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1 – 10 of over 15000Zhiyun Zou, Yao Xiao and Jianzhi Gao
The purpose of this paper is to attempt to realize the optimization of cascading failure process of urban transit network based on Load‐Capacity model, for better evaluating and…
Abstract
Purpose
The purpose of this paper is to attempt to realize the optimization of cascading failure process of urban transit network based on Load‐Capacity model, for better evaluating and improving the operation of transit network.
Design/methodology/approach
Robustness is an essential index of stability performance for urban transit systems. In this paper, firstly, the static robustness of transit networks is analyzed based on the complex networks theory. Aiming at random and intentional attack, a concrete algorithm process is proposed on the basis of Dijstra algorithm. Then, the dynamic robustness of the networks, namely cascading failure, is analyzed, and the algorithm process is presented based on the Load‐Capacity model. Finally, the space‐of‐stations is adopted to build the network topology of Foshan transit network, and then the simulation analyses of static and dynamic robustness are realized.
Findings
Results show that transit network is robust to random attack when considering static robustness, but somewhat vulnerable to intentional attack. For dynamic robustness analysis, a large‐scale cascade of transit network may be triggered when the tolerance parameter α is less than a value, so that the robustness of transit network can be improved through some reasonable measures.
Practice implications
The results of this study provide useful information for urban transit network robustness optimization.
Originality/value
An effective method for analyzing the static and dynamic robustness of transit network is provided in this paper.
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Mingwei Sun, Zenghui Wang and Zengqiang Chen
– This paper aims to present a fast, economical and practical attitude control design approach for flight vehicles operating within wide envelopes.
Abstract
Purpose
This paper aims to present a fast, economical and practical attitude control design approach for flight vehicles operating within wide envelopes.
Design/methodology/approach
Based on a linear disturbance observer, an enhanced proportional-derivative (PD) control scheme is proposed. Utilizing the data from the onboard gyro, the observer can treat the entire response of the system, with the exception of the control term, as a disturbance, and use the estimation of the disturbance to cancel out this response and thereby to effectively simplify the control channel. Using the stability margin tester, the explicit graphical tuning rules are given in a consistent way for the longitudinal dynamics based on the induction method. Mathematical simulations are performed for a highly maneuverable flight vehicle to test the proposed method, which are compared with the traditional PD and H8 control algorithms.
Findings
The proposed strategy for attitude control can be reformulated as a static-dynamic control algorithm and the robust synthesis method can be employed to determine the control parameters according to a specific performance configuration. The remarkable control performance robustness can be achieved as shown in the comparative simulations.
Practical implications
There is a sole parameter, steady gain, needed to be scheduled and it can be estimated with a high accuracy.
Originality/value
This paper applies the linear active disturbance rejection control scheme to flight control scenario. The proposed method can reduce the design and implementation complexity of attitude control for flight vehicles operating within a wide envelope, which originates from diverse time-varying flight dynamics. The new method converts the attitude control problem to a sole parameter gain scheduling problem, and there is no complicated and time-consuming multi-dimension interpolation needed for the control parameters.
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A number of studies have examined the role of typical demand supply factors in explaining inflation. The contribution in this chapter is to investigate the possible role of…
Abstract
A number of studies have examined the role of typical demand supply factors in explaining inflation. The contribution in this chapter is to investigate the possible role of product market imperfections on inflation and inflation persistence, especially among emerging market economies. Using a backward-looking Phillips curve framework in a dynamic panel framework of 105 countries over the 2008–2011 period, our findings suggest that product market competition, as measured by the World Economic Forum’s measure of goods market imperfections do have a significant impact on inflation persistence. On average, higher competition and efficiency in product markets reduces the inflation persistence effect especially in the MENA region and countries at lower stages of development.
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Nipan Kumar Das Das and Mrinal Buragohain
The power framework has become a vital part in the day-to-day life and exhibits a rapid development in this current era. Due to the fact of huge power utilization, the power…
Abstract
Purpose
The power framework has become a vital part in the day-to-day life and exhibits a rapid development in this current era. Due to the fact of huge power utilization, the power frameworks fall under several power transmission-related concerns. Precisely, frequency deviation has generated a huge impact during power transmission; this in turn highly reduces the power system stability as well as reliability too.
Design/methodology/approach
To boost the system’s efficacy, this study proposes a neoteric closed loop feedback controller in which a control algorithm named correlative-elemental-curvature algorithm is introduced with a constant threshold.
Findings
With the aim of mitigating frequency deviation, a stability analysis technique called Retrofit Lyapunov’s method is deployed in the controller. This would simultaneously reduce the load disturbances along with tie-line synchronization issues faced with the prior controllers. Optimization is carried out with the aid of duelist optimization algorithm, which tunes the controller parameters thereby mitigating the complexities while designing a loop feedback controller power framework.
Originality/value
The efficacy of the proposed work is assessed with the aid of metrics, such as integral absolute error, accuracy and settling time. Thus, the proposed work enhances the system reliability as well as the stability by mitigating the frequency deviation related issues and guarantees reliable power transmission.
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Anas Iftikhar, Imran Ali and Mark Stevenson
This study aims to analyse whether the presence of supply chain complexity (SCC) influences firms to improve their supply chain (SC) resilience and SC robustness capability. This…
Abstract
Purpose
This study aims to analyse whether the presence of supply chain complexity (SCC) influences firms to improve their supply chain (SC) resilience and SC robustness capability. This study also examines an important paradox: whether investing in both exploitation and exploration practices is conflicting or complementary to enabling SC resilience and robustness in the presence of SCC.
Design/methodology/approach
The authors used a survey-based approach to collect 242 useful responses from SC professionals of Pakistani firms, an important emerging economy context. The data were analysed with covariance-based structural equation modelling to statistically validate the model.
Findings
The analysis reveals several key findings: the presence of SCC has a direct, positive influence on SC resilience and SC robustness; while exploitation practices only partially mediate the nexus between SCC and SC resilience, they fully mediate the relationship between SCC and SC robustness; while exploration practices partially mediate the nexus between SCC and SC resilience, they do not mediate the relationship between SCC and SC robustness and SCC has a significant influence on SC resilience and SC robustness sequentially through exploitation and exploration (i.e. one after the other).
Practical implications
These findings help to reconcile the exploitation versus exploration paradox in cultivating SC resilience and SC robustness in the presence of SCC. The findings assist SC managers in determining how to deploy their limited resources most effectively to enhance SC resilience and SC robustness while facing SCC.
Originality/value
The authors devise and empirically validate a unique framework that demonstrates how the presence of SCC works as a stimulus to build SC resilience and SC robustness.
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Rosa Hendijani and Mahdis Norouzi
In recent years, the COVID-19 pandemic has become one of the most impactful disruptions which has imposed high levels of uncertainty on supply chains around the world. Supply…
Abstract
Purpose
In recent years, the COVID-19 pandemic has become one of the most impactful disruptions which has imposed high levels of uncertainty on supply chains around the world. Supply chain integration (SCI) is highly recommended as an underlying mechanism that can facilitate the development of resilience and robustness as two dynamic capabilities. They can in turn positively influence firm performance and success during the disruptive conditions of COVID-19 era. The study aims to examine whether SCI as an enabler of resilience and robustness can improve firm performance during COVID-19 pandemic.
Design/methodology/approach
A theoretical model is developed to elaborate the relationship between SCI dimensions, resilience and robustness and firm’s operational and financial performance during the COVID-19 pandemic. A survey method is then used to empirically examine the model using a sample of 94 companies in the food industry in the province of Tehran, Iran, during the COVID-19 pandemic. This study makes several contributions. It provides a novel theoretical model on the relationship between SCI, resilience and robustness and firm performance and tests this model in a less-studied yet critical context (i.e. Iranian food industry) and during a disruptive era (i.e. COVID-19 pandemic).
Findings
The results support the positive effect of three SCI dimensions of internal, product and process integration on operational and financial performance during corona virus pandemic. Furthermore, internal and process integration have positive effects on resilience. Internal, product and process integration have positive effects on robustness. In addition, resilience mediates the effects of internal and product integration on both operational and financial performance, whereas robustness mediates the effect of internal and product integration on financial performance.
Research limitations/implications
This study was conducted in the Province of Tehran. To test and generalize the results, it is recommended to conduct this study in other places and countries.
Originality/value
These results highlight the importance of SCI dimensions as vital enablers of resilience and robustness and their consequent impact on firm’s performance during the COVID-19 pandemic.
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Qamar Ul Islam, Haidi Ibrahim, Pan Kok Chin, Kevin Lim and Mohd Zaid Abdullah
Many popular simultaneous localization and mapping (SLAM) techniques have low accuracy, especially when localizing environments containing dynamically moving objects since their…
Abstract
Purpose
Many popular simultaneous localization and mapping (SLAM) techniques have low accuracy, especially when localizing environments containing dynamically moving objects since their presence can potentially cause inaccurate data associations. To address this issue, the proposed FADM-SLAM system aims to improve the accuracy of SLAM techniques in environments containing dynamically moving objects. It uses a pipeline of feature-based approaches accompanied by sparse optical flow and multi-view geometry as constraints to achieve this goal.
Design/methodology/approach
FADM-SLAM, which works with monocular, stereo and RGB-D sensors, combines an instance segmentation network incorporating an intelligent motion detection strategy (iM) with an optical flow technique to improve location accuracy. The proposed AS-SLAM system comprises four principal modules, which are the optical flow mask and iM, the ego motion estimation, dynamic point detection and the feature-based extraction framework.
Findings
Experiment results using the publicly available RGBD-Bonn data set indicate that FADM-SLAM outperforms established visual SLAM systems in highly dynamic conditions.
Originality/value
In summary, the first module generates the indication of dynamic objects by using the optical flow and iM with geometric-wise segmentation, which is then used by the second module to compute the starting point of a posture. The third module, meanwhile, first searches for the dynamic feature points in the environment, and second, eliminates them from further processing. An algorithm based on epipolar constraints is implemented to do this. In this way, only the static feature points are retained, which are then fed to the fourth module for extracting important features.
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Yawen Li, Guangming Song, Shuang Hao, Juzheng Mao and Aiguo Song
The prerequisite for most traditional visual simultaneous localization and mapping (V-SLAM) algorithms is that most objects in the environment should be static or in low-speed…
Abstract
Purpose
The prerequisite for most traditional visual simultaneous localization and mapping (V-SLAM) algorithms is that most objects in the environment should be static or in low-speed locomotion. These algorithms rely on geometric information of the environment and restrict the application scenarios with dynamic objects. Semantic segmentation can be used to extract deep features from images to identify dynamic objects in the real world. Therefore, V-SLAM fused with semantic information can reduce the influence from dynamic objects and achieve higher accuracy. This paper aims to present a new semantic stereo V-SLAM method toward outdoor dynamic environments for more accurate pose estimation.
Design/methodology/approach
First, the Deeplabv3+ semantic segmentation model is adopted to recognize semantic information about dynamic objects in the outdoor scenes. Second, an approach that combines prior knowledge to determine the dynamic hierarchy of moveable objects is proposed, which depends on the pixel movement between frames. Finally, a semantic stereo V-SLAM based on ORB-SLAM2 to calculate accurate trajectory in dynamic environments is presented, which selects corresponding feature points on static regions and eliminates useless feature points on dynamic regions.
Findings
The proposed method is successfully verified on the public data set KITTI and ZED2 self-collected data set in the real world. The proposed V-SLAM system can extract the semantic information and track feature points steadily in dynamic environments. Absolute pose error and relative pose error are used to evaluate the feasibility of the proposed method. Experimental results show significant improvements in root mean square error and standard deviation error on both the KITTI data set and an unmanned aerial vehicle. That indicates this method can be effectively applied to outdoor environments.
Originality/value
The main contribution of this study is that a new semantic stereo V-SLAM method is proposed with greater robustness and stability, which reduces the impact of moving objects in dynamic scenes.
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Emmanuel Sawyerr and Christian Harrison
The purpose of this explorative research is to analyse the resilience of the United Kingdom's (UK) healthcare supply chains from a customer’s perspective in the light of the…
Abstract
Purpose
The purpose of this explorative research is to analyse the resilience of the United Kingdom's (UK) healthcare supply chains from a customer’s perspective in the light of the coronavirus pandemic.
Design/methodology/approach
Using the capabilities of preparedness, robustness, recovery and adaptability as the foundational percept for supply chain resilience, 22 healthcare professionals in 17 of the UK's National Health Scheme (NHS) Trusts were interviewed to explore their personal and organisational approaches adopted relative to the provision of eye protection, gloves, gowns, aprons, masks and respirators. The Dynamic Capabilities View is mapped to the resilience capabilities and used to analyse the data from a transformational supply chain research perspective.
Findings
The supply chains were largely unprepared, which was not particularly surprising even though the availability of gloves was significantly better compared to the other personal protective equipment (PPE). Techniques adopted to ensure robustness and recovery revealed the use of unsanctioned methods such as extended use of PPE beyond recommended use, redefinition of guidelines, protocols and procedures by infection control and the use of expired PPE – all of which compromised customer well-being.
Research limitations/implications
As the paper views resilience through the lens of customers, it does not provide the perspectives of the supply chain practitioners as to the reasons for the findings and the challenges within these supply chains.
Practical implications
The compromise of the well-being of healthcare workers due to the vulnerabilities of healthcare supply chains is highlighted to managers and prescriptions for post-disruption adaptability are made.
Originality/value
This paper introduces transformative research to supply chain resilience research by uniquely looking at resilience from the customers' well-being perspective.
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A.V. Thomas and Biswajit Mahanty
This study aims to examine the interrelationship between resilience, robustness and bullwhip effect using an inventory- and order-based production control system being subjected…
Abstract
Purpose
This study aims to examine the interrelationship between resilience, robustness and bullwhip effect using an inventory- and order-based production control system being subjected to operational disruption in the customer demand process.
Design/methodology/approach
Control engineering techniques and simulation are employed for the supply chain dynamics study.
Findings
The results show that resilience and robustness are two conflicting performance characteristics and therefore, a tradeoff can be established between them. It is also observed that improvement in resilience and reduction of bullwhip effect can be achieved simultaneously through a proper selection of control parameters.
Originality/value
The work establishes a relationship between the resilient behavior of a supply chain and bullwhip effect.
Details