37,024 research outputs found
Coral symbiodinium community composition across the Belize Mesoamerican barrier reef system is influenced by host species and thermal variability
Accepted manuscrip
Frustration Driven Stripe Domain Formation in Co/Pt Multilayer Films
We report microscopic mechanisms for an unusual magnetization reversal
behavior in Co/Pt multilayers where some of the first-order reversal curves
protrude outside of the major loop. Transmission x-ray microscopy reveals a
fragmented stripe domain topography when the magnetic field is reversed prior
to saturation, in contrast to an interconnected pattern when reversing from a
saturated state. The different domain nucleation and propagation behaviors are
due to unannihilated domains from the prior field sweep. These residual domains
contribute to random dipole fields that impede the subsequent domain growth and
prevent domains from growing as closely together as for the interconnected
pattern.Comment: 13 pages, 3 figures, to appear in AP
The detection of FIR emission from high redshift star-forming galaxies in the ECDF-S
ABRIDGED: We have used the LABOCA Survey of the ECDF-S (LESS) to investigate
rest-frame FIR emission from typical SF systems (LBGs) at redshift 3, 4, and 5.
We initially concentrate on LBGs at z~3 and select three subsamples on stellar
mass, extinction corrected SF and rest-frame UV-magnitude. We produce composite
870micron images of the typical source in our subsamples, obtaining ~4sigma
detections and suggesting a correlation between FIR luminosity and stellar
mass. We apply a similar procedure to our full samples at z~3, 4, 4.5 and 5 and
do not obtain detections - consistent with a simple scaling between FIR
luminosity and stellar mass. In order to constrain the FIR SED of these systems
we explore their emission at multiple wavelengths spanning the peak of dust
emission at z~3 using the Herschel SPIRE observations of the field. We obtain
detections at multiple wavelengths for both our stellar mass and UV-magnitude
selected samples, and find a best-fit SED with T_dust in the ~33-41K range. We
calculate L_FIR, obscured SFRs and M_dust, and find that a significant fraction
of SF in these systems is obscured. Interestingly, our extinction corrected SFR
sample does not display the large FIR fluxes predicted from its red UV-spectral
slope. This suggests that the method of assuming an intrinsic UV-slope and
correcting for dust attenuation may be invalid for this sample - and that these
are not in fact the most actively SF systems. All of our z~3 samples fall on
the `main sequence' of SF galaxies at z~3 and our detected subsamples are
likely to represent the high obscuration end of LBGs at their epoch. We compare
the FIR properties of our subsamples with various other populations, finding
that our stellar mass selected sample shows similar FIR characteristics to SMGs
at the same epoch and therefore potentially represents the low L_FIR end of the
high redshift FIR luminosity function.Comment: 18 pages, 10 figure, MNRAS accepted, corrected typos,
acknowledgements adde
Development and acceptability of a co-produced online intervention to prevent alcohol misuse in adolescents: A think aloud study
Background: The prototype willingness model (PWM) may offer an appropriate basis for explaining and preventing adolescent alcohol misuse. An intervention was developed using a co-production approach, and consisted of an online quiz featuring 10 questions linked to the PWM.
Objective: This study sought to determine the acceptability and relevance of the intervention content to young people, to incorporate their feedback into a final version.
Methods: A qualitative think aloud study with follow-up semistructured interviews was undertaken with 16 young people aged 11-15 (50%). Transcripts were analyzed using thematic analysis.
Results: The following 3 main themes relating the acceptability of the intervention were identified: “challenging expectations of alcohol education”; “motivations for drinking or not drinking,” and “the inevitability of drinking.” Participants found the intervention appealing because it was counter to their expectations. The content appeared to reflect their experiences of social pressure and drinking encounters. There was evidence that a focus on drinker/nondrinker prototypes was too narrow and that because adolescents perceived drinking as inevitable, it would be challenging to enact any plans to resist pressure to drink.
Conclusions: An online intervention based on the PWM has the potential to engage and interest adolescents. A wide range of alcohol prototypes should be targeted and a focus on short-term harms should ensure that the intervention is credible to young people
Time-of-arrival probabilities and quantum measurements: II Application to tunneling times
We formulate quantum tunneling as a time-of-arrival problem: we determine the
detection probability for particles passing through a barrier at a detector
located a distance L from the tunneling region. For this purpose, we use a
Positive-Operator-Valued-Measure (POVM) for the time-of-arrival determined in
quant-ph/0509020 [JMP 47, 122106 (2006)]. This only depends on the initial
state, the Hamiltonian and the location of the detector. The POVM above
provides a well-defined probability density and an unambiguous interpretation
of all quantities involved. We demonstrate that for a class of localized
initial states, the detection probability allows for an identification of
tunneling time with the classic phase time. We also establish limits to the
definability of tunneling time.
We then generalize these results to a sequential measurement set-up: the
phase space properties of the particles are determined by an unsharp sampling
before their attempt to cross the barrier. For such measurements the tunneling
time is defined as a genuine observable. This allows us to construct a
probability distribution for its values that is definable for all initial
states and potentials. We also identify a regime, in which these probabilities
correspond to a tunneling-time operator.Comment: 26 pages--revised version, small changes, to appear in J. Math. Phy
Reionization history constraints from neural network based predictions of high-redshift quasar continua
Observations of the early Universe suggest that reionization was complete by
, however, the exact history of this process is still unknown. One
method for measuring the evolution of the neutral fraction throughout this
epoch is via observing the Ly damping wings of high-redshift quasars.
In order to constrain the neutral fraction from quasar observations, one needs
an accurate model of the quasar spectrum around Ly, after the spectrum
has been processed by its host galaxy but before it is altered by absorption
and damping in the intervening IGM. In this paper, we present a novel machine
learning approach, using artificial neural networks, to reconstruct quasar
continua around Ly. Our QSANNdRA algorithm improves the error in this
reconstruction compared to the state-of-the-art PCA-based model in the
literature by 14.2% on average, and provides an improvement of 6.1% on average
when compared to an extension thereof. In comparison with the extended PCA
model, QSANNdRA further achieves an improvement of 22.1% and 16.8% when
evaluated on low-redshift quasars most similar to the two high-redshift quasars
under consideration, ULAS J1120+0641 at and ULAS J1342+0928 at
, respectively. Using our more accurate reconstructions of these two
quasars, we estimate the neutral fraction of the IGM using a homogeneous
reionization model and find at
and at . Our
results are consistent with the literature and favour a rapid end to
reionization
Near-infrared integral field spectroscopy of Massive Young Stellar Objects
We present medium resolution () -band integral field
spectroscopy of six MYSOs. The targets are selected from the RMS survey, and we
used the NIFS on the Gemini North telescope. The data show various spectral
line features including Br, CO, H, and \mbox{He\,{\sc i}}. The
Br line is detected in emission in all objects with
-- 200 kms. V645 Cyg shows a high-velocity
P-Cygni profile between -800 kms and -300 kms. We performed
three-dimensional spectroastrometry to diagnose the circumstellar environment
in the vicinity of the central stars using the Br line. We measured the
centroids of the velocity components with sub-mas precision. The centroids
allow us to discriminate the blueshifted and redshifted components in a roughly
east--west direction in both IRAS 18151--1208 and S106 in Br. This lies
almost perpendicular to observed larger scale outflows. We conclude, given the
widths of the lines and the orientation of the spectroastrometric signature,
that our results trace a disc wind in both IRAS 18151--1208 and S106. The CO
absorption lines at low transitions are detected in IRAS
18151--1208 and AFGL 2136. We analysed the velocity structure of the neutral
gas discs. In IRAS 18151--1208, the absorption centroids of the blueshifted and
redshifted components are separated in a direction of north-east to south-west,
nearly perpendicular to that of the larger scale jet. The
position-velocity relations of these objects can be reproduced with central
masses of 30 M_{\sun} for IRAS 18151--1208 and 20 M_{\sun} for AFGL 2136.
We also detect CO bandhead emission in IRAS 18151--1208, S106 and
V645 Cyg. The results can be fitted reasonably with a Keplerian rotation model,
with masses of 15, 20 and 20 M_{\sun} respectively.Comment: 17 pages, 10 figures, accepted by MNRA
The origin of the red luminescence in Mg-doped GaN
Optically-detected magnetic resonance (ODMR) and positron annihilation
spectroscopy (PAS) experiments have been employed to study magnesium-doped GaN
layers grown by metal-organic vapor phase epitaxy. As the Mg doping level is
changed, the combined experiments reveal a strong correlation between the
vacancy concentrations and the intensity of the red photoluminescence band at
1.8 eV. The analysis provides strong evidence that the emission is due to
recombination in which electrons both from effective mass donors and from
deeper donors recombine with deep centers, the deep centers being
vacancy-related defects.Comment: 4 pages, 3 figure
Concept study for a high-efficiency nanowire-based thermoelectric
Materials capable of highly efficient, direct thermal-to-electric energy
conversion would have substantial economic potential. Theory predicts that
thermoelectric efficiencies approaching the Carnot limit can be achieved at low
temperatures in one-dimensional conductors that contain an energy filter such
as a double-barrier resonant tunneling structure. The recent advances in growth
techniques suggest that such devices can now be realized in heterostructured,
semiconductor nanowires. Here we propose specific structural parameters for
InAs/InP nanowires that may allow the experimental observation of near-Carnot
efficient thermoelectric energy conversion in a single nanowire at low
temperature
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