A data mining approach for understanding topographic control on climate-induced inter-annual vegetation variability over the United States

The complex feedback relationship between climate variability and vegetation dynamics is a subject of intense investigation for its implications in furthering our understanding of the global biogeochemical cycle. We address an important question in this context: “How does topography influence the vegetation's response to natural climate fluctuations?” We explore this issue through the analysis of inter-annual vegetation variability over a very large area (continental United States) using long-term (13-year period of 1989-2001), monthly averaged, biweekly maximum value composite normalized difference vegetation index (NDVI) data. These data are obtained from satellite remote sensing at 1-km resolution. Through the novel implementation of data mining techniques, we show that the Northern Pacific climate oscillation and the ENSO phenomena influence the year-to-year vegetation variability over an extensive geographical domain. Further, the vegetation response to these fluctuations depends on a variety of topographic attributes such as elevation, slope, aspect, and proximity to moisture convergence zones, although the first two are the predominant controls. Therefore, the dynamic response of terrestrial vegetation to climate fluctuations, which shows tremendous spatial heterogeneity, is closely linked to the variability induced by the topography. These findings suggest that the representation of vegetation dynamics in existing climate models, which do not incorporate such dependencies, may be inadequate. Therefore, climate models that are regularly employed to guide policy decisions need to better incorporate these dependencies for the assessment of terrestrial carbon sequestration under evolving climate scenarios.     

形貌优化在机枪枪管频率设计中的应用以及射击精度改进研究

为了提高机枪系统射击精度,将瞬态动力学与模态分析技术相结合,为枪管结构形貌优化选择了合适的目标模态,并对其进行了形貌优化。并采用刚柔耦合动力学与外弹道计算对优化前后机枪系统动力学响应特性、射击精度进行了对比研究。结果表明：采用优化后的枪管结构后,枪口高低方向振动位移、速度、射角最大值分别减少了40%、52%、46%左右,效果良好。并且,机枪射击精度指标R50、R70分别由原先的7.7cm、11.6cm下降为2.6cm、6.4cm,射击精度指标分别提高了66%、44%左右,提升效果较为明显。本文研究,可为同类武器结构设计提供参考。     

基于Daubechies小波和工件面形误差的机床导轨误差相关性分析

提出一种基于Daubechies小波和车削面形误差的导轨误差辨识的新方法,根据检测结果的特征分析结果,识别出引起此特征的机床误差源。为了了解小波分析的误差,对工件面形检测信号用不同紧支集的Daubechies小波族在1～9尺度下进行分解和重构,对比重构信号和原始信号发现,紧支集为[0,1]的Db1小波用于工件面形信号分解时误差最小。误差源对加工结果影响的仿真结果与实际加工工件的面形检测结果对比,分离出的表面形貌的单尺度上的信息与原信息除了会有相位时移外,还有很多特征相关性。利用小波的变焦特性,采用特征相关性分析方法,从检测结果中确定出引起加工结果的机床误差源。     

Effect of Bed Armoring on Bed Topography of Channel Bends

The two-dimensional numerical model previously developed by the writers for modeling the bed variations in a channel bend with uniform sediment is upgraded to incorporate the nonuniformity of sediment particles as well as bed armoring. In this model, the two-dimensional, depth-averaged, unsteady flow equations along with the bed-load mass conservation equation are solved in a body-fitted coordinate system by using the Beam and Warming alternating-direction implicit (ADI) scheme. A one-dimensional bed surface armoring approach is extended herein for application to a two-dimensional domain. The model is applied to a 180° bend with a constant radius under unsteady flow conditions. Numerical simulations are carried out to study the effect of bed armoring on the bed deformations in channel bends. Results show that bed armoring reduces scour in channel bends.     

曲面形貌轮廓仪传感器的机构设计

介绍一种适于曲面形貌测量的新型触针式轮廓仪的传感机构。它采用顶尖支承作为测杆的支承形式，并以测杆自重为传感器的测力源，无导头。本文分析了其动态特性和动态测力问题。     

Thin film flow over spinning discs: The effect of surface topography and flow rate modulation

We examine the effect of disc topography and time modulation of the liquid flow rate at the inlet on the dynamics of a thin film flowing over a spinning disc. We use a combination of boundary-layer theory and the Kármán-Polhausen approximation to derive coupled equations for the film thickness, and radial and azimuthal flow rates. Substrate patterning is taken into account in the limit of small-amplitude topography. Our numerical results indicate that the combined effects of flow rate modulation at the inlet and disc patterning can lead to a significant increase in interfacial waviness, which greatly exceeds that associated with the constant flow rate, smooth disc case.     

Sequential colour mapping system of brain potentials

We present a colour mapping system for the visualization of both the spatial scalp distribution and the temporal evolution of brain potentials. The system is applicable to recordings of auditory, visual and somatosensory potentials. It uses a Tektronix 4113 colour terminal connected to a Solar 16 (SEMS) mini-computer. The brain potentials are recorded on up to 16 scalp electrodes. The gain and the baseline are corrected separately on each channel. At each point of the scalp the potential is reconstructed by a linear interpolation of the measured potentials of the four nearest electrodes. Simultaneously n2 (1 less than n less than 8) colour maps can be presented on the screen. This allows the study of the temporal evolution of full scalp evoked potentials. The user chooses the two extreme latencies defining the time window to be explored and the latencies of the maps are regularly time-spaced within this window. In a typical case, in which four maps are desired, the latencies of the maps can be chosen independently. The 16-colour palette is predetermined but the user has three possibilities to establish the correspondence between the electrical potential and the colours. Examples are shown in the visual and somatosensory stimulation modalities. The advantages and limitations of such a representation are discussed.     

Coupled distance sensor systems for high-accuracy topography measurement: Accounting for scanning stage and systematic sensor errors

Scanning topography measurements using systems of coupled distance sensors suffer from the presence of scanning stage and systematic sensor errors. While scanning stage errors can be estimated for suitably-designed sensor systems, it is usually not possible to simultaneously estimate both scanning stage and systematic sensor errors. Additional angular scanning stage measurements can solve this problem, and potentials and limitations of such a proceeding will be assessed.It is shown that perfect topography reconstruction can be achieved in the presence of systematic sensor and certain scanning stage errors provided that the measurements are noise-free and no further systematic errors emerge. In general, the topography is reconstructed by the application of least-squares, and the uncertainty associated with the reconstructed topography is derived. Resulting topography accuracies are evaluated for different noise levels of the distance sensor and angular scanning stage measurements, and practical considerations are discussed. The gain in accuracy due to accounting for scanning stage and systematic sensor errors can be large, and high accuracies can be reached.     

Transmission electron microscopy and x-ray topography study of mercury-cadmium-telluride

The fault structure of MCT crystals was studied by means of X-ray topography and transmission electron microscopy. Subgrain boundaries were revealed and identified by both techniques, and their tilt angle was calculated to be of the order of 10^-3 rad. The dislocations which form the subgrain boundaries were identified by TEM to have Burger‘s vectors parallel to the <110> directions. Twins in large numbers were observed by TEM. The twins were identified to have a {111} habit plane.     

Divergence Form for Bed Slope Source Term in Shallow Water Equations

A novel technique is presented for the treatment of the bed slope source terms within the numerical solution of the shallow water equations. The proposed method consists of writing the bed slope source term as the divergence of a proper matrix, related to the static force due to bottom slope. Such a technique is founded on analytical reasoning and is physically based, so that it can be easily applied to a wide range of numerical models, as it is completely independent of any adopted discretization technique, and requires a minimum computational effort. Herein, we show an application to a Godunov-type model, second order accurate both in space and time, based on the finite-volume method. The presented technique leads to a strong improvement in the source terms numerical treatment, especially for steady states, in which flux gradients are exactly balanced by source terms. A surprising degree of simplicity is maintained, with respect to different existing methods. The numerical model has been applied to a set of classical test cases and to a selected laboratory experiment, in order to verify its stability, accuracy, and applicability to practical real-world cases.