The Effect of Thermal Shocks on the Stresses in a Sapphire Wafer

Sapphire wafers can experience temperature variations during processing in a furnace, which in turn can cause large deformation and stresses in the wafers. This paper aims to reveal the mechanism of stress development and evolution in sapphire wafers during thermal shocks, as well as the dependence of the stresses on some process parameters. Finite-element stress analysis was conducted on a single sapphire wafer subjected to thermal shocks. The results show that the thermal gradient in the radial direction induces high stresses even in mechanically unrestrained wafers. The largest stress components occur at the wafer edge as the largest normal stresses are circumferential; whereas the maximum tensile stress is realized upon cooling, the highest value of the maximum shear stress and the minimum compressive stress eventuate in the heating-up phase. The normal stresses have a parabolic distribution in the radial direction. It was found that holding the furnace temperature leads to a more uniform temperature distribution across the wafer but brings about higher tensile stresses in the cooling phase     

Left atrial appendage flow velocity and spontaneous echo contrast in patients with rheumatic mitral stenosis: a multiplane transesophageal echocardiographic study

BACKGROUND: Left atrial spontaneous echo contrast (LASEC), a putative marker of thrombo-embolic risk, is commonly located in the left atrial appendage (LAA). The aims of this work were to evaluate, using multiplane transesophageal echography, the echocardiographic determinants, specifically LAA outflow Doppler velocity, in the presence of SEC in patients with rheumatic MS. METHODS: Transthoracic and transesophageal echocardiographic tests were performed on 61 patients. The patients were divided into 3 groups based on the presence and type of valvular disease. Patients in group I (n = 28) presented with rheumatic mitral stenosis (MS). Patients in group II (n = 18) presented with valvular heart disease other than MS, and patients in group III (n = 15) had no history of valvular heart disease. The left atrium and appendage were examined for the presence of spontaneous echocontrast and thrombus, using multiplane echo scopy with transducer rotation. Minimal and maximal appendage areas were measured, on a computer-assisted bablet, by tracing a line from the top of the limbus of the left upper pulmonary vein to the appendage endocardial border. The LAA ejection fraction was calculated according to the formula: (maximal area-minimal area)/maximal area. Mitral valvular condition was evaluated with transthoracic and transesophageal echocardiography. Left atrial appendage blood flow velocity profiles were obtained with pulsed-wave Doppler at the orifice of the LAA. RESULTS: LASEC was present in 18 of 28 patients with mitral stenosis (64.3%). Patients with LASEC showed a greater incidence of atrial fibrillation (14/18 vs 12/43, p < 0.005), larger LAD (53.67 +/- 8.74 vs 40.54 +/- 14.85, p < 0.005), smaller LAAEF (38.7 +/- 1.53 vs 69.5 +/- 24.0, p < 0.05), smaller LAAMEV (20.28 +/- 10.07 vs 2.95 +/- 25.11, p < 0.005) and smaller LAAMFV (24.6 +/- 12.23 vs 36.00 +/- 11.01, p < 0.01), when compared with patients without LASEC. For group I, LAAEF, LAAMEV and LAAFV were smaller in patients with SEC than in patients without SEC (p < 0.005, p < 0.05, p < 0.01). However LAD values were similar for patients with and without SEC (53.67 +/- 8.75 vs 54.20 +/- 18.81, p = NS). Both LAAMEV and LAAMFV were related to SEC in patients with atrial fibrillation. However, LAD did not show the same trend. CONCLUSIONS: LASEC is more commonly observed in patients with rheumatic mitral stenosis or atrial fibrillation. Both LAAMEV and LAAMFV are associated with SEC in these patients.     

Temperature Distribution in Walls and Roofs

Temperatures in the walls and roofs of an experimental shed were measured. An “average” mathematical model was established for the determination of heat flow through wall and roof elements with different surface finishes. The input meteorological data and parameters used in calculation are discussed. The measured data were used to calibrate the model and check the assumptions involved. Based on the established model, heat flow through wall and roof elements and efficiency of different surface finishes are compared. The thermal inertia of a 150-mm-thick concrete wall is significant. Heat transmitted through a wall also depends greatly on the color of its surface. The insulation layers reduce heat flow into the interior and increase considerably the thermal inertia of a roof. The study focused on the summer period.     

Noise limit in heterodyne Interferometer demodulator for FBG-based sensors

This paper reports the results of a recent investigation on the noise-limited performance in heterodyne interferometric demodulation systems for fiber Bragg grating strain sensors. Theoretical and simulation results are presented and compared with experimental results.     

Flux observer with online tuning of stator and rotor resistancesfor induction motors

This paper proposes an adaptive flux observer for induction motors, where stator and rotor resistances are estimated in online environments. The variation of motor parameters during operation degrades the performance of the controller and the flux observer. Among the parameters of induction motors, rotor resistance is a crucial one for flux estimation, and stator resistance also becomes critical in the low-speed region. Under the persistent excitation condition, the proposed method estimates the actual values of stator and rotor resistances simultaneously, which guarantees the exact estimation of the rotor flux. The persistent excitation condition is not satisfied when the electric torque of an induction motor is absent due to the lack of rotor currents. Even in this case, the proposed method achieves the correct estimation of the rotor flux. Simulations and actual experiments show that the rotor flux is estimated in all operating conditions and that both resistances converge to their actual values when the electrical motor torque exists     

A fully automated four-probe d.c. conductivity technique for investigating solid electrolytes

A fully automated four-probe d.c. conductivity technique has been described for investigating the conductivity of solid electrolytes as a function of temperature and time. The technique is equally applicable to semiconducting and superconducting materials. With full automation, the time for data acquisition is very short and the reproducibility is high. Several uncertainties associated with manual recording of data are reduced. Some applications of the technique have been described. Various sources of error associated with collection of data have been considered and limitations and advantages of the techniques have been discussed.     

Efficient method for estimating directions-of-arrival of partiallypolarized signals with electromagnetic vector sensors

We have developed a high-resolution ESPRIT-based method for estimating the directions-of-arrival of partially polarized signals with electromagnetic vector sensors, each of which provides measurements of the complete electric and magnetic fields induced by electromagnetic signals. The method is computationally efficient since unlike many high-resolution methods, it does not involve searching across a multidimensional array manifold. In addition, the method has two variants, of which one is applicable to scenarios where a priori information about the array system, such as the sensor positions, is unavailable     

Reliability analysis for the design of an inflator

Product reliability is determined at its design stage and must be identified to adequately evaluate the feasibility of the current design. Reliability prediction provides the means to design verification and optimum modification. A design team must detect any potential reliability problems before the completion of the product design. This paper presents an approach to include the use of a reliability block diagram for reliability prediction, a fault tree analysis for detecting possible failures, and the axiomatic design procedure in the product design evaluation process. The discussion includes the reliability analysis of a passenger side airbag inflator design. The modification of the current inflator design is also discussed.     

Bid Compensation Decision Model for Projects with Costly Bid Preparation

For projects with high bid preparation cost, it is often suggested that the owner should consider paying bid compensation to the most highly ranked unsuccessful bidders to stimulate extra effort or inputs in bid preparation. Whereas the underlying idea of using bid compensation is intuitively sound, there is no theoretical basis or empirical evidence for such suggestion. Because costly bid preparation often implies a larger project scale, the issue of bid compensation strategy is important to practitioners and an interest of study. This paper aims to study the impacts of bid compensation and to develop appropriate bid compensation strategies. Game theory is applied to analyze the behavioral dynamics between competing bidders and project owners. A bid compensation model based on game theoretic analysis is developed in this study. The model provides equilibrium solutions under bid compensation, quantitative formula, and qualitative implications for the formation of bid compensation strategies.     

Cognitive-behavioral therapy for bulimia nervosa: Time course and mechanisms of change.

Cognitive-behavioral therapy (CBT) is an effective treatment of bulimia nervosa, but its mechanisms of action have not been established. In this study the authors analyzed the results of a randomized control trial comparing CBT with Interpersonal Psychotherapy (IPT) to identify possible mediators of change of CBT for BN and its time course of action. Reduction in dietary restraint as early as Week 4 mediated posttreatment improvement in both binge eating and vomiting. Measures of self-efficacy concerning eating behavior, negative affect, and body shape and weight at midtreatment were also significantly associated with posttreatment outcome at 20 wks. No evidence was found that the therapeutic alliance mediated treatment outcome. CBT had a significantly more rapid treatment effect than IPT, with 62% of posttreatment improvement evident by Week 6. (PsycINFO Database Record (c) 2010 APA, all rights reserved)