A finite element study of microstructure-sensitive plasticity and crack nucleation in fretting

This paper is concerned with finite element modelling of microstructure-sensitive plasticity and crack initiation in fretting. The approach adopted is based on an existing method for microstructure-sensitive (uniaxial) fatigue life prediction, which proposes the use of a unit cell crystal plasticity model to identify the critical value of accumulated plastic slip associated with crack initiation. This approach is successfully implemented here, using a FCC unit cell crystal plasticity model, to predict the plain low-cycle fatigue behaviour of a stainless steel. A crystal plasticity frictional contact model for stainless steel is developed for microstructure-sensitive fretting analyses. A methodology for microstructure-sensitive fretting crack initiation is presented, based on identification of the number of cycles in the fretting contact at which the identified critical value of accumulated plastic slip is achieved. Significant polycrystal plasticity effects in fretting are predicted, leading to significant effects on contact pressure, fatigue indicator parameters and microstructural accumulated slip. The crystal plasticity fretting predictions are compared with J₂ continuum plasticity predictions. It is argued that the microstructural accumulated plastic slip parameter has the potential to unify the prediction of wear and fatigue crack initiation, leading in some cases, e.g. gross slip, to wear, via a non-localised distribution of critical crystallographic slip, and in other cases, e.g. partial slip, to fatigue crack initiation, via a highly-localised distribution of critical crystallographic slip with preferred orientation (cracking locations and directions).     

Filtration effectiveness of HVAC systems at near‐roadway schools

Concern for the exposure of children attending schools located near busy roadways to toxic, traffic‐related air pollutants has raised questions regarding the environmental benefits of advanced heating, ventilation, and air‐conditioning (HVAC) filtration systems for near‐road pollution. Levels of black carbon and gaseous pollutants were measured at three indoor classroom sites and at seven outdoor monitoring sites at Las Vegas schools. Initial HVAC filtration systems effected a 31–66% reduction in black carbon particle concentrations inside three schools compared with ambient air concentrations. After improved filtration systems were installed, black carbon particle concentrations were reduced by 74–97% inside three classrooms relative to ambient air concentrations. Average black carbon particle concentrations inside the schools with improved filtration systems were lower than typical ambient Las Vegas concentrations by 49–96%. Gaseous pollutants were higher indoors than outdoors. The higher indoor concentrations most likely originated at least partially from indoor sources, which were not targeted as part of this intervention.     

Supercritical CO<Subscript>2</Subscript>-assisted,silicone-modified wood for enhanced fire resistance

A composite fabrication method is reported that incorporates silicones into bulk aspen substrates and subsequently crosslinks the additives in situ. This process utilizes supercritical CO₂, a non-toxic and easily recoverable solvent, as a transport and reaction medium resulting in aspen composites that have been uniformly infused with silicone. Flexure properties of aspen–silicone composites were determined to be indistinguishable from those of aspen. However, after thermal degradation, the residual flexure properties of the composite char were significantly improved compared to the virgin aspen char. Energy release rate, total energy released, and char yield of aspen and aspen–silicone composites were measured and a significant improvement in all three of these fire-resistance parameters was observed after the incorporation of silicone. Samples were also exposed to a controlled thermo-oxidative environment under an applied stress to measure lifetimes of each sample at given temperatures and stress levels. This data were subjected to an Arrhenius analysis and show a good linear correlation. Composite systems demonstrate significantly longer lifetimes than virgin aspen and the slopes of all lines are nearly identical, suggesting that no change in the chemical degradation mechanism has occurred.     

A Plan for the Development of Fusion Energy

This is the final report of a panel set up by the U.S. Department of Energy (DOE) Fusion Energy Sciences Advisory Committee (FESAC) in response to a charge letter dated September 10, 2002 from Dr. Ray Orbach, Director of the DOE's Office of Science. In that letter, Dr. Orbach asked FESAC to develop a plan with the end goal of the start of operation of a demonstration power plant in approximately 35 years. This report, submitted March 5, 2003, presents such a plan, leading to commercial application of fusion energy by mid-century. The plan is derived from the necessary features of a demonstration fusion power plant and from the time scale defined by President Bush. It identifies critical milestones, key decision points, needed major facilities and required budgets. The report also responds to a request from DOE to FESAC to describe what new or upgraded fusion facilities will best serve our purposes over a time frame of the next twenty years.     

Frequency Stabilization of a Ho:Tm:YLF Laser to Absorption Lines of Carbon Dioxide

A single-frequency Ho:Tm:YLF laser, operating at an eye-safe wavelength of 2 mum, has been developed with tuning characteristics optimized for spectroscopy of absorption features. The laser frequency was stabilized to three different absorption lines of carbon dioxide by a wavelength modulation technique. Long-term frequency drift has been eliminated from the laser, and shorter-term jitter has been reduced to within 13.5 MHz of the absorption line center. This stabilized laser is an ideal injection seed source for a differential absorption lidar system for measurement of atmospheric gases.     

Modifications to methods for the enumeration and detection of injured Escherichia coli O157:H7 in foods

Reliable methods are required for the detection and enumeration of potentially injured E. coli O157 in food in the presence of outnumbering competing bacteria. Selective agents can prevent or inhibit the recovery and subsequent multiplication of injured cells and direct inoculation, either into selective enrichment broths or onto selective agar plates is still used in many methods for E. coli O157 detection and enumeration. When compared with tryptone soya agar (TSA), sorbitol MacConkey agar (SMAC) was shown to underestimate the concentration of viable E. coli O157:H7 subjected to low pH and high NaCl concentration. Using a resuscitation stage on TSA followed by membrane transfer to SMAC improved recovery to levels obtained on TSA. The membrane method was used to monitor the numbers of artificially contaminated E. coli O157:H7 during the fermentation of a meat product and demonstrated better survival when compared to counts on SMAC. Six rapid methods for the detection of E. coli O157 in food (BAX E. coli O157, Reveal 8 E. coli O157-H7 screening test, VIP EHEC, VIDAS E. coli O157 (ECO), EHEC-Tek and Tecra E. coli O157 visual immunoassay), were evaluated using beetburgers, parsley and fermented meat artificially contaminated with injured cells. Methods using direct selective enrichment, with or without an elevated incubation temperature gave false-negative results. The incorporation of a non-selective pre-enrichment medium improved the detection rates of these assays by up to ten fold.     

Folding pathway of a lattice model for proteins

The folding of a protein-like heteropolymer is studied by using direct simulation of a lattice model that folds rapidly to a well-defined "native" structure. The details of each molecular folding event depend on the random initial conformation as well as the random thermal fluctuations of the polymer. By analyzing the statistical properties of hundreds of folding events, a classical folding "pathway" for such a polymer is found that includes partially folded, on-pathway intermediates that are shown to be metastable equilibrium states of the polymer. These results are discussed in the context of the "classical" and "new" views of folding.     

Kinematic data on primate head and neck posture: implications for the evolution of basicranial flexion and an evaluation of registration planes used in paleoanthropology

Kinematic data on primate head and neck posture were collected by filming 29 primate species during locomotion. These were used to test whether head and neck posture are significant influences on basicranial flexion and whether the Frankfurt plane can legitimately be employed in paleoanthropological studies. Three kinematic measurements were recorded as angles relative to the gravity vector, the inclination of the orbital plane, the inclination of the neck, and the inclination of the Frankfurt plane. A fourth kinematic measurement was calculated as the angle between the neck and the orbital plane (the head-neck angle [HNA]). The functional relationships of basicranial flexion were examined by calculating the correlations and partial correlations between HNA and craniometric measurements representing basicranial flexion, orbital kyphosis, and relative brain size (Ross and Ravosa [1993] Am. J. Phys. Anthropol. 91:305-324). Significant partial correlations were observed between relative brain size and basicranial flexion and between HNA and orbital kyphosis. This indicates that brain size, rather than head and neck posture, is the primary influence on flexion, while the degree of orbital kyphosis may act to reorient the visual field in response to variation in head and neck posture. Regarding registration planes, the Frankfurt plane was found to be horizontal in humans but inclined in all nonhuman primates. In contrast, nearly all primates (including humans) oriented their orbits such that they faced anteriorly and slightly inferiorly. These results suggest that for certain functional craniometric studies, the orbital plane may be a more suitable registration plane than Frankfurt "Horizontal."