Showing papers by "Stevens Institute of Technology published in 1990"

The interface in binary mixtures of polymers containing a corresponding block copolymer: Effects of industrial mixing processes and of coalescence

Abstract: In theories of the minor phase (domain) formation in polyblends rendered as emulsions it is usually assumed that the size and shape of the domains are the result of melt viscosity effects (Taylor, Wu) or viscoelasticity effects (VanOene, Elmendorp) being balanced by interfacial tension. This assumption would predict a monotonic decrease of the domain size to a final limiting size with increasing energy of mixing. However, a systematic study of the dependence of domain morphology on industrial mixing processes which was carried out on a “model” LDPE/PS (2/1) mixture and the related polyalloy (i.e., the same mixture with a corresponding block copolymer as compatibilizer) does not support this expectation. Doirain size was found to go through a minimum as mixing energy was increased. A similar minimum was seen in data on specific volume of the melt vs. mixing energy, which indicates a correlation between melt specific volume and domain size. Calculation of the approximate surface area of the domains using a simple model of domain shape indicated that total interfacial energy in the polyblend and/or polyalloy is a trivial part of the mixing energy introduced. These calculations also indicated that if compatibilizer was located entirely at the interface, the surface layer would have a thickness of about 90 nm. Some micrographs seem to show such a surface layer. We propose that an abrasion mechanism is responsible for the early stage of the dispersion process, and that the final domain size may be controlled by a dispersion-coalescence equilibrium. This is compared with the theories of final particle size proposed by VanOene and Wu.

An examination of the effects of using behavior checklists on the construct validity of assessment center dimensions

Abstract: Although research has established the criterion-related validity of assessment centers for selection purposes, the construct validity of dimension ratings has not been demonstrated. A quasi-experimental design was used to investigate the influence of retranslated behavior checklists on the construct validity of dimension ratings for two assessment center exercises. Assessor use of behavior checklists increased the average convergent (i.e., same dimension across exercise) validity from .24 to .43 while decreasing the average discriminant (i.e., different dimension within exercise) validity (.47 to .41). Behavior checklist sums were moderately correlated with corresponding dimension ratings and demonstrated a comparable level of construct validity. It is suggested that using behavior checklists may improve dimension construct validity by reducing the cognitive demands placed on raters.

Polypropylene/polyethylene terephthalate blends compatibilized through functionalization

Abstract: In attempts to improve the compatibility of polypropylene with polyethylene terephthalate, an acrylic acid functionalized polypropylene was evaluated as the blend component in polyblends containing 40 percent by weight polyethylene terephthalate and compared with an unmodified polypropylene. The preliminary experiments in a batch laboratory mixer were followed by compounding in a co-rotating twin-screw extruder. Additives such as magnesium acetate and p-toluenesulfonic acid were evaluated as catalysts for potential interchange or esterification reactions that could occur in the melt. The blends were characterized through scanning electron microscopy, infrared spectroscopy, differential scanning calorimetry, and for mechanical properties. The results show that the functionalized polypropylene promotes a fine dispersed phase morphology, improves processability and mechanical properties, and modifies the crystallization behavior of the polyester component. These effects are attributed to enhanced phase interactions resulting in reduced interfacial tension (calculated as a 4-fold decrease). The presence of the additives does not, in general, improve any further the blend morphology and properties, or its processability.

A photonic variable RF delay line for phased array antennas

Abstract: It is shown that by applying spatial frequency-dependent phase compensation in an optical heterodyne process a variable RF delay line can be synthesized over a prescribed frequency band. Experimental results which demonstrate the performance of the delay line with regard to both maximum delay and resolution over a broad bandwidth are presented. A spatially integrated optical system is proposed for control of phased array antennas. The integrated system provides mechanical stability essentially eliminates the drift problems associated with freespace optical systems, and can provide high-packing density. The approach uses a class of spatial light modulator known as a deformable mirror device and leads to a steerable arbitrary antenna radiation pattern of the true time-delay type. >

Laminar secondary flows in curved rectangular ducts

Abstract: The occurrence of secondary flow in curved ducts due to the centrifugal forces can often significantly influence the flow rate. In the present work, the secondary flow of an incompressible viscous fluid in a curved duct is studied by using a finite-volume method. It is shown that as the Dean number is increased the secondary flow structure evolves into a double vortex pair for low-aspect-ratio ducts and roll cells for ducts of high aspect ratio. A stability diagram is obtained in the domain of curvature ratio and Reynolds number. It is found that for ducts of high curvature the onset of transition from single vortex pair to double vortex pair or roll cells depends on the Dean number and the curvature ratio, while for ducts of small curvature the onset can be characterized by the Dean number alone. A comparison with the available theoretical and experimental results indicates good agreement. A correlation for the friction factor as a function of the Dean number and aspect ratio is developed and is found to be in good agreement with the available experimental and computational results for a wide range of parameters.

Nondispersive membrane solvent back extraction of Phenol

Abstract: Nondispersive back extraction of phenol from methyl isobutyl ketone into caustic solutions has been studied using microporous polymeric membranes in flat as well as hollow-fiber form Dispersion-free reactive back extraction was successfully achieved using the correct phase pressure difference The predictive capabilities of the mathematical models developed for such a system have been investigated This study indicates that the overall mass transfer can be controlled by boundary layer resistance and/or the membrane transfer resistance, depending on the flow configuration, the nature of the membrane, and the regime of caustic concentration Individual film transfer coefficients on the shell side and the tube side have been isolated for different hollow-fiber modules A commercially available 15 cm long module containing hydrophobic microporous hollow fibers has provided very low values of height of transfer unit (HTU) and very high phenol recoveries The experimentally obtained HTUs of this module have been predicted with significant accuracy

A neural network approach to infrared spectrum interpretation

Abstract: The simple linear neural network model was investigated as a method for automated interpretation of infrared spectra. The model was trained using a database of infrared spectra of organic compounds of known structure. The model was able to learn, without any prior input of spectrum-structure correlations, to recognize and identify 76 functional groupings with accuracies ranging from fair to excellent. The effect of network input parameters and of training set composition were studied, and several sources of spurious correlations were identified and corrected.

The σ-game and cellular automata

Abstract: 1. SummaryIn an article in this journal Don Pelletier discussed the mathematics involved in a little battery operated toy called Merlin (see [3], and also the “Addenda” in this Monthly, Dec. 1987, page 994). Several years ago Stephen Wolfram, in another article that appeared in the Monthly, analyzed a number of simple cellular automata and the fractal patterns generated by some of these automata (see [6]). In this article we point out the close connection between MERLIN-type games and a class of cellular automata related to the ones described by Wolfram. We introduce a game played on directed graphs and give a detailed analysis of the special case where the graph is a rectangular grid. Our analysis uses linear algebra as well as ideas from the theory of cellular automata.

Ethanol production in a microporous hollow-fiber-based extractive fermentor with immobilized yeast.

Abstract: Microporous-membrane-based extractive product recovery in product-inhibited fermentations allows in situ recovery of inhibitory products in a nondispersive fashion. A tubular bioreactor with continuous strands of hydrophobic microporous hollow fibers having extracting solvent flowing in fiber lumen was utilized for yeast fermentation of glucose to ethanol. Yeast was effectively immobilized on the shell side in small lengths of chopped microporous hyrophilic hollow fibers. The beneficial effects of in situ dispersion-free solvent ex (oleyl alcohol and dibutyl phthalate) were demonstrated for a 300 g/L glucose substrate feed. Outlet glucose concentration dropped drastically from 123 to 41 g/L as solvent/ substrate flow ratio was increased from 0 to 3 at 9 mL/h of substrate flow rate with oleyl alcohol as extracting solvent. The significant productivity increase with in situ solvent extraction became more evident as solvent/ substrate flow ratio increased. A model of the locally integrated extractive bioreactor describes the observed fermentor performance quite well.

A characterization of partial 3-trees

Abstract: A k-tree is defined recursively as follows: The complete graph Kk on k points is a k-tree. Given a k-tree G on n ≤ k points, a k-tree on n + 1 points is obtained by adding a new point u and edges connecting u to every point of a Kk in G. A graph is a partial k-tree if it is a subgraph of some k-tree. In this paper, we establish some interesting properties of partial 3-trees and show that a graph is a partial 3-tree if and only if it has no subgraph contractible to K5, K2.2.2C8(1, 4), or K2 ≤ C5. A graph G is said to be contractible to a graph H if H can be obtained from G by a sequence of edge contractions. hitherto, such a characterization of partial k-trees was known only for the values of k ≤ 2.

Finite-Element Analysis in Design with Rubber

Abstract: The application of finite-element analysis in rubber technology has been discussed. The intent has been to combine features of a tutorial, an exposition, and a survey. Attention has been limited to homogeneous cured rubber products. The finite-element method is a prime constituent of computer-aided engineering, and, as such, it is a powerful resource for the design and analysis of rubber components. Owing to rapid progress and greater availability of computer hardware and software and, in particular, computer-aided design systems, finite-element analysis is eminently practical. Difficulties such as incompressibility and large deformation, the subjects of a substantial literature, appear to have been successfully addressed. Finite-element analyses of rubber products such as seals and bearings have been published widely, often along with experimental validation. However, note that the implementation of the hyperelastic element in major codes has occurred recently. And, at the time of this review, i...

A deformable mirror-based optical beamforming system for phased array antennas

Abstract: Microwave carrier generation along with the signal processing required for dynamic beamsteering of a high-resolution phased array antenna with an arbitrary radiation pattern is accomplished using optical components. It is shown that a deformable mirror type spatial light modulator can establish a truly arbitrary continuous optical phasefront which is directly converted to spatial RF phase information by an optical heterodyne system. Experimental results simulating the performance of the actual system are presented. A spatially integrated optical implementation providing mechanical stability and essentially eliminating the drift problems usually encountered in free space systems is presented. >

Discrete black and white object recognition via morphological functions

Abstract: Two morphological algorithms that attempt to recognize a black and white object directly in its discrete domain are presented. The first algorithm is based on covariance functions, while the second is based on a variant of size distribution functions. In both these algorithms, the scale correction has been automated. Also presented is a complete geometric and algebraic characterization of objects that are identical with respect to the proposed methodologies, and it is shown that the induced equivalent classes over binary images contain objects that are structurally very similar. This has been accomplished by introducing the notions of a strongly attached pixel, discrete structure of an image, and a structure preserving operation. An outcome of the analysis is the insight into the relationship between the discrete structure of an image and the induced equivalence classes. >

Composition Rules for Building Linear Programming Models from Component Models

Abstract: This paper describes some rules for combining component modelsinto complete linear programs The objective is to lay thefoundations for systems that give users flexibility in designingnew models and reusing old ones, while at the same time,providing better documentation and better diagnostics thancurrently available The results presented here rely on twodifferent sets of properties of LP models: first, the syntacticrelationships among indices that define the rows and columns ofthe LP, and second, the meanings attached to these indicesThese two kinds of information allow us to build a completealgebraic statement of a model from a collection of componentsprovided by the model builder

Aspects of the Zel'dovich-Sunyaev mechanism.

Abstract: In this paper we treat aspects of the Compton distortion of the cosmic background radiation (CBR)---what is known as the Zel'dovich-Sunyaev mechanism---which do not appear to have been fully explored in the literature. These include a novel solution to the so-called Kompaneets equation, a treatment of the simultaneous heating and cooling of free electrons, a discussion of electron-proton "recombination," and a demonstration of the ingredients necessary for efficient energy transfer. These matters are illustrated in a scenario in which the excess CBR energy observed by Matsumoto et al. is supplied by a radiatively decaying heavy lepton, so we also provide a careful analytic treatment of the photon spectrum produced by a heavy particle decaying in the early Universe.

Peroxide modified polyolefin blends: Part I. Effects on ldpe/pp blends with components of similar initial viscosities

Abstract: As part of a broader research effort to prepare polyolefin blends with controlled rheological and mechanical behavior, LDPE/PP blends were peroxide modified through reactive processing in intensive batch mixers. Polymers with similar initial viscosities and elasticities were first melt mixed and then simultaneously reacted and mixed to produce blends whose reaction-modified components had very different molecular weights and molecular weight distributions. The rheological behavior of the blends in both shear and elongational flow were found to depend on composition, peroxide concentration, and, possibly, on the relative response rate of the individual components to peroxide attack. In general, the rheological properties of the reacted blends differed significantly from those of blends compounded in the absence of peroxide, and they were influenced by the presence of two components with vastly different structural and rheological characteristics: the degraded PP of low viscosity and elasticity, and a branched or crosslinked LDPE with increased viscosity and increased melt elasticity. Data from the batch experiments of this work are useful in defining process requirements for continuous reactive extrusion compounding, such as component characteristics, length of mixing/reaction zones, screw geometry, and sequence of feeding, as they relate to product characteristics.

Least reliable networks and the reliability domination

Abstract: A well-known model in communication network reliability consists of an undirected graph G whose edges operate independently with the same probability p. Then the reliability, R(G,p) of G, is the probability that G is connected. It is known that R(G,p) is a polynomial in p and its coefficient of the least-order term is the number of spanning trees t(G), while the coefficient of the highest-order term is the reliability domination d(G) of G. Presented is a complete characterization of graphs that achieve the minimum absolute value mod d(G) mod over the class of n-node, e-edge connected graphs. Furthermore, the class of graphs that yield minimum t(G) is shown to minimize mod d(G) mod . The results have applications in the synthesis of least-reliable networks. >

Comparison of simultaneous wet milling and enzymatic hydrolysis of cellulose in ball mill and attrition mill reactors

Abstract: Simultaneous wet milling and enzymatic hydrolysis of newsprint in a ball mill reactor (BMR) and in an attrition mill reactor (AMR) were studied. The effect of milling on the enzyme deactivation was also investigated. Variables studied included milling media size, material, and the presence or absence of an air–liquid interface in the reactor. At a reaction temperature of 45°C and a pH of 4.5 and in the presence of an air–liquid interface, the amount of reducing sugars produced by hydrolysis using a BMR was typically 5 to 15%less than the amount produced using an AMR. Without an air–liquid interface there was no significant difference. The effect of an air–;liquid interface on enzyme deactivation without any substrate was also studied. Enzyme activity after six hours of milling ranged from 1 to 85% ofthe starting activity. In both the AMR and the BMR, the extent of enzyme deactivation was 20 to 50% greater with an air–liquid interface present than with the air–liquid interface absent.

A Computer-Based Methodology for the Form Synthesis and Optimal Design of Robot Manipulators

Abstract: The study reported in this paper deals with the development of a generalized computer-based methodology for the form synthesis and optimal design of robot manipulators. The developed computer program to implement the methodology operates in two separate modes. The first deals with the synthesis of user defined topologies and in the second mode, the designer provides only the required task, then the program will generate optimum manipulator configuration by systematic evaluation and ranking of plausible alternatives. The methodology simultaneously incorporates kinematic and dynamic synthesis as well as optimal actuation and stress analysis in an integrated design process. The procedure relies on the systematic composition of manipulator configurations from tabulated basic elements. The optimization strategy for synthesis and control utilizes a dynamic programming approach which makes it possible to select the optimum parameters in a stage-wise manner without sacrificing the interactions inherent in such highly coupled nonlinear systems.

Numerical study of turbulent secondary flows in curved ducts

Abstract: The pressure driven, fully-developed turbulent flow of an incompressible viscous fluid in curved ducts of square cross-section is studied numerically by making use of a finite volume method. A nonlinear Kappa - Iota model is used to represent the turbulence. The results for both straight and curved ducts are presented. For the case of fully-developed turbulent flow in straight ducts, the secondary flow is characterized by an eight-vortex structure for which the computed flowfield is shown to be in good agreement with available experimental data. The introduction of moderate curvature is shown to cause a substantial increase in the strength of the secondary flow and to change the secondary flow pattern to either a double-vortex or a four-vortex configuration.

Ab initio properties of electronic states of Be69

Abstract: Results of ab initio Hartree-Fock calculations are presented for the nine-coordination-shell cluster Be{sub 69}. Binding energy, ionization potential, electrical field gradient, nuclear-electrostatic potential, diamagnetic shielding constant, second moments of charge, and Mulliken populations are reported for several electronic states. Properties centered at the innermost Be atoms exhibit convergence toward bulk Be metal values.

On the perfect accuracy of an approximate subscript analysis test

Abstract: The Banerjee test is commonly considered to be the more accurate of the two major approximate data dependence tests used in automatic vectorization/parallelization of loops, the other being the GCD test. From its derivation, however, there is no simple explanation of why the Banerjee test should be nearly as accurate as it is given credit for. We present a set of sufficient conditions for the Banerjee test's accuracy, and explain its perceived accuracy in actual practice by proving that under circumstances which occur extremely frequently in actual code, the Banerjee test is, in fact, not approximate, but perfectly accurate.