Novel thick-foam ferroelectret with engineered voids for energy harvesting applications

This work reports a novel thick-foam ferroelectret which is designed and engineered for energy harvesting applications. We fabricated this ferroelectret foam by mixing a chemical blowing agent with a polymer solution, then used heat treatment to activate the agent and create voids in the polymer foam. The dimensions of the foam, the density and size of voids can be well controlled in the fabrication process. Therefore, this ferroelectret can be engineered into optimized structure for energy harvesting applications

Investigation of a scale-up manufacturing approach for nanostructures by using a nanoscale multi-tip diamond tool

Increasing interest in commercializing functional nanostructured devices heightens the need for cost-effective manufacturing approaches for nanostructures. This paper presents an investigation of a scale-up manufacturing approach for nanostructures through diamond turning using a nanoscale multi-tip diamond tool (four tip tool with tip width of 150 nm) fabricated by focused ion beam (FIB). The manufacturing capacity of this new technique is evaluated through a series of cutting trials on copper substrates under different cutting conditions (depth of cut 100–500 nm, spindle speed 12–120 rpm). The machined surface roughness and nanostructure patterns are measured by using a white light interferometer and a scanning electron microscope, respectively. Results show that the form accuracy and integrity of the machined nanostructures were degraded with the increase of the depth of cut and the cutting speed. The burr and the structure damage are two major machining defects. High precision nano-grooves (form error of bottom width < 6.7 %) was achieved when a small depth of cut of 100 nm was used (spindle speed = 12 rpm). Initial tool wear was found at both the clearance cutting edge and the side edges of tool tips after a cutting distance of 2.5 km. Moreover, the nanometric cutting process was emulated by molecular dynamic (MD) simulations. The research findings obtained from MD simulation reveal the underlying mechanism for machining defects and the initialization of tool wear observed in experiments

On Finite Time Singularity and Global Regularity of an Axisymmetric Model for the 3D Euler Equations

We investigate the large time behavior of an axisymmetric model for the 3D Euler equations. In \cite{HL09}, Hou and Lei proposed a 3D model for the axisymmetric incompressible Euler and Navier-Stokes equations with swirl. This model shares many properties of the 3D incompressible Euler and Navier-Stokes equations. The main difference between the 3D model of Hou and Lei and the reformulated 3D Euler and Navier-Stokes equations is that the convection term is neglected in the 3D model. In \cite{HSW09}, the authors proved that the 3D inviscid model can develop a finite time singularity starting from smooth initial data on a rectangular domain. A global well-posedness result was also proved for a class of smooth initial data under some smallness condition. The analysis in \cite{HSW09} does not apply to the case when the domain is axisymmetric and unbounded in the radial direction. In this paper, we prove that the 3D inviscid model with an appropriate Neumann-Robin boundary condition will develop a finite time singularity starting from smooth initial data in an axisymmetric domain. Moreover, we prove that the 3D inviscid model has globally smooth solutions for a class of large smooth initial data with some appropriate boundary condition.Comment: Please read the published versio

Light deflection by photonic crystals

When propagating through periodically structured media, i. e. photonic crystals, optical waves will be modulated with the periodicity. As a result, the dispersion of waves will no longer behave as in a free space, and so called frequency band structures appear. Under certain conditions, waves may be prohibited from propagation in certain or all directions, corresponding to partial and complete bandgaps respectively. Here we report a new fascinating phenomenon associated with the partial gaps, that is, deflection of optical waves. This phenomenon will render novel applications in manipulating light flows.Comment: 3 pages, 4 figure