排序方式： 共有2条查询结果，搜索用时 0 毫秒
1
1.
We present an optofluidic microvalve utilizing an embedded, surface plasmon-enhanced fiber optic microheater. The fiber optic microheater is formed by depositing a titanium thin film on the roughened end-face of a silica optical fiber that serves as a waveguide to deliver laser light to the titanium film. The nanoscale roughness at the titanium-silica interface enables strong light absorption enhancement in the titanium film through excitation of localized surface plasmons as well as facilitates bubble nucleation. Our experimental results show that due to the unique design of the fiber optic heater, the threshold laser power required to generate a bubble is greatly reduced and the bubble growth rate is significantly increased. By using the microvalve, stable vapor bubble generation in the microchannel is demonstrated, which does not require complex optical focusing and alignment. The generated vapor bubble is shown to successfully block a liquid flow channel with a size of 125 μm × 125 μm and a flow rate of ∼10 μl/min at ∼120 mW laser power. 相似文献
2.
Grading and the Ethos of Effort 总被引：1，自引：0，他引：1
Using quantitative and qualitative data from a project to improve middle-school girls' engagement with science, mathematics
and technology, this study examined the ways in which grading practices worked to augment the messages about achievement and
compliance conveyed in more and less troubled schools. In particular, the study revealed differences in the extent to which
different kinds of schools embedded achievement and non-achievement factors in the grades awarded to middle school girls.
The study linked these differences to school-level differences in teachers' overall orientation toward grading. Grading in
the more troubled schools - those with a more custodial orientation toward control - appeared to reflect teachers' tendency
to subscribe to an 'ethos of effort'. Acting on the basis of this 'ethos', teachers in the troubled schools tended to confound
achievement and non-achievement factors in the determination of report-card grades. In the less troubled school, by contrast,
teachers did not rely as heavily on non-achievement factors when they determined students' grades. Given limitations associated
with sampling, however, findings from the study were viewed cautiously. Nevertheless, the research appeared to support the
claim that there could be systematic associations between school-level climate characteristics and particular instructional
practices.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
1