Showing papers by "Missouri University of Science and Technology published in 1973"

Interval Estimation for the Two-parameter Double Exponential Distribution

Abstract: Confidence intervals based on the maximum likelihood estimators are given for the location and scale parameters of the Double Exponential distribution. These intervals are obtained by determining the distribution of the pivotal quantities ( – θ)/ and /σ. Exact distributions are determined for n = 3 and n = .5, and approximate distributions are provided for larger n. The asymptotic distributions are also given and the accluacy of these approximations are investigated. The powers of the associated tests of hypotheses are given and tolerance limits for the population are also provided. Some possible applications are indicated.

Cold-Formed Steel Members with Perforated Elements

Abstract: In cold-formed steel structural members, holes are sometimes provided in webs, or flanges, or both of beams and columns for duct work, piping, ease of handling, and for other purposes. The presence of such holes may result in a reduction in strength of individual component elements or the overall strength of the member, or in both. At present, only a limited amount of design information is available for relatively heavy steel sections with perforated elements; however, no provisions are included in the American Iron and Steel Institute specification for the design of cold-formed steel members with perforated elements. The structural behavior of cold-formed steel beams and columns with a single circular or square hole in the web or flange has been studied in this preliminary investigation. Design formulas subject to a limited scope have been developed from this study for possible determination of effective design width and load-carrying capacities.

Subcritical bifurcation of plane Poiseuille flow

Abstract: We apply the perturbation theory which was recently developed and justified by Joseph & Sattinger (1972) to determine the form of the time-periodic solutions which bifurcate from plane Poiseuille flow. The results a t lowest significant order seem to be in good agreement with those following from the formal perturbation method of Stuart (1960) as extended by Reynolds & Potter (1967). Given the numerical results of the present calculation, the rigorous theory guarantees that the only time-periodic solution which bifurcates from laminar Poiseuille flow is a two-dimensional wave. The wave which bifurcates at the lowest Reynolds number exists, but it is unstable when its amplitude is small. Solutions which escape the small domain of attraction of laminar Poiseuille flow snap through this unstable time-periodic solution with a small amplitude to solutions of larger amplitudes.

Magnetic properties of HoFe3

Abstract: The magnetic structure of HoFe3 has been determined by powder neutron diffraction techniques. The moments of the holmium and the iron atoms are colinear, ferrimagnetically coupled, and parallel to the basal plane of the hexagonal structure. X-ray diffraction of the powder, oriented in a magnetic field, has shown that the easy direction of magnetization is the b-axis. Molecular field coefficients and average exchange fields for holmium and iron atoms have been calculated from the thermal variation of the magnetization and the paramagnetic susceptibility. The interactions between iron atoms are strong whereas the holmium-holmium and holmium-iron interactions are weak.

Neutron diffraction study of the Th(Co 1-x Fe x ) 5 alloys

Abstract: We have studied the ordering of Fe atoms and the magnetic properties of Th(Co 1-x Fe x ) 5 alloys with the CaCu 5 - type structure. From the neutron diffraction analysis it is concluded that the larger Fe atoms prefer to occupy the site 3g whereas the smaller Co prefer to occupy the site 2c. The ordering between Fe and Co in these alloys is mainly determined by stearic considerations. The Curie temperatures are found to be sensitive to the type of heat treatment. Although the bulk anisotropy of the alloys up to x \leq 0.7 remains essentially unchanged, the coercivity decreases with increasing iron concentration. The possibility of disordered substitution of a Th atom by a pair of transition metal atoms and its role on the structural and magnetic properties is discussed.

Dynamic Matrix of Timoshenko Beam Columns

Abstract: This paper describes the dynamic behavior of general structural frameworks subjected to lateral time-dependent excitations and static axial loads. Different static axial loads may be applied to various members which are simultaneously subjected to lateral harmonic excitations applied as nodal forces, uniform and nonuniform loads, or foundation movements. All the matrix equations are expressed in nondimensional parameters representing various effects of rotary inertia, axial load, and shear and bending deformations. The individual parameter may be dropped when the appropriate effect is not considered. Consequently, the formulation and the computer program developed may be applied to various cases of dynamic response as bending deformation only; bending deformation and axial load; rotatory inertia, bending and shear deformations; rotatory inertia, bending and shear deformations, and axial loads; etc.

Two-Dimensional Radiative Equilibrium: A Semi-Infinite Medium Subjected to Cosine Varying Radiation

Abstract: Exact numerical solutions are presented for the radiative flux and emissive power at the boundary of a semi-infinite, two-dimensional, planar, absorbing-emitting, gray medium subjected to cosine-varying collimated and cosine-varying diffuse boundary radiation, respectively. The emissive power at the boundary due to the cosine varying collimated boundary condition is shown to be a generalized H -function which is analogous to the H -function of Chandrasekhar. The nonlinear integral equation of the Chandrasekhar type is developed for the generalized H -function and solved for a wide range of the parameters. The emissive power and radiative flux at the boundary for the cosine-varying diffuse model, as well as the radiative flux for the cosine-varying collimated model, are expressed in terms of the generalized H -function and solved numerically.

Transient Hydraulic Simulation of Breached Earth Dams

Abstract: A conceptual method to alleviate flood damages due to overtopping failures of future small earthfill dams is the incorporation of a relatively thin erosion retarding layer within the dam. This paper investigates the potential reduction in the reservoir release due to the proposed erosion retarding layer. The paper provides a method for the determination of an optimal location of the layer so as to minimize the maximum possible reservoir release due to a gradually breached earth dam. The transient reservoir flow is simulated by a numerical model, based upon the solution of the one-dimensional St. Venant unsteady open-channel flow equations. These equations are solved by the method of characteristics, with appropriate boundary conditions incorporated into the solution procedure. The numerical simulation model is used to determine the reduction in reservoir release due to a single retarding layer and its optimal location for a wide range of pertinent geometric, hydraulic and dynamic parameters.

Infrared absorption of small silicon particles with oxide overlayers

Abstract: The infrared optical absorption coefficient for spherical particles coated with a dielectric mantel and imbedded in a nonabsorbing dielectric medium has been predicted based on calculations of the average dielectric function. The theory represents an extension of the continuum, volume-averaging model of Genzel and Martin. The average dielectric function is calculated, and the consequences are considered for the case of Si-SiO2 dispersed in CsI. The average absorption coefficient is displayed for intrinsic and doped Si spheres with a range of oxide mantel thicknesses. The absorption spectra are seen to be dominated by the absorption of the SiO2, even for very thin layers. Structure is predicted in the average absorption coefficient between 1100 and 1300 cm−1 which has no counterpart in either SiO2 or Si (with or without free carriers). The structures, though different in origin, are reminiscent of the “antiresonance” and nearby high frequency strong absorption previously found only for surface plasmon-surface phonon interactions in small spheres. Der Infrarot-Absorptionskoeffizient von kugelformigen Teilchen mit dielektrischer Oberflachenschicht, eingebettet in einem nichtleitenden Dielektrikum, wird aus Berechnungen der gemittelten dielektrischen Funktion vorhergesagt. Diese Theorie stellt eine Erweiterung des Kontinuumsmodells mit Volumenmittelung von Genzel und Martin dar. Die mittlere dielektrische Funktion wird berechnet und das Ergebnis auf Si-SiO2, dispergiert in CsJ, angewandt. Der mittlere Absorptionskoeffizient fur reines und dotiertes Si wird fur verschiedene Dicken der Oxydschicht dargestellt. Es zeigt sich, das die SiO2-Absorption selbst fur sehr dunne Schichten das Absorptionsspektrum bestimmt. Zwischen 1100 und 1300 cm−1 wird eine Struktur im Absorptionskoeffizienten vorausgesagt, fur die sich weder bei SiO2 noch bei Si (mit oder ohne freie Ladungstrager) ein Gegenstuck findet. Die Strukturen erinnern, obgleich sie anderen Ursprungs sind, an die “Antiresonanz” und ihrer benachbarten hoherfrequenten starken Absorption, die kurzlich fur reine Oberflachenplasmon-Oberflachenphonon-Wechselwirkung in kleinen Kugeln gefunden wurden.

Oxidation of Tetragonal PbO in Air

Abstract: Isothermal oxidation of tetragonal PbO in air produced multiphase assemblages with apparent equilibrium compositions which varied linearly with temperature from PbO1.548 at 286°C to PbO1.333 at 351°C. Oxidation at each temperature was relatively rapid to PbO1.40 and very slow from PbO1.40 to apparent equilibrium values. Pseudocubic PbO1+x, with compositions between PbO1.41 and PbO1.57, was indexed on a cubic unit cell at the lower O/Pb ratios and on a tetragonal unit cell at the higher ratios. Linear changes in lattice parameters and deviation from cubic symmetry accompanied reversible oxidation and reduction of the phase. Pseudocubic PbO1+x was reduced irreversibly to Pb3O4 below the composition PbO1.41. Hexagonal PbO1+x, with compositions between PbO1.333 and PbO1.41, developed to a maximum of 60% at intermediate temperatures. The hexagonal phase oxidized irreversibly to pseudocubic PbO1+x at lower temperatures and reduced irreversibly to Pb3O4 at higher temperatures. The extent of oxidation at a given temperature was greater in PbO with a mean diameter of 0.52 μm than in PbO with a mean diameter of 2.89 μm, indicating a metastable assemblage. Linear variation of oxidation limits with temperature across the composition boundary between the PbO1+x phases suggests that the free energies are equal at PbO1.41, with the lower limit of pseudocubic PbO1+x determined by tolerance of the structure for oxygen vacancies.

Polynary silicon arsenic chalcogenide glasses with high softening temperatures

Abstract: The introduction of Ag in SiAsTe glasses permits the incorporation of Se, otherwise volatile and/or degradable as a constituent in Si-containing chalcogenide glasses. SiAsAgTeSe glasses exhibit much higher softening ranges and glass transition temperatures than encountered in known chalgogenide systems. A glass Si35As15Ag10Te20Se20 had the viscosity log ν = 13 at about 500°C, as compared to 370°C for the base glass Si35As25Te40, the viscosity of log ν = 9.8 at about 560°C, as compared to 442°C for the base glass. Phase separation occurs in the system SiAsAgTeSe and becomes manifest in two glass transitions indicated by changes in the slopes of the expansion curves and breaks in the softening point-composition relations. The existence and behavior SiAsAgTeSe glasses suggests the possible development of higher Tg i.r. transparencies and higher Tg semiconductor glasses than described so far.

Synthesis and characterization of poly(p‐phenylene pyromellitamic acid)

Abstract: Poly(p-phenylene pyromellitamic acid)s were synthesized over the weight-average molecular weight range 8,000 to 22,000. The polymers were recovered as amorphous powders composed of 3–4 × 1–2 μ platelets 0.1–0.2 μ thick containing 20–30% associated solvent. Consumption of reactants and attainment of the ultimate molecular weight of the polymer were found to occur within the first few minutes of reaction. The polymers were characterized by scanning electron microscopy; ultraviolet, visible, near-infrared, and infrared spectroscopy; x-ray analysis; viscometry; and light-scattering photometry. The intrinsic viscosity–molecular weight relation for the polymer in DMF was .

Emittance of Semi-Infinite Absorbing and Isotropically Scattering Medium with Refractive Index Greater Than Unity

Abstract: An approximate solution is presented for the integrodifferential equation that governs the radiant intensity and the source function within a semi-infinite absorbing-scattering medium with an index of refraction different from unity. The exponential kernel substitution has been used to develop a closed form analytical expression for the directional emittance as a function of the refractive index and the scattering albedo. The scattering has been considered as isotropic, and the Fresnel relations have been used to evaluate the reflection and the transmission at the interface. The directional and the hemispherical emittances are presented for a refractive index range between 1 and 2 and for scattering albedo between 0 and 1. The results indicate that the directional and hemispherical emittances of a medium with a refractive index larger than unity can be either smaller, because of interface reflection, or larger, because of scattering, than that associated with a medium of a unity index of refraction. A generalized graph is presented from which an approximate value for the directional emittance can be obtained for a wide range of optical conditions. Based on other applications in the field of radiative transfer with similar geometry and on comparison, when possible, with exact solutions, the approximate method which has been used should be accurate in predicting directional and hemispherical emittances to within 10%.

Some Evidence on the Value of Instructors in Teaching Economic Principles

Abstract: Using data collected from three universities, the authors of this article attempt to show that student attitude is “an important dimension of learning” and that the quality of instruction is indeed associated with attitude. The attitude referred to here is that of student opinions toward economics (as measured by Karstensson's “Questionnaire on Student Attitude Toward Economics”) rather than opinions on economic issues. Posttest scores on the TUCE and the attitude instrument were the dependent variables, while scores on the TUCE pretest, ACT scores, sex, major field, economics background, university attended, and quality of instruction were used as independent variables.

Absolute Differential Elastic- and Inelastic-Scattering Cross Sections in 25-140 keV He + + He Collisions

Abstract: Data obtained as energy-loss spectra at angles from 0 to 7.3\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}3}$ rad (c.m.) with typical energy-loss resolution of 0.7 eV and angular resolution of 2\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}3}$ rad (c.m.) were used to calculate average differential cross sections ${〈\frac{d\ensuremath{\sigma}}{d\ensuremath{\Omega}}〉}_{\mathrm{av}}$ for elastic scattering, direct excitation of the individual $\mathrm{He}(n=2)$ states, and direct excitation of the ${\mathrm{He}}^{+}(n=2)$ states. The total cross section for excitation of the $\mathrm{He}(n=2)$ states obtained by integrating the differential cross sections was found to be 20\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}18}$ ${\mathrm{cm}}^{2}$ at 25 keV (lab) decreasing to 7\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}18}$ ${\mathrm{cm}}^{2}$ at 140 keV. At incident lab energies below 100 keV the $\mathrm{He}(2^{2}S)$ and $\mathrm{He}(2^{3}P)$ states dominate the $\mathrm{He}(n=2)$ structure at angles close to zero, while the $\mathrm{He}(2^{1}P)$ state dominates at larger angles. The contribution of the $\mathrm{He}(2^{1}S)$ state remains below 25% at all angles and energies.

An Improved Single Flight Technique for Radar Stereo

Abstract: An improved technique for obtaining stereo radar image pairs is described. The technique uses a unique combination of two different radar beam pattern characteristics. The resulting stereo radar images are illuminated from very nearly the same aircraft position which results in radar shadow and backscatter characteristics which are very similar and in improved image registration possibilities. The reduction in illumination angle and aircraft position differences is shown to be nearly an order of magnitude or more when compared with a previously proposed single flight technique which used two vertical fan beam patterns at different azimuth angles. As a related sidelight it is shown that this previous technique requlres the two fan beam patterns to generate parallax on the images and thus can not be implemented with synthetic arrays squinted at two different squint angles.

Oxidation State Control of Volatile Species in Sintering

Abstract: The hinderance to sintering created by oxidation state changes which produce volatile phases is well known. The chromium-oxygen system provides an excellent example to illustrate the problems associated with these types of phase changes. Chromium sesquioxide is an attractive refractory material with three other oxides in the system as well as chromium metal having a considerable vapor pressure. Attempts to sinter chromium sesquioxide powders must include provisions for the stabilization of this phase if sintering to high density is to be successful.(1)

Drag Reduction of Solid-Liquid Suspensions in Pipe Flow

Abstract: WHEN the pressure drop of a fluid-additive system in conduit flow is less than that of the fluid alone at the same volumetric flow rate, drag reduction is said to occur.

On the effect of cesium in photoionization laser plasmas

Abstract: A number of photoionization mechanisms and how they can be used to generate large-volume laser plasmas are discussed. Reaction rates for two-step photoionization of the cesium atoms as well as formation of molecular ions (Cs 2 +) are estimated. The necessary cross-section data were obtained from related research in thermionic energy converters.

Radiative transfer through carbon ablation layers

Abstract: The composition, emittance, and transmittance of carbon plasmas have been calculated for temperatures of 3000 and 5000°K, thicknesses from 0.01 to 1.0 cm, and pressures from 0.1 to 10.0 atmospheres. The carbon plasmas are assumed to be isothermal and in local thermodynamic equilibrium. The radiation includes molecular bands, atomic lines, and continuum processes. The calculations consider molecular carbon molecules, atomic and singly ionized carbon atoms, and electrons. The emittance and transmittance results are applied to a simple model of the ablation layer in the stagnation shock layer for two cases: (1) Jupiter entry and (2) Earth entry. The results show that the molecular carbon bands are most effective in blocking the high-energy stagnation shock layer radiation when the ablation shock-layer temperature is low. For high ablation-layer temperatures, the photoionization process in atomic carbon becomes very effective in reducing the radiation to the vehicle.