System dynamics is an approach to understanding the behaviour of complex systems over time. It deals with internal feedback loops and time delays that affect the behaviour of the entire system. What makes using system dynamics different from other approaches to studying complex systems is the use of feedback loops and stocks and flows. These elements help describe how even seemingly simple systems display baffling nonlinearity. Wikipedia.
Aoki S.,University of Tokyo |
Ito M.,University of Tokyo |
Iwasaki W.,System Dynamics
Molecular Biology and Evolution | Year: 2013
Although many α- And some β-proteobacterial species are symbiotic with legumes, the evolutionary origin of nitrogenfixing nodulation remains unclear. We examined α- And β-proteobacteria whose genomes were sequenced using largescale phylogenetic profiling and revealed the evolutionary origin of two nodulation genes. These genes, nodI and nodJ (nodIJ), play key roles in the secretion of Nod factors, which are recognized by legumes during nodulation.We found that only the nodulating β-proteobacteria, including the novel strains isolated in this study, possess both nodIJ and their paralogous genes (DRA-ATPase/permease genes). Contrary to the widely accepted scenario of the α-proteobacterial origin of rhizobia, our exhaustive phylogenetic analysis showed that the entire nodIJ clade is included in the clade of Burkholderiaceae DRA-ATPase/permease genes, that is, the nodIJ genes originated from gene duplication in a lineage of the β-proteobacterial family. After duplication, the evolutionary rates of nodIJ were significantly accelerated relative to those of homologous genes, which is consistent with their novel function in nodulation. The likelihood analyses suggest that this accelerated evolution is not associated with changes in either nonsynonymous/synonymous substitution rates or transition/transversion rates, but rather, in the GC content. Although the low GC content of the nodulation genes has been assumed to reflect past horizontal transfer events from donor rhizobial genomes with low GC content, no rhizobial genome with such low GC content has yet been found. Our results encourage a reconsideration of the origin of nodulation and suggest new perspectives on the role of the GC content of bacterial genes in functional adaptation. © The Author 2013.
Levis S.,System Dynamics
Wiley Interdisciplinary Reviews: Climate Change | Year: 2010
Land surfacemodelingwas invented to represent the atmosphere's lower boundary over continental areas in climate models. Mass, momentum, and energy cross this boundary via biogeochemical and biogeophysical processes often involving plants. Scientific research with models and in the field strives to refine how the changing face of the land interacts with climate change. Discussed here are methods by which we simulate the vegetation and land use in global models and ways by which vegetation and land use affect climate. Model simulations suggest that global land cover changes due to land use play a greater role in affecting 20thand 21st-century climate than changes in unmanaged vegetation. Among the biogeochemical and biogeophysical effects of land use, biogeochemical ones seem to dominate and enhance 20th- and 21st- century warming. Among the effects of natural vegetation, the positive biogeophysical snow-vegetation-albedo feedback of the high latitudes is expected to increasingly influence global climate in response to increasing vegetation density. Still, human or natural disturbances and other not well-understood processes may alter expected outcomes. Interactive nitrogen is one of the newer additions to our models. Nitrogen is found to buffer the terrestrial biosphere's response to forcings, such as changing CO 2 or climate. We still have much to learn about nitrogen's role in the Earth System. Yet, if land use dominates the effects of land cover change on climate, then human behavior will be our greatest uncertainty, which includes management choices that are not easy to predict, such as urbanization, deforestation and afforestation, crop expansion or abandonment, as well as crop rotation, irrigation, and fertilization. © 2010 John Wiley & Sons, Ltd.
Shigarov A.O.,System Dynamics
Expert Systems with Applications | Year: 2014
The paper discusses issues on the conversion of tabular data from unstructured to structured form. Particularly, we propose an approach to table understanding (i.e. recovering semantic relationships in a table), which is designed for unstructured tabular data integration. Our approach is based on using a rule engine. It is assumed that spatial, style (typographical), and natural language information can be used for table analysis and interpretation. The CELLS system based on the approach has been developed for integrating unstructured tabular data presented in Excel spreadsheet format. Experimental results show that the approach and system can be applied to a wide range of tables from statistical and financial reports. © 2014 Elsevier Ltd. All rights reserved.
System Dynamics | Date: 2012-10-01
A method of controlling a combination vehicle for road transport of heavy goods, said vehicle comprising a motor vehicle at the front and a trailer attached so as to be towed behind the motor vehicle, said trailer comprising:
Agency: GTR | Branch: EPSRC | Program: | Phase: Research Grant | Award Amount: 3.44M | Year: 2013
Compared to many parts of the world, the UK has under-invested in its infrastructure in recent decades. It now faces many challenges in upgrading its infrastructure so that it is appropriate for the social, economic and environmental challenges it will face in the remainder of the 21st century. A key challenge involves taking into account the ways in which infrastructure systems in one sector increasingly rely on other infrastructure systems in other sectors in order to operate. These interdependencies mean failures in one system can cause follow-on failures in other systems. For example, failures in the water system might knock out electricity supplies, which disrupt communications, and therefore transportation, which prevent engineers getting to the original problem in the water infrastructure. These problems now generate major economic and social costs. Unfortunately they are difficult to manage because the UK infrastructure system has historically been built, and is currently operated and managed, around individual infrastructure sectors. Because many privatised utilities have focused on operating infrastructure assets, they have limited experience in producing new ones or of understanding these interdependencies. Many of the old national R&D laboratories have been shut down and there is a lack of capability in the UK to procure and deliver the modern infrastructure the UK requires. On the one hand, this makes innovation risky. On the other hand, it creates significant commercial opportunities for firms that can improve their understanding of infrastructure interdependencies and speed up how they develop and test their new business models. This learning is difficult because infrastructure innovation is undertaken in complex networks of firms, rather than in an individual firm, and typically has to address a wide range of stakeholders, regulators, customers, users and suppliers. Currently, the UK lacks a shared learning environment where these different actors can come together and explore the strengths and weaknesses of different options. This makes innovation more difficult and costly, as firms are forced to learn by doing and find it difficult to anticipate technical, economic, legal and societal constraints on their activity before they embark on costly development projects. The Centre will create a shared, facilitated learning environment in which social scientists, engineers, industrialists, policy makers and other stakeholders can research and learn together to understand how better to exploit the technical and market opportunities that emerge from the increased interdependence of infrastructure systems. The Centre will focus on the development and implementation of innovative business models and aims to support UK firms wishing to exploit them in international markets. The Centre will undertake a wide range of research activities on infrastructure interdependencies with users, which will allow problems to be discovered and addressed earlier and at lower cost. Because infrastructure innovations alter the social distribution of risks and rewards, the public needs to be involved in decision making to ensure business models and forms of regulation are socially robust. As a consequence, the Centre has a major focus on using its research to catalyse a broader national debate about the future of the UKs infrastructure, and how it might contribute towards a more sustainable, economically vibrant, and fair society. Beneficiaries from the Centres activities include existing utility businesses, entrepreneurs wishing to enter the infrastructure sector, regulators, government and, perhaps most importantly, our communities who will benefit from more efficient and less vulnerable infrastructure based services.