pH Measurement of Flame-Hydrolysed Silica Suspensions

Various pH measurements on silica suspensions have been made. The changes in pH of HCl/NaOH solutions caused by increasing amounts of dispersed phase were determined. The differences in pH between the suspensions and their supernatants were also measured. The reasons for these differences are discussed and the most suitable method for pH measurement outlined.     

Double channel electrodes and the measurement of heterogeneous reaction rates at the solid-liquid interface

The theory of collection efficiency measurements (under steady-state conditions) at double channel electrodes is extended to include the case where the species generated at the upstream electrode undergoes a heterogeneous reaction on the surface of the gap between the two electrodes. The problem is treated numerically using the Backwards Implicit method, which allows the collection efficiency to be related to the corresponding value of the rate constant for the heterogeneous process for chosen double electrode geometries and solution flow rates. The use of the technique is illustrated with experiments in which bromine, generated at the upstream electrode by the oxidation of bromide ions (in 0.5 M sulphuric acid), reacts with a cloth dyed with Direct Red 80, and is subsequently collected at the downstream electrode through transport-controlled reduction to bromide. Good agreement is found between theory and experiment.     

Effects of dietary gossypol consumption on metabolic homeostasis and reproductive endocrine function in beef heifers and cows

Our objectives were to determine the effects of incremental increases in dietary gossypol on metabolic homeostasis and reproductive endocrine function in postpubertal beef heifers and the long-term effects of elevated dietary gossypol on various metabolic and reproductive endocrine characteristics in mature cows. In Exp. 1, heifers (n = 6/group) were fed either 0, .5, 2.5, 5, 10, or 20 g.animal-1 x d-1 of dietary free gossypol for 62 d. Erythrocyte membrane osmotic fragility was increased (P < .0001) in both the 10- and 20-g groups. Slight alterations in plasma concentrations of sorbitol dehydrogenase and K+ were also detected in the latter group. Treatment did not affect ADG, body condition scores, or concentrations of progesterone during the estrous cycle; however, mean concentrations of LH were higher (P < .001) in heifers fed 20 g/d of gossypol than in heifers in all other groups. In Exp. 2, lactating cows (n = 17) exhibiting regular estrous cycles were fed a control (no gossypol, n = 8) or high-gossypol (20 mg.kg BW-1 x d-1 free gossypol, n = 9) diet for 33 wk. Mean BW and body condition scores did not differ during the feeding period. Erythrocyte membrane fragility was greater (P < .05) in the high-gossypol than in the control group. Magnitude of the preovulatory LH surge, luteal phase concentrations of progesterone, follicular fluid concentrations of estradiol and progesterone, in vitro granulosa cell estradiol production, and 60-d pregnancy rates were similar between groups. The amounts of gossypol fed in these experiments are not likely to affect reproductive performance adversely in beef heifers or cows.     

Numerical analysis of injection molding of glass fiber reinforced thermoplastics. Part 2: Fiber orientation

Numerical predictions of fiber orientation during injection molding of fiber-filled thermoplastics are compared to measurements. The numerical work successfully describes the flow of fiber-filled plastic during injection molding, using finite-difference solutions for the transport equations and marker particles to track the flow front. The flow is modeled as a 2-D, non-isothermal, free-surface flow with a new viscosity model dependent upon temperature, pressure, and fiber concentration. The fiber orientation is based upon solution to the Fokker-Planke equation. The comparison demonstrates fair agreement between predicted fiber orientation and experimental results for slow and fast injection speeds. For the slow speed case at 10 and 20 wt% fibers, the numerical and experimental works show that the fibers are more random at the flow front than at the centerline, and that the fibers become more aligned as they flow from the gate to the midstream region. At fast injection speeds, the agreement between the numerical and experimental works is not as good as at slow injection speed. Possible explanations for the discrepancies are that the flow is assumed to be simple shear when injection molding is known to be a pressure-driven flow, the fibers have an initial orientation for the runner rather than the assumed random orientation, the fibers that were displayed from the camera were more oriented just behind the flow front (owing to the fast injection speed), and the orientation requires more than a 2-D video image to represent a 3-D fiber orientation.     

A study of microwave transmission,reflection, absorption,and shielding effectiveness of conducting polypyrrole films

Microwave transmission, reflection, and absorption behavior and the shielding effectiveness of electrochemically synthesized polypyrrole films with dc conductivities ranging from 0.001 to 50 S/cm are presented. Results show that the electrical conductivity of the doped polypyrrole films has a significant effect on transmission, reflection, and absorption of microwaves. Heavily doped, conducting films were highly reflective, whereas lightly doped, semiconducting films had very high transmission. Intermediate conductivity polypyrrole samples were highly absorptive. The agreement between experimental data and theoretical modeling provided confidence to extend the modeling to include the effect of sample thickness on the transmission, reflection, and absorption properties of films with a wide range of conductivity values, hence, providing valuable information for the design of microwave devices and fundamental understanding of the material properties. A method of measuring the far-field sheilding effectiveness of polypyrrole films is also presented. Results of shielding experiments indicated the potential for such applications. © 1994 John Wiley & Sons, Inc.     

Gallium-loaded zeolites for light paraffin aromatization: evidence for exchanged gallium cation active centers

It is shown that certain metal-loaded zeolites (e.g., Ga-MFI) initially prepared as separate metal-containing and zeolite phases are reducible, resulting in solid-state transfer of the metal to the zeolite. The final material is similar to those initially prepared as ‘unsegregated’ by methods such as aqueous impregnation. Reduction occurs either through appropriate pretreatment or onstream in certain hydrocarbon reactions. First, preparation methods leading to one or the other type of material are examined. Then it is shown that reduced catalysts give far higher ratios of dehydrogenation to cracking rates (for alkanes) than either segregated or unsegregated but unreduced systems. The product distributions of the propane reaction at low partial pressure and low conversion are also reviewed, and new data presented for unsegregated, reduced catalysts. There are great differences in the distribution obtained using reduced 1/1 metal/A1 catalysts from corresponding distributions for the H-form zeolites or for segregated systems. The differences suggest a mechanism which may be entirely independent of catalysis by protons.     

Sensory and cognitive components of visual information acquisition.

Describes a theory of visual information acquisition and visual memory. The theory has 2 major components. First, the visual system's initial sensory response to a short-duration, low-contrast stimulus is generated by a linear, low-pass temporal filter that operates on the stimulus's temporal waveform. Second, information is acquired from a stimulus through an independent-sampling process whose sampling rate at time t following stimulus onset is jointly proportional to (1) the magnitude by which the sensory response exceeds some threshold and (2) the proportion of still unacquired information. The theory was successfully tested in 5 variants of a digit recall task in which temporal waveform of the stimulus was systematically manipulated. In a final experiment, the theory simultaneously accounted for performance in detection and identification tasks. Implications for visual information processing, low-contrast detection, and binocular combination of information are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)