Rheology-processing-property relationships in tubular blown film extrusion. I. High-pressure low-density polyethylene

Three different grades of high-pressure low-density polyethylene resin were used to establish relationships between tubular film blowability and the molecular parameters, namely, the molecular weight distribution (MWD) and the degree of long-chain branching (LCB), and also between the processing conditions and the mechanical properties of the tubular blown films produced. For the study, both the shearing and elongational flow properties of the resins were determined. During the tubular film blowing experiment we measured the freeze-line position, the tubular bubble diameter, the takeup speed, the axial tension, the pressure inside the tubular bubble, and the mass flow rate of the resin. The thickness of the tubular blown films was measured from the samples collected. In order to determine the tubular film blowability, we measured the maximum takeup speed at which the tubular blown bubble broke, for various blowup ratios. The measurements described above permitted us to calculate the tensile stresses at the freeze line, in both the machine and transverse directions, and they were found to be correlatable to the processing conditions employed. It has been found that the tubular film blowability is increased as the resin's MWD becomes narrower and the degree of LCB is less. It has been found further that a resin having lower elongational viscosity tends to give a greater draw-down ratio, indicating a better tubular film blowability. Finally, the tensile properties of the tubular blown films were found correlatable to the processing variables, namely, blowup and takeup ratios.     

Adrenocortical pregnenolone binding activity resides with estrogen sulfotransferase

Cytosol prepared from Chinese hamster ovary (CHO)-K1 cells transfected with guinea pig estrogen sulfotransferase (EST) cDNA demonstrated high affinity binding activity for pregnenolone as well as 17 beta-estradiol but failed to bind dehydroepiandrosterone or testosterone. In contrast, cytosol prepared from nontransfected CHO-K1 cells did not demonstrate steroid binding activity. Additionally, the binding activity for pregnenolone and 17 beta-estradiol was dependent on the presence of the cofactor adenosine-3',5'-diphosphate. Pregnenolone and 17 beta-estradiol effectively competed with each other for binding. On the other hand, pregnenolone, which was not sulfonated, did not inhibit the sulfonation of 17 beta-estradiol by expressed EST.     

Rheology-processing-property relationships in tubular blown film extrusion. II. Low-pressure low-density polyethylene

An experimental investigation was undertaken to establish rheology-processing-property relationships in the tubular blown film extrusion of low-pressure low-density polyethylene (LP-LDPE). For the study, three commercial LP-LDPE resins, each from a different resin manufacturer, were used in producing tubular films, by employing the apparatus described in Paper I of this series. Both molecular and rheological characterizations of the resin were conducted, enabling us to interpret the tubular film blowing characteristics of the resins. Correlations were obtained between the processing variables (namely, blowup and takeup ratios) and the tensile properties of the films. The tubular film blowing characteristics of LP-LDPE and HP-LDPE resins are compared. Differences in the rheological properties (namely, elongational viscosity) of the two types of resin are used in explaining the experimentally observed differences in their tubular film blowability.     

Empirical correlations of turbulent friction factors and heat transfer coefficients for viscoelastic fluids

Empirical correlations for the friction factor and the dimensionless heat transfer coefficients are proposed as functions of the Reynolds and Weissenberg numbers. If the rheological properties of the polymer solution including the characteristic time are known, the friction factor and dimensionless heat transfer coefficient of a polymer solution in a circular pipe can be estimated. Additionally, these empirical correlations can be used to determine the characteristic time of a dilute or highly degraded polymer solution with a simple pressure drop measurement.     

New method to determine characteristic time of viscoelastic fluids

An extra dimensionless parameter involving the ratio of the elastic and viscous forces, the Weissenberg number, is necessary to correlate the friction and heat transfer behavior of viscoelastic fluids. The evaluation of the Weissenberg number requires a measurement of the first normal force difference or, alternatively, the determination of the characteristic time of the fluid. We suggest that the characteristic time of viscoelastic fluids can be determined by a simple pressure drop measurement. The basis for the proposed method is presented. More detailed measurements are required to validate the procedure.     

Characteristics of pixel arrangements in various rhombuses for full-parallax three-dimensional image generation

In full-parallax three-dimensional (3-D) imaging systems, the pixel cells often have the shape of a rhombus. Proper arrangement of pixels in these rhombic-shaped cells is important to maximize the quality of displayable 3-D images with a given display panel. The possible number of pixel arrangements in a rhombic cell with a definite dimension is found by considering the number of possible crossings between parallel line families forming the pixel cells, when the slopes of the lines are approximated by the ratio between the number of pixels in the vertical and horizontal directions. To make the rhombic cell have a uniquely defined pixel arrangement, its horizontal and vertical dimensions should be equal to the even multiple of the pixel dimension in their corresponding direction.     

Reaction modeling on the phosphorous-treated Ru/Co/Zr/SiO2 Fischer-Tropsch catalyst with the estimation of kinetic parameters and hydrocarbon distribution

The catalytic performances and the kinetics model of the cobalt-based Fischer-Tropsch (FT) catalyst were investigated on Ru/Co/Zr/SiO₂ with different amounts of phosphorous. The preliminary analysis of the CO conversion, the hydrocarbon selectivity and the activation energy revealed that the 0.5 wt.% phosphorous-treated Ru/Co/Zr/SiO₂ catalyst was found to have the highest catalytic activity because of the good dispersion of the cobalt species and the suppressed aggregation during the FT reaction. Kinetics model was concomitantly developed on the selected catalyst. The model that was reported in the literature was modified in order to explain the characteristics that were observed in the experimental studies, and the kinetic parameters were estimated to fit the experimental data under various reaction conditions. The simulation results along with the estimated kinetic parameters satisfactorily predicted the effects of the operating conditions on both the CO conversion and the entire hydrocarbon distribution.     

Nanoscale two-bit/cell NAND silicon-oxide-nitride-oxide-silicon devices with a separated double-gate saddle-type structure

Nanoscale two-bit/cell NAND silicon-oxide-nitride-oxide-silicon flash memory devices based on a separated double-gate (SDG) saddle structure with a recess channel region had two different doping regions in silicon-fin channel to operate two-bit per cell. A simulation results showed that the short channel effect, the cross-talk problem between cells, and the increase in threshold voltage distribution were minimized, resulting in the enhancement of the scaling-down characteristics and the program/erase speed.