398 research outputs found
Anisotropic Extra Dimensions
We consider the scenario where in a five-dimensional theory, the extra
spatial dimension has different scaling than the other four dimensions. We find
background maximally symmetric solutions, when the bulk is filled with a
cosmological constant and at the same time it has a three-brane embedded in it.
These background solutions are reminiscent of Randall-Sundrum warped metrics,
with bulk curvature depending on the parameters of the breaking of
diffeomorphism invariance. Subsequently, we consider the scalar perturbation
sector of the theory and show that it has certain pathologies and the striking
feature that in the limit where the diffeomorphism invariance is restored,
there remain ghost scalar mode(s) in the spectrum.Comment: 12 pages, no figures, comments and references added, published
versio
Multi-Brane Worlds and modification of gravity at large scales
We discuss the implications of multi-brane constructions involving
combinations of positive and negative tension brane and show how anomalously
light KK states emerge when negative tension ''-'' branes are sandwiched
between ''+'' branes. We present a detailed study of a ''+--+'' brane
assignment which interpolates between two models that have been previously
proposed in which gravity is modified at large scales due to the anomalously
light states. We show that it has the peculiar characteristic that gravity
changes from four dimensional (4D) to 5D at large distances and returns to 4D
at even larger scales. We also consider a crystalline universe which leads to a
similar structure for gravity. The problems associated with intermediate
negative tension branes are discussed and a possible resolution suggested.Comment: 28 pages, 6 figures,references adde
Human Papillomavirus in Endometrial Adenocarcinomas: Infectious Agent or a Mere “Passenger”?
Aims. To investigate the possible association
of human papillomavirus (HPV) with endometrial hyperplasias and
neoplasia. Does HPV play any role in the initiation or
prognosis of endometrial adenocarcinomas?
Methods. Twenty-five endometrial adenocarcinomas
of the endometrioid cell type, with and without squamous
differentiation, and twenty-four endometrial hyperplasias of various
forms (simple, complex, and atypical) were analyzed for the
presence of type 16 and 18 HPV by the polymerase chain
reaction (PCR). The results were related to histopathological
features of the tumour, and the patients' age, and
prognosis. Results. Six of 25 endometrial
adenocarcinomas were HPV 16-positive
(24%),
and 5 of 25
(20%)
were HPV 18-positive. Simple endometrial hyperplasias was
associated somewhat more commonly with HPV 16 and 18 (2/8 and
1/8 cases, resp.) than hyperplasias progressing to
endometrial adenocarcinomas, namely, atypical endometrial
hyperplasia (1/8 and 0/8 cases, resp.). None of the
positive cases in the series, whether hyperplastic or
neoplastic, demonstrated cytological evidence of HPV
infection. There was no relation between HPV-positive cases
and squamous differentiation, depth of myometrial invasion,
lymphatic involvement, lymphocytic response, patients' age,
or prognosis. Conclusion. It appears that the
presence of HPV in the endometrium, as detected by PCR, does
not play any role in the initiation or prognosis of
endometrial adenocarcinoma
Hadrons in Dense Resonance-Matter: A Chiral SU(3) Approach
A nonlinear chiral SU(3) approach including the spin 3/2 decuplet is
developed to describe dense matter. The coupling constants of the baryon
resonances to the scalar mesons are determined from the decuplet vacuum masses
and SU(3) symmetry relations. Different methods of mass generation show
significant differences in the properties of the spin-3/2 particles and in the
nuclear equation of state.Comment: 28 pages, 9 figure
The Impact of Aortic Occlusion Balloon on Mortality After Endovascular Repair of Ruptured Abdominal Aortic Aneurysms: A Meta-analysis and Meta-regression Analysis
INTRODUCTION:We aimed to investigate whether the use of aortic occlusion balloon (AOB) has an impact on mortality of patients undergoing endovascular repair of ruptured abdominal aortic aneurysms (RAAAs).METHODS:A meta-analysis of the English-language literature was undertaken through February 2013. Articles reporting data on outcome after endovascular repair of RAAAs were identified and information regarding the use of AOB was sought.RESULTS:Included in this meta-analysis were 39 eligible studies reporting 1277 patients. The pooled perioperative mortality was 21.6% (95% CI 18.1-25.1%). There was significant within-study heterogeneity (I(2) 50.2%, P < 0.001). A total of 200 patients required AOB with an estimated pooled proportion of 14.1% (8.9-19.3%). Individual random-effects meta-regression investigating the effect of AOB and other risk factors on mortality revealed a significant linear association of hemodynamic instability, bifurcated endograft approach, and primary conversion to open repair with mortality and a nonlinear (second degree polynomial) association of AOB with mortality. On multivariable meta-regression models, both hemodynamic instability and AOB were found to be statistically significant, independent predictors of mortality. In particular, there was a statistically significant negative correlation between AOB and mortality and a positive effect of hemodynamic instability on mortality. In practical terms, mortality was significantly higher in studies with a higher proportion of hemodynamically unstable patients and lower in studies with a higher rate of AOB use.CONCLUSION:This study provides meta-analytical evidence that the use of an AOB in unstable RAAA patients undergoing endovascular repair may improve the results
Cosmological Evolution of a Purely Conical Codimension-2 Brane World
We study the cosmological evolution of isotropic matter on an infinitely thin
conical codimension-two brane-world. Our analysis is based on the boundary
dynamics of a six-dimensional model in the presence of an induced gravity term
on the brane and a Gauss-Bonnet term in the bulk. With the assumption that the
bulk contains only a cosmological constant Lambda_B, we find that the isotropic
evolution of the brane-universe imposes a tuned relation between the energy
density and the brane equation of state. The evolution of the system has fixed
points (attractors), which correspond to a final state of radiation for
Lambda_B=0 and to de Sitter state for Lambda_B>0. Furthermore, considering
anisotropic matter on the brane, the tuning of the parameters is lifted, and
new regions of the parametric space are available for the cosmological
evolution of the brane-universe. The analysis of the dynamics of the system
shows that, the isotropic fixed points remain attractors of the system, and for
values of Lambda_B which give acceptable cosmological evolution of the equation
of state, the line of isotropic tuning is a very weak attractor. The initial
conditions, in this case, need to be fine tuned to have an evolution with
acceptably small anisotropy.Comment: 20 pages, 4 figures, typo correcte
The m->0 limit for massive graviton in dS_4 and AdS_4. How to circumvent the van Dam-Veltman-Zakharov discontinuity
We show that, by considering physics in dS_4 or AdS_4 spacetime, one can
circumvent the van Dam - Veltman - Zakharov theorem which requires that the
extra polarization states of a massive graviton do not decouple in the massless
limit. It is shown that the smoothness of the m->0 limit is ensured if the H
(``Hubble'') parameter, associated with the horizon of the dS_4 or AdS_4 space,
tends to zero slower than the mass of the graviton m.Comment: 11 pages, references added, minor typos correcte
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