盐城地区大棚反季节蔬菜生产的温度条件及其应用   总被引：3，自引：2，他引：3       下载免费PDF全文

蒋名淑  朱傅详等 《气象科学》2002,22(2):236-241

通过平行对比观测试验，分析得出了我市塑料大棚不同层次的增温效应，以及晴雨天气转换时大棚内的各项温度的变化情况，并根据大彬的几种主要蔬菜适宜生长的气象指标，对我市沿海地区大棚的反季节蔬菜生产作出各类蔬菜棚内的适宜生长期，为利用大棚进行反季节蔬菜生产提供了科学依据。  相似文献   

柔性断层错动产物的微观研究方法初探   总被引：2，自引：0，他引：2  

姚大全  汤有标 《地震研究》1992,15(1):63-69

柔性断层错动产物一般尚未固结,难以对其进行定向取样,固化和磨制薄片,笔者经过长期努力提出解决这个问题的方法并将其应用于郯—庐断裂带赤山段晚更新世以来活动性的研究中。笔者按总结出的方法定向采取断层泥,对其固化并磨制定向薄片,在镜下仔细观测,发现众多变形现象和由其反映的运动学和动力学方面的重要信息。属脆性变形的有:长英质矿物颗粒被错移并形成棋盘格式构造,脆—塑或塑性变形发生在粘土和云母类的矿物中,尤其是“帚”状扭折和先扭后错现象在云母中非常普遍。恢复薄片的自然产状后,宏微观构造具统一性。据变形产物赋存的地质时代,它们应是断裂晚更新世以来活动的微观证据。文中笔者除系统介绍了柔性断层产物的采样、固结、磨片和应用此种技术的实例外,还探讨了显微构造分析在活断层研究中应有的地位和作用。  相似文献   

Long-term changes in the type,but not amount,of ingested plastic particles in short-tailed shearwaters in the southeastern Bering Sea     

Vlietstra LS  Parga JA 《Marine pollution bulletin》2002,44(9):945-955

We report the current (1997-1999, 2001) incidence and amount of ingested plastic in short-tailed shearwaters (Puffinus tenuirostris) in the southeastern Bering Sea and compare our results with plastic reported in shearwaters during 1970-1978. We also examine correlations between plastic loads and shearwater body mass. We found that 84% (N = 330) of shearwaters sampled in 1997-1999 and 2001 contained plastic. The incidence and amount of ingested plastic have not significantly changed since the 1970s. In contrast, the predominant type of plastic has changed over time, from industrial plastic to user plastic. S,asonal patterns in the incidence and amount of ingested plastic also changed from peak levels during early and late summer in the 1970s to mid summer in the late 1990s and 2001. We suggest that the availability of neuston plastic to seabirds in the Bering Sea has undergone a shift in composition since the 1970s. Shearwater body mass appears little if at all impaired by plastic, at least at present levels of consumption.  相似文献   

Plastic debris as nesting material in a Kittiwake-(Rissa tridactyla)-colony at the Jammerbugt, Northwest Denmark     

Hartwig E  Clemens T  Heckroth M 《Marine pollution bulletin》2007,54(5):595-597

This paper continues the investigations of Clemens and Hartwig from 1992 on the proportion of garbage used as nesting material in the Kittiwake colony at Bulbjerg in the Jammerbugt in Northwest Denmark. Whereas in the year 1992 plastic garbage items were included in 39.3% of 466 Kittiwake nests in the Bulbjerg colony, in 2005 57.2% of 311 nests contained plastic debris. Although it has been forbidden to dispose of plastic garbage into the marine environment since the implementation of the MARPOL 73/78-Agreement/Annex V (Regulation for the Prevention of Pollution by Ship Waste) of 1989 and especially since the declaration of the North Sea as a MARPOL-Special Area for garbage in 1991, the pollution of the oceans and the North Sea is still an ubiquitous problem, particularly with regard to plastic waste. Plastic waste is presumably not used preferentially for nest-building, but in the context of available nesting material in the waters surrounding the breeding colony. Therefore the share of garbage parts in nests of certain species of birds is an indicator of the amount of waste in the natural environment in the vicinity of their breeding site.  相似文献   

成都花卉塑料薄膜大棚热量平衡初探     

黄斌  罗秀陵 《成都信息工程学院学报》1993,(3)

本文在测量的基础上,对热量平衡各分量在大棚内、外的差异,进行了比较与分析,对大棚生产管理有重要参考价值。  相似文献   

板钉连接CFST柱-RC梁节点梁端塑性铰区受力性能数值模拟     

马华  阚吉平  赵玉坤  李振宝 《震灾防御技术》2022,17(2):381-391

建立竖板-栓钉连接钢管混凝土（CFST）柱-钢筋混凝土（RC）梁节点试件（SSJD）拟静力加载试验有限元模型,并在节点损伤情况、梁端荷载-位移曲线等数值模拟结果与试验结果吻合较好的基础上,进一步开展了RC梁混凝土强度、配筋率ρ_s和连接竖板长度L_b及界面连接情况等对CFST柱-RC梁节点梁端塑性铰区域力学性能的影响。研究结果表明,RC梁混凝土强度对试件SSJD塑性铰区域受力性能的影响较小;适筋范围内RC梁配筋率增加可适当提高试件SSJD承载力和延性;随着连接竖板长度的增加,梁端塑性铰区域外移,梁破坏荷载增大;本研究给出的RC梁与CFST柱之间的界面抗剪承载力模拟值与计算值吻合较好,可用于界面抗剪设计。  相似文献   

土钉支护现场测试及三维数值模拟分析   总被引：12，自引：3，他引：9  

李志刚秦四清  张冰峰 《工程地质学报》2004,12(1):69-73

在进行土钉轴力和边坡位移测试的基础上 ,进行了土钉支护的三维数值模拟研究 ,对边坡位移、土钉轴力、塑性区分布等分别作了较为深入的探讨 ,认识到土钉与土体相互作用形成了一个完整的支护体系 ;基坑失稳破坏并非传统意义上的土体和土钉的破坏 ,而是土钉支护体系的整体性破坏 ;土钉支护体系的形成正是通过土钉的分担作用、应力传递与扩散作用来实现的 ,这是土钉支护作用的实质.  相似文献   

后生浮游动物摄食对太湖夏季微囊藻水华形成的作用     

周健  杨桂军  秦伯强  张光生  王丽君  高映海  李鸿毅  陈满意  钟春妮 《湖泊科学》2013,25(3):398-405

为了了解后生浮游动物的摄食作用在太湖夏季微囊藻水华形成中的作用,2009年7月15日至8月14日取太湖梅梁湾湖水开展了后生浮游动物对微囊藻水华形成作用的野外模拟实验.实验期间,未过滤掉后生浮游动物的对照组出现了漂浮在水面、肉眼可见的微囊藻水华,而过滤掉后生浮游动物的实验组没有出现微囊藻水华.结果显示,对照组整个实验期间都有后生浮游动物存在,共发现了9种后生浮游动物;而实验组在实验第6 d发现有后生浮游动物出现,整个实验期间共发现了3种后生浮游动物.浮游动物生物多样性分析显示对照组显著高于实验组.实验后期(21～30 d),对照组微囊藻平均密度显著高于实验组.整个实验期间,惠氏微囊藻(Microcystis wesenbergii)和水华微囊藻(Microcystis flos-aquae)密度均显著高于实验组,且惠氏微囊藻密度占对照组微囊藻总密度的60.79%.研究结果表明,太湖夏季后生浮游动物摄食并不能控制太湖蓝藻水华,相反,后生浮游动物特别是大型浮游动物能促进蓝藻水华的形成.同时表明,后生浮游动物群落结构可能是影响微囊藻水华形成的重要因素.  相似文献   

Generalized failure envelope for caisson foundations in cohesive soil: Static and dynamic loading     

《Soil Dynamics and Earthquake Engineering》2015

The response of massive caisson foundations to combined vertical (N), horizontal (Q) and moment (M) loading is investigated parametrically by a series of three-dimensional finite element analyses. The study considers foundations in cohesive soil, with due consideration to the caisson-soil contact interface conditions. The ultimate limit states are presented by failure envelopes in dimensionless and normalized forms and the effects of the embedment ratio, vertical load and interface friction on the bearing capacity are studied in detail. Particular emphasis is given on the physical and geometrical interpretation of the kinematic mechanisms that accompany failure, with respect to the loading ratio M/Q. Exploiting the numerical results, analytical expressions are derived for the capacities under pure horizontal, moment and vertical loading, for certain conditions. For the case of fully bonded interface conditions, comparison is given with upper bound limit equilibrium solutions based on Brinch Hansen theory for the ultimate lateral soil reaction. A generalized closed-form expression for the failure envelope in M–Q–N space is then proposed and validated for all cases examined. It is shown that the incremental displacement vector of the caisson at failure follows an associated flow rule, with respect to the envelope, irrespective of: (a) the caisson geometry, and (b) the interface conditions. A simplified geometrical explanation and physical interpretation of the associativity in M-Q load space is also provided. Finally, the derived failure envelope is validated against low (0.67 Hz) and high frequency (5 Hz) dynamic loading tests and the role of radiation damping on the response of the caisson at near failure conditions is unraveled.  相似文献   

Effects of mechanical and chemical processes on the degradation of plastic beach debris on the island of Kauai, Hawaii   总被引：3，自引：0，他引：3  

David A Cooper  Patricia L Corcoran 《Marine pollution bulletin》2010,60(5):650-654

Plastic debris is accumulating on the beaches of Kauai at an alarming rate, averaging 484 pieces/day in one locality. Particles sampled were analyzed to determine the effects of mechanical and chemical processes on the breakdown of polymers in a subtropical setting. Scanning electron microscopy (SEM) indicates that plastic surfaces contain fractures, horizontal notches, flakes, pits, grooves, and vermiculate textures. The mechanically produced textures provide ideal loci for chemical weathering to occur which further weakens the polymer surface leading to embrittlement. Fourier transform infrared spectroscopy (FTIR) results show that some particles have highly oxidized surfaces as indicated by intense peaks in the lower wavenumber region of the spectra. Our textural analyses suggest that polyethylene has the potential to degrade more readily than polypropylene. Further evaluation of plastic degradation in the natural environment may lead to a shift away from the production and use of plastic materials with longer residence times.  相似文献