295 research outputs found
ALMA CO J=6-5 observations of IRAS16293-2422: Shocks and entrainment
Observations of higher-excited transitions of abundant molecules such as CO
are important for determining where energy in the form of shocks is fed back
into the parental envelope of forming stars. The nearby prototypical and
protobinary low-mass hot core, IRAS16293-2422 (I16293) is ideal for such a
study. The source was targeted with ALMA for science verification purposes in
band 9, which includes CO J=6-5 (E_up/k_B ~ 116 K), at an unprecedented spatial
resolution (~0.2", 25 AU). I16293 itself is composed of two sources, A and B,
with a projected distance of 5". CO J=6-5 emission is detected throughout the
region, particularly in small, arcsecond-sized hotspots, where the outflow
interacts with the envelope. The observations only recover a fraction of the
emission in the line wings when compared to data from single-dish telescopes,
with a higher fraction of emission recovered at higher velocities. The very
high angular resolution of these new data reveal that a bow shock from source A
coincides, in the plane of the sky, with the position of source B. Source B, on
the other hand, does not show current outflow activity. In this region, outflow
entrainment takes place over large spatial scales, >~ 100 AU, and in small
discrete knots. This unique dataset shows that the combination of a
high-temperature tracer (e.g., CO J=6-5) and very high angular resolution
observations is crucial for interpreting the structure of the warm inner
environment of low-mass protostars.Comment: Accepted for publication in A&A Letter
Magnetic excitations in the metallic single-layer Ruthenates Ca(2-x)Sr(x)RuO(4) studied by inelastic neutron scattering
By inelastic neutron scattering, we have analyzed the magnetic correlations
in the paramagnetic metallic region of the series Ca(2-x)Sr(x)RuO(4),
0.2<=x<=0.62. We find different contributions that correspond to 2D
ferromagnetic fluctuations and to fluctuations at incommensurate wave vectors
(0.11,0,0), (0.26,0,0) and (0.3,0.3,0). These components constitute the
measured response as function of the Sr-concentration x, of the magnetic field
and of the temperature. A generic model is applicable to metallic
Ca(2-x)Sr(x)RuO(4) close to the Mott transition, in spite of their strongly
varying physical properties. The amplitude, characteristic energy and width of
the incommensurate components vary only little as function of x, but the
ferromagnetic component depends sensitively on concentration, temperature and
magnetic field. While ferromagnetic fluctuations are very strong in
Ca1.38Sr0.62RuO4 with a low characteristic energy of 0.2 meV at T=1.5 K, they
are strongly suppressed in Ca1.8Sr0.2RuO4, but reappear upon the application of
a magnetic field and form a magnon mode above the metamagnetic transition. The
inelastic neutron scattering results document how the competition between
ferromagnetic and incommensurate antiferromagnetic instabilities governs the
physics of this system
Kinetics of the Multiferroic Switching in MnWO
The time dependence of switching multiferroic domains in MnWO has been
studied by time-resolved polarized neutron diffraction. Inverting an external
electric field inverts the chiral magnetic component within rise times ranging
between a few and some tens of milliseconds in perfect agreement with
macroscopic techniques. There is no evidence for any faster process in the
inversion of the chiral magnetic structure. The time dependence is well
described by a temperature-dependent rise time suggesting a well-defined
process of domain reversion. As expected, the rise times decrease when heating
towards the upper boundary of the ferroelectric phase. However, switching also
becomes faster upon cooling towards the lower boundary, which is associated
with a first-order phase transition
The Earliest Phases of Star formation (EPoS): Temperature, density, and kinematic structure of the star-forming core CB 17
Context: The initial conditions for the gravitational collapse of molecular
cloud cores and the subsequent birth of stars are still not well constrained.
The characteristic cold temperatures (about 10 K) in such regions require
observations at sub-millimetre and longer wavelengths. The Herschel Space
Observatory and complementary ground-based observations presented in this paper
have the unprecedented potential to reveal the structure and kinematics of a
prototypical core region at the onset of stellar birth.
Aims: This paper aims to determine the density, temperature, and velocity
structure of the star-forming Bok globule CB 17. This isolated region is known
to host (at least) two sources at different evolutionary stages: a dense core,
SMM1, and a Class I protostar, IRS.
Methods: We modeled the cold dust emission maps from 100 micron to 1.2 mm
with both a modified blackbody technique to determine the optical
depth-weighted line-of-sight temperature and column density and a ray-tracing
technique to determine the core temperature and volume density structure.
Furthermore, we analysed the kinematics of CB17 using the high-density gas
tracer N2H+.
Results: From the ray-tracing analysis, we find a temperature in the centre
of SMM1 of 10.6 K, a flat density profile with radius 9500 au, and a central
volume density of n(H) = 2.3x10^5 cm-3. The velocity structure of the N2H+
observations reveal global rotation with a velocity gradient of 4.3 km/s/pc.
Superposed on this rotation signature we find a more complex velocity field,
which may be indicative of differential motions within the dense core.
Conclusions: SMM is a core in an early evolutionary stage at the verge of
being bound, but the question of whether it is a starless or a protostellar
core remains unanswered.Comment: published in A&
Field-induced paramagnons at the metamagnetic transition in Ca1.8Sr0.2RuO4
The magnetic excitations in Ca1.8Sr0.2RuO4 were studied across the
metamagnetic transition and as a function of temperature using inelastic
neutron scattering. At low temperature and low magnetic field the magnetic
response is dominated by a complex superposition of incommensurate
antiferromagnetic fluctuations. Upon increasing the magnetic field across the
metamagnetic ransition, paramagnon and finally well-defined magnon scattering
is induced, partially suppressing the incommensurate signals. The high-field
phase in Ca1.8Sr0.2RuO4 has, therefore, to be considered as an intrinsically
ferromagnetic state stabilized by the magnetic field
Equine recurrent uveitis - A spontaneous horse model of uveitis
Equine recurrent uveitis (ERU) is an autoimmune disease that occurs with a high prevalence (10%) in horses. ERU represents the only reliable spontaneous model for human autoimmune uveitis. We already identified and characterized novel autoantigens (malate dehydrogenase, recoverin, CRALBP) by analyzing the autoantibody-binding pattern of horses affected by spontaneous recurrent uveitis (ERU) to the retinal proteome. CRALBP also seems to be relevant to human autoimmune uveitis. Proteomic screening of vitreous and retinal samples from ERU diseased cases in comparison to healthy controls has led to the identification of a series of differentially regulated proteins, which are functionally linked to the immune system and the maintenance of the blood-retinal barrier. Copyright (c) 2008 S. Karger AG, Basel
Gas-phase CO depletion and N2H+ abundances in starless cores
Seven isolated, nearby low-mass starless molecular cloud cores have been
observed as part of the Herschel key program Earliest Phases of Star formation
(EPoS). By applying a ray-tracing technique to the obtained continuum emission
and complementary (sub)mm emission maps, we derive the physical structure
(density, dust temperature) of these cloud cores. We present observations of
the 12CO, 13CO, and C18O (2-1) and N2H+ (1-0) transitions towards the same
cores. Based on the density and temperature profiles, we apply time-dependent
chemical and line-radiative transfer modeling and compare the modeled to the
observed molecular emission profiles. CO is frozen onto the grains in the
center of all cores in our sample. The level of CO depletion increases with
hydrogen density and ranges from 46% up to more than 95% in the core centers in
the core centers in the three cores with the highest hydrogen density. The
average hydrogen density at which 50% of CO is frozen onto the grains is
1.1+-0.4 10^5 cm^-3. At about this density, the cores typically have the
highest relative abundance of N2H+. The cores with higher central densities
show depletion of N2H+ at levels of 13% to 55%. The chemical ages for the
individual species are on average 2+-1 10^5 yr for 13CO, 6+-3 10^4 yr for C18O,
and 9+-2 10^4 yr for N2H+. Chemical modeling indirectly suggests that the gas
and dust temperatures decouple in the envelopes and that the dust grains are
not yet significantly coagulated. We observationally confirm chemical models of
CO-freezeout and nitrogen chemistry. We find clear correlations between the
hydrogen density and CO depletion and the emergence of N2H+. The chemical ages
indicate a core lifetime of less than 1 Myr.Comment: 24 pages, 25 figures, Accepted for publication in Astronomy and
Astrophysic
ALMA observations of the molecular gas in the debris disk of the 30 Myr old star HD 21997
The 30 Myr old A3-type star HD 21997 is one of the two known debris dust
disks having a measurable amount of cold molecular gas. With the goal of
understanding the physical state, origin, and evolution of the gas in young
debris disks, we obtained CO line observations with the Atacama Large
Millimeter/submillimeter Array (ALMA). Here we report on the detection of 12CO
and 13CO in the J=2-1 and J=3-2 transitions and C18O in the J=2-1 line. The gas
exhibits a Keplerian velocity curve, one of the few direct measurements of
Keplerian rotation in young debris disks. The measured CO brightness
distribution could be reproduced by a simple star+disk system, whose parameters
are r_in < 26 AU, r_out = 138 +/- 20 AU, M_*=1.8 +0.5 -0.2 M_Sun, and i = 32.6
+/- 3.1 degrees. The total CO mass, as calculated from the optically thin C18O
line, is about (4-8) x 10^-2 M_Earth, while the CO line ratios suggest a
radiation temperature on the order of 6-9 K. Comparing our results with those
obtained for the dust component of the HD 21997 disk from the ALMA continuum
observations by Mo\'or et al., we conclude that comparable amounts of CO gas
and dust are present in the disk. Interestingly, the gas and dust in the HD
21997 system are not co-located, indicating a dust-free inner gas disk within
55 AU of the star. We explore two possible scenarios for the origin of the gas.
A secondary origin, which involves gas production from colliding or active
planetesimals, would require unreasonably high gas production rates and would
not explain why the gas and dust are not co-located. We propose that HD 21997
is a hybrid system where secondary debris dust and primordial gas coexist. HD
21997, whose age exceeds both the model predictions for disk clearing and the
ages of the oldest T Tauri-like or transitional gas disks in the literature,
may be a key object linking the primordial and the debris phases of disk
evolution.Comment: 8 pages, 4 figures, accepted for publication in Ap
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Neural correlates of the rubber hand illusion in amputees: a report of two cases
One of the current challenges in the field of advanced prosthetics is the development of artificial limbs that provide
the user with detailed sensory feedback. Sensory feedback from our limbs is not only important for proprioceptive
awareness and motor control, but also essential for providing us with a feeling of ownership or simply put, the
sensation that our limbs actually belong to ourselves. The strong link between sensory feedback and ownership
has been repeatedly demonstrated with the so-called rubber hand illusion (RHI), during which individuals are
induced with the illusory sensation that an artificial hand is their own. In healthy participants, this occurs via
integration of visual and tactile signals, which is primarily supported by multisensory regions in premotor and
intraparietal cortices. Here, we describe a functional magnetic resonance imaging (fMRI) study with two upper
limb amputees, showing for the first time that the same brain regions underlie ownership sensations of an artificial
hand in this population. Albeit preliminary, these findings are interesting from both a theoretical as well as a clinical
point of view. From a theoretical perspective, they imply that even years after the amputation, a few seconds of
synchronous visuotactile stimulation are sufficient to activate hand-centered multisensory integration mechanisms.
From a clinical perspective, they show that a very basic sensation of touch from an artificial hand can be obtained
by simple but precisely targeted stimulation of the stump, and suggest that a similar mechanism implemented in
prosthetic hands would greatly facilitate ownership sensations and in turn, acceptance of the prosthesis
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