Infrared spectra in polarized light of crystalline chloroform

High resolution spectra in polarized light of oriented crystalline films of chloroform at 77°K were obtained. The ratio of intensities of Davydov components for different angles of polarization were also determined. Comparison with the oriented gas model approximation allowed the assignment of components to the proper representations of the D 2h factor group : all bands were assigned to the infrared active factor group symmetry species B 1u, B 2u, and B 3u corresponding to vibrations along a, b, and c crystallographic axes. Comparison with results of measurements in solid solutions in argon made by King allowed the distinction between crystallographic effect and isotopic shifts.Fil:Pomposiello, C. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina

Polysaccharide Layer-by-Layer Coating for Polyimide-Based Neural Interfaces

Implantable flexible neural interfaces (IfNIs) are capable of directly modulating signals of the central and peripheral nervous system by stimulating or recording the action potential. Despite outstanding results in acute experiments on animals and humans, their long-term biocompatibility is hampered by the effects of foreign body reactions that worsen electrical performance and cause tissue damage. We report on the fabrication of a polysaccharide nanostructured thin film as a coating of polyimide (PI)-based IfNIs. The layer-by-layer technique was used to coat the PI surface due to its versatility and ease of manufacturing. Two different LbL deposition techniques were tested and compared: dip coating and spin coating. Morphological and physiochemical characterization showed the presence of a very smooth and nanostructured thin film coating on the PI surface that remarkably enhanced surface hydrophilicity with respect to the bare PI surface for both the deposition techniques. However, spin coating offered more control over the fabrication properties, with the possibility to tune the coating’s physiochemical and morphological properties. Overall, the proposed coating strategies allowed the deposition of a biocompatible nanostructured film onto the PI surface and could represent a valid tool to enhance long-term IfNI biocompatibility by improving tissue/electrode integration

Intrinsic instability of lean hydrogen/ammonia premixed flames: Influence of Soret effect and pressure

The addition of hydrogen in ammonia/air mixtures can lead to the onset of intrinsic flame instabilities at conditions of technical relevance. The length and time scales of intrinsic instabilities can be estimated by means of linear stability analysis of planar premixed flames by evaluating the dispersion relation. In this work, we perform such linear stability analysis for hydrogen-enriched ammonia/air flames (50%H2-50%NH3 by volume) using direct numerical simulation with a detailed chemical kinetic mechanism. The impact of pressure and the inclusion of the Soret effect in the governing equations is assessed by comparing the resulting dispersion relation at atmospheric pressure and 10 atm. Our data indicate that both pressure and the Soret effects promote the onset of intrinsic instabilities. Comparisons with available numerical literature data as well as theoretical models are also discussed

Warm Molecular Layers in Protoplanetary Disks

We have investigated molecular distributions in protoplanetary disks, adopting a disk model with a temperature gradient in the vertical direction. The model produces sufficiently high abundances of gaseous CO and HCO+ to account for line observations of T Tauri stars using a sticking probability of unity and without assuming any non-thermal desorption. In regions of radius R > 10 AU, with which we are concerned, the temperature increases with increasing height from the midplane. In a warm intermediate layer, there are significant amounts of gaseous molecules owing to thermal desorption and efficient shielding of ultraviolet radiation by the flared disk. The column densities of HCN, CN, CS, H2CO, HNC and HCO+ obtained from our model are in good agreement with the observations of DM Tau, but are smaller than those of LkCa15. Molecular line profiles from our disk models are calculated using a 2-dimensional non-local-thermal-equilibrium (NLTE) molecular-line radiative transfer code for a direct comparison with observations. Deuterated species are included in our chemical model. The molecular D/H ratios in the model are in reasonable agreement with those observed in protoplanetary disks.Comment: 11 pages, Latex (aa.cls), to be published in Astronomy and Astrophysic

Use of Preputial Skin as Cutaneous Graft after Nevus Excision

We report a four-year-old boy with a nevus covering all the plantar side of his second finger on the left foot. He was also affected by congenital phimosis. Surgical excision of the nevus was indicated, but the skin defect would have been too large to be directly closed. The foreskin was taken as a full-thickness skin graft to cover the cutaneous defect of the finger. The graft intake was favourable and provided a functional repair with good aesthetic characteristic

The complete catalogue of gamma-ray bursts observed by the Wide Field Cameras on board BeppoSAX

We present the complete on-line catalogue of gamma-ray bursts observed by the two Wide Field Cameras on board \sax in the period 1996-2002. Our aim is to provide the community with the largest published data set of GRB's prompt emission X-ray light curves and other useful data. This catalogue (BS-GRBWFCcat) contains data on 77 bursts and a collection of the X-ray light curves of 56 GRB discovered or noticed shortly after the event and of other additional bursts detected in subsequent searches. Light curves are given in the three X-ray energy bands (2-5, 5-10, 10-26 keV). The catalogue can be accessed from the home web page of the ASI Science Data Center-ASDC (http://www.asdc.asi.it)Comment: 4 pages, 3 figure

Unveiling the Structure of Pre-Transitional Disks

In the past few years, several disks with inner holes that are empty of small dust grains have been detected and are known as transitional disks. Recently, Spitzer has identified a new class of "pre-transitional disks" with gaps; these objects have an optically thick inner disk separated from an optically thick outer disk by an optically thin disk gap. A near-infrared spectrum provided the first confirmation of a gap in the pre-transitional disk of LkCa 15 by verifying that the near-infrared excess emission in this object was due to an optically thick inner disk. Here we investigate the difference between the nature of the inner regions of transitional and pre-transitional disks using the same veiling-based technique to extract the near-infrared excess emission above the stellar photosphere. We show that the near-infrared excess emission of the previously identified pre-transitional disks of LkCa 15 and UX Tau A in Taurus as well as the newly identified pre-transitional disk of ROX 44 in Ophiuchus can be fit with an inner disk wall located at the dust destruction radius. We also model the broad-band SEDs of these objects, taking into account the effect of shadowing by the inner disk on the outer disk, considering the finite size of the star. The near-infrared excess continua of these three pre-transitional disks, which can be explained by optically thick inner disks, are significantly different from that of the transitional disks of GM Aur, whose near-infrared excess continuum can be reproduced by emission from sub-micron-sized optically thin dust, and DM Tau, whose near-infrared spectrum is consistent with a disk hole that is relatively free of small dust. The structure of pre-transitional disks may be a sign of young planets forming in these disks and future studies of pre-transitional disks will provide constraints to aid in theoretical modeling of planet formation.Comment: Accepted for publication in ApJ on May 10, 2010; 29 page

Radiatively heated, protoplanetary discs with dead zones. I. Dust settling and thermal structure of discs around M stars

The irradiation of protoplanetary discs by central stars is the main heating mechanism for discs, resulting in their flared geometric structure. In a series of papers, we investigate the deep links between 2D self-consistent disc structure and planetary migration in irradiated discs, focusing particularly on those around M stars. In this first paper, we analyse the thermal structure of discs that are irradiated by an M star by solving the radiative transfer equation by means of a Monte Carlo code. Our simulations of irradiated hydrostatic discs are realistic and self-consistent in that they include dust settling with multiple grain sizes (N=15), the gravitational force of an embedded planet on the disc, and the presence of a dead zone (a region with very low levels of turbulence) within it. We show that dust settling drives the temperature of the mid-plane from an $r^{-3/5}$ distribution (well mixed dust models) toward an $r^{-3/4}$. The dead zone, meanwhile, leaves a dusty wall at its outer edge because dust settling in this region is enhanced compared to the active turbulent disc at larger disc radii. The disc heating produced by this irradiated wall provides a positive gradient region of the temperature in the dead zone in front of the wall. This is crucially important for slowing planetary migration because Lindblad torques are inversely proportional to the disc temperature. Furthermore, we show that low turbulence of the dead zone is self-consistently induced by dust settling, resulting in the Kelvin-Helmholtz instability (KHI). We show that the strength of turbulence arising from the KHI in the dead zone is $\alpha=10^{-5}$.Comment: 19 pages, 20 figures, 3 tables, accepted for publication in MNRA

A Spitzer IRS Survey of NGC 1333: Insights into disk evolution from a very young cluster

We report on the {\lambda} = 5-36{\mu}m Spitzer Infrared Spectrograph spectra of 79 young stellar objects in the very young nearby cluster NGC 1333. NGC 1333's youth enables the study of early protoplanetary disk properties, such as the degree of settling as well as the formation of gaps and clearings. We construct spectral energy distributions (SEDs) using our IRS data as well as published photometry and classify our sample into SED classes. Using "extinction-free" spectral indices, we determine whether the disk, envelope, or photosphere dominates the spectrum. We analyze the dereddened spectra of objects which show disk dominated emission using spectral indices and properties of silicate features in order to study the vertical and radial structure of protoplanetary disks in NGC 1333. At least nine objects in our sample of NGC 1333 show signs of large (several AU) radial gaps or clearings in their inner disk. Disks with radial gaps in NGC 1333 show more-nearly pristine silicate dust than their radially continuous counterparts. We compare properties of disks in NGC 1333 to those in three other well studied regions, Taurus-Auriga, Ophiuchus and Chamaeleon I, and find no difference in their degree of sedimentation and dust processing.Comment: 67 pages, 20 figures, accepted to The Astrophysical Journal Supplement Serie