Novel Design for High Speed and Resolution Delta-sigma A/D Converter

The delta-sigma converter is one of the high speed and resolution analog-to-digital modulators. Its implementation needs the low oversampling technique and the multi-bit D/A converter. The noise induced by the multi-bit D/A converter becomes one of the key factors deteriorating the signal-to-noise rate of the delta- sigma A/D converter. A novel structure with signal unity transfunction, dynamic element matching（DEM） and noise-shaping is discussed. The method is investigated to design converter based on the proposed structure. The behavior simulation indicates that the structure and the design method are feasible.     

基于小波分解和ROI的数字高程模型表面建模

将小波多尺度分解和ROI应用于数字高程模型(DEM)的表面建模中,首先用非均匀B样条曲面进行数字高程模型地形表面建模,然后用小波多尺度的特征将地表曲面进行压缩和光顺处理.对复杂地表曲面,可能只对某些局部区域感兴趣,因此在小波多尺度分解过程中要结合感兴趣区域(ROI)的方法.本文阐述了地表曲面小波分解和ROI多分辨率表示的原理,给出了具体曲面的小波分解算法和实现结果,有效减少了曲面存储所需的空间并提高了曲面的光顺程度.     

基于小波的地形连续快速绘制技术*

利用小波变换的多分辨率特性构建了地面高程数据的动态多分辨率模型，通过小波渐近重构算法解决了多分辨率模型间的平滑过渡问题，通过缝补解决了不同分辨率地形块间的裂缝问题，实现了对大规模地形的视点相关的连续快速绘制，通过实验进行了验证。     

STREAM RESTORATION AND CRIBWALL PERFORMANCE: A CASE STUDY OF CRIBWALL MONITORING IN SOUTHERN ONTARIO

Stream restoration focusing on adaptable natural and inert material use has been implemented through soil bioengineering designs aimed at the stabilization of urbanized streams. Within each design application materials such as large wood, sediment fill and vegetation must be suited to diverse settings. This paper discusses the application of cribwalls as soil bioengineering designs found in two Southern Ontario watersheds and the criteria that influence their performance. Field measurements of cribwall cuttings, sediment sampling, erosion pin monitoring, and computer‐generated stream power analysis are used to compare design performance at several sites. It is determined that the technical specifications of the design and site characteristics such as stream power distribution, sediment, and channel planform are equally involved in long‐term streambank stability. The results indicate that cribwalls with dense cutting growth perform well on streambanks that offer a greater amount of soil cohesion, nutrients, and infiltration in the mid and upper sections of the bank. In streams with moderate channel slopes and stream power distribution that is above the watershed mean, streams with well‐developed floodplains, sinuous channel planforms, and low bank height ratios perform better than those that are confined, straightened, and have greater bank height ratios. Throughout the comparison of several cribwall sites, the implication of this work is to demonstrate how to assess the fitness of similar soil bioengineering designs for application to diverse stream settings and to further validate their significance in stream restoration as designs that are multifunctional. Copyright © 2013 John Wiley & Sons, Ltd.     

Inter-tablet coating variability: Tablet residence time variability

This paper investigates inter-tablet coating variability, specifically, the variability of tablet residence times within the spray zone of a horizontal coating pan. Results from experiments, discrete element method (DEM) computer simulations, and an analytical model developed to describe the coating mass distribution are presented.The simulations indicate that the coefficient of variation of tablet residence times, and subsequently, of coating mass, decreases with time following a power law relation. The theoretical model demonstrates that the coefficient of variation of residence time for a randomly mixed tablet bed is inversely proportional to the square root of the number of coating “trials”. DEM simulations show that during each pan revolution, tablets in the spray zone remain in a quasi-segregated state from tablets located outside the spray zone for some time period termed Δt_seg. Increasing the pan's Froude number, the spray zone aspect ratio, and the tablet-tablet and tablet-pan friction coefficient all act to decrease Δt_seg, leading to more uniform residence times and less inter-tablet coating variability for a given operating time. The relationship between Δt_seg and tablet load is more complex due changes in bed dynamics. In addition to the variability studies, a model is developed that relates coating fraction, effective mass flow rate, Δt_seg, and the desired coating mass to the allowable fraction of tablets with a coating mass lying outside of a specified range of coating masses.     

Simulating macroscopic behavior of self-compacting mixtures with DEM

Development of proper rheological models and suitable numerical methods are necessary for a thorough understanding of the basic flow properties of fresh mortar or concrete. Main challenge for models is to find a quantitative correlation between the model parameters and the properties and proportions of the mix ingredients. This paper presents a modeling approach for the rheological behavior of fresh self-compacting mixtures using a Discrete Element Method (DEM). The employed method is based on a conceptual idea where the grain-paste-grain interactions are explicitly described as an interactive two-phase paste-bridge system. Each mixture is considered to be an assembly of mutually interacting “grain-paste-grain” systems which can be characterized according to the mix composition with help of the “excess paste theory”. Macroscopic slump flow predictions are evaluated by laboratory tests. Simulations and experimental test results show good agreement.     

Comparison research on the neighbor list algorithms: Verlet table and linked-cell

A Discrete Element Method (DEM) simulation program of gravity driven granular collapse is developed to compare the performance of Verlet table and linked-cell algorithms. Focusing on the simulation efficiency, the two neighbor list algorithms' parameters are discussed such as search radius Rs, cell edge Lc, updating interval time step (UPTime) and the number of particles in simulation system N. The results show that appropriate parameters will improve the simulation efficiency, while the inappropriate parameters will debase the simulation efficiency, even leading to the simulation system crash. The results and discussions presented in this paper will be useful not only for parameters adjustment of DEM but also for Molecular Dynamics (MD) simulations. It will be beneficial to improving the simulation efficiency, especially for the researchers who intend to carry out DEM or MD simulation.     

SPOT5-HRS digital elevation models and the monitoring of glacier elevation changes in North-West Canada and South-East Alaska

Monitoring the response of land ice to climate change requires accurate and repeatable topographic surveys. The SPOT5-HRS (High Resolution Stereoscopic) instrument covers up to 120 km by 600 km in a single pass and has the potential to accurately map the poorly known topography of most glaciers and ice caps. The acquisition of a large HRS archive over ice-covered regions is planned by the French Space Agency (CNES) and Spotimage, France during the 2007–2008 International Polar Year (IPY). Here, we report on the accuracy and value of HRS digital elevation model (DEM) over ice and snow surfaces.

A DEM is generated by combining tools available from CNES with the PCI Orthoengine^SE software, using HRS images acquired in May 2004 over South-East Alaska (USA) and northern British Columbia (Canada). The DEM is evaluated through comparison with shuttle radar topographic mission (SRTM) DEM and ICESAT data, on and around the glaciers. A horizontal shift of 50 m is found between the HRS and SRTM DEMs and is attributed to errors in the SRTM DEM. Over ice-free areas, HRS elevations are 7 m higher than those of SRTM, with a standard deviation of ± 25 m for the difference between the two DEMs. The 7-m difference is partly attributed to the differential penetration of the electromagnetic waves (visible for HRS; microwave for SRTM) in snow and vegetation.

We also report on the application of sequential DEMs (SRTM DEM in February 2000 and HRS DEM in May 2004) for the monitoring of glacier elevation changes. We map the topographic changes induced by a surge of one tributary of Ferris Glacier. Maximum surface lowering of 42 (± 10) m and rising of 77 (± 10) m are observed in the 4 years time interval. Thinning rates up to 10 (± 2.5) m/yr are observed at low altitudes and confirm the ongoing wastage of glaciers in South-East Alaska.     

Characterization and Evaluation of Elevation Data Uncertainty in Water Resources Modeling with GIS

Grid based digital elevation models (DEM) are commonly used in water resources modeling. The quality of readily available DEM, however, varies from source to source in terms of horizontal resolution and vertical accuracy which are the two important aspects of elevation uncertainty in the modeling with raster GIS. This paper addresses the issue of elevation data uncertainty in GIS supported hydrologic simulations. The essential role of elevation data in the modeling is revealed by presenting DEM processing processes in distributed and semi-distributed hydrologic analyses. It is very difficult to examine the elevation uncertainties analytically due to complexities of the hydrologic models. An ideal approach is to assess the effect of the DEM uncertainty by applying varying resolutions or accuracies of elevation data in the modeling. Different grid sizes of DEM are used in observing DEM resolution dependence and resulting model outputs are compared to obtain a profile of its effect. Impact of DEM vertical accuracy is explored by Monte Carlo simulation with a large number of DEM realizations generated based on different levels of specified error. The approach is implemented in a case study with a topography based hydrologic model on an experimental watershed to analyze both aspects of the uncertainty. The results show that both DEM grid size and vertical accuracy could have profound effect on hydrologic modeling performance. The impact can be compensated by model calibrations due to interactions between model parameters and spatial factors. The study indicates that the DEM uncertainty can be effectively evaluated using the applied method. The work is to provide some insight into the characterization of elevation data quality and the association between topography and water resources models.     

Single and bulk compressions of soft granules: Experimental study and DEM evaluation

The characterisation of mechanical properties of particulate solids (e.g. yield pressure and failure strength) is often done by an analysis of bulk compression. However, the relationship between bulk compression behaviour and the physical and mechanical parameters of single particles is not well understood. In this paper the deformation and failure behaviour of soft synthetic detergent granules is investigated experimentally using single granule and bulk compression analyses. Furthermore, the bulk compression of soft spheres, with the properties, which are the same as those of single granules used here, is simulated by distinct element method (DEM) and the predictions are compared with the experimental results. Both the experimental and simulation analyses are for a range of low pressures, less than 30 kPa, with the aim of characterising the yield pressure (limiting contact pressure) of the individual granules using the bulk compression models of Heckel, Kawakita and Lüdde and Adams and co-workers. It is shown that the ratio of the yield pressure of single granules to the Heckel parameter for this type of granules is less than one, and is about 0.5. Furthermore, a relationship is developed among the above three models of bulk compression, in which the above ratio is related to parameters such as the inter-particle and particle wall friction coefficients, initial porosity of the bed and lateral to axial pressure ratio of the particles in the bed. Therefore the use of bulk compression method to infer single particle properties should be made with great caution.