应用声强测试技术对发动机噪声源识别的研究   总被引：1，自引：0，他引：1  

谢裕智  徐凌  李捷辉  赵哲  黄国彧 《农机化研究》2007,(1):193-196

通过对一台增压柴油机的噪声进行声强测试,将测试得到的数据用STARAcoustics声强软件进行处理和分析,得出发动机各个包络面的等声强分布、声强矢量分布和声功率的计算结果;利用这些结果着重分析和识别了该发动机的主要噪声源,确定了其噪声源的位置、主要噪声频率成分和声功率的贡献,为降低发动机噪声提供了改进依据.结果表明,通过与9点法试验结果的定性比较,能够更准确地判断噪声源的位置及其频率分布.  相似文献   

减弱光照强度对水稻叶片气孔性状的影响   总被引：9，自引：0，他引：9  

孟雷  陈温福  李磊鑫  徐正进  刘丽霞  孙静文 《沈阳农业大学学报》2002,33(2):87-89

采用改良刮制法研究了典型粳稻，典型籼稻，偏籼型，偏粳型和陆稻等10个水稻品种的气孔性状，研究结果发现，剑叶的气孔密度在水稻类型间和品种间具有明显差异。是一个品种特性，光照强度减弱使各品种上三叶的气孔密度明显减少。其原因是由于叶面积增大，气孔行数减少和每一行中相邻气孔间距离增大共同作用的结果。品种不同，其气孔密度对光强变化的反应亦不同，光照强度减弱对剑叶气孔大小有显影响。  相似文献   

湖北省1961年以来气温和降水变化趋势及分布   总被引：10，自引：0，他引：10  

覃军  王海军 《华中农业大学学报》1997,16(4):405-410

１９６１年以来湖北省年平均气温变化小，冬变暖夏变凉趋势明显，冬变暖区域集中在江汉平原南部及鄂东大部，夏变凉区域集中在鄂西北。年平均民政部下最高气温有下降趋势，最低气温有升高趋势，夏季的最高气温下降幅度最大、中心在鄂西北、冬季的最低气温增加幅度最大、中心在武汉附近。年降水量有增加趋势，其分布格局是东增西减，南增北减。  相似文献   

不同采伐强度对闽西常绿阔叶林林分结构稳定性的影响   总被引：3，自引：0，他引：3  

罗永福 《华东森林经理》2012,(3):1-5,13

应用多样性分析方法和改进后的 M.Godron 稳定性测定方法研究常绿阔叶林5种不同强度采伐(弱度9.8%、中度24.5%,强度46.8%和极强度72.3%和皆伐)作业10 a后林分结构稳定性.结果表明,择伐林地林分处于稳定状态,随着择伐强度的增强,林分的稳定性开始逐渐降低.皆伐林地林分处于不稳定状态.对于常绿阔叶林的科学经营,从稳定性出发,应尽量采取择伐方式,尤其是中低强度的择伐方式.  相似文献   

坡度和降雨强度对坡耕地入渗的影响   总被引：6，自引：0，他引：6  

卫喜国  严昌荣  魏永霞  李娜  陆永玲 《灌溉排水学报》2009,(4)

利用人工模拟降雨对黑龙江西部半干旱区坡耕地不同坡度和不同降雨强度下的土壤水分入渗规律进行了试验研究,采用产流历时和稳定入渗速率二项指标进行分析,发现随着地面坡度的增大,产流历时提前,稳定入渗速率逐渐减小,坡面产流历时与坡度呈对数函数关系,土壤稳渗速率与坡度呈幂函数关系;随着降雨强度的增大,产流历时提前,稳定入渗速率逐渐增大;坡面产流历时与降雨强度呈指数函数关系,土壤稳定入渗速率与降雨强度也呈指数关系。  相似文献   

Removal of Vegetative Clippings Reduces Dissolved Phosphorus Loss in Runoff     

《Communications in Soil Science and Plant Analysis》2012,43(11):1555-1564

Rainfall simulation was used to study the vegetative filter strip (VFS) conditions under which losses of total dissolved phosphorus (TDP) and dissolved reactive phosphorus (DRP) leaching occur. Boxes containing silt loam soil were planted with ryegrass and cut at two different intervals prior to simulated rainfall 14 days apart. Grass clippings were either removed or retained. During the second simulated rainfall, runoff TDP and DRP were greater for treatments cut the day before irrigation with clippings retained as compared to treatments cut the same day as irrigation with clippings retained. Removing clippings yielded the lowest mean TDP and DRP concentrations. Increasing the senesced vegetative surface area for contact with water, and the amount of time for leaching to occur, resulted in the greatest DRP loss. The VFS management implications should consider clipping removal or no or reduced mowing during the growing season followed by end-of-season removal to reduce DRP leaching losses.  相似文献   

The effects of applied crop residues on losses of Fe, Mn, Cu and Zn in run-off from a soil prone to crusting     

J. M. Mirás Avalos  I. Bertol    P. Sande Fouz  C. Carballeira  Díaz  E. Vidal Vázquez  & A. Paz  Gonzalez 《Soil Use and Management》2009,25(2):193-200

Tillage practices may reduce the organic matter content in near-surface soil horizons causing crust formation. Surface conditions may cause an increase in surface run-off, thus enhancing contaminant transfer of heavy metals or an acceleration in nutrient loss. This study examines the effect of applying crop residues to the surface of tilled soils on heavy metal losses by run-off. Losses in iron (Fe), manganese (Mn), zinc (Zn) and copper (Cu) were analysed. Run-off and sediment yield were measured on 1 m² plots using a rainfall simulator with a constant 65 mm/h intensity. Four successive rainfall applications were performed, the first three at 25 mm each and the last at 65 mm. Added corn straw varied between 0 and 4 t/ha in the five studied treatments. After 140 mm cumulative rainfall, total heavy metal losses were as follows: Fe from 137 to 950 mg/L, Mn from 2.3 to 12.83 mg/L, Cu from 0.09 to 0.72 mg/L and Zn from 0.31 to 2.46 mg/L. Dissolved fractions were as follows: Fe from 0.014 to 0.229 mg/L, Mn from 0.034 to 1.45 mg/L, Cu from 0.002 to 0.013 mg/L and Zn from 0.02 to 0.12 mg/L. Total concentrations of the studied elements decreased exponentially due to the effect of corn straw on soil loss. However, dissolved contents of Fe and Cu scarcely varied. Significant positive linear correlations were observed between total heavy metal content and soil and sediment loss by run-off. It is concluded that the addition of straw to a soil of low fertility prevents heavy metal loss.  相似文献   

覆盖对粘重土壤中苜蓿出苗的影响     

毛玉林 《草业学报》1999,8(2):76-80

紧实土壤降雨后常由于板结而严重影响作物出苗，导致建植不良乃至失败本实验采用遮阳膜覆盖、麦秸覆盖、不覆盖、土壤稳定剂４个表面处理和快速干燥、缓慢干燥２个干燥速度处理，研究芷蓉播后模拟降水条件一出苗情况，不同的覆盖及土壤处理条件下芷蓿出苗具有显著的处理效应，处理效应主要在出苗早期形成，遮阳膜覆盖比其他出苗显著要高；干燥速度地芷蓿出苗无影响。土壤剂和麦秸对苜蓿出苗的影响需要进一步的研究。  相似文献   

覆膜甜椒干物质积累与养分吸收分配规律的研究   总被引：2，自引：0，他引：2  

蔡绍珍  陈建美 《山东农业科学》1990,(1):15-19

地膜覆盖栽培提高了土壤的供肥能力,促进了甜椒对养分的吸收。在甜椒整个生育过程中,土壤养分含量前期较高,以后逐减,与植株养分吸收强度成负相关。覆膜甜椒前期需肥较少,吸肥高峰出现在采收至采收盛期,此间养分供需存在尖锐矛盾。对覆膜甜椒增施半腐熟有机肥,磷、钾化肥与有机肥混合栽前全层施入,结果至采收期分次适当多追氮素化肥,将有助子产量的提高。  相似文献   

CONTRAST-ENHANCED ULTRASONOGRAPHY IN NORMAL CANINE LIVER. EVALUATION OF IMAGING AND SAFETY PARAMETERS     

Helena T. Nyman  Annemarie T. Kristensen  Mads Kjelgaard-Hansen  Fintan J. McEvoy 《Veterinary radiology & ultrasound》2005,46(3):243-250

Contrast-enhanced ultrasonography, a new imaging modality in veterinary medicine, can provide data on tissue perfusion. The objective of this study was to use the ultrasonographic contrast agent SonoVue to evaluate various transit time indices in the normal canine liver, to examine the effect of anesthesia on these parameters, and to evaluate the safety of this agent in dogs. The liver of 11 healthy dogs was studied by ultrasound during an intravenous bolus injection of SonoVue. Each dog underwent the examination twice, first with and later without the use of anesthesia. A time-intensity curve was generated from a selected region of interest within the liver from each scanning session. Ratios derived from peak enhancement, time to peak enhancement, up-slope and full-width half-maximum (FWHM) of the curve were calculated from the time-intensity curves, and are reported. There were no statistically significant differences (P > 0.05) in peak enhancement, up-slope and FWHM between dogs that were anesthetized and dogs that were not. Time to peak enhancement, however, was significantly shorter when the dogs were anesthetized than when they were nonanesthetized (P < 0.05). There were no biologically significant changes in clinical laboratory findings. This study indicates that contrast-enhanced ultrasound using SonoVue gives reproducible liver perfusion data, and appears to be a safe and well-tolerated agent for use in dogs. When considering normal values, the use of anesthetic drugs has to be considered.  相似文献