2,174 research outputs found
Intrinsic Magnetism in Nanosheets of SnO: A First-principles Study
We propose intrinsic magnetism in nanosheets of SnO, based on
first-principles calculations. The electronic structure and spin density reveal
that orbitals of the oxygen atoms, surrounding Sn vacancies, have a non
itinerant nature which gives birth to localized magnetism. A giant decrease in
defect formation energies of Sn vacancies in nanosheets is observed. We,
therefore, believe that native defects can be stabilized without any chemical
doping. Nanosheets of different thicknesses are also studied, and it is found
that it is easier to create vacancies, which are magnetic, at the surface of
the sheets. SnO nanosheets can, therefore, open new opportunities in the
field of spintronics.Comment: J. Magn. Magn. Mate. 2012 (Accepted
Effects of bonding type and interface geometry on coherent transport through the single-molecule magnet Mn12
We examine theoretically coherent electron transport through the
single-molecule magnet Mn, bridged between Au(111) electrodes, using the
non-equilibrium Green's function method and the density-functional theory. We
analyze the effects of bonding type, molecular orientation, and geometry
relaxation on the electronic properties and charge and spin transport across
the single-molecule junction. We consider nine interface geometries leading to
five bonding mechanisms and two molecular orientations: (i) Au-C bonding, (ii)
Au-Au bonding, (iii) Au-S bonding, (iv) Au-H bonding, and (v) physisorption via
van der Waals forces. The two molecular orientations of Mn correspond to
the magnetic easy axis of the molecule aligned perpendicular [hereafter denoted
as orientation (1)] or parallel [orientation (2)] to the direction of electron
transport. We find that the electron transport is carried by the lowest
unoccupied molecular orbital (LUMO) level in all the cases that we have
simulated. Relaxation of the junction geometries mainly shifts the relevant
occupied molecular levels toward the Fermi energy as well as slightly reduces
the broadening of the LUMO level. As a result, the current slightly decreases
at low bias voltage. Our calculations also show that placing the molecule in
the orientation (1) broadens the LUMO level much more than in the orientation
(2), due to the internal structure of the Mn. Consequently, junctions
with the former orientation yield a higher current than those with the latter.
Among all of the bonding types considered, the Au-C bonding gives rise to the
highest current (about one order of magnitude higher than the Au-S bonding),
for a given distance between the electrodes. The current through the junction
with other bonding types decreases in the order of Au-Au, Au-S, and Au-H.
Importantly, the spin-filtering effect in all the nine geometries stays robust
and their ratios of the majority-spin to the minority-spin transmission
coefficients are in the range of 10 to 10. The general trend in
transport among the different bonding types and molecular orientations obtained
from this study may be applied to other single-molecular magnets.Comment: Accepted for publication in Phys. Rev. B
Stabilizing intrinsic defects in SnO
TThe magnetism and electronic structure of Li-doped SnO are
investigated using first-principles LDA/LDA calculations. We find that Li
induces magnetism in SnO when doped at the Sn site but becomes
non-magnetic when doped at the O and interstitial sites. The calculated
formation energies show that Li prefers the Sn site as compared with the O
site, in agreement with previous experimental works. The interaction of Li with
native defects (Sn V and O V vacancies) is also
studied, and we find that Li not only behaves as a spin polarizer, but also a
vacancy stabilizer, i.e. Li significantly reduces the defect formation energies
of the native defects and helps the stabilization of magnetic oxygen vacancies.
The electronic densities of states reveals that these systems, where the Fermi
level touches the conduction (valence) band, are non-magnetic
(magnetic).cancies. The electronic densities of states reveal that those
systems, where the Fermi levels touch the conduction (valence) band, are
non-magnetic (magnetic).Comment: Phys. Rev. B (2013), Accepte
Design of a Segmentation and Classification System for Seed Detection Based on Pixel Intensity Thresholds and Convolutional Neural Networks
Due to the computational power and memory of modern computers, computer vision techniques and neural networks can be used to develop a visual inspection system of agricultural products to satisfy product quality requirements. This chapter employs artificial vision techniques to classify seeds in RGB images. As a first step, an algorithm based on pixel intensity threshold is developed to detect and classify a set of different seed types, such as rice, beans, and lentils. Then, the information inferred by this algorithm is exploited to develop a neural network model, which successfully achieves learning classification and detection tasks through a semantic-segmentation scheme. The applicability and satisfactory performance of the proposed algorithms are illustrated by testing with real images, achieving an average accuracy of 92% in the selected set of classes. The experimental results verify that both algorithms can directly detect and classify the proposed set of seeds in input RGB images. © 2023, The Author(s), under exclusive license to Springer Nature Switzerland AG
Detection of solar-like oscillations from Kepler photometry of the open cluster NGC 6819
Asteroseismology of stars in clusters has been a long-sought goal because the
assumption of a common age, distance and initial chemical composition allows
strong tests of the theory of stellar evolution. We report results from the
first 34 days of science data from the Kepler Mission for the open cluster NGC
6819 -- one of four clusters in the field of view. We obtain the first clear
detections of solar-like oscillations in the cluster red giants and are able to
measure the large frequency separation and the frequency of maximum oscillation
power. We find that the asteroseismic parameters allow us to test
cluster-membership of the stars, and even with the limited seismic data in
hand, we can already identify four possible non-members despite their having a
better than 80% membership probability from radial velocity measurements. We
are also able to determine the oscillation amplitudes for stars that span about
two orders of magnitude in luminosity and find good agreement with the
prediction that oscillation amplitudes scale as the luminosity to the power of
0.7. These early results demonstrate the unique potential of asteroseismology
of the stellar clusters observed by Kepler.Comment: 5 pages, 4 figures, accepted by ApJ (Lett.
Measurement of the cosmic ray spectrum above eV using inclined events detected with the Pierre Auger Observatory
A measurement of the cosmic-ray spectrum for energies exceeding
eV is presented, which is based on the analysis of showers
with zenith angles greater than detected with the Pierre Auger
Observatory between 1 January 2004 and 31 December 2013. The measured spectrum
confirms a flux suppression at the highest energies. Above
eV, the "ankle", the flux can be described by a power law with
index followed by
a smooth suppression region. For the energy () at which the
spectral flux has fallen to one-half of its extrapolated value in the absence
of suppression, we find
eV.Comment: Replaced with published version. Added journal reference and DO
Energy Estimation of Cosmic Rays with the Engineering Radio Array of the Pierre Auger Observatory
The Auger Engineering Radio Array (AERA) is part of the Pierre Auger
Observatory and is used to detect the radio emission of cosmic-ray air showers.
These observations are compared to the data of the surface detector stations of
the Observatory, which provide well-calibrated information on the cosmic-ray
energies and arrival directions. The response of the radio stations in the 30
to 80 MHz regime has been thoroughly calibrated to enable the reconstruction of
the incoming electric field. For the latter, the energy deposit per area is
determined from the radio pulses at each observer position and is interpolated
using a two-dimensional function that takes into account signal asymmetries due
to interference between the geomagnetic and charge-excess emission components.
The spatial integral over the signal distribution gives a direct measurement of
the energy transferred from the primary cosmic ray into radio emission in the
AERA frequency range. We measure 15.8 MeV of radiation energy for a 1 EeV air
shower arriving perpendicularly to the geomagnetic field. This radiation energy
-- corrected for geometrical effects -- is used as a cosmic-ray energy
estimator. Performing an absolute energy calibration against the
surface-detector information, we observe that this radio-energy estimator
scales quadratically with the cosmic-ray energy as expected for coherent
emission. We find an energy resolution of the radio reconstruction of 22% for
the data set and 17% for a high-quality subset containing only events with at
least five radio stations with signal.Comment: Replaced with published version. Added journal reference and DO
Measurement of the Radiation Energy in the Radio Signal of Extensive Air Showers as a Universal Estimator of Cosmic-Ray Energy
We measure the energy emitted by extensive air showers in the form of radio
emission in the frequency range from 30 to 80 MHz. Exploiting the accurate
energy scale of the Pierre Auger Observatory, we obtain a radiation energy of
15.8 \pm 0.7 (stat) \pm 6.7 (sys) MeV for cosmic rays with an energy of 1 EeV
arriving perpendicularly to a geomagnetic field of 0.24 G, scaling
quadratically with the cosmic-ray energy. A comparison with predictions from
state-of-the-art first-principle calculations shows agreement with our
measurement. The radiation energy provides direct access to the calorimetric
energy in the electromagnetic cascade of extensive air showers. Comparison with
our result thus allows the direct calibration of any cosmic-ray radio detector
against the well-established energy scale of the Pierre Auger Observatory.Comment: Replaced with published version. Added journal reference and DOI.
Supplemental material in the ancillary file
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