Search results for "Polarization"
showing 10 items of 1884 documents
Theoretical study of the electronic spectrum of magnesium-porphyrin
1999
Multiconfigurational self-consistent field (SCF) and second order perturbation methods have been used to study the electronic spectrum of magnesium-porphyrin (MgP). An extended ANO-type basis set including polarization functions on all heavy atoms has been used. Four allowed singlet states of E1u symmetry have been computed and in addition a number of forbidden transitions and a few triplet states. The results lead to a consistent interpretation of the electronic spectrum, where the Q band contains one transition, the B band two, and the N band one. The computed transition energies are consistently between 0.1 and 0.5 too low compared to the measured band maxima. The source of the discrepan…
Assessment of a single-acquisition imaging sequence for oxygen-sensitive (3)He-MRI.
2001
MRI of the lungs using hyperpolarized helium-3 (3He) allows the determination of intrapulmonary oxygen partial pressures (pO2). The need to separate competing processes of signal loss has hitherto required two different imaging series during two different breathing maneuvers. In this work, a new imaging strategy to measure pO2 by a single series of consecutive scans is presented. The feasibility of the method is demonstrated in three healthy human volunteers. Maps and histograms of intrapulmonary pO2 are calculated. Changes in the oxygen concentration of the inhaled gas mixture are well reproduced in the histograms. Monte Carlo (MC) simulations of the temporal evolution of 3He hyperpolariza…
<title>Level-crossing spectroscopy of the 7, 9, and 10D states of Cs in an external electric field</title>
2007
We discuss experimental and theoretical studies of coherent excitation of magnetic sublevels in n D states of cesium that cross in an external electric field. Crossings of mF magnetic sublevels of hyperfine F levels with ΔmF = ±2 lead to resonances in the linearly polarized laser induced fluorescence, while crossings with ΔmF = ±1 lead to resonances in the circularly polarized laser induced fluorescence. These resonances can be exploited to observe alignment to orientation conversion. From the level crossing signals it is possible to measure atomic properties, such as the tensor polarizability α2 and the hyperfine constant A . Alignment to orientation conversion involves the deformation of …
Fe 2p photoemission magnetic dichroism with linearly polarized synchrotron radiation and with unpolarized A1 Kα radiation
1997
We report on the measurements and analysis of Fe 2p magnetic dichroism in the angular distribution of the photoelectrons from remanently magnetized Fe(100)surfaces with unpolarized, monochromatized A1 Kα X-rays of 1486 eV energy (MDAD)and with linearly polarized synchrotron radiation of energy 800 eV (LMDAD). The two experiments verify the atomic photoionization model of (L)MDAD including the dichroism effect between field-averaged experiments of different chirality.
Human Embryonic Stem Cell-Derived and Fetal Macrophages Exhibit Mainly Features of Alternative (M2) Polarization.
2009
Abstract Abstract 4598 Monocyte heterogeneity has long been recognized and 2 functional subsets of human monocytes that exert specific roles in homeostasis and inflammation in vivo, M1 and M2 monocytes, has been described. The different monocyte subsets seem to reflect developmental stages with distinct physiological roles but few is known whether the macrophage diversity arises in early ontogeny. Human embryonic stem cells (hESC) provide an unique model for in vitro studies of the early ontogeny of the hematopoietic system. Human embryonic monocytes were obtained from embryoid bodies cultured for 3 weeks in the presence of BMP4, VEGF and a mixture of hematopoietic cytokines. The sorted CD1…
The e-ASTROGAM gamma-ray space observatory for the multimessenger astronomy of the 2030s
2018
e-ASTROGAM is a concept for a breakthrough observatory space mission carrying a gamma-ray telescope dedicated to the study of the non-thermal Universe in the photon energy range from 0.15 MeV to 3 GeV. The lower energy limit can be pushed down to energies as low as 30 keV for gamma-ray burst detection with the calorimeter. The mission is based on an advanced space-proven detector technology, with unprecedented sensitivity, angular and energy resolution, combined with remarkable polarimetric capability. Thanks to its performance in the MeV-GeV domain, substantially improving its predecessors, e-ASTROGAM will open a new window on the non-thermal Universe, making pioneering observations of the…
Accessibility of Protein-Bound Chlorophylls Probed by Dynamic Electron Polarization
2018
The possibility to probe the accessibility of sites of proteins represents an important point to explore their interactions with specific substrates in solution. The dynamic electron polarization of nitroxide radicals induced by excited triplet states of organic molecules is a phenomenon that is known to occur in aqueous solutions. The interaction within the radical-triplet pair causes a net emissive dynamic electron polarization of the nitroxide radical, that can be detected by means of time-resolved electron paramagnetic resonance (TR-EPR) spectroscopy. We have exploited this effect to prove the accessibility of chlorophylls bound to a protein, namely, the water-soluble chlorophyll protei…
Hierarchical Self-Organization of Perylene Bisimide–Melamine Assemblies to Fluorescent Mesoscopic Superstructures
2000
A series of three perylene tetracarboxylic acid bisimide dyes 3a-c bearing phenoxy substituents at the four bay positions of the perylene core were synthesized and their complexation behavior to complementary ditopic dialkyl melamines 8a-c was investigated. Binding constants and Gibbs binding energies for the hydrogen bonds between the imide and the complementary melamine moiety have been determined in several solvents by NMR and UV/Vis titration experiments with monotopic model compounds 5 and 9. The effects of the solvent polarity and specific solvent-solute interactions on the degree of polymerization of (3 x 8)n are discussed, and a general formula to estimate the chain length of [AA-BB…
Antennas for the detection of radio emission pulses from cosmic-ray induced air showers at the Pierre Auger Observatory.
2012
The Pierre Auger Observatory is exploring the potential of the radio detection technique to study extensive air showers induced by ultra-high energy cosmic rays. The Auger Engineering Radio Array (AERA) addresses both technological and scientific aspects of the radio technique. A first phase of AERA has been operating since September 2010 with detector stations observing radio signals at frequencies between 30 and 80 MHz. In this paper we present comparative studies to identify and optimize the antenna design for the final configuration of AERA consisting of 160 individual radio detector stations. The transient nature of the air shower signal requires a detailed description of the antenna s…
Characterization of gramicidin A in an inverted micellar environment. A combined high-performance liquid chromatographic and spectroscopic study
1992
We have investigated the conformational adaptability of gramicidin A incorporated into reverse micelles of sodium bis(2-ethylhexyl)sulfosuccinate (AOT)/isooctane/water, a so far unexplored "host" membrane-mimetic model system for this peptide. A high-performance liquid chromatographic strategy previously developed for the study of gramicidin in phospholipid vesicles and normal micelles [Bañó et al. (1989) FEBS Lett. 250, 67; Bañó et al. (1991) Biochemistry 30, 886] has been successfully extended to this system. The method has permitted the separation of peptide conformational species, namely, double-stranded dimers and monomers, and an accurate quantitation of their proportion in the invert…