1,079 research outputs found
Symmetry Breaking Using Value Precedence
We present a comprehensive study of the use of value precedence constraints
to break value symmetry. We first give a simple encoding of value precedence
into ternary constraints that is both efficient and effective at breaking
symmetry. We then extend value precedence to deal with a number of
generalizations like wreath value and partial interchangeability. We also show
that value precedence is closely related to lexicographical ordering. Finally,
we consider the interaction between value precedence and symmetry breaking
constraints for variable symmetries.Comment: 17th European Conference on Artificial Intelligenc
Bubbles Unbound: Bubbles of Nothing Without Kaluza-Klein
I present analytic time symmetric initial data for five dimensions describing
``bubbles of nothing'' which are asymptotically flat in the higher dimensional
sense, i.e. there is no Kaluza-Klein circle asymptotically. The mass and size
of these bubbles may be chosen arbitrarily and in particular the solutions
contain bubbles of any size which are arbitrarily light. This suggests the
solutions may be important phenomenologically and in particular I show that at
low energy there are bubbles which expand outwards, suggesting a new possible
instability in higher dimensions. Further, one may find bubbles of any size
where the only region of high curvature is confined to an arbitrarily small
volume.Comment: 27 pages, 2 figures, v2: minor changes, published versio
Comparing different freeze-out scenarios in azimuthal hadron correlations induced by fast partons
I review the linearized hydrodynamical treatment of a fast parton traversing
a perturbative quark-gluon plasma. Using numerical solutions for the medium's
response to the fast parton, I obtain the medium's distribution function which
is then used in a Cooper-Frye freeze-out prescription to obtain an azimuthal
particle spectrum. Two different freeze-out scenarios are considered which
yield significantly different results. I conclude that any meaningful
comparison of azimuthal hadron correlation functions to RHIC data requires
implementing a realistic freeze-out scenario in an expanding medium.Comment: Contribution to the Proceedings for 2008 Hot Quarks in Estes Park,
CO, as accepted for publication in EPJ-
Depinning of a superfluid vortex line by Kelvin waves
We measure the interaction of a single superfluid vortex with surface
irregularities. While vortex pinning in superconductors usually becomes weaker
at higher temperatures, we find the opposite behavior. The pinning steadily
increases throughout our measurement range, from 0.15Tc to over 0.5Tc. We also
find that moving the other end of the vortex decreases the pinning, so we
propose Kelvin waves along the vortex as a depinning mechanism.Comment: 5 figures; substantial revision including 2 new figure
R^2 Corrections to Asymptotically Lifshitz Spacetimes
We study corrections to five-dimensional asymptotically Lifshitz
spacetimes by adding Gauss-Bonnet terms in the effective action. For the
zero-temperature backgrounds we obtain exact solutions in both pure
Gauss-Bonnet gravity and Gauss-Bonnet gravity with non-trivial matter. The
dynamical exponent undergoes finite renormalization in the latter case. For the
finite-temperature backgrounds we obtain black brane solutions perturbatively
and calculate the ratio of shear viscosity to entropy density . The KSS
bound is still violated but unlike the relativistic counterparts, the causality
of the boundary field theory cannot be taken as a constraint.Comment: 24 pages, Latex, typos fixed, accepted by JHE
A Lifshitz Black Hole in Four Dimensional R^2 Gravity
We consider a higher derivative gravity theory in four dimensions with a
negative cosmological constant and show that vacuum solutions of both Lifshitz
type and Schr\"{o}dinger type with arbitrary dynamical exponent z exist in this
system. Then we find an analytic black hole solution which asymptotes to the
vacuum Lifshitz solution with z=3/2 at a specific value of the coupling
constant. We analyze the thermodynamic behavior of this black hole and find
that the black hole has zero entropy while non-zero temperature, which is very
similar to the case of BTZ black holes in new massive gravity at a specific
coupling. In addition, we find that the three dimensional Lifshitz black hole
recently found by E. Ayon-Beato et al. has a negative entropy and mass when the
Newton constant is taken to be positive.Comment: 11 pages, no figure; v2, a minor error correcte
Non-relativistic metrics with extremal limits
We present solutions of type IIB supergravity with z=2 Schrodinger
asymptotics that admit an extremal limit, i.e. the black hole horizon has a
double zero. These solutions are obtained as TsT transformations of the charged
planar black hole in AdS_5 \times S^5. Unlike the uncharged solution, the
Ramond-Ramond two-form is turned on. We study the thermodynamic properties of
these new solutions, and we show that the ratio of shear viscosity to entropy
density is 1/4\pi even in the extremal limit. We also consider the
TsT-transformed soliton and show that, for a special radius of the compact
circle, there is a confinement-deconfinement phase transition at zero
temperature between the soliton and black hole phases.Comment: 23 pages, references and clarifications added, typos corrected,
restriction in phase transition due to equation 6.5 emphasized; published
versio
Some No-go Theorems for String Duals of Non-relativistic Lifshitz-like Theories
We study possibilities of string theory embeddings of the gravity duals for
non-relativistic Lifshitz-like theories with anisotropic scale invariance. We
search classical solutions in type IIA and eleven-dimensional supergravities
which are expected to be dual to (2+1)-dimensional Lifshitz-like theories.
Under reasonable ansaetze, we prove that such gravity duals in the
supergravities are not possible. We also discuss a possible physical reason
behind this.Comment: 18 pages, Latex, flux conditions clarified (v2), brief summary of
results added (v3
Hypoglycaemic unawareness: A systematic review of qualitative studies of significant others' (SO) supportive interventions for patients with diabetes mellitus
BackgroundHypoglycemia unawareness (HU) has been attributed to both a downward shift in central nervous system (CNS)-triggered sympatho-adrenal responses to low glycaemic thresholds and a subsequent loss of adrenergic symptoms, which, in addition, to cerebral cortex adaptations permit normal function under hypoglycaemic conditions. Both of these mechanisms are brought about by recurring hypoglycemic events (hypoglycemia-associate autonomic failure, HAAF). This can contribute to repetitive cycles of increasingly severe hypoglycaemia, the consequences of which have considerable impact on relatives and significant others (SO) when providing care to patients with diabetes.MethodsA Systematic Review (SR) of 639 qualitative studies was carried out in accordance with the Preferred Reporting Items for Systematic Review (PRISMA) principles. The search strategy was developed using MeSH terms for a range of electronic databases: CINAHL, Pubmed, EMBASE, Medline, AMED and ASSIA were systematically searched in order to identify a variety of literature relevant to the review topic. Four duplicate studies were removed and a further 630 studies were excluded due to being irrelevant. Five qualitative studies were retained and analysed.ResultsThe three resultant findings from the literature appraised were i) Experiences and views of Significant Others' (SO) with adult relatives that have HU ii) Support needs of SO and iii) Health professionals interventions to address SO support needs and improve overall HU care. A clear finding was that SO experience difficulties managing HU and this can impact on the relationships that SO and HU patients have. Support needs of SO highlighted were both educational and psychological in nature, with there being a requirement for additional raised awareness within the wider community.ConclusionIt is essential that healthcare professionals offer support, such as teaching and support groups. In addition, providing interventions into improving family knowledge of diabetes and support with regard to psychosocial, behavioural and practical support for the person with diabetes. Moreover, improving resources for families to improve diabetes care. However, as the literature was of a qualitative nature, future recommendations would be quantitative research into these suggested nursing implementations to quantitatively assess their usefulness in practice
Enhanced stability of layered phases in parallel hard-spherocylinders due to the addition of hard spheres
There is increasing evidence that entropy can induce microphase separation in
binary fluid mixtures interacting through hard particle potentials. One such
phase consists of alternating two dimensional liquid-like layers of rods and
spheres. We study the transition from a uniform miscible state to this ordered
state using computer simulations and compare results to experiments and theory.
We conclude that (1) there is stable entropy driven microphase separation in
mixtures of parallel rods and spheres, (2) adding spheres smaller then the rod
length decreases the total volume fraction needed for the formation of a
layered phase, therefore small spheres effectively stabilize the layered phase;
the opposite is true for large spheres and (3) the degree of this stabilization
increases with increasing rod length.Comment: 11 pages, 9 figures. Submitted to Phys. Rev. E. See related website
http://www.elsie.brandeis.ed
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