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21.
In this second part of the study, ideal shock theory in two‐layer stratified flow is extended to include a third passive layer (i.e., a two and a half layer system). With the presence of a passive layer, two linear wave modes and "viscous tail modes" exist, complicating the solubility conditions and uniqueness proofs for two layer shocks. It is found however, that shocks can be unambiguously classified as external or internal based on the states of criticality that they connect. The steepening condition, while still necessary, provides a less restrictive constraint than it did with a rigid lid. Thus, we have to rely more on solutions to the full viscous shock equations to establish shock existence. The detailed structure, momentum exchange, and Bernoulli loss in a viscous shock are examined using an analytical weak shock solution and a set of numerical solutions for shocks with finite amplitudes. A shock regime diagram ( F 1 by F 2 ) is constructed based on the numerical integration of the full viscous shock equations. For strong external jumps, a cusp region (i.e., in the sense of catastrophe theory) is identified on the regime diagram. For pre‐shock states within the cusp, three end states are possible and two of these are realizable. The cusp has several physical implications. It indicates that an equal distribution of dissipation between the two layers in shocks is mathematically possible but physically inaccessible. It also allows hysteresis in time varying flows, and promotes the occurrence of double shocks (i.e., closely spaced shocks of different character). The results are compared with classical shock solutions and a set of time dependent numerical experiments. 相似文献
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RONALD F. ABLER 《International journal of geographical information science》2013,27(4):303-326
Abstract The National Science Foundation will soon establish a National Center devoted to geographical research and education based on geographical information systems (GIS). The Center will be located at a university chosen on the basis of competitive proposals that will be evaluated primarily on the quality of their research agendas. The winning institution will be expected to involve government agencies and private firms in Center operations and programmes, and it will be expected to serve the national GIS community. The Center arose from a suggestion made by a member of the GIS research community. A large-scale database initiative and a Foundation commitment to Science and Technology Centers provided an institutional environment hospitable to the Center. There are similarities and differences in the approach taken toward GIS research, policy and applications in the United Kingdom (UK) and in the United States (US). Those similarities and differences offer promising topics for collaborative research on GIS itself and on GIS as an information technology affecting the discipline of geography. Cross-national UK-US research would be a productive step toward the globalization of GIS and GIS research. 相似文献
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Examination of the accuracy of a tangent linear model 总被引：1，自引：0，他引：1
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Large portions of the spectra of singular values are determined for both moist and dry versions of a tangent linear, regional model for 4 different synoptic cases. Norms considered include the usual energy norm and versions of a norm measuring only the energy in some set of rotational mode perturbations. At most, only a few percent of the singular vectors possible with any of the norms are growing ones. Inclusion of moist physics in the tangent linear model greatly affects the leading singular vectors but does not increase the number of growing singular vectors much. Most singular vectors are damping ones, and therefore random perturbations drawn from a white‐noise distribution will likely damp during the 24‐h forecast periods considered. Only a few singular vectors are required to explain a significant portion of the final‐time variance of such perturbations, however, because the leading singular values are so large compared with the rest. The truncated rotational mode norm is shown to be very useful for investigating these properties. 相似文献
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ABSTRACT. In the public‐space discourse Los Angeles is usually portrayed as more “anti‐city” than city. Its landscape is overrun by houses, “private‐public” squares and plazas, theme parks, shopping malls, and so on and lacks inclusive public places. Yet this discourse has essentially disdained to contemplate a major public space that contradicts its general thesis: the Los Angeles coast. The coast is meaningful public place in two specific senses. First, it symbolizes Los Angeles as a whole and therefore provides a basis for regional public identity. Second, Angelinos themselves take the coast seriously as a public place, and they have striven to make it inclusive in practice. 相似文献
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