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Abstract This comment concerns the doubtful new auxiliary equation method (Khater method) included in the above paper. We prove by simple calculation that this method is wrong. The exact solutions of the proposed nonlinear equation obtained in the above paper are all wrong. Highlights • The new auxiliary equation method is called Khater method. • We prove by simple calculation that Khater method is wrong. • We show that the exact solutions obtained in the above paper are all wrong. [ABSTRACT FROM AUTHOR]

This paper explores the dynamic behavior of metamaterial-like structures by investigating the evolution of their band gap under the influence of geometrical nonlinearities in the large displacement/rotations field. The study employs a unified framework based on the Carrera Unified Formulation (CUF) and a total Lagrangian approach to develop higher-order one-dimensional beam theories that account for geometric nonlinearities. The axis discretization is achieved through a finite element approximation. The equations of motion are solved around nonlinear static equilibrium states, which are determined using a Newton–Raphson algorithm combined with a path-following method of arc-length type. The CUF approach introduces two key innovations that are highly suitable for the evolution of the band gap: (1) Thin-walled structures can be effectively represented using a single one-dimensional beam model, overcoming the common limitations of standard finite elements. This is crucial as three-dimensional solid elements would result in significant computational costs, and two-dimensional elements based on von Kármán theory pose limitations for this type of investigation. Moreover, employing one-dimensional finite elements usually requires a combination of elements, leading to additional mathematical complexities in their connections and lacking geometric precision. (2) CUF enables the use of the full Green–Lagrange strain tensor without the need for assumptions, as is the case with von Kármán nonlinearities. The paper specifically compares results obtained with linear and nonlinear stiffness matrices, highlighting the differences. Numerical investigations are conducted on thin-walled structures composed of repeatable cells, assessing mode changes under traction and compression loading. Additionally, the paper presents a more complex metamaterial-like structure. The findings emphasize that the band gap is an inherent property of the equilibrium state, underscoring the necessity of a proper nonlinear analysis for accurately evaluating frequency transitions. • Dynamics of metamaterial-like structures investigating the evolution of band gap. • Analysis of the mode and frequency change in the geometrical nonlinear field. • CUF for 1D Finite element model of thin-walled metamaterial-like structures. • Lagrange polynomials for the description of complex geometries. • Comparison between linear and nonlinear approaches. [ABSTRACT FROM AUTHOR]

Flow-induced structural noise is an important component of hydrodynamic noise of underwater structures. Local resonance metamaterials are considered to have excellent performance and enormous potential in the field of low-frequency vibration and noise control. To verify its potential, the paper derived the underwater band gap of a lateral local resonance (LLR) plate through the plane wave expansion (PWE). Then, utilizing the modal superposition approach and Rayleigh integral technique, the vibro-acoustic response of a LLR plate under a turbulent boundary layer (TBL) excitation is obtained. Finite element certification is also conducted through an uncorrelated wall plane wave technique. Parametric study is conducted to analyse the factors which influence the control effects. The result shows that the plate exhibits excellent suppression performance for flow-induced vibration at band gap frequencies. The band gaps and suppression ranges generated by the underwater metamaterial plate, are dramatically narrowed due to the thick fluid load. The paper provides theoretical guidance for the control of flow-induced structural vibration and the application of acoustic metamaterials. [ABSTRACT FROM AUTHOR]

Photocatalysis, as an alternative for treating persistent water pollutants, holds immense promise. However, limitations hinder sustained treatment and recycling under varying light conditions. This comprehensive review delves into the novel paradigm of metal and non-metal doping to overcome these challenges. It begins by discussing the fundamental principles of photocatalysis and its inherent limitations. Understanding these constraints is crucial for developing effective strategies. Band gap narrowing by metal and non-metal doping modifies the band gap, enabling visible-light absorption. Impurity energy levels and oxygen vacancies influenced the doping energy levels and surface defects. Interfacial electron transfer and charge carrier recombination are the most important factors that impact overall efficiency. The comparative analysis of nanomaterials are reviewed on various, including nanometal oxides, nanocarbon materials, and advanced two-dimensional structures. The synthesis process are narratively presented, emphasizing production yields, selectivity, and efficiency. The review has potential applications in the environment for efficient pollutant removal and water purification, economic cost-effective and scalable production and technological advancement catalyst design, in spite of its challenges in material stability, synthesis methods and optimizing band gaps. The novelty of the review paper is on the proposal of a new paradigm of heterojunctions of doped metal and non-metal photocatalysts to promise highly efficient water treatment. This review bridges the gap between fundamental research and practical applications, offering insights into tailored nano photocatalysts. [Display omitted] • Characterization of metal and non-metal-doped heteroatom photocatalysts. • Compare doped heteroatom nanomaterials in photocatalysis. • Future challenges in heteroatom-doped nanomaterials. [ABSTRACT FROM AUTHOR]

Single-crystal-to-single-crystal (SCSC) transformation provides a good platform for obtaining new functional coordination polymers. In this study, we demonstrate a violent and rapid structural transformation between two d10 coordination polymers (CPs). The complex 1 [Zn(3,5-thbzc) 2 (C 2 H 6 O) 2 ] transformed into the complex 2 {[Zn(3,5-thbzc) 2 (H 2 O) 2 ]·C 3 H 7 NO·2H 2 O} (where t = tbutyl, hbzc− = 2-Hydroxybenzoato) triggered by deionized water under standard temperature and pressure conditions in solid state. The transformation reaction was confirmed using single-crystal XRD, PXRD and SEM. The results showed that complex 1 adopts a bidentate chelate six-coordination mode, and complex 2 adopts a monodentate four-coordination mode. SEM clearly showed that complex 2 was in the form of random nanowire clusters, suggesting that their transformation required degradation of the entire crystal structure. UV–Vis–NIR spectra were used to calculate the band gaps of complexes 1 and 2 , which demonstrated wide-bandgap semiconductor-like materials with ∼3.2 eV band gap widths. The results of dielectric studies of complex 1 revealed that it possessed a medium dielectric constant (κ = 6.08 at 1 kHz), while complex 2 displayed an even higher dielectric constant (κ = 7.97 at 1 kHz) at room temperature. Interestingly, parent complex 1 exhibited a small ladder-like dielectric anomaly at 188 °C, while progeny complex 2 did not. This paper describes a new strategy for preparing adjustable functional dielectric materials. Through solid-state transformation triggered by deionized water, the parent bidentate six-coordination complex 1 generates the progeny monodentate four-coordination complex 2. This transformation process involves the cleavage and regeneration of coordination bonds. Complex 2 has a high dielectric constant due to the substitution of water ligands. [Display omitted] • Ligand-substituted SCSC transformation between complexes 1 and 2 was triggered by deionized water. • The transformation process involves the cleavage and regeneration of coordination bonds. • The coordination number of Zn2+ changes from six-coordination to four-coordination. • The introduction of H 2 O ligands can significantly improve the dielectric constants of Zn-CPs. • Complex 1 shows a ladder-like dielectric anomaly at 188 °C. [ABSTRACT FROM AUTHOR]

[Display omitted] The fundamental mechanistic understanding of the working principle of metal phthalocyanine (MPc) + H 2 O 2 system, at molecular level, is in its nascent stage. In this paper, a green strategy was employed for the immobilization of sulfonated cobalt phthalocyanine (CoPc) onto reduced graphene with assistance of bio-synthesized nanocellulose, and the resulting graphene-supported-CoPc (CoPc&G) was applied for the catalytic degradation of phenol solution with H 2 O 2 as oxidant. More than 90% of phenol can be removed within 75 min, and the existence of graphene clearly has a positive effect on the catalytic activity. Theoretical calculations were conducted to unveil the catalytic nature of CoPc&G. H 2 O 2 was favorably chemisorbed onto CoPc&G in the form of OOH−, hydroxyl radicals were favorably formed by homolytic cleavage of O O bonds, and ΔG value for the formation of reactive species was decreased with the existence of graphene. Density of states (DOS) analysis shows that graphene could effectively boost the electronic activity, reduce HOMO-LUMO gap, and strengthen the polarizability of the catalyst, thereby lower the free energy gap for the enhanced generation of reactive species. A detailed catalytic degradation route of phenol with CoPc&G + H 2 O 2 system was established based on the combination of theoretical calculations and experimental results. [ABSTRACT FROM AUTHOR]

Abstract Quasi-periodic structures have been widely studied, notably in the atomic vibration domain. In this paper a beam structure based on Octagonal quasi-periodic tiling is studied. We provide a complete description of its vibrational response, including the density of its vibrational states, a detailed description of its vibration modes, and the computation of the dynamical structure factor (spectral density of energy) for transverse and for longitudinal waves. It is shown that quasi-periodic structures exhibit localized low frequency vibration modes that are due to resonant vibrations of isolated patterns in the quasi-periodic structure, but in opposite, high-frequency modes are (non-trivially) extended. Moreover, the paper shows the possible existence of band gaps in the vibrational response of periodic and quasi-periodic beam lattices as a function of the ratio between the bending and the tensile stiffness of the beams. [ABSTRACT FROM AUTHOR]

In this paper, we investigate the graphene field effect transistor (G-FET) to enhance the drain current saturation and to minimize the drain conductance (g d ) using numerical simulation. This work focus on suppressing the drain conductance using silicon substrate. We studied the impact of different substrate on the performance of band gap engineered G-FET device. We used a non-equilibrium green function with mode space (NEGF_MS) to model the transport behavior of carriers for 10 nm channel length G-FET device. We compared the drain current saturation of G-FET at higher drain voltage regime on silicon, SiC, and the SiO 2 substrate. This paper clearly demonstrates the effect of substrate on an electric field near drain region of G-FET device. It is shown that the substrate of G-FET is not only creating a band gap in graphene, which is important for current saturation and g d minimization, but also selection of suitable substrate can suppress generation of carrier concentration near drain region is also important. [ABSTRACT FROM AUTHOR]

This paper presents the synthesis of visible light-responsive ternary nanocomposites composed of cuprous oxide (Cu 2 O), tungsten trioxide (WO 3), and titanium dioxide (TiO 2) with varying weight percentages (wt.%) of the Cu 2 O. The resulting Cu 2 O/WO 3 /TiO 2 (CWT) nanocomposites exhibited band gap energy ranging from 2.35 to 2.90 eV. Electrochemical and photoelectrochemical (PEC) studies confirmed a reduced recombination rate of photoexcited charge carriers in the CWT nanocomposites, facilitated by a direct Z-scheme heterojunction. The 0.50CWT nanocomposite demonstrated superior photodegradation activity (2.29 × 10−2 min−1) against Reactive Black 5 (RB5) dye under visible light activation. Furthermore, the 0.50CWT nanocomposite exhibited excellent stability with 80.51% RB5 photodegradation retention after five cycles. The 0.50CWT electrode achieved a maximum specific capacitance of 66.32 F/g at 10 mA/g current density, with a capacitance retention of 95.17% after 1000 charge-discharge cycles, affirming its stable and efficient supercapacitor performance. This was supported by well-defined peaks in cyclic voltammetry (CV) and galvanostatic charge-discharge (GCD) curves, indicating pseudocapacitive properties. • Direct Z-scheme heterojunction facilitates separation of photoexcited charge carriers. • Photoelectrochemical study proved reduction of charge carriers recombination rate. • Nanocomposite showed excellent chemical and photostability for dye photodegradation. • Chemical oxygen demand test proved complete mineralization of dye by photocatalysis. • High capacitance retention and specific capacitance proved effective supercapacitor. [ABSTRACT FROM AUTHOR]

• The precise parameters transfer matrix method exhibits excellent accuracy and applicability. • The effect of moment of inertia on the band calculation accuracy is smaller than that of shear deformation. • Both Young's modulus difference and density difference jointly affect the bandgap characteristics. • The appropriate axial wall pressure is beneficial for the low-frequency broadband design. The phononic crystal theory provides a novel approach for effectively controlling the bending vibrations in fluid-filled pipelines. This paper innovatively proposes the precise parameters transfer matrix method to investigate the band calculation accuracy and bandgap characteristics of fluid-filled periodic pipelines with various beam types. Firstly, the differential equations for bending vibration of fluid-filled pipelines are established based on deformation and force analysis. The parameters of the system state are precisely represented by the structural form of multiplying the constitutive matrix with the derivative matrix. Combined with Bloch's theorem, the novel precise parameters transfer matrix method for calculating the band structure is proposed. Secondly, the validity of this method is verified through a comparison with finite element simulation results. A detailed analysis is provided regarding the mechanism of bandgap formation and the effect of fluid filling on the band structure. Then, the influence of shear deformation, moment of inertia, and their coupling on the band calculation accuracy for fluid-filled periodic pipelines is studied based on various beam theories. Finally, it delves into the bandgap characteristics of fluid-filled periodic pipelines under different material parameters, structural parameters, and excitation conditions. This research offers valuable insights for the structural design and vibration damping application in fluid-filled periodic pipelines, providing theoretical support for accurately determining their bandgaps. [Display omitted] [ABSTRACT FROM AUTHOR]

This paper develops an asymptotic method to predict the dispersion curves of a weakly disordered medium. The disordered coefficients of the original acoustic equation are related to periodic coefficients through a change of variables, assumed asymptotically close to the identity. At leading order in the amplitude of the disorder, the medium is driven by an acoustic equation with periodic coefficients, which can be analyzed through a classical Floquet–Bloch approach. At first order, with simple eigenvalues, a simple post-processing of the periodic eigenvalues and eigenfunctions of the leading order allows to account for the weakly disordered character of the original coefficients. In the case of repeated eigenvalues (for instance, at Dirac points), a residual is introduced, whose minimization allows to recover the opening of the band gaps with the loss of periodicity. Examples in 1D and 2D illustrate the validity of our asymptotic approach, by comparing its results with eigenmodes and dispersion curves computed over much larger periods for reference. • Dispersion curves and wave modes in weakly non-periodic media are analyzed. • An asymptotic method to predict them is developed. • Opening of the band gaps generated by the loss of periodicity is well reproduced. • Only cell-scale solutions of the periodic medium are needed. [ABSTRACT FROM AUTHOR]

The aim of this paper is to show both analytically and numerically the existence of a subwavelength phononic bandgap in bubble phononic crystals. The key result is an original formula for the quasi-periodic Minnaert resonance frequencies of an arbitrarily shaped bubble. The main findings in this paper are illustrated with a variety of numerical experiments. [ABSTRACT FROM AUTHOR]

• A mathematical model of the local resonance elastic metamaterial beam with multiple resonators is established by the EPWE method. • Broadening the vibration attenuation region without changing the total mass of the resonators. • The effects of frequency spacing, damping, and mass ratio on the vibration attenuation characteristics are analyzed, and their critical values are observed. Enhancing vibration isolation with local resonance metamaterials has attracted widespread attention due to the low-frequency band gap. However, the narrow band gaps limit its application. To improve vibration suppression properties over a wide frequency range under the constraints of space and mass in engineering, this paper presents the modeling techniques and design strategies for a local resonance elastic metamaterial beam with multiple resonators. The local resonance sub-system contains multi-degree-of-freedom resonators and is periodically mounted on the elastic beam. Two special cases, the elastic metamaterial beam with one-degree-of-freedom local resonator sub-system (1-DOF) and two-degree-of-freedom local resonator sub-system (2-DOF) are used to investigate the vibration attenuation characteristics in detail. Results are presented in the form of attenuation constant, which are calculated by the extended plane wave expansion (EPWE) method. The effects of frequency spacing, damping and mass ratio on the vibration attenuation characteristics of elastic metamaterial beams are comprehensively investigated. The results show that a wider and more stable attenuation range can be obtained by reasonably adjusting these three parameters. Finally, the comparison of experimental and simulation results demonstrates that the design strategies proposed in this paper can broaden the vibration attenuation regions. The theoretical approaches and design schemes can provide effective guidance for passive vibration control. [ABSTRACT FROM AUTHOR]

The dynamic characterization of complex structures raises the need for a robust experiment-based wavenumber identification method, especially when they are tested under complex conditions. To this end, this paper presents an optimized Algebraic Wavenumber Identification (AWI) method and describes the dynamic behavior of three complex structures under a series of complex conditions through AWI. The first novelty of this paper is to optimize AWI in terms of computation efficiency and accuracy by two solutions: (a) the multiple integral of AWI, which acts as a filter, is explicitly solved by the least squares fitting method, significantly reducing the computation cost, especially when multiple samples are used as input parameters; (b) a sampling strategy is provided to further improve the robustness of the AWI to measurement errors. On this basis, an AWI implementation procedure is proposed for experimental tests under complex conditions. The second novelty of this paper is on the applications of AWI in wave propagation parameters identification of complex structures, including the damping loss factor estimation of a viscoelastic beam and a honeycomb sandwich beam, the band gap identification of a meta-structure, and experimental dispersion curves extraction of these three complex structures. The third novelty of this paper is the experimental validation of AWI under a series of complex conditions, including signal noise, non-periodic sampling, and uncertainty of measuring points' geometric coordinates. The experimental and numerical results have been compared to two popular inverse methods, namely, Inhomogeneous Wave Correlation (IWC) and INverse COnvolution MEthod (INCOME), demonstrating the validity of the AWI implementation procedure proposed in this paper. • A robust and low-cost experimental-based wavenumber identification method. • Experimental dispersion curves and damping loss factor identification of three complex structures. • Investigations of wavenumber identification under three complex conditions. • Investigations of the impact of measurement variability on the wavenumber identification. • Comparison of three inverse methods for extraction of complex wavenumbers. [ABSTRACT FROM AUTHOR]

[Display omitted] Exploring high performance photocatalysts is of great importance to relieve the environment pollution issues. In this paper, we introduce a facile antisolvent solvothermal method to synthesize methylammonium lead tribromide perovskite (MAPbBr 3) nanocrystals and successfully employ them as efficient photocatalysts. Compared to the room temperature synthesized MAPbBr 3 (RT-MAPbBr 3), the antisolvent solvothermal synthesized MAPbBr 3 (AS-MAPbBr 3) has multiple outstanding properties, such as improved crystallinity with lower grain boundary density, enhanced light absorption in visible range, suitable band gap of 2.31 eV and extended photoluminescence (PL) lifetime as long as 2627.82 ns. By taking advantages of the above merits, the AS-MAPbBr 3 exhibits efficient photocatalytic performance by decomposition of methyl orange under solar light. A high apparent rate constant of 101.2 × 10−3 is achieved along with excellent cyclability, which significantly outperforms the RT-MAPbBr 3 (56.0 × 10−3) and P25 (16.5 × 10−3). The underlying mechanism for MO photocatalytic degradation is deeply explored and proposed. Our present study suggests that the antisolvent solvothermal method can be a promising method to synthesize perovskite nanocrystals, and might also provide some insights in developing a series of high performance perovskite based photocatalysts. [ABSTRACT FROM AUTHOR]

This paper introduces a computer image processing-based method called the rasterized plane wave expansion method (RPWEM). This method improves the conventional plane wave expansion method (CPWEM) and reduces its formula derivation cost in the case of 2-D phononic crystals with complex inclusions. In addition, for 2-D phononic crystals with arbitrary multiphase materials, this method can also simplify the calculation process. By employing the proposed RPWEM, successful calculations of band gaps are conducted for planar phononic crystals with the hexagonal unit cell as well as phononic crystals featuring integrated circuit-like structures. The results further validate the expanded applicability of the RPWEM in comparison to the CPWEM. In the end, a potential application similar to DIC (Digital Image Correlation) for predicting band structures of phononic crystals is proposed, and its feasibility is briefly validated. [ABSTRACT FROM AUTHOR]

• A new MRE metamaterial plate with continuous programmable properties was proposed. • A real-time tunable and fast response local resonant band gap was generated. • The plane wave expansion method and the finite element method were implemented. • The vibration manipulation functionalities were experimentally verified. Metamaterial plates have attracted considerable attention due to their unprecedented elastic wave manipulation abilities. Currently, the band gap and other properties of traditional metamaterial plates are fixed, and the material parameters of most metamaterials cannot be dynamically and continuously adjusted. To address this issue, a two-dimensional (2D) magnetorheological elastomer (MRE) programmable metamaterial plate (MREPMP) with local resonance was proposed. The proposed MREPMP was composed of a thin steel plate and a periodic array of resonators, consisting of MREs and electromagnetic mass blocks. It not only has a compact structural design, but also enables real-time vibration control and programming wave manipulation by altering the amplitude of the current. The dispersion relation of the proposed MREPMP was theoretically calculated based on the plane wave expansion (PWE) method and the simulated transmissibility was numerically calculated using the finite element method in COMSOL. Subsequently, a prototype of the MREPMP was fabricated, and vibration tests were conducted to assess its programmable vibration manipulation functionalities. Two different types of defect paths were used as excitations and the corresponding real-time vibration manipulation performance was analyzed. The simulation results agree with the experimental results, showing that the MREPMP can dynamically tune the band gap and activate different waveguides through continuous online programming. This paper opens up a new idea for tunable manipulation of wave propagation. [Display omitted] [ABSTRACT FROM AUTHOR]

Dispersion relation reflects the dependence of wave frequency on its wave vector when the wave passes through certain materials. It demonstrates the properties of this material and thus it is critical. However, dispersion relation reconstruction is very time-consuming and expensive. To address this bottleneck, we propose in this paper an efficient dispersion relation reconstruction scheme based on global polynomial interpolation for the approximation of two-dimensional photonic band functions. Our method relies on the fact that the band functions are piecewise analytic with respect to the wave vector in the Brillouin zone. We utilize suitable sampling points in the Brillouin zone at which we solve the eigenvalue problem involved in the band function calculation, and then employ Lagrange interpolation to approximate the band functions on the whole Brillouin zone. Numerical results show that our proposed method can significantly improve the computational efficiency. [ABSTRACT FROM AUTHOR]

In this paper, the structural phase transition, surface morphologies, ferromagnetic and optical properties have been observed in [K 1/2 Na 1/2 NbO 3 ] 1- x [BaNi 1/2 Nb 1/2 O 3-δ ] x (KNBNNO, 0 ​≤ ​ x ​≤ ​1) films. X-ray diffraction indicated that the KNBNNO films undergo a phase transition process with increasing BaNi 1/2 Nb 1/2 O 3-δ content from 0 to 1, which mainly stems from the Ni2+ doping-induced local lattice strain. Moreover, with an increase in BaNi 1/2 Nb 1/2 O 3-δ content, the band-gap of the KNBNNO films shows a non-linear variation, namely, a premier sharp decline for x from 0 to 0.3 and a remarkable elevating between 0.3 and 1.0. Additionally, with increasing x from 0 to 1, the magnetism transition behavior from diamagnetism to ferromagnetism for KNBNNO films may originate from ferromagnetic exchange interaction between the magnetic Ni2+ ions and a spin-polarized electron trapped at oxygen vacancy. These results are helpful in deeper understanding of structural transition, magnetic, and optical properties in perovskite oxides, which show that the materials can play potential roles in multiferroic applications and solar energy devices. In this paper, the structural phase transition, surface morphologies, ferromagnetic and optical properties have been observed in [K 1/2 Na 1/2 NbO 3 ] 1- x [BaNi 1/2 Nb 1/2 O 3-δ ] x (KNBNNO, 0 ​≤ ​ x ​≤ ​1) films. The KNBNNO films undergo a phase transition process with increasing BaNi 1/2 Nb 1/2 O 3-δ content from 0 to 1. The band-gap of the KNBNNO films shows a non-linear variation, namely, a premier sharp decline for x from 0 to 0.3 and a remarkable elevating between 0.3 and 1.0. Additionally, with increasing x from 0 to 1, the magnetism transition behavior from diamagnetism to ferromagnetism for KNBNNO films. [Display omitted] • KNBNNO films were deposited on the quartz substrates for the first time. • KNBNNO films undergo a phase transition process with increasing BNNO content. • KNBNNO films exhibit a magnetism conversion phenomena increasing BNNO content. • The optical band gap of KNBNNO films could be tuned by BNNO content. [ABSTRACT FROM AUTHOR]

• Comprehend the dual resonance mechanism of a train moving over a row of equal-span bridges. • Develop an active pitching resonator (APR) for resonance reduction of a moving train. • Propose an active vibration cancelation method to broaden the frequency bandgaps of wave attenuation in a train. • Present a closed-form dispersion relation of an APR-controlled train to reveal the key factors affecting the formation of dispersion bandgaps. • Examine the wave attenuation performance of using the optimal APR to reduce resonance of a moving train. The dynamic interaction of a moving train over a series of railway bridges with equal spans can result in a coupled vibration problem of wave transmission between two periodic structures. Dual resonance occurs when both systems vibrate in phase and the train travels at a resonant speed. The objectives of this paper are to (1) develop an active pitching resonator (APR) to attenuate resonance waves in a train; (2) study the dispersion relation for pitching motion control of periodically linked train cars; (3) investigate the key parameters that affect the dispersion band gaps of wave attenuation in a train; (4) present an active vibration cancellation method to enhance the control performance of the APR; and (5) demonstrate the effectiveness of using the optimal APRs to reduce resonance of a moving train. Through dispersion analysis, the optimum APR can not only shift the target frequency level away from resonance of a moving train, but also create a wide resonance band gap to reduce wave transmission in the train. Finally, the effectiveness of the optimum APR unit in reducing the resonance and attenuating the waves of a train travelling over multiple-span simple beams is demonstrated by dynamic finite element analysis of the train-bridge interaction. [ABSTRACT FROM AUTHOR]

Oxygen vacancy is an inherent defect of aquamarine crystals. The concentration and properties of this defect have an essential influence on aquamarine crystals and optical properties. This paper reports that blue in aquamarine crystals is due to the interaction between Fe2+ and oxygen vacancy. Infrared and Raman spectra showed that more Fe2+ replaced Al3+ in dark sample A than in light sample B. Oxygen vacancies were found in all samples. Dark sample A strongly absorbed the 830 nm band associated with Fe2+ in the UV–Vis–NIR absorption spectrum. The band gap of dark sample A was smaller than that of light sample B, and the difference in band gap was related to the concentration of oxygen vacancies. X-ray Photoelectron Spectroscopy showed that the oxygen vacancy concentration in sample A was higher than that in sample B, which showed that the oxygen vacancy concentration affected the color depth of aquamarines. [Display omitted] • Experimental tests address oxygen vacancies affect the color depth of aquamarine crystals. • More Fe2+ are found in dark sample to replace Al3+, resulting in more oxygen vacancies. • Oxygen vacancies have two functions: balancing electricity prices and introducing defect energy levels into the band gap, reducing bandwidth and improving light absorption performance. • The experimental results show more oxygen vacancies in darker aquamarine crystals. [ABSTRACT FROM AUTHOR]

Periodic structures feature frequency band gaps in which the propagation of certain waves will be attenuated. Therefore, they are widely applied in the vibration control of structures. The premise of this theory is that the structure should be perfectly periodic. However, this must be broken more or less due to inevitable deviations, leading structures to disorder. The vibration reduction performance can be significantly altered by the disorder, as reported by various authors. Moreover, the disorder pattern plays an important role in such a performance change. In this paper, we study the influence of the disorder patterns and explore a general permutation to retune the disordered periodic structures which means to reduce the deviation of the dynamic characteristics between the nominal and disordered structures. This research is conducted through three stages. In the first stage, a diatomic lumped-mass model is used. We study the implication of the disorder and propose a sorting strategy inspired by global sensitivity analysis (GSA). In the second stage, the sorting strategy is corroborated with numerical simulations by a finite element (FE) model of beam. We use the wave finite element method (WFEM) to calculate the band gaps. A thousand samples are generated randomly to test the sorting strategy and the contrarian strategy. In the third stage, the sorting strategy is verified by an experimental structure of beam. We set up an experimental system and scheme to measure and analyze the effects of the strategy for 5 groups of experiments. We show that vibration suppression may deteriorate statistically due to disorder for periodic structures. Specifically, vibration mitigation is most sensitive to the deviation in the first unit cell from the excitation. Inspired by this finding, a retuning strategy is proposed for the first time, i.e. the unit cell with the smallest deviation should be arranged in the position nearest to the excitation. The results in all stages show that the strategy can significantly improve the similarity of the dynamic characteristics between the nominal and disordered structures. [Display omitted] • Vibration suppression may deteriorate statistically due to disorder for periodic structures. • A retuning strategy is proposed for the first time and verified experimentally. • The unit cell with minimum deviation should be arranged near the excitation. • The influence of disorder is reduced by an order of magnitude after retuning. [ABSTRACT FROM AUTHOR]

• Stress-stiffening in local resonances of rotating acoustic metamaterials can be captured using a stress stiffening function. • Rotating acoustic metamaterials with beam-tip-mass resonators support band gaps that depend linearly on the rotational speed. • Resonator parameters can be chosen such that band gaps of the metamaterial self-adjust to the synchronous vibration frequency, resulting in attenuation over a wide range of frequencies and thus rotational speeds. The rotation of mechanical systems can greatly change their modal and wave propagation response. In the classic example of the Foucault pendulum, the Coriolis force from the Earth's rotation causes the pendulum path to appear deflected to an observer on Earth. More recently, Coriolis forces and gyroscopic effects from rotation have been shown to break time-reversal symmetry, induce non-reciprocity, and change the band structure of phononic crystals. However, rotation also introduces centrifugal forces that can considerably affect the vibration response through stress stiffening and spin softening effects. Although this is well studied in the field of rotor dynamics, the effects of centrifugal forces on the dynamic behavior of acoustic metamaterials (AMs) are still unexplored. In this paper, we study the dependence of torsional band gaps on rotational speed in a rotating shaft with attached local resonances. Different from previous studies, we explicitly consider the effects of stress stiffening in local resonances by introducing a stress stiffening function in a reduced order model of the rotating AM. We then calculate the stress stiffening function for beam-tip-mass resonators and show that these resonators have a resonant frequency that scales linearly with the rotational speed in the asymptotic limit, which in turn causes the band gaps of the AM to depend linearly on the rotational speed. Motivated by the presence of synchronous vibrations in rotating machinery, in which frequency is also linearly dependent on rotational speed, we show that this rotating AM supports band gaps that self-adjust to the synchronous vibration frequency, resulting in attenuation over a wide range of frequencies and thus rotational speeds. Finally, we validate the reduced order model of the rotating AM using 3D finite element analysis. This work contributes a foundational understanding of the effects of rotation in AMs and builds a connection between the AM and rotor dynamics communities, with the potential to introduce novel vibration control in rotor dynamics problems. [ABSTRACT FROM AUTHOR]

Abstract: This paper investigates the bandgap properties of two-dimensional phononic crystal slabs with cross-like holes by using the finite element method. The effects of the slab thickness and the geometry parameters of the holes on the bandgaps are discussed. No bandgap appears in the system with the square holes if the symmetry of the holes is the same as that of the lattice. However if the square holes are replaced with the cross-like holes, multiple wide bandgaps at lower frequencies are generated. The bandgaps are significantly dependent on the slab thickness and the geometry (including the size, shape and rotation) of the cross-like holes. The vibration modes at the bandgap edges are computed and analyzed to clarify the mechanism of the bandgap generation. It is found that the generation of the bandgap is due to the flexural vibration localized in the lumps or connectors. The appearances of the higher modes with the cut-off frequencies which decrease with the thickness increasing result in the decrease of the upper bandgap edge, and finally lead to vanishing of the bandgap. The study in this paper could be indispensable to practical applications of phononic crystal slabs such as bandgap tuning. [Copyright &y& Elsevier]

Abstract: In this paper, a quantum transport theory for describing photonic dissipative transport dynamics in nanophotonics is developed. The nanophotonic devices concerned in this paper consist of on-chip all-optical integrated circuits incorporating photonic bandgap waveguides and driven resonators embedded in nanostructured photonic crystals. The photonic transport through waveguides is entirely determined from the exact master equation of the driven resonators, which is obtained by explicitly eliminating all the degrees of freedom of the waveguides (treated as reservoirs). Back-reactions from the reservoirs are fully taken into account. The relation between the driven photonic dynamics and photocurrents is obtained explicitly. The non-Markovian memory structure and quantum decoherence dynamics in photonic transport can then be fully addressed. As an illustration, the theory is utilized to study the transport dynamics of a photonic transistor consisting of a nanocavity coupled to two waveguides in photonic crystals. The controllability of photonic transport through the external driven field is demonstrated. [Copyright &y& Elsevier]

In this paper, we present a detailed theoretical study of structural, electronic and optical properties of two-dimensional (2D) Al x B 1-x N monolayer compounds for 0 ≤ x ≤ 1. All possible arrangement of atoms have been determined for five concentration (x = 0, 0.25, 0.50, 0.75 and 1). Stabilities of all configurations are demonstrated by cohesive energies. In addition, we have investigated the composition dependence of the lattice constants a (x) and b (x), and band gaps Eg(x). The results show that the incorporation of aluminum (Al) atoms increases the lattice parameters in both zigzag and armchair direction. The cohesive energies and band gap values decreases with increasing (Al) composition. Cohesive energy and band gap bowing are more significant then bowing lattices. Monolayer of Al 0.50 B 0.50 N exhibits a direct band gap at Γ point with energy value of about 3.3 eV. Calculation of optical properties suggests potential characteristics for UV applications. • Possible arrangement of atoms in two-dimensional (2D) Al x B 1-x N monolayer compounds have been determined for five concentration (x = 0, 0.25, 0.50, 0.75 and 1). • Stabilities of all configurations are demonstrated by cohesive energies. • Band gap transition of Al x B 1-x N monolayer from indirect (0 ≤ x < 0.50) to direct (x = 0.50) and again to indirect (0.50 > x ≥ 1). • Calculated lattice bowing parameters are found to be small compared to the obtained cohesive and band gap bowings. • UV light-emitting diodes and detectors. [ABSTRACT FROM AUTHOR]

In this paper, we study electrical properties of AB-stacked bilayer graphene-DNA hybrid nanostructure connected to two semi-infinite monolayer graphene nanoribbon leads. We investigated two types of devices with both zigzag and armchair edges and the results are evaluated by replacing the junction position. Our calculations are based on the tight-binding approximation and the Green's function method in which the electrical transmission, the density of states (DOS) and the local density of states (LDOS) are calculated numerically. In the metallic bilayer graphene device via creating a nanopore and translocating the DNA molecule, the electron transmission reduces and an energy gap opens, so that, the metal-semiconductor phase transition occurs. Also, our results indicate that the model AC leads to a more considerable energy gap than model AB. Our results have important applications in DNA sensing. . • The electron transmission, electron density of states and local density of states of AB-stacked bilayer graphene-DNA hybrid nanostructure (zigzag and armchair edges) connected to two metallic monolayer graphene nanoribbon leads, have been calculated. • By creating translocating DNA molecule in bilayer graphene nanostructures, the electron transmission decreased and energy gap was opened. • We indicated that the model AC causes a more considerable energy gap than model AB. • Results have important application for DNA sensing. [ABSTRACT FROM AUTHOR]

Highlights • Geometric nonlinearity is used to form a negative-stiffness (NS) mechanism. • The stiffness of resonator can be reduced to any low values by NS mechanism. • A very low band gap of longitudinal wave can be created by HSLDS resonator. • A sufficient number of unit cells are needed to obtain good wave attenuations. Abstract In this paper, a local resonant (LR) rod with high-static-low-dynamic-stiffness (HSLDS) resonators is proposed to create a very low-frequency band gap for longitudinal wave propagation along the rod. The HSLDS resonator is devised by employing geometrical nonlinearity, and attached onto a periodic rod composed of rigid frames and rubbers to construct a LR rod. To reveal the band gaps, the LR rod is modeled as a lumped mass-spring chain. The effects of damping and nonlinearity of the HSLDS resonator on the dispersion relation is studied analytically by the Harmonic Balance method. The analytical results indicate that the damping mainly affects the width and depth of the band gap, while the nonlinearity can influence the central frequency and width of the band gap. In addition, both multi-body dynamic analyses and numerical simulations are conducted to predict longitudinal wave propagation along the LR rod, and thus to validate the very low-frequency band gap. The results show that the periodic rod with HSLDS resonators can create a very low-frequency band gap for longitudinal waves propagating along the rod. [ABSTRACT FROM AUTHOR]

Abstract In China, one of the major causes of energy performance gaps observed in green office buildings is the incompetent operations management, which is not distinguished from that of traditional buildings on both facilities and occupants. In this paper, a system dynamics model was established to simulate the interactions (primarily through communications) between facility managers and occupants and to find out targeted operations management strategies to narrow energy performance gaps. The model identifies different types of occupants and uses the Monte Carlo method to address the uncertainty between energy consumption and indoor environment quality satisfaction of occupants. Through a comparison of scenarios in which different types of occupants were each involved, differences in energy performance gaps were found and more-targeted operations management strategies were tailored. The model was applied to a specific case in China. The results indicate that facility managers could pay less attention to austerity occupants while paying more attention to communications with standard occupants to enhance their energy-saving awareness. The results also reveal that the wasteful occupants have the most potential for narrowing the gaps, which can be realized by combining communications and the heating, ventilation and air conditioning (HVAC) system equipment with zonal control. Highlights • The interaction between occupants and facility managers of green office buildings is simulated. • System dynamics modeling is used to assess the interactive effects on energy performance gaps. • Occupants are differentiated and scenarios are compared to find the differences in the gaps. • A differentiated communication strategy for the austerity and standard occupants is tailored. • A targeted management portfolio for the wasteful occupants is drawn. [ABSTRACT FROM AUTHOR]

Abstract This paper aims to optimize the synthesis of in-situ CBD CdS thin films deposited on flexible substrates. The deposition temperature is a sensitive parameter which strongly affects the optical and structural properties and needs to be as low as possible to be compatible with flexible substrates technology. We show that it is possible to allow good quality of thin CdS films on plastic foil and polymer (PE-LD) substrates. Experimental analyses based on X-Ray diffraction confirm the pure cubic structure with (111) as unique preferential orientation. However, the crystallinity of the films depends strongly on the deposition temperature in the range 45–95 °C and it has been found that 65 °C is the optimal deposition temperature. SEM micrographs show homogeneous, compact and smooth surface with remarkable average grain sizes varying from 22 to 32 nm depending on the bath temperature. The optical analyses based on the UV–Visible measurements, performed on the films deposited on flexible substrates, reveal the highest transmittance (∼90%) at the optimized bath temperature of 65 °C, with band gap energy around 2.42 eV. These results demonstrate that the CBD in-situ growth on flexible substrates (polymer and plastic type), at the optimized temperature, improves the physical properties of the films and paves the way to integrate this process in the embedded application systems. Graphical abstract Image 10131285 Highlights • High crystalline CdS films growth performed at an optimal low temperature. • CdS layer deposition on different flexible substrates. • Detailed optical, structural and morphological characterizations. [ABSTRACT FROM AUTHOR]

Abstract In this paper, optical properties of silicene and germanene under compressive homogeneous strain are investigated within the density function theory. Results show that the optical-field response are strongly depend on the amount of applied strain. As the strain increases, the amount of optical absorption increases. In fact, by applying the compressive strain in the silicene and germanene, the band gap at the Dirac points decreases where ultimately reaches zero. Depending on the amount of strain, absorption peak shows red and blue shifts by increasing the strain. This can be realized by considering the change of the band gap energy and transition rates by the strain. In both of these graphene-like structures, the light absorption along zigzag direction is greater than that of the armchair direction. Highlights • Strain induced red and blue shifts of the silicene and gemanene photon absorption. • DFT based optical calculations in strained graphene-like materials. • Realization of the different absorption frequency ranges based on their response to strain. [ABSTRACT FROM AUTHOR]

Abstract In this paper, four types of compounds are considered: ideal wurtzite (B N), N vacancies in B N (B N − V N), A l doped ideal B N (A l : B N) and A l doped B N with N vacancies(A l : B N − V N). The structural, electronic and magnetic properties are calculated by using the density functional theory (DFT) based on the generalized gradient approximation implemented in Quantum-Espresso code. Our results show that the nitrogen vacancies and the aliminium impurities are responsible of the magnetic properties in these compounds. We have also found that aluminium impurities have a remarkable effect on the optical band gap. Our results are in good agreement with experimental and other theoretical studies. We can conclude from this study, that this material can be used as diluted magnetic semiconductors. Highlights • The DFT method has been used to study the Al doped (w−BN). • The lattice parameters increase with the incorporation of Al in the BN supercell. • The Al impurities decrease the value of the band gap. • Al and N vacancy induce magnetic properties. [ABSTRACT FROM AUTHOR]

Abstract Three-dimensional time-harmonic wave motion in a layered functionally graded (FG) piezoelectric periodic composite (phononic crystal) composed of a finite or an infinite number of unit-cells is considered. A longitudinal or transverse plane waves incident obliquely to the interfaces of a finite phononic crystal between two half-spaces is studied. The paper proposes a semi-analytical method to simulate and analyse the wave fields in a phononic crystal in the case of arbitrary angles of incidence. It is shown that the method is numerically stable for an arbitrary number of unit-cells in finite phononic crystals. Several kinds of pass-bands and band-gaps can be distinguished by employing the derived semi-analytical expressions: band-gaps, pass-bands, low transmission pass-bands, quasi-longitudinal and quasi-transverse band-gaps. Using the present approach a detailed parametric analysis of the influences of the type and incidence angle of an incident wave, and the material and geometrical parameters of the FG interlayers on wave propagation is conducted. [ABSTRACT FROM AUTHOR]

Abstract The combined characteristics of periodic and locally resonant features in metamaterial structures, or meta-structures, give rise to unique wave propagation characteristics such as relatively low and wide band gaps. These meta-structures have a fixed geometry and thus a fixed behavior, however applications that require structural vibration mitigation such as spacecraft and automotive components have variable vibration mitigation requirements over a range of operation and external conditions. In this paper, we propose a method to thermally tune the band gaps of composite meta-structures, which combine a periodic lattice and locally-resonant inclusions, through changes in temperature of the structure. The concept primarily takes advantage of the different moduli of the two materials in the meta-structure that have drastically different temperature dependences, to preferentially tune the modulus of the lattice material compared to the resonant inclusion. We introduce an additional concept, termed thermal partitioning, to partially or fully open and close band gaps by locally controlling the temperature within the meta-structure. We demonstrate these results numerically with finite element simulations. [ABSTRACT FROM AUTHOR]

Abstract In this paper, we consider elastic wave propagation in two dimensional periodic lattices that include an alternating pattern of linear springs and nonlinear bistable springs. Because of the bistable springs, these lattices have multiple stable equilibrium configurations. An analytical model that takes into account both nonlinear geometrical effects and nonlinearity of the springs is developed for the total potential energy of the system. After finding the stable equilibrium configurations of the unit cell by minimizing its potential energy, the propagation of waves of small amplitude is analyzed in each of these stable configurations using Bloch theorem. Examination of the band diagrams demonstrates that, depending on the model parameters, directional or complete band gaps can be observed in some of the deformed configurations, particularly for deformed configurations that are close to a critical point. Furthermore, analysis of the iso-frequency contours of the dispersion surfaces and of polar plots of the phase and group velocities indicates that the low frequency wave directionality of the lattice is tunable. For some designs, switching from one configuration to another configuration makes it possible to dramatically alter the preferred direction of wave propagation. Simulations of the response of lattices of finite size confirm that these lattices can be used as reconfigurable phononic crystals with tunable directivity, both in the low frequency range and within the directional band gaps. [ABSTRACT FROM AUTHOR]

• Metamaterials, origami structures, and their applications to vibration control are discussed. • Metamaterials with abnormal features are reviewed based on the unusual values of elastic constants. • Auxetic, band gap and pentamode metamaterials are reviewed for vibration and sound control. • Origami structures are discussed on their capacities for vibration control. • Future research directions are given for this emerging interdisciplinary research field. Vibration and sound control is critical to many practical engineering systems in order to minimise the detrimental effects caused by unavoidable vibrations and noises. Metamaterials and origami-based structures, which have attracted increasing interests in interdisciplinary research fields, possess many peculiar physical properties, including negative Poisson's ratios, bi- or multi-stable states, nonlinear and tuneable stiffness features, and thus offer promising applications for vibration and sound control. This paper presents a review of metamaterials and origami-based structures as well as their applications to vibration and sound control. Metamaterials are artificially engineered materials having extremal properties which are not found in conventional materials. Metamaterials with abnormal features are firstly discussed on the basis of the unusual values of their elastic constants. Recent advances of auxetic, band gap and pentamode metamaterials are reviewed together with their applications to vibration and sound mitigations. Origami, as the ancient Japanese art of paper folding, has emerged as a new design paradigm for different applications. Origami-based structures can be adopted for vibration isolation by using their multi-stable states and desirable stiffness characteristics. Different origami patterns are reviewed to show their configurations and base structures. Special features, such as bi- or multi-stable states, dynamic Poisson's ratios, and nonlinear force–displacement relationships are discussed for their applications for vibration control. Finally, possible future research directions are elaborated for this emerging and promising interdisciplinary research field. [ABSTRACT FROM AUTHOR]

• The chiral buckling unit cell has two stable states. • The axial stiffness of the unit cell in two states has an order-of-magnitude difference. • Low band gap frequency and wide band gap can be obtained by changing the states of the outer and inner stiffness structures. • The metamaterial can be used for low-frequency vibration isolation and has the potential for energy absorption, tensile-torsion material and dynamic logic gates. • The hybrid supercells can further broaden the band gap width, lower the band gap frequency, and have up to 16 different dynamic responses. This paper proposes a tunable local resonance metamaterial with chiral buckling structures for low-frequency vibration isolation. The unit cell consists of the inner and outer buckling stiffness structure, basic structure, and local resonator. The bistability of three kinds of unit cells with different initial shapes of beams is investigated and compared via the elliptic integral method and finite element analysis. Then, their axial stiffness in different states is studied. The dynamic responses of the metamaterial with simple unit cells and hybrid supercells are theoretically derived and analyzed by Bloch's theorem and transfer coefficient method. Theoretical, numerical, and experimental results demonstrate that the unit cell with initially convex downward beams has strong bistability and determinate deformation modes. The axial stiffness of the unit cell in two stable states differs by an order of magnitude. Changing some specific parameters broadens the gap in the axial stiffness between the two stable states. The axial negative stiffness characteristics and rotation effect of the unit cell have the potential for energy dissipation and tensile-torsion material. The metamaterial with simple unit cells has tunable and wide band gap and low-frequency vibration isolation via the stable states switching of the inner and outer buckling stiffness structures. The metamaterial with hybrid supercells can further broaden the band gap width and lower the band gap frequency, which has up to 16 different band gap characteristics. [Display omitted] [ABSTRACT FROM AUTHOR]

Abstract In this paper, a band-pass filter based on photonic crystals is designed by using the principle of frequency domain superposition. The influence of the heterostructure position, period numbers and incidence angles on transmission spectrums are analyzed. The filter can achieve efficient filtering in 240–280 nm solar-blind ultraviolet band, with an average transmittance of 72.2%. Simultaneously, a good band-stop appears in near ultraviolet and visible region (300–700 nm) and its average transmittance is below 3.4%. It provides a choice in the application of solar-blind ultraviolet detection technology. Highlights • A solar-blind ultraviolet filter based on frequency domain superposition is devised. • The filter achieves efficient filtering (72.2%) in SBUV band. • There is a wide band gap in 300–700 nm and the average transmittance is below 3.4%. • It has some significance for the development of ultraviolet filter. [ABSTRACT FROM AUTHOR]

Metal dopants play an important role in the resistive switching mechanism of HfO 2 -based resistive random access memory (RRAM), which can improve the performance of the RRAM device. Although Cu and Gd ions as metal dopants were widely explored, Au dopant is little focused so far. So the effects of Au doping in defect-free m -HfO 2 using the first-principles calculation were investigated in this paper, with the purpose of revealing the contribution of dopants in the forming process of conducting filaments (CFs). Based on the first principle, the statistical models are firstly built to simulate the system of the Au-doped m -HfO 2 with and without an oxygen vacancy (Vo). Then the electronic properties, the charge transfer of atoms, and the interaction between Au dopants and Vos are calculated and analyzed. The results show that the formation energy of the Au-dopant at the interstitial site is 5.673eV less than that of the Au-dopant at the substitutional site, which means the interstitial site is found to be the more stable position. Moreover, the interstitial Au dopant induces gap states of Hf and O atoms into the band gap of m -HfO 2 . As a result, the conductivity of the Au-HfO 2 and the Au-HfO 2 -Vo systems is enhanced substantially. The results of the DOS, the band structure and the partial charge density show that the intermediate energy level crosses over the Fermi level and the electrons could connect the Au-dopant with nearby Hf atoms. According to these results, it is found that the Au CFs can be generated in the process of doping. In addition, the Vos at different positions near the Au-dopant have diverse formation energies, which highly indicate that these Vos are involved in the forming of the CFs. It may be concluded that the Vos CFs and the Au-dopants can be formed and play a role in the process of the resistive switching. [ABSTRACT FROM AUTHOR]

In this paper, highly uniform and band gap tunable CH 3 NH 3 PbI 3-x Br x perovskite film was successfully prepared by a polymer blends (Polyvinyl Pyrrolidone/polyethylene glycol) modified sequential deposition method in ambient atmosphere. Moreover, the influences of the Br content on the surface morphology, structure, optical absorption and luminescence properties of CH 3 NH 3 PbI 3-x Br x films and the photovoltaic performance of the corresponding perovskite solar cells based on ZnO-TiO 2 nanorod arrays were investigated. The results revealed that introducing bromine ion can decrease the convert rate from PbI 2 to CH 3 NH 3 PbI 3 . Furthermore, bromine doping can expand the bang gap of the CH 3 NH 3 PbI 3 , which is benefit to the improvement of open-circuit voltage. The CH 3 NH 3 PbI 3-x Br x perovskite solar cell shows the best device performance with an open-circuit voltage ( Voc ) of 0.87 V, a short-circuit current density ( Jsc ) of 17.41 mA/cm 2 , fill factor ( FF ) of 0.6 and power conversion efficiency of 9.12% when the molar ratio of PbBr 2 /PbI 2  = 15/85. [ABSTRACT FROM AUTHOR]

A periodic vibration suppressor with multiple secondary oscillators is examined in this paper to reduce the low-frequency vibration. The band-gap properties of infinite periodic structure and vibration transmission properties of finite periodic structure attached with secondary oscillators with arbitrary degree of freedom are thoroughly analyzed by the plane-wave-expansion method. A simply supported plate with a periodic rectangular array of vibration suppressors is considered. The dynamic model of this periodic structure is established and the equation of harmonic vibration response is theoretically derived and numerically examined. Compared with the simply supported plate without attached suppressors, the proposed plate can obtain better vibration control, and the vibration response can be effectively reduced in several frequency bands owing to the multiple band-gap property. By analyzing the modal properties of the periodic vibration suppressors, the relationship between modal frequencies and the parameters of spring stiffness and mass is established. With the numerical results, the design guidance of the locally resonant structure with multiple secondary oscillators is proposed to provide practical guidance for application. Finally, a practical periodic specimen is designed and fabricated, and then an experiment is carried out to validate the effectiveness of periodic suppressors in the reality. The results show that the experimental band gaps have a good coincidence with those in the theoretical model, and the low-frequency vibration of the plate with periodic suppressors can be effectively reduced in the tuned band gaps. Both the theoretical results and experimental results prove that the design method is effective and the structure with periodic suppressors has a promising application in engineering. [ABSTRACT FROM AUTHOR]

Graphene nanoribbon (GNR), a new 2D carbon nanomaterial, has some unique features and special properties that offer a great potential for interconnect, nanoelectronic devices, optoelectronics, and nanophotonics. This paper reports the structural analysis, electronic properties, and band gaps of a GNR considering different chirality combinations obtained using the p z orbital tight binding model. In structural analysis, the analytical expressions for GNRs have been developed and verified using the simulation for the first time. It has been found that the total number of unit cells and carbon atoms within an overall unit cell and molecular structure of a GNR have been changed with the change in their chirality values which are similar to the values calculated using the developed analytical expressions thus validating both the simulation as well as analytical results. Further, the electronic band structures at different chirality values have been shown for the identification of metallic and semiconductor properties of a GNR. It has been concluded that all zigzag edge GNRs are metallic with very small band gaps range whereas all armchair GNRs show both the metallic and semiconductor nature with very small and high band gaps range. Again, the total number of subbands in each electronic band structure is equal to the total number of carbon atoms present in overall unit cell of the corresponding GNR. The semiconductors GNRs can be used as a channel material in field effect transistor suitable for advanced CMOS technology whereas the metallic GNRs could be used for interconnect. [ABSTRACT FROM AUTHOR]

Properties of shear waves in a piezoelectric stratified periodic structure with a defect layer are studied for a superlattice with identical piezoelectric materials in a unit cell. Due to the electro-mechanical coupling in piezoelectric materials the structure exhibits defect modes in the superlattice with full transmission peaks both for full contact and electrically shorted interfaces. The results show an existence of one or two transmission peaks depending on the interfacial conditions. In the long wavelength region where coupling between electro-magnetic and elastic waves creates frequency band gaps the defect layer introduces one or two defect modes transmitting both electro-magnetic and elastic energies. Other parameters affecting the defect modes are the thickness of the defect layer, differences in refractive indexes and the magnitude of the angle of the incident wave. The results of the paper may be useful in the design of narrow band filters or multi-channel piezoelectric filters. [ABSTRACT FROM AUTHOR]

In this paper, the CH 3 NH 3 PbI 3−x Br x films with various Br-doping contents were successfully prepared by solution processed deposition and followed by annealing process. This method simultaneously modified the morphology and composition of the CH 3 NH 3 PbI 3 film. The effects of annealing treatment of CH 3 NH 3 PbI 3−x Br x films under N 2 and DMSO conditions on the microstructure of films and photoelectric properties of the solar cells were systematically investigated. The relationship of the component ratio of R Br/I = CH 3 NH 3 PbI 3−x Br x /CH 3 NH 3 PbI 3 in the resulting perovskite versus CH 3 NH 3 Br concentration also was explored. The results revealed that the CH 3 NH 3 PbI 3−x Br x films annealed under DMSO exhibited increased grain sizes, enhanced crystallinity, enlarged bandgap and reduced defect density compared with that of the N 2 annealing. It also was found that the R Br/I linearly increased in the resulting perovskite with the increased of CH 3 NH 3 Br concentration in the methylammonium halide mixture solutions. Furthermore, the photovoltaic performances of devices fabricated using DMSO precursor solvent were worse than that of DMF under N 2 annealing atmosphere. When CH 3 NH 3 Br concentration was 7.5 mg ml −1 , the planar perovskite solar cell based on CH 3 NH 3 PbI 3−x Br x annealed under DMSO showed the best efficiency of 13.7%. [ABSTRACT FROM AUTHOR]

This paper deals with the reflection and transmission of SH waves at a very rough interface separating two dissimilar isotropic elastic solids. The interface oscillates between two straight lines. By means of homogenization, the domain containing the very rough interface is replaced by an effective material layer whose elastic constants depend on the thickness variable. The reflection and transmission of SH waves at the very rough interface is then reduced to the ones at a FGM layer. The exact analytical formulas for the reflection and transmission coefficients have been derived. Based on them, the dependence of the reflection and transmission coefficients on the incident angle, the wave frequency, the material constants and the geometry of the rough interface are examined. Remarkably, it has been shown that a very rough interface of comb-type with the comb-tooth width varying periodically can produce band-gaps to SH waves. With this fact, many potential applications can be expected coming from very rough interfaces of comb-type with periodic comb-tooth width. It is also shown that the width and the location of band-gaps depend strongly on the contrast of rigidities of two half-spaces, the amplitude of the variation of the comb-tooth width, the incident angle of SH waves and the number of periods of comb-tooth. [ABSTRACT FROM AUTHOR]

The realization of unidirectional acoustic transmission (UAT) has recently aroused great attention owing to the versatile possibility in acoustics-based applications. This paper extends the bi-directional evolutionary structural optimization (BESO) method to the design of phononic crystal (PC) for achieving UAT. The optimization objective is to enlarge the minimum imaginary part of wave vectors along Γ-X while keep that along Γ-M less than the constraint value. We systematically studied the design of symmetric and asymmetric PCs at various frequencies. Numerical examples demonstrate that the proposed optimization algorithm is effective for creating the partial band gap at the specified frequency. The UAT with high rectifying efficiency is then successfully realized by placing the optimized PC in a bend wave guide. The results also show that the asymmetric PCs are more favorable for the design of broadband UAT devices compared with symmetric ones. [ABSTRACT FROM AUTHOR]

The objective of this paper is to use transfer functions to comprehend the formation of band gaps in locally resonant acoustic metamaterials. Identifying a recursive approach for any number of serially arranged locally resonant mass in mass cells, a closed form expression for the transfer function is derived. Analysis of the end-to-end transfer function helps identify the fundamental mechanism for the band gap formation in a finite metamaterial. This mechanism includes (a) repeated complex conjugate zeros located at the natural frequency of the individual local resonators, (b) the presence of two poles which flank the band gap, and (c) the absence of poles in the band-gap. Analysis of the finite cell dynamics are compared to the Bloch-wave analysis of infinitely long metamaterials to confirm the theoretical limits of the band gap estimated by the transfer function modeling. The analysis also explains how the band gap evolves as the number of cells in the metamaterial chain increases and highlights how the response varies depending on the chosen sensing location along the length of the metamaterial. The proposed transfer function approach to compute and evaluate band gaps in locally resonant structures provides a framework for the exploitation of control techniques to modify and tune band gaps in finite metamaterial realizations. [ABSTRACT FROM AUTHOR]

Earth-abundant Cu 2 ZnSn(S,Se) 4 (CZTSSe) thin film photovoltaic absorber layers were fabricated by co-evaporated Cu, ZnS, SnS and Se sources in a vacuum chamber followed by annealing at tubular furnace for 30 min at 550 °C. In this paper, we investigated the metal elements with stoichiometric ratio film to study the effect of annealing conditions of Se, SnS + Se, S and SnS + S atmosphere on the structure, surface morphological, optical and electrical properties of Cu 2 ZnSn(S,Se) 4 thin films respectively. These films were characterized by Inductively Coupled Plasma-Mass Spectrometer, scanning electron microscopy, X-ray diffraction to investigate the composition, morphological and crystal structural properties. The grain size of samples were found to increase after annealing. XRD patterns confirmed the formation of pure polycrystalline CZTSSe thin films at S atmosphere, the optical band gaps are 1.02, 1.05, 1.23, 1.35 eV for Se, SnS + Se, SnS + S and S atmosphere respectively. [ABSTRACT FROM AUTHOR]

This paper reports on a theoretical model of one-dimensional (1D) periodic graded metacomposites for investigating and enlarging the bandgaps in which wave propagation is not allowed. The unit-cell of the acoustic metamaterial consists of external mass, spring and internal mass. Different from the conventional infinite mass-in-mass lattice structure, the periodic metacomposite has graded internal masses in each period. Referring to lumped-mass method and on the basis of Bloch theorem, the general formula for calculating the dispersion curve of the 1D periodic graded metacomposites is derived. Furthermore, the effects of the unit-cell's parameters including the mass and the spring constants are also investigated. Numerical results show that the number of the bandgaps is closely related to the number of the unit-cells in each period. The width and the location of the bandgaps are determined by the arrangement and the values of the mass and spring constants. [ABSTRACT FROM AUTHOR]

This paper models the scattering limited electron transport in a nano-dimensional In 0 . 52 Al 0.48 As/In 0.53 Ga 0.47 As/InP heterostructure. An analytical model for temperature dependent sheet carrier concentration and carrier mobility in a two dimensional electron gas, confined in a triangular potential well has been developed. The model accounts for all the major scattering process including ionized impurity scattering and lattice scattering. Quantum mechanical variational technique is employed for studying the intrasubband scattering mechanism in the two dimensional electron gas. Results of various scattering limited structural parameters such as energy band-gap and functional parameters such as sheet carrier concentration, scattering rate and mobility are presented. The model corroborates the dominance of ionized impurity scattering mechanism at low temperatures and that of lattice scattering at high temperatures, both in turn limiting the carrier mobility. Net mobility obtained taking various scattering mechanisms into account has been found in agreement with earlier reported results, thus validating the model. [ABSTRACT FROM AUTHOR]