4,372 research outputs found
Chiral nature of magnetic monopoles in artificial spin ice
Micromagnetic properties of monopoles in artificial kagome spin ice systems
are investigated using numerical simulations. We show that micromagnetics
brings additional complexity into the physics of these monopoles that is, by
essence, absent in spin models: besides a fractionalized classical magnetic
charge, monopoles in the artificial kagome ice are chiral at remanence. Our
simulations predict that the chirality of these monopoles can be controlled
without altering their charge state. This chirality breaks the vertex symmetry
and triggers a directional motion of the monopole under an applied magnetic
field. Our results also show that the choice of the geometrical features of the
lattice can be used to turn on and off this chirality, thus allowing the
investigation of chiral and achiral monopoles.Comment: 10 pages, 4 figure
Wide range and tunable linear TMR sensor using two exchange pinned electrodes
A magnetic tunnel junction sensor is proposed, with both the detection and
the reference layers pinned by IrMn. Using the differences in the blocking
temperatures of the IrMn films with different thicknesses, crossed anisotropies
can be induced between the detection and the reference electrodes. The pinning
of the sensing electrode ensures a linear and reversible output. It also allows
tuning both the sensitivity and the linear range of the sensor. The authors
show that the sensitivity varies linearly with the ferromagnetic thickness of
the detection electrode. It is demonstrated that an increased thickness leads
to a rise of sensitivity and a reduction of the operating range
Unveiling the near-infrared structure of the massive-young stellar object NGC 3603 IRS 9A with sparse aperture masking and spectroastrometry
Contemporary theory holds that massive stars gather mass during their initial
phases via accreting disk-like structures. However, conclusive evidence for
disks has remained elusive for the most massive young objects. This is mainly
due to significant observational challenges. Incisive studies, even targeting
individual objects, are therefore relevant to the progression of the field. NGC
3603 IRS 9A* is a young massive stellar object still surrounded by an envelope
of molecular gas. Previous mid-infrared observations with long-baseline
interferometry provided evidence for a disk of 50 mas diameter at its core.
This work aims at a comprehensive study of the physics and morphology of IRS 9A
at near-infrared wavelengths. New sparse aperture masking interferometry data
taken with NACO/VLT at Ks and Lp filters were obtained and analysed together
with archival CRIRES spectra of the H2 and BrG lines. The calibrated
visibilities recorded at Ks and Lp bands suggest the presence of a partially
resolved compact object of 30 mas at the core of IRS 9A, together with the
presence of over-resolved flux. The spectroastrometric signal of the H2 line
shows that this spectral feature proceeds from the large scale extended
emission (300 mas) of IRS 9A, while the BrG line appears to be formed at the
core of the object (20 mas). This scenario is consistent with the brightness
distribution of the source for near- and mid-infrared wavelengths at various
spatial scales. However, our model suffers from remaining inconsistencies
between SED modelling and the interferometric data. Moreover, the BrG
spectroastrometric signal indicates that the core of IRS 9A exhibits some form
of complexity such as asymmetries in the disk. Future high-resolution
observations are required to confirm the disk/envelope model and to flesh out
the details of the physical form of the inner regions of IRS 9A.Comment: Accepted to be published in Astronomy & Astrophysics, 13 pages, 14
figure
beta Pic b position relative to the Debris Disk
Context. We detected in 2009 a giant, close-by planet orbiting {\beta} Pic, a
young star surrounded with a disk, extensively studied for more than 20 years.
We showed that if located on an inclined orbit, the planet could explain
several peculiarities of {\beta} Pictoris system. However, the available data
did not permit to measure the inclination of {\beta} Pic b with respect to the
disk, and in particular to establish in which component of the disk - the main,
extended disk or the inner inclined component/disk-, the planet was located.
Comparison between the observed planet position and the disk orientation
measured on previous imaging data was not an option because of potential biases
in the measurements. Aims. Our aim is to measure precisely the planet location
with respect to the dust disk using a single high resolution image, and
correcting for systematics or errors that degrades the precision of the disk
and planet relative position measurements. Methods. We gathered new NaCo data
at Ks band, with a set-up optimized to derive simultaneously the orientation(s)
of the disk(s) and that of the planet. Results. We show that the projected
position of {\beta} Pic b is above the midplane of the main disk. With the
current data and knowledge on the system, this implies that {\beta} Pic b
cannot be located in the main disk. The data rather suggest the planet being
located in the inclined component.Comment: 13 pages, 6 figures, to appear in Astronomy and Astrophysic
Effects of exposure to hypoxia on the signal-averaged electrocardiogram in healthy subjects
The effects of hypoxia on the signal-averaged ECG (SAECG) were investigated in 26 healthy active subjects with no suggestion of cardiac disease. The SAECG was recorded in each resting subject in normoxic and hypoxic normobaric conditions (inspired O2 fraction 20.7 vs 10.0%) which lowered resting arterial O2 saturation from 98.6 +0.6% to 77.7 ± 8%. Recordings from four subjects (three men) met the definition of abnormal late potentials at baseline; in all these subjects but one, who exhibited an improved but still abnormal QRS duration, these parameters returned to normal in hypoxic conditions. The duration of the filtered QRS was significantly reduced (from 107.6 ±13.2 to 101.6 ± 11.3 ms, P<001), the duration of the low amplitude signals in the terminal portion of the QRS <40 Ό V (LAS) significantly decreased (from 26.5 ± 9.5 to 22.7 ± 7.9 ms, P<005) and the root mean square voltage in the last 40 ms (Term-RMS) increased non-significantly (from 55.8±40.2 to 69.1±38.3 ΌV, P=0.058). Hypoxia determined a higher (P<0.05) heart rate increase in subjects with abnormal records than in normal subjects. These data could be related to a sympathic discharge. They suggest that: (1) variation in heart rate could affect the SAECG; (2) exposure to hypoxia improves SAECG parameters in healthy subjects, possibly related to sympathetic discharge; (3) abnormal records collected during sinus bradycardia could represent a type of false-positive expression of late potentials in young active adult
The interferometric baselines and GRAVITY astrometric error budget
GRAVITY is a new generation beam combination instrument for the VLTI. Its
goal is to achieve microarsecond astrometric accuracy between objects separated
by a few arcsec. This accuracy on astrometric measurements is the most
important challenge of the instrument, and careful error budget have been
paramount during the technical design of the instrument. In this poster, we
will focus on baselines induced errors, which is part of a larger error budget.Comment: SPIE Meeting 2014 -- Montrea
Importance of the Saharan heat low in controlling the North Atlantic free tropospheric humidity budget deduced from IASI <i>ÎŽ</i>D observations
The isotopic composition of water vapour in the North Atlantic free
troposphere is investigated with Infrared Atmospheric Sounding Interferometer
(IASI) measurements of the DâŻââŻH ratio (ÎŽD) above the ocean. We
show that in the vicinity of West Africa, the seasonality of ÎŽD is
particularly strong (130âŻâ°), which is related with the influence of
the Saharan heat low (SHL) during summertime. The SHL indeed largely
influences the dynamic in that region by producing deep turbulent mixing
layers, yielding a specific water vapour isotopic footprint. The influence of
the SHL on the isotopic budget is analysed on various time and space scales
and is shown to be large, highlighting the importance of the SHL dynamics on
the moistening and the HDO enrichment of the free troposphere over the North
Atlantic. The potential influence of the SHL is also investigated on the
inter-annual scale as we also report important variations in ÎŽD above
the Canary archipelago region. We interpret the variability in the
enrichment, using backward trajectory analyses, in terms of the ratio of air
masses coming from the North Atlantic and air masses coming from the African
continent. Finally, the interest of IASI high sampling capabilities is
further illustrated by presenting spatial distributions of ÎŽD and
humidity above the North Atlantic from which we show that the different
sources and dehydration pathways controlling the humidity can be disentangled
thanks to the added value of ÎŽD observations. More generally, our
results demonstrate the utility of ÎŽD observations obtained from the
IASI sounder to gain insight into the hydrological cycle processes in the
West African region
The near-infrared spectral energy distribution of {\beta} Pictoris b
A gas giant planet has previously been directly seen orbiting at 8-10 AU
within the debris disk of the ~12 Myr old star {\beta} Pictoris. The {\beta}
Pictoris system offers the rare opportunity to study the physical and
atmospheric properties of an exoplanet placed on a wide orbit and to establish
its formation scenario. We obtained J (1.265 {\mu}m), H (1.66 {\mu}m), and M'
(4.78 {\mu}m) band angular differential imaging of the system between 2011 and
2012. We detect the planetary companion in our four-epoch observations. We
estimate J = 14.0 +- 0.3, H = 13.5 +- 0.2, and M' = 11.0 +- 0.3 mag. Our new
astrometry consolidates previous semi-major axis (sma=8-10 AU) and excentricity
(e <= 0.15) estimates of the planet. These constraints, and those derived from
radial velocities of the star provides independent upper limits on the mass of
{\beta} Pictoris b of 12 and 15.5 MJup for semi-major axis of 9 and 10 AU. The
location of {\beta} Pictoris b in color-magnitude diagrams suggests it has
spectroscopic properties similar to L0-L4 dwarfs. This enables to derive
Log10(L/Lsun) = -3.87 +- 0.08 for the companion. The analysis with 7
PHOENIX-based atmospheric models reveals the planet has a dusty atmosphere with
Teff = 1700 +- 100 K and log g = 4.0+- 0.5. "Hot-start" evolutionary models
give a new mass of 10+3-2 MJup from Teff and 9+3-2 MJup from luminosity.
Predictions of "cold-start" models are inconsistent with independent
constraints on the planet mass. "Warm-start" models constrain the mass to M >=
6MJup and the initial entropies to values (Sinit >= 9.3Kb/baryon), intermediate
between those considered for cold/hot-start models, but likely closer to those
of hot-start models.Comment: 19 pages, accepted in Astronomy and Astrophysic
Starlight Demonstration of the Dragonfly Instrument: an Integrated Photonic Pupil Remapping Interferometer for High Contrast Imaging
In the two decades since the first extra-solar planet was discovered, the
detection and characterization of extra-solar planets has become one of the key
endeavors in all of modern science. Recently direct detection techniques such
as interferometry or coronography have received growing attention because they
reveal the population of exoplanets inaccessible to Doppler or transit
techniques, and moreover they allow the faint signal from the planet itself to
be investigated. Next-generation stellar interferometers are increasingly
incorporating photonic technologies due to the increase in fidelity of the data
generated. Here, we report the design, construction and commissioning of a new
high contrast imager; the integrated pupil-remapping interferometer; an
instrument we expect will find application in the detection of young faint
companions in the nearest star-forming regions. The laboratory characterisation
of the instrument demonstrated high visibility fringes on all interferometer
baselines in addition to stable closure phase signals. We also report the first
successful on-sky experiments with the prototype instrument at the 3.9-m
Anglo-Australian Telescope. Performance metrics recovered were consistent with
ideal device behaviour after accounting for expected levels of decoherence and
signal loss from the uncompensated seeing. The prospect of complete
Fourier-coverage coupled with the current performance metrics means that this
photonically-enhanced instrument is well positioned to contribute to the
science of high contrast companions.Comment: 10 pages, 7 figures, accepted to Mon. Not. of Roy. Ast. Soc., 201
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