115 research outputs found
Electric Polarizability of Hadrons
The electric polarizability of a hadron allows an external electric field to
shift the hadron mass. We try to calculate the electric polarizability for
several hadrons from their quadratic response to the field at a=0.17fm using an
improved gauge field and the clover quark action. Results are compared to
experiment where available.Comment: 3 pgs, 5 figs, LATTICE2002(spectrum
Transient outburst events from tidally disrupted asteroids near white dwarfs
We discuss the possibility of observing the transient formation event of an
accretion disk from the tidal destruction process of an asteroid near a white
dwarf (WD). This scenario is commonly proposed as the explanation for dusty
disks around WDs. We find that the initial formation phase lasts for about a
month and material that ends in a close orbit near the WD forms a gaseous disk
rather than a dusty disk. The mass and size of this gaseous accretion disk is
very similar to that of Dwarf Novae (DNe) in quiescence. The bolometric
luminosity of the event at maximum is estimated to be 0.001-0.1Lsun. Based on
the similarity with DNe we expect that transient outburst events such as
discussed here will be observed at wavelengths ranging from visible to the
X-ray, and be detected by present and future surveys.Comment: Accepted by New Astronom
Mental representation and motor imagery training
Schack T, Essig K, Frank C, Koester D. Mental representation and motor imagery training. Frontiers in Human Neuroscience. 2014;8(328):1-10.Research in sports, dance and rehabilitation has shown that basic action concepts (BACs) are fundamental building blocks of mental action representations. BACs are based on chunked body postures related to common functions for realizing action goals. In this paper, we outline issues in research methodology and an experimental method, the structural dimensional analysis of mental representation (SDA-M), to assess action-relevant representational structures that reflect the organization of BACs. The SDA-M reveals a strong relationship between cognitive representation and performance if complex actions are performed. We show how the SDA-M can improve motor imagery training and how it contributes to our understanding of coaching processes. The SDA-M capitalizes on the objective measurement of individual mental movement representations before training and the integration of these results into the motor imagery training. Such motor imagery training based on mental representations (MTMR) has been applied successfully in professional sports such as golf, volleyball, gymnastics, windsurfing, and recently in the rehabilitation of patients who have suffered a stroke
Satellite Kinematics I: A New Method to Constrain the Halo Mass-Luminosity Relation of Central Galaxies
Satellite kinematics can be used to probe the masses of dark matter haloes of
central galaxies. In order to measure the kinematics with sufficient
signal-to-noise, one uses the satellite galaxies of a large number of central
galaxies stacked according to similar properties (e.g., luminosity). However,
in general the relation between the luminosity of a central galaxy and the mass
of its host halo will have non-zero scatter. Consequently, this stacking
results in combining the kinematics of satellite galaxies in haloes of
different masses, which complicates the interpretation of the data. In this
paper we present an analytical framework to model satellite kinematics,
properly accounting for this scatter and for various selection effects. We show
that in the presence of scatter in the halo mass-luminosity relation, the
commonly used velocity dispersion of satellite galaxies can not be used to
infer a unique halo mass-luminosity relation. In particular, we demonstrate
that there is a degeneracy between the mean and the scatter of the halo
mass-luminosity relation. We present a new technique that can break this
degeneracy, and which involves measuring the velocity dispersions using two
different weighting schemes: host-weighting (each central galaxy gets the same
weight) and satellite-weighting (each central galaxy gets a weight proportional
to its number of satellites). The ratio between the velocity dispersions
obtained using these two weighting schemes is a strong function of the scatter
in the halo mass-luminosity relation, and can thus be used to infer a unique
relation between light and mass from the kinematics of satellite galaxies.Comment: 8 pages, 3 figures, MNRAS submitte
Global Models of Runaway Accretion in White Dwarf Debris Disks
A growing sample of white dwarfs (WDs) with metal-enriched atmospheres are
accompanied by excess infrared emission, indicating that they are encircled by
a compact dusty disk of solid debris. Such `WD debris disks' are thought to
originate from the tidal disruption of asteroids or other minor bodies, but the
precise mechanism(s) responsible for transporting matter to the WD surface
remains unclear, especially in those systems with the highest inferred metal
accretion rates dM_Z/dt ~ 1e8-1e10 g/s. Here we present global time-dependent
calculations of the coupled evolution of the gaseous and solid components of WD
debris disks. Solids transported inwards (initially due to PR drag) sublimate
at tens of WD radii, producing a source of gas that accretes onto the WD
surface and viscously spreads outwards in radius, where it overlaps with the
solid disk. If the aerodynamic coupling between the solids and gaseous disks is
sufficiently strong (and/or the gas viscosity sufficiently weak), then gas
builds up near the sublimation radius faster than it can viscously spread away.
Since the rate of drag-induced solid accretion increases with gas density, this
results in a runaway accretion process, during which the WD accretion rate
reaches values orders of magnitude higher than can be achieved by PR drag
alone. We explore the evolution of WD debris disks across a wide range of
physical conditions and calculate the predicted distribution of observed
accretion rates dM_Z/dt, finding reasonable agreement with the current sample.
Although the conditions necessary for runaway accretion are at best marginally
satisfied given the minimal level of aerodynamic drag between circular gaseous
and solid disks, the presence of other stronger forms of solid-gas
coupling---such as would result if the gaseous disk is only mildly
eccentric---substantially increase the likelihood of runaway accretion.Comment: 23 pages, 20 figures, submitted to MNRA
Inspection of Electronics Components for Cryogenic Temperature Operation
Electronics operating at cryogenic temperatures play a critical role in future science experiments and space exploration programs. The Deep Underground Neutrino Experiment (DUNE) uses a cold electronics system for data taking. Specifically, it utilizes custom-designed Application Specific Integrated Circuits (ASICs). The main challenge is that these circuits will be immersed in liquid Argon and that they need to function for 20+ years without any access. Ensuring quality is critical, and issues may arise due to thermal stress, packaging, and manufacturing-related defects: if undetected, these could lead to long-term reliability and performance problems. This paper reports an investigation into non-destructive evaluation techniques to assess their potential use in a comprehensive quality control process during prototyping, testing, and commissioning of the DUNE cold electronics system. Scanning acoustic microscopy (SAM) was used to investigate permanent structural changes in the ASICs associated with thermal cycling between room and cryogenic temperatures. Data are assessed using a correlation analysis, which can detect even minimal changes happening inside the ASICs
Constraints on new interactions from neutron scattering experiments
Constraints for the constants of hypothetical Yukawa-type corrections to the
Newtonian gravitational potential are obtained from analysis of neutron
scattering experiments. Restrictions are obtained for the interaction range
between 10^{-12} and 10^{-7} cm, where Casimir force experiments and atomic
force microscopy are not sensitive. Experimental limits are obtained also for
non-electromagnetic inverse power law neutron-nucleus potential. Some
possibilities are discussed to strengthen these constraints.Comment: 18 pages, 3 figure
Probing Hot Gas in Galaxy Groups through the Sunyaev-Zeldovich Effect
We investigate the potential of exploiting the Sunyaev-Zeldovich effect (SZE)
to study the properties of hot gas in galaxy groups. It is shown that, with
upcoming SZE surveys, one can stack SZE maps around galaxy groups of similar
halo masses selected from large galaxy redshift surveys to study the hot gas in
halos represented by galaxy groups. We use various models for the hot halo gas
to study how the expected SZE signals are affected by gas fraction, equation of
state, halo concentration, and cosmology. Comparing the model predictions with
the sensitivities expected from the SPT, ACT and Planck surveys shows that a
SPT-like survey can provide stringent constraints on the hot gas properties for
halos with masses M ~> 10^{13} h^{-1}Msun. We also explore the idea of using
the cross correlation between hot gas and galaxies of different luminosity to
probe the hot gas in dark matter halos without identifying galaxy groups to
represent dark halos. Our results show that, with a galaxy survey as large as
the Sloan Digital Sky Survey and with the help of the conditional luminosity
function (CLF) model, one can obtain stringent constraints on the hot gas
properties in halos with masses down to 10^{13} h^{-1}Msun. Thus, the upcoming
SZE surveys should provide a very promising avenue to probe the hot gas in
relatively low-mass halos where the majority of L*-galaxies reside.Comment: 22 pages, 16 figures, accepted for publication on MNRA
Are Brightest Halo Galaxies Central Galaxies?
It is generally assumed that the central galaxy in a dark matter halo, that
is, the galaxy with the lowest specific potential energy, is also the brightest
halo galaxy (BHG), and that it resides at rest at the centre of the dark matter
potential well. This central galaxy paradigm (CGP) is an essential assumption
made in various fields of astronomical research. In this paper we test the
validity of the CGP using a large galaxy group catalogue constructed from the
Sloan Digital Sky Survey. For each group we compute two statistics,
and , which quantify the offsets of the line-of-sight velocities and
projected positions of brightest group galaxies relative to the other group
members. By comparing the cumulative distributions of and to those obtained from detailed mock group catalogues, we rule out the
null-hypothesis that the CGP is correct. Rather, the data indicate that in a
non-zero fraction of all haloes of mass the BHG is not the
central galaxy, but instead, a satellite galaxy. In particular, we find that
increases from in low mass haloes (10^{12} h^{-1}
{\rm M_{\odot}} \leq M \lsim 2 \times 10^{13} h^{-1}{\rm M_{\odot}}) to in massive haloes (M \gsim 5 \times 10^{13} h^{-1} {\rm M_{\odot}}). We
show that these values of are uncomfortably high compared to
predictions from halo occupation statistics and from semi-analytical models of
galaxy formation. We end by discussing various implications of a non-zero
, with an emphasis on the halo masses inferred from satellite
kinematics.Comment: 17 pages, 11 figures. Axes labels of Fig. 3 fixe
Skunk River Fall 1998
https://openspace.dmacc.edu/skunkriver/1019/thumbnail.jp
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