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341.
在印度洋中部查戈斯礁群的大多数珊瑚死亡之后3年,对30m水深以浅珊瑚的侵蚀和恢复情况进行了研究.北部环礁15m水深以浅、中部和南部环礁>35m处的珊瑚差不多全部死亡.由于密集珊瑚丛的损失,一些礁体"表面"下降了1 5m.珊瑚的生物侵蚀情况严重,减少了三维礁体"结构"并形成松散的碎石.幼年珊瑚数量众多,尽管大部分是在侵蚀的或不稳定的基底上,并且稳定种较少.在15m的深度,礁体间鱼类丰度和多样性仍旧较高;依赖于珊瑚生存的物种减少,而一些食草动物和食碎屑动物则增加.一个新的海面温度(SST)数据集表明,平均SST自1950年以来升高了0.65℃.造成查戈斯珊瑚礁死亡的临界SST是29.9℃. 相似文献
342.
Cooperative prey retrieval in the monomorphic ant Formica schaufussi is carried out by workers that perform functionally distinct roles which persist only for the duration of a single retrieval event. A forager (scout) that locates prey too large to retrieve individually organizes cooperative prey transport by recruiting nestmates (recruits) to assist in retrieval. The scout and recruit roles appear to be determined by whether a worker activates recruitment or is recruited from the nest. Scouts organize recruitment and play a key role in maintaining the cohesion of the retrieval group. If a scout that has initiated group transport is experimentally removed, the recruited workers composing the retrieval group typically abandon the prey and cooperative foraging is terminated. In this context, recruits are unable to function as scouts and reorganize group transport. Individuals marked as recruits in one prey retrieval, however, can switch and act as scouts in subsequent retrievals. Because the roles of individuals persist within but not between retrieval events, the specialization involved in cooperative prey retrieval cannot easily be explained as a response associated with age-related or genetic predispositions. This transient division-of-labor, in which individual roles may persist only for the duration of a single group action, represents a novel type of short-term individual specialization. 相似文献
343.
R.H. Field S. Benke K. Bdonyi R.B. Bradbury 《Agriculture, ecosystems & environment》2007,120(2-4):399-404
Bird use of conservation tillage-established (CT—seedbed preparation without soil inversion) crops was assessed at two adjacent sites in western Hungary, in comparison with conventionally established (mouldboard ploughed—P) fields. Bird abundance was assessed in a typical rotation of spring-sown maize and winter wheat in three consecutive winters. In the first winter, several species and the guild of seed-eating passerines were significantly more abundant on CT established plots, in both crop types. In the second winter, only starlings were more abundant on CT plots. In the third winter, only skylarks favoured CT over P plots. In combination with agri-environment scheme measures designed to provide resources for biodiversity, conservation tillage could play a role in softening the impact of agriculture on farmland birds in Hungary and elsewhere in Eastern Europe, in addition to its potential for reducing soil erosion and diffuse pollution. 相似文献
344.
J. Caspar Rüegg 《Die Naturwissenschaften》1998,85(12):575-582
2+ concentrations tropomyosin is located at the edge of the thin filament, thereby interfering with the formation of strong
actin-myosin linkages (blocked state). An increase in Ca2+ activity causes an azimuthal shift of tropomyosin around the filament (by about 30°), thereby increasing the probability
of low-force crossbridge interaction, a process which by cooperative effects induces further tropomyosin movement (by an additional
10°) which results in the open state of the filament characterized by forceful crossbridge interaction. (This mechanism may
be analogous to that in ligand-gated ion channels, where ligand binding increases the open probability of the pore.) The extent
of activation then depends on the free Ca2+ concentration and on the calcium sensitivity of the thin filament that may be affected by protein phosphorylation, crossbridge
attachment, the troponin isoform composition of the filament, and novel calcium-sensitizing drugs that act on the contractile
or regulatory proteins and thus increase the force of the heart. 相似文献
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349.
In several branches of science and technology a gaseous phase is dispersed into a liquid in the form of bubbles, a gaseous
component then dissolves into the liquid and subsequently undergoes chemical reaction. The overall process performance can
be improved substantially when the area of gas–liquid contact is increased. By subjecting the liquid phase to low frequency
vibrations, the bubbles are shown to suffer significant breakage, induced by resonance. When the vibration is properly tuned,
the interfacial area is found to increase by a factor of 1.8–2.4, depending on the properties of the liquid. Resonance-induced
bubble breakage phenomena have a great potential for improving the rates of chemical processes involving fast reactions, with
minimal energy input.
Received: 7 July 2000 / Accepted in revised form: 28 August 2000 相似文献
350.
This paper investigates the current treatment of environmental issues by two companies within the large made-to-order sector. Fifty questionnaires were issued to the design team of each company to assess current practice in the integration of environmental issues with design activities, awareness of environmental issues, awareness of existing environmental design tools and the preferred format for a potential clean design tool. 相似文献