空套螺母的设计参数对横纹夹持梓木构件极限抗拔力的影响     

郝景新  周腾飞  刘文金  黄彬 《中南林业科技大学学报(自然科学版)》2015,(2):100-102

采用正交试验法系统研究了不同空套螺母的设计参数对梓木构件径向极限抗拔力的影响规律。结果表明:螺纹长度、螺纹间距、螺纹高度对梓木构件径向极限抗拔力的影响显著,而螺母底径的影响不显著。随着螺纹长度和螺纹高度的增加,螺纹间距的减小,极限抗拔力呈上升趋势。如果要提高空套螺母连接件的抗拔力,比较有效的方法是延长螺纹的长度而不是增加螺母的底径。  相似文献   

区域尺度灌溉用水效率考核指标及计算方法     

邵东国  何思聪  李浩鑫 《灌溉排水学报》2015,34(1):9-12,32

随着节水灌溉尺度效应的深入研究,灌溉回归水重复利用被认为是导致农业用水效率尺度效应的重要因素之一。传统的基于田间试验或统计得到的单位面积灌溉用水量指标并未考虑回归水的重复利用。针对这一问题,考虑灌区管理部门干支渠灌溉系统管理的实际需求,分析了中等尺度区域灌溉回归水重复利用过程,首次提出了农业用水效率考核新指标"千公顷灌溉取水量"的概念,给出了相应的计算依据、方法及适用条件。经湖北省漳河灌区千公顷典型区域水平衡试验观测与模拟模型计算,论证了回归水利用在提高农业用水效率中的重要作用,表明"千公顷灌溉取水量"作为我国中等尺度区域特别是南方长藤结瓜灌溉系统农业用水效率考核指标,是必要和可行的。  相似文献   

水库低温水的生态影响及工程对策研究   总被引：1，自引：0，他引：1  

张士杰  刘昌明  谭红武  李国强 《中国生态农业学报》2011,19(6):1412-1416

大型水库低温水下泄对农业生态和水生生态产生较大不利影响, 国内在高坝大库设计中多采用叠梁门表层取水结构来获取满足农作物的灌溉水温和鱼类生活史需求水温, 其运用的下泄水温调节效果多采用立面二维或垂向一维水温模型进行模拟。文中利用MIKE3软件建立研究水库的三维水温数学模型, 精确模拟水库采用叠梁门分层取水和单层进水口两种取水方案下的水库水温结构及下泄水温。预测结果表明叠梁门分层取水方案能有效地提高水库泄水温度, 3~9月出现的水库低温水温度比单层进水口提高2~4 ℃, 并在5月份就能达到鱼类产卵要求的18.4 ℃。叠梁门分层取水结构能够有效地提高水库泄水温度, 最大程度减缓水库低温水下泄的生态影响, 实现生态环境保护和经济效益的较好协调, 叠梁门结构比较适合作为国内生态友好型大型水库工程建设的生态修复和保护措施。  相似文献   

土拉霉素在猪体内残留消除规律的研究     

倪姮佳  黄显会  贺利民  方炳虎  赵永达 《畜牧兽医学报》2011,42(4)

本研究旨在分析土拉霉素在猪体内的残留消除规律并为制定休药期提供依据。采用猪颈部一次性肌内注射土拉霉素注射液,注射剂量为2.5mg.kg-1体质量,分别在给药后第0.5,5,12,18,25,36,48天,各宰杀5头取样。样品经乙腈提取,正己烷脱脂,C18固相萃取柱(SPE)净化后用高效液相色谱—串联质谱仪分析。结果显示,给药后第0.5天注射部位药物浓度最高,第36天所有组织的药物浓度均低于最高残留限量(MRL)。用WinNonlin软件分析各组织中的消除动力学参数,消除快慢依次为注射部位,肝脏,皮脂,肌肉,肺脏和肾脏,其消除半衰期(t1/2β)分别为117.06,193.14,197.60,207.64,228.99和232.61h。肺脏的药时曲线下面积(AUC)为1 220.59μg.h.g-1仅次于注射部位及肾脏,显著高于肌肉,肝脏及皮脂。由于肾脏为代谢器官,因此可确定肺脏为土拉霉素作用的靶部位。根据欧美等国家对土拉霉素制定的最高残留限量,计算得注射部位的休药期最长,为33d。结果提示土拉霉素注射液吸收迅速,体内分布广,作用时间长。建议休药期为33d。  相似文献   

Effects of CCK-8 and its receptor antagonists on expression of CREB and pCREB in prefrontal cortex and hippocampus of morphine withdrawal rats     

GAO Ping-rui  MA Xing-you  WEN Di  YANG Sheng-chang  YU Feng  NI Zhi-yu  LI Shu-jin  MA Chun-ling  CONG Bin 《园艺学报》2014,30(7):1158-1165

AIM：To observe the effects of cholecystokinin octapeptide (CCK-8) and its receptor antagonists on cAMP response element binding protein (CREB) and phosphorylated CREB (pCREB） expression in frontal cortex and hippocampus of morphine withdrawal rats, which aim to explore the post-receptor mechanism through which CCK-8 regulates morphine withdrawal. METHODS：After the morphine dependence and naloxone-precipitated withdrawal animal models were established, the effects of CCK-8, L-364718 (CCK1 receptor antagonist) and LY-288513 (CCK2 receptor antagonist) pretreatment on CREB and pCREB expression in frontal cortex and hippocampus were observed by Western blotting and immunohistochemistry. RESULTS：In rat frontal cortex neuron, CREB was expressed in both cytoplasm and nucleus, but pCREB was only highly expressed in the nucleus. In the pyramidal cell layer of hippocampal CA1 region, CREB showed high expression in the cytoplasm and low expression in the nucleus, while pCREB was only expressed in the nu-cleus. No obvious change of CREB was observed after either chronic morphine treatment or naloxone withdrawal. The pCREB expression was increased after chronic morphine treatment and further increased after naloxone withdrawal. Compared with the withdrawal group, chronic pretreatment with CCK-8, L-364718 and LY-288513 had no effect on CREB expression in the frontal cortex, but obviously decreased the pCREB expression. In the hippocampus, pretreatment with L-364718 and LY-288513 decreased CREB and pCREB expression, but only the pCREB expression was decreased after CCK-8 treatment. CONCLUSION：CCK-8 and CCK receptor antagonists may alleviate morphine withdrawal symptoms by regulating CREB, with specificity in different brain regions.  相似文献   

A comparison of the withdrawal resistance load of nails using experimental and interference approaches     

《Wood material science & engineering》2013,8(4):213-218

Abstract

The objective of this study was to determine and predict the withdrawal resistance or pull-out load of common wire nails embedded in radial, tangential and cross-sectional grain orientation of Douglas fir (Presudotsuga menziesii) and sugar maple (Acer sacharum) samples. Four lead-hole diameters of 1.5, 2.0, 2.5 and 3.0 mm were used to create various interference fits. Nails with a diameter of 3.38 mm were driven into the samples to a depth of 10 mm for the experiments. The overall withdrawal resistance of Douglas fir samples was found to be lower than that of maple samples. Strength values of each sample increased with decreasing lead-hole diameters. No significant difference was found between withdrawal resistance values from radial and tangential sections in either species. However, significantly lower values were obtained for the cross-sections of the samples than for the two other sections. Ratios between predicted pull-out load values of the nails from both species based on the finite element numerical interference approach were very close to experimental measurements, with ratios ranging from 0.93 to 1.09. The results provide better understanding of the behaviour and performance of pull-out resistance for building systems.  相似文献   

Evaluation of the Local Analgesic Effects of a Commercial Aqueous Extract of Sarracenia purpurea and Ammonium Sulfate in the Equine Abaxial Sesamoid Block Model     

Gerardo J. Campos  Tony C. Chacón  Francisco J. Cova  Sergio A. Flores  Jesús A. Rojas  Arnaldo J. Risso  Hector A. Zerpa González 《Journal of Equine Veterinary Science》2013

Sarracenia purpurea is a carnivorous plant whose aqueous extracts have been proposed to exert analgesic effects by neurolytical action on peripheral nerves. The aim of this study was to determine the local analgesic effects of a commercially available aqueous extract solution of S. purpurea (P-Bloc, St. Joseph, Missouri) and a 1% ammonium sulfate solution, using the horse abaxial sesamoid block model. Twenty horses were randomly assigned to two groups. The first group (n = 10) was used to evaluate the effect of P-Bloc. The horses received a bilateral (medial and lateral) abaxial sesamoid block with 5 mL of P-Bloc in one random forelimb, while in the contralateral forelimb, they received either 5 mL of 2% lidocaine as a positive control (n = 5) or 5 mL of 0.9% NaCl as a negative control (n = 5). The second group (n = 10) was treated as the first but received 5 mL of 1% ammonium sulfate in NaCl (0.9% NaCl) solution instead of P-Bloc. The period of hoof withdrawal reflex latency (HWRL, in seconds) was measured using a custom-made heat projector lamp as a source of a noxious skin heating stimulus applied to the pastern. Lidocaine (2%) prolonged (P ≤ .05) the HWRL period, returning to the negative control basal values after 240 minutes. Neither the treatment with P-Bloc nor 1% ammonium sulfate modified the HWRL period. The lack of effect of these compounds in this model reinforces the results reported elsewhere and suggests a nonlocal anesthetic mechanism of action for the aqueous extract of S. purpurea in the horse.  相似文献   

恩诺沙星注射液在猪体内的残留消除研究   总被引：1，自引：0，他引：1  

黄耀凌  徐士新 《中国兽药杂志》2017,51(3):48-54

为研究恩诺沙星在猪体内的残留消除规律,验证休药期,以2.5 mg/kg体重肌内注射10%恩诺沙星注射液,每日2次,连续3 d。在最后一次给药后0、3、5、7、10 d时间点,采集肌肉、肝脏、肾脏、脂肪和注射部位肌肉,HPLC法测定组织中的恩诺沙星及其代谢物环丙沙星的残留量,并用WT1.4软件计算休药期。结果显示,恩诺沙星在猪肌肉、肝脏、肾脏、脂肪和注射部位肌肉的休药期分别是5.6、13.4、8.2、3.0、5.5 d。为保证兽药使用安全、消费者健康和食品安全,推荐恩诺沙星注射液在猪的休药期为14 d。  相似文献   

落叶松规格材的钉连接性能     

王春明  费本华  林利民  刘一楠  高大宏 《木材工业》2010,24(3)

钉连接是木结构中常用的连接方式之一。依据美国钉连接的试验方法及设计值的确定方法,对我国东北地区落叶松的钉连接性能进行了检测。结果表明,随着圆钉直径的增大,落叶松的抗拔出力和抗剪切力基本呈上升趋势。并对东北地区落叶松钉连接的参考设计值进行了分析。  相似文献   

磺胺间甲氧嘧啶钠对厚颌鲂幼鱼SOD活性和MDA含量的影响   总被引：1，自引：0，他引：1  

周梦  郑永华  胡文达  唐洪玉  李洪泽  黎学练 《淡水渔业》2016,(2):55-59

以(30±2.3)g/尾的厚颌鲂(Megalobrama pellegrini)幼鱼为研究对象,采用一次性胸腔注射法,通过观察磺胺间甲氧嘧啶钠对厚颌鲂幼鱼超氧化物歧化酶(SOD)活性和丙二醛(MDA)含量的影响,探讨磺胺间甲氧嘧啶钠对厚颌鲂幼鱼各组织酶活性的影响变化及其休药期。结果显示,在同一浓度下,随着给药时间的延长,肝脏、肌肉和鳃组织SOD活性出现先降后升再降的趋势,而随着浓度的增加,则出现先升后降的趋势;肝脏、肌肉和鳃组织MDA,随着给药时间的延长和浓度的增加,均出现先升后降的趋势;厚颌鲂各组织SOD和MDA受磺胺间甲氧嘧啶钠影响最小的是肌肉,其次是鳃、肝脏;通过SOD和MDA变化情况,确定休药期为28 d左右。  相似文献