欧洲的氮状况

欧洲(不包括前苏联)的氮收支表明,欧洲氮循环加速的三个主要驱动力是肥料生产(14MtN/a)、矿物燃料燃烧及其它工业(3.3MtN/a)和各种产品中的氮输入(7.6MtN/a).本文估计了欧洲粮食、能源和工业产品系统中活性氮元素的各种泄漏,评估了它们对人类健康及水陆生态系统的影响.考虑到氮流转中的可能后果,未来欧洲有关封闭氮循环和减少活性氮泄漏的环境政策措施最好集中于三个主要驱动力.在确定氮排放上限和制定氯流控制的综合政策方面,如肥料使用、输入和氮水平,临界负载可能是非常有用的工具.     

Gamergates in the myrmicine genus <Emphasis Type="Italic">Metapone</Emphasis> (Hymenoptera:Formicidae)

Gamergates (i.e. mated reproductive workers) are mostly known from ant species within the Ponerinae. We report here the discovery of gamergates in two species of the subfamily Myrmicinae. Until now, mated reproductive females in colonies of myrmicine species have been considered morphologically distinct from the worker caste. However, in two species of the myrmicine Metapone (Metapone madagascarica and a newly discovered, not yet described Metapone species) all workers have six ovarioles and a spermatheca; and some of them are mated. There are no morphological differences between mated and non-mated workers. Field observations and laboratory studies indicate that colonies of the Metapone species can reproduce with gamergates only.     

Cardiac Contractility: How Calcium Activates the Myofilaments

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.     

Carbon Budget Implications of the Transition from Natural to Managed Disturbance Regimes in Forest Landscapes

Land-use change from an unmanaged to a managed forested landscape in northern forests is associated with a reduction of the area annually affected by natural disturbances (wildfires and forest insects) and the introduction of harvesting as a new disturbance. This study examined the impacts of changes in the disturbance regime-the frequency and type of disturbance-on landscape-level carbon (C) content and fluxes. The Carbon Budget Model of the Canadian Forest Sector was used to assess these impacts in six representative landscapes (100,000 ha each) with a range of disturbance regimes that are characteristic of conditions in coastal British Columbia, the interior of British Columbia, and the eastern boreal forest in Canada. The model was used to simulate ecosystem C fluxes during a period of natural disturbances, a 50-year transition period during which harvesting replaced natural disturbances, followed by 150 years of harvesting. The initial landscape-level biomass C content under natural disturbance regimes in the six example landscapes was 22 to 75% of their potential maximum content which is often used as the reference or baseline case. After 200 years of forest management, the C stored in the landscape plus the C retained in forest products manufactured from harvested biomass was between 58 and 101% of the landscape C content prior to the onset of harvesting. Landscape-level ecosystem C content was found to be affected by changes in the disturbance frequency, the age-dependence of the disturbance probabilities, and the disturbance-specific impacts on ecosystem C content. The results indicate that using the potential maximum C content of a landscape as the baseline always overestimates the actual C release due to land use change. A more meaningful procedure would be to assess the actual differences in landscape-level C content between the natural and the managed disturbance regime.     

重金属在牡蛎(Crassostrea virginica)中的生物积累及其影响因素的研究

牡蛎软体，贝壳和沉积物中Ｃｄ、Ｃｒ、Ｃｕ、Ｆｅ、Ｍｎ、Ｐｂ和Ｚｎ等重金属元素被同步分析研究，研究结果表明，重金属在牡蛎中的生物积累是牡自身的新陈代谢、重金属元素的地球化学性质和环境诸因素综合影响的结果，其中牡蛎斩生理作用对重金属在软体中的积累产生的影响尤为重要，而贝壳中重金属的积累对来自环境的影响更为敏感。     

Utilisation of bubble resonance phenomena to improve gas–liquid contact

 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