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The thermal transport properties of the electrons in stanene nanoribbons (SNRs) and graphene nanoribbons (GNRs) are studied using a nonequilibrium Green’s function approach in which the effects of electron-phonon coupling are considered. The results demonstrate that the electron thermal conductance values in both SNRs and GNRs are closely related to both the temperature T and the chemical potential l. Comparison with the thermal transport properties of GNRs shows that the quantized thermal conductance plateau in SNRs is narrower at low temperatures, while the thermal conductance is also greater at higher temperatures in SNRs. The periodic strain-induced electron-phonon coupling can modulate the thermal conductance periodically in both SNRs and GNRs. [ABSTRACT FROM AUTHOR]

We have found theoretically that nearly total absorption in a wideband of frequencies and a large range of angles of incidence for both polarizations can be realized in a heterostructure consisting of a highly absorptive metal film and a truncated photonic crystal. Furthermore, the width of the absorption band is broadened with increase of the incident angle for the transverse electric polarization. Such properties are significant for designing near-perfect broadband and wide-angle absorbers in the visible and near infrared regions. [ABSTRACT FROM AUTHOR]

We demonstrated that transmittance and field intensities of a thick metal sandwiched between two dielectric photonic crystals (PCs) can be enhanced by more than two orders of magnitude and by nearly 20 times, respectively, compared to a single metal layer with the same thickness. Under the tunneling mechanism, the light can enter the sandwiched structure without reflection and localizes at the two interfaces of the metal film and PCs. This configuration of fields facilitates the reduction of absorption in the metal. Experimental results are in good agreement with simulations. [ABSTRACT FROM AUTHOR]

We investigated the swelling behavior and density distributions of polyion segments and multivalent counterions in polyelectrolyte brushes within a primitive model that represents both polyion segments and salt ions as charged spheres and the solvent as a continuous dielectric medium. The numerical performance of a previously proposed nonlocal density functional theory (NLDFT) was tested with Monte Carlo simulations for multivalent systems and compared with the Poisson–Boltzmann equation that ignores the ionic size and electrostatic correlations. The NLDFT predicts that in the limit of low salt concentration, trivalent counterions can self-organize into a one-dimensional wavelike structure within the oppositely charged polyelectrolyte brush. Multivalent counterions introduce electrostatic correlations responsible for the nonmonotonic swelling of the brush which is qualitatively different from that in a monovalent solution. While in a monovalent solution the brush thickness increases monotonically with the grafting density, in a trivalent solution the swelling behavior resembles that for a neutral brush in a poor solvent. The NLDFT was also used to investigate the effects of ionic size on the brush swelling and counterion organization. [ABSTRACT FROM AUTHOR]

We present a hybrid method to investigate the isotropic-nematic (I-N) transition in athermal solutions of rod-coil copolymers. This method incorporates the scaled-particle theory for semiflexible chains with two-chain Monte Carlo simulation for the osmotic second virial coefficient and for the angle-dependent excluded volume. We compare the theoretical prediction with Monte Carlo simulations for fused rod-coil copolymers and find good agreement for both the equation of state and the orientational order parameter. The theory is also used to examine the effects of the bond length, the chain length, and the chain composition on orientational ordering in athermal solutions of rod-coil block copolymers. It predicts I-N transition in rod-coil copolymers with fixed rod length but a variable flexible tail in good agreement with experiments. [ABSTRACT FROM AUTHOR]

A hybrid method is proposed to investigate the microstructure of various polymeric fluids confined between two parallel surfaces. The hybrid method combines a single-chain Monte Carlo (MC) simulation for the ideal-gas part of the Helmholtz energy and a density functional theory (DFT) for the excess part that arises from nonbonded intersegment interactions. The latter consists of a modified fundamental measure theory for excluded-volume effect, the first-order thermodynamics perturbation theory for chain connectivity, and a mean-field approximation for the van der Waals attraction. In comparison with a conventional DFT, the hybrid method avoids calculation of the time-consuming recursive functions and is directly applicable to polymers with arbitrary molecular architecture. Its numerical performance has been validated by extensive comparisons with MC data for the density distributions of totally flexible, semiflexible, or rigid polymers and those with starlike architecture. Special attention is also given to the formation of a nematic monolayer by rigid molecules laying perpendicular to a planar surface. The hybrid method predicts the surface pressure versus surface coverage in good agreement with experiment. [ABSTRACT FROM AUTHOR]

Random invariant manifolds are geometric objects useful for understanding complex dynamics under stochastic influences. But these random objects are difficult to be visualized geometrically or computed numerically. The current work provides a perturbation approach to approximate these random invariant manifolds. We first discuss the existence of a random invariant manifold for a class of stochastic evolutionary equations. Then, we approximate the random invariant manifold by the invariant manifold of a new system with smooth colored noise (i.e., integrated Ornstein-Uhlenbeck processes). The convergence in a pathwiseWong-Zakai sense is shown. [ABSTRACT FROM AUTHOR]

Monopole patch antenna systems, which can generate orbital angular momentum (OAM) waves at 2.4GHz, are proposed in this paper. The proposed antenna systems have advantages of simple planar structure and small size of antenna element. Design, simulation, fabrication and measurement of the proposed antenna systems are presented. Two feeding networks, which constitute the proposed antenna systems with monopole patch antenna array, are designed to generate modes 1 and 2 of OAM waves. The antenna systems for both modes are shown to be effective in generating OAM waves of modes 1 and 2 from both simulation and three types of measurement: radiation pattern, phase distribution and phase gradient. Simulation and measurement results of radiation pattern and phase distribution have shown very close results. Phase gradient measurement results has verified that the generated waves from the antenna systems are indeed OAM waves. [ABSTRACT FROM AUTHOR]

Triboelectric nanogenerators attract more and more research attention, for their high efficiency, low fabrication cost, and high flexibility. However, the mechanism about triboelectrification remains highly debated. In this work, we constructed a liquid-metal based triboelectric nanogenerator (LM-TENG) and investigated the influence of the gas atmosphere on the triboelectrification between the liquid metal and the dielectric materials, such as PTFE, Kapton, and Nylon. It was found that the dielectric materials were negatively charged on contact with the liquid metal in ambient air. But in the nitrogen conditions, the polarity of the charges was reversed. Oxygen was excluded, which is responsible for the polarity reversal in contact electrification. Based on X-ray photoelectron spectroscopy, energy-dispersive X-ray, and SKFM data, a possible mechanism was proposed. [ABSTRACT FROM AUTHOR]

By integrating a triboelectric nanogenerator (TENG) and a thin film dielectric elastomer actuator (DEA), the DEA can be directly powered and controlled by the output of the TENG, which demonstrates a self-powered actuation system toward various practical applications in the fields of electronic skin and soft robotics. This paper describes a method to construct a physical model for this integrated TENG-DEA system on the basis of nonequilibrium thermodynamics and electrostatics induction theory. The model can precisely simulate the influences from both the viscoelasticity and current leakage to the output performance of the TENG, which can help us to better understand the interaction between TENG and DEA devices. Accordingly, the established electric field, the deformation strain of the DEA, and the output current from the TENG are systemically analyzed by using this model. A comparison between real measurements and simulation results confirms that the proposed model can predict the dynamic response of the DEA driven by contact-electrification and can also quantitatively analyze the relaxation of the tribo-induced strain due to the leakage behavior. Hence, the proposed model in this work could serve as a guidance for optimizing the devices in the future studies. [ABSTRACT FROM AUTHOR]

We present a novel design of two-dimensional (2D) angular-resolved spectrometer for full beam characterization of ultrashort intense laser driven proton sources. A rotated 2D pinhole array was employed, as selective entrance before a pair of parallel permanent magnets, to sample the full proton beam into discrete beamlets. The proton beamlets are subsequently dispersed without overlapping onto a planar detector. Representative experimental result of protons generated from femtosecond intense laser interaction with thin foil target is presented. [ABSTRACT FROM AUTHOR]

A non-uniform buncher and a depth-tunable collector have been proposed to improve the power capacity and conversion efficiency of the coaxial foilless transit-time oscillator (TTO) in our previous work. Recently, our Ku-band coaxial TTO with low guiding magnetic field is improved by employing them, and the related experimental investigations are carried out on the TORCH-01 accelerator. It is shown that the non-uniform buncher plays a key role in the enhancement of microwave pulse duration. The influences of the collector's depth on characteristics of the device indicate that the conversion efficiency can be improved by optimizing the collector's depth in the experiments. With the diode voltage 460 kV, the beam current 8.7 kA, and the guiding magnetic field of 0.6 T, a radiation power of 1 GW with the conversion efficiency of 25% at 14.3 GHz is generated by our improved TTO. The output pulse duration is 26 ns and no obvious pulse shortening is observed. The experimental results demonstrate the abilities of this improved Ku-band device to generate gigawatt-class Ku-band microwave with low guiding magnetic field. [ABSTRACT FROM AUTHOR]

Terahertz quantum cascade lasers with a record output power up to ∼0.23 W in continuous wave mode were obtained. We show that the optimal 2.9-mm-long device operating at 3.11 THz has a low threshold current density of 270 A/cm2 at ∼15 K. The maximum operating temperature arrived at ∼65 K in continuous wave mode and the internal quantum efficiencies decreased from 0.53 to 0.19 for the devices with different cavity lengths. By using one convex lens with the effective focal length of 13 mm, the beam profile was collimated to be a quasi Gaussian distribution. [ABSTRACT FROM AUTHOR]

Abnormal percolative transport properties have been studied in (011)-oriented La0.325Pr0.3Ca0.375MnO3 (LPCMO)/0.68Pb(Mg1/3Nb2/3)O3-0.32PbTiO3 (PMN-PT) heterostructure. By introducing a dynamic electric field-induced in-plane anisotropic strain-field in phase separated LPCMO film, we observed a significant promotion of the thermal hysteresis (~68 K) and a positive colossal electroresistance (~8450%). Such abnormal hysteresis is believed to be associated with anisotropic strain induced strong pinning effect in the material. This work unambiguously evidenced the importance of the anisotropic strain on the abnormal transport and meanwhile provides alternative opportunity for well understanding the percolation mechanism in inhomogeneous systems. [ABSTRACT FROM AUTHOR]

An improved Ku-band magnetically insulated transmission line oscillator is proposed and investigated experimentally. In the particle-in-cell simulation, the Ku-band MILO generates the microwave with a power of 1.62GW and a frequency of 13 GHz at the input voltage of 474 kV. The device is fabricated based on the simulation results, and an experiment system is designed. In the preliminary experiments, output microwave with frequency of 13.02 GHz, power of 150MW, and pulse width of 17 ns is generated, under the diode voltage of 450 kV. Analysis on the experiment results shows that plasma produced due to the large current hitting to the outside of the collection tank is the essential cause for the low amplitude of the microwave power and short pulse width. [ABSTRACT FROM AUTHOR]

A self-powered field emission device (FED) driven by a single-electrode tribo-electric nanogenerator (TENG) is demonstrated. The mechanical motion works as both a power supply to drive the FED and a control unit to regulate the amount of emitted electrons. By using the Fowler-Nordheim equation and Kirchhoff laws, a theoretical model of this self-powered FED is proposed, and accordingly the real-time output characteristics of the device are systematically investigated. It is found that the motion distance of the TENG controls switch-on of the FED and determines the charge amount for emission, while the motion velocity regulates the amplitude of emission current. The minimum contact area for the TENG to generate field emission is about 9 cm², which can be improved by optimizing FED structure and the tribo-materials of TENG. The demonstrated concept of this self-powered FED as well as the proposed physical analysis can serve as guidance for further applications of FED in such fields of self-powered electronics and soft electronics. [ABSTRACT FROM AUTHOR]

A relativistic Ku-band coaxial transit-time oscillator has been proposed in our previous work. In the experiments, we find that the asymmetric competition mode in the device limits the microwave power with the increase of the input electric power. For solving such a problem, the methods for analysis and suppression of the asymmetric competition mode in the device are investigated theoretically and experimentally. It is shown that the structure and the material of the collector, the concentricity, and the electron emission uniformity play an important part in the suppression of the asymmetric competition mode in the relativistic Ku-band transit-time oscillator. In the subsequent experiments, the asymmetric mode was suppressed effectively. At a low guiding magnetic field of 0.7 T, a microwave pulse with power of 1 GW, frequency of 14.3 GHz close to the simulation one, and efficiency of 20% was generated. [ABSTRACT FROM AUTHOR]

An improved foilless Ku-band transit-time oscillator with low guiding magnetic field is proposed and investigated in this paper. With a non-uniform buncher and a coaxial TM02 mode dual-resonant reflector, this improved device can output gigawatt level Ku-band microwave with relatively compact radial dimensions. Besides the above virtue, this novel reflector also has the merits of high TEM reflectance, being more suitable for pre-modulating the electron beam and enhancing the conversion efficiency. Moreover, in order to further increase the conversion efficiency and lower the power saturation time, a depth-tunable coaxial collector and a resonant cavity located before the extractor are employed in our device. Main structure parameters of the device are optimized by particle in cell simulations. The typical simulation result is that, with a 380kV, 8.2kA beam guided by a magnetic field of about 0.6T, 1.15GW microwave pulse at 14.25 GHz is generated, yielding a conversion efficiency of about 37%. [ABSTRACT FROM AUTHOR]

Magnetic and resistive anisotropies have been studied for the La0.325Pr0.3Ca0.375MnO3 films with different thicknesses grown on low symmetric (011)-oriented (LaAlO3)0.3(SrAl0.5Ta0.5O3)0.7 substrates. In the magnetic and electronic phase separation region, a colossal anisotropic resistivity (AR) of ~105% and an anomalous large anisotropic magnetoresistance can be observed for 30 nm film. However, for 120 nm film, the maximum AR decreases significantly (~2×10³%) due to strain relaxation. The colossal AR is strongly associated with the oriented formation of magnetic domains, and the features of the strain effects are believed to be useful for the design of artificial materials and devices. [ABSTRACT FROM AUTHOR]

In this letter, a very simple metallic subwavelength cell is designed for constructing left-handed metamaterial. The conductive current mode inside the metallic resonator of this cell imitates one reported displacement current mode inside a dielectric subwavelength resonator. We show by simulation and experiments that an artificial metamaterial composed of cells with such kind of current mode can behave simultaneously negative permittivity and permeability. The metallic cell with double negative property obtained in this letter is suitable for the applications in the high frequency band, such as in millimeter or even terahertz bands. [ABSTRACT FROM AUTHOR]

The nonlinear properties of a metamaterial sample composed of double-layer metallic patterns and voltage controllable diodes are experimentally investigated. Second harmonics and spectrum modulations are clearly observed in a wide band of microwave frequencies, showing that this kind of metamaterial is not only tunable by low dc bias voltage but also behaves strong nonlinear property under a small power incidence. These properties are difficult to be found in normal naturally occurring materials. [ABSTRACT FROM AUTHOR]

A left-handed metamaterial based on a bianisotropic S-ring resonator is fabricated. By shorting some of the horizontal arms of the paired S-rings, net electric (magnetic) dipoles accumulate under certain magnetic (electric) field induction, which results in a magnetoelectric coupling effect. Free space experimental measurements are carried out and the experimental results demonstrate the cross polarization effect around the left-handed pass band of the metamaterial. The simple planar configuration of the structure also indicates the superiority of this inclusion in the realization of bianisotropic left-handed metamaterials. [ABSTRACT FROM AUTHOR]