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991.
针对高热通量芯片的冷却散热问题,利用具有巨大升华潜热以及极低初始温度的干冰作为散热流体,通过建立干冰冷却的散热器模型,对散热器散热空间内干冰冷却降温过程的热流场进行模拟仿真,对干冰冷却的芯片降温特性进行分析,得出:干冰入口半径为6 mm,散热器针柱直径为2 mm、11×11均匀分布的散热效果最好。随着干冰流速逐渐增大,芯片温度达到稳定时间越快,流速为0.20 m/s时稳定温度为15.49℃,远低于芯片结温,0.06 m/s的流速即可达到芯片安全温度。干冰流速为0.20 m/s,在10 s时散热空间内已充满干冰,降温效果更好。功率为125 W时,干冰冷却也可将芯片中心测点(A点)温度稳定控制在49.47℃之下。此外,对比分析了P0=65 W下的水冷式冷却降温与P0=95 W下的干冰冷却降温性能,得出水冷式冷却稳定后的温度停留在74.2℃,干冰冷却稳定后的温度为15.49℃,干冰冷却降温的芯片整体温度分布更均匀,冷却效果更好。研究结果为进一步深入研究高热通量芯片干冰冷却降温系统打下基础。 相似文献
992.
993.
研究了以粉状聚丙烯(PP)为原料、以羧甲基纤维素(CMC)为稳定剂的旋转成型用水性浆液料的干燥行为.实验结果表明,PP/CMC浆液料体系由于CMC的成膜作用而导致干燥过程复杂化,表现出与普通干燥过程不同的特点.出现了该体系所特有的变速干燥阶段. 相似文献
994.
干气密封启停阶段的端面接触是不可避免的,为了揭示端面发生接触时的力学特性以保证干气密封稳定运行,运用统计学接触理论和等效阻尼思想,考虑密封环材料属性,推导出适用于分析干气密封干摩擦界面法向动态接触刚度和动态接触阻尼的解析模型,并通过实验测得密封环真实表面形貌,确定了接触模型的初始参数。探究干气密封端面发生接触时动态接触刚度和接触阻尼等参数的变化规律。结果表明,动态接触刚度随接触比压、扰动振幅的增大而增大。扰动频率对动态接触刚度的作用效果远小于接触比压或振幅对接触刚度的作用效果。动态接触阻尼随接触比压的增大而增大,随扰动频率和振幅的增大而减小。通过与多种经典接触模型对比,当前的计算结果与GW模型更为接近。针对干气密封碳化硅作为动环、石墨作为静环的配对方式,在端面未发生磨损时,结合面的微扰动态特性以动态接触刚度为主,动态接触阻尼较弱。法向接触特性的变化主要考虑50%临界脱开转速之前的接触阶段。 相似文献
995.
996.
997.
French PD 《Journal of dairy science》2006,89(3):1057-1061
An experiment was conducted using 14 multiparous Holstein and 14 multiparous Jersey cows to determine if dry matter intake (DMI), specifically the decline in prepartum DMI and plasma parameters differed between breeds. Cows were blocked by expected calving date and received a dry cow total mixed ration (15% crude protein and 39% neutral detergent fiber) beginning 30 d before expected calving date. At calving, cows were switched to a lactation total mixed ration (17% crude protein and 33% neutral detergent fiber). Data were collected from d 23 prepartum to d 1 postpartum. Body weight was greater for Holsteins compared with Jerseys, but body condition score did not differ between breeds. Dry matter intake decreased for both Holsteins and Jerseys as parturition approached. The interaction of breed × day prepartum was significant for DMI with the magnitude of depression being greater for Holsteins compared with Jerseys. Plasma glucose and β-hydroxy-butyrate was similar between breeds. Plasma nonesterified fatty acids (NEFA) were similar for the two breeds up to d 5 prepartum, but greater for Holsteins compared with Jerseys thereafter. The decline in prepartum DMI was positively correlated to plasma NEFA for Holsteins, but not for Jerseys. These results indicate that breed differences exist for the decline in prepartum DMI and plasma NEFA. In addition, these data show an association between prepartum DMI depression and plasma NEFA but do not suggest a causal relationship. 相似文献
998.
Dann HM Litherland NB Underwood JP Bionaz M D'Angelo A McFadden JW Drackley JK 《Journal of dairy science》2006,89(9):3563-3577
The objectives of this study were to determine the effects of far-off and close-up diets on prepartum metabolism, postpartum metabolism, and postpartum performance of multiparous Holstein cows. From dry-off to −25 d relative to expected parturition (far-off dry period), cows were fed a control diet to meet National Research Council (NRC) recommendations for net energy for lactation (NEL) at ad libitum intake (100NRC; n = 25) or a higher nutrient density diet, which was fed for either ad libitum intake to provide at least 150% of calculated NEL requirement (150NRC; n = 25) or at restricted intake to provide 80% of calculated NEL requirements (80NRC; n = 24). From −24 d relative to expected parturition until parturition (close-up period), cows were fed a diet that met or exceeded NRC nutrient recommendations at either ad libitum intake (n = 38) or restricted intake (n = 36) to provide 80% of the calculated NEL requirement. After parturition, all cows were fed a lactation diet and measurements were made through 56 d in milk (DIM). Prepartum metabolism was consistent with the plane of nutrition. During the first 10 DIM, far-off treatments had significant carryover effects on dry matter intake, energy balance, serum nonesterified fatty acid (NEFA) concentration, and serum β-hydroxybutyrate concentration. Cows with the lower energy balance during the far-off period (100NRC and 80NRC) had higher dry matter intake and energy balance and lower serum NEFA and β-hydroxybutyrate during the first 10 DIM. There were no effects of close-up diet and no interactions of far-off and close-up treatments. During the first 56 DIM, there were no residual effects of far-off or close-up diets on dry matter intake, milk yield or composition, body weight, body condition score, serum glucose and insulin concentrations, or muscle lipid concentration. Serum NEFA was higher for 150NRC than 80NRC; 100NRC was intermediate. Thus, the effects of far-off and close-up treatments on postpartum variables diminished as lactation progressed. Overfeeding during the far-off period had a greater negative impact on peripartum metabolism than did differences in close-up period nutrition. 相似文献
999.
1000.
Kuhn C Kuhn A Rykow K Osten B 《Hemodialysis international. International Symposium on Home Hemodialysis》2006,10(1):68-72
To assess the dry weight of chronic hemodialysis (HD) patients, the extravascular lung water index (ELWI) as a volume parameter was investigated to identify fluid overload. Forty-two patients (30 males, 12 females) with a mean age of 55.7+/-13.0 years who were clinically not overhydrated were connected to the PiCCO system before starting HD treatment. We determined ELWI (normal range 3-7 mL/kg) and the following parameters: global end-diastolic volume index (GEDI, normal range 680-800 mL/m(2)) and intrathoracic blood volume index (ITBI, normal range 850-1000 mL/m(2)) before and after HD to assess the volume status. Brain natriuretic peptide (BNP), aldosterone, and renin as vasoactive hormones were measured at the beginning and at the end of HD treatment as well. In 28 of the 42 patients (67%), elevated values of ELWI were found, indicating interstitial volume overload. There were significant correlations between ELWI and cardiac function index (p=0.003; Pearson's coefficient -0.451), global ejection fraction (p=0.012; Pearson's coefficient -0.389), ITBI (p=0.004; Pearson's coefficient 0.437), and GEDI (p=0.004; Pearson's coefficient 0.437). No significant relations among ELWI and mean arterial pressure (MAP), BNP, aldosterone, and renin were found. In conclusion, the use of ELWI is safe in chronic HD patients and identifies fluid-overloaded patients, who show no obvious signs of hypervolemia. The determination of ELWI is an excellent method to quantify the exact volume in chronic HD patients. 相似文献