25,824 research outputs found
From Microscales to Macroscales in 3D: Selfconsistent Equation of State for Supernova and Neutron Star Models
First results from a fully self-consistent, temperature-dependent equation of
state that spans the whole density range of neutron stars and supernova cores
are presented. The equation of state (EoS) is calculated using a mean-field
Hartree-Fock method in three dimensions (3D). The nuclear interaction is
represented by the phenomenological Skyrme model in this work, but the EoS can
be obtained in our framework for any suitable form of the nucleon-nucleon
effective interaction. The scheme we employ naturally allows effects such as
(i) neutron drip, which results in an external neutron gas, (ii) the variety of
exotic nuclear shapes expected for extremely neutron heavy nuclei, and (iii)
the subsequent dissolution of these nuclei into nuclear matter. In this way,
the equation of state is calculated across phase transitions without recourse
to interpolation techniques between density regimes described by different
physical models. EoS tables are calculated in the wide range of densities,
temperature and proton/neutron ratios on the ORNL NCCS XT3, using up to 2000
processors simultaneously.Comment: 6 pages, 11 figures. Published in conference proceedings Journal of
Physics: Conference Series 46 (2006) 408. Extended version to be submitted to
Phys. Rev.
Finite Nuclei in the Quark-Meson Coupling (QMC) Model
We report the first use of the effective QMC energy density functional (EDF),
derived from a quark model of hadron structure, to study a broad range of
ground state properties of even-even nuclei across the periodic table in the
non-relativistic Hartree-Fock+BCS framework. The novelty of the QMC model is
that the nuclear medium effects are treated through modification of the
internal structure of the nucleon. The density dependence is microscopically
derived and the spin-orbit term arises naturally. The QMC EDF depends on a
single set of four adjustable parameters having clear physical basis. When
applied to diverse ground state data the QMC EDF already produces, in its
present simple form, overall agreement with experiment of a quality comparable
to a representative Skyrme EDF. There exist however multiple Skyrme paramater
sets, frequently tailored to describe selected nuclear phenomena. The QMC EDF
set of fewer parameters, as derived in this work, is not open to such
variation, chosen set being applied, without adjustment, to both the properties
of finite nuclei and nuclear matter.Comment: 9 pages, 1 table, 4 figures; in print in Phys. Rev. Letters. A minor
change in the abstract, a few typos corrected and some small technical
adjustments made to comply with the journal regulation
Flight test evaluation of a separate surface attitude command control system on a Beech 99 airplane
A joint NASA/university/industry program was conducted to flight evaluate a potentially low cost separate surface implementation of attitude command in a Beech 99 airplane. Saturation of the separate surfaces was the primary cause of many problems during development. Six experienced professional pilots who made simulated instrument flight evaluations experienced improvements in airplane handling qualities in the presence of turbulence and a reduction in pilot workload. For ride quality, quantitative data show that the attitude command control system results in all cases of airplane motion being removed from the uncomfortable ride region
Field Dependent Phase Diagram of the Quantum Spin Chain (CH3)2NH2CuCl3
Although (CH3)2NH2CuCl3 (MCCL) was first examined in the 1930's [1], there
are open questions regarding the magnetic dimensionality and nature of the
magnetic properties. MCCL is proposed to be a S=1/2 alternating ferromagnetic
antiferromagnetic spin chain alternating along the crystalline a-axis [2,3].
Proposed ferromagnetic (JFM =1.3 meV) and antiferromagnetic (JAFM =1.1 meV)
exchange constants make this system particularly interesting for experimental
study. Because JFM and JAFM are nearly identical, the system should show
competing behavior between S=1/2 (AFM) and S=1(FM) effects. We report low
temperature magnetic field dependent susceptibility, chi(H), and specific heat,
Cp, of MCCL. These provide an initial magnetic-field versus temperature phase
diagram. A zero-field phase transition consistent with long range magnetic
order is observed at T=0.9 K. The transition temperature can be reduced via
application of a magnetic field. We also present comparisons to a FM/AFM dimer
model that accounts for chi(T,H=0) and Cp(H,T).Comment: 2 pages, 1 figure included in text. Submitted to proceedings of 24th
International Conference on Low Temperature Physics, August 200
Edge helicons and repulsion of fundamental edge magnetoplasmons in the quantum Hall regime
A quasi-microscopic treatment of edge magnetoplasmons (EMP) is presented for
very low temperatures and confining potentials smooth on the scale of the
magnetic length but sufficiently steep at the edges such that Landau
level (LL) flattening can be discarded. The profile of the unperturbed electron
density is sharp and the dissipation taken into account comes only from
electron intra-edge and intra-LL transitions due to scattering by acoustic
phonons. For wide channels and filling factors and 2, there exist
independent EMP modes spatially symmetric and antisymmetric with respect to the
edge. Some of these modes, named edge helicons, can propagate nearly undamped
even when the dissipation is strong. Their density profile changes
qualitatively during propagation and is given by a rotation of a complex vector
function. For the Coulomb coupling between the LLs leads to a
repulsion of the uncoupled fundamental LL modes: the new modes have very
different group velocities and are nearly undamped. The theory accounts well
for the experimentally observed plateau structure of the delay times as well as
for the EMP's period and decay rates.Comment: 12 pages, 6 figure
Fast drift kilometric radio bursts and solar proton events
Initial results of a comparative study of major fast drift kilometric bursts and solar proton events from Sep. 1978 to Feb. 1983 are presented. It was found that only about half of all intense, long duration ( 40 min above 500 sfu) 1 MHz bursts can be associated with F 20 MeV proton events. However, for the subset of such fast drift bursts accompanied by metric Type 2 and/or 4 activity (approximately 40% of the total), the degree of association with 20 MeV events is 80%. For the reverse association, it was found that proton events with J( 20 MeV) 0.01 1 pr cm(-2)s(-1)sr(-1)MeV(-1) were typically (approximately 80% of the time) preceded by intense 1 MHz bursts that exceeded the 500 sfu level for times 20 min (median duration approximately 35 min)
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