32,536 research outputs found

    EAGLE 2006 – Multi-purpose, multi-angle and multi-sensor in-situ and airborne campaigns over grassland and forest

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    EAGLE2006 - an intensive field campaign - was carried out in the Netherlands from the 8th until the 18th of June 2006. Several airborne sensors - an optical imaging sensor, an imaging microwave radiometer, and a flux airplane – were used and extensive ground measurements were conducted over one grassland (Cabauw) site and two forest sites (Loobos & Speulderbos) in the central part of the Netherlands, in addition to the acquisition of multi-angle and multi-sensor satellite data. The data set is both unique and urgently needed for the development and validation of models and inversion algorithms for quantitative surface parameter estimation and process studies. EAGLE2006 was led by the Department of Water Resources of the International Institute for Geo-Information Science and Earth Observation and originated from the combination of a number of initiatives coming under different funding. The objectives of the EAGLE2006 campaign were closely related to the objectives of other ESA Campaigns (SPARC2004, Sen2Flex2005 and especially AGRISAR2006). However, one important objective of the campaign is to build up a data base for the investigation and validation of the retrieval of bio-geophysical parameters, obtained at different radar frequencies (X-, C- and L-Band) and at hyperspectral optical and thermal bands acquired over vegetated fields (forest and grassland). As such, all activities were related to algorithm development for future satellite missions such as Sentinels and for satellite validations for MERIS, MODIS as well as AATSR and ASTER thermal data validation, with activities also related to the ASAR sensor on board ESA’s Envisat platform and those on EPS/MetOp and SMOS. Most of the activities in the campaign are highly relevant for the EU GEMS EAGLE project, but also issues related to retrieval of biophysical parameters from MERIS and MODIS as well as AATSR and ASTER data were of particular relevance to the NWO-SRON EcoRTM project, while scaling issues and complementary between these (covering only local sites) and global sensors such as MERIS/SEVIRI, EPS/MetOP and SMOS were also key elements for the SMOS cal/val project and the ESA-MOST DRAGON programme. This contribution describes the mission objectives and provides an overview of the airborne and field campaigns

    Local Density of States and Angle-Resolved Photoemission Spectral Function of an Inhomogeneous D-wave Superconductor

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    Nanoscale inhomogeneity seems to be a central feature of the d-wave superconductivity in the cuprates. Such a feature can strongly affect the local density of states (LDOS) and the spectral weight functions. Within the Bogoliubov-de Gennes formalism we examine various inhomogeneous configurations of the superconducting order parameter to see which ones better agree with the experimental data. Nanoscale large amplitude oscillations in the order parameter seem to fit the LDOS data for the underdoped cuprates. The one-particle spectral function for a general inhomogeneous configuration exhibits a coherent peak in the nodal direction. In contrast, the spectral function in the antinodal region is easily rendered incoherent by the inhomogeneity. This throws new light on the dichotomy between the nodal and antinodal quasiparticles in the underdoped cuprates.Comment: 5 pages, 9 pictures. Phys. Rev. B (in press

    Magnetic control of the pair creation in spatially localized supercritical fields

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    We examine the impact of a perpendicular magnetic field on the creation mechanism of electron-positron pairs in a supercritical static electric field, where both fields are localized along the direction of the electric field. In the case where the spatial extent of the magnetic field exceeds that of the electric field, quantum field theoretical simulations based on the Dirac equation predict a suppression of pair creation even if the electric field is supercritical. Furthermore, an arbitrarily small magnetic field outside the interaction zone can bring the creation process even to a complete halt, if it is sufficiently extended. The mechanism for this magnetically induced complete shutoff can be associated with a reopening of the mass gap and the emergence of electrically dressed Landau levels

    Lie bialgebras of generalized Witt type

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    In a paper by Michaelis a class of infinite-dimensional Lie bialgebras containing the Virasoro algebra was presented. This type of Lie bialgebras was classified by Ng and Taft. In this paper, all Lie bialgebra structures on the Lie algebras of generalized Witt type are classified. It is proved that, for any Lie algebra WW of generalized Witt type, all Lie bialgebras on WW are coboundary triangular Lie bialgebras. As a by-product, it is also proved that the first cohomology group H1(W,W⊗W)H^1(W,W \otimes W) is trivial.Comment: 14 page

    Mott-Peierls Transition in the extended Peierls-Hubbard model

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    The one-dimensional extended Peierls-Hubbard model is studied at several band fillings using the density matrix renormalization group method. Results show that the ground state evolves from a Mott-Peierls insulator with a correlation gap at half-filling to a soliton lattice with a small band gap away from half-filling. It is also confirmed that the ground state of the Peierls-Hubbard model undergoes a transition to a metallic state at finite doping. These results show that electronic correlations effects should be taken into account in theoretical studies of doped polyacetylene. They also show that a Mott-Peierls theory could explain the insulator-metal transition observed in this material.Comment: 4 pages with 3 embedded eps figure

    Liquid-gas Phase Transition in Strange Hadronic Matter with Weak Y-Y Interaction

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    The liquid-gas phase transition in strange hadronic matter is reexamined by using the new parameters about the Λ−Λ\Lambda - \Lambda interaction deduced from recent observation of ΛΛ6He^{6}_{\Lambda\Lambda}He double hypernucleus. The extended Furnstahl-Serot-Tang model with nucleons and hyperons is utilized. The binodal surface, the limit pressure, the entropy, the specific heat capacity and the Caloric curves are addressed. We find that the liquid-gas phase transition can occur more easily in strange hadronic matter with weak Y-Y interaction than that of the strong Y-Y interaction.Comment: 10 pages, 7 figure

    Design, Synthesis and Relaxivity Behaviour of mRNA Targeting Contrast Agents

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    Introduction: Magnetic Resonance Imaging (MRI) is one of the most important diagnostic tools available in medicine. The specificity and sensitivity of MRI can be further enhanced by the introduction of contrast agents (CAs). As many clinically valuable targets reside inside the cell membrane, the development of efficient intracellular targeted MR contrast agent is required. Potential intracellular targets would be DNA, mRNA or protein/enzymes. The prerequisite for the intracellular targeting is not only the efficient delivery of probes inside the cell but also the colocalization with the target. The objective of the present study is to design and synthesize efficient intracellular MR contrast agents [1] which include three functional domains (i) Gd based MR reporter part (ii) antisense PNA to target mRNA (iii) cell penetrating peptide (CPP) or cholesterol as the delivery agent. The antisense PNA can hybridize uniquely to the complementary mRNA and provides cell specific targeting for cells containing the mRNA. Thus, the expression of the corresponding gene can be visualized non invasively by in vivo MR imaging. Methods: The conjugates were synthesized by continuous solid phase synthesis. Cellular uptake was confirmed by fluorescence microscopy, spectroscopy and MRI of labeled cells. Results: CPP conjugated mRNA targeting CAs were taken up efficiently into cells by an exclusively endosomal mechanism. A subtoxic labeling concentration at low micromolar range was sufficient to enhance significant MR imaging contrast. Cell free binding assays proved a specific interaction with a synthetic target. However, because of the vesicular entrapment, it can be expected that there would be a lack of specific interaction between CA and mRNA located in the cytosol. In order to overcome this problem, cholesterol conjugated CAs are designed and synthesized [2]. The idea behind cholesterol coupling was from the already published report [3] where covalent conjugates of cholesterol and siRNAs were facilitating cellular import and were able to silence protein expression effectively. Initial results have shown that these agents were delivered more efficiently than CPP conjugated CAs. Unfortunately, they were also entrapped in vesicles. Both types of CA were able to enhance contrast in labeled target containing as well as non-targeted parent cells. However, there was not efficient colocalization and specific interaction of CA and target mRNA achievable to be exploited for MR imaging purposes. Conclusion: CPP or lipid coupled CAs are internalized efficiently into cells. However, vesicular entrapment prevented sufficient specific interaction between CA and mRNA. Further modifications are required to achieve the release from endosomes or a direct uptake into the cytosol
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