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Red blood cells (RBCs) are important to dictate hemorheological properties of blood. The
shear-thinning effect of blood is mainly attributed to the characteristics of the RBCs. Variations
in hemorheological properties alter flow resistance and wall shear stress in blood vessels. Therefore, detailed
understanding of the relationship between the hemorheological and hemodynamic properties is of great
importance. In this study, blood viscosity and blood
flow were simultaneously measured in the same microfluidic device by monitoring the
flow-switching phenomenon. To investigate blood flows according to hemorheological variations, the flow rate of blood samples (RBCs
suspended in autologous plasma, dextran-treated plasma, and in phosphate buffered saline solution)
was precisely controlled with a syringe pump. Velocity profiles of blood flows were measured by using a micro-particle image
velocimetry technique. The
shape of velocity profiles
was quantified by using a curve-fitting equation. It is found that the shape of the velocity profiles is highly correlated with
blood viscosity. To
demonstrate the relationship under ex vivo conditions, biophysical properties and
velocity profiles were
measured in an extracorporeal rat bypass loop. Experimental results show that
increased blood viscosity seems to induce blunt velocity profile with high velocity component at the wall of the microchannel. Simultaneous
measurement of blood viscosity and velocity profile would be useful for understanding the effects of hemorheological
features on the hemodynamic
characteristics in capillary blood vessels. 相似文献
2.
This case study attempts to examine basic education expansion and curriculum reform policies in Indonesia during the last
decade. The study focuses on the context of educational reform to understand its rationale as well as the content and process
of the reform policies, and the main barriers to effective reform implementation. The study is based on a review of policy
documents and interviews with key participants in the decision-making and monitoring process. The reforms in the 1990s were
concerned with providing quality-basic-education opportunities through basic education expansion and decentralizing the administrative
structure of curriculum development. The expansion of basic education has been very successful. However there were a number
of problems associated with the decentralization of the curriculum and it ’s implementation: the implementation gap between
the province and district level, the lack of appropriate teacher training, the teachers ’ passive attitudes toward the policy,
and the scarcity of resources and funding.
This paper is part of the Secondary Education Reform Case Studies Project directed by professor Clementina Acedo at the Institute
for International Studies, University of Pittsburgh, sponsored by USAID. We would like to thank Professor Mark B. Ginsburg
(University of Pittsburgh), Professor Emeritus Don Adams (University of Pittsburgh) and John Hatch (USAID), who gave us meaningful
comments helpful in finalizing this paper. 相似文献
3.
Blood viscosity has been considered as one of important biophysical parameters for effectively monitoring variations in physiological and pathological conditions of circulatory disorders. Standard previous methods make it difficult to evaluate variations of blood viscosity under cardiopulmonary bypass procedures or hemodialysis. In this study, we proposed a unique microfluidic device for simultaneously measuring viscosity and flow rate of whole blood circulating in a complex fluidic network including a rat, a reservoir, a pinch valve, and a peristaltic pump. To demonstrate the proposed method, a twin-shaped microfluidic device, which is composed of two half-circular chambers, two side channels with multiple indicating channels, and one bridge channel, was carefully designed. Based on the microfluidic device, three sequential flow controls were applied to identify viscosity and flow rate of blood, with label-free and sensorless detection. The half-circular chamber was employed to achieve mechanical membrane compliance for flow stabilization in the microfluidic device. To quantify the effect of flow stabilization on flow fluctuations, a formula of pulsation index (PI) was analytically derived using a discrete fluidic circuit model. Using the PI formula, the time constant contributed by the half-circular chamber is estimated to be 8 s. Furthermore, flow fluctuations resulting from the peristaltic pumps are completely removed, especially under periodic flow conditions within short periods (T < 10 s). For performance demonstrations, the proposed method was applied to evaluate blood viscosity with respect to varying flow rate conditions [(a) known blood flow rate via a syringe pump, (b) unknown blood flow rate via a peristaltic pump]. As a result, the flow rate and viscosity of blood can be simultaneously measured with satisfactory accuracy. In addition, the proposed method was successfully applied to identify the viscosity of rat blood, which circulates in a complex fluidic network. These observations confirm that the proposed method can be used for simultaneous measurement of viscosity and flow rate of whole blood circulating in the complex fluid network, with sensorless and label-free detection. Furthermore, the proposed method will be used in evaluating variations in the viscosity of human blood during cardiopulmonary bypass procedures or hemodialysis. 相似文献
4.
The bubble-free and pulse-free fluid delivery is critical to reliable operation of microfluidic devices. In this study, we propose a new method for stable bubble-free and pulse-free fluid delivery in a microfluidic device. Gas bubbles are separated from liquid by using the density difference between liquid and gas in a closed cavity. The pulsatile flow caused by a peristaltic pump is stabilized via gas compressibility. To demonstrate the proposed method, a fluidic chamber which is composed of two needles for inlet and outlet, one needle for a pinch valve and a closed cavity is carefully designed. By manipulating the opening or closing of the pinch valve, fluids fill up the fluidic chamber or are delivered into a microfluidic device through the fluidic chamber in a bubble-free and pulse-free manner. The performance of the proposed method in bubble-free and pulse-free fluid delivery is quantitatively evaluated. The proposed method is then applied to monitor the temporal variations of fluidic flows of rat blood circulating within a complex fluidic network including a rat, a pinch valve, a reservoir, a peristaltic pump, and the microfluidic device. In addition, the deformability of red blood cells and platelet aggregation are quantitatively evaluated from the information on the temporal variations of blood flows in the microfluidic device. These experimental demonstrations confirm that the proposed method is a promising tool for stable, bubble-free, and pulse-free supply of fluids, including whole blood, into a microfluidic device. Furthermore, the proposed method will be used to quantify the biophysical properties of blood circulating within an extracorporeal bypass loop of animal models. 相似文献
5.
Sam Robinson Dawne Clark Ji-Sook Yeom Joy-Ruth Mickelson Diane C. Hodges Jim Paul 《Interchange》1996,27(3-4):361-373
6.
This paper compares how educational reform documents in Korea and the U.S.A. conceptualize teachers and teacher education
and examines how, if at all, the discourses of one country appear to influence those of the other. Special attention is paid
to the ways in which reform documents incorporate different conceptions of professionalism in framing and in proposing remedies
for the problems with teachers and teacher education. Eighteen reform documents issued in the two countries by national governmental
and non-governmental organizations since the 1980s were selected and analyzed. It was found that while both Korean and American
documents seem to draw on elements of the functionalist (or trait theory) conception of professionalism, Korean documents
put more emphasis on issues related to the power/autonomy of teachers. Regarding cross-country influence, Korea seems to have
appropriated ideas and moved toward the structures and practices evidenced in the U.S.A. during an earlier period. 相似文献
7.
Heng Yuan Kyu-jin Kin Won-seok Kang Byoung-ho Kang Se-hyuk Yeom Jae-ho Kim Shin-won Kang 《浙江大学学报(A卷英文版)》2011,12(5):368-373
This paper presents a high-efficiency technique based on dielectrophoresis (DEP) for assembling metal, semiconductor, and
polymer nanorods, which are synthesized by electrochemical deposition (ECD). The assembly patterns of these nanorods (width:
20 nm; length: 7 μm) were designed using a finite element method (FEM) simulation tool. Further, these nanorods were used
in our experiment after their assembly patterns were fabricated. The assembly yield was found to be approximately 70% at an
AC voltage of 30 Vp-p and at frequencies of 20 and 30 kHz, and the DC voltage prevented the random alignment of the nanorods at the edge of the
assembly pattern. Moreover, the above-mentioned nanorods, which had different permittivities, were found to have similar assembly
yields. The proposed method can be improved and applied to nanostructure device fabrication. 相似文献
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