Search results

The purpose of this paper is to present a simple and effective method to search the optimal turn-on and turn-off angles on-line for the control of the switched reluctance motor (SRM). The optimal turn-on and turn-off angles are defined as the ones that can meet torque production requirements with minimum copper loss.

The optimal turn-on and turn-off angles are first defined based on the analysis of the SRM losses and torque production principles. Then the algorithm for optimal angles searching is developed, and the searching parameters are determined through analytical computation. The optimal angles are approached on-line with iterative process. Simulation and experiments are finally performed to verify the proposed method.

The presented method can meet torque production requirements while copper loss is minimized. The optimal turn-on and turn-off angles are generally approached within five phase cycles for most of the SRM operation modes. Furthermore, the SRM drive system using the presented method exhibits good dynamics during starting and sudden load operations.

The presented method is simple, and implementation of it is easy. It is an eligible candidate for industrial applications where energy conversion efficiency is crucial.

The optimal turn-off angle definition that considers both torque production and copper loss minimization is proposed. The turn-on and turn-off angles are searched independently on-line with little SRM geometrical information. The searching steps are derived through analytical computation and qualitative analysis so that both the searching speed and algorithm convergence are balanced.

This study aims to propose an adaptive fractional-order sliding mode controller to solve the problem of train speed tracking control and position interval control under disturbance environment in moving block system, so as to improve the tracking efficiency and collision avoidance performance.

The mathematical model of information interaction between trains is established based on algebraic graph theory, so that the train can obtain the state information of adjacent trains, and then realize the distributed cooperative control of each train. In the controller design, the sliding mode control and fractional calculus are combined to avoid the discontinuous switching phenomenon, so as to suppress the chattering of sliding mode control, and a parameter adaptive law is constructed to approximate the time-varying operating resistance coefficient.

The simulation results show that compared with proportional integral derivative (PID) control and ordinary sliding mode control, the control accuracy of the proposed algorithm in terms of speed is, respectively, improved by 25% and 75%. The error frequency and fluctuation range of the proposed algorithm are reduced in the position error control, the error value tends to 0, and the operation trend tends to be consistent. Therefore, the control method can improve the control accuracy of the system and prove that it has strong immunity.

The algorithm can reduce the influence of external interference in the actual operating environment, realize efficient and stable tracking of trains, and ensure the safety of train control.

The track impedance is one of the most important parameters in designing the track circuit which is widely used in the railway signal control system to detect the presence of a train. This paper aims to calculate the ballastless track impedance by taking account of the influence of reinforcement bars.

This paper proposes a two-step decomposition approach to calculate the ballastless track impedance. The basic idea is evaluating the track impedance without the reinforcement bars by using two-dimensional (2D) finite element method (FEM), and the incremental impedance, because of the reinforcement bar, is calculated by the partial element equivalent circuit (PEEC) method.

The numerical examples show that the proposed approach can guarantee the accuracy and largely reduce the computing time, at least 20 times, compared with the direct three-dimensional (3D) FEM method.

The study provides a fast approach to calculate the ballastless track impedance. However, compared with the 3D FEM method, the results are less accurate because of the approximation and assumption adopted in the method. A future study should pay more attention to improve accuracy of the model.

A fast approach is proposed to calculate the ballastless track impedance taking account of the influence of the reinforcement bars. The computing time can be largely reduced by using the method. With the proposed approach, the influence of insulation of the reinforcement bars on track impedance can be analyzed.

The flammability of epoxy resin is a major disadvantage in applications that require flame resistance. Epoxy monomers and hardeners containing flame-retardant elements are molecularly incorporated in the resin network are expected to exhibit better flame resistance than those borne on an additive approach. In recent years, because of health and environmental regulation, the use of waterborne coatings has received many attentions. However, waterborne epoxy resin curing agent with excellent flame retardancy has been seldom reported. The paper aims to study the preparation of waterborne P-N-containing epoxy resin curing agent and its performances (P-N – phosphorous and nitrogen).

Waterborne P-N-containing epoxy curing agent was prepared in this study using reactive flame retardant 10-(2,5-dihydroxyphenyl)-9,10-dihydro-9-xa-10-phosphaphenanthrene-10-oxide, liquid epoxy resin, triethylenetetramine and butyl glycidyl ether at the mole ratio of 1.0:2.0:2.0:2.0.

The results show that the epoxy thermoset from the prepared P-N-containing curing agent presents good flame retardancy and can pass the V-1 rating, and the cured epoxy thermoset film presents excellent performances such as water resistance, adhesion, impact resistance and pencil hardness. This study provides useful suggestions for the application of the water-borne flame retardancy epoxy resins in coating industry.

Each step of products during the preparation of waterborne P-N-containing epoxy curing agent cannot be accurately tested.

This method for synthesis of waterborne P-N-containing epoxy curing agent is novel and could be used for various applications in epoxy coating industry.

The purpose of this paper is to summarize the latest research of BIM adoption in construction engineering and management (CEM) and propose research directions for future scholarly work. During the recent decade, building information modeling (BIM) has gained increasing applications and research interest in the construction industry. Although there have been review-based studies that summarized BIM-based research in the overall architecture, engineering and construction (AEC) area, there is limited review that evaluates the current stage of BIM-based research specifically in the CEM sub-area.

CEM falls into the scope of AEC. It involves construction-related tasks, activities and processes (e.g. scheduling and cost estimates), issues (e.g. constructability), as well as human factors (e.g. collaboration). This study adopted a holistic literature review approach that incorporates bibliometric search and scientometric analysis. A total of 276 articles related to BIM applied in CEM were selected from Scopus as the literature sample for the scientometric analysis.

Some key CEM research areas (e.g. CEM pedagogy, integrated project delivery, lean and off-site construction) were identified and evaluated. Research trends in these areas were identified, and analyses were carried out with regard to how they could be integrated with BIM. For example, BIM, as a data repository for ACE facilities, has substantial potential to be integrated with a variety of other digital technologies, project delivery methods and innovative construction techniques throughout the whole process of CEM.

As BIM is one of the key technologies and digital platforms to improve the construction productivity and collaboration, it is important for industry practitioners to be updated of the latest movement and progress of the academic research. The industry, academics and governmental authorities should work with joint effort to fill the gap by first recognizing the current needs, limitations and trends of applying BIM in the construction industry. For example, it needs more understanding about how to address technical interoperability issues and how to introduce the integrated design and construction delivery approach for BIM implementation under the UK BIM Level 2/3 framework.

This study contributed to the body of knowledge in BIM by proposing a framework leading to research directions including the differences of BIM effects between design-bid-build and other fast-track project delivery methods; the integration of BIM with off-site construction; and BIM pedagogy in CEM. It also addressed the need to investigate the similarities and differences between academia and industry toward perceiving the movement of BIM in construction field work.

Although voice behavior is important for team performance, scholars have yet to identify its underlying mechanisms and boundary conditions. Using the theory of social information processing (SIP), this study explores how and when team voice influences team performance by considering team learning as a mediator and contingent reward transactional (CRT) leadership as a moderator.

The authors conducted a survey in China using a questionnaire to collect the data. The study sample consisted of 78 leaders and 441 employees nested in 78 teams.

Results showed that team voice was positively related to team performance. The results also proved that the positive relationship between team voice and team performance was mediated by team learning. Additionally, CRT leadership enhanced the effect of team voice on team learning.

First, managers should consider individuals high in voice behavior when selecting team members. Second, leaders need to focus on enhancing the learning process. Third, the authors’ findings suggest that when selecting persons as team leaders, managers should pay additional attention to their leadership style.

The primary contribution of this study is that the research sheds light on the specific team process (i.e. team learning), through which team voice is related to team performance. Moreover, the current study deepens the authors’ understanding of the role of leadership in the voice process by identifying the moderating role of CRT leadership.

The purpose of this paper is to investigate how boundary-spanning search affects sustainable competitive advantage under the conditions that competitors also search and to test the moderating role of knowledge integration capability.

This paper classifies boundary-spanning search into proactive search and responsive search by considering competition and develops a theoretical model in which knowledge integration capability moderates the effects of proactive and responsive searches on sustainable competitive advantage. Empirical analyses were conducted on the data of 245 Chinese advanced manufacturing firms.

The results show that proactive and responsive searches have inverted U-shaped relationships with sustainable competitive advantage. Moreover, the relationships between proactive and responsive searches and sustainable competitive advantage are moderated by knowledge integration capability. Specifically, as knowledge integration capability increases, the inverted U-shaped relationship between proactive search and sustainable competitive advantage becomes flatter, whereas the inverted U-shaped relationship between responsive search and sustainable competitive advantage becomes almost linear.

This paper enriches the research of boundary-spanning search by considering competition and uncovers how boundary-spanning search affects sustainable competitive advantage under the conditions that competitors also search. Furthermore, this paper sheds light on that the effects of proactive and responsive searches on sustainable competitive advantage are even more complex than inverted U-shaped patterns and provides a contingent viewpoint to deeply understand the relationship between boundary-spanning search and sustainable competitive advantage.

The flammability of poly-acrylate (PA) resin is a major disadvantage in applications that require flame resistance. It has been reported that a flame-retardant PA resin could be prepared by covalent incorporate phosphorous containing monomer with vinyl group via free radical polymerization, and the prepared modified PA resin is expected to exhibit better flame resistance than those by an additive approach. However, the phosphorus-containing monomers reported previously are made from expensive or toxic materials, and the production procedure is tedious and under harsh reaction conditions, which are not feasible for industrial application. Therefore, the purpose of this paper is the preparation of flame-retardant PA resin modified by epoxy resin phosphorous acid (EPPA) and the study of its flame retardancy.

EPPA is first prepared by epoxy resin E-51 and phosphorous acid and then used to prepare phosphorous containing PA resin by free radical polymerization. The flame retardancy of the prepared EPPA-modified PA (EPPA-PA) resin is studied.

The results show that EPPA can graft onto the PA polymer chain by free radical polymerization, the flame retardancy of the EPPA-PA resin increases as the EPPA content increasing. The flame retardancy of EPPA-PA resin prepared reaches 27.8% and can pass the V-0 rating in the UL-94 test when EPPA content is 30.0%. SEM and EDS results indicate that phosphorous element in the EPPA-PA resin shows a condensed-phase flame retardant effect.

The grafting degree of EPPA cannot be accurately tested.

It is expected that the large-scale production of this epoxy resin phosphoric acid modified PA resin will enable practical industrial applications.

This method for synthesis of epoxy resin phosphoric acid modified PA resin is newfrangled.

The purpose of this paper is to examine the relationship between price movements of target firms’ stocks and behaviors of local individual, local institutional and foreign investors in trading target firms’ stocks around mergers and acquisitions announcements in Korea.

This study uses event study methodology and cross-sectional regressions for abnormal returns.

Results reveal that the average abnormal return becomes significantly positive three days prior to the announcement date and becomes insignificant after the announcement date. Results also show that local individual investors tend to sell more intensely prior to announcements for target firms with larger wealth effects. In contrast, foreign investors tend to buy target stocks with larger wealth effects more intensely prior to the announcement date, and then they sell them more intensely in the post-announcement period.

This paper provides evidence that foreign investors are able to identify target stocks with large wealth effects prior to the announcement date and they realize short-term profits by selling them following the announcement.

With an increasing number of Chinese private firms establishing primary level CPC Party committees, it is important to study the role of Party organizations in these firms. Using a nationwide survey of private firms in 2006, we empirically study the firm-level CCP committee's effect on workers' benefits and firm performance.

To overcome the potential endogeneity, we employ the regression discontinuity approach by utilizing the following rule from the Constitution of the CCP: Primary party committees should be established in any basic work unit with more than 3 full party members.

Our empirical results show that party committees in private firms have positive and statistically significant effects on many types of workers' benefits, including pension, unemployment insurance and workplace safety.

This paper highlights CCP committees as an important alternative mechanism in coordinating labor relationships in China when formal labor protecting institutions are weak.