OSCILLOGRAPH STUDY OF DIELECTRIC PROPERTIES OF BARIUM TITANATE

A disk of barium titanate was fired to 1350°C. for six hours in an electric furnace. Silvered electrodes were then fired on the disk at 650°C. A cathode-ray oscillograph measurement was made of the dielectric properties in order to analyze the whole charging and discharging cycle. The material showed saturation of the dielectric flux density or charge with increase of field strength or voltage and is therefore a new type of ferroelectric material. The dielectric properties of such a nonlinear circuit element was studied over a temperature range from –175° to +140°C. at field strengths of 59, 134,234, 580, and 4300 volts per cm. Peaks in the dielectric constant were observed near –70°, +10°, and 120°C. As the field strength was increased, the two lower peaks increased in magnitude and all peaks shifted slightly to lower temperature.     

Control policies for an industrial acetylene hydrogenation reactor

This paper addresses the problem of finding optimal operational policies for an acetylene reactor for day to day operation. A lumped parameter model based on four main reactions is developed and used to examine the effects of the reactor manipulated variables on key reaction parameters. An optimal and a sub-optimal operational policy which minimize the ethylene loss over time are formulated and the solution techniques are presented. The results indicate that the reactor model is in good agreement with industrial plant data. The performance of the optimal control policy is very similar to the performance of the sub-optimal control policy. However, the sub-optimal formulation, while retaining the dominant features of the optimal response, reduces the computational requirements. Finally, some issues concerning the real-time implementation of an advanced acetylene reactor control scheme are presented. These include the estimation of the optimum regeneration cycle, a recursive model update algorithm, the process optimizer and their overall coordination. A preliminary analysis of the benefits associated with the advanced control scheme suggests a considerable reduction in the yearly ethylene loss.     

Effects of fatty acid concentration and positional specificity on maize triglyceride structure

The effects of fatty acid concentration and positional specificity on maize triglyceride structure were evaluated from the stereospecific analyses of triglycerides from 12 genotypes. The fatty acids at each position were influenced by the fatty acid concentration in the total triglyceride except for the saturates in the 2 position. The fatty acid concentration had the greatest effect on the fatty acid composition of position 3. The existence of positional specificity was evident from the nonrandom distribution of the fatty acids among the three positions of the triglycerides. The concentration and positional specificity effects could be separated in selected genotypes and their crosses. This indicated different genetic controls for each effect.     

The selective utilization of diglyceride species into maize triglycerides

The maize triglycerides were resolved into species by silver nitrate thin layer chromatography. The distribution of the fatty acids among the 1, 2 and 3 positions of each triglyceride species was determined by stereospecific analysis. From these data the relative amounts of each positional isomer were calculated. The results indicate that esterification of the fatty acids at each position proceeds with a specificity that is correlated with the composition of the other positions of the triglyceride.     

Fractional turbidimetric analysis of the molar substitution of hydroxyethyl cellulose

High quality packaging films from hydroxyethyl cellulose of low degree of substitution (DS) are being produced commercially in this country and abroad. Increasing demand for this and a variety of other applications requires a rapid and simple production control method for determining hydroxyethyl substitution of cellulose. None of the known analytical methods fulfills these requirements. The present paper describes a method which is based on the relationship between the solubility and the molar hydroxyethyl substitution of hydroxyethyl cellulose. A washed and dried sample of hydroxyethyl cellulose is dissolved in 7% aqueous sodium hydroxide. Methyl alcohol, a nonsolvent, is used to precipitate a fraction of the sample. The turbidity of the equilibrium system is determined and optical density readings are related to molar substitution. The method is most useful in low DS ranges of 2–8% EtO but is susceptile to broader application through adjustment of the composition of the solvent–nonsolvent mixture. Relatively large variations in DP can be tolerated. The molar substitution level of an hydroxyethyl cellulose sample can be obtained in 40 min. by this method, making it a practical production control technique.     

Analysis of oil content of maize by wide-line NMR

A series of experiments to define feasibility, accuracy, and precision of wide-line nuclear magnetic resonance spectroscopy as a nondestructive analytical tool for the oil content of living seeds is described. Corn samples, ranging from single seeds to 25 g, were scanned by NMR and gravimetrically analyzed. A high positive correlation (r = 0.99⁺) was invariably encountered. Single, 30-sec NMR scans on 25-g corn samples gave estimates within ±33 ing of the “true” oil content 95% of the time. Error associated with single, 30-sec scans of individual corn kernels amounted to ±1.3 mg of oil at the same confidence level. Samples containing more than 4.5% moisture contribute to the NMR signal, and therefore oil content is overestimated. A new dimension is added to the breeding and genetics of oil crops by the application of the NMR technique in that the process is non-destructive and feasible even for single seeds. The usefulness of the technique in studies involving the nature of water and its surrounding medium is suggested.     

ALUMINA-SILICA RELATIONSHIP IN GLASS*

Assuming from a consideration of silicate minerals that aluminum should replace silicon in silicates, the authors investigated the system Na₂O-CaO-SiO₂-Al₂O₃. Densities and refractive indices have been determined and molecular refractions have been calculated. Partial molecular refractivities of Al₂O₃ indicate a coordination number of 4 for aluminum and deviate appreciably from values for compounds in which aluminum has a coordination number of 6. Interionic distances have been calculated for Si—O and Al—O. As a result of these studies, it is concluded that the aluminum atom isomorphously replaces the silicon atom in the random fetrahedral network. With this replacement, Ca⁺⁺ can increasingly replace Na⁺ in the interstices of the open structure.     

Mechanical properties of non-cohesive polygonal particle aggregates

We numerically investigate the effective material properties of aggregates consisting of soft convex polygonal particles, using the discrete element method. First, we construct two types of “sand piles” by two different procedures. Then we measure the averaged stress and strain, the latter via imposing a 10% reduction of gravity, as well as the fabric tensor. Furthermore, we compare the vertical normal strain tensor between sand piles qualitatively and show how the construction history of the piles affects their strain distribution as well as the stress distribution. In the next step, elastic constants are determined, assuming Hooke’s law to be locally valid throughout the sand piles. We determine the relationship between invariants of the stress and strain tensor, observing that the behaviour is nonlinear. While linear elastic behaviour near the centre of the pile is compatible with our data, nonlinearity signals the transition to plastic behaviour near its surface. A similar behaviour was assumed by Cantelaube et al. (Static multiplicity of stress states in granular heaps. Proc R Soc Lond A 456:2569–2588, 2000). We find that the macroscopic stress and fabric tensors are not collinear in the sand pile and that the elastic behaviour is anisotropic in an essential way.