激光雷达监测北京城区冬季边界层气溶胶

运用一种新型边界层气溶胶监测激光雷达,在北京丰台区进行了外场实验,探讨了大气边界层内气溶胶消光系数时空分布的特点.实验结果表明:1)冬季北京城区气溶胶源多且变化快;2)北京城区气溶胶污染白天比晚上严重,中午达到顶峰;3)气象条件对气溶胶的扩散和分布影响很大.实验结论对北京城区的环境治理具有较高的参考价值.     

珠海2009年夏季激光雷达探测大气边界层高度数据处理

2009年6月20日~7月20日,中国海洋大学利用研制的可移式多普勒激光雷达系统在珠海市国家气候观象台（N22º 4’54”,E113º 12’50”）进行了为期一月的大气观测实验。报道了可移式多普勒激光雷达系统及观测实验,介绍了大气边界层高度检测原理及应用。利用一阶导数方法,对该系统实测数据进行了大气边界层高度检测和分析,讨论了有云存在时如何同时检测云高和大气边界层高度问题。实验结果表明,该区域和时间周期内的大气边界层高度范围在0.3~1.2km之间,平均高度为0.66km。     

激光雷达探测大气边界层高度分布的梯度法应用研究

为了研究合肥地区大气边界层结构变化特征,利用偏振拉曼-米散射激光雷达进行了连续探测.首先介绍利用激光雷达回波信号提取大气边界层高度的梯度法,并分析该方法的优缺点.然后对梯度法进行修正,给出具体的实例分析及对比结果.最后利用修正后的梯度法对激光雷达连续测量数据进行大气边界层高度提取,得到合肥地区观测站上空大气边界层的高度分布及时间变化特征.结果表明,实验期间合肥地区的大气边界层高度主要分布在1～1.5 km范围内,平均高度约为(1.28±0.2) km.     

北京城区奥运期间与其他时段激光雷达观测实例分析

为了研究北京城区在北京奥运会期间大气边界层变化特征及大气边界层内气溶胶的消光特性,2008年8月利用MPL激光雷达对北京城区的大气边界层进行了系统观测.反演出了测站地域上空大气气溶胶的消光特性垂直分布以及大气边界层的高度.同往年北京城区的雷达监测数据进行了系统的对比,并与设在北京南郊梨花村的清洁对照点数据进行了比较.观测数据表明:北京城区奥运期间大气边界层日变化趋势明显,呈早晚低、午间高的特点.大气边界层高度相对稳定,多分布在2.0 km下,平均值为0.79km.奥运期间气溶胶粒子浓度水平较往年有明显下降.观测点处气溶胶浓度水平每天呈周期性变化.     

激光雷达监测北京城区夏季边界层气溶胶

运用一种新型边界层气溶胶监测激光雷达,在北京丰台区进行了外场实验,探讨了大气边界层(PBL)内气溶胶消光系数与湿度、风速等气象条件的关系,并给出了消光系数的时空分布。实验结果表明,水平大气气溶胶消光系数与黑碳质量浓度、地面风速等近地气象因子均有较好的相关性;边界层气象因子直接影响气溶胶的时空扩散和分布;在近地面风速较小等条件下,北京城区气溶胶污染在凌晨和上午较下午和前半夜严重。     

2008年北京奥运期间大气颗粒物激光雷达观测研究

大气区域性污染及其区域输送研究是当前研究的热点问题,2008年北京奥运会的举行为研究北京及其周边大气区域输送提供了机会。主要利用双波长三通道激光雷达和风廓线雷达对颗粒物大气颗粒物区域输送进行研究,介绍了双波长三通道激光雷达的特征及主要参数,讨论了大气颗粒物质量浓度垂直分布的反演方法,并结合风廓线雷达数据论述了颗粒物区域输送的反演,实现了对大气颗粒物输送通量的估算和输送方向的判断。最后,对监测期间典型时间段的大气颗粒物区域输送通量和总量进行估算,并结合SO2实测数据进行了对比分析。     

测量大气边界层高度的激光雷达数据反演方法研究

大气边界层与人类关系最为密切,它的高度分布直接反映了近地面的大气状况.而今激光雷达已成为探测大气边界层时空演变特征的最有效手段,但如何从大量的测量数据中精确提取大气边界层高度则成为限制其应用的主要问题.介绍了四种常用的大气边界层高度提取方法,即梯度法、标准偏差法、曲线拟合法和小波协方差变换法,并结合自行研制的偏振拉曼-米散射激光雷达的实测数据,分别对四种方法的提取结果进行分析.结果表明:四种方法各有优缺点,梯度法、标准偏差法和小波协方差变换法比较相近,准确性高但不稳定;而曲线拟合法的稳定性好,但提取结果相对折中.总体而言,曲线拟合法更适用于大量数据的批处理运算.     

Mie散射激光雷达研究成都地区大气边界层特性

基于Mie散射激光雷达,对成都地区大气边界层结构随时间的变化特性进行了研究.利用Mie散射激光雷达测量大气回波信号,由改进的Klett算法反演获得大气后向散射系数,应用误差函数拟合法并参照位温廊线获得并分析了成都地区大气边界层高度以及卷夹层厚度等特性.     

Mie散射激光雷达研究成都地区大气边界层结构

基于Mie散射大气激光雷达,对成都地区大气边界层结构随时间变化的特性进行了研究。首先,应用Klett算法对大气激光雷达回波信号进行了反演,得到大气消光系数和后向散射系数。然后,通过对大气后向散射系数曲线进行拟合得到大气边界层混合层高度以及卷夹层厚度等特征参量。基于实测数据对成都地区大气回波信号进行了反演,结果表明,成都地区大气边界层混合层高度较低,卷夹层厚度较薄,且随时间变化的趋势较缓慢,这与成都地区特殊的地理状况有关。     

基于激光雷达观测网的杭州及周边地区颗粒物污染特征研究

激光雷达观测网是研究区域大气颗粒物污染分布特征的有力工具。长三角地区激光雷达观测网部分站点的激光雷达资料与地面气象数据、PM2.5、PM10质量浓度数据,以及HYSPLIT后向轨迹模型模拟的后向轨迹相结合,对2016年9月杭州及其周边地区一次颗粒物污染的来源和成因进行了分析。分析结果表明,9月8日杭州颗粒物污染过程是该地区局地污染与高空输送共同作用的结果,且粗粒子主要来源于西北方向。杭州地区SO$_2$浓度整体较低,PM2.5浓度与NO$_2$浓度呈正相关,细颗粒物主要以硝酸盐为主。较高的NO$_2$浓度和高湿度、低风速的不利气象条件,是该地区局地细粒子快速增长的主要原因。     

Grain boundary barrier height in base and space charge regions

The influence of grain boundary barrier height is of great importance for polycrystalline electronic devices and solar cells. The g.b. barrier height is computed in a forward biased one-sided step junction. Within the base, it is calculated by means of analytical expressions which depend on the interface state distribution. Within the space charge region, the population of the interface states is considerably changed on taking the band bending into account. In this region, the g.b. barrier height is obtained by means of a numerical solution of the two-dimensional Poisson's equation. The energy band diagram of the junction in the vicinity of the boundary is given. The variation of the g.b. barrier height as a function of the distance from the junction has been determined for monoenergetic and uniform interface state distributions and for different direct bias voltages.     

Quantum effects in Si n-MOS inversion layer at high substrate concentration

The charge distribution at the semiconductgor-insulator interface is calculated for electrons by solving Schrödinger's and Poisson's equations self-consistently for particles obeying Fermi-Dirac statistics at 300 K. The results are applied to carriers in the channel of a crystalline MOSFET with the (100) axis perpendicular to the gate oxide. The inversion charge density calculated quantum mechanically is smaller than that calculated classically. This affects the shift of the subthreshold curves. The shift is larger at higher substrate impurity concentrations, and is especially pronounced at more than 10¹⁷ cm⁻³, which is the concentration used in recent MOS devices. The shift is as large as 0.18 V when the substrate impurity concentration is 8.5 × 10¹⁷ cm⁻³. Comparisons with measurement are also shown and it agrees well with quantum mechanical calculations. The inversion layer depth is compared, and a new efficient method is derived by transferring the quantum mechanical effect into the classical calculation. The results of this new method agree well with the quantum mechanical calculations and with the measurements.     

Thermal sounding of the atmospheric boundary layer in the oxygenabsorption band center at 60 GHz

A sensitive radiometer that allows the measurement of the radiobrightness temperature with an error not greater than δT _b≈0.06 K is described. It provides the facility for the remote temperature sensing of the boundary layer. According to numerical experiments, the accuracy of the temperature profile recovery is about 0.2 K in the case of a simple profile, and about 0.5 K in the case of a profile with an inversion. Field experiments were conducted with the radiometer in elevation angle scanning mode. In situ temperature measurements were carried out simultaneously with the remote sensing     

北京上空中层顶区域重力波参数关系的激光雷达研究

基于子午工程项目北京钠激光雷达的长期观测数据(2010年4月到2011年9月), 采用Yang等人(2008)的重力波参数提取方法,提取了在253个夜晚2 208 h的有效观测时间里出现的162个钠层单色重力波的垂直波长、周期、幅度值和幅度增长因子参数值.统计分析显示激光雷达所观测到的中层顶区域重力波具有系统性的参数关系,z=0.226Tob0.530、KE=6.6610-10 kz-3.091和KE=8.9710-6 fob-1.696.这些实验观测结果验证了Gardner(1994)扩散滤波理论的结果,但同时发现仅认为波致涡流扩散是重力波衰减的主要途径是不完全正确的,其它因素引起的衰减在重力波的饱和和耗散机制中也起到了重要作用.     

内陆和沿海地区大气气溶胶标高的测量分析

在大气气溶胶粒子浓度随高度指数下降的假定下,气溶胶标高反映了大气边界层气溶胶的特征厚度。为了得到气溶胶标高随时空、季节和地域变化情况,根据整层大气光学厚度和近地面水平能见度的测量结果,分析了内地和沿海地区气溶胶标高的实际变化,初步得到了气溶胶标高随时间、地域及季节改变的规律。     

DTMB-A与ATSC 3.0物理层关键技术对比浅析

DTMB-A是中国自主研发的地面数字电视广播传输标准,其主要的性能指标达到并超越了欧洲的第二代地面数字电视标准DVB-T2.美国ATSC3.0作为广播与宽带的混合网络,它的诞生引起了业界的极大关注.主要对DTMB-A和ATSC 3.0物理层所采用的关键技术进行一个简要对比分析,不仅比较了这两种标准共有的前向纠错编码、星座映射、比特交织等技术,还介绍了ATSC 3.0标准中BICM、LDM等技术.论文总结了DTMB-A和ATSC 3.0各自的特点,这对探讨我国数字电视标准的发展具有一定的参考意义.     

地铁颗粒物PM2.5的SEM和微束XRF分析

采用扫描电镜和X-射线能谱分析(SEM-EDS)以及同步辐射X射线荧光分析(SR-XRF)技术,对地铁PM2.5颗粒物样品进行了形貌及元素成分分析。SEM结果表明地铁颗粒物形貌不同于室外颗粒物,地铁颗粒物粒径较大,形状不规则,具有片状刮擦特性。EDS分析表明地铁单颗粒物中Fe、O元素成分含量最高,铁氧化物是地铁颗粒物的主要成分。结果表明,地铁大气环境明显有别于地铁外环境,地铁在运行过程中产生了大量富含对人体有害的金属颗粒物。地铁环境对城市人群健康的影响需要引起重视。     

Role of Schottky barrier height at source/drain contact for electrical improvement in high carrier concentration amorphous InGaZnO thin film transistors

We report the fabrication of bottom-gate thin film transistors (TFTs) at various carrier concentrations of an amorphous InGaZnO (a-IGZO) active layer from ~10¹⁶ to ~10¹⁹ cm⁻³, which exceeds the limit of the concentration range for a conventional active layer in a TFT. Using the Schottky TFTs configuration yielded high TFT performance with saturation mobility (μ_sat), threshold voltage (V_TH), and on off current ratio (I_ON/I_OFF) of 16.1 cm²/V s, −1.22 V, and 1.3×10⁸, respectively, at the highest carrier concentration active layer of 10¹⁹ cm⁻³. Other carrier concentrations (<10¹⁹ cm⁻³) of IGZO resulted in a decrease of its work function and increase in activation energy, which changes the source/drain (S/D) contact with the active layer behavior from Schottky to quasi Ohmic, resulting in achieving conventional TFT. Hence, we successfully manipulate the barrier height between the active layer and the S/D contact by changing the carrier concentration of the active layer. Since the performance of this Schottky type TFT yielded favorable results, it is feasible to explore other high carrier concentration ternary and quaternary materials as active layers.     

Conductivity of the insulating (oxide) layer on the surface of a semiconductor caused by electron-ion interaction at the insulator-semiconductor boundary

The creation of neutral electron-ion complexes at the boundary between the semiconductor and its surface insulating layer, the diffusion of these complexes, and their decay in the bulk of the insulator are discussed. An ion that appears after the decay of one of these complexes either returns to the semiconductor-insulator (SI) boundary or drifts toward the opposite electrode under the action of the electric field in the insulator layer, depending on the direction of this field. In the first case, a peculiar ion circulation takes place at the surface of the semiconductor within a layer whose thickness is of the same order of magnitude as the diffusion length for electron-ion complexes. This circulation manifests itself in the form of a stationary current through the insulator that depends only slightly on the electric field. In the second case, the transient ion current acquires a component that is independent of the magnitude of the electric field; this component is attributable to the diffusion and decay of the complexes. These effects are observed in insulating layers on silicon MOS structures. Fiz. Tekh. Poluprovodn. 33, 933–939 (August 1999)     

Comparative study on the influence of Al component at GaAlAs layer for GaAs/AlGaAs photocathode

We designed two transmission-mode GaAs/AlGaAs photocathodes with different AlxGa_1-xAs layers, one has an Al_xGa_1-xAs layer with the Al component ranging from 0.9 to 0, and the other has a fixed Al component 0.7. Using the first-principle method, we calculated the electronic structure and absorption spectrum of Al_xGa_1-xAs at x=0, 0.25, 0.5, 0.75 and 1, calculation results suggest that with the increase of the Al component, the band gap of Al_xGa_1-xAs increases. Then we activated the two samples, and obtained the spectral response curves and quantum efficiency curves; it is found that sample 1 has a better shortwave response and higher quantum efficiency at short wavelengths. Combined with the band structure diagram of the transmission-mode GaAs/AlGaAs photocathode and the fitted performance parameters, we analyze the phenomenon. It is found that the transmission-mode GaAs/AlGaAs photocathode with variable Al component and various doping structure can form a two-stage built-in electric field, which improves the probability of shortwave response photoelectrons escaping to the vacuum. In conclusion, such a structure reduces the influence of back-interface recombination, improves the shortwave response of the transmission-mode photocathode.