559 research outputs found
Could natural selection change the geographic range limits of light brown apple moth (Lepidoptera, Tortricidae) in North America?
We artificially selected for increased freeze tolerance in the invasive light brown apple moth. Our results suggest that, by not accounting for adaptation to cold, current models of potential geographic distributions could underestimate the areas at risk of exposure to this species
Letter, Addressed to William Easton Hutchison from Ida Callery, May 1916
A letter written by Ida Callery sent to an unidentified person on May 28, 1916
Fatigue Behavior of a Zirconium-Based Bulk Metallic Glass
Although the mechanical behavior of Zr-based bulk metallic glasses (BMGs) has been studied, fatigue studies in controlled environments and testing conditions have not been adequately performed or understood. Early fatigue examinations of rectangular bar specimens tested in bending had resulted in fatigue strengths substantially lower than anticipated [1,2,3,4,5]. Preliminary work performed by Peter et al. and Wang et al. on uniaxial button-head specimens have yielded in very different fatigue behavior with fatigue-endurance limits comparable to conventional high-strength, crystalline alloys [6,7,8,9,10]. Between all S-N results studied, the fatigue-endurance limits for Zr-based BMGs have been observed to range from 150 MPa to 1 GPa [1,2,3,4,5,6,7,8,9,10]. Testing conditions, sample preparation, and the quality of the amorphous alloy may provide the understanding for this variability in fatigue behavior.
In the following thesis, several investigations were engaged to better understand changeability in the fatigue behavior of a Zr-based BMG, Zr52.5Al10Ti5Cu17.9Ni14.6 (at. %). The studies were primarily conducted to explain how the loading conditions, the sample preparation, the quality of the glass materials, the test environment, or the chemical composition affect the degradation behavior of BMGs. Fabrication, corrosion, metallography, and cyclic loading were types of investigations performed.
Fatigue testing was conducted in air and vacuum environments. By comparing the results, the environmental effects due to water vapor (in air) on the fatigue lifetime of BMG-11 were evaluated. It was concluded that water vapor does not have a detrimental effect on the fatigue lifetime of BMG-11. Indeed, the observed lifetimes in vacuum were shorter than those in air. Early fatigue tests in vacuum with and without the use of an ionization gauge seemed to indicate that the dissociation of the residual water vapor to atomic hydrogen in vacuum via a hot tungsten-filament ionization gauge could be a factor in the shorter fatigue lifetimes in vacuum than in air. Further testing has disproved this hypothesis. Closer examinations of the surface of multiple samples has led to the discovery of mechanical wear and fused copper (from copper grips) near the crack initiation site.
Because of the possible impact the ionization gauge may have had on the fatigue behavior of BMG-11, hydrogen-charged samples were tested in air and compared to uncharged samples in order to understand any detrimental effects hydrogen may have on the fatigue lifetime around the fatigue-endurance limit. Though the ionization gauge did not seem to play a detrimental role in the fatigue lifetime of amorphous samples tested in vacuum, charged hydrogen embrittles the material with increases in hardness values and lower fatigue lifetimes for cathodically-charged samples. These results could impact Zr-based BMGs’ usefulness in hydrogen-rich environments.
Fatigue studies were performed on button head, uniaxial specimens with different surface finishes in order to better understand the influence the average surface roughness and/or critical surface defects may have on the fatigue behavior. It was hypothesized that geometric, surface flaws could lower the observed life of a BMG sample by shortening the crack initiation phase and providing local stress concentrators. Careful studies of surface conditions indicate that fatigue-endurance limits are greatly impacted by the average surface roughness with possible reductions over fifty percent. Lastly, a rectangular bend-bar sample was finished with a coarse grit paper on the tension side of the sample, and observed for the location of crack initiation.
Four-point and three-point bending fatigue studies were conducted to observe the effect of variability in loading conditions versus uniaxial tension studies, and to observe any impact from testing volume on the fatigue life of BMG-11. Both, three point and four point bend results seemed to exhibit slightly better fatigue behavior compared to the uniaxial tests. However, little difference was observed between three-and four-point bending. These results are similar to those found with a preliminary study of uniaxial specimens with varying testing gauge lengths.
Lastly, a study was performed to better understand the effect crystallinity has on the fatigue behavior of Zr-based bulk metallic glasses. The crystalline phases of BMG-11 have an extremely low ultimate bending strength, around 100 MPa, and are very brittle. Any interfaces between crystalline impurities and the glassy matrix are prime locations for crack-initiation sites. A large volume fraction of crystallinity has been shown to dramatically lower the fatigue lifetime of a Zr-based BMG. This careful study of fatigue behavior leads to the conclusion that the detrimental effect crystallinity and geometrical surface defects have on the fatigue-endurance limit and the fatigue lifetime explain the variability in previously reported results
Synthesis of new antimalarial drugs - pyridoacridines derived from 5-, 6-, and 7-aminoquinolines
Effect of Preventive Primary Care Outreach on Health Related Quality of Life Among Older Adults at Risk of Functional Decline: Randomised Controlled Trial
Objective: To evaluate the impact of a provider initiated primary care outreach intervention compared with usual care among older adults at risk of functional decline.
Design: Randomised controlled trial.
Setting: Patients enrolled with 35 family physicians in five primary care networks in Hamilton, Ontario, Canada.
Participants: Patients were eligible if they were 75 years of age or older and were not receiving home care services. Of 3166 potentially eligible patients, 2662 (84%) completed the validated postal questionnaire used to determine risk of functional decline. Of 1724 patients who met the risk criteria, 769 (45%) agreed to participate and 719 were randomised.
Intervention: The 12 month intervention, provided by experienced home care nurses in 2004-6, consisted of a comprehensive initial assessment using the resident assessment instrument for home care; collaborative care planning with patients, their families, and family physicians; health promotion; and referral to community health and social support services.
Main outcome measures: Quality adjusted life years (QALYs), use and costs of health and social services, functional status, self rated health, and mortality.
Results: The mean difference in QALYs between intervention and control patients during the study period was not statistically significant (0.017, 95% confidence interval ?0.022 to 0.056; P=0.388). The mean difference in overall cost of prescription drugs and services between the intervention and control groups was not statistically significant, (-162), 95% confidence interval -$16 214; P=0.984). Changes over 12 months in functional status and self rated health were not significantly different between the intervention and control groups. Ten patients died in each group.
Conclusions: The results of this study do not support adoption of this preventive primary care intervention for this target population of high risk older adults
The sulfur isotope evolution of magmatic-hydrothermal fluids : insights into ore-forming processes
This project was supported by the European Union’s Horizon 2020 research and innovation programme under grant agreement No. 689909. W.H. also acknowledges support from a UKRI Future Leaders Fellowship (MR/S033505/1). A.J.B. is funded by the NERC National Environment Isotope Facility award (NE/S011587/1) and the Scottish Universities Environmental Research Centre.Metal-rich fluids that circulate in magmatic-hydrothermal environments form a wide array of economically significant ore deposits. Unravelling the origins and evolution of these fluids is crucial for understanding how Earth’s metal resources form and one of the most widely used tools for tracking these processes is sulfur isotopes. It is well established that S isotopes record valuable information about the source of the fluid, as well as its physical and chemical evolution (i.e. changing pH, redox and temperature), but it is often challenging to unravel which of these competing processes drives isotopic variability. Here we use thermodynamic models to predict S isotope fractionation for geologically realistic hydrothermal fluids and attempt to disentangle the effects of fluid sources, physico-chemical evolution and S mineral disequilibrium. By modelling a range of fluid compositions, we show that S isotope fingerprints are controlled by the ratio of oxidised to reduced S species (SO42−/H2S), and this is most strongly affected by changing temperature, fO2 and pH. We show that SO42−/H2S can change dramatically during cooling and our key insight is that S isotopes of individual sulfide or sulfate minerals can show large fractionations (up to 20 ‰) even when pH is constant and fO2 fixed to a specific mineral redox buffer. Importantly, while it is commonly assumed that SO42−/H2S is constant throughout fluid evolution, our analysis shows that this is unlikely to hold for most natural systems. We then compare our model predictions to S isotope data from porphyry and epithermal deposits, seafloor hydrothermal vents and alkaline igneous bodies. We find that our models accurately reproduce the S isotope evolution of porphyry and high sulfidation epithermal fluids, and that most require magmatic S sources between 0 and 5 ‰. The S isotopes of low sulfidation epithermal fluids and seafloor hydrothermal vents do not fit our model predictions and reflect disequilibrium between the reduced and oxidised S species and, for the latter, significant S input from seawater and biogenic sources. Alkaline igneous fluids match model predictions and confirm magmatic S sources and a wide range of temperature and redox conditions. Of all these different ore deposits, porphyry and alkaline igneous systems are particularly well-suited to S isotope investigation because they show relationships between redox, alteration and ore mineralogy that could be useful for exploration and prospecting. Ultimately, our examples demonstrate that S isotope forward models are powerful tools for identifying S sources, flagging disequilibrium processes, and validating hypotheses of magmatic fluid evolution.Publisher PDFPeer reviewe
The development of Hydatigera (Taenia) taeniaeformis (Cestoda, Cyclophyllidae) in vivo
Abstract Not Provided
The eruptive history and magmatic evolution of Aluto volcano: new insights into silicic peralkaline volcanism in the Ethiopian rift
The silicic peralkaline volcanoes of the East African Rift are some of the least studied volcanoes on Earth. Here we bring together new constraints from fieldwork, remote sensing, geochronology and geochemistry to present the first detailed account of the eruptive history of Aluto, a restless silicic volcano located in a densely populated section of the Main Ethiopian Rift. Prior to the growth of the Aluto volcanic complex (before 500 ka) the region was characterized by a significant period of fault development and mafic fissure eruptions. The earliest volcanism at Aluto built up a trachytic complex over 8 km in diameter. Aluto then underwent large-volume ignimbrite eruptions at 316 ± 19 ka and 306 ± 12 ka developing a ~ 42 km2 collapse structure. After a hiatus of ~ 250 ka, a phase of post-caldera volcanism initiated at 55 ± 19 ka and the most recent eruption of Aluto has a radiocarbon age of 0.40 ± 0.05 cal. ka BP. During this post-caldera phase highly-evolved peralkaline rhyolite lavas, ignimbrites and pumice fall deposits have erupted from vents across the complex. Geochemical modelling is consistent with rhyolite genesis from protracted fractionation (> 80%) of basalt that is compositionally similar to rift-related basalts found east of the complex. Based on the style and volume of recent eruptions we suggest that silicic eruptions occur at an average rate of 1 per 1000 years, and that future eruptions of Aluto will involve explosive emplacement of localised pumice cones and effusive obsidian coulees of volumes in the range 1–100 × 106 m3
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