Robust and adaptive path following for underactuated autonomous underwater vehicles

This paper proposes a nonlinear robust adaptive control strategy to force a six degrees of freedom underactuated underwater vehicle with only four actuators to follow a predefined path at a desired speed despite of the presence of environmental disturbances and vehicle’s unknown physical parameters. The proposed controller is designed using Lyapunov’s direct method, the popular backstepping and parameter projection techniques. The closed loop path following errors can be made arbitrarily small. Interestingly, it is shown that our developed control strategy is easily extendible to situations of practical importance such as parking and point-to-point navigation. Numerical simulations are provided to illustrate the effectiveness of the proposed methodology.     

编译BASIC语言编程质量的控制

本文利用编译BASIC语言具有的某些特殊功能,结合具体课题研究实践,从编程技术的模块化、坚固性和可用性三方面进行了实验,采用覆盖技术、“出误陷阱”等技术,使得在较小的内存中运行较大的程序并捕获可能发生的各种随机事件,达到了控制编程质量的目的。     

The evolution of the electronics industry in Johor (Malaysia): Strategic coupling,adaptiveness, adaptation,and the role of agency

Bringing together concepts from the global production networks and evolutionary economic geography literature, this article empirically examines the trajectory of the electrical and electronics industry in Johor (Malaysia). Based on trends in firm entries and exit as well as interviews with companies, we find limited robustness in the industry’s trajectory. While there is evidence of the role of ‘structure’ in this outcome, we argue that human agency – particularly the actions of subnational policy-makers – is key. This is manifest in a preference for fostering regional ‘adaptiveness’ through the often uncritical promotion of a diversity of economic sectors. This compromises the meaningful pursuit of regional ‘adaptation’ in the form of new and more complex branches emerging from existing industries. This arrested development, in turn, hinders an effective strategic coupling between the regional economy and multinational corporations, thus undermining regional resilience.     

Integer estimation in the presence of biases

 Carrier phase ambiguity resolution is the key to fast and high-precision GNSS (Global Navigation Satellite System) kinematic positioning. Critical in the application of ambiguity resolution is the quality of the computed integer ambiguities. Unsuccessful ambiguity resolution, when passed unnoticed, will too often lead to unacceptable errors in the positioning results. Very high success rates are therefore required for ambiguity resolution to be reliable. Biases which are unaccounted for will lower the success rate and thus increase the chance of unsuccessful ambiguity resolution. The performance of integer ambiguity estimation in the presence of such biases is studied. Particular attention is given to integer rounding, integer bootstrapping and integer least squares. Lower and upper bounds, as well as an exact and easy-to-compute formula for the bias-affected success rate, are presented. These results will enable the evaluation of the bias robustness of ambiguity resolution. Received: 28 September 2000 / Accepted: 29 March 2001     

Robust geotechnical design of shield-driven tunnels

This paper presents a fuzzy set-based robust geotechnical design (RGD) methodology for the design of shield-driven tunnels. Here, uncertain geotechnical parameters required for analysis of tunnel performance (referred to herein as the structure safety and serviceability performance of tunnel cross section) are represented as fuzzy sets. Given fuzzy input parameters, the performance of a shield-driven tunnel will be uncertain, which is expressed in this study as a fuzzy factor of safety, according to the analysis of vertex method. Then, the fuzzy factor of safety for a given design is used to evaluate the failure probability and design robustness, which are, in turn, employed in the proposed RGD framework. Note that a design is considered robust if the performance of the shield-driven tunnel is insensitive to the variation of its uncertain geotechnical parameters. Within the RGD framework, each candidate design in the design space is analyzed for its safety state (in terms of failure probability), design robustness, and cost. The goal of the RGD of a shield-driven tunnel is to bring the safety state to an acceptable level, while maximizing the robustness and cost efficiency simultaneously. To this end, a multi-objective optimization is performed and a Pareto front is obtained, which provides a trade-off that may be used to select the most preferred design. Through an illustrative case, the effectiveness and significance of this new robust design methodology is demonstrated.     

Robustness of the holistic seismic risk evaluation in urban centers using the USRi

The Urban Seismic Risk index (USRi) published in a previous article (Carreño et al., Nat Hazards 40:137–172, 2007) is a composite indicator that measures risk from an integrated perspective and guides decision-making for identifying the main interdisciplinary factors of vulnerability to be reduced or intervened. The first step of the method is the evaluation of the potential physical damage (hard approach) as a result of the convolution of the seismic hazard with the physical vulnerability of buildings and infrastructure. Subsequently, a set of social context conditions that aggravate the physical effects is also considered (soft approach). According to this procedure, the physical risk index is evaluated for each unit of analysis from existing loss scenarios, whereas the total risk index is obtained by multiplying the former index by an impact factor using an aggravating coefficient, based on variables associated with the socio-economic conditions of each unit of analysis. The USRi has been developed using the underlying holistic and multi-hazard approach of the Urban Risk Index framework proposed for the evaluation of disaster risk in different megacities worldwide. This article presents the sensitivity analysis of the index to different parameters such as input data, weights and transformation functions used for the scaling or normalization of variables. This analysis has been performed using the Monte Carlo simulation to validate the robustness of this composite indicator, understanding as robustness how the cities maintain the ranking as well as predefined risk level ranges, when compared with the deterministic results of risk. Results are shown for different cities of the world.     

Calibration of the specific barrier model to Iranian plateau earthquakes and development of physically based attenuation relationships for Iran

Earthquake ground-motion relationships for soil and rock sites in Iran have been developed based on the specific barrier model (SBM) used within the context of the stochastic modeling and calibrated against up-to-date Iranian strong-motion data. A total of 171 strong-motion accelerograms recorded at distances of up to 200 km from 24 earthquakes with moment magnitudes ranging from Mw 5.2 to 7.4 are used to determine the region-specific source parameters of this model. Regression analysis was conducted using the “random effects” methodology that considers both earthquake-to-earthquake (inter-event) variability and within-earthquake (intra-event) variability to effectively handle the problem of weighting observations from different earthquakes. The minimization of the error function in each iteration of the “random effects” procedure was performed using the genetic algorithm method. The residuals are examined against available Iranian strong-motion data to confirm that the model predictions are unbiased and that there are no significant residual trends with distance and magnitude. No evidence of self-similarity breakdown is observed between the source radius and its seismic moment. To verify the robustness of the results, tests were performed to confirm that the results are unchanged if the number of observations is changed by removing different randomly selected datasets from the original database. Stochastic simulations, using the derived SBM, are then performed to predict peak ground-motion and response spectra parameters for a wide range of magnitudes and distances. The stochastic SBM predictions agree well with the new empirical regression equations proposed for Iran, Europe and Middle East in the magnitude–distance ranges well represented by the data. It has been shown that the SBM of this study provides unbiased ground-motion estimates over the entire frequency range of most engineering interests (1–10 Hz) for the Iranian earthquakes. Our results are also important for the assessment of hazards in other seismically active environments in the Middle East and Mediterranean regions.     

一种矢量线数据零水印算法

为了满足矢量地理空间数据高精度和零扰动的实用性需要,该文提出一种零水印算法。首先利用Logistic混沌映射置乱原始水印图像;然后对原始矢量线数据进行离散傅里叶变换,获得离散傅里叶变换后的相位值,并将相位值由弧度值转换为角度值;接着随机选取均匀分布的角度值,向下取整后转换为相应的二进制形式,得到二值矩阵;最后将置乱后的水印图像与由相位值构成的二值矩阵进行异或操作,从而构造出零水印图像。实验结果表明,该算法能够抵抗常见的平移、缩放等几何攻击,并且对数据格式转换攻击、投影变换攻击具有较好的鲁棒性。     

Quantifying urban water supply security under global change

Urban water supply security is commonly measured in terms of per capita water availability at the city level. However, the actual services that citizens receive are influenced by several components, including (1) a city's access to water, (2) infrastructure for its treatment, storage and distribution, (3) financial capital for building and maintaining infrastructure, and (4) management efficacy for regulating and operating the water system. These four types of "capital" are required for the provision of public water supply services. A fifth capital “community adaptation” is needed when public services are insufficient. Here, we develop and test an integrated framework for the quantification of urban water supply security based on these five capitals. “Security” involves three dimensions: 1) the level of system function (i.e., supply services); 2) risks to these services; and 3) robustness of system functioning. We apply this Capital Portfolio Approach (CPA) to seven urban case studies selected from a wide range of hydro-climatic and socio-economic regions on four continents. Detailed data on urban water infrastructure and services were collected in two cities, and key stakeholder interviews and household surveys were conducted in one city. Additional cities were assessed based on publicly available utility and globally available datasets. We find that in cities with high levels of public services, adaptive capacity remains inactive, while cities with high levels of water insecurity rely on community adaptation for self-provision of services. Inequality in the capacity to adapt leads to variable levels of urban water security and the vulnerability of the urban poor. Results demonstrate the applicability of the presented framework for the assessment of individual urban water systems, as well as for cross-city comparison of any type of cities. We discuss implications for policy and decision-making.