首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到10条相似文献,搜索用时 156 毫秒
1.
岳平*  张强  李耀辉  王润元  王胜  孙旭映 《物理学报》2013,62(9):99202-099202
本文利用锡林郭勒草原2008年春季近地层涡旋相关系统和铁塔的风、 温平均梯度观测资料, 分析了总体输送系数随梯度Richardson数的变化特征, 建立了动量总体输送系数随大气稳定度、近地层风速以及感热总体输送系数随大气稳定度和近地层气温的关系. 中性条件下, 半干旱草原植被下垫面动量总体输送系数与近地层大气动力状态之间存在明显的相互作用, 总体输送系数与近地面层风速之间满足二次曲线拟合关系; 风速较小时, 大气动力特征对地表粗糙度长度的改变不是很明显, 动量总体输送系数随气流增强而增大; 而当风速较大时, 强风速会使植被高度发生改变, 动量总体输送系数随气流增强而减小. 另外, 感热总体输送系数与近地层气温之间也存在二次曲线关系. 动量总体输送系数与近地层风速之间的关系、感热总体输送系数与近地层气温之间关系的建立为总体输送系数参数化提供了重要途径, 同时该方案避免了对动力学粗糙度长度和热力学粗糙度长度的求解. 关键词: 总体输送系数 参数化 湍流通量 相似性函数  相似文献   

2.
(火积)的宏观物理意义及其应用   总被引:3,自引:0,他引:3       下载免费PDF全文
赵甜  陈群 《物理学报》2013,62(23):234401-234401
提高传热过程的性能是解决能源问题的重要途径之一. 本文通过与力学中相关概念进行对比,分析了传热过程性能优化的新物理量——(火积)的宏观物理意义. 通过(火积)与物体对外传热能力、(火积)定义的传热过程效率以及(火积)与热量传递驱动力的关系三方面分析,发现(火积)具有的宏观物理意义是物体包含的热量在温度场中所具有的势能. 并且,通过对流换热的(火积)理论优化介绍了(火积)理论在工程实际中的应用. 关键词: (火积) 宏观物理意义 势能 对流换热  相似文献   

3.
何志聪  李芳  李牧野  魏来 《物理学报》2015,64(4):46802-046802
以波长为780 nm、重复频率为76 MHz、脉宽为130 fs的飞秒激光作为激发光源, 采用超快时间分辨光谱技术研究了CdTe量子点-铜酞菁复合体系的荧光共振能量转移. 实验结果表明, 在780 nm的双光子激发条件下, 复合体系中CdTe量子点的荧光寿命随着铜酞菁溶液浓度的增加而减少, 荧光共振能量转移效率增加. 同时也研究了激发功率对荧光共振能量转移效率的影响. 结果表明, 随着激发光功率的增加, 复合体系溶液中CdTe量子点的荧光寿命增加, 荧光共振能量转移效率减小, 其物理机理是因为高激发功率下的热效应和由双光子诱导的高阶激发态的跃迁. 当激发光功率为200 mW时, 双光子荧光共振能量转移效率为43.8%. 研究表明CdTe量子点-铜酞菁复合体系是非常有潜力的第三代光敏剂.  相似文献   

4.
This paper presents the numerical modeling of complex flows and heat transfer. The Finite Analytic method is used to discretize the transport equations. The diagonal Cartesian method is proposed to model fluid flows and heat transfer over complex geometries. A three-dimensional channel flow with conjugate heat transfer is simulated. By the diagonal Cartesian method and 5-point Finite Analytic scheme, a grooved channel flow and flow in a casting bank at different Reynolds numbers are modeled. Simulations by both the diagonal Cartesian method and the traditional saw-tooth Cartesian method indicates the diagonal Cartesian method improves the modeling of flows, due to the more accurate approximation of complex boundaries. Heat transfer in two-dimensional finned compact heat exchanger is also studied. An improved heat exchanger is proposed based on the numerical prediction of heat transfer.  相似文献   

5.
In this work, the relationship between the structure and the radical scavenging activity of seven hydroxycoumarins and their sulfured analogs was investigated for the first time by density functional theory calculation in the gas phase, benzene, and water. Our investigation includes hydrogen atom transfer, single‐electron transfer–proton transfer, and sequential proton loss electron transfer mechanisms. The results revealed that the bond dissociation enthalpy values of sulfured coumarins were lower than those of hydroxylated analogs. The obtained results were in a good agreement with the experimental results. The hydrogen atom transfer mechanism is dominant in both benzene and vacuum. The sequential proton loss electron transfer mechanism represents the most thermodynamically preferred reaction pathway in water. However, single‐electron transfer–proton transfer mechanism is not the most preferred one in all media. Finally, this work contributes to the understanding of the pharmacological activity of the compounds studied. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

6.
An investigation of the luminescence properties of TbAl3B4O12 in the temperature region 1.4–300 K is reported. Laser site-selection and time-resolution techniques were used.The results show that energy migration among Tb3+ ions on the regular crystallographic sites occurs. The transfer characteristics at room temperature are consistent with a diffusion-limited transfer process to Mo3+ quenching centres. The diffusion constant and the critical transfer distance for Tb3+ → Mo3+ transfer are derived. The rate of diffusion increases for decreasing temperature. At about 60 K a transition from diffusion-limited transfer to trapping-limited transfer occurs. This behaviour is due to the variation in the diffusion constant with temperature. In the temperature region below 60 K transfer to Tb3+ traps is observed. The intensity of the emission from the traps increases exponentially with decreasing temperature. However, the overall transfer rate to Mo3+ and traps remains roughly constant. A simple model including time-independent transfer rates and back transfer from traps to intrinsic Tb3+ ions is proposed to explain the results. The rates of transfer to Mo3+ and traps are obtained.  相似文献   

7.
低温绝热气瓶颈管传热的数值模拟与试验   总被引:1,自引:0,他引:1  
利用数值模拟的方法建立模型来分析高真空多层绝热气瓶容器的漏热量,与理论计算相比,能更精确分析颈管传热包括颈管导热和气体换热所占的份额及液体充满率对颈管传热的影响。模型中还考虑了不规则内筒壁的导热和容器气相空间的传热,并且模拟结果与通过试验测试不同液位高度时绝热气瓶的漏热量吻合良好。  相似文献   

8.
载人登月转移轨道偏差传播机理分析与稳健性设计   总被引:2,自引:0,他引:2       下载免费PDF全文
贺波勇  李海阳  张波 《物理学报》2013,62(19):190505-190505
载人登月转移轨道具有飞行时间长, 动力学模型复杂, 非线性强且变系数的特点, 而载人登月工程对转移轨道可靠性要求极高, 研究地月转移轨道偏差传播机理和轨道稳健性设计不仅具有工程意义, 更具有探索地月空间复杂引力场对轨道偏差作用的科学意义. 本文首先分析了日地月中心引力和地球J2项摄动等主要作用力对转移轨道偏差的作用范围与影响大小, 其次提出了一种基于标称轨道数据的变系数非线性动力学系统偏差传播机理解析分析方法, 最后构建了基于偏差传播矩阵的转移轨道稳健性评价指标, 并基于NSGA-II (Nondominated Sorting Genetic Algorithms)算法求解了载人登月转移轨道稳健性优化设计问题. 仿真结果表明, 本文提出的偏差传播机理分析方法能快速准确地求解出载人登月转移轨道偏差传播矩阵, 利用偏差传播矩阵进行协方差分析和中途修正脉冲计算是简单准确的, 考虑稳健性的转移轨道优化设计可以提高标称轨道品质. 关键词: 载人登月 转移轨道 偏差分析 稳健性设计  相似文献   

9.
佘银柱  秦慧斌  吕明 《应用声学》2015,34(5):425-432
变厚度圆板和环板是在工程设计中经常遇到的一类构件,与等厚度板相比,通过适当的沿径向厚度的变化,这种变厚度板在振动、失稳、弯曲等方面能起到更好的效果。将沿径向任意变厚度圆板、环板划分为一系列等厚度环板单元,基于Mindlin中厚板理论采用逆向推导的方式推导了其传递矩阵,建立起变厚度圆板、环板的频率方程。通过计算线性变厚度环板自由振动时的频率,并与ANSYS模态分析结果相比较,验证了计算模型的精确性。逆向推导法避免了高阶数传递矩阵推导复杂的问题,是对传递矩阵法的很好推广。  相似文献   

10.
The role of water’s H-bond percolation network in acid-assisted proton transfer was studied in water and glycerol solutions and in sugar glasses. Proton transfer rates were determined by the fluorescence of pyrene-1-carboxylate, a compound with a higher pK in its excited state relative to the ground state. Excitation of pyrene-1-COO produces fluorescence from pyrene-1-COOH when a proton is accepted during the excited singlet state lifetime of pyrene-1-COO. The presence of glycerol as an aqueous cosolvent decreases proton transfer rates from phosphoric and acetic acid in a manner that does not follow the Stokes relationship on viscosity. In sugar glass composed of trehalose and sucrose, proton transfer occurs when phosphate is incorporated in the glass. Sugar glass containing phosphate retains water and it is suggested that proton transfer requires this water. The infrared (IR) frequency of water bending mode in sugar glass and in aqueous solution is affected by the presence of phosphate and the IR spectral bands of all phosphate species in water are temperature dependent; both results are consistent with H-bonding between water and phosphate. The fluorescence results, which studied the effect of cosolvent, highlight the role of water in assisting proton transfer in reactions involving biological acids, and the IR results, which give spectroscopic evidence for H-bonding between water and phosphate, are consistent with a mechanism of proton transfer involving H-bonding. The possibility that the phosphate-rich surface of membranes assists in proton equilibration in cells is discussed.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号