Showing papers by "Stevens Institute of Technology published in 1988"

Dispersion‐free solvent extraction with microporous hollow‐fiber modules

Abstract: Determination experimentale des coefficients de transfert de matiere pour des modules hydrophobes ou hydrophiles. Mise en place d'une correlation pour decrire les resultats

Interfacial agents for multiphase polymer systems: Recent advances

Abstract: The rapid growth in the use of multiphase polymer systems (blends and composites) is undoubtedly related to the availability of methods of controlling the physical and chemical interactions at the interface. Compounds acting as interfacial agents are commonly known as “compatibilizers” in blends, or “coupling agents” in composites; their function is to promote adhesion and enhance overall properties. This paper is a review of recent advances in the use of these compounds in immiscible polymer blends and thermoplastic composites. Polymeric compatibilizers are classified according to their method of addition (in situformation vs. separate addition) and reactivity. Reactive low molecular weight compounds are also listed and their various coupling mechanisms are discussed. It is demonstrated that common routes to enhanced adhesion exist for some types of blends and composites. For example, reactive graft copolymers and certain crosslinklng agents are equally effective as adhesion promoters in blends and composites containing a polyolefin phase.

Spin-Orbit Coupling and Other Relativistic Effects in Atoms and Molecules

Abstract: Publisher Summary This chapter focuses on the recommended method for the inclusion of spin-orbit coupling and other relativistic effects for molecules containing heavy elements, considering computational complexity and accuracy factors that is one based on ab initio REPS. The calculation of accurate wave functions for systems containing heavy elements requires addressing the difficulties of the treatment of large numbers of electrons and the subtleties of electron correlation. This is not intended as a general review of relativity in chemistry or quantum mechanics, nor even of effective potential procedures, but is rather a critical discussion, including a limited number of applications, of the background, approximations, and implications of techniques developed by the present authors and collaborators and colleagues. The underlying assumption behind all methods for defining effective core potentials (EP) is the frozen core approximation. That is, the intrinsic reliability of core-valence separability. However, substantial savings are not realized by this approximation alone because of the radical oscillations of the valence orbitals in the region near the nuclei. An accurate procedure for performing calculations that incorporate spinorbit and other relativistic effects, and that represents intermediate coupling states for molecules containing heavy atoms, is based on A-S coupling in conjunction with the use of the ab initio REP-based spin-orbit operator and extended configuration interaction.

Observation of 4.2-K equilibrium-noise squeezing via a Josephson-parametric amplifier.

Abstract: We have demonstrated 42% squeezing of 4.2-K thermal noise using a Josephson-parametric amplifier operated at 19.4 GHz. The amplifier has been operated at 0.1 K with an excess noise of 0.28 K referred to the input port. This is less than the vacuum fluctuation noise h\ensuremath{ u}/2k=0.47 K at 19.4 GHz. The amplifier thus is less noise than a linear phase-insensitive amplifier such as a maser could in principle be.

The face-detection effect: configuration enhances detection.

Abstract: We have found that a picture of a face is more easily detected than is a pattern of arbitrarily rearranged facial features. An upright face is also more detectable than an inverted face. Using two-alternative forced-choice visual masking paradigms, we have found that this face-detection effect (FDE) can be produced with line drawings and with photocopies of a picture of a face. Our results suggest that a face, as an organized, meaningful pattern, is a more potent stimulus than an arbitrary assemblage of the same visual features. It may be that the FDE is a visual configuration effect. Previous visual configuration effects have been documented only with recognition responses. The FDE, by contrast, documents a configuration effect that affects the detectability of a stimulus.

Separation of solutes from aqueous solutions by contained liquid membranes

Abstract: The hollow fiber contained liquid membrane (CLM) is a thin liquid film contained in the interstices of two sets of intermingled microporous hollow fine fibers. Organic CLM-s have been used here for the separation of solutes from an aqueous feed into an aqueous strip. Solutes studied are phenol and acetic acid. The separations are carried out in either hydrophilic or hydrophobic hollow fiber CLM permeator modules, using a variety of organic liquids (e.g., decanol, methyl isobutyl ketone, xylene) as membranes. First-order models have been developed to predict the overall solute transfer coefficients adequately. The transfer coefficient can be enhanced significantly when a chemical reaction is carried out on the strip side using NaOH. The advantages of the CLM structure include operational stability, independent control of membrane phase pressure, automatic replenishment of the lost membrane liquid, and absence of the need for preequilibration. These features are demonstrated here, even for systems with considerable aqueous-organic mutual solubilities.

A new liquid membrane technique for gas separation

Abstract: A new liquid membrane separation technique for gas mixtures has been developed: feed and sweep gases flow through the lumen of two different sets of hydrophobic microporous hollow fibers while a liquid on the shell side acts as the membrane. This membrane is identified as the contained liquid membrane (CLM). Major shortcomings of immobilized liquid membrane techniques are eliminated. The novel separation device is identified as the hollow fiber contained liquid membrane (HFCLM) permeator. Experimental studies are made with different CO2-N2 feed mixtures and a pure helium sweep stream, with special emphasis on model landfill gas purification. Either pure water or an aqueous solution of K2CO3 is used as membrane. The effects of several variables on the performance of the HFCLM permeator have been studied. A three-component permeation model, incorporating axial pressure drop, is developed for binary mixture separation in a HFCLM permeator having a sweep gas stream. The experimental data show good agreement with the theoretical predictions.

Pulsed Electrodeposition of Ni‐Mo Alloys

Abstract: The effect of pulsing the current on the composition, the internal stress, and mechanical properties of Ni-Mo electrodeposits was investigated. The molybdenum, content increased with increasing peak current density and to a lesser degree with decreasing duty cycle. A reduction in the internal stresses was explained in terms of the relaxation of those due to crystallite or fine grain coalescence during the off-time and an expansion of the surface layer when hydrogen diffused into it at the start of each on-time. The mechanical properties were improved by high frequency pulse plating. Deposits consisting of alternate layers of different composition annealed at 300/sup 0/C exhibited further improvement of their mechanical properties.

Network Architecture and Modulus of Miscible Heteropolymer Blends

Abstract: The architecture and entanglement density of a multicomponent polymer network composed of miscible, flexible chains is related to the corresponding properties and concentrations of the pure components. It is assumed that the coupling frequency between different chain species is proportional to their fractional participation in the blend and that the entanglement ability of polymers can be affected by the presence of heteropolymer neighbors. The theory, equally applicable to temporary and permanent networks, estimates the molecular weight between entanglements and their total number along a chain in the blend. This information is used in establishing a mixing law for the rubbery plateau modulus of a fluid polymer blend and in deriving a relationship for the equilibrium modulus of an interpenetrating polymer network containing trapped entanglements and dangling segments. The theoretical predictions are compared with experimental results from the literature on several miscible polymer blends.

Motion planning among time dependent obstacles

Abstract: In this paper we study the problem of motion planning in the presence of time dependent, i.e. moving, obstacles. More specifically, we will consider the problem: given a bodyB and a collection of moving obstacles inD-dimensional space decide whether there is a continuous, collision-free movement ofB from a given initial position to a target position subject to the condition thatB cannot move any faster than some fixed top-speedc. As a discrete, combinatorial model for the continuous, geometric motion planning problem we introduce time-dependent graphs. It is shown that a path existence problem in time-dependent graphs is PSPACE-complete. Using this result we will demonstrate that a version of the motion planning problem (where the obstacles are allowed to move periodically) is PSPACE-hard, even ifD=2, B is a square and the obstacles have only translational movement. ForD=1 it is shown that motion planning is NP-hard. Furthermore we introduce the notion of thec-hull of an obstacle: thec-hull is the collection of all positions in space-time at which a future collision with an obstacle cannot be avoided. In the low-dimensional situationD=1 andD=2 we develop polynomial-time algorithms for the computation of thec-hull as well as for the motion planning problem in the special case where the obstacles are polyhedral. In particular forD=1 there is aO(n lgn) time algorithm for the motion planning problem wheren is the number of edges of the obstacle.

Asymmetrically-wettable porous membrane process

Abstract: An asymmetrically-wettable, porous membrane has a hydrophilic side and a hydrophobic side. The membrane has pores which pass through the membrane to provide communication between the hydrophilic side and the hydrophobic side. The membrane can be used in a process for transferring a solute from a liquid feed solution to a liquid extractant which is substantially immiscible with the feed solution. The process comprises contacting the hydrophilic side of the membrane with one solution and contacting the hydrophobic side of the membrane with the other solution. The interface between the feed solution and the extractant is substantially immobilized at the porous membrane. Solute is transferred from the feed solution to the extractant through the pores of the membrane.

Development of experimental techniques and simulation methods to analyze mixing in co‐rotating twin screw extrusion

Abstract: Currently, the selection of elements and operating conditions in the mixing of various materials in a corotating twin screw extruder is an art which requires previous experimental studies. In this report, we outline various experimental and theoretical tools developed to investigate the mixing process in a fully intermeshing corotating twin screw extruder. The thermomechanical history of mixing is simulated employing the finite element method. To verify the numerical findings, experimental techniques were developed to investigate the goodness of mixing of samples collected from a 50.8 mm, “clam shell” design, Baker-Perkins twin screw extruder.

Reduction of residual amplitude modulation in frequency-modulation spectroscopy by using harmonic frequency modulation

Abstract: A new technique to improve the sensitivity of frequency-modulation laser absorption spectroscopy is reported. Theoretical analysis and experimental demonstration show that the application of two harmonically related, appropriately phase-shifted rf waves to the electro-optic modulator can reduce the residual amplitude-modulation background signal in the photodetector output current without reducing the absorption-induced signal. When the new method was used, the residual amplitude-modulation background was reduced by a factor of 4. Our results suggest that shot-noise-limited detection sensitivity may eventually be achieved without using dual-beam compensation or dc-biased modulators.

Graph theoretic reliability analysis for the Boolean n cube networks

Abstract: Two graph-theoretic results concerning Boolean n-cube network reliability are presented. First, a simple formula for the number of spanning trees of the Boolean n-cube network is derived. As a result, the reliability function for large failure rate can be readily computed. Second, the Boolean n-cube network is proved to have the super-line-connectivity property. Thus the number of line-disconnecting sets (a set of lines the removal of which results in a disconnected or trivial graph) or order lambda for the Boolean n-cube network is equal to 2/sup n/. >

Separation of Liquid Solutions by Contained Liquid Membranes

Abstract: The technique of contained liquid membranes (CLM) for liquid solution separation is discussed. The CLM is obtained by confining the membrane liquid between two sets of microporous hollow fibers (MHF). The lumen of the hollow fiber carries the feed or the strip solution under proper phase pressure condition vis-a-vis the membrane phase. Various possible structural configurations of the CLM are illustrated with respect to the nature of microporous hollow fiber substrate, the feed solution and the liquid membrane. The contributions of different resistances to the solute transport rate are identified. Some basic experimental data obtained in small CLM permeators are presented for two systems with organic liquid membranes to illustrate how steady state separation is achieved after an initial unsteady period. The considerable advantages of the CLM structure over more traditional liquid membrane techniques such as supported liquid membrane (SLM) with respect to membrane stability, membrane regeneration ...

Commitment and Academic Success.

Abstract: The predictors of academic success usually include aptitude and previous achievement measures. In the present study we used a modified version of Rusbult and Farrell’s (1983) commitment questionnaire to predict final grades in a university setting. As part of a larger study on the relationship between attitudes and study behaviors, 39 students completed the 5 parts of the Rusbult and Farrell questionnaire. Responses were then correlated with 3 dependent measures: a final course grade in calculus, grade point average (GPA), and the grade in a humanities course. Results showed that adjusted R 2 values of .38 and .40 were obtained with the first 2 criteria. The implications of using affective variables for predicting academic achievement are discussed.

Pulsed electrodeposition of layered brass structures

Abstract: The mechanical properties of electroplated alpha and beta brasses and of deposits consisting of alternate layers of the two phases were determined. The alternate-layer deposits were stronger than the single-phase ones only if the latter were coarse grained. Some alternate-layer deposits of ordered and disordered beta brass exhibited high ductilities, apparently due to a strain-induced martensitic reaction which inhibited necking. The friction coefficients of alternate-layer deposits being lower than those of the single-phase ones indicated weak bonding between the alpha and beta layers.

Video transmission in optical fiber communication systems using pulse frequency modulation

Abstract: A design procedure has been developed to determine the required operating conditions for a pulse-frequency modulation (PFM) system (modulation index, required system bandwidth, and receiver carrier-to-noise ratio (CNR) for a specified receiver SNR (signal-to-noise ratio) and number of clicks per second. The PFM processing gain (=SNR/CNR) was measured to be 40 dB for a modulation index of beta =2.5, which agrees closely with the theory. The theoretical processing gain advantage of PFM over FM is 15.9 dB for a modulation index of beta =2.5 with receiver bandwidth B/sub rx/=50 MHz. >

Tribochemical Lubricious Oxides on Silicon Nitride

Abstract: The concept of lubrication by a tribochemically generated oxide layer on the surface of silicon nitride is further investigated. Previous work has shown that low friction coefficients (μ≈0.1) are obtained in a range of sliding velocities and loads when otherwise unlubricated silicon nitride slides in humid air at temperatures between 150 and 650oC. In order to verify the hypothesis that this behavior results from a competition between the growth of an oxide layer (with growth kinetics accelerated by friction) and its removal by wear, we have performed model experiments at room temperature, wherethe oxide layer is grown statically (i.e. without friction) and the friction coefficient and its evolution in time are subsequently measured. In order to avoid high friction by plowing, ultraflat surfaces were first prepared by sliding in water. The experiments showed that the oxide layer growing in humid air on silicon nitride produces a friction coefficient as low as μ≈0.05 that survives about 30 Newton meter of sliding, which corresponds to several hundred passes of the counterface. When sliding in water, the surface acquires a high friction coefficient (μ≈0.7) very rapidly. The difference in the lubricating properties of tribochemical surface layers on aluminum oxide and silicon nitride can be understood on the basis of the differing surface chemistries of these materials. We offer a tentative lubrication mechanism based on low adhesion between the oxide surface and the silicon nitride counterface and the structure of oxides grown inhumid ambients.

Vibrational-rotational analysis of ab initio potential energy surfaces for symmetric-top molecules: application to ammonia isotopomers

Abstract: Author Institution: Lever Research, Inc., Edgewater; Department of Chemistry and Chemical Engineering, Stevens Institute of Technology

Rheology and processing of linear low density polyethylene resins as affected by alpha‐olefin comonomers

Abstract: The effects of the higher alpha-olefin comonomers on the rheology and processing behavior of linear low density polyethylenes were investigated. Four linear low density polyethylene resins polymerized with butene, hexene and octene comonomers and a low density polyethylene were characterized in terms of their shear viscosity, first normal stress difference, storage and loss moduli, shear stress growth, stress relaxation upon step strain, stress relaxation upon the cessation of steady shear, and uniaxial extensional stress growth material functions. Differences in first normal stress difference, relaxation moduli, damping function parameters, and uniaxial extensional stress growth behavior were noted. The observations were elucidated in terms of the processability considerations in blown film extrusion process.

A model for irreversible adsorption hysteresis

Abstract: A model is proposed which is capable of describing non‐linear irreversible adsorption hysteresis with a single set of coefficients. The model is predicated on the assumption that two types of adsorption sites are present on the sorbent. At the first type of sites, solutes are irreversibly adsorbed in an amount related to the highest concentration at which the sorbent was exposed. Adsorption at the other sites is completely reversible and non‐hysteretic. The total adsorption is the sum of the two. However, when the equilibrium concentration is decreased, only the reversible component desorbs. Experimental protocol and mathematical techniques are presented for calibrating and verifying the model. The model is capable of predicting continuous flow column behavior based upon batch isotherm data.