33,831 research outputs found
Initial Shock Waves for Explosive Nucleosynthesis in Type II Supernova
We have performed 1-dimensional calculations for explosive nucleosynthesis in
collapse-driven supernova and investigated its sensitivity to the initial form
of the shock wave. We have found the tendency that the peak temperature becomes
higher around the mass cut if the input energy is injected more in the form of
kinetic energy rather than internal energy. Then, the mass cut becomes larger,
and, as a result, neutron-rich matter is less included in the ejecta; this is
favorable for producing the observational data compared with a previous model.
Our results imply that the standard method to treat various processes for
stellar evolution, such as convection and electron capture during the silicon
burning stage, are still compatible with the calculation of explosive
nucleosynthesis.Comment: 20 pages, 6 figures, LaTe
Stripe Formation in Fermionic Atoms on 2-D Optical Lattice inside a Box Trap: DMRG Studies for Repulsive Hubbard Model with Open Boundary Condition
We suggest that box shape trap enables to observe intrinsic properties of the
repulsive Hubbard model in a fixed doping in contrast to the harmonic trap
bringing about spatial variations of atom density profiles. In order to predict
atomic density profile under the box trap, we apply the directly-extended
density-matrix renormalization group method to 4-leg repulsive Hubbard model
with the open boundary condition. Consequently, we find that stripe formation
is universal in a low hole doping range and the stripe sensitively changes its
structure with variations of and the doping rate. A remarkable change is
that a stripe formed by a hole pair turns to one by a bi-hole pair when
entering a limited strong range. Furthermore, a systematic calculation
reveals that the Hubbard model shows a change from the stripe to the Friedel
like oscillation with increasing the doping rate
Experimental determination of optimum coil pitch for a planar mesh-type micromagnetic sensor
To overcome the directional properties of a planar meander-type sensor, a new planar micromagetic sensor having mesh-type configuration is reported in this paper. Analytical models are usually used for the characterization of the planar-type sensors. Sensors having mesh-type configuration have been fabricated for the derivation of the optimum coil pitch
R-Process Nucleosynthesis In Neutrino-Driven Winds From A Typical Neutron Star With M = 1.4 Msun
We study the effects of the outer boundary conditions in neutrino-driven
winds on the r-process nucleosynthesis. We perform numerical simulations of
hydrodynamics of neutrino-driven winds and nuclear reaction network
calculations of the r-process. As an outer boundary condition of hydrodynamic
calculations, we set a pressure upon the outermost layer of the wind, which is
approaching toward the shock wall. Varying the boundary pressure, we obtain
various asymptotic thermal temperature of expanding material in the
neutrino-driven winds for resulting nucleosynthesis. We find that the
asymptotic temperature slightly lower than those used in the previous studies
of the neutrino-driven winds can lead to a successful r-process abundance
pattern, which is in a reasonable agreement with the solar system r-process
abundance pattern even for the typical proto-neutron star mass Mns ~ 1.4 Msun.
A slightly lower asymptotic temperature reduces the charged particle reaction
rates and the resulting amount of seed elements and lead to a high
neutron-to-seed ratio for successful r-process. This is a new idea which is
different from the previous models of neutrino-driven winds from very massive
(Mns ~ 2.0 Msun) and compact (Rns ~ 10 km) neutron star to get a short
expansion time and a high entropy for a successful r-process abundance pattern.
Although such a large mass is sometimes criticized from observational facts on
a neutron star mass, we dissolve this criticism by reconsidering the boundary
condition of the wind. We also explore the relation between the boundary
condition and neutron star mass, which is related to the progenitor mass, for
successful r-process.Comment: 14 pages, 2 figure
Universal Finite-Size Scaling Function of the Ferromagnetic Heisenberg Chain in a Magnetic Field,
The finite-size scaling function of the magnetization of the ferromagnetic
Heisenberg chain is argued to be universal with respect to the magnitude of the
spin. The finite-size scaling function is given explicitly by an analytical
calculation in the classical limit The universality is checked for
and by means of numerical calculations. Critical exponents are
obtained as well. It is concluded that this universal scaling function
originates in the universal behavior of the correlation function.Comment: 14 pages (revtex 2.0) + 8 PS figures upon request
Hydrodynamics of Internal Shocks in Relativistic Outflows
We study the hydrodynamical effects of two colliding shells, adopted to model
internal shocks in various relativistic outflows such as gamma-ray bursts and
blazars. We find that the density profiles are significantly affected by the
propagation of rarefaction waves. A split-feature appears at the contact
discontinuity of the two shells. The shell spreading with a few ten percent of
the speed of light is also shown to be a notable aspect. The conversion
efficiency of the bulk kinetic energy to internal one shows deviations from the
widely-used inelastic two-point-mass-collision model. Observational
implications are also shortly discussed.Comment: 6 pages, 4 figures, Proceeding of International Symposium on High
Energy Gamma-ray Astronomy (July 26-30, 2004, Heidelberg, Germany
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