Two applications of a numerical approach of heat transfer process within rock beds

A general method for solving the differential equations describing the heat transfer process within a rock bed is presented. A numerical model accounting for secondary phenomena such as thermal losses and conduction effect is developed. The results of the study are presented in the form of curves and empirical equations. Two applications of this theoretical model are then investigated. One is the elaboration of a new calculation method for the volumetric convective heat transfer coefficient using the compared results of theoretical modeling and experimental tests. The second application is a design method for solar applications of rock-bed storage with determination of optimal values for parameters such as air velocity, particle diameter and geometrical aspects of the storage unit.     

Fatigue crack initiation and propagation in austenitic stainless steels for light water reactors

The determination of fatigue life of components containing defects usually takes into account crack propagation only. In a real situation, a number of cycles are often required to reach fatigue crack initiation and predictive evaluation of fatigue crack initiation phases of real defects in austenitic stainless steel welded joints are presented. Fatigue crack growth rates in wrought and cast austenitic stainless steels and associated welds are also presented. Effects of various mechanical parameters (R ratio and variable amplitude loading) of a PWR environment and of metallurgical factors (δ ferrite content and ageing in cast austenitic stainless steels) are discussed.     

Microstructure and Nanoscale Piezoelectric/Ferroelectric Properties in La2Ti2O7 Thin Films Grown on (110)‐Oriented Doped Nb:SrTiO3 Substrates

(00l)‐Oriented La₂Ti₂O₇ (LTO) thin films with monoclinic perovskite‐layer structure [a = 7.806(2) Å, b = 5.552(3) Å, c = 13.015(5) Å, β = 98.62(2)°] have been grown by a sol–gel route on conducting (110)‐oriented doped Nb:SrTiO₃ (STO) substrates. The narrow rocking curves (0.24° width for 004_LTO peak) demonstrate the sharp mosaïcity of the films. Using high‐resolution X‐ray diffraction (HR‐XRD), epitaxial relationships between the LTO, and the STO substrate are given. In addition, HR‐XRD evidences the existence of (212)‐oriented crystallites 1.5° disoriented with respect to the plane of the substrate. We confirm, by DFT calculations, that the polarization vector lies in the b‐axis of the LTO cell and consequently, the existence of these (212)‐oriented crystallites enables to explain the origin of the various contrasts observed both on the in‐plane and out‐of‐plane images when collected by piezoresponse force microscopy. Finally, both successful poling experiments performed via the tip of atomic force microscope and the existence of local piezoloops within the domains, unambiguously confirm the ferroelectric state of the films at the nanoscale level. Once again, this study demonstrates that a clear understanding of nanoscale piezoelectric/ferroelectric phenomena in oriented thin films passes through a carefully structural analysis as performed by HR‐XRD.     

Toughening of epoxy matrices with reduced single-walled carbon nanotubes

Reduced single-walled carbon nanotubes (r-SWCNT) are shown to react readily at room temperature under inert atmosphere conditions with epoxide moieties, such as those in triglycidyl p-amino phenol (TGAP), to produce a soft covalently bonded interface around the SWCNT. The soft interface is compatible with the SWCNT-free cross-linked cured matrix and acts as a toughener for the composite. Incorporation of 0.2 wt % r-SWCNT enhances the ultimate tensile strength, toughness and fracture toughness by 32, 118, and 40%, respectively, without change in modulus. A toughening rate (dK(IC)/dwt(f)) of 200 MPa m(0.5) is obtained. The toughening mechanism is elucidated through dynamic mechanical analyses, Raman spectroscopy and imaging, and stress-strain curve analyses. The method is scalable and applicable to epoxy resins and systems used commercially.     

Reproducing the experimental pull-out and shear strength of clinched sheet metal connections using FEA

Clinching, commonly referred to as press-joining, is a mechanical joining technique which involves severe local plastic deformation of two or more sheet metal parts resulting in a permanent mechanical interlock or joint. This interlock is achieved by using simple tools like a die, a punch and a blank holder. Since no additional elements are used, the strength of the clinched connection is entirely determined by the clinch geometry, and, consequently, by the geometry of die and punch. As a result, for each combination of material and sheet thickness an optimal geometry of the tools can be derived. This can be done either through extensive experimental testing or, more cost-effectively, with the aid of numerical simulations. However, for these results to be useful they have to be able to reproduce the experimental strength of the connection. In this paper we investigate the possibility of predicting the shear and pull-out strength of a clinched sheet metal assembly using FEA. Numerical difficulties associated with these simulations and the preceding forming operation are discussed. A comparison between experimental data and simulation is provided.     

State of the art of high temperature power electronics

High temperature power electronics has become possible with the recent availability of silicon carbide devices. This material, as other wide-bandgap semiconductors, can operate at temperatures above 500 °C, whereas silicon is limited to 150-200 °C. Applications such as transportation or a deep oil and gas wells drilling can benefit. A few converters operating above 200 °C have been demonstrated, but work is still ongoing to design and build a power system able to operate in harsh environment (high temperature and deep thermal cycling).     

Junction fabrication by shadow evaporation without a suspended bridge

We present a novel shadow evaporation technique for the realization of junctions and capacitors. The design by e-beam lithography of strongly asymmetric undercuts on a bilayer resist enables in situ fabrication of junctions and capacitors without the use of the well-known suspended bridge (Dolan 1977 Appl. Phys. Lett. 31 337-9). The absence of bridges increases the mechanical robustness of the resist mask as well as the accessible range of the junction size, from 10(-2) μm(2) to more than 10(4) μm(2). We have fabricated Al/AlO(x)/Al Josephson junctions, phase qubit and capacitors using a 100 kV e-beam writer. Although this high voltage enables a precise control of the undercut, implementation using a conventional 20 kV e-beam is also discussed. The phase qubit coherence times, extracted from spectroscopy resonance width, Rabi and Ramsey oscillation decays and energy relaxation measurements, are longer than the ones obtained in our previous samples realized by standard techniques. These results demonstrate the high quality of the junction obtained by this bridge-free technique.     

Sources of self-efficacy: An investigation of elementary school students in France.

The purpose of this study was to assess the influence of Bandura's (1997) theorized sources of self-efficacy on the academic and self-regulatory efficacy beliefs of 3rd-grade elementary school students (N = 395) in France, to examine whether classroom context might explain a significant portion of the variation in self-efficacy, and to assess whether these sources differ as a function of sex. Hierarchical linear modeling revealed that mastery experience, social persuasions, and mean classroom-level self-efficacy predicted mathematics self-efficacy. Mastery experience, social persuasions, physiological state, and mean classroom-level self-efficacy predicted French self-efficacy. All 4 sources predicted self-efficacy for self-regulated learning in both subjects, with the exception of vicarious experience in French. Classroom-level variables did not predict self-efficacy for self-regulated learning in either subject. Boys outperformed girls in mathematics and reported higher mathematics self-efficacy, self-regulatory efficacy, mastery experience, social persuasions, and lower physiological arousal. In French, girls outperformed boys but reported lower self-efficacy. Findings support and refine the theoretical tenets of Bandura's social cognitive theory. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Determination of pre-impact occupant postures and analysis of consequences on injury outcome--part II: biomechanical study

This paper considers pre-impact vehicle maneuvers and analyzes the resulting driver motion from their comfort seating position. Part I of this work consisted of analyzing the driver behavior during a simulated crash in a car driving simulator. The configuration of the virtual accident led to an unavoidable frontal crash with a truck. The typical response to this type of emergency event was to brace rearward into the seat and to straighten the arms against the steering wheel, or, to swerve to attempt to avoid the impacting vehicle. In a turn crossover maneuvers, the forearm is directly positioned on the airbag module at time of crash. This position represents a potential injurious situation and is investigated in this Part II.Static airbag-deployment tests were realized in collaboration with Zodiac using conventional airbag (sewn cushion, pyrotechnical system and open event) and a Hybrid III 50th Male Dummy seated with the left arm positioned in the path of the deploying airbag. These experiments were numerically reproduced with Madymo^® and the ellipsoid Hybrid III dummy model. The dummy arm interaction with airbag was correlated with experiments. Then, a numerical simulation of a frontal collision at 56 km/h was realized. The results of the computational runs put forward injurious situations when the driver's arm was in front of the steering wheel. Indeed, in this case, the arm could hit the head under airbag deployment and induced serious neck bending and violent head launching.To mitigate head and neck trauma in this out-of-position situation, an airbag prototype (bonded cushion, two pure helium cold gas generators allowing mono- or multi-stage inflating, patented silicone membrane) was proposed by Zodiac. The results of static airbag-deployment tests with conventional and prototype airbags showed a significant reduction of the maximum linear head acceleration and neck bending with airbag prototype when a dual stage inflating was ignited, due to a reduced ‘flinging’ of the arm.     

Experimental evaluation of solar thermosyphons with heat exchangers

The advantages of solar thermosyphons in terms of simplicity, reliability and cost have long been recognized. Recent studies have also shown their thermal performance to be comparable with that of equivalent active systems. When pump power is considered, the energy savings of domestic hot water thermosyphons can be significantly superior to active systems. In spite of these advantages, use of solar thermosyphons in the United States is almost negligible compared to their widespread use in other countries. A major limitation to the use of thermosyphons in the United States is lack of effective, reliable freeze protection. One technique for reliable, passive freeze protection is to use a heat exchanger in the storage tank and a nonfreezing fluid in the collector. Previous analytical work indicates that the performance penalty for these systems with practical-sized heat exchangers may be small enough to make these systems economically feasible. A full-scale, residential-size test facility has been constructed for testing this concept and validating the theoretical models. This paper describes results of testing comparing the performance of a horizontal tank with and without heat exchanger to a baseline case of a vertical tank without heat exchanger. An analytical expression for a “heat exchanger penalty factor” for these systems is derived and compared with the experimental results.