Morphological evolution through multiple cis-regulatory mutations at a single gene

One central, and yet unsolved, question in evolutionary biology is the relationship between the genetic variants segregating within species and the causes of morphological differences between species. The classic neo-darwinian view postulates that species differences result from the accumulation of small-effect changes at multiple loci. However, many examples support the possible role of larger abrupt changes in the expression of developmental genes in morphological evolution. Although this evidence might be considered a challenge to a neo-darwinian micromutationist view of evolution, there are currently few examples of the actual genes causing morphological differences between species. Here we examine the genetic basis of a trichome pattern difference between Drosophila species, previously shown to result from the evolution of a single gene, shavenbaby (svb), probably through cis-regulatory changes. We first identified three distinct svb enhancers from D. melanogaster driving reporter gene expression in partly overlapping patterns that together recapitulate endogenous svb expression. All three homologous enhancers from D. sechellia drive expression in modified patterns, in a direction consistent with the evolved svb expression pattern. To test the influence of these enhancers on the actual phenotypic difference, we conducted interspecific genetic mapping at a resolution sufficient to recover multiple intragenic recombinants. This functional analysis revealed that independent genetic regions upstream of svb that overlap the three identified enhancers are collectively required to generate the D. sechellia trichome pattern. Our results demonstrate that the accumulation of multiple small-effect changes at a single locus underlies the evolution of a morphological difference between species. These data support the view that alleles of large effect that distinguish species may sometimes reflect the accumulation of multiple mutations of small effect at select genes.     

A reversible wet/dry adhesive inspired by mussels and geckos

The adhesive strategy of the gecko relies on foot pads composed of specialized keratinous foot-hairs called setae, which are subdivided into terminal spatulae of approximately 200 nm (ref. 1). Contact between the gecko foot and an opposing surface generates adhesive forces that are sufficient to allow the gecko to cling onto vertical and even inverted surfaces. Although strong, the adhesion is temporary, permitting rapid detachment and reattachment of the gecko foot during locomotion. Researchers have attempted to capture these properties of gecko adhesive in synthetic mimics with nanoscale surface features reminiscent of setae; however, maintenance of adhesive performance over many cycles has been elusive, and gecko adhesion is greatly diminished upon full immersion in water. Here we report a hybrid biologically inspired adhesive consisting of an array of nanofabricated polymer pillars coated with a thin layer of a synthetic polymer that mimics the wet adhesive proteins found in mussel holdfasts. Wet adhesion of the nanostructured polymer pillar arrays increased nearly 15-fold when coated with mussel-mimetic polymer. The system maintains its adhesive performance for over a thousand contact cycles in both dry and wet environments. This hybrid adhesive, which combines the salient design elements of both gecko and mussel adhesives, should be useful for reversible attachment to a variety of surfaces in any environment.     

Spin-based logic in semiconductors for reconfigurable large-scale circuits

Research in semiconductor spintronics aims to extend the scope of conventional electronics by using the spin degree of freedom of an electron in addition to its charge. Significant scientific advances in this area have been reported, such as the development of diluted ferromagnetic semiconductors, spin injection into semiconductors from ferromagnetic metals and discoveries of new physical phenomena involving electron spin. Yet no viable means of developing spintronics in semiconductors has been presented. Here we report a theoretical design that is a conceptual step forward-spin accumulation is used as the basis of a semiconductor computer circuit. Although the giant magnetoresistance effect in metals has already been commercially exploited, it does not extend to semiconductor/ferromagnet systems, because the effect is too weak for logic operations. We overcome this obstacle by using spin accumulation rather than spin flow. The basic element in our design is a logic gate that consists of a semiconductor structure with multiple magnetic contacts; this serves to perform fast and reprogrammable logic operations in a noisy, room-temperature environment. We then introduce a method to interconnect a large number of these gates to form a 'spin computer'. As the shrinking of conventional complementary metal-oxide-semiconductor (CMOS) transistors reaches its intrinsic limit, greater computational capability will mean an increase in both circuit area and power dissipation. Our spin-based approach may provide wide margins for further scaling and also greater computational capability per gate.     

供热设计方案综合评价与优选研究

多目标综合效果测度法是一种非常有效的系统优化评价方法。从方案的经济性、技术性及对环境的影响等角度,对5种供热方案进行分析,运用多目标综合效果测度法对备选方案进行评价,确定污水源热泵系统为最佳方案。     

电磁阻尼器性能参数试验研究

电磁阻尼器性能与多种因素有关,在电磁阻尼器基本性能试验研究基础上,制作了一个电磁阻尼器模型,进行了涡流板厚度参数影响的试验研究:做了3种厚度涡流板在不同频率、不同位移情况下的试验,得到了涡流板厚度对阻尼器性能影响的定性结论。     

粘土基防渗浆材的实验研究

针对目前常用浆材的局限性和工程应用的需要,采用正交优化的实验方法研究一种以粘土为主的粘土基防渗浆材,浆材具有良好的稳定性和可灌性,其结石体具有低渗透性和较低强度,适用于非加固型的防渗注浆工程。     

QY25起重机行星变速箱优化设计

根据产品要求,对起重机起升机构中的行星变速箱进行优化设计,主要对变速箱中的齿轮进行高度变位计算,从而达到减轻整机的重量和体积,合理地确定已有参数,以期达到最佳设计的目的。     

一种包边模边界缩进控制方法

 将确定性优化方法用于板料包边设计.汽车板料包边仿真中变形区域小导致有限元模型在变形区域的网格很小,模型计算时间太长.本文针对影响板料包边后边界缩进较大的3个参数,建立目标函数的径向基函数近似模型,并用确定性优化方法对近似模型进行优化,近似模型计算效率高,提高了优化方法计算效率,使板料包边的优化设计成为可能,并为生产中的汽车板料控制包边后的边界缩进提供了一种新的思路.     

某类重特大火灾数值模拟研究

某酒吧火灾、深圳舞王俱乐部火灾和福建长乐拉丁酒吧火灾的发生场所和火灾原因类似,且短时间就造成大量人员伤亡,研究这类火灾防控措施有较好的意义。本文利用FDS软件构造某酒吧的火灾模型,合理分析场所的人员情况设定疏散模拟参数,根据火场情况设定合适的火灾场景,分析热辐射、烟气温度、烟气毒性、烟气能见度等参数的变化过程,并得到可用疏散时间。结合CFE软件进行人员疏散过程模拟,模拟的预期火灾人员伤亡与实际情况较好相符;并对不同的可燃物类型、消防设施状况和待疏散人数进行火灾后果分析,可燃物分析结果说明装修用聚氨酯泡沫吸音棉是造成火灾极速蔓延的直接原因,这类材料产生大量的有毒浓烟,很快就造成人员伤亡;不同消防设施模拟分析的结果体现了自动消防设施的重要作用,公共娱乐场所的自动喷水灭火系统应推广快速响应喷头,未按国家标准安装自动消防设施是造成重大火灾人员伤亡的成灾原因;对酒吧不同待疏散人数的火灾预期伤亡数定量分析证明了公共娱乐场所定员管理的重要意义;模拟分析的结果可用于此类火灾成因分析和火灾防控措施研究。     

飞机电热除冰的研究进展与展望

 飞机在结冰气象条件下容易发生结冰现象,冰的存在会破坏飞机气动特性,影响飞行安全,严重结冰可导致机毁人亡,故必须及时将冰移除。电热除冰是目前最常考虑的除冰方式之一,本文系统介绍了电热除冰装置及其工作原理。首先,主要围绕除冰过程的传热特性、冰层力学特性和冰脊的形成,详细阐述了国内外电热除冰研究的发展。然后,针对国内外研究存在的一些问题,提出了几点对电热除冰研究的粗略想法,电热除冰数值计算方法和模拟技术研究、热力耦合特性对冰层融化和力学特性的影响研究、冰脱落准则和运动规律研究是未来研究需要重视的方向。