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Probabilistic safety assessment of self-centering steel braced frame

Navid RAHGOZAR, Nima RAHGOZAR, Abdolreza S. MOGHADAM

《结构与土木工程前沿（英文）》 2018年第12卷第1期页码 163-182 doi: 10.1007/s11709-017-0384-z

摘要： The main drawback of conventional braced frames is implicitly accepting structural damage under the design earthquake load, which leads to considerable economic losses. Controlled rocking self-centering system as a modern low-damage system is capable of minimizing the drawbacks of conventional braced frames. This paper quantifies main limit states and investigates the seismic performance of self-centering braced frame using a Probabilistic Safety Assessment procedure. Margin of safety, confidence level, and mean annual frequency of the self-centering archetypes for their main limit states, including PT yield, fuse fracture, and global collapse, are established and are compared with their acceptance criteria. Considering incorporating aleatory and epistemic uncertainties, the efficiency of the system is examined. Results of the investigation indicate that the design of low- and mid-rise self-centering archetypes could provide the adequate margin of safety against exceeding the undesirable limit-states.

关键词： self-centering steel braced frame mean annual frequency safety assessment confidence level margin of safety

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针对异构隐式反馈的置信度估计方法 Article

Jing WANG, Lan-fen LIN, Heng ZHANG, Jia-qi TU, Peng-hua YU

《信息与电子工程前沿（英文）》 2017年第18卷第11期页码 1817-1827 doi: 10.1631/FITEE.1601468

摘要：隐式反馈是指用户通过行为间接表达用户的意见。由于其在现实世界中的易得性和丰富性，越来越受到推荐系统领域的关注。使用隐式反馈的常见做法是把隐式反馈当做正面或者负面的用户偏好，并附带不同的置信度。这类方法大多认为，与隐式反馈相关的数值（例如观看的时间）反映了置信度的大小，并且数值越大代表置信度越大。这种假设只适合只有一种隐式反馈的场景。然而在现实世界中，经常同时存在多种隐式反馈，称为异构隐式反馈。现有方法无法有效地从异构隐式反馈中推测出置信度。本文提出了一种新颖的利用异构隐式反馈预测置信度的方法，把预测的置信度应用到“基于点的”和“基于对的”矩阵分解模型中，并提出了一种更通用的方法来为“基于对的”方法选择有效的训练样本。在天猫提供的真实电商数据集上的实验表明，本文方法在多个指标上的效果均要优于现有的方法。

关键词：推荐系统；异构隐式反馈；置信度；协同过滤；电商

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用考虑置信区间长度影响的最小二乘法拟合S-N曲线

杨晓华,金平,姚卫星

《中国工程科学》 2004年第6卷第4期页码 41-43

摘要：

S-N曲线是用名义应力法预测结构疲劳寿命的基础。基于试验疲劳寿命分散的物理机制，提出了一个S-N曲线试验数据处理的加权最小二乘法，此方法中每组数据的权重与该组数据的置信区间成反比。计算结果表明用考虑置信区间长度影响的最小二乘法拟合得到的S-N曲线比用一般最小二乘法得到的S-N曲线具有更高的可靠度，给出的寿命预测结果也更安全。

关键词：置信区间疲劳寿命最小二乘法 S-N曲线

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基于自适应置信度校准的交互式医疗图像分割框架

沈楚云,李文浩,徐琪森,胡斌,金博,蔡海滨,朱凤平,李郁欣,王祥丰

《信息与电子工程前沿（英文）》 2023年第24卷第9期页码 1332-1348 doi: 10.1631/FITEE.2200299

摘要：基于人机交互的医疗图像分割方法是一种新的范式，其通过引入专家交互信息来指导算法完成图像分割任务。然而，现有医疗图像分割模型往往容易产生“交互误解”，即无法合理权衡短期和长期交互信息的重要性。为更好地利用不同时间尺度上的交互信息，本文提出一种基于自适应置信度校准的交互式医疗图像分割框架MECCA，其结合了基于分割决策的置信度学习技术和多智能体强化学习技术，并通过预测分割决策与短期交互信息的对齐水平来学习一个新颖的置信度网络。随后，提出一种基于置信度的奖励塑造机制，在策略梯度计算中引入置信度，从而直接纠正模型产生的交互误解。MECCA还通过标签生成和交互指导来降低交互强度和难度，从而实现用户友好交互。实验结果表明，MECCA在不同分割任务中可以显著提高短期和长期交互信息的利用效率，且仅需较少的标注样本。演示视频可通过https://bit.ly/mecca-demo-video访问。

关键词：医疗图像分割交互式分割多智能体强化学习置信度学习半监督学习

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Simulation of heterogeneous two-phase media using random fields and level sets

George STEFANOU

《结构与土木工程前沿（英文）》 2015年第9卷第2期页码 114-120 doi: 10.1007/s11709-014-0267-5

摘要： The accurate and efficient simulation of random heterogeneous media is important in the framework of modeling and design of complex materials across multiple length scales. It is usually assumed that the morphology of a random microstructure can be described as a non-Gaussian random field that is completely defined by its multivariate distribution. A particular kind of non-Gaussian random fields with great practical importance is that of translation fields resulting from a simple memory-less transformation of an underlying Gaussian field with known second-order statistics. This paper provides a critical examination of existing random field models of heterogeneous two-phase media with emphasis on level-cut random fields which are a special case of translation fields. The case of random level sets, often used to represent the geometry of physical systems, is also examined. Two numerical examples are provided to illustrate the basic features of the different approaches.

关键词： microstructure random fields level sets shape recovery two-phase media

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The effect of sea level rise on beach morphology of caspian sea coast

M. A. Lashteh NESHAEI, F. GHANBARPOUR

《结构与土木工程前沿（英文）》 2017年第11卷第4期页码 369-379 doi: 10.1007/s11709-017-0398-6

摘要： Study of beach morphology has been one of the most important issues in coastal engineering research projects. Because of the existence of two important coastal areas located in the north and south parts of the Iran, in the present study an analysis of the coastal zone behaviour is made. Bed level elevations are measured and compared with the theoretical equilibrium profile. It is shown that the behaviour of the coastal zone in the region is consistent with the Dean (1991) equilibrium profile. In the next stage, following extensive investigations, the bed level changes due to arise in sea level at different locations in the surf zone are estimated. The mechanism of beach re-treatment due to a rise in sea level is considered based on the simplified model of Dean (1991) in which the mass balance of the sediments is taken into account. Comparison of the equilibrium profiles for different cases of sea level rise, clearly shows that because of the sediment transport induced by the fluctuation of the water level, the beach profile in the surf zone changes accordingly resulting in an erosion in the inner region of the surf zone and an accumulation of sediments towards the offshore.

关键词： wave coastal zone beach morphology evolution equilibrium profile sea level rise

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Level set band method: A combination of density-based and level set methods for the topology optimization

Peng WEI, Wenwen WANG, Yang YANG, Michael Yu WANG

《机械工程前沿（英文）》 2020年第15卷第3期页码 390-405 doi: 10.1007/s11465-020-0588-0

摘要： The level set method (LSM), which is transplanted from the computer graphics field, has been successfully introduced into the structural topology optimization field for about two decades, but it still has not been widely applied to practical engineering problems as density-based methods do. One of the reasons is that it acts as a boundary evolution algorithm, which is not as flexible as density-based methods at controlling topology changes. In this study, a level set band method is proposed to overcome this drawback in handling topology changes in the level set framework. This scheme is proposed to improve the continuity of objective and constraint functions by incorporating one parameter, namely, level set band, to seamlessly combine LSM and density-based method to utilize their advantages. The proposed method demonstrates a flexible topology change by applying a certain size of the level set band and can converge to a clear boundary representation methodology. The method is easy to implement for improving existing LSMs and does not require the introduction of penalization or filtering factors that are prone to numerical issues. Several 2D and 3D numerical examples of compliance minimization problems are studied to illustrate the effects of the proposed method.

关键词： level set method topology optimization density-based method level set band

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钢塔节段水平预拼装关键技术研究

张永利,顾碧峰

《中国工程科学》 2010年第12卷第4期页码 48-52

摘要：

通过对泰州长江公路大桥钢塔柱预拼装方案的选择和关键工艺的研究，提出结构形式复杂的钢塔节段预拼装工艺选择原则。在研究了钢塔节段预拼环境的影响、支撑条件、金属接触率等水平预拼装关键工艺控制项点后，成功地解决了泰州桥钢塔节段水平预拼装中的技术难题。钢塔节段水平预拼装填补了我国钢塔制造的技术空白，为后续复杂钢塔节段水平预拼装方案选择提供了有力基础。

关键词：钢塔水平预拼装支撑控制水平力施加

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Two-level uncapacitated lot-sizing problem considering the financing cost of working capital requirement

Yuan BIAN, David LEMOINE, Thomas G. YEUNG, Nathalie BOSTEL

《工程管理前沿（英文）》 2020年第7卷第2期页码 248-258 doi: 10.1007/s42524-019-0069-5

摘要： During financial crisis, companies constantly need free cash flows to efficiently react to any uncertainty, thus ensuring solvency. Working capital requirement (WCR) has been recognized as a key factor for releasing tied up cash in companies. However, in literatures related to lot-sizing problem, WCR has only been studied in the single-level supply chain context. In this paper, we initially adopt WCR model for a multi-level case. A two-level (supplier–customer) model is established on the basis of the classic multi-level lot-sizing model integrated with WCR financing cost. To tackle this problem, we propose sequential and centralized approaches to solve the two-level case with a serial chain structure. The ZIO (Zero Inventory Ordering) property is further confirmed valid in both cases. This property allows us to establish a dynamic programming-based algorithm, which solves the problem in O(T ). Finally, numerical tests show differences in optimal plans obtained by both approaches and the influence of varying delays in payment on the WCR of both actors.

关键词： two-level ULS problem lot-sizing working capital requirement ZIO property infinite production capacity

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Understanding the demand predictability of bike share systems: A station-level analysis

《工程管理前沿（英文）》页码 551-565 doi: 10.1007/s42524-023-0279-8

摘要： Predicting demand for bike share systems (BSSs) is critical for both the management of an existing BSS and the planning for a new BSS. While researchers have mainly focused on improving prediction accuracy and analysing demand-influencing factors, there are few studies examining the inherent randomness of stations’ observed demands and to what degree the demands at individual stations are predictable. Using Divvy bike-share one-year data from Chicago, USA, we measured demand entropy and quantified the station-level predictability. Additionally, to verify that these predictability measures could represent the performance of prediction models, we implemented two commonly used demand prediction models to compare the empirical prediction accuracy with the calculated entropy and predictability. Furthermore, we explored how city- and system-specific temporally-constant features would impact entropy and predictability to inform estimating these measures when historical demand data are unavailable. Our results show that entropy of demands across stations is polarized as some stations exhibit high uncertainty (a low entropy of 0.65) and others have almost no check-out demand uncertainty (a high entropy of around 1.0). We also validated that the entropy and predictability are a priori model-free indicators for prediction error, given a sequence of bike usage demands. Lastly, we identified that key factors contributing to station-level entropy and predictability include per capita income, spatial eccentricity, and the number of parking lots near the station. Findings from this study provide more fundamental understanding of BSS demand prediction, which can help decision makers and system operators anticipate diverse station-level prediction errors from their prediction models both for existing stations and for new ones.

关键词： bike share systems demand prediction prediction errors machine learning entropy

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Conceptual design of compliant mechanisms using level set method

Shi-kui CHEN, Michael Yu WANG

《机械工程前沿（英文）》 2006年第1卷第2期页码 131-145 doi: 10.1007/s11465-006-0018-y

摘要： We propose a level set method-based framework for the conceptual design of compliant mechanisms. In this method, the compliant mechanism design problem is recast as an infinite dimensional optimization problem, where the design variable is the geometric shape of the compliant mechanism and the goal is to find a suitable shape in the admissible design space so that the objective functional can reach a minimum. The geometric shape of the compliant mechanism is represented as the zero level set of a one-higher dimensional level set function, and the dynamic variations of the shape are governed by the Hamilton-Jacobi partial differential equation. The application of level set methods endows the optimization process with the particular quality that topological changes of the boundary, such as merging or splitting, can be handled in a natural fashion. By making a connection between the velocity field in the Hamilton-Jacobi partial differential equation with the shape gradient of the objective functional, we go further to transform the optimization problem into that of finding a steady-state solution of the partial differential equation. Besides the above-mentioned methodological issues, some numerical examples together with prototypes are presented to validate the performance of the method.

关键词： splitting minimum dimensional optimization Hamilton-Jacobi topological

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System engineering for water pollution control at the watershed level in China

Wei MENG,

《环境科学与工程前沿（英文）》 2009年第3卷第4期页码 443-452 doi: 10.1007/s11783-009-0037-0

摘要： The present water pollution situation at watershed level in China has been systematically analyzed. The causes of water pollution are attributed to the extensive economic developmental pattern, poor wastewater treatment, and a lack of nonpoint pollution control. The problems of water pollution control at watershed level include a lack of thought and approach, developmental delay in the environmental standard system, an inadequate monitoring ability, and an inefficient implementation of laws and regulations. From 2006 to 2020, water pollution control and governance will be a national key specific project of science and technology in China. The strategies of this project include establishing a water pollution control system at watershed level, orienting a healthy aquatic ecosystem, conducting risk management, and using comprehensive methods. The goal is to establish and complete a technological system of pollution control and management in three five-year phases. The main tasks are to develop common technologies, management systems, and mechanisms for lake eutrophication control, river pollution control, urban water environmental pollution control, potable water safety, and water environmental management. The bottlenecks of water pollution control and management in China could be systematically removed, and the demonstration of the system engineering approach will be conducted at selected key watersheds.

关键词： water pollution control watershed system engineering sustainability integrated watershed management key specific project of science and technology

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Analysis of inventory level under procurement constraints in supply chain

CHANG Guangshu

《机械工程前沿（英文）》 2007年第2卷第3期页码 361-363 doi: 10.1007/s11465-007-0063-1

摘要： Because the inventory is one of the major factors that affect the performance of the supply chain system, efficient reduction of an inventory can effectively reduce the cost level of the total supply chain. Therefore, inventory management is an important means to optimize the operation of a supply chain and enhance the competitive advantage. Considering the (, ) policy in an inventory management, this paper establishes a model of the inventory level. Then, the change of the inventory level with and without the procurement constraints is analyzed, and their expectation and variance calculated. Consequently, the order point can be determined accurately to reduce the inventory level and the operation risk.

关键词： supply efficient reduction system expectation procurement

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Effect of fly ash replacement level on the fracture behavior of concrete

Mahdi AREZOUMANDI, Jeffery S. VOLZ

《结构与土木工程前沿（英文）》 2013年第7卷第4期页码 411-418 doi: 10.1007/s11709-013-0228-4

摘要： The production of portland cement–the key ingredient in concrete–generates a significant amount of carbon dioxide. However, due to its incredible versatility, availability, and relatively low cost, concrete is the most consumed manmade material on the planet. One method of reducing concrete’s contribution to greenhouse gas emissions is the use of fly ash to replace a significant amount of the cement. ?This study presents the results of an experimental investigation that evaluates effect of fly ash replacement level on the fracture energy of concrete. This study includes four mixes with 0%, 30%, 50%, and 70% fly ash as a cement replacement. This experimental program consisted of 32 fracture beams to study the fracture behavior of concrete. The experimental fracture energies were compared with the fracture energy provisions of different design codes and also different analytical equations. Furthermore, statistical data analyses (parametric and non-parametric) were performed to evaluate whether or not there is any statistically significant difference between the experimental fracture energies of different mixes. Results of these statistical tests show that the mix with higher level of fly ash replacement level has higher fracture energy.

关键词： concrete fracture energy fly ash