1,881 research outputs found
Formation of pure two-electron triplet states in weakly coupled quantum dots attached to ferromagnetic leads
Weakly coupled quantum dots in the Pauli spin blockade regime are considered
with respect to spin-dependent transport. By attaching one half-metallic and
one non-magnetic lead, the Pauli spin blockade if formed by a pure triplet
state with spin moment or -1. Furthermore, additional spin blockade
regimes emerge because of full occupation in states with opposite spin to that
of the half-metallic lead.Comment: 6 pages, 2 figures, 1 table, minor changes to appear as publishe
Detection of spin reversal and nutations through current measurements
The dynamics of a single spin embedded in a the tunnel junction between
ferromagnetic contacts is strongly affected by the exchange coupling to the
tunneling electrons. Moment reversal of the local spin induced by the bias
voltage across the junction is shown to have a measurable effect on the
tunneling current. Furthermore, the frequency of a harmonic bias voltage is
picked up by the local spin dynamics and transferred back to the current
generating a double frequency component.Comment: 5 pages, 5 figures; published version (with minor corrections
Detection of exchange interaction in STM measurements through Fanolike interference effects
We address Fano-like interference effects in scanning tunneling microscopy
(STM) measurements of nanoscale systems, e.g. two-level systems. Common for
these systems is that second order tunneling contributions give rise to
interference effects that cause suppressed transmission through the system for
certain energies. The suppressed transmission is measurable either in the
differential conductance or in the bias voltage derivative thereof.Comment: 9 pages, 3 figures, submitted: in addition to the results published
in Phys. Rev. B, 75, 153309 (2007), this paper contains a more thorough
discussion on the used transport formalism, studies of asymmetric couplings
to the substrate, and discussion of non-resonant levels. The non-resonant
case is related to spin-dependent tunnelin
Modeling the Radio and X-ray Emission of SN 1993J and SN 2002ap
Modeling of radio and X-ray observations of supernovae interacting with their
circumstellar media are discussed, with special application to SN 1993J and SN
2002ap. We emphasize the importance of including all relevant physical
mechanisms, especially for the modeling of the radio light curves. The
different conclusions for the absorption mechanism (free-free or synchrotron
self-absorption), as well as departures from an CSM, as
inferred by some authors, are discussed in detail. We conclude that the
evidence for a variation in the mass loss rate with time is very weak. The
results regarding the efficiencies of magnetic field generation and
relativistic particle acceleration are summarized.Comment: 10 pages, 2 figures. Uses svmult.cls. To appear in proceedings of IAU
Colloquium 192 "Supernovae (10 years of SN 1993J)", April 2003, Valencia,
Spain, eds. J. M. Marcaide and K. W. Weile
Lithiation of InSb and CuSb : A Theoretical Investigation
In this work the mechanism of Li insertion/intercalation in the anode
materials InSb and CuSb is investigated by means of the first principles
total energy calculations. The total charge densities for the lithiated
products of the two compounds are presented. Based on these results the change
in the bonding character on lithiation is discussed. Further, the isomer shift
for InSb and CuSb and there various lithiated products is reported. The
average insertion/intercalation voltage and volume expansion for transitions
from InSb to LiInSb and CuSb to LiCuSb are calculated and found to
be in good agreement with the experimental values. These findings help to
resolve the controversy regarding the lithiation mechanism in InSb.Comment: 5 pages 3 figure
X-ray emission from radiative shocks in Type II supernovae
The X-ray emission from the circumstellar interaction in Type II supernovae
with a dense circumstellar medium is calculated. In Type IIL and Type IIn
supernovae mass loss rates are generally high enough for the region behind the
reverse shock to be radiative, producing strong radiation, particularly in
X-rays. We present a model for the emission from the cooling region in the case
of a radiative reverse shock. Under the assumption of a stationary flow, a
hydrodynamic model is combined with time dependent ionization balance and
multilevel calculations. The applicability of the steady state approximation is
discussed for various values of the ejecta density gradient and different sets
of chemical composition. We show how the emerging spectrum depends strongly on
the reverse shock velocity and the composition of the shocked gas. We discuss
differences between a spectrum produced by this model and a single-temperature
spectrum. Large differences for especially the line emission are found, which
seriously can affect abundance estimates. We also illustrate the effects of
absorption in the cool shocked ejecta. The applicability of our model for
various types of supernovae is discussed.Comment: 25 pages, 15 figures, 4 tables. Accepted for publication in A&
Adaptive Optics Discovery of Supernova 2004ip in the Nuclear Regions of the Luminous Infrared Galaxy IRAS 18293-3413
We report a supernova discovery in Ks-band images from the NAOS CONICA
adaptive optics (AO) system on the ESO Very Large Telescope (VLT). The images
were obtained as part of a near-infrared search for highly-obscured supernovae
in the nuclear regions of luminous and ultraluminous infrared galaxies. SN
2004ip is located within a circumnuclear starburst at 1.4 arcsec (or 500 pc)
projected distance from the K-band nucleus of the luminous infrared galaxy IRAS
18293-3413. The supernova luminosity and light curve are consistent with a
core-collapse event suffering from a host galaxy extinction of up to about 40
magnitudes in V-band which is as expected for a circumnuclear starburst
environment. This is the first supernova to be discovered making use of AO
correction and demonstrates the potential of the current 8-meter class
telescopes equipped with AO in discovering supernovae from the innermost
nuclear regions of luminous and ultraluminous infrared galaxies.Comment: 4 pages, 3 figures, ApJ Letters (accepted
Circumstellar Emission from Type Ib and Ic Supernovae
The presumed Wolf-Rayet star progenitors of Type Ib/c supernovae have fast,
low density winds and the shock waves generated by the supernova interaction
with the wind are not expected to be radiative at typical times of observation.
The injected energy spectrum of radio emitting electrons typically has an
observed index p=3, which is suggestive of acceleration in cosmic ray dominated
shocks. The early, absorbed part of the radio light curves can be attributed to
synchrotron self-absorption, which leads to constraints on the magnetic field
in the emitting region and on the circumstellar density. The range of
circumstellar densities inferred from the radio emission is somewhat broader
than that for Galactic Wolf-Rayet stars, if similar efficiencies of synchrotron
emission are assumed in the extragalactic supernovae. For the observed and
expected ranges of circumstellar densities to roughly overlap, a high
efficiency of magnetic field production in the shocked region is required
(epsilon_B ~ 0.1). For the expected densities around a Wolf-Rayet star, a
nonthermal mechanism is generally required to explain the observed X-ray
luminosities of Type Ib/c supernovae. Although the inverse Compton mechanism
can explain the observed X-ray emission from SN 2002ap if the wind parameters
are taken from the radio model, the mechanism is not promising for other
supernovae unless the postshock magnetic energy density is much smaller than
the electron energy density. In some cases another mechanism is definitely
needed and we suggest that it is X-ray synchrotron emission in a case where the
shock wave is cosmic ray dominated so that the electron energy spectrum
flattens at high energy. More comprehensive X-ray observations of a Type Ib/c
supernova are needed to determine whether this suggestion is correct.Comment: 31 pages, 2 figures, ApJ, accepted, corrected typ
Job strain and the risk of stroke: an individual-participant data meta-analysis
Background and Purpose—Psychosocial stress at work has been proposed to be a risk factor for cardiovascular disease. However, its role as a risk factor for stroke is uncertain.
Methods—We conducted an individual-participant-data meta-analysis of 196 380 males and females from 14 European cohort studies to investigate the association between job strain, a measure of work-related stress, and incident stroke.
Results—In 1.8 million person-years at risk (mean follow-up 9.2 years), 2023 first-time stroke events were recorded. The age- and sex-adjusted hazard ratio for job strain relative to no job strain was 1.24 (95% confidence interval, 1.05;1.47) for ischemic stroke, 1.01 (95% confidence interval, 0.75;1.36) for hemorrhagic stroke, and 1.09 (95% confidence interval, 0.94;1.26) for overall stroke. The association with ischemic stroke was robust to further adjustment for socioeconomic status.
Conclusion—Job strain may be associated with an increased risk of ischemic stroke, but further research is needed to determine whether interventions targeting job strain would reduce stroke risk beyond existing preventive strategies
Near-infrared evolution of the equatorial ring of SN 1987A
We use adaptive-optics imaging and integral field spectroscopy from the Very
Large Telescope, together with images from the \emph{Hubble Space Telescope},
to study the near-infrared (NIR) evolution of the equatorial ring (ER) of
SN~1987A. We study the NIR line and continuum flux and morphology over time in
order to lay the groundwork for \emph{James Webb Space Telescope} observations
of the system. We also study the differences in the interacting ring structure
and flux between optical, NIR and other wavelengths, and between line and
continuum emission, to constrain the underlying physical processes. Mostly the
evolution is similar in the NIR and optical. The morphology of the ER has been
skewed toward the west side (with roughly 2/3 of the NIR emission originating
there) since around 2010. A steady decline in the ER flux, broadly similar to
the MIR and the optical, is ongoing since roughly this time as well. The
expansion velocity of the ER hotspots in the NIR is fully consistent with the
optical. However, continuum emission forms roughly 70 per cent of the NIR
luminosity, and is relatively stronger outside the hotspot-defined extent of
the ER than the optical emission or NIR line emission since 2012--2013,
suggesting a faster-expanding continuum component. We find that this outer NIR
emission can have a significant synchrotron contribution. Even if emission from
hot (2000~K) dust is dominant within the ER, the mass of this dust must
be vanishingly small (a few ~M) compared to the total
dust mass in the ER (~M) to account for the observed
flux. The NIR continuum emission, however, expands slower than the more
diffuse 180-K dust emission that dominates in the MIR, indicating a different
source, and the same hot dust component cannot account for the -band
emission.Comment: 17 pages, 17 figures. Accepted for publication in Astronomy &
Astrophysic
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