Continuum modeling of localized deformation in irradiated bcc materials

A continuum constitutive crystal plasticity framework is implemented to model the post-irradiation tensile behavior of bcc structural materials, accounting for localized deformation due to the formation of dislocation channels. Both the mechanical response and deformed microstructure of the material are modeled for quasi-static tensile loading. The latter is studied to identify the stages of dislocation channel formation during localization, specifically with respect to the evolution of dislocations and irradiation-induced defects. Parametric studies of the cross-slip and flow softening (due to annihilation of irradiation-induced defects) models are performed to study their effects on the localization behavior. Results are compared to available experimental data.     

Exercise improves executive function and achievement and alters brain activation in overweight children: A randomized, controlled trial.

Objective: This experiment tested the hypothesis that exercise would improve executive function. Design: Sedentary, overweight 7- to 11-year-old children (N = 171, 56% girls, 61% Black, M ± SD age = 9.3 ± 1.0 years, body mass index [BMI] = 26 ± 4.6 kg/m2, BMI z-score = 2.1 ± 0.4) were randomized to 13 ± 1.6 weeks of an exercise program (20 or 40 min/day), or a control condition. Main Outcome Measures: Blinded, standardized psychological evaluations (Cognitive Assessment System and Woodcock-Johnson Tests of Achievement III) assessed cognition and academic achievement. Functional MRI measured brain activity during executive function tasks. Results: Intent to treat analysis revealed dose-response benefits of exercise on executive function and mathematics achievement. Preliminary evidence of increased bilateral prefrontal cortex activity and reduced bilateral posterior parietal cortex activity attributable to exercise was also observed. Conclusion: Consistent with results obtained in older adults, a specific improvement on executive function and brain activation changes attributable to exercise were observed. The cognitive and achievement results add evidence of dose-response and extend experimental evidence into childhood. This study provides information on an educational outcome. Besides its importance for maintaining weight and reducing health risks during a childhood obesity epidemic, physical activity may prove to be a simple, important method of enhancing aspects of children's mental functioning that are central to cognitive development. This information may persuade educators to implement vigorous physical activity. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Evaluating copper lysine and copper sulfate sources for heifers

The effects of feeding different sources and quantities of Cu to heifers were evaluated in a 211-d experiment. Forty crossbred predominantly Brahman x Hereford heifers averaging 13.5 mo of age and 301 kg were initially depleted of Cu. The depletion diet was fed for 70 d and consisted of low Cu and high antagonist minerals, Fe, S, and Mo at 1000 mg/kg, 0.5%, and 5 mg/kg (dry basis), respectively. On d 71, heifers continued to receive the antagonistic minerals and were allotted equally to five Cu treatments: 1) control, no additional Cu source; 2) 8 mg of Cu/kg from CuSO4; 3) 16 mg of Cu/kg from CuSO4; 4) 8 mg of Cu/kg from Cu lysine; and 5) 16 mg of Cu/kg from Cu lysine. When no notable change in concentration of Cu in the liver was observed, d 169, a second diet was formulated. The heifers were fed the same Cu treatments, but S and Mo were removed and Fe was lowered to 50 mg/kg. This diet was then fed for the final 42 d of the experiment. In addition to performance, concentrations of Cu, Fe, and Zn in the plasma and liver, plasma ceruloplasmin, hemoglobin, superoxide dismutase (SOD) activity of neutrophils and lymphocytes, and a cell mediated immune response (phytohemagglutinin-P, PHA) were measured. Heifers in this study had increased growth over time, but there were no treatment differences for growth and average daily gain. Liver and plasma Cu concentrations were not greatly influenced by different supplemental Cu sources. However, compared with other treatments, Cu lysine (16 mg/kg) increased liver Cu in cattle that were deficient and tended to increase plasma Cu in animals that were marginally deficient in Cu. Iron concentrations decreased over time in liver and plasma, but there was no difference in Fe and Zn concentrations in liver and plasma among treatments. Differences in ceruloplasmin and hemoglobin concentrations were significant over time but not among treatments. The SOD activity in neutrophils did not change over time, but SOD activity of lymphocytes increased over time. For the PHA immune response test, there was no effect of time or a time by treatment interaction. These data suggest that all Cu sources were available, but Cu at 16 mg/kg from Cu lysine was more beneficial than were other sources and particularly for heifers with low Cu status.     

Prevalence and numbers of Escherichia coli O157 on bovine hides at a beef slaughter plant

In this study, we investigated the prevalence and numbers of Escherichia coli O157 on bovine hides. Samples (n = 1,500) were collected over a 17-month period (30 samples per week) by sponge swabbing approximately 122-cm2 areas of the bovine rump of slaughtered cattle at an early stage of carcass processing (first legging). Sponge samples (n = 1,500) were stomached in buffered peptone water supplemented with novobiocin, directly plated on sorbitol MacConkey with Cefixime tellurite (SMAC-CT), enriched for 24 h, extracted by immunomagnetic separation, and plated onto SMAC-CT agar. Presumptive E. coli O157 colonies from SMAC-CT plates were confirmed by PCR for the presence of eaeA, hlyA, fliCh7, vt1, vt2, and portions of the rfb (O-antigen encoding) region of E. coli O157. Overall, E. coli O157 was recovered from 109 samples (7.3%) at concentrations ranging from less than 0.13 to 4.24 log CFU/100 cm2. PCR analysis revealed a wide diversity of genetic profiles among recovered isolates of verocytotoxigenic E. coli. Of the isolates recovered, 99 of 109 contained the attaching and effacing gene (eaeA) and the hemolysin gene (hlyA), and 78 of 109 had the flagellar H7 antigen-encoding gene (fliCh7). Only 6 of 109 isolates contained both verotoxin-producing genes (vt1 and vt2); 91 of 109 contained the vt2 gene only, whereas 1 of 109 contained the vt1 gene only. The remaining 11 of 109 contained neither vt1 nor vt2.     

Comparison of a real-time PCR and an IMS/culture method to detect Escherichia coli O26 and O111 in minced beef in the Republic of Ireland

This study compared an immuno-magnetic separation (IMS)/culture method and a real-time PCR method to detect Verocytotoxigenic Escherichia coli (VTEC) serovar O26 and/or O111 in minced beef. A total of 65 samples were examined, 40 of which were frozen beef samples previously established as containing E. coli O157, and 25 were samples of fresh minced beef, purchased from butcher shops in the Dublin area. After selective enrichment, all samples were (a) subjected to IMS, plated on differential media and identified as E. coli O26 or O111 using biochemical and immuno-logical methods; and (b) subjected to DNA extraction and real-time PCR analysis using primers and probes against E. coli O111 and O26 serovar specific genes, and verotoxin genes. Overall, from the 65 minced beef samples collected, three were positive for E. coli O26 by real-time PCR, with only one of these samples positive for E. coli O26 by the culture method. One sample was positive for E. coli O111 by both real-time PCR and the culture method. The two samples found positive for E. coli O26 by real-time PCR method but not by culture method belonged to the group of frozen beef samples, indicating that the previously developed culture method for the detection of E. coli O26 may not be suitable for the detection of freeze injured cells. In conclusion, this study highlights the role of beef meat in the transmission of non-O157 VTEC. The results of the study emphasize that the analyses for emergent pathogens should be included in food safety surveillance systems and that the development of standard methods for the detection of E. coli O26 and O111 in routine food testing is needed in order to reduce the consumer exposure to contaminated food.     

Thermal inactivation of Yersinia enterocolitica in pork slaughter plant scald tank water

The objective of this study was to establish the time–temperature combinations required to ensure the thermal inactivation of Yersinia enterocolitica during scalding of pork carcasses. A 2 strain cocktail of Y. enterocolitica (bioserotypes 2/O:5,27 and 1A/O:6,30) was heat treated at 50, 55 and 60 °C in samples of scald tank water obtained from a commercial pork slaughter plant. Samples were removed at regular intervals and surviving cells enumerated using (i) Cefsulodin–Irgasan–Novobiocin Agar (CIN) supplemented with ampicillin and arabinose and (ii) Tryptone Soya Agar (TSA), overlaid with CIN agar with ampicillin and arabinose. The data generated was used to estimate D- and z-values and the formula D_x = log^− 1(log D₆₀ − ((t₂ − t₁)/z)) was applied to calculate thermal death time–temperature combinations from 55 to 65 °C. D₅₀, D₅₅ and D₆₀-values of 45.9, 10.6 and 2.7 min were calculated from the cell counts obtained on CIN agar, respectively. The corresponding D-values calculated from the TSA/CIN counts were 45.1, 11 and 2.5 min, respectively. The z-value was 7.8. It was concluded that a time–temperature combination of 2.7 min at 60 °C is required to achieve a 1 log reduction in Y. enterocolitica in pork scald tank water. The predicted equivalent at 65 °C was 0.6 min. This study provides data and a model to enable pork processors to identify and apply parameters to limit the risk of carcass cross-contamination with Y. enterocolitica in pork carcass scald tanks.     

Microstructure-sensitive notch root analysis for dwell fatigue in Ni-base superalloys

Macroscopic viscoplastic constitutive models for γ–γ′ Ni-base superalloys typically do not contain an explicit dependence on the underlying microstructure. Microstructure-sensitive models are of interest in many applications since microstructure can vary in components, whether intentional or not. In such cases, the use of experiments from one microstructure condition to fit macroscopic models may be too limiting. The principal microstructure attributes that can significantly affect the cyclic stress–strain response of γ–γ′ Ni-base superalloys are the grain size and γ′ precipitate volume fraction and size distributions. An artificial neural network (ANN) is used to correlate the material parameters of a macroscale internal state variable cyclic viscoplasticity model with these microstructure attributes using a combination of limited experiments augmented by polycrystal plasticity calculations performed on other (virtual) microstructures within the range characterized experimentally. The trained model is applied to an example of a component fatigue notch root analysis with dwell periods at peak load to demonstrate the methodology and explore the potential impact of microstructure-sensitive constitutive models on life prediction for notched structures subjected to realistic load histories.     

3D modeling of subsurface fatigue crack nucleation potency of primary inclusions in heat treated and shot peened martensitic gear steels

A computational strategy is developed to characterize the driving force for fatigue crack nucleation at subsurface primary inclusions in carburized and shot peened C61^® martensitic gear steels. Experimental investigation revealed minimum fatigue strength to be controlled by subsurface fatigue crack nucleation at inclusion clusters under cyclic bending. An algorithm is presented to simulate residual stress distribution induced through the shot peening process following carburization and tempering. A methodology is developed to analyze potency of fatigue crack nucleation at subsurface inclusions. Rate-independent 3D finite element analyses are performed to evaluate plastic deformation during processing and service. The specimen is subjected to reversed bending stress cycles with R = 0.05, representative of loading on a gear tooth. The matrix is modeled as an elastic–plastic material with pure nonlinear kinematic hardening. The inclusions are modeled as isotropic, linear elastic. Idealized inclusion geometries (ellipsoidal) are considered to study the fatigue crack nucleation potency at various subsurface depths. Three distinct types of second-phase particles (perfectly bonded, partially debonded, and cracked) are analyzed. Parametric studies quantify the effects of inclusion size, orientation and clustering on subsurface crack nucleation in the high cycle fatigue (HCF) or very high cycle fatigue (VHCF) regimes. The nonlocal average values of maximum plastic shear strain amplitude and Fatemi–Socie (FS) parameter calculated in the proximity of the inclusions are considered as the primary driving force parameters for fatigue crack nucleation and microstructurally small crack growth. The simulations indicate a strong propensity for crack nucleation at subsurface depths in agreement with experiments in which fatigue cracks nucleated at inclusion clusters, still in the compressive residual stress field. It is observed that the gradient from the surface of residual stress distribution, bending stress, and carburized material properties play a pivotal role in fatigue crack nucleation and small crack growth at subsurface primary inclusions. The fatigue potency of inclusion clusters is greatly increased by prior interfacial damage during processing.     

Fatigue behaviour of porous polysulphone surface coatings for orthopaedic applications

Porous polysulphone (PPSF) has recently been selected as a candidate material for use as a prosthetic surface coating in orthopaedic applications to acommodate ‘bone ingrowth’ for fixation to the skeletal system. The tension-loaded fatigue behaviour of PPSF was characterized based on the interpretation of stress/life (S/N) data. Results of this investigation indicate that the fatigue life of PPSF is governed by crack propagation across the sintered necks of the porous structure. In addition, experimental data revealed that the fatigue strength-reduction factor, K_f, remains equivalent to the tensile notch strength-reduction factor for a wide range of fatigue lives. However, analytical results indicate that the material has a low notch sensitivity and that a single application of a theoretical elastic stress-concentration factor in a fatigue analysis would be inappropriate.     

Computerized container-ship load planning: A methodology and evaluation

A heuristic is developed to plan loads for containerized cargo ships. It is designed to serve a port which uses gantry cranes (transtainers) and trucks to handle containers. The model recognizes constraints on ship stability, placing containers in a bay with the proper length, limits on stack height in under-deck bays, limits on stack weight in on-deck bays, refrigerated containers, and the need for support under a container. Provisions are made for the operator to handle overstowage of cargo for different ports and placement of oversize cargo. The model uses minimization of transtainer movement time and minimization of rehandles in the yard as an objective. The heuristic uses strategies for container placement similar to those used in manual load planning. A test of two ships and four voyages at the Port of Portland produced feasible load plans for each voyage. Transtainer movement and rehandling time varied for the four voyages; but on the average, the heuristic reduced a composite material handling measure by 4.8%.