Efficiently sampling exchangeable Cuadras-Augé copulas in high dimensions

An n-dimensional random vector is constructed whose survival copula is given by a copula that was first presented in Cuadras and Augé [C.M. Cuadras, J. Augé, A continuous general multivariate distribution and its properties, Communications in Statistics - Theory and Methods 10 (4) (1981) 339-353]. This construction adds a Poisson subordinator as mixing variable to initially independent exponentially distributed random variables. It is shown how the choice of Poisson process relates to the parameter of the induced Cuadras-Augé copula. Based on this construction, a sampling algorithm for this multivariate distribution is presented which has average computational efficiency O(nloglogn).     

Design and analysis for the Gaussian process model

In an effort to speed the development of new products and processes, many companies are turning to computer simulations to avoid the time and expense of building prototypes. These computer simulations are often complex, taking hours to complete one run. If there are many variables affecting the results of the simulation, then it makes sense to design an experiment to gain the most information possible from a limited number of computer simulation runs. The researcher can use the results of these runs to build a surrogate model of the computer simulation model. The absence of noise is the key difference between computer simulation experiments and experiments in the real world. Since there is no variability in the results of computer experiments, optimal designs, which are based on reducing the variance of some statistic, have questionable utility. Replication, usually a ‘good thing’, is clearly undesirable in computer experiments. Thus, a new approach to experimentation is necessary. Published in 2009 by John Wiley & Sons, Ltd.     

Air Quality Monitoring Network Design to Control Nitrogen Dioxide and Ozone,Applied in Granada,Spain

This paper describes a method to design air quality monitoring networks for nitrogen dioxide and ozone and its application in Granada, a city located in Andalusia, southern Spain. The city has a population of 236,988 inhabitants, and traffic is its main source of air pollution. Sampling campaigns with passive diffusion samplers at 88 sites were carried out to obtain information on the pollution distribution in Granada. The average concentrations found for NO₂ and O₃ were 36.5 μg/m³ and 51.6 μg/m³, respectively. Maximum values of up to 57.1 μg/m³ NO₂ were found in Granada city center and O₃ reached 77.2 μg/m³ downwind from the emission source. After spatial interpolation of the obtained values with Geographical Information Systems, a selection of the best locations for the monitoring stations was made, in line with the macro- and microscale siting requirements of the European Directive 2008/50/EC on ambient air quality and cleaner air for Europe. Another sampling campaign with diffusive samplers was carried out in 2007 to determine if the locations of the air quality assessment stations were still representative for their zone. A correction was made in the control network following results of this verification campaign.     

HBV模型与新安江模型在黄河源区的应用比较

为强化黄河源区水资源管理及生态环境规划等问题,采用HBV模型、新安江模型对其流量过程进行模拟。HBV模型中共有15个参数,参数率定采用蒙特卡罗法(MC)和遗传算法(GA),发现敏感参数有5个,且HBV模型中应用遗传算法计算得到的结果与实测过程更加接近。新安江模型共有17个参数,参数率定采用了蒙特卡罗法(MC)、拉丁超立方分层抽样(LHS)、次数多的蒙特卡罗法,发现敏感参数共有10个,大多数时候拉丁超立方方法率定结果与实测值更接近。两个模型应用结果对比发现,HBV模型对枯季的模拟流量偏低,新安江模型对枯水年的模拟比HBV模型好,且对枯水年的模拟均处于可接受范围之内。     

Sustainability of biofuels in Latin America: Risks and opportunities

Several Latin American countries are setting up biofuel programmes to establish alternative markets for agricultural commodities. This is mainly triggered by the current success of Brazilian bioethanol production for the domestic market and for export. Furthermore, the global biofuel market is expected to increase due to ambitious biofuel programmes in the EU and in the USA. Colombia, Venezuela, Costa Rica and Guatemala are focusing on bioethanol production from sugarcane whereas biofuel production in Argentina is based on soy biodiesel. Recent developments of the biofuel sector take place extremely rapid especially in Argentina, which became one of the five largest biodiesel producers in the world in 2008. Till date no specific biofuel sustainability certification systems have been implemented in Latin American, as well as on global level. This fact and the predominant use of food crops for biofuel production raise concerns about the sustainability of biofuel production related to environmental and social aspects. This paper provides an overview of the hotspots of conflicts in biofuel production in Latin America. It investigates presently available sustainability tools and initiatives to ensure sustainable biofuel production in Latin America. Finally, it provides an outlook on how to integrate sustainability in the Latin American biofuel sector.     

Characterization of carbonaceous materials in PM2.5 and PM10 size fractions in Morogoro, Tanzania, during 2006 wet season campaign

Atmospheric aerosol samples in PM10 and PM2.5 size fractions were collected in parallel at a rural site in Morogoro during wet season in March and April 2006. All samples were analysed for the particulate matter mass, for organic, elemental, and total carbon (OC, EC, and TC), and for water-soluble OC (WSOC). The average PM10 and PM2.5 mass concentrations and associated standard deviations were 14 ± 13 μg/m³ and 7.3 ± 4 μg/m³ respectively. On average, TC accounted for 33% of the PM10 mass and 44% of the PM2.5 mass for the campaign. The average OC/PM percentage ratios were 27% and 33% in PM10 and PM2.5 size fractions respectively and a larger fraction of the OC was water-soluble. The observed low EC/TC mean percentage ratios of 10-14% respectively for PM10 and PM2.5 fractions indicate that the carbonaceous aerosol originates mainly from biogenic aerosols and/or biomass burning. A simple source apportionment approach was used to apportion the OC to biofuel and charcoal burning. On average, 93% of the PM10 OC was attributed to biofuel and 7% to charcoal burning in the 2006 wet season campaign. However, it is suggested that a contribution to the OC at Morogoro could also come from other natural biogenic matter, and/or biomass burning aerosols. The results for the sources of OC at Morogoro should therefore be considered with great caution.     

Research Validation: Challenges and Opportunities in the Construction Domain

Validation of the research methodology and its results is a fundamental element of the process of scholarly endeavor. Approaches used for construction engineering and management research have included experiments, surveys and observational studies, modeling and simulation, theory building, case studies, and various subtypes thereof. Some studies use more than one approach. A particular contribution of this paper is that it reviews different types of validation using examples of studies, analyzes the specific challenges that were found to be significant, and presents how they were successfully overcome in each case. Another contribution is that it describes new opportunities for research validation that are emerging at the horizon as well as ongoing collaborative efforts to enhance the access of construction researchers to validation tools. This paper increases the awareness of the paramount role that validation techniques play in scholarly work by providing readers with recommendations to properly validate their own research efforts.     

Observations on Limit Equilibrium–Based Slope Reliability Problems with Inclined Weak Seams

This study addresses the complexity of slope reliability problems based on limit equilibrium methods (LEMs). The main focus is on the existence of multiple failure modes that poses difficulty to many LEM-based slope reliability methods. In particular, when weak seams are present, the failure modes associated with those seams may be difficult to detect. A systematic way of searching the failure modes is proposed, and its robustness over slopes with or without weak seams is demonstrated. It is found that in the presence of weak seams, assuming circular slip surfaces may cause underestimation of slope failure probability. The conclusion of the study promotes the use of finite elements as the stability method for reliability evaluation because it is not necessary to search for failure surfaces in finite-element stability analysis.     

Role of Stream Restoration on Improving Benthic Macroinvertebrates and In-Stream Water Quality in an Urban Watershed: Case Study

Many stream restoration projects do not include a requirement for long-term monitoring after the project has been completed, resulting in a lack of information about the success or failure of certain restoration techniques. The National Risk Management Research Laboratory, part of the U.S. EPA Office of Research and Development, evaluated the effectiveness of stream bank and channel restoration as a means of improving in-stream water quality and biological habitat in Accotink Creek, Fairfax City, Va., using discrete sampling and continuous monitoring techniques before and after restoration. This project monitored the effects of a 549 m (1,800 linear-ft) restoration of degraded stream channel in the North Fork of Accotink Creek. Restoration, which was intended to restore the stream channel to a stable condition, thereby reducing stream bank erosion and sediment loads in the stream, included installation of native plant materials along the stream and bioengineering structures to stabilize the stream channel and bank. Results of sampling and monitoring for 2 years after restoration indicated a slight improvement in biological quality for macroinvertebrate indices such as Virginia Stream Condition Index, Hilsenhoff Biotic Index, and Ephemeroptera, Plecoptera, Trichoptera taxa; the differences were statistically significant at 90% level of confidence with the power of greater than 0.8. However, indices were all below the impairment level, indicating poor water quality conditions. No statistically significant differences in chemical constituents and bacteriological indicator organisms were found before and after restoration as well as upstream and downstream of the restoration. The results indicated that stream restoration alone had little effect in improving the conditions of in-stream water quality and biological habitat, though it has lessened further degradation of stream banks in critical areas where the properties were at risk. Control of storm-water flows by placing best management practices in the watershed might reduce and delay discharge to the stream and may ultimately improve habitat and water quality conditions.     

基于非均匀采样的相关系数最大化曲线排齐方法*

在函数型数据分析中,为提高曲线排齐效率,提出如下2种非均匀采样方法对函数曲线进行排齐:基于斜率的非均匀采样(SBNS)和基于弧长的非均匀采样(ALBNS).SBNS按照函数曲线的斜率大小采样,ALBNS在函数曲线的弧长上采样.这两种方法都不是在时间轴上均匀采样,而是根据曲线的形状特征进行采样,因此可在一定程度上克服均匀采样方法由于采样点数量和位置分配不当而产生的缺陷,提高曲线排齐效果.在模拟数据和真实数据上的实验表明,两种方法在时间效率和效果上均优于均匀采样方法.