Las curvas tensión-deformación de hormigones ensayados bajo compresión uniaxial monotónica: una revisión sistemática

The existence of more than thirty different mathematical expressions that claims to represent the stress-strain relationship of a concrete specimen under monotonic and uniaxial compression (including those proposed in the official regulations of different countries that have regulated by law the use of concrete as structural material), seems to require an additional effort in formulating a universally accepted equation. As a first step toward that goal, in this paper we show and analyze systematically the different dynasties of equations that have been published, since the first proposals of Ritter and Bach (1897-1899), through the, more or less complicated, polynomial truncations of the Smith and Young’s equation (1956), continuing with the contributions based on statistical distributions of the damage model, and concluding with the analysis of the approach to the issue by the successive versions of the Model Code and the Spanish Structural Concrete Instruction (EHE-08).La existencia de más de una treintena de expresiones matemáticas distintas que pretenden representar la evolución tenso- deformacional de una probeta de hormigón sometida a compresión uniaxial monotónica (incluidas las propuestas en las normativas oficiales de los distintos países que tienen regulado por ley el empleo del hormigón como material estructural), parece requerir un esfuerzo adicional a la hora de formular una expresión universalmente aceptada. Como primer paso hacia ese objetivo, en este trabajo se muestran y analizan de manera sistemática las distintas dinastías de ecuaciones publicadas, desde las primeras propuestas de Ritter y Bach (1897- 1899), pasando por los truncamientos polinómicos más o menos complejos de la ecuación de Smith y Young (1956), hasta las aportaciones basadas en distribuciones estadísticas del modelo de daño, concluyendo con el análisis del tratamiento dado a la cuestión por las distintas versiones del Código Modelo y la Instrucción de Hormigón Estructural española (EHE-08)

Perturbations of Gauss-Bonnet Black Strings in Codimension-2 Braneworlds

We derive the Lichnerowicz equation in the presence of the Gauss-Bonnet term. Using the modified Lichnerowicz equation we study the metric perturbations of Gauss-Bonnet black strings in Codimension-2 Braneworlds.Comment: 26 pages, no figures, clarifying comments and one reference added, to be published in JHE

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

Geodesics, the Equivalence Principle and Singularities in Higher-dimensional General Relativity and Braneworlds

The geodesics of a spacetime seldom coincide with those of an embedded submanifold of codimension one. We investigate this issue for higher-dimensional general relativity-like models, firstly in the simpler case without branes to isolate which features are already present, and then in the more complicated case with branes. The framework in which we consider branes is general enough to include asymmetric braneworlds but not thick branes. We apply our results on geodesics to study both the equivalence principle and cosmological singularities. Among the models we study these considerations favour $Z_2$ symmetric braneworlds with a negative bulk cosmological constant.Comment: 20 pages, 2 figures. Accepted by JCAP. Minor proofreading corrections; several references adde

Absorption cross section in Lifshitz black hole

We derive the absorption cross section of a minimally coupled scalar in the Lifshitz black hole obtained from the new massive gravity. The absorption cross section reduces to the horizon area in the low energy and massless limit of s-wave mode propagation, indicating that the Lifshitz black hole also satisfies the universality of low energy absorption cross section for black holes.Comment: 13 pages, 1 figure, version to appear in EPJ

Microvessel changes after post-ischemic benign and malignant hyperemia: experimental study in rats

<p>Abstract</p> <p>Background</p> <p>The present investigation was designed to elucidate the use of dynamic contrast enhanced perfusion MR imaging (DCE pMRI) in characterizing hyperemia, including microvessel changes, and to examine whether DCE pMRI can predict benign or malignant hyperemia.</p> <p>Methods</p> <p>Sprague-Dawley rats underwent middle cerebral artery occlusion (MCAO) by intraluminal suture placement. All rats were randomized to 4 groups: MCAO for 0.5 hours followed by saline treatment (10 ml/kg; group 1); MCAO for 3 hours followed by treatment with saline (group 2) or urokinase (25000 IU/kg; group 3); and MCAO for 6 hours followed by urokinase treatment (group 4). Relative cerebral blood volume (rCBV) and relative maximum slope of increase of the signal intensity time curve (rMSI) were quantitatively analyzed from MRI. Microvessel diameter and blood-brain barrier disruption obtained by laser scanning confocal microscopy (LSCM) as well as transmission electron microscopy (TEM) were obtained for correlative study.</p> <p>Results</p> <p>Benign hyperemia was noticed only in group 1; malignant hyperemia was seen in group 3. Although the rCBV of malignant hyperemia was slightly higher than in benign hyperemia (<it>P </it>> 0.05), the rMSI, on the other hand, was significantly lower (<it>P </it>< 0.05). Fluoro-isothiocyanate dextran (FITC-dextran) extravasations, marked glial end-foot process swelling, and significant vasodilatation were seen in malignant hyperemia, while no or mild leakage of FITC-dextran and slight glial end-foot process swelling occurred in benign hyperemia.</p> <p>Conclusion</p> <p>Our findings indicate that DCE pMRI can characterize post-ischemic hyperemia and correlates well with microvascular damage.</p