Search results for "electromagnetic"
showing 10 items of 1595 documents
Modeling particle acceleration and non-thermal emission in supernova remnants
2021
According to the most popular model for the origin of cosmic rays (CRs), supernova remnants (SNRs) are the site where CRs are accelerated. Observations across the electromagnetic spectrum support this picture through the detection of non-thermal emission that is compatible with being synchrotron or inverse Compton radiation from high energy electrons, or pion decay due to proton-proton interactions. These observations of growing quantity and quality promise to unveil many aspects of CRs acceleration and require more and more accurate tools for their interpretation. Here, we show how multi-dimensional MHD models of SNRs, including the effects on shock dynamics due to back-reaction of acceler…
Electromagnetically generated extracorporeal shock waves for gallstone lithotripsy: in vitro experiments and clinical relevance.
1989
. First generation shock wave sources have been proved to disintegrate gallstones effectively, but they require the immersion of the patient's body in a tank of water. A recently developed second generation shock wave source (Siemens-Lithostar, Erlangen, FRG) generates shock waves electromagnetically. It presents several novel features. In particular the waterbath can be omitted and due to lower shock wave pressure general anaesthesia is not required. In vitro studies showed that 36 out of 38 gallstones (11–30 mm in diameter) could be disintegrated. Two concrements resisting lithotripsy were pure white cholesterol stones. Independent of shape, size, and composition (cholesterol or pigment) …
A fluorescence retrieval method for the flex sentinel-3 tandem mission
2014
A new fluorescence retrieval method is proposed to support ESA's 8th Earth Explorer Fluorescence EXplorer (FLEX) candidate mission. Most hyperspectral fluorescence retrieval algorithms available in the literature are very sensitive to true reflectance modelization and/or they assume the atmospheric status as known. The proposed algorithm delivers the retrieval of full fluorescence spectrum at canopy level by using only Top Of Atmosphere (TOA) radiances as input. The proposed method starts with (1) the atmospheric correction of TOA radiances, characterizing the state of the atmosphere without assuming any a-priori classification on aerosols models, (2) performing a first estimation of fluore…
Multi-spectral mapping of in vivo skin hemoglobin and melanin
2010
The multi-spectral imaging technique has been used for distant mapping of in-vivo skin chromophores by analyzing spectral data at each reflected image pixel and constructing 2-D maps of the relative concentrations of oxy-/deoxyhemoglobin and melanin. Instead of using a broad visible-NIR spectral range, this study focuses on narrowed spectral band 500-700 nm, so speeding-up the signal processing procedure. Regression analysis confirmed that superposition of three Gaussians is optimal analytic approximation for the oxy-hemoglobin absorption tabular spectrum in this spectral band, while superposition of two Gaussians fits well for deoxy-hemoglobin absorption and exponential function - for mela…
Probing the radio emission from air showers with polarization measurements
2014
The emission of radio waves from air showers has been attributed to the so-called geomagnetic emission process. At frequencies around 50 MHz this process leads to coherent radiation which can be observed with rather simple setups. The direction of the electric field induced by this emission process depends only on the local magnetic field vector and on the incoming direction of the air shower. We report on measurements of the electric field vector where, in addition to this geomagnetic component, another component has been observed which cannot be described by the geomagnetic emission process. The data provide strong evidence that the other electric field component is polarized radially wit…
Investigation of optical and radiation properties of oxygen deficient silica glasses
1999
The deficiency of oxygen in pure silica manifests an absorption band at 5 eV as well as an absorption band of higher intensity at 7.6 eV. The band at 5 eV is associated with lone twofold-coordinated silicon centers. The nature of the main band at 7.6 eV has been studied using silica samples with different levels of oxygen deficiency. The excitation via the 7.6 eV band produces a photoelectric response as well as inner center and recombination type luminescence. Two main luminescence bands of the twofold-coordinated silicon center appear: a blue band (2.7 eV) and a UV band (4.4 eV). Induced absorption with several bands as well as thermally stimulated luminescence with complex peak structure…
Fluorine laser-induced silicon hydride SiH groups in silica
2007
Abstract Formation and destruction of silicon hydride (Si–H) groups in silica by F 2 laser irradiation and their vacuum ultraviolet (VUV) optical absorption was examined by infrared (IR) and VUV spectroscopy. Photoinduced creation of Si–H groups in H 2 -impregnated oxygen deficient silica is accompanied by a growth of infrared absorption band at 2250 cm −1 and by a strong increase of VUV transmission at 7.9 eV. Photolysis of Si–H groups by 7.9 eV photons in this glass was not detected when the irradiation was performed at temperature 80 K. However, a slight destruction of Si–H groups under 7.9 eV irradiation was observed at the room temperature. This finding gives a tentative estimate of VU…
Practical formula for the evaluation of high-order multiphoton absorption in thin nonlinear media
2009
We present an analytical formula for the fast and accurate evaluation of nonlinear absorption in materials exhibiting an admixture of different multiphoton processes. This approach is specifically addressed for its use in thin films when the slowly varying envelope approximation applies. The contribution of absorptions of distinct order is conveniently averaged in order to use well-known expressions for a single multiphoton process. In the latter case, therefore, our simple expression is reduced toward the exact solution.
Influence of doped charge transport layers on efficient perovskite solar cells
2018
Planar vacuum deposited p–i–n methyl ammonium lead tri-iodide perovskite solar cells are prepared with different electron and hole transporting layers, either doped or undoped. The effect of these layers on the solar cells performance (efficiency and stability) is studied. The main benefit of using doped layers lies in the formation of barrier free charge extraction contacts to the electrodes. However, this comes at the cost of increased residual absorption (reducing the current density and efficiency of the cells) and a decreased stability. A generic solar cell structure using undoped charge extraction layers is presented, containing a thin layer of a strong electron acceptor in between th…
Extended conjugation in stilbenoid squaraines
2019
Abstract Squaraines, two-fold condensation products in 1,3-position of squaric acid, represent dyes or pigments of high actuality. After their first boom in electrophotography diverse applications are presently studied in a wide area of research, which reaches from electrooptical materials to biosensors and compounds used in photodynamic therapy. Absorption and/or emission ranges in the NIR are mandatory for many of these techniques. The present article deals with stilbenoid squaraines, which feature an extended conjugation in their biradicaloid D-π-A-π-D structure. Due to the charge-transfer character of the excitation, boundaries are set for the optimal length of the conjugation. The abso…