4,485 research outputs found
Cold neutrons trapped in external fields
The properties of inhomogeneous neutron matter are crucial to the physics of
neutron-rich nuclei and the crust of neutron stars. Advances in computational
techniques now allow us to accurately determine the binding energies and
densities of many neutrons interacting via realistic microscopic interactions
and confined in external fields. We perform calculations for different external
fields and across several shells to place important constraints on
inhomogeneous neutron matter, and hence the large isospin limit of the nuclear
energy density functionals that are used to predict properties of heavy nuclei
and neutron star crusts. We find important differences between microscopic
calculations and current density functionals; in particular the isovector
gradient terms are significantly more repulsive than in traditional models, and
the spin-orbit and pairing forces are comparatively weaker.Comment: 5 pages, 4 figures, final version. Additional material reference
added in the published versio
Phase Transitions in a Dusty Plasma with Two Distinct Particle Sizes
In semiconductor manufacturing, contamination due to particulates
significantly decreases the yield and quality of device fabrication, therefore
increasing the cost of production. Dust particle clouds can be found in almost
all plasma processing environments including both plasma etching devices and in
plasma deposition processes. Dust particles suspended within such plasmas will
acquire an electric charge from collisions with free electrons in the plasma.
If the ratio of inter-particle potential energy to the average kinetic energy
is sufficient, the particles will form either a liquid structure with short
range ordering or a crystalline structure with long range ordering. Otherwise,
the dust particle system will remain in a gaseous state. Many experiments have
been conducted over the past decade on such colloidal plasmas to discover the
character of the systems formed, but more work is needed to fully understand
these structures. The preponderance of previous experiments used monodisperse
spheres to form complex plasma systems
Quantum Monte Carlo study of inhomogeneous neutron matter
We present an ab-initio study of neutron drops. We use Quantum Monte Carlo
techniques to calculate the energy up to 54 neutrons in different external
potentials, and we compare the results with Skyrme forces. We also calculate
the rms radii and radial densities, and we find that a re-adjustment of the
gradient term in Skyrme is needed in order to reproduce the properties of these
systems given by the ab-initio calculation. By using the ab-initio results for
neutron drops for close- and open-shell configurations, we suggest how to
improve Skyrme forces when dealing with systems with large isospin-asymmetries
like neutron-rich nuclei.Comment: 8 pages, 6 figures, talk given at Horizons on Innovative Theories,
Experiments, and Supercomputing in Nuclear Physics 2012, (HITES2012), New
Orleans, Louisiana, June 4-7, 2012; to appear in Journal of Physics:
Conference Series (JPCS
Solar Protons and Magnetic Storms in July 1961
Injun i satellite observations of solar protons and magnetic storm
Quantum Monte Carlo calculations of excited states in A = 6--8 nuclei
A variational Monte Carlo method is used to generate sets of orthogonal trial
functions, Psi_T(J^pi,T), for given quantum numbers in various light p-shell
nuclei. These Psi_T are then used as input to Green's function Monte Carlo
calculations of first, second, and higher excited (J^pi,T) states. Realistic
two- and three-nucleon interactions are used. We find that if the physical
excited state is reasonably narrow, the GFMC energy converges to a stable
result. With the combined Argonne v_18 two-nucleon and Illinois-2 three-nucleon
interactions, the results for many second and higher states in A = 6--8 nuclei
are close to the experimental values.Comment: Revised version with minor changes as accepted by Phys. Rev. C. 11
page
Tensor Forces and the Ground-State Structure of Nuclei
Two-nucleon momentum distributions are calculated for the ground states of
nuclei with mass number , using variational Monte Carlo wave functions
derived from a realistic Hamiltonian with two- and three-nucleon potentials.
The momentum distribution of pairs is found to be much larger than that of
pairs for values of the relative momentum in the range (300--600) MeV/c
and vanishing total momentum. This order of magnitude difference is seen in all
nuclei considered and has a universal character originating from the tensor
components present in any realistic nucleon-nucleon potential. The correlations
induced by the tensor force strongly influence the structure of pairs,
which are predominantly in deuteron-like states, while they are ineffective for
pairs, which are mostly in S states. These features should be
easily observable in two-nucleon knock-out processes, such as and .Comment: 4 pages including 3 figure
Dependence of two-nucleon momentum densities on total pair momentum
Two-nucleon momentum distributions are calculated for the ground states of
3He and 4He as a function of the nucleons' relative and total momenta. We use
variational Monte Carlo wave functions derived from a realistic Hamiltonian
with two- and three-nucleon potentials. The momentum distribution of pp pairs
is found to be much smaller than that of pn pairs for values of the relative
momentum in the range (300--500) MeV/c and vanishing total momentum. However,
as the total momentum increases to 400 MeV/c, the ratio of pp to pn pairs in
this relative momentum range grows and approaches the limit 1/2 for 3He and 1/4
for 4He, corresponding to the ratio of pp to pn pairs in these nuclei. This
behavior should be easily observable in two-nucleon knock-out processes, such
as A(e,e'pN).Comment: 3 pages, 3 figure
Analysis of the Expression of Human Endogenous Retroviruses in Chronic Fatigue Syndrome
Chronic fatigue syndrome or myalgic encephalomyelitis (CFS/ME) is a poorly understood condition that affects between .007% and 2.8% of the US population. Characterized by fatigue without a clear cause persisting for at least six months, CFS/ME has never had a precise cause identified. Despite this, researchers have often focused on one of several potential disease mechanisms. While early studies focused on actual pathogens, immune abnormalities in patients with CFS/ME have recently suggested that there may be an autoimmune component to the condition. Given recent research suggesting that the expression of endogenous retroviral elements (ERV) may play a role in activating the innate immune system. I conducted a study to determine whether ERVs might be expressed at greater levels in patients with CFS/ME. To do this, I used a bioinformatic approach to identify ERVs in RNA sequencing data derived from patients diagnosed with CFS/ME as well as controls. Data were processed using the ERVmap scripts and analyzed each ERV identified using a two-sample T test. I identified 49 ERVs that showed a significant positive (p \u3c.05) correlation with CFS/ME. Although my results would be stronger with a larger sample size, they generally show evidence of a connection between expression of ERVs and CFS/ME. Future research should focus on whether inhibiting the specific innate immunity pathways decreases the severity of CFS/ME symptoms
Challenging social systems under the threat of pollution: Replication and extension of Eadeh and Chang (2019)
I replicated and extended Eadeh and Chang (2019; Study 2) who found that reading a story about pollution harming a child increased self-reported liberalism and increased support for environmental regulation policies through greater negative affect (i.e., anger and disgust) (Hypothesis 1). Eadeh and Chang’s (2019) threat-affordance model posits that perceived threat can increase greater support for liberalism or greater support for conservatism, depending on the type of threat. In contrast, Jost and colleagues’ (2003) system justification theory posits that perceived threat asymmetrically predicts greater support for conservatism and greater systemsupporting collective action. This article advances a synthesis of these two theoretical perspectives such that the threat of environmental pollution (a) increases system-challenging collective action intentions and donation behavior through negative affect (Hypothesis 2) and (b) increases liberalism, support for environmental regulation, collection action intentions, and donation behavior through lower system justification (moderated by empathy), greater perceived injustice, and greater negative affect (in order; Hypothesis 3)
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