Measurement of polarization with the Degree Angular Scale Interferometer

Measurements of the cosmic microwave background (CMB) radiation can reveal with remarkable precision the conditions of the Universe when it was approximately 400,000 years old. The three most fundamental properties of the CMB are its frequency spectrum (which determines the temperature), and the fluctuations in both the temperature and polarization across a range of angular scales. The frequency spectrum has been well determined, and considerable progress has been made in measuring the power spectrum of the temperature fluctuations. But despite many efforts to measure the polarization, detection of this property of the CMB has hitherto been beyond the reach of even the most sensitive observations. Here we describe the Degree Angular Scale Interferometer (DASI), an array of radio telescopes, which for the past two years has conducted polarization-sensitive observations of the CMB from the Amundsen-Scott South Pole research station.     

宇宙微波背景辐射检验CPT对称性

电荷共轭-宇称-时间反演（CPT）联合对称性是粒子物理中的一种基本对称性.检验CPT对称性是检验标准模型及发现新物理等基础科学研究的重要途径.本文将介绍利用高精度的宇宙微波背景辐射（CMB）的观测和实验检验CPT对称性的方法,以及最新进展.通过与其他实验的比较我们发现CMB对CPT对称性的检验精度更高.     

A correlation between the cosmic microwave background and large-scale structure in the Universe

Observations of distant supernovae and the fluctuations in the cosmic microwave background (CMB) indicate that the expansion of the Universe may be accelerating under the action of a 'cosmological constant' or some other form of 'dark energy'. This dark energy now appears to dominate the Universe and not only alters its expansion rate, but also affects the evolution of fluctuations in the density of matter, slowing down the gravitational collapse of material (into, for example, clusters of galaxies) in recent times. Additional fluctuations in the temperature of CMB photons are induced as they pass through large-scale structures and these fluctuations are necessarily correlated with the distribution of relatively nearby matter. Here we report the detection of correlations between recent CMB data and two probes of large-scale structure: the X-ray background and the distribution of radio galaxies. These correlations are consistent with those predicted by dark energy, indicating that we are seeing the imprint of dark energy on the growth of structure in the Universe.     

A flat Universe from high-resolution maps of the cosmic microwave background radiation

The blackbody radiation left over from the Big Bang has been transformed by the expansion of the Universe into the nearly isotropic 2.73 K cosmic microwave background. Tiny inhomogeneities in the early Universe left their imprint on the microwave background in the form of small anisotropies in its temperature. These anisotropies contain information about basic cosmological parameters, particularly the total energy density and curvature of the Universe. Here we report the first images of resolved structure in the microwave background anisotropies over a significant part of the sky. Maps at four frequencies clearly distinguish the microwave background from foreground emission. We compute the angular power spectrum of the microwave background, and find a peak at Legendre multipole Ipeak = (197 +/- 6), with an amplitude delta T200 = (69 +/- 8) microK. This is consistent with that expected for cold dark matter models in a flat (euclidean) Universe, as favoured by standard inflationary models.     

The cosmic microwave background radiation temperature at a redshift of 2.34

The existence of the cosmic microwave background radiation is a fundamental prediction of hot Big Bang cosmology, and its temperature should increase with increasing redshift. At the present time (redshift z = 0), the temperature has been determined with high precision to be T(CMBR)(0) = 2.726 +/- 0.010 K. In principle, the background temperature can be determined using measurements of the relative populations of atomic fine-structure levels, which are excited by the background radiation. But all previous measurements have achieved only upper limits, thus still formally permitting the radiation temperature to be constant with increasing redshift. Here we report the detection of absorption lines from the first and second fine-structure levels of neutral carbon atoms in an isolated cloud of gas at z = 2.3371. We also detected absorption due to several rotational transitions of molecular hydrogen, and fine-structure lines of singly ionized carbon. These constraints enable us to determine that the background radiation was indeed warmer in the past: we find that T(CMBR)(z = 2.3371) is between 6.0 and 14 K. This is in accord with the temperature of 9.1 K predicted by hot Big Bang cosmology.     

宇宙微波背景辐射对超高能宇宙线流强的影响

文章指出：（１）在Ｅ＝５＊１０＾１９ｅＶ附近，对所有ｘ（ｘ是宇宙线飞行的距离），超高能宇宙线流强略有增强；（２）在１．０＊１０＾２０ｅＶ≤Ｅ≤５．０＊１０＾２４ｅＶ能区内，宇宙微波背景辐射的作用仅使超高能宇宙线流强有所减弱，在ｘ≤２０００Ｍｐｃ区域内，减弱系数Ｆ（Ｘ，Ｅ）＝ｊ（ｘ，Ｅ）／ｊ（０，Ｅ）≥０．３４。     

Dodecahedral space topology as an explanation for weak wide-angle temperature correlations in the cosmic microwave background

The current 'standard model' of cosmology posits an infinite flat universe forever expanding under the pressure of dark energy. First-year data from the Wilkinson Microwave Anisotropy Probe (WMAP) confirm this model to spectacular precision on all but the largest scales. Temperature correlations across the microwave sky match expectations on angular scales narrower than 60 degrees but, contrary to predictions, vanish on scales wider than 60 degrees. Several explanations have been proposed. One natural approach questions the underlying geometry of space--namely, its curvature and topology. In an infinite flat space, waves from the Big Bang would fill the universe on all length scales. The observed lack of temperature correlations on scales beyond 60 degrees means that the broadest waves are missing, perhaps because space itself is not big enough to support them. Here we present a simple geometrical model of a finite space--the Poincaré dodecahedral space--which accounts for WMAP's observations with no fine-tuning required. The predicted density is Omega(0) approximately 1.013 > 1, and the model also predicts temperature correlations in matching circles on the sky.     

用横向剪切干涉仪测量部分相干度

本文提出了用横向剪切干涉仪测量光的部分相干度的方法;用非相干光照明的圆孔作为实际光源,测量了不同剪切量的部分相干度,所得实验结果与理论计算一致。     

带转角自由度平面单元的不完备性

讨论了有限元法中带转角自由度的平面单元的收敛性。证明了其位移模式不同满足收敛条件,是不完备的。     

Tracing the first stars with fluctuations of the cosmic infrared background

The deepest space- and ground-based observations find metal-enriched galaxies at cosmic times when the Universe was less than 1 Gyr old. These stellar populations had to be preceded by the metal-free first stars, known as 'population III'. Recent cosmic microwave background polarization measurements indicate that stars started forming early--when the Universe was < or =200 Myr old. It is now thought that population III stars were significantly more massive than the present metal-rich stellar populations. Although such sources will not be individually detectable by existing or planned telescopes, they would have produced significant cosmic infrared background radiation in the near-infrared, whose fluctuations reflect the conditions in the primordial density field. Here we report a measurement of diffuse flux fluctuations after removing foreground stars and galaxies. The anisotropies exceed the instrument noise and the more local foregrounds; they can be attributed to emission from population III stars, at an era dominated by these objects.     

偏振失配对非线性光纤环镜微波光子开关的影响

基于考虑偏振态的耦合非线性薛定谔方程,采用分步傅立叶法分析了控制光与信号光偏振失配对双耦合器非线性光纤环境(NOLM)微波光子开关性能的影响.研究表明,偏振失配造成NOLM输出信号强度波动,严重影响NOLM性能,尤其是在大调制带宽时NOLM对偏振失配极为敏感.偏振失配造成NOLM输出眼图和信噪比急剧恶化并导致较大的强度波动.     

涡旋光束的轨道角动量的测量

理论分析拓扑电荷数大小相等、符号相反的两束拉盖尔高斯型涡旋光束的干涉,并从实验上研究拉盖尔高斯型涡旋光束的拓扑电荷数的改变及干涉特性.结果表明,采用加道威棱镜的马赫曾德尔干涉方法,可以容易地分辨涡旋光束的拓扑电荷数,并降低检测的误差.研究还发现,干涉后的光斑图样有缓慢的旋转现象.     

真空开关管内真空度检测的研究

真空灭弧室内真空度将直接影响真空开关的性能。利用自行设计建立的真空实验测试系统研究了灭弧室内真空度与放电电流,两极电压,触头开距之间的关系。尤其是在灭弧室两侧加一横向磁场情况下,它对真空灭弧室内真空度测量的作用,得到了一些有益的结论,为真空灭弧室内真空度的检测提供了有效的途径。     

聊城市土地利用程度的县乡尺度区域差异分析

土地利用程度是反映区域人类活动对土地自然状态改变的综合指标,文章基于全国第二次土地调查聊城市2010年变更数据,对其土地利用程度及县乡尺度区域差异进行研究.结果表明:聊城市土地利用程度指数为305.70.各县市区土地利用程度介于296.97-311.57之间,县级土地利用程度与农村居民点用地、水工用地和农村人口的相关性显著;乡镇级土地利用程度变化于280.20-358.58之间,与城镇用地、林地、耕地、水工用地、水域、农村居民点用地、其他土地、交通运输用地相关性显著.县乡尺度土地利用程度的联系表现为土地利用程度高的乡镇分布于县城、重点(中心)镇、交通干线沿线.     

激光激发干涉仪检测涂层/基底的黏结特性

将脉冲激光器产生的激光直接照射到环氧涂层/铝基底的界面激发声波,并在铝基底的后表面上利用光学干涉仪对位移进行检测.实验结果表明,直达波和反射波的幅度比值与界面黏结质量相关,利用该方法可对类似结构的黏结质量进行评价分析.     

A test of the nature of cosmic acceleration using galaxy redshift distortions

Observations of distant supernovae indicate that the Universe is now in a phase of accelerated expansion the physical cause of which is a mystery. Formally, this requires the inclusion of a term acting as a negative pressure in the equations of cosmic expansion, accounting for about 75 per cent of the total energy density in the Universe. The simplest option for this 'dark energy' corresponds to a 'cosmological constant', perhaps related to the quantum vacuum energy. Physically viable alternatives invoke either the presence of a scalar field with an evolving equation of state, or extensions of general relativity involving higher-order curvature terms or extra dimensions. Although they produce similar expansion rates, different models predict measurable differences in the growth rate of large-scale structure with cosmic time. A fingerprint of this growth is provided by coherent galaxy motions, which introduce a radial anisotropy in the clustering pattern reconstructed by galaxy redshift surveys. Here we report a measurement of this effect at a redshift of 0.8. Using a new survey of more than 10,000 faint galaxies, we measure the anisotropy parameter beta = 0.70 +/- 0.26, which corresponds to a growth rate of structure at that time of f = 0.91 +/- 0.36. This is consistent with the standard cosmological-constant model with low matter density and flat geometry, although the error bars are still too large to distinguish among alternative origins for the accelerated expansion. The correct origin could be determined with a further factor-of-ten increase in the sampled volume at similar redshift.     

Tripling the capacity of wireless communications using electromagnetic polarization

Wireless communications are a fundamental part of modern information infrastructure. But wireless bandwidth is costly, prompting a close examination of the data channels available using electromagnetic waves. Classically, radio communications have relied on one channel per frequency, although it is well understood that the two polarization states of planar waves allow two distinct information channels; techniques such as 'polarization diversity' already take advantage of this. Recent work has shown that environments with scattering, such as urban areas or indoors, also possess independent spatial channels that can be used to enhance capacity greatly. In either case, the relevant signal processing techniques come under the heading of 'multiple-input/multiple-output' communications, because multiple antennae are required to access the polarization or spatial channels. Here we show that, in a scattering environment, an extra factor of three in channel capacity can be obtained, relative to the conventional limit using dual-polarized radio signals. The extra capacity arises because there are six distinguishable electric and magnetic states of polarization at a given point, rather than two as is usually assumed.     

大米加工精度检测方法的研究进展

大米加工精度是衡量大米品质的重要指标,本文综述了大米加工精度检测方法的研究进展．     

基于灰色关联度的本地生活服务O2O市场交易规模影响因素研究

随着互联网经济的快速发展和各种交互工具的普及,基于本地生活服务的O2O行业呈现了迅猛发展的态势。在确定本地生活服务O2O市场交易规模影响因素的基础上,利用灰色关联度分析法进行计算分析,得到各个因素对本地生活服务O2O市场交易规模的影响力度,以期为政府和电商企业的科学合理决策提供参考。