A spherically symmetric and stationary universe from a weak modification of general relativity

It is shown that a weak modification of general relativity, in the linearized approach, renders a spherically symmetric and stationary model of the universe. This is due to the presence of a third mode of polarization in the linearized gravity in which a "curvature" energy term is present. Such an energy can, in principle, be identified as the Dark Energy. The model can also help to a better understanding of the framework of the Einstein-Vlasov system.Comment: Accepted for publication by Europhysics Letter

Removing black-hole singularities with nonlinear electrodynamics

We propose a way to remove black hole singularities by using a particular nonlinear electrodynamics Lagrangian that has been recently used in various astrophysics and cosmological frameworks. In particular, we adapt the cosmological analysis discussed in a previous work to the black hole physics. Such analysis will be improved by applying the Oppenheimer-Volkoff equation to the black hole case. At the end, fixed the radius of the star, the final density depends only on the introduced quintessential density term $\rho_{\gamma}$ and on the mass.Comment: In this last updated version we correct two typos which were present in Eqs. (21) and (22) in the version of this letter which has been published in Mod. Phys. Lett. A 25, 2423-2429 (2010). In the present version, both of Eqs. (21) and (22) are dimensionally and analytically correc

Definition of critical conditions for obtaining of a macromodel of ceramic matrix composites

The necessity for development of an approach to studying the phase composition and physico-chemical processes occurring during the firing of ceramic materials with a matrix structure based on technogenic and natural materials is substantiated. The study results on definition of critical conditions for obtaining of a ceramic matrix composites macromodel are presented

Theory of x-ray absorption by laser-dressed atoms

An ab initio theory is devised for the x-ray photoabsorption cross section of atoms in the field of a moderately intense optical laser (800nm, 10^13 W/cm^2). The laser dresses the core-excited atomic states, which introduces a dependence of the cross section on the angle between the polarization vectors of the two linearly polarized radiation sources. We use the Hartree-Fock-Slater approximation to describe the atomic many-particle problem in conjunction with a nonrelativistic quantum-electrodynamic approach to treat the photon-electron interaction. The continuum wave functions of ejected electrons are treated with a complex absorbing potential that is derived from smooth exterior complex scaling. The solution to the two-color (x-ray plus laser) problem is discussed in terms of a direct diagonalization of the complex symmetric matrix representation of the Hamiltonian. Alternative treatments with time-independent and time-dependent non-Hermitian perturbation theories are presented that exploit the weak interaction strength between x rays and atoms. We apply the theory to study the photoabsorption cross section of krypton atoms near the K edge. A pronounced modification of the cross section is found in the presence of the optical laser.Comment: 13 pages, 3 figures, 1 table, RevTeX4, corrected typoe

An Improved Implementation and Abstract Interface for Hybrid

Hybrid is a formal theory implemented in Isabelle/HOL that provides an interface for representing and reasoning about object languages using higher-order abstract syntax (HOAS). This interface is built around an HOAS variable-binding operator that is constructed definitionally from a de Bruijn index representation. In this paper we make a variety of improvements to Hybrid, culminating in an abstract interface that on one hand makes Hybrid a more mathematically satisfactory theory, and on the other hand has important practical benefits. We start with a modification of Hybrid's type of terms that better hides its implementation in terms of de Bruijn indices, by excluding at the type level terms with dangling indices. We present an improved set of definitions, and a series of new lemmas that provide a complete characterization of Hybrid's primitives in terms of properties stated at the HOAS level. Benefits of this new package include a new proof of adequacy and improvements to reasoning about object logics. Such proofs are carried out at the higher level with no involvement of the lower level de Bruijn syntax.Comment: In Proceedings LFMTP 2011, arXiv:1110.668

Inflation from R^2 gravity: a new approach using nonlinear electrodynamics

We discuss another approach regarding the inflation from the R^2 theory of gravity originally proposed by Starobinski. A non-singular early cosmology is proposed, where, adding a nonlinear electrodynamics Lagrangian to the high-order action, a bouncing is present and a power-law inflation is obtained. In the model the Ricci scalar works like an inflaton field.Comment: Definitive version to be published in Astroparticle Physics during 2011, 9 page

The effectiveness of neuromuscular warm-up strategies, that require no additional equipment, for preventing lower limb injuries during sports participation: a systematic review

PMCID: PMC3408383The electronic version of this article is the complete one and can be found online at: http://www.biomedcentral.com/1741-7015/10/75. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited

Detection of Active Mammalian GH31 α-Glucosidases in Health and Disease Using In-Class, Broad-Spectrum Activity-Based Probes

The development of small molecule activity-based probes (ABPs) is an evolving and powerful area of chemistry. There is a major need for synthetically accessible and specific ABPs to advance our understanding of enzymes in health and disease. α-Glucosidases are involved in diverse physiological processes including carbohydrate assimilation in the gastrointestinal tract, glycoprotein processing in the endoplasmic reticulum (ER), and intralysosomal glycogen catabolism. Inherited deficiency of the lysosomal acid α-glucosidase (GAA) causes the lysosomal glycogen storage disorder, Pompe disease. Here, we design a synthetic route for fluorescent and biotin-modified ABPs for in vitro and in situ monitoring of α-glucosidases. We show, through mass spectrometry, gel electrophoresis, and X-ray crystallography, that α-glucopyranose configured cyclophellitol aziridines label distinct retaining α-glucosidases including GAA and ER α-glucosidase II, and that this labeling can be tuned by pH. We illustrate a direct diagnostic application in Pompe disease patient cells, and discuss how the probes may be further exploited for diverse applications