53 research outputs found
Influence of joint line remnant on crack paths under static and fatigue loadings in friction stir welded Al-Mg-Sc alloy
The influence of the joint line remnant (JLR) on tensile and fatigue fracture behaviour has been investigated in a friction stir welded Al-Mg-Sc alloy. JLR is one of the microstructural features formed in friction stir welds depending on welding conditions and alloy systems. It is attributed to initial oxide layer on butting surfaces to be welded. In this study, two different tool travel speeds were used. JLR was formed in both welds but its spatial distribution was different depending on the tool travel speeds. Under the tensile test, the weld with the higher heat input fractured partially along JLR, since strong microstructural inhomogeneity existed in the vicinity of JLR in this weld and JLR had weak bonding. Resultantly, the mechanical properties of this weld were deteriorated compared with the other weld. Fatigue crack initiation was not affected by the existence of JLR in all welds. But the crack propagated preferentially along JLR in the weld of the higher heat input, when it initiated on the retreating side. Consequently, such crack propagation behaviour along JLR could bring about shorter fatigue lives in larger components in which crack growth phase is dominant
Herschel/PACS far-infrared photometry of two z>4 quasars
We present Herschel far-infrared (FIR) observations of two sub-mm bright
quasars at high redshift: SDSS J1148+5251 (z=6.42) and BR 1202-0725 (z=4.69)
obtained with the PACS instrument. Both objects are detected in the PACS
photometric bands. The Herschel measurements provide additional data points
that constrain the FIR spectral energy distributions (SEDs) of both sources,
and they emphasise a broad range of dust temperatures in these objects. For
lambda_rest ~< 20mu, the two SEDs are very similar to the average SEDs of
quasars at low redshift. In the FIR, however, both quasars show excess emission
compared to low-z QSO templates, most likely from cold dust powered by vigorous
star formation in the QSO host galaxies. For SDSS J1148+5251 we detect another
object at 160mu with a distance of ~10 arcseconds from the QSO. Although no
physical connection between the quasar and this object can be shown with the
available data, it could potentially confuse low-resolution measurements, thus
resulting in an overestimate of the FIR luminosity of the z=6.42 quasar.Comment: 4 pages, 3 figures, accepted for publication in the A&A special issue
on Hersche
A Herschel PACS and SPIRE study of the dust content of the Cassiopeia A supernova remnant
Using the 3.5-m Herschel Space Observatory, imaging photometry of Cas A has been obtained in six bands between 70 and 500 μm with the PACS and SPIRE instruments, with angular resolutions ranging from 6 to 37”. In the outer regions of the remnant the 70-μm PACS image resembles the 24-μm image Spitzer image, with the emission attributed to the same warm dust component, located in the reverse shock region. At longer wavelengths, the three SPIRE bands are increasingly dominated by emission from cold interstellar dust knots and filaments, particularly across the central, western and southern parts of the remnant. Nonthermal emission from the northern part of the remnant becomes prominent at 500 μm. We have estimated and subtracted the contributions from the nonthermal, warm dust and cold interstellar dust components. We confirm and resolve for the first time a cool (~35 K) dust component, emitting at 70-160 μm, that is located interior to the reverse shock region, with an estimated mass of 0.075
A cool dust factory in the Crab Nebula: a Herschel study of the filaments
Whether supernovae are major sources of dust in galaxies is a long-standing debate. We present infrared and submillimeter photometry and spectroscopy from the Herschel Space Observatory of the Crab Nebula between 51 and 670 μm as part of the Mass Loss from Evolved StarS program. We compare the emission detected with Herschel with multiwavelength data including millimeter, radio, mid-infrared, and archive optical images. We carefully remove the synchrotron component using the Herschel and Planck fluxes measured in the same epoch. The contribution from line emission is removed using Herschel spectroscopy combined with Infrared Space Observatory archive data. Several forbidden lines of carbon, oxygen, and nitrogen are detected where multiple velocity components are resolved, deduced to be from the nitrogen-depleted, carbon-rich ejecta. No spectral lines are detected in the SPIRE wavebands; in the PACS bands, the line contribution is 5% and 10% at 70 and 100 μm and negligible at 160 μm. After subtracting the synchrotron and line emission, the remaining far-infrared continuum can be fit with two dust components. Assuming standard interstellar silicates, the mass of the cooler component is 0.24+0.32 – 0.08 M ☉ for T = 28.1+5.5 – 3.2 K. Amorphous carbon grains require 0.11 ± 0.01 M ☉ of dust with T = 33.8+2.3 – 1.8 K. A single temperature modified blackbody with 0.14 M ☉ and 0.08 M ☉ for silicate and carbon dust, respectively, provides an adequate fit to the far-infrared region of the spectral energy distribution but is a poor fit at 24-500 μm. The Crab Nebula has condensed most of the relevant refractory elements into dust, suggesting the formation of dust in core-collapse supernova ejecta is efficient
Dust in Historical Galactic Type Ia Supernova Remnants with Herschel
The origin of interstellar dust in galaxies is poorly understood,
particularly the relative contributions from supernovae and the cool stellar
winds of low-intermediate mass stars. Here, we present Herschel PACS and SPIRE
photometry at 70-500um of the historical young supernova remnants: Kepler and
Tycho; both thought to be the remnants of Type Ia explosion events. We detect a
warm dust component in Kepler's remnant with T = 82K and mass 0.0031Msun; this
is spatially coincident with thermal X-ray emission optical knots and
filaments, consistent with the warm dust originating in the circumstellar
material swept up by the primary blast wave of the remnant. Similarly for
Tycho's remnant, we detect warm dust at 90K with mass 0.0086Msun. Comparing the
spatial distribution of the warm dust with X-rays from the ejecta and swept-up
medium, and Ha emission arising from the post-shock edge, we show that the warm
dust is swept up interstellar material. We find no evidence of a cool (25-50 K)
component of dust with mass >0.07Msun as observed in core-collapse remnants of
massive stars. Neither the warm or cold dust components detected here are
spatially coincident with supernova ejecta material. We compare the lack of
observed supernova dust with a theoretical model of dust formation in Type Ia
remnants which predicts dust masses of 0.088(0.017)Msun for ejecta expanding
into surrounding densities of 1(5)cm-3. The model predicts that silicon- and
carbon-rich dust grains will encounter the interior edge of the observed dust
emission at 400 years confirming that the majority of the warm dust originates
from swept up circumstellar or interstellar grains (for Kepler and Tycho
respectively). The lack of cold dust grains in the ejecta suggests that Type Ia
remnants do not produce substantial quantities of iron-rich dust grains and has
important consequences for the 'missing' iron mass observed in ejecta.Comment: 17 pages, 14 figures, accepted for publication in MNRAS, final
version including corrected typos and reference
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Resilience, Motivational Factors, and Medication Adherence Among Rural Older Adults
Adherence to hypertension medications has been explored in previous studies; however, these studies focused on individuals who reside in urban areas. More information regarding demographic characteristics and relationships to motivational factors among rural older adults with hypertension is needed. The purpose of this study was to explore medication adherence among rural older adults with hypertension and constructs identified in self-determination theory (SDT) including motivation (autonomous versus controlled), perceived competence, perceived autonomy support and basic needs satisfaction. Rural nursing theory (RNT) was used to include the concept of resilience. This cross-sectional study included a sample of 80 older adults (≥ 65 years of age) prescribed at least one medication to control hypertension. Participants ranged in age from 65 to 89 (M=74.04, SD=6.18) from rural communities in the northwest. A demographic questionnaire, a measure of medication adherence and questionnaires to assess perceived autonomy support, basic needs satisfaction, autonomous and controlled motivation, perceived competence, and resilience were used. Correlational analysis and multiple regression were used to examine associations with adherence and to predict adherence. Perceived autonomy support, resilience, cost of medication and medication regimen complexity were the only variables significantly associated with medication adherence and predicted antihypertensive medication adherence. Overall, the measure used to assess medication adherence indicated high levels of adherence
Observations of infrared echoes around Cassiopeia A with WISE
Context. Light echoes of supernovae have proven to be a viable tool for characterizing both the supernova explosion mechanism and the surrounding circumstellar and interstellar medium.
Aims. We explore new possibilities for identifying infrared echoes with WISE data and extend the area of known echoes around the supernova remnant Cassiopeia A in different illumination conditions.
Methods. Preliminary release WISE data around Cassiopeia A is analyzed and compared to Spitzer-MIPS data. While Spitzer-WISE difference images directly show evidence of infrared light echoes, they can also be identified according to their 22/12 μm flux ratio.
Results. We find that WISE allows the detection of previously unknown infrared echoes in various illumination conditions. For the first time, infrared echoes at distances greater than 800 pc from a supernova remnant have been found. The 22/12 μm flux ratio criterion can be used as a conceptual factor for identifying infrared echoes around other supernovae as well as providing insights into the dust processing conditions of the interstellar medium
Influence of joint line remnant on crack paths under static and fatigue loadings in friction stir welded Al-Mg-Sc alloy
The influence of the joint line remnant (JLR) on tensile and fatigue fracture behaviour has been
investigated in a friction stir welded Al-Mg-Sc alloy. JLR is one of the microstructural features formed in
friction stir welds depending on welding conditions and alloy systems. It is attributed to initial oxide layer on
butting surfaces to be welded. In this study, two different tool travel speeds were used. JLR was formed in both
welds but its spatial distribution was different depending on the tool travel speeds. Under the tensile test, the
weld with the higher heat input fractured partially along JLR, since strong microstructural inhomogeneity
existed in the vicinity of JLR in this weld and JLR had weak bonding. Resultantly, the mechanical properties of
this weld were deteriorated compared with the other weld. Fatigue crack initiation was not affected by the
existence of JLR in all welds. But the crack propagated preferentially along JLR in the weld of the higher heat
input, when it initiated on the retreating side. Consequently, such crack propagation behaviour along JLR could
bring about shorter fatigue lives in larger components in which crack growth phase is dominant
The direct observation of copper segregation at the broad faces of η’ and η precipitates in AA7010 aluminium alloy
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