Showing papers by "Missouri University of Science and Technology published in 1995"
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17 Aug 1995TL;DR: Ceramic fabrication processes -an introductory overview synthesis of powders powder characterization science of colloidal processing sol-gel processing powder consolidation and forming of ceramics sintering of ceramic materials.
Abstract: Ceramic fabrication processes - an introductory overview synthesis of powders powder characterization science of colloidal processing sol-gel processing powder consolidation and forming of ceramics sintering of ceramics - fundamentals theory of viscous sintering grain growth and microstructural control liquid-phase sintering problems of sintering densification process variables and densification practice.
1,384 citations
TL;DR: In this article, the electrical conductivity and Seebeck coefficient as a function of the Co Fe ratio and temperature were investigated in the La0.8Sr0.2Co1−yFeyO3 with 0 ≤ y ≤ 1.
746 citations
TL;DR: In this paper, a semi-empirical model was developed which took into account the thermally activated disproportionation of Co 3+ ions into Co 4+ and Co 2+ pairs, and the ionic compensation of oxygen vacancies formed at high temperatures.
667 citations
TL;DR: It appears that teicoplanin is a widely applicable, highly effective chiral selector for HPLC enantioseparations.
305 citations
TL;DR: A new method for measurement of glutathione and other biological thiols utilizing reverse-phase high-performance liquid chromatography to separate and quantify these derivatives is described, offering some advantages over the currently accepted techniques, including specificity, speed, sensitivity, and ease of use.
211 citations
TL;DR: In this article, nanocrystalline CeO{sub 2} powders were prepared electrochemically by the cathodic electrogeneration of base, and their sintering behavior was investigated.
Abstract: Nanocrystalline CeO{sub 2} powders were prepared electrochemically by the cathodic electrogeneration of base, and their sintering behavior was investigated. X-ray diffraction and transmission electron microscopy revealed that the as-prepared powders were crystalline cerium(IV) oxide with the cubic fluorite structure. The lattice parameter of the electrogenerated material was 0.5419 nm. The powders consisted of nonaggregated, faceted particles. The average crystallite size was a function of the solution temperature. It increased from 10 nm at 29 C to 14 nm at 80 C. Consolidated powders were sintered in air at both a constant heating rate of 10 C/min and under isothermal conditions. The temperature at which sintering started (750 C) for nanocrystalline CeO{sub 2} powders was only about 100 C lower than that of coarser-grained powders (850 C). However, the sintering rate was enhanced. The temperature at which shrinkage stopped was 200--300 C lower with the nanoscale powder than with micrometer-sized powders. A sintered specimen with 99.8% of theoretical density and a grain size of about 350 nm was obtained by sintering at 1,300 C for 2 h.
169 citations
TL;DR: Some basic concepts of fuzzy methods are reviewed, some philosophical and practical problems are pointed out, and simpler alternatives based on traditional probability and statistical theory are offered.
Abstract: Fuzzy set theory has primarily been associated with control theory and with the representation of uncertainty in applications in artificial intelligence. More recently, fuzzy methods have been proposed as alternatives to traditional statistical methods in statistical quality control, linear regression, and forecasting, among other areas. We review some basic concepts of fuzzy methods, point out some philosophical and practical problems, and offer simpler alternatives based on traditional probability and statistical theory. Applications in control theory and statistical quality control serve as our primary examples.
167 citations
TL;DR: In this article, the four optimum rotation angles for a polarimeter consisting of a quarter-wave plate in conjunction with a linear polarizer are found by using the determinant and condition numbers of the system measurement matrix as objective functions in a minimization procedure.
Abstract: The four optimum rotation angles for a polarimeter consisting of a quarter-wave plate in conjunction with a linear polarizer are found. This is done by using the determinant and condition numbers of the system measurement matrix as objective functions in a minimization procedure. The four angles so found result in the polarimeter's estimate of the incident Stokes vector to have a minimum sensitivity with respect to fluctuations in the detected flux and errors in the angular position of the optical components constituting the polarimeter. Four optimal angles are presented. These four angles also retain a simplicity of form for the measurement matrix.
161 citations
TL;DR: The use and optimization of ristocetin A as a chiral selector in capillary electrophoresis (CE) is discussed.
142 citations
TL;DR: It was found that adding sodium dodecyl sulfate to the run buffer increased efficiency by over 1 order of magnitude, decreased analysis times, and reversed the elution order of the enantiomers.
Abstract: Vancomycin (an oligophenolic, glycopeptide, macrocyclic antibiotic) has been shown to be a superb chiral selector for anionic and neutral compounds. It was found that adding sodium dodecyl sulfate to the run buffer increased efficiency by over 1 order of magnitude, decreased analysis times, and reversed the elution order of the enantiomers. This allows for control of the retention order as well as the resolution of enantiomers in complex mixtures in a single run. A mechanism is proposed which explains all of the observed effects and is verified experimentally. Since vancomycin is present in both the micelle and in free solution, previously proposed micelle-selector models are, at best, limiting cases. A general equation is derived which can be used to describe all possible interactions, including those with the capillary wall, if needed. Also, it is shown that electrophoretic mobilities and not migration times must be used to calculate binding constants of a solute to the micelle, the chiral selector, or both. Furthermore, it is shown that a neutral marker molecule cannot be used to accurately correct mobilities that have been altered due to changes in solution viscosity. While this work utilizes the practical vancomycin-micelle system, the general conclusions and theory apply to most other analogous CE systems as well.
109 citations
TL;DR: In this article, the reaction sintering of equimolar mixtures of ZnO and Al{sub 2}O{sub 3} powders was investigated as a function of primary processing parameters such as the temperature, heating rate, green density, and particle size.
Abstract: The reaction sintering of equimolar mixtures of ZnO and Al{sub 2}O{sub 3} powders was investigated as a function of primary processing parameters such as the temperature, heating rate, green density, and particle size. The powder mixtures were prepared by two different methods. In one method, the ZnO and Al{sub 2}O{sub 3} powders were ball-milled. In the other method, the ZnO powder was chemically precipitated onto the Al{sub 2}O{sub 3} particles dispersed in a solution of zinc chloride. The sintering characteristics of the compacted powders prepared by each method were compared with those for a pre-reacted single-phase powder of zinc aluminate, ZnAl{sub 2}O{sub 4}. The chemical reaction between ZnO and Al{sub 2}O{sub 3} occurred prior to densification of the powder compact and was accompanied by fairly large expansion. The mixing procedure had a significant effect on the densification rate during reaction sintering. The densification rate of the compact formed from the ball-milled powder was strongly inhibited compared to that for the single-phase ZnAl{sub 2}O{sub 4} powder. However, the densification rate of the compact formed from the chemically precipitated mixture was almost identical to that for the ZnAl{sub 2}O{sub 4} powder. The difference in sintering between the ball-milled mixture and the chemicallymore » precipitated mixture is interpreted in terms of differences i the microstructural uniformity of the initial powder compacts resulting from the different preparation procedures.« less
TL;DR: In this paper, a model friction material was formulated with a cashew modified phenolic resin, short carbon fiber, phenolic particles, barytes and steel fiber, and the coefficient of friction was found to vary between 0.2 and 0.5 with lower values associated with higher loads, speeds and drum temperatures.
TL;DR: In this article, an overview of the clouds comprehensively studied by ground-based and airborne sensors from Coffeyville, Kansas, during the 5-6 December 1992 First ISCCP Regional Experiment (FIRE) intensive field observation (IFO) case study period, evidence is provided that volcanic aerosols from the June 1991 Pinatubo eruptions may have significantly influenced the formation and maintenance of the cirrus.
Abstract: In presenting an overview of the cirrus clouds comprehensively studied by ground based and airborne sensors from Coffeyville, Kansas, during the 5-6 December 1992 First ISCCP Regional Experiment (FIRE) intensive field observation (IFO) case study period, evidence is provided that volcanic aerosols from the June 1991 Pinatubo eruptions may have significantly influenced the formation and maintenance of the cirrus. Following the local appearance of a spur of stratospheric volcanic debris from the subtropics, a series of jet streaks subsequently conditioned the troposphere through tropopause foldings with sulfur based particles that became effective cloud forming nuclei in cirrus clouds. Aerosol and ozone measurements suggest a complicated history of stratospheric-tropospheric exchanges embedded with the upper level flow, and cirrus cloud formation was noted to occur locally at the boundaries of stratospheric aerosol enriched layers that became humidified through diffusion, precipitation, or advective processes. Apparent cirrus cloud alterations include abnormally high ice crystal concentrations (up to approximately 600 L(exp. 1)), complex radial ice crystal types, and relatively large haze particles in cirrus uncinus cell heads at temperatures between -40 and -50 degrees C. Implications for volcanic-cirrus cloud climate effects and unusual (nonvolcanic) aerosol jet stream cirrus cloud formation are discussed.
TL;DR: A semiempirical model of the Seebeck coefficient for a small polaron hopping conductor is presented and cobalt ion valence populations predicted by the model are used to calculate effective paramagnetic moments for LaCoO{sub 3}, which are favorably compared to those found experimentally.
Abstract: A semiempirical model of the Seebeck coefficient for a small polaron hopping conductor is presented. The population of small polarons is allowed to change as a function of temperature via the mechanism of charge disproportionation. The energy required for polaron formation by the disproportionation mechanism is modeled as screened by a Coulomb interaction with nearby small polarons. The charge carrier site occupancies generated by the model are used to successfully predict the electrical conductivity and Seebeck coefficient for compositions in the ${\mathrm{La}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Ca}}_{\mathit{x}}$${\mathrm{CoO}}_{3}$ system. Cobalt ion valence populations predicted by the model are used to calculate effective paramagnetic moments for ${\mathrm{LaCoO}}_{3}$, which are favorably compared to those found experimentally.
TL;DR: In this article, the generation and evolution of the flow vorticity established by instream injector ramps in a high Mach number/high enthalpy scramjet combustor flow-field are described in detail for a number of computational cases.
Abstract: The generation and evolution of the flow vorticity established by instream injector ramps in a high Mach number/high enthalpy scramjet combustor flow-field are described in detail for a number of computational cases. Classical fluid dynamic circulation is presented for these cases in order to clarify the spatial distribution and convection of the vorticity. The ability of the simulations to accurately represent Stokes Law of circulation is discussed and shown. In addition, the conservation of swirl (effectively the moment-of-momentum theorem) is presented for these flows. The impact of both turbulent diffusion and the vortex/ramp non-uniformity on the downstream mixing rate is clearly illustrated. A correlation over the length of the combustor between fuel-air mixing and a parameter called the vortex stirring length is demonstrated. Finally, computational results for a representative ramp injector are compared with experimental data. Influence of the stream vorticity on the effective turbulent Prandtl number used in the simulation is discussed.
TL;DR: In this paper, phase stability, oxygen content, electrical conductivity, and Seebeck coefficient of La{sub 1-x}Sr{sub x}Co{sub 0.2, 0.4] were studied as a function of temperature and oxygen activity.
TL;DR: In this article, the influence of high pressure waterjet delivered into tool-chip interface in two different methods, namely, waterjet injected directly into the toolchip interface through a hole in the tool rake face, and water jet injected into tool chip interface through an external nozzle, was explored in terms of cutting force, surface finish, chip shape and tool wear.
Abstract: The efficiency of the metal cutting operations depends upon the thermal/frictional conditions at the tool-chip interface. The use of high pressure waterjet as a coolant/lubricant to improve the thermal/frictional conditions in milling operations was studied here. The influence of high pressure waterjet delivered into tool-chip interface in two different methods, namely, waterjet injected directly into the tool-chip interface through a hole in the tool rake face, and waterjet injected into tool-chip interface through an external nozzle, was explored in this study. The effectiveness of these developed methods was evaluated in terms of cutting force, surface finish, chip shape and tool wear.
TL;DR: In this paper, a method for estimating the axial distribution of thrust performance potential in a supersonic combustor is described, and a complementary technique for illustrating the spatial evolution and distribution of the thrust potential and loss mechanisms in reacting flows is developed.
Abstract: A method for estimating the axial distribution of thrust performance potential in a supersonic combustor is described. A complementary technique for illustrating the spatial evolution and distribution of thrust potential and loss mechanisms in reacting flows is developed. A wall jet case and swept ramp injector case for Mach 17 and Mach 13.5 flight enthalpy inflow conditions, respectively, are numerically modeled and analyzed using these techniques.
TL;DR: In this article, the primary and secondary drying stages of the freeze-drying of pharmaceutical crystalline and amorphous solutes in vials are constructed and presented in a dynamic and spatially multi-dimensional mathematical model.
Abstract: Dynamic and spatially multi-dimensional mathematical models of the primary and secondary drying stages of the freeze-drying of pharmaceutical crystalline and amorphous solutes in vials, are constructed and presented in this work. The models account for the removal of free and bound water and could also provide the geometric shape of the moving interface and its position. It is proved that the temperature of the moving interface can not be constant if the flux of heat flow to the sides of the vial is not zero. It is also proved that the slope of the free surface (moving interface) at the edge of the vial is always curved downward. The numerical solution of the nonlinear partial differential equations of the models would allow model simulations that could indicate design conditions, operating conditions, and control strategies that could provide high drying rates and could lead to a series of novel experiments in freeze-drying.
TL;DR: The magnetic properties of a series of Ce2Fe17−xAlx solid solutions with x equal to 0.62 have been studied by magnetic measurements, neutron diffraction, and Mossbauer spectroscopy as discussed by the authors.
Abstract: The magnetic properties of a series of Ce2Fe17−xAlx solid solutions with x equal to 0.00, 0.88, 2.06, 2.81, 3.98, 5.15, 6.08, 7.21, 8.20, 9.08, 9.84, and 10.62 have been studied by magnetic measurements, neutron diffraction, and Mossbauer spectroscopy. The compounds crystallize in the rhombohedral Th2Zn17‐type structure. Magnetization studies indicate that the Curie temperature increases uniformly from 238 K for Ce2Fe17 to 384 K for Ce2Fe14Al3 and then decreases at higher aluminum content. Powder neutron diffraction results, obtained at 295 K, indicate that aluminum avoids the 9d site for all x values and preferentially occupies the 18h site at low aluminum content. Aluminum shows a marked preference for the 6c site for x≳6. The room‐temperature iron magnetic moments increase from x=0 to 2 and then decrease for x≳2. The Mossbauer spectra have been fit with a binomial distribution of the near‐neighbor environments in terms of a maximum hyperfine field, Hmax, for an iron with zero aluminum near neighbors, a...
TL;DR: In this article, the properties and structural role of nitrogen in phosphorus oxynitride glasses are reported, including the dissolution rate in water, thermal expansion coefficient, viscosity and refractive index.
Abstract: The properties and structural role of nitrogen in phosphorus oxynitride glasses are reported. Properties summarized for several compositions include the dissolution rate in water, thermal expansion coefficient, viscosity and refractive index. The bonding and coordination number of nitrogen in the glass network has been deduced from nuclear magnetic resonance, X-ray photoelectron spectroscopy and Raman spectroscopy. The existing evidence shows that nitrogen replaces oxygen in the PO4 network as doubly coordinated (=N-) and triply coordinated (> N-) N3− ions. The measured properties are consistent with these network structural features.
TL;DR: In this paper, the effects of the cation concentration size and valency on the densification and grain growth of the compacted powders were examined during sintering at a constant heating rate of 10 degrees C/min.
Abstract: Ultra-fine CeO2 powders (particle size approximate to 10-15 nm) containing up to 20 at% of various divalent and trivalent cations (Mg2+, Ca2+, SC3+, Y3+ and Nd3+) were prepared by chemical precipitation under hydrothermal conditions. The effects of the cation concentration size and valency on the densification and grain growth of the compacted powders were examined during sintering at a constant heating rate of 10 degrees C/min. Compared to undoped CeO2, all of the additive cations caused a shift in the densification curve to higher temperatures. However, the density and grain size achieved after sintering depended significantly on the elemental composition of the additive. When the radii of the additive cations were larger than that of the host Ce4+ cation, (i.e. Ca2+, Y3+ and Nd-3), nearly full density and ultrafine grain size were achieved. Under identical sintering conditions lower density (approximate to 93-95% of the theoretical) and larger grain size were achieved when the radii of the additive cations were smaller than that of the host, (i.e. Mg2+ and SC3+). Powders doped simultaneously with two cations, (e.g. Ca2+ and Mg2+) showed sintering and grain growth characteristics which were intermediate between those for the powders doped with single cations at the equivalent concentration.
TL;DR: This paper presents a meta-analyses of the response of the immune system to x-ray diffraction and shows clear patterns in response to the presence of X-ray fluorescence.
Abstract: We have developed a new kind of recoil ion momentum spectroscopy technique, using a precooled supersonic gas jet target, to determine state selective, scattering angle dependent cross sections for swift ion-atom collisions ( $0.25,\dots{},1\mathrm{MeV}{\mathrm{He}}^{2+}$ on He), by measuring the transverse and longitudinal momentum of the recoil ion. A longitudinal momentum resolution of $\ifmmode\pm\else\textpm\fi{}0.13\mathrm{a}.\mathrm{u}.$ was achieved, about a factor of 30 better than ever obtained before, which enables a clear separation of K and L shell capture. In the transverse direction a resolution corresponding to a projectile scattering angle uncertainty of $\ensuremath{\Delta}{\ensuremath{\vartheta}}_{P}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}\ifmmode\pm\else\textpm\fi{}1\ensuremath{\mu}\mathrm{rad}$ was obtained.
TL;DR: First measurements of the fast confined $\ensuremath{\alpha}$-particle energy distribution in a fusion plasma are reported, and stochastic ripple effects are responsible for steepening the energy distribution outside the plasma core.
Abstract: This Letter reports the first measurements of the fast confined $\ensuremath{\alpha}$-particle energy distribution in a fusion plasma. The pellet charge exchange technique shows the fusion generated $\ensuremath{\alpha}$'s in the core of the Tokamak Fusion Test Reactor plasma slow down classically, and appear to be well confined. Preliminary indications are that stochastic ripple effects are responsible for steepening the energy distribution outside the plasma core $(r/a\ensuremath{\gtrsim}0.35)$. Sawteeth mixing of fast $\ensuremath{\alpha}$'s is suggested in data during the post-beam-heating plasma decay.
TL;DR: In this paper, a constitutive model for creep that incorporates reinforcement spacing for creeping fibers in a creeping matrix was found to describe the creep behaviour of the eutectic, i.e. ∈αλ withm = 1.09 μm.
Abstract: The high temperature deformation behaviour of MoSi2-Mo5Si3 eutectics has been investigated as a function of lamellar spacing over the temperature range 1100–1400°C and strain rates (∈) of 1 × 10−4 to 1 × 10−6 s−1. Specimens with lamellar morphologies were produced by directional solidification using the Czochralski method at pull rates of 25–210 mm/h giving lamellar spacings (λ) of 2.6 to 1.09 μm. The measured flow stress was found to increase as the lamellar spacing decreased for a given strain rate. A constitutive model for creep that incorporates reinforcement spacing for creeping fibers in a creeping matrix was found to describe the creep behaviour of the eutectic, i.e. ∈αλ withm = 1. Creep deformation of the eutectic was controlled by ½〈110〉 (001) partial dislocations in the Mo5Si3 phase. The creep behaviour of a [314] oriented Mo5Si3 single crystal was also investigated.
TL;DR: In this paper, the authors present a formulation of the stability problem for a rectangular composite plate reinforced by two types of fibers, one of them being both stiffer and more expensive than the other.
TL;DR: In this paper, a numerical model of the acoustic radiated field from a turbofan engine inlet in the presence of a mean flow has been constructed with conventional finite elements in near field and wave envelope elements in far field.
Abstract: Improvements have been made in the finite element model of the acoustic radiated field from a turbofan engine inlet in the presence of a mean flow. The problem of acoustic radiation from a turbofan engine inlet is difficult to model numerically because of the large domain and high frequencies involved. A numerical model with conventional finite elements in the near field and wave envelope elements in the far field has been constructed. By employing an irrotational mean flow assumption, both the mean flow and the acoustic perturbation problem have been posed in an axisymmetric formulation in terms of the velocity potential; thereby minimizing computer storage and time requirements. The finite element mesh has been altered in search of an improved solution. The mean flow problem has been reformulated with new boundary conditions to make it theoretically rigorous. The sound source at the fan face has been modeled as a combination of positive and negative propagating duct eigenfunctions. Therefore, a finite element duct eigenvalue problem has been solved on the fan face and the resulting modal matrix has been used to implement a source boundary condition on the fan face in the acoustic radiation problem. In the post processing of the solution, the acoustic pressure has been evaluated at Gauss points inside the elements and the nodal pressure values have been interpolated from them. This has significantly improved the results. The effect of the geometric position of the transition circle between conventional finite elements and wave envelope elements has been studied and it has been found that the transition can be made nearer to the inlet than previously assumed.
01 Jan 1995
TL;DR: The overall polarity of 22 chiral stationary phases used in capillary open tubular gas chromatography columns was estimated using the first five Rohrschneider-McReynolds constants and their average values and it was found that the derivatized cyclodextrin CSP polarity increased with the CD ring size.
Abstract: The overall polarity of 22 chiral stationary phases (CSPs) used in capillary open tubular gas chromatography columns was estimated using the first five Rohrschneider-McReynolds constants. Most of the columns (i.e., 18) were wall-coated, and four were of the wall-immobilized or of the so-called "bonded" type. A wall-coated capillary squalane column was specially prepared as a polarity reference column. All but two of the CSPs were based on derivatized cyclodextrins (CDs) of different sizes. The overall properties of the CSPs are discussed in terms of the five Rohrschneider-McReynolds constants and their average values. It was found that the derivatized cyclodextrin CSP polarity increased with the CD ring size. The bonded CSPs were significantly less polar than their coated homologues due to the apolar polymer used to immobilize the CD rings. The retention behavior of 14 compounds was studied at 100 degrees C on the capillary columns. Retention parameters are clearly related to the McReynolds constants. Conversely, the enantiomeric resolution capability of a given stationary phase is not related to the constants. The enantioselective resolution mechanism critically depends on the solute structure and on the nature of the CSP.