沥青混合料的黏弹性性能与温度、时间及其胶结料的状态等参数密切相关,而在路面的使用过程中沥青容易受到老化的影响,进一步影响沥青混合料的黏弹性性能。为了让路面设计过程中的参数更为具体,在实验室内对不同老化状态下的SBS改性沥青...沥青混合料的黏弹性性能与温度、时间及其胶结料的状态等参数密切相关,而在路面的使用过程中沥青容易受到老化的影响,进一步影响沥青混合料的黏弹性性能。为了让路面设计过程中的参数更为具体,在实验室内对不同老化状态下的SBS改性沥青混合料进行多个频率及温度下的单轴动态模量试验。采用William, Landel and Ferry(WLF)公式对不同温度下的频率进行时温等效转换,然后基于分数阶模型(2S2P1D模型)建立了动态模量及相位角主曲线,分析老化对沥青混合料黏弹性能的影响特征。研究结果表明:2S2P1D模型能够较好地拟合不同老化状态下的SBS改性沥青混合料的动态模量的数据,相关系数大于0.9;沥青混合料的2S2P1D模型中的玻璃态模量Eg和与粘度相关的β参数随着老化程度的增加显著增大。然而,静态模量E0、分数阶指数k及h随着老化程度的增加而减小。基于该模型建立的储存模量及损失模量的主曲线表明:低频时老化对于沥青混合料的储存模量及损失模量具有不同的影响,当频率趋近于0时,老化对储存模量的影响基本不存在,但是随着老化程度的加深损失模量会显著增强。展开更多
The main purpose of this article is to choose among advanced rheological models used in the French rational design, one that best represents the viscoelastic behavior of asphalt mixtures mixed with aggregates of Seneg...The main purpose of this article is to choose among advanced rheological models used in the French rational design, one that best represents the viscoelastic behavior of asphalt mixtures mixed with aggregates of Senegal. The model chosen will be the basis for the development of computational tools for stress and strain for Senegal. However, the calibration of these models needs complex modulus test results. In opposition to mechanical models the complex modulus can directly characterize the viscoelastic behavior of bituminous materials. Here determination is performed in the laboratory by using several types of tests divided into two groups: homogeneous tests and non-homogeneous tests. The choice of model will be carried out by statistical analysis through the least squares method. To this end, a study was carried out to “Laboratory of Pavement and Bituminous Materials” (LCMB) with asphalt concrete mixed with aggregate from Senegal named basalt of Diack and quartzite of Bakel. In this study, the test used to measure the complex modulus is the Canadian test method LC 26-700 (Determination of the complex modulus by tension-compression). There mainly exist two viewing complex modulus planes for laboratory test results: the Cole and Cole plane and the Black space. The uniqueness of the data points in these two areas means that studied asphalt concretes are thermorheologically simple and that the principle of time-temperature superposition can be applied. This means that the master curve may be drawn and that the same modulus value can be obtained for different pairs (frequency-temperature). These master curves are fitted during the calibration process by the advanced rheological models. One of the most used software in the French rational design for the visualization of complex modulus test results and calibration of rheological models developed tools is named Visco-analysis. In this study, its use in interpreting the complex modulus test results and calibration models shows that, the studied asphalt concretes are thermorheologically simple, because they present good uniqueness of their Black and Cole and Cole and Black diagrams. They allow a good application of the principle of time temperature superposition. The statistical analysis of calibration models by the least squares method has shown that the three studied models are suitable for modeling the linear viscoelastic behavior of asphalt mixtures formulated with the basalt of Diack and the quartzite of Bakel. Indeed their calibration has very similar precision values of “Sum of Squared Deviation” (SSD) about 0.185. However, the lower precision value (0.169) is obtained with the 2S2P1D model.展开更多
Nowadays,sustainability and circular economy are two principles to be pursued in all fields.In road pavement engineering,they can be put into practice through the partial substitution of bitumen with industrial residu...Nowadays,sustainability and circular economy are two principles to be pursued in all fields.In road pavement engineering,they can be put into practice through the partial substitution of bitumen with industrial residues and by-products deriving from renewable materials.Within this framework,this paper presents an extensive investigation of the chemical,morphological and rheological properties of bio-binders obtained by mixing a conventional 50/70 bitumen with different percentages by weight(0,5%,10%and 15%)of a renewable bio-oil,generated as a residue in the processing of wood into pulp and paper.Results show that overall the bio-oil provides a softening effect,which,in terms of performance,leads to an improvement of the low-temperature behaviour and fatigue resistance with respect to the control bitumen,in spite of an increased tendency to permanent deformation.Although no chemical reaction appears to occur after blending,the peculiarities of the bio-oil affect the chemistry of the resulting bio-binders,whereas no phase separation is observed from the microscopic analysis.In addition,a Newtonian behaviour,an unchanged temperature susceptibility and a good fitting of 1 S2 P1 D model to the rheological data are found,regardless of the bio-oil percentage considered.These promising outcomes suggest that such bio-binders can be favourably employed for several applications in road pavements.展开更多
Energy levels of a donor impurity in the ZnO parabolic quantum well under the magnetic field are investigated using the variational method.The binding energy of the ground state,the energies of 2p±state and 1 s→...Energy levels of a donor impurity in the ZnO parabolic quantum well under the magnetic field are investigated using the variational method.The binding energy of the ground state,the energies of 2p±state and 1 s→2p±transition energies of a hydrogenic donor in the ZnO parabolic quantum well are numerically calculated as a function of the strength of magnetic field for different parabolic potential fields.The results show that the external magnetic field has an obvious influence on the binding energies and the 1 s→2p±transition energies of a hydrogenic donor.The Is to 2p±transition energy increases linearly with the strength of magnetic field,but the Is to 2p;transition energy decreases when the strength of magnetic field increases for the small field strength. Compared to the GaAs parabolic well,the donors are more tightly bound to the ZnO parabolic well and the influence of external magnetic field on the binding energy of a donor is much stronger in the ZnO parabolic well.展开更多
Optical selection rules fundamentally determine the optical transitions between energy states in a variety of physical systems,from hydrogen atoms to bulk crystals such as gallium arsenide.These rules are important fo...Optical selection rules fundamentally determine the optical transitions between energy states in a variety of physical systems,from hydrogen atoms to bulk crystals such as gallium arsenide.These rules are important for optoelectronic applications such as lasers,energy-dispersive X-ray spectroscopy,and quantum computation.Recently,single-layer transition metal dichalcogenides have been found to exhibit valleys in momentum space with nontrivial Berry curvature and excitons with large binding energy.However,there has been little study of how the unique valley degree of freedom combined with the strong excitonic effect influences the nonlinear optical excitation.Here,we report the discovery of nonlinear optical selection rules in monolayer WS2,an important candidate for visible 2D optoelectronics because of its high quantum yield and large direct bandgap.We experimentally demonstrated this principle for second-harmonic generation and two-photon luminescence(TPL).Moreover,the circularly polarized TPL and the study of its dynamics evince a sub-ps interexciton relaxation(2p R 1s).The discovery of this new optical selection rule in a valleytronic 2D system not only considerably enhances knowledge in this area but also establishes a foundation for the control of optical transitions that will be crucial for valley optoelectronic device applications such as 2D valley-polarized THz sources with 2p–1s transitions,optical switches,and coherent control for quantum computing.展开更多
文摘沥青混合料的黏弹性性能与温度、时间及其胶结料的状态等参数密切相关,而在路面的使用过程中沥青容易受到老化的影响,进一步影响沥青混合料的黏弹性性能。为了让路面设计过程中的参数更为具体,在实验室内对不同老化状态下的SBS改性沥青混合料进行多个频率及温度下的单轴动态模量试验。采用William, Landel and Ferry(WLF)公式对不同温度下的频率进行时温等效转换,然后基于分数阶模型(2S2P1D模型)建立了动态模量及相位角主曲线,分析老化对沥青混合料黏弹性能的影响特征。研究结果表明:2S2P1D模型能够较好地拟合不同老化状态下的SBS改性沥青混合料的动态模量的数据,相关系数大于0.9;沥青混合料的2S2P1D模型中的玻璃态模量Eg和与粘度相关的β参数随着老化程度的增加显著增大。然而,静态模量E0、分数阶指数k及h随着老化程度的增加而减小。基于该模型建立的储存模量及损失模量的主曲线表明:低频时老化对于沥青混合料的储存模量及损失模量具有不同的影响,当频率趋近于0时,老化对储存模量的影响基本不存在,但是随着老化程度的加深损失模量会显著增强。
文摘The main purpose of this article is to choose among advanced rheological models used in the French rational design, one that best represents the viscoelastic behavior of asphalt mixtures mixed with aggregates of Senegal. The model chosen will be the basis for the development of computational tools for stress and strain for Senegal. However, the calibration of these models needs complex modulus test results. In opposition to mechanical models the complex modulus can directly characterize the viscoelastic behavior of bituminous materials. Here determination is performed in the laboratory by using several types of tests divided into two groups: homogeneous tests and non-homogeneous tests. The choice of model will be carried out by statistical analysis through the least squares method. To this end, a study was carried out to “Laboratory of Pavement and Bituminous Materials” (LCMB) with asphalt concrete mixed with aggregate from Senegal named basalt of Diack and quartzite of Bakel. In this study, the test used to measure the complex modulus is the Canadian test method LC 26-700 (Determination of the complex modulus by tension-compression). There mainly exist two viewing complex modulus planes for laboratory test results: the Cole and Cole plane and the Black space. The uniqueness of the data points in these two areas means that studied asphalt concretes are thermorheologically simple and that the principle of time-temperature superposition can be applied. This means that the master curve may be drawn and that the same modulus value can be obtained for different pairs (frequency-temperature). These master curves are fitted during the calibration process by the advanced rheological models. One of the most used software in the French rational design for the visualization of complex modulus test results and calibration of rheological models developed tools is named Visco-analysis. In this study, its use in interpreting the complex modulus test results and calibration models shows that, the studied asphalt concretes are thermorheologically simple, because they present good uniqueness of their Black and Cole and Cole and Black diagrams. They allow a good application of the principle of time temperature superposition. The statistical analysis of calibration models by the least squares method has shown that the three studied models are suitable for modeling the linear viscoelastic behavior of asphalt mixtures formulated with the basalt of Diack and the quartzite of Bakel. Indeed their calibration has very similar precision values of “Sum of Squared Deviation” (SSD) about 0.185. However, the lower precision value (0.169) is obtained with the 2S2P1D model.
文摘Nowadays,sustainability and circular economy are two principles to be pursued in all fields.In road pavement engineering,they can be put into practice through the partial substitution of bitumen with industrial residues and by-products deriving from renewable materials.Within this framework,this paper presents an extensive investigation of the chemical,morphological and rheological properties of bio-binders obtained by mixing a conventional 50/70 bitumen with different percentages by weight(0,5%,10%and 15%)of a renewable bio-oil,generated as a residue in the processing of wood into pulp and paper.Results show that overall the bio-oil provides a softening effect,which,in terms of performance,leads to an improvement of the low-temperature behaviour and fatigue resistance with respect to the control bitumen,in spite of an increased tendency to permanent deformation.Although no chemical reaction appears to occur after blending,the peculiarities of the bio-oil affect the chemistry of the resulting bio-binders,whereas no phase separation is observed from the microscopic analysis.In addition,a Newtonian behaviour,an unchanged temperature susceptibility and a good fitting of 1 S2 P1 D model to the rheological data are found,regardless of the bio-oil percentage considered.These promising outcomes suggest that such bio-binders can be favourably employed for several applications in road pavements.
基金Project supported by the National Natural Science Foundation of China(No.10647006)the Youth Science Foundation of Lanzhou University of Technology,China(No.QN200805)
文摘Energy levels of a donor impurity in the ZnO parabolic quantum well under the magnetic field are investigated using the variational method.The binding energy of the ground state,the energies of 2p±state and 1 s→2p±transition energies of a hydrogenic donor in the ZnO parabolic quantum well are numerically calculated as a function of the strength of magnetic field for different parabolic potential fields.The results show that the external magnetic field has an obvious influence on the binding energies and the 1 s→2p±transition energies of a hydrogenic donor.The Is to 2p±transition energy increases linearly with the strength of magnetic field,but the Is to 2p;transition energy decreases when the strength of magnetic field increases for the small field strength. Compared to the GaAs parabolic well,the donors are more tightly bound to the ZnO parabolic well and the influence of external magnetic field on the binding energy of a donor is much stronger in the ZnO parabolic well.
基金This work was supported by the“Light-Material Interactions in Energy Conversion”Energy Frontier Research Center funded by the U.S.Department of Energy,Office of Science,Office of Basic Energy Sciences under Award Number DE-AC02-05CH11231.
文摘Optical selection rules fundamentally determine the optical transitions between energy states in a variety of physical systems,from hydrogen atoms to bulk crystals such as gallium arsenide.These rules are important for optoelectronic applications such as lasers,energy-dispersive X-ray spectroscopy,and quantum computation.Recently,single-layer transition metal dichalcogenides have been found to exhibit valleys in momentum space with nontrivial Berry curvature and excitons with large binding energy.However,there has been little study of how the unique valley degree of freedom combined with the strong excitonic effect influences the nonlinear optical excitation.Here,we report the discovery of nonlinear optical selection rules in monolayer WS2,an important candidate for visible 2D optoelectronics because of its high quantum yield and large direct bandgap.We experimentally demonstrated this principle for second-harmonic generation and two-photon luminescence(TPL).Moreover,the circularly polarized TPL and the study of its dynamics evince a sub-ps interexciton relaxation(2p R 1s).The discovery of this new optical selection rule in a valleytronic 2D system not only considerably enhances knowledge in this area but also establishes a foundation for the control of optical transitions that will be crucial for valley optoelectronic device applications such as 2D valley-polarized THz sources with 2p–1s transitions,optical switches,and coherent control for quantum computing.
