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Search Results: 1 - 10 of 8423 matches for " Kun Men "
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Research on the Transient Power Characteristics of the Inverter for Yun-Guang UHVDC  [PDF]
Chengjun Xia, Haiwen Lan, Kun Men, Guokai Liang
Journal of Power and Energy Engineering (JPEE) , 2014, DOI: 10.4236/jpee.2014.29025
Abstract:

During the transient period of large-disturbance of the received power grid, the power features of the inverter are of great important for the security and stability of the system. The research before is defective in that the constant control mode assumption and the rough HVDC simulation model. The paper establishes the PSCAD/EMTDC model for Yun-Guang EHVDC system, and analysis the transient real power and the reactive power of the inverter. With the analysis of logic for control mode, the author also introduces the physical processes of the peak of the reactive power. At last, the paper puts forward several strategies for suppressing the peak of the dynamic reactive power and real power recovery acceleration.

Study on Identification of Inductive-Motors Load Partition Based on Coherence  [PDF]
Chengjun Xia, Yun Zhou, Kun Men, Yinggeng Xie
Journal of Power and Energy Engineering (JPEE) , 2014, DOI: 10.4236/jpee.2014.29023
Abstract:

A new inductive motors load equivalence algorithm based on coherence is proposed in this paper. In order to partite motors load rapidly and accurately, fuzzy c-means clustering along with particle swarm optimization (PSO-FCM) algorithm is proposed to identify coherent motors base on its physical essence of fuzziness. The merits of PSO algorithm are independent to initial value and convergent to optimum value rapidly, and the validity function is constructed to assess clustering validity. The test on IEEE 39-Bus System is presented to evaluate the effectiveness of the new algorithm, the membership matrix definite not only coherence group of motors but also correlation value of coherence between motors. The algorithm can be used to partite motor load based on coherency in dynamic equivalence with power system operating on different modes.

Analysis of Commutation Failure in Multi-Infeed HVDC System under Different Load Models  [PDF]
Chengjun Xia, Zhongchao Yang, Kun Men, Yong Zhao
Journal of Power and Energy Engineering (JPEE) , 2014, DOI: 10.4236/jpee.2014.29022
Abstract:

HVDC technology has been widely used in modern power system. On one hand, HVDC has the advantages of economy, high efficiency and strong controllability. While on the other hand, it makes the dynamic characteristics of the power system becoming more and more complex. That puts forward a new challenge to system stability and raises new questions for power system simulation. This paper focuses on the interaction between AC and DC systems, especially the problem of commutation failure caused by AC system fault. Based on the data of China Southern Power Grid, this paper calculates the fault regions that may cause commutation failure and calculates the system critical clearance time under different load models, analyzes the impacts of different load models on commutation failure and the stability of AC/DC hybrid system.

The Analysis of the Differences between Electromechanical Transients Simulation and Electromagnetic Transients Simulation  [PDF]
Chengjun Xia, Haoyu Huang, Kun Men, Cuiqiong Chen
Journal of Power and Energy Engineering (JPEE) , 2014, DOI: 10.4236/jpee.2014.29020
Abstract:

The paper firstly interprets the differences between electromechanical transients program BPA and electromagnetic transients program EMTDC in the field of principle, model and algorithm. Then the authors carry out the simulation based on single-machine infinite-bus system and draw some conclusions. The time consumption of the simulation using EMTDC is much longer than the simulation using BPA under the same length of time. The results of BPA are close to those of EMTDC under steady conditions. The fundamental frequency component of the EMTDC results seems closer to the BPA results than its original value, but they still away from completely consistent. In this simulation of single-machine infinite-bus system, the transient stability results of BPA and EMTDC are close, but the results of BPA are apt to be more conservative. All the conclusions above have a certain reference value to both hybrid simulation and comprehensive analysis method in the study of the AC/DC digital simulation of large power grid.

A Nonlinear Dynamic Approach Reveals a Long-Term Stroke Effect on Cerebral Blood Flow Regulation at Multiple Time Scales
Kun Hu ,Men-Tzung Lo ,Chung-Kang Peng,Yanhui Liu,Vera Novak
PLOS Computational Biology , 2012, DOI: 10.1371/journal.pcbi.1002601
Abstract: Cerebral autoregulation (CA) is an important vascular control mechanism responsible for relatively stable cerebral blood flow despite changes of systemic blood pressure (BP). Impaired CA may leave brain tissue unprotected against potentially harmful effects of BP fluctuations. It is generally accepted that CA is less effective or even inactive at frequencies >~0.1 Hz. Without any physiological foundation, this concept is based on studies that quantified the coupling between BP and cerebral blood flow velocity (BFV) using transfer function analysis. This traditional analysis assumes stationary oscillations with constant amplitude and period, and may be unreliable or even invalid for analysis of nonstationary BP and BFV signals. In this study we propose a novel computational tool for CA assessment that is based on nonlinear dynamic theory without the assumption of stationary signals. Using this method, we studied BP and BFV recordings collected from 39 patients with chronic ischemic infarctions and 40 age-matched non-stroke subjects during baseline resting conditions. The active CA function in non-stroke subjects was associated with an advanced phase in BFV oscillations compared to BP oscillations at frequencies from ~0.02 to 0.38 Hz. The phase shift was reduced in stroke patients even at > = 6 months after stroke, and the reduction was consistent at all tested frequencies and in both stroke and non-stroke hemispheres. These results provide strong evidence that CA may be active in a much wider frequency region than previously believed and that the altered multiscale CA in different vascular territories following stroke may have important clinical implications for post-stroke recovery. Moreover, the stroke effects on multiscale cerebral blood flow regulation could not be detected by transfer function analysis, suggesting that nonlinear approaches without the assumption of stationarity are more sensitive for the assessment of the coupling of nonstationary physiological signals.
Impaired Cerebral Autoregulation Is Associated with Brain Atrophy and Worse Functional Status in Chronic Ischemic Stroke
Mikio C. Aoi, Kun Hu, Men-Tzung Lo, Magdy Selim, Mette S. Olufsen, Vera Novak
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0046794
Abstract: Dynamic cerebral autoregulation (dCA) is impaired following stroke. However, the relationship between dCA, brain atrophy, and functional outcomes following stroke remains unclear. In this study, we aimed to determine whether impairment of dCA is associated with atrophy in specific regions or globally, thereby affecting daily functions in stroke patients. We performed a retrospective analysis of 33 subjects with chronic infarctions in the middle cerebral artery territory, and 109 age-matched non-stroke subjects. dCA was assessed via the phase relationship between arterial blood pressure and cerebral blood flow velocity. Brain tissue volumes were quantified from MRI. Functional status was assessed by gait speed, instrumental activities of daily living (IADL), modified Rankin Scale, and NIH Stroke Score. Compared to the non-stroke group, stroke subjects showed degraded dCA bilaterally, and showed gray matter atrophy in the frontal, parietal and temporal lobes ipsilateral to infarct. In stroke subjects, better dCA was associated with less temporal lobe gray matter atrophy on the infracted side ( = 0.029), faster gait speed ( = 0.018) and lower IADL score (0.002). Our results indicate that better dynamic cerebral perfusion regulation is associated with less atrophy and better long-term functional status in older adults with chronic ischemic infarctions.
Clinical Microbiology Laboratory in the Control of Healthcare-Associated Infections
Güne? ?enol,Meral Co?kun,Ayriz Gündüz,Can Bi?men
Klimik Journal , 2012,
Abstract: Objective: Clinical Microbiology Laboratory is one of the basic components of an effective infection control program. In this study, the importance of early detection and reporting of clusters by our Hospital Microbiology Laboratory in the prevention of epidemics was emphasized.Methods: Clinical samples obtained by bronchoscopic aspiration in our Hospital Bronchoscopy Unit were investigated prospectively and retrospectively. Bacteriological analysis was performed from the bronchoscope and also the rinse tanks. Antimicrobial effects of disinfectant used in the bronchoscopy unit were tested.Results: Although microscopic findings were not compatible, Pseudomonas aeruginosa isolates with the same phenotypic characteristics and antibiotic susceptibility patterns were reported from the Microbiology Laboratory P. aeruginosa was yielded in 37 clinical samples by the Infection Control Team. Contamination or colonization was detected in 34 cases, but infection findings were identified in 3 patients. Identical P. aeruginosa strains were yielded in both rinse water samples and bronchoscopic samples. As a result of investigations, low disinfectant activity and technical failure in one of the bronchoscopes were detected. Contamination was ended by changing disinfectant and bronchoscope. Conclusion: Early reporting of the clusters of microorganisms by Microbiology Laboratory resulted in prevention of a possible outbreak of P. aeruginosa.
Sarcoidosis of the Breast
Hayrettin G??MEN,Funda CO?KUN,?aduman BALABAN ADIM,Esra UZASLAN
Trakya Universitesi Tip Fakultesi Dergisi , 2009,
Abstract: Sarcoidosis is a granulomatous disease which might affect many systems. Less than 1% of the cases suffer breast involvement. There are about 33 cases involving breast in the literature. In many cases, systemic symptoms mask breast involvement of sarcoidosis, that was generally recognized in result of surgical operation for malignancy. Breast and skin involvement together is rather rare in sarcoidosis. A 49-yearold female patient with mediastinoscopic diagnosis of sarcoidosis has been followed since 1999. Patient was treated with systemic corticosteroid twice due to skin involvement of sarcoidosis in 2002 and 2004. In 2006 macronodular lesions were found in both of her breast. Nodule excision and reduction mammoplasty were performed with pathological result of noncaseous granulomatous sarcoid inflammation. Patient was admitted as pulmonary sarcoidosis stage II with skin and breast involvement. Since lung, breast and skin involvement together is very rare in sarcoidosis we presented this case.
Multimodal Pressure-Flow Analysis: Application of Hilbert Huang Transform in Cerebral Blood Flow Regulation
Men-Tzung Lo,Kun Hu,Yanhui Liu,C.-K. Peng
EURASIP Journal on Advances in Signal Processing , 2008, DOI: 10.1155/2008/785243
Abstract: Quantification of nonlinear interactions between two nonstationary signals presents a computational challenge in different research fields, especially for assessments of physiological systems. Traditional approaches that are based on theories of stationary signals cannot resolve nonstationarity-related issues and, thus, cannot reliably assess nonlinear interactions in physiological systems. In this review we discuss a new technique called multimodal pressure flow (MMPF) method that utilizes Hilbert-Huang transformation to quantify interaction between nonstationary cerebral blood flow velocity (BFV) and blood pressure (BP) for the assessment of dynamic cerebral autoregulation (CA). CA is an important mechanism responsible for controlling cerebral blood flow in responses to fluctuations in systemic BP within a few heart-beats. The MMPF analysis decomposes BP and BFV signals into multiple empirical modes adaptively so that the fluctuations caused by a specific physiologic process can be represented in a corresponding empirical mode. Using this technique, we showed that dynamic CA can be characterized by specific phase delays between the decomposed BP and BFV oscillations, and that the phase shifts are significantly reduced in hypertensive, diabetics and stroke subjects with impaired CA. Additionally, the new technique can reliably assess CA using both induced BP/BFV oscillations during clinical tests and spontaneous BP/BFV fluctuations during resting conditions.
Application of LINGO in Water Resources Optimization Teaching Based on Integer Programming  [PDF]
Baohui Men, Shiyang Yin
Creative Education (CE) , 2018, DOI: 10.4236/ce.2018.915190
Abstract: Objective: To improve the teaching quality of water resources optimization teaching and train students to master advanced and quick methods or techniques to solve the problems of integer programming of engineering projects. Method: This paper introduces LINGO software to solve integer programming problems in integer programming teaching, and explains the entire process with the example. Results: Through the construction of the example model and the use of LINGO software, it shows that: the LINGO software programming language is clear; the solution to the programming problem is simple; the solution speed is fast; and the accuracy is high. Conclusion: LINGO software can solve complex integer programming models more easily and quickly. It has a wide range of applications and has a strong application value.
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