Reactive processing of LLDPES in corotating intermeshing twin-screw extruder. II. Effect of peroxide treatment on processability

Commercial ethylene–octene linear low-density polyethylenes (LLDPEs) were reactively extruded with low levels of a peroxide [2,5-dimethyl-2,5-di(t-butylperoxy)hexane] to modify polymer molecular structure and processing properties. Peroxide levels were kept low to avoid crosslinking. This article reports the effects of this reactive extrusion on viscoelastic properties. Rheological properties are more sensitive than are molecular structure characteristics to the changes produced by reactions of very low peroxide concentrations. Complex viscosity increases are seen, especially at low frequencies. Shear-thining behavior is also accentuated. The crossover between G′ and G″ moves to lower frequencies. A modified Cole–Cole presentation of these data shows that the elastic component is more predominant for extrusion-reacted materials. Peroxide-modified materials all have higher Bagley end correction values than those of barefoot resins. The former exhibit lower power indices (more shear thinning). All these properties indicate more long-chain branching and higher melt elasticity. However, die swell decreased as a function of peroxide concentration. Peroxide treatment results in an enhancement of elongational viscosity, both under isothermal and cooling conditions, along with a decrease in drawdown ability. The rheological changes parallel those reported earlier in molecular characteristics but are more sensitive and suitable to evaluate the effects of reactive processing. The effectiveness of the reactive extrusion process for improving processability of LLDPEs depends critically on the extrusion conditions. © 1995 John Wiley & Sons, Inc.     

Structure and Mechanical Properties of Copper/Niobium Multilayers

Copper/niobium multilayers prepared by sputtering onto Si substrates with layer thicknesses ranging from 11 to 5000 have been characterized by transmission electron microscopy and nanoindentation. The films are strongly textured with {110} close-packed planes of the bcc Nb parallel to the {111} close-packed planes of the fcc Cu and close-packed directions tending to be parallel as well. For the 11 layers, the Cu is found to grow pseudomorphically on Nb in the bcc structure. It is thought that, for thicker layers, the bcc Cu loses coherency and transforms martensitically to the fcc phase, thus resulting in the observed KurdjumovSachs orientation relationship. As the layer thickness, d , decreases from 5000 to 500, the hardness increases as d ^−1/2; i.e., it follows a HallPetch relationship so that hardening is due to grain boundaries and interfaces. The slope is the same as in pure Cu, but there is a large intercept which is ascribed to internal stresses and a large dislocation density. As the layer thickness decreases from 100 to 11, the hardness increases as (1/ d ) ℓn (0.69 d ), which is a line tension formulation such as would be expected for Orowan dislocation bowing between the layers. Again there is a large intercept which is ascribed to cutting through the Cu/Nb interfaces. The interfacial energy is calculated to be 0.46 J/m².     

Zur Berechnung des Gleichgangs von Asynchronoder Synchronmaschinen mit Kolbenmaschinen

Zusammenfassung Im I. Teil der Arbeit wird gezeigt, wie man auf einfache Weise unter Benützung von Ortskurven die GleichgangverhÄltnisse bei Kolbenmaschinen mit Drehstrom-Asynchronmaschinen untersuchen kann. Die rein rechnerische Behandlung mit der Zielsetzung, alle den Gleichgang betreffenden Teilfragen und für die ma\gebendsten Teilmomente des Drehkraftdiagramms zu untersuchen, scheitert zunÄchst an dem damit verbundenen Rechen- und Zeitaufwand und vor allem an der Unmöglichkeit, den Einflu\ auch nur der wichtigsten, den Gleichgang bestimmenden Parameter klar zu überblicken.Zur Untersuchung genügt für jedes Teilmoment die Kenntnis irgend eines Ortskreises, z. B. des Ortskreises, der die AbhÄngigkeit vom Schwungmoment des Schwungrades ( _{2 v} -Kreise) oder von der Drehfederzahl des Wellenstranges (C -Kreise) angibt, um alle mechanischen und elektrischen Fragen ohne weitere Rechnung zu beantworten. Die zwischen den Ortskurven für die verschiedenen Parameter bestehenden Beziehungen werden gezeigt und die Grenzen für die Werte des Schwungmomentes des Schwungrades und der Drehfederzahl des Wellenstranges bzw. einer einzubauenden, elastischen Kupplung, angegeben, innerhalb der eine Verbesserung des Gleichganges erreicht werden kann. An zwei Beispielen wird die Anwendung des Verfahrens gezeigt und insbesondere der Einflu\ einer elastischen Kupplung auf den Gleichgang untersucht.     

Analyzing and Synthesizing Images by Evolving Curves with the Osher-Sethian Method

Numerical analysis of conservation laws plays an important role in the implementation of curve evolution equations. This paper reviews the relevant concepts in numerical analysis and the relation between curve evolution, Hamilton-Jacobi partial differential equations, and differential conservation laws. This close relation enables us to introduce finite difference approximations, based on the theory of conservation laws, into curve evolution. It is shown how curve evolution serves as a powerful tool for image analysis, and how these mathematical relations enable us to construct efficient and accurate numerical schemes. Some examples demonstrate the importance of the CFL condition as a necessary condition for the stability of the numerical schemes.     

Contributions of frontal system dysfunction to memory and perceptual abilities in Parkinson's disease.

Tested (1) the hypothesis that Parkinson's disease (PD), thought to result in disturbed neuronal outflow from the striatum, leads to circumscribed deficits in cognitive functions presumed to be dependent on the functional integrity of the frontal lobes and (2) whether such deficits could account for previously reported memory and visuoperceptual difficulties in PD. 19 nondemented PD patients were demographically matched to 19 normal elderly control Ss. Three categories of tests were given: (1) tests sensitive to frontal system dysfunction, (2) tests of learning and memory, and (3) tests of visuoperceptual and visuoconstructive skills. Nondemented PD patients demonstrated selective deficits on frontal system tasks; tests of learning and memory and of visuoperceptual and visuoconstructive skill were not significantly impaired once performance on the frontal related tasks was statistically covaried. Results are consistent with the striatofrontal outflow model of neuropsychological impairment in nondemented PD patients. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

n-octane dehydrocyclisation on monofunctional and bifunctional Pt/Al2O3 catalyst

The dehydrocyclisation of n-octane to iso-octane, ethylbenzene and o-, m- and p-xylene was investigated on monofunctional (non-acidic) and bifunctional (acidic) Pt/Al₂O₃ catalyst in a microcatalytic reactor with hydrogen as carrier at 1.8 atm and 563–673 K. On bifunctional Pt/Al₂O₃, the total conversion of n-octane started from a high value and decreased with increasing temperature for all pulse sizes investigated. The primary product of n-octane conversion on acidic Pt/Al₂O₃ was iso-octane. The product yield-temperature profiles showed a large initial production of iso-octane which decreased to a minimum as the catalyst temperature increased due to its conversion to ethylbenzene and o-xylene. On non-acidic Pt/Al₂O₃, the total conversion of n-octane increased initially and then went through a maximum as the catalyst temperature increased. The primary products of the reaction were found to be ethylbenzene and o-xylene, indicative of the activity of the metal to effect these ring closure reactions.     

Nonlinear Kirchhoff Circuits and Relativity Theory

Kirchhoff circuits consist of interconnections of elements. They are of importance not only for studying electrical phenomena but are ideally suited to model a broad range of physical systems for purposes where conservation of power and energy and related concepts such as passivity and losslessness are of paramount importance. In order to properly characterize such properties in the nonlinear case, the defining relations for nonlinear inductances etc. must have a specific form, but the classical relation for a relativistic mass is not of this type. It is shown that, preserving the classical relativistic kinematics and imposing a very reasonable requirement concerning work done, thus energy rather than momentum, one is naturally led to an expression for force in terms of mass and velocity whose form is in full agreement with that referred to for a nonlinear inductance. This alternative way of modifying Newton's second law requires Newton's third law to be also modified. These two modifications combined produce the same conservation of momentum and the same dynamics of particles in fields as classical relativity. The expression for kinetic energy, however, is different. Logically consistent derivations are presented, and a theoretical and an experimental result are pointed out that tend to offer some support to the alternative theory, or at least do not outrightly contradict it, as implausible as that theory may a priori appear to be. The paper updates earlier results on the subject.     

International Mentoring

Abstract

Despite some obvious differences between the two countries, Australian experience and approaches are proving useful in technical assistance to current reforms in the Sri Lankan water sector. A system of bulk water allocation through transferable entitlements is proposed in a policy package being considered by government. Demand management measures, including sharing of water management costs, are also proposed. Integrated planning of basin water resources is expected to play an important part in the new water management strategy. Institutional recommendations have also been prepared. An apex National Water Resources Authority along with an inter-ministerial Water Resources Council and an appeal resolution Water Resources Tribunal are proposed to carry out planning, regulatory, co-ordination, and related functions. River basin committees are recommended for basin level coordination in many areas, while the Mahaweli Authority, a major irrigation-oriented development agency, is being restructured along the lines of a river basin authority with Australian and other national guidance. A long-term, bilateral relationship has also been proposed as a means of capacity building and technical support for emerging issues.     

The Effects of Groundwater and Surface Water Use on Total Water Availability and Implications for Water Management: The Case of Lake Naivasha, Kenya

This study discusses the effects of water abstractions from two alternative sources on the available water volume around Lake Naivasha, Kenya: the lake itself and a connected aquifer. An estimation of the water abstraction pattern for the period 1999–2010 is made and its effect on the available water volume in Lake Naivasha and its connected aquifer is evaluated using a simple water balance modeling approach. This study shows that accurate estimates of annual volume changes of Lake Naivasha can be made using a simple monthly water balance approach that takes into account the exchange of water between the lake and its connected aquifer. The amount of water that is used for irrigation in the area around Lake Naivasha has a substantial adverse effect on the availability of water. Simulation results of our simple water balance model suggests that abstractions from groundwater affect the lake volume less than direct abstractions from the lake. Groundwater volumes, in contrast, are much more affected by groundwater abstractions and therefore lead to much lower groundwater levels. Moreover, when groundwater is used instead of surface water, evaporation losses from the lake are potentially higher due to a larger lake surface area. If that would be the case then the overall water availability in the area is more strongly affected by the abstraction of groundwater than by the abstraction of surface water. Therefore water managers should be cautious when using lake levels as the only indicator of water availability for restricting water abstractions.