180 research outputs found
New Types of Thermodynamics from -Dimensional Black Holes
For normal thermodynamic systems superadditivity , homogeneity \H and
concavity \C of the entropy hold, whereas for -dimensional black holes
the latter two properties are violated. We show that -dimensional black
holes exhibit qualitatively new types of thermodynamic behaviour, discussed
here for the first time, in which \C always holds, \H is always violated
and may or may not be violated, depending of the magnitude of the black
hole mass. Hence it is now seen that neither superadditivity nor concavity
encapsulate the meaning of the second law in all situations.Comment: WATPHYS-TH93/05, Latex, 10 pgs. 1 figure (available on request), to
appear in Class. Quant. Gra
Flat Information Geometries in Black Hole Thermodynamics
The Hessian of either the entropy or the energy function can be regarded as a
metric on a Gibbs surface. For two parameter families of asymptotically flat
black holes in arbitrary dimension one or the other of these metrics are flat,
and the state space is a flat wedge. The mathematical reason for this is traced
back to the scale invariance of the Einstein-Maxwell equations. The picture of
state space that we obtain makes some properties such as the occurence of
divergent specific heats transparent.Comment: 14 pages, one figure. Dedicated to Rafael Sorkin's birthda
Quasi-Homogeneous Thermodynamics and Black Holes
We propose a generalized thermodynamics in which quasi-homogeneity of the
thermodynamic potentials plays a fundamental role. This thermodynamic formalism
arises from a generalization of the approach presented in paper [1], and it is
based on the requirement that quasi-homogeneity is a non-trivial symmetry for
the Pfaffian form . It is shown that quasi-homogeneous
thermodynamics fits the thermodynamic features of at least some
self-gravitating systems. We analyze how quasi-homogeneous thermodynamics is
suggested by black hole thermodynamics. Then, some existing results involving
self-gravitating systems are also shortly discussed in the light of this
thermodynamic framework. The consequences of the lack of extensivity are also
recalled. We show that generalized Gibbs-Duhem equations arise as a consequence
of quasi-homogeneity of the thermodynamic potentials. An heuristic link between
this generalized thermodynamic formalism and the thermodynamic limit is also
discussed.Comment: 39 pages, uses RevteX. Published version (minor changes w.r.t. the
original one
Thermodynamic curvature and black holes
I give a relatively broad survey of thermodynamic curvature , one spanning
results in fluids and solids, spin systems, and black hole thermodynamics.
results from the thermodynamic information metric giving thermodynamic
fluctuations. has a unique status in thermodynamics as being a geometric
invariant, the same for any given thermodynamic state. In fluid and solid
systems, the sign of indicates the character of microscopic interactions,
repulsive or attractive. gives the average size of organized mesoscopic
fluctuating structures. The broad generality of thermodynamic principles might
lead one to believe the same for black hole thermodynamics. This paper explores
this issue with a systematic tabulation of results in a number of cases.Comment: 27 pages, 10 figures, 7 tables, 78 references. Talk presented at the
conference Breaking of Supersymmetry and Ultraviolet Divergences in extended
Supergravity, in Frascati, Italy, March 27, 2013. v2 corrects some small
problem
Black Strings, Black Rings and State-space Manifold
State-space geometry is considered, for diverse three and four parameter
non-spherical horizon rotating black brane configurations, in string theory and
-theory. We have explicitly examined the case of unit Kaluza-Klein momentum
black strings, circular strings, small black rings and black
supertubes. An investigation of the state-space pair correlation functions
shows that there exist two classes of brane statistical configurations, {\it
viz.}, the first category divulges a degenerate intrinsic equilibrium basis,
while the second yields a non-degenerate, curved, intrinsic Riemannian
geometry. Specifically, the solutions with finitely many branes expose that the
two charged rotating black strings and three charged rotating small
black rings consort real degenerate state-space manifolds. Interestingly,
arbitrary valued -dipole charged rotating circular strings and Maldacena
Strominger Witten black rings exhibit non-degenerate, positively curved,
comprehensively regular state-space configurations. Furthermore, the
state-space geometry of single bubbled rings admits a well-defined, positive
definite, everywhere regular and curved intrinsic Riemannian manifold; except
for the two finite values of conserved electric charge. We also discuss the
implication and potential significance of this work for the physics of black
holes in string theory.Comment: 41 pages, Keywords: Rotating Black Branes; Microscopic
Configurations; State-space Geometry, PACS numbers: 04.70.-s Physics of black
holes; 04.70.Bw Classical black holes; 04.70.Dy Quantum aspects of black
holes, evaporation, thermodynamic
State-space Manifold and Rotating Black Holes
We study a class of fluctuating higher dimensional black hole configurations
obtained in string theory/ -theory compactifications. We explore the
intrinsic Riemannian geometric nature of Gaussian fluctuations arising from the
Hessian of the coarse graining entropy, defined over an ensemble of brane
microstates. It has been shown that the state-space geometry spanned by the set
of invariant parameters is non-degenerate, regular and has a negative scalar
curvature for the rotating Myers-Perry black holes, Kaluza-Klein black holes,
supersymmetric black holes, - configurations and the
associated BMPV black holes. Interestingly, these solutions demonstrate that
the principal components of the state-space metric tensor admit a positive
definite form, while the off diagonal components do not. Furthermore, the ratio
of diagonal components weakens relatively faster than the off diagonal
components, and thus they swiftly come into an equilibrium statistical
configuration. Novel aspects of the scaling property suggest that the
brane-brane statistical pair correlation functions divulge an asymmetric
nature, in comparison with the others. This approach indicates that all above
configurations are effectively attractive and stable, on an arbitrary
hyper-surface of the state-space manifolds. It is nevertheless noticed that
there exists an intriguing relationship between non-ideal inter-brane
statistical interactions and phase transitions. The ramifications thus
described are consistent with the existing picture of the microscopic CFTs. We
conclude with an extended discussion of the implications of this work for the
physics of black holes in string theory.Comment: 44 pages, Keywords: Rotating Black Holes; State-space Geometry;
Statistical Configurations, String Theory, M-Theory. PACS numbers: 04.70.-s
Physics of black holes; 04.70.Bw Classical black holes; 04.70.Dy Quantum
aspects of black holes, evaporation, thermodynamics; 04.50.Gh
Higher-dimensional black holes, black strings, and related objects. Edited
the bibliograph
Trials and tribulations of recruiting 2,000 older women onto a clinical trial investigating falls and fractures : vital D study
Background Randomised, placebo-controlled trials are needed to provide evidence demonstrating safe, effective interventions that reduce falls and fractures in the elderly. The quality of a clinical trial is dependent on successful recruitment of the target participant group. This paper documents the successes and failures of recruiting over 2,000 women aged at least 70 years and at higher risk of falls or fractures onto a placebo-controlled trial of six years duration. The characteristics of study participants at baseline are also described for this study.Methods The Vital D Study recruited older women identified at high risk of fracture through the use of an eligibility algorithm, adapted from identified risk factors for hip fracture. Participants were randomised to orally receive either 500,000 IU vitamin D3 (cholecalciferol) or placebo every autumn for five consecutive years. A variety of recruitment strategies were employed to attract potential participants.Results Of the 2,317 participants randomised onto the study, 74% (n = 1716/2317) were consented onto the study in the last five months of recruiting. This was largely due to the success of a targeted mail-out. Prior to this only 541 women were consented in the 18 months of recruiting. A total of 70% of all participants were recruited as a result of targeted mail-out. The response rate from the letters increased from 2 to 7% following revision of the material by a public relations company. Participant demographic or risk factor profile did not differ between those recruited by targeted mail-outs compared with other methods.Conclusion The most successful recruitment strategy was the targeted mail-out and the response rate was no higher in the local region where the study had extensive exposure through other recruiting strategies. The strategies that were labour-intensive and did not result in successful recruitment include the activities directed towards the GP medical centres. Comprehensive recruitment programs employ overlapping strategies simultaneously with ongoing assessment of recruitment rates. In our experience, and others direct mail-outs work best although rights to privacy must be respected. <br /
Drug-gene interactions of antihypertensive medications and risk of incident cardiovascular disease: a pharmacogenomics study from the CHARGE consortium
Background
Hypertension is a major risk factor for a spectrum of cardiovascular diseases (CVD), including myocardial infarction, sudden death, and stroke. In the US, over 65 million people have high blood pressure and a large proportion of these individuals are prescribed antihypertensive medications. Although large long-term clinical trials conducted in the last several decades have identified a number of effective antihypertensive treatments that reduce the risk of future clinical complications, responses to therapy and protection from cardiovascular events vary among individuals.
Methods
Using a genome-wide association study among 21,267 participants with pharmaceutically treated hypertension, we explored the hypothesis that genetic variants might influence or modify the effectiveness of common antihypertensive therapies on the risk of major cardiovascular outcomes. The classes of drug treatments included angiotensin-converting enzyme inhibitors, beta-blockers, calcium channel blockers, and diuretics. In the setting of the Cohorts for Heart and Aging Research in Genomic Epidemiology (CHARGE) consortium, each study performed array-based genome-wide genotyping, imputed to HapMap Phase II reference panels, and used additive genetic models in proportional hazards or logistic regression models to evaluate drug-gene interactions for each of four therapeutic drug classes. We used meta-analysis to combine study-specific interaction estimates for approximately 2 million single nucleotide polymorphisms (SNPs) in a discovery analysis among 15,375 European Ancestry participants (3,527 CVD cases) with targeted follow-up in a case-only study of 1,751 European Ancestry GenHAT participants as well as among 4,141 African-Americans (1,267 CVD cases).
Results
Although drug-SNP interactions were biologically plausible, exposures and outcomes were well measured, and power was sufficient to detect modest interactions, we did not identify any statistically significant interactions from the four antihypertensive therapy meta-analyses (Pinteraction > 5.0×10−8). Similarly, findings were null for meta-analyses restricted to 66 SNPs with significant main effects on coronary artery disease or blood pressure from large published genome-wide association studies (Pinteraction ≥ 0.01). Our results suggest that there are no major pharmacogenetic influences of common SNPs on the relationship between blood pressure medications and the risk of incident CVD
A genome-wide association study identifies protein quantitative trait loci (pQTLs)
There is considerable evidence that human genetic variation influences gene expression. Genome-wide studies have revealed that mRNA levels are associated with genetic variation in or close to the gene coding for those mRNA transcripts - cis effects, and elsewhere in the genome - trans effects. The role of genetic variation in determining protein levels has not been systematically assessed. Using a genome-wide association approach we show that common genetic variation influences levels of clinically relevant proteins in human serum and plasma. We evaluated the role of 496,032 polymorphisms on levels of 42 proteins measured in 1200 fasting individuals from the population based InCHIANTI study. Proteins included insulin, several interleukins, adipokines, chemokines, and liver function markers that are implicated in many common diseases including metabolic, inflammatory, and infectious conditions. We identified eight Cis effects, including variants in or near the IL6R (p = 1.8×10 -57), CCL4L1 (p = 3.9×10-21), IL18 (p = 6.8×10-13), LPA (p = 4.4×10-10), GGT1 (p = 1.5×10-7), SHBG (p = 3.1×10-7), CRP (p = 6.4×10-6) and IL1RN (p = 7.3×10-6) genes, all associated with their respective protein products with effect sizes ranging from 0.19 to 0.69 standard deviations per allele. Mechanisms implicated include altered rates of cleavage of bound to unbound soluble receptor (IL6R), altered secretion rates of different sized proteins (LPA), variation in gene copy number (CCL4L1) and altered transcription (GGT1). We identified one novel trans effect that was an association between ABO blood group and tumour necrosis factor alpha (TNF-alpha) levels (p = 6.8×10-40), but this finding was not present when TNF-alpha was measured using a different assay , or in a second study, suggesting an assay-specific association. Our results show that protein levels share some of the features of the genetics of gene expression. These include the presence of strong genetic effects in cis locations. The identification of protein quantitative trait loci (pQTLs) may be a powerful complementary method of improving our understanding of disease pathways. © 2008 Melzer et al
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