8,214 research outputs found
Local Statistics of Realizable Vertex Models
We study planar "vertex" models, which are probability measures on edge
subsets of a planar graph, satisfying certain constraints at each vertex,
examples including dimer model, and 1-2 model, which we will define. We express
the local statistics of a large class of vertex models on a finite hexagonal
lattice as a linear combination of the local statistics of dimers on the
corresponding Fisher graph, with the help of a generalized holographic
algorithm. Using an torus to approximate the periodic infinite
graph, we give an explicit integral formula for the free energy and local
statistics for configurations of the vertex model on an infinite bi-periodic
graph. As an example, we simulate the 1-2 model by the technique of Glauber
dynamics
Low Mass Stars and Brown Dwarfs around Sigma Orionis
We present optical spectroscopy of 71 photometric candidate low-mass members
of the cluster associated with Sigma Orionis. Thirty-five of these are found to
pass the lithium test and hence are confirmed as true cluster members, covering
a mass range of <0.055-0.3M_{sun}, assuming a mean cluster age of <5 Myr. We
find evidence for an age spread on the (I, I-J) colour magnitude diagram,
members appearing to lie in the range 1-7 Myr. There are, however, a
significant fraction of candidates that are non-members, including some
previously identified as members based on photometry alone. We see some
evidence that the ratio of spectroscopically confirmed members to photometric
candidates decreases with brightness and mass. This highlights the importance
of spectroscopy in determining the true initial mass-function.Comment: To appear in the 12th Cambridge Workshop on Cool Stars Stellar
Systems and the Su
The interaction of a gap with a free boundary in a two dimensional dimer system
Let be a fixed vertical lattice line of the unit triangular lattice in
the plane, and let \Cal H be the half plane to the left of . We
consider lozenge tilings of \Cal H that have a triangular gap of side-length
two and in which is a free boundary - i.e., tiles are allowed to
protrude out half-way across . We prove that the correlation function of
this gap near the free boundary has asymptotics ,
, where is the distance from the gap to the free boundary. This
parallels the electrostatic phenomenon by which the field of an electric charge
near a conductor can be obtained by the method of images.Comment: 34 pages, AmS-Te
Planet formation around stars of various masses: Hot super-Earths
We consider trends resulting from two formation mechanisms for short-period
super-Earths: planet-planet scattering and migration. We model scenarios where
these planets originate near the snow line in ``cold finger'' circumstellar
disks. Low-mass planet-planet scattering excites planets to low periastron
orbits only for lower mass stars. With long circularisation times, these
planets reside on long-period eccentric orbits. Closer formation regions mean
planets that reach short-period orbits by migration are most common around
low-mass stars. Above ~1 Solar mass, planets massive enough to migrate to
close-in orbits before the gas disk dissipates are above the critical mass for
gas giant formation. Thus, there is an upper stellar mass limit for
short-period super-Earths that form by migration. If disk masses are
distributed as a power law, planet frequency increases with metallicity because
most disks have low masses. For disk masses distributed around a relatively
high mass, planet frequency decreases with increasing metallicity. As icy
planets migrate, they shepherd interior objects toward the star, which grow to
~1 Earth mass. In contrast to icy migrators, surviving shepherded planets are
rocky. Upon reaching short-period orbits, planets are subject to evaporation
processes. The closest planets may be reduced to rocky or icy cores. Low-mass
stars have lower EUV luminosities, so the level of evaporation decreases with
decreasing stellar mass.Comment: Accepted to ApJ. 13 pages of emulateap
Correlations Between Ego Identity Development and Career Development
There are numerous ways in which people choose their occupation. Some choose a career by simply asking their parents or friends for their opinion on what would be a good occupation. Others may talk to people in the occupation, or go to the library to gather information about occupations that are of interest. Because of the importance of the career choice to the individual\u27s well-being and productivity in a career, some try a more organized approach. A career counselor, who can utilize tests to aid in the search process as well as provide information on occupations, can be a valuable resource
The discovery of a low mass, pre-main-sequence stellar association around gamma Velorum
We report the serendipitous discovery of a population of low mass, pre-main
sequence stars (PMS) in the direction of the Wolf-Rayet/O-star binary system
gamma^{2} Vel and the Vela OB2 association. We argue that gamma^{2} Vel and the
low mass stars are truly associated, are approximately coeval and that both are
at distances between 360-490 pc, disagreeing at the 2 sigma level with the
recent Hipparcos parallax of gamma^{2} Vel, but consistent with older distance
estimates. Our results clearly have implications for the physical parameters of
the gamma^{2} Vel system, but also offer an exciting opportunity to investigate
the influence of high mass stars on the mass function and circumstellar disc
lifetimes of their lower mass PMS siblings.Comment: Monthly Notices of the Royal Astronomical Society, Letters - in pres
Quadri-tilings of the plane
We introduce {\em quadri-tilings} and show that they are in bijection with
dimer models on a {\em family} of graphs arising from rhombus
tilings. Using two height functions, we interpret a sub-family of all
quadri-tilings, called {\em triangular quadri-tilings}, as an interface model
in dimension 2+2. Assigning "critical" weights to edges of , we prove an
explicit expression, only depending on the local geometry of the graph ,
for the minimal free energy per fundamental domain Gibbs measure; this solves a
conjecture of \cite{Kenyon1}. We also show that when edges of are
asymptotically far apart, the probability of their occurrence only depends on
this set of edges. Finally, we give an expression for a Gibbs measure on the
set of {\em all} triangular quadri-tilings whose marginals are the above Gibbs
measures, and conjecture it to be that of minimal free energy per fundamental
domain.Comment: Revised version, minor changes. 30 pages, 13 figure
Habituation to novel visual vestibular environments with special reference to space flight
The etiology of space motion sickness and the underlying physiological mechanisms associated with spatial orientation in a space environment were investigated. Human psychophysical experiments were used as the basis for the research concerning the interaction of visual and vestibular cues in the development of motion sickness. Particular emphasis is placed on the conflict theory in terms of explaining these interactions. Research on the plasticity of the vestibulo-ocular reflex is discussed
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