Quasi-invariance of analytic measures on compact groups

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Modification of crystallinity and structure in powder processing of polytetra fluoroethylene

The modification of structure, crystallinity and orientation have been studied in powder processed polytetrafluoroethylene by various techniques. It was found that crystallinity (as determined from regression curve analysis) in unsintered samples decreased with increase of compaction pressure while in sintered specimen it increased with increase of pressure. The crystallinity was also found to vary inversely with logarithm of cooling rate. Microfocus X-ray diffraction revealed the orientation of c-axis lying preferentially in the plane perpendicular to applied pressure. There was slight variation in the lattice dimension especially the c-axis in completely sintered specimen. The infrared studies showed the presence of some of the bands depended upon the molding/sintering conditions. These various findings have been explained on the basis of compaction and recrystallization behaviour under constrained conditions

A study of the solid-state polymerization of trithiane

The temperature dependence of the rate of solid-state polymerization of trithiane was investigated in conjunction with calorimetric measurements of the heat capacity of the irradiated monomer as a function of temperature. It was found that the rate of change of entropy with temperature exhibited a maximum at about 175°C. The curve of per cent polymerization versus isochronal, post-irradiation polymerization temperature also peaked at some 175°C. Finally, the existence of a crystalline phase-transition in the monomer at about 194°C was discovered by DSC and was confirmed by X-ray powder diffraction and by optical microscopy. Two models which may interrelate this set of phenomena are suggested

An application of Martingale convergence theorem to analyse company data

Martingale Convergence Theorem, in a slightly general form, when applied to the process of investor's fortune tells that an investor with a limited aim of enhancing her fortune k-fold will, in due course, either attain her aim or lose the entire initial investment. We verify and apply this theorem to analyse certain company data

Hamel bases and measurability

This is a note - set in the background of some historic comments - discussing the relationship between measurability and Hamel bases for R over Q. We explicitly note that such a basis must necessarily fail to be Borel measurable (or even 'analytic' in the sense of descriptive set theory). We also discuss some constructions in the literature which yield Hamel bases which even fail to be Lebesgue measurable, and discussan elementary construction of a Hamel basis which is Lebesgue measurable

From melt flow index to rheogram

A knowledge of the complete flow curve or rheogram of a polymeric melt depicting the variation of the melt viscosity over industrially relevant range of shear rate and temperature is essential in the design of polymer processing equipment, process optimization and trouble-shooting. These data are generated on sophisticated rheometers that are beyond the financial and technical means of most plastics processors. The only flow parameter available to the processor is the melt flow index of the material. In the present work, a method has been proposed to estimate the rheograms of a melt at temperatures relevant to its processing conditions with the use of a master curve, knowing the melt flow index and glass transition temperature of the material. Master curves that coalesce rheograms of different grades at various temperatures have been generated and presented for low density polyethylene, high density polyethylene, polypropylene, polystyrene and styrene-acrylonitrile copolymer

Effect of processing condition and composition on the microhardness of Cu-(2.5-10)vol.%Al₂O₃ nanocomposite powder particles produced by high energy mechanical milling

Nanostructured Cu-(2.5-10vol.%)Al₂O₃ nanocomposites were produced using high energy mechanical milling. For the as-milled Cu- Al₂O₃ composite powder particles having Al₂O₃ volume fractions of 2.5% and 5%, the increase in average microhardness is significant with the increase of milling time from 12 hours to 24 hours. With the increase of the content of Al₂O₃ nanoparticles the microhardness increases and in the range of 255HV-270HV. The milled nanocomposite powders were heat treated at 150, 300, 400 and 500°C for 1 hour, respectively, to determine the thermal stability of the powder particles as a function of annealing temperature. The average microhardness increased/decreased for the Cu- Al₂O₃ composites after annealing at 150°C due to the dislocation density, while increasing the annealing temperature to 300°C and 400°C the average microhardness almost remained mostly unchanged. Further increasing the annealing temperature to 500°C causes significant decrease in average microhardness due to reduction in dislocation density and coarsening of Cu grains of the Cu- Al₂O₃ composite powders produced after 24 hours of milling. This paper is to report and discuss the changes of the microhardness of the material, caused by the compositions and processing conditions, used to fabricate the Cu-(2.5-10)vol.% Al₂O₃ nanocomposite powders

Rheograms for asphalt from single viscosity measurement

Asphalt materials are used in a variety of applications such as road paving, waterproofing, roofing membranes, adhesive binders, rust proofing and water resistant coatings. There are available in a number of grades distinguished in terms of their softening point and flow resistance. The selection of the proper grade of asphalt for a particular application is governed by the desired flow behaviour. A knowledge of the complete flow curve depicting the variation of melt viscosity with shear rate at the relevant temperatures is necessary not only for proper grade selection, but also for specifying processing conditions for aggregate mixing and spraying. The rheological data are also useful in assessing end use performance. The scientific techniques for generating the rheological data involve the use of expensive, sophisticated instruments. Generation of the necessary flow data using these instruments is beyond the financial and technical means of most processors of asphalt materials. The engineering techniques involving the use of inexpensive vacuum viscometers are relatively easy, but provide a single point viscosity measurement at low shear rate. In the present work, a method is proposed for unifying the viscosity versus shear rate a data at various temperatures for a number of asphalt grades. A master curve has been generated that is independent of the grade of asphalt and the temperature of viscosity measurement. The master curve can be used to generate rheograms at desired temperatures for the asphalt grade of interest, knowing its zero-shear viscosity at that temperature

Rheology of nylon 6 containing metal halides

Addition of metal halides to nylons has been shown to be advantageous in a number of ways. The decrease in melting temperature, increase in glass transition temperature and melt viscosity by such additions have allowed more convenient processing of low molecular weight polymers and thermally unstable polymers. Rheological data depicting the variation of melt viscosity with shear rate at temperatures relevant to processing are necessary in optimizing and trouble-shooting plastics processing operations. In the present paper, a method has been proposed to estimate, complete flow curves or rheograms of nylon-metal halide systems with the use of a master curve knowing the melt flow index and glass transition temperature of the system. The validity of the approach has been verified for the nylon 6-lithium chloride system and shown to hold good for any nylon-metal halide combination