Electrical power free, low dead volume, pressure-driven pumping for microfluidic applications

This paper presents a simple-to-construct, low dead volume pump capable of generating a wide range of positive and negative pressures for microfluidic applications. The pump generates pressure or vacuum by changing the volume of air confined inside a syringe and is able to generate pressures between -95 and +300 kPa with a resolution as high as 1 Pa. Different from syringe pumps and electrokinetic pumping, which are capable of controlling flow rates only, our pump can be used to generate constant flow rates or constant pressures, which are required for certain applications such as the aspiration of biological cells for biophysical characterization. Compared to syringe pumps, the new pump has almost zero dead volume and does not exhibit pulsatile flows. Additionally, the system does not require electrical power and is cost effective (～$100). To demonstrate the capabilities of the pump, we used it to aspirate osteoblasts (MC3T3-E1 cells) and to determine Young's modulus of the cells, to generate a concentration gradient, and to produce variable-sized droplets in microchannels using hydrodynamic focusing.     

税收,撬动风投的杠杆--美国风险投资税收经验谈

给点说服投资的理由 合理的税收政策是说服和鼓励风险投资者投资的办法之一。     

Conceptual change and anomalous data: A case study in the domain of natural sciences

Cognitive conflict has been proposed as a strategy to promote conceptual change. The history and philosophy of science have shown the importance of anomalous data to change scientific theories and to the progress of science. Often, scientists use anomalous data to develop new interpretations that lead to new conceptualizations and finally, to a deep conceptual change. To be aware of contradiction seems to be a first step in the process of conceptual change. A study to explore novice students responses to anomalous data has been carried out. Sixty nine ninth graders, fifty seven eleventh graders and sixty three twelfth graders participated in the study. A paper and pencil task about the origin of life on the Earth was designed. Subjects were divided into two conditions. In condition “A” only anomalous data were presented to the subjects. In condition “A+B”, both anomalous and confirmatory data were presented. Results indicated that younger students were less aware of contradiction than older students when both anomalous and confirmatory data were presented. However, no differences have been found among them when just anomalous data were presented (condition A). Twelfth graders were aware of contradiction in both conditions. Some students’ epistemological beliefs influenced their response to anomalous data. Although no conceptual change (weak or strong restructuring) was achieved, as it could be predicted by the low domain-specific knowledge of the subjects and the complexity of the topic, presenting anomalous data facilitated the achievement of the first steps of the conceptual change process.     

Students' preconceptions of the nature of gases

A total of 1098 students, from second graders to university chemistry students, drew representations of highly magnified views of air at 1.0 atmosphere of pressure and at 0.5 atmosphere of pressure. The drawings were classified and the authors inferred from them a relatively limited number of preconceptions of the nature of gases. Several major trends occurred in the frequencies of these inferred preconceptions held at different grade levels. The majority of the drawings that were not in fairly close agreement with atomic theory seemed to reflect one or more of the following misconceptions: (a) air is a continuous (nonparticulate) substance, (b) gas behavior is similar to liquid behavior, and (c) there is relatively little space between gas particles. The number of drawings that gave evidence of particulate views ranged from 8% for Grades 2–4 to 85% for university chemistry students. However, 33% of the university students' drawings showed highly packed particles, and only 37% showed particles in an approximately correct geometrical distribution. The authors suggest a technique for promoting conceptual change among students who possess alternative views of the nature of gases.     

Open-field behavior of young chicks (Gallus gallus): Antipredatory responses,social reinstatement motivation,and gender effects

Two experiments investigating sex differences in the open-field behavior of young chicks are reported. In the first experiment, ambulation latencies of 10-day-old male and female chicks in a novel environment were measured. Half of the chicks were kept in social isolation for 2 days prior to testing; the other half were socially reared until tested. Results showed that in socially reared chicks ambulation latencies were significantly higher in males than in females, whereas in isolation-reared chicks there were no significant sex differences. In the second experiment, latencies of ambulation were measured in socially reared 10-day-old chicks placed in a novel environment with or without a visible predator (i.e., a human being). Sex differences were evident in both conditions, with males showing higher ambulation latencies than females. It is argued that sex differences in open-field behavior of chicks may be due to a stronger motivation for social reinstatement in females, which reduces the usual antipredatory reactions of chicks placed in a novel environment.     

畅想无线网络的应用

2005年7月,美国国家自然科学基金会NSF资助了一个项目。这个项目的目标是:整合大学、公司和政府中无线移动和传感器网络研究者的研究成果,创新网络结构,并且整理这些成果成为一个连贯的议程。这个计划极大地促进了无线网络的研究发展。这些研究者汇聚在一起,被称为NSF无线移动计划编制组WMPG。不久前,工作组发表了该项目的报告。从本期起,本刊将选择报告中的重点内容进行连续登载。     

Auflösung der Vorbereitungsfragen zur Facharztprüfung aus Heft 3–4/2009

Aufl?sung

Aufl?sung der Vorbereitungsfragen zur Facharztprüfung aus Heft 3–4/2009