Bimodal distribution measurements using different

Table II. Bimodal Distribution Measurements Using Different...

One characteristic of shear banded flow is the presence of fluctuations in the flow field. Such fluctuations also occur in some glassy colloidal materials at colloid volume fractions close to the glass transition. One such system is the soft gel formed by crowded monodisperse multiarm (122) star 1,4-polybutadienes in decane. Using NMR velocimetry Holmes et al. [23] found evidence for fluctuations in the flow behavior across the gap of a wide gap concentric cylindrical Couette device, in association with a degree of apparent slip at the inner wall. The timescale of these fluctuations appeared to be rapid (with respect to the measurement time per shear rate in the flow curve), in the order of tens to hundreds of milliseconds. As a result, the velocity distributions, measured at different points across the cell, exhibited bimodal behavior, as apparent in Figure 2.8.13. These workers interpreted their data... 

This value is considerably higher than the experimental value (0.17) obtained from rate measurements on different size particles, but several factors may be invoked to explain the inconsistency. There will be a distribution of both pore radii and pore lengths present in the actual catalyst rather than uniquely specified values. Alumina catalysts often have a bimodal pore-size distribution. Our estimate of an apparent first-order rate constant using the method outlined above will be somewhat in error. The catalyst surface may not be equally active throughout if selective deactivation has taken place and the peripheral region is less active than the catalyst core. Other sources of error are the... 

Before proceeding to a discussion of blood levels of MMPs and TIMPs in various diseases, it will be useful for the reader to critically examine the technical limitations of measuring these antigens in blood. An important consideration of measurements of MMPs in disease is the bimodal distribution of blood levels of MMPs in healthy subjects this is especially noted with plasma MMP-9, where 20% of healthy individuals have MMP-9 levels that are twice that of the remainder of the population (Fig. 2). We have noted that MMP levels are relatively constant in each individual over time. Genetic differences within the population probably account for much of this... 

Particle Sizing has been performed on the different PFC emulsions. Three vials were selected at random from each formulated batch. Vials were vortexed for 5 seconds and 10 uL aliquots of the liquid formulation were removed by syringe, injected into 3mL cuvettes containing 2mL of a phosphate buffered saline diluent (of known viscosity), and chilled in an ice batch. The cuvettes were covered and gently inverted 3 times. The temperature of the sample was then measured and each sample was analyzed using a Malvern Zetasizer HSIOO at temperature and viscosity settings determined. Because it was the main focus of this study, only the DDFPe particle size was monitored over a 6 month time period. The initial average particle diameters were determined to be 215 56 nm, 103 8 nm and 155 6 nm for DDFPe, PFDe and PFOBe, respectively. Fig. 1 shows that the DDFPe particle size remains stable at a diameter below 400 nm for 6 months at room temperature (23°C 2°C). Note that the open diamonds represent less than 2% of the particles in the sample and these bimodal distributions were only observed for the first two months. 

Based on the gas permeation measurement results on a variety of silica membranes, we have also reported similar findings [7]. We reported that the pore size distribution of sol-gel silica membranes appear to be bimodal with majority pores with sizes around 0.3 nm and some pores with much larger sizes formed due to the opaqueness of silica polymer clusters. Figure 16.5 shows the permeation results of silica membranes. The four membranes used in the study had been tailored with different porosity values. In spite of the differences in porosity values between the membranes, all the membranes showed ability to separate He from other molecules but the ability to separate between molecules of sizes greater than 0.3 nm was poor. Figure 16.6 shows a schematic representation of the separation behavior exhibited by silica membranes in comparison to a zeolite ZSM-5 membrane [7, 16, 36]. 

The CCD curve shown in Fig. 15 contains all the information on composition distribution and it is a common practice to compare the CCD curves of the different resins to be evaluated In addition to the CCD curve, it is convenient to work with some easy-to-use average parameters. In the case of multiple peaks (like those shown in Fig. 15), integration of the peaks is most appropriate. In bimodal LLDPE, the most important parameters to measure are the homopolymer (linear) and soluble fraction percentages. Calculation of moments similar to... 

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