319 research outputs found
The structure of disks around intermediate-mass young stars from mid-infrared interferometry. Evidence for a population of group II disks with gaps
The disks around Herbig Ae/Be stars are commonly divided into group I and
group II based on their far-infrared spectral energy distribution, and the
common interpretation for that is flared and flat disks. Recent observations
suggest that many flaring disks have gaps, whereas flat disks are thought to be
gapless. The different groups of objects can be expected to have different
structural signatures in high-angular-resolution data. Over the past 10 years,
the MIDI instrument on the Very Large Telescope Interferometer has collected
observations of several tens of protoplanetary disks. We model the large set of
observations with simple geometric models. A population of radiative-transfer
models is synthesized for interpreting the mid-infrared signatures. Objects
with similar luminosities show very different disk sizes in the mid-infrared.
Restricting to the young objects of intermediate mass, we confirm that most
group I disks are in agreement with being transitional. We find that several
group II objects have mid-infrared sizes and colors overlapping with sources
classified as group I, transition disks. This suggests that these sources have
gaps, which has been demonstrated for a subset of them. This may point to an
intermediate population between gapless and transition disks. Flat disks with
gaps are most likely descendants of flat disks without gaps. Gaps, potentially
related to the formation of massive bodies, may therefore even develop in disks
in a far stage of grain growth and settling. The evolutionary implications of
this new population could be twofold. Either gapped flat disks form a separate
population of evolved disks, or some of them may further evolve into flaring
disks with large gaps. The latter transformation may be governed by the
interaction with a massive planet, carving a large gap and dynamically exciting
the grain population in the disk.Comment: 24 pages, 11 figures, A&A in pres
The evolved circumbinary disk of AC Her: a radiative transfer, interferometric and mineralogical study
We aim to constrain the structure of the circumstellar material around the
post-AGB binary and RV Tauri pulsator AC Her. We want to constrain the spatial
distribution of the amorphous as well as of the crystalline dust. We present
very high-quality mid-IR interferometric data that were obtained with
MIDI/VLTI. We analyse the MIDI data and the full SED, using the MCMax radiative
transfer code, to find a good structure model of AC Her's circumbinary disk. We
include a grain size distribution and midplane settling of dust
self-consistently. The spatial distribution of crystalline forsterite in the
disk is investigated with the mid-IR features, the 69~m band and the
11.3~m signatures in the interferometric data. All the data are well
fitted. The inclination and position angle of the disk are well determined at
i=50+-8 and PA=305+-10. We firmly establish that the inner disk radius is about
an order of magnitude larger than the dust sublimation radius. Significant
grain growth has occurred, with mm-sized grains being settled to the midplane
of the disk. A large dust mass is needed to fit the sub-mm fluxes. By assuming
{\alpha}=0.01, a good fit is obtained with a small grain size power law index
of 3.25, combined with a small gas/dust ratio <10. The resulting gas mass is
compatible with recent estimates employing direct gas diagnostics. The spatial
distribution of the forsterite is different from the amorphous dust, as more
warm forsterite is needed in the surface layers of the inner disk. The disk in
AC Her is very evolved, with its small gas/dust ratio and large inner hole.
Mid-IR interferometry offers unique constraints, complementary to mid-IR
features, for studying the mineralogy in disks. A better uv coverage is needed
to constrain in detail the distribution of the crystalline forsterite in AC
Her, but we find strong similarities with the protoplanetary disk HD100546.Comment: update with final version published in A&
Preoperative portal vein embolization with a combination of trisacryl microspheres, gelfoam and coils
AbstractPurposeTo evaluate the safety and efficiency of preoperative portal vein embolization (PVE) with a combination of trisacryl microspheres, gelfoam and coils for inducing lobar hypertrophy in hepatobiliary malignancy patients.Materials and methodsPVE was performed by a percutaneous left approach in 63 patients with hepatic malignancy (hepatocarcinoma=38, colorectal metastasis=14, cholangiocarcinoma=11). The indication of PVE and surgery was evaluated by hepatic tumor board take into consideration to the tumor extension and the hepatic volume on initial and post-embolization CT-scans. The total functional liver volume (TELV) and future liver remnant (FLR) volume were measured before and 24±5days after PVE to assess FLR, TELV and FLR/TELV ratios. Efficiency evaluation was based on FLR increase, the ability to perform the hepatectomy and the hepatic function after surgery. Safety evaluation was determined by clinical and biological follow-up after embolization and surgery.ResultsPVE was successful in all the patients. The mean FLR volume increases by 57±56% after embolization (449±180cm3 to 663±254cm3) (P<0.0001). The FLR/TELV ratio increases by 11% after PVE (25±8% to 36±12%). Three minors’ complications were registered without impact on surgery, and four patients developed portal hypertension. Forty-nine patients underwent hepatectomy; none of them developed liver failure. Surgery was not performed in 14 patients due to tumor progression (n=9), inadequate hypertrophy of FLR (n=1) and portal hypertension (n=4).ConclusionPreoperative PVE with a combination of trisacryl microspheres, gelfoam and coils is a safe and effective method for inducing contralateral hypertrophy before right hepatectomy in patients with advanced hepatobiliary malignancy
A mid-IR interferometric survey with MIDI/VLTI: resolving the second-generation protoplanetary disks around post-AGB binaries
We present a mid-IR interferometric survey of the circumstellar environment
of a specific class of post-Asymptotic Giant Branch (post-AGB) binaries. For
this class the presence of a compact dusty disk has been postulated on the
basis of various spatially unresolved measurements. Our interferometric survey
was performed with the MIDI instrument on the VLTI. In total 19 different
systems were observed using variable baseline configurations. Combining all the
visibilities at a single wavelength at 10.7 micron, we fitted two parametric
models to the data: a uniform disk (UD) and a ring model mimicking a
temperature gradient. We compared our observables of the whole sample, with
synthetic data computed from a grid of radiative transfer models of passively
irradiated disks in hydrostatic equilibrium. These models are computed with a
Monte Carlo code that has been widely applied to describe the structure of
protoplanetary disks around young stellar objects (YSO). The spatially resolved
observations show that the majority of our targets cluster closely together in
the distance-independent size-colour diagram, and have extremely compact N-band
emission regions. The typical uniform disk diameter of the N-band emission
region is about 40 mass which corresponds to a typical brightness temperature
of 400-600~K. The resolved objects display very similar characteristics in the
interferometric observables and in the spectral energy distributions.
Therefore, the physical properties of the disks around our targets must be
similar. The grid of protoplanetary disk models covers very well the observed
objects. Much like for young stars, the spatially resolved N-band emission
region is determined by the hot inner rim of the disk. Continued comparisons
between post-AGB and protoplanetary disks will help to understand grain growth
and disk evolution processes,Comment: 30 pages, 21 figures, in press in Astronomy and Astrophysic
N-Nitrosodimethylamine Formation from Treatment of Seasonally and Spatially Varying Source Water
N-nitrosodimethylamine (NDMA) is a disinfection by-product (DBP) that has been classified as a probable human carcinogen in multiple risk assessments. NDMA presence in drinking water is widespread and dependent on source water, disinfectant type, precursors, and water treatment strategies. The objectives of this study were to investigate NDMA formation potential in a modeled monochloramine water treatment plant (WTP) fed by seasonally and spatially varying source water; and to optimize DBP precursor removal by combining conventional and additional treatment techniques. After NDMA analysis, it was found that NDMA formation was significantly dependent on source water type and monochloramine contact time (CT); e.g., at 24 h CT, Cork Brook produced 12.2 ng/L NDMA and Bailey Brook produced 4.2 ng/L NDMA, compared with 72 h CT, Cork Brook produced 4.1 ng/L NDMA and Bailey Brook produced 3.4 ng/L NDMA. No correlations were found between traditional DBP precursors such as total organic carbon and total nitrogen, and the formation of NDMA. The laboratory bench-top treatment system was highly effective at removing traditional DBP precursors, highlighting the need for WTPs to alter their current treatment methods to best accommodate the complex system of DBP control
Transition Metal Diazoalkane Complexes. Synthesis, Structure, and Photochemistry of Rh[C(N_2)SiMe_3](PEt_3)_3
Reaction of RhCl(PR_3)_n (R = Me (n = 4), Et (n = 3)) and RhCl(CO)(PEt_3)_2 with (trimethylsilyl)diazomethyl lithium at −78 °C in ether yields the three complexes Rh[C(N_2)SiMe_3](PEt_3)_3 (1), Rh[C(N_2)SiMe_3](PMe_3)_4 (2), and Rh[C(N_2)SiMe_3](CO)(PEt_3)_2 (3). 2 could not be isolated as a solid at room temperature but 1 was precipitated as red crystals that were stable enough to be handled under argon. X-ray work on 1 reveals a tetrahedrally distorted square-planar geometry with the planar (trimethylsilyl)diazomethyl ligand roughly perpendicular to the P3RhC coordination plane. This distortion makes the PEt3 ligands nonequivalent in the crystal and produces an ABB‘X pattern in the solid-state ^(31)P NMR spectrum. Photolysis of Rh[C(N_2)SiMe_3](PEt_3)_3 leads quantitatively to the dimer [Rh{C(SiMe_3)(PEt_3)}(PEt_3)_2]_2 (4). The presence of the two ylide bridges and terminal phosphines is deduced from the COSY ^(31)P−^(31)P NMR spectrum. This photochemical reactivity suggests that the transient carbene (PEt_3)_3RhC̈(SiMe_3) is electrophilic, which is typical of a singlet carbene. We believe the singlet state is stabilized by the presence of the electron-rich low-spin Rh(PEt3)3 fragment. Reaction with ^nBuNC and ^tBuNC leads to stereo- and regioselective formation of a triazole that is σ bonded to the rhodium center. The X-ray structure of the ^tBuNC derivative Rh[CC(SiMe_3)N_2N^tBu](^tBuNC)_2(PEt_3) (5) shows a distorted square-planar geometry around Rh with the planar triazolato ligand roughly orthogonal to this plane. The probable reaction mechanism involves addition and substitution reactions of isocyanides at Rh followed by insertion into the Rh−C bond
Antitumour and antiangiogenic effects of Aplidin® in the 5TMM syngeneic models of multiple myeloma
Aplidin® is an antitumour drug, currently undergoing phase II evaluation in different haematological and solid tumours. In this study, we analysed the antimyeloma effects of Aplidin in the syngeneic 5T33MM model, which is representable for the human disease. In vitro, Aplidin inhibited 5T33MMvv DNA synthesis with an IC50 of 3.87 nM. On cell-cycle progression, the drug induced an arrest in transition from G0/G1 to S phase, while Western blot showed a decreased cyclin D1 and CDK4 expression. Furthermore, Aplidin induced apoptosis by lowering the mitochondrial membrane potential, by inducing cytochrome c release and by activating caspase-9 and caspase-3. For the in vivo experiment, 5T33MM-injected C57Bl/KaLwRij mice were intraperitoneally treated with vehicle or Aplidin (90 μg kg−1 daily). Chronic treatment with Aplidin was well tolerated and reduced serum paraprotein concentration by 42% (P<0.001), while BM invasion with myeloma cells was decreased by 35% (P<0.001). Aplidin also reduced the myeloma-associated angiogenesis to basal values. This antiangiogenic effect was confirmed in vitro and explained by inhibition of endothelial cell proliferation and vessel formation. These data indicate that Aplidin is well tolerated in vivo and its antitumour and antiangiogenic effects support the use of the drug in multiple myeloma
The orbits of subdwarf B + main-sequence binaries. I: The sdB+G0 system PG 1104+243
The predicted orbital period histogram of an sdB population is bimodal with a
peak at short ( 250 days) periods. Observationally, there
are many short-period sdB systems known, but only very few long-period sdB
binaries are identified. As these predictions are based on poorly understood
binary interaction processes, it is of prime importance to confront the
predictions to observational data. In this contribution we aim to determine the
absolute dimensions of the long-period sdB+MS binary system PG1104+243.
High-resolution spectroscopy time-series were obtained with HERMES at the
Mercator telescope at La Palma, and analyzed to obtain radial velocities of
both components. Photometry from the literature was used to construct the
spectral energy distribution (SED) of the binary. Atmosphere models were used
to fit this SED and determine the surface gravity and temperature of both
components. The gravitational redshift provided an independent confirmation of
the surface gravity of the sdB component. An orbital period of 753 +- 3 d and a
mass ratio of q = 0.637 +- 0.015 were found from the RV-curves. The sdB
component has an effective temperature of Teff = 33500 +- 1200 K and a surface
gravity of logg = 5.84 +- 0.08 dex, while the cool companion is found to be a
G-type star with Teff = 5930 +- 160 K and logg = 4.29 +- 0.05 dex. Assuming a
canonical mass of Msdb = 0.47 Msun, the MS component has a mass of 0.74 +- 0.07
Msun, and its Teff corresponds to what is expected for a terminal age
main-sequence star with sub-solar metalicity. PG1104+243 is the first
long-period sdB binary in which accurate physical parameters of both components
could be determined, and the first sdB binary in which the gravitational
redshift is measured. Furthermore, PG1104+243 is the first sdB+MS system that
shows consistent evidence for being formed through stable Roche-lobe overflow.Comment: Accepted by A&A on 05-10-201
On the structure of the transition disk around TW Hya
For over a decade, the structure of the inner cavity in the transition disk
of TW Hydrae has been a subject of debate. Modeling the disk with data obtained
at different wavelengths has led to a variety of proposed disk structures.
Rather than being inconsistent, the individual models might point to the
different faces of physical processes going on in disks, such as dust growth
and planet formation. Our aim is to investigate the structure of the transition
disk again and to find to what extent we can reconcile apparent model
differences. A large set of high-angular-resolution data was collected from
near-infrared to centimeter wavelengths. We investigated the existing disk
models and established a new self-consistent radiative-transfer model. A
genetic fitting algorithm was used to automatize the parameter fitting. Simple
disk models with a vertical inner rim and a radially homogeneous dust
composition from small to large grains cannot reproduce the combined data set.
Two modifications are applied to this simple disk model: (1) the inner rim is
smoothed by exponentially decreasing the surface density in the inner ~3 AU,
and (2) the largest grains (>100 um) are concentrated towards the inner disk
region. Both properties can be linked to fundamental processes that determine
the evolution of protoplanetary disks: the shaping by a possible companion and
the different regimes of dust-grain growth, respectively. The full
interferometric data set from near-infrared to centimeter wavelengths requires
a revision of existing models for the TW Hya disk. We present a new model that
incorporates the characteristic structures of previous models but deviates in
two key aspects: it does not have a sharp edge at 4 AU, and the surface density
of large grains differs from that of smaller grains. This is the first
successful radiative-transfer-based model for a full set of interferometric
data.Comment: 22 pages, 12 figures, accepted for publication in Astronomy &
Astrophysic
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