X线双能量骨密度仪模拟研究

双能量Ｘ线吸收骨密度测量仪是对骨质疏松症进行诊治的重要手段。由于Ｘ线源通常具有一个较宽的能谱，因而骨密度测量值的计算比较复杂。对如何在仪器研制中获得足够高的测量精度问题，本文进行了详细的计算机模拟工作，给出了模拟计算的方法及定量的结果。     

LnCl/MCl熔盐体系能量不对称性 (Ln=稀土元素，M=碱金属元素)

LnCl/MCl熔体中，库仑效应、Van der Waals效应和极化效应起着主导作用，导致溶液热力学性质相对理想溶液呈负偏差，并在x     

能量法确定桩的承载力和沉陷

为了推导出桩的承载力和沉陷值之间的关系,应用能量法,由收锤时桩的贯入度以及由桩的静压实验提供的载荷Q/沉陷s关系曲线得到相应的计算方法。为了证明本文方法的正确性,在实际工程中应用了据此制定的收锤标准。实践证明,这种方法对节省桩长、工时以及工程费用有一定的实践意义。     

How cat lands: insights into contribution of the forelimbs and hindlimbs to attenuating impact force

To safely land after different drops, cats can perfectly use their limbs as dampers to dissipate impact forces. Yet, we know little about the contribution of the forelimbs and hindlimbs of cats to attenuating the impact forces during landing. In order to investigate this, we analyzed the landing impulses and energy absorption based on the ground reaction forces and high-speed video recordings of cats performing self-initiated jump downs at different heights. Our results show that the distribution of impact forces between forelimbs and hindlimbs exhibits a landing height-dependent manner. Furthermore, combining the experimental measurements and the inverted pendu- lum-spring model, we find that variation in landing angle is correlated with the distribution manner. This posture- dependent actuation allows the animal to tune the distri- bution of energy absorption between forelimbs and hind- limbs. These findings highlight how cats perfectly jump down using their limbs, providing fundamental insights into the importance of control mechanisms that attenuate landing impulses safely and efficiently.     

实现“两个转换”,打造思政课高效课堂

在新课程标准下,要提高中学思政课教师的教学能力与教学效果,打造高效课堂,就必须转变教育观念、创新教学内容、优化教学方式,实现从＂教材体系＂向＂教学体系＂的转换以及从＂教学体系＂向＂学生能力—素质体系＂的转换,即实现＂两个转换＂。     

Different effects of substrates on the morphologies of single-walled carbon nanotubes

In this work, different effects of substrates on the morphologies of single-walled carbon nanotubes （SWNTs） are studied. SWNTs were produced by floating catalytic chemical vapor deposition using CH4 as carbon source gas and Ar as carrier gas. Then the SWNTs were deposited on lithography-patterned different substrates. The as-grown SWNTs at the boundaries between SiO2 and metal were characterized by scanning electron microscopy, atomic force spectroscopy and Raman spectroscopy. It is found that SWNTs deposited on low-conductivity substrates trend to have curved morphologies and some of them form rings, while SWNTs deposited on metal sub- strates remain straight and orientated. The mechanism of these effects was also discussed, which is closely related to the thermal conductivities and the principle of energy dissipation.     

为什么男性的鼻子比女性的大

正科学家最近研究发现,男性的鼻子平均而言比女性的大10%(即便两者的体重一样)。科学家推测,这种差异源自两性的不同体格和能量需求:男性的肌肉量总体而言更高,肌肉的生长和保持需要更多的氧;更大的鼻子意味着,吸入的氧以及在血液中供应给肌肉的氧更多。科学家还发现,男女两性从大约11岁起即青春期开始时便显示出鼻     

Lagrange方程在振动系统中的应用

介绍了从系统能量的观点出发去分析一个系统,运用Lagrange方程建立结构动力学基本方程,并特别地推导了考虑轴向力的欧拉粱振动模态与系统质量矩阵、刚度矩阵的关系.最后进行了算例分析.     

双岭特大桥连续梁悬臂施工控制技术

连续梁桥采用悬臂施工方法施工时,桥梁结构不仅要经历T型刚构阶段形成主梁的过程,还要经历体系转换的过程,桥梁结构经历了相当复杂的受力过程,为了确保整个桥梁施工过程的安全性,必须对桥梁施工过程的应力、线形以及影响因素进行严格的控制;否则就会出现受力不合理,线形控制不好,使桥梁合龙困难,影响桥梁的质量和使用寿命。因此,为了保证桥梁施工的安全与质量,桥梁施工控制是不可缺少的。