Hydrogel discs for digital microfluidics

Hydrogels are networks of hydrophilic polymer chains that are swollen with water, and they are useful for a wide range of applications because they provide stable niches for immobilizing proteins and cells. We report here the marriage of hydrogels with digital microfluidic devices. Until recently, digital microfluidics, a fluid handling technique in which discrete droplets are manipulated electromechanically on the surface of an array of electrodes, has been used only for homogeneous systems involving liquid reagents. Here, we demonstrate for the first time that the cylindrical hydrogel discs can be incorporated into digital microfluidic systems and that these discs can be systematically addressed by droplets of reagents. Droplet movement is observed to be unimpeded by interaction with the gel discs, and gel discs remain stationary when droplets pass through them. Analyte transport into gel discs is observed to be identical to diffusion in cases in which droplets are incubated with gels passively, but transport is enhanced when droplets are continually actuated through the gels. The system is useful for generating integrated enzymatic microreactors and for three-dimensional cell culture. This paper demonstrates a new combination of techniques for lab-on-a-chip systems which we propose will be useful for a wide range of applications.     

Peer rejection and HPA activity in middle childhood: friendship makes a difference

Exclusion and victimization by classmates were related to levels and diurnal change in cortisol in 97 fourth graders (53% boys, M = 9.3 years). Number and quality of friendships were considered as moderators. Salivary cortisol was collected 5 times daily on 2 school days. Excluded children had elevated cortisol levels at school and a flattened diurnal cortisol curve, suggesting hypothalamic-pituitary-adrenocortical (HPA) axis dysregulation. This effect was weaker for children with more friends or better friendships. Victimization was not associated with cortisol level or change. The results demonstrate the role of HPA activity in peer group processes and indicate that group and dyadic factors interact in predicting stress in the peer group.     

A tool for monitoring the development of written English: T-unit analysis using the SAWL

The article reports the development of the Structural Analysis of Written Language (SAWL), an instrument designed for use by classroom teachers in objectively documenting the ability of children to write in English. The SAWL allows teachers to use T-unit analysis to quantitatively assess language improvement regardless of whether the student writes perfect English, flawed English, and/or generates "wordstrings" with minimal English structure. The SAWL introduces two new indexes of linguistic maturity, morphemes per T-unit (MTU) and the word efficiency ratio (WER). The SAWL also allows teachers to (a) objectively compare a child's written composition with printed material and (b) make a seamless comparison of a student's written English across his or her academic life using the same indexes of measurement.     

Dynamic in situ chromosome immobilisation and DNA extraction using localized poly(N-isopropylacrylamide) phase transition

A method of in situ chromosome immobilisation and DNA extraction in a microfluidic polymer chip was presented. Light-induced local heating was used to induce poly(N-isopropylacrylamide) phase transition in order to create a hydrogel and embed a single chromosome such that it was immobilised. This was achieved with the use of a near-infrared laser focused on an absorption layer integrated in the polymer chip in close proximity to the microchannel. It was possible to proceed to DNA extraction while holding on the chromosome at an arbitrary location by introducing protease K into the microchannel.     

贾兰坡:在石头中寻找人类的足迹

1993年6月,在“七运会”组委会的一次会议上,当讨论到“七运会”的圣火炎种应当到我们的祖先——“北京猿人”栖息的洞中去点时,有人提到半个多世纪以前发掘“北京猿人”化石的老科学家贾兰坡还健在,现已85岁高龄。 组委会当即同拍案:“太好了！就请这位老科学家来点！” 贾兰坡,中国科学院学部委员,当时正在京西宾馆参加预选新一届学     

四川西部中、晚三叠世腹足类化石

四川省地质局区域地质调查队的同志们,近年从事川西高原地区二十万分一区域地质测量工作过程中,在该区中、晚三叠世地层内采获了大批腹足动物化石。本文对其中之一部进行了描述,共7属10种,其中包括3个新种,其名称及产地层位如下表(75页)所示。这些化石中,Undulcria scalata v. Schlotheim, Loxonema obsoletum v. Ziethen与Neritaria sphaeroidica E.Picard原产于德国中三叠统(壳灰统)下部,Toxoconcha brockii Stoppani, Crgptonerita elliptica Kittl与Neritaria candida Kittl原产于     

科学大师的教育艺术──《另一种人生——当代中国科学家随感》读后

科学大师的教育艺术《另一种人生———当代中国科学家随感》读后●潘云唐上海“东方出版中心”于１９９８年３月推出了卢嘉锡为主编、李真真为副主编的《另一种人生———当代中国科学家随感》一书。此书收录了５０位著名科学家（其中４８位是中国科学院院士）的１２３篇...     

科学家的人生——爱国、拼搏与奉献

在这“信息时代”、“知识经济时代”,科学家成了历史舞台上的重要角色。科学家从来就是时代最高精神境界的代表。在我国地球科学界,人们常常怀念一位卓越的地质学家——中国科学院院士李春昱,他是风靡全球的“板块构造学说”在中国最杰出的研究者。去年是他逝世10周年,今年又是他诞辰95周年。在他身上,闪耀着爱国、拼搏、奉献精神的光辉。