Volcanic Water Vapour Abundance Retrieved Using Hypespectral Data

In the present study a remote sensing differential absorption technique, already developed to calculate the atmospheric water vapour abundance, has been adapted to calculate water vapour columnar abundance in tropospheric volcanic plume. Water vapour is the most abundant gas of a volcanic plume released into the atmosphere from an active volcanic system. The technique is based on the correlation between the dip in the spectral curve measured by the spectrometer were water vapour absorptions bands are presents, and the precipitable water content in the column. Airborne and satellite remote sensing images in the infrared wavelength range were used. The technique has been applied to data acquired over two different degassing volcanoes. The Airborne Visible and Infrared Imaging Spectrometer (AVIRIS) acquired data over the Hawaiian Pu’u’O’o Vent cone of the Kilauea volcano on April 2000. The Hyperion sensor on EO-1 satellite has been requested to acquire data on July 2003, during a ground-based measurements campaign on Mt. Etna (Italy). The result is the spatial distribution of water vapour abundance of the Mt. Etna and of the Pu`u` O`o Vent volcanic plumes. A comparison between the two results has been done, showing the differences in the volcanic activity. The algorithm produces reliable results compared to the ground based measurements in the plume area acquired during a measurements campaign over Mt. Etna

Nucleation and growth of single wall carbon nanotubes

The nucleation and growth of single wall carbon nanotubes from a carbon-saturated catalytic particle surrounded by a single sheet of graphene is described qualitatively by using a very restricted number of elementary processes, namely Stone-Wales defects and carbon bi-interstitials. Energies of the different configurations are estimated by using a Tersoff energy minimization scheme. Such a description is compatible with a broad variety of size or helicity of the tubes. Several mechanisms of growth of the embryos are considered: one of them is made more favourable when the tubes embryos are arranged in an hexagonal network in the graphene plane. All the proposed mechanisms can be indefinitely repeated for the growth of the nanotubes.Comment: Solid state communications, in pres

Characterization of volcanic thermal anomalies by means of sub-pixel temperature distribution analysis

Abstract: The simultaneous solution of the Planck equation (involving the widely used “dual-band” technique) using two shortwave infrared (SWIR) bands allows for an estimate of the fractional area of the hottest part of an active lava flow (fh), and the background temperature of the cooler crust (Tc). The use of a high spectral and spatial resolution imaging spectrometer with a wide dynamic range of 15 bits (DAIS 7915) in the wavelength range from 0.501 to 12.67 µm resulted in the identification of crustal temperature and fractional areas for an intra-crater hot spot at Mount Etna, Italy. This study indicates the existence of a relationship between these Tc and fh extracted from DAIS and Landsat TM data. When the dual band equation system is performed on a lava flow, a logarithmic distribution is obtained from a plot of the fractional area of the hottest temperature versus the temperature of the cooler crust. An entirely different distribution is obtained over active degassing vents, where increases in Tc occur without any increase in fh. This result indicates that we can use scatter plots of Tc vs. fh to discriminate between different types of volcanic activity, in this case between degassing vents and lava flows, using satellite thermal data

Temperature distribution analysis of July 2001 Mt. Etna eruption observed by the airborne hyperspectral sensor MIVIS

On 17th and 18th July 2001, several fractures opened on Mt. Etna southern flank generating different lava flows spreading both in Valle del Bove and towards Nicolosi. On 29th July the image spectrometer MIVIS was flown over Mt. Etna to acquire high-resolution images of the eruption. The MIVIS airborne campaign was planned simultaneously with TERRA, EO-1 and Landsat 7 satellite acquisitions, in order to compare hyperspectral and multispectral data referred to active lavas. This work focuses on the thermal mapping of lava flows, taking advantage of MIVIS sensor high technical performances. The MIVIS high spatial resolution allows a detailed analysis of the lava flow topographic distribution. Its 12 bit dynamic range consents an estimate of the temperature even for the «hottest» pixels. The main target of this work is the evaluation of the energy flux by means of remote-sensing techniques. Surface temperature analysis was performed on distinct lava flows using the dualband technique. These quantities were compared with the integrated temperatures retrieved using the MIVIS thermal infrared bands. The influence of topography was also considered in the flux calculation using a Digital Elevation Model (DEM) of Mt. Etna

Band Structure and Quantum Conductance of Nanostructures from Maximally-Localized Wannier Functions: The Case of Functionalized Carbon Nanotubes

We have combined large-scale, $\Gamma$-point electronic-structure calculations with the maximally-localized Wannier functions approach to calculate efficiently the band structure and the quantum conductance of complex systems containing thousands of atoms while maintaining full first-principles accuracy. We have applied this approach to study covalent functionalizations in metallic single-walled carbon nanotubes. We find that the band structure around the Fermi energy is much less dependent on the chemical nature of the ligands than on the $sp^3$ functionalization pattern disrupting the conjugation network. Common aryl functionalizations are more stable when paired with saturating hydrogens; even when paired, they still act as strong scattering centers that degrade the ballistic conductance of the nanotubes already at low degrees of coverage.Comment: To be published in Phys. Rev. Let

First principle theory of correlated transport through nano-junctions

We report the inclusion of electron-electron correlation in the calculation of transport properties within an ab initio scheme. A key step is the reformulation of Landauer's approach in terms of an effective transmittance for the interacting electron system. We apply this framework to analyze the effect of short range interactions on Pt atomic wires and discuss the coherent and incoherent correction to the mean-field approach.Comment: 5 pages, 3 figure

Wavelength influence in sub-pixel temperature retrieval using the dual-band technique

The thermal model proposed by Crisp and Baloga (1990) for active lava flows considers thermal flux as a function of the fractional area of two thermally distinct radiant surfaces. In this model, the larger surface area corresponds to the cooler crust of the flow and the other, much smaller to fractures in the crust. These cracks temperature is much higher than the crust one and approaches the temperature of the molten or plastic interior flow. The dual-band method needs two distinct SWIR (short wave infrared) bands to formulate a two equations system from the simultaneous solution of the Planck equation in each band. The system solutions consist in the crust temperature and the fractional area of the hot component. The dual band technique originally builds on data acquired by sensors (such as Landsat TM) with two SWIR bands only. The use of hyperspectral imaging spectrometers allows us to test the dual-band technique using different wavelengths in the SWIR range of the spectrum. DAIS 7915 is equipped with 40 bands into the range 1.54-2.49 nm which represent potential input in dual band calculation. This study aims to compare results derived by inserting assorted couples of wavelengths into the equation system. The analysis of these data provides useful information on dual-band technique accuracy

Macroscopic polarization and band offsets at nitride heterojunctions

Ab initio electronic structure studies of prototypical polar interfaces of wurtzite III-V nitrides show that large uniform electric fields exist in epitaxial nitride overlayers, due to the discontinuity across the interface of the macroscopic polarization of the constituent materials. Polarization fields forbid a standard evaluation of band offsets and formation energies: using new techniques, we find a large forward-backward asymmetry of the offset (0.2 eV for AlN/GaN (0001), 0.85 eV for GaN/AlN (0001)), and tiny interface formation energies.Comment: RevTeX 4 pages, 2 figure

Spectral emissivity and temperature maps of the Solfatara crater from DAIS hyperspectral images

Quantitative maps of surface temperature and spectral emissivity have been retrieved on the Solfatara crater at Pozzuoli (Naples) from remote sensing hyperspectral data. The present study relies on thermal infrared images collected on July 27, 1997 by the DAIS hyperspectral sensor owned by the German aerospace center (DLR). The Emissivity Spectrum Normalization method was used to make temperature and emissivity estimates. Raw data were previously transformed in radiance and corrected for the atmospheric contributions using the MODTRAN radiative transfer code and the sensor response functions. During the DAIS flight a radiosonde was launched to collect the atmospheric profiles of pressure, temperature and humidity used as input to the code. Retrieved temperature values are in good agreement with temperature measurements performed in situ during the campaign. The spectral emissivity map was used to classify the image in different geo-mineralogical units with the Spectral Angle Mapper method. Areas of geologic interest were previously selected using a mask obtained from an NDVI image calculated with two channels of the visible (red) and the near infrared respectively

Electric Field Induced Phase Transitions in Polymers: A Novel Mechanism for High Speed Energy Storage

This article discusses electric field induced phase transitions in polymers