GRBs and the thermalization process of electron-positron plasmas

We discuss the temporal evolution of the pair plasma created in Gamma-Ray Burst sources. A particular attention is paid to the relaxation of the plasma into thermal equilibrium. We also discuss the connection between the dynamics of expansion and the spatial geometry of the plasma. The role of the baryonic loading parameter is emphasized.Comment: 4 pages, 3 figures, in the Proceedings of the "Gamma Ray Bursts 2007" meeting, November 5-9, 2007, Santa Fe, New Mexico, US

Effects of partial rootzone drying and rootstock vigour on growth and fruit quality of 'Pink Lady' apple trees in Mediterranean environments

We investigated the effects of partial rootzone drying (PRD) and rootstock vigor on water relations, vegetative and productive performance of \u2018Pink Lady\u2019 apple (Malus domestica Borkh.) trees in central Sicily. In a first field trial, trees on MM.106 rootstock were subjected to: Conventional irrigation (CI), maintaining soil moisture above 80% of field capacity; PRD irrigation, where only one alternated side of the rootzone received 50% of the CI irrigation water; and continuous deficit irrigation (DI), where 50% of the CI water was equally applied to both sides of the rootzone. In a second trial, trees on M.9 or MM.106 were subjected to CI and PRD irrigation. PRD reduced stomatal conductance (gs) more consistently in trees on MM.106 than in trees on M.9, but maintained relative water content (RWC) to the levels of CI. DI induced greater gs reductions than PRD and lower RWC than CI and PRD. Rootstock vigor did not influence plant response to irrigation strategy. PRD induced some reduction in fruit number but no change in yields and fruit quality compared to CI, whereas DI reduced fruit size and marketable yields. Significant reductions in shoot and leaf growth were induced by DI, whereas only leaf growth was affected by PRD. Our observations indicate that responses induced by PRD are due to a combination of the amount and way of applying water, and not just to reductions in irrigation volumes, suggesting a possible use of PRD for increasing apple water use efficiency in Mediterranean environments

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

Three dimensional mechanical model for simulating the NSM FRP strips shear strength contribution to RC beams

Shear strengthening of Reinforced Concrete (RC) beams by means of Near Surface Mounted (NSM) Fiber Reinforced Polymer (FRP) strips is an emerging technique for structural rehabilitation that is gaining increasing interest in the FRP community mainly because of some advantages it provides with respect to the better consolidated technique of the Externally Bonded Reinforcement (EBR). Those advantages encompass, mainly, a better exploitation of material and a higher protection against vandalism along with a relative faster applicability. Yet, the behavior of such NSM FRP strips is extremely complex, as can be gathered by experimental evidence, due to the complex geometry, the non linear mechanical properties of bond, and the scatter affecting the concrete tensile properties along with their non-linearity. In an attempt to provide valuable contribution to a better understanding of their behavior, a three dimensional mechanical model for simulating the shear strength contribution provided by a system of NSM FRPs to a RC beam throughout the loading process was recently developed. Its upgraded version is herein presented along with the main findings. It correctly interprets the experimental evidence taking into account complex phenomena such as the interaction between bond transferred force and concrete fracture along with the interaction between adjacent strips.The authors of the present work wish to acknowledge the support provided by the "Empreiteiros Casais", S&P(R), degussa (R) 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 no. 13-05-04-FDR-00031. Also, this work was carried out under the auspices of the Italian DPC-ReLuis Project (repertory no. 540), Research Line 8, whose financial support is greatly appreciated

Shear strengthening of RC beams by means of NSM FRP strips : constitutive law of a single strip

The need to provide a rational explanation to the observed peculiar failure mode affecting the behaviour, at ultimate, of a Reinforced Concrete (RC) beam strengthened in shear by Near Surface Mounted (NSM) Fibre Reinforced Polymer (FRP) strips, led the authors to develop a comprehensive numerical model for simulating the NSM shear strength contribution to RC beams throughout the entire loading process as function of the Critical Diagonal Crack (CDC) opening angle. That model was respectful of equilibrium, ki-nematic compatibility and constitutive laws. Despite its high level of prediction accuracy, taking into account all of the possible failure modes, as well as the interaction among adjacent strips, that model resulted rela-tively complex to be easily implemented in a practitioners-addressed building regulations code. Yet, it can be conveniently simplified into a more user-friendly and closed-form design formula. Crucial point of that sim-plification is the development of a reliable constitutive analytical law providing the single strip strength as function of the imposed end slip. This paper presents the modelling strategy adopted to determine that consti-tutive law, as well as its final analytical expression.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 no 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

Parametric studies of the NSM FRP strips shear strength contribution to a RC beam

A three dimensional mechanical model was recently developed to simulate the shear strength contribution provided by a system of Near Surface Mounted (NSM) Fiber Reinforced Polymer (FRP) strips to a Reinforced Concrete (RC) beam throughout its loading process. It was developed fulfilling equilibrium, kinematic compatibility and constitutive laws of both materials, concrete and FRP, and local bond between themselves. In the present paper, that model is first appraised on the basis of some of the most recent experimental results and then is applied to carry out parametric studies. The influence of each of the involved parameters on the contribution provided by a system of NSM FRP strips to the shear strength of a RC beam is investigated. The results of those studies are presented along with the main findings.(undefined)The authors of the present work wish to acknowledge the support provided by the “Empreiteiros Casais”, S&P®, degussa® Portugal, and Secil (Unibetão, Braga). The study reported in this paper forms a part of the research program “CUTINEMO” supported by FCT, PTDC/ECM/73099/2006. Also, this work was carried out under the auspices of the Italian DPC-ReLuis Project (repertory n. 540), Research Line 8, whose financial support is greatly appreciated

Design formula to evaluate the NSM FRP strips shear strength contribution to a RC beam

This paper presents the closing step of a synthesis process aiming at deriving, from a previously developed more complex model, a simple design formula to evaluate the shear strength contribution provided by a system of Near Surface Mounted (NSM) Fiber Reinforced Polymer (FRP) strips to a Reinforced Concrete (RC) beam. 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 the two previous and more sophisticated versions of the same modeling strategy. Monte Carlo simulations are carried out in order to appraise the sensitivity of the NSM shear strength contribution prediction to the value assumed by the input parameters.Fundação para a Ciência e a Tecnologia (FCT