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51.
9月29日,中铝郑州企业领导李天庚、王立建、吕子剑、纪行带领有关部门负责人深 入长城铝职工总医院看望并慰问病困员职工,为他们送去了中铝郑州企业的关心和温暖。 相似文献
52.
By proposing a two-dimensional triggering model with concentrically circular closed magnetic field line structure, numerical research is made on the asymmetric propagation feature of coronal mass ejection (CME) in two cases emerging at the solar northern latitudes 10° and 45° respectively. The numerical results can qualitatively explain some features of CME event observed by the spacecraft SOHO and show that: (i) In these two cases, the triggering model can initiate CME with an asymmetric closed magnetic field structure, (ii) Closed magnetic structure of CME event will keep deflecting to the current sheet when it propagates away from the sun and this deflecting effect mostly happens within tens of solar radii before CME travels finally along the current sheet, (iii) The triggering model emerging at different locations can introduce CME events with different magnetic shapes. This shape happens to be circular and crescent when the triggering model emerges at the northern latitudes 10° and 45°, respecti 相似文献
53.
Injuries trends of passenger car drivers in head-on collisions are identified based on crash data extracted from the National Automotive Sampling System. Annual injury incidence levels are estimated for years 1990-2007. Over that period, the number of crashes is predicted to rise by 71%. However, the number of serious injuries to drivers is expected to rise by only 41% and driver fatalities are anticipated to decrease by 9%. Meantime, the types of injuries suffered by drivers are changing. Year-to-year shifts in injury patterns result from changes in vehicle size classes within the US vehicle fleet population and increases in seat belt use and air bag availability. The effectiveness of air bags in saving lives is estimated to be 30%, and with more air bag-equipped cars on the road, the probability of sustaining a life-threatening head or a torso injury is reduced. Air bags, however, are not as effective in preventing upper and lower extremity injuries, and thus arm and leg injuries will become more prevalent in years to come. 相似文献
54.
用带孔边裂纹的三种岩石的厚壁筒试件,以水压致裂法测定了不同条件下岩石的断裂韧度K_(IC).结果表明,孔隙压力、预裂纹深度及加载途径等对岩石的K_(IC)有明显的影响。 相似文献
55.
叙述了软件工程的发展过程,论述了软件工程的概念。就目前软件界有影响的几种软件开发模拟进行了分析和比较。同时说明我国软件产业的出路在力推行软件工程化管理。 相似文献
56.
57.
The sterol substrate analog 25-thialanosterol and its corresponding sulfonium salt were evaluated for their ability to serve
as antifungal agents and to inhibit sterol methyltransferase (SMT) activity in Candida albicans. Both compounds inhibited cell proliferation, were fungistatic, interrupted the yeastlike-form to germ-tube-form transition,
and resulted in the accumulation of zymosterol and related Δ24-sterols concurrent with a decrease in ergosterol, as was expected for the specific inhibition of SMT activity. Feedback on
sterol synthesis was evidenced by elevated levels of cellular sterols in treated vs. control cultures. However, neither farnesol
nor squalene accumulated in significant amounts in treated cultures, suggesting that carbon flux is channeled from the isoprenoid
pathway to the sterol pathway with minor interruption or redirection until blockage at the C-methylation step. Activity assays using solubilized C. albicans SMT confirmed the inhibitors impair SMT action. Kinetic analysis indicated that 25-thialanosterol inhibited SMT with the
properties of a time-dependent mechanismbased inactivator K
i of 5 =gmM and apparent k
inact of 0.013 min−1, whereas the corresponding sulfonium salt was a reversible-type transition state analog exhibiting a K
i of 20 nM. The results are interpreted to imply changes in ergosterol homeostasis as influenced by SMT activity can control
growth and the morphological transition in C. albicans, possibly affecting disease development. 相似文献
58.
Evidence for a Male-Produced Sex Pheromone in the Western Flower Thrips Frankliniella occidentalis 总被引:4,自引:0,他引:4
Olfactometer bioassays of walking adult western flower thrips Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae) showed that virgin females (1- to 3-d postemergence) were attracted to the odor of 25 adult males, but not to the odor of 25 adult females, providing behavioral evidence for a male-produced sex pheromone in this species. In contrast to earlier findings, mixed-age adult males were attracted to the odor of adult males. GC analysis of odors collected on SPME fibers revealed two major components and five minor components that were present in the male odor and not in the female odor. The compounds were not present in hexane extracts of males, indicating that these compounds are produced on demand and not stored. 相似文献
59.
As medical ultrasound imaging moves to larger apertures and higher frequencies, tissue sound-speed variations continue to limit resolution. In geophysical imaging, a standard approach for estimating near-surface aberrating delays is to analyze the time shifts between common-midpoint signals. This requires complete data-echoes from every source/receiver pair in the array. Unfocused common-midpoint signals remain highly correlated in the presence of delay aberrations; there is also tremendous redundancy in the data. In medical ultrasound, this technique has been impaired by the wide-angle, random-scattering nature of tissue. This has made it difficult to estimate azimuth-dependent aberration profiles or to harness the full redundancy in the complete data. Prefiltering the data with two-dimensional fan filters mitigates these problems, permitting highly overdetermined, least-squares solutions for the aberration profiles at many steering angles. In experiments with a tissue-mimicking phantom target and silicone rubber aberrators at nonzero stand-off distances from a one-dimensional phased array, this overdetermined, fan-filtering algorithm significantly outperformed other phase-screen algorithms based on nearest-neighbor cross-correlation, speckle brightness maximization, and common-midpoint signal analysis. Our results imply that there is still progress to be made in imaging with single-valued focusing operators. It also appears that the signal-to-noise penalty for using complete data sets is partially compensated by the overdetermined nature of the problem. 相似文献
60.
A probabilistic model called the potential source contribution function (PSCF) has been used to estimate atmospheric source regions of polycyclic aromatic hydrocarbons (PAHs), chlorinated pesticides, and polychlorinated biphenyls (PCBs) to the Great Lakes. This model allows us to map each compound's source region on a 0.5 degrees x 0.5 degrees latitude/longitude grid centered over the Great Lakes basin. PCBs primarily have urban sources, the strengths of which vary. Like PCBs, PAHs show a strong urban signature, but these compounds also seem to come from rural sites. The source regions of PAH become less distinct as the molecular weight of the compound increases. Since reactivity increases with PAH size, this diminishing trend may be an indication that atmospheric degradation plays a large role in PAH transport. The pesticides have the strongest source regions and are typically transported the farthest, often from areas distant from the Great Lakes basin. 相似文献