粉末材料压制过程的DEM分析

应用离散单元法(DEM)研究了粉末材料在开口容器中受到刚性凸模压制时的流动特点,获得了压制过程中颗粒的运动轨迹、运动速度以及粉末密度分布等重要信息;总结了几种典型的粉末流动模式,并在相关实验中得到了印证,说明了应用DEM分析具有强剪切行为的粉末流动是可行的,结论可供粉末冶金工艺和模具设计人员参考.     

在基本的认知物理学习系统中相互作用的多媒体的应用(上)

现代社会要求理工科学生在大学教育中逐渐掌握各种科学研究的手段及个人技能,以满足21世纪的需要.我们描述了一个帮助学生发展这种技能及在实际科学研究中的认知过程,系统技术在这个学习系统的许多方面起到非常重要的作用,我们描述了在各种国际测量表中描述的教育目标,描述了部分满足这个目标的学习系统,描述了技术在这个系统中的作用以及这个学习系统的有效性评估.     

A C. elegans Ror receptor tyrosine kinase regulates cell motility and asymmetric cell division.

Ror kinases are a family of orphan receptors with tyrosine kinase activity that are related to muscle specific kinase (MuSK), a receptor tyrosine kinase that assembles acetylcholine receptors at the neuromuscular junction. Although the functions of Ror kinases are unknown, similarities between Ror and MuSK kinases have led to speculation that Ror kinases regulate synaptic development. Here we show that the Caenorhabditis elegans gene cam-1 encodes a member of the Ror kinase family that guides migrating cells and orients the polarity of asymmetric cell divisions and axon outgrowth. We find that tyrosine kinase activity is required for some of the functions of CAM-1, but not for its role in cell migration. CAM-1 is expressed in cells that require its function, and acts cell autonomously in migrating neurons. Overexpression and loss of cam-1 function result in reciprocal cell-migration phenotypes, indicating that levels of CAM-1 influence the final positions of migrating cells. Our results raise the possibility that Ror kinases regulate cell motility and asymmetric cell division in organisms as diverse as nematodes and mammals.     

The finished DNA sequence of human chromosome 12

Human chromosome 12 contains more than 1,400 coding genes and 487 loci that have been directly implicated in human disease. The q arm of chromosome 12 contains one of the largest blocks of linkage disequilibrium found in the human genome. Here we present the finished sequence of human chromosome 12, which has been finished to high quality and spans approximately 132 megabases, representing approximately 4.5% of the human genome. Alignment of the human chromosome 12 sequence across vertebrates reveals the origin of individual segments in chicken, and a unique history of rearrangement through rodent and primate lineages. The rate of base substitutions in recent evolutionary history shows an overall slowing in hominids compared with primates and rodents.     

Observation of the radiative decay mode of the free neutron

The theory of quantum electrodynamics (QED) predicts that beta decay of the neutron into a proton, electron and antineutrino should be accompanied by a continuous spectrum of soft photons. While this inner bremsstrahlung branch has been previously measured in nuclear beta and electron capture decay, it has never been observed in free neutron decay. Recently, the photon energy spectrum and branching ratio for neutron radiative decay have been calculated using two approaches: a standard QED framework and heavy baryon chiral perturbation theory (an effective theory of hadrons based on the symmetries of quantum chromodynamics). The QED calculation treats the nucleons as point-like, whereas the latter approach includes the effect of nucleon structure in a systematic way. Here we observe the radiative decay mode of free neutrons, measuring photons in coincidence with both the emitted electron and proton. We determined a branching ratio of (3.13 +/- 0.34) x 10(-3) (68 per cent level of confidence) in the energy region between 15 and 340 keV, where the uncertainty is dominated by systematic effects. The value is consistent with the predictions of both theoretical approaches; the characteristic energy spectrum of the radiated photons, which differs from the uncorrelated background spectrum, is also consistent with the calculated spectrum. This result may provide opportunities for more detailed investigations of the weak interaction processes involved in neutron beta decay.     

工业炸药管道效应的一般规律

本文在分析实验数据的基础上,通过计算炸药中的冲击波,提出了炸药受超前冲击压缩而纯感的冲量准则;并得出了管道效应的存在界限和计算传爆长度的经验公式。     

VARIATION OF WOVEN FABRIC GEOMETRY——Non-uniform Flattening of Yarns

In previous research much effort has been devoted to the geometry of woven fabrics and relat-ed problems under the assumption of constant yarn configuration in fabric.This paper will first re-port that image crimp (yarn crimp measured by an image analysis method) seems larger than actualvalue.From the explanation of this result,the variation of yarn configuration in woven fabric dueto the non-uniform flattening is revealed.The significance of this actual structure of woven fabricsis discussed.It is believed that the variation of yarn configuration is very important for fabric per-formance,and may be an advantage for fabric quality.     

Inclusive fitness theory and eusociality

Arising from M. A. Nowak, C. E. Tarnita & E. O. Wilson 466, 1057-1062 (2010); Nowak et al. reply. Nowak et al. argue that inclusive fitness theory has been of little value in explaining the natural world, and that it has led to negligible progress in explaining the evolution of eusociality. However, we believe that their arguments are based upon a misunderstanding of evolutionary theory and a misrepresentation of the empirical literature. We will focus our comments on three general issues.     

Extinction risk from climate change

Climate change over the past approximately 30 years has produced numerous shifts in the distributions and abundances of species and has been implicated in one species-level extinction. Using projections of species' distributions for future climate scenarios, we assess extinction risks for sample regions that cover some 20% of the Earth's terrestrial surface. Exploring three approaches in which the estimated probability of extinction shows a power-law relationship with geographical range size, we predict, on the basis of mid-range climate-warming scenarios for 2050, that 15-37% of species in our sample of regions and taxa will be 'committed to extinction'. When the average of the three methods and two dispersal scenarios is taken, minimal climate-warming scenarios produce lower projections of species committed to extinction ( approximately 18%) than mid-range ( approximately 24%) and maximum-change ( approximately 35%) scenarios. These estimates show the importance of rapid implementation of technologies to decrease greenhouse gas emissions and strategies for carbon sequestration.     

Nova regulates brain-specific splicing to shape the synapse

Alternative RNA splicing greatly increases proteome diversity and may thereby contribute to tissue-specific functions. We carried out genome-wide quantitative analysis of alternative splicing using a custom Affymetrix microarray to assess the role of the neuronal splicing factor Nova in the brain. We used a stringent algorithm to identify 591 exons that were differentially spliced in the brain relative to immune tissues, and 6.6% of these showed major splicing defects in the neocortex of Nova2-/- mice. We tested 49 exons with the largest predicted Nova-dependent splicing changes and validated all 49 by RT-PCR. We analyzed the encoded proteins and found that all those with defined brain functions acted in the synapse (34 of 40, including neurotransmitter receptors, cation channels, adhesion and scaffold proteins) or in axon guidance (8 of 40). Moreover, of the 35 proteins with known interaction partners, 74% (26) interact with each other. Validating a large set of Nova RNA targets has led us to identify a multi-tiered network in which Nova regulates the exon content of RNAs encoding proteins that interact in the synapse.