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71.
介绍了江西省数字化雷达回波拼图的技术方法。该方法主要包括回波资料的预处理、拼图投影处理。它具有资料同一性、准确性好、方便灵活、适合业务使用等特点。 相似文献
72.
Armin Freundt 《Bulletin of Volcanology》1998,59(6):414-435
High-grade ignimbrites are thought to be deposited by pyroclastic flows at temperatures exceeding minimum welding temperature
or even solidus temperature. Corresponding pyroclastic-flow particles range from plastic to partially liquid and are able
to aggregate or coalesce. This contrasts with particles in pyroclastic flows producing unwelded ignimbrite, which are capable
of elastic grain interactions. The low aspect ratio and great areal extent of high-grade ignimbrites requires transport in
a particulate state either by (a) high-concentration mass flow facilitated by fluidizing gas reducing internal friction, or
by (b) expanded turbulent flow of low but downward increasing concentration. This paper presents experiments designed to investigate
the effects of plastic to liquid particles on these two contrasting transport mechanisms. Gas fluidization experiments using
polyethyleneglycole (PEG) powders heated above minimum sintering (Tms) and melting (Tm) temperatures cover a wide range of fluidization velocities (Umf>Ua>0.6·Ut) but are always in the bubbly fluidization regime similar to fluidized ignimbrite ash, where particle volume concentration
outside the bubbles is high (≈10–1). When the powders reach a critical temperature Tm≥T≥Tms, defluidization by catastrophic particle aggregation immediately commences in both stationary and laterally moving fluidized
beds as well as in experiments using mixtures of high- and low-Tm (≥30 wt.%) PEG powders, when T≥Tms of the lower-Tm powder. This indicates that extended particulate transport at T≥Tms is not possible at such high particle concentrations. In the turbulent flow experiments, liquid sprays of molten PEG or water,
vertically injected into a high-Re (>104) horizontal air flow, form a low-concentration (10–5 to 10–4) turbulent suspension current. Proximal formation of partially coalesced aggregates, which settle faster than individual
particles, causes the measured downstream decay of sedimentation rate to be steeper than predicted by theory of single solid-particle
sedimentation from turbulent suspensions. As particles become finer downstream and coalescence efficiency decreases in response
to cooling, more distally formed aggregates become too small and rare to modify sedimentation-rate decay from that of suspension
flows containing solid particles. The key difference between the two transport systems is particle concentration, C. Since
particle collision rate Rcoll∝C2, collision rates in fluidized beds are so high that all particles immediately aggregate when coalescence efficiency (1≥Ecoal≥0) is larger than 10-3. Low-concentration suspensions, on the other hand, require much higher values of Ecoal for significant aggregation to occur. Dilute pyroclastic flows will have higher particle volume fractions (≈10–3) than the experimental currents, but then viscous pyroclasts should have lower coalescence efficiencies than PEG droplets.
Experimental results thus support an expanded turbulent transport mechanism of pyroclastic flows generating extensive high-grade
ignimbrite sheets.
Received: 28 August 1996 / Accepted: 3 December 1997 相似文献
73.
河西地区非均匀下垫面的大气变性过程 总被引:14,自引:6,他引:14
利用HEIFE野外观测资料,分析了河西地区黑河流域夏半年下面动力和热力特性的不均匀 ;并以个别具有一定代表性的晴天观测资料为例,客观地分析了绿洲与沙漠或戈壁下垫面突变所产生的近地层大气变性过程;初步解释发绿洲近地层逆温和沙漠或戈壁近地层逆湿的形成机制,同时也讨论了绿洲和沙的水汽输送过程。 相似文献
74.
75.
In natural waters arsenic normally occurs in the oxidation states +III (arsenite) and +V (arsenate). The removal of As(III) is more difficult than the removal of As(V). Therefore, As(III) has to be oxidized to As(V) prior to its removal. The oxidation in the presence of air or pure oxygen is slow. The oxidation rate can be increased by ozone, chlorine, hypochlorite, chlorine dioxide, or H2O2. The oxidation of As(III) is also possible in the presence of manganese oxide coated sands or by advanced oxidation processes. Arsenic can be removed from waters by coprecipitation with Fe(OH)3, MnO2 or during water softening. Fixed‐bed filters have successfully been applied for the removal of arsenic.The effectiveness of arsenic removal was tested in the presence of adsorbents such as FeOOH, activated alumina, ferruginous manganese ore, granular activated carbon, or natural zeolites. Other removal technologies are anion exchange, electrocoagulation, and membrane filtration by ultrafiltration, nanofiltration or reverse osmosis. 相似文献
76.
资源学、环境学与经济学是相对独立的学科,但它们之间又具有密切的内部联系。资源(自然资源)、经济和环境是现代社会发展中的三个重要方面。本文试图用综合发展的观点,分析资源、环境、经济三者之间的相互矛盾、相互依赖、相互影响、相互作用的规律,论述处理好资源、环境与经济相互协调、发展的关系。这也是社会经济可持续发展的时代要求。 相似文献
77.
78.
以地震次生水灾为研究对象,构建了地震次生水灾的指标体系,在此基础上应用层次分析法建立数学模型,初步研究了地震次生水灾区划的方法和过程。 相似文献
79.
Erick R. Burns Maria I. Dragila John S. Selker Ronald B. Guenther Jean-Yves Parlange Noam Weisbrod 《Advances in water resources》2007
The Buckingham–Darcy Law is used to describe fluid flow in unsaturated porous media at low Reynolds number. In order to provide a priori corrections to this law, a process thermodynamic approach is utilized to ascertain the functional dependence. Using this knowledge, corrections to the hydraulic conductivity coefficient are proposed and compared with available data. The proposed corrections substantially predict the observed behavior of flow of high concentration (saturated) sodium chloride solutions in porous media. During the derivation, physical principles consistent with the thermodynamics of the system were utilized. A review of these principles and their results provides an alternative form of the generalized Gibbs–Duhem Relation for continuous processes, indicating that the identical equivalence to zero is unlikely to occur for dissipative processes. Further, the postulated Gibbs and Gibbs–Duhem Relations indicate that special differential operators need to be used for continuous processes rather than the usual use of a generic differential. 相似文献
80.
基于遥感和GIS的中国土地潜力资源的研究 总被引:26,自引:0,他引:26
在对中国土地资源综合研究基础上,利用已有研究成果,借助GIS工具,利用层次分析法,对中国土地地潜力资源进行了综合分析和评价,在评价基础上,对中国土地资源的耕地潜力、生产潜力、生产潜力总量、人口容量潜力及综合潜力的大小和空间展布特征进行分析。结论为:中国土地资源潜力很力,但时空分布不均,在开发利用中,应因地制宜,采取不同的开发、利用的战略方针,在保护好现有土地资源和合理科学利用的基础上,谨慎开发,以 相似文献