New classes of test polynomials of polynomial algebras

A polynomialp in a polynomial algebra over a field is called a test polynomial if any endomorphism of the polynomial algebra that fixesp is an automorphism. some classes of new test polynomials recognizing nonlinear automorphisms of polynomial algebras are given. In the odd prime characteristic case, test polynomials recognizing non-semisimple automorphisms are also constructed. Project supported by the National Natural Science Foundation of China (Grant No. 19631100) and University of Hong Kong RGC Fundable Grant 344/024/0004.     

Localized 3D-structural features of dynamic-chemical processes of urban air pollution in Beijing winter

The Beijing City Air Pollution Observation Field Experiment (BECAPEX) is described with emphases on the “point-surface” research approach and composite analysis. The analysis results of measurements from four observation sites across the Beijing urban area from January to March indicate that the overall impact of urban emission sources in the heating season is significant, and the staggered impact of urban emission sources has different features at observation sites over different parts of Beijing in both heating and non-heating seasons. The pollutants NOx, SO2 and CO in the urban boundary layer have the in-phase variation features over a large area. 03 concentrations at different sites have the same variation trend but its change is reversed phases with above pollutants. The pollutants over the urban area in heating and non-heating seasons also have the synchronous variation trend. The comprehensive sounding of BECAPEX indicates that pollutants and aerosol verticalprofiles are closely correlated to the vertical structure of the large-scale inversion layer in the urban boundary layer over the urban area. The localized 3D-structural features of local urban polluting processes associated with the peripheral areas are discussed with a “point-surface” comprehensive sounding technique.     

适于反演陆面大气气溶胶光学厚度的物理量

针对水平均一的晴天大气、朗伯下垫面的特殊条件,在一定理论分析的基础上,利用具有“频率相近、但气体吸收系数相差很大”特征的一对观测频率,构造了一个对地面反照率不敏感,但对气溶胶光学厚度敏感的无量纲物理量．进而借助ＬｏｗｔｒａｎＤｉｓｏｒｔ 耦合模式的数值实验,确定了观测的最佳方位,并比较了最佳观测方位下对地面反照率和气溶胶光学厚度的不同敏感性．     

GPS蒙特卡罗三维水汽层析算法敏感性试验和研究

以布设在天津的由13部地基GPS组成的高密度小尺度探测网为基础, 对蒙特卡罗层析算法中GPS平均站距、层析时间间隔以及蒙特卡罗随机次数3个影响层析算法的关键参数进行敏感性实验和分析。实验表明, 层析解算精度随着平均站距的降低和蒙特卡罗次数的增加而提高, 增加层析时间间隔对提高层析算法结果的精度作用不明显。同时提出采用“最优+次优”的两组残差最小水汽场的平均作为最终层析场的方法, 使得水汽场绝对偏差较前人所采用的只取残差最小水汽场的方法减少约30%。     

Characteristics of distribution and seasonal variation of aerosol optical depth in eastern China with MODIS products

The accuracy of MODIS aerosol products from the NASA Terra Satellite is validated in comparison with the results of sun-photometer observations in Beijing and Hong Kong. By analyzing the MODIS aerosol products within the period of August 2000 to April 2003, it is believed that human activities are the main source of aerosols in the eastern part of China. This is based on the facts that all areas with relatively high values are consistent with regions of dense population and fast economic development, such as the North China Plain, the Sichuan Basin and the Pearl River Delta. It is also supported by the distribution of 舗gstr鰉 exponents showing that most aerosols in the eastern part of China are closely related to human activities, excepting the strong sandstorm episodes occurring in spring, fall and winter. In contrast to developed countries, the 舗gstr鰉 exponent of urban area in China is lower than its surroundings, indicating that the contribution of local floating dust and soot attributed to human activities is significant. Results presented in this paper provide important data for further research on climatic change and environmental study.     

MODIS气溶胶光学厚度产品在地面PM_(10)监测方面的应用研究

利用MODIS(中分辨率成像光谱仪)两年的气溶胶光学厚度(AOD)产品与北京地区API转化得到的PM10质量浓度、北京大学站点直接监测的PM10质量浓度以及香港元朗站点监测的PM10质量浓度做相关性分析,发现二者的直接相关程度较低。将AOD除以气溶胶季节标高,得到地面消光系数,与地面PM10质量浓度相关性提高。对地面消光系数进行相对湿度订正,得到计算的质量浓度,与地面实际观测的PM10质量浓度相关性进一步提高。经过两年时间资料的对比分析,证实气溶胶遥感光学厚度经过垂直和湿度影响订正后,可以应用于地面PM10监测。     

Low-Noise Intensity Amplification of a Bright Entangled Beam

We experimentally demonstrate a low-noise phase-sensitive amplifier(PSA) scheme that is able to amplify bright entangled beams at a high level intensity gain of up to 4.4.Moreover,we demonstrate that the PSA scheme introduces much less uncorrelated extra noise to the entangled state than the phase-insensitive amplifier scheme with the same intensity gain.This PSA scheme has potential applications for quantum communication in continuous variable regimes.     

Remote sensing precipitable water with GPS

The principle and method of remote sensing precipitable water (PW) by the Global Positioning System (GPS) are introduced. A series of tropospheric delay have been obtained from the dual frequency receiver’s data of global tracking stations in East Asia and precise satelllte ephemeris of IGS from July 31 to August 20, 1997. The continuous PW at the interval of 30 min have been estimated at Shanghai and Wuhan GPS sites. The results are compared with PW from conventional radiosonde during the same period, and the RMS is about 0.50 cm.     

Optimization of Quantum Correlation in Cascaded Four-Wave Mixing

We propose a measurement strategy that can be used to optimize quantum correlation for a cascaded four-wave mixing (FWM) structure. By calculating the covariance matrix of a cascaded FWM structure, we can get all the correlations between any two parties in the outputs. We then calculate the eigenvalues and corresponding eigenmodes of the covariance matrix to find the squeezing degrees of the squeezed modes. Our theoretical model can explain our previous experimental results very well and is useful to optimize the squeezing degree in the cascaded FWM structure.     

MODIS卫星监测中国东部地区地面颗粒物的样本时间代表性分析

选取2011年中国东部地区428个测站的PM10质量浓度资料,用Terra和Aqua MODIS AOD产品的时间分布作为指示数据,检验日、月、季、年时间尺度下,卫星过境时刻地面PM数据(SATPM)对地面所有时刻数据平均值(ALLPM)的代表性。结果发现,在东部大部分地区,SATPM与ALLPM的相对误差在±20%以内,且Aqua-MODIS代表性更好。此外,结合两颗卫星的数据,经拟合订正获得了新的日、年时间尺度上PM10质量浓度数据,将其与ALLPM的相关系数从0.87和0.83提高到0.90。此检验结果对于检验卫星数据反演的PM2.5的代表性也有一定指导意义。