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Articles 2191 - 2220 of 2359

Full-Text Articles in Engineering

Steady-State Modeling Of A Parallel-Plate Electrochemical Fluorination Reactor, Kamal Jha, Gerald L. Bauer, John W. Weidner Jan 1998

Steady-State Modeling Of A Parallel-Plate Electrochemical Fluorination Reactor, Kamal Jha, Gerald L. Bauer, John W. Weidner

Faculty Publications

A steady-state mathematical model of a parallel-plate reactor was developed for studying the electrochemical fluorination of organic compounds dissolved in anhydrous hydrogen fluoride. The model incorporates two-phase flow with differential material, energy, and pressure balances. Profiles of temperature, pressure, vapor volume fraction, and current density in the reactor are presented at two inlet temperatures to provide insight into the operation of the reactor. The effects of the inlet temperature, feed flow rate, and cell current on the cell pack voltage and current efficiency of the reactor are presented to determine problematic operating regions for the reactor. Optimum operating currents based …

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The Effect Of Particle Size On The Discharge Performance Of A Nickel-Metal Hydride Cell, Jussi M. Heikonen, Harry J. Ploehn, Ralph E. White Jan 1998

The Effect Of Particle Size On The Discharge Performance Of A Nickel-Metal Hydride Cell, Jussi M. Heikonen, Harry J. Ploehn, Ralph E. White

Faculty Publications

We investigate the effect of particle size on the discharge performance of a nickel-metal hydride cell with a mathematical model. Electrodes with uniform as well as with nonuniform particle sizes are studied. With uniform particle size, the dependence of the particle-to-particle resistance on the particle size is taken into account. The optimal particle size depends on the discharge rate. Moreover, we show that under certain conditions it is advantageous to use a nonuniform particle size. In general, the higher the discharge current density, the more the particle size affects the electrode performance.

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Measurement Of Thin Liquid Film Drainage Using A Novel High-Speed Impedance Analyzer, Kevin O. Hool, Robert C. Saunders, Harry J. Ploehn Jan 1998

Measurement Of Thin Liquid Film Drainage Using A Novel High-Speed Impedance Analyzer, Kevin O. Hool, Robert C. Saunders, Harry J. Ploehn

Faculty Publications

This work describes the design and implementation of a new instrument, called the thin film impedance analyzer, which measures the rate of drainage of thin oil films. The instrument forms an oil film by elevating a planar oil–water interface into a water drop hanging from a stainless steel capillary tube immersed in the oil. The instrument measures the magnitude of the impedance of the matter between the capillary tube and a screen electrode immersed in the lower water phase. Under appropriate conditions, the capacitance of the oil film dominates the impedance. The instrument records the increase in the magnitude of …

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Agent Jurisprudence, Michael N. Huhns, Munindar P. Singh Jan 1998

Agent Jurisprudence, Michael N. Huhns, Munindar P. Singh

Faculty Publications

The agent metaphor comes packaged with a number of powerful abstractions. Some of these are psychological, such as beliefs, knowledge, and intentions-abstractions that were traditionally studied in AI. However, there are a number of other abstractions that the agent metaphor brings to the fore. Of these, one has been emphasizing the social abstractions. Close cousins of the social abstractions are the ethical and legal abstractions. These too are being recognized as increasingly important in developing agents that are not only sociable, but also well behaved.

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Electrode Performance Test On Single Ceramic Fuel Cells Using As Electrolyte Sr‐ And Mg‐Doped Lagao3, Kevin Huang, Man Feng, John B. Goodenough, Christopher Milliken Oct 1997

Electrode Performance Test On Single Ceramic Fuel Cells Using As Electrolyte Sr‐ And Mg‐Doped Lagao3, Kevin Huang, Man Feng, John B. Goodenough, Christopher Milliken

Faculty Publications

The electrode performance of a single solid oxide fuel cell was evaluated using a 500 μm thick La0.9Sr0.1Ga0.8Mg0.2O2.85 (LSGM) as the electrolyte membrane. Comparison of La0.6Sr0.4CoO3-δ (LSCo) and La0.9Sr0.1MnO3 (LSM) as cathodes showed LSCo gave an exchange current density two orders of magnitude higher than that of LSM. Comparison of CeO2/Ni and LSGM/Ni as anodes showed a degradation of the latter with time, and studies of the anode‐electrolyte interface and the reactivity of NiO and LSGM suggest better anode …

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A Novel Laboratory Course On Advanced Chemical Engineering Experiments, Jochen A. Lauterbach, S. White, X. Lui, G. M. Bodner, W. N. Delgass Oct 1997

A Novel Laboratory Course On Advanced Chemical Engineering Experiments, Jochen A. Lauterbach, S. White, X. Lui, G. M. Bodner, W. N. Delgass

Faculty Publications

The chemical engineering curriculum in the United States has trained generations of technical experts who have successfully optimized chemical processes and products once they entered the chemical industry. The U.S. chemical industry, however, has entered a critical stage in which it must be able to create new and differentiated value through technical innovations that arc essential for long-term survival. This innovation process will require new skills that go far beyond the traditional expertise for the optimization of tasks possessed by young chemical engineers. The innovators must be able to identify new opportunities, explore the boundaries of technology, evaluate critical issues, …

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An Ontology Tool For Distributed Information Environments, Kuhanandha Mahalingam, Michael N. Huhns Jun 1997

An Ontology Tool For Distributed Information Environments, Kuhanandha Mahalingam, Michael N. Huhns

Faculty Publications

This paper describes how ontologies can be used for query formulation and semantic reconciliation in large distributed information environments. It presents a tool, written in Java, that can be used to create and browse ontologies, and construct ontology-based queries. The tool incorporates several abstraction mechanisms that enable users to manage large ontologies, which are typical of large information environments. The tool is being applied to an information system for healthcare administrators, which spans hospitals, clinics, and governmental health departments.

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Chemical Stability Study Of Bace0.9Nd0.1O3−Α High Temperature Proton-Conducting Ceramic, Fanglin Chen, O. Toft Sorensen, Guangyao Meng, Dingkum Peng Jan 1997

Chemical Stability Study Of Bace0.9Nd0.1O3−Α High Temperature Proton-Conducting Ceramic, Fanglin Chen, O. Toft Sorensen, Guangyao Meng, Dingkum Peng

Faculty Publications

BaCe0.9Nd0.1O3−a (BCN) ceramic is known to be an excellent high-temperature proton conductor and is a candidate electrolyte for use in solid oxide fuel cells, hydrogen or steam sensors and steam electrolysers. In this work, the chemical stability of BCN was investigated systematically by combining XRD and DTA–TG techniques to study its processing compatibility and its feasibility in potential applications. It was found that above 1200 °C, BCN reacted with alumina or zirconia, leading to the loss of barium and an excess of cerium. In cold water, both sintered BCN disks and powder samples had very …

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Ellipsometric And Raman Spectroscopic Study Of Thermally Formed Films On Titanium, E. Hristova, Lj. Arsov, Branko N. Popov, Ralph E. White Jan 1997

Ellipsometric And Raman Spectroscopic Study Of Thermally Formed Films On Titanium, E. Hristova, Lj. Arsov, Branko N. Popov, Ralph E. White

Faculty Publications

Thermal films on titanium surfaces were formed by heating titanium samples in air at atmospheric pressure. The optical constants, thickness, and structure of the formed films at various temperatures and times of heating were investigated by ellipsometry and Raman spectroscopy. The complex index of refraction and the thickness of generated films were determined by comparing the experimental loci and obtained by ellipsometric measurements with theoretical computed vs. curves. It was found that the thickness in homogeneity and porosity of formed films increase with increasing temperature and the duration of the thermal treatment. Beyond a certain critical temperature, the appearance of …

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The Effects Of Organic Compounds On Inhibition Of Hydrogen Permeation Through A Mild Steel Membrane, H. A. Duarte, D. M. See, Branko N. Popov, Ralph E. White Jan 1997

The Effects Of Organic Compounds On Inhibition Of Hydrogen Permeation Through A Mild Steel Membrane, H. A. Duarte, D. M. See, Branko N. Popov, Ralph E. White

Faculty Publications

The effectiveness of 5-(4-pyridyl)-2,7-nonadiene, and 1 phenyl-2-propyn-ol (PP) on inhibition of the hydrogen evolution reaction on a 1010 steel membrane and on the degree of hydrogen ingress into the membrane was determined. Hydrogen evolution rates and permeation currents were monitored as a function of time at different applied potentials. In the presence of 0.5 g/liter PP in the electrolyte, the hydrogen discharge and permeation current density were inhibited by 98 and95%, respectively.

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The Agent Test, Michael N. Huhns, Munindar P. Singh Jan 1997

The Agent Test, Michael N. Huhns, Munindar P. Singh

Faculty Publications

The authors consider agents on the World Wide Web, including information retrieval agents. They propose a test for agenthood, involving communication in multi-agent systems.

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Internet-Based Agents: Applications And Infrastructure, Munindar P. Singh, Michael N. Huhns Jan 1997

Internet-Based Agents: Applications And Infrastructure, Munindar P. Singh, Michael N. Huhns

Faculty Publications

Software agents are mitigating the complexity of modern information systems—technically by providing a locus for managing information subsets, and psychologically by providing an abstraction for human interaction with them.

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Mobile Agents, Michael N. Huhns, Munindar P. Singh Jan 1997

Mobile Agents, Michael N. Huhns, Munindar P. Singh

Faculty Publications

A lot of agents are executing on the Web, and some of them are starting to move around. While most agents are static (existing as a single process or thread on one host), others can pick up and move their code and data to a new host where they resume executing.

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Conversational Agents, Michael N. Huhns, Munindar P. Singh Jan 1997

Conversational Agents, Michael N. Huhns, Munindar P. Singh

Faculty Publications

When you build or buy an agent for the Web, you want it to perform as well as possible. Increasingly, this means your agent should take advantage not only of the Web's information resources, but also of all the other agents that might be operating there.

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Agents Are Everywhere!, Michael N. Huhns, Munindar P. Singh Jan 1997

Agents Are Everywhere!, Michael N. Huhns, Munindar P. Singh

Faculty Publications

A decade ago this claim would have evoked images from the Cold War—and probably gotten this column classified! Today, it describes one of the hottest technical areas on the Internet.

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Hierarchical Classification As An Aid To Browsing, John R. Rose, Caroline M. Eastman Jan 1997

Hierarchical Classification As An Aid To Browsing, John R. Rose, Caroline M. Eastman

Faculty Publications

An approach to browsing large chemical reaction databases is presented. The method that is described builds on earlier work in which unsupervised hierarchical classification was used to extract generalizations of reaction classes from reaction databases for use in reaction knowledge bases. The method described in this paper involves classification based on both semantic and topological features. It supports the creation of deep hierarchies in which succeeding levels represent increasing degrees of abstraction. The creation of a hierarchy allows the user to quickly locate interesting items or classes of items by performing a tree traversal as opposed to sequentially scanning a …

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Ontologies For Agents, Michael N. Huhns, Munindar P. Singh Jan 1997

Ontologies For Agents, Michael N. Huhns, Munindar P. Singh

Faculty Publications

An ontology is a computational model of some portion of the world. It is often captured in some form of a semantic network-a graph whose nodes are concepts or individual objects and whose arcs represent relationships or associations among the concepts. This network is augmented by properties and attributes, constraints, functions, and rules that govern the behavior of the concepts. Formally, an ontology is an agreement about a shared conceptualization, which includes frameworks for modeling domain knowledge and agreements about the representation of particular domain theories. Definitions associate the names of entities in a universe of discourse (for example, classes, …

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Preparation Of Nd-Doped Baceo3 Proton-Conducting Ceramics By Homogeneous Oxalate Coprecipitation, Fanglin Chen, Ping Wang, O. Toft Sorensen, Guangyao Meng, Dingkum Peng Jan 1997

Preparation Of Nd-Doped Baceo3 Proton-Conducting Ceramics By Homogeneous Oxalate Coprecipitation, Fanglin Chen, Ping Wang, O. Toft Sorensen, Guangyao Meng, Dingkum Peng

Faculty Publications

Nd-doped BaCeO3 have been obtained from homogeneous coprecipitated oxalates when calcined at temperatures T≥1000 °C. Ball-milling of the calcined powders well disperses the agglomerates and consequently has a beneficial effect in the densification process. The calcination temperature has a major influence on the sintering process and powders calcined at 1100 °C possess good sinterabilities. The pressure applied to press the green pellets has no apparent influence on the sintered density at sintering temperatures of T≥1400 °C. By controlling the processing variables it was possible to obtain near fully dense Nd-doped BaCeO3 ceramics with homogeneous microstructure at a sintering …

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Governing Equations For Transport In Porous Electrodes, Pauline De Vidts, Ralph E. White Jan 1997

Governing Equations For Transport In Porous Electrodes, Pauline De Vidts, Ralph E. White

Faculty Publications

No abstract provided.

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Mathematical Modeling Of Proton‐Exchange‐Membrane Fuel‐Cell Stacks, Dhanwa Thirumalai, Ralph E. White Jan 1997

Mathematical Modeling Of Proton‐Exchange‐Membrane Fuel‐Cell Stacks, Dhanwa Thirumalai, Ralph E. White

Faculty Publications

No abstract provided.

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Electrowinning Of Nonnoble Metals With Simultaneous Hydrogen Evolution At Flow-Through Porous Electrodes Iii. Time Effects, Mahmoud M. Saleh, John W Weidner, Bahgat E. El-Anadouli, Badr G. Ateya Jan 1997

Electrowinning Of Nonnoble Metals With Simultaneous Hydrogen Evolution At Flow-Through Porous Electrodes Iii. Time Effects, Mahmoud M. Saleh, John W Weidner, Bahgat E. El-Anadouli, Badr G. Ateya

Faculty Publications

The electrowinning of zinc from a recirculating alkaline zincate solution at a flow-through porous electrode was investigated. Experimental results were obtained to test the predictions of a mathematical model. The effects of electrolyte flow rate, cell current, and electrode thickness on the concentration-time relations and coulombic efficiency-time relations were studied. The experimental results show that the highest recovery rate was obtained at both high flow rates and cell currents. There is, however, a practical limit for increasing both the cell current and the electrolyte flow rate. Reasonable agreement between the model predictions and experimental results was obtained. A case study …

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An Electrochemical Route For Making Porous Nickel Oxide Electrochemical Capacitors, Venkat Srinivasan, John W. Weidner Jan 1997

An Electrochemical Route For Making Porous Nickel Oxide Electrochemical Capacitors, Venkat Srinivasan, John W. Weidner

Faculty Publications

Porous nickel oxide films were prepared by electrochemically precipitating nickel hydroxide and heating the hydroxide in air at 300°C. The resulting nickel oxide films behave as an electrochemical capacitor with a specific capacitance of 59 F/g electrode material. These nickel oxide films maintain high utilization at high rates of discharge (i.e., high power density) and have excellent cycle life. Porous cobalt oxide films were also synthesized. Although the specific capacitances of these films are approximately one-fifth that of the nickel oxide films, the results demonstrate the versatility of fabricating a wide range of porous metal oxide films using …

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Molecular-Level Modeling Of The Viscoelasticity Of Crosslinked Polymers: Effect Of Time And Temperature, Philip P. Simon, Harry J. Ploehn Jan 1997

Molecular-Level Modeling Of The Viscoelasticity Of Crosslinked Polymers: Effect Of Time And Temperature, Philip P. Simon, Harry J. Ploehn

Faculty Publications

We present a new molecular-level picture of chain dynamics for describing the viscoelasticity of crosslinked polymers. The associated mathematical model consists of a time-dependent momentum balance on a representative polymer segment in the crosslinked network, plus phenomenological expressions for forces acting on the segments. These include a cohesive force that accounts for intermolecular attraction, an entropic force describing the thermodynamics governing chain conformations, and a frictional force that captures the temperature dependence of relative chain motion. We treat the case of oscillatory uniaxial deformation. Solution of the model equations in the frequency domain yields the dynamic moduli as functions of …

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Detection For A Statistically-Known, Time-Varying Dispersive Channel, David W. Matolak, S. G. Wilson Dec 1996

Detection For A Statistically-Known, Time-Varying Dispersive Channel, David W. Matolak, S. G. Wilson

Faculty Publications

Detection for the statistically known channel (SKC) is aimed at obtaining good performance in situations where our statistical knowledge of a time-varying channel is good, and where other equalization/detection schemes are either too complex to implement, or their performance is limited due to the rapidity of channel fading, or where we are simply unable to perform channel estimation. By using a statistical characterization of the channel, we develop a new detector that performs maximum-likelihood sequence estimation (MLSE) (given the channel model) on blocks of N symbols. Both symbol-spaced and fractionally spaced samples are used, to obtain two different detectors, that …

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Characterization Of Sr‐Doped Lamno3 And Lacoo3 As Cathode Materials For A Doped Lagao3 Ceramic Fuel Cell, Kevin Huang, Man Feng, John B. Goodenough, Michael Schmerling Nov 1996

Characterization Of Sr‐Doped Lamno3 And Lacoo3 As Cathode Materials For A Doped Lagao3 Ceramic Fuel Cell, Kevin Huang, Man Feng, John B. Goodenough, Michael Schmerling

Faculty Publications

Energy dispersive spectrometry line scan and ac impedance spectroscopy were used in this study to investigate the chemical reactions between two cathode materials, La0.84Sr0.16MnO3 (LSM), La0.5Sr0.5CoO3-δ (LSC), and the electrolyte La0.9Sr0.1Ga0.8Mg0.2O2.85 (LSGM). Significant interdiffusions of Co into LSGM and Ga into LSC were found at an LSC/LSGM interface even at relatively low fabrication temperatures. In contrast, only small interdiffusions of Mn into LSGM and Ga into LSM were detected at the LSM/LSGM interface even though it was fired at 1470°C. The …

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Characterization Of The Si/Sio2 Interface Formed By Remote Plasma Enhanced Chemical Vapor Deposition From Sih4/N2O With Or Without Chlorine Addition, Young-Bae Park, Xiaodong Li, Shi-Woo Rhee Jul 1996

Characterization Of The Si/Sio2 Interface Formed By Remote Plasma Enhanced Chemical Vapor Deposition From Sih4/N2O With Or Without Chlorine Addition, Young-Bae Park, Xiaodong Li, Shi-Woo Rhee

Faculty Publications

The Si/SiO2interface formed by remote plasma enhanced chemical vapor deposition (RPECVD) at low temperature with SiH4/N2O or SiH4/N2O/Cl2 was studied and compared with thermal oxidation. The interface of the CVD SiO2 without chlorine addition is rougher than that with chlorine addition. But the surface roughness of CVD SiO2 films increases with chlorine addition. The thermal oxidation induces strong interface strains, and the strains generated by the CVD SiO2 without chlorine addition are stronger and are distributed more nonuniformly than those by the chlorinated SiO2. …

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Microstructure And Deposition Rate Of Aluminum Thin Films From Chemical Vapor Deposition With Dimethylethylamine Alane, Byoung-Youp Kim, Xiaodong Li, Shi-Woo Rhee Jun 1996

Microstructure And Deposition Rate Of Aluminum Thin Films From Chemical Vapor Deposition With Dimethylethylamine Alane, Byoung-Youp Kim, Xiaodong Li, Shi-Woo Rhee

Faculty Publications

Deposition of aluminumfilm from DMEAA in the temperature range of 100–300 °C has been studied. In this temperature range, there is a maximum deposition rate at around 150 °C. The film deposited at 190 °C has elongated blocklike grain shapes, which are ∼600 nm in width and 930 nm in length. Grains in the film deposited at 150 °C showed an equiaxed structure with grain size in the range of 100–300 nm in a film with 600 nm thickness. Aluminum oxide particle inclusion was observed especially at high deposition temperature. Plausible reaction pathways of DMEAA dissociation were suggested to explain …

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Low-Frequency Noise In 4h-Silicon Carbide Junction Field Effect Transistors, J. W. Palmour, M. E. Levinshtein, S. L. Rumyantsev, Grigory Simin May 1996

Low-Frequency Noise In 4h-Silicon Carbide Junction Field Effect Transistors, J. W. Palmour, M. E. Levinshtein, S. L. Rumyantsev, Grigory Simin

Faculty Publications

Low frequency noise in 4H‐silicon carbide junction field effect transistors (JFETs) has been investigated. JFETs with a buried p + n junction gate were manufactured by CREE Research Inc. Very low noise level has been observed in the JFETs. At 300 K the value of Hooge constant α is as small as α∼10−5 and the α value can be decreased by an appropriate annealing to α∼2×10−6. It has been shown that even these extremely low noise values are determined not by the volume noise sources but by the noise at the SiC–SiO2 interface.

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Variable-Complexity Trellis Decoding Of Binary Convolutional Codes, David W. Matolak, S. G. Wilson Feb 1996

Variable-Complexity Trellis Decoding Of Binary Convolutional Codes, David W. Matolak, S. G. Wilson

Faculty Publications

Considers trellis decoding of convolutional codes with selectable effort, as measured by decoder complexity. Decoding is described for single parent codes with a variety of complexities, with performance "near" that of the optimal fixed receiver complexity coding system. Effective free distance is examined. Criteria are proposed for ranking parent codes, and some codes found to be best according to the criteria are tabulated, Several codes with effective free distance better than the best code of comparable complexity were found. Asymptotic (high SNR) performance analysis and error propagation are discussed. Simulation results are also provided.

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Galvanostatic Pulse And Pulse Reverse Plating Of Zinc–Nickel Alloys From Sulfate Electrolytes On A Rotating Disc Electrode, Branko Popov, M. Ramasubramanian, S. N. Popova, Ralph E. White, Ken-Ming Yin Jan 1996

Galvanostatic Pulse And Pulse Reverse Plating Of Zinc–Nickel Alloys From Sulfate Electrolytes On A Rotating Disc Electrode, Branko Popov, M. Ramasubramanian, S. N. Popova, Ralph E. White, Ken-Ming Yin

Faculty Publications

Galvanostatic pulse and pulse reverse techniques have been used to study the plating of zinc–nickel alloys in the presence of nonyl phenyl polyethylene oxide. The effects of average current density, rotation speed of disc electrode and the presence of nonyl phenyl polyethylene oxide in the electrolyte on deposition of zinc–nickel alloys were evaluated. Zinc–nickel plating bath solution chemistry was studied by determining the equilibrium concentrations at various pH levels. It was found that the alloy composition was determined by solution equilibria, mass transfer of the electroactive species within the diffusion layer and by the surface coverage of nonyl phenyl polyethylene …

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