Density-dependent separation of encapsulated cells in a microfluidic channel by using a standing surface acoustic wave

This study presents a method for density-based separation of monodisperse encapsulated cells using a standing surface acoustic wave (SSAW) in a microchannel. Even though monodisperse polymer beads can be generated by the state-of-the-art technology in microfluidics, the quantity of encapsulated cells cannot be controlled precisely. In the present study, mono-disperse alginate beads in a laminar flow can be separated based on their density using acoustophoresis. A mixture of beads of equal sizes but dissimilar densities was hydrodynamically focused at the entrance and then actively driven toward the sidewalls by a SSAW. The lateral displacement of a bead is proportional to the density of the bead, i.e., the number of encapsulated cells in an alginate bead. Under optimized conditions, the recovery rate of a target bead group (large-cell-quantity alginate beads) reached up to 97% at a rate of 2300 beads per minute. A cell viability test also confirmed that the encapsulated cells were hardly damaged by the acoustic force. Moreover, cell-encapsulating beads that were cultured for 1 day were separated in a similar manner. In conclusion, this study demonstrated that a SSAW can successfully separate monodisperse particles by their density. With the present technique for separating cell-encapsulating beads, the current cell engineering technology can be significantly advanced.     

电子治理的演进及持续挑战

电子治理是指运用信息与通讯技术（ICTs）来支撑公共服务、政府管理、民主程序、并改善公民、公民社会、私有部门与国家之间的关系。经过20余年的技术创新与政策回应,电子治理的发展可以用5个具有内在关联的目标来描述：建立政策框架、提升公共服务、高质量低成本的政府运作、民主程序中的公民参与、行政和体制改革。本文对美国州政府和地方政府电子治理的总结评估表明：在提升公共服务和改善政府运作方面的投资力度最大,进步最明显;政策制定也已在多个方面取得进步,但新的政策议题不断使问题愈趋复杂;进展最小是在提升民主,以及探索电子治理对行政和体制改革的启示这两个方面。在可以预见的未来,以信息通讯技术为手段的电子治理将会继续发展,并为不断的研究与实践提供一个动态的环境。     

我国高校教师发明披露问题——现状、制度原因及改进对策

以2002—2012年间我国35所重点高校2002名在职教师的18435项发明专利为样本,调查了我国高校教师的发明披露现状,并从政府和高校两个层面分析了制度设计对教师披露意愿的影响.研究发现,约13.16%的教师发明专利没有被完全分配给所在高校,高质量教师发明更可能被披露给校外机构和个人.分析表明,我国高校的发明权属、职务发明认定和收益分配制度,以及地方政府专利资助政策无助于激励教师向高校披露高质量发明,而高校的发明质量审查体系和绩效考核机制也难以有效抑制教师的低质量发明披露冲动.最后,本文从政府和高校层面提出相关的制度改进建议,以期为政策制订者提供参考.     

量子力学中的微扰展开

微扰级数在量子力学教学中很重要,这对于研究生层次的教学尤为重要。标准教科书[1]、[2]推导量子力学中与时间有关的微扰级数,将含时薛定谔方程变为相互作用绘景下的微分方程,然后再转变成积分方程,其解由迭代法给出,从而得到与时间有关的相互作用绘景下的波函数相应的微扰级数。本文结果表明:对于含时薛定谔波函数,找出其用微扰参数的递次幂表示的形式泰勒级数,可以得到微扰级数。泰勒级数中的系数由波函数对微扰参数     

Treatment outcomes for students with learning disabilities: how important are internal and external validity?

This study analyzed the magnitude of experimental intervention outcomes as a function of violations in internal and external validity for studies that included students with learning disabilities. The results indicated that treatment outcomes were significantly affected by the following violations: teacher effects, establishing criterion levels of instructional performance, reliance on experimental measures, using different measures between pretest and posttest, using a sample heterogenous in age, and using incorrect units of analysis. Furthermore, the underreporting of information related to ethnicity, locale of the study, psychometric data, and teacher applications positively inflated the magnitude of treatment outcomes. A weighted hierarchical regression analysis revealed that composite scores of the aforementioned high-risk variables accounted for 16% of the total variance in effect size. The implications for interpreting intervention research to practice are discussed.     

Studying enzymatic bioreactions in a millisecond microfluidic flow mixer

In this study, the pre-steady state development of enzymatic bioreactions using a microfluidic mixer is presented. To follow such reactions fast mixing of reagents (enzyme and substrate) is crucial. By using a highly efficient passive micromixer based on multilaminar flow, mixing times in the low millisecond range are reached. Four lamination layers in a shallow channel reduce the diffusion lengths to a few micrometers only, enabling very fast mixing. This was proven by confocal fluorescence measurements in the channel’s cross sectional area. Adjusting the overall flow rate in the 200 μm wide and 900 μm long mixing and observation channel makes it possible to investigate enzyme reactions over several seconds. Further, the device enables changing the enzyme/substrate ratio from 1:1 up to 3:1, while still providing high mixing efficiency, as shown for the enzymatic hydrolysis using β-galactosidase. This way, the early kinetics of the enzyme reaction at multiple enzyme/substrate concentrations can be collected in a very short time (minutes). The fast and easy handling of the mixing device makes it a very powerful and convenient instrument for millisecond temporal analysis of bioreactions.     

An evaluation of searching the German CCMed database for the production of systematic reviews

Objectives: National databases may be useful sources in the production of a systematic review (SR). The aim of this study was to assess the potential benefit of a systematic search in the German database ‘Current Contents Medizin’ (CCMed ). Methods: The study was conducted on the basis of published SRs that included CCMed as a literature source. Eligible SRs were identified through a systematic search in medline , embase and The Cochrane Library. The websites of German Health Technology Assessment agencies were also screened. Citations of primary studies included as relevant in the SRs were extracted and then categorised. Results: The search yielded 52 eligible SRs. A total of 1505 relevant citations were extracted. Seventy‐seven of these articles were published in journals indexed in CCMed . Thirty‐two of the 77 citations were indexed in CCMed , but only eight of the 32 were unique. Of these eight citations, seven were not identified by a systematic search, but by handsearching. Only one unique citation, an observational study, was identified in CCMed by a systematic search. Conclusions: In the production of SRs, a systematic search in CCMed identifies relevant studies only in exceptional cases. Therefore, the routine inclusion of this database in systematic searches does not appear meaningful.     

Oxygen and nitrogen plasma hydrophilization and hydrophobic recovery of polymers

PLASMA HYDROPHILIZATION AND SUBSEQUENT HYDROPHOBIC RECOVERY ARE STUDIED FOR TEN DIFFERENT POLYMERS OF MICROFABRICATION INTEREST: polydimethylsiloxane (PDMS), polymethylmethacrylate, polycarbonate, polyethylene, polypropylene, polystyrene, epoxy polymer SU-8, hybrid polymer ORMOCOMP, polycaprolactone, and polycaprolactone/D,L-lactide (P(CL/DLLA)). All polymers are treated identically with oxygen and nitrogen plasmas, in order to make comparisons between polymers as easy as possible. The primary measured parameter is the contact angle, which was measured on all polymers for more than 100 days in order to determine the kinetics of the hydrophobic recovery for both dry stored and rewashed samples. Clear differences and trends are observed both between different polymers and between different plasma parameters.     

Manipulating single annealed polyelectrolyte under alternating current electric fields: Collapse versus accumulation

Effective manipulation and understanding of the structural and dynamic behaviors of a single polyelectrolyte (PE) under alternating current (AC) electric fields are of great scientific and technological importance because of its intimate relevance to emerging bionanotechnology. In this work, we employ fluorescence correlation spectroscopy (FCS) to study the conformational and AC-electrokinetic behaviors of a model annealed PE, poly(2-vinyl pyridine) (P2VP) under both spatially uniform and non-uniform AC fields at a single molecule level. Under spatially uniform AC-fields, we observe a gradual and continuous coil-to-globule conformational transition (CGT) of single P2VP at varied AC-frequency when a critical AC-field strength is exceeded, in contrast to the pH-induced abrupt CGT in the absence of AC-fields. On the contrary, under spatially non-uniform AC-fields, we observe field-driven net flow and accumulation of P2VP near high AC-field regions due to combined AC electro-osmosis and dielectrophoresis but surprisingly no conformational change. Thus, distinct AC-electric polarization effect on single annealed PE subject to AC-field homogeneity is suggested.     

Vimentin networks at tunable ion-concentration in microfluidic drops

The structure and function of biological systems, for example, cells and proteins, depend strongly on their chemical environment. To investigate such dependence, we design a polydimethylsiloxane-based microfluidic device to encapsulate biological systems in picoliter-sized drops. The content of each individual drop is tuned in a defined manner. As a key feature of our method, the individual chemical composition is determined and related to the drop content. In our case, the drop content is imaged using microscopy methods, while the drops are immobilized to allow for long-time studies. As an application of our device, we study the influence of divalent ions on vimentin intermediate filament networks in a quantitative way by tuning the magnesium concentration from drop to drop. This way we are able to directly image the effect of magnesium on the fluorescently tagged protein in a few hundreds of drops. Our study shows that with increasing magnesium concentration in the drops, the compaction of the networks becomes more pronounced. The degree of compaction is characterized by different morphologies; freely fluctuating networks are observed at comparatively low magnesium concentrations of 5–10 mM, while with increasing magnesium concentration reaching 16 mM they develop into fully aggregated networks. Our approach demonstrates how a systematic study of interactions in biological systems can benefit from the exceptional controllability of microfluidic methods.