Showing papers by "University of Delaware published in 1973"

Chemistry and engineering of catalytic hydrodesulfurization

Abstract: A review with 74 refs. on catalytic hydrodesulfurization of pure compds. and petroleum feedstocks, with emphasis on reaction intermediates and structures of Al2O3-supported Ni-W and Co-Mo catalysts. [on SciFinder (R)]

Kinetics of crystallite sintering during heat treatment of supported metal catalysts

Abstract: Models are developed to describe sintering of metal crystallites during heat treatment. The growth rate of such crystallites is assumed to depend upon particle migration over the surface of the support as well as on the rate the colliding particles merge (sinter) into a single unit. The theory predicts that the rate of decay of exposed metal surface area S is given as in Equation (1a). The exponent n is related to the assumed size dependence of the diffusion coefficients or of the rate constant of the merging process. It varies from 4 to 8 for diffusion controlled decay and it is less than 3 for sintering controlled decay, that is, when the rate controlling step is the merging of two colliding particles. Diffusion control is associated with strong interactions between the metal and the support, but in sintering control there is a weaker metal-support interaction.

Tricritical Behavior in a Liquid-Crystal System

Abstract: The isotropic-cholesteric and cholesteric-smectic-$A$ phase transitions in cholesteryl oleyl carbonate have been studied for pressures up to 7 kbar. The latter transition possesses a tricritical point at 2.66 kbar and 60.3\ifmmode^\circ\else\textdegree\fi{}C, where the behavior changes from first to second order.

Kinetics of Self-Trapped Holes in Alkali-Halide Crystals: Experiments in NaI(Tl) and KI(Tl)

Abstract: A previous model calculation of the kinetics of hole diffusion in thallium-activated alkali iodides led to predictions concerning the role of binary electron-hole diffusion in the energy transport associated with the scintillation process. In this paper we report the resuls of time-resolved emission and absorption measurements on KI(Tl) and NaI(Tl) at various temperatures and compare these results with the model calculation. By absorption spectroscopy we recorded the growth and decay of the ${\mathrm{Tl}}^{++}$ absorption band following excitation by pulse of electrons. The characteristic diffusion time of the self-trapped hole was obtained from the growth curve, and recombination kinetics (due to electrons thermally excited from ${\mathrm{Tl}}^{0}$) were obtained from the decay curve. The luminescence intensity was also recorded as a function of time and this function was correlated with the diffusion and recombination processes. Experimental results are in accord with the principal conclusions of the diffusion calculation, and permit definitive statements regarding the mechanism of energy transport. In particular, it is concluded that nearly all of the energy transport in KI(Tl) occurs by electron-hole diffusion.

Accumulation and depuration of mercury in the American oyster Crassostrea virginica

Abstract: To study the kinetics of mercury uptake in oysters, adult Crassostrea virginica (Gmelin) were held in seawater containing 10 μg mercury/l (ppb) or 100 μg mercury/l (ppb), added in the form of mercuric acetate, for 60 days. Mercury concentration in tissues was determined by analysis of individually homogenized oyster meats, using wet digestion and flameless absorption spectrophotometry. After 45 days, average mercury tissue concentration was 140,000 μg mercury/kg tissue (ppb) and 28,000 μg mercury/kg tissue (ppb) in the 100 ppb and 10 ppb experimental groups, respectively. After this time, concentrations dropped sharply, probably due to spawning. Clearance of mercury from tissue was studied by exposing treated adults to estuarine water (with no additions) for 30 days (100 ppb group) and 160 days (10 ppb group). Tissue concentrations in the 100 ppb mercury environment group declined from 115,000 to 65,000 ppb, and those of the 10 ppb group declined from 18,000 to 15,000 ppb, in 18 days; there-after, no further decline occurred in either group. Oysters accumulated mercury 1,400 times and 2,800 times above the environmental concentrations of 100 and 10 ppb mercury, respectively. Total self-purification was not achieved over a 6 month cleansing period.

Solvents for and purification of chitin

Abstract: New solvents for chitin comprising dimethylacetamide, N-methylpyrrolidone or mixtures of these in combination with a minor proportion of lithium chloride, and their use in the purification of chitin for regeneration in the form of films and fibers are described.

Investigation of the effect of amylose/iodine complexation on the conformation of amylose in aqueous solution†

Abstract: Using a potato amylose fraction of 8 × 105, molecular-weight viscosity studies were carried out at 25°C on solutions containing 0.176–0.042% polymer, 8.67 mM KI, 1% ethanol, and different concentrations of iodine. By a novel extrapolation method, the intrinsic viscosities of the amylose/iodine complex were determined under various conditions of iodine binding (0–0.133 g I2/g amylose). Contrary to the view long held in this research area, it was found that the intrinsic viscosity of amylose solutions decreases significantly upon complex formation with iodine. Taking into account the results of our previous kinetic studies, the present findings are interpreted in terms of an amylose model characterized by loose, extended helical regions which are interrupted by short disordered regions. It is proposed that the intrinsic viscosity decrease observed is due to a shortening of the linear dimension of the polymer chain. This conformation change is apparently caused by the contraction of loose helical regions of the amylose macromolecule due to the entrapment of iodine (and perhaps other) atoms inside the helical cavities.

A model incorporating reversible immobilization for sorption and diffusion in glassy polymers

Abstract: A model incorporating reversible, bimolecular immobilization for diffusion and sorption in glassy polymers is developed. Sorption is considered to occur by two distinct mechanisms: ordinary diffusion-controlled sorption and sorption resulting from the immobilization of diffusing gas molecules by prexisting sites in the polymer. Expressions are obtained for equilibrium sorption, transient sorption, and time lag. The effects of kinetic parameters of the model are illustrated and discussed.

Distribution of the Fiddler Crabs,Uca pugnax andUca minax, in Relation to Salinity in Delaware Rivers

Abstract: The distribution and abundance of the fiddler crabs,Uca pugnax andU. minax were determined in relation to salinity in three tidal tributaries of Delaware Bay, U.S.A. OnlyUca pugnax was present in high salinity (21–29 o/oo) whileU. minax was present in lower salinities and even in fresh water. Their distributions overlapped along the salinity gradient and both species were equally abundant in salinities of 8–12 o/oo. There was a statistically significant positive association between abundance and salinity forUca pugnax and a negative association forU. minax.

Studies on the Oyster Community in Delaware: The Effects of the Estuarine Environment on the Associated Fauna

Abstract: The purpose of this study was to determine the composition of the associated fauna of Delaware's oyster beds. Moreover the relative position of Delaware's oyster producing tributaries lends itself to testing the classic hypothesis concerning the effect of salinity on faunal distribution. Interaction of substrate was also studied. The local oyster beds are termed the bay beds which include planted and natural populations, and the river beds. From 1967 to 1971 approximately 800 samples have been collected and the majority of these were from the bay beds. In 1968 and 1969, 132 samples were systematically collected from the river beds and 19 from the bay beds. These were returned to the laboratory for special care in identification. Samples from fouling panels and oyster rafts provided additional species. 152 species were identified but only 133 species were statistically analysed because they were from the systematic collections. Nonparametric statistics were used. In order to facilitate analysis the top 23 species were selected for special treatment. In order of decreasing frequency of occurrence the species were: Sabellaria vulgaris, Conopeum tenuissimum, Panopeus herbsti, Nereis succinea, Palaemonetes vulgaris, Crassostrea virginica, Nassarius obsoletus, Polydora websteri, Membranipora tenuis, Garveia fransiscana, Bulanus improvisus, Diadumene leucolena, Aiptasiomorpha luciae, Melita nitida, Obelia longicyatha, Alcyonidium polyoum, Sertularia argentea, Crangon septemspinosa, Hydroides dianthus, Eurypanopeus depressus, Modiolus demissus, Parapleustes sp., and Hartlaubella gelatinosa. The diversity of species decreases up the estuary with decreasing salinity. Substrate can alter this pattern in particular cases. Within a given salinity range the presence of any firm substrate or mud influenced the nature of the community from epifaunal to infaunal. Four faunal units were recognized: the planted and natural beds, the four southern rivers, the Leipsic River, the Woodland Beach area. The Leipsic River area marks a critical transition zone with a rapid reduction in species. North of Woodland Beach brackish water conditions begin to prevail. The fauna was more diverse in late spring than in the fall but seasonality was not as marked as expected. The faunal composition of Delaware's oyster beds agrees with the cosmopolitan view of estuaries. The stability — time hypothesis proposed by SANDERS provides a theoretical basis to explain faunal distributions in Delaware's oyster community. The hardy nature and geologic history of this oyster community makes it a likely candidate as a sensitive indicator of environmental degradation in the estuary.

Language, Communication and Culture.

Abstract: details was not to tell you how pre-reading should be taught, but to suggest that prereading studies be expanded to welcome the imaginative contribution of students as they begin to say something in a foreign language I want to free us from feeling that we are "taking time" from the book when we give students time and freedom to tell their own ideas in their new loose-fitting language At the same time vocabulary aimed at a specific reading or listening assignment gives the teacher a handle by which he can guide and control the conversation toward disciplined language development The time spent reacting to the word list with students is the central activity and emphasizes studying to express their reactions to words and pictures in a second language Anyone talks willingly about himself; he may talk fluently if his expression is valued as an end in itself When students contribute to the development of the central theme of class discussion and are kept aware of the significance of their contributions, they will surely progress more rapidly to mature use of the language and will maintain interest in learning the language instead of taking a

Nitrate and nitrite in the surface waters of two delaware salt marshes

Abstract: The distribution of nitrate and nitrite in two Delaware salt marshes was studied from July 1966 through December 1967. Canary Creek Marsh, located near the mouth of Delaware Bay, was characterized by high salinity, low nitrate water. The Murderkill Marsh, in central Delaware, was characterized by low salinity, high nitrate water. Man-made control structures in the Murderkill Marsh inhibited free tidal exchange and modified the distribution of nitrate and nitrite. Maximum nitrate concentrations occurred in the winter, while minimum concentrations were observed during the summer. Summer nitrate concentrations in the Canary Creek Marsh ranged from undetectable (<2 μg-at/1) to 8 μg-at/1. Winter values were generally between 10 and 25 μg-at/1. At the Murderkill Marsh winter nitrate concentrations ranged from 40 to 100 μg-at/1, and the summer concentrations were generally in the range of 5 to 20 μg-at/1. Nitrite concentrations in both areas rarely exceeded 1.5 μg-at/1, and exhibited no discernable seasonable pattern.

Kinetics of structural changes in thixotropic fluids

Abstract: Thixotropic behavior is analyzed on the basis of the kinetics of breakdown and recovery of the structural elements of a “multicomponent mixture.” The analysis is based on the assumption that the components consist of elements containing different numbers of the same structural unit. The rate of breakdown is calculated by assuming equal rupture probability for each bond between the structural units. The growth process takes into account the possible recovery of bonds due to the collision between the elements of the various components. The rate of recovery is calculated as in coagulation theory. The rate constants are expressed as functions of the shear stress and the rate of shear. The equilibrium and transient viscosity functions are derived by means of the kinetic equations and from a rule expressing the viscosity of a mixture as a function of the viscosities of the components. Illustrative calculations show the general shape of the resulting curves. Ways are indicated to determine the model parameters and to check the validity of the assumptions.

Energetics of phase transformations in polyethylene

Abstract: The molecular mechanisms involved in the orthorhombic-to-monoclinic phase transformation in polyethylene were investigated by the computer simulation of a structure–energy map based on empirically justified intermolecular potential functions. Stable packing structures for the orthorhombic and monoclinic form were isolated as relative minima, cohesive energies were determined from the energy minima, specific chain motions involved in the transformation were identified by the minimum energy path connecting the packing minima, and the activation energy for the transformation was determined from the energy barrier along the minimum energy transformation path. The packing structure parameters predicted from the energy map were in excellent agreement with unit cell dimensions observed near 0°K. The activation energy predicted for the transformation is relatively low (∼0.5 kcal/mole of ethylene at 0°K and 0.25 kcal/mole of ethylene near the melting point, 411°K). Monoclinic packing was predicted to be slightly more stable than orthorhombic. Since this result is inconsistent with a large body of observations, we propose that the intramolecular energy of chain folds plays a dominant role in establishing chain-packing geometry. The inclusion of fold-transition energetics could give rise to transformation mechanisms which differ in details from those proposed in this work.

Extensional flow induced crystallization from solution

Abstract: An experimental apparatus and technique were developed for studying the crystallization of polyethylene from solutions undergoing an oscillatory, constant stretch rate, extensional flow. Investigation of the resulting fiber morphology, obtained at various temperatures and stretch rates, shows that the fibers exhibit a bead and stringlike appearance. Study of the melting, acid etching, and selective dissolution behavior of the fibers leads to the conclusion that fiber growth occurs in a fashion which directly results in the bead and string morphology and that the morphology is not a result of secondary, epitaxial crystal growth as previously believed. A model for the growth process, as suggested by the data, is presented. Evidence is also presented to suggest that at certain temperatures and stretch rates, a triclinic phase transformation occurs during the flow process. The effect is to produce two separate melting entities which appear to be stretch rate sensitive, in line with previously published studies on the effects of stretching on the behavior of bulk polymer.