A unified integro-differential nonlocal model Khodabakhshi, Parisa; Reddy, J.N.
International journal of engineering science,
October 2015, 2015-10-00, 20151001, Volume:
95
Journal Article
Peer reviewed
Open access
In this paper a unified integro-differential nonlocal elasticity model is presented and its use in the bending analysis of Euler–Bernoulli beams is illustrated. A general (for an elastic continuum) ...finite element formulation for the two-phase integro-differential form of Eringen nonlocal model is provided. The equations are specialized for the case of the Euler–Bernoulli beam theory. Several numerical examples, including the paradoxical cantilever beam problem that eluded other researchers, are provided to show how the present nonlocal model affects the transverse displacement of beams. The examples show that Eringen nonlocal constitutive relation has a softening effect on the beam, except for the case of the simply supported beam. A brief discussion on the applicability of the integro-differential model to other problems is also presented. Finally, the transition from the stiffened nonlocal simply supported beam to the softened nonlocal clamped beam is also investigated.
•Segmented arc-shaped piezoelectric energy harvester is proposed.•A new distributed-parameter electromechanical coupling model is developed.•The analytical solutions are validated with FEM and ...experiments.•Energy harvester characteristics with optimal parameters to generate maximum output voltage of 50 V are fully investigated.
Advances in energy harvesting techniques, along with low-power electronic devices open up the possibility of developing self-powered engineering systems. Most existing energy harvesters are constructed with beams such as cantilevers, fully-clamped beams and buckled beams. Here we present an attempt to add a new design dimension to the piezoelectric energy harvesters (PEHs) by exploiting a curved-beam structure. This design will be shown to dramatically improve the contemporary harvester performance. To establish an analytical base for curved PEHs, we take a variable-curvature unimorph as the general modelling object and derive its governing equations based on the Timoshenko beam theory. Using the mode expansion method with the consideration of boundary conditions and continuous conditions, we present analytical solutions of the electrical and mechanical response of the PEH. The model developed is verified via the finite element method and it can accurately estimate the modal response of the curved PEH. Prototypes are fabricated and tested to validate the analytical model and solutions. Furthermore, we comprehensively analyzed the key parameter effects including the length of the straight beam, thickness ratio and Young’s modulus on the performance of the PEH. The proposed analytical model provides an analytical guidance for composite arc-shaped PEHs with variable curvature and it also helps in the design and optimization of new PEHs.
We report on the generation of a narrow divergence (θ_{γ}<2.5 mrad), multi-MeV (E_{max}≈18 MeV) and ultrahigh peak brilliance (>1.8×10^{20} photons s^{-1} mm^{-2} mrad^{-2} 0.1% BW) γ-ray beam ...from the scattering of an ultrarelativistic laser-wakefield accelerated electron beam in the field of a relativistically intense laser (dimensionless amplitude a_{0}≈2). The spectrum of the generated γ-ray beam is measured, with MeV resolution, seamlessly from 6 to 18 MeV, giving clear evidence of the onset of nonlinear relativistic Thomson scattering. To the best of our knowledge, this photon source has the highest peak brilliance in the multi-MeV regime ever reported in the literature.
We investigate the influence of a tilted laser-pulse-intensity front on laser-wakefield acceleration. Such asymmetric light pulses may be exploited to obtain control over the electron-bunch-pointing ...direction and in our case allowed for reproducible electron-beam steering in an all-optical way within an 8 mrad opening window with respect to the initial laser axis. We also discovered evidence of collective electron-betatron oscillations due to off-axis electron injection into the wakefield induced by a pulse-front tilt. These findings are supported by 3D particle-in-cell simulations.
All forms of waves can contain phase singularities. In the case of optical waves, a light beam with a phase singularity carries orbital angular momentum, and such beams have found a range of ...applications in optical manipulation, quantum information and astronomy. Here we report the generation of an electron beam with a phase singularity propagating in free space, which we achieve by passing a plane electron wave through a spiral phase plate constructed naturally from a stack of graphite thin films. The interference pattern between the final beam and a plane electron wave in a transmission electron microscope shows the 'Y'-like defect pattern characteristic of a beam carrying a phase singularity with a topological charge equal to one. This fundamentally new electron degree of freedom could find application in a number of research areas, as is the case for polarized electron beams.
Optical tweezers, a simple and robust implementation of optical micromanipulation technologies, have become a standard tool in biological, medical and physics research laboratories. Recently, with ...the utilization of holographic beam shaping techniques, more sophisticated trapping configurations have been realized to overcome current challenges in applications. Holographically generated higher‐order light modes, for example, can induce highly structured and ordered three‐dimensional optical potential landscapes with promising applications in optically guided assembly, transfer of orbital angular momentum, or acceleration of particles along defined trajectories. The non‐diffracting property of particular light modes enables the optical manipulation in multiple planes or the creation of axially extended particle structures. Alongside with these concepts which rely on direct interaction of the light field with particles, two promising adjacent approaches tackle fundamental limitations by utilizing non‐optical forces which are, however, induced by optical light fields. Optoelectronic tweezers take advantage of dielectrophoretic forces for adaptive and flexible, massively parallel trapping. Photophoretic trapping makes use of thermal forces and by this means is perfectly suited for trapping absorbing particles. Hence the possibility to tailor light fields holographically, combined with the complementary dielectrophoretic and photophoretic trapping provides a holistic approach to the majority of optical micromanipulation scenarios.
Optical tweezers, a simple and robust implementation of optical micromanipulation technologies, have become a standard tool in biological, medical and physics research laboratories. Recently, with the utilization of holographic beam shaping techniques, more sophisticated trapping configurations have been realized to overcome current challenges in applications. Holographically generated higher‐order light modes, for example, can induce highly structured and ordered three‐dimensional optical potential landscapes with promising applications in optically guided assembly, transfer of orbital angular momentum, or acceleration of particles along defined trajectories. The non‐diffracting property of particular light modes enables the optical manipulation in multiple planes or the creation of axially extended particle structures. Alongside with these concepts which rely on direct interaction of the light field with particles, two promising adjacent approaches tackle fundamental limitations by utilizing non‐optical forces which are, however, induced by optical light fields. Optoelectronic tweezers take advantage of dielectrophoretic forces for adaptive and flexible, massively parallel trapping. Photophoretic trapping makes use of thermal forces and by this means is perfectly suited for trapping absorbing particles. Hence the possibility to tailor light fields holographically, combined with the complementary dielectrophoretic and photophoretic trapping provides a holistic approach to the majority of optical micromanipulation scenarios.
In this article, we proposed a new class of light beam which arose from the combination of the symmetric Airy beams and vortex or vector beams. We called them symmetric Airy vortex beam and symmetric ...Airy vector beam. In our experiments, we combined vortex phase and symmetric spatially cubic phase to fabricate liquid crystal q-symmetric-Airy plate. It can directly generate the symmetric Airy vortex or symmetric Airy vector beams by controlling the polarisation of incident Gaussian beam. This work may provide a versatile candidate for many potential optical applications in the areas of optical micromanipulation, optical communication and paves the way for the future researches of symmetric Airy vortex and symmetric Airy vector beams.
Electron beams with helical wavefronts carrying orbital angular momentum are expected to provide new capabilities for electron microscopy and other applications. We used nanofabricated diffraction ...holograms in an electron microscope to produce multiple electron vortex beams with well-defined topological charge. Beams carrying quantized amounts of orbital angular momentum (up to 100Planck's over 2pi) per electron were observed. We describe how the electrons can exhibit such orbital motion in free space in the absence of any confining potential or external field, and discuss how these beams can be applied to improved electron microscopy of magnetic and biological specimens.
PDF
