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561.
Eckehard W. Mielke 《General Relativity and Gravitation》2008,40(6):1311-1325
The curvature-squared model of gravity, in the affine form proposed by Weyl and Yang, is deduced from a topological action
in 4D. More specifically, we start from the Pontrjagin (or Euler) invariant. Using the BRST antifield formalism with a double
duality gauge fixing, we obtain a consistent quantization in spaces of double dual curvature as classical instanton type background. However,
exact vacuum solutions with double duality properties exhibit a ‘vacuum degeneracy’. By modifying the duality via a scale breaking term, we demonstrate that only Einstein’s equations with an induced cosmological constant emerge for the topology of the macroscopic background. This may have repercussions on the problem of ‘dark energy’ as well as ‘dark matter’ modeled
by a torsion induced quintaxion. 相似文献
562.
Subir Sarkar 《General Relativity and Gravitation》2008,40(2-3):269-284
Several kinds of astronomical observations, interpreted in the framework of the standard Friedmann–Robertson–Walker cosmology,
have indicated that our universe is dominated by a Cosmological Constant. The dimming of distant Type Ia supernovae suggests
that the expansion rate is accelerating, as if driven by vacuum energy, and this has been indirectly substantiated through
studies of angular anisotropies in the cosmic microwave background (CMB) and of spatial correlations in the large-scale structure
(LSS) of galaxies. However there is no compelling direct evidence yet for (the dynamical effects of) dark energy. The precision CMB data can be equally well fitted without dark energy
if the spectrum of primordial density fluctuations is not quite scale-free and if the Hubble constant is lower globally than
its locally measured value. The LSS data can also be satisfactorily fitted if there is a small component of hot dark matter,
as would be provided by neutrinos of mass ∼0.5 eV. Although such an Einstein–de Sitter model cannot explain the SNe Ia Hubble
diagram or the position of the “baryon acoustic oscillation” peak in the autocorrelation function of galaxies, it may be possible
to do so, e.g. in an inhomogeneous Lemaitre–Tolman–Bondi cosmology where we are located in a void which is expanding faster
than the average. Such alternatives may seem contrived but this must be weighed against our lack of any fundamental understanding
of the inferred tiny energy scale of the dark energy. It may well be an artifact of an oversimplified cosmological model,
rather than having physical reality. 相似文献
563.
开路光伏空间孤子的动态行为 总被引:1,自引:1,他引:0
从理论上研究了开路情况下一维光伏空间孤子的时间演化过程.采用数值方法,通过研究有无背景光辐照下光伏空间亮(暗)孤子的含时空间电荷场,分别得到了光伏空间亮(暗)孤子的孤子波形强度微分方程.在此基础上研究了开路情况下通过增加均匀背景光辐照强度对光伏空间孤子及其半峰全宽的影响.结果显示,通过增加均匀背景光辐照强度,光伏空间孤子随时间的演化过程比没有均匀背景光时加快的倍数为均匀背景光强与暗辐照光强之比.光伏空间孤子的半峰全宽达到稳态所需的时间随孤子峰值强度和暗辐照与均匀背景光强度之和的比值的增大而变短. 相似文献
564.
研究了不同响应波长的HgCdTe器件在不同背景辐射条件下的噪声变化.随着背景辐射的增加,甚长波器件的噪声减小,而中波器件相反.噪声频谱测量表明,产生-复合噪声分量和1/f噪声分量是器件的主要噪声来源,并且这两个分量随背景的变化趋势相同.非平衡载流子和器件有效寿命的理论分析,表明器件噪声随背景辐射的变化存在一个极大值,而中波和甚长波器件处在不同的作用区域内,接受到的背景辐射对载流子浓度和器件有效寿命的影响不同,从而噪声变化表现不同.在此基础上,提出了"临界背景通量密度"的概念. 相似文献
565.
566.
XUE Zhen SHAN Qing XU Zi-Zong WANG Xiao-Lian WU Jian WANG Yong-Gang ZHANG Tao HU Tao CAI Xiao WANG Yi-Fang 《中国物理C(英文版)》2010,34(4):487-491
The fast luminosity monitor counting the γ photons above a given energy threshold emitted from radiative Bhabha scattering has been operated in the BEPCⅡ to measure the relative luminosity bunch by bunch for the first time and used successfully in beam tuning of BEPCⅡ.In the relative mode the monitor is able to deliver the relative luminosities with an accuracy of 0.8 %.By steering the electron beam while observing the counting rate changes of the monitor the horizontal and vertical sizes of the bunch spots can be estimated as:sxe+ =sxe-=0.356 mm,sye+ =sye-=0.011 mm. 相似文献
567.
568.
569.
本文介绍了应用ICP-动态背景校正法测定催化剂中钯和铂的方法。并分析了几个主要元素的光谱干扰情况。 相似文献
570.
Summary We discuss a SN model with s-matter in the core, compatible with the set of experimental results obtained on SN 1987A by ν-detectors
and gravitational antennas. 相似文献