双极荷电粉尘颗粒凝聚的初步研究

采取将含尘气体并行分别通过正负放电电场 ,然后再合二为一 ,空间大尺度范围依靠湍流输运 ,近距离依靠库仑力及范德瓦力的双极荷电凝聚方式 ,以滑石粉和锅炉飞灰为实验粉尘 ,初步研究了气流速度、含尘浓度、正负放电强度配合等因素对凝聚效率的影响 ,得到了双极荷电可使沉降收集效率提高约 10 %的静电凝聚效果。     

Predator inspection behaviour in three-spined sticklebacks (<Emphasis Type="Italic">Gasterosteus aculeatus</Emphasis>): body size,local predation pressure and cooperation

The apparently maladaptive tendency of fish to approach and inspect potential predators has been explained in terms of useful information gathering or as a signal to the predator that it has been seen. We examined this behaviour in 16 populations of wild-caught stickleback (Gasterosteus aculeatus) from ponds with and without predatory perch (Perca fluviatilis). Three large and three small individuals per population were each exposed to three model predators differing in realism. A final cooperative treatment entailed pairing subjects with a second individual from the same population, but of the alternative size class, during predator presentation. As might be expected, predator inspection behaviour was much greater in the predator-sympatric populations, and only these fish increased their level of inspection as the models became incrementally more realistic. This suggests that reductions occur in the level of costly inspection behaviour in populations without predators. Subject body size had no effect on inspection effort, which suggests a limited role for experience (we assumed larger fish to be older than smaller fish), at least over the relative age differences utilized. However, small predator-sympatric fish were the only subjects to increase inspection significantly when in a cooperative context, perhaps reflecting the inherent value of a relatively larger partner in this context. These results confirm that levels of predator inspection are both population- and situation-dependent, suggesting a trade-off in the potential costs and benefits of this behaviour.Communicated by C. St. Mary     

Patterns of fluctuating asymmetry in beetle horns: an experimental examination of the honest signalling hypothesis

Recent theoretical arguments have claimed that negative relationships between the size and symmetry of secondary sexual traits are indicative of honest signalling of male quality. The patterns of fluctuating asymmetry in beetle horns have been proposed to support the honest signalling hypothesis. Here we examine three assumptions of the hypothesis, (1) that traits are costly to produce; (2) the levels of fluctuating asymmetry are indicative of stress imposed during development; and (3) that males with larger traits should have more symmetrical traits, using the horned beetle, Onthophagus taurus. Experimental manipulations of brood mass were used to manipulate horn size and asymmetry. The development of horns was found to be environmentally determined and costly in terms of delayed development and increased risk of pre-adult mortality. Decreasing resource availability increased relative horn asymmetry. However, horn height was positively related to absolute horn asymmetry. While the results do support the hypothesis that sexual selection on secondary sexual traits should increase levels of fluctuating asymmetry, they provide no support for the notion that the patterns of asymmetry honestly signal male quality. Horns are used in disputes between males and may be indicative of male parental investment. Thus, we conclude that while horn size may be an indication of male quality, the patterns of fluctuating asymmetry are not. Received: 16 December 1996 / Accepted after revision: 5 May 1997     

超临界直流电站锅炉水冷壁开裂原因分析及改进措施

本文介绍了超临界直流电站锅炉检验中发现的水冷壁开裂、变形,调风器鳍片烧损变形,集箱管接头角焊缝裂纹,刚性梁固定耳板处拉裂、变形等问题。对产生这些问题的原因进行了分析和研究,认为各水冷壁管子内水汽温度不均匀是造成拉裂、变形的主要原因。针对产生问题的原因,提出要预防此类问题发生就必须控制水冷壁超温和降低水冷壁各管子间温度差。并详细地论述了控制水冷壁超温和降低水冷壁各管子间温度差的八项具体改进措施。     

锂离子电池电解液火灾的烟雾探测方法研究

基于散射不对称比的气溶胶识别方法,采用单个入射波长和两个散射角的方式测定了电解液火灾、正庚烷火、棉绳阴燃三种火灾烟雾和D90粉尘的前后向散射不对称比。结果表明,在红外LED光源作用下,前向散射角为45°和后向散射角为135°时,不同类型气溶胶的散射不对称比的均值和变化率存在差异,这可以用于区分火灾烟雾和干扰气溶胶。此外,在进行锂离子电池火灾烟雾探测器的光源选择时发现,在电解液火灾初期,短波长作用下的烟雾不对称比变化率更大,由此提出了采用405 nm～525 nm单波长光源和双散射角的电解液火灾烟雾探测方法。     

征税,还是补贴--对当前环境经济政策的反思

现行环境经济政策的目标在于纠正经济主体的外部不经济性，具体是通过税收或产权交易使外部成本内部化，本文称其为环境经济政策的“不对称性”。因为外部效应除了外部不经济以外，还有外部经济，现行的环境经济政策只考虑了前者却完全忽视了后者，只强调了外部成本的内部化却忽视了外部收益也应该内部化。以此为出发点，文章从现行政策的对立面出发，探讨了围绕外部收益内部化制定环境经济政策的必要性和可行性。最后作者分析了目前排污权交易存在的严重问题，并给出了解决问题的方法。     

Influence of an oblique path of staircase descent on toe placement and foot clearance

During their commute, pedestrians encounter a variety of staircase designs. One such design is the oblique staircase that allows pedestrians to descend at an angle. The purpose of this study was to assess the influence of an oblique path of descent on heel and toe clearance, and toe placement on a step. Sixteen participants descended a staircase on an angled path at three angles: 0° (perpendicular), 25°, and 45°. Toe placement and foot clearances were compared between the descent angles and feet. An increase in descent angle demonstrated increased clearance of the heel apex compared with straight descent; however, the aspect of the foot closest to the stair changes in angled descent, moving from the apex to the side of the heel. A greater portion of the foot was placed on the stair tread during angled descent. Future work should address the influence of angled descent on fall risk.     

The effect of air pollution and other environmental stressors on leaf fluctuating asymmetry and specific leaf area of Salix alba L

We aimed at evaluating the effect of low-level air pollution on leaf area fluctuating asymmetry (FAA) and specific leaf area (SLA) of Salix alba L., taking into account other environmental factors. Cuttings were grown in standardized conditions in the near vicinity of air quality measuring stations in Belgium. Variability of SLA and FAA between measuring stations explained 83% and 7.26%, respectively, of the total variability. FAA was not influenced by air pollution or environmental factors such as shading, herbivory, air temperature and humidity. SLA was increased by an increase in shadow, while NO_x and O₃ concentrations had only a marginal influence. The influence of SO₂ concentration was negligible. Although our data analysis suggests a relationship between SLA and NO_x/O₃ concentration, the absence of a straightforward relationship between FAA and SLA and air pollution still questions the usefulness of these bio-indicators for monitoring air pollution.     

Effect of modulated microwave radiation on human EEG asymmetry

This study is aimed to investigation of the effect of modulated 450 MHz microwave radiation on the EEG inter-hemispheric asymmetry. Ten cycles of the microwave exposure (1 min off and 1 min on) at fixed modulation frequency were applied on two groups of healthy volunteers. The first group of 13 subjects was exposed to microwave radiation modulated at 14 Hz and the second group of 15 subjects at 40 Hz frequency. The peak specific absorption rate (SAR) average over 1 g was 0.303 W/kg. Differences in SAR between hemispheres were up to 20 dB. Rod antenna was located from the left side of the head. Differences of relative changes in EEG energy between symmetric channels FP1–FP2, T3–T4, P3–P4 and O1–O2 in exposed and sham conditions were analysed. The results showed increase in EEG energy from the left side caused by microwave exposure. Statistical analysis done for the whole group of subjects didn’t reveal significant differences in inter-hemispheres asymmetry between exposed and sham conditions. However, statistical analysis performed for individual subjects detected significant differences in asymmetry caused by exposure for 15–35% of individuals.     

Distribution of Calculated Indices and an Attempt of Its Biological Interpretation Using the Production Characteristics of Grass Communities

The distribution of indices characterizing the productivity structure of natural, semicultivated, and cultivated grass communities has been analyzed. The proportion of normally distributed series accounts for more than half of all series in wheat fields and herb–reedgrass meadows and less than one-third of all series in sown grass mixtures.