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1.
基于TMS320F240 DSP的电网谐波抑制全数字化控制的研究 总被引:1,自引:0,他引:1
为治理电力系统谐波污染 ,提高电力系统运行的安全稳定性 ,笔者对混合式并联有源电力滤波系统的结构和工作原理进行了分析和研究。该系统由无源滤波器和小容量有源滤波器串联构成 ,与被补偿的谐波负载并联连接。基于TMS32 0F2 4 0DSP开发套件 ,设计数字控制器主程序和中断服务子程序。实验结果表明 ,采用TMS32 0F2 4 0DSP编程方便并直观 ,运算精度高 ,控制器参数调整方便 ,易于实现各种控制策略。研究成果对DSP在有源电力滤波系统中的应用有重要参考价值。 相似文献
2.
爆堆块度评价方法研究的进展 总被引:4,自引:1,他引:4
林大泽 《中国安全科学学报》2003,13(9):9-13
爆堆矿岩的块度分布是评价爆破效果的一项重要依据。对爆堆矿岩的块度大小与块度构成情况进行准确、可靠的定量描述 ,不仅可为验证、改进爆破工艺与参数 ,进而为改善爆破效果提供直接的参考依据 ,而且也是开展爆破优化研究的重要技术基础。通常使用手工方法去评估爆堆矿岩的块度 ,它能在一定程度上对爆破块度分布进行定量的评价。但这些方法还都存在着某些缺陷。而爆堆矿岩块度的计算机图像分析法则可弥补上述诸方法的种种缺陷 ,近年来 ,该研究在国内外得到了越来越广泛的关注和应用。笔者在总结各种测定爆破块度分布的理论和方法的基础上 ,详细分析和研究了当前计算机图像处理分析爆破块度方法。 相似文献
3.
4.
Jurgen Garbrecht Lawrence W. Martz 《Journal of the American Water Resources Association》1993,29(6):909-916
ABSTRACT: An automated extraction of channel network and sub-watershed characteristics from digital elevation models (DEM) is performed by model DEDNM. This model can process DEM data of limited vertical resolution representing low relief terrain. Such representations often include ill-defined drainage boundaries and indeterminate flow paths. The application watershed is an 84 km2 low relief watershed in southwestern Oklahoma. The standard for validation is the network and subwatershed parameters defined by the blue line method on USGS 7.5–minute topographic maps. Evaluation of the generated and validation networks by visual comparisons shows a high degree of correlation. Comparison of selected network parameters (channel length, slope, drainage density, etc.) and of drainage network composition (bifurcation, length, slope, and area ratios) shows that, on the average, the generated parameters are within 5 percent of those derived from the validation network. The largest discrepancies were found for the channel slope values. The results of this application demonstrate that DEDNM effectively addresses network definition problems often encountered in low relief terrain and that it can generate accurate network and subwatershed parameters under those conditions. 相似文献
5.
基于证书权威(CA)中心的时间戳服务系统的实现 总被引:5,自引:3,他引:2
介绍了数字签名不具有抗抵赖的问题 ,以及数据抗抵赖在信息安全中的重要性。在对原有的时间戳协议缺乏可靠的身份认证和可信性分析后 ,提出了一种新的基于证书权威 (CA)中心的时间戳服务协议。利用CA中心的信任原理和数字证书的身份认证作用 ,使提供时间戳服务的服务方具备了可靠的身份鉴别和可信性。并利用XML标记对时间戳的数据内容进行描述 ,形成简单、直观的时间戳 ,且无需复杂的编解码过程。通过正确和可信的时间戳可以判定用户数据产生的时间 ,防止用户事后的抵赖行为 ,为网络应用提供更为安全的数据。 相似文献
6.
A comparison of current techniques for measuring elevations in the beach and near-shore zones is presented. Techniques considered
include traditional methods such as ground survey along transects and airborne stereophotogrammetry, and also newer methods
based on remote sensing such as airborne scanning laser altimetry (LiDAR). The approach taken was to identify a representative
group of users of beach elevation data, elicit their requirements regarding these data, then assess how well the different
methods met these requirements on both technical and financial grounds.
Potential users of beach height measurements include those concerned with coastal defence, coastal environmental management
economic exploitation of the intertidal zone, and coastal flood forecasting. Three test areas in the UK were identified covering
a range of such users and also different beach types. A total of 17 basic user requirements were elicited. For each requirement
each method was scored according to the degree to which it could meet the requirement. Total scores were calculated and each
method ranked. This was undertaken for all the requirements together, for a subset relating to survey of narrow beaches, and
for a subset relating to survey of wide beaches. Approximate costs were also established for the top six methods.
Airborne stereophotogrammetry proved to be the best method technically, but was also the most expensive. Ground survey provides
very good technical performance on narrower beaches at moderate cost. Airborne LiDAR can achieve good technical performance
on both narrow and wide beaches at lower cost than ground survey. The satellite-based waterline method was also inexpensive
and gave good results on wide beaches. An overall conclusion is that, while the traditional methods of ground survey and airborne
stereophotogrammetry remain the best for engineering-related surveys requiring high levels of accuracy, airborne LiDAR in
particular looks set to have a significant impact on beach survey for applications for which a vertical accuracy of 20 cm
is acceptable, provided that its technology evolves satisfactorily. 相似文献
7.
Public rangelands in North America are typically managed under a multiple use policy that includes livestock grazing and wildlife
management. In this article we report on the landscape level extent of grassland loss to shrub encroachment in a portion of
the Rocky Mountain Forest Reserve in southwestern Alberta, Canada, and review the associated implications for simultaneously
supporting livestock and wildlife populations while maintaining range health on this diminishing vegetation type. Digitized
aerial photographs of 12 km of valley bottom from 1958 and 1974 were co-registered to ortho-rectified digital imagery taken
in 1998, and an un-supervised classification used to determine areas associated with grassland and shrubland in each year.
Field data from 2002 were over-layed using GPS coordinates to refine the classification using a calibration-validation procedure.
Over the 40-year study period, open grasslands declined from 1,111 ha in 1958 to 465 ha in 1998, representing a 58% decrease.
Using mean production data for grass and shrub dominated areas we then quantified aggregate changes in grazing capacity of
both primary (grassland) and secondary (shrubland) habitats for livestock and wildlife. Total declines in grazing capacity
from 1958 to 1998 totaled 2,744 Animal Unit Months (AUMs) of forage (−39%), including a 58% decrease in primary (i.e., open
grassland) range, which was only partly offset by the availability of 1,357 AUMs within less productive and less accessible
shrubland habitats. Our results indicate shrub encroachment has been extensive and significantly reduced forage availability
to domestic livestock and wildlife, and will increase the difficulty of conserving remaining grasslands. Although current
grazing capacities remain marginally above those specified by regulated grazing policies, it is clear that continued habitat
change and decreases in forage availability are likely to threaten the condition of remaining grasslands. Unless shrub encroachment
is arrested or grassland restoration initiated, reductions in aggregate ungulate numbers may be necessary.
相似文献
Edward W. BorkEmail: |
8.
由于上游超量用水,导致石羊河下游的民勤县绿洲无水可用,生态环境严重恶化,成为我国的第四大沙尘暴策源地.本文提出了建立"数字石羊河"的概念,认为石羊河流域要建立公平的用水机制,在技术上要建立"数字石羊河",最后对"数字石羊河"在沙尘暴防治中的应用作了分析. 相似文献
9.
Apps are small task-orientated programs with the potential to integrate the computational and sensing capacities of smartphones with the power of cloud computing, social networking, and crowdsourcing. They have the potential to transform how humans interact with nature, cause a step change in the quantity and resolution of biodiversity data, democratize access to environmental knowledge, and reinvigorate ways of enjoying nature. To assess the extent to which this potential is being exploited in relation to nature, we conducted an automated search of the Google Play Store using 96 nature-related terms. This returned data on ~36 304 apps, of which ~6301 were nature-themed. We found that few of these fully exploit the full range of capabilities inherent in the technology and/or have successfully captured the public imagination. Such breakthroughs will only be achieved by increasing the frequency and quality of collaboration between environmental scientists, information engineers, computer scientists, and interested publics. 相似文献
10.
Vulnerability assessment and adaptation to the impacts of sea level rise on the Kingdom of Bahrain 总被引:2,自引:0,他引:2
S. Al-Jeneid M. Bahnassy S. Nasr M. El Raey 《Mitigation and Adaptation Strategies for Global Change》2008,13(1):87-104
This paper assesses quantitatively the impact of sea level rise (SLR) at the global and regional scale as a result of climate
change (CC) on the coastal areas of the Kingdom of Bahrain’s islands (36 Islands). The standard Intergovernmental Panel on
Climate Change (IPCC) guidelines was modified as appropriate for the situation of the study area. Geographic Information Systems
(GIS) coupled with Remote Sensing (RS) were used as the main techniques of collecting, analyzing, modeling simulating and
disseminating information to build SLR scenarios in a geographically referenced context. Also, these tools were used to assess
vulnerability and risk of the coastal area of the islands with the expectation that coastal planner and government authorities
will profit from integrating these knowledge into a broad based environmental decision making. Three SLR scenarios: low, moderate
and high were developed to examine the impacts from SLR on all islands. The low SLR scenario (Optimistic) assumes a 0.5-m
rise above current sea level, the moderate scenario (Intermediate) assumes a one meter rise, and the high scenario (Pessimistic)
assumes a 1.5 m rise in sea level. Two more SLR scenarios were assumed to perform risk analysis, a 2 and 5 meter rise above
current sea level. The simulation of SLR are quite straightforward, emphasizing on the uses of both of the data that are incorporated
from the satellite images and the created Digital Elevation Model (DEM) to estimate SLR scenarios that are adapted in the
study. These data were used to predict consequences of the possibility of the rise in sea level at different scenarios which
may alter the landuse and patterns of human communities. Results indicate that low-lying coastal areas of Bahrain islands
are at risk from the effects of any SLR resulting from CC. These islands are vulnerable under different SLR Scenarios. More
than 17% of the country total area may be inundated under 1.5 m SLR in 2100. The total area that might be lost under different
sea level scenarios will vary from more than 77 km2 if SLR reaches 0.5 m, to about 100 km2 under 1.0 m SLR and may reach 124 km2 under 1.5 m SLR scenario. The total inundated areas due to risk scenarios will reach 133 km2, if the SLR rises to 2.0 m, and it is estimated to be more than (22%) of the main island total area. Under the second scenario,
if the SLR reaches 5.0 m, the main islands will lose approximately half of its area (47%) equal to 280 km2. Hawar islands group will lose about (30%) of its total area under 2.0 m SLR, which is about 15.5 km2.A SLR adaptation policy framework (APF) and adaptation policy initiatives (APIs) are suggested for planners to build upon
for reducing the likely effects of SLR in the Kingdom of Bahrain. The framework is composed of four steps namely, acquisition
of information, planning and design, implementation and monitoring and evaluation. A general policy framework for a national
response to SLR is suggested. Additionally, a range of policy adaptation options/initiatives to sustain coastal developments
under the likely effects of SLR are recommended. 相似文献