Analysis of a laminar-flow diffusional mixer for directed self-assembly of liposomes

The present work describes the operation and simulation of a microfluidic laminar-flow mixer. Diffusive mixing takes place between a core solution containing lipids in ethanol and a sheath solution containing aqueous buffer, leading to self assembly of liposomes. Present device architecture hydrodynamically focuses the lipid solution into a cylindrical core positioned at the center of a microfluidic channel of 125 × 125-μm² cross-section. Use of the device produces liposomes in the size range of 100–300 nm, with larger liposomes forming at greater ionic strength in the sheath solution and at lower lipid concentration in the core solution. Finite element simulations compute the concentration distributions of solutes at axial distances of greater than 100 channel widths. These simulations reduce computation time and enable computation at long axial distances by utilizing long hexahedral elements in the axial flow region and fine tetrahedral elements in the hydrodynamic focusing region. Present meshing technique is generally useful for simulation of long microfluidic channels and is fully implementable using comsol Multiphysics. Confocal microscopy provides experimental validation of the simulations using fluorescent solutions containing fluorescein or enhanced green fluorescent protein.     

Challenges to Institutionalizing Participatory Extension: The Case of Farmer Livestock Schools in Vietnam

Abstract

Purpose: The objective of this article is to analyze the introduction of participatory extension approaches (PEA) in the predominantly supply-driven, hierarchical Vietnamese extension system. Drawing on the case of the so-called Farmer Livestock School (FLS) concept, the authors investigate the potential and challenges of scaling up and out the FLS/PEA principles of participatory training methods, encompassing intensive and interactive training sessions, group-based sharing of experience, practical learning, and learning-by-doing processes.

Design/Methodology/Approach: The article is based on data collected and synthesized from 36 pilot communes from 2000 to 2007 and draws on the extensive insider experience of two of its authors during their work for a DANIDA-funded livestock project.

Findings: At the micro-scale and with external support, FLS has been a successful experiment of using participatory extension approaches in farmer training and extension in the livestock sector. Yet, possibilities of scaling up and institutionalizing FLS remain a challenge given the capacity and resource limitations and the resistance at various levels within the Vietnamese extension system.

Practical Implications: The starting point for successfully institutionalizing participatory extension approaches should be to assess the existing system's root problems and capacities and then gradually and systematically introduce institutional innovations rather than aiming at a complete overhaul of a system that may result in the creation of a parallel universe.

Originality/Value: The FLS project provided a unique opportunity to study the enabling and constraining factors of institutionalizing participatory extension approaches in a traditionally top-down oriented extension system beyond the immediate duration of an externally orchestrated project.     

Three Levels of Goal Orientation in Learning

Sixteen adult volunteers provided thinking-aloud protocols while undergoing a 10-hr individually administered course in BASIC (beginner's all-purpose symbolic instruction code) programming. Three levels of goals were identified as operative in the learning situation: task-completion goals, instructional goals, and personal knowledge-building goals. Although protocol statements indicating knowledge-building goals were infrequent, students exhibiting a relatively high proportion of them were distinctive in several ways. They did significantly better on a posttest. Their performance in goal cue selections differed from that of other participants in ways consistent with their orientation: They responded more often to learning goal cues than to task goal cues. They actively related new learning to prior knowledge and they posed and tried to solve problems and questions. Students oriented toward instructional goals tended to focus on what was explicitly taught. Students oriented toward task-completion goals tended to equate learning with successful completion of assigned tasks. Level of goal orientation and posttest performance were unrelated to level of education and prior computer experience but were positively related to previous experience of independent learning.     

IMPACT OF FULL-TIME VERSUS PART-TIME INSTRUCTOR STATUS ON COLLEGE STUDENT RETENTION AND ACADEMIC PERFORMANCE IN SEQUENTIAL COURSES

The primary purpose of this study was to examine the relation between full - time or part - time instructor status and college student retention and academic performance in sequential courses . Results indicate that for either developmental or regular courses, college students who take the first course in a sequence from a part - time instructor , and who take the second course in the sequence from a full - time instructor seem underprepared for the second course. By contrast to students experiencing other instructor status combinations (part - time / part - time , full - time / part - time , or full - time / full - time), these students are significantly less likely to either complete or achieve a grade of "C" or better in the second course. Sequential course instructor status, therefore, seems to be a predictor of college student success. Implications for practice pertaining to further research, college students, and institutions are discussed.