Caging dynamics in a granular fluid

We report an experimental investigation of the caging motion in a uniformly heated granular fluid, for a wide range of filling fractions, $\phi$. At low $\phi$ the classic diffusive behavior of a fluid is observed. However, as $\phi$ is increased, temporary cages develop and particles become increasingly trapped by their neighbors. We statistically analyze particle trajectories and observe a number of robust features typically associated with dense molecular liquids and colloids. Even though our monodisperse and quasi-2D system is known to not exhibit a glass transition, we still observe many of the precursors usually associated with glassy dynamics. We speculate that this is due to a process of structural arrest provided, in our case, by the presence of crystallization.Comment: 4 pages, 5 figures, submitted to Phys. Rev. Let

Simulations of Time-Resolved X-Ray Diffraction in Laue Geometry

A method of computer simulation of Time-Resolved X-ray Diffraction (TRXD) in asymmetric Laue (transmission) geometry with an arbitrary propagating strain perpendicular to the crystal surface is presented. We present two case studies for possible strain generation by short-pulse laser irradiation: (i) a thermoelastic-like analytic model; (ii) a numerical model including effects of electron-hole diffusion, Auger recombination, deformation potential and thermal diffusion. A comparison with recent experimental results is also presented.Comment: 9 pages, 11 figure

Rotação de culturas. XXIII. Efeitos das culturas de inverno sobre o rendimento de grãos e sobre algumas características agronômicas de plantas de soja, num período de nove anos.

bitstream/item/133654/1/ID12354-1988-1989sojaresultados-p88-99.pdfTrabalho apresentado na XVII Reunião de Pesquisa de Soja da Região Sul, Porto Alegre, 1989

Advanced mimetic materials for meniscus tissue engineering : targeting segmental vascularization

Meniscus lesions are among the most common orthopaedic injuries which can ultimately lead to degeneration of the knee articular cartilage. The human meniscus has a limited healing potential, partly due to a poor vasculature, and thus meniscus regeneration using tissue engineering strategies has recently been investigated as a promising alternative to total/partial meniscectomy [1]. Advanced scaffolds for tissue engineering of meniscus should be able to mimic and preserve the asymmetric vascular network of this complex tissue, i.e. enable controlling the segmental vascularization during the regeneration process. Novel scaffolds were produced combining a silk polymeric matrix (12 wt%) [2] and the methacrylated gellan gum hydrogel (iGG-MA), which has been shown to be able to prevent the ingrowth of endothelial cells and blood vessels into the hydrogels [3,4]. The angiogenic/ anti-angiogenic potential of acellular and cell-laden silk-12 scaffolds combined with iGG-MA hydrogel was investigated in vivo, using the chick embryo chorioallantoic membrane (CAM) assay. For producing the cell-laden scaffolds, human meniscus cells (HMC¢s) were isolated from morphologically intact human menisci using an enzymatic-based digestion and expanded using standard culture conditions. The HMC’sladen hydrogel/silk scaffolds were produced by encapsulating the HMC’s into a 2 wt% GG-MA hydrogel, followed by impregnation onto the 12 wt% silk scaffold and ionic-crosslinking in a saline solution. A CAM assay was used to investigate the control of segmental vascularization of the acellular and HMC¢s-laden hydrogel/silk scaffolds by the effect of GG-MA hydrogel, until day 14 of embryonic development. The in vivo study allowed investigating the number of macroscopic blood vessels converging to the implants. The evaluation of possible inflammation and endothelial cells ingrowths was performed by histological (haematoxylin and eosin - H&E - staining) and immunohistochemical methods (SNA-lectin staining). When the silk-12 scaffold was combined with the hydrogel, an inhibitory effect was observed as demonstrated by the low number of convergent blood vessels. Results have shown that iGG-MA hydrogel prevented the endothelial cells adhesion and blood vessels infiltration into the HMC’s hydrogel/silk scaffolds, after 4 days of implantation. This study showed that the hydrogel/silk scaffolds enabled controlling the segmental vascularization, thus it can possibly mimic the native vasculature architecture during meniscus regeneration

FUZZY LOGIC CONTROL APPLIED TO A PHOTOVOLTAIC SYSTEM CONNECTED TO CITY NETWORK FOR RESIDENTIAL USE

A simplified topology using power electronics and fuzzy logic control techniques for developing a photovoltaic generation system, at a low cost, to be used in residential systems, connected to the local distribution grid is herein proposed. A technique for determining maximum power points on photovoltaic panels, in order to transfer the powerful generated to the load, is studied, so to impart a minimum energy loss in the whole system. In the fuzzy logic controller development the relevant functions to the input and output photovoltaic system variables and the rules to be used in this controller is established and obtained from other photovoltaic systems, adapted to the system. Simulation results are obtained always focusing maximum power search by a fuzzy logic controller, through intelligent changes into control variables that will carry the work cycle of increasing converter and the inverter bridge. It is shown that while exists solar radiation variation and low voltage available on photovoltaic module, the increasing converter will supply necessary voltage to the inverter bridge operation

A damage parameter for HCF and VHCF based on hysteretic damping

The fatigue limit of materials, due to the improvement of fatigue life of structures and mechanical components should be extended from the traditional 106–107 cycles up to 109 and more, but with traditional testing hardware this is a difficult technical task due to the length of time needed for the completion of tests. Ultrasonic fatigue testing machines seem to be adequate for very high cycle fatigue (VHCF) tests. We propose here to evaluate the behavior of the hysteretic damping in an attempt to associate that with damage parameter. The approach here presented is based on the fact that the fatigue issue can be understood in terms of the energy available for irreversible process triggering. This nonconservative energy will be involved in micro-structural changes in the material before being dissipated as thermal energy. In fact, the balance between the energy supplied to and returned by the material is positive and the hysteretic damping factor represents the inelastic fraction of energy in each cycle. Aiming at building a model to correlate the hysteretic cycle parameters and the fatigue process, both energy loss and material response of the specimens are measured during the fatigue test. The fatigue tests are carried out with an ultrasonic machine test, operated at 20 kHz with amplitude or temperature control, under HCF and VHCF for copper specimens. The results show the behavior of hysteretic damping parameter during fatigue life, the equivalent dissipated energy per cycle and a good correlation between the hysteretic damping factor parameter and the fatigue process S–N curve, suggesting that factor as a promising fatigue life parameter useful for some cases of fatigue life prediction.info:eu-repo/semantics/publishedVersio