Gravitational coupling,dynamical changes of units and the cosmological constant problem

A spacetime interval connecting two neighbouring points can be measured in different unit systems.For instance,it can be measured in atomic unit defined in terms of fundamental constants existing in quantum theories.It is also possible to use a gravitational unit which is defined by the use of properties of macroscopic objects.These two unit systems are usually regarded as indistinguishable up to a constant conversion factor.Here we consider the possibility that these two units are related by an epoch-dependent conversion factor.This is a dynamical changes of units.Regarding a conformal transformation as a local unit transformation,we use a gravitational model in which the gravitational and the matter sectors are given in different conformal frames(or unit systems).It is relevant to the cosmological constant problem,namely the huge discrepancy between the estimated and the observational values of the cosmological constant in particle physics and cosmology,respectively.We argue that the problem arises when one ignores evolution of the conversion factor relating the two units during expansion of the Universe.Connection of the model with violation of equivalence principle and possible variation of fundamental constants are also discussed.     

Extremely large-amplitude oscillation of soft pipes conveying fluid under gravity

In this work, the nonlinear behaviors of soft cantilevered pipes containing internal fluid flow are studied based on a geometrically exact model, with particular focus on the mechanism of large-amplitude oscillations of the pipe under gravity. Four key parameters, including the flow velocity, the mass ratio, the gravity parameter, and the inclination angle between the pipe length and the gravity direction, are considered to affect the static and dynamic behaviors of the soft pipe. The stability analyses show that, provided that the inclination angle is not equal to π, the soft pipe is stable at a low flow velocity and becomes unstable via flutter once the flow velocity is beyond a critical value. As the inclination angle is equal to π, the pipe experiences, in turn,buckling instability, regaining stability, and flutter instability with the increase in the flow velocity. Interestingly, the stability of the pipe can be either enhanced or weakened by varying the gravity parameter, mainly dependent on the value of the inclination angle.In the nonlinear dynamic analysis, it is demonstrated that the post-flutter amplitude of the soft pipe can be extremely large in the form of limit-cycle oscillations. Besides,the oscillating shapes for various inclination angles are provided to display interesting dynamical behaviors of the inclined soft pipe conveying fluid.     

Einstein-Maxwell-dilaton引力模型中的5维宇宙膜解

获得了Einstein-Maxwell-dilaton引力模型中的一种新型的5维 宇宙膜解，并分析和讨论了这种解的物理含义. 关键词： Einstein-Maxwell-dilaton引力模型 5维时空 宇宙膜解     

气垫导轨测重力加速度时空气粘滞阻力的影响

本文通过理论推导，得出在考虑空气粘滞阻力的情况下，用气垫导轨测重力加速度的实验近似公式，并给出重力加速度的修正项。     

单摆实验数据处理方法的研究简

分析了单摆实验中数据处理的列表法、图解法、最小二乘法,同时提出了逐差法和软件拟合法。在讨论和比较这五种实验数据的基础上,提出如何根据单摆实验目的进行科学选择数据处理方法。     

非旋转性前进波Euler与Lagrange解间的转换

对等深水中非旋转性的前进重力波动场,以求得的Euler与Lagrange两种形式至第三阶的解,按照同一流体质点在相同时间与位置处其流速唯一与质量守恒性及在自由表面水位处Euler形式解与Lagrange形式解为同一值的特性,来推导二者可相互转换.由连续的Taylor级数展开,考虑波动场中各流体质点的运动轨迹与运动周期,将已知的Euler形式解转换成完全未知的Lagrange形式解,解决了以往成果中出现含时间的不合理的共振项,以及无法得到与Euler系统不同的Lagrange形式的流体质点运动频率与平均运动 关键词： 非旋转性前进波 Euler-Lagrange转换 质点运动轨迹 质点运动频率     

旋转液体综合实验设计

提出了一种根据旋转液体特性用光学方法测量重力加速度和液体黏度的综合实验设计方案,该实验已作为开放、设计性实验内容在教学中应用．     

绝对重力仪的技术发展:光学干涉和原子干涉

绝对重力仪是直接开展绝对重力测量的精密计量仪器.绝对重力测量是指对地球表面重力加速度值的直接测量,其在地球科学和计量科学等领域都有十分重要的应用.历史上最早的绝对重力测量约在1590年.1590～1960年,主要利用摆仪的摆长和自由摆周期来开展绝对重力测量.自1960年起,随着激光技术的发明,高精度绝对重力测量有了新的...     

胶体粒子Boltzmann分布对测试结果产生的误差分析

胶体粒子是自然科学中一类非常重要的研究对象。由于重力势场的作用,胶体粒子并不是均匀分布的(假设为Boltzmann分布)。为了考察Boltzmann分布对测试结果产生的影响,通过理论计算讨论了3种粒径(20 nm、50 nm、100 nm)的二氧化硅在重力势场作用下的Boltzmann分布,即浓度随高度的变化,并与平均浓度相比较。结果表明,粒子越大,重力势场对粒子分布的影响越大,对测试结果产生的误差也越大。最后,通过理论计算指出合理选择粒子种类和粒子大小,可以降低Boltzmann分布对测试结果产生的影响。