Size-dependent Electroelastic Properties of Piezoelectric Nanoplates

With the development of nanotechnology, piezoelectric nanostructures have attracted a surge of interests in research communities for the potential applications as transistors, sensors, actuators, resonators and energy harvesters in nanoelectromechanical systems (NEMS) due to their high electromechanical coupling and unique features at the nano-scale. Piezoelectric nanomaterials have been characterized to possess size-dependent electromechanical coupling properties from both experimental and theoretical perspectives. Therefore it is of great importance to investigate the physical mechanisms of these distinct nano-scale structure features in order to fulfill the design and application of those piezoelectricity-based nanodevices. Due to large surface to volume ratio and manifest strain gradients typically present in nanostructures, surface effects and flexoelectricity are commonly believed to be responsible for the size-dependent electromechanical properties of piezoelectric nanomaterials. This thesis aims to develop modified continuum mechanics models with the consideration of the surface effects and the flexoelectricity to theoretically investigate such size effects. Based on the classical Kirchhoff plate model and the extended linear piezoelectricity theory, the influence of flexoelectricity on the static bending and the transverse vibration of a piezoelectric nanoplate (PNP) is firstly examined. Then the surface effects including the residual surface stress, the surface elasticity and the surface piezoelectricity are further incorporated to develop a more comprehensive modified Kirchhoff plate model in addition to the flexoelectricity. Variational principle is adopted to derive the governing equations and the corresponding boundary conditions for a clamped PNP. Ritz approximate solutions for the static bending and the free vibration of the PNP indicate that the influence of the flexoelectricity and the surface effects is more prominent for thinner plates with smaller thickness. The simulation results also demonstrate that such size effects on the electromechanical coupling behaviors of the PNP are sensitive to the surface material properties, the applied electrical load and the plate dimensions. Moreover, it also suggests that the possible frequency tuning of PNP-based resonators through the applied electric voltage could be modified by either the flexoelectricity or the surface effects. The current work is claimed to provide increased understanding on the fundamental physics of the size-dependent electromechanical coupling properties of piezoelectric nanostructures and thus benefit the design and applications of PNP-based nanodevices

Intrinsic energy conversion mechanism via telescopic extension and retraction of concentric carbon nanotubes

The conversion of other forms of energy into mechanical work through the geometrical extension and retraction of nanomaterials has a wide variety of potential applications, including for mimicking biomotors. Here, using molecular dynamic simulations, we demonstrate that there exists an intrinsic energy conversion mechanism between thermal energy and mechanical work in the telescopic motions of double-walled carbon nanotubes (DWCNTs). A DWCNT can inherently convert heat into mechanical work in its telescopic extension process, while convert mechanical energy into heat in its telescopic retraction process. These two processes are thermodynamically reversible. The underlying mechanism for this reversibility is that the entropy changes with the telescopic overlapping length of concentric individual tubes. We find also that the entropy effect enlarges with the decreasing intertube space of DWCNTs. As a result, the spontaneously telescopic motion of a condensed DWCNT can be switched to extrusion by rising the system temperature above a critical value. These findings are important for fundamentally understanding the mechanical behavior of concentric nanotubes, and may have general implications in the application of DWCNTs as linear motors in nanodevices

An improved image segmentation algorithm for salient object detection

Semantic object detection is one of the most important and challenging problems in image analysis. Segmentation is an optimal approach to detect salient objects, but often fails to generate meaningful regions due to over-segmentation. This paper presents an improved semantic segmentation approach which is based on JSEG algorithm and utilizes multiple region merging criteria. The experimental results demonstrate that the proposed algorithm is encouraging and effective in salient object detection

Protective effect of Salvia miltiorrhiza in rheumatoid arthritis patients: A randomized, single-blind, placebocontrolled trial

Purpose: To study the protective effect of Salvia miltiorrhiza (SM) against rheumatoid arthritis (RA) in RA patients.Methods: Sixty RA patients were divided into two groups: SM (n = 30) and placebo (n =30) groups given SM at a dose of 250 mg/kg (3 capsules/day), and placebo (3 capsule/day), respectively, for 12 weeks. Patient responses based on American College of Rheumatology (ACR), health assessmentquestionnaire (HAQ) score, and global assessment of disease (GAD) were recorded. Moreover, Disease Activity Score (DAS) 28, pain score (visual analogue score, VAS), rheumatoid factor (Rh factor), and inflammatory cytokines (markers) were determined.Results: After 12 weeks of intervention with SM, ACR20 (30 %)/ACR50 patient response (13.3%, i.e., score for swelling and tenderness of joints), was significantly improved. There were considerable reductions in GAD, HAQ, DAS 28, pain score (VAS), and levels of erythrocyte sedimentation rate(ESR), acute phase reaction protein (CRP), Rh factor (IgM) and inflammatory cytokines (IL-1β, IL-6 and TNF-α), when compared to placebo (p < 0.01). Treatment with SM produced milder adverse effects than treatment with placebo (p < 0.01).Conclusion: Overall, SM produces better anti-RA effect than placebo by significantly altering ACR patient response, reducing GAD, HAQ, DAS 28 scores, Rh factor, ESR, CRP and inflammatory cytokines in RA patients. However, a large-scale clinical trial is needed before SM can be recommended for combating RA and its related symptoms. Keywords: Salvia miltiorrhiza, Rheumatoid arthritis, DAS 28, Adverse effec

Direct Simulation of Low-Re Flow around a Square Cylinder by Numerical Manifold Method for Navier-Stokes Equations

Numerical manifold method was applied to directly solve Navier-Stokes (N-S) equations for incompressible viscous flow in this paper, and numerical manifold schemes for N-S equations coupled velocity and pressure were derived based on Galerkin weighted residuals method as well. Mixed cover with linear polynomial function for velocity and constant function for pressure was employed in finite element cover system. As an application, mixed cover 4-node rectangular manifold element has been used to simulate the incompressible viscous flow around a square cylinder in a channel. Numerical tests illustrate that NMM is an effective and high-order accurate numerical method for incompressible viscous flow N-S equations

Effects of water content change path on laboratory and field compaction of lime stabilized expansive soil

Generally, the soil requires to be compacted in highway construction. The expansive soil is a special type of soil that is highly susceptible to variations in water content, which affects the degree of compaction at the same compaction energy. In the present study, a series of wet compaction tests and dry compaction tests were carried out in the laboratory. Laboratory test results show that dry compaction will produce a higher optimum water content and a higher maximum dry unit weight compared to wet compaction, because its matric suction is smaller. Field compaction tests were also conducted, the results showed that there might be a risk of under-compacting soils during construction caused by different water content change path in actual field conditions

Static and dynamic crushing of novel porous crochet-sintered metal and its filled composite tube

© 2018 Elsevier Ltd A novel porous crochet-sintered metal (PCSM) is fabricated by rolling a crocheted porous cloth and subsequent vacuum sintering using a continual single super-fine soft 304 rope twisted by 49 fibers as raw material. This work investigates the quasi-static and dynamic axial crushing response of PCSMs and their filled composite tubes. The pore structures of PCSMs are formed by inter-crocheted and multiple inter-locked rope skeletons and metallurgical bonds. The PCSMs have almost no initial impact effects with a high crushing force efficiency. Filling the PCSMs changes the deformation model of 6063 tube, improves the static crashworthiness parameters of 6063 tube by 8–25% with almost no increasing initial impact effect, and doesn't always play a positive role in dynamic absorption. Porosity has obvious influence on the quasi-static and dynamic behavior and crashworthiness of PCSMs and their filled composite tube, and the effect of porosity on dynamic crashworthiness of composite tube is greater than that on quasi-static crashworthiness of composite tube. The PCSMs and their composite tubes show great potential for application in energy absorbers. The method of filling PCSM into bare tube is possible to improve the energy absorption ability of thin-walled tube with almost no increase in the initial peak force

Increased concentrations of soluble B7-H3 and interleukin 36 in bronchoalveolar lavage fluid of Children with Mycoplasma pneumoniae pneumonia

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