272 research outputs found
Proper motions and velocity asymmetries in the RW Aur jet
We present adaptive optics spectro-imaging observations of the RW Aur jet in
optical forbidden lines, at an angular resolution of 0.4 arcsec. Comparison
with HST data taken 2 years later shows that proper motions in the blueshifted
and redshifted lobes are in the same ratio as their radial velocities, a direct
proof that the velocity asymmetry in this jet is real and not an emissivity
effect. The inferred jet inclination to the line of sight is i = 46 +/- 3
degrees. The inner knot spacing appears best explained by time variability with
at least two modes: one irregular and asymmetric (possibly random) on
timescales of <3-10 yr, and another more regular with ~ 20 yr period. We also
report indirect evidence for correlated velocity and excitation gradients in
the redshifted lobe, possibly related to the blue/red velocity and brightness
asymmetry in this system.Comment: 4 pags, 3 figure
Tomographic reconstruction of the three-dimensional structure of the HH30 jet
The physical parameters of Herbig-Haro jets are usually determined from
emission line ratios, obtained from spectroscopy or narrow band imaging,
assuming that the emitting region is homogeneous along the line of sight. Under
the more general hypothesis of axisymmetry, we apply tomographic reconstruction
techniques to the analysis of Herbig-Haro jets. We use data of the HH30 jet
taken by Hartigan & Morse (2007) with the Hubble space telescope using the
slitless spectroscopy technique. Using a non-parametric Tikhonov regularization
technique, we determine the volumetric emission line intensities of the
[SII]6716,6731, [OI]6300 and [NII]6583 forbidden emission lines. From our
tomographic analysis of the corresponding line ratios, we produce
"three-dimensional" images of the physical parameters. The reconstructed
density, temperature and ionization fraction present much steeper profiles than
those inferred using the assumption of homogeneity. Our technique reveals that
the reconstructed jet is much more collimated than the observed one close to
the source (a width ~ 5 AU vs. ~ 20 AU at a distance of 10 AU from the star),
while they have similar widths at larger distances. In addition, our results
show a much more fragmented and irregular jet structure than the classical
analysis, suggesting that the the ejection history of the jet from the
star-disk system has a shorter timescale component (~ some months) superimposed
on a longer, previously observed timescale (of a few years). Finally, we
discuss the possible application of the same technique to other stellar jets
and planetary nebulae.Comment: 13 pages, 9 figures, accepted by Ap
Formation of Flavanol-aldehyde Adducts in Barrel-aged White Wine – Possible Contribution of These Products to Colour
This paper describes the formation and diversity of new compounds resulting from the polymerisation of furanic andphenolic flavanol-aldehydes with HPLC‑DAD and LC‑ES/MS analysis. Polymerisation, resulting from nucleophilicreactions, formed dimers, trimers, soluble and insoluble polymers. Reactions in hydroalcoholic solution with purealdehydes (phenolic and furanic) and flavanols (catechin) were studied. The study was repeated with differentaldehydes in white wine. This research focused particularly on the colour properties of the released products and theirpotential impact on the colour of white wine. Some products were purified and isolated; these were mainly catechinfurfuraldehyde,catechin-methyl-5-furfuraldehyde, catechin-hydroxymethyl-furfuraldehyde,catechin-vanillin, andcatechin-syringaldehyde dimers. The most powerful coloured products resulted from furanic aldehydes. Over thecourse of the experiment, the reaction produced dimers, trimers and oligomers. After 50 to 60 days, the colour of thesolution was mainly due to soluble polymeric forms. In addition, the role of SO2, generally used during vinificationand ageing, was studied. The influence of SO2 on the kinetics of the reaction was limited
Formation of Flavanol-aldehyde Adducts in Barrel-aged White Wine - Possible Contribution of These Products to Colour
[EN] This paper describes the formation and diversity of new compounds resulting from the polymerisation of furanic and
phenolic flavanol-aldehydes with HPLCÂżDAD and LCÂżES/MS analysis. Polymerisation, resulting from nucleophilic
reactions, formed dimers, trimers, soluble and insoluble polymers. Reactions in hydroalcoholic solution with pure
aldehydes (phenolic and furanic) and flavanols (catechin) were studied. The study was repeated with different
aldehydes in white wine. This research focused particularly on the colour properties of the released products and their
potential impact on the colour of white wine. Some products were purified and isolated; these were mainly catechinfurfuraldehyde,
catechin-methyl-5-furfuraldehyde, catechin-hydroxymethyl-furfuraldehyde, catechin-vanillin, and
catechin-syringaldehyde dimers. The most powerful coloured products resulted from furanic aldehydes. Over the
course of the experiment, the reaction produced dimers, trimers and oligomers. After 50 to 60 days, the colour of the
solution was mainly due to soluble polymeric forms. In addition, the role of SO2
, generally used during vinification
and ageing, was studied. The influence of SO2 on the kinetics of the reaction was limited.Vivas, N.; Nonier, MFB.; Absalon, C.; Lizama Abad, V.; Jamet, F.; De Gaulejac, NV.; Vitry, C.... (2008). Formation of Flavanol-aldehyde Adducts in Barrel-aged White Wine - Possible Contribution of These Products to Colour. South African journal of enology and viticulture. 29(2):98-108. http://hdl.handle.net/10251/105310S9810829
Emission lines from rotating proto-stellar jets with variable velocity profiles. I. Three-dimensional numerical simulation of the non-magnetic case
Using the Yguazu-a three-dimensional hydrodynamic code, we have computed a
set of numerical simulations of heavy, supersonic, radiatively cooling jets
including variabilities in both the ejection direction (precession) and the jet
velocity (intermittence). In order to investigate the effects of jet rotation
on the shape of the line profiles, we also introduce an initial toroidal
rotation velocity profile, in agreement with some recent observational evidence
found in jets from T Tauri stars which seems to support the presence of a
rotation velocity pattern inside the jet beam, near the jet production region.
Since the Yguazu-a code includes an atomic/ionic network, we are able to
compute the emission coefficients for several emission lines, and we generate
line profiles for the H, [O I]6300, [S II]6716 and [N II]6548 lines. Using
initial parameters that are suitable for the DG Tau microjet, we show that the
computed radial velocity shift for the medium-velocity component of the line
profile as a function of distance from the jet axis is strikingly similar for
rotating and non-rotating jet models. These findings lead us to put forward
some caveats on the interpretation of the observed radial velocity distribution
from a few outflows from young stellar objects, and we claim that these data
should not be directly used as a doubtless confirmation of the
magnetocentrifugal wind acceleration models.Comment: 15 pages, 8 figures. Accepted to publication in Astronomy and
Astrophysic
Three-Dimensional Simulations of Jets from Keplerian Disks: Self--Regulatory Stability
We present the extension of previous two-dimensional simulations of the
time-dependent evolution of non-relativistic outflows from the surface of
Keplerian accretion disks, to three dimensions. The accretion disk itself is
taken to provide a set of fixed boundary conditions for the problem. The 3-D
results are consistent with the theory of steady, axisymmetric, centrifugally
driven disk winds up to the Alfv\'en surface of the outflow. Beyond the
Alfv\'en surface however, the jet in 3-D becomes unstable to non-axisymmetric,
Kelvin-Helmholtz instabilities. We show that jets maintain their long-term
stability through a self-limiting process wherein the average Alfv\'enic Mach
number within the jet is maintained to order unity. This is accomplished in at
least two ways. First, poloidal magnetic field is concentrated along the
central axis of the jet forming a ``backbone'' in which the Alfv\'en speed is
sufficiently high to reduce the average jet Alfv\'enic Mach number to unity.
Second, the onset of higher order Kelvin-Helmholtz ``flute'' modes (m \ge 2)
reduce the efficiency with which the jet material is accelerated, and transfer
kinetic energy of the outflow into the stretched, poloidal field lines of the
distorted jet. This too has the effect of increasing the Alfv\'en speed, and
thus reducing the Alfv\'enic Mach number. The jet is able to survive the onset
of the more destructive m=1 mode in this way. Our simulations also show that
jets can acquire corkscrew, or wobbling types of geometries in this relatively
stable end-state, depending on the nature of the perturbations upon them.
Finally, we suggest that jets go into alternating periods of low and high
activity as the disappearance of unstable modes in the sub-Alfv\'enic regime
enables another cycle of acceleration to super-Alfv\'enic speeds.Comment: 57 pages, 22 figures, submitted to Ap
Gemini Observations of Disks and Jets in Young Stellar Objects and in Active Galaxies
We present first results from the Near-infrared Integral Field Spectrograph
(NIFS) located at Gemini North. For the active galaxies Cygnus A and Perseus A
we observe rotationally-supported accretion disks and adduce the existence of
massive central black holes and estimate their masses. In Cygnus A we also see
remarkable high-excitation ionization cones dominated by photoionization from
the central engine. In the T-Tauri stars HV Tau C and DG Tau we see
highly-collimated bipolar outflows in the [Fe II] 1.644 micron line, surrounded
by a slower molecular bipolar outflow seen in the H_2 lines, in accordance with
the model advocated by Pyo et al. (2002).Comment: Invited paper presented at the 5th Stromlo Symposium. 9 pages, 7
figures. Accepted for publication in Astrophysics & Space Scienc
Nonradial and nonpolytropic astrophysical outflows IX. Modeling T Tauri jets with a low mass-accretion rate
Context: A large sample of T Tauri stars exhibits optical jets, approximately
half of which rotate slowly, only at ten per cent of their breakup velocity.
The disk-locking mechanism has been shown to be inefficient to explain this
observational fact.
Aims: We show that low mass accreting T Tauri stars may have a strong stellar
jet component that can effectively brake the star to the observed rotation
speed.
Methods: By means of a nonlinear separation of the variables in the full set
of the MHD equations we construct semi- analytical solutions describing the
dynamics and topology of the stellar component of the jet that emerges from the
corona of the star.
Results: We analyze two typical solutions with the same mass loss rate but
different magnetic lever arms and jet radii. The first solution with a long
lever arm and a wide jet radius effectively brakes the star and can be applied
to the visible jets of T Tauri stars, such as RY Tau. The second solution with
a shorter lever arm and a very narrow jet radius may explain why similar stars,
either Weak line T Tauri Stars (WTTS) or Classical T Tauri Stars (CTTS) do not
all have visible jets. For instance, RY Tau itself seems to have different
phases that probably depend on the activity of the star.
Conclusions: First, stellar jets seem to be able to brake pre-main sequence
stars with a low mass accreting rate. Second, jets may be visible only part
time owing to changes in their boundary conditions. We also suggest a possible
scenario for explaining the dichotomy between CTTS and WTTS, which rotate
faster and do not have visible jets
Risk factors for upper-extremity musculoskeletal disorders in the working population.
OBJECTIVE: To assess the relative importance of personal and occupational risk factors for upper-extremity musculoskeletal disorders in the working population.
METHODS: A total of 3,710 workers (58% men) participating in a surveillance program of musculoskeletal disorders in a French region in 2002-2005 were included. Upper-extremity musculoskeletal disorders were diagnosed by 83 trained occupational physicians performing a standardized physical examination. Personal factors and work exposure were assessed by a self-administered questionnaire. Statistical associations between musculoskeletal disorders, personal, and occupational factors were analyzed using logistic regression modeling.
RESULTS: A total of 472 workers experienced at least 1 upper-extremity musculoskeletal disorder. The risk of upper-extremity musculoskeletal disorders increased with age for both sexes (P < 0.001, odds ratio [OR] < or =4.9 in men and < or =5.0 in women), and in cases of prior history of upper-extremity musculoskeletal disorders (OR 3.1 and 5.0, respectively, P < 0.001). In men, upper-extremity musculoskeletal disorders were associated with obesity (OR 2.2, P = 0.014), high level of physical demand (OR 2.0, P < 0.001), high repetitiveness of the task (OR 1.5, P = 0.027), postures with the arms at or above shoulder level (OR 1.7, P = 0.009) or with full elbow flexion (OR 1.6, P = 0.006), and high psychological demand (OR 1.5, P = 0.005). In women, upper-extremity musculoskeletal disorders were associated with diabetes mellitus (OR 4.9, P = 0.001), postures with extreme wrist bending (OR 2.0, P < 0.001), use of vibrating hand tools (OR 2.2, P = 0.025), and low level of decision authority (OR 1.4, P = 0.042).
CONCLUSION: Personal and work-related physical and psychosocial factors were strongly associated with clinically diagnosed upper-extremity musculoskeletal disorders
- …