Showing papers by "Rensselaer Polytechnic Institute published in 1981"

Introduction to Polymers

Abstract: CONCEPTS, NOMENCLATURE AND SYNTHESIS OF POLYMERS Concepts and Nomenclature The Origins of Polymer Science and the Polymer Industry Basic Definitions and Nomenclature Molar Mass and Degree of Polymerization Principles of Polymerization Introduction Classification of Polymerization Reactions Monomer Functionality and Polymer Skeletal Structure Functional Group Reactivity and Molecular Size: The Principle of Equal Reactivity Step Polymerization Introduction Linear Step Polymerization Non-Linear Step Polymerization Radical Polymerization Introduction to Radical Polymerization The Chemistry of Conventional Free-Radical Polymerization Kinetics of Conventional Free-Radical Polymerization Free-Radical Polymerization Processes Reversible-Deactivation ('Living') Radical Polymerizations Non-Linear Radical Polymerizations Ionic Polymerization Introduction to Ionic Polymerization Cationic Polymerization Anionic Polymerization Group-Transfer Polymerization Stereochemistry and Coordination Polymerization Introduction to Stereochemistry of Polymerization Tacticity of Polymers Geometric Isomerism in Polymers Prepared from Conjugated Dienes Ziegler-Natta Coordination Polymerization Metallocene Coordination Polymerization Ring-Opening Polymerization Introduction to Ring-Opening Polymerization Cationic Ring-Opening Polymerization Anionic Ring-Opening Polymerization Free-Radical Ring-Opening Polymerization Ring-Opening Metathesis Polymerization Specialized Methods of Polymer Synthesis Introduction Solid-State Topochemical Polymerization Polymerization by Oxidative Coupling Precursor Routes to Intractable Polymers Supramolecular Polymerization (Polyassociation) Copolymerization Introduction Step Copolymerization Chain Copolymerization Block Copolymer Synthesis Graft Copolymer Synthesis CHARACTERIZATION OF POLYMERS Theoretical Description of Polymers in Solution Introduction Thermodynamics of Polymer Solutions Chain Dimensions Frictional Properties of Polymer Molecules in Dilute Solution Number-Average Molar Mass Introduction to Measurements of Number-Average Molar Mass Membrane Osmometry Vapour Pressure Osmometry Ebulliometry and Cryoscopy End-Group Analysis Effects of Low Molar Mass Impurities upon Mn Scattering Methods Introduction Static Light Scattering Dynamic Light Scattering Small-Angle X-Ray and Neutron Scattering Frictional Properties of Polymers in Solution Introduction Dilute Solution Viscometry Ultracentrifugation Molar Mass Distribution Introduction Fractionation Gel Permeation Chromatography Field-Flow Fractionation Mass Spectroscopy Chemical Composition and Molecular Microstructure Introduction Principles of Spectroscopy Ultraviolet and Visible Light Absorption Spectroscopy Infrared Spectroscopy Raman Spectroscopy Nuclear Magnetic Resonance Spectroscopy Mass Spectroscopy PHASE STRUCTURE AND MORPHOLOGY OF BULK POLYMERS The Amorphous State Introduction The Glass Transition Factors Controlling the Tg Macromolecular Dynamics The Crystalline State Introduction Determination of Crystal Structure Polymer Single Crystals Semi-Crystalline Polymers Liquid Crystalline Polymers Defects in Crystalline Polymers Crystallization Melting Multicomponent Polymer Systems Introduction Polymer Blends Block Copolymers PROPERTIES OF BULK POLYMERS Elastic Deformation Introduction Elastic Deformation Elastic Deformation of Polymers Viscoelasticity Introduction Viscoelastic Mechanical Models Boltzmann Superposition Principle Dynamic Mechanical Testing Frequency Dependence of Viscoelastic Behaviour Transitions and Polymer Structure Time-Temperature Superposition Effect of Entanglements Non-Linear Viscoelasticity Elastomers Introduction Thermodynamics of Elastomer Deformation Statistical Theory of Elastomer Deformation Stress-Strain Behaviour of Elastomers Factors Affecting Mechanical Behaviour Yield and Crazing Introduction Phenomenology of Yield Yield Criteria Deformation Mechanisms Crazing Fracture and Toughening Introduction Fundamentals of Fracture Mechanics of Fracture Fracture Phenomena Toughened Polymers Polymer Composites Introduction to Composite Materials Matrix Materials Types of Reinforcement Composite Composition Particulate Reinforcement Fibre Reinforcement Nanocomposites Electrical Properties Introduction to Electrical Properties Dielectric Properties Conduction in Polymers Polymer Electronics Answers to Problems Index Problems and Further Reading appear at the end of each chapter.

Superquadrics and Angle-Preserving Transformations

Abstract: A new and powerful family of parametric shapes extends the basic quadric surfaces and solids, yielding a variety of useful forms.

Capacitated arc routing problems

Abstract: A capacitated node routing problem, known as the vehicle routing or dispatch problem, has been the focus of much research attention On the other hand, capacitated arc routing problems have been comparatively neglected Both classes of problems are extremely rich in theory and applications Our intent in this paper is to define a capacitated arc routing problem, to provide mathematical programming formulations, to perform a computational complexity analysis, and to present an approximate solution strategy for this class of problems In addition, we identify several related routing problems and develop tight lower bounds on the optimal solution

The paralanguage of caregiving: Baby talk to the institutionalized aged.

Abstract: A field study was conducted at a nursing home to (a) obtain descriptive information on the speech environment of the institutionalized elderly and (b) provide speech samples with which to conduct judgment studies on the paralinguistic features of caregiver communication. Three kinds of speech were differentiated: baby talk, speech to the elderly that was not in baby talk, and speech between caregivers, which was assumed to be normal adult speech. Over 22% of the sentences were reliably categorized as baby talk speech. Caregivers' ratings of the characteristics of the care receivers did not predict the amount of baby talk that was directed toward individual care receivers. In Judgment Study 1, content-filtered baby talk was identified as speech to children regardless of the actual status, adult or child, of the target. In Judgment Study 2, content-filtered speech samples were rated on four dimensions: comfort, pleasantness, irritation, and arousal. Baby talk was rated positive, adult speech received intermediate ratings, and non-baby-talk was rated negative. The findings suggest that baby talk is a speech register conveying affection, and it is proposed that non-baby-talk to the elderly is an "institutional" register denoting and promoting dependency.

Time, distance, and feature trade-offs in visual apparent motion.

Abstract: A model of visual apparent motion is derived from four observations on path selection in ambiguous displays in which apparent motion of illuminated dots could, in principle, be perceived along many possible paths: (a) Whereas motion over each path is clearly visible when its stimulus is presented in isolation, motion is usually seen over only one path when two or more such stimuli are combined (competition), (b) Path selection is nearly independent of viewing distance (scale invariance). (c) At transition points between paths (' and j (where apparent motion is equally likely to be perceived along / and j), the time t and distance d between successive points along the paths are described by a log linear d/t relationship; that is, t = A - B log (d/d,). (d) When successive elements along a path differ in orientation or size, the perceived motion along this path is not necessarily weaker than motion along a path composed entirely of identical elements. The model is a form of strength theory in which the path with greatest strength 5 becomes the dominant path. From scale invariance, we prove that the contributions of time and distance to stimulus strength are independent. From the log linear d/t relationship, we derive the precise trade-off function between d and / and show the existence of an optimal interstimulus interval to maximize the strength for any path. The model accounts well for the path-selection data and suggests a neural interpretation in which motion perception is based on the outputs of elementary detectors that are scaled replicas of each other, all having the same geometry and time delays, and differing only in size and orientation. A visual stimulus, such as a bar or a disk, which is flashed first at one position and then flashed again nearby, may evoke a powerful illusion of movement, provided the spacing and timing of the two flashes is chosen appropriately. The vividness of this apparent motion depends strongly on the spatial and temporal separation of the stimuli and only weakly on the figural similarity of one stimulus to the other (see Kolers, 1972, for a review). However, efforts by Korte (1915), Neuhaus (1930), and others to discover a

A lens and aperture camera model for synthetic image generation

Abstract: This paper extends the traditional pin-hole camera projection geometry, used in computer graphics, to a more realistic camera model which approximates the effects of a lens and an aperture function of an actual camera. This model allows the generation of synthetic images which have a depth of field, can be focused on an arbitrary plane, and also permits selective modeling of certain optical characteristics of a lens. The model can be expanded to include motion blur and special effect filters. These capabilities provide additional tools for highlighting important areas of a scene and for portraying certain physical characteristics of an object in an image.

Effects of Nonlinear Strain-Dependent Permeability and Rate of Compression on the Stress Behavior of Articular Cartilage

Abstract: The compressive viscoelastic behavior of articular cartilage, a fiber-reinforced, porous, permeable solid matrix filled with water, is predominately governed by the flow of the interstitial water within the tissue and its exudation across the articular surface. The fluid flow is in turn governed by the permeability of the tissue and the loading imposed upon its surface. But for articular cartilage, the permeability depends nonlinearly on the strain; k = ko exp (Me). Here, M is the nonlinear flow-limiting parameter and e is the dilatation. In this investigation, we studied the influence of M and Ro = koHA/Uh (where HA is the elastic equilibrium modulus of the solid matrix, h is the tissue's thickness and U is the rate of compression applied onto the surface via a rigid, porous, free-draining filter) on the stress history of circular plugs of cartilage specimens attached to the bone. It was found that these two parameters have profound effects on the predicted compressive stress history. For very large Ro, the fluid flow effects become negligible. For small Ro and large M, large instantaneous compressive stresses several times larger than those observed at equilibrium are predicted. This amplification of compressive stress is due to the increase of importance of the relative fluid flow effect, i.e., Ro leads to 0, and nonlinear flow-limit effect, i.e., M greater than 0. Also, the theoretical curves predict that the rate of increase of stress initially decreases (convex) and finally becomes a constant. The results of our 5 percent offset compression experiments are in good agreement with the theoretical predictions.

Direct Fourier reconstruction in computer tomography

Abstract: Direct Fourier transform (FT) reconstruction of images in computerized tomography (CT) is not widely used because of the difficulty of precisely interpolating from polar to Cartesian samples. In this paper, an exact interpolation scheme is proposed which, in practice, can be approached with arbitrary accuracy using well-conditioned algorithms. Several features of the direct FT method are discussed. A method that allows angular band limiting of the data before processing -to avoid angular aliasing artifacts in the reconstructed image-is discussed and experimentally verified. The experimental results demonstrate the feasibility of direct FT reconstruction of CT data.

Kalman filtering in two dimensions: Further results

Abstract: The two-dimensional reduced update Kalman filter was recently introduced. The corresponding scalar filtering equations were derived for the case of estimating a Gaussian signal in white Gaussian noise and were shown to constitute a general nonsymmetric half-plane recursive filter. This paper extends the method to the deconvolution problem of image restoration. This paper also provides a more thorough treatment of the uniquely two-dimensional boundary condition problems. Numerical and subjective examples are presented.

A general two‐dimensional, graphical finite element preprocessor utilizing discrete transfinite mappings

Abstract: Finite element preprocessor programs have been developed in recent years in order to expedite the task of data preparation. A key decision in the design of these programs is the choice of a method for automated mesh generation. Three popular methods (Laplacian, isoparametric and transfinite mappings) are compared. Transfinite mappings with boundary information represented in discrete form are found to possess distinct advantages for the task of mesh generation. A two-dimensional preprocessor program utilizing the discrete transfinite mappings is described. Interactive computer graphics techniques are used extensively to facilitate data preparation and display. The geometry-generating routines are general, and may be used in any finite element application. A specialized graphical ‘attribute editor’ for structural mechanics problems is also described. This editor provides an efficient method of specifying boundary conditions, material properties, loads, etc.

An analysis of the commuter departure time decision

Abstract: Transportation planners and transit operators alike have become increasingly aware of the need to diffuse the concentration of peak period travel in an effort to improve gasoline economy and reduce peak load requirements. An evaluation of the potential effectiveness of strategies directed to achieve this end requires an understanding of factors which affect commuter trip timing decisions. The research discussed in this article addresses this particular problem through the development and estimation of a commuter departure time (to work) choice model. A number of conclusions were drawn based on the departure time model results and related analyses. It was found that work schedule flexibility, mode, occupation, income, age, and transportation level of service all influence departure time choice. The uncertainty in work arrival time and the consequences of various work arrival times may also be determinants of commuter departure time choice. The estimated model represents improvements over previous work in that it more explicitly considers work arrival time uncertainty and travelers' perceived loss associated with varying work arrival times, and additional socio-demographic factors which can potentially affect departure time choice. Furthermore, the estimated model includes consideration of transit commuters, in addition to single occupant auto and carpool work travelers. The inclusion of transit commuters represents a particularly important contribution for policy analysis, since the model could potentially be used to study the effect of service and employment policies on transit system peak load requirements.

Combined Source-Channel Coding of Images Using the Block Cosine Transform

Abstract: An approach is described for exploiting the tradeoffs between source and channel coding in the context of image transmission. The source encoder employs two-dimensional (2-D) block transform coding using the discrete cosine transform (DCT). This technique has proven to be an efficient and readily implementable source coding technique in the absence of channel errors. In the presence of channel errors, however, the performance degrades rapidly, requiring some form of error-control protection if high quality image reconstruction is to be achieved. This channel coding can be extremely wasteful of channel bandwidth if not applied judiciously. The approach described here provides a rationale for combined source-channel coding which provides improved quality image reconstruction without sacrificing transmission bandwidth. This approach is shown to result in a relatively robust design which is reasonably insensitive to channel errors and yet provides performance approaching theoretical performance limits. Analytical results are provided for assumed 2-D autoregressive image models, while simulation results are provided for real-world images.

The influence of coherency strain on the elevated temperature tensile behavior of Ni-15Cr-AI-Ti-Mo alloys

Abstract: The effect of coherency strain on elevated temperature tensile strength was examined in a model, two-phase y’-strengthened Ni-15Cr-Al-Ti-Mo alloy series. The temperature dependence of coherency strain as represented by the γ-γ’ mismatch was determined over the temperature range 25 to 800 °C. The flow stress incrementAσγ, due to precipitation of γ’, was found to correlate well to the magnitude of the γ-γ’ mismatch over the same temperature interval. The correlation was strongest for high misfit alloys regardless of the Antiphase Boundary Energy (APBE). The predominance of by-pass type dislocation-particle interactions in high coherency alloys confirms that strengthening is primarily due to coherency strains. Conversely, alloys with low misfit exhibit two distinct particle shear mechanisms believed to be dependent upon the relative APBE and matrix stacking fault energy of the alloy.

The Significance of Electromechanical and Osmotic Forces in the Nonequilibrium Swelling Behavior of Articular Cartilage in Tension

Abstract: Studies were conducted of some of the nonequilibrium, electrolyte-activated, electromechanical and osmotic processes that can affect the tensile properties of articular cartilage. We measured changes in tensile force that were induced by altering the ionic environment of strips of cartilage held at fixed length. We compared the kinetics of changes in these macroscopically measured isometric tensile forces to theoretical estimates of the time constants that characterize the underlying physical and chemical mechanisms occurring within the cartilage specimens during the experiment. Changes in the tensile force induced by changing the bath neutral salt concentration surrounding the specimen appear to be rate-limited by the diffusion of the salt into the specimen. That is, the mechanical stress relaxation process resulting from changes in salt concentration seems to be occurring at least as rapidly as the diffusion of salt into the matrix. When the bath concentration of CaCl2 or HCl is varied, the rate of change in the resulting isometric stresses indicates that Ca++ and H+ ions are binding to the cartilage matrix macromolecules.

Morphine antagonists and consummatory behaviors

Abstract: Opiate antagonists were tested for their effects upon either drinking or eating in eight experiments. Naloxone, nalorphine, and the active isomer of WIN 44,441 all reduce drinking. Neither an analog of nalorphine that does not cross the blood-brain barrier, nor the inactive isomer of WIN 44,441 is effective in reducing water intake. These data provide support for the conclusion that these antagonists ahve stereospecific effects within the central nervous system. Naloxone suppresses drinking following procedures inducing osmotic, volemic, or hormonal thirst. Naloxone suppresses eating following procedures inducing glucoprivation but does not alter eating elicited by tail-pressure. Collectively, these data lead to the conclusion that endorphins play a role in the organization of ingestive behavior following challenges to homeostasis.

An Investigation of Computerized Tomography by Direct Fourier Inversion and Optimum Interpolation

Abstract: In this paper an exact interpolation formula forms the basis for reconstructing computerized tomographic (CT) imagery by direct Fourier methods. Practical variations of exact interpolation are compared with other interpolation methods (i.e., nearest neighbor, etc.) and are shown to yield superior imagery. Images produced by the direct Fourier approach using near-exact interpolation are shown to be equal in quality with those produced by filtered convolution backprojection (FCBP). Moreover, the direct Fourier approach computes an image in O(N2 log N) time versus O(N3) for the FCBP method.

Effect of ionizing radiation on the chemical composition, crystalline content and structure, and flow properties of polytetrafluoroethylene

Abstract: This article describes a study of ionizing radiation-induced changes in the chemical composition, crystalline content and structure, and flow properties in polytetrafluoroethylene (PTFE). Irradiations conducted in the presence of oxygen cause acid fluoride end groups to be formed, which on exposure to water vapor hydrolyze to form carboxylic acid end groups. Analyses by infrared (IR) spectroscopy indicate that when irradiated in a vacuum PTFE exhibits defect absorption bands which have been attributed to branch and crosslink formation. The crystalline content of PTFE which increases after exposure to radiation was monitored by IR spectroscopy, density, x-ray diffraction on unoriented samples, and differential scanning calorimetry (DSC) as the measurement probes. The melt viscosity of PTFE exposed to various radiation doses in air decreases dramatically after irradiation. Between 2.5 and 5 Mrd an increase in viscosity is attributed to the formation of branches and crosslinks. The effects of preirradiation crystallinity and postirradiation heat treatment were studied. A model is presented to explain the mechanism of the observed radiation effects.

Two-Treatment Crossover Designs for Estimating a Variety of Effects

Abstract: The variances of contrasts among direct, residual, and cumulative treatment effects are compared for a variety of two-treatment crossover designs. Estimation of contrasts among second-order residual effects and among direct-by-period and direct-by-first-order-residual interaction effects is also considered.

Analysis of the Precision of Generalized Chain Codes for the Representation of Planar Curves

Abstract: This paper examines a set of line-segment approximation codes for the representation of planar curves (the so-called generalized chain codes) and shows that the average quantization error (measure of code's precision) is directly proportional to the grid size and is independent of the form of the code. Thus, to achieve a desired level of precision for the representation of a line drawing, only the size of the grid need be determined; the form of the code can be chosen on the basis of other criteria, such as compactness, smoothness, or relative ease of encoding and processing.

Effects of inhibitors of spermidine and spermine synthesis on polyamine concentrations and growth of transformed mouse fibroblasts

Abstract: 1. A number of compounds known to inhibit polyamine biosynthesis at various steps in the biosynthetic pathway were tested for their ability to inhibit growth and decrease polyamine concentrations in virally transformed mouse fibroblasts (SV-3T3 cells). 2. Virtually complete inhibition of growth was produced by the inhibitors of ornithine decarboxylase α-methylornithine and α-difluoromethylornithine and by the inhibitors of S-adenosylmethionine decarboxylase 1,1′-[(methylethanediylidene)dinitrilo]diguanidine and 1,1′-[(methylethanediylidene)dinitrilo]bis-(3-aminoguanidine). The former inhibitors decreased putrescine and spermidine contents in the cells to very low values, whereas the latter substantially increased putrescine but decreased spermidine concentrations. The inhibitory effects of all of these inhibitors on cell growth could be prevented by the addition of spermidine, suggesting that spermidine depletion is the underlying cause of their inhibition of growth. 3. α-Difluoromethylornithine, which is an irreversible inhibitor of ornithine decarboxylase, was a more potent inhibitor of growth and polyamine production (depleting spermidine almost completely and spermine significantly) than α-methylornithine, which is a competitive inhibitor. This was not the case with the inhibitors of S-adenosylmethionine decarboxylase where 1,1′-[(methylethanediylidene)dinitrilo]diguanidine, a reversible inhibitor, was more active than 1,1′-[(methylethanediylidene)dinitrilo]bis-(3-aminoguanidine), an irreversible inhibitor. It is suggested that this effect may be due to the lesser uptake and/or greater chemical reactivity of the latter compound. 4. Various nucleoside derivatives of S-adenosylhomocysteine that inhibited spermidine synthase in vitro did not have significant inhibitory action against polyamine accumulation in the cell. These compounds, which included S-adenosylhomocysteine sulphone, decarboxylated S-adenosylhomocysteine sulphone, decarboxylated S-adenosylhomocysteine sulphoxide and S-adenosyl-4-thio-butyric acid sulphone did not inhibit cell growth or polyamine content until cytotoxic concentrations were added. 5. 5′-Methylthioadenosine, 5′-isobutylthioadenosine and 5′-methylthiotubercidin, which inhibit aminopropyltransferase activity in vitro, all inhibited cell growth and decreased spermidine content. Although these compounds were most active against spermine synthase in vitro, they acted in the cell primarily to decrease spermidine content. Cell growth could not be restored to normal values by addition of spermidine, suggesting that these nucleosides have another inhibitory action towards cellular proliferation. 6. 5′-Methylthioadenosine and 5′-isobutylthioadenosine are degraded by a phosphorylase present in SV3T3 cells, yielding 5-methylthioribose-1-phosphate and 5-isobutylthioribose-1-phosphate respectively, and adenine. This degradation appears to decrease the inhibitory action towards cell growth, suggesting that the nucleosides themselves are exerting the inhibitory action. 5′-Methylthiotubercidin, which is not a substrate for the phosphorylase and is a competitive inhibitor of it, was the most active of these nucleosides in inhibiting cell growth and spermidine content. 5′-Methylthiotubercidin and α-difluoromethylornithine had additive effects on retarding cell growth, but not on cellular spermine accumulation, also suggesting that the primary growth-inhibiting action of the nucleoside was not on polyamine production. 7. These results support the concept that 5′-methylthioadenosine phosphorylase plays an important role in permitting cell growth to continue by preventing the build-up of inhibitory intracellular concentrations of 5′-methylthioadenosine.

Estimation and identification of two-dimensional images

Abstract: Estimation of image pixel density can be performed using a reduced update Kalman filter provided that a mathematical model for the image generating process is available. To this effect various algorithms suitable for identifying the parameters of autoregressive image models are discussed and evaluated in terms of the mean-squared error between the true and filtered images. Algorithms considered include general and bias-compensated least-square procedures, a correlation-based algorithm, and procedures involving the simultaneous estimation of both the image model coefficient vector and pixel estimates. Experiments using two real images and two random fields indicate that bias-compensated least squares and correlation-based procedures might be most useful for image identification and adaptive filtering.

Controllability of distributed bilinear systems

Abstract: A discussion of recent results of Ball, Marsden, & Slemrod [1] for controllability of distributed bilinear systems will be given.