7,116 research outputs found
Numerical Study on GRB-Jet Formation in Collapsars
Two-dimensional magnetohydrodynamic simulations are performed using the
ZEUS-2D code to investigate the dynamics of a collapsar that generates a GRB
jet, taking account of realistic equation of state, neutrino cooling and
heating processes, magnetic fields, and gravitational force from the central
black hole and self gravity. It is found that neutrino heating processes are
not so efficient to launch a jet in this study. It is also found that a jet is
launched mainly by B_\phi fields that are amplified by the winding-up effect.
However, since the ratio of total energy relative to the rest mass energy in
the jet is not so high as several hundred, we conclude that the jets seen in
this study are not be a GRB jet. This result suggests that general relativistic
effects, which are not included in this study, will be important to generate a
GRB jet. Also, the accretion disk with magnetic fields may still play an
important role to launch a GRB jet, although a simulation for much longer
physical time (\sim 10-100 s) is required to confirm this effect. It is shown
that considerable amount of 56Ni is synthesized in the accretion disk. Thus
there will be a possibility for the accretion disk to supply sufficient amount
of 56Ni required to explain the luminosity of a hypernova. Also, it is shown
that neutron-rich matter due to electron captures with high entropy per baryon
is ejected along the polar axis. Moreover, it is found that the electron
fraction becomes larger than 0.5 around the polar axis near the black hole by
\nu_e capture at the region. Thus there will be a possibility that r-process
and r/p-process nucleosynthesis occur at these regions. Finally, much neutrons
will be ejected from the jet, which suggests that signals from the neutron
decays may be observed as the delayed bump of afterglow or gamma-rays.Comment: 54 pages with 19 postscript figures. Accepted for publication in ApJ.
High resolution version is available at
http://www2.yukawa.kyoto-u.ac.jp/~nagataki/collapsar.pd
New N=1 Extended Superconformal Algebras with Two and Three Generators
In this paper we consider extensions of the super Virasoro algebra by one and
two super primary fields. Using a non-explicitly covariant approach we compute
all SW-algebras with one generator of dimension up to 7 in addition to the
super Virasoro field. In complete analogy to W-algebras with two generators
most results can be classified using the representation theory of the super
Virasoro algebra. Furthermore, we find that the SW(3/2, 11/2)-algebra can be
realized as a subalgebra of SW(3/2, 5/2) at c = 10/7. We also construct some
new SW-algebras with three generators, namely SW(3/2, 3/2, 5/2), SW(3/2, 2, 2)
and SW(3/2, 2, 5/2).Comment: 30 pages (Plain TeX), BONN-HE-92-0
The distribution of supermassive black holes in the nuclei of nearby galaxies
The growth of supermassive black holes by merging and accretion in
hierarchical models of galaxy formation is studied by means of Monte Carlo
simulations. A tight linear relation between masses of black holes and masses
of bulges arises if if the mass accreted by supermassive black holes scales
linearly with the mass forming stars and if the redshift evolution of mass
accretion tracks closely that of star formation. Differences in redshift
evolution between black hole accretion and star formation introduce
considerable scatter in this relation. A non-linear relation between black hole
accretion and star formation results in a non-linear relation between masses of
remnant black holes and masses of bulges. The relation of black hole mass to
bulge luminosity obseved in nearby galaxies and its scatter are reproduced
reasonably well by models in which black hole accretion and star formation are
linearly related but do not track each other in redshift. This suggests that a
common mechanism determines the efficiency for black hole accretion and the
efficiency for star formation, especially for bright bulges.Comment: 6 pages, 3 figures, submitted to MNRA
Focused Deterrence and the Prevention of Violent Gun Injuries: Practice, Theoretical Principles, and Scientific Evidence
Focused deterrence strategies are a relatively new addition to a growing portfolio of evidence-based violent gun injury prevention practices available to policy makers and practitioners. These strategies seek to change offender behavior by understanding the underlying violence-producing dynamics and conditions that sustain recurring violent gun injury problems and by implementing a blended strategy of law enforcement, community mobilization, and social service actions. Consistent with documented public health practice, the focused deterrence approach identifies underlying risk factors and causes of recurring violent gun injury problems, develops tailored responses to these underlying conditions, and measures the impact of implemented interventions. This article reviews the practice, theoretical principles, and evaluation evidence on focused deterrence strategies. Although more rigorous randomized studies are needed, the available empirical evidence suggests that these strategies generate noteworthy gun violence reduction impacts and should be part of a broader portfolio of violence prevention strategies available to policy makers and practitioners
Constraints on B and Higgs Physics in Minimal Low Energy Supersymmetric Models
We study the implications of minimal flavor violating low energy
supersymmetry scenarios for the search of new physics in the B and Higgs
sectors at the Tevatron collider and the LHC. We show that the already
stringent Tevatron bound on the decay rate B_s -> mu+ mu- sets strong
constraints on the possibility of generating large corrections to the mass
difference Delta M_s of the B_s eigenstates. We also show that the B_s -> mu+
mu- bound together with the constraint on the branching ratio of the rare decay
b -> s gamma has strong implications for the search of light, non-standard
Higgs bosons at hadron colliders. In doing this, we demonstrate that the former
expressions derived for the analysis of the double penguin contributions in the
Kaon sector need to be corrected by additional terms for a realistic analysis
of these effects. We also study a specific non-minimal flavor violating
scenario, where there are flavor changing gluino-squark-quark interactions,
governed by the CKM matrix elements, and show that the B and Higgs physics
constraints are similar to the ones in the minimal flavor violating case.
Finally we show that, in scenarios like electroweak baryogenesis which have
light stops and charginos, there may be enhanced effects on the B and K mixing
parameters, without any significant effect on the rate of B_s -> mu+ mu-.Comment: 40 pages, 14 figures; added references and note about recent
measurement
Report of the 2005 Snowmass Top/QCD Working Group
This report discusses several topics in both top quark physics and QCD at an
International Linear Collider (ILC). Issues such as measurements at the
threshold, including both theoretical and machine requirements, and
the determination of electroweak top quark couplings, are reviewed. New results
concerning the potential of a 500 GeV collider for measuring
couplings and the top quark Yukawa coupling are presented. The status of higher
order QCD corrections to jet production cross sections, heavy quark form
factors, and longitudinal gauge boson scattering, needed for percent-level
studies at the ILC, are reviewed. A new study of the measurement of the
hadronic structure of the photon at a collider is presented. The
effects on top quark properties from several models of new physics, including
composite models, Little Higgs theories, and CPT violation, are studied.Comment: 39 pages, many figs; typos fixed and refs added. Contributed to the
2005 International Linear Collider Physics and Detector Workshop and 2nd ILC
Accelerator Workshop, Snowmass, Colorado, 14-27 Aug 200
Lentiviral vector transduction of spermatozoa as a tool for the study of early development
Spermatozoa and lentiviruses are two of natureās most efficient gene delivery vehicles. Both can be genetically modified and used independently for the generation of transgenic animals or gene transfer/therapy of inherited disorders. Here we show that mature spermatozoa can be directly transduced with various pseudotyped lentiviral vectors and used in in vitro fertilisation studies. Lentiviral vectors encoding Green Fluorescent Protein (GFP) were shown to be efficiently processed and expressed in sperm. When these transduced sperm were used in in vitro fertilisation studies, GFP expression was observed in arising blastocysts. This simple technique of directly transducing spermatozoa has potential to be a powerful tool for the study of early and pre-implantation development and could be used as a technique in transgenic development and vertical viral transmission studies
Particle-In-Cell Simulations of a Nonlinear Transverse Electromagnetic Wave in a Pulsar Wind Termination Shock
A 2.5-dimensional particle-in-cell code is used to investigate the
propagation of a large-amplitude, superluminal, nearly transverse
electromagnetic (TEM) wave in a relativistically streaming electron-positron
plasma with and without a shock. In the freestreaming, unshocked case, the
analytic TEM dispersion relation is verified, and the streaming is shown to
stabilize the wave against parametric instabilities. In the confined, shocked
case, the wave induces strong, coherent particle oscillations, heats the
plasma, and modifies the shock density profile via ponderomotive effects. The
wave decays over skin depths; the decay length scale depends
primarily on the ratio between the wave frequency and the effective plasma
frequency, and on the wave amplitude. The results are applied to the
termination shock of the Crab pulsar wind, where the decay length-scale (at
least 0.05") might be comparable to the thickness of filamentary, variable
substructure observed in the optical and X-ray wisps and knots.Comment: 10 pages, 4 figures. Accepted for publication in ApJ (2005
Architecture of a Silicon Strip Beam Position Monitor
A collaboration between Fermilab and the Institute for High Energy Physics
(IHEP), Beijing, has developed a beam position monitor for the IHEP test beam
facility. This telescope is based on 5 stations of silicon strip detectors
having a pitch of 60 microns. The total active area of each layer of the
detector is about 12x10 cm2. Readout of the strips is provided through the use
of VA1` ASICs mounted on custom hybrid printed circuit boards and interfaced to
Adapter Cards via copper-over-kapton flexible circuits. The Adapter Cards
amplify and level-shift the signal for input to the Fermilab CAPTAN data
acquisition nodes for data readout and channel configuration. These nodes
deliver readout and temperature data from triggered events to an analysis
computer over gigabit Ethernet links.Comment: Submitted to TWEPP 201
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