Showing papers by "Missouri University of Science and Technology published in 1988"

Accelerating the convergence of the back-propagation method

Abstract: The utility of the back-propagation method in establishing suitable weights in a distributed adaptive network has been demonstrated repeatedly. Unfortunately, in many applications, the number of iterations required before convergence can be large. Modifications to the back-propagation algorithm described by Rumelhart et al. (1986) can greatly accelerate convergence. The modifications consist of three changes:1) instead of updating the network weights after each pattern is presented to the network, the network is updated only after the entire repertoire of patterns to be learned has been presented to the network, at which time the algebraic sums of all the weight changes are applied:2) instead of keeping ź, the "learning rate" (i.e., the multiplier on the step size) constant, it is varied dynamically so that the algorithm utilizes a near-optimum ź, as determined by the local optimization topography; and3) the momentum factor ź is set to zero when, as signified by a failure of a step to reduce the total error, the information inherent in prior steps is more likely to be misleading than beneficial. Only after the network takes a useful step, i.e., one that reduces the total error, does ź again assume a non-zero value. Considering the selection of weights in neural nets as a problem in classical nonlinear optimization theory, the rationale for algorithms seeking only those weights that produce the globally minimum error is reviewed and rejected.

Optical properties of Al, Fe, Ti, Ta, W, and Mo at submillimeter wavelengths.

Abstract: Measurements of the optical constants of metals at submillimeter wavelengths are sparse. We have used a nonresonant cavity to measure, at room temperature, the angle averaged absorptance spectra P(omega) of aluminum, molybdenum, tantalum, titanium, tungsten, and iron in the 30-300-cm(-1) wavenumber region. The real part of the normalized surface impedance spectrum, z(omega) = r(omega) + ix(omega), was determined from P(omega). Measurements were also made on iron from 400 to 4000 cm(-1) using standard reflectance techniques. The r(omega) spectrum was combined with previous measurements by others at higher frequencies and Kramers-Kronig analyses of the resultant combined r(omega) spectra provided epsilon(omega) = epsilon(1)(omega) + iepsilon(2)(omega) and N(omega) = n(omega) + ik(omega).

Mixed Convection in Stagnation Flows Adjacent to Vertical Surfaces

Abstract: Laminar mixed convection in two-dimensional stagnation flows around heated surfaces is analyzed for both cases of an arbitrary wall temperature and arbitrary surface heat flux variations. The two-dimensional Navier-Stokes equations and the energy equation governing the flow and thermal fields are reduced to a dimensionless form by appropriate transformations and the resulting system of ordinary differential equations is solved in the buoyancy assisting and opposing regions. Numerical results are obtained for the special cases for which locally similar solutions exist as a function of the buoyancy parameter. Local wall shear stress and heat transfer rates as well as velocity and temperature distributions are presented. It is found that the local Nusselt number and wall shear stress increase as the value of the buoyancy parameter increases in the buoyancy assisting flow region. A reverse flow region develops in the buoyancy opposing flow region, and dual solutions are found to exist in that flow regime for a certain range of the buoyancy parameter.

Self‐Serving Attributions for Performance in Naturalistic Settings: A Meta‐Analytic Review1

Abstract: The study of self-serving attributions in sports settings is fertile ground for testing the validity of self-serving attributional phenomena. This paper reports the results of a meta-analytic review of research examining self-serving attributions in the context of sports events. A total of 91 distinct hypothesis tests were located, comprising five dimensions of attribution: ability (N= 21), effort (N= 21), task difficulty (N= 21), luck (N= 21), and a general internal-external dimension (N= 7). The meta-analytic combination of significance levels indicated that the combined results were unlikely to occur if the null hypothesis of no effect were true (for each of the five dimensions of attribution). The internal-external dimension and the ability dimension produced effects of moderate magnitude, whereas effort, difficulty and luck produced effects of small magnitude. Meta-anaiytic focused comparisons revealed that self-serving attributions (ended to be more extreme in the context of larger team sizes, and for attribution measures focused upon the team rather than the individual. Discussion considers the implications of these findings and develops and explanation for the finding that ability is the specific attribution dimension exhibiting the greatest self-serving attribution effects.

A study of surface dynamics of polymers. II. Investigation by plasma surface implantation of fluorine–containing moieties

Abstract: Macromolecules at the surface of a polymeric solid have considerable mobility, and the specific arrangement of functional groups of macromolecules at the surface is dictated by the environmental conditions in which the surface is placed. Consequently, the change of environmental conditions, such as immersion in water or placement in a biological surrounding, could cause a cosiderable degree of change in the surface characteristics of a polymer from those evaluated in the laboratory against ambient air. The mobile nature of a polymer surface can be investigated by surface-implanting fluorine-containing moieties, mainly—CF3, by the plasma implantation technique and following the disappearance and reappearance of fluorine atoms on the surface. The disappearance rates (based on the immersion time in water at room temperature) of ESCA F1s signals, the decay rates of (advancing) contact angle of water, and the recovery of these values on heat treatment of water-immersed samples were measured as a function of crystallinity of polymer samples (at three levels of crystallinity) for poly(ethylene terephthalate) and nylon 6.

Surface energy of liquid copper and single-crystal sapphire and the wetting behavior of copper on sapphire

Abstract: The wetting behavior of liquid copper on sapphire is affected by the crystallographic orientation of the sapphire surface, the oxygen partial pressure, and the temperature. The influences of each of these conditions have been studied by the sessile drop technique over the oxygen partial pressure range 10-2-10-20 atm at temperatures of 1100 and 1250°C. The effect of oxygen partial pressure on the liquid copper surface energy follows the Gibbs-Langmuir law. The contact angle varies with the crystallographic orientation of the sapphire surface. This variation is more significant at higher oxygen partial pressures, but is eliminated at higher temperatures. The liquid copper surface energy was determined to be γlv = 1.757-3.3 x 10-4T(°C) J/m2. The solid surface energy of sapphire was estimated as γsv = 1.961-4.7x 10-4T(°C) J/m2, which applies only to the temperature range 927-2077°C.

Natural Convection Along Slender Vertical Cylinders With Variable Surface Temperature

Abstract: Natural convection in laminar boundary layers along slender vertical cylinders is analyzed for the situation in which the wall temperature T{sub w}(x) varies arbitrarily with the axial coordinate x. The governing boundary layer equations along with the boundary conditions are first cast into a dimensionless form by a nonsimilar transformation and the resulting system of equations is then solved by a finite difference method in conjunction with the cubic spline interpolation technique. As an example, numerical results were obtained for the case of T{sub w}(x) = T{infinity} + ax{sup n}, a power-law wall temperature variation. They cover Prandtl numbers of 0.1, 0.7, 7, and 100 over a wide range of values of the surface curvature parameter. Representative local Nusselt number as well as velocity and temperature profiles are presented. Correlation equations for the local and average Nusselt numbers are also given.

Blood compatibility of surfaces modified by plasma polymerization.

Abstract: Tubular blood-contacting polymeric materials were modified by plasma polymerization and evaluated in the baboon with respect to their capacity to induce both acute and chronic arterial thrombosis. Polymer surface composition was determined by electron spectroscopy for chemical analysis. Steady-state arterial thromboembolism was initiated by introducing tubular segments into chronic arteriovenous shunts. Rates of platelet destruction induced by the test materials were calculated from 111In-platelet survival measurements. Nine plasma polymers based on tetrafluoroethylene, hexafluoroethane, hexafluoroethane/H2, and methane, when deposited on silicone rubber, consumed platelets at rates ranging from 1.1-5.6 x 10(8) platelets/cm2-day. Since these values were near the lower detection limit for this test system, the plasma polymers were considered relatively nonthrombogenic. Acute thrombus formation was initiated by inserting expanded Teflon (Gore-Tex PTFE) vascular grafts into the shunt system. 111In-platelet deposition was measured by scintillation camera imaging over a 1-h exposure period. Standard PTFE grafts (10 cm x 4 mm i.d.) accumulated approximately 1 x 10(10) platelets over this interval. While modification of PTFE grafts with a plasma polymer based on hexafluoroethane/H2 did not alter graft surface morphology, platelet deposition was reduced by 87% as compared to the controls (p less than 0.001). We conclude that both the surface chemistry and texture of prosthetic materials influence thrombogenesis. The method of plasma polymerization may be useful for assessing the importance of these variables independently and, perhaps, for minimizing certain adverse blood-material interactions.

Oxygen bonding in nitrided sodium- and lithium-metaphosphate glasses

Abstract: Oxygen bonding in nitrided alkali metaphosphate glasses was characterized by X-ray photoelectron spectroscopy. Bridging-to-nonbridging oxygen ratios (BO/NBO) were determined from deconvoluted O1s spectra. As the nitrogen contents of the metaphosphate glasses increased, the BO/NBO ratios decreased. A mechanism based on the equal reactivity of bridging and nonbridging oxygens during the nitridation process is used to explain the observed trends in the oxygen bonding.

Fluid dynamics in bubble stirred ladles: Part I. experiments

Abstract: Air is supplied through a porous plug placed in the center axis of a cylindrical perspex-water model of a ladle. A Laser-Doppler system is employed to measure radial and axial mean and fluctuating velocities. Velocities in the two-phase bubbly region can also be determined. Velocities are measured near the bottom, half-way up, and near the free surface. It is shown that the bubbles contribute to production of turbulence. The ladle has recirculation zones near the bottom, where the mean velocities are very low. Close to the free surface the radial mean and turbulent velocities are high, promoting mass transfer through the interface. The present measured velocity profiles cannot be reduced to a single profile by employing similarity scaling.

Siderite formation in anoxic deep-sea sediments: A synergetic bacteria controlled process with improtant implications in paleomagnetism

Abstract: Recent work on magnetic properties of limestones has demonstrated that the mineral siderite can be very important in paleomagnetism, for two reasons. First, oxidation of siderite produces secondary (daughter) magnetic minerals (magnetite, maghemite, and hematite), either before, during, or after sampling. These daughter products can completely change the magnetic properties of limestone samples and if unrecognized may be one of the primary reasons why many paleomagnetic studies of limestones, especially Paleozoic limestones, are unsuccessful. Second, siderite in weakly magnetized rocks may indicate the potential for successful paleomagnetic results. Because the presence of siderite indicates that the primary magnetic carriers are still intact, appropriate demagnetization methods should yield successful results. We conclude that microenvironmental conditions in anoxic marine sediments may permit the formation of siderite from iron (II) produced during bacterial dissimilatory iron reduction.

The Behavior of Thin Walled Structures: Beams, Plates, and Shells

Abstract: 1. Equations of Linear Elasticity in Cartesian Coordinates.- 1.1 Stresses.- 1.2 Displacements.- 1.3 Strains.- 1.4 Isotropy and Its Elastic Constants.- 1.5 Equilibrium Equations.- 1.6 Stress-Strain Relations.- 1.7 Linear Strain-Displacement Relations.- 1.8 Compatibility Equations.- 1.9 Summary.- 1.10 References.- 1.11 Problems.- 2. Derivation of the Governing Equations for Beams and Rectangular Plates.- 2.1 Assumptions of Plate Theory.- 2.2 Derivation of the Equilibrium Equations for a Plate.- 2.3 Derivation of Plate Moment-Curvature Relations and Integrated Stress Resultant- Displacement Relations.- 2.4 Derivation of the Governing Equations for a Plate.- 2.5 Boundary Conditions.- 2.6 Stress Distribution within a Plate.- 2.7 References.- 2.8 Problems.- 3. Beams and Rods.- 3.1 General Remarks.- 3.2 Development of the Governing Equations.- 3.3 Solutions for the Beam Equation.- 3.4 Stresses in Beams - Rods - Columns.- 3.5 Example: Clamped-Clamped Beam with a Constant Lateral Load, q(x) = -q0.- 3.6 Example: Cantilevered Beam with a Uniform Lateral Load, q(x) = -q0.- 3.7 Example: Simply Supported Beam with a Uniform Load over Part of Its Length.- 3.8 Beam with an Abrupt Change in Stiffness.- 3.9 Beam Subjected to Concentrated Loads.- 3.10 Solutions by Green's Functions.- 3.11 Tapered Beam Solution Using Galerkin's Method.- 3.12 Problems.- 4. Solutions to Problems of Rectangular Plates.- 4.1 Some General Solutions to the Biharmonic Equation.- 4.2 Double Series Solution (Navier Solution).- 4.3 Single Series Solution (Method of M. Levy).- 4.4 Example of Plate with Edges Supported by Beams.- 4.5 Summary.- 4.6 References.- 4.7 Problems.- 5. Thermal Stresses in Plates.- 5.1 General Considerations.- 5.2 Derivation of the Governing Equations for a Thermoelastic Plate.- 5.3 Boundary Conditions.- 5.4 General Treatment of Plate Nonhomogeneous Boundary Conditions.- 5.5 Thermoelastic Effects on Beams.- 5.6 Self-Equilibration of Thermal Stresses.- 5.7 References.- 5.8 Problems.- 6. Circular Plates.- 6.1 Introduction.- 6.2 Derivation of the Governing Equations.- 6.3 Axially Symmetric Circular Plates.- 6.4 Solutions for Axially Symmetric Circular Plates.- 6.5 Circular Plate, Simply Supported at the Outer Edge, Subjected to a Uniform Lateral Loading, p0.- 6.6 Circular Plate, Clamped at the Outer Edge, Subjected to a Uniform Lateral Loading, p0.- 6.7 Annular Plate, Simply Supported at the Outer Edge, Subjected to a Stress Couple, M, at the Inner Boundary.- 6.8 Annular Plate, Simply Supported at the Outer Edge, Subjected to a Shear Resultant, Q0, at the Inner Boundary.- 6.9 General Remarks.- 6.10 Problems.- 7. Buckling of Columns and Plates.- 7.1 Derivation of the Plate Governing Equations for Buckling.- 7.2 Buckling of Columns Simply Supported at Each End.- 7.3 Column Buckling with Other Boundary Conditions.- 7.4 Buckling of Plates Simply Supported on All Four Edges.- 7.5 Buckling of Plates with Other Loads and Boundary Conditions.- 7.6 References.- 7.7 Problems.- 8. The Vibrations of Beams and Plates.- 8.1 Introduction.- 8.2 Natural Vibrations of Beams.- 8.3 Natural Vibrations of Plates.- 8.4 Forced Vibrations of Beams and Plates.- 8.5 References.- 8.6 Problems.- 9. Energy Methods in Beams, Columns and Plates.- 9.1 Introduction.- 9.2 Theorem of Minimum Potential Energy.- 9.3 Analysis of Beams Subjected to a Lateral Load.- 9.4 The Buckling of Columns.- 9.5 Vibration of Beams.- 9.6 Minimum Potential Energy for Rectangular Plates.- 9.7 The Buckling of a Plate under Uniaxial Load, Simply Supported on Three Sides, and Free on an Unloaded Edge.- 9.8 Functions to Assume in the Use of Minimum Potential Energy for Solving Beam, Column, and Plate Problems.- 9.9 Problems.- 10. Cylindrical Shells.- 10.1 Cylindrical Shells under General Loads.- 10.2 Circular Cylindrical Shells under Axially Symmetric Loads.- 10.3 Edge Load Solutions.- 10.4 A General Solution for Cylindrical Shells under Axially Symmetric Loads.- 10.5 Sample Solutions.- 10.6 Circular Cylindrical Shells under Asymmetric Loads.- 10.7 Shallow Shell Theory (Donnell'1. Equations of Linear Elasticity in Cartesian Coordinates.- 1.1 Stresses.- 1.2 Displacements.- 1.3 Strains.- 1.4 Isotropy and Its Elastic Constants.- 1.5 Equilibrium Equations.- 1.6 Stress-Strain Relations.- 1.7 Linear Strain-Displacement Relations.- 1.8 Compatibility Equations.- 1.9 Summary.- 1.10 References.- 1.11 Problems.- 2. Derivation of the Governing Equations for Beams and Rectangular Plates.- 2.1 Assumptions of Plate Theory.- 2.2 Derivation of the Equilibrium Equations for a Plate.- 2.3 Derivation of Plate Moment-Curvature Relations and Integrated Stress Resultant- Displacement Relations.- 2.4 Derivation of the Governing Equations for a Plate.- 2.5 Boundary Conditions.- 2.6 Stress Distribution within a Plate.- 2.7 References.- 2.8 Problems.- 3. Beams and Rods.- 3.1 General Remarks.- 3.2 Development of the Governing Equations.- 3.3 Solutions for the Beam Equation.- 3.4 Stresses in Beams - Rods - Columns.- 3.5 Example: Clamped-Clamped Beam with a Constant Lateral Load, q(x) = -q0.- 3.6 Example: Cantilevered Beam with a Uniform Lateral Load, q(x) = -q0.- 3.7 Example: Simply Supported Beam with a Uniform Load over Part of Its Length.- 3.8 Beam with an Abrupt Change in Stiffness.- 3.9 Beam Subjected to Concentrated Loads.- 3.10 Solutions by Green's Functions.- 3.11 Tapered Beam Solution Using Galerkin's Method.- 3.12 Problems.- 4. Solutions to Problems of Rectangular Plates.- 4.1 Some General Solutions to the Biharmonic Equation.- 4.2 Double Series Solution (Navier Solution).- 4.3 Single Series Solution (Method of M. Levy).- 4.4 Example of Plate with Edges Supported by Beams.- 4.5 Summary.- 4.6 References.- 4.7 Problems.- 5. Thermal Stresses in Plates.- 5.1 General Considerations.- 5.2 Derivation of the Governing Equations for a Thermoelastic Plate.- 5.3 Boundary Conditions.- 5.4 General Treatment of Plate Nonhomogeneous Boundary Conditions.- 5.5 Thermoelastic Effects on Beams.- 5.6 Self-Equilibration of Thermal Stresses.- 5.7 References.- 5.8 Problems.- 6. Circular Plates.- 6.1 Introduction.- 6.2 Derivation of the Governing Equations.- 6.3 Axially Symmetric Circular Plates.- 6.4 Solutions for Axially Symmetric Circular Plates.- 6.5 Circular Plate, Simply Supported at the Outer Edge, Subjected to a Uniform Lateral Loading, p0.- 6.6 Circular Plate, Clamped at the Outer Edge, Subjected to a Uniform Lateral Loading, p0.- 6.7 Annular Plate, Simply Supported at the Outer Edge, Subjected to a Stress Couple, M, at the Inner Boundary.- 6.8 Annular Plate, Simply Supported at the Outer Edge, Subjected to a Shear Resultant, Q0, at the Inner Boundary.- 6.9 General Remarks.- 6.10 Problems.- 7. Buckling of Columns and Plates.- 7.1 Derivation of the Plate Governing Equations for Buckling.- 7.2 Buckling of Columns Simply Supported at Each End.- 7.3 Column Buckling with Other Boundary Conditions.- 7.4 Buckling of Plates Simply Supported on All Four Edges.- 7.5 Buckling of Plates with Other Loads and Boundary Conditions.- 7.6 References.- 7.7 Problems.- 8. The Vibrations of Beams and Plates.- 8.1 Introduction.- 8.2 Natural Vibrations of Beams.- 8.3 Natural Vibrations of Plates.- 8.4 Forced Vibrations of Beams and Plates.- 8.5 References.- 8.6 Problems.- 9. Energy Methods in Beams, Columns and Plates.- 9.1 Introduction.- 9.2 Theorem of Minimum Potential Energy.- 9.3 Analysis of Beams Subjected to a Lateral Load.- 9.4 The Buckling of Columns.- 9.5 Vibration of Beams.- 9.6 Minimum Potential Energy for Rectangular Plates.- 9.7 The Buckling of a Plate under Uniaxial Load, Simply Supported on Three Sides, and Free on an Unloaded Edge.- 9.8 Functions to Assume in the Use of Minimum Potential Energy for Solving Beam, Column, and Plate Problems.- 9.9 Problems.- 10. Cylindrical Shells.- 10.1 Cylindrical Shells under General Loads.- 10.2 Circular Cylindrical Shells under Axially Symmetric Loads.- 10.3 Edge Load Solutions.- 10.4 A General Solution for Cylindrical Shells under Axially Symmetric Loads.- 10.5 Sample Solutions.- 10.6 Circular Cylindrical Shells under Asymmetric Loads.- 10.7 Shallow Shell Theory (Donnell's Equations).- 10.8 Inextensional Shell Theory.- 10.9 Membrane Shell Theory.- 10.10 Examples of Membrane Theory.- 10.11 References.- 10.12 Problems.- 11. Elastic Stability of Shells.- 11.1 Buckling of Isotropic Circular Cylindrical Shells under Axially Symmetric Axial Loads.- 11.2 Buckling of Isotropic Circular Cylindrical Shells under Axially Symmetric Axial Loads and an Internal Pressure.- 11.3 Buckling of Isotropic Circular Cylindrical Shells under Bending.- 11.4 Buckling of Isotropic Circular Cylindrical Shells under Lateral Pressures.- 11.5 Buckling of Isotropic Circular Cylindrical Shells in Torsion.- 11.6 Buckling of Isotropic Circular Cylindrical Shells under Combined Axial Loads and Bending Loads.- 11.7 Buckling of Isotropic Circular Cylindrical Shells under Combined Axial Load and Torsion.- 11.8 Buckling of Isotropic Circular Cylindrical Shells under Combined Bending and Torsion.- 11.9 Buckling of Isotropic Circular Cylindrical Shells under Combined Bending and Transverse Shear.- 11.10 Buckling of Isotropic Circular Cylindrical Shells under Combined Axial Compression, Bending and Torsion.- 11.11 Buckling of Isotropic Spherical Shells under External Pressure.- 11.12 Buckling of Anisotropic and Sandwich Cylindrical Shells.- 11.13 References.- 11.14 Problems.- 12. The Vibration of Cylindrical Shells.- 12.1 Governing Differential Equations for Natural Vibrations.- 12.2 Hamilton's Principle for Determining the Natural Vibrations of Cylindrical Shells.- 12.3 Reference.- Appendix 1. Properties of Useful Engineering Materials.- Appendix 2. Answers to Selected Problems.

Dynamic Timoshenko Beam‐Columns on Elastic Media

Abstract: Two approaches are used to derive differential equations, stiffness coefficients, and fixed‐end forces for the analysis of structural systems composed of Timoshenko beam‐columns that may be supported by an elastic foundation. The analysis is for the evaluation of the critical static axial load and buckling mode‐shapes of a structure with consideration of elastic media, bending, and shear deformations. The two approaches differ in terms of the assumed shear component of the static axial load on the cross section. The first approach is based on the assumption that the shear component of the axial load is calculated from the total slope, which consists of the bending and shear slope. In the second approach, the shear component of the axial load, however, is calculated only from the bending slope. Analytical expressions for a typical simple beam are derived to show the influence of a foundation parameter on the buckling modes. It is observed that the critical axial loads are significantly reduced when shear d...

Single-electron – removal processes in collisions of positrons and protons with helium at intermediate velocities

Abstract: Total cross sections for single ionization and charge transfer have been calculated using the classical-trajectory Monte Carlo (CTMC) technique for collisions of both positrons and protons with helium. Analysis of the classical trajectories has helped to explain the differences in the collision mechanisms responsible for the observed relative magnitudes of the positron and proton electron-removal cross sections. In the intermediate collision velocity range (1.5 a.u.lvl4.5 a.u.) it is found that because the positron is much smaller in mass than the proton, two dynamical effects occur leading to differences in their efficiency in electron removal. First, positrons are less likely to singly ionize helium than are protons since they possess less kinetic energy above the ionization threshold and accordingly there is a lower probability for ionization. Second, positrons are more likely to remove an electron from helium by charge transfer than are protons since they may be deflected by the target to large positive or negative scattering angles and be accelerated or decelerated to more readily momentum-vector match with an orbital electron. In the large-velocity regime (vg4.5 a.u.) positrons and protons are found to be equally likely to singly ionize helium, but positrons remain at least half an order of magnitude more likely to remove an electron by charge transfer.

Biospecific adsorption in fixed and periodic countercurrent beds.

Abstract: A mathematical model that describes the adsorption and wash stages of biospecific adsorption (affinity chromatography) in a packed column is presented. The model expressions account for film and pre diffusion mass transfer as well as for different mechanisms of interaction between the adsorbate(s) and the ligand. The model equations may be applicable to single and multi-component biospecific adsorption systems involving both monovalent and multivalent adsorbates. The results obtained from model simulations show that the breakthrough time of the adsorbate is significantly influenced by the rate of the interaction step between the adsorbate and the ligand. The results indicate that when short beds are employed, then the choice of ligand with respect to its rate of interaction with the adsorbate may be of paramount importance. In certain systems involving bivalent adsorbates, the adsorbate may be displaced from the one-site complex, reenter the flowing fluid stream, and increase the effluent adsorbate concentration above its inlet value. It is also shown that when a single column is divided into two beds operating in a periodic counter current mode, the ligand utilization can be almost four times higher than that obtained in a column of the same length operating in the fixed bed mode. The studies on the wash stage indicate that the reduction of the concentration of the contaminant to a specified low level may be accomplished for certain systems in a shorter time, if the direction of flow in the wash stage is opposite to that used in the adsorption stage. However, a larger amount of product will be lost, in general, when the direction of flow of the washing medium is opposite to that employed during the adsorption stage.

Centrifugal Partition Chromatography. I. General Features

Abstract: Centrifugal Partition Chromatography (CPC) is a variant of countercurrent chromatography (CCC). As in CCC, two immiscible liquids are used. The first liquid is the stationary phase, the second is the mobile phase. The liquid stationary phase is held in channels engraved in several polychlorotrifluoroethylene (PCTFE) plates. One hundred channels are engraved on each PCTFE plate. Four PCTFE plates are assembled together in a cartridge. Up to 12 cartridges (4800 channels) can be loaded in the rotor of a centrifuge. The centrifugal field, generated by the spinning rotor, holds the stationary phase sufficiently that a mobile phase can be pumped through it. This system is analyzed in detail. The stationary phase evolution versus time is studied. A complete derivation is made of the relationship linking system pressure to the spin and flow rate as well as to the physico-chemical properties of the two liquids, i.e., density and viscosity.

Steady state penetration of thermoviscoplastic targets

Abstract: Steady state thermomechanical deformations of a target hit by a rigid cylindrical penetrator with an ellipsoidal nose are studied. The material of the target is assumed to be thermally softening but strain and strain-rate hardening. Results computed and presented graphically include the pressure distribution on the nose of the penetrator, dependence of the axial resisting force upon the speed of the penetrator, and the variation of field quantities such as the temperature and strain-rate in the target. Computed results show that the ratio of the major to minor axes of the ellipsoidal nose has a significant effect on the deformations of the target particles in the vicinity of the penetrator nose.

Effect of Excess PbO on the Sintering Characteristics and Dielectric Properties of Pb(Mg1/3Nb2/3)O3–PbTiO3-Based Ceramics

Abstract: Additions of excess PbO to the perovskite Pb[(Mg1/3Nb2/3)0.92Ti0.08]O3 solid solution enhanced the formation of a liquid phase at 840°C, which served as a densification aid for the ceramics. The liquid phase allowed elimination of pores and promoted grain growth during sintering. With additions of 1 to 2 wt% excess PbO, densities in excess of 97% of theoretical were obtained at a sintering temperature of 950°C. The peak dielectric constants of the resulting ceramics were over 18 000 at 30°C and dissipation factors less than 1%. Additions of PbO in excess of 2 wt% resulted in inferior dielectric properties due mainly to the dilution of the ferroelectric phase.

Enantiomeric Separations in Chromatography

Abstract: I. INTRODUCTION The resolution of enantiomers (nonsuperimposable, mirror-image isomers) has traditionally been considered one of the more difficult problems in separation science. Enantiomers have identical physical and chemical properties in an isotropic environment except that they rotate the plane of polarized light in opposite directions. A mixture containing equal amounts of enantiomers is referred to as a racemic mixture. Neither racemic mixtures nor solutions of achiral compounds are able to rotate the plane of polarized light.

A study of surface dynamics of polymers. III. Surface dynamic stabilization by plasma polymerization

Abstract: As demonstrated in Part II of this series of studies, the hydrophobic character of CF4 plasma-treated Nylon 6 and poly(ethylene terephthalate) (PET) decay with time of water immersion, and the rate of decay can be used as a measure for the surface mobility of (substrate) polymers. The same method of using fluorine-containing moieties introduced by CF4 plasma treatment as surface labeling is applied to investigate the influence of a thin layer of plasma polymer of methane applied onto the surface of those polymers. An ultrathin layer of plasma polymer provides a barrier to the rotational and diffusional migration of the introduced chemical moieties from the surface into the bulk of the film. The influence of operational parameters of plasma polymerization on the surface dynamic stability are examined by measuring the decay rate constants for (subsequently) CF4 plasma-treated samples. The rate constant was found to decrease sharply with increasing value of plasma energy input manifested by J/kg monomer, and no decay was observed as the energy input reached a threshold value (about 6.5 GJ/kg for PET, about 7.0 GJ/kg for Nylon 6), indicating that unperturbable surfaces can be created by means of plasma polymerization.

Ultrathin coating of plasma polymer of methane applied on the surface of silicone contact lenses.

Abstract: Silicone rubber has great advantages as a contact lens material because of its very high oxygen permeability, softness, and excellent mechanical strength and durability. Practical application is hampered by inherent characteristics of elastomers, i.e., high tackiness and highly hydrophobic surface properties. By applying a thin layer, e.g., 5 nm, of plasma polymer of methane, it was found that all these disadvantages can be eliminated without sacrificing high oxygen permeation rate, e.g., less than 15% reduction. Optimization of operational parameters to achieve this task has been investigated. It was also found that under optimum conditions the coating withstood severe and repeated flexing of the contact lens.