工时定额动态参数建模及可视化研究

工时定额数据获取的快速基于动态参数的工时定额计算方法.对影响工时定额计算结果 的诸多参数进行分析,根据参数的性和准确性影响着制造成本和作业计划.传统计算方法效率低、准确性差,为解决这一问题提出了信息表达方式进行分类,建立动态参数计算模型.利用VRML技术构造可视化加工特征模型,将动态参数映射到加工特征模型上,实现工时定额计算参数的图形化拾取.该技术已应用于企业生产过程中,取得良好的效果.     

Polyimides Based on Flexible Diamines:Synthesis, Characterization and Thermal Properties

1 Results and DiscussionTwo diamines 1,4-phenylene di(oxy-4,4′-aniline) and 4-aminophenyloxy-N-4-[(4-amiophenyloxy)benzylidene]aniline were prepared via the nucleopilic substitution reaction and were polymerized with 3,3′,4,4′-benzophenonetetracarboxylic acid dianhydride (BP), 4,4′-(hexafluoroisopropylidene)diphthalic anhydride (HF) , 3,4,9,10-perylenetetracarboxylic acid dianhydride (PD) and pyromellitic dianhydride (PMDA) either by one step solution polymerization reaction or two step procedure. The l...     

Supernova--remnant origin of cosmic rays?

It is thought that Galactic cosmic-ray nuclei are gradually accelerated to high energies (up to about 300 TeV per nucleon, where 1 TeV is 10(12) eV) in the expanding shock waves connected with the remnants of powerful supernova explosions. However, this conjecture has eluded direct observational confirmation since it was first proposed in 1953 (ref. 3). Enomoto et al. claim to have finally found definitive evidence that corroborates this model, proposing that very-high-energy, TeV-range, gamma-rays from the supernova remnant (SNR) RX J1713.7-3946 are due to the interactions of energetic nuclei in this region. Here we argue that their claim is not supported by the existing multiwavelength spectrum of this source. The search for the origin(s) of Galactic cosmic-ray nuclei may be closing in on the long-suspected supernova-remnant sources, but it is not yet over.     

Unexpected inhibition of fusion in nucleus-nucleus collisions

Unstable heavy atomic nuclei not found in nature can be created by fusing two stable nuclei, in a process analogous to colliding charged droplets of liquid. Recently, the formation of a handful of super-heavy nuclei with atomic numbers 114 (ref. 1) and 116 (ref. 2) has been achieved by fusion of heavy nuclei. The electrostatic energy of such systems is very large (which is the reason super-heavy nuclei are unstable), so although the two nuclei may initially be captured by the nuclear potential, rather than fusing, they almost always separate after transfer of mass to the lighter nucleus. This process, called quasi-fission, can inhibit fusion by many orders of magnitude. Understanding this inhibition may hold the key to forming more super-heavy elements. Theoretically, inhibition is predicted (ref. 5 and references therein) when the product Z1Z2 of the charges of the projectile and target nuclei is larger than about 1,600. Here we report measurements of three fusion reactions with Z1Z2 around half this value, each forming 216 88Ra. We find convincing model-independent evidence both of inhibition of fusion, and of the presence of quasi-fission. These results defy interpretation within the standard picture of nuclear fusion and fission.     

Pixel switching of epitaxial Pd/YHx/CaF2 switchable mirrors

Exposure of rare-earth films to hydrogen can induce a metal-insulator transition, accompanied by pronounced optical changes. This 'switchable mirror' effect has received considerable attention from theoretical, experimental and technological points of view. Most systems use polycrystalline films, but the synthesis of yttrium-based epitaxial switchable mirrors has also been reported. The latter form an extended self-organized ridge network during initial hydrogen loading, which results in the creation of micrometre-sized triangular domains. Here we observe homogeneous and essentially independent optical switching of individual domains in epitaxial switchable mirrors during hydrogen absorption. The optical switching is accompanied by topographical changes as the domains sequentially expand and contract; the ridges block lateral hydrogen diffusion and serve as a microscopic lubricant for the domain oscillations. We observe the correlated changes in topology and optical properties using in situ atomic force and optical microscopy. Single-domain phase switching is not observed in polycrystalline films, which are optically homogeneous. The ability to generate a tunable, dense pattern of switchable pixels is of technological relevance for solid-state displays based on switchable mirrors.     

大叶白麻叶化学成分的研究

从大叶白麻[poacynumhendersonii(Hookf)woodson]叶中分得2个木脂素类化舍物,经理化常数测定和光谱分析,分别鉴定为(-)-丁香脂素[(-)-Syringaresino1]和( )-松脂素-4-O-β-D-葡萄糖甙[( )-Pinoresionol-4-0-β-D-glucopyranoside].     

Molecular dialogue between the human gut microbiota and the host: a Lactobacillus and Bifidobacterium perspective

The human gut represents a highly complex ecosystem, which is densely colonized by a myriad of microorganisms that influence the physiology, immune function and health status of the host. Among the many members of the human gut microbiota, there are microorganisms that have co-evolved with their host and that are believed to exert health-promoting or probiotic effects. Probiotic bacteria isolated from the gut and other environments are commercially exploited, and although there is a growing list of health benefits provided by the consumption of such probiotics, their precise mechanisms of action have essentially remained elusive. Genomics approaches have provided exciting new opportunities for the identification of probiotic effector molecules that elicit specific responses to influence the physiology and immune function of their human host. In this review, we describe the current understanding of the intriguing relationships that exist between the human gut and key members of the gut microbiota such as bifidobacteria and lactobacilli, discussed here as prototypical groups of probiotic microorganisms.