2,611 research outputs found
Interferometric detection of spin-polarized transport in the depletion layer of a metal-GaAs Schottky barrier
It is shown that the Kerr rotation of spin-polarized electrons is modulated
by the distance of the electrons from the sample surface. Time-resolved Kerr
rotation of optically-excited spin-polarized electrons in the depletion layer
of n-doped GaAs displays fast oscillations that originate from an interference
between the light reflected from the semiconductor surface and from the front
of the electron distribution moving into the semiconductor. Using this effect,
the dynamics of the photogenerated charge carriers in the depletion layer of
the biased Schottky barrier is measured.Comment: 10 pages, 4 figure
Signatures of dynamically polarized nuclear spins in all-electrical lateral spin transport devices
The effect of nuclear spins in Fe/GaAs all-electrical spin-injection devices
is investigated. At temperatures below 50 K, strong modifications of the
non-local spin signal are found that are characteristic for hyperfine coupling
between conduction electrons and dynamically polarized nuclear spins. The
perpendicular component of the nuclear Overhauser field depolarizes electron
spins near zero in-plane external magnetic field, and can suppress such
dephasing when antialigned with the external field, leading to satellite peaks
in a Hanle measurement. The features observed agree well with a Monte Carlo
simulation of the spin diffusion equation including hyperfine interaction, and
are used to study the nuclear spin dynamics and relate it to the spin
polarization of injected electrons.Comment: 6 pages, 4 figure
Temperature dependence of the nonlocal voltage in an Fe/GaAs electrical spin injection device
The nonlocal spin resistance is measured as a function of temperature in a
Fe/GaAs spin-injection device. For nonannealed samples that show minority-spin
injection, the spin resistance is observed up to room temperature and decays
exponentially with temperature at a rate of 0.018\,K. Post-growth
annealing at 440\,K increases the spin signal at low temperatures, but the
decay rate also increases to 0.030\,K. From measurements of the
diffusion constant and the spin lifetime in the GaAs channel, we conclude that
sample annealing modifies the temperature dependence of the spin transfer
efficiency at injection and detection contacts. Surprisingly, the spin transfer
efficiency increases in samples that exhibit minority-spin injection.Comment: 10 pages, 4 figure
The Space Environment and Atmospheric Joule Heating of the Habitable Zone Exoplanet TOI700-d
We investigate the space environment conditions near the Earth-size planet
TOI~700~d using a set of numerical models for the stellar corona and wind, the
planetary magnetosphere, and the planetary ionosphere. We drive our simulations
using a scaled-down stellar input and a scaled-up solar input in order to
obtain two independent solutions. We find that for the particular parameters
used in our study, the stellar wind conditions near the planet are not very
extreme -- slightly stronger than that near the Earth in terms of the stellar
wind ram pressure and the intensity of the interplanetary magnetic field. Thus,
the space environment near TOI700-d may not be extremely harmful to the
planetary atmosphere, assuming the planet resembles the Earth. Nevertheless, we
stress that the stellar input parameters and the actual planetary parameters
are unconstrained, and different parameters may result in a much greater effect
on the atmosphere of TOI700-d. Finally, we compare our results to solar wind
measurements in the solar system and stress that modest stellar wind conditions
may not guarantee atmospheric retention of exoplanets.Comment: accepted to Ap
Hydrated lime matrix decreases ruminal biohydrogenation of flaxseed fatty acids
Omega-3 fatty acids are essential nutrients for humans, but dietary intake of these
nutrients by many Americans is inadequate due to low consumption of omega-3-rich
foods such as fish, walnuts, and flaxseed. In contrast, per capita consumption of red
meat is relatively high, but these products normally contain only small amounts of
omega-3 fatty acids. Feeding cattle diets that contain omega-3 fatty acids has consistently
increased the proportion of the desirable fats that accumulate in beef. Unfortunately,
the proportion of dietary omega-3 fats that are deposited into beef tissues is
relatively low, because microorganisms within the rumen biohydrogenate the unsaturated
omega-3 fatty acids extensively to produce the saturated fats that are characteristic
of beef fat. Encapsulation of fats has been proposed as a method for improving efficiency
of transfer of omega-3 fats into beef. Encapsulation processes apply a protective
barrier on the surface of fats or fat-containing feeds, which theoretically decreases fats’
susceptibility to microbial biohydrogenation. Protective coatings must remain intact to
retain their functionality, and physical damage to the coatings that occurs with normal
handling can result in poor efficacy because the core material is exposed to microorganisms
in the rumen. Embedding feed particles within a homogeneous protective matrix
constitutes a potentially useful alternative to protective surface barriers. The matrix is
created by mixing feed particles that are to be protected with a suitable matrix material
that is resistant to microbial digestion and subsequently forming the mixture into pills.
In cases where physical damage occurs, exposure of the core material is confined to the
broken surface, and the remainder of the matrix retains its ruminal stability.
The objective of this study was to determine if embedding flaxseed within a matrix of
hydrated dolomitic lime could be used as a method to decrease biohydrogenation of
polyunsaturated omega-3 fatty acids, thus improving efficiency of omega-3 fatty acids
absorption into the bloodstream
Unraveling the Historical Economies of Scale and Learning Effects for Desalination Technologies
As a technology develops and matures, both economies of scale and the lessons learned through experience drive down the cost over time. This article analyzes and separates the effects of economies of scale and learning through experience on historical cost reductions for three mature desalination technologies: multi‐effect distillation (MED), multi‐stage flash (MSF) distillation, and reverse osmosis (RO). The analysis suggests that learning has been the dominant driver for cost reductions, with learning rates of 23%, 30%, and 12% for MED, MSF, and RO, respectively, when the effects of scale are removed. The highest influence of economies of scale is found for MED, with an exponential scale coefficient of 0.71 and the largest difference between a traditional or scale‐free estimation of the learning rate. MSF and RO showed smaller differences between the traditional and de‐scaled learning rates (only 3%), pointing at learning as the main factor driving their historical cost reductions. However, a trend break observed over the last 10 years mirrors an exhaustion of the potential for technical improvements, as well as an increasing complexity and nonlinearity of the factors influencing the systems' cost. The findings provide useful data and insights for integrated and economic modeling frameworks, while providing guidance to prevent overestimations of the learning effect due to the confounding influence of economies of scale effects associated to historical unit upscaling processes
Activity and Magnetic Field Structure of the Sun-Like Planet Hosting Star HD 1237
We analyse the magnetic activity characteristics of the planet hosting
Sun-like star, HD 1237, using HARPS spectro-polarimetric time-series data. We
find evidence of rotational modulation of the magnetic longitudinal field
measurements consistent with our ZDI analysis, with a period of 7 days. We
investigate the effect of customising the LSD mask to the line depths of the
observed spectrum and find that it has a minimal effect on shape of the
extracted Stokes V profile but does result in a small increase in the S/N
( 7%). We find that using a Milne-Eddington solution to describe the
local line profile provides a better fit to the LSD profiles in this slowly
rotating star, which also impacts the recovered ZDI field distribution. We also
introduce a fit-stopping criterion based on the information content (entropy)
of the ZDI maps solution set. The recovered magnetic field maps show a strong
(+90 G) ring-like azimuthal field distribution and a complex radial field
dominating at mid latitudes (45 degrees). Similar magnetic field maps are
recovered from data acquired five months apart. Future work will investigate
how this surface magnetic field distribution impacts the coronal magnetic field
and extended environment around this planet-hosting star.Comment: Accepted for publication in A&
Network theory approach for data evaluation in the dynamic force spectroscopy of biomolecular interactions
Investigations of molecular bonds between single molecules and molecular
complexes by the dynamic force spectroscopy are subject to large fluctuations
at nanoscale and possible other aspecific binding, which mask the experimental
output. Big efforts are devoted to develop methods for effective selection of
the relevant experimental data, before taking the quantitative analysis of bond
parameters. Here we present a methodology which is based on the application of
graph theory. The force-distance curves corresponding to repeated pulling
events are mapped onto their correlation network (mathematical graph). On these
graphs the groups of similar curves appear as topological modules, which are
identified using the spectral analysis of graphs. We demonstrate the approach
by analyzing a large ensemble of the force-distance curves measured on:
ssDNA-ssDNA, peptide-RNA (system from HIV1), and peptide-Au surface. Within our
data sets the methodology systematically separates subgroups of curves which
are related to different intermolecular interactions and to spatial
arrangements in which the molecules are brought together and/or pulling speeds.
This demonstrates the sensitivity of the method to the spatial degrees of
freedom, suggesting potential applications in the case of large molecular
complexes and situations with multiple binding sites
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