1,255 research outputs found
Effects of hydrogen/deuterium absorption on the magnetic properties of Co/Pd multilayers
The effects of hydrogen (H2) and deuterium (D2) absorption were studied in
two Co/Pd multilayers with perpendicular magnetic anisotropy (PMA) using
polarized neutron reflectivity (PNR). PNR was measured in an external magnetic
field H applied in the plane of the sample with the magnetization M confined in
the plane for {\mu}_o H= 6.0 T and partially out of plane at 0.65 T. Nominal
thicknesses of the Co and Pd layers were 2.5 {\AA} and 21 {\AA}, respectively.
Because of these small values, the actual layer chemical composition,
thickness, and interface roughness parameters were determined from the nuclear
scattering length density profile ({\rho}_n) and its derivative obtained from
both x-ray reflectivity and PNR, and uncertainties were determined using Monte
Carlo analysis. The PNR {\rho}_n showed that although D2 absorption occurred
throughout the samples, absorption in the multilayer stack was modest (0.02 D
per Pd atom) and thus did not expand. Direct magnetometry showed that H2
absorption decreased the total M at saturation and increased the component of M
in the plane of the sample when not at saturation. The PNR magnetic scattering
length density ({\rho}_m) revealed that the Pd layers in the multilayer stack
were magnetized and that their magnetization was preferentially modified upon
D2 absorption. In one sample, a modulation of M with twice the multilayer
period was observed at {\mu}_o H= 0.65 T, which increased upon D2 absorption.
These results indicate that H2 or D2 absorption decreases both the PMA and
total magnetization of the samples. The lack of measurable expansion during
absorption indicates that these changes are primarily governed by modification
of the electronic structure of the material.Comment: to appear in Physics review B, 201
Sputtering of Oxygen Ice by Low Energy Ions
Naturally occurring ices lie on both interstellar dust grains and on
celestial objects, such as those in the outer solar system. These ices are
continu- ously subjected to irradiation by ions from the solar wind and/or
cosmic rays, which modify their surfaces. As a result, new molecular species
may form which can be sputtered off into space or planetary atmospheres. We
determined the experimental values of sputtering yields for irradiation of
oxygen ice at 10 K by singly (He+, C+, N+, O+ and Ar+) and doubly (C2+, N2+ and
O2+) charged ions with 4 keV kinetic energy. In these laboratory experiments,
oxygen ice was deposited and irradiated by ions in an ultra high vacuum chamber
at low temperature to simulate the environment of space. The number of
molecules removed by sputtering was observed by measurement of the ice
thickness using laser interferometry. Preliminary mass spectra were taken of
sputtered species and of molecules formed in the ice by temperature programmed
desorption (TPD). We find that the experimental sputtering yields increase
approximately linearly with the projectile ion mass (or momentum squared) for
all ions studied. No difference was found between the sputtering yield for
singly and doubly charged ions of the same atom within the experimental
uncertainty, as expected for a process dominated by momentum transfer. The
experimental sputter yields are in good agreement with values calculated using
a theoretical model except in the case of oxygen ions. Preliminary studies have
shown molecular oxygen as the dominant species sputtered and TPD measurements
indicate ozone formation.Comment: to be published in Surface Science (2015
Clergy Interest in Innovative Collaboration with Psychologists
What forms of innovative collaboration are possible between clergy and psychologists? A total of 117 clergypersons (63% response rate) rated 6 scenarios of collaboration, indicating their level of interest and the extent to which they would like to remain involved with the psychologist. The scenarios were derived from two categories of collaboration articulated by in previous research: mental health services and enhancing parish life. Overall, clergy expressed relatively modest levels of interest in innovative collaboration, though they were somewhat interested in mental health consultation services. Many clergy refer troubled parishioners to clinical or counseling psychologists for treatment, but appear less interested in more innovative forms of collaboration
Resource User Perceptions of Marine Governance and Coral Reef Management in the Bay Islands, Honduras
Exploring the Role of Different Actors in Caribbean Coral Reef Governance Through Multi-level Social Networks
2P/Encke, the Taurid complex NEOs and the Maribo and Sutter’s Mill meteorites
Aims. 2P/Encke is a short period comet that was discovered in 1786 and has been extensively observed and studied for more than 200 years. The Taurid meteoroid stream has long been linked with 2P/Encke owing to a good match of their orbital elements, even though the comet’s activity is not strong enough to explain the number of observed meteors. Various small near-Earth objects (NEOs) have been discovered with orbits that can be linked to 2P/Encke and the Taurid meteoroid stream. Maribo and Sutter’s Mill are CM type carbonaceous chondrite that fell in Denmark on January 17, 2009 and April 22, 2012, respectively. Their pre-atmospheric orbits place them in the middle of the Taurid meteoroid stream, which raises the intriguing possibility that comet 2P/Encke could be the parent body of CM chondrites.
Methods. To investigate whether a relationship between comet 2P/Encke, the Taurid complex associated NEOs, and CM chondrites exists, we performed photometric and spectroscopic studies of these objects in the visible wavelength range. We observed 2P/Encke and 10 NEOs on August 2, 2011 with the FORS instrument at the 8.2 m Very Large Telescope on Cerro Paranal (Chile).
Results. Images in the R filter, used to investigate the possible presence of cometary activity around the nucleus of 2P/Encke and the NEOs, show that no resolved coma is present. None of the FORS spectra show the 700 nm absorption feature due to hydrated minerals that is seen in the CM chondrite meteorites. All objects show featureless spectra with moderate reddening slopes at λ10 and 1999 VT25, which show a flatter spectrum, the spectral slope of the observed NEOs is compatible with that of 2P/Encke. However, most of the NEOs show evidence of a silicate absorption in lower S/N data at λ> 800 nm, which is not seen in 2P/Encke, which suggests that they are not related.
Conclusions. Despite similar orbits, we find no spectroscopic evidence for a link between 2P/Encke, the Taurid complex NEOs and the Maribo and Sutter’s Mill meteorites. However, we cannot rule out a connection to the meteorites either, as the spectral differences may be caused by secondary alteration of the surfaces of the NEOs
Rotation of Cometary Nuclei New Lightcurves and an Update of the Ensemble Properties of Jupiter-Family Comets
We report new lightcurves and phase functions for nine Jupiter-family comets
(JFCs). They were observed in the period 2004-2015 with various ground
telescopes as part of the Survey of Ensemble Physical Properties of Cometary
Nuclei (SEPPCoN) as well as during devoted observing campaigns. We add to this
a review of the properties of 35 JFCs with previously published rotation
properties.
The photometric time-series were obtained in Bessel R, Harris R and SDSS r'
filters and were absolutely calibrated using stars from the Pan-STARRS survey.
This specially-developed method allowed us to combine data sets taken at
different epochs and instruments with absolute-calibration uncertainty down to
0.02 mag. We used the resulting time series to improve the rotation periods for
comets 14P/Wolf, 47P/Ashbrook-Jackson, 94P/Russell, and 110P/Hartley 3 and to
determine the rotation rates of comets 93P/Lovas and 162P/Siding-Spring for the
first time. In addition to this, we determined the phase functions for seven of
the examined comets and derived geometric albedos for eight of them.
We confirm the known cut-off in bulk densities at 0.6 g
if JFCs are strengthless. Using the model of Davidsson
(2001) for prolate ellipsoids with typical density and elongations, we conclude
that none of the known JFCs require tensile strength larger than 10-25 Pa to
remain stable against rotational instabilities. We find evidence for an
increasing linear phase function coefficient with increasing geometric albedo.
The median linear phase function coefficient for JFCs is 0.046 mag/deg and the
median geometric albedo is 4.2 per cent.Comment: 38 pages, accepted for publication in MNRA
Magnetic Structure in Fe/Sm-Co Exchange Spring Bilayers with Intermixed Interfaces
The depth profile of the intrinsic magnetic properties in an Fe/Sm-Co bilayer
fabricated under nearly optimal spring-magnet conditions was determined by
complementary studies of polarized neutron reflectometry and micromagnetic
simulations. We found that at the Fe/Sm-Co interface the magnetic properties
change gradually at the length scale of 8 nm. In this intermixed interfacial
region, the saturation magnetization and magnetic anisotropy are lower and the
exchange stiffness is higher than values estimated from the model based on a
mixture of Fe and Sm-Co phases. Therefore, the intermixed interface yields
superior exchange coupling between the Fe and Sm-Co layers, but at the cost of
average magnetization.Comment: 16 pages, 6 figures and 1 tabl
Collaborate With Whom? Clergy Responses to Psychologist Characteristics (Chapter 2 of Psychology and the Church)
Some clergy and psychologists are willing to collaborate in providing for people under their care and some are reticent. The purpose of this research is to see if clergy are more likely to collaborate with psychologists of a particular sex or training background. Six groups of clergy were given written descriptions of a psychologist that varied on these two dimensions-the institution from which the psychologist received training and sexand were then asked to rate how likely they would be to participate in 7 collaborative scenarios with the psychologist. No group differences were found. Furthermore, clergy characteristics were not significantly related to their likelihood of collaborating with psychologists. Differences were observed among the 7 collaborative scenarios, suggesting that clergy are more interested in some forms of collaboration than others. It appears that idiographic relational factors are ultimately more important than general demographic categories in establishing clergy-psychologist collaboration
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