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Sample records for absorption fine-structure xafs

  1. The 16th International Conference on X-ray Absorption Fine Structure (XAFS16)

    NASA Astrophysics Data System (ADS)

    Grunwaldt, J.-D.; Hagelstein, M.; Rothe, J.

    2016-05-01

    This preface of the proceedings volume of the 16th International Conference on X- ray Absorption Fine Structure (XAFS16) gives a glance on the five days of cutting-edge X-ray science which were held in Karlsruhe, Germany, August 23 - 28, 2015. In addition, several satellite meetings took place in Hamburg, Berlin and Stuttgart, a Sino-German workshop, three data analysis tutorials as well as special symposia on industrial catalysis and XFELs were held at the conference venue.

  2. Sorption mechanisms of zinc to calcium silicate hydrate: X-ray absorption fine structure (XAFS) investigation.

    PubMed

    Ziegler, F; Scheidegger, A M; Johnson, C A; Dähn, R; Wieland, E

    2001-04-01

    In this study, X-ray absorption fine structure (XAFS) spectroscopy has been used to further elucidate the binding mechanisms of Zn(II) to calcium silicate hydrate (C-S-H), the quantitatively most important cement mineral. Such knowledge is essential for the assessment of the longterm behavior of cement-stabilized waste materials. XAFS spectra of the Zn(II) equilibrated with C-S-H(I) for up to 28 days are best modeled by tetrahedral coordination of Zn(II) by four O atoms in the first atomic shell. Beyond the first coordination shell, data analysis of more highly concentrated samples suggests the presence of two distinct Zn distances and possibly the presence of an Si shell. On the basis of the comparison with a set of reference compounds, this coordination environment can be reasonably related to the structure of hemimorphite, a naturally occurring zinc silicate, and/or the presence of gamma-Zn(OH)2. At the lowest Zn uptake, the above fitting approach failed and data could be described best with a Zn-Si and a Zn-Ca shell. Previous work has been able to show that Zn(II) diffuses into the C-S-H(I) particles and does not form discrete precipitates, so the findings appear to confirm the incorporation of Zn(II) in the interlayer of C-S-H(I).

  3. PREFACE: The 15th International Conference on X-ray Absorption Fine Structure (XAFS15)

    NASA Astrophysics Data System (ADS)

    Wu, Z. Y.

    2013-04-01

    The 15th International Conference on X-ray Absorption Fine Structure (XAFS15) was held on 22-28 July 2012 in Beijing, P. R. China. About 340 scientists from 34 countries attended this important international event. Main hall Figure 1. Main hall of XAFS15. The rapidly increasing application of XAFS to the study of a large variety of materials and the operation of the new SR source led to the first meeting of XAFS users in 1981 in England. Following that a further 14 International Conferences have been held. Comparing a breakdown of attendees according to their national origin, it is clear that participation is spreading to include attendees from more and more countries every year. The strategy of development in China of science and education is increasing quickly thanks to the large investment in scientific and technological research and infrastructure. There are three Synchrotron Radiation facilities in mainland China, Hefei Light Source (HLS) in the National Natural Science Foundation of China (NSRL), Beijing Synchrotron Radiation Facility (BSRF) in the Institute of High Energy Physics, and Shanghai Synchrotron Radiation Facility (SSRF) in the Shanghai Institute of Applied Physics. More than 10000 users and over 5000 proposals run at these facilities. Among them, many teams from the USA, Japan, German, Italy, Russia, and other countries. More than 3000 manuscript were published in SCI journals, including (incomplete) Science (7), Nature (10), Nature Series (7), PNAS (3), JACS (12), Angew. Chem. Int. Ed. (15), Nano Lett. (2), etc. In XAFS15, the participants contributed 18 plenary invited talks, 16 parallel invited talks, 136 oral presentations, 12 special talks, and 219 poster presentations. Wide communication was promoted in the conference halls, the classical banquet restaurant, and the Great Wall. Parallel hallCommunicationPoster room Figure 2. Parallel hallFigure 3. CommunicationFigure 4. Poster room This volume contains 136 invited and contributed papers

  4. Speciation of arsenic in pyrite by micro-X-ray absorption fine- structure spectroscopy (XAFS)

    SciTech Connect

    Paktunc, D.

    2008-09-30

    Pyrite (FeS2) often contains variable levels of arsenic, regardless of the environment of formation. Arsenian pyrite has been reported in coals, sediments and ore deposits. Arsenian pyrite having As concentrations of up to 10 wt % in sedimentary rocks (Kolker et al. 1997), about 10 wt% in gold deposits (Fleet et al. 1993), 12 wt % in a refractory gold ore (Paktunc et al. 2006) and 20 wt % in a Carlin-type gold deposit in Nevada (Reich et al. 2005) have been reported. Arsenian pyrite is the carrier of gold in hydrothermal Carlin-type gold deposits, and gold concentrations of up to 0.9 wt % have been reported (Reich et al. 2005; Paktunc et al. 2006). In general, high Au concentrations correlate with As-rich zones in pyrite (Paktunc et al. 2006). Pyrite often ends up in mining and metallurgical wastes as an unwanted mineral and consititutes one of the primary sources of As in the wastes. Arsenic can be readily released to the environment due to rapid oxidative dissolution of host pyrite under atmospheric conditions. Pyrite is also the primary source of arsenic in emissions and dust resulting from combustion of bituminous coals. Despite the importance of arsenian pyrite as a primary source of anthropogenic arsenic in the environment and its economic significance as the primary carrier of gold in Carlin-type gold deposits, our understanding of the nature of arsenic in pyrite is limited. There are few papers dealing with the mode of occurrence of arsenic by bulk XAFS in a limited number of pyrite-bearing samples. The present study documents the analysis of pyrite particles displaying different morphologies and a range of arsenic and gold concentrations to determine the nature and speciation of arsenic.

  5. Application of x-ray absorption fine structure (XAFS) to local-order analysis in Fe-Cr maghemite-like materials

    SciTech Connect

    Montero-Cabrera, M. E. Fuentes-Cobas, L. E.; Macías-Ríos, E.; Fuentes-Montero, M. E.

    2015-07-23

    The maghemite-like oxide system γ-Fe{sub 2-x}Cr{sub x}O{sub 3} (x=0.75, 1 and 1.25) was studied by X-ray absorption fine structure (XAFS) and by synchrotron radiation X-ray diffraction (XRD). Measurements were performed at the Stanford Synchrotron Radiation Lightsource at room temperature, at beamlines 2-1, 2-3 and 4-3. High-resolution XRD patterns were processed by means of the Rietveld method. In cases of atoms being neighbors in the Periodic Table, the order/disorder degree of the considered solutions is indiscernible by “normal” (absence of “anomalous scattering”) diffraction experiments. Thus, maghemite-like materials were investigated by XAFS in both Fe and Cr K-edges to clarify, via short-range structure characterization, the local ordering of the investigated system. Athena and Artemis graphic user interfaces for IFEFFIT and FEFF8.4 codes were employed for XAFS spectra interpretation. Pre-edge decomposition and theoretical modeling of X-ray absorption near edge structure (XANES) transitions were performed. By analysis of the Cr K-edge XANES, it has been confirmed that Cr is located in an octahedral environment. Fitting of the extended X-ray absorption fine structure (EXAFS) spectra was performed under the consideration that the central atom of Fe is allowed to occupy octa- and tetrahedral positions, while Cr occupies only octahedral ones. Coordination number of neighboring atoms, interatomic distances and their quadratic deviation average were determined for x=1, by fitting simultaneously the EXAFS spectra of both Fe and Cr K-edges. The results of fitting the experimental spectra with theoretical standards showed that the cation vacancies tend to follow a regular pattern within the structure of the iron-chromium maghemite (FeCrO{sub 3})

  6. Application of x-ray absorption fine structure (XAFS) to local-order analysis in Fe-Cr maghemite-like materials

    NASA Astrophysics Data System (ADS)

    Montero-Cabrera, M. E.; Fuentes-Cobas, L. E.; Macías-Ríos, E.; Fuentes-Montero, M. E.

    2015-07-01

    The maghemite-like oxide system γ-Fe2-xCrxO3 (x=0.75, 1 and 1.25) was studied by X-ray absorption fine structure (XAFS) and by synchrotron radiation X-ray diffraction (XRD). Measurements were performed at the Stanford Synchrotron Radiation Lightsource at room temperature, at beamlines 2-1, 2-3 and 4-3. High-resolution XRD patterns were processed by means of the Rietveld method. In cases of atoms being neighbors in the Periodic Table, the order/disorder degree of the considered solutions is indiscernible by "normal" (absence of "anomalous scattering") diffraction experiments. Thus, maghemite-like materials were investigated by XAFS in both Fe and Cr K-edges to clarify, via short-range structure characterization, the local ordering of the investigated system. Athena and Artemis graphic user interfaces for IFEFFIT and FEFF8.4 codes were employed for XAFS spectra interpretation. Pre-edge decomposition and theoretical modeling of X-ray absorption near edge structure (XANES) transitions were performed. By analysis of the Cr K-edge XANES, it has been confirmed that Cr is located in an octahedral environment. Fitting of the extended X-ray absorption fine structure (EXAFS) spectra was performed under the consideration that the central atom of Fe is allowed to occupy octa- and tetrahedral positions, while Cr occupies only octahedral ones. Coordination number of neighboring atoms, interatomic distances and their quadratic deviation average were determined for x=1, by fitting simultaneously the EXAFS spectra of both Fe and Cr K-edges. The results of fitting the experimental spectra with theoretical standards showed that the cation vacancies tend to follow a regular pattern within the structure of the iron-chromium maghemite (FeCrO3).

  7. X-ray absorption fine structure (XAFS) analyses of Ni species trapped in graphene sheet of carbon nanofibers

    SciTech Connect

    Ushiro, Mayuko; Uno, Kanae; Fujikawa, Takashi; Sato, Yoshinori; Tohji, Kazuyuki; Watari, Fumio; Chun, W.-J.; Koike, Yuichiro; Asakura, Kiyotaka

    2006-04-01

    Metal impurities in the carbon nanotubes and carbon nanofibers play an important role in understanding their physical and chemical properties. We apply the Ni K-edge x-ray absorption fine structure analyses to the local electronic and geometric structures around embedded Ni impurities used as catalysts in a carbon nanofiber in combination with multiple scattering analyses. We find almost Ni catalysts as metal particles are removed by the purification treatment. Even after the purification, residual 100 ppm Ni species are still absorbed; most of them are in monomer structure with Ni-C bond length 1.83 A, and each of them is substituted for a carbon atom in a graphene sheet.

  8. X-ray absorption fine structure (XAFS) studies of copper (II) mixed ligand complexes having tetramethylethylenediamine as one of the ligands

    NASA Astrophysics Data System (ADS)

    Sharma, Sharad; Joshi, S. K.; Shrivastava, B. D.; Hinge, V. K.; Prasad, J.; Srivastava, K.

    2014-09-01

    X-ray absorption fine structure (XAFS) has been studied at the K-edge of copper in copper(II) mixed ligand complexes, having tetramethylethylenediamine (tmen) as one of the ligands, viz., Cu(tmen)(gly)ClO4, Cu(tmen)(bipy)(ClO4)2 and Cu(tmen)(phen)(ClO4)2. The spectra have been recorded at the dispersive XAFS beamline (BL-8) at the 2.5 GeV INDUS-2 synchrotron, RRCAT, Indore, India. The data obtained has been processed and analyzed using the computer program Athena. It has been observed that K-edge has been found to split in two edges, K and K', in each of the complex. The chemical shift has been utilized to determine the oxidation state of copper in the complexes and also the effective nuclear charge (ENC). The EXAFS data has been analyzed to obtain the bond lengths in the complexes using Levy's, Lytle's and Lytle, Sayers and Stern's (LSS) methods. The first peak in the Fourier transform of the spectra gives the value of first shell phase uncorrected bond length. The results obtained from the Fourier transformation and LSS methods are in good agreement.

  9. Separable-spherical-wave approximation: Application to x-ray-absorption fine-structure multiple scattering in ReO3

    NASA Astrophysics Data System (ADS)

    Houser, B.; Ingalls, R.; Rehr, J. J.

    1992-04-01

    Rehr and Albers have shown that the exact x-ray-absorption fine-structure (XAFS) propagator may be expanded in a separable matrix form, and that the lowest-order term in the expansion yields XAFS formulas that contain spherical-wave corrections, yet retain the simplicity of the plane-wave approximation. This separable-spherical-wave approximation was used to model the multiple-scattering contributions to the XAFS spectrum of rhenium trioxide. We report a modest improvement over the plane-wave approximation.

  10. Note: Construction of x-ray scattering and x-ray absorption fine structure beamline at the Pohang Light Source

    SciTech Connect

    Lee, Ik-Jae; Yu, Chung-Jong; Yun, Young-Duck; Lee, Chae-Soon; Seo, In Deuk; Kim, Hyo-Yun; Lee, Woul-Woo; Chae, Keun Hwa

    2010-02-15

    A new hard x-ray beamline, 10B KIST-PAL beamline (BL10B), has been designed and constructed at the Pohang Light Source (PLS) in Korea. The beamline, operated by Pohang Accelerator Laboratory-Korean Institute of Science and Technology consortium, is dedicated to x-ray scattering (XRS) and x-ray absorption fine structure (XAFS) experiments. X rays with photon energies from 4.0 to 16.0 keV are delivered to the experimental station passing a collimating mirror, a fixed-exit double-crystal Si(111) monochromator, and a toroidal mirror. Basic experimental equipments for XAFS measurement, a high resolution diffractometry, an image plate detector system, and a hot stage have been prepared for the station. From our initial commissioning and performance testing of the beamline, it is observed that BL10B beamline can perform XRS and XAFS measurements successfully.

  11. The Effect of X-Ray Absorption Fine Structure in Soft X-ray Astronomical Telescopes

    NASA Astrophysics Data System (ADS)

    Owens, Alan; Denby, Michael; Wells, Alan; Keay, Adam; Graessle, Dale E.; Blake, Richard L.

    1997-02-01

    Recent in-orbit measurements by high resolution soft X-ray telescopes have revealed low-level fine structure in target spectra that cannot be attributed to a celestial source. Ultimately, this can be traced to the ability of the new high spectral resolution silicon detectors to resolve X-ray absorption fine structure (XAFS) produced in the various detection subsystems. Based on measurements taken at the Daresbury Synchrotron Radiation Source (SRS) and the National Synchrotron Light Source (NSLS), we have modeled the full-up response function of the Joint European X-ray Telescope (JET-X), taking into account edge structure generated in the detectors, filters, and mirrors. It is found that unfolding celestial source spectra using a response function in which the detailed edge shapes are calculated from standard absorption cross sections leads to the generation of spectral artifacts at every absorption edge. These in turn produce unacceptably high values of χ2 in model fits for total source fluxes above ~4 × 104 counts. For JET-X, this corresponds to a source strength of ~0.4 millicrab observed for 105 s. Statistically significant ``linelike'' features are introduced into the derived source spectra with amplitudes as great as 10% of the source flux. For JET-X, these features rise above the 3 σ level for integral source exposures above ~5 × 104 source counts. The largest deviations in the residuals arise near 0.5 keV and 2.2 keV and are attributed to XAFS produced in the oxide surface layers of the CCD and the gold reflective surface of the mirrors, respectively. These results are significant for data interpretation tasks with the ASCA, JET-X, XMM, and Advanced X-Ray Astrophysics Facility (AXAF) telescopes.

  12. The forms of trace metals in an Illinois basin coal by x-ray absorption fine structure spectroscopy

    USGS Publications Warehouse

    Chou, I.-Ming; Bruinius, J.A.; Lytle, J.M.; Ruch, R.R.; Huggins, Frank E.; Huffman, G.P.; Ho, K.K.

    1997-01-01

    Utilities burning Illinois coals currently do not consider trace elements in their flue gas emissions. After the US EPA completes an investigation on trace elements, however, this may change and flue gas emission standards may be established. The mode of occurrence of a trace element may determine its cleanability and Hue gas emission potential. X-ray Absorption Fine Structure (XAFS) is a spectroscopic technique that can differentiate the mode of occurrence of an element, even at the low concentrations that trace elements are found in coal. This is principally accomplished by comparing the XAFS spectra of a coal to a database of reference sample spectra. This study evaluated the technique as a potential tool to examine six trace elements in an Illinois #6 coal. For the elements As and Zn, the present database provides a definitive interpretation on their mode of occurrence. For the elements Ti, V, Cr, and Mn the database of XAFS spectra of trace elements in coal was still too limited to allow a definitive interpretation. The data obtained on these elements, however, was sufficient to rule out several of the mineralogical possibilities that have been suggested previously. The results indicate that XAFS is a promising technique for the study of trace elements in coal.

  13. Extended x-ray absorption fine structure studies of hemoglobin

    SciTech Connect

    Shulman, R.G.

    1987-02-01

    Results of extended x-ray absorption fine structure (EXAFS) studies of the iron atom in deoxygenated hemoglobin are reviewed. It is shown that the iron-porphinato nitrogen distance has been determined to be 2.06 +/- 0.01 A by two independent investigations. Difficulties experienced in using this distance to calculate the iron's distance above the plane by triangulation are shown to be due to ignoring differences between ferrous and ferric hemes. It is concluded that the iron is 0.2 +/- 0.1/0.2 A above the plane of the nitrogens as originally shown.

  14. Extended X-ray absorption fine structure of bimetallic nanoparticles

    PubMed Central

    2011-01-01

    Summary Electronic and magnetic properties strongly depend on the structure of the material, especially on the crystal symmetry and chemical environment. In nanoparticles, the break of symmetry at the surface may yield different physical properties with respect to the corresponding bulk material. A useful tool to investigate the electronic structure, magnetic behaviour and local crystallographic structure is X-ray absorption spectroscopy. In this review, recent developments in the field of extended X-ray absorption fine structure measurements and in the analysis methods for structural investigations of bimetallic nanoparticles are highlighted. The standard analysis based on Fourier transforms is compared to the relatively new field of wavelet transforms that have the potential to outperform traditional analysis, especially in bimetallic alloys. As an example, the lattice expansion and inhomogeneous alloying found in FePt nanoparticles is presented, and this is discussed below in terms of the influence of employed density functional theory calculations on the magnetic properties. PMID:21977436

  15. Photoconductivity measurements of x-ray absorption fine structures in liquids in the soft x-ray region: Si and Cl K-edge

    SciTech Connect

    Sham, T.K.; Xiong, J.Z.; Feng, X.H.; Holroyd, R.A.; Yang, B.X.

    1992-12-31

    Photoconductivity measurements of X-ray absorption fine structures (XAFS) at the Si and Cl K-edge have been carried out in a liquid cell for (CH{sub 3}){sub 4},Si [(CH{sub 3}){sub 3}Si]{sub 4}Si and eitheras a pure liquid or 2,2,4-trimethylpentane solution. It is found that for the pure liquids and their concentrated hydrocarbon solutions, all K-edge XAFS spectra are inverted as expected under the condition of total absorption. A sharp conductivity dip is also observed in CCl{sub 4} at the Cl K-edge. The concentration dependence of the XAFS spectrum of CCl{sub 4} is reported. These results are discussed in terms of soft X-ray induced ion yields of the solute and solvent molecules in liquids.

  16. Photoconductivity measurements of x-ray absorption fine structures in liquids in the soft x-ray region: Si and Cl K-edge

    SciTech Connect

    Sham, T.K.; Xiong, J.Z.; Feng, X.H. . Dept. of Chemistry); Holroyd, R.A. ); Yang, B.X. )

    1992-01-01

    Photoconductivity measurements of X-ray absorption fine structures (XAFS) at the Si and Cl K-edge have been carried out in a liquid cell for (CH[sub 3])[sub 4],Si [(CH[sub 3])[sub 3]Si][sub 4]Si and eitheras a pure liquid or 2,2,4-trimethylpentane solution. It is found that for the pure liquids and their concentrated hydrocarbon solutions, all K-edge XAFS spectra are inverted as expected under the condition of total absorption. A sharp conductivity dip is also observed in CCl[sub 4] at the Cl K-edge. The concentration dependence of the XAFS spectrum of CCl[sub 4] is reported. These results are discussed in terms of soft X-ray induced ion yields of the solute and solvent molecules in liquids.

  17. Mechanism of Pb Adsorption to Fatty Acid Langmuir Monolayers Studied by X-ray Absorption Fine Structure Spectroscopy

    SciTech Connect

    Boyanov, M.I.; Kmetko, J.; Shibata, T.; Datta, A.; Dutta, P.; Bunker, B.A.

    2010-09-30

    The local atomic environment of lead (Pb) adsorbed to a CH{sub 3}(CH{sub 2}){sub 19}COOH Langmuir monolayer was investigated in situ using grazing-incidence X-ray absorption fine structure (GI-XAFS) spectroscopy at the Pb L{sub III} edge. Measurements were performed at pH 6.5 of the 10{sup -5} M PbCl{sub 2} solution subphase, a condition under which grazing incidence diffraction (GID) revealed a large-area commensurate superstructure underneath the close-packed organic monolayer. The XAFS results indicate covalent binding of the Pb cations to the carboxyl headgroups, and the observed Pb-Pb coordination suggests that the metal is adsorbed as a hydrolysis polymer, rather than as individual Pb{sup 2+} ions. The data are consistent with a bidentate chelating mechanism and a one Pb atom to one carboxyl headgroup binding stoichiometry. We discuss how this adsorption model can explain the peculiarities observed with Pb in previous metal-Langmuir monolayer studies. A systematic study of lead perchlorate and lead acetate aqueous solutions is presented and used in the analysis. XAFS multiple scattering effects from alignment of the Pb-C-C atoms in the lead acetate solutions are reported.

  18. X-ray absorption fine structure and X-ray excited optical luminescence studies of II-VI semiconducting nanostructures

    NASA Astrophysics Data System (ADS)

    Murphy, Michael Wayne

    2010-06-01

    Various II-VI semiconducting nanomaterials such as ZnO-ZnS nanoribbons (NRs), CdSxSe1-x nanostructures, ZnS:Mn NRs, ZnS:Mn,Eu nanoprsims (NPs), ZnO:Mn nanopowders, and ZnO:Co nanopowders were synthesized for study. These materials were characterized by techniques such as scanning electron microscopy, transmission electron microscopy, element dispersive X-ray spectroscopy, selected area electron diffraction, and X-ray diffraction. The electronic and optical properties of these nanomaterials were studied by X-ray absorption fine structure (XAFS) spectroscopy and X-ray excited optical luminescence (XEOL) techniques, using tuneable soft X-rays from a synchrotron light source. The complementary nature ofthe XAFS and XEOL techniques give site, element and chemical specific measurements which allow a better understanding of the interplay and role of each element in the system. Chemical vapour deposition (CVD) of ZnS powder in a limited oxygen environment resulted in side-by-side biaxial ZnO-ZnS NR heterostructures. The resulting NRs contained distinct wurtzite ZnS and wurtzite ZnO components with widths of 10--100 nm and 20 --500 nm, respectively and a uniform interface region of 5-15 nm. XAFS and XEOL measurements revealed the luminescence of ZnO-ZnS NRs is from the ZnO component. The luminescence of CdSxSe1-x nanostructures is shown to be dependent on the S to Se ratio, with the band-gap emission being tunable between that of pure CdS and CdSe. Excitation of the CdSxSe 1-x nanostructures by X-ray in XEOL has revealed new de-excitation channels which show a defect emission band not seen by laser excitation. CVD of Mn2+ doped ZnS results in nanostructures with luminescence dominated by the yellow Mn2+ emission due to energy transfer from the ZnS host to the Mn dopant sites. The addition of EuCl3 to the reactants in the CVD process results in a change in morphology from NR to NP. Zn1-xMnxO and Zn1-xCOxO nanopowders were prepared by sol-gel methods at dopant concentrations

  19. X-ray Absorption Fine Structure Studies of Mn Coordination in Doped Perovskite SrTiO3

    SciTech Connect

    Levin, I.; Krayzman, V; Woicik, J; Tkach, A; Vilarinho, P

    2010-01-01

    The coordination of Mn in doped SrTiO{sub 3} ceramics having nominal compositions SrTi{sub 0.98}Mn{sub 0.02}O{sub 3} and Sr{sub 0.98}Mn{sub 0.02}TiO{sub 3} was analyzed using x-ray absorption fine structure (XAFS) measurements. As expected, Mn{sup 4+} substitution for Ti{sup 4+} leads to Mn occupancy of the octahedral B-sites of ABO{sub 3} perovskite lattice with a Mn-O bond distance of 1.902 {angstrom} (compared to 1.953 {angstrom} for Ti-O) and no significant local distortions around the Mn atoms. In contrast, for the composition Sr{sub 0.98}Mn{sup 0.02}TiO{sub 3}, Mn segregates to both the A-sites (as Mn{sup 2+}) and the B-sites (predominantly as Mn{sup 4+}). Extended XAFS confirms strong ({approx} 0.77 {angstrom}) displacements of Mn{sup 2+} cations off the ideal A-site positions along <001> directions with a significant distortion of several coordination shells around the dopant atoms.

  20. Mercury Speciation by X-ray Absorption Fine Structure Spectroscopy and Sequential Chemical Extractions: A Comparison of Speciation Methods

    USGS Publications Warehouse

    Kim, C.S.; Bloom, N.S.; Rytuba, J.J.; Brown, Gordon E.

    2003-01-01

    Determining the chemical speciation of mercury in contaminated mining and industrial environments is essential for predicting its solubility, transport behavior, and potential bioavailability as well as for designing effective remediation strategies. In this study, two techniques for determining Hg speciation-X-ray absorption fine structure (XAFS) spectroscopy and sequential chemical extractions (SCE)-are independently applied to a set of samples with Hg concentrations ranging from 132 to 7539 mg/kg to determine if the two techniques provide comparable Hg speciation results. Generally, the proportions of insoluble HgS (cinnabar, metacinnabar) and HgSe identified by XAFS correlate well with the proportion of Hg removed in the aqua regia extraction demonstrated to remove HgS and HgSe. Statistically significant (> 10%) differences are observed however in samples containing more soluble Hg-containing phases (HgCl2, HgO, Hg3S2O 4). Such differences may be related to matrix, particle size, or crystallinity effects, which could affect the apparent solubility of Hg phases present. In more highly concentrated samples, microscopy techniques can help characterize the Hg-bearing species in complex multiphase natural samples.

  1. Chromium oxide as a metal diffusion barrier layer: An x-ray absorption fine structure spectroscopy study

    NASA Astrophysics Data System (ADS)

    Ahamad Mohiddon, Md.; Lakshun Naidu, K.; Ghanashyam Krishna, M.; Dalba, G.; Ahmed, S. I.; Rocca, F.

    2014-01-01

    The interaction at the interface between chromium and amorphous Silicon (a-Si) films in the presence of a sandwich layer of chromium oxide is investigated using X-ray absorption fine structure (XAFS) spectroscopy. The oxidized interface was created, in situ, prior to the deposition of a 400 nm tick a-Si layer over a 50 nm tick Cr layer. The entire stack of substrate/metallic Cr/Cr2O3/a-Si was then annealed at temperatures from 300 up to 700 °C. Analysis of the near edge and extended regions of each XAFS spectrum shows that only a small fraction of Cr is able to diffuse through the oxide layer up to 500 °C, while the remaining fraction is buried under the oxide layer in the form of metallic Cr. At higher temperatures, diffusion through the oxide layer is enhanced and the diffused metallic Cr reacts with a-Si to form CrSi2. At 700 °C, the film contains Cr2O3 and CrSi2 without evidence of unreacted metallic Cr. The activation energy and diffusion coefficient of Cr are quantitatively determined in the two temperature regions, one where the oxide acts as diffusion barrier and another where it is transparent to Cr diffusion. It is thus demonstrated that chromium oxide can be used as a diffusion barrier to prevent metal diffusion into a-Si.

  2. Applications of x ray absorption fine structure to the in situ study of the effect of cobalt in nickel hydrous oxide electrodes for fuel cells and rechargeable batteries

    NASA Technical Reports Server (NTRS)

    Kim, Sunghyun; Tryk, Donald A.; Scherson, Daniel A.; Antonio, Mark R.

    1993-01-01

    Electronic and structural aspects of composite nickel-cobalt hydrous oxides have been examined in alkaline solutions using in situ X-ray absorption fine structure (XAFS). The results obtained have indicated that cobalt in this material is present as cobaltic ions regardless of the oxidation state of nickel in the lattice. Furthermore, careful analysis of the Co K-edge Extended X-ray absorption fine structure data reveals that the co-electrodeposition procedure generates a single phase, mixed metal hydrous oxide, in which cobaltic ions occupy nickel sites in the NiO2 sheet-like layers and not two intermixed phases each consisting of a single metal hydrous oxide.

  3. Portable ultrahigh-vacuum sample storage system for polarization-dependent total-reflection fluorescence x-ray absorption fine structure spectroscopy

    SciTech Connect

    Watanabe, Yoshihide Nishimura, Yusaku F.; Suzuki, Ryo; Beniya, Atsushi; Isomura, Noritake; Uehara, Hiromitsu; Asakura, Kiyotaka; Takakusagi, Satoru; Nimura, Tomoyuki

    2016-03-15

    A portable ultrahigh-vacuum sample storage system was designed and built to investigate the detailed geometric structures of mass-selected metal clusters on oxide substrates by polarization-dependent total-reflection fluorescence x-ray absorption fine structure spectroscopy (PTRF-XAFS). This ultrahigh-vacuum (UHV) sample storage system provides the handover of samples between two different sample manipulating systems. The sample storage system is adaptable for public transportation, facilitating experiments using air-sensitive samples in synchrotron radiation or other quantum beam facilities. The samples were transferred by the developed portable UHV transfer system via a public transportation at a distance over 400 km. The performance of the transfer system was demonstrated by a successful PTRF-XAFS study of Pt{sub 4} clusters deposited on a TiO{sub 2}(110) surface.

  4. A Modern Laboratory XAFS Cookbook

    NASA Astrophysics Data System (ADS)

    Seidler, GT; Mortensen, DR; Ditter, AS; Ball, NA; Remesnik, AJ

    2016-05-01

    We have recently demonstrated a very favorable, inexpensive modernization of lab- based x-ray absorption fine structure (XAFS) and high-resolution x-ray emission spectroscopy (XES) using only commercially-available optics and x-ray tube sources. Here, we survey several proven instrument designs that can be readily implemented in any laboratory setting to achieve synchrotron-quality XAFS and XES for many systems in the 5 keV to 10 keV energy range. These approaches are based on our immediate experience with the development of: (1) an inexpensive, low-powered monochromator capable of performing either XAFS or XES, (2) a mid-scale XAFS user facility having 106/sec flux with sub-eV bandwidth on each of two independent beamlines, and (3) multiple XES spectrometers having outstanding performance that can complement synchrotron XAFS studies in battery and actinide research.

  5. Improved self-absorption correction for extended x-ray absorption fine-structure measurements

    SciTech Connect

    Booth, C.H.; Bridges, F.

    2003-06-04

    Extended x-ray absorption fine-structure (EXAFS) data collected in the fluorescence mode are susceptible to an apparent amplitude reduction due to the self-absorption of the fluorescing photon by the sample before it reaches a detector. Previous treatments have made the simplifying assumption that the effect of the EXAFS on the correction term is negligible, and that the samples are in the thick limit. We present a nearly exact treatment that can be applied for any sample thickness or concentration, and retains the EXAFS oscillations in the correction term.

  6. Clarifying the chemical state of additives in membranes for polymer electrolyte fuel cells by X-ray absorption fine structure

    NASA Astrophysics Data System (ADS)

    Tanuma, Toshihiro; Itoh, Takanori

    2016-02-01

    Cerium and manganese compounds are used in the membrane for polymer electrolyte fuel cells (PEFCs) as radical scavengers to mitigate chemical degradation of the membrane. The chemical states of cerium and manganese in the membrane were investigated using a fluorescence X-ray absorption fine structure (XAFS) technique. Membrane electrode assemblies (MEAs) were subjected to open circuit voltage (OCV) condition, under which hydroxyl radicals attack the membrane; a shift in absorption energy in X-ray absorption near edge structure (XANES) spectra was compared between Ce- and Mn-containing membranes before and after OCV testing. In the case of the Ce-containing MEA, there was no significant difference in XANES spectra before and after OCV testing, whereas in the case of the Mn-containing MEA, there was an obvious shift in XANES absorption energy after OCV testing, indicating that Mn atoms with higher valence state than 2+ exist in the membrane after OCV testing. This can be attributed to the difference in the rate of reduction; the reaction of Ce4+ with ·OOH is much faster than that of Mn3+ with ·OOH, leaving some of the Mn atoms with higher valence state. It was confirmed that cerium and manganese redox couples reduced the attack from radicals, mitigating membrane degradation.

  7. An X-ray Absorption Fine Structure study of Au adsorbed onto the non-metabolizing cells of two soil bacterial species

    SciTech Connect

    Song, Zhen; Kenney, Janice P.L.; Fein, Jeremy B.; Bunker, Bruce A.

    2015-02-09

    Gram-positive and Gram-negative bacterial cells can remove Au from Au(III)-chloride solutions, and the extent of removal is strongly pH dependent. In order to determine the removal mechanisms, X-ray Absorption Fine Structure (XAFS) spectroscopy experiments were conducted on non-metabolizing biomass of Bacillus subtilis and Pseudomonas putida with fixed Au(III) concentrations over a range of bacterial concentrations and pH values. X-ray Absorption Near Edge Structure (XANES) and Extended X-ray Absorption Fine Structure (EXAFS) data on both bacterial species indicate that more than 90% of the Au atoms on the bacterial cell walls were reduced to Au(I). In contrast to what has been observed for Au(III) interaction with metabolizing bacterial cells, no Au(0) or Au-Au nearest neighbors were observed in our experimental systems. All of the removed Au was present as adsorbed bacterial surface complexes. For both species, the XAFS data suggest that although Au-chloride-hydroxide aqueous complexes dominate the speciation of Au in solution, Au on the bacterial cell wall is characterized predominantly by binding of Au atoms to sulfhydryl functional groups and amine and/or carboxyl functional groups, and the relative importance of the sulfhydryl groups increases with increasing pH and with decreasing Au loading. The XAFS data for both microorganism species suggest that adsorption is the first step in the formation of Au nanoparticles by bacteria, and the results enhance our ability to account for the behavior of Au in bacteria-bearing geologic systems.

  8. Fluorescence x-ray absorption fine structure studies of Fe-Ni-S and Fe-Ni-Si melts to 1600 K

    SciTech Connect

    Manghnani, M.H.; Hong, X.; Balogh, J.; Amulele, G.; Sekar, M.; Newville, M.

    2008-04-29

    We report Ni K-edge fluorescence x-ray absorption fine structure spectra (XAFS) for Fe{sub 0.75}Ni{sub 0.05}S{sub 0.20} and Fe{sub 0.75}Ni{sub 0.05}Si{sub 0.20} ternary alloys from room temperature up to 1600 K. A high-temperature furnace designed for these studies incorporates two x-ray transparent windows and enables both a vertical orientation of the molten sample and a wide opening angle, so that XAFS can be measured in the fluorescence mode with a detector at 90{sup o} with respect to the incident x-ray beam. An analysis of the Ni XAFS data for these two alloys indicates different local structural environments for Ni in Fe{sub 0.75}Ni{sub 0.05}S{sub 0.20} and Fe{sub 0.75}Ni{sub 0.05}Si{sub 0.20} melts, with more Ni-Si coordination than Ni-S coordination persisting from room temperature through melting. These results suggest that light elements such as S and Si may impact the structural and chemical properties of Fe-Ni alloys with a composition similar to the earth's core.

  9. Insights from arsenate adsorption on rutile (110): grazing-incidence X-ray absorption fine structure spectroscopy and DFT+U study.

    PubMed

    Yan, Li; Hu, Shan; Duan, Jinming; Jing, Chuanyong

    2014-07-03

    Insights into the bonding of As(V) at the metal oxide/aqueous interface can further our understanding of its fate and transport in the environment. The motivation of this work is to explore the interfacial configuration of As(V) on single crystal rutile (110) using grazing-incidence X-ray absorption fine structure spectroscopy (GI-XAFS) and planewave density functional calculations with on-site repulsion (DFT+U). In contrast to the commonly considered corner-sharing bidentate binuclear structure, tetrahedral As(V) binds as an edge/corner-sharing tridentate binuclear complex on rutile (110), as evidenced by observation of three As-Ti distances at 2.83, 3.36, and 4.05 Å. In agreement with the GI-XAFS analysis, our DFT+U calculations for this configuration resulted in the lowest adsorption energy among five possible alternatives. In addition, the electron density difference further demonstrated the transfer of charge between surface Ti atoms and O atoms in AsO4. This charge transfer consequently induced the formation of a chemical bond, which is also confirmed by the partial density of states analysis. Our results may shed new light on coupling the GI-XAFS and DFT approaches to explore molecular-scale adsorption mechanisms on single crystal surfaces.

  10. Curium analysis in plutonium uranium mixed oxide by x-ray fluorescence and absorption fine structure spectroscopy.

    PubMed

    Degueldre, C; Borca, C; Cozzo, C

    2013-10-15

    Plutonium uranium mixed oxide (MOX) fuels are being used in commercial nuclear reactors. The actinides in these fuels need to be analyzed after irradiation for assessing their behaviour with regards to their environment and the coolant. In this work the study of the local occurrence, speciation and next-neighbour environment of curium (Cm) in the (Pu,U)O2 lattice within an irradiated (60 MW d kg(-1) average burn-up) MOX sample was performed employing micro-x-ray fluorescence (µ-XRF) and micro-x-ray absorption fine structure (µ-XAFS) spectroscopy. The chemical bonds, valences and stoichiometry of Cm (≈ 0.7 wt% in the rim and ≈ 0.03 wt% in the centre) are determined from the experimental data gained for the irradiated fuel material examined in its centre and peripheral (rim) zones of the fuel. Curium occurrence is also reduced from the centre (hot) to the periphery (colder) because of the condensation of these volatile oxides. In the irradiated sample Cm builds up as Cm(3+) species (>90%) within a [CmO8](13-) or [CmO7](11-) coordination environment and no (<10%) Cm(IV) can be detected in the rim zone. Curium dioxide is reduced because of the redox buffering activity of the uranium dioxide matrix and of its thermodynamic instability.

  11. In situ X-ray absorption fine structure studies of a manganese dioxide electrode in a rechargeable MnO{sub 2}/Zn alkaline battery environment

    SciTech Connect

    Mo, Y.; Hu, Y.; Bae, I.T.; Miller, B.; Scherson, D.A.; Antonio, M.R.

    1996-12-31

    Electronic and structural aspects of a MnO{sub 2} electrode in a rechargeable MnO{sub 2}/Zn battery environment have been investigated by in situ Mn K-edge X-ray absorption fine structure (XAFS). The relative amplitudes of the three major Fourier transform shells of the EXAFS (extended XAFS) function of the rechargeable MnO{sub 2} electrode in the undischarged state were found to be similar to those found for ramsdellite, a MnO{sub 2} polymorph with substantial corner-sharing linkages among the basic MnO{sub 6} octahedral units. The analyses of the background-subtracted pre-edge peaks and absorption edge regions for the nominally 1-e{sup {minus}} discharged electrode were consistent with Mn{sup 3+} as being the predominant constituent species, rather than a mixture of Mn{sup 4+} and Mn{sup 2+} sites. Furthermore, careful inspection of both the XANES (X-ray absorption near edge structure) and EXAFS indicated that the full recharge of MnO, which had been previously discharged either by a 1- or 2-equivalent corner-sharing linkages compared to the original undischarged MnO{sub 2}.

  12. X-ray absorption fine structure study of heavily P doped (111) and (001) diamond

    NASA Astrophysics Data System (ADS)

    Shikata, Shinichi; Yamaguchi, Koji; Fujiwara, Akihiko; Tamenori, Yusuke; Yahiro, Jumpei; Kunisu, Masahiro; Yamada, Takatoshi

    2017-02-01

    X-ray absorption fine structure (XANES) measurements were carried out for P doped (111) and (001) diamond films, and the results were compared with those from simulations. For the (111) spectrum, the main strong peak observed at 2147.0 eV and three broad peaks centered at 2150 eV, 2157 eV, and 2165 eV were observed. The assignment with the estimation by the simulation of the XANES peaks showed the interstitial sites additional to the substitutional site. The Extended X-ray Absorption Fine Structure (EXAFS) result of the P doped (111) diamond showed that the first and second neighboring peaks are observed at 1.21 A and 2.0 A, respectively. The assignment with the estimation by the simulation of the EXAFS peaks also showed the interstitial sites additional to the substitutional site. Overall, P in diamonds presumably has dopant sites in both the substitutional and interstitial sites.

  13. PRELIMINARY IN-SITU X-RAY ABSORPTION FINE STRUCTURE EXAMINATION OF PT/C AND PTCO/C CATHODE CATALYSTS IN AN OPERATIONAL POLYMER ELECTROLYTE FUEL CELL

    SciTech Connect

    Phelan, B.T.; Myers, D.J.; Smith, M.C.

    2009-01-01

    State-of-the-art polymer electrolyte fuel cells require a conditioning period to reach optimized cell performance. There is insuffi cient understanding about the behavior of catalysts during this period, especially with regard to the changing environment of the cathode electrocatalyst, which is typically Pt nanoparticles supported on high surface area Vulcan XC-72 carbon (Pt/C). The purpose of this research was to record preliminary observations of the changing environment during the conditioning phase using X-Ray Absorption Fine Structure (XAFS) spectroscopy. XAFS was recorded for a Pt/C cathode at the Pt L3-edge and a PtCo/C cathode at both the Pt L3-edge and Co K-edge. Using precision machined graphite cell-blocks, both transmission and fl uorescence data were recorded at Sector 12-BM-B of Argonne National Laboratory’s Advanced Photon Source. The fl uorescence and transmission edge steps allow for a working description of the changing electrocatalyst environment, especially water concentration, at the anode and cathode as functions of operating parameters. These features are discussed in the context of how future analysis may correlate with potential, current and changing apparent thickness of the membrane electrode assembly through loss of catalyst materials (anode, cathode, carbon support). Such direct knowledge of the effect of the conditioning protocol on the electrocatalyst may lead to better catalyst design. In turn, this may lead to minimizing, or even eliminating, the conditioning period.

  14. X-Ray Absorption Fine Structure Study for Fe60Ni40 Alloy

    SciTech Connect

    Yang, Dong-Seok; Oh, Kyuseung; Na, Wonkyung; Kim, Nayoung; Yoo, Yong-Goo; Min, Seung-Gi; Yu, Seong-Cho

    2007-02-02

    Fe60Ni40 alloys were fabricated by the mechanical alloying process with process periods of 1, 2, 4, 6, 12 and 24 hours, respectively. The formation of alloy and the structural evolution of the alloy were examined by X-ray diffraction and extended X-ray absorption fine structure methods. With increase of alloying time the BCC phase of iron was changed significantly during the mechanical alloying process. The alloying was activated in about 6 hours and completed in about 24 hours.

  15. Extended X-ray absorption fine structure (EXAFS) study of CaSO 4:Dy phosphors

    NASA Astrophysics Data System (ADS)

    Bhattacharyya, D.; Bakshi, A. K.; Ciatto, G.; Aquilanti, G.; Pradhan, A. S.; Pascarelli, S.

    2006-03-01

    Extended X-ray absorption fine structure (EXAFS) measurements have been carried out on CaSO 4:Dy phosphors at the Dy L 3 edge with synchrotron radiation. The data have been analysed to find out the Dy-S and Dy-O bond lengths in the neighborhood of the Dy atoms. Measurements have been carried out over several samples thermally annealed for different cycles at 400 °C in air for 1 h and the change in bond lengths in samples with increasing number of annealing cycles have been studied by analyzing the EXAFS data.

  16. Novel angular encoder for a quick-extended x-ray absorption fine structure monochromator

    SciTech Connect

    Stoetzel, J.; Luetzenkirchen-Hecht, D.; Frahm, R.; Fonda, E.; De Oliveira, N.; Briois, V.

    2008-08-15

    New concepts for time-resolved x-ray absorption spectroscopy using the quick-extended x-ray absorption fine structure (QEXAFS) method are presented. QEXAFS is a powerful tool to gain structural information about, e.g., fast chemical reactions or phase transitions on a subsecond scale. This can be achieved with a monochromator design that employs a channel-cut crystal on a cam driven tilt table for rapid angular oscillations of the Bragg angle. A new angular encoder system and a new data acquisition were described and characterized that were applied to a QEXAFS monochromator to get spectra with a directly measured accurate energy scale. New electronics were designed to allow a fast acquisition of the Bragg angle values and the absorption data during the measurements simultaneously.

  17. Spiky Fine Structure of Type III-like Radio Bursts in Absorption

    NASA Astrophysics Data System (ADS)

    Chernov, G. P.; Yan, Y. H.; Tan, C. M.; Chen, B.; Fu, Q. J.

    2010-03-01

    An uncommon fine structure in the radio spectrum consisting of bursts in absorption was observed with the Chinese Solar Broadband Radiospectrometer (SBRS) in the frequency range of 2.6 - 3.8 GHz during an X3.4/4B flare on 13 December 2006 in active region NOAA 10930 (S05W33). Usual fine structures in emission such as spikes, zebra stripes, and drifting fibers were observed at the peak of every new flare brightening. Within an hour at the decay phase of the event we observed bursts consisting of spikes in absorption, which pulsated periodically in frequency. Their instantaneous frequency bandwidths were found to be in the 75 MHz range. Moreover, in the strongest Type III-like bursts in absorption, the spikes showed stripes of the zebra-pattern (ZP) that drifted to higher frequencies. All spikes had the duration as short as down to the limit of the instrument resolution of ≈8 ms. The TRACE 195 Å images indicate that the magnetic reconnection at this moment occurred in the western edge of the flare loop arcade. Taking into account the presence of the reverse-drifting bursts in emission, in the course of the restoration of the magnetic structures in the corona, the acceleration of the beams of fast particles must have occurred both upward and downward at different heights. The upward beams will be captured by the magnetic trap, where the loss-cone distribution of fast particles (responsible for the emission of continuum and ZP) were formed. An additional injection of fast particles will fill the loss-cone later, breaking the loss-cone distribution. Therefore, the generation of continuum will be quenched at these moments, which was evidenced by the formation of bursts in absorption.

  18. Extended X-ray absorption fine structural studies of copper and nickel ferrites

    NASA Astrophysics Data System (ADS)

    Malviya, P. K.; Sharma, P.; Mishra, Ashutosh; Bhalse, D.

    2014-09-01

    The Cu-Ni ferrites with general formula Cu1-xNix Fe2O4 (where x=0.0, 0.05, 0.10, 0. 15, 0.20) were prepared by solid state root method. X-ray, K- absorption fine structural measurements were carried out. EXAFS spectra have been recorded at the K-edge of Fe using the dispersive EXAFS (DEXAFS) beam line at 2.5GeV Indus-2 synchrotron radiation source RRCAT, Indore, India. The EXAFS data have been analysed using the computer software Athena. These have been used to determine the bond lengths in these ferrites with the help of four different methods, namely, Levy's, Lytle's and Lytle, Sayers and Stern's (LSS) methods.

  19. The coefficient of bond thermal expansion measured by extended x-ray absorption fine structure.

    PubMed

    Fornasini, P; Grisenti, R

    2014-10-28

    The bond thermal expansion is in principle different from the lattice expansion and can be measured by correlation sensitive probes such as extended x-ray absorption fine structure (EXAFS) and diffuse scattering. The temperature dependence of the coefficient α(bond)(T) of bond thermal expansion has been obtained from EXAFS for CdTe and for Cu. A coefficient α(tens)(T) of negative expansion due to tension effects has been calculated from the comparison of bond and lattice expansions. Negative lattice expansion is present in temperature intervals where α(bond) prevails over α(tens); this real-space approach is complementary but not equivalent to the Grüneisen theory. The relevance of taking into account the asymmetry of the nearest-neighbours distribution of distances in order to get reliable bond expansion values and the physical meaning of the third cumulant are thoroughly discussed.

  20. Local structure studies of some cobalt (II) complexes using extended X-ray absorption fine structure

    NASA Astrophysics Data System (ADS)

    Mishra, Ashutosh; Ninama, Samrath; Trivedi, Apurva

    2014-09-01

    Extended X-ray Absorption Fine Structure (EXAFS) analysis of Cobalt (II) complex as a ligand of 2 -methyl-3-[(bis-aniline(R) phenyl]-3H-l,5 benzodiazepine for finding local structure using conventional method .The Co(II) complexes were prepared by chemical root method. The EXAFS spectra were recorded at Cobalt K-edge i.e.; 7709 eV using Dispersive EXFAS beam line at 2.5GeV Indus-2 Synchrotron Radiation Source(SRS) at RRCAT, Indore, India. The recorded EXAFS data were analysed using the computer software Athena for determine the nearest neighbouring distances (bond lengths) of these complexes with conventional methods and it compared with Fourier transform(FT) analysis. The Fourier Transform convert EXAFS data signal into r-space or k-space. This is useful for visualizing the major contributions to the EXAFS spectrum.

  1. Vibronic fine structure in high-resolution x-ray absorption spectra from ion-bombarded boron nitride nanotubes

    SciTech Connect

    Petravic, Mladen; Peter, Robert; Varasanec, Marijana; Li Luhua; Chen Ying; Cowie, Bruce C. C.

    2013-05-15

    The authors have applied high-resolution near-edge x-ray absorption fine structure measurements around the nitrogen K-edge to study the effects of ion-bombardment on near-surface properties of boron nitride nanotubes. A notable difference has been observed between surface sensitive partial electron yield (PEY) and bulk sensitive total electron yield (TEY) fine-structure measurements. The authors assign the PEY fine structure to the coupling of excited molecular vibrational modes to electronic transitions in NO molecules trapped just below the surface. Oxidation resistance of the boron nitride nanotubes is significantly reduced by low energy ion bombardment, as broken B-N bonds are replaced by N-O bonds involving oxygen present in the surface region. In contrast to the PEY spectra, the bulk sensitive TEY measurements on as-grown samples do not exhibit any fine structure while the ion-bombarded samples show a clear vibronic signature of molecular nitrogen.

  2. XAFS SPECTROSCOPY RESULTS FOR PM SAMPLES FROM RESIDUAL FUEL OIL

    EPA Science Inventory

    X-ray absorption fine structure (XAFS spectroscopy data were obtained from particulate samples produced by the combustion of residual fuel oil in a 732-kW fire-tube boiler at EPA's National Risk Management Research Laboratory in North Carolina. Residual oil flyash (ROFA) from fo...

  3. Extended x-ray absorption fine structure studies of IBS Fe--Tb alloy films

    SciTech Connect

    Harris, V.G.; Aylesworth, K.D.; Kim, K.H.; Elam, W.T.; Koon, N.C. )

    1991-11-15

    We have employed extended x-ray absorption fine structure (EXAFS) analysis to study the compositional dependence of the atomic structure in Fe--Tb alloy films. Fourier transforms of EXAFS data, relative to both the Fe {ital K} and the Tb {ital L}{sub III} absorption edges, provide information about the local atomic environments relative to each atom. Results indicate the Fe EXAFS data to be dominated by Fe--Fe correlations, and consists of contributions from two Fe atomic shells at radial distances near 2.47 and 2.66 A and a Tb shell near 2.91 A. The coordination number of the Fe shells are measured to increase, while radial distances decrease, with increased Fe content. The Tb EXAFS data was found to have an atomic shells of Fe and Tb at 2.91 and 3.47 A, respectively. Analysis suggests that the Fe shell is very disordered and is comprised of approximately 9.5 atoms while the Tb shell has {approx}3 atoms.

  4. Near-Edge X-ray Absorption Fine Structure Spectroscopy of Diamondoid Thiol Monolayers on Gold

    SciTech Connect

    Willey, T M; Fabbri, J; Lee, J I; Schreiner, P; Fokin, A A; Tkachenko, B A; Fokina, N A; Dahl, J; Carlson, B; Vance, A L; Yang, W; Terminello, L J; van Buuren, T; Melosh, N

    2007-11-27

    Diamondoids, hydrocarbon molecules with cubic-diamond-cage structures, have unique properties with potential value for nanotechnology. The availability and ability to selectively functionalize this special class of nanodiamond materials opens new possibilities for surface-modification, for high-efficiency field emitters in molecular electronics, as seed crystals for diamond growth, or as robust mechanical coatings. The properties of self-assembled monolayers (SAMs) of diamondoids are thus of fundamental interest for a variety of emerging applications. This paper presents the effects of thiol substitution position and polymantane order on diamondoid SAMs on gold using near-edge X-ray absorption fine structure spectroscopy (NEXAFS) and X-ray photoelectron spectroscopy (XPS). A framework to determine both molecular tilt and twist through NEXAFS is presented and reveals highly ordered diamondoid SAMs, with the molecular orientation controlled by the thiol location. C 1s and S 2p binding energies are lower in adamantane thiol than alkane thiols on gold by 0.67 {+-} 0.05 eV and 0.16 {+-} 0.04 eV respectively. These binding energies vary with diamondoid monolayer structure and thiol substitution position, consistent with different amounts of steric strain and electronic interaction with the substrate. This work demonstrates control over the assembly, in particular the orientational and electronic structure, providing a flexible design of surface properties with this exciting new class of diamond clusters.

  5. Constraining the variation of the fine-structure constant with observations of narrow quasar absorption lines

    SciTech Connect

    Songaila, A.; Cowie, L. L.

    2014-10-01

    The unequivocal demonstration of temporal or spatial variability in a fundamental constant of nature would be of enormous significance. Recent attempts to measure the variability of the fine-structure constant α over cosmological time, using high-resolution spectra of high-redshift quasars observed with 10 m class telescopes, have produced conflicting results. We use the many multiplet (MM) method with Mg II and Fe II lines on very high signal-to-noise, high-resolution (R = 72, 000) Keck HIRES spectra of eight narrow quasar absorption systems. We consider both systematic uncertainties in spectrograph wavelength calibration and also velocity offsets introduced by complex velocity structure in even apparently simple and weak narrow lines and analyze their effect on claimed variations in α. We find no significant change in α, Δα/α = (0.43 ± 0.34) × 10{sup –5}, in the redshift range z = 0.7-1.5, where this includes both statistical and systematic errors. We also show that the scatter in measurements of Δα/α arising from absorption line structure can be considerably larger than assigned statistical errors even for apparently simple and narrow absorption systems. We find a null result of Δα/α = (– 0.59 ± 0.55) × 10{sup –5} in a system at z = 1.7382 using lines of Cr II, Zn II, and Mn II, whereas using Cr II and Zn II lines in a system at z = 1.6614 we find a systematic velocity trend that, if interpreted as a shift in α, would correspond to Δα/α = (1.88 ± 0.47) × 10{sup –5}, where both results include both statistical and systematic errors. This latter result is almost certainly caused by varying ionic abundances in subcomponents of the line: using Mn II, Ni II, and Cr II in the analysis changes the result to Δα/α = (– 0.47 ± 0.53) × 10{sup –5}. Combining the Mg II and Fe II results with estimates based on Mn II, Ni II, and Cr II gives Δα/α = (– 0.01 ± 0.26) × 10{sup –5}. We conclude that spectroscopic measurements of

  6. Constraining the Variation of the Fine-structure Constant with Observations of Narrow Quasar Absorption Lines

    NASA Astrophysics Data System (ADS)

    Songaila, A.; Cowie, L. L.

    2014-10-01

    The unequivocal demonstration of temporal or spatial variability in a fundamental constant of nature would be of enormous significance. Recent attempts to measure the variability of the fine-structure constant α over cosmological time, using high-resolution spectra of high-redshift quasars observed with 10 m class telescopes, have produced conflicting results. We use the many multiplet (MM) method with Mg II and Fe II lines on very high signal-to-noise, high-resolution (R = 72, 000) Keck HIRES spectra of eight narrow quasar absorption systems. We consider both systematic uncertainties in spectrograph wavelength calibration and also velocity offsets introduced by complex velocity structure in even apparently simple and weak narrow lines and analyze their effect on claimed variations in α. We find no significant change in α, Δα/α = (0.43 ± 0.34) × 10-5, in the redshift range z = 0.7-1.5, where this includes both statistical and systematic errors. We also show that the scatter in measurements of Δα/α arising from absorption line structure can be considerably larger than assigned statistical errors even for apparently simple and narrow absorption systems. We find a null result of Δα/α = (- 0.59 ± 0.55) × 10-5 in a system at z = 1.7382 using lines of Cr II, Zn II, and Mn II, whereas using Cr II and Zn II lines in a system at z = 1.6614 we find a systematic velocity trend that, if interpreted as a shift in α, would correspond to Δα/α = (1.88 ± 0.47) × 10-5, where both results include both statistical and systematic errors. This latter result is almost certainly caused by varying ionic abundances in subcomponents of the line: using Mn II, Ni II, and Cr II in the analysis changes the result to Δα/α = (- 0.47 ± 0.53) × 10-5. Combining the Mg II and Fe II results with estimates based on Mn II, Ni II, and Cr II gives Δα/α = (- 0.01 ± 0.26) × 10-5. We conclude that spectroscopic measurements of quasar absorption lines are not yet capable of

  7. Local Thermodynamic Measurements of Dilute Binary Alloys Using XAFS

    NASA Astrophysics Data System (ADS)

    Newville, Matthew George

    1995-01-01

    Temperature-dependent x-ray-absorption fine-structure (XAFS) measurements are presented for pure Ag, pure Au, and the minority component of several dilute binary alloys with majority components of Ag or Au. The analyses of the XAFS data at and above room temperature are used to determine local thermodynamic quantities for the impurity -host bonds. Thermodynamic quantities are determined for interatomic bonds from the XAFS measurements using a one-dimensional anharmonic model for the interatomic potential between near-neighbor atoms. The effect on the XAFS for two atoms bound by such a potential is found in terms of the force constants of the potential. This formalism is then used in the analyses of the experimental XAFS data to find the force constants of the various interatomic bonds. Thermodynamic properties are written in terms of the force constants for this potential. The results of the XAFS analyses are used in this way to determine thermodynamic properties of the interatomic bonds between near-neighbors. The XAFS measurements of the thermodynamic parameters for pure Ag and Au are in reasonable agreement with bulk measurements. Based on this agreement, the newly developed ability of XAFS to determine thermodynamic properties of interatomic bonds is combined with the well-established ability of XAFS to measure impurity-host bonds in dilute alloys. This allows previously unavailable local thermodynamic parameters for interatomic bonds in dilute binary alloys to be determined. XAFS analysis techniques have been developed to exploit theoretical calculations from the computer code scFEFF. These techniques use the scFEFF calculations as theoretical standards to determine physical parameters about the atomic structure from the experimentally measured XAFS spectra. An R-space description of XAFS, based on the Fourier transform, is used in the analysis. This suggests a natural approach to the information content of XAFS data, and simplifies the estimation of the

  8. Radiation effects in water ice: a near-edge x-ray absorption fine structure study.

    PubMed

    Laffon, C; Lacombe, S; Bournel, F; Parent, Ph

    2006-11-28

    The changes in the structure and composition of vapor-deposited ice films irradiated at 20 K with soft x-ray photons (3-900 eV) and their subsequent evolution with temperatures between 20 and 150 K have been investigated by near-edge x-ray absorption fine structure spectroscopy (NEXAFS) at the oxygen K edge. We observe the hydroxyl OH, the atomic oxygen O, and the hydroperoxyl HO(2) radicals, as well as the oxygen O(2) and hydrogen peroxide H(2)O(2) molecules in irradiated porous amorphous solid water (p-ASW) and crystalline (I(cryst)) ice films. The evolution of their concentrations with the temperature indicates that HO(2), O(2), and H(2)O(2) result from a simple step reaction fuelled by OH, where O(2) is a product of HO(2) and HO(2) a product of H(2)O(2). The local order of ice is also modified, whatever the initial structure is. The crystalline ice I(cryst) becomes amorphous. The high-density amorphous phase (I(a)h) of ice is observed after irradiation of the p-ASW film, whose initial structure is the normal low-density form of the amorphous ice (I(a)l). The phase I(a)h is thus peculiar to irradiated ice and does not exist in the as-deposited ice films. A new "very high density" amorphous phase-we call I(a)vh-is obtained after warming at 50 K the irradiated p-ASW ice. This phase is stable up to 90 K and partially transforms into crystalline ice at 150 K.

  9. An X-Ray Absorption Fine Structure Study of Ordering in Polythiophene Thin Films

    DTIC Science & Technology

    1993-09-01

    within experimental error. As a result. XAFS spectroscopy has been shown to be a useful technique for investigating the molecular structure of an...3413300 13400 13500 13600 Energy (eV) Figure 19: Br K-edge X-ray . . bsorption Near Edge Structure for 2,5 dibromothiophene collected in transmission...Structure spectroscopy as a useful technique for investigating structures of materials with potential laser- hardening applications. The near-atomic

  10. Tin Oxide Crystals Exposed by Low-Energy {110} Facets for Enhanced Electrochemical Heavy Metal Ions Sensing: X-ray Absorption Fine Structure Experimental Combined with Density-Functional Theory Evidence.

    PubMed

    Jin, Zhen; Yang, Meng; Chen, Shao-Hua; Liu, Jin-Huai; Li, Qun-Xiang; Huang, Xing-Jiu

    2017-02-21

    Herein, we revealed that the electrochemical behaviors on the detection of heavy metal ions (HMIs) would largely rely on the exposed facets of SnO2 nanoparticles. Compared to the high-energy {221} facet, the low-energy {110} facet of SnO2 possessed better electrochemical performance. The adsorption/desorption tests, density-functional theory (DFT) calculations, and X-ray absorption fine structure (XAFS) studies showed that the lower barrier energy of surface diffusion on {110} facet was critical for the superior electrochemical property, which was favorable for the ions diffusion on the electrode, and further leading the enhanced electrochemical performance. Through the combination of experiments and theoretical calculations, a reliable interpretation of the mechanism for electroanalysis of HMIs with nanomaterials exposed by different crystal facets has been provided. Furthermore, it provides a deep insight into understanding the key factor to improve the electrochemical performance for HMIs detection, so as to design high-performance electrochemical sensors.

  11. Confocal micrometer-scale X-ray fluorescence and X-ray absorption fine structure studies of uranium speciation in a tertiary sediment from a waste disposal natural analogue site.

    PubMed

    Denecke, Melissa A; Janssens, Koen; Proost, Kristof; Rothe, Jörg; Noseck, Ulrich

    2005-04-01

    Investigations by micrometer-scale X-ray fluorescence and X-ray absorption fine structure (micro-XRF and micro-XAFS) recorded in a confocal geometry on a bore core section of a uranium-rich tertiary sediment are performed in order to assess mechanisms leading to immobilization of the uranium during diagenesis. Results show uranium to be present as a tetravalent phosphate and that U(IV) is associated with As(V). Arsenic present is either As(V) or As(O); we found no evidence for As(III). The As(O) is observed to be intimately associated with the surface of Fe(II) nodules and likely arsenopyrite. A hypothesis for the mechanism of uranium immobilization is proposed, where arsenopyrite acted as reductant of groundwater-dissolved U(VI), leading to precipitation of less soluble U(IV) and thereby forming As(V).

  12. Structural characterization of poorly-crystalline scorodite, iron(III)-arsenate co-precipitates and uranium mill neutralized raffinate solids using X-ray absorption fine structure spectroscopy

    NASA Astrophysics Data System (ADS)

    Chen, N.; Jiang, D. T.; Cutler, J.; Kotzer, T.; Jia, Y. F.; Demopoulos, G. P.; Rowson, J. W.

    2009-06-01

    X-ray absorption fine structure (XAFS) is used to characterize the mineralogy of the iron(III)-arsenate(V) precipitates produced during the raffinate (aqueous effluent) neutralization process at the McClean Lake uranium mill in northern Saskatchewan, Canada. To facilitate the structural characterization of the precipitated solids derived from the neutralized raffinate, a set of reference compounds were synthesized and analyzed. The reference compounds include crystalline scorodite, poorly-crystalline scorodite, iron(III)-arsenate co-precipitates obtained under different pH conditions, and arsenate-adsorbed on goethite. The poorly-crystalline scorodite (prepared at pH 4 with Fe/As = 1) has similar As local structure as that of crystalline scorodite. Both As and Fe K-edge XAFS of poorly-crystalline scorodite yield consistent results on As-Fe (or Fe-As) shell. From As K-edge analysis the As-Fe shell has an inter-atomic distance of 3.33 ± 0.02 Å and coordination number of 3.2; while from Fe K-edge analysis the Fe-As distance and coordination number are 3.31 ± 0.02 Å and 3.8, respectively. These are in contrast with the typical arsenate adsorption on bidentate binuclear sites on goethite surfaces, where the As-Fe distance is 3.26 ± 0.03 Å and coordination number is close to 2. A similar local structure identified in the poorly-crystalline scorodite is also found in co-precipitation solids (Fe(III)/As(V) = 3) when precipitated at the same pH (pH = 4): As-Fe distance 3.30 ± 0.03 Å and coordination number 3.9; while at pH = 8 the co-precipitate has As-Fe distance of 3.27 ± 0.03 Å and coordination number about 2, resembling more closely the adsorption case. The As local structure in the two neutralized raffinate solid series (precipitated at pH values up to 7) closely resembles that in the poorly-crystalline scorodite. All of the raffinate solids have the same As-Fe inter-atomic distance as that in the poorly-crystalline scorodite, and a systematic decrease in the

  13. Characterization of fossil remains using XRF, XPS and XAFS spectroscopies

    NASA Astrophysics Data System (ADS)

    Zougrou, I. M.; Katsikini, M.; Pinakidou, F.; Brzhezinskaya, M.; Papadopoulou, L.; Vlachos, E.; Tsoukala, E.; Paloura, E. C.

    2016-05-01

    Synchrotron radiation micro-X-Ray Fluorescence (μ-XRF), X-ray photoelectron (XPS) and X-ray Absorption Fine Structure (XAFS) spectroscopies are applied for the study of paleontological findings. More specifically the costal plate of a gigantic terrestrial turtle Titanochelon bacharidisi and a fossilized coprolite of the cave spotted hyena Crocuta crocuta spelaea are studied. Ca L 2,3-edge NEXAFS and Ca 2p XPS are applied for the identification and quantification of apatite and Ca containing minerals. XRF mapping and XAFS are employed for the study of the spatial distribution and speciation of the minerals related to the deposition environment.

  14. Photoluminescence and extended X-ray absorption fine structure studies on cadmium telluride material

    NASA Astrophysics Data System (ADS)

    Liu, Xiangxin

    The direct-band-gap semiconductor CdTe is an important material for fabricating high efficiency, polycrystalline thin-film solar cells in a heterojunction configuration. The outstanding physical properties of this material such as its good band-gap match to the solar spectrum, ease of fabrication of stoichiometric films, and easy grain boundary passivation make it an important candidate for large area, thin-film solar cells. However, there are several poorly understood processing steps that are commonly utilized in cell fabrication. One of these is a CdCl2 treatment near 400°C in the presence of oxygen, which can improve the cell efficiency a factor of two or more. Another factor is the role of copper in cell performance. In high performance CdS/CdTe thin-film solar cells, copper is usually included in the fabrication of low-resistance back contacts to obtain heavy p-type doping of the absorber CdTe at the contact. However, most of the copper is not electrically active. For example, secondary ion mass spectroscopy (SIMS) on typical CdTe cells has shown Cu concentrations of 1019 atoms/cm3 and even higher, although capacitance-voltage (C-V) measurements indicate typical ionized acceptor levels on the order of 1014/cm 3. Thus, there is great interest in the location and role of this inactive copper in CdTe photovoltaic (PV) devices. In this thesis, I will describe results obtained on magnetron-sputtered CdTe films that were diffused with copper following the procedure used for creating a cell back contact. Extended X-ray Absorption Fine Structure (EXAFS) measurements identified the chemical environment of the majority of the copper and show major differences depending on whether the CdTe film has been treated with chloride prior to the Cu diffusion. The EXAFS data indicate that the Cu chemistry is strongly affected by the chloride treatments---predominantly Cu2Te when Cu was diffused into the as-deposited CdTe film, but a Cu2O environment when Cu was diffused after

  15. XAFS SPECTROSCOPY ANALYSIS OF SELECTED HAP ELEMENTS IN FINE PM DERIVED FROM COAL COMBUSTION

    EPA Science Inventory

    X-ray absorption fine structure (XAFS) spectroscopy has been used to investigate the valence states and molecular structures of sulfur (S), chromium (Cr), arsenic (As), and zinc (Zn) in fine particulate matter (PM) separated from coal flyash produced in a realistic combustion sys...

  16. Study on the Coordination Structure of Pt Sorbed on Bacterial Cells Using X-Ray Absorption Fine Structure Spectroscopy

    PubMed Central

    Tanaka, Kazuya; Watanabe, Naoko

    2015-01-01

    Biosorption has been intensively investigated as a promising technology for the recovery of precious metals from solution. However, the detailed mechanism responsible for the biosorption of Pt on a biomass is not fully understood because of a lack of spectroscopic studies. We applied X-ray absorption fine structure spectroscopy to elucidate the coordination structure of Pt sorbed on bacterial cells. We examined the sorption of Pt(II) and Pt(IV) species on bacterial cells of Bacillus subtilis and Shewanella putrefaciens in NaCl solutions. X-ray absorption near-edge structure and extended X-ray absorption fine structure (EXAFS) of Pt-sorbed bacteria suggested that Pt(IV) was reduced to Pt(II) on the cell’s surface, even in the absence of an organic material as an exogenous electron donor. EXAFS spectra demonstrated that Pt sorbed on bacterial cells has a fourfold coordination of chlorine ions, similar to PtCl42-, which indicated that sorption on the protonated amine groups of the bacterial cells. This work clearly demonstrated the coordination structure of Pt sorbed on bacterial cells. The findings of this study will contribute to the understanding of Pt biosorption on biomass, and facilitate the development of recovery methods for rare metals using biosorbent materials. PMID:25996945

  17. Near Edge X-Ray Absorption Fine Structure Spectroscopy with X-Ray Free-Electron Lasers

    SciTech Connect

    Bernstein, D.P.; Acremann, Y.; Scherz, A.; Burkhardt, M.; Stohr, J.; Beye, M.; Schlotter, W.F.; Beeck, T.; Sorgenfrei, F.; Pietzsch, A.; Wurth, W.; Fohlisch, A.; /Hamburg U.

    2009-12-11

    We demonstrate the feasibility of Near Edge X-ray Absorption Fine Structure (NEXAFS) spectroscopy on solids by means of femtosecond soft x-ray pulses from a free-electron laser (FEL). Our experiments, carried out at the Free-Electron Laser at Hamburg (FLASH), used a special sample geometry, spectrographic energy dispersion, single shot position-sensitive detection and a data normalization procedure that eliminates the severe fluctuations of the incident intensity in space and photon energy. As an example we recorded the {sup 3}D{sub 1} N{sub 4,5}-edge absorption resonance of La{sup 3+}-ions in LaMnO{sub 3}. Our study opens the door for x-ray absorption measurements on future x-ray FEL facilities.

  18. X-ray absorption fine structure spectroscopic determination of plutonium speciation at the Rocky Flats environmental technology

    SciTech Connect

    Lezama-pacheco, Juan S; Conradson, Steven D; Clark, David L

    2008-01-01

    X-ray Absorption Fine Structure spectroscopy was used to probe the speciation of the ppm level Pu in thirteen soil and concrete samples from the Rocky Flats Environmental Technology Site in support of the site remediation effort that has been successfully completed since these measurements. In addition to X-ray Absorption Near Edge Spectra, two of the samples yielded Extended X-ray Absorption Fine Structure spectra that could be analyzed by curve-fits. Most of these spectra exhibited features consistent with PU(IV), and more specificaJly, PuO{sub 2+x}-type speciation. Two were ambiguous, possibly indicating that Pu that was originally present in a different form was transforming into PuO{sub 2+x}, and one was interpreted as demonstrating the presence of an unusual Pu(VI) compound, consistent with its source being spills from a PUREX purification line onto a concrete floor and the resultant extreme conditions. These experimental results therefore validated models that predicted that insoluble PuO{sub 2+x} would be the most stable form of Pu in equilibrium with air and water even when the source terms were most likely Pu metal with organic compounds or a Pu fire. A corollary of these models' predictions and other in situ observations is therefore that the minimal transport of Pu that occurred on the site was via the resuspension and mobilization of colloidal particles. Under these conditions, the small amounts of diffusely distributed Pu that were left on the site after its remediation pose only a negligible hazard.

  19. Antimony(III) complexing with O-bearing organic ligands in aqueous solution: An X-ray absorption fine structure spectroscopy and solubility study

    NASA Astrophysics Data System (ADS)

    Tella, Marie; Pokrovski, Gleb S.

    2009-01-01

    The stability and structure of aqueous complexes formed by trivalent antimony (Sb III) with carboxylic acids (acetic, adipic, malonic, lactic, oxalic, tartaric, and citric acid), phenols (catechol), and amino acids (glycine) having O- and N-functional groups (carboxyl, alcoholic hydroxyl, phenolic hydroxyl and amine) typical of natural organic matter, were determined at 20 and 60 °C from solubility and X-ray absorption fine structure (XAFS) spectroscopy measurements. In organic-free aqueous solutions and in the presence of acetic, adipic, malonic acids and glycine, both spectroscopic and solubility data are consistent with the dominant formation of Sb III hydroxide species, Sb(OH)3-nn+,Sb(OH)30andSb(OH)4-, at strongly acid, acid-to-neutral and basic pH, respectively, demonstrating negligible complexing with mono-functional organic ligands (acetic) or those having non adjacent carboxylic groups (adipic, malonic). In contrast, in the presence of poly-functional carboxylic and hydroxy-carboxylic acids and catechol, Sb III forms stable 1:1 and 1:2 complexes with the studied organic ligands over a wide pH range typical of natural waters (3 < pH < 9). XAFS spectroscopy measurements show that in these species the central Sb III atom has a distorted pseudo-trigonal pyramidal geometry composed of the lone pair of 5s 2 electrons of Sb and four oxygen atoms from two adjacent functional groups of the ligand (O dbnd C-OH and/or C sbnd OH), forming a five-membered bidendate chelate cycle. Stability constants for these species, generated from Sb 2O 3 (rhomb.) solubility experiments, were used to model Sb complexing with natural humic acids possessing the same functional groups as those investigated in this study. Our predictions show that in an aqueous solution of pH between 2 and 10, containing 1 μg/L of Sb and 5 mg/L of dissolved organic carbon (DOC), up to 35% of total dissolved Sb binds to aqueous organic matter via carboxylic and hydroxy-carboxylic groups. This amount of

  20. X-ray absorption fine-structure spectroscopy studies of Fe sites in natural human neuromelanin and synthetic analogues.

    PubMed Central

    Kropf, A J; Bunker, B A; Eisner, M; Moss, S C; Zecca, L; Stroppolo, A; Crippa, P R

    1998-01-01

    X-ray absorption fine-structure spectroscopy is used to study the local environment of the iron site in natural (human) neuromelanin extracted from substantia nigra tissue and in various synthetic neuromelanins. All the materials show Fe centered in a nearest neighbor sixfold (distorted) oxygen octahedron; the Fe-O distances, while slightly different in the natural and synthetic neuromelanin, are both approximately 2.0 A. Appreciable differences arise, however, in the second (and higher) coordination shells. In this case the synthetic melanin has the four planar oxygens bound to carbon rings with Fe-C distances of approximately 2.82 and 4.13 A; the human sample does not show the 2.82 A link but instead indicates a double shell at approximately 3.45 and 3.78 A. PMID:9826634

  1. Local Structure Around Te in Heavily Doped GaAs:Te using X-Ray Absorption Fine Structure

    SciTech Connect

    Pietnoczka, A.; Bacewicz, R.; Slupinski, T.; Antonowicz, J.; Wei, Su-Huai

    2012-04-01

    The annealing of heavily doped GaAs:Te can significantly change the free electron concentration in a reversible manner. These changes of electrical properties are accompanied by the structural changes of GaAs:Te solid solution. We used X-ray Absorption Fine Structure at K-edge of tellurium to determine local changes around Te atoms for different states of the GaAs:Te crystals caused by the annealing corresponding to different electron concentrations. The best EXAFS fit for the samples with high electron concentration was obtained for the substitutional Te{sub As} model with elongated Te-Ga bonds (as compared to the As-Ga distance). For the samples in the low concentration state the best fit was for the pairs of Te atoms forming a rhombohedral symmetry double-DX centre, with the proportional admixture of the substitutional tellurium.

  2. Applications of extended X-ray absorption fine-structure spectroscopy to studies of bimetallic nanoparticle catalysts.

    PubMed

    Frenkel, Anatoly I

    2012-12-21

    Extended X-ray absorption fine structure (EXAFS) spectroscopy has been used to study short range order in heterometallic alloys for almost four decades. In this critical review, experimental, theoretical and data analytical approaches are revisited to examine their power, and limitations, in studies of bimetallic nanocatalysts. This article covers the basics of EXAFS experiments, data analysis, and modelling of nanoscale clusters. It demonstrates that, in the best case scenario, quantitative information about the nanocatalyst's size, shape, details of core-shell architecture, as well as static and dynamic disorder in metal-metal bond lengths can be obtained. The article also emphasizes the main challenge accompanying such insights: the need to account for the statistical nature of the EXAFS technique, and discusses corrective strategies.

  3. Iron distances in hemoglobin: comparison of x-ray crystallographic and extended x-ray absorption fine structure studies

    SciTech Connect

    Fermi, G.; Perutz, M.F.; Shulman, R.G.

    1987-09-01

    A comparison is presented of the structures obtained around the iron atom in deoxyhemoglobin (Hb). The data come from extended x-ray absorption fine structure (EXAFS) studies of the iron, which gave Fe-porphyrin nitrogen distances of 2.06 +- 0.01 A, and from the most recent high-resolution x-ray crystallographic study, which gave exactly the same distance-2.06 +- 0.02 A. The distance of Fe above the plane of the porphyrin nitrogens was 0.38 +- 0.04 A from the crystallographic study; this value is not far from the upper limit of the distances 0.20 +- /sub 0.20//sup 0.10/ A calculated from the EXAFS experiment by triangulation. These distances above the nitrogen plane are shorter than those estimated in the earliest x-ray structures

  4. Modeling the structure and composition of nanoparticles by extended X-Ray absorption fine-structure spectroscopy

    SciTech Connect

    Frenkel, Anatoly I.; Yevick, Aaron; Cooper, Chana; Vasic, Relja

    2011-07-19

    Many metal clusters in the 1-nm size range are catalytically active, and their enhanced reactivity is often attributed to their size, structure, morphology, and details of alloying. Synchrotron sources provide a wide range of opportunities for studying catalysis. Among them, extended X-ray absorption fine-structure (EXAFS) spectroscopy is the premier method for investigating structure and composition of nanocatalysts. In this review, we summarize common methods of EXAFS analysis for geometric and compositional characterization of nanoparticles. We discuss several aspects of the experiments and analyses that are critical for reliably modeling EXAFS data. The most important are sample homogeneity, the width of the size and compositional distribution functions, and accounting for multiple-scattering contributions to EXAFS. We focus on the contribution of structural disorder and structural/compositional heterogeneity to the accuracy of three-dimensional modeling.

  5. Local structure of Se in cancrinite: X-ray absorption fine structure theoretical analysis

    NASA Astrophysics Data System (ADS)

    Soldatov, A. V.; Yalovega, G. E.

    2000-04-01

    A theoretical "ab initio" analysis of the polarized X-ray absorption spectrum of selenium in a cancrinite matrix based on a full multiple-scattering theory has been performed. Comparison of the theoretical spectra with the experimental results shows that Se atoms form dimerized chains in the channels of the cancrinite matrix with an interchain distance of about 4.8 Å. In addition the distribution of unoccupied partial s-, p- and d- electronic states of Se has been obtained. Density of states analysis provides some insight into the chemical bonding of Se in cancrinite. The results suggest that the interaction of Se atoms with the matrix is the cause of the unusually large Se-Se distance in dimers.

  6. Near-edge x-ray absorption fine structure measurements using a laboratory-scale XUV source

    NASA Astrophysics Data System (ADS)

    Peth, Christian; Barkusky, Frank; Mann, Klaus

    2008-05-01

    We present a compact setup for near-edge x-ray absorption spectroscopy at the carbon K-edge based on a laser-driven plasma source. To generate the required broad-band emission in the spectral range of the 'water window' (λ = 2.2-4.4 nm) a krypton gas puff target was used. The table-top setup consisting basically of the laser-plasma source and a flat-field spectrometer can be used for near-edge x-ray absorption fine structure experiments in transmission as well as reflection under grazing incidence conditions (ReflEXAFS). The latter method offers the advantage that thin film preparation is not necessary and that the surface sensitivity is strongly enhanced. The results obtained for thin polymer films show good agreement with synchrotron data. Furthermore, we use the ReflEXAFS method to investigate changes in the chemical composition of PMMA induced by extreme ultraviolet (EUV) radiation. The spectra indicate a loss of the carbonyl functional group upon irradiation as well as crosslinking effects at high EUV radiation doses.

  7. Structural analysis of ultrafast extended x-ray absorption fine structure with subpicometer spatial resolution: Application to spin crossover complexes

    SciTech Connect

    Gawelda, W.; Bressler, C.; Pham, V.-T.; Veen, R. M. van der; Chergui, M.; Grolimund, D.; Abela, R.

    2009-03-28

    We present a novel analysis of time-resolved extended x-ray absorption fine structure (EXAFS) spectra based on the fitting of the experimental transients obtained from optical pump/x-ray probe experiments. We apply it to the analysis of picosecond EXAFS data on aqueous [Fe{sup II}(bpy){sub 3}]{sup 2+}, which undergoes a light induced conversion from its low-spin (LS) ground state to the short-lived ({tau}{approx_equal}650 ps) excited high-spin (HS) state. A series of EXAFS spectra were simulated for a collection of possible HS structures from which the ground state fit spectrum was subtracted to generate transient difference absorption (TA) spectra. These are then compared with the experimental TA spectrum using a least-squares statistical analysis to derive the structural change. This approach reduces the number of required parameters by cancellation in the differences. It also delivers a unique solution for both the fractional population and the extracted excited state structure. We thus obtain a value of the Fe-N bond elongation in the HS state with subpicometer precision (0.203{+-}0.008 A)

  8. Structural analysis of ultrafast extended x-ray absorption fine structure with subpicometer spatial resolution: application to spin crossover complexes.

    PubMed

    Gawelda, W; Pham, V-T; van der Veen, R M; Grolimund, D; Abela, R; Chergui, M; Bressler, C

    2009-03-28

    We present a novel analysis of time-resolved extended x-ray absorption fine structure (EXAFS) spectra based on the fitting of the experimental transients obtained from optical pump/x-ray probe experiments. We apply it to the analysis of picosecond EXAFS data on aqueous [Fe(II)(bpy)(3)](2+), which undergoes a light induced conversion from its low-spin (LS) ground state to the short-lived (tau approximately 650 ps) excited high-spin (HS) state. A series of EXAFS spectra were simulated for a collection of possible HS structures from which the ground state fit spectrum was subtracted to generate transient difference absorption (TA) spectra. These are then compared with the experimental TA spectrum using a least-squares statistical analysis to derive the structural change. This approach reduces the number of required parameters by cancellation in the differences. It also delivers a unique solution for both the fractional population and the extracted excited state structure. We thus obtain a value of the Fe-N bond elongation in the HS state with subpicometer precision (0.203+/-0.008 A).

  9. Quick extended x-ray absorption fine structure instrument with millisecond time scale, optimized for in situ applications.

    PubMed

    Khalid, S; Caliebe, W; Siddons, P; So, I; Clay, B; Lenhard, T; Hanson, J; Wang, Q; Frenkel, A I; Marinkovic, N; Hould, N; Ginder-Vogel, M; Landrot, G L; Sparks, D L; Ganjoo, A

    2010-01-01

    In order to learn about in situ structural changes in materials at subseconds time scale, we have further refined the techniques of quick extended x-ray absorption fine structure (QEXAFS) and quick x-ray absorption near edge structure (XANES) spectroscopies at beamline X18B at the National Synchrotron Light Source. The channel cut Si (111) monochromator oscillation is driven through a tangential arm at 5 Hz, using a cam, dc motor, pulley, and belt system. The rubber belt between the motor and the cam damps the mechanical noise. EXAFS scan taken in 100 ms is comparable to standard data. The angle and the angular range of the monochromator can be changed to collect a full EXAFS or XANES spectrum in the energy range 4.7-40.0 KeV. The data are recorded in ascending and descending order of energy, on the fly, without any loss of beam time. The QEXAFS mechanical system is outside the vacuum system, and therefore changing the mode of operation from conventional to QEXAFS takes only a few minutes. This instrument allows the acquisition of time resolved data in a variety of systems relevant to electrochemical, photochemical, catalytic, materials, and environmental sciences.

  10. SYNCHROTRON RADIATION, FREE ELECTRON LASER, APPLICATION OF NUCLEAR TECHNOLOGY, ETC.: A new cell for X-ray absorption spectroscopy study under high pressure

    NASA Astrophysics Data System (ADS)

    Zheng, Li-Rong; Che, Rong-Zheng; Liu, Jing; Du, Yong-Hua; Zhou, Ying-Li; Hu, Tian-Dou

    2009-08-01

    X-ray absorption fine structure (XAFS) spectroscopy is a powerful technique for the investigation of the local environment around selected atoms in condensed matter. XAFS under pressure is an important method for the synchrotron source. We design a cell for a high pressure XAFS experiment. Sintered boron carbide is used as the anvils of this high pressure cell in order to obtain a full XAFS spectrum free from diffraction peaks. In addition, a hydraulic pump was adopted to make in-suit pressure modulation. High quality XAFS spectra of ZrH2 under high pressure (up to 13 GPa) were obtained by this cell.

  11. Extended x-ray absorption fine structure measurements of quasi-isentropically compressed vanadium targets on the OMEGA laser

    SciTech Connect

    Yaakobi, B.; Boehly, T. R.; Sangster, T. C.; Meyerhofer, D. D.; Remington, B. A.; Allen, P. G.; Pollaine, S. M.; Lorenzana, H. E.; Lorenz, K. T.; Hawreliak, J. A.

    2008-06-15

    The use of in situ extended x-ray absorption fine structure (EXAFS) for characterizing nanosecond laser-shocked vanadium, titanium, and iron has recently been demonstrated. These measurements are extended to laser-driven, quasi-isentropic compression experiments (ICE). The radiation source (backlighter) for EXAFS in all of these experiments is obtained by imploding a spherical target on the OMEGA laser [T. R. Boehly et al., Rev. Sci. Instrum. 66, 508 (1995)]. Isentropic compression (where the entropy is kept constant) enables to reach high compressions at relatively low temperatures. The absorption spectra are used to determine the temperature and compression in a vanadium sample quasi-isentropically compressed to pressures of up to {approx}0.75 Mbar. The ability to measure the temperature and compression directly is unique to EXAFS. The drive pressure is calibrated by substituting aluminum for the vanadium and interferometrically measuring the velocity of the back target surface by the velocity interferometer system for any reflector (VISAR). The experimental results obtained by EXAFS and VISAR agree with each other and with the simulations of a hydrodynamic code. The role of a shield to protect the sample from impact heating is studied. It is shown that the shield produces an initial weak shock that is followed by a quasi-isentropic compression at a relatively low temperature. The role of radiation heating from the imploding target as well as from the laser-absorption region is studied. The results show that in laser-driven ICE, as compared with laser-driven shocks, comparable compressions can be achieved at lower temperatures. The EXAFS results show important details not seen in the VISAR results.

  12. Non-patchy strategy for inter-atomic distances from Extended X-ray Absorption Fine Structure

    PubMed Central

    Xu, Gu; Li, Guifang; LI, Xianya; Liang, Yi; Feng, Zhechuan

    2017-01-01

    Extended X-ray Absorption Fine Structure (EXAFS) has been one of the few structural probes available for crystalline, non-crystalline and even highly disordered specimens. However, the data analysis involves a patchy and tinkering process, including back-and-forth fitting and filtering, leading to ambiguous answers sometimes. Here we try to resolve this long standing problem, to extract the inter-atomic distances from the experimental data by a single step minimization, in order to replace the tedious and tinkering process. The new strategy is built firmly by the mathematical logic, and made straightforward and undeniable. The finding demonstrates that it is possible to break off from the traditional patchy model fitting, and to remove the logical confusion of a priori prediction of the structure to be matched with experimental data, making it a much more powerful technique than the existing methods. The new method is expected to benefit EXAFS users covering all disciplines. Also, it is anticipated that the current work to be the motivation and inspiration to the further efforts. PMID:28181529

  13. Non-patchy strategy for inter-atomic distances from Extended X-ray Absorption Fine Structure

    NASA Astrophysics Data System (ADS)

    Xu, Gu; Li, Guifang; Li, Xianya; Liang, Yi; Feng, Zhechuan

    2017-02-01

    Extended X-ray Absorption Fine Structure (EXAFS) has been one of the few structural probes available for crystalline, non-crystalline and even highly disordered specimens. However, the data analysis involves a patchy and tinkering process, including back-and-forth fitting and filtering, leading to ambiguous answers sometimes. Here we try to resolve this long standing problem, to extract the inter-atomic distances from the experimental data by a single step minimization, in order to replace the tedious and tinkering process. The new strategy is built firmly by the mathematical logic, and made straightforward and undeniable. The finding demonstrates that it is possible to break off from the traditional patchy model fitting, and to remove the logical confusion of a priori prediction of the structure to be matched with experimental data, making it a much more powerful technique than the existing methods. The new method is expected to benefit EXAFS users covering all disciplines. Also, it is anticipated that the current work to be the motivation and inspiration to the further efforts.

  14. High-precision limit on variation in the fine-structure constant from a single quasar absorption system

    NASA Astrophysics Data System (ADS)

    Kotuš, S. M.; Murphy, M. T.; Carswell, R. F.

    2017-01-01

    The brightest southern quasar above redshift z = 1, HE 0515-4414, with its strong intervening metal absorption line system at zabs = 1.1508, provides a unique opportunity to precisely measure or limit relative variations in the fine-structure constant (Δα/α). A variation of just ˜3 parts per million (ppm) would produce detectable velocity shifts between its many strong metal transitions. Using new and archival observations from the Ultraviolet and Visual Echelle Spectrograph (UVES), we obtain an extremely high signal-to-noise ratio spectrum (peaking at S/N ≈ 250 pix-1). This provides the most precise measurement of Δα/α from a single absorption system to date, Δα/α = -1.42 ± 0.55stat ± 0.65sys ppm, comparable with the precision from previous, large samples of ˜150 absorbers. The largest systematic error in all (but one) previous similar measurements, including the large samples, was long-range distortions in the wavelength calibration. These would add an ˜2 ppm systematic error to our measurement and up to ˜10 ppm to other measurements using Mg and Fe transitions. However, we corrected the UVES spectra using well-calibrated spectra of the same quasar from the High Accuracy Radial velocity Planet Searcher, leaving a residual 0.59 ppm systematic uncertainty, the largest contribution to our total systematic error. A similar approach, using short observations on future well-calibrated spectrographs to correct existing high S/N spectra, would efficiently enable a large sample of reliable Δα/α measurements. The high-S/N UVES spectrum also provides insights into analysis difficulties, detector artefacts and systematic errors likely to arise from 25-40-m telescopes.

  15. Artificial intelligence applied to the automatic analysis of absorption spectra. Objective measurement of the fine structure constant

    NASA Astrophysics Data System (ADS)

    Bainbridge, Matthew B.; Webb, John K.

    2017-01-01

    A new and automated method is presented for the analysis of high-resolution absorption spectra. Three established numerical methods are unified into one `artificial intelligence' process: a genetic algorithm (Genetic Voigt Profile FIT, gvpfit); non-linear least-squares with parameter constraints (vpfit); and Bayesian model averaging (BMA). The method has broad application but here we apply it specifically to the problem of measuring the fine structure constant at high redshift. For this we need objectivity and reproducibility. gvpfit is also motivated by the importance of obtaining a large statistical sample of measurements of Δα/α. Interactive analyses are both time consuming and complex and automation makes obtaining a large sample feasible. In contrast to previous methodologies, we use BMA to derive results using a large set of models and show that this procedure is more robust than a human picking a single preferred model since BMA avoids the systematic uncertainties associated with model choice. Numerical simulations provide stringent tests of the whole process and we show using both real and simulated spectra that the unified automated fitting procedure out-performs a human interactive analysis. The method should be invaluable in the context of future instrumentation like ESPRESSO on the VLT and indeed future ELTs. We apply the method to the zabs = 1.8389 absorber towards the zem = 2.145 quasar J110325-264515. The derived constraint of Δα/α = 3.3 ± 2.9 × 10-6 is consistent with no variation and also consistent with the tentative spatial variation reported in Webb et al. and King et al.

  16. Artificial intelligence applied to the automatic analysis of absorption spectra. Objective measurement of the fine structure constant.

    NASA Astrophysics Data System (ADS)

    Bainbridge, Matthew B.; Webb, John K.

    2017-01-01

    A new and automated method is presented for the analysis of high-resolution absorption spectra. Three established numerical methods are unified into one "artificial intelligence" process: a genetic algorithm (GVPFIT); non-linear least-squares with parameter constraints (VPFIT); and Bayesian Model Averaging (BMA). The method has broad application but here we apply it specifically to the problem of measuring the fine structure constant at high redshift. For this we need objectivity and reproducibility. GVPFIT is also motivated by the importance of obtaining a large statistical sample of measurements of Δα/α. Interactive analyses are both time consuming and complex and automation makes obtaining a large sample feasible. In contrast to previous methodologies, we use BMA to derive results using a large set of models and show that this procedure is more robust than a human picking a single preferred model since BMA avoids the systematic uncertainties associated with model choice. Numerical simulations provide stringent tests of the whole process and we show using both real and simulated spectra that the unified automated fitting procedure out-performs a human interactive analysis. The method should be invaluable in the context of future instrumentation like ESPRESSO on the VLT and indeed future ELTs. We apply the method to the zabs = 1.8389 absorber towards the zem = 2.145 quasar J110325-264515. The derived constraint of Δα/α = 3.3 ± 2.9 × 10-6 is consistent with no variation and also consistent with the tentative spatial variation reported in Webb et al. (2011) and King et al. (2012).

  17. Extended x-ray absorption fine structure studies of the atomic structure of nanoparticles in different metallic matrices.

    PubMed

    Baker, S H; Roy, M; Gurman, S J; Binns, C

    2009-05-06

    It has been appreciated for some time that the novel properties of particles in the size range 1-10 nm are potentially exploitable in a range of applications. In order to ultimately produce commercial devices containing nanosized particles, it is necessary to develop controllable means of incorporating them into macroscopic samples. One way of doing this is to embed the nanoparticles in a matrix of a different material, by co-deposition for example, to form a nanocomposite film. The atomic structure of the embedded particles can be strongly influenced by the matrix. Since some of the key properties of materials, including magnetism, strongly depend on atomic structure, the ability to determine atomic structure in embedded nanoparticles is very important. This review focuses on nanoparticles, in particular magnetic nanoparticles, embedded in different metal matrices. Extended x-ray absorption fine structure (EXAFS) provides an excellent means of probing atomic structure in nanocomposite materials, and an overview of this technique is given. Its application in probing catalytic metal clusters is described briefly, before giving an account of the use of EXAFS in determining atomic structure in magnetic nanocomposite films. In particular, we focus on cluster-assembled films comprised of Fe and Co nanosized particles embedded in various metal matrices, and show how the crystal structure of the particles can be changed by appropriate choice of the matrix material. The work discussed here demonstrates that combining the results of structural and magnetic measurements, as well as theoretical calculations, can play a significant part in tailoring the properties of new magnetic cluster-assembled materials.

  18. High resolution spectrometer for extended x-ray absorption fine structure measurements in the 6 keV to 15 keV energy range

    NASA Astrophysics Data System (ADS)

    Seely, J. F.; Hudson, L. T.; Henins, Albert; Feldman, U.

    2016-11-01

    A Cauchois transmission-crystal spectrometer has been developed with high crystal resolving power in the 6 keV-15 keV energy range and sufficient sensitivity to record single-shot spectra from the Lawrence Livermore National Laboratory (LLNL) Titan laser and other comparable or more energetic lasers. The spectrometer capabilities were tested by recording the W L transitions from a laboratory source and the extended x-ray absorption fine structure (EXAFS) spectrum through a Cu foil.

  19. Geometric Structure Determination of N694C Lipoxygenase: a Comparative Near-Edge X-Ray Absorption Spectroscopy And Extended X-Ray Absorption Fine Structure Study

    SciTech Connect

    Sarangi, R.; Hocking, R.K.; Neidig, M.L.; Benfatto, M.; Holman, T.R.; Solomon, E.I.; Hodgson, K.O.; Hedman, B.

    2009-05-27

    The mononuclear nonheme iron active site of N694C soybean lipoxygenase (sLO1) has been investigated in the resting ferrous form using a combination of Fe-K-pre-edge, near-edge (using the minuit X-ray absorption near-edge full multiple-scattering approach), and extended X-ray absorption fine structure (EXAFS) methods. The results indicate that the active site is six-coordinate (6C) with a large perturbation in the first-shell bond distances in comparison to the more ordered octahedral site in wild-type sLO1. Upon mutation of the asparigine to cystiene, the short Fe-O interaction with asparigine is replaced by a weak Fe-(H{sub 2}O), which leads to a distorted 6C site with an effective 5C ligand field. In addition, it is shown that near-edge multiple scattering analysis can give important three-dimensional structural information, which usually cannot be accessed using EXAFS analysis. It is further shown that, relative to EXAFS, near-edge analysis is more sensitive to partial coordination numbers and can be potentially used as a tool for structure determination in a mixture of chemical species.

  20. XAFS beam lines at Aichi Synchrotron Radiation Center dedicated to industrial use

    NASA Astrophysics Data System (ADS)

    Takeda, Yoshikazu

    2016-05-01

    Aichi Synchrotron Radiation Center was designed for industrial use following five years of discussion among academia, industry and local government in the Aichi area. Among the six beam lines constructed, those that facilitated X-ray absorption fine structure (XAFS) analysis were given first priority. In addition to the hardware, attention was given to the development of operating procedures that were quick and user-friendly. The facility entered public service in March 2013. In the year 2013, 55% of the experiments involved XAFS analysis (hard X-ray, soft X-ray and vacuum ultraviolet regions) and in 2014 it was 57%. The range of research fields is very broad, emphasizing the importance of the XAFS beam lines.

  1. Cyclic voltammetry and near edge X-ray absorption fine structure spectroscopy at the Ag L3-edge on electrochemical halogenation of Ag layers on Au(111)

    NASA Astrophysics Data System (ADS)

    Endo, Osamu; Nakamura, Masashi

    2011-05-01

    One to three layers of Ag grown on a Au(111) electrode were studied by cyclic voltammetry in chloride and bromide solutions and by ex-situ near-edge X-ray absorption fine structure spectroscopy at the Ag L3-edge (Ag L3-NEXAFS). The one and two layers obtained by underpotential deposition exhibited reduced intensity at the absorption edge in the Ag L3-NEXAFS spectra, which suggests the gain of d-electrons in these layers. The cyclic voltammograms and the Ag L3-NEXAFS spectra indicate that the second and third layers of Ag halogenated at positive potentials, whereas the first layer remained in metallic form.

  2. Calculation of near-edge x-ray-absorption fine structure at finite temperatures: spectral signatures of hydrogen bond breaking in liquid water.

    PubMed

    Hetényi, Balázs; De Angelis, Filippo; Giannozzi, Paolo; Car, Roberto

    2004-05-08

    We calculate the near-edge x-ray-absorption fine structure of H(2)O in the gas, hexagonal ice, and liquid phases using heuristic density-functional based methods. We present a detailed comparison of our results with experiment. The differences between the ice and water spectra can be rationalized in terms of the breaking of hydrogen bonds around the absorbing molecule. In particular the increase in the pre-edge absorption feature from ice to water is shown to be due to the breaking of a donor hydrogen bond. We also find that in water approximately 19% of hydrogen bonds are broken.

  3. Analysis of the near-edge X-ray-absorption fine-structure of anthracene: A combined theoretical and experimental study

    SciTech Connect

    Klues, Michael; Witte, Gregor; Hermann, Klaus

    2014-01-07

    The near-edge fine structure of the carbon K-edge absorption spectrum of anthracene was measured and theoretically analyzed by density functional theory calculations implemented in the StoBe code. It is demonstrated that the consideration of electronic relaxation of excited states around localized core holes yields a significant improvement of the calculated excitation energies and reproduces the experimentally observed fine structure well. The detailed analysis of excitation spectra calculated for each symmetry inequivalent excitation center allows in particular to examine the influence of chemical shifts and core hole effects on the excitation energies. Moreover, the visualization of final states explains the large variations in the oscillator strength of various transitions as well as the nature of Rydberg-states that exhibit a notable density of states below the ionization potentials.

  4. Effect of Iron(II) on Arsenic Sequestration by δ-MnO2: Desorption Studies Using Stirred-Flow Experiments and X-Ray Absorption Fine-Structure Spectroscopy.

    PubMed

    Wu, Yun; Li, Wei; Sparks, Donald L

    2015-11-17

    Arsenic (As) mobility in the environment is greatly affected by its oxidation state and the degree to which it is sorbed on metal oxide surfaces. Manganese (Mn) and iron (Fe) oxides are ubiquitous solids in terrestrial systems and have high sorptive capacities for many trace metals, including As. Although numerous studies have studied the effects of As adsorption and desorption onto Fe and Mn oxides individually, the fate of As within mixed systems representative of natural environments has not been resolved. In this research, As(III) was initially reacted with a poorly crystalline phyllomanganate (δ-MnO2) in the presence of Fe(II) prior to desorption. This initial reaction resulted in the sorption of both As(III) and As(V) on mixed Fe/Mn-oxides surfaces. A desorption study was carried out using two environmentally significant ions, phosphate (PO4(3-)) and calcium (Ca(2+)). Both a stirred-flow technique and X-ray absorption fine-structure spectroscopy (XAFS) analysis were used to investigate As desorption behavior. Results showed that when As(III)/Fe(II) = 1:1 in the initial reaction, only As(V) was desorbed, agreeing with a previous study showing that As(III) is not associated with the Fe/Mn-oxides. When As(III)/Fe(II) = 1:10 in the initial reaction, both As(III) and As(V) can be desorbed from the Fe/Mn-oxide surface, and more As(III) is desorbed than As(V). Neither of the desorbents used in this study completely removed As(III) or As(V) from the Fe/Mn-oxides surface. However, the As desorption fraction decreases with increasing Fe(II) concentration in the initial reactions.

  5. Evolution of fcc Cu clusters and their structure changes in the soft magnetic Fe85.2Si1B9P4Cu0.8 (NANOMET) and FINEMET alloys observed by X-ray absorption fine structure

    NASA Astrophysics Data System (ADS)

    Matsuura, M.; Nishijima, M.; Takenaka, K.; Takeuchi, A.; Ofuchi, H.; Makino, A.

    2015-05-01

    It is known that Cu plays an essential role in reducing the grain size of precipitated bcc Fe(Si) nanocrystallites in a nanocrystalline soft-magnetic Fe85.2Si1B9P4Cu0.8 (NANOMET®) alloys like as an Fe73.5Si13.5B9Nb3Cu1 (FINEMET®). However, significant differences are there between two alloys; NANOMET has much higher iron content (˜85%) than FINEMET (73.5%) and the former contains P instead of Nb for the latter. In the present work, the local structure around Cu in FINEMET was measured by X-ray absorption fine structure (XAFS) at 20 K and compared with those of NANOMET during nanocrystallization. Definite differences between NANOMET and FINEMET are found in the way of the evolution of Cu clusters during nanocrystallization. In FINEMET, an fcc structure of Cu is recognized in an as-quenched ribbon indicating existence of a small number of Cu clusters or a very small size of Cu clusters which is stable up to 450 °C, while the fcc Cu clusters are developed rapidly above 450 °C. An fcc structure of the Cu clusters in FINEMET is retained all the way to the end of the nanocrystallization. On the contrary, for NANOMET the local structure around Cu changes in a sequence as "amorphous → fcc → bcc → fcc" by annealing. The reasons of such different behaviors of the local structure around Cu during nanocrystallization are discussed in terms of different contributions of Cu clusters in bcc Fe precipitation between FINEMET and NANOMET. A significantly fast crystallization process with an extraordinary large heat release can be another reason for the transition of the local structure around Cu from fcc to bcc for NANOMET.

  6. Operando characterization of batteries using x-ray absorption spectroscopy: advances at the beamline XAFS at synchrotron Elettra

    NASA Astrophysics Data System (ADS)

    Aquilanti, Giuliana; Giorgetti, Marco; Dominko, Robert; Stievano, Lorenzo; Arčon, Iztok; Novello, Nicola; Olivi, Luca

    2017-02-01

    X-ray absorption spectroscopy is a synchrotron radiation based technique that is able to provide information on both local structure and electronic properties in a chemically selective manner. It can be used to characterize the dynamic processes that govern the electrochemical energy storage in batteries, and to shed light on the redox chemistry and changes in structure during galvanostatic cycling to design cathode materials with improved properties. Operando XAS studies have been performed at beamline XAFS at Elettra on different systems. For Li-ion batteries, a multiedge approach revealed the role of the different cathode components during the charge and discharge of the battery. In addition, Li-S batteries for automotive applications were studied. Operando sulfur K-edge XANES and EXAFS analysis was used to characterize the redox chemistry of sulfur, and to relate the electrochemical mechanism to its local structure.

  7. Interaction of Isophorone with Pd(111): A Combination of Infrared Reflection–Absorption Spectroscopy, Near-Edge X-ray Absorption Fine Structure, and Density Functional Theory Studies

    PubMed Central

    2014-01-01

    Atomistic level understanding of interaction of α,β-unsaturated carbonyls with late transition metals is a key prerequisite for rational design of new catalytic materials with the desired selectivity toward C=C or C=O bond hydrogenation. The interaction of this class of compounds with transition metals was investigated on α,β-unsaturated ketone isophorone on Pd(111) as a prototypical system. In this study, infrared reflection–absorption spectroscopy (IRAS), near-edge X-ray absorption fine structure (NEXAFS) experiments, and density functional theory calculations including van der Waals interactions (DFT+vdW) were combined to obtain detailed information on the binding of isophorone to palladium at different coverages and on the effect of preadsorbed hydrogen on the binding and adsorption geometry. According to these experimental observations and the results of theoretical calculations, isophorone adsorbs on Pd(111) in a flat-lying geometry at low coverages. With increasing coverage, both C=C and C=O bonds of isophorone tilt with respect to the surface plane. The tilting is considerably more pronounced for the C=C bond on the pristine Pd(111) surface, indicating a prominent perturbation and structural distortion of the conjugated π system upon interaction with Pd. Preadsorbed hydrogen leads to higher tilting angles of both π bonds, which points to much weaker interaction of isophorone with hydrogen-precovered Pd and suggests the conservation of the in-plane geometry of the conjugated π system. The results of the DFT+vdW calculations provide further insights into the perturbation of the molecular structure of isophorone on Pd(111). PMID:26089998

  8. Interaction of Isophorone with Pd(111): A Combination of Infrared Reflection-Absorption Spectroscopy, Near-Edge X-ray Absorption Fine Structure, and Density Functional Theory Studies.

    PubMed

    Dostert, Karl-Heinz; O'Brien, Casey P; Riedel, Wiebke; Savara, Aditya; Liu, Wei; Oehzelt, Martin; Tkatchenko, Alexandre; Schauermann, Swetlana

    2014-12-04

    Atomistic level understanding of interaction of α,β-unsaturated carbonyls with late transition metals is a key prerequisite for rational design of new catalytic materials with the desired selectivity toward C=C or C=O bond hydrogenation. The interaction of this class of compounds with transition metals was investigated on α,β-unsaturated ketone isophorone on Pd(111) as a prototypical system. In this study, infrared reflection-absorption spectroscopy (IRAS), near-edge X-ray absorption fine structure (NEXAFS) experiments, and density functional theory calculations including van der Waals interactions (DFT+vdW) were combined to obtain detailed information on the binding of isophorone to palladium at different coverages and on the effect of preadsorbed hydrogen on the binding and adsorption geometry. According to these experimental observations and the results of theoretical calculations, isophorone adsorbs on Pd(111) in a flat-lying geometry at low coverages. With increasing coverage, both C=C and C=O bonds of isophorone tilt with respect to the surface plane. The tilting is considerably more pronounced for the C=C bond on the pristine Pd(111) surface, indicating a prominent perturbation and structural distortion of the conjugated π system upon interaction with Pd. Preadsorbed hydrogen leads to higher tilting angles of both π bonds, which points to much weaker interaction of isophorone with hydrogen-precovered Pd and suggests the conservation of the in-plane geometry of the conjugated π system. The results of the DFT+vdW calculations provide further insights into the perturbation of the molecular structure of isophorone on Pd(111).

  9. State of manganese in the photosynthetic apparatus. 1. Extended x-ray absorption fine structure studies on chloroplasts and di-.mu.-oxo-bridged dimanganese model compounds

    SciTech Connect

    Kirby, J. A.; Robertson, A. S.; Smith, J. P.; Thompson, A. C.; Cooper, S. R.; Klein, M. P.

    1981-09-01

    In this paper, extended X-ray absorption fine structure studies on the manganese contained in spinach chloroplasts and on certain di-p-oxo-bridged manganese dimers of the form (X2Mn)O2(MnX2) (X = 2,2'-bipyridine and 1 ,10-phenanthroline) are reported. From these studies, the manganese associated with photosynthetic oxygen evolution is suggested to occur as a bridged transition-metal dimer with most likely another manganese. Finally, extensive details on the analysis are included.

  10. XAFS studies of radiation damage in nuclear materials

    NASA Astrophysics Data System (ADS)

    Olive, Daniel Thomas

    The growing demand for nuclear energy places a high importance on the development of new materials capable of withstanding higher temperatures and harsher irradiation conditions than those used in existing reactors. By supporting the development of next generation reactors it also becomes possible to close the nuclear fuel cycle, greatly reducing the amount of waste sent for disposal in deep geologic repositories, where its interaction with the environment is also a matter of interest. In this thesis, X-ray absorption fine structure (XAFS) spectroscopy is used to investigate the local atomic structure of systems of interest to nuclear energy. First, two XAFS studies on environmental materials are presented. Granular activated carbon (GAC) was treated with iron to improve its water remediation properties, specifically with respect to arsenic. XAFS was used to determine the nature of iron coating on the GAC surface, and the method of arsenic bonding to the treated surface. Next, a neodymium precipitate from solubility studies carried out for the Waste Isolation Pilot Plant (WIPP) was analyzed. Neodymium was used as an analog for plutonium in brine solutions. XAFS fitting indicated that the neodymium substituted for calcium in a gypsum lattice, providing information useful for future geochemical modeling. XAFS was also used to study radiation damage in materials. A candidate material for advanced reactor structural materials, modified 9Cr--1Mo, was irradiated to 1, 4, and 10 displacements per atom (dpa). XAFS analyses were performed on the Fe, Mo, and Nb K-edges. Irradiation caused a reduction in coordination for all three elements, but the exact behavior was element specific. Damage around Fe atoms was linear with dose, while damage around Mo atoms saturated at or before 1 dpa. XAFS was shown to provide a useful atomic level description of radiation damage for a complex alloy system. Finally, zirconium carbide and zirconium nitride, candidate materials for advanced

  11. A new limit on the variation of the fine-structure constant using absorption line multiplets in the early universe

    NASA Astrophysics Data System (ADS)

    Thong, Le Duc

    2015-08-01

    One of the key questions of modern physics concerns the possibility that physical constants vary over space and time during the history of the universe. The Standard Model of physics is built on these constants, but it does not provide any explanation for their values, nor requires their constancy over space and time. Here we set a new limit on possible spatial and temporal variations of the fine-structure constant , by comparing transitions line multiplets in an ensemble of Fe II 1608, 2344, 2374, 2383, 2587 and 2600 observed in the early universe with those measured in the laboratory. Based on the optical spectra observations of QSO HE 0515-4414, we deduced a constraint of at redshift z = 1.15. This is at present the tightest limit on at early cosmological epochs compared to the published results in the literature.

  12. Low-temperature adsorption of H2S on Ni(001) studied by near-edge- and surface-extended-x-ray-absorption fine structure

    NASA Astrophysics Data System (ADS)

    McGrath, R.; MacDowell, A. A.; Hashizume, T.; Sette, F.; Citrin, P. H.

    1989-11-01

    The adsorption of H2S on Ni(001) has been studied with surface-extended x-ray-absorption fine structure and near-edge x-ray-absorption fine structure (NEXAFS) using the AT&T Bell Laboratories X15B beamline at the National Synchrotron Light Source. At 95 K and full saturation coverage, ~0.45 monolayer (ML) of S atoms in fourfold-hollow sites are produced, characteristic of room-temperature adsorption, accompanied by ~0.05 ML of oriented molecular H2S. Both these atomic and molecular chemisorbed species are buried under ~0.9 ML of disordered physisorbed H2S. No evidence for HS is found. Above 190 K the two molecular H2S phases desorb, leaving only dissociated S. These findings differ from previously reported interpretations of data obtained with high-resolution electron-energy-loss spectroscopy. They also exemplify the utility of NEXAFS for identifying and quantifying atomic and molecular surface species even when their difference involves only H and the two species coexist.

  13. A Stringent Limit on Variation of the Fine-Structure Constant Using Absorption Line Multiplets in the Early Universe

    NASA Astrophysics Data System (ADS)

    Le, T. D.

    2016-06-01

    One of the key questions of modern physics concerns the possibility that physical constants have varied throughout the history of the Universe. The standard model of physics is built on these constants, but it does not provide any explanation for their values, nor does it require their constancy over space and time. Here, we set a new limit on possible spatial and temporal variations of the fine-structure constant α = e 2/4πɛ0 ħc by comparing transitions and line multiplets in an ensemble of Fe II λ 1608, λ 2344, λ 2374, λ 2383, λ 2587, and λ 2600 observed in the early Universe with those measured in the laboratory. Based on the optical spectrum observations of QSO HE 0515-4414, we deduce a constraint of Δα/α = (-0.157± 0.300)×10-6 at redshift z = 1.15. At present, this represents the tightest limit on Δα/α in early cosmological epochs compared to the published results in the literature.

  14. Fine structure in krypton excimer

    SciTech Connect

    Hemici, M.; Saoudi, R.; Descroix, E.; Audouard, E.; Laporte, P. ); Spiegelmann, F. )

    1995-04-01

    By using laser reduced fluorescence techniques, molecular absorption from the first relaxed excited excimer states of krypton is obtained in the 960--990-nm wavelength range. Five bands are observed and analyzed by comparison with an [ital ab] [ital initio] calculated spectrum. The fine structure is thus evidenced.

  15. X-ray absorption fine structure measurement with a 9 V electric battery x-ray emitter

    SciTech Connect

    Mitsuya, Shota; Ishii, Hideshi; Kawai, Jun; Tanaka, Keiichi

    2006-09-25

    X-ray absorption spectral analysis is a well known technique for analyzing the chemical environment of an element in a specimen. It has been believed that high intensity and monochromatized x rays such as the synchrotron radiation are required for an x-ray absorption experiment. In the present study, however, we demonstrate that the x-ray absorption spectral measurement of transition metal foils with an energy resolution of 10 eV is possible with a combination of a 9 V dry electric battery pyroelectric x-ray generator and a superconducting microcalorimeter.

  16. XRD, IR and XAFS studies of cobalt complexes having amino pyrazole dicarboxylate (APD) as ligand

    NASA Astrophysics Data System (ADS)

    Mishra, Ashutosh; Jain, Garima; Patil, H.

    2014-09-01

    X-ray absorption fine structure spectroscopic (XAFS) studies have been done on two cobalt complexes using APD (diethyl 4-amino-1-phenyl-1H-pyrazole-3,5 dicarboxylate) as ligand. The X-ray absorption spectra of the complexes have been recorded on beam line of synchrotron at Raja Ramanna Centre for Advanced Technology (RRCAT), Indore (India). The X-ray diffraction of the samples has also been carried out. FTIR studies of two samples were also reported in the present communication.

  17. Extended x-ray-absorption fine-structure study of the position of Zr within the unit cell of Sm sub 2 Co sub 17

    SciTech Connect

    Rabenberg, L. ); Barrera, E.V. ); Maury, C.E.; Allibert, C.H. , ENSEEG, B. P. 75, 38402 St. Martin-d'Heres, ); Heald, S.M. )

    1991-04-15

    Extended x-ray-absorption fine-structure spectroscopy (EXAFS) has been used to determine the position of Zr within the unit cell of Sm{sub 2}Co{sub 17}. Induction-melted Sm{sub 2}Co{sub 17}:Zr ternary alloys, aged at 1180 {degree}C, then quenched, consisted of intimately mixed H2:17 and R2:17 having Zr in solid solution as well some regions of R2:17 that were poor in Zr. EXAFS spectroscopy of these specimens indicates that the most probable position for Zr is a site having 2 Sm near-neighbor atoms and 11 Co atoms distributed over three different interatomic distances. This is consistent with a direct substitution of Zr for Co in the Co site in the mixed planes (12{ital j} in {ital P}6{sub 3}/{ital mmc} or 18{ital f} in {ital R}3{ital m}).

  18. Thermal and magnetic anomalies of α-iron: an exploration by extended x-ray absorption fine structure spectroscopy and synchrotron x-ray diffraction.

    PubMed

    Boccato, Silvia; Sanson, Andrea; Kantor, Innokenty; Mathon, Olivier; Dyadkin, Vadim; Chernyshov, Dmitry; Carnera, Alberto; Pascarelli, Sakura

    2016-09-07

    The local structure and dynamics of α-iron have been investigated by extended x-ray absorption fine structure (EXAFS) spectroscopy and x-ray diffraction (XRD) in order to shed light on some thermal and magnetic anomalies observed in the last decades. The quantitative EXAFS analysis of the first two coordination shells reveals a peculiar local vibrational dynamics of α-iron: the second neighbor distance exhibits anharmonicity and vibrational anisotropy larger than the first neighbor distance. We search for possible distortions of the bcc structure to justify the unexplained magnetostriction anomalies of α-iron and provide a value for the maximum dislocation of the central Fe atom. No thermal anomalies have been detected from the current XRD data. On the contrary, an intriguing thermal anomaly at about 150 K, ascribed to a stiffening of the Fe-Fe bonds, was found by EXAFS.

  19. The structure of Mn-doped tris(8-hydroxyquinoline)gallium by extended x-ray absorption fine structure spectroscopy and first principles calculations

    NASA Astrophysics Data System (ADS)

    Fang, Shaojie; Pang, Zhiyong; Du, Yonghua; Zheng, Lirong; Zhang, Xijian; Wang, Fenggong; Yuan, Huimin; Han, Shenghao

    2012-12-01

    Metal-Mqx (M = Al, Ga, Zn, Be, and Ca, x = 2 or 3) complexes play a key role in organic spintronics and organic optoelectronics. However, the accurate structure determination of these complexes has been a challenge for a long time. Here, we report the structure of Mn-Gaq3 investigated by using first-principle density functional theory (DFT) calculations and extended X-ray absorption fine structure (EXAFS) spectroscopy. First, the structures of Mn-Gaq3 were predicted by first-principle DFT calculations. Then, all reasonable structures achieved from the calculations were used to fit the EXAFS spectra. By this method, the structure of Mn-Gaq3 is well obtained. We believe this method is also applicable to other metal-Mqx films.

  20. Thermal and magnetic anomalies of α-iron: an exploration by extended x-ray absorption fine structure spectroscopy and synchrotron x-ray diffraction

    NASA Astrophysics Data System (ADS)

    Boccato, Silvia; Sanson, Andrea; Kantor, Innokenty; Mathon, Olivier; Dyadkin, Vadim; Chernyshov, Dmitry; Carnera, Alberto; Pascarelli, Sakura

    2016-09-01

    The local structure and dynamics of α-iron have been investigated by extended x-ray absorption fine structure (EXAFS) spectroscopy and x-ray diffraction (XRD) in order to shed light on some thermal and magnetic anomalies observed in the last decades. The quantitative EXAFS analysis of the first two coordination shells reveals a peculiar local vibrational dynamics of α-iron: the second neighbor distance exhibits anharmonicity and vibrational anisotropy larger than the first neighbor distance. We search for possible distortions of the bcc structure to justify the unexplained magnetostriction anomalies of α-iron and provide a value for the maximum dislocation of the central Fe atom. No thermal anomalies have been detected from the current XRD data. On the contrary, an intriguing thermal anomaly at about 150 K, ascribed to a stiffening of the Fe-Fe bonds, was found by EXAFS.

  1. Absolute determination of charge-coupled device quantum detection efficiency using Si K-edge x-ray absorption fine structure

    SciTech Connect

    Dunn, J; Steel, A B

    2012-05-06

    We report a method to determine the quantum detection efficiency and the absorbing layers on a front-illuminated charge-coupled device (CCD). The CCD under study, as part of a crystal spectrometer, measures intense continuum x-ray emission from a picosecond laser-produced plasma and spectrally resolves the Si K-edge x-ray absorption fine structure features due to the electrode gate structure of the device. The CCD response across the Si K-edge shows a large discontinuity as well as a number of oscillations that are identified individually and uniquely from Si, SiO{sub 2}, and Si{sub 3}N{sub 4} layers. From the spectral analysis of the structure and K-edge discontinuity, the active layer thickness and the different absorbing layers thickness can be determined precisely. A precise CCD detection model from 0.2-10 keV can be deduced from this highly sensitive technique.

  2. Communication: Near edge x-ray absorption fine structure spectroscopy of aqueous adenosine triphosphate at the carbon and nitrogen K-edges.

    PubMed

    Kelly, Daniel N; Schwartz, Craig P; Uejio, Janel S; Duffin, Andrew M; England, Alice H; Saykally, Richard J

    2010-09-14

    Near edge x-ray absorption fine structure (NEXAFS) spectroscopy at the nitrogen and carbon K-edges was used to study the hydration of adenosine triphosphate in liquid microjets. The total electron yield spectra were recorded as a function of concentration, pH, and the presence of sodium, magnesium, and copper ions (Na(+)/Mg(2+)/Cu(2+)). Significant spectral changes were observed upon protonation of the adenine ring, but not under conditions that promote π-stacking, such as high concentration or presence of Mg(2+), indicating that NEXAFS is insensitive to the phenomenon. Intramolecular inner-sphere association of Cu(2+) did create observable broadening of the nitrogen spectrum, whereas outer-sphere association with Mg(2+) did not.

  3. Particle Formation from Pulsed Laser Irradiation of SootAggregates studied with scanning mobility particle sizer, transmissionelectron microscope and near-edge x-ray absorption fine structure.

    SciTech Connect

    Michelsen, Hope A.; Tivanski, Alexei V.; Gilles, Mary K.; vanPoppel, Laura H.; Dansson, Mark A.; Buseck, Peter R.; Buseck, Peter R.

    2007-02-20

    We investigated the physical and chemical changes induced in soot aggregates exposed to laser radiation using a scanning mobility particle sizer, a transmission electron microscope, and a scanning transmission x-ray microscope to perform near-edge x-ray absorption fine structure spectroscopy. Laser-induced nanoparticle production was observed at fluences above 0.12 J/cm(2) at 532 nm and 0.22 J/cm(2) at 1064 nm. Our results indicate that new particle formation proceeds via (1) vaporization of small carbon clusters by thermal or photolytic mechanisms, followed by homogeneous nucleation, (2) heterogeneous nucleation of vaporized carbon clusters onto material ablated from primary particles, or (3) both processes.

  4. Time dependent density functional theory study of the near-edge x-ray absorption fine structure of benzene in gas phase and on metal surfaces.

    PubMed

    Asmuruf, Frans A; Besley, Nicholas A

    2008-08-14

    The near-edge x-ray absorption fine structure of benzene in the gas phase and adsorbed on the Au(111) and Pt(111) surfaces is studied with time dependent density functional theory. Excitation energies computed with hybrid exchange-correlation functionals are too low compared to experiment. However, after applying a constant shift the spectra are in good agreement with experiment. For benzene on the Au(111) surface, two bands arising from excitation to the e(2u)(pi(*)) and b(2g)(pi(*)) orbitals of benzene are observed for photon incidence parallel to the surface. On Pt(111) surface, a broader band arises from excitation to benzene orbitals that are mixed with the surface and have both sigma(*)(Pt-C) and pi(*) characters.

  5. Time-resolved near-edge x-ray absorption fine structure spectroscopy on photo-induced phase transitions using a tabletop soft-x-ray spectrometer

    NASA Astrophysics Data System (ADS)

    Grossmann, P.; Rajkovic, I.; Moré, R.; Norpoth, J.; Techert, S.; Jooss, C.; Mann, Klaus

    2012-05-01

    We present a table-top soft-x-ray spectrometer for the wavelength range λ = 1-5 nm based on a stable laser-driven x-ray source, making use of a gas-puff target. With this setup, optical light-pump/soft-x-ray probe near-edge x-ray absorption fine structure (NEXAFS) experiments with a temporal resolution of about 230 ps are feasible. Pump-probe NEXAFS measurements were carried out in the "water-window" region (2.28 nm-4.36 nm) on the manganite Pr0.7Ca0.3MnO3, investigating diminutive changes of the oxygen K edge that derive from an optically induced phase transition. The results show the practicability of the table-top soft-x-ray spectrometer on demanding investigations so far exclusively conducted at synchrotron radiation sources.

  6. X-ray absorption fine structure analysis of molybdenum added to BaTiO3-based ceramics used for multilayer ceramic capacitors

    NASA Astrophysics Data System (ADS)

    Ogata, Yoichiro; Shimura, Tetsuo; Ryu, Minoru; Iwazaki, Yoshiki

    2017-04-01

    The effect of slight molybdenum doping of perovskite-type BaTiO3-based ceramics on the reliability of a multilayer ceramic capacitor (MLCC) and on the valence state of molybdenum in the BaTiO3-based ceramics has been investigated by highly accelerated lifetime tests and X-ray absorption fine structure analysis. The molybdenum added to the BaTiO3-based ceramics is located at Ti sites and improves the highly accelerated lifetime and lowers the initial dielectric resistivity in MLCCs. Through sintering in a reducing atmosphere, which is an important process in the fabrication of BaTiO3-based MLCCs, the oxidation state of the molybdenum added could be adjusted from +6 to a value close to +4.

  7. Dopant activation mechanism of Bi wire-δ-doping into Si crystal, investigated with wavelength dispersive fluorescence x-ray absorption fine structure and density functional theory.

    PubMed

    Murata, Koichi; Kirkham, Christopher; Shimomura, Masaru; Nitta, Kiyofumi; Uruga, Tomoya; Terada, Yasuko; Nittoh, Koh-Ichi; Bowler, David R; Miki, Kazushi

    2017-04-20

    We successfully characterized the local structures of Bi atoms in a wire-δ-doped layer (1/8 ML) in a Si crystal, using wavelength dispersive fluorescence x-ray absorption fine structure at the beamline BL37XU, in SPring-8, with the help of density functional theory calculations. It was found that the burial of Bi nanolines on the Si(0 0 1) surface, via growth of Si capping layer at 400 °C by molecular beam epitaxy, reduced the Bi-Si bond length from [Formula: see text] to [Formula: see text] Å. We infer that following epitaxial growth the Bi-Bi dimers of the nanoline are broken, and the Bi atoms are located at substitutional sites within the Si crystal, leading to the shorter Bi-Si bond lengths.

  8. Dopant activation mechanism of Bi wire-δ-doping into Si crystal, investigated with wavelength dispersive fluorescence x-ray absorption fine structure and density functional theory

    NASA Astrophysics Data System (ADS)

    Murata, Koichi; Kirkham, Christopher; Shimomura, Masaru; Nitta, Kiyofumi; Uruga, Tomoya; Terada, Yasuko; Nittoh, Koh-ichi; Bowler, David R.; Miki, Kazushi

    2017-04-01

    We successfully characterized the local structures of Bi atoms in a wire-δ-doped layer (1/8 ML) in a Si crystal, using wavelength dispersive fluorescence x-ray absorption fine structure at the beamline BL37XU, in SPring-8, with the help of density functional theory calculations. It was found that the burial of Bi nanolines on the Si(0 0 1) surface, via growth of Si capping layer at 400 °C by molecular beam epitaxy, reduced the Bi–Si bond length from 2.79+/- 0.01~{\\mathring{\\text{A}}} to 2.63+/- 0.02 Å. We infer that following epitaxial growth the Bi–Bi dimers of the nanoline are broken, and the Bi atoms are located at substitutional sites within the Si crystal, leading to the shorter Bi–Si bond lengths.

  9. The fate of silver ions in the photochemical synthesis of gold nanorods: an extended X-ray absorption fine structure analysis.

    PubMed

    Giannici, Francesco; Placido, Tiziana; Curri, Maria Lucia; Striccoli, Marinella; Agostiano, Angela; Comparelli, Roberto

    2009-12-14

    Water-soluble gold nanorods (Au NRs) were synthesized using a silver-ion mediated photochemical route under UV irradiation. Extended X-ray Absorption Fine Structure (EXAFS) measurements on the Ag K-edge were performed on samples obtained at different Ag/Au ratios and at increasing irradiation times in order to investigate the fate of silver ions during the growth of Au NRs. EXAFS measurements allowed to probe the chemical state and the local environment of silver in the final product. Experimental data suggest that Ag atoms are placed on top of the Au particles as metallic Ag(0), while no significant contribution to the EXAFS spectra comes from AgBr or other Ag(+) based species. The reported results strongly support the deposition of Ag(0) islands on the (110) surfaces of the Au particles, thus driving the anisotropic growth via the (111) surfaces.

  10. Study of atomic clusters in neutron irradiated reactor pressure vessel surveillance samples by extended X-ray absorption fine structure spectroscopy

    NASA Astrophysics Data System (ADS)

    Cammelli, S.; Degueldre, C.; Kuri, G.; Bertsch, J.; Lützenkirchen-Hecht, D.; Frahm, R.

    2009-03-01

    Copper and nickel impurities in nuclear reactor pressure vessel (RPV) steel can form nano-clusters, which have a strong impact on the ductile-brittle transition temperature of the material. Thus, for control purposes and simulation of long irradiation times, surveillance samples are submitted to enhanced neutron irradiation. In this work, surveillance samples from a Swiss nuclear power plant were investigated by extended X-ray absorption fine structure spectroscopy (EXAFS). The density of Cu and Ni atoms determined in the first and second shells around the absorber is affected by the irradiation and temperature. The comparison of the EXAFS data at Cu and Ni K-edges shows that these elements reside in arrangements similar to bcc Fe. However, the EXAFS analysis reveals local irradiation damage in the form of vacancy fractions, which can be determined with a precision of ∼5%. There are indications that the formation of Cu and Ni clusters differs significantly.

  11. Extended x-ray absorption fine structure spectroscopy and first-principles study of SnWO4

    NASA Astrophysics Data System (ADS)

    Kuzmin, A.; Anspoks, A.; Kalinko, A.; Timoshenko, J.; Kalendarev, R.

    2014-04-01

    The local atomic structure in α- and β-SnWO4 was studied by synchrotron radiation W L3-edge x-ray absorption spectroscopy at 10 and 300 K. Strongly distorted WO6 octahedra were found in α-SnWO4, whereas nearly regular WO4 tetrahedra were observed in β-SnWO4, confirming previous results. The structural results obtained were supported by the first-principles calculations, suggesting that the second-order Jahn-Teller effect is responsible for octahedral distortion.

  12. Versatile plug flow catalytic cell for in situ transmission/fluorescence x-ray absorption fine structure measurements

    NASA Astrophysics Data System (ADS)

    Centomo, P.; Meneghini, C.; Zecca, M.

    2013-05-01

    A novel flow-through catalytic cell has been developed for in situ x-ray absorption spectroscopy (XAS) experiments on heterogeneous catalysts under working conditions and in the presence of a liquid and a gas phase. The apparatus allows to carry out XAS measurements in both the transmission and fluorescence modes, at moderate temperature (from RT to 50-80 °C) and low-medium gas pressure (up to 7-8 bars). The materials employed are compatible with several chemicals such as those involved in the direct synthesis of hydrogen peroxide (O2, H2, H2O2, methanol). The versatile design of the cell allows to fit it to different experimental setups in synchrotron radiation beamlines. It was used successfully for the first time to test nanostructured Pd catalysts during the direct synthesis of hydrogen peroxide (H2O2) in methanol solution from dihydrogen and dioxygen.

  13. In-situ extended X-ray absorption fine structure study of electrostriction in Gd doped ceria

    SciTech Connect

    Korobko, Roman; Wachtel, Ellen; Lubomirsky, Igor; Lerner, Alyssa; Li, Yuanyuan; Frenkel, Anatoly I.

    2015-01-26

    Studying electric field-induced structural changes in ceramics is challenging due to the very small magnitude of the atomic displacements. We used differential X-ray absorption spectroscopy, an elementally specific and spatially sensitive method, to detect such changes in Gd-doped ceria, recently shown to exhibit giant electrostriction. We found that the large electrostrictive stress generation can be associated with a few percent of unusually short Ce-O chemical bonds that change their length and degree of order under an external electric field. The remainder of the lattice is reduced to the role of passive spectator. This mechanism is fundamentally different from that in electromechanically active materials currently in use.

  14. Extended X-ray absorption fine structure data analysis of copper (II) hydroxamic acid mixed ligand complexes

    NASA Astrophysics Data System (ADS)

    Parsai, N.; Mishra, A.; Shrivastava, B. D.

    2014-09-01

    The X-ray absorption spectra of copper mixed ligand complexes, having hydroxamic acid as one of the ligands, have been recorded at the K-edge of copper at BL-8 Dispersive EXAFS beamline at the 2.5 GeV INDUS-2 Synchrotron, RRCAT, Indore, India. For the analysis of EXAFS data, crystallographic data of the complex or of its analog is required, which is not available. Hence, for the analysis of EXAFS data, theoretical EXAFS data of the studied complexes have been generated using the EXAFS equation employing computer software program Mathcad. Firstly, the experimental data has been processed using the computer program Athena to obtain the normalized absorption versus energy data. From the experimental EXAFS data, the phase shift parameter (an energy independent constant 5) has been computed using Lytle, Sayers and Stern's (LSS) method. The backscattering amplitude has been taken from the available theoretical tabulations and other parameters have been taken from crystallographic data of the copper metal. Fourier transforms of both the experimental and theoretical data have been computed, and the two Fourier transforms are found to agree with each other for all the complexes. The position of the first peak in the Fourier transform gives the value of the first shell bond length, which is shorter than the actual bond length as a result of energy dependence of the phase factor (5(k)) in the sine function of the EXAFS equation. Since, the Fourier transform method and LSS method both are uncorrected for phase and other parameters of the EXAFS equation, the present method gives phase uncorrected bond length of the first coordination shell.

  15. Extended X-ray absorption fine structure data analysis of copper (II) hydroxamic acid mixed ligand complexes

    NASA Astrophysics Data System (ADS)

    Parsai, N.; Mishra, A.; Shrivastava, B. D.

    2014-09-01

    The X-ray absorption spectra of copper mixed ligand complexes, having hydroxamic acid as one of the ligands, have been recorded at the K-edge of copper at BL-8 Dispersive EXAFS beamline at the 2.5 GeV INDUS-2 Synchrotron, RRCAT, Indore, India. For the analysis of EXAFS data, crystallographic data of the complex or of its analog is required, which is not available. Hence, for the analysis of EXAFS data, theoretical EXAFS data of the studied complexes have been generated using the EXAFS equation employing computer software program Mathcad. Firstly, the experimental data has been processed using the computer program Athena to obtain the normalized absorption versus energy data. From the experimental EXAFS data, the phase shift parameter (an energy independent constant 5) has been computed using Lytle, Sayers and Stern's (LSS) method. The backscattering amplitude has been taken from the available theoretical tabulations and other parameters have been taken from crystallographic data of the copper metal. Fourier transforms of both the experimental and theoretical data have been computed, and the two Fourier transforms are found to agree with each other for all the complexes. The position of the first peak in the Fourier transform gives the value of the first shell bond length, which is shorter than the actual bond length as a result of energy dependence of the phase factor (δ(k)) in the sine function of the EXAFS equation. Since, the Fourier transform method and LSS method both are uncorrected for phase and other parameters of the EXAFS equation, the present method gives phase uncorrected bond length of the first coordination shell.

  16. Electronic structure of individual hybrid colloid particles studied by near-edge X-ray absorption fine structure (NEXAFS) spectroscopy in the X-ray microscope.

    PubMed

    Henzler, Katja; Guttmann, Peter; Lu, Yan; Polzer, Frank; Schneider, Gerd; Ballauff, Matthias

    2013-02-13

    The electronic structure of individual hybrid particles was studied by nanoscale near-edge X-ray absorption spectromicroscopy. The colloidal particles consist of a solid polystyrene core and a cross-linked poly-N-(isopropylacrylamide) shell with embedded crystalline titanium dioxide (TiO(2)) nanoparticles (d = 6 ± 3 nm). The TiO(2) particles are generated in the carrier network by a sol-gel process at room temperature. The hybrid particles were imaged with photon energy steps of 0.1 eV in their hydrated environment with a cryo transmission X-ray microscope (TXM) at the Ti L(2,3)-edge. By analyzing the image stacks, the obtained near-edge X-ray absorption fine structure (NEXAFS) spectra of our individual hybrid particles show clearly that our synthesis generates TiO(2) in the anastase phase. Additionally, our spectromicroscopy method permits the determination of the density distribution of TiO(2) in single carrier particles. Therefore, NEXAFS spectroscopy combined with TXM presents a unique method to get in-depth insight into the electronic structure of hybrid materials.

  17. Versatile plug flow catalytic cell for in situ transmission/fluorescence x-ray absorption fine structure measurements

    SciTech Connect

    Centomo, P.; Zecca, M.; Meneghini, C.

    2013-05-15

    A novel flow-through catalytic cell has been developed for in situ x-ray absorption spectroscopy (XAS) experiments on heterogeneous catalysts under working conditions and in the presence of a liquid and a gas phase. The apparatus allows to carry out XAS measurements in both the transmission and fluorescence modes, at moderate temperature (from RT to 50-80 Degree-Sign C) and low-medium gas pressure (up to 7-8 bars). The materials employed are compatible with several chemicals such as those involved in the direct synthesis of hydrogen peroxide (O{sub 2}, H{sub 2}, H{sub 2}O{sub 2}, methanol). The versatile design of the cell allows to fit it to different experimental setups in synchrotron radiation beamlines. It was used successfully for the first time to test nanostructured Pd catalysts during the direct synthesis of hydrogen peroxide (H{sub 2}O{sub 2}) in methanol solution from dihydrogen and dioxygen.

  18. XAFS study on structural order in highly monodispersed thiol-stabilized Au nanoparticles

    NASA Astrophysics Data System (ADS)

    Huang, Y.; Liu, W.; Yang, L.; Huang, T.; Jiang, Y.; Yao, T.; Wei, S.

    2016-05-01

    Understanding the influence of thiol on nanoparticle size and structure is essential for the fundamental and applied researches. Here, using x-ray absorption fine structure (XAFS) spectroscopy, we investigate the structural order of Au nanoparticles (NPs) in the protection of thiol ligands with different contents. We found that besides protecting Au NPs against aggregation and growth, thiolates can effectively eliminate the dangling bonds of unsaturated Au atoms, and thus increase the structural order. This work enriches our knowledge of Au-S interface interaction and guides the way towards preparing size-controllable nanoparticles with specific physical/chemical properties.

  19. Study of Catalytic Reaction at Electrode-Electrolyte Interfaces by a CV-XAFS Method

    NASA Astrophysics Data System (ADS)

    Kusano, Shogo; Matsumura, Daiju; Asazawa, Koichiro; Kishi, Hirofumi; Sakamoto, Tomokazu; Yamaguchi, Susumu; Tanaka, Hirohisa; Mizuki, Jun'ichiro

    2017-01-01

    A method combining cyclic voltammetry (CV) with x-ray absorption fine structure (XAFS) spectroscopy, viz. CV-XAFS, has been developed to enable in situ real-time investigation of atomic and electronic structures related to electrochemical reactions. We use this method to study the reaction of a Pt/C cathode catalyst in the oxygen reduction reaction (ORR) in an alkaline electrolyte, using x-ray energies near the Pt LIII edge for XAFS measurements. It was found that the current induced by the ORR was first observed at approximately 0.08 V versus Hg/HgO, although the Pt valence, which is reflected in the oxidation states, remained almost unchanged. The electronic structure of the catalytic surface in the ORR was observed to be different in the negative and positive scan directions of CV measurements. Hydrogen adsorption is also discussed on the basis of the observation of this spectral change. We have demonstrated that CV-XAFS provides dynamical structural and electronic information related to electrochemical reactions and can be used for in situ real-time measurements of a catalyst.

  20. Development of dispersive XAFS system for analysis of time-resolved spatial distribution of electrode reaction.

    PubMed

    Katayama, Misaki; Miyahara, Ryota; Watanabe, Toshiki; Yamagishi, Hirona; Yamashita, Shohei; Kizaki, Terue; Sugawara, Yoshimi; Inada, Yasuhiro

    2015-09-01

    Apparatus for a technique based on the dispersive optics of X-ray absorption fine structure (XAFS) has been developed at beamline BL-5 of the Synchrotron Radiation Center of Ritsumeikan University. The vertical axis of the cross section of the synchrotron light is used to disperse the X-ray energy using a cylindrical polychromator and the horizontal axis is used for the spatially resolved analysis with a pixel array detector. The vertically dispersive XAFS (VDXAFS) instrument was designed to analyze the dynamic changeover of the inhomogeneous electrode reaction of secondary batteries. The line-shaped X-ray beam is transmitted through the electrode sample, and then the dispersed transmitted X-rays are detected by a two-dimensional detector. An array of XAFS spectra in the linear footprint of the transmitted X-ray on the sample is obtained with the time resolution of the repetition frequency of the detector. Sequential measurements of the space-resolved XAFS data are possible with the VDXAFS instrument. The time and spatial resolutions of the VDXAFS instrument depend on the flux density of the available X-ray beam and the size of the light source, and they were estimated as 1 s and 100 µm, respectively. The electrode reaction of the LiFePO4 lithium ion battery was analyzed during the constant current charging process and during the charging process after potential jumping.

  1. EXAFS (Extended X-ray Absorption Fine-Structure Spectroscopy) study of the position of Zr within the unit cell of Sm sub 2 Co sub 17

    SciTech Connect

    Rabenberg, L. . Center for Materials Science and Engineering); Barrera, E.V. . Dept. of Mechanical Engineering and Materials Science); Maury, C.E.; Allibert, C.H. . Lab. de Thermodynamique et PhysicoChimie Metallurgiques); Heald, S.M. (Brookhaven National Lab

    1990-01-01

    Extended X-ray Absorption Fine-Structure Spectroscopy (EXAFS) has been used to determine the position of Zr within the unit cell of Sm{sub 2}Co{sub 17}. Zr is routinely added to Sm{sub 2}Co{sub 17} permanent magnet alloys because of its effects on their metallurgical development, but the details of its behavior remain controversial. Induction melted Sm{sub 2}Co{sub 17}:Zr ternary alloys, aged at 1180{degrees}C, then quenched, consisted of intimately mixed H2:17 and R2:17 having Zr in solid solution as well some regions of R2:17 that were poor in Zr. EXAFS spectroscopy of these specimens indicates that the most probable position for Zr is a site having two Sm near neighbor atoms and 11 Co atoms distributed over three different interatomic distances. This is consistent with a direct substitution of Zr for Co in the Co site in the mixed planes (12j in P6{sub 3}/mmc, or 18f in R3m). These results are discussed in terms of the metallurgy of 2:17 magnet alloys. 20 refs., 2 figs.

  2. Effect of site occupancy disorder on martensitic properties of Mn2NiIn type alloys: X-ray absorption fine structure study

    NASA Astrophysics Data System (ADS)

    Lobo, D. N.; Priolkar, K. R.; Koide, A.; Emura, S.

    2017-02-01

    We have carried out ab-initio calculations of the local structure of Mn and Ni in the Mn2Ni1.5In0.5 alloy with different site occupancies in order to understand the similarities in martensitic and magnetic properties of Mn2Ni1+xIn1-x and Ni2Mn1+xIn1-x alloys. Our results show that in Mn2Ni1+xIn1-x alloys, there is a strong possibility of Mn atoms occupying all the three X, Y, and Z sites of the X2YZ Heusler structure, while Ni atoms preferentially occupy the X sites. Such a site occupancy disorder of Mn atoms is in addition to a local structural disorder due to size differences between Mn and In atoms, which is also present in Ni2Mn1+xIn1-x alloys. Further, a comparison of the calculations with experimental x-ray absorption fine structure at the Mn and Ni K edges in Mn2-yNi1.6+yIn0.4 (-0.08 ≤ y ≤ 0.08) indicates a strong connection between martensitic transformation and occupancy of Z sites by Mn atoms.

  3. Local vibrational dynamics of hematite (α-Fe{sub 2}O{sub 3}) studied by extended x-ray absorption fine structure and molecular dynamics

    SciTech Connect

    Sanson, A.; Mathon, O.; Pascarelli, S.

    2014-06-14

    The local vibrational dynamics of hematite (α-Fe{sub 2}O{sub 3}) has been investigated by temperature-dependent extended x-ray absorption fine structure spectroscopy and molecular dynamics simulations. The local dynamics of both the short and long nearest-neighbor Fe–O distances has been singled out, i.e., their local thermal expansion and the parallel and perpendicular mean-square relative atomic displacements have been determined, obtaining a partial agreement with molecular dynamics. No evidence of the Morin transition has been observed. More importantly, the strong anisotropy of relative thermal vibrations found for the short Fe–O distance has been related to its negative thermal expansion. The differences between the local dynamics of short and long Fe–O distances are discussed in terms of projection and correlation of atomic motion. As a result, we can conclude that the short Fe–O bond is stiffer to stretching and softer to bending than the long Fe–O bond.

  4. Local vibrational dynamics of hematite (α-Fe₂O₃) studied by extended x-ray absorption fine structure and molecular dynamics.

    PubMed

    Sanson, A; Mathon, O; Pascarelli, S

    2014-06-14

    The local vibrational dynamics of hematite (α-Fe2O3) has been investigated by temperature-dependent extended x-ray absorption fine structure spectroscopy and molecular dynamics simulations. The local dynamics of both the short and long nearest-neighbor Fe-O distances has been singled out, i.e., their local thermal expansion and the parallel and perpendicular mean-square relative atomic displacements have been determined, obtaining a partial agreement with molecular dynamics. No evidence of the Morin transition has been observed. More importantly, the strong anisotropy of relative thermal vibrations found for the short Fe-O distance has been related to its negative thermal expansion. The differences between the local dynamics of short and long Fe-O distances are discussed in terms of projection and correlation of atomic motion. As a result, we can conclude that the short Fe-O bond is stiffer to stretching and softer to bending than the long Fe-O bond.

  5. Nearest-neighbor nitrogen and oxygen distances in the iron(II)-DNA complex studied by extended X-ray absorption fine structure.

    PubMed

    Bertoncini, Clelia R A; Meneghini, Rogerio; Tolentino, Helio

    2010-11-01

    In mammalian cells, DNA-bound Fe(II) reacts with H₂O₂ producing the highly reactive hydroxyl radical (OH) in situ. Since ·OH attacks nearby DNA residue generating oxidative DNA damage, many questions have arisen regarding iron-DNA complex formations and their implication in pre-malignant mutations and aging. In this work, a solid sample of Fe(II)-DNA complex containing one Fe(II) per 10 nucleotides was analyzed from extended X-ray absorption fine structure (EXAFS) spectra collected in a synchrotron radiation light source. Best fitting parameters of the EXAFS signal for the first two shells provide evidence of five oxygen atoms at 1.99 ± 0.02 Å and one nitrogen atom at 2.20 ± 0.02 Å in the inner coordination sphere of the Fe(II)-DNA complex. Considering that both purine base moieties bearing nitrogen atoms are prone to chelate iron, these results are consistent with the previously observed lower levels of DNA damage in cytosine nucleotides relative to adenine and guanine sites in cells under more physiological conditions of Fe(II) Fenton reaction.

  6. Extended X- ray absorption fine structure study at the K-edge of copper in mixed ligand complexes having benzimidazole as one of the ligands

    NASA Astrophysics Data System (ADS)

    Hinge, V. K.; Joshi, S. K.; Nitin Nair, N.; Singh Verma, Vikram; Shrivastava, B. D.; Prasad, J.; Srivastava, K.

    2014-09-01

    Extended X-ray absorption fine structure (EXAFS) spectra have been studied at the K-edge of copper in some of its biologically important complexes, viz., [Cu(BzImH)4X2] and [Cu(BzIm)2], where X= Cl, Br, 1/2SO4, ClO4, NO3, and BzIm = Benzimidazolato anion. The spectra have been recorded using a bent crystal 0.4 m Cauchois-type transmission spectrograph. The positions of EXAFS maxima and minima have been used to determine the bond lengths in the complexes with the help of three different methods, namely, Levy's, Lytle's and Lytle, Sayers and Stern's (L.S.S.) methods. The phase uncorrected bond lengths have also been determined from Fourier transforms of the experimental spectra. The results obtained from these methods have been discussed and it has been found that the results obtained by L.S.S. method are comparable with the results obtained by Fourier transformation method and that these two methods give phase uncorrected bond lengths.

  7. Determination of bond lengths from extended X-ray absorption fine structure in cobalt(III)-oxo cubane-like clusters

    NASA Astrophysics Data System (ADS)

    Nitin Nair, N.; Shrivastava, B. D.; Das, Birinchi Kumar

    2016-10-01

    The extended X-ray absorption fine structure (EXAFS) at the K-edge of cobalt has been studied in two cobalt complexes having Co(III)-oxo cubane-like clusters of the type Co4O4(O2CR)4L4 where R is CH3 and L is pyridine (py) in one of the complex and ammonia (NH3) in the other complex. The spectra have been recorded at BL-9 scanning EXAFS beamline at the 2.5-GeV INDUS-2 Synchrotron, RRCAT, Indore, India. The positions of EXAFS maxima and minima have been reported. Using this data, the bond length has been determined by simple bond determination methods, viz., Levy's, Lytle's and Lytle, Sayers and Stern's (LSS) methods. The normalized EXAFS spectra have been Fourier transformed and the value of the bond length has also been determined from the position of the first peak in the Fourier transform. This distance is the phase-uncorrected bond length. LSS method also gives such bond length. The results obtained from Fourier transform and LSS methods have been found to be comparable to each other. For the pyridine complex, the value obtained from Levy's method has been found to be in agreement with the available crystallographic value.

  8. Near-edge X-ray Absorption Fine Structure (NEXAFS) Spectroscopy study on Chlorinated Graphene through Plasma-based Surface Functionalization

    NASA Astrophysics Data System (ADS)

    Zhang, Xu; Schiros, Theanne; Nordlund, Dennis; Shin, Yong Cheol; Kong, Jing; Dresselhaus, Mildred; Palacios, Tomas; MIT/Columbia University/SLAC Collaboration

    2015-03-01

    Plasma-based chlorination is a promising technique to realize controllable doping in graphene, while maintaining its high mobility. Meanwhile, synchrotron-based X-ray spectroscopy provides us a sensitive probe to investigate the surface states of functionalizing dopants in graphene. Here, we systematically studied the electronic states of chlorinated graphene on different substrates, including surface binding energy, dopant concentration and work function shift by use of Near Edge X-ray Absorption Fine Structure (NEXAFS) spectroscopy, XPS and photoemission threshold measurements. The concentration of absorbed chlorine is high enough to generate a distinct NEXAFS resonance at 286.2 eV (1s -> π* transition for C-Cl bonds). It is remarkable that the sp2 carbon core-hole exciton (291.85eV) retained its sharpness even after treatment, indicating the long-range periodicity in graphene is largely preserved. This distinguishes our approach as a noninvasive and effective doping method. The interaction between Cl and graphene also exhibits strong substrate effects: for Cu, graphene's Fermi level is shifted downwards by 0.35eV, while for graphene on SiO2, the much (4-5 times) higher chlorine concentration causes EF to shift by 0.9eV.

  9. Strain in epitaxial MnSi films on Si(111) in the thick film limit studied by polarization-dependent extended x-ray absorption fine structure

    NASA Astrophysics Data System (ADS)

    Figueroa, A. I.; Zhang, S. L.; Baker, A. A.; Chalasani, R.; Kohn, A.; Speller, S. C.; Gianolio, D.; Pfleiderer, C.; van der Laan, G.; Hesjedal, T.

    2016-11-01

    We report a study of the strain state of epitaxial MnSi films on Si(111) substrates in the thick film limit (100-500 Å) as a function of film thickness using polarization-dependent extended x-ray absorption fine structure (EXAFS). All films investigated are phase-pure and of high quality with a sharp interface between MnSi and Si. The investigated MnSi films are in a thickness regime where the magnetic transition temperature Tc assumes a thickness-independent enhanced value of ≥43 K as compared with that of bulk MnSi, where Tc≈29 K . A detailed refinement of the EXAFS data reveals that the Mn positions are unchanged, whereas the Si positions vary along the out-of-plane [111] direction, alternating in orientation from unit cell to unit cell. Thus, for thick MnSi films, the unit cell volume is essentially that of bulk MnSi—except in the vicinity of the interface with the Si substrate (thin film limit). In view of the enhanced magnetic transition temperature we conclude that the mere presence of the interface, and its specific characteristics, strongly affects the magnetic properties of the entire MnSi film, even far from the interface. Our analysis provides invaluable information about the local strain at the MnSi/Si(111) interface. The presented methodology of polarization dependent EXAFS can also be employed to investigate the local structure of other interesting interfaces.

  10. Extended x-ray absorption fine structure and micro-Raman spectra of Bridgman grown Cd1-xZnxTe ternary alloys

    NASA Astrophysics Data System (ADS)

    Talwar, Devki N.; Feng, Zhe Chuan; Lee, Jyh-Fu; Becla, P.

    2014-03-01

    We have performed low-temperature micro-Raman scattering and extended x-ray absorption fine-structure (EXAFS) measurements on the Bridgman-grown bulk zinc-blende Cd1-x Zn x Te (1.0 ≧̸ x ≧̸ 0.03) ternary alloys to comprehend their structural and lattice dynamical properties. The micro-Raman results are carefully appraised to authenticate the classical two-phonon mode behavior insinuated by far-infrared (FIR) reflectivity study. The composition-dependent EXAFS experiments have revealed a bimodal distribution of the nearest-neighbor bond lengths—its analysis by first-principles bond-orbital model enabled us to estimate the lattice relaxations around Zn/Cd atoms in CdTe/ZnTe to help evaluate the necessary force constant variations for constructing the impurity-perturbation matrices. The simulated results of impurity vibrational modes by average-t-matrix Green’s function (ATM-GF) theory has put our experimental findings of the gap mode ˜153 cm-1 near x ≈ 1 on a much firmer ground.

  11. Unrelaxation of the semiconductor surface at low-coverage Ag/InP(110) interfaces as determined by photoemission extended x-ray-absorption fine structure

    NASA Astrophysics Data System (ADS)

    Choudhary, K. M.; Mangat, P. S.; Kilday, D.; Margaritondo, G.

    1990-04-01

    The atomic geometries of Ag/InP(110) interfaces for metal coverages in the cluster regime have been determined by photoemission extended x-ray-absorption fine structure (PEXAFS). P 2p PEXAFS for InP(110)+0.5 Å Ag and InP(110)+1 Å Ag (at room temperature) were acquired. The data were analyzed by conventional Fourier-transform methods using the theoretical backscattering phase function of McKale et al. plus the absorber phase function of Teo and Lee. For both noble-metal coverages on the semiconductor surface, our measurements show that the relaxation (about 4% contraction) in the P-In bond length of the clean InP(110) surface is mostly removed. This is in contrast to our recent PEXAFS results, reported in the literature, for reactive-metal Al/InP(110) or Na/InP(110) interfaces, where low-coverage metal-induced reconstruction of the P-In bond length has been observed. The low-coverage noble-metal-induced unrelaxation of the P-In bond length might contribute to Fermi-level movements during Schottky-barrier formation.

  12. Lead is not off center in PbTe: the importance of r-space phase information in extended x-ray absorption fine structure spectroscopy.

    PubMed

    Keiber, T; Bridges, F; Sales, B C

    2013-08-30

    PbTe is a well-known thermoelectric material. Recent x-ray total scattering studies suggest that Pb moves off center along 100 in PbTe, by ∼0.2  Å at 300 K, producing a split Pb-Te pair distribution. We present an extended x-ray absorption fine structure spectroscopy (EXAFS) study of PbTe (and Tl doped PbTe) to determine if Pb or Te is off center. EXAFS provides sensitive r- or k-space phase information which can differentiate between a split peak for the Pb-Te distribution (indicative of off-center Pb) and a thermally broadened peak. We find no evidence for a split peak for Pb-Te or Te-Pb. At 300 K, the vibration amplitude for Pb-Te (or Te-Pb) is large; this thermally induced disorder is indicative of weak bonds, and the large disorder is consistent with the low thermal conductivity at 300 K. We also find evidence of an anharmonic potential for the nearest Pb-Te bonds, consistent with the overall anharmonicity found for the phonon modes. This effect is modeled by a "skew" factor (C3) which significantly improves the fit of the Pb-Te and Te-Pb peaks for the high temperature EXAFS data; C3 becomes significant above approximately 150-200 K. The consequences of these results will be discussed.

  13. Nearest-neighbor oxygen distances in liquid water and ice observed by x-ray Raman based extended x-ray absorption fine structure.

    PubMed

    Bergmann, Uwe; Di Cicco, Andrea; Wernet, Philippe; Principi, Emiliano; Glatzel, Pieter; Nilsson, Anders

    2007-11-07

    We report the nearest-neighbor oxygen-oxygen radial distribution function (NN O-O RDF) of room temperature liquid water and polycrystalline ice Ih (-16.8 degrees C) obtained by x-ray Raman based extended x-ray absorption fine structure (EXAFS) spectroscopy. The spectra of the two systems were taken under identical experimental conditions using the same procedures to obtain the NN O-O RDFs. This protocol ensured a measurement of the relative distance distribution with very small systematic errors. The NN O-O RDF of water is found to be more asymmetric (tail extending to longer distances) with longer average distance (2.81 A for water and 2.76 A for ice) but a slightly shorter peak position (2.70 A for water and 2.71 A for ice). The refinement also showed a small but significant contribution from the linear O-H-O multiple scattering signal. The high sensitivity to short range distances of the EXAFS probe will set further restrictions to the range of possible models of liquid water.

  14. Near-Edge X-ray Absorption Fine Structure Studies of Electrospun Poly(dimethylsiloxane)/Poly (methyl methacrylate)/Multiwall Carbon Nanotube Composites

    PubMed Central

    Winter, A. Douglas; Larios, Eduardo; Alamgir, Faisal M.; Jaye, Cherno; Fischer, Daniel; Campo, Eva M.

    2014-01-01

    This work describes the near conduction band edge structure of electrospun mats of MWCNT-PDMS-PMMA by near edge X-Ray absorption fine structure (NEXAFS) spectroscopy. Effects of adding nanofillers of different sizes were addressed. Despite observed morphological variations and inhomogeneous carbon nanotube distribution, spun mats appeared homogeneous under NEXAFS analysis. Spectra revealed differences in emissions from glancing and normal spectra; which may evidence phase separation within the bulk of the micron-size fibers. Further, dichroic ratios show polymer chains did not align, even in the presence of nanofillers. Addition of nanofillers affected emissions in the C-H, C=O and C-C regimes, suggesting their involvement in interfacial matrix-carbon nanotube bonding. Spectral differences at glancing angles between pristine and composite mats suggest that geometric conformational configurations are taking place between polymeric chains and carbon nanotubes. These differences appear to be carbon nanotube-dimension dependent, and are promoted upon room temperature mixing and shear flow during electrospinning. CH-π bonding between polymer chains and graphitic walls, as well as H-bonds between impurities in the as-grown CNTs and polymer pendant groups are proposed bonding mechanisms promoting matrix conformation. PMID:24308286

  15. Extended x-ray absorption fine structure in Ga1-xMnxN/SiC films with high Mn content

    NASA Astrophysics Data System (ADS)

    Sancho-Juan, O.; Martínez-Criado, O.; Cantarero, A.; Garro, N.; Salomé, M.; Susini, J.; Olguín, D.; Dhar, S.; Ploog, K.

    2011-05-01

    In this study, the local atomic structure of highly homogeneous Ga1-xMnxN alloy films (0.03absorption fine structure measurements. From the curve fitting, the structural parameters corresponding to the first two atomic shells surrounding both Ga and Mn atoms are reported. In the Ga1-xMnxN films, grown by molecular beam epitaxy, the Mn atoms are in tetrahedral configuration, independent of the Mn concentration; that is, they are in a substitutional site, MnGa, in the wurtzite structure. A small increase in the interatomic distances has been found with increasing Mn content. The Debye-Waller factor does not show a significant trend as Mn content increases, which suggests the presence of short-range disorder in the GaN lattice. Ab initio calculations of the structural parameter for two different Mn concentrations are consistent with the experimental results.

  16. Surface Structure and Chemical Switching of Thioctic Acid Adsorbed on Au(111) as Observed Using Near-Edge X-ray Absorption Fine Structure

    SciTech Connect

    Meulenberg, R W; van Buuren, T; Vance, A L; Terminello, L J; Willey, T M; Bostedt, C; Fadley, C S

    2004-01-06

    Thioctic acid (alpha-lipoic acid) is a molecule with a large disulfide-containing base, a short alkyl-chain with four CH{sub 2} units, and a carboxyl termination. Self-assembled monolayer (SAM) films of thioctic acid adsorbed on Au(111) have been investigated with near-edge x-ray absorption fine structure (NEXAFS) spectroscopy and x-ray photoelectron spectroscopy (XPS) to determine film quality, bonding and morphology. Using standard preparation protocols for SAMs, that is, dissolving thioctic acid in ethanol and exposing gold to the solution, results in poor films. These films are highly disordered, contain a mixture of carboxyl and carboxylate terminations, have more than monolayer coverage, and exhibit unbound disulfide. Conversely, forming films by dissolving 1 mmol thioctic acid into 5% acetic acid in ethanol (as previously reported with carboxyl-terminated alkyl-thiols) forms ordered monolayers with small amounts of unbound sulfur. NEXAFS indicates tilted over endgroups with the carboxyl group normal on average 38{sup o} from the surface normal. Slight dichroism in other features indicates alkyl chains statistically more upright than prostrate on the surface. Reflection-absorption Fourier transform infrared (RA-FTIR) spectra indicate hydrogen bonding between neighboring molecules. In such well-formed monolayers, a stark reorientation occurs upon deprotonation of the endgroup by rinsing in a KOH solution. The carboxylate plane normal is now about 66{sup o} from sample normal, a much more upright orientation. Data indicate this reorientation may also cause a more upright orientation to the alkyl portion of the molecules.

  17. A fluorescence XAFS measurement instrument in the soft x-ray region toward observation under operando conditions

    SciTech Connect

    Honda, M. Baba, Y.; Shimoyama, I.; Sekiguchi, T.

    2015-03-15

    X-ray absorption fine structure (XAFS) measurements are widely used for the analysis of electronic structure. Generally, XAFS in the soft X-ray region is measured under vacuum, but chemical structures under vacuum are typically different from those under operando conditions, where chemical species exhibit their function. Here, we developed an XAFS measurement instrument, as a step toward operando fluorescent, which yields XAFS measurement using synchrotron radiation in the soft X-ray region. We applied this method to analyze the local electronic structure of the sulfur atoms in L-cysteine in different pH solutions. In water at pH 7, the hydrogen atom does not dissociate from the thiol (-SH) group in L-cysteine, which forms a structure surrounded by and interacting with water molecules. The XAFS spectrum of L-cysteine in solution was altered by changing the pH. At pH 9, the hydrogen atom dissociated and a thiolate anion was formed. Although the -SH group was oxidized to SO{sub 4}{sup 2−} when L-cysteine was adsorbed on a metal surface and dried, no oxidation was observed in solution. This may be because the water molecules were densely packed and protected the -SH group from oxidation. Our results show that this instrument aimed toward operando fluorescence XAFS measurements in the soft X-ray region is useful for structural analysis of sulfur atoms in organic molecules in air and in solution. The instrument will be applied to the structural analysis of materials containing elements that have absorption edges in soft X-ray region, such as phosphorus and alkali metals (potassium and cesium). It will be also particularly useful for the analysis of samples that are difficult to handle under vacuum and materials that have specific functions in solution.

  18. [Spectrum characterization and fine structure of copper phthalocyanine-doped TiO2 microcavities].

    PubMed

    Liu, Cheng-lin; Zhang, Xin-yi; Zhong, Ju-hua; Zhu, Yi-hua; He, Bo; Wei, Shi-qiang

    2007-10-01

    Copper phthalocyanine-doped TiO2 microcavities were fabricated by chemistry method. Their spectrum characterization was studied by Fourier transform infrared (FTIR) and Raman spectroscopy, and their fine structure was analyzed by X-ray absorption fine structure (XAFS). The results show that there is interaction of copper phthalocyanine (CuPc) and TiO2 microcavities after TiO2 microcavities was doped with CuPc. For example, there is absorption at 900.76 cm(-1) in FTIR spectra, and the "red shift" of both OH vibration at 3392.75 cm(-1) and CH vibration at 2848.83 cm(-1). There exist definite peak shifts and intensity changes in infrared absorption in the C-C or C-N vibration in the planar phthalocyanine ring, the winding vibration of C-H inside and C-N outside plane of benzene ring. In Raman spectrum, there are 403.4, 592.1 and 679.1 cm(-1) characterized peaks of TiO2 in CuPc-doped TiO2 microcavities, but their wave-numbers show shifts to anatase TiO2. The vibration peaks at 1586.8 and 1525.6 cm(-1) show that there exists the composite material of CuPc and TiO2. These changes are related to the plane tropism of the molecule structure of copper phthalocyanine. XAFS showed tetrahedron TiO4 structure of Ti in TiO2 microcavities doped with copper phthalocyanine, and the changes of inner "medial distances" and the surface structure of TiO2 microcavities.

  19. Systematic Oxidation of Polystyrene by Ultraviolet-Ozone, Characterized by Near-Edge X-ray Absorption Fine Structure and Contact Angle

    SciTech Connect

    Klein,R.; Fischer, D.; Lenhart, J.

    2008-01-01

    The process of implanting oxygen in polystyrene (PS) via exposure to ultraviolet-ozone (UV-O) was systematically investigated using the characterization technique of near-edge X-ray absorption fine structure (NEXAFS). Samples of PS exposed to UV-O for 10-300 s and washed with isopropanol were analyzed using the carbon and oxygen K-edge NEXAFS partial electron yields, using various retarding bias voltages to depth-profile the oxygen penetration into the surface. Evaluation of reference polymers provided a scale to quantify the oxygen concentration implanted by UV-O treatment. We find that ozone initially reacts with the double bonds on the phenyl rings, forming carbonyl groups, but within 1 min of exposure, the ratio of double to single oxygen bonds stabilizes at a lower value. Oxygen penetrates the film with relative ease, creating a fairly uniform distribution of oxygen within at least the first 4 nm (the effective depth probed by NEXAFS here). Before oxygen accumulates in large concentrations, however, it preferentially degrades the uppermost layer of the film by removing oxygenated low-molecular-weight oligomers. The failure to accumulate high concentrations of oxygen is seen in the nearly constant carbon edge jump, the low concentration of oxygen even at 5 min exposure (58% of that in poly(4-acetoxystyrene), the polymer with the most similarities to UV-O-treated PS), and the relatively high contact angles. At 5 min exposure the oxygen concentration contains ca. 7 atomic % oxygen. The oxygen species that are implanted consist predominantly of single O-C bonds and double OC bonds but also include a small fraction of O-H. UV-O treatment leads a plateau after 2 min exposure in the water contact angle hysteresis, at a value of 67 {+-} 2, due primarily to chemical heterogeneity. Annealing above Tg allows oxygenated species to move short distances away from the surface but not diffuse further than 1-2 nm.

  20. Spectroscopic analysis of small organic molecules: A comprehensive near-edge x-ray-absorption fine-structure study of C{sub 6}-ring-containing molecules

    SciTech Connect

    Kolczewski, C.; Puettner, R.; Martins, M.; Schlachter, A.S.; Snell, G.; Sant'Anna, M.M.; Hermann, K.; Kaindl, G.

    2006-01-21

    We report high-resolution C 1s near-edge x-ray-absorption fine-structure (NEXAFS) spectra of the C{sub 6}-ring-containing molecules benzene (C{sub 6}H{sub 6}), 1,3- and 1,4-cyclohexadiene (C{sub 6}H{sub 8}), cyclohexene (C{sub 6}H{sub 10}), cyclohexane (C{sub 6}H{sub 12}), styrene (C{sub 8}H{sub 8}), and ethylbenzene (C{sub 8}H{sub 10}) which allow us to examine the gradual development of delocalization of the corresponding {pi} electron systems. Due to the high experimental resolution, vibrational progressions can be partly resolved in the spectra. The experimental spectra are compared with theoretical NEXAFS spectra obtained from density-functional theory calculations where electronic final-state relaxation is accounted for. The comparison yields very good agreement between theoretical spectra and experimental results. In all cases, the spectra can be described by excitations to {pi}*- and {sigma}*-type final-state orbitals with valence character, while final-state orbitals of Rydberg character make only minor contributions. The lowest C 1s{yields}1{pi}* excitation energy is found to agree in the (experimental and theoretical) spectra of all molecules except for 1,3-cyclohexadiene (C{sub 6}H{sub 8}) where an energy smaller by about 0.6 eV is obtained. The theoretical analysis can explain this result by different binding properties of this molecule compared to the others.

  1. Near-edge X-ray absorption fine structure (NEXAFS) spectroscopy for mapping nano-scale distribution of organic carbon forms in soil: Application to black carbon particles

    NASA Astrophysics Data System (ADS)

    Lehmann, Johannes; Liang, Biqing; Solomon, Dawit; Lerotic, Mirna; LuizãO, Flavio; Kinyangi, James; SchäFer, Thorsten; Wirick, Sue; Jacobsen, Chris

    2005-03-01

    Small-scale heterogeneity of organic carbon (C) forms in soils is poorly quantified since appropriate analytical techniques were not available up to now. Specifically, tools for the identification of functional groups on the surface of micrometer-sized black C particles were not available up to now. Scanning Transmission X-ray Microscopy (STXM) using synchrotron radiation was used in conjunction with Near-Edge X-ray Absorption Fine Structure (NEXAFS) spectroscopy to investigate nano-scale distribution (50-nm resolution) of C forms in black C particles and compared to synchrotron-based FTIR spectroscopy. A new embedding technique was developed that did not build on a C-based embedding medium and did not pose the risk of heat damage to the sample. Elemental sulfur (S) was melted to 220°C until it polymerized and quenched with liquid N2 to obtain a very viscous plastic S in which the black C could be embedded until it hardened to a noncrystalline state and was ultrasectioned. Principal component and cluster analysis followed by singular value decomposition was able to resolve distinct areas in a black carbon particle. The core of the studied biomass-derived black C particles was highly aromatic even after thousands of years of exposure in soil and resembled the spectral characteristics of fresh charcoal. Surrounding this core and on the surface of the black C particle, however, much larger proportions of carboxylic and phenolic C forms were identified that were spatially and structurally distinct from the core of the particle. Cluster analysis provided evidence for both oxidation of the black C particle itself as well as adsorption of non-black C. NEXAFS spectroscopy has great potential to allow new insight into black C properties with important implications for biogeochemical cycles such as mineralization of black C in soils and sediments, and adsorption of C, nutrients, and pollutants as well as transport in the geosphere, hydrosphere, and atmosphere.

  2. Optimizing the crystal environment through extended x-ray absorption fine structure to increase the luminescent lifetimes of Er3+ doped Y2O3 nanoparticles

    NASA Astrophysics Data System (ADS)

    Dorman, James A.; Choi, Ju H.; Kuzmanich, Gregory; Bargar, John R.; Chang, Jane P.

    2012-04-01

    To predict and optimize luminescence efficiency of rare-earth ion doped (RE) nanophosphors, a relationship between the RE-concentration and the luminescent parameters is often obtained by Judd-Ofelt analysis, where the quality factor (χ =Ω4/Ω6) depends on the Er interactions with other RE elements in the second nearest neighboring shell. In this work, a detailed analysis of the local bonding environment by extended x-ray absorption fine structure (EXAFS) analyses is shown as effective as the Judd-Ofelt analysis to quantify the Er↔RE interaction in the second nearest neighboring shell (ρN=IREr↔RE2/IREr↔RE1). As the physical basis of ρN is consistent to that of χ, the EXAFS analysis becomes a viable alternative to replace Judd-Ofelt analysis to predict the optimum dopant concentration. This approach was corroborated based on analysis of Er3+:Y2O3 and core-shell Er3+:Y2O3|Y2O3 (5 nm shell) nanoparticles (NPs), with Er3+ concentrations up to 20 mol %. The ρN ratio from EXAFS analysis was shown to strongly correlate to the lifetimes extracted from the Judd-Ofelt analysis, both predicting the optimal dopant concentrations to be at 5 mol % and 2 mol % for the Er3+:Y2O3 and core-shell NPs, respectively. This confirms that EXAFS analysis can be used as a more time efficient method to achieve the same outcome typically obtained by Judd-Ofelt analysis, enabling the optimization of the luminescent lifetimes of RE doped nano-phosphors.

  3. Speciation and localization of Zn in the hyperaccumulator Sedum alfredii by extended X-ray absorption fine structure and micro-X-ray fluorescence.

    PubMed

    Lu, Lingli; Liao, Xingcheng; Labavitch, John; Yang, Xiaoe; Nelson, Erik; Du, Yonghua; Brown, Patrick H; Tian, Shengke

    2014-11-01

    Differences in metal homeostasis among related plant species can give important information of metal hyperaccumulation mechanisms. Speciation and distribution of Zn were investigated in a hyperaccumulating population of Sedum alfredii by using extended X-ray absorption fine structure and micro-synchrotron X-ray fluorescence (μ-XRF), respectively. The hyperaccumulator uses complexation with oxygen donor ligands for Zn storage in leaves and stems, and variations in the Zn speciation was noted in different tissues. The dominant chemical form of Zn in leaves was most probably a complex with malate, the most prevalent organic acid in S. alfredii leaves. In stems, Zn was mainly associated with malate and cell walls, while Zn-citrate and Zn-cell wall complexes dominated in the roots. Two-dimensional μ-XRF images revealed age-dependent differences in Zn localization in S. alfredii stems and leaves. In old leaves of S. alfredii, Zn was high in the midrib, margin regions and the petiole, whereas distribution of Zn was essentially uniform in young leaves. Zinc was preferentially sequestered by cells near vascular bundles in young stems, but was highly localized to vascular bundles and the outer cortex layer of old stems. The results suggest that tissue- and age-dependent variations of Zn speciation and distribution occurred in the hyperaccumulator S. alfredii, with most of the Zn complexed with malate in the leaves, but a shift to cell wall- and citric acid-Zn complexes during transportation and storage in stems and roots. This implies that biotransformation in Zn complexation occurred during transportation and storage processes in the plants of S. alfredii.

  4. A combined fit of total scattering and extended x-ray absorption fine structure data for local-structure determination in crystalline materials

    SciTech Connect

    Proffen, Thomas E; Krayzman, Victor; Levin, Igor; Tucker, Matt

    2009-01-01

    Reverse Monte Carlo (RMC) refinements of local structure using a simultaneous fit of X-ray/neutron total scattering and extended X-ray absorption fine structure (EXAFS) data were developed to incorporate an explicit treatment of both single- and multiple-scattering contributions to EXAFS. The refinement algorithm, implemented as an extension to the public domain computer software RMCProfile, enables accurate modeling of EXAFS over distances encompassing several coordination shells around the absorbing species. The approach was first tested on Ni, which exhibits extensive multiple scattering in EXAFS, and then applied to perovskite-like SrAl{sub 1/2}Nb{sub 1/2}O{sub 3}. This compound crystal1izes with a cubic double-perovskite structure but presents a challenge for local-structure determination using a total pair-distribution function (PDF) alone because of overlapping peaks of the constituent partial PDFs (e.g. Al-O and Nb-O or Sr-O and O-O). The results obtained here suggest that the combined use of the total scattering and EXAFS data provides sufficient constraints for RMC refinements to recover fine details of local structure in complex perovskites. Among other results, it was found that the probability density distribution for Sr in SrAl{sub 1/2}Nb{sub 1/2}O{sub 3} adopts T{sub d} point-group symmetry for the Sr sites, determined by the ordered arrangement of Al and Nb, as opposed to a spherical distribution commonly assumed in traditional Rietveld refinements.

  5. Near-Edge X-ray Absorption Fine Structure Imaging of Spherical and Flat Counterfaces of Ultrananocrystalline Diamond Tribological Contacts: A Correlation of Surface Chemistry and Friction

    SciTech Connect

    A Konicek; C Jaye; M Hamilton; W Sawyer; D Fischer; R Carpick

    2011-12-31

    A recently installed synchrotron radiation near-edge X-ray absorption fine structure (NEXAFS) full field imaging electron spectrometer was used to spatially resolve the chemical changes of both counterfaces from an ultra-nanocrystalline diamond (UNCD) tribological contact. A silicon flat and Si{sub 3}N{sub 4} sphere were both coated with UNCD, and employed to form two wear tracks on the flat in a linear reciprocating tribometer. The first wear track was produced using a new, unconditioned sphere whose surface was thus conditioned during this first experiment. This led to faster run-in and lower friction when producing a second wear track using the conditioned sphere. The large depth of field of the magnetically guided NEXAFS imaging detector enabled rapid, large area spectromicroscopic imaging of both the spherical and flat surfaces. Laterally resolved NEXAFS data from the tribological contact area revealed that both substrates had an as-grown surface layer that contained a higher fraction of sp{sup 2}-bonded carbon and oxygen which was mechanically removed. Unlike the flat, the film on the sphere showed evidence of having graphitic character, both before and after sliding. These results show that the graphitic character of the sphere is not solely responsible for low friction and short run-in. Rather, conditioning the sphere, likely by removing asperities and passivating dangling bonds, leads to lower friction with less chemical modification of the substrate in subsequent tests. The new NEXAFS imaging spectroscopy detector enabled a more complete understanding of the tribological phenomena by imaging, for the first time, the surface chemistry of the spherical counterface which had been in continual contact during wear track formation.

  6. Synthesis of 1 nm Pd Nanoparticles in a Microfluidic Reactor: Insights from in Situ X ray Absorption Fine Structure Spectroscopy and Small-Angle X ray Scattering

    SciTech Connect

    Karim, Ayman M.; Al Hasan, Naila M.; Ivanov, Sergei A.; Siefert, Soenke; Kelly, Ryan T.; Hallfors, Nicholas G.; Benavidez, Angelica D.; Kovarik, Libor; Jenkins, Aaron; Winans, R. E.; Datye, Abhaya K.

    2015-06-11

    In this paper we show that the temporal separation of nucleation and growth is not a necessary condition for the colloidal synthesis of monodisperse nanoparticles. The synthesis mechanism of Pd nanoparticles was determined by in situ XAFS and SAXS in a microfluidic reactor capable of millisecond up to an hour time resolution. The SAXS results showed two autocatalytic growth phases, a fast growth phase followed by a very slow growth phase. The steady increase in the number of particles throughout the two growth phases indicates the synthesis is limited by slow continuous nucleation. The transition from fast to slow growth was caused by rapid increase in bonding with the capping agent as shown by XAFS. Based on this fundamental understanding of the synthesis mechanism, we show that 1 nm monodisperse Pd nanoparticles can be synthesized at low temperature using a strong binding capping agent such as trioctylphosphine (TOP).

  7. X-ray absorption fine structure spectroscopic studies of Octakis(DMSO)lanthanoid(III) complexes in solution and in the solid iodides.

    PubMed

    Persson, Ingmar; Risberg, Emiliana Damian; D'Angelo, Paola; De Panfilis, Simone; Sandström, Magnus; Abbasi, Alireza

    2007-09-17

    Octakis(DMSO)lanthanoid(III) iodides (DMSO = dimethylsulfoxide), [Ln(OS(CH3)2)8]I3, of most lanthanoid(III) ions in the series from La to Lu have been studied in the solid state and in DMSO solution by extended X-ray absorption fine structure (EXAFS) spectroscopy. L3-edge and also some K-edge spectra were recorded, which provided mean Ln-O bond distances for the octakis(DMSO)lanthanoid(III) complexes. The agreement with the average of the Ln-O bond distances obtained in a separate study by X-ray crystallography was quite satisfactory. The crystalline octakis(DMSO)lanthanoid(III) iodide salts have a fairly broad distribution of Ln-O bond distances, ca. 0.1 A, with a few disordered DMSO ligands. Their EXAFS spectra are in excellent agreement with those obtained for the solvated lanthanoid(III) ions in DMSO solution, both of which show slightly asymmetric distributions of the Ln-O bond distances. Hence, all lanthanoid(III) ions are present as octakis(DMSO)lanthanoid(III) complexes in DMSO solution, with the mean Ln-O distances centered at 2.50 (La), 2.45 (Pr), 2.43 (Nd), 2.41 (Sm), 2.40 (Eu), 2.39 (Gd), 2.37 (Tb), 2.36 (Dy), 2.34 (Ho), 2.33 (Er), 2.31 (Tm), and 2.29 A (Lu). This decrease in the Ln-O bond distances is larger than expected from the previously established ionic radii for octa-coordination. This indicates increasing polarization of the LnIII-O(DMSO) bonds with increasing atomic number. However, the S(1s) electron transition energies in the sulfur K-edge X-ray absorption near-edge structure (XANES) spectra, probing the unoccupied molecular orbitals of lowest energy of the DMSO ligands for the [Ln(OS(CH3)2)8](3+) complexes, change only insignificantly from Ln = La to Lu. This indicates that there is no appreciable change in the sigma-contribution to the S-O bond, probably due to a corresponding increase in the contribution from the sulfur lone pair to the bonding.

  8. X-Ray Absorption Fine Structure Spectroscopic Studies of Octakis(DMSO)Lanthanoid(III) Complexes in Solution And in the Solid Iodides

    SciTech Connect

    Persson, I.; Risberg, E.Damian; D'Angelo, P.; Panfilis, S.De; Sandstrom, M.; Abbasi, A.

    2009-06-04

    Octakis(DMSO)lanthanoid(III) iodides (DMSO = dimethylsulfoxide), [Ln(OS(CH{sub 3}){sub 2}){sub 8}]I{sub 3}, of most lanthanoid(III) ions in the series from La to Lu have been studied in the solid state and in DMSO solution by extended X-ray absorption fine structure (EXAFS) spectroscopy. L{sub 3}-edge and also some K-edge spectra were recorded, which provided mean Ln-O bond distances for the octakis(DMSO)lanthanoid(III) complexes. The agreement with the average of the Ln-O bond distances obtained in a separate study by X-ray crystallography was quite satisfactory. The crystalline octakis(DMSO)lanthanoid(III) iodide salts have a fairly broad distribution of Ln-O bond distances, ca. 0.1 {angstrom}, with a few disordered DMSO ligands. Their EXAFS spectra are in excellent agreement with those obtained for the solvated lanthanoid(III) ions in DMSO solution, both of which show slightly asymmetric distributions of the Ln-O bond distances. Hence, all lanthanoid(III) ions are present as octakis(DMSO)lanthanoid(III) complexes in DMSO solution, with the mean Ln-O distances centered at 2.50 (La), 2.45 (Pr), 2.43 (Nd), 2.41 (Sm), 2.40 (Eu), 2.39 (Gd), 2.37 (Tb), 2.36 (Dy), 2.34 (Ho), 2.33 (Er), 2.31 (Tm), and 2.29 {angstrom} (Lu). This decrease in the Ln-O bond distances is larger than expected from the previously established ionic radii for octa-coordination. This indicates increasing polarization of the Ln{sup III}-O(DMSO) bonds with increasing atomic number. However, the S(1s) electron transition energies in the sulfur K-edge X-ray absorption near-edge structure (XANES) spectra, probing the unoccupied molecular orbitals of lowest energy of the DMSO ligands for the [Ln(OS(CH{sub 3}){sub 2}){sub 8}]{sup 3+} complexes, change only insignificantly from Ln = La to Lu. This indicates that there is no appreciable change in the ?-contribution to the S-O bond, probably due to a corresponding increase in the contribution from the sulfur lone pair to the bonding.

  9. Structural Studies of Clean Semiconductor Surfaces and Metal-Semiconductor Interfaces by Photoemission Extended X-Ray Absorption Fine Structure Spectroscopy.

    NASA Astrophysics Data System (ADS)

    Mangat, Pawitterjit Singh

    We determined the atomic geometries for clean InP(110)-(1 x 1) and Si(111)-(2 x 1) surfaces and Al/InP(110), Ag/InP(110), Bi/InP(110), Na/InP(110) and Al/Si(111) interfaces by photoemission extended x-ray absorption fine structure (PEXAFS) spectroscopy to understand the correlation between electrical Schottky barrier heights and interfacial structure. P 2p PEXAFS for the InP(110) surface and Si 2p PEXAFS for the Si(111) surface were acquired which yielded information on the short range order of substrate atoms on the surface or at the interface. For Al/Si(111) interfaces, we also obtained Al 2p PEXAFS. The data analyzed by Fourier analysis and curve-fitting procedures. The theoretical backscattering phase function of McKale et al. (J. Am. Chem. Soc. 110, 3763 (1988)) and absorber phase function of Teo and Lee (J. Am. Chem. Soc. 101, 2815 (1979)) were used for phase analysis to determine the interatomic bond lengths. For the clean InP(110) surface, we observed surface relaxation. For the Si(111)-(2 x 1) surface, we found 10% contraction in the second near neighborhood Si-Si distance which is not reported in any model. For low coverage reactive metal (Al, Na)/InP(110) interfaces, we observed metal induced surface structural changes which involve removal of relaxation and change in the basis of the surface unit mesh of the substrate. For Ag/InP(110) interfaces, the noble metal atoms were found to remove the relaxation of the first P-In bond length at the interface. These changes in the substrate might bring in interface states within the semiconductor band gap and, consequently, influencing Fermi-level pinning during the Schottky barrier formation. For the Bi/InP(110) interfaces, the relaxation of the clean InP(110) surface is not removed by the deposited Bi atoms. Hence, the Bi/InP(110) interface might not have Fermi-level pinning by interface states due to the interfacial structure of InP. For Al/Si(111) interfaces, the Al atoms do not induce drastic surface

  10. Characterization of Functionalized Self-Assembled Monolayers and Surface-Attached Interlocking Molecules Using Near-Edge X-ray Absorption Fine Structure Spectroscopy

    SciTech Connect

    Willey, Trevor M.

    2004-04-01

    Quantitative knowledge of the fundamental structure and substrate binding, as well as the direct measurement of conformational changes, are essential to the development of self-assembled monolayers (SAMs) and surface-attached interlocking molecules, catenanes and rotaxanes. These monolayers are vital to development of nano-mechanical, molecular electronic, and biological/chemical sensor applications. This dissertation investigates properties of functionalized SAMs in sulfur-gold based adsorbed molecular monolayers using quantitative spectroscopic techniques including near-edge x-ray absorption fine structure spectroscopy (NEXAFS) and x-ray photoelectron spectroscopy (XPS). The stability of the gold-thiolate interface is addressed. A simple model SAM consisting of dodecanethiol adsorbed on Au(111) degrades significantly in less than 24 hours under ambient laboratory air. S 2p and O 1s XPS show the gold-bound thiolates oxidize to sulfinates and sulfonates. A reduction of organic material on the surface and a decrease in order are observed as the layer degrades. The effect of the carboxyl vs. carboxylate functionalization on SAM structure is investigated. Carboxyl-terminated layers consisting of long alkyl-chain thiols vs. thioctic acid with short, sterically separated, alkyl groups are compared and contrasted. NEXAFS shows a conformational change, or chemical switchability, with carboxyl groups tilted over and carboxylate endgroups more upright. Surface-attached loops and simple surface-attached rotaxanes are quantitatively characterized, and preparation conditions that lead to desired films are outlined. A dithiol is often insufficient to form a molecular species bound at each end to the substrate, while a structurally related disulfide-containing polymer yields surface-attached loops. Similarly, spectroscopic techniques show the successful production of a simple, surface-attached rotaxane that requires a ''molecular riveting'' step to hold the mechanically attached

  11. Extended x-ray-absorption and electron-energy-loss fine-structure studies of the local atomic structure of amorphous unhydrogenated and hydrogenated silicon carbide

    NASA Astrophysics Data System (ADS)

    Kaloyeros, Alain E.; Rizk, Richard B.; Woodhouse, John B.

    1988-12-01

    Extended x-ray-absorption (EXAFS) and electron-energy-loss fine-structure (EXELFS) measurements have been performed on amorphous unhydrogenated silicon carbide, a-SiC, and amorphous hydrogenated silicon carbide, a-SiC:H. Two hydrogenated samples with hydrogen concentrations corresponding, respectively, to H flows of 4 sccm (20% of argon flow) and 8 sccm (40% of argon flow) during the reactive sputtering process, were analyzed (sccm denotes standard cubic centimeters per minute at STP). It is found that short-range order (SRO), consisting of the same tetrahedrally coordinated units present in cubic crystalline c-SiC (zinc-blende structure), where a Si atom is surrounded by nearly four C atoms and vice versa, does exist in all the amorphous samples. This SRO, however, is detected only at a level of the first C and Si coordination shells in a-SiC and a-SiC:H. The structural disorder of the first Si and C coordination shells in all forms of amorphous SiC is somewhat greater than c-SiC, and it decreases appreciably as hydrogen is added. The a-SiC sample exhibits large Si and C coordination numbers, almost identical to c-SiC, a low atomic density, and virtually the same Si-C bond length as c-SiC. These results indicate that a relatively small concentration of large voids exist in a highly disordered a-SiC matrix. The a-SiC:H samples, on the other hand, exhibit a decrease in the C coordination number relative to a-SiC, which is independent of H concentration, low Si and C atomic densities, comparable to a-SiC, and virtually the same Si coordination number as a-SiC. These EXAFS-EXELFS results are consistent with a model where part of the H is substituting for Si in the local tetrahedra surrounding C atoms, while the rest is located inside internal voids in the a-SiC:H samples. The surface of the voids is composed of C atoms which have at least one bond to H, and of Si atoms. Finally, a straightforward computational procedure is applied to estimate the size of these voids

  12. Surface complexation and precipitate geometry for aqueous Zn(II) sorption on ferrihydrite I: X-ray absorption extended fine structure spectroscopy analysis

    USGS Publications Warehouse

    Waychunas, G.A.; Fuller, C.C.; Davis, J.A.

    2002-01-01

    "Two-line" ferrihydrite samples precipitated and then exposed to a range of aqueous Zn solutions (10-5 to 10-3 M), and also coprecipitated in similar Zn solutions (pH 6.5), have been examined by Zn and Fe K-edge X-ray absorption spectroscopy. Typical Zn complexes on the surface have Zn-O distances of 1.97(0.2) A?? and coordination numbers of about 4.0(0.5), consistent with tetrahedral oxygen coordination. This contrasts with Zn-O distances of 2.11(.02) A?? and coordination numbers of 6 to 7 in the aqueous Zn solutions used in sample preparation. X-ray absorption extended fine structure spectroscopy (EXAFS) fits to the second shell of cation neighbors indicate as many as 4 Zn-Fe neighbors at 3.44(.04) A?? in coprecipitated samples, and about two Zn-Fe neighbors at the same distance in adsorption samples. In both sets of samples, the fitted coordination number of second shell cations decreases as sorption density increases, indicating changes in the number and type of available complexing sites or the onset of competitive precipitation processes. Comparison of our results with the possible geometries for surface complexes and precipitates suggests that the Zn sorption complexes are inner sphere and at lowest adsorption densities are bidentate, sharing apical oxygens with adjacent edge-sharing Fe(O,OH)6 octahedra. Coprecipitation samples have complexes with similar geometry, but these are polydentate, sharing apices with more than two adjacent edge-sharing Fe(O,OH)6 polyhedra. The results are inconsistent with Zn entering the ferrihydrite structure (i.e., solid solution formation) or formation of other Zn-Fe precipitates. The fitted Zn-Fe coordination numbers drop with increasing Zn density with a minimum of about 0.8(.2) at Zn/(Zn + Fe) of 0.08 or more. This change appears to be attributable to the onset of precipitation of zinc hydroxide polymers with mainly tetrahedral Zn coordination. At the highest loadings studied, the nature of the complexes changes further

  13. XAF/XANES studies of plutonium-loaded sodalite/glass composite waste forms.

    SciTech Connect

    Aase, S. B.; Kropf, A. J.; Lewis, M. A.; Reed, D. T.; Richmann, M. K.

    1999-07-14

    A sodalite/glass ceramic waste form has been developed to immobilize highly radioactive nuclear wastes in chloride form, as part of an electrochemical cleanup process. Simulated waste forms have been fabricated which contain plutonium and are representative of the salt from the electrometallurgical process to recover uranium from spent nuclear fuel. X-ray absorption fine structure spectroscopy (XAFS) and x-ray absorption near-edge spectroscopy (XANES) studies were performed to determine the location, oxidation state and form of the plutonium within these waste forms. Plutonium, in the non-fission-element case, was found to segregate as plutonium(IV) oxide with a crystallite size of at least 20 nm. With fission elements present, the crystallite size was about 2 nm. No plutonium was observed within the sodalite or glass in the waste form.

  14. Analysis of Diffraction Anomalous Fine Structure

    NASA Astrophysics Data System (ADS)

    Cross, Julie Olmsted

    This thesis presents a systematic study of the application of DAFS to determine site-specific local structural and chemical information in complex materials, and the first application of state-of-the-art theoretical XAFS calculations using the computer program scFEFF to model DAFS data. In addition, the iterative dispersion analysis method, first suggested by Pickering, et al., has been generalized to accommodate the off-resonance anomalous scattering from heavy atoms in the unit cell. The generalized algorithm scKKFIT was applied to DAFS data from eight (00 l) reflections of the high-T _{c} superconductor YBa _2Cu_3O_ {6.8} to obtain the weighted complex resonant scattering amplitudes Delta f_{ rm w}(Q, E). The fine-structure functions chi_{rm w}(Q, E) isolated from the Delta f_{ rm w}(Q, E) are linear combinations of the individual site fine structure functions chi _{rm w}(Q, E) = Sigma_{i}W_{i,{ bf Q}}chi_{i}(E) from the two inequivalent Cu sites, added together according to the structure factor for the Cu sublattice. The chi_{rm w}(Q, E) were fit en masse using the XAFS analysis program scFEFFIT under a set of constraints on the coefficients W _{i,{bf Q}} based on the structure factor for kinematic scattering. The W_{i,{bf Q}} determined by scFEFFIT were used to obtain the fully separated complex resonant scattering amplitudes Delta f(E) for the two Cu sites. The theoretical connection between DAFS and XAFS is used to justify the application of state-of-the-art theoretical XAFS calculations to DAFS analysis. The polarization dependence of DAFS is described in terms of individual virtual photoelectron scattering paths in the Rehr-Albers separable curved-wave formalism. Polarization is shown to be an important factor in all DAFS experiments. Three experimental constraints are found necessary for obtaining site-separated Delta f(E) from DAFS data by linear inversion of the W_{i, {bf Q}} matrix and scKKFIT isolated Delta f_{rm w }(Q, E): (1) The diffraction must be

  15. Adsorption and stability of malonic acid on rutile TiO2 (110), studied by near edge X-ray absorption fine structure and photoelectron spectroscopy

    NASA Astrophysics Data System (ADS)

    Syres, Karen L.; Thomas, Andrew G.; Graham, Darren M.; Spencer, Ben F.; Flavell, Wendy R.; Jackman, Mark J.; Dhanak, Vinod R.

    2014-08-01

    The adsorption of malonic acid on rutile TiO2 (110) has been studied using photoelectron spectroscopy and C K-edge, near edge X-ray fine structure spectroscopy (NEXAFS). Analysis of the O 1s and Ti 2p spectra suggest that the molecule adsorbs dissociatively in a doubly-bidentate adsorption geometry as malonate. The data are unable to distinguish between a chelating bonding mode with the backbone of the molecule lying along the [001] azimuth or a bridging geometry along the direction. Work carried out on a wiggler beamline suggests that the molecule is unstable under irradiation by high-flux synchrotron radiation from this type of insertion device.

  16. Investigation on the stability of water-soluble ZnO quantum dots in KB cells by X-ray fluorescence and absorption methods

    NASA Astrophysics Data System (ADS)

    Lu, P.; Zhang, H.; Satoh, T.; Ohkubo, T.; Yamazaki, A.; Takano, K.; Kamiya, T.; Zhu, L.; Huang, Y.; Jiang, Z.; Zheng, Yi; Yang, M.; Mi, Y.; Ren, Q.; Shen, H.

    2011-09-01

    The structural stability of water-soluble ZnO quantum dots (QDs) in oral epidermoid carcinoma (KB) cells was studied by the External Micro Proton Induced X-ray Emission (External Micro-PIXE) technique and the X-ray absorption fine structure (XAFS) measurement. The External Micro-PIXE and XAFS experiments were respectively performed at the JAEA and the Shanghai Synchrotron Radiation Facility. The elements' distributions were detected by the External Micro-PIXE technique. The XAFS method was applied to obtain information about zinc (Zn) K-edge spectra. The fits of the XAFS data showed that the Zn-O bond structure of water-soluble ZnO QDs was stable after being absorbed by KB cells. Its local structural parameters were almost identical with those of the standard wurtzite structure. Water-soluble ZnO QDs had good structural stability in KB cells.

  17. Uranium XAFS analysis of kidney from rats exposed to uranium.

    PubMed

    Kitahara, Keisuke; Numako, Chiya; Terada, Yasuko; Nitta, Kiyohumi; Shimada, Yoshiya; Homma-Takeda, Shino

    2017-03-01

    The kidney is the critical target of uranium exposure because uranium accumulates in the proximal tubules and causes tubular damage, but the chemical nature of uranium in kidney, such as its chemical status in the toxic target site, is poorly understood. Micro-X-ray absorption fine-structureXAFS) analysis was used to examine renal thin sections of rats exposed to uranyl acetate. The U LIII-edge X-ray absorption near-edge structure spectra of bulk renal specimens obtained at various toxicological phases were similar to that of uranyl acetate: their edge position did not shift compared with that of uranyl acetate (17.175 keV) although the peak widths for some kidney specimens were slightly narrowed. µXAFS measurements of spots of concentrated uranium in the micro-regions of the proximal tubules showed that the edge jump slightly shifted to lower energy. The results suggest that most uranium accumulated in kidney was uranium (VI) but a portion might have been biotransformed in rats exposed to uranyl acetate.

  18. Uranium XAFS analysis of kidney from rats exposed to uranium

    PubMed Central

    Kitahara, Keisuke; Numako, Chiya; Terada, Yasuko; Nitta, Kiyohumi; Homma-Takeda, Shino

    2017-01-01

    The kidney is the critical target of uranium exposure because uranium accumulates in the proximal tubules and causes tubular damage, but the chemical nature of uranium in kidney, such as its chemical status in the toxic target site, is poorly understood. Micro-X-ray absorption fine-structureXAFS) analysis was used to examine renal thin sections of rats exposed to uranyl acetate. The U L III-edge X-ray absorption near-edge structure spectra of bulk renal specimens obtained at various toxicological phases were similar to that of uranyl acetate: their edge position did not shift compared with that of uranyl acetate (17.175 keV) although the peak widths for some kidney specimens were slightly narrowed. µXAFS measurements of spots of concentrated uranium in the micro-regions of the proximal tubules showed that the edge jump slightly shifted to lower energy. The results suggest that most uranium accumulated in kidney was uranium (VI) but a portion might have been biotransformed in rats exposed to uranyl acetate. PMID:28244440

  19. XAFS studies of monodisperse Au nanoclusters formation in the etching process

    NASA Astrophysics Data System (ADS)

    Yang, Lina; Huang, Ting; Liu, Wei; Bao, Jie; Huang, Yuanyuan; Cao, Yuanjie; Yao, Tao; Sun, Zhihu; Wei, Shiqiang

    2016-05-01

    Understanding the formation mechanism of gold nanoclusters is essential to the development of their synthetic chemistry. Here, by using x-ray absorption fine-structure (XAFS) spectroscopy, UV-Vis and MS spectra, the formation process of monodisperse Au13 nanoclusters is investigated. We find that a critical step involving the formation of smaller Au8-Au11 metastable intermediate clusters induced by the HCl + HSR etching of the polydisperse Aun precursor clusters occurs firstly. Then these intermediate species undergo a size-growth to Au13 cores, followed by a slow structure rearrangement to reach the final stable structure. This work enriches the understanding of cluster formation chemistry and may guide the way towards the design and the controllable synthesis of nanoclusters.

  20. Experimental study of germanium adsorption on goethite and germanium coprecipitation with iron hydroxide: X-ray absorption fine structure and macroscopic characterization

    NASA Astrophysics Data System (ADS)

    Pokrovsky, O. S.; Pokrovski, G. S.; Schott, J.; Galy, A.

    2006-07-01

    Adsorption of germanium on goethite was studied at 25 °C in batch reactors as a function of pH (1-12), germanium concentration in solution (10 -7 to 0.002 M) and solid/solution ratio (1.8-17 g/L). The maximal surface site density determined via Ge adsorption experiments at pH from 6 to 10 is equal to 2.5 ± 0.1 μmol/m 2. The percentage of adsorbed Ge increases with pH at pH < 9, reaches a maximum at pH ˜ 9 and slightly decreases when pH is further increased to 11. These results allowed generation of a 2-p K Surface Complexation Model (SCM) which implies a constant capacitance of the electric double layer and postulates the presence of two Ge complexes, >FeO-Ge(OH)30 and >FeO-GeO(OH)2-, at the goethite-solution interface. Coprecipitation of Ge with iron oxy(hydr)oxides formed during Fe(II) oxidation by atmospheric oxygen or by Fe(III) hydrolysis in neutral solutions led to high Ge incorporations in solid with maximal Ge/Fe molar ratio close to 0.5. The molar Ge/Fe ratio in precipitated solid is proportional to that in the initial solution according to the equation (Ge/Fe) solid = k × (Ge/Fe) solution with 0.7 ⩽ k ⩽ 1.0. The structure of adsorbed and coprecipitated Ge complexes was further characterized using XAFS spectroscopy. In agreement with previous data on oxyanions adsorption on goethite, bi-dentate bi-nuclear surface complexes composed of tetrahedrally coordinated Ge attached to the corners of two adjacent Fe octahedra represent the dominant contribution to the EXAFS signal. Coprecipitated samples with Ge/Fe molar ratios >0.1, and samples not aged in solution (<1 day) having intermediate Ge/Fe ratios (0.01-0.1) show 4 ± 0.3 oxygen atoms at 1.76 ± 0.01 Å around Ge. Samples less concentrated in Ge (0.001 < Ge/Fe < 0.10) and aged longer times in solution (up to 280 days) exhibit a splitting of the first atomic shell with Ge in both tetrahedral ( R = 1.77 ± 0.02 Å) and octahedral ( R = 1.92 ± 0.03 Å) coordination with oxygen. In these samples

  1. Capturing Transient Electronic and Molecular Structures in Liquids by Picosecond X-Ray Absorption Spectroscopy

    SciTech Connect

    Gawelda, W.; Pham, V. T.; El Nahhas, A.; Kaiser, M.; Zaushitsyn, Y.; Bressler, C.; Chergui, M.; Johnson, S. L.; Grolimund, D.; Abela, R.; Hauser, A.

    2007-02-02

    We describe an advanced setup for time-resolved x-ray absorption fine structure (XAFS) Spectroscopy with picosecond temporal resolution. It combines an intense femtosecond laser source synchronized to the x-ray pulses delivered into the microXAS beamline of the Swiss Light Source (SLS). The setup is applied to measure the short-lived high-spin geometric structure of photoexcited aqueous Fe(bpy)3 at room temperature.

  2. High quality x-ray absorption spectroscopy measurements with long energy range at high pressure using diamond anvil cell

    SciTech Connect

    Hong, X.; Newville, M.; Prakapenka, V.B.; Rivers, M.L.; Sutton, S.R.

    2009-07-31

    We describe an approach for acquiring high quality x-ray absorption fine structure (XAFS) spectroscopy spectra with wide energy range at high pressure using diamond anvil cell (DAC). Overcoming the serious interference of diamond Bragg peaks is essential for combining XAFS and DAC techniques in high pressure research, yet an effective method to obtain accurate XAFS spectrum free from DAC induced glitches has been lacking. It was found that these glitches, whose energy positions are very sensitive to the relative orientation between DAC and incident x-ray beam, can be effectively eliminated using an iterative algorithm based on repeated measurements over a small angular range of DAC orientation, e.g., within {+-}3{sup o} relative to the x-ray beam direction. Demonstration XAFS spectra are reported for rutile-type GeO{sub 2} recorded by traditional ambient pressure and high pressure DAC methods, showing similar quality at 440 eV above the absorption edge. Accurate XAFS spectra of GeO{sub 2} glass were obtained at high pressure up to 53 GPa, providing important insight into the structural polymorphism of GeO{sub 2} glass at high pressure. This method is expected be applicable for in situ XAFS measurements using a diamond anvil cell up to ultrahigh pressures.

  3. Two-channel opto-acoustic diode laser spectrometer and fine structure of methane absorption spectra in 6070-6180 cm-1 region.

    PubMed

    Kapitanov, V A; Ponomarev, Yu N; Tyryshkin, I S; Rostov, A P

    2007-04-01

    We describe the hardware and software of the high-sensitive two-channel opto-acoustic spectrometer with a near infrared diode laser. A semiconductor TEC-100 laser with outer resonator generates a continuous single-frequency radiation in the range of 6040-6300 cm-1 with spectral resolution better that 10 MHz. The newly designed model of photo-acoustic cells in the form of a ring type resonator was used in the spectrometer, and the system allows the measurement of a weak absorption coefficient equal to 1.4x10(-7) cm-1 Hz-1/2 with a laser radiation power of 0.003 W. The methane absorption spectra within a range of 6080-6180 cm-1 were measured with a spectral resolution of 10 MHz and the signal to noise ratio more than 10(3). Six hundred absorption lines were recorded, which is twice as many as in HITRAN-2004. The accurate measurements of the half-width and shift of methane unresolved triplet R3 of 2nu3 band permit us to determine values of the broadening and shift coefficients for CH4-air, CH4-N2, and CH4-SF6 mixtures.

  4. Complex polarization propagator approach in the restricted open-shell, self-consistent field approximation: the near K-edge X-ray absorption fine structure spectra of allyl and copper phthalocyanine.

    PubMed

    Linares, Mathieu; Stafström, Sven; Rinkevicius, Zilvinas; Ågren, Hans; Norman, Patrick

    2011-05-12

    A presentation of the complex polarization propagator in the restricted open-shell self-consistent field approximation is given. It rests on a formulation of a resonant-convergent, first-order polarization propagator approach that makes it possible to directly calculate the X-ray absorption cross section at a particular frequency without explicitly addressing the excited states. The quality of the predicted X-ray spectra relates only to the type of density functional applied without any separate treatment of dynamical relaxation effects. The method is applied to the calculation of the near K-edge X-ray absorption fine structure spectra of allyl and copper phthalocyanine. Comparison is made between the spectra of the radicals and those of the corresponding cations and anions to assess the effect of the increase of electron charge in the frontier orbital. The method offers the possibility for unique assignment of symmetry-independent atoms. The overall excellent spectral agreement motivates the application of the method as a routine precise tool for analyzing X-ray absorption of large systems of technological interest.

  5. An XAFS Study of Tantalum Chloride in the Ionic Liquid 1-ethyl-3-methyl Imidazolium Chloride/ aluminum Chloride

    SciTech Connect

    D Roeper; K Pandya; G Cheek; W OGrady

    2011-12-31

    Tantalum chloride was studied with extended X-ray absorption fine structure spectroscopy (XAFS) in acidic and basic aluminum chloride/1-ethyl-3-methyl imidazolium chloride ionic liquids (ILs). Anhydrous Ta2Cl10 is more soluble in the basic solution than in the acidic solution and the X-ray absorption data shows that the coordination shell of chlorides around the tantalum is larger in the basic solution. In the acidic solution, tantalum has five chlorides in its coordination shell while in the basic solution; the tantalum is coordinated by seven chlorides. This indicates that the Lewis acidity of the tantalum chloride causes the Ta to coordinate differently in the acidic and the basic solutions.

  6. Hydrothermal diamond anvil cell for XAFS studies of first-row transition elements in aqueous solutions up to supercritical conditions

    USGS Publications Warehouse

    Bassett, William A.; Anderson, Alan J.; Mayanovic, Robert A.; Chou, I.-Ming

    2000-01-01

    A hydrothermal diamond anvil cell (HDAC) has been modified by drilling holes with a laser to within 150 ??m of the anvil face to minimize the loss of X-rays due to absorption and scatter by diamond. This modification enables acquisition of K-edge X-ray absorption fine structure (XAFS) spectra from first-row transition metal ions in aqueous solutions at temperatures ranging from 25??C to 660??C and pressures up to 800 MPa. These pressure-temperature (P-T) conditions are more than sufficient for carrying out experimental measurements that can provide data valuable in the interpretation of fluid inclusions in minerals found in ore-forming hydrothermal systems as well as other important lithospheric processes involving water. (C) 2000 Elsevier Science B.V. All rights reserved.

  7. A new device for XAFS data collection up to 2000 K (or 3700 K under vacuum)

    NASA Astrophysics Data System (ADS)

    Farges, F.; Itié, J.-P.; Fiquet, G.; Andrault, D.

    1995-08-01

    A new device to collect high- to ultra high temperature X-ray absorption fine structure (XAFS) data is presented. The experimental XAFS data is collected in the energy-dispersive mode using the heating wire technique. The X-ray beam is focused on a 500 μm ⊘ hole (drilled within a Pt 90Rh 10 heating wire) that contains the sample (100-300 μm thickness). The wire is heated by the Joule effect. The actual temperature is measured using an optical pyrometer and an electrical power-temperature calibration, based on 10 model compound melting points ( T is ± 20 K on the average). The maximum possible temperature is that of the wire melting point (˜ 2000 K for the Pt 90Rh 10 alloy). However, much higher temperatures can be achieved by the use of Ir, W, Ta (etc.) wires under inert atmosphere (to prevent the wire from oxidation by air). Data collection at all temperatures is rather fast (3 s/spectrum for a 3-13 Å -1k-domain used) and can be performed every 20 K. Therefore, in situ, high temperature kinetics can also be studied as a function of time such as phase transitions, oxidation reactions or melting phenomena. The study of GeO 2 polymorphs as a function of temperature will be shown to give an example of the possibilities offered by this technique.

  8. XAFS Studies of Silver Environments in Ion-Exchanged Glasses

    SciTech Connect

    Yang, X. C.; Dubiel, M.

    2007-02-02

    The X-ray absorption fine structure (XAFS) technique was used to analyze the structural geometry of Ag atoms introduced into soda-lime silicate glass and soda aluminosilicate glass by ion-exchange methods. The results show that Ag+ ions in aluminosilicate glass are coordinated by about two oxygens and the nearest-neighbor Ag-O distance increases when the Ag+-for-Na+ ion-exchange ratio is larger than 0.47. When the exchange ratio is low, the introduced Ag+ ions are stabilized at the non-bridge oxygen (NBO) site with a Ag-O distance of 2.20 A, and the Na+ ions in the AlO4 site are exchanged by Ag+ ions after full replacement of the NBO sites with a Ag-O distance of 2.28 A. The disorder of Ag-O coordination increases with increasing ion-exchange ratio in aluminosilicate glass where Ag+ ions are coordinated by NBO and bridge oxygen (BO)

  9. Prospects for X-ray absorption with the super-bright light sources of the future.

    PubMed

    Norman, D

    2001-03-01

    The immense growth in applications of X-ray absorption spectroscopy (XAS) has been enabled by the widespread availability of intense tunable X-rays from synchrotron radiation sources. Recently, new concepts have been proposed for fourth-generation light sources, such as the SASE (self-amplified stimulated emission) X-ray free-electron lasers (XFELs) being pursued at Hamburg (TESLA) and Stanford (LCLS), and the recirculator ring (MARS) at Novosibirsk. These sources offer expected gains of many orders of magnitude in instantaneous brilliance, which will unlock opportunities for qualitatively different science. Examples of new or greatly expanded techniques in XAS could include Raman X-ray absorption fine structure (XAFS), pump-probe experiments, time-resolved XAFS and small-spot X-ray spectromicroscopy, although the limited tunability of the sources might not allow conventional XAFS measurements. Multi-photon X-ray absorption could become a new field of study. There should not be a collective stampede to these new sources, however, and it is likely that storage rings will continue to be necessary for most XAFS applications. The extreme brightness of these future light sources will present difficult challenges in instrumentation, especially detectors and sample containment. Practitioners will also have to exercise caution, because the intensity of the beam will surely destroy many samples and in some cases there will be so many photons absorbed per atom that XAFS will be impossible.

  10. In Situ X-ray Absorption Fine Structure Studies on the Effect of pH on Pt Electronic Density during Aqueous Phase Reforming of Glycerol

    SciTech Connect

    Karim, Ayman M.; Howard, Christopher J.; Roberts, Benjamin Q.; Kovarik, Libor; Zhang, Liang; King, David L.; Wang, Yong

    2012-10-30

    In situ x-ray absorption spectroscopy (XAS) results on correlating the Pt local coordination and electronic structure with the Pt/C catalyst activity and selectivity during aqueous reforming of glycerol at different pH are reported. The results show that both low and high pH favor C-O cleavage over that of C-C. However, the selectivity towards C-O bond cleavage was higher under the acidic conditions. XANES measurements under reaction conditions showed that low pH increased the Pt electron density while the effect of basic conditions was minimal. ΔXANES was used to estimate the coverage of adsorbates under reaction conditions and the results suggest a change in the adsorbates coverage by the acidic conditions, resulting in higher electron density on Pt

  11. In situ back-side illumination fluorescence XAFS (BI-FXAFS) studies on platinum nanoparticles deposited on a HOPG surface as a model fuel cell: a new approach to the Pt-HOPG electrode/electrolyte interface.

    PubMed

    Uehara, Hiromitsu; Uemura, Yohei; Ogawa, Takafumi; Kono, Kentaro; Ueno, Ryoichi; Niwa, Yasuhiro; Nitani, Hiroaki; Abe, Hitoshi; Takakusagi, Satoru; Nomura, Masaharu; Iwasawa, Yasuhiro; Asakura, Kiyotaka

    2014-07-21

    We measured the in situ polarization-dependent X-ray absorption fine structure of platinum nanoparticles (PtNPs) deposited on a flat highly oriented pyrolytic graphite (HOPG) substrate under electrochemical conditions using a back-side illumination method. In this method, the thin HOPG substrate with PtNPs deposited on one side was used as a window for incident and fluorescent X-rays, as well as an electrode. A bent crystal Laue analyzer (BCLA) was applied to the extraction of the Pt Lα fluorescent X-ray signals from strong scattered X-rays. Pt L3 edge XAFS spectra were observed for various electrode potentials and polarization directions.

  12. Refinement of DNA structures through near-edge X-ray absorption fine structure analysis: applications on guanine and cytosine nucleobases, nucleosides, and nucleotides.

    PubMed

    Hua, Weijie; Gao, Bin; Li, Shuhua; Agren, Hans; Luo, Yi

    2010-10-21

    In this work we highlight the potential of NEXAFS—near-edge X-ray absorption fine structure—analysis to perform refinements of hydrogen-bond structure in DNA. For this purpose we have carried out first-principle calculations of the N1s NEXAFS spectra of the guanine and cytosine nucleobases and their tautomers, nucleosides, and nucleotides in the gas phase, as well as for five crystal structures of guanine, cytosine, or guanosine. The spectra all clearly show imine (π1*) and amine (π2*) nitrogen absorption bands with a characteristic energy difference (Δ). Among all of the intramolecule covalent connections, the tautomerism of hydrogens makes the largest influence, around ±0.4−0.5 eV change of Δ, to the spectra due to a switch of single−double bonds. Deoxyribose and ribose sugars can cause at most 0.2 eV narrowing of Δ, while the phosphate groups have nearly negligible effects on the spectra. Two kinds of intermolecule interactions are analyzed, the hydrogen bonds and the stacking effect, by comparing “compressed” and “expanded” models or by comparing models including or excluding the nearest stacking molecules. The shortening of hydrogen-bond length by 0.2−0.3 Å can result in the reduction of Δ by 0.2−0.8 eV. This is because the hydrogen bonds make the electrons more delocalized, and the amine and imine nitrogens become less distinguishable. Moreover, the hydrogen bond has a different ability to influence the spectra of different crystals, with guanine crystals as the largest (change by 0.8 eV) and the guanosine crystal as the smallest (change by 0.2 eV). The stacking has negligible effects on the spectra in all studied systems. A comparison of guanosine to guanine crystals shows that the sugars in the crystal could create “blocks” in the π-and hydrogen bonds network of bases and thus makes the imine and amine nitrogens more distinguishable with a larger Δ. Our theoretical calculations offer a good match with experimental findings

  13. XAFS Model Compound Library

    DOE Data Explorer

    Newville, Matthew

    The XAFS Model Compound Library contains XAFS data on model compounds. The term "model" compounds refers to compounds of homogeneous and well-known crystallographic or molecular structure. Each data file in this library has an associated atoms.inp file that can be converted to a feff.inp file using the program ATOMS. (See the related Searchable Atoms.inp Archive at http://cars9.uchicago.edu/~newville/adb/) This Library exists because XAFS data on model compounds is useful for several reasons, including comparing to unknown data for "fingerprinting" and testing calculations and analysis methods. The collection here is currently limited, but is growing. The focus to date has been on inorganic compounds and minerals of interest to the geochemical community. [Copied, with editing, from http://cars9.uchicago.edu/~newville/ModelLib/

  14. Structural kinetics of a Pt/C cathode catalyst with practical catalyst loading in an MEA for PEFC operating conditions studied by in situ time-resolved XAFS.

    PubMed

    Ishiguro, Nozomu; Saida, Takahiro; Uruga, Tomoya; Sekizawa, Oki; Nagasawa, Kensaku; Nitta, Kiyofumi; Yamamoto, Takashi; Ohkoshi, Shin-ichi; Yokoyama, Toshihiko; Tada, Mizuki

    2013-11-21

    The structural kinetics of surface events on a Pt/C cathode catalyst in a membrane electrode assembly (MEA) with a practical catalyst loading (0.5 mgPt cm(-2)) for a polymer electrolyte fuel cell were investigated by in situ time-resolved X-ray absorption fine structure analysis (XAFS; time resolution: 100 ms) for the first time. The rate constants of structural changes in the Pt/C cathode catalyst in the MEA during voltage cycling were successfully estimated. For voltage-cycling processes, all reactions (electrochemical reactions and structural changes in the Pt catalyst) in the MEA were found to be much faster than those in an MEA with a thick cathode catalyst layer, but the in situ time-resolved XAFS analysis revealed that significant time lags similarly existed between the electrochemical reactions and the structural changes in the Pt cathode catalyst. The time-resolved XAFS also revealed differences in the structural kinetics of the Pt/C cathode catalyst for the voltage-cycling processes under N2 and air flows at the cathode.

  15. On the distribution and bonding environment of Zn and Fe in glasses containing electric arc furnace dust: a mu-XAFS and mu-XRF study.

    PubMed

    Pinakidou, F; Katsikini, M; Paloura, E C; Kavouras, P; Kehagias, Th; Komninou, Ph; Karakostas, Th; Erko, A

    2007-04-02

    We apply synchrotron radiation assisted X-ray fluorescence (SR-XRF), SR-XRF mapping as well as micro- and conventional X-ray absorption fine structure (mu-XAFS and XAFS) spectroscopies in order to study the bonding environment of Fe and Zn in vitrified samples that contain electric arc furnace dust from metal processing industries. The samples are studied in the as-cast state as well as after annealing at 900 degrees C. The SR-XRF results demonstrate that annealing does not induce any significant changes in the distribution of either Fe or Zn, in both the as-cast and annealed glasses. The mu-XAFS spectra recorded at the Fe-K and Zn-K edges reveal that the structural role of both Fe and Zn remains unaffected by the annealing procedure. More specifically, Fe forms both FeO(6) and FeO(4) polyhedra, i.e. acts as an intermediate oxide while Zn occupies tetrahedral sites.

  16. Determination of iron-ligand bond lengths in ferric and ferrous horse heart cytochrome c using multiple-scattering analyses of XAFS data

    SciTech Connect

    Cheng, M.C.; Rich, A.M.; Armstrong, R.S.; Ellis, P.J.; Lay, P.A.

    1999-12-13

    Cytochrome c (cyt c) is a small heme protein (MW 12 384) that functions as a biological electron-transfer agent. It consists of a single polypeptide chain and a prosthetic heme group and provides a pathway for the transfer of electrons from cyt c reductase to cyt c oxidase in the mitochondrial respiratory chain (oxidative phosphorylation). The protein participates in oxidation-reduction reactions with the heme iron alternating between the oxidized (ferric, Fe{sup III}) state and the reduced (ferrous, Fe{sup II}) state. X-ray absorption fine structure (XAFS) data were obtained from frozen aqueous solutions (10 K) of horse heart ferri- and ferrocyt c. Models of the structure about the Fe center were refined to optimize the fit between the observed XAFS in the range 0 {le} k {le} 16.3 {angstrom}{sup {minus}1} and the XAFS calculated using both single-scattering (SS) and multiple-scattering (MS) calculations. The bond lengths obtained are more accurate and precise than those determined previously for cyt c from various species using X-ray crystallography. The Fe-N bond lengths are 1.98--1.99 {angstrom} for both oxidation states of cyt c. The Fe-S bond of derricyt c (2.33 {angstrom}) is significantly longer than that of ferrocyt c (2.29 {angstrom}). The small changes in the bond lengths are consistent with the small reorganizational energy required for the fast electron-transfer reaction of cyt c.

  17. Lead, Uranium, and Nickel Compound Data from the XAFS Library at the Stanford Synchrotron Radiation Laboratory (SSRL)

    DOE Data Explorer

    The x-ray absorption fine structure spectroscopy (XAFS) library at the Stanford Synchrotron Radiation Laboratory is intended to be a reference library of XAFS spectra for various lead, uranium, and nickel compounds. Compounds are organized by central atom and all spectra are transmission data. Molecular Environmental Science (MES) research at SSRL focuses on the fundamental interfacial, molecular- and nano-scale processes that control contaminant and nutrient cycling in the biosphere with the goal of elucidating global elemental cycles and anthropogenic influences on the environment. Key areas of investigation include the: (a) Structural chemistry of water and dissolved solutes, (b) Structural chemistry and reactivity of complex natural environmental materials with respect to heavy metals and metalloids (biominerals, Fe- and Mn-oxides, biofilms, and organic materials), (c) Reactions at environmental interfaces, including sorption, precipitation and dissolution processes that affect the bioavailability of heavy metals and other contaminants, and (d) Microbial transformations of metals and anions. SSRL-based MES research utilizes synchrotron-based x-ray absorption spectroscopy (XAS), x-ray diffraction (XRD), small-angle x-ray scattering (SAXS), x-ray standing wave (XSW) spectroscopy, and photoemission spectroscopy (PES) because of their unique capabilities to probe structure/composition relationships in complex, non-crystalline, and dilute materials. [copied from http://www-ssrl.slac.stanford.edu/mes/index.html

  18. Structural Analysis of the Mn(IV)/Fe(III) Cofactor of Chlamydia Trachomatis Ribonucleotide Reductase By Extended X-Ray Absorption Fine Structure Spectroscopy And Density Functional Theory Calculations

    SciTech Connect

    Younker, J.M.; Krest, C.M.; Jiang, W.; Krebs, C.; Bollinger, J.M.Jr.; Green, M.T.

    2009-05-28

    The class Ic ribonucleotide reductase from Chlamydia trachomatis (C{bar A}) uses a stable Mn(lV)/ Fe(lll) cofactor to initiate nucleotide reduction by a free-radical mechanism. Extended X-ray absorption fine structure (EXAFS) spectroscopy and density functional theory (DFT) calculations are used to postulate a structure for this cofactor. Fe and Mn K-edge EXAFS data yield an intermetallic distance of -2.92 {angstrom}. The Mn data also suggest the presence of a short 1.74 {angstrom} Mn-O bond. These metrics are compared to the results of DFT calculations on 12 cofactor models derived from the crystal structure of the inactive Fe2(lll/ III) form of the protein. Models are differentiated by the protonation states of their bridging and terminal OH{sub x} ligands as well as the location of the Mn(lV) ion (site 1 or 2). The models that agree best with experimental observation feature a{mu}-1, 3-carboxylate bridge (E120), terminal solvent (H{sub 2}O/OH) to site 1, one {mu}-O bridge, and one {mu}-OH bridge. The site-placement of the metal ions cannot be discerned from the available data.

  19. Surface metallization on Si(001) at elevated temperatures studied by angle-resolved photoemission spectroscopy and near-edge x-ray absorption fine structure: Effect of thermal adatoms

    NASA Astrophysics Data System (ADS)

    Jeon, C.; Hwang, C. C.; Kang, T.-H.; Kim, K.-J.; Kim, B.; Kim, Y.; Noh, D. Y.; Park, C.-Y.

    2009-10-01

    We report the metallization of the Si(001)2×1 surface at elevated temperatures using angle-resolved photoemission spectroscopy (ARPES) and near-edge x-ray absorption fine structure (NEXAFS). A metallic state (Sm) over the EF , which corresponds to the empty (π∗) state of the 2×1 asymmetric dimer model, increases in the ARPES spectra, while the π∗ state decreases in the NEXAFS spectra with increasing temperature. Since Sm is observed even at 400 K, the structural phase transition at ˜900K [Phys. Rev. Lett. 91, 126103 (2003); Phys. Rev. Lett. 77, 3869 (1996)] is not related to the metallization. Thermal excitation seems to be too small to detect in ARPES in initial stage of the metallization and cannot account for the different behavior of Sm and the filled surface state of the up-dimer upon oxidation. We suggest, based on the existence of Sm even at 400 K and the oxidation behavior, that the metallization is attributed to thermal adatoms.

  20. Nondestructive Speciation Depth Profiling of Complex TiOx Nanolayer Structures by Grazing Incidence X-ray Fluorescence Analysis and Near Edge X-ray Absorption Fine Structure Spectroscopy.

    PubMed

    Pollakowski, Beatrix; Beckhoff, Burkhard

    2015-08-04

    An important challenge of modern material science is the depth-sensitive and nondestructive analysis of the chemical binding state of complex structures consisting of multiple thin layers. In general, the correlation of the material functionality and underlying chemical and physical properties is the key question in view of directed device development, performance, and quality control. It has been shown that the combined method grazing incidence X-ray fluorescence analysis (GIXRF) and near edge X-ray absorption fine structure spectroscopy (NEXAFS) can significantly contribute to the nondestructive chemical analysis of buried thin films and interface structures regarding chemical speciation. Recently, we have enhanced the method to allow for a depth-resolved analysis of multilayered nanoscaled thin film structures. By means of appropriate model systems, the methodology has been developed and successfully validated. The model systems basically consist of a carbon cap layer, two titanium layers differing in their oxidation states and separated by a thin carbon layer, and a silicon substrate covered with molybdenum and a carbon layer. A differential approach has been developed to derive the chemical species of each of the titanium layers.

  1. Interrogation of Surface, Skin, and Core Orientation in Thermotropic Liquid-Crystalline Copolyester Moldings by Near-Edge X-ray Absorption Fine Structure and Wide-Angle X-ray Scattering

    SciTech Connect

    Rendon,S.; Bubeck, R.; Thomas, L.; Burghardt, W.; Hexemer, A.; Fischer, D.

    2007-01-01

    Injection molding thermotropic liquid-crystalline polymers (TLCPs) usually results in the fabrication of molded articles that possess complex states of orientation that vary greatly as a function of thickness. 'Skin-core' morphologies are often observed in TLCP moldings. Given that both 'core' and 'skin' orientation states may often differ both in magnitude and direction, deconvolution of these complex orientation states requires a method to separately characterize molecular orientation in the surface region. A combination of two-dimensional wide-angle X-ray scattering (WAXS) in transmission and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy is used to probe the molecular orientation in injection molded plaques fabricated from a 4,4'-dihydroxy-{alpha}-methylstilbene (DH{alpha}MS)-based thermotropic liquid crystalline copolyester. Partial electron yield (PEY) mode NEXAFS is a noninvasive ex situ characterization tool with exquisite surface sensitivity that samples to a depth of 2 nm. The effects of plaque geometry and injection molding processing conditions on surface orientation in the regions on- and off- axis to the centerline of injection molded plaques are presented and discussed. Quantitative comparisons are made between orientation parameters obtained by NEXAFS and those from 2D WAXS in transmission, which are dominated by the microstructure in the skin and core regions. Some qualitative comparisons are also made with 2D WAXS results from the literature.

  2. A high-resolution near-edge x-ray absorption fine structure investigation of the molecular orientation in the pentacene/poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) pentacene/system.

    PubMed

    Casu, M B; Cosseddu, P; Batchelor, D; Bonfiglio, A; Umbach, E

    2008-01-07

    We present x-ray photoemission spectroscopy and highly resolved near-edge x-ray absorption fine structure spectroscopy measurements taken on pentacene thin films of different thicknesses deposited on a spin coated poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) substrate. Thin films of pentacene were prepared by using organic molecular beam deposition in situ using strictly controlled evaporation conditions. Our investigations show that pentacene thin films on PEDOT:PSS are characterized by upright standing molecules. Due to the strong dichroic behavior, the calculated values of the molecular orientation give a clear indication not only of the real molecular arrangement in the films but also of a high orientational order. This high degree of molecular orientation order is a characteristic already of the first layer. The films show the tendency to grow on the PEDOT:PSS substrate following an island-fashion mode, with a relatively narrow intermixing zone at the interface between the pentacene and the polymer blend. The peculiarity of the growth of pentacene on PEDOT:PSS is due to the fact that the substrate does not offer any template for the nucleated films and thus exerts a lateral order toward the crystal structure arrangement. Under these conditions, the upright orientation of the molecules in the films minimizes the energy required for the system stability.

  3. Metal (Hydr)oxides for the removal of Cr(VI) from drinking water: a XAFS study

    NASA Astrophysics Data System (ADS)

    Pinakidou, F.; Kaprara, E.; Katsikini, M.; Paloura, E. C.; Simeonidis, K.; Mitrakas, M.

    2016-05-01

    The reduction mechanism and adsorption behaviour of Cr(VI) onto Tin(II) oxy- hydroxides are investigated using Cr-K edge X-ray absorption fine structure (XAFS) spectroscopies. The synthesis of the Sn oxy-hydroxide proceeds via hydrolysis of SnSO4. The successful reduction of Cr(VI) was identified by the analysis of the Cr-K edge XANES spectra where only Cr(III) species in octahedral sites are detected. According to the Cr-K edge EXAFS analysis results, Cr(III) forms bidentate inner sphere (binuclear (2C) and mononuclear (2E)) complexes. However, the surface coverage of Cr affects the type of Cr(III)-complexes formed: as the Cr-loading increases, Cr(III)-oxy-anions preferentially sorb in a “combined” 2C and 1V configuration, at the expense of the existing 2E sorption geometry.

  4. The BioCAT Microprobe for X-Ray Fluorescence Imaging, MicroXAFS and Microdiffraction Studies on Biological Samples

    SciTech Connect

    Barrea, R.A.; Gore, D.; Kondrashkina, E.; Weng, T.; Heurich, R.; Vukonich, M.; Orgel, J.; Davidson, M.; Collingwood, J.F.; Mikhaylova, A.; Irving, T.C.

    2007-07-31

    Microbeam capabilities have been recently added to the Biophysics Collaborative Access Team (BioCAT) beamline 18-ID at the Advanced Photon Source to allow x-ray elemental mapping, micro x-ray absorption fine structure and microdiffraction studies on biological samples. The microprobe setup comprises a pair of platinum coated silicon KB mirrors; a sample holder mounted in a high precision positioner (100 nm accuracy); fluorescence detectors including a Si drift detector, Fe and Zn Bent Laue analyzers and a Ge detector; and a CCD detector for micro-diffraction experiments. The energy range of the microprobe is from 3.5 keV up to 17 keV. The fast scanning capabilities of the Bio-CAT beamline facilitate rapid acquisition of x-ray elemental images and micro-XAFS spectra. This paper reports the results of commissioning the KB mirror system and its performance in initial x-ray fluorescence mapping and micro-diffraction studies.

  5. MAX: Multiplatform Applications for XAFS

    NASA Astrophysics Data System (ADS)

    Alain, Michalowicz; Jacques, Moscovici; Diane, Muller-Bouvet; Karine, Provost

    2009-11-01

    MAX is a new EXAFS and XANES analysis package, replacing our old "EXAFS pour le Mac" software suite. The major improvement is the ability to work with strictly the same code, compiled at once for Microsoft Windows, Apple MacOSX and LINUX systems, justifying the title "Multiplatform Applications for XAFS". It is organized as four modules: ABSORBIX (X-ray absorbance and fluorescence self-absorption calculations), CHEROKEE (EXAFS and XANES data treatment), ROUNDMIDNIGHT (EXAFS modeling and fit) and CRYSTALFFREV (from crystal structures and molecular modeling to FEFF EXAFS and XANES theoretical calculations). Most features developed in "EXAFS pour le Mac" are still available, but with much improvements in the user's interface, data treatment algorithms and new functionalities.

  6. Invited article: The fast readout low noise camera as a versatile x-ray detector for time resolved dispersive extended x-ray absorption fine structure and diffraction studies of dynamic problems in materials science, chemistry, and catalysis

    NASA Astrophysics Data System (ADS)

    Labiche, Jean-Claude; Mathon, Olivier; Pascarelli, Sakura; Newton, Mark A.; Ferre, Gemma Guilera; Curfs, Caroline; Vaughan, Gavin; Homs, Alejandro; Carreiras, David Fernandez

    2007-09-01

    Originally conceived and developed at the European Synchrotron Radiation Facility (ESRF) as an "area" detector for rapid x-ray imaging studies, the fast readout low noise (FReLoN) detector of the ESRF [J.-C. Labiche, ESRF Newsletter 25, 41 (1996)] has been demonstrated to be a highly versatile and unique detector. Charge coupled device (CCD) cameras at present available on the public market offer either a high dynamic range or a high readout speed. A compromise between signal dynamic range and readout speed is always sought. The parameters of the commercial cameras can sometimes be tuned, in order to better fulfill the needs of specific experiments, but in general these cameras have a poor duty cycle (i.e., the signal integration time is much smaller than the readout time). In order to address scientific problems such as time resolved experiments at the ESRF, a FReLoN camera has been developed by the Instrument Support Group at ESRF. This camera is a low noise CCD camera that combines high dynamic range, high readout speed, accuracy, and improved duty cycle in a single image. In this paper, we show its application in a quasi-one-dimensional sense to dynamic problems in materials science, catalysis, and chemistry that require data acquisition on a time scale of milliseconds or a few tens of milliseconds. It is demonstrated that in this mode the FReLoN can be applied equally to the investigation of rapid changes in long range order (via diffraction) and local order (via energy dispersive extended x-ray absorption fine structure) and in situations of x-ray hardness and flux beyond the capacity of other detectors.

  7. Invited article: The fast readout low noise camera as a versatile x-ray detector for time resolved dispersive extended x-ray absorption fine structure and diffraction studies of dynamic problems in materials science, chemistry, and catalysis

    SciTech Connect

    Labiche, Jean-Claude; Mathon, Olivier; Pascarelli, Sakura; Newton, Mark A.; Ferre, Gemma Guilera; Curfs, Caroline; Vaughan, Gavin; Homs, Alejandro; Carreiras, David Fernandez

    2007-09-15

    Originally conceived and developed at the European Synchrotron Radiation Facility (ESRF) as an 'area' detector for rapid x-ray imaging studies, the fast readout low noise (FReLoN) detector of the ESRF [J.-C. Labiche, ESRF Newsletter 25, 41 (1996)] has been demonstrated to be a highly versatile and unique detector. Charge coupled device (CCD) cameras at present available on the public market offer either a high dynamic range or a high readout speed. A compromise between signal dynamic range and readout speed is always sought. The parameters of the commercial cameras can sometimes be tuned, in order to better fulfill the needs of specific experiments, but in general these cameras have a poor duty cycle (i.e., the signal integration time is much smaller than the readout time). In order to address scientific problems such as time resolved experiments at the ESRF, a FReLoN camera has been developed by the Instrument Support Group at ESRF. This camera is a low noise CCD camera that combines high dynamic range, high readout speed, accuracy, and improved duty cycle in a single image. In this paper, we show its application in a quasi-one-dimensional sense to dynamic problems in materials science, catalysis, and chemistry that require data acquisition on a time scale of milliseconds or a few tens of milliseconds. It is demonstrated that in this mode the FReLoN can be applied equally to the investigation of rapid changes in long range order (via diffraction) and local order (via energy dispersive extended x-ray absorption fine structure) and in situations of x-ray hardness and flux beyond the capacity of other detectors.

  8. Quantitative chemical imaging of element diffusion into heterogeneous media using laser ablation inductively coupled plasma mass spectrometry, synchrotron micro-X-ray fluorescence, and extended X-ray absorption fine structure spectroscopy.

    PubMed

    Wang, H A O; Grolimund, D; Van Loon, L R; Barmettler, K; Borca, C N; Aeschlimann, B; Günther, D

    2011-08-15

    Quantitative chemical imaging of trace elements in heterogeneous media is important for the fundamental understanding of a broad range of chemical and physical processes. The primary aim of this study was to develop an analytical methodology for quantitative high spatial resolution chemical imaging based on the complementary use of independent microanalytical techniques. The selected scientific case study is focused on high spatially resolved quantitative imaging of major elements, minor elements, and a trace element (Cs) in Opalinus clay, which has been proposed as the host rock for high-level radioactive waste repositories. Laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS), providing quantitative chemical information, and synchrotron radiation based micro-X-ray fluorescence (SR-microXRF), providing high spatial resolution images, were applied to study Cs migration into Opalinus clay rock. The results indicate that combining the outputs achievable by the two independent techniques enhances the imaging capabilities significantly. The qualitative high resolution image of SR-microXRF is in good agreement with the quantitative image recorded with lower spatial resolution by LA-ICPMS. Combining both techniques, it was possible to determine that the Opalinus clay sample contains two distinct domains: (i) a clay mineral rich domain and (ii) a calcium carbonate dominated domain. The two domains are separated by sharp boundaries. The spatial Cs distribution is highly correlated to the distribution of the clay. Furthermore, extended X-ray absorption fine structure analysis indicates that the trace element Cs preferentially migrates into clay interlayers rather than into the calcite domain, which complements the results acquired by LA-ICPMS and SR-microXRF. By using complementary techniques, the quantification robustness was improved to quantitative micrometer spatial resolution. Such quantitative, microscale chemical images allow a more detailed

  9. Effect of different thickness crystalline SiC buffer layers on the ordering of MgB{sub 2} films probed by extended x-ray absorption fine structure

    SciTech Connect

    Putri, W. B. K.; Tran, D. H.; Kang, B.; Lee, O. Y.; Kang, W. N.; Miyanaga, T.; Yang, D. S.

    2014-03-07

    Extended X-ray absorption fine structure (EXAFS) spectroscopy is a powerful method to investigate the local structure of thin films. Here, we have studied EXAFS of MgB{sub 2} films grown on SiC buffer layers. Crystalline SiC buffer layers with different thickness of 70, 100, and 130 nm were deposited on the Al{sub 2}O{sub 3} (0001) substrates by using a pulsed laser deposition method, and then MgB{sub 2} films were grown on the SiC buffer layer by using a hybrid physical-chemical vapor deposition technique. Transition temperature of MgB{sub 2} film decreased with increasing thickness of SiC buffer layer. However, the T{sub c} dropping went no farther than 100 nm-thick-SiC. This uncommon behavior of transition temperature is likely to be created from electron-phonon interaction in MgB{sub 2} films, which is believed to be related to the ordering of MgB{sub 2} atomic bonds, especially in the ordering of Mg–Mg bonds. Analysis from Mg K-edge EXAFS measurements showed interesting ordering behavior of MgB{sub 2} films. It is noticeable that the ordering of Mg–B bonds is found to decrease monotonically with the increase in SiC thickness of the MgB{sub 2} films, while the opposite happens with the ordering in Mg–Mg bonds. Based on these results, crystalline SiC buffer layers in MgB{sub 2} films seemingly have evident effects on the alteration of the local structure of the MgB{sub 2} film.

  10. Local atomic and electronic structures in ferromagnetic topological insulator Cr-doped (BixSb1-x) 2Te3 studied by XAFS and ab initio calculations

    NASA Astrophysics Data System (ADS)

    Liu, Zhen; Wei, Xinyuan; Wang, Jiajia; Pan, Hong; Ji, Fuhao; Ye, Mao; Yang, Zhongqin; Qiao, Shan

    2015-09-01

    The local atomic and electronic structures around the dopants in Cr-doped (BixSb1 -x )2Te3 are studied by x-ray absorption fine structure (XAFS) measurements and first-principles calculations. Both Cr and Bi are confirmed substituting Sb sites (CrSb and BiSb). The six nearest Te atoms around Cr move towards Cr and shorten the Cr-Te bond lengths to 2.76 Å and 2.77 Å for x =0.1 and x =0.2 , respectively. Importantly, we reveal the hybridization between the Sb/Te p states and Cr d states by the presence of a pre-edge peak at Cr K -absorption edge, which is also supported by our ab initio calculations. These findings provide important clues to understand the mechanism of ferromagnetic order in this system with quantum anomalous Hall effect.

  11. Fine structures at pore boundary

    NASA Astrophysics Data System (ADS)

    Bharti, L.; Quintero Noda, C.; Joshi, C.; Rakesh, S.; Pandya, A.

    2016-10-01

    We present high resolution observations of fine structures at pore boundaries. The inner part of granules towards umbra show dark striations which evolve into a filamentary structure with dark core and `Y' shape at the head of the filaments. These filaments migrate into the umbra similar to penumbral filaments. These filaments show higher temperature, lower magnetic field strength and more inclined field compared to the background umbra. The optical depth stratification of physical quantities suggests their similarity with penumbral filaments. However, line-of-sight velocity pattern is different from penumbral filaments where they show downflows in the deeper layers of the atmosphere while the higher layers show upflows. These observations show filamentation in a simple magnetic configuration.

  12. 3D WHOLE-PROMINENCE FINE STRUCTURE MODELING

    SciTech Connect

    Gunár, Stanislav; Mackay, Duncan H.

    2015-04-20

    We present the first 3D whole-prominence fine structure model. The model combines a 3D magnetic field configuration of an entire prominence obtained from nonlinear force-free field simulations, with a detailed description of the prominence plasma. The plasma is located in magnetic dips in hydrostatic equilibrium and is distributed along multiple fine structures within the 3D magnetic model. Through the use of a novel radiative transfer visualization technique for the Hα line such plasma-loaded magnetic field model produces synthetic images of the modeled prominence comparable with high-resolution observations. This allows us for the first time to use a single technique to consistently study, in both emission on the limb and absorption against the solar disk, the fine structures of prominences/filaments produced by a magnetic field model.

  13. Study of the Local Structure of GALLIUM(X)INDIUM(1 -X)ARSENIDE(Y)ANTIMONY(1-Y), a Quaternary Iii-V Semiconductor Alloy, Using the Extended X-Ray Absorption Fine Structure (exafs) Technique.

    NASA Astrophysics Data System (ADS)

    Islam, Shaheen Momtaz

    The technological importance of quaternary semiconductor alloys has stimulated considerable interest in the basic physics of these materials. Understanding of the local structure of these alloys is of fundamental importance. In this work, the extended x-ray absorption fine structure (EXAFS) technique has been used to investigate the atomic-scale structure of the III-V quaternary alloy series Ga_{rm x}In _{rm 1-x}As _{rm y}Sb_ {rm 1-y}, where Ga and In atoms occupy one sublattice and As and Sb atoms are distributed over the other sublattice. Two series of these alloys were studied with varying x (from 0.05 to 0.95) and keeping y constant (y = 0.05 or y = 0.10). The samples were polycrystalline powders of various compositions. EXAFS data were obtained at the As K-edge at room temperature for all these alloys. Our measurements reveal the number and types of atoms and the nearest neighbor distances about the average As atom. Our results show a consistent deviation from random site occupation in all these alloys, with Ga-As (and therefore In-Sb) pairs being clearly preferred over In-As and Ga -Sb pairs. This result is consistent with a theoretical model based on the pair approximation. From EXAFS measurements we also observe that the variation of Ga-As and In-As near-neighbor distances with composition is linear and that the bond-lengths remain nearly constant, closer to those in the pure binary compounds and varying only by 0.03 to 0.05A. On the other hand, the x-ray diffraction results show that the average cation -anion distance in the alloys changes by as much as 0.165A in accordance with Vegard's law. This linear variation of lattice constant with composition between the end members suggests that the atomic volume is conserved regardless of the details of the local distortions of lattice.

  14. Structural characterization of Bi{sub 2}Te{sub 3} and Sb{sub 2}Te{sub 3} as a function of temperature using neutron powder diffraction and extended X-ray absorption fine structure techniques

    SciTech Connect

    Mansour, A. N.; Wong-Ng, W.; Huang, Q.; Tang, W.; Thompson, A.; Sharp, J.

    2014-08-28

    The structure of Bi{sub 2}Te{sub 3} (Seebeck coefficient Standard Reference Material (SRM™ 3451)) and the related phase Sb{sub 2}Te{sub 3} have been characterized as a function of temperature using the neutron powder diffraction (NPD) and the extended X-ray absorption fine structure (EXAFS) techniques. The neutron structural studies were carried out from 20 K to 300 K for Bi{sub 2}Te{sub 3} and from 10 K to 298 K for Sb{sub 2}Te{sub 3}. The EXAFS technique for studying the local structure of the two compounds was conducted from 19 K to 298 K. Bi{sub 2}Te{sub 3} and Sb{sub 2}Te{sub 3} are isostructural, with a space group of R3{sup ¯}m. The structure consists of repeated quintuple layers of atoms, Te2-M-Te1-M-Te2 (where M = Bi or Sb) stacking along the c-axis of the unit cell. EXAFS was used to examine the bond distances and static and thermal disorders for the first three shells of Bi{sub 2}Te{sub 3} and Sb{sub 2}Te{sub 3} as a function of temperature. The temperature dependencies of thermal disorders were analyzed using the Debye and Einstein models for lattice vibrations. The Debye and Einstein temperatures for the first two shells of Bi{sub 2}Te{sub 3} are similar to those of Sb{sub 2}Te{sub 3} within the uncertainty in the data. However, the Debye and Einstein temperatures for the third shell of Bi-Bi are significantly lower than those of the third shell of Sb-Sb. The Einstein temperature for the third shell is consistent with a soft phonon mode in both Bi{sub 2}Te{sub 3} and Sb{sub 2}Te{sub 3}. The lower Einstein temperature of Bi-Bi relative to Sb-Sb is consistent with the lower value of thermal conductivity of Bi{sub 2}Te{sub 3} relative to Sb{sub 2}Te{sub 3}.

  15. Multiple Scattering Theory of XAFS

    NASA Astrophysics Data System (ADS)

    Zabinsky, Steven Ira

    A multiple scattering theory of XAFS for arbitrary materials with convergence to full multiple scattering calculations and to experiment is presented. It is shown that the multiple scattering expansion converges with a small number of paths. The theory is embodied in an efficient automated computer code that provides accurate theoretical multiple scattering standards for use in experimental analysis. The basis of this work is a new path enumeration and filtering algorithm. Paths are constructed for an arbitrary cluster in order of increasing path length. Filters based on the relative importance of the paths in the plane wave approximation and on the random phase approximation limit the number of paths so that all important paths with effective path length up to the mean free path length (between 10 and 20 A) can be considered. Quantitative expressions for path proliferation and relative path importance are presented. The calculations are compared with full multiple scattering calculations for Cu and Al. In the case of fcc Cu, the path filters reduce the number of paths from 60 billion to only 56 paths in a cluster of radius 12.5 A. These 56 paths are sufficient to converge the calculation to within the uncertainty inherent in the band structure calculation. Based on an analysis of these paths, a new hypothesis is presented for consideration: Single scattering, double scattering, and all orders of scattering that involve only forward or back scattering are sufficient to describe XAFS. Comparison with experiment in Cu, Pt and Ti demonstrate the accuracy of the calculation through the fourth shell. The correlated Debye model is used to determine Debye-Waller factors--the strengths and weaknesses of this approach are discussed. Preliminary results for calculations of the x -ray absorption near edge structure (XANES) have been done. The calculations compare well with Cu, Pt and Ti experiments. The white line in the Pt absorption edge is calculated correctly. There are

  16. Fine Structure of Plasmaspheric Hiss

    NASA Astrophysics Data System (ADS)

    Summers, D.; Omura, Y.; Nakamura, S.; Kletzing, C.

    2014-12-01

    Plasmaspheric hiss plays a key role in controlling the structure and dynamics of Earth's radiation belts.The quiet time slot region between the inner and outer belts can be explained as a steady-state balance between earthward radial diffusion and pitch-angle scattering loss of energetic electrons to the atmosphere induced by plasmaspheric hiss. Plasmaspheric hiss can also induce gradual precipitation loss of MeV electrons from the outer radiation belt. Plasmaspheric hiss has been widely regarded as a broadband,structureless,incoherent emission. Here, by examining burst-mode vector waveform data from the EMFISIS instrument on the Van Allen Probes mission,we show that plasmaspheric hiss is a coherent emission with complex fine structure. Specifically, plasmaspheric hiss appears as discrete rising tone and falling tone elements. By means of waveform analysis we identify typical amplitudes,phase profiles,and sweep rates of the rising and falling tone elements. The new observations reported here can be expected to fuel a re-examination of the properties of plasmaspheric hiss, including a further re-analysis of the generation mechanism for hiss.

  17. XAFS Data Interchange: A single spectrum XAFS data file format

    NASA Astrophysics Data System (ADS)

    Ravel, B.; Newville, M.

    2016-05-01

    We propose a standard data format for the interchange of XAFS data. The XAFS Data Interchange (XDI) standard is meant to encapsulate a single spectrum of XAFS along with relevant metadata. XDI is a text-based format with a simple syntax which clearly delineates metadata from the data table in a way that is easily interpreted both by a computer and by a human. The metadata header is inspired by the format of an electronic mail header, representing metadata names and values as an associative array. The data table is represented as columns of numbers. This format can be imported as is into most existing XAFS data analysis, spreadsheet, or data visualization programs. Along with a specification and a dictionary of metadata types, we provide an application-programming interface written in C and bindings for programming dynamic languages.

  18. XAFS Data Interchange: A single spectrum XAFS data file format.

    PubMed

    Ravel, B; Newville, M

    We propose a standard data format for the interchange of XAFS data. The XAFS Data Interchange (XDI) standard is meant to encapsulate a single spectrum of XAFS along with relevant metadata. XDI is a text-based format with a simple syntax which clearly delineates metadata from the data table in a way that is easily interpreted both by a computer and by a human. The metadata header is inspired by the format of an electronic mail header, representing metadata names and values as an associative array. The data table is represented as columns of numbers. This format can be imported as is into most existing XAFS data analysis, spreadsheet, or data visualization programs. Along with a specification and a dictionary of metadata types, we provide an application-programming interface written in C and bindings for programming dynamic languages.

  19. In situ XAFS of the Li{sub x}Ni{sub 0.8}Co{sub 0.2} cathode for lithium-ion batteries

    SciTech Connect

    Kropf, J.; Johnson, C. S.

    2000-01-17

    The layered LiNi{sub 0.8}Co{sub 0.2}O{sub 2} system is being considered as a new cathode material for the lithium-ion battery. Compared with LiCoO{sub 2}, the standard cathode formulation, it possesses improved electrochemical performance at a projected lower cost. In situ x-ray absorption fine-structure spectroscopy (XAFS) measurements were conducted on a cell cycled at a moderate rate and normal Li-ion operating voltages (3.0--4.1 V). The XAFS data collected at the Ni and Co edges approximately every 30 min. revealed details about the response of the cathode to Li insertion and extraction. These measurements on the Li{sub x}Ni{sub 0.8}Co{sub 0.2}O{sub 2} cathode (0.29 < x < 0.78) demonstrated the excellent reversibility of the cathode's short-range structure. However, the Co and Ni atoms behaved differently in response to Li insertion. This study corroborates previous work that explains the XAFS of the Ni atoms in terms of a Ni{sup 3+} Jahn-Teller ion. An analysis of the metal-metal distances suggests, contrary to a qualitative analysis of the x-ray absorption near-edge structure (XANES), that the Co{sup 3+} is oxidized to the maximum extent possible (within the Li content range of this experiment) at x = 0.47 {+-} 0.04, and further oxidation occurs at the Ni site.

  20. The O2-Evolving Complex of Photosystem II: Recent Insights from Quantum Mechanics/Molecular Mechanics (QM/MM), Extended X-ray Absorption Fine Structure (EXAFS), and Femtosecond X-ray Crystallography Data.

    PubMed

    Askerka, Mikhail; Brudvig, Gary W; Batista, Victor S

    2017-01-17

    Efficient photoelectrochemical water oxidation may open a way to produce energy from renewable solar power. In biology, generation of fuel due to water oxidation happens efficiently on an immense scale during the light reactions of photosynthesis. To oxidize water, photosynthetic organisms have evolved a highly conserved protein complex, Photosystem II. Within that complex, water oxidation happens at the CaMn4O5 inorganic catalytic cluster, the so-called oxygen-evolving complex (OEC), which cycles through storage "S" states as it accumulates oxidizing equivalents and produces molecular oxygen. In recent years, there has been significant progress in understanding the OEC as it evolves through the catalytic cycle. Studies have combined conventional and femtosecond X-ray crystallography with extended X-ray absorption fine structure (EXAFS) and quantum mechanics/molecular mechanics (QM/MM) methods and have addressed changes in protonation states of μ-oxo bridges and the coordination of substrate water through the analysis of ammonia binding as a chemical analog of water. These advances are thought to be critical to understanding the catalytic cycle since protonation states regulate the relative stability of different redox states and the geometry of the OEC. Therefore, establishing the mechanism for substrate water binding and the nature of protonation/redox state transitions in the OEC is essential for understanding the catalytic cycle of O2 evolution. The structure of the dark-stable S1 state has been a target for X-ray crystallography for the past 15 years. However, traditional X-ray crystallography has been hampered by radiation-induced reduction of the OEC. Very recently, a revolutionary X-ray free electron laser (XFEL) technique was applied to PSII to reveal atomic positions at 1.95 Å without radiation damage, which brought us closer than ever to establishing the ultimate structure of the OEC in the S1 state. However, the atom positions in this crystal

  1. Cosmological constant, fine structure constant and beyond

    NASA Astrophysics Data System (ADS)

    Wei, Hao; Zou, Xiao-Bo; Li, Hong-Yu; Xue, Dong-Ze

    2017-01-01

    In the present work, we consider the cosmological constant model Λ ∝ α ^{-6}, which is well motivated from three independent approaches. As is well known, the hint of varying fine structure constant α was found in 1998. If Λ ∝ α ^{-6} is right, it means that the cosmological constant Λ should also be varying. Here, we try to develop a suitable framework to model this varying cosmological constant Λ ∝ α ^{-6}, in which we view it from an interacting vacuum energy perspective. Then we consider the observational constraints on these models by using the 293 Δ α /α data from the absorption systems in the spectra of distant quasars. We find that the model parameters can be tightly constrained to the very narrow ranges of O(10^{-5}) typically. On the other hand, we can also view the varying cosmological constant model Λ ∝ α ^{-6} from another perspective, namely it can be equivalent to a model containing "dark energy" and "warm dark matter", but there is no interaction between them. We find that this is also fully consistent with the observational constraints on warm dark matter.

  2. Surface speciation of Cd(II) and Pb(II) on kaolinite by XAFS spectroscopy.

    PubMed

    Gräfe, Markus; Singh, Balwant; Balasubramanian, Mahalingam

    2007-11-01

    Little spectroscopic evidence exists in the literature describing the surface complexation of cadmium (Cd) and lead (Pb) on kaolinite, the dominant clay mineral present in highly weathered soils of tropical and humid climates. X-ray absorption fine structure (XAFS) spectroscopy data at the Cd K and Pb L(III) edges were collected on Cd- and Pb-sorbed kaolinite samples and compared to a suite of reference materials including Pb and Cd sorbed on amorphous (am-)gibbsite. Cadmium formed dominantly (>75%) outer sphere complexes on kaolinite and a small fraction of CdOHCl complexes. In contrast Cd adsorbed as an inner sphere complex on gibbsite, suggesting that the Si tetrahedral sheet hindered Cd sorption to the Al octahedral sheet on kaolinite. Lead formed polymeric complexes, which bonded to kaolinite via edge sharing with surface Al octahedra. Two distinct Pb-Al edge-sharing distances on am-gibbsite, as opposed to one on kaolinite, suggested a similar steric hindrance effect for the surface complexation of polymeric Pb complexes on kaolinite. The results of this study show that the Si tetrahedral sheet limited the surface complexation of Cd and Pb on kaolinite, elevating kaolinite's permanent negative charge properties in retaining these heavy metals at its surface.

  3. New XAFS spectroscopic investigations in the 1-2 keV region. Final report on LDRD program

    SciTech Connect

    Wong, J.; Froba, M.; Tamura, E.

    1996-03-01

    Until recently x-ray absorption fine structure (XAFS) measurements in the 1-2 keV region remained a challenging experimental task. This was primarily due to the lack of an adequate monochromator crystal that possessed both the required x-ray properties (large d-spacing, high resolution and reflectivity) and materials properties (ultra-high vacuum (UHV) capability, damage resistance in a synchrotron radiation beam, absence of constituent element absorption edges and stability, both thermal and mechanical). Traditionally, XAFS spectra in this photon energy range have been measured in a piece-wise fashion using a combination of monochromator crystals. Very recently, we have an experimental breakthrough in XAFS spectroscopy in this soft x-ray region. This energy region is of great importance for materials and basic research since the K-edges of Na (1070 eV), Mg (1303 eV), Al (1557 eV) and Si (1839 eV), the L-edges of some 4p elements from Ga to Sr and the M-edges of the rare-earth elements fall within this energy window of the electromagnetic spectrum. YB{sub 66}, a complex binary semiconducting yttrium boride having a cubic crystal structure with a lattice constant of 23.44 {angstrom} has been singled out as a candidate monochromator material for synchrotron radiation in the 1-2 keV region. There is no intrinsic absorption by the constituent elements in this region, which can adequately be dispersed by the (400) reflection having a 2d value of 11.76 {angstrom}. In terms of vacuum compatibility, resistance to radiation damage, thermal and mechanical stability, YB{sub 66} satisfies all the material requirements for use as a monochromator in a synchrotron beam. In the past few years, LLNL in collaboration with a number of other research institutes has pioneered the development of this unique man-made crystal for use as soft x-ray monochromator with synchrotron light sources for materials science studies. 23 refs., 4 figs.

  4. Ceria-based Catalysts for the Production of H2 Through the Water-gas-shift Reaction: Time-Resolved XRD and XAFS Studies

    SciTech Connect

    Wang,X.; Rodriguez, J.; Hanson, J.; Gamarra, D.; Marinez-Arias, A.; Fernandez-Garcia, M.

    2008-01-01

    Hydrogen is a potential alternate energy source for satisfying many of our energy needs. In this work, we studied H2 production from the water-gas-shift (WGS) reaction over Ce1-x Cu x O2 catalysts, prepared with a novel microemulsion method, using two synchrotron-based techniques: time-resolved X-ray diffraction (XRD) and X-ray absorption fine structure (XAFS). The results are compared with those reported for conventional CuO x /CeO2 and AuO x /CeO2 catalysts obtained through impregnation of ceria. For the fresh Ce1-x Cu x O2 catalysts, the results of XAFS measurements at the Cu K-edge indicate that Cu is in an oxidation state higher than in CuO. Nevertheless, under WGS reaction conditions the Ce1-x Cu x O2 catalysts undergo reduction and the active phase contains very small particles of metallic Cu and CeO2-x . Time-resolved XRD and XAFS results also indicate that Cud+ and Aud+ species present in fresh CuO x /CeO2 and AuO x /CeO2 catalysts do not survive above 200 C under the WGS conditions. In all these systems, the ceria lattice displayed a significant increase after exposure to CO and a decrease in H2O, indicating that CO reduced ceria while H2O oxidized it. Our data suggest that H2O dissociation occurred on the Ovacancy sites or the Cu-Ovacancy and Au-Ovacancy interfaces. The rate of H2 generation by a Ce0.95Cu0.05O2 catalyst was comparable to that of a 5 wt% CuO x /CeO2 catalyst and much bigger than those of pure ceria or CuO.

  5. Formation of layered single- and double-metal hydroxide precipitates at the mineral/water interface: A multiple-scattering XAFS analysis

    SciTech Connect

    Scheinost, A.C.; Sparks, D.L.

    2000-03-15

    Spectroscopic and microscopic studies have shown that Ni and Co sorption by clay minerals may proceed via formation of surface precipitates. Several studies employing X-ray absorption fine structure (XAFS) spectroscopy suggested the formation of turbostratic, a-type metal hydroxides, of layered double hydroxides (LDH) with Al-for-metal substitution, and of 1:1 or 2:1 phyllosilicates. Distinction of these phases is difficult because they have low crystallinity and/or a small mass compared to the sorbents, and because they have similar metal-metal distances in their hydroxide layers/sheets. Distinction of these phases is crucial, however, because they have substantially differing solubilities. In this paper the authors show that an XAFS beat pattern at about 8 {angstrom} {sup {minus}1} can be used as a fingerprint to unequivocally distinguish LDH from the {alpha}-type hydroxides and phyllosilicates. Full multiple-scattering simulations and experimental spectra of model compounds indicate that the beat pattern is due to focused multiple scattering at Me/Al ratios between 1 and 4(Me = Ni,Co). By applying the fingerprint method to new and to already published XAFS data on Ni and Co surface precipitates, the authors found that LDH preferentially forms in the presence of the Al-containing sorbents pyrophyllite, illite, kaolinite, gibbsite, and alumina above pH 7.0. However, {alpha}-type metal hydroxides form in the presence of the Al-free sorbents talc, silica, and rutile, and in the presence of the Al-containing clay minerals montmorillonite and vermiculite. The authors believe, that the high permanent charge of these latter minerals prevents or retards the release of Al. When Al is available, the formation of LDH seems to be thermodynamically and/or kinetically favored over the formation of {alpha}-type hydroxides.

  6. Fine structure of the exciton electroabsorption in semiconductor superlattices

    NASA Astrophysics Data System (ADS)

    Monozon, B. S.; Schmelcher, P.

    2017-02-01

    Wannier-Mott excitons in a semiconductor layered superlattice (SL) are investigated analytically for the case that the period of the superlattice is much smaller than the 2D exciton Bohr radius. Additionally we assume the presence of a longitudinal external static electric field directed parallel to the SL axis. The exciton states and the optical absorption coefficient are derived in the tight-binding and adiabatic approximations. Strong and weak electric fields providing spatially localized and extended electron and hole states, respectively, are studied. The dependencies of the exciton states and the exciton absorption spectrum on the SL parameters and the electric field strength are presented in an explicit form. We focus on the fine structure of the ground quasi-2D exciton level formed by the series of closely spaced energy levels adjacent from the high frequencies. These levels are related to the adiabatically slow relative exciton longitudinal motion governed by the potential formed by the in-plane exciton state. It is shown that the external electric fields compress the fine structure energy levels, decrease the intensities of the corresponding optical peaks and increase the exciton binding energy. A possible experimental study of the fine structure of the exciton electroabsorption is discussed.

  7. Identifying barriers to charge-carriers in the bulk and surface regions of Cu2ZnSnS4 nanocrystal films by x-ray absorption fine structures (XAFSs)

    NASA Astrophysics Data System (ADS)

    Turnbull, Matthew J.; Vaccarello, Daniel; Yiu, Yun Mui; Sham, Tsun-Kong; Ding, Zhifeng

    2016-11-01

    Solar cell performance is most affected by the quality of the light absorber layer. For thin-film devices, this becomes a two-fold problem of maintaining a low-cost design with well-ordered nanocrystal (NC) structure. The use of Cu2ZnSnS4 (CZTS) NCs as the light absorber films forms an ideal low-cost design, but the quaternary structure makes it difficult to maintain a well-ordered layer without the use of high-temperature treatments. There is little understanding of how CZTS NC structures affect the photoconversion efficiency, the charge-carriers, and therefore the performance of the device manufactured from it. To examine these relationships, the measured photoresponse from the photo-generation of charge-carrier electron-hole pairs was compared against the crystal structure, as short-range and long-range crystal orders for the films. The photoresponse simplifies the electronic properties into three basic steps that can be associated with changes in energy levels within the band structure. These changes result in the formation of barriers to charge-carrier flow. The extent of these barriers was determined using synchrotron-based X-ray absorbance fine structure to probe the individual metal centers in the film, and comparing these to molecular simulations of the ideal extended x-ray absorbance fine structure scattering. This allowed for the quantification of bond lengths, and thus an interpretation of the distortions in the crystal lattice. The various characteristics of the photoresponse were then correlated to the crystallographic order and used to gain physical insight into barriers to charge-carriers in the bulk and surface regions of CZTS films.

  8. Identifying barriers to charge-carriers in the bulk and surface regions of Cu2ZnSnS4 nanocrystal films by x-ray absorption fine structures (XAFSs).

    PubMed

    Turnbull, Matthew J; Vaccarello, Daniel; Yiu, Yun Mui; Sham, Tsun-Kong; Ding, Zhifeng

    2016-11-28

    Solar cell performance is most affected by the quality of the light absorber layer. For thin-film devices, this becomes a two-fold problem of maintaining a low-cost design with well-ordered nanocrystal (NC) structure. The use of Cu2ZnSnS4 (CZTS) NCs as the light absorber films forms an ideal low-cost design, but the quaternary structure makes it difficult to maintain a well-ordered layer without the use of high-temperature treatments. There is little understanding of how CZTS NC structures affect the photoconversion efficiency, the charge-carriers, and therefore the performance of the device manufactured from it. To examine these relationships, the measured photoresponse from the photo-generation of charge-carrier electron-hole pairs was compared against the crystal structure, as short-range and long-range crystal orders for the films. The photoresponse simplifies the electronic properties into three basic steps that can be associated with changes in energy levels within the band structure. These changes result in the formation of barriers to charge-carrier flow. The extent of these barriers was determined using synchrotron-based X-ray absorbance fine structure to probe the individual metal centers in the film, and comparing these to molecular simulations of the ideal extended x-ray absorbance fine structure scattering. This allowed for the quantification of bond lengths, and thus an interpretation of the distortions in the crystal lattice. The various characteristics of the photoresponse were then correlated to the crystallographic order and used to gain physical insight into barriers to charge-carriers in the bulk and surface regions of CZTS films.

  9. XAFS study of copper and silver nanoparticles in glazes of medieval middle-east lustreware (10th-13th century)

    NASA Astrophysics Data System (ADS)

    Padovani, S.; Puzzovio, D.; Sada, C.; Mazzoldi, P.; Borgia, I.; Sgamellotti, A.; Brunetti, B. G.; Cartechini, L.; D'Acapito, F.; Maurizio, C.; Shokoui, F.; Oliaiy, P.; Rahighi, J.; Lamehi-Rachti, M.; Pantos, E.

    2006-06-01

    It has recently been shown that lustre decoration of medieval and Renaissance pottery consists of silver and copper nanoparticles dispersed in the glassy matrix of the ceramic glaze. Here the findings of an X-ray absorption fine structure (XAFS) study on lustred glazes of shards belonging to 10th and 13rd century pottery from the National Museum of Iran are reported. Absorption spectra in the visible range have been also measured in order to investigate the relations between colour and glaze composition. Gold colour is mainly due to Ag nanoparticles, though Ag+, Cu+ and Cu2+ ions can be also dispersed within the glassy matrix, with different ratios. Red colour is mainly due to Cu nanoparticles, although some Ag nanoparticles, Ag+ and Cu+ ions can be present. The achievement of metallic Cu and the absence of Cu2+ indicate a higher reduction of copper in red lustre. These findings are in substantial agreement with previous results on Italian Renaissance pottery. In spite of the large heterogeneity of cases, the presence of copper and silver ions in the glaze confirms that lustre formation is mediated by a copper- and silver-alkali ion exchange, followed by nucleation and growth of metal nanoparticles.

  10. Characterization of the Cu(Π) and Zn(Π) binding to the Amyloid-β short peptides by both the Extended X-ray Absorption Fine Structure and the Synchrotron Radiation Circular Dichroism spectroscopy

    NASA Astrophysics Data System (ADS)

    Zhang, Zhiyin; Sun, Shuaishuai; Xu, Jianhua; Zhang, Jing; Huang, Yan; Zhang, Bingbing; Tao, Ye

    2013-04-01

    Alzheimer's disease (AD) is a progressive and devastating neurodegenerative pathology, clinically characterized by dementia, cognitive impairment, personality disorders and memory loss. It is generally accepted that, misfolding of Aβ peptides is the key element in pathogenesis and the secondary structure of Aβ can be changed to major β-strand with reasons unknown yet. Many studies have shown that the misfolding may be linked with some biometals, mainly copper and zinc ions. To characterize interactions of Aβ and metal ions, we utilized both the extended X-ray fine structure spectroscopy (EXAFS) and the synchrotron radiation circular dichroism spectroscopy (SRCD). Aβ (13-22), Aβ (13-21), Aβ (E22G) and Aβ(HH-AA) were selected to study the mechanism of copper and zinc binding to Aβ. We found that Cu interaction with H13 and H14 residues led to the disappearance of the PPΠ, while the Cu binding E22 residue caused a remarkable conformation change to β-sheet enrichment. The Zn ion, in contrast, made little effect on the conformation and it coordinated to only one histidine (H residue) or not.

  11. A Geometric and Electrostatic Study of the [4Fe-4S] Cluster of Adenosine-5´-Phosphosulfate Reductase from Broken Symmetry Density Functional Calculations and Extended X-ray Absorption Fine Structure Spectroscopy

    PubMed Central

    Bhave, Devayani P.; Han, Wen-Ge; Pazicni, Samuel; Penner-Hahn, James E.; Carroll, Kate S.; Noodleman, Louis

    2011-01-01

    Adenosine-5’-phosphosulfate reductase (APSR) is an iron-sulfur protein that catalyses the reduction of adenosine-5’-phosphosulfate (APS) to sulfite. APSR coordinates to a [4Fe-4S] cluster via a conserved CC-X~80-CXXC motif and the cluster is essential for catalysis. Despite extensive functional, structural and spectroscopic studies, the exact role of the iron-sulfur cluster in APS reduction remains unknown. To gain an understanding into the role of the cluster, density functional theory (DFT) analysis and extended X-ray fine structure spectroscopy (EXAFS) have been performed to reveal insights into the coordination, geometry and electrostatics of the [4Fe-4S] cluster. XANES data confirms that the cluster is in the [4Fe-4S]2+ state in both native and substrate-bound APSR while EXAFS data recorded at ~0.1 Å resolution indicates that there is no significant change in the structure of the [4Fe-4S] cluster between the native and substrate-bound forms of the protein. On the other hand, DFT calculations provide an insight into the subtle differences between the geometry of the cluster in the native and APS-bound forms of APSR. A comparison between models with and without the tandem cysteine pair coordination of the cluster suggests a role for the unique coordination in facilitating a compact geometric structure and ‘fine-tuning’ the electronic structure to prevent reduction of the cluster. Further, calculations using models in which residue Lys144 is mutated to Ala confirm the finding that Lys144 serves as a crucial link in the interactions involving the [4Fe-4S] cluster and APS. PMID:21678934

  12. THE FINE STRUCTURE OF DIPLOCOCCUS PNEUMONIAE

    PubMed Central

    Tomasz, Alexander; Jamieson, James D.; Ottolenghi, Elena

    1964-01-01

    The fine structure of an unencapsulated strain of Diplococcus pneumoniae is described. A striking feature of these bacteria is an intracytoplasmic membrane system which appears to be an extension of septa of dividing bacteria. The possible function of these structures and their relationship to the plasma membrane and other types of intracytoplasmic membranes found in pneumococcus is discussed. PMID:14203390

  13. THE FINE STRUCTURE OF THE RAT CEREBELLUM

    PubMed Central

    Herndon, Robert M.

    1964-01-01

    This paper describes the fine structure of the granule cells, stellate neurons, astrocytes, Bergmann glia, oligodendrocytes, and microglia of the rat cerebellum after fixation by perfusion with buffered 1 per cent osmium tetroxide. Criteria are given for differentiating the various cell types, and the findings are correlated with previous light microscope and electron microscope studies of the cerebellum. PMID:14222815

  14. Extended electron energy loss fine structure simulation of the local boron environment in sodium aluminoborosilicate glasses containing gadolinium

    SciTech Connect

    Qian, Morris; Li, Hong; Li, Liyu ); Strachan, Denis M. )

    2003-10-15

    Gadolinium can be dissolved in sodium-alumino-borosilicate glasses up to 47 wt% in a baseline borosilicate glass (mol%) 20 B2O3, 5 Al2O3, 60 SiO2,and 20 Na2O. Understanding of Gd dissolution in borosilicate melts is important in glass formulation optimization. Electron energy loss fine structure (ELFS) spectroscopy is chosen, which provides well resolved local atomic structure information for both amorphous and crystalline materials with high sensitivity to low Z elements such as Al, B, Na, O, and Si where the x-ray absorption fine structure (XAFS) technique faces experimental difficulty. In this study, we report our results of boron K-edge ELFS study. Two borosilicate glass samples with 30 and 47 mass% Gd2O3, B20Gd30 and B20Gd47were chosen for B K-edge ELFS study. EEL spectra were acquired on a Philips 430 TEM equipped with Gatan PEELS system 666 and EL/P 2.1 software with Custom function AcqLong. The ELFS data analysis was performed using UWELFS, UWXAFS and FEFF software. From our Gd solubility study, the local structure of Gd in the borate environment possibly resembles double chain structure found in crystalline Gd(BO2)3 as proposed by Chakraborty et al. The B/Gd ratio's in both glasses are smaller then 3, which means the excess Gd atoms in the Si-sites would be 17 and 60 mol% of the total Gd atoms, respectively according to the model, yet the local environment of borate sites saturated with Gd should be remained. To verity above hypothesis, the double chain structure model was applied to fit boron K-edge. The model was shown to well fit experimental boron K-edge EELS spectra for both glasses with some degree of distance distortion which is understandable in amorphous structure. Therefore, it is very likely that Gd stabilized in borate sites has a local structure resembling the double chain Gd(BO2)3 structure as proposed by our solubility study and literature.

  15. MAX (Multiplatform Applications for XAFS) New Features

    NASA Astrophysics Data System (ADS)

    Michalowicz, A.; Moscovici, J.; Muller-Bouvet, D.; Provost, K.

    2013-04-01

    MAX is a complete suite of XAFS data analysis computer programs, written with the cross-platform object scripting langage Livecode [1] working on Windows, MacOSX and Linux systems, freely available on our web site since 2007 [2]. The 2009 version presentation is available in the XAFS14 conference proceedings [3] and regularly updated on the www.xafs.org web site [4].

  16. High-resolution Measurement of Contact Ion-pair Structures in Aqueous RbCl Solutions from the Simultaneous Corefinement of their Rb and Cl K-edge XAFS and XRD Spectra

    SciTech Connect

    Pham, Van-Thai; Fulton, John L.

    2016-06-21

    In concentrated solutions of aqueous RbCl, all of the Rb+ and Cl- ions exist as contact ion pairs. This full structural assessment is derived from the refinement of three independent experimental measurements: the Rb and Cl K-edge x-ray absorption fine structure (XAFS) and the x-ray diffraction spectra (XRD). This simultaneous refinement of the XAFS and XRD data provides high accuracy since each method probes the structure of different local regions about the ions with high sensitivity. At high RbCl concentration (6 m (mol/kg )) the solution is dominated by Rb+ - Cl- contact ion pairs yielding an average of 1.5 pairs at an Rb-Cl distance of 3.24 Å. Upon formation of these ion pairs, approximately 1.1 waters molecules are displaced from the Rb+ and 1.4 water molecules from Cl-. The hydration shells about both the cation and anion are also determined. These results greatly improve the understanding of monovalent ions and provide a basis for testing the Rb+-Cl- interaction potentials used in molecular dynamics (MD) simulation. This research was supported by the US Department of Energy, Office of Science, Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences, and Biosciences.

  17. Origin of Photoluminescence and XAFS Study of (ZnS)1-x(AgInS2)x Nanocrystals.

    PubMed

    Rao, M Jagadeeswara; Shibata, Tomohiro; Chattopadhyay, Soma; Nag, Angshuman

    2014-01-02

    Donor-Acceptor transition was previously suggested as a mechanism for luminescence in (ZnS)1-x(AgInS2)x nanocrystals. Here we show the participation of delocalized valence/conduction band in the luminescence. Two emission pathways are observed: Path-1 involves transition between a delocalized state and a localized state exhibiting higher energy and shorter lifetime (∼25 ns) and Path-2 (donor-acceptor) involves two localized defect states exhibiting lower emission energy and longer lifetime (>185 ns). Surprisingly, Path-1 dominates (82% for x = 0.33) for nanocrystals with lower x, in sharp difference with prior assignment. Luminescence peak blue shifts systematically by 0.57 eV with decreasing x because of this large contribution from Path-1. X-ray absorption fine structure (XAFS) study of (ZnS)1-x(AgInS2)x nanocrystals shows larger AgS4 tetrahedra compared with InS4 tetrahedra with Ag-S and In-S bond lengths 2.52 and 2.45 Å respectively, whereas Zn-S bond length is 2.33 Å along with the absence of second nearest-neighbor Zn-S-metal correlation.

  18. Extended X-ray absorption fine structure studies of Zn/sub 2/Fe/sub 2/ hybrid hemoglobins: absence of heme bond length changes in half-ligated species

    SciTech Connect

    Simolo, K.; Korszun, Z.R.; Stucky, G.; Moffat, K.; McLendon, G.

    1986-07-01

    Metal hybrid hemoglobins, in which Zn(II) replaces Fe(II), have been structurally characterized by extended X-ray absorption structure (EAFS) studies. Since Zn and Fe have very different K absorption edge energies, the structures of the ligated (Fe) and unligated (Zn) sites could be examined independently within a single molecule that mimics an intermediate ligation state. The observed EXAFS spectra and associated structural parameters are compared among the ligand free (..cap alpha..Zn)/sub 2/(..beta..Zn)/sub 2/, half-ligated (..cap alpha..FeCO)/sub 2/(..beta..Zn)/sub 2/ and (..cap alpha..Zn)/sub 2/(..beta..FeCO)/sub 2/, and fully ligated (..cap alpha..FeCO)/sub 2/(..beta..FeCO)/sub 2/ systems.

  19. THE FINE STRUCTURE OF THE PURKINJE CELL

    PubMed Central

    Herndon, Robert M.

    1963-01-01

    This paper describes the fine structure of the Purkinje cell of the rat cerebellum after fixation by perfusion with 1 per cent buffered osmium tetroxide. Structures described include a large Golgi apparatus, abundant Nissl substance, mitochondria, multivesicular bodies, osmiophilic granules, axodendritic and axosomatic synapses, the nucleus, the nucleolus, and the nucleolar body. A new and possibly unique relationship between mitochondria and subsurface cisterns is described. Possible functional correlations are discussed. PMID:13953993

  20. Theoretical analysis of x-ray-absorption near-edge fine structure at the O and metal K edges of LaFeO{sub 3} and LaCoO{sub 3}

    SciTech Connect

    Wu, Z.Y.; Pedio, M.; Cimino, R.; Mobilio, S. |; Barman, S.R. |; Maiti, K.; Sarma, D.D. |

    1997-07-01

    We present experimental x-ray-absorption spectra at the oxygen and 3d transition-metal K edges of LaFeO{sub 3} and LaCoO{sub 3}. We interpret the experimental results in terms of detailed theoretical calculations based on multiple-scattering theory. Along with providing an understanding of the origin of various experimental features, we investigate the effects of structural distortions and the core-hole potential in determining the experimental spectral shape. The results indicate that the core-hole potential as well as many-body effects within the valence electrons do not have any strong effect on the spectra suggesting that the spectral features can be directly interpreted in terms of the electronic structure of such compounds. {copyright} {ital 1997} {ital The American Physical Society}

  1. Preliminary optical design of a varied line-space spectrograph for the multi-channel detection of near-edge X-ray absorption fine structure (NEXAFS) spectra in the 280-550 eV energy range

    SciTech Connect

    Wheeler, B.S.; McKinney, W.R.; Hussain, Z.; Padmore, H.

    1996-07-01

    The optical design of a varied line-space spectrograph for the multi-channel recording of NEXAFS spectra in a single {open_quotes}snapshot{close_quotes} is proposed. The spectrograph is to be used with a bending magnet source on beamline 7.3.2 at the Advanced Light Source (ALS). Approximately 20 volts of spectra are simultaneously imaged across a small square of material sample at each respective K absorption edge of carbon, nitrogen, and oxygen. Photoelectrons emitted from the material sample will be collected by an electron imaging microscope, the view field of which determines the sampling size. The sample also forms the exit slit of the optical system. This dispersive method of NEXAFS data acquisition is three to four orders of magnitude faster than the conventional method of taking data point-to-point using scanning of the grating. The proposed design is presented along with the design method and supporting SHADOW raytrace analysis.

  2. High pressure experiments at the XAFS Beamline, INDUS-2

    NASA Astrophysics Data System (ADS)

    Ramanan, Nitya; Lahiri, Debdutta; Garg, Nandini; Bhattacharyya, D.; Jha, S. N.; Sahoo, N. K.; Sharma, Surinder M.

    2012-07-01

    The dispersive XAFS beamline BL-08 at the INDUS-2 synchrotron radiation source, RRCAT, Indore uses a bent Si (111) crystal as dispersive-cum-focusing element and a position sensitive CCD detector to enable instantaneous measurement of the whole XAFS spectrum around the absorption edge of interest. This beamline is ideal for characterisation of materials under high pressure using Diamond Anvil Cell with ~50 μm spot size. For this setup, the theoretically determined spot size (Horizontal × Vertical) varies between 17 × 137 μm and 37 × 142 μm for the x-ray energy range 5 keV-20 keV. To reduce the vertical spot size to <50 μm, we have designed an additional focusing mirror between the polychromator and sample position. The mirror, procured from SESO (France), will be installed shortly. Meanwhile, we have developed a dummy mirror bender setup at CDM (B ARC) and have carried out feasibility tests to confirm reduction in spot size using the same. We have also conducted preliminary XAFS experiments (at BL-08) on SrRuO3 at ~16 keV, under ambient conditions and inside diamond anvil cell, in order to assess the signal intensity and quality. We have obtained reasonably good signal.

  3. Universal fine structure of nematic hedgehogs

    NASA Astrophysics Data System (ADS)

    Kralj, Samo; Virga, Epifanio G.

    2001-02-01

    We study in a Landau-de Gennes approach the biaxial structure of a nematic point defect with topological charge M = + 1. We aim to illuminate the role of the confining boundaries in determining the fine structure of the defect. We show that there are different regimes associated with different values of the ratio between the typical size R of the region in space occupied by the material and the biaxial correlation length ξb. For R/ξb>20 the core structure is already qualitatively universal, that is, independent of the confining geometry, while also for R/ξb>200 any quantitative difference is unlikely to be detected.

  4. Adding diffuse reflectance infrared Fourier transform spectroscopy capability to extended x-ray-absorption fine structure in a new cell to study solid catalysts in combination with a modulation approach

    NASA Astrophysics Data System (ADS)

    Chiarello, Gian Luca; Nachtegaal, Maarten; Marchionni, Valentina; Quaroni, Luca; Ferri, Davide

    2014-07-01

    We describe a novel cell used to combine in situ transmission X-ray absorption spectroscopy (XAS) with diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) in a single experiment. The novelty of the cell design compared to current examples is that both radiations are passed through an X-ray and IR transparent window in direct contact with the sample. This innovative geometry also offers a wide surface for IR collection. In order to avoid interference from the crystalline IR transparent materials (e.g., CaF2, MgF2, diamond) a 500 μm carbon filled hole is laser drilled in the center of a CaF2 window. The cell is designed to represent a plug flow reactor, has reduced dead volume in order to allow for fast exchange of gases and is therefore suitable for experiments under fast transients, e.g., according to the concentration modulation approach. High quality time-resolved XAS and DRIFTS data of a 2 wt.% Pt/Al2O3 catalyst are obtained in concentration modulation experiments where CO (or H2) pulses are alternated to O2 pulses at 150 °C. We show that additional information can be obtained on the Pt redox dynamic under working conditions thanks to the improved sensitivity given by the modulation approach followed by Phase Sensitive Detection (PSD) analysis. It is anticipated that the design of the novel cell is likely suitable for a number of other in situ spectroscopic and diffraction methods.

  5. Angle-resolved photoemission extended fine structure

    SciTech Connect

    Barton, J.J.

    1985-03-01

    Measurements of the Angle-Resolved Photoemission Extended Fine Structure (ARPEFS) from the S(1s) core level of a c(2 x 2)S/Ni(001) are analyzed to determine the spacing between the S overlayer and the first and second Ni layers. ARPEFS is a type of photoelectron diffraction measurement in which the photoelectron kinetic energy is swept typically from 100 to 600 eV. By using this wide range of intermediate energies we add high precision and theoretical simplification to the advantages of the photoelectron diffraction technique for determining surface structures. We report developments in the theory of photoelectron scattering in the intermediate energy range, measurement of the experimental photoemission spectra, their reduction to ARPEFS, and the surface structure determination from the ARPEFS by combined Fourier and multiple-scattering analyses. 202 refs., 67 figs., 2 tabs.

  6. Solar Prominence Fine Structure and Dynamics

    NASA Astrophysics Data System (ADS)

    Berger, Thomas

    2014-01-01

    We review recent observational and theoretical results on the fine structure and dynamics of solar prominences, beginning with an overview of prominence classifications, the proposal of possible new ``funnel prominence'' classification, and a discussion of the recent ``solar tornado'' findings. We then focus on quiescent prominences to review formation, down-flow dynamics, and the ``prominence bubble'' phenomena. We show new observations of the prominence bubble Rayleigh-Taylor instability triggered by a Kelvin-Helmholtz shear flow instability occurring along the bubble boundary. Finally we review recent studies on plasma composition of bubbles, emphasizing that differential emission measure (DEM) analysis offers a more quantitative analysis than photometric comparisons. In conclusion, we discuss the relation of prominences to coronal magnetic flux ropes, proposing that prominences can be understood as partially ionized condensations of plasma forming the return flow of a general magneto-thermal convection in the corona.

  7. Revisit to diffraction anomalous fine structure

    PubMed Central

    Kawaguchi, T.; Fukuda, K.; Tokuda, K.; Shimada, K.; Ichitsubo, T.; Oishi, M.; Mizuki, J.; Matsubara, E.

    2014-01-01

    The diffraction anomalous fine structure (DAFS) method that is a spectroscopic analysis combined with resonant X-ray diffraction enables the determination of the valence state and local structure of a selected element at a specific crystalline site and/or phase. This method has been improved by using a polycrystalline sample, channel-cut monochromator optics with an undulator synchrotron radiation source, an area detector and direct determination of resonant terms with a logarithmic dispersion relation. This study makes the DAFS method more convenient and saves a large amount of measurement time in comparison with the conventional DAFS method with a single crystal. The improved DAFS method has been applied to some model samples, Ni foil and Fe3O4 powder, to demonstrate the validity of the measurement and the analysis of the present DAFS method. PMID:25343791

  8. Substitution behavior of x(Na0.5K0.5)NbO3-(1 - x)BaTiO3 ceramics for multilayer ceramic capacitors by a near edge x-ray absorption fine structure analysis

    NASA Astrophysics Data System (ADS)

    Ha, Jooyeon; Ryu, Jiseung; Lee, Heesoo

    2014-06-01

    The doping effect of (Na0.5K0.5)NbO3 (NKN) as alternatives for rare-earth elements on the electrical properties of BaTiO3 has been investigated, in terms of their substitution behavior. The dielectric constant of a specimen with x = 0.05 was about 79% higher than that of pure BaTiO3, and the temperature coefficient of capacitance was satisfied by the X7R specification. The specimen with x = 0.05 showed the lowest tetragonality among the four compositions and had a fine grain size of <2 μm. Although the addition of NKN decreased the specimen's tetragonality, the electrical properties were enhanced by the formation of defect dipoles and conduction electrons, which resulted from an acceptor and donor substitution behavior. Through O K-edge near edge x-ray absorption fine structure spectroscopy, the practical substitution behavior was defined by the change in Ti 3d orbital states. The energy separation of the Ti 3d orbitals was more apparent with the specimen of x = 0.05, which is related to the donor level from the donor substitution of Nb5+ ion for Ti-sites. Therefore, the simultaneous substitution of Na+/K+ and Nb5+ ions into BaTiO3 can improve dielectric properties, based on the charge-transfer process.

  9. The fine structure of developing elastic cartilage.

    PubMed Central

    Cox, R W; Peacock, M A

    1977-01-01

    The fine structure of the elastic cartilage of the pinna has been examined in young rabbits aged from 1 day to 1108 days. Changes associated with growth and development are related not only to age but also to the actual situation in the pinna. In the midline, progressive changes are seen from the tip to the base. The changes in the chondroblasts with time are compared with those described in hyaline cartilage. Structures occur that, except for the presence of crystals, are apparently morphologically identical with the matrix vesicles of calcifying cartilage. These matrix vesicles, however, become very prominent with age, and aggregations of them appear to be released into the intercellular tissue from vacuoles at the periphery of the chondroblasts. There is no obvious association with calcification. Occasional single cilia, desmosomes and giant mitochondria are seen. Elastica is present at birth, and eventually every cell is separated from its neighbours by a partial investment of elastica. The quantity of matrix seems to increase with time, and with distance from the tip of the ear. This is accompanied by a marked increase in cell size with time. Images Fig. 1 Fig. 2 Fig. 3 Fig. 4 Fig. 5 Fig. 6 Fig. 7 Fig. 8 PMID:870470

  10. Beta environmental fine structure characterization of defects

    NASA Astrophysics Data System (ADS)

    Benedek, G.; Fiorini, E.; Giuliani, A.; Milani, P.; Monfardini, A.; Nucciotti, A.; Prandoni, M. L.; Sancrotti, M.

    1999-04-01

    The fine structure of beta emission (BEFS) due to the interference with the scattered waves from neighboring atoms, analogous to EXAFS, is known to produce oscillations in the Kurie plot. Here we suggest the use of BEFS for characterizing the lattice environment of β-emitting defects located at a distance from the crystal surface not exceeding the mean free path of β-electrons. Examples of defective structures in semiconductors whose atomic arrangement could be conveniently studied with BEFS are tritium-passivated dangling bonds, β-radioactive ions implanted in the crystal lattice or segregated at extended defects such as dislocations, grain boundaries or radiation damage. Also 14C-doped diamond-like materials and other exotic carbon forms, as well as the atomic environment of ions in metal alloys could be good candidate for BEFS. In this work we have calculated the fractional BEFS modulation for 187Re in its ordinary hcp crystal lattice for which experimental data by Cosulich et al. are available. The good correspondence between theory and experiment permits to conclude that BEFS experiments at low temperature are accessible to the present bolometric detection techniques and can provide an expedient method, as compared to EXAFS, for an accurate structural assessment of extended defects in solids.

  11. Molecular Eigensolution Symmetry Analysis and Fine Structure

    PubMed Central

    Harter, William G.; Mitchell, Justin C.

    2013-01-01

    Spectra of high-symmetry molecules contain fine and superfine level cluster structure related to J-tunneling between hills and valleys on rovibronic energy surfaces (RES). Such graphic visualizations help disentangle multi-level dynamics, selection rules, and state mixing effects including widespread violation of nuclear spin symmetry species. A review of RES analysis compares it to that of potential energy surfaces (PES) used in Born–Oppenheimer approximations. Both take advantage of adiabatic coupling in order to visualize Hamiltonian eigensolutions. RES of symmetric and D2 asymmetric top rank-2-tensor Hamiltonians are compared with Oh spherical top rank-4-tensor fine-structure clusters of 6-fold and 8-fold tunneling multiplets. Then extreme 12-fold and 24-fold multiplets are analyzed by RES plots of higher rank tensor Hamiltonians. Such extreme clustering is rare in fundamental bands but prevalent in hot bands, and analysis of its superfine structure requires more efficient labeling and a more powerful group theory. This is introduced using elementary examples involving two groups of order-6 (C6 and D3~C3v), then applied to families of Oh clusters in SF6 spectra and to extreme clusters. PMID:23344041

  12. Internal Fine Structure of Ellerman Bombs

    NASA Astrophysics Data System (ADS)

    Hashimoto, Yuki; Kitai, Reizaburo; Ichimoto, Kiyoshi; Ueno, Satoru; Nagata, Shin'ichi; Ishii, Takako T.; Hagino, Masaoki; Komori, Hiroyuki; Nishida, Keisuke; Matsumoto, Takuma; Otsuji, Kenichi; Nakamura, Tahei; Kawate, Tomoko; Watanabe, Hiroko; Shibata, Kazunari

    2010-08-01

    We conducted coordinated observations of Ellerman bombs (EBs) between Hinode Satellite and Hida Observatory (HOP12). CaII H broad-band filter images of NOAA 10966 on 2007 August 9 and 10 were obtained with the Solar Optical Telescope (SOT) aboard the Hinode Satellite, and many bright points were observed. We identified a total of 4 bright points as EBs, and studied the temporal variation of their morphological fine structures and spectroscopic characteristics. With high-resolution CaII H images of SOT, we found that the EBs, thus far thought of as single bright features, are composed of a few of fine subcomponents. Also, by using Stokes I/V filtergrams with Hinode/SOT, and CaII H spectroheliograms with Hida/Domeless Solar Telescope (DST), our observation showed: (1) The mean duration, the mean width, the mean length, and the mean aspect ratio of the subcomponents were 390 s, 170 km, 450 km, and 2.7, respectively. (2) Subcomponents started to appear on the magnetic neutral lines, and extended their lengths from the original locations. (3) When the CaII H line of EBs showed the characteristic blue asymmetry, they are associated with the appearance or re-brightening of subcomponents. Summarizing our results, we obtained an observational view that elementary magnetic reconnections take place one by one successively and intermittently in EBs, and that their manifestation is the fine subcomponents of the EB phenomena.

  13. Terahertz Fine Structure Lines toward NGC 2024

    NASA Astrophysics Data System (ADS)

    Graf, U. U.; Simon, R.; Stutzki, J.; Güsten, R.

    2016-05-01

    We present 1.9 THz [Cii] and 4.7 THz [Oi] measurements of the star forming region NGC 2024 observed with GREAT on SOFIA. Velocity resolved spectroscopy reveals the strong foreground absorption, which conceals most of the intrinsic line brightness of the dense PDR region. Modelling of the line shapes allows disentangling the foreground absorption from the strong background emission.

  14. Structural characterization of CO-inhibited Mo-nitrogenase by combined application of nuclear resonance vibrational spectroscopy, extended X-ray absorption fine structure, and density functional theory: new insights into the effects of CO binding and the role of the interstitial atom.

    PubMed

    Scott, Aubrey D; Pelmenschikov, Vladimir; Guo, Yisong; Yan, Lifen; Wang, Hongxin; George, Simon J; Dapper, Christie H; Newton, William E; Yoda, Yoshitaka; Tanaka, Yoshihito; Cramer, Stephen P

    2014-11-12

    The properties of CO-inhibited Azotobacter vinelandii (Av) Mo-nitrogenase (N2ase) have been examined by the combined application of nuclear resonance vibrational spectroscopy (NRVS), extended X-ray absorption fine structure (EXAFS), and density functional theory (DFT). Dramatic changes in the NRVS are seen under high-CO conditions, especially in a 188 cm(-1) mode associated with symmetric breathing of the central cage of the FeMo-cofactor. Similar changes are reproduced with the α-H195Q N2ase variant. In the frequency region above 450 cm(-1), additional features are seen that are assigned to Fe-CO bending and stretching modes (confirmed by (13)CO isotope shifts). The EXAFS for wild-type N2ase shows evidence for a significant cluster distortion under high-CO conditions, most dramatically in the splitting of the interaction between Mo and the shell of Fe atoms originally at 5.08 Å in the resting enzyme. A DFT model with both a terminal -CO and a partially reduced -CHO ligand bound to adjacent Fe sites is consistent with both earlier FT-IR experiments, and the present EXAFS and NRVS observations for the wild-type enzyme. Another DFT model with two terminal CO ligands on the adjacent Fe atoms yields Fe-CO bands consistent with the α-H195Q variant NRVS. The calculations also shed light on the vibrational "shake" modes of the interstitial atom inside the central cage, and their interaction with the Fe-CO modes. Implications for the CO and N2 reactivity of N2ase are discussed.

  15. Fine Structure and Function in Stentor polymorphus

    PubMed Central

    Randall, J. T.; Jackson, Sylvia Fitton

    1958-01-01

    The fine structure of the ciliate Stentor has been studied by means of the electron microscope and the results have been correlated with observations made on the living organism by means of light microscopy; special reference has been made to structural features which may be responsible for contraction and extension in Stentor. Descriptions have been given of the structure of the macronucleus, the vacuolated cytoplasm, mitochondria and the pellicle; a detailed study has also been made of the adoral membranelles. About 250 membranelles encircle the peristomal cap and each is composed of 3 rows of cilia, with 20 to 25 cilia in each row; a fibrillar root system connected with the membranelles depends into the endoplasm for about 20 µ and each is essentially in the shape of a fan, the terminal ends of each root bifurcating to connect to neighbouring roots. The membranelles thus form a cohesive unit and this morphological arrangement may have a bearing on the motion and coordination of the whole system. Two structural features extending throughout the length of the animal have been identified per cortical stripe in the body wall of Stentor; first, km fibres lying just beneath the pellicle are composed of stacks of fibrillar sheets and are identical with the birefringent fibres observed in the living animal. The individual fibrils of the sheets are in turn connected to the kinetosomes of the body cilia; thus the km fibres are homologous to kinetodesmata. Secondly, M bands lie beneath the km fibres and form an interconnected system in contact with the surrounding vacuolated cytoplasm; the thickness of the M bands is greatest at the base of a contracted animal. The contractile and extensile properties of these organelles have been discussed in the light of experimental results and theoretical considerations. PMID:13610947

  16. Fine structure and function in Stentor polymorphous.

    PubMed

    RANDALL, J T; JACKSON, S F

    1958-11-25

    The fine structure of the ciliate Stentor has been studied by means of the electron microscope and the results have been correlated with observations made on the living organism by means of light microscopy; special reference has been made to structural features which may be responsible for contraction and extension in Stentor. Descriptions have been given of the structure of the macronucleus, the vacuolated cytoplasm, mitochondria and the pellicle; a detailed study has also been made of the adoral membranelles. About 250 membranelles encircle the peristomal cap and each is composed of 3 rows of cilia, with 20 to 25 cilia in each row; a fibrillar root system connected with the membranelles depends into the endoplasm for about 20 micro and each is essentially in the shape of a fan, the terminal ends of each root bifurcating to connect to neighbouring roots. The membranelles thus form a cohesive unit and this morphological arrangement may have a bearing on the motion and coordination of the whole system. Two structural features extending throughout the length of the animal have been identified per cortical stripe in the body wall of Stentor; first, km fibres lying just beneath the pellicle are composed of stacks of fibrillar sheets and are identical with the birefringent fibres observed in the living animal. The individual fibrils of the sheets are in turn connected to the kinetosomes of the body cilia; thus the km fibres are homologous to kinetodesmata. Secondly, M bands lie beneath the km fibres and form an interconnected system in contact with the surrounding vacuolated cytoplasm; the thickness of the M bands is greatest at the base of a contracted animal. The contractile and extensile properties of these organelles have been discussed in the light of experimental results and theoretical considerations.

  17. A novel surface-sensitive X-ray absorption spectroscopic detector to study the thermal decomposition of cathode materials for Li-ion batteries

    NASA Astrophysics Data System (ADS)

    Nonaka, Takamasa; Okuda, Chikaaki; Oka, Hideaki; Nishimura, Yusaku F.; Makimura, Yoshinari; Kondo, Yasuhito; Dohmae, Kazuhiko; Takeuchi, Yoji

    2016-09-01

    A surface-sensitive conversion-electron-yield X-ray absorption fine structure (CEY-XAFS) detector that operates at elevated temperatures is developed to investigate the thermal decomposition of cathode materials for Li-ion batteries. The detector enables measurements with the sample temperature controlled from room temperature up to 450 °C. The detector is applied to the LiNi0.75Co0.15Al0.05Mg0.05O2 cathode material at 0% state of charge (SOC) and 50% SOC to examine the chemical changes that occur during heating in the absence of an electrolyte. The combination of surface-sensitive CEY-XAFS and bulk-sensitive transmission-mode XAFS shows that the reduction of Ni and Co ions begins at the surface of the cathode particles at around 150 °C, and propagates inside the particle upon further heating. These changes with heating are irreversible and are more obvious at 50% SOC than at 0% SOC. The fraction of reduced Ni ions is larger than that of reduced Co ions. These results demonstrate the capability of the developed detector to obtain important information for the safe employment of this cathode material in Li-ion batteries.

  18. Damping of Magnetohydrodynamic Waves in Solar Prominence Fine Structures

    NASA Astrophysics Data System (ADS)

    Soler, Roberto

    2010-05-01

    High-resolution observations of solar filaments and prominences reveal that these large-scale coronal structures are formed by a myriad of long and thin ribbons, here called threads, which are piled up to form the prominence body. Evidences suggest that these fine structures are magnetic flux tubes anchored in the solar photosphere, which are partially filled with the cool and dense prominence material. Individual and collective oscillations of prominence and filament fine structures are frequently reported by means of oscillatory variations in Doppler signals and spectral line intensity. Common features of these observations are that the reported oscillatory periods are usually in a narrow range between 2 and 10 minutes, that the velocity amplitudes are smaller than ˜3 km/s, and that the oscillations seem to be strongly damped after a few periods. Typically, the ratio of the damping time, tD, to the period, P, is tD/P < 10. While the oscillations have been interpreted in the context of the magnetohydrodynamic (MHD) theory, i.e., in terms of the MHD normal modes supported by the filament thread body and/or propagating MHD waves, the mechanism or mechanisms responsible for the damping are not well-known and a comparative study between different damping mechanisms is needed. In this Thesis, we study the efficiency of several physical mechanisms for the damping of MHD oscillations in prominence fine structures. Both individual and collective oscillations of threads are analyzed. We model a filament thread as a straight cylindrical magnetic flux tube with prominence conditions, embedded in a magnetized environment representing the solar coronal medium. The basic MHD equations are applied to the model and contain non-ideal terms accounting for effects as, e.g., non-adiabatic mechanisms, magnetic diffusion, ion-neutral collisions, etc., that may be of relevance in prominence plasmas and whose role on the damping of the oscillations is assessed. Our method combines

  19. SEISMOLOGY OF STANDING KINK OSCILLATIONS OF SOLAR PROMINENCE FINE STRUCTURES

    SciTech Connect

    Soler, R.; Arregui, I.; Oliver, R.; Ballester, J. L.

    2010-10-20

    We investigate standing kink magnetohydrodynamic (MHD) oscillations in a prominence fine structure modeled as a straight and cylindrical magnetic tube only partially filled with the prominence material and with its ends fixed at two rigid walls representing the solar photosphere. The prominence plasma is partially ionized and a transverse inhomogeneous transitional layer is included between the prominence thread and the coronal medium. Thus, ion-neutral collisions and resonant absorption are the damping mechanisms considered. Approximate analytical expressions of the period, the damping time, and their ratio are derived for the fundamental mode in the thin tube and thin boundary approximations. We find that the dominant damping mechanism is resonant absorption, which provides damping ratios in agreement with the observations, whereas ion-neutral collisions are irrelevant for damping. The values of the damping ratio are independent of both the prominence thread length and its position within the magnetic tube, and coincide with the values for a tube fully filled with the prominence plasma. The implications of our results in the context of the MHD seismology technique are discussed, pointing out that the reported short-period (2-10 minutes) and short-wavelength (700-8000 km) thread oscillations may not be consistent with a standing mode interpretation and could be related to propagating waves. Finally, we show that the inversion of some prominence physical parameters, e.g., Alfven speed, magnetic field strength, transverse inhomogeneity length scale, etc., is possible using observationally determined values of the period and damping time of the oscillations along with the analytical approximations of these quantities.

  20. Uranium speciation as a function of depth in contaminated hanford sediments--a micro-XRF, micro-XRD, and micro- and bulk-XAFS study.

    PubMed

    Singer, David M; Zachara, John M; Brown, Gordon E

    2009-02-01

    The distribution and speciation of U and Cu in contaminated vadose zone and aquifer sediments from the U.S. DOE Hanford site (300 Area) were determined using a combination of synchrotron-based micro-X-ray fluorescence (microXRF) imaging, micro-X-ray absorption near edge structure (microXANES) spectroscopy, and micro-X-ray diffraction (microXRD) techniques combined with bulk U LIII-edge X-ray absorption fine structure (XAFS) spectroscopy. Samples were collected from within the inactive North Process Pond (NPP2) at 8 ft (2.4 m, NPP2-8) depth and 12 ft (3.7 m, NPP2-12) depth in the vadose zone, and fines were isolated from turbid groundwater just below the water Table (12-14 ft, approximately 4 m, NPP2-GW). microXRF imaging, microXRD, and microXANES spectroscopy revealed two major U occurrences within the vadose and groundwater zones: (1) low to moderate concentrations of U(VI) associated with fine-textured grain coatings that were consistently found to contain clinochlore (referred to here as chlorite) observed in all three samples, and (2) U(VI)-Cu(II) hotspots consisting of micrometer-sized particles associated with surface coatings on grains of muscovite and chlorite observed in samples NPP2-8' and NPP2-GW. In the aquifer fines (NPP2-GW), these particles were identified as cuprosklodowskite (cps: Cu[(UO2)(SiO2OH)]2 x 6H2O) and metatorbernite (mtb: Cu(UO2)2(PO4)2 x 8H2O). In contrast, the U-Cu-containing particles in the vadose zone were X-ray amorphous. Analyses of U LIII-edge XAFS spectra by linear-combination fitting indicated that U speciation consisted of (1) approximately 75% uranyl sorbed to chlorite and approximately 25% mtb-like X-ray amorphous U-Cu-phosphates (8 ft depth), (2) nearly 100% sorbed uranyl (12 ft depth), and (3) approximately 70% uranyl sorbed to chlorite and approximately 30% cps/mtb (groundwater zone). These findings suggest that dissolution of U(VI)-Cu(II)-bearing solids as well as desorption of U(VI), mainly from phyllosilicates, are

  1. Fine Structure of Solar Acoustic Oscillations Due to Rotation

    NASA Technical Reports Server (NTRS)

    Goode, P. R.; Dziembowski, W.

    1984-01-01

    The nature of the fine structure of high order, low degree five minute period solar oscillations following from various postulated forms of spherical rotation is predicted. The first and second order effects of rotation are included.

  2. The fine-structure constant before quantum mechanics

    NASA Astrophysics Data System (ADS)

    Kragh, Helge

    2003-03-01

    This paper focuses on the early history of the fine-structure constant, largely the period until 1925. Contrary to what is generally assumed, speculations concerning the interdependence of the elementary electric charge and Planck's constant predated Arnold Sommerfeld's 1916 discussion of the dimensionless constant. This paper pays particular attention to a little known work from 1914 in which G N Lewis and E Q Adams derived what is effectively a numerical expression for the fine-structure constant.

  3. A Newtonian Explanation of the Hydrogen Fine Structure

    NASA Astrophysics Data System (ADS)

    Fisher, Paul; Espinosa, James; Woodyard, James

    2010-10-01

    The Hydrogen spectrum as seen by low dispersion spectrometers is correctly described by a classical theory founded on Ritz's magnetic model. With increasingly powerful instruments, individual lines are split into smaller groupings that are three orders of magnitude smaller. Arnold Sommerfeld was the first to develop a theory based on the mass variation of the electron to correctly describe this ``fine'' structure. A few years later, Vannevar Bush pointed out that Weber's force law could be used instead of Einstein's theory of relativity. We will utilize this line of approach to present a purely classical theory of the fine structure of the Hydrogen atom. Ritz's theory of electromagnetism replaces Weber's law; we will summarize all the other atomic physics experiments that our classical theory already describes correctly. Finally we will show how this fine structure theory logically paves the way for an explanation of the linear Stark effect.

  4. XAFS and bond-valence determination of the structures and compositions of surface functional groups and Pb(II) and Co(II) sorption products on single-crystal {alpha}-Al{sub 2}O{sub 3}

    SciTech Connect

    Bargar, J.R.; Towle, S.N.; Parks, G.A.; Brown, G.E. Jr.

    1997-01-15

    The structures and compositions of Pb(II) adsorption complexes and surface binding sites on {alpha}-Al{sub 2}O{sub 3} (0001) and (1{bar 1}02) surfaces were investigated in the presence of water using grazing-incidence X-ray absorption fine structure (GI-XAFS) spectroscopy. Pb(II) ions were found to adsorb in an inner-sphere mode on {alpha}-Al{sub 2}O{sub 3} (1{bar 1}02) but as outer-sphere complexes on {alpha}-Al{sub 2}O{sub 3} (0001). The distance between the outer-sphere complexes and the surface places useful constraints on double-layer properties of water. A bond-valence model is described that relates the reactivities of surface functional groups and adsorption complexes to their molecular structures and compositions, and places constraints on the stoichiometries of adsorption reactions, including proton release. The EXAFS and modeling results suggest that Pb(II) and Co(II) ions bond to [3Al--O{sup {minus}1/2}] and [Al--OH{sub 2}{sup +1/2}] surface functional groups. In contrast, [2Al--OH] groups complex Co(II) but not Pb(II). The results indicate the importance of using structurally defined surface sites to describe reactions at oxide-water interfaces.

  5. XAFSmass: a program for calculating the optimal mass of XAFS samples

    NASA Astrophysics Data System (ADS)

    Klementiev, K.; Chernikov, R.

    2016-05-01

    We present a new implementation of the XAFSmass program that calculates the optimal mass of XAFS samples. It has several improvements as compared to the old Windows based program XAFSmass: 1) it is truly platform independent, as provided by Python language, 2) it has an improved parser of chemical formulas that enables parentheses and nested inclusion-to-matrix weight percentages. The program calculates the absorption edge height given the total optical thickness, operates with differently determined sample amounts (mass, pressure, density or sample area) depending on the aggregate state of the sample and solves the inverse problem of finding the elemental composition given the experimental absorption edge jump and the chemical formula.

  6. Strained spiral vortex model for turbulent fine structure

    NASA Technical Reports Server (NTRS)

    Lundgren, T. S.

    1982-01-01

    A model for the intermittent fine structure of high Reynolds number turbulence is proposed. The model consists of slender axially strained spiral vortex solutions of the Navier-Stokes equation. The tightening of the spiral turns by the differential rotation of the induced swirling velocity produces a cascade of velocity fluctuations to smaller scale. The Kolmogorov energy spectrum is a result of this model.

  7. Temporal Fine Structure and Applications to Cochlear Implants

    ERIC Educational Resources Information Center

    Li, Xing

    2013-01-01

    Complex broadband sounds are decomposed by the auditory filters into a series of relatively narrowband signals, each of which conveys information about the sound by time-varying features. The slow changes in the overall amplitude constitute envelope, while the more rapid events, such as zero crossings, constitute temporal fine structure (TFS).…

  8. The origin of the distortion product otoacoustic emission fine structure

    NASA Astrophysics Data System (ADS)

    Piskorski, Pawel

    Distortion-product otoacoustic emissions (DPOAEs) are sounds detected in the ear canal which are generated by the nonlinear processes in the inner ear (cochlea) in response to the external stimulation of two or more tones (primaries). Their generation region in the cochlea can be systematically changed by varying the primary frequencies, and they are currently being evaluated for possible clinical use in screening for hearing defects. The phase and amplitude of various orders of DPOAEs of frequencies, f/sb [dp]=f1-n(f2-f1),/ (n=1,2,/...), were measured in human subjects for two- tone stimuli of frequencies f1 and f2 (>f1). A number of experimental paradigms (fixed primary ratio f2/f1, fixed f1, fixed f2, and fixed f/sb [dp]) were used to investigate the nature of peaks and valleys (fine structure) of DPOAEs in their phase and amplitude dependence on the primary frequencies. This fine structure must be taken into account in any potential clinical applications of DPOAEs. The experimental results largely support a model in which the fine structure stems from interference at the base of the cochlea between distortion product (DP) components coming from the primary DPOAE source region (around the f2 tonotopic place) and components coming from the DP tonotopic place (via reflection of an apically moving DP wave). The spectral periodicity of the fine structures for several orders of apical DPOAEs corresponds to a tonotopic displacement of about 0.4 mm along the basilar membrane (BM) (0.4 bark). In agreement with the reaction model, this spectral spacing is also characteristic of synchronous evoked and spontaneous otoacoustic emission spectra as well as the microstructure of the hearing threshold. Approximate analytic expressions for the mechanisms which are responsible for the fine structure are used to interpret the data.

  9. Arsenic Speciation in Multiple Metal Environments: I. Bulk-XAFS Spectroscopy of Model and Mixed Compounds

    SciTech Connect

    Grafe,M.; Tappero, R.; Marcus, M.; Sparks, D.

    2008-01-01

    X-ray absorption fine structure (XAFS) spectroscopy was employed to determine the bonding environment of As(V) in the presence of Cu(II) and Zn(II) on goethite and gibbsite. In addition, several mineral species and precipitates derived from homogeneous and heterogeneous (presence of ?-Cr2O3) super-saturations were studied. Structural parameters were determined after resolving the broad second shells in r-space by differential k-weighting (1, 2 or 3) and k-ranging (2.5- vs 3.5-12.75 Angstroms) of the raw EXAFS functions. In precipitates, AsO4 was incorporated in the metal-hydroxides forming clinoclase-like and koettigite-like structures in the presence of Cu(II) and Zn(II), respectively. In the presence of both Cu(II) and Zn(II), the clinoclase structure formed preferentially over the koettigite structure under homogeneous oversaturated solution conditions and in the presence of eskolaite (?-Cr2O3). Silica promoted the formation of koettigite-like zinc-arsenate precipitates from initial As(V) and Zn(II) solution concentrations of 500 ?M. On goethite and gibbsite, 750 ?M As(V) formed mainly bidentate binuclear surface species in accordance with many previous findings even in the presence of equimolar Cu(II) and or Zn(II) concentrations. Copper was readily identified in the second shell environment of As(V) sorbed on gibbsite, but not on goethite. We hypothesize that this complex formed on the basis of Cu(II)'s ability to form polymeric species in solution and at the mineral-water interface in agreement with previous studies. The effects of Zn(II) on the coordination environment of As(V) on gibbsite and goethite could not be ascertained with As K-edge EXAFS spectroscopy. In addition to bidentate binuclear surface complexes, As(V) formed edge-sharing complexes with Fe, Al, and Cu atoms, which we could differentiate on the basis of the inter-atomic distances, phase shifts between wavefunctions of Fourier-filtered peaks, and differences in amplitude of the absorption

  10. Interstellar dust grain composition from high-resolution X-ray absorption edge structure

    NASA Astrophysics Data System (ADS)

    Corrales, Lia

    2016-06-01

    X-ray light is sufficient to excite electrons from n=1 (K-shell) and n=2 (L-shell) energy levels of neutral interstellar metals, causing a sharp increase in the absorption cross-section. Near the ionization energy, the shape of the photoelectric absorption edge depends strongly on whether the atom is isolated or bound in molecules or minerals (dust). With high resolution X-ray spectroscopy, we can directly measure the state of metals and the mineral composition of dust in the interstellar medium. In addition, the scattering contribution to the X-ray extinction cross-section can be used to gauge grain size, shape, and filling factor. In order to fully take advantage of major advances in high resolution X-ray spectroscopy, lab measurements of X-ray absorption fine structure (XAFS) from suspected interstellar minerals are required. Optical constants derived from the absorption measurements can be used with Mie scattering or anomalous diffraction theory in order to model the full extinction cross-sections from the interstellar medium. Much like quasar spectra are used to probe other intergalactic gas, absorption spectroscopy of Galactic X-ray binaries and bright stars will yield key insights to the mineralogy and evolution of dust grains in the Milky Way.

  11. Cytochrome c in a Dry Trehalose Matrix: Structural and Dynamical Effects Probed by X-Ray Absorption Spectroscopy

    PubMed Central

    Giachini, Lisa; Francia, Francesco; Cordone, Lorenzo; Boscherini, Federico; Venturoli, Giovanni

    2007-01-01

    We report on the structure and dynamics of the Fe ligand cluster of reduced horse heart cytochrome c in solution, in a dried polyvinyl alcohol (PVA) film, and in two trehalose matrices characterized by different contents of residual water. The effect of the solvent/matrix environment was studied at room temperature using Fe K-edge x-ray absorption fine structure (XAFS) spectroscopy. XAFS data were analyzed by combining ab initio simulations and multi-parameter fitting in an attempt to disentangle structural from disorder parameters. Essentially the same structural and disorder parameters account adequately for the XAFS spectra measured in solution, both in the absence and in the presence of glycerol, and in the PVA film, showing that this polymer interacts weakly with the embedded protein. Instead, incorporation in trehalose leads to severe structural changes, more prominent in the more dried matrix, consisting of 1), an increase up to 0.2 Å of the distance between Fe and the imidazole N atom of the coordinating histidine residue and 2), an elongation up to 0.16 Å of the distance between Fe and the fourth-shell C atoms of the heme pyrrolic units. These structural distortions are accompanied by a substantial decrease of the relative mean-square displacements of the first ligands. In the extensively dried trehalose matrix, extremely low values of the Debye Waller factors are obtained for the pyrrolic and for the imidazole N atoms. This finding is interpreted as reflecting a drastic hindering in the relative motions of the Fe ligand cluster atoms and an impressive decrease in the static disorder of the local Fe structure. It appears, therefore, that the dried trehalose matrix dramatically perturbs the energy landscape of cyrochrome c, giving rise, at the level of local structure, to well-resolved structural distortions and restricting the ensemble of accessible conformational substates. PMID:17142287

  12. Speciation of Energy Critical Elements in Marine Ferromanganese Crusts and Nodules by Principal Component Analysis and Least-squares fits to XAFS Spectra

    NASA Astrophysics Data System (ADS)

    Foster, A. L.; Klofas, J. M.; Hein, J. R.; Koschinsky, A.; Bargar, J.; Dunham, R. E.; Conrad, T. A.

    2011-12-01

    Marine ferromanganese crusts and nodules ("Fe-Mn crusts") are considered a potential mineral resource due to their accumulation of several economically-important elements at concentrations above mean crustal abundances. They are typically composed of intergrown Fe oxyhydroxide and Mn oxide; thicker (older) crusts can also contain carbonate fluorapatite. We used X-ray absorption fine-structure (XAFS) spectroscopy, a molecular-scale structure probe, to determine the speciation of several elements (Te, Bi, Mo, Zr, Pt) in Fe-Mn crusts. As a first step in analysis of this dataset, we have conducted principal component analysis (PCA) of Te K-edge and Mo K-edge, k3-weighted XAFS spectra. The sample set consisted of 12 homogenized, ground Fe-Mn crust samples from 8 locations in the global ocean. One sample was subjected to a chemical leach to selectively remove Mn oxides and the elements associated with it. The samples in the study set contain 50-205 mg/kg Te (average = 88) and 97-802 mg/kg Mo (average = 567). PCAs of background-subtracted, normalized Te K-edge and Mo K-edge XAFS spectra were performed on a data matrix of 12 rows x 122 columns (rows = samples; columns = Te or Mo fluorescence value at each energy step) and results were visualized without rotation. The number of significant components was assessed by the Malinowski indicator function and ability of the components to reconstruct the features (minus noise) of all sample spectra. Two components were significant by these criteria for both Te and Mo PCAs and described a total of 74 and 75% of the total variance, respectively. Reconstruction of potential model compounds by the principal components derived from PCAs on the sample set ("target transformation") provides a means of ranking models in terms of their utility for subsequent linear-combination, least-squares (LCLS) fits (the next step of data analysis). Synthetic end-member models of Te4+, Te6+, and Mo adsorbed to Fe(III) oxyhydroxide and Mn oxide were

  13. Variations in the fine-structure constant constraining gravity theories

    NASA Astrophysics Data System (ADS)

    Bezerra, V. B.; Cunha, M. S.; Muniz, C. R.; Tahim, M. O.; Vieira, H. S.

    2016-08-01

    In this paper, we investigate how the fine-structure constant, α, locally varies in the presence of a static and spherically symmetric gravitational source. The procedure consists in calculating the solution and the energy eigenvalues of a massive scalar field around that source, considering the weak-field regime. From this result, we obtain expressions for a spatially variable fine-structure constant by considering suitable modifications in the involved parameters admitting some scenarios of semi-classical and quantum gravities. Constraints on free parameters of the approached theories are calculated from astrophysical observations of the emission spectra of a white dwarf. Such constraints are finally compared with those obtained in the literature.

  14. Fine Structure of Dark Energy and New Physics

    DOE PAGES

    Jejjala, Vishnu; Kavic, Michael; Minic, Djordje

    2007-01-01

    Following our recent work on the cosmological constant problem, in this letter we make a specific proposal regarding the fine structure (i.e., the spectrum) of dark energy. The proposal is motivated by a deep analogy between the blackbody radiation problem, which led to the development of quantum theory, and the cosmological constant problem, for which we have recently argued calls for a conceptual extension of the quantum theory. We argue that the fine structure of dark energy is governed by a Wien distribution, indicating its dual quantum and classical nature. We discuss observational consequences of such a picture of darkmore » energy and constrain the distribution function.« less

  15. Analysis of fine structure in the nuclear continuum

    SciTech Connect

    Shevchenko, A.; Kalmykov, Y.; Neumann-Cosel, P. von; Ponomarev, V. Yu.; Richter, A.; Wambach, J.; Carter, J.; Usman, I.; Cooper, G. R. J.; Fearick, R. W.

    2008-02-15

    Fine structure has been shown to be a general phenomenon of nuclear giant resonances of different multipolarities over a wide mass range. In this article we assess various techniques that have been proposed to extract quantitative information from the fine structure in terms of characteristic scales. These include the so-called local scaling dimension, the entropy index method, Fourier analysis, and continuous and discrete wavelet transforms. As an example, results on the isoscalar giant quadrupole resonance in {sup 208}Pb from high-energy-resolution inelastic proton scattering and calculations with the quasiparticle-phonon model are analyzed. Wavelet analysis, both continuous and discrete, of the spectra is shown to be a powerful tool to extract the magnitude and localization of characteristic scales.

  16. Assigning {gamma} deformation from fine structure in exotic nuclei

    SciTech Connect

    Ferreira, L. S.; Maglione, E.; Arumugam, P.

    2011-10-28

    The nonadiabatic quasiparticle model for triaxial shapes is used to perform calculations for decay of {sup 141}Ho, the only known odd-Z even-N deformed nucleus for which fine structure in proton emission from both ground and isomeric states has been observed. All experimental data corresponding to this unique case namely, the rotational spectra of parent and daughter nuclei, decay widths and branching ratios for ground and isomeric states, could be well explained with a strong triaxial deformation {gamma}{approx}20. The recent experimental observation of fine structure decay from the isomeric state, can be explained only with an assignment of I{sup {pi}} = 3/2{sup +} as the decaying state, in contradiction with the previous assignment, of I{sup {pi}} 1/2{sup +}, based on adiabatic calculations. This study reveals that proton emission measurements could be a precise tool to probe triaxial deformations and other structural properties of exotic nuclei beyond the proton dripline.

  17. Fine structures in the light diffraction pattern of striated muscle.

    PubMed

    Leung, A F

    1984-10-01

    Single skeletal muscle fibres of frog were illuminated with a He-Ne, argon-ion or rhodamine 6G dye laser. The fine structures lying within the diffraction columns moved parallel to the fibre axis without changing their pattern when either the wavelength or the incident angle of the laser beam was varied, or when the fibre was stretched slightly. However, their pattern remained nearly constant when the fibre was submerged in hypotonic or hypertonic solution. As the illumination of about 1 mm or 0.1 mm width scanned along the length of the fibre, new structures emerged while others faded away giving rise to the notion that the diffraction columns were moving in the direction of the scan. A decrease in the illumination width caused the structures lying on the periphery of the diffraction column to disappear and the width of the remaining structures to increase. Measurements rule out the existence of large diffraction planes in these muscles. In addition, they indicate that the fine structures come from the diffraction of the whole rather than independent components of the illuminated volume. The origin of the fine structures is explained by two diffraction models.

  18. 3D WHOLE-PROMINENCE FINE STRUCTURE MODELING. II. PROMINENCE EVOLUTION

    SciTech Connect

    Gunár, Stanislav; Mackay, Duncan H.

    2015-10-20

    We use the new three-dimensional (3D) whole-prominence fine structure model to study the evolution of prominences and their fine structures in response to changes in the underlying photospheric magnetic flux distribution. The applied model combines a detailed 3D prominence magnetic field configuration with a realistic description of the prominence plasma distributed along multiple fine structures. In addition, we utilize an approximate Hα visualization technique to study the evolution of the visible cool prominence plasma both in emission (prominence) and absorption (filament). We show that the initial magnetic field configuration of the modeled prominence is significantly disturbed by the changing position of a single polarity of a magnetic bipole as the bipole is advected toward the main body of the filament. This leads to the creation of a barb, which becomes the dominant feature visible in the synthetic Hα images of both the prominence and filament views. The evolution of the bipole also creates conditions that lead to the disappearance and reappearance of large portions of the main body. We also show that an arch-like region containing a dark void (a bubble) can be naturally produced in the synthetic prominence Hα images. While not visible in terms of the magnetic field lines, it is due to a lack of Hα emission from low-pressure, low-density plasma located in shallow magnetic dips lying along the lines of sight intersecting the dark void. In addition, a quasi-vertical small-scale feature consisting of short and deep dips, piled one above the other, is produced.

  19. Local structure and optical absorption characteristic investigation on Fe doped TiO2 nanoparticles

    NASA Astrophysics Data System (ADS)

    Zhao, Tian-Xing; Feng, Ya-Juan; Huang, Jun-Heng; He, Jin-Fu; Liu, Qing-Hua; Pan, Zhi-Yun; Wu, Zi-Yu

    2015-02-01

    The local structures and optical absorption characteristics of Fe doped TiO2 nanoparticles synthesized by the sol-gel method were characterized by X-ray diffraction (XRD), X-ray absorption fine structure spectroscopy (XAFS) and ultraviolet-visible absorption spectroscopy (UV-Vis). XRD patterns show that all Fe-doped TiO2 samples have the characteristic anatase structure. Accurate Fe and Ti K-edge EXAFS analysis further reveal that all Fe atoms replace Ti atoms in the anatase lattice. The analysis of UV-Vis data shows a red shift to the visible range. According to the above results, we claim that substitutional Fe atoms lead to the formation of structural defects and new intermediate energy levels appear, narrowing the band gap and extending the optical absorption edge towards the visible region. Supported by National Basic Research Program of China (2012CB825801), Science Fund for Creative Research Groups of NSFC (11321503), National Natural Science Foundation of China (11321503, 11179004) and Guangdong Natural Science Foundation (S2011040003985)

  20. Fine structure of a resonantly excited p -shell exciton in a CdTe quantum dot

    NASA Astrophysics Data System (ADS)

    Smoleński, T.; Kazimierczuk, T.; Goryca, M.; Wojnar, P.; Kossacki, P.

    2016-05-01

    We present a polarization-resolved photoluminescence excitation study of the absorption spectrum of a p -shell neutral exciton in a single CdTe/ZnTe quantum dot. We find that the fine structure of the p -shell exciton is completely analogous to the fine structure of the s -shell exciton, including the selection rules and the effects of a magnetic field applied in Faraday and Voigt configurations. The energy spectrum of the p -shell exciton is found to be well described by introducing respective isotropic and anisotropic constants of the exchange interaction between a p -shell electron and a p -shell hole. The typical values of these exchange constants averaged over several randomly selected quantum dots yield δ0p p=(0.92 ±0.16 ) meV and δ1p p=(0.58 ±0.25 ) meV. Additionally, we demonstrate that the nonresonant relaxation of the p -shell exciton conserves the exciton spin to a very high degree for both bright and dark exciton configurations.

  1. A simple cosmology with a varying fine structure constant.

    PubMed

    Sandvik, Håvard Bunes; Barrow, John D; Magueijo, João

    2002-01-21

    We investigate the cosmological consequences of a theory in which the electric charge e can vary. In this theory the fine structure "constant," alpha, remains almost constant in the radiation era, undergoes a small increase in the matter era, but approaches a constant value when the universe starts accelerating because of a positive cosmological constant. This model satisfies geonuclear, nucleosynthesis, and cosmic microwave background constraints on time variation in alpha, while fitting the observed accelerating Universe and evidence for small alpha variations in quasar spectra. It also places specific restrictions on the nature of the dark matter. Further tests, involving stellar spectra and Eötvös experiments, are proposed.

  2. New Tests for Variations of the Fine Structure Constant

    NASA Technical Reports Server (NTRS)

    Prestage, John D.

    1995-01-01

    We describe a new test for possible variations of the fine structure constant, by comparisons of rates between clocks based on hyperfine transitions in alkali atomos with different atomic number Z. H- maser, Cs and Hg+ clocks have a different dependence on ia relativistic contributions of order (Z. Recent H-maser vs Hg+ clock comparison data improves laboratory limits on a time variation by 100-fold to giveFuture laser cooled clocks (Be+, Rb, Cs, Hg+, etc.), when compared, will yield the most senstive of all tests for.

  3. Topological Quantization in Units of the Fine Structure Constant

    SciTech Connect

    Maciejko, Joseph; Qi, Xiao-Liang; Drew, H.Dennis; Zhang, Shou-Cheng; /Stanford U., Phys. Dept. /Stanford U., Materials Sci. Dept. /SLAC

    2011-11-11

    Fundamental topological phenomena in condensed matter physics are associated with a quantized electromagnetic response in units of fundamental constants. Recently, it has been predicted theoretically that the time-reversal invariant topological insulator in three dimensions exhibits a topological magnetoelectric effect quantized in units of the fine structure constant {alpha} = e{sup 2}/{h_bar}c. In this Letter, we propose an optical experiment to directly measure this topological quantization phenomenon, independent of material details. Our proposal also provides a way to measure the half-quantized Hall conductances on the two surfaces of the topological insulator independently of each other.

  4. QED Based Calculation of the Fine Structure Constant

    SciTech Connect

    Lestone, John Paul

    2016-10-13

    Quantum electrodynamics is complex and its associated mathematics can appear overwhelming for those not trained in this field. Here, semi-classical approaches are used to obtain a more intuitive feel for what causes electrostatics, and the anomalous magnetic moment of the electron. These intuitive arguments lead to a possible answer to the question of the nature of charge. Virtual photons, with a reduced wavelength of λ, are assumed to interact with isolated electrons with a cross section of πλ2. This interaction is assumed to generate time-reversed virtual photons that are capable of seeking out and interacting with other electrons. This exchange of virtual photons between particles is assumed to generate and define the strength of electromagnetism. With the inclusion of near-field effects the model presented here gives a fine structure constant of ~1/137 and an anomalous magnetic moment of the electron of ~0.00116. These calculations support the possibility that near-field corrections are the key to understanding the numerical value of the dimensionless fine structure constant.

  5. SOLAR RADIO BURSTS WITH SPECTRAL FINE STRUCTURES IN PREFLARES

    SciTech Connect

    Zhang, Yin; Tan, Baolin; Huang, Jing; Tan, Chengming; Karlický, Marian; Mészárosová, Hana; Simões, Paulo J.A.

    2015-01-20

    Good observations of preflare activities are important for us to understand the origin and triggering mechanism of solar flares, and to predict the occurrence of solar flares. This work presents the characteristics of microwave spectral fine structures as preflare activities of four solar flares observed by the Ondřejov radio spectrograph in the frequency range of 0.8-2.0 GHz. We found that these microwave bursts which occurred 1-4 minutes before the onset of flares have spectral fine structures with relatively weak intensities and very short timescales. They include microwave quasi-periodic pulsations with very short periods of 0.1-0.3 s and dot bursts with millisecond timescales and narrow frequency bandwidths. Accompanying these microwave bursts are filament motions, plasma ejection or loop brightening in the EUV imaging observations, and non-thermal hard X-ray emission enhancements observed by RHESSI. These facts may reveal certain independent, non-thermal energy releasing processes and particle acceleration before the onset of solar flares. They may help us to understand the nature of solar flares and to predict their occurrence.

  6. Fine structure in the cluster decays of the translead nuclei

    SciTech Connect

    Dumitrescu, O. |; Cioaca, C.

    1995-06-01

    Within the one level {ital R}-matrix approach several hindrance factors for the radioactive decays in which are emitted {sup 4}He, {sup 14}C, and {sup 20}O atomic nuclei are calculated. The interior wave functions are supposed to be given by the recently proposed enlarged superfluid model, an extension of the JINR-Dubna`s quasiparticle phonon nuclear model. The spectroscopic factors are expanded in terms of products of cluster overlaps and intrinsic overlap integrals. The cluster overlaps are equivalents of the generalized coefficients of fractional parentage, while for the intrinsic overlap integrals we construct a model, which is an extension of the usual models for simple particle decay such as deuteron, triton, and {alpha} decay. The exterior wave functions are calculated from a cluster-nucleus double-folding model potential obtained with the {ital M}3{ital Y} interaction. As examples of the cluster decay fine structure we analyzed the particular cases of {alpha} decay of {sup 255}Fm, {sup 14}C decay of {sup 223}Ra and {sup 20}O decay of {sup 229}Th and {sup 255}Fm. A relatively good agreement with the experimental data is obtained especially in the case of the {alpha}-decay fine structure.

  7. `Fingerprint' Fine Structure in the Solar Decametric Radio Spectrum Solar Physics

    NASA Astrophysics Data System (ADS)

    Zlotnik, E. Y.; Zaitsev, V. V.; Melnik, V. N.; Konovalenko, A. A.; Dorovskyy, V. V.

    2015-07-01

    We study a unique fine structure in the dynamic spectrum of the solar radio emission discovered by the UTR-2 radio telescope (Kharkiv, Ukraine) in the frequency band of 20 - 30 MHz. The structure was observed against the background of a broadband type IV radio burst and consisted of parallel drifting narrow bands of enhanced emission and absorption on the background emission. The observed structure differs from the widely known zebra pattern at meter and decimeter wavelengths by the opposite directions of the frequency drift within a single stripe at a given time. We show that the observed properties can be understood in the framework of the radiation mechanism by virtue of the double plasma resonance effect in a nonuniform coronal magnetic trap. We propose a source model providing the observed frequency drift of the stripes.

  8. Astronomical constraints on the cosmic evolution of the fine structure constant and possible quantum dimensions.

    PubMed

    Carilli, C L; Menten, K M; Stocke, J T; Perlman, E; Vermeulen, R; Briggs, F; de Bruyn, A G; Conway, J; Moore, C P

    2000-12-25

    We present measurements of absorption by the 21 cm hyperfine transition of neutral hydrogen toward radio sources at substantial look-back times. These data are used in combination with observations of rotational transitions of common interstellar molecules to set limits on the evolution of the fine structure constant: alpha/ alpha<3.5x10(-15) yr(-1), to a look-back time of 4.8 Gyr. In the context of string theory, the limit on the secular evolution of the scale factor of the compact dimensions, R, is &Rdot/ R<10(-15) yr(-1). Including terrestrial and other astronomical measurements places 2sigma limits on slow oscillations of R from the present to the epoch of cosmic nucleosynthesis, just seconds after the big bang, of DeltaR /R<10(-5).

  9. Low Temperature XRF-yield XAFS of low concentration Mo in steel

    NASA Astrophysics Data System (ADS)

    Nagoshi, M.; Kawano, T.; Sato, K.; Funakawa, Y.

    2013-04-01

    Low temperature x-ray fluorescence yield x-ray absorption fine structure measurements have been carried out for 0.2 mass% Mo in steel and carbides extracted from a steel sample. The increase in amplitude of the extended x-ray absorption fine structure, at 8 K, was larger for Mo in bcc-Fe matrix than for Mo in carbides. This is explained by the differences in distortion of the local structure around Mo atoms between the two chemical states. The Ratio method was applied to the EXAFS, measured at 8 K, for the Fe atoms surrounding the Mo in the bcc-Fe matrix. The atomic fraction of the Mo in solution and Mo as carbides in steel was determined by this technique.

  10. Thermal stability analysis of the fine structure of solar prominences

    NASA Technical Reports Server (NTRS)

    Demoulin, Pascal; Malherbe, Jean-Marie; Schmieder, Brigitte; Raadu, Mickael A.

    1986-01-01

    The linear thermal stability of a 2D periodic structure (alternatively hot and cold) in a uniform magnetic field is analyzed. The energy equation includes wave heating (assumed proportional to density), radiative cooling and both conduction parallel and orthogonal to magnetic lines. The equilibrium is perturbed at constant gas pressure. With parallel conduction only, it is found to be unstable when the length scale 1// is greater than 45 Mn. In that case, orthogonal conduction becomes important and stabilizes the structure when the length scale is smaller than 5 km. On the other hand, when the length scale is greater than 5 km, the thermal equilibrium is unstable, and the corresponding time scale is about 10,000 s: this result may be compared to observations showing that the lifetime of the fine structure of solar prominences is about one hour; consequently, our computations suggest that the size of the unresolved threads could be of the order of 10 km only.

  11. Exploring the fine structure at the limb in coronal holes

    NASA Technical Reports Server (NTRS)

    Karovska, Magarita; Blundell, Solon F.; Habbal, Shadia Rifai

    1994-01-01

    The fine structure of the solar limb in coronal holes is explored at temperatures ranging from 10(exp 4) to 10(exp 6) K. An image enhancement algorithm orignally developed for solar eclipse observations is applied to a number of simultaneous multiwavelength observations made with the Harvard Extreme Ultraviolet Spectrometer experiment on Skylab. The enhanced images reveal the presence of filamentary structures above the limb with a characteristic separation of approximately 10 to 15 sec . Some of the structures extend from the solar limb into the corona to at least 4 min above the solar limb. The brightness of these structures changes as a function of height above the limb. The brightest emission is associated with spiculelike structures in the proximity of the limb. The emission characteristic of high-temperature plasma is not cospatial with the emission at lower temperatures, indicating the presence of different temperature plasmas in the field of view.

  12. Atomic Clocks and Variations of the FIne Structure Constant

    NASA Technical Reports Server (NTRS)

    Prestage, John D.; Tjoelker, Robert L.; Maleki, Lute

    1995-01-01

    We describe a new test for possible variations of the fine structure constant alpha by comparisons of rates between clocks based on hyperfine transitions in alkali atoms with different atomic number Z. H-maser, Cs, and Hg(+) clocks have a different dependence on alpha via relativistic contributions of order (Z-alpha)(sup 2). Recent H-maser vs Hg(+) clock comparison data improve laboratory limits on a time variation by 100-fold to give dot-alpha less than or equal to 3.7 x 10(exp -14)/yr. Future laser cooled clocks (Be(+), Rb, Cs, Hg(+), etc.), when compared, will yield the most sensitive of all tests for dot-alpha/alpha.

  13. HERSCHEL GALACTIC PLANE SURVEY OF [N ii] FINE STRUCTURE EMISSION

    SciTech Connect

    Goldsmith, Paul F.; Yıldız, Umut A.; Langer, William D.; Pineda, Jorge L.

    2015-12-01

    We present the first large-scale high angular resolution survey of ionized nitrogen in the Galactic Plane through emission of its two fine structure transitions ([N ii]) at 122 and 205 μm. The observations were largely obtained with the PACS instrument onboard the Herschel Space Observatory. The lines of sight were in the Galactic plane, following those of the Herschel OTKP project GOT C+. Both lines are reliably detected at the 10{sup −8}–10{sup −7} Wm{sup −2} sr{sup −1} level over the range –60° ≤ l ≤ 60°. The rms of the intensity among the 25 PACS spaxels of a given pointing is typically less than one third of the mean intensity, showing that the emission is extended. [N ii] is produced in gas in which hydrogen is ionized, and collisional excitation is by electrons. The ratio of the two fine structure transitions provides a direct measurement of the electron density, yielding n(e) largely in the range 10–50 cm{sup −3} with an average value of 29 cm{sup −3} and N{sup +} column densities 10{sup 16}–10{sup 17} cm{sup −2}. [N ii] emission is highly correlated with that of [C ii], and we calculate that between 1/3 and 1/2 of the [C ii] emission is associated with the ionized gas. The relatively high electron densities indicate that the source of the [N ii] emission is not the warm ionized medium (WIM), which has electron densities more than 100 times smaller. Possible origins of the observed [N ii] include the ionized surfaces of dense atomic and molecular clouds, the extended low-density envelopes of H ii regions, and low-filling factor high-density fluctuations of the WIM.

  14. Herschel Galactic Plane Survey of [NII] Fine Structure Emission

    NASA Astrophysics Data System (ADS)

    Goldsmith, Paul F.; Yıldız, Umut A.; Langer, William D.; Pineda, Jorge L.

    2015-12-01

    We present the first large-scale high angular resolution survey of ionized nitrogen in the Galactic Plane through emission of its two fine structure transitions ([N ii]) at 122 and 205 μm. The observations were largely obtained with the PACS instrument onboard the Herschel Space Observatory. The lines of sight were in the Galactic plane, following those of the Herschel OTKP project GOT C+. Both lines are reliably detected at the 10-8-10-7 Wm-2 sr-1 level over the range -60° ≤ l ≤ 60°. The rms of the intensity among the 25 PACS spaxels of a given pointing is typically less than one third of the mean intensity, showing that the emission is extended. [N ii] is produced in gas in which hydrogen is ionized, and collisional excitation is by electrons. The ratio of the two fine structure transitions provides a direct measurement of the electron density, yielding n(e) largely in the range 10-50 cm-3 with an average value of 29 cm-3 and N+ column densities 1016-1017 cm-2. [N ii] emission is highly correlated with that of [C ii], and we calculate that between 1/3 and 1/2 of the [C ii] emission is associated with the ionized gas. The relatively high electron densities indicate that the source of the [N ii] emission is not the warm ionized medium (WIM), which has electron densities more than 100 times smaller. Possible origins of the observed [N ii] include the ionized surfaces of dense atomic and molecular clouds, the extended low-density envelopes of H ii regions, and low-filling factor high-density fluctuations of the WIM.

  15. Vertical fine structure observations in the eastern equatorial Pacific

    SciTech Connect

    Hayes, S.P.

    1981-11-20

    Measurements of vertical displacement and horizontal velocity finestructure near the equator at 110/sup 0/W in the eastern Pacific Ocean are reported. Profiles were scaled to a constant Bruent-Vaeisaelae frequency ocean (N/sub 0/ = 1 cph) in accordance with a WKBJ approximation. A total of 57 CTD casts between 3/sup 0/N and 3/sup 0/S taken during five cruises in 1979 were analyzed. Results show an equatorial enhancement of vertical displacement is similar variance for vertical wavelengths longer than 50 sdbar (stretched decibars). This enhancement is similar to that which has been reported at 125/sup 0/W and 179/sup 0/E. Difference between locations can be accounted for by the observed temporal variability at 110/sup 0/W. Coherence between vertical displacement profiles separated in time by dealys of 2 hours to 120 hour indicate that the high wave number structures were largely associated with time scales of 4 days and less. Meridionally, vertical structures longer than 300 sdbar were coherent within 50 km of the equator. We interpret this vertical displacement fine structure enhancement as high wave number equatorially trapped inertial-gravity waves. The velocity fine structure measurements in July 1979 also indicate equatorially enhanced horizontal kinetic energy for vertical wave lengths longer than 100 sdbar. The velocity structures persisted over the 56 hour of measurement and appeared to have longer time scales than the vertical displacements. Meridional energy measurement and appeared to have longer time scales than the vertical displacements. Meridional energy exceeded zonal energy; however, the two components were coherent. We interpret these velocity structures as inertial-gravity waves which were produced off the equator and are propagating through the equatorial region.

  16. Effect of heat treatment on the far-infrared emission spectra and fine structures of black tourmaline.

    PubMed

    Meng, Junping; Liang, Jinsheng; Liu, Jie; Ding, Yan; Gan, Kun

    2014-05-01

    Mineral black tourmaline powders were heat-treated at different temperatures. Their crystal structure was studied by X-ray diffractometer. Their infrared absorption and emission spectra before and after the heat treatment were analyzed by the Fourier transform infrared spectrometer. The corresponding fine structures were discussed in detail. The results showed that the powders possessed higher infrared emissivity at the band where they showed stronger infrared absorption. However, there is no certain correlation between the peak intensity of infrared absorption and emissivity values at the same frequency. Because of the crystal shrinkage of c-axis, the electronic transitions were stimulated between different energy levels, and the abilities of infrared absorption and emission were enhanced with increasing the temperature of heat treatment.

  17. [Study on the fine structure of K-feldspar of Qichun granite].

    PubMed

    Du, Deng-Wen; Hong, Han-Lie; Fan, Kan; Wang, Chao-Wen; Yin, Ke

    2013-03-01

    Fine structure of K-feldspar from the Qichun granite was investigated using X-ray diffraction (XRD), Fourier infrared absorption spectroscopy (FTIR), and inductively coupled plasma mass spectrometry methods to understand the evolution of the granitic magmatism and its correlation to molybdenite mineralization. The XRD results showed that K-feldspar of the potassic alteration veins has higher ordering index and triclinicity and is namely microcline with triclinic symmetry. K-feldspar of the early cretaceous granite has relatively lower ordering index and has widening [131] peak and is locally triclinic ordering. K-feldspar of the late cretaceous granite has lowest ordering index and sharp [131] peak and is honiogeneously monoclinic. The FTIR results showed that the IR spectra of the Qichun K-feldspar are similar to that of orthoclase reported by Farmer (1974). The 640 cm-1 absorption band increases while the 540 cm-' absorption band decreases with increase in K-feldspar ordering index, also, the 1,010 cm-1 absorption band separates into 1,010 and 1,046 cm-1 absorption bands, with a change in the band shape from widening to sharp outline. The ICP-MS results suggested that K-feldspar of the early cretaceous granite has relatively higher metal elements and rare earth elements, and the granite exhibits better mineralization background, K-feldspar of the potassic alteration veins has markedly lower Sr and Ba, indicating that the alteration fluid originated from the granitic magmatism, and hence, potassic alteration is a good indicator for molybdenite exploration.

  18. Fine structure of the nucleus of the galaxy NGC 1275

    NASA Astrophysics Data System (ADS)

    Matveyenko, L. I.; Seleznev, S. V.

    2016-04-01

    The fine structure of the nucleus of the Seyfert galaxy NGC 1275 was investigated in 2005-2010 at a wavelength of 2 cm with a resolution as high as 50 μas. The structure consists of two parallel identical systems, eastern and western, spaced 0.5 pc apart in the plane of the sky. Each of them contains an ejector and a bipolar outflow. There are extended regions, lobes, at the extension of the bipolar outflows in the -10° and 170° directions at distances of 5 pc northward and 6.5 pc southward of the active zone. The observed difference between the jet and counterjet sizes by a factor of ~3 and between the distances to the lobes by a factor of 0.8 is determined by the difference between their velocities and by the change of sign of the outflow acceleration in the period of silence. The high-velocity bipolar outflows are surrounded by three pairs of low-velocity components. The diameters of the low-velocity coaxial outflows and the third component are Ø1 ≈ 0.3 pc, Ø2 ≈ 0.8 pc, and Ø3 ≈ 1.4 pc at the detection limit. The outer low-velocity components of the outflows encompass both high-velocity outflows. The velocities of the outflows and their brightness temperatures increase exponentially as the center of the high-velocity outflows is approached. The brightness temperatures of the high-velocity outflows at the ejector exit are T b > 1012 K. The spectral line velocities in the nuclear region differ by ~600 km s-1 due to the velocity difference between the two systems. In the case of Keplerian motion, the revolution period is ~5 × 103 yr, and the mass of the central massive bodies, black holes, is M ≈ 107M⊙. The fine structure suggests a vortical nature of the formation. In the case under consideration, two parallel vortices spaced ~0.5 pc apart and shifted by ~0.5 pc relative to each other were formed. The surrounding material inflows onto the disk of each system, is transferred in a spiral to the center, and is ejected in the -10° and 170

  19. Americium characterization by X-ray fluorescence and absorption spectroscopy in plutonium uranium mixed oxide

    SciTech Connect

    Degueldre, Claude Cozzo, Cedric; Martin, Matthias; Grolimund, Daniel; Mieszczynski, Cyprian

    2013-06-01

    Plutonium uranium mixed oxide (MOX) fuels are currently used in nuclear reactors. The actinides in these fuels need to be analyzed after irradiation for assessing their behaviour with regard to their environment and the coolant. In this work the study of the atomic structure and next-neighbour environment of Am in the (Pu,U)O₂ lattice in an irradiated (60 MW d kg⁻¹) MOX sample was performed employing micro-X-ray fluorescence (µ-XRF) and micro-X-ray absorption fine structure (µ-XAFS) spectroscopy. The chemical bonds, valences and stoichiometry of Am (~0.66 wt%) are determined from the experimental data gained for the irradiated fuel material examined in its peripheral zone (rim) of the fuel. In the irradiated sample Am builds up as Am³⁺ species within an [AmO₈]¹³⁻ coordination environment (e.g. >90%) and no (<10%) Am(IV) or (V) can be detected in the rim zone. The occurrence of americium dioxide is avoided by the redox buffering activity of the uranium dioxide matrix. - Graphical abstract: Americium LIII XAFS spectra recorded for the irradiated MOX sub-sample in the rim zone for a 300 μm×300 μm beam size area investigated over six scans of 4 h. The records remain constant during multi-scan. The analysis of the XAFS signal shows that Am is found as trivalent in the UO₂ matrix. This analytical work shall open the door of very challenging analysis (speciation of fission product and actinides) in irradiated nuclear fuels. - Highlights: • Americium was characterized by microX-ray absorption spectroscopy in irradiated MOX fuel. • The americium redox state as determined from XAS data of irradiated fuel material was Am(III). • In the sample, the Am³⁺ face an AmO₈¹³⁻coordination environment in the (Pu,U)O₂ matrix. • The americium dioxide is reduced by the uranium dioxide matrix.

  20. PDR modeling of the LWS fine-structure lines in ultraluminous galaxies

    NASA Technical Reports Server (NTRS)

    Luhman, M. L.; Satyapal, S.; Fischer, J.; Wolfire, M. G.

    1997-01-01

    The observations performed onboard the Infrared Space Observatory (ISO) long wavelength spectrometer (LWS) on the fine structure lines in ultraluminous galaxies are reported on. The C II 158 micrometer, the O I 63 and 146 micrometer fine structure lines were detected. These lines were compared to the results of the revised theoretical models of extragalactic photodissociation regions (PDRs). The PDR origin of the fine structure lines and the physical properties of the PDR component are discussed.

  1. A Simple Model for Fine Structure Transitions in Alkali-Metal Noble-Gas Collisions

    DTIC Science & Technology

    2015-03-01

    fine- structure transition rates of the alkali atoms . The integration of this integral is primarily performed nu- merically, using an adaptive Romberg...Previous work on the fine structure transitions of alkali atoms as they collide with noble gas atoms includes a full quantum mechanical calculation of...adiabaticity in alkali atom fine structure mixing”. SPIE LASE, 896207–896207. International Society for Optics and Photonics, 2014. 4. Griffiths, David J

  2. Urban Airborne Lead: X-Ray Absorption Spectroscopy Establishes Soil as Dominant Source

    PubMed Central

    Pingitore, Nicholas E.; Clague, Juan W.; Amaya, Maria A.; Maciejewska, Beata; Reynoso, Jesús J.

    2009-01-01

    Background Despite the dramatic decrease in airborne lead over the past three decades, there are calls for regulatory limits on this potent pediatric neurotoxin lower even than the new (2008) US Environmental Protection Agency standard. To achieve further decreases in airborne lead, what sources would need to be decreased and what costs would ensue? Our aim was to identify and, if possible, quantify the major species (compounds) of lead in recent ambient airborne particulate matter collected in El Paso, TX, USA. Methodology/Principal Findings We used synchrotron-based XAFS (x-ray absorption fine structure) to identify and quantify the major Pb species. XAFS provides molecular-level structural information about a specific element in a bulk sample. Pb-humate is the dominant form of lead in contemporary El Paso air. Pb-humate is a stable, sorbed complex produced exclusively in the humus fraction of Pb-contaminated soils; it also is the major lead species in El Paso soils. Thus such soil must be the dominant source, and its resuspension into the air, the transfer process, providing lead particles to the local air. Conclusions/Significance Current industrial and commercial activity apparently is not a major source of airborne lead in El Paso, and presumably other locales that have eliminated such traditional sources as leaded gasoline. Instead, local contaminated soil, legacy of earlier anthropogenic Pb releases, serves as a long-term reservoir that gradually leaks particulate lead to the atmosphere. Given the difficulty and expense of large-scale soil remediation or removal, fugitive soil likely constrains a lower limit for airborne lead levels in many urban settings. PMID:19340295

  3. Fine structure analysis of Salmonella typhimurium glutamate synthase genes.

    PubMed Central

    Madonna, M J; Fuchs, R L; Brenchley, J E

    1985-01-01

    Glutamate synthase activity is required for the growth of Salmonella typhimurium on media containing a growth-rate-limiting nitrogen source. Mutations that alter glutamate synthase activity had been identified in the gltB gene, but it was not known which of the two nonidentical subunits of the enzyme was altered. To examine the gene-protein relationship of the glt region, two nonsense mutations were identified and used to demonstrate that gltB encodes the large subunit of the enzyme. Six strains with independent Mu cts d1 (lac bla) insertions were isolated, from which a collection of deletion mutations was obtained. The deletions were transduced with the nonsense mutations and 38 other glt point mutations to construct a fine-structure genetic map. Chromosome mobilization studies, mediated by Hfr derivatives of Mu cts d1 lysogens, showed that gltB is transcribed in a clockwise direction, as shown in the S. typhimurium linkage map. Studies of the polar effects of three Mu cts d1 insertions indicated that the gene for the small subunit maps clockwise to gltB and that the two genes are cotranscribed to form a glt operon. Images PMID:3881392

  4. FINE STRUCTURES AND OVERLYING LOOPS OF CONFINED SOLAR FLARES

    SciTech Connect

    Yang, Shuhong; Zhang, Jun; Xiang, Yongyuan

    2014-10-01

    Using the Hα observations from the New Vacuum Solar Telescope at the Fuxian Solar Observatory, we focus on the fine structures of three confined flares and the issue why all the three flares are confined instead of eruptive. All the three confined flares take place successively at the same location and have similar morphologies, so can be termed homologous confined flares. In the simultaneous images obtained by the Solar Dynamics Observatory, many large-scale coronal loops above the confined flares are clearly observed in multi-wavelengths. At the pre-flare stage, two dipoles emerge near the negative sunspot, and the dipolar patches are connected by small loops appearing as arch-shaped Hα fibrils. There exists a reconnection between the small loops, and thus the Hα fibrils change their configuration. The reconnection also occurs between a set of emerging Hα fibrils and a set of pre-existing large loops, which are rooted in the negative sunspot, a nearby positive patch, and some remote positive faculae, forming a typical three-legged structure. During the flare processes, the overlying loops, some of which are tracked by activated dark materials, do not break out. These direct observations may illustrate the physical mechanism of confined flares, i.e., magnetic reconnection between the emerging loops and the pre-existing loops triggers flares and the overlying loops prevent the flares from being eruptive.

  5. Bumblebee Homing: The Fine Structure of Head Turning Movements

    PubMed Central

    Boeddeker, Norbert; Mertes, Marcel; Dittmar, Laura; Egelhaaf, Martin

    2015-01-01

    Changes in flight direction in flying insects are largely due to roll, yaw and pitch rotations of their body. Head orientation is stabilized for most of the time by counter rotation. Here, we use high-speed video to analyse head- and body-movements of the bumblebee Bombus terrestris while approaching and departing from a food source located between three landmarks in an indoor flight-arena. The flight paths consist of almost straight flight segments that are interspersed with rapid turns. These short and fast yaw turns (“saccades”) are usually accompanied by even faster head yaw turns that change gaze direction. Since a large part of image rotation is thereby reduced to brief instants of time, this behavioural pattern facilitates depth perception from visual motion parallax during the intersaccadic intervals. The detailed analysis of the fine structure of the bees’ head turning movements shows that the time course of single head saccades is very stereotypical. We find a consistent relationship between the duration, peak velocity and amplitude of saccadic head movements, which in its main characteristics resembles the so-called "saccadic main sequence" in humans. The fact that bumblebee head saccades are highly stereotyped as in humans, may hint at a common principle, where fast and precise motor control is used to reliably reduce the time during which the retinal images moves. PMID:26352836

  6. FINE STRUCTURE OF THE EYE OF A CHAETOGNATH.

    PubMed

    EAKIN, R M; WESTFALL, J A

    1964-04-01

    Electron microscopy reveals a star-like pigment cell at the center of the eye of the arrow-worm, Sagitta scrippsae. Between the arms of the pigment cell are clusters of photoreceptor cell processes, each process consisting of: (1) a tubular segment containing longitudinally arranged microtubules about 500 A in diameter and 20 micro in length; (2) a remarkable conical body, composed of cords and large granules, situated at the base of the tubular segment; and (3) a connecting piece which, like that of rods and cones, connects the process with the sensory cell proper and through which runs a fibrillar apparatus consisting of nine peripheral double tubules. Beneath the connecting piece lies a typical centriole with a striated rootlet. The receptor cell process is deeply recessed into the sensory cell which may possess a corona of microvilli at its inner surface. A nerve fiber arises from the outer end of the cell and passes into the optic nerve. Additional features are some supporting cells, an external layer of flattened epithelial cells, and an over-all investment of basement membrane and thick fibrous capsule. The fine structure and function of these elements of the eye are discussed in relation to earlier studies with the light microscope. The ciliary nature of the photoreceptor cell process in S. scrippsae points to a probable evolutionary relationship of chaetognaths to echinoderms and chordates.

  7. Varying fine structure 'constant' and charged black holes

    SciTech Connect

    Bekenstein, Jacob D.; Schiffer, Marcelo

    2009-12-15

    Speculation that the fine-structure constant {alpha} varies in spacetime has a long history. We derive, in 4-D general relativity and in isotropic coordinates, the solution for a charged spherical black hole according to the framework for dynamical {alpha} J. D. Bekenstein, Phys. Rev. D 25, 1527 (1982).. This solution coincides with a previously known one-parameter extension of the dilatonic black hole family. Among the notable properties of varying-{alpha} charged black holes are adherence to a 'no hair' principle, the absence of the inner (Cauchy) horizon of the Reissner-Nordstroem black holes, the nonexistence of precisely extremal black holes, and the appearance of naked singularities in an analytic extension of the relevant metric. The exteriors of almost extremal electrically (magnetically) charged black holes have simple structures which makes their influence on applied magnetic (electric) fields transparent. We rederive the thermodynamic functions of the modified black holes; the otherwise difficult calculation of the electric potential is done by a shortcut. We confirm that variability of {alpha} in the wake of expansion of the universe does not threaten the generalized second law.

  8. THE FINE STRUCTURE OF VON EBNER'S GLAND OF THE RAT

    PubMed Central

    Hand, Arthur R.

    1970-01-01

    The fine structure of von Ebner's gland was studied in untreated rats and rats stimulated to secrete by fasting-refeeding or injection of pilocarpine. Cytological features were similar to those reported for pancreas and parotid gland. Abundant granular endoplasmic reticulum filled the basal portion of the cell, a well-developed Golgi complex was located in the vicinity of the nucleus, and the apical portion of the cell was filled with dense secretory granules. Dense heterogeneous bodies resembling lysosomes were closely associated with the Golgi complex. Coated vesicles were seen in the Golgi region and also in continuity with the cell membrane. Granule discharge occurred by fusion of the granule membrane with the cell membrane at the secretory surface. Successive fusion of adjacent granules to the previously fused granule formed a connected string of granules in the apical cytoplasm. Myoepithelial cells were present within the basement membrane, and nerve processes were seen adjacent to acinar and myoepithelial cells. Duct cells resembled the intercalated duct cells of the major salivary glands. PMID:5411078

  9. THE FINE STRUCTURE OF STREPTOMYCES VIOLACEORUBER (S. COELICOLOR)

    PubMed Central

    Glauert, Audrey M.; Hopwood, David A.

    1961-01-01

    A study of thin sections of hyphae of Streptomyces violaceoruber in the electron microscope showed that the structure of the walls and the mode of formation of cross-walls are similar to those of Gram-positive bacteria. A beaded structure was seen in some regions of the wall, and the significance of this observation is discussed in relation to previous studies of the fine structure of bacterial cell walls. Elements of the intracytoplasmic membrane system appear to be involved in the process of cross-wall formation. The walls of the hyphae of the aerial mycelium divide into two layers before the spores are formed, and only the inner component of the wall grows inwards to form the cross-walls and so delimit the spores. The outer component remains intact for a time and acts as a sheath around the developing spores. Finally the sheath breaks and the spores are liberated. This process is contrasted with the formation of endospores in eubacteria. When the spores germinate, the walls of the germ tubes are continuous with those of the spores. PMID:13705984

  10. Fine structure behaviour of VVER-1000 RPV materials under irradiation

    NASA Astrophysics Data System (ADS)

    Gurovich, B. A.; Kuleshova, E. A.; Shtrombakh, Ya. I.; Erak, D. Yu.; Chernobaeva, A. A.; Zabusov, O. O.

    2009-06-01

    Changes in the fine structure and mechanical properties of the base metal (BM) and weld metal (WM) of VVER-1000 pressure vessels during accumulation of neutron dose in the range of fluences ˜(3.2-15) × 10 23 m -2 ( E > 0.5 MeV) at 290 °C are studied using methods of transmission electron microscopy, fractographic analysis, and Auger electron spectroscopy. A correlation was found between the changes of mechanical properties and the micro- and nano-structures of the studied steels. Accumulation of neutron dose considerably raises the strength characteristics and transition temperature of VVER-1000 pressure vessel steels. The rate of changes in the mechanical properties of the weld metal is significantly higher than that of the base metal. The slower growth of strength characteristics and transition temperature shift of the base metal under irradiation as compared with the weld metal is due to the slower growth of the density of radiation defects and radiation-induced precipitates. The level of intergranular embrittlement under irradiation in the weld metal is not higher then in the base metal in spite of the higher content of nickel.

  11. Hymenolepis nana: the fine structure of the embryonic envelopes.

    PubMed

    Fairweather, I; Threadgold, L T

    1981-06-01

    The fine structure of the envelopes surrounding hatched and unhatched oncospheres of Hymenolepis nana has been investigated by transmission and scanning electron microscopy (SEM), together with light microscope histochemical observations of JB-4 embedded material. The oncosphere is surrounded by 3 layers--the capsule, the outer envelope and the inner envelope, the latter giving rise to the embryophore and the 'oncospheral membrane'. An additional layer--the polar filament layer--lies between the 'oncospheral membrane' and the oncosphere. Shell material is deposited on the capsule as a thin layer. It is secreted by the outer envelope, which degenerates once shell formation is complete. The uterus may also contribute to shell formation. The embryophore forms a thin incomplete and peripheral layer within the inner envelope. In the basal region of this envelope, partial development of an 'oncospheral membrane' takes place, but it does not become detached as a separate layer. The polar filaments, which are characteristic of the oncosphere of H. nana, are derived from the epithelial covering of the oncosphere itself, which delaminates to form a separate polar filament layer. The filaments arise from knob-like projections at opposite poles of this layer. The design of the embryonic envelopes in H. nana show a number of modifications from the basic cyclophyllidean pattern, and these can be related to the demands of its 'direct' life-cycle.

  12. THE FINE STRUCTURE OF THE ELECTRIC ORGAN OF TORPEDO MARMORATA

    PubMed Central

    Sheridan, Michael N.

    1965-01-01

    The fine structure of the electric organ of the fish Torpedo marmorata has been examined after osmium tetroxide or potassium permanganate fixation, acetone dehydration, and Araldite embedment. This organ consists of stacks of electroplaques which possess a dorsal noninnervated and a ventral richly innervated surface. Both surfaces are covered with a thin basement membrane. A tubular membranous network whose lumen is continuous with the extracellular space occupies the dorsal third of the electroplaque. Nerve endings, separated from the ventral surface of the electroplaque by a thin basement membrane, contain synaptic vesicles (diameter 300 to 1200 A), mitochondria, and electron-opaque granules (diameter 300 A). Projections from the nerve endings occupy the lumina of the finger-like invaginations of the ventral surface. The cytoplasm of the electroplaques contains the usual organelles. A "cellular cuff" surrounds most of the nerve fibers in the intercellular space, and is separated from the nerve fibre and its Schwann cell by a space containing connective tissue fibrils. The connective tissue fibrils and fibroblasts in the intercellular space are primarily associated with the dorsal surface of the electroplaque. PMID:14286287

  13. Fine structure genetic analysis of a beta-globin promoter.

    PubMed

    Myers, R M; Tilly, K; Maniatis, T

    1986-05-02

    A novel procedure for saturation mutagenesis of cloned DNA was used to obtain more than 100 single base substitutions within the promoter of the mouse beta-major globin gene. The effects of these promoter substitutions on transcription were determined by transfecting the cloned mutant genes into HeLa cells on plasmids containing an SV40 transcription enhancer, and measuring the levels of correctly initiated beta-globin transcripts after 2 days. Mutations in three regions of the promoter resulted in a significant decrease in the level of transcription: (i) the CACCC box, located between -87 and -95, (ii) the CCAAT box, located between -72 and -77, and (iii) the TATA box, located between -26 and -30 relative to the start site of transcription. In contrast, two different mutations in nucleotides immediately upstream from the CCAAT box resulted in a 3- to 3.5-fold increase in transcription. With two minor exceptions, single base substitutions in all other regions of the promoter had no effect on transcription. These results precisely delineate the cis-acting sequences required for accurate and efficient initiation of beta-globin transcription, and they establish a general approach for the fine structure genetic analysis of eukaryotic regulatory sequences.

  14. Fine structure of A and M antigens from Brucella biovars.

    PubMed

    Meikle, P J; Perry, M B; Cherwonogrodzky, J W; Bundle, D R

    1989-09-01

    Brucella A and M epitopes were found on single O-polysaccharide chains of all biotype strains of this species. Lipopolysaccharides from the type and reference strains of five of the six Brucella species, B. abortus, B. melitensis, B. suis, B. canis, and B. neotomae, were extracted and purified. Analysis by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, in conjunction with silver staining and immunoblotting developed by monoclonal antibodies, showed bands characteristic of A, M, or mixed A and M antigens. The A antigen previously described as an exclusively alpha 1,2-linked homopolymer of 4,6-dideoxy-4-formamido-D-mannopyranose was shown by 1H and 13C nuclear magnetic resonance spectroscopy to possess a fine structure consistent with the low-frequency occurrence of alpha 1, 3-linked 4,6-dideoxy-4-formamido-D-mannopyranose residues. This feature was previously attributed only to the M antigen, which is also a homopolymer of the same sugar. B. melitensis biotype 3 and B. suis biotype 4 lipopolysaccharides showed characteristics of mixed A and M antigens. Immunoabsorption of these O polysaccharides on a column of immobilized A-antigen-specific monoclonal antibody enriched polymer chains with A-antigen characteristics but did not eliminate M epitopes. Composite A- and M-antigen characteristics resulted from O polysaccharides in which the frequency of alpha 1,3 linkages, and hence, M-antigen characteristics, varied. All biotypes assigned as A+ M- expressed one or two alpha 1,3-linked residues per polysaccharide O chain. M antigens (M+ A-) also possessed a unique M epitope as well as a tetrasaccharide determinant common to A-antigen structures. B. canis and B. abortus 45/20, both rough strains, expressed low-molecular-weight A antigen.

  15. A New Physical Meaning of Sommerfeld Fine Structure Constant

    NASA Astrophysics Data System (ADS)

    Sohrab, Siavash

    2015-04-01

    Identifying physical space or Casimir vacuum as a compressible tachyon fluid, Planck compressible ether, leads to stochastic definitions of Planck h = mk <λk > c and Boltzmann k = mk <νk > c constants, finite photon mass mk = (hk/c3)1/2 , amu = mk c2 = (hkc)1/2 , and modified Avogadro-Loschmidt number No = 1/(hkc)1/2 = 6.03766 x1023 mole-1 . Thus, Lorentz-FitzGerald contractions now result from compressibility of physical space and become causal (Pauli) in accordance with Poincaré-Lorentz dynamic theory of relativity as opposed to Einstein kinematic theory of relativity. At thermodynamic equilibrium he = me <λe > ve = hk = mk <λk > c = h, Compton wavelength can be expressed as λc = h/me c = (ve /c)h <λe > /(me <λe > ve) = αλe . Hence, Sommerfeld fine structure constant α is identified as the ratio of electron to photon speeds α = e2/(2ɛo hc) = ve/c = 1/137.036. The mean thermal speed of electron at equilibrium with photon gas is ve = 2.187640x106 m/s and its de Broglie wavelength is λe = 3.3250x10-10 m. Also, electron kinetic energy for oscillations in two directions < x + > and < x- > or ɛe = hνe = me ve2= kTe results in electron temperature Te = 3.15690x105 K.

  16. Fine structure of high-power microwave-induced resistance oscillations

    NASA Astrophysics Data System (ADS)

    Shi, Q.; Zudov, M. A.; Dmitriev, I. A.; Baldwin, K. Â. W.; Pfeiffer, L. Â. N.; West, K. Â. W.

    2017-01-01

    We report on observation of a fine structure of microwave-induced resistance oscillations in an ultraclean two-dimensional electron gas. This fine structure is manifested by multiple secondary sharp extrema, residing beside the primary ones, which emerge at high radiation power. Theoretical considerations reveal that this fine structure originates from multiphoton-assisted scattering off short-range impurities. Unique properties of the fine structure allow us to access all experimental parameters, including microwave power, and to separate different contributions to photoresistance. Furthermore, we show that the fine structure offers a convenient means to quantitatively assess the correlation properties of the disorder potential in high-quality systems, allowing separation of short- and long-range disorder contributions to the electron mobility.

  17. Assessment of XAF1 as A Biomarker to Differentiate Hepatocellular Carcinoma from Nonneoplastic Liver Tissues

    PubMed Central

    Lin, Ying

    2012-01-01

    Objective XIAP-associated factor 1 (XAF1) expression has been shown to be related with apoptosis in hepatocellular carcinoma (HCC). However, the correlation of XAF1 expression with HCC tumor grade has not been intensively assessed. XIAP-associated factor-1 (XAF1) is an important apoptosis inducer in human HCC. The aim of this study is to determine the correlation between XAF1 expression and HCC histopathological grades. Methods The mRNA levels of XAF1 in 24 paired HCC-nonneoplastic specimens were quantified by real-time reverse transcription PCR (RT-PCR). Protein levels of XAF1 in 110 paired HCC-noncancer tissues were investigated by immunostaining specimens on a tissue microarray (TMA). Correlations between XAF1 mRNA levels or protein expression and clinicopathological features were assessed by statistical analysis. Results Both XAF1 mRNA and protein were significantly under-expressed in HCC tissues compared to their non-neoplastic counterparts. No significant relationship was found between XAF1 mRNA or protein expression and histological tumor grade. Conclusion All these data suggest that XAF1 is a potential biomarker for differentiating HCC with noncancerous tissues. PMID:23358741

  18. Fine structure of the 2003 geomagnetic jerk near China

    NASA Astrophysics Data System (ADS)

    Ou, J.; Du, A.

    2015-12-01

    The 2003 jerk has an abrupt change in the geomagnetic secular variation (SV), and was recognized as a local phenomenon of internal origin from the satellite observations (Olsen and Mandea, 2007). Notable strength of the 2003 jerk is located near China. The temporal and spatial features at this area are important to resolve the Earth's core fluid flow dynamics at local scale (e.g. Wardinski et al., 2008). We investigate the temporal-spatial development of the 2003 jerk in more detail near China with the ground-based observations and CHAOS-3 core field model. We select the data in the international geomagnetic quiet days to calculate the monthly means. In order to reduce the influence of the external field, we adopt a function comprising the terms associated with the indices of the geomagnetic activity, and the terms of the periodic signals on the observatory monthly means data (Stewart and Whaler, 1992). We then use an empirical AR-2 model to represent the internal field signals in the observatory data. The extreme detection is applied to identify the jerk in the SV time series. The onset time and the strength of the 2003 jerk are obtained through the detection for geomagnetic field component, X, Y and Z. The maximum of the strength of the 2003 jerk is located under the Indian mainland. The onset time of this jerk propagates approximately southeastward. Two jerks in 2001 and 2003 for the Z component are further compared and they are confirmed as independent processes. We suggest the jerk in 2001 identical to the well known 1999 jerk in Europe (Mandea et al., 2000). Our results reveal the fine structures of the 2003 jerk that corroborate the conclusions in previous studies. The larger scale time-spatial structure given by the AR-2 model constructed from ground observatory data (monthly values) is consistent with the results from the CHAOS-3 model. This structure can be applied for further inversion of the local core surface fluid flow motions.

  19. Excited state molecular structure determination in disordered media using laser pump/x-ray probe time-domain x-ray absorption spectroscopy.

    SciTech Connect

    Chen, L. X.; Chemistry

    2003-01-01

    Advances in X-ray technologies provide opportunities for solving structures of photoexcited state molecules with short lifetimes. Using X-ray pulses from a modern synchrotron source, the structure of a metal-to-ligand-charge-transfer (MLCT) excited state of CuI(dmp)2+ (dmp 1/4 2,9-dimethyl-1,10-phenanthroline) was investigated by laser pump/X-ray probe X-ray absorption fine structure (LPXP-XAFS) in fluid solution at room temperature on a nanosecond time scale. The experimental requirements for such pump-probe XAFS are described in terms of technical challenges: (1) conversion of optimal excited state population, (2) synchronization of the pump laser pulse and probe Xray pulse, and (3) timing of the detection. Using a laser pump pulse for the photoexcitation, a photoluminescent MLCT excited state of CuI(dmp)2(BArF), (dmp 1/4 2,9-dimethyl-1,10-phenanthroline), BArF 1/4 tetrakis(3,5-bis(trifluoromethylphenyl)borate) with a lifetime of 98{+-}5 ns was created. Probing the structure of this state at its optimal concentration using an X-ray pulse cluster with a total duration of 14.2 ns revealed that (1) a Cu{sup II} center was generated via a whole charge transfer; (2) the copper in the MLCT state bound an additional ligand to form a penta-coordinate complex with a likely trigonal bipyramidal geometry; and (3) the average Cu-N bond length increases in the MLCT excited state by 0.07 . In contrast to previously reported literature, the photoluminescence of this pentacoordinate MLCT state was not quenched upon ligation with the fifth ligand. On the basis of experimental results, we propose that the absorptive and emissive states have distinct geometries. The results represent X-ray characterization of a molecular excited state in fluid solution on a nanosecond time scale.

  20. Surface structure of CdSe Nanorods revealed by combined X-rayabsorption fine structure measurements and ab-initio calculations

    SciTech Connect

    Aruguete, Deborah A.; Marcus, Matthew A.; Li, Liang-shi; Williamson, Andrew; Fakra, Sirine; Gygi, Francois; Galli, Giulia; Alivisatos, A. Paul

    2006-01-27

    We report orientation-specific, surface-sensitive structural characterization of colloidal CdSe nanorods with extended X-ray absorption fine structure spectroscopy and ab-initio density functional theory calculations. Our measurements of crystallographically-aligned CdSe nanorods show that they have reconstructed Cd-rich surfaces. They exhibit orientation-dependent changes in interatomic distances which are qualitatively reproduced by our calculations. These calculations reveal that the measured interatomic distance anisotropy originates from the nanorod surface.

  1. Emission wavelength tuning of fluorescence by fine structural control of optical metamaterials with Fano resonance

    PubMed Central

    Moritake, Y.; Kanamori, Y.; Hane, K.

    2016-01-01

    We demonstrated fine emission wavelength tuning of quantum dot (QD) fluorescence by fine structural control of optical metamaterials with Fano resonance. An asymmetric-double-bar (ADB), which was composed of only two bars with slightly different bar lengths, was used to obtain Fano resonance in the optical region. By changing the short bar length of ADB structures with high dimensional accuracy in the order of 10 nm, resonant wavelengths of Fano resonance were controlled from 1296 to 1416 nm. Fluorescence of QDs embedded in a polymer layer on ADB metamaterials were modified due to coupling to Fano resonance and fine tuning from 1350 to 1376 nm was observed. Wavelength tuning of modified fluorescence was reproduced by analysis using absorption peaks of Fano resonance. Tuning range of modified fluorescence became narrow, which was interpreted by a simple Gaussian model and resulted from comparable FWHM in QD fluorescence and Fano resonant peaks. The results will help the design and fabrication of metamaterial devices with fluorophores such as light sources and biomarkers. PMID:27622503

  2. Nonlinear Schrödinger-Poisson definition of fine-structure-constant's value ~1/137

    NASA Astrophysics Data System (ADS)

    Reinisch, G.

    2010-06-01

    By numerically investigating the nonlinear Schrödinger-Poisson eigenstates of a condensed Bose gas of charged particles that is confined in a two-dimensional axisymmetric parabolic potential ½meω2r2 (e.g. quantum-dot helium), it is shown that the probability amplitude between two nonlinear—and hence non-orthogonal—eigenstates displays an interference pattern scaled (within 0.03 %) by graphic equation Since α = e2/hbarc ~ 1/137 is the fine structure constant, this stunning result—indeed velocity of light c does not enter the present non-relativistic model—is tentatively explained by the existence of a "nonlinear" bound state of the trapped particle-particle interaction Coulomb field whose energy cal E = half pi hbar omega defines the induced emission or absorption equilibrium processes between two appropriate chemical potentials. Besides, a non-decoherence quantum-classical transition with increasing nonlinearity is pointed out. As a possible experimental test for the present theory, the 0s2 → 1s2 nonlinear transition in an hbarω = 1.66meV GaAs quantum-dot helium is emphasized.

  3. Impact of instrumental systematic errors on fine-structure constant measurements with quasar spectra

    NASA Astrophysics Data System (ADS)

    Whitmore, Jonathan B.; Murphy, Michael T.

    2015-02-01

    We present a new `supercalibration' technique for measuring systematic distortions in the wavelength scales of high-resolution spectrographs. By comparing spectra of `solar twin' stars or asteroids with a reference laboratory solar spectrum, distortions in the standard thorium-argon calibration can be tracked with ˜10 m s-1 precision over the entire optical wavelength range on scales of both echelle orders (˜50-100 Å) and entire spectrographs arms (˜1000-3000 Å). Using archival spectra from the past 20 yr, we have probed the supercalibration history of the Very Large Telescope-Ultraviolet and Visible Echelle Spectrograph (VLT-UVES) and Keck-High Resolution Echelle Spectrograph (HIRES) spectrographs. We find that systematic errors in their wavelength scales are ubiquitous and substantial, with long-range distortions varying between typically ±200 m s-1 per 1000 Å. We apply a simple model of these distortions to simulated spectra that characterize the large UVES and HIRES quasar samples which previously indicated possible evidence for cosmological variations in the fine-structure constant, α. The spurious deviations in α produced by the model closely match important aspects of the VLT-UVES quasar results at all redshifts and partially explain the HIRES results, though not self-consistently at all redshifts. That is, the apparent ubiquity, size and general characteristics of the distortions are capable of significantly weakening the evidence for variations in α from quasar absorption lines.

  4. Fine Structure of Starch-Clay Composites as Biopolymers

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Midsol 50 wheat starch and 5% Cloisite clay with or without the addition of glycerin were used to prepare biopolymers in a twin-screw extruder. Early trials of sectioning the unembedded biopolymer resulted in the immediate absorption of water and subsequent dissolution of the sample due to the the ...

  5. Relative importance of temporal envelope and fine structure in lexical-tone perception (L)

    NASA Astrophysics Data System (ADS)

    Xu, Li; Pfingst, Bryan E.

    2003-12-01

    The relative importance of temporal envelope and fine structure in speech and music perception was investigated by Smith et al. [Nature (London) 416, 87-90 (2002)] using ``auditory chimera'' in which the envelope from one sound was paired with the fine structure of another. Smith et al. found that, when 4 to 16 frequency bands were used, recognition of English speech was dominated by the envelope, whereas recognition of melody was dominated by the fine structure. In the present study, Mandarin Chinese monosyllables were divided into 4, 8, or 16 frequency bands and the fine structure and envelope of one tone pattern were exchanged with those of another tone pattern of the same monosyllable. Five normal-hearing native Mandarin Chinese speakers completed a four-alternative forced-choice tone-identification task. In the vast majority of trials, subjects based their identification of the monosyllables on the fine structure rather than the envelope. Thus, the relative importance of envelope and fine structure for lexical-tone perception resembled that for melody recognition rather than that for English speech recognition. Delivering fine-structure information in cochlear implant stimulation could be particularly beneficial for lexical-tone perception.

  6. THE FINE STRUCTURE OF CORTICAL COMPONENTS OF PARAMECIUM MULTIMICRONUCLEATUM

    PubMed Central

    Sedar, Albert W.; Porter, Keith R.

    1955-01-01

    additional fiber system, the infraciliary lattice system, which is separate and distinct from the kinetodesmal system. This system consists of a fibrous network of irregular polygons and runs roughly parallel to the surface of the animal. Mitochondria have a fine structure similar in general features to that described for a number of mammalian cell types, but different in certain details. The structures corresponding to cristae mitochondriales appear as finger-like projections or microvilli extending into the matrix of the organelle from the inner membrane of the paired mitochondrial membrane. The cortical cytoplasm contains also a particulate component and a system of vesicles respectively comparable to the nucleoprotein particles and to the endoplasmic reticulum described in various metazoan cell types. An accessory kinetosome has been observed in oblique sections of a number of non-dividing specimens slightly removed from the ciliary kinetosome and on the same meridional line as the cilia and trichocysts. Its position corresponds to the location of the kinetosome of the newly formed cilium in animals selected as being in the approaching fission stage of the life cycle. PMID:13278368

  7. On the 1s24d Fine Structures of B III and Ne VIII

    NASA Astrophysics Data System (ADS)

    Wang, Zhiwen; Z, W. Wang; Kwong, T. Chung; Zhu, Xiaowei

    1995-01-01

    The fine structure of lithium-like 1s24d states in the literature behaves irregularly as a function of Z. The fine structures of the B III and Ne VIII fall well below the isoelectronic curve. The term energies of these two systems in the data tables also give worse agreement with the theoretical prediction. In this work, we show that the reason for this unusual situation is caused by a misidentification in the original spectra. When the correct identifications are made, the fine structures of both systems fall on the isoelectronic curve and the agreement between theory and experiment is excellent.

  8. Measurement of the lithium 10p fine structure interval and absolute energy

    SciTech Connect

    Oxley, Paul; Collins, Patrick

    2010-02-15

    We report a measurement of the fine structure interval of the {sup 7}Li 10p atomic state with a precision significantly better than previous measurements of fine structure intervals of Rydberg {sup 7}Li p states. Our result of 74.97(74) MHz provides an experimental value for the only n=10 fine structure interval which is yet to be calculated. We also report a measurement of the absolute energy of the 10p state and its quantum defect, which are, respectively, 42379.498(23)cm{sup -1} and 0.04694(10). These results are in good agreement with recent calculations.

  9. Fine structure of the amide i band in acetanilide

    NASA Astrophysics Data System (ADS)

    Careri, G.; Gratton, E.; Shyamsunder, E.

    1988-05-01

    Their absorption spectrum of both single crystals and powdered samples of acetanilide (a model system for proteins) has been studied in the amide i region, where a narrow band has been identified as a highly trapped soliton state. The powder-sample spectra have been decomposed using four Lorentzian bands. A strong temperature dependence has been found for the intensity of two of the subbands, which also show a complementary behavior. Polarization studies performed on thin crystals have shown that the subbands have the same polarization. Low-temperature spectra of partially deuterated samples show the presence of the subbands at the same absorption frequencies found using the fitting procedure in the spectra of nondeuterated samples. The soliton model currently proposed to explain the origin of the anomalous amide i component at 1650 cm-1 still holds, but some modification of the model is required to account for the new features revealed by this study.

  10. Comparative XAFS studies of some Cobalt complexes of (3-N- phenyl -thiourea-pentanone-2)

    NASA Astrophysics Data System (ADS)

    soni, Namrata; Parsai, Neetu; Mishra, Ashutosh

    2016-10-01

    XAFS spectroscopy is a useful method for determining the local structure around a specific atom in disordered systems. XAFS study of some cobalt complexes of (3-N-phenyle- thiourea-pentanon-2) is carried out using the latest XAFS analysis software Demeter with Strawberry Perl. The same study is also carried out theoretically using Mathcad software. It is found that the thiourea has significant influence in the spectra and the results obtained experimentally and theoretically are in agreement. Fourier transform of the experimental and theoretically generated XAFS have been taken to obtain first shell radial distance. The values so obtained are in agreement with each other.

  11. Americium characterization by X-ray fluorescence and absorption spectroscopy in plutonium uranium mixed oxide

    NASA Astrophysics Data System (ADS)

    Degueldre, Claude; Cozzo, Cedric; Martin, Matthias; Grolimund, Daniel; Mieszczynski, Cyprian

    2013-06-01

    Plutonium uranium mixed oxide (MOX) fuels are currently used in nuclear reactors. The actinides in these fuels need to be analyzed after irradiation for assessing their behaviour with regard to their environment and the coolant. In this work the study of the atomic structure and next-neighbour environment of Am in the (Pu,U)O2 lattice in an irradiated (60 MW d kg-1) MOX sample was performed employing micro-X-ray fluorescence (µ-XRF) and micro-X-ray absorption fine structure (µ-XAFS) spectroscopy. The chemical bonds, valences and stoichiometry of Am (˜0.66 wt%) are determined from the experimental data gained for the irradiated fuel material examined in its peripheral zone (rim) of the fuel. In the irradiated sample Am builds up as Am3+ species within an [AmO8]13- coordination environment (e.g. >90%) and no (<10%) Am(IV) or (V) can be detected in the rim zone. The occurrence of americium dioxide is avoided by the redox buffering activity of the uranium dioxide matrix.

  12. XAFS study of americium sorbed onto groundwater colloids.

    PubMed

    Degueldre, Claude; Reed, Donald; Kropf, A Jeremy; Mertz, Carol

    2004-03-01

    The sorption of americium, as Am(III), onto groundwater colloids obtained from a marl aquifer was studied in 2 x 10(-2)M sodium bicarbonate groundwater and 2 x 10(-2)M sodium chloride bicarbonate-free solutions. At the in situ groundwater pH of 8.6, the americium was strongly sorbed onto the colloids. XAFS analyses were performed on these sorbed Am species to establish the oxidation state and its near-neighbour bonding. These XAFS data, obtained at 400 mg l(-1) colloid concentrations and total Am concentration of 1.53 x 10(-5)M (dissolved and onto colloids), indicated that Am remains trivalent, and that surface complexes are formed with the colloids without surface precipitation. This conclusion is based on the absence of Am-Am interactions in the second or third shells. The surface complexes generated by the Am(III) sorbed onto active sites are described on the basis of the XAFS data. They include the presence of about seven water molecules around the ternary surface complexes of this trivalent actinide.

  13. MacXAFS: An EXAFS analysis package for the Macintosh

    NASA Astrophysics Data System (ADS)

    Bouldin, C.; Furenlid, L.; Elam, T.

    1995-02-01

    We present an EXAFS analysis package that runs on the Apple Macintosh. (Certain commercial products are identified in the article for the sake of completeness. This does not constitute and endorsement by the National Institute of Standards and Technology, the Naval Research Laboratory, or Broohaven National Lab.) The MacXAFS package is derived from a suite of EXAFS analysis programs originally written at the University of Washington. The MacXAFS package preserves the portable computational kernel of this well-tested group of programs and adds a graphical interface by using HyperCard. Communication between the core analysis programs and the HyperCard interface is done by using ASCII script files that direct the execution of the FORTRAN-based analysis programs. The user is largely insulated from the FORTRAN code, but instead interacts with the more intuitive Hypercard interface. This implementation preserves the portability of the ANSI FORTRAN programs, while taking full advantage of the platform-specific user interface features of the Macintosh. Computationally intensive programs, such as the ab initio XAFS calculation program FEFF can be executed remotely via a TCP/IP connection. Due to the clean separation of the interface and the computational kernel, this package is readily extensible by writing new programs, in FORTRAN or any other language, and adding the corresponding interface element in the HyperCard stack.

  14. Sulphur speciation in bitumens and asphaltenes by X-ray absorption fine structure spectroscopy

    SciTech Connect

    Kasrai, M.; Bancroft, G.M.; Brunner, R.W. ); Jonasson, R.G. ); Tan, K.H.; Feng, X. ); Brown, J.R.

    1994-07-01

    The S L-edge and K-edge XANES spectra were collected on bitumen and asphaltene samples as well as model compounds in order to determine the feasibility of monitoring transformations of organic sulphur in bitumen during genesis, processing, and upgrading. Using the spectra of model compounds as fingerprints, it was possible to speciate the sulphur forms in bitumen and asphaltene. The reduced form of sulphur such as thiophenes are the predominant form of sulphur in the bitumen and asphaltene samples analyzed. No significant amounts of oxidized sulphur forms could be detected. Spectra collected using total electron yield and fluorescence yield were identical, confirming that there is no preferential partitioning at the bitumen/air interface, or oxidation during sample handling. Also important was the finding that bitumen could be analyzed at moderately high vacuum (10[sup [minus]8] torr). Thus XANES represents a rapid, nondestructive mean of characterizing specific classes of compounds in complex matrices, such as bitumen.

  15. PLUTONIUM CONTAMINATION VALENCE STATE DETERMINATION USING X-RAY ABSORPTION FINE STRUCTURE PERMITS CONCRETE RECYCLE

    SciTech Connect

    Ervin, P. F.; Conradson, S. D.

    2002-02-25

    This paper describes the determination of the speciation of plutonium contamination present on concrete surfaces at the Rocky Flats Environmental Technology Site (RFETS). At RFETS, the plutonium processing facilities have been contaminated during multiple events over their 50 year operating history. Contamination has resulted from plutonium fire smoke, plutonium fire fighting water, milling and lathe operation aerosols, furnace operations vapors and plutonium ''dust'' diffusion.

  16. Near-Edge X-ray Absorption Fine Structure within Multilevel Coupled Cluster Theory.

    PubMed

    Myhre, Rolf H; Coriani, Sonia; Koch, Henrik

    2016-06-14

    Core excited states are challenging to calculate, mainly because they are embedded in a manifold of high-energy valence-excited states. However, their locality makes their determination ideal for local correlation methods. In this paper, we demonstrate the performance of multilevel coupled cluster theory in computing core spectra both within the core-valence separated and the asymmetric Lanczos implementations of coupled cluster linear response theory. We also propose a visualization tool to analyze the excitations using the difference between the ground-state and excited-state electron densities.

  17. Magnetic diffusion instability and the fine structures of soler active region

    NASA Astrophysics Data System (ADS)

    Zhou, Dao-qi; Qian, Jing-kui; Ai, Guo-xiang

    1990-03-01

    Continuous observations over five days with the magnetic field telescope at Huairou yielded some clear characteristics of the fine structures in sunspot active regions. Starting from magnetic diffusivity being a function of temperature and using the induction equation we investigated the cause of the fine structures. Using linear perturbation of the MHD equations we found the instability mode. This gives rise to inhomogeneous structures in the originally smooth magnetic field and is the cause of the fine structures. Our observed fibrilles are about 1.5″ to 3.0″, or 1000 to 2000km in size, whereas, with certain typical values of sunspot parameters the theoretical lower limit for the fine structures is about 220km, in agreement with some observational estimates.

  18. Fine structural characterization of microbodies and Woronin bodies in Trichophyton mentagrophytes.

    PubMed

    Vannini, G L; Mares, D

    1975-08-15

    Microbodies and Woronin bodies, organelles surrounded by a single unit membrane, were identified in the hyphal cells of Trichophyton mentagrophytes by employing a fixative containing TAPO. The fine structure of the organelles is described and their possible significance discussed.

  19. Impaired perception of temporal fine structure and musical timbre in cochlear implant users.

    PubMed

    Heng, Joseph; Cantarero, Gabriela; Elhilali, Mounya; Limb, Charles J

    2011-10-01

    Cochlear implant (CI) users demonstrate severe limitations in perceiving musical timbre, a psychoacoustic feature of sound responsible for 'tone color' and one's ability to identify a musical instrument. The reasons for this limitation remain poorly understood. In this study, we sought to examine the relative contributions of temporal envelope and fine structure for timbre judgments, in light of the fact that speech processing strategies employed by CI systems typically employ envelope extraction algorithms. We synthesized "instrumental chimeras" that systematically combined variable amounts of envelope and fine structure in 25% increments from two different source instruments with either sustained or percussive envelopes. CI users and normal hearing (NH) subjects were presented with 150 chimeras and asked to determine which instrument the chimera more closely resembled in a single-interval two-alternative forced choice task. By combining instruments with similar and dissimilar envelopes, we controlled the valence of envelope for timbre identification and compensated for envelope reconstruction from fine structure information. Our results show that NH subjects utilize envelope and fine structure interchangeably, whereas CI subjects demonstrate overwhelming reliance on temporal envelope. When chimeras were created from dissimilar envelope instrument pairs, NH subjects utilized a combination of envelope (p = 0.008) and fine structure information (p = 0.009) to make timbre judgments. In contrast, CI users utilized envelope information almost exclusively to make timbre judgments (p < 0.001) and ignored fine structure information (p = 0.908). Interestingly, when the value of envelope as a cue was reduced, both NH subjects and CI users utilized fine structure information to make timbre judgments (p < 0.001), although the effect was quite weak in CI users. Our findings confirm that impairments in fine structure processing underlie poor perception of musical timbre in CI

  20. Path integral formalism for the spectral line shape in plasmas: Lyman-{alpha} with fine structure

    SciTech Connect

    Bedida, N.; Meftah, M. T.; Boland, D.; Stamm, R.

    2008-10-22

    We examine in this work the expression of the dipolar autocorrelation function for an emitter in the plasma using the path integrals formalism. The results for Lyman alpha lines with fine structure are retrieved in a compact formula. The expression of the dipolar autocorrelation function takes into account the ions dynamics and the fine structure effects. The electron's effect is represented by the impact operator {phi}{sub e} in the final formula.

  1. Globular Clusters as Tracers of Fine Structure in the Dramatic Shell Galaxy NGC 474

    NASA Astrophysics Data System (ADS)

    Lim, Sungsoon; Peng, Eric W.; Duc, Pierre-Alain; Fensch, Jérémy; Durrell, Patrick R.; Harris, William E.; Cuillandre, Jean-Charles; Gwyn, Stephen; Lançon, Ariane; Sánchez-Janssen, Rúben

    2017-02-01

    Globular clusters (GCs) are some of the most visible tracers of the merging and accretion histories of galaxy halos. Metal-poor GCs, in particular, are thought to arrive in massive galaxies largely through dry, minor merging events, but it is rare to see a direct connection between GCs and visible stellar streams. NGC 474 is a post-merger early-type galaxy with dramatic fine structures made of concentric shells and radial streams that have been more clearly revealed by deep imaging. We present a study of GCs in NGC 474 to better establish the relationship between merger-induced fine structure and the GC system. We find that many GCs are superimposed on visible streams and shells, and about 35% of GCs outside 3{R}{{e},{galaxy}} are located in regions of fine structure. The spatial correlation between GCs and fine structure is significant at the 99.9% level, which shows that this correlation is not coincidental. The colors of GCs on fine structures are mostly blue, and we also find an intermediate-color population that is dominant in the central region and that will likely passively evolve to have colors consistent with a traditional metal-rich GC population. The association of the blue GCs with fine structures is direct confirmation that many metal-poor GCs are accreted onto massive galaxy halos through merging events and that the progenitors of these mergers are sub-{L}\\star galaxies.

  2. Nickel speciation of residual oil fly ash and ambient particulate matter using X-ray absorption spectroscopy.

    PubMed

    Galbreath, K C; Toman, D L; Zygarlicke, C J; Huggins, F E; Huffman, G P; Wong, J L

    2000-11-01

    The chemical speciation of Ni in fly ash produced from approximately 0.85 wt % S residual (no. 6 fuel) oils in laboratory (7 kW)- and utility (400 MW)-scale combustion systems was investigated using X-ray absorption fine structure (XAFS) spectroscopy, X-ray diffraction (XRD), and acetate extraction [1 M NaOAc-0.5 M HOAc (pH 5) at 25 degrees C]-anodic stripping voltammetry (ASV). XAFS was also used to determine the Ni speciation of ambient particulate matter (PM) sampled near the 400-MW system. Based on XAFS analyses of bulk fly ash and their corresponding acetate extraction residue, it is estimated that > 99% of the total Ni (0.38 wt %) in the experimentally produced fly ash occurs as NiSO4.xH2O, whereas > 95% of the total Ni (1.70 and 2.25 wt %) in two fly ash samples from the 400-MW system occurs as NiSO4.xH2O and Ni-bearing spinel, possibly NiFe2O4. Spinel was also detected using XRD. Acetate extracts most of the NiSO4.xH2O and concentrates insoluble NiFe2O4 in extraction residue. Similar to fly ash, ambient PM contains NiSO4.xH2O and NiFe2O4; however, the proportion of NiSO4.xH2O relative to NiFe2O4 is much greater in the PM. Results from this and previous investigations indicate that residual oil ash produced in the 7-kW combustion system lack insoluble Ni (e.g., NiFe2O4) but are enriched in soluble NiSO4.xH2O relative to fly ash from utility-scale systems. This difference in Ni speciation is most likely related to the lack of additive [e.g., Mg(OH)2] injection and residence time in the 7-kW combustion system.

  3. Quantifying envelope and fine-structure coding in auditory nerve responses to chimaeric speech.

    PubMed

    Heinz, Michael G; Swaminathan, Jayaganesh

    2009-09-01

    Any sound can be separated mathematically into a slowly varying envelope and rapidly varying fine-structure component. This property has motivated numerous perceptual studies to understand the relative importance of each component for speech and music perception. Specialized acoustic stimuli, such as auditory chimaeras with the envelope of one sound and fine structure of another have been used to separate the perceptual roles for envelope and fine structure. Cochlear narrowband filtering limits the ability to isolate fine structure from envelope; however, envelope recovery from fine structure has been difficult to evaluate physiologically. To evaluate envelope recovery at the output of the cochlea, neural cross-correlation coefficients were developed that quantify the similarity between two sets of spike-train responses. Shuffled auto- and cross-correlogram analyses were used to compute separate correlations for responses to envelope and fine structure based on both model and recorded spike trains from auditory nerve fibers. Previous correlogram analyses were extended to isolate envelope coding more effectively in auditory nerve fibers with low center frequencies, which are particularly important for speech coding. Recovered speech envelopes were present in both model and recorded responses to one- and 16-band speech fine-structure chimaeras and were significantly greater for the one-band case, consistent with perceptual studies. Model predictions suggest that cochlear recovered envelopes are reduced following sensorineural hearing loss due to broadened tuning associated with outer-hair cell dysfunction. In addition to the within-fiber cross-stimulus cases considered here, these neural cross-correlation coefficients can also be used to evaluate spatiotemporal coding by applying them to cross-fiber within-stimulus conditions. Thus, these neural metrics can be used to quantitatively evaluate a wide range of perceptually significant temporal coding issues relevant to

  4. Effects of contralateral acoustic stimulation on spontaneous otoacoustic emissions and hearing threshold fine structure.

    PubMed

    Dewey, James B; Lee, Jungmee; Dhar, Sumitrajit

    2014-12-01

    Medial olivocochlear (MOC) influence on cochlear mechanics can be noninvasively, albeit indirectly, explored via the effects of contralateral acoustic stimulation (CAS) on otoacoustic emissions. CAS-mediated effects are particularly pronounced for spontaneous otoacoustic emissions (SOAEs), which are typically reduced in amplitude and shifted upward in frequency by CAS. We investigated whether similar frequency shifts and magnitude reductions were observed behaviorally in the fine structure of pure-tone hearing thresholds, a phenomenon thought to share a common underlying mechanism with SOAEs. In normal-hearing listeners, fine-resolution thresholds were obtained over a narrow frequency range centered on the frequency of an SOAE, both in the absence and presence of 60-dB SPL broadband CAS. While CAS shifted threshold fine structure patterns and SOAEs upward in frequency by a comparable amount, little reduction in the presence or depth of fine structure was observed at frequencies near those of SOAEs. In fact, CAS typically improved thresholds, particularly at threshold minima, and increased fine structure depth when reductions in the amplitude of the associated SOAE were less than 10 dB. Additional measurements made at frequencies distant from SOAEs, or near SOAEs that were more dramatically reduced in amplitude by the CAS, revealed that CAS tended to elevate thresholds and reduce threshold fine structure depth. The results suggest that threshold fine structure is sensitive to MOC-mediated changes in cochlear gain, but that SOAEs complicate the interpretation of threshold measurements at nearby frequencies, perhaps due to masking or other interference effects. Both threshold fine structure and SOAEs may be significant sources of intersubject and intrasubject variability in psychoacoustic investigations of MOC function.

  5. (Research at and operation of the material science x-ray absorption beamline (X-11) at the National Synchrotron Light Source)

    SciTech Connect

    Not Available

    1992-01-01

    This report discusses three projects at the Material Science X-Ray Absorption Beamline. Topics discussed include: XAFS study of some titanium silicon and germanium compounds; initial XAS results of zirconium/silicon reactions; and low angle electron yield detector.

  6. [Research at and operation of the material science x-ray absorption beamline (X-11) at the National Synchrotron Light Source]. Progress report

    SciTech Connect

    Not Available

    1992-08-01

    This report discusses three projects at the Material Science X-Ray Absorption Beamline. Topics discussed include: XAFS study of some titanium silicon and germanium compounds; initial XAS results of zirconium/silicon reactions; and low angle electron yield detector.

  7. ISO-SWS observations of OMC-1: H_2 and fine structure lines

    NASA Astrophysics Data System (ADS)

    Rosenthal, D.; Bertoldi, F.; Drapatz, S.

    2000-04-01

    Using the Short-Wavelength-Spectrometer on the Infrared Space Observatory (ISO), we obtained near- and mid-infrared spectra toward the brightest H_2 emission peak of the Orion OMC-1 outflow. A wealth of emission and absorption features were detected, dominated by 56 H_2 ro-vibrational and pure rotational lines reaching from H_2 0-0 S(1) to 0-0 S(25). The spectra also show a number of H i recombination lines, atomic and ionic fine structure lines, and molecular lines of CO and H_2O. Between 6 and 12 μm the emission is dominated by PAH features. The extinction toward the molecular and atomic line emitting regions is estimated from relative line intensities, and it is found that the H_2 emission arises from within the OMC-1 cloud at an average K-band extinction of 1.0 mag, whereas the atomic hydrogen emission and much of the fine structure emission comes from the foreground H ii region and its bounding photodissociation front. H_2 1-0 S(1) emission of the OMC-1 outflow as seen with the NICMOS camera aboard the HST (Schultz et al. 1999). Overlaid are the various apertures of our ISO-SWS observations, which were centered on alpha_2000 . = 5h 35m 13.s 67, delta_2000 . = -5 degr 22 arcmin 8. arcsec 5, with an aperture of 14 arcsec x 20 arcsec for lambda < 12 μm, 14 arcsec x 27 arcsec at 12 to 27.5μm, 20 arcsec x 27 arcsec at 27.5 to 29μm, and 20 arcsec x 33 arcsec at 29 to 45.2μm. The total H_2 luminosity in the ISO-SWS aperture is estimated at (17 +/- 5) Lsun , and extrapolated to the entire outflow, (120 +/- 60) Lsun . The H_2 level column density distribution shows no signs of fluorescent excitation or a deviation from an ortho-to-para ratio of three. It shows an excitation temperature which increases from about 600 K for the lowest rotational and vibrational levels to about 3200 K at level energies E(v,J)/k > 14 000 K. No single steady state shock model can reproduce the observed H_2 excitation. The higher energy H_2 levels may be excited either thermally in non

  8. A simulation for gravity fine structure recovery from high-low GRAVSAT SST data

    NASA Technical Reports Server (NTRS)

    Estes, R. H.; Lancaster, E. R.

    1976-01-01

    Covariance error analysis techniques were applied to investigate estimation strategies for the high-low SST mission for accurate local recovery of gravitational fine structure, considering the aliasing effects of unsolved for parameters. Surface density blocks of 5 deg x 5 deg and 2 1/2 deg x 2 1/2 deg resolution were utilized to represent the high order geopotential with the drag-free GRAVSAT configured in a nearly circular polar orbit at 250 km. altitude. GEOPAUSE and geosynchronous satellites were considered as high relay spacecraft. It is demonstrated that knowledge of gravitational fine structure can be significantly improved at 5 deg x 5 deg resolution using SST data from a high-low configuration with reasonably accurate orbits for the low GRAVSAT. The gravity fine structure recoverability of the high-low SST mission is compared with the low-low configuration and shown to be superior.

  9. Excited-state energies and fine structure of highly charged lithiumlike ions

    NASA Astrophysics Data System (ADS)

    Li, Jin-ying; Ding, Da-jun; Wang, Zhi-wen

    2013-10-01

    The full-core-plus-correlation method (FCPC) is extended to calculate the energies and fine structures of 1s2nd and 1s2nf (n≤5) states for the lithiumlike systems with high nuclear charge from Z = 41 to 50. In calculating energy, the higher-order relativistic contribution is estimated under a hydrogenic approximation. The nonrelativistic energies and wave functions are calculated by the Rayleigh-Ritz method. The mass polarization and the relativistic corrections including the kinetic energy correction, the Darwin term, the electron-electron contact term, and the orbit-orbit interaction are calculated perturbatively as the first-order correction. The quantum-electrodynamics contributions to the energy and to the fine-structure splitting are estimated by using the effective nuclear charge formula. The excited energies, the fine structures, and other relevant term energies are given and compared with the data available in the literature.

  10. Is it homogeneous or heterogeneous catalysis derived from [RhCp*Cl2]2? In operando XAFS, kinetic, and crucial kinetic poisoning evidence for subnanometer Rh4 cluster-based benzene hydrogenation catalysis.

    PubMed

    Bayram, Ercan; Linehan, John C; Fulton, John L; Roberts, John A S; Szymczak, Nathaniel K; Smurthwaite, Tricia D; Özkar, Saim; Balasubramanian, Mahalingam; Finke, Richard G

    2011-11-23

    Determining the true, kinetically dominant catalytically active species, in the classic benzene hydrogenation system pioneered by Maitlis and co-workers 34 years ago starting with [RhCp*Cl(2)](2) (Cp* = [η(5)-C(5)(CH(3))(5)]), has proven to be one of the most challenging case studies in the quest to distinguish single-metal-based "homogeneous" from polymetallic, "heterogeneous" catalysis. The reason, this study will show, is the previous failure to use the proper combination of: (i) in operando spectroscopy to determine the dominant form(s) of the precatalyst's mass under catalysis (i.e., operating) conditions, and then crucially also (ii) the previous lack of the necessary kinetic studies, catalysis being a "wholly kinetic phenomenon" as J. Halpern long ago noted. An important contribution from this study will be to reveal the power of quantitiative kinetic poisoning experiments for distinguishing single-metal, or in the present case subnanometer Rh(4) cluster-based catalysis, from larger, polymetallic Rh(0)(n) nanoparticle catalysis, at least under favorable conditions. The combined in operando X-ray absorption fine structure (XAFS) spectroscopy and kinetic evidence provide a compelling case for Rh(4)-based, with average stoichiometry "Rh(4)Cp*(2.4)Cl(4)H(c)", benzene hydrogenation catalysis in 2-propanol with added Et(3)N and at 100 °C and 50 atm initial H(2) pressure. The results also reveal, however, that if even ca. 1.4% of the total soluble Rh(0)(n) had formed nanoparticles, then those Rh(0)(n) nanoparticles would have been able to account for all the observed benzene hydrogenation catalytic rate (using commercial, ca. 2 nm, polyethyleneglycol-dodecylether hydrosol stabilized Rh(0)(n) nanoparticles as a model system). The results--especially the poisoning methodology developed and employed--are of significant, broader interest since determining the nature of the true catalyst continues to be a central, often vexing issue in any and all catalytic reactions

  11. Transition wavelengths and fine structure for the doublet states of Be/sup +/

    SciTech Connect

    Davis, B.F.; Chung, K.T.

    1984-05-01

    Seventeen bound and core-excited states of Be/sup +/ are calculated using configuration-interaction wave functions. Relativistic and mass-polarization correction are included. The relativistic corrections considered are correction to the kinetic energy, Darwin term, contact terms, and retardation effect. The fine structure is calculated by using spin-orbit and spin-other-orbit operators. The wavelengths computed for the transitions from the core-excited states improve the agreement between theory and experiment. The lifetimes for these states are also calculated. Our calculated transition wavelengths and fine structures for the bound states agree well in most cases with the experimental data tabulated by Bashkin and Stoner.

  12. Enhancement of speech intelligibility in reverberant rooms: role of amplitude envelope and temporal fine structure.

    PubMed

    Srinivasan, Nirmal Kumar; Zahorik, Pavel

    2014-06-01

    The temporal envelope and fine structure of speech make distinct contributions to the perception of speech in normal-hearing listeners, and are differentially affected by room reverberation. Previous work has demonstrated enhanced speech intelligibility in reverberant rooms when prior exposure to the room was provided. Here, the relative contributions of envelope and fine structure cues to this intelligibility enhancement were tested using an open-set speech corpus and virtual auditory space techniques to independently manipulate the speech cues within a simulated room. Intelligibility enhancement was observed only when the envelope was reverberant, indicating that the enhancement is envelope-based.

  13. A note on chromospheric fine structure at active region polarity boundaries.

    NASA Technical Reports Server (NTRS)

    Prata, S. W.

    1971-01-01

    High resolution H-alpha filtergrams from Big Bear Solar Observatory reveal that some filamentary features in active regions have fine structure and hence magnetic field transverse to the gross structure and the zero longitudinal field line. These features are distinct from the usual active region filament, in which fine structure, magnetic field, and filament are all parallel to the zero longitudinal field line. The latter occur on boundaries between regions of weaker fields, while the former occur at boundaries between regions of stronger field.

  14. Modification of DPOAE Fine Structure Stemming from Changes in Outer and Middle Ear Function

    NASA Astrophysics Data System (ADS)

    Long, Glenis R.; Henin, Simon; Thompson, Suzanne

    2011-11-01

    High resolution DPOAE fine structure was evaluated when the output impedance of the cochlea was modified by: (1) Changes in outer ear volume, due to accumulation of cerumen, which does not modify input impedance. (2) Manipulation of middle ear pressure and scarring of the tympanic membrane (which modify both input and output impedance). At high primary levels a wider and deeper DPOAE structure combined with (and sometimes dominated) DPOAE level fine structure. The group delay was also modified, sometimes giving rise to negative group delay. The data can be modeled by assuming that the increased impedance at the oval widow produces reflections back into the cochlea which can be re-reflected.

  15. Progress towards a precision measurement of the n=2 triplet P fine structure of atomic helium

    NASA Astrophysics Data System (ADS)

    Kato, K.; Fitzakerley, D. W.; George, M. C.; Vutha, A. C.; Storry, C. H.; Hessels, E. A.

    2016-05-01

    We report progress on the measurement of the J = 1 to J = 2 23 P fine-structure interval of atomic helium. The measurement uses a liquid-nitrogen-cooled DC discharge source of metastable helium and the atomic beam is laser cooled in the transverse directions. The atoms are excited to 23 P by a 1083-nm diode laser, and the fine-structure transition is driven by microwaves using the frequency-offset separated oscillatory fields technique. The transition is detected by further laser excitation to a Rydberg state, followed by Stark ionization. This work is supported by NSERC, CRC.

  16. Suppression of fine-structure splitting and oscillator strength of sodium D-line in a Debye plasma

    SciTech Connect

    Basu, Joyee Ray, Debasis

    2014-01-15

    We investigate theoretically the influence of static plasma screening on relativistic spin-orbit interaction-induced fine-structure splitting of the D-line doublet arising from the transitions 3p{sub 1/2}–3s{sub 1/2} and 3p{sub 3/2}–3s{sub 1/2} of the valence electron of a sodium atom embedded in a model plasma environment. The many-electron atomic problem is formulated first as an effective one-electron problem in which the interaction between the optically active valence electron and the atomic ion core is represented by an accurate parametric model potential including core-polarization correction, and then the plasma effect on the atomic system is simulated by the Debye-screening model for the valence-core interaction. It is observed that the magnitude of spin-orbit energy shift reduces for both the upper component 3p{sub 3/2} and the lower component 3p{sub 1/2} with increasing plasma screening strength, thereby reducing the spin-orbit energy separation between these two components as the screening becomes stronger. As a consequence, the magnitude of fine-structure splitting between the D{sub 1} and D{sub 2} line energies of sodium drops significantly with stronger plasma screening. The optical (absorption) oscillator strength for 3s → 3p transition is seen to reduce with stronger screening and this leads to a screening-induced gradual suppression of the 3p → 3s spontaneous decay rate.

  17. Fine structure of the subradular organ of Lepidochitona cinereus (L), (Mollusca, Polyplacophora).

    PubMed

    Boyle, P R

    1975-10-13

    Electron microscopy of the subradular organ of the chiton Lepidochitona cinereus (L) reveals at least three cell types, microvillous, ciliated and mucus-secreting, situated in a single epithelium. The base of the epithelium is abundantly innervated and supplied with muscle cells. The fine structure is consistent with a chemosensory function for the subradular organ.

  18. Site-specific ionisation edge fine-structure of Rutile in the electron microscope.

    PubMed

    Hetaba, Walid; Löffler, Stefan; Willinger, Marc-Georg; Schuster, Manfred Erwin; Schlögl, Robert; Schattschneider, Peter

    2014-08-01

    Combined Bloch-wave and density functional theory simulations are performed to investigate the effects of different channelling conditions on the fine-structure of electron energy-loss spectra. The simulated spectra compare well with experiments. Furthermore, we demonstrate that using this technique, the site-specific investigation of atomic orbitals is possible. This opens new possibilities for chemical analyses.

  19. Photoionization modeling of the LWS fine-structure lines in IR bright galaxies

    NASA Technical Reports Server (NTRS)

    Satyapal, S.; Luhman, M. L.; Fischer, J.; Greenhouse, M. A.; Wolfire, M. G.

    1997-01-01

    The long wavelength spectrometer (LWS) fine structure line spectra from infrared luminous galaxies were modeled using stellar evolutionary synthesis models combined with photoionization and photodissociation region models. The calculations were carried out by using the computational code CLOUDY. Starburst and active galactic nuclei models are presented. The effects of dust in the ionized region are examined.

  20. Accuracy of mapping the Earth's gravity field fine structure with a spaceborne gravity gradiometer mission

    NASA Technical Reports Server (NTRS)

    Kahn, W. D.

    1984-01-01

    The spaceborne gravity gradiometer is a potential sensor for mapping the fine structure of the Earth's gravity field. Error analyses were performed to investigate the accuracy of the determination of the Earth's gravity field from a gravity field satellite mission. The orbital height of the spacecraft is the dominating parameter as far as gravity field resolution and accuracies are concerned.

  1. Comment on ``Interpretation of the fine structure in the 14C radioactive decay of 223'

    NASA Astrophysics Data System (ADS)

    Hussonnois, M.; Le Du, J. F.; Brillard, L.; Ardisson, G.

    1991-12-01

    Priority of our interpretation of the fine structure in the 14C radioactive decay of 223Ra is asserted. It seems that the deformation parameter values, used in the framework of ARM to interpret properties of both 223Ra ground and excited states, partly allow for the qualitative interpretation of the experimental hindrance factors to the 209Pb states.

  2. X.a.f.s. studies of chicken dicupric ovotransferrin.

    PubMed Central

    Garratt, R C; Evans, R W; Hasnain, S S; Lindley, P F; Sarra, R

    1991-01-01

    A comparison of Cu K-edge x.a.f.s. spectra with that of the equivalent Fe K-edge for chicken ovotransferrin (COT) indicates that the metal ions occupy essentially the same binding sites in the protein. However, in the case of the Cu2+ complex the metal appears to have reduced co-ordination. Changes are observed in the x.a.f.s. of 90%-saturated COT (Cu1.8COT) on freeze-drying. The three-dimensional X-ray structures of rabbit serum transferrin and human lactoferrin have shown that the ferric cations are co-ordinated by four protein ligands and a bidentate carbonate anion in a distorted octahedral arrangement [Anderson, Baker, Dodson, Norris, Rumball, Waters & Baker (1987) Proc. Natl. Acad. Sci. U.S.A. 84, 1768-1774; Anderson, Baker, Norris, Rice and Baker (1989) J. Mol. Biol. 209, 711-734; Bailey, Evans, Garratt, Gorinsky, Hasnain, Horsburgh, Jhoti, Lindley, Mydin, Sarra & Watson (1988) Biochemistry 27, 5804-5812]. This structural information, together with the differences in e.x.a.f.s. spectra for solution and freeze-dried samples of diferric COT [Hasnain, Evans, Garratt & Lindley (1987) Biochem. J. 247, 369-375] suggests that the synergistic carbonate anion may be capable of behaving as a unidentate linkage to the Cu2+ in the dicupric complex. Data for Cu1.8COT are consistent with only three protein ligands bound to Cu2+, monodentate binding of the synergistic anion in one lobe and its bidentate binding in the other lobe. Such flexibility in the anion co-ordination may be a requirement for the uptake and release of metals by the transferrins. PMID:1660264

  3. X.a.f.s. studies of chicken dicupric ovotransferrin.

    PubMed

    Garratt, R C; Evans, R W; Hasnain, S S; Lindley, P F; Sarra, R

    1991-11-15

    A comparison of Cu K-edge x.a.f.s. spectra with that of the equivalent Fe K-edge for chicken ovotransferrin (COT) indicates that the metal ions occupy essentially the same binding sites in the protein. However, in the case of the Cu2+ complex the metal appears to have reduced co-ordination. Changes are observed in the x.a.f.s. of 90%-saturated COT (Cu1.8COT) on freeze-drying. The three-dimensional X-ray structures of rabbit serum transferrin and human lactoferrin have shown that the ferric cations are co-ordinated by four protein ligands and a bidentate carbonate anion in a distorted octahedral arrangement [Anderson, Baker, Dodson, Norris, Rumball, Waters & Baker (1987) Proc. Natl. Acad. Sci. U.S.A. 84, 1768-1774; Anderson, Baker, Norris, Rice and Baker (1989) J. Mol. Biol. 209, 711-734; Bailey, Evans, Garratt, Gorinsky, Hasnain, Horsburgh, Jhoti, Lindley, Mydin, Sarra & Watson (1988) Biochemistry 27, 5804-5812]. This structural information, together with the differences in e.x.a.f.s. spectra for solution and freeze-dried samples of diferric COT [Hasnain, Evans, Garratt & Lindley (1987) Biochem. J. 247, 369-375] suggests that the synergistic carbonate anion may be capable of behaving as a unidentate linkage to the Cu2+ in the dicupric complex. Data for Cu1.8COT are consistent with only three protein ligands bound to Cu2+, monodentate binding of the synergistic anion in one lobe and its bidentate binding in the other lobe. Such flexibility in the anion co-ordination may be a requirement for the uptake and release of metals by the transferrins.

  4. Exciton fine structure and spin relaxation in semiconductor colloidal quantum dots.

    PubMed

    Kim, Jeongho; Wong, Cathy Y; Scholes, Gregory D

    2009-08-18

    Quantum dots (QDs) have discrete quantum states isolated from the environment, making QDs well suited for quantum information processing. In semiconductor QDs, the electron spins can be coherently oriented by photoexcitation using circularly polarized light, creating optical orientation. The optically induced spin orientation could serve as a unit for data storage and processing. Carrier spin orientation is also envisioned to be a key component in a related, though parallel, field of semiconductor spintronics. However, the oriented spin population rapidly loses its coherence by interaction with the environment, thereby erasing the prepared information. Since long-lasting spin orientation is desirable in both areas of investigation, spin relaxation is the central focus of investigation for optimization of device performance. In this Account, we discuss a topic peripherally related to these emerging areas of investigation: exciton fine structure relaxation (EFSR). The radiationless transition occurring in the exciton fine structure not only highlights a novel aspect of QD exciton relaxation but also has implications for carrier spin relaxation in QDs. We focus on examining the EFSR in connection with optical spin orientation and subsequent ultrafast relaxation of electron and hole spin densities in the framework of the exciton fine structure basis. Despite its significance, the study of exciton fine structure in colloidal QDs has been hampered by the experimental challenge arising from inhomogeneous line broadening that obscures the details of closely spaced fine structure states in the frequency domain. In this Account, we show that spin relaxation occurring in the fine structure of CdSe QDs can be probed by a time-domain nonlinear polarization spectroscopy, circumventing the obstacles confronted in the frequency-domain spectroscopy. In particular, by combining polarization sequences of multiple optical pulses with the unique optical selection rules of

  5. Using XAFS, EDAX and AFM in comparative study of various natural and synthetic emeralds

    NASA Astrophysics Data System (ADS)

    Parikh, P.; Saini, N. L.; Dalela, S.; Bhardwaj, D. M.; Fernandes, S.; Gupta, R. P.; Garg, K. B.

    2003-01-01

    We have performed XAFS, EDAX and AFM studies on some natural and synthetic emeralds. While the XAFS results yield information on changes in the valence of the Cr ion and the n-n distance the AFM is used to determine the areal atomic density on surface of the crystals. It is a pilot study to explore if the three techniques can offer a possible way of distinguishing between the natural and synthetic emeralds and the results are promising.

  6. An XAFS Study of Niobium chloride in the ionic liquid 1-ethyl-3-methyl imidazolium chloride/ aluminum chloride

    SciTech Connect

    D Roeper; K Pandya; G Cheek; W OGrady

    2011-12-31

    Niobium chloride was studied with extended X-ray absorption fine structure spectroscopy (EXAFS) in acidic and basic aluminum chloride/1-ethyl-3-methyl imidazolium chloride (EMIC) ionic liquids. Although anhydrous Nb2Cl10 is more soluble in the basic melt than in the acidic melt, the EXAFS data shows that the coordination shell around the niobium does not change in the different ionic liquids. Both the acidic and basic melts show a coordination of five chlorides in the first shell. This indicates that in this series of ionic liquids, the Nb2Cl10 breaks up into two NbCl5 entities in both the acidic and the basic melts.

  7. Fine structure in plasma waves and radiation near the plasma frequency in Earth's foreshock

    NASA Technical Reports Server (NTRS)

    Cairns, Iver H.

    1994-01-01

    Novel observations are presented of intrunsic fine structure in the frequency spectrum of electomagnetic (EM) radiation and plasma waves near the electron plasma frequency f(sub p) during a period of unusually high interplanetary magnetic field strength. Measured using the wideband receiver on the International Sun-Earth Explorer (ISEE) 1 spacecraft, fine-structured emissions are observed both in the solar wind and the foreshock, The fine structure is shown to correspond to emissions spaced above f(sub p) near half harmonies of the electon cyclotron frequency f(sub ce), i.e., near f(sub p) + nf(sub ce)/2. These appear to be the first space physics observations of emissions spaced by f(sub ce)/2. Indirect but strong arguments are used to discriminate between EM and electrostatic (ES) signals, to identify whether ISEE 1 is in the solar wind or the foreshock, and to determine the relative frequencies of the emissions and the local f(sub p). The data are consistent with generation of the ES and EM emissions in the foreshock, with subsequent propagation of the EM emissions into the solar wind. It remains possible that some emissions currently identified as ES have significant EM character. The ES and EM emisions often merge into one another with minimal changes in frequency, arguing that their source regions and generation mechanisms are related and imposing significant constraints on theories. The f(sub ce)/2 ES and EM fine structures observed may be intrinsic to the emission mechanisms or to superposition of two series of signals with f(sub ce) spacing that differ in starting frequency by f(sub ce)/2. Present theories for nonlinear wave coupling processes, cyclotron maser emission, and other linear instability processes are all unable to explain multiple EM and/or ES components spaced by approximately f(sub ce)/2 above f(sub p) for f(sub p)/f(sub ce) much greater than 1 and typical for shock beams parameters. Suitable avenues for further theoretical research are

  8. The fine-structure intervals of (N-14)+ by far-infrared laser magnetic resonance

    NASA Technical Reports Server (NTRS)

    Brown, John M.; Varberg, Thomas D.; Evenson, Kenneth M.; Cooksy, Andrew L.

    1994-01-01

    The far-infrared laser magnetic resonance spectra associated with both fine-structure transitions in (N-14)+ in its ground P-3 state have been recorded. This is the first laboratory observation of the J = 1 left arrow 0 transition and its frequency has been determined two orders of magnitude more accurately than previously. The remeasurement of the J = 2 left arrow 1 spectrum revealed a small error in the previous laboratory measurements. The fine-structure splittings (free of hyperfine interactions) determined in this work are (delta)E(sub 10) = 1461.13190 (61) GHz, (delta)E(sub 21) = 2459.38006 (37) GHz. Zero-field transition frequencies which include the effects of hyperfine structure have also been calculated. Refined values for the hyperfine constants and the g(sub J) factors have been obtained.

  9. Fine-structure deletion map of the Escherichia coli L-arabinose operon.

    PubMed

    Schleif, R

    1972-11-01

    A fine-structure deletion map of the L-arabinose operon of E. coli was constructed by mapping deletion endpoints against point mutations. Of 350 independent deletions with average endpoint separation of ten nucleotides, 51 ended in the control region between the C and B genes, and the rest ended in the structural genes A, B, C, and D. If deletion endpoints are randomly distributed, the C and B genes are separated by about 510 nucleotides. Deletion endpoints and locations of point mutations in fact do appear randomly interspersed in the C and B genes, but no point mutations were found in the control region between them. Deletions were isolated with the aid of a heat-inducible lambda phage inserted into leucine genes adjacent to the arabinose genes. A high-capacity mating technique was developed for rapidly generating fine structure maps from many deletions and point mutations.

  10. Relation Between Basophilia and Fine Structure of Cytoplasm in the Fungus Allomyces macrogynus Em

    PubMed Central

    Blondel, Benigna; Turian, Gilbert

    1960-01-01

    In a fungus, Allomyces macrogynus Em., staining tests have revealed changes in the location of cytoplasmic basophilia following different phases of the developmental cycle. These variations in location were used to observe which fine structures correspond to basophile and non-basophile areas of the cytoplasm. Hyphae, gametangia, zygotes, and plants were fixed at various developmental stages in OsO4, pH 6.1, and embedded in vestopal. Sections were examined in the electron microscope. Comparison of basophile and non-basophile cytoplasms leads to the conclusion that cytoplasmic particles of 150 to 200 A in diameter are responsible for basophilia. The possibility of these particles being ribosomes is discussed and confirmed. The present paper also describes some observations on the fine structure of other cellular components of this fungus, such as nuclei, mitochondria, various granules, and flagella. PMID:13801597

  11. Fine structure of a biexciton in a single quantum dot with a magnetic impurity

    NASA Astrophysics Data System (ADS)

    Trojnar, Anna H.; Korkusinski, Marek; Mendes, Udson C.; Goryca, Mateusz; Koperski, Maciej; Smolenski, Tomasz; Kossacki, Piotr; Wojnar, Piotr; Hawrylak, Pawel

    2013-05-01

    We show theoretically and experimentally that the ground state of a biexciton in a CdTe self-assembled quantum dot with a magnetic Mn impurity exhibits a fine structure due to electron-electron Coulomb and electron-Mn exchange interactions. Results of exact diagonalization of the microscopic biexciton-manganese-ion model predict a pattern of three pairs of states in the ground-state manifold, each pair labeled by the projection of Mn spin. We show that the fine structure determines the ordering of the biexciton emission maxima and can be derived from the biexciton and exciton emission spectra. Theoretical predictions are successfully compared with measured biexciton and exciton emission spectra of a single CdTe dot with a Mn ion in its center.

  12. Solar Cycle Fine Structure and Surface Rotation from Ca II K-Line Time Series Data

    NASA Technical Reports Server (NTRS)

    Scargle, Jeff; Keil, Steve; Worden, Pete

    2011-01-01

    Analysis of three and a half decades of data from the NSO/AFRL/Sac Peak K-line monitoring program yields evidence for four components to the variation: (a) the solar cycle, with considerable fine structure and a quasi-periodicity of 122.4 days; (b) a stochastic process, faster than (a) and largely independent of it, (c) a quasi-periodic signal due to rotational modulation, and of course (d) observational errors (shown to be quite small). Correlation and power spectrum analyses elucidate periodic and aperiodic variation of these chromospheric parameters. Time-frequency analysis is especially useful for extracting information about differential rotation, and in particular elucidates the connection between its behavior and fine structure of the solar cycle on approximately one-year time scales. These results further suggest that similar analyses will be useful at detecting and characterizing differential rotation in stars from stellar light-curves such as those being produced at NASA's Kepler observatory.

  13. Topological map of the Hofstadter butterfly: Fine structure of Chern numbers and Van Hove singularities

    NASA Astrophysics Data System (ADS)

    Naumis, Gerardo G.

    2016-04-01

    The Hofstadter butterfly is a quantum fractal with a highly complex nested set of gaps, where each gap represents a quantum Hall state whose quantized conductivity is characterized by topological invariants known as the Chern numbers. Here we obtain simple rules to determine the Chern numbers at all scales in the butterfly fractal and lay out a very detailed topological map of the butterfly by using a method used to describe quasicrystals: the cut and projection method. Our study reveals the existence of a set of critical points that separates orderly patterns of both positive and negative Cherns that appear as a fine structure in the butterfly. This fine structure can be understood as a small tilting of the projection subspace in the cut and projection method and by using a Chern meeting formula. Finally, we prove that the critical points are identified with the Van Hove singularities that exist at every band center in the butterfly landscape.

  14. MCDHF calculations of isotope shifts of even-parity fine-structure levels in neutral osmium

    NASA Astrophysics Data System (ADS)

    Palmeri, P.; Quinet, P.; Bouazza, S.

    2016-12-01

    Ab initio multiconfiguration Dirac-Hartree-Fock (MCDHF) calculations have been carried out in order to determine the isotope shifts of all the fine-structure levels belonging to the even-parity configurations (5d+6s)8 in neutral osmium, Os I. The theoretical predictions have been compared to laser spectroscopy measurements available in the literature showing a good agreement between theory and experiment.

  15. Enhanced effect of temporal variation of the fine-structure constant in diatomic molecules

    SciTech Connect

    Flambaum, V. V.

    2006-03-15

    We show that the relative effect of variation of the fine-structure constant in microwave transitions between very close and narrow rotational-hyperfine levels may be enhanced 2-3 orders of magnitude in diatomic molecules with unpaired electrons like LaS, LaO, LuS, LuO, YbF, and similar molecular ions. The enhancement is result of cancellation between the hyperfine and rotational intervals.

  16. HRTS observations of the fine structure and dynamics of the solar chromosphere and transition zone

    NASA Technical Reports Server (NTRS)

    Dere, K. P.

    1983-01-01

    Arc-second UV observations of the Sun by the NRL High Resolution Telescope and Spectrograph (HRTS) have led to the discovery of dynamic fine structures such as 400 km/s coronal jets and chromospheric jets (spicules) and have provided new information about the structure and dynamics of the transition zone. These observations are reviewed and their relevance to the origin of the solar wind is discussed.

  17. Cosmological variation of the fine-structure constant versus a new interaction

    SciTech Connect

    Angstmann, E.J.; Flambaum, V.V.; Karshenboim, S.G.

    2004-10-01

    We show that using the modified form of the Dirac Hamiltonian as suggested by Bekenstein does not affect the analysis of QSO data pertaining to a measurement of {alpha} variation. We obtain the present time limit on Bekenstein's parameter, tan{sup 2} {chi}=(0.2{+-}0.7)x10{sup -6}, from the measurement of the hydrogen 2p fine structure using a value of {alpha} obtained from different experiments.

  18. Atomic oxygen fine-structure splittings with tunable far-infrared spectroscopy

    NASA Technical Reports Server (NTRS)

    Zink, Lyndon R.; Evenson, Kenneth M.; Matsushima, Fusakazu; Nelis, Thomas; Robinson, Ruth L.

    1991-01-01

    Fine-structure splittings of atomic oxygen (O-16) in the ground state have been accurately measured using a tunable far-infrared spectrometer. The 3P0-3pl splitting is 2,060,069.09 (10) MHz, and the 3Pl-3P2 splitting is 4,744,777.49 (16) MHz. These frequencies are important for measuring atomic oxygen concentration in earth's atmosphere and the interstellar medium.

  19. Current Work to Improve Precision in Measurements of Helium Fine Structure

    NASA Astrophysics Data System (ADS)

    Hassan Rezaeian, Nima; Shiner, Davis

    2013-05-01

    With the recent improvement on the 23P Helium fine structure calculation by Pachucki and the quest for finding the most precise value for α, spectroscopic measurement of the helium atom has a great advantage to find this primary constant. Distinctively, the 32 GHz atomic fine structure of 23P J2 to J0 interval with uncertainty of 100Hz leads a factor of three better than the best current value of α and an impulsion to the theory to evaluate the largest term of order mα8 is our ambition. This measurement not only tests the quantum electrodynamics, but also establishes the fine structure constant α with uncertainty of 1.6 ppb. The electron g-factor measurement of α, even though, is by far more accurate at 0.37 ppb, our end result would be a examination to the best alternative atom recoil measurements with different approach. To reach on this level of accuracy, we implement our frequency selector with precision better than 1 to 100 along with laser cooling mechanism to enhance the signal to noise ratio by increasing the signal strength. This work is supported by NSF grant.

  20. Current Work to Improve Precision in Measurements of Helium Fine Structure

    NASA Astrophysics Data System (ADS)

    Hassan Rezaeian, Nima; Shiner, David

    2013-06-01

    With the recent improvement on the 23P Helium fine structure calculation by Pachucki and the quest for finding the most precise value for α, spectroscopic measurement of the helium atom has a great advantage to find this primary constant. Distinctively, the 32 GHz atomic fine structure of 23P J2 to J0 interval with uncertainty of 100Hz leads a factor of three better than the best current value of α and an impulsion to the theory to evaluate the largest term of order mα8 is our ambition. This measurement not only tests the quantum electrodynamics, but also establishes the fine structure constant α with uncertainty of 1.6 ppb. The electron g-factor measurement of α, even though, is by far more accurate at 0.37 ppb, our end result would be a examination to the best alternative atom recoil measurements with different approach. To reach on this level of accuracy, we implement our frequency selector with precision better than 1 to 100 along with laser cooling mechanism to enhance the signal to noise ratio by increasing the signal strength. This work is supported by NSF grant.

  1. Exciton fine structure and spin/valley dynamics in nanosystems (Presentation Recording)

    NASA Astrophysics Data System (ADS)

    Glazov, Mikhail M.

    2015-09-01

    In my invited talk the fine structure of neutral and charged excitons for GaAs/AlGaAs quantum dots (QDs) grown on (111) plane as well for transition metal dichalcogenides (TMDCs) monolayers will be discussed. These, at first glance, different systems posses similar trigonal symmetry, which makes exciton fine structure and spin dynamics unusual compared with standard low-dimensional semiconductors. The effects of long-range exchange interaction induced mixing of excitons in two valleys of TMDCs and of magneto-induced mixing of bright and dark excitonic states in trigonal QDs are predicted and confirmed experimentally. Manifestations of excitonic spin/valley dynamics in photoluminescence, pump-probe Kerr rotation and spin noise are discussed. The presentation will be based on the following references: [1] G. Sallen, B. Urbaszek, M. M. Glazov, et al., Dark-Bright Mixing of Interband Transitions in Symmetric Semiconductor Quantum Dots, Phys. Rev. Lett. 107, 166604 (2011). [2] L. Bouet, M. Vidal, T. Mano, N. Ha, T. Kuroda, M. V. Durnev, M. M. Glazov, et al., Charge tuning in [111] grown GaAs droplet quantum dots, Appl. Phys. Lett. 105, 082111 (2014). [3] M. M. Glazov, et al., Exciton fine structure and spin decoherence in monolayers of transition metal dichalcogenides Phys. Rev. B 89, 201302(R) (2014). [4] C. R. Zhu, K. Zhang, M. Glazov, et al., Exciton valley dynamics probed by Kerr rotation in WSe2 monolayers, Phys. Rev. B 90, 161302(R) (2014).

  2. Effective collision strengths for fine-structure transitions in Si VII

    SciTech Connect

    Sossah, A. M.; Tayal, S. S.

    2014-05-20

    The effective collision strengths for electron-impact excitation of fine-structure transitions in Si VII are calculated as a function of electron temperature in the range 5000-2,000,000 K. The B-spline Breit-Pauli R-matrix method has been used to calculate collision strengths by electron impact. The target wave functions have been obtained using the multi-configuration Hartree-Fock method with term-dependent non-orthogonal orbitals. The 92 fine-structure levels belonging to the 46 LS states of 2s {sup 2}2p {sup 4}, 2s2p {sup 5}, 2p {sup 6}, 2s {sup 2}2p {sup 3}3s, 2s {sup 2}2p {sup 3}3p, 2s {sup 2}2p {sup 3}3d, and 2s2p {sup 4}3s configurations are included in our calculations of oscillator strengths and collision strengths. There are 4186 possible fine-structure allowed and forbidden transitions among the 92 levels. The present excitation energies, oscillator strengths, and collision strengths have been compared with previous theoretical results and available experimental data. Generally, a good agreement is found with the 6 LS-state close-coupling approximation results of Butler and Zeippen and the 44 LS-state distorted wave calculation of Bhatia and Landi.

  3. Helium induced fine structure in the electronic spectra of anthracene derivatives doped into superfluid helium nanodroplets

    SciTech Connect

    Pentlehner, D.; Slenczka, A.

    2015-01-07

    Electronic spectra of organic molecules doped into superfluid helium nanodroplets show characteristic features induced by the helium environment. Besides a solvent induced shift of the electronic transition frequency, in many cases, a spectral fine structure can be resolved for electronic and vibronic transitions which goes beyond the expected feature of a zero phonon line accompanied by a phonon wing as known from matrix isolation spectroscopy. The spectral shape of the zero phonon line and the helium induced phonon wing depends strongly on the dopant species. Phonon wings, for example, are reported ranging from single or multiple sharp transitions to broad (Δν > 100 cm{sup −1}) diffuse signals. Despite the large number of example spectra in the literature, a quantitative understanding of the helium induced fine structure of the zero phonon line and the phonon wing is missing. Our approach is a systematic investigation of related molecular compounds, which may help to shed light on this key feature of microsolvation in superfluid helium droplets. This paper is part of a comparative study of the helium induced fine structure observed in electronic spectra of anthracene derivatives with particular emphasis on a spectrally sharp multiplet splitting at the electronic origin. In addition to previously discussed species, 9-cyanoanthracene and 9-chloroanthracene will be presented in this study for the first time.

  4. Atomistic theory of excitonic fine structure in InAs/InP nanowire quantum dot molecules

    NASA Astrophysics Data System (ADS)

    Świderski, M.; Zieliński, M.

    2017-03-01

    Nanowire quantum dots have peculiar electronic and optical properties. In this work we use atomistic tight binding to study excitonic spectra of artificial molecules formed by a double nanowire quantum dot. We demonstrate a key role of atomistic symmetry and nanowire substrate orientation rather than cylindrical shape symmetry of a nanowire and a molecule. In particular for [001 ] nanowire orientation we observe a nonvanishing bright exciton splitting for a quasimolecule formed by two cylindrical quantum dots of different heights. This effect is due to interdot coupling that effectively reduces the overall symmetry, whereas single uncoupled [001 ] quantum dots have zero fine structure splitting. We found that the same double quantum dot system grown on [111 ] nanowire reveals no excitonic fine structure for all considered quantum dot distances and individual quantum dot heights. Further we demonstrate a pronounced, by several orders of magnitude, increase of the dark exciton optical activity in a quantum dot molecule as compared to a single quantum dot. For [111 ] systems we also show spontaneous localization of single particle states in one of nominally identical quantum dots forming a molecule, which is mediated by strain and origins from the lack of the vertical inversion symmetry in [111 ] nanostructures of overall C3 v symmetry. Finally, we study lowering of symmetry due to alloy randomness that triggers nonzero excitonic fine structure and the dark exciton optical activity in realistic nanowire quantum dot molecules of intermixed composition.

  5. Strong limit on the spatial and temporal variations of the fine-structure constant

    NASA Astrophysics Data System (ADS)

    Le, T. D.

    2016-10-01

    Observed spectra of quasars provide a powerful tool to test the possible spatial and temporal variations of the fine-structure constant α = e 2/ћc over the history of the Universe. It is demonstrated that high sensitivity to the variation of α can be obtained from a comparison of the spectra of quasars and laboratories. We reported a new constraint on the variation of the fine-structure constant based on the analysis of the optical spectra of the fine-structure transitions in [NeIII], [NeV], [OIII], [OI] and [SII] multiplets from 14 Seyfert 1.5 galaxies. The weighted mean value of the α-variation derived from our analysis over the redshift range 0.035 < z < 0.281 Δα/α= (4.50 +/- 5.53) \\times 10-5. This result presents strong limit improvements on the constraint on Δα/α compared to the published in the literature

  6. Accurate modeling of spectral fine-structure in Earth radiance spectra measured with the Global Ozone Monitoring Experiment.

    PubMed

    van Deelen, Rutger; Hasekamp, Otto P; Landgraf, Jochen

    2007-01-10

    We present what we believe to be a novel approach to simulating the spectral fine structure (<1 nm) in measurements of spectrometers such as the Global Ozone Monitoring Experiment (GOME). GOME measures the Earth's radiance spectra and daily solar irradiance spectra from which a reflectivity spectrum is commonly extracted. The high-frequency structures contained in such a spectrum are, apart from atmospheric absorption, caused by Raman scattering and by a shift between the solar irradiance and the Earth's radiance spectrum. Normally, an a priori high-resolution solar spectrum is used to simulate these structures. We present an alternative method in which all the required information on the solar spectrum is retrieved from the GOME measurements. We investigate two approaches for the spectral range of 390-400 nm. First, a solar spectrum is reconstructed on a fine spectral grid from the GOME solar measurement. This approach leads to undersampling errors of up to 0.5% in the modeling of the Earth's radiance spectra. Second, a combination of the solar measurement and one of the Earth's radiance measurement is used to retrieve a solar spectrum. This approach effectively removes the undersampling error and results in residuals close to the GOME measurement noise of 0.1%.

  7. The Effect of Quantum-Mechanical Interference on Precise Measurements of the n = 2 Triplet P Fine Structure of Helium

    SciTech Connect

    Marsman, A.; Horbatsch, M.; Hessels, E. A.

    2015-09-15

    For many decades, improvements in both theory and experiment of the fine structure of the n = 2 triplet P levels of helium have allowed for an increasingly precise determination of the fine-structure constant. Recently, it has been observed that quantum-mechanical interference between neighboring resonances can cause significant shifts, even if such neighboring resonances are separated by thousands of natural widths. The shifts depend in detail on the experimental method used for the measurement, as well as the specific experimental parameters employed. Here, we review how these shifts apply for the most precise measurements of the helium 2{sup 3}P fine-structure intervals.

  8. X-ray absorption spectroscopy identifies calcium-uranyl-carbonate complexes at environmental concentrations.

    SciTech Connect

    Kelly, S. D.; Kemner, K. M.; Brooks, S. C.; Biosciences Division; ORNL

    2007-01-01

    Current research on bioremediation of uranium-contaminated groundwater focuses on supplying indigenous metal-reducing bacteria with the appropriate metabolic requirements to induce microbiological reduction of soluble uranium(VI) to poorly soluble uranium(IV). Recent studies of uranium(VI) bioreduction in the presence of environmentally relevant levels of calcium revealed limited and slowed uranium(VI) reduction and the formation of a Ca-UO{sub 2}-CO{sub 3} complex. However, the stoichiometry of the complex is poorly defined and may be complicated by the presence of a Na-UO{sub 2}-CO{sub 3} complex. Such a complex might exist even at high calcium concentrations, as some UO{sub 2}-CO{sub 3} complexes will still be present. The number of calcium and/or sodium atoms coordinated to a uranyl carbonate complex will determine the net charge of the complex. Such a change in aqueous speciation of uranium(VI) in calcareous groundwater may affect the fate and transport properties of uranium. In this paper, we present the results from X-ray absorption fine structure (XAFS) measurements of a series of solutions containing 50 {micro}M uranium(VI) and 30 mM sodium bicarbonate, with various calcium concentrations of 0-5 mM. Use of the data series reduces the uncertainty in the number of calcium atoms bound to the UO{sub 2}-CO{sub 3} complex to approximately 0.6 and enables spectroscopic identification of the Na-UO{sub 2}-CO{sub 3} complex. At nearly neutral pH values, the numbers of sodium and calcium atoms bound to the uranyl triscarbonate species are found to depend on the calcium concentration, as predicted by speciation calculations.

  9. X-ray Absorption Spectroscopy Identifies Calcium-Uranyl-Carbonate Complexes at Environmental Concentrations

    SciTech Connect

    Kelly, Shelly D; Kemner, Kenneth M; Brooks, Scott C

    2007-01-01

    Current research on bioremediation of uranium-contaminated groundwater focuses on supplying indigenous metal-reducing bacteria with the appropriate metabolic requirements to induce microbiological reduction of soluble uranium(VI) to poorly soluble uranium(IV). Recent studies of uranium(VI) bioreduction in the presence of environmentally relevant levels of calcium revealed limited and slowed uranium(VI) reduction and the formation of a Ca-UO2-CO3 complex. However, the stoichiometry of the complex is poorly defined and may be complicated by the presence of a Na-UO2-CO3 complex. Such a complex might exist even at high calcium concentrations, as some UO2-CO3 complexes will still be present. The number of calcium and/or sodium atoms coordinated to a uranyl carbonate complex will determine the net charge of the complex. Such a change in aqueous speciation of uranium(VI) in calcareous groundwater may affect the fate and transport properties of uranium. In this paper, we present the results from X-ray absorption fine structure (XAFS) measurements of a series of solutions containing 50 lM uranium(VI) and 30 mM sodium bicarbonate, with various calcium concentrations of 0-5 mM. Use of the data series reduces the uncertainty in the number of calcium atoms bound to the UO2-CO3 complex to approximately 0.6 and enables spectroscopic identification of the Na-UO2-CO3 complex. At nearly neutral pH values, the numbers of sodium and calcium atoms bound to the uranyl triscarbonate species are found to depend on the calcium concentration, as predicted by speciation calculations.

  10. Global investigation of the fine structure of the isoscalar giant quadrupole resonance

    SciTech Connect

    Shevchenko, A.; Burda, O.; Kalmykov, Y.; Neumann-Cosel, P. von; Ponomarev, V. Yu.; Richter, A.; Wambach, J.; Carter, J.; Sideras-Haddad, E.; Cooper, G. R. J.; Fearick, R. W.; Foertsch, S. V.; Lawrie, J. J.; Neveling, R.; Smit, F. D.; Fujita, H.; Fujita, Y.; Lacroix, D.

    2009-04-15

    Fine structure in the region of the isoscalar giant quadrupole resonance (ISGQR) in {sup 58}Ni, {sup 89}Y, {sup 90}Zr, {sup 120}Sn, {sup 166}Er, and {sup 208}Pb has been observed in high-energy-resolution ({delta}E{sub 1/2}{approx_equal}35-50 keV) inelastic proton scattering measurements at E{sub 0}=200 MeV at iThemba LABS. Calculations of the corresponding quadrupole excitation strength functions performed within models based on the random-phase approximation (RPA) reveal similar fine structure when the mixing of one-particle one-hole states with two-particle two-hole states is taken into account. A detailed comparison of the experimental data is made with results from the quasiparticle-phonon model (QPM) and the extended time-dependent Hartree-Fock (ETDHF) method. For {sup 208}Pb, additional theoretical results from second RPA and the extended theory of finite Fermi systems (ETFFS) are discussed. A continuous wavelet analysis of the experimental and the calculated spectra is used to extract dominant scales characterizing the fine structure. Although the calculations agree with qualitative features of these scales, considerable differences are found between the model and experimental results and amongst different models. Within the framework of the QPM and ETDHF calculations it is possible to decompose the model spaces into subspaces approximately corresponding to different damping mechanisms. It is demonstrated that characteristic scales mainly arise from the collective coupling of the ISGQR to low-energy surface vibrations.

  11. Fine Structure in the Mm-Wavelength Spectra of the Active Region

    NASA Astrophysics Data System (ADS)

    Sawant, H. S.; Cecatto, J. R.

    1990-11-01

    RESUMEN. Faltan observaciones solares espectrosc6picas en la longitud de onda milimetrica. Hay sugerencias de que se puede superponer una fi na estructura en frecuencia a la componente-S de la regi6n solar activa, asi como a la componente del brote en las longitudes de onda milimetri- cas. Se ha desarrollado un receptor de alta sensibilidad de pasos de frecuencia que opera en el intervalo de 23-18 GHz con una resoluci6n de 1 GHz y resoluci6n de tiempo variable entre 1.2 y 96 sec, usando la an- tena de Itapetinga de 13.7-m para estudiar la estructura fina en frecuencia y tiempo. Discutimos el espectro en longitud de onda-mm en re- giones activas y su evoluci6n en el tiempo. El estudio de Ia evoluci6n en el tiempo de la regi6n activa en AR 5569 observada el 29 de junio de 1989, sugiere la existencia de estructuras finas como funci6n deltiempo. ABSTRACT. There is a lack of mm-wavelength spectroscopic solar observations. There are suggestions that a fine structure in frequency may be superimposed on the S-component of solar active region as well as on the burst component at inm-wavelengths. To study fine structure in frequency and time, a high sensitivity step frequency receiver operating in the frequency range 23-18 GHz with frequency resolution of 1 GHz and variable time resolution 1.2 to 96 sec, using 13.7 m diameter Itapetinga radome covered antenna, has been developed. Here, we discuss mm-wavelength spectra of active regions and their time evolution. Study of time evolution of an active region AR 5569 observed on 29th June, 1989 suggests existence of fine structures as a function of time. ( Ck : SUN-ACTIVITY - SUN-RADIO RADIATION

  12. On the fine-structure constant in a plasma model of the fluctuating vacuum substratum

    NASA Technical Reports Server (NTRS)

    Cragin, B. L.

    1986-01-01

    The existence of an intimate connection between the quivering motion of electrons and positrons (Zitterbewegung), predicted by the Dirac equation, and the zero-point fluctuations of the vacuum is suggested. The nature of the proposed connection is discussed quantitatively, and an approximate self-consistency relation is derived, supplying a purely mathematical expression that relates the dimensionless coupling strengths (fine-structure constants) alpha sub e and alpha sub g of electromagnetism and gravity. These considerations provide a tentative explanation for the heretofore puzzling number 1/alpha sub e of about 137.036 and suggest that attempts to unify gravity with the electroweak and strong interactions will ultimately prove successful.

  13. A cascade interpretation of Lundgren's stretched spiral vortex model for turbulent fine structure

    NASA Astrophysics Data System (ADS)

    Gilbert, Andrew D.

    1993-11-01

    Lundgren's [Phys. Fluids 25, 2193 (1982)] model for turbulent fine structure comprises coherent vortices which wind up vorticity variations into spiral structures; simultaneously the vortices are stretched axially by a background strain field. The model predicts a k-5/3 energy spectrum and is remarkably robust to the form of the coherent vortices and the form of the vorticity variations. To understand this the present article introduces a simple cascade argument which illuminates how the dynamical processes of vortex stretching and reduction of scale conspire to give this Kolmogorov spectrum. Some generalizations are considered.

  14. Sensitivity of ultracold-atom scattering experiments to variation of the fine-structure constant

    SciTech Connect

    Borschevsky, A.; Beloy, K.; Flambaum, V. V.; Schwerdtfeger, P.

    2011-05-15

    We present numerical calculations for cesium and mercury to estimate the sensitivity of the scattering length to the variation of the fine-structure constant {alpha}. The method used follows the ideas of Chin and Flambaum [Phys. Rev. Lett. 96, 230801 (2006)], where the sensitivity to the variation of the electron-to-proton mass ratio {beta} was considered. We demonstrate that for heavy systems, the sensitivity to the variation of {alpha} is of the same order of magnitude as to the variation of {beta}. Near narrow Feshbach resonances, the enhancement of the sensitivity may exceed nine orders of magnitude.

  15. The fine structure of muscle attachments in a spider (Latrodectus mactans, Fabr.).

    PubMed

    Smith, D S; Järlfors, U; Russell, F E

    1969-01-01

    The fine structure of a spider myo-apodeme junction is described, and discussed in terms of other arthropod muscle attachments. This is contrasted with the situation in the venom gland, equipped with muscle fibers that control expulsion of the secreted material. The latter involves a cell-free collagenous matrix, lying between the muscle cells and the sheath of the gland. As in other arthropods, skeletal fibers are attached to the apodeme cuticle via specialized epidermal cells, containing oriented microtubules. Interdigitations between these cells and muscle, basally, and cuticle, apically, are described. Extracellular tonofibrillae described elsewhere are inconspicuous in the apodeme cuticle.

  16. Domain Dynamics in Piezoresponse Force Spectroscopy: Quantitative Deconvolution and Hysteresis Loop Fine Structure

    SciTech Connect

    Bdikin, Igor; Kholkin, Andrei; Morozovska, A. N.; Svechnikov, S. V.; Kim, S.-H.; Kalinin, Sergei V

    2008-01-01

    Domain dynamics in the Piezoresponse Force Spectroscopy (PFS) experiment is studied using the combination of local hysteresis loop acquisition with simultaneous domain imaging. The analytical theory for PFS signal from domain of arbitrary cross-section and length is developed for the analysis of experimental data on Pb(Zr,Ti)O3 polycrystalline films. The results suggest formation of oblate domain at early stage of the nucleation and growth, consistent with efficient screening of depolarization field. The fine structure of the hysteresis loop is shown to be related to the observed jumps in the domain geometry during domain wall propagation (nanoscale Barkhausen jumps), indicative of strong domain-defect interactions.

  17. The fine structure of the sperm of the round goby (Neogobius melanostomus)

    USGS Publications Warehouse

    Allen, Jeffrey D.; Walker, Glenn K.; Nichols, Susan J.; Sorenson, Dorothy

    2004-01-01

    The fine structural details of the spermatozoon of the round goby are presented for the first time in this study. Scanning and transmission electron microscopic examination of testis reveals an anacrosomal spermatozoon with a slightly elongate head and uniformly compacted chromatin. The midpiece contains a single, spherical mitochondrion. Two perpendicularly oriented centrioles lie in a deep, eccentric nuclear fossa with no regularly observed connection to the nucleus. The flagellum develops bilateral fins soon after emerging from the fossa; each extends approximately 1 A?m from the axoneme and persists nearly the length of the flagellum.

  18. Quantum field theory and classical optics: determining the fine structure constant

    NASA Astrophysics Data System (ADS)

    Leuchs, Gerd; Hawton, Margaret; Sánchez-Soto, Luis L.

    2017-01-01

    The properties of the vacuum are described by quantum physics including the response to external fields such as electromagnetic radiation. Of the two parameters that govern the details of the electromagnetic field dynamics in vacuum, one is fixed by the requirement of Lorentz invariance c = 1/\\sqrt {ε 0 μ 0 } . The other one, Z0 = \\sqrt {μ 0 /ε 0 } = 1/(cε 0 ) and its relation to the quantum vacuum, is discussed in this contribution. Deriving ε 0 from the properties of the quantum vacuum implies the derivation of the fine structure constant.

  19. Biology of Budding Bacteria III. Fine Structure of Rhodomicrobium and Hyphomicrobium spp

    PubMed Central

    Conti, S. F.; Hirsch, Peter

    1965-01-01

    Conti, S. F. (Dartmouth Medical School, Hanover, N.H.), and Peter Hirsch. Biology of budding bacteria. III. Fine structure of Rhodomicrobium and Hyphomicrobium spp. J. Bacteriol. 89:503–512. 1965.—The ultrastructure of 14 strains of hyphomicrobia, and of Rhodomicrobium vannielii, was investigated by means of electron microscopy of thin sections. The majority of the strains of hyphomicrobia possessed a well-developed internal membrane system, which appeared to be derived by invagination from the cytoplasmic membrane. The subcellular organization of the hyphomicrobia and R. vannielii was investigated. Images PMID:14255720

  20. Enhanced Laboratory Sensitivity to Variation of the Fine-Structure Constant using Highly Charged Ions

    SciTech Connect

    Berengut, J. C.; Dzuba, V. A.; Flambaum, V. V.

    2010-09-17

    We study atomic systems that are in the frequency range of optical atomic clocks and have enhanced sensitivity to potential time variation of the fine-structure constant {alpha}. The high sensitivity is due to coherent contributions from three factors: high nuclear charge Z, high ionization degree, and significant differences in the configuration composition of the states involved. Configuration crossing keeps the frequencies in the optical range despite the large ionization energies. We discuss a few promising examples that have the largest {alpha} sensitivities seen in atomic systems.

  1. Simple surface structure determination from Fourier transforms of angle-resolved photoemission extended fine structure

    SciTech Connect

    Zheng, Y. |; Shirley, D.A.

    1995-02-01

    The authors show by Fourier analyses of experimental data, with no further treatment, that the positions of all the strong peaks in Fourier transforms of angle-resolved photoemission extended fine structure (ARPEFS) from adsorbed surfaces can be explicitly predicted from a trial structure with an accuracy of about {+-} 0.3 {angstrom} based on a single-scattering cluster model together with the concept of a strong backscattering cone, and without any additional analysis. This characteristic of ARPEFS Fourier transforms can be developed as a simple method for determining the structures of adsorbed surfaces to an accuracy of about {+-} 0.1 {angstrom}.

  2. Tailoring the exciton fine structure of cadmium selenide nanocrystals with shape anisotropy and magnetic field.

    PubMed

    Sinito, Chiara; Fernée, Mark J; Goupalov, Serguei V; Mulvaney, Paul; Tamarat, Philippe; Lounis, Brahim

    2014-11-25

    We use nominally spheroidal CdSe nanocrystals with a zinc blende crystal structure to study how shape perturbations lift the energy degeneracies of the band-edge exciton. Nanocrystals with a low degree of symmetry exhibit splitting of both upper and lower bright state degeneracies due to valence band mixing combined with the isotropic exchange interaction, allowing active control of the level splitting with a magnetic field. Asymmetry-induced splitting of the bright states is used to reveal the entire 8-state band-edge fine structure, enabling complete comparison with band-edge exciton models.

  3. Ground-based and spaceborn observations of the type II burst with developed fine structure

    NASA Astrophysics Data System (ADS)

    Dorovskyy, V.; Melnik, V.; Konovalenko, A.; Brazhenko, A.; Rucker, H.; Stanislavskyy, A.; Panchenko, M.

    2012-09-01

    The combination of two huge ground-based radio telescopes (UTR-2 and URAN-2) operated in decameter wavelengths with three spatially separated spacecrafts (SOHO, STEREO-A and STEREO-B) equipped with white light coronagraphs, UV telescopes and decameter-hectometer band radio telescopes created a unique opportunity to investigate the high energy solar transients, such as CMEs and their manifestations in radio bands - type II bursts. In this paper we made detailed analysis of the powerful and complex event occurred on 7 June 2011 consisted of Halo-CME and type II burst with rich fine structure.

  4. Fine structure of transient waves in a random medium: The correlation and spectral density functions

    NASA Technical Reports Server (NTRS)

    Wenzel, Alan R.

    1994-01-01

    This is essentially a progress report on a theoretical investigation of the propagation of transient waves in a random medium. The emphasis in this study is on applications to sonic-boom propagation, particularly as regards the effect of atmospheric turbulence on the sonic-boom waveform. The analysis is general, however, and is applicable to other types of waves besides sonic-boom waves. The phenomenon of primary concern in this investigation is the fine structure of the wave. A figure is used to illustrate what is meant by finestructure.

  5. Enhanced laboratory sensitivity to variation of the fine-structure constant using highly charged ions.

    PubMed

    Berengut, J C; Dzuba, V A; Flambaum, V V

    2010-09-17

    We study atomic systems that are in the frequency range of optical atomic clocks and have enhanced sensitivity to potential time variation of the fine-structure constant α. The high sensitivity is due to coherent contributions from three factors: high nuclear charge Z, high ionization degree, and significant differences in the configuration composition of the states involved. Configuration crossing keeps the frequencies in the optical range despite the large ionization energies. We discuss a few promising examples that have the largest α sensitivities seen in atomic systems.

  6. New determination of the fine structure constant from the electron value and QED.

    PubMed

    Gabrielse, G; Hanneke, D; Kinoshita, T; Nio, M; Odom, B

    2006-07-21

    Quantum electrodynamics (QED) predicts a relationship between the dimensionless magnetic moment of the electron (g) and the fine structure constant (alpha). A new measurement of g using a one-electron quantum cyclotron, together with a QED calculation involving 891 eighth-order Feynman diagrams, determine alpha(-1)=137.035 999 710 (96) [0.70 ppb]. The uncertainties are 10 times smaller than those of nearest rival methods that include atom-recoil measurements. Comparisons of measured and calculated g test QED most stringently, and set a limit on internal electron structure.

  7. X-ray Absorption Spectroscopy

    SciTech Connect

    Yano, Junko; Yachandra, Vittal K.

    2009-07-09

    This review gives a brief description of the theory and application of X-ray absorption spectroscopy, both X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS), especially, pertaining to photosynthesis. The advantages and limitations of the methods are discussed. Recent advances in extended EXAFS and polarized EXAFS using oriented membranes and single crystals are explained. Developments in theory in understanding the XANES spectra are described. The application of X-ray absorption spectroscopy to the study of the Mn4Ca cluster in Photosystem II is presented.

  8. Fine-structure splittings in high-lying {sup 2}F states of rubidium via three-step laser spectroscopy

    SciTech Connect

    Brandenberger, J. R.; Malyshev, G. S.

    2010-03-15

    Three-step laser spectroscopy has been used to measure six additional fine-structure splittings in the n {sup 2}F states of {sup 87}Rb for 11{<=}n{<=}16. When combined with our previous measurements for 4{<=}n{<=}10, they constitute a continuous sequence of 13 measurements suitable for comparison to fine-structure calculations in heavy alkali-metal atoms where relativistic effects, core polarization, configuration mixing, and electron correlation are important.

  9. A comparative study of distortion-product-otoacoustic-emission fine structure in human newborns and adults with normal hearing.

    PubMed

    Dhar, Sumitrajit; Abdala, Carolina

    2007-10-01

    Distortion product otoacoustic emissions (DPOAE) measured in human newborns are not adult-like. More than a decade of work from various investigators has created a well-developed body of evidence describing these differences but the putative anatomy or physiology has only been partially explained. Recently, Abdala and Keefe [J. Acoust. Soc. Am. 120, 3832-3842 (2006)] have identified outer and middle ear immaturities that at least partially describe the differences observed between newborn and adult input-output functions and suppression tuning curves. DPOAE fine structure characteristics and their maturation have not been examined to any extent in the literature. Fine structure characteristics in two groups of ten newborns and young adults with normal hearing sensitivity are compared here. Consistent with previous reports, the newborns show higher DPOAE levels; greater fine structure depth and wider fine structure spacing is also observed in the newborns. Differences in fine structure morphology are also observed between the two age groups. While some of these findings are attributable to an immature outer and middle ear system in the newborns, it is argued that some observed differences in fine structure characteristics might be due to remnant immaturities in passive motion of the basilar membrane in the newborn cochlea.

  10. Time variation of the fine structure constant in the early universe and the Bekenstein model

    NASA Astrophysics Data System (ADS)

    Mosquera, M. E.; Scóccola, C. G.; Landau, S. J.; Vucetich, H.

    2008-02-01

    Aims:We calculate the bounds on the variation in the fine structure constant at the time of primordial nucleosynthesis and at the time of neutral hydrogen formation. We used these bounds and other bounds from the late universe to test the Bekenstein model. Methods: We modified the Kawano code, CAMB, and CosmoMC to include the possible variation in the fine structure constant. We used observational primordial abundances of D, ^4He, and ^7Li, recent data from the cosmic microwave background, and the 2dFGRS power spectrum, to obtain bounds on the variation in α. We calculated a piecewise solution to the scalar field equation of the Bekenstein model in two different regimes: i) matter and radiation, ii) matter and cosmological constant. We match both solutions with the appropriate boundary conditions. We performed a statistical analysis, using the bounds obtained from the early universe and other bounds from the late universe to constrain the free parameters of the model. Results: Results are consistent with no variation in α for the early universe. Limits on α are inconsistent with the scale length of the theory l being larger than the Planck scale. Conclusions: In order to fit all observational and experimental data, the assumption l > Lp implied in Bekenstein's model has to be relaxed.

  11. Accurate Electron Affinity of Iron and Fine Structures of Negative Iron ions

    PubMed Central

    Chen, Xiaolin; Luo, Zhihong; Li, Jiaming; Ning, Chuangang

    2016-01-01

    Ionization potential (IP) is defined as the amount of energy required to remove the most loosely bound electron of an atom, while electron affinity (EA) is defined as the amount of energy released when an electron is attached to a neutral atom. Both IP and EA are critical for understanding chemical properties of an element. In contrast to accurate IPs and structures of neutral atoms, EAs and structures of negative ions are relatively unexplored, especially for the transition metal anions. Here, we report the accurate EA value of Fe and fine structures of Fe− using the slow electron velocity imaging method. These measurements yield a very accurate EA value of Fe, 1235.93(28) cm−1 or 153.236(34) meV. The fine structures of Fe− were also successfully resolved. The present work provides a reliable benchmark for theoretical calculations, and also paves the way for improving the EA measurements of other transition metal atoms to the sub cm−1 accuracy. PMID:27138292

  12. Julius Edgar Lilienfeld Prize Talk: Measuring the Electron Magnetic Moment and the Fine Structure Constant

    NASA Astrophysics Data System (ADS)

    Gabrielse, Gerald

    2011-05-01

    The electron magnetic moment in Bohr magnetons has been measured to a precision of 3 parts in 1013. This measurement, with quantum electrodynamics (AED) theory, provides the most precise value of the fine structure constant. This measurement, with a value of the fine structure from other measurements, also tests QED and sets a limit on the internal structure of the electron. A one-electron quantum cyclotron is at the heart of the measurement -- an electron suspended in a magnetic field and cooled enough that its lowest cyclotron and spin quantum states can be deduced with quantum nondemolition (QND) measurements. A cylindrical Penning trap cavity inhibits spontaneous emission and feedback methods make the electron excite and sustain its own motion for detection. A new apparatus is being commissioned in pursuit of more precise measurements. Adapted methods are promising for observing a proton spin flip, which should make it possible to compare the antiproton and proton magnetic moments a million times more accurately than is currently possible.

  13. A Potential Link Between the Cosmological Constant and the Fine-structure Constant

    NASA Astrophysics Data System (ADS)

    Goradia, Shantilal

    2008-04-01

    The age of the universe, about 10^60 Planck times, makes the spherical radius (R) of its space 10^60 Planck lengths, as the light moves one Planck length per one Planck time. The fine-structure constant (α) closely equals the natural logarithm of the square root of the reciprocal of the cosmological constant (λ), making α ln (1/λ), where λ = 1/ R^2 as originally introduced by Einstein in equation number (14) in his 1917 paper: Cosmological Considerations on the General Theory of Relativity. This confirms the time-dependent variation of fine-structure constant in [1], but does not address the issue of dark energy. While [1] invokes negative entropy (-Q/T), so it also invokes dark energy simply. The problem still remains that no theory, as yet, combines the probabilistic aspect of quantum mechanics with gravity. In the meanwhile, we can link [1] with the quantum information theory as information links to entropy. [1] Goradia S. Preprint at (http://www.arxiv.org/physics/0210040 v3 (Jan 2007).

  14. Fine structure of the red luminescence band in undoped GaN

    SciTech Connect

    Reshchikov, M. A.; Usikov, A.; Helava, H.; Makarov, Yu.

    2014-01-20

    Many point defects in GaN responsible for broad photoluminescence (PL) bands remain unidentified. Their presence in thick GaN layers grown by hydride vapor phase epitaxy (HVPE) detrimentally affects the material quality and may hinder the use of GaN in high-power electronic devices. One of the main PL bands in HVPE-grown GaN is the red luminescence (RL) band with a maximum at 1.8 eV. We observed the fine structure of this band with a zero-phonon line (ZPL) at 2.36 eV, which may help to identify the related defect. The shift of the ZPL with excitation intensity and the temperature-related transformation of the RL band fine structure indicate that the RL band is caused by transitions from a shallow donor (at low temperature) or from the conduction band (above 50 K) to an unknown deep acceptor having an energy level 1.130 eV above the valence band.

  15. Position-sensitive change in the transition metal L-edge fine structures

    SciTech Connect

    Gulec, Ahmet; Phillips, Patrick J.; Klie, Robert F.

    2015-10-05

    Studying the structure and composition of solid-state materials on the atomic scale has become nearly routine in transmission electron microscopy with the development of novel electron optics and electron sources. In particular, with spatial resolutions better than 0.1 nm and energy resolution smaller than 100 meV, the stoichiometry, bonding, and coordination can now be examined on similar scales. Aberration-corrected scanning transmission electron microscopy and electron energy-loss spectroscopy (EELS) have played a crucial role in identifying charge ordering, valence, and as spin state transitions in transition metal perovskite oxides. In this letter, we investigate the effects of ever-decreasing electron-probe sizes on the measured near-edge fine-structure of the transition metal core-loss edge using EELS. We find that for certain transition metal perovskites, the position of the electron probe with respect to the atomic column is crucial in determining the correct valence state. Several reasons for the observed position-sensitive EELS fine-structure are discussed.

  16. THE FINE STRUCTURE OF THE NUCLEOLUS DURING MITOSIS IN THE GRASSHOPPER NEUROBLAST CELL

    PubMed Central

    Stevens, Barbara J.

    1965-01-01

    The behavior of the nucleolus during mitosis was studied by electron microscopy in neuroblast cells of the grasshopper embryo, Chortophaga viridifasciata. Living neuroblast cells were observed in the light microscope, and their mitotic stages were identified and recorded. The cells were fixed and embedded; alternate thick and thin sections were made for light and electron microscopy. The interphase nucleolus consists of two fine structural components arranged in separate zones. Concentrations of 150 A granules form a dense peripheral zone, while the central regions are composed of a homogeneous background substance. Observations show that nucleolar dissolution in prophase occurs in two steps with a preliminary loss of the background substance followed by a dispersal of the granules. Nucleolar material reappears at anaphase as small clumps or layers at the chromosome surfaces. These later form into definite bodies, which disappear as the nucleolus grows in telophase. Evidence suggests both a collecting and a synthesizing role for the nucleolus-associated chromatin. The final, mature nucleolar form is produced by a rearrangement of the fine structural components and an increase in their mass. PMID:14326121

  17. The variation of the fine-structure constant from disformal couplings

    SciTech Connect

    De Bruck, Carsten van; Mifsud, Jurgen; Nunes, Nelson J. E-mail: jmifsud1@sheffield.ac.uk

    2015-12-01

    We study a theory in which the electromagnetic field is disformally coupled to a scalar field, in addition to a usual non-minimal electromagnetic coupling. We show that disformal couplings modify the expression for the fine-structure constant, α. As a result, the theory we consider can explain the non-zero reported variation in the evolution of α by purely considering disformal couplings. We also find that if matter and photons are coupled in the same way to the scalar field, disformal couplings itself do not lead to a variation of the fine-structure constant. A number of scenarios are discussed consistent with the current astrophysical, geochemical, laboratory and the cosmic microwave background radiation constraints on the cosmological evolution of α. The models presented are also consistent with the current type Ia supernovae constraints on the effective dark energy equation of state. We find that the Oklo bound in particular puts strong constraints on the model parameters. From our numerical results, we find that the introduction of a non-minimal electromagnetic coupling enhances the cosmological variation in α. Better constrained data is expected to be reported by ALMA and with the forthcoming generation of high-resolution ultra-stable spectrographs such as PEPSI, ESPRESSO, and ELT-HIRES. Furthermore, an expected increase in the sensitivity of molecular and nuclear clocks will put a more stringent constraint on the theory.

  18. Accurate Electron Affinity of Iron and Fine Structures of Negative Iron ions.

    PubMed

    Chen, Xiaolin; Luo, Zhihong; Li, Jiaming; Ning, Chuangang

    2016-05-03

    Ionization potential (IP) is defined as the amount of energy required to remove the most loosely bound electron of an atom, while electron affinity (EA) is defined as the amount of energy released when an electron is attached to a neutral atom. Both IP and EA are critical for understanding chemical properties of an element. In contrast to accurate IPs and structures of neutral atoms, EAs and structures of negative ions are relatively unexplored, especially for the transition metal anions. Here, we report the accurate EA value of Fe and fine structures of Fe(-) using the slow electron velocity imaging method. These measurements yield a very accurate EA value of Fe, 1235.93(28) cm(-1) or 153.236(34) meV. The fine structures of Fe(-) were also successfully resolved. The present work provides a reliable benchmark for theoretical calculations, and also paves the way for improving the EA measurements of other transition metal atoms to the sub cm(-1) accuracy.

  19. Infrared fine-structure line diagnostics of shrouded active galactic nuclei

    NASA Technical Reports Server (NTRS)

    Voit, G. M.

    1993-01-01

    Far-infrared spectroscopy of celestial objects will improve dramatically in the coming decade, allowing astronomers to use fine-structure line emission to probe photoionized regions obscured in the optical band by thick clouds of dust. The ultraluminous far-IR galaxies revealed by IRAS, quasar-like in luminosity but smothered in molecular gas, probably conceal either immense starbursts or luminous active nuclei. In both scenarios, these objects ought to produce copious infrared fine-structure emission with several lines comparable to H(beta) in luminosity. This paper shows how these lines, if detected, can be used to determine the electron densities and far-IR obscurations of shrouded photoionized regions and to constrain the shape and ionization parameter of the ionizing spectra. The presence of (Ne V) emission in particular will distinguish shrouded AGN's from shrouded starbursts. Since all active galaxies photoionize at least some surrounding material, these diagnostics can also be applied to active galaxies in general and will aid in studying how an active nucleus interacts with the interstellar medium of its host galaxy.

  20. Retinular fine structure in compound eyes of diurnal and nocturnal sphingid moths.

    PubMed

    Eguchi, E

    1982-01-01

    Retinular fine structure has been compared in the superposition compound eyes of three sphingid moths, one nocturnal, Cechenena, and two diurnal, Cephonodes and Macroglossum. Cechenena and Cephonodes have tiered retinas with three kinds of retinular cells: two distal, six regular and one basal. The distal retinular cells in Cechenena are special in having a complex partially intracellular rhabdomere not present in Cephonodes. Macroglossum lacks the distal retinular cell. In Cephonodes a unique rhabdom type, formed by the six regular retinular cells in the middle region of the retinula, is divided into three separate longitudinal plates arranged closely parallel to one another. Their constituent microvilli are consequently all nearly unidirectional. The ratio of rhabdom volume to retinular cell volume in the two diurnal sphingids is 10-27%; this is about the same as that (25%) of skipper butterflies, but significantly smaller than in the nocturnal Cechenena (60%). In the diurnal sphingids retinular cell membranes show elongate meandering profiles with septate junctions between adjacent retinular cells. From the comparative fine structure of their eyes the diurnal sphingids and the skippers would appear to be phylogenetically closely related.

  1. On the mechanisms involved in the recovery of envelope information from temporal fine structure

    PubMed Central

    Apoux, Frédéric; Millman, Rebecca E.; Viemeister, Neal F.; Brown, Christopher A.; Bacon, Sid P.

    2011-01-01

    Three experiments were designed to provide psychophysical evidence for the existence of envelope information in the temporal fine structure (TFS) of stimuli that were originally amplitude modulated (AM). The original stimuli typically consisted of the sum of a sinusoidally AM tone and two unmodulated tones so that the envelope and TFS could be determined a priori. Experiment 1 showed that normal-hearing listeners not only perceive AM when presented with the Hilbert fine structure alone but AM detection thresholds are lower than those observed when presenting the original stimuli. Based on our analysis, envelope recovery resulted from the failure of the decomposition process to remove the spectral components related to the original envelope from the TFS and the introduction of spectral components related to the original envelope, suggesting that frequency- to amplitude-modulation conversion is not necessary to recover envelope information from TFS. Experiment 2 suggested that these spectral components interact in such a way that envelope fluctuations are minimized in the broadband TFS. Experiment 3 demonstrated that the modulation depth at the original carrier frequency is only slightly reduced compared to the depth of the original modulator. It also indicated that envelope recovery is not specific to the Hilbert decomposition. PMID:21786897

  2. Perceptual weighting of individual and concurrent cues for sentence intelligibility: Frequency, envelope, and fine structure

    PubMed Central

    Fogerty, Daniel

    2011-01-01

    The speech signal may be divided into frequency bands, each containing temporal properties of the envelope and fine structure. For maximal speech understanding, listeners must allocate their perceptual resources to the most informative acoustic properties. Understanding this perceptual weighting is essential for the design of assistive listening devices that need to preserve these important speech cues. This study measured the perceptual weighting of young normal-hearing listeners for the envelope and fine structure in each of three frequency bands for sentence materials. Perceptual weights were obtained under two listening contexts: (1) when each acoustic property was presented individually and (2) when multiple acoustic properties were available concurrently. The processing method was designed to vary the availability of each acoustic property independently by adding noise at different levels. Perceptual weights were determined by correlating a listener’s performance with the availability of each acoustic property on a trial-by-trial basis. Results demonstrated that weights were (1) equal when acoustic properties were presented individually and (2) biased toward envelope and mid-frequency information when multiple properties were available. Results suggest a complex interaction between the available acoustic properties and the listening context in determining how best to allocate perceptual resources when listening to speech in noise. PMID:21361454

  3. Features of sound propagation in the ocean with fine-structure inhomogeneities

    NASA Astrophysics Data System (ADS)

    Gostev, V. S.; Mikryukov, A. V.; Popov, O. E.

    2016-09-01

    We analyze the results of an experiment using an explosive sound source in the tropical part of the Indian Ocean. We consider the time structure of sound signals in geometric shadow zones to a distance of 270 km and the scheme of how the sound field in the shadow zone is formed by rays reflected from horizontally extended fine-structured sound velocity layers. From the results of calculation using a wave program that realizes the method of psuedodifferential parabolic equations, we analyze the influence of signal scattering by fine-structure sound velocity inhomogeneities on the sound field distribution in a waveguide. We show that the field formed by spots of light in each of the shadow zones is generated by a regular field and propagates in parallel to it, taking energy from the regular zone in the near field and in each subsequent convergence zone. This mechanism causes an additional decrease in the field in illuminated zones, which can be interpreted as additional attenuation of the regular sound field.

  4. Fine structure of synaptic sites and circuits in mushroom bodies of insect brains.

    PubMed

    Schürmann, Friedrich-Wilhelm

    2016-09-01

    In the insect brain, mushroom bodies represent a prominent central neuropil for multisensory integration and, crucially, for learning and memory. For this reason, special attention has been focused on its small chemical synapses. Early studies on synaptic types and their distribution, using conventional electron microscopy, and recent publications have resolved basic features of synaptic circuits. More recent studies, using experimental methods for resolving neurons, such as immunocytochemistry, genetic labelling, high resolution confocal microscopy and more advanced electron microscopy, have revealed many new details about the fine structure and molecular contents of identifiable neurons of mushroom bodies and has led to more refined modelling of functional organisation. Synaptic circuitries have been described in most detail for the calyces. In contrast, the mushroom bodies' columnar peduncle and lobes have been explored to a lesser degree. In dissecting local microcircuits, the scientist is confronted with complex neuronal compartmentalisation and specific synaptic arrangements. This article reviews classical and modern studies on the fine structure of synapses and their networks in mushroom bodies across several insect species.

  5. Frequency-dependent fine structure in the frequency-following response: The byproduct of multiple generators.

    PubMed

    Tichko, Parker; Skoe, Erika

    2017-01-28

    The frequency-following response (FFR) is an auditory-evoked response recorded at the scalp that captures the spectrotemporal properties of tonal stimuli. Previous investigations report that the amplitude of the FFR fluctuates as a function of stimulus frequency, a phenomenon thought to reflect multiple neural generators phase-locking to the stimulus with different response latencies. When phase-locked responses are offset by different latencies, constructive and destructive phase interferences emerge in the volume-conducted signals, culminating in an attenuation or amplification of the scalp-recorded response in a frequency-specific manner. Borrowing from the literature on the audiogram and otoacoustic emissions (OAEs), we refer to this frequency-specific waxing and waning of the FFR amplitude as fine structure. While prior work on the human FFR was limited by small sets of stimulus frequencies, here, we provide the first systematic investigation of FFR fine structure using a broad stimulus set (90 + frequencies) that spanned the limits of human pitch perception. Consistent with predictions, the magnitude of the FFR response varied systematically as a function of stimulus frequency between 16.35 and 880 Hz. In our dataset, FFR high points (local maxima) emerged at ∼44, 87, 208, and 415 Hz with FFR valleys (local minima) emerging ∼62, 110, 311, and 448 Hz. To investigate whether these amplitude fluctuations are the result of multiple neural generators with distinct latencies, we created a theoretical model of the FFR that included six putative generators. Based on the extant literature on the sources of the FFR, our model adopted latencies characteristic of the cochlear microphonic (0 ms), cochlear nucleus (∼1.25 ms), superior olive (∼3.7 ms), and inferior colliculus (∼5 ms). In addition, we included two longer latency putative generators (∼13 ms, and ∼25 ms) reflective of the characteristic latencies of primary and non-primary auditory

  6. Local ordering of nanostructured Pt probed by multiple-scattering XAFS

    SciTech Connect

    Witkowska, Agnieszka; Di Cicco, Andrea; Principi, Emiliano

    2007-09-01

    We present detailed results of a multiple-scattering (MS) extended x-ray absorption fine structure (EXAFS) data analysis of crystalline and nanocrystalline platinum. Advanced MS EXAFS analysis has been applied to raw x-ray absorption data including the background, using the expansion of the absorption cross section in terms of local two-body and three-body configurations. Present EXAFS results on bulk Pt are found to be in agreement with previous structural and vibrational data, and has been used as a reference for reliable structural refinement of nanosized systems. EXAFS structural refinement of Pt nanoparticles has been performed in combination with electron microscopy and x-ray diffraction, showing the importance of considering the actual size distribution and morphology of the samples. Present samples were unsupported and supported Pt nanocrystalline systems with size distributions showing clusters of quasispherical shape in the 1-7 nm range. In particular, EXAFS spectra have been analyzed accounting for the reduction of the coordination number and degeneracy of three-body configurations, resulting from the measured size distribution and expected surface atom contributions. The importance of a correct account of the reduction of the number of neighbors for calculating MS contributions is emphasized in the paper. EXAFS results have been found compatible with x-ray diffraction and transmission electron microscopy investigations. We estimate that EXAFS could be used to study cluster shapes only for sizes below 2 nm using present methods and quality of the experimental data. We have also shown that the local distribution of distances and angles probed by EXAFS is broader than in bulk Pt, with first-neighbor bond length variance and asymmetry increasing upon reducing the particle size. Methods and results presented in this paper have been found to be successful for a robust structural refinement of monatomic nanocrystalline systems and represents a solid starting

  7. Far-Infrared Rotational and Fine-Structure Transition Frequencies and Molecular Constants of 14NO and 15NO in the X2Pi (v = 0) State.

    PubMed

    Varberg; Stroh; Evenson

    1999-07-01

    We have made highly accurate measurements of the absorption spectrum of the 14NO and 15NO isotopomers of nitric oxide in the far-infrared. Pure rotational transitions up to J" = 3712 within the 2Pi1/2 and 2Pi3/2 spin components and several 2Pi3/2 <-- 2Pi1/2 fine-structure transitions were recorded within the ground vibrational state. A least-squares fit to these data combined with some lambda-doubling and rotational transitions measured by previous workers has resulted in accurate values for the rotational, fine, and hyperfine parameters of these two isotopomers. Most of the far-infrared transitions reported here have an experimental uncertainty of about 20 kHz and will be useful for astronomers and atmospheric scientists studying this important molecule. The more accurate calculated frequencies will also be useful as spectroscopic calibration standards. Copyright 1999 Academic Press.

  8. Effect of atomic vibrations in XANES: polarization-dependent damping of the fine structure at the Cu K-edge of (creat)2CuCl4.

    PubMed

    Šipr, Ondřej; Vackář, Jiří; Kuzmin, Alexei

    2016-11-01

    Polarization-dependent damping of the fine structure in the Cu K-edge spectrum of creatinium tetrachlorocuprate [(creat)2CuCl4] in the X-ray absorption near-edge structure (XANES) region is shown to be due to atomic vibrations. These vibrations can be separated into two groups, depending on whether the respective atoms belong to the same molecular block; individual molecular blocks can be treated as semi-rigid entities while the mutual positions of these blocks are subject to large mean relative displacements. The effect of vibrations can be efficiently included in XANES calculations by using the same formula as for static systems but with a modified free-electron propagator which accounts for fluctuations in interatomic distances.

  9. WAVELENGTH ACCURACY OF THE KECK HIRES SPECTROGRAPH AND MEASURING CHANGES IN THE FINE STRUCTURE CONSTANT

    SciTech Connect

    Griest, Kim; Whitmore, Jonathan B.; Wolfe, Arthur M.; Prochaska, J. Xavier; Howk, J. Christopher; Marcy, Geoffrey W. E-mail: jonathan.b.whitmore@gmail.co

    2010-01-01

    We report on an attempt to accurately wavelength calibrate four nights of data taken with the Keck HIRES spectrograph on QSO PHL957, for the purpose of determining whether the fine structure constant was different in the past. Using new software and techniques, we measured the redshifts of various Ni II, Fe II, Si II, etc. lines in a damped Lyalpha system at z = 2.309. Roughly half the data were taken through the Keck iodine cell which contains thousands of well calibrated iodine lines. Using these iodine exposures to calibrate the normal Th-Ar Keck data pipeline output, we found absolute wavelength offsets of 500 m s{sup -1} to 1000 m s{sup -1} with drifts of more than 500 m s{sup -1} over a single night, and drifts of nearly 2000 m s{sup -1} over several nights. These offsets correspond to an absolute redshift of uncertainty of about DELTAz approx 10{sup -5}(DELTAlambda approx 0.02 A), with daily drifts of around DELTAz approx 5 x 10{sup -6} (DELTAlambda approx 0.01 A), and multiday drifts of nearly DELTAz approx 2 x 10{sup -5}(approx0.04 A). The causes of the wavelength offsets are not known, but since claimed shifts in the fine structure constant would result in velocity shifts of less than 100 m s{sup -1}, this level of systematic uncertainty may make it difficult to use Keck HIRES data to constrain the change in the fine structure constant. Using our calibrated data, we applied both our own fitting software and standard fitting software to measure DELTAalpha/alpha, but discovered that we could obtain results ranging from significant detection of either sign, to strong null limits, depending upon which sets of lines and which fitting method were used. We thus speculate that the discrepant results on DELTAalpha/alpha reported in the literature may be due to random fluctuations coming from underestimated systematic errors in wavelength calibration and fitting procedure.

  10. Low temperature XAFS investigation on the lutetium binding changes during the 2-line ferrihydrite alteration process.

    PubMed

    Dardenne, K; Schäfer, T; Lindqvist-Reis, P; Denecke, M A; Plaschke, M; Rothe, J; Kim, J I

    2002-12-01

    The time dependent changes of Lu speciation (used as Am(III) homologue), initially sorbed onto 2-line ferrihydrite at pH 5.9, during tempering (70 degrees C) to stable crystalline transformation products, goethite and hematite, is studied. Microscopies (AFM, SEM), XRD and FTIR spectroscopy confirm transformation to both goethite and hematite, with a predominance of hematite. XRD investigation of another transformation series at pH 8.0 (75 degrees C, [Lu(III)initial] 7 times higher) shows that the cell volume of hematite increases, suggesting the incorporation of Lu in the crystal structure. Extended X-ray absorption fine structure (EXAFS) (pH 5.9 series, 70 degrees C) reveals a shortening of the Lu-O bond distance and an increase in asymmetry of the first shell with increasing tempering time in the intermediate temper time samples. The intensity of the second peak in the Fourier transform (FT) of the EXAFS increases and splits into two components. The EXAFS data of the end product can be modeled well using a hematite-like cluster, with an isotropic expansion of distances to account for incorporation of Lu into the hematite structure. These results demonstrate that the Lu is incorporated in the crystal lattice of the transformation product, as opposed to being occluded or remaining a sorbed species on the surface.

  11. A study on adsorption mechanism of organoarsenic compounds on ferrihydrite by XAFS

    NASA Astrophysics Data System (ADS)

    Tanaka, M.; Takahashi, Y.; Yamaguchi, N.

    2013-04-01

    Anthropogenic organoarsenic compounds which were used such as agrochemicals, pesticides, and herbicides can have a potential as a source of arsenic pollution in water. In the process, the adsorption of arsenic onto mineral surface in soil may play an important role to affect arsenic distribution in solid-water interface. However, adsorption structures of organoarsenic compounds on the iron-(oxyhydr)oxides are not well known. In this study, extended X-ray absorption fine structure (EXAFS) spectroscopy was employed to know the adsorption structure of methyl- and phenyl-substituted organoarsenic compounds (methylarsonic acid (MMA), dimethylarsinic acid (DMA), phenylarsonic acid (PAA), and diphenylarsinic acid (DPAA) onto ferrihydrite which can be a strong adsorbent of arsenic. EXAFS analysis suggests that the formation of inner-sphere surface complex for all organoarsenic compounds with ferrihydrite regardless of the organic functional groups and the number of substitution. The As-Fe distances are around 3.27 , which suggests both mono-and bi-dentate inner-sphere complexes by DFT calculations. The corresponding coordination numbers (CNs) are less than two, suggesting that coexistence of both structures of inner-sphere complexes.

  12. Glucose and Fluoxetine Induce Fine Structural Change in Human Serum Albumin

    PubMed Central

    Shahani, Minoo; Daneshi-Mehr, Fatemeh; Tadayon, Roya; Hoseinzade Salavati, Behrooz; Akbar Zadeh-Baghban, Ali-Reza; Zamanian, Abbas; Rezaei-Tavirani, Mostafa

    2013-01-01

    Human serum albumin has been used as a model protein for protein folding and ligand binding studies over many decades. Due to its long life period and high concentration in plasma, HSA is highly sensitive to glycation. It is reported that 175 mg/dL glucose concentration is a threshold of kidney activity for the beginning of excretion of glucose. pH denaturation of HSA in absence and presence of different concentrations of glucose is studied and based on the Pace two-state model, the findings are analyzed. In addition, florescence emission data of albumin range in the period of 300-500 nm was depicted. The amounts of free energy change and [D]1/2 parameters of unfolding in correspond to florescence date indicate that glucose induces fine structural change in human serum albumin. Results showed that 175 mg/dL glucose concentration is a critical point for albumin structural and functional alteration. PMID:24250587

  13. Fine structure of the dogfish egg case: a unique collagenous material.

    PubMed

    Knight, D P; Hunt, S

    1976-01-01

    The fine structure of the dogfish egg case is described with special reference to the highly ordered, unique, collagen-containing fibrils. The outer layer of the case wall contains densely packed, amorphous granules, rich in tyrosine while approximately 98% of the thickness of the case is built up from orthogonally stacked laminae of closely packed, collagen-containing fibrils. These fibrils show a paracrystalline three-dimensional construction. A model for the structure of the B band of the fibril is proposed, based on appearances in transverse sections of different thickness and on two projection seen in longitudinal sections. The transverse projection of the unit cell appears to be a square lattice with sides approximately 110 A possibly containing a pseudocell with sides (see article). The structure of these fibrils is discussed in relation to those of rat tail tendon collagen.

  14. Impact of heavy hole-light hole coupling on the exciton fine structure in quantum dots

    NASA Astrophysics Data System (ADS)

    Tsitsishvili, E.

    2017-03-01

    We present analytical results which describe the properties of the exciton ground state in a single semiconductor quantum dot (QD). Calculations are performed within the Luttinger-Kohn and Bir-Pikus Hamiltonian theory. We show in an explicit form that an interplay of the exchange interaction and the heavy hole-light hole coupling, which is due to the in-plane asymmetries of the dot shape and the strain distribution, plays an essential role. For both the bright and dark exciton, this combined effect leads to a dependence of the fine structure splitting and polarizations on the main anisotropy axis direction relative to the dot orientation. Basing on the obtained analytical expressions, we discuss some special cases in details.

  15. The role of temporal fine structure in harmonic segregation through mistuning.

    PubMed

    Moore, Brian C J; Glasberg, Brian R

    2010-01-01

    Bernstein and Oxenham [(2008). J. Acoust. Soc. Am. 124, 1653-1667] measured thresholds for discriminating the fundamental frequency, F0, of a complex tone that was passed through a fixed bandpass filter. They found that performance worsened when the F0 was decreased so that only harmonics above the tenth were audible. However, performance in this case was improved by mistuning the odd harmonics by 3%. Bernstein and Oxenham considered whether the results could be explained in terms of temporal fine structure information available at the output of a single auditory filter and concluded that their results did not appear to be consistent with such an explanation. Here, it is argued that such cues could have led to the improvement in performance produced by mistuning the odd harmonics.

  16. Enhanced sensitivity to the fine-structure-constant variation in the Th IV atomic clock transition

    SciTech Connect

    Flambaum, V. V.; Porsev, S. G.

    2009-12-15

    Our calculations have shown that the 5f{sub 5/2}-7s{sub 1/2} 23 131 cm{sup -1} transition from the ground state in the ion Th{sup 3+} is very sensitive to the temporal variation of the fine-structure constant alpha=e{sup 2}/(Planck constant/2pi)c (q=-75 300 cm{sup -1}). The line is very narrow, the ion has been trapped and laser cooled, and the positive shifter line 5f{sub 5/2}-5f{sub 7/2} 4325 cm{sup -1} (q=+2900 cm{sup -1}) may be used as a reference. A comparison may also be made with a positive shifter in another atom or ion. This makes Th{sup 3+} a good candidate to search for the alpha variation.

  17. High resolution telescope and spectrograph observations of solar fine structure in the 1600 A region

    NASA Technical Reports Server (NTRS)

    Cook, J. W.; Brueckner, G. E.; Bartoe, J.-D. F.

    1983-01-01

    High spatial resolution spectroheliograms of the 1600 A region obtained during the HRTS rocket flight of 1978 February 13 are presented. The morphology, fine structure, and temporal behavior of emission bright points (BPs) in active and quiet regions are illustrated. In quiet regions, network elements persist as morphological units, although individual BPs may vary in intensity while usually lasting the flight duration. In cell centers, the BPs are highly variable on a 1 minute time scale. BPs in plages remain more constant in brightness over the observing sequence. BPs cover less than 4 percent of the quiet surface. The lifetime and degree of packing of BPs vary with the local strength of the magnetic field.

  18. New limit on the present temporal variation of the fine structure constant

    SciTech Connect

    Peik, E.; Lipphardt, B.; Schnatz, H.; Schneider, T.; Tamm, Chr.; Karshenboim, S.G.

    2005-05-05

    A comparison of different atomic frequency standards over time can be used to perform a measurement of the present value of the temporal derivative of the fine structure constant {alpha} in a model-independent way without assumptions on constancy or variability of other parameters. We have measured an optical transition frequency at 688 THz in Yb+ with a cesium atomic clock at two times separated by 2.8 years and find that a variation of this frequency can be excluded within a 1{sigma} relative uncertainty of 4.4{center_dot}10-15 yr-1. Combined with recently published values for the constancy of other transition frequencies this measurement provides a limit on the present variability of {alpha} at the level of 2.0{center_dot}10-15 yr-1. Constraints are also derived for the drift rates of other fundamental constants like the electron/proton mass ratio and the proton g-factor.

  19. The tardigrade cuticle. I. Fine structure and the distribution of lipids.

    PubMed

    Wright, J C

    1988-01-01

    Fine structure and lipid distribution are studied in cuticles of five tardigrade species using TEM and SEM. Double osmication using partitioning methods reveals a substantial lipid component in the intracuticle and in irregular granular regions within the procuticle. These results are substantiated by the loss of osmiophily following lipid extraction with chloroform and methanol. Other lipid components are revealed by osmication following unmasking of lipo-protein complexes with thymol. These occur in the outer epicuticle and in the trilaminar layer lying between the epi- and intracuticles. Anhydrous fixation of dehydrated tardigrades (tuns) reveals dense, superficial masses of osmiophilic material, apparently concentrated lumps of the surface mucopolysaccharide ('flocculent coat'). However, cryo-SEMs of tuns reveal similar dense aggregations which apparently exude from pores (not visible) and are removed by chloroform. These results suggest extruded lipids since the flocculent coat is unaffected by chloroform; likely functions of such lipids are discussed.

  20. Domain Dynamics in Piezoresponse Force Microscopy: Quantitative Deconvolution and Hysteresis Loop Fine Structure

    SciTech Connect

    Bdikin, Igor; Kholkin, Andrei; Morozovska, A. N.; Svechnikov, S. V.; Kim, S.-H.; Kalinin, Sergei V

    2008-01-01

    Domain dynamics in the Piezoresponse Force Spectroscopy (PFS) experiment is studied using the combination of local hysteresis loop acquisition with simultaneous domain imaging. The analytical theory for PFS signal from domain of arbitrary cross-section is developed and used for the analysis of experimental data on Pb(Zr,Ti)O3 polycrystalline films. The results suggest formation of oblate domain at early stage of the domain nucleation and growth, consistent with efficient screening of depolarization field within the material. The fine structure of the hysteresis loop is shown to be related to the observed jumps in the domain geometry during domain wall propagation (nanoscale Barkhausen jumps), indicative of strong domain-defect interactions.

  1. The fine structure of pulmonary contusion and the effect of various drugs.

    PubMed Central

    Casley-Smith, J. R.; Eckert, P.; Földi-Börcsök, E.

    1976-01-01

    The results of contusion were examined by electron and light microscopy in the lungs of rats. It was found that the results here were very similar to those elsewhere in the body, with a few minor modifications due to the unique structure of the lung. Densitometry of protein concentration and visual estimation of oedema were used to quantitate the effects on the injury. The benzo-pyrone drug Venalot had a considerable effect in reducing the protein concentration in the air spaces and the interstitial tissue, and of the oedema in the latter. Neither the proteinase inhibitor Trasylol nor the pectin-based plasma expander HAS had any significant effect on the fine structural alterations of pulmonary contusion. Images Fig. 1 Fig. 2 Fig. 3 Fig. 4 Fig. 5 Fig. 6 Fig. 7 Fig. 8 Fig. 9 Fig. 10 PMID:1087159

  2. Fine-structural changes in the midgut of old Drosophila melanogaster

    NASA Technical Reports Server (NTRS)

    Anton-Erxleben, F.; Miquel, J.; Philpott, D. E.

    1983-01-01

    Senescent fine-structural changes in the midgut of Drosophila melanogaster are investigated. A large number of midgut mitochondria in old flies exhibit nodular cristae and a tubular system located perpendicular to the normal cristae orientation. Anterior intestinal cells show a senescent accumulation of age pigment, either with a surrounding two-unit membrane or without any membrane. The predominant localization of enlarged mitochondria and pigment in the luminal gut region may be related to the polarized metabolism of the intestinal cells. Findings concur with previous observations of dense-body accumulations and support the theory that mitochondria are involved in the aging of fixed post-mitotic cells. Demonstrated by statistical analyses is that mitochondrial size increase is related to mitochondrial variation increase.

  3. THE FINE STRUCTURE OF STALKED BACTERIA BELONGING TO THE FAMILY CAULOBACTERACEAE.

    PubMed

    STOVEPOINDEXTER, J L; COHEN-BAZIRE, G

    1964-12-01

    The fine structure of a series of stalked bacteria belonging to the genera Caulobacter and Asticcacaulis has been examined in thin sections. The cell wall has the multilayered structure typical of many Gram-negative bacteria, and continues without interruption throughout the length of the stalk. The core of the stalk, continuous with the cytoplasmic region of the cell, is enclosed in an extension of the cell membrane, and contains a system of internal membranes: it is devoid of ribosomes and nucleoplasm. A membranous organelle occupies the juncture of stalk and cell, separating the ribosomal region from the core of the stalk. Typical mesosomes also occur in the cell, being particularly frequent at the plane of division. The secreted holdfast is located at the tip of the stalk in Caulobacter, and at the pole of the cell adjacent to the stalk in Asticcacaulis.

  4. Confocal imaging reveals three-dimensional fine structure difference between ventral and dorsal nerve roots.

    PubMed

    Wu, Yuxiang; Sui, Tao; Cao, Xiaojian; Lv, Xiaohua; Zeng, Shaoqun; Sun, Peng

    2011-05-01

    Peripheral nerve injury repair is one of the most challenging problems in neurosurgery, partially due to lack of knowledge of three-dimensional (3-D) fine structure and organization of peripheral nerves. In this paper, we explored the structures of nerve fibers in ventral and dorsal nerves with a laser scanning confocal microscopy. Thick tissue staining results suggested that nerve fibers have a different 3-D structure in ventral and dorsal nerves, and reconstruction from serial sectioning images showed that in ventral nerves the nerve fibers travel in a winding form, while in dorsal nerves, the nerve fibers form in a parallel cable pattern. These structural differences could help surgeons to differentiate ventral and dorsal nerves in peripheral nerve injury repair, and also facilitate scientists to get a deeper understanding about nerve fiber organization.

  5. Fine structure in RF spectra of lightning return stroke wave forms

    NASA Technical Reports Server (NTRS)

    Lanzerotti, L. J.; Thomson, D. J.; Maclennan, C. G.; Rinnert, K.; Krider, E. P.

    1988-01-01

    The power spectra of the wide-band (10 Hz to 100 kHz) magnetic-field signals for a number of lightning return strokes measured during a thunderstorm which occurred in Lindau in August, 1984 have been calculated. The RF magnetic field data are obtained with the engineering unit of the Galileo Jupiter Probe lightning experiment. Each return stroke data stream is passed through an adaptive filter designed to whiten its spectrum. The spectra of the magnetic field data definitely show fine structure, with two or three distinct peaks in the spectra of many of the waveforms. A peak at f of about 60-70 kHz is often seen in the power spectra of the waveform time segments preceding and following the rise-to-peak amplitude of the return stroke.

  6. New determination of the fine structure constant and test of the quantum electrodynamics.

    PubMed

    Bouchendira, Rym; Cladé, Pierre; Guellati-Khélifa, Saïda; Nez, François; Biraben, François

    2011-02-25

    We report a new measurement of the ratio h/m(Rb) between the Planck constant and the mass of (87)Rb atom. A new value of the fine structure constant is deduced, α(-1)=137.035999037(91) with a relative uncertainty of 6.6×10(-10). Using this determination, we obtain a theoretical value of the electron anomaly a(e)=0.00115965218113(84), which is in agreement with the experimental measurement of Gabrielse [a(e)=0.00115965218073(28)]. The comparison of these values provides the most stringent test of the QED. Moreover, the precision is large enough to verify for the first time the muonic and hadronic contributions to this anomaly.

  7. Engineering quantum dots for electrical control of the fine structure splitting

    NASA Astrophysics Data System (ADS)

    Pooley, M. A.; Bennett, A. J.; Farrer, I.; Ritchie, D. A.; Shields, A. J.

    2013-07-01

    We have studied the variation in fine-structure splitting (FSS) under application of vertical electric field in a range of quantum dots grown by different methods. In each sample, we confirm that this energy splitting changes linearly over the field range we can access. We conclude that this linear tuning is a general feature of self-assembled quantum dots, observed under different growth conditions, emission wavelengths, and in different material systems. Statistical measurements of characteristic parameters such as emission energy, Stark shift, and FSS tuning are presented which may provide a guide for future attempts to increase the yield of quantum dots that can be tuned to a minimal value of FSS with vertical electric field.

  8. Gravity field fine structure estimation techniques for a spaceborne gravity gradiometer

    NASA Technical Reports Server (NTRS)

    Kahn, W. D.; Englar, T. S., Jr.

    1987-01-01

    Use of standard estimation techniques to recover geopotential fine structure from gradiometer data requires the adjustment of small subsets of parameters while constraining others to their a priori values in order to minimize the computational load. Here, gravitational anomalies are selected as a parametrization of the gravity field which permits such an approach. Techniques coupled with numerical results for a spaceborne gravity gradiometer mission simulation are described which demonstrate that if a satellite is in a polar/circular orbit at an altitude of 160 km, 1 deg mean free air gravity anomalies can be recovered to an accuracy of 0.4 mgal, where 1 mgal = 0.001 cm/sq s.

  9. THE FINE STRUCTURE OF STALKED BACTERIA BELONGING TO THE FAMILY CAULOBACTERACEAE

    PubMed Central

    Stove Poindexter, Jeanne L.; Cohen-Bazire, Germaine

    1964-01-01

    The fine structure of a series of stalked bacteria belonging to the genera Caulobacter and Asticcacaulis has been examined in thin sections. The cell wall has the multilayered structure typical of many Gram-negative bacteria, and continues without interruption throughout the length of the stalk. The core of the stalk, continuous with the cytoplasmic region of the cell, is enclosed in an extension of the cell membrane, and contains a system of internal membranes: it is devoid of ribosomes and nucleoplasm. A membranous organelle occupies the juncture of stalk and cell, separating the ribosomal region from the core of the stalk. Typical mesosomes also occur in the cell, being particularly frequent at the plane of division. The secreted holdfast is located at the tip of the stalk in Caulobacter, and at the pole of the cell adjacent to the stalk in Asticcacaulis. PMID:14245437

  10. Fine structural changes in the lateral vestibular nucleus of aging rats

    NASA Technical Reports Server (NTRS)

    Johnson, J. E., Jr.; Miquel, J.

    1974-01-01

    The fine structure of the lateral vestibular nucleus was investigated in Sprague-Dawley rats, that were sacrified at 4 weeks, 6-8 weeks, 6-8 months, and 18-20 months of age. In the neuronal perikaria, the following age-associated changes were seen with increasing frequency with advancing age: rodlike nuclear inclusions and nuclear membrane invaginations; cytoplasmic dense bodies with the characteristics of lipofuscin; and moderate disorganization of the granular endoplasmic reticulum. Dense bodies were also seen in glial cells. Rats 18 to 20 months old showed dendritic swellings, axonal degeneration, and an apparent increase in the number of axosomatic synaptic terminals containing flattened vesicles (presumed to be inhibitory in function).

  11. Infrared fine-structure line diagnostics of shrouded active galactic nuclei

    NASA Technical Reports Server (NTRS)

    Voit, G. M.

    1992-01-01

    The ultraluminous far-IR galaxies revealed by IRAS, quasar-like in luminosity but smothered in molecular gas, probably conceal either immense starbursts or luminous active nuclei. In both scenarios, these objects ought to produce copious infrared fine-structure emission with several lines comparable to H-beta in luminosity. We show how these lines, if detected, can be used to determine the electron densities and far-IR obscurations of shrouded photoionized regions and to constrain the shape and ionization parameter of the ionizing spectra. The presence of Ne v emission in particular will distinguish shrouded AGNs from shrouded starbursts. Since all active galaxies photoionize at least some surrounding material, these diagnostics can also be applied to active galaxies in general and will aid in studying how an active nucleus interacts with the interstellar medium of its host galaxy.

  12. Automated fine structure image analysis method for discrimination of diabetic retinopathy stage using conjunctival microvasculature images

    PubMed Central

    Khansari, Maziyar M; O’Neill, William; Penn, Richard; Chau, Felix; Blair, Norman P; Shahidi, Mahnaz

    2016-01-01

    The conjunctiva is a densely vascularized mucus membrane covering the sclera of the eye with a unique advantage of accessibility for direct visualization and non-invasive imaging. The purpose of this study is to apply an automated quantitative method for discrimination of different stages of diabetic retinopathy (DR) using conjunctival microvasculature images. Fine structural analysis of conjunctival microvasculature images was performed by ordinary least square regression and Fisher linear discriminant analysis. Conjunctival images between groups of non-diabetic and diabetic subjects at different stages of DR were discriminated. The automated method’s discriminate rates were higher than those determined by human observers. The method allowed sensitive and rapid discrimination by assessment of conjunctival microvasculature images and can be potentially useful for DR screening and monitoring. PMID:27446692

  13. Fine structure of the isoscalar giant quadrupole resonance in 28Si and 27Al

    NASA Astrophysics Data System (ADS)

    Usman, I. T.; Buthelezi, Z.; Carter, J.; Cooper, G. R. J.; Fearick, R. W.; Förtsch, S. V.; Fujita, H.; Fujita, Y.; von Neumann-Cosel, P.; Neveling, R.; Papakonstantinou, P.; Pysmenetska, I.; Richter, A.; Roth, R.; Sideras-Haddad, E.; Smit, F. D.

    2016-08-01

    The isoscalar giant quadrupole resonance in 28Si and 27Al has been investigated with high-energy-resolution proton inelastic scattering at Ep=200 MeV and at scattering angles close to the maximum of Δ L =2 angular distributions with the K600 magnetic spectrometer of iThemba LABS, South Africa. Characteristic scales are extracted from the observed fine structure with a wavelet analysis and compared for 28Si with random-phase approximation and second random phase approximation calculations with an interaction derived from the Argonne V18 potential by a unitary transformation. A recent extension of the method to deformed nuclei provides the best description of the data, suggesting the significance of Landau damping.

  14. Highly charged ions for atomic clocks and search for variation of the fine structure constant

    NASA Astrophysics Data System (ADS)

    Dzuba, V. A.; Flambaum, V. V.

    2015-11-01

    We review a number of highly charged ions which have optical transitions suitable for building extremely accurate atomic clocks. This includes ions from Hf 12+ to U 34+, which have the 4 f 12 configuration of valence electrons, the Ir 17+ ion, which has a hole in almost filled 4 f subshell, the Ho 14+, Cf 15+, Es 17+ and Es 16+ ions. Clock transitions in most of these ions are sensitive to variation of the fine structure constant, α (α = e2/hbar c). E.g., californium and einsteinium ions have largest known sensitivity to α-variation while holmium ion looks as the most suitable ion for experimental study. We study the spectra of the ions and their features relevant to the use as frequency standards.

  15. Systematics of fine structure in the α decay of deformed odd-mass nuclei

    NASA Astrophysics Data System (ADS)

    Ren, Zhongzhou; Ni, Dongdong

    2014-12-01

    We present a detailed analysis of the a-decay fine structure in 32 deformed odd-mass nuclei from Z = 93 to Z = 102. The α-decay half-lives are systematically calculated within the multichannel cluster model (MCCM), which turns out to well reproduce the experimental data and show the neutron deformed shell structure. The branching ratios for various daughter states are investigated in the MCCM and in the WKB barrier penetration approach, respectively. It is found that the MCCM results agree well with the experimental data, while the WKB results have relatively large deviations from the experimental data for the α transitions to the high-lying members of the rotational band.

  16. Half-lives and fine structure for the α decay of deformed even-even nuclei

    NASA Astrophysics Data System (ADS)

    Ni, DongDong; Ren, ZhongZhou

    2011-08-01

    The α-decay properties of well-deformed even-even nuclei are systematically calculated within the multichannel cluster model (MCCM). Instead of working in the WKB framework, the quasibound solution to the coupled Schrödinger equation is presented with outgoing wave boundary conditions, and the coupling potential is taken into full account in terms of the general quantum theories. The calculated α-decay half-lives are found to agree well with the experimental data with a mean factor of less than 2. The fine structure observed in α decay is also well reproduced by the four-channel microscopic calculation. Very strikingly, the MCCM can give relatively precise descriptions of the branching ratio to excited 4+ states, which is often overestimated in the usual WKB calculations. We expect it to be a significant development of theoretical models toward quantitative descriptions of α transitions to high-spin daughter states.

  17. Theoretical description of fine structure in the α decay of heavy odd-odd nuclei

    NASA Astrophysics Data System (ADS)

    Ni, Dongdong; Ren, Zhongzhou

    2013-02-01

    The newly developed multichannel cluster model (MCCM), based on the coupled-channel Schrödinger equation with outgoing wave boundary conditions, is extended to study the α-decay fine structure in heavy odd-odd nuclei. Calculations are performed for the α transitions to favored rotational bands where the unpaired nucleons remain unchanged. The simple WKB barrier penetration formula is also used to evaluate the branching ratios for various daughter states. It is found that the WKB formula seems to overestimate the branching ratios for the second and third members of the favored rotational band, while the MCCM gives a precise description of them without any adjustable parameters. Moreover, the experimental total α-decay half-lives are well reproduced within the MCCM.

  18. Confocal imaging reveals three-dimensional fine structure difference between ventral and dorsal nerve roots

    NASA Astrophysics Data System (ADS)

    Wu, Yuxiang; Sui, Tao; Cao, Xiaojian; Lv, Xiaohua; Zeng, Shaoqun; Sun, Peng

    2011-05-01

    Peripheral nerve injury repair is one of the most challenging problems in neurosurgery, partially due to lack of knowledge of three-dimensional (3-D) fine structure and organization of peripheral nerves. In this paper, we explored the structures of nerve fibers in ventral and dorsal nerves with a laser scanning confocal microscopy. Thick tissue staining results suggested that nerve fibers have a different 3-D structure in ventral and dorsal nerves, and reconstruction from serial sectioning images showed that in ventral nerves the nerve fibers travel in a winding form, while in dorsal nerves, the nerve fibers form in a parallel cable pattern. These structural differences could help surgeons to differentiate ventral and dorsal nerves in peripheral nerve injury repair, and also facilitate scientists to get a deeper understanding about nerve fiber organization.

  19. Hemicellulose fine structure is affected differently during ripening of tomato lines with contrasted texture.

    PubMed

    Lahaye, Marc; Quemener, Bernard; Causse, Mathilde; Seymour, Graham B

    2012-11-01

    The impact of genetic and fruit ripening on hemicelluloses fine structure was studied in twelve near isogenic lines of tomato fruits harboring firmness QTL. The sugar composition and the MALDI-TOF MS oligosaccharides profile after glucanase hydrolysis of the cell walls were determined from all green and red fruits pericarp tissue. MS profiles showed two major series of oligomers attributed to xyloglucan (XG) and glucomannan (GM) with minor peaks for xylan and ions attributed to galacto-oligomers. The oligosaccharides MS intensity varied significantly with the fruit genetic and ripening status. Correlations between MS intensity indicated structural regulations of both XG and GM structures with genetics and ripening. These results point to a region on the tomato chromosome 9 controlling cell wall galactose metabolism.

  20. Observation of fine structures in laser-driven electron beams using coherent transition radiation.

    PubMed

    Glinec, Y; Faure, J; Norlin, A; Pukhov, A; Malka, V

    2007-05-11

    We have measured the coherent optical transition radiation emitted by an electron beam from laser-plasma interaction. The measurement of the spectrum of the radiation reveals fine structures of the electron beam in the range 400-1000 nm. These structures are reproduced using an electron distribution from a 3D particle-in-cell simulation and are attributed to microbunching of the electron bunch due to its interaction with the laser field. When the radiator is placed closer to the interaction point, spectral oscillations have also been recorded, signature of the interference of the radiation produced by two electron bunches delayed by 74 fs. The second electron bunch duration is shown to be ultrashort to match the intensity level of the radiation. Whereas transition radiation was used at longer wavelengths in order to estimate the electron bunch length, this study focuses on the ultrashort structures of the electron beam.

  1. Fine structure of all-particle energy spectrum in the knee region

    NASA Astrophysics Data System (ADS)

    Garyaka, A.; Martirosov, R.; Ter-Antonyan, S.; Babayan, H.; Erlykin, A.; Gallant, Y.; Jones, L.; Kempa, J.; Nikolskaya, N.; Pattison, B.; Procureur, J.; Sokhoyan, S.; Vardanyan, H.

    2013-02-01

    All-particle energy spectrum in the knee region obtained from extensive air shower (EAS) measurements (GAMMA experiment, 700 g/cm2, Armenia) is presented. Energies of primary particles in the range of 106-108 GeV were evaluated on the basis of observed shower parameters Nch,Nμ, s, θ and corresponding parameterisation of CORSIKA simulated database for SIBYLL interaction model. All shower detection and reconstruction uncertainties were included in the simulated showers for four kinds (H, He, O, Fe) of primary nuclei. The reliability of observed all-particle energy spectrum is investigated from viewpoint of methodical errors and statistical fluctuations. Observed fine structure of all-particle energy spectrum can be interpreted by the rigidity-dependent steepening Galactic diffuse nuclei flux and an additional iron component in the region of 70-80 PeV primary energies most likely originated from nearby pulsars.

  2. Photoexcited State Molecular Structures in Solution Studied by Pump-Probe XAFS

    NASA Astrophysics Data System (ADS)

    Chen, Lin

    2002-03-01

    The photoexcitation causes displacement of electron densities within or among molecules, which consequently leads to nuclear movements. Such nuclear displacements often occur in transient states with short lifetimes. Knowing transient molecular structures during photochemical reactions is important for understanding fundamental aspects of solar energy conversion and storage. Fast x-ray techniques provide direct probes for these transient structures. Using x-ray pulses from the Advanced Photon Source at Argonne, a laser pulse pump, x-ray pulse probe XAFS technique has been developed to capture transient molecular structures in disordered media with nanosecond time resolution. We have carried out several pump-probe XAFS measurements on 1)identifying a transient molecular structure of the photodissociation product of nickel-tetraphenylporphyrin with piperidine axial ligands (NiTPP-L2); 2)determination of the MLCT state structure of Bis(2,9-dimethyl-1,10-phenanthroline) Copper(I) [Cu(I)(dmp)2]+, and 3) triplet state molecular structures of metalloporphyrins. These studies not only prove the feasibility of the technique, but also gain structural information that otherwise will not be available. Future studies include probing transient structures in electron donor-acceptor complexes and optical polarization selected XAFS (OPS-XAFS) using the same technique with a 100-ps time resolution. This work is supported by the Division of Chemical Sciences, Office of Basic Energy Sciences, U. S. Department of Energy, under contract W-31-109-Eng-38.

  3. Direct comparison of XAFS spectroscopy and sequential extraction for arsenic speciation in coal

    USGS Publications Warehouse

    Huggins, Frank E.; Huffman, G.P.; Kolker, A.; Mroczkowski, S.; Palmer, C.A.; Finkelman, R.B.

    2000-01-01

    The speciation of arsenic in an Ohio bituminous coal and a North Dakota lignite has been examined by the complementary methods of arsenic XAFS spectroscopy and sequential extraction by aqueous solutions of ammonium acetate, HCl, HF, and HNO3. In order to facilitate a more direct comparison of the two methods, the arsenic XAFS spectra were obtained from aliquots of the coal prepared after each stage of the leaching procedure. For the aliquots, approximately linear correlations (r2 > 0.98 for the Ohio coal, > 0.90 for the ND lignite) were observed between the height of the edge-step in the XAFS analysis and the concentration of arsenic measured by instrumental neutron activation analysis. Results from the leaching sequence indicate that there are two major arsenic forms present in both coals; one is removed by leaching with HCl and the other by HNO3. Whereas the XAFS spectral signatures of the arsenic leached by HCl are compatible with arsenate for both coals, the arsenic leached by HNO3 is identified as arsenic associated with pyrite for the Ohio coal and as an As3+ species for the North Dakota lignite. Minor arsenate forms persist in both coals after the final leaching with nitric acid. The arsenate forms extracted in HCl are believed to be oxidation products derived from the other major arsenic forms upon exposure of the pulverized coals to air.

  4. Comparison of fine structures of electron cyclotron harmonic emissions in aurora

    NASA Astrophysics Data System (ADS)

    LaBelle, J.; Dundek, M.

    2015-10-01

    Recent discoveries of higher harmonic cyclotron emissions in aurora occurring under daylight conditions motivated the modification of radio receivers at South Pole Station, Antarctica, to measure fine structure of such emissions during two consecutive austral summers, 2013-2014 and 2014-2015. The experiment recorded 347 emission events over 376 days of observation. The seasonal distribution of these events reveals that successively higher harmonics require higher solar zenith angles for occurrence, as expected if they are generated at the matching condition fuh = Nfce, which for higher N requires higher electron densities which are associated with higher solar zenith angles. This result implies that generation of higher harmonics from lower harmonics via wave-wave processes explains only a minority of events. Detailed examination of 21 cases in which two harmonics occur simultaneously shows that in almost all events the higher harmonic comes from higher altitudes, and only for a small fraction of events is it plausible that the frequencies of the fine structures of the emissions are correlated and in exact integer ratio. This observation puts an upper bound of 15-20% on the fraction of emissions which can be explained by wave-wave interactions involving Z mode waves at fce and, combined with consideration of source altitudes, puts an upper bound of 75% on the fraction explained by coalescence of Z mode waves at 2fce. Taken together, these results suggest that the dominant mechanism for the higher harmonics is independent generation at the matching points fuh = Nfce and that the wave-wave interaction mechanisms explain a relatively small fraction of events.

  5. On the Visibility of Prominence Fine Structures at Radio Millimeter Wavelengths

    NASA Astrophysics Data System (ADS)

    Heinzel, P.; Berlicki, A.; Bárta, M.; Karlický, M.; Rudawy, P.

    2015-07-01

    Prominence temperatures have so far mainly been determined by analyzing spectral line shapes, which is difficult when the spectral lines are optically thick. The radio spectra in the millimeter range offer a unique possibility to measure the kinetic temperature. However, studies in the past used data with insufficient spatial resolution to resolve the prominence fine structures. The aim of this article is to predict the visibility of prominence fine structures in the submillimeter/millimeter (SMM) domain, to estimate their brightness temperatures at various wavelengths, and to demonstrate the feasibility and usefulness of future high-resolution radio observations of solar prominences with ALMA ( Atacama Large Millimeter-submillimeter Array). Our novel approach is the conversion of H coronagraphic images into microwave spectral images. We show that the spatial variations of the prominence brightness both in the H line and in the SMM domain predominantly depend on the line-of-sight emission measure of the cool plasma, which we derive from the integrated intensities of the observed H line. This relation also offers a new possibility to determine the SMM optical thickness from simultaneous H observations with high resolution. We also describe how we determine the prominence kinetic temperature from SMM spectral images. Finally, we apply the ALMA image-processing software Common Astronomy Software Applications (CASA) to our simulated images to assess what ALMA would detect at a resolution level that is similar to the coronagraphic H images used in this study. Our results can thus help in preparations of first ALMA prominence observations in the frame of science and technical verification tests.

  6. Fine-structure energy levels, radiative rates and lifetimes in Si-like nickel

    NASA Astrophysics Data System (ADS)

    Gupta, G. P.; Msezane, A. Z.

    2012-07-01

    Large scale CIV3 calculations of excitation energies from ground state as well as of oscillator strengths and radiative decay rates for all electric-dipole-allowed and intercombination transitions among the fine-structure levels of the terms belonging to the (1s22s22p6)3s23p2, 3s3p3, 3p4, 3s23p3d, 3s23p4s, 3s23p4p, 3s23p4d and 3s23p4f configurations of Ni XV, are performed using very extensive configuration-interaction wave functions. The relativistic effects in intermediate coupling are incorporated by means of the Breit-Pauli Hamiltonian. In order to keep our calculated energy splittings as close as possible to the National Institute of Standard and Technology (NIST) values, we have made small adjustments to the diagonal elements of the Hamiltonian matrices. Our calculated excitation energies, including their ordering, are in excellent agreement with the available NIST results. From our radiative decay rates we have also calculated radiative lifetimes of the fine-structure levels. It is noted that our calculated radiative rates show significant disagreement (23-30%) with those calculated by Ishikawa and Vilkas (2002 Phys. Scr. 65 219) for the transitions involving the 3s3p3(5S2) level. For this high spin level 3s3p3(5S2) our calculated lifetime is found to be in excellent agreement with the experimental value of Träbert et al (1989 Z. Phys. D 11 207). In this calculation, we also predict many additional new and accurate data for various optically allowed and intercombination transitions to complete the void in the existing data.

  7. Comparison of Fine Structures of Electron Cyclotron Harmonic Emissions in Aurora

    NASA Astrophysics Data System (ADS)

    Labelle, J. W.; Dundek, M.

    2015-12-01

    Recent discoveries of emissions at four and five times the electron cyclotron frequency in aurora occuring under daylit conditions motivated the modification of radio receivers at South Pole Station, Antarctica, to measure fine structure of such emissions during two consecutive austral summers, 2013-4 and 2014-5. The experiment recorded 347 emission events over 376 days of observation. The seasonal distribution of these events revealed that successively higher harmonics require higher solar zenith angles for occurrence, as expected if they are generated at locations where the upper hybrid frequency matches the cyclotron harmonic, which for higher harmonics requires higher electron densities which are associated with higher solar zenith angles. Detailed examination of 21 cases in which two harmonics occur simultaneously showed that only rarely, about ten percent of the time, are the frequencies of the fine structures of the emissions in exact integer ratio (e.g., 3:2, 4:3, or 5:4 depending on which combination of harmonics is observed). In the remaining approximately ninety percent of the cases, the higher harmonic occurred at a lower ratio than the appropriate integer ratio, as expected if the harmonics are generated independently at their separate matching conditions in the bottomside ionosphere, where the upper hybrid frequency increases with altitude while the gyroharmonics decrease with altitude. (The bottomside is the most likely source of the emissions, since from there the mode converted Z-modes have access to ground-level.) Taken together, these results suggest that the dominant mechanism for the higher harmonics is independent generation at locations where the upper hybrid frequency matches each harmonic, i.e., at a separate source altitude for each harmonic. Generation of higher harmonics through coalescence of lower harmonic waves explains at most a small minority of events.

  8. Hydrogenic Lamb shift in iron Fe{sup 25+} and fine-structure Lamb shift

    SciTech Connect

    Chantler, C. T.; Laming, J. M.; Dietrich, D. D.; Hallett, W. A.; McDonald, R.; Silver, J. D.

    2007-10-15

    1s-2p Lyman {alpha} transitions in hydrogenic iron Fe{sup 25+} have been observed from a beam-foil source in fourth-order diffraction off ADP 101 and PET 002 crystals, simultaneously with the n=2 to n=4 Balmer {beta} transitions diffracted in first order. Calibration of the local dispersion relation of the spectrometer using Balmer {beta} lines provides measurements of Lyman {alpha} wavelengths. The approach of fitting the full two-dimensional dispersion relation, including other members of Balmer and Lyman series, limits random and systematic correlation of parameters, and reveals a major systematic due to dynamical diffraction depth penetration into a curved crystal. The development of a theory of x-ray diffraction from mosaic crystals was necessary for the accurate interpretation of the experimental data. Photographic theory was also developed in the process of this research. Several systematics are discussed and quantified for the first time for these medium-Z QED comparisons. 2s-1s and 4f-2p satellites are explicitly investigated, and a dominant systematic is uncovered, which is due to the variable location of spectral emission downstream of the beam-foil target. 1s-2p{sub 3/2}, 1s-2p{sub 1/2} iron Lamb shifts are measured to be 35 376{+-}1900 cm{sup -1} and 35 953{+-}1800 cm{sup -1}. These agree with but lie higher than theory. This represents a 5.7% measurement of the hydrogenic 1s-2p{sub 1/2} Lamb shift in iron. The technique also reports the iron 2p{sub 3/2}-2p{sub 1/2} fine structure as 171 108 cm{sup -1}{+-}180 cm{sup -1}, which represents a 51% measurement of the hydrogenic iron fine-structure Lamb shift, and reports measurements of secondary lines.

  9. Fine Structure of Tibetan Kefir Grains and Their Yeast Distribution, Diversity, and Shift

    PubMed Central

    Lu, Man; Wang, Xingxing; Sun, Guowei; Qin, Bing; Xiao, Jinzhou; Yan, Shuling; Pan, Yingjie; Wang, Yongjie

    2014-01-01

    Tibetan kefir grains (TKGs), a kind of natural starter for fermented milk in Tibet, China, host various microorganisms of lactic acid bacteria, yeasts, and occasionally acetic acid bacteria in a polysaccharide/protein matrix. In the present study, the fine structure of TKGs was studied to shed light on this unusual symbiosis with stereomicroscopy and thin sections. The results reveal that TKGs consist of numerous small grain units, which are characterized by a hollow globular structure with a diameter between 2.0 and 9.0 mm and a wall thickness of approximately 200 µm. A polyhedron-like net structure, formed mainly by the bacteria, was observed in the wall of the grain units, which has not been reported previously to our knowledge. Towards the inside of the grain unit, the polyhedron-like net structures became gradually larger in diameter and fewer in number. Such fine structures may play a crucial role in the stability of the grains. Subsequently, the distribution, diversity, and shift of yeasts in TKGs were investigated based on thin section, scanning electron microscopy, cloning and sequencing of D1/D2 of the 26S rRNA gene, real-time quantitative PCR, and in situ hybridization with specific fluorescence-labeled oligonucleotide probes. These show that (i) yeasts appear to localize on the outer surface of the grains and grow normally together to form colonies embedded in the bacterial community; (ii) the diversity of yeasts is relatively low on genus level with three dominant species – Saccharomyces cerevisiae, Kluyveromyces marxianus, and Yarrowia lipolytica; (iii) S. cerevisiae is the stable predominant yeast species, while the composition of Kluyveromyces and Yarrowia are subject to change over time. Our results indicate that TKGs are relatively stable in structure, and culture conditions to some extent shape the microbial community and interaction in kefir grains. These findings pave the way for further study of the specific symbiotic associations between S

  10. Production of fine structures in type III solar radio bursts due to turbulent density profiles

    SciTech Connect

    Loi, Shyeh Tjing; Cairns, Iver H.; Li, Bo

    2014-07-20

    Magnetic reconnection events in the corona release energetic electron beams along open field lines, and the beams generate radio emission at multiples of the electron plasma frequency f{sub p} to produce type III solar radio bursts. Type III bursts often exhibit irregularities in the form of flux modulations with frequency and/or local temporal advances and delays, and a type IIIb burst represents the extreme case where a type III burst is fragmented into a chain of narrowband features called striae. Remote and in situ spacecraft measurements have shown that density turbulence is ubiquitous in the corona and solar wind, and often exhibits a Kolmogorov power spectrum. In this work, we numerically investigate the effects of one-dimensional macroscopic density turbulence (along the beam direction) on the behavior of type III bursts, and find that this turbulence produces stria-like fine structures in the dynamic spectra of both f{sub p} and 2 f{sub p} radiation. Spectral and temporal fine structures in the predicted type III emission are produced by variations in the scattering path lengths and group speeds of radio emission, and in the locations and sizes of emitting volumes. Moderate turbulence levels yield flux enhancements with much broader half-power bandwidths in f{sub p} than 2 f{sub p} emission, possibly explaining the often observed type IIIb-III harmonic pairs as being where intensifications in 2 f{sub p} radiation are not resolved observationally. Larger turbulence levels producing trough-peak regions in the plasma density profile may lead to broader, resolvable intensifications in 2 f{sub p} radiation, which may account for the type IIIb-IIIb pairs that are sometimes observed.

  11. Retention of Nickel in Soils: Sorption-Desorption and Extended X-ray Absorption Fine Structure Experiments

    EPA Science Inventory

    Adsorption and desorption of heavy metals in soils are primary factors that influence their bioavailability and mobility in the soil profile. To examine the characteristics of nickel (Ni) adsorption-desorption in soils, kinetic batch experiments were carried out followed by Ni re...

  12. A grazing incidence surface X-ray absorption fine structure (GIXAFS) study of alkanethiols adsorbed on Au, Ag, and Cu

    NASA Astrophysics Data System (ADS)

    Floriano, Pierre N.; Schlieben, Olaf; Doomes, Edward E.; Klein, Ingo; Janssen, J.; Hormes, Josef; Poliakoff, E. D.; McCarley, Robin L.

    2000-04-01

    Self-assembled monolayers of n-alkanethiols, CH 3-(CH 2) x-SH, on Au, Ag, and Cu have been studied with GIXAFS at the sulfur K-edge. For both pentanethiol and decanethiol monolayers on Ag and Cu, the three-fold hollow site is found to be the most probable sulfur binding site. However, observations for octadecanethiol indicate that the three-fold hollow site is not the exclusive binding site. In addition, the possible existence of disulfide bonds on the metal surface (adsorbed dialkyldisulfides) is not supported by the data. Preliminary results from monolayers on Au are also reported.

  13. Local order in hydrogenated amorphous germanium thin films studied by extended x-ray absorption fine-structure spectroscopy

    NASA Astrophysics Data System (ADS)

    Dalba, G.; Fornasini, P.; Grisenti, R.; Rocca, F.; Chambouleyron, I.; Graeff, C. F. O.

    1997-07-01

    The effect of hydrogenation on the local order in amorphous germanium has been studied by EXAFS. Measurements have been carried out on sputtered a-Ge:H films with hydrogen concentrations of 0, 7, 10, and 15 at.%, as a function of temperature in the range 11 - 300 K. The first-shell EXAFS data were analysed by the ratio method based on cumulant expansion. The asymmetric distributions reconstructed from cumulants are in very good agreement with a parametrized distribution obtained by other researchers using calculated phase-shifts. For the unhydrogenated a-Ge (deposited at 0953-8984/9/27/017/img7), increases of the interatomic distance, 0953-8984/9/27/017/img8 at 11 K, static disorder, 0953-8984/9/27/017/img9, and thermal disorder, 0953-8984/9/27/017/img10, have been found with respect to those for c-Ge. Both the static and the thermal disorder are smaller than for an evaporated sample (deposited at 0953-8984/9/27/017/img11) previously studied. The insertion of hydrogen in a-Ge produces a sharp reduction of the interatomic distance, static disorder, and asymmetry of the distribution already at the lowest H concentration (7%); then these parameters decrease almost linearly when the hydrogen content increases. No appreciable influence of hydrogenation on the thermal disorder has been detected.

  14. XAFS study of copper(II) complexes with square planar and square pyramidal coordination geometries

    NASA Astrophysics Data System (ADS)

    Gaur, A.; Klysubun, W.; Nitin Nair, N.; Shrivastava, B. D.; Prasad, J.; Srivastava, K.

    2016-08-01

    X-ray absorption fine structure of six Cu(II) complexes, Cu2(Clna)4 2H2O (1), Cu2(ac)4 2H2O (2), Cu2(phac)4 (pyz) (3), Cu2(bpy)2(na)2 H2O (ClO4) (4), Cu2(teen)4(OH)2(ClO4)2 (5) and Cu2(tmen)4(OH)2(ClO4)2 (6) (where ac, phac, pyz, bpy, na, teen, tmen = acetate, phenyl acetate, pyrazole, bipyridine, nicotinic acid, tetraethyethylenediamine, tetramethylethylenediamine, respectively), which were supposed to have square pyramidal and square planar coordination geometries have been investigated. The differences observed in the X-ray absorption near edge structure (XANES) features of the standard compounds having four, five and six coordination geometry points towards presence of square planar and square pyramidal geometry around Cu centre in the studied complexes. The presence of intense pre-edge feature in the spectra of four complexes, 1-4, indicates square pyramidal coordination. Another important XANES feature, present in complexes 5 and 6, is prominent shoulder in the rising part of edge whose intensity decreases in the presence of axial ligands and thus indicates four coordination in these complexes. Ab initio calculations were carried out for square planar and square pyramidal Cu centres to observe the variation of 4p density of states in the presence and absence of axial ligands. To determine the number and distance of scattering atoms around Cu centre in the complexes, EXAFS analysis has been done using the paths obtained from Cu(II) oxide model and an axial Cu-O path from model of a square pyramidal complex. The results obtained from EXAFS analysis have been reported which confirmed the inference drawn from XANES features. Thus, it has been shown that these paths from model of a standard compound can be used to determine the structural parameters for complexes having unknown structure.

  15. Degradation mechanism of a high-performance real micro gas sensor, as determined by spatially resolved XAFS.

    PubMed

    Wada, Takahiro; Murata, Naoyoshi; Uehara, Hiromitsu; Suzuki, Takuya; Nitani, Hiroaki; Niwa, Yasuhiro; Uo, Motohiro; Asakura, Kiyotaka

    2016-03-14

    Of late, battery-driven high-performance gas sensors have gained acceptability in practical usage, whose atomic-scale structure has been revealed by μ-fluorescence X-ray absorption fine structure analysis. We studied the chemical distribution of Pd species in the Pd/Al2O3 catalyst overlayer in the real gas sensor at various degrees of deterioration. In a freshly prepared sensor, all Pd species were in the PdO form; in a heavily deteriorated sensor, Pd/Al2O3 in the external region changed to metallic Pd particles, while the PdO structure in the inner region near the heater remained unchanged. The Pd species distribution was in agreement with the simulated thermal distribution. Temperature control was crucial to maintain the high performance of the gas sensor. The improved sensor allows homogeneous heating and has a lifetime of more than 5 years.

  16. FINE STRUCTURAL OBSERVATIONS RELATING TO THE PRODUCTION OF COLOR BY THE IRIDOPHORES OF A LIZARD, ANOLIS CAROLINENSIS

    PubMed Central

    Rohrlich, Susannah T.; Porter, Keith R.

    1972-01-01

    This paper presents the results of light and electron microscopy done on iridophores in the dorsal skin of the lizard Anolis carolinensis. New fine-structural details are revealed, and their importance is discussed. Of some interest is the complex of filaments between crystalline sheets in the cell. It is proposed that this complex is involved in the arrangement of crystals into crystalline sheets, and that the crystal arrangement and spacing are critical for the production of the cells' blue-green color. Tyndall scattering and thin-film interference are discussed as possible explanations for iridophore color production in relation to the fine-structural data obtained. PMID:5013601

  17. Fine Structure of the Gamow-Teller Resonance in {sup 90}Nb and Level Density of 1{sup +} States

    SciTech Connect

    Kalmykov, Y.; Neumann-Cosel, P. von; Ponomarev, V.Yu.; Richter, A.; Shevchenko, A.; Wambach, J.; Adachi, T.; Fujita, Y.; Shimbara, Y.; Berg, G.P.A.; Fujita, K.; Hatanaka, K.; Kamiya, J.; Nakanishi, K.; Sakamoto, N.; Sakemi, Y.; Shimizu, Y.; Wakasa, T.; Fujita, H.; Smit, F.D.

    2006-01-13

    The fine structure of the Gamow-Teller resonance in a medium-heavy nucleus is observed for the first time in a high-resolution {sup 90}Zr({sup 3}He,t){sup 90}Nb experiment at the Research Center for Nuclear Physics, Osaka. Using a novel wavelet analysis technique, it is possible to extract characteristic energy scales and to quantify their relative importance for the generation of the fine structure. This method combined with the selectivity of the reaction permits an extraction of the level density of 1{sup +} states in {sup 90}Nb.

  18. XAFS measurements on zinc chloride aqueous solutions from ambient to supercritical conditions using the diamond anvil cell

    USGS Publications Warehouse

    Mayanovic, Robert A.; Anderson, Alan J.; Bassett, William A.; Chou, I.-Ming

    1999-01-01

    The structure and bonding properties of metal complexes in subcritical and supercritical fluids are still largely unknown. Conventional high pressure and temperature cell designs impose considerable limitations on the pressure, temperature, and concentration of metal salts required for measurements on solutions under supercritical conditions. In this study, we demonstrate the first application of the diamond anvil cell, specially designed for x-ray absorption studies of first-row transition metal ions in supercritical fluids. Zn K-edge XAFS spectra were measured from aqueous solutions of 1-2m ZnCl2 and up to 6m NaCl, at temperatures ranging from 25-660 ??C and pressures up to 800 MPa. Our results indicate that the ZnCl42- complex is predominant in the 1m ZnCl2/6m NaCl solution, while ZnCl2(H2O)2 is similarly predominant in the 2m ZnCl2 solution, at all temperatures and pressures. The Zn-Cl bond length of both types of chlorozinc(II) complexes was found to decrease at a rate of about 0.01 A??/100 ??C.

  19. Electron yield XAFS study of evaporated Co/Pd multilayers with various thickness ratios of Co to Pd sublayers: Simulations of the Co K-edge XAFS and fourier transforms

    SciTech Connect

    Choi, M. . Dept. of Physics); Joo, J.H. . Materials Design Lab.); Kim, S.K.; Kang, J.S.; Lee, Y.P. ); Shin, S.C. ); Heald, S.M.

    1992-01-01

    Electron-yield XAFS measurements using the NSLS were made on e-beam evaporated Co/Pd multilayers with various sublayer thicknesses and different thickness ratios of Co to Pd sublayers. The Co K-edge and the Pd K-edge XAFS data were obtained for the Co/Pd multilayers with sublayer thicknesses of 3[Angstrom]/ 4[Angstrom], 15[Angstrom]/4[Angstrom], 3[Angstrom]/15[Angstrom], 2.1[Angstrom]/13.5[Angstrom], and 2.2[Angstrom]/4.5[Angstrom]. Fourier transforms of Co K XAFS for most samples show a splitting of major peak, and the magnitude ratio of these split peaks varies systematically with the thickness ratio of the Pd sublayer to the Co sublayer, whereas the Fourier transforms of the Pd K XAFS for the same samples do not show a splitting of peaks. As a preliminary analysis, the Co K XAFS and the split peaks in the Fourier transform for the Co/Pd(3[Angstrom]/4[Angstrom]) case were simulated by using the FEFF calculations, and the Co K XAFS and the major peak in the fourier transform for the Co/Pd(15[Angstrom]/4[Angstrom]) case were also simulated consistently.

  20. Electron yield XAFS study of evaporated Co/Pd multilayers with various thickness ratios of Co to Pd sublayers: Simulations of the Co K-edge XAFS and fourier transforms

    SciTech Connect

    Choi, M.; Joo, J.H.; Kim, S.K.; Kang, J.S.; Lee, Y.P.; Shin, S.C.; Heald, S.M.

    1992-11-01

    Electron-yield XAFS measurements using the NSLS were made on e-beam evaporated Co/Pd multilayers with various sublayer thicknesses and different thickness ratios of Co to Pd sublayers. The Co K-edge and the Pd K-edge XAFS data were obtained for the Co/Pd multilayers with sublayer thicknesses of 3{Angstrom}/ 4{Angstrom}, 15{Angstrom}/4{Angstrom}, 3{Angstrom}/15{Angstrom}, 2.1{Angstrom}/13.5{Angstrom}, and 2.2{Angstrom}/4.5{Angstrom}. Fourier transforms of Co K XAFS for most samples show a splitting of major peak, and the magnitude ratio of these split peaks varies systematically with the thickness ratio of the Pd sublayer to the Co sublayer, whereas the Fourier transforms of the Pd K XAFS for the same samples do not show a splitting of peaks. As a preliminary analysis, the Co K XAFS and the split peaks in the Fourier transform for the Co/Pd(3{Angstrom}/4{Angstrom}) case were simulated by using the FEFF calculations, and the Co K XAFS and the major peak in the fourier transform for the Co/Pd(15{Angstrom}/4{Angstrom}) case were also simulated consistently.

  1. Ion-pairing in aqueous CaCl2 and RbBr solutions. Simultaneous structural refinement of XAFS and XRD data

    SciTech Connect

    Pham, Thai V.; Fulton, John L.

    2013-01-22

    We present a new methodology involving the simultaneous refinement of both x-ray absorption and x-ray diffraction spectra (X-ray Absorption/Diffraction Structural Refinement,XADSR), to study hydration and ion pair structure of CaCl2 and RbBr salts in concentrated aqueous solutions. The XADSR analysis includes the XAFS spectra analysis of both the cation and anion as a probe of their short-range structure with an XRD spectral analysis as a probe of the global structural. Together they deliver a comprehensive picture of the cation and anion hydration, the contact ion pair (CIP) structure and the solvent-separated ion pair (SSIP) structure. XADSR analysis of 6.0 m aqueous CaCl2 reveals that there are an insignificant number of Ca2+-Cl- CIP’s, but there are approximately 3.4 SSIP’s separated by about 4.99 Å. In contrast XADSR analysis of aqueous RbBr yields about 0.7 pair CIP at a bond length 3.51 Å. The present work demonstrates a new approach for a direct co-refinement of XRD and XAFS spectra in a simple and reliable fashion, opening new opportunities for analysis in various disordered and crystalline systems. This work was supported by the U.S. Department of Energy (DOE), Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences and Biosciences. Pacific Northwest National Laboratory (PNNL) is operated for the U.S. Department of Energy by Battelle.

  2. Fine structure of the mineralized teeth of the chiton Acanthopleura echinata (Mollusca: Polyplacophora).

    PubMed

    Wealthall, Rosamund J; Brooker, Lesley R; Macey, David J; Griffin, Brendan J

    2005-08-01

    The major lateral teeth of the chiton Acanthopleura echinata are composite structures composed of three distinct mineral zones: a posterior layer of magnetite; a thin band of lepidocrocite just anterior to this; and apatite throughout the core and anterior regions of the cusp. Biomineralization in these teeth is a matrix-mediated process, in which the minerals are deposited around fibers, with the different biominerals described as occupying architecturally discrete compartments. In this study, a range of scanning electron microscopes was utilized to undertake a detailed in situ investigation of the fine structure of the major lateral teeth. The arrangement of the organic and biomineral components of the tooth is similar throughout the three zones, having no discrete borders between them, and with crystallites of each mineral phase extending into the adjacent mineral zone. Along the posterior surface of the tooth, the organic fibers are arranged in a series of fine parallel lines, but just within the periphery their appearance takes on a "fish scale"-like pattern, reflective of the cross section of a series of units that are overlaid, and offset from each other, in adjacent rows. The units are approximately 2 microm wide and 0.6 microm thick and comprise biomineral plates separated by organic fibers. Two types of subunits make up each "fish scale": one is elongate and curved and forms a trough, in which the other, rod-like unit, is nestled. Adjacent rod and trough units are aligned into large sheets that define the fracture plane of the tooth. The alignment of the plates of rod-trough units is complex and exhibits extreme spatial variation within the tooth cusp. Close to the posterior surface the plates are essentially horizontal and lie in a lateromedial plane, while anteriorly they are almost vertical and lie in the posteroanterior plane. An understanding of the fine structure of the mineralized teeth of chitons, and of the relationship between the organic and

  3. Rotational and Fine Structure of Pseudo-Jahn Molecules with C_1 Symmetry

    NASA Astrophysics Data System (ADS)

    Liu, Jinjun

    2016-06-01

    It has been found in our previous works that rotational and fine-structure analysis of spectra involving nearly degenerate electronic states may aid in interpretation and analysis of the vibronic structure, specifically in the case of pseudo-Jahn-Teller (pJT) molecules with C_s symmetry. The spectral analysis of pJT derivatives (isopropoxy and cyclohexoxy of a prototypical JT molecule (the methoxy radical) allowed for quantitative determination of various contributions to the energy separation between the nearly degenerate electronic states, including the relativistic spin-orbit (SO) effect, the electrostatic interaction, and their zero-point energy difference. These states are coupled by SO and Coriolis interactions, which can also be determined accurately in rotational and fine structure analysis. Most recently, the spectroscopic model for rotational analysis of pJT molecules has been extended for analysis of molecules with C_1 symmetry, i.e., no symmetry. This model includes the six independently determinable components of the spin-rotation (SR) tensor and the three components of the SO and Coriolis interactions. It has been employed to simulate and fit high-resolution laser-induced fluorescence (LIF) spectra of jet-cooled alkoxy radicals with C_1 symmetry, including the 2-hexoxy and the 2-pentoxy radicals, as well as previously recorded LIF spectrum of the trans-conformer (defined by its OCCC dihedral angle) of the 2-butoxy radical. Although the LIF spectra can be reproduced by using either the SR constants or SO and Coriolis constants, the latter simulation offers results that are physically more meaningful whereas the SR constants have to be regarded as effective constants. Furthermore, we will review the SO and Coriolis constants of alkoxy radicals that have been investigated, starting from the well-studied methoxy radical (CH_3O). J. Liu, D. Melnik, and T. A. Miller, J. Chem. Phys. 139, 094308 (2013) J. Liu and T. A. Miller, J. Phys. Chem. A 118, 11871

  4. Hall effect and fine structures in magnetic reconnection with high plasma {beta}

    SciTech Connect

    Jin, S.P.; Yang, H.A.; Wang, X.G.

    2005-04-15

    Magnetic reconnection with various plasma {beta} (the ratio of plasma pressure to the magnetic pressure) is studied numerically using a 2.5 dimensional Hall magnetohydrodynamics (MHD) code developed from a multistep implicit scheme. The initial state of the Hall MHD simulation is an equilibrium Harris sheet with L{sub c}=0.5d{sub i} (where L{sub c} is the half-width of the equilibrium current layer and d{sub i} is the ion inertial length) and a zero guide field (i.e., B{sub y0}=0 at t=0). Driven by a constant boundary inflow a quasisteady fast reconnection occurs in the plasma with a low uniform resistivity. The out-of-plane magnetic field component B{sub y} is then spontaneously generated and its quadrupolar structure is shown around the X point. It is demonstrated by the comparing studies that the reconnection dynamics is controlled by the Hall effect and the effect of scalar electron pressure gradient is negligible in the generalized Ohm's law. It is also found that the openness of the magnetic separatrix angle and associated quadrupolar B{sub y} structure is enlarged as {beta} increases. When {beta}>2.0 fine structures of B{sub y} contours with reversed sign emerge. The numerical results indicate that the variations in electron velocity V{sub e} are greater than those in ion velocity V{sub i} and the decoupling of electron and ion occurs in larger scale lengths than d{sub i} as {beta} increases. Clearly, the reserve current, which is associated with the relative motion between electrons and ions, generates the fine structures of B{sub y} contours in the outflow region. Then the corresponding profile of B{sub y} component exhibits a static whistler wave signature. Enhanced wave activities observed during a Cluster crossing of the high-{beta} exterior cusp region [Y. Khotyaintsev, A. Vaivads, Y. Ogawa, B. Popielawska, M. Andre, S. Buchert, P. Decreau, B. Lavraud, and H. Reme, Ann. Geophys. 22, 2403 (2004)] might be related to the Hall effects of magnetic

  5. Speciation and characterization of arsenic in gold ores and cyanidation tailings using X-ray absorption spectroscopy

    USGS Publications Warehouse

    Paktunc, D.; Foster, A.; Heald, S.; Laflamme, G.

    2004-01-01

    The knowledge of mineralogy and molecular structure of As is needed to better understand the stability of As in wastes resulting from processing of gold ores. In this study, optical microscopy, scanning electron microscopy, electron microprobe, X-ray diffraction and X-ray absorption fine structure (XAFS) spectroscopy (including both XANES and EXAFS regimes) were employed to determine the mineralogical composition and local coordination environment of As in gold ores and process tailings from bench-scale tests designed to mimic a common plant practice. Arsenic-bearing minerals identified in the ores and tailings include iron (III) oxyhydroxides, scorodite (FeAsO4??2H2O), ferric arsenates, arseniosiderite (Ca2Fe3 (AsO4)3O2??3H2O), Ca-Fe arsenates, pharmacosiderite (KFe4 (AsO4)3(OH)4??6-7H2O), jarosite (K2Fe6(SO4)4 (OH)12) and arsenopyrite (FeAsS). Iron (III) oxyhydroxides contain variable levels of As from trace to about 22 wt% and Ca up to approximately 9 wt%. Finely ground ore and tailings samples were examined by bulk XAFS and selected mineral grains were analyzed by microfocused XAFS (micro-EXAFS) spectroscopy to reconcile the ambiguities of multiple As sources in the complex bulk EXAFS spectra. XANES spectra indicated that As occurs as As5+in all the samples. Micro-EXAFS spectra of individual iron (III) oxyhydroxide grains with varying As concentrations point to inner-sphere bidentate-binuclear arsenate complexes as the predominant form of As. There are indications for the presence of a second Fe shell corresponding to bidentate-mononuclear arrangement. Iron (III) oxyhydroxides with high As concentrations corresponding to maximum adsorption densities probably occur as nanoparticles. The discovery of Ca atoms around As in iron (III) oxyhydroxides at interatomic distances of 4.14-4.17 A?? and the coordination numbers suggest the formation of arseniosiderite-like nanoclusters by coprecipitation rather than simple adsorption of Ca onto iron (III) oxyhydroxides

  6. A tale of two pectins: Diverse fine structures can result from identical processive PME treatments on similar high DM subtrates

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The effects of a processive pectin-methylesterase treatment on two different pectins, both possessing a high degree of methylesterification, were investigated. While the starting samples were purportedly very similar in fine structure, and even though the sample-averaged degree of methylesterificati...

  7. Properties of the prominence magnetic field and plasma distributions as obtained from 3D whole-prominence fine structure modeling

    NASA Astrophysics Data System (ADS)

    Gunár, S.; Mackay, D. H.

    2016-07-01

    Aims: We analyze distributions of the magnetic field strength and prominence plasma (temperature, pressure, plasma β, and mass) using the 3D whole-prominence fine structure model. Methods: The model combines a 3D magnetic field configuration of an entire prominence, obtained from non-linear force-free field simulations, with a detailed semi-empirically derived description of the prominence plasma. The plasma is located in magnetic dips in hydrostatic equilibrium and is distributed along multiple fine structures within the 3D magnetic model. Results: We show that in the modeled prominence, the variations of the magnetic field strength and its orientation are insignificant on scales comparable to the smallest dimensions of the observed prominence fine structures. We also show the ability of the 3D whole-prominence fine structure model to reveal the distribution of the prominence plasma with respect to its temperature within the prominence volume. This provides new insights into the composition of the prominence-corona transition region. We further demonstrate that the values of the plasma β are small throughout the majority of the modeled prominences when realistic photospheric magnetic flux distributions and prominence plasma parameters are assumed. While this is generally true, we also find that in the region with the deepest magnetic dips, the plasma β may increase towards unity. Finally, we show that the mass of the modeled prominence plasma is in good agreement with the mass of observed non-eruptive prominences.

  8. Variation in beta-glucan fine structure, extractability, and flour slurry viscosity in oats due to genotype and environment

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Effects of genotype and environment on oats on beta-glucan extractability,flour slurry viscosity, and beta-glucan polymer fine structure were tested. Certain environments had unpredictable catastrophic effects on slurry viscosity. Learning the cause of such viscosity loss should be of high priority ...

  9. Characteristics of the starch fine structure and pasting properties of waxy rice during storage.

    PubMed

    Huang, Yu-Chan; Lai, Hsi-Mei

    2014-01-01

    Two waxy rice (TNW1 and TCSW1, exhibiting high and low amylase activity, respectively), were stored at 4 and 17 °C (polished rice) and at room temperature (paddy rice) for 15 months. The fine structure of starch isolated from the aged rice and the pasting properties of starch and rice flour were studied. After storage, the percentage of short amylopectin (AP) chains increased in TNW1, and no uniform changing pattern was observed in the chain-length (CL) distribution of TCSW1. The viscosity of starch isolated from the aged rice increased as the storage temperature and duration increased. We hypothesised that this increase was due to the hydrolysis of AP by endogenous amylase and the generation of small clusters during storage, which caused the simple dissociation of AP and a high swelling degree of starch granules during gelatinisation. Factor analysis of the first two factors associated with the characteristics of viscograms and the CL of AP explained 72% of the total variation.

  10. Fine structure of the landers fault zone: Segmentation and the rupture process

    USGS Publications Warehouse

    Li, Y.-G.; Vidale, J.E.; Aki, K.; Marone, C.J.; Lee, W.H.K.

    1994-01-01

    Observations and modeling of 3- to 6-hertz seismic shear waves trapped within the fault zone of the 1992 Landers earthquake series allow the fine structure and continuity of the zone to be evaluated. The fault, to a depth of at least 12 kilometers, is marked by a zone 100 to 200 meters wide where shear velocity is reduced by 30 to 50 percent. This zone forms a seismic waveguide that extends along the southern 30 kilometers of the Landers rupture surface and ends at the fault bend about 18 kilometers north of the main shock epicenter. Another fault plane waveguide, disconnected from the first, exists along the northern rupture surface. These observations, in conjunction with surface slip, detailed seismicity patterns, and the progression of rupture along the fault, suggest that several simple rupture planes were involved in the Landers earthquake and that the inferred rupture front hesitated or slowed at the location where the rupture jumped from one to the next plane. Reduction in rupture velocity can tentatively be attributed to fault plane complexity, and variations in moment release can be attributed to variations in available energy.

  11. Fine structure of the entanglement entropy in the O(2) model

    NASA Astrophysics Data System (ADS)

    Yang, Li-Ping; Liu, Yuzhi; Zou, Haiyuan; Xie, Z. Y.; Meurice, Y.

    2016-01-01

    We compare two calculations of the particle density in the superfluid phase of the O(2) model with a chemical potential μ in 1+1 dimensions. The first relies on exact blocking formulas from the Tensor Renormalization Group (TRG) formulation of the transfer matrix. The second is a worm algorithm. We show that the particle number distributions obtained with the two methods agree well. We use the TRG method to calculate the thermal entropy and the entanglement entropy. We describe the particle density, the two entropies and the topology of the world lines as we increase μ to go across the superfluid phase between the first two Mott insulating phases. For a sufficiently large temporal size, this process reveals an interesting fine structure: the average particle number and the winding number of most of the world lines in the Euclidean time direction increase by one unit at a time. At each step, the thermal entropy develops a peak and the entanglement entropy increases until we reach half-filling and then decreases in a way that approximately mirrors the ascent. This suggests an approximate fermionic picture.

  12. Sensitivity to temporal fine structure and hearing-aid outcomes in older adults

    PubMed Central

    Perez, Elvira; McCormack, Abby; Edmonds, Barrie A.

    2014-01-01

    Objective: To investigate the effect of sensitivity to temporal fine structure (TFS) on subjective measures of hearing aid outcome. Design: Prior to receiving hearing aids, participants completed a test to assess sensitivity to TFS and two self-assessment questionnaires; the Glasgow Hearing Aid Benefit Profile (GHABP), and the Speech, Spatial and Qualities of hearing (SSQ-A). Follow-up appointments, comprised three self-assessment questionnaires; the GHABP, the SSQ-B, and the International Outcome Inventory for Hearing Aid Outcomes (IOI-HA). Study sample: 75 adults were recruited from direct referral clinics. Results: Two thirds of participants were found to have good sensitivity to TFS; listeners with good sensitivity to TFS rated their hearing abilities higher at pre-fitting (SSQ-A) than those with poor sensitivity to TFS. At follow-up, participants with good sensitivity to TFS showed a smaller improvement on SSQ-B over listeners with poor sensitivity to TFS. Among the questionnaires, only the SSQ showed greater sensitivity to measure subjective differences between listeners with good and poor sensitivity to TFS. Conclusions: The clinical identification of a patient's ability to process TFS information at an early stage in the treatment pathway could prove useful in managing expectations about hearing aid outcomes. PMID:24550769

  13. THE FINE STRUCTURE OF SYMPATHETIC NEURONS IN X-IRRADIATED FROGS

    PubMed Central

    Pick, Joseph

    1965-01-01

    The effects of whole body x-irradiation on the fine structure of sympathetic neurons were studied in 15 unanesthetized adult frogs (Rana pipiens), as seen at intervals ranging from 1 hour to 2 weeks after single exposures to 1000 r and 2000 r. Using standard procedures, the lumbar sympathetic ganglia of experimental and 20 control animals were prepared for electron microscope examination. Radiation produced conspicuous but irregular and variable deterioration, swelling, and clearing of neuronal lysosomes. These changes may have been due to an increased permeability of lysosomal membranes, causing the entry of fluid into lysosomes and their swelling and deterioration, but a pronounced escape of lysosomal enzymes into the cytoplasm was questionable. Less frequent were the dilatation and the parallel layering or complete fusion and tight packing of the rough-edged endoplasmic reticulum. The number of vacuoles, probably derived from Golgi cisternae, was somewhat increased. These vacuoles were conjectured to serve the "sequestration" of damaged cytoplasmic areas. Abnormal amounts of presumptive glycogen granules occupied some axons of myelinated and unmyelinated fibers, especially of presynaptic nerve fibers. This was assumed to be due to a decreased breakdown of glycogen and probably caused the interruption of the transmission of nerve impulses in presynaptic fibers. The maximal incidence of these alterations seemingly occurred 8 days after exposure to 1000 r, and 1 hour after x-irradiation with 2000 r. Signs of recovery appeared 2 weeks after exposure to 2000 r. PMID:5865928

  14. Dual-carrier processing to convey temporal fine structure cues: Implications for cochlear implants

    PubMed Central

    Apoux, Frédéric; Youngdahl, Carla L.; Yoho, Sarah E.; Healy, Eric W.

    2015-01-01

    Speech intelligibility in noise can be degraded by using vocoder processing to alter the temporal fine structure (TFS). Here it is argued that this degradation is not attributable to the loss of speech information potentially present in the TFS. Instead it is proposed that the degradation results from the loss of sound-source segregation information when two or more carriers (i.e., TFS) are substituted with only one as a consequence of vocoder processing. To demonstrate this segregation role, vocoder processing involving two carriers, one for the target and one for the background, was implemented. Because this approach does not preserve the speech TFS, it may be assumed that any improvement in intelligibility can only be a consequence of the preserved carrier duality and associated segregation cues. Three experiments were conducted using this “dual-carrier” approach. All experiments showed substantial sentence intelligibility in noise improvements compared to traditional single-carrier conditions. In several conditions, the improvement was so substantial that intelligibility approximated that for unprocessed speech in noise. A foreseeable and potentially promising implication for the dual-carrier approach involves implementation into cochlear implant speech processors, where it may provide the TFS cues necessary to segregate speech from noise. PMID:26428784

  15. Characterization of a bioactive polysaccharide from Ganoderma atrum: Re-elucidation of the fine structure.

    PubMed

    Zhang, Hui; Nie, Shaoping; Cui, Steve W; Xu, Ming; Ding, Huihuang; Xie, Mingyong

    2017-02-20

    The fine structure in terms of backbone and branch chain features of a bioactive polysaccharide from Ganoderma atrum (PSG-1) was re-elucidated systematically using high performance anion-exchange chromatography (HPAEC), methylation and GLC-MS analysis, and 1D & 2D NMR spectroscopy. Monosaccharide composition analysis revealed that PSG-1-F0.2 fraction mainly consisted of glucose (73.8%) and glucuronic acid (15.3%), with small amount of mannose (5.7%) and galactose (5.2%). Based on methylation, multistep partial acid hydrolysis and NMR study, were proposed to substitute at the O-6 position of β-(1→3)-glucan. The small amount of mannose and galactose residues were considered to be from the other fraction in PSG which was very difficult to be separated from PSG-1-F0.2. This revised structure as an acidic β-(1→3, 1→6)-glucan is considered to be more accurate than the previous proposal of PSG-1.

  16. Electronic fine structure in the nickel carbide superconductor Th2NiC2

    NASA Astrophysics Data System (ADS)

    Quan, Y.; Pickett, W. E.

    2013-07-01

    The recently reported nickel carbide superconductor body centered tetragonal I4/mmm Th2NiC2 with Tc=8.5 K increasing to 11.2 K upon alloying Th with Sc is found to have very fine structure in its electronic spectrum, according to density functional based first-principles calculations. The filled Ni 3d band complex is hybridized with C 2p and Th character to and through the Fermi level (EF), and a sharply structured density of states arises only when spin-orbit coupling is included, which splits a zone-center degeneracy, leaving a very flat band edge lying at the Fermi level. The flat part of the band corresponds to an effective mass mz*→∞ with large and negative mx*=my*. Although the region over which the effective mass characterization applies is less than 1% of the zone volume, it supplies on the order of half the states at (or just above) the Fermi level. The observed increase of Tc by hole doping is accounted for if the reference as-synthesized sample is minutely hole doped, which decreases the Fermi level density of states and will provide some stabilization. In this scenario, electron doping will increase the Fermi level density of states and the superconducting critical temperature. Vibrational properties are presented, and enough coupling to the C-Ni-C stretch mode at 70 meV is obtained to imply that superconductivity is electron-phonon mediated.

  17. Helical Motions of Fine-structure Prominence Threads Observed by Hinode and IRIS

    NASA Astrophysics Data System (ADS)

    Okamoto, Takenori J.; Liu, Wei; Tsuneta, Saku

    2016-11-01

    Fine-structure dynamics in solar prominences holds critical clues to understanding their physical nature of significant space-weather implications. We report evidence of rotational motions of horizontal helical threads in two active-region prominences observed by the Hinode and/or Interface Region Imaging Spectrograph satellites at high resolution. In the first event, we found transverse motions of brightening threads at speeds up to 55 km s-1 seen in the plane of the sky. Such motions appeared as sinusoidal space-time trajectories with a typical period of ˜390 s, which is consistent with plane-of-sky projections of rotational motions. Phase delays at different locations suggest the propagation of twists along the threads at phase speeds of 90-270 km s-1. At least 15 episodes of such motions occurred in two days, none associated with an eruption. For these episodes, the plane-of-sky speed is linearly correlated with the vertical travel distance, suggestive of a constant angular speed. In the second event, we found Doppler velocities of 30-40 km s-1 in opposite directions in the top and bottom portions of the prominence, comparable to the plane-of-sky speed. The moving threads have about twice broader line widths than stationary threads. These observations, when taken together, provide strong evidence for rotations of helical prominence threads, which were likely driven by unwinding twists triggered by magnetic reconnection between twisted prominence magnetic fields and ambient coronal fields.

  18. Atomic transition energies and the variation of the fine-structure constant {alpha}

    SciTech Connect

    Borschevsky, Anastasia; Eliav, Ephraim; Ishikawa, Yasuyuki; Kaldor, Uzi

    2006-12-15

    Relativistic energy shifts of atomic excitation energies, showing the dependence of these energies on the value of the fine-structure constant {alpha}, are needed to extract past changes in {alpha} from spectra of distant quasars. These shifts are calculated by the Fock-space coupled cluster method and its extrapolated intermediate Hamiltonian extension, which allow high-accuracy treatment of electron correlation. The accuracy of the method is tested by comparing 33 transition energies in heavy atoms (obtained with the laboratory {alpha}) with experiment; the average error is 258 cm{sup -1}, and the largest error is 711 cm{sup -1}. This may be compared with an average error of 432 cm{sup -1} and a maximum error of 2150 cm{sup -1} in the work of Dzuba et al., who reported most of the available energy shift calculations. The enhanced accuracy is due to more extensive inclusion of electron correlation. To obtain the energy shifts, we repeated the calculations with different values of {alpha} (within 0.1% of the current value). Our shifts differ by up to 30% from the values given by Dzuba et al., with an average difference of 9%. Based on the better quality of the present-day excitation energies, we believe the energy shifts reported here are more accurate than earlier work.

  19. Angle-resolved photoemission extended fine structure: Multiple layers of emitters and multiple initial states

    SciTech Connect

    Huff, W.R.A.; Kellar, S.A.; Moler, E.J. |; Chen, Y.; Wu, H.; Shirley, D.A.; Hussain, Z.

    1995-08-01

    Recently, angle-resolved photoemission extended fine structure (ARPEFS) has been applied to experimental systems involving multiple layers of emitters and non-s core-level photoemission in an effort to broaden the utility of the technique. Most of the previous systems have been comprised of atomic or molecular overlayers adsorbed onto a single-crystal, metal surface and the photoemission data were taken from an s atomic core-level in the overlayer. For such a system, the acquired ARPEFS data is dominated by the p{sub o} final state wave backscattering from the substrate atoms and is well understood. In this study, we investigate ARPEFS as a surface-region structure determination technique when applied to experimental systems comprised of multiple layers of photoemitters and arbitrary initial state core-level photoemission. Understanding the data acquired from multiple layers of photoemitters is useful for studying multilayer interfaces, ''buried'' surfaces, and clean crystals in ultra- high vacuum. The ability to apply ARPEFS to arbitrary initial state core-level photoemission obviously opens up many systems to analysis. Efforts have been ongoing to understand such data in depth. We present clean Cu(111) 3s, 3p, and 3d core-level, normal photoemission data taken on a high resolution soft x-ray beamline 9.3.2 at the Advanced Light Source in Berkeley, California and clean Ni(111) 3p normal photoemission data taken at the National Synchrotron Light Source in Upton, New York, USA.

  20. The Effects of Instrumental Elliptical Polarization on Stellar Point Spread Function Fine Structure

    NASA Technical Reports Server (NTRS)

    Carson, Joseph C.; Kern, Brian D.; Breckinridge, James B.; Trauger, John T.

    2005-01-01

    We present procedures and preliminary results from a study on the effects of instrumental polarization on the fine structure of the stellar point spread function (PSF). These effects are important to understand because the the aberration caused by instrumental polarization on an otherwise diffraction-limited will likely have have severe consequences for extreme high contrast imaging systems such as NASA's planned Terrestrial Planet Finder (TPF) mission and the proposed NASA Eclipse mission. The report here, describing our efforts to examine these effects, includes two parts: 1) a numerical analysis of the effect of metallic reflection, with some polarization-specific retardation, on a spherical wavefront; 2) an experimental approach for observing this effect, along with some preliminary laboratory results. While the experimental phase of this study requires more fine-tuning to produce meaningful results, the numerical analysis indicates that the inclusion of polarization-specific phase effects (retardation) results in a point spread function (PSF) aberration more severe than the amplitude (reflectivity) effects previously recorded in the literature.

  1. New limits on variation of the fine-structure constant using atomic dysprosium.

    PubMed

    Leefer, N; Weber, C T M; Cingöz, A; Torgerson, J R; Budker, D

    2013-08-09

    We report on the spectroscopy of radio-frequency transitions between nearly degenerate, opposite-parity excited states in atomic dysprosium (Dy). Theoretical calculations predict that these states are very sensitive to variation of the fine-structure constant α owing to large relativistic corrections of opposite sign for the opposite-parity levels. The near degeneracy reduces the relative precision necessary to place constraints on variation of α, competitive with results obtained from the best atomic clocks in the world. Additionally, the existence of several abundant isotopes of Dy allows isotopic comparisons that suppress common-mode systematic errors. The frequencies of the 754-MHz transition in 164Dy and 235-MHz transition in 162Dy are measured over the span of two years. The linear variation of α is α·/α=(-5.8±6.9([1σ]))×10(-17)  yr(-1), consistent with zero. The same data are used to constrain the dimensionless parameter kα characterizing a possible coupling of α to a changing gravitational potential. We find that kα=(-5.5±5.2([1σ]))×10(-7), essentially consistent with zero and the best constraint to date.

  2. Fine structure and immunocytochemistry of a new chemosensory system in the Chiton larva (Mollusca: Polyplacophora).

    PubMed

    Haszprunar, Gerhard; Friedrich, Stefan; Wanninger, Andreas; Ruthensteiner, Bernhard

    2002-02-01

    Combined electron microscopy and immunocytochemistry of the larvae of several polyplacophoran species (Chiton olivaceus, Lepidochitona aff. corrugata, Mopalia muscosa) revealed a sensory system new to science, a so-called "ampullary system." The cells of the "ampullary system" are arranged in four symmetrically situated pairs lying dorsolaterally and ventrolaterally in the pretrochal part of the trochophore-like larva and they send axons into the cerebral commissure. They are lost at metamorphosis. The fine structure of these cells strongly resembles that of so-called "ampullary cells" known from various sensory organs of other molluscs, such as the apical complex of gastropod and bivalve larvae, osphradia of vetigastropods, and olfactory organs of cephalopods, and nuchal organs of certain polychaetes. The ampullary cells and their nerves are densely stained by anti-FMRF-amide fluorescence dyes, whereas antiserotonin staining is only weak. While cytological homology of the ampullary cells with those of other organs is probable, the ampullary system as a whole is regarded as a synapomorphy of the Polyplacophora or Chitonida.

  3. Scattering pulse of label free fine structure cells to determine the size scale of scattering structures.

    PubMed

    Zhang, Lu; Chen, Xingyu; Zhang, Zhenxi; Chen, Wei; Zhao, Hong; Zhao, Xin; Li, Kaixing; Yuan, Li

    2016-04-01

    Scattering pulse is sensitive to the morphology and components of each single label-free cell. The most direct detection result, label free cell's scattering pulse is studied in this paper as a novel trait to recognize large malignant cells from small normal cells. A set of intrinsic scattering pulse calculation method is figured out, which combines both hydraulic focusing theory and small particle's scattering principle. Based on the scattering detection angle ranges of widely used flow cytometry, the scattering pulses formed by cell scattering energy in forward scattering angle 2°-5° and side scattering angle 80°-110° are discussed. Combining the analysis of cell's illuminating light energy, the peak, area, and full width at half maximum (FWHM) of label free cells' scattering pulses for fine structure cells with diameter 1-20 μm are studied to extract the interrelations of scattering pulse's features and cell's morphology. The theoretical and experimental results show that cell's diameter and FWHM of its scattering pulse agree with approximate linear distribution; the peak and area of scattering pulse do not always increase with cell's diameter becoming larger, but when cell's diameter is less than about 16 μm the monotone increasing relation of scattering pulse peak or area with cell's diameter can be obtained. This relationship between the features of scattering pulse and cell's size is potentially a useful but very simple criterion to distinguishing malignant and normal cells by their sizes and morphologies in label free cells clinical examinations.

  4. Preferred Compression Speed for Speech and Music and Its Relationship to Sensitivity to Temporal Fine Structure.

    PubMed

    Moore, Brian C J; Sęk, Aleksander

    2016-09-07

    Multichannel amplitude compression is widely used in hearing aids. The preferred compression speed varies across individuals. Moore (2008) suggested that reduced sensitivity to temporal fine structure (TFS) may be associated with preference for slow compression. This idea was tested using a simulated hearing aid. It was also assessed whether preferences for compression speed depend on the type of stimulus: speech or music. Twenty-two hearing-impaired subjects were tested, and the stimulated hearing aid was fitted individually using the CAM2A method. On each trial, a given segment of speech or music was presented twice. One segment was processed with fast compression and the other with slow compression, and the order was balanced across trials. The subject indicated which segment was preferred and by how much. On average, slow compression was preferred over fast compression, more so for music, but there were distinct individual differences, which were highly correlated for speech and music. Sensitivity to TFS was assessed using the difference limen for frequency at 2000 Hz and by two measures of sensitivity to interaural phase at low frequencies. The results for the difference limens for frequency, but not the measures of sensitivity to interaural phase, supported the suggestion that preference for compression speed is affected by sensitivity to TFS.

  5. Influence of dense quantum plasmas on fine-structure splitting of Lyman doublets of hydrogenic systems

    SciTech Connect

    De, Madhab Ray, Debasis

    2015-05-15

    Relativistic calculations are performed to study the effects of oscillatory quantum plasma screening on the fine-structure splitting between the components of Lyman-α and β line doublets of atomic hydrogen and hydrgen-like argon ion within dense quantum plasmas, where the effective two-body (electron–nucleus) interaction is modeled by the Shukla–Eliasson oscillatory exponential cosine screened-Coulomb potential. The numerical solutions of the radial Dirac equation for the quantum plasma-embedded atomic systems reveal that the oscillatory quantum screening effect suppresses the doublet (energy) splitting substantially and the suppression becomes more prominent at large quantum wave number k{sub q}. In the absence of the oscillatory cosine screening term, much larger amount of suppression is noticed at larger values of k{sub q}, and the corresponding results represent the screening effect of an exponential screened-Coulomb two-body interaction. The Z{sup 4} scaling of the Lyman doublet splitting in low-Z hydrogen isoelectronic series of ions in free space is violated in dense quantum plasma environments. The relativistic data for the doublet splitting in the zero screening (k{sub q} = 0) case are in very good agreement with the NIST reference data, with slight discrepancies (∼0.2%) arising from the neglect of the quantum electrodynamic effects.

  6. Preferred Compression Speed for Speech and Music and Its Relationship to Sensitivity to Temporal Fine Structure

    PubMed Central

    Sęk, Aleksander

    2016-01-01

    Multichannel amplitude compression is widely used in hearing aids. The preferred compression speed varies across individuals. Moore (2008) suggested that reduced sensitivity to temporal fine structure (TFS) may be associated with preference for slow compression. This idea was tested using a simulated hearing aid. It was also assessed whether preferences for compression speed depend on the type of stimulus: speech or music. Twenty-two hearing-impaired subjects were tested, and the stimulated hearing aid was fitted individually using the CAM2A method. On each trial, a given segment of speech or music was presented twice. One segment was processed with fast compression and the other with slow compression, and the order was balanced across trials. The subject indicated which segment was preferred and by how much. On average, slow compression was preferred over fast compression, more so for music, but there were distinct individual differences, which were highly correlated for speech and music. Sensitivity to TFS was assessed using the difference limen for frequency at 2000 Hz and by two measures of sensitivity to interaural phase at low frequencies. The results for the difference limens for frequency, but not the measures of sensitivity to interaural phase, supported the suggestion that preference for compression speed is affected by sensitivity to TFS. PMID:27604778

  7. Fine structure of extracellular fibers in primo-nodes and vessels.

    PubMed

    Jung, Jong Hyun; Sung, Baeckkyoung; Soh, Kwang-Sup

    2011-01-01

    To investigate the extracellular matrices in the primo-nodes (PNs) and vessels (PVs) (Bonghan corpuscles and ducts), fine structure of the fibers comprising the extracellular matrices was studied in relation to the diameter and the periodicity to identify the types of the fibers. Electron micrographs of the fibers from the previously published works on the PNs and PVs were analyzed by using MATLAB programming and ImageJ software. The extracellular fibrous components of the PNs and PVs could be classified generally into two groups--thin collagen fibrils and thick non-collagenous wavy bent fibers. The thick bent fibers were fibrin-like. The diameters of the thick bent fibers were 30-200 nm and they were highly bent. This group included organ surface PNs and lymphatic PNs/PVs. The diameters of the collagen fibrils were 30-70 nm. Organ surface, heart, and hypodermis PVs were categorized in this group. The periodicity of bent fibers in an organ surface PN was 16.1 +/- 0.2 (SE) nm, and the periodicity of collagen fibrils in the hypodermis PVs was 37.4 +/- 0.5 (SE) nm. Further investigations are required to reveal the physiological implications of the two types of fibers in the PNs and PVs.

  8. FINE STRUCTURAL ALTERATIONS OF INTERPHASE NUCLEI OF LYMPHOCYTES STIMULATED TO GROWTH ACTIVITY IN VITRO

    PubMed Central

    Tokuyasu, K.; Madden, S. C.; Zeldis, L. J.

    1968-01-01

    This report describes fine structural changes of interphase nuclei of human peripheral blood lymphocytes stimulated to growth by short-term culture with phytohemagglutinin. Chromatin is found highly labile, its changes accompanying the sequential increases of RNA and DNA synthesis which are known to occur in lymphocyte cultures. In "resting" lymphocytes, abundant condensed chromatin appears as a network of large and small aggregates. Early in the response to phytohemagglutinin, small aggregates disappear during increase of diffuse chromatin regions. Small aggregates soon reappear, probably resulting from disaggregation of large masses of condensed chromatin. Loosened and highly dispersed forms then appear prior to the formation of prophase chromosomes. The loosened state is found by radioautography to be most active in DNA synthesis. Small nucleoli of resting lymphocytes have concentric agranular, fibrillar, and granular zones with small amounts of intranucleolar chromatin. Enlarging interphase nucleoli change chiefly (1) by increase in amount of intranucleolar chromatin and alteration of its state of aggregation and (2) by increase in granular components in close association with fibrillar components. PMID:5699935

  9. The fine structure of Langmuir waves observed upstream of the bow shock at Venus

    NASA Technical Reports Server (NTRS)

    Hospodarsky, G. B.; Gurnett, D. A.; Kurth, W. S.; Kivelson, M. G.; Strangeway, R. J.; Bolton, S. J.

    1994-01-01

    Highly structured Langmuir waves, also known as electron plasma oscillations, have been observed in the foreshock of Venus using the plasma wave experiment on the Galileo spacecraft during the gravity assist flyby on February 10, 1990. The Galileo wideband sampling system provides digital electric field waveform measurements at sampling rates up to 201,600 samples per second, much higher than any previous instrument of this type. The main Langmuir wave emission band occurs near the local electron plasma frequency, which was approximately 43 kHz. The Langmuir waves are observed to shift above and below the plasma frequency, sometimes by as much as 20 kHz. The shifts in frequency are closely correlated with the downstream distance from the tangent field line, implying that the shifts are controlled by the electron beam velocity. Considerable fine structure is also evident, with time scales as short as 0.15 milliseconds, corresponding to spatial scales of a few tens of Debye lengths. The frequency spectrum often consists of beat-type waveforms, with beat frequencies ranging from 0.2 to 7 kHz, and in a few cases, isolated wavepackets. The peak electric field strengths are approximately 1 mV/m. These field strengths are too small for strongly nonlinear processes to be important. The beat-type waveforms are suggestive of a parametric decay process.

  10. Properties and Modeling of Unresolved Fine Structure Loops Observed in the Solar Transition Region by IRIS

    NASA Astrophysics Data System (ADS)

    Brooks, David H.; Reep, Jeffrey W.; Warren, Harry P.

    2016-08-01

    Recent observations from the Interface Region Imaging Spectrograph (IRIS) have discovered a new class of numerous low-lying dynamic loop structures, and it has been argued that they are the long-postulated unresolved fine structures (UFSs) that dominate the emission of the solar transition region. In this letter, we combine IRIS measurements of the properties of a sample of 108 UFSs (intensities, lengths, widths, lifetimes) with one-dimensional non-equilibrium ionization simulations, using the HYDRAD hydrodynamic model to examine whether the UFSs are now truly spatially resolved in the sense of being individual structures rather than being composed of multiple magnetic threads. We find that a simulation of an impulsively heated single strand can reproduce most of the observed properties, suggesting that the UFSs may be resolved, and the distribution of UFS widths implies that they are structured on a spatial scale of 133 km on average. Spatial scales of a few hundred kilometers appear to be typical for a range of chromospheric and coronal structures, and we conjecture that this could be an important clue for understanding the coronal heating process.

  11. Sensitivity of bilateral cochlear implant users to fine-structure and envelope interaural time differences.

    PubMed

    Noel, Victor A; Eddington, Donald K

    2013-04-01

    Bilateral cochlear implant users have poor sensitivity to interaural time differences (ITDs) of high-rate pulse trains, which precludes use of these stimuli to convey fine-structure ITD cues. However, previous reports of single-neuron recordings in cats demonstrated good ITD sensitivity to 1000 pulses-per-second (pps) pulses when the pulses were sinusoidally amplitude modulated. The ability of modulation to restore ITD sensitivity to high-rate pulses in humans was tested by measuring ITD thresholds for three conditions: ITD encoded in the modulated carrier pulses alone, in the envelope alone, and in the whole waveform. Five of six subjects were not sensitive to ITD in the 1000-pps carrier, even with modulation. One subject's 1000-pps carrier ITD sensitivity did significantly improve due to modulation. Sensitivity to ITD encoded in the envelope was also measured as a function of modulation frequency, including at frequencies from 4 to 16 Hz where much of the speech envelope's energy and information resides. Sensitivity was best at the modulation frequency of 100 Hz and degraded rapidly outside of a narrow range. These results provide little evidence to support encoding ITD in the carrier of current bilateral processors, and suggest envelope ITD sensitivity is poor for an important segment of the speech modulation spectrum.

  12. Fine structure analysis and sintering properties of Si-doped hydroxyapatite.

    PubMed

    Qiu, Z Y; Li, G; Zhang, Y Q; Liu, J; Hu, W; Ma, J; Zhang, S M

    2012-08-01

    Si-doped hydroxyapatite (Si-HA) has been intensively investigated as a promising bone biomaterial because of the biomineralization and bone formation benefit from silicon addition. In the current work, Si-HA samples were synthesized by the aqueous precipitation method. The sintering property of Si-HA was studied in terms of phase composition and transition, which was influenced by the Si doping percentage and sintering temperature. The results indicate that all the as-prepared and sintered low Si doping samples (Si% ≤ 1.6 wt%) possess HA phases; while the high Si doping samples (Si% ≥ 2 wt%) present amorphous phases as prepared, and largely or even completely transform to β-tricalcium phosphate (β-TCP) phase after sintering at 1250 °C. The Rietveld refinement on x-ray diffraction patterns was conducted to determine the particle sizes, microstrain factors and anisotropic distributions. According to the refined results, the calculated anisotropic particle sizes correspond to the observations made by transmission electron microscopy. The microstrains also present anisotropic distributions in all refinements. The accurate variation in the fine structure of Si-HA has been studied by the improved refinements after considering the anisotropic distribution.

  13. Retinal pigment epithelial fine structure in the great blue heron (Ardea herodias).

    PubMed

    Braekevelt, C R; Young, D L

    1994-09-01

    The fine structure of the retinal epithelium (RPE), choriocapillaris and Bruch's membrane (complexus basalis) has been studied by light and electron microscopy in the great blue heron (Ardea herodias). In this species the RPE consists of a single layer of cuboidal cells which display numerous basal (scleral) infoldings and plentiful apical (vitreal) processes which surround photoreceptor outer segments. These epithelial cells are joined laterally by a series of tight junctions located in the mid to basal region. Within the epithelial cells, smooth endoplasmic reticulum is very abundant while rough ER is not. Mitochondria (some of which are ring-shaped) and polysomes are abundant. In light-adaptation the RPE nuclei are large vesicular and basally located while the melanosomes of these cells are almost exclusively located within the apical processes. Myeloid bodies are large and numerous and often show ribosomes on their outer surface. Bruch's membrane (complexus basalis) shows the typical pentalaminate structure noted in the majority of vertebrates except teleosts. The choriocapillary endothelium is very thin facing Bruch's membrane but is only moderately fenestrated. The majority of these fenestrations show a single-layered diaphragm but double-layered diaphragms are also noted.

  14. Supratentorial intracerebral epithelial (ependymal) cysts: review, case reports, and fine structure.

    PubMed Central

    Friede, R L; Yasargil, M G

    1977-01-01

    The paper concerns the rare supratentorial, intracerebral or convexity cysts in adults having a wall lined with an epithelium resembling ependyma. The clincopathological aspects of such cysts are reviewed from 15 published cases and two specimens of the authors which could be examined with the electronmicroscope. These cysts manifest at a median age of 46 years as progressive, space occupying lesions with a fairly rapid clinical course of about one to two years. Twelve of 17 cysts were located in the frontal lobes, most were unequivocally intracerebral and none communicated with the lateral ventricle. Microscopic examination of the cyst wall disclosed some variance in structure, the most common feature being a monolayer of ciliated cells sitting on a very thin collagen membrane. One of the present cases was unique in that the compression by the cyst had caused a shell of infarction in the encompassing tissue. The fine structure of the cysts is described and compared with that of potential host tissues from which such cysts may originate. It is concluded that the cysts arise from displaced segments of the wall of the neural tube which correspond to the sites from which the tela chorioidea forms. Images PMID:864476

  15. Elongation pattern and fine structure of the sheaths formed by Thiothrix nivea and Thiothrix fructosivorans.

    PubMed

    Kawasaki, Yuta; Endo, Tomoyuki; Fujiwara, Atsuo; Kondo, Keiko; Katahira, Masato; Nittami, Tadashi; Sato, Michio; Takeda, Minoru

    2017-02-01

    Thiothrix strains are filamentous sulfur-oxidizing bacteria common in activated sludge. Some of the members, including Thiothrix nivea and T. fructosivorans, are known to form a microtubular sheath that covers a line of cells. The sheaths are assemblages of [→4)-β-d-GlcN-(1→4)-β-d-Glc-(1→]n modified with unusual deoxy sugars. In an attempt to elucidate the sheath-forming mechanism, the patterns of sheath formation and cell proliferation were determined in this study. Prior to analysis, both sheaths were confirmed to be highly de-N-acetylated. Sheaths in viable filaments were N-biotinylated followed by cultivation and then fluorescently immunostained. Epifluorescence microscopy of the filaments revealed ubiquitous elongation of the sheaths. For visualization of the cell proliferation pattern, the cell membrane was fluorescently stained. The epifluorescence images demonstrated that cell proliferation also proceeds ubiquitously, suggesting that sheath elongation proceeds surrounding an elongating cell. In addition, the fine structure of the Thiothrix filaments was analyzed by transmission electron microscopy employing a freeze-substitution technique. The micrographs of freeze-substituted filaments showed that the sheaths were thin and single layered. In contrast, the sheaths in chemically fixed filaments appeared thick and multilayered. Treatment with glutaraldehyde probably caused deformation of the sheaths. Supporting this possibility, the sheaths were found to be deformed or solubilized by N-acetylation.

  16. On the quantitative method for measurement and analysis of the fine structure of Fraunhofer line profiles

    NASA Astrophysics Data System (ADS)

    Kuli-Zade, D. M.

    The methods of measurement and analysis of the fine structure of weak and moderate Fraunhofer line profiles are considered. The digital spectral materials were obtained using rapid scanning high dispersion and high resolution double monochromators. The methods of asymmetry coefficient, bisector method and new quantitative method pro- posed by the author are discussed. The new physical values of differential, integral, residual and relative asymmetries are first introduced. These quantitative values permit us to investigate the dependence of asymmetry on microscopic (atomic) and macro- scopic (photospheric) values. It is shown that the integral profile asymmetries grow appreciably with increase in line equivalent width. The average effective depths of the formation of used Fraunhofer lines in the photosphere of the Sun are determined. It is shown that with the increasing of the effective formation depths of the lines integral and residual asymmetries of the lines profiles noticeably decrease. It is in fine agree- ment with the results of intensity dependence of asymmetry. The above-mentioned methods are critically compared and the advantages of author's method are shown. The computer program of calculation of the line-profile asymmetry parameters has been worked out.

  17. Fine-Structure Branching in N 2 C 4 1 Sigma + U (0)

    NASA Astrophysics Data System (ADS)

    Shemansky, D. E.; Kanik, I.; Ajello, J. M.

    1995-10-01

    We report a quantitative measurement of the predissociation fraction in the N2c'41Σ+u-X1Σ+g (0, 0) band, with an experimental determination of rotational line strengths. The fine structure of the N2(c'4-X) (0, 0) band has been analyzed in optically thin laboratory emission spectra obtained from crossed electron and N2 beams. The distortion of the emission envelope from calculations based on constant rotational level radiative transition probabilities and a thermalized ground state source population has been used to obtain an estimated predissociation loss fraction of 0.15 + -0.045+0.01 for the N2 c'4 (0) level averaged over rotational structure at a neutral gas temperature of 300 K. The analysis has been aided by measurements at gas temperatures depressed over a range from 300 to 30 K. The predissociation rate is temperature dependent, caused by nonuniform predissociation at intermediate and high rotational levels. The coupling of the rotational branches, also measured quantitatively for N2 c'4 (0) for the first time in this experiment, is complicated by configuration mixing with the c3 1Πu and b1Πu states forcing strong departures from Hönl-London factors.

  18. Influence of dense quantum plasmas on fine-structure splitting of Lyman doublets of hydrogenic systems

    NASA Astrophysics Data System (ADS)

    De, Madhab; Ray, Debasis

    2015-05-01

    Relativistic calculations are performed to study the effects of oscillatory quantum plasma screening on the fine-structure splitting between the components of Lyman-α and β line doublets of atomic hydrogen and hydrgen-like argon ion within dense quantum plasmas, where the effective two-body (electron-nucleus) interaction is modeled by the Shukla-Eliasson oscillatory exponential cosine screened-Coulomb potential. The numerical solutions of the radial Dirac equation for the quantum plasma-embedded atomic systems reveal that the oscillatory quantum screening effect suppresses the doublet (energy) splitting substantially and the suppression becomes more prominent at large quantum wave number kq. In the absence of the oscillatory cosine screening term, much larger amount of suppression is noticed at larger values of kq, and the corresponding results represent the screening effect of an exponential screened-Coulomb two-body interaction. The Z4 scaling of the Lyman doublet splitting in low-Z hydrogen isoelectronic series of ions in free space is violated in dense quantum plasma environments. The relativistic data for the doublet splitting in the zero screening (kq = 0) case are in very good agreement with the NIST reference data, with slight discrepancies (˜0.2%) arising from the neglect of the quantum electrodynamic effects.

  19. Fine structure and synaptology of the nitrergic neurons in medial septum of the rat brain.

    PubMed

    Halasy, Katalin; Szőke, Balázs; Janzsó, Gergely

    2017-03-01

    The nitrergic neuron population and certain aspects of their connectivity (peptidergic inputs, co-localization with GABA, synaptic target distribution) were studied in the medial septum of the rat brain. The histochemical localization of NADPH diaphorase and immunohistochemical identification of nNOS at light and electron microscopic level was applied. Double-labeling experiments with galanin and leucine enkephalin, moreover the postembedding GABA immunogold staining was also carried out. NADPH diaphorase- and nNOS-immunopositive neurons could be identified inside the borders of medial septum. Out of their peptidergic inputs galanin- and leucine enkephaline-immunopositive varicose fibers were found in close apposition with nNOS-immunopositive neurons. Based on fine structural characteristics (large indented nucleus, thin cytoplasmic rim, lack of axosomatic synapses) the nitrergic neurons are suggested to be identical with the septal cholinergic nerve cells. Their boutons established asymmetrical synapses mainly on dendritic shafts and spines, some of which were also nNOS-immunopositive. A lower amount of nNOS-immunopositive boutons of presumably extrinsic origin were found to be GABAergic.

  20. The fine structure of electron irradiation induced EL2-like defects in n-GaAs

    NASA Astrophysics Data System (ADS)

    Tunhuma, S. M.; Auret, F. D.; Legodi, M. J.; Diale, M.

    2016-04-01

    Defects induced by electron irradiation in n-GaAs have been studied using deep level transient spectroscopy (DLTS) and Laplace DLTS (L-DLTS). The E0.83 (EL2) is the only defect observed prior to irradiation. Ru/n-GaAs Schottky diodes were irradiated with high energy electrons from a Sr-90 radionuclide up to a fluence of 2.45 × 1013 cm-2. The prominent electron irradiation induced defects, E0.04, E0.14, E0.38, and E0.63, were observed together with the metastable E0.17. Using L-DLTS, we observed the fine structure of a broad base EL2-like defect peak. This was found to be made up of the E0.75, E0.83, and E0.85 defects. Our study reveals that high energy electron irradiation increases the concentration of the E0.83 defect and introduces a family of defects with electronic properties similar to those of the EL2.