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181.
提出了一种基于限制编程(Constraint programmmg)的信息模型内在一致性检查方法,重点描述了EXPRESS信息模型的一致性及其检查。EXPRESS语言,作为标准制造数据交换的一个重要部分,广泛地应用于制造与信息业。中提到的一致性检查包括三个步骤:EXPRESS模型形式化,限制满足性问题(CSP)从形式化模型中的抽取和CSP的可满足性测试。本同时揭示了限制编程的一个新的应用领域:模型验证。 相似文献
182.
观察到碘分子在光谱线514.5nm感应作用下的荧光谱,同时得到了在514.5nm附近碘分子的激发光谱。这两种谱的测量和研究表明,两能极模型对碘分子是一个很好的近似,普通光感应的碘分子荧光谱明显不同于激光感应的碘分子荧光谱。 在上面测量和研究的基础上,建立了新的物理模型以应用到激光感应荧光测量技术中。在488.0~544.0nm间,观察到了碘分子的激光感应荧光。 相似文献
183.
本文给出了正态分布可靠寿命的又一个经典近似下限,经验证,本文所给出的结果的精度比已有的结果精度要高,可提供给可靠性工程人员使用。 相似文献
184.
有机高分子絮凝剂处理高浊度原水效果和机理研究 总被引:2,自引:0,他引:2
本文研究了有机高分子絮凝剂PAM、CTAB及它们的复配PAM+CTAB处理高浊度原水的最佳实验条件、絮凝性能、效果和机理,为有机高分子絮凝剂的选择和管式絮凝器的研制提供了理论依据。 相似文献
185.
H.F. Swift R. Bamford R. Chen 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1982,2(12):219-234
Dual-layer meteroid shields consisting of sacrificial bumper plates spaced some distance outboard from the vehicle hull are the most effective structures yet conceived for protecting space vehicles from supervelocity meteroid impacts. This paper presents a new analysis for designing dual-layer shields. The analysis is based upon energy and momentum conservation, fundamental electromagnetic radiation physics, and observation of results from extensive experimental impact investigations conducted at relatively low velocities (near 7 km/s). One important conclusion is that most of the kinetic energy of a meteoroid striking a dual-layer shield is expended as radiation at the stagnation zone on the face plate of the underlying structure. The analysis includes systematic procedures to evaluate the response of shield designs for a given impact threat. Similar applications of the analysis can be used to support a mathematically rigorous procedure for optimum shield design. The research described here supported the Halley Intercept Mission Project at the Jet Propulsion Laboratory, C.I.T., under Contract No. NAS 7–100, sponsored by the National Aeronautics and Space Administration. 相似文献
186.
187.
The martian surface environment exhibits extremes of salinity, temperature, desiccation, and radiation that would make it difficult for terrestrial microbes to survive. Recent evidence suggests that martian soils contain high concentrations of MgSO? minerals. Through warming of the soils, meltwater derived from subterranean ice-rich regolith may exist for an extended period of time and thus allow the propagation of terrestrial microbes and create significant bioburden at the near surface of Mars. The current report demonstrates that halotolerant bacteria from the Great Salt Plains (GSP) of Oklahoma are capable of growing at high concentrations of MgSO? in the form of 2 M solutions of epsomite. The epsotolerance of isolates in the GSP bacterial collection was determined, with 35% growing at 2 M MgSO?. There was a complex physiological response to mixtures of MgSO? and NaCl coupled with other environmental stressors. Growth also was measured at 1 M concentrations of other magnesium and sulfate salts. The complex responses may be partially explained by the pattern of chaotropicity observed for high-salt solutions as measured by agar gelation temperature. Select isolates could grow at the high salt concentrations and low temperatures found on Mars. Survival during repetitive freeze-thaw or drying-rewetting cycles was used as other measures of potential success on the martian surface. Our results indicate that terrestrial microbes might survive under the high-salt, low-temperature, anaerobic conditions on Mars and present significant potential for forward contamination. Stringent planetary protection requirements are needed for future life-detection missions to Mars. 相似文献
188.
Microbially induced iron precipitation associated with a neutrophilic spring at Borra Caves, Vishakhapatnam, India 总被引:1,自引:0,他引:1
The present investigation uncovers various pieces of evidence for the possible biologically induced mineralization in iron mats associated with a pH-neutral spring in the Borra caves, Vishakhapatnam, India. Electron microscopy [scanning electron microscopy (SEM) and transmission electron microscopy (TEM)] demonstrated large numbers of (i) hollow tubes (diameter ~1?μm) resembling sheaths of the iron-oxidizing bacteria Leptothrix, (ii) thin (diameter <1?μm) solid fibers of uncertain origin, (iii) nanoscale subspherical to irregularly shaped particles encrusting tubes and fibers, and (iv) aggregates of broken and partially disintegrated sheaths, fibers, and particles embedded in extracellular polymeric substances (EPS) occasionally including microbial cells. X-ray microanalyses by energy dispersive spectroscopy (EDS) revealed that the mat accumulated largely Fe but also smaller amounts of Si and traces of P and Ca. Particles rich in Si and Al (possibly kaolinite) and Ca (carbonate) were also observed. High-resolution TEM/EDS of unstained ultrathin sections suggests that microbial sheaths were highly mineralized by amorphous to cryptocrystalline Fe-rich phases and less frequently by other fine-grained and fibrous authigenic claylike minerals. Total number of microorganisms in the iron mats was 5.8×10(5) cells, g sed(-1) (wet weight). Analysis of the 16S rRNA gene diversity revealed microorganisms assigned to eight different phyla [Proteobacteria (62%), Chloroflexi (8%), Bacteroidetes (7%), Planctomycetes (1%), Actinobacteria (5%), Acidobacteria (6%), Nitrospira (1%), Firmicutes (5%)]. Within the Proteobacteria, Betaproteobacteria was the predominant class, which accounted for 28% of the sequences. Within this class some obvious similarities between the obtained sequences and sequences from other cave systems could be seen, especially sequences affiliated with Leptothrix, Siderooxidans, Crenothrix, Comamonadaceae, Dechloromonas, and many uncultured Betaproteobacteria. Four (4%) of the sequences could not be assigned to phylum level but were affiliating with the candidate division TM7 (2%), candidate division OP11 (1%), and candidate division WWE3 (1%). The results allow us to infer a possible relationship of microbial sheaths, EPS, and the iron precipitates to microbial community diversity in the Borra cave springs. Understanding biogenic iron oxides in caves has important astrobiological applications as it provides a potential tool for the detection of extraterrestrial life. 相似文献
189.
Cottin H Guan YY Noblet A Poch O Saiagh K Cloix M Macari F Jérome M Coll P Raulin F Stalport F Szopa C Bertrand M Chabin A Westall F Chaput D Demets R Brack A 《Astrobiology》2012,12(5):412-425
The PROCESS (PRebiotic Organic ChEmistry on the Space Station) experiment was part of the EXPOSE-E payload outside the European Columbus module of the International Space Station from February 2008 to August 2009. During this interval, organic samples were exposed to space conditions to simulate their evolution in various astrophysical environments. The samples used represent organic species related to the evolution of organic matter on the small bodies of the Solar System (carbonaceous asteroids and comets), the photolysis of methane in the atmosphere of Titan, and the search for organic matter at the surface of Mars. This paper describes the hardware developed for this experiment as well as the results for the glycine solid-phase samples and the gas-phase samples that were used with regard to the atmosphere of Titan. Lessons learned from this experiment are also presented for future low-Earth orbit astrochemistry investigations. 相似文献
190.
To prevent forward contamination and maintain the scientific integrity of future life-detection missions, it is important to characterize and attempt to eliminate terrestrial microorganisms associated with exploratory spacecraft and landing vehicles. Among the organisms isolated from spacecraft-associated surfaces, spores of Bacillus pumilus SAFR-032 exhibited unusually high resistance to decontamination techniques such as UV radiation and peroxide treatment. Subsequently, B. pumilus SAFR-032 was flown to the International Space Station (ISS) and exposed to a variety of space conditions via the European Technology Exposure Facility (EuTEF). After 18 months of exposure in the EXPOSE facility of the European Space Agency (ESA) on EuTEF under dark space conditions, SAFR-032 spores showed 10-40% survivability, whereas a survival rate of 85-100% was observed when these spores were kept aboard the ISS under dark simulated martian atmospheric conditions. In contrast, when UV (>110?nm) was applied on SAFR-032 spores for the same time period and under the same conditions used in EXPOSE, a ~7-log reduction in viability was observed. A parallel experiment was conducted on Earth with identical samples under simulated space conditions. Spores exposed to ground simulations showed less of a reduction in viability when compared with the "real space" exposed spores (~3-log reduction in viability for "UV-Mars," and ~4-log reduction in viability for "UV-Space"). A comparative proteomics analysis indicated that proteins conferring resistant traits (superoxide dismutase) were present in higher concentration in space-exposed spores when compared to controls. Also, the first-generation cells and spores derived from space-exposed samples exhibited elevated UVC resistance when compared with their ground control counterparts. The data generated are important for calculating the probability and mechanisms of microbial survival in space conditions and assessing microbial contaminants as risks for forward contamination and in situ life detection. 相似文献