Search results for "RAY"
showing 10 items of 8009 documents
Element-Selective Magnetic Imaging in Exchange-Coupled Systems by Magnetic Photoemission Microscopy
1998
We have used a photoemission microscope to obtain element-resolved magnetic contrast in stacked magnetic thin film systems. Magnetic information is thereby provided by X-ray magnetic circular dichroism. Elemental sensitivity, which is crucial for studying magnetic coupling phenomena in systems with several different layers, is achieved by tuning the energy of the illuminating photons to atomic absorption edges. We present measurements of a Ni-coated Co micropattern on Cu(001), and a wedged Co/Cr/Fe(001) sample. In the former sample the Ni magnetization is seen to follow the magnetization of the Co pattern, thereby changing from an out-of-plane easy axis in areas without underlying Co to in…
Reactivity of Distibanes toward Trialkylalanes and -gallanes: Syntheses and X-ray Structures of Bisadducts and Heterocycles
2001
Reactions between distibanes of the type Sb2R4 and trialkylalanes and -gallanes R‘3M in 1:2 stoichiometry yield eight bisadducts of the type [Sb2R4][MR‘3]2 (R = Me, R‘ = t-Bu, M = Al 1, Ga 2; R = Et, M = Al, R‘ = Me 3, Et 4, t-Bu 5; M = Ga, R‘ = Me 6, Et 7, t-Bu 8), which were characterized by multinuclear NMR studies and elemental analysis. In addition, 1, 2, 5, and 8 are the first structurally characterized neutral main group Lewis acid−distibane bisadducts. 1−8 are unstable in solution toward the formation of heterocycles of the type [R2SbMR‘2]x. [Me2SbGa(t-Bu)2]3 (9) and [Et2SbGa(t-Bu)2]2 (10) have been isolated and their solid state structures determined by single-crystal X-ray diffrac…
Photoelectrochemical study of passive films on stainless steel in neutral solutions
1991
Abstract Passive films formed on AISI 304 stainless steel in neutral solutions are studied using photoelectrochemical technique. Photocurrents were investigated as a function of the wavelength of the incident light, the electrode potential and the time. The results of the measurements together with capacity measurements indicate that the passive film on AISI 304 shows characteristics of a highly doped amorphous or highly disordered n-type semiconductor. The potential dependence of the optical gap values and of the photocurrent transients can be interpreted assuming that the passive film is an iron-chromium oxide solid solution.
Crystal structures, infrared-spectra, and thermal behavior of calcium hydrogenselenite monohydrate, Ca(HSeO3)2 · H2O, and dicalcium diselenite bis(hy…
1986
Abstract Calcium hydrogenselenite monohydrate and dicalcium diselenite bis(hydrogenselenite) were synthesized and their crystal structures determined. Crystal data for Ca(HSeO3)2 · H2O: a = 6.911(2), b = 7.369(2), c = 6.739(2) A, α = 90.51(3)°, β = 90.93(3)°, γ = 107.46(2)°, V = 327.3(2) A3, space group P 1 (No. 2), dcalcd = 3.19 M gm−3, Z = 2, and R = 0.036 for 1503 reflections. Data for Ca2(HSeO3)2(Se2O5): a = 14.719(4), b = 7.059(2), c = 11.793(2) A, β = 117.96(2)°, V = 1082.3(4) A3, space group C2 c (No. 15), dcalcd = 3.52 Mg m−3, Z = 4, and R = 0.047 for 1251 reflections. Both structures form a three-dimensional network. The coordination polyhedron around calcium is a monocapped trigon…
Defects in yttrium aluminium perovskite and garnet crystals: atomistic study
2000
Native and impurity point defects in both yttrium aluminium perovskite (YAP) and garnet (YAG) crystals are studied in the framework of the pair-potential approximation coupled with the shell model description of the lattice ions. The calculated formation energies for native defects suggest that the antisite disorder is preferred over the Frenkel and Schottky-like disorder in both YAP and YAG. The calculated values of the distortion caused by the antisite YAl x in the lattice turn out to be in an excellent agreement with the EXAFS measurements. In non-stoichiometric compounds, the calculated reaction energies indicate that excess Y2 O3 or Al2 O3 is most likely to be accommodated by the forma…
New Regularization Method for EXAFS Analysis
2007
As an alternative to the analysis of EXAFS spectra by conventional shell fitting, the Tikhonov regularization method has been proposed. An improved algorithm that utilizes a priori information about the sample has been developed and applied to the analysis of U L3‐edge spectra of soddyite, (UO2)2SiO4⋅2H2O, and of U(VI) sorbed onto kaolinite. The partial radial distribution functions g1(UU), g2(USi), and g3(UO) of soddyite agree with crystallographic values and previous EXAFS results.
CONSTRUCTION OF METASTABLE STATES IN QUANTUM ELECTRODYNAMICS
2004
In this paper, we construct metastable states of atoms interacting with the quantized radiation field. These states emerge from the excited bound states of the non-interacting system. We prove that these states obey an exponential time-decay law. In detail, we show that their decay is given by an exponential function in time, predicted by Fermi's Golden Rule, plus a small remainder term. The latter is proportional to the (4+β)th power of the coupling constant and decays algebraically in time. As a result, though it is small, it dominates the decay for large times. A central point of the paper is that our remainder term is significantly smaller than the one previously obtained in [1] and as…
Simulations of Array Configurations for the Square Kilometre Array (SKA)
2010
The Square Kilometre Array (SKA) is a new generation radio telescope for the next decades, working at metre to centimetre wavelengths. The SKA will be operational at the same time than other new optical, X-ray and Gamma-ray telescopes. It is of extreme importance that the SKA becomes competitive and complementary to those instruments. An extensive study of technologies and possible configurations involved is needed to ensure the SKA will reach the design specifications. To compare imaging capabilities between different SKA configurations or between the SKA and other instruments, we have implemented figures of merit based on several characteristics of these instruments. In this work we are p…
Cytosporones, coumarins, and an alkaloid from the endophytic fungus Pestalotiopsis sp. isolated from the Chinese mangrove plant Rhizophora mucronata
2009
Chemical examination of the endophytic fungus Pestalotiopsis sp., isolated from the leaves of the Chinese mangrove Rhizophora mucronata, yielded 11 new compounds including cytosporones J-N (1-3, 5-6), five new coumarins pestalasins A-E (8-12), and a new alkaloid named pestalotiopsoid A (14), along with the known compounds cytosporone C (4), dothiorelone B (7), and 3-hydroxymethyl-6,8-dimethoxycoumarin (13). The structures of the new compounds were unambiguously elucidated on the basis of extensive spectroscopic data analysis.
Compact all-diffractive setup for spectral synthesis with non-uniform illumination
2009
Optical filters based on diffractive optical elements (DOE) have received increased attention since the development of the first synthetic spectrum as a tool for correlation spectroscopy [1]. The production of a synthetic spectrum requires the design of a DOE that transforms the spectrum associated with the incident light into the spectrum of interest. Based on this procedure, several approaches have been reported in the literature [1–4]. In general, these configurations employ angular dispersion elements for spectrum tailoring, so they are restricted to working off-axis, and most of them need an extra focusing refractive lens.