The activity of Main Belt comets

Main Belt comets represent a recently discovered class of objects. They are quite intriguing because, while having a Tisserand invariant value higher than 3, are showing cometary activity. We study the activity of the Main Belt comets making the assumption that they are icy-bodies and that the activity has been triggered by an impact. We determine the characteristics of this activity and if the nowadays impact rate in the Main Asteroid Belt is compatible with the hypothesis of an activity triggered by a recent impact. Due to the fact that the Main Belt comets can be considered as a kind of comets, we apply a thermal evolution model developed for icy bodies in order to simulate their activity. We also apply a model to derive the impact rate, with respect to the size of the impactor, in the Main Belt. We demonstrate that a stable activity can result from a recent impact, able to expose ice-rich layers, and that the impact rate in the Main Belt is compatible with this explanation.Comment: 9 pages, 7 figure

Water in Comet 2/2003 K4 (LINEAR) with Spitzer

We present sensitive 5.5 to 7.6 micron spectra of comet C/2003 K4 (LINEAR) obtained on 16 July 2004 (r_{h} = 1.760 AU, Delta_{Spitzer} = 1.409 AU, phase angle 35.4 degrees) with the Spitzer Space Telescope. The nu_{2} vibrational band of water is detected with a high signal-to-noise ratio (> 50). Model fitting to the best spectrum yields a water ortho-to-para ratio of 2.47 +/- 0.27, which corresponds to a spin temperature of 28.5^{+6.5}_{-3.5} K. Spectra acquired at different offset positions show that the rotational temperature decreases with increasing distance from the nucleus, which is consistent with evolution from thermal to fluorescence equilibrium. The inferred water production rate is (2.43 +/- 0.25) \times 10^{29} molec. s^{-1}. The spectra do not show any evidence for emission from PAHs and carbonate minerals, in contrast to results reported for comets 9P/Tempel 1 and C/1995 O1 (Hale-Bopp). However, residual emission is observed near 7.3 micron the origin of which remains unidentified.Comment: 33 pages, including 11 figures, 2 tables, ApJ 2007 accepte

Bioelectrical impedance analysis in patients with posterior vitreous detachment

OBJECTIVE: the purpose of the study is to assess body hydration in patients with posterior vitreous detachment (PVD) by bioelectrical impedance analysis (BIA). PVD, one of the most common eye diseases, is associated in both research and the collective image with reduced daily water intake, but this finding is not supported by strong evidence in the literature. PATIENTS AND METHODS: based on spectral domain optical coherence tomography (SD-OCT) evaluation, different PVD stages are identified: absent posterior vitreous detachment, partial posterior vitreous detachment (P-PVD), or complete posterior vitreous detachment (C-PVD). BIA is a simple, non-invasive bedside method used to assess body composition. patients underwent BIA and completed a floaters symptoms. 30 patients were enrolled and divided into two groups according to the degree of vitreous detachment, in P-PVD (n=12) and C-PVD (n=18). patients underwent BIA and completed a floaters symptoms questionnaire. BIA measured the resistance (R), reactance (Xc), phase angle (PhA), total body water (TBW), extracellular water (ECW), fat mass (FM), fat-free mass (FFM), and body cell mass Index (BCMI). finally, patients received a test to assess adherence to the mediterranean diet (mediterranean diet test score, MDTS) with the addition of daily water intake. RESULTS: relevant data were obtained from the BIA evaluation: the values of R and Xc were lower in the P-PVD group than C-PVD group (respectively 417.08±58.12 Ω vs. 476.94±51.29 Ω p=0.006 and 41.33±8.23 Ω vs. 50.61±7.98 Ω p=0.004). instead, patients in the P-PVD group reported higher values of TBW and ECW than C-PVD group (respectively 44.13±7.57 L vs. 37.96±6.27 L p=0.021 and 21.03±4.06 L vs. 17.24±2.63 L p=0.004). CONCLUSIONS: In the present study, we reported a significant correlation between vitreous pathology and anthropometric and BIA measurements

Mesosiderites on Vesta: A Hyperspectral VIS-NIR Investigation

The discussion about the mesosiderite origin is an open issue since several years. Mesosiderites are mixtures of silicate mineral fragments or clasts, embedded in a FeNi metal matrix. Silicates are very similar in mineralogy and texture to howardites [1]. This led some scientists to conclude that mesosiderites could come from the same parent parent asteroid of the howardite, eucrite and diogenite (HED) meteorites [2, 3]. Other studies found a number of differences between HEDs and mesosiderite silicates that could be explained only by separate parent asteroids [4]. Recently, high precision oxygen isotope measurements of m esosiderites silicate fraction were found to be isotopically identical to the HEDs, requiring common parent body, i.e. 4 Vesta [5]. Another important element in favor of a common origin was given by the identification of a centimeter-sized mesosiderite clast in a howardite (Dar al Gani 779): a metal-rich inclusion with fragments of olivine, anorthite, and orthopyroxene plus minor amounts of chromite, tridymite, and troilite [6]. The Dawn mission with its instruments, the Infrared Mapping Spectrometer (VIR) [7], the Framing Camera [8] and the Gamma-Ray and Neutron Detector (GRaND) [9] confirmed that Vesta has a composition fully compatible with HED meteorites [10]. We investigate here the possibility to discern mesosiderite rich locations on the surface of Vesta by means of hyperspectral IR images

nanoscale characterisation of hybrid photovoltaic cells based on c61 capped cdse qds

Hybrid solar cells based on 1,2 methanofullerene (C61) capped CdSe and poly (3-hexylthiophene) (P3HT) were been investigated through a range of techniques. High resolution transmission electron microscopy (HRTEM) was used to characterize size, morphology and crystal structure of as-grown and C61-capped CdSe quantum dots. Cross sectional lamellar specimens were prepared from full photovoltaic devices using a focused ion beam milling approach. The sections were analysed by high angle annular dark field imaging in scanning TEM mode to determine the morphology of the device, in particular the intermixing of P3HT and capped quantum dots

First mineralogical maps of 4 Vesta

Before Dawn arrived at 4 Vesta only very low spatial resolution (~50 km) albedo and color maps were available from HST data. Also ground-based color and spectroscopic data were utilized as a first attempt to map Vesta’s mineralogical diversity [1-4]. The VIR spectrometer [5] onboard Dawn has ac-quired hyperspectral data while the FC camera [6] ob-tained multi-color data of the Vestan surface at very high spatial resolutions, allowing us to map complex geologic, morphologic units and features. We here re-port about the results obtained from a preliminary global mineralogical map of Vesta, based on data from the Survey orbit. This map is part of an iterative map-ping effort; the map is refined with each improvement in resolution

Thermal maps and properties of comet 67P as derived from Rosetta/VIRTIS data

After a 10-year cruise, the Rosetta spacecraft began a close exploration of its main target, comet 67P/Churyumov-Gerasimenko, in July 2014. Since then, the Visible InfraRed Thermal Imaging Spectrometer (VIRTIS) acquired hyperspectral images of the comet’s surface with an unprecedented spatial resolution. VIRTIS data are routinely used to map the surface composition and to retrieve surface temperatures on the dayside of the comet. The thermal behavior of the surface of comet 67P is related to composition and physical properties that provide information about the nature and evolution of those materials. Here we present temperature maps of comet 67P that were observed by Rosetta under different illumination conditions and different local solar times

Non-Abelian Vortices, Super-Yang-Mills Theory and Spin(7)-Instantons

We consider a complex vector bundle E endowed with a connection A over the eight-dimensional manifold R^2 x G/H, where G/H = SU(3)/U(1)xU(1) is a homogeneous space provided with a never integrable almost complex structure and a family of SU(3)-structures. We establish an equivalence between G-invariant solutions A of the Spin(7)-instanton equations on R^2 x G/H and general solutions of non-Abelian coupled vortex equations on R^2. These vortices are BPS solitons in a d=4 gauge theory obtained from N=1 supersymmetric Yang-Mills theory in ten dimensions compactified on the coset space G/H with an SU(3)-structure. The novelty of the obtained vortex equations lies in the fact that Higgs fields, defining morphisms of vector bundles over R^2, are not holomorphic in the generic case. Finally, we introduce BPS vortex equations in N=4 super Yang-Mills theory and show that they have the same feature.Comment: 14 pages; v2: typos fixed, published versio

Mapping Vesta: First Results from Dawn’s Survey Orbit

The geologic objectives of the Dawn Mission [1] are to derive Vesta’s shape, map the surface geology, understand the geological context and contribute to the determination of the asteroids’ origin and evolution.Geomorphology and distribution of surface features will provide evidence for impact cratering, tectonic activity, volcanism, and regolith processes. Spectral measurements of the surface will provide evidence of the compositional characteristics of geological units. Age information, as derived from crater sizefrequency distributions, provides the stratigraphic context for the structural and compositional mapping results, thus revealing the geologic history of Vesta. We present here the first results of the Dawn mission from data collected during the approach to Vesta, and its first discrete orbit phase – the Survey Orbit, which lasts 21 days after the spacecraft had established a circular polar orbit at a radius of ~3000 km with a beta angle of 10°-15°