Conversion of amorphous TiO2 coatings into their crystalline form using a novel microwave plasma treatment

Crystalline titanium dioxide (TiO₂) coatings have been widely used in photo-electrochemical solar cell applications. In this study, TiO₂ and carbon-doped TiO₂ coatings were deposited onto unheated titanium and silicon wafer substrates using a DC closed-field magnetron sputtering system. The resultant coatings had an amorphous structure and a post-deposition heat treatment is required to convert this amorphous structure into the photoactive crystalline phase(s) of TiO₂. This study investigates the use of a microwave plasma heat treatment as a means of achieving this crystalline conversion. The treatment involved placing the sputtered coatings into a 2.45 GHz microwave-induced nitrogen plasma where they were heated to approximately 550 °C. It was observed that for treatment times as short as 1 min, the 0.25-μm thick coatings were converted into the anatase crystalline phase of TiO₂. The coatings were further transformed into the rutile crystalline phase after treatments at higher temperatures. The doping of TiO₂ with carbon was found to result in a reduction in this phase transformation temperature, with higher level of doping (up to 5.8% in this study) leading to lower anatase-to-rutile transition temperature. The photoactivity performance of both doped and un-doped coatings heat-treated using both furnace and microwave plasma was compared. The carbon-doped TiO₂ exhibited a 29% increase in photocurrent density compared to that observed for the un-doped coating. Comparing carbon-doped coatings heat-treated using the furnace and microwave plasma, it was observed that the latter yielded a 19% increase in photocurrent density. This enhanced performance may be correlated to the differences in the coatings' surface morphology and band gap energy, both of which influence the coatings' photoabsorption efficiency.     

Supervisory fault‐tolerant control with mutual performance optimization

The problem of active fault‐tolerant control with reconfiguration mechanism for uncertain linear systems with external disturbances is addressed applying the supervisory control approach. A key feature of the proposed approach is establishment of a set of conditions providing mutual performance in the sense of taking into account the interaction of the fault detection, isolation, and accommodation subsystems in order to achieve global fault‐tolerance performance with guaranteed global stability. The efficiency of the approach is demonstrated in an example of computer simulation for a flight system benchmark. Copyright © 2012 John Wiley & Sons, Ltd.     

Using Superconducting Magnet to Reproduce Quick Variations of Gravity in Liquid Oxygen

A ground based facility (OLGA), providing magnetic compensation of gravity in oxygen, has been developed. A 2-T superconducting magnetic solenoid is used to create the required magnetic field. A novel electrical supply permits to quickly vary the magnetic field, leading to rapid variation of the acceleration forces applied to oxygen. These variations can be made from overcompensation of gravity (−0.5g) to zero gravity or from zero gravity to reduced gravity (0.4g) with a time constant of 340 ms. This time is typical of the cutoff or reignition of spacecraft engines. Preliminary results on the transient flows induced by these acceleration variations in a reservoir filled with liquid and gaseous oxygen are presented.     

Linking Contradictions and Laws of Engineering System Evolution within the TRIZ Framework

Tools and methods developed during the era of quality and optimization have shown their limitations and become inappropriate in the context of the requirements of innovation. Nowadays the need to rebuild design practices in enterprises is strongly felt both in terms of human skills and methodological expertise. In part, a way to face the innovation era's difficulties has been provided through the theory of inventive problem solving. This theory represents a significant breakthrough in driving problem statement and solving in a direction that is expressed through the idea that technical systems are driven by objective laws. A second postulate concerns the notion of contradiction, but so far only few contributions have addressed the relations between laws and contradictions. This paper, through a qualitative approach, presents a solution to this limitation and proposes a possible use of laws within the choice of the appropriate conflicting pair, prior to the use of any TRIZ solving techniques. Tests to observe the impact of the proposed approach were conducted in a French engineering ‘grande école’ during three semesters with 180 engineers. The contribution of this paper is twofold. On the one hand, there is a theoretical contribution to the theory of inventive problem solving. In addition, the proposed method offers especially TRIZ practitioners new ways for problem understanding and problem formulation.     

Processing radio frequency ultrasound images: a robust method for local spectral features estimation by a spatially constrained parametric approach

Spectral estimation is a major component in studies aiming at characterizing biological tissues through the analysis of backscattered radio frequency (RF) ultrasonic signals and images. However, conventional spectral estimation techniques yield a well-known trade-off between spatial resolution and variance. The backscattered signals are stochastic by nature, so short-term local analysis results in a high variance of the estimates, which cannot efficiently be reduced through conventional spatial averaging. We address this issue by describing a spectral estimation technique that reduces the variance of the estimates (by smoothing the local estimates in spectrally homogeneous regions) while preserving spectral discontinuities (i.e., the smoothing is not performed across regions with different spectral contents). The proposed approach is set in a Bayesian framework and is based on local autoregressive (AR) estimation, constrained by smoothness priors. These smoothness priors are introduced through a Markov random field in which the associated potential functions are nonquadratic, allowing thereby to preserve discontinuity. The method is validated on simulated RF images and tested on echocardiographic images acquired in vivo. The results are compared to the estimates provided by the conventional Burg technique. These results clearly demonstrate the ability of the proposed approach to improve spectral estimation in terms of variance reduction and discontinuity detection.     

The three-dimensional model of Dictyostelium discoideum racE based on the human rhoA-GDP crystal structure

The three-dimensional structure of racE was modeled using several homologous small G proteins, and the best model obtained using the human rhoA as modeling template is reported. The three-dimensional fold of the racE model is remarkably similar to the cellular form of human ras p21 crystal structure. Its secondary structure consists of six alpha-helices, six beta-strands and three 3(10) helices. The model retains its secondary structure after a 300 K, 300 ps molecular dynamics (MD) simulation. Important domains of the protein include its effector loop (residues 34-46), the insertion domain (residues 121-136), and the polybasic motif (between 210 and 220) not modeled in the current structure. The effector loop is inherently flexible and the structure docked with GDP exhibits the effector loop moving significantly closer to the nucleotide binding pocket, forming a tighter complex with the bound GDP. The mobility of the effector loop is conferred by a single residue 'hinge' point at residue 34Asp, also allowing the Switch I region, immediately preceding the effector loop, to be equally mobile. In comparison, the Switch II region shows average mobility. The insertion domain is highly flexible, with the insertion taking the form of a helical domain, with several charged residues forming a complex charged interface over the entire insertion region. While the GDP moiety is loosely held in the active site, the metal cation is extensively co-ordinated. The critical residue 38Thr exhibits high mobility, and is seen interacting directly with the metal ion at a distance of 2.64 A, and indirectly via an intervening water molecule. 64Gln, a key residue involved in GTP hydrolysis in ras, is seen facing the beta-phosphate group and the metal ion. Certain residues (i.e. 51Asn, 38Thr and 65Glu) exhibit unique characteristics and these residues, together with 158Val, may play important roles in the maintenance of the protein's integrity and function. There is strong consensus of secondary structural elements between models generated using various templates, such as h-rac1, h-rhoA and h-cdc42 bound to RhoGDI, all sharing only 50-55% sequence identity with racE, which suggests that this model is in all probability an accurate prediction of the true tertiary structure of racE.