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Rashmi,Siddaganga Institute of Technology | Shivakumar K.N.,&ate University
International Journal of Materials Research | Year: 2013

Polymer nanocomposites were prepared by mixing Epoxy resin with 2, 5 and 7 wt.% of organically modified montmorillonite clay using a high shear mixer. Microstructural analysis of the nanocomposites was performed with transmission electron microscopy and X-ray diffraction. The effects of voltage, frequency, temperature and seawater ageing on electrical conductivity and impedance of the nanocomposites were evaluated. The transmission electron microscopy and X-ray diffraction results indicate that montmorillonite clay nanoparticles were uniformly dispersed in the Epoxy matrix. Experimental results show higher conductivity and lower impedance with the addition of 2 wt.% montmorillonite clay in the Epoxy matrix with respect to frequency, temperature and seawater ageing. On the other hand, with further increase in filler loading (5 and 7 wt.%) a reverse trend was observed with respect to conductivity and impedance. The obtained values of capacitance and resistance were found to be well correlated. © 2013 Carl Hanser Verlag. Source


Chartier T.P.,Davidson College | Ellison V.,&ate University | Langville A.N.,College of Charleston
4OR | Year: 2014

This paper presents a multi-objective linear integer program that assigns student volunteers to present lectures at participating classes in local schools. A student’s class assignment is based upon his or her availability to teach at that time as well as several additional factors including student preferences regarding commuting and partners as well as the institution’s goal of creating diverse student groups. This case study shows that the proposed mathematical program dramatically improves the assignments of students to classes and provides increased flexibility for modeling other goals and factors in future years. In addition, this multi-phase model can be applied in other contexts, such as crew scheduling or the scheduling of parallel sessions of large conferences. © 2014, Springer-Verlag Berlin Heidelberg. Source


Gong Y.,Henan Polytechnic University | Liu L.,&ate University
AIP Conference Proceedings | Year: 2010

A generalized component modal analytical method for space mega frames of super tall buildings is developed. The components used herein are not the actual components, but they are conceptual ones. They are actually the nodal lines employed to discretize the computational model of the structure, a three dimensional model with continuously distributed mass and stiffness. One-variable functions defined on the nodal lines selected by the analyst are unknown functions (eigenfunctions) employed to describe the behavior of the model. By a Hamiltonian principle, the governing equations of the modal analysis can be obtained, which are a set of Ordinary Differential Equations (ODE) of the eigenfunctions with their corresponding boundary conditions. The desired eigenvalues and corresponding eigenfunctions (eigenmode) can be obtained by numerically solving the system of ODEs with boundary conditions. The method is applied to the space-mega-frame system of super tall buildings. The results from the illustration example show that the method is rational and powerful for the modal analysis of space-mega-frame systems. © 2010 American Institute of Physics. Source


Kasanaboina P.K.,North Carolina A&T State University | Ojha S.K.,North Carolina A&T State University | Sami S.U.,&ate University | Lewis Reynolds C.,North Carolina State University | And 3 more authors.
Journal of Electronic Materials | Year: 2016

GaAs/GaAsSb nanowire (NW) arrays are ideally suited to meet the demands of the next generation infrared (IR) photodetectors with potential for improving detection. NWs in a core–shell geometry have the advantage of providing axial direction for a long optical path for enhanced optical absorption and a short radial path for charge diffusion and collection. For the Ga-assisted molecular beam epitaxial growth of vertical, dense and uniform GaAs core NWs on Si (111), the effects of substrate surface preparation in combination with growth parameter variation were examined. On the epiready substrate without any surface preparation, both initial Ga shutter opening duration and V/III beam equivalent pressure ratio play a vital role in achieving almost all vertical NWs with moderate density ~107 cm−2. Also the spatial uniformity of the NWs was poor. Substrate surface preparation by chemical cleaning followed by oxidation in air led to highly vertical and uniform NWs with high density (8 × 108 cm−2). The GaAsSb shell was then successfully grown around the highly dense and vertical core GaAs NWs at growth temperatures ranging from 550°C to 590°C. It was found that growth temperature has a strong influence on Sb incorporation in the NWs and, hence, the NW morphology and 4K photoluminescence (PL) spectra. The presence of x-ray diffraction peaks corresponding to (111) reflection only and its higher-order reflections attest to the vertical alignment of NWs. Strain in the NWs as estimated using the Williamson–Hall isotropic strain model increases with Sb incorporation, which results in bending of the NWs with increasing Sb. Structural properties of these NWs using scanning transmission electron microscopy (STEM) are also presented. The temperature dependence PL of the NWs exhibited “S-curve” behavior, which is a well-known signature of localized excitons and a room temperature band edge PL emission occurring at ~1.3 μm. © 2016 The Minerals, Metals & Materials Society Source


Kasanaboina P.K.,North Carolina A&T State University | Ojha S.K.,North Carolina A&T State University | Sami S.U.,&ate University | Lewis Reynolds C.,North Carolina State University | And 3 more authors.
Journal of Electronic Materials | Year: 2016

GaAs/GaAsSb nanowire (NW) arrays are ideally suited to meet the demands of the next generation infrared (IR) photodetectors with potential for improving detection. NWs in a core–shell geometry have the advantage of providing axial direction for a long optical path for enhanced optical absorption and a short radial path for charge diffusion and collection. For the Ga-assisted molecular beam epitaxial growth of vertical, dense and uniform GaAs core NWs on Si (111), the effects of substrate surface preparation in combination with growth parameter variation were examined. On the epiready substrate without any surface preparation, both initial Ga shutter opening duration and V/III beam equivalent pressure ratio play a vital role in achieving almost all vertical NWs with moderate density ~107 cm−2. Also the spatial uniformity of the NWs was poor. Substrate surface preparation by chemical cleaning followed by oxidation in air led to highly vertical and uniform NWs with high density (8 × 108 cm−2). The GaAsSb shell was then successfully grown around the highly dense and vertical core GaAs NWs at growth temperatures ranging from 550°C to 590°C. It was found that growth temperature has a strong influence on Sb incorporation in the NWs and, hence, the NW morphology and 4K photoluminescence (PL) spectra. The presence of x-ray diffraction peaks corresponding to (111) reflection only and its higher-order reflections attest to the vertical alignment of NWs. Strain in the NWs as estimated using the Williamson–Hall isotropic strain model increases with Sb incorporation, which results in bending of the NWs with increasing Sb. Structural properties of these NWs using scanning transmission electron microscopy (STEM) are also presented. The temperature dependence PL of the NWs exhibited “S-curve” behavior, which is a well-known signature of localized excitons and a room temperature band edge PL emission occurring at ~1.3 μm. © 2016, The Minerals, Metals & Materials Society. Source

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