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On the measurement procedures for the assessment of the specific absorption rate (SAR) from MIMO cellular-equipment of fast varying relative phases 快速变相MIMO蜂窝设备比吸收率(SAR)的测量方法研究
IF 1.4 4区 物理与天体物理 Q3 Physics and Astronomy Pub Date : 2021-03-31 DOI: 10.5802/CRPHYS.64
M. Teniou, Mehdi Ramdani, O. Jawad, T. Julien, S. Pannetrat, L. Aberbour
This article introduces a measurement methodology for the evaluation of the specific absorption rate (SAR) of MIMO systems (multiple-input and multiple-output) in which the relative phases between the antennas are rapidly changing and in very short durations. This measurement methodology is enabled by SAR systems that uses vector field measurements combined with a vector spectral analysis of the measured radiofrequency signals for SAR assessment. By exploiting the equivalence principle and the uniqueness of the solution of Maxwell’s equation, the proposed approach allows for an accurate SAR assessment of complex MIMO systems in a very short duration (few seconds).
本文介绍了一种用于评估MIMO系统(多输入和多输出)的特定吸收率(SAR)的测量方法,其中天线之间的相对相位快速变化且持续时间很短。这种测量方法是由SAR系统实现的,该系统使用矢量场测量和测量射频信号的矢量频谱分析来进行SAR评估。通过利用等效原理和麦克斯韦方程解的唯一性,所提出的方法允许在很短的持续时间(几秒钟)内对复杂MIMO系统进行准确的SAR评估。
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引用次数: 0
Light-control of materials via nonlinear phononics 材料的非线性声子光控制
IF 1.4 4区 物理与天体物理 Q3 Physics and Astronomy Pub Date : 2021-03-26 DOI: 10.5802/crphys.44
A. Subedi
Nonlinear phononics is the phenomenon in which a coherent dynamics in a material along a set of phonons is launched after its infrared-active phonons are selectively excited using external light pulses. The microscopic mechanism underlying this phenomenon is the nonlinear coupling of the pumped infrared-active mode to other phonon modes present in a material. Nonlinear phonon couplings can cause finite time-averaged atomic displacements with or without broken crystal symmetries depending on the order, magnitude and sign of the nonlinearities. Such coherent lattice displacements along phonon coordinates can be used to control the physical properties of materials and even induce transient phases with lower symmetries. Light-control of materials via nonlinear phononics has become a practical reality due to the availability of intense mid-infrared lasers that can drive large-amplitude oscillations of the infrared-active phonons of materials. Mid-infrared pump induced insulator-metal transitions and spin and orbital order melting have been observed in pump-probe experiments. First principles based microscopic theory of nonlinear phononics has been developed, and it has been used to better understand how the lattice evolves after a mid-infrared pump excitation of infrared-active phonons. This theory has been used to predict light-induced switching of ferroelectric polarization as well as ferroelectricity in paraelectrics and ferromagnetism in antiferromagnets, which have been partially confirmed in recent experiments. This review summarizes the experimental and theoretical developments within this emerging field.
非线性声子是一种现象,在使用外部光脉冲选择性地激发材料的红外活性声子后,沿着一组声子的材料中的相干动力学被启动。这种现象背后的微观机制是泵浦的红外活性模式与材料中存在的其他声子模式的非线性耦合。非线性声子耦合可以引起有限的时间平均原子位移,无论是否具有破坏的晶体对称性,这取决于非线性的阶数、大小和符号。这种沿着声子坐标的相干晶格位移可以用于控制材料的物理性质,甚至可以诱导具有较低对称性的瞬态相。由于强中红外激光器的可用性,通过非线性声子对材料的光控制已成为现实,该激光器可以驱动材料的红外有源声子的大振幅振荡。在泵浦探针实验中观察到了中红外泵浦诱导的绝缘体-金属跃迁以及自旋和轨道有序熔化。基于第一性原理的非线性声子微观理论已经发展起来,并被用来更好地理解在红外有源声子的中红外泵浦激发后晶格是如何演化的。这一理论已被用于预测铁电极化的光致开关,以及顺电体中的铁电性和反铁磁体中的铁磁性,这在最近的实验中得到了部分证实。这篇综述总结了这一新兴领域的实验和理论发展。
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引用次数: 6
Grain size effects and weakest link theory in 3D crystal plasticity simulations of polycrystals 三维多晶塑性模拟中的晶粒尺寸效应和最薄弱环节理论
IF 1.4 4区 物理与天体物理 Q3 Physics and Astronomy Pub Date : 2021-03-26 DOI: 10.5802/CRPHYS.53
L. Gélébart
The weakest link theory, sometimes proposed to analyze size effects on the plastic behaviour of single crystals, is introduced in 3D numerical simulations of polycrystals. The approach relies on a random distribution of sources in space and strength associated to a crystal plasticity law with constant per layer Critical Resolved Shear Stresses (CRSS). It is able to reproduce: (1) the grain size dependence of the yield stress given by the Hall–Petch law, (2) intense slip band localization patterns as often observed at the grains surface, especially pronounced in quenched or irradiated metals, but difficult to reproduce by numerical simulation.
将最薄弱环节理论引入到多晶的三维数值模拟中,该理论有时被用于分析尺寸对单晶塑性行为的影响。该方法依赖于源在空间中的随机分布以及与晶体塑性定律相关的强度,该定律具有恒定的每层临界分解剪切应力(CRSS)。它能够再现:(1)霍尔-佩奇定律给出的屈服应力对晶粒尺寸的依赖关系;(2)在晶粒表面经常观察到的强烈的滑移带局部化模式,特别是在淬火或辐照金属中,但难以通过数值模拟再现。
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引用次数: 2
A numerical study of reversible plasticity using continuum dislocation mechanics 基于连续位错力学的可逆塑性数值研究
IF 1.4 4区 物理与天体物理 Q3 Physics and Astronomy Pub Date : 2021-03-26 DOI: 10.5802/CRPHYS.54
S. Berbenni, R. Lebensohn
In this contribution, an elasto-viscoplastic fast Fourier transform-based (EVPFFT) numerical implementation of the Mesoscale Field Dislocation Mechanics (MFDM) formulation, called MFDM-EVPFFT, is applied to study the reversible plastic behavior of periodic two-phase crystalline composites with an elastoviscoplastic plastic matrix and a purely elastic second phase. Periodic laminate microstructures of this kind with different periods (i.e. sizes) are considered to examine the size dependence of the Bauschinger effect and hardening during cyclic loading. Comparisons with classic composite effects obtained with conventional crystal plasticity are discussed. Specifically, the MFDM-EVPFFT results shed light on the hardening mechanisms due to piling-up/unpiling-up of geometrically-necessary dislocations (GND) during reverse loading.
在这篇贡献中,一个基于弹粘塑性快速傅立叶变换(EVPFFT)的中尺度场位错力学(MFDM)公式的数值实现,称为MFDM-EVPFFT,用于研究具有弹粘塑性塑性基体和纯弹性第二相的周期性两相结晶复合材料的可逆塑性行为。考虑了这种具有不同周期(即尺寸)的周期性层状微结构,以研究循环加载过程中鲍辛格效应和硬化的尺寸依赖性。讨论了与传统晶体塑性得到的经典复合效应的比较。具体来说,MFDM-EVPFFT结果揭示了由于反向加载期间几何必要位错(GND)的堆积/解堆积而导致的硬化机制。
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引用次数: 1
Elasto-plastic behavior of amorphous materials: a brief review 非晶材料的弹塑性行为:综述
IF 1.4 4区 物理与天体物理 Q3 Physics and Astronomy Pub Date : 2021-03-26 DOI: 10.5802/CRPHYS.49
A. Tanguy
Disordered materials, like metallic glasses or silicate glasses, have an atomistic amorphous structure preventing the formation of extended defects such as dislocations. Irreversible deformation in these materials is thus localized, but can organize along shear bands. In this brief review, based on recent publications, we will see if local plasticity can be measured and predicted in disordered atomic assemblies, and in what conditions it can be related to preexisting structural defects. We will then draw a general picture of the plastic mechanical behaviour within the theoretical framework of mechanical instabilities. Finally, we will focus our attention on different scenarii for shear banding in glasses.
无序材料,如金属玻璃或硅酸盐玻璃,具有原子无定形结构,防止形成扩展缺陷,如位错。因此,这些材料中的不可逆变形是局部的,但可以沿着剪切带组织。在这篇简短的综述中,基于最近的出版物,我们将看到局部塑性是否可以在无序原子组装中测量和预测,以及在什么条件下它可以与预先存在的结构缺陷相关。然后,我们将在力学不稳定性的理论框架内绘制塑性力学行为的一般图像。最后,我们将重点关注玻璃剪切带的不同场景。
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引用次数: 14
Nanomechanics serving polymer-based composite research 纳米力学服务于聚合物基复合材料的研究
IF 1.4 4区 物理与天体物理 Q3 Physics and Astronomy Pub Date : 2021-03-26 DOI: 10.5802/CRPHYS.56
T. Pardoen, Nathan Klavzer, S. Gayot, F. Loock, J. Chevalier, X. Morelle, Vincent Destoop, F. Lani, P. Camanho, L. Brassart, B. Nysten, C. Bailly
Tremendous progress in nanomechanical testing and modelling has been made during the last two decades. This progress emerged from different areas of materials science dealing with the mechanical behaviour of thin films and coatings, polymer blends, nanomaterials or microstructure constituents as well as from the rapidly growing field of MEMS. Nanomechanical test methods include, among others, nanoindentation, in-situ testing in a scanning or transmission electron microscope coupled with digital image correlation, atomic force microscopy with new advanced dynamic modes, micropillar compression or splitting, on-chip testing, or notched microbeam bending. These methods, when combined, reveal the elastic, plastic, creep, and fracture properties at the microand even the nanoscale. Modelling techniques including atomistic simulations and several coarse graining methods have been enriched to a level that allows treating complex size, interface or surface effects in a realistic way. Interestingly, the transfer of this paradigm to advanced long fibre-reinforced polymer composites has not been as intense compared to other fields. Here, we show that these methods put together can offer new perspectives for an improved characterisation of the response at the elementary fibre-matrix level, involving the interfaces and interphases. Yet, there are still many open issues left to resolve. In addition, this is the length scale, typically below 10 micrometres, ∗Corresponding author. ISSN (electronic) : 1878-1535 https://comptes-rendus.academie-sciences.fr/physique/
在过去的二十年里,纳米力学测试和建模取得了巨大的进步。这一进展来自材料科学的不同领域,涉及薄膜和涂层、聚合物混合物、纳米材料或微结构成分的机械行为,以及快速发展的MEMS领域。纳米力学测试方法包括纳米压痕,在扫描或透射电子显微镜下进行原位测试,结合数字图像相关,原子力显微镜与新的先进动态模式,微柱压缩或分裂,芯片上测试,或缺口微束弯曲。当这些方法结合在一起时,可以揭示微观甚至纳米尺度上的弹性、塑性、蠕变和断裂性能。包括原子模拟和几种粗粒度方法在内的建模技术已经丰富到可以以现实的方式处理复杂尺寸,界面或表面效果的水平。有趣的是,与其他领域相比,将这种模式转移到先进的长纤维增强聚合物复合材料并没有那么激烈。在这里,我们表明,这些方法放在一起可以为在基本纤维基质水平(包括界面和界面相)改进响应特征提供新的视角。然而,仍有许多悬而未决的问题有待解决。此外,这是长度尺度,通常低于10微米,*通讯作者。ISSN(电子):1878-1535 https://comptes-rendus.academie-sciences.fr/physique/
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引用次数: 7
Loop currents in quantum matter 量子物质中的回路电流
IF 1.4 4区 物理与天体物理 Q3 Physics and Astronomy Pub Date : 2021-03-24 DOI: 10.5802/crphys.84
P. Bourges, D. Bounoua, Y. Sidis
In many quantum materials, strong electron correlations lead to the emergence of new states of matter. In particular, the study in the last decades of the complex phase diagram of high temperature superconducting cuprates highlighted intra-unit-cell electronic instabilities breaking discrete Ising-like symmetries, while preserving the lattice translation invariance. Polarized neutron diffraction experiments have provided compelling evidences supporting a new form of intra-unit-cell magnetism, emerging concomitantly with the so-called pseudogap state of these materials. This observation is currently interpreted as the magnetic hallmark of an intra-unit-cell loop current order, breaking both parity and time-reversal symmetries. More generally, this magneto-electric state is likely to exist in a wider class of quantum materials beyond superconducting cuprates. For instance, it has been already observed in hole-doped Mott insulating iridates or in the spin liquid state of hole-doped 2-leg ladder cuprates.
在许多量子材料中,强电子相关性导致物质新状态的出现。特别是,近几十年来对高温超导铜酸盐复杂相图的研究突出了单元内电子不稳定性,打破了离散的类伊辛对称性,同时保持了晶格平移不变性。极化中子衍射实验提供了令人信服的证据,支持一种新的单位胞内磁性形式,伴随着这些材料的所谓赝隙状态而出现。这一观察结果目前被解释为单位胞内环电流顺序的磁性标志,打破了宇称和时间反转对称性。更一般地说,这种磁电状态可能存在于比超导铜更广泛的量子材料中。例如,已经在空穴掺杂的莫特绝缘铱酸盐或空穴掺杂的两腿阶梯铜酸盐的自旋液态中观察到这种现象。
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引用次数: 13
Insights from the quantitative calibration of an elasto-plastic model from a Lennard-Jones atomic glass Lennard-Jones原子玻璃弹塑性模型定量校准的见解
IF 1.4 4区 物理与天体物理 Q3 Physics and Astronomy Pub Date : 2021-03-01 DOI: 10.5802/CRPHYS.48
D. F. Castellanos, S. Roux, S. Patinet
We compare the macroscopic and the local plastic behavior of a model amorphous solid based on two radically different numerical descriptions. On the one hand, we simulate glass samples by atomistic simulations. On the other, we implement a mesoscale elasto-plastic model based on a solid-mechanics description. The latter is extended to consider the anisotropy of the yield surface via statistically distributed local and discrete weak planes on which shear transformations can be activated. To make the comparison as quantitative as possible, we consider the simple case of a quasistatically driven two-dimensional system in the stationary flow state and compare mechanical observables measured on both models over the same length scales. We show that the macroscale response, including its fluctuations, can be quantitatively recovered for a range of elasto-plastic mesoscale parameters. Using a newly developed method that makes it possible to probe the local yield stresses in atomistic simulations, we calibrate the local mechanical response of the elasto-plastic model at different coarse-graining scales. In this case, the calibration shows a qualitative agreement only for an optimized subset of mesoscale parameters and for sufficiently coarse probing length scales. This calibration allows us to establish a length scale for the mesoscopic elements that corresponds to an upper bound of the shear transformation size, a key physical parameter in elasto-plastic models. We find that certain properties naturally emerge from the elasto-plastic model. In particular, we show that the elasto-plastic model reproduces the Bauschinger effect, namely the plasticity-induced anisotropy in the stress-strain response. We discuss the successes and failures of our approach, the impact of different model ingredients and propose future research directions for quantitative multi-scale models of amorphous plasticity.
基于两种完全不同的数值描述,我们比较了模型非晶固体的宏观和局部塑性行为。一方面,我们通过原子模拟来模拟玻璃样品。另一方面,我们实现了一个基于固体力学描述的中尺度弹塑性模型。后者被扩展为通过统计分布的局部和离散弱平面来考虑屈服面的各向异性,在这些弱平面上可以激活剪切变换。为了使比较尽可能定量,我们考虑了准静态驱动的二维系统在静止流动状态下的简单情况,并比较了在相同长度尺度上在两个模型上测量的机械可观察性。我们表明,对于一系列弹塑性中尺度参数,宏观尺度响应,包括其波动,可以定量恢复。使用一种新开发的方法,可以在原子模拟中探测局部屈服应力,我们校准了弹塑性模型在不同粗粒度尺度下的局部力学响应。在这种情况下,校准仅对中尺度参数的优化子集和足够粗的探测长度尺度显示出定性一致性。这种校准使我们能够为介观单元建立一个长度尺度,该尺度对应于剪切变换尺寸的上限,剪切变换尺寸是弹塑性模型中的一个关键物理参数。我们发现某些性质自然地从弹塑性模型中显现出来。特别是,我们表明弹塑性模型再现了Bauschinger效应,即应力-应变响应中塑性诱导的各向异性。我们讨论了我们的方法的成功和失败,不同模型成分的影响,并提出了非晶塑性定量多尺度模型的未来研究方向。
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引用次数: 13
Moiré excitons at line defects in transition metal dichalcogenides heterobilayers 过渡金属二硫族化合物异质层中线缺陷处的振动子
IF 1.4 4区 物理与天体物理 Q3 Physics and Astronomy Pub Date : 2021-03-01 DOI: 10.5802/CRPHYS.50
Jianju Tang, Hongyi Yu, C. Shih, W. Yao
In heterobilayers of 2D semiconductors, moiré pattern forms due to the inevitable lattice mismatch and twisting. Earlier works have shown that interlayer excitons in long-period moiré pattern experience a pronounced superlattice potential and have nanoscale patterned light-coupling properties. This leads to remarkable new possibilities to explore exciton physics and tailor optical properties. Line defects such as twin domain boundaries are commonly found in semiconducting transition metal dichalcogenides monolayer, which, in the context of a heterobilayer, leads to an interface between the R-stacking moiré and H-stacking moiré. Here, we show that such interface created by twin-domain boundary realizes a line-defect in the moiré superlattices for interlayer excitons, which localises a one-dimensional exciton mode of topological origin. The defect configuration in the moiré exciton superlattices can be continuously tuned by the interlayer translation and twisting angle, and is also a reflection of the atomic configuration of the domain boundary. The dispersion, wavefunction, and light coupling properties of the interface exciton modes are investigated at different superlattice defect configurations.
在二维半导体的异质层中,由于不可避免的晶格错配和扭曲而形成波纹图案。早期的研究表明,长周期莫尔条纹的层间激子具有明显的超晶格势,并具有纳米尺度的图案光耦合特性。这为探索激子物理和定制光学特性带来了非凡的新可能性。在半导体过渡金属二硫族化合物单层中,双畴边界等线缺陷是常见的,在异质层的情况下,这导致了r层和h层之间的界面。在这里,我们证明了这种由双畴边界产生的界面实现了层间激子的摩尔超晶格中的线缺陷,它定位了拓扑起源的一维激子模式。莫尔激子超晶格中的缺陷构型可以通过层间平移和扭转角度连续调谐,也是畴边界原子构型的反映。研究了不同超晶格缺陷构型下界面激子模的色散、波函数和光耦合特性。
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引用次数: 0
Sub-picosecond C=C bond photo-isomerization: evidence for the role of excited state mixing 亚皮秒C=C键光异构化:激发态混合作用的证据
IF 1.4 4区 物理与天体物理 Q3 Physics and Astronomy Pub Date : 2021-03-01 DOI: 10.5802/CRPHYS.41
D. Agathangelou, P. Roy, M. D. C. Marín, N. Ferré, M. Olivucci, T. Buckup, J. Léonard, S. Haacke
Sub-picosecond photo-isomerization is the major primary process of energy conversion in retinal proteins and has as such been in the focus of extensive theoretical and experimental work over the past decades. In this review article, we revisit the long-standing question as to how the protein tunes the isomerization speed and quantum yield. We focus on our recent contributions to this field, which underscore the concept of a delicate mixing of reactive and non-reactive excited states, as a result of steric properties and electrostatic interactions with the protein environment. Further avenues and new approaches are outlined which hold promise for advancing our understanding of these intimately coupled chromophore-protein systems.
亚皮秒光异构化是视网膜蛋白质能量转换的主要过程,在过去的几十年里一直是广泛的理论和实验工作的焦点。在这篇综述文章中,我们重新审视了长期存在的问题,即蛋白质如何调节异构化速度和量子产率。我们将重点介绍我们最近在这一领域的贡献,这些贡献强调了反应性和非反应性激发态的微妙混合概念,这是由于与蛋白质环境的空间性质和静电相互作用的结果。进一步的途径和新方法概述了有希望推进我们对这些密切耦合的发色团-蛋白质系统的理解。
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引用次数: 4
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Comptes Rendus Physique
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