642 research outputs found
Noncommutative Einstein Equations
We study a noncommutative deformation of general relativity where the
gravitational field is described by a matrix-valued symmetric two-tensor field.
The equations of motion are derived in the framework of this new theory by
varying a diffeomorphisms and gauge invariant action constructed by using a
matrix-valued scalar curvature. Interestingly the genuine noncommutative part
of the dynamical equations is described only in terms of a particular tensor
density that vanishes identically in the commutative limit. A noncommutative
generalization of the energy-momentum tensor for the matter field is studied as
well.Comment: 17 Pages, LaTeX, reference adde
Non-Perturbative One-Loop Effective Action for Electrodynamics in Curved Spacetime
In this paper we explicitly evaluate the one-loop effective action in four
dimensions for scalar and spinor fields under the influence of a strong,
covariantly constant, magnetic field in curved spacetime. In the framework of
zeta function regularization, we find the one-loop effective action to all
orders in the magnetic field up to linear terms in the Riemannian curvature. As
a particular case, we also obtain the one-loop effective action for massless
scalar and spinor fields. In this setting, we found that the vacuum energy of
charged spinors with small mass becomes very large due entirely by the
gravitational correction.Comment: LaTeX, 23 page
Acute Disseminated Encephalomyelitis followed by Optic Neuritis: A Rare Syndrome of Uncertain Treatment and Prognosis
Aim Acute Disseminated Encephalomyelitis followed by optic neuritis (ADEM-ON), first described in 2013, is a rare demyelinating syndrome, typical of the pediatric age. We conducted a mini review of the existing literature, focusing on clinical, laboratory, radiological, therapeutic, and prognostic aspects in order to improve the identification of new cases. Methods We searched PubMed and Cochrane Library for studies on ADEM-ON between 2013 and 2018. Results Examination of the reported cases (three case reports and eight observational studies) established the following features. Time between ADEM and ON is highly variable. Almost all patients show antimyelin oligodendrocyte glycoprotein antibody (MOG-abs) seropositivity. High-dose intravenous steroid and plasmapheresis efficacy is reported for the acute phase; oral prednisone and other maintenance drugs may be useful in avoiding relapses. The clinical history may lead to a complete recovery but also to residual deficits. Conclusion MOG-abs detection strongly supports ADEM-ON diagnosis, confirming this entity as part of MOG-abs spectrum disorder. Owing to the very small number of cases so far reported, predicting clinical evolution is very difficult
Results of the fifth international spectroradiometer comparison for improved solar spectral irradiance measurements and related impact on reference solar cell calibration
This paper reports on the results of the fifth spectral irradiance measurement intercomparison and the impact these results have on the spread of spectral mismatch calculations in the outdoor characterization of reference solar cell and photovoltaic (PV) devices. Ten laboratories and commercial partners with their own instruments were involved in the comparison. Solar spectral irradiance in clear sky condition was measured with both fast fixed and slow rotating grating spectroradiometers. This paper describes the intercomparison campaign, describes different statistical analysis used on acquired data, reports on the results, and analyzes the impact these results would have on the primary calibration of a c-Si PV reference cell under natural sunlight
Non-commutative Corrections in Spectral Matrix Gravity
We study a non-commutative deformation of general relativity based on
spectral invariants of a partial differential operator acting on sections of a
vector bundle over a smooth manifold. We compute the first non-commutative
corrections to Einstein equations in the weak deformation limit and analyze the
spectrum of the theory. Related topics are discussed as well.Comment: 32 Pages, LaTex. Some nonessential typos in intermediate calculations
in sect. 3 and 4 are corrected. The final results are the sam
Spectral asymptotics of Euclidean quantum gravity with diff-invariant boundary conditions
A general method is known to exist for studying Abelian and non-Abelian gauge
theories, as well as Euclidean quantum gravity, at one-loop level on manifolds
with boundary. In the latter case, boundary conditions on metric perturbations
h can be chosen to be completely invariant under infinitesimal diffeomorphisms,
to preserve the invariance group of the theory and BRST symmetry. In the de
Donder gauge, however, the resulting boundary-value problem for the Laplace
type operator acting on h is known to be self-adjoint but not strongly
elliptic. The latter is a technical condition ensuring that a unique smooth
solution of the boundary-value problem exists, which implies, in turn, that the
global heat-kernel asymptotics yielding one-loop divergences and one-loop
effective action actually exists. The present paper shows that, on the
Euclidean four-ball, only the scalar part of perturbative modes for quantum
gravity are affected by the lack of strong ellipticity. Further evidence for
lack of strong ellipticity, from an analytic point of view, is therefore
obtained. Interestingly, three sectors of the scalar-perturbation problem
remain elliptic, while lack of strong ellipticity is confined to the remaining
fourth sector. The integral representation of the resulting zeta-function
asymptotics is also obtained; this remains regular at the origin by virtue of a
spectral identity here obtained for the first time.Comment: 25 pages, Revtex-4. Misprints in Eqs. (5.11), (5.14), (5.16) have
been correcte
Redox status assessment in infertile patients with nonâobstructive azoospermia undergoing testicular sperm extraction: A prospective study
AbstractBackgroundOxidative stress (OS) is one of the most prevalent causes of sperm damage, through the toxic effects of endogenously generated hydrogen peroxide, superoxide anion, and hydroxyl radicals. Peripheral leukocytes represent a feasible model for studying the pathophysiology of OSâmediated homeostasis, which can be responsible for cell dysfunction and cell injury.ObjectiveTo evaluate the redox status in patients with nonâobstructive azoospermia (NOA), establishing the potential role exerted by reactive oxygen species (ROS) in the genesis of testicular secretory injury.Material and methodsFrom May 2018 to March 2019, 39 patients were enrolled in this prospective singleâcenter cohort study and divided into two groups. Group 1 included 19 patients with NOA, and Group 2 included 20 normozoospermic men, partners of women with infertility tubal factor. All patients underwent serum blood tests. NOA underwent testicular sperm extraction (TeSE). ROS production (in lymphocytes, monocytes, and granulocytes) was assessed by fluorescenceâactivated cell sorting (FACS) analysis. Plasma oxidative stress was evaluated by lipid peroxidation markers (MDA) and total antioxidant capacity (TAC) both assessed by fluorometric techniques.ResultsMean lymphocyte ROS production resulted 967.0 ± 224.5 vs 728.0 ± 98.0 (NOA vs Controls, P .05).ConclusionROS production can be directly related to disorders of spermatogenesis, leading to severe conditions of male infertility, including azoospermia
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