不倒塔的实验探究

对圆盘对心堆叠而成的塔被敲击下端后的相关运动过程进行分析,将塔身的复杂运动分为3个阶段,采用控制变量的方法进行了大量实验.理论上通过堆塔原理来判断塔是否能够保持直立不倒,并对塔运动的全过程进行数值模拟,将实验结果和数值模拟结合,得到相关参量与塔稳定性之间的关系.     

拉离平板实验的创新与探索

利用排水方法,使水面稳定下降,通过力传感器测定物体所受拉力随时间的变化曲线.改进后的实验装置,可以观察到水块的变化过程,能够直观获得拉力的变化情况及其最大值,并探究其他因素对实验的影响.     

超导磁悬浮力的理论研究与实验分析

本文通过理论研究和实验分析了超导磁悬浮力的变化规律.首先,基于超导体局部模型,从理论上建立了永磁-超导系统磁悬浮力的计算方法,得到的悬浮力为实用高温超导体的最大磁悬浮力,为判断超导块材的性能提供理论依据.利用该方法全面分析了系统参数对磁悬浮力的影响,结果与实验结果吻合,为超导磁悬浮系统的优化设计提供重要的理论指导.其次,采用基于超导体临界态Bean模型的有限元法仿真分析了超导块材磁悬浮力变化的规律.最后,在西北有色金属研究院的超导磁悬浮力测试台上对超导块材在不同场冷条件下的磁悬浮力变化进行了测试,对仿真结果进行了验证,并得到不同冷却方式、不同的场冷高度对超导磁悬浮力的影响.这些结论为超导块材的实际应用提供了重要的理论依据.     

惯性与力

人类进行生产劳动时,源于推、拉、提、抛等的肌肉活动,就认识了力．从此,力便与运动关联在一起．在我国,《墨子》里有这样的记述：“力,形之所以奋也”,古人认为力是物体奋起运动的原因．在西方,当亚里士多德的“有力才有运动”的理论被伽利略的“小车实验”推翻的同时,林利略提出的惯性原理认为：物体不受外力作用时将保持匀速直线运动．而牛顿呢,他的惯性定律这样描述：任何物体都保持静止或匀速直线运动状态,直到其他物体所作用的力迫使它改变这种状态为止．于是,历史进入了牛顿力学时代． 然而,随着历史在时空中的穿梭,自…     

自制的力的平衡四边形定测演示器

验证力的平行四边形定则实验是最基本的实验之一.过去的教学表明,学生在物体共点力的合成与分解,力的平衡,以及物体受力分析等方面出现的问题,追究其根源,就是教师没有重视验证力的平行四边形定则实验.教师借故弹簧秤数量不足而且误差大,所以只做了演示实验或定性说明,导致学生对于力的矢量性理解不深刻.     

公式W=Flcosθ的六种内在特性

做功是能量转化的过程,功是能量转化的量度,所以,功在机械能的教学中十分重要.从能量转化的角度看,如果在力的作用下物体的能量发生了变化,那么这个力一定对物体做了功;从运动的角度看,一个物体受到力的作用并在力的方向上发生了一段位移,则这个力一定对物体做了功.     

利用力传感器探究功与速度变化关系

运用力传感器和数字实验平台对"功与物体速度变化的关系"进行了有效性探究.     

一道动力学问题的求解

文献[1]中有这样一道力学习题.如图1所示,在一质量为M的小车上放一质量为m1的物块,它用细绳通过固定在小车上的滑轮与质量为m2的物块相连,物块m2靠在小车的前壁上而使悬线竖直.忽略所有摩擦.(1)当用水平力F推小车使之沿水平桌面加速前进时,小车的加速度多大?(2)如果要保持m2的高度不变,力F应多大?     

摩擦力实验的改进

1引言 　　摩擦力是力学教学的难点和重点之一,通常的摩擦力演示实验是用弹簧测力计直接拉木块或其他物体进行.这种方法演示易出现弹簧测力计抖动、偏斜、不水平,由于刻度小造成可见度小,不便讲解,学生从演示中收获很小.鉴于这种情况我们自制了一套摩擦力实验装置,该装置克服了以上不足,可在动态下测得一个比较稳定的滑动摩擦力数值,并使实验数据放大,读数暂留,可见度增大,便于课堂讲解.……     

滚动摩擦成因分析

分析了刚体在水平软支承面上做纯滚动和软物体在水平刚性支承面上做纯滚动两种情况下的滚动摩擦成因,分析表明滚动摩擦是一个物体在另一物体上滚动或有滚动趋势时,支承面对滚动物体作用力的不对称分布所引起的一种阻碍滚动的作用,并对滚动摩擦和滚动摩擦力的概念进行了阐释.     

One step hologram calculation for multi-plane objects based on nonuniform sampling (Invited Paper)

The nonuniform sampling method in hologram plane is proposed to reconstruct objects on multi-plane simultaneously. The hologram is nonuniformly sampled by decomposing it into several parts with various sampling rates. The hologram is calculated based on the nonuniform fast Fourier transform （NUFFT） algorithm. In the experiment, we load this nonuniformly sampled hologram on phases-only spatial light modulator （SLM）, and by illumination with collimated light objects with different sampling rates are reconstructed at different distant planes simultaneously. Both of the numerically simulation and optical experiments are performed to demonstrate the feasibility of our method. The experiment also shows that our proposed nonuniform sampled hologram for multi-plane objects is calculated by only one step, better than conventional method that needs several steps of calculation proportional to the numbers of object planes.     

Effect of wind on performance of a dry-cooling tower

The influence of cross-winds on the performance of a natural draft dry-cooling tower is investigated by means of full scale measurements. By monitoring all the relevant independent variables, the results of these measurements allow direct comparison with the wind effect predicted by a numerical procedure employing the PHOENICS code. It is shown that results obtained on full scale towers can be successfully reproduced provided that the effects of all tower components are included in the analysis. In practical cooling towers rectangular heat exchanger bundles are arranged either vertically around the circumference of the tower or in the horizontal inlet cross-section of the tower and the wind is found to be dependent on the particular layout.     

底部加热空气层自然对流的可视化实验研究

本文对底部加热的水平空气层的自然对流换热进行了可视化实验研究,采用实时全息干涉照相技术获得了温度场的激光干涉图及流场的烟可视化图象。实验结果表明,这种水平空气层自然对流换热是非稳态的,并且在空间上是三维的。     

Minimum Query Set for Decision Tree Construction

A new two-stage method for the construction of a decision tree is developed. The first stage is based on the definition of a minimum query set, which is the smallest set of attribute-value pairs for which any two objects can be distinguished. To obtain this set, an appropriate linear programming model is proposed. The queries from this set are building blocks of the second stage in which we try to find an optimal decision tree using a genetic algorithm. In a series of experiments, we show that for some databases, our approach should be considered as an alternative method to classical ones (CART, C4.5) and other heuristic approaches in terms of classification quality.     

Mathematical description of leader channel propagation for selection of model experiment parameters and lightning guard systems

A statistical model of the leader channel propagating toward the Earth with consideration for its orientation relative to grounded objects is proposed, and the results obtained are compared with the predictions of model experiments. Recommendations of how to optimize model experiment conditions for gaining insight into the electric mechanism of the leader channel orientation relative to ground objects are given. The probability of hitting an area protected by a lightning conductor is calculated, and possible ways of improving lightning protection devices are outlined.     

基于DISLab平抛运动实验的改进

利用＂数字信息系统实验室＂（DISLab）对物体的平抛运动进行了实验研究,并针对实验装置中存在问题提出了改进方案,最后将改进后的实验装置与原实验装置的实验结果进行比较研究,结果表明改进后的实验装置明显地提高了测量精度。     

Analyses of cooling tower dynamics

A finite element method for analyzing accurately the free vibrations of cooling towers (with column-supports) is shown to give results that are in good agreement with the experimental data obtained on both a full scale cooling tower and the corresponding model structure, and as far as the author is aware, this agreement is appreciably better than that heretofore reported for comparable studies in the literature by other workers. The theoretical method is also used successfully to explain the apparent discrepancies between the respective experimental results obtained for both model and full scale structures. The effect of foundation elasticity can be included in the method and it is shown to have a significant effect on the lower modes of a cooling tower. The usefulness of the method as a design tool is demonstrated, and as an example, the effects of changing the dimensions of the cornice, ring-beam and column-supports are studied. The angle a column-support makes with the horizontal is shown to have a noticeable effect on the lowest mode of vibration. Varying the value of Poisson's ratio is shown to have only a small effect; this vindicates the use of material in a model cooling tower that does not have quite the same value of Poisson's ratio as the full scale structure. Whilst the free vibration of cooling towers is discussed in this paper, the method can be used to analyze other rotationally periodic structures such as chimneys, and can be extended to analyze the behaviour of rotationally periodic structures subjected to seismic disturbances, impacting missiles or wind-forces.     

锥束射线RT扫描大视场三维CT成像方法研究

受探测器尺寸和重建锥角的限制,基于单圆轨道扫描和FDK算法的三维CT成像方法难以对大物体进行三维CT成像。提出了一种基于平板探测器,采用锥束RT扫描方式的成像方法,推导了其三维CT成像算法。首先把对回转物体进行三次锥束平移透照的投影数据重新排成为更大范围的倾斜平行投影数据,然后经过加权滤波和反投影重建,获得物体的三维层析结果。仿真结果表明,该方法在重构大物体图像时,获得了满意的图像质量。水平方向视场是单圆轨道FDK算法视场的2.88倍,在垂直方向减少了锥角过大形成的伪影,提高了物体的重构精度。     

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在自行设计与建造的液态锂铅合金鼓泡器实验系统上,开展了气-液接触法提取液态锂铅合金中的氢。实验结果表明,氦气比氩气更适合作填料塔的载带气;塔温越高,塔出口端氢含量越大;载气流速对出口端氢含量的影响呈锯齿状,无明显规律。实验结果虽然与文献数据有差别,但可以认为采用气-液接触法提取液态锂铅中的氢同位素是可行的,提取效率是随液态锂铅在填料塔中滞留的时间增长而增大的。     

Stokes参量数字全息法实现相位物体成像

为实现对相位物体的无损检测和成像,克服数字同轴全息相位物体成像技术在消除零级像和孪生像的干扰时存在的系列问题,提出一种基于Stokes参量的新的数字同轴全息技术。该方法区别于传统的利用干涉光场来记录原始像项的数字全息方法,通过测量物参光合成光束的Stokes参量来分别得到这两束光的振幅和相位差,从而准确、唯一地获得原始像项;再利用数字再现即可重构物光的振幅和相位信息。实验中对弱吸收的相位样品进行了测量,得到样品清晰的振幅和相位分布。结果表明,采用该方法对相位物体进行数字全息再现,可以克服传统同轴全息图中零级像和共轭像对相位物体信息的严重干扰,对于提取相位物体的振幅和相位信息是可行和有效的。