Showing papers by "Missouri University of Science and Technology published in 2003"
TL;DR: In this paper, the grain structure, dislocation density and second phase particles in various regions including the dynamically recrystallized zone (DXZ), thermo-mechanically affected zone (TMAZ), and heat-affected zone (HAZ) of a friction stir weld aluminum alloy 7050-T651 were investigated and compared with the unaffected base metal.
934 citations
TL;DR: In this article, the results of a study of the structure and electrical properties of nanocrystalline cerium oxide sensor are presented, where the relationship between the resistance of the thin film ceria and oxygen partial pressure is shown.
Abstract: The results of a study of the structure and the electrical properties of nanocrystalline cerium oxide sensor are presented. The relationship between the resistance of the thin film ceria and oxygen partial pressure is shown. In the range of oxygen concentration from 10 ppm to 100% the conductivity of the ceria follows (PO2)−1/4 behavior. The response time of the sensor and its cross-sensitivity to nitrogen dioxide and sulfur dioxide is investigated.
487 citations
TL;DR: It is shown that chiral surfaces can be produced through electrodeposition, a relatively simple solution-based process that resembles biomineralization in that organic molecules adsorbed on surfaces have profound effects on the morphology of the inorganic deposits.
Abstract: Many biomolecules are chiral--they can exist in one of two enantiomeric forms that only differ in that their structures are mirror images of each other. Because only one enantiomer tends to be physiologically active while the other is inactive or even toxic, drug compounds are increasingly produced in an enantiomerically pure form using solution-phase homogeneous catalysts and enzymes. Chiral surfaces offer the possibility of developing heterogeneous enantioselective catalysts that can more readily be separated from the products and reused. In addition, such surfaces might serve as electrochemical sensors for chiral molecules. To date, chiral surfaces have been obtained by adsorbing chiral molecules or slicing single crystals so that they exhibit high-index faces, and some of these surfaces act as enantioselective heterogeneous catalysts. Here we show that chiral surfaces can also be produced through electrodeposition, a relatively simple solution-based process that resembles biomineralization in that organic molecules adsorbed on surfaces have profound effects on the morphology of the inorganic deposits. When electrodepositing a copper oxide film on an achiral gold surface in the presence of tartrate ion in the deposition solution, the chirality of the ion determines the chirality of the deposited film, which in turn determines the film's enantiospecificity during subsequent electrochemical oxidation reactions.
326 citations
TL;DR: In this article, a microelectromechanical system-based multiaxis cellular force sensor has been used to conduct mouse ZP force sensing, establishing a quantitative relationship between applied forces and biomembrane structural deformations on both mouse oocytes and embryos.
Abstract: Previous intracytoplasmic sperm injection (ICSI) studies have indicated significant variation in ICSI success rates among different species. In mouse ICSI, the zona pellucida (ZP) undergoes a "hardening" process at fertilization in order to prevent subsequent sperm from penetrating. There have been few studies investigating changes in the mechanical properties of mouse ZP post fertilization. To characterize mouse ZP mechanical properties and quantitate the mechanical property differences of the ZP before and after fertilization, a microelectromechanical systems-based multiaxis cellular force sensor has been developed. A microrobotic cell manipulation system employing the multiaxis cellular force sensor is used to conduct mouse ZP force sensing, establishing a quantitative relationship between applied forces and biomembrane structural deformations on both mouse oocytes and embryos. An analytical biomembrane elastic model is constructed to describe biomembrane mechanical properties. The characterized elastic modulus of embryos is 2.3 times that of oocytes, and the measured forces for puncturing embryo ZP are 1.7 times those for oocyte ZP. The technique and model presented in this paper can be applied to investigations into the mechanical properties of other biomembranes, such as the plasma membrane of oocytes or other cell types.
294 citations
01 Jan 2003
TL;DR: In this paper, a method of RBD with the mixture of random variables with distributions and uncertain variables with intervals is proposed, where the reliability is considered under the condition of the worst combination of interval variables.
Abstract: In Reliability-Based Design (RBD), uncertainties usually imply for randomness. Nondeterministic variables are assumed to follow certain probability distributions. However, in real engineering applications, some of distributions may not be precisely known or uncertainties associated with some uncertain variables are not from randomness. These nondeterministic variables are only known within intervals. In this paper, a method of RBD with the mixture of random variables with distributions and uncertain variables with intervals is proposed. The reliability is considered under the condition of the worst combination of interval variables. In comparison with traditional RBD, the computational demand of RBD with the mixture of random and interval variables increases dramatically. To alleviate the computational burden, a sequential single-loop procedure is developed to replace the computationally expensive double-loop procedure when the worst case scenario is applied directly. With the proposed method, the RBD is conducted within a series of cycles of deterministic optimization and reliability analysis. The optimization model in each cycle is built based on the Most Probable Point (MPP) and the worst case combination obtained in the reliability analysis in previous cycle. Since the optimization is decoupled from the reliability analysis, the computational amount for MPP search is decreased to the minimum extent. The proposed method is demonstrated with a structural design example.Copyright © 2003 by ASME
245 citations
12 Oct 2003
TL;DR: A new voltage balancing control for the diode-clamped multilevel rectifier/inverter system that regulates the DC bus voltage, balances the capacitors, and decreases the harmonic components of the voltage and current is presented.
Abstract: This paper presents a new voltage balancing control for the diode-clamped multilevel rectifier/inverter system. A complete analysis of the voltage balance theory for a 5-level back-to-back system is given. The analysis is based on fundamental frequency switching control and then extended to pulse-width modulation. The method involves obtaining optimal switching angles; a process which is described in detail in this paper. The proposed control strategy regulates the DC bus voltage, balances the capacitors, and decreases the harmonic components of the voltage and current. Simulation and experimental results demonstrate the validity of the optimizing method and control theory.
206 citations
TL;DR: Three-dimensional images of the complete electron emission pattern for the single ionization of helium by the impact of C6+ ions of energy 100 MeV per a.m.u. (a four-body system) are reported and a higher-order ionization mechanism, involving the interaction between the projectile and the target nucleus, is proposed to explain these features.
Abstract: To understand the physical processes that occur in nature we need to obtain a solid concept about the ‘fundamental’ forces acting between pairs of elementary particles. It is also necessary to describe the temporal and spatial evolution of many mutually interacting particles under the influence of these forces. This latter step, known as the few-body problem, remains an important unsolved problem in physics. Experiments involving atomic collisions represent a useful testing ground for studying the few-body problem. For the single ionization of a helium atom by charged particle impact, kinematically complete experiments have been performed1,2,3,4,5,6 since 1969 (ref. 7). The theoretical analysis of such experiments was thought to yield a complete picture of the basic features of the collision process, at least for large collision energies8,9,10,11,12,13,14. These conclusions are, however, almost exclusively based on studies of restricted electron-emission geometries1,2,3. Here, we report three-dimensional images of the complete electron emission pattern for the single ionization of helium by the impact of C6+ ions of energy 100 MeV per a.m.u. (a four-body system) and observe features that have not been predicted by any published theoretical model. We propose a higher-order ionization mechanism, involving the interaction between the projectile and the target nucleus, to explain these features.
189 citations
TL;DR: The need for obesity trials, the assumptions that must be made regarding missing data in such trials, and some modern statistical methods for analysing data containing missing repeated measurements are reviewed.
Abstract: This paper brings together some modern statistical methods to address the problem of missing data in obesity trials with repeated measurements. Such missing data occur when subjects miss one or more follow-up visits, or drop out early from an obesity trial. A common approach to dealing with missing data because of dropout is 'last observation carried forward' (LOCF). This method, although intuitively appealing, requires restrictive assumptions to produce valid statistical conclusions. We review the need for obesity trials, the assumptions that must be made regarding missing data in such trials, and some modern statistical methods for analysing data containing missing repeated measurements. These modern methods have fewer limitations and less restrictive assumptions than required for LOCF. Moreover, their recent introduction into current releases of statistical software and textbooks makes them more readily available to the applied data analyses.
188 citations
TL;DR: A charge exchange emission model is developed that successfully reproduces the soft x-ray spectrum of comet Linear C/1999 S4, observed with the Chandra X-ray Observatory.
Abstract: In laboratory experiments using the engineering spare microcalorimeter detector from the ASTRO-E satellite mission, we recorded the x-ray emission of highly charged ions of carbon, nitrogen, and oxygen, which simulates charge exchange reactions between heavy ions in the solar wind and neutral gases in cometary comae. The spectra are complex and do not readily match predictions. We developed a charge exchange emission model that successfully reproduces the soft x-ray spectrum of comet Linear C/1999 S4, observed with the Chandra X-ray Observatory.
167 citations
TL;DR: Heat capacity measurements on Tl0.8Co4Sb11Sn as compared to CoSb3 are consistent with the presence of a localized vibrational mode associated with the "rattling" thallium atoms in this filled skutterudite compound, providing perhaps the clearest example of local mode behavior in a concentrated metallic system.
Abstract: Inelastic neutron scattering measurements on several Tl filled skutterudites (Tl0.5Co3.5Fe0.5Sb12, Tl0.8Co3FeSb12, and Tl0.8Co4Sb11Sn) all show a sharp peak in the vibrational density of states at 57+/-2 K, which is absent in the unfilled skutterudite CoSb3. Heat capacity measurements on Tl0.8Co4Sb11Sn as compared to CoSb3 are consistent with the presence of a localized vibrational mode associated with the "rattling" thallium atoms in this filled skutterudite compound. Both results are well described by a localized Einstein mode model with an Einstein temperature Theta(E) of 53+/-1 K. These data provide perhaps the clearest example of local mode behavior in a concentrated metallic system.
157 citations
TL;DR: The thiosemicarbazone derivative of 9,10-phenanthrenequinone, 1, and its metal complexes were synthesized and the X-ray crystal structure confirms the presence of the E tautomeric arrangement in this compound.
TL;DR: In this paper, the contribution of megacities to sulfur emissions and pollution in Asia is studied over a 25-year period (1975-2000) using a multi-layer Lagrangian puff transport model.
TL;DR: Research presented here demonstrates that TCE is taken up by trees and volatilized to the atmosphere, and TCE diffusion along the transpiration pathway is shown to be the primary process for TCE volatILization, although vol atilization can occur from both stems and leaves.
Abstract: The phytoremediation of trichloroethylene (TCE) and other chlorinated compounds has been studied over the past decade, and full-scale systems are in place. The results regarding TCE fates and removal pathways are inconclusive and conflicting, particularly the results regarding volatilization to the atmosphere. Research presented here demonstrates that TCE is taken up by trees and volatilized to the atmosphere. TCE diffusion along the transpiration pathway is shown to be the primary process for TCE volatilization, although volatilization can occur from both stems and leaves. Two concurrent processes influence the eventual fate: transport with transpiration stream through xylem tissues and diffusion from transpiration stream to atmosphere. TCE diffusion flux invariably decreased with height for trees planted in soil or grown hydroponically. In both laboratory experiments and field sampling, TCE concentrations in the transpiration stream (e.g., xylem tissues) decreased with elevation. In field samples, TCE ...
TL;DR: In this article, the authors report on the North American state-of-the-art in the use of FRP composites in concrete structures, including parking garages, multi-purpose convention centers, office buildings and silos.
TL;DR: In this paper, the discharge current and the transient fields of an ESD generator in the contact mode are numerically simulated using the finite-difference time-domain method, and the simulated data are used to study the effect of design choices on the current and fields.
Abstract: The discharge current and the transient fields of an electrostatic discharge (ESD) generator in the contact mode are numerically simulated using the finite-difference time-domain method. At first the static field is established. Then the conductivity of the relay contact is changed, which initiates the discharge process. The simulated data are used to study the effect of design choices on the current and fields. They are compared to measured field and current data using a multidecade broadband field and current sensors. The model allows accurate prediction of the fields and currents of ESD generators, thus it can be used to evaluate different design choices.
TL;DR: In this article, the authors present the theoretical foundations of a matrix-based approach to derive similarities that exist between different failure modes, by mapping observed failure modes to the functionality of each component, and applies it to a simple design example.
Abstract: When designing aerospace systems, it is essential to provide crucial failure information for failure prevention. Failure modes and effects types of analyses and prior engineering knowledge and experience are commonly used to determine the potential modes of failures a product might encounter during its lifetime. When new products are being considered and designed, this knowledge and information is expanded upon to help designers extrapolate based on their similarity with existing products and the potential design tradeoffs. In this work, we aim to enhance this process by providing design-aid tools which derive similarities between functionality and failure modes. Specifically, this paper presents the theoretical foundations of a matrix-based approach to derive similarities that exist between different failure modes, by mapping observed failure modes to the functionality of each component, and applies it to a simple design example. The function–failure mode method is proposed to design new products or redesign existing ones with solutions for functions that eliminate or reduce the potential of a failure mode.
TL;DR: Future space farmers will have to adapt their practices to accommodate microgravity, high and low extremes in ambient temperatures, reduced atmospheric pressures, atmospheres containing high volatile organic carbon contents, and elevated to super-elevated CO2 concentrations.
25 Jun 2003-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this article, the superplastic deformation behavior of FSP Al-4Mg-1Zr alloy was investigated in strain rate range of 1×10−3 to 1 s−1 and temperature range of 350-550°C and compared with that of as-rolled one.
Abstract: Al–4Mg–1Zr extruded bar was subjected to friction stir processing (FSP), resulting in generation of a fine microstructure of 1.5 μm grain size. Superplastic deformation behavior of FSP Al–4Mg–1Zr alloy was investigated in strain rate range of 1×10−3 to 1 s−1 and temperature range of 350–550 °C and compared with that of as-rolled one. It is indicated that the FSP alloy exhibited significantly enhanced superplasticity at a high strain rate of 1×10−1 s−1, and a maximum elongation of 1280% was obtained at 525 °C and 1×10−1 s−1. Further, the FSP Al–4Mg–1Zr alloy exhibited excellent thermal stability at high temperature, and a large elongation of 1210% was observed at 550 °C and 1×10−1 s−1. Moreover, FSP resulted in a significant decrease in the flow stress in Al–4Mg–1Zr alloy. At a strain rate of 1×10−2 s−1, the flow stress (∼7 MPa) of FSP Al–4Mg–1Zr at 450 °C was comparable to that of as-rolled alloy at 550 °C.
TL;DR: The described method of retrieving particle-containing brine from fluid inclusions offers a robust approach for assessing the antiquity of microorganisms associated with evaporites.
Abstract: Halite crystals were selected from a 186 m subsurface core taken from the Badwater salt pan, Death Valley, California to ascertain if halophilic Archaea and their associated 16S rDNA can survive over several tens of thousands of years. Using a combined microscope microdrill/micropipette system, fluids from brine inclusions were aseptically extracted from primary, hopper texture, halite crystals from 8 and 85 metres below the surface (mbls). U-Th disequilibrium dating indicates that these halite layers were deposited at 9,600 and 97,000 years before present (ybp) respectively. Extracted inclusions were used for polymerase chain reaction (PCR) analysis with haloarchaea-specific 16S rDNA primers or placed into haloarchaea culture medium. Enrichment cultures were obtained from 97 kyr halite crystal inclusion fluid and haloarchaea-containing prepared crystals (positive controls), whereas inclusions from crystals of 9.6 kyr halite and the haloarchaea-free halite crystals (negative controls) resulted in no growth. Phylogenetic analysis (16S rDNA) of the 97 kyr isolate, designated BBH 001, revealed a homology of 100% with Halobacterium salinarum. DNA-DNA hybridization experiments confirmed that BBH 001 was closely related to H. salinarum (81-75% hybridization) and its ascription to this haloarchaea species. The described method of retrieving particle-containing brine from fluid inclusions offers a robust approach for assessing the antiquity of microorganisms associated with evaporites.
TL;DR: An experimental study of magnetic dipole (M1) transitions in highly charged argon ions in the visible spectral range using an electron beam ion trap shows great potential for the study of QED effects in relativistic few-electron systems.
Abstract: We present the results of an experimental study of magnetic dipole ($M1$) transitions in highly charged argon ions (Ar X, Ar XI, Ar XIV, Ar XV) in the visible spectral range using an electron beam ion trap. Their wavelengths were determined with, for highly charged ions, unprecedented accuracy up to the sub-ppm level and compared with theoretical calculations. The QED contributions, calculated in this Letter, are found to be 4 orders of magnitude larger than the experimental error and are absolutely indispensable to bring theory and experiment to a good agreement. This method shows great potential for the study of QED effects in relativistic few-electron systems.
TL;DR: In this article, an iron phosphate glass with 30 wt% of a high sodium and sulfur Hanford low-activity waste (LAW) simulant was successfully melted in electric furnaces at 1000-1050 °C for 2-3 h.
Abstract: Iron phosphate glasses containing 30 w% of a high sodium and sulfur Hanford low-activity waste (LAW) simulant was successfully melted in electric furnaces at 1000–1050 °C for 2–3 h. No sulfate salt segregation or crystalline phases were detectable in the glassy wasteform when examined by scanning electron microscope and X-ray diffractometer. This suggests that the waste loading in the iron phosphate glasses will not be limited by the SO 3 content of the LAW as is currently the case in borosilicate glasses. At 30 wt% LAW, the iron phosphate glass wasteform satisfies DOE’s product consistency test and vapor hydration test requirements for aqueous chemical durability, but the chemical durability depends upon the overall composition. The high fluidity and electrical conductivity of the iron phosphate melts suggest that iron phosphate wasteforms can be melted in a hot or cold crucible induction melter as an alternative to melting in a joule-heated melter. These properties combined with a significantly higher waste loading offer a considerable savings in time, energy and cost for vitrifying the Hanford LAW in iron phosphate glasses.
02 Nov 2003
TL;DR: In this paper, the authors focus on emergent phenomena and the utilization of computer simulations, basically agent-based modeling to understand emergent phenomenon, and highlight how artificial life and management can be brought together to develop decision making aid tools.
Abstract: This paper focuses on emergent phenomena and the utilization of computer simulations, basically agent-based modeling to understand emergent phenomena Agent-based simulation models have a promising future in the social sciences, from management to economies, political science, sociology and anthropology This paper attempts to realize their full scientific potential by reviewing recent applications in engineering management and addresses the set of challenges confronted by this method Common methodology for constructing an agent-based model is also discussed with the aim of highlighting how artificial life and management can be brought together to develop decision making aid tools
TL;DR: In this paper, the size, morphology, and volume fraction of soot particles within the fuel-rich regions of a non-premixed turbulent jet flame fueled by ethylene/air at atmospheric pressure were investigated.
TL;DR: Unlike discrete decoupling capacitors, whose effective frequency range is generally limited to a few hundred megahertz due to interconnect inductance, embedded capacitance was found to efficiently reduce power-bus noise over the entire frequency range evaluated (up to 5 GHz).
Abstract: This paper experimentally investigates the effectiveness of embedded capacitance for reducing power-bus noise in high-speed printed circuit board designs. Boards with embedded capacitance employ closely spaced power-return plane pairs separated by a thin layer of dielectric material. In this paper, test boards with four embedded capacitance materials are evaluated. Power-bus input impedance measurements and power-bus noise measurements are presented for boards with various dimensions and layer stack ups. Unlike discrete decoupling capacitors, whose effective frequency range is generally limited to a few hundred megahertz due to interconnect inductance, embedded capacitance was found to efficiently reduce power-bus noise over the entire frequency range evaluated (up to 5 GHz).
TL;DR: The influence of quenched disorder on quantum phase transitions in systems with overdamped dynamics is studied and the behavior based on Lifshitz-tail arguments is discussed and illustrated by simulations of a model system.
Abstract: We study the influence of quenched disorder on quantum phase transitions in systems with over-damped dynamics. For Ising order-parameter symmetry disorder destroys the sharp phase transition by rounding because a static order parameter can develop on rare spatial regions. This leads to an exponential dependence of the order parameter on the coupling constant. At finite temperatures the static order on the rare regions is destroyed. This restores the phase transition and leads to a double-exponential relation between critical temperature and coupling strength. We discuss the behavior based on Lifshitz-tail arguments and illustrate the results by simulations of a model system.
TL;DR: In this paper, the authors present the design and practical hardware implementation of optimal neurocontrollers that replace the conventional automatic voltage regulator (AVR) and the turbine governor of turbogenerators on multimachine power systems.
Abstract: This paper presents the design and practical hardware implementation of optimal neurocontrollers that replace the conventional automatic voltage regulator (AVR) and the turbine governor of turbogenerators on multimachine power systems. The neurocontroller design uses a powerful technique of the adaptive critic design (ACD) family called dual heuristic programming (DHP). The DHP neurocontrollers' training and testing are implemented on the Innovative Integration M67 card consisting of the TMS320C6701 processor. The measured results show that the DHP neurocontrollers are robust and their performance does not degrade unlike the conventional controllers even when a power system stabilizer (PSS) is included, for changes in system operating conditions and configurations. This paper also shows that it is possible to design and implement optimal neurocontrollers for multiple turbogenerators in real time, without having to do continually online training of the neural networks, thus avoiding risks of instability.
TL;DR: Examining the use of a computerized patient record system in an intensive care unit of a U.S. hospital presents two sociotechnical requirements, awareness and coordination, embedded in the users' work, based on observation.
Abstract: Summary Objective: We explore sociotechnical requirements by examining the use of a computerized patient record system in an intensive care unit of a U.S. hospital and present two sociotechnical requirements, awareness and coordination, embedded in the users’ work. Method: The study is based on observation during seven months of the use of a computerized patient record system in a surgical intensive care unit. During that period semi-formal interviews, informal interviews were held. Results and Conclusions: A key step in the design of clinical systems is the development and analysis of requirements. However, traditional requirements analysis is based on a set of assumptions that break down in the highly collaborative, exception-filled clinical domain. Sociotechnical requirement analysis enabled the designers to gather a much richer description of the environment surrounding the computer system, highlighting awareness and coordination, embedded in the users’ work.
TL;DR: A simulated sodium bearing waste (SBW) was successfully vitrified in iron phosphate glasses (IPG) at a maximum waste loading of 40 wt% using conventional and cold crucible induction melting (CCIM) techniques.
TL;DR: In this paper, the vertical profiles of the horizontal mass flux of blown sand are investigated experimentally using a passive vertical array in a wind tunnel and the measured longitudinal profiles are similar to the measured vertical profiles.
TL;DR: In this paper, the authors define various terms (intrinsic and extrinsic strength and inert and environmental fatigue) and analyze techniques for their measurement and illustrate and evaluate these parameters by means of literature data on silica and E-glass.
Abstract: Recent studies on the strength of glass fibers suggest that the time is ripe for new, fundamental studies in this area which may significantly advance our understanding of the intrinsic strength of glasses. In order to set the stage, in this paper we define various terms (intrinsic and extrinsic strength and inert and environmental fatigue) and analyze techniques for their measurement. We illustrate and evaluate these parameters by means of literature data on silica and E-glass. In addition we present some preliminary new data on E-glass fibers using 2-point bending. These new data report higher strength than previously reported and some possible reasons for this are given. While these comments deal primarily with the science of strength, a better understanding of these issues may lead to improvements in glass technology and glass products.