3,480 research outputs found
Thermodynamics of phase transition in higher dimensional AdS black holes
We investigate the thermodynamics of phase transition for
dimensional Reissner Nordstrom (RN)-AdS black holes using a grand canonical
ensemble. This phase transition is characterized by a discontinuity in specific
heat. The phase transition occurs from a lower mass black hole with negative
specific heat to a higher mass black hole with positive specific heat. By
exploring Ehrenfest's scheme we show that this is a second order phase
transition. Explicit expressions for the critical temperature and critical mass
are derived. In appropriate limits the results for dimensional
Schwarzschild AdS black holes are obtained.Comment: LaTex, 11 pages, 5 figures, To appear in JHE
Structural basis for oligomerization and glycosaminoglycan binding of CCL5 and CCL3.
CC chemokine ligand 5 (CCL5) and CCL3 are critical for immune surveillance and inflammation. Consequently, they are linked to the pathogenesis of many inflammatory conditions and are therapeutic targets. Oligomerization and glycosaminoglycan (GAG) binding of CCL5 and CCL3 are vital for the functions of these chemokines. Our structural and biophysical analyses of human CCL5 reveal that CCL5 oligomerization is a polymerization process in which CCL5 forms rod-shaped, double-helical oligomers. This CCL5 structure explains mutational data and offers a unified mechanism for CCL3, CCL4, and CCL5 assembly into high-molecular-weight, polydisperse oligomers. A conserved, positively charged BBXB motif is key for the binding of CC chemokines to GAG. However, this motif is partially buried when CCL3, CCL4, and CCL5 are oligomerized; thus, the mechanism by which GAG binds these chemokine oligomers has been elusive. Our structures of GAG-bound CCL5 and CCL3 oligomers reveal that these chemokine oligomers have distinct GAG-binding mechanisms. The CCL5 oligomer uses another positively charged and fully exposed motif, KKWVR, in GAG binding. However, residues from two partially buried BBXB motifs along with other residues combine to form a GAG-binding groove in the CCL3 oligomer. The N termini of CC chemokines are shown to be involved in receptor binding and oligomerization. We also report an alternative CCL3 oligomer structure that reveals how conformational changes in CCL3 N termini profoundly alter its surface properties and dimer-dimer interactions to affect GAG binding and oligomerization. Such complexity in oligomerization and GAG binding enables intricate, physiologically relevant regulation of CC chemokine functions
All solutions of the localization equations for N=2 quantum black hole entropy
We find the most general bosonic solution to the localization equations
describing the contributions to the quantum entropy of supersymmetric black
holes in four-dimensional N=2 supergravity coupled to n_v vector multiplets.
This requires the analysis of the BPS equations of the corresponding off-shell
supergravity (including fluctuations of the auxiliary fields) with AdS2 \times
S2 attractor boundary conditions. Our work completes and extends the results of
arXiv:1012.0265 that were obtained for the vector multiplet sector, to include
the fluctuations of all the fields of the off-shell supergravity. We find that,
when the auxiliary SU(2) gauge field strength vanishes, the most general
supersymmetric configuration preserving four supercharges is labelled by n_v+1
real parameters corresponding to the excitations of the conformal mode of the
graviton and the scalars of the n_v vector multiplets. In the general case, the
localization manifold is labelled by an additional SU(2) triplet of one-forms
and a scalar function.Comment: 27 page
The Bregman chord divergence
Distances are fundamental primitives whose choice significantly impacts the
performances of algorithms in machine learning and signal processing. However
selecting the most appropriate distance for a given task is an endeavor.
Instead of testing one by one the entries of an ever-expanding dictionary of
{\em ad hoc} distances, one rather prefers to consider parametric classes of
distances that are exhaustively characterized by axioms derived from first
principles. Bregman divergences are such a class. However fine-tuning a Bregman
divergence is delicate since it requires to smoothly adjust a functional
generator. In this work, we propose an extension of Bregman divergences called
the Bregman chord divergences. This new class of distances does not require
gradient calculations, uses two scalar parameters that can be easily tailored
in applications, and generalizes asymptotically Bregman divergences.Comment: 10 page
Extended phase space thermodynamics for charged and rotating black holes and Born-Infeld vacuum polarization
We investigate the critical behaviour of charged and rotating AdS black holes
in d spacetime dimensions, including effects from non-linear electrodynamics
via the Born-Infeld action, in an extended phase space in which the
cosmological constant is interpreted as thermodynamic pressure. For
Reissner-Nordstrom black holes we find that the analogy with the Van der Walls
liquid-gas system holds in any dimension greater than three, and that the
critical exponents coincide with those of the Van der Waals system. We find
that neutral slowly rotating black holes in four space-time dimensions also
have the same qualitative behaviour. However charged and rotating black holes
in three spacetime dimensions do not exhibit critical phenomena. For
Born-Infeld black holes we define a new thermodynamic quantity B conjugate to
the Born-Infeld parameter b that we call Born-Infeld vacuum polarization. We
demonstrate that this quantity is required for consistency of both the first
law of thermodynamics and the corresponding Smarr relation.Comment: 23 pages, 32 figures, v2: minor changes, upgraded reference
A two-year participatory intervention project with owners to reduce lameness and limb abnormalities in working horses in Jaipur, India
Participatory methods are increasingly used in international human development, but scientific evaluation of their efficacy versus a control group is rare. Working horses support families in impoverished communities. Lameness and limb abnormalities are highly prevalent in these animals and a cause for welfare concern. We aimed to stimulate and evaluate improvements in lameness and limb abnormalities in horses whose owners took part in a 2-year participatory intervention project to reduce lameness (PI) versus a control group (C) in Jaipur, India.In total, 439 owners of 862 horses participated in the study. PI group owners from 21 communities were encouraged to meet regularly to discuss management and work practices influencing lameness and poor welfare and to track their own progress in improving these. Lameness examinations (41 parameters) were conducted at the start of the study (Baseline), and after 1 year and 2 years. Results were compared with control horses from a further 21 communities outside the intervention. Of the 149 horses assessed on all three occasions, PI horses showed significantly (P<0.05) greater improvement than C horses in 20 parameters, most notably overall lameness score, measures of sole pain and range of movement on limb flexion. Control horses showed slight but significantly greater improvements in four parameters, including frog quality in fore and hindlimbs.This participatory intervention succeeded in improving lameness and some limb abnormalities in working horses, by encouraging changes in management and work practices which were feasible within ownersâ socioeconomic and environmental constraints. Demonstration of the potentially sustainable improvements achieved here should encourage further development of participatory intervention approaches to benefit humans and animals in other contexts
A unified picture of phase transition: from liquid-vapour systems to AdS black holes
Based on fundamental concepts of thermodynamics we examine phase transitions
in black holes defined in Anti-de Sitter (AdS) spaces. The method is in line
with that used a long ago to understand the liquid-vapour phase transition
where the first order derivatives of Gibbs potential are discontinuous and
Clausius-Clapeyron equation is satisfied. The idea here is to consider the AdS
black holes as grand-canonical ensembles and study phase transition defined by
the discontinuity of second order derivatives of Gibbs potential. We
analytically check that this phase transition between the `smaller' and
`larger' mass black holes obey Ehrenfest relations defined at the critical
point and hence confirm a second order phase transition. This include both the
rotating and charged black holes in Einstein gravity.Comment: v3; JHEP style, 11 pages, 1 figure; title is changed, paper rewritten
but basic results are unchanged, to appear in JHE
Reâdefining the virtual reality dental simulator: Demonstrating concurrent validity of clinically relevant assessment and feedback
Introduction
Virtual reality (VR) dental simulators are gaining momentum as a useful tool to educate dental students. To date, no VR dental simulator exercise has been designed which is capable of reliably providing validated, meaningful clinical feedback to dental students. This study aims to measure the concurrent validity of the assessment, and the provision of qualitative feedback, pertaining to cavity preparations by VR dental simulators.
Methods
A cavity preparation exercise was created on a VR dental simulator, and assessment criteria for cavity preparations were developed. The exercise was performed 10 times in order to demonstrate a range of performances and for each, the simulator feedback was recorded. The exercises were subsequently threeâdimensionally printed and 12 clinical teachers were asked to assess the preparations according to the same criteria. Interârater reliability (IRR) between clinical teachers was measured using a freeâmarginal multirater kappa value. Clinical teacher assessment responses were compared with the VR simulator responses and percentage agreements calculated.
Results
IRR values for each exercise ranged from 0.39â0.77 (69.39â88.48%). The assessment of smoothness (Îșfree0.58, 78.79%) and ability to follow the outline (Îșfree0.56, 77.88%) demonstrated highest agreement between clinical teachers, whilst the assessment of undercut (Îșfree0.15, 57.58%) and depth (Îșfree 0.28, 64.09%) had the lowest agreement. The modal percentage agreement between clinical teachers and the VR simulator was, on average, 78% across all exercises.
Conclusion
The results of this study demonstrate that it is possible to provide reliable and clinically relevant qualitative feedback via a VR dental simulator. Further research should look to employ this technique across a broader range of exercises that help to develop other complex operative dental skills
BPS black holes in N=2 D=4 gauged supergravities
We construct and analyze BPS black hole solutions in gauged N=2, D=4
supergravity with charged hypermultiplets. A class of solutions can be found
through spontaneous symmetry breaking in vacua that preserve maximal
supersymmetry. The resulting black holes do not carry any hair for the scalars.
We demonstrate this with explicit examples of both asymptotically flat and
anti-de Sitter black holes. Next, we analyze the BPS conditions for
asymptotically flat black holes with scalar hair and spherical or axial
symmetry. We find solutions only in cases when the metric contains ripples and
the vector multiplet scalars become ghost-like. We give explicit examples that
can be analyzed numerically. Finally, we comment on a way to circumvent the
ghost-problem by introducing also fermionic hair.Comment: 40 pages, 2 figures; v2 references added; v3 minor changes, published
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