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991.
992.
Analyze the Present Status in the Calculation Methods of Lightning Protection Performance for Transmission Line 总被引:1,自引:0,他引:1
Lightning is the main reason that endangers transmission line working safety and reliabilty today. The theory and characteristic of methods that not only estimate the lightning performance for back strike such as standard method, traveling wave method, Monte Carlo technique, treeing fault method, EMTP and so on but also for the shielding failure such as standard method, EGM, leader progression model and so on are summarized. The criterion of flashover for insulators is referred simply, furthermore, it gives the opinion that the development of research for the future. 相似文献
993.
Chen Zhonglin 《保鲜与加工》1989,(1)
According to the definition of luminous flux, and on the basisof the probability of fuzzy stechastic events in fuzzy mathematies, this paperstudies the fuzzy phenomena of the luminous flux increment obtained by thereciprocal reflection of light on indoor surfaces. This paper also suggests a newway to compute the transmission of luminous flux. 相似文献
994.
995.
Thomas Davies Cliona Skelly Antonella Puggioni Catherine D'Helft Susan Connolly Seamus Hoey 《Veterinary radiology & ultrasound》2020,61(2):137-146
Multiple published studies involving computed tomographic (CT) examinations of the equine head utilise a wide range of mAs parameters for image acquisition. This prospective, experimental study assessed the effects of lowering mAs during CT image acquisition on image quality and scatter radiation on 10 cadaver equine heads. Each head was scanned three times at 300, 225, and 150 mAs, with all other scanning parameters remaining constant between series. An anthropomorphic phantom was positioned adjacent to each equine head during image acquisition, mimicking a human bystander, with an ionization chamber attached to the phantom at eye level. Each series was reconstructed using filtered back projection, using medium (H30) and high (H80) frequency reconstruction algorithms. Quantitative image quality assessment was performed by calculating signal to noise ratio (SNR) and contrast to noise ratio (CNR). Two qualitative image quality assessments were performed independently by three blinded board certified veterinary radiologists with a 4 week interval, using a visual grade analysis model adapted from peer reviewed medical literature. Ionization chamber measurements, calculated volume CT dose index (CTDIvol), and dose‐length product (DLP) were recorded. Halving radiation dose during image acquisition from 300 to 150mAs resulted in comparable image quality between series. There was a statistically significant and linear relationship between mAs and scatter radiation to the bystander; halving mAs during image acquisition resulted in halving of scatter radiation. Results of this cadaveric study support the use of lower mAs settings during standing CT examinations of the equine head. 相似文献
996.
Jonathon D. Kotwa David L. Pearl Mats Isaksson Claire M. Jardine Olaf Berke Nicola J. Mercer Eva Osterman‐Lind Andrew S. Peregrine 《Zoonoses and public health》2020,67(5):546-553
Echinococcus multilocularis was recently reported in wild canids across southern Ontario, a newly recognized endemic area in Canada. In such areas, a comprehensive understanding of factors associated with infection in definitive hosts (wild canids) is critical for mitigating risk of transmission to humans. However, little is known about the transmission dynamics of the parasite in definitive hosts for this region. A study was therefore carried out to investigate the association of host‐level (sex, body condition), environmental (southern Ontario region, land cover), temporal (season, hunting season, calendar year) and extraneous factors (submitter type) with E. multilocularis infection in coyotes in southern Ontario. Between November 2015 and March 2017, 416 coyotes were collected from across the region as part of a study that investigated the prevalence and distribution of the parasite in wild canids; approximately 24% of coyotes were positive for E. multilocularis. Associations between infection and factors of interest were assessed via a mixed‐effects logistic regression model with a random intercept for submitter to account for clustering. Coyotes with poor body condition were at greater odds of E. multilocularis infection than those in good condition (odds ratio [OR] 2.14; 95% CI: 1.08–4.26; p = .030). A negative association was observed between infection in coyotes and the proportion of natural land in a coyote's estimated home range (OR: 0.67; 95% CI: 0.52–0.85; p = .001). Coyotes from the western region of southern Ontario had lower odds of infection compared to coyotes from the central region (OR: 0.26; 95% CI: 0.12–0.55; p < .001). These results can be used to help guide future public health prevention strategies for human alveolar echinococcosis. 相似文献
997.
Zhe SUN Zhibin ZHANG Qiyong LIU Baolei LYU Xiye FANG Shuchun WANG Jianguo XU Lei XU Bing XU 《Integrative zoology》2020,15(1):69-78
Plague, a devastating infectious disease caused by Yersinia pestis, has killed millions of people in the past and is still active in the natural foci of the world today. Understanding the spatiotemporal patterns of plague outbreaks in history is critically important, as it may help to facilitate prevention and control of potential future outbreaks. In this study, we explored spatiotemporal clusters of human plague occurrences in China using a machine‐learning clustering method and reconstructed the potential transmission pattern during the Third Pandemic (1772–1964). We succeeded in identifying 6 clusters in the space domain (2D) and 13 clusters in the spatiotemporal domain (3D). Our results suggest that there were several temporal outbreaks and transmissions of plague in different spatial clusters. Together with the spatiotemporal nearest neighbor approach (ST‐NNA), this method could allow us to have a clearer look at the spatiotemporal patterns of plague. 相似文献
998.
玉米冠层光分布农业气象模式的研究 总被引:5,自引:0,他引:5
利用气象学、天文学和农业气象学知识建立了用日总辐射量反演辐射日变化过程来推算玉米冠层光分布状况的农业气象模型。利用实测资料进行验证,模拟误差在24%~87%之间。对冠层分层研究的结果表明,模拟误差随分层数的增加呈指数递减。实际应用中冠层分为3~5层较为合适。 相似文献
999.
对行星齿轮传动装置的性能、特点和丰富多变的结构形式以及在开发设计制造中采用的新技术和新工艺进行了介绍。 相似文献
1000.
黄瓜花叶病毒(CMV)土壤非介体传播研究 总被引:3,自引:0,他引:3
对黄瓜花叶病毒(CMV)土壤非介体传播的试验结果表明,土壤非介体传播是CMV传播的新途径,不同作物间的传播效率有差异,一般CMV传入根部后多数地上部不表现症状,但根系生长明显受到影响。文章还分析了CMV能够以土壤非介体方式传播的原因。 相似文献