10,205 research outputs found
Spin pumping damping and magnetic proximity effect in Pd and Pt spin-sink layers
We investigated the spin pumping damping contributed by paramagnetic layers
(Pd, Pt) in both direct and indirect contact with ferromagnetic
NiFe films. We find a nearly linear dependence of the
interface-related Gilbert damping enhancement on the heavy-metal
spin-sink layer thicknesses t in direct-contact
NiFe/(Pd, Pt) junctions, whereas an exponential dependence is
observed when NiFe and (Pd, Pt) are separated by \unit[3]{nm} Cu.
We attribute the quasi-linear thickness dependence to the presence of induced
moments in Pt, Pd near the interface with NiFe, quantified using
X-ray magnetic circular dichroism (XMCD) measurements. Our results show that
the scattering of pure spin current is configuration-dependent in these systems
and cannot be described by a single characteristic length
Socioeconomic indicators of health inequalities and female mortality: a nested cohort study within the United Kingdom Collaborative Trial of Ovarian Cancer Screening (UKCTOCS)
Evidence is mounting that area-level socioeconomic indicators are important tools for predicting health outcomes. However, few studies have examined these alongside individual-level education. This nested cohort study within the control arm of the United Kingdom Collaborative Trial of Ovarian Cancer Screening (UKCTOCS) assesses the association of mutually adjusted individual (education) and area-level (Index of Multiple Deprivation-IMD 2007) socioeconomic status indicators and all-cause female mortality
The oscillator model for the Lie superalgebra sh(2|2) and Charlier polynomials
We investigate an algebraic model for the quantum oscillator based upon the
Lie superalgebra sh(2|2), known as the Heisenberg-Weyl superalgebra or "the
algebra of supersymmetric quantum mechanics", and its Fock representation. The
model offers some freedom in the choice of a position and a momentum operator,
leading to a free model parameter gamma. Using the technique of Jacobi
matrices, we determine the spectrum of the position operator, and show that its
wavefunctions are related to Charlier polynomials C_n with parameter gamma^2.
Some properties of these wavefunctions are discussed, as well as some other
properties of the current oscillator model.Comment: Minor changes and some additional references added in version
Data Reduction Techniques for High Contrast Imaging Polarimetry. Applications to ExPo
Imaging polarimetry is a powerful tool for detecting and characterizing
exoplanets and circumstellar environments. Polarimetry allows a separation of
the light coming from an unpolarized source such as a star and the polarized
source such as a planet or a protoplanetary disk. Future facilities like SPHERE
at the VLT or EPICS at the E-ELT will incorporate imaging polarimetry to detect
exoplanets. The Extreme Polarimeter (ExPo) is a dual-beam imaging polarimeter
that currently can reach contrast ratios of 10^5, enough to characterize
circumstellar environments. We present the data reduction steps for a dual-beam
imaging polarimeter that can reach contrast ratios of 10^5. The data obtained
with ExPo at the William Herschel Telescope (WHT) are analyzed. Instrumental
artifacts and noise sources are discussed for an unpolarized star and for a
protoplanetary disk (AB Aurigae). The combination of fast modulation and
dual-beam techniques allow us to minimize instrumental artifacts. A proper data
processing and alignment of the images is fundamental when dealing with large
contrasts. Imaging polarimetry proves to be a powerful method to resolve
circumstellar environments even without a coronagraph mask or an Adaptive
Optics system.Comment: 9 pages, 12 Figures, Accepted for publication in A&
Volume-energy correlations in the slow degrees of freedom of computer-simulated phospholipid membranes
Constant-pressure molecular-dynamics simulations of phospholipid membranes in
the fluid phase reveal strong correlations between equilibrium fluctuations of
volume and energy on the nanosecond time-scale. The existence of strong
volume-energy correlations was previously deduced indirectly by Heimburg from
experiments focusing on the phase transition between the fluid and the ordered
gel phases. The correlations, which are reported here for three different
membranes (DMPC, DMPS-Na, and DMPSH), have volume-energy correlation
coefficients ranging from 0.81 to 0.89. The DMPC membrane was studied at two
temperatures showing that the correlation coefficient increases as the phase
transition is approached
The unusual volatile composition of the Halley-type comet 8P/Tuttle: Addressing the existence of an Inner Oort Cloud
We measured organic volatiles (CH4, CH3OH, C2H6, H2CO), CO, and water in
comet 8P/Tuttle, a comet from the Oort cloud reservoir now in a short-period
Halley-type orbit. We compare its composition with two other comets in
Halley-type orbits, and with comets of the "organics-normal" and
"organics-depleted" classes. Chemical gradients are expected in the
comet-forming region of the proto-planetary disk, and an individual comet
should reflect its specific heritage. If Halley-type comets came from the inner
Oort cloud as proposed, we see no common characteristics that could distinguish
such comets from those that were stored in the outer Oort cloud.Comment: 14 pages, including 1 figure and 2 Table
Covers of acts over monoids II
In 1981 Edgar Enochs conjectured that every module has a flat cover and
finally proved this in 2001. Since then a great deal of effort has been spent
on studying different types of covers, for example injective and torsion free
covers. In 2008, Mahmoudi and Renshaw initiated the study of flat covers of
acts over monoids but their definition of cover was slightly different from
that of Enochs. Recently, Bailey and Renshaw produced some preliminary results
on the `other' type of cover and it is this work that is extended in this
paper. We consider free, divisible, torsion free and injective covers and
demonstrate that in some cases the results are quite different from the module
case
Choice of activity-intensity classification thresholds impacts upon accelerometer-assessed physical activity-health relationships in children
It is unknown whether using different published thresholds (PTs) for classifying physical activity (PA) impacts upon activity-health relationships. This study explored whether relationships between PA (sedentary [SED], light PA [LPA], moderate PA [MPA], moderate-to-vigorous PA, vigorous PA [VPA]) and health markers differed in children when classified using three different PTs
The TWINS exospheric neutral H-density distribution under solar minimum conditions
Terrestrial exospheric atomic hydrogen (H) resonantly
scatters solar Lyman-α (121.567 nm) radiation, observed as the glow of the
H-geocorona. The Two Wide-angle Imaging Neutral-atom Spectrometers (TWINS)
satellites are equiped with two Lyman-α line-of-sight Detectors (LADs) each.
Since during the past solar minimum conditions the relevant solar control
parameters practically did not vary, we are using LAD data between June and
September 2008 to create a time averaged hydrogen geocorona model
representative for these solar minimum conditions. In this averaged model we
assume that the H-geocorona is longitudinally symmetric with respect to the
earth-sun line. We find a 3-dimensional H-density distribution in the range
from 3 to 8 earth radii which with some caution can also be extrapolated to
larger distances. For lower geocentric distances than 3 earth radii a best
fitting r-dependent Chamberlain (1963)-like model is adapted. Main findings
are larger than conventionally expected H-densities at heights above 5 <I>R</I><sub>E</sub> and a pronounced day-to-night side H-density asymmetry. The
H-geocorona presented here should serve as a reference H-atmosphere for the
earth during solar minimum conditions
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