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( Hongtao Zhang ),( Zihua Yang ),( Yunfan Ye ) 한국인터넷정보학회 2016 KSII Transactions on Internet and Information Syst Vol.10 No.11
Femtocells are envisioned as a key solution to embrace the ever-increasing high data rate and thus are extensively deployed. However, the dense and random deployments of femtocell access points (FAPs) induce severe intercell inference that in turn may degrade the performance of spectral efficiency. Hence, unrestrained proliferation of FAPs may not acquire a net throughput gain. Besides, given that numerous FAPs deployed in ultra-dense networks (UDNs) lead to significant energy consumption, the amount of FAPs deployed is worthy of more considerations. Nevertheless, little existing works present an analytical result regarding the optimal FAP density for a given User Equipment (UE) density. This paper explores the realistic scenario of randomly distributed FAPs in UDN and derives the coverage probability via Stochastic Geometry. From the analytical results, coverage probability is strictly increasing as the FAP-to-UE ratio increases, yet the growing rate of coverage probability decreases as the ratio grows. Therefore, we can consider a specific FAP-to-UE ratio as the point where further increasing the ratio is not cost-effective with regards to the requirements of communication systems. To reach the optimal FAP density, we can deploy FAPs in line with peak traffic and randomly switch off FAPs to keep the optimal ratio during off-peak hours. Furthermore, considering the unbalanced nature of traffic demands in the temporal and spatial domain, dynamically and carefully choosing the locations of active FAPs would provide advantages over randomization. Besides, with a huge FAP density in UDN, we have more potential choices for the locations of active FAPs and this adds to the demand for a strategic sleeping policy.
Design and Analysis of a Segmental Rotor Type 12/8 Switched Reluctance Motor
Zhang, Hongtao,Lee, Dong-Hee,Lee, Chee-Woo,Ahn, Jin-Woo The Korean Institute of Power Electronics 2014 JOURNAL OF POWER ELECTRONICS Vol.14 No.5
In this paper, a novel 12/8 segmental rotor type switched reluctance motor (SRM) is proposed for cooling fan applications. Unlike conventional structures, the rotor of the proposed structure is constructed from a series of discrete segments, and the stator is constructed from two types of stator poles: exciting and auxiliary poles. Moreover, in this structure, short flux paths are taken and no flux reversion exists in the stator. While the auxiliary poles are not wound by the windings, which only provide the flux return path. When compared with the conventional SRM, the proposed structure increases the electrical utilization of the machine and decreases the core losses, which may lead to a higher efficiency. To verify the proposed structure, the finite element method (FEM) and Matlab-Simulink are employed to get the static and dynamic characteristics of the proposed SRM. Finally, a prototype of the proposed motor was tested for characteristic comparisons.
Design and Analysis of a Segmental Rotor Type 12/8 Switched Reluctance Motor
Hongtao Zhang,Dong-Hee Lee,Chee-Woo Lee,Jin-Woo Ahn 전력전자학회 2014 JOURNAL OF POWER ELECTRONICS Vol.14 No.5
In this paper, a novel 12/8 segmental rotor type switched reluctance motor (SRM) is proposed for cooling fan applications. Unlike conventional structures, the rotor of the proposed structure is constructed from a series of discrete segments, and the stator is constructed from two types of stator poles: exciting and auxiliary poles. Moreover, in this structure, short flux paths are taken and no flux reversion exists in the stator. While the auxiliary poles are not wound by the windings, which only provide the flux return path. When compared with the conventional SRM, the proposed structure increases the electrical utilization of the machine and decreases the core losses, which may lead to a higher efficiency. To verify the proposed structure, the finite element method (FEM) and Matlab-Simulink are employed to get the static and dynamic characteristics of the proposed SRM. Finally, a prototype of the proposed motor was tested for characteristic comparisons.
Zhang, Hongtao Materials Research Society of Korea 2019 한국재료학회지 Vol.29 No.9
The widespread use of automobiles has greatly increased energy demand and exhaust gas pollution. In order to save energy, reduce emissions and protect the environment, making lightweights automobiles is an effective measure. In this paper, carbon fiber composites and automobile B-pillars are briefly introduced, and then the mechanical properties and impact resistance of the DC590 steel B-pillars and carbon fiber composites B-pillars are simulated by the ABAQUS finite element software. The results show that the quality of compound B-pillars is reduced by 50.76 % under the same dimensions, and the mechanical property of unit mass is significantly better than that of metal B-pillars. In the course of a collision, the kinetic energy of the two B-pillars is converted into internal energy, but the total energy remains the same; the converted internal energy of the composite B-pillars is greater, the deformation is smaller and the maximum intrusion and intrusion speed is also smaller, indicating that the anti-collision performance of the composite B-pillars is excellent. In summary, the carbon fiber composites can not only reduce the quality of the B-pillars, but also improve their anti-collision performance.
A Unify Unbalance Compensation Strategy for Islanded Microgrid with Unbalanced Condition
Hongtao Shi,Fang Zhuo,Zhiqing Geng,Dong zhang 전력전자학회 2015 ICPE(ISPE)논문집 Vol.2015 No.6
Due to the unbalance condition, the voltage of microgrid would be deteriorated. In this paper, a unify unbalance compensation strategy is proposed to suppress the unbalanced voltage and the voltage variation for islanded microgrid with unbalanced condition. Comparing to the traditional compensation strategy, where only negative sequence components of voltage are suppressed, in the proposed scheme, the voltage and frequency variations resulted from the unbalanced condition are also eliminated. A simulation model of microgrid is developed in PSIM and the simulation and experimental results verify the effectiveness of the proposed method.
A data-driven approach for real-time prediction of thermal gradient in engineered structures
Hongtao Ban,Yongqiang Zhang,Shizhe Feng 대한기계학회 2022 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.36 No.3
Predicting thermal gradient of engineered structures with uncertain parameters is crucial for the safety. Many numerical computation methods have been developed in literatre;however, a practical approach is still pursued. To bridge this research gap, a data-driven approach is proposed to realize real-time prediction of thermal gradient in engineered structures with uncertain parameters. First, tetrahedral elements are used to build structures with complex geometry, and the face-based smoothed finite element method (FS-FEM) is employed to calculate the thermal response of the structures. By doing so, a good trade-off between the efficiency and accuracy for modelling the structures can be achieved. Then, the generated datasets are used for training a back propagation neural network (BPNN) model, and real-time prediction of thermal gradient in engineered structures can be performed without knowing the exact distribution functions of stochastic parameters. Lastly, two case studies were investigated to evaluate the performance of the proposed approach. The analysis results demonstrate that the proposed data-driven approach is able to offer accurate predictions of the thermal gradient for the engineered structures with uncertain parameters.
( Hongtao Yu ),( Lijun Sun ),( Fuzhi Zhang ) 한국인터넷정보학회 2019 KSII Transactions on Internet and Information Syst Vol.13 No.9
Collaborative filtering recommender systems are vulnerable to shilling attacks in which malicious users may inject biased profiles to promote or demote a particular item being recommended. To tackle this problem, many robust collaborative recommendation methods have been presented. Unfortunately, the robustness of most methods is improved at the expense of prediction accuracy. In this paper, we construct a robust Bayesian probabilistic matrix factorization model for collaborative filtering recommender systems by incorporating the detection of user anomaly rating behaviors. We first detect the anomaly rating behaviors of users by the modified K-means algorithm and target item identification method to generate an indicator matrix of attack users. Then we incorporate the indicator matrix of attack users to construct a robust Bayesian probabilistic matrix factorization model and based on which a robust collaborative recommendation algorithm is devised. The experimental results on the MovieLens and Netflix datasets show that our model can significantly improve the robustness and recommendation accuracy compared with three baseline methods.
Shengbo Zhang,Huan Hu,Hongtao Yu,Yawen Huang,Junxiao Yang 한국고분자학회 2017 Macromolecular Research Vol.25 No.4
Low dielectric materials show great application potential in future microelectronic industry. In this study, benzocyclobutene-functionalized polycarbosilane derived block copolymer, poly(carbosilane-b-lactide), was synthesized via sequential anionic polymerization of silacyclobutene and ring-opening polymerization of lactide. The block copolymer revealed microphase-separation behavior to form a well-defined morphology. Simultaneously, the sacrifice of polylactide blocks by thermal decomposition and thermally-induced reaction of benzocyclobutene produces cross-linked nanoporous polycarbosilane (PBCS). The dielectric constant of this nanoporous material reaches to around 2.1.