16,166 research outputs found
A direct approach to the ultradiscrete KdV equation with negative
A generalisation of the ultra-discrete KdV equation is investigated using a direct approach. We
show that evolution through one time step serves to reveal the entire solitonic content of the system
Bilinear Equations and B\"acklund Transformation for Generalized Ultradiscrete Soliton Solution
Ultradiscrete soliton equations and B\"acklund transformation for a
generalized soliton solution are presented. The equations include the
ultradiscrete KdV equation or the ultradiscrete Toda equation in a special
case. We also express the solution by the ultradiscrete permanent, which is
defined by ultradiscretizing the signature-free determinant, that is, the
permanent. Moreover, we discuss a relation between B\"acklund transformations
for discrete and ultradiscrete KdV equations.Comment: 11 page
Noise-Induced Synchronization of a Large Population of Globally Coupled Nonidentical Oscillators
We study a large population of globally coupled phase oscillators subject to
common white Gaussian noise and find analytically that the critical coupling
strength between oscillators for synchronization transition decreases with an
increase in the intensity of common noise. Thus, common noise promotes the
onset of synchronization. Our prediction is confirmed by numerical simulations
of the phase oscillators as well as of limit-cycle oscillators
Magnetic phases in the correlated Kondo-lattice model
We study magnetic ordering of an extended Kondo-lattice model including an
additional on-site Coulomb interaction between the itinerant states. The model
is solved in the dynamical mean-field theory using Wilson's numerical
renormalization group approach as impurity solver. For a bipartite lattice we
find at half filling the expected antiferromagnetic phase. Upon doping this
phase is gradually suppressed and hints towards phase separation are observed.
For large doping the model exhibits ferromagnetism, the appearance of which can
at first sight be explained by Rudermann-Kittel-Kasuya-Yosida interaction.
However, for large values of the Kondo coupling significant differences to
a simple Rudermann-Kittel-Kasuya-Yosida picture can be found. We furthermore
observe signs of quantum critical points for antiferromagnetic Kondo coupling
between the local spins and band states
Engaging non-alumni advisory board members in hospitality education
Hospitality education programs within higher education institutions often rely upon members of the hospitality industry to serve as volunteer advisory board members. A common role for volunteers of an academic program advisory board is to serve as a credible link between the formal education and degree earning process to the hospitality industry, provide insight and advice on current issues and trends, assist in developing industry relationships, and share their time and resources to help promote the program (Edwards, 2008; Merrill, 2003). While volunteer advisory boards within higher education are often made up of both alumni and non-alumni, this study focused on the non-alumni volunteers.
The purpose of this qualitative study was to explore the self-reported motivations, experiences, and engagement levels of non-alumni volunteers to a hospitality education program. The participants were drawn from those who were executives in the hospitality industry and served as current volunteers on the International Advisory Board for the College of Hotel Administration at the University of Nevada, Las Vegas. In-depth interviews were conducted with participants both in-person and by phone. Participants were grouped into two cases of five people each; Case 1 consisted of newer advisory board members and Case 2 consisted of longer-serving advisory board members. A within-case comparison as well as a cross-case analysis was applied to the participant responses to better understand their motivations for volunteering and motivations to continue as volunteers.
The results of the study found that non-alumni volunteers, through their involvement with their fellow advisory board members, college administrators, and perhaps most importantly, interaction with students, developed emotional connections and pride in serving the institution. This led most volunteers to have a level of engagement that was meaningful to them and resulted in their desire to continue as volunteers. The participants acknowledged a variety of factors related to their experiences that influenced their overall feelings of engagement, factors that either contributed toward or hindered their satisfaction levels, emotional attachment, and identification with the advisory board. Implications of these findings for theory, practice and future research are discussed in the final chapter
Discovery of a wandering radio jet base after a large X-ray flare in the blazar Markarian 421
We investigate the location of the radio jet bases ("radio cores") of blazars
in radio images, and their stationarity by means of dense very long baseline
interferometry (VLBI) observations. In order to measure the position of a radio
core, we conducted 12 epoch astrometric observation of the blazar Markarian 421
with the VLBI Exploration of Radio Astrometry at 22 GHz immediately after a
large X-ray flare, which occurred in the middle of 2011 September. For the
first time, we find that the radio core is not stationary but rather changes
its location toward 0.5 mas downstream. This angular scale corresponds to the
de-projected length of a scale of Schwarzschild radii (Rs) at the
distance of Markarian~421. This radio-core wandering may be a new type of
manifestation associated with the phenomena of large X-ray flares.Comment: 6 pages, 4 figures, 1 table, has been published in ApJ Letter
Quantifying properties of ICM inhomogeneities
We present a new method to identify and characterize the structure of the
intracluster medium (ICM) in simulated galaxy clusters. The method uses the
median of gas properties, such as density and pressure, which we show to be
very robust to the presence of gas inhomogeneities. In particular, we show that
the radial profiles of median gas properties are smooth and do not exhibit
fluctuations at locations of massive clumps in contrast to mean and mode
properties. It is shown that distribution of gas properties in a given radial
shell can be well described by a log-normal PDF and a tail. The former
corresponds to a nearly hydrostatic bulk component, accounting for ~99% of the
volume, while the tail corresponds to high density inhomogeneities. We show
that this results in a simple and robust separation of the diffuse and clumpy
components of the ICM. The FWHM of the density distribution grows with radius
and varies from ~0.15 dex in cluster centre to ~0.5 dex at 2r_500 in relaxed
clusters. The small scatter in the width between relaxed clusters suggests that
the degree of inhomogeneity is a robust characteristic of the ICM. It broadly
agrees with the amplitude of density perturbations in the Coma cluster. We
discuss the origin of ICM density variations in spherical shells and show that
less than 20% of the width can be attributed to the triaxiality of the cluster
gravitational potential. As a link to X-ray observations of real clusters we
evaluated the ICM clumping factor with and without high density
inhomogeneities. We argue that these two cases represent upper and lower limits
on the departure of the observed X-ray emissivity from the median value. We
find that the typical value of the clumping factor in the bulk component of
relaxed clusters varies from ~1.1-1.2 at r_500 up to ~1.3-1.4 at r_200, in
broad agreement with recent observations.Comment: 16 pages, 12 figure, accepted to MNRA
Effects of Galaxy Formation on Thermodynamics of the Intracluster Medium
We present detailed comparisons of the intracluster medium (ICM) in
cosmological Eulerian cluster simulations with deep Chandra observations of
nearby relaxed clusters. To assess the impact of galaxy formation, we compare
two sets of simulations, one performed in the non-radiative regime and another
with radiative cooling and several physical processes critical to various
aspects of galaxy formation: star formation, metal enrichment and stellar
feedback. We show that the observed ICM properties outside cluster cores are
well-reproduced in the simulations that include cooling and star formation,
while the non-radiative simulations predict an overall shape of the ICM
profiles inconsistent with observations. In particular, we find that the ICM
entropy in our runs with cooling is enhanced to the observed levels at radii as
large as half of the virial radius. We also find that outside cluster cores
entropy scaling with the mean ICM temperature in both simulations and Chandra
observations is consistent with being self-similar within current error bars.
We find that the pressure profiles of simulated clusters are also close to
self-similar and exhibit little cluster-to-cluster scatter. The X-ray
observable-total mass relations for our simulated sample agree with the Chandra
measurements to \~10%-20% in normalization. We show that this systematic
difference could be caused by the subsonic gas motions, unaccounted for in
X-ray hydrostatic mass estimates. The much improved agreement of simulations
and observations in the ICM profiles and scaling relations is encouraging and
the existence of tight relations of X-ray observables, such as Yx, and total
cluster mass and the simple redshift evolution of these relations hold promise
for the use of clusters as cosmological probes.Comment: 14 pages, 6 figures. Matches version accepted to Ap
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