Experimental study and numerical simulation of the behaviour of concrete dapped-end beams

One of the commonly used advantages in the construction of bridges is the possibility of dividing beams into two prefabricated sections imposing thus a hinge without significantly altering the distribution of internal forces with respect to that of a continuous beam. However, a weakness of this solution is the possibility of premature cracking in the re-entrant corner of the dapped-end beam, which may in turn lead to the infiltration of water. For the purpose of this study, three scaled specimens were built and subjected to service load. The first specimen was reinforced according to the guidelines given in PCI design Handbook [1], a longitudinal post-tension was applied to the second one while diagonal bars were placed in the third specimen. The obtained results allow the conclusion that the post-tensioned specimen had a better behaviour, i.e. the post-tensioning is positively correlated with the reduction of cracking. Three-dimensional nonlinear finite element models were created to simulate the cracking of concrete under service load. To this end, smeared crack and discrete crack approach were adopted. The values for cracking obtained by the numerical models showed satisfactory agreement with the experimental tests. It was concluded that in case the necessary parameters for simulation of cracks are obtained from experimental tests, the discrete crack model can be applied to the study of local fracture in reinforced or prestressed concrete structures

Evolution of Global Relativistic Jets: Collimations and Expansion with kKHI and the Weibel Instability

One of the key open questions in the study of relativistic jets is their interaction with the environment. Here, we study the initial evolution of both electron-proton and electron-positron relativistic jets, focusing on their lateral interaction with the ambient plasma. We trace the generation and evolution of the toroidal magnetic field generated by both kinetic Kelvin-Helmholtz (kKH) and Mushroom instabilities (MI). This magnetic field collimates the jet. We show that in electron-proton jet, electrons are perpendicularly accelerated with jet collimation. The magnetic polarity switches from the clockwise to anti-clockwise in the middle of jet, as the instabilities weaken. For the electron-positron jet, we find strong mixture of electron-positron with the ambient plasma, that results in the creation of a bow shock. Merger of magnetic field current filaments generate density bumps which initiate a forward shock. The strong mixing between jet and ambient particles prevents full development of the jet on the studied scale. Our results therefore provide a direct evidence for both jet collimation and particle acceleration in the created bow shock. Differences in the magnetic field structures generated by electron-proton and electron-positron jets may contribute to observable differences in the polarized properties of emission by electrons.Comment: 25 pages, 12 figures, ApJ, accepte

Magnetic Field Generation in Core-Sheath Jets via the Kinetic Kelvin-Helmholtz Instability

We have investigated magnetic field generation in velocity shears via the kinetic Kelvin-Helmholtz instability (kKHI) using a relativistic plasma jet core and stationary plasma sheath. Our three-dimensional particle-in-cell simulations consider plasma jet cores with Lorentz factors of 1.5, 5, and 15 for both electron-proton and electron-positron plasmas. For electron-proton plasmas we find generation of strong large-scale DC currents and magnetic fields which extend over the entire shear-surface and reach thicknesses of a few tens of electron skin depths. For electron-positron plasmas we find generation of alternating currents and magnetic fields. Jet and sheath plasmas are accelerated across the shear surface in the strong magnetic fields generated by the kKHI. The mixing of jet and sheath plasmas generates transverse structure similar to that produced by the Weibel instability.Comment: 28 pages, 12 figures, in press, ApJ, September 10, 201

Peroxisome proliferator-activated receptor alpha plays a crucial role in behavioral repetition and cognitive flexibility in mice

Acknowledgments We thank Luca Giordano, Giovanni Esposito and Angelo Russo for technical assistance and Dr. Livio Luongo (Second University of Naples–Italy) for critical discussions. This work was supported by a Grant PRIN from Ministry of Education, Universities and Research (MIUR), Italy, to A.C. and the Wellcome Trust (WT098012) to L.K.H. and BBSRC (BB/K001418/1) to L.K.H. and G.D’A. G.D’A. received partial supports from a “FORGIARE” post-doctoral fellowship cofounded by the Polo delle Scienze e Tecnologie per la Vita, University of Naples Federico II and Compagnia di San Paolo Foundation, Turin, Italy (2010–2012).Peer reviewedPublisher PD