Because there is no literature on the effect of thermal loadings on guided wave propagation in FG plates, the present paper is to fill the gap. In the present paper, the wave propagation analysis of ...porous FG plates with clamped ends in thermal environments based on first order shear deformation theory are presented. The plates are exposed to various types of thermal loading including uniform and non-uniform temperature changes, the material properties of FG plates are temperature- and porosity-dependent. Using the Galerkin method, we obtain the dispersion relation of thermoelastic waves in porous functionally graded plates. Compared with the previous results, the correctness of the present work is verified. In the end, the effects of the temperature changes, porosity as well as power law index on the phase velocity and group velocity of the guided wave are investigated.
Celotno besedilo
Dostopno za:
BFBNIB, DOBA, GIS, IJS, IZUM, KILJ, KISLJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
In this paper, attention is paid to the prediction of vibration characteristics of two-dimensional functionally graded (2D-FG) tubes based on higher order theory. The tubes are formed of two ...different materials, and the material properties of the nano-scaled tubes vary both in the length and radial direction. To incorporate the size effect, the nonlocal strain gradient theory is employed. The thermal force is considered to be uniform temperature across the radial of the nonlocal tube, on the basis of the Hamilton's principle, the size-dependent governing equations are derived. After solving these equations using the generalized differential quadrature method (GDQM), the impact of the nonlocal parameter, strain gradient parameter, temperature variations, material variation on the vibration characteristic of the tubes with various boundary conditions are discussed in details.
•Postbuckling characteristics of geometrically imperfect FG-GPLRC microtubes are investigated.•A size-dependent nonlinear tube model with consideration of the initial geometrical imperfection is ...developed.•Analytical solutions for postbuckling responses of FG-GPLRC microtubes under different boundary conditions are derived.•Microstructure effect and initial geometrical imperfection on the postbuckling behaviors are examined.•The ideal distribution pattern, weight fraction, aspect ratio and width-to-thickness ratio of GPLs reinforcements are explored.
Graphene reinforced composites have attracted a great deal of attention in recent years due to their outstanding mechanical properties. The present work focuses on the size-dependent postbuckling characteristics of functionally graded (FG) graphene platelets reinforced composite (GPLRC) multilayer microtubes containing initial geometrical imperfection. It is assumed that the distribution of GPL reinforcements in microtubes is uniform or layer-wise change across the radial direction, and five typical distribution patterns (i.e., UD, FG-X, FG-O, FG-V and FG-A) are considered. Based on the modified couple stress theory and a refined higher-order beam theory, the non-classical governing equations with the account of von Kármán geometrical non‐linearity for postbuckling analysis are derived by employing the principle of minimum potential energy and solved by using an analytical method. After validating the analytical solutions by comparing with results reported in the literature, the influences of various important parameters on the postbuckling of FG-GPLRC multilayer microtubes are investigated. It is found that the microstructure effect on the postbuckling behavior is significant when the outer radius of the microtube is comparable to the material length scale parameter. Moreover, the initial geometrical imperfection decreases the postbuckling load-carrying capacity at small deflection, but increases it at large deflection. Additionally, our results indicate that the FG-V distribution pattern produces the highest postbuckling load-carrying capacity for FG-GPLRC multilayer tubes, which differs from the cases for FG-GPLRC multilayer beams, plates and thin shells where the FG-X distribution pattern always has the best reinforcing effect. The present work could provide theoretical guidelines for the optimal design and safety assessment of graphene reinforced composite tubular structures, and may find potential application in microscale engineering devices and systems.
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Abstract
Photocatalytic reduction of CO
2
is a promising approach to achieve solar-to-chemical energy conversion. However, traditional catalysts usually suffer from low efficiency, poor stability, ...and selectivity. Here we demonstrate that a large porous and stable metal-organic framework featuring dinuclear Eu(III)
2
clusters as connecting nodes and Ru(phen)
3
-derived ligands as linkers is constructed to catalyze visible-light-driven CO
2
reduction. Photo-excitation of the metalloligands initiates electron injection into the nodes to generate dinuclear {Eu(II)}
2
active sites, which can selectively reduce CO
2
to formate in a two-electron process with a remarkable rate of 321.9 μmol h
−1
mmol
MOF
−1
. The electron transfer from Ru metalloligands to Eu(III)
2
catalytic centers are studied via transient absorption and theoretical calculations, shedding light on the photocatalytic mechanism. This work highlights opportunities in photo-generation of highly active lanthanide clusters stabilized in MOFs, which not only enables efficient photocatalysis but also facilitates mechanistic investigation of photo-driven charge separation processes.
In traditional analysis, several studies have discussed the vibration behavior of electric machines from the point of view of radial force. With the increasingly strict vibroacoustic index, the ...tangential force effects on the vibration are analyzed and investigated, and it shows the contribution of tangential force on electromagnetic vibration cannot be ignored. However, these studies are based mainly on finite element multi-physics models, and experiments are not conducted. Furthermore, the mechanism of tangential force is not clearly explained. In this paper, a special motor stator structure is proposed to explore the effect of tangential force on vibration. First, the analytical calculation of the tangential force and the tangential effect on motor vibration are described. Next, the Theorem of Translation of A Force is introduced to convert the effective tangential tooth force to a radial force couple acting on the stator yoke. Then, a novel motor stator is proposed to investigate the vibration characteristics caused only by tangential force, and the simulation is analyzed. Finally, a vibration test of the prototype is conducted and the result shows the tangential force can induce the radial vibration with corresponding order.
Aspect-based sentiment analysis is a fine-grained sentiment analysis task, which needs to detection the sentiment polarity towards a given aspect. Recently, graph neural models over the dependency ...tree are widely applied for aspect-based sentiment analysis. Most existing works, however, they generally focus on learning the dependency information from contextual words to aspect words based on the dependency tree of the sentence, which lacks the exploitation of contextual affective knowledge with regard to the specific aspect. In this paper, we propose a graph convolutional network based on SenticNet to leverage the affective dependencies of the sentence according to the specific aspect, called Sentic GCN. To be specific, we explore a novel solution to construct the graph neural networks via integrating the affective knowledge from SenticNet to enhance the dependency graphs of sentences. Based on it, both the dependencies of contextual words and aspect words and the affective information between opinion words and the aspect are considered by the novel affective enhanced graph model. Experimental results on multiple public benchmark datasets illustrate that our proposed model can beat state-of-the-art methods.
Channel estimation for downlink millimeter wave (mmWave) multiuser multiple-input-multiple-output (MU-MIMO) communications over a time-varying channel is demandingly challenging. This is due to a ...massive number of channel coefficients to be estimated and the severe propagation loss of mmWave transmissions. To tackle this problem, this paper proposes an effective channel estimation scheme for time-varying mmWave channels. Discovering the property that the variations of angles of arrival/departure (AoAs/AoDs) are much slower than that of path gains, we propose a novel transmission frame structure, where the channel estimation is decoupled into two separated stages including AoAs/AoDs estimation followed by path gains estimation. In the first stage, the sparse nature of mmWave channels is leveraged to formulate the AoAs/AoDs estimation into a block-sparse signal recovery problem, and we develop an adaptive angle estimation algorithm to estimate the AoAs/AoDs. In the second stage, the pilot beamforming based on the estimated AoAs/AoDs is designed aiming for maximizing the desired pilot power so that the path gains can be accurately estimated. Simulation results demonstrate that the proposed scheme can effectively estimate the time-varying mmWave channels with a small number of pilots.
In this paper, the forced resonance vibration analysis of curved micro-size beams made of graphene nanoplatelets (GNPs) reinforced polymer composites is presented. The approximating of the effective ...material properties is on the basis of Halpin–Tsai model and a modified rule of mixture. The Timoshenko beam theory is applied to describe the displacement field for the microbeam. To incorporate small-size effects, the modified strain gradient theory, possessing three independent length scale coefficients, is employed. Hamilton principle is applied to formulate the size-dependent governing motion equations, which then is solved by Navier solution method. Ultimately, the influences of length scale coefficients, opening angle, weight fraction and the total number of layers in GNPs on composite curved microbeams corresponding to different GNPs distribution are discussed in detail through parametric studies. It is shown that, the resonance position is significantly affected by changing these parameters.
•The resonances of curved microbeams reinforced with GNPs are studied.•The modified strain gradient theory is used to build the size-dependent model.•The Navier-type solution procedure is utilized to solve the whole problems.•Three different types of GPNs distributions are considered.
Three Cu(I) coordination networks, namely, {Cu2(bpz)2(CN)X·CH3CN} n , (X = Cl, 1; I, 3), {Cu6(bpz)6(CH3CN)3(CN)3Br·2OH·14CH3CN} n , (2, bpz = 3,3′,5,5′-tetramethyl-4,4′-bipyrazole), were ...prepared by using solvothermal method. The cyanide ligands in these networks were generated in situ by cleavage of C–C bond of MeCN under solvothermal condition. The structures of these networks are dependent on halogen anions. Complex 1 is a ladderlike structure with μ2-CN– as rung and μ2-bpz as armrest. The Cl– in 1 is at terminal position but does not extend the one-dimensional (1D) ladder to higher dimensionalities. Complex 2 is a three-dimensional (3D) framework comprised of novel planar Cu3Br triangle and single Cu nodes, which are extended by μ2-bpz and μ2-CN– to form a novel (3,9)-connected gfy network. Density functional theory calculations showed that single-electron delocalization of Br atom induces the plane structure of Cu3Br. Complex 3 also possesses a similar ladderlike subunit as in 1, but the I– acts as bidentate bridge to extend the ladder to 3D framework with a four-connected sra topology. The three networks show notable catalytic activity on the click reaction. The compared catalytic results demonstrate that complex 2 possesses the best catalysis performance among three complexes, which is ascribed to the largest solvent-accessible void (porosity: 2 (29.4%) > 1 (25.7%) > 3 (17.6%)) and the more Cu(I) active sites in 2. The present combined structure–property studies provide not only a new synthetic route to obtain a new kind of catalyst for click reaction but also the new insights on catalyst structure–function relationships.
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