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Colorado H.A.,University of California at Los Angeles | Colorado H.A.,University of Medellin | Colorado H.A.,Phase IV Engineering, Inc. | Hiel C.,Composite Support and Solutions Inc. | Hahn H.T.,University of California at Los Angeles
Bulletin of Materials Science | Year: 2011

Mechanical properties and microstructures of a chemically bonded phosphate ceramic (CBPC) and its composite with 1.0 wt% graphite nanoplatelets (GNPs) reinforcement have been investigated. Microstructure was identified by using optical and scanning electron microscopes, X-ray tomography, and X-ray diffraction. In addition, weight loss of the resin at room temperature was studied. The microstructure characterization shows that CBPC is itself a composite with several crystalline (wollastonite and brushite) and amorphous phases. SEM and micro tomography show a homogeneous distribution of crystalline phases. Bending and compression strength of the CBPC was improved by reducing bubbles via preparation in vacuum. © Indian Academy of Sciences.

Kim H.C.,Korea Atomic Energy Research Institute | Hahn H.T.,Phase IV Engineering, Inc. | Yang Y.S.,Korea Atomic Energy Research Institute
Journal of Composite Materials | Year: 2013

In an effort to fabricate prototypes with improved mechanical properties in the selective laser sintering process, functionalized graphite nanoplatelets were added to polyamide-12 powder to produce a nanocomposite powder. The polyamide-12 powder was chosen as the matrix polymer because it has features conducive to laser sintering, such as a low melting temperature and high mechanical properties. As fillers, the graphite nanoplatelets were oxidized through a nitric acid treatment to improve the interfacial bonding. For the syntheses of the nanocomposite solution, intercalation in an autoclave was conducted to obtain good dispersion and manufacturability. The micro/nanostructures of the synthesized nanocomposites were examined through scanning electron microscopy. The distribution of particles was also analyzed to look at the feasibility for the selective laser sintering process. The synthesized nanocomposite powder was layered and sintered by a laser. The mechanical properties for specimens made of neat polyamide-12, polyamide-12/TiO2, and polyamide-12/functionalized graphite nanoplatelet were tested and compared. The results indicate that the functionalization of nanofiller reinforces interfacial bonding force. For this reason, a small amount of nanofiller, which does not influence the thermal and rheological behavior, can improve the material properties. © The Author(s) 2012.

Abbasi S.,Phase IV Engineering, Inc. | Healy P.,University of Limerick | Rextin A.,University of Limerick
Information Processing Letters | Year: 2010

We consider the standard algorithm by Bertolazzi et al. to test the upward planarity of embedded digraphs. We show how to improve its running time from O (n + r2) to O (n + rfrac(3, 2)), where r is the number of sources and sinks in the digraph. We also discuss an application of this technique: improving the running time of getting a quasi-upward planar drawing for an embedded digraph with minimum number of bends. © 2010 Elsevier B.V. All rights reserved.

Yusoff A.R.B.M.,Federal University of Parana | Shuib S.A.,Phase IV Engineering, Inc.
Electrochimica Acta | Year: 2011

In this paper, we present a simple method for electropolymerization process that combines aniline-silane (C6H5NHC3H 6Si(OMe)3) surface modified indium-tin-oxide (ITO) to prepare thin, polyaniline (PANI) films with good surface coverage. The modified surface enhances the growth of PANI film resulting in a smoother surface, dense, strongly adhered film, higher electropolymerization activity and stability than those deposited on unmodified ITO substrates. PANI film deposited on modified ITO substrate was used as a modified base terminal in a metal-base-transistor (MBT), which used tris(8-hydroxyquinoline) aluminum (Alq3) as an emitter layer, LiF as a buffer layer, and Al as a cathode. The MBT, tested at in ambient atmosphere, and without the presence of magnetic-field, has a comparable but stable current gain, 6.5 than that of a device with a sulfonated polyaniline (SPANI) based metal-base transistor. With this simple and easy electropolymerization method, the on-to-off current ratio achieved 6.9 × 104. © 2011 Elsevier Ltd. All rights reserved.

Kuester D.,Phase IV Engineering, Inc. | Popovic Z.,University of Colorado
IEEE Microwave Magazine | Year: 2013

Passive ultra-high-frequency (UHF) radio-frequency identification (RFID) has developed rapidly over the past two decades. In 2012 alone, about 4 billion tags were sold worldwide [1]. Manufacture and deployment at this volume has been made possible by minimizing tag cost, making a strong disincentive for the added expense of RF performance testing. As a result, performance metrics and test methods are not yet unified or generally adopted. Large customers in industry and government, however, wish to compare products with parameters like read range and inventory rate, so this problem is attracting more attention, and test standards are improving. This article discusses the history, state of the art, and some future challenges in this rapidly evolving area of study. In particular, we consider two metrics for digitally modulated backscatter of passive UHF RFID tags and how tests can be simplified for reduced costs. Examples for some 860-960 MHz commercial tags and applications are given to illustrate the method. © 2000-2012 IEEE.

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