热超构材料的研究进展

由于光波、声波、地震波和水波都遵循波动方程,所以,2006年光学隐身衣(optical cloak)原理在Science杂志上发表后,光学隐身衣的设想很快就从最初的光波推广到了声波、地震波和水波,至今方兴未艾.由于热传导满足的是扩散方程,并且波动方程与扩散方程在物理机制上迥异,这就使得把光学隐身衣推广到热学隐身衣的尝试不得不面临来自原理上的挑战,可能也正因为如此,国际上对热超构材料的研究非常缓慢:早在2008年,就有学者在光学隐身衣的启发下,通过有限元模拟,揭示了热学隐身衣和热流反转等反常热功能或热现象,从而提出热超构材料(thermal metamaterial)的概念,但是,直到2012年,这个概念才被实验验证.由于其中蕴含着巨大的潜在应用价值,该实验工作发表后,热超构材料开始得到国际同行的广泛关注.文章的主要目的就是向读者介绍这一类新型功能材料——热超构材料的物理原理、发展历程及其理论和实验研究进展.     

热隐身：小概念，大用途

热隐身这个概念的提出,无论从应用角度,还是从学术层面,皆有其异乎寻常的重要性。文章简介了热隐身的来龙去脉,在介绍概念的同时,重点阐述其在地下掩体中红外热防护方面的特殊应用价值——其在领域内已经发展十五年,广为人知,而在领域外尚显陌生。至于热隐身的特殊学术价值,也在文末一并介绍,并着重介绍基于其进行的概念延拓,即从“热隐身”这个小概念,推广到“热超构材料”这个大概念,再进一步推广到“扩散超构材料”这个更大的概念。此外,文章对热隐身的制备方法和原理亦有述及。     

胶体铁磁流体的光子特性研究(英文)

这篇综述回顾了我们近年来在铁磁流体方面的一些研究工作。铁磁流体是一种纳米铁磁颗粒或亚铁磁颗粒悬浮在基液(如:水或煤油)中形成的悬浮液。铁磁流体之所以受到广泛关注,是因为它们在许多方面都有着潜在应用,例如在机械工程和生物医学等领域。在此综述中,我们首先介绍了铁磁流体的场感应各向异性结构,然后,介绍了几种铁磁流体基软物质材料的光学性质,即:光学负折射、磁控光子带隙和非线性光学响应。我们采用的研究方法主要是分子动力学模拟,有效媒质近似和有限元模拟。     

Unprecedentedly rapid transport of single-file rolling water molecules

The realization of rapid and unidirectional single-file water-molecule flow in nanochannels has posed a challenge to date. Here, we report unprecedentedly rapid unidirectional single-file water-molecule flow under a translational terahertz electric field, which is obtained by developing a Debye doublerelaxation theory. In addition, we demonstrate that all the single-file molecules undergo both stable translation and rotation, behaving like high-speed train wheels moving along a railway track. Independent molecular dynamics simulations help to confirm these theoretical results. The mechanism involves the resonant relaxation dynamics of H and O atoms. Further, an experimental demonstration is suggested and discussed. This work has implications for the design of high-efficiency nanochannels or smaller nanomachines in the field of nanotechnology, and the findings also aid in the understanding and control of water flow across biological nanochannels in biology-related research.     

Many-body dipole-induced dipole model for electrorheological fluids

Theoretical investigations on electrorheological (ER) fluids usually rely on computer simulations. An initial approach for these studies would be the point-dipole (PD) approximation, which is known to err considerably when the particles approach and finally touch each other due to many-body and multipolar interactions. Thus various works have attempted to go beyond the PD model. Being beyond the PD model, previous attempts have been restricted to either local-field effects only or multipolar effects only, but not both. For instance, we recently proposed a dipole-induced-dipole (DID) model which is shown to be both more accurate than the PD model and easy to use. This work is necessary because the many-body (local-field) effect is included to put forth the many-body DID model. The results show that the multipolar interactions can indeed be dominant over the dipole interaction, while the local-field effect may yield a correction.     

Equilibrium state and non-equilibrium steady state in an isolated human system

The principle of increasing entropy （PIE） is commonly considered as a universal physical law tbr natural systems. It also means that a non-equilibrium steady state （NESS） must not appear in any isolated natural systems. Here we experimentally investigate an isolated human social system with a clustering effect. We report that the PIE cannot always hold, and that NESSs can come to appear. Our study highlights the role of human adaptability in the PIE, and makes it possible to study human social systems by using some laws originating from traditional physics.     

Robustness of critical points in a complex adaptive system: Effects of hedge behavior

In our recent papers, we have identified a class of phase transitions in the market-directed resource-allocation game, and found that there exists a critical point at which the phase transitions occur. The critical point is given by a certain resource ratio. Here, by performing computer simulations and theoretical analysis, we report that the critical point is robust against various kinds of human hedge behavior where the numbers of herds and contrarians can be varied widely. This means that the critical point can be independent of the total number of participants composed of normal agents, herds and contrarians, under some conditions. This finding means that the critical points we identified in this complex adaptive system (with adaptive agents) may also be an intensive quantity, similar to those revealed in traditional physical systems (with non-adaptive units).     

Controlling Thermal Conduction by Graded Materials

Manipulating thermal conductivities are fundamentally important for controlling the conduction of heat at will. Thermal cloaks and concentrators, which have been extensively studied recently, are actually graded materials designed according to coordinate transformation approaches, and their effective thermal conductivity is equal to that of the host medium outside the cloak or concentrator. Here we attempt to investigate a more general problem: what is the effective thermal conductivity of graded materials? In particular, we perform a first-principles approach to the analytic exact results of effective thermal conductivities of materials possessing either power-law or linear gradation profiles. On the other hand, by solving Laplace's equation, we derive a differential equation for calculating the effective thermal conductivity of a material whose thermal conductivity varies along the radius with arbitrary gradation profiles. The two methods agree with each other for both external and internal heat sources, as confirmed by simulation and experiment. This work provides different methods for designing new thermal metamaterials (including thermal cloaks and concentrators), in order to control or manipulate the transfer of heat.     

Dust-Induced Regulation of Thermal Radiation in Water Droplets

Accurate and fast prediction of thermal radiation properties of materials is crucial for their potential applications.However, some models assume that the media are made up of pure water droplets, which do not account for the increasing deviations caused by volcanic eruptions, pollution, and human activities that exacerbate dust production. The distinct radiation properties of water and dust particles make it challenging to determine the thermal radiation properties of water droplets containing ...