Monthly Joint Operations for the Nakdong Multi-reservoir System in Korea

Abstract

This study applies a state-of-art optimization technique, SSDP/ESP (Sampling Stochastic Dynamic Programming with Ensemble Streamflow Prediction), to derive a monthly joint operating policy for the Nakdong multi-reservoir system in Korea. A rainfall-runoff model, SSARR (Streamflow Synthesis And Reservoir Regulation), is linked to the SSDP/ESP model to provide ESP scenarios for runoff during the next month in the Nakdong River basin. The primary advantage of the SSDP/ESP is that it updates the derived operating policy as new ESP forecasts become available. Another SSDP model that employs historical runoff scenarios (SSDP/Hist) is also developed. The main difference between the two SSDP models is that SSDP/Hist is an off-line model whereas the SSDP/ESP is on-line. The developed operating policies are tested with a simulation model using an object-oriented simulation software, STELLA. The simulation results show that SSDP/ESP is superior to SSDP/Hist with respect to the water supply criterion, although both models perform similarly with respect to the hydroelectric energy production criterion.     

Prediction of in vivo drug performance using in vitro dissolution coupled with STELLA: a study with selected drug products

Prediction of the in vivo performance of the drug product from the in vitro studies is the major challenging job for the pharmaceutical industries. From the current regulatory perspective, biorelevant dissolution media should now be considered as quality control media in order to avoid the risk associated. Physiological based pharmacokinetic models (PBPK) coupled with biorelevant dissolution medium is widely used in simulation and prediction of the plasma drug concentration and in vivo drug performance. The present investigation deals with the evaluation of biorelevant dissolution media as well as in vivo drug performance by PBPK modelling using STELLA® simulation software. The PBPK model was developed using STELLA® using dissolution kinetics, solubility, standard gastrointestinal parameters and post-absorptive disposition parameters. The drug product selected for the present study includes Linezolid film-coated immediate-release tablets (Zyvox), Tacrolimus prolonged-release capsules (Advagraf), Valganciclovir tablets (Valcyte) and Mesalamine controlled-release capsules (Pentasa) each belonging to different biopharmaceutics classification system (BCS). The simulated plasma drug concentration was analyzed and pharmacokinetic parameters were calculated and compared with the reported values. The result from the present investigation indicates that STELLA® when coupled with biorelevant dissolution media can predict the in vivo performance of the drug product with prediction error less than 20% irrespective of the dosage form (immediate release versus modified release) and BCS Classification. Thus, STELLA® can be used for in vivo drug prediction which will be helpful in generic drug development.     

“It was an artefact not the result”: A note on systems dynamic model development tools

Environmental modelling is done more and more by practising ecologists rather than computer scientists or mathematicians. This is because there is a broad spectrum of development tools available that allows graphical coding of complex models of dynamic systems and help to abstract from the mathematical issues of the modelled system and the related numerical problems for estimating solutions. In this contribution, we study how different modelling tools treat a test system, a highly non-linear predator–prey model, and how the numerical solutions vary. We can show that solutions (a) differ if different development tools are chosen but the same numerical procedure is selected; (b) depend on undocumented implementation details; (c) vary even for the same tool but for different versions; and (d) are generated but with no notifications on numerical problems even if these could be identified. We conclude that improved documentation of numeric methods used in the modelling software is essential to make sure that process based models formulated in terms of these modelling packages do not become “black box” models due to uncertainty in integration methods.     

What is the limit of Chinese coal supplies—A STELLA model of Hubbert Peak

American geophysicist M. King Hubbert in 1956 first introduced a logistic equation to estimate the peak and lifetime production for oil of USA. In his 1956 article “Nuclear Energy and the Fossil Fuels”, in which he predicted the production peak for the USA, Hubbert used 80 pages of differential equations to draw his conclusions. That earned him some criticism, because only those with profound mathematical knowledge could understand. Hubbert presented in his 1982 article, “Techniques of Prediction as Applied to the Production of Oil and Gas” an alternative method that was much more accessible. Since then, a fierce debate ensued on the so-called Hubbert Peak, including also its methodology.     

Sixth form students' ability to engage in computational modelling

Abstract  The paper presents the main conclusions of an exploratory study of the ability of Sixth form students in England to use some different approaches to computational modelling. The research involves a questionnaire survey of causal diagraming and mathematical knowledge, which aims at characterizing students' model building capability. Also, it includes an intensive study with pairs of students doing exploratory and expressive tasks using two modelling systems: IQON and STELLA. Data was gathered through written notes from observation, written answers given to questionnaires and data recorded in the computer. Overlapping questionnaires connected the survey and the intensive study, and comparisons between the use of causal diagrams and IQON were carried out. Results suggest that Sixth form students can undertake valuable work with both computational systems.     

Emergy synthesis and simulation for Macao

Macao is a tourist city with a dense population and has a shortage of natural resources. Almost all of the city's life-support systems thus depend on imports of external resources. During the past 20 years, Macao has experienced an economic boom accompanied by rapid social development, in which the gambling industry and related tourism services have become the main economic activity. This paper employs emergy flow analysis to investigate and characterize the evolution and development of Macao from 1983 to 2003. In addition, Macao has experienced six periods of land reclamation since 1866, supported by large-scale importation of sand and rocks from China. By simulating the emergy trends using the STELLA dynamic modeling software, we predicted the evolution of Macao's development and trends in the coming 20 years. In 2025, the city's economy is estimated to be 15 times its current size as a result of Macao's territorial expansion. The exported emergy will increase slowly and then stabilize, the population will reach 593 185, and the area covered by Macao will expand to 38.91 km².     

基于 STELLA 的水资源供需系统模拟和预警分析——以山东省为例

科学预测区域水资源供需变化并提出合理的应对方案对区域可持续发展有重要意义,但现有研究多未合理考虑区域的生态需水量。本文以山东省水资源供需系统为研究对象,考虑城市生态建设及河流生态需水,利用系统动力学软件STELLA模拟预测了山东省2015-2030年水资源供需状况的动态变化,利用支撑度构建水资源短缺预警等级,并进行预警分析;基于敏感性分析结果从重视经济、节水、开源、综合协调4个角度提出发展应对方案。结果表明:当前山东省生态缺水严重,至2030年水资源供需差额将达90×108m3,并有10×108m3会影响到当地生产生活,全省将处于Ⅲ级缺水状态;重视经济和节水型方案均不利于山东省可持续发展,而综合协调型方案将建立兼顾社会经济与生态环境的水资源利用模式,为缓解水资源供需矛盾、优化水资源配置提供科学依据,对水生态文明建设也具有重要意义。     

基于STELLA和输出系数法的流域非点源负荷预测及污染控制措施

以汾河流域为研究对象,综合考虑非点源污染与农村生活、社会经济、土地利用之间的因果关系,利用输出系数法和系统动力学理论建立流域非点源污染的STELLA模型,对汾河流域非点源污染TN负荷进行估算,并提出缓解方案。结果表明,2014年汾河流非点源污染TN负荷为8.961×10~4t,农村生活污染贡献最大;当前发展模式无法实现TN负荷的有效控制,至2030年将增长6.83%;强化农村水废处理和改善土地利用方式对TN负荷有明显的削减效果,且综合型发展方案比单一倾向性措施更具现实意义。     

基于STELLA的安徽省水资源供需预测研究

利用系统动力学软件STELLA建立由水资源供给和居民、工业、农业、生态环境、公共需水等子系统组成的水资源供需系统模型,对安徽省2012-2030年水资源供需情势进行模拟分析,模拟效果较好。参数灵敏度分析表明,模型结果对工业增加值增长率、万元工业增加值用水量、农田有效灌溉系数的变化最为敏感。基于此提出应对水资源短缺问题的3种综合调控方案(方案I,方案Ⅱ和方案Ⅲ)。结果表明:与现有发展模式相比,方案I和方案Ⅱ延迟了水资源短缺的时间;以经济平稳增长、生态环境友好为目标的方案Ⅲ则会有效地解决未来水资源供需矛盾。最后在各种模式的基础上提出了应对水资源问题措施,为缓解安徽省水资源矛盾、优化水资源配置提供参考。