376 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&
Parametric FEM simulation of composite barrier FTJs under external bias at room temperature
A study on a parametrized model of a composite barrier FTJ (three-interface
system, with a non-polar dielectric layer) under an external bias voltage and
at room temperature, using FEM-based simulations, was performed. The approach
involves the Thomas-Fermi model assuming incomplete screening of polarization
charges for building the energy barrier profile, and numerically simulates the
electron transport through the barrier by bias-voltage-dependent tunneling,
using Tsu-Esaki formulation. That naturally include the temperature dependent
contributions to the total current density. The TER coefficient and current
densities are computed considering variation of a large set of parameters that
describe the composite barrier FTJ system in realistic physical range of values
with respect to a reference (prototypical) system. In this study, the
parametric simulations were performed starting from selected data reported on
the SRO/STO/BTO/SRO heterostructure. The most important results of our work can
be stated as follows: i) The FEM simulations prove to be reliable approach when
we are interested in the prediction of FTJ characteristics at temperatures
close to 300 K, and ii) We show that several configurations with large TER
values may be predicted, but at the expense of very low current densities in
the ON state. We suggest that the results may be useful for assessing the FTJ
performances at ambient temperature, as well as to design preoptimized FTJs by
using different combinations of materials to comply with a set of properties of
a specific model
Does 'relationship intelligence' make big brains in birds?
Lately, Emery et al. developed a bird-specific modification of the “social brain hypothesis”, termed “relationship intelligence hypothesis”. Although the idea may be valuable, we doubt that it is supported by sufficient evidence and critically discuss some of the arguments raised by the authors in favour of their new idea
Early lung ultrasonography predicts the occurrence of acute respiratory distress syndrome in blunt trauma patients
PURPOSE: Extent of lung contusion on initial computed tomography (CT) scan predicts the occurrence of acute respiratory distress syndrome (ARDS) in blunt chest trauma patients. We hypothesized that lung ultrasonography (LUS) on admission could also predict subsequent ARDS. METHODS: Forty-five blunt trauma patients were prospectively studied. Clinical examination, chest radiography, and LUS were performed on arrival at the emergency room. Lung contusion extent was quantified using a LUS score and compared to CT scan measurements. The ability of the LUS score to predict ARDS was tested using the area under the receiver operating characteristic curve (AUC-ROC). The diagnostic accuracy of LUS was compared to that of combined clinical examination and chest radiography for pneumothorax, lung contusion, and hemothorax, with thoracic CT scan as reference. RESULTS: Lung contusion extent assessed by LUS on admission was predictive of the occurrence of ARDS within 72 h (AUC-ROC = 0.78 [95 % CI 0.64-0.92]). The extent of lung contusion on LUS correlated well with CT scan measurements (Spearman\u27s coefficient = 0.82). A LUS score of 6 out of 16 was the best threshold to predict ARDS, with a 58 % [95 % CI 36-77] sensitivity and a 96 % [95 % CI 76-100] specificity. The diagnostic accuracy of LUS was higher than that of combined clinical examination and chest radiography: (AUC-ROC) 0.81 [95 % CI 0.50-1.00] vs. 0.74 [0.48-1.00] (p = 0.24) for pneumothorax, 0.88 [0.76-1.00] vs. 0.69 [0.47-0.92] (p < 0.05) for lung contusion, and 0.84 [0.59-1.00] vs. 0.73 [0.51-0.94] (p < 0.05) for hemothorax. CONCLUSIONS: LUS on admission identifies patients at risk of developing ARDS after blunt trauma. In addition, LUS allows rapid and accurate diagnosis of common traumatic thoracic injuries
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
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
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
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