High resolution infrared absorption spectra, crystal field, and relaxation processes in CsCdBr_3:Pr^3+

High resolution low-temperature absorption spectra of 0.2% Pr^3+ doped CsCdBr_3 were measured in the spectral region 2000--7000 cm-1. Positions and widths of the crystal field levels within the 3H5, 3H4, 3F2, and 3F3 multiplets of the Pr^3+ main center have been determined. Hyperfine structure of several spectral lines has been found. Crystal field calculations were carried out in the framework of the semiphenomenological exchange charge model (ECM). Parameters of the ECM were determined by fitting to the measured total splittings of the 3H4 and 3H6 multiplets and to the observed in this work hyperfine splittings of the crystal field levels. One- and two-phonon relaxation rates were calculated using the phonon Green's functions of the perfect (CsCdBr_3) and locally perturbed (impurity dimer centers in CsCdBr_3:Pr^3+) crystal lattice. Comparison with the measured linewidths confirmed an essential redistribution of the phonon density of states in CsCdBr_3 crystals doped with rare-earth ions.Comment: 16 pages, 5 tables, 3 figure

A Broadly Applicable Strategy for Entry into Homogeneous Nickel(0) Catalysts from Air-Stable Nickel(II) Complexes

A series of air-stable nickel complexes of the form L[subscript 2]Ni(aryl) X (L = monodentate phosphine, X = Cl, Br) and LNi(aryl)X (L = bis-phosphine) have been synthesized and are presented as a library of precatalysts suitable for a wide variety of nickel-catalyzed transformations. These complexes are easily synthesized from low-cost NiCl[subscript 2]·6H[subscript 2]O or NiBr[subscript 2]·3H[subscript 2]O and the desired ligand followed by addition of 1 equiv of Grignard reagent. A selection of these complexes were characterized by single-crystal X-ray diffraction, and an analysis of their structural features is provided. A case study of their use as precatalysts for the nickel-catalyzed carbonyl-ene reaction is presented, showing superior reactivity in comparison to reactions using Ni(cod)[subscript 2]. Furthermore, as the precatalysts are all stable to air, no glovebox or inert-atmosphere techniques are required to make use of these complexes for nickel-catalyzed reactions.National Institute of General Medical Sciences (U.S.) (GM63755)National Science Foundation (U.S.). Graduate Research Fellowshi

Electronic absorption spectra, optical line strengths, and crystal-field energy-level structure of Nd3+ in hexagonal [Nd(H2O)9](CF3SO3)3

Optical absorption measurements are used to locate and assign 79 crystal-field (Stark) levels split out of the 4f3 electronic configuration of Nd3+ in single crystals of neodymium nonahydrate tris(trifluoromethanesulfonate), [Nd(H2O)9](CF3SO3)3, denoted hereafter as NdTRF. Line strengths are determined for 56 transitions between Stark levels. Single crystals of NdTRF have hexagonal, P63/m(C6h2) space-group symmetry, and each Nd3+ ion is coordinated to nine water molecules in a slightly distorted tri-capped trigonal prism structure of C3h symmetry. The energy-level structure of 4f3 (Nd3+) in NdTRF is analyzed in terms of a model Hamiltonian that includes consideration of both one-electron crystal-field and two-electron correlation-crystal-field interactions, the latter interactions making important contributions to the energy-level structures of several 4f3 [SL]J multiplet manifolds. Line strength data obtaibned for NdTRF is analyzed in terms of a general 4f → 4f transition intensity model in which the details of the 4f-electron/crystal-field/electric-dipolar radiation-field interactions are represented in parametric form. The derived parameters provide information about structural properties and interaction mechanisms that contribute to 4f → 4f transition intensities. The general crystal-field and intensity parameters are further analyzed in terms of a set of ‘intrinsic’ parameters that are related to contributions from individual Nd3+ OH2 pairwise interactions

Localization of the glutamine transporter SNAT1 in rat cerebral cortex and neighboring structures, with a note on its localization in human cortex

ABSTRACT SNAT1 mediates glutamine (Gln) influx into neurons and is believed to replenish the transmitters pools of glutamate (Glu) and γ-aminobutyric acid (GABA). We investigated its distribution and cellular localization in the cerebral cortex and neighboring regions of rats and humans using light and electron microscopic immunocytochemical methods with specific antibodies. In the first somatic sensory cortex of rats and in areas 9, 10, 21 and 46 of the human cortex, numerous SNAT1-positive (+) cells were present in the cortical parenchyma and in the white matter; >95% of SNAT1+ cells were neurons, but some were astrocytes. Most SNAT1+ cells were pyramidal neurons, but numerous non-pyramidal neurons were also observed: SNAT1/ GABA double-labeling studies showed that SNAT1 is expressed in all GABA+ neurons. SNAT1/synaptophysin studies showed that <0.1% of all synaptophysin+ puncta coexpressed SNAT1. SNAT1 immunoreactivity (ir) was also in leptomeninges, ependymal cells and choroid plexus. Electron microscopic studies showed that neuronal SNAT1 ir was almost exclusively observed in perikarya and dendritic profiles. SNAT1 ir was also in distal astrocytic processes, including end feet profiles, and in leptomeninges. These findings suggest that the major function of SNAT1 is not to replenish the transmitter pools of Glu and GABA

Laserterapia Fotodinamica nella degenerazione maculare correlata all'et\ue0: risultati funzionali.

Scopo del presente lavoro \ue8 di riferire l'esperienza personale nel laser trattamento fotodinamico della Degenerazione Maculare Legata all'Et\ue0 (DMLA) complicata da neovascolarizzazioni coroideali subfoveali

The e-h plasma in direct-gap GaAlas under 3-d confinement

Uniformely excited e-h plasma in direct-gap Ga1 12xAlxAs under 3-D confinement has been measured by photoluminescence at 2 K. A satisfactory fit to experiment in the whole range of densities investigated is given by a theoretical model with k-conservation and collision broadening, using a single value of density and temperature throughout the excited region. The fitted renormalized gap matches closely current theoretical values, independent of composition x