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1.
A precise knowledge of the Newtonian gravitational constant G has an important role in physics and is of considerable meteorological interest. Although G was the first physical constant to be introduced and measured in the history of science, it is still the least precisely
determined of all the fundamental constants of nature. The 2002 CODATA recommended value for G, G = (6.6742 ± 0.0010) × 10−11m3 · kg−1 · s−2, has an uncertainty of 150 parts per million (ppm), much larger than that of all other fundamental constants. Reviewed here
is the status of our knowledge of the absolute value of G, methods for determining G, and recent high precision experiments for determining G. 相似文献
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A set of general expressions for photoionization cross sections of atoms or molecules embedded in a medium and a dielectric influence function are derived based on Maxwell‘s equations and the Beer-Lambert‘s law in this work.The applications are performed for the photoionization process of solid gold both in the Clausius-Mossotti (virtual cavity) model and the Glauber-Lewenstein (real cavity) model firstly. The results show that the present theoretical expressions of photoionization cross section can be used to describe the photoionization process of atoms in condensed matter properly. 相似文献
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Durmu? A. Demir 《Physics letters. [Part B]》2011,701(4):496-502
We study gravitational properties of vacuum energy by erecting a geometry on the stress-energy tensor of vacuum, matter and radiation. Postulating that the gravitational effects of matter and radiation can be formulated by an appropriate modification of the spacetime connection, we obtain varied geometrodynamical equations which properly comprise the usual gravitational field equations with, however, Planck-suppressed, non-local, higher-dimensional additional terms. The prime novelty brought about by the formalism is that, the vacuum energy does act not as the cosmological constant but as the source of the gravitational constant. The formalism thus deafens the cosmological constant problem by channeling vacuum energy to gravitational constant. Nevertheless, quantum gravitational effects, if any, restore the problem via the graviton and graviton-matter loops, and the mechanism proposed here falls short of taming such contributions to cosmological constant. 相似文献
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We comment on the paper “ISLAND – Inverse-Square-Law Acceleration Measurement using Inertial Drift,” by Lockerbie, N.A.: Gen.
Rel. Grav. 36, 593–600 (2004). 相似文献
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D Narasimha 《Pramana》1999,53(6):921-931
There is some consensus emerging on the values of the basic parameters of classical cosmology. The baryon number density estimated
from the light element abundance or X-ray gas in galaxy clusters tends towards 5% of closure density; the dark matter content
based on a number of independent methods appears to be somewhat less than half the closure density; Hubble constant obtained
from local measurements, gravitational lens or Sunyaev Zeldovich method are all probably centred around 60 km/sec/Mpc and
the age of the Universe is generally agree to be around 14 Gyr — all specified with bearable error bars. The supernova projects
and CMBR anisotropy together favour a finite cosmological constant, and gravitational lens statistics support the same conclusion. 相似文献
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Constants of Motion for Several One-Dimensional Systems and Problems Associated with Getting Their Hamiltonians 总被引:1,自引:1,他引:0
G. López L. A. Barrera Y. Garibo H. Hernández J. C. Salazar C. A. Vargas 《International Journal of Theoretical Physics》2004,43(10):2009-2021
The constants of motion of the following systems are deduced: a relativistic particle with linear dissipation; a no-relativistic particle with a time explicitly depending force; a no-relativistic particle with a constant force and time depending mass; and a relativistic particle under a conservative force with position depending mass. The Hamiltonian for these systems, which is determined by getting the velocity as a function of position and generalized linear momentum, can be found explicitly at first approximation for the first system. The Hamiltonians for the other systems are kept implicitly in their expressions for their constants of motion. 相似文献
10.
The Planck constant h is one of the most significant constants in quantum physics.Recently,the precision measurement of the value of h has been a hot issue due to its important role for the establishment of both a new SI and a revised fundamental physical constant system.Up to date,two approaches,the watt balance and counting atoms,have been employed to determine the Planck constant at a level of several parts in 108.In this paper,the principle and progress on precision measurement of the Planck constant using watt balance and counting atoms at national metrology institutes are reviewed.Further improvement in determining the Planck constant and possible developments of a revised physical constant system in future are discussed. 相似文献
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采用基于第一性原理的赝势平面波方法系统地计算了LiBX2 (B= Ga, In; X= S,Se,Te) 晶体的光学性质与力学性质. 由禁带宽度推断出晶体抗激光损伤阈值的大小顺序为LiGaS2 > LiInS2 > LiGaSe2 > LiInSe2 > LiGaTe2 > LiInTe2. 六种晶体在常压下均满足机械力学稳定性要求, 且铟化合物可塑性及延展性强于镓化合物. 这些晶体的静态电介电常数 ε1(0)、静态折射率n(0)和双折射率Δn 理论计算值与实验值相符. LiGaS2, LiInS2, LiGaSe2, LiInSe2和LiGaTe2五种化合物双折射率较高, 并且它们的吸收谱与反射谱在中远红外区是透过的, 因此可推断出这五种化合物可以成为优异的中远红外非线性光学材料. 相似文献
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对O原子以aug-cc-pvTZ为基组,Sn原子以aug-cc-pvTZ-PP为基组,分别采用多参考组态相互作用方法(MRCI)及运用Davidson修正的多参考组态相互作用方法对SnO分子基态X~1Σ~+及两个激发态a~3Π和A~1Π态的势能曲线进行计算,进而得到了各态的平衡键长R_e,谐振频率w_2,非谐振常数ω_ex_e,转动常数B_r,垂直跃迁能T_e以及离解能D_e,通过群论原理确定了各电子状态和离解通道,计算结果表明:3个电子态有共同的离解通道,即Sn(~3p)+O(~3p);利用Level程序对势能曲线进行拟合得到的光谱数据表明,MRCI方法的计算结果与实验值符合更好;通过求解核运动的Schrodinger方程得到了J=0时这三个电子态的前30个振动态的B_v和D_v等分子常数和振动能级E。 相似文献
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研究了各种表面活性剂存在下,8-羟基-1,3,6-三磺酸芘钠盐(HPTS)的荧光光谱,结果表明、表面活性剂对其荧光特性的影响可分为两种类型:单分子猝灭(CMC以下)和胶束作用(CMC以上)。它们分别服从相应的Stern-Volmer稳态猝灭和溶质-胶束作用线性方程。按导出方程对应作图,求得CTMAB的单分子猝灭常数K=2.4×10~5L/mol;CTMAB胶束和TX100胶束对HPTS的键合常数分别为7.4×10~5L/mol和7.0×10~3L/mol。阴离子表而活性剂十二烷基硫酸钠,由于其电性与HPTS阴离子电性的不相容性,对HPTS荧光未见明显影响。 相似文献
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采用Davidson修正的内收缩多参考组态相互作用方法及Dunning等的相关一致基aug-cc-pV6Z计算了B2分子X3∑g-和A3Πu电子态的势能曲线.利用总能量外推公式,将两个电子态的总能量分别外推至完全基组极限.对势能曲线进行核价相关修正及相对论修正计算,得到了同时考虑两种效应修正的外推势能曲线.通过同位素质量识别,得到了主要的同位素分子11B11B和10B11B的X3Σg-和A3Ⅱu电子态的光谱常数Te,Re,ωe,ωexe,ωeye,Be,βe和γe.求解双原子分子核运动的径向Schr(o|¨)dinger方程,找到了无转动的同位素分子11B2(X3Σg-,A3Πu)和10B11B(X3∑g-,A3Πu)的全部振动态.针对每一同位素分子的每一振动态,分别计算了其振动能级和惯性转动常数等分子常数,它们均与已有的实验结果较为一致.其中,10B11B(AΠu)分子的光谱常数和分子常数属首次报道. 相似文献
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利用Davidson修正的内收缩多参考组态相互作用(MRCI+Q)方法,结合相关一致全电子基aug-cc-pw CV5Z优化计算了MgH分子5个低激发电子态(5Λ–S)的势能曲线.为了得到高精确的光谱性质,计算中引入核价电子相关和相对论效应修正.利用LEVEL8.0程序拟合修正的Λ-S束缚态的势能曲线,得到了相应的光谱常数、振动能级和分子常数,结果与近来的理论计算相比,本文的数值更接近实验值.这些结果说明高精度的计算方法和引入相关修正对分析光谱性质是非常必要的,为进一步研究MgH分子高激发态的光谱和跃迁特性提供可靠的实验和理论参考. 相似文献
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基于电磁模式的色散方程,研究了有损金属圆波导中电磁模式的传输问题.在考虑了损耗层厚度影响的情况下,得到了各模式传输常数的近似解析表达式,此式适用于截止频率附近.通过解析表达式和波导模式色散方程,对衰减常数和相位常数进行了大量数值计算,得到了它们随损耗层厚度、频率以及损耗层电导率的变化规律,两种方法所获得的结果有较好的一致性.研究表明,损耗强度和损耗层厚度的变化会改变波导中电磁模式的色散和简并特性,对于改善高功率回旋行波放大器中注波互作用带宽和模式竞争非常有益.
关键词:
有损圆波导
相位常数
衰减常数
色散方程 相似文献
18.
利用Davidson修正的内收缩多参考组态相互作用(MRCI+Q)方法,结合相关一致全电子基aug-cc-pwCV5Z优化计算了MgH分子5个低激发电子态(5Λ–S)的势能曲线. 为了得到高精确的光谱性质,计算中引入核价电子相关和相对论效应修正. 利用LEVEL8.0程序拟合修正的Λ-S束缚态的势能曲线,得到了相应的光谱常数、振动能级和分子常数,结果与近来的理论计算相比,本文的数值更接近实验值. 这些结果说明高精度的计算方法和引入相关修正对分析光谱性质是非常必要的,为进一步研究MgH分子高激发态的光谱和跃迁特性提供可靠的实验和理论参考. 相似文献
19.
测量了10种典型溶剂中β胡萝卜素分子的紫外-可见吸收谱和共振拉曼光谱.结果表明:溶剂的极化率、介电常数都对β胡萝卜素分子的电子-振动耦合有影响;随着极化率的增大,β胡萝卜素分子的黄昆因子、电子-振动耦合常数减小,拉曼截面增加,且这些影响与溶剂极性无关;随着溶剂介电常数的增加,对于非极性溶剂,β胡萝卜素分子的黄昆因子、电子-振动耦合常数减小,拉曼截面增加,对于极性溶剂,没有获得比较好的规律.给出了溶剂性质对电子-振动耦合的影响规律,为分子的电子-振动耦合研究中溶剂的选择提供了参考. 相似文献
20.
Yousef Bisabr 《International Journal of Theoretical Physics》2004,43(10):2137-2148
We investigate a conformal invariant gravitational model which is taken to hold at early universe. The conformal invariance allows us to make a dynamical distinction between the two unit systems (or conformal frames) usually used in cosmology and elementary particle physics. In this model we argue that when the universe suffers phase transition, the resulting mass scale introduced by particle physics should have a variable contribution to vacuum energy density. This variation is controlled by the conformal factor which is taken as a dynamical field. We then deal with the cosmological consequences of this model. In particular, we shall show that there is an inationary phase at early times. At late times, on the other hand, it provides a mechanism which makes a large effective cosmological constant relax to a sufficiently small value. Moreover, we shall show that the conformal factor acts as a quintessence field that leads the universe to accelerate at late times. 相似文献