Stress accumulation is a key factor leading to sodium storage performance deterioration for NiSe_(2)-based anodes.Therefore,inhibiting the concentrated local stress during the sodiataion/desodiation process is crucial...Stress accumulation is a key factor leading to sodium storage performance deterioration for NiSe_(2)-based anodes.Therefore,inhibiting the concentrated local stress during the sodiataion/desodiation process is crucial for acquiring stable NiSe2-based materials for sodium-ion batteries(SIBs),Herein,a stress dissipation strategy driven by architecture engineering is proposed,which can achieve ultrafast and ultralong sodium storage properties.Different from the conventional sphere-like or rod-like architecture,the three-dimensional(3D)flower-like NiSe_(2)@C composite is delicately designed and assembled with onedimensional nanorods and carbon framework.More importantly,the fundamental mechanism of improved structure stability is unveiled by simulations and experimental results simultaneously.It demonstrates that this designed multidimensional flower-like architecture with dispersed nanorods can balance the structural mismatch,avoid concentrated local strain,and relax the internal stress,mainly induced by the unavoidable volume variation during the repeated conversion processes.Moreover,it can provide more Na^(+)-storage sites and multi-directional migration pathways,leading to a fast Na^(+)-migration channel with boosted reaction kinetic.As expected,it delivers superior rate performance(441 mA h g^(-1)at 5.0 A g^(-1))and long cycling stability(563 mA h g^(-1)at 1.0 A g^(-1)over 1000 cycles)for SIBs.This work provides useful insights for designing high-performance conversion-based anode materials for SIBs.展开更多
This paper is devoted to understanding the stability of perturbations around the hydrostatic equilibrium of the Boussinesq system in order to gain insight into certain atmospheric and oceanographic phenomena.The Bouss...This paper is devoted to understanding the stability of perturbations around the hydrostatic equilibrium of the Boussinesq system in order to gain insight into certain atmospheric and oceanographic phenomena.The Boussinesq system focused on here is anisotropic,and involves only horizontal dissipation and thermal damping.In the 2D case R^(2),due to the lack of vertical dissipation,the stability and large-time behavior problems have remained open in a Sobolev setting.For the spatial domain T×R,this paper solves the stability problem and gives the precise large-time behavior of the perturbation.By decomposing the velocity u and temperatureθinto the horizontal average(ū,θ)and the corresponding oscillation(ū,θ),we can derive the global stability in H~2 and the exponential decay of(ū,θ)to zero in H^(1).Moreover,we also obtain that(ū_(2),θ)decays exponentially to zero in H^(1),and thatū_(1)decays exponentially toū_(1)(∞)in H^(1)as well;this reflects a strongly stratified phenomenon of buoyancy-driven fluids.In addition,we establish the global stability in H^(3)for the 3D case R^(3).展开更多
Thermal management of nanoscale quantum dots(QDs)in light-emitting devices is a long-lasting challenge.The existing heat transfer reinforcement solutions for QDs-polymer composite mainly rely on thermal-conductive fil...Thermal management of nanoscale quantum dots(QDs)in light-emitting devices is a long-lasting challenge.The existing heat transfer reinforcement solutions for QDs-polymer composite mainly rely on thermal-conductive fillers.However,this strategy failed to deliver the QDs’heat generation across a long distance,and the accumulated heat still causes considerable temperature rise of QDs-polymer composite,which eventually menaces the performance and reliability of lightemitting devices.Inspired by the radially aligned fruit fibers in oranges,we proposed to eliminate this heat dissipation challenge by establishing long-range ordered heat transfer pathways within the QDs-polymer composite.Ultrahigh molecular weight polyethylene fibers(UPEF)were radially aligned throughout the polymer matrix,thus facilitating massive efficient heat dissipation of the QDs.Under a UPEF filling fraction of 24.46 vol%,the in-plane thermal conductivity of QDs-radially aligned UPEF composite(QDs-RAPE)could reach 10.45 W m^(−1) K^(−1),which is the highest value of QDs-polymer composite reported so far.As a proof of concept,the QDs’working temperature can be reduced by 342.5℃ when illuminated by a highly concentrated laser diode(LD)under driving current of 1000 mA,thus improving their optical performance.This work may pave a new way for next generation high-power QDs lighting applications.展开更多
To conveniently calculate the Wigner function of the optical cumulant operator and its dissipation evolution in a thermal environment, in this paper, the thermo-entangled state representation is introduced to derive t...To conveniently calculate the Wigner function of the optical cumulant operator and its dissipation evolution in a thermal environment, in this paper, the thermo-entangled state representation is introduced to derive the general evolution formula of the Wigner function, and its relation to Weyl correspondence is also discussed. The method of integration within the ordered product of operators is essential to our discussion.展开更多
The zero dissipation limit of the compressible heat-conducting Navier–Stokes equations in the presence of the shock is investigated. It is shown that when the heat conduction coefficient κ and the viscosity coeffici...The zero dissipation limit of the compressible heat-conducting Navier–Stokes equations in the presence of the shock is investigated. It is shown that when the heat conduction coefficient κ and the viscosity coefficient ε satisfy κ = O（ε）, κ/ε≥ c 〉 0, as ε→ 0 （see （1.3））, if the solution of the corresponding Euler equations is piecewise smooth with shock wave satisfying the Lax entropy condition, then there exists a smooth solution to the Navier–Stokes equations, which converges to the piecewise smooth shock solution of the Euler equations away from the shock discontinuity at a rate of ε. The proof is given by a combination of the energy estimates and the matched asymptotic analysis introduced in [3].展开更多
Metal rubber （MR） is a kind of homogeneous poroelastic damping material made of metal wire. In this paper, by ana- lyzing the forces on the MR isolator and the MR element, the hysteresis loops of the force and defor...Metal rubber （MR） is a kind of homogeneous poroelastic damping material made of metal wire. In this paper, by ana- lyzing the forces on the MR isolator and the MR element, the hysteresis loops of the force and deformation are studied and verified by experiments. The results show that the force and displacement hysteresis loop of the MR isolator is described by the force and deformation hysteresis loops of the MR elements. In addition, the relationship between the energy dissipation coefficient of the MR element and that of the MR isolator is derived. The energy dissipation coefficient is programmed and calculated by MATLAB using experimental data, and the results are compared with the theoretical value. It is the basis for the design and applied research of the MR isolator in a future study.展开更多
In this article, we mainly study the local equation of energy for weak solutions of 3D MHD equations. We define a dissipation term D（u, B） that steins from an eventual lack of smoothness in the solution, and then ob...In this article, we mainly study the local equation of energy for weak solutions of 3D MHD equations. We define a dissipation term D（u, B） that steins from an eventual lack of smoothness in the solution, and then obtain a local equation of energy for weak solutions of 3D MHD equations. Finally, we consider the 2D case at the end of this article.展开更多
We discuss the effects of dissipation on the behavior of single photon transport in a system of coupled cavity arrays, with the two nearest cavities nonlocally coupled to a two-level atom. The single photon transmissi...We discuss the effects of dissipation on the behavior of single photon transport in a system of coupled cavity arrays, with the two nearest cavities nonlocally coupled to a two-level atom. The single photon transmission amplitude is solved exactly by employing the quasi-boson picture. We investigate two different situations of local and nonlocal couplings, respectively. Comparing the dissipative case with the nondissipative one reveals that the dissipation of the system increases the middle dip and lowers the peak of the single photon transmission amplitudes, broadening the line width of the transport spectrum. It should be noted that the influence of the cavity dissipation to the single photon transport spectrum is asymmet- ric. By comparing the nonlocal coupling with the local one, one can find that the enhancement of the middle dip of single photon transmission amplitudes is mostly caused by the atom dissipation and that the reduced peak is mainly caused by the cavity dissipation, no matter whether it is a nonlocal or local coupling case. Whereas in the nonlocal coupling case, when the coupling strength gets stronger, the cavity dissipation has a greater effect on the single photon transport spectrum and the atom dissipation affection becomes weak, so it can be ignored.展开更多
Because the larger metallic surrounds are heated by the eddy current, which is generated by the AC current flowing through the AC busbar in the International Thermonuclear ExperimentM Reactor （ITER） poloidal field ...Because the larger metallic surrounds are heated by the eddy current, which is generated by the AC current flowing through the AC busbar in the International Thermonuclear ExperimentM Reactor （ITER） poloidal field （PF） converter system, shielding of the AC busbar is required to decrease the temperature rise of the surrounds to satisfy the design requirement. Three special types of AC busbar with natural cooling, air cooling and water cooling busbar structure have been proposed and investigated in this paper. For each cooling scheme, a 3D finite model based on the proposed structure has been developed to perform the electromagnetic and thermal analysis to predict their operation behavior. Comparing the analysis results of the three different cooling patterns, water cooling has more advantages than the other patterns and it is selected to be the thermal dissipation pattern for the AC busbar of ITER PF converter unit. The approach to qualify the suitable cooling scheme in this paper can be provided as a reference on the thermal dissipation design of AC busbar in the converter system.展开更多
The zero dissipation limit to the contact discontinuities for one-dimensional com- pressible Navier-Stokes equations was recently proved for ideal polytropic gas （see Huang et al. [15, 22] and Ma [31]）, but there is...The zero dissipation limit to the contact discontinuities for one-dimensional com- pressible Navier-Stokes equations was recently proved for ideal polytropic gas （see Huang et al. [15, 22] and Ma [31]）, but there is few result for general gases including ideal polytropic gas. We prove that if the solution to the corresponding Euler system of general gas satisfying （1.4） is piecewise constant with a contact discontinuity, then there exist smooth solutions to Navier-Stokes equations which converge to the inviscid solutions at a rate of k1/4 as the heat-conductivity coefficient k tends to zero. The key is to construct a viscous contact wave of general gas suitable to our proof （see Section 2）. Notice that we have no need to restrict the strength of the contact discontinuity to be small.展开更多
The equivalent circuit with complex physical constants for a piezoelectric ceramic in thickness mode is established. In the equivalent circuit, electric components （equivalent circuit parameters） are connected to re...The equivalent circuit with complex physical constants for a piezoelectric ceramic in thickness mode is established. In the equivalent circuit, electric components （equivalent circuit parameters） are connected to real and imaginary parts of complex physical coefficients of piezoelectric materials. Based on definitions of dissipation factors, three of them （dielectric, elastic and piezoelectric dissipation factors） are represented by equivalent circuit parameters. Since the equivalent circuit parameters are detectable, the dissipation factors can be easily obtained. In the experiments, the temperature and the stress responses of the three dissipation factors are measured.展开更多
We presented 980-nm oxide-confined vertical-cavity surface-emitting lasers （VCSELs） with a 16 -um oxide aperture. Optical power, voltage, and emission wavelength are measured in an ambient temperature range of 5 ℃-...We presented 980-nm oxide-confined vertical-cavity surface-emitting lasers （VCSELs） with a 16 -um oxide aperture. Optical power, voltage, and emission wavelength are measured in an ambient temperature range of 5 ℃-80 ℃. Measurements combined with an empirical model are used to analyse the power dissipation in the device and the physical mechanism contributing to the thermal rollover phenomenon in VCSEL. It is found that the carrier leakage induced selfheating in the active region and the Joule heating caused by the series resistance are the main sources of power dissipation. In addition, carrier leakage induced self-heating increases as the injection current increases, resulting in a rapid decrease of the internal quantum efficiency, which is a dominant contribution to the thermal rollover of the VCSEL at a larger current. Our study provides useful guidelines to design a 980-nm oxide-confined VCSEL for thermal performance enhancement.展开更多
The power dissipation characteristics of pulsed power switch reversely switched dynistors （RSDs） are investigated in this paper. According to the expressions of voltage on RSD, derived from the plasma bipolar drift ...The power dissipation characteristics of pulsed power switch reversely switched dynistors （RSDs） are investigated in this paper. According to the expressions of voltage on RSD, derived from the plasma bipolar drift model and the RLC circuit equations of RSD main loop, the simulation waveforms of current and voltage on RSD are acquired through iterative calculation by using the fourth order Runge-Kutta method, then the curve of transient power on RSD versus time is obtained. The result shows that the total dissipation on RSD is trivial compared with the pulse discharge energy and the commutation dissipation can be nearly ignored compared with the quasi-static dissipation. These characteristics can make the repetitive frequency of RSD increase largely. The experimental results prove the validity of simulation calculations. The influence factors on power dissipation are discussed. The power dissipation increases with the increase of the peak current and the n-base width and with the decrease of n-base doping concentration. In order to keep a low power dissipation, it is suggested that the n-base width should be smaller than 320μm when doping concentration is 1.0×10^14cm^-3 while the doping concentration should be higher than 5.8×10^13cm^-3 when n-base width is 270μm.展开更多
The physical and mechanical change processes of coal and rock are closely related to energy transformation,and the destruction and failure of coal and rock is an instability phenomena driven by energy change.However,t...The physical and mechanical change processes of coal and rock are closely related to energy transformation,and the destruction and failure of coal and rock is an instability phenomena driven by energy change.However,the energy change of large-scale coal rock in the mine site is hardly calculated accurately,making it difficult to monitor coal-rock systematic failure and collapse from the perspective of energy.By the energy dissipation EMR monitoring system,we studied the damage and failure of coal and rock with bursting liability from the energy dissipation point using the geophysical method-EMR,and explored the energy dissipation characteristics during uniaxial compression and their main influencing factors.The results show that under displacement-control loading mode,there are 2 types of energy dissipation trends for both coal and rock with bursting liability.The type Ⅰ trend is a steady increase one during the whole process,therein,the energy dissipation of rock samples is accelerated at the peak load.The type Ⅱ trend energy is a W-shaped fluctuating one containing 6 stages.Under load-control loading mode,there is one energy dissipation trend of shock downward-steady rise.Besides that,rock samples also present a trend of 4 stages.The energy dissipation characteristics of coal and rockduring loading failure process can be used as effective criteria to assess whether they are in a stable or destructive stage.The factors influencing energy dissipation in the loading failure process of coal and rock mainly include strength,homogeneity,and energy input efficiency.展开更多
On the basis of quantization of charge, the loop equations of quantum circuits are investigated by using the Helsenberg motion equation for a mesoscopic dissipation transmission line. On the supposition that the syste...On the basis of quantization of charge, the loop equations of quantum circuits are investigated by using the Helsenberg motion equation for a mesoscopic dissipation transmission line. On the supposition that the system has a symmetry under translation in charge space, the quantum current and the quantum energy spectrum in the mesoscopic transmission llne are given by solving their eigenvalue equations. Results show that the quantum current and the quantum energy spectrum are not only related to the parameters of the transmission llne, but also dependent on the quantized character of the charge obviously.展开更多
A numerical study is performed to investigate the flow and heat transfer at the surface of a permeable wedge immersed in a copper （Cu）-water-based nanofluid in the presence of magnetic field and viscous dissipation ...A numerical study is performed to investigate the flow and heat transfer at the surface of a permeable wedge immersed in a copper （Cu）-water-based nanofluid in the presence of magnetic field and viscous dissipation using a nanofluid model proposed by Tiwari and Das （Tiwari I K and Das M K 2007 Int. J. HeatMass Transfer 50 2002）. A similarity solution for the transformed governing equation is obtained, and those equations are solved by employing a numerical shooting technique with a fourth-order Runge-Kutta integration scheme. A comparison with previously published work is carried out and shows that they are in good agreement with each other. The effects of velocity ratio parameter ~, solid volume fraction tp, magnetic field M, viscous dissipation Ec, and suction parameter Fw on the fluid flow and heat transfer characteristics are discussed. The unique and dual solutions for self-similar equations of the flow and heat transfer are analyzed numerically. Moreover, the range of the velocity ratio parameter for which the solution exists increases in the presence of magnetic field and suction parameter.展开更多
Dynamic disasters in Chinese coal mines pose a significant threat to coal productivity. Thus, a thorough understanding of the deformation and failure processes of coal is necessary. In this study, the energy dissipati...Dynamic disasters in Chinese coal mines pose a significant threat to coal productivity. Thus, a thorough understanding of the deformation and failure processes of coal is necessary. In this study, the energy dissipation rate is proposed as a novel indicator of coal deformation and failure under static and dynamic compressive loads. The relationship between stress-strain, uniaxial compressive strength, displacement rate, loading rate, fractal dimension, and energy dissipation rate was investigated through experiments conducted using the MTS C60 tests(static loads) and split Hopkinson pressure bar system(dynamic loads). The results show that the energy dissipation rate peaks are associated with stress drop during coal deformation, and also positively related to the uniaxial compressive strength. A higher displacement rate of quasi-static loads leads to an initial increase and then a decrease in energy dissipation rate, whereas a higher loading rate of dynamic loads results in larger energy dissipation rate. Theoretical analysis indicates that a sudden increase in energy dissipation rate suggests partial fracture occurring within coal under both quasi-static and dynamic loads. Hence, the energy dissipation rate is an essential indicator of partial fracture and final failure within coal, as well as a prospective precursor for catastrophic failure in coal mine.展开更多
Rock joints exhibit hysteresis shearing behavior and produce energy dissipation under shear cyclic loads,which however cannot be accurately depicted by existing constitutive models. This paper establishes a constituti...Rock joints exhibit hysteresis shearing behavior and produce energy dissipation under shear cyclic loads,which however cannot be accurately depicted by existing constitutive models. This paper establishes a constitutive model for hysteresis shearing and associated energy dissipation of rock joints. Analytical expressions of the model during cyclic shearing processes are derived. Derivation of the model indicates no energy dissipation in the elastic stage. When the shear load exceeds elastic boundary, nonlinear energy dissipation takes place. Validations with experiments show that the proposed model provides good conformities with direct shear curves and hysteresis loops, and can predict the energy dissipation characteristics of rock joints under different working conditions. Compared to the constitutive models using Weibull's distribution, the proposed one is smooth at the elastic boundary and can accurately capture the maximum shear stress. Unlike the existing incremental-type models, the proposed one provides clear and direct analytical expressions for both shear stress and energy dissipation during the whole displacement domain, which is more convenient in application.展开更多
A method of non-uniform finger spacing is proposed to enhance thermal stability of a multiple finger power SiGe heterojunction bipolar transistor under different power dissipations. Temperature distribution on the emi...A method of non-uniform finger spacing is proposed to enhance thermal stability of a multiple finger power SiGe heterojunction bipolar transistor under different power dissipations. Temperature distribution on the emitter fingers of a multi-finger SiGe heterojunction bipolar transistor is studied using a numerical electro-thermal model. The results show that the SiGe heterojunction bipolar transistor with non-uniform finger spacing has a small temperature difference between fingers compared with a traditional uniform finger spacing heterojunction bipolar transistor at the same power dissipation. What is most important is that the ability to improve temperature non-uniformity is not weakened as power dissipation increases. So the method of non-uniform finger spacing is very effective in enhancing the thermal stability and the power handing capability of power device. Experimental results verify our conclusions.展开更多
This article considers the global regularity to the initial-boundary value problem for the 2D incompressible MHD with mixed partial dissipation and magnetic diffusion. To overcome the difficulty caused by the vanishin...This article considers the global regularity to the initial-boundary value problem for the 2D incompressible MHD with mixed partial dissipation and magnetic diffusion. To overcome the difficulty caused by the vanishing viscosities, we first establish the elliptic system for ux and by, which are estimated by 7 × us and × by, respectively. Then, we establish the global estimates for × u and ×b.展开更多
基金the financial support from the Guangxi Natural Science Foundation(grant no.2021GXNSFDA075012,2023GXNSFGA026002)National Natural Science Foundation of China(52104298,22075073,52362027,52462029)Fundamental Research Funds for the Central Universities(531107051077).
文摘Stress accumulation is a key factor leading to sodium storage performance deterioration for NiSe_(2)-based anodes.Therefore,inhibiting the concentrated local stress during the sodiataion/desodiation process is crucial for acquiring stable NiSe2-based materials for sodium-ion batteries(SIBs),Herein,a stress dissipation strategy driven by architecture engineering is proposed,which can achieve ultrafast and ultralong sodium storage properties.Different from the conventional sphere-like or rod-like architecture,the three-dimensional(3D)flower-like NiSe_(2)@C composite is delicately designed and assembled with onedimensional nanorods and carbon framework.More importantly,the fundamental mechanism of improved structure stability is unveiled by simulations and experimental results simultaneously.It demonstrates that this designed multidimensional flower-like architecture with dispersed nanorods can balance the structural mismatch,avoid concentrated local strain,and relax the internal stress,mainly induced by the unavoidable volume variation during the repeated conversion processes.Moreover,it can provide more Na^(+)-storage sites and multi-directional migration pathways,leading to a fast Na^(+)-migration channel with boosted reaction kinetic.As expected,it delivers superior rate performance(441 mA h g^(-1)at 5.0 A g^(-1))and long cycling stability(563 mA h g^(-1)at 1.0 A g^(-1)over 1000 cycles)for SIBs.This work provides useful insights for designing high-performance conversion-based anode materials for SIBs.
基金supported by National Natural Science Foundation of China(12071391,12231016)the Guangdong Basic and Applied Basic Research Foundation(2022A1515010860)。
文摘This paper is devoted to understanding the stability of perturbations around the hydrostatic equilibrium of the Boussinesq system in order to gain insight into certain atmospheric and oceanographic phenomena.The Boussinesq system focused on here is anisotropic,and involves only horizontal dissipation and thermal damping.In the 2D case R^(2),due to the lack of vertical dissipation,the stability and large-time behavior problems have remained open in a Sobolev setting.For the spatial domain T×R,this paper solves the stability problem and gives the precise large-time behavior of the perturbation.By decomposing the velocity u and temperatureθinto the horizontal average(ū,θ)and the corresponding oscillation(ū,θ),we can derive the global stability in H~2 and the exponential decay of(ū,θ)to zero in H^(1).Moreover,we also obtain that(ū_(2),θ)decays exponentially to zero in H^(1),and thatū_(1)decays exponentially toū_(1)(∞)in H^(1)as well;this reflects a strongly stratified phenomenon of buoyancy-driven fluids.In addition,we establish the global stability in H^(3)for the 3D case R^(3).
基金supported by the National Natural Science Foundation of China(52106089).
文摘Thermal management of nanoscale quantum dots(QDs)in light-emitting devices is a long-lasting challenge.The existing heat transfer reinforcement solutions for QDs-polymer composite mainly rely on thermal-conductive fillers.However,this strategy failed to deliver the QDs’heat generation across a long distance,and the accumulated heat still causes considerable temperature rise of QDs-polymer composite,which eventually menaces the performance and reliability of lightemitting devices.Inspired by the radially aligned fruit fibers in oranges,we proposed to eliminate this heat dissipation challenge by establishing long-range ordered heat transfer pathways within the QDs-polymer composite.Ultrahigh molecular weight polyethylene fibers(UPEF)were radially aligned throughout the polymer matrix,thus facilitating massive efficient heat dissipation of the QDs.Under a UPEF filling fraction of 24.46 vol%,the in-plane thermal conductivity of QDs-radially aligned UPEF composite(QDs-RAPE)could reach 10.45 W m^(−1) K^(−1),which is the highest value of QDs-polymer composite reported so far.As a proof of concept,the QDs’working temperature can be reduced by 342.5℃ when illuminated by a highly concentrated laser diode(LD)under driving current of 1000 mA,thus improving their optical performance.This work may pave a new way for next generation high-power QDs lighting applications.
基金Project supported by the Foundation for Young Talents in College of Anhui Province, China (Grant Nos. gxyq2021210 and gxyq2019077)the Natural Science Foundation of the Anhui Higher Education Institutions, China (Grant Nos. 2022AH051580 and 2022AH051586)。
文摘To conveniently calculate the Wigner function of the optical cumulant operator and its dissipation evolution in a thermal environment, in this paper, the thermo-entangled state representation is introduced to derive the general evolution formula of the Wigner function, and its relation to Weyl correspondence is also discussed. The method of integration within the ordered product of operators is essential to our discussion.
基金the Knowledge Innovation Program of the Chinese Academy of Sciences
文摘The zero dissipation limit of the compressible heat-conducting Navier–Stokes equations in the presence of the shock is investigated. It is shown that when the heat conduction coefficient κ and the viscosity coefficient ε satisfy κ = O（ε）, κ/ε≥ c 〉 0, as ε→ 0 （see （1.3））, if the solution of the corresponding Euler equations is piecewise smooth with shock wave satisfying the Lax entropy condition, then there exists a smooth solution to the Navier–Stokes equations, which converges to the piecewise smooth shock solution of the Euler equations away from the shock discontinuity at a rate of ε. The proof is given by a combination of the energy estimates and the matched asymptotic analysis introduced in [3].
文摘Metal rubber （MR） is a kind of homogeneous poroelastic damping material made of metal wire. In this paper, by ana- lyzing the forces on the MR isolator and the MR element, the hysteresis loops of the force and deformation are studied and verified by experiments. The results show that the force and displacement hysteresis loop of the MR isolator is described by the force and deformation hysteresis loops of the MR elements. In addition, the relationship between the energy dissipation coefficient of the MR element and that of the MR isolator is derived. The energy dissipation coefficient is programmed and calculated by MATLAB using experimental data, and the results are compared with the theoretical value. It is the basis for the design and applied research of the MR isolator in a future study.
基金Supported by NSFC (10976026)supported by the Fundamental Research Funds for the Central Universities (11QZR18)the Research Funds for high-level talents of Huaqiao University (12BS232)
文摘In this article, we mainly study the local equation of energy for weak solutions of 3D MHD equations. We define a dissipation term D（u, B） that steins from an eventual lack of smoothness in the solution, and then obtain a local equation of energy for weak solutions of 3D MHD equations. Finally, we consider the 2D case at the end of this article.
基金Project supported by the National Natural Science Foundation of China (Grant Nos.10704031,10874235,11274148,and 10934010)
文摘We discuss the effects of dissipation on the behavior of single photon transport in a system of coupled cavity arrays, with the two nearest cavities nonlocally coupled to a two-level atom. The single photon transmission amplitude is solved exactly by employing the quasi-boson picture. We investigate two different situations of local and nonlocal couplings, respectively. Comparing the dissipative case with the nondissipative one reveals that the dissipation of the system increases the middle dip and lowers the peak of the single photon transmission amplitudes, broadening the line width of the transport spectrum. It should be noted that the influence of the cavity dissipation to the single photon transport spectrum is asymmet- ric. By comparing the nonlocal coupling with the local one, one can find that the enhancement of the middle dip of single photon transmission amplitudes is mostly caused by the atom dissipation and that the reduced peak is mainly caused by the cavity dissipation, no matter whether it is a nonlocal or local coupling case. Whereas in the nonlocal coupling case, when the coupling strength gets stronger, the cavity dissipation has a greater effect on the single photon transport spectrum and the atom dissipation affection becomes weak, so it can be ignored.
基金supported by National Natural Science Foundation of China(No.51407179)
文摘Because the larger metallic surrounds are heated by the eddy current, which is generated by the AC current flowing through the AC busbar in the International Thermonuclear ExperimentM Reactor （ITER） poloidal field （PF） converter system, shielding of the AC busbar is required to decrease the temperature rise of the surrounds to satisfy the design requirement. Three special types of AC busbar with natural cooling, air cooling and water cooling busbar structure have been proposed and investigated in this paper. For each cooling scheme, a 3D finite model based on the proposed structure has been developed to perform the electromagnetic and thermal analysis to predict their operation behavior. Comparing the analysis results of the three different cooling patterns, water cooling has more advantages than the other patterns and it is selected to be the thermal dissipation pattern for the AC busbar of ITER PF converter unit. The approach to qualify the suitable cooling scheme in this paper can be provided as a reference on the thermal dissipation design of AC busbar in the converter system.
文摘The zero dissipation limit to the contact discontinuities for one-dimensional com- pressible Navier-Stokes equations was recently proved for ideal polytropic gas （see Huang et al. [15, 22] and Ma [31]）, but there is few result for general gases including ideal polytropic gas. We prove that if the solution to the corresponding Euler system of general gas satisfying （1.4） is piecewise constant with a contact discontinuity, then there exist smooth solutions to Navier-Stokes equations which converge to the inviscid solutions at a rate of k1/4 as the heat-conductivity coefficient k tends to zero. The key is to construct a viscous contact wave of general gas suitable to our proof （see Section 2）. Notice that we have no need to restrict the strength of the contact discontinuity to be small.
基金Project supported by the National Natural Science Foundation of China （Grant No 50278098）.
文摘The equivalent circuit with complex physical constants for a piezoelectric ceramic in thickness mode is established. In the equivalent circuit, electric components （equivalent circuit parameters） are connected to real and imaginary parts of complex physical coefficients of piezoelectric materials. Based on definitions of dissipation factors, three of them （dielectric, elastic and piezoelectric dissipation factors） are represented by equivalent circuit parameters. Since the equivalent circuit parameters are detectable, the dissipation factors can be easily obtained. In the experiments, the temperature and the stress responses of the three dissipation factors are measured.
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 60908012 and 61076148)the Foundation of Beijing Municipal Education Commission, China (Grant No. KM201010005030)
文摘We presented 980-nm oxide-confined vertical-cavity surface-emitting lasers （VCSELs） with a 16 -um oxide aperture. Optical power, voltage, and emission wavelength are measured in an ambient temperature range of 5 ℃-80 ℃. Measurements combined with an empirical model are used to analyse the power dissipation in the device and the physical mechanism contributing to the thermal rollover phenomenon in VCSEL. It is found that the carrier leakage induced selfheating in the active region and the Joule heating caused by the series resistance are the main sources of power dissipation. In addition, carrier leakage induced self-heating increases as the injection current increases, resulting in a rapid decrease of the internal quantum efficiency, which is a dominant contribution to the thermal rollover of the VCSEL at a larger current. Our study provides useful guidelines to design a 980-nm oxide-confined VCSEL for thermal performance enhancement.
基金supported by the National Natural Science Foundation of China (Grant Nos 50277016 and 50577028)supported by the Specialized Research Fund for the Doctoral Program of Higher Education of China (Grant No 20050487044)
文摘The power dissipation characteristics of pulsed power switch reversely switched dynistors （RSDs） are investigated in this paper. According to the expressions of voltage on RSD, derived from the plasma bipolar drift model and the RLC circuit equations of RSD main loop, the simulation waveforms of current and voltage on RSD are acquired through iterative calculation by using the fourth order Runge-Kutta method, then the curve of transient power on RSD versus time is obtained. The result shows that the total dissipation on RSD is trivial compared with the pulse discharge energy and the commutation dissipation can be nearly ignored compared with the quasi-static dissipation. These characteristics can make the repetitive frequency of RSD increase largely. The experimental results prove the validity of simulation calculations. The influence factors on power dissipation are discussed. The power dissipation increases with the increase of the peak current and the n-base width and with the decrease of n-base doping concentration. In order to keep a low power dissipation, it is suggested that the n-base width should be smaller than 320μm when doping concentration is 1.0×10^14cm^-3 while the doping concentration should be higher than 5.8×10^13cm^-3 when n-base width is 270μm.
基金supported by Youth Science Foundation of the National Natural Science Foundation of China(No.51104156)the Fundamental Research Funds for the Central Universities of China(No.2013QNB02)the 12th Five Year National Science and Technology Support Key Project of China(Nos. 2012BAK04B07-2 and 2012BAK09B01-04)
文摘The physical and mechanical change processes of coal and rock are closely related to energy transformation,and the destruction and failure of coal and rock is an instability phenomena driven by energy change.However,the energy change of large-scale coal rock in the mine site is hardly calculated accurately,making it difficult to monitor coal-rock systematic failure and collapse from the perspective of energy.By the energy dissipation EMR monitoring system,we studied the damage and failure of coal and rock with bursting liability from the energy dissipation point using the geophysical method-EMR,and explored the energy dissipation characteristics during uniaxial compression and their main influencing factors.The results show that under displacement-control loading mode,there are 2 types of energy dissipation trends for both coal and rock with bursting liability.The type Ⅰ trend is a steady increase one during the whole process,therein,the energy dissipation of rock samples is accelerated at the peak load.The type Ⅱ trend energy is a W-shaped fluctuating one containing 6 stages.Under load-control loading mode,there is one energy dissipation trend of shock downward-steady rise.Besides that,rock samples also present a trend of 4 stages.The energy dissipation characteristics of coal and rockduring loading failure process can be used as effective criteria to assess whether they are in a stable or destructive stage.The factors influencing energy dissipation in the loading failure process of coal and rock mainly include strength,homogeneity,and energy input efficiency.
基金Project supported by the Science Foundation of Jiangsu Provincial Education 0ffice, China （Grant No 05KJD140035）.
文摘On the basis of quantization of charge, the loop equations of quantum circuits are investigated by using the Helsenberg motion equation for a mesoscopic dissipation transmission line. On the supposition that the system has a symmetry under translation in charge space, the quantum current and the quantum energy spectrum in the mesoscopic transmission llne are given by solving their eigenvalue equations. Results show that the quantum current and the quantum energy spectrum are not only related to the parameters of the transmission llne, but also dependent on the quantized character of the charge obviously.
文摘A numerical study is performed to investigate the flow and heat transfer at the surface of a permeable wedge immersed in a copper （Cu）-water-based nanofluid in the presence of magnetic field and viscous dissipation using a nanofluid model proposed by Tiwari and Das （Tiwari I K and Das M K 2007 Int. J. HeatMass Transfer 50 2002）. A similarity solution for the transformed governing equation is obtained, and those equations are solved by employing a numerical shooting technique with a fourth-order Runge-Kutta integration scheme. A comparison with previously published work is carried out and shows that they are in good agreement with each other. The effects of velocity ratio parameter ~, solid volume fraction tp, magnetic field M, viscous dissipation Ec, and suction parameter Fw on the fluid flow and heat transfer characteristics are discussed. The unique and dual solutions for self-similar equations of the flow and heat transfer are analyzed numerically. Moreover, the range of the velocity ratio parameter for which the solution exists increases in the presence of magnetic field and suction parameter.
基金provided by the National Natural Science Foundation of China (No. 51574231)the Youth Fund of Anhui University of Technology (No. QZ201718)
文摘Dynamic disasters in Chinese coal mines pose a significant threat to coal productivity. Thus, a thorough understanding of the deformation and failure processes of coal is necessary. In this study, the energy dissipation rate is proposed as a novel indicator of coal deformation and failure under static and dynamic compressive loads. The relationship between stress-strain, uniaxial compressive strength, displacement rate, loading rate, fractal dimension, and energy dissipation rate was investigated through experiments conducted using the MTS C60 tests(static loads) and split Hopkinson pressure bar system(dynamic loads). The results show that the energy dissipation rate peaks are associated with stress drop during coal deformation, and also positively related to the uniaxial compressive strength. A higher displacement rate of quasi-static loads leads to an initial increase and then a decrease in energy dissipation rate, whereas a higher loading rate of dynamic loads results in larger energy dissipation rate. Theoretical analysis indicates that a sudden increase in energy dissipation rate suggests partial fracture occurring within coal under both quasi-static and dynamic loads. Hence, the energy dissipation rate is an essential indicator of partial fracture and final failure within coal, as well as a prospective precursor for catastrophic failure in coal mine.
基金supported by the National Natural Science Foundation of China (No. 51974171)the Major Program of Shandong Provincial Natural Science Foundation (No. ZR2019ZD13)the Major Scientific and Technological Innovation Project of Shandong Provincial Key Research Development Program (No. 2019SDZY02)。
文摘Rock joints exhibit hysteresis shearing behavior and produce energy dissipation under shear cyclic loads,which however cannot be accurately depicted by existing constitutive models. This paper establishes a constitutive model for hysteresis shearing and associated energy dissipation of rock joints. Analytical expressions of the model during cyclic shearing processes are derived. Derivation of the model indicates no energy dissipation in the elastic stage. When the shear load exceeds elastic boundary, nonlinear energy dissipation takes place. Validations with experiments show that the proposed model provides good conformities with direct shear curves and hysteresis loops, and can predict the energy dissipation characteristics of rock joints under different working conditions. Compared to the constitutive models using Weibull's distribution, the proposed one is smooth at the elastic boundary and can accurately capture the maximum shear stress. Unlike the existing incremental-type models, the proposed one provides clear and direct analytical expressions for both shear stress and energy dissipation during the whole displacement domain, which is more convenient in application.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.60776051,61006059and61006044)the Beijing Municipal Natural Science Foundation,China(Grant No.4082007)the Beijing Municipal Education Committee,China(Grant Nos.KM200710005015and KM200910005001)
文摘A method of non-uniform finger spacing is proposed to enhance thermal stability of a multiple finger power SiGe heterojunction bipolar transistor under different power dissipations. Temperature distribution on the emitter fingers of a multi-finger SiGe heterojunction bipolar transistor is studied using a numerical electro-thermal model. The results show that the SiGe heterojunction bipolar transistor with non-uniform finger spacing has a small temperature difference between fingers compared with a traditional uniform finger spacing heterojunction bipolar transistor at the same power dissipation. What is most important is that the ability to improve temperature non-uniformity is not weakened as power dissipation increases. So the method of non-uniform finger spacing is very effective in enhancing the thermal stability and the power handing capability of power device. Experimental results verify our conclusions.
基金supported by the Scientific Research Funds of Huaqiao University(14BS309)the National Natural Science Foundation of China(11526091)
文摘This article considers the global regularity to the initial-boundary value problem for the 2D incompressible MHD with mixed partial dissipation and magnetic diffusion. To overcome the difficulty caused by the vanishing viscosities, we first establish the elliptic system for ux and by, which are estimated by 7 × us and × by, respectively. Then, we establish the global estimates for × u and ×b.
