Coordination control method to block cascading failure of a renewable generation power system under line dynamic security

The large application of renewable energy generation (REG) has increased the risk of cascading failures in the power system. At the same time REG also provides the possibility of new approaches for the suppression of such failures. However, the capacity and position of the synchronous generator (SG) involved in regulation limit the power regulation speed (PRS) of REG to the overload line which is the main cause of cascading failures, while the PRS of SG is related to the position and shedding power. REG and SGs have difficulty in achieving effective cooperation under constraints of system power balance. Particularly, the dynamic variation of line flow during power regulation causes new problems for the accurate evaluation of line thermal safety under overload. Therefore, a new strategy for quantitatively coordinating shedding power and power regulation to block cascading failures in the dynamic security domain is proposed in this paper. The control capability and dynamic security domain of the overload line are modeled, and the coordination control method based on power regulation is then proposed to minimize shedding power. The algorithm for the optimal control scheme considers the constraints of load capacity, power source capacity and bus PRS. The correctness of the proposed method is verified using case studies.     

Optimizing the Oxygen-Catalytic Performance of Zn–Mn–Co Spinel by Regulating the Bond Competition at Octahedral Sites

By using the more electro-negative Mn³⁺ ion to partially replace Co³⁺ at the octahedral site of spinel ZnCo₂O₄, i.e., forming ternary Zn–Mn–Co spinel oxide, the electrocatalytic oxygen reduction/evolution activity is found to be significantly increased. Considering the physical characterization and theoretical calculations, it demonstrated that the bond competition played a key role in regulating the cobalt valence state and the electrocatalytic activity. The partial replacement of octahedral-site-occupied Co³⁺ by Mn³⁺ can effectively modulate the adjacent Co–O bond and induce the Jahn–Teller effect, thus changing the originally stable crystal structure and optimizing the binding strength between the active center and reaction intermediates. Certainly, the Mn-substituted ZnMn_1.4Co_0.6O₄/NCNTs exhibit higher electrocatalytic oxygen reduction reaction (ORR) activity than that of ZnCo₂O₄/NCNTs and ZnMn₂O₄/NCNTs, supporting that the Co–O bond covalency determines the ORR activity of spinel ZnCo₂O₄. This study offers the competition between adjacent Co–O and Mn–O bonds via the B_Oh–O–B_Oh edge-sharing geometry. The ion substitution at octahedral sites by less electronegative cations can be a new and effective way to improve the electrocatalytic performance of cobalt-based spinel oxides.     

Social-path embedding-based transformer for graduation development prediction

As the education of students attracts more and more attention, the task of graduation development prediction has gradually become a hot topic in academia and industry. The task of graduation development prediction aims to predict the employment category of students in advance via academic achievement data, which can help administrators understand students’ learning status and set up a reasonable learning plan. However, existing research ignores the potential impact of social relationships on students’ graduation development choices. To fully explore social relationships among students, we propose a Social-path Embedding-based Transformer Neural Network (SPE-TNN) for the task of graduation development prediction in this paper. Specifically, SPE-TNN is divided into the Social-path selection layer, the Social-path embedding layer, the Transformer layer, and the Multi-layer projection layer. Firstly, the Social-path selection layer is designed to find social relationships that impact graduation development and embed them into the student’s performance features through the Social-path embedding layer. Secondly, the Transformer layer is adopted to balance the weights of the students’ features. Finally, the Multi-layer projection layer is used to achieve the student graduation development prediction. Experimental results on the real-world datasets show that SPE-TNN outperforms the existing popular approaches.

     

Ferromagnetism and the Optical Properties of Mn-Doped CdSe with the Wurtzite Structure

The geometrical structure of CdSe was optimized by using the ultrasoft pseudopotential method of a total energy plane wave based on density functional theory. The band structure, density of states, and optical properties were calculated and discussed in detail. The Mn-doped CdSe is found to be a half-metallic ferromagnet with 100% carrier spin polarization at the Fermi level. At a Mn concentration of 12.5%, the calculated total energy of the spin-polarized state is 614 meV lower than that of the nonspin-polarized state. The net magnetic moment of 5 μ _B is found per supercell for 12.5% Mn-doped CdSe. The estimated Curie temperature of 748.6 K for Mn-doped CdSe is above room temperature. The ferromagnetic ground state in Mn-doped CdSe can be explained in terms of the p ? d hybridization mechanism. These results suggest that Mn-doped CdSe may present a promising dilute magnetic semiconductor, and may have potential applications in the field of spintronics.     

A Prediction Region‐based Approach to Model Uncertainty for Multi‐response Optimization

Multi‐response optimization methods rely on empirical process models based on the estimates of model parameters that relate response variables to a set of design variables. However, in determining the optimal conditions for the design variables, model uncertainty is typically neglected, resulting in an unstable optimal solution. This paper proposes a new optimization strategy that takes model uncertainty into account via the prediction region for multiple responses. To avoid obtaining an overly conservative design, the location and dispersion performances are constructed based on the best‐case strategy and the worst‐case strategy of expected loss. We reveal that the traditional loss function and the minimax/maximin strategy are both special cases of the proposed approach. An example is illustrated to present the procedure and the effectiveness of the proposed loss function. The results show that the proposed approach can give reasonable results when both the location and dispersion performances are important issues. Copyright © 2015 John Wiley & Sons, Ltd.     

UV Photodetectors Based on BiOCl Nanosheet Arrays: The Effects of Morphologies and Electrode Configurations

A facile chemical bath method is adopted to grow bismuth oxychloride (BiOCl) nanosheet arrays on a piece of Cu foil (denoted as BiOCl‐Cu) and isolated BiOCl nanosheets are collected by ultrasonication. A self‐supporting BiOCl film is obtained by the removal of Cu foil. Photodetectors (PDs) based on these BiOCl materials are assembled and the effects of morphologies and electrode configurations on the photoelectric performance of these PDs are examined. The BiOCl nanosheet PD achieves high responsivities in the spectral range from 250 to 350 nm, while it presents quite a small photocurrent and slow response speed. The BiOCl film PD yields low photocurrents and near‐unity on–off ratios, demonstrating poor photoelectric performance. The photocurrent of the BiOCl‐Cu PD with both electrodes on the BiOCl film is much higher than those of these above‐mentioned PDs, and the response times are fast. Meanwhile, the BiOCl‐Cu PD with separate electrodes on the BiOCl film and Cu foil achieves even higher photocurrents and presents a self‐powering characteristic, depicting the improved photodetecting performances induced by the specific morphology and distinct electrode configuration. These results would promote the applications of BiOCl nanostructures in the photoelectric devices.     

Relationship between fracture parameters from two parameter fracture model and from size effect model

This paper studies the relationship between the two parameter fracture model and the size effect model. An equivalency between two models is first established based on infinitely large size specimens. Based on this equivalency, relationships between material fracture parameters (K _Ic ^s , CTOD_c) and (G _f, c_f) are derived. Using these relationships, values of (K _Ic ^s , CTOD_c) and (G _f, c_f) can be predicted from each other. It is found that the relationship betweenCTOD _c andc _f theoretically depends on both specimen geometry and initial crack length. However this dependency is numerically insignificant, except for tensile plate with a short center notch. The obtained results may explain why both the two parameter fracture model and the size effect model can reasonably predict fracture behavior of quasi-brittle materials.     

Dynamic mix zone: location data sanitizing in assisted environments

Pervasive technology has been widely used in assistive environments and aware homes. The issue of how to preserve the privacy of patients being monitored has been attracting more public concerns. In assistive environments, location data of patients are collected through sensors for behavior patterns analysis, and they can also be shared among researchers for further research for early disease diagnosis. However, location information, even though de-identified, also introduces the risk of privacy leakage. A series of consecutive location samples can be considered as a trajectory of a single person, and this may leak private information if obtained by malicious users. This paper discusses this problem and proposes a location randomization algorithm to protect users’ location privacy. Two privacy metrics according to location privacy are defined and used to evaluate the proposed approach. A method using dynamic mix zones is proposed to confound trajectories of two or more persons.     

基于RFID技术的网络式汽车安防系统的设计

为了降低汽车的失窃率,满足人们对于智能化防盗的需求,设计出了一种融合射频识别技术和全球移动通信网络的汽车安防系统;系统以德州仪器公司的八位车用微控制器STM8AF51AA为控制核心,恩智浦公司的射频读卡芯片MF RC522能迅速识别车主的身份,实现无钥进入和无钥启动功能,热释电红外传感器和振动传感器完成现场监控功能,Simcom公司的GSM模块SIM300DZ实现短信或电话设防和解防,并通过AT命令远程控制汽车的状态;实践表明,与传统的汽车防盗系统相比,系统能唯一识别车主身份,安全性和可靠性提高,实现了智能化防盗和远程控制的统一。     

Diverse community: Demand differentiation in P2P live streaming

Peer-to-Peer (P2P) technology has become an attractive approach for enabling large-scale video streaming applications, but the factor of users’ subjective preferences is not paid enough attention in such networks. As users have various demand on video qualities, we can provide them with video streams at different resolutions without impairing their satisfaction. The adaptive streaming rate technique is a promising method. However, in providing adaptive streaming rate services, P2P live streaming design faces the following challenge: how to provide all users with uninterrupted video with their desired qualities in case that their demand dynamically changes? To shed more light on this problem, we first derive a model and formulate the problem as a resource demand vs supply problem. Then we present a framework to address the challenge via efficient bandwidth allocation and group cooperation. Through comprehensive simulations, we evaluate the effectiveness of the proposed framework, and conclude that it effectively helps existing solutions, such as Partial Participation Scheme (PPS), achieve better performance.