95 research outputs found
Observed and Physical Properties of Core-Collapse Supernovae
I use photometry and spectroscopy data for 24 Type II plateau supernovae to
examine their observed and physical properties. This dataset shows that these
objects encompass a wide range of ~5 mag in their plateau luminosities, their
expansion velocities vary by x5, and the nickel masses produced in these
explosions go from 0.0016 to 0.26 Mo. From a subset of 16 objects I find that
the explosion energies vary between 0.6x and 5.5x10^51 ergs, the ejected masses
encompass the range 14-56 Mo, and the progenitors' radii go from 80 to 600 Ro.
Despite this great diversity several regularities emerge, which reveal that
there is a continuum in the properties of these objects from the faint,
low-energy, nickel-poor SNe 1997D and 1999br, to the bright, high-energy,
nickel-rich SN 1992am. This study provides evidence that more massive
progenitors produce more energetic explosions, thus suggesting that the outcome
of the core collapse is somewhat determined by the envelope mass. I find also
that supernovae with greater energies produce more nickel. Similar
relationships appear to hold for Type Ib/c supernovae, which suggests that both
Type II and Type Ib/c supernovae share the same core physics. When the whole
sample of core collapse objects is considered, there is a continous
distribution of energies below 8x10^51 ergs. Far above in energy scale and
nickel production lies the extreme hypernova 1998bw, the only supernova firmly
associated to a GRB.Comment: 25 pages, 7 figures, accepted for Part 1 of Astrophysical Journa
Extra-Legal and Shadow Functioning of Public Authorities
This article discusses the various forms of public authorities functioning and state authorities functioning in particular. The authors argue that in addition to the institutional and regulatory and structural and functional characteristics, public authority realizes in extra-legal form, which acts as a complex concept correlating with such forms as "informal", "shadow", "unlawful." It is proved that this form of governmental authority is not mediated by law and can have both formal public and informal, shadow and non-legal nature. The matter of this article shows that extralegal forms of activity lead not only to negative, but also to positive effects - to the development of the system of state power, political forms and regime, methods of state and legal impact on the political, economic, social and other systems of society. Thus, in some cases extralegal but legitimated by society forms of state influence on the political process can get institutional and regulatory clearance. Moreover, the authors identify the causes and factors of the development of this form, as well as provide a meaningful analysis of the informal authorities’ activity, their shadow interaction and shadow forms of relations, illegal practices, unlawful sphere and shadow law.
DOI: 10.5901/mjss.2015.v6n3p38
A Parameter Study of Type II Supernova Light Curves Using 6 M_odot He Cores
Results of numerical calculations of Type II supernova light curves are
presented. The model progenitor stars have 6 cores and various
envelopes, originating from a numerically evolved 20 star. Five
parameters that affect the light curves are examined: the ejected mass, the
progenitor radius, the explosion energy, the Ni mass, and the extent of
Ni mixing. The following affects have been found: 1) the larger the
progenitor radius the brighter the early--time light curve, with little affect
on the late--time light curve, 2) the larger the envelope mass the fainter the
early light curve and the flatter the slope of the late light curve, 3) the
larger the explosion energy the brighter the early light curve and the steeper
the slope of the late light curve, 4) the larger the Ni mass the
brighter the overall light curve after 20 to 50 days, with no affect on the
early light curve, 5) the more extensive the Ni mixing the brighter the
early light curve and the steeper the late light curve. The primary parameters
affecting the light curve shape are the progenitor radius and the ejected mass.
The secondary parameters are the explosion energy, Ni mass and Ni
mixing. I find that while in principle the general shape and absolute magnitude
of a light curve indicate a unique set of parameters, in practice it is
difficult to avoid some ambiguity in the parameters. I find that the
nickel--powered diffusion wave and the recombination of helium produce a
prominent secondary peak in all our calculations. The feature is less prominent
when compositional mixing, both Ni mixing and mixing between the
hydrogen and helium layers, occurs. The model photospheric temperatures and
velocities are presented, for comparison to observation.Comment: 39 pages, 15 figures. Astrophysical Journal (Accepted, Dec. 20, 2004
Covariant response theory beyond RPA and its application
The covariant particle-vibration coupling model within the time blocking
approximation is employed to supplement the Relativistic Random Phase
Approximation (RRPA) with coupling to collective vibrations. The Bethe-Salpeter
equation in the particle-hole channel with an energy dependent residual
particle-hole (p-h) interaction is formulated and solved in the shell-model
Dirac basis as well as in the momentum space. The same set of the coupling
constants generates the Dirac-Hartree single-particle spectrum, the static part
of the residual p-h interaction and the particle-phonon coupling amplitudes.
This approach is applied to quantitative description of damping phenomenon in
even-even spherical nuclei with closed shells Pb and Sn. Since
the phonon coupling enriches the RRPA spectrum with a multitude of
phphonon states a noticeable fragmentation of giant monopole and
dipole resonances is obtained in the examined nuclei. The results are compared
with experimental data and with results of the non-relativistic approach.Comment: 12 pages, 4 figures, Proceedings of the NSRT06 Conferenc
The development of attenuation compensation models of fluorescence spectroscopy signals
This study examines the effect of blood absorption on the endogenous fluorescence signal intensity of biological tissues. Experimental studies were conducted to identify these effects. To register the fluorescence intensity, the fluorescence spectroscopy method was employed. The intensity of the blood flow was measured by laser Doppler flowmetry. We proposed one possible implementation of the Monte Carlo method for the theoretical analysis of the effect of blood on the fluorescence signals. The simulation is constructed as a four-layer skin optical model based on the known optical parameters of the skin with different levels of blood supply. With the help of the simulation, we demonstrate how the level of blood supply can affect the appearance of the fluorescence spectra. In addition, to describe the properties of biological tissue, which may affect the fluorescence spectra, we turned to the method of diffuse reflectance spectroscopy (DRS). Using the spectral data provided by the DRS, the tissue attenuation effect can be extracted and used to correct the fluorescence spectra
Pygmy dipole resonance in 208Pb
Scattering of protons of several hundred MeV is a promising new spectroscopic
tool for the study of electric dipole strength in nuclei. A case study of 208Pb
shows that at very forward angles J^pi = 1- states are strongly populated via
Coulomb excitation. A separation from nuclear excitation of other modes is
achieved by a multipole decomposition analysis of the experimental cross
sections based on theoretical angular distributions calculated within the
quasiparticle-phonon model. The B(E1) transition strength distribution is
extracted for excitation energies up to 9 MeV, i.e., in the region of the
so-called pygmy dipole resonance (PDR). The Coulomb-nuclear interference shows
sensitivity to the underlying structure of the E1 transitions, which allows for
the first time an experimental extraction of the electromagnetic transition
strength and the energy centroid of the PDR.Comment: submitted to Phys. Rev.
SN 2006bp: Probing the Shock Breakout of a Type II-P Supernova
HET optical spectroscopy and unfiltered ROTSE-III photometry spanning the
first 11 months since explosion of the Type II-P SN 2006bp are presented. Flux
limits from the days before discovery combined with the initial rapid
brightening suggest the supernova was first detected just hours after shock
breakout. Optical spectra obtained about 2 days after breakout exhibit narrow
emission lines corresponding to HeII 4200, HeII 4686, and CIV 5805 in the rest
frame, and these features persist in a second observation obtained 5 hours
later; however, these emission lines are not detected the following night nor
in subsequent observations. We suggest that these lines emanate from material
close to the explosion site, possibly in the outer layers of the progenitor
that have been ionized by the high energy photons released at shock breakout. A
P-Cygni profile is observed around 4450 A in the +2 and +3 day spectra.
Previous studies have attributed this feature to high velocity H-beta, but we
discuss the possibility that this profile is instead due to HeII 4687. Further
HET observations (14 nights in total) covering the spectral evolution across
the photometric plateau up to 73 days after breakout and during the nebular
phase around day +340 are presented, and expansion velocities are derived for
key features. The measured decay slope for the unfiltered light curve is 0.0073
+/- 0.0004 mag/day between days +121 and +335, which is significantly slower
than the decay of rate 56Co. We combine our HET measurements with published
X-ray, UV, and optical data to obtain a quasi-bolometric light curve through
day +60. We see a slow cooling over the first 25 days, but no sign of an early
sharp peak; any such feature from the shock breakout must have lasted less than
~1 day.[ABRIDGED]Comment: ApJ accepted, 43 page
Complete electric dipole response and the neutron skin in 208Pb
A benchmark experiment on 208Pb shows that polarized proton inelastic
scattering at very forward angles including 0{\deg} is a powerful tool for
high-resolution studies of electric dipole (E1) and spin magnetic dipole (M1)
modes in nuclei over a broad excitation energy range to test up-to-date nuclear
models. The extracted E1 polarizability leads to a neutron skin thickness
r_skin = 0.156+0.025-0.021 fm in 208Pb derived within a mean-field model [Phys.
Rev. C 81, 051303 (2010)], thereby constraining the symmetry energy and its
density dependence, relevant to the description of neutron stars.Comment: 5 pages, 5 figures, revised mansucrip
Radiation hydrodynamics of SN 1987A: I. Global analysis of the light curve for the first 4 months
The optical/UV light curves of SN 1987A are analyzed with the multi-energy
group radiation hydrodynamics code STELLA. The calculated monochromatic and
bolometric light curves are compared with observations shortly after shock
breakout, during the early plateau, through the broad second maximum, and
during the earliest phase of the radioactive tail. We have concentrated on a
progenitor model calculated by Nomoto & Hashimoto and Saio, Nomoto, & Kato,
which assumes that 14 solar masses of the stellar mass is ejected. Using this
model, we have updated constraints on the explosion energy and the extent of
mixing in the ejecta. In particular, we determine the most likely range of E/M
(explosion energy over ejecta mass) and R_0 (radius of the progenitor). In
general, our best models have energies in the range E = (1.1 +/- 0.3) x 10^{51}
ergs, and the agreement is better than in earlier, flux-limited diffusion
calculations for the same explosion energy. Our modeled B and V fluxes compare
well with observations, while the flux in U undershoots after about 10 days by
a factor of a few, presumably due to NLTE and line transfer effects. We also
compare our results with IUE observations, and a very good quantitative
agreement is found for the first days, and for one IUE band (2500-3000 A) as
long as for 3 months. We point out that the V flux estimated by McNaught &
Zoltowski should probably be revised to a lower value.Comment: 27 pages AASTeX v.4.0 + 35 postscript figures. ApJ, accepte
Quantifying the importance and location of SARS-CoV-2 transmission events in large metropolitan areas
Detailed characterization of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) transmission across different settings can help design less disruptive interventions. We used real-time, privacy-enhanced mobility data in the New York City, NY and Seattle, WA metropolitan areas to build a detailed agent-based model of SARS-CoV-2 infection to estimate the where, when, and magnitude of transmission events during the pandemic’s first wave. We estimate that only 18% of individuals produce most infections (80%), with about 10% of events that can be considered superspreading events (SSEs). Although mass gatherings present an important risk for SSEs, we estimate that the bulk of transmission occurred in smaller events in settings like workplaces, grocery stores, or food venues. The places most important for transmission change during the pandemic and are different across cities, signaling the large underlying behavioral component underneath them. Our modeling complements case studies and epidemiological data and indicates that real-time tracking of transmission events could help evaluate and define targeted mitigation policies. Copyright © 2022 the Author(s
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