大庆HDPE装置改扩建可行性分析

大庆石化总厂规划在“九五”期间将30万t/a乙烯装置扩建到48万t/a,HDPE装置是主要的乙烯使用装置。根据该装置几年来的生产实践及与日本三井油化同类装置生产情况的对比,并经过对主要操作单元的详细计算,对该装置设计能力由14万t/a扩建到24万t/a进行了可行性分析,提出了通过对部分设备进行改造后,产量提高10万t/a是可行的。     

Hypercube sandwich approach to conferencing

This paper presents a novel cascaded conference network that provides distributed processing and signal transmission among members of disjoint sets of generic send/receive devices called conferees. It assumes an online request model in which idle groups of conferees may request the formation of a conference interconnection. Once a conference is established, all conferees remain connected until the entire conference is dissolved. The Hypercube Sandwich Network (HSN) consists of two components. A bidirectional permutation network is used for routing purposes to and from a hypercube of special processing elements for the purpose of conference formation. The HSN achieves strictly nonblocking performance for N conferees using O(Nlog N) processing elements, and this is shown to be tight to within a log ^1/4 N factor. Previous constructions required a quadratic number of processing elements for strictly nonblocking performance or could only provide wide-sense nonblocking conferencing. If the stronger requirement is made that the communication delay is logarithmic in the conference size, a simple algorithm is presented for wide-sense nonblocking conferencing in an HSN with O(N log N) processing elements.An earlier version of this paper was presented at the 1995 International Conference on Parallel Processing Techniques and Applications.     

基于静态路由的ISP负载均衡解决方案

传统的ISP负载均衡方法主要有2种,一是使用开启BGP协议的高端防火墙;二是使用专业负载均衡设备.本论文建立了1套新型的基于静态路由的ISP负载均衡解决方案.本文首先通过Whois协议获得ISP的AS号码,在公网BGP路由器数据库中根据这个AS号码查询属于不同ISP的全部BGP路由条目;之后将不同ISP(例如中国电信和中国联通)的路由条目导入园区网边界防火墙,使得用户访问实现负载分担和路由备份.本方案适用于大中型企业和大型居民小区园区网,相比传统的负载均衡方法,本方案能够节省大量设备投资.     

基于DDS的低通滤波器设计与仿真

分析了几种经典滤波器特性,重点研究了DDS系统中低通滤波器的设计方法。根据DDS的结构特点和输出杂散频谱特性,结合滤波器技术指标使用了归一化法完成了一个九阶椭圆函数低通滤波器的设计,使其通带截至频率为120MHz、通带内最大衰减为0.2dB、在135MHz处阻带内最小衰减为66dB。通过Multisim10对其进行仿真后可以得出,使用此种方法设计的低通滤波器过渡带陡峭、幅频特性仿真良好,并且能够很好地满足预期的技术指标。     

A guided local search procedure for the multi-compartment capacitated arc routing problem

In this paper, we introduce and study the multi-compartment capacitated arc routing problem—an extension of the classical capacitated arc routing problem, but where the required edges have a demand for different products, and multi-compartment vehicles are available to co-distribute these commodities. We present a local search algorithm that exploits well-known moves (2-opt, re-insert, relocate, exchange and cross). We take advantage of speed up tricks such as marking and neighbour lists, and we combine the procedure with the guided local search meta-heuristic in order to reach high quality solutions. We report on results from extensive computational experiments. Our aim is to reveal in what situations co-distribution by partitioned vehicles saves in routing costs as compared with separate distribution with un-partitioned trucks. We explore sensitivities in key problem characteristics including, the number of commodities, the vehicle capacity, the location of the depot and required edges, the density of required edges, and the demand per commodity for the required edges.     

改进的FCM与局部信息相结合的图像分割

传统的EM算法和FCM算法分割精度低,时间消耗大。为解决以上不足,提出了一种基于EM、FCM和KCN三种算法相结合的全新的图像分割算法。该算法有较好的分割精度。考虑到图像会受到噪声的干扰,在改进算法的基础上又引入图像的局部信息。首先利用图像的局部信息重塑图像的灰度直方图,增强了像素的类间散布性和类内紧凑性,然后让改进的算法在重塑图像上执行。实验结果表明,该算法具有很好的分割效果和较强的抗噪性能。     

A new data fusion model for high spatial- and temporal-resolution mapping of forest disturbance based on Landsat and MODIS

Investigating the temporal and spatial pattern of landscape disturbances is an important requirement for modeling ecosystem characteristics, including understanding changes in the terrestrial carbon cycle or mapping the quality and abundance of wildlife habitats. Data from the Landsat series of satellites have been successfully applied to map a range of biophysical vegetation parameters at a 30 m spatial resolution; the Landsat 16 day revisit cycle, however, which is often extended due to cloud cover, can be a major obstacle for monitoring short term disturbances and changes in vegetation characteristics through time.The development of data fusion techniques has helped to improve the temporal resolution of fine spatial resolution data by blending observations from sensors with differing spatial and temporal characteristics. This study introduces a new data fusion model for producing synthetic imagery and the detection of changes termed Spatial Temporal Adaptive Algorithm for mapping Reflectance Change (STAARCH). The algorithm is designed to detect changes in reflectance, denoting disturbance, using Tasseled Cap transformations of both Landsat TM/ETM and MODIS reflectance data. The algorithm has been tested over a 185 × 185 km study area in west-central Alberta, Canada. Results show that STAARCH was able to identify spatial and temporal changes in the landscape with a high level of detail. The spatial accuracy of the disturbed area was 93% when compared to the validation data set, while temporal changes in the landscape were correctly estimated for 87% to 89% of instances for the total disturbed area. The change sequence derived from STAARCH was also used to produce synthetic Landsat images for the study period for each available date of MODIS imagery. Comparison to existing Landsat observations showed that the change sequence derived from STAARCH helped to improve the prediction results when compared to previously published data fusion techniques.     

基于信息素质培养的高校计算机基础教学改革探讨

应用型普通高校计算机基础教学应以学生信息素质培养为目标,为此对计算机基础课程体系构建、教学内容选择、教学模式优化等方面进行了深入分析、探讨和改革实践,实践证明该教学改革有效地提升了学生的信息素质。     

Optimization of Geoscience Laser Altimeter System waveform metrics to support vegetation measurements

The Geoscience Laser Altimeter System (GLAS) has collected over 250 million measurements of vegetation height over forests globally. Accurate vegetation heights can be determined using waveform metrics that include vertical extent and extent of the waveform's trailing and leading edges. All three indices are highly dependent upon the signal strength, background noise and signal-to-noise ratio of the waveform, as the background noise contribution to the waveforms has to be removed before their calculation. Over the last six years, GLAS has collected data during thirteen observation periods using illumination from three different lasers. The power levels of these lasers have changed over time, resulting in variable signal power and noise characteristics. Atmospheric conditions vary continuously, also influencing signal power and noise.To minimize these effects, we optimized a noise coefficient which could be constant or vary according to observation period or noise metric. This parameter is used with the mean and standard deviation of the background noise to determine a noise level threshold that is removed from each waveform. An optimization analysis was used with a global dataset of waveforms that are near-coincident with waveforms from other observation periods; the goal of the optimization was to minimize the difference in vertical extent between spatially overlapping GLAS observations. Optimizations based on absolute difference in height led to situations in which the total extent was minimized as well; further optimizations reduced a normalized difference in height extent. The simplest optimizations were based on a constant value to be applied to all observations; noise coefficients of 2.7, 3.2, 3.4 and 4.0 were determined for datasets consisting of global forests, global vegetation, forest in the legal Amazon basin and boreal forests respectively. Optimizations based on the power level or the signal-to-noise ratio of waveforms best minimized differences in waveform extent, decreasing the percent root mean squared height difference by 25-54% over the constant value approach. Further development of methods to ensure temporal consistency of waveform indices will be necessary to support long-term satellite lidar missions and will result in more accurate and precise estimates of canopy height.     

Effects of age and illumination on night driving: a road test

OBJECTIVE: This study investigated the effects of drivers' age and low light on speed, lane keeping, and visual recognition of typical roadway stimuli. BACKGROUND: Poor visibility, which is exacerbated by age-related changes in vision, is a leading contributor to fatal nighttime crashes. There is little evidence, however, concerning the extent to which drivers recognize and compensate for their visual limitations at night. METHOD: Young, middle-aged, and elder participants drove on a closed road course in day and night conditions at a "comfortable" speed without speedometer information. During night tests, headlight intensity was varied over a range of 1.5 log units using neutral density filters. RESULTS: Average speed and recognition of road signs decreased significantly as functions of increased age and reduced illumination. Recognition of pedestrians at night was significantly enhanced by retroreflective markings of limb joints as compared with markings of the torso, and this benefit was greater for middle-aged and elder drivers. Lane keeping showed nonlinear effects of lighting, which interacted with task conditions and drivers' lateral bias, indicating that older drivers drove more cautiously in low light. CONCLUSION: Consistent with the hypothesis that drivers misjudge their visual abilities at night, participants of all age groups failed to compensate fully for diminished visual recognition abilities in low light, although older drivers behaved more cautiously than the younger groups. APPLICATION: These findings highlight the importance of educating all road users about the limitations of night vision and provide new evidence that retroreflective markings of the limbs can be of great benefit to pedestrians' safety at night.