Implications of a Sub-Threshold Resonance for Stellar Beryllium Depletion

Abundance measurements of the light elements lithium, beryllium, and boron are playing an increasingly important role in the study of stellar physics. Because these elements are easily destroyed in stars at temperatures 2--4 million K, the abundances in the surface convective zone are diagnostics of the star's internal workings. Standard stellar models cannot explain depletion patterns observed in low mass stars, and so are not accounting for all the relevant physical processes. These processes have important implications for stellar evolution and primordial lithium production in big bang nucleosynthesis. Because beryllium is destroyed at slightly higher temperatures than lithium, observations of both light elements can differentiate between the various proposed depletion mechanisms. Unfortunately, the reaction rate for the main destruction channel, 9Be(p,alpha)6Li, is uncertain. A level in the compound nucleus 10B is only 25.7 keV below the reaction's energetic threshold. The angular momentum and parity of this level are not well known; current estimates indicate that the resonance entrance channel is either s- or d-wave. We show that an s-wave resonance can easily increase the reaction rate by an order of magnitude at temperatures of approximately 4 million K. Observations of sub-solar mass stars can constrain the strength of the resonance, as can experimental measurements at lab energies lower than 30 keV.Comment: 9 pages, 1 ps figure, uses AASTeX macros and epsfig.sty. Reference added, typos corrected. To appear in ApJ, 10 March 199

Quantification and classification of potassium and calcium disorders with the electrocardiogram: What do clinical studies, modeling, and reconstruction tell us?

Diseases caused by alterations of ionic concentrations are frequently observed challenges and play an important role in clinical practice. The clinically established method for the diagnosis of electrolyte concentration imbalance is blood tests. A rapid and non-invasive point-of-care method is yet needed. The electrocardiogram (ECG) could meet this need and becomes an established diagnostic tool allowing home monitoring of the electrolyte concentration also by wearable devices. In this review, we present the current state of potassium and calcium concentration monitoring using the ECG and summarize results from previous work. Selected clinical studies are presented, supporting or questioning the use of the ECG for the monitoring of electrolyte concentration imbalances. Differences in the findings from automatic monitoring studies are discussed, and current studies utilizing machine learning are presented demonstrating the potential of the deep learning approach. Furthermore, we demonstrate the potential of computational modeling approaches to gain insight into the mechanisms of relevant clinical findings and as a tool to obtain synthetic data for methodical improvements in monitoring approaches

A search for stable strange quark matter nuggets in helium

A search for stable strange quark nuggets has been conducted in helium and argon using a high sensitivity mass spectrometer. The search was guided by a mass formula for strange quark nuggets which suggested that stable strange helium might exist at a mass around 65 u. The chemical similarity of such ``strangelets'' to noble gas atoms and the gravitational unboundedness of normal helium result in a large enhancement in the sensitivity of such a search. An abundance limit of no more than $2 \cdot 10^{-11}$ strangelets per normal nucleus is imposed by our search over a mass region from 42 to 82 u, with much more stringent limits at most (non-integer) masses.Comment: 11 pages RevTeX, Accepted for publication in Physics Letters B. 2 updated references added. Air abundance to cosmic abundance ratios now reflect updated references. No change in results or figures. Also see ftp://www-physics.mps.ohio-state.edu/pub/nucex/sq

The rp-process and new measurements of beta-delayed proton decay of light Ag and Cd isotopes

Recent network calculations suggest that a high temperature rp-process could explain the abundances of light Mo and Ru isotopes, which have long challenged models of p-process nuclide production. Important ingredients to network calculations involving unstable nuclei near and at the proton drip line are $\beta$-halflives and decay modes, i.e., whether or not $\beta$-delayed proton decay takes place. Of particular importance to these network calculation are the proton-rich isotopes $^{96}$Ag, $^{98}$Ag, $^{96}$Cd and $^{98}$Cd. We report on recent measurements of $\beta$-delayed proton branching ratios for $^{96}$Ag, $^{98}$Ag, and $^{98}$Cd at the on-line mass separator at GSI.Comment: 4 pages, uses espcrc1.sty. Proceedings of the 4th International Symposium Nuclei in the Cosmos, June 1996, Notre Dame/IN, USA, Ed. M. Wiescher, to be published in Nucl.Phys.A. Also available at ftp://ftp.physics.ohio-state.edu/pub/nucex/nic96-gs

The metallicities of UM151, UM408 and A1228+12 revisited

We present the results of new spectrophotometry and heavy element abundance determinations for 3 dwarf galaxies UM151, UM408 and A1228+12 (RMB132). These galaxies have been claimed in the literature to have very low metallicities, corresponding to log(O/H)+12 < 7.65, that are in the metallicity range of some candidate local young galaxies. We present higher S/N data for these three galaxies. UM151 and UM408 have significantly larger metallicities: log(O/H)+12 = 8.5 and 7.93, respectively. For A1228+12 our new log(O/H)+12 = 7.73 is close to that recalculated from earlier data (7.68). Thus, the rederived metallicities allow us to remove these objects from the list of galaxies with Z < 1/20 Z_Sun.Comment: LaTeX, 8 pages with 3 Postscript figures, A&A in pres

The temporal and spatial evolution of the starburst in ESO 338-IG04 as probed by its star clusters

In this paper we use ultra-violet (UV) and optical HST photometry in five bands, and an extensive set of spectral evolutionary synthesis scenarios to investigate the age and masses of 124 star clusters in the luminous blue compact galaxy ESO338-IG04 (Tololo 1924-416). The very small internal reddening makes ESO 338-IG04 an excellent laboratory for studying the formation of massive star clusters. We have used the star clusters to trace the temporal and spatial evolution of the starburst, and to put constraints on the star formation activity over a cosmological time-scale. The present starburst has been active for about 40 Myr. A standard Salpeter initial mass function (IMF) extending up to 120 solar masses provides the best fit to the data, although a flatter IMF cannot be excluded. The compact star clusters provide 30-40 percent of the UV luminosity and star formation activity. We find no evidence for dust obscuration even among the youngest (< 1 Myr) clusters. The fraction of stellar mass contained in compact star clusters is found to be several percent, which is an unusually high value. The intermediate age clusters show a flattened space distribution which agrees with the isophotal shape of the galaxy, whereas the oldest clusters seem to have a spherical distribution.(abridged)Comment: Accepted for publication in A&

Astrophysical Reaction Rates for 10^{10}B(p,α\alpha)7^{7}Be and 11^{11}B(p,α\alpha)8^{8}Be From a Direct Model

The reactions $^{10}$B(p,$\alpha$)$^{7}$Be and $^{11}$B(p,$\alpha$)$^{8}$Be are studied at thermonuclear energies using DWBA calculations. For both reactions, transitions to the ground states and first excited states are investigated. In the case of $^{10}$B(p,$\alpha$)$^{7}$Be, a resonance at $E_{Res}=10$ keV can be consistently described in the potential model, thereby allowing the extension of the astrophysical $S$-factor data to very low energies. Strong interference with a resonance at about $E_{Res}=550$ keV require a Breit-Wigner description of that resonance and the introduction of an interference term for the reaction $^{10}$B(p,$\alpha_1$)$^{7}$Be$^*$. Two isospin $T=1$ resonances (at $E_{Res1}=149$ keV and $E_{Res2}=619$ keV) observed in the $^{11}$B+p reactions necessitate Breit-Wigner resonance and interference terms to fit the data of the $^{11}$B(p,$\alpha$)$^{8}$Be reaction. $S$-factors and thermonuclear reaction rates are given for each reaction. The present calculation is the first consistent parametrization for the transition to the ground states and first excited states at low energies.Comment: 27 pages, 5 Postscript figures, uses RevTex and aps.sty; preprint also available at http://quasar.physik.unibas.ch/ Phys. Rev. C, in pres

Reaction rates for Neutron Capture Reactions to C-, N- and O-isotopes to the neutron rich side of stability

The reaction rates of neutron capture reactions on light nuclei are important for reliably simulating nucleosynthesis in a variety of stellar scenarios. Neutron capture reaction rates on neutron-rich C-, N-, and O-isotopes are calculated in the framework of a hybrid compound and direct capture model. The results are tabulated and compared with the results of previous calculations as well as with experimental results.Comment: 33 pages (uses revtex) and 9 postscript figures, accepted for publication in Phys. Rev.

GMASS Ultradeep Spectroscopy of Galaxies at redshift z~2. I. The stellar metallicity

Context: Galaxy metallicities have been measured to redshift z~2 by gas-phase oxygen abundances of the interstellar medium using the R23 and N2 methods. Galaxy stellar metallicities provide crucial data for chemical evolution models but have not been assessed reliably much outside the local Universe. Aims: We determine the iron-abundance, stellar metallicity of star-forming galaxies (SFGs) at redshift z~2, observed as part of the Galaxy Mass Assembly ultra-deep Spectroscopic Survey (GMASS). Methods: We compute the equivalent width of a rest-frame mid-ultraviolet, photospheric absorption-line index, the 1978 index found to vary monotonically with stellar metallicity by Rix and collaborators. We normalise and combine 75 SFG spectra from the GMASS survey to produce a spectrum corresponding to a total integration time 1652.5 hours (and a signal-to-noise ratio ~100 for our 1.5 angstrom binning) of FORS2 spectroscopic observations at the Very Large Telescope. Results: We measure an iron-abundance, stellar metallicity of log (Z/Zsolar) = -0.574+/-0.159 for our spectrum representative of a galaxy of stellar mass 9.4 x 10^9 Msolar assuming a Chabrier IMF. We find that the R04 model SFG spectrum for log (Z/Zsolar) = -0.699 solar metallicity provides the best description of our GMASS coadded spectrum. For similar galaxy stellar mass, our stellar metallicity is ~0.25 dex lower than the oxygen-abundance, gas-phase metallicity quantified by Erb and collaborators for UV-selected star-forming galaxies at z=2. Conclusions: We conclude that we are witnessing the establishment of a light-element overabundance in galaxies as they are being formed at redshift z~2. Our measurements are reminiscent of the alpha-element enhancement seen in low-redshift, galactic bulges and early-type galaxies. (Abridged)Comment: Accepted for publication in Astronomy and Astrophysics on 18 December 2007, 9 pages, 8 figures, aa.bst and aa.cls A&A style file

A Salivary Urea Nitrogen Dipstick to Detect Obstetric-Related Acute Kidney Disease in Malawi

Introduction: Obstetric-related acute kidney injury (AKI) is associated with adverse outcomes for mother and fetus, particularly in low-income countries. However, laboratory-independent tools to facilitate diagnosis are lacking. We assessed the diagnostic performance of a salivary urea nitrogen (SUN) dipstick to detect obstetric-related acute kidney disease in Malawi. / Methods: Women at high risk for AKI admitted to an obstetric unit in Blantyre, Malawi, were recruited between 21 September and 11 December 2015. Patients underwent serum creatinine (SCr) testing alongside measurement of SUN using a dipstick on admission, and every 48 hours thereafter if evidence of kidney disease was found. / Results: A total of 301 patients were included (mean age 25.9 years, 11% HIV positive). Of the patients, 23 (7.6%) had AKI, stage 1 in 47.8%, most commonly due to preeclampsia/eclampsia. Mean presenting SCr values were 108.8 ± 21.8 μmol/l (1.23 ± 0.25 mg/dl), 118 ± 34.45 μmol/l (1.33 ± 0.39 mg/dl), and 136.1 ± 30.4 μmol/l (1.54 ± 0.34 mg/dl) in AKI stages 1 to 3 respectively. SUN > 14 mg/dl had a sensitivity of 12.82% and a specificity of 97.33% to detect acute kidney disease; the area under the receiver operating characteristic curve was 0.551. In patients with normal SUN on admission, perinatal mortality was 11.8%, and was 25.0% if SUN was?> 14 mg/dl (P = 0.18). / Conclusion: The SUN dipstick was specific but insensitive when used to diagnose obstetric-related AKI. Limited biochemical derangement and low salivary urea concentrations due to physiological changes in pregnancy, as opposed to a technical limitation of the dipstick itself, are the likely reason for the lack of sensitivity in this study