Showing papers by "Missouri University of Science and Technology published in 1985"

Optical properties of fourteen metals in the infrared and far infrared: Al, Co, Cu, Au, Fe, Pb, Mo, Ni, Pd, Pt, Ag, Ti, V, and W.

Abstract: Infrared optical constants collected from the literature are tabulated for Mo and V. New data are presented for Cu, Fe, and Ni. Drude model parameters ωτ and ωp are given for the fourteen metals Al, Co, Cu, Au, Fe, Pb, Mo, Ni, Pd, Pt, Ag, Ti, V, and W. The Drude model parameters for Cu are revised from our earlier tabulation due to the availability of additional data. Refinements in our fitting technique have resulted in only slight changes in the Drude model parameters for Al, Au, Ag, and W. The Drude model parameters for Pb correct a numerical error in our earlier tabulation. For all fourteen metals, the optical resistivity has been calculated from the Drude model parameters ωτ and ωp and compared to handbook values for the dc resistivity.

An analysis of the lyophilization process using a sorption-sublimation model and various operational policies

Abstract: The freeze-drying process is studied under various operational policies through the use of a sorption-sublimation model. The operational policy that provides the shortest drying times keeps the pressure at its lowest value. The upper and lower heating plates are independently controlled so that the material constraints are encountered and held throughout the free water removal phase. Under certain conditions, and for the case of samples of small thickness, the sorbed water profiles may have segments whose bound water concentrations are higher than those at the start of the free water removal phase. It is shown that the criterion used in terminating the freeze-drying process is of extreme importance, since it may lead to an undesirable sorbed water profile which may deteriorate the quality of the dried product.

Magnesium-doped lithium niobate for higher optical power applications

Abstract: Compositions of lithium niobate containing 4.5 at.% or more MgO have the ability to transmit, without distortion, light 100 times as intense as undopecl compositions. Holographic diffraction measurements of photorefraction have demonstrated that the improved performance is due to a hundredfold increase in the photoconductivity, rather than to a decrease in the Glass current. The damage-resistant compositions are also distinguished by a thermal activation energy of 0.1 eV for the diffraction efficiency, an OH-stretch vibration at 2.83 Am, a lattice phonon absorption at 21.2 Am, an electron spin resonance signal for Fe impurities at 1500 G, and, after reduction by heating in a vacuum, an optical absorption band at 1.2 um. (The corresponding values for undopedl LiNbO3 are 0.5 eV, 2.87 um, 21.8 um, 790 G, and 0.5 um, respectively.) The high photoconductivity is thus related to a distinctive electronic environment for impurities in the damage-resistant crystals. The photoconductivity strongly affects the impedance and time constants of signal processing devices made of LiNbO3.

Opportunistic scheduling for robotic assembly

Abstract: Impressive strides have been made in dealing with the spatial complexity of robotic assembly tasks. Unfortunately, advances in dealing with temporal complexity have not kept pace. It is proposed that one reason for this deficiency is the unnecessary confounding of planning and scheduling. These two activities are differentiated on the basis of knowledge required/knowledge available at robot programming time. It is suggested that giving the robot the ability to reason opportunistically over knowledge of part availability at run time is a practical, efficient way to streamline assembly tasks. Initial experimental results are presented to substantiate this conclusion.

Structure‐Property Relations in Lanthanide Borate Glasses

Abstract: Glass formation in the system Ln2O3-B2O3 (Ln = Nd, Sm) was studied. Glasses could be formed in the range from 0 to 28 mol pct rare-earth oxide (Ln2O3), but liquid immiscibility in these systems limits the range of homogeneous glasses to 0 to 1.5 and 25 to 28 mol pct Ln2O3. The infrared spectra indicate that the rare-earth-rich glasses are structurally similar to rare-earth metaborates (LnB3O6) which contain (B3O6)-infinity chains. The variation in density, transformation temperature, thermal expansion coefficient, and transformation-range viscosity of these glasses with the size of the rare-earth ion is discussed. Glasses near the metaborate composition have a transformation temperature of about 700 C, which is high for binary borate glasses. Glasses could not be formed in the systems Eu2O3-, Gd2O3-, Ho2O3-, and Er2O3-B2O3, even by quenching at 1300 C/s. The sudden lack of glass formation in the system Ln2O3-B2O3 with Ln(3+) ions smaller than Sm(3+) is explained on the basis of the size effect of the Ln(3+) ion on the stability of (B3O6)-infinity chains in these metaborates.

Plasma polymerization investigated by the substrate temperature dependence

Abstract: Plasma polymerization of tetra fluoroethylene (TFE), perfluoro-2-butyl-tetrahydrofuran (PFBTHF), ethylene, and styrene were investigated in various combinations of monomer flow rates and discharge wattages for the substrate temperature range of −50 to 80°C. The polymer deposition rates can be generally expressed by k0 = Ae−bt, where k0 is the specific deposition rate given by k0 = (deposition rate)/(mass flow rate of monomer), A is the preexponential factor representing the extrapolated value of k0 at zero absolute temperature, and b is the temperature-dependence coefficient. It was found that the value of b is not dependent on the condensibility of monomer but depends largely on the group of monomer; that is, perfluorocarbons versus hydrocarbons. The values of A are dependent on domains of plasma polymerization. In the energy deficient region A is given by A = α(W/FM)n, where α is the proportionality constant, W is discharge wattage, FM is the mass flow rate, and n is close to unity. In the monomer deficient region A becomes a constant. The kinetic equation is discussed in view of the bicyclic rapid step-growth polymerization mechanisms.

Tests for an Increasing Trend in the Intensity of a Poisson Process: A Power Study

Abstract: This article concerns a comparison of several tests for testing the hypothesis of a constant intensity against the alternative of an increasing intensity function in a nonhomogeneous Poisson process (NHPP). The study includes the well-known Laplace test statistic, the most powerful test for the shape parameter in a Poisson process with Weibull intensity, the likelihood ratio test against arbitrary NHPP alternatives, two nonparametric tests for trends based on Kendall's tau and Spearman's rho, and a test based on an F statistic. The powers of the tests are determined by Monte Carlo simulation against alternatives that are increasing at an exponential rate, a power rate (Weibull intensity), and a logarithmic rate. Alternatives that are step functions with one jump are also considered. In a few cases, the exact powers are also obtained analytically.

A polynomial time generator for minimal perfect hash functions

Abstract: A perfect hash function PHF is an injection F from a set W of M objects into the set consisting of the first N nonnegative integers where N g M. If N = M, then F is a minimal perfect hash function, MPHF. PHFs are useful for the compact storage and fast retrieval of frequently used objects such as reserved words in a programming language or commonly employed words in a natural language.The mincycle algorithm for finding PHFs executes with an expected time complexity that is polynomial in M and has been used successfully on sets of cardinality up to 512. Given three pseudorandom functions h0, h1, and h2, the mincycle algorithm searches for a function g such that F(w) = (h0(w) + g ° h1(w) + g ° h2(w)) mod N is a PHF.

Equations linking different sets of optical properties for nonmagnetic materials.

Abstract: Pour caracteriser les proprietes optiques des materiaux on utilise: l'indice de refraction complexe, la fonction dielectrique complexe, l'impedance complexe normalisee et la conductivite complexe. On presente les relations entre ces quatre quantites dans le modele de Drude pour les metaux

Effect of R3+ Ions on the Structure and Properties of Lanthanum Borate Glasses

Abstract: The present investigation of glass formation in the (mole percent) systems 25La2O3 (x)R2O3 (75-x)B2O3, where R = Al, Ga, and (25-x)La2O3 (x)Ln2O3 75B2O3, where Ln = Gd, Er, Y, notes that up to 25 mol pct Al2O3 or Ga2O3 can be substituted for B2O3, while no more than about 5 mol pct Ln2O3, substituted for La2O3, caused macro-phase separation. The substitution of either R2O3 or Ln2O3 in the lanthanum borate system changes the separation distance between adjacent B3O6 chains. The effect of this structural change on the molar volume, transformation temperature, thermal expansion coefficient, and transformation-range viscosity is discussed.

Dirac-delta function approximations to the scattering phase function

Abstract: Dirac-delta function approximations are used to represent the single scattering phase function of large spherical particles or voids. The phase function for a spherical particle or void can be represented by a series of Legendre polynomials; however, as the diameter is increased, forward scattering becomes dominant and the number of terms in the series becomes very large. A Dirac-delta function approximation consists of a Dirac-delta function in the forward direction plus a finite series of Legendre polynomials. The Dirac-delta function accounts for strong forward scattering. Particular attention is given to large ice spheres and spherical voids in ice. The Dirac-delta function is shown effective in reducing the number of terms needed to describe the phase function.

Internal material damping of polymer matrix composites under off-axis loading

Abstract: The objective of this paper is to determine theoretically the material damping of short fibre-reinforced polymer matrix composites. The major damping mechanism in such composites is the viscoelastic behaviour of the polymer matrix. The analysis was carried out by developing a finite-element program which is capable of evaluating the stress and strain distribution of short fibre composites under axial loading (see Fig. 1a). Using the concept of balance of force we can express the modulusE x along the loading direction as a function of the mechanical properties of the fibre and matrix materials, fibre aspect ratio,l/d, loading angle,θ, and fibre volume fraction,V f. Then we apply the elastic-viscoelastic correspondence principle to replace all the mechanical properties of the composite, fibre and matrix materials such asE x,E f,E m,G m, by the corresponding complex moduli such asE x ′ +iE x ″ , andE f ′ +iE f ″ . After separation of the real and imaginary parts, we can expressE ' x/t' andE x t" as functions of the fibre aspect ratio,l/d, loading angle,θ, stiffness ratio,E f/E m, fibre volume fraction,V f, and damping properties of the fibre and matrix materials such asη f andη m. Numerical results of the composite storage modulus,E x ′ , loss modulus,E x ″ , and loss factor (damping),η C, are plotted as functions of parameters such asl/d,θ,V f, and are discussed in terms of variations ofl/d,θ, andE f/E m, in detail. It is observed that for a given composite, there exist optimum values ofl/d andθ at whichE x ″ andη c are maximized. The results of this paper can be used to optimize the performance of composite structures.

Experimental study of the interaction of multiple jets with a cross flow

Abstract: This paper discusses the results from an experimental study of twin jets injected normal to a cross flow at a jet:cross-flow velocity ratio of 2. Turbulence data from hot-wire anemometry are presented and comparison is made with single-jet data of the present and earlier studies. The profiles of mean velocities and Reynolds stresses for the single and tandem jets show very similar behavior, indicating that the turbulent nature of the jet/s is caused by the same mechanism/s for both configurations.

Contributions to the Finite Element Solution of the Fan Noise Radiation Problem

Abstract: The radiation of fan generated noise to the far field from a nacelle of realistic geometry is investigated using the finite element method. Several innovations have been introduced to minimize the computational requirements and create a highly efficient numerical scheme. The innovations include: (1) formulation of the problem in terms of velocity potential and density in such a way that no inlet mean flow velocity derivatives are required in the field equations, (2) the use of 'wave envelope' elements in an outer region permitting a grid much coarser than would be used for conventional finite elements, (3) the use of a mesh which deforms with an increase of forward flight speed so that mesh lines are always lines of constant phase and rays for a point source, permitting the use of wave envelope elements and simple boundary conditions for any case of forward velocity, (4) an efficient scheme for introducing the noise source via modal amplitude coefficients, and (5) the use of a frontal solution technique which for physically realistic problems drastically reduces the active storage requirements. The finite element scheme is outlined, as are the specific details of the innovations. Results are given for cases where comparable experimental data are available.

Coupling the circuit equations to the non-linear time dependent field solution in inverter driven induction motors

Abstract: The conventional way of analysing electric machinery has been to impose currents or current densities, to calculate from them the electromagnetic field and from that the self and mutual inductances of the windings. Circuit equations using these inductances would give correct values for the currents in the windings. In this paper, the field and circuit equations are coupled, giving a time dependent set of nonlinear equations, the solution of which gives the magnetic vector potential at every point in the cross section of the machine and the electric field intensity at the cross section of the conductors. The method is of particular interest when the harmonic content of the excitation is large, prohibiting the calculation of permeability of iron from only the fundamental.

Two-Dimensional Linearly Anisotropic Scattering in a Finite-Thick Cylindrical Medium Exposed to a Laser Beam

Abstract: Integro-differential equations are developed for the source function, flux and intensity at the boundaries of a two-dimensional finite-thick medium which scatters in a linear fashion. The incident radiation is collimated, normal to the upper surface of the medium and dependent only on the radial coordinate. Two radial distributions are investigated: (1) a Bessel function and (2) a Gaussian laser beam. The solution for the Gaussian beam is constructed from the Bessel solution. Numerical results are presented in graphical and tabular forms for both boundary conditions. Comparisons are made between forward and isotropic scattering and between the finite and semi-infinite cases.

Use of indicator variograms for an enhanced spatial analysis

Abstract: Flat variograms often are interpreted as representing a lack of spatial autocorrelation. Recent research in earthquake engineering shows that nearby field noise can substantially mask a prominent spatial autocorrelation and result in what appears to be a purely random spatial process. A careful selection of threshold in assigning an indicator function can yield an indicator variogram which reveals underlying spatial autocorrelation. Although this application involves use of seismic data, the results are relevant to geostatistical applications in general.