The unreasonable effectiveness of experiments in constraining nova nucleosynthesis

Classical nova explosions arise from thermonuclear ignition in the envelopes of accreting white dwarfs in close binary star systems. Detailed observations of novae have stimulated numerous studies in theoretical astrophysics and experimental nuclear physics. These phenomena are unusual in nuclear astrophysics because most of the thermonuclear reaction rates thought to be involved are constrained by experimental measurements. This situation allows for rather precise statements to be made about which measurements are still necessary to improve the nuclear physics input to astrophysical models. We briefly discuss desired measurements in these environments with an emphasis on recent experimental progress made to better determine key rates.Postprint (published version

Determination of Global Extractives in Polyethylene Terephthalate by Heating the Solvent in a Microwave Oven

DETERMINATION OF GLOBAL EXTRACTIVES IN POLYETHYLENE TEREPHTHALATE BY HEATING THE SOLVENT IN A MICROWAVE OVEN By Anuj Vinodchandra Parikh The purpose of this research is to evaluate a method of determining extractives. Instead of a conventional oven, a microwave oven is used to heat the solvent. Attempts are made to duplicate the extraction methodology proposed by the Food and Drug Administration (FDA) in a way that it can be used to determine extractives for microwave-only packages. A test package consisting of crystalline polyethylene terephthalate and paper was selected for the test. A product consisting of a dehydrated mix of pasta and cheese sauce was evaluated to determine the test parameters including the solvent, time, and temperature. Distilled deionized water was selected as a solvent. It was exposed in two different package shapes to counter any microwave heating irregularities. The solvent was heated in packages for 10 minutes in a 700 watt microwave oven at maximum power. The extractives, in each case, were obtained by evaporating the solution under reduced temperature of 60°F (15.5°C) and in vacuum, a method commonly referred to as vacuo. A Rotavapor machine was used for this purpose. The extractives were then dried and weighed. They were further dissolved in chloroform. Chloroform-insoluble extractives were filtered out and further extraction was performed on the solution. The temperature was maintained at 35°F (1.7°C). It was found that the amount of extractives obtained by the conventional FDA method were comparable to the ones obtained by this procedure. In both cases the amount of total extractives for this package fell within the specified limits set by the FDA in milligrams per square inch of contact surface

Non-extensive statistics to the cosmological lithium problem

Big Bang nucleosynthesis (BBN) theory predicts the abundances of the light elements D, 3He, 4He, and 7Li produced in the early universe. The primordial abundances of D and 4He inferred from observational data are in good agreement with predictions, however, BBN theory overestimates the primordial 7Li abundance by about a factor of three. This is the so-calledPeer ReviewedPostprint (author's final draft

The Effects of Variations in Nuclear Interactions on Nucleosynthesis in Thermonuclear Supernovae

The impact of nuclear physics uncertainties on nucleosynthesis in thermonuclear supernovae has not been fully explored using comprehensive and systematic studies with multiple models. To better constrain predictions of yields from these phenomena, we have performed a sensitivity study by post-processing thermodynamic histories from two different hydrodynamic, Chandrasekhar-mass explosion models. We have individually varied all input reaction and, for the first time, weak interaction rates by a factor of ten and compared the yields in each case to yields using standard rates. Of the 2305 nuclear reactions in our network, we find that the rates of only 53 reactions affect the yield of any species with an abundance of at least 10^-8 M_sun by at least a factor of two, in either model. The rates of the 12C(a,g), 12C+12C, 20Ne(a,p), 20Ne(a,g) and 30Si(p,g) reactions are among those that modify the most yields when varied by a factor of ten. From the individual variation of 658 weak interaction rates in our network by a factor of ten, only the stellar 28Si(b+)28Al, 32S(b+)32P and 36Ar(b+)36Cl rates significantly affect the yields of species in a model. Additional tests reveal that reaction rate changes over temperatures T > 1.5 GK have the greatest impact, and that ratios of radionuclides that may be used as explosion diagnostics change by a factor of less than two from the variation of individual rates by a factor of 10. Nucleosynthesis in the two adopted models is relatively robust to variations in individual nuclear reaction and weak interaction rates. Laboratory measurements of a limited number of reactions would help to further constrain predictions. As well, we confirm the need for a consistent treatment for relevant stellar weak interaction rates since simultaneous variation of these rates (as opposed to individual variation) has a significant effect on yields in our models.Comment: accepted by A&A, 14 pages, 5 figures, 2 table

Constraints on the mass and radius of the accreting neutron star in the Rapid Burster

The Rapid Burster (MXB 1730-335) is a unique object, showing both type I and type II X-ray bursts. A type I burst of the Rapid Burster was observed with Swift/XRT on 2009 March 5, showing photospheric radius expansion for the first time in this source. We report here on the mass and radius determination from this photospheric radius expansion burst using a Bayesian approach. After marginalization over the likely distance of the system (5.8-10 kpc) we obtain M=1.1+/-0.3 M_sun and R=9.6+/-1.5 km (1-sigma uncertainties) for the compact object, ruling out the stiffest equations of state for the neutron star. We study the sensitivity of the results to the distance, the color correction factor, and the hydrogen mass fraction in the envelope. We find that only the distance plays a crucial role.Comment: 7 pages, 8 figures, Accepted for publication in The Astrophysical Journa

Immediate complications and subsequent reproductive outcome after medical abortion: hospital based cross sectional study

Background: Medical abortion is considered to be a safe, effective and reliable method for termination of pregnancy. The procedure has stood the test of time very well over the last 10 years in terms of results and immediate complications but there are not many reports regarding the subsequent reproductive outcome of these women. Thus, it was decided to conduct a study with special focus on subsequent reproductive outcome in women undergoing medical abortion. The objectives of the study were to determine the source of health care provider for women seeking medical abortion, to study immediate complications of medical abortion, to study acceptance of family planning methods post medical abortion in the study subjects and to study subsequent reproductive outcomes in women who underwent medical abortion.Methods: A cross sectional institution based study was conducted after ethics committee approval in the Obstetrics and Gynecology outpatient department of a tertiary care institute from January 2014 to December 2014. 94 newly registered patients in the age group of 18-35 years who came to the Obstetrics and Gynecology OPD during the study period were interviewed. Amongst these those who have undergone medical abortion in the period between 2010 and 2011 and were willing to participate in the study were enrolled. Diagnosed cases of Diabetes Mellitus, Hypertension and any other major medical or surgical illness were excluded from the study.Study subjects were interviewed with a revalidated, pretested semi structured Questionnaire with due privacy to maintain confidentiality. The data was analyzed by SPSS version 16 software.Results: 13.8% study subjects took their medicines from chemists without consulting any medical professional and 9.5% of them were prescribed these medicines by general practitioners. Prevalence of immediate complications that is incomplete abortion, need for surgical evacuation and excessive bleeding in the study were 17%, 11.7% and 1.1% respectively. Proportion of women who accepted family planning post medical abortion was 62.8%. Prevalence of subsequent reproductive outcomes in females who did not use permanent method of sterilization or got copper T inserted were infertility (7.1%), abortion (8.9%), ectopic pregnancy (3.6%), PIH (10.7%), IUGR (3.6%) and preterm labour (10.7%).Conclusions: Medical abortion using Mifepristone and Misoprostol is a reliable and safe method of termination of early pregnancy (up to 7 weeks period of gestation). These findings are relevant while counseling patients for medical abortion

Scattering and Diffraction in Magnetospheres of Fast Pulsars

We apply a theory of wave propagation through a turbulent medium to the scattering of radio waves in pulsar magnetospheres. We find that under conditions of strong density modulation the effects of magnetospheric scintillations in diffractive and refractive regimes may be observable. The most distinctive feature of the magnetospheric scintillations is their independence on frequency. Results based on diffractive scattering due to small scale inhomogeneities give a scattering angle that may be as large as 0.1 radians, and a typical decorrelation time of $10^{-8}$ seconds. Refractive scattering due to large scale inhomogeneities is also possible, with a typical angle of $10^{-3}$ radians and a correlation time of the order of $10^{-4}$ seconds. Temporal variation in the plasma density may also result in a delay time of the order of $10^{-4}$ seconds. The different scaling of the above quantities with frequency may allow one to distinguish the effects of propagation through a pulsar magnetosphere from the interstellar medium. In particular, we expect that the magnetospheric scintillations are relatively more important for nearby pulsars when observed at high frequencies.Comment: 19 pages, 1 Figur

Recent advances in the modelling of classical novae and type I X-ray bursts

Classical nova outbursts and type I X-ray bursts are thermonuclear stellar explosions driven by charged-particle reactions. Extensive numerical simulations of nova explosions have shown that the accreted envelopes attain peak temperatures between 0.1 and 0.4 GK, for about several hundred seconds, and therefore, their ejecta is expected to show signatures of significant nuclear activity. Indeed, it has been claimed that novae play some role in the enrichment of the interstellar medium through a number of intermediate-mass elements. This includes 17O, 15N, and 13C, systematically overproduced in huge amounts with respect to solar abundances, with a lower contribution to a number of species with A<40, such as 7Li, 19F, or 26Al. In this review, we present new 1-D hydrodynamic models of classical nova outbursts, from the onset of accretion up to the explosion and ejection phases. Special emphasis is put on their gross observational properties (including constraints from meteoritic presolar grains and potential gamma-ray signatures) and on their associated nucleosynthesis. Multidimensional models of mixing at the core-envelope interface during outbursts will also be presented. The impact of nuclear uncertainties on the final yields will be also outlined. Detailed analysis of the relevant reactions along the main nuclear path for type I X-ray bursts has only been scarcely addressed, mainly in the context of parameterized one-zone models. Here, we present a detailed study of the nucleosynthesis and nuclear processes powering type I X-ray bursts. The reported bursts have been computed by means of a spherically symmetric (1D), Lagrangian, hydrodynamic code, linked to a nuclear reaction network that contains 325 isotopes (from 1H to 107Te), and 1392 nuclear processes. These evolutionary sequences, followed from the onset of accretion up to the explosion and expansion stages, have been performed for two different metallicities to explore the dependence between the extension of the main nuclear flow and the initial metal content. We carefully analyze the physical parameters that determine the light curve (including recurrence times, ratios between persistent and burst luminosities, or the extent of the envelope expansion). Results are in qualitative agreement with the observed properties of some well-studied bursting sources.Postprint (published version

Hydrodynamic Models of Type I X-Ray Bursts: Metallicity Effects

Type I X-ray bursts are thermonuclear stellar explosions driven by charged-particle reactions. In the regime for combined H/He-ignition, the main nuclear flow is dominated by the rp-process (rapid proton-captures and beta+ decays), the 3 alpha-reaction, and the alpha-p-process (a suite of (alpha,p) and (p,gamma) reactions). The main flow is expected to proceed away from the valley of stability, eventually reaching the proton drip-line beyond A = 38. Detailed analysis of the relevant reactions along the main path has only been scarcely addressed, mainly in the context of parameterized one-zone models. In this paper, we present a detailed study of the nucleosynthesis and nuclear processes powering type I X-ray bursts. The reported 11 bursts have been computed by means of a spherically symmetric (1D), Lagrangian, hydrodynamic code, linked to a nuclear reaction network that contains 325 isotopes (from 1H to 107Te), and 1392 nuclear processes. These evolutionary sequences, followed from the onset of accretion up to the explosion and expansion stages, have been performed for 2 different metallicities to explore the dependence between the extension of the main nuclear flow and the initial metal content. We carefully analyze the dominant reactions and the products of nucleosynthesis, together with the the physical parameters that determine the light curve (including recurrence times, ratios between persistent and burst luminosities, or the extent of the envelope expansion). Results are in qualitative agreement with the observed properties of some well-studied bursting sources. Leakage from the predicted SbSnTe-cycle cannot be discarded in some of our models. Production of 12C (and implications for the mechanism that powers superbursts), light p-nuclei, and the amount of H left over after the bursting episodes will also be discussed.Comment: 78 pages (pdf), including 34 figures. Accepted for publication in The Astrophysical Journal Suppl. Serie

The Sensitivity of Nucleosynthesis in Type I X-ray Bursts to Thermonuclear Reaction-Rate Variations

We examine the sensitivity of nucleosynthesis in Type I X-ray bursts to variations in nuclear rates. As a large number of nuclear processes are involved in these phenomena -with the vast majority of reaction rates only determined theoretically due to the lack of any experimental information- our results can provide a means for determining which rates play significant roles in the thermonuclear runaway. These results may then motivate new experiments. For our studies, we have performed a comprehensive series of one-zone post-processing calculations in conjunction with various representative X-ray burst thermodynamic histories. We present those reactions whose rate variations have the largest effects on yields in our studies.Comment: 8 pages, accepted for publication in New Astronomy Reviews, Special Issue on "Astronomy with Radioactivities VI" workshop, Ringberg Castle, Germany, Jan. 200