Showing papers by "Lehigh University published in 1978"

Nonlinear Systems Analysis

Abstract: Introduction. Non-linear Differential Equations. Second-Order Systems. Approximate Analysis Methods. Lyapunov Stability. Input-Output Stability. Differential Geometric Methods. Appendices: Prevalence of Differential Equations with Unique Solutions, Proof of the Kalman-Yacubovitch Lemma and Proof of the Frobenius Theorem.

Mixed boundary value problems in mechanics

Abstract: Definitions in the case of multiple series equations and multiple integral equations are examined. In considering the solution of a given mixed boundary value problem perhaps the simplest technique is the direct application of the method of complex potentials provided the problem admits such potentials and the domain and the boundary conditions are suitable for such an application. The direct application of complex potentials is described with the aid of examples, taking into account a problem in potential theory, the case of periodic cuts, and an elasticity problem for a nonhomogeneous plane. The reduction to singular integral equations is discussed along with the numerical solution of singular integral equations of the first kind, integral equations with generalized Cauchy kernels, and singular integral equations of the second kind.

Segregation in Social Networks

Abstract: The intuitive literature on segregation is reviewed and a segregation measure, S, is constructed to embody existing intuitions. S measures segregation over a network of symmetrical social relations. Distributional problems are explored and two kinds of applications are illustrated.

Fracture Mechanics and Surface Chemistry Studies of Subcritical Crack Growth in AISI 4340 Steel.

Abstract: Coordinated fracture mechanics and surface chemistry experiments were carried out to develop further understanding of environment enhanced subcritical crack growth in high strength steels. The kinetics of crack growth were determined for an AISI 4340 steel (tempered at 204°C) in hydrogen and in water, and the kinetics for the reactions of water with the same steel were also determined. A regime of rate limited (Stage II) crack growth was observed in each of the environments. Stage II crack growth was found to be thermally activated, with an apparent activation energy of 14.7 ±2.9 kJ/mole for crack growth in hydrogen, and 33.5 ± 5.0 kJ/mole in water. Fractographic evidence indicated that the fracture path through the microstructure was the same for these environments, and suggested hydrogen to be the embrittling species for environment enhanced crack growth in hydrogen and in water/water vapor. A slow step in the surface reaction of water vapor with steel was identified, and exhibited an activation energy of 36 ± 14 kJ/ mole. This reaction step was identified to be that for the nucleation and growth of oxide. The hydrogen responsible for embrittlement was presumed to be produced during this reaction. On the basis of a comparison of the activation energies, in conjunction with other supporting data, this slow step in the water/metal surface reaction was unambiguously identified as the rate controlling process for crack growth in water/water vapor. The inhibiting effect of oxygen and the influence of water vapor pressure on environment enhanced subcritical crack growth were considered. The influence of segregation of alloying and residual impurity elements on crack growth was also considered.

Diffusion modeling of the carburization process

Abstract: Mathematical models have been developed for simulating the carburization process. One model simulates carburization in low alloy steels where temperature, time, surface carbon content, and diffusion coefficient vary during the process. Two step and vacuum carburization are among the treatments considered. The other model simulates the ef-fect of major ternary alloying additions such as Mn, Cr, Ni and Si during carburization. The importance of the off diagonal or cross diffusion coefficientD 12 3 on carbon diffusion is calculated. The Crank-Nicolson finite difference equations are used to provide numeri-cal stability and flexability. Calculated carbon profiles for low alloy steels were com-pared with experimental data available in the literature. Agreement between calculated and measured data was very good. Chromium and silicon have large cross coefficient ef-fects and it is predicted that they have a large influence on the amount of carburization which will occur. Experimental data for carburization treatments of Fe-C-Cr alloys are in excellent agreement with model predictions of major increases in effective surface carbon content and the formation of carbides in austenite at the carburization tempera-ture. These computer models are relatively easy to apply and can be used to design car-burization treatments for specific alloy steels.

Load and Resistance Factor Design Criteria for Connectors

Abstract: Design criteria based on the Load and Resistance Factor Design (LRFD) approach must include a treatment of connections. The nominal resistance and resistance factor terms for the principal structural steel fastening elements (welds, high-strength bolts, and ordinary bolts) are developed. Sufficient statistical information relative to the development is given so that a critical evaluation of the choices presented can be made. The work shows that current design values for different connectors provide substantially different levels of reliability.

Tensile, impact and fatigue behavior of an amine‐cured epoxy resin

Abstract: Although crosslinked networks are commonly used as adhesives and composite matrixes, structure-property relationships are not as well established as with thermoplastics. For this reason, an extensive study was begun to systematically examine effects of stoichiometry, morphology, and distribution of crosslink density on viscoelastic behavior and ultimate properties. The system selected was based on a bisphenol-A-type epoxy cured with methylene dianiline. This paper describes and discusses results obtained for resins in which the amine/epoxy ratio ranged between 0.7 and 2.2. In agreement with reports by others, the tensile strength, modulus, and ultimate elongation were relatively insensitive to stoichiometry but did not show slight maxima or minima when the amine was somewhat in excess. Impact strengths, tensile energies-to-break and fracture toughness were, in contrast, quite sensitive, though the patterns of each differed significantly. Both fracture toughness and the stress intensity factor required to drive the crack at a given rate varied directly with the amine/epoxy ratio, as did estimates of the characteristic flaw size. Fatigue striations were observed on the fracture surfaces and corresponded to the incremental advance of the crack in one loading cycle.

Electronic energy-band structure of α quartz

Abstract: The electronic energy bands of silicon dioxide in the $\ensuremath{\alpha}$-quartz structure have been calculated at several p\^oints of high symmetry in the Brillouin zone by the mixed-basis method. A tight-binding interpolation scheme has been used to determine complete valence bands and their state densities. The results are compared with experiment and with calculations on the higher-symmetry $\ensuremath{\beta}$-cristobalite. The quartz and cristobalite bands share many properties; for example, in both cases the optical-absorption edge is predicted to be direct but forbidden. These results are in partial agreement with pseudopotential calculations by Chelikowsky and Schluter (CS). The major disagreements are that CS predict an indirect absorption edge, and their conduction bands are much wider than ours. Possible reasons for these disagreements are suggested.

Technical aspects of the rheological properties of microbial cultures

Abstract: The rheological properties of culture fluids have a profound effect on the course of a fermentation, the response and reliability of sensors, and on the difficulty of recovery processes. In addition, the rheological properties can be sensitive indicators of the state of a fermentation and can be useful for purposes of control and monitoring. In this paper the fundamentals and important nomenclature of rheology are introduced, the merits of various experimental methods for measuring rheological properties are discussed, critical evaluations are presented of past studies of the rheological properties of culture fluids and the effects of these properties, and suggestions are made for further investigation and development.

The Role of Lysosomal Hydrolases in Molluscan Cellular Response to Immunologic Challenge

Abstract: Although considerable new information has been contributed in recent years to our knowledge of the biochemistry and physiology of phagocytosis by invertebrate hemocytes, especially those of insects and molluscs (see Cheng, 1975, and Anderson, 1977, for reviews), little new information has been contributed to our understanding of what is generally considered a second type of cellular reaction in molluscs to invading nonself materials, i. e., encapsulation or granuloma formation. Since the comprehensive review of what is known about this process and related phenomena in molluscs by Cheng and Rifkin (1970), new inf ormat ion has been contributed only by Harris and Cheng (1975a,b), Harris (1975), Rachford (1976), Krupa et al. (1977), Cheng and Garrabrant (1977), and Cheng (1978).

A Thick-Walled Cylinder With an Axisymmetric Internal or Edge Crack

Abstract: The paper considers the elastostatic axisymmetric problem for a long thick-walled cylinder containing a ring-shaped internal or edge crack. Using the standard transform technique the problem is formulated in terms of an integral equation which has a simple Cauchy kernel for the internal crack and a generalized Cauchy kernel for the edge crack as the dominant part. As examples the uniform axial load and the steady-state thermal stress problems have been solved and the related stress-intensity factors have been calculated. Among other findings the results show that in the cylinder under uniform axial stress containing an internal crack the stress-intensity factor at the inner tip is always greater than that at the outer tip for equal net ligament thicknesses and in the cylinder with an edge crack which is under a state of thermal stress the stress-intensity factor is a decreasing function of the crack depth, tending to zero as the crack depth approaches the wall thickness.

Age-at-acquisition and word recognition

Abstract: Recent investigations have shown that the latency in object naming is affected by when in life the naming word is learned—the age-at-acquisition of the naming word. The present study investigated the effect of age-at-acquisition in the recognition of tachistoscopically presented words. It was found that, with word frequency controlled, words judged to be of early acquisition had a significantly lower recognition threshold than words judged to be of later acquisition.

The influence of vibration on Poiseuille flow of a non-Newtonian fluid, I.

Abstract: Manero and Mena (1) have published experiments in which a non-Newtonian fluid flows through a tube of circular cross-section under a uniform time-independent pressure head, the tube being simultaneously vibrated sinusoidally in the longitudinal direction. They found that the effect of the vibration is to produce an increase in the mean rate of discharge of fluid through the tube. This increase in the rate of discharge depends on the frequency and amplitude of the vibration and may be many times that which exists in the absence of a superposed vibration.

An analysis of flow separation in hydrodynamic chromatography of polymer latexes

Abstract: An analysis is presented for the flow separation process in hydrodynamic chromatography along with comparisons to experimental data. The flow separation model is based on calculations for the convected Brownian motion of colloidal particles in a capillary tube in the presence of a force field. The results indicate the role of the relevant experimental parameters in the separation process.

Fatigue crack propagation in polyacetal

Abstract: The fatigue crack propagation characteristics of a typical commercial homopolymer and copolymer polyacetal were determined. These materials were found to be the most fatigue resistant plastics examined to date, thus confirming the generally high fatigue resistance of all crystalline polymers. A discontinuous fatigue cracking process was identified at all test frequencies in the acetal copolymer and at high frequencies in the homopolymer, while continuous crack propagation occurred at low test frequencies in the homopolymer. The discrete advance increments of the crack in the discontinuous mode were equal to the dimension of the prevailing crack-tip plastic zone. On a more local scale, the crack path is seen to be mainly trans-spherulitic in nature.

Flux pinning by grain boundaries in niobium bicrystals

Abstract: Bicrystals of niobium with symmetric tilt boundaries grown directly from the melt with bicrystal seeds have been used as a model system to measure the resistive critical current Ic as a function of...