475 research outputs found
A low optical depth region in the inner disk of the HerbigAe star HR5999
Circumstellar disks surrounding young stars are known to be the birthplaces
of planets, and the innermost astronomical unit is of particular interest. We
present new long-baseline spectro-interferometric observations of the HerbigAe
star, HR5999, obtained in the H and K bands with the AMBER instrument at the
VLTI, and aim to produce near-infrared images at the sub-AU spatial scale. We
spatially resolve the circumstellar material and reconstruct images using the
MiRA algorithm. In addition, we interpret the interferometric observations
using models that assume that the near-infrared excess is dominated by the
emission of a circumstellar disk. We compare the images reconstructed from the
VLTI measurements to images obtained using simulated model data. The K-band
image reveals three main elements: a ring-like feature located at ~0.65 AU, a
low surface brightness region inside, and a central spot. At the maximum
angular resolution of our observations (1.3 mas), the ring is resolved while
the central spot is only marginally resolved, preventing us from revealing the
exact morphology of the circumstellar environment. We suggest that the ring
traces silicate condensation, i.e., an opacity change, in a circumstellar disk
around HR 5999. We build a model that includes a ring at the silicate
sublimation radius and an inner disk of low surface brightness responsible for
a large amount of the near-infrared continuum emission. The model successfully
fits the SED, visibilities, and closure phases, and provides evidence of a low
surface brightness region inside the silicate sublimation radius. This study
provides additional evidence that in HerbigAe stars, there is material in a low
surface brightness region, probably a low optical depth region, located inside
the silicate sublimation radius and of unknown nature.Comment: 11 pages, 10 figure
The spatial location of laser-driven, forward-propagating waves in a National-Ignition-Facility-relevant plasma
Ion acoustic and electron plasma waves, associated with backward-propagating stimulated Brillouin scattering and stimulated Raman scattering, have been diagnosed in a long-scale-length, nearly homogenous plasma with transverse flow. Thomson scattered light from a probe beam is employed to show that these waves are well localized in space and for a time much shorter than the laser pulse duration. These plasma conditions are relevant to hohlraum design for the National Ignition Facility inertial confinement fusion laser system. [R. Sawicki et al., Fusion Technol. 34, 1097 (1998)]. © 2000 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/71338/2/PHPAEN-7-1-323-1.pd
Revisiting the chemistry of apple pomace polyphenols
Hot water is an easily implementable process for polyphenols extraction. To evaluate the effect of this process on apple pomace, the overall polyphenolic composition was assessed before and after hot water extraction, followed by extractions with aqueous/organic solutions. As determined by UHPLC-DAD, flavan-3-ols were the main apple native polyphenols. Their amount decreased 50% after hot water extraction, while the other classes remained unchanged. Dihydrochalcones and hydroxycinnamic acid oxidation products, were also observed, alongside with non-extractable oxidised procyanidins that represented more than 4-fold the amount of native apple polyphenols in the pomace. Microwave superheated-water extraction of the insoluble cell wall material in water/acetone solutions and the high amounts of polyphenols that were insoluble in water/ethanol solutions suggested that oxidised procyanidins could be covalently linked to polysaccharides. These complexes represented up to 40% of the available polyphenols from apple pomace, potentially relevant for agro-food waste valuation.publishe
The STAR Silicon Strip Detector (SSD)
The STAR Silicon Strip Detector (SSD) completes the three layers of the
Silicon Vertex Tracker (SVT) to make an inner tracking system located inside
the Time Projection Chamber (TPC). This additional fourth layer provides two
dimensional hit position and energy loss measurements for charged particles,
improving the extrapolation of TPC tracks through SVT hits. To match the high
multiplicity of central Au+Au collisions at RHIC the double sided silicon strip
technology was chosen which makes the SSD a half million channels detector.
Dedicated electronics have been designed for both readout and control. Also a
novel technique of bonding, the Tape Automated Bonding (TAB), was used to
fullfill the large number of bounds to be done. All aspects of the SSD are
shortly described here and test performances of produced detection modules as
well as simulated results on hit reconstruction are given.Comment: 11 pages, 8 figures, 1 tabl
Design and synthesis of imidazoline derivatives active on glucose homeostasis in a rat model of type II diabetes.2. Syntheses and biological activities of 1,4-dialkyl-,1,4-dibenzyl and 1-benzyl-4-alkyl-2-(4',5'-dihydro-1' H-imidazol-2'yl)piperazines and isosteric analogues of imidazoline
International audienc
Pre-maximum spectro-imaging of the Mira star T Lep with AMBER/VLTI
Diffuse envelopes around Mira variables are among the most important sources
influencing the chemical evolution of galaxies. However they represent an
observational challenge because of their complex spectral features and their
rapid temporal variability. We constrained the exact brightness distribution of
the Mira star TLep with a model-independent analysis. We obtained single-epoch
interferometric observations with a dataset continuous in the spectral domain
(1.5-2.4mum) and in the spatial domain (baselines ranging from 11 to 96m). We
performed a model independent image reconstruction for each spectral bin using
the MIRA software. We completed the analysis by modeling the data with a simple
star+layer model inspired from the images. Reconstructed images confirm the
general picture of a central star partially obscured by the surrounding
molecular shell of changing opacity. At 1.7mum, the shell becomes optically
thin, with corresponding emission appearing as a ring circling the star. This
is the first direct evidence of the spherical morphology of the molecular
shell. Model fitting confirmed a spherical layer of constant size and changing
opacity over the wavelengths. Rough modeling points to a continuum opacity
within the shell, in addition to the CO and H2O features. Accordingly, it
appeared impossible to model the data by a photosphere alone in any of the
spectral bins.Comment: Accepted in A&
Hole doping and disorder effects on the one-dimensional Kondo lattice, for ferromagnetic Kondo couplings
We investigate the one-dimensional Kondo lattice model (1D KLM) for
ferromagnetic Kondo couplings. The so-called ferromagnetic 2-leg spin ladder
and the S=1 antiferromagnet occur as new one-dimensional Kondo insulators. Both
exhibit a spin gap. But, in contrast to the strong coupling limit, the Haldane
state which characterizes the 2-leg spin ladder Kondo insulator cannot fight
against very weak exterior perturbations. First, by using standard bosonization
techniques, we prove that an antiferromagnetic ground state occurs by doping
with few holes; it is characterized by a form factor of the spin-spin
correlation functions which exhibits two structures respectively at and
. Second, we prove precisely by using renormalization group methods
that the Anderson-localization inevitably takes place in that weak-coupling
Haldane system, by the introduction of quenched randomness; the spin-fixed
point rather corresponds to a ``glass'' state. Finally, a weak-coupling
``analogue'' of the S=1 antiferromagnet Kondo insulator is proposed; we show
that the transition into the Anderson-localization state may be avoided in that
unusual weak-coupling Haldane system.Comment: 22 pages, TEX and 2 figures (long version); to be published in Phys.
Rev. B (December 97
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