Stress-strain response of a cast 319-T6 aluminum under thermomechanical loading

The stress-strain behavior of cast 319-T6 aluminum-copper alloys with three different secondary dendrite arm spacings (SDASs) was studied at high temperatures and under thermomechanical deformation, exposing marked cyclic softening. A two state-variable unified inelastic constitutive model proposed earlier was modified to describe the stress-strain responses of these alloys by considering the variation of hardening and recovery functions of back-stress and drag stress. The SDAS was incorporated in the model as a length-scale parameter, and the material constants were determined systematically from experiments on a cast 319-T6 aluminum with small and large SDASs. The capabilities of the constitutive model were checked by the comparisons of simulations to experiments in the small-strain regime (<0.005). The results show that the model provides successful simulations for material response after thermal exposure at high temperature and cyclic transient stress-strain behavior. The causes of mechanical behaviors at the macro scale are discussed based on microstructural changes during thermal exposure.     

Exploring the construct validity of the eating disorder continuum.

Although many counseling psychologists conceptualize eating disturbances along a continuum of degree, there appears to be a dearth of research exploring the construct validity of this eating disorder continuum hypothesis (L. B. Mintz et al., 1997). Specific psychological, behavioral, and cognitive characteristics known to be related to clinical eating disorders (C. Fairburn, 1995; D. M. Garner, 1991) were examined in 2 studies undertaken to explore whether these characteristics vary by eating disorder continuum placement. In Study 1, Neuroticism, as measured by the NEO–Five Factor Inventory (FFI), was found to vary by continuum placement in a sample of 169 women. In Study 2, 8 out of 9 Eating Disorder Inventory–2 (EDI–2) subscales and dieting locus of control varied significantly by continuum placement for a sample of 135 women. Scores on Neuroticism and many EDI–2 subscales (i.e., on which higher scores are more indicative of disordered eating) increased in a linear fashion, and women adopted a more internal dieting locus of control as the severity of disturbed eating increased, supporting the construct validity of the eating disorder continuum. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Autobiographical remembering and hypermnesia: A comparison of older and younger adults.

This study examined age differences in autobiographical memory and extended findings concerning hypermnesia in laboratory tasks to a real world event, the announcement of the verdict in the O. J. Simpson murder trial. Older and younger adults repeatedly recalled the event in a single session. Interviews were coded for amount and type of accurate information and for errors. The age groups did not differ in ability to recall the gist of the event or in the number of errors made. Younger adults were better at remembering when the event had occurred. Both age groups showed hypermnesia. The results are discussed in terms of the importance of autobiographical memory across the life span and the phenomenon of hypermnesia in everyday memory. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Trust-Assisted Handover Approach in Hybrid Wireless Networks

In Next-Generation (NG) hybrid wireless networks, Mobile-Controlled Handover (MCHO) is expected to be employed as the handover control mechanism, in contrast to Network-Controlled Handover (NCHO) used in homogeneous wireless networks. As more independent network operators get involved in providing Internet access, roaming mobile users would have to deal with complex trust relationships between heterogeneous network domains. The state-of-the-art handover approaches just take into account Quality of Service (QoS), but ignore the complexities arising from the coexistence of multiple network operators in the NG networks. The existence of a complex trust relationship between networks may lead to unnecessary handover attempts in service roaming. In this regard, this paper introduces a novel approach of dynamically retrieving network trust information, and using it in MCHO. We show how network trust information can be utilised to obtain a 35% reduction in handover delay, meanwhile retain QoS in a handover. The proposed scheme does not need bulk storage in mobile handsets, and can react to changes to network topology and trust relationships dynamically. Analytical results are provided to demonstrate how roaming mobile users make more intelligent and reliable handover if implementing the proposed handover approach in a multi-operator and multi-technology environment.     

The metabolism and analysis of isoflavones and other dietary polyphenols in foods and biological systems

Polyphenols in dietary and botanical matrices are usually present as simple and complex O-glycosides. In fermented dietary materials, the glycosidic moiety is removed and accompanied in some cases by more complex changes to the polyphenol. As for most xenobiotics, polyphenols undergo phase II conjugation in the intestinal wall during their absorption from the gut. In contrast, a few polyphenols, such as puerarin in the kudzu vine, are C-glycosides and are stable in the gut and during absorption, distribution and excretion. Large bowel bacteria reduce polyphenol aglycones, causing opening of the heterocyclic B-ring and ring cleavage. The products are mostly absorbed and enter the bloodstream. Phase I and II metabolism events occur in the intestine and the liver - most polyphenols predominantly circulate as β-glucuronides and sulfate esters with very little as the aglycones, the presumed active forms. In addition, metabolism can occur in non-hepatic tissues and cells including breast tumor cells that have variable amounts of cytochrome P450s, sulfatase and sulfotransferase activities. Inflammatory cells produce chemical oxidants (HOCl, HOBr, ONO(2)(-)) that will react with polyphenols. The isoflavones daidzein and genistein and the flavonol quercetin form mono- and dichlorinated products in reaction with HOCl. Genistein is converted to 3'-nitrogenistein in the lung tissue of lipopolysaccharide-treated rats. Whereas polyphenols that can be converted to quinones or epoxides react with glutathione (GSH) to form adducts, chlorinated isoflavones do not react with GSH; instead, they are converted to β-glucuronides and are excreted in bile. Analysis of polyphenols and their metabolites is routinely carried out with great sensitivity, specificity and quantification by LC-tandem mass spectrometry. Critical questions about the absorption and tissue uptake of complex polyphenols such as the proanthocyanins can be answered by labeling these polyphenols with (14)C-sucrose in plant cell culture and then purifying them for use in animal experiments. The (14)C signature is quantified using accelerator mass spectrometry, a technique capable of detecting one (14)C atom in 10(15) carbon atoms. This permits the study of the penetration of the polyphenols into the interstitial fluid, the fluid that is actually in contact with non-vascular cells.     

Electrophysiological and ultrasonic correlates of reproductive behavior in the male rat.

Monitored the ultrasonic vocalizations of 13 male Long-Evans rats and determined the correlation of these vocalizations with electrophysiological activity measured by chronically implanted hippocampal and cortical electrodes during mating with a female rat. Hippocampal theta rhythms were significantly correlated with high activity, mounting, intromissions, and preejaculatory excitatory behavior and were also significantly associated with 50-kHz short ultrasonic vocalizations. Postmount or postintromission behaviors (grooming, exploration) were closely correlated with an absence of ultrasonic vocalizations and the onset of irregular low-amplitude hippocampal EEG recordings. Long 22-kHz vocalizations occurred during the postejaculatory refractory period. Shorter 22-kHz vocalizations occurred during mating and were associated with unsuccessful intromissions or mounting attempts. Postejaculatory long 22-kHz vocalizations were significantly associated with irregular high-amplitude hippocampal EEG tracings, while preejaculatory short 22-kHz vocalizations were also accompanied by sleeplike irregular high-amplitude hippocampal EEG tracings with cortical spindling. Findings suggest that ultrasonic vocalizations are indicators of the sexual arousal of mating rats. (14 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

EFFECTS OF FLOW DYNAMICS ON THE AQUATIC‐TERRESTRIAL TRANSITION ZONE (ATTZ) OF LOWER MISSOURI RIVER SANDBARS WITH IMPLICATIONS FOR SELECTED BIOTA

Sandbars are an important aquatic terrestrial transition zone (ATTZ) in the active channel of rivers that provide a variety of habitat conditions for riverine biota. Channelization and flow regulation in many large rivers have diminished sandbar habitats and their rehabilitation is a priority. We developed sandbar‐specific models of discharge‐area relationships to determine how changes in flow regime affect the area of different habitat types within the submerged sandbar ATTZ (depth) and exposed sandbar ATTZ (elevation) for a representative sample of Lower Missouri River sandbars. We defined six different structural habitat types within the sandbar ATTZ based on depth or exposed elevation ranges that are important to different biota during at least part of their annual cycle for either survival or reproduction. Scenarios included the modelled natural flow regime, current managed flow regime and two environmental flow options, all modelled within the contemporary river active channel. Thirteen point and wing‐dike sandbars were evaluated under four different flow scenarios to explore the effects of flow regime on seasonal habitat availability for foraging of migratory shorebirds and wading birds, nesting of softshell turtles and nursery of riverine fishes. Managed flows provided more foraging habitat for shorebirds and wading birds and more nursery habitat for riverine fishes within the channelized reach sandbar ATTZ than the natural flow regime or modelled environmental flows. Reduced summer flows occurring under natural and environmental flow alternatives increased exposed sandbar nesting habitat for softshell turtle hatchling emergence. Results reveal how management of channelized and flow regulated large rivers could benefit from a modelling framework that couples hydrologic and geomorphic characteristics to predict habitat conditions for a variety of biota. Published in 2011 by John Wiley & Sons, Ltd.     

Analysis of a radial crack in a circular ring segment

The problem considered is a segment of a circular ring with a radial crack emanating frorn the surface with the smaller radius. Pure bending and three-point loading are chosen for solution. The problem is solved usiag the ‘modified mapping-collocation’ technique and partitioning. Numerical data is presented for varying crack lengths and thicknesses.     

A grain-scale study of spall in brittle materials

The evolution of spall for a brittle material is investigated under variance of anisotropy, grain boundary fracture energy, and loading. Because spall occurs in the interior of the specimen, fundamental studies of crack nucleation and growth are needed to better understand surface velocity measurements. Within a cohesive approach to fracture, we illustrate that for anisotropic materials, increases in the fracture energy cause a transition in crack nucleation from triple-points to entire grain boundary facets. Analysis of idealized flaws reveals that while crack initiation and acceleration are strong functions of the fracture energy, flaws soon reach speeds on the order of the Rayleigh wave speed. Finally, simulated surface velocities of spalled configurations are correlated with microstructural evolution. These fundamental studies of nucleation, growth, and spall attempt to link atomic separation to the macroscopic spall strength and provide a computational framework to examine the evolution of spall and the impact on the simulated surface velocity field.