3D modeling of high temperature superconducting staggered array undulator

A 3-D model of a superconducting staggered array undulator has been built, which could serve as a powerful tool to solve electromagnetic problems and to realize field optimization of such design. Given the limitation of 2-D simulation for irregular shapes and complex geometries, 3-D models are more desirable for a comprehensive investigation. An optimization method for the undulator peak field is proposed; up to 32% enhancement can be achieved by introducing major segment bulks. Some improvements of the undulator design are obtained by careful analyzing of the simulation results. © 2002-2011 IEEE.

A performance evaluation of volumetric 3D interest point detectors

This paper presents the first performance evaluation of interest points on scalar volumetric data. Such data encodes 3D shape, a fundamental property of objects. The use of another such property, texture (i.e. 2D surface colouration), or appearance, for object detection, recognition and registration has been well studied; 3D shape less so. However, the increasing prevalence of 3D shape acquisition techniques and the diminishing returns to be had from appearance alone have seen a surge in 3D shape-based methods. In this work, we investigate the performance of several state of the art interest points detectors in volumetric data, in terms of repeatability, number and nature of interest points. Such methods form the first step in many shape-based applications. Our detailed comparison, with both quantitative and qualitative measures on synthetic and real 3D data, both point-based and volumetric, aids readers in selecting a method suitable for their application. © 2012 Springer Science+Business Media, LLC.

A simple criterion for filament break-up in drop-on-demand inkjet printing

Jets from drop-on-demand inkjet print-heads consist of a main drop with a trailing filament, which either condenses into the main drop, or breaks up into satellite drops. Filament behaviour is quantitatively similar to that of larger, free symmetrical filamentscan be predicted from the aspect ratio and Ohnesorge number. Symmetrical filaments generated from inkjet print-heads show the same behaviour. A simple model, based on competition between the processes of axial shortening and radial necking, predicts the critical aspect ratio below which the jet condenses into a single drop. The success of this simple criterion supports the underlying physical model. © 2013 American Institute of Physics.

Aerodynamic effects in ink-jet printing on a moving web

The airflow between the fast-moving substrate and stationary print heads in a web print press may cause print quality issues in high-speed, roll-to-roll printing applications. We have studied the interactions between ink drops and the airflow in the gap between the printhead and substrate, by using an experimental flow channel and high-speed imaging. The results show: 1) the gap airflow is well approximated by a standard Couette flow profile; 2) the effect of gap airflow on the flight paths of main drops and satellites is negligible; and 3) the interaction between the gap airflow and the wakes from the printed ink drops should be investigated as the primary source of aerodynamically- related print quality issues. ©2012 Society for Imaging Science and Technology.

Fabrication, densification, and replica molding of 3D carbon nanotube microstructures

The introduction of new materials and processes to microfabrication has, in large part, enabled many important advances in microsystems, labon- a-chip devices, and their applications. In particular, capabilities for cost-effective fabrication of polymer microstructures were transformed by the advent of soft lithography and other micromolding techniques 1,2, and this led a revolution in applications of microfabrication to biomedical engineering and biology. Nevertheless, it remains challenging to fabricate microstructures with well-defined nanoscale surface textures, and to fabricate arbitrary 3D shapes at the micro-scale. Robustness of master molds and maintenance of shape integrity is especially important to achieve high fidelity replication of complex structures and preserving their nanoscale surface texture. The combination of hierarchical textures, and heterogeneous shapes, is a profound challenge to existing microfabrication methods that largely rely upon top-down etching using fixed mask templates. On the other hand, the bottom-up synthesis of nanostructures such as nanotubes and nanowires can offer new capabilities to microfabrication, in particular by taking advantage of the collective self-organization of nanostructures, and local control of their growth behavior with respect to microfabricated patterns. Our goal is to introduce vertically aligned carbon nanotubes (CNTs), which we refer to as CNT "forests", as a new microfabrication material. We present details of a suite of related methods recently developed by our group: fabrication of CNT forest microstructures by thermal CVD from lithographically patterned catalyst thin films; self-directed elastocapillary densification of CNT microstructures; and replica molding of polymer microstructures using CNT composite master molds. In particular, our work shows that self-directed capillary densification ("capillary forming"), which is performed by condensation of a solvent onto the substrate with CNT microstructures, significantly increases the packing density of CNTs. This process enables directed transformation of vertical CNT microstructures into straight, inclined, and twisted shapes, which have robust mechanical properties exceeding those of typical microfabrication polymers. This in turn enables formation of nanocomposite CNT master molds by capillary-driven infiltration of polymers. The replica structures exhibit the anisotropic nanoscale texture of the aligned CNTs, and can have walls with sub-micron thickness and aspect ratios exceeding 50:1. Integration of CNT microstructures in fabrication offers further opportunity to exploit the electrical and thermal properties of CNTs, and diverse capabilities for chemical and biochemical functionalization 3. © 2012 Journal of Visualized Experiments.

Diverse 3D microarchitectures made by capillary forming of carbon nanotubes.

A new technology called capillary forming enables transformation of vertically aligned nanoscale filaments into complex three-dimensional microarchitectures. We demonstrate capillary forming of carbon nanotubes into diverse forms having intricate bends, twists, and multidirectional textures. In addition to their novel geometries, these structures have mechanical stiffness exceeding that of microfabrication polymers, and can be used as masters for replica molding

Programmable transformation of vertically aligned carbon nanotubes into 3D microstructures

Capillary forming of carbon nanotubes (CNTs) enables the fabrication of unique 3D microstructures over large areas. In this paper we focus on the simulation as well as on the integration of these structures in MEMS devices. We developed finite element models (FEM) that enables qualitative prediction of shape transformations caused by capillary forming; and show how capillary formed CNT structured can be integrated with conventional lithographic processing for patterning of polymers and metals in concert with CNTs. © 2011 IEEE.