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Low-cost sensorless control of four-switch,brushless DC motor drive with direct back-EmF detection

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Journal of Zhejiang university-Science A(Applied Physics & Engineering) 2009年第2期10卷 201-208页

作者： Abolfazl HALVAEI NIASAR Abolfazl VAHEDI Hassan mOGHBELLI Department of Electrical Engineering Faculty of EngineeringUniversity of Kashan Center of Excellence for Power System Automation and Operation Iran University of Science and Technology Department of Science and mathematics Texas A&M University at Qatar

We propose a position sensorless control scheme for a four-switch,three-phase brushless DC motor drive,based on the zero crossing point detection of phase back-EmF voltages using newly defined error functions(EFs). The commutation in-stants are 30° after detected zero crossing points of the EFs. Developed EFs have greater magnitude rather than phase or line voltages so that the sensorless control can work at a lower speed range. moreover,EFs have smooth transitions around zero voltage level that reduces the commutation errors. EFs are derived from the filtered terminal voltages vao and vbo of two low-pass filters,which are used to eliminate high frequency noises for calculation of the average terminal voltages. The feasibility of the proposed sensorless control is demonstrated by simulation and experimental results.

关键词： Brushless DC motor Four-switch inverter Sensorless control Back-EmF voltage sensing DSP

A deep neural network regressor for phase constitution estimation in the high entropy alloy system Al-Co-Cr-Fe-mn-Nb-Ni

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npj Computational materials 2023年第1期9卷 1661-1674页

作者： G.Vazquez S.Chakravarty R.Gurrola R.Arróyave Department of materials Science and Engineering Texas A&M UniversityCollege Station 77843 TXUSA Department of mechanical Engineering Texas A&M UniversityCollege Station 77843 TXUSA Department of Industrial and Systems Engineering Texas A&M UniversityCollege Station 77843 TXUSA

High Entropy Alloys(HEAs)are composed of more than one principal element and constitute a major paradigm in metals *** HEA space is vast and an exhaustive exploration is ***,a thorough estimation of the phases present in the HEA is of paramount importance for alloy *** Learning presents a feasible and non-expensive method for predicting possible new HEAs on-the-fly.A deep neural network(DNN)model for the elemental system of:mn,Ni,Fe,Al,Cr,Nb,and Co is developed using a dataset generated by high-throughput computational thermodynamic calculations using *** features list used for the neural network is developed based on literature and freely available databases.A feature significance analysis matches the reported HEAs phase constitution trends on elemental properties and further expands it by providing so far-overlooked *** final regressor has a coefficient of determination(r^(2))greater than 0.96 for identifying the most recurrent phases and the functionality is tested by running optimization tasks that simulate those required in alloy *** DNN developed constitutes an example of an emulator that can be used in fast,real-time materials discovery/design tasks.

关键词： alloy neural network

Predicting upslope expansion of sub-alpine forest in the makalu Barun National Park, Eastern Nepal, with a hybrid cartographic model

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Journal of Forestry Research 2018年第1期29卷 129-137页

作者： Parveen Kumar Chhetri Department of Geography Texas A&M UniversityCollege Station

The natural upper boundary of a forest（forest line） in mountain environments is an indicator of climate conditions. An increase in global average temperatures has resulted in an upward advance of the forest line. This advance may result in fragmentation of the alpine ecosystem and a loss of biodiversity. Therefore, it is important to identify potential areas where current forests can advance under scenarios of future climate change. I used expert knowledge and cartographic modeling to create a hybrid cartographic model considering five topographic variables to predict areas where forest line can expand in the *** prediction accuracy of the model is around 82%. The model is able to predict areas above the current forest line that are suitable or unsuitable for future forest *** inclusion of high-resolution satellite imagery and digital elevation models, as well as field-based information into the model can help to improve the model accuracy.

关键词： Climate change Forest line Forest line advance Hybrid cartographic model makalu Barun National Park

Contemporary and Historic Population Structure of Abies spectabilis at Treeline in Barun Valley,Eastern Nepal Himalaya

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Journal of mountain Science 2015年第3期12卷 558-570页

作者： Parveen Kumar CHHETRI David m.CAIRNS Department of Geography Texas A&M UniversityCollege Station

Treeline ecotone dynamics of Abies spectabilis （D. Don） mirb. in the Barun valley, makalu Barun National Park, eastern Nepal Himalaya were studied by establishing seven plots （20 m x variable length） from the foresfline to the tree species limit： three plots on the south- and north-facing slopes each （S1-S3, N1-N3）, and one plot on the east- facing slope （E） in the relatively undisturbed forests. A dendroecological method was used to study treeline advance rate and recruitment pattern. In all the plots, most trees established in the early 20th century, and establishment in the second half of the 20th century was confined to the foresfline area. Treeline position has not advanced substantially in the Barun valley, with 0nly 22 m average elevational shift in the last 13o years, and with average current shifting rate of 14 cm/yr. moreover, no significant relationship was found between tree age and elevation on the south-, north-, and east-facing slopes. The number of seedlings and saplings in near the treeline area was negligible compared to that near the foresfline area. Therefore, A. spectabilis treeline response to the temperature change was slow, despite the increasing temperature trend in the region. Beside the temperature change, factors such as high inter-annual variability in temperature, dense shrub cover, and local topography also play an important role in treeline advance and controlling recruitment pattern above the treeline.

关键词： Climate change Treeline ecotone Treeline advance Recruitment pattern

Performance Prediction of a multi-Stage Wind Tower for Indoor Cooling

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Journal of Thermal Science 2012年第4期21卷 327-335页

作者： Roy J. Issa Byungik Chang Department of Engineering and Computer Science West Texas A&M University Canyon

A theoretical model is developed to establish an indepth understanding of the performance of a three-stage wind tower with a bypass system for indoor cooling in rural dry and hot climates. model simulations are presented for a wide range of ambient conditions that include inlet wind speed, inlet temperature and relative humidity. Simulation results provide an insight into the desirable water flow rates and air-to-water loadings for comfort zone tem-peratures and relative humidity levels at the exit of the wind tower. Simulations show wind towers with variable cross-sections provide an increase in the cooling power for the same inlet wind speed, inlet air temperature and relative humidity when compared to wind towers with a constant cross-section. The study shall lead to a better understanding to designing wind towers that are both environmentally friendly and energy efficient.

关键词： Wind tower Cooling power Cooling effectiveness Relative humidity

CFD Simulation of a container ship in random waves using a coupled level-set and volume of fluid method

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Journal of Hydrodynamics 2023年第2期35卷 222-231页

作者： Hamn-Ching Chen Chia-Rong Chen Zachry Department of Civil and Environmental Engineering Texas A&M UniversityCollege StationTexasUSA

The coupled level-set and volume of fluid(CLSVOF)method is an advanced interface-capturing method that has been extended to handle overset grid ***,artificial uneven interface may be observed across block boundaries of different sizes and *** present an improved inter-grid VOF interpolation and mass correction scheme to address the *** demonstrate the capability of the improved CLSVOF method,it is applied to the simulation of a container ship in pitch and heave motions under both head sea and following sea irregular wave *** simulation proves that the improved CLSVOF method is capable of revealing detailed physics difficult to see with other *** phenomena simulated in our work include the extensive greenwater propagation on the ship deck,the breakup of overtopping waves into small droplets,and the formation and collapse of air pockets in sudden bow and stern slamming which cause strong and highly localized impacts on the ship bow,stern,and rudder.

关键词： Computational fluid dynamics(CFD) couple level-set and volume of fluid(CLSVOF)method random waves overset grid system violent free surface flow bow and stern slamming

Thermoelastic rotating contact of an FGm coating with temperature-dependent and arbitrary varying properties

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Science China(Technological Sciences) 2023年第4期66卷 1038-1049页

作者： ZHOU JiaLin SHEN Fei LIU Jing EL-BORGI Sami KE LiaoLiang Department of mechanics School of Mechanical EngineeringTianjin UniversityTianjin 300350China College of Engineering Huazhong Agricultural UniversityWuhan 430070Chin mechanical Engineering Program Engineering BuildingTexas A&M University at QatarP.O.Box 23874Qatar

This paper investigates the frictional thermoelastic contact of a rigid spherical punch and functionally graded material(FGm)coated half-space with arbitrarily varying material *** material parameters include the elastic modulus,Poisson’s ratio,heat conduction parameter,and thermal expansion *** material parameters of the FGm coating and half-space are assumed to be temperature *** spherical punch is rotated in the FGm-coated half-space at a constant angular *** generated frictional heat is related to the friction coefficient,contact radius,angular velocity,and contact pressure.A theoretical formula for the thermoelastic rotating contact problem is established and solved using the finite element *** main objective of this paper is to investigate the effects of temperature dependence,gradient index,friction coefficient,angular velocity,and gradient form on the surface temperature and stresses.

关键词： rotating punch frictional heat functionally graded materials temperature dependence arbitrary properties

Distributed hybrid optimization for multi-agent systems

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Science China(Technological Sciences) 2022年第8期65卷 1651-1660页

作者： TAN XueGang YUAN Yang HE WangLi CAO JinDe HUANG TingWen School of mathematics Southeast UniversityNanjing 210096China Key Laboratory of Smart manufacturing in Energy Chemical Process Ministry of EducationEast China University of Science and TechnologyShanghai 200237China Department of Science Texas A&M University at QatarDoha 23874Qatar

This paper addresses the distributed optimization problems of multi-agent systems using a distributed hybrid impulsive *** objective is to ensure the agents achieve the state consensus and optimize the aggregate objective functions assigned for each agent with distributed manner. We establish two criteria related to the optimality condition and the impulsive gain upper estimation, and propose a distributed hybrid impulsive optimal protocol, which includes two terms: the local averaging term in the continuous interval and the term involving the gradient information at impulsive instants. The simulation results show that the optimal consensus can be realized under the distributed hybrid impulsive optimization algorithm.

关键词： multi-agent systems hybrid impulsive strategy optimal consensus distributed optimization

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Sudden enhancement of sedimentation flux of^(210)Pb_(ex) as anindicator of lake productivity as exemplified by Lake Chenghai

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Science China Earth Sciences 2005年第4期48卷 484-495页

作者： P. H. Santschi Department of marine Sciences Texas A&M University Galveston Texas 77551 USA

The fundamental assumption of 210Pbsediment dating is the stable flux of 210Pbse, which was derived from atmosphere and then transferred into sediments via lake water. When the sedimentation rate is relatively constant, the 210Pbse activity in sediments will be exponentially reduced with sedimentation age. 210Pbse in lake water is incorporated into sediments mainly via organic particulates. If the sedimentation flux of organic matter in lake water is suddenly in- creased, 210Pbse will be significantly deposited and then transferred into sediments. On the one hand such sudden purification effect is obviously unfit for the fundamental assumption of 210Pbse dating; on the other hand, the sudden enhancement of 210Pbse flux would be indicative of the conspicuous variation of primary productivity of lake water. This problem will be discussed in accordance with the variation trend of 210Pbex in the vertical profile of recent sediments of Lake Chenghai, Yunnan Province. The sediment core was collected from the deep-water area of Lake Chenghai in June 1997. The vertical profile of 137 Cs activity is characterized by a tree-peak pat- tern. This profile gave reliable ages, and also showed the stability of sediment accumulation in the recent ten years. The vertical profile of210Pbse activity displays a specific distribution of peaks, and is similar to the vertical profile of Corg. This phenomenon seems to be related to the mecha- nism of constraining the transfer of 210Pbse into lake sediments. The average atomic ratios of Horg/Corg and Corg/Norg in Lake Chenghai sediments are 5.51 and 7.04, respectively, indicating that the organic matter was predominantly derived from the remains of endogenic algae. In terms of the three-stage evolutionary characteristics of organic matter in sediments, i.e., “deposition-de- composition-accumulation”, the sedimentation fluxes （F（Corg）） of organic carbon （Corg） since 1970 were calculated by modeling. The sedimentation fluxes of 210Pbse (F(210P

关键词： sudden purification effect, 210Pbex, primary productivity of lake, Lake Chenghai.