1,240 research outputs found
Realistic Neutrino Opacities for Supernova Simulations With Correlations and Weak Magnetism
Advances in neutrino transport allow realistic neutrino interactions to be
incorporated into supernova simulations. We add tensor couplings to
relativistic RPA calculations of neutrino opacities. Our results reproduce
free-space neutrino-nucleon cross sections at low density, including weak
magnetism and recoil corrections. In addition, our opacities are
thermodynamically consistent with relativistic mean field equations of state.
We find antineutrino mean free paths that are considerably larger then those
for neutrinos. This difference depends little on density. In a supernova, this
difference could lead to an average energy of that is larger than
that for by an amount that is comparable to the energy difference
between and Comment: 15 pages, 10 figures, submitted to PRC, minor changes to figs. (9,10
Cell culture device using spatial light modulator
Spatial light modulator is introduced for cell culturing and related illumination experiment. Two kinds of designs were used. The first type put the cell along with the bio-medium directly on top of the analyzer of the microdisplay and set a cover glass on it to retain the medium environment, which turned the microdisplay into a bio-container. The second type introduced an optical lens system placed below the spatial light modulator to focus the light spots on specific position. Details of the advantages and drawbacks for the two different approaches are discussed, and the human melanocyte cell (HMC) is introduced to prove the feasibility of the concept. Results indicate that the second type is much more suitable than the first for precision required application
Phantom Cosmology with Non-minimally Coupled Real Scalar Field
We find that the expansion of the universe is accelerating by analyzing the
recent observation data of type \textsc{I}a supernova(SN-Ia) .It indicates
that the equation of state of the dark energy might be smaller than -1,which
leads to the introduction of phantom models featured by its negative kinetic
energy to account for the regime of equation of state parameter .In this
paper the possibility of using a non-minimally coupled real scalar field as
phantom to realize the equation of state parameter is discussed.The main
equations which govern the evolution of the universe are obtained.Then we
rewrite them with the observable quantities.Comment: 12 pages, 2 figures. Accepted for publication in Gen.Rel.Gra
Algebraic Quantization, Good Operators and Fractional Quantum Numbers
The problems arising when quantizing systems with periodic boundary
conditions are analysed, in an algebraic (group-) quantization scheme, and the
``failure" of the Ehrenfest theorem is clarified in terms of the already
defined notion of {\it good} (and {\it bad}) operators. The analysis of
``constrained" Heisenberg-Weyl groups according to this quantization scheme
reveals the possibility for new quantum (fractional) numbers extending those
allowed for Chern classes in traditional Geometric Quantization. This study is
illustrated with the examples of the free particle on the circumference and the
charged particle in a homogeneous magnetic field on the torus, both examples
featuring ``anomalous" operators, non-equivalent quantization and the latter,
fractional quantum numbers. These provide the rationale behind flux
quantization in superconducting rings and Fractional Quantum Hall Effect,
respectively.Comment: 29 pages, latex, 1 figure included with EPSF. Revised version with
minor changes intended to clarify notation. Acepted for publication in Comm.
Math. Phy
Cluster Formation and The Virial Equation of State of Low-Density Nuclear Matter
We present the virial equation of state of low-density nuclear matter
composed of neutrons, protons and alpha particles. The virial equation of state
is model-independent, and therefore sets a benchmark for all nuclear equations
of state at low densities. We calculate the second virial coefficients for
nucleon-nucleon, nucleon-alpha and alpha-alpha interactions directly from the
relevant binding energies and scattering phase shifts. The virial approach
systematically takes into account contributions from bound nuclei and the
resonant continuum, and consequently provides a framework to include
strong-interaction corrections to nuclear statistical equilibrium models. The
virial coefficients are used to make model-independent predictions for a
variety of properties of nuclear matter over a range of densities, temperatures
and compositions. Our results provide constraints on the physics of the
neutrinosphere in supernovae. The resulting alpha particle concentration
differs from all equations of state currently used in supernova simulations.
Finally, the virial equation of state greatly improves our conceptual
understanding of low-density nuclear matter.Comment: 15 pages, 17 figures, minor revisions, to appear in Nucl. Phys.
Cosmic ray induced explosive chemical desorption in dense clouds
Wetensch. publicatieFaculteit der Wiskunde en Natuurwetenschappe
Interplanetary and Geomagnetic Consequences of Interacting CMEs of 13-14 June 2012
We report on the kinematics of two interacting CMEs observed on 13 and 14
June 2012. Both CMEs originated from the same active region NOAA 11504. After
their launches which were separated by several hours, they were observed to
interact at a distance of 100 Rs from the Sun. The interaction led to a
moderate geomagnetic storm at the Earth with Dst index of approximately, -86
nT. The kinematics of the two CMEs is estimated using data from the Sun Earth
Connection Coronal and Heliospheric Investigation (SECCHI) onboard the Solar
Terrestrial Relations Observatory (STEREO). Assuming a head-on collision
scenario, we find that the collision is inelastic in nature. Further, the
signatures of their interaction are examined using the in situ observations
obtained by Wind and the Advance Composition Explorer (ACE) spacecraft. It is
also found that this interaction event led to the strongest sudden storm
commencement (SSC) (approximately 150 nT) of the present Solar Cycle 24. The
SSC was of long duration, approximately 20 hours. The role of interacting CMEs
in enhancing the geoeffectiveness is examined.Comment: 17 pages, 5 figures, Accepted in Solar Physics Journa
Partial wave analysiss of pbar-p -> piminus-piplus, pizero-pizero, eta-eta and eta-etaprime
A partial wave analysis is presented of Crystal Barrel data on pbar-p ->
pizero-pizero, eta-eta and eta-etaprime from 600 to 1940 MeV/c, combined with
earlier data on d\sigma /d\Omega and P for pbar-p->piminus-piplus. The
following s-channel I=0 resonances are identified: (i) J^{PC} = 5^{--} with
mass and width (M,\Gamma) at (2295+-30,235^{+65}_{-40}) MeV, (ii) J^{PC} =
4^{++} at (2020+-12, 170+-15) MeV and (2300+-25, 270+-50) MeV, (iii) 3D3 JPC =
3^{--} at (1960+-15, 150+-25) MeV and (2210+-4$, 360+-55) MeV, and a 3G3 state
at (2300 ^{+50}_{-80}, 340+-150) MeV, (iv) JPC = 2^{++} at (1910+-30, 260+-40)
MeV, (2020+-30, 275+-35) MeV, (2230+-30, 245+-45) MeV, and (2300+-35, 290+-50)
MeV, (v) JPC = 1^{--} at (2005+-40, 275+-75) MeV, and (2165+-40, 160
^{+140}_{-70}) MeV, and (vi) JPC = 0^{++} at (2005+-30, 305+-50) MeV,
(2105+-15, 200+-25) MeV, and (2320+-30, 175+-45) MeV. In addition, there is a
less well defined 6^{++} resonance at 2485+-40 MeV, with Gamma = 410+-90 MeV.
For every JP, almost all these resonances lie on well defined linear
trajectories of mass squared v. excitation number. The slope is 1.10+-0.03
Gev^2 per excitation. The f_0(2105) has strong coupling to eta-\eta, but much
weaker coupling to pizero-pizero. Its flavour mixing angle between q-qbar and
s-sbar is (59-71.6)deg, i.e. dominant decays to s-sbar. Such decays and its
strong production in pbar-p interactions strongly suggest exotic character.Comment: Makes available the combined fit to Crystal Barrel data on pbar-p ->
2-body final states. 29 pages, 11 figures. Typo corrected in version
Influence of entrance-channel magicity and isospin on quasi-fission
The role of spherical quantum shells in the competition between fusion and
quasi-fission is studied for reactions forming heavy elements. Measurements of
fission fragment mass distributions for different reactions leading to similar
compound nuclei have been made near the fusion barrier. In general, more
quasi-fission is observed for reactions with non-magic nuclei. However, the
Ca+Pb reaction is an exception, showing strong evidence for
quasi-fission, though both nuclei are doubly magic. Time-dependent Hartree-Fock
calculations predict fast equilibration of in the two fragments early in
the collision. This transfer of nucleons breaks the shell effect, causing this
reaction to behave more like a non-magic one in the competition between fusion
and quasi-fission. Future measurements of fission in reactions with exotic
beams should be able to test this idea with larger asymmetries.Comment: accepted for publication in Physics Letters
Genetic clustering on the hippocampal surface for genome-wide association studies
Imaging genetics aims to discover how variants in the human genome influence brain measures derived from images. Genome-wide association scans (GWAS) can screen the genome for common differences in our DNA that relate to brain measures. In small samples, GWAS has low power as individual gene effects are weak and one must also correct for multiple comparisons across the genome and the image. Here we extend recent work on genetic clustering of images, to analyze surface-based models of anatomy using GWAS. We performed spherical harmonic analysis of hippocampal surfaces, automatically extracted from brain MRI scans of 1254 subjects. We clustered hippocampal surface regions with common genetic influences by examining genetic correlations (rg) between the normalized deformation values at all pairs of surface points. Using genetic correlations to cluster surface measures, we were able to boost effect sizes for genetic associations, compared to clustering with traditional phenotypic correlations using Pearson's r
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