Ultrafast microfluidics using surface acoustic waves

We demonstrate that surface acoustic waves (SAWs), nanometer amplitude Rayleigh waves driven at megahertz order frequencies propagating on the surface of a piezoelectric substrate, offer a powerful method for driving a host of extremely fast microfluidic actuation and micro∕bioparticle manipulation schemes. We show that sessile drops can be translated rapidly on planar substrates or fluid can be pumped through microchannels at 1–10 cm∕s velocities, which are typically one to two orders quicker than that afforded by current microfluidic technologies. Through symmetry-breaking, azimuthal recirculation can be induced within the drop to drive strong inertial microcentrifugation for micromixing and particle concentration or separation. Similar micromixing strategies can be induced in the same microchannel in which fluid is pumped with the SAW by merely changing the SAW frequency to rapidly switch the uniform through-flow into a chaotic oscillatory flow by exploiting superpositioning of the irradiated sound waves from the sidewalls of the microchannel. If the flow is sufficiently quiescent, the nodes of the transverse standing wave that arises across the microchannel also allow for particle aggregation, and hence, sorting on nodal lines. In addition, the SAW also facilitates other microfluidic capabilities. For example, capillary waves excited at the free surface of a sessile drop by the SAW underneath it can be exploited for micro∕nanoparticle collection and sorting at nodal points or lines at low powers. At higher powers, the large accelerations off the substrate surface as the SAW propagates across drives rapid destabilization of the drop free surface giving rise to inertial liquid jets that persist over 1–2 cm in length or atomization of the entire drop to produce 1–10 μm monodispersed aerosol droplets, which can be exploited for ink-jet printing, mass spectrometry interfacing, or pulmonary drug delivery. The atomization of polymer∕protein solutions can also be used for the rapid synthesis of 150–200 nm polymer∕protein particles or biodegradable polymeric shells in which proteins, peptides, and other therapeutic molecules are encapsulated within for controlled release drug delivery. The atomization of thin films behind a translating drop containing polymer solutions also gives rise to long-range spatial ordering of regular polymer spots whose size and spacing are dependent on the SAW frequency, thus offering a simple and powerful method for polymer patterning without requiring surface treatment or physical∕chemical templating.     

Rapid production of protein-loaded biodegradable microparticles using surface acoustic waves

We present a straightforward and rapid surface acoustic wave (SAW) atomization-based technique for encapsulating proteins into 10 μm order particles composed of a biodegradable polymeric excipient, using bovine serum albumin (BSA) as an exemplar. Scans obtained from confocal microscopy provide qualitative proof of encapsulation and show the fluorescent conjugated protein to be distributed in a relatively uniform manner within the polymer shell. An ELISA assay of the collected particles demonstrates that the BSA survives the atomization, particle formation, and collection process with a yield of approximately 55%. The SAW atomization universally gave particles with a textured morphology, and increasing the frequency and polymer concentration generally gave smaller particles (to 3 μm average) with reduced porosity.     

Vocational Interests and Career Efficacy Expectations in Relation to Occupational Sex-Typing Beliefs for Eighth Grade Students

Following the recommendations of Lent, Brown and Hackett's Social Cognitive Career Theory (2000), we measured eighth grade boys' and girls' perception of the proportion of men and women employed in occupations and their level of interest and self-efficacy for those occupations. Results indicated that eighth grade boys and girls expressed stronger career interest in and higher self-efficacy for those occupations that they rated as employing more of their own gender. The study highlights how career practitioners can work with adolescents to widen their perceived range of occupational choices.     

Social Work Intervention with White Collared Employees and Their Families

This investigation presents a framework for understanding and also to test the efficacy of Social Work intervention on the well being of the white collared employee (industrial employee) and his/her family. A comprehensive and intensive personal- family exploration was done to uncover the relatedness of seemingly disparate areas of the clients lives. A total of 80 executives (industrial employees) served as subjects. A baseline assessment was done using structured, standardized interview-schedules/questionnaires. The results of the study can be enumerated as follows: After the Social Work intervention, the executives in occupational profile, there were significant changes in Role perception, overload, role conflict, low status and poor peer relations. In coping strategies there was significant improvement in sub-scales like problem solving and unproductive coping. Significant reduction was noticed in their proneness to heart disease, depression, inadequate mental mastery, and perceived ill health. There was significant improvement in their family group support, and in their expressiveness, achievement, orientation, active-recreational and organizational characteristics.     

Variables related to career commitment,mastery motivation,and level of career aspiration among college students

The authors wish to express appreciation for the statistical help provided by James Wardrop and Ya-Mei Chen; and for the support provided by the Bureau of Educational Research and the Campus Research Board, University of Illinois. Also several persons helped with the development of the measures and data collection including Carole Ames, Mary Z. Anderson, Cindy Glidden, Fu-lin Y. Lee, Kirsten Peterson, and Barbara Powell. Requests for reprints may be addressed to the first author at the Educational Psychology Department, University of Illinois, 1310 South Sixth St., Champaign, IL 61820.     

Stability of switching linear systems with switching signals driven by stochastic processes

This paper presents conditions to assure the exponential stability in probability for autonomous switching linear systems. The switching signal acting on the autonomous system produces intervals that follow independent, identically distributed stochastic processes—the stability then follows by verifying simple-to-check linear matrix inequalities.     

Robust self-triggered MPC with fast convergence for constrained linear systems

In this paper, a robust self-triggered model predictive control (MPC) scheme is proposed for linear discrete-time systems subject to additive disturbances, state and control constraints. To reduce the amount of computation on controller sides, MPC optimization problems are only solved at certain sampling instants which are determined by a novel self-triggering mechanism. The main idea of the self-triggering mechanism is to choose inter-sampling times by guaranteeing a fast decrease in optimal costs. It implies a fast convergence of system states to a compact set where it is ultimately bounded and a reduction of computation times to stabilize the system. Once the state enters a terminal region, the system can be stabilized to a robust invariant set by a state feedback controller. Robust constraint satisfaction is ensured by utilizing the worst-case set-valued predictions of future states in such a way that recursive feasibility is guaranteed for all possible realisations of disturbances. In the case where a priority is given to reducing communication costs rather than improvement in control performance in a neighborhood of the origin, a feedback control law based on nominal state predictions is designed in the terminal region to avoid frequent feedback. Performances of the closed-loop system are demonstrated by a simulation example.     

Chinese students at an English-Language university: Prediction of academic performance

There is a paucity of systematic research on prediction of success at the tertiary education level for Asian students, despite the important role that universities play in Asian communities, and despite the increasing numbers of such students who are coming to the West to study. This study reviews evidence collected over the past ten to fifteen years, which relates to the issue of prediction of academic performance of Chinese students at an English-Language and Western-oriented university - the University of Hong Kong. This review is complemented by an analysis of data collected longitudinally over a five year period, using multiple regression, multiple correlation, path analysis and canonical correlation analyses. The results provide evidence of factors which are important in determining the ability of a student to adapt to the foreign cultural and language barriers that exist at this university. In particular, ability in English language and mathematics provides good and reasonably independent predictors of success. The data show the importance of considering the cultural background of students when assessing their aptitude for study, and offer information for Western universities regarding their admissions procedures for Chinese students.