Modelling and calculation of the current density distribution evolution at vertical gas-evolving electrodes

During industrial electrolysis, for hydrogen, dichloride or aluminium production, there is bubbles creation at one or two electrodes which imply a great hydrodynamic acceleration but also a quite important electrical field disturbance. This disturbance can lead to the modification of the local current density and to anode effects for example. There is few works concerning the local modelling of coupled electro active species transport and electrochemical processes in a biphasic electrolyte. There are also few local experimental measurements in term of chemical composition, temperature or current density which would allow the numerical calculations validation. Nevertheless, effects like the anode effect, particularly expensive on the point of the process efficiency, should need a better understanding. Nowadays, the respective roles of the local temperature increases, the electro active specie composition or the transport properties modification due to bubbles are not known.The goal of the present work is the modelling and the numerical simulation of the vertical electrode configuration for a biphasic electrolysis process. Bubbles presence is supposed to modify the electrical properties, and then the electro active species diffusive transport and the current density. Bubbles are also motion sources for the electrolysis cell flow, and then hydrodynamic properties are strongly coupled with species transport and electrical field. The present work shows hydrodynamic and electrical properties in a laboratory scale electrolysis cell with a vertical electrode. The numerical algorithm used was the finite volume used in the computational fluid dynamic software Fluent^®.     

Effect of Helium Elasticity on Torsional Oscillator Measurements

In 2004 Kim and Chan performed a torsional oscillator measurement of the rotational inertia of solid helium-4. They found frequency changes which were interpreted in terms of a non-classical rotational inertia, that is a partial superfluidity or ??supersolidity?? of solid helium-4. Since then there have been many further studies using various versions of this technique. One important question that arises in these experiments is the possible effect on the oscillator frequency of changes in the elasticity of the solid helium; this can produce a change in frequency that adds to any effect due to superfluidity. In this paper we give a general discussion of the effect of changes in elasticity on the oscillator frequency and consider how the magnitude of the effect is influenced by the oscillator design. Our results should help make it possible to discriminate between frequency changes due to changes in elasticity and changes due to supersolidity.     

Modelling the effect of carbon on deformation behaviour of twinning induced plasticity steels

In this article, a physical model describing the deformation behaviour of Twinning Induced Plasticity (TWIP) steels has been extended to include the effect of carbon content. The experimental validation and the analysis show that carbon mainly controls the maximum number of dislocations piled up at the twin boundary, resulting in the increase of back-stresses (i.e. kinematic hardening) and therefore the work hardening rate. This explanation seems to be in agreement with recent TEM observations.     

How the psychological theory of action identification can offer new advances for research in cognitive engineering

We present the psychological theory of action identification as a framework for a more in-depth understanding of a human operator's cognitive activity in the scope of cognitive engineering. A comparison of theoretical models and findings shows that both frameworks are founded on a similar theory of cognitive control based on an ontological viewpoint of means–ends relationships with the proposal that an individual mentally ‘navigates’ or ‘moves’ through a hierarchical arrangement of these relationships. However, whilst cognitive engineering begins the analysis from a viewpoint on affordances coming from the external work domain, the action identification theory starts from a viewpoint on action identities internally attributed to actions by individuals. We show that the conceptual articulation of these two approaches leads to confirming qualitative findings on an agent's cognitive activity and to proposing general cognitive principles that would explain a single agent's mental navigation through the abstraction hierarchy.     

Pulsed Electroplating: a Derivate Form of Electrodeposition for Improvement of (Bi1?xSbx)2Te3 Thin Films

Bismuth antimony telluride (Bi_1−x Sb _x )₂Te₃ thermoelectric compounds were synthesized by pulse plating. Due to the large number of parameters available (pulse waveform, on/off pulse time, applied current density), this advanced form of electrodeposition allows better control of the interfacial supply and electrochemical reactions and offers effective ways to improve macroscopic properties such as adhesion and to produce crack-free hard deposits and fine-grained films with higher uniformity and lower porosity. The influence of pulse parameters (pulse time t _on, cathodic current density J _c) on the stoichiometry, roughness, and crystallography of deposits was studied. The thermoelectric properties (electrical resistivity and Seebeck coefficient) of the films were measured. The results revealed that deposits have p-type conductivity directly after electroplating (Seebeck coefficient around 150 μV K⁻¹), in contrast to films synthesized by direct current, which require annealing. An improvement of resistivity was observed: for a direct-current-deposited film the resistivity is around 5000 μΩ m, whereas for a pulse-deposited film the resistivity was around 200 μΩ m.     

A comprehensive cardiac motion estimation framework using both untagged and 3-D tagged MR images based on nonrigid registration

In this paper, we present a novel technique based on nonrigid image registration for myocardial motion estimation using both untagged and 3-D tagged MR images. The novel aspect of our technique is its simultaneous usage of complementary information from both untagged and 3-D tagged MR images. To estimate the motion within the myocardium, we register a sequence of tagged and untagged MR images during the cardiac cycle to a set of reference tagged and untagged MR images at end-diastole. The similarity measure is spatially weighted to maximize the utility of information from both images. In addition, the proposed approach integrates a valve plane tracker and adaptive incompressibility into the framework. We have evaluated the proposed approach on 12 subjects. Our results show a clear improvement in terms of accuracy compared to approaches that use either 3-D tagged or untagged MR image information alone. The relative error compared to manually tracked landmarks is less than 15% throughout the cardiac cycle. Finally, we demonstrate the automatic analysis of cardiac function from the myocardial deformation fields.     

3D Ordering at the Liquid–Solid Polar Interface of Nanowires

The nature of the liquid–solid interface determines the characteristics of a variety of physical phenomena, including catalysis, electrochemistry, lubrication, and crystal growth. Most of the established models for crystal growth are based on macroscopic thermodynamics, neglecting the atomistic nature of the liquid–solid interface. Here, experimental observations and molecular dynamics simulations are employed to identify the 3D nature of an atomic-scale ordering of liquid Ga in contact with solid GaAs in a nanowire growth configuration. An interplay between the liquid ordering and the formation of a new bilayer is revealed, which, contrary to the established theories, suggests that the preference for a certain polarity and polytypism is influenced by the atomic structure of the interface. The conclusions of this work open new avenues for the understanding of crystal growth, as well as other processes and systems involving a liquid–solid interface.     

High-frequency homogenization for checkerboard structures: defect modes, ultrarefraction, and all-angle negative refraction

The counterintuitive properties of photonic crystals, such as all-angle negative refraction (AANR) [J. Mod. Opt.34, 1589 (1987)] and high-directivity via ultrarefraction [Phys. Rev. Lett.89, 213902 (2002)], as well as localized defect modes, are known to be associated with anomalous dispersion near the edge of stop bands. We explore the implications of an asymptotic approach to uncover the underlying structure behind these phenomena. Conventional homogenization is widely assumed to be ineffective for modeling photonic crystals as it is limited to low frequencies when the wavelength is long relative to the microstructural length scales. Here a recently developed high-frequency homogenization (HFH) theory [Proc. R. Soc. Lond. A466, 2341 (2010)] is used to generate effective partial differential equations on a macroscale, which have the microscale embedded within them through averaged quantities, for checkerboard media. For physical applications, ultrarefraction is well described by an equivalent homogeneous medium with an effective refractive index given by the HFH procedure, the decay behavior of localized defect modes is characterized completely, and frequencies at which AANR occurs are all determined analytically. We illustrate our findings numerically with a finite-size checkerboard using finite elements, and we emphasize that conventional effective medium theory cannot handle such high frequencies. Finally, we look at light confinement effects in finite-size checkerboards behaving as open resonators when the condition for AANR is met [J. Phys. Condens. Matter 15, 6345 (2003)].     

Increased Sulfur Precursors and Volatiles Production by the Leek <Emphasis Type="Italic">Allium porrum</Emphasis> in Response to Specialist Insect Attack

To defend themselves against herbivory, plants use a variety of direct and indirect strategies involving induced increases in secondary substances. Species of the Allium genus (Alliaceae), such as the leek Allium porrum (L.), produce nonprotein sulfur amino acids derived from cysteine, i.e., alk(en)yl-cysteine sulfoxides that are precursors of volatile thiosulfinates and disulfides. These defend most species including the specialist leek moth, Acrolepiopsis assectella. We determined by measuring the increase in the sulfur precursor propyl-cysteine sulfoxide (PCSO) if production of this precursor is induced in response to moth attack and mechanical wounding. The concentration of PCSO was determined by HPLC in 2- or 6-mo-old leeks after attacks of various intensity either by the specialist leek moth or by a generalist moth, Agrotis ipsilon. Injury-induced release of sulfur volatiles was measured by GC/MS after the attacks. Results showed an increase in the production of sulfur compounds in both the precursor and volatile form, occurring only in association with intensive attacks by leek moths. The increase in sulfur precursors also led to an increase in the release of sulfur volatiles. This induced response may provide an effective defense strategy against the plant’s main natural enemy, both directly and indirectly by attracting entomophagous insects.