An efficient ABAQUS solid shell element implementation for low velocity impact analysis of FGM plates

The main objective of this paper is to develop a numerical model susceptible to solve the numerical locking problems that may appear when applying the conventional solid and shell finite elements of ABAQUS. This model is based on a hexahedral solid shell element. The formulation of this element relays on the combination of the enhanced assumed strain (EAS) and assumed natural strain (ANS) methods with modified First Shear Deformation Theory (FSDT). The developed element is implemented into the ABAQUS user element (UEL) interface. The performance of this element is demonstrated by different benchmark tests from the literature. Our contribution consists on applying a single solid shell element through the thickness direction to predict the low velocity impact behavior on functionally graded material (FGM) circular plates.

     

The Role of Nuclear Power in Reducing Risk of the Fossil Fuel Prices and Diversity of Electricity Generation in Tunisia: A Portfolio Approach

This paper applies real options and mean–variance portfolio theories to analyze the electricity generation planning into presence of nuclear power plant for the Tunisian case. First, we analyze the choice between fossil fuel and nuclear production. A dynamic model is presented to illustrate the impact of fossil fuel cost uncertainty on the optimal timing to switch from gas to nuclear. Next, we use the portfolio theory to manage risk of the electricity generation portfolio and to determine the optimal fuel mix with the nuclear alternative. Based on portfolio theory, the results show that there is other optimal mix than the mix fixed for the Tunisian mix for the horizon 2010–2020, with lower cost for the same risk degree. In the presence of nuclear technology, we found that the optimal generating portfolio must include 13% of nuclear power technology share.     

The Signaling Role of CD40 Ligand in Platelet Biology and in Platelet Component Transfusion

The CD40 ligand (CD40L) is a transmembrane molecule of crucial interest in cell signaling in innate and adaptive immunity. It is expressed by a variety of cells, but mainly by activated T-lymphocytes and platelets. CD40L may be cleaved into a soluble form (sCD40L) that has a cytokine-like activity. Both forms bind to several receptors, including CD40. This interaction is necessary for the antigen specific immune response. Furthermore, CD40L and sCD40L are involved in inflammation and a panoply of immune related and vascular pathologies. Soluble CD40L is primarily produced by platelets after activation, degranulation and cleavage, which may present a problem for transfusion. Soluble CD40L is involved in adverse transfusion events including transfusion related acute lung injury (TRALI). Although platelet storage designed for transfusion occurs in sterile conditions, platelets are activated and release sCD40L without known agonists. Recently, proteomic studies identified signaling pathways activated in platelet concentrates. Soluble CD40L is a good candidate for platelet activation in an auto-amplification loop. In this review, we describe the immunomodulatory role of CD40L in physiological and pathological conditions. We will focus on the main signaling pathways activated by CD40L after binding to its different receptors.     

Influence of the velocity of Pt ablated species on the structural and electrocatalytic properties of Pt thin films

Platinum was deposited by pulsed laser deposition at different kinetic energy by varying the He background pressure in the deposition chamber. As a result, the porosity of the film varies from 5 to 86% as the He pressure is increased. This yields to an increase of the electrochemically active surface area and to an increased resistance to poisoning by CO, as evidenced by a 45 mV shift of the peak potential of the CO stripping peak towards less positive values. Similarly, the electrocatalytic activity of the films for the oxygen reduction reaction, as measured by the potential at half limiting diffusion current, is enhanced. However, a comparison between the intrinsic electrocatalytic activities of the films show that they have similar values (within a factor of 1.8) and do not significantly differ from that of a polycrystalline Pt disk, indicating that the increased activity for the ORR is mainly due to a geometric (electrochemically active surface area) effect.     

Value-at-risk estimations of energy commodities via long-memory,asymmetry and fat-tailed GARCH models

In this paper, we evaluate the value-at-risk (VaR) and the expected shortfalls for some major crude oil and gas commodities for both short and long trading positions. Classical VaR estimations as well as RiskMetrics and other extensions to cases considering for long-range memory, asymmetry and fat-tail in energy markets volatility were conducted. We computed the VaR for three ARCH/GARCH-type models including FIGARCH, FIAPARCH and HYGARCH. These models were estimated in the presence of three alternative innovation’s distributions: normal, Student and skewed Student. Our results show that considering for long-range memory, fat-tails and asymmetry performs better in predicting a one-day-ahead VaR for both short and long trading positions. Moreover, the FIAPARCH model outperforms the other models in the VaR’s prediction. These results present several potential implications for energy markets risk quantifications and hedging strategies.     

Low-loss CaxBa1−xNb2O6 ridge waveguide for electro-optic devices

Optical ridge waveguide using calcium barium niobate (CBN) on silicon substrate for the first time is designed, fabricated and characterized for future integrated electro-optic devices. To obtain single-mode propagation, the CBN thin strip is designed to be surrounded by thick silicon dioxide layer forming a ridge waveguide. Deposition of CBN film on profiled silicon dioxide introduces spatial separation which solves the CBN etching problem. Fabrication, edge polishing and near-field mode profile measurement of the waveguide are carried out. The measurement is in good agreement with the simulation and an exact loss as low as 2.15 dB/cm was obtained for the fabricated waveguide.     

Voltage and frequency dependent dielectric properties of BST-0.5 thin films on alumina substrates

Dielectric properties of Ba/sub 0.5/Sr/sub 0.5/TiO/sub 3/ (BST-0.5) polycrystalline thin films, deposited on alumina substrates by means of reactive pulsed laser deposition (PLD), were measured at GHz frequencies using an interdigital capacitor (IDC). By applying a voltage up to 40 V between the two groups of fingers at room temperature, a high tunability of /spl sim/27% was achieved at 5 GHz. A relative dielectric constant of /spl sim/500 (consistent with the low-frequency IDC measurements) has been obtained using coplanar waveguides by means of the through-reflect-line (TRL) analysis combined with either a conformal mapping model or a full wave calculation. The BST loss tangent was estimated as /spl sim/0.05 in the range 3-16 GHz.     

Experimental study of the influences substitution from Ni by Co,Al and Mn on the hydrogen storage properties of LaNi3.6Mn0.3Al0.4Co0.7 alloy

The hydrogen storage properties of LaNi_3.6Mn_0.3Al_0.4Co_0.7 alloy were improved by the addition of Co, Mn and Al. The phase compositions and crystal structures of this alloy were characterized via X-ray diffraction and Scanning Electron Microscopy. The gravimetric study showed that the average size of the particles was about 10 μm. The isotherms of reactions and the hydrogen absorption capacity were measured in the temperature range of 20–40 °C. Hence, the enthalpy (ΔH) and entropy (ΔS) were also calculated. The obtained experimental results showed that this compound can absorb and desorb hydrogen in a reversible way in normal operating conditions (temperature T = 20 °C and pressure P = 6 bar). The hydrogen sorption measurements revealed the effect of the partial substitution of Ni by Al, Mn and Co on the crystal structure of our compound. This substitution led to a significant reduction of hysteresis between hydriding and dehydriding. Thus, the substitution of Ni by these elements led to a larger size of interstitial voids and, therefore, the possibility of a higher number of hydrogen atoms in the cell.