635 research outputs found
Time-Dependent Behavior of a Graphite/Thermoplastic Composite and the Effects of Stress and Physical Aging
Experimental studies were performed to determine the effects of stress and physical aging on the matrix dominated time dependent properties of IM7/8320 composite. Isothermal tensile creep/aging test techniques developed for polymers were adapted for testing of the composite material. Time dependent transverse and shear compliance's for an orthotropic plate were found from short term creep compliance measurements at constant, sub-T(8) temperatures. These compliance terms were shown to be affected by physical aging. Aging time shift factors and shift rates were found to be a function of temperature and applied stress
The effects of physical aging at elevated temperatures on the viscoelastic creep on IM7/K3B
Physical aging at elevated temperature of the advanced composite IM7/K3B was investigated through the use of creep compliance tests. Testing consisted of short term isothermal, creep/recovery with the creep segments performed at constant load. The matrix dominated transverse tensile and in-plane shear behavior were measured at temperatures ranging from 200 to 230 C. Through the use of time based shifting procedures, the aging shift factors, shift rates and momentary master curve parameters were found at each temperature. These material parameters were used as input to a predictive methodology, which was based upon effective time theory and linear viscoelasticity combined with classical lamination theory. Long term creep compliance test data was compared to predictions to verify the method. The model was then used to predict the long term creep behavior for several general laminates
Time dependent behavior of a graphite/thermoplastic composite and the effects of stress and physical aging
Two complimentary studies were performed to determine the effects of stress and physical aging on the matrix dominated time dependent properties of IM7/8320 composite. The first of these studies, experimental in nature, used isothermal tensile creep/aging test techniques developed for polymers and adapted them for testing of the composite material. From these tests, the time dependent transverse (S22) and shear (S66) compliance's for an orthotropic plate were found from short term creep compliance measurements at constant, sub-T(sub g) temperatures. These compliance terms were shown to be affected by physical aging. Aging time shift factors and shift rates were found to be a function of temperature and applied stress. The second part of the study relied upon isothermal uniaxial tension tests of IM7/8320 to determine the effects of physical aging on the nonlinear material behavior at elevated temperature. An elastic/viscoplastic constitutive model was used to quantify the effects of aging on the rate-independent plastic and rate-dependent viscoplastic response. Sensitivity of the material constants required by the model to aging time were determined for aging times up to 65 hours. Verification of the analytical model indicated that the effects of prior aging on the nonlinear stress/strain/time data of matrix dominated laminates can be predicted
Observations of quasar host galaxies with laser guide star AO
We report on observations of two quasar host galaxies made with the Lick Observatory adaptive optic system using a laser guide star tuned to the wavelength of the sodium D lines. A brief outline of the system is given, and a description of its performance when obtaining science data. We discuss techniques for obtaining calibration of the point spread function and the analysis steps required to obtain useful scientific results. We present H-band images of quasar host galaxies made with the system. Estimates of the host galaxy magnitudes and central black hole masses were made from these data. These are the first observations of quasar host galaxies with a sodium laser guide star
Does a monetary incentive improve the response to a postal questionnaire in a randomised controlled trial? : the MINT incentive study
Background: Sending a monetary incentive with postal questionnaires has been found to improve
the proportion of responders, in research in non-healthcare settings. However, there is little
research on use of incentives to improve follow-up rates in clinical trials, and existing studies are
inconclusive. We conducted a randomised trial among participants in the Managing Injuries of the
Neck Trial (MINT) to investigate the effects on the proportion of questionnaires returned and
overall non-response of sending a £5 gift voucher with a follow-up questionnaire.
Methods: Participants in MINT were randomised to receive either: (a) a £5 gift voucher (incentive
group) or (b) no gift voucher (no incentive group), with their 4 month or 8 month follow-up
questionnaire. We recorded, for each group, the number of questionnaires returned, the number
returned without any chasing from the study office, the overall number of non-responders (after
all chasing efforts by the study office), and the costs of following up each group.
Results: 2144 participants were randomised, 1070 to the incentive group and 1074 to the no
incentive group. The proportion of questionnaires returned (RR 1.10 (95% CI 1.05, 1.16)) and the
proportion returned without chasing (RR 1.14 (95% CI 1.05, 1.24) were higher in the incentive
group, and the overall non-response rate was lower (RR 0.68 (95% CI 0.53, 0.87)). Adjustment for
injury severity and hospital of recruitment to MINT made no difference to these results, and there
were no differences in results between the 4-month and 8-month follow up questionnaires.
Analysis of costs suggested a cost of £67.29 per additional questionnaire returned.
Conclusion: Monetary incentives may be an effective way to increase the proportion of postal
questionnaires returned and minimise loss to follow-up in clinical trials
The Spitzer mid-infrared AGN survey. II-the demographics and cosmic evolution of the AGN population
We present luminosity functions derived from a spectroscopic survey of AGN
selected from Spitzer Space Telescope imaging surveys. Selection in the
mid-infrared is significantly less affected by dust obscuration. We can thus
compare the luminosity functions of the obscured and unobscured AGN in a more
reliable fashion than by using optical or X-ray data alone. We find that the
AGN luminosity function can be well described by a broken power-law model in
which the break luminosity decreases with redshift. At high redshifts
(), we find significantly more AGN at a given bolometric luminosity than
found by either optical quasar surveys or hard X-ray surveys. The fraction of
obscured AGN decreases rapidly with increasing AGN luminosity, but, at least at
high redshifts, appears to remain at \% even at bolometric
luminosities . The data support a picture in which the
obscured and unobscured populations evolve differently, with some evidence that
high luminosity obscured quasars peak in space density at a higher redshift
than their unobscured counterparts. The amount of accretion energy in the
Universe estimated from this work suggests that AGN contribute about 12\% to
the total radiation intensity of the Universe, and a high radiative accretion
efficiency is required to match current
estimates of the local mass density in black holes.Comment: 14 pages, accepted by Ap
Efficacy of Targeted Mist-Netting to Capture Northern Bobwhites During the Non-Breeding Season in Ohio
Baited funnel traps and nightlighting are well established northern bobwhite (Colinus virginianus) capture techniques, but their use is not always appropriate, particularly on private land where cooperating landowners may place constraints on research activities. Alternative capture techniques may be more effective under conditions considered to be unfavorable for established techniques (e.g., periods with abundant natural food). Targeted mist-netting, where mist nets are erected near the known location of specific individuals, has been used to capture gallinaceous species and may be an effective alternative to established bobwhite capture techniques. We evaluated the effectiveness of using targeted mist-netting to capture bobwhites during the non-breeding season in Ohio. We tested for differences in survival and age and sex ratios of individuals captured with targeted netting and baited funnel traps. We captured 257 individuals with targeted netting during 1 October-28 February 2009–2011 and concurrently captured 253 individuals with baited funnel traps. There was a short-term influence of capture and handling, but there was no significant difference in post-capture survival of bobwhites captured with targeted netting or trapping. Capture rates of age and sex classes were similar (P 1⁄4 0.488 and P 1⁄4 0.973, respectively) between targeted netting and trapping. Body mass of bobwhites captured by targeted netting was less than that of bobwhites captured by trapping (P 1⁄4 0.009) suggesting that netting may provide more accurate estimates of body mass. We used targeted netting to capture bobwhites in a variety of situations where use of funnel traps was ineffective or problematic. Targeted netting was effective and often more compatible with constraints of working on private land than established capture techniques
Transcriptional and Environmental Control of Bacterial Denitrification and N2O Emissions
In oxygen-limited environments, denitrifying bacteria can switch from oxygen-dependent respiration to nitrate (NO3−) respiration in which the NO3− is sequentially reduced via nitrite (NO2−), nitric oxide (NO) and nitrous oxide (N2O) to dinitrogen (N2). However, atmospheric N2O continues to rise, a significant proportion of which is microbial in origin. This implies that the enzyme responsible for N2O reduction, nitrous oxide reductase (NosZ), does not always carry out the final step of denitrification either efficiently, or in synchrony with the rest of the pathway. Despite a solid understanding of the biochemistry underpinning denitrification, there is a relatively poor understanding of how environmental signals and respective transcriptional regulators control expression of the denitrification apparatus. This mini-review will describe the current picture for transcriptional regulation of denitrification in the model bacterium, Paracoccus denitrificans, highlighting differences in other denitrifying bacteria where appropriate, as well as gaps in our understanding. Alongside this, the emerging role of small regulatory RNAs (sRNAs) in regulation of denitrification will be discussed. We will conclude by speculating how this information, aside from providing a better understanding of the denitrification process, can be translated into development of novel greenhouse gas mitigation strategies
School Leadership Interventions Under the Every Student Succeeds Act: Evidence Review - Updated and Expanded
This RAND analysis offers guidance to states and districts on how they can choose to use the Every Student Succeeds Act to help achieve their school improvement goals by supporting principals and other school leaders
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