Non-uniqueness in the Inverse Gravity Problem for Infinite Polygonal Cylinders

The inverse problem of potential theory is discussed and conditionsare examined under which it is possible for two different uniforminfinite cylinders with polygonal crosssection to produce exactlythe same external gravity field.     

Approximate Operators and Dual Extremum Principles for Linear Problems

The use of approximate operators in the theory of dual extremumprinciples is investigated for certain linear problems. If second-ordertrial functions to certain approximate Lagrangian equationscan be found, bounds which are improvements on the dual boundingfunctions can be constructed. Some simple applications to apartial differential equation and an integral equation are given.It is shown that both upper and lower bounds follow from onetrial function.     

变温核磁共振对壳聚糖/磷酸甘油盐温敏性水凝胶的初步研究

采用变温核磁共振技术对壳聚糖/磷酸甘油盐温敏性水凝胶体系的凝胶化过程进行跟踪研究. 实验结果表明, 壳聚糖中氢和磷酸甘油盐中磷的化学位移均随着温度的升高而变化, 其中壳聚糖中氢的化学位移向高场移动而磷酸甘油盐中磷的化学位移向低场移动. 在凝胶温度附近, 壳聚糖中H-2(D)的化学位移变化出现转折点, 表明其所处的化学环境发生了突变. 随着体系中磷酸甘油盐含量的增加或者pH值的增大, 壳聚糖中H-2(D)的化学位移愈加偏向高场, 体系的凝胶温度则越低. 由此, 我们提出如下壳聚糖/磷酸甘油盐温敏性水凝胶的凝胶机理: 随着温度的升高, 壳聚糖通过氨基正离子与磷酸甘油盐形成的静电吸引被破坏, 随之由于壳聚糖分子链间形成大量氢键而发生凝胶化.     

THE USE OF TELESCOPING SPATIAL SCALES TO CAPTURE INSHORE TO SLOPE DYNAMICS IN MARINE ECOSYSTEM MODELING

Abstract Ecosystem processes function at many scales, and capturing these processes is a challenge for ecosystem models. Nevertheless, it is a necessary step for considering many management issues pertaining to shelf and coastal systems. In this paper, we explore one method of modeling large areas with a focus at a range of scales. We develop an ecosystem model that can be used for strategic management decision support by modeling the waters off southeastern Australia using a polygon telescoping approach, which incorporates fine‐scale detail at the coastal zone, increasing in scale to a very coarse scale in the offshore areas. This telescoping technique is a useful tool for incorporating a wide range of habitats at different scales into a single model.     

FISHING YIELD,CURVATURE AND SPATIAL BEHAVIOR: IMPLICATIONS FOR MODELING MARINE RESERVES

ABSTRACT. Given a paucity of empirical data, policymakers are forced to rely on modeling to assess potential impacts of creating marine reserves to manage fisheries. Many modeling studies of reserves conclude that fishing yield will increase (or decrease only modestly) after creating a reserve in a heavily exploited fishery. However, much of the marine reserves modeling ignores the spatial heterogeneity of fishing behavior. Contrary to empirical findings in fisheries science and economics, most models assume explicitly or implicitly that fishing effort is distributed uniformly over space. This paper demonstrates that by ignoring this heterogeneity, yield‐per‐recruit models systematically overstate the yield gains (or understate the losses) from creating a reserve in a heavily exploited fishery. Conversely, at very low levels of exploitation, models that ignore heterogeneous fishing effort overstate the fishing yield losses from creating a reserve. Starting with a standard yield‐per‐recruit model, the paper derives a yield surface that maps spatially differentiated fishing effort into total long‐run fishing yield. It is the curvature of this surface that accounts for why the spatial distribution of fishing effort so greatly affects predicted changes from forming a reserve. The results apply generally to any model in which the long‐run fishing yield has similar curvature to a two‐patch Beverton‐Holt model. A simulation of marine reserve formation in the California red sea urchin fishery with Beverton‐Holt recruitment, eleven patches, and common larval pool dispersal dynamics reinforces these results.