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A novel process using ultrasonics to enhance the exfoliation and dispersion of clay platelets in polypropylene-based nanocomposites has been proposed and investigated. The materials studied were isotactic polypropylene of various molecular weights reinforced with organophilic montmorillonite clay (nanoclay) at 4-6 wt% loadings. X-ray diffraction (XRD) and rheological measurements, on a model system of nanoclay in mineral oil, were first used to determine ultrasonic energy requirements. The effectiveness of the proposed ultrasonic processing technique on polypropylene nanocomposites was evaluated by XRD and transmission electron microscopy (TEM). The effects of added maleic anhydride-grafted polypropylene compatibilizer, polypropylene molecular weight, and pretreatment of the nanoclays on the nanocomposite exfoliation were also investigated. Results indicate that ultrasonic processing of polymer nanocomposites in the melt state is an effective method for improving exfoliation and dispersion of nanoclays. Issues regarding molecular weight degradation, optimization, mechanical properties, and continuous processing are beyond the scope of the present study and are currently being investigated in our laboratory. Polym. Eng. Sci. 44:1773-1782, 2004. [c] 2004 Society of Plastics Engineers., INTRODUCTION The class of materials known as nanocomposites has enjoyed increased interest since the initial development of a nylon-based material by Usuki et al. at Toyota in 1993 (1). In [...]

The analysis of resonant converters including the capacitance of the switches is presented. New dc characteristics are obtained for the series, parallel, and series-parallel resonant converters (SPRC). The operating regions where the converters operate with zero-voltage switching (ZVS) are determined as a function of the switch capacitance. The more pronounced effect can be seen in the series resonant converter (SRC), while the parallel resonant converter (PRC) is the most insensitive. The results of the analysis have been verified on an experimental prototype.

Background: Minimally invasive surgical techniques expose surgeons to a variety of occupational hazards that may promote musculoskeletal disorders. Telerobotic systems for minimally invasive surgery may help to reduce these stressors. The objective of this study was to compare manual and telerobotic endoscopic surgery in terms of postural and mental stress.Methods: Thirteen participants with no experience as primary surgeons in endoscopic surgery performed a set of simulated surgical tasks using two different techniques--a telerobotic master--slave system and a manual endoscopic surgery system. The tasks consisted of passing a soft spherical object through a series of parallel rings, suturing along a line 5-cm long, running a 32-in ribbon, and cannulation. The Job Strain Index (JSI) and Rapid Upper Limb Assessment (RULA) were used to quantify upper extremity exposure to postural and force risk factors. Task duration was quantified in seconds. A questionnaire provided measures of the participants' intuitiveness and mental stress.Results: The JSI and RULA scores for all four tasks were significantly lower for the telerobotic technique than for the manual one. Task duration was significantly longer for telerobotic than for manual tasks. Participants reported that the telerobotic technique was as intuitive as, and no more stressful than, the manual technique.Conclusions: Given identical tasks, the time to completion is longer using the telerobotic technique than its manual counterpart. For the given simulated tasks in the laboratory setting, the better scores for the upper extremity postural analysis indicate that telerobotic surgery provides a more comfortable environment for the surgeon without any additional mental stress. [ABSTRACT FROM AUTHOR]