Production of submicron SiC particles by d.c. thermal plasma: a systematic approach based on injection parameters

Aiming at producing high temperature structural ceramics, ultra-fine SiC powders were synthesized by the gas phase reaction of silicon tetrachloride with methane in a d.c. thermal plasma. The influence of parameters as the SiCl₄ feeding rate, C/Si and H₂/C molar ratios and internal pressure on the powder properties were investigated. The SiC powders were characterized by chemical analysis, Fourier transform infrared spectroscopy, X-ray diffraction and scanning electronic microscopy. The experimental set-up allows the production of β-SiC powders at a rate of 200 g h⁻¹ with particle size around 0.1 μm. The main impurities in the as-produced powder handled at ambient atmosphere are: oxygen (1.8–2.5%) and free carbon (3–4%). Interesting relationships were found between the SiCl₄ feeding rate and the H₂/C molar ratio and between the C/Si molar ratio and the internal pressure. The internal pressure plays a major role in controlling the particle size.     

Thickness control in structural optimization via a level set method

In the context of structural optimization via a level-set method we propose a framework to handle geometric constraints related to a notion of local thickness. The local thickness is calculated using the signed distance function to the shape. We formulate global constraints using integral functionals and compute their shape derivatives. We discuss different strategies and possible approximations to handle the geometric constraints. We implement our approach in two and three space dimensions for a model of linearized elasticity. As can be expected, the resulting optimized shapes are strongly dependent on the initial guesses and on the specific treatment of the constraints since, in particular, some topological changes may be prevented by those constraints.     

Second-order shape derivatives along normal trajectories,governed by Hamilton-Jacobi equations

In this paper we introduce a new variant of shape differentiation which is adapted to the deformation of shapes along their normal direction. This is typically the case in the level-set method for shape optimization where the shape evolves with a normal velocity. As all other variants of the original Hadamard method of shape differentiation, our approach yields the same first order derivative. However, the Hessian or second-order derivative is different and somehow simpler since only normal movements are allowed. The applications of this new Hessian formula are twofold. First, it leads to a novel extension method for the normal velocity, used in the Hamilton-Jacobi equation of front propagation. Second, as could be expected, it is at the basis of a Newton optimization algorithm which is conceptually simpler since no tangential displacements have to be considered. Numerical examples are given to illustrate the potentiality of these two applications. The key technical tool for our approach is the method of bicharacteristics for solving Hamilton-Jacobi equations. Our new idea is to differentiate the shape along these bicharacteristics (a system of two ordinary differential equations).     

Hypogastric arterial aneurysms associated with abdominal aortic aneurysms

The purpose of this study was to compare the physiological responses of professional and elite road cyclists during an incremental cycle ergometer test. Twenty-five elite cyclists (EC; 23+/-1 yr) and 25 professional cyclists (PC; 25+/-2yr) performed a ramp protocol (increases of 25 W x min(-1)) during which the following parameters were measured: oxygen consumption (VO2), pulmonary ventilation (VE), ventilatory equivalents for oxygen and carbon dioxide (VE x VO2(-1) and VE x VCO2(-1), respectively), respiratory exchange ratio (RER), ventilatory thresholds 1 and 2 (VT1 and VT2, respectively), blood lactate, and electromyographic activity (EMG) of the vastus lateralis. Significant differences existed between the two groups mainly at submaximal intensities, since both VT1 and VT2 occurred at a higher exercise intensity (p<0.001) in PC than in EC (VT2: 80.4+/-6.6 vs 87.0+/- 5.9% VO2max in EC and PC, respectively). Lactate levels showed a similar response in both groups at low-to-moderate intensities (< 300 W), and thereafter blood lactate was significantly higher in EC. Finally, the "electromyographic threshold" (EMGT) occurred at a significantly higher intensity (p < 0.05) in PC when compared to EC (64.7+/-14.2 vs 56.0+/-14.9% VO2max, respectively). It was concluded that, in comparison with EC, PC exhibit some remarkable physiological characteristics such as a high VT2, an important reliance on fat metabolism even at high power outputs, and several neuromuscular adaptations.     

Introducing a level-set based shape and topology optimization method for the wear of composite materials with geometric constraints

The wear of materials continues to be a limiting factor in the lifetime and performance of mechanical systems with sliding surfaces. As the demand for low wear materials grows so does the need for models and methods to systematically optimize tribological systems. Elastic foundation models offer a simplified framework to study the wear of multimaterial composites subject to abrasive sliding. Previously, the evolving wear profile has been shown to converge to a steady-state that is characterized by a time-independent elliptic equation. In this article, the steady-state formulation is generalized and integrated with shape optimization to improve the wear performance of bi-material composites. Both macroscopic structures and periodic material microstructures are considered. Several common tribological objectives for systems undergoing wear are identified and mathematically formalized with shape derivatives. These include (i) achieving a planar wear surface from multimaterial composites and (ii) minimizing the run-in volume of material lost before steady-state wear is achieved. A level-set based topology optimization algorithm that incorporates a novel constraint on the level-set function is presented. In particular, a new scheme is developed to update material interfaces; the scheme (i) conveniently enforces volume constraints at each iteration, (ii) controls the complexity of design features using perimeter penalization, and (iii) nucleates holes or inclusions with the topological gradient. The broad applicability of the proposed formulation for problems beyond wear is discussed, especially for problems where convenient control of the complexity of geometric features is desired.     

A prospective randomized comparison of epidural infusion of fentanyl and intravenous administration of morphine by patient-controlled analgesia after radical retropubic prostatectomy

In a prospective, randomized study, continuous infusion of epidural fentanyl citrate (group E) was compared with patient-controlled intravenously administered morphine sulfate (group P) for analgesia in 66 men after radical retropubic prostatectomy. Although both methods provided satisfactory analgesia, the mean comfort level scores were lower (that is, greater comfort) in group E than in group P at all observation times. The difference in mean resting comfort level scores between groups E and P was statistically significant (P < or = 0.05) at 9 of the 11 observation times. In addition, significant differences in comfort level scores were noted at 8 of the 11 observation times during deep breathing, 5 of 11 during coughing, and 3 of 9 during ambulation. Maximal and minimal comfort level scores recorded by each patient during the course of the study were significantly lower (that is, less pain) in group E than in group P for all four categories of activity. The percentage of patients who reported no pain was significantly higher in group E than in group P at 9 of 11 observation times during resting and 5 of 11 observation times during deep breathing. No significant differences were noted in side effect profiles or duration of hospital stay. In summary, when two effective methods of analgesia used after radical retropubic prostatectomy were compared prospectively, patients who received epidural infusion of fentanyl were more comfortable than those with patient-controlled intravenous administration of morphine, as evidenced by lower mean, maximal, and minimal comfort level scores and a greater proportion of patients with complete relief of pain.     

Afterload reduction in the management of postinfarction ventricular septal defect

The primary goal in the medical management of ventricular septal defect complicating myocardial infarction is to support cardiac function and control symptoms, if possible, for a period of 4 to 6 weeks. If the patient survives this period, surgical correction of the defect is technically easier and safer. In many cases, However, cardiac function is severly compromised, intractable biventricular failure develops,early operation is necessary and the likelihood of successful repair is diminished.     

Relative Efficiency of Selection Methods for Profit in Dairy Cows

Selection singly on milk yield and calculated profitability traits, selection indexes, and regression indexes were compared for the relative gains in expected profit to 72 mo of age or life time profit. Indexes consisted of five traits of the first lactation: milk, fat percent, days in milk, number of breedings, and age at first calving. The study was on 1806 Holstein cows sired by 404 bulls in 38 California herds. Genetic gain in total profit was 13 to 14% greater when selection was on estimated profit to 41 mo than on milk yield to 305 days in the first lactation. Selection on traits of estimated profit on three bases, to 305 days in first lactation, to end of first lactation, and to 41 mo of age was 2 to 14% more efficient for genetic gain in total profit than selection on corresponding traits of milk yield or selection indexes. Regression indexes were 3 to 19% more efficient than selection indexes for predicting subsequent cumulative profit. In contrast, selection indexes were 6 to 20% more efficient than regression indexes for genetic gain in total profit. Heritabilities for estimated profit and traits of milk yield in the first lactation ranged from .26 to .49 for cows with two or more calvings. Heritabilities for profit to end of first lactation and to 41 mo of age exceeded comparable milk yield traits by 15 to 27%. The economic value of a 1-mo decrease in age at first calving was equivalent to an increase of 138 kg milk yield to the end of the first lactation for gain in total profit to 72 mo of age. Similarly, the genetic effects, or relative selection value, of a 1-mo decrease in age at first calving is valued at approximately 471 kg milk.     

Physics-based modeling strategies for diagnostic and prognostic application in aerospace systems

This paper presents physics-based models as a key component of prognostic and diagnostic algorithms of health monitoring systems. While traditionally overlooked in condition-based maintenance strategies, these models potentially offer a robust alternative to experimental or other stochastic modeling data. Such a strategy is particularly useful in aerospace applications, presented in this paper in the context of a helicopter transmission model. A lumped parameter, finite element model of a widely used helicopter transmission is presented as well as methods of fault seeding and detection. Fault detection through diagnostic vibration parameters is illustrated through the simulation of a degraded rolling-element bearing supporting the transmission’s input shaft. Detection in the time domain and frequency domain is discussed. The simulation shows such modeling techniques to be useful tools in health monitoring analysis, particularly as sources of information for algorithms to compare with real-time or near real-time sensor data.     

Refractory Lining for Alumina Electrolytic Cells

This paper provides the specifications of a refractory lining for alumina electrolytic cells capable of ensuring good resistance to corrosion by the cell chemicals, while maintaining desirable thermal characteristics during service.
Several refractory materials were tested in the Alcan's standard electrolysis bath test. Also, using Alcan's standard procedures, different insulating refractory products were tested for their gain in thermal conductivity after compression.