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Acta Mechanica Sinica 2010年第4期26卷 509-520页

作者： yan-Lai Zhang mao Sun Ministry-of-Education Key Laboratory of Fluid Mechanics Institute of Fluid Mechanics Beihang University 100191 Beijing China

In the present paper, the longitudinal dynamic flight stability properties of two model insects are predicted by an approximate theory and computed by numerical sim- ulation. The theory is based on the averaged model （which assumes that the frequency of wingbeat is sufficiently higher than that of the body motion, so that the flapping wings＇ degrees of freedom relative to the body can be dropped and the wings can be replaced by wingbeat-cycle-average forces and moments）; the simulation solves the complete equations of motion coupled with the Navier-Stokes equations. Comparison between the theory and the simulation provides a test to the validity of the assumptions in the theory. One of the insects is a model dronefly which has relatively high wingbeat frequency （164 Hz） and the other is a model hawkmoth which has relatively low wingbeat frequency （26 Hz）. The results show that the averaged model is valid for the hawkmoth as well as for the dronefly. Since the wingbeat frequency of the hawkmoth is relatively low （the characteristic times of the natural modes of motion of the body divided by wingbeat period are relatively large） compared with many other insects, that the theory based on the averaged model is valid for the hawkmoth means that it could be valid for many insects.

关键词： Insect Hovering Dynamic flight stability Averaged model Equations-of-motion Navier-Stokes simulation

Dimensionless study on outlet flow characteristics of an air-driven booster

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Journal of Zhejiang University-Science A(Applied Physics & Engineering) 2012年第6期13卷 481-490页

作者： yan SHI mao-lin CAI School of Automation Science and Electrical Engineering Beihang UniversityBeijing 100191China

Air-driven boosters are widely used to obtain high-pressure gas. Through analysis of the boosting process of an air-driven booster, the basic mathematical model of working processes can be set up. By selecting the appropriate reference values, the basic mathematical model is transformed to a dimensionless expression. Using MATLAB/Simulink for simulation and studying the booster experimentally, the dimensionless outlet flow characteristics of the booster were obtained and the simulation results agree well with the experimental results. Through analysis, it can be seen that the dimensionless outlet flow of the booster is mainly determined by the dimensionless input pressure of the driving chamber, the dimensionless outlet condition pressure of the booster and the dimensionless area of the piston in the driving chamber. The dimensionless average outlet flow becomes larger with an increasing dimensionless input pressure of the driving chamber, but it becomes smaller with an increase in the dimen- sionless outlet condition pressure of the booster. Especially when the dimensionless outlet condition pressure is approximately 1.4, the dimensionless average outlet flow reaches zero. With an increase in the dimensionless area of the piston in the driving chamber, the dimensionless average outlet flow increases and peaks at approximately 1.89, and after this peak, it starts to decrease. This research can be referred to in the design of air-driven boosters.

关键词： Air-driven booster Outlet flow Pneumatic system Compressed air

Stabilization control of a hovering model insect:lateral motion

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Acta Mechanica Sinica 2011年第5期27卷 823-832页

作者： yan-Lai Zhang mao Sun Ministry-of-Education Key Laboratory of Fluid Mechanics Beihang University 100191 Beijing China

Our previous study shows that the lateral disturbance motion of a model drone fly does not have inherent stability （passive stability）,because of the existence of an unstable divergence *** drone flies are observed to fly *** active control must be applied to stabilize the *** this study,we investigate the lateral stabilization control of the model drone *** method of computational fluid dynamics is used to compute the lateral control derivatives and the techniques of eigenvalue and eigenvector analysis and modal decomposition are used for solving the equations of *** analysis shows that although inherently unstable,the lateral disturbance motion is *** feeding back the state variables （*** translation velocity,yaw rate,roll rate and roll angle,which can be measured by the sensory system of the insect） to produce anti-symmetrical changes in stroke amplitude and/or in angle of attack between the left and right wings,the motion can be stabilized,explaining why the drone flies can fly stably even if the flight is passively unstable.

关键词： Hovering drone fly Lateral motion Flight stability Stabilization control Modal analysis

Modular assembly of Co4-thiacalix[4]arene units and Keggin-type SiW12O40 for visible-light photothermal conversion

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Tungsten 2025年第1期 112-119页

作者： Jia-Hui Li Qing Zhao Dong-Ao mao Kun Zhou Bao-Kuan Chen yan-Feng Bi School of Petrochemical Engineering Liaoning Petrochemical University

The construction of metal-organic coordination clusters（MCCs） using modular secondary building units is an important method for preparing functional *** this study,two new MCCs modularly assembled from Keggin-type {SiW12O40}H4TC4A=p-tert-Butylthiacalix[4]arene(SiW12) units and thiacalixarene-supported Co4-thiacalix[4]arene(Co4-TC4A polynuclear second-building units（PSBUs,H4TC4A=p-tert-Butylthiacalix[4]arene） are *** two MCCs,abbreviated as Co4-SiW12and Co8-SiW12,were structurally characterized by single-crystal X-ray *** Co4-SiW12is a supramolecular structure involving cation-anion interactions between Co4-TC4A PSBUs and ***8-SiW12features "barbell-like" shapes with two Co4-TC4A coordinatively linked to a Keggin-type SiW12unit on opposite via W-O_t-Co *** coordination of Co4-TC4A to SiW12in Co8-SiW12resulted in significantly improved photothermal conversion performances compared with Co4-SiW12and pure SiW12or ***-gap determination and photophysical analysis combined with density functional theory calculations indicated the binding mode between Co4-TC4A PSBUs and SiW12,which considerably influences the way of electron transport and the conversion ability of visible light to heat.

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A computational study of the wing-wing and wing-body interactions of a model insect

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Acta Mechanica Sinica 2009年第4期25卷 421-431页

作者： Xin yu mao Sun Institute of Applied Physics and Computational Mathematics Beihang University 100191 Beijing China Institute of Fluid Mechanics Beihang University 100191 Beijing China

The aerodynamic interaction between the contralateral wings and between the body and wings of a model insect are studied, by using the method of numerically solving the Navier-Stokes equations over moving overset grids, under typical hovering and forward flight conditions. Both the interaction between the contralateral wings and the interaction between the body and wings are very weak, e.g. at hovering, changes in aerodynamic forces of a wing due to the present of the other wing are less than 3% and changes in aerodynamic forces of the wings due to presence of the body are less than 2%. The reason for this is as following. During each down- or up-stroke, a wing produces a vortex ring, which induces a relatively large jet-like flow inside the ring but very small flow outside the ring. The vortex rings of the left and right wings are on the two sides of the body. Thus one wing is outside vortex ring of the other wing and the body is outside the vortex rings of the left and right wings, resulting in the weak interactions.

关键词： Insect Aerodynamics Wing/winginteraction Wing/body interaction

Identification of the active sites and mechanism for partial methane oxidation to methanol over copper-exchanged CHA zeolites

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Science China Chemistry 2020年第6期63卷 850-859页

作者： yu mao P.Hu School of Chemistry and Chemical Engineering The Queen’s University of BelfastBelfastUK

To make methane a suitable energy carrier and transport less costly,it is an urgent and challenging task for us to convert methane to liquid under mild conditions *** this study,we explored partial methane oxidation to methanol by density functional theory(DFT)calculations using a hybrid functional(HSE06)with van der Waals(vdW)*** stabilities of different active sites over SSZ-13 and SAPO-34,two CHA type zeolites,are thoroughly investigated by ab initio molecular dynamics(AIMD)simulations and ab initio thermodynamics *** possible active sites,namely[CuOHCu]2+,[Cu(OH)2Cu]2+,[CuOCu]2+and[CuOH]+,are identified ***-to-methanol reaction mechanisms are further studied upon these most stable active sites,among which[CuOCu]2+and[CuOH]+are proved to be *** migration of species among zeolite pores are also discussed,which accounts for the activity on[CuOH]+*** concept may represent a more complete picture of catalytic reactions over zeolites in general.

关键词： DFT heterogeneous catalysis methane-to-methanol CHA zeolites

Review: Progress in the Preparation of Iron Based Magnetic Nanoparticles for Biomedical Applications

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Journal of Harbin Institute of Technology(New Series) 2019年第2期26卷 1-18页

作者： yu mao yan Li Ning Gu State Key Laboratory of Bioelectronics Jiangsu Key Laboratory for Biomaterials and DevicesSchool of Biological Sciences and Medical EngineeringSoutheast University

With unique physical properties, chemical properties, and biological effects, magnetic nanomaterials are important functional materials in many fields. In the past decades, iron based magnetic nanomaterials have attracted much attention in the biomedicine field due to their superior magnetic properties and great potential in biomedical applications. In particular, magnetic iron oxide nanoparticles(MIONPs) have been playing a crucial role in the biomedicine field because of their diagnostic and therapeutic functions. Meanwhile, MIONPs are benign, low toxic, biocompatible, and biodegradable, so they are the only inorganic magnetic nanomaterials approved by the U.S. Food and Drug Administration(FDA) for clinical use at present. In this review, we mainly introduce the progress in the preparation of iron based magnetic nanomaterials for biomedical applications, including pure iron nanoparticles, iron-based alloy nanoparticles, and MIONPs, with a focus on MIONPs. Also, we summarize the preparation methods of MIONPs and point out the importance of their developments.

关键词： iron based magnetic nanomaterials biomedical applications MIONPs diagnostic and therapeutic functions preparation methods

Correlating Photovoltaic Performance of Dye-Sensitized Solar Cell to the Film Thickness of Titania via Numerical Drift-Diffusion Simulations

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Chinese Journal of Chemical Physics 2016年第6期29卷 735-741,I0002页

作者： yu-dan Wang Zhe Sun Ya-jun Ren yan Zhang mao Liang Song Xue TianjinKeyLaboratoryofOrganicSolarCellsandPhotochemicalConversion SchoolofChemistryChemicalEnEineerinETianjinUniversityofTechnologyTianjin300384China SchoolofElectricEngineering TianjinUniversityofTechnologyTianjin300384China

The thickness of TiO2 film is vital to realize the optimization on photovoltaic performance of dye sensitized solar cells （DSSCs）. Herein, the process of charge separation in DSSCs was simulated by using a drift-diffusion model. This model allows multiple-trapping diffu- sion of photo-generated electrons, as well as the back reaction with the electron acceptors in electrolyte, to be mimicked in both steady and non-steady states. Numerical results on current-voltage characteristics allow power conversion efficiency to be maximized by varying the thickness of TiO2 film. Charge collection efficiency is shown to decrease with film thick- ness, whereas the flux of electron injection benefits from the film thickening. The output of photocurrent is actually impacted by the two factors. Furthermore, recombination rate constant is found to affect the optimized film thickness remarkably. Thicker TiO2 film is suitable to the DSSCs in which back reaction is suppressed sufficiently. On the contrary, the DSSCs with the redox couple showing fast electron interception require thinner film to alleviate the charge loss via recombination. At open circuit, electron density is found to decrease with film thickness, which engenders not only the reduction of photovoltage but also the increase of electron lifetime.

关键词： Dye-sensitized solar cells Titania Film thickness Simulation

Deep Learning Based Channel Estimation in Fog Radio Access Networks

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China Communications 2019年第11期16卷 16-28页

作者： Zhendong mao Shi yan State Key Laboratory of Networking and Switching Technology Beijing University of Posts and Telecommunications

As a promising paradigm of the fifth generation networks,fog radio access network(F-RAN)has attracted lots of attention *** fully utilize the promising gain of F-RANs,the acquisition of accurate channel state information is ***,conventional channel estimation approaches are not suitable in F-RANs due to the large training and feedback *** this paper,we consider the channel estimation in F-RANs with fog access point(F-AP)equipped with massive *** to the computing ability of F-AP and the sparsity of channel matrices in angular domain,Gated Recurrent Unit(GRU),a data-driven based channel estimation is proposed at F-AP to reduce the training and feedback *** GRU-based method can capture the hidden sparsity structure automatically through the network ***,to further improve the channel estimation,a bidirectional GRU based method is proposed,whose target channel structure is decided by previous and subsequent *** compare the performance of our proposed channel estimation with traditional methods(Orthogonal Matching Pursuit(OMP)and Simultaneous OMP(SOMP)).Simulation results show that the proposed approaches have better performance compared with the traditional OMP and SOMP methods.

关键词： fog radio access network(F-RAN) massive MIMO compressive sensing deep learning gated recurrent unit(GRU)

Composite Hierachical Linear Quantile Regression

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Acta Mathematicae Applicatae Sinica 2014年第1期30卷 49-64页

作者： yan-liang CHEN mao-zai TIAN Ke-ming yu Jian-xin PAN Center for Applied Statistics School of StatisticsRenmin University of China School of Business Shihezi University Mathematical Sciences John Crank 209Brunel University School of Mathematics The University of Manchester School of Statistics and Mathematics Yunnan University of Finance and Economics

Multilevel （hierarchical） modeling is a generalization of linear and generalized linear modeling in which regression coefficients are modeled through a model, whose parameters are also estimated from data. Multilevel model fails to fit well typically by the use of the EM algorithm once one of level error variance （like Cauchy distribution） tends to infinity. This paper proposes a composite multilevel to combine the nested structure of multilevel data and the robustness of the composite quantile regression, which greatly improves the efficiency and precision of the estimation. The new approach, which is based on the Gauss-Seidel iteration and takes a full advantage of the composite quantile regression and multilevel models, still works well when the error variance tends to infinity, We show that even the error distribution is normal, the MSE of the estimation of composite multilevel quantile regression models nearly equals to mean regression. When the error distribution is not normal, our method still enjoys great advantages in terms of estimation efficiency.

关键词： multilevel model composite quantile regression E-CQ algorithm, fixed effects, random effects