Testing the Equivalence Principle in the Quantum Regime

We consider possible tests of the Einstein Equivalence Principle for physical systems in which quantum-mechanical vacuum energies cannot be neglected. Specific tests include a search for the manifestation of non-metric effects in Lamb-shift transitions of hydrogenic atoms and in anomalous magnetic moments of massive leptons. We discuss how current experiments already set bounds on the violation of the equivalence principle in this sector and how new (high-precision) measurements of these quantities could provide further information to this end.     

A General-Relativistic Fermat Principle for Extended Light Sources and Extended Receivers

In an arbitrary Lorentzian manifold, we fix a spacelike submanifold P and a timelike submanifold . We interpret P as (the surface of) a light source at a particular instant of time, and we interpret as the history of (the surface of) a receiver. We prove the following version of Fermat's principle. Among all lightlike curves from P to , the lightlike geodesics which are perpendicular to P and spatially perpendicular to are characterized by stationary arrival time. Here, the arrival time is defined with the help of an arbitrary time function on . Moreover, we show that the second variation of the arrival time at a stationary point is characterized by a Morse index theorem.     

三原子分子振转激发态成簇现象理论研究

在只考虑弯曲振动与总角动量的耦合,而冻结伸缩振动的模型下,采用Jacobi多项式作为弯曲振动的基函数,用严格的变分法研究了H~2O分子的振转激发态的成簇现象。本文计算了H~2O分子的振转能级和函数,研究了振动激发态下转动高激发态中出现的成簇态。     

Mach's Principle and Minkowski Spacetime

It is shown that when the Minkowski metric is approached by a limiting process using two different static, spherically-symmetric, closed cosmological models, that although the energy-stress tensors for the Einstein-Friedmann field equations vanishes, their integral does not. Since part of this integral consists of the mass of the incoherent dust background, which is the same in both models, the Minkowski metric obtained by this limiting process cannot be regarded as anti-Machian, since there is an infinite amount of ponderable matter in the background, albeit at vanishing density. One of the models is the Einstein static universe with its cosmological term. The other model does not employ this term, but instead uses a tensor that has vanishing trace, negative energy density and negative pressure. Gravitational energy is also studied, and it is pointed out that for both models, this energy becomes infinitely negative in the Minkowski limit.     

中药有效成分三维结构数据库的开发和研究

介绍了北京大学中药有效成分三维结构数据库软件系统的结构、功能及开发步骤。该数据库系统不仅仅提供6500个中草药有效成分的二维和三维结构以及其它各类相关信息,同时拥有功能强大的数据库查询、维护及分子表达系统。在该系统中,用户可以交互式地实现多种分子特征的查询以及二维子结构的查询。查询得到的分子可以直接在北京大学药物设计系统(PKUDDS)中进行三维结构的显示和分析。该数据库系统和我们科研组开发的北京大学药物设计系统以及中草药信息系统构成了完整的基于中药的药物设计系统。该系统已经用于NS3-NS4A蛋白酶抑制剂以及其它体系的研究并取得了很好的结果。     

Local and Global Light Bending in Einstein's and Other Gravitational Theories

To remedy a certain confusion in the literature, we stress the distinction between local and global light bending. Local bending is a purely kinematic effect between mutually accelerating reference frames tracking the same signal, and applies via Einstein's equivalence principle exactly and equally in Newton's, Einstein's, Nordström's and other gravitational theories, independently of all field equations. Global bending, on the other hand, arises as an integral of local bending and depends critically on the conformal spacetime structure and thus on the specific field equations of a given theory.     

Radiation from a Uniformly Accelerated Charge

The emission of radiation by a uniformly accelerated charge is analyzed. According to the standard approach, a radiation is observed whenever there is a relative acceleration between the charge and the observer. Analyzing difficulties that arose in the standard approach, we propose that a radiation is created whenever a relative acceleration between the charge and its own electric field exists. The electric field induced by a charge accelerated by an external (nongravitational) force is not accelerated with the charge. Hence the electric field is curved in the instantaneous rest frame of the accelerated charge. This curvature gives rise to a stress force, and the work done to overcome the stress force is the source of the energy carried by the radiation. In this way, the energy balance paradox finds its solution.     

Machian Mechanics with Isotropic Inertia

A nonrelativistic theory is discussed here which contains an interaction which produces isotropic inertia for anisotropic matter distributions. The interaction is a 4-body interaction and it is explained why it is necessary to have this type of interaction. The consequences of the theory are discussed for celestial mechanics including the predicted perihelion precession. Frame dragging effects are calculated and compared with other theories. Possible ways to extend the theory to noninstantaneous interactions are briefly discussed. This theory demonstrates that Mach's principle in the form considered here is not necessarily inconsistent with isotropic inertia.