66 research outputs found
Identifying rotation in SASI-dominated core-collapse supernovae with a neutrino gyroscope
Measuring the rotation of core-collapse supernovae (SN) and of their
progenitor stars is extremely challenging. Here it is demonstrated that
neutrinos may potentially be employed as stellar gyroscopes, if phases of
activity by the standing accretion-shock instability (SASI) affect the neutrino
emission prior to the onset of the SN explosion. This is shown by comparing the
neutrino emission properties of self-consistent, three-dimensional (3D) SN
simulations of a 15 M_sun progenitor without rotation as well as slow and fast
rotation compatible with observational constraints. The explosion of the fast
rotating model gives rise to long-lasting, massive polar accretion downflows
with stochastic time-variability, detectable e.g. by the IceCube Neutrino
Observatory for any observer direction. While spectrograms of the neutrino
event rate of non-rotating SNe feature a well-known sharp peak due to SASI for
observers located in the proximity of the SASI plane, the corresponding
spectrograms of rotating models show activity over a wide range of frequencies,
most notably above 200 Hz for rapid rotation. In addition, the Fourier power
spectra of the event rate for rotating models exhibit a SASI peak with lower
power than in non-rotating models. The spectra for the rotating models also
show secondary peaks at higher frequencies with greater relative heights
compared to the main SASI peak than for non-rotating cases. These rotational
imprints will be detectable for SNe at 10 kpc or closer.Comment: 10 pages, including 6 figures. Minor changes in the text, matches
version accepted for publication in Phys. Rev. D. Animated visualizations
available at: https://wwwmpa.mpa-garching.mpg.de/ccsnarchive/data/Walk2018
Effects of the standing accretion-shock instability and the lepton-emission self-sustained asymmetry in the neutrino emission of rotating supernovae
Rotation of core-collapse supernovae (SNe) affects the neutrino emission
characteristics. By comparing the neutrino properties of three
three-dimensional SN simulations of a 15 M_sun progenitor (one non-rotating
model and two models rotating at different velocities), we investigate how the
neutrino emission varies with the flow dynamics in the SN core depending on the
different degrees of rotation. The large-amplitude sinusoidal modulations due
to the standing accretion-shock instability (SASI) are weaker in both the
rotating models than in the non-rotating case. The SN progenitor rotation
reduces the radial velocities and radial component of the kinetic energy
associated with convection interior to the proto-neutron star. This effect
seems to disfavor the growth of the hemispheric neutrino-emission asymmetries
associated with the lepton-emission self-sustained asymmetry (LESA). An
investigation of the multipole expansion of the neutrino luminosity and the
electron neutrino lepton number flux shows a dominant quadrupolar mode in
rotating SN models. Our findings highlight the power of using neutrinos as
probes of SN hydrodynamics.Comment: 21 pages, including 17 figures. Characterization of LESA in rotating
models expanded; conclusions unchanged. Animated visualizations available at:
https://wwwmpa.mpa-garching.mpg.de/ccsnarchive/data/Walk2018
Neutrino emission characteristics of black hole formation in three-dimensional simulations of stellar collapse
Neutrinos are unique probes of core-collapse supernova dynamics, especially
in the case of black hole (BH) forming stellar collapses, where the
electromagnetic emission may be faint or absent. By investigating two 3D
hydrodynamical simulations of BH-forming stellar collapses of mass 40 and 75
M_sun, we identify the physical processes preceding BH formation through
neutrinos, and forecast the neutrino signal expected in the existing IceCube
and Super-Kamiokande detectors, as well as in the future generation DUNE
facility. Prior to the abrupt termination of the neutrino signal corresponding
to BH formation, both models develop episodes of strong and long-lasting
activity by the spiral standing accretion shock instability (SASI). We find
that the spiral SASI peak in the Fourier power spectrum of the neutrino event
rate will be distinguishable at 3 sigma above the detector noise for distances
up to O(30) kpc in the most optimistic scenario, with IceCube having the
highest sensitivity. Interestingly, given the long duration of the spiral SASI
episodes, the spectrograms of the expected neutrino event rate carry clear
signs of the evolution of the blue spiral SASI frequency as a function of time,
as the shock radius and post-shock fluid velocity evolve. Due to the high
accretion luminosity and its large-amplitude SASI-induced modulations, any
contribution from asymmetric (dipolar or quadrupolar) neutrino emission
associated with the lepton emission self-sustained asymmetry (LESA) is far
subdominant in the neutrino signal.Comment: 25 pages, including 19 figures. Discussion on LESA expanded;
conclusions unchanged. Matches version accepted for publication in Phys. Rev.
D. Animated visualizations available at:
https://wwwmpa.mpa-garching.mpg.de/ccsnarchive/data/Walk2019
Diffuse Supernova Neutrino Background from extensive core-collapse simulations of - progenitors
We revisit the diffuse supernova neutrino background in light of recent
systematic studies of stellar core collapse that reveal the quantitative
impacts of the progenitor conditions on the collapse process. In general, the
dependence of the progenitor on the core-collapse neutrino emission is not
monotonic in progenitor initial mass, but we show that it can, at first order,
be characterized by the core compactness. For the first time, we incorporate
the detailed variations in the neutrino emission over the entire mass range
-, based on (i) a long-term simulation of the core
collapse of a O-Ne-Mg core progenitor, (ii) over 100
simulations of iron core collapse to neutron stars, and (iii) half a dozen
simulations of core collapse to black holes (the "failed channel"). The
fraction of massive stars that undergo the failed channel remains uncertain,
but in view of recent simulations which reveal high compactness to be conducive
to collapse to black holes, we characterize the failed fraction by considering
a threshold compactness above which massive stars collapse to black holes and
below which the final remnant is a neutron star. We predict that future
detections of the diffuse supernova neutrino background may have the power to
reveal this threshold compactness, if its value is relatively small as
suggested by interpretations of several recent astronomical observations.Comment: 14 pages, 8 figures, accepted for publication in MNRA
East Bay Coalition for the Homeless: Branding Study and Marketing Strategy
There are a number of potential positioning strategies. The two which make the most sense for the EBCH are to “position the EBCH away from others in the category” and to “position the EBCH as unique.” These strategies have the advantage of setting the EBCH apart from the other organizations that address homelessness. Occupying its own “position” in the minds of potential and current donors is not only an effective communications/marketing strategy but also a less costly one because it avoids head-to-head competition and comparisons
A quality metric for homology modeling: the H-factor
<p>Abstract</p> <p>Background</p> <p>The analysis of protein structures provides fundamental insight into most biochemical functions and consequently into the cause and possible treatment of diseases. As the structures of most known proteins cannot be solved experimentally for technical or sometimes simply for time constraints, <it>in silico </it>protein structure prediction is expected to step in and generate a more complete picture of the protein structure universe. Molecular modeling of protein structures is a fast growing field and tremendous works have been done since the publication of the very first model. The growth of modeling techniques and more specifically of those that rely on the existing experimental knowledge of protein structures is intimately linked to the developments of high resolution, experimental techniques such as NMR, X-ray crystallography and electron microscopy. This strong connection between experimental and <it>in silico </it>methods is however not devoid of criticisms and concerns among modelers as well as among experimentalists.</p> <p>Results</p> <p>In this paper, we focus on homology-modeling and more specifically, we review how it is perceived by the structural biology community and what can be done to impress on the experimentalists that it can be a valuable resource to them. We review the common practices and provide a set of guidelines for building better models. For that purpose, we introduce the H-factor, a new indicator for assessing the quality of homology models, mimicking the R-factor in X-ray crystallography. The methods for computing the H-factor is fully described and validated on a series of test cases.</p> <p>Conclusions</p> <p>We have developed a web service for computing the H-factor for models of a protein structure. This service is freely accessible at <url>http://koehllab.genomecenter.ucdavis.edu/toolkit/h-factor</url>.</p
Modellierung hochenergetischer Beobachtungsgrößen von Supernova-Explosionen
In this work, high-energy observables arising during different phases of SN explosions are studied with respect to their potential for allowing conclusions on suggested explosion scenarios and physical mechanisms that are thought to influence the evolution of SNe in a major way. The focus on selected observables at keV and MeV energies is motivated by the appearance of large degeneracies that can even be found for disparate scenarios in many wavelength regimes. Since the discussed emission in the high-energy regime is directly linked to nuclear processes being usually very distinct for different suggested physical models, the signatures at keV and MeV energies allow for meaningful comparisons of simulations with observations.In der vorliegenden Arbeit werden Hochenergie-Beobachtungsgrößen, die während verschiedener Phasen von Supernova-Explosionen entstehen, hinsichtlich der Möglichkeit von Rückschlüssen auf vorgeschlagene Explosionsszenarien und physikalische Mechanismen, welche einen wichtigen
Einfluss auf die Entwicklung dieser Explosionen ausüben, untersucht. Die Schwerpunktsetzung auf Beobachtungsgrößen im keV- und MeV-Energiebereich ist dabei durch die großen Ähnlichkeiten begründet, die grundverschiedene Szenarien in ihrer Emission in vielen Wellenlängenbereichen zeigen. Da die diskutierten Beobachtungsgrößen im Hochenergie-Bereich direkt mit nuklearen Prozessen verknüpft sind, die bei unterschiedlichen physikalischen Modellen sehr charakteristisch ausgeprägt sein können, eignen sich gerade die vorgestellten Signaturen im keV- und MeV-Bereich
für aussagekräftige Vergleiche von Simulationen und Beobachtungen
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