Characterization of Culturable PAH and BTEX Degrading Bacteria from Heavy Oil of the Rancho La Brea Tarpits

Novel petroleum degrading bacteria have been identified in heavy oil from natural asphalt seeps using DNA-based methods, but there is little knowledge of the extent to which these bacteria can be cultured by selective enrichments on different aromatic hydrocarbons. Here we report the species composition of bacterial communities from a 40,000 yr-old asphalt deposit that could be grown on selected petroleum compounds. Species compositions of the degrader communities determined by PCR-DGGE and 16S rDNA sequencing showed that selective enrichment using (PAHs) and BTEX (benzene, toluene, ethyl benzene, and xylene) as growth substrates produced relatively simple degrader communities, and included a predominant species, Pseudomonas stutzeri, which grew on multiple compounds. PCR-based techniques further identified genes encoding naphthalene dioxygenase and catechol 2,3-dioxygenase from P. stutzeri in the enrichment cultures. The results suggest that only a small portion of the asphalt-inhabiting community can be cultured under aerobic conditions on individual substrates. Within these communities were several new species that merit further characterization as consortia, as well as new isolates of the cosmopolitan degrader, P. stutzeri.     

The relationship between social distance and treatment attrition for juvenile offenders

Although recent work has begun to identify factors associated with risk of treatment attrition for juvenile offenders, few of these studies have considered how community context is related to the completion of juvenile offender treatment. The current work examines the relationship between social distance and treatment attrition for juvenile offenders. Analyzing a data set of 5,517 juvenile offenders adjudicated in Philadelphia, the results of cross‐classified hierarchical models indicate that social distance, operationalized in two ways that consider perceptions of both the ethnic composition and level of disadvantage within neighborhoods, does not directly predict the likelihood of treatment attrition. However, when considered with the ethnicity of the juvenile offenders in the form of an interaction effect, social distance based on perceptions of ethnicity within neighborhoods is shown to predict the likelihood of treatment attrition, and to be more acute for young non‐White offenders. The implications of these findings are discussed.     

High-Temperature Stress Corrosion Cracking in Ceramics

Single-phase ceramics are shown to be susceptible to stress corrosion cracking at elevated temperatures in the presence of a wetting amorphous deposit. Crack arrest occurs when the crack is depleted of amorphous material, provided that the stress intensity is below a "blunting" threshold. A preliminary model of such cracking has been developed. The model considers stress corrosion as a process wherein the corrosive medium, by virtue of its wetting characteristics, allows the crack to propagate along grain boundaries. A crack velocity that depends sensitively on the dihedral angle is predicted. Furthermore, since the corrosive medium acts as a conduit for rapid atom transport to the crack tip, the crack velocity also exhibits a strong dependence on the viscosity of the fluid medium. Implications for such stress corrosion processes on premature failure are discussed.     

Cryptotype,Overgeneralization and Competition: A Connectionist Model of the Learning of English Reversive Prefixes

This study examined the role of covert semantic classes or 'cryptotypes' in determining children's overgeneralizations of reversive prefixes such as un - in *unsqueeze or *unpress . A training corpus of 160 English verbs was presented incrementally to a backpropagation network. In three simulations, we showed that the network developed structured representations for the semantic cryptotype associated with the use of the reversive prefix un- . Overgeneralizations produced by the network, such as *unbury or *unpress , match up well with actual overgeneralizations observed in human children, showing that structured cryptotypic semantic representations underlie this overgeneralization behaviour. Simulation 2 points towards a role of lexical competition in morphological acquisition and overgeneralizations. Simulation 3 provides insight into the relationship between plasticity in network learning and the ability to recover from overgeneralizations. Together, these analyses paint a dynamic picture in which competing morphological devices work together to provide the best possible match to underlying covert semantic structures.     

THERE AND THERE - A COLUMN

Abstract

Henry L. Stimson is best known to readers of this journal for his quote, “Gentlemen do not read each other's mail,” and his shutting down of Herbert O. Yardley's black chamber. The present piece reveals a second cryptologic episode from his life. During WWII, Stimson made a request of hundreds of libraries that they withdraw all material on explosives, secret inks, and ciphers from circulation and report the names of anyone requesting these materials to the local office of the Federal Bureau of Investigation (FBI). A pair of original documents is reproduced for the first time along with some references. A list of libraries contacted is also provided.     

Stress and Fracture Behavior of Monolithic Fuel Cell Tapes

This paper summarizes the stress and fracture analyses of a three-layer ceramic composite which is a fundamental building block for the monolithic solid oxide fuel tell currently being developed at Argonne National Laboratory. A small difference in the coefficients of thermal expansion of different layers can result in large stresses and cause cracking parallel to the plane of the layers. A simple fracture model for a three-layer composite has been developed. The cracking behavior predicted by the model is in reasonably good agreement with the fabrication experience to date.     

Theory of Fatigue for Brittle Flaws Originating from Residual Stress Concentrations

A theory is formulated for the general fatigue response of brittle flaws which experience residual stress concentrations. The indentation crack is taken as a model flaw system for the purpose of setting up the basic fracture mechanics equations, but the essential results are expected to have a wider range of applicability in the strength characterization of ceramics. A starting fatigue differential equation is first set up by combining an appropriate stress intensity factor for point- or line-contact flaws with a power-law crack velocity function. Analytical solutions are then obtained for the case of static fatigue. The resulting relation between lifetime and failure stress is shown to have exactly the same power-law form as the conventional solution for Griffith (residual-stress-free) flaws. This "equivalence" is used as a basis for extending the results to dynamic fatigue. A comparison of these analytical solutions with numerical counterparts defines the limits of accuracy of the theoretical procedure. However, while the form of the lifetime relation remains invariant, the values of the exponent and coefficient differ significantly for flaws with and without residual stress. Accordingly, the application of conventional fatigue theory to evaluate crack velocity parameters, without due regard for the nature of the critical flaw, can lead to serious errors. Explicit conversion formulas are given for transforming "apparent" velocity parameters for indentation flaws directly into "true" parameters. The implications of these results concerning the use of the indentation method for materials evaluation are discussed.     

EFFECTS OF LIQUID VISCOSITY ON RHEOLOGY OF CONCENTRATED SUSPENSIONS

ABSTRACT

This paper presents the experimental results on the effects of liquid viscosity on the rheology of concentrated suspensions of solid particles in Newtonian liquids. Specifically, the relative viscosity of a pseudoplastic suspension decreases as the viscosity of the suspending liquid increases, indicating excess energy dissipation in a less viscous liquid. In contrast, the relative viscosity of a Newtonian suspension is only slightly affected by the liquid viscosity. It is in excellent agreement with the value predicted from the rigid sphere model which neglects nonhydrodynamic interactions, and assumes zero particle-to-liquid relative velocity. The flow behavior indices of both concentrated suspensions are independent of the liquid viscosity.