Showing papers in "Chinese Physics B in 2020"

Moisture-sensitive torsional cotton artificial muscle and textile*

Abstract: Developing moisture-sensitive artificial muscles from industrialized natural fibers with large abundance is highly desired for smart textiles that can respond to humidity or temperature change. However, currently most of fiber artificial muscles are based on non-common industrial textile materials or of a small portion of global textile fiber market. In this paper, we developed moisture-sensitive torsional artificial muscles and textiles based on cotton yarns. It was prepared by twisting the cotton yarn followed by folding in the middle point to form a self-balanced structure. The cotton yarn muscle showed a torsional stroke of 42.55 °/mm and a rotational speed of 720 rpm upon exposure to water moisture. Good reversibility and retention of stroke during cyclic exposure and removal of water moisture were obtained. A moisture-sensitive smart window that can close when it rains was demonstrated based on the torsional cotton yarn muscles. This twist-based technique combining natural textile fibers provides a new insight for construction of smart textile materials.

Hidden attractors in a new fractional-order discrete system: Chaos, complexity, entropy, and control

Abstract: This paper studies the dynamics of a new fractional-order discrete system based on the Caputo-like difference operator. This is the first study to explore a three-dimensional fractional-order discrete chaotic system without equilibrium. Through phase portrait, bifurcation diagrams and largest Lyapunov exponents, it is shown that the proposed fractional-order discrete system exhibits a range of different dynamical behaviors. Also, different tests are used to confirm the existence of chaos such as 0-1 test and C 0 complexity. In addition, the quantification of the level of chaos in the new fractional-order discrete system is measured by the approximate entropy technique. Furthermore, based on the fractional linearization method, a one-dimensional controller to stabilize the new system is proposed. Numerical results are presented to validate the findings of the paper.

Memristor-based hyper-chaotic circuit for image encryption

Abstract: The memristor is a kind of non-linear element with memory function, which can be applied to chaotic systems to increase signal randomness and complexity. In this paper, a new four-dimensional hyper-chaotic system is designed based on a flux controlled memristor model, which can generate complex chaotic attractors. The basic dynamic theory analysis and numerical simulations of the system, such as the stability of equilibrium points, the Lyapunov exponents and dimension, Poincare maps, the power spectrum, and the waveform graph prove that it has rich dynamic behaviors. Then, the circuit implementation of this system is established. The consistency of simulation program with integrated circuit emphasis (SPICE) simulation and numerical analysis proves the ability to generate chaos. Finally, a new image encryption scheme is designed by using the memristor-based hyper-chaotic system proposed in this paper. The scheme involves a total of two encryptions. By using different security analysis factors, the proposed algorithm is compared with other image encryption schemes, including correlation analysis, information entropy, etc. The results show that the proposed image encryption scheme has a large key space and presents a better encryption effect.

Identifying influential spreaders in complex networks based on entropy weight method and gravity law

Abstract: In complex networks, identifying influential spreader is of great significance for improving the reliability of networks and ensuring the safe and effective operation of networks. Nowadays, it is widely used in power networks, aviation networks, computer networks, and social networks, and so on. Traditional centrality methods mainly include degree centrality, closeness centrality, betweenness centrality, eigenvector centrality, k-shell, etc. However, single centrality method is one-sided and inaccurate, and sometimes many nodes have the same centrality value, namely the same ranking result, which makes it difficult to distinguish between nodes. According to several classical methods of identifying influential nodes, in this paper we propose a novel method that is more full-scaled and universally applicable. Taken into account in this method are several aspects of node's properties, including local topological characteristics, central location of nodes, propagation characteristics, and properties of neighbor nodes. In view of the idea of the multi-attribute decision-making, we regard the basic centrality method as node's attribute and use the entropy weight method to weigh different attributes, and obtain node's combined centrality. Then, the combined centrality is applied to the gravity law to comprehensively identify influential nodes in networks. Finally, the classical susceptible-infected-recovered (SIR) model is used to simulate the epidemic spreading in six real-society networks. Our proposed method not only considers the four topological properties of nodes, but also emphasizes the influence of neighbor nodes from the aspect of gravity. It is proved that the new method can effectively overcome the disadvantages of single centrality method and increase the accuracy of identifying influential nodes, which is of great significance for monitoring and controlling the complex networks.

Topological Anderson insulator in two-dimensional non-Hermitian systems

Abstract: We study the characterization and realization of higher-order topological Anderson insulator (HOTAI) in non-Hermitian systems, where the non-Hermitian mechanism ensures extra symmetries as well as gain and loss disorder. We illuminate that the quadrupole moment Qxy can be used as the real space topological invariant of non-Hermitian higher-order topological insulator (HOTI). Based on the biorthogonal bases and non-Hermitian symmetries, we prove that Qxy can be quantized to 0 or 0.5. Considering the disorder effect, we find the disorder-induced phase transition from normal insulator to non-Hermitian HOTAI. Furthermore, we elucidate that the real space topological invariant Qxy is also applicable for systems with the non-Hermitian skin effect. Our work enlightens the study of the combination of disorder and non-Hermitian HOTI.

Perpendicular magnetization switching by large spin-orbit torques from sputtered Bi2Te3

Abstract: Spin-orbit torque (SOT) effect is considered as an efficient way to switch the magnetization and can inspire various high-performance spintronic devices. Recently, topological insulators (TIs) have gained extensive attention, for they are demonstrated to maintain a large effective spin Hall angle (θ SH eff ), even at room temperature. However, molecular beam epitaxy (MBE), as a precise deposition method, is required to guarantee favorable surface states of TI, which hinders the prospect of TIs towards industrial application. In this paper, we demonstrate that Bi2Te3 films grown by magnetron sputtering can provide a notable SOT effect in the heterostructure with perpendicular magnetic anisotropy CoTb ferrimagnetic alloy. By harmonic Hall measurement, a high SOT efficiency (8.7±0.9 Oe/(109A/m2)) and a large θ SH eff (3.3±0.3) are obtained at room temperature. Besides, we also observe an ultra-low critical switching current density (9.7×109 A/m2). Moreover, the low-power characteristic of sputtered Bi2Te3 film is investigated by drawing a comparison with different sputtered SOT sources. Our work may provide an alternative to leverage chalcogenides as a realistic and efficient SOT source in future spintronic devices.

Quantum teleportation of particles in an environment

Abstract: We discuss the teleportation of particles in an environment of an N-body system. In this case, we can change a many-body system into an arbitrary shape in space by teleporting some or all the constituent particles, and thus we call the quantum teleportation under this circumstance as quantum tele-transformation (QTT). The particular feature of QTT is that the wave function of the internal degrees of freedom remains the same, while the spatial wave function experiences a drastic change. The notion of QTT provides conceptual and pedagogical convenience for quantum information processing. In view of QTT, teleportation is the change of a single particle in space, while entanglement swapping is the change of one particle of an entangled pair.

Optoelectronic memristor for neuromorphic computing

Abstract: With the need of the internet of things, big data, and artificial intelligence, creating new computing architecture is greatly desired for handling data-intensive tasks. Human brain can simultaneously process and store information, which would reduce the power consumption while improve the efficiency of computing. Therefore, the development of brain-like intelligent device and the construction of brain-like computation are important breakthroughs in the field of artificial intelligence. Memristor, as the fourth fundamental circuit element, is an ideal synaptic simulator due to its integration of storage and processing characteristics, and very similar activities and the working mechanism to synapses among neurons which are the most numerous components of the brains. In particular, memristive synaptic devices with optoelectronic responding capability have the benefits of storing and processing transmitted optical signals with wide bandwidth, ultrafast data operation speed, low power consumption, and low cross-talk, which is important for building efficient brain-like computing networks. Herein, we review recent progresses in optoelectronic memristor for neuromorphic computing, including the optoelectronic memristive materials, working principles, applications, as well as the current challenges and the future development of the optoelectronic memristor.

Electron beam irradiation on novel coronavirus (COVID-19): A Monte-Carlo simulation

Abstract: The novel coronavirus pneumonia triggered by COVID-19 is now raging the whole world. As a rapid and reliable killing COVID-19 method in industry, electron beam irradiation can interact with virus molecules and destroy their activity. With the unexpected appearance and quickly spreading of the virus, it is urgently necessary to figure out the mechanism of electron beam irradiation on COVID-19. In this study, we establish a virus structure and molecule model based on the detected gene sequence of Wuhan patient, and calculate irradiated electron interaction with virus atoms via a Monte Carlo simulation that track each elastic and inelastic collision of all electrons. The characteristics of irradiation damage on COVID-19, atoms' ionizations and electron energy losses are calculated and analyzed with regions. We simulate the different situations of incident electron energy for evaluating the influence of incident energy on virus damage. It is found that under the major protecting of an envelope protein layer, the inner RNA suffers the minimal damage. The damage for a ~100-nm-diameter virus molecule is not always enhanced by irradiation energy monotonicity, for COVID-19, the irradiation electron energy of the strongest energy loss damage is 2 keV.

A novel (2+1)-dimensional integrable KdV equation with peculiar solution structures

Abstract: The celebrated (1+1)-dimensional Korteweg de-Vries (KdV) equation and its (2+1)-dimensional extension, the Kadomtsev-Petviashvili (KP) equation, are two of the most important models in physical science. The KP hierarchy is explicitly written out by means of the linearized operator of the KP equation. A novel (2+1)-dimensional KdV extension, the cKP3-4 equation, is obtained by combining the third member (KP3, the usual KP equation) and the fourth member (KP4) of the KP hierarchy. The integrability of the cKP3-4 equation is guaranteed by the existence of the Lax pair and dual Lax pair. The cKP3-4 system can be bilinearized by using Hirota's bilinear operators after introducing an additional auxiliary variable. Exact solutions of the cKP3-4 equation possess some peculiar and interesting properties which are not valid for the KP3 and KP4 equations. For instance, the soliton molecules and the missing D'Alembert type solutions (the arbitrary travelling waves moving in one direction with a fixed model dependent velocity) including periodic kink molecules, periodic kink-antikink molecules, few cycle solitons and envelope solitons are existed for the cKP3-4 equation but not for the separated KP3 equation and the KP4 equation.

Twistronics in graphene-based van der Waals structures

Abstract: The electronic properties of van der Waals (vdW) structures can be substantially modified by the moire superlattice potential, which strongly depends on the twist angle among the compounds. In twisted bilayer graphene (TBG), two low-energy Van Hove singularities (VHSs) move closer with decreasing twist angles and finally become highly non-dispersive flat bands at the magic angle (~ 1.1 degree). When the Fermi level lies within the flat bands of the TBG near the magic angle, Coulomb interaction is supposed to exceed the kinetic energy of the electrons, which can drive the system into various strongly correlated phases. Moreover, the strongly correlated states of flat bands are also realized in other graphene-based vdW structures with an interlayer twist. In this article, we mainly review the recent experimental advances on the strongly correlated physics of the magic-angle TBG (MATBG) and the small-angle twisted multilayer graphene. Lastly we will give out a perspective of this field.

Multiple Fano resonances in metal–insulator–metal waveguide with umbrella resonator coupled with metal baffle for refractive index sensing*

Abstract: A single baffle metal–insulator–metal (MIM) waveguide coupled with a semi-circular cavity and a cross-shaped cavity is proposed based on the multiple Fano resonance characteristics of surface plasmon polaritons (SPPs) subwavelength structure. The isolated state formed by two resonators interferes with the wider continuous state mode formed by the metal baffle, forming Fano resonance that can independently be tuned into five different modes. The formation mechanism of Fano resonance is analyzed based on the multimode interference coupled mode theory (MICMT). The finite element method (FEM) and MICMT are used to simulate the transmission spectra of this structure and analyze the influence of structural parameters on the refractive index sensing characteristics. And the transmission responses calculated by the FEM simulation are consistent with the MICMT theoretical results very well. The results show that the figure of merit (FOM) can reach 193 and the ultra-high sensitivity is 1600 nm/RIU after the structure parameters have been optimized, and can provide theoretical basis for designing the high sensitive refractive index sensors based on SPPs waveguide for high-density photonic integration with excellent performance in the near future.

Understanding the Li diffusion mechanism and positive effect of current collector volume expansion in anode free batteries

Abstract: In anode free batteries (AFBs), the current collector acts as anode simultaneously and has large volume expansion which is generally considered as a negative effect decreasing structural stability of a battery. Moreover, despite many studies on the fast lithium diffusion in the current collector materials of AFB such as copper and aluminum, the involved Li diffusion mechanism in these materials remains poorly understood. Through first-principles calculation and stress-assisted diffusion equations, here we study the Li diffusion mechanism in several current collectors and related alloys and clarify the effect of volume expansion on Li diffusion, respectively. It is suggested that due to the lower Li migration barriers in aluminum and tin, they should be more suitable to be used as AFB anodes, compared to copper, silver and lead. The Li diffusion facilitation in copper with a certain number of vacancies is proposed to explain why the use of copper with a thickness of ≤ 100 nm as the protective coating on anode improves the lifetime of batteries. We show that the volume expansion has a positive effect on Li diffusion via mechanical-electrochemical coupling. Namely, the volume expansion caused by Li diffusion will further induce stress which in turn affects the diffusion. These findings not only provide in-depth insight into the operating principle of AFBs, but also open a new route toward design of improved anode through utilizing the positive effect of mechanical-electrochemical coupling.

Efficient manipulation of terahertz waves by multi-bit coding metasurfaces and further applications of such metasurfaces

Abstract: Yunping Qi(祁云平)1,† Baohe Zhang(张宝和)1, Jinghui Ding(丁京徽)1, Ting Zhang(张婷)1, Xiangxian Wang(王向贤)2, and Zao Yi(易早)3 1College of Physics and Electronic Engineering, Northwest Normal University, Lanzhou 730070, China 2School of Science, Lanzhou University of Technology, Lanzhou 730050, China 3Joint Laboratory for Extreme Conditions Matter Properties, Southwest University of Science and Technology, Mianyang 621900, China