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The prospects of using gravitational waves for constraining the anisotropy of the Universe
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作者 赵志超 林海南 常哲 《中国物理C:英文版》 SCIE CAS CSCD 2019年第7期112-117,共6页
The observation of GW150914 gave a new independent measurement of the luminosity distance of a gravitational wave event. In this paper, we constrain the anisotropy of the Universe by using gravitational wave events.We... The observation of GW150914 gave a new independent measurement of the luminosity distance of a gravitational wave event. In this paper, we constrain the anisotropy of the Universe by using gravitational wave events.We simulate hundreds of events of binary neutron star merger that may be observed by the Einstein Telescope. Full simulation of the production process of gravitational wave data is employed. We find that 200 binary neutron star merging events with the redshift in (0,1) observed by the Einstein Telescope may constrain the anisotropy with an accuracy comparable to that from the Union2.1 supernovae. This result shows that gravitational waves can be a powerful tool for investigating cosmological anisotropy. 展开更多
关键词 GRAVITATIONAL WAVE ANISOTROPIC SPACE-TIME GRAVITATIONAL WAVE detector
Three-Dimensional Growth of Coherent Ferrite in Austenite:A Molecular Dynamics Study
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作者 Zhi-Peng Sun Fu-Zhi Dai +1 位作者 Ben Xu Wen-Zheng Zhang 《金属学报:英文版》 SCIE EI CAS CSCD 2019年第6期669-676,共8页
Coherent second phase often exhibits anisotropic morphology with specifi c orientations with respect to both the second and the matrix phases.As a key feature of microstructure,the morphology of the coherent particles... Coherent second phase often exhibits anisotropic morphology with specifi c orientations with respect to both the second and the matrix phases.As a key feature of microstructure,the morphology of the coherent particles is essential for understanding the second-phase strengthening eff ect in various industrial alloys.This letter reports anisotropic growth of coherent ferrite from austenite matrix in pure iron based on molecular dynamics simulation.We found that the ferrite grain tends to grow into an elongated plate-like shape,independent of its initial confi guration.The fi nal shape of the ferrite is closely related to the misfi t between the two phases,with the longest direction and the broad facet of the plate being,respectively,consistent with the best matching direction and the best matching plane calculated via the Burgers vector content(BVC)method.The strain energy calculation in the framework of Eshelby’s inclusion theory verifi es that the simulated orientation of the coherent ferrite is energetically favorable.It is anticipated that the BVC method will be applicable in analysis of anisotropic growth and morphology of coherent second phase in other phase transformation systems. 展开更多
关键词 COHERENT FERRITE Anisotropic GROWTH Molecular dynamics simulation BURGERS vector content Eshelby’s inclusion theory
基于双径向流模型的产能计算及射孔优化技术 预览
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作者 关利军 李纪智 +1 位作者 何泽俊 林炳南 《石油化工应用》 CAS 2019年第5期35-42,60共9页
应用等值渗流阻力法和双径向流模型,分射穿污染带与未射穿污染带两种情况,推导出各向同性油藏射孔直井的产能公式,考虑了孔深、孔密、孔径、相位、压实带、污染带等因素对产能的影响。在此基础上,根据各向异性油藏渗流理论,得到各向异... 应用等值渗流阻力法和双径向流模型,分射穿污染带与未射穿污染带两种情况,推导出各向同性油藏射孔直井的产能公式,考虑了孔深、孔密、孔径、相位、压实带、污染带等因素对产能的影响。在此基础上,根据各向异性油藏渗流理论,得到各向异性油藏射孔直井产能公式。利用推导的公式对射孔直井产能进行参数敏感性分析,结果表明:射孔直井产能随着孔深、孔径、孔密、相位、垂向渗透率等参数的增大而增大,随着压实带厚度和压实程度的增大而减小;各参数在射穿污染带时的敏感性小于未射穿污染带时的敏感性;孔深、孔密、压实程度、垂向渗透率对产能的影响比较大。工程设计时,应优先考虑孔深、孔密,并避免压实损害程度过高,矿场应用时,结合储层物性特征和作业实际需求,选用合适的射孔器材,形成一套具有针对性的射孔优化技术。 展开更多
关键词 双径向流模型 等值渗流阻力法 各向异性 产能 射孔
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基于三维各向异性拉普拉斯滤波的随机噪声压制方法及应用 预览
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作者 刘宏杰 毛海波 +2 位作者 杨晓海 李文捷 蒋立 《石油地球物理勘探》 EI CSCD 北大核心 2019年第3期522-528,484共8页
准噶尔盆地叠后地震资料随机噪声压制主要采用三维空间预测滤波(FXY)方法。由于假设同相轴在短距离内是线性的,因此该方法在提高强能量信号信噪比的同时,也会损伤相对弱小信号,模糊断层和裂缝等线性相关性较差的地质体的信号特征。为此... 准噶尔盆地叠后地震资料随机噪声压制主要采用三维空间预测滤波(FXY)方法。由于假设同相轴在短距离内是线性的,因此该方法在提高强能量信号信噪比的同时,也会损伤相对弱小信号,模糊断层和裂缝等线性相关性较差的地质体的信号特征。为此,基于GeoEast系统研发了利用三维各向异性拉普拉斯滤波的随机噪声压制方法。模型试验和在准噶尔盆地不同地区的实际资料应用结果均表明,本文方法对随机噪声的压制效果优于FXY方法,能明显提高地震资料信噪比、较好地保护有效信号、清晰展现地质体边缘特征细节及提高断层成像精度,为后续储层反演和精细地震资料解释夯实了基础。 展开更多
关键词 各向异性 拉普拉斯滤波 随机噪声压制 信噪比 FXY滤波法
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Behavior of noncircular tunnels excavated in stratified rock masses-Case of underground coal mines 预览
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作者 Ngoc Anh Do Daniel Dias +4 位作者 Van Diep Dinh Tien Tung Tran Van Canh Dao Viet Doan Dao Phuc Nhan Nguyen 《岩石力学与岩土工程学报:英文版》 CSCD 2019年第1期99-110,共12页
The amount of tunnels excavated along stratified/sedimentary rock masses in Quangninh coal mine area,Vietnam,is gradually increasing.Rock mass in Quangninh is characterized by beddings between rock layers.The behavior... The amount of tunnels excavated along stratified/sedimentary rock masses in Quangninh coal mine area,Vietnam,is gradually increasing.Rock mass in Quangninh is characterized by beddings between rock layers.The behavior of stratified rock masses surrounding the tunnels depends on both the intact rock and the beddings between rock layers.The main characteristics of stratified rock masses that need to be considered are their heterogeneity and anisotropy.Depending on the dip angle of rock layers,movements and failure zones developed surrounding the tunnels can be asymmetrical over the vertical axis of tunnel.This asymmetry causes adverse behaviors of the tunnel structures.The objective of this study is to highlight convergences and yielded zones developed in rock masses surrounding noncircular tunnels in Quangninh coal mine area using a finite element method.The presence of bedding joints is explicitly simulated.The numerical results indicated that with the increase in dip angle of bedding joints,the stress asymmetry over the tunnel vertical axis increases.It gradually leads to an asymmetry of the failure zone surrounding the tunnel.An increase of rock mass quality means a decrease of rock mass sensitivity to the discontinuities.In addition,a dip angle of the bedding joints of approximately 45 could be considered as the critical angle at which the rock mass mechanism changes between sliding and bending. 展开更多
关键词 TUNNEL BEDDING STRATIFICATION ANISOTROPIC HETEROGENEITY
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各向异性密度函数的小波估计
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作者 曹凯凯 《山东大学学报:理学版》 CAS CSCD 北大核心 2019年第6期99-105,共7页
基于小波方法在各向异性 Besov 空间中研究了非紧支密度函数的估计问题,给出线性小波估计器,并证明其在 Lp ( 2≤ p <+∞)风险意义下的上界。进一步地,假定密度函数具有独立结构来降低维数灾难,并给出相应上界证明。
关键词 小波 密度估计 各向异性 独立结构 BESOV 空间
Influence of temperature cycling and pore fluid on tensile strength of chalk 预览
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作者 T.Voake A.Nermoen +2 位作者 C.Ravnas R.I.Korsnes I.L.Fabricius 《岩石力学与岩土工程学报:英文版》 CSCD 2019年第2期277-288,共12页
Calcite has a highly anisotropic thermal expansion coefficient,and repeated heating and cooling cycles can potentially destabilize chalks by breaking cement bonds between neighboring particles.Based on tensile strengt... Calcite has a highly anisotropic thermal expansion coefficient,and repeated heating and cooling cycles can potentially destabilize chalks by breaking cement bonds between neighboring particles.Based on tensile strength measurements,we investigated how temperature cycles induce weakening of chalk.Tensile strength tests were performed on chalk specimens sampled from Kansas(USA)and Mons(Belgium),each with differing amounts of contact cement.Samples of the two chalk types were tested in dry and water-saturated states,and then exposed to 0,15,and 30 temperature cycles in order to find out under what circumstances thermally induced tensile strength reduction occurs.The testing results show that the dry samples were not influenced by temperature cycling in either of the chalk types.However,in the water-saturated state,tensile strength is increasingly reduced with progressive numbers of temperature cycles for both chalk samples,especially for the more cemented Kansas chalk.The Kansas chalk demonstrated higher initial tensile strength compared to the less cemented Mons chalk,but the strength of both chalks was reduced by the same relative proportion when undergoing thermal cycles in the water-saturated state. 展开更多
关键词 TENSILE strength WEAKENING by heating and COOLING cycles ANISOTROPIC thermal EXPANSION
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Understanding the need for pre-injection from permeability measurements:What is the connection? 预览
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作者 Nick Barton Eda Quadros 《岩石力学与岩土工程学报:英文版》 CSCD 2019年第3期576-597,共22页
Pre-grouting ahead of tunnels has three main functions:to control water inflow into the tunnel,to limit groundwater drawdown above the tunnel,and to make tunnelling progress more predictable since rock mass quality is... Pre-grouting ahead of tunnels has three main functions:to control water inflow into the tunnel,to limit groundwater drawdown above the tunnel,and to make tunnelling progress more predictable since rock mass quality is effectively improved.It helps to avoid settlement damage caused by consolidation of clay deposits beneath built-up areas,since towns tend to be built where terrain is more flat,due to the clay deposits.There are so many instances of settlement damage that the profession needs to take note of the need for high-pressure pre-grouting,to use micro-cements and micro-silica additives.The use of highpressure injection may cause joint jacking,but this is local in extent when the rapid pressure decay away from an injection hole is understood.This effect is variable and depends on the geometrical parameters of the joints.This pressure-decay advantage must not be violated by maintaining high pressure when grout flow from the injection hole has ceased.The latter can cause damage to the grouting already achieved.Simplified methods of estimating mean hydraulic apertures(e)from Lugeon testing are described,and from more sophisticated three-dimensional(3D)permeability measurement.The estimation of the larger mean physical joint apertures(E)is based on the joint roughness coefficient(JRC).Comparison is then made with the empirical aperture-particle size criterion E>4d95,where d95 represents almost the largest cement particle size.Depending on joint set orientations and on the available micro-cements,the decision must be made of which range of pre-injection pressure should be aimed for,using successive reductions of the water-cement ratio w/c.More simple estimation of permeability,also with depth dependence,can be made with the empirical link between a modified rock mass quality Q and permeability,which is termed QH2O.The value of this parameter can be based on core-logging or intunnel face logging.The 3D before-and-after-grouting permeability measurements have been used to justify the quantification of rock mass qua 展开更多
关键词 Pre-grouting Micro-cement Hydraulic APERTURES Physical JOINT APERTURES JOINT ROUGHNESS Particle size ANISOTROPIC PERMEABILITY
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Anisotropic Cu@Cu-BTC core-shell nanostructure for memory device
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作者 Yiqi Luo Zhengdong Liu +5 位作者 Geng Wu Guanzhong Wang Tingting Chao Hai Li Juqing Liu Xun Hong 《中国化学快报:英文版》 SCIE CAS CSCD 2019年第5期1093-1096,共4页
The activity and stability of Cu nanostructures strongly depend on their sizes,morphology and structures.Here we report the preparation of two-dimensional(2 D)Cu@Cu-BTC core-shell nanosheets(NSs).The thickness of the ... The activity and stability of Cu nanostructures strongly depend on their sizes,morphology and structures.Here we report the preparation of two-dimensional(2 D)Cu@Cu-BTC core-shell nanosheets(NSs).The thickness of the Cu NSs could be tuned to sub-10 nm through a mild etching process,in which the Cu-BTC in situ grow along with the oxidation on the surface of the Cu NSs.This unique strategy can also be extended to synthesize one-dimensional(1 D)Cu@Cu-BTC nanowires(NWs).Furthermore,the obtained Cu@Cu-BTC NSs could be applied as an effective material to the memory device with the write-onceread-many times(WORM)behavior and the high ION/I(OFF)ratio(>2.7×103). 展开更多
关键词 Copper ANISOTROPIC CORE-SHELL MOF MEMORY DEVICE
Analyze the Dose Results Calculated with AAA Algorithm in Eclipse Software of New Treatment Planning System 预览
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作者 Soai DANG QUOC Quang BUI VINH +2 位作者 Cuong BUI XUAN Toan HOANG VAN Truong VU 《药剂与药理学:英文版》 2019年第6期309-315,共7页
In this paper,the authors investigate the differences between the dose results calculated with AAA(Anisotropic Analytical Algorithm)algorithm in Eclipse 13.0 treatment planning system,which has just commissioned,with ... In this paper,the authors investigate the differences between the dose results calculated with AAA(Anisotropic Analytical Algorithm)algorithm in Eclipse 13.0 treatment planning system,which has just commissioned,with the measured doses.The AAA algorithm in the Eclipse software is used to calculate the absolute dose,relative dose in profile line,and percent depth dose of some specific field size in Blue Phantom.The calculated dose results were compared with measured dose based on Technical Reports Series No.430 of International Atomic Energy Agency(IAEA No.430).The authors have used CC13 ion chamber,Famer Chamber,water phantom,and Omnipro software to measure relative,absolute doses of these fields size.The AAA algorithm was also used to calculate the doses in IMRT(Intensity Modulated Radiotherapy)plan of fifty head and neck cancer patients.These IMRT plans were controlled quality in some points with plastic phantom,and famer chamber FC65.The differences between calculated dose,and measured doses are in the limit of IAEA 430 report.The results of the QA IMRT plan processing are fitting with ESTRO(European Society Therapeutic Radiation Oncology)Booklet No.9. 展开更多
关键词 Analytical ANISOTROPIC ALGORITHM DOSIMETRY relative DOSE ABSOLUTE DOSE
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Constitutive modeling of viscoelastic-viscoplastic behavior of short fiber reinforced polymers coupled with anisotropic damage and moisture effects 预览
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作者 Ge He Yucheng Liu +1 位作者 Xingqiao Deng Lei Fan 《力学学报:英文版》 SCIE EI CAS CSCD 2019年第3期495-506,共12页
In this paper, a combined viscoelasticity-viscoplasticity model, coupled with anisotropic damage and moisture effects, is developed for short fiber reinforced polymers (SFRPs) with different fiber contents and subject... In this paper, a combined viscoelasticity-viscoplasticity model, coupled with anisotropic damage and moisture effects, is developed for short fiber reinforced polymers (SFRPs) with different fiber contents and subjected to a variety of strain rates. In our model, a rate-dependent yield surface for the matrix phase is employed to identify initial yielding of the material. When an SFRP is loaded at small deformation before yielding, its viscoelastic behavior can be described using the generalized Maxwell model, while when plasticity occurs, a scalar internal state variable (ISV) is used to capture the hardening behavior caused by the polymeric constituent of the composite. The material degradation due to the moisture absorption of the composite is modeled by employing another type of ISV with different evolution equations. The complicated damage state of the SFRPs is captured by a second rank tensor, which is further decomposed to model the subscale damage mechanisms of micro-voids/cracks nucleation, growth and coalescence. It is concluded that the proposed constitutive model can be used to accurately describe complicated behaviors of SFRPs because the results predicted from the model are in good agreement with the experimental data. 展开更多
关键词 SHORT fiber reinforced polymer Internal state variable Anisotropic damage MOISTURE effect Viscoelasticity-viscoplasticity
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低温裂隙岩体的各向异性传热模型
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作者 刘乃飞 李宁 +1 位作者 宋战平 李国锋 《岩石力学与工程学报》 EI CAS CSCD 北大核心 2019年第A01期2625-2635,共11页
低温裂隙岩体属于典型的非连续介质,其传热特性具有明显的各向异性特性和时变性。从传热学的基本原理出发,对含冰–水相变低温裂隙岩体的传热特性进行了研究。首先通过类比电阻,推导考虑冰水相变及热对流作用的低温单裂隙热阻模型。在... 低温裂隙岩体属于典型的非连续介质,其传热特性具有明显的各向异性特性和时变性。从传热学的基本原理出发,对含冰–水相变低温裂隙岩体的传热特性进行了研究。首先通过类比电阻,推导考虑冰水相变及热对流作用的低温单裂隙热阻模型。在此基础上,根据能量守恒定律并考虑对流换热作用对裂隙岩体等效传热特性的影响,推导低温单裂隙代表性体元的传热模型。基于传热性能的可叠加性,构建含多组优势节理低温岩体的各向异性传热模型,从而实现低温裂隙岩体传热性能的等效连续化处理。最后通过一个含水平裂隙岩样和理想岩质边坡对各向异性传热模型进行了验证,最大误差不超过1.0℃。该传热模型的精度满足实际低温裂隙岩体工程的要求。 展开更多
关键词 岩石力学 裂隙岩体 各向异性 传热模型 冰–水相变
聚氯乙烯膜材各向异性超弹性本构模型
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作者 徐俊豪 张营营 +2 位作者 赵玉帅 周祎 张其林 《建筑结构学报》 EI CAS CSCD 北大核心 2019年第2期198-205,共8页
为反映聚氯乙烯(PVC)膜材在拉剪耦合应力作用下呈现的大变形、非线性和各向异性等力学特性,基于纤维增强复合材料连续介质力学理论,将应变能解耦为经、纬向纤维束的拉伸变形能和两向纤维束间角度变化产生的剪切变形能,建立了各向异性超... 为反映聚氯乙烯(PVC)膜材在拉剪耦合应力作用下呈现的大变形、非线性和各向异性等力学特性,基于纤维增强复合材料连续介质力学理论,将应变能解耦为经、纬向纤维束的拉伸变形能和两向纤维束间角度变化产生的剪切变形能,建立了各向异性超弹性本构模型。推导了适用于PVC膜材偏轴拉伸的本构模型表达式,给出了获取模型参数的具体方法,并通过堆载试验进行了验证分析。结果表明:该模型能够很好地预测PVC膜材偏轴拉伸应力.应变曲线,且较CECS158:2015中建议模型的计算精度更高。 展开更多
关键词 聚氯乙烯(PVC)膜材 各向异性 超弹性本构关系 拉剪耦合
Drag reduction of turbulent channel flows over an anisotropic porous wall with reduced spanwise permeability 预览
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作者 Qingxiang LI Ming PAN +1 位作者 Quan ZHOU Yuhong DONG 《应用数学和力学:英文版》 SCIE EI CSCD 2019年第7期1041-1052,共12页
The direct numerical simulation (DNS) is carried out for the incompressible viscous turbulent flows over an anisotropic porous wall. Effects of the anisotropic porous wall on turbulence modifications as well as on the... The direct numerical simulation (DNS) is carried out for the incompressible viscous turbulent flows over an anisotropic porous wall. Effects of the anisotropic porous wall on turbulence modifications as well as on the turbulent drag reduction are investigated. The simulation is carried out at a friction Reynolds number of 180, which is based on the averaged friction velocity at the interface between the porous medium and the clear fluid domain. The depth of the porous layer ranges from 0.9 to 54 viscous units. The permeability in the spanwise direction is set to be lower than the other directions in the present simulation. The maximum drag reduction obtained is about 15.3% which occurs for a depth of 9 viscous units. The increasing of drag is addressed when the depth of the porous layer is more than 25 wall units. The thinner porous layer restricts the spanwise extension of the streamwise vortices which suppresses the bursting events near the wall. However, for the thicker porous layer, the wall-normal fluctuations are enhanced due to the weakening of the wall-blocking effect which can trigger strong turbulent structures near the wall. 展开更多
关键词 direct numerical simulation (DNS) ANISOTROPIC POROUS medium drag reduction TURBULENT open channel flow
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Direct numerical simulation of turbulent boundary layer over an anisotropic compliant wall 预览
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作者 Qian-Jin Xia Wei-Xi Huang Chun-Xiao Xu 《力学学报:英文版》 SCIE EI CAS CSCD 2019年第2期384-400,共17页
Direct numerical simulation of a spatially developing turbulent boundary layer over a compliant wall with anisotropic wall material properties is performed. The Reynolds number varies from 300 to approximately 860 alo... Direct numerical simulation of a spatially developing turbulent boundary layer over a compliant wall with anisotropic wall material properties is performed. The Reynolds number varies from 300 to approximately 860 along the streamwise direction, based on the external flow velocity and the momentum thickness. Eight typical cases are selected for numerical investigation under the guidance of the monoharmonic analysis. The instantaneous flow fields exhibit the traveling wavy motion of the compliant wall, and the frequency-wavenumber power spectrum of wall pressure fluctuation is computed to quantify the mutual influence of the wall compliance and the turbulent flow at different wave numbers. It is shown that the Reynolds shear stress and the pressure fluctuation are generally enhanced by the wall compliance with the parameters considered in the present study. A dynamical decomposition of the skin-friction coefficient is derived, and a new term (CW) appears due to the wall-induced Reynolds shear stress. The influence of the anisotropic compliant wall motion on the turbulent boundary layer through the wall-induced negative Reynolds shear stress is discussed. To elucidate the underlying mechanism, the budget analysis of the Reynolds stresses transportation is further carried out. The impact of the wall compliance on the turbulent flow is disclosed by examining the variations of the diffusion and velocity-pressure correlation terms. It is shown that increase of the Reynolds stresses inside the flow domain is caused by enhancement of the velocity-pressure correlation term, possibly through the long-range influence of the wall compliance on the pressure field, rather than diffusion of the wall-induced Reynolds shear stress into the fluid flow. 展开更多
关键词 TURBULENT boundary layer ANISOTROPIC compliant WALL Direct numerical simulation Skin-friction coefficient REYNOLDS shear stress
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Anisotropic Transport on Monolayer and Multilayer Phosphorene in the Presence of an Electric Field
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作者 付谷风 程芳 《中国物理快报:英文版》 SCIE CAS CSCD 2019年第5期71-74,共4页
We demonstrate theoretically the anisotropic quantum transport of electrons through an electric field on monolayer and multilayer phosphorene. Using the long-wavelength Hamiltonian with continuum approximation, we fin... We demonstrate theoretically the anisotropic quantum transport of electrons through an electric field on monolayer and multilayer phosphorene. Using the long-wavelength Hamiltonian with continuum approximation, we find that the transmission probability for transport through an electric field is an oscillating function of incident angle, electric field intensity, as well as the incident energy of electrons. By tuning the electric field intensity and incident angle, the channels can be transited from opaque to transparent. The conductance through the quantum waveguides depends sensitively on the transport direction because of the anisotropic effective mass, and the anisotropy of the conductance can be tuned by the electric field intensity and the number of layers. These behaviors provide us an efficient way to control the transport of phosphorene-based microstructures. 展开更多
关键词 BP ANISOTROPIC Transport on MONOLAYER and MULTILAYER Phosphorene in the PRESENCE of AN Electric Field
Global strong solutions to 3-D Navier-Stokes system with strong dissipation in one direction Dedicated to Professor Jean-Yves Chemin on the Occasion of His 60th Birthday
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作者 Marius Paicu Ping Zhang 《中国科学:数学英文版》 SCIE CSCD 2019年第6期1175-1204,共30页
We consider three-dimensional incompressible Navier-Stokes equations(NS) with different viscous coefficients in the vertical and horizontal variables. In particular, when one of these viscous coefficients is large eno... We consider three-dimensional incompressible Navier-Stokes equations(NS) with different viscous coefficients in the vertical and horizontal variables. In particular, when one of these viscous coefficients is large enough compared with the initial data, we prove the global well-posedness of this system. In fact, we obtain the existence of a global strong solution to(NS) when the initial data verifies an anisotropic smallness condition which takes into account the different roles of the horizontal and vertical viscosity. 展开更多
关键词 anisotropic NAVIER-STOKES equations LITTLEWOOD-PALEY theory WELL-POSEDNESS
Excitation of extremely low-frequency chorus emissions:The role of background plasma density 预览
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作者 XiongDong Yu ZhiGang Yuan +4 位作者 ShiYong Huang Fei Yao Zheng Qiao John R.Wygant Herbert O.Funsten 《地球与行星物理:英文版》 CSCD 2019年第1期1-7,共7页
Low-frequency chorus emissions have recently attracted much attention due to the suggestion that they may play important roles in the dynamics of the Van Allen Belts.However,the mechanism(s)generating these low-freque... Low-frequency chorus emissions have recently attracted much attention due to the suggestion that they may play important roles in the dynamics of the Van Allen Belts.However,the mechanism(s)generating these low-frequency chorus emissions have not been well understood.In this letter,we report an interesting case in which background plasma density lowered the lower cutoff frequency of chorus emissions from above 0.1 fce(typical ordinary chorus)to 0.02 fce(extremely low-frequency chorus).Those extremely low-frequency chorus waves were observed in a rather dense plasma,where the number density Ne was found to be several times larger than has been associated with observations of ordinary chorus waves.For suprathermal electrons whose free energy is supplied by anisotropic temperatures,linear growth rates(calculated using in-situ plasma parameters measured by the Van Allen Probes)show that whistler mode instability can occur at frequencies below 0.1 fce when the background plasma density Ne increases.Especially when Ne reaches 90 cm^-3 or more,the lowest unstable frequency can extend to 0.02 fce or even less,which is consistent with satellite observations.Therefore,our results demonstrate that a dense background plasma could play an essential role in the excitation of extremely lowfrequency chorus waves by controlling the wave growth rates. 展开更多
关键词 LOW-FREQUENCY CHORUS EMISSIONS anisotropic temperature instability WHISTLER mode Van Allen Probes linear growth rate
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不同屈服准则对热轧结构钢各向异性行为预测精度对比
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作者 夏亮亮 陈维晋 +1 位作者 宋鸿武 张士宏 《塑性工程学报》 CAS CSCD 北大核心 2019年第2期259-265,共7页
实验测试了酸洗汽车结构钢QSt E系列热轧钢板不同方向(与轧向分别成0°、45°和90°)的单向拉伸力学性能,获得了其各向异性屈服行为。依据Hill48、Hill90和Barlat89各向异性屈服准则及其参数计算方法,分别建立了QSt E系列... 实验测试了酸洗汽车结构钢QSt E系列热轧钢板不同方向(与轧向分别成0°、45°和90°)的单向拉伸力学性能,获得了其各向异性屈服行为。依据Hill48、Hill90和Barlat89各向异性屈服准则及其参数计算方法,分别建立了QSt E系列钢种的各向异性屈服模型,并将模型预测的不同方向屈服应力及r值与实验结果进行对比分析。结果表明,经优化后的参数求解方法可很好的同时预测单向屈服应力和r值。在r值的预测能力上,不论r值呈抛物线型变化还是单调递增变化,Hill48屈服准则均能很好的预测,Hill90屈服准则仅能很好的预测单调递增变化的情况,而Barlat89屈服准则对两种情况下的预测能力均较弱。 展开更多
关键词 各向异性 屈服准则 参数求解 优化 热轧结构钢
Optical and electrical properties of two-dimensional anisotropic materials 预览
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作者 Ziqi Zhou Yu Cui +2 位作者 Ping-Heng Tan Xuelu Liu Zhongming Wei 《半导体学报:英文版》 EI CAS CSCD 2019年第6期7-17,共11页
Two-dimensional(2D) anisotropic materials, such as B-P, B-As, GeSe, GeAs, ReSe2, KP15 and their hybrid systems, exhibit unique crystal structures and extraordinary anisotropy. This review presents a comprehensive comp... Two-dimensional(2D) anisotropic materials, such as B-P, B-As, GeSe, GeAs, ReSe2, KP15 and their hybrid systems, exhibit unique crystal structures and extraordinary anisotropy. This review presents a comprehensive comparison of various 2D anisotropic crystals as well as relevant FETs and photodetectors, especially on their particular anisotropy in optical and electrical properties. First, the structure of typical 2D anisotropic crystal as well as the analysis of structural anisotropy is provided. Then, recent researches on anisotropic Raman spectra are reviewed. Particularly, a brief measurement principle of Raman spectra under three typical polarized measurement configurations is introduced. Finally, recent progress on the electrical and photoelectrical properties of FETs and polarization-sensitive photodetectors based on 2D anisotropic materials is summarized for the comparison between different 2D anisotropic materials. Beyond the high response speed, sensitivity and on/off ratio, these 2D anisotropic crystals exhibit highly conduction ratio and dichroic ratio which can be applied in terms of polarization sensors, polarization spectroscopy imaging, optical radar and remote sensing. 展开更多
关键词 TWO-DIMENSIONAL ANISOTROPIC RAMAN SPECTRA polarization-sensitive PHOTODETECTORS
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