Increase in tropospheric nitrogen dioxide over China observed from space

Emissions from fossil fuel combustion and biomass burning reduce local air quality and affect global tropospheric chemistry. Nitrogen oxides are emitted by all combustion processes and play a key part in the photochemically induced catalytic production of ozone, which results in summer smog and has increased levels of tropospheric ozone globally. Release of nitrogen oxide also results in nitric acid deposition, and--at least locally--increases radiative forcing effects due to the absorption of downward propagating visible light. Nitrogen oxide concentrations in many industrialized countries are expected to decrease, but rapid economic development has the potential to increase significantly the emissions of nitrogen oxides in parts of Asia. Here we present the tropospheric column amounts of nitrogen dioxide retrieved from two satellite instruments GOME and SCIAMACHY over the years 1996-2004. We find substantial reductions in nitrogen dioxide concentrations over some areas of Europe and the USA, but a highly significant increase of about 50 per cent-with an accelerating trend in annual growth rate-over the industrial areas of China, more than recent bottom-up inventories suggest.     

Internal motions of a quasiparticle governing its ultrafast nonlinear response

A charged particle modifies the structure of the surrounding medium: examples include a proton in ice, an ion in a DNA molecule, an electron at an interface, or an electron in an organic or inorganic crystal. In turn, the medium acts back on the particle. In a polar or ionic solid, a free electron distorts the crystal lattice, displacing the atoms from their equilibrium positions. The electron, when considered together with its surrounding lattice distortion, is a single quasiparticle, known as the Fr?hlich polaron. The basic properties of polarons and their drift motion in a weak electric field are well known. However, their nonlinear high-field properties--relevant for transport on nanometre length and ultrashort timescales--are not understood. Here we show that a high electric field in the terahertz range drives the polaron in a GaAs crystal into a highly nonlinear regime where, in addition to the drift motion, the electron is impulsively moved away from the centre of the surrounding lattice distortion. In this way, coherent lattice vibrations (phonons) and concomitant drift velocity oscillations are induced that persist for several hundred femtoseconds. They modulate the optical response at infrared frequencies between absorption and stimulated emission. Such quantum coherent processes directly affect high-frequency transport in nanostructures and may be exploited in novel terahertz-driven optical modulators and switches.     

一种综合时频分布在mc-PPS检测中的应用

为解决多分量多项式相位信号(mc-PPS)的检测问题,提出乘积性谱图-WVD(PSWVD)变换的多分量PPS信号检测方法.综合谱图和WVD变换的优势,在去除WVD变换交叉项的同时保持了良好的频率聚集性和优良的低信噪比性能.为抑制噪声和交叉项,设置了自适应门限,大幅减少了后续Radon变换的计算量.对三分量线性调频(LFM)、双分量非线性调频(NLFM)和强弱分量PPS信号的仿真结果表明,PSWVD算法具有优良的检测性能.     

度量空间中的拟近标准点及度量空间的非标准完备化

研究了度量空间中的拟近标准点和度量空间的非标准完备化.在K-饱和的非标准模型下.采用非标准分析方法,提出了度量空间中的拟近标准点的定义,得到了非标准度量空间中的点是拟近标准点的充要条件是它属于某一个标准点的每一个*-开球,证明了度量空间的非标准完备化恰是该空间的非标准扩张中拟近标准点集的商空间.     

一个新的函数空间的紧致性

借助于Kurzweil-Henstock积分建立了一个新的函数空间K，并证明了它的紧致性，为讨论x′=g(x,t) h(t)型方程局部动力系统问题做了基础性工作。     

The interface between silicon and a high-k oxide

The ability of the semiconductor industry to continue scaling microelectronic devices to ever smaller dimensions (a trend known as Moore's Law) is limited by quantum mechanical effects: as the thickness of conventional silicon dioxide (SiO(2)) gate insulators is reduced to just a few atomic layers, electrons can tunnel directly through the films. Continued device scaling will therefore probably require the replacement of the insulator with high-dielectric-constant (high-k) oxides, to increase its thickness, thus preventing tunnelling currents while retaining the electronic properties of an ultrathin SiO(2) film. Ultimately, such insulators will require an atomically defined interface with silicon without an interfacial SiO(2) layer for optimal performance. Following the first reports of epitaxial growth of AO and ABO(3) compounds on silicon, the formation of an atomically abrupt crystalline interface between strontium titanate and silicon was demonstrated. However, the atomic structure proposed for this interface is questionable because it requires silicon atoms that have coordinations rarely found elsewhere in nature. Here we describe first-principles calculations of the formation of the interface between silicon and strontium titanate and its atomic structure. Our study shows that atomic control of the interfacial structure by altering the chemical environment can dramatically improve the electronic properties of the interface to meet technological requirements. The interface structure and its chemistry may provide guidance for the selection process of other high-k gate oxides and for controlling their growth.     

火烧油层试验的压力时频分析

为了解决火烧油层燃烧前缘监测问题,对室内一维燃烧管试验所采集的压力数据,运用Daubechies一阶小波提取其高频分量并进行对比分析.结果表明:压力波动的小波低频分量表征了燃烧管内压力水平的整体变化,而高频分量则与流体流动和燃烧稳定性变化一致;燃烧稳定时,压力波动的小波高频分量幅值基本恒定,而燃烧不稳定时,小波高频分量幅值波动较大;利用压力信号的高频分量能够监测火烧油层燃烧的稳定性.     

Characteristics of magnetocardiography and electrocardiography in the time-frequency domain

As the carriers of electromagnetic information about the cardiac system,both magnetocardiography(MCG) and electrocardiography(ECG) are non-stationary signals(NSS).The essential and crucial features of NSS are the local time-frequency characteristics(LTFCH).Under the constraint of the uncertainty principle in the time-frequency domain(TFD),the LTFCH of those non-stationary signals can be determined by evolutionary spectrum analysis(ESA).In this paper,by analyzing the QRS complexes of both MCG and ECG data from healthy volunteers,we have derived some characteristic parameters(CHPs) in the TFD,such as the quality factor(Q) and center frequency(fz).According to the experiment results,we believe that there are threshold ranges of Q and fz values in the dynamic behavior of the cardiac system for healthy projects.If the CHPs are in the proper ranges,the cardiac system is in a normal condition and homeostasis can be self-correcting.In contrast,if the values of the CHPs are less than the proper ranges,the homeostasis of the cardiac system is lost and some cardiac diseases may result.The assumption of the threshold ranges is verified by sample data from different cardiac diseases,and the results support the assumption.The CHPs are not only a kind of new reference criterion for ECG in clinical diagnosis,but also afford a technological route for the application of MCGs in cardiology.     

三维Minkowski空间中非类光曲线的从切可展曲面的奇点分类

给出了曲线的法向距离函数概念,建立了由此函数诱导的奇点和曲线的几何不变量之间的联系,并且给出了三维Minkowski空间中非类光曲线的从切可展曲面的奇点分类.     

Banach空间上的单值延拓性质

设A为Banach空间X上的一个有界线性算子. 给出了算子A具有单值延拓性质的特征;利用算子的单值延拓性质, 研究了正则算子的摄动和线性算子的分解.     

概率空间上的盒维数

在概率空间（Ω,ξ,μ）上定义关于卢的上、下盒维数,并给出了上、下盒维数的另一等价定义,讨论了概率空间上关于产的上、下盒维数与关于μ的Hausdorff维数、预填充维数及填充维数之间的关系．     

时频分析在语言想像脑机接口中的应用

为了分析语言想像所诱导的脑电信号的时间和频率特性,利用事件相关谱扰动(ERSP)对信号进行时频分析.首先,经ERSP确定能量波动的频率范围;然后,根据该频率范围计算信号的事件相关(去)同步(ERD/ERS),并利用共空间模式和支持向量机分别对单次实验数据的特征值进行提取和分类.对8位被试的试验结果分析表明,被试间的频率范围具有显著的差异,其中4位被试的频率范围含有α波,3位被试含有α波和β波,1位被试的脑电信号在默读汉字时无明显变化.2个汉字默读时的脑电信号可产生相似的ERD/ERS.优化频率范围后针对这2个汉字的平均分类正确率分别提高了2.25%和1.39%.时频分析能更好地显示脑电信号的能量变化率,并能改善语言想像脑机接口的性能.