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发生全内反射时,入射到介质分界面上的能量全部反射回到第一介质内.可是,当计算折射波平均能流时,发现其沿界面的分量并不为零.这部分能量是哪里来的?本文将回答这一问题,给出全内反射现象中能量流动的图象. 相似文献
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对理想流体一维绝热稳定流动作了讨论.对一般理想流体(可压缩或不可压缩),用两种方法推出了能量方程.在此基础上,讨论了流动可逆性及不同流体性质对流动参数的影响. 相似文献
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本文用“剖面不变性”确定等效电子热导系数,研究了TCA装置上阿尔芬波加热的能量平衡,结果与实验符合很好。证明本文所用的方法对不同装置、不同加热方式都适用。 相似文献
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本文对前人提出的计算激光焊接深熔焊过程中熔池尺寸的方法进行了检验、改进与推广。从激光焊接过程中的能量平衡出发,预报了不同焊接工况下熔池的尺寸,并与实验数据进行了比较,得到了符合得比较好的结果。 相似文献
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讨论考虑洪特耦合的两带赫伯德模型得到的一维自旋轨道模型中自旋-轨道能隙的产生.运用SU(4)赝费米子表象下的平均场理论,计算求得价键序参数、准粒子激发谱能隙和自旋、轨道密度-密度关联函数随系统耦合参数变化的结果.随洪特耦合相互作用由零开始增强,系统激发谱能隙逐渐打开,并且系统在参数取值为J1/J2=1/3处由具有阻错的无序状态相变到自旋铁磁有序和轨道反铁磁有序的状态. 相似文献
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针对大多数现有的无线传感器网络设计方法通常仅找到给定图的最短路径而导致只能优化单个用户性能的问题,提出了一种寻找节点之间的最短路径和最低能耗的路由优化模型,该模型约束WSNs的特定资源,考虑多种约束条件:多周期、最短距离和低能耗。本文按照混合整数线性规划,使用11.0 ILOG CPLEX优化引擎的ILOG OPL开发工具5.5进行编码和求解本文的优化模型。实验结果表明,相比一般可行网络,本文模型的节点的总距离和能耗均有明显降低,此外,在三个不同周期和约束条件数下,每组实验花费的时间均少于10s,完全满足资源有限的无线网络应用要求。 相似文献
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通过对三相电压型PWM整流器传统直接功率控制(DPC)引起的开关频率不固定,网侧电流谐波分量高,系统调节时间长等问题的分析,提出一种电压型三相PWM整流器模型预测直接功率控制方法,应用模型预测理论构建目标函数并对目标函数进行求偏导,对下一个采样周期的有功功率和无功功率变化进行预测,将模型预测理论与二阶拉格朗日插值法相结合进行功率修正,实现了有功和无功功率的实际值与预测值的误差最小,并采用空间矢量脉宽调制(SVPWM)产生PWM信号驱动整流器功率开关,实现固定的开关频率;仿真结果表明,本方法具有良好的动态和稳态性能,系统对电感参数的变化不敏感,有效降低了交流测电流总谐波失真(THD),提高了交流侧功率因数。 相似文献
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Hironobu Sakagawa 《Journal of statistical physics》2000,98(3-4):949-959
It is proved that, under appropriate conditions on the jump rate and potential, one- and two-dimensional stochastic lattice-gas models (exclusion process with speed change) have only canonical Gibbs measures as their stationary measures. This extends the previously known result, which treats only a special jump rate and potential. 相似文献
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The energy gradient method has been proposed with the aim of better
understanding the mechanism of flow transition from laminar flow to
turbulent flow. In this method, it is demonstrated that the transition
to turbulence depends on the relative magnitudes of the transverse gradient
of the total mechanical energy which amplifies the disturbance and the energy
loss from viscous friction which damps the disturbance, for given imposed
disturbance. For a given flow geometry and fluid properties, when the maximum
of the function $K$ (a function standing for the ratio of the gradient of total
mechanical energy in the transverse direction to the rate of energy loss due to
viscous friction in the streamwise direction) in the flow field is larger than a
certain critical value, it is expected that instability would occur for some
initial disturbances. In this paper, using the energy gradient analysis, the
equation for calculating the energy gradient function $K$ for plane Couette flow
is derived. The result indicates that $K$ reaches the maximum at the moving walls.
Thus, the fluid layer near the moving wall is the most dangerous position to generate
initial oscillation at sufficient high $\operatorname{Re}$ for given same level of
normalized perturbation in the domain. The critical value of $K$ at turbulent transition,
which is observed from experiments, is about 370 for plane Couette flow when two walls
move in opposite directions (anti-symmetry). This value is about the same as that for
plane Poiseuille flow and pipe Poiseuille flow (385-389). Therefore, it is concluded
that the critical value of $K$ at turbulent transition is about 370-389 for wall-bounded
parallel shear flows which include both pressure (symmetrical case) and shear driven
flows (anti-symmetrical case). 相似文献
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针对游梁式抽油机平衡装置效果不理想的问题,设计了风光储联合供电的抽油机自动平衡装置;该装置由伺服电机驱动平衡块,根据油井工况实时调节其位置,实现抽油机的最佳平衡;针对平衡装置耗电量大的不足,设计了由风光储联合供电的模式,真正实现抽油机节能;最后,对该装置设计了模糊PD自适应控制器,由模糊控制器在线调节PD控制器参数;在实验室试验10 h,该装置可将抽油机平衡度从1.61减小到1.03以内,白天由太阳能电池供电,夜间由蓄电池供电,其电压从12 V降到9.3 V,表明供电系统完全能满足要求。 相似文献