Swartz C.H.,Texas State University |
Noriega O.C.,Texas State University |
Jayathilaka P.A.R.D.,Texas State University |
Edirisooriya M.,Texas State University |
And 9 more authors.
2014 IEEE 40th Photovoltaic Specialist Conference, PVSC 2014 | Year: 2014
Confocal photoluminescence is shown to be a powerful tool for analyzing defect structure in epitaxial CdTe appropriate for photovoltaic applications. Non-radiative defects such as dislocations are easily mapped and quantified. Photoluminescence intensity measurements are shown to be a valuable tool for quantifying interface state density. Very low dislocation density and twin content can be achieved for epitaxial CdTe, and low interface state densities result from using CdMgTe barriers. © 2014 IEEE.
Neerukatti R.K.,School for Engineering of Matter |
Rajadas A.,School for Engineering of Matter |
Borkowski L.,School for Engineering of Matter |
Chattopadhyay A.,School for Engineering of Matter |
Huff D.W.,Boeing Company
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2016
Advanced composite structures, such as foam core carbon fiber reinforced polymer composites, are increasingly being used in applications which require high strength, high in-plane and flexural stiffness, and low weight. However, the presence of in situ damage due to manufacturing defects and/or service conditions can complicate the failure mechanisms and compromise their strength and reliability. In this paper, the capability of detecting damages such as delaminations and foam-core separations in X-COR composite structures using non-destructive evaluation (NDE) and structural health monitoring (SHM) techniques is investigated. Two NDE techniques, flash thermography and low frequency ultrasonics, were used to detect and quantify the damage size and locations. Macro fiber composites (MFCs) were used as actuators and sensors to study the interaction of Lamb waves with delaminations and foam-core separations. The results indicate that both flash thermography and low frequency ultrasonics were capable of detecting damage in X-COR sandwich structures, although low frequency ultrasonic methods were capable of detecting through thickness damages more accurately than flash thermography. It was also observed that the presence of foam-core separations significantly changes the wave behavior when compared to delamination, which complicates the use of wave based SHM techniques. Further, a wave propagation model was developed to model the wave interaction with damages at different locations on the X-COR sandwich plate. © COPYRIGHT SPIE. Downloading of the abstract is permitted for personal use only.
Stith J.L.,U.S. National Center for Atmospheric Research |
Twohy C.H.,Oregon State University |
Demott P.J.,Colorado State University |
Baumgardner D.,National Autonomous University of Mexico |
And 3 more authors.
Atmospheric Chemistry and Physics | Year: 2011
In situ airborne sampling of refractory black carbon (rBC) particles and Ice Nuclei (IN) was conducted in and near an extratropical cyclonic storm in the western Pacific Ocean during the Pacific Dust Experiment, PACDEX, in the spring of 2007. Airmass origins were from Eastern Asia. Clouds associated primarily with the warm sector of the storm were sampled at various locations and altitudes. Cloud hydrometeors were evaporated by a counterflow virtual impactor (CVI) and the residuals were sampled by a single particle soot photometer (SP2) instrument, a continuous flow diffusion chamber ice nucleus detector (CFDC) and collected for electron microscope analysis. In clouds containing large ice particles, multiple residual particles were observed downstream of the CVI for each ice particle sampled on average. The fraction of rBC compared to total particles in the residual particles increased with decreasing condensed water content, while the fraction of IN compared to total particles did not, suggesting that the scavenging process for rBC is different than for IN. In the warm sector storm midlevels at temperatures where heterogeneous freezing is expected to be significant (here ĝ̂'24 to ĝ̂'29 Â°C), IN concentrations from ice particle residuals generally agreed with simultaneous measurements of total ice concentrations or were higher in regions where aggregates of crystals were found, suggesting heterogeneous freezing as the dominant ice formation process in the mid levels of these warm sector clouds. Lower in the storm, at warmer temperatures, ice concentrations were affected by aggregation and were somewhat less than measured IN concentrations at colder temperatures. The results are consistent with ice particles forming at storm mid-levels by heterogeneous freezing on IN, followed by aggregation and sedimentation to lower altitudes. Compositional analysis of the aerosol and back trajectories of the air in the warm sector suggested a possible biomass burning source for much of the aerosol. Comparison of the particles from the CFDC with the other aerosol in the residuals of ice particles suggested that the largest portion of IN had similar inferred origins (from biomass burning with minor amounts of rBC) as the other aerosol, but contained slightly elevated amounts of calcium and less influence from sea salt. © 2011 Author(s).
Deshpande S.,Arizona State University |
Rivera D.E.,School for Engineering of Matter
Proceedings of the IEEE Conference on Decision and Control | Year: 2014
Data-centric system identification approaches generate a local function approximation from a database of regressors at a given operating point. This paper studies the design of input signals for data-centric identification of highly interactive multivariable systems which show strong gain directionality. The input signal design formulation aims to develop uniform coverage in the output space by addressing the optimal distribution of time-indexed output points under general operating constraints on the manipulated input and measured output signals. The solution of resulting nonconvex quadratic program is proposed using semidefinite and nonlinear programming methods. A numerical example is shown to highlight the benefit of proposed design in comparison to the input design based on Weyl's criterion for data of finite length. © 2014 IEEE.
Cheng Q.,School for Engineering of Matter |
Song Z.,School for Engineering of Matter |
Ma T.,School for Engineering of Matter |
Smith B.B.,School for Engineering of Matter |
And 4 more authors.
Nano Letters | Year: 2013
Paper folding techniques are used in order to compact a Li-ion battery and increase its energy per footprint area. Full cells were prepared using Li 4Ti5O12 and LiCoO2 powders deposited onto current collectors consisting of paper coated with carbon nanotubes. Folded cells showed higher areal capacities compared to the planar versions with a 5 × 5 cell folded using the Miura-ori pattern displaying a ∼14× increase in areal energy density. © 2013 American Chemical Society.
Deshpande S.,Arizona State University |
Rivera D.E.,School for Engineering of Matter
Proceedings of the IEEE Conference on Decision and Control | Year: 2013
This paper examines the design of input signals for identification of Hammerstein systems in a data-centric framework by addressing the optimal distribution of regressors. Data-centric estimation methods such as Model-on-Demand (MoD) generate local function approximations from a database of regressors at the current operating point. The data-centric input signal design formulation aims to develop sufficient support in the regressor space for the MoD estimator, while addressing time-domain constraints on the input and output signals. A numerical example is shown to highlight the benefit of proposed design over classical Pseudo Random Binary Sequence (PRBS), Multi Level Pseudo Random Sequence (MLPRS) and uniform random input designs. © 2013 IEEE.
Yadav A.,School for Engineering of Matter |
Lind M.L.,School for Engineering of Matter |
Ma X.,School for Engineering of Matter |
Lin Y.S.,School for Engineering of Matter
Industrial and Engineering Chemistry Research | Year: 2013
Separation of alcohols from dilute aqueous solutions is important to enable continuous microbial production of biofuels. Pervaporation is a process with great potential for continuous extraction of alcohols from biological fermentation broths. Here, we report on the synthesis and pervaporation performance of thin, supported pure polydimethylsiloxane (PDMS) and silicalite-1/PDMS nanocomposite membranes with nanoparticle contents of 10, 20, and 30 wt %. Using a batch pervaporation system, we measured flux and separation factors of the membranes for solutions of 4 wt % ethanol in water at 25 °C, 50 °C, and 65 °C. With increased nanosilicalite loadings in the nanocomposite membranes, we obtained both increased flux and increased alcohol separation factors. © 2013 American Chemical Society.