Double white dwarf mergers and elemental surface abundances in extreme helium and R Coronae Borealis stars

The surface abundances of extreme helium (EHe) and R Coronae Borealis (RCB) stars are discussed in terms of the merger of a carbon-oxygen white dwarf with a helium white dwarf. The model is expressed as a linear mixture of the individual layers of both constituent white dwarfs, taking account of the specific evolution of each star. In developing this recipe from previous versions, particular attention has been given to the inter-shell abundances of the asymptotic giant branch star which evolved to become the carbon-oxygen white dwarf. Thus the surface composition of the merged star is estimated as a function of the initial mass and metallicity of its progenitor. The question of whether additional nucleosynthesis occurs during the white dwarf merger has been examined. The high observed abundances of carbon and oxygen must either originate by dredge-up from the core of the carbon-oxygen white dwarf during a cold merger or be generated directly by alpha-burning during a hot merger. The presence of large quantities of O18 may be consistent with both scenarios, since a significant O18 pocket develops at the carbon/helium boundary in a number of our post-AGB models. The production of fluorine, neon and phosphorus in the AGB intershell produces n overabundance at the surface of the merged stars, but generally not in sufficient quantity. However, the evidence for an AGB origin for these elements points to progenitor stars with initial masses in the range 1.9 - 3 solar masses. There is not yet sufficient information to discriminate the origin (fossil or prompt) of all the abundance anomalies observed in EHe and RCB stars. Further work is required on argon and s-process elements in the AGB intershell, and on the predicted yields of all elements from a hot merger.Comment: 20 pages, 8 figures, 3 tables, MNRAS in pres

Air-sea exchange of halocarbons: the influence of diurnal and regional variations and distribution of pigments

Diurnal cycles of halocarbons, except methyl bromide and methyl chloride, were observed at six 24-h stations occupied in three different regions, the Summer Ice Edge, the Winter Ice Edge, and the Antarctic Polar Front, in the Atlantic sector of the Southern Ocean during a Swedish-South African expedition in 1997/1998. The diurnal cycles contained three phases; a productive phase, a phase of losses and a phase with steady state. The duration of the different phases varied for the different stations as well as for individual compounds. The measured production and losses of organo-halogens in the Antarctic Ocean based on values from each station, were in the order of a few to hundreds of Tg yr(-1). Bromochloromethane, tribromomethane, trichloroethene and diiodomethane were the four compounds found in highest concentrations throughout the investigation, and they were found to be the major contributors of organohalogens. Only the presence of the photosynthetic pigment 19'-hexanoyloxyfucoxanthin, biomarker pigment of haptophytes, could explain some of the variations in the distribution and production of halocarbons, and then only for iodinated compounds. The flux of organo-halogens from the oceans to the atmosphere was estimated in two ways, either based on calculations according to models or based on the measured concentrations. Large discrepancies were found, which could not be explained by chemical or biological degradation or adsorption to particles. This investigation, therefore, shows the need for assessing the rates of degradation and the air-sea exchange more accurately. (C) 2004 Elsevier Ltd. All rights reserved

Characteristics of lithium-ion batteries during fire tests

Commercial lithium-ion battery cells are exposed to a controlled propane fire in order to evaluate heat release rate (HRR), emission of toxic gases as well as cell temperature and voltage under this type of abuse. The study includes six abuse tests on cells having lithium-iron phosphate (LFP) cathodes and, as a comparison, one test on conventional laptop battery packs with cobalt based cathode. The influence of different state of charge (SOC) is investigated and a limited study of the effect of water mist application is also performed. The total heat release (THR) per battery energy capacity are determined to be 28-75 kJ Wh(-1) and the maximum HRR values to 110-490 W Wh(-1). Hydrogen fluoride (HF) is found in the released gases for all tests but no traceable amounts of phosphorous oxyfluoride (POF3) or phosphorus pentafluoride (PF5) are detected. An extrapolation of expected HF emissions for a typical automotive 10 kWh battery pack exposed to fire gives a release of 400-1200 g HF. If released in a confined environment such emissions of HF may results in unacceptable exposure levels

Surface-enhanced Raman scattering imaging of single living lymphocytes with multivariate evaluation

This paper is aimed to show the possibility to determine individual organic compounds introduced into single living cells with surface-enhanced Raman spectroscopy (SERS). Surface enhancement was achieved with gold colloids that were allowed to diffuse into lymphocytes. An introduced analyte, rhodamine 6G, could be imaged together with for example nucleotides and amino acids of the cell. Multivariate evaluation of surface-enhanced Raman images proved to be a powerful tool for the separation of spectral information of various intracellular components. The principal component analysis (PCA) enabled identification of spectra containing different chemical information and separation of the spectral contribution of rhodamine 6G from the complex cellular matrix

Self-assembled monolayer coating for normalization of surface enhanced Raman spectra

We demonstrate that the use of a self-assembled monolayer, consisting of a thiol derivative of Dabcyl, can be used to normalize surface enhanced Raman signals (SERS) with respect to varying enhancement. Chaotic assemblies of gold nanoparticles exhibit large spatial variation in enhancement. Our work shows that in such a system the signals from the reporting molecules in the SAM co-vary with the signal from the analyte solution. With this knowledge, a normalization procedure was used to increase the precision of the analyte signal by 1 order of magnitude, to 8-13%, fully acceptable for quantitative work

Feasibility of quantitative determination of doxorubicin with surface-enhanced Raman spectroscopy

Surface-enhanced Raman spectroscopy (SERS) was performed using excitation at 488 nm in a blood plasma-doxorubicin-silver colloid system. With a blood plasma content of 1%, a partial least-squares calibration of the doxorubicin was made in the 10-750 nM range. Predictions for a test set generated a root mean square error of prediction of 70 nM. The use of SERS and chemometrics in complex systems made it possible to use the highly informative Raman signals even at low concentrations without the need for sample pretreatment such as extraction. Copyright © 2001 John Wiley & Sons, Ltd

Growth-limiting role of endothelial cells in endoderm development.

Endoderm development is dependent on inductive signals from different structures in close vicinity, including the notochord, lateral plate mesoderm and endothelial cells. Recently, we demonstrated that a functional vascular system is necessary for proper pancreas development, and that sphingosine-1-phosphate (S1P) exhibits the traits of a blood vessel-derived molecule involved in early pancreas morphogenesis. To examine whether S1P(1)-signaling plays a more general role in endoderm development, S1P(1)-deficient mice were analyzed. S1P(1) ablation results in compromised growth of several foregut-derived organs, including the stomach, dorsal and ventral pancreas and liver. Within the developing pancreas the reduction in organ size was due to deficient proliferation of Pdx1(+) pancreatic progenitors, whereas endocrine cell differentiation was unaffected. Ablation of endothelial cells in vitro did not mimic the S1P(1) phenotype, instead, increased organ size and hyperbranching were observed. Consistent with a negative role for endothelial cells in endoderm organ expansion, excessive vasculature was discovered in S1P(1)-deficient embryos. Altogether, our results show that endothelial cell hyperplasia negatively influences organ development in several foregut-derived organs