417 research outputs found
Spectral properties of the largest asteroids associated with Taurid Complex
We obtained spectra of six of the largest asteroids (2201, 4183, 4486, 5143,
6063, and 269690) associated with Taurid complex. The observations were made
with the IRTF telescope equipped with the spectro-imager SpeX. Their taxonomic
classification is made using Bus-DeMeo taxonomy. The asteroid spectra are
compared with the meteorite spectra from the Relab database. Mineralogical
models were applied to determine their surface composition. All the spectral
analysis is made in the context of the already published physical data.
Five of the objects studied in this paper present spectral characteristics
similar to the S taxonomic complex. The spectra of ordinary chondrites
(spanning H, L, and LL subtypes) are the best matches for these asteroid
spectra. {\bf The asteroid} (269690) 1996 RG3 presents a flat featureless
spectrum which could be associated to a primitive C-type object. The increased
reflectance above 2.1 microns constrains its geometrical albedo to a value
around 0.03.
While there is an important dynamical grouping among the Taurid Complex
asteroids, the spectral data of the largest objects do not support a common
cometary origin. Furthermore, there are significant variations between the
spectra acquired until now.Comment: Accepted for publication in A&
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Charged polymers transport under applied electric fields in periodic channels
By molecular dynamics simulations, we investigated the transport of charged polymers in applied electric fields in confining environments, which were straight cylinders of uniform or non-uniform diameter. In the simulations, the solvent was modeled explicitly and, also, the counterions and coions of added salt. The electrophoretic velocities of charged chains in relation to electrolyte friction, hydrodynamic effects due to the solvent, and surface friction were calculated. We found that the velocities were higher if counterions were moved away from the polymeric domain, which led to a decrease in hydrodynamic friction. The topology of the surface played a key role in retarding the motion of the polyelectrolyte and, even more so, in the presence of transverse electric fields. The present study showed that a possible way of improving separation resolution is by controlling the motion of counterions or electrolyte friction effects
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Charge inversion effects in electrophoresis of polyelectrolytes in the presence of multivalent counterions and transversal electric fields
By molecular dynamics simulations we investigate the transport of charged polymers in confinement, under externally applied electric fields, in straight cylinders of uniform diameter and in the presence of monovalent or multivalent counterions. The applied electric field has two components; a longitudinal component along the axis of the cylinder and a transversal component perpendicular to the cylinder axis. The direction of electrophoretic velocity depends on the polyelectrolyte length, valency of the counterions present in solution and transversal electric field value. A statistical model is put forward in order to explain these observations
Aortic injuries following stents in bariatric surgery: our experience
Background: Due to the large number of laparoscopic sleeve gastrectomy (LSG) performed over the last decade, the management of the leak following LSG has been increasingly reported. The role of covered Self Expandable Metal Stents (cSEMS) for the treatment of the leak is still controversial because of the poor tolerance and high risk of complications. Objectives: The aim of the present study was to analyze the foregut wall perforation and aorta injuries, a very rare but potentially fatal complication, related to the treatment of the leak following LSG using cSEMS. Setting: Private hospital, France. Methods: An audit was conducted in 2 French tertiary bariatric endoscopic centers focusing on aortic injuries after cSEMS use for leak. We examined and classified the initial procedure, leak characteristics, primary endoscopic treatment, and outcome of endoscopic complication for each eligible case. Results: A total of 5 patients were identified with foregut wall perforation and aorta injuries. All stents were deployed for staple line leak following LSG. The recorded mortality in case of esophageal-aortic injuries related to cSEMS use was 80%. Conclusion: cSEMS are potentially effective tools for the management of foregut leaks in bariatric surgery. The biggest challenges with this approach are stent migration and poor quality of life. Caution is required due to the risk of fatal complications such as foregut wall perforation and aortic injury
Near-infrared colors of minor planets recovered from VISTA - VHS survey (MOVIS)
The Sloan Digital Sky Survey (SDSS) and Wide-field Infrared Survey Explorer
(WISE) provide information about the surface composition of about 100,000 minor
planets. The resulting visible colors and albedos enabled us to group them in
several major classes, which are a simplified view of the diversity shown by
the few existing spectra. We performed a serendipitous search in VISTA-VHS
observations using a pipeline developed to retrieve and process the data that
corresponds to solar system objects (SSo). The colors and the magnitudes of the
minor planets observed by the VISTA survey are compiled into three catalogs
that are available online: the detections catalog (MOVIS-D), the magnitudes
catalog (MOVIS-M), and the colors catalog (MOVIS-C). They were built using the
third data release of the survey (VISTA VHS-DR3). A total of 39,947 objects
were detected, including 52 NEAs, 325 Mars Crossers, 515 Hungaria asteroids,
38,428 main-belt asteroids, 146 Cybele asteroids, 147 Hilda asteroids, 270
Trojans, 13 comets, 12 Kuiper Belt objects and Neptune with its four
satellites. The colors found for asteroids with known spectral properties
reveal well-defined patterns corresponding to different mineralogies. The
distributions of MOVIS-C data in color-color plots shows clusters identified
with different taxonomic types. All the diagrams that use (Y-J) color separate
the spectral classes more effectively than the (J-H) and (H-Ks) plots used
until now: even for large color errors (<0.1), the plots (Y-J) vs (Y-Ks) and
(Y-J) vs (J-Ks) provide the separation between S-complex and C-complex. The end
members A, D, R, and V-types occupy well-defined regions.Comment: 19 pages, 16 figure
Quantum well infrared photodetectors hardiness to the non ideality of the energy band profile
We report results on the effect of a non-sharp and disordered potential in
Quantum Well Infrared Photodetectors (QWIP). Scanning electronic transmission
microscopy is used to measure the alloy profile of the structure which is shown
to present a gradient of composition along the growth axis. Those measurements
are used as inputs to quantify the effect on the detector performance (peak
wavelength, spectral broadening and dark current). The influence of the random
positioning of the doping is also studied. Finally we demonstrate that QWIP
properties are quite robust with regard to the non ideality of the energy band
profile
Nonlinear sigma model study of a frustrated spin ladder
A model of two-leg spin-S ladder with two additional frustrating diagonal
exchange couplings J_{D}, J_{D}' is studied within the framework of the
nonlinear sigma model approach. The phase diagram has a rich structure and
contains 2S gapless phase boundaries which split off the boundary to the fully
saturated ferromagnetic phase when J_{D} and J_{D}' become different. For the
S=1/2 case, the phase boundaries are identified as separating two topologically
distinct Haldane-type phases discussed recently by Kim et al.
(cond-mat/9910023).Comment: revtex 4 pages, figures embedded (psfig
Optimizing end-labeled free-solution electrophoresis by increasing the hydrodynamic friction of the drag-tag
We study the electrophoretic separation of polyelectrolytes of varying
lengths by means of end-labeled free-solution electrophoresis (ELFSE). A
coarse-grained molecular dynamics simulation model, using full electrostatic
interactions and a mesoscopic Lattice Boltzmann fluid to account for
hydrodynamic interactions, is used to characterize the drag coefficients of
different label types: linear and branched polymeric labels, as well as
transiently bound micelles.
It is specifically shown that the label's drag coefficient is determined by
its hydrodynamic size, and that the drag per label monomer is largest for
linear labels. However, the addition of side chains to a linear label offers
the possibility to increase the hydrodynamic size, and therefore the label
efficiency, without having to increase the linear length of the label, thereby
simplifying synthesis. The third class of labels investigated, transiently
bound micelles, seems very promising for the usage in ELFSE, as they provide a
significant higher hydrodynamic drag than the other label types.
The results are compared to theoretical predictions, and we investigate how
the efficiency of the ELFSE method can be improved by using smartly designed
drag-tags.Comment: 32 pages, 11 figures, submitted to Macromolecule
Applications of phase-contrast velocimetry sequences in cardiovascular imaging.
AIMS: To describe and illustrate the main applications of phase-contrast flow quantification in cardiovascular imaging.
CONCLUSION: Phase-contrast velocimetry sequences provide an accurate, reliable, reproducible and non-invasive study of blood flow, information which is sometimes not available from other investigation methods. The haemodynamic information obtained from these complement MRI angiography images. They appear to have a range of clinical applications, firstly improving pathophysiological understanding but also contributing to the treatment and follow-up strategy after surgical or endovascular treatment
Near infra-red spectroscopy of the asteroid 21 Lutetia. II. Rotationally resolved spectroscopy of the surface
Reproduced with permission. Copyright ESO. Article published by EDP Sciences and available at http://www.aanda.orgInternational audienceAims. In the framework of the ground-based science campaign dedicated to the encounter with the Rosetta spacecraft, the mineralogy of the asteroid (21) Lutetia was investigated. Methods. Near-infrared (NIR) spectra of the asteroid in the 0.8−2.5 μm spectral range were obtained with SpeX/IRTF in remote observing mode from Meudon, France in March and April 2006. We analysed these data together with previously acquired spectra - March 2003, August 2004. I-band relative photometric data obtained on 20 January 2006 using the 105 cm telescope from Pic du Midi, France has been used to build the ephemeris for physical observations. A χ2 test using meteorite spectra from the RELAB database was performed in order to find the best fit of complete visible + infrared (VNIR) spectra of Lutetia. Results. The new spectra reveal no absorption features. We find a clear spectral variation (slope), and a good correspondence between spectral variations and rotational phase. Two of the most different spectra correspond to two opposite sides of the asteroid (sub-Earth longitude difference around 180◦). For the neutral spectra a carbonaceous chondrite spectrum yields the best fit, while for those with a slightly positive slope the enstatitic chondrite spectra are the best analog. Based on the chosen subset of the meteorite samples, our analysis suggests a primitive, chondritic nature for (21) Lutetia. Differences in spectra are interpreted in terms of the coexistence of several lithologies on the surface where the aqueous alteration played an important role
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