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考虑到含间隙运动副副元素的碰撞接触时的边界条件,采用非线性弹簧力和非线性阻尼描述副无素的碰撞接触过程,以此为基础建立了含间隙内燃机曲柄滑块机构的动力学模型;通过数值仿真研究了运动副间隙对机构动态特性的影响,并指出在机构高运转条件下,运动副元素存在连续变形接触现象。 相似文献
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3种滤食性贝类对塔玛亚历山大藻的摄食研究 总被引:4,自引:0,他引:4
20 0 3年 4月在实验室内采用静水法 ,研究了长牡蛎、紫贻贝、栉孔扇贝对塔玛亚历山大藻的清滤率 (CR)和摄食率 (IR) ,实验时间持续 3d ,水温 17℃。实验中每 1种贝都分别投喂 :(1)叉鞭金藻 (对照藻 ) ,(2 )叉鞭金藻 +塔玛亚历山大藻去藻过滤液 1.5L ,(3)叉鞭金藻 +塔玛亚历山大藻细胞。结果表明 ,塔玛亚历山大藻过滤液 ,对 3种贝的清滤率的无明显影响 (P >0 .0 5 ) ;3种贝对塔玛亚历山大藻和叉鞭金藻混合液的清滤率与对照组相比明显降低 (P <0 .0 1) ;而对塔玛亚历山大藻的摄食率和保留率 3d间无显著变化 ;实验期间 ,随时间的变化 ,牡蛎对混合液的清滤率变化最大 ,贻贝次之 ,扇贝则无明显著变化 (P >0 .0 5 ) ;如果以摄食率作为指标 ,贻贝在控制赤潮方面的潜力较大 ,值得今后进一步研究。 相似文献
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The influence of dietary restriction on the negative feedback potency of 17-beta-estradiol (E2) was evaluated in both castrated male (wethers) and female sheep (OVX ewes) during the breeding season. In study 1, OVX ewes received maintenance or restricted dietary energy for 7 weeks or maintenance energy for 6 weeks prior to a 5 day fast (n=12ewes/feeding group). Estradiol (0.31microg E2/50kg/h) or vehicle (10% EtOH-saline) was continuously infused into half the animals in each dietary treatment for the final 54h of the study. The dynamic pattern of LH secretion was assessed during the final 6h of infusion. Estradiol inhibited luteinizing hormone (LH) pulse amplitude independent of nutrition (P=0.02); fasting increased mean LH, LH peak height, and LH nadir in the absence of E2 (P=0.004, P=0.02, and P=0.02, respectively); while E2 inhibited pulse frequency (P=0.02) and increased peak width (P=0.04) in restricted ewes. Interestingly, despite uniform E2 delivery, serum concentrations of E2 differed with feeding status. Therefore, 12 wethers were infused with 0.31microg E2/50kg/h (6 fed, 6 fasted) and six wethers received 0.19microg E2/50kg/h (fasted) to establish similar serum concentrations of E2 in fed (0.31microg/50kg/h) and fasted (0.19microg/50kg/h) wethers. When fed and fasted wethers had uniform serum concentrations of E2 LH pulse frequency was suppressed (P<0.05) in fasted relative to fed animals, supporting the postulate that energy restriction enhances the E2 negative feedback potency. Collectively, these studies demonstrate that nutrition affects E2 feedback potency and clearance. 相似文献
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本试验以日照红茶为材料,在单因素试验基础上,采用Box-Behnken响应面设计法对茶多酚超声波辅助提取清除DPPH的工艺进行优化,建立了乙醇体积分数、超声时间、超声温度、乙酸乙酯萃取静置时间4因素与DPPH清除率之间的回归优化模型,确定了最佳提取工艺为:乙醇体积分数86.54%,超声时间69.61min,超声温度60℃,静置萃取时间82.26min,在优化后的最佳工艺参数下,红茶茶多酚对DPPH的清除率最高可达74.84%,研究表明红茶茶多酚具有较强的清除DPPH的能力。 相似文献
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K. Wotman P.A. Wilkins J.E. Palmer R.C. Boston 《Journal of veterinary internal medicine / American College of Veterinary Internal Medicine》2009,23(3):598-605
Background: Lactate concentration in blood or plasma ([LAC]) and change in [LAC] are associated with survival in sick foals. Hypothesis: [LAC] and change in [LAC] over time are associated with survival at 96 hours and discharge in neonatal foals. Furthermore [LAC] and change in [LAC] over time correlate with blood culture results and blood pressure at admission. Animals: Two hundred and twenty‐five foals consecutively admitted to a Neonatal Intensive Care Unit. Methods: Retrospective case review. Foals ≤30 days of age with [LAC] from arterial (190) or umbilical (35) blood gas analysis ([LAC]BG) at admission, 24, and 48 hours. [LAC]BG, blood pressure, blood culture status, and outcome (survival versus nonsurvival at 96 hours and discharge) were recorded. Change in [LAC]BG over time ([LAC]BGΔT) was calculated. Results: [LAC]BG was lower in survivors (96 hours and discharge) at all times. [LAC]BGΔT was larger for survivors (96 hours). Odds of survival (96 hours and discharge) decreased 18, 39, 53 and 22, 38, and 47%, respectively, at each sample time for every 1 mmol/L increment in [LAC]BG and increased 156% for each 1.0/day increment in [LAC]BGΔT from admission to 24 hours at 96 hours. Blood pressure and [LAC]BG were not correlated (P= .196) until removal of selected foals (mean arterial pressure <60 mmHg, admission [LAC]BG <5.5 mmol/L) (P < .001). Bacteremia was not associated with [LAC]BG. Proposed admission [LAC]BG cut‐points for future studies were 6.5 mmol/L (96 hours) and 5.5 mmol/L (discharge). Conclusions and Clinical Importance: Prospective studies evaluating [LAC], [LAC]BGΔT, and cut‐points in sick foals are warranted. 相似文献
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研究了反应时间、提取液浓度、pH 和温度对刺五加提取液抗 NO2-的作用的影响,结果发现:在反应30min,提取液浓度0.297 mg /ml 以上,pH =3,37℃条件下,清除率可达50%以上。 相似文献
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含泄水孔混流式水轮机间隙流动数值模拟 总被引:3,自引:0,他引:3
建立了包括混流式水轮机转轮上冠和顶盖间的空腔、泄水孔以及转轮前密封间隙流道中的水体模型在内的全流道几何模型,通过三维数值模拟,研究了主流道内速度和压力分布以及空腔、泄水孔和密封间隙内的流动特征,揭示了混流式水轮机上部空腔压力与泄漏水量随不同密封间隙尺寸、不同泄水孔直径和数目的变化规律。根据数值模拟结果,最终确定水轮机泄水孔数目为6个,直径为40 mm,间隙宽度为1 mm,该模型额定工况下流量为5 109 m3/h,间隙泄漏水量占机组流量的0.3%,水轮机效率为86.75%,与试验测试结果基本一致,表明所研究的间隙流计算方法可为水轮机泄水孔直径、数目以及密封间隙等细部结构尺寸的权衡确定提供参考依据。 相似文献