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231.
控制超塑胀形件的壁厚变薄和改善其壁厚分布的均匀性,是超塑胀形一个十分重要的工艺问题。此文提出了一种能在超塑胀形过程中同时进行拉深的新工艺——超塑性拉深胀形组合新工艺。通过对供应态的TC4板材的超塑性拉深胀形试验表明:该工艺在很大程度上改善了超塑胀形件壁厚分布的均匀性,降低了其变薄率。 相似文献
232.
《环境科学学报(英文版)》2023,35(4):58-69
Co-exposure to heavy metal and antibiotic pollution might result in complexation and synergistic interactions, affecting rice growth and further exacerbating pollutant enrichment. Therefore, our study sought to clarify the influence of different Tetracycline (TC) and Cadmium(Cd) concentration ratios (both alone and combined) on rice growth, pollutant accumulation, and transportation during the tillering stage in hydroponic system. Surprisingly, our findings indicated that the interaction between TC and Cd could alleviate the toxic effects of TC/Cd on aerial rice structures and decrease pollutant burdens during root elongation. In contrast, TC and Cd synergistically promoted the accumulation of TC/Cd in rice roots. However, their interaction increased the accumulation of TC in roots while decreasing the accumulation of Cd when the toxicant doses increased. The strong affinity of rice to Cd promoted its upward transport from the roots, whereas the toxic effects of TC reduced TC transport. Therefore, the combined toxicity of the two pollutants inhibited their upward transport. Additionally, a low concentration of TC promoted the accumulation of Cd in rice mainly in the root tip. Furthermore, a certain dose of TC promoted the upward migration of Cd from the root tip. Laser ablation-inductively coupled plasma mass spectrometry demonstrated that Cd mainly accumulated in the epidermis and stele of the root, whereas Fe mainly accumulated in the epidermis, which inhibited the absorption and accumulation of Cd by the rice roots through the generation of a Fe plaque. Our findings thus provide insights into the effects of TC and Cd co-exposure on rice growth. 相似文献
233.
Raimundo Real A. Márcia Barbosa J. Mario Vargas 《Environmental and Ecological Statistics》2006,13(2):237-245
Logistic regression is a statistical tool widely used for predicting species’ potential distributions starting from presence/absence
data and a set of independent variables. However, logistic regression equations compute probability values based not only
on the values of the predictor variables but also on the relative proportion of presences and absences in the dataset, which
does not adequately describe the environmental favourability for or against species presence. A few strategies have been used
to circumvent this, but they usually imply an alteration of the original data or the discarding of potentially valuable information.
We propose a way to obtain from logistic regression an environmental favourability function whose results are not affected
by an uneven proportion of presences and absences. We tested the method on the distribution of virtual species in an imaginary
territory. The favourability models yielded similar values regardless of the variation in the presence/absence ratio. We also
illustrate with the example of the Pyrenean desman’s (Galemys pyrenaicus) distribution in Spain. The favourability model yielded more realistic potential distribution maps than the logistic regression
model. Favourability values can be regarded as the degree of membership of the fuzzy set of sites whose environmental conditions
are favourable to the species, which enables applying the rules of fuzzy logic to distribution modelling. They also allow
for direct comparisons between models for species with different presence/absence ratios in the study area. This makes them
more useful to estimate the conservation value of areas, to design ecological corridors, or to select appropriate areas for
species reintroductions.
Received: June 2005 / Revised: July 2005 相似文献
234.
重金属铜和放射性核素^3H在鲫鱼体内的分布规律及比较 总被引:1,自引:0,他引:1
对重金属铜和放射性核素^3H在鲫鱼不同组织和器官内的分布规律进行了研究并作了比较。结果表明:①铜在鲫鱼不同组织和器官内的分布规律为:肝>鳃>骨赂肌肉;②放射性核素^3H在鲫鱼不同组织和器官内的分布规律为:内脏>鳃>尾鳍≈肌肉;③两种毒物在鲫鱼不同组织和器官内的分布规律大致相同。 相似文献
235.
236.
A. M. Avis 《Journal of Coastal Conservation》1995,1(1):41-50
A total of 17 sites along the eastern Cape coastline, which had been established with indigenous species, were sampled to
assess species composition and abundance. The areas sampled ranged from small blowout dunes of 1 ha, to extensive transverse
dune fields of 134 ha; age at the time of sampling ranged from 2 to 20 yr. The total mean percentage cover and density, alpha
diversity and importance values of all the species were calculated and used to describe each site. A TWINSPAN analysis grouped
sites of similar localities, mainly on the basis of their species composition. A DECORANA plot revealed that axis 1 corresponded
to the position of sites along the coastline rather than other factors, such as age. The variability in species composition
was related more to the types of species used for stabilization, rather than the natural distribution of the indigenous dune
vegetation. The species ordination showed a similar gradient, and it was possible from this analysis to determine which species
were more commonly used and better suited for dune stabilization. It is concluded that successful stabilization can be achieved
using indigenous species. 相似文献
237.
本文介绍了近几年来对我国部分煤矿采煤工作面粉尘状况的调查,测试和煤矿粉尘粒度分布分析结果。通过测试分析证明,不同煤种的煤被外部能量破碎时,它的产尘量、产生的粉尘的粒度分布及粉尘中呼吸性粉尘含量不同;各种煤直接破碎产生的粉尘和矿井空气的浮游粉尘的粒度分布均符合罗辛——拉姆勒(Rosin——Rammlar)分布规律;采用一般常规防尘措施(如煤体注水、洒水、喷雾降尘等),对粒度较粗的粉尘有一定降尘效果,可改善粉尘作业环境,而对工人身体健康影响较大的呼吸性粉尘降尘效果不显著,造成矿井浮游粉尘中呼吸性粉尘含量增加。为此,今后防尘工作重点应加强对呼吸性粉尘控制技术的研究,推广、应用对呼吸性粉尘除尘效率高的防尘措施,大幅度降低矿井中呼吸性粉尘.使煤矿尘肺病发病率有较大降低。 相似文献
238.
Assessing the effects of pseudo-absences on predictive distribution model performance 总被引:4,自引:0,他引:4
Modelling species distributions with presence data from atlases, museum collections and databases is challenging. In this paper, we compare seven procedures to generate pseudo-absence data, which in turn are used to generate GLM-logistic regressed models when reliable absence data are not available. We use pseudo-absences selected randomly or by means of presence-only methods (ENFA and MDE) to model the distribution of a threatened endemic Iberian moth species (Graellsia isabelae). The results show that the pseudo-absence selection method greatly influences the percentage of explained variability, the scores of the accuracy measures and, most importantly, the degree of constraint in the distribution estimated. As we extract pseudo-absences from environmental regions further from the optimum established by presence data, the models generated obtain better accuracy scores, and over-prediction increases. When variables other than environmental ones influence the distribution of the species (i.e., non-equilibrium state) and precise information on absences is non-existent, the random selection of pseudo-absences or their selection from environmental localities similar to those of species presence data generates the most constrained predictive distribution maps, because pseudo-absences can be located within environmentally suitable areas. This study shows that if we do not have reliable absence data, the method of pseudo-absence selection strongly conditions the obtained model, generating different model predictions in the gradient between potential and realized distributions. 相似文献
239.
The sequential extraction procedures described by Tessier et al., McGrath and Cegarra, and Gimeno-García et al. were compared
to investigate trace element (As, Cr, Cu, Pb, and Zn) partitioning patterns and extraction efficiency in three contaminated
soils from Mediterranean regions of Spain. Soils were selected from Onda (Castellón) (S1), Aznalcóllar (Sevilla) (S2), and
Silla (Valencia) (S3). S1 was a soil contaminated with Pb and Zn after dumping of wastes from the manufacture of ceramic tiles,
S2 was polluted accidentally with a highly acid and As-concentrated sludge from mining activities, and S3 was a soil with
a high Cr content from tannery sludge disposal. Trace element distribution in the soils—soluble, exchangeable, organically
bound, precipitated with carbonates, bound to iron and manganese oxides, and precipitated with sulfides fractions—varied significantly
according to the extraction procedure used. In addition, different extraction efficiencies were found for the three sequential
extraction procedures compared. Finally, the trace elements studied showed different and specific distribution patterns between
the various soil fractions examined. 相似文献
240.
关于RosinRammler粒径分布函数的研究 总被引:1,自引:0,他引:1
Rosin Ramm ler分布函数是最常用的描述粉尘粒径分布的一种形式 ,本文对表达式中系数 a与指数 n之间的关系进行了分析 ,导出了二者之间的关系式。 相似文献