Two-dimensional spatial manipulation of microparticles in continuous flows in acoustofluidic systems

We report a modeling and experimental study of techniques to acoustically focus particles flowing through a microfluidic channel. Our theoretical model differs from prior works in that we solve an approximate 2-D wave transmission model that accounts for wave propagation in both the solid and fluid phases. Our simulations indicate that particles can be effectively focused at driving frequencies as high as 10% off of the resonant condition. This conclusion is supported by experiments on the acoustic focusing of particles in nearly square microchannels, which are studied for different flow rates, driving frequencies and placements of the lead zirconate titanate transducer, either underneath the microchannel or underneath a parallel trough. The relative acoustic potential energy and the resultant velocity fields for particles with positive acoustic contrast coefficients are estimated in the 2-D limit. Confocal microscopy was used to observe the spatial distribution of the flowing microparticles in three dimensions. Through these studies, we show that a single driving frequency from a single piezoelectric actuator can induce the 2-D concentration of particles in a microchannel with a nearly square cross section, and we correlate these behaviors with theoretical predictions. We also show that it is possible to control the extent of focusing of the microparticles, and that it is possible to decouple the focusing of microparticles in the vertical direction from the lateral direction in rectangular channels with anisotropic cross sections. This study provides guidelines to design and operate microchip-based acoustofluidic devices for precise control over the spatial arrangement of microparticles for applications such as flow cytometry and cellular sorting.     

PDA power at the bedside

George Washington University's Himmelfarb Health Sciences Library was investigating adding PDA resources to the collection when a medical education grant was received. Funds were used for a pilot project to compare PDA use by third-year medical students (MSIII), fourth-year medical students (MSIV), second-year physician assistant (PAII) students, and residents in the clinical setting. The PDA Committee evaluated various titles by the following criteria: both Palm and PocketPC operating systems compatibility, ease of use, depth of information, product cost, and a wide target audience. Griffith's 5 Minute Clinical Consult by Skyscape was selected. Library registration was required to receive the software and PDA downloading instructions. A short, Web-based questionnaire was developed to evaluate the product's use in the clinical setting. A low response rate of 74 questionnaires (23% of participants) was received and analyzed in March 2004. As additional funding becomes available, PDA software will be seriously considered as additions to the collection.     

Viewing the changing world of educational technology from a different perspective: Present realities,past lessons,and future possibilities

This review paper focuses on likely reasons for the rhetoric-reality gap in the use of educational information and communication technology. It is based on the assumption that the present challenges being experienced with educational ICT might be avoided in the future if we look at the current challenges from a different perspective, by revisiting past research to gain insights from the history of innovations in educational technology. Seven major lessons emerging from the review could inform future directions so that the future does not simply replicate the disappointing results achieved thus far. We argue that the vision for ICT has been unrealistically ambitious, and review reasons to justify this point of view. We suggest that setting more attainable goals, based on the actuality of educational contexts, might be a more pragmatic way to go in a future of constantly changing educational technology.     

Kinematic parameters contributing to the production of spin in elite finger spin bowling

ABSTRACT

The aim of this study was to identify the key kinematic parameters which contribute to higher spin rates in elite finger spin bowling. Kinematic data were collected for twenty-three elite male finger spin bowlers with thirty kinematic parameters calculated for each delivery. Stepwise linear regression and Pearson product moment correlations were used to identify kinematic parameters linked to spin rate. Pelvis orientation at front foot contact (r = 0.674, p < 0.001) and ball release (r = 0.676, p < 0.001) were found to be the biggest predictors of spin rate, with both individually predicting 43% of the observed variance in spin rate. Other kinematic parameters correlated with spin rate included: shoulder orientation at ball release (r = 0.462, p = 0.027), and pelvis-shoulder separation angle at front foot contact (r = 0.521, p = 0.011). The bowlers with the highest spin rates adopted a mid-way pelvis orientation angle, a larger pelvis-shoulder separation angle and a shoulder orientation short of side-on at front foot contact. The segments then rotated sequentially, starting with the pelvis and finishing with the pronation of the forearm. This knowledge can be translated to coaches to provide a better understanding of finger spin bowling technique.     

Teacher and Classroom Context Effects on Student Achievement: Implications for Teacher Evaluation

The Tennessee Value-Added Assessment System (TVAAS) has been designed to use statistical mixed-model methodologies to conduct multivariate, longitudinal analyses of student achievement to make estimates of school, class size, teacher, and other effects. This study examined the relative magnitude of teacher effects on student achievement while simultaneously considering the influences of intraclassroom heterogeneity, student achievement level, and class size on academic growth. The results show that teacher effects are dominant factors affecting student academic gain and that the classroom context variables of heterogeneity among students and class sizes have relatively little influence on academic gain. Thus, a major conclusion is that teachers make a difference. Implications of the findings for teacher evaluation and future research are discussed.