Quantifying uncertainty in high-resolution coupled hydrodynamic-ecosystem models

Marine ecosystem models are becoming increasingly complex and sophisticated, and are being used to estimate the effects of future changes in the earth system with a view to informing important policy decisions. Despite their potential importance, far too little attention has been, and is generally, paid to model errors and the extent to which model outputs actually relate to real-world processes. With the increasing complexity of the models themselves comes an increasing complexity among model results. If we are to develop useful modelling tools for the marine environment we need to be able to understand and quantify the uncertainties inherent in the simulations. Analysing errors within highly multivariate model outputs, and relating them to even more complex and multivariate observational data, are not trivial tasks. Here we describe the application of a series of techniques, including a 2-stage self-organising map (SOM), non-parametric multivariate analysis, and error statistics, to a complex spatio-temporal model run for the period 1988–1989 in the Southern North Sea, coinciding with the North Sea Project which collected a wealth of observational data. We use model output, large spatio-temporally resolved data sets and a combination of methodologies (SOM, MDS, uncertainty metrics) to simplify the problem and to provide tractable information on model performance. The use of a SOM as a clustering tool allows us to simplify the dimensions of the problem while the use of MDS on independent data grouped according to the SOM classification allows us to validate the SOM. The combination of classification and uncertainty metrics allows us to pinpoint the variables and associated processes which require attention in each region. We recommend the use of this combination of techniques for simplifying complex comparisons of model outputs with real data, and analysis of error distributions.     

Carbonate chemistry dynamics and carbon dioxide fluxes across the atmosphere–ice–water interfaces in the Arctic Ocean: Pacific sector of the Arctic

Climatic changes in the Northern Hemisphere have led to remarkable environmental changes in the Arctic Ocean, which is surrounded by permafrost. These changes include significant shrinking of sea-ice cover in summer, increased time between sea-ice break-up and freeze-up, and Arctic surface water freshening and warming associated with melting sea-ice, thawing permafrost, and increased runoff. These changes are commonly attributed to the greenhouse effect resulting from increased atmospheric carbon dioxide (CO₂) concentration and other non-CO₂ radiatively active gases (methane, nitrous oxide). The greenhouse effect should be most pronounced in the Arctic where the largest air CO₂ concentrations and winter–summer variations in the world for a clean background environment were detected. However, the air–land–shelf interaction in the Arctic has a substantial impact on the composition of the overlying atmosphere; as the permafrost thaws, a significant amount of old terrestrial carbon becomes available for biogeochemical cycling and oxidation to CO₂. The Arctic Ocean's role in determining regional CO₂ balance has been ignored, because of its small size (only  4% of the world ocean area) and because its continuous sea-ice cover is considered to impede gaseous exchange with the atmosphere so efficiently that no global climate models include CO₂ exchange over sea-ice. In this paper we show that: (1) the Arctic shelf seas (the Laptev and East-Siberian seas) may become a strong source of atmospheric CO₂ because of oxidation of bio-available eroded terrestrial carbon and river transport; (2) the Chukchi Sea shelf exhibits the strong uptake of atmospheric CO₂; (3) the sea-ice melt ponds and open brine channels form an important spring/summer air CO₂ sink that also must be included in any Arctic regional CO₂ budget. Both the direction and amount of CO₂ transfer between air and sea during open water season may be different from transfer during freezing and thawing, or during winter when CO₂ accumulates beneath Arctic sea-ice; (4) direct measurements beneath the sea ice gave two initial results. First, a drastic pCO₂ decrease from 410 μatm to 288 μatm, which was recorded in February–March beneath the fast ice near Barrow using the SAMI-CO₂ sensor, may reflect increased photosynthetic activity beneath sea-ice just after polar sunrise. Second, new measurements made in summer 2005 beneath the sea ice in the Central Basin show relatively high values of pCO₂ ranging between 425 μatm and 475 μatm, values, which are larger than the mean atmospheric value in the Arctic in summertime. The sources of those high values are supposed to be: high rates of bacterial respiration, import of the Upper Halocline Water (UHW) from the Chukchi Sea (CS) where values of pCO₂ range between 400 and 600 μatm, a contribution from the Lena river plume, or any combination of these sources.     

Use of an activity diary survey to examine travel and activity reporting in a home interview survey: An example using data from Adelaide,Australia

Research presented in this paper uses results from an acitivity diary survey to comment on the quality of data collected in a home interview travel survey. The two surveys were conducted in Adelaide, Australia. Evidence is presented to suggest that although a period of slightly more than three years separated the two surveys, the samples were reasonably similar with respect to their socio-demographic composition and real mobility levels. There was, however, a much higher level of travel and out-of-home activity reporting in the activity diary when compared to the home interview survey. Differences in reporting rates are examined in detail and areas of deficiency with the home interview survey are identified. The paper concludes with a short discussion of the possible implications of these deficiencies when home interview survey data is used to investigate a range of urban transport issues.     

LC/CL/LCL滤波的电压源和电流源逆变器多环控制策略分析

多环控制策略已被广泛应用于电压源和电流源的逆变器控制中,包括UPS和分布式发电.但是,对于特殊的应用,这些控制策略将被发展和评价,并作为独立的新发展.通过几个常见的系统,文章分析了用不同反馈变量的不同多环控制方法,强调了其相似性,证明了通用的优化变量选择法可用于大部分多环控制逆变系统.通过Matlab仿真和实验室的试验,不同逆变系统的时域波形图十分相似,验证了文中提出的优化变量选择方法的可行性.     

Perceptions of new electronic media for business communication

A model of communications media choice in business organizations is formulated based upon the results of exploratory interviews and the consumer choice literature. Choice is modelled as a function of organizational characteristics, individual characteristics, communication activity characteristics, communication initiator-recipient relationships and perceptions and feelings about available media. Hypotheses concerning media perceptions are developed from the exploratory interviews and tested using survey results from two firms in the Chicago region. The methodology developed in this research provides a useful approach to exploring preferences for and choices of communication media. As a paradigm for future research, it can be used to extend our understanding of communications media usage.     

Optimal roll control of an articulated vehicle: theory and model validation

This paper investigates optimal roll control of an experimental articulated vehicle. The test vehicle and the mathematical model used to design the control strategies are presented. The vehicle model is validated against experimental data from the test vehicle in passive configuration. The initial controller design, performed by Sampson (Sampson, D.J.M. and Cebon, D., 2003a, Achievable roll stability of heavy road vehicles. Proc. Instn. Mech. Engrs, Part D, J. Automobile Engineering, 217(4), 269-287), is reviewed and adapted for the experimental vehicle. The effect of not controlling all the axles on the vehicle is investigated and a variable vehicle speed controller is designed by interpolating between constant speed controllers. Substantial reduction in normalized load transfer is achieved for a range of manoeuvres, both in steady-state and transient conditions.     

Grounding experiments on soft bottoms

To verify a theoretical analysis procedure for calculation of the hull girder response of ships running aground, a series of large-scale ship grounding experiments was performed on an artificial island made of engineered fill. The tests were conducted by running a condemned fishing vessel up on selected beaches of the island with velocities ranging between 2m/s and 5.5m/s. During the tests, surge, heave, and pitch accelerations were measured and also the deformations of the beach and the ship bow. Based on these accelerations, rigid body velocities and motions were determined. The forces arising from the interaction between the bow of the vessel and the seabed were determined by solving the equations of motions. This article describes the analysis of the measured results and a comparison of the results from the full-scale measurements with results from a recently developed analysis procedure for grounding on soft bottoms. Presented at the International Conference on Technology for Marine Environment Preservation (MARIENV '95), Tokyo, Japan, September 24–29, 1995.     

Human-Centered Design of an Acc-With-Braking and Forward-Crash-Warning System

This paper addresses the development of driver assistance systems whose functional purposes are to provide both adaptive cruise control (ACC) and forward collision warning (FCW). The purpose of the paper is to combine concepts from human factors psychology, vehicle-dynamics, and control theory, thereby contributing to the body of knowledge and understanding concerning human-centered approaches for designing and evaluating driver assistance systems. Conceptual and experimental results pertaining to driving manually and with the assistance of ACC and FCW are presented. The following human-centered aspects of driver-assistance systems are analyzed and presented: the looming effect; including rule-based and skill-based behavior in the design of ACC systems; using desired dynamics in controlling the driving process; braking rules that trade headway range for deceleration level; and collision-warning rules based on two different stress indicators. Field-test data are examined to justify and verify the parametric values selected for use in human-centered ACC systems. Measured data from on-road driving are used to evaluate the performance of proposed FCW systems in braking situations. The paper concludes with observations concerning the difficulty of developing a clear understanding of when and why drivers brake.     

Adaptive control of the shifting process in automatic transmissions

This paper focuses on the way of keeping shift quality of automatic transmissions consistent in mass production and with mileage accumulation. We investigate the main factors influencing the consistency of shift quality. Test results show that the torque to pressure (T2P) and pressure to current (P2I) characteristics of shifting elements are easily affected. A simulation model of an 8-speed automatic transmission is established to simulate the dynamic process of clutch-to-clutch shift. Simulation results demonstrate that the change of T2P and P2I characteristics has a significant influence on shift quality. In order to compensate for the influences, we develop two adaptive control strategies, i.e., the adaptive control strategies for torque phase and inertia phase. They make use of the measured speed information and time information to evaluate shift quality. Then the control parameters are tuned to adapt to the change of T2P and P2I characteristics. Vehicle tests verify that the developed adaptive control strategies are effective to keep shift quality consistent in mass production and with mileage accumulation.