Torsion balances with fibres of zero length

Torsion balances have good immunity to tilt and low rotational stiffness. However precise control of the position of the suspended torsion ‘bob’ is difficult in the presence of ground vibrations and tilt and this is a limiting factor in applications where Casimir forces or putative non-Newtonian short-range forces are being measured. We describe how the desirable characteristics of torsion balances can be reproduced in a rigid body that is suspended using applied forces rather than a torsion fibre. The suspension system can then provide a more precise control of the degrees of freedom of the suspended body. We apply these ideas to a superconducting levitated torsion balance, developed by the authors, and a generic electrostatic suspension. We present results of preliminary experiments that provide support for our analyses.     

直接键连原子间的NMR偶合常数的自然杂化轨道研究V.~(13)C-~(13)C和~(13)C-~(31)P核自旋偶合常数~1J_(CC)和~1J_(CP)

在前文工作的基础上，结合ＭＮＤＯ／ＥＨＭＯ分子轨道方法和自然杂化轨道方法，具体计算了ＣＣ键和ＣＰ键的核自旋偶合常数．计算结果表明，１ＪＣＣ和１ＪＣＰ主要由成键原子的轨道杂化作用和键极性这两种结构因素所决定．为从简单价键理论角度解释和计算１ＪＣＣ和１ＪＣＰ值提供了简便直观的方法．     

具有切向控制的局部四点插值曲线设计方法

Ｎｉｒａ Ｄｙｎ等提出的四点插值法是一种典型的自由曲线离散造型方法，但该方法不能控制插值点的切向。本文利用薄板样很可能 量的极小化原理给出了具有切向控制的四点分插值条件。用户可以方便地交互控制任一插值点的切向，使得四点插值法更为有效和实用。     

New constraints on short-range forces coupling mass to intrinsic spin

A new device that we refer to as the spherical superconducting torsion balance has been used to search for a new force coupling mass to intrinsic spin. Our experimental approach also employs a novel spin-source geometry that allows unprecedented sensitivity in the range 100 mum10 mm at 1sigma confidence. At a range of 1 mm our most relaxed limit is g_{p};{e}g_{s}<1.5x10;{-24}.     

The Feasibility of Testing the Inverse Square Law of Gravitation at Newtonian Strength and at Mass Separations of 1 μm

We examine the feasibility of searching for violations of the inverse square law of gravitation with Newtonian strength and at particle separations of 1 m. We discuss systematic uncertainties, such as spurious forces due to the Casimir force, and various sources of random uncertainty, including those due to patch fields and detector noise. Our analysis suggests that a cryogenic, drag-free space environment is necessary to make the experiment feasible, as thermal and vibrational noise could potentially be reduced to the required level in such an environment.     

Forces between conducting surfaces due to spatial variations of surface potential

We describe analytical and numerical methods for calculating forces between conductors due to variations of electrostatic surface potential across their surfaces. In the simple case where the spatial variation of surface potential gives rise to uniform power spectra, we show that the electrostatic force can be large in comparison with, and scale in approximately the same way with distance of closest approach as, the Casimir force. Patch potentials that are consistent with existing experimental data could give rise to forces with a magnitude of 4% of the Casimir force at separations of 0.1 microm.     

A new determination of G using two methods

We present the results of a measurement of G made with a torsion-strip balance used in two substantially independent ways. The two results agree to within their respective uncertainties; the correlation coefficient of the two methods is -0.18. The result is G = 6.675 59(27)x10(-11) m(3) kg(-1) s(-2) with a standard uncertainty of 4.1 parts in 10(5). Our result is 2 parts in 10(4) higher than the recent result of Gundlach and Merkowitz.