Core-collapse supernovae and gravitational waves

Core-collapse supernovae are dramatic events with a rich phenomenology, including gravitational radiation. Simulations of these events in multiple spatial dimensions with energy- and angle-dependent neutrino transport are still in their infancy. Core collapse and bounce in a supernova in our galaxy may well be visible by first-generation LIGO, but detailed understanding waits on improvements in modeling both stellar progenitors and the supernova process.Comment: 3 pages. Talk presented in the Parallel Session on Gravity and Gravitational Waves at TAUP2003, September 5 - 9, 2003, University of Washington, Seattle, Washingto

Non-spherical core collapse supernovae III. Evolution towards homology and dependence on the numerical resolution

(abridged) We study the hydrodynamic evolution of a non-spherical core-collapse supernova in two spatial dimensions. We find that our model displays a strong tendency to expand toward the pole. We demonstrate that this expansion is a physical property of the low-mode, SASI instability. The SASI leaves behind a large lateral velocity gradient in the post shock layer which affects the evolution for minutes and hours later. This results in a prolate deformation of the ejecta and a fast advection of Ni-rich material from moderate latitudes to the polar regions. This effect might actually be responsible for the global asymmetry of the nickel lines in SN 1987A. The simulations demonstrate that significant radial and lateral motions in the post-shock region, produced by convective overturn and the SASI during the early explosion phase, contribute to the evolution for minutes and hours after shock revival. They lead to both later clump formation, and a significant prolate deformation of the ejecta which are observed even as late as one week after the explosion. As pointed out recently by Kjaer et al., such an ejecta morphology is in good agreement with the observational data of SN 1987A. Systematic future studies are needed to investigate how the SASI-induced late-time lateral expansion depends on the dominant mode of the SASI, and to which extent it is affected by the dimensionality of the simulations. The impact on and importance of the SASI for the distribution of iron group nuclei and the morphology of the young SNR argues for future three-dimensional explosion and post-explosion studies on singularity-free grids that cover the entire sphere. Given the results of our 2D resolution study, present 3D simulations must be regarded as underresolved, and their conclusions must be verified by a proper numerical convergence analysis in three dimensions.Comment: 16 pages, 20 figures, accepted for publication in Astronomy & Astrophysic

Trends in the concentration and distribution of health care expenditures in the US, 2001-2018

Importance: The concentration of health care expenditures has important implications for managing risk pools, drug benefit design, and care management. Objective: To examine trends in the concentration of health care spending in different population groups and expenditure categories in the US between 2001 and 2018. Design, Setting, and Participants: This study is a cross-sectional analysis of Medical Expenditure Panel Surveys (MEPS) collected between 2001 and 2018. The MEPS is a household survey of medical expenditures weighted to represent national estimates in the US. Respondents were a nationally representative sample of the US civilian noninstitutionalized population. Data analysis was performed from December 2020 to February 2021. Main Outcomes and Measures: The main outcome is the concentration of health care expenditures as measured by the cumulative percentage of health expenditure vs percentage of ranked population. This study reports trends in the distribution of populations across 4 concentration curve parameters: top 50% expenditure (high spenders), next 49% expenditure (medium spenders), next 1% expenditure (low spenders), and nonspenders. Results: The mean sample size of the MEPS surveys used in the analysis was 34539 individuals, and the sample size varied between 30461 and 39165 individuals over the years studied. On the basis of data from 30461 MEPS respondents (15867 women [52.1%]; mean [SD] age, 38.9 [24.0] years) in 2018, the top 4.6% (95% CI, 4.3%-4.9%) of the US population by spending accounted for 50% of health care expenditures. Although this fraction varied across population groups or expenditure categories, it remained remarkably stable over time with one exception: the concentration of spending on prescription drugs. In 2001, one-half of all expenditures on prescription drugs were concentrated in 6.0% (95% CI, 5.6%-6.4%) of the US population, but by 2018, this proportion had decreased to 2.3% (95% CI, 2.1%-2.5%). This change does not appear to be associated with a change in the overall share of prescription drug expenses, which increased by only a small amount, from 20.4% in 2001 to 24.8% in 2018. Conclusions and Relevance: The overall concentration of health care expenditures remained stable between 2001 and 2018, but these findings suggest that there has been a sharp increase in the concentration of spending on prescription drugs in the US. This coincides with the genericization of many primary care drugs, along with a shift in focus of the biopharmaceutical industry toward high-cost specialty drugs targeted at smaller populations. If this trend continues, it will have implications for the minimum scale of risk-bearing and drug management needed to operate efficiently, as well as the optimal cost-sharing features of insurance products.

Modeling The Nucleosynthesis Of Massive Stars

This overview discusses issues relevant to modeling nucleosynthesis in type II supernovae and implications of detailed studies of the ejecta. After a brief presentation of the most common approaches to stellar evolution and parameterized explosions, the relevance of a number of nuclei to obtain information on the evolution and explosion mechanisms is discussed. The paper is concluded by an outlook on multi-dimensional simulations.Comment: Invited talk at the workshop "Astronomy with Radioactivities IV", Seeon, Germany, June 2003; 6 pages, to appear in New Astronomy Review

Analysis of Actin FLAP Dynamics in the Leading Lamella

BACKGROUND. The transport of labeled G-actin from the mid-lamella region to the leading edge in a highly motile malignant rat fibroblast line has been studied using fluorescence localization after photobleaching or FLAP, and the transit times recorded in these experiments were so fast that simple diffusion was deemed an insufficient explanation (see Zicha et al., Science, v. 300, pp. 142-145 [1]). METHODOLOGY/PRINCIPAL FINDINGS. We re-examine the Zicha FLAP experiments using a two-phase reactive interpenetrating flow formalism to model the cytoplasm and the transport dynamics of bleached and unbleached actin. By allowing an improved treatment of effects related to the retrograde flow of the cytoskeleton and of the geometry and finite thickness of the lamella, this new analysis reveals a mechanism that can realistically explain the timing and the amplitude of all the FLAP signals observed in [1] without invoking special transport modalities. CONCLUSIONS/SIGNIFICANCE. We conclude that simple diffusion is sufficent to explain the observed transport rates, and that variations in the transport of labeled actin through the lamella are minor and not likely to be the cause of the observed physiological variations among different segments of the leading edge. We find that such variations in labeling can easily arise from differences and changes in the microscopic actin dynamics inside the edge compartment, and that the key dynamical parameter in this regard is the so-called "dilatation rate" (the velocity of cytoskeletal retrograde flow divided by a characteristic dimension of the edge compartment where rapid polymerization occurs). If our dilatation hypothesis is correct, the transient kinetics of bleached actin relocalization constitute a novel and very sensitive method for probing the cytoskeletal dynamics in leading edge micro-environments which are otherwise very difficult to directly interrogate.Whitaker biomedical engineering research grant (RG-02-0714); National Institutes of Health (RO1 GM7200

Protrusive Push versus Enveloping Embrace: Computational Model of Phagocytosis Predicts Key Regulatory Role of Cytoskeletal Membrane Anchors

Encounters between human neutrophils and zymosan elicit an initially protrusive cell response that is distinct from the thin lamella embracing antibody-coated targets. Recent experiments have led us to hypothesize that this behavior has its mechanistic roots in the modulation of interactions between membrane and cytoskeleton. To test and refine this hypothesis, we confront our experimental results with predictions of a computer model of leukocyte mechanical behavior, and establish the minimum set of mechanistic variations of this computational framework that reproduces the differences between zymosan and antibody phagocytosis. We confirm that the structural linkages between the cytoskeleton and the membrane patch adherent to a target form the “switchboard” that controls the target specificity of a neutrophil's mechanical response. These linkages are presumably actin-binding protein complexes associating with the cytoplasmic domains of cell-surface receptors that are engaged in adhesion to zymosan and Fc-domains

Merging White Dwarf/Black Hole Binaries and Gamma-Ray Bursts

The merger of compact binaries, especially black holes and neutron stars, is frequently invoked to explain gamma-ray bursts (GRB's). In this paper, we present three dimensional hydrodynamical simulations of the relatively neglected mergers of white dwarfs and black holes. During the merger, the white dwarf is tidally disrupted and sheared into an accretion disk. Nuclear reactions are followed and the energy release is negligible. Peak accretion rates are ~0.05 Msun/s (less for lower mass white dwarfs) lasting for approximately a minute. Many of the disk parameters can be explained by a simple analytic model which we derive and compare to our simulations. This model can be used to predict accretion rates for white dwarf and black hole (or neutron star) masses which are not simulated in this paper. Although the mergers studied here create disks with larger radii, and longer accretion times than those from the merger of double neutron stars, a larger fraction of the merging star's mass becomes part of the disk. Thus the merger of a white dwarf and a black hole could produce a long duration GRB. The event rate of these mergers may be as high as 1/Myr per galaxy.Comment: 17 pages text + 9 figures, minor corrections to text and tables, added references, accepted by Ap

Supernova neutrino challenges

A principal `supernova neutrino challenge' is the computational difficulty of six-dimensional neutrino radiation hydrodynamics. The variety of resulting approximations has provoked a long history of uncertainty in the core-collapse supernova explosion mechanism, but recent work highlighting low-mode convection and a newly-recognized instability in spherical accretion shocks may signal (yet another) resolution. As part of its goal of elucidating the explosion mechanism, the Terascale Supernova Initiative is committed to meeting the full complexity of the computational challenge. The understanding of supernova neutrino emission gained in detailed simulations provides a potential basis for learning about two major remaining unknowns in neutrino flavor mixing: the value of the mixing angle $\theta_{13}$, and distinguishing between ``normal'' and ``inverted'' mass hierarchies.Comment: 6 pages. Contribution to the proceedings of NOW2004, Conca Specchiulla (Otranto, Italy), September 11-17, 2004, to be published by Nucl. Phys. B (Proc. Suppl.), ed. P. Bernardini, G.L. Fogli, and E. Lis