The individual of a species is the basic unit which responds to climate and UV-B changes, and it responds over a wide range of time scales. The diversity of animal, plant and microbial species appears to be low in the Arctic, and decreases from the boreal forests to the polar deserts of the extreme North but primitive species are particularly abundant. This latitudinal decline is associated with an increase in super-dominant species that occupy a wide range of habitats. Climate warming is expected to reduce the abundance and restrict the ranges of such species and to affect species at their northern range boundaries more than in the South: some Arctic animal and plant specialists could face extinction. Species most likely to expand into tundra are boreal species that currently exist as outlier populations in the Arctic. Many plant species have characteristics that allow them to survive short snow-free growing seasons, low solar angles, permafrost and low soil temperatures, low nutrient availability and physical disturbance. Many of these characteristics are likely to limit species' responses to climate warming, but mainly because of poor competitive ability compared with potential immigrant species. Terrestrial Arctic animals possess many adaptations that enable them to persist under a wide range of temperatures in the Arctic. Many escape unfavorable weather and resource shortage by winter dormancy or by migration. The biotic environment of Arctic animal species is relatively simple with few enemies, competitors, diseases, parasites and available food resources. Terrestrial Arctic animals are likely to be most vulnerable to warmer and drier summers, climatic changes that interfere with migration routes and staging areas, altered snow conditions and freeze-thaw cycles in winter, climate-induced disruption of the seasonal timing of reproduction and development, and influx of new competitors, predators, parasites and diseases. Arctic microorganisms are also well adapted to the Arctic's climate: some can metabolize at temperatures down to -39 degrees C. Cyanobacteria and algae have a wide range of adaptive strategies that allow them to avoid, or at least minimize UV injury. Microorganisms can tolerate most environmental conditions and they have short generation times which can facilitate rapid adaptation to new environments. In contrast, Arctic plant and animal species are very likely to change their distributions rather than evolve significantly in response to warming. 相似文献
Accidental electrostatic sparks in industrial plant producing/handling powders/dusts occur whenever a non-earthed electrically conducting object has been charged tribo-electrically to a high voltage and suddenly discharges its energy to earth via an air gap of appropriate length. When assessing the electrostatic spark ignition hazard in an industrial plant, the parameters of prime concern are the capacitances C of electrically conducting plant items that may become charged tribo-electrically, the voltages U to which they may become charged, and the minimum electric spark ignition energies (MIE) of the dust clouds of concern. Whenever , there is a possibility of accidental electrostatic spark ignition.
Current standard apparatuses for determining MIE of dust clouds have a lower spark energy limit of 2–3 mJ. In an investigation by the present authors, discussed in detail elsewhere, a new spark generator capable of producing synchronized capacitive sparks of energies down to the order of 0.01 mJ was developed and used for testing a selection of ignition-sensitive powders for MIE. Several of the MIEs found were 1–2 orders of magnitude lower than the lower energy limit of current standard test apparatus. Other experiments by the present authors, also reported elsewhere, have shown that quite low MIEs can be found for some dusts even with a less optimal synchronization mechanism, which may occur accidentally in practice.
The main object of the present paper is to discuss possible practical concerns arising from the finding that clouds in air of some dusts can have very low MIEs. In such cases, one may have to pay attention to even minor C values, i.e. minor plant items. Alternatively, with larger C values, even quite low voltages may give rise to hazardous spark discharges.
However, some types of fine metal powders of low MIEs will quite readily form electrically conductive layers on the solid surfaces with which they make contact. Hence, electrostatic spark ignition inside process equipment containing such dusts may be less probable than in the case of process equipment containing non-conducting dusts of correspondingly low MIEs.
There may be a need for a new standard test method for determination of MIEs of dust clouds in the <1 mJ range. 相似文献
The full-depth vertical distributions of males, females and juveniles of Lucicutia grandis and Calanoides carinatus are presented from the surface down to depths of 3,900 m in the central Arabian Sea at the end of the NE monsoon and the
February and October inter-monsoonal periods. L. grandis is a steady component and C. carinatus is a temporal resident of the central Arabian Sea oxygen minimum zone. Maximum abundances of C. carinatus and L. grandis juveniles were found at depths around 600 m, whereas the center of the distribution of L. grandis adults was somewhat deeper at 950 m. Both copepods are indicator species which can help to understand the functioning of
the mesopelagic Arabian Sea ecosystem. 相似文献
There is little known data characterizing the biomechanical responses of the human head and neck under direct head loading conditions. However, the evaluation of the appropriateness of current crash test dummy head-neck systems is easily accomplished. Such an effort, using experimental means, generates and provides characterizations of human head-neck response to several direct head loading conditions. Low-level impact loads were applied to the head and face of volunteers and dummies. The resultant forces and moments at the occipital condyle were calculated. For the volunteers, activation of the neck musculature was determined using electromyography (EMG). In addition, cervical vertebral motions of the volunteers have been taken by means of X-ray cineradiography. The Ethics Committee of Tsukuba University approved the protocol of the experiments in advance. External force of about 210 N was applied to the head and face of five volunteers with an average age of 25 for the duration of 100 msec or so, via a strap at one of four locations in various directions: (1) an upward load applied to the chin, (2) a rearward load applied to the chin without facial mask, (3) a rearward load applied to the chin with the facial mask, and (4) a rearward load applied to the forehead. The same impact force as those for the human volunteers was also applied to HY-III, THOR, and BioRID. We found that cervical vertebral motions differ markedly according to the difference in impact loading condition. Some particular characteristics are also found, such as the flexion or extension of the upper cervical vertebrae (C0, C1, and C2) or middle cervical vertebrae (C3-C4), showing that the modes of cervical vertebral motions are markedly different among the different loading conditions. We also found that the biofidelity of dummies to neck response characteristics of the volunteers at the low-level impact loads is in the order of BioRID, THOR, and HY-III. It is relevant in this regard that the BioRID dummy was designed for a low-severity impact environment, whereas THOR and HY-III were optimized for higher-severity impacts. 相似文献