Multi-axial perfectly matched layer(M-PML),known to have lost the perfect-matching property owing to multi-axial coordinate stretching,has been numerically validated to be long-time stable and it is thus used extensiv...Multi-axial perfectly matched layer(M-PML),known to have lost the perfect-matching property owing to multi-axial coordinate stretching,has been numerically validated to be long-time stable and it is thus used extensively in linear anisotropic wave simulation and in isotropic cases where the PML becomes unstable.We are concerned with the construction of the M-PML for anisotropic wave simulation based on a second order wave equation implemented with the displacement-based numerical method.We address the benefit of the incorrect chain rule,which is implicitly adopted in the previous derivation of the M-PML.We show that using the frequency-shifted stretching function improves the absorbing efficiency of the M-PML for near-grazing incident waves.Then,through multi-axial complex-coordinate stretching the second order anisotropic wave equation in a weak form,we derive a time-domain multi-axial unsplit frequency-shifted PML(M-UFSPML)using the frequency-shifted stretching function and the incorrect chain rule.A new approach is provided to reduce the number of memory variables needed for computing convolution terms in the M-UFSPML.The obtained M-UFSPML is well suited for implementation with a finite element or the spectral element method.By providing several typical examples,we numerically verify the accuracy and long-time stability of the implementation of our M-UFSPML by utilizing the Legendre spectral element method.展开更多
For joining high Cr,Ni and Mo austenitic stainless steel(AISI 316)by direct drive friction welding(DDFW),with friction weld-ing conditions:rotation speed of 3000 r/min,friction time of 10 s,friction pressure of 130 MP...For joining high Cr,Ni and Mo austenitic stainless steel(AISI 316)by direct drive friction welding(DDFW),with friction weld-ing conditions:rotation speed of 3000 r/min,friction time of 10 s,friction pressure of 130 MPa,forge time of 5 s and forge pressure of 260 MPa.The results of microstructure showed that the temperature at the interface reached 819℃while forge applied between 357-237℃,which subdivided welded joint into four distinct regions of highly plastically deformed zone(HPDZ),thermo-mechanically affected zone(TMAZ),heat affected zone(HAZ)and the base metal,with grain size about 10µm,100µm,90µm and 30µm respectively.These re-gions were created due to dynamic recrystallization(DRX)at the interface and thermo-mechanical deformation with heat diffusion in the neighboring regions.Whereas,high level of microhardness about 300 HV0.1 and hardness roughly 240 Hv10 at the interface due to HPDZ creation while low level of 240 HV0.1 for microhardness and moderately of 205 HV10 for hardness in neighboring regions.展开更多
Thrombosis plays a crucial role in atherosclerosis or in haemostasis when a blood vessel is injured.This article focuses on using a meshless particle-based Lagrangian numerical technique,the smoothed particles hydrody...Thrombosis plays a crucial role in atherosclerosis or in haemostasis when a blood vessel is injured.This article focuses on using a meshless particle-based Lagrangian numerical technique,the smoothed particles hydrodynamic(SPH)method,to study the flow behaviour of blood and to explore the flow parameters that induce formation of a thrombus in a blood vessel.Due to its simplicity and effectiveness,the SPH method is employed here to simulate the process of thrombogenesis and to study the effect of various blood flow parameters.In the present SPH simulation,blood is modelled by two sets of particles that have the characteristics of plasma and of platelet,respectively.To simulate coagulation of platelets which leads to a thrombus,the so-called adhesion and aggregation mechanisms of the platelets during this process are modelled by an inter-particle force model.The transport of platelets in the flowing blood,platelet adhesion and aggregation processes are coupled with viscous blood flow for various low Reynolds number scenarios.The numerical results are compared with the experimental observations and a good agreement is found between the simulated and experimental results.展开更多
In statistical modeling area, the Akaike information criterion AIC, is a widely known and extensively used tool for model choice. The φ-divergence test statistic is a recently developed tool for statistical model sel...In statistical modeling area, the Akaike information criterion AIC, is a widely known and extensively used tool for model choice. The φ-divergence test statistic is a recently developed tool for statistical model selection. The popularity of the divergence criterion is however tempered by their known lack of robustness in small sample. In this paper the penalized minimum Hellinger distance type statistics are considered and some properties are established. The limit laws of the estimates and test statistics are given under both the null and the alternative hypotheses, and approximations of the power functions are deduced. A model selection criterion relative to these divergence measures are developed for parametric inference. Our interest is in the problem to testing for choosing between two models using some informational type statistics, when independent sample are drawn from a discrete population. Here, we discuss the asymptotic properties and the performance of new procedure tests and investigate their small sample behavior.展开更多
Abstract Accurate simulation of seismic wave propaga- tion in complex geological structures is of particular interest nowadays. However conventional methods may fail to simulate realistic wavefields in environments wi...Abstract Accurate simulation of seismic wave propaga- tion in complex geological structures is of particular interest nowadays. However conventional methods may fail to simulate realistic wavefields in environments with great and rapid structural changes, due for instance to the presence of shadow zones, diffractions and/or edge effects. Different methods, developed to improve seismic model- ing, are typically tested on synthetic configurations against analytical solutions for simple canonical problems or ref- erence methods, or via direct comparison with real data acquired in situ. Such approaches have limitations,especially if the propagation occurs in a complex envi- ronment with strong-contrast reflectors and surface irreg- ularities, as it can be difficult to determine the method which gives the best approximation of the ＂real＂ solution, or to interpret the results obtained without an a priori knowledge of the geologic environment. An alternative approach for seismics consists in comparing the synthetic data with high-quality data collected in laboratory experi- ments under controlled conditions for a known configuration. In contrast with numerical experiments, laboratory data possess many of the characteristics of field data, as real waves propagate through models with no numerical approximations. We thus present a comparison of laboratory-scaled measurements of 3D zero-offset wave reflection of broadband pulses from a strong topographic environment immersed in a water tank with numerical data simulated by means of a spectral-element method and a discretized Kirchhoff integral method. The results indicate a good quantitative fit in terms of time arrivals and acceptable fit in amplitudes for all datasets.展开更多
The neuropsychiatric disease named obsessive-compulsive disorder is composed by obsessions and/or compulsions.Obsessive-compulsive disorder etiologies are undefined.However,numerous mechanisms in several localizations...The neuropsychiatric disease named obsessive-compulsive disorder is composed by obsessions and/or compulsions.Obsessive-compulsive disorder etiologies are undefined.However,numerous mechanisms in several localizations are implicated.Some studies showed that both glutamate,inflammatory factors and oxidative stress could have main functions in obsessive-compulsive disorder.Glycogen synthase kinase-3β,the major negative controller of the WNT/β-catenin pathway is upregulated in obsessive-compulsive disorder.In obsessive-compulsive disorder,some studies presented the actions of the different circadian clock genes.WNT/β-catenin pathway and circadian clock genes appear to be intricate.Thus,this review focuses on the interaction between circadian clock genes and the WNT/β-catenin pathway in obsessive-compulsive disorder.展开更多
In our study, we investigate the differences between the combustion of different hydrocarbon fuels CH4, C3H8, C4H10. A numerical simulation of an impinging jet diffusion flames is used. The jet injector has a 10 mm in...In our study, we investigate the differences between the combustion of different hydrocarbon fuels CH4, C3H8, C4H10. A numerical simulation of an impinging jet diffusion flames is used. The jet injector has a 10 mm in diameter and the distance between the jet flame and the vertical wall is 2 time half diameter. The fuel jet velocity was fixed for 11.8 m/s, corresponding to a Reynolds number of 6881. The flame characteristics varied from hydrocarbon to another for the same Reynolds number. The combustion products of CO, CO2, NO, OH, are depending on the methane and propane and butane flames for the same conditions. The temperature of the flame was varied from hydrocarbon to another the same as for the chemical species production rate. The concentration of the thermal and prompt NO pollutant depends on the temperature flow field and on the thermochemical characteristics of the hydrocarbon fuels.展开更多
The scattering strength of isotropic and anisotropic rough surfaces was experimentally and theoretically investigated for high frequencies about 500 kHz. Emphasis was placed on studying the response from three two-dim...The scattering strength of isotropic and anisotropic rough surfaces was experimentally and theoretically investigated for high frequencies about 500 kHz. Emphasis was placed on studying the response from three two-dimensional rough surfaces which roughness was either isotropic (characterized by a Gaussian distribution) or anisotropic (characterized by a modified-sine surface). Theoretical predictions rely on the first-order small slope approximation either including a Gaussian structure function or a quasi-periodic structure function. The combination of true data and theoretical results indicates the importance of taking into account the anisotropy of a surface in a scattering prediction process. It is shown that the scattering strength varies a lot depending on the propagation plane. In the longitudinal direction of ripples, scattering strength is mostly in the specular direction, whereas in the transversal direction of the ripples, the scattering strength is spread in a very different way related to the particular features of the ripples, with several maxima and minima independent of the specular direction. Contrary to the isotropic surface, the scattering strength from an anisotropic rough surface is modified from one propagation plane to another, which explains why the entire rough surface should be taken into account without any simplification as it is often seen when dealing with scattering models. Compared to such a surface, positions of the emitter and of the receiver are naturally significant when measuring scattering strength.展开更多
Film-boiling heat transfer is a key phenomenon governing severe accident sequence in a sodium-cooled fast reactor. Experimental the fuel-coolant interaction process which may occur during a and theoretical work on fil...Film-boiling heat transfer is a key phenomenon governing severe accident sequence in a sodium-cooled fast reactor. Experimental the fuel-coolant interaction process which may occur during a and theoretical work on film-boiling heat transfer in sodium has hardly been carried out in the past. An experiment has been conducted in the early seventies to investigate sodium pool boiling. In this experiment, a hot tantalum sphere was immersed into subcooled liquid sodium. Film boiling was obtained for various sets of parameters： sodium subcooling from 4.1 K to 29. 1 K, initial sphere temperature ranging from 1,802.6 K to 2,633.7 K, sphere diameters of 1.27, 1.91 and 2.54 cm and sodium depths of 7.6 cm and 11.4 cm. In the present work, a simplified analysis based on the boundary layer theory is developed to describe pool film-boiling heat transfer on a hot sphere in liquid sodium. Two extreme cases are considered depending on sodium subcooling. In the case of high subcooling, most of the heat lost by the sphere is used to heat the sodium while for low subcooling, it is used to vaporize the liquid at the liquid-vapor interface. It will be shown that the scaling analysis predicts the heat fluxes within the order of magnitude when compared to the available experimental data. Besides, it allows an estimation of the contribution of these fluxes to the liquid heating and vaporization processes.展开更多
We report on a Te-seeded epitaxial growth of ultrathin Bi2Te3 nanoplates （down to three quintuple layers （QL）） with large planar sizes （up to tens of micrometers） through vapor transport. Optical contrast has be...We report on a Te-seeded epitaxial growth of ultrathin Bi2Te3 nanoplates （down to three quintuple layers （QL）） with large planar sizes （up to tens of micrometers） through vapor transport. Optical contrast has been systematically investigated for the as-grown Bi2Te3 nanoplates on the SiO2/Si substrates, experimentally and computationally. The high and distinct optical contrast provides a fast and convenient method for the thickness determination of few-QL Bi2Te3 nanoplates. By aberration-corrected scanning transmission electron microscopy, a hexagonal crystalline structure has been identified for the Te seeds, which form naturally during the growth process and initiate an epitaxial growth of the rhombohedral- structured Bi2Te3 nanoplates. The epitaxial relationship between Te and Bi2T% is identified to be perfect along both in-plane and out-of-plane directions of the layered nanoplate. Similar growth mechanism might be expected for other bismuth chalcogenide layered materials.展开更多
Strain engineering provides an effective mean of tuning the fundamental properties of semiconductors for electric and optoelectronic applications. Here we report on how the applied strain changes the emission properti...Strain engineering provides an effective mean of tuning the fundamental properties of semiconductors for electric and optoelectronic applications. Here we report on how the applied strain changes the emission properties of hetero- structures consisting of different crystalline phases in the same CdS nanobelts. The strained portion was found to produce an additional emission peak on the low-energy side that was blueshifted with increasing strain. Furthermore, the additional emission peak obeyed the Varshni equation with temperature and exhibited the band-filling effect at high excitation power. This new emission peak may be attributed to spatially indirect exciton recombination between different crystalline phases of CdS. First-principles calculations were performed based on the spatially indirect exciton recombination, and the calculated and experimental results agreed with one another. Strain proved to be capable of enhancing the anti-Stokes emission, suggesting that the efficiency of laser cooling may be improved by strain engineering.展开更多
We propose a new Absorbing Boundary Condition(ABC)for the acoustic wave equation which is derived from a micro-local diagonalization process formerly defined by M.E.Taylor and which does not depend on the geometry of ...We propose a new Absorbing Boundary Condition(ABC)for the acoustic wave equation which is derived from a micro-local diagonalization process formerly defined by M.E.Taylor and which does not depend on the geometry of the surface bearing the ABC.By considering the principal symbol of the wave equation both in the hyperbolic and the elliptic regions,we show that a second-order ABC can be constructed as the combination of an existing first-order ABC and a Fourier-Robin condition.We compare the new ABC with other ABCs and we show that it performs well in simple configurations and that it improves the accuracy of the numerical solution without increasing the computational burden.展开更多
We present a new high ordermethod in space and time for solving the wave equation,based on a newinterpretation of the“Modified Equation”technique.Indeed,contrary to most of the works,we consider the time discretizat...We present a new high ordermethod in space and time for solving the wave equation,based on a newinterpretation of the“Modified Equation”technique.Indeed,contrary to most of the works,we consider the time discretization before the space discretization.After the time discretization,an additional biharmonic operator appears,which can not be discretized by classical finite elements.We propose a new Discontinuous Galerkinmethod for the discretization of this operator,andwe provide numerical experiments proving that the new method is more accurate than the classicalModified Equation technique with a lower computational burden.展开更多
We are interested in the modeling of wave propagation in an infinite bilayered acoustic/poroelastic media. We consider the biphasic Biot’s model in the poroelastic layer. The first part was devoted to the calculation...We are interested in the modeling of wave propagation in an infinite bilayered acoustic/poroelastic media. We consider the biphasic Biot’s model in the poroelastic layer. The first part was devoted to the calculation of analytical solution in twodimensions, thanks to Cagniard de Hoop method. In the first part (Diaz and Ezziani,Commun. Comput. Phys., Vol. 7, pp. 171-194) solution to the two-dimensional problem is considered. In this second part we consider the 3D case.展开更多
Thanks to the Cagniard-de Hoop’s method we derive the solution to theproblem of wave propagation in an infinite bilayered acoustic/poroelastic media, wherethe poroelastic layer is modelled by the biphasic Biot’s mod...Thanks to the Cagniard-de Hoop’s method we derive the solution to theproblem of wave propagation in an infinite bilayered acoustic/poroelastic media, wherethe poroelastic layer is modelled by the biphasic Biot’s model. This first part is dedi-cated to solution to the two-dimensional problem. We illustrate the properties of thesolution, which will be used to validate a numerical code.展开更多
This work pertains to numerical aspects of a finite element method based discontinuous functions.Our study focuses on the Interior Penalty Discontinuous Galerkin method(IPDGM)because of its high-level of flexibility f...This work pertains to numerical aspects of a finite element method based discontinuous functions.Our study focuses on the Interior Penalty Discontinuous Galerkin method(IPDGM)because of its high-level of flexibility for solving the full wave equation in heterogeneousmedia.We assess the performance of IPDGMthrough a comparison study with a spectral element method(SEM).We show that IPDGM is as accurate as SEM.In addition,we illustrate the efficiency of IPDGM when employed in a seismic imaging process by considering two-dimensional problems involving the Reverse Time Migration.展开更多
We investigate through this research the numerical inversion technique for the Laplace transforms cooperated by the integration Boubaker polynomials operational matrix.The efficiency of the presented approach is demon...We investigate through this research the numerical inversion technique for the Laplace transforms cooperated by the integration Boubaker polynomials operational matrix.The efficiency of the presented approach is demonstrated by solving some differential equations.Also,this technique is combined with the standard Laplace Homotopy Per-turbation Method.The numerical results highlight that there is a very good agreement between the estimated solutions with exact solutions.展开更多
A new solution methodology is proposed for solving efficiently Helmholtz problems.The proposed method falls in the category of the discontinuous Galerkin methods.However,unlike the existing solution methodologies,this...A new solution methodology is proposed for solving efficiently Helmholtz problems.The proposed method falls in the category of the discontinuous Galerkin methods.However,unlike the existing solution methodologies,this method requires solving(a)well-posed local problems to determine the primal variable,and(b)a global positive semi-definite Hermitian system to evaluate the Lagrange multiplier needed to restore the continuity across the element edges.Illustrative numerical results obtained for two-dimensional interior Helmholtz problems are presented to assess the accuracy and the stability of the proposed solution methodology.展开更多
Using the averaging theory of first and second order we study the maximum number of limit cycles of generalized Linard differential systems{x = y ＋ εhl1（x） ＋ ε2hl2（x）,y=-x- ε（fn1（x）y（2p＋1） ＋ gm1（x））...Using the averaging theory of first and second order we study the maximum number of limit cycles of generalized Linard differential systems{x = y ＋ εhl1（x） ＋ ε2hl2（x）,y=-x- ε（fn1（x）y（2p＋1） ＋ gm1（x）） ＋ ∈2（fn2（x）y（2p＋1） ＋ gm2（x））,which bifurcate from the periodic orbits of the linear center x = y,y=-x,where ε is a small parameter.The polynomials hl1 and hl2 have degree l;fn1and fn2 have degree n;and gm1,gm2 have degree m.p ∈ N and[·]denotes the integer part function.展开更多
基金Scientific Research Fund of Institute of Engineering Mechanics,China Earthquake Administration under Grant No.2021EEEVL0102National Natural Science Foundation of China under Grant Nos.U2039209 and 51808516+1 种基金the National Key R&D Program of China under Grant No.2018YFC1504004Distinguished Young Scholars Program of the Natural Science Foundation of Heilongjiang province,China under Grant No.YQ2020E005。
文摘Multi-axial perfectly matched layer(M-PML),known to have lost the perfect-matching property owing to multi-axial coordinate stretching,has been numerically validated to be long-time stable and it is thus used extensively in linear anisotropic wave simulation and in isotropic cases where the PML becomes unstable.We are concerned with the construction of the M-PML for anisotropic wave simulation based on a second order wave equation implemented with the displacement-based numerical method.We address the benefit of the incorrect chain rule,which is implicitly adopted in the previous derivation of the M-PML.We show that using the frequency-shifted stretching function improves the absorbing efficiency of the M-PML for near-grazing incident waves.Then,through multi-axial complex-coordinate stretching the second order anisotropic wave equation in a weak form,we derive a time-domain multi-axial unsplit frequency-shifted PML(M-UFSPML)using the frequency-shifted stretching function and the incorrect chain rule.A new approach is provided to reduce the number of memory variables needed for computing convolution terms in the M-UFSPML.The obtained M-UFSPML is well suited for implementation with a finite element or the spectral element method.By providing several typical examples,we numerically verify the accuracy and long-time stability of the implementation of our M-UFSPML by utilizing the Legendre spectral element method.
文摘For joining high Cr,Ni and Mo austenitic stainless steel(AISI 316)by direct drive friction welding(DDFW),with friction weld-ing conditions:rotation speed of 3000 r/min,friction time of 10 s,friction pressure of 130 MPa,forge time of 5 s and forge pressure of 260 MPa.The results of microstructure showed that the temperature at the interface reached 819℃while forge applied between 357-237℃,which subdivided welded joint into four distinct regions of highly plastically deformed zone(HPDZ),thermo-mechanically affected zone(TMAZ),heat affected zone(HAZ)and the base metal,with grain size about 10µm,100µm,90µm and 30µm respectively.These re-gions were created due to dynamic recrystallization(DRX)at the interface and thermo-mechanical deformation with heat diffusion in the neighboring regions.Whereas,high level of microhardness about 300 HV0.1 and hardness roughly 240 Hv10 at the interface due to HPDZ creation while low level of 240 HV0.1 for microhardness and moderately of 205 HV10 for hardness in neighboring regions.
文摘Thrombosis plays a crucial role in atherosclerosis or in haemostasis when a blood vessel is injured.This article focuses on using a meshless particle-based Lagrangian numerical technique,the smoothed particles hydrodynamic(SPH)method,to study the flow behaviour of blood and to explore the flow parameters that induce formation of a thrombus in a blood vessel.Due to its simplicity and effectiveness,the SPH method is employed here to simulate the process of thrombogenesis and to study the effect of various blood flow parameters.In the present SPH simulation,blood is modelled by two sets of particles that have the characteristics of plasma and of platelet,respectively.To simulate coagulation of platelets which leads to a thrombus,the so-called adhesion and aggregation mechanisms of the platelets during this process are modelled by an inter-particle force model.The transport of platelets in the flowing blood,platelet adhesion and aggregation processes are coupled with viscous blood flow for various low Reynolds number scenarios.The numerical results are compared with the experimental observations and a good agreement is found between the simulated and experimental results.
文摘In statistical modeling area, the Akaike information criterion AIC, is a widely known and extensively used tool for model choice. The φ-divergence test statistic is a recently developed tool for statistical model selection. The popularity of the divergence criterion is however tempered by their known lack of robustness in small sample. In this paper the penalized minimum Hellinger distance type statistics are considered and some properties are established. The limit laws of the estimates and test statistics are given under both the null and the alternative hypotheses, and approximations of the power functions are deduced. A model selection criterion relative to these divergence measures are developed for parametric inference. Our interest is in the problem to testing for choosing between two models using some informational type statistics, when independent sample are drawn from a discrete population. Here, we discuss the asymptotic properties and the performance of new procedure tests and investigate their small sample behavior.
基金the INSIS Institute of the French CNRS,Aix-Marseille Universitythe Carnot Star Institute,the VISTA Projectthe Norwegian Research Council through the ROSE Project for financial support
文摘Abstract Accurate simulation of seismic wave propaga- tion in complex geological structures is of particular interest nowadays. However conventional methods may fail to simulate realistic wavefields in environments with great and rapid structural changes, due for instance to the presence of shadow zones, diffractions and/or edge effects. Different methods, developed to improve seismic model- ing, are typically tested on synthetic configurations against analytical solutions for simple canonical problems or ref- erence methods, or via direct comparison with real data acquired in situ. Such approaches have limitations,especially if the propagation occurs in a complex envi- ronment with strong-contrast reflectors and surface irreg- ularities, as it can be difficult to determine the method which gives the best approximation of the ＂real＂ solution, or to interpret the results obtained without an a priori knowledge of the geologic environment. An alternative approach for seismics consists in comparing the synthetic data with high-quality data collected in laboratory experi- ments under controlled conditions for a known configuration. In contrast with numerical experiments, laboratory data possess many of the characteristics of field data, as real waves propagate through models with no numerical approximations. We thus present a comparison of laboratory-scaled measurements of 3D zero-offset wave reflection of broadband pulses from a strong topographic environment immersed in a water tank with numerical data simulated by means of a spectral-element method and a discretized Kirchhoff integral method. The results indicate a good quantitative fit in terms of time arrivals and acceptable fit in amplitudes for all datasets.
文摘The neuropsychiatric disease named obsessive-compulsive disorder is composed by obsessions and/or compulsions.Obsessive-compulsive disorder etiologies are undefined.However,numerous mechanisms in several localizations are implicated.Some studies showed that both glutamate,inflammatory factors and oxidative stress could have main functions in obsessive-compulsive disorder.Glycogen synthase kinase-3β,the major negative controller of the WNT/β-catenin pathway is upregulated in obsessive-compulsive disorder.In obsessive-compulsive disorder,some studies presented the actions of the different circadian clock genes.WNT/β-catenin pathway and circadian clock genes appear to be intricate.Thus,this review focuses on the interaction between circadian clock genes and the WNT/β-catenin pathway in obsessive-compulsive disorder.
文摘In our study, we investigate the differences between the combustion of different hydrocarbon fuels CH4, C3H8, C4H10. A numerical simulation of an impinging jet diffusion flames is used. The jet injector has a 10 mm in diameter and the distance between the jet flame and the vertical wall is 2 time half diameter. The fuel jet velocity was fixed for 11.8 m/s, corresponding to a Reynolds number of 6881. The flame characteristics varied from hydrocarbon to another for the same Reynolds number. The combustion products of CO, CO2, NO, OH, are depending on the methane and propane and butane flames for the same conditions. The temperature of the flame was varied from hydrocarbon to another the same as for the chemical species production rate. The concentration of the thermal and prompt NO pollutant depends on the temperature flow field and on the thermochemical characteristics of the hydrocarbon fuels.
文摘The scattering strength of isotropic and anisotropic rough surfaces was experimentally and theoretically investigated for high frequencies about 500 kHz. Emphasis was placed on studying the response from three two-dimensional rough surfaces which roughness was either isotropic (characterized by a Gaussian distribution) or anisotropic (characterized by a modified-sine surface). Theoretical predictions rely on the first-order small slope approximation either including a Gaussian structure function or a quasi-periodic structure function. The combination of true data and theoretical results indicates the importance of taking into account the anisotropy of a surface in a scattering prediction process. It is shown that the scattering strength varies a lot depending on the propagation plane. In the longitudinal direction of ripples, scattering strength is mostly in the specular direction, whereas in the transversal direction of the ripples, the scattering strength is spread in a very different way related to the particular features of the ripples, with several maxima and minima independent of the specular direction. Contrary to the isotropic surface, the scattering strength from an anisotropic rough surface is modified from one propagation plane to another, which explains why the entire rough surface should be taken into account without any simplification as it is often seen when dealing with scattering models. Compared to such a surface, positions of the emitter and of the receiver are naturally significant when measuring scattering strength.
文摘Film-boiling heat transfer is a key phenomenon governing severe accident sequence in a sodium-cooled fast reactor. Experimental the fuel-coolant interaction process which may occur during a and theoretical work on film-boiling heat transfer in sodium has hardly been carried out in the past. An experiment has been conducted in the early seventies to investigate sodium pool boiling. In this experiment, a hot tantalum sphere was immersed into subcooled liquid sodium. Film boiling was obtained for various sets of parameters： sodium subcooling from 4.1 K to 29. 1 K, initial sphere temperature ranging from 1,802.6 K to 2,633.7 K, sphere diameters of 1.27, 1.91 and 2.54 cm and sodium depths of 7.6 cm and 11.4 cm. In the present work, a simplified analysis based on the boundary layer theory is developed to describe pool film-boiling heat transfer on a hot sphere in liquid sodium. Two extreme cases are considered depending on sodium subcooling. In the case of high subcooling, most of the heat lost by the sphere is used to heat the sodium while for low subcooling, it is used to vaporize the liquid at the liquid-vapor interface. It will be shown that the scaling analysis predicts the heat fluxes within the order of magnitude when compared to the available experimental data. Besides, it allows an estimation of the contribution of these fluxes to the liquid heating and vaporization processes.
文摘We report on a Te-seeded epitaxial growth of ultrathin Bi2Te3 nanoplates （down to three quintuple layers （QL）） with large planar sizes （up to tens of micrometers） through vapor transport. Optical contrast has been systematically investigated for the as-grown Bi2Te3 nanoplates on the SiO2/Si substrates, experimentally and computationally. The high and distinct optical contrast provides a fast and convenient method for the thickness determination of few-QL Bi2Te3 nanoplates. By aberration-corrected scanning transmission electron microscopy, a hexagonal crystalline structure has been identified for the Te seeds, which form naturally during the growth process and initiate an epitaxial growth of the rhombohedral- structured Bi2Te3 nanoplates. The epitaxial relationship between Te and Bi2T% is identified to be perfect along both in-plane and out-of-plane directions of the layered nanoplate. Similar growth mechanism might be expected for other bismuth chalcogenide layered materials.
文摘Strain engineering provides an effective mean of tuning the fundamental properties of semiconductors for electric and optoelectronic applications. Here we report on how the applied strain changes the emission properties of hetero- structures consisting of different crystalline phases in the same CdS nanobelts. The strained portion was found to produce an additional emission peak on the low-energy side that was blueshifted with increasing strain. Furthermore, the additional emission peak obeyed the Varshni equation with temperature and exhibited the band-filling effect at high excitation power. This new emission peak may be attributed to spatially indirect exciton recombination between different crystalline phases of CdS. First-principles calculations were performed based on the spatially indirect exciton recombination, and the calculated and experimental results agreed with one another. Strain proved to be capable of enhancing the anti-Stokes emission, suggesting that the efficiency of laser cooling may be improved by strain engineering.
文摘We propose a new Absorbing Boundary Condition(ABC)for the acoustic wave equation which is derived from a micro-local diagonalization process formerly defined by M.E.Taylor and which does not depend on the geometry of the surface bearing the ABC.By considering the principal symbol of the wave equation both in the hyperbolic and the elliptic regions,we show that a second-order ABC can be constructed as the combination of an existing first-order ABC and a Fourier-Robin condition.We compare the new ABC with other ABCs and we show that it performs well in simple configurations and that it improves the accuracy of the numerical solution without increasing the computational burden.
基金supported by the Conseil General des Pyrenees Atlantiques.
文摘We present a new high ordermethod in space and time for solving the wave equation,based on a newinterpretation of the“Modified Equation”technique.Indeed,contrary to most of the works,we consider the time discretization before the space discretization.After the time discretization,an additional biharmonic operator appears,which can not be discretized by classical finite elements.We propose a new Discontinuous Galerkinmethod for the discretization of this operator,andwe provide numerical experiments proving that the new method is more accurate than the classicalModified Equation technique with a lower computational burden.
基金This work was partially supported by the ANR project“AHPI”(ANR-07-BLAN-0247-01).
文摘We are interested in the modeling of wave propagation in an infinite bilayered acoustic/poroelastic media. We consider the biphasic Biot’s model in the poroelastic layer. The first part was devoted to the calculation of analytical solution in twodimensions, thanks to Cagniard de Hoop method. In the first part (Diaz and Ezziani,Commun. Comput. Phys., Vol. 7, pp. 171-194) solution to the two-dimensional problem is considered. In this second part we consider the 3D case.
文摘Thanks to the Cagniard-de Hoop’s method we derive the solution to theproblem of wave propagation in an infinite bilayered acoustic/poroelastic media, wherethe poroelastic layer is modelled by the biphasic Biot’s model. This first part is dedi-cated to solution to the two-dimensional problem. We illustrate the properties of thesolution, which will be used to validate a numerical code.
基金support by TOTAL/INRIA strategic action DIP(Depth Imaging Partnership).
文摘This work pertains to numerical aspects of a finite element method based discontinuous functions.Our study focuses on the Interior Penalty Discontinuous Galerkin method(IPDGM)because of its high-level of flexibility for solving the full wave equation in heterogeneousmedia.We assess the performance of IPDGMthrough a comparison study with a spectral element method(SEM).We show that IPDGM is as accurate as SEM.In addition,we illustrate the efficiency of IPDGM when employed in a seismic imaging process by considering two-dimensional problems involving the Reverse Time Migration.
文摘We investigate through this research the numerical inversion technique for the Laplace transforms cooperated by the integration Boubaker polynomials operational matrix.The efficiency of the presented approach is demonstrated by solving some differential equations.Also,this technique is combined with the standard Laplace Homotopy Per-turbation Method.The numerical results highlight that there is a very good agreement between the estimated solutions with exact solutions.
基金support by TOTAL and INRIA/CSUN Associate Team Magic,INRIA Bordeaux Sud-Ouest Center.Any opinions,findings,and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of TOTAL,INRIA or CSUN.
文摘A new solution methodology is proposed for solving efficiently Helmholtz problems.The proposed method falls in the category of the discontinuous Galerkin methods.However,unlike the existing solution methodologies,this method requires solving(a)well-posed local problems to determine the primal variable,and(b)a global positive semi-definite Hermitian system to evaluate the Lagrange multiplier needed to restore the continuity across the element edges.Illustrative numerical results obtained for two-dimensional interior Helmholtz problems are presented to assess the accuracy and the stability of the proposed solution methodology.
文摘Using the averaging theory of first and second order we study the maximum number of limit cycles of generalized Linard differential systems{x = y ＋ εhl1（x） ＋ ε2hl2（x）,y=-x- ε（fn1（x）y（2p＋1） ＋ gm1（x）） ＋ ∈2（fn2（x）y（2p＋1） ＋ gm2（x））,which bifurcate from the periodic orbits of the linear center x = y,y=-x,where ε is a small parameter.The polynomials hl1 and hl2 have degree l;fn1and fn2 have degree n;and gm1,gm2 have degree m.p ∈ N and[·]denotes the integer part function.
