基于地形分区的射线跟踪法加速方法的研究

通过分析影响射线跟踪法计算效率的因素,提出一种基于多线程的用于开放地理环境中的射线跟踪加速方法,以提高射线跟踪法在计算机仿真中的计算效率。该方法应用于特定复杂战场电磁环境,根据电磁波射线传播特性,采用对地形分区的途径减少射线与规则三角面地形面的求交次数,同时使用多线程追踪单个辐射源的射线路径。经过对方法进行仿真计算,验证该方法的有效性。     

基于Daubechies4小波变换地形滤波的复杂电磁环境仿真加速方法

本文提出了一种基于射线追踪算法的复杂电磁环境仿真计算的加速方法,同时结合并行系统来共同加速仿真计算。对地形DEM数据进行Daubechies4二维离散小波变换,地形滤波在一定范围内有效降低了其复杂度。继而搭建并行计算系统,将滤波后的地形应用到多个辐射源的仿真建模并行计算,提高复杂电磁环境仿真计算速度。经过对该方法进行多次实验,验证了该方法可以在一定精度范围内提高复杂电磁环境计算速度。     

复杂电磁环境仿真软件中的电磁态势显示计算技术研究

在复杂电磁环境仿真软件中，电磁态势显示是一个重要的功能，而传统的单PC机仿真软件很难满足电磁态势显示大数据量和高计算精度的要求。从分布式计算以及接收区域模型化两个方面对传统的射线追踪算法加以改进，使其更加适合电磁态势仿真场景，以达到提升仿真效率的目的。     

基于射线追踪法的态势计算的优化

区域态势仿真通常会采用在既定区域内放置大量的点状接收机来接收电磁信号,分析计算信号功率与场强,从而达到模拟态势区域的目的。这就要求每个点状接收机都需要进行信号的处理与计算,计算上的重复性很大。采用n米采点投影的方法,假定接收区域投影为长方形,将其划分成n*n米2的小正方形。发出射线后,从射线进入接收区域的位置开始,每隔n米对射线信号进行取样。该方法可以大幅度提高计算效率,且在仿真应用中得到了较好的效果。     

射线追踪中与地形的加速技术研究

在采用射线追踪方法的仿真软件中，一般都会判断射线与地形的交点，从而判断射线与哪块地形发生相交和反射、绕射。目前地形多采用三角面的形式来模拟。而一条射线对较大地形所有三角面进行一次相交的判定的过程较长。就射线与地形判断相交和确定交点的位置的过程中估计射线路径从而减少与三角面的相交判断从而进行加速，从而使得射线追踪时间能够大幅度的缩短，提高了软件仿真的效率。     

基于射线弹跳法的常见电磁仿真模型的地形剖分加速算法

电磁环境仿真中,针对一种常见的电磁仿真模型,提出了一种地形剖分方法来加快射线追踪计算。当发射机与接收机相距较远时,将包含发射机的较小区域和包含接收机的较小区域分别用较密的网格进行剖分,其他的地形用较粗的网格进行剖分。大量的仿真测试证明了该加速算法的高效性,其能在保证仿真精度的情况下减少仿真时间。     

一种航空电子设备的隔振设计

为确保一种安装在某型高振动量级飞机上的电子设备能正常工作,提出了需要被动隔振的方法。介绍了振动及隔振的基本理论,用计算和仿真的方法确定了隔振系统的基本参数,定制合适的隔振器,将隔振系统进行了振动实验。结果表明:隔振效率达到76.8 %。理论计算结合仿真、实验的方法能够解决工程中隔振设计问题,为提高航电设备可靠性奠定基础。     

旁路二极管对热斑效应的抑制效果仿真研究

在光伏电池产业迅速发展的背景下,光伏电池板在阴影遮蔽时产生的热板效应也逐渐受到关注。本文首先分析了热板效应产生的原理,基于PSCAD仿真平台建立了光伏发电系统的等效模型,并根据工程实际选取合适的参数。继而对无阴影遮挡电池板和有阴影遮挡时的光伏电池板进行仿真研究,对比后分析得出加装旁路二极管对热斑效应的抑制效果。     

基于CNN算法的地下水位动态变化特征识别方法研究

为解决地下水位特征识别中存在的识别效果较差的问题，提出基于CNN算法的地下水位动态变化特征识别方法。首先分析地质结构与水化学特性，获取地下水储存层与水的种类；其次计算地下水位关联维度，从初始时间序列内挑选时间延迟；再次根据圆形颜色确定识别的地下水位图像，将图像转换成YCrCb色彩空间格式，并通过二值化转换挑选自适应色调阈值，最后借助CNN卷积架构将地下水位图像进行分层，通过CNN判据的两次确定，实现地下水位动态变化特征的识别。实验证明：所提方法在正常时刻和地震纵波影响下采集到的水位特征较为一致，且能够量化识别结果，一天内其监测水位最大误差仅为0.07m,具有较好的监测性能，有效提高地下水治理效果，值得推广应用。     

有限元动态模型的修正方法综述

结构在进行有限元仿真分析时,对比计算结果与实际测试数据,往往存在一定的偏离。针对有限元动态模型,基于实际测试获取的少量数据,采用一定的修正算法,从而减小模型修正后的仿真结果与实测响应数据的误差。通过文献调研,对有限元模型修正的一般方法及其发展进行了归纳和总结。     

AN APPLICATION RUNOFF MODEL STRATEGY FOR UNGAGED WATERSHEDS1

ABSTRACT: Mathematical models for predicting watershed surface flow responses are available, most of which are elaborate nonlinear numerical surface and channel flow models linked with infiltration models. Such models may be used to make predictions for ungaged areas, assuming an acceptable fitting of the model to the topography and roughness of the real system. For some application purposes, these models are impractical because of their complexity and expensive computer solutions. A procedure is developed that uses a complex model of an ungaged area to derive a simpler parametric nonlinear system model for repetitious simulation with input sequences. The predicted flow outputs are obtained with the simpler model at significant savings of money and time. The procedures for constructing a complex kinematic model of a 40 acre (161,880 m²) reference watershed and deriving the simpler system model are outlined. The results of predictions from both models are compared with a selected set of measured events, all having essentially the same initial conditions. Peak discharges ranged from 3 to 118 ft³/sec (0.085 to 3.34 m³/sec), which includes the largest event of record. The inherent limitations of lumped systems models are demonstrated, including the bias caused by their inability to model infiltration losses after rainfall ceases. Computer costs and times for the models were compared. The derived simple model has a cost advantage when repeated use of a model is required. Such an applications hydrologic model has an engineering tradeoff of reduced accuracy, and lumping bias, but is more economical for certain design purposes.     

Conversion of temperate forests into heaths: Role of ecosystem disturbance and ericaceous plants

Fire and logging in nutrient-poor temperate forests with certain ericaceous understory plants may convert the forests into heaths. The process of disturbance-induced heath formation is documented by using examples ofCalluna in western Europe,Kalmia in Newfoundland, andGaultheria (salal) in coastal British Columbia. In a cool, temperate climate, rapid vegetative growth ofCalluna, Kalmia, and salal following disturbance results in increasing organic accumulation (paludification), nutrient sequestration, soil acidification, and allelochemicals. These are thought to be the main reasons to conifer regeneration failure in disturbed habitats. If continuation in forest is a land-use objective, then temperate forests with an ericaceous understory should not be logged unless effective silvicultural methods are devised to control the ericaceous plants and restore forest regeneration. Preharvest vegetation control may be considered as an option. Failure to control the understory plants may lead to a long-term vegetation shift, from forest to heathland, particularly in nutrient-poor sites. Successful methods of controllingKalmia andGaultheria, however, have yet to be developed. While theKalmia- andGaultheria- dominated heathlands are undesirable in Canada and the Pacific Northwest, a wide range ofCalluna heathlands of western Europe are being conserved as natural and seminatural vegetation.     

Using Paleo Reconstructions to Improve Streamflow Forecast Lead Time in the Western United States

In water stressed regions, water managers are exploring new horizons that would help in long‐range streamflow forecasts. Oceanic‐atmospheric oscillations have been shown to influence streamflow variability. In this study, long‐lead time streamflow forecasts are made using a multiclass kernel‐based data‐driven support vector machine (SVM) model. The extended streamflow records based on tree ring reconstructions were used to provide a longer time series data. Reconstructed data were used from 1658 to 1952 and the instrumental record was used from 1953 to 2007. Reconstructions for oceanic‐atmospheric oscillations included the El Niño‐Southern Oscillation, Pacific Decadal Oscillation, Atlantic Multidecadal Oscillation, and North Atlantic Oscillation. Streamflow forecasts using all four oscillations were made with one‐year to five‐year lead times for 21 gages in the western United States. This is the first study that uses both instrumental and reconstructed data of oscillations in SVM model to improve streamflow forecast lead time. SVM model was able to provide “satisfactory” to “very good” forecasts with one‐ to five‐year lead time for the selected gages. The use of all the oscillation indices helped in achieving better predictability compared to using individual oscillations. The SVM modeling results are better when compared with multiple linear regression model forecasts. The findings are statistical in nature and are expected to be useful for long‐term water resources planning and management.     

Urban ecological systems: scientific foundations and a decade of progress

Urban ecological studies, including focus on cities, suburbs, and exurbs, while having deep roots in the early to mid 20th century, have burgeoned in the last several decades. We use the state factor approach to highlight the role of important aspects of climate, substrate, organisms, relief, and time in differentiating urban from non-urban areas, and for determining heterogeneity within spatially extensive metropolitan areas. In addition to reviewing key findings relevant to each state factor, we note the emergence of tentative "urban syndromes" concerning soils, streams, wildlife and plants, and homogenization of certain ecosystem functions, such as soil organic carbon dynamics. We note the utility of the ecosystem approach, the human ecosystem framework, and watersheds as integrative tools to tie information about multiple state factors together. The organismal component of urban complexes includes the social organization of the human population, and we review key modes by which human populations within urban areas are differentiated, and how such differentiation affects environmentally relevant actions. Emerging syntheses in land change science and ecological urban design are also summarized. The multifaceted frameworks and the growing urban knowledge base do however identify some pressing research needs.     

Neighbourhood characteristics and urban gardens in the Toledo metropolitan area: staffing and voluntarism,food production,infrastructure, and sustainability practices

Urban gardens are important sources of sustenance for communities with limited access to food. Hence, this study focuses on food production in gardens in the Toledo metropolitan area in Northwest Ohio. We administered surveys to 150 garden managers from November 2014 to February 2015 in our attempt to better understand how neighbourhood racial composition and poverty levels are related to staffing and voluntarism, food production and distribution, the development of infrastructure, and the adoption of sustainability practices in urban gardens. The results from 30 gardens are presented in this paper. We used Geographic Information Systems to map the gardens and overlay the map with 2010 census data so that we could conduct demographic analyses of the neighbourhoods in which the gardens were located. Though the gardens were small – two acres or less – up to 46 varieties of food were grown in a single garden. Gardens also operated on small budgets. Food from the gardens was gifted or shared with friends, family, and neighbourhood residents. Gardens in predominantly minority neighbourhoods tended to have fewer institutional partners, less garden infrastructure, and had adopted fewer sustainable practices than gardens in predominantly White neighbourhoods. Nonetheless, residents of predominantly minority and high-poverty neighbourhoods participated in garden activities and influenced garden operations. Volunteering and staffing were racialised and gendered.     

Predicting deer-vehicle collisions in an urban area

Collisions with deer and other large animals are increasing, and the resulting economic costs and risks to public safety have made mitigation measures a priority for both city and wildlife managers. We created landscape models to describe and predict deer-vehicle collision (DVCs) within the City of Edmonton, Alberta. Models based on roadside characteristics revealed that DVCs occurred frequently where roadside vegetation was both denser and more diverse, and that DVCs were more likely to occur when the groomed width of roadside right-of-ways was smaller. No DVCs occurred where the width of the vegetation-free or manicured roadside buffer was greater than 40 m. Landscape-based models showed that DVCs were more likely in more heterogeneous landscapes where road densities were lower and speed limits were higher, and where non-forested vegetation such as farmland was in closer proximity to larger tracts of forest. These models can help wildlife and transportation managers to identify locations of high collision frequency for mitigation. Modifying certain landscape and roadside habitats can be an effective way to reduce deer-vehicle collisions.     

BIOLOGICAL INDICATORS AND BIOLOGICAL EFFECTS OF ESTUARINE/COASTAL POLLUTION1

ABSTRACT: Sustained interest in and concern about the health status of the aquatic environment has resulted in extensive research focused on (1) effects of pollution on survival, growth, and reproduction of resource species at all life stages; (2) diseases of fish and shellfish, as they may be related to pollution and as they may serve as indicators of environmental stress; and (3) contaminant body burdens in fish and shellfish - their effects on the aquatic animals and their potential effects on humans. Effects, lethal and sublethal, of pollutants on life history stages of fish and shellfish have been documented, as have impacts on local stocks in badly degraded habitats, but as yet there has been no adequate quantitative demonstration of effects on entire aquatic species - probably because of the difficulty in sorting out relative effects of the many environmental factors that influence abundance. Sublethal effects, especially those that result in disease, have been examined intensively, and some diseases and disease syndromes have been associated statistically with pollution. Other pollution indicators (biochemical, physiological, genetic, behavioral, and ecological) have also received some attention, as have body burdens of contaminants in aquatic species. Research, especially that conducted during the past decade, has done much to clarify the many pathways and toxic effects of contaminants on aquatic animals, and has also helped to identify mechanisms for survival of fish and shellfish in the presence of environmental changes caused by human activities.     

Biodiversity and biotechnology

The maintenance of biodiversity is urged from many quarters and on grounds ranging from aesthetic considerations to its usefulness, particularly for biotechnology. But regardless of the grounds for preserving biodiversity, writers are generally in agreement that it should be preserved. But, in examining the various references biodiversity, such as species diversity, genetic diversity, and habitat diversity, it is apparent that we cannot aim to preserve biodiversityas such, since there are a number of conflicts in any such undertaking. In preserving one aspect of biodiversity, we damage another aspect. Five arguments which attempt to ground our moral concern for biodiversity are reviewed and critiqued, not only for their consistency but also for their power to move us to action. The final section of the paper shows how conflicts in the values of personal and environmental health can impair ethical action and especially policy formation.An earlier version of this paper was read at the conference on Agriculture, Food, and Human Values: Tradition and Change, Orlando, Florida, October 7–9, 1987.     

Journalists' views of advertiser pressures on agricultural news

All major journalism ethical codes explicitly state that journalists should protect editorial copy from undue influence by outside sources. However, much of the previous research on agricultural information has concentrated on what information various media communicate (gatekeeping studies) or communication's role in increasing innovation adoption (diffusion studies). Few studies have concentrated specifically on organizational and structural constraints that might adversely affect agricultural journalists' ethical standards; those that have, focus largely on farm magazines. A study of newspaper reporters who cover agricultural news found that the most pressing ethical concern is the effect of advertiser (agri-business) pressure on editorial copy, and that their concerns in general parallel those of farm magazine writers and editors. The majority reported being in situations in which they might be exposed to advertiser pressure, including pressures to change or withhold editorial copy. Large minorities suggested that advertising pressures affect the overall environment in which agricultural journalists work, and more than one in ten said they allow advertiser pressures to influence editorial decisions. The newspaper reporters who cover agricultural beats showed slightly more resistance to advertiser pressure than did farm magazine editors in a parallel study.     

Definition Procedures Have Little Effect on Performance of Environmental Classifications of Streams and Rivers

Mapped environmental classifications are defined using various procedures, but there has been little evaluation of the differences in their ability to discriminate variation in independent ecological characteristics. We tested the performance of environmental classifications of the streams and rivers of France that had been defined from the same environmental data using geographic regionalization and numerical classification of individual river valley segments. Test data comprised invertebrate assemblages, water chemistry, and hydrological indexes obtained from sites throughout France. Classification performance was measured by analysis of similarity (ANOSIM). Geometric regions defined by a regular grid and without regard to environmental variables and a posteriori classifications based on clustering the test datasets defined lower and upper bounds of performance for a given number of classes. Differences in classification performances were generally small. The ANOSIM statistics for the a posteriori classifications were around twice that of all environmental classifications, including geometrically defined regions. The hydro-ecoregions performed slightly better for the invertebrate data and the network classification performed slightly better for the chemistry and hydrological data. Our results indicate that environmental classifications that are defined using different procedures can be comparable in terms of their ability to discriminate variation of ecological characteristics and that alleged differences in performance arising from different classification procedures can be small relative to unexplained variation. We conclude that definition procedures might have little effect on the performance of large-scale environmental classifications and decisions over which procedures to use should be based primarily on pragmatic considerations.