Gravitation as Anholonomy

A gravitational field can be seen as the anholonomy of the tetrad fields. This is more explicit in the teleparallel approach, in which the gravitational field-strength is the torsion of the ensuing Weitzenboeck connection. In a tetrad frame, that torsion is just the anholonomy of that frame. The infinitely many tetrad fields taking the Lorentz metric into a given Riemannian metric differ by point-dependent Lorentz transformations. Inertial frames constitute a smaller infinity of them, differing by fixed-point Lorentz transformations. Holonomic tetrads take the Lorentz metric into itself, and correspond to Minkowski flat spacetime. An accelerated frame is necessarily anholonomic and sees the electromagnetic field strength with an additional term.Comment: RevTeX4, 10 pages, no figures. To appear in Gen. Rel. Gra

The Equivalence Principle Revisited

A precise formulation of the strong Equivalence Principle is essential to the understanding of the relationship between gravitation and quantum mechanics. The relevant aspects are reviewed in a context including General Relativity, but allowing for the presence of torsion. For the sake of brevity, a concise statement is proposed for the Principle: "An ideal observer immersed in a gravitational field can choose a reference frame in which gravitation goes unnoticed". This statement is given a clear mathematical meaning through an accurate discussion of its terms. It holds for ideal observers (time-like smooth non-intersecting curves), but not for real, spatially extended observers. Analogous results hold for gauge fields. The difference between gravitation and the other fundamental interactions comes from their distinct roles in the equation of force.Comment: RevTeX, 18 pages, no figures, to appear in Foundations of Physic

Comportamento de painéis de alvenaria reforçados com FRCM sujeitos a ações no plano: Estudo da interface

O presente trabalho dedica-se à caracterização do comportamento de modelos de alvenaria reforçada com FRCM (fiber reinforced cementitious matrix) quando sujeitos a ações que atuam no plano da parede. O sistema de reforço, composto por uma camada de argamassa cimentícia reforçada com uma malha de CFRP (carbon fiber reinforced polymer), foi aplicado a modelos de alvenaria de tijolo furado. Considerando a importância da interface entre a camada de reforço e o substrato para a eficiência do sistema de reforço, procedeu-se à caracterização do comportamento mecânico da interface por intermédio de ensaios de corte direto, com os quais foi possível definir as superfícies de cedência e de rotura da interface. Os resultados obtidos permitiram a quantificação dos parâmetros que caracterizam a interface entre o material cerâmico e uma argamassa do tipo PFRM (polypropylene fibre reinforced mortar) quando sujeita a cargas de corte combinadas com cargas normais à interface. Através de expressões analíticas e do critério de rotura de Mohr-Coloumb foi analisada a adequação de um critério baseado numa aproximação linear, aos dados obtidos experimentalmente.Projeto InoTec - Material inovador de ultra-alta ductilidade para a reabilitação do património construído, financiado pelo COMPETE / QREN / FEDER (NORTE-07-0202-FEDER-02302

Influência da idade nos parâmetros de fractura do betão auto-compactável reforçado com fibras de aço

No presente trabalho apresenta-se a estratégia numérica desenvolvida para a determinação das propriedades de fractura do betão auto-compactável reforçado com fibras de aço de distintas idades. Para tal foram utilizados resultados obtidos num programa experimental e um software de análise não linear material baseado nas técnicas dos elementos finitos, sendo a fendilhação simulada por intermédio de um modelo de fendas discretas.FEDER - "PABERFIA - Painéis sandwich prefabricados de betão reforçado com fibras”. Fundação para a Ciência e Tecnologia (FCT) -"PABERFIA - Painéis sandwich prefabricados de betão reforçado com fibras”. Prégaia. Civitest. Secil. Bettor MBT. Bekaert. Comital

Compression and bending behavior of steel fiber reinforced self-compacting concrete

A method to design cost competitive steel fiber reinforced self-compacting concrete (SFRSCC) for precasting industrial applications is described in this paper. Since demolding the elements as soon as possible is an important requirement in this industry, the influence of the age on the resistance and toughness of the designed SFRSCC was assessed carrying out an experimental program. Based on the force-deflection relationship obtained in the three point bending notched beam tests performed according to the RILEM TC 162-TDF recommendations, the stress-crack opening relationship of the SFRSCC was determined. The influence of the SFRSCC age on the fracture parameters of this material was analyzed.Inserido no programa de pesquisa suportado pelo FEDER e o Ministério da Ciência e Tecnologia (MCT) e promovido pelo Agencia de Inovação (ADI)

Steel fibre reinforced concrete for elements failing in bending and in shear

Discrete steel fibres can increase significantly the bending and the shear resistance of concrete structural elements when Steel Fibre Reinforced Concrete (SFRC) is designed in such a way that fibre reinforcing mechanisms are optimized. To assess the fibre reinforcement effectiveness in shallow structural elements failing in bending and in shear, experimental and numerical research were performed. Uniaxial compression and bending tests were executed to derive the constitutive laws of the developed SFRC. Using a cross-section layered model and the material constitutive laws, the deformational behaviour of structural elements failing in bending was predicted from the moment-curvature relationship of the representative cross sections. To evaluate the influence of the percentage of fibres on the shear resistance of shallow structures, three point bending tests with shallow beams were performed. The applicability of the formulation proposed by RILEM TC 162-TDF for the prediction of the shear resistance of SFRC elements was evaluated. Inverse analysis was adopted to determine indirectly the values of the fracture mode I parameters of the developed SFRC. With these values, and using a softening diagram for modelling the crack shear softening behaviour, the response of the SFRC beams failing in shear was predicted.Fundação para a Ciência e a Tecnologia (FCT

Self-compacting steel fibre reinforced concrete for precasted sandwich panels : experimental and numerical research

In Portugal, steel fibres are the most used for concrete reinforcement, and flooring and tunnelling are the main applications of fibre reinforced concrete (FRC). In last years the prefabrication industry is showing more interest in collaborating in FRC research projects. The research carried out in consortium by University of Minho (UM) and two private companies for the development of self-compacting steel fibre reinforced concrete (SCSFRC) is an example of this new strategy. This research has the following main tasks: conceive a rational mix design method; evaluate the most relevant material properties and the structural behaviour of laminar elements; develop numerical tools. This paper intends to show the research strategy adopted in the SCSFRC project, since it is a typical example of the methodology followed by the UM research group, the most active in Portugal, in the FRC domain.FEDER. MCT. ADI. PREGAIA. CIVITEST. MBT. SECIL. Bekaert. Comital

Protein-energy malnutrition halts hemopoietic progenitor cells in the G0/G1 cell cycle stage, thereby altering cell production rates

Protein energy malnutrition (PEM) is a syndrome that often results in immunodeficiency coupled with pancytopenia. Hemopoietic tissue requires a high nutrient supply and the proliferation, differentiation and maturation of cells occur in a constant and balanced manner, sensitive to the demands of specific cell lineages and dependent on the stem cell population. In the present study, we evaluated the effect of PEM on some aspects of hemopoiesis, analyzing the cell cycle of bone marrow cells and the percentage of progenitor cells in the bone marrow. Two-month-old male Swiss mice (N = 7-9 per group) were submitted to PEM with a low-protein diet (4%) or were fed a control diet (20% protein) ad libitum. When the experimental group had lost about 20% of their original body weight after 14 days, we collected blood and bone marrow cells to determine the percentage of progenitor cells and the number of cells in each phase of the cell cycle. Animals of both groups were stimulated with 5-fluorouracil. Blood analysis, bone marrow cell composition and cell cycle evaluation was performed after 10 days. Malnourished animals presented anemia, reticulocytopenia and leukopenia. Their bone marrow was hypocellular and depleted of progenitor cells. Malnourished animals also presented more cells than normal in phases G0 and G1 of the cell cycle. Thus, we conclude that PEM leads to the depletion of progenitor hemopoietic populations and changes in cellular development. We suggest that these changes are some of the primary causes of pancytopenia in cases of PEM.FAPESPCNP