Showing papers by "Stevens Institute of Technology published in 1991"
TL;DR: In this paper, the authors introduce the notion of Dymanic Order and Choas (DOC) for the stochastic layer of a stochastically ordered graph, and describe two types of spatial patterns: two-dimensional hydrodynamic patterns with symmetry and quasi-symmetry.
Abstract: Part I. General Concepts: Hamiltonian dynamics Stability and chaos Part II. Dymanic Order and Choas: The stochastic layer Stochastic layer - stochastic sea transition The stochastic web Uniform web Part III. Spatial Patterns: Two-dimensional patterns with quasi-symmetry Two-dimensional hydrodynamic patterns with symmetry and quasi-symmetry Chaos and streamlines Part IV. Miscellanea: Patterns in art and nature References Index.
325 citations
TL;DR: In this article, a review examines some recent developments in the field of reactive compatibilization of polymer blends by melt processing in extruders and intensive batch mixers, including the use of suitably functionalized blend constituents, the incorporation of polymeric compatiblizers, and the addition of low molecular weight compounds.
Abstract: This review examines some recent developments in the field of reactive compatibilization of polymer blends by melt processing in extruders and intensive batch mixers. Three routes to reactive compatibilization are considered, namely, the use of suitably functionalized blend constituents, the incorporation of polymeric compatibilizers, and the addition of low molecular weight compounds. Representative systems from the recent patent and open literature are classified according to method and assumed mechanism of compatibilization, and the types of chemical reactions involved. A variety of polymer blends are discussed, including impact modified thermoplastics, polymer modified engineering thermoplastics, dynamically vulcanized thermoplastic elastomers, and co-crosslinked rubber/rubber blends. Examples of potential opportunities in reactive compatibilization are also presented.
322 citations
TL;DR: It is shown that it is undecidable to which class in the hierarchy a cellular automaton belongs and whether all spatially periodic configurations evolve to a fixed point, and there is no computable bound on the period lengths of these configurations.
197 citations
175 citations
TL;DR: In this paper, the wear rates of a silicon nitride ball and a diamond-like carbon (DLC) film were measured using a pin-on-disk tribometer in argon and air with varying relative humidity.
Abstract: Diamond-like carbon (DLC) films were prepared on Si(100) wafers by plasma-assisted chemical vapor deposition at a pressure of 900 mTorr. Their wear rates and friction coefficients against a silicon nitride ball were measured in a pin-on-disk tribometer in argon and air with varying relative humidities. In 50% relative humidity, the measured wear rates of the ball and DLC were of the order of 10−8 mm3 N−1 m−1 and 10−7 mm3 N−1 m−1 respectively. In dry argon, dry air and 100% humid air, the wear rates of DLC were 10−9, 10−9 and 10−8 mm3 N−1 m−1, but that of the ball was below the detection limit. The measured friction coefficients were 0.06 in dry argon, 0.08 in 50% humid air and 0.09 in 100% humid argon, and around 0.2 in 50% humid argon, dry and 100% in humid air. In dry argon, the contact area of the ball was covered with material transferred from the DLC film during sliding; the low friction coefficient and wear rate measured in dry argon are attributed to this material. In dry and humid air, surface layers of DLC were oxidized by a tribochemical reaction forming a CO bond. They covered the contact area of both the DLC film and the ball. This film increased friction coefficients, but it acted as a protective coating when its thickness was sufficient to prevent direct contact of the DLC film against the ball in 100% humid air.
161 citations
01 Jan 1991
126 citations
TL;DR: Bloch electron conductivity perpendicular to the layers of a superlattice (period d) is evaluated using an extension of the balance-equation approach X to narrow-band transport.
Abstract: Bloch equation conductivity perpendicular to the layers of a superlattice (period d) is evaluated using an extension of the balance-equation approach [X. L. Lei and C. S. Ting, Phys. Rev. B 32, 1112 (1985)] to narrow-band transport. The perpendicular peak drift velocity ${\mathit{v}}_{\mathit{p}}$ and the critical field ${\mathit{E}}_{\mathit{c}}$, at which the drift velocity peaks, are analyzed as functions of miniband width. Our theoretical prediction that ${\mathit{E}}_{\mathit{c}}$d increases with decreasing miniband width agrees well with the data of Sibille et al. [Phys. Rev. Lett. 64, 52 (1990)], even for the samples of narrowest miniband width in their experiment.
124 citations
TL;DR: In this article, restricted Hartree-Fock ab initio calculations using relativistic core potentials were performed on C60M (M=O, F, K, Ca, Mn, Cs, Ba, La, Eu, U) complexes with M as the central atom in the C60 truncated icosahedron.
Abstract: Restricted Hartree–Fock ab initio calculations using relativistic core potentials were performed on C60M (M=O, F, K, Ca, Mn, Cs, Ba, La, Eu, U) complexes with M as the central atom in the C60 truncated icosahedron. The icosahedral symmetry was used to great advantage in the calculations. The ground and excited states of both neutral complexes and their positive ions were studied, and the population analyses for the ground states of the complexes were obtained. The C60 cage accepts one or two electrons from electropositive elements in a formal sense, but the actual charge is usually less. Electrons in large‐radius s orbitals on the central atom tend to move outward to the carbon cage or inward to smaller‐radius d orbitals on the central atom. For the larger central atoms, ionization occurs from a cage orbital so that the ionization potentials of these complexes are almost constant.
107 citations
TL;DR: It is shown that the I test is useful when, in the event that a positive result must be reported, a definitive positive is of more use than a tentative positive and when insufficient loop iterations are known for the Banerjee test to apply.
Abstract: The I test is a subscript dependence test which extends both the range of applicability and the accuracy of the GCD and Banerjee tests (U. Banerjee, 1976), standard subscript dependence tests used to determine whether loops may be parallelized/vectorized. It is shown that the I test is useful when, in the event that a positive result must be reported, a definitive positive is of more use than a tentative positive and when insufficient loop iterations are known for the Banerjee test to apply. >
98 citations
TL;DR: In this article, the hollow fiber contained liquid membrane (HFCLM) technique was used for facilitated transport of citric acid from an aqueous solution using hollow fibers, and a mathematical model of facilitated solute transport through HFCLM that accounts for the interfacial reversible reaction kinetics and diffusion process inherent in carrier facilitated transport was presented.
Abstract: Citric acid was successfully separated from an aqueous solution using the hollow fiber contained liquid membrane (HFCLM) technique. In this technique, the organic liquid membrane is contained in the shell side between two sets of hollow fibers; feed solution flows through one set of fibers and the strip solution flows through the other set. Tri-n-octylamine diluted in various organic solvents was used as a complexing agent for facilitated transport of citric acid from an aqueous solution. Pure water and aqueous sodium hydroxide were used as stripping agents. Membrane life and stability problems encountered in supported liquid membranes are eliminated. A mathematical model of facilitated solute transport through HFCLM that accounts for the interfacial reversible reaction kinetics and diffusion process inherent in carrier-facilitated transport is presented. Experimental data agreed well with the theoretical predictions for permeators achieving almost complete solute recovery.
93 citations
TL;DR: This work considers the possibility of the existence of a fixed graph that is optimal for all possible ρ, and shows that such graphs exist when e = n − 1, or n, and that they also exist whene = n + 1 and n + 2.
Abstract: A well-known model for network reliability studies consists of an undirected graph with perfectly reliable nodes and equal and independent edge failure probabilities. The measure of reliability is then defined to be the probability that the graph is connected. A well-defined synthesis problem is to find the graph that minimizes the failure probability given the number of nodes n, the number of edges e, and the edge failure rate ρ. In this work, we consider the possibility of the existence of a fixed graph that is optimal for all possible ρ. It is simple to verify that such graphs exist when e = n − 1, or n. Herein, we show that they also exist when e = n + 1 and n + 2.
TL;DR: This treatment shows how the Goldstone bosons of a spontaneously broken symmetry and the quasiparticles of the nonrelativistic gas emerge as special cases of one general formula in a relativistic Bose-Einstein gas.
Abstract: We calculate the partition function for a relativistic Bose-Einstein gas. The excitation energies are identified and compared with known results in various limits. In particular, this treatment shows how the Goldstone bosons of a spontaneously broken symmetry and the quasiparticles of the nonrelativistic gas emerge as special cases of one general formula. New results are obtained for the spectrum of Goldstone modes in a medium of nonzero density, and the fully relativistic case is discussed along with a possible cosmological application.
TL;DR: In this article, a neural network model with a layer of hidden units is described which can identify functional groups in organic compounds, based on their infrared spectra, which shows substantially better performance than the simple linear model reported earlier.
Abstract: A neural network model having a layer of hidden units is described which can identify functional groups in organic compounds, based on their infrared spectra. This network shows substantially better performance than the simple linear model reported earlier. The effect of the training set size and composition, the number of hidden units used, and the training time were studied.
TL;DR: In this paper, the peroxide-initiated controlled degradation of polypropylene, such as concentration of peroxide, reaction temperature, and reaction time, are investigated under in situ uniform, microsegregation, and macrosegregation conditions.
Abstract: Parameters affecting the process efficiency of the peroxide-initiated controlled degradation of polypropylene, such as concentration of peroxide, reaction temperature, and reaction time, are investigated under in situ uniform, microsegregation, and macrosegregation conditions. Reactions were carried out under static (no mixing) and dynamic conditions on model samples and samples processed in batch mixers, respectively. As expected, MW and MWD decrease with increasing peroxide concentration. Low- and mid-MW fractions increase at the expense of the high-MW fractions. Localization of peroxide occurs under macrosegregation conditions and causes overall loss of peroxide efficiency and side reactions. MW and MWD undergo no further change after three to four times the half-life of the peroxide. A kinetic model developed using the quasisteady-state approximation on free radicals successfully simulates the degradation reaction kinetics for peroxide uniformly mixed. The method of moments is used to calculate the molecular weight averages. The results of this work confirm the importance of mixing uniformity as a parameter controlling the product characteristics in reactive processing.
TL;DR: In this article, the sources of nonlinear elements, often associated with physical and chemical interactions, in designs and their control systems are examined for the equality constraints and nonlinear programs in phase and chemical equilibria, in reactors and separators, and in the simulation and optimization of flowsheets.
Abstract: As steady-state and dynamic simulators with optimal controllers have evolved, tools for nonlinear analysis have been developed by reactor and thermophysical property specialists. Designers lag behind in developing and utilizing these tools, as many design strategies assume idealized behavior even though processes contain an increasing number of nonlinear elements. This article examines the sources of the nonlinear elements, often associated with physical and chemical interactions, in designs and their control systems. Promising methods for nonlinear analysis are reviewed.
In each design activity, involving simulation, economic optimization, projections of controllability and operability, emphasis is on the sources of nonlinearities and solution methods. These are examined for the equality constraints and nonlinear programs in phase and chemical equilibria, in reactors and separators, and in the simulation and optimization of flowsheets. Also examined are the impact of non-linear predictive control in screening designs and methods to insure operability, in the face of uncertainties.
TL;DR: It is proven that the problem of computing the residual connectedness reliability is NP-hard by showing that the problems of counting the number of node induced connected subgraphs of a given graph is-complete.
Abstract: This paper considers a probabilistic network in which the edges are perfectly reliable but the nodes fail with some known probabilities. The network is in an operational state if the surviving nodes induce a connected graph. The residual node connectedness reliability $R(G)$ of a network G is the probability that the graph induced by the surviving nodes is connected. This reliability measure is very different from the widely studied K-terminal network reliability measure. It is proven that the problem of computing the residual connectedness reliability is NP-hard by showing that the problem of counting the number of node induced connected subgraphs of a given graph is $# {\bf P}$-complete. The problem remains $# {\bf P}$-complete for split graphs as well as planar and bipartite graphs.
TL;DR: In this paper, the large amplitude oscillatory shear behavior of a concentrated suspension was found to be significantly affected by the screw configuration employed and the location of the location, and the volume fraction of the entrained air increased with geometries and operating conditions.
Abstract: Samples of a concentrated suspension were systematically collected from the mixing volume of a continuous processor. The large amplitude oscillatory shear behavior of the samples was found to be significantly affected by the screw configuration employed and the location. Microstructural analyses employing nuclear magnetic resonance imaging, wide-angle X-ray diffraction and X-ray radioscopy revealed substantial entrainment of air into the suspension during continuous processing. The volume fraction of the entrained air increased with geometries and operating conditions leading to partially full channels. Overall, air entrainment is identified as a dominant factor in the development of the microstructure and the rheology of concentrated suspensions and should be considered in their optimum processing.
TL;DR: The authors explored the relationship between Condorcet and Jefferson to gain insight into the early development of social choice theory and identified the intellectual intermediaries and a different perspective on the creation of Social choice theory in the French Academy of Sciences.
Abstract: This paper explores the relationship between Condorcet and Jefferson to gain insight into the early development of social choice theory. Jefferson does not seem to have read or understood Condorcet's theoretical work, but studying the relationship leads to the identification of intellectual intermediaries and a different perspective on the creation of social choice theory in the French Academy of Sciences.
TL;DR: In this article, the authors reviewed the literature in the area of dilatancy of concentrated suspensions and investigated the shear viscosity of a Newtonian polymeric liquid filled with 60 vol. percent ammonium sulfate.
Abstract: Suspensions filled close to their maximum packing fraction present special challenges in their processing and in their rheological characterization. In this report, the literature in the area of dilatancy of concentrated suspensions is reviewed. Furthermore, the shear viscosity of a Newtonian polymeric liquid filled with 60 vol. percent of ammonium sulfate has been investigated. Both capillary and parallel disk torsional flows, were employed, spanning three decades in shear stress. Upon correction for slip, the suspension exhibited shear thinning at low shear stresses and shear thickening at higher shear stresses. Above a critical wall shear stress, the shear viscosity of the suspension increased unboundedly and the flow became pluglike with apparent slip at the wall. These findings have important ramifications in the processing of composites from such concentrated suspensions.
01 Feb 1991
TL;DR: In this article, the ability of two-equation models to accurately predict separated flows is analyzed from a combined theoretical and computational standpoint, and it is found that the errors in the reported predictions of the k-epsilon model have two major origins: (1) numerical problems arising from inadequate resolution, and (2) inaccurate predictions for normal Reynolds stress differences arising from the use of an isotropic eddy viscosity.
Abstract: The ability of two-equation models to accurately predict separated flows is analyzed from a combined theoretical and computational standpoint. Turbulent flow past a backward facing step is chosen as a test case in an effort to resolve the variety of conflicting results that were published during the past decade concerning the performance of two-equation models. It is found that the errors in the reported predictions of the k-epsilon model have two major origins: (1) numerical problems arising from inadequate resolution, and (2) inaccurate predictions for normal Reynolds stress differences arising from the use of an isotropic eddy viscosity. Inadequacies in near wall modelling play a substantially smaller role. Detailed calculations are presented which strongly indicate the standard k-epsilon model - when modified with an independently calibrated anisotropic eddy viscosity - can yield surprisingly good predictions for the backstep problem.
TL;DR: It is shown that the bound on NC in the result of Faudree et al. can be lowered to 1 3 (2n−1) , which is best possible, and G is shown to have a cycle of length at least min{ n, 2(NC2)} if G is 2-connected and σ 3 ⩾ n +2.
TL;DR: In this paper, a numerical study of fully-developed turbulent flow past a backward-facing step is performed to analyze the effect of mesh refinement on the computed results, and the time averaged equations of conservation of mass and momentum are solved by a finite-volume method using two versions of the K-e model of turbulence.
TL;DR: In this article, the melting behavior of reactor-made isotactic polypropylene (PP) and various controlled rheology (CR-PP) samples crystallized under both isothermal and non-isothermal conditions were studied by differential scanning calorimetry and the crystal structure of isothermally crystallized samples at 120°C was investigated using wide angle X-ray diffraction.
TL;DR: In this paper, the Hartree-Fock method was used to model the beryllium surface and the effect of electron spin coupling on the adsorption process was discussed.
Abstract: Hydrogen adsorption on the (0001) beryllium surface is modeled using a Be45 cluster containing seven layers. The ab initio Hartree–Fock calculations employ effective core potentials and full D3h point group symmetry. Six low‐lying electron configurations are investigated and the effect of electron spin coupling on the adsorption process is discussed. The adsorption of H on Be is calculated to be stable by 20 kcal/mol and lowers the work function by 1.3 eV.
TL;DR: This work proves a sufficient condition for the Banerjee test's accuracy and explains the test's perceived superiority by showing that under circumstances which occur extremely frequently in actual code, it is, in fact, not approximate, but perfectly accurate.
TL;DR: In this article, the authors established that 12C(d,n)13N and 14N(d-n,n)-15O reaction yields inside 12C+D, 14N+D plasmas of focused discharges are ≈ 1% of the simultaneous D-D fusion yield for 10% of 12C and/or 14N atoms doped into D2 gas.
TL;DR: This paper shows that partial correctness logic can be viewed as a special case of the equational logic of iteration theories, and the familiar rules for the structured programming constructs of composition, if-then-else and while-do are shown valid in all guarded iteration theories.
Abstract: What is special about the rules of Hoare logic? This paper shows that partial correctness logic can be viewed as a special case of the equational logic of iteration theories [6, 7, 24]. It is shown how to formulate a partial correctness assertion {a} f { /3} as an equation between iteration theory terms. The guards (a, ~) that appear in partial correctness assertions are equationally axiomatized, and a new representation theorem for Boolean algebras is derived. The familiar rules for the structured programming constructs of composition, if-then-else and while-do are shown valid in all guarded iteration theories. A new system of partial correctness logic is described that applies to all flowchart programs. The invariant guard condition, weaker than the well-known condition of expressiveness. is found to be both necessary and sufficient for the completeness of these rules. The Cook completeness theorem [19] follows as an easy corollary. The role played by weakest liberal preconditions in connection with completeness is examined.
TL;DR: In this paper, the effects of blending low-density polyethylene (LDPE) with linear low-dimensional polyethylenes (LLDPE), as well as haze, were studied on extrusion blown films, and the impact energies of the LLDPE and the LDPE were approximately the same.
Abstract: Effects of blending low-density polyethylene (LDPE) with linear low-density polyethylene (LLDPE) were studied on extrusion blown films. The tensile strength, the tear strength, the elongation at break, as well as haze showed more or less additivity between the properties of LDPE and LLDPE except in the range of 20–40% where synergistic effects were observed. The LLDPE had higher tensile strength and elongation at break than did the LDPE in both test directions, as well as higher tear strength in the transverse direction. The impact energies of the LLDPE and the LDPE were approximately the same, but the tear strength of the LLDPE was lower than that of LDPE in the machine direction. The comparative mechanical properties strongly depend on the processing conditions and structural parameters such as the molecular weight and the molecular weight distribution of both classes of materials. The LLDPE in this study had a higher molecular weight in comparison to the LDPE of the study, as implied from its lower melt flow index (MFI) in comparison to that of the LDPE. The effects of processing conditions such as the blow-up ratio (BUR) and the draw-down ratio (DDR) were also studied at 20/80 (LLDPE/LDPE) ratio. Tensile strength, elongation at break, and tear strength in both directions became equalized, and the impact energy decreased as the BUR and the DDR approached each other.
TL;DR: La perte d'energie est traitee a la fois pour le mouvement parallele aux faces du barreau et pour the penetration a l'interieur dubarreau dans l'approximation de phase aleatoire.
Abstract: La perte d'energie est traitee a la fois pour le mouvement parallele aux faces du barreau et pour la penetration a l'interieur du barreau. On emploie l'approximation diagonale pour la reponse dielectrique inverse dans l'approximation de phase aleatoire. Les electrons du plasma sont soumis a une condition aux limites de reflexion speculaire
TL;DR: In this paper, high-c -axis oriented, highly dense, low carbon YBa 2 Cu 3 O x superconducting thin films have been formed in-situ at a reduced substrate temperature as low as 570°C by a novel plasma enhanced metalorganic chemical vapor deposition process.