A unified constrained inversion model for ultrasonic flaw sizing

Equivalent flaw sizing using ultrasonic waves is an approach whereby shape and orientation information of a defect are obtained in terms of a best-fit simple geometry that is able to represent the major aspects of the flaw. Separate examples of this approach have previously been developed for volumetric flaws and cracks using the Born and Kirchhoff approximations, respectively. Here, these separate algorithms are unified into a single algorithm capable of sizing both volumetric flaws and cracks. Some examples of the performance of this unified algorithm on both synthetic and experimental data are also given.     

The effects of accumulated experience on radiofrequency ablation of accessory pathways

Increasing experience in radiofrequency ablation for accessory pathways appears to reduce the procedure time, radiation time and radiofrequency pulse number, and results in a higher success rate. However, the effect of a learning curve on this procedure from the perspective of location and conduction direction of accessory pathways has not been reported before. The purpose of this study was to determine the effect of accumulated experience on the outcomes of radiofrequency ablation for accessory pathways and on the duration of the procedure parameters by analyzing the results of a dedicated ablation team. The first 512 patients with a single accessory pathway treated in this laboratory were included for analysis of the procedure parameters with respect to locations and conduction directions of accessory pathways. The results showed that the average procedure time, radiation time, and radiofrequency pulse number differed significantly among the different subgroups (left free wall, right free wall, posteroseptal and anteromidseptal location; manifest or concealed conduction). All subgroups except the anteromidseptal pathways showed a significant improvement of the procedure parameters with increased ablation experience. Although the initial rate of improvement was similar among the different subgroups, the rate of improvement in left free wall pathways nearly reached a plateau after 120 ablation procedures. Thus it was concluded that a certain number of ablation procedures was necessary before achievement of a high success rate with shorter procedure and radiation times and a lower radiofrequency pulse number.     

The effects of binders and heating temperatures on the properties of preforms

The use of binders in fabricating ceramic fiber preforms is essential when producing metal-matrix com-posites via squeeze casting or liquid metal infiltration. The binder is not only used to stabilize the shape of the preform, but also to increase its strength. A strong preform is needed to make a net shape or near-net shape casting so that many post-machining processes can be reduced or eliminated. However, very lit-tle attention has been paid to preform fabrication, subsequent processing, and its characterization. This work focuses on the relation between preform processing (selection of binder, heat treatment of the pre-form, etc.) and the properties of the resulting preforms. Silica and phosphate binders were used to make short alumina fiber preforms. The use of binders and the heat treatments used were correlated to the properties of the resulting preforms. The results showed that the heat treating temperature, as well as the amount of binder, is relevant to the resulting properties of the preform. Correlations among the use of binders, heat treatment condition, composition of the binders, and the properties of the preforms were investigated.     

Studies of the cellular mechanisms underlying the vasorelaxant effects of rutaecarpine, a bioactive component extracted from an herbal drug

We conducted studies to investigate the nature and underlying mechanisms of the vascular effects of rutaecarpine (Rut), an alkaloid isolated from the Chinese herbal drug Evodia rutaecarpa. By using largely the effects on phenylephrine (PE)-induced contraction in the isolated rat aorta as the experimental index and by comparison with several known vascular muscle relaxants such as acetylcholine (ACh), histamine, and A23187, Rut relaxed PE-precontracted aorta in concentration-(10(-7)-10(-4) M) and endothelium-dependent manners. Studies with appropriate antagonists indicated that this was coupled to nitric oxide (NO) and guanylyl cyclase. Extracellular Ca2+ removal and treatment with the intracellular Ca2+ antagonist, 8-(N,N-diethylamino)octyl-3,4,5-trimethoxybenzoate (TMB-8), suggested that influx of extracellular Ca2+ was the major factor contributing to the action of Rut. Pertussis toxin suppressed the relaxation potency of histamine but had no effects on the actions of Rut. NaF, the G proteins activator, attenuated the actions of ACh, but only minimally affected Na-NP, A23187, and Rut. 1-[6-{[17 beta-3-methoxyestra-1,2,3(10)-trien-17-yl]amino} hexyl]-1H-pyrrole-2,5-dione (U73122), the phospholipase C inhibitor, again suppressed the actions of ACh but had few effects on A23187 and Rut. Taken together, these results suggest that these vasorelaxants had different cellular mechanisms and that neither pertussis toxin-sensitive Gi protein, other G proteins, nor phospholipase C activation was involved in the cellular response to rutaecarpine.     

Lapping of ultra-precision ball surfaces. Part I. Concentric V-groove lapping system

A general closed-form analytical solution is derived for the lapping tracks with its kinematics for the concentric V-groove lapping system. Based on the kinematics, the theoretical prediction in the prediction of the ball-spin angle β is in very good agreement with the experimental results from the observation of the contact track, where a small slip ratio occurs at the contact points. The lapping tracks on the ball surface for the three contact points are fixed circles, and their lengths of the lapping tracks are linearly proportional to |sin(θ₁+β)|, |sin(θ₂+β)|, and |cos β|, respectively. To understand the generation mechanism of spherical surface, the ball is enforced to rotate a certain degree of δ with respect to its previous orientation when it enters the lap again. Results show that the lapped area ratio, Lr, is significantly influenced by the angular speed ratio, w_b/Ω_b, and δ. When the angular speed ratio is integer and δ is small enough or randomized, the lapped area ratios at the contact points of A, B, and C are linearly proportional to [sin θ+sin(θ+2β)], [sin θ+sin(θ−2β)], and (1+cos 2β), respectively. In practice, if the orientation is randomized as the ball enters the lap again, then the distribution of the lapping tracks are dense after many cycles, and the larger the lapping length in each cycle, the smaller is the number of cycles required to achieve the maximum lapped area ratio. In the geometry design of ball lapping, the V-groove half-angle should be larger than 45°, but to prevent the splash of abrasives, it should be less than 75°.     

Nitride-based flip-chip p-i-n photodiodes

Nitride-based flip-chip p-i-n photodiodes were fabricated and characterized. It was found that we could achieve a small dark current of 5/spl times/10/sup -10/ A at -5 V and a large rejection ratio larger than three orders of magnitude. It was also found that the photodiodes only detect optical signals with wavelengths between 365 and 378 nm. Furthermore, it was found that peak responsivity occurs at around 370 nm with a value of 0.21 A/W at zero bias which corresponds to 70% external quantum efficiency.     

Conceptual Structural Design in SEED

Although there are many computer-based tools for analyzing structures whose geometry, topology, and member properties have already been determined, there are very few general-purpose tools to assist structural designers in synthesizing structural configurations to be subsequently sized, analyzed, and detailed. The comceptual-structural-design submodule of the Software Environment to Support the Early Phases in Building Design (SEED-Config) is intended to fill this void. The process starts with a geometric model of the building's massing, a set of functional requirements to be satisfied, and a toolkit of technologies capable of generating potential structural system and subsystem alternatives. Structural alternatives can be rapidly generated under designer control to the level of detail desired and evaluated against a range of criteria. Provisions are made to store design cases as well as to retrieve and adapt these to meet new requirements.     

Electromechanical and electrothermal behaviours of carbon whisker reinforced elastomer composites

The electromechanical and electrothermal properties of conducting carbon whisker reinforced thermoplastic elastomer (TPE) composites were investigated. The carbon whiskers were derived by a catalytic chemical vapour Deposition (CCVD) process and the TPE was a styrene-ethylene-butylene-styrene (S-EB-S) block copolymer. The electrical resistivity (ϱ) of the composites can be varied either by uniaxial deformation (10¹–10⁸ Ω cm) or by temperature (10¹–10⁵ Ω cm). The temperature-resistivity studies indicated that the resistivity of these composites was influenced by the glass transition temperature (T _g) of the TPE. The ϱ versus 1/T curves exhibited two distinct regimes each with a different negative slope which intersected at the T _g of the elastomer. This was correlated to the T _gof the EB segments in the S-EB-S block copolymer (∼ -50°C) by the dynamic mechanical thermal analysis. Further, uniaxial deformation studies at room temperature (20 °C) demonstrated that the resistivity increased exponentially with the deformation. Processing technique considerations and electron micrographs of the morphology of the composites indicated the formation of polymeric film on the carbon whiskers. Thus, the electrical conduction between carbon whiskers in these highly loaded (33 and 52 vol % fraction) composites occurred through the elastomeric film by electron tunnelling. This is explained on the basis of Mott's electron hopping theory, for conduction through several carbon-polymer-carbon (C-P-C) junctions. Further studies by scanning electron microscopy, dielectric thermal analysis and voltage-current characteristics confirmed this observation. Mechanical and electrical properties of the composites indicated that CCVD carbon whiskers can be used to improve the strength and electrical conductivity of TPEs. The change in resistivity (up to five orders of magnitude) of the composites with respect to the deformation or temperature can find use in electromechanical and electrothermal device applications.