Elongational viscosity of LDPEs and polystyrenes using entrance loss data

For two low‐density polyethylenes and two polystyrenes, axisymmetric and planar elongational viscosities are estimated using entrance loss data from capillary and slit rheometers, respectively. The elongational viscosity is estimated by optimizing the values of various parameters in the Sarkar–Gupta elongational viscosity model such that the entrance loss predicted by a finite element simulation agrees with the corresponding experimental data. The predicted entrance loss is in good agreement with the experimental data at high flow rates. The difference in the experimental and predicted entrance loss at lower flow rates might have been caused by large error in the experimental data in this range. POLYM. ENG. SCI., 2008. © 2007 Society of Plastics Engineers     

Coefficients of dynamic friction and the mechanical melting mechanism for vinylidene chloride copolymers

Previous research and this research indicate that the mechanical melting for poly(vinylidene chloride) copolymers (PVDC) is complex. Mechanical melting is defined as the melting (or devitrification) of a polymer when a significant portion of the thermal energy originates from a mechanical energy dissipative process. PVDC mechanically melted on a moving metal surface at temperatures of the test instrument that were considerably lower than the differential scanning calorimetry (DSC) onset melting temperature. PVDC formulated with low levels of high density polyethylene (HDPE), however, melted at metal temperatures near the DSC onset melting temperature. Two different mechanical melting mechanisms are proposed to explan the data, and the frictional data are discussed with respect to solids conveying in a single-screw, plasticating extruder.     

A species of Plasmodium from sandhill cranes in Florida

Infections of a species of Plasmodium (subgenus Giovannolaia) were diagnosed in 3 sandhill cranes (Grus canadensis) from north-central Florida. This parasite is close morphometrically to Plasmodium polare; this finding constitutes the first report of a species of Plasmodium from sandhill cranes in North America.     

Temperature gradients in the channels of a single‐screw extruder

We used a temperature‐sensitive fluorescent dye, perylene, to monitor the true resin temperature during extrusion of polycarbonate. The measurement involved doping polycarbonate with perylene and detecting fluorescence with an optical sensor that accesses a standard instrumentation port on a barrel of a single‐screw extruder. The sensor's confocal optics design permits fluorescence intensity measurements as a function of position. Using a previously established calibration function, temperature and temperature gradients were obtained from the measured fluorescence. Because the origin of the measurement is the fluorescent dye molecule that is soluble in the resin, this method allows temperature measurement of the polymer without interference from the surrounding metal parts. With the sensor looking over the screw, temperature profiles from the barrel wall to the core of the screw were obtained as a function of screw speed, screw design and resin melt flow rate. Polym. Eng. Sci. 44:2148–2157, 2004. © 2004 Society of Plastics Engineers.

1 This paper is a contribution from the National Institute of Standards and Technology, and, thus, is not subject to copyright in the United States.

     

Postural changes in plasma renin activity and responses to vasoactive drugs in a case of Shy-Drager syndrome

A male aged 47 years with gross autonomic insufficiency as part of the Shy-Drager syndrome is described. He did not sweat normally when warmed, and his circulatory responses to mental arithmetic, the Valsalva manoeuvre, and head-up tilt were abnormal indicating severe sympathetic failure. During head-up tilt there was a rise in plasma renin activity and plasma aldosterone. It is argued that plasma renin activity is not dependent on sympathetic nervous activity and may be mediated by renal baroreceptors. These rises may help sustain the blood pressure in such patients during repeated head-up tilts. Infusions of L-noradrenaline and angiotension produced greater hypertension, and injections of isoprenaline greater hypotension than in controls. Although it is difficult to exclude the possibility that one factor in this may be hypersensitivity of receptors in blood vessel walls, the principal factor is likely to be the absence of those baroreflexes of which the efferent pathways are in the sympathetic nervous system.     

Performance of uprated substations in contaminated environments

Uprated substations have proven to be a viable economic alternative to rebuilding in order to increase power system capacity. The key economic factor in uprated designs is the use of lower than traditional insulation margins in high voltage substations. The experience of these uprated substations has been good and insulation design procedures for uprated substations have been developed to show other engineers how to take advantage of this design alternative. While these design procedures and other publications including the results of actual tests have given ample evidence of the success of the uprated designs, it has been noted that several areas need more study and testing. Among those areas which need further study are the effects of the dynamic forces caused by higher fault currents in the uprated substations and the ability of the reduced creepage distances of the uprated design to withstand pollution severity. This study covers the pollution severity issue by examining the results of flashover tests on the uprated substation insulators under various contamination conditions. The tests, which were done at the EPRI Power Deliver Center at Lenox, USA, are believed to be the only flashover tests ever conducted with uprated insulators. As might be expected, the uprated design is shown to be very sensitive to pollution severity. Sites chosen for uprating should include a pollution severity assessment as part of the design review     

CARIN theory reanalysis reanalyzed: A comment on Maguire, Devereux, Costello, and Cater (2007).

P. Maguire, B. Devereux, F. Costello, and A. Cater (see record 2007-08734-012) discussed the Gagné and Shoben (1997) CARIN theory of conceptual combination and, after presenting a sample drawn from the British National Corpus and comparing the two corpora, concluded that the Gagné and Shoben corpus is too small and unrepresentative. They then discussed the mathematical model presented by Gagné and Shoben and claimed that the model does not incorporate relational competition. In this article, the authors present critical aspects of the mathematical model not considered by Maguire et al. and show that the mathematical instantiation of CARIN presented by Gagń and Shoben is, in fact, very sensitive to the number of strong competing relations. The authors then present some new comparisons between the corpora, showing that they correspond surprisingly well. (PsycINFO Database Record (c) 2010 APA, all rights reserved)