A variable magnetization(VM) motor by incorporating magnets that can be flexibly configured with variable magnetization process is proposed to meet the emerging requirements on motor efficiency and actuator compliance...A variable magnetization(VM) motor by incorporating magnets that can be flexibly configured with variable magnetization process is proposed to meet the emerging requirements on motor efficiency and actuator compliance in robotic applications. A generalized spin torque model is established which provides a relationship between the motor torque and two different types of motor inputs, the current inputs and the magnet magnetizations. Avariable magnetization process is proposed based on the study of the hysteresis properties of the magnetic materials and the design criteria for implementing the variable magnetization process with current pulses are established. The feasibility of the variable magnetization is validated with experimental data and the motor functions and performances are numerically demonstrated and evaluated. The results show that the VM motor can maintain high efficiency by switching between two actuation modes. Controllable stiffness at different equilibria can be also achieved with the VM motor with instantaneous magnetizing current pulses.展开更多
A new normalized least mean square(NLMS) adaptive filter is first derived from a cost function, which incorporates the conventional one of the NLMS with a minimum-disturbance(MD)constraint. A variable regularization f...A new normalized least mean square(NLMS) adaptive filter is first derived from a cost function, which incorporates the conventional one of the NLMS with a minimum-disturbance(MD)constraint. A variable regularization factor(RF) is then employed to control the contribution made by the MD constraint in the cost function. Analysis results show that the RF can be taken as a combination of the step size and regularization parameter in the conventional NLMS. This implies that these parameters can be jointly controlled by simply tuning the RF as the proposed algorithm does. It also demonstrates that the RF can accelerate the convergence rate of the proposed algorithm and its optimal value can be obtained by minimizing the squared noise-free posteriori error. A method for automatically determining the value of the RF is also presented, which is free of any prior knowledge of the noise. While simulation results verify the analytical ones, it is also illustrated that the performance of the proposed algorithm is superior to the state-of-art ones in both the steady-state misalignment and the convergence rate. A novel algorithm is proposed to solve some problems. Simulation results show the effectiveness of the proposed algorithm.展开更多
Cluster state is the basic resource for one-way quantum computation and a valuable resource for establishing quantum network, because it has a flexible and varied composition form. We present measurement-device-indepe...Cluster state is the basic resource for one-way quantum computation and a valuable resource for establishing quantum network, because it has a flexible and varied composition form. We present measurement-device-independent quantum secret sharing(QSS) and quantum conference(QC) schemes based on continuous variable(CV) four-mode cluster state with different structures. The users of the protocol prepare their own Einstein-Podolsky-Rosen(EPR) states, respectively. One mode of these EPR states is sent to an untrusted relay where a generalized Bell measurement creates different types of CV cluster states among four users, while the other mode is kept at their own station. We show that a shared secret key for QSS and QC schemes is distilled based on the shared quantum correlation among four users. QC and four users QSS are implemented based on the star shape CV cluster state. QSS with three users are implemented based on the linear or square shape CV cluster states. The results show that the secure transmission distance for an asymmetric network, where the transmission distances between the users and relay are different, is longer than that of a symmetric network, where the transmission distances between the users and relay are the same. The presented schemes provide concrete references for establishing quantum network with the CV cluster state.展开更多
A novel variable C-band radio-frequency (RF) power splitter was designed at Shanghai Institute of Applied Physics, Chinese Academy of Sciences. Using three RF impedance combiners, an H-bend, and an RF polarizer, this ...A novel variable C-band radio-frequency (RF) power splitter was designed at Shanghai Institute of Applied Physics, Chinese Academy of Sciences. Using three RF impedance combiners, an H-bend, and an RF polarizer, this new power splitter is much more compact than a traditionally designed splitter, which comprises three 3-dB hybrids. The parameters were optimized to achieve good matching and minimize reflection. Here, the RF design of the new C-band variable power splitter is presented.展开更多
The oil-return system plays an important role in the variable refrigerant flow (VRP) systems because it ensures the reliable operation of the VRF systems. The oil-gas separator is the most essential component of the o...The oil-return system plays an important role in the variable refrigerant flow (VRP) systems because it ensures the reliable operation of the VRF systems. The oil-gas separator is the most essential component of the oil- return system, and the separation efficiency of the separator directly influences the performance of the VRF systems. Therefore, in this paper, a test rig was built to measure the oil discharge ratio of the compressor and the separation efficiency of the oil-gas separator. A sound velocity transducer was used to measure the oil mass concentration instantaneously, because the sound velocity was changed with the mass ratio of oil to refrigerant. The separation efficiency of the separator could be obtained by comparing the mass fraction of oil to refrigerant before and after the separator was connected to the system.展开更多
This paper presents a two-dimensional unsteady laminar boundary layer mixed convection flow heat and mass transfer along a vertical plate filled with Casson nanofluid located in a porous quiescent medium that contains...This paper presents a two-dimensional unsteady laminar boundary layer mixed convection flow heat and mass transfer along a vertical plate filled with Casson nanofluid located in a porous quiescent medium that contains both nanoparticles and gyrotactic microorganisms. This permeable vertical plate is assumed to be moving in the same direction as the free stream velocity. The flow is subject to a variable heat flux, a zero nanoparticle flux and a constant density of motile microorganisms on the surface. The free stream velocity is time-dependent resulting in a non-similar solution. The transport equations are solved using the bivariate spectral quasilinearization method. A grid independence test for the validity of the result is given. The significance of the inclusion of motile microorganisms to heat transfer processes is discussed. We show, inter alia, that introducing motile microorganisms into the flow reduces the skin friction coefficient and that the random motion of the nanoparticles improves the rate of transfer of the motile microorganisms.展开更多
Accuracy is a key factor in high-resolution remote sensing and photogrammetry. The factors that affect accuracy are imaging system errors and data processing errors. Due to the complexity of aerial camera errors, this...Accuracy is a key factor in high-resolution remote sensing and photogrammetry. The factors that affect accuracy are imaging system errors and data processing errors. Due to the complexity of aerial camera errors, this paper focuses on the design of digital aerial camera systems and the means to reduce system error and data processing inefficiencies. There are many kinds of digital aerial camera systems at present;however, these systems lack a unified physical model, which ultimately leads to more complicated designs and multi-camera modes. Such a system is complex and costly, as it is easily affected by factors such as vibration and temperature. Thus, the installed accuracy can only reach the millimeter level. Here, we describe a unified physical structure for a digital aerial camera that imitates an out-of-field multi-charge-coupled device (CCD), an in-field multi-CCD, and once-imaging and twice-imaging digital camera systems. This model is referred to as the variable baseline-height ratio spatiotemporal model. The variable ratio allows the opto-mechanical spatial parameters to be linked with height accuracy, thus providing a connection to the surface elevation. The twice-imaging digital camera prototype system and the wideband limb imaging spectrometer provide a transformation prototype from the current multi-rigid once-imaging aerial camera to a single rigid structure. Thus, our research lays a theoretical foundation and prototype references for the construction and industrialization of digital aerial systems.展开更多
Monitoring high-dimensional multistage processes becomes crucial to ensure the quality of the final product in modern industry environments. Few statistical process monitoring (SPC) approaches for monitoring and contr...Monitoring high-dimensional multistage processes becomes crucial to ensure the quality of the final product in modern industry environments. Few statistical process monitoring (SPC) approaches for monitoring and controlling quality in highdimensional multistage processes are studied. We propose a deviance residual-based multivariate exponentially weighted moving average (MEWMA) control chart with a variable selection procedure. We demonstrate that it outperforms the existing multivariate SPC charts in terms of out-of-control average run length (ARL) for the detection of process mean shift.展开更多
The multi-dimensional system of nonlinear partial differential equations is considered. In two-dimensional case, this system describes process of vein formation in higher plants. Variable directions finite difference ...The multi-dimensional system of nonlinear partial differential equations is considered. In two-dimensional case, this system describes process of vein formation in higher plants. Variable directions finite difference scheme is constructed. The stability and convergence of that scheme are studied. Numerical experiments are carried out. The appropriate graphical illustrations and tables are given.展开更多
A switching disturbance rejection attitude control law is proposed for a near space vehicle (NSV) with variable structure. The multiple flight modes, system uncertainties and disturbances of the NSV are taken into acc...A switching disturbance rejection attitude control law is proposed for a near space vehicle (NSV) with variable structure. The multiple flight modes, system uncertainties and disturbances of the NSV are taken into account based on switched nonlinear systems. Compared with traditional backstepping design methods, the proposed method utilizes the added integrals of attitude angle and angular rate tracking errors to further decrease the tracking errors. Moreover, to reduce the computation complexity, a rapid convergent differentiator is employed to obtain the derivative of the virtual control command. Finally, for disturbance rejection, based on the idea from the extended state observer (ESO), two disturbance observers are designed by using non-smooth functions to estimate the disturbances in the switched nonlinear systems. All signals of the closed-loop system are proven to be uniformly ultimately bounded under the Lyapunov function framework. Simulation results demonstrate the effectiveness of the proposed control scheme.展开更多
Numerical investigation of the dusty Williamson fluid with the dependency of time has been done in current disquisition. The flow of multiphase liquid/particle suspension saturating the medium is caused by stretching ...Numerical investigation of the dusty Williamson fluid with the dependency of time has been done in current disquisition. The flow of multiphase liquid/particle suspension saturating the medium is caused by stretching of porous surface. The influence of magnetic field and heat generation/absorption is observed. It is assumed that particle has a spherical shape and distributed uniformly in fluid matrix. The unsteady two-dimensional problems are modeled for both fluid and particle phase using conservation of mass, momentum and heat transfer. The finalized model generates the non-dimensioned parameters, namely Weissenberg number, unsteadiness parameter, magnetic parameter,heat generation/absorption parameter, Prandtl number, fluid particle interaction parameter, and mass concentration parameters. The numerical solution is obtained. Locality of skin friction and Nusselt number is deliberately focused to help of tables and graphs. While inferencing the current article it is clearly observed that increment of Williamson parameter, unsteadiness parameter, magnetic parameter, volume fraction parameter, and mass concentration parameter reduces the velocity profile of fluid and solid particles as well. And increment of Prandtl number, unsteadiness parameter,volume fraction parameter, and mass concentration parameter reduces the temperature profile of fluid and solid particles as well.展开更多
It is significant to study thermal balance of diesel engine under different variable geometry turbocharger(VGT)vane openings at variable altitudes,which is helpful to assess the heat distribution,control the heat load...It is significant to study thermal balance of diesel engine under different variable geometry turbocharger(VGT)vane openings at variable altitudes,which is helpful to assess the heat distribution,control the heat load and improve the heat efficiency of the diesel engine.A thermal balance test system was built to study the influence of the VGT vane opening angles on a regulated two-stage turbocharged(RTST)diesel engine’s thermal balance performance.The experiment was conducted under full load operating conditions at different altitudes(0 m,3500 m and 5500 m).Results indicated that the heat load of engine increased and the thermal efficiency decreased with the increase of altitudes under all operating conditions.As the VGT vane openings increased,the exhaust and maximum combustion temperature increased,while the maximum cylinder combustion pressure decreased.In particular,the maximum combustion temperature was more than 2000 K when the VGT vane openings were greater than 70%at the altitude of 5500 m,and the maximum combustion pressure exceeded 17 MPa when the opening of VGT vane was 70%at 0 m.The thermal efficiency of the engine decreased with the increase of VGT vane openings at the altitudes of 0 m and 5500 m,but the thermal efficiency increased and then decreased at the altitude of 3500 m.It was finally obtained that the best openings of VGT vane was 80%,60%and 50%under the engine speed of 2100 r/min at 0 m,3500 m and 5500 m,respectively.展开更多
Over the past four decades of reform and opening up since 1978, China’s GDP has been growing at 9.5% on an annual average basis. While some scholars believe that China’s economic growth is systematically overestimat...Over the past four decades of reform and opening up since 1978, China’s GDP has been growing at 9.5% on an annual average basis. While some scholars believe that China’s economic growth is systematically overestimated, this paper carries out an estimation of China’s underground economy and finds that due to the existence of the underground economy, China’s real GDP is systematically underestimated. China’s official GDP statistics generally reflect a real picture of its economic growth. The size of China’s underground economy is significantly influenced by total electricity consumption, the selfemployed ratio, labor participation rate and money supply. These findings are of great significance for policy-making.展开更多
Two-dimensional (2D) nanomaterials have attracted great attention in next generation electronic and optoelectronic technologies due to the unique layered structure and excellent physical and chemical properties. Howev...Two-dimensional (2D) nanomaterials have attracted great attention in next generation electronic and optoelectronic technologies due to the unique layered structure and excellent physical and chemical properties. However, the mechanism of transmission along the vertical direction of 2D semiconductor materials has not been investigated. Here, we use first-principles calculations to explore the bandgap energies along different directions, and fabricate a vertical, a lateral and a mixture-structured black phosphorus field effect transistor (BPFET) to study the electrical characteristics along different directions under variable temperatures. The variable temperature test indicates that the mixture-structured device performs more like a lateral device, while the conductanee along the vertical direction is hard to be tuned by temperature and electrical field. The unchanged conductance under electric field and variable temperatures allows the vertical device to act as a fixed resistor, promising possible application for the prospective electronic and optoelectronic devices.展开更多
The paper presents a direct numerical simulation(DNS)for the drag-reducing channel flow using the Giesekus model with variable parameters.It is assumed that the relaxation time in the constitutive equation is varied d...The paper presents a direct numerical simulation(DNS)for the drag-reducing channel flow using the Giesekus model with variable parameters.It is assumed that the relaxation time in the constitutive equation is varied depending on the local shear rate.The maximal drag reduction rate is obtained when variable parameters are applied in the Giesekus model at a high Weissenberg number.The Reynolds shear stress is reduced when the Weissenberg number increases.In this case,the turbulence generation and transportation are further weakened and increasingly approach to the values in the experiments.展开更多
This paper proposes a hybrid architecture based on Multi-disciplinary Design Optimization(MDO) with the Variable Complexity Modeling(VCM) method, to solve the problem of general design optimization for a stratosphere ...This paper proposes a hybrid architecture based on Multi-disciplinary Design Optimization(MDO) with the Variable Complexity Modeling(VCM) method, to solve the problem of general design optimization for a stratosphere airship. Firstly, MDO based on the Concurrent SubSpace Optimization(CSSO) strategy is improved for handling the subsystem coupling problem in stratosphere airship design which contains aerodynamics, structure, and energy. Secondly, the VCM method based on the surrogate model is presented for reducing the computational complexity in high-fidelity modeling without loss of accuracy. Moreover, the global-to-local optimization strategy is added to the architecture to enhance the process. Finally, the result gives a prominent stratosphere airship general solution that validates the feasibility and efficiency of the optimization architecture. Besides, a sensitivity analysis is conducted to outline the critical impact upon stratosphere airship design.展开更多
We study a degenerate elliptic system with variable exponents. Using the variational approach and some recent theory on weighted Lebesgue and Sobolev spaces with variable exponents, we prove the existence of at least ...We study a degenerate elliptic system with variable exponents. Using the variational approach and some recent theory on weighted Lebesgue and Sobolev spaces with variable exponents, we prove the existence of at least two distinct nontrivial weak solutions of the system. Several consequences of the main theorem are derived;in particular, the existence of at lease two distinct nontrivial non-negative solutions is established for a scalar degenerate problem. One example is provided to show the applicability of our results.展开更多
基金The National Natural Science Foundation of China (Grant Nos.51675194,U1713204).
文摘A variable magnetization(VM) motor by incorporating magnets that can be flexibly configured with variable magnetization process is proposed to meet the emerging requirements on motor efficiency and actuator compliance in robotic applications. A generalized spin torque model is established which provides a relationship between the motor torque and two different types of motor inputs, the current inputs and the magnet magnetizations. Avariable magnetization process is proposed based on the study of the hysteresis properties of the magnetic materials and the design criteria for implementing the variable magnetization process with current pulses are established. The feasibility of the variable magnetization is validated with experimental data and the motor functions and performances are numerically demonstrated and evaluated. The results show that the VM motor can maintain high efficiency by switching between two actuation modes. Controllable stiffness at different equilibria can be also achieved with the VM motor with instantaneous magnetizing current pulses.
基金the National Natural Science Foundation of China (6157113111604055).
文摘A new normalized least mean square(NLMS) adaptive filter is first derived from a cost function, which incorporates the conventional one of the NLMS with a minimum-disturbance(MD)constraint. A variable regularization factor(RF) is then employed to control the contribution made by the MD constraint in the cost function. Analysis results show that the RF can be taken as a combination of the step size and regularization parameter in the conventional NLMS. This implies that these parameters can be jointly controlled by simply tuning the RF as the proposed algorithm does. It also demonstrates that the RF can accelerate the convergence rate of the proposed algorithm and its optimal value can be obtained by minimizing the squared noise-free posteriori error. A method for automatically determining the value of the RF is also presented, which is free of any prior knowledge of the noise. While simulation results verify the analytical ones, it is also illustrated that the performance of the proposed algorithm is superior to the state-of-art ones in both the steady-state misalignment and the convergence rate. A novel algorithm is proposed to solve some problems. Simulation results show the effectiveness of the proposed algorithm.
基金National Natural Science Foundation of China(Grant Nos.11504024,11834010,61602045,11522433,61502041,61602046)National Key Research and Development Program of China(Grant No.2016YFA0302600,2018YFA0306404,2016YFA0301402)Program of Youth Sanjin Scholar.
文摘Cluster state is the basic resource for one-way quantum computation and a valuable resource for establishing quantum network, because it has a flexible and varied composition form. We present measurement-device-independent quantum secret sharing(QSS) and quantum conference(QC) schemes based on continuous variable(CV) four-mode cluster state with different structures. The users of the protocol prepare their own Einstein-Podolsky-Rosen(EPR) states, respectively. One mode of these EPR states is sent to an untrusted relay where a generalized Bell measurement creates different types of CV cluster states among four users, while the other mode is kept at their own station. We show that a shared secret key for QSS and QC schemes is distilled based on the shared quantum correlation among four users. QC and four users QSS are implemented based on the star shape CV cluster state. QSS with three users are implemented based on the linear or square shape CV cluster states. The results show that the secure transmission distance for an asymmetric network, where the transmission distances between the users and relay are different, is longer than that of a symmetric network, where the transmission distances between the users and relay are the same. The presented schemes provide concrete references for establishing quantum network with the CV cluster state.
基金the National Natural Science Foundation of China (No. 11675249).
文摘A novel variable C-band radio-frequency (RF) power splitter was designed at Shanghai Institute of Applied Physics, Chinese Academy of Sciences. Using three RF impedance combiners, an H-bend, and an RF polarizer, this new power splitter is much more compact than a traditionally designed splitter, which comprises three 3-dB hybrids. The parameters were optimized to achieve good matching and minimize reflection. Here, the RF design of the new C-band variable power splitter is presented.
文摘The oil-return system plays an important role in the variable refrigerant flow (VRP) systems because it ensures the reliable operation of the VRF systems. The oil-gas separator is the most essential component of the oil- return system, and the separation efficiency of the separator directly influences the performance of the VRF systems. Therefore, in this paper, a test rig was built to measure the oil discharge ratio of the compressor and the separation efficiency of the oil-gas separator. A sound velocity transducer was used to measure the oil mass concentration instantaneously, because the sound velocity was changed with the mass ratio of oil to refrigerant. The separation efficiency of the separator could be obtained by comparing the mass fraction of oil to refrigerant before and after the separator was connected to the system.
文摘This paper presents a two-dimensional unsteady laminar boundary layer mixed convection flow heat and mass transfer along a vertical plate filled with Casson nanofluid located in a porous quiescent medium that contains both nanoparticles and gyrotactic microorganisms. This permeable vertical plate is assumed to be moving in the same direction as the free stream velocity. The flow is subject to a variable heat flux, a zero nanoparticle flux and a constant density of motile microorganisms on the surface. The free stream velocity is time-dependent resulting in a non-similar solution. The transport equations are solved using the bivariate spectral quasilinearization method. A grid independence test for the validity of the result is given. The significance of the inclusion of motile microorganisms to heat transfer processes is discussed. We show, inter alia, that introducing motile microorganisms into the flow reduces the skin friction coefficient and that the random motion of the nanoparticles improves the rate of transfer of the motile microorganisms.
基金The National Major Plan Research and Development Project(2017YFB0503003)The National Natural Science Foundation of China(11174017)+1 种基金The National 863 Subject(2007AA12Z111,2006AA12Z119)The Special Research Fund for Doctoral Programs in Colleges and Universities(20130001110046).
文摘Accuracy is a key factor in high-resolution remote sensing and photogrammetry. The factors that affect accuracy are imaging system errors and data processing errors. Due to the complexity of aerial camera errors, this paper focuses on the design of digital aerial camera systems and the means to reduce system error and data processing inefficiencies. There are many kinds of digital aerial camera systems at present;however, these systems lack a unified physical model, which ultimately leads to more complicated designs and multi-camera modes. Such a system is complex and costly, as it is easily affected by factors such as vibration and temperature. Thus, the installed accuracy can only reach the millimeter level. Here, we describe a unified physical structure for a digital aerial camera that imitates an out-of-field multi-charge-coupled device (CCD), an in-field multi-CCD, and once-imaging and twice-imaging digital camera systems. This model is referred to as the variable baseline-height ratio spatiotemporal model. The variable ratio allows the opto-mechanical spatial parameters to be linked with height accuracy, thus providing a connection to the surface elevation. The twice-imaging digital camera prototype system and the wideband limb imaging spectrometer provide a transformation prototype from the current multi-rigid once-imaging aerial camera to a single rigid structure. Thus, our research lays a theoretical foundation and prototype references for the construction and industrialization of digital aerial systems.
基金Qatar National Research Fund (NPRP5-364-2-142NPRP7-1040-2-293).
文摘Monitoring high-dimensional multistage processes becomes crucial to ensure the quality of the final product in modern industry environments. Few statistical process monitoring (SPC) approaches for monitoring and controlling quality in highdimensional multistage processes are studied. We propose a deviance residual-based multivariate exponentially weighted moving average (MEWMA) control chart with a variable selection procedure. We demonstrate that it outperforms the existing multivariate SPC charts in terms of out-of-control average run length (ARL) for the detection of process mean shift.
文摘The multi-dimensional system of nonlinear partial differential equations is considered. In two-dimensional case, this system describes process of vein formation in higher plants. Variable directions finite difference scheme is constructed. The stability and convergence of that scheme are studied. Numerical experiments are carried out. The appropriate graphical illustrations and tables are given.
基金National Natural Science Foundation of China (61374012)the Aeronautical Science Foundation of China (2016ZA51011).
文摘A switching disturbance rejection attitude control law is proposed for a near space vehicle (NSV) with variable structure. The multiple flight modes, system uncertainties and disturbances of the NSV are taken into account based on switched nonlinear systems. Compared with traditional backstepping design methods, the proposed method utilizes the added integrals of attitude angle and angular rate tracking errors to further decrease the tracking errors. Moreover, to reduce the computation complexity, a rapid convergent differentiator is employed to obtain the derivative of the virtual control command. Finally, for disturbance rejection, based on the idea from the extended state observer (ESO), two disturbance observers are designed by using non-smooth functions to estimate the disturbances in the switched nonlinear systems. All signals of the closed-loop system are proven to be uniformly ultimately bounded under the Lyapunov function framework. Simulation results demonstrate the effectiveness of the proposed control scheme.
文摘Numerical investigation of the dusty Williamson fluid with the dependency of time has been done in current disquisition. The flow of multiphase liquid/particle suspension saturating the medium is caused by stretching of porous surface. The influence of magnetic field and heat generation/absorption is observed. It is assumed that particle has a spherical shape and distributed uniformly in fluid matrix. The unsteady two-dimensional problems are modeled for both fluid and particle phase using conservation of mass, momentum and heat transfer. The finalized model generates the non-dimensioned parameters, namely Weissenberg number, unsteadiness parameter, magnetic parameter,heat generation/absorption parameter, Prandtl number, fluid particle interaction parameter, and mass concentration parameters. The numerical solution is obtained. Locality of skin friction and Nusselt number is deliberately focused to help of tables and graphs. While inferencing the current article it is clearly observed that increment of Williamson parameter, unsteadiness parameter, magnetic parameter, volume fraction parameter, and mass concentration parameter reduces the velocity profile of fluid and solid particles as well. And increment of Prandtl number, unsteadiness parameter,volume fraction parameter, and mass concentration parameter reduces the temperature profile of fluid and solid particles as well.
基金Machinery Industry Key Laboratory of Engine Plateau Adaptation.
文摘It is significant to study thermal balance of diesel engine under different variable geometry turbocharger(VGT)vane openings at variable altitudes,which is helpful to assess the heat distribution,control the heat load and improve the heat efficiency of the diesel engine.A thermal balance test system was built to study the influence of the VGT vane opening angles on a regulated two-stage turbocharged(RTST)diesel engine’s thermal balance performance.The experiment was conducted under full load operating conditions at different altitudes(0 m,3500 m and 5500 m).Results indicated that the heat load of engine increased and the thermal efficiency decreased with the increase of altitudes under all operating conditions.As the VGT vane openings increased,the exhaust and maximum combustion temperature increased,while the maximum cylinder combustion pressure decreased.In particular,the maximum combustion temperature was more than 2000 K when the VGT vane openings were greater than 70%at the altitude of 5500 m,and the maximum combustion pressure exceeded 17 MPa when the opening of VGT vane was 70%at 0 m.The thermal efficiency of the engine decreased with the increase of VGT vane openings at the altitudes of 0 m and 5500 m,but the thermal efficiency increased and then decreased at the altitude of 3500 m.It was finally obtained that the best openings of VGT vane was 80%,60%and 50%under the engine speed of 2100 r/min at 0 m,3500 m and 5500 m,respectively.
文摘Over the past four decades of reform and opening up since 1978, China’s GDP has been growing at 9.5% on an annual average basis. While some scholars believe that China’s economic growth is systematically overestimated, this paper carries out an estimation of China’s underground economy and finds that due to the existence of the underground economy, China’s real GDP is systematically underestimated. China’s official GDP statistics generally reflect a real picture of its economic growth. The size of China’s underground economy is significantly influenced by total electricity consumption, the selfemployed ratio, labor participation rate and money supply. These findings are of great significance for policy-making.
基金National Key Research and Development from Minister of Scie nee and Tech no logy of China (2016YFA0202703)National Natural Science Foundation of China (51622205, 61675027, 51432005, 61505010, 51672106, 11704081, and 51502018)+1 种基金Beijing City Committee of Science and Technology (Z171100002017019, and Z181100004418004)Beijing Natural Science Foundation (4181004, 4182080, 4184110, and 2184131).
文摘Two-dimensional (2D) nanomaterials have attracted great attention in next generation electronic and optoelectronic technologies due to the unique layered structure and excellent physical and chemical properties. However, the mechanism of transmission along the vertical direction of 2D semiconductor materials has not been investigated. Here, we use first-principles calculations to explore the bandgap energies along different directions, and fabricate a vertical, a lateral and a mixture-structured black phosphorus field effect transistor (BPFET) to study the electrical characteristics along different directions under variable temperatures. The variable temperature test indicates that the mixture-structured device performs more like a lateral device, while the conductanee along the vertical direction is hard to be tuned by temperature and electrical field. The unchanged conductance under electric field and variable temperatures allows the vertical device to act as a fixed resistor, promising possible application for the prospective electronic and optoelectronic devices.
基金by National Natural Science Foundation of China(Grant Nos.51106095,11575113).
文摘The paper presents a direct numerical simulation(DNS)for the drag-reducing channel flow using the Giesekus model with variable parameters.It is assumed that the relaxation time in the constitutive equation is varied depending on the local shear rate.The maximal drag reduction rate is obtained when variable parameters are applied in the Giesekus model at a high Weissenberg number.The Reynolds shear stress is reduced when the Weissenberg number increases.In this case,the turbulence generation and transportation are further weakened and increasingly approach to the values in the experiments.
基金the National Key R&D Program of China (No.2016YFB1200100).
文摘This paper proposes a hybrid architecture based on Multi-disciplinary Design Optimization(MDO) with the Variable Complexity Modeling(VCM) method, to solve the problem of general design optimization for a stratosphere airship. Firstly, MDO based on the Concurrent SubSpace Optimization(CSSO) strategy is improved for handling the subsystem coupling problem in stratosphere airship design which contains aerodynamics, structure, and energy. Secondly, the VCM method based on the surrogate model is presented for reducing the computational complexity in high-fidelity modeling without loss of accuracy. Moreover, the global-to-local optimization strategy is added to the architecture to enhance the process. Finally, the result gives a prominent stratosphere airship general solution that validates the feasibility and efficiency of the optimization architecture. Besides, a sensitivity analysis is conducted to outline the critical impact upon stratosphere airship design.
基金supported in part by a University of Tennessee at Chattanooga SimCenter-Center of Excellence in Applied Computational Science and Engineering (CEACSE) grant.
文摘We study a degenerate elliptic system with variable exponents. Using the variational approach and some recent theory on weighted Lebesgue and Sobolev spaces with variable exponents, we prove the existence of at least two distinct nontrivial weak solutions of the system. Several consequences of the main theorem are derived;in particular, the existence of at lease two distinct nontrivial non-negative solutions is established for a scalar degenerate problem. One example is provided to show the applicability of our results.