Germ-line transmission of genes introduced into cultured pluripotential cells by retroviral vector

Embryonic stem cells isolated directly from mouse embryos can be cultured for long periods in vitro and subsequently repopulate the germ line in chimaeric mice. During the culture period these embryonic cells are accessible for experimental genetic manipulation. Here we report the use of retroviral vectors to introduce exogenous DNA sequences into a stem-cell line and show that these modified cells contribute extensively to the somatic and germ-cell lineages in chimaeric mice. Compared with current methods for manipulation of the mouse genome, this approach has the advantage that powerful somatic-cell genetic techniques can be used to modify and to select cells with germ-line potential, allowing the derivation of transgenic strains with pre-determined genetic changes. We have by this means inserted many proviral vector sequences that provide new chromosomal molecular markers for linkage studies in the mouse and that also may cause insertional mutations.     

枢纽港投资方案与安全运输通道同步优化模型

针对西非大陆独特特性,考虑货主与港口经营者博弈、各枢纽港间相互关系以及西非地缘风险等因素的影响,基于用户均衡原理,以区域综合运输成本最低为目标,构建混合整数规划模型,协同优化枢纽港投资方案(包括枢纽港投资对象选择,投资港口数,投资额度)以及内陆安全通道设计方案.基于遗传算法提出一种遗传Frank-Wolf混合算法.计算结果表明,模型能够在考虑安全风险因素的要求下,同步优化枢纽港投资对象选择、投资额度以及相应的内陆安全运输通道网络.     

Trading zones and interactional expertise

The phrase ‘trading zone’ is often used to denote any kind of interdisciplinary partnership in which two or more perspectives are combined and a new, shared language develops. In this paper we distinguish between different types of trading zone by asking whether the collaboration is co-operative or coerced and whether the end-state is a heterogeneous or homogeneous culture. In so doing, we find that the voluntary development of a new language community—what we call an inter-language trading zone—represents only one of four possible configurations. In developing this argument we show how different modes of collaboration result in different kinds of trading zone, how different kinds of trading zone may be ‘nested’ inside each other and discuss how a single collaboration might move between different kinds of trading zone over time. One implication of our analysis is that interactional expertise is a central component of at least one class of trading zone.     

Experiments with interactional expertise

‘Interactional expertise’ is developed through linguistic interaction without full scale practical immersion in a culture. Interactional expertise is the medium of communication in peer review in science, in review committees, and in interdisciplinary projects. It is also the medium of specialist journalists and of interpretative methods in the social sciences. We describe imitation game experiments designed to make concrete the idea of interactional expertise. The experiments show that the linguistic performance of those well socialized in the language of a specialist group is indistinguishable from those with full blown practical socialization but distinguishable from those who are not well socialized. The imitation game can also be used to indicate whether an individual can enter an esoteric domain and master the interactional expertise, a skill required by interpretative sociologists of science, anthropologists, ethnographers, and the like.     

Selective antagonism by Mg2+ of amino acid-induced depolarization of spinal neurones.

In the isolated frog or rat spinal cord, low concentrations of Mg2+ (0.5-1.00 mM) markedly depress, in a substantially Ca2+-independent manner, ventral root depolarizations produced by dorsal root stimulation and by certain amino acids (e.g. N-methyl-D-aspartate and L-homocysteate) but do not depress depolarizations produced by other excitatory amino acids (e.g. kainate and quisqualate). L-Aspartate-induced depolarizations are more sensitive to Mg2+ then are L-glutamate-induced depolarizations.