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1.
R.S.K. Barnes 《Journal of Natural History》2018,52(1-2):87-113
Areas of the Knysna estuarine bay in the Western Cape are dominated by three endemic South African truncatelloid microgastropods, temporarily known as ‘Hydrobia’ knysnaensis (Krauss), ‘Assiminea’ capensis (Sowerby) and ‘Assiminea’ globulus Connolly. Although first described 80–170 years ago and present in abundance (up to 100,000 m?2), they remain surrounded by confusion and still await taxonomic assignment, largely because they appear most atypical members of their groups by virtue of anatomy and/or biogeography and/or habitat. This study contributes in-life perspectives to morphological and phylogenetic analyses known to be on-going. At Knysna, they are syntopic: at least two occurring in >85% and all three in >40% of individual 0.0026 m2 samples from their region of dominance. Nevertheless, they tend to greater abundance in divergent microhabitats; ‘A.’ globulus dominating higher tidal levels, and ‘A.’ capensis and ‘Hydrobia’ lower ones; the former especially unvegetated sediment, the latter, if anything, seagrass. Interspecific feeding interactions appear unlikely to be responsible for these patterns, other evidence suggesting that all are maintained below carrying capacity. Field biology of ‘H.’ knysnaensis generally appears equivalent to that of northern-hemisphere intertidal hydrobiids and that of ‘A.’ globulus is typically assimineid, albeit at atypically low shore height. Unlike assimineids, however, ‘A.’ capensis is truly aquatic. The success of these truncatelloids in unusual circumstances may be consequent on the absence from South Africa of other microgastropod groups that fill their niches elsewhere in the southern hemisphere. 相似文献
2.
This paper studies the optimal investment problem for an insurer and a reinsurer. The basic claim process is assumed to follow a Brownian motion with drift and the insurer can purchase proportional reinsurance from the reinsurer. The insurer and the reinsurer are allowed to invest in a risk-free asset and a risky asset. Moreover, the authors consider the correlation between the claim process and the price process of the risky asset. The authors ?rst study the optimization problem of maximizing the expected exponential utility of terminal wealth for the insurer. Then with the optimal reinsurance strategy chosen by the insurer, the authors consider two optimization problems for the reinsurer: The problem of maximizing the expected exponential utility of terminal wealth and the problem of minimizing the ruin probability. By solving the corresponding Hamilton-Jacobi-Bellman equations, the authors derive the optimal reinsurance and investment strategies, explicitly. Finally, the authors illustrate the equality of the reinsurer's optimal investment strategies under the two cases. 相似文献
3.
In this paper, views of investor are described in fuzzy sets, and two fuzzy Black-Litterman models are constructed with fuzzy views and fuzzy random views respectively. In the models, expected returns and uncertainty matrix of views are redefined and the views are formulated by fuzzy approaches suitably. Then the models are tested with data from Chinese financial markets. Empirical results show that the fuzzy random views model performs the best, and both the fuzzy models are better than the traditional ones, demonstrating that the fuzzy approaches can contain more information in the views and measure the uncertainty more correctly. 相似文献
4.
目的:探讨等候区手术患者家属的心理影响因素及其干预措施.方法:通过临床护理实践及查阅相关文献进行总结分析.结果:影响因素及其干预措施包括详解病情及手术风险性;对手术环境及术中情况的告知;完善急诊手术患者家属心理干预;根据不同文化水平进行健康宣教;尽量以病情为主,设计最经济有效的治疗方案;提高医护人员从业技能及道德品质.结论:对等候区手术患者家属进行积极有效的心理干预,可很大程度上减轻患者家属的焦虑程度,缓和医患关系,一定程度上提升了医疗质量. 相似文献
5.
针对希望进一步掌握普通话口语学习的外国学习者,该研究提出了一种普通话游戏学习系统.系统的学习模式结合了计算机技术和语言学研究成果,打破了传统的教学模式的限制,对学习者进行实时评测,提供学习报告与口语学习的最终评定结果.结果表明,该系统能够较为有效地辅助外国学习者的普通话口语学习. 相似文献
6.
In this paper,the new development of three basic theories of Extenics,incluing basic-element theory,extension set theory and extension logic theory ,has been introduced.And the new theoretical frame of Extenics has also been set forth. 相似文献
7.
文章以调查典型县现状年灌溉用水定额为基础 ,以当地灌溉水可利用量为控制条件 ,采用逐级平衡的办法 ,制定吕梁区主要作物的灌溉用水定额 相似文献
8.
以介绍中美综合大学本科课程改革的概况为比较的背景,以复旦大学和哈佛大学物理学专业本科课程设置为例,比较中美综合大学本科课程设置的异同,分析其形成的原因,从中得出对我国综合大学本科课程设置改革的启示。 相似文献
9.
赵育林 《宝鸡文理学院学报(自然科学版)》1996,16(3):4-7
本文给出原点为细焦点的三次系统{x=-y+ax^3+βx^2y+λxy^2 y=x+ρx^3+αx^2y+βxy^2+λy^3 (1)当ρ〉0时存在或不存在极限环的条件。 相似文献
10.
Ten-day treatment with nicotine (5, 25 or 50 micrograms/ml drinking water) dose-dependently intensified gastric ulceration induced by cold-restraint, and emptying rate. Stomach contractions produced by graded doses of bethanechol i.v. were elevated further by nicotine treatment. It is suggested that chronic nicotine administration produces hypersensitivity of the gastric muscarinic receptors; stomach hypermotility contributes to the ulcer-worsening action of the alkaloid. 相似文献