Engineering Commons^™

Effective Ionic Conductivity Of A Novel Intermediate-Temperature Mixed Oxide-Ion And Carbonate-Ion Conductor, Xue Li, Guoliang Xiao, Kevin Huang

Faculty Publications

A systematic investigation on the effective ionic conductivity (σ_m) of a novel intermediate-temperature mixed oxide-ion and carbonate-ion conductor MOCC consisting of a ceria phase and a carbonate phase is reported. The study explicitly shows that the observed remarkable temperature-dependent σ_m is primarily the result of softening/melting of the carbonate phase as the physical state of the carbonate phase transforms from solid, softened to molten. Differential scanning calorimetry analysis complements the understanding of the observed electrical behavior by revealing temperatures of melting and solidification in agreement with the onset temperatures of σ_m. In addition, the …

Optimization Design Of Electrodes For Anode-Supported Solid Oxide Fuel Cells Via Genetic Algorithm, Junxiang Shi, Xingjian Xue

Faculty Publications

Porous electrode is the critical component of solid-oxide fuel cells (SOFCs) and provides a functional material backbone for multi-physicochemical processes. Model based electrode designs could significantly improve SOFC performance. This task is usually performed via parameter studies for simple case and assumed property distributions for graded electrodes. When nonlinearly coupled multiparameters of electrodes are considered, it could be very difficult for the model based parameter study method to effectively and systematically search the design space. In this research, the optimization approach with a genetic algorithm is demonstrated for this purpose. An anode-supported proton conducting SOFC integrated with a fuel supply …

Geometry-Dependent Oxygen Diffusion Flux And Limiting Current Density Of The Cathode In A Cathode-Supported Solid Oxide Fuel Cell, Kevin Huang, James L. Shull

Faculty Publications

An analysis is performed on the diffusion of oxygen through tubular porous cathode substrates having several different geometries. It is shown that the flux of oxygen as it diffuses through these different substrate geometries can be explicitly expressed by a general analytical form with a unique geometric factor for each type of substrate geometry. Experimental measurements of the geometry-independent term, oxygen diffusivity, were conducted for two representative geometries: cylindrical and triangular tubes. These measurements show good agreement between samples with similar porosities and thus favorably support the oxygen flux equations presented. Formulations for the limiting current density were also derived …

Structures Of Human Thymidylate Synthase R163k With Dump, Fdump And Glutathione Show Asymmetric Ligand Binding, Lydia M. Gibson, Lesa R. Celeste, Leslie L. Lovelace, Lukasz Lebioda

Faculty Publications

Thymidylate synthase (TS) is a well validated target in cancer chemotherapy. Here, a new crystal form of the R163K variant of human TS (hTS) with five subunits per asymmetric part of the unit cell, all with loop 181-197 in the active conformation, is reported. This form allows binding studies by soaking crystals in artificial mother liquors containing ligands that bind in the active site. Using this approach, crystal structures of hTS complexes with FdUMP and dUMP were obtained, indicating that this form should facilitate high-throughput analysis of hTS complexes with drug candidates. Crystal soaking experiments using oxidized glutathione revealed that …

Doping Dependence Of Electronic And Mechanical Properties Of Gase1−XTeX And Ga1−XInXSe From First Principles, Zs. Rak, S. D. Mahanti, K. C. Mandal, N. C. Fernelius

Faculty Publications

No abstract provided.

Cathode Polarizations Of A Cathode-Supported Solid Oxide Fuel Cell, Kevin Huang, Alessandro Zampieri, Martin Ise

Faculty Publications

The concentration, activation, and total polarizations of the cathode in a cathode-supported solid oxide fuel cell (SOFC) were theoretically and experimentally investigated. In the theoretical analysis, the exchange current density of the charge transfer was considered to be dependent on the P_O2 determined by the preceding O₂ diffusion, resulting in an interrelationship between activation and concentration polarizations. The established nonlinear polarization equations were then applied to solve the key parameters with area specific resistances and overpotentials of the polarizations experimentally measured by electrochemical impedance spectroscopy on an operating cathode-supported SOFC. To ensure the consistency and meaningfulness of …

Modelling And Verification Of Response Of Rc Slabs Strengthened In Flexure With Mechanically Fastened Frp Laminates, Annalisa Napoli, Fabio Matta, Enzo Martinelli, Antonio Nanni, Roberto Realfonzo

Faculty Publications

Mechanically fastened fibre-reinforced polymer laminate systems are emerging as a promising means for the repair and strengthening of reinforced concrete members. This technology entails the use of pultruded carbon- and glass- vinyl ester fibre-reinforced polymer laminates with enhanced longitudinal bearing strength that are connected to the concrete substrate by means of steel anchors. Attractive applications are those for emergency repairs where constructability and speed of installation are critical requirements. In this paper, an experimental investigation is first presented that included laboratory testing of scaled reinforced concrete slabs strengthened with four different combinations of laminate lengths and fastener layouts to study …

A Miniature Energy Harvesting Device For Wireless Sensors In Electric Power System, Rashed H. Bhuiyan, Roger A. Dougal, Mohammod Ali

Faculty Publications

A novel energy harvesting device called the energy coupler is proposed which can provide power to small wireless sensors in a power system. The energy coupler when coupled electromagnetically to a nearby current carrying conductor scavenges ac power from the conductor. The proposed energy coupler converts the harvested ac power into dc using a passive voltage multiplier circuit. The design of the energy coupler is such that the dc power obtained is adequate to charge a miniature 1.2-V rechargeable battery. It is demonstrated that the energy coupler is capable of delivering 10 mW of dc power to a 50-Ω load. …

5 Ghz Band Vehicle-To-Vehicle Channels: Models For Multiple Values Of Channel Bandwidth, Qiong Wu, David W. Matolak, Indranil Sen

Faculty Publications

In Sen and Matolak's earlier paper, 5-GHz-band vehicle-to-vehicle (V2V) channel models were presented for channel bandwidths of 5 and 10 MHz. In this paper, we provide additional tapped delay line models for bandwidths of 1, 20, 33.33, and 50 MHz based upon the data used in Sen and Matolak's paper. We provide tables of channel parameters for five types of V2V channel classes and also include example tap correlation coefficients. Root-mean-square delay spread values are summarized, as are values of bandwidth for which the channel frequency correlation takes values of 0.7 and 0.5. As with the results from Sen and …

Fpga Acceleration Of The Phylogenetic Likelihood Function For Bayesian Mcmc Inference Methods, Stephanie Zierke, Jason D. Bakos

Faculty Publications

Background
Likelihood (ML)-based phylogenetic inference has become a popular method for estimating the evolutionary relationships among species based on genomic sequence data. This method is used in applications such as RAxML, GARLI, MrBayes, PAML, and PAUP. The Phylogenetic Likelihood Function (PLF) is an important kernel computation for this method. The PLF consists of a loop with no conditional behavior or dependencies between iterations. As such it contains a high potential for exploiting parallelism using micro-architectural techniques. In this paper, we describe a technique for mapping the PLF and supporting logic onto a Field Programmable Gate Array (FPGA)-based co-processor. By leveraging …

Reverberation-Chamber Test Environment For Outdoor Urban Wireless Propagation Studies, Helge Fielitz, Kate A. Remley, Christopher L. Holloway, Qian Zhang, Qiong Wu, David W. Matolak

Faculty Publications

We introduce a test environment to replicate the well-known clustering of reflections in power delay profiles arising from late-time delays and reflections. Urban wireless propagation environments are known to exhibit such clustering. The test setup combines discrete reflections generated by a fading simulator with the continuous distribution of reflections created in a reverberation chamber. We describe measurements made in an urban environment in Denver, CO, that illustrate these multiple distributions of reflections. Our comparison of measurements made in the urban environment to those made in the new test environment shows good agreement.

Adhesion At Diamond /Metal Interfaces: A Density Functional Theory Study, Haibo Guo, Yue Qi, Xiaodong Li

Faculty Publications

To understand the basic material properties required in selecting a metallic interlayer for enhanced adhesion of diamondcoatings on the substrates, the interfaces between diamond and metals with different carbide formation enthalpies (Cu, Ti, and Al) are studied using density functional theory. It is found that the work of separation decreases, while the interface energy increases, with the carbide formation enthalpy ΔHf (Tiy_s (Ti>Cu>Al), is needed to achieve a higher overall interface strength. In addition, when the surface energy is larger than the interface energy, a wetted diamond/metal interface is formed during diamondnucleation, providing the strongest adhesion …

Statistical Approach For Yield Optimization For Minimum Energy Operation In Subthreshold Circuits Considering Variability Issues, Md. Waliullah Khan Nomani, Mohab Anis, Goutam Koley

Faculty Publications

The supply voltage (V-dd) and threshold voltage (V-th) are two significant design variables that directly impact the performance and power consumption of circuits. The scaling of these voltages has become a popular option to satisfy performance and low power requirements. Subthreshold operation is a compelling approach for energy-constrained applications where processor speed is less important. However, subthreshold designs show dramatically increased sensitivity to process variations due to the exponential relationship of subthreshold drive current with V-th variation and drastically growing leakage power. If there is uncertainty in the value of the threshold or supply voltage, the power advantages of this …

Far-Field Optical Nanoscopy Based On Continuous Wave Laser Stimulated Emission Depletion, C. Kuang, Wei Zhao, Guiren Wang

Faculty Publications

Stimulated emission depletion (STED) microscopy is one of the breakthrough technologies that belong to far-field optical microscopy and can achieve nanoscale spatial resolution. We demonstrate a far-field optical nanoscopy based on continuous wave lasers with different wavelengths, i.e., violet and green lasers for excitation and STED, respectively. Fluorescent dyes Coumarin 102 and Atto 390 are used for validating the depletion efficiency. Fluorescent nanoparticles are selected for characterizing the spatial resolution of the STED system. Linear scanning of the laser beams of the STED system along one line of a microscope slide, which is coated with the nanoparticles, indicates that a …

High-Performance Heterogeneous Computing With The Convey Hc-1, Jason D. Bakos

Faculty Publications

Unlike other socket-based reconfigurable coprocessors, the Convey HC-1 contains nearly 40 field-programmable gate arrays, scatter-gather memory modules, a high-capacity crossbar switch, and a fully coherent memory system.

Multimetallic Electrocatalysts Of Pt, Ru, And Ir Supported On Anatase And Rutile Tio2 For Oxygen Evolution In An Acid Environment, Roderick E. Fuentes, Jake Farell, John W. Weidner

Faculty Publications

Anatase and rutile TiO2 were investigated as stable supports for different multimetallic nanoparticles (i.e., Pt:Ru, Pt:Ir, Pt:Ru:Ir, and Ir:Ru) and tested for activity toward the oxygen evolution reaction (OER). Overall, Ir:Ru had the highest activity toward OER (i.e., current per gram of metal) compared to the other multimetallic combinations studied. This bimetallic supported on anatase TiO2 had a 53% higher current per gram of metal than an unsupported electrocatalyst of the same composition. The higher catalyst utilization of the supported electrocatalysts for OER is consistent with small, well-dispersed nanoparticles, which were observed in high resolution transmission electron microscopy images.

Quantifying Individual Potential Contributions Of The Hybrid Sulfur Electrolyzer, John A. Staser, Maximilian B. Gorensek, John W. Weidner

Faculty Publications

The hybrid sulfur cycle has been investigated as a means to produce clean hydrogen efficiently on a large scale by first decomposing H₂SO₄ to SO₂, O₂, and H₂O and then electrochemically oxidizing SO₂ back to H₂SO₄ with the cogeneration of H₂. Thus far, it has been determined that the total cell potential for the hybrid sulfur electrolyzer is controlled mainly by water transport in the cell. Water is required at the anode to participate in the oxidation of SO₂ to H₂SO_{4 …}

Maximizing The Life Of A Lithium-Ion Cell By Optimization Of Charging Rates, Saeed Khaleghi Rahimian, Sean Rayman, Ralph E. White

Faculty Publications

Using a dynamic optimization method, the optimum charge currents as a function of cycle number during cycling for the lithium-ion cell are obtained. A single particle physics-based model, which includes capacity fade, was applied to simulate the cell performance under low earth-orbit (LEO) cycling conditions. Useful cell life is defined as the number of cycles before the end of discharge voltage drops below 3.0 V or the cell discharge capacity becomes less than 20% of the original discharge capacity. The simulated useful cell life can be increased by ∼29.28% by varying the charge current.

Structural Health Monitoring With Piezoelectric Wafer Active Sensors--Predictive Modeling And Simulation, Victor Giurgiutiu

Faculty Publications

This paper starts a review of the state of the art in structural health monitoring with piezoelectric wafer active sensors and follows with highlighting the limitations of the current approaches which are predominantly experimental. Subsequently, the paper examines the needs for developing a predictive modeling methodology that would allow to perform extensive parameter studies to determine the sensing method’s sensitivity to damage and insensitivity to confounding factors such as environmental changes, vibrations, and structural manufacturing variability. The thesis is made that such a predictive methodology should be multi-scale and multi-domain, thus encompassing the modeling of structure, sensors, electronics, and power …

A Novel Far-Field Nanoscopic Velocimetry For Nanofluidics, C. Kuang, Guiren Wang

Faculty Publications

For the first time we have been able to measure the flow velocity profile for nanofluidics with a spatial resolution better than 70 nm. Due to the diffraction resolution barrier, traditional optical methods have so far failed in measuring the velocity profile in a nanocapillary or a closed nanochannel without an opened sidewall. A novel optical point measurement method is presented which applies stimulated emission depletion (STED) microscopy to laser induced fluorescence photobleaching anemometer (LIFPA) techniques to measure flow velocity. Herein we demonstrate this far-field nanoscopic velocimetry method by measuring the velocity profile in a nanocapillary with an inner diameter …

Structural Health Monitoring With Piezoelectric Wafer Active Sensors—Predictive Modeling And Simulation, Victor Giurgiutiu

Faculty Publications

This paper starts a review of the state of the art in structural health monitoring with piezoelectric wafer active sensors and follows with highlighting the limitations of the current approaches which are predominantly experimental. Subsequently, the paper examines the needs for developing a predictive modeling methodology that would allow to perform extensive parameter studies to determine the sensing method’s sensitivity to damage and insensitivity to confounding factors such as environmental changes, vibrations, and structural manufacturing variability. The thesis is made that such a predictive methodology should be multi-scale and multi-domain, thus encompassing the modeling of structure, sensors, electronics, and power …

Comparison Of Stabilization Methods For Fixed-Speed Wind Generator Systems, Mohammod Ali, Bin Wu

Faculty Publications

Static Synchronous Compensator (STATCOM), Pitch control system, Braking Resistor (BR), and Superconducting Magnetic Energy Storage (SMES) have recently been reported as stabilization methods for fixed-speed wind generator systems. although the individual technologies are well documented, a comparative study of these systems has not been reported so far. This paper aims to fill in the gap, and provides a comprehensive analysis of these stabilization methods for fixed-speed wind generator systems. The analysis is performed in terms of transient stability enhancement, controller complexity, and cost. a novel feature of this work is that the transient stability analysis of wind generator system is …

Genome3d: A Viewer-Model Framework For Integrating And Visualizing Multi-Scale Epigenomic Information Within A Three-Dimensional Genome, Thomas M. Asbury, Matt Mitman, Jijun Tang, W. Jim Zheng

Faculty Publications

Background
New technologies are enabling the measurement of many types of genomic and epigenomic information at scales ranging from the atomic to nuclear. Much of this new data is increasingly structural in nature, and is often difficult to coordinate with other data sets. There is a legitimate need for integrating and visualizing these disparate data sets to reveal structural relationships not apparent when looking at these data in isolation.

Results
We have applied object-oriented technology to develop a downloadable visualization tool, Genome3D, for integrating and displaying epigenomic data within a prescribed three-dimensional physical model of the human genome. In order …

Using Jackknife To Assess The Quality Of Gene Order Phylogenies, Jian Shi, Yiwei Zhang, Haiwei Luo, Jijun Tang

Faculty Publications

Background
In recent years, gene order data has attracted increasing attention from both biologists and computer scientists as a new type of data for phylogenetic analysis. If gene orders are viewed as one character with a large number of states, traditional bootstrap procedures cannot be applied. Researchers began to use a jackknife resampling method to assess the quality of gene order phylogenies.

Results
In this paper, we design and conduct a set of experiments to validate the performance of this jackknife procedure and provide discussions on how to conduct it properly. Our results show that jackknife is very useful to …

Integrated Circuit Implementation For A Gan Hfet Driver Circuit, Bo Wang, Jason D. Bakos, Antonello Monti

Faculty Publications

This paper presents the design and implementation of a new integrated circuit (IC) that is suitable for driving the new generation of high-frequency GaN HFETs. The circuit, based upon a resonant switching transition technique, is first briefly described and then discussed in detail, focusing on the design process practical considerations. A new level-shifter topology, used to generate the zero and negative gate-source voltages required to switch the GaN HFET, is introduced and analyzed. The experimental measurements included in this paper report the results of tests carried out on an IC designed and fabricated as part of the multiproject die in …

Mesoporous Tin Oxide As An Oxidation-Resistant Catalyst Support For Proton Exchange Membrane Fuel Cells, Peng Zhang, Sheng-Yang Huang, Branko N. Popov

Faculty Publications

Mesoporous catalyst support based on tin oxide (SnO₂) is synthesized with high surface area of 205 m² g⁻¹ and with narrow pore size distribution. Modified polyol method is used to deposit platinum on SnO₂. The physical properties of the support and the SnO₂-supported Pt catalyst (Pt/SnO₂) are characterized by using the Brunauer, Emmett, and Teller method, X-ray diffraction, and transmission electron microscopy. The electrochemical stability and durability of the Pt/SnO₂ catalyst are investigated by the accelerated stress tests proposed by the U.S. Department of Energy. Pt/SnO₂ catalyst exhibits …

Theoretical Analysis Of Stresses In A Lithium Ion Cell, Sindhuja Renganathan, Godfrey Sikha, Shriram Santhanagopalan, Ralph E. White

Faculty Publications

A mathematical model to simulate the generation of mechanical stress during the discharge process in a dual porous insertion electrode cell sandwich comprised of lithium cobalt oxide and carbon is presented. The model attributes stress buildup within intercalation electrodes to two different aspects: changes in the lattice volume due to intercalation and phase transformation during the charge/discharge process. The model is used to predict the influence of cell design parameters such as thickness, porosity, and particle size of the electrodes on the magnitude of stress generation. The model developed in this study can be used to understand the mechanical degradation …

An Efficient Electrochemical–Thermal Model For A Lithium-Ion Cell By Using The Proper Orthogonal Decomposition Method, Long Cai, Ralph E. White

Faculty Publications

The proper orthogonal decomposition method was applied to develop an efficient, reduced order electrochemical–thermal model for a lithium-ion cell. This model was validated for discharge simulations over a wide range of C rates and various cooling conditions of the cell. The reduced order model agrees well with the COMSOL model, a commercial finite element method solver, and requires times less computation time than the COMSOL model. The model predictions indicate that the discharge time or percent of capacity removed from the cell at an end of discharge voltage of 3.0 V depends on the rate of the discharge and heat …