Finite element simulations of hydrodynamic trapping in microfluidic particle-trap array systems

Computational fluid dynamic (CFD) simulation is a powerful tool in the design and implementation of microfluidic systems, especially for systems that involve hydrodynamic behavior of objects such as functionalized microspheres, biological cells, or biopolymers in complex structures. In this work, we investigate hydrodynamic trapping of microspheres in a novel microfluidic particle-trap array device by finite element simulations. The accuracy of the time-dependent simulation of a microsphere''s motion towards the traps is validated by our experimental results. Based on the simulation, we study the fluid velocity field, pressure field, and force and stress on the microsphere in the device. We further explore the trap array''s geometric parameters and critical fluid velocity, which affect the microsphere''s hydrodynamic trapping. The information is valuable for designing microfluidic devices and guiding experimental operation. Besides, we provide guidelines on the simulation set-up and release an openly available implementation of our simulation in one of the popular FEM softwares, COMSOL Multiphysics. Researchers may tailor the model to simulate similar microfluidic systems that may accommodate a variety of structured particles. Therefore, the simulation will be of particular interest to biomedical research involving cell or bead transport and migration, blood flow within microvessels, and drug delivery.     

Facet design and smallest space analysis of teachers' instructional behavior

The essence of research in the behavioral sciences is to help in forming theories that will enhance understanding of behavior. In this study an attempt is made to construct such a theory of students' perceptions of their teachers' instructional behaviors and to verify it by empirical evidence. Guttman's definition of a theory was adopted here: “An hypothesis of a correspondence between a definitional system for a universe of observation and an aspect of the empirical structure of those observations, together with a rationale for such an hypothesis” (Shye, 1978). Data was collected through a questionnaire administered to two thousand highschool students. Facet design and smallest space analysis (SSA) were used to construct a theory that was then verified by empirical evidence. The results are consistent with previous studies done by Bar-On (Bar-On & Perlberg, 1976; Klinging & Bar-On, 1975) which employed also facet design and smallest space analysis.     

Sources of stress in academe - the Israeli case

The effects of stress on the physical and psychological well being of people in different professions and occupations have become, in the last decade, the focal interest of researchers and clinicians. There is a growing body of evidence that stress, adversely affects the performance, productivity, job satisfaction, health and the general quality of life of professionals and people in general (Farber, 1983; Lazarus & Folkman, 1984). Originally, research on stress focused on the helping professions and human services occupations (Cherniss, 1980; Farber, 1983). More recently, other occupations which involve continuous, intensive interpersonal relationships between people, have been investigated and were found to be a potential source of stress (Holt, 1982). The growing interest in the study of stress and its manifestations resulted among others in newly defined concepts such as: burnout, tedium, wear and tear, deadwoods, midlife crisis, etc. (Maslach and Jackson, 1979; Manuso, 1979; Freudenberger, 1980; Pines, Aronson and Kafry, 1981; Farber, 1983).     

Evaluation of instruction in higher education: Some critical issues

Critical issues arising from the evaluation of instruction in higher education are reviewed. The purposes of evaluation (for reward and accountability, for improvement of instruction) and identity of the evaluations (students, reporters, peers, administrators, consultants) are discussed and a plea made for tying evaluation to systematic training schemes.