Vacancy defects induced in the track region of 132 MeV C irradiated SiC

Positron annihilation lifetime spectroscopy (PALS) and electron paramagnetic resonance (EPR) have been used in this work to investigate vacancy defects induced in the track region of 132 MeV ¹²C irradiated silicon carbide. Irradiations have been performed at room temperature at a fluence of 2.5 × 10¹⁴ cm⁻² in N-low doped 6H–SiC and 3C–SiC monocrystals. Silicon monovacancies have been detected in both polytypes using EPR. Their charge state and concentration have been determined in the track and cascade region of the C⁺ ions. PALS measurements performed as a function of temperature have shown the presence of V_Si–C divacancies in the track region for both polytypes.     

Pulsed Laser Deposition of Zr1-xCexO2 and Ce1-xLaxO2-x/2 for Buffer Layers and Insulating Barrier in Oxide Heterostructures

We have studied the pulsed laser deposition (PLD) of Zr_1-xCexO₂ and Ce_1-xLa_xO₂-x/2 initially to grow buffer layers for perovskite films deposited on Si, LaAlO₃, SrTiO₃ and MgO and then to produce tunneling barriers for cuprate or manganite heterostructures. On (1 0 0) Si, the deposition of Zr_1-xCexO₂ (x = 0.12) produces a smooth epitaxial layer (R _RMS = 0.25/1m²), which allows the further deposition of high quality YBa₂Cu₃O₇ (Tc 88 K) and La_0.7Sr_0.3MnO₃ films. On the other hand, the use of Ce_1-xLa_xO_2-x/2 (0 x 0.4) makes it possible to match the YBa₂Cu₃O₇ and La_0.7Sr_0.3MnO₃ layers to various substrates. The buffer layers are epitaxially grown with a 45° rotation of the in-plane axes with respect to those of the substrate, and the smoothness is high (R _RMS = 0.25/1m²). In the case of an ultra-thin barrier (2.5 nm) of Ce_1-xLa_xO_2-x/2 sandwiched in a La_0.7Sr_0.3MnO₃, the out-of-plane mismatch of 2 induces distortions at the interface steps, which propagate into the topmost La_0.7Sr_0.3MnO₃ layer. This is in contrast to the case of SrTiO₃ barriers where an ideal crystal continuity in the growth direction is observed.     

High-Quality Adaptive Soft Shadow Mapping

The recent soft shadow mapping technique [ [GBP06] ] allows the rendering in real-time of convincing soft shadows on complex and dynamic scenes using a single shadow map. While attractive, this method suffers from shadow overestimation and becomes both expensive and approximate when dealing with large penumbrae. This paper proposes new solutions removing these limitations and hence providing an efficient and practical technique for soft shadow generation. First, we propose a new visibility computation procedure based on the detection of occluder contours, that is more accurate and faster while reducing aliasing. Secondly, we present a shadow map multi-resolution strategy keeping the computation complexity almost independent on the light size while maintaining high-quality rendering. Finally, we propose a view-dependent adaptive strategy, that automatically reduces the screen resolution in the region of large penumbrae, thus allowing us to keep very high frame rates in any situation.     

Al0.3Ga0.7As-GaAs microwave resonant tunneling oscillator

We describe the design of a microwave oscillator using resonant tunneling diodes. The devices are fabricated from Al_0.3Ga_0.7As-GaAs double barrier hetero-structures grown by molecular beam epitaxy. Design criteria improving current drivability are established from a theoretical study of tunneling transmission probabilities. Very high peak current densities up to 3.10⁴ A/cm², favorable for high frequency operation as an oscillator, have been achieved experimentally. The devices exhibit stable oscillations at liquid nitrogen temperature and at room temperature when the tunnel diode oscillator is constructed with a stabilizing network.     

Towards a better assessment of the ecological status of coastal waters using satellite-derived chlorophyll-a concentrations

The application of the new Water Framework Directive (WFD) of the European Union will require a dense and frequent monitoring of chlorophyll-a near the coast. Not counting the transitional water bodies located in the vicinity of estuaries, not less than seventy four coastal water bodies have to be monitored along the coast of the French Atlantic continental shelf and the English Channel. All the available data have to be gathered to implement a comprehensive monitoring scheme. To this purpose, we evaluate the capacity of ocean colour imagery to complete the conventional in situ data set collected in coastal networks. Satellite-derived chlorophyll-a concentration is obtained by the application of a coastal Look-Up-Table to water-leaving radiance of the Sea-viewing Wide Field Instrument Sensor (SeaWiFS) for the 1998–2004 period. Seven years of satellite-derived and in situ chlorophyll-a concentrations are compared at seven representative stations of different water bodies. These comparisons show that the satellite products are reliable in most of the situations studied and throughout the seasons. Then the satellite imagery is used to classify the coastal waters following the eutrophication risk criterion of the WFD. This classification is made according to the percentile-90 of chlorophyll-a calculated during the productive season, from March to October. Despite a lack of sensor coverage over a small fraction of the near shore waters, this work shows that the satellite monitoring can considerably ease the application of the WFD.     

Progress on large area n‐type silicon solar cells with front laser doping and a rear emitter

We report on the progress of imec's n‐type passivated emitter, rear totally diffused rear junction silicon solar cells. Selective laser doping has been introduced in the flow, allowing the implementation of a shallow diffused front surface field and a reduction of the recombination current in the contact area. Simplifications have been implemented towards a more industrial annealing sequence, by replacing expensive forming gas annealing steps with a belt furnace annealing. By applying these improvements, together with an advanced texturing process and emitter passivation by atomic layer deposition of Al₂O₃, 22.5% efficient cells (three busbars) have been realized on commercial 156 · 156 mm² Czochralski‐Si. This result has been independently confirmed by ISE CalLab. Copyright © 2016 John Wiley & Sons, Ltd.     

Invasion percolation with inlet multiple injections and the water management problem in proton exchange membrane fuel cells

Liquid water transport in the diffusion porous layers of polymer electrolyte membrane fuel cells (PEMFC) is analyzed as a process of quasi-static invasion from multiple interfacial injection sources. From pore network simulations based on a new version of the invasion percolation algorithm it is shown that a porous layer acts as a two-phase filter: the number of breakthrough points is significantly lower that the number of injection points owing to the merging of liquid paths within the porous layer. The number of breakthrough points at the gas diffusion layer/gas channel interface obtained with this model is consistent with the available experimental observations.     

Can transplantation of neurons facilitate motor recovery in paraplegics? Study of an animal model

This review strives forward at least two goals. First, to take from the literature the arguments demonstrating that hindlimbs locomotion is controlled by a spinal network of neurons (the so-called Central Pattern Generator for locomotion--CPG) known to be able to generate locomotor activity independently of the control of supraspinal nervous structures, as it is after thoracic lesions of the spinal cord. The principles of work of the CPG and its intrinsic possibilities to adapt its working are reviewed. Special reference is made to the various ways used during experiments to activate the CPG in spinal animals or clinical practice in paraplegic men: training to walk, electrical stimulations, pharmacological stimulations. Second, to show, from our own results, obtained from the study of an animal model of paraplegia, the adult spinal rat, how it could be possible to take advantage of the autonomy of the CPG, with special reference to its sensibility to monoamines, to obtain locomotor recovery in hindlimbs after section of the thoracic spinal cord, by means of transplantation of noradrenergic and/or serotonergic embryonic neurons in the lumbo-sacral spinal cord. Section of the spinal cord at a thoracic level results in an important locomotor deficit in hindlimbs, likely linked to degeneration of monoaminergic terminals in the lumbar enlargement. In the adult spinal rat, sub-lesional injection of a suspension of embryonic nervous cells, taken from either locus coeruleus or raphe sites, leads to reinnervation of the lumbar enlargement with monoaminergic terminals. Despite the fact that connections with supraspinal structures are not reestablished, transplanted animals recover progressively a posture convenient for locomotion. The hindlimbs, which are in an extended position a few days after the lesion, become progressively flexed and able to support the body weight. This evolution does not appear in spinal but non transplanted animals. But, the main point is that transplanted animals develop, within the few weeks that follow transplantation, a good-quality locomotor activity in hindlimbs which had no equivalent in spinal but non transplanted animals. The reality of a lumbar CPG for locomotion and the efficacy of pharmacological treatments and training to walk, to elicit recovery of stepping, are discussed in man, in connection with the relevance to use transplantation of monoaminergic nervous cells in the spinal cord of paraplegics.