701 research outputs found
Pseudo Goldstone Bosons Phenomenology in Minimal Walking Technicolor
We construct the non-linear realized Lagrangian for the Goldstone Bosons
associated to the breaking pattern of SU(4) to SO(4). This pattern is expected
to occur in any Technicolor extension of the standard model featuring two Dirac
fermions transforming according to real representations of the underlying gauge
group. We concentrate on the Minimal Walking Technicolor quantum number
assignments with respect to the standard model symmetries. We demonstrate that
for, any choice of the quantum numbers, consistent with gauge and Witten
anomalies the spectrum of the pseudo Goldstone Bosons contains electrically
doubly charged states which can be discovered at the Large Hadron Collider.Comment: 25 pages, 5 figure
Predictions for Triple Stars with and without a Pulsar in Star Clusters
Though about 80 pulsar binaries have been detected in globular clusters so
far, no pulsar has been found in a triple system in which all three objects are
of comparable mass. Here we present predictions for the abundance of such
triple systems, and for the most likely characteristics of these systems. Our
predictions are based on an extensive set of more than 500 direct simulations
of star clusters with primordial binaries, and a number of additional runs
containing primordial triples. Our simulations employ a number N_{tot} of equal
mass stars from N_{tot}=512 to N_{tot}=19661 and a primordial binary fraction
from 0-50%. In addition, we validate our results against simulations with
N=19661 that include a mass spectrum with a turn-off mass at 0.8 M_{sun},
appropriate to describe the old stellar populations of galactic globular
clusters. Based on our simulations, we expect that typical triple abundances in
the core of a dense cluster are two orders of magnitude lower than the binary
abundances, which in itself already suggests that we don't have to wait too
long for the first comparable-mass triple with a pulsar to be detected.Comment: 11 pages, minor changes to match MNRAS accepted versio
The M/L ratio of massive young clusters
We point out a strong time-evolution of the mass-to-light conversion factor
\eta commonly used to estimate masses of dense star clusters from observed
cluster radii and stellar velocity dispersions. We use a gas-dynamical model
coupled with the Cambridge stellar evolution tracks to compute line-of-sight
velocity dispersions and half-light radii weighted by the luminosity. Stars at
birth are assumed to follow the Salpeter mass function in the range [0.15--17
M_\sun]. We find that , and hence the estimated cluster mass, increases
by factors as large as 3 over time-scales of 20 million years. Increasing the
upper mass limit to 50 M_\sun leads to a sharp rise of similar amplitude but
in as little as 10 million years.
Fitting truncated isothermal (Michie-King) models to the projected light
profile leads to over-estimates of the concentration par ameter c of compared to the same functional fit applied to the proj ected
mass density.Comment: Draft version of an ApJ lette
The Journey through Perspective Transformation: Learning Nursing Theory
Through the use of grounded theory, educational methods most useful for nurses to achieve a perspective transformation, as exemplified by learning nursing theory were examined. Perspective transformation is a theory originally developed by Mezirow (1978) in a study of older women returning to college for additional education. Mezirow defined perspective transformation as the alteration or change of meaning perspectives. Perspective transformation in an individual can be compared to a paradigm change within a scientific community. Within the nursing literature on perspective transformation, most articles related to the perspective transformation needed for nurses to learn to use nursing theory as the framework for patient care. Little has been written on how nurses learn nursing theory, none found from the perspective of the learner. The experiences of 21 working nurses who had made a perspective transformation by learning nursing theory and practicing within a nursing theoretical framework were examined. One hour interviews were taped and transcribed. Data were coded using Level 1 open coding, Level 2 axial coding, and Level 3 selective coding. Study findings indicated that nurses achieving perspective transformation go through three nonlinear stages: (a) becoming aware, (b) developing meaning, and (c) perspective transformation. Those evolving beyond perspective transformation to self-actualization go through a fourth stage. During this stage, they combined theoretical models to create a personal nursing model for patient care. Nursing needs to operate within its own theoretical base. Nursing theory helps describe, explain, predict, or prescribe the phenomenon that are the reality of nursing. This study is important because it examined the most useful methods to help nurses learn nursing theory, incorporate theory into practice, and achieve perspective transformation. Future research studies should continue to pursue: (a) how to help nurses learn to incorporate nursing theoretical models into practice, (b) how to encourage organizational support of nursing theoretical frameworks, (c) satisfaction of patients cared for within the framework of nursing theoretical models, (d) the improvement of patient care through the use of nursing theory in practice, and (e) the professional growth of nurses practicing through the use of nursing theoretical frameworks
Models of core reconstruction for the 90-degree partial dislocation in semiconductors
We compare the models that have been proposed in the literature for the
atomic structure of the 90-degree partial dislocation in the homopolar
semiconductors, silicon, diamond, and germanium. In particular, we examine the
traditional single-period and our recently proposed double-period core
structures. Ab-initio and tight-binding results on the core energies are
discussed, and the geometries are compared in light of the available
experimental information about dislocations in these systems. The double-period
geometry is found to be the ground-state structure in all three materials. We
address boundary-conditions issues that have been recently raised about these
results. The structures of point excitations (kinks, solitons, and kink-soliton
complexes) in the two geometries are also reviewed.Comment: 9 pages, with 3 postscript figures embedded. Uses REVTEX and epsf
macros. Also available at
http://www.physics.rutgers.edu/~dhv/preprints/rn_eds/index.htm
HST Observations of the Central-Cusp Globular Cluster NGC 6752. The Effect of Binary Stars on the Luminosity Function in the Core
We consider the effect of binary stars on the main-sequence luminosity
functions observed in the core of globular clusters, with specific reference to
NGC 6752. We find that mass segregation results in an increased binary fraction
at fainter magnitudes along the main-sequence. If this effect is not taken into
account when analyzing luminosity functions, erroneous conclusions can be drawn
regarding the distribution of single stars, and the dynamical state of the
cluster. In the core of NGC 6752, our HST data reveal a flat luminosity
function, in agreement with previous results. However, when we correct for the
increasing binary fraction at faint magnitudes, the LF begins to fall
immediately below the turn-off. This effect appears to be confined to the inner
core radius of the cluster.Comment: 10 pages, 3 figures Accepted to ApJ Lett Vol 513 Number
Planets in triple star systems--the case of HD188753
We consider the formation of the recently discovered ``hot Jupiter'' planet
orbiting the primary component of the triple star system HD188753. Although the
current outer orbit of the triple is too tight for a Jupiter-like planet to
have formed and migrated to its current location, the binary may have been much
wider in the past. We assume here that the planetary system formed in an open
star cluster, the dynamical evolution of which subsequently led to changes in
the system's orbital parameters and binary configuration. We calculate cross
sections for various scenarios that could have led to the multiple system
currently observed, and conclude that component A of HD188753 with its planet
were most likely formed in isolation to be swapped in a triple star system by a
dynamical encounter in an open star cluster. We estimate that within 500pc of
the Sun there are about 1200 planetary systems which, like Hd188753, have
orbital parameters unfavorable for forming planets but still having a planet,
making it quite possible that the HD188753 system was indeed formed by a
dynamical encounter in an open star cluster.Comment: ApJ Letters in pres
Atomic structure of dislocation kinks in silicon
We investigate the physics of the core reconstruction and associated
structural excitations (reconstruction defects and kinks) of dislocations in
silicon, using a linear-scaling density-matrix technique. The two predominant
dislocations (the 90-degree and 30-degree partials) are examined, focusing for
the 90-degree case on the single-period core reconstruction. In both cases, we
observe strongly reconstructed bonds at the dislocation cores, as suggested in
previous studies. As a consequence, relatively low formation energies and high
migration barriers are generally associated with reconstructed
(dangling-bond-free) kinks. Complexes formed of a kink plus a reconstruction
defect are found to be strongly bound in the 30-degree partial, while the
opposite is true in the case of 90-degree partial, where such complexes are
found to be only marginally stable at zero temperature with very low
dissociation barriers. For the 30-degree partial, our calculated formation
energies and migration barriers of kinks are seen to compare favorably with
experiment. Our results for the kink energies on the 90-degree partial are
consistent with a recently proposed alternative double-period structure for the
core of this dislocation.Comment: 12 pages, two-column style with 8 postscript figures embedded. Uses
REVTEX and epsf macros. Also available at
http://www.physics.rutgers.edu/~dhv/preprints/index.html#rn_di
The surface density profile of NGC 6388: a good candidate for harboring an intermediate-mass black hole
We have used a combination of high resolution (HST ACS-HRC, ACS-WFC, and
WFPC2) and wide-field (ESO-WFI) observations of the galactic globular cluster
NGC 6388 to derive its center of gravity, projected density profile, and
central surface brightness profile. While the overall projected profiles are
well fit by a King model with intermediate concentration (c=1.8) and sizable
core radius (rc=7"), a significant power law (with slope \alpha=-0.2) deviation
from a flat core behavior has been detected within the inner 1 arcsecond. These
properties suggest the presence of a central intermediate mass black hole. The
observed profiles are well reproduced by a multi-mass isotropic, spherical
model including a black hole with a mass of ~5.7x10^3 Msol.Comment: ApJ Letter in pres
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