Transient Nucleation near the Mean-Field Spinodal

Nucleation is considered near the pseudospinodal in a one-dimensional $\phi^4$ model with a non-conserved order parameter and long-range interactions. For a sufficiently large system or a system with slow relaxation to metastable equilibrium, there is a non-negligible probability of nucleation occurring before reaching metastable equilibrium. This process is referred to as transient nucleation. The critical droplet is defined to be the configuration of maximum likelihood that is dynamically balanced between the metastable and stable wells. Time-dependent droplet profiles and nucleation rates are derived, and theoretical results are compared to computer simulation. The analysis reveals a distribution of nucleation times with a distinct peak characteristic of a nonstationary nucleation rate. Under the quench conditions employed, transient critical droplets are more compact than the droplets found in metastable equilibrium simulations and theoretical predictions.Comment: 7 Pages, 5 Figure

Global aspects of gravitomagnetism

We consider global properties of gravitomagnetism by investigating the gravitomagnetic field of a rotating cosmic string. We show that although the gravitomagnetic field produced by such a configuration of matter vanishes locally, it can be detected globally. In this context we discuss the gravitational analogue of the Aharonov-Bohm effect.Comment: 10 pages - Typeset using REVTE

Clival chordomas: The endoscopic transnasal transsphenoidal approach

Os cordomas da base do crânio são tumores raros, localmente destrutivos, que constituem um desafio cirúrgico pela proximidade a estruturas neurovasculares vitais e ao elevado potencial de recidiva. Os autores descrevem o caso de uma mulher de 45 anos, com quadro de cefaleias, anisocória e diplopia, com cinco meses de evolução, cujos exames complementares de diagnóstico revelaram uma volumosa lesão expansiva dos 2/3 superiores do clivus, com preenchimento do seio esfenoidal, destruição selar e extensão para ambos os seios cavernosos. Procedeu-se a excisão da lesão, após biopsia diagnóstica compatível com cordoma, por abordagem endoscópica endonasal transesfenoidal (EET), guiada por neuronavegação. Com 3 meses de seguimento, a doente encontra-se clinicamente bem e a ressonância magnética revela eventual resíduo tumoral no seio cavernoso direito. A cirurgia EET constitui uma alternativa minimamente invasiva na abordagem de lesões expansivas da base do crânio, possibilitando, em casos seleccionados, resultados similares e com menor morbilidade, relativamente às técnicas cirúrgicas clássicas.info:eu-repo/semantics/publishedVersio

Influence of the concrete mechanical properties on the efficacy of the shear strengthening intervention on RC beams by NSM technique

The occurrence of a failure mode, different from debonding, consisting on the detachment, from the beam core, of “two concrete lateral walls” containing the glued laminates, highlights the paramount importance of concrete mechanical properties on the effectiveness of NSM shear strengthening technique. A new mechanical-analytical interpretation of the phenomenon affecting the ultimate behaviour of RC beams NSM-strengthened in shear is presented along with the main findings. This approach takes into account the possibility that the shear strengthening contribution of the NSM laminates can be limited by the three following failure modes: debonding, concrete tensile fracture and laminates’ tensile rupture. The interaction between laminates can be also accounted for. The proposed mechanical interpretation of the NSM laminates behaviour can be extended to NSM rods.Fundação para a Ciência e a Tecnologia (FCT) - programa “CUTINSHEAR - Performance assessment of an innovative structural FRP strengthening technique using an integrated system based on optical fiber sensors” s, POCTI/ECM/59033/2004. This work has been partially carried out under the program “Dipartimento di Protezione Civile – Consorzio RELUIS”, signed on 2005-07-11 (n. 540), Research Line 8, whose financial support is greatly appreciatePrograma “Dipartimento di Protezione Civile – Consorzio RELUIS” nº 540Research Line 8Empreiteiros CasaisS&P®Secil (Unibetão, Braga)Degussa

Theoretical model and computacional procedure to evaluate the NSM FRP strips shear strength contribution to a RC beam

This paper presents a closed-form procedure to evaluate the shear strength contribution provided to a Reinforced Concrete (RC) beam by a system of Near Surface Mounted (NSM) Fiber Reinforced Polymer (FRP) strips. This procedure is based on the evaluation of: a) the constitutive law of the average-available-bond-length NSM FRP strip effectively crossing the shear crack and b) the maximum effective capacity it can attain during the loading process of the strengthened beam. Due to complex phenomena, such as: a) interaction between forces transferred through bond to the surrounding concrete and the concrete fracture, and b) interaction among adjacent strips, the NSM FRP strip constitutive law is largely different than the linear elastic one characterizing the FRP behavior in tension. Once the constitutive law of the average-available-bond-length NSM strip is reliably known, its maximum effective capacity can be determined by imposing a coherent kinematic mechanism. The self-contained and ready-to-implement set of analytical equations and logical operations is presented along with the main underlying physical-mechanical principles and assumptions. The formulation proposed is appraised against some of the most recent experimental results, and its predictions are also compared with those obtained by a recently developed more sophisticated model.Fundação para a Ciência e a Tecnologia (FCT) - CUTINEMO - Carbon fiber laminates applied according to the near surface mounted technique to increase the flexural resistance to negative moments of continuous reinforced concrete structures” (PTDC/ECM/73099/2006

NSM FRP strips shear strength contribution to a RC beam : a design procedure

This paper presents a closed-form procedure to evaluate the shear strength contribution provided to a Reinforced Concrete (RC) beam by a system of Near Surface Mounted (NSM) Fiber Reinforced Polymer (FRP) strips. This procedure is based on the evaluation of: a) the constitutive law of the average-available-bond-length NSM FRP strip effectively crossing the shear crack and b) the maximum effective capacity it can attain during the loading process of the strengthened beam. Due to complex phenomena, such as: a) interaction between forces transferred through bond to the surrounding concrete and concrete fracture, and b) interaction among adjacent strips, the NSM FRP strip constitutive law is largely different than the linear elastic one characterizing the FRP behavior in tension. Once the constitutive law of the average-available-bond-length NSM strip is reliably known, its maximum effective capacity can be determined by imposing a coherent kinematic mechanism. The self-contained and ready-to-implement set of analytical equations and logical operations is presented along with the main underlying physical-mechanical principles and assumptions. The formulation proposed is appraised against some of the most recent experimental results and its predictions are also compared with those obtained by a recently developed more sophisticated model.(undefined

A new approach for modelling the NSM shear strengthening contribution in reinforced concrete beams

Empreiteiros CasaisDegussa PortugalSecil (Unibetão, Braga)S&P®Fundação para a Ciência e a Tecnologia (FCT) - POCTI/ECM/59033/200

Mechanical model to simulate the NSM FRP strips shear strength contribution to RC beams

A three dimensional mechanical model has been recently developed to simulate the Near Sur-face Mounted (NSM) Fibre Reinforced Polymer (FRP) strips shear strength contribution to Reinforced Con-crete (RC) beams throughout the entire loading process, as function of the Critical Diagonal Crack (CDC) opening angle. It was developed by fulfilling equilibrium, kinematic compatibility and constitutive laws of both intervening materials and bond between them. It takes into consideration all of possible failure modes that can affect the behaviour, at ultimate, of a single NSM strip, namely: loss of bond (debonding), semi-conical concrete tensile fracture, rupture of the strip itself and a mixed shallow-semi-cone-plus-debonding failure. Besides, it allows the interaction among adjacent strips to be accounted for. The numerical results, in terms of both shear strength contribution and predicted cracking scenario are presented and compared with experimental evidence regarding some of the most recent experimental programs. From that comparison, a satisfactory level of prediction accuracy, regardless of the main parameters such as concrete mechanical prop-erties, amount and inclination of strips, arises. The main findings, as well as the influence of some of the main intervening parameters, are shown.The authors of the present work wish to acknowledge the support provided by the Empreiteiros Casais, S&P.., degussa.. Portugal, and Secil (Unibetao, Braga).The study reported in this paper forms a part of the research program SmartReinforcement Carbon fibre laminates for the strengthening and monitoring of reinforced concrete structures supported by ADI-IDEIA, Project n.. 13-05-04-FDR-00031. This work was also carried out under the auspices of the Italian DPC-ReLuis Project (repertory n. 540), Research Line 8, whose financial support is greatly appreciated