纵向岭谷区高速公路沿线生态系统健康评价     

刘杰  陈帆  耿海清  仇昕昕  蔡斌彬 《水土保持通报》2010,30(2):31-36

将生态系统健康理论引入路边生态系统,选择纵向岭谷区大保(大理-保山)和思小(思茅-小勐养)两段高速公路作为案例工程,采用生态系统距离指数、协调指数和健康指数对高速公路沿线生态系统的健康状态进行了尝试性评价,进而分析了高速公路建设对沿线生态系统健康的影响.结果表明,高速公路建设对沿线生态系统健康产生了一定程度的影响,其影响范围可能在200m内,且距离高速公路越近,其影响强度越大;不同地理位置和地貌条件下高速公路建设对沿线生态系统健康的影响强度不同,大保高速公路的影响作用强于思小高速公路(除山腰路段沿线0～50 m),不同地貌条件下其影响程度的强弱比较满足:山腰>山顶.  相似文献   

Variability of acetone in milk in a large low-production dairy herd: a longitudinal case study     

Heuer C  Wangler A  Schukken YH  Noordhuizen JP 《Veterinary journal (London, England : 1997)》2001,161(3):314-321

The objective of this study was to relate acetone in milk with cow and management factors in one low producing dairy herd (5260 kg milk per 305-day lactation). Milk acetone was measured in regular monthly milk samples one to three times within 100 days of lactation in 4433 lactations (2639 cows, 7800 measurements) from one herd over a period of 32 months (1988-91). Associations between milk acetone and cow factors and surrogate measures of management were evaluated by variance components of multiple fixed effect models. Lactation stage, calendar month of study, production groups and milk yield were strong, and percentage milk fat and parity were weak predictors of milk acetone. There was a trend of increasing body weight loss from the first to the second month of lactation with increasing milk acetone level. A substantial increase in milk production in 1991 was accompanied by an almost twofold rise in milk acetone. It was concluded that environmental parameters had strong relationships with milk acetone even in this low-producing herd.  相似文献   

Effect of lamellas annual-ring orientation on cracking of glulam beams investigated with computer tomography and image processing     

《Wood material science & engineering》2013,8(3):166-174

Abstract

Cracks in glulam beams can reduce their strength, depending on the crack's depth, length, and location and can also be a passage for the accumulation of water and dirt. To avoid cracks, the relationship between cracks (area of cracks, mm²) and annual-ring orientation in glulam beams of spruce (Picea abies), and pine (Pinus sylvestris) with different dimensions and surface treatments was investigated using RGB images of the surface and tomography images of the cross-sections. Image processing was used to measure characteristics visible in the photos such as crack area and lamella position in the beam. Combination of lamellas in lay up was measured from computer tomography images. Four types of combinations were defined; type 1 (pith side facing outward), types 2 and 3 (pith to the same side), and type 4 (pith sides meet pith side). It was found that the area close to the glue line in the lamellas in combination type 4 is the most subject to cracking, whereas combinations of type 1 show the highest resistance to cracking. This means that type 4 should not be used in glulam beams, because the lamellas shrink apart from each other causing stresses and resulting cracks.  相似文献   

胶合木T梁弯曲承载力试验研究     

杨涛  王解军  宁凡  饶真宇 《中南林业科技大学学报(自然科学版)》2019,(5):124-131

为了增强结构整体性与耐久性,节省材料,降低造价,提出一种理论上适合工程应用的正交胶合木T梁这一新的构件形式。采用兴安落叶松板材和结构胶,制作了正交T梁、平行T梁(高跨比1/7.6)及矩形梁(高跨比1/9.2)共3组试件,进行静力弯曲承载力试验,对比分析各类构件的应变、挠度及极限承载力。结果表明:1)3类梁受弯时均为中部顺纹剪切破坏,正交T梁的抗弯承载力比矩形梁提高了33%,比平行T梁低30%;2)基于刚度等效原则,提出了将正交T梁等效为平行T梁,然后采用Rammer抗剪强度公式来计算其弯曲剪切强度的策略;3)分析表明所提出的策略合理、可靠,扩展了Rammer公式的适用范围。研究成果可为工程应用提供理论依据。  相似文献   

Exercise-induced pulmonary haemorrhage in Thoroughbred racehorses: a longitudinal study     

E. J. Crispe  C. J. Secombe  D. I. Perera  A. A. Manderson  B. A. Turlach  G. D. Lester 《Equine veterinary journal》2019,51(1):45-51

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豫北地区苹果树干皮缝中越冬的节肢动物种类调查初报     

柴立英  刘春元 《河南农业大学学报》1998,32(1):52-54

通过２ａ的调查结果表明,豫北地区苹果树干皮缝中越冬的节肢动物数量大,且种类繁多,其中包括农林作物和果树害虫及其天敌。统计分析表明,害虫占总数的８．３４％,天敌占总数的９１．６６％,蜘蛛类占天敌总数的４５．４５％,传统的冬季刮老树皮防治果树害虫的方法,能消灭部害虫,也能杀伤大量的害虫天敌、建议尽量不要刮树干老皮。  相似文献   

基于Prescan自动紧急制动系统分级控制策略研究     

尤本隆 《农业装备与车辆工程》2022,60(1):54-59

为提高汽车跟车行为的安全性,提出一种基于有限状态机理论的自动紧急制动(AEB)控制策略.制定了分级预警和分级制动策略,通过碰撞时间模型(TTC)和安全距离模型确定出AEB系统的预警时机、制动时机和制动强度.在2021版C-NCAP主动安全测试场景下,通过PreScan和MATLAB/Simulink软件对提出的控制策略...  相似文献   

玉米应力裂纹扩展的分形模型及动力学分析     

朱文学  张玉先  李栋  曹崇文 《农业机械学报》1999,30(3):48-52

对玉米应力裂纹分形分析表明,裂纹具有近似的自相似性,即分形特征,因此,可以用分形理论进行研究。建立了应力裂纹４种扩展机制的分形模型,给出了生成元维数,并进行了应力裂纹扩展的动力学分析,表明裂纹沿晶扩展需要的扩展力最小,分叉扩展需要的扩展力最大。  相似文献   

螺旋焊管与直缝焊管裂纹断裂分析     

董绍华  吕英民 《油气储运》1999,18(12):24-27

根据最大位应力理论,分析了焊管在受内压及裂余应力的作用下,焊缝区Ⅰ／Ⅱ混合型裂纹开裂角θ０与裂纹角β的关系,并分析限具有不同裂纹缺陷时,螺旋管与直缝管的断裂破坏强度。  相似文献   

Prospective longitudinal studies of salmonid alphavirus infections on two Atlantic salmon farms in Ireland; evidence for viral persistence     

D A Graham  E Fringuelli  C Wilson  H M Rowley  A Brown  H Rodger  M F McLoughlin  C McManus  E Casey  L J McCarthy  N M Ruane 《Journal of fish diseases》2010,33(2):123-135

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