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就通风空调工程中具有特殊应用的环形风道的摩擦阻力计算问题进行了分析,根据流体力学原理,提出了采用流量当量直径法和直接利用圆形风道计算图风道的比摩阻2种方法,第2种计算方法与流量当量直径法比较,查表时更直接。 相似文献
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木材是唯一可再生的主要工业材料,对环境最为友好,是人类历史中的一种重要的建筑材料;但作为一种生物材料,木材具有易燃性,要确保木结构安全,就得充分重视木结构的防火设计。我国传统建筑主要是木结构建筑,其防火问题在我国很早就引起了重视,首先回顾了传统的防火设计方法;然后介绍了1h火灾防护方法,并详细分析了国内外不同木结构体系防火的设计、研究和思路等;其次简要介绍了木材的化学阻燃方法;最后总结木结构各种防火设计方法,提出存在的问题和未来研究的方向。 相似文献
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对目前性能化防火设计中常用的4种火灾作用模型进行了分析和总结,并运用这4种模型对钢结构交错桁架在火灾时的热环境进行了模拟,分析不同火灾作用模型下该体系的结构响应,研究不同火灾作用模型对交错桁架结构性能化抗火设计的适用性。研究表明:火源功率、火灾载及火灾持续时间等因素对钢结构交错桁架的抗火分析具有重要影响。国际标准升温曲线和参数化室内升温曲线不考虑火源功率、建筑通风口等因素,缺乏针对性,分析结果偏于保守;区域模型所得温度偏低,不宜用于交错桁架结构的性能化抗火设计;场模型考虑了火源功率及环境温度分布的不均匀性,和实际火灾较接近,计算结果相对较为准确,可用于结构的性能化防火设计。 相似文献
287.
Vânia Santos Braz Jéssica Aparecida Silva Moretto Ana Flavia Tonelli Fernandes 《Journal of environmental science and health. Part. B》2019,54(4):290-293
The extensive use of pesticides represents a risk to human health and to the environment. This study aimed to investigate if the exposure to atrazine and diuron, two herbicides widely used in Brazil, could induce changes in the susceptibility profile to aztreonam, colistin and polymyxin B antimicrobials in isolates of P. aeruginosa obtained from soil samples by using the determination of minimum inhibitory concentration (MIC) test. Three isolates had an increase of MIC to aztreonam after exposure to both herbicides and one isolate did not show any MIC change. The MexAB-OprM efflux pump has already been upregulated in these isolates and the herbicides atrazine and diuron did not increase MexAB-OprM overexpression. Therefore, the decrease in aztreonam susceptibility was not directly related to this pump, suggesting that probably other mechanisms should be involved. 相似文献
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This study examines what happens when contentious lay citizens harness the technical-ecological repertoire of experts as means of challenging nature conservation policy. The causes, manifestations, and implications of this phenomenon are elucidated through a critical discourse analysis. The case study is based on the wolf reintroduction project in Europe, with particular focus on Sweden, using illegal hunting discussions as a point of entry within the hunting community. It reveals the deployment of three topoi, which are defined as stock arguments situated within a discourse. Analysis shows how while some topoi often incur short-term gains in the debate because of their scientific guise, they are fundamentally relegated as folk science (or “barstool biology”) by government experts and, in some cases, contribute to the further marginalization of other knowledges. Acquiescence to this discourse is shown to greatly impede the debate. Finally, the study shows how lack of trust in the public dialog, which hunters openly recognize to be colonized by ecological expertise, results in increasingly noncommunicative forms of resistance toward policy. 相似文献
289.
Pierangeli G. Vital Marie Bernadine D. Caballes Windell L. Rivera 《Journal of environmental science and health. Part. B》2017,52(9):683-689
Foodborne diseases associated with fresh produce consumption have escalated worldwide, causing microbial safety of produce of critical importance. Bacteria that have increasingly been detected in fresh produce are Escherichia coli and Salmonella spp., both of which have been shown to progressively display antimicrobial resistance. The study focused on the assessment of antimicrobial resistance of these enteric bacteria from different kinds of fresh produce from various open air markets and supermarkets in the Philippines. Using the disk diffusion assay on a total of 50 bacterial isolates obtained from 410 fresh produce surveyed, monoresistance to tetracycline was observed to be the most prevalent (38%), followed by multidrug resistance to tetracycline, chloramphenicol, ciprofloxacin, and nalidixic acid (4%), and lastly by dual resistance to tetracycline and chloramphenicol (2%). Using multiplex and simplex polymerase chain reaction (PCR) assays, tetA (75%) and tetB (9%) were found in tetracycline resistant isolates, whereas catI (67%) and catIII (33%) were detected in chloramphenicol resistant isolates. Sequence analysis of gyr and par genes from the ciprofloxacin and nalidixic acid resistant isolates revealed different mutations. Based on the results, fresh produce act as a reservoir of these antibiotic resistant bacteria which may pose health threat to consumers. 相似文献
290.
随着抗生素抗性污染日益严重,快速评估环境中典型病原菌与条件性致病菌的抗生素抗性水平,对掌握区域环境抗生素抗性污染状况、揭示抗性污染传播规律至关重要。通过以最低抑菌浓度浸入抗生素改进MI、VJ培养基,并结合滤膜法,建立了针对近岸海洋环境中指示性病原微生物大肠杆菌(Escherichia coli,E.coli)与金黄色葡萄球菌(Staphylococcus aureus,S.aureus)的抗生素抗性监测方法。水体和沉积物样品抗生素抗性水平评估实验结果显示,该方法具有较好重现性(水体和沉积物中E.coli和S.aureus抗生素抗性水平的相对标准偏差分别为11%、8%)与准确度(水体和沉积物中E.coli和S.aureus的平均回收率分别为83.5%、68.4%;相对于CLSI药敏试验的偏离度为±0.1)。且与CLSI药敏实验相比,该方法过程简便、耗时短(36 h/84 h),能最大限度节约经济和人员成本提高抗性评价效率。应用该方法评估辽河口与莱州湾环境中2种病原微生物磺胺类抗生素抗性水平,结果显示辽河口水体中E.coli和S.aureus磺胺二甲嘧啶的平均抗性率分别为27.0%、28.4%,沉积物中分别为35.5%、34.6%;莱州湾水体中E.coli和S.aureus磺胺二甲嘧啶的平均抗性率分别为26.0%、14.5%,沉积物中分别为12.0%、32.9%。该方法适用于河口、近岸海洋及入海排污口水体与沉积物样品中E.coli与S.aureus的快速分析及抗生素抗性水平评估。 相似文献