Measurement and analysis of critical crack tip processes during fatigue crack growth

The mechanics of fatigue crack growth under constant-amplitudes and variable-amplitude loading were examined. Critical loading histories involving relatively simple overload and overload/underload cycles were studied to provide a basic understanding of the underlying physical processes controlling crack growth. The material used for this study was 7091-T7E69, a powder metallurgy aluminum alloy. Local crack-tip parameters were measured at various times before, during, and after the overloads, these include crack-tip opening loads and displacements, and crack-tip strain fields. The latter were useed, in combination with the materials cyclic and monotonic stress-strain properties, to compute crack-tip residual stresses. The experimental results are also compared with analytical predictions obtained using the FAST-2 computer code. The sensitivity of the analytical model to constant-amplitude fatigue crack growth rate properties and to through-thickness constrain are studied

A comparison of single-cycle versus multiple-cycle proof testing strategies

An evaluation of single-cycle and multiple-cycle proof testing (MCPT) strategies for SSME components is described. Data for initial sizes and shapes of actual SSME hardware defects are analyzed statistically. Closed-form estimates of the J-integral for surface flaws are derived with a modified reference stress method. The results of load- and displacement-controlled stable crack growth tests on thin IN-718 plates with deep surface flaws are summarized. A J-resistance curve for the surface-cracked configuration is developed and compared with data from thick compact tension specimens. The potential for further crack growth during large unload/reload cycles is discussed, highlighting conflicting data in the literature. A simple model for ductile crack growth during MCPT based on the J-resistance curve is used to study the potential effects of key variables. The projected changes in the crack size distribution during MCPT depend on the interactions between several key parameters, including the number of proof cycles, the nature of the resistance curve, the initial crack size distribution, the component boundary conditions (load vs. displacement control), and the magnitude of the applied load or displacement. The relative advantages of single-cycle and multiple-cycle proof testing appear to be specific, therefore, to individual component geometry, material, and loading

Cognitive Speed of Processing Training Can Promote Community Mobility among Older Adults: A Brief Review

Background. Community mobility is crucial for maintaining independent functioning and quality of life for older adults. Purpose. The present paper describes the relationship of cognition, particularly speed of processing as measured by the Useful Field of View Test, to mobility as indicated by driving behaviors, life space, and falls among healthy older adults. Research examining the impact of cognitive speed of processing training (SOPT) on older adults' community mobility (i.e., driving behaviors) is also summarized. Key Issues. Even slight cognitive declines can place older adults at risk for mobility limitations. However, cognitive interventions like SOPT can mitigate declines in driving mobility. Implications. The potential of SOPT to sustain community mobility among older adults is discussed

Measurement and analysis of critical crack tip processes associated with variable amplitude fatigue crack growth

Crack growth retardation following overloads can result in overly conservative life predictions in structures subjected to variable amplitude fatigue loading when linear damage accumulation procedures are employed. Crack closure is believed to control the crack growth retardation, although the specific closure mechanism is debatable. Information on the relative contributions to crack closure from: (1) plasticity left in the wake of the advancing crack and (2) crack tip residual stresses is provided. The delay period and corresponding crack growth rate transients following overloads are systematically measured as a function of load ratio (R) and overload magnitude. These responses are correlated in terms of the local 'driving force' for crack growth as measured by crack tip opening loads and delta K sub eff. The latter measurements are obtained using a scanning electron microscope equipped with a cyclic loading stage; measurements are quantified using a relatively new stereoimaging technique. Combining experimental results with analytical predictions suggests that both plastic wake and residual stress mechanism are operative, the latter becoming predominate as R increases

Relative cost-effectiveness of using a liquid human milk fortifier in preterm infants in the US

Objective: To estimate the cost-effectiveness of using a liquid human milk fortifier (LHMF) compared to a powdered human milk fortifier (PHMF) in preterm infants in the US from the perspective of third-party payers and parents. Methods: This was a decision modelling study using patient data obtained from a random- ized controlled trial comparing a LHMF with a PHMF in preterm infants, supplemented with additional data obtained by performing a chart review among 79% of the trial patients. The model estimated the cost-effectiveness of LHMF versus PHMF in US$at 2014/2015 prices. Results: More infants in the LHMF group were discharged home (92$10,497 per infant less in the LHMF group than the PHMF group ($240,928 versus$251,425). Conclusion: Using LHMF instead of PHMF in preterm infants enabled resources to be freed-up for alternative use within the system. There is no health economic reason why LHMF should not be used in preference to PHMF in the NICU

Potential Hazards of Wind Energy For Rare, Threatened, and Endangered Birds and Batsin Texas

This article discusses the potential hazards of wind energy for rare, threatened, and endangered birds and bats in Texas

Efficacy of recombinant human granulocyte colony stimulating factor in very-low-birth-weight infants with early neutropenia

Background/PurposeNeutropenia is a risk factor for nosocomial infections (NI) in very-low-birth-weight (VLBW) infants. Although recombinant human granulocyte colony stimulating factor (rhG-CSF) increases the neutrophil counts in neutropenic VLBW infants, its long-term efficacy for early neutropenia (EN) remains unknown.MethodsIn this case-controlled study, charts of VLBW recipients of rhG-CSF for EN (total neutrophil count <1.5 × 109/L during first 7 days) were reviewed and compared to gestational age, total neutrophil count, and birth weight matched infants unexposed to rhG-CSF.ResultsTwenty-seven infants were identified in each group. Mortality and morbidity did not differ between the two groups. Rate of NI (16/27 vs. 4/27, p = 0.002, odds ratio = 8.36) as well as the total number of episodes of NI (22 vs. 4, p = 0.007) were higher in rhG-CSF (+) group than in the rhG-CSF (–) group.ConclusionOur experience does not show benefit in empirical use of rhG-CSF in preventing NI in VLBW infants with EN

Analysis of small crack behavior for airframe applications

The small fatigue crack problem is critically reviewed from the perspective of airframe applications. Different types of small cracks-microstructural, mechanical, and chemical-are carefully defined and relevant mechanisms identified. Appropriate analysis techniques, including both rigorous scientific and practical engineering treatments, are briefly described. Important materials data issues are addressed, including increased scatter in small crack data and recommended small crack test methods. Key problems requiring further study are highlighted

Workforce Characteristics, Perceptions, Stress, and Satisfaction among Staff in Green House and Other Nursing Homes

OBJECTIVE: To compare workforce characteristics and staff perceptions of safety, satisfaction, and stress between Green House (GH) and comparison nursing homes (CNHs). DATA SOURCES/STUDY SETTING: Primary data on staff perceptions of safety, stress, and satisfaction from 13 GHs and 8 comparison NHs in 11 states; secondary data from human resources records on workforce characteristics, turnover, and staffing from 01/01/2011-06/30/2012. STUDY DESIGN: Observational study. DATA COLLECTION METHODS: Workforce data were from human resources offices; staff perceptions were from surveys. PRINCIPAL FINDINGS: Few significant differences were found between GH and CNHs. Exceptions were GH direct caregivers were older, provided twice the normalized hours per week budgeted per resident than CNAs in CNHs or Legacy NHs, and trended toward lower turnover. CONCLUSIONS: GH environment may promote staff longevity and does not negatively affect worker's stress, safety perceptions, or satisfaction. Larger studies are needed to confirm findings

Use of 2d-video Disdrometer to Derive Mean Density-size and Ze-SR Relations: Four Snow Cases from the Light Precipitation Validation Experiment

The application of the 2D-video disdrometer to measure fall speed and snow size distribution and to derive liquid equivalent snow rate, mean density-size and reflectivity-snow rate power law is described. Inversion of the methodology proposed by Bhm provides the pathway to use measured fall speed, area ratio and '3D' size measurement to estimate the mass of each particle. Four snow cases from the Light Precipitation Validation Experiment are analyzed with supporting data from other instruments such as Precipitation Occurrence Sensor System (POSS), Snow Video Imager (SVI), a network of seven snow gauges and three scanning C9 band radars. The radar-based snow accumulations using the 2DVD-derived Ze-SR relation are in good agreement with a network of seven snow gauges and outperform the accumulations derived from a climatological Ze-SR relation used by the Finnish Meteorological Institute (FMI). The normalized bias between radar-derived and gauge accumulation is reduced from 96% when using the fixed FMI relation to 28% when using the Ze-SR relations based on 2DVD data. The normalized standard error is also reduced significantly from 66% to 31%. For two of the days with widely different coefficients of the Ze-SR power law, the reflectivity structure showed significant differences in spatial variability. Liquid water path estimates from radiometric data also showed significant differences between the two cases. Examination of SVI particle images at the measurement site corroborated these differences in terms of unrimed versus rimed snow particles. The findings reported herein support the application of Bhm's methodology for deriving the mean density-size and Ze-SR power laws using data from 2D-video disdrometer