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21.
A preliminary theoretical and experimental study was conducted on internal wave modes and their weak nonlinear resonant interaction
in a nonlinearly stratified fluid. An asymptotical solution of the modes and a dispersion relation of internal waves in a
stratified fluid with density profile
similar to that in our experiment were obtained theoretically. The resonant-interaction mechanism to 2nd order approximation
is also discussed. The resonant interaction of the 3rd and 4th mode internal waves excited by the unstable 1st mode wave is
analyzed on the basis of data obtained by conductivity probes. The resonant-interaction condition, i.e.,
,k
1+k
3+k
4=0, is examined. It is shown that the resonant instability increases with pycnocline thickness and wave maker driving frequency.
This work is supported by the National Natural Science Foundation of China. 相似文献
22.
A model is presented for the emplacement of intermediate volume ignimbrites based on a study of two 6 km3 volume ignimbrites on Roccamonfina Volcano, Italy. The model considers that the flows were slow moving, and quickly deflated from turbulent to non-turbulent conditions. Yield strength and density increased whereas fluidisation decreased with time and runout of the pyroclastic flows. In proximal locations, on the caldera rim, heterogeneous exposures including discontinuous lithic breccias, stratified and cross-stratified units interbedded with massive ignimbrite suggest deposition from turbulent flows. In medial locations thick, massive ignimbrite occurs associated with three types of co-ignimbrite lithic breccia which we interpret as being emplaced by non-turbulent flows. Multiple grading of different breccia/lithic concentration types within single flow units indicates that internal shear occurred producing overriding or overlapping of the rear of the flow onto the slower-moving front part. This overriding of different parts of non-turbulent pyroclastic flows could be caused by at least two different mechanisms: (1) changes in flow regime, such as hydraulic jumps that may occur at breaks in slope; and (2) periods of increased discharge rate, possibly associated with caldera collapse, producing fresh pulses of lithic-rich material that sheared onto the slower-moving part of the flow in front.We propose that ground surge deposits enriched in pumice compared with their associated ignimbrite probably formed by a flow separation mechanism from the top and front of the pyroclastic flow. These turbulent clouds moved ahead of the non-turbulent lower part of the flow to form stratified pumice-rich deposits. In distal regions well-developed coarse, often clast-supported, pumice concentrations zones and coarse intra-flow-unit lithic concentrations occur within the massive ignimbrite. We suggest that the flows were non-turbulent, possessed a relatively high yield strength and may have moved by plug flow prior to emplacement. 相似文献
23.
列举了企业内邵会计控制存在的内部会计系统控制机制不健全,监督、考核机制乏力,财务控制存在漏洞、公司企业治理结构不完善等目前企业内部会计控制现状及重点存在问题。提出了完善企业的内部会计控制环境.不相容职务必须分离,强化监督,督促实施,加强会计基础工作,完善会计电算化管理,规范业务处理程序等具体改进建议。 相似文献
24.
25.
Mark E. Reisinger 《The Professional geographer》2003,55(3):383-395
This research is grounded in notions of differential economic restructuring across employment sectors and geographic space, as well as migration selectivity by occupation. A series of unconstrained competing‐destinations models were employed to analyze the response by workers in thirteen occupational categories to sectoral employment change, average wages, and distance. As was hypothesized, workers in occupations that require high levels of education and skills are more responsive, in terms of migration, to economic opportunities in alternative labor‐market areas. However, the results do not support the hypothesis that highly educated and skilled workers migrate longer distances. Further investigation suggests that opportunities for highly educated and skilled workers may be clustering in relatively few areas that are in relatively close proximity. 相似文献
26.
笔者应用地球化学块体理论,对全省化探数据进行综合分析处理。圈出14种元素地球化学块体173个,其中地球化学巨省25个,地球化学省148个。总结地球化学块体在空间上的分布规律。通过研究地球化学块体内部结构,追踪大型至特大型矿床可能存在的地点。利用块体内已探明的金属储量,计算其成矿率,预测其他元素或其他地段的金属资源总量,固定成矿远景区,确定巨型矿床找矿靶区7处。通过不同级别地球化学块体与成矿区带的关系研究,对重要地球化学块体、子块体与成矿亚带、矿田进行对比,对地球化学块体内区域矿产资源潜力作出评价。 相似文献
27.
目的:探讨CT在长骨测量中的应用价值.方法:经X线检查证实的肱骨、股骨、胫骨骨折患者600多例,其中302例临床行髓内钉固定术,并在术前进行了健侧骨的CT定位扫描,测量其两点之间骨干长度及骨髓腔最窄处的宽度。结果 依据术前CT定位测量数据而选择的髓内钉在手术中完全适用。结论:此方法操作简便测量数据准确为临床提供可靠依据。 相似文献
28.
29.
中国南方风化磷块岩研究 总被引:3,自引:2,他引:3
中国南方风化磷块岩中的风化磷矿的自然类型可分为两类七种型式,其中以“原位面型风化磷矿”和“位移溶洞砂砾磷矿”为主。风化磷矿是由其原矿的自身特性与外部适宜条件(水文地质条件为主导)综合作用的产物。根据碳酸盐、磷酸盐矿物分解、淋失程度可划分为弱风化、风化、强风化三个阶段。可用直接法、间接法和数学法3类共13种方法加以判别 相似文献
30.
现代企业必须建立严密的、完善的控制系统,严格的、科学的管理制度,有效的、畅通的运行机制,才能保证经营目标的实现。内部审计可以及时发现经营管理中的薄弱环节和存在的漏洞,及时、准确提醒企业决策者采取措施加以改进,有利于企业不断发展壮大。 相似文献