLTE Ne abundance. We show that the derived abundances of these key elements, including Ne, are well matched with semi-quantitative predictions for the EHe resulting from a cold merger (i.e., no nucleosynthesis during the merger) of a He white dwarf with a C-O white dwarf.Comment: Astrophysical Journal, accepte

Behavior and weight correlates of weight-control efforts in Australian women living in disadvantage : the READI study

BackgroundWith increasing obesity rates worldwide, more and more people are actively attempting to lose weight or avoid weight gain, but relatively little is known about what specific behaviors comprise these efforts and which, if any, are associated with better weight control over time.MethodsThis paper reports relationships between body weight, weight-control efforts and related behaviors over a three-year period in 1,634 Australian women. The women were purposefully recruited from 80 disadvantaged neighborhoods in Victoria, Australia. Weight loss efforts were categorized as trying to lose weight, trying to prevent weight gain and no weight-control efforts. Behavioral correlates examined included different kinds of physical activity and consumption of a number of specific foods types.Results and discussionSelf-reported body weight at baseline was higher in women trying to lose weight. Frequency of consumption of low energy density foods was positively associated with reported weight-control efforts, as was frequency of reported total and leisure-time physical activity. Longitudinal associations between changes in weight-control efforts and changes in behaviors were consistent with the cross-sectional findings. At three-year follow up, however, weight-control efforts were not associated with change in body weight. More detailed analyses of specific food choices suggested that part of the explanation of no effect of reported weight-control efforts and weight over time might be that people are not as well-informed as they should be about the energy density of some common foods. In particular, those reporting engagement in weight-control efforts reported reducing consumption of carbohydrate-containing foods such as bread and potatoes more than is justified by their energy content, while they reported increasing consumption of some high energy density foods (e.g., cheese and nuts).ConclusionIt is tentatively concluded that women living in disadvantaged neighborhoods understand messages about weight-control (more activity and foods with lower fat and lower energy density) but that some foods eaten more by women engaged in weight control may reduce the effectiveness of these efforts.<br /

Further Studies on Fire Retardant Polystyrene by Friedel–Crafts Chemistry

The combination of a copolymer of 4-vinylbenzyl alcohol and styrene with 2-ethylhexyldiphenylphosphate (DPP) and with metal chlorides has been studied by TGA, radiative gasification, Cone Calorimetry, and oxygen index measurements. Evidence is presented in support of a cross-linking reaction with the additives and the copolymer, which proceeds through a Friedel–Crafts mechanism. This approach reduces the peak heat release rate (HRR) by 60% as measured in the Cone Calorimeter. There is a significant reduction in the mass loss rate during the thermal degradation, and evidence of char formation is observed in the radiative gasification experiments

Current Assessment and Future Prediction of Forest Cover Change in Cumberland and Morgan Counties, Tennessee: A Modeling Technique

Determining the relationship between human disturbance of the environment and natural forest change is critical for sound natural resource planning. Improved land cover modeling techniques that incorporate geographic information systems and statistical models are needed to assist in this analysis. Continued forest fragmentation due to increasing population and urbanization has created a growing interest in forest protection for the Cumberland Plateau of Tennessee. Specifically, Cumberland and Morgan Counties have seen unprecedented population growth over the last two decades, resulting in fragmentation of forestland. This study developed a model to determine the probability of exurbia development and its resulting forest fragmentation. Geographic data used in the research included satellite imagery from 1992 and 2000, U.S. Census population and demographic estimates, and road and water coverages for the two counties. The first objective of this study was to develop an accurate and efficient procedure for the development of a land cover map for use in a forest change detection system for Cumberland and Morgan Counties, Tennessee. A unique method was developed to generate this procedure by combining post-classification and image differencing. The second objective of the study was to determine the relationship between urbanization and forest loss in Cumberland and Morgan Counties, Tennessee, and to predict current and future land cover patterns. Logistic regression analysis suggested that demographic variables such as education and population along with spatial factors such as slope, distance to water, distance to interstate junctions, and gravity index factors of nearby urban retail centers, significantly influenced the transition of forest to urban cover. Of these parameters, a high gravity index, a suburban designation, and unsloped terrain had the greatest impact on forest to urban conversion. In addition, spatial factors such as parcel distance to water, and parcel distance to interstate junctions significantly influenced the probability of development. Finally, using population density predictions, the model identified the probability that forest land would be urbanized by 2010