Knudsen Cell Studies of the Vaporization of Samarium Dicarbide

The vapor pressure of SmC₂ in equilibrium with graphite was measured by the Mnudsen effusion technique. Rates of weight loss from the cells were measured with an automatic recording balance. The apparent pressures varied with orifice size, and equilibrium pressures were calculated by extrapolation to zero orifice area. This work was combined with other studies to obtain log₁₀ P(atm) = - 13.869 × 10³/T + 3.752 (1300°-2050°K) for the Sm vapor pressure above SmC₂-C. Estimates of S°₂₉₈ and c_p were made for SmC₂, and δH°₂₉₈ was calculated to be 72.0 ± 2 kcal/mol for the reaction SmC₂(s) = Sm(g) + 2C(s). This value combined with δH°_{v, 298}= 48.6 kcal/mol for Sm gives a δ°_f298 for SmC₂ of 23.4 ± 2 kcal/mol.     

VISCOMETRIC MEASUREMENT OF CHROMIUM(III)-POLYACRYLAMIDE GELS†

Gelled polymers are being used increasingly to modify the movement of injected fluids in secondary and enhaced oil recovery processes. A common gelation process involves the reduction of Cr(VI) to Cr(III) in the presence of polyacrylamide. The Cr(III) reacts or interacts with the polymer to form a gel network. Although correlations of gelation time with principal process variables have been obtained, viscometric data have not been reported during or after gelation. These data are needed for fluid flow calculations in surface equipment and estimation of flow behaviour in reservoir rocks.

A Weissenberg Rheogoniometer, with cone and plate geometry, was used to obtain viscometric data for the gelation of polyacrylamide and chromium (III). Solutions consisting of polyacrylamide polymer, sodium dichromate-dihydrate and sodium bisulfite were gelled under a steady shear field at constant temperature. The shear stress versus time profile for the galation process was interpreted to define a gelation time and to determine the apparent viscosity of the gelled fluid. The gelation time decreased as the applied shear rate increased up to about 14.25 sec^?1 and was affected by shear rate history. Viscometric properties of the gelled solutions were determined. Apparent viscosity of the gelled solutions decreased as the shear rate under which they were formed increased.

Post gelation studies indicated that gels exhibited a residual stress at zero shear rate and behaved as Bingham plastics under steady shear. Gels formed at low shear rates were more viscous than gels formed at high shear rates. However, the structure of these gels was susceptible to shear degradation.     

A Direct Test for Cointegration Between a Pair of Time Series

In this paper we introduce a new test of the null hypothesis of no cointegration between a pair of time series. For a very simple generating model, our test compares favourably with the Engle–Granger/Dickey–Fuller test and the Johansen trace test. Indeed, shortcomings of the former motivated the development of our test. The applicability of our test is extended to series generated by low-order vector autoregressions. Again, we find evidence that this general version of our test is more powerful than the Johansen test. The paper concludes with an empirical example in which the new test finds strong evidence of cointegration, but the Johansen test does not.     

Comparison of three‐dimensional analysis and stereological techniques for quantifying lithium‐ion battery electrode microstructures

Lithium‐ion battery performance is intrinsically linked to electrode microstructure. Quantitative measurement of key structural parameters of lithium‐ion battery electrode microstructures will enable optimization as well as motivate systematic numerical studies for the improvement of battery performance. With the rapid development of 3‐D imaging techniques, quantitative assessment of 3‐D microstructures from 2‐D image sections by stereological methods appears outmoded; however, in spite of the proliferation of tomographic imaging techniques, it remains significantly easier to obtain two‐dimensional (2‐D) data sets. In this study, stereological prediction and three‐dimensional (3‐D) analysis techniques for quantitative assessment of key geometric parameters for characterizing battery electrode microstructures are examined and compared. Lithium‐ion battery electrodes were imaged using synchrotron‐based X‐ray tomographic microscopy. For each electrode sample investigated, stereological analysis was performed on reconstructed 2‐D image sections generated from tomographic imaging, whereas direct 3‐D analysis was performed on reconstructed image volumes. The analysis showed that geometric parameter estimation using 2‐D image sections is bound to be associated with ambiguity and that volume‐based 3‐D characterization of nonconvex, irregular and interconnected particles can be used to more accurately quantify spatially‐dependent parameters, such as tortuosity and pore‐phase connectivity.     

胶接接头在静态负载条件下的蠕变和松弛行为

Modern high performance adhesives are designed to offer an optimized balance of elasticity,toughness and plastic deformation capacity for the individual fields of application in e.g. the building and construction or transportation and vehicle industry. The long-term life prediction for adhesive joints based on laboratory tests requiring only days,weeks,or months is still a demanding challenge. Testing in practice is carried out with the intention of accelerating time dependent aging effects that may occur in a bonded joint during its service time. Initial strength values of bonded joints,such as shear or peel properties can often be obtained from the adhesive manufacturers or retrieved from literature. They are useful to compare different adhesives and to demonstrate the effect of parameters such as bond line thickness,overlap length or curing conditions,and,in some cases,the surface state. On the other hand only few data are available describing the mechanical long-term properties of adhesives related to creep and relaxation under static load conditions. Due to the nature of the polymer network of organic adhesives their viscoelastic-plastic deformation behavior is strongly time-and temperature dependent. The objective of this paper is to illustrate effective methods for investigating and predicting the creep and relaxation properties of adhesively bonded joints in the long-term region and for creating basic data for the design and engineering with adhesives.     

OPTICAL ASSESSMENT OF CORN OIL DETERIORATION DURING FRYING

The ultraviolet (UV), visible and near-infrared (NIR) absorption changes in corn oil were measured during processes simulating deep fat frying. Corn oil, maintained at 185C, was exposed to various treatments with nitrogen, air, water injection, air with water injection, and steam. Autoxidation due to a combination of air and high temperature in the simulated frying trials caused visible absorption changes between 400 and 580 nm as the oil deteriorated similar to those observed in potato frying experiments. These absorption changes were found to be associated with changes in an ultraviolet absorption band with a maximum near 270 nm. Second-derivative calibration equations developed at various visible and NIR absorption wavelengths successfully predicted the percentage of total polar materials (%TPM) which accumulated in the corn oil during simulated trials of autoxidation (R values from 0.93 to 0.98). Using spectral data from repetitive potato frying experiments, the predicted %TPM calculated with these equations correlated well with kinematic viscosity measurements (R values from 086 to 0.97).     

MECHANICAL PROPERTIES OF AN IMMERSION FRIED POTATO STARCH-GLUTEN GEL DURING POSTFRYING PERIOD

Moisture profiles in fried samples of potato starch with different gluten contents were determined during postfrying storage. Over time, moisture migrated from the core to the crust of the sample, and the moisture content of the crust region increased. The addition of gluten caused a significant increase in oil uptake in the crust. The initial hardness of the crust significantly decreased as the gluten content increased to 10 and 30%, during the first 30 min of storage. With longer storage time (> 240 min), the crust hardness tended to increase, due to an increase in firmness of the starch sample. This behavior was less pronounced for samples with 10 and 30% gluten. The range of linear viscoelastic behavior (up to 14% strain) was determined from the initial linear zone of the stress-strain curves. Stress relaxation tests were performed in the linear and nonlinear viscoelastic regions, with a strain level of 5% and 40%, respectively. According to stress relaxation curves, samples became less elastic with the addition of gluten and more elastic with the time of storage.     

ESCHERICHIA COLI O157 IN IRISH FEEDLOT CATTLE: A LONGITUDINAL STUDY INVOLVING PREHARVEST AND HARVEST PHASES OF THE FOOD CHAIN

The aim of this study was to investigate fecal shedding and transmission of E. coli O157 in cohorts of cattle within a feedlot, to assess subsequent contamination of carcasses with this pathogen and to identify risk factors associated with fecal shedding of E. coli O157. A cohort of 133 heifers housed infour adjacent pens was examined over a five month period, from entering the feedlot to slaughter. Individual rectal fecal samples and pen environmental samples were taken at monthly intervals. The entire outer and inner surfaces of a carcass side of each animal were swabbed immediately following slaughter.
E. coli O157 was isolated from 136 (23%) of the 600 rectal fecal samples; 96% of which contained virulent markers. One hundred and sixty environmental samples were examined and E. coli O157 was isolated from 46 (29%), all of which contained virulent markers. E. coli O157 was not isolated from any of the dressed carcasses. The prevalence of E. coli O157 fecal shedding may be related to the pen and E. coli O157 contamination of the pen floor feces, water trough and feed.
E. coli O157 should be considered as a pathogen shed in the feces of a substantial proportion of feedlot cattle. However, with good hygienic practice at harvest, a very low level of this pathogen can be achieved on dressed carcasses.     

Methods used to study non-starter microorganisms in cheese: a review

The significance of non-starter lactic acid bacteria (NSLAB), which become the dominant organ-isms in hard cheese varieties during ripening, is still controversial, but they have been shown to contribute to the release of amino acids and to influence flavour development. Since the NSLAB population is essentially uncontrolled, it is likely that at least some of the variability in cheese quality is due to the NSLAB. Several approaches used to assess the significance of NSLAB in cheese ripening are reviewed in this paper.