Null test for cosmic curvature using Gaussian process

The cosmic curvature \begin{document}$ \Omega_{K,0} $\end{document}, which determines the spatial geometry of the universe, is an important parameter in modern cosmology. Any deviation from \begin{document}$ \Omega_{K,0}=0 $\end{document} would have a profound impact on the primordial inflation paradigm and fundamental physics. In this work, we adopt a cosmological model-independent method to test whether \begin{document}$ \Omega_{K,0} $\end{document} deviates from zero. We use the Gaussian process to reconstruct the reduced Hubble parameter \begin{document}$ E(z) $\end{document} and the derivative of the distance \begin{document}$ D'(z) $\end{document} from observational data and then determine \begin{document}$ \Omega_{K,0} $\end{document} with a null test relation. The cosmic chronometer (CC) Hubble data, baryon acoustic oscillation (BAO) Hubble data, and supernovae Pantheon sample are considered. Our result is consistent with a spatially flat universe within the domain of reconstruction \begin{document}$ 0<z<2.3 $\end{document}, at the \begin{document}$ 1\sigma $\end{document} confidence level. In the redshift interval \begin{document}$ 0<z<1 $\end{document}, the result favors a flat universe, while at \begin{document}$ z>1 $\end{document}, it tends to favor a closed universe. In this sense, there is still a possibility for a closed universe. We also carry out the null test of the cosmic curvature at \begin{document}$ 0<z<4.5 $\end{document} using the simulated gravitational wave standard sirens, CC+BAO, and redshift drift Hubble data. The result indicates that in the future, with the synergy of multiple high-quality observations, we can tightly constrain the spatial geometry or exclude the flat universe.     

附加运动约束提高GPS/INS导航参数估计精度

针对GPS/INS组合数据融合处理中存在的仅利用GPS观测信息不能准确估计全部状态参数的问题,提出了将不同运动环境或运动条件下部分参数满足一些特定的条件作为虚拟观测输入滤波器,形成附加运动约束的GPS/INS组合模式的新思路,其关键是如何对附加的运动信息建立准确的函数模型和合理定权。以倍受人们关注的GPS卫星不足4颗时,附加速度高程约束的GPS/INS紧组合模式为例,详细介绍新算法的实施过程。结果表明,新算法能有效提高GPS部分中断情况下的组合系统的导航精度。     

Testing the interaction model with cosmological data and gamma-ray bursts

We use the new gamma-ray bursts (GRBs) data, combined with the baryon acoustic oscillation (BAO) observation from the spectroscopic Sloan digital sky survey (SDSS) data release, the newly obtained A   parameter at z=0.6$z=0.6$ from the WiggleZ dark energy survey, the cosmic microwave background (CMB) observations from the 7-year Wilkinson microwave anisotropy probe (WMAP7) results, and the type Ia supernovae (SNeIa) from Union2 set, to constrain a phenomenological model describing possible interactions between dark energy and dark matter, which was proposed to alleviate the coincidence problem of the standard ΛCDM model. By using the Markov chain Monte Carlo (MCMC) method, we obtain the marginalized 1σ   constraints _Ωm=0.2886±0.0135${\Omega }_m=0.2886\pm 0.0135$, _rm=−0.0047±0.0046$r_m=-0.0047\pm 0.0046$, and _wX=−1.0658±0.0564$w_X=-1.0658\pm 0.0564$. We also consider other combinations of these data for comparison. These results show that: (1) the energy of dark matter is slightly transferring to that of dark energy; (2) even though the GRBs + BAO + CMB data present less stringent constraints than SNe + BAO + CMB data do, the GRBs can help eliminate the degeneracies among parameters.     

Mysteries of R^ik=0： A novel paradigm in Einstein＇s theory of gravitation

Despite a century-long effort, a proper energy-stress tensor of the gravitational field, could not have been discovered. Furthermore, it has been discovered recently that the standard formulation of the energy-stress tensor of matter, suffers from various inconsistencies and paradoxes, concluding that the tensor is not consistent with the geometric formulation of gravitation [Astrophys. Space Sci., 2009, 321： 151; Astrophys. Space Sei., 2012, 340： 373]. This perhaps hints that a consistent theory of gravitation should not have any bearing on the energy-stress tensor. It is shown here that the so-called ＂vacuum＂ field equations Rik = 0 do not represent an empty spacetime, and the energy, momenta and angular momenta of the gravitational and the matter fields are revealed through the geometry, without including any formulation thereof in the field equations. Though, this novel discovery appears baffling and orthogonal to the usual understanding, is consistent with the observations at all scales, without requiring the Moreover, the resulting theory circumvents the besides explaining some unexplained puzzles. hypothetical dark matter, dark energy or inflation long-standing problems of the standard cosmology     

Exploring neutrino mass and mass hierarchy in the scenario of vacuum energy interacting with cold dark matter

We investigate the constraints on total neutrino mass in the scenario of vacuum energy interacting with cold dark matter. We focus on two typical interaction forms, i.e., Q=βHρ_c and Q=βHρ_∧. To avoid the occurrence of large-scale instability in interacting dark energy cosmology, we adopt the parameterized post-Friedmann approach to calculate the perturbation evolution of dark energy. We employ observational data, including the Planck cosmic microwave background temperature and polarization data, baryon acoustic oscillation data, a JLA sample of type Ia supernovae observation, direct measurement of the Hubble constant, and redshift space distortion data. We find that, compared with those in the ∧CDM model, much looser constraints on ∑m_ν are obtained in the Q=βHρ_c model, whereas slightly tighter constraints are obtained in the Q=βHρ_∧ model. Consideration of the possible mass hierarchies of neutrinos reveals that the smallest upper limit of ∑m_ν appears in the degenerate hierarchy case. By comparing the values of χ_min², we find that the normal hierarchy case is favored over the inverted one. In particular, we find that the difference △χ_min² ≡ χ_{IH; min}²-χ_{NH; min}² > 2 in the Q=βHρ_c model. In addition, we find that β=0 is consistent with the current observations in the Q=βHρ_c model, and β < 0 is favored at more than the 1σ level in the Q=βHρ_∧ model.     

基于前向散射核函数拟合冰雪反射光谱各向异性

对地表反射光谱的各向异性进行建模和拟合,是遥感对地观测的重要研究内容。传统的线性核驱动模型拟合方法使用的核函数是基于植被覆盖地表辐射传输模型导出的,因此难以准确地描述冰雪覆盖地表前向散射强的特征。提出一种在线性核驱动模型中增加前向散射核函数的拟合方法,并采用地面多角度观测架测量的冰雪反射光谱对该方法的有效性进行了验证。验证结果表明该方法能够较好地拟合冰雪反射光谱的各向异性(R2=0.997 5, RMSE=0.022 6),准确地反映冰雪前向散射较强的特征。通过对提出的方法与经验函数法、传统线性核驱动模型拟合方进行比较,可以发现线性核驱动模型方法明显优于经验函数拟合法,其中增加前向散射核函数能够显著提高对冰雪覆盖地表二向反射因子的拟合精度,并在各波段都有稳定的拟合效果。     

Constraining cosmological parameters through Sunyaev-Zel’dovich surveys

For cold dark matter models, images of temperature fluctuations in the cosmic microwave background (CMB), due to Sunyaev Zel’dovich (SZ) effect have been been simulated taking a cosmolgical distribution of clusters into account. All the models are normalised to the 4-year COBE data. The image statistics are compared with the ATCA limits on arcmin scale anisotropy. The comparison appears to favour low-Ω₀ open universe models.     

On inconsistency of the common rate difference estimators from sparse follow-up data

It has been shown that the unconditional maximum likelihood estimator of the common odds ratio, risk ratio and risk difference parameters are inconsistent in sparse statification. Under a Poisson sparse-data model, the maximum likelihood estimator for the rate difference, which is the difference of the disease incidence rates among the exposed and the unexposed, is also shown to be biased. The sparse-data asymptotic bias of the maximum likelihood estimator is evaluated numerically and compared with that of the weighted least squares estimators.     

The ALTAIR cryogenic gravitational-wave experiment

Summary We report on the experimental results obtained with the cryogenic Gravitational-Wave resonant detector ALTAIR located in Frascati (Italy) at the Istituto di Fisica dello Spazio Interplanetario of Consiglio Nazionale delle Ricerche. The peculiarity of this experiment is its working frequency. The first longitudinal mode of resonance of the antenna is at 1.8 kHz. The antenna, now equipped with a resonant capacitive transducer and a d.c. SQUID preamplifier, after a first test in November 1989, has operated almost continuously from May 1990. The best sensitivity, recently reached, expressed in terms of the effective noise temperatureT _eff, is 20 mK, corresponding, for a short pulse of gravitational wave, to a metric perturbationh of 3×10⁻¹⁸. In the last period of measurements (from April 1991 to March 1992) two other antennas were operating: the Explorer antenna (2300 kg,T=2.0 K) at CERN in Geneva and the LSU antenna (2500 kg,T=4.2 K) at Louisiana State University in USA, both having a resonant frequency below 1 kHz. The data of these three detectors can be remote observed, in real time, by the international computer network. Coincidence analysis between the data of these three detectors is in progress. Paper presented at the V Cosmic Physics National Conference, S. Miniato, November 27–30, 1990 (updated version).     

Real time observation of oxygen chemisorption states on Si(0 0 1)-2×1 during supersonic oxygen molecular beam irradiation

Employing Si 2p and O 1s photoemission spectroscopy using monochromated synchrotron radiation and the supersonic molecular beam technique, we have performed real time in situ observations of oxidation states on Si(0 0 1)-2×1 at room temperature. High-resolution Si 2p photoemission spectra, which unambiguously resolve oxide components [Si¹⁺, Si²⁺, Si³⁺ and Si⁴⁺], were successfully measured requiring only 43 s per spectrum. We found that the Si⁴⁺ species gradually increases to reach the oxide thickness of 0.57 nm just after the saturation of Si¹⁺, Si²⁺ and Si³⁺ species with a translational energy of 2.9 eV.