Geometrical effects in microfluidic-based microarrays for rapid, efficient single-cell capture of mammalian stem cells and plant cells

In this paper, a detailed numerical and experimental investigation into the optimisation of hydrodynamic micro-trapping arrays for high-throughput capture of single polystyrene (PS) microparticles and three different types of live cells at trapping times of 30 min or less is described. Four different trap geometries (triangular, square, conical, and elliptical) were investigated within three different device generations, in which device architecture, channel geometry, inter-trap spacing, trap size, and trap density were varied. Numerical simulation confirmed that (1) the calculated device dimensions permitted partitioned flow between the main channel and the trap channel, and further, preferential flow through the trap channel in the absence of any obstruction; (2) different trap shapes, all having the same dimensional parameters in terms of depth, trapping channel lengths and widths, main channel lengths and widths, produce contrasting streamline plots and that the interaction of the fluid with the different geometries can produce areas of stagnated flow or distorted field lines; and (3) that once trapped, any motion of the trapped particle or cell or a shift in its configuration within the trap can result in significant increases in pressures on the cell surface and variations in the shear stress distribution across the cell’s surface. Numerical outcomes were then validated experimentally in terms of the impact of these variations in device design elements on the percent occupancy of the trapping array (with one or more particles or cells) within these targeted short timeframes. Limitations on obtaining high trap occupancies in the devices were shown to be primarily a result of particle aggregation, channel clogging and the trap aperture size. These limitations could be overcome somewhat by optimisation of these device design elements and other operational variables, such as the average carrier fluid velocity. For example, for the 20 μm polystyrene microparticles, the number of filled traps increased from 32% to 42% during 5–10 min experiments in devices with smaller apertures. Similarly, a 40%–60% reduction in trapping channel size resulted in an increase in the amount of filled traps, from 0% to almost 90% in 10 min, for the human bone marrow derived mesenchymal stem cells, and 15%–85% in 15 min for the human embryonic stem cells. Last, a reduction of the average carrier fluid velocity by 50% resulted in an increase from 80% to 92% occupancy of single algae cells in traps. Interestingly, changes in the physical properties of the species being trapped also had a substantial impact, as regardless of the trap shape, higher percent occupancies were observed with cells compared to single PS microparticles in the same device, even though they are of approximately the same size. This investigation showed that in microfluidic single cell capture arrays, the trap shape that maximizes cell viability is not necessarily the most efficient for high-speed single cell capture. However, high-speed trapping configurations for delicate mammalian cells are possible but must be optimised for each cell type and designed principally in accordance with the trap size to cell size ratio.     

An undergraduate course to bridge the gap between textbooks and scientific research

This article reports on a one-semester Advanced Cell Biology course that endeavors to bridge the gap between gaining basic textbook knowledge about cell biology and learning to think and work as a researcher. The key elements of this course are 1) learning to work with primary articles in order to get acquainted with the field of choice, to learn scientific reasoning, and to identify gaps in our current knowledge that represent opportunities for further research; 2) formulating a research project with fellow students; 3) gaining thorough knowledge of relevant methodology and technologies used within the field of cell biology; 4) developing cooperation and leadership skills; and 5) presenting and defending research projects before a jury of experts. The course activities were student centered and focused on designing a genuine research program. Our 5-yr experience with this course demonstrates that 1) undergraduate students are capable of delivering high-quality research designs that meet professional standards, and 2) the authenticity of the learning environment in this course strongly engages students to become self-directed and critical thinkers. We hope to provide colleagues with an example of a course that encourages and stimulates students to develop essential research thinking skills.     

Developing POPTRAN,a population modelling package

Collaboration between subject matter specialists, computer programmers and educational technologists has resulted in the production of POPTRAN, a computer assisted learning package designed to teach the basic concepts of population studies. Its evaluation in developing countries, with both naive and specialist users, and subsequent revision, has produced a package of both academic quality and teaching effectiveness.     

Decrease in Ammonia Excretion by Boleophthalmus Boddaerti(Mudskipper) Exposed to Cyanide

ThetoleranceofthemudskipperBoleophthalmusboddaertitocyanideishigherthanthoseofotherfishes[1].Suchahightolerancetocyanidedoesnotinvoveareductionofmetabolicrateoranenhancedanaerobicmetabolism,oracyanide-insensitiverespiratorypathway.Instead,itisaresultofthepresenceofasurplusofcytochromeoxidaseandinduciblecyanide-detoxifyingmechanisms,tumingcyanideinthiocyanate,inthismudskipper[1].ThoughCN-isdetoxifiedtoSCN-,realizingbiomembranesaremorepermeabletoHCNthanCN-,wedecidedtoinvestigateiftheprotondi…     

利用心率测定无氧阈

本文以自行车运动员为研究对象,在现场采用定量增加车速的方法来研究运动员心率随车速变化的规律。发现在达到某一负荷速度之前,运动员的心率与车速的增加呈直线相关,而在这种负荷速度之后,上述直线关系明显地发生变化。这种现象在其他竞速运动项目中也被重复,所以称这个速度为偏转速度。偏转速度出现的时间恰与运动员体内血乳酸开始大量堆积的时间相吻合,故作者认为可以利用偏转速度的测定来确定运动员的无氧阈。     

Awareness, use and opinions of methodological search filters used for the retrieval of evidence-based medical literature-a questionnaire survey

The aim of this study was to determine the level of awareness of methodological search filters among health and academic librarians in the UK and Ireland, their use of filters and views on the perceived benefits, limitations and ways to increase usage of search filters. A random proportional sample of health and academic librarians were surveyed by telephone and fax. Overall, 88% (196/224) completed the telephone survey to establish awareness and use of filters. Eighty-four per cent (51/61) completed a fax survey focusing in more depth on usability issues surrounding filters. Results indicate a high level of awareness of methodological filters, but low level of usage. Furthermore, a high level of awareness did not necessarily correlate with a high level of knowledge or understanding. Examination of responses revealed limitations and recommendations beyond those reported in the literature and highlights the relationship between understanding and effective use of filters. Improved dissemination and publication of filters is required to better inform librarians on the concept of filters and how to use them effectively.     

Child protection and justice systems processing of serious child abuse and neglect cases

OBJECTIVE: The aim of this study was to examine the trajectory of cases through four systems: child protection, law enforcement, the dependency courts, and the criminal courts. METHOD: This study focused on a county selected from a 41-county telephone survey conducted for the National Incidence Study of Child Abuse and Neglect (NIS-3). For this analysis prospective samples were drawn from law enforcement (n=225) and the county child protection (CPS) agency (n=225) and followed through in-depth case tracking across all agencies and through both the dependency and criminal court systems. RESULTS: The percentage of CPS cases opened in dependency court was similar to prior studies (29%), but the acceptance and prosecution rates were much higher--92% of the cases referred from CPS, including many cases of physical abuse. Compared to referrals from CPS to law enforcement (93%), few cases were referred from law enforcement to CPS (17%). Anecdotally, case referral patterns appeared to be influenced by communication patterns and mutual positive regard, regardless of the collaborative protocols in place. One of the most instructive findings was the degree of difficulty in tracking cases across organizations and the types of obstacles that impeded success. Disorganization was not an issue, rather internal structures set up to facilitate intra-organizational processing were the same structures that actually impeded cross-organizational case finding. CONCLUSIONS: It is not sufficient to rely on the existence of multi-disciplinary teams or Child Advocacy Centers to ensure collaboration. More attention to daily tasks and activities as well as the nature and quality of communication is warranted. On the technical side, use of common case identifiers on cases that are cross-referred is strongly recommended. Future studies should broaden the scope of inquiry to include the consequences of all case trajectories, rather than solely focusing on the justice system.     

明星与政治

Bono vs.Pretty Much Eyerything博诺vs .几乎每件事Bono befriends O’Neill and Ghana President JohnKufuor. His Case:You name it,he’s trying to fix it:hunger,education,health care,orphans,whatever makes peopleunhappy;lately,he's pushing debt relief for the ThirdWorld nations and stopping the spread of AIDS in Africa.     

Adaptive progressive download based on the MPEG-4 file format

In this paper we describe how progressive download and adaptive streaming can be combined into a simple and efficient streaming framework. Based on the MPEG-4 file format (MP4) we use HTTP for transport and argue that these two components are sufficient for specifying an open streaming architecture. The client selects appropriate chunks from the MP4 file to be transferred based on (1) the header information (i.e. the "moov" box) in the first part of the file and (2) his observation of network throughput. The framework is completely client driven which allows for better server scalability and reduces signalling overhead. We discuss architecture and implementation issues such as complexity, interoperability and scalability and compare to 3GPP PSS Re1-6 adaptive streaming when appropriate. Measurements from a simple MP4/HTTP streaming client are presented showing that appropriate chunks are selected such that increased reliability is achieved.