817 research outputs found
Viscous Brane Cosmology with a Brane-Bulk Energy Interchange Term
We assume a flat brane located at y=0, surrounded by an AdS space, and
consider the 5D Einstein equations when the energy flux component of the
energy-momentum tensor is related to the Hubble parameter through a constant Q.
We calculate the metric tensor, as well as the Hubble parameter on the brane,
when Q is small. As a special case, if the brane is tensionless, the influence
from Q on the Hubble parameter is absent. We also consider the emission of
gravitons from the brane, by means of the Boltzmann equation. Comparing the
energy conservation equation derived herefrom with the energy conservation
equation for a viscous fluid on the brane, we find that the entropy change for
the fluid in the emission process has to be negative. This peculiar effect is
related to the fluid on the brane being a non-closed thermodynamic system. The
negative entropy property for non-closed systems is encountered in other areas
in physics also, in particular, in connection with the Casimir effect at finite
temperature.Comment: 12 pages, latex, no figure
Metabolic Syndrome Derived from Principal Component Analysis and Incident Cardiovascular Events: The Multi Ethnic Study of Atherosclerosis (MESA) and Health, Aging, and Body Composition (Health ABC).
Background. The NCEP metabolic syndrome (MetS) is a combination of dichotomized interrelated risk factors from predominantly Caucasian populations. We propose a continuous MetS score based on principal component analysis (PCA) of the same risk factors in a multiethnic cohort and compare prediction of incident CVD events with NCEP MetS definition. Additionally, we replicated these analyses in the Health, Aging, and Body composition (Health ABC) study cohort. Methods and Results. We performed PCA of the MetS elements (waist circumference, HDL, TG, fasting blood glucose, SBP, and DBP) in 2610 Caucasian Americans, 801 Chinese Americans, 1875 African Americans, and 1494 Hispanic Americans in the multiethnic study of atherosclerosis (MESA) cohort. We selected the first principal component as a continuous MetS score (MetS-PC). Cox proportional hazards models were used to examine the association between MetS-PC and 5.5 years of CVD events (n = 377) adjusting for age, gender, race, smoking and LDL-C, overall and by ethnicity. To facilitate comparison of MetS-PC with the binary NCEP definition, a MetS-PC cut point was chosen to yield the same 37% prevalence of MetS as the NCEP definition (37%) in the MESA cohort. Hazard ratio (HR) for CVD events were estimated using the NCEP and Mets-PC-derived binary definitions. In Cox proportional models, the HR (95% CI) for CVD events for 1-SD (standard deviation) of MetS-PC was 1.71 (1.54-1.90) (P < 0.0001) overall after adjusting for potential confounders, and for each ethnicity, HRs were: Caucasian, 1.64 (1.39-1.94), Chinese, 1.39 (1.06-1.83), African, 1.67 (1.37-2.02), and Hispanic, 2.10 (1.66-2.65). Finally, when binary definitions were compared, HR for CVD events was 2.34 (1.91-2.87) for MetS-PC versus 1.79 (1.46-2.20) for NCEP MetS. In the Health ABC cohort, in a fully adjusted model, MetS-PC per 1-SD (Health ABC) remained associated with CVD events (HR = 1.21, 95%CI 1.12-1.32) overall, and for each ethnicity, Caucasian (HR = 1.24, 95%CI 1.12-1.39) and African Americans (HR = 1.16, 95%CI 1.01-1.32). Finally, when using a binary definition of MetS-PC (cut point 0.505) designed to match the NCEP definition in terms of prevalence in the Health ABC cohort (35%), the fully adjusted HR for CVD events was 1.39, 95%CI 1.17-1.64 compared with 1.46, 95%CI 1.23-1.72 using the NCEP definition. Conclusion. MetS-PC is a continuous measure of metabolic syndrome and was a better predictor of CVD events overall and in individual ethnicities. Additionally, a binary MetS-PC definition was better than the NCEP MetS definition in predicting incident CVD events in the MESA cohort, but this superiority was not evident in the Health ABC cohort
Influence of a Brane Tension on Phantom and Massive Scalar Field Emission
We elaborate the signature of the extra dimensions and brane tension in the
process of phantom and massive scalar emission in the spacetime of
(4+n)-dimensional tense brane black hole. Absorption cross section, luminosity
of Hawking radiation and cross section in the low-energy approximation were
found. We envisage that parameter connected with the existence of a brane
imprints its role in the Hawking radiation of the considered fields.Comment: 7 pages, * figures, RevTex, to be published in General Relativity and
Gravitatio
X chromosome dosage of histone demethylase KDM5C determines sex differences in adiposity
Males and females differ in body composition and fat distribution. Using a mouse model that segregates gonadal sex (ovaries and testes) from chromosomal sex (XX and XY), we showed that XX chromosome complement in combination with a high-fat diet led to enhanced weight gain in the presence of male or female gonads. We identified the genomic dosage of Kdm5c, an X chromosome gene that escapes X chromosome inactivation, as a determinant of the X chromosome effect on adiposity. Modulating Kdm5c gene dosage in XX female mice to levels that are normally present in males resulted in reduced body weight, fat content, and food intake to a degree similar to that seen with altering the entire X chromosome dosage. In cultured preadipocytes, the levels of KDM5C histone demethylase influenced chromatin accessibility (ATAC-Seq), gene expression (RNA-Seq), and adipocyte differentiation. Both in vitro and in vivo, Kdm5c dosage influenced gene expression involved in extracellular matrix remodeling, which is critical for adipocyte differentiation and adipose tissue expansion. In humans, adipose tissue KDM5C mRNA levels and KDM5C genetic variants were associated with body mass. These studies demonstrate that the sex-dependent dosage of Kdm5c contributes to male/female differences in adipocyte biology and highlight X-escape genes as a critical component of female physiology
Cosmology of intersecting brane world models in Gauss-Bonnet gravity
We study the cosmological properties of a codimension two brane world that
sits at the intersection between two four branes, in the framework of six
dimensional Einstein-Gauss-Bonnet gravity. Due to contributions of the
Gauss-Bonnet terms, the junction conditions require the presence of localized
energy density on the codimension two defect. The induced metric on this
surface assumes a FRW form, with a scale factor associated to the position of
the brane in the background; we can embed on the codimension two defect the
preferred form of energy density. We present the cosmological evolution
equations for the three brane, showing that, for the case of pure AdS
backgrounds, they acquire the same form of the ones for the Randall-Sundrum II
model. When the background is different from pure AdS, the cosmological
behavior is potentially modified in respect to the typical one of codimension
one brane worlds. We discuss, in a particular model embedded in an AdS
black hole, the conditions one should satisfy in order to obtain standard
cosmology at late epochs.Comment: 19 pages, no figures, JHEP style. v2: Typos corrected and references
adde
Brane-bulk matter relation for a purely conical codimension-2 brane world
We study gravity on an infinitely thin codimension-2 brane world, with purely
conical singularities and in the presence of an induced gravity term on the
brane. We show that in this approximation, the energy momentum tensor of the
bulk is strongly related to the energy momentum tensor of the brane and thus
the gravity dynamics on the brane are induced by the bulk content. This is in
contrast with the gravity dynamics on a codimension-1 brane. We show how this
strong result is relaxed after including a Gauss-Bonnet term in the bulk.Comment: 12 pages, mistake corrected, references adde
Brane cosmological solutions in six-dimensional warped flux compactifications
We study cosmology on a conical brane in the six-dimensional
Einstein-Maxwell-dilaton system, where the extra dimensions are compactified by
a magnetic flux. We systematically construct exact cosmological solutions using
the fact that the system is equivalently described by (6+n)-dimensional pure
Einstein-Maxwell theory via dimensional reduction. In particular, we find a
power-law inflationary solution for a general dilatonic coupling. When the
dilatonic coupling is given by that of Nishino-Sezgin chiral supergravity, this
reduces to the known solution which is not inflating. The power-law solution is
shown to be the late-time attractor. We also investigate cosmological tensor
perturbations in this model using the (6+n)-dimensional description. We obtain
the separable equation of motion and find that there always exist a zero mode,
while tachyonic modes are absent in the spectrum. The mass spectrum of
Kaluza-Klein modes is obtained numerically.Comment: 12 pages, 2 figures; v2: references added; v3: version published in
JCA
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Genetically Determined Plasma Lipid Levels and Risk of Diabetic Retinopathy: A Mendelian Randomization Study.
Results from observational studies examining dyslipidemia as a risk factor for diabetic retinopathy (DR) have been inconsistent. We evaluated the causal relationship between plasma lipids and DR using a Mendelian randomization approach. We pooled genome-wide association studies summary statistics from 18 studies for two DR phenotypes: any DR (N = 2,969 case and 4,096 control subjects) and severe DR (N = 1,277 case and 3,980 control subjects). Previously identified lipid-associated single nucleotide polymorphisms served as instrumental variables. Meta-analysis to combine the Mendelian randomization estimates from different cohorts was conducted. There was no statistically significant change in odds ratios of having any DR or severe DR for any of the lipid fractions in the primary analysis that used single nucleotide polymorphisms that did not have a pleiotropic effect on another lipid fraction. Similarly, there was no significant association in the Caucasian and Chinese subgroup analyses. This study did not show evidence of a causal role of the four lipid fractions on DR. However, the study had limited power to detect odds ratios less than 1.23 per SD in genetically induced increase in plasma lipid levels, thus we cannot exclude that causal relationships with more modest effect sizes exist
Hybrid compactifications and brane gravity in six dimensions
We consider a six-dimensional axisymmetric Einstein-Maxwell model of warped
braneworlds. The bulk is bounded by two branes, one of which is a conical
3-brane and the other is a 4-brane wrapped around the axis of symmetry. The
latter brane is assumed to be our universe. If the tension of the 3-brane is
fine-tuned, it folds the internal two-dimensional space in a narrow cone,
making sufficiently small the Kaluza-Klein circle of the 4-brane. An arbitrary
energy-momentum tensor can be accommodated on this ring-like 4-brane. We study
linear perturbations sourced by matter on the brane, and show that weak gravity
is apparently described by a four-dimensional scalar-tensor theory. The extra
scalar degree of freedom can be interpreted as the fluctuation of the internal
space volume (or that of the circumference of the ring), the effect of which
turns out to be suppressed at long distances. Consequently, four-dimensional
Einstein gravity is reproduced on the brane. We point out that as in the
Randall-Sundrum model, the brane bending mode is crucial for recovering the
four-dimensional tensor structure in this setup.Comment: 15 pages, 2 figures; v2: references added; v3: accepted for
publication in Class. Quant. Gra
Holographic Cosmic Quintessence on Dilatonic Brane World
Recently quintessence is proposed to explain the observation data of
supernova indicating a time-varying cosmological constant and accelerating
universe. Inspired by this and its mysterious origin, we look for the
possibility of quintessence as the holographic dark matters dominated in the
late time in the brane world scenarios. We consider both the cases of static
and moving brane in a dilaton gravity background. For the static brane we use
the Hamilton-Jacobi method motivated by holographic renormalization group to
study the intrinsic FRW cosmology on the brane and find out the constraint on
the bulk potential for the quintessence. This constraint requires a negative
slowly varying bulk potential which implies an anti-de Sitter-like bulk
geometry and could be possibly realized from the higher dimensional
supergravities or string theory. We find the similar constraint for the moving
brane cases and that the quintessence on it has the effect as a mildly
time-varying Newton constant.Comment: 16pages, no figure, Latex; revised version, references added, typos
corrected, abstract and comments improved; final version, will appear in PR
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