The material removal rate and required work- piece surface quality of thin-walled structure milling are greatly limited due to its severe vibration, which is directly associated with the dynamic characteristics of the...The material removal rate and required work- piece surface quality of thin-walled structure milling are greatly limited due to its severe vibration, which is directly associated with the dynamic characteristics of the system. Therefore, the suppression of vibration is an unavoidable problem during milling. A novel partial surface damping method is proposed to modify the mode of the thin walled cantilever plate and to suppress vibration during milling. Based on classical plate theory, the design criterion is analyzed and configuration of the partial surface damper is introduced, in which viscoelastic plate and constraining plate are attached to the surface of the plate to increase the system＇s natural frequency and loss factor. In order to obtain the energy expression of the cutting system, the Ritz method is used to describe the unknown displacements. Then, with Lagrange＇s equation, the natural frequency and loss factor are calculated. In addition, the plate is divided into a finite number of square elements, and the regulation of treated position is studied based on theoretic and experimental analysis. The milling tests are conducted to verify its damping performance and the experimentalresults show that with treatment of partial surface damper, the deformation of the hare plate is reduced from 0.27 mm to 0.1 mm, while the vibration amplitude of the bare plate is reduced from 0.08 mm to 0.01 mm. The proposed research provides the instruction to design partial surface damper.展开更多
The partial potential energy surface of the I ＋ HI →IH ＋ I reaction involving the translational and vibrational motions has been constructed at the QCISD（ T ）//MP4SDQ level with the pseudo potential method that i...The partial potential energy surface of the I ＋ HI →IH ＋ I reaction involving the translational and vibrational motions has been constructed at the QCISD（ T ）//MP4SDQ level with the pseudo potential method that is helpful to interpreting the scattering resonance states. The lifetimes of the scattering resonance states in the title reaction obtained from the partial potential energy surface are about 90-120 fs, which agrees with the result of high-resolved threshold photodetachment spectroscopy of anion IHI^- measured by Neumark.展开更多
Based on the vibrational potential curves coupled with the minimum energy reaction path, the partial potential energy surface of the reaction I＋HI→IH＋I was constructed at the QCISD（T）//MP4SDQ level with pseudo po...Based on the vibrational potential curves coupled with the minimum energy reaction path, the partial potential energy surface of the reaction I＋HI→IH＋I was constructed at the QCISD（T）//MP4SDQ level with pseudo potential method. And the formation mechanism of the scattering resonance states of this reaction was well interpreted with the partial potential energy surface. The scattering resonance states of this reaction should belong to Feshbach resonance because of the coupling of the vibrational mode and the translational mode. With the one-dimensional square potential well model, the resonance width and lifetime of the I＋HI（v=0）→IH（v＇=0）＋I state-to-state reaction were calculated, which preferably explained the high-resolved threshold photodetachment spectroscopy of the IHI- anion performed by Neumark et al..展开更多
The partial potential energy surface was constructed by ab initio method [QCISD（T）/6- 311＋＋G（2df,2pd）]for F＋CH4→HF＋CH3 reaction system. It not only explained the reaction mechanism brought forward by Diego Tr...The partial potential energy surface was constructed by ab initio method [QCISD（T）/6- 311＋＋G（2df,2pd）]for F＋CH4→HF＋CH3 reaction system. It not only explained the reaction mechanism brought forward by Diego Troya by means of quasiclassical trajectory （QCT） but also successfully validated Kopin Liu＇s experimental phenomena about the existence of the reactive resonance. The lifetime of the scattering resonance state was about 0.07 ps. All these were in agreement with the experiments.展开更多
In this paper,the design of a resonator rectenna,based on metamaterials and capable of harvesting radio-frequency energy at 2.45 GHz to power any low-power devices,is presented.The proposed design uses a simple and in...In this paper,the design of a resonator rectenna,based on metamaterials and capable of harvesting radio-frequency energy at 2.45 GHz to power any low-power devices,is presented.The proposed design uses a simple and inexpensive circuit consisting of a microstrip patch antenna with a mushroom-like electromagnetic band gap(EBG),partially reflective surface(PRS)structure,rectifier circuit,voltage multiplier circuit,and 2.45 GHzWi-Fi module.The mushroom-like EBG sheet was fabricated on an FR4 substrate surrounding the conventional patch antenna to suppress surface waves so as to enhance the antenna performance.Furthermore,the antenna performance was improved more by utilizing the slotted I-shaped structure as a superstrate called a PRS surface.The enhancement occurred via the reflection of the transmitted power.The proposed rectenna achieved a maximum directive gain of 11.62 dBi covering the industrial,scientific,and medical radio band of 2.40–2.48 GHz.A Wi-Fi 4231 access point transmitted signals in the 2.45 GHz band.The rectenna,located 45◦anticlockwise relative to the access point,could achieve a maximum power of 0.53μW.In this study,the rectenna was fully characterized and charged to low-power devices.展开更多
Fabry-Perot(FP)antennas have characteristics of planar structures combined with high gain,and they have been widely used in wireless communications.With the progress of ongoing research,FP antennas have achieved vario...Fabry-Perot(FP)antennas have characteristics of planar structures combined with high gain,and they have been widely used in wireless communications.With the progress of ongoing research,FP antennas have achieved various capabilities,but many of them are still under development,such as lowprofile,wideband,circular polarization,multi-band,low-radar cross section(RCS)and reconfigurable features.This paper discusses the theoretical analysis methods and research progress of FP antennas,and explains the realization methods of different features of FP antennas.In order to indicate different technologies for realizing various capabilities,the key technologies and features of some of the latest designs are described.Finally,the research situation and prospects of FP antennas are summarized to guide their research directions in the future.展开更多
In this article we define a surface finite element method （SFEM） for the numerical solution of parabolic partial differential equations on hypersurfaces F in R^n＋1. The key idea is based on the approximation of F b...In this article we define a surface finite element method （SFEM） for the numerical solution of parabolic partial differential equations on hypersurfaces F in R^n＋1. The key idea is based on the approximation of F by a polyhedral surface Гh consisting of a union of simplices （triangles for n = 2, intervals for n = 1） with vertices on Г. A finite element space of functions is then defined by taking the continuous functions on Гh which are linear affine on each simplex of the polygonal surface. We use surface gradients to define weak forms of elliptic operators and naturally generate weak formulations of elliptic and parabolic equations on Г. Our finite element method is applied to weak forms of the equations. The computation of the mass and element stiffness matrices are simple and straightforward. We give an example of error bounds in the case of semi-discretization in space for a fourth order linear problem. Numerical experiments are described for several linear and nonlinear partial differential equations. In particular the power of the method is demorrstrated by employing it to solve highly nonlinear second and fourth order problems such as surface Allen-Cahn and Cahn-Hilliard equations and surface level set equations for geodesic mean curvature flow.展开更多
A correlation study between the observed surface morphology using high-resolution scanning electron microscopy(HRSEM) and the observed structural imperfections using transmission electron microscopy(TEM) has been cond...A correlation study between the observed surface morphology using high-resolution scanning electron microscopy(HRSEM) and the observed structural imperfections using transmission electron microscopy(TEM) has been conducted for a-plane Ga N. There are three different sized asymmetric surface pits: large pit of 500 nm–2 ?m in side length, medium pit of 50 nm in side length, and small pit with side lengths of less than 5 nm, which originate from incomplete island coalescence, screw dislocation, and partial dislocation(PD), respectively. Both screw dislocation and PD can produce pits on the free surface because they have a perpendicular line tension to the surface, which must remain in balance with the surface tension. The two types of dislocation lead to distinctive pit sizes because the PD has a smaller Burgers vector component along the dislocation line than the pure screw dislocation. A pit that is produced in the island-coalescing process is much larger than those caused by dislocations because island coalescence is a kinetic process that involves large-scale mass transportation, whereas the dislocation mediates the surface in the local area. These three types of surface pits sometimes interact with one another in space. The coalescence of the island determines the surface morphology at large scales, whereas the defects affect the details.展开更多
Imbalance arises when the Roe＇s method is directly applied in the shallow water simulation.The reasons are different for the continuity equation and the momentum equations.Based on the Roe＇s method,a partial surface...Imbalance arises when the Roe＇s method is directly applied in the shallow water simulation.The reasons are different for the continuity equation and the momentum equations.Based on the Roe＇s method,a partial surface method is proposed for a perfect balance for the continuity equation.In order to generate a mathematically hyperbolic formulation,the momentum equations are split,which causes incompatibility in the calculation of the momentum equations.In this article a numerical approach named the Slop Flux Method（SFM）is proposed to balance the source terms and the flux gradient based on the finite volume method.The method is first applied to shallow water equations.The model is verified by analytical results of classical test cases with good agreement.Finally the method is applied to a steady flow simulation over a practical complicated topography and the result shows good balance and conservation.展开更多
One of the biggest obstacles to the application of orbital angular momentum(OAM)in the microwave field is its divergence problem.This paper presents a full analysis of generating and focusing OAM waves using original ...One of the biggest obstacles to the application of orbital angular momentum(OAM)in the microwave field is its divergence problem.This paper presents a full analysis of generating and focusing OAM waves using original and improved Fabry-Perot(F-P)cavities.Utilizing combination of microstrip antenna and original F-P cavity,the gain of the OAM antenna is enhanced from 4.0 dBi to 9.3 dBi and the corresponding divergence angle is decreased from 41to 24.To further improve the performance of the OAM antenna,the improved F-P cavity is introduced.The simulated results show that the gain is further enhanced to 12.0 dBi and the divergence angle is further decreased to be 15.展开更多
We introduce a dual-polarized(DP)Fabry–Perot cavity(FPC)antenna operating at the millimeter-wave(mmWave)frequency band with high-gain and wideband characteristics.A DP feeding source and a partially reflective surfac...We introduce a dual-polarized(DP)Fabry–Perot cavity(FPC)antenna operating at the millimeter-wave(mmWave)frequency band with high-gain and wideband characteristics.A DP feeding source and a partially reflective surface(PRS)integrated with a Fresnel zone lens are suggested to realize dual-polarization wave radiation over a wide impedance bandwidth.The feeding source provides vertical and horizontal polarizations while keeping high isolation between the two polarizations.PRS is used to realize Fabry cavity to produce a directive beam radiation.The integrated Fresnel zone rings are introduced for phase correction,leading to a significant gain enhancement for the antenna.For verification,a 60-GHz FPC antenna prototype with DP radiation is designed and fabricated with measurement results.It consists of a feeding source,a PRS integrated with a Fresnel zone lens,a quasi-curved reflector,and four three-dimensional printed supporters.The results illustrate that the peak gains of vertical and horizontal polarizations are 18.4 and 17.6 dBi,respectively.The impedance matching bandwidth for the two polarizations is 14%.The performance ensures that the proposed DP FPC antenna is a promising candidate for the fifth-generation wireless communication systems in the mmWave band.展开更多
基金Supported by National Natural Science Foundation of China(Grant No.51575319)Young Scholars Program of Shandong University(Grant No.2015WLJH31)+1 种基金Major National Science and Technology Project of China(Grant No.2014ZX04012-014)Tai Shan Scholar Foundation,China(Grant No.TS20130922)
文摘The material removal rate and required work- piece surface quality of thin-walled structure milling are greatly limited due to its severe vibration, which is directly associated with the dynamic characteristics of the system. Therefore, the suppression of vibration is an unavoidable problem during milling. A novel partial surface damping method is proposed to modify the mode of the thin walled cantilever plate and to suppress vibration during milling. Based on classical plate theory, the design criterion is analyzed and configuration of the partial surface damper is introduced, in which viscoelastic plate and constraining plate are attached to the surface of the plate to increase the system＇s natural frequency and loss factor. In order to obtain the energy expression of the cutting system, the Ritz method is used to describe the unknown displacements. Then, with Lagrange＇s equation, the natural frequency and loss factor are calculated. In addition, the plate is divided into a finite number of square elements, and the regulation of treated position is studied based on theoretic and experimental analysis. The milling tests are conducted to verify its damping performance and the experimentalresults show that with treatment of partial surface damper, the deformation of the hare plate is reduced from 0.27 mm to 0.1 mm, while the vibration amplitude of the bare plate is reduced from 0.08 mm to 0.01 mm. The proposed research provides the instruction to design partial surface damper.
基金Supported by the National Natural Science Foundation of China(No. 20173032) Ph. D. Special Research Foundation ofMinistry of Education of China(No. 20020422027).
文摘The partial potential energy surface of the I ＋ HI →IH ＋ I reaction involving the translational and vibrational motions has been constructed at the QCISD（ T ）//MP4SDQ level with the pseudo potential method that is helpful to interpreting the scattering resonance states. The lifetimes of the scattering resonance states in the title reaction obtained from the partial potential energy surface are about 90-120 fs, which agrees with the result of high-resolved threshold photodetachment spectroscopy of anion IHI^- measured by Neumark.
基金Ⅴ. ACKN0WLEDGMENTS This work was supported by the National Natural Science Foundation of China （No.20573064） and Ph.D. Special Research Foundation of Chinese Education Department.
文摘Based on the vibrational potential curves coupled with the minimum energy reaction path, the partial potential energy surface of the reaction I＋HI→IH＋I was constructed at the QCISD（T）//MP4SDQ level with pseudo potential method. And the formation mechanism of the scattering resonance states of this reaction was well interpreted with the partial potential energy surface. The scattering resonance states of this reaction should belong to Feshbach resonance because of the coupling of the vibrational mode and the translational mode. With the one-dimensional square potential well model, the resonance width and lifetime of the I＋HI（v=0）→IH（v＇=0）＋I state-to-state reaction were calculated, which preferably explained the high-resolved threshold photodetachment spectroscopy of the IHI- anion performed by Neumark et al..
基金the support of the Grant from the National Natural Science Foundation of China No.20573064 Ph.D.Special Research Foundation of Chinese Education Department.
文摘The partial potential energy surface was constructed by ab initio method [QCISD（T）/6- 311＋＋G（2df,2pd）]for F＋CH4→HF＋CH3 reaction system. It not only explained the reaction mechanism brought forward by Diego Troya by means of quasiclassical trajectory （QCT） but also successfully validated Kopin Liu＇s experimental phenomena about the existence of the reactive resonance. The lifetime of the scattering resonance state was about 0.07 ps. All these were in agreement with the experiments.
基金supported by the Rajamangala University of Technology Thanyaburi research and development fund.
文摘In this paper,the design of a resonator rectenna,based on metamaterials and capable of harvesting radio-frequency energy at 2.45 GHz to power any low-power devices,is presented.The proposed design uses a simple and inexpensive circuit consisting of a microstrip patch antenna with a mushroom-like electromagnetic band gap(EBG),partially reflective surface(PRS)structure,rectifier circuit,voltage multiplier circuit,and 2.45 GHzWi-Fi module.The mushroom-like EBG sheet was fabricated on an FR4 substrate surrounding the conventional patch antenna to suppress surface waves so as to enhance the antenna performance.Furthermore,the antenna performance was improved more by utilizing the slotted I-shaped structure as a superstrate called a PRS surface.The enhancement occurred via the reflection of the transmitted power.The proposed rectenna achieved a maximum directive gain of 11.62 dBi covering the industrial,scientific,and medical radio band of 2.40–2.48 GHz.A Wi-Fi 4231 access point transmitted signals in the 2.45 GHz band.The rectenna,located 45◦anticlockwise relative to the access point,could achieve a maximum power of 0.53μW.In this study,the rectenna was fully characterized and charged to low-power devices.
基金supported by the National Natural Science Foundation of China(61671238,61471368)the Fundamental Research Funds for the Central Universities(NJ20160008,56XAA19052)+2 种基金the Jiangsu Planned Projects for Postdoctoral Research Funds(1601009B)the Equipment Advanced Research Foundation of China(61402090103)the Natural Sciences and Engineering Research Council(NSERC)of Canada.
文摘Fabry-Perot(FP)antennas have characteristics of planar structures combined with high gain,and they have been widely used in wireless communications.With the progress of ongoing research,FP antennas have achieved various capabilities,but many of them are still under development,such as lowprofile,wideband,circular polarization,multi-band,low-radar cross section(RCS)and reconfigurable features.This paper discusses the theoretical analysis methods and research progress of FP antennas,and explains the realization methods of different features of FP antennas.In order to indicate different technologies for realizing various capabilities,the key technologies and features of some of the latest designs are described.Finally,the research situation and prospects of FP antennas are summarized to guide their research directions in the future.
文摘In this article we define a surface finite element method （SFEM） for the numerical solution of parabolic partial differential equations on hypersurfaces F in R^n＋1. The key idea is based on the approximation of F by a polyhedral surface Гh consisting of a union of simplices （triangles for n = 2, intervals for n = 1） with vertices on Г. A finite element space of functions is then defined by taking the continuous functions on Гh which are linear affine on each simplex of the polygonal surface. We use surface gradients to define weak forms of elliptic operators and naturally generate weak formulations of elliptic and parabolic equations on Г. Our finite element method is applied to weak forms of the equations. The computation of the mass and element stiffness matrices are simple and straightforward. We give an example of error bounds in the case of semi-discretization in space for a fourth order linear problem. Numerical experiments are described for several linear and nonlinear partial differential equations. In particular the power of the method is demorrstrated by employing it to solve highly nonlinear second and fourth order problems such as surface Allen-Cahn and Cahn-Hilliard equations and surface level set equations for geodesic mean curvature flow.
基金supported by the National Natural Science Foundation of China(Grant Nos.11204009&61204011)Beijing Municipal Natural Science Foundation(Grant No.4142005)
文摘A correlation study between the observed surface morphology using high-resolution scanning electron microscopy(HRSEM) and the observed structural imperfections using transmission electron microscopy(TEM) has been conducted for a-plane Ga N. There are three different sized asymmetric surface pits: large pit of 500 nm–2 ?m in side length, medium pit of 50 nm in side length, and small pit with side lengths of less than 5 nm, which originate from incomplete island coalescence, screw dislocation, and partial dislocation(PD), respectively. Both screw dislocation and PD can produce pits on the free surface because they have a perpendicular line tension to the surface, which must remain in balance with the surface tension. The two types of dislocation lead to distinctive pit sizes because the PD has a smaller Burgers vector component along the dislocation line than the pure screw dislocation. A pit that is produced in the island-coalescing process is much larger than those caused by dislocations because island coalescence is a kinetic process that involves large-scale mass transportation, whereas the dislocation mediates the surface in the local area. These three types of surface pits sometimes interact with one another in space. The coalescence of the island determines the surface morphology at large scales, whereas the defects affect the details.
基金supported by the National Basic Research and Development Program of China(973Program,Grant No.2011CB409901)the Special Funds for Public Welfare Project(Grant No.200901014)the"12th Five-Year Plan"to Support Science and Technology Project(Grant No.2012BAB02B01)
文摘Imbalance arises when the Roe＇s method is directly applied in the shallow water simulation.The reasons are different for the continuity equation and the momentum equations.Based on the Roe＇s method,a partial surface method is proposed for a perfect balance for the continuity equation.In order to generate a mathematically hyperbolic formulation,the momentum equations are split,which causes incompatibility in the calculation of the momentum equations.In this article a numerical approach named the Slop Flux Method（SFM）is proposed to balance the source terms and the flux gradient based on the finite volume method.The method is first applied to shallow water equations.The model is verified by analytical results of classical test cases with good agreement.Finally the method is applied to a steady flow simulation over a practical complicated topography and the result shows good balance and conservation.
基金This work was supported by the National Natural Science Foundation(Grant Nos.61571298,61671416 and 61571289)the Natural Science Foundation of Shanghai(Grant No.17ZR1414300).
文摘One of the biggest obstacles to the application of orbital angular momentum(OAM)in the microwave field is its divergence problem.This paper presents a full analysis of generating and focusing OAM waves using original and improved Fabry-Perot(F-P)cavities.Utilizing combination of microstrip antenna and original F-P cavity,the gain of the OAM antenna is enhanced from 4.0 dBi to 9.3 dBi and the corresponding divergence angle is decreased from 41to 24.To further improve the performance of the OAM antenna,the improved F-P cavity is introduced.The simulated results show that the gain is further enhanced to 12.0 dBi and the divergence angle is further decreased to be 15.
基金Project supported by the Research Grant Council of the Hong Kong SAR,China(No.CityU11218318)the CityU Strategic Research Grant,China(No.SRG-Fd 7005446)。
文摘We introduce a dual-polarized(DP)Fabry–Perot cavity(FPC)antenna operating at the millimeter-wave(mmWave)frequency band with high-gain and wideband characteristics.A DP feeding source and a partially reflective surface(PRS)integrated with a Fresnel zone lens are suggested to realize dual-polarization wave radiation over a wide impedance bandwidth.The feeding source provides vertical and horizontal polarizations while keeping high isolation between the two polarizations.PRS is used to realize Fabry cavity to produce a directive beam radiation.The integrated Fresnel zone rings are introduced for phase correction,leading to a significant gain enhancement for the antenna.For verification,a 60-GHz FPC antenna prototype with DP radiation is designed and fabricated with measurement results.It consists of a feeding source,a PRS integrated with a Fresnel zone lens,a quasi-curved reflector,and four three-dimensional printed supporters.The results illustrate that the peak gains of vertical and horizontal polarizations are 18.4 and 17.6 dBi,respectively.The impedance matching bandwidth for the two polarizations is 14%.The performance ensures that the proposed DP FPC antenna is a promising candidate for the fifth-generation wireless communication systems in the mmWave band.
