Engineering Commons^™

Self-Healing Of Ionomeric Polymers With Carbon Fibers From Medium-Velocity Impact And Resistive Heating, Vishnu Baba Sundaresan, Andrew Morgan, Matt Castellucci

Mechanical and Nuclear Engineering Publications

Self-healing materials science has seen significant advances in the last decade. Recent efforts have demonstrated healing in polymeric materials through chemical reaction, thermal treatment, and ultraviolet irradiation. The existing technology for healing polymeric materials through the aforementioned mechanisms produces an irreversible change in the material and makes it unsuitable for subsequent healing cycles. To overcome these disadvantages, we demonstrate a new composite self-healing material made from an ionomer (Surlyn) and carbon fiber that can sustain damage from medium-velocity impact and heal from the energy of the impact. Furthermore, the carbon fiber embedded in the polymer matrix results in resistive heating …

A Hierarchical Method For Removal Of Baseline Drift From Biomedical Signals: Application In Ecg Analysis, Yurong Luo, Rosalyn H. Hargraves, Ashwin Belle, Ou Bai, Xuguang Qi, Kevin R. Ward, Michael Paul Pfaffenberger, Kayvan Najarian

Computer Science Publications

Noise can compromise the extraction of some fundamental and important features from biomedical signals and hence prohibit accurate analysis of these signals. Baseline wander in electrocardiogram (ECG) signals is one such example, which can be caused by factors such as respiration, variations in electrode impedance, and excessive body movements. Unless baseline wander is effectively removed, the accuracy of any feature extracted from the ECG, such as timing and duration of the ST-segment, is compromised. This paper approaches this filtering task from a novel standpoint by assuming that the ECG baseline wander comes from an independent and unknown source. The technique …

Electrospun Polymer-Fiber Solar Cell, Shinobu Nagata, Gary M. Atkinson, Dmitry Pestov, Gary C. Tepper, James T. Mcleskey Jr.

Mechanical and Nuclear Engineering Publications

A novel electrospun polymer-fiber solar cell was synthesized by electrospinning a 1 : 2.5 weight% ratio mixture of poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) and [6,6]-phenyl C₆₁ butyric acid methyl ester (PCBM) resulting in bulk heterojunctions. Electrospinning is introduced as a technique that may increase polymer solar cell efficiency, and a list of advantages of the technique applied to solar cells is discussed. The device achieved a power conversion efficiency of η = 3.08 x 10^-7%. The absorption and photoluminescence of MEH-PPV nanofibers are compared to thin films of the same material. Electrospun nanofibers are discussed as a favorable structure for …

Effect Of Substrate Stiffness On Early Human Embryonic Stem Cell Differentiation, Nikolai Eroshenko, Rukmani Ramachandran, Vamsi K. Yadavalli, Raj R. Rao

Chemical and Life Science Engineering Publications

Background

The pluripotency and self renewing properties of human embryonic stem cells (hESC) make them a valuable tool in the fields of developmental biology, pharmacology and regenerative medicine. Therefore, there exists immense interest in devising strategies for hESC propagation and differentiation. Methods involving simulation of the native stem cell microenvironment, both chemical and physical, have received a lot of attention in recent years. Equally important is evidence that cells can also sense the mechanical properties of their microenvironment. In this study, we test the hypothesis that hESCs accept mechanical cues for differentiation from the substrate by culturing them on flexible …

Ennet: Inferring Large Gene Regulatory Networks From Expression Data Using Gradient Boosting, Janusz Slawek, Tomasz Arodź

Computer Science Publications

Background

The regulation of gene expression by transcription factors is a key determinant of cellular phenotypes. Deciphering genome-wide networks that capture which transcription factors regulate which genes is one of the major efforts towards understanding and accurate modeling of living systems. However, reverse-engineering the network from gene expression profiles remains a challenge, because the data are noisy, high dimensional and sparse, and the regulation is often obscured by indirect connections.

Results

We introduce a gene regulatory network inference algorithm ENNET, which reverse-engineers networks of transcriptional regulation from a variety of expression profiles with a superior accuracy compared to the state-of-the-art …

An Entropy-Based Automated Cell Nuclei Segmentation And Quantification: Application In Analysis Of Wound Healing Process, Varun Oswal, Ashwin Belle, Robert Diegelmann, Kayvan Najarian

Computer Science Publications

The segmentation and quantification of cell nuclei are two very significant tasks in the analysis of histological images. Accurate results of cell nuclei segmentation are often adapted to a variety of applications such as the detection of cancerous cell nuclei and the observation of overlapping cellular events occurring during wound healing process in the human body. In this paper, an automated entropy-based thresholding system for segmentation and quantification of cell nuclei from histologically stained images has been presented. The proposed translational computation system aims to integrate clinical insight and computational analysis by identifying and segmenting objects of interest within histological …

On Applications And Limitations Of One-Dimensional Capillarity Formulations For Media With Heterogeneous Wettability, T. M. Bucher, H. Vahedi Tafreshi

Mechanical and Nuclear Engineering Publications

Force-balance-based one-dimensional algebraic formulations that are often used in characterizing the capillarity of a multi-component system (e.g., predicting capillary height rise inporous media) are discussed. It is shown that such formulations fail to provide accurate predictions when the distribution of wetting (or non-wetting) surfaces is not homogeneous. A more general mathematical formulation is suggested and used to demonstrate that for media with heterogeneous wettability, hydrophilic (or hydrophobic) surfaces clustered in groups will have less contribution to the overall capillarity of the system.

Amelogenin Peptide Extract Increases Differentiation And Angiogenic And Local Factor Production And Inhibits Apoptosis In Human Osteoblasts, Rene Olivares-Navarrete, Sharon L. Hyzy, Argelia Almaguer-Flores, Corinna Mauth, Anja C. Gemperli, Barbara D. Boyan, Zvi Schwartz

Biomedical Engineering Publications

Enamel matrix derivative (EMD), a decellularized porcine extracellular matrix (ECM), is used clinically in periodontal tissue regeneration. Amelogenin, EMD’s principal component, spontaneously assembles into nanospheres in vivo, forming an ECM complex that releases proteolytically cleaved peptides. However, the role of amelogenin or amelogenin peptides in mediating osteoblast response to EMD is not clear. Human MG63 osteoblast-like cells or normal human osteoblasts were treated with recombinant human amelogenin or a 5 kDa tyrosine-rich amelogenin peptide (TRAP) isolated from EMD and the effect on osteogenesis, local factor production, and apoptosis assessed. Treated MG63 cells increased alkaline phosphatase specific activity and levels of …

Degradation In Algan/Gan Heterojunction Field Effect Transistors Upon Electrical Stress: Effects Of Field And Temperature, C. Y. Zhu, F. Zhang, Romualdo A. Ferreyra, U. Ozgur, Hadis Morkoç

Electrical and Computer Engineering Publications

AlGaN/GaN heterojunction field effect transistors (HFETs) with 2 μm gate length were subjected to on-state-high-field (high drain bias and drain current) and reverse-gate-bias (no drain currentand reverse gate bias) stress at room and elevated temperatures for up to 10 h. The resulting degradation of the HFETs was studied by direct current and uniquely phase noise before and after stress. A series of drain and gate voltages was applied during the on-state-high-field and reverse-gate-bias stress conditions, respectively, to examine the effect of electric field on degradation of the HFET devices passivated with SiNx. The degradation behaviors under these two types of …

The Effect Of Stair Case Electron Injector Design On Electron Overflow In Ingan Light Emitting Diodes, F. Zhang, X. Li, S. Hafiz, S. Okur, Vitaliy Avrutin, U. Ozgur, Hadis Morkoç, A. Matulionis

Electrical and Computer Engineering Publications

Effect of two-layer (In0.04Ga0.96N and In0.08Ga0.92N) staircase electron injector (SEI) on quantum efficiency of light-emitting-diodes (LEDs) in the context of active regions composed of single and quad 3 nm double heterostructures (DHs) is reported. The experiments were augmented with the first order model calculations of electron overflow percentile. Increasing the two-layer SEI thickness from 4 + 4 nm up to 20 + 20 nm substantially reduced, if not totally eliminated, the electron overflow in single DH LEDs at low injections without degrading the material quality evidenced by the high optical efficiency observed at 15K and room temperature. The improvement in …

Ultra-Low-Energy Non-Volatile Straintronic Computing Using Single Multiferroic Composites, Kuntal Roy

Electrical and Computer Engineering Publications

The primary impediment to continued downscaling of traditional charge-based electronic devices in accordance with Moore's law is the excessive energy dissipation that takes place in the device during switching of bits. One very promising solution is to utilize multiferroicheterostructures, comprised of a single-domain magnetostrictive nanomagnet strain-coupled to a piezoelectric layer, in which the magnetization can be switched between its two stable states while dissipating minuscule amount of energy. However, no efficient and viable means of computing is proposed so far. Here we show that such single multiferroic composites can act as universal logic gates for computing purposes, which we demonstrate …

Reliability Of Algan/Gan High Electron Mobility Transistors On Low Dislocation Density Bulk Gan Substrate: Implications Of Surface Step Edges, N. Killat, M. Montes Bajo, T. Paskova, K. R. Evans, J. Leach, X. Li, Ü. Özgür, Hadis Morkoç, K. D. Chabak, A. Crespo, J. K. Gillespie, R. Fitch, M. Kossler, D. E. Walker, M. Trejo, G. D. Via, J. D. Blevins, M. Kuball

Electrical and Computer Engineering Publications

To enable gaining insight into degradation mechanisms of AlGaN/GaN high electron mobility transistors, devices grown on a low-dislocation-density bulk-GaN substrate were studied. Gateleakage current and electroluminescence (EL) monitoring revealed a progressive appearance of EL spots during off-state stress which signify the generation of gate current leakage paths.Atomic force microscopy evidenced the formation of semiconductor surface pits at the failure location, which corresponds to the interaction region of the gate contact edge and the edges ofsurface steps.

Acoustically Assisted Spin-Transfer-Torque Switching Of Nanomagnets: An Energy-Efficient Hybrid Writing Scheme For Non-Volatile Memory, Ayan K. Biswas, Supriyo Bandyopadhyay, Jayasimha Atulasimha

Electrical and Computer Engineering Publications

We show that the energy dissipated to write bits in spin-transfer-torque random access memory can be reduced by an order of magnitude if a surface acoustic wave (SAW) is launched underneath the magneto-tunneling junctions (MTJs) storing the bits. The SAW-generated strain rotates the magnetization of every MTJs' soft magnet from the easy towards the hard axis, whereupon passage of a small spin-polarized current through a target MTJ selectively switches it to the desired state with > 99.99% probability at room temperature, thereby writing the bit. The other MTJs return to their original states at the completion of the SAW cycle.

Correlation Between Si Doping And Stacking Fault Related Luminescence In Homoepitaxial M-Plane Gan, S. Khromov, B. Monemar, Vitaliy Avrutin, Hadis Morkoç, L. Hultman, G. Pozina

Electrical and Computer Engineering Publications

Si-doped GaN layers grown by metal organic vapor phase epitaxy on m-plane GaN substrates were investigated by low-temperature cathodoluminescence (CL). We have observed stacking fault (SF) related emission in the range of 3.29–3.42 eV for samples with moderate doping, while for the layers with high concentration of dopants, no CL lines related to SFs have been noted. Perturbation of the SF potential profile by neighboring impurity atoms can explain localization ofexcitons at SFs, while this effect would vanish at high doping levels due to screening.

Microscopic Distribution Of Extended Defects And Blockage Of Threading Dislocations By Stacking Faults In Semipolar (1101)(1101)()(1101)() Gan Revealed From Spatially Resolved Luminescence, S. Okur, S. Metzner, N. Izyumskaya, F. Zhang, Vitaliy Avrutin, C. Karbaum, F. Bertram, J. Christen, Hadis Morkoç, Ü. Özgür

Electrical and Computer Engineering Publications

Spatial distribution of extended defects in semipolar -oriented GaN layers grown on patterned(001) Si substrates with striped grooves of varying width was investigated by optical means only using near-field scanning optical microscopy (NSOM) and cathodoluminescence (CL). A high density of basal and prismatic stacking faults was observed in the c⁻ wings, and the threadingdislocations in c+ wings, which appear as dark patterns in the NSOM and CL images, were found to bend toward the surface during the initial stages of growth. In the case when growingc+ front of GaN made contact with the SiO2 masking layer during growth, stacking …

Strain Induced Variations In Band Offsets And Built-In Electric Fields In Ingan/Gan Multiple Quantum Wells, L. Dong, J. V. Mantese, Vitaliy Avrutin, Ü. Özgür, H. Morkoç, S. P. Alpay

Electrical and Computer Engineering Publications

The band structure, quantum confinement of charge carriers, and their localization affect the optoelectronic properties of compound semiconductor heterostructures and multiple quantum wells (MQWs). We present here the results of a systematic first-principles based density functional theory (DFT) investigation of the dependence of the valence band offsets and band bending in polar and non-polar strain-free and in-plane strained heteroepitaxial In x Ga1- xN(InGaN)/GaN multilayers on the In composition and misfit strain. The results indicate that for non-polar m-plane configurations with [12¯10]InGaN // [12¯10]GaN and [0001]InGaN // [0001]GaN epitaxial alignments, the valence band offset changes linearly from 0 to 0.57 eV …

Enhanced Microwave Dielectric Tunability Of Ba0.5sr0.5tio3 Thin Films Grown With Reduced Strain On Dysco3 Substrates By Three-Step Technique, Hongrui Liu, Vitaliy Avrutin, Congyong Zhu, Ümit Özgür, Juan Yang, Changzhi Lu, Hadis Morkoç

Electrical and Computer Engineering Publications

Tunable dielectric properties of epitaxial ferroelectric Ba_0.5Sr_0.5TiO₃ (BST) thin films deposited on nearly lattice-matched DyScO₃ substrates by radio frequency magnetron sputtering have been investigated at microwave frequencies and correlated with residual compressive strain. To reduce the residual strain of the BST films caused by substrate clamping and improve their microwave properties, a three-step deposition method was devised and employed. A high-temperature deposition at 1068 K of the nucleation layer was followed by a relatively low-temperature deposition (varied in the range of 673–873 K) of the BST interlayer and a high-temperature deposition at 1068 K …

Spectral Distribution Of Excitation-Dependent Recombination Rate In An In0.13ga0.87n Epilayer, K. Jarašiūnas, S. Nargelas, R. Aleksiejūnas, S. Miasojedovas, M. Vengris, S. Okur, H. Morkoç, Ü Özgür, C. Giesen, Ö. Tuna, M. Heuken

Electrical and Computer Engineering Publications

Time-resolved optical techniques of photoluminescence (PL), light-induced transient grating(LITG), and differential transmission spectroscopy were used to investigate carrier dynamics in a single 50-nm thick In_0.13Ga_0.97N epilayer at high photoexcitation levels. Data in wide spectral, temporal, excitation, and temperature ranges revealed novel features in spectral distribution of recombination rates as follows: at low injection levels, an inverse correlation of carrier life time increasing with temperature and diffusivity decreasing with temperature confirmed a mechanism of diffusion-limited nonradiative recombination at extended defects. Carrier dynamics in the spectral region below the absorption edge but ∼70 meV above the PL band …

Optical Studies Of Strain And Defect Distribution In Semipolar (1(1)Over-Bar01) Gan On Patterned Si Substrates, N. Izyumskaya, F. Zhang, S. Okur, T. Selden, V. Avrutin, Ü. Özgür, S. Metzner, C. Karbaum, F. Bertram, J. Christen, H. Morkoç

Electrical and Computer Engineering Publications

Formation of defects in semipolar ( 11¯01 )-oriented GaN layers grown by metal-organic chemical vapor deposition on patterned Si (001) substrates and their effects on optical properties were investigated by steady-state and time-resolved photoluminescence (PL) and spectrally and spatially resolved cathodoluminescence (CL). Near-band edge emission is found to be dominant in the c +-wings of semipolar ( 11¯01 )GaN, which are mainly free from defect-related emission lines, while the c – wings contain a large number of basal stacking faults. When the advancing c+ and c — fronts meet to coalesce into a continuous film, the existing stacking faults contained …

Extending Device Performance In Photonic Devices Using Piezoelectric Properties, Gregory Edward Triplett

Electrical and Computer Engineering Publications

This study focuses on the influence of epi-layer strain and piezoelectric effects in asymmetric GaInAs/GaAlAs action regions that potentially lead to intra-cavity frequency mixing. The theoretical limits for conduction and valence band offsets in lattice-matched semiconductor structures have resulted in the deployment of non-traditional approaches such as strain compensation to extend wavelength in intersubband devices, where strain limits are related to misfit dislocation generation. Strain and piezoelectric effects have been studied and verified using select photonic device designs. Metrics under this effort also included dipole strength, oscillator strength, and offset of energy transitions, which are strongly correlated with induced piezoelectric …

Pseudomorphic Growth Of Inas On Misoriented Gaas For Extending Quantum Cascade Laser Wavelength, Gregory Edward Triplett, Charles Meyer, Emily Cheng, Justin Grayer, David Mueller, Denzil Roberts, Samuel Graham

Electrical and Computer Engineering Publications

The authors have studied the impact of epilayer strain on the deposition of InAs/GaAs on (100) and (111)B with 2 degrees offset toward 2-1-1 surfaces. Consequences of a 7% lattice mismatch between these orientations in the form of three-dimensional growth are less apparent for (111)B with 2 degrees offset toward 2-1-1 surfaces compared to (100). By exploring a range of molecular beam epitaxy process parameters for InAs/GaAs growth and utilizing scanning electron microscopy, atomic force microscopy, and Raman spectroscopy to evaluate the quality of these strained layers, the authors develop empirical models that describe the influence of the process conditions …

Producing Children's Toys Through 3-D Printing: A Multidisciplinary Approach, Rebekah Rifareal

Auctus: The Journal of Undergraduate Research and Creative Scholarship

One of the things that first attracted me to VCU was the opportunity for interdisciplinary discussions and interactions. I saw HSURP as a way to push my boundaries and interact with peers from different disciplines. When I saw the Social Design and 3-D Printing project, it just clicked. I saw the opportunity for engineering, for arts, for research, for graphic design. All of the things I was interested in learning about all came together.