1,613 research outputs found
Breaking Symmetries in Graph Representation
There are many complex combinatorial problems
which involve searching for an undirected graph
satisfying a certain property. These problems are
often highly challenging because of the large number
of isomorphic representations of a possible solution.
In this paper we introduce novel, effective
and compact, symmetry breaking constraints for
undirected graph search. While incomplete, these
prove highly beneficial in pruning the search for a
graph. We illustrate the application of symmetry
breaking in graph representation to resolve several
open instances in extremal graph theory
End of a Dark Age?
We argue that dark matter and dark energy phenomena associated with galactic
rotation curves, X-ray cluster mass profiles, and type Ia supernova data can be
accounted for via small corrections to idealized general relativistic spacetime
geometries due to disordered locality. Accordingly, we fit THINGS rotation
curve data rivaling modified Newtonian dynamics, ROSAT/ASCA X-ray cluster mass
profile data rivaling metric-skew-tensor gravity, and SCP Union2.1 SN Ia data
rivaling CDM without non-baryonic dark matter or a cosmological
constant. In the case of dark matter, we geometrically modify proper mass
interior to the Schwarzschild solution. In the case of dark energy, we modify
proper distance in Einstein-deSitter cosmology. Therefore, the phenomena of
dark matter and dark energy may be chimeras created by an errant belief that
spacetime is a differentiable manifold rather than a disordered graph.Comment: This version was accepted for publication in the International
Journal of Modern Physics D; revised version of an essay that won Honorable
Mention in the Gravity Research Foundation 2016 Awards for Essays on
Gravitation. 10 pages, 3 figures. arXiv admin note: text overlap with
arXiv:1509.0928
The Missing Mass Problem as a Manifestation of GR Contextuality
In Newtonian gravity, mass is an intrinsic property of matter while in
general relativity (GR), mass is a contextual property of matter, i.e., matter
can simultaneously possess two different values of mass when it is responsible
for two different spatiotemporal geometries. Herein, we explore the possibility
that the astrophysical missing mass attributed to non-baryonic dark matter (DM)
actually obtains because we have been assuming the Newtonian view of mass
rather than the GR view. Since an exact GR solution for realistic astrophysical
situations is not feasible, we explore GR-motivated ansatzes relating proper
mass and dynamic mass for one and the same baryonic matter, as justified by GR
contextuality. We consider four GR alternatives and find that the GR ansatz
motivated by metric perturbation theory works well in fitting galactic rotation
curves (THINGS data), the mass profiles of X-ray clusters (ROSAT and ASCA data)
and the angular power spectrum of the cosmic microwave background (CMB, Planck
2015 data) without DM. We compare our galactic rotation curve fits to modified
Newtonian dynamics (MOND), Burkett halo DM and Navarro-Frenk-White (NFW) halo
DM. We compare our X-ray cluster mass profile fits to metric skew-tensor
gravity (MSTG) and core-modified NFW DM. We compare our CMB angular power
spectrum fit to scalar-tensor-vector gravity (STVG) and CDM. Overall,
we find our fits to be comparable to those of MOND, MSTG, STVG, CDM,
Burkett, and NFW. We present and discuss correlations and trends for the best
fit values of our fitting parameters. For the most part, the correlations are
consistent with well-established results at all scales, which is perhaps
surprising given the simple functional form of the GR ansatz.Comment: 18 pages text. Twice revised per referee/reviewer comments. Fit of
CMB angular power spectrum and dark matter halo fits adde
Abelian Higgs Cosmic Strings: Small Scale Structure and Loops
Classical lattice simulations of the Abelian Higgs model are used to
investigate small scale structure and loop distributions in cosmic string
networks. Use of the field theory ensures that the small-scale physics is
captured correctly. The results confirm analytic predictions of Polchinski &
Rocha [1] for the two-point correlation function of the string tangent vector,
with a power law from length scales of order the string core width up to
horizon scale with evidence to suggest that the small scale structure builds up
from small scales. An analysis of the size distribution of string loops gives a
very low number density, of order 1 per horizon volume, in contrast with
Nambu-Goto simulations. Further, our loop distribution function does not
support the detailed analytic predictions for loop production derived by Dubath
et al. [2]. Better agreement to our data is found with a model based on loop
fragmentation [3], coupled with a constant rate of energy loss into massive
radiation. Our results show a strong energy loss mechanism which allows the
string network to scale without gravitational radiation, but which is not due
to the production of string width loops. From evidence of small scale structure
we argue a partial explanation for the scale separation problem of how energy
in the very low frequency modes of the string network is transformed into the
very high frequency modes of gauge and Higgs radiation. We propose a picture of
string network evolution which reconciles the apparent differences between
Nambu-Goto and field theory simulations.Comment: 16 pages, 17 figure
Coming in Warm: Qualitative Study and Concept Map to Cultivate PatientāCentered Empathy in Emergency Care
Background
Increased empathy may improve patient perceptions and outcomes. No training tool has been derived to teach empathy to emergency care providers. Accordingly, we engaged patients to assist in creating a concept map to teach empathy to emergency care providers.
Methods
We recruited patients, patient caretakers and patient advocates with emergency department experience to participate in three separate focus groups (n = 18 participants). Facilitators guided discussion about behaviors that physicians should demonstrate in order to rapidly create trust, enhance patient perception that the physician understood the patient's point of view, needs, concerns, fears, and optimize patient/caregiver understanding of their experience. Verbatim transcripts from the three focus groups were read by the authors and by consensus, 5 major themes with 10 minor themes were identified. After creating a codebook with thematic definitions, one author reviewed all transcripts to a library of verbatim excerpts coded by theme. To test for interārater reliability, two other authors similarly coded a random sample of 40% of the transcripts. Authors independently chose excerpts that represented consensus and strong emotional responses from participants.
Results
Approximately 90% of opinions and preferences fell within 15 themes, with five central themes: Provider transparency, Acknowledgement of patient's emotions, Provider disposition, Trust in physician, and Listening. Participants also highlighted the need for authenticity, context and individuality to enhance empathic communication. For empathy map content, patients offered example behaviors that promote perceptions of physician warmth, respect, physical touch, knowledge of medical history, explanation of tests, transparency, and treating patients as partners. The resulting concept map was named the āEmpathy Circleā.
Conclusions
Focus group participants emphasized themes and tangible behaviors to improve empathy in emergency care. These were incorporated into the āEmpathy Circleā, a novel concept map that can serve as the framework to teach empathy to emergency care providers
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