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.     

A computer science and robotics integration model for primary school: evaluation of a large-scale in-service K-4 teacher-training program

Education and Information Technologies - Integrating computer science (CS) into school curricula has become a worldwide preoccupation. Therefore, we present a CS and Robotics integration model and...     

Assessing Fat Mass of Adolescent Swimmers Using Anthropometric Equations: A DXA Validation Study

Purpose: The aim of the present study was to determine which of the published anthropometric equations is the most appropriate to estimate body-fat percentage (BF_%) in adolescent swimmers. Method: Eighty-eight swimmers (45 boys, 43 girls) participated in this study. Following the recommendations of the International Society of the Advancement of Kinanthropometry, biceps, triceps, subscapular, iliac-crest, supraspinale, front-thigh, and medial calf skinfold thicknesses were measured. Waist, hip, midthigh, calf, relaxed arm, and arm flexed and tensed girths were also registered. BF_% was measured with dual-energy X-ray absorptiometry (DXA) to obtain the reference value. Existing anthropometric equations were applied, and BF_% results obtained from anthropometric equations were compared to DXA BF_% results with the modified Bland-Altman. Results: The Flavel, Durnin-Rahaman-Siri, and Durnin-Rahaman-Brozek were the only equations that did not demonstrate statistically significant differences when compared with DXA. Conclusion: The present study showed that the best anthropometric equation from existing literature to estimate BF_% in swimmers is that proposed by Durnin-Rahaman (independently of applying the Siri or Brozek equation).     

The location of the tibial accelerometer does influence impact acceleration parameters during running

Tibial accelerations have been associated with a number of running injuries. However, studies attaching the tibial accelerometer on the proximal section are as numerous as those attaching the accelerometer on the distal section. This study aimed to investigate whether accelerometer location influences acceleration parameters commonly reported in running literature. To fulfil this purpose, 30 athletes ran at 2.22, 2.78 and 3.33 m · s^–1 with three accelerometers attached with double-sided tape and tightened to the participants’ tolerance on the forehead, the proximal section of the tibia and the distal section of the tibia. Time-domain (peak acceleration, shock attenuation) and frequency-domain parameters (peak frequency, peak power, signal magnitude and shock attenuation in both the low and high frequency ranges) were calculated for each of the tibial locations. The distal accelerometer registered greater tibial acceleration peak and shock attenuation compared to the proximal accelerometer. With respect to the frequency-domain analysis, the distal accelerometer provided greater values of all the low-frequency parameters, whereas no difference was observed for the high-frequency parameters. These findings suggest that the location of the tibial accelerometer does influence the acceleration signal parameters, and thus, researchers should carefully consider the location they choose to place the accelerometer so that equivalent comparisons across studies can be made.     

金发碧眼的对决 第二届国务总理杯世界业余围棋锦标赛

看到对局者的姓名,估计大家有些不适应,看棋谱习惯了看中文名字,突然看到两个老外名字,多多少少有点新鲜。这一期介绍了欧洲围棋的发展,下面我们将通过国务总理杯世界围棋锦标赛的一盘对局来具体了解一下欧洲棋手的实力。黑棋比利时的Ramon是那届比赛的一匹黑马,是前四轮仅有的保持全胜的五名棋手之一。而白棋罗马尼亚的Pop则是欧洲非常有名的棋手,他的水平应该代表了目前欧洲的最高水平。