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Sample records for absorption edge energy

  1. An energy and intensity monitor for X-ray absorption near-edge structure measurements

    NASA Astrophysics Data System (ADS)

    de Jonge, Martin D.; Paterson, David; McNulty, Ian; Rau, Christoph; Brandes, Jay A.; Ingall, Ellery

    2010-07-01

    An in-line X-ray beam energy and intensity monitor has been developed for use in focussed X-ray absorption near-edge spectroscopy (XANES) measurements. The monitor uses only the X-ray intensity that would otherwise bypass our zone-plate focussing optic and relies on a measurement of photoemission current. The monitor is inexpensive, easy to align, and provides valuable feedback about the X-ray energy. Operation of the monitor is demonstrated for measurements of phosphorus XANES. The precision of the energy determination is around 0.5 eV.

  2. Failure of Energy Transfer between Identical Aromatic Molecules on Excitation at the Long Wave Edge of the Absorption Spectrum

    PubMed Central

    Weber, Gregorio; Shinitzky, Meir

    1970-01-01

    Electronic energy transfer among identical molecules has been followed by the depolarization of the fluorescence in concentrated solutions as well as in dimers, polymers, and micelle systems. In the many aromatic fluorophores examined, unlike a few nonaromatic ones, transfer is much decreased or altogether undetectable on excitation at the red edge of the absorption spectrum. The phenomenon is not due to the transfer taking place during a small fraction of the total fluorescence lifetime, nor is it explainable by a decrease in overlap of absorption and emission upon edge excitation. PMID:16591825

  3. The electronic absorption edge of petroleum

    SciTech Connect

    Mullins, O.C.; Mitra-Kirtley, S.; Zhu, Yifu

    1992-09-01

    The electronic absorption spectra of more than 20 crude oils and asphaltenes are examined. The spectral location of the electronic absorption edge varies over a wide range, from the near-infrared for heavy oils and asphaltenes to the near-UV for gas condensates. The functional form of the electronic absorption edge for all crude oils (measured) is characteristic of the {open_quotes}Urbach tail,{close_quotes} a phenomenology which describes electronic absorption edges in wide-ranging materials. The crude oils all show similar Urbach widths, which are significantly larger than those generally found for various materials but are similar to those previously reported for asphaltenes. Monotonically increasing absorption at higher photon energy continues for all crude oils until the spectral region is reached where single-ring aromatics dominate absorption. However, the rate of increasing absorption at higher energies moderates, thereby deviating from the Urbach behavior. Fluorescence emission spectra exhibit small red shifts from the excitation wavelength and small fluorescence peak widths in the Urbach regions of different crude oils, but show large red shifts and large peak widths in spectral regions which deviate from the Urbach behavior. This observation implies that the Urbach spectral region is dominated by lowest-energy electronic absorption of corresponding chromophores. Thus, the Urbach tail gives a direct measure of the population distribution of chromophores in crude oils. Implied population distributions are consistent with thermally activated growth of large chromophores from small ones. 12 refs., 8 figs.

  4. Core-hole effects on theoretical electron-energy-loss near-edge structure and near-edge x-ray absorption fine structure of MgO

    NASA Astrophysics Data System (ADS)

    Mizoguchi, Teruyasu; Tanaka, Isao; Yoshiya, Masato; Oba, Fumiyasu; Ogasawara, Kazuyoshi; Adachi, Hirohiko

    2000-01-01

    First-principles molecular orbital calculations using model clusters are made in order to reproduce and interpret experimental electron-energy-loss near-edge structure and near-edge x-ray absorption fine structure of MgO at Mg K, L2,3 and O K edges. Ground-state calculations using a model cluster composed of 125 atoms and by a band-structure method are in good agreement, but they do not reproduce the experimental spectra satisfactory. They are well reproduced only by the cluster calculations for the Slater transition state, where a half-electron is removed from a core orbital and placed into the lowest unoccupied molecular orbital. The core-hole effect is therefore essential for theoretical reproduction of the spectral shapes. A large supercell is required to reproduce the experimental spectra when one uses a band-structure method. The origin of peaks appearing in the experimental spectra is interpreted in terms of orbital interactions using overlap-population diagrams. Some features of the spectra at different edges are pointed out to have common origins. Experimental spectra are aligned accordingly. The transition energies and qualitative features of experimental spectra are found to be reproduced even using a smaller cluster composed of 27 atoms, although some of fine structure is missing.

  5. Absorption-edge calculations of inorganic nonlinear optical crystals

    NASA Astrophysics Data System (ADS)

    Wu, Kechen; Chen, Chuangtian

    1992-03-01

    A theoretical model suitable for calculating absorption edges of inorganic nonlinear optical (NLO) crystals is introduced. This model is proved to be useful to elucidate the relationship between electronic structures of NLO-active groups and macroscopic properties of absorption edges on the UV side of most of the inorganic nonlinear optical crystals. A systematic calculation of absorption edges on the UV side for several important inorganic NLO crystals is carried out by means of DV-SCM-Xα method and all calculated results are in good agreement with experimental data. These inorganic NLO crystals include LiB3O5(LBO), β-BaB2O4(BBO), KB5, KDP, Na2SbF5, Ba2TiSi2O8, iodate and NaNO2. The calculated energy level structures of LiB3O5 and β-BaB2O4 crystals are compared with the measured XPS spectra. The unusual transparent spectra of KB5 and KDP crystals are partly explained from the microstructure point of view. The effect of lone electron pair in iodate and NaNO2 crystals on their absorption edges are discussed. All these results show that Anionic Group Theory of Nonlinear Optical Crystals is useful to evaluate the absorption edges of the inorganic nonlinear optical crystal and is a powerful tool in a Molecular Engineering approach to search for new nonlinear optical materials.

  6. Urbach absorption edge in epitaxial erbium-doped silicon

    SciTech Connect

    Shmagin, V. B. Kudryavtsev, K. E.; Shengurov, D. V.; Krasilnik, Z. F.

    2015-02-07

    We investigate the dependencies of the photocurrent in Si:Er p-n junctions on the energy of the incident photons. The exponential absorption edge (Urbach edge) just below fundamental edge of silicon was observed in the absorption spectra of epitaxial Si:Er layers grown at 400–600 C. It is shown that the introduction of erbium significantly enhances the structural disorder in the silicon crystal which was estimated from the slope of the Urbach edge. We discuss the possible nature of the structural disorder in Si:Er and a new mechanism of erbium excitation, which does not require the presence of deep levels in the band gap of silicon.

  7. Theoretical X-ray production cross sections at incident photon energies across L{sub i} (i=1-3) absorption edges of Br

    SciTech Connect

    Puri, Sanjiv

    2015-08-28

    The X-ray production (XRP) cross sections, σ{sub Lk} (k = l, η, α, β{sub 6}, β{sub 1}, β{sub 3}, β{sub 4}, β{sub 9,10}, γ{sub 1,5}, γ{sub 2,3}) have been evaluated at incident photon energies across the L{sub i}(i=1-3) absorption edge energies of {sub 35}Br using theoretical data sets of different physical parameters, namely, the L{sub i}(i=1-3) sub-shell the X-ray emission rates based on the Dirac-Fock (DF) model, the fluorescence and Coster Kronig yields based on the Dirac-Hartree-Slater (DHS) model, and two sets of the photoionisation cross sections based on the relativistic Hartree-Fock-Slater (RHFS) model and the Dirac-Fock (DF) model, in order to highlight the importance of electron exchange effects at photon energies in vicinity of absorption edge energies.

  8. Collisionless absorption in sharp-edged plasmas

    SciTech Connect

    Gibbon, P. ); Bell, A.R. )

    1992-03-09

    The absorption of subpicosecond, obliquely incident laser light is studied using a 11/2D particle-in-cell code. Density scale lengths from {ital L}/{lambda}=0.01 to 2 and laser irradiances between {ital I}{lambda}{sup 2}=10{sup 14} and 10{sup 18} W cm{sup {minus}2} {mu}m{sup 2} are considered. Vacuum heating'' (F. Brunel, Phys. Rev. Lett. 59, 52 (1987)) dominates over resonance absorption for scale lengths {ital L}/{lambda}{lt}0.1, and is most efficient when {ital v}{sub osc}/{ital c}{congruent}3.1({ital L}/{lambda}){sup 2}. Absorbed energy is carried mainly by a superhot'' electron population with {ital U}{sub hot}{similar to}({ital I}{lambda}{sup 2}){sup 1/3--1/2}.

  9. Temperature dependence of the absorption edge of vitreous silica

    NASA Technical Reports Server (NTRS)

    Bates, C. W., Jr.

    1976-01-01

    During an investigation of the optical properties of high-purity vitreous silica (fused quartz), which is being developed by NASA as a reflective and ablative heat shield, some interesting properties of theoretical and experimental nature have become apparent which otherwise may have remained unnoticed. Of particular interest for the NASA application is the shift of the absorption edge toward longer wavelengths with increasing temperature. The results of studies of this shift and of the spectral dependence of the absorption edge are summarized in the present paper. Plots of the absorption edge and the absorption spectrum of fused quartz vs temperature are given and discussed.

  10. Determination of the K absorption edge energy of Ho in element and its compounds using the bremsstrahlung technique

    NASA Astrophysics Data System (ADS)

    Niranjana, K. M.; Badiger, N. M.

    2013-05-01

    The K shell binding energies of Ho in element and in compounds Ho2O3 and HoF3 have been measured for the first time by adopting a novel method. The method involves a weak beta source, an external bremsstrahlung (EB) converter, element and compound targets and a high-resolution HPGe detector coupled to a 16K multichannel analyser. A spectrum of continuous EB photons, produced by the interaction of beta particles from a 90Sr-90Y radioactive source with an iron foil, is allowed to pass through the element and compound targets of Ho. The spectrum of transmitted EB photons is measured with a high-resolution HPGe detector spectrometer. The transmitted spectrum shows a sudden drop in intensity at K shell binding energy of the target. Such a sudden drop, which is essentially due to the onset of the K shell photoelectric effect, has been used to determine the K shell binding energy of Ho in element. The K shell binding energies of Ho in Ho2O3 and HoF3 compounds have also been determined using the same technique. From these data, the chemical shift in the K shell binding energy has been measured. It is found to be positive for Ho2O3 and negative for HoF3, indicating the dependence of the chemical shift on the crystal structure.

  11. Photonic band-edge-induced enhancement in absorption and emission

    NASA Astrophysics Data System (ADS)

    Ummer, Karikkuzhi Variyath; Vijaya, Ramarao

    2015-01-01

    An enhancement in photonic band-edge-induced absorption and emission from rhodamine-B dye doped polystyrene pseudo gap photonic crystals is studied. The band-edge-induced enhancement in absorption is achieved by selecting the incident angle of the excitation beam so that the absorption spectrum of the emitter overlaps the photonic band edge. The band-edge-induced enhancement in emission, on the other hand, is possible with and without an enhancement in band-edge-induced absorption, depending on the collection angle of emission. Through a simple set of measurements with suitably chosen angles for excitation and emission, we achieve a maximum enhancement of 70% in emission intensity with band-edge-induced effects over and above the intrinsic emission in the case of self-assembled opals. This is a comprehensive effort to interpret tunable lasing in opals as well as to predict the wavelength of lasing arising as a result of band-edge-induced distributed feedback effects.

  12. The yields of free radicals induced by monochromatic soft X-rays with energy of the K-absorption edge of bromine in BrdU/dThd complexes

    SciTech Connect

    Kuwabara, M.; Sawamura, S.; Inanami, O.; Kobayashi, K.

    1995-12-31

    Biological Auger effects have been found not only in Br-substituted plasmid DNA (Menke et al. 1991) but also in cells with Br-DNA when they are exposed to soft X-rays with energies above and below the K-absorption edge of Br. These biological Auger effects were sometimes correlated to enhanced DNA damage such as single- or double-strand breaks in these studies. Free radicals induced in DNA are regarded as precursors of base damage and strand breaks. Therefore, it is of interest to examine whether the Auger effects are also reflected in free-radical formation in Br-substituted DNA when they are exposed to soft X-rays with energy corresponding to the K-absorption edge of Br. In the present study BrdU{center_dot}dThd complexes were employed as Br-substituted DNA models, and the yields of free radicals were measured by ESR after irradiating them in the solid state with soft X-rays having energies above and below the K-absorption edge of Br.

  13. Investigating Actinide Molecular Adducts From Absorption Edge Spectroscopy

    SciTech Connect

    Den Auwer, C.; Conradson, S.D.; Guilbaud, P.; Moisy, P.; Mustre de Leon, J.; Simoni, E.; /SLAC, SSRL

    2006-10-27

    Although Absorption Edge Spectroscopy has been widely applied to the speciation of actinide elements, specifically at the L{sub III} edge, understanding and interpretation of actinide edge spectra are not complete. In that sense, semi-quantitative analysis is scarce. In this paper, different aspects of edge simulation are presented, including semi-quantitative approaches. Comparison is made between various actinyl (U, Np) aquo or hydroxy compounds. An excursion into transition metal osmium chemistry allows us to compare the structurally related osmyl and uranyl hydroxides. The edge shape and characteristic features are discussed within the multiple scattering picture and the role of the first coordination sphere as well as contributions from the water solvent are described.

  14. Search for Lyman Limit Absorption Edge in Quasar Continuum

    NASA Astrophysics Data System (ADS)

    Sun, W.-H.; Malkan, M. A.; Chang, Thomas H. W.

    1993-12-01

    We examine the low resolution UV spectra of the 37 quasars in HST Key Project to search for intrinsic Lyman absorption edge which may be a signature of thermal accretion disks. Only 28 QSOs have proper redshifts to place the region of interest in the G160L window. We fit the L_β with two gaussians to remove the line. We then avoid 20 and 50 Angstroms on the blue and red sides of 912 Angstroms in the rest frame, and take 80 Angstroms bins (rest frame) on both sides but further out for analysis. We compare the single power-law fitting (to the entire range across the edge), with the two power-law fitting to blue and red bands. We also measure the percentage drop of flux over the Lyman limit. There are 7 objects with intrinsically noisy spectra, which were presumably caused by intervening Lyman absorption systems. Applying the two methods on the rest 21 objects, we found {24%} candidates to have possible rest frame Lyman limit absorption edges. Same analyses have also been performed on optical spectra of medium- to high-redshift QSOs from Lick Observatory and Hale Observatory. Similar results were also found.

  15. Soft X-ray Absorption Edges in LMXBs

    NASA Technical Reports Server (NTRS)

    2004-01-01

    The XMM observation of LMC X-2 is part of our program to study X-ray absorption in the interstellar medium (ISM). This program includes a variety of bright X-ray binaries in the Galaxy as well as the Magellanic Clouds (LMC and SMC). LMC X-2 is located near the heart of the LMC. Its very soft X-ray spectrum is used to determine abundance and ionization fractions of neutral and lowly ionized oxygen of the ISM in the LMC. The RGS spectrum so far allowed us to determine the O-edge value to be for atomic O, the EW of O-I in the ls-2p resonance absorption line, and the same for O-II. The current study is still ongoing in conjunction with other low absorption sources like Sco X-1 and the recently observed X-ray binary 4U 1957+11.

  16. Nitrogen K-edge x-ray absorption near edge structure of pyrimidine-containing nucleotides in aqueous solution

    SciTech Connect

    Shimada, Hiroyuki Minami, Hirotake; Okuizumi, Naoto; Sakuma, Ichiro; Ukai, Masatoshi; Fujii, Kentaro; Yokoya, Akinari; Fukuda, Yoshihiro; Saitoh, Yuji

    2015-05-07

    X-ray absorption near edge structure (XANES) was measured at energies around the N K-edge of the pyrimidine-containing nucleotides, cytidine 5′-monophosphate (CMP), 2′-deoxythymidine 5′-monophosphate (dTMP), and uridine 5′-monophosphate (UMP), in aqueous solutions and in dried films under various pH conditions. The features of resonant excitations below the N K-edge in the XANES spectra for CMP, dTMP, and UMP changed depending on the pH of the solutions. The spectral change thus observed is systematically explained by the chemical shift of the core-levels of N atoms in the nucleobase moieties caused by structural changes due to protonation or deprotonation at different proton concentrations. This interpretation is supported by the results of theoretical calculations using density functional theory for the corresponding nucleobases in the neutral and protonated or deprotonated forms.

  17. Nitrogen K-edge x-ray absorption near edge structure of pyrimidine-containing nucleotides in aqueous solution

    NASA Astrophysics Data System (ADS)

    Shimada, Hiroyuki; Minami, Hirotake; Okuizumi, Naoto; Sakuma, Ichiro; Ukai, Masatoshi; Fujii, Kentaro; Yokoya, Akinari; Fukuda, Yoshihiro; Saitoh, Yuji

    2015-05-01

    X-ray absorption near edge structure (XANES) was measured at energies around the N K-edge of the pyrimidine-containing nucleotides, cytidine 5'-monophosphate (CMP), 2'-deoxythymidine 5'-monophosphate (dTMP), and uridine 5'-monophosphate (UMP), in aqueous solutions and in dried films under various pH conditions. The features of resonant excitations below the N K-edge in the XANES spectra for CMP, dTMP, and UMP changed depending on the pH of the solutions. The spectral change thus observed is systematically explained by the chemical shift of the core-levels of N atoms in the nucleobase moieties caused by structural changes due to protonation or deprotonation at different proton concentrations. This interpretation is supported by the results of theoretical calculations using density functional theory for the corresponding nucleobases in the neutral and protonated or deprotonated forms.

  18. Room-Temperature Absorption Edge of InGaN/GaN Quantum Wells Characterized by Photoacoustic Measurement

    NASA Astrophysics Data System (ADS)

    Takeda, Yosuke; Takagi, Daigo; Sano, Tatsuji; Tabata, Shin; Kobayashi, Naoki; Shen, Qing; Toyoda, Taro; Yamamoto, Jun; Ban, Yuzaburo; Matsumoto, Kou

    2008-12-01

    The absorption edges of five periods of InxGa1-xN (3 nm)/GaN (15 nm) (x=0.07-0.23) quantum wells (QWs) are characterized by photoacoustic (PA) measurement at room temperature. The absorption edge is determined by differentiating the PA signal curve to obtain the inflection point on the assumption that the signal curve consists of Urbach tail in the low-energy region and Elliott's equation in the high-energy region. The constant absorption edge of GaN is observed at 3.4 eV and an absorption edge redshift with increasing In composition is observed for InGaN QWs. As a result, the Stokes shift increases with In composition and the highest shift of 435 meV is observed at x=0.23. From the energy calculation of optical transition in the InGaN/GaN QWs under an internal polarization field, the transition between the ground states confined in the well with a triangular potential causes a low-energy shift in the photoluminescence peak from the bulk band-gap energy, and the excited bound states whose wave functions are confined by the step-linear potential extending over the GaN barrier lead to the high-energy shift in the absorption edge.

  19. Multiwavelength anomalous diffraction analysis at the M absorption edges of uranium

    PubMed Central

    Liu, Yee; Ogata, Craig M.; Hendrickson, Wayne A.

    2001-01-01

    The multiwavelength anomalous diffraction (MAD) method for phase evaluation is now widely used in macromolecular crystallography. Successful MAD structure determinations have been carried out at the K or L absorption edges of a variety of elements. In this study, we investigate the anomalous scattering properties of uranium at its MIV (3.326 Å) and MV (3.490 Å) edge. Fluorescence spectra showed remarkably strong anomalous scattering at these edges (f′ = −70e, f′′ = 80e at the MIV edge and f′ = −90e, f′′ = 105e at the MV edge), many times higher than from any anomalous scatterers used previously for MAD phasing. However, the large scattering angles and high absorption at the low energies of these edges present some difficulties not found in typical crystallographic studies. We conducted test experiments at the MIV edge with crystals of porcine elastase derivatized with uranyl nitrate. A four-wavelength MAD data set complete to 3.2-Å Bragg spacings was collected from a single small frozen crystal. Analysis of the data yielded satisfactory phase information (average difference of 0ϕT − 0ϕA for replicated determinations is 32°) and produced an interpretable electron-density map. Our results demonstrate that it is practical to measure macromolecular diffraction data at these edges with current instrumentation and that phase information of good accuracy can be extracted from such experiments. We show that such experiments have potential for the phasing of very large macromolecular assemblages. PMID:11526210

  20. Local environment of metal ions in phthalocyanines: K-edge X-ray absorption spectra.

    PubMed

    Rossi, G; d'Acapito, F; Amidani, L; Boscherini, F; Pedio, M

    2016-09-14

    We report a detailed study of the K-edge X-ray absorption spectra of four transition metal phthalocyanines (MPc, M = Fe, Co, Cu and Zn). We identify the important single and multiple scattering contributions to the spectra in the extended energy range and provide a robust treatment of thermal damping; thus, a generally applicable model for the interpretation of X-ray absorption fine structure spectra is proposed. Consistent variations of bond lengths and Debye Waller factors are found as a function of atomic number of the metal ion, indicating a variation of the metal-ligand bond strength which correlates with the spatial arrangement and occupation of molecular orbitals. We also provide an interpretation of the near edge spectral features in the framework of a full potential real space multiple scattering approach and provide a connection to the local electronic structure. PMID:27510989

  1. The effects of dust scattering on high-resolution X-ray absorption edge structure

    NASA Astrophysics Data System (ADS)

    Corrales, L.; García, J.; Wilms, J.; Baganoff, F.

    2016-06-01

    High energy studies of astrophysical dust complement observations of dusty interstellar gas at other wavelengths. With high resolution X-ray spectroscopy, dust scattering significantly enhances the total extinction optical depth and alters the shape of photoelectric absorption edges. This effect is modulated by the dust grain size distribution, spatial location along the line of sight, and the imaging resolution of the X-ray telescope. At soft energies, the spectrum of scattered light is likely to have significant features at the 0.3 keV (C-K), 0.5 keV (O-K), and 0.7 keV (Fe-L) photoelectric absorption edges. This direct probe of ISM dust grain elements will be important for (i) understanding the relative abundances of graphitic grains or PAHs versus silicates, and (ii) measuring the depletion of gas phase elements into solid form. We focus in particular on the Fe-L edge, fitting a template for the total extinction to the high resolution spectrum of three X-ray binaries from the Chandra archive: GX 9+9, XTE J1817-330, and Cyg X-1. We discuss ways in which spectroscopy with XMM can yield insight into dust obscured objects such as stars, binaries, AGN, and foreground quasar absorption line systems.

  2. Resonant diffraction in stishovite near the K absorption edge of silicon

    SciTech Connect

    Dmitrienko, V. E.; Ovchinnikova, E. N.

    2011-05-15

    The X-ray resonant diffraction in a stishovite crystal near the K absorption edge of silicon (E{sub K} = 1839 eV) is studied theoretically. For such a long wavelength, the only possible Bragg reflection is the 100 reflection, which is forbidden by the space group of the crystal. It can be excited solely due to anisotropy of the X-ray scattering amplitude. The crystal symmetry is used to determine the polarization and azimuthal dependence of the reflection intensity. Since this reflection is single, it can be detected upon diffraction from a powder, which substantially widens the possibilities of investigations. The numerical calculations of the energy dependences of the forbidden reflection intensity and the absorption coefficient demonstrate that the dipole-quadrupole, quadrupole-quadrupole, and dipole-octupole contributions to the resonant diffraction and absorption are small and that the dipole-dipole contribution is the most important one.

  3. Absorption-edge transmission technique using Ce- 139 for measurement of stable iodine concentration.

    PubMed

    Sorenson, J A

    1979-12-01

    We have investigated a technique for measuring stable iodine concentrations by absorption-edge transmission measurements using a Ce 139 radiation source. The lanthanum daughter emits characteristic x-rays whose energies just bracket the absorption edge of iodine at 33.2 keV. Relative transmission of these x-rays is sensitive to iodine concentration in the sample, but is relatively insensitive to other elements. By applying energy-selective beam filtration, it is possible to determine the relative transmission of these closely spaced x-ray energies with NaI(Tl) detectors. Optimizations of sample thickness, detector thickness, and Ce-139 source activity are discussed. Using sample volumes of about 10 ml, one can determine iodine concentration to an uncertainty (standard deviation) of +/- 5 microgram/ml with a 5-mCi source in a measurement time of 400 sec. Potential clinical applications of the in vitro technique are discussed, along with comparative aspects of the Ce-139 technique and other absorption and fluorescence techniques for measuring stable iodine. PMID:536797

  4. Absorption edge shift, optical conductivity, and energy loss function of nano thermal-evaporated N-type anatase TiO2 films

    NASA Astrophysics Data System (ADS)

    El-Nahass, M. M.; Soliman, H. S.; El-Denglawey, A.

    2016-08-01

    Thermal evaporation technique was used to deposit 263 nm of TiO2 films on a quartz substrate. XRD of powder TiO2 reveals anatase phase characterized by nanostructure with crystallite size within a range of 4-10 nm. The increase in annealing temperature (400-800 °C) increases the crystallite size up to 43.1 nm. SEM micrograph shows grains of annealed TiO2 films within nanoscale. Optical gap, refractive index, dielectric constants, porosity, ratio of carrier concentration to the effective mass, dispersion, and oscillation energy were determined as well as optical conductivity and energy loss function. All parameters are affected by annealing. Current theoretical ideas were used to discuss the obtained results.

  5. 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.

  6. Near edge X-ray absorption mass spectrometry on coronene

    SciTech Connect

    Reitsma, G.; Deuzeman, M. J.; Hoekstra, R.; Schlathölter, T.; Boschman, L.; Hoekstra, S.

    2015-01-14

    We have investigated the photoionization and photodissociation of free coronene cations C{sub 24}H{sub 12}{sup +} upon soft X-ray photoabsorption in the carbon K-edge region by means of a time-of-flight mass spectrometry approach. Core excitation into an unoccupied molecular orbital (below threshold) and core ionization into the continuum both leave a C 1s vacancy, that is subsequently filled in an Auger-type process. The resulting coronene dications and trications are internally excited and cool down predominantly by means of hydrogen emission. Density functional theory was employed to determine the dissociation energies for subsequent neutral hydrogen loss. A statistical cascade model incorporating these dissociation energies agrees well with the experimentally observed dehydrogenation. For double ionization, i.e., formation of intermediate C{sub 24}H{sub 12}{sup 3+⋆}trications, the experimental data hint at loss of H{sup +} ions. This asymmetric fission channel is associated with hot intermediates, whereas colder intermediates predominantly decay via neutral H loss.

  7. X-ray Absorption Spectroscopy Systematics at the Tungsten L-Edge

    PubMed Central

    2015-01-01

    A series of mononuclear six-coordinate tungsten compounds spanning formal oxidation states from 0 to +VI, largely in a ligand environment of inert chloride and/or phosphine, was interrogated by tungsten L-edge X-ray absorption spectroscopy. The L-edge spectra of this compound set, comprised of [W0(PMe3)6], [WIICl2(PMePh2)4], [WIIICl2(dppe)2][PF6] (dppe = 1,2-bis(diphenylphosphino)ethane), [WIVCl4(PMePh2)2], [WV(NPh)Cl3(PMe3)2], and [WVICl6], correlate with formal oxidation state and have usefulness as references for the interpretation of the L-edge spectra of tungsten compounds with redox-active ligands and ambiguous electronic structure descriptions. The utility of these spectra arises from the combined correlation of the estimated branching ratio of the L3,2-edges and the L1 rising-edge energy with metal Zeff, thereby permitting an assessment of effective metal oxidation state. An application of these reference spectra is illustrated by their use as backdrop for the L-edge X-ray absorption spectra of [WIV(mdt)2(CO)2] and [WIV(mdt)2(CN)2]2– (mdt2– = 1,2-dimethylethene-1,2-dithiolate), which shows that both compounds are effectively WIV species even though the mdt ligands exist at different redox levels in the two compounds. Use of metal L-edge XAS to assess a compound of uncertain formulation requires: (1) Placement of that data within the context of spectra offered by unambiguous calibrant compounds, preferably with the same coordination number and similar metal ligand distances. Such spectra assist in defining upper and/or lower limits for metal Zeff in the species of interest. (2) Evaluation of that data in conjunction with information from other physical methods, especially ligand K-edge XAS. (3) Increased care in interpretation if strong π-acceptor ligands, particularly CO, or π-donor ligands are present. The electron-withdrawing/donating nature of these ligand types, combined with relatively short metal–ligand distances, exaggerate the difference

  8. Parametric distortion of the optical absorption edge of a magnetic semiconductor by a strong laser field

    SciTech Connect

    Nunes, O.A.C.

    1985-09-15

    The influence of a strong laser field on the optical absorption edge of a direct-gap magnetic semiconductor is considered. It is shown that as the strong laser intensity increases the absorption coefficient is modified so as to give rise to an absorption tail below the free-field forbidden gap. An application is made for the case of the EuO.

  9. The irradiation of ammonia ice studied by near edge x-ray absorption spectroscopy

    SciTech Connect

    Parent, Ph.; Bournel, F.; Lasne, J.; Laffon, C.; Carniato, S.; Lacombe, S.; Strazzulla, G.; Gardonio, S.; Lizzit, S.; Kappler, J.-P.; Joly, L.

    2009-10-21

    A vapor-deposited NH{sub 3} ice film irradiated at 20 K with 150 eV photons has been studied with near-edge x-ray absorption fine structure (NEXAFS) spectroscopy at the nitrogen K-edge. Irradiation leads to the formation of high amounts (12%) of molecular nitrogen N{sub 2}, whose concentration as a function of the absorbed energy has been quantified to 0.13 molecule/eV. The stability of N{sub 2} in solid NH{sub 3} has been also studied, showing that N{sub 2} continuously desorbs between 20 and 95 K from the irradiated ammonia ice film. Weak concentrations (<1%) of other photoproducts are also detected. Our NEXAFS simulations show that these features own to NH{sub 2}, N{sub 2}H{sub 2}, and N{sub 3}{sup -}.

  10. 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.

  11. Relativistic Effects Around Black Holes: Smearing Absorption Edges

    NASA Technical Reports Server (NTRS)

    Zhang, X. L.; Feng, Y. X.; Zhang, S. N.; Yao, Y.

    2002-01-01

    Broad iron absorption structures have been observed in the X-ray spectra of both AGNs and black hole X-ray binaries (BHXBs). A correctly modeled absorption structure can reveal the physical condition of the source, help to determine the continuum spectra and thus help to estimate other spectral lifes more accurately. The absorption structures are usually thought to be caused by the reflection of X-rays by the accretion disks around the central black holes, and the broadening can be a ttributed to the ionization states of the disk and relativistic effects.

  12. X-ray absorption and reflection as probes of the GaN conduction bands: Theory and experiment of the N K-edge and Ga M{sub 2,3} edges

    SciTech Connect

    Lambrecht, W.R.L.; Rashkeev, S.N.; Segall, B.; Lawniczak-Jablonska, K.; Suski, T.; Gullikson, E.M.; Underwood, J.H.; Perera, R.C.C.; Rife, J.C.

    1997-12-31

    X-ray absorption and glancing angle reflectivity measurements in the energy range of the Nitrogen K-edge and Gallium M{sub 2,3} edges are reported. Linear muffin-tin orbital band-structure and spectral function calculations are used to interpret the data. Polarization effects are evidenced for the N-K-edge spectra by comparing X-ray reflectivity in s- and p-polarized light.

  13. Quantitative analysis of deconvolved X-ray absorption near-edge structure spectra: a tool to push the limits of the X-ray absorption spectroscopy technique.

    PubMed

    D'Angelo, Paola; Migliorati, Valentina; Persson, Ingmar; Mancini, Giordano; Della Longa, Stefano

    2014-09-15

    A deconvolution procedure has been applied to K-edge X-ray absorption near-edge structure (XANES) spectra of lanthanoid-containing solid systems, namely, hexakis(dmpu)praseodymium(III) and -gadolinium(III) iodide. The K-edges of lanthanoids cover the energy range 38 (La)-65 (Lu) keV, and the large widths of the core-hole states lead to broadening of spectral features, reducing the content of structural information that can be extracted from the raw X-ray absorption spectra. Here, we demonstrate that deconvolution procedures allow one to remove most of the instrumental and core-hole lifetime broadening in the K-edge XANES spectra of lanthanoid compounds, highlighting structural features that are lost in the raw data. We show that quantitative analysis of the deconvolved K-edge XANES spectra can be profitably used to gain a complete local structural characterization of lanthanoid-containing systems not only for the nearest neighbor atoms but also for higher-distance coordination shells. PMID:25171598

  14. Prediction of Iron K-Edge Absorption Spectra Using Time-Dependent Density Functional Theory

    SciTech Connect

    George, S.DeBeer; Petrenko, T.; Neese, F.

    2009-05-14

    Iron K-edge X-ray absorption pre-edge features have been calculated using a time-dependent density functional approach. The influence of functional, solvation, and relativistic effects on the calculated energies and intensities has been examined by correlation of the calculated parameters to experimental data on a series of 10 iron model complexes, which span a range of high-spin and low-spin ferrous and ferric complexes in O{sub h} to T{sub d} geometries. Both quadrupole and dipole contributions to the spectra have been calculated. We find that good agreement between theory and experiment is obtained by using the BP86 functional with the CP(PPP) basis set on the Fe and TZVP one of the remaining atoms. Inclusion of solvation yields a small improvement in the calculated energies. However, the inclusion of scalar relativistic effects did not yield any improved correlation with experiment. The use of these methods to uniquely assign individual spectral transitions and to examine experimental contributions to backbonding is discussed.

  15. THE STATE OF MANGANESE IN THE PHOTOSYNTHETIC APPARATUS. II. X-RAY ABSORPTION EDGE STUDIES ON MANGANESE IN PHOTOSYNTHETIC MEMBRANES

    SciTech Connect

    Kirby, J. A.; Goodin, D. B.; Wydrzynski, T.; Robertson, A. S.; Klein, M. P.

    1980-11-01

    X-ray absorption spectra at the Manganese K-edge are presented for spinach chloroplasts, and chloroplasts which have been Tris-treated and hence unable to evolve oxygen. A significant change in the electronic environment of manganese is observed and is attributed to the release of manganese from the thylakoid membranes with a concomitant change in oxidation state. A correlation of the K-edge energy, defined as the energy at the first inflection point, with coordination charge has been established for a number of manganese compounds of known structure and oxidation state. Comparison of the manganese K-edge energies of the chloroplast samples with the reference compounds places the average oxidation state of the chloroplasts between +2 and +3. Using the edge spectra for Tris-treated membranes which were osmotically shocked to remove the released manganese, difference edge spectra were synthesized to approximate the active pool of manganese. Coordination charge predictions for this fraction are consistent with an average resting oxidation state higher than +2. The shape at the edge is also indicative of heterogeneity of the manganese site, of low symmetry, or both.

  16. Attenuation studies near K-absorption edges using Compton scattered 241 Am gamma rays

    NASA Astrophysics Data System (ADS)

    Abdullah, K. K.; Ramachandran, N.; Karunakaran Nair, K.; Babu, B. R. S.; Joseph, Antony; Thomas, Rajive; Varier, K. M.

    2008-04-01

    We have carried out photon attenuation measurements at several energies in the range from 49.38 keV to 57.96 keV around the K-absorption edges of the rare earth elements Sm, Eu, Gd, Tb, Dy and Er using 59.54 keV gamma rays from ^{241}Am source after Compton scattering from an aluminium target. Pellets of oxides of the rare earth elements were chosen as mixture absorbers in these investigations. A narrow beam good geometry set-up was used for the attenuation measurements. The scattered gamma rays were detected by an HPGe detector. The results are consistent with theoretical values derived from the XCOM package.

  17. 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.

  18. Correction of absorption-edge artifacts in polychromatic X-ray tomography in a scanning electron microscope for 3D microelectronics

    SciTech Connect

    Laloum, D.; Printemps, T.; Bleuet, P.; Lorut, F.

    2015-01-15

    X-ray tomography is widely used in materials science. However, X-ray scanners are often based on polychromatic radiation that creates artifacts such as dark streaks. We show this artifact is not always due to beam hardening. It may appear when scanning samples with high-Z elements inside a low-Z matrix because of the high-Z element absorption edge: X-rays whose energy is above this edge are strongly absorbed, violating the exponential decay assumption for reconstruction algorithms and generating dark streaks. A method is proposed to limit the absorption edge effect and is applied on a microelectronic case to suppress dark streaks between interconnections.

  19. Correction of absorption-edge artifacts in polychromatic X-ray tomography in a scanning electron microscope for 3D microelectronics

    NASA Astrophysics Data System (ADS)

    Laloum, D.; Printemps, T.; Lorut, F.; Bleuet, P.

    2015-01-01

    X-ray tomography is widely used in materials science. However, X-ray scanners are often based on polychromatic radiation that creates artifacts such as dark streaks. We show this artifact is not always due to beam hardening. It may appear when scanning samples with high-Z elements inside a low-Z matrix because of the high-Z element absorption edge: X-rays whose energy is above this edge are strongly absorbed, violating the exponential decay assumption for reconstruction algorithms and generating dark streaks. A method is proposed to limit the absorption edge effect and is applied on a microelectronic case to suppress dark streaks between interconnections.

  20. Energy absorption by polymer crazing

    NASA Technical Reports Server (NTRS)

    Pang, S. S.; Zhang, Z. D.; Chern, S. S.; Hsiao, C. C.

    1983-01-01

    During the past thirty years, a tremendous amount of research was done on the development of crazing in polymers. The phenomenon of crazing was recognized as an unusual deformation behavior associated with a process of molecular orientation in a solid to resist failure. The craze absorbs a fairly large amount of energy during the crazing process. When a craze does occur the surrounding bulk material is usually stretched to several hundred percent of its original dimension and creates a new phase. The total energy absorbed by a craze during the crazing process in creep was calculated analytically with the help of some experimental measurements. A comparison of the energy absorption by the new phase and that by the original bulk uncrazed medium is made.

  1. Fluid absorption solar energy receiver

    NASA Technical Reports Server (NTRS)

    Bair, Edward J.

    1993-01-01

    A conventional solar dynamic system transmits solar energy to the flowing fluid of a thermodynamic cycle through structures which contain the gas and thermal energy storage material. Such a heat transfer mechanism dictates that the structure operate at a higher temperature than the fluid. This investigation reports on a fluid absorption receiver where only a part of the solar energy is transmitted to the structure. The other part is absorbed directly by the fluid. By proportioning these two heat transfer paths the energy to the structure can preheat the fluid, while the energy absorbed directly by the fluid raises the fluid to its final working temperature. The surface temperatures need not exceed the output temperature of the fluid. This makes the output temperature of the gas the maximum temperature in the system. The gas can have local maximum temperatures higher than the output working temperature. However local high temperatures are quickly equilibrated, and since the gas does not emit radiation, local high temperatures do not result in a radiative heat loss. Thermal radiation, thermal conductivity, and heat exchange with the gas all help equilibrate the surface temperature.

  2. Electronic structure investigation of highly compressed aluminum with K edge absorption spectroscopy.

    PubMed

    Benuzzi-Mounaix, A; Dorchies, F; Recoules, V; Festa, F; Peyrusse, O; Levy, A; Ravasio, A; Hall, T; Koenig, M; Amadou, N; Brambrink, E; Mazevet, S

    2011-10-14

    The electronic structure evolution of highly compressed aluminum has been investigated using time resolved K edge x-ray absorption spectroscopy. A long laser pulse (500 ps, I(L)≈8×10(13) W/cm(2)) was used to create a uniform shock. A second ps pulse (I(L)≈10(17)  W/cm(2)) generated an ultrashort broadband x-ray source near the Al K edge. The main target was designed to probe aluminum at reshocked conditions up to now unexplored (3 times the solid density and temperatures around 8 eV). The hydrodynamical conditions were obtained using rear side visible diagnostics. Data were compared to ab initio and dense plasma calculations, indicating potential improvements in either description. This comparison shows that x-ray-absorption near-edge structure measurements provide a unique capability to probe matter at these extreme conditions and severally constrains theoretical approaches currently used. PMID:22107398

  3. Single shot near edge x-ray absorption fine structure spectroscopy in the laboratory

    NASA Astrophysics Data System (ADS)

    Mantouvalou, I.; Witte, K.; Martyanov, W.; Jonas, A.; Grötzsch, D.; Streeck, C.; Löchel, H.; Rudolph, I.; Erko, A.; Stiel, H.; Kanngießer, B.

    2016-05-01

    With the help of adapted off-axis reflection zone plates, near edge X-ray absorption fine structure spectra at the C and N K-absorption edge have been recorded using a single 1.2 ns long soft X-ray pulse. The transmission experiments were performed with a laser-produced plasma source in the laboratory rendering time resolved measurements feasible independent on large scale facilities. A resolving power of E/ΔE ˜ 950 at the respective edges could be demonstrated. A comparison of single shot spectra with those collected with longer measuring time proves that all features of the used reference samples (silicon nitrate and polyimide) can be resolved in 1.2 ns. Hence, investigations of radiation sensitive biological specimen become possible due to the high efficiency of the optical elements enabling low dose experiments.

  4. Shift of optical absorption edge in SnO2 films with high concentrations of nitrogen grown by chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Jiang, Jie; Lu, Yinmei; Meyer, Bruno K.; Hofmann, Detlev M.; Eickhoff, Martin

    2016-06-01

    The optical and electrical properties of n-type SnO2 films with high concentrations of nitrogen (SnO2:N) grown by chemical vapor deposition are studied. The carrier concentration increases from 4.1 × 1018 to 3.9 × 1019 cm-3 and the absorption edge shifts from 4.26 to 4.08 eV with increasing NH3 flow rate. Typical Urbach tails were observed from the absorption spectra and the Urbach energy increases from 0.321 to 0.526 eV with increasing NH3 flow rate. An "effective" absorption edge of about 4.61 eV was obtained for all investigated samples from fitting the extrapolations of the Urbach tails. Burstein-Moss effect, electron-impurity, and electron-electron interactions are shown to play a minor role for the shift of the absorption edges in SnO2:N thin films.

  5. Defects forming the optical absorption edge in TlGaSe2 layered crystal

    NASA Astrophysics Data System (ADS)

    Seyidov, MirHasan Yu.; Suleymanov, Rauf A.; Şale, Yasin

    2016-09-01

    In this work, we present the results of optical experiments designed to investigate the changes in optical absorption spectra of TlGaSe2 ferroelectric-semiconductor with incommensurate (INC) phase in experimental conditions where crystal is kept several hours within the INC-phase (the regime of so called "memory" effect). The fundamental absorption of TlGaSe2, experimentally investigated by optical transmission measurements performed in the temperature range 15-300 K. An extraordinary modification of the optical absorption edge in the range of Urbach's tail is discovered as a result of the annealing within the INC-phase. The role of native defects forming the band edge in the observed phenomena in TlGaSe2 is discussed.

  6. Iron speciation in human cancer cells by K-edge total reflection X-ray fluorescence-X-ray absorption near edge structure analysis

    NASA Astrophysics Data System (ADS)

    Polgári, Zs.; Meirer, F.; Sasamori, S.; Ingerle, D.; Pepponi, G.; Streli, C.; Rickers, K.; Réti, A.; Budai, B.; Szoboszlai, N.; Záray, G.

    2011-03-01

    X-ray absorption near edge structure (XANES) analysis in combination with synchrotron radiation induced total reflection X-ray fluorescence (SR-TXRF) acquisition was used to determine the oxidation state of Fe in human cancer cells and simultaneously their elemental composition by applying a simple sample preparation procedure consisting of pipetting the cell suspension onto the quartz reflectors. XANES spectra of several inorganic and organic iron compounds were recorded and compared to that of different cell lines. The XANES spectra of cells, independently from the phase of cell growth and cell type were very similar to that of ferritin, the main Fe store within the cell. The spectra obtained after CoCl 2 or NiCl 2 treatment, which could mimic a hypoxic state of cells, did not differ noticeably from that of the ferritin standard. After 5-fluorouracil administration, which could also induce an oxidative-stress in cells, the absorption edge position was shifted toward higher energies representing a higher oxidation state of Fe. Intense treatment with antimycin A, which inhibits electron transfer in the respiratory chain, resulted in minor changes in the spectrum, resembling rather the N-donor Fe-α,α'-dipyridyl complex at the oxidation energy of Fe(III), than ferritin. The incorporation of Co and Ni in the cells was followed by SR-TXRF measurements.

  7. Near-Edge X-Ray Absorption Fine Structure Spectroscopy of Diamondoid Thiol Monolayers on Gold

    SciTech Connect

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

    2009-05-26

    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 and 0.16 {+-} 0.04 eV, respectively. These binding energies vary with diamondoid monolayer structure and thiol substitution position, consistent with different degrees 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 nanoparticles.

  8. 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.

  9. Mechanism of Pressure-Induced Phase Transitions, Amorphization, and Absorption-Edge Shift in Photovoltaic Methylammonium Lead Iodide.

    PubMed

    Szafrański, Marek; Katrusiak, Andrzej

    2016-09-01

    Our single-crystal X-ray diffraction study of methylammonium lead triiodide, MAPbI3, provides the first comprehensive structural information on the tetragonal phase II in the pressure range to 0.35 GPa, on the cubic phase IV stable between 0.35 and 2.5 GPa, and on the isostructural cubic phase V observed above 2.5 GPa, which undergoes a gradual amorphization. The optical absorption study confirms that up to 0.35 GPa, the absorption edge of MAPbI3 is red-shifted, allowing an extension of spectral absorption. The transitions to phases IV and V are associated with the abrupt blue shifts of the absorption edge. The strong increase of the energy gap in phase V result in a spectacular color change of the crystal from black to red around 3.5 GPa. The optical changes have been correlated with the pressure-induced strain of the MAPbI3 inorganic framework and its frustration, triggered by methylammonium cations trapped at random orientations in the squeezed voids. PMID:27538989

  10. Direct Correlation Between Aromatization of Kerogen in Organic Shales during Maturation and Its Visible Absorption Edge

    NASA Astrophysics Data System (ADS)

    Ferralis, N.; Liu, Y.; Pomerantz, A.; Grossman, J.

    2014-12-01

    The evolution of the electronic visible-range optical absorption edge of isolated kerogens type 1, 2 (from organic shales) and 3 is characterized by diffuse reflectance UV-Visible absorption spectroscopy. The functional form of the electronic absorption edge for all kerogens measured is in excellent agreement with the "Urbach tail" phenomenology. The Urbach decay width extracted from the exponential fit within the visible range is strongly correlated with the aliphatic/aromatic ratio in isolated kerogen, regardless of the kerogen type. The direct correlation is confirmed by density functional theory calculations on proxy ensemble models of kerogen. The correlation of the decay width with conventional maturity indicators such as vitrinite reflectance is found to be good within a particular kerogen type, but not consistent across different kerogen types. This is explained in terms of the evolution of the population of aromatic constituents in kerogen, which is instead directly measured through the Urbach decay. The optical absorption edge and the Urbach decay width are therefore presented as excellent candidates for the evaluation of thermal maturity in kerogen.

  11. X-ray absorption near edge structure investigation ofvanadium-doped ZnO thin films

    SciTech Connect

    Faiz, M.; Tabet, N.; Mekki, A.; Mun, B.S.; Hussain, Z.

    2006-05-11

    X-ray absorption near edge structure spectroscopy has beenused to investigate the electronic and atomic structure of vanadium-dopedZnO thin films obtained by reactive plasma. The results show no sign ofmetallic clustering of V atoms, +4 oxidation state of V, 4-foldcoordination of Zn in the films, and a secondary phase (possibly VO2)formation at 15 percent V doping. O K edge spectra show V 3d-O 2p and Zn4d-O 2p hybridization, and suggest that V4+ acts as electron donor thatfills the sigma* band.

  12. General Method for Determination of the Surface Composition in Bimetallic Nanoparticle Catalysts from the L Edge X-ray Absorption Near-Edge Spectra

    SciTech Connect

    Wu, Tiapin; Childers, David; Gomez, Carolina; Karim, Ayman M.; Schweitzer, Neil; Kropf, Arthur; Wang, Hui; Bolin, Trudy B.; Hu, Yongfeng; Kovarik, Libor; Meyer, Randall; Miller, Jeffrey T.

    2012-10-08

    Bimetallic PtPd on silica nano-particle catalysts have been synthesized and their average structure determined by Pt L3 and Pd K-edge extended X-ray absorption finestructure (EXAFS) spectroscopy. The bimetallic structure is confirmed from elemental line scans by STEM for the individual 1-2 nm sized particles. A general method is described to determine the surface composition in bimetallic nanoparticles even when both metals adsorb, for example, CO. By measuring the change in the L3 X-ray absorption near-edge structure (XANES) spectra with and without CO in bimetallic particles and comparing these changes to those in monometallic particles of known size the fraction of surface atoms can be determined. The turnover rates (TOR) and neopentane hydrogenolysis and isomerization selectivities based on the surface composition suggest that the catalytic and spectroscopic properties are different from those in monometallic nano-particle catalysts. At the same neo-pentane conversion, the isomerization selectivity is higher for the PtPd catalyst while the TOR is lower than that of both Pt and Pd. As with the catalytic performance, the infrared spectra of adsorbed CO are not a linear combination of the spectra on monometallic catalysts. Density functional theory calculations indicate that the Pt-CO adsorption enthalpy increases while the Pd-CO bond energy decreases. The ability to determine the surface composition allows for a better understanding of the spectroscopic and catalytic properties of bimetallic nanoparticle catalysts.

  13. Light harvesting in photonic crystals revisited: why do slow photons at the blue edge enhance absorption?

    PubMed

    Deparis, O; Mouchet, S R; Su, B-L

    2015-11-11

    Light harvesting enhancement by slow photons in photonic crystal catalysts or dye-sensitized solar cells is a promising approach for increasing the efficiency of photoreactions. This structural effect is exploited in inverse opal TiO2 photocatalysts by tuning the red edge of the photonic band gap to the TiO2 electronic excitation band edge. In spite of many experimental demonstrations, the slow photon effect is not fully understood yet. In particular, observed enhancement by tuning the blue edge has remained unexplained. Based on rigorous couple wave analysis simulations, we quantify light harvesting enhancement in terms of absorption increase at a specific wavelength (monochromatic UV illumination) or photocurrent increase (solar light illumination), with respect to homogeneous flat slab of equivalent material thickness. We show that the commonly accepted explanation relying on light intensity confinement in high (low) dielectric constant regions at the red (blue) edge is challenged in the case of TiO2 inverse opals because of the sub-wavelength size of the material skeleton. The reason why slow photons at the blue edge are also able to enhance light harvesting is the loose confinement of the field, which leads to significant resonantly enhanced field intensity overlap with the skeleton in both red and blue edge tuning cases, yet with different intensity patterns. PMID:26517229

  14. Virtual edge illumination and one dimensional beam tracking for absorption, refraction, and scattering retrieval

    SciTech Connect

    Vittoria, Fabio A. Diemoz, Paul C.; Endrizzi, Marco; Olivo, Alessandro; Wagner, Ulrich H.; Rau, Christoph; Robinson, Ian K.

    2014-03-31

    We propose two different approaches to retrieve x-ray absorption, refraction, and scattering signals using a one dimensional scan and a high resolution detector. The first method can be easily implemented in existing procedures developed for edge illumination to retrieve absorption and refraction signals, giving comparable image quality while reducing exposure time and delivered dose. The second method tracks the variations of the beam intensity profile on the detector through a multi-Gaussian interpolation, allowing the additional retrieval of the scattering signal.

  15. Intracellular nanoparticles mass quantification by near-edge absorption soft X-ray nanotomography

    NASA Astrophysics Data System (ADS)

    Conesa, Jose Javier; Otón, Joaquín; Chiappi, Michele; Carazo, Jose María; Pereiro, Eva; Chichón, Francisco Javier; Carrascosa, José L.

    2016-03-01

    We used soft X-ray three-dimensional imaging to quantify the mass of superparamagnetic iron oxide nanoparticles (SPION) within whole cells, by exploiting the iron oxide differential absorption contrast. Near-edge absorption soft X-ray nanotomography (NEASXT) combines whole-cell 3D structure determination at 50 nm resolution, with 3D elemental mapping and high throughput. We detected three-dimensional distribution of SPIONs within cells with 0.3 g/cm3 sensitivity, sufficient for detecting the density corresponding to a single nanoparticle.

  16. A high resolution x-ray fluorescence spectrometer for near edge absorption studies

    SciTech Connect

    Stojanoff, V.; Hamalainen, K.; Siddons, D.P.; Hastings, J.B.; Berman, L.E.; Cramer, S.; Smith, G.

    1991-01-01

    A high resolution fluorescence spectrometer using a Johann geometry in a back scattering arrangement was developed. The spectrometer, with a resolution of 0.3 eV at 6.5 keV, combined with an incident beam, with a resolution of 0.7 eV, form the basis of a high resolution instrument for measuring x-ray absorption spectra. The advantages of the instrument are illustrated with the near edge absorption spectrum of dysprosium nitrate. 10 refs., 4 figs.

  17. A high resolution x-ray fluorescence spectrometer for near edge absorption studies

    SciTech Connect

    Stojanoff, V.; Hamalainen, K.; Siddons, D.P.; Hastings, J.B.; Berman, L.E.; Cramer, S.; Smith, G.

    1991-12-31

    A high resolution fluorescence spectrometer using a Johann geometry in a back scattering arrangement was developed. The spectrometer, with a resolution of 0.3 eV at 6.5 keV, combined with an incident beam, with a resolution of 0.7 eV, form the basis of a high resolution instrument for measuring x-ray absorption spectra. The advantages of the instrument are illustrated with the near edge absorption spectrum of dysprosium nitrate. 10 refs., 4 figs.

  18. Intracellular nanoparticles mass quantification by near-edge absorption soft X-ray nanotomography

    PubMed Central

    Conesa, Jose Javier; Otón, Joaquín; Chiappi, Michele; Carazo, Jose María; Pereiro, Eva; Chichón, Francisco Javier; Carrascosa, José L.

    2016-01-01

    We used soft X-ray three-dimensional imaging to quantify the mass of superparamagnetic iron oxide nanoparticles (SPION) within whole cells, by exploiting the iron oxide differential absorption contrast. Near-edge absorption soft X-ray nanotomography (NEASXT) combines whole-cell 3D structure determination at 50 nm resolution, with 3D elemental mapping and high throughput. We detected three-dimensional distribution of SPIONs within cells with 0.3 g/cm3 sensitivity, sufficient for detecting the density corresponding to a single nanoparticle. PMID:26960695

  19. Intracellular nanoparticles mass quantification by near-edge absorption soft X-ray nanotomography.

    PubMed

    Conesa, Jose Javier; Otón, Joaquín; Chiappi, Michele; Carazo, Jose María; Pereiro, Eva; Chichón, Francisco Javier; Carrascosa, José L

    2016-01-01

    We used soft X-ray three-dimensional imaging to quantify the mass of superparamagnetic iron oxide nanoparticles (SPION) within whole cells, by exploiting the iron oxide differential absorption contrast. Near-edge absorption soft X-ray nanotomography (NEASXT) combines whole-cell 3D structure determination at 50 nm resolution, with 3D elemental mapping and high throughput. We detected three-dimensional distribution of SPIONs within cells with 0.3 g/cm(3) sensitivity, sufficient for detecting the density corresponding to a single nanoparticle. PMID:26960695

  20. Oscillator strength of the peptide bond {pi}* resonances at all relevant x-ray absorption edges

    SciTech Connect

    Kummer, K.; Vyalikh, D. V.; Molodtsov, S. L.; Sivkov, V. N.; Nekipelov, S. V.; Maslyuk, V. V.; Mertig, I.; Blueher, A.; Mertig, M.; Bredow, T.

    2009-10-15

    Absolute x-ray absorption cross sections of a regular bacterial surface-layer protein deposited on a naturally oxidized silicon substrate were determined experimentally. Upon separation of the partial cross sections of the three relevant 1s absorption edges, the oscillator strengths of the 1s{yields}{pi}* excitations within the peptide-backbone unit were extracted. Comparison with results of first-principles calculations revealed their close correlation to the topology of {pi}{sub peptide}* orbitals of the peptide backbone.

  1. Multiple-scattering calculations of the uranium L3-edge x-ray-absorption near-edge structure

    NASA Astrophysics Data System (ADS)

    Hudson, E. A.; Rehr, J. J.; Bucher, J. J.

    1995-11-01

    A theoretical study of the uranium L3-edge x-ray absorption near-edge structure (XANES) is presented for several uranium compounds, including oxides, intermetallics, uranyl fluoride, and α-uranium. Calculations were performed using feff6, an ab initio multiple-scattering (MS) code that includes the most important features of current theories. The results, which account for both the fine structure χ and the atomiclike background μ0 of the absorption coefficient μ, are compared to new and previously measured experimental spectra, reavealing very good agreement for most systems. For several compounds, a more detailed theoretical analysis determined the influence of cluster size and scattering order upon the calculated spectra. Results indicate that MS paths and scattering paths that include rather distant atoms make significant contributions for UO2, whereas XANES for crystals with lower symmetry and density can be modeled using only shorter single-scattering paths. In most cases, assumption of a screened final state in the calculation gives better agreement with experiment than use of an unscreened final state. The successful modeling of spectra for a variety of different uranium compounds, with differing spectral features, indicates that the semirelativistic treatment of XANES used here is adequate even for heavy elements. The well-known resonance, observed experimentally for uranyl (UO2+2) compounds ~=15 eV above the white line, is successfully modeled here for the first time, using multiple-scattering paths within the O-U-O axial bonds. Overlapping muffin-tin spheres were required in the calculation, probably as a result of the short uranyl axial bonds.

  2. Microanalysis of iron oxidation state in iron oxides using X Ray Absorption Near Edge Structure (XANES)

    NASA Technical Reports Server (NTRS)

    Sutton, S. R.; Delaney, J.; Bajt, S.; Rivers, M. L.; Smith, J. V.

    1993-01-01

    An exploratory application of x ray absorption near edge structure (XANES) analysis using the synchrotron x ray microprobe was undertaken to obtain Fe XANES spectra on individual sub-millimeter grains in conventional polished sections. The experiments concentrated on determinations of Fe valence in a suite of iron oxide minerals for which independent estimates of the iron speciation could be made by electron microprobe analysis and x ray diffraction.

  3. X-ray phase-amplitude contrast mapping of single-crystal alloys near the absorption edge of the alloy impurity

    NASA Astrophysics Data System (ADS)

    Nikulin, A. Yu.; Davis, J. R.; Jones, N. T.; Zaumseil, P.

    1998-11-01

    An experimental-analytical method for the nondestructive structural and chemical composition mapping of single-crystal alloys is proposed, implemented, and successfully tested. The technique is based on analytical measurements of phase and amplitude changes in a narrow polychromatic region near the absorption edge of the alloy impurity. Synchrotron radiation energies of 11.096-11.105 keV were used to measure the Bragg diffraction profiles near the absorption edge of germanium at 11.103 keV in SiGe/Si crystal alloy superstructures. Physical dimensions and chemical composition of SiGe alloys were determined with a spatial resolution 8.6 Å.

  4. Photoelectron Experiments and Studies of X-Ray Absorption Near Edge Structure in Alkaline-Earth and Rare - Fluorides.

    NASA Astrophysics Data System (ADS)

    Gao, Yuan

    Alkaline-earth fluorides and rare-earth trifluorides possess technological importance for applications in multi -layer electronic device structures and opto-electronic devices. Interfaces between thin films of YbF _3 and Si(111) substrates were studied by photoelectron spectroscopy and x-ray absorption spectroscopy using synchrotron radiation. Results of YbF_3 /Si(111) were compared with those of TmF _3/Si(111). While electrons in the Si valence band are prevented from occupying the empty 4f levels in TmF_3 at the interface by the on -site Coulomb repulsion energy, the charge transfer from Si to YbF_3 is possible because the totally filled 4f states in Yb still lie below the Si valence band maximum. The theory of x-ray absorption near edge structure (XANES) is incomplete except for a few particularly simple special cases. A Bragg reflection model was developed to qualitatively explain the oscillations in XANES, in terms of the scattering of the photoelectron wave between families of lattice planes as set out by the Bragg condition for backscattering. The model was found to represent the data for systems with nearly free electron like conduction bands reasonably well. High resolution CaF_2 fluorine K edge XANES was used as a prototype to understand XANES in more depth on systems with strong core hole effects. Unlike previous work which involved multiple scattering cluster calculations that include only short range order effects, both the long range order and the symmetry breaking core holes are included in a new bandstructure approach in which the core hole is treated with a supercell technique. A first principles calculation with the use of pseudopotentials successfully reproduced all the main features of the first 15 eV of the fluorine K edge in CaF_2 which had not been explained with the cluster calculations. A comparison of the theoretical and experimental fluorine K edges in CaF_2 and BaF _2 was used to identify the structure related features. The possibility

  5. Atomic form factors and photoelectric absorption cross-sections near absorption edges in the soft X-ray region

    NASA Astrophysics Data System (ADS)

    Chantler, C. T.

    2003-01-01

    Reliable knowledge of the complex X-ray form factor [Re(f) and Im(f)] and the photoelectric attenuation coefficient (σPE) is required for crystallography, medical diagnosis, radiation safety and XAFS studies. Key discrepancies in earlier theoretical work are due to the smoothing of edge structure, the use of non-relativistic wave functions, and the lack of appropriate convergence of wave functions. These discrepancies lead to significant corrections for most comprehensive (i.e. all-Z) tabulations. This work has led to a major comprehensive database tabulation [Chantler, C. T. (2000). J. Phys. Chem. Ref. Data, 29, 597-1048] which serves as a sequel and companion to earlier relativistic Dirac-Fock computations [Chantler, C. T. (1995). J. Phys. Chem. Ref. Data, 24, 71-643]. The paper finds that earlier work needs improvement in the near-edge region for soft X-ray energies, and derives new theoretical results of substantially higher accuracy in near-edge soft X-ray regions. Fine grids near edges are tabulated demonstrating the current comparison with alternate theory and with available experimental data. The best experimental data and the observed experimental structure as a function of energy are strong indicators of the validity of the current approach. New developments in experimental measurement hold great promise in making critical comparisons with theory in the near future. This work forms the latest component of the FFAST NIST database [http://physics.nist.gov/PhysRefData/FFast02/Text/cover.html].

  6. Reduced chromium in olivine grains from lunar basalt 15555 - X-ray Absorption Near Edge Structure (XANES)

    NASA Technical Reports Server (NTRS)

    Sutton, S. R.; Jones, K. W.; Gordon, B.; Rivers, M. L.; Bajt, S.; Smith, J. V.

    1993-01-01

    The oxidation state of Cr in 200-micron regions within individual lunar olivine and pyroxene grains from lunar basalt 15555 was inferred using X-ray Absorption Near Edge Structure (XANES). Reference materials had previously been studied by optical absorption spectroscopy and included Cr-bearing borosilicate glasses synthesized under controlled oxygen fugacity and Cr-doped olivines. The energy dependence of XANES spectral features defined by these reference materials indicated that Cr is predominantly divalent in the lunar olivine and trivalent in the pyroxene. These results, coupled with the apparent f(02)-independence of partitioning coefficients for Cr into olivine, imply that the source magma was dominated by divalent Cr at the time of olivine crystallization.

  7. Water ice self-absorption in three Ophiuchus edge-on disks

    NASA Astrophysics Data System (ADS)

    Duchene, Gaspard; Beck, Tracy; Grosso, Nicolas; McCabe, Caer; Menard, Francois; Pinte, Christophe

    2008-02-01

    We propose to use NIRI to measure the depth and shape of the 3(micron) water ice absorption feature in three edge-on disks in the Ophiuchus molecular cloud. This will provide us with an estimate of the total column density of ice in these disks and an indication of the thermal processing it has experienced. In protoplanetary disks, water ice coats dust grains in the majority of the disk volume and plays a major role in favoring grain-grain sticking during collisions, a key phenomenon towards the formation of planetesimals. In edge-on disks, the disk near- infrared thermal radiation, arising from the innermost regions, provides a continuous background that can be absorbed by water ice in the cold outer regions of the disks. These systems therefore offer a unique opportunity to probe water ice in protoplanetary disks. The proposed observations will double the number of edge-on disks with detected water ice absorption and represent the first such observations in the Ophiuchus molecular cloud.

  8. High-resolution molybdenum K-edge X-ray absorption spectroscopy analyzed with time-dependent density functional theory.

    PubMed

    Lima, Frederico A; Bjornsson, Ragnar; Weyhermüller, Thomas; Chandrasekaran, Perumalreddy; Glatzel, Pieter; Neese, Frank; DeBeer, Serena

    2013-12-28

    X-ray absorption spectroscopy (XAS) is a widely used experimental technique capable of selectively probing the local structure around an absorbing atomic species in molecules and materials. When applied to heavy elements, however, the quantitative interpretation can be challenging due to the intrinsic spectral broadening arising from the decrease in the core-hole lifetime. In this work we have used high-energy resolution fluorescence detected XAS (HERFD-XAS) to investigate a series of molybdenum complexes. The sharper spectral features obtained by HERFD-XAS measurements enable a clear assignment of the features present in the pre-edge region. Time-dependent density functional theory (TDDFT) has been previously shown to predict K-pre-edge XAS spectra of first row transition metal compounds with a reasonable degree of accuracy. Here we extend this approach to molybdenum K-edge HERFD-XAS and present the necessary calibration. Modern pure and hybrid functionals are utilized and relativistic effects are accounted for using either the Zeroth Order Regular Approximation (ZORA) or the second order Douglas-Kroll-Hess (DKH2) scalar relativistic approximations. We have found that both the predicted energies and intensities are in excellent agreement with experiment, independent of the functional used. The model chosen to account for relativistic effects also has little impact on the calculated spectra. This study provides an important calibration set for future applications of molybdenum HERFD-XAS to complex catalytic systems. PMID:24197060

  9. Experiment to Determine the Absorption Coefficient of Gamma Rays as a Function of Energy.

    ERIC Educational Resources Information Center

    Ouseph, P. J.; And Others

    1982-01-01

    Simpler than x-ray diffractometer experiments, the experiment described illustrates certain concepts regarding the interaction of electromagnetic rays with matter such as the exponential decrease in the intensity with absorber thickness, variation of the coefficient of absorption with energy, and the effect of the K-absorption edge on the…

  10. Quantitative investigation of two metallohydrolases by X-ray absorption spectroscopy near-edge spectroscopy

    NASA Astrophysics Data System (ADS)

    Zhao, W.; Chu, W. S.; Yang, F. F.; Yu, M. J.; Chen, D. L.; Guo, X. Y.; Zhou, D. W.; Shi, N.; Marcelli, A.; Niu, L. W.; Teng, M. K.; Gong, W. M.; Benfatto, M.; Wu, Z. Y.

    2007-09-01

    The last several years have witnessed a tremendous increase in biological applications using X-ray absorption spectroscopy (BioXAS), thanks to continuous advancements in synchrotron radiation (SR) sources and detector technology. However, XAS applications in many biological systems have been limited by the intrinsic limitations of the Extended X-ray Absorption Fine Structure (EXAFS) technique e.g., the lack of sensitivity to bond angles. As a consequence, the application of the X-ray absorption near-edge structure (XANES) spectroscopy changed this scenario that is now continuously changing with the introduction of the first quantitative XANES packages such as Minut XANES (MXAN). Here we present and discuss the XANES code MXAN, a novel XANES-fitting package that allows a quantitative analysis of experimental data applied to Zn K-edge spectra of two metalloproteins: Leptospira interrogans Peptide deformylase ( LiPDF) and acutolysin-C, a representative of snake venom metalloproteinases (SVMPs) from Agkistrodon acutus venom. The analysis on these two metallohydrolases reveals that proteolytic activities are correlated to subtle conformation changes around the zinc ion. In particular, this quantitative study clarifies the occurrence of the LiPDF catalytic mechanism via a two-water-molecules model, whereas in the acutolysin-C we have observed a different proteolytic activity correlated to structural changes around the zinc ion induced by pH variations.

  11. The effects of dust scattering on high-resolution X-ray absorption edge structure

    NASA Astrophysics Data System (ADS)

    Corrales, Lia; Garcia, Javier; Wilms, Joern; Baganoff, Frederick K.

    2016-04-01

    In high resolution X-ray spectroscopy, dust scattering significantly enhances the total extinction optical depth and alters the shape of photoelectric absorption edges. This effect is modulated by the dust grain size distribution, spatial location along the line of sight, and the imaging resolution of the X-ray telescope. We focus in particular on the Fe L-edge at 0.7 keV, fitting a template for the total extinction to the high resolution spectrum of three X-ray binaries from the Chandra archive: GX 9+9, XTE J1817-330, and Cyg X-1. In cases where dust is intrinsic to the source, a covering factor based on the angular extent of the dusty material must be applied to the extinction curve, regardless of imaging resolution. We discuss the various astrophysical cases in which scattering effects need to be taken into account.

  12. Three Dimensional Mapping of Nicle Oxidation States Using Full Field Xray Absorption Near Edge Structure Nanotomography

    SciTech Connect

    Nelson, G.J.; Chu, Y.; Harris, W.M.; Izzo, J.R.; Grew, K.N., Chiu, W.K.S.; Yi, J.; Andrews, J.C.; Liu, Y., Pierro, P.

    2011-04-28

    The reduction-oxidation cycling of the nickel-based oxides in composite solid oxide fuel cells and battery electrodes is directly related to cell performance. A greater understanding of nickel redox mechanisms at the microstructural level can be achieved in part using transmission x-ray microscopy (TXM) to explore material oxidation states. X-ray nanotomography combined with x-ray absorption near edge structure (XANES) spectroscopy has been applied to study samples containing distinct regions of nickel and nickel oxide (NiO) compositions. Digitally processed images obtained using TXM demonstrate the three-dimensional chemical mapping and microstructural distribution capabilities of full-field XANES nanotomography.

  13. Near-Edge X-Ray Absorption Fine Structures Revealed in Core Ionization Photoelectron Spectroscopy

    NASA Astrophysics Data System (ADS)

    Nakano, M.; Selles, P.; Lablanquie, P.; Hikosaka, Y.; Penent, F.; Shigemasa, E.; Ito, K.; Carniato, S.

    2013-09-01

    Simultaneous core ionization and core excitation have been observed in the C2H2n (n=1, 2, 3) molecular series using synchrotron radiation and a magnetic bottle time-of-flight electron spectrometer. Rich satellite patterns corresponding to (K-2V) core excited states of the K-1 molecular ions have been identified by detecting in coincidence the photoelectron with the two Auger electrons resulting from the double core hole relaxation. A theoretical model is proposed providing absolute photoionization cross sections and revealing clear signatures of direct (monopolar) and conjugate (dipolar near-edge x-ray absorption fine structure) shakeup lines of comparable magnitude.

  14. Near-edge x-ray absorption fine structures revealed in core ionization photoelectron spectroscopy.

    PubMed

    Nakano, M; Selles, P; Lablanquie, P; Hikosaka, Y; Penent, F; Shigemasa, E; Ito, K; Carniato, S

    2013-09-20

    Simultaneous core ionization and core excitation have been observed in the C(2)H(2n) (n=1, 2, 3) molecular series using synchrotron radiation and a magnetic bottle time-of-flight electron spectrometer. Rich satellite patterns corresponding to (K(-2)V) core excited states of the K(-1) molecular ions have been identified by detecting in coincidence the photoelectron with the two Auger electrons resulting from the double core hole relaxation. A theoretical model is proposed providing absolute photoionization cross sections and revealing clear signatures of direct (monopolar) and conjugate (dipolar near-edge x-ray absorption fine structure) shakeup lines of comparable magnitude. PMID:24093255

  15. Double conical crystal x-ray spectrometer for high resolution ultrafast x-ray absorption near-edge spectroscopy of Al K edge

    NASA Astrophysics Data System (ADS)

    Levy, A.; Dorchies, F.; Fourment, C.; Harmand, M.; Hulin, S.; Santos, J. J.; Descamps, D.; Petit, S.; Bouillaud, R.

    2010-06-01

    An x-ray spectrometer devoted to dynamical studies of transient systems using the x-ray absorption fine spectroscopy technique is presented in this article. Using an ultrafast laser-induced x-ray source, this optical device based on a set of two potassium acid phthalate conical crystals allows the extraction of x-ray absorption near-edge spectroscopy structures following the Al absorption K edge. The proposed experimental protocol leads to a measurement of the absorption spectra free from any crystal reflectivity defaults and shot-to-shot x-ray spectral fluctuation. According to the detailed analysis of the experimental results, a spectral resolution of 0.7 eV rms and relative fluctuation lower than 1% rms are achieved, demonstrated to be limited by the statistics of photon counting on the x-ray detector.

  16. Near-edge X-ray absorption spectroscopy signature of image potential states in multilayer epitaxial graphene

    NASA Astrophysics Data System (ADS)

    Coelho, P. M.; dos Reis, D. D.; Matos, M. J. S.; Mendes-de-Sa, T. G.; Goncalves, A. M. B.; Lacerda, R. G.; Malachias, A.; Magalhaes-Paniago, R.

    2016-02-01

    Single layer behavior in multilayer epitaxial graphene has been a matter of intense investigation. This is due to the layer decoupling that occurs during growth of graphene on some types of substrates, such as carbon-terminated silicon carbide. We show here that near-edge X-ray absorption spectroscopy can be used to observe the signature of this decoupling. To this end, samples of multilayer graphene from silicon carbide sublimation were grown with different degrees of decoupling. Raman spectroscopy was used to infer the degree of structural decoupling. X-ray grazing-incidence diffraction and scanning tunneling microscopy showed that growth initiates with the presence of bilayer graphene commensurate structures, while layer decoupling is associated to the formation of incommensurate structures observed for longer sublimation time. Near-edge X-ray absorption spectroscopy was used to probe the electronic states above the Fermi energy. Besides the σ* and π* empty states, image potential states are observed and show a clear change of intensity as a function of incident angle. These image potential states evolve from a graphite- to graphene-like behavior as a function of growth time and can be used to infer the degree of structural coupling among layers.

  17. An asymmetric BODIPY triad with panchromatic absorption for high-performance red-edge laser emission.

    PubMed

    Duran-Sampedro, Gonzalo; Agarrabeitia, Antonia R; Garcia-Moreno, Inmaculada; Gartzia-Rivero, Leire; de la Moya, Santiago; Bañuelos, Jorge; López-Arbeloa, Íñigo; Ortiz, María J

    2015-07-21

    A rational design of an unprecedented asymmetric cassette triad based entirely on BODIPY chromophores allows efficient light harvesting over the UV-vis spectral region, leading to a bright and stable red-edge laser emission via efficient energy-transfer processes. PMID:26084606

  18. Correction of absorption-edge artifacts in polychromatic X-ray tomography in a scanning electron microscope for 3D microelectronics.

    PubMed

    Laloum, D; Printemps, T; Lorut, F; Bleuet, P

    2015-01-01

    X-ray tomography is widely used in materials science. However, X-ray scanners are often based on polychromatic radiation that creates artifacts such as dark streaks. We show this artifact is not always due to beam hardening. It may appear when scanning samples with high-Z elements inside a low-Z matrix because of the high-Z element absorption edge: X-rays whose energy is above this edge are strongly absorbed, violating the exponential decay assumption for reconstruction algorithms and generating dark streaks. A method is proposed to limit the absorption edge effect and is applied on a microelectronic case to suppress dark streaks between interconnections. PMID:25638086

  19. Sub-gap and band edge optical absorption in a-Si:H by photothermal deflection spectroscopy

    NASA Astrophysics Data System (ADS)

    Jackson, W. B.; Amer, N. M.

    1981-07-01

    Using photothermal deflection spectroscopy, the optical absorption of various a-Si:H films was investigated in the range of 2.1 to 0.6 eV. An absorption shoulder which depends on deposition conditions and on doping was found and was attributed to dangling bonds. The exponential edge broadens with increasing spin density.

  20. Energy absorption of composite material and structure

    NASA Technical Reports Server (NTRS)

    Farley, Gary L.

    1987-01-01

    Results are presented from a joint research program on helicopter crashworthiness conducted by the U.S. Army Aerostructures Directorate and NASA Langley. Through the ongoing research program an in-depth understanding has been developed on the cause/effect relationships between material and architectural variables and the energy-absorption capability of composite material and structure. Composite materials were found to be efficient energy absorbers. Graphite/epoxy subfloor structures were more efficient energy absorbers than comparable structures fabricated from Kevlar or aluminum. An accurate method of predicting the energy-absorption capability of beams was developed.

  1. AKARI observations of ice absorption bands towards edge-on young stellar objects

    NASA Astrophysics Data System (ADS)

    Aikawa, Y.; Kamuro, D.; Sakon, I.; Itoh, Y.; Terada, H.; Noble, J. A.; Pontoppidan, K. M.; Fraser, H. J.; Tamura, M.; Kandori, R.; Kawamura, A.; Ueno, M.

    2012-02-01

    Context. Circumstellar disks and envelopes of low-mass young stellar objects (YSOs) contain significant amounts of ice. Such icy material will evolve to become volatile components of planetary systems, such as comets in our solar system. Aims: To investigate the composition and evolution of circumstellar ice around low-mass young stellar objects (YSOs), we observed ice absorption bands in the near infrared (NIR) towards eight YSOs ranging from class 0 to class II, among which seven are associated with edge-on disks. Methods: We performed slit-less spectroscopic observations using the grism mode of the InfraRed Camera (IRC) on board AKARI, which enables us to obtain full NIR spectra from 2.5 μm to 5 μm, including the CO2 band and the blue wing of the H2O band, which are inaccessible from the ground. We developed procedures to carefully process the spectra of targets with nebulosity. The spectra were fitted with polynomial baselines to derive the absorption spectra. The molecular absorption bands were then fitted with the laboratory database of ice absorption bands, considering the instrumental line profile and the spectral resolution of the grism dispersion element. Results: Towards the class 0-I sources (L1527, IRC-L1041-2, and IRAS 04302), absorption bands of H2O, CO2, CO, and XCN are clearly detected. Column density ratios of CO2 ice and CO ice relative to H2O ice are 21-28% and 13-46%, respectively. If XCN is OCN-, its column density is as high as 2-6% relative to H2O ice. The HDO ice feature at 4.1 μm is tentatively detected towards the class 0-I sources and HV Tau. Non-detections of the CH-stretching mode features around 3.5 μm provide upper limits to the CH3OH abundance of 26% (L1527) and 42% (IRAS 04302) relative to H2O. We tentatively detect OCS ice absorption towards IRC-L1041-2. Towards class 0-I sources, the detected features should mostly originate in the cold envelope, while CO gas and OCN- could originate in the region close to the protostar

  2. Tailoring of absorption edge by thermal annealing in tin oxide thin films

    SciTech Connect

    Thakur, Anup; Gautam, Sanjeev; Kumar, Virender; Chae, K. H.; Lee, Ik-Jae; Shin, Hyun Joon

    2015-05-15

    Tin oxide (SnO{sub 2}) thin films were deposited by radio-frequency (RF) magnetron sputtering on silicon and glass substrates in different oxygen-to-argon gas-flow ratio (O{sub 2}-to-Ar = 0%, 10%, 50%). All films were deposited at room temperature and fixed working pressures, 10 mTorr. The X-ray diffraction (XRD) measurement suggests that all films were crystalline in nature except film deposited in argon environment. Thin films were annealed in air at 200 °C, 400 °C and 600 °C for two hours. All films were highly transparent except the film deposited only in the argon environment. It was also observed that transparency was improved with annealing due to decrease in oxygen vacancies. Atomic force microscopy (AFM), results showed that the surface of all the films were highly flat and smooth. Blue shift was observed in the absorption edge with annealing temperature. It was also observed that there was not big change in the absorption edge with annealing for films deposited in 10% and 50% oxygen-to-argon gas-flow ratio.

  3. Photon interference effect in x-ray absorption spectra over a wide energy range

    NASA Astrophysics Data System (ADS)

    Nishino, Y.; Ishikawa, T.; Suzuki, M.; Kawamura, N.; Kappen, P.; Korecki, P.; Haack, N.; Materlik, G.

    2002-09-01

    We consider fundamental structures in x-ray absorption spectra over a wide energy range. We formulate the elastic scattering in addition to the photoelectric absorption in recently reported photon interference x-ray absorption fine structure (πXAFS). The simulations show excellent agreement with experimental x-ray absorption spectra for platinum and tungsten powders far above and below the L absorption edges. πXAFS can be as big as in the order of 10% of XAFS, and cannot be easily neglected in detailed analysis of XAFS and related phenomena.

  4. AKARI observations of ice absorption bands towards edge-on YSOs

    NASA Astrophysics Data System (ADS)

    Aikawa, Y.; Kamuro, D.; Sakon, I.; Itoh, Y.; Noble, J. A.; Pontoppidan, K. M., Fraser, H. J.; Terada, H.; Tamura, M.; Kandori, R.; Kawamura, A.; Ueno, M.

    2011-05-01

    Circumstellar disks and envelopes of low-mass YSOs contain significant amounts of ice. Such icy material will evolve to volatile components of planetary systems, such as comets in our solar system. In order to investigate the composition and evolution of circumstellar ice around low-mass YSOs, we have observed ice absorption bands towards eight YSOs ranging from class 0 to class II, among which seven are associated with edge-on disks. Slit-less spectroscopic observations are performed using the grism mode of Infrared Camera (IRC) on board AKARI, which enables us to obtain full NIR spectra from 2.5 μm to 5 μm, including the CO_2 band and the blue wing of the H_2O band, which are not accessible from the ground. We developed procedures to reduce the spectra of targets with nebulosity. The spectra are fitted with polynomial baselines to derive the absorption spectra. Then we fit the molecular absorption bands with the laboratory spectra from the database, considering the instrumental line profile and the spectral resolution of the dispersion element. Towards the Class 0-I sources, absorption bands of H_2O, CO_2, CO and XCN (OCN^-) are clearly detected. Weak features of 13CO_2, HDO, the C-H band, and gaseous CO are detected as well. OCS ice absorption is tentatively detected towards IRC-L1041-2. The detected features would mostly originate in the cold envelope, while CO gas and OCN^- could originate in the region close to the protostar. Towards class II stars, H_2O ice band is detected. We also detected H_2O ice, CO_2 ice and tentative CO gas features of the foreground component of class II stars.

  5. The origin of luminescence from di[4-(4-diphenylaminophenyl)phenyl]sulfone (DAPSF), a blue light emitter: an X-ray excited optical luminescence (XEOL) and X-ray absorption near edge structure (XANES) study.

    PubMed

    Zhang, Duo; Zhang, Hui; Zhang, Xiaohong; Sham, Tsun-Kong; Hu, Yongfeng; Sun, Xuhui

    2016-02-24

    The electronic structure and optical properties of di[4-(4-diphenylaminophenyl)phenyl]sulfone (denoted as DAPSF), a highly efficient fluorophor, have been investigated using X-ray excited optical luminescence (XEOL) and X-ray absorption near edge structure (XANES) spectroscopy at excitation energies across the C, N, O K-edges and the sulfur K-edge. The results indicate that the blue luminescence is mainly related to the sulfur functional group. PMID:26866785

  6. Extension to Low Energies (<7keV) of High Pressure X-Ray Absorption Spectroscopy

    SciTech Connect

    Itie, J.-P.; Flank, A.-M.; Lagarde, P.; Idir, M.; Polian, A.; Couzinet, B.

    2007-01-19

    High pressure x-ray absorption has been performed down to 3.6 keV, thanks to the new LUCIA beamline (SLS, PSI) and to the use of perforated diamonds or Be gasket. Various experimental geometries are proposed, depending on the energy of the edge and on the concentration of the studied element. A few examples will be presented: BaTiO3 at the titanium K edge, Zn0.95 Mn0.05O at the manganese K edge, KCl at the potassium K edge.

  7. Oxygen K-edge absorption spectra of small molecules in the gas phase

    SciTech Connect

    Yang, B.X.; Kirz, J.; Sham, T.K.

    1986-01-01

    The absorption spectra of O/sub 2/, CO, CO/sub 2/ and OCS have been recorded in a transmission mode in the energy region from 500 to 950 eV. Recent observation of EXAFS in these molecules is confirmed in this study. 7 refs., 3 figs.

  8. Quantum Monte Carlo for the x-ray absorption spectrum of pyrrole at the nitrogen K-edge

    SciTech Connect

    Zubarev, Dmitry Yu.; Austin, Brian M.; Lester, William A. Jr.

    2012-04-14

    Fixed-node diffusion Monte Carlo (FNDMC) is used to simulate the x-ray absorption spectrum of a gas-phase pyrrole molecule at the nitrogen K-edge. Trial wave functions for core-excited states are constructed from ground-state Kohn-Sham determinants substituted with singly occupied natural orbitals from configuration interaction with single excitations calculations of the five lowest valence-excited triplet states. The FNDMC ionization potential (IP) is found to lie within 0.3 eV of the experimental value of 406.1 {+-} 0.1 eV. The transition energies to anti-bonding virtual orbitals match the experimental spectrum after alignment of IP values and agree with the existing assignments.

  9. Molybdenum X-ray absorption edges from 200 to 20,000eV: the benefits of soft X-ray spectroscopy for chemical speciation.

    PubMed

    George, Simon J; Drury, Owen B; Fu, Juxia; Friedrich, Stephan; Doonan, Christian J; George, Graham N; White, Jonathan M; Young, Charles G; Cramer, Stephen P

    2009-02-01

    We have surveyed the chemical utility of the near-edge structure of molybdenum X-ray absorption edges from the hard X-ray K-edge at 20,000eV down to the soft X-ray M(4,5)-edges at approximately 230eV. We compared, for each edge, the spectra of two tetrahedral anions, MoO(4)(2-) and MoS(4)(2-). We used three criteria for assessing near-edge structure of each edge: (i) the ratio of the observed chemical shift between MoO(4)(2-) and MoS(4)(2-) and the linewidth, (ii) the chemical information from analysis of the near-edge structure and (iii) the ease of measurement using fluorescence detection. Not surprisingly, the K-edge was by far the easiest to measure, but it contained the least information. The L(2,3)-edges, although harder to measure, had benefits with regard to selection rules and chemical speciation in that they had both a greater chemical shift as well as detailed lineshapes which could be theoretically analyzed in terms of Mo ligand field, symmetry, and covalency. The soft X-ray M(2,3)-edges were perhaps the least useful, in that they were difficult to measure using fluorescence detection and had very similar information content to the corresponding L(2,3)-edges. Interestingly, the soft X-ray, low energy ( approximately 230eV) M(4,5)-edges had greatest potential chemical sensitivity and using our high-resolution superconducting tunnel junction (STJ) fluorescence detector they appear to be straightforward to measure. The spectra were amenable to analysis using both the TT-multiplet approach and FEFF. The results using FEFF indicate that the sharp near-edge peaks arise from 3d-->5p transitions, while the broad edge structure has predominately 3d-->4f character. A proper understanding of the dependence of these soft X-ray spectra on ligand field and site geometry is necessary before a complete assessment of the utility of the Mo M(4,5)-edges can be made. This work includes crystallographic characterization of sodium tetrathiomolybdate. PMID:19041140

  10. Molybdenum X-Ray Absorption Edges from 200 – 20,000 eV, The Benefits of Soft X-Ray Spectroscopy for Chemical Speciation

    PubMed Central

    George, Simon J.; Drury, Owen B.; Fu, Juxia; Friedrich, Stephan; Doonan, Christian J.; George, Graham N.; White, Jonathan M.; Young, Charles G.; Cramer, Stephen P.

    2009-01-01

    We have surveyed the chemical utility of the near-edge structure of molybdenum x-ray absorption edges from the hard x-ray K-edge at 20,000 eV down to the soft x-ray M4,5-edges at ~230 eV. We compared, for each edge, the spectra of two tetrahedral anions, MoO4 and MoS42-. We used three criteria for assessing near-edge structure of each edge: (i) the ratio of the observed chemical shift between MoO42- and MoS42- and the linewidth, (ii) the chemical information from analysis of the near-edge structure and (iii) the ease of measurement using fluorescence detection. Not surprisingly, the K-edge was by far the easiest to measure, but it contained the least information. The L2,3-edges, although harder to measure, had benefits with regard to selection rules and chemical speciation in that they had both a greater chemical shift as well as detailed lineshapes which could be theoretically analyzed in terms of Mo ligand field, symmetry, and covalency. The soft x-ray M2,3-edges were perhaps the least useful, in that they were difficult to measure using fluorescence detection and had very similar information content to the corresponding L2,3-edges. Interestingly, the soft x-ray, low energy (~230 eV) M4,5-edges had greatest potential chemical sensitivity and using our high resolution superconducting tunnel junction (STJ) fluorescence detector they appear to be straightforward to measure. The spectra were amenable to analysis using both the TT-multiplet approach and FEFF. The results using FEFF indicate that the sharp near-edge peaks arise from 3d → 5p transitions, while the broad edge structure has predominately 3d → 4f character. A proper understanding of the dependence of these soft x-ray spectra on ligand field and site geometry is necessary before a complete assessment of the utility of the Mo M4,5-edges can be made. This work includes crystallographic characterization of sodium tetrathiomolybdate. PMID:19041140

  11. X-ray absorption near edge spectroscopy with a superconducting detector for nitrogen dopants in SiC

    PubMed Central

    Ohkubo, M.; Shiki, S.; Ukibe, M.; Matsubayashi, N.; Kitajima, Y.; Nagamachi, S.

    2012-01-01

    Fluorescence-yield X-ray absorption fine structure (FY-XAFS) is extensively used for investigating atomic-scale local structures around specific elements in functional materials. However, conventional FY-XAFS instruments frequently cannot cover trace light elements, for example dopants in wide gap semiconductors, because of insufficient energy resolution of semiconductor X-ray detectors. Here we introduce a superconducting XAFS (SC-XAFS) apparatus to measure X-ray absorption near-edge structure (XANES) of n-type dopant N atoms (4 ×1019 cm−3) implanted at 500°C into 4H-SiC substrates annealed subsequently. The XANES spectra and ab initio multiple scattering calculations indicate that the N atoms almost completely substitute for the C sites, associated with a possible existence of local CN regions, in the as-implanted state. This is a reason why hot implantation is necessary for dopant activation in ion implantation. The SC-XAFS apparatus may play an important role in improving doping processes for energy-saving wide-gap semiconductors and other functional materials. PMID:23152937

  12. Parameters Influencing Sulfur Speciation in Environmental Samples Using Sulfur K-Edge X-Ray Absorption Near-Edge Structure

    PubMed Central

    Pongpiachan, Siwatt; Thumanu, Kanjana; Kositanont, Charnwit; Schwarzer, Klaus; Prietzel, Jörg; Hirunyatrakul, Phoosak; Kittikoon, Itthipon

    2012-01-01

    This paper aims to enhance the credibility of applying the sulfur K-edge XANES spectroscopy as an innovative “fingerprint” for characterizing environmental samples. The sensitivities of sulfur K-edge XANES spectra of ten sulfur compound standards detected by two different detectors, namely, Lytle detector (LyD) and Germanium detector (GeD), were studied and compared. Further investigation on “self-absorption” effect revealed that the maximum sensitivities of sulfur K-edge XANES spectra were achieved when diluting sulfur compound standards with boron nitride (BN) at the mixing ratio of 0.1%. The “particle-size” effect on sulfur K-edge XANES spectrum sensitivities was examined by comparing signal-to-noise ratios of total suspended particles (TSP) and particulate matter of less than 10 millionths of a meter (PM10) collected at three major cities of Thailand. The analytical results have demonstrated that the signal-to-noise ratios of sulfur K-edge XANES spectra were positively correlated with sulfate content in aerosols and negatively connected with particle sizes. The combination of hierarchical cluster analysis (HCA) and principal component analysis (PCA) has proved that sulfur K-edge XANES spectrum can be used to characterize German terrestrial soils and Andaman coastal sediments. In addition, this study highlighted the capability of sulfur K-edge XANES spectra as an innovative “fingerprint” to distinguish tsunami backwash deposits (TBD) from typical marine sediments (TMS). PMID:23193498

  13. NO binding kinetics in myoglobin investigated by picosecond Fe K-edge absorption spectroscopy

    PubMed Central

    Silatani, Mahsa; Lima, Frederico A.; Penfold, Thomas J.; Rittmann, Jochen; Reinhard, Marco E.; Rittmann-Frank, Hannelore M.; Borca, Camelia; Grolimund, Daniel; Milne, Christopher J.; Chergui, Majed

    2015-01-01

    Diatomic ligands in hemoproteins and the way they bind to the active center are central to the protein’s function. Using picosecond Fe K-edge X-ray absorption spectroscopy, we probe the NO-heme recombination kinetics with direct sensitivity to the Fe-NO binding after 532-nm photoexcitation of nitrosylmyoglobin (MbNO) in physiological solutions. The transients at 70 and 300 ps are identical, but they deviate from the difference between the static spectra of deoxymyoglobin and MbNO, showing the formation of an intermediate species. We propose the latter to be a six-coordinated domed species that is populated on a timescale of ∼200 ps by recombination with NO ligands. This work shows the feasibility of ultrafast pump–probe X-ray spectroscopic studies of proteins in physiological media, delivering insight into the electronic and geometric structure of the active center. PMID:26438842

  14. Variation in optical-absorption edge in SiN{sub x} layers with silicon clusters

    SciTech Connect

    Efremov, M. D. Volodin, V. A.; Marin, D. V.; Arzhannikova, S. A.; Kamaev, G. N.; Kochubei, S. A.; Popov, A. A.

    2008-02-15

    Using optical methods, data on optical constants are obtained for silicon nitride films synthesized by plasma-chemical vapor deposition (PCVD). Models for calculating the permittivity in the model of inhomogeneous phase mixture of silicon and silicon nitride are considered. It is found that the optical-absorption edge (E{sub g}) and the photoluminescence peak shift to longer wavelengths with increasing nitrogen atomic fraction x in sin{sub x} films. When x approaches the value 4/3 characteristic for stoichiometric silicon nitride Si{sub 3}N{sub 4}, a nonlinear sharp increase in E{sub g} is observed. Using Raman scattering, Si-Si bonds are revealed, which confirms the direct formation of silicon clusters during the film deposition. The relation between the composition of nonstoichiometric silicon nitride films, values of permittivity, and the optical-band width is established for light transmission.

  15. Structural analysis of sulfur in natural rubber using X-ray absorption near-edge spectroscopy.

    PubMed

    Pattanasiriwisawa, Wanwisa; Siritapetawee, Jaruwan; Patarapaiboolchai, Orasa; Klysubun, Wantana

    2008-09-01

    X-ray absorption near-edge spectroscopy (XANES) has been applied to natural rubber in order to study the local environment of sulfur atoms in sulfur crosslinking structures introduced in the vulcanization process. Different types of chemical accelerators in conventional, semi-efficient and efficient vulcanization systems were investigated. The experimental results show the good sensitivity and reproducibility of XANES to characterize the local geometry and electronic environment of the sulfur K-shell under various conditions of vulcanization and non-vulcanization of natural rubber. Several applications of XANES in this study demonstrate an alternative way of identifying sulfur crosslinks in treated natural rubber based on differences in their spectra and oxidation states. PMID:18728323

  16. Role of exciton-phonon interactions and disordering processes in the formation of the absorption edge in Cu6P(S1- x Sex)5Br crystals

    NASA Astrophysics Data System (ADS)

    Studenyak, I. P.; Kranjcec, M.; Suslikov, L. M.; Kovacs, D. Sh.; Pan'ko, V. V.

    2002-04-01

    The absorption edge in Cu6P(S1- x Sex)5Br crystals has been studied for strong absorption in the temperature range of 77 330 K. The parameters of the Urbach absorption edge and exciton-phonon interactions in Cu6P(S1- x Sex)5Br crystals are determined and their effect on the composition disorder is studied.

  17. A microsecond time resolved x-ray absorption near edge structure synchrotron study of phase transitions in Fe undergoing ramp heating at high pressure

    SciTech Connect

    Marini, C.; Mathon, O.; Pascarelli, S.; Occelli, F.; Torchio, R.; Recoules, V.; Loubeyre, P.

    2014-03-07

    We report a microsecond time-resolved x-ray absorption near edge structure study using synchrotron radiation to dynamically detect structural phase transitions in Fe undergoing rapid heating along a quasi-isochoric path. Within a few ms, we observed two structural phase transitions, which transform the ambient bcc phase of Fe into the fcc phase, and then into the liquid phase. This example illustrates the opportunities offered by energy dispersive x-ray absorption spectroscopy in the study of matter under extreme dynamic conditions. Advanced simulations are compared to these data.

  18. Time-Dependent Density Functional Calculations of Ligand K-Edge X-Ray Absorption Spectra

    SciTech Connect

    DeBeer George, S.; Petrenko, T.; Neese, F.

    2007-07-10

    X-ray absorption spectra (XAS) at the Cl and S K edge and Mo L edge have been calculated at the TDDFT level for a series of dioxomolybdenum complexes LMoO{sub 2}X (L = hydrotris(3,5-dimethyl-1-pyrazolyl)borate, X = Cl, SCH{sub 2}Ph, OPh), which play an important role in modeling the catalytic cycle of the sulfite oxidase enzyme. Also, the XAS spectra of model molecules of the Mo complexes have been simulated and interpreted in terms of the Mo 4d orbital splitting, in order to find possible correlations with the spectral pattern of the complexes. Comparison with the available experimental data allows us to assess the performances of the present computational scheme to describe the core excitations in large bioinorganic systems. The theoretical interpretation of the spectral features of both the metal and ligand core excitations in terms of the oscillator strength distribution provides important insight into the covalency of the metal-ligand bond.

  19. Evaluation of iron-containing carbon nanotubes by near edge X-ray absorption technique

    NASA Astrophysics Data System (ADS)

    Osorio, A. G.; Bergmann, C. P.

    2015-10-01

    The synthesis of carbon nanotubes (CNTs) via Chemical Vapor Deposition method with ferrocene results in CNTs filled with Fe-containing nanoparticles. The present work proposes a novel route to characterize the Fe phases in CNTs inherent to the synthesis process. CNTs were synthesized and, afterwards, the CNTs were heat treated at 1000 °C for 20 min in an inert atmosphere during a thermogravimetric experiment. X-Ray Absorption Spectroscopy (XAS) experiments were performed on the CNTs before and after the heat treatment and, also, during the heat treatment, e.g., in situ tests were performed while several Near-Edge X-Ray Absorption (XANES) spectra were collected during the heating of the samples. The XAS technique was successfully applied to evaluate the phases encapsulated by CNTs. Phase transformations of the Fe-based nanoparticles were also observed from iron carbide to metallic iron when the in situ experiments were performed. Results also indicated that the applied synthesis method guarantees that Fe phases are not oxidize. In addition, the results show that heat treatment under inert atmosphere can control which phase remains encapsulated by the CNTs.

  20. Isoabsorption and spectrometric studies of optical absorption edge in Cu6AsS5I superionic crystal

    NASA Astrophysics Data System (ADS)

    Studenyak, I. P.; Kayla, M. I.; Kranjčec, M.; Kokhan, O. P.; Minets, Yu. V.

    2011-12-01

    Cu6AsS5I single crystals were grown using chemical vapour transport method. Two low-temperature phase transitions (PT) are observed from isoabsorption studies: a first-order PT at ТІ=153±1 K and a second-order PT in the temperature interval TІI=260-280 K. At low temperatures and high absorption levels an excitonic absorption band was revealed in the range of direct optical transitions. At Т>ТІ, the absorption edge has an exponential shape and a characteristic Urbach bundle is observed. The influence of the cationic P→As substitution on the parameters of the Urbach absorption edge, parameters of exciton-phonon interaction, and phase transitions temperatures are studied.

  1. First-principles study of phonon effects in x-ray absorption near-edge structure spectroscopy

    NASA Astrophysics Data System (ADS)

    Nemausat, R.; Brouder, Ch; Gervais, Ch; Cabaret, D.

    2016-05-01

    Usually first-principles x-ray absorption near-edge structure (XANES) calculations are performed in the Born-Oppenheimer approximation assuming a static lattice, whereas the nuclear motion undoubtedly impacts XANES spectra notably at the K pre-edge of light elements in oxides. Here, an efficient method based on density-functional theory to account for quantum thermal fluctuations of nuclei is developed and is successfully applied to the K edge of corundum for temperatures up to 930 K. The zero-point motion influence is estimated. Comparison is made with previous theoretical approaches also developed to account for vibrations in XANES.

  2. Nitrogen K-edge X-ray absorption near edge structure (XANES) spectra of purine-containing nucleotides in aqueous solution

    NASA Astrophysics Data System (ADS)

    Shimada, Hiroyuki; Fukao, Taishi; Minami, Hirotake; Ukai, Masatoshi; Fujii, Kentaro; Yokoya, Akinari; Fukuda, Yoshihiro; Saitoh, Yuji

    2014-08-01

    The N K-edge X-ray absorption near edge structure (XANES) spectra of the purine-containing nucleotide, guanosine 5'-monophosphate (GMP), in aqueous solution are measured under various pH conditions. The spectra show characteristic peaks, which originate from resonant excitations of N 1s electrons to π* orbitals inside the guanine moiety of GMP. The relative intensities of these peaks depend on the pH values of the solution. The pH dependence is explained by the core-level shift of N atoms at specific sites caused by protonation and deprotonation. The experimental spectra are compared with theoretical spectra calculated by using density functional theory for GMP and the other purine-containing nucleotides, adenosine 5'-monophosphate, and adenosine 5'-triphosphate. The N K-edge XANES spectra for all of these nucleotides are classified by the numbers of N atoms with particular chemical bonding characteristics in the purine moiety.

  3. Probing Warm Dense Matter electronic structure using X-ray absorption Near Edge Spectroscopy (XANES)

    NASA Astrophysics Data System (ADS)

    Benuzzi Mounaix, Alessandra

    2011-06-01

    The behavior and physical properties of warm dense matter, fundamental for various branches of physics including planetology and Inertial Confinement Fusion, are non trivial to simulate either theoretically, numerically or experimentally. Despite important progress obtained in the last decade on macroscopic characterization (e.g. equations of state), microscopic studies are today necessary to investigate finely the WDM structure changes, the phase transitions and to test physical hypothesis and approximations commonly used in calculations. In this work, highly compressed aluminum has been investigated with the aim of bringing information on the evolution of its electronic structure by using K-edge shift and XANES. The experiment was performed at LULI laboratory where we used one long pulse (500 ps, IL ~ 8 1013 W/cm2) to create a uniform shock and a second ps beam (IL ~ 1017 W/cm2) to generate an ultra-short broadband X-ray source near the Al K-edge. The spectra were registered by using two conical KAP Bragg crystals. The main target was designed to probe the Aluminum in reshocked conditions allowing us to probe and to test theories in an extreme regime up to now unexplored (ρ ~ 3 ρ0 and T ~ 8 eV). The hydrodynamical Al conditions were measured by using VISARs interferometers and self-emission diagnostics. By increasing the delay between the two beams, we have been able to observe the modification of absorption spectra for unloading Al conditions (ρ >= 0.5 g/cc), and to put in evidence the relocalization of the 3p valence electrons occurring in the metal-non metal transition. All data have been compared to ab initio and dense plasma calculations.

  4. 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.

  5. Link between K absorption edges and thermodynamic properties of warm dense plasmas established by an improved first-principles method

    NASA Astrophysics Data System (ADS)

    Zhang, Shen; Zhao, Shijun; Kang, Wei; Zhang, Ping; He, Xian-Tu

    2016-03-01

    A precise calculation that translates shifts of x-ray K absorption edges to variations of thermodynamic properties allows quantitative characterization of interior thermodynamic properties of warm dense plasmas by x-ray absorption techniques, which provides essential information for inertial confinement fusion and other astrophysical applications. We show that this interpretation can be achieved through an improved first-principles method. Our calculation shows that the shift of K edges exhibits selective sensitivity to thermal parameters and thus would be a suitable temperature index to warm dense plasmas. We also show with a simple model that the shift of K edges can be used to detect inhomogeneity inside warm dense plasmas when combined with other experimental tools.

  6. Absorption edge and the refractive index dispersion of carbon-nickel composite films at different annealing temperatures

    NASA Astrophysics Data System (ADS)

    Dalouji, Vali; Elahi, Seyed Mohammad; Solaymani, Shahram; Ghaderi, Atefeh

    2016-04-01

    In this paper, the optical properties of carbon-nickel films annealed at different temperatures 300, 500, 800 and 1000 ° C, with a special emphasis on the absorption edge, were investigated. The optical transmittance spectra in the wavelength range 300-1000nm were used to compute the absorption coefficient. The optical dispersion parameters were calculated according to Wemple and DiDomenico (WDD) single-oscillator model. Photoluminescence (PL) measurements of carbon-nickel films exhibit two main peaks at about 2.5 and 3.3eV which correspond to the fundamental indirect and direct gap, respectively. The field emission scanning electron microscopy (FESEM) showed that the absorption edge in the films was controlled by the nanoparticle size. The films annealed at 500 ° C have minimum indirect optical band gap and maximum disorder.

  7. Ligand K-edge x-ray absorption spectroscopy as a probe of ligand-metal bonding: Charge donation and covalency in copper-chloride systems

    SciTech Connect

    Shadle, S.E.; Hedman, B.; Solomon, E.I.; Hodgson, K.O.

    1994-09-14

    X-ray absorption spectra (XAS) have been measured at the chloride K-edge for a series of complexes containing chloride ligands bound to open shell d{sup 9} copper ions in order to probe ligand-metal bonding. The intensity of the pre-edge feature in these spectra reflects the covalency in the half-occupied d{sub x}{sup 2-}{sub y}{sup 2-} derived molecular orbital (HOMO) of the complex. The energy of the pre-edge feature as well as the energy of the rising absorption edge provides quantitative information about the covalency of the ligand-metal interaction, the charge donated by the chloride, and the energy of the copper d-manifold. The results demonstrate that ligand K-edge XAS features can be used to obtain information about ligand-metal bonding. The results also identify the chemical basis for trends in the XAS data for the following complexes: D{sub 4h} CuCl{sub 4}{sup 2-}, D{sub 2d} CuCl{sub 4}{sup 2-}, planar trans-CuCl{sub 2-} (pdmp){sub 2} (pdmp = N-phenyl-3,5-dimethylpyrazole), square pyramidal CuCl{sub 5}{sup 3-}, the planar dimer KCuCl{sub 3}, the distorted tetrahedral dimer (Ph{sub 4}P)CuCl{sub 3}, and two dimers with mixed ligation, one containing a bridging chloride, and the other, containing terminally bound chloride. Several of these results are supported by independent spectral data or by basic ligand field concepts. A geometric distortion from square planar to distorted tetrahedral results in a decrease in the chloride-copper HOMO covalency but an increase in the total charge donation by the chlorides. While the geometry can maximize the overlap for a highly covalent HOMO, this does not necessarily reflect the overall charge donation.

  8. Iron near absorption edge X-ray spectroscopy at aqueous-membrane interfaces

    SciTech Connect

    Wang, Wenjie; Kuzmenko, Ivan; Vaknin, David

    2014-01-01

    Employing synchrotron X-ray scattering, we systematically determine the absorption near-edge spectra (XANES) of iron in its ferrous (Fe2+) and ferric (Fe3+) states both as ions in aqueous solutions and as they bind to form a single layer to anionic templates that consist of carboxyl or phosphate groups at aqueous/vapor interfaces. While the XANES of bulk iron ions show that the electronic state and coordination of iron complexes in the bulk are isotropic, the interfacial bound ions show a signature of a broken inversion-symmetry environment. The XANES of Fe2+ and Fe3+ in the bulk possess distinct profiles however, upon binding they practically exhibit similar patterns. This indicates that both bound ions settle into a stable electronic and coordination configuration with an effective fractional valence (for example, Fe[2+nu]+, 0 < nu < 1) at charged organic templates. Such two dimensional properties may render interfacial iron, abundant in living organisms, a more efficient and versatile catalytic behavior.

  9. Tunable Q-switched fiber laser based on saturable edge-state absorption in few-layer molybdenum disulfide (MoS₂).

    PubMed

    Woodward, R I; Kelleher, E J R; Howe, R C T; Hu, G; Torrisi, F; Hasan, T; Popov, S V; Taylor, J R

    2014-12-15

    We fabricate a few-layer molybdenum disulfide (MoS₂) polymer composite saturable absorber by liquid-phase exfoliation, and use this to passively Q-switch an ytterbium-doped fiber laser, tunable from 1030 to 1070 nm. Self-starting Q-switching generates 2.88 μs pulses at 74 kHz repetition rate, with over 100 nJ pulse energy. We propose a mechanism, based on edge states within the bandgap, responsible for the wideband nonlinear optical absorption exhibited by our few-layer MoS₂ sample, despite operating at photon energies lower than the material bandgap. PMID:25607060

  10. Simulating Ru L3-Edge X-ray Absorption Spectroscopy with Time-Dependent Density Functional Theory: Model Complexes and Electron Localization in Mixed-Valence Metal Dimers

    SciTech Connect

    Kuiken, Benjamin E. Van; Valiev, Marat; Daifuku, Stephanie L.; Bannan, Caitlin; Strader, Matthew L.; Cho, Hana; Huse, Nils; Schoenlein, Robert W.; Govind, Niranjan; Khalil, Munira

    2013-04-26

    Ruthenium L3-edge X-ray absorption (XA) spectroscopy probes unoccupied 4d orbitals of the metal atom and is increasingly being used to investigate the local electronic structure in ground and excited electronic states of Ru complexes. The simultaneous development of computational tools for simulating Ru L3-edge spectra is crucial for interpreting the spectral features at a molecular level. This study demonstrates that time-dependent density functional theory (TDDFT) is a viable and predictive tool for simulating ruthenium L3-edge XA spectroscopy. We systematically investigate the effects of exchange correlation functional and implicit and explicit solvent interactions on a series of RuII and RuIII complexes in their ground and electronic excited states. The TDDFT simulations reproduce all of the experimentally observed features in Ru L3-edge XA spectra within the experimental resolution (0.4 eV). Our simulations identify ligand-specific charge transfer features in complicated Ru L3-edge spectra of [Ru(CN)6]4- and RuII polypyridyl complexes illustrating the advantage of using TDDFT in complex systems. We conclude that the B3LYP functional most accurately predicts the transition energies of charge transfer features in these systems. We use our TDDFT approach to simulate experimental Ru L3-edge XA spectra of transition metal mixed-valence dimers of the form [(NC)5MII-CN-RuIII(NH3)5] (where M = Fe or Ru) dissolved in water. Our study determines the spectral signatures of electron delocalization in Ru L3-edge XA spectra. We find that the inclusion of explicit solvent molecules is necessary for reproducing the spectral features and the experimentally determined valencies in these mixed-valence complexes. This study validates the use of TDDFT for simulating Ru 2p excitations using popular quantum chemistry codes and providing a powerful interpretive tool for equilibrium and ultrafast Ru L3-edge XA spectroscopy.

  11. Characterization of Oxygen Containing Functional Groups on Carbon Materials with Oxygen K-edge X-ray Absorption Near Edge Structure Spectroscopy

    SciTech Connect

    K Kim; P Zhu; L Na; X Ma; Y Chen

    2011-12-31

    Surface functional groups on carbon materials are critical to their surface properties and related applications. Many characterization techniques have been used to identify and quantify the surface functional groups, but none is completely satisfactory especially for quantification. In this work, we used oxygen K-edge X-ray absorption near edge structure (XANES) spectroscopy to identify and quantify the oxygen containing surface functional groups on carbon materials. XANES spectra were collected in fluorescence yield mode to minimize charging effect due to poor sample conductivity which can potentially distort XANES spectra. The surface functional groups are grouped into three types, namely carboxyl-type, carbonyl-type, and hydroxyl-type. XANES spectra of the same type are very similar while spectra of different types are significantly different. Two activated carbon samples were analyzed by XANES. The total oxygen contents of the samples were estimated from the edge step of their XANES spectra, and the identity and abundance of different functional groups were determined by fitting of the sample XANES spectrum to a linear combination of spectra of the reference compounds. It is concluded that oxygen K-edge XANES spectroscopy is a reliable characterization technique for the identification and quantification of surface functional groups on carbon materials.

  12. Calibration of scalar relativistic density functional theory for the calculation of sulfur K-edge X-ray absorption spectra.

    PubMed

    Debeer George, Serena; Neese, Frank

    2010-02-15

    Sulfur K-edge X-ray absorption spectroscopy has been proven to be a powerful tool for investigating the electronic structures of sulfur-containing coordination complexes. The full information content of the spectra can be developed through a combination of experiment and time-dependent density functional theory (TD-DFT). In this work, the necessary calibration is carried out for a range of contemporary functionals (BP86, PBE, OLYP, OPBE, B3LYP, PBE0, TPSSh) in a scalar relativistic (0(th) order regular approximation, ZORA) DFT framework. It is shown that with recently developed segmented all-electron scalar relativistic (SARC) basis sets one obtains results that are as good as with large, uncontracted basis sets. The errors in the calibrated transition energies are on the order of 0.1 eV. The error in calibrated intensities is slightly larger, but the calculations are still in excellent agreement with experiment. The behavior of full TD-DFT linear response versus the Tamm-Dancoff approximation has been evaluated with the result that two methods are almost indistinguishable. The inclusion of relativistic effects barely changes the results for first row transition metal complexes, however, the contributions become visible for second-row transition metals and reach a maximum (of an approximately 10% change in the calibration parameters) for third row transition metal species. The protocol developed here is approximately 10 times more efficient than the previously employed protocol, which was based on large, uncontracted basis sets. The calibration strategy followed here may be readily extended to other edges. PMID:20092349

  13. Inorganic iodine incorporation into soil organic matter: evidence from iodine K-edge X-ray absorption near-edge structure.

    PubMed

    Yamaguchi, Noriko; Nakano, Masashi; Takamatsu, Rieko; Tanida, Hajime

    2010-06-01

    The transformation of inorganic iodine (I(-) and IO(3)(-)) incubated in soils with varying amounts of organic matter (Andosols from the surface layer of an upland field and forest, as well as Acrisols from surface and subsurface layers of an upland field) was investigated by using the iodine K-edge X-ray absorption near-edge structure (XANES). After 60d of reaction, both I(-) and IO(3)(-) were transformed into organoiodine in surface soils containing sufficient amounts of organic matter, whereas IO(3)(-) remained unchanged in the subsurface soil of Acrisols with low organic matter contents. Transformation of IO(3)(-) into organoiodine was not retarded when the microbial activity in soil was reduced by gamma-ray irradiation, suggesting that microbial activity was not essential for the transformation of inorganic iodine into organoiodine. Soil organic matter has the ability to transform inorganic iodine into organoiodine. PMID:18640749

  14. 14 CFR 29.727 - Reserve energy absorption drop test.

    Code of Federal Regulations, 2014 CFR

    2014-01-01

    ... 14 Aeronautics and Space 1 2014-01-01 2014-01-01 false Reserve energy absorption drop test. 29.727 Section 29.727 Aeronautics and Space FEDERAL AVIATION ADMINISTRATION, DEPARTMENT OF TRANSPORTATION....727 Reserve energy absorption drop test. The reserve energy absorption drop test must be conducted...

  15. 14 CFR 23.727 - Reserve energy absorption drop test.

    Code of Federal Regulations, 2014 CFR

    2014-01-01

    ... 14 Aeronautics and Space 1 2014-01-01 2014-01-01 false Reserve energy absorption drop test. 23.727... Construction Landing Gear § 23.727 Reserve energy absorption drop test. (a) If compliance with the reserve energy absorption requirement in § 23.723(b) is shown by free drop tests, the drop height may not be...

  16. 14 CFR 27.727 - Reserve energy absorption drop test.

    Code of Federal Regulations, 2014 CFR

    2014-01-01

    ... 14 Aeronautics and Space 1 2014-01-01 2014-01-01 false Reserve energy absorption drop test. 27.727 Section 27.727 Aeronautics and Space FEDERAL AVIATION ADMINISTRATION, DEPARTMENT OF TRANSPORTATION... Reserve energy absorption drop test. The reserve energy absorption drop test must be conducted as...

  17. 14 CFR 27.727 - Reserve energy absorption drop test.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ... 14 Aeronautics and Space 1 2010-01-01 2010-01-01 false Reserve energy absorption drop test. 27.727 Section 27.727 Aeronautics and Space FEDERAL AVIATION ADMINISTRATION, DEPARTMENT OF TRANSPORTATION... Reserve energy absorption drop test. The reserve energy absorption drop test must be conducted as...

  18. 14 CFR 29.727 - Reserve energy absorption drop test.

    Code of Federal Regulations, 2013 CFR

    2013-01-01

    ... 14 Aeronautics and Space 1 2013-01-01 2013-01-01 false Reserve energy absorption drop test. 29.727 Section 29.727 Aeronautics and Space FEDERAL AVIATION ADMINISTRATION, DEPARTMENT OF TRANSPORTATION....727 Reserve energy absorption drop test. The reserve energy absorption drop test must be conducted...

  19. 14 CFR 29.727 - Reserve energy absorption drop test.

    Code of Federal Regulations, 2012 CFR

    2012-01-01

    ... 14 Aeronautics and Space 1 2012-01-01 2012-01-01 false Reserve energy absorption drop test. 29.727 Section 29.727 Aeronautics and Space FEDERAL AVIATION ADMINISTRATION, DEPARTMENT OF TRANSPORTATION....727 Reserve energy absorption drop test. The reserve energy absorption drop test must be conducted...

  20. 14 CFR 23.727 - Reserve energy absorption drop test.

    Code of Federal Regulations, 2011 CFR

    2011-01-01

    ... 14 Aeronautics and Space 1 2011-01-01 2011-01-01 false Reserve energy absorption drop test. 23.727... Construction Landing Gear § 23.727 Reserve energy absorption drop test. (a) If compliance with the reserve energy absorption requirement in § 23.723(b) is shown by free drop tests, the drop height may not be...

  1. 14 CFR 27.727 - Reserve energy absorption drop test.

    Code of Federal Regulations, 2013 CFR

    2013-01-01

    ... 14 Aeronautics and Space 1 2013-01-01 2013-01-01 false Reserve energy absorption drop test. 27.727 Section 27.727 Aeronautics and Space FEDERAL AVIATION ADMINISTRATION, DEPARTMENT OF TRANSPORTATION... Reserve energy absorption drop test. The reserve energy absorption drop test must be conducted as...

  2. 14 CFR 23.727 - Reserve energy absorption drop test.

    Code of Federal Regulations, 2013 CFR

    2013-01-01

    ... 14 Aeronautics and Space 1 2013-01-01 2013-01-01 false Reserve energy absorption drop test. 23.727... Construction Landing Gear § 23.727 Reserve energy absorption drop test. (a) If compliance with the reserve energy absorption requirement in § 23.723(b) is shown by free drop tests, the drop height may not be...

  3. 14 CFR 27.727 - Reserve energy absorption drop test.

    Code of Federal Regulations, 2011 CFR

    2011-01-01

    ... 14 Aeronautics and Space 1 2011-01-01 2011-01-01 false Reserve energy absorption drop test. 27.727 Section 27.727 Aeronautics and Space FEDERAL AVIATION ADMINISTRATION, DEPARTMENT OF TRANSPORTATION... Reserve energy absorption drop test. The reserve energy absorption drop test must be conducted as...

  4. 14 CFR 29.727 - Reserve energy absorption drop test.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ... 14 Aeronautics and Space 1 2010-01-01 2010-01-01 false Reserve energy absorption drop test. 29.727 Section 29.727 Aeronautics and Space FEDERAL AVIATION ADMINISTRATION, DEPARTMENT OF TRANSPORTATION....727 Reserve energy absorption drop test. The reserve energy absorption drop test must be conducted...

  5. 14 CFR 27.727 - Reserve energy absorption drop test.

    Code of Federal Regulations, 2012 CFR

    2012-01-01

    ... 14 Aeronautics and Space 1 2012-01-01 2012-01-01 false Reserve energy absorption drop test. 27.727 Section 27.727 Aeronautics and Space FEDERAL AVIATION ADMINISTRATION, DEPARTMENT OF TRANSPORTATION... Reserve energy absorption drop test. The reserve energy absorption drop test must be conducted as...

  6. 14 CFR 23.727 - Reserve energy absorption drop test.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ... 14 Aeronautics and Space 1 2010-01-01 2010-01-01 false Reserve energy absorption drop test. 23.727... Construction Landing Gear § 23.727 Reserve energy absorption drop test. (a) If compliance with the reserve energy absorption requirement in § 23.723(b) is shown by free drop tests, the drop height may not be...

  7. 14 CFR 23.727 - Reserve energy absorption drop test.

    Code of Federal Regulations, 2012 CFR

    2012-01-01

    ... 14 Aeronautics and Space 1 2012-01-01 2012-01-01 false Reserve energy absorption drop test. 23.727... Construction Landing Gear § 23.727 Reserve energy absorption drop test. (a) If compliance with the reserve energy absorption requirement in § 23.723(b) is shown by free drop tests, the drop height may not be...

  8. 14 CFR 29.727 - Reserve energy absorption drop test.

    Code of Federal Regulations, 2011 CFR

    2011-01-01

    ... 14 Aeronautics and Space 1 2011-01-01 2011-01-01 false Reserve energy absorption drop test. 29.727 Section 29.727 Aeronautics and Space FEDERAL AVIATION ADMINISTRATION, DEPARTMENT OF TRANSPORTATION....727 Reserve energy absorption drop test. The reserve energy absorption drop test must be conducted...

  9. Structural changes of nucleic acid base in aqueous solution as observed in X-ray absorption near edge structure (XANES)

    NASA Astrophysics Data System (ADS)

    Shimada, Hiroyuki; Fukao, Taishi; Minami, Hirotake; Ukai, Masatoshi; Fujii, Kentaro; Yokoya, Akinari; Fukuda, Yoshihiro; Saitoh, Yuji

    2014-01-01

    X-ray absorption near edge structure (XANES) spectra for adenine-containing nucleotides, adenosine 5‧-monophosphate (AMP) and adenosine 5‧-triphosphate (ATP) in aqueous solutions at the nitrogen K-edge region were measured. The two intense peaks in XANES spectra are assigned to transitions of 1s electrons to the π∗ orbitals of different types of N atoms with particular bonding characteristics. The difference between their spectra is ascribed to protonation of a particular N atom. Similarity observed in XANES spectra of guanosine 5‧-monophosphate (GMP) and ATP is also interpreted as similar bonding characters of the N atoms in the nucleobase moiety.

  10. Study on Coloration Mechanism of Chinese Ancient Ceramics by X-ray Absorption Near-edge Structure

    NASA Astrophysics Data System (ADS)

    Peng, Y. H.; Xie, Z.; He, J. F.; Liu, Q. H.; Pan, Z. Y.; Cheng, W. R.; Wei, S. Q.

    2013-04-01

    The Fe K-edge X-ray absorption near-edge structure (XANES) spectra of a series of ceramic shards were measured by fluorescence mode to reveal the color-generating techniques of Chinese porcelain. The analysis disclosed relationships among the chemical form of the iron, the firing conditions and the colors of the ceramics. The results indicate that the coloration for different ceramics depend on the valence states of iron as the main color element in glaze and the proportion of Fe2+ and Fe3+ was attributed to the baking technology. The findings provide important information for archaeologist on the coloration researches.

  11. Angle-resolved x-ray absorption near edge structure study of vertically aligned single-walled carbon nanotubes

    NASA Astrophysics Data System (ADS)

    Li, Zhongrui; Zhang, Liang; Resasco, Daniel E.; Mun, Bongjin Simon; Requejo, Félix G.

    2007-03-01

    Vertically aligned single-walled carbon nanotube (SWNT) forest was studied by using angular-dependent C K-edge x-ray absorption near edge structure (XANES) with linearly polarized x-ray beam. The XANES analysis found a crust of entangled nanotubes on top of the forest formed at the first stage of the forest growth, which shapes the morphology of the entire forest and constricts the nanotubes to grow to the same length. It indicates that this type of SWNT forest has a different growth mechanism from the multiwalled carbon nanotube forest.

  12. Electronic transitions and fermi edge singularity in polar heterostructures studied by absorption and emission spectroscopy

    NASA Astrophysics Data System (ADS)

    Pandey, S.; Cavalcoli, D.; Minj, A.; Fraboni, B.; Cavallini, A.; Gamarra, P.; Poisson, M. A.

    2012-12-01

    Optically induced electronic transitions in nitride based polar heterostructures have been investigated by absorption and emission spectroscopy. Surface photovoltage (SPV), photocurrent (PC), and photo luminescence spectroscopy have been applied to high quality InAlN/AlN/GaN structures to study the optical properties of two dimensional electron gas. Energy levels within the two dimensional electron gas (2DEG) well at the interface between the GaN and AlN have been directly observed by SPV and PC. Moreover, a strong enhancement of the photoluminescence intensity due to holes recombining with electrons at the Fermi Energy, known as fermi energy singularity, has been observed. These analyses have been carried out on InAlN/AlN/GaN heterojunctions with the InAlN barrier layer having different In content, a parameter which affects the energy levels within the 2DEG well as well as the optical signal intensity. The measured energy values are in a very good agreement with the ones obtained by Schrödinger-Poisson simulations.

  13. Speciation of sulfur in humic and fulvic acids using X-ray Absorption Near-Edge Structures (XANES) spectroscopy

    SciTech Connect

    Morra, M.J.; Fendorf, S.E.; Brown, P.D.

    1997-02-01

    Sulfur species in soils and sediments have previously been determined indirectly using destructive techniques. A direct and more accurate method for S speciation would improve our understanding of S biogeochemistry. X-ray absorption near edge structure (XANES) spectroscopy was performed on purified humic and fulvic acids from terrestrial and aquatic environments. This methodology allows direct determination of S species using the relationship that exists with the energy required for core electron transitions and in some cases, correlation with additional spectral features. Soil, peat, and aquatic humic acids were dominated by sulfonates with an oxidation state of +5, but also contained ester-bonded sulfates with an oxidation state of +6. Leonardite humic acid contained ester-bonded sulfate and an unidentified S compound with an oxidation state of +4.0. In contrast, high-valent S in soil, peat, and aquatic fulvic acids was exclusively in the form of sulfonic acids. Reduced S species were also present in both humic and fulvic acids. XANES is a valuable method for the speciation of S in humic materials and of potential use in S speciation of unfractionated soils. 27 refs., 4 figs., 3 tabs.

  14. Speciation of sulfur in humic and fulvic acids using X-ray absorption near-edge structure (XANES) spectroscopy

    NASA Astrophysics Data System (ADS)

    Morra, Matthew J.; Fendorf, Scott E.; Brown, Paul D.

    1997-02-01

    Sulfur species in soils and sediments have previously been determined indirectly using destructive techniques. A direct and more accurate method for S speciation would improve our understanding of S biogeochemistry. X-ray absorption near edge structure (XANES) spectroscopy was performed on purified humic and fulvic acids from terrestrial and aquatic environments. This methodology allows direct determination of S species using the relationship that exists with the energy required for core electron transitions and in some cases, correlation with additional spectral features. Soil, peat, and aquatic humic acids were dominated by sulfonates with an oxidation state of +5, but also contained ester-bonded sulfates with an oxidation state of +6. Leonardite humic acid contained ester-bonded sulfate and an unidentified S compound with an oxidation state of +4.0. In contrast, high-valent S in soil, peat, and aquatic fulvic acids was exclusively in the form of sulfonic acids. Reduced S species were also present in both humic and fulvic acids. XANES is a valuable method for the speciation of S in humic materials and of potential use in S speciation of unfractionated soils.

  15. Ab initio x-ray absorption study of copper K-edge XANES spectra in Cu(II) compounds

    SciTech Connect

    Chaboy, Jesus; Munoz-Paez, Adela; Carrera, Flora; Merkling, Patrick; Marcos, Enrique Sanchez

    2005-04-01

    This work reports a theoretical study of the x-ray absorption near-edge structure spectra at the Cu K edge in several Cu(II) complexes with N-coordinating ligands showing a square-planar arrangement around metal cation. It is shown that single-channel multiple-scattering calculations are not able to reproduce the experimental spectra. The comparison between experimental data and ab initio computations indicates the need of including the contribution of two electronic configurations (3d{sup 9} and 3d{sup 10}L) to account for a proper description of the final state during the photoabsorption process. The best agreement between theory and experiment is obtained by considering a relative weight of 68% and 32% for the two absorption channels 3d{sup 10}L and 3d{sup 9}, respectively.

  16. Sulfur 1s near-edge x-ray absorption fine structure (NEXAFS) of thiol and thioether compounds

    SciTech Connect

    Beyhan, Shirin; Urquhart, Stephen G.; Hu Yongfeng

    2011-06-28

    The speciation and quantification of sulfur species based on sulfur K-edge x-ray absorption spectroscopy is of wide interest, particularly for biological and petroleum science. These tasks require a firm understanding of the sulfur 1s near-edge x-ray absorption fine structure (NEXAFS) spectra of relevant species. To this end, we have examined the gas phase sulfur 1s NEXAFS spectra of a group of simple thiol and thioether compounds. These high-resolution gas phase spectra are free of solid-state broadening, charging, and saturation effects common in the NEXAFS spectra of solids. These experimental data have been further analyzed with the aid of improved virtual orbital Hartree-Fock ab initio calculations. The experimental sulfur 1s NEXAFS spectra show fine features predicted by calculation, and the combination of experiment and calculation has been used to improve assignment of spectroscopic features relevant for the speciation and quantification of the sulfur compounds.

  17. Temperature and high-pressure dependent x-ray absorption of SmNiO3 at the Ni K and Sm L3 edges

    NASA Astrophysics Data System (ADS)

    Massa, Néstor E.; Ramos, Aline Y.; Tolentino, Helio C. N.; Sousa-Neto, Narcizo M.; Fonseca, Jairo, Jr.; Alonso, José Antonio

    2015-12-01

    We report on x-ray absorption near-edge structure (XANES) and extended x-ray absorption fine structure (EXAFS) measurements of SmNiO3 from 20 K to 600 K and up to 38 GPa at the Ni K and Sm L3 edges. A multiple component pre-Ni K edge tail is understood, originating from 1 s transitions to 3d-4p states while a post-edge shoulder increases distinctively smoothly, at about the insulator to metal phase transition (TIM), due to the reduction of electron-phonon interactions as the Ni 3d and O 2p band overlap triggers the metallic phase. This effect is concomitant with pressure-induced Ni-O-Ni angle increments toward more symmetric Ni3+ octahedra of the rhombohedral R¯3c space group. Room temperature pressure-dependent Ni white line peak energies have an abrupt ˜3.10 ± 0.04 GPa valence discontinuity from non-equivalent Ni3+δ + Ni3-δ charge disproportionate net unresolved absorber turning at ˜TIM into Ni3+ of the orthorhombic Pbnm metal oxide phase. At 20 K the overall white line response, still distinctive at TIM ˜8.1 ± 0.6 GPa is much smoother due to localization. Octahedral bond contraction up to 38 GPa and at 300 K and 20 K show breaks in its monotonic increase at the different structural changes. The Sm L3 edge does not show distinctive behaviors either at 300 K or 20 K up to about 35 GPa but the perovskite Sm cage, coordinated to eight oxygen atoms, undergoes strong uneven bond contractions at intermediate pressures where we found the coexistence of octahedral and rhombohedral superexchange angle distortions. We found that the white line pressure-dependent anomaly may be used as an accurate alternative for delineating pressure-temperature phase diagrams.

  18. Theory of x-ray absorption and linear dichroism at the Ca L23-edge of CaCO3

    NASA Astrophysics Data System (ADS)

    Krüger, Peter; Natoli, Calogero R.

    2016-05-01

    X-ray absorption calculations of Ca L23-edge spectra of calcium carbonate in its two main crystal phases, calcite and aragonite, are reported. The multichannel multiple scattering theory with a correlated particle-hole wave function and a partially screened core-hole potential is used. Very good agreement with experiment for both CaCO3 phases is obtained, while the independent particle approximation completely fails. For aragonite, appreciable linear dichroism is predicted in agreement with recent observations.

  19. C 1s Near Edge X-ray Absorption Fine Structure (NEXAFS) of substituted benzoic acids: a theoretical and experimental study

    SciTech Connect

    Baldea,I.; Schimmelpfennig, B.; Plaschke, M.; Rothe, J.; Schirmer, J.; Trofimov, A.; Fanghaenel, T.

    2007-01-01

    Ab initio calculations are performed to explain the discrete transitions in experimental C 1s-NEXAFS (near edge X-ray absorption fine structure) spectra of various benzoic acid derivates. Transition energies and oscillator strengths of the contributing C 1s-{pi}* excitations are computed using the ADC(2) (second-order algebraic-diagrammatic construction) method. This method is demonstrated to be well suited for the finite electronic systems represented by these simple organic acids. There is good agreement between experiment and theory reproducing all the relevant spectral features. Some transitions can only be assigned based on a theoretical foundation. Remaining discrepancies between experimental and computed spectra are discussed.

  20. Final report on the energy edge impact evaluation of 28 new, low-energy commercial buildings

    SciTech Connect

    Piette, M.A.; Diamond, R.; Nordman, B.

    1994-08-01

    This report presents the findings of the Energy Edge Impact Evaluation. It is the fourth and final report in a series of project impact evaluation reports. Energy Edge is a research-oriented demonstration of energy efficiency in 28 new commercial buildings. Beginning in 1985,the project, sponsored by the Bonneville Power Administration (BPA), was developed to evaluate the potential for electricity conservation in new commercial buildings. By focusing on the construction of new commercial buildings, Energy Edge meets the region`s goal of capturing otherwise lost opportunities to accomplish energy conservation. That is, the best time to add an energy-efficiency measure to a building is during the construction phase.

  1. 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. PMID:23360082

  2. Nitrogen K-edge X-ray absorption near edge structure (XANES) spectra of purine-containing nucleotides in aqueous solution

    SciTech Connect

    Shimada, Hiroyuki; Fukao, Taishi; Minami, Hirotake; Ukai, Masatoshi; Fujii, Kentaro; Yokoya, Akinari; Fukuda, Yoshihiro; Saitoh, Yuji

    2014-08-07

    The N K-edge X-ray absorption near edge structure (XANES) spectra of the purine-containing nucleotide, guanosine 5{sup ′}-monophosphate (GMP), in aqueous solution are measured under various pH conditions. The spectra show characteristic peaks, which originate from resonant excitations of N 1s electrons to π* orbitals inside the guanine moiety of GMP. The relative intensities of these peaks depend on the pH values of the solution. The pH dependence is explained by the core-level shift of N atoms at specific sites caused by protonation and deprotonation. The experimental spectra are compared with theoretical spectra calculated by using density functional theory for GMP and the other purine-containing nucleotides, adenosine 5{sup ′}-monophosphate, and adenosine 5{sup ′}-triphosphate. The N K-edge XANES spectra for all of these nucleotides are classified by the numbers of N atoms with particular chemical bonding characteristics in the purine moiety.

  3. Experimental and theoretical comparison between absorption, total electron yield, and fluorescence spectra of rare-earth M{sub 5} edges

    SciTech Connect

    Pompa, M.; Flank, A.M.; Lagarde, P.; Rife, J.C.; Stekhin, I.; Nakazawa, M.; Ogasawara, H.; Kotani, A.

    1997-07-01

    Besides the now well-known self-absorption effect, several phenomena related to the multiplet structure of the intermediate state may occur which render x-ray fluorescence different from the true absorption in 3d transition metals at the L edge and at the M{sub 4,5} edges of rare earths. Special selection rules of the radiative de-excitation process play an important role there. We have measured the absorption coefficient of thin films of lanthanum, samarium, and thulium deposited on an aluminum foil, at room temperature, through the simultaneous detection of the transmission, total electron yield, and 150-eV bandwidth fluorescence yield. The latter result shows differences as compared to the other two, and exhibits polarization effects depending upon the angle between incident and outgoing photons. The resonant x-ray fluorescence spectrum is calculated using an atomic model, and then integrated over the emitted energy, to predict the fluorescence yield spectrum. Very good agreement is obtained between the theory and experiment. {copyright} {ital 1997} {ital The American Physical Society}

  4. Identification of B-K near edge x-ray absorption fine structure peaks of boron nitride thin films prepared by sputtering deposition

    SciTech Connect

    Niibe, Masahito; Miyamoto, Kazuyoshi; Mitamura, Tohru; Mochiji, Kozo

    2010-09-15

    Four {pi}{sup *} resonance peaks were observed in the B-K near edge x-ray absorption fine structure spectra of boron nitride thin films prepared by magnetron sputtering. In the past, these peaks have been explained as the K-absorption of boron atoms, which are present in environment containing nitrogen vacancies, the number of which is 1-3 corresponding to the three peaks at higher photon energy. However, the authors found that there was a strong correlation between the intensities of these three peaks and that of O-K absorption after wide range scanning and simultaneous measurement of nitrogen and oxygen K-absorptions of the BN films. Therefore, the authors conclude that these three peaks at the higher energy side correspond to boron atoms bound to one-to-three oxygen atoms instead of three nitrogen atoms surrounding the boron atom in the h-BN structure. The result of the first-principles calculation with a simple cluster model supported the validity of this explanation.

  5. The C 1s and N 1s near edge x-ray absorption fine structure spectra of five azabenzenes in the gas phase.

    PubMed

    Vall-llosera, G; Gao, B; Kivimäki, A; Coreno, M; Alvarez Ruiz, J; de Simone, M; Agren, H; Rachlew, E

    2008-01-28

    Near edge x-ray absorption fine structure spectra have been measured and interpreted by means of density functional theory for five different azabenzenes (pyridine, pyridazine, pyrimidine, pyrazine, and s-triazine) in the gas phase. The experimental and theoretical spectra at the N 1s and C 1s edges show a strong resonance assigned to the transition of the 1s electron in the respective N or C atoms to the lowest unoccupied molecular orbital with pi(*) symmetry. As opposed to the N 1s edge, at the C 1s edge this resonance is split due to the different environments of the core hole atom in the molecule. The shift in atomic core-level energy due to a specific chemical environment is explained with the higher electronegativity of the N atom compared to the C atom. The remaining resonances below the ionization potential (IP) are assigned to sigma or pi [corrected] orbitals with mixed valence/Rydberg [corrected] character. Upon N addition, a reduction of intensity is observed in the Rydberg region at both edges as compared to the intensity in the continuum. Above the IP one or more resonances are seen and ascribed here to transitions to sigma(*) orbitals. Calculating the experimental and theoretical Delta(pi) term values at both edges, we observe that they are almost the same within +/-1 eV as expected for isoelectronic bonded pairs. The term values of the pi(*) and sigma(*) resonances are discussed in terms of the total Z number of the atoms participating in the bond. PMID:18247958

  6. Mechanical Energy Absorption of Pectin Films

    NASA Astrophysics Data System (ADS)

    Zsivanovits, G.

    2007-04-01

    Pectin film samples were prepared from HM, LM and amidated pectins produced by CP Kelco and Danisco, with acidic and enzymatic de-esterification and amidation. The swelling of samples were indicated by hydration before the experiments for 24 h by PEG20000 solution, on known osmotic pressure, with Ca, Mg and K ions with different concentrations. Mechanical tests were followed by Stable Micro Systems penetrometer, with stress-relaxation method, in elastic deformation section. Results show, that the energy absorption depends on the pectin type, on the hydration and the ion concentration. Based on this type experiments it is possible to choose the best pectin type for different uses - as a packaging material in different occasions, or modeling pectin changes during physiological changing in the cell-wall etc.

  7. Radiative ablation with two ionizing fronts when opacity displays a sharp absorption edge.

    PubMed

    Poujade, Olivier; Bonnefille, Max; Vandenboomgaerde, Marc

    2015-11-01

    The interaction of a strong flux of photons with matter through an ionizing front (I-front) is an ubiquitous phenomenon in the context of astrophysics and inertial confinement fusion (ICF) where intense sources of radiation put matter into motion. When the opacity of the irradiated material varies continuously in the radiation spectral domain, only one single I-front is formed. In contrast, as numerical simulations tend to show, when the opacity of the irradiated material presents a sharp edge in the radiation spectral domain, a second I-front (an edge front) can form. A full description of the mechanism behind the formation of this edge front is presented in this article. It allows us to understand extra shocks (edge-shocks), displayed by ICF simulations, that might affect the robustness of the design of fusion capsules in actual experiments. Moreover, it may have consequences in various domains of astrophysics where ablative flows occur. PMID:26651800

  8. Radiative ablation with two ionizing fronts when opacity displays a sharp absorption edge

    NASA Astrophysics Data System (ADS)

    Poujade, Olivier; Bonnefille, Max; Vandenboomgaerde, Marc

    2015-11-01

    The interaction of a strong flux of photons with matter through an ionizing front (I-front) is an ubiquitous phenomenon in the context of astrophysics and inertial confinement fusion (ICF) where intense sources of radiation put matter into motion. When the opacity of the irradiated material varies continuously in the radiation spectral domain, only one single I-front is formed. In contrast, as numerical simulations tend to show, when the opacity of the irradiated material presents a sharp edge in the radiation spectral domain, a second I-front (an edge front) can form. A full description of the mechanism behind the formation of this edge front is presented in this article. It allows us to understand extra shocks (edge-shocks), displayed by ICF simulations, that might affect the robustness of the design of fusion capsules in actual experiments. Moreover, it may have consequences in various domains of astrophysics where ablative flows occur.

  9. Tuning semiconductor band edge energies for solar photocatalysis via surface ligand passivation.

    PubMed

    Yang, Shenyuan; Prendergast, David; Neaton, Jeffrey B

    2012-01-11

    Semiconductor photocatalysts capable of broadband solar photon absorption may be nonetheless precluded from use in driving water splitting and other solar-to-fuel related reactions due to unfavorable band edge energy alignment. Using first-principles density functional theory and beyond, we calculate the electronic structure of passivated CdSe surfaces and explore the opportunity to tune band edge energies of this and related semiconductors via electrostatic dipoles associated with chemisorbed ligands. We predict substantial shifts in band edge energies originating from both the induced dipole at the ligand/CdSe interface and the intrinsic dipole of the ligand. Building on important induced dipole contributions, we further show that, by changing the size and orientation of the ligand's intrinsic dipole moment via functionalization, we can control the direction and magnitude of the shifts of CdSe electronic levels. Our calculations suggest a general strategy for enabling new active semiconductor photocatalysts with both optimal opto-electronic, and photo- and electrochemical properties. PMID:22192078

  10. Multiple-scattering calculations of the uranium {ital L}{sub 3}-edge x-ray-absorption near-edge structure

    SciTech Connect

    Hudson, E.A.; Rehr, J.J.; Bucher, J.J.

    1995-11-15

    A theoretical study of the uranium {ital L}{sub 3}-edge x-ray absorption near-edge structure (XANES) is presented for several uranium compounds, including oxides, intermetallics, uranyl fluoride, and {alpha}-uranium. Calculations were performed using FEFF6, an {ital ab} {ital initio} multiple-scattering (MS) code that includes the most important features of current theories. The results, which account for both the fine structure {chi} and the atomiclike background {mu}{sub 0} of the absorption coefficient {mu}, are compared to new and previously measured experimental spectra, reavealing very good agreement for most systems. For several compounds, a more detailed theoretical analysis determined the influence of cluster size and scattering order upon the calculated spectra. Results indicate that MS paths and scattering paths that include rather distant atoms make significant contributions for UO{sub 2}, whereas XANES for crystals with lower symmetry and density can be modeled using only shorter single-scattering paths. In most cases, assumption of a screened final state in the calculation gives better agreement with experiment than use of an unscreened final state. The successful modeling of spectra for a variety of different uranium compounds, with differing spectral features, indicates that the semirelativistic treatment of XANES used here is adequate even for heavy elements. The well-known resonance, observed experimentally for uranyl (UO{sub 2}{sup 2+}) compounds {approx}15 eV above the white line, is successfully modeled here for the first time, using multiple-scattering paths within the O-U-O axial bonds. Overlapping muffin-tin spheres were required in the calculation, probably as a result of the short uranyl axial bonds.

  11. Energy conservation in regenerated chemical absorption processes

    SciTech Connect

    Thompson, R.E.

    1986-01-01

    Energy savings from split-flow design modifications or the installation of absorber intercoolers are quantified for solvent-based separation processes. Absorber-stripper systems that use aqueous monoethanolamine (MEA) or diethanolamine (DEA) to remove CO/sub 2/ or H/sub 2/S from natural gas streams are modeled. Use of split flow in regenerated chemical absorption processes with isothermal columns resulted in energy savings of over 50% for systems with large solute-recovery fractions. The energy savings are a linear function of the logarithm of percent unrecovered solute. Optimal values are found for the flow rate and withdrawal point of the split-flow stream. The optimal design and operating conditions for CO/sub 2/ systems with adiabatic columns are determined by the stripper column; the stripper exhibits a steam-consumption minimum with respect to the total solvent flow rate and the composition of the lean-solvent stream. In contrast, optimal conditions for H/sub 2/S systems are set by the absorber. These absorber-limited systems exhibit a steam consumption minimum for the lowest solvent flow which can achieve the specified solute recovery in the absorber. Absorber intercoolers conserve energy by reducing the solvent flow rate required for a specified solute recovery. The optimal intercooler location is near an acid-gas-to-amine ratio halfway between the same ratios for the lean and rich solvent streams. The intercooler location is near an acid-gas-to-amine ratio halfway between the same ratios for the lean and rich solvent streams. The intercooler is optically sized by equating the absorber-solvent-feed temperature, the absorber-intercooler process-outlet temperature, and the cooling-water effluent temperature.

  12. Local environment of Mn dopant in ZnO by near-edge x-ray absorption fine structure analysis

    NASA Astrophysics Data System (ADS)

    Kunisu, Masahiro; Oba, Fumiyasu; Ikeno, Hidekazu; Tanaka, Isao; Yamamoto, Tomoyuki

    2005-03-01

    High-resolution near-edge x-ray absorption fine structure (NEXAFS) at MnK edge is employed to probe the local environment of Mn dopant in ZnO. First-principles supercell calculations are systematically made to obtain theoretical NEXAFS. Mn is found to substitute for Zn up to 5at. %Mn in polycrystalline samples sintered at 1623K in air. Presence of Mn3O4 is apparent for samples with higher Mn content. The NEXAFS does not change in the range of Mn concentration from 0.01 to 5at.%, indicating the absence of Mn precipitates. The results are confirmed by examining the polarization dependence of the NEXAFS for a 5at.%-doped ZnO thin film.

  13. Micro-x-ray absorption near-edge structure imaging for detecting metallic Mn in GaN

    NASA Astrophysics Data System (ADS)

    Martínez-Criado, G.; Somogyi, A.; Homs, A.; Tucoulou, R.; Susini, J.

    2005-08-01

    In this study, we report the application of a synchrotron radiation microprobe to the analysis of Mn valencies in GaN. X-ray absorption near-edge structure (XANES) images taken around MnK-edge in fluorescence detection mode reveal the concentration of oxidation states of Mn centers. By fitting the XANES curve for each point of the image, the distributions of the Mn0, Mn2+, and Mn3+ oxidation states are obtained. At low Mn concentrations, there is a homogeneous mixture of Mn2+ and Mn3+ centers, while at high Mn content strong spatial-dependent Mn0 and Mn2+ distributions characterize the XANES maps. In a supplementary way with respect to Mn2+, the Mn0 pattern suggests the presence of specific cluster-like features, indicating surface segregation of metallic Mn centers.

  14. Energy gap of novel edge-defected graphene nanoribbons

    NASA Astrophysics Data System (ADS)

    Yuan, Weiqing; Wen, Zhongquan; Li, Min; Chen, Li; Chen, Gang; Ruan, Desheng; Gao, Yang

    2016-08-01

    Herein, the effects of width and boundary defects on the energy gap of graphene nanoribbons (GNRs) have been explored and theoretically investigated by means of semi-empirical atomic basis Extended Hückel method. Due to the existence of boundary defects, the energy gap of GNRs is mainly determined by the width of graphene nanoribbons for armchair graphene nanoribbons (AGNRs) or zigzag graphene nanoribbons (ZGNRs). Interestingly, the energy gap of AGNRs with a 120° V-type defect displays the monotone decreasing tendency when the width reaches to 2 nm, while the energy gap of intrinsic AGNRs is oscillatory. At the same time, the energy gap of U-type defected ZGNRs is opened, which differs from the zero energy gap characteristics of the intrinsic zigzag graphene. Furthermore, the size of energy gap of the defected AGNRs and ZGNRs with the same width is proved to be very close. Calculation results demonstrate that the energy gap of GNRs is just inversely proportional to the width and has little to do with the crystallographic direction. All the findings above provide a basis for energy gap engineering with different edge defects in GNRs and signify promising prospects in graphene-based semiconductor electronic devices.

  15. Calibration of Energy-Specific TDDFT for Modeling K-edge XAS Spectra of Light Elements.

    PubMed

    Lestrange, Patrick J; Nguyen, Phu D; Li, Xiaosong

    2015-07-14

    X-ray absorption spectroscopy (XAS) has become a powerful technique in chemical physics, because of advances in synchrotron technology that have greatly improved its temporal and spectroscopic resolution. Our recent work on energy-specific time-dependent density functional theory (ES-TDDFT) allows for the direct calculation of excitation energies in any region of the absorption spectrum, from UV-vis to X-ray. However, the ability of different density functional theories to model X-ray absorption spectra (XAS) of light elements has not yet been verified for ES-TDDFT. This work is a calibration of the ability of existing DFT kernels and basis sets to reproduce experimental K-edge excitation energies. Results were compared against 30 different transitions from gas-phase experiments. We focus on six commonly used density functionals (BHandHLYP, B3LYP, PBE1PBE, BP86, HSE06, LC-ωPBE) and various triple-ζ basis sets. The effects of core and diffuse functions are also investigated. PMID:26575736

  16. Three-dimensional mapping of nickel oxidation states using full field x-ray absorption near edge structure nanotomography

    SciTech Connect

    Nelson, George J.; Harris, William M.; Izzo, John R. Jr.; Grew, Kyle N.; Chiu, Wilson K. S.; Chu, Yong S.; Yi, Jaemock; Andrews, Joy C.; Liu Yijin; Pianetta, Piero

    2011-04-25

    The reduction-oxidation cycling of the nickel-based oxides in composite solid oxide fuel cells and battery electrodes is directly related to cell performance. A greater understanding of nickel redox mechanisms at the microstructural level can be achieved in part using transmission x-ray microscopy (TXM) to explore material oxidation states. X-ray nanotomography combined with x-ray absorption near edge structure (XANES) spectroscopy has been applied to study samples containing distinct regions of nickel and nickel oxide (NiO) compositions. Digitally processed images obtained using TXM demonstrate the three-dimensional chemical mapping and microstructural distribution capabilities of full-field XANES nanotomography.

  17. Three-dimensional mapping of nickel oxidation states using full field x-ray absorption near edge structure nanotomography

    NASA Astrophysics Data System (ADS)

    Nelson, George J.; Harris, William M.; Izzo, John R.; Grew, Kyle N.; Chiu, Wilson K. S.; Chu, Yong S.; Yi, Jaemock; Andrews, Joy C.; Liu, Yijin; Pianetta, Piero

    2011-04-01

    The reduction-oxidation cycling of the nickel-based oxides in composite solid oxide fuel cells and battery electrodes is directly related to cell performance. A greater understanding of nickel redox mechanisms at the microstructural level can be achieved in part using transmission x-ray microscopy (TXM) to explore material oxidation states. X-ray nanotomography combined with x-ray absorption near edge structure (XANES) spectroscopy has been applied to study samples containing distinct regions of nickel and nickel oxide (NiO) compositions. Digitally processed images obtained using TXM demonstrate the three-dimensional chemical mapping and microstructural distribution capabilities of full-field XANES nanotomography.

  18. Solving local structure around dopants in metal nanoparticles with ab initio modeling of X-ray absorption near edge structure

    DOE PAGESBeta

    Timoshenko, J.; Shivhare, A.; Scott, R. W.; Lu, D.; Frenkel, A. I.

    2016-06-30

    We adopted ab-initio X-ray Absorption Near Edge Structure (XANES) modelling for structural refinement of local environments around metal impurities in a large variety of materials. Our method enables both direct modelling, where the candidate structures are known, and the inverse modelling, where the unknown structural motifs are deciphered from the experimental spectra. We present also estimates of systematic errors, and their influence on the stability and accuracy of the obtained results. We illustrate our approach by following the evolution of local environment of palladium atoms in palladium-doped gold thiolate clusters upon chemical and thermal treatments.

  19. Final-State Projection Method in Charge-Transfer Multiplet Calculations: An Analysis of Ti L-Edge Absorption Spectra.

    PubMed

    Kroll, Thomas; Solomon, Edward I; de Groot, Frank M F

    2015-10-29

    A projection method to determine the final-state configuration character of all peaks in a charge transfer multiplet calculation of a 2p X-ray absorption spectrum is presented using a d(0) system as an example. The projection method is used to identify the most important influences on spectral shape and to map out the configuration weights. The spectral shape of a 2p X-ray absorption or L2,3-edge spectrum is largely determined by the ratio of the 2p core-hole interactions relative to the 2p3d atomic multiplet interaction. This leads to a nontrivial spectral assignment, which makes a detailed theoretical description of experimental spectra valuable for the analysis of bonding. PMID:26226507

  20. Development of Palladium L-Edge X-Ray Absorption Spectroscopy And Its Application for Chloropalladium Complexes

    SciTech Connect

    Boysen, R.B.; Szilagyi, R.K.

    2009-05-12

    X-ray absorption spectroscopy (XAS) is a synchrotron-based experimental technique that provides information about geometric and electronic structures of transition metal complexes. Combination of metal L-edge and ligand K-edge XAS has the potential to define the complete experimental ground state electronic structures for metal complexes with unoccupied d manifolds. We developed a quantitative treatment for Pd L-edge spectroscopy on the basis of the well-established chlorine K-edge XAS for a series of chloropalladium complexes that are pre-catalysts in various organic transformations. We found that Pd-Cl bonds are highly covalent, such as 24 {+-} 2%, 34 {+-} 3%, and 48 {+-} 4% chloride 3p character for each Pd-Cl bond in [PdCl{sub 4}]{sup 2-}, [PdCl{sub 6}]{sup 2-}, and PdCl{sub 2}, respectively. Pd(2p {yields} 4d) transition dipole integrals of 20.8 (SSRL)/16.9 (ALS) eV and 14.1 (SSRL)/11.9 (ALS) eV were determined using various combinations of L-edges for Pd(II) and Pd(IV), respectively. Application of metal-ligand covalency and transition dipole integrals were demonstrated for the example of bridging chloride ligands in PdCl{sub 2}. Our work lays the foundation for extending the quantitative treatment to other catalytically important ligands, such as phosphine, phosphite, olefin, amine, and alkyl in order to correlate the electronic structures of palladium complexes with their catalytic activity.

  1. X-ray absorption spectra of nucleotides (AMP, GMP, and CMP) in liquid water solutions near the nitrogen K-edge

    NASA Astrophysics Data System (ADS)

    Ukai, Masatoshi; Yokoya, Akinari; Fujii, Kentaro; Saitoh, Yuji

    2010-07-01

    The X-ray absorption of nucleotides (adenosine-5'-monophosphate, guanosine 5'-monophosphate, and cytidine 5'-monophosphate) are measured in both water solutions and thin solid films at X-ray energies near the nitrogen K-edge in the 'water-window' region. Each spectrum corresponds to the selective excitation of a nucleobase site in a nucleotide, and thus has features similar to the spectrum of the corresponding nucleobase. An additional new peak in the energy region of the nitrogen 1s → π* resonance is observed for each nucleotide. No significant difference between the water solutions and thin solid films is found, which might be attributable to the hydrophobic properties of a nucleobase in a nucleotide.

  2. Long-Range Chemical Sensitivity in the Sulfur K-Edge X-ray Absorption Spectra of Substituted Thiophenes

    PubMed Central

    2015-01-01

    Thiophenes are the simplest aromatic sulfur-containing compounds and are stable and widespread in fossil fuels. Regulation of sulfur levels in fuels and emissions has become and continues to be ever more stringent as part of governments’ efforts to address negative environmental impacts of sulfur dioxide. In turn, more effective removal methods are continually being sought. In a chemical sense, thiophenes are somewhat obdurate and hence their removal from fossil fuels poses problems for the industrial chemist. Sulfur K-edge X-ray absorption spectroscopy provides key information on thiophenic components in fuels. Here we present a systematic study of the spectroscopic sensitivity to chemical modifications of the thiophene system. We conclude that while the utility of sulfur K-edge X-ray absorption spectra in understanding the chemical composition of sulfur-containing fossil fuels has already been demonstrated, care must be exercised in interpreting these spectra because the assumption of an invariant spectrum for thiophenic forms may not always be valid. PMID:25116792

  3. Log spiral of revolution highly oriented pyrolytic graphite monochromator for fluorescence x-ray absorption edge fine structure

    SciTech Connect

    Pease, D. M.; Daniel, M.; Budnick, J. I.; Rhodes, T.; Hammes, M.; Potrepka, D. M.; Sills, K.; Nelson, C.; Heald, S. M.; Brewe, D. I.

    2000-09-01

    We have constructed an x-ray monochromator based on a log spiral of revolution covered with highly oriented pyrolytic graphite. Such a monochromator is used for obtaining x-ray absorption edge fine structure by the fluorescence method, and is particularly useful for measuring the fine structure of dilute element A in a concentrated matrix of element B, where B is to the left of A in the Periodic Table. Using the log spiral monochromator, we measure good Cr x-ray fine structure in an alloy of 1% Cr in a V matrix, whereas the corresponding spectrum is severely distorted by the V background if nonmonochromatized fluorescence is used. We also obtain excellent rejection of Mn fluorescence relative to Cr fluorescence in a Cr{sub 80}Mn{sub 20} alloy, and can tune the monochromator such that the entire Mn step height is significantly smaller than the Cr x-ray absorption edge fine structure oscillations for this system. (c) 2000 American Institute of Physics.

  4. Physical properties of the interstellar medium using high-resolution Chandra spectra: O K-edge absorption

    SciTech Connect

    Gatuzz, E.; Mendoza, C.; García, J.; Kallman, T. R.; Bautista, M. A.; Gorczyca, T. W. E-mail: claudio@ivic.gob.ve E-mail: manuel.bautista@wmich.edu E-mail: timothy.r.kallman@nasa.gov

    2014-08-01

    Chandra high-resolution spectra toward eight low-mass Galactic binaries have been analyzed with a photoionization model that is capable of determining the physical state of the interstellar medium. Particular attention is given to the accuracy of the atomic data. Hydrogen column densities are derived with a broadband fit that takes into account pileup effects, and in general are in good agreement with previous results. The dominant features in the oxygen-edge region are O I and O II Kα absorption lines whose simultaneous fits lead to average values of the ionization parameter of log ξ = –2.90 and oxygen abundance of A{sub O} = 0.70. The latter is given relative to the standard by Grevesse and Sauval, but rescaling with the revision by Asplund et al. would lead to an average abundance value fairly close to solar. The low average oxygen column density (N{sub O} = 9.2 × 10{sup 17} cm{sup –2}) suggests a correlation with the low ionization parameters, the latter also being in evidence in the column density ratios N(O II)/N(O I) and N(O III)/N(O I) that are estimated to be less than 0.1. We do not find conclusive evidence for absorption by any other compound but atomic oxygen in our oxygen-edge region analysis.

  5. Angular Resolved X-Ray Absorption Near Edge Structure Investigation of Adsorbed Alkanethiol Monolayers on III-V(110) Surfaces

    NASA Astrophysics Data System (ADS)

    Chassé, T.; Zerulla, D.; Hallmeier, K. H.

    The structure of alkanethiol monolayers on III-V(110) surfaces was studied by analyzing the X-ray absorption near edge structure (XANES) of the carbon K edge. Pronounced absorption maxima were observed for special orientations of the polarization vector of the radiation as revealed from angular-dependent measurements, suggesting a rather well-defined molecular axis of the alkyl chains. From quantitative evaluations of these angular dependences the chains were found to be tilted from the normal towards the [001] direction of the (110) surfaces by 34° and 15° in the case of hexadecanethiol (HDT) adsorption on InP and GaP, respectively. The similarities as well as the differences in tilt angles between the substrates are dicussed in terms of constraints imposed by the surface structure and lattice constants as well as the space requirements of the van der Waals spheres of the adsorbed thiols. A unique feature observed on these monolayers is the nearly complete alignment of the alkyl chains with respect to the azimuthal orientation. We suggest that this adsorbate system represents the case of a single domain orientation within the organic monolayer.

  6. Energy Absorption in a Shear-Thickening Fluid

    NASA Astrophysics Data System (ADS)

    Afeshejani, Seyed Hossein Amiri; Sabet, Seyed Ali Reza; Zeynali, Mohammad Ebrahim; Atai, Mohammad

    2014-09-01

    This study investigates energy absorption in a shear-thickening fluid (STF) containing nano-size fumed silica as a suspending material. Fumed silica particles in 20, 30, and 40 wt.% were used in polyethylene glycol and ethylene glycol. Three areas were studied, namely: energy absorption of STF pre-impregnated aramid fabric, neat STF under high-velocity impact, and flexible foam soaked in STF under low-velocity drop weight impact. Results showed moderate energy absorption in STF pre-impregnated aramid fabric compared to dry fabric. High-velocity impact tests also revealed higher fabric weave density, and multi-layered target plays vital role in optimum performance of SFT impregnated targets. High-velocity impact tests on the neat STF showed good energy absorption at velocities near STF critical shear rate. Low-velocity drop weight impact test on flexible foam soaked in STF also indicated significant energy absorption.

  7. Energy Absorption in a Shear-Thickening Fluid

    NASA Astrophysics Data System (ADS)

    Afeshejani, Seyed Hossein Amiri; Sabet, Seyed Ali Reza; Zeynali, Mohammad Ebrahim; Atai, Mohammad

    2014-12-01

    This study investigates energy absorption in a shear-thickening fluid (STF) containing nano-size fumed silica as a suspending material. Fumed silica particles in 20, 30, and 40 wt.% were used in polyethylene glycol and ethylene glycol. Three areas were studied, namely: energy absorption of STF pre-impregnated aramid fabric, neat STF under high-velocity impact, and flexible foam soaked in STF under low-velocity drop weight impact. Results showed moderate energy absorption in STF pre-impregnated aramid fabric compared to dry fabric. High-velocity impact tests also revealed higher fabric weave density, and multi-layered target plays vital role in optimum performance of SFT impregnated targets. High-velocity impact tests on the neat STF showed good energy absorption at velocities near STF critical shear rate. Low-velocity drop weight impact test on flexible foam soaked in STF also indicated significant energy absorption.

  8. Absorption Of Crushing Energy In Square Composite Tubes

    NASA Technical Reports Server (NTRS)

    Farley, Gary L.

    1992-01-01

    Report describes investigation of crash-energy-absorbing capabilities of square-cross-section tubes of two matrix/fiber composite materials. Both graphite/epoxy and Kevlar/epoxy tubes crushed in progressive and stable manner. Ratio between width of cross section and thickness of wall determined to affect energy-absorption significantly. As ratio decreases, energy-absorption capability increases non-linearly. Useful in building energy-absorbing composite structures.

  9. Design for Manufacturing for Energy Absorption Systems

    SciTech Connect

    Del Prete, A.; Primo, T.; Papadia, G.; Manisi, B.

    2011-05-04

    In the typical scenario of a helicopter crash, impact with the ground is preceded by a substantially vertical drop, with the result that a seated occupant of a helicopter experiences high spinal loads and pelvic deceleration during such crash due to the sudden arresting of vertical downward motion. It has long been recognized that spinal injuries to occupants of helicopters in such crash scenario can be minimized by seat arrangements which limit the deceleration to which the seated occupant is subjected, relative to the helicopter, to a predetermined maximum, by allowing downward movement of the seated occupant relative to the helicopter, at the time of impact with the ground, under a restraining force which, over a limited range of such movement, is limited to a predetermined maximum. In practice, significant benefits, in the way of reduced injuries and reduced seriousness of injuries, can be afforded in this way in such crash situations even where the extent of such controlled vertical movement permitted by the crashworthy seat arrangement is quite limited. Important increase of accident safety is reached with the installation of crashworthy shock absorbers on the main landing gear, but this solution is mostly feasible on military helicopters with long fixed landing gear. Seats can then give high contribution to survivability. Commonly, an energy absorber is a constant load device, if one excludes an initial elastic part of the load-stroke curve. On helicopter seats, this behavior is obtained by plastic deformation of a metal component or scraping of material. In the present work the authors have studied three absorption systems, which differ in relation to their shape, their working conditions and their constructive materials. All the combinations have been analyzed for applications in VIP helicopter seats.

  10. Design for Manufacturing for Energy Absorption Systems

    NASA Astrophysics Data System (ADS)

    Del Prete, A.; Primo, T.; Papadia, G.; Manisi, B.

    2011-05-01

    In the typical scenario of a helicopter crash, impact with the ground is preceded by a substantially vertical drop, with the result that a seated occupant of a helicopter experiences high spinal loads and pelvic deceleration during such crash due to the sudden arresting of vertical downward motion. It has long been recognized that spinal injuries to occupants of helicopters in such crash scenario can be minimized by seat arrangements which limit the deceleration to which the seated occupant is subjected, relative to the helicopter, to a predetermined maximum, by allowing downward movement of the seated occupant relative to the helicopter, at the time of impact with the ground, under a restraining force which, over a limited range of such movement, is limited to a predetermined maximum. In practice, significant benefits, in the way of reduced injuries and reduced seriousness of injuries, can be afforded in this way in such crash situations even where the extent of such controlled vertical movement permitted by the crashworthy seat arrangement is quite limited. Important increase of accident safety is reached with the installation of crashworthy shock absorbers on the main landing gear, but this solution is mostly feasible on military helicopters with long fixed landing gear. Seats can then give high contribution to survivability. Commonly, an energy absorber is a constant load device, if one excludes an initial elastic part of the load-stroke curve. On helicopter seats, this behavior is obtained by plastic deformation of a metal component or scraping of material. In the present work the authors have studied three absorption systems, which differ in relation to their shape, their working conditions and their constructive materials. All the combinations have been analyzed for applications in VIP helicopter seats.

  11. Seasonal Solar Thermal Absorption Energy Storage Development.

    PubMed

    Daguenet-Frick, Xavier; Gantenbein, Paul; Rommel, Mathias; Fumey, Benjamin; Weber, Robert; Gooneseker, Kanishka; Williamson, Tommy

    2015-01-01

    This article describes a thermochemical seasonal storage with emphasis on the development of a reaction zone for an absorption/desorption unit. The heat and mass exchanges are modelled and the design of a suitable reaction zone is explained. A tube bundle concept is retained for the heat and mass exchangers and the units are manufactured and commissioned. Furthermore, experimental results of both absorption and desorption processes are presented and the exchanged power is compared to the results of the simulations. PMID:26842331

  12. The Protonation States of Oxo-Bridged MnIV-Dimers Resolved by Experimental and Computational Mn K Pre-Edge X-Ray Absorption Spectroscopy

    PubMed Central

    Krewald, Vera; Lassalle-Kaiser, Benedikt; Boron, Thaddeus T.; Pollock, Christopher J.; Kern, Jan; Beckwith, Martha A.; Yachandra, Vittal K.; Pecoraro, Vincent L.; Yano, Junko; Neese, Frank; DeBeer, Serena

    2013-01-01

    In nature, the protonation of oxo bridges is a commonly encountered mechanism for fine-tuning chemical properties and reaction pathways. Often, however, the protonation states are difficult to establish experimentally. This is of particular importance in the oxygen evolving complex of Photosystem II, where identification of the bridging oxo protonation states is one of the essential requirements toward unraveling the mechanism. In order to establish a combined experimental and theoretical protocol for the determination of protonation states, we have systematically investigated a series of Mn model complexes by Mn K pre-edge X-ray absorption spectroscopy. An ideal test case for selective bis-μ-oxo-bridge protonation in a Mn-dimer is represented by the system [MnIV2(salpn)2(μ-OH(n))2](n+). Although the three species [MnIV2(salpn)2(μ-O)2], [MnIV2(salpn)2(μ-O)(μ-OH)]+ and [MnIV2(salpn)2(μ-OH)2]2+ differ only in the protonation of the oxo bridges, they exhibit distinct differences in the pre-edge region while maintaining the same edge energy. The experimental spectra are correlated in detail to theoretical ly calculated spectra. A time-dependent density functional theory approach for calculating the pre-edge spectra of molecules with multiple metal centers is presented, using both high-spin (HS) and broken-symmetry (BS) electronic structure solutions. The most intense pre-edge transitions correspond to an excitation of the Mn-1s core electrons into the unoccupied orbitals of local eg character (dz2 and dxy based in the chosen coordinate system). The lowest by energy experimental feature is dominated by excitations of 1s-α electrons and the second observed feature is primarily attributed to 1s-β electron excitations. The observed energetic separation is due to spin polarization effects in spin-unrestricted density functional theory and models final state multiplet effects. The effects of spin polarization on the calculated Mn K pre-edge spectra, in both the HS

  13. Energy absorption in composite materials for crashworthy structures

    NASA Technical Reports Server (NTRS)

    Farley, Gary L.

    1987-01-01

    Crash energy-absorption processes in composite materials have been studied as part of a research program aimed at the development of energy absorbing subfloor beams for crashworthy military helicopters. Based on extensive tests on glass/epoxy, graphite/epoxy, and Kevlar/epoxy composites, it is shown that the energy-absorption characteristics and crushing modes of composite beams are similar to those exhibited by tubular specimens of similar material and architecture. The crushing mechanisms have been determined and related to the mechanical properties of the constituent materials and specimen architecture. A simple and accurate method for predicting the energy-absorption capability of composite beams has been developed.

  14. Lead uptake in diverse plant families: a study applying X-ray absorption near edge spectroscopy.

    PubMed

    Bovenkamp, Gudrun L; Prange, Alexander; Schumacher, Wolfgang; Ham, Kyungmin; Smith, Aaron P; Hormes, Josef

    2013-05-01

    The chemical environment of lead in roots and leaves of plants from four different plant families and a lichen from a former lead mining site in the Eifel Mountains in Germany was determined by Pb L3-edge XANES measurements using solid reference compounds and also aqueous solutions of different ionic strength simulating the plant environment. Pb(2+) ions in the plants were found to have two major coordinations, one with nine oxygen atoms in the first coordination shell similar to outer-sphere complexation and a second coordination with just three oxygen atoms similar to inner-sphere complexation. This can be interpreted assuming that lead is sorbed on the surface of cell walls depending on the concentration of lead in the soil solution. Pb L3-edge XANES spectra of dried and fresh plant samples are very similar because sorption does not change with removal of water but only because of the initial ionic strength. No bonding to biologically important groups (-S, - N) or precipitation (-PO4) was found. PMID:23517351

  15. Energy absorption studied to reduce aircraft crash forces

    NASA Technical Reports Server (NTRS)

    1981-01-01

    The NASA/FAA aircraft safety reseach programs for general aviation aircraft are discussed. Energy absorption of aircraft subflooring and redesign of interior flooring are being studied. The testing of energy absorbing configurations is described. The three NASA advanced concepts performed at neary the maximum possible amount of energy absorption, and one of two minimum modifications concepts performed well. Planned full scale tests are described. Airplane seat concepts are being considered.

  16. Evidence for 5d-σ and 5d-π covalency in lanthanide sesquioxides from oxygen K-edge X-ray absorption spectroscopy.

    PubMed

    Altman, Alison B; Pacold, Joseph I; Wang, Jian; Lukens, Wayne W; Minasian, Stefan G

    2016-06-14

    The electronic structure in the complete series of stable lanthanide sesquioxides, Ln2O3 (Ln = La to Lu, except radioactive Pm), has been evaluated using oxygen K-edge X-ray absorption spectroscopy (XAS) with a scanning transmission X-ray microscope (STXM). The experimental results agree with recent synthetic, spectroscopic and theoretical investigations that provided evidence for 5d orbital involvement in lanthanide bonding, while confirming the traditional viewpoint that there is little Ln 4f and O 2p orbital mixing. However, the results also showed that changes in the energy and occupancy of the 4f orbitals can impact Ln 5d and O 2p mixing, leading to several different bonding modes for seemingly identical Ln2O3 structures. On moving from left to right in the periodic table, abrupt changes were observed for the energy and intensity of transitions associated with Ln 5d and O 2p antibonding states. These changes in peak intensity, which were directly related to the amounts of O 2p and Ln 5d mixing, were closely correlated to the well-established trends in the chemical accessibility of the 4f orbitals towards oxidation or reduction. The unique insight provided by the O K-edge XAS is discussed in the context of several recent theoretical and physical studies on trivalent lanthanide compounds. PMID:26979662

  17. Simulations of iron K pre-edge X-ray absorption spectra using the restricted active space method.

    PubMed

    Guo, Meiyuan; Sørensen, Lasse Kragh; Delcey, Mickaël G; Pinjari, Rahul V; Lundberg, Marcus

    2016-01-28

    The intensities and relative energies of metal K pre-edge features are sensitive to both geometric and electronic structures. With the possibility to collect high-resolution spectral data it is important to find theoretical methods that include all important spectral effects: ligand-field splitting, multiplet structures, 3d-4p orbital hybridization, and charge-transfer excitations. Here the restricted active space (RAS) method is used for the first time to calculate metal K pre-edge spectra of open-shell systems, and its performance is tested against on six iron complexes: [FeCl6](n-), [FeCl4](n-), and [Fe(CN)6](n-) in ferrous and ferric oxidation states. The method gives good descriptions of the spectral shapes for all six systems. The mean absolute deviation for the relative energies of different peaks is only 0.1 eV. For the two systems that lack centrosymmetry [FeCl4](2-/1-), the ratios between dipole and quadrupole intensity contributions are reproduced with an error of 10%, which leads to good descriptions of the integrated pre-edge intensities. To gain further chemical insight, the origins of the pre-edge features have been analyzed with a chemically intuitive molecular orbital picture that serves as a bridge between the spectra and the electronic structures. The pre-edges contain information about both ligand-field strengths and orbital covalencies, which can be understood by analyzing the RAS wavefunction. The RAS method can thus be used to predict and rationalize the effects of changes in both the oxidation state and ligand environment in a number of hard X-ray studies of small and medium-sized molecular systems. PMID:26742851

  18. The effect of nanocrystallite size in monoclinic HfO{sub 2} films on lattice expansion and near-edge optical absorption

    SciTech Connect

    Cisneros-Morales, M. C.; Aita, C. R.

    2010-05-10

    Nanocrystalline monoclinic HfO{sub 2} films were sputter deposited on fused silica substrates, air annealed at 573 to 1273 K to affect crystallite growth, and analyzed by x-ray diffraction and spectrophotometry. Lattice expansion occurs with diminishing crystallite size. O 2p->Hf 5d interband absorption dominates the optical edge at energy E>=6.24 eV, with an optical band gap, E{sub o}=5.48+-0.023, which is independent of crystallite size. However, the strength of a localized resonant band, with onset at 5.65 eV and maximum at 5.94 eV, is affected by crystallite size. Its polaronic origin in a perfect HfO{sub 2} lattice is discussed.

  19. A laboratory-based hard x-ray monochromator for high-resolution x-ray emission spectroscopy and x-ray absorption near edge structure measurements.

    PubMed

    Seidler, G T; Mortensen, D R; Remesnik, A J; Pacold, J I; Ball, N A; Barry, N; Styczinski, M; Hoidn, O R

    2014-11-01

    We report the development of a laboratory-based Rowland-circle monochromator that incorporates a low power x-ray (bremsstrahlung) tube source, a spherically bent crystal analyzer, and an energy-resolving solid-state detector. This relatively inexpensive, introductory level instrument achieves 1-eV energy resolution for photon energies of ∼5 keV to ∼10 keV while also demonstrating a net efficiency previously seen only in laboratory monochromators having much coarser energy resolution. Despite the use of only a compact, air-cooled 10 W x-ray tube, we find count rates for nonresonant x-ray emission spectroscopy comparable to those achieved at monochromatized spectroscopy beamlines at synchrotron light sources. For x-ray absorption near edge structure, the monochromatized flux is small (due to the use of a low-powered x-ray generator) but still useful for routine transmission-mode studies of concentrated samples. These results indicate that upgrading to a standard commercial high-power line-focused x-ray tube or rotating anode x-ray generator would result in monochromatized fluxes of order 10(6)-10(7) photons/s with no loss in energy resolution. This work establishes core technical capabilities for a rejuvenation of laboratory-based hard x-ray spectroscopies that could have special relevance for contemporary research on catalytic or electrical energy storage systems using transition-metal, lanthanide, or noble-metal active species. PMID:25430123

  20. A laboratory-based hard x-ray monochromator for high-resolution x-ray emission spectroscopy and x-ray absorption near edge structure measurements

    SciTech Connect

    Seidler, G. T. Mortensen, D. R.; Remesnik, A. J.; Pacold, J. I.; Ball, N. A.; Barry, N.; Styczinski, M.; Hoidn, O. R.

    2014-11-15

    We report the development of a laboratory-based Rowland-circle monochromator that incorporates a low power x-ray (bremsstrahlung) tube source, a spherically bent crystal analyzer, and an energy-resolving solid-state detector. This relatively inexpensive, introductory level instrument achieves 1-eV energy resolution for photon energies of ∼5 keV to ∼10 keV while also demonstrating a net efficiency previously seen only in laboratory monochromators having much coarser energy resolution. Despite the use of only a compact, air-cooled 10 W x-ray tube, we find count rates for nonresonant x-ray emission spectroscopy comparable to those achieved at monochromatized spectroscopy beamlines at synchrotron light sources. For x-ray absorption near edge structure, the monochromatized flux is small (due to the use of a low-powered x-ray generator) but still useful for routine transmission-mode studies of concentrated samples. These results indicate that upgrading to a standard commercial high-power line-focused x-ray tube or rotating anode x-ray generator would result in monochromatized fluxes of order 10{sup 6}–10{sup 7} photons/s with no loss in energy resolution. This work establishes core technical capabilities for a rejuvenation of laboratory-based hard x-ray spectroscopies that could have special relevance for contemporary research on catalytic or electrical energy storage systems using transition-metal, lanthanide, or noble-metal active species.

  1. Experimental station for laser-based picosecond time-resolved x-ray absorption near-edge spectroscopy

    SciTech Connect

    Dorchies, F. Fedorov, N.; Lecherbourg, L.

    2015-07-15

    We present an experimental station designed for time-resolved X-ray Absorption Near-Edge Spectroscopy (XANES). It is based on ultrashort laser-plasma x-ray pulses generated from a table-top 100 mJ-class laser at 10 Hz repetition rate. A high transmission (10%–20%) x-ray beam line transport using polycapillary optics allows us to set the sample in an independent vacuum chamber, providing high flexibility over a wide spectral range from 0.5 up to 4 keV. Some XANES spectra are presented, demonstrating 1% noise level in only ∼1 mn and ∼100 cumulated laser shots. Time-resolved measurements are reported, indicating that the time resolution of the entire experimental station is 3.3 ± 0.6 ps rms.

  2. Extremely asymmetric diffraction as a method of determining magneto-optical constants for X-rays near absorption edges

    SciTech Connect

    Andreeva, M. A.; Repchenko, Yu. L.; Smekhova, A. G.; Dumesnil, K.; Wilhelm, F.; Rogalev, A.

    2015-06-15

    The spectral dependence of the Bragg peak position under conditions of extremely asymmetric diffraction has been analyzed in the kinematical and dynamical approximations of the diffraction theory. Simulations have been performed for the L{sub 3} absorption edge of yttrium in a single-crystal YFe{sub 2} film; they have shown that the magneto-optical constants (or, equivalently, the dispersion corrections to the atomic scattering factor) for hard X-rays can be determined from this dependence. Comparison with the experimental data obtained for a Nb(4 nm)/YFe{sub 2}(40 nm〈110〉)/Fe(1.5 nm)/Nb(50 nm)/sapphire sample at the European Synchrotron Radiation Facility has been made.

  3. 3D Imaging of Nickel Oxidation States using Full Field X-ray Absorption Near Edge Structure Nanotomography

    SciTech Connect

    Nelson, George; Harris, William; Izzo, John; Grew, Kyle N.

    2012-01-20

    Reduction-oxidation (redox) cycling of the nickel electrocatalyst phase in the solid oxide fuel cell (SOFC) anode can lead to performance degradation and cell failure. A greater understanding of nickel redox mechanisms at the microstructural level is vital to future SOFC development. Transmission x-ray microscopy (TXM) provides several key techniques for exploring oxidation states within SOFC electrode microstructure. Specifically, x-ray nanotomography and x-ray absorption near edge structure (XANES) spectroscopy have been applied to study samples of varying nickel (Ni) and nickel oxide (NiO) compositions. The imaged samples are treated as mock SOFC anodes containing distinct regions of the materials in question. XANES spectra presented for the individual materials provide a basis for the further processing and analysis of mixed samples. Images of composite samples obtained are segmented, and the distinct nickel and nickel oxide phases are uniquely identified using full field XANES spectroscopy. Applications to SOFC analysis are discussed.

  4. Experimental station for laser-based picosecond time-resolved x-ray absorption near-edge spectroscopy

    NASA Astrophysics Data System (ADS)

    Dorchies, F.; Fedorov, N.; Lecherbourg, L.

    2015-07-01

    We present an experimental station designed for time-resolved X-ray Absorption Near-Edge Spectroscopy (XANES). It is based on ultrashort laser-plasma x-ray pulses generated from a table-top 100 mJ-class laser at 10 Hz repetition rate. A high transmission (10%-20%) x-ray beam line transport using polycapillary optics allows us to set the sample in an independent vacuum chamber, providing high flexibility over a wide spectral range from 0.5 up to 4 keV. Some XANES spectra are presented, demonstrating 1% noise level in only ˜1 mn and ˜100 cumulated laser shots. Time-resolved measurements are reported, indicating that the time resolution of the entire experimental station is 3.3 ± 0.6 ps rms.

  5. Extremely asymmetric diffraction as a method of determining magneto-optical constants for X-rays near absorption edges

    NASA Astrophysics Data System (ADS)

    Andreeva, M. A.; Repchenko, Yu. L.; Smekhova, A. G.; Dumesnil, K.; Wilhelm, F.; Rogalev, A.

    2015-06-01

    The spectral dependence of the Bragg peak position under conditions of extremely asymmetric diffraction has been analyzed in the kinematical and dynamical approximations of the diffraction theory. Simulations have been performed for the L 3 absorption edge of yttrium in a single-crystal YFe2 film; they have shown that the magneto-optical constants (or, equivalently, the dispersion corrections to the atomic scattering factor) for hard X-rays can be determined from this dependence. Comparison with the experimental data obtained for a Nb(4 nm)/YFe2(40 nm<110>)/Fe(1.5 nm)/Nb(50 nm)/sapphire sample at the European Synchrotron Radiation Facility has been made.

  6. Tracking Drug Loading Capacities of Calcium Silicate Hydrate Carrier: A Comparative X-ray Absorption Near Edge Structures Study.

    PubMed

    Guo, Xiaoxuan; Wang, Zhiqiang; Wu, Jin; Yiu, Yun-Mui; Hu, Yongfeng; Zhu, Ying-Jie; Sham, Tsun-Kong

    2015-08-01

    Mesoporous spheres of calcium silicate hydrate (MS-CSH) have been prepared by an ultrasonic method. Following an earlier work in which we have revealed the interactions between ibuprofen (IBU) and CSH carriers with different morphologies by X-ray absorption near edge structures (XANES) analysis. In the present investigation, two new drug molecules, alendronate sodium (ALN) and gentamicin sulfate (GS), were incorporated into MS-CSH, and their drug loading capacities (DLCs) were measured using thermogravimetric analysis to establish the relationship between drug-carrier interactions and DLCs. The XANES spectra clearly indicate that acidic functional groups of the drug molecules linked to the active sites (Ca-OH and Si-OH groups) of MS-CSH on the surface by electrostatic interactions. In addition, it is found that the stoichiometric ratio of Ca(2+) ions of CSH carriers and the functional groups of drug molecules may significantly influence the DLCs. PMID:26162602

  7. Anisotropy of Chemical Bonds in Collagen Molecules Studied by X-ray Absorption Near-Edge Structure (XANES) Spectroscopy

    PubMed Central

    Lam, Raymond S.K.; Metzler, Rebecca A.; Gilbert, Pupa U.P.A.; Beniash, Elia

    2012-01-01

    Collagen type I fibrils are the major building blocks of connective tissues. Collagen fibrils are anisotropic supra-molecular structures, and their orientation can be revealed by polarized light microscopy and vibrational microspectroscopy. We hypothesized that the anisotropy of chemical bonds in the collagen molecules, and hence their orientation, might also be detected by X-ray photoemission electron spectromicroscopy (X-PEEM) and X-ray absorption near-edge structure (XANES) spectroscopy, which use linearly polarized synchrotron light. To test this hypothesis, we analyzed sections of rat-tail tendon, composed of parallel arrays of collagen fibrils. The results clearly indicate that XANES-PEEM is sensitive to collagen fibril orientation and, more specifically, to the orientations of carbonyl and amide bonds in collagen molecules. These data suggest that XANES-PEEM is a promising technique for characterizing the chemical composition and structural organization at the nanoscale of collagen-based connective tissues, including tendons, cartilage, and bone. PMID:22148847

  8. Electrospun nanofibers of Er{sup 3+}-doped TiO{sub 2} with photocatalytic activity beyond the absorption edge

    SciTech Connect

    Zheng, Yali; Wang, Wenzhong

    2014-02-15

    Er{sup 3+}-doped TiO{sub 2} nanofibers with different Er{sup 3+} contents were prepared via electrospinning and characterized by X-ray diffraction, scanning electron microscopy, ultraviolet–visible diffuse reflectance spectroscopy and photocurrent measurement. Photocatalytic activities of the as-prepared samples were evaluated by the decolorization of methyl orange aqueous solution under simulated solar light irradiation. The results indicated that the photocatalytic activity of Er{sup 3+}-doped TiO{sub 2} nanofibers was much higher than that of the undoped one, and the optimal dosage of Er{sup 3+} at 1 mol% achieved the highest degradation rate. Moreover, the photocatalytic activity of Er{sup 3+}-doped TiO{sub 2} nanofibers under the irradiation of light with the wavelength beyond the absorption edge of TiO{sub 2} was explored by the decolorization of a dye, rhodamine B and the photodegradation of a typical colorless pollutant, phenol. The results further revealed the mechanism of the enhanced photocatalytic activity through Er{sup 3+} doping in TiO{sub 2} nanofibers. - Graphical abstract: Display Omitted - Highlights: ●Er{sup 3+}:TiO{sub 2} nanofibers with different Er{sup 3+} contents were prepared via electrospinning. ●The photocatalytic activity of Er{sup 3+}:TiO{sub 2} was much higher than that of undoped one. ●Er{sup 3+}:TiO{sub 2} could be activated by the light with wavelength beyond the absorption edge.

  9. Ligand and Charge Dependence for Absorption Edge in XANES Spectra of TPP[Fe(Pc)L2]2 Systems

    NASA Astrophysics Data System (ADS)

    Takahashi, Kei; Watanabe, Akie; Niki, Kaori; Hanasaki, Noriaki; Kanda, Akinori; Fujikawa, Takashi

    We apply real space full multiple scattering theory to interpret the Fe K-edge XANES spectra of TPP[Fe(Pc)L2]2 (L = CN, Cl and Br) systems, which show the giant magnetoresistance (GMR) at the low temperatures. In the previous paper, we have reported the absorption edge shift of the XANES spectra, whose origin remains unclear, for TPP[Fe(Pc)L2]2 systems. In order to clarify the relation between the charge of the Fe atom, the local structure of the axial ligand and the XANES spectra, we improve the calculation of the XANES spectra by taking into account the wider region including the neighboring Fe(Pc)L2 and TPP molecules. Our multiple scattering analyses suggest that the spectral shape is strongly influenced by the distance between a central Fe and axial ligands L. The number of Fe 3d electrons obtained by density functional theory calculations show weak dependence on the axial ligands L. The EXAFS spectra, the polarization dependence and the temperature dependence of the XANES spectra are also discussed.

  10. Near-edge X-ray absorption fine-structure spectroscopy of naphthalene diimide-thiophene co-polymers

    SciTech Connect

    Gann, Eliot; McNeill, Christopher R.; Szumilo, Monika; Sirringhaus, Henning; Sommer, Michael; Maniam, Subashani; Langford, Steven J.; Thomsen, Lars

    2014-04-28

    Near-edge X-ray absorption fine-structure (NEXAFS) spectroscopy is an important tool for probing the structure of conjugated polymer films used in organic electronic devices. High-performance conjugated polymers are often donor-acceptor co-polymers which feature a repeat unit with multiple functional groups. To facilitate better application of NEXAFS spectroscopy to the study of such materials, improved understanding of the observed NEXAFS spectral features is required. In order to examine how the NEXAFS spectrum of a donor-acceptor co-polymer relates to the properties of the sub-units, a series of naphthalene diimide-thiophene-based co-polymers have been studied where the nature and length of the donor co-monomer has been systematically varied. The spectra of these materials are compared with that of a thiophene homopolymer and naphthalene diimide monomer enabling peak assignment and the influence of inter-unit electronic coupling to be assessed. We find that while it is possible to attribute peaks within the π* manifold as arising primarily due to the naphthalene diimide or thiophene sub-units, very similar dichroism of these peaks is observed indicating that it may not be possible to separately probe the molecular orientation of the separate sub-units with carbon K-edge NEXAFS spectroscopy.

  11. X-ray absorption near-edge structure micro-spectroscopy study of vanadium speciation in Phycomyces blakesleeanus mycelium.

    PubMed

    Žižić, Milan; Dučić, Tanja; Grolimund, Daniel; Bajuk-Bogdanović, Danica; Nikolic, Miroslav; Stanić, Marina; Križak, Strahinja; Zakrzewska, Joanna

    2015-09-01

    Vanadium speciation in the fungus Phycomyces blakesleeanus was examined by X-ray absorption near-edge structure (XANES) spectroscopy, enabling assessment of oxidation states and related molecular symmetries of this transition element in the fungus. The exposure of P. blakesleeanus to two physiologically important vanadium species (V(5+) and V(4+)) resulted in the accumulation of this metal in central compartments of 24 h old mycelia, most probably in vacuoles. Tetrahedral V(5+), octahedral V(4+), and proposed intracellular complexes of V(5+) were detected simultaneously after addition of a physiologically relevant concentration of V(5+) to the mycelium. A substantial fraction of the externally added V(4+) remained mostly in its original form. However, observable variations in the pre-edge-peak intensities in the XANES spectra indicated intracellular complexation and corresponding changes in the molecular coordination symmetry. Vanadate complexation was confirmed by (51)V NMR and Raman spectroscopy, and potential binding compounds including cell-wall constituents (chitosan and/or chitin), (poly)phosphates, DNA, and proteins are proposed. The evidenced vanadate complexation and reduction could also explain the resistance of P. blakesleeanus to high extracellular concentrations of vanadium. PMID:26253227

  12. Quasi-static energy absorption of hollow microlattice structures

    SciTech Connect

    Liu, YL; Schaedler, TA; Jacobsen, AJ; Chen, X

    2014-12-01

    We present a comprehensive modeling and numerical study focusing on the energy quasi-static crushing behavior and energy absorption characteristics of hollow tube microlattice structures. The peak stress and effective plateau stress of the hollow microlattice structures are deduced for different geometrical parameters which gives volume and mass densities of energy absorption, D-v and D-m, scale with the relative density, (rho) over bar, as D-v similar to (rho) over bar (1) (5) and D-m similar to (rho) over bar (0 5), respectively, fitting very well to the experimental results of both 60 degrees inclined and 90 degrees predominately microlattices. Then the strategies for energy absorption enhancement are proposed for the engineering design of microlattice structures. By introducing a gradient in the thickness or radius of the lattice members, the buckle propagation can be modulated resulting in an increase in energy absorption density that can exceed 40%. Liquid filler is another approach to improve energy absorption by strengthening the microtruss via circumference expansion, and the gain may be over 100% in terms of volume density. Insight into the correlations between microlattice architecture and energy absorption performance combined with the high degree of architecture control paves the way for designing high performance microlattice structures for a range of impact and impulse mitigation applications for vehicles and structures. (C) 2014 Elsevier Ltd. All rights reserved.

  13. FREQUENCY-DEPENDENT ABSORPTION OF ELECTROMAGNETIC ENERGY IN BIOLOGICAL TISSUE

    EPA Science Inventory

    The frequency-dependent absorption of electromagnetic energy in biological tissue is illustrated by use of the Debye equations, model calculations for different irradiation conditions, and measured electrical properties (conductivity and permittivity) of different tissues. Four s...

  14. Energy calibration of superconducting transition edge sensors for x-ray detection using pulse analysis

    SciTech Connect

    Hollerith, C.; Simmnacher, B.; Weiland, R.; Feilitzsch, F. v.; Isaila, C.; Jochum, J.; Potzel, W.; Hoehne, J.; Phelan, K.; Wernicke, D.; May, T.

    2006-05-15

    Transition edge sensors (TESs) have been developed to be used as high-resolution x-ray detectors. They show excellent energy resolution and can be used in many applications. TESs are a special kind of calorimeters that can determine small temperature changes after x-ray absorption. Such a temperature change causes a strong resistance change (superconducting to normal-conducting phase transition) that can be measured. The energy calibration of a TES based spectrometer is problematic due to the nonlinear behavior of the detector response. In this article, a method is introduced to calibrate the energy scale of TES spectra. This is accomplished by calculating the energy dependence of the response of the detector operated in electrothermal feedback mode. Using this method a calibration accuracy of a few eV for an x-ray energy of 6 keV can be achieved. Examples of energy dispersive x-ray spectroscopy (EDS) measurements demonstrate the high quality of this method for everyday use of TES EDS detectors in material analysis. However, because the method relies only on a few very general assumptions, it should also be useful for other kinds of TES detectors.

  15. 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

  16. Characterization of hydrophobic nanoporous particle liquids for energy absorption

    NASA Astrophysics Data System (ADS)

    Hsu, Yi; Liu, Yingtao

    2016-04-01

    Recently, the development of hydrophobic nanoporous technologies has drawn increased attention, especially for the applications of energy absorption and impact protection. Although significant amount of research has been conducted to synthesis and characterize materials to protect structures from impact damage, the tradition methods focused on converting kinetic energy to other forms, such as heat and cell buckling. Due to their high energy absorption efficiency, hydrophobic nanoporous particle liquids (NPLs) are one of the most attractive impact mitigation materials. During impact, such particles directly trap liquid molecules inside the non-wetting surface of nanopores in the particles. The captured impact energy is simply stored temporarily and isolated from the original energy transmission path. In this paper we will investigate the energy absorption efficiency of combinations of silica nanoporous particles and with multiple liquids. Inorganic particles, such as nanoporous silica, are characterized using scanning electron microscopy. Small molecule promoters, such as methanol and ethanol, are introduced to the prepared NPLs. Their effects on the energy absorption efficiency are studied in this paper. NPLs are prepared by dispersing the studied materials in deionized water. Energy absorption efficiency of these liquids are experimentally characterized using an Instron mechanical testing frame and in-house develop stainless steel hydraulic cylinder system.

  17. Sulfur K-edge X-ray absorption spectroscopy and time-dependent density functional theory of arsenic dithiocarbamates.

    PubMed

    Donahue, Courtney M; Pacheco, Juan S Lezama; Keith, Jason M; Daly, Scott R

    2014-06-28

    S K-edge X-ray absorption spectroscopy (XAS) and time-dependent density functional theory (TDDFT) calculations were performed on a series of As[S2CNR2]3 complexes, where R2 = Et2, (CH2)5 and Ph2, to determine how dithiocarbamate substituents attached to N affect As[S2CNR2]3 electronic structure. Complimentary [PPh4][S2CNR2] salts were also studied to compare dithiocarbamate bonding in the absence of As. The XAS results indicate that changing the orientation of the alkyl substituents from trans to cis (R2 = Et2vs. (CH2)5) yields subtle variations whereas differences associated with a change from alkyl to aryl are much more pronounced. For example, despite the differences in As 4p mixing, the first features in the S K-edge XAS spectra of [PPh4][S2CNPh2] and As[S2CNPh2]3 were both shifted by 0.3 eV compared to their alkyl-substituted derivatives. DFT calculations revealed that the unique shift observed for [PPh4][S2CNPh2] is due to phenyl-induced splitting of the π* orbitals delocalized over N, C and S. A similar phenomenon accounts for the shift observed for As[S2CNPh2]3, but the presence of two unique S environments (As-S and As···S) prevented reliable analysis of As-S covalency from the XAS data. In the absence of experimental values, DFT calculations revealed a decrease in As-S orbital mixing in As[S2CNPh2]3 that stems from a redistribution of electron density to S atoms participating in weaker As···S interactions. Simulated spectra obtained from TDDFT calculations reproduce the experimental differences in the S K-edge XAS data, which suggests that the theory is accurately modeling the experimental differences in As-S orbital mixing. The results highlight how S K-edge XAS and DFT can be used cooperatively to understand the electronic structure of low symmetry coordination complexes containing S atoms in different chemical environments. PMID:24811926

  18. Radiant energy absorption studies for laser propulsion. [gas dynamics

    NASA Technical Reports Server (NTRS)

    Caledonia, G. E.; Wu, P. K. S.; Pirri, A. N.

    1975-01-01

    A study of the energy absorption mechanisms and fluid dynamic considerations for efficient conversion of high power laser radiation into a high velocity flow is presented. The objectives of the study are: (1) to determine the most effective absorption mechanisms for converting laser radiation into translational energy, and (2) to examine the requirements for transfer of the absorbed energy into a steady flow which is stable to disturbances in the absorption zone. A review of inverse Bremsstrahlung, molecular and particulate absorption mechanisms is considered and the steady flow and stability considerations for conversion of the laser power to a high velocity flow in a nozzle configuration is calculated. A quasi-one-dimensional flow through a nozzle was formulated under the assumptions of perfect gas.

  19. 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.

  20. 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. PMID:27182829

  1. Electrosynthesis of ZnO nanorods and nanotowers: Morphology and X-ray Absorption Near Edge Spectroscopy studies

    NASA Astrophysics Data System (ADS)

    Sigircik, Gokmen; Erken, Ozge; Tuken, Tunc; Gumus, Cebrail; Ozkendir, Osman M.; Ufuktepe, Yuksel

    2015-06-01

    Deposition mechanism of nano-structured ZnO films has been investigated in the absence and presence of chloride ions from aqueous solution. The resulting opto-electronic properties were interpreted extensively, using X-ray diffraction (XRD), X-ray Absorption Near Edge Spectroscopy (XANES), field emission scanning electron microscopy (FE-SEM), UV-Visible spectroscopy and four probe techniques. The ZnO deposition is mass transport controlled process and the interaction of chloride ions with the surface has great influence on diffusion kinetics, considering the substantial species (Zn2+ and OH-) involved in the construction of ZnO film. This effect does not change major lattice parameters, as shown with detailed analysis of XRD data. However, the texture coefficient (Tc) (0 0 2) value is higher in presence of chloride ions containing synthesis solution which gave vertically aligned, well defined and uniformly dispersed nanorods structure. The calculated Eg values are in the range 3.28-3.41 eV and 3.22-3.31 eV for ZnO nanorods and nanotowers synthesized at different deposition periods, respectively. Furthermore, the charge mobility values regarding the deposition periods were measured to be in the ranges from 130.4 to 449.2 cm2 V-1 s-1 and 126.2 to 204.7 cm2 V-1 s-1 for nanorods and nanotowers, respectively. From XANES results, it was shown that the Zn K-edge spectrum is dominated by the transition of Zn 1s core electrons into the unoccupied Zn 4p states of the conduction band. Comparing the rod and tower nano-structured ZnO thin films, the excitation behavior of valence band electrons is different. Moreover, the density states of Zn 4p are higher for ZnO nanorods.

  2. Scattering with absorptive interaction: Energy-dependent potentials

    NASA Astrophysics Data System (ADS)

    Cassing, W.; Stingl, M.; Weiguny, A.

    1983-05-01

    The energy dependence and analytic structure of the effective interaction for elastic scattering of composite particles are investigated using Feshbach's projection technique. A generalized Levinson theorem is established for complex, nonlocal, and energy-dependent interactions. The analytical results are illustrated by means of Argand diagrams for a solvable model and the effect of energy averaging is discussed. NUCLEAR REACTIONS Scattering theory, S matrix for absorptive, energy-dependent potentials, Levinson theorem.

  3. Terahertz absorption spectra and potential energy distribution of liquid crystals.

    PubMed

    Chen, Zezhang; Jiang, Yurong; Jiang, Lulu; Ma, Heng

    2016-01-15

    In this work, the terahertz (THz) absorption spectra of a set of nematic liquid crystals were studied using the density functional theories (DFT). An accurate assignment of the vibrational modes corresponding to absorption frequencies were performed using potential energy distribution (PED) in a frequency range of 0-3 THz. The impacts of different core structures on THz absorption spectra were discussed. The results indicate that scope of application must be considered in the LC-based THz device designing. This proposed work may give a useful suggestion on the design of novel liquid crystal material in THz wave. PMID:26476072

  4. Energy absorption capabilities of composite sandwich panels under blast loads

    NASA Astrophysics Data System (ADS)

    Sankar Ray, Tirtha

    As blast threats on military and civilian structures continue to be a significant concern, there remains a need for improved design strategies to increase blast resistance capabilities. The approach to blast resistance proposed here is focused on dissipating the high levels of pressure induced during a blast through maximizing the potential for energy absorption of composite sandwich panels, which are a competitive structural member type due to the inherent energy absorption capabilities of fiber reinforced polymer (FRP) composites. Furthermore, the middle core in the sandwich panels can be designed as a sacrificial layer allowing for a significant amount of deformation or progressive failure to maximize the potential for energy absorption. The research here is aimed at the optimization of composite sandwich panels for blast mitigation via energy absorption mechanisms. The energy absorption mechanisms considered include absorbed strain energy due to inelastic deformation as well as energy dissipation through progressive failure of the core of the sandwich panels. The methods employed in the research consist of a combination of experimentally-validated finite element analysis (FEA) and the derivation and use of a simplified analytical model. The key components of the scope of work then includes: establishment of quantified energy absorption criteria, validation of the selected FE modeling techniques, development of the simplified analytical model, investigation of influential core architectures and geometric parameters, and investigation of influential material properties. For the parameters that are identified as being most-influential, recommended values for these parameters are suggested in conceptual terms that are conducive to designing composite sandwich panels for various blast threats. Based on reviewing the energy response characteristic of the panel under blast loading, a non-dimensional parameter AET/ ET (absorbed energy, AET, normalized by total energy

  5. Energy absorption characteristics of nano-composite conical structures

    NASA Astrophysics Data System (ADS)

    Silva, F.; Sachse, S.; Njuguna, J.

    2012-09-01

    The effect of the filler material on the energy absorption capabilities of polyamide 6 composite structures is studied in details in the present paper. The axial dynamic and quasi-static collapse of conical structures was conducted using a high energy drop tower, as well as Instron 5500R electro-mechanical testing machine. The impact event was recorded using a high-speed camera and the fracture surface was investigated using scanning electron microscopy (SEM). The obtained results indicate an important influence of filler material on the energy absorption capabilities of the polymer composites. A significant increase in specific energy absorption (SEA) is observed in polyamide 6 (PA6) reinforced with nano-silica particles (SiO2) and glass-spheres (GS), whereas addition of montmorillonite (MMT) did not change the SEA parameter.

  6. Local disorder investigation in NiS(2-x)Se(x) using Raman and Ni K-edge x-ray absorption spectroscopies.

    PubMed

    Marini, C; Joseph, B; Caramazza, S; Capitani, F; Bendele, M; Mitrano, M; Chermisi, D; Mangialardo, S; Pal, B; Goyal, M; Iadecola, A; Mathon, O; Pascarelli, S; Sarma, D D; Postorino, P

    2014-11-12

    We report on Raman and Ni K-edge x-ray absorption investigations of a NiS(2-x)Se(x) (with x = 0.00, 0.50/0.55, 0.60, and 1.20) pyrite family. The Ni K-edge absorption edge shows a systematic shift going from an insulating phase (x = 0.00 and 0.50) to a metallic phase (x = 0.60 and 1.20). The near-edge absorption features show a clear evolution with Se doping. The extended x-ray absorption fine structure data reveal the evolution of the local structure with Se doping which mainly governs the local disorder. We also describe the decomposition of the NiS(2-x)Se(x) Raman spectra and investigate the weights of various phonon modes using Gaussian and Lorentzian profiles. The effectiveness of the fitting models in describing the data is evaluated by means of Bayes factor estimation. The Raman analysis clearly demonstrates the disorder effects due to Se alloying in describing the phonon spectra of NiS(2-x)Se(x) pyrites. PMID:25320052

  7. Local disorder investigation in NiS2-xSex using Raman and Ni K-edge x-ray absorption spectroscopies

    NASA Astrophysics Data System (ADS)

    Marini, C.; Joseph, B.; Caramazza, S.; Capitani, F.; Bendele, M.; Mitrano, M.; Chermisi, D.; Mangialardo, S.; Pal, B.; Goyal, M.; Iadecola, A.; Mathon, O.; Pascarelli, S.; Sarma, D. D.; Postorino, P.

    2014-11-01

    We report on Raman and Ni K-edge x-ray absorption investigations of a NiS2-xSex (with x = 0.00, 0.50/0.55, 0.60, and 1.20) pyrite family. The Ni K-edge absorption edge shows a systematic shift going from an insulating phase (x = 0.00 and 0.50) to a metallic phase (x = 0.60 and 1.20). The near-edge absorption features show a clear evolution with Se doping. The extended x-ray absorption fine structure data reveal the evolution of the local structure with Se doping which mainly governs the local disorder. We also describe the decomposition of the NiS2-xSex Raman spectra and investigate the weights of various phonon modes using Gaussian and Lorentzian profiles. The effectiveness of the fitting models in describing the data is evaluated by means of Bayes factor estimation. The Raman analysis clearly demonstrates the disorder effects due to Se alloying in describing the phonon spectra of NiS2-xSex pyrites.

  8. Understanding of Edge Plasmas in Magnetic Fusion Energy Devices

    SciTech Connect

    Rognlien, T

    2004-11-01

    A limited overview is given of the theoretical understanding of edge plasmas in fusion devices. This plasma occupies the thin region between the hot core plasma and material walls in magnetically confinement configurations. The region is often formed by a change in magnetic topology from close magnetic field lines (i.e., the core region) and open field lines that contact material surfaces (i.e., the scrape-off layer [SOL]), with the most common example being magnetically diverted tokamaks. The physics of this region is determined by the interaction of plasma with neutral gas in the presence of plasma turbulence, with impurity radiation being an important component. Recent advances in modeling strong, intermittent micro-turbulent edge-plasma transport is given, and the closely coupled self-consistent evolution of the edge-plasma profiles in tokamaks. In addition, selected new results are given for the characterization of edge-plasmas behavior in the areas of edge-pedestal relaxation and SOL transport via Edge-Localize Modes (ELMs), impurity formation including dust, and magnetic field-line stochasticity in tokamaks.

  9. Probing Variable Amine/Amide Ligation in NiIIN2S2 Complexes Using Sulfur K-Edge and Nickel L-Edge X-ray Absorption Spectroscopies: Implications for the Active Site of Nickel Superoxide Dismutase

    SciTech Connect

    Shearer,J.; Dehestani, A.; Abanda, F.

    2008-01-01

    Nickel superoxide dismutase (NiSOD) is a recently discovered metalloenzyme that catalyzes the disproportionation of O2* into O2 and H2O2. In its reduced state, the mononuclear NiII ion is ligated by two cis-cysteinate sulfurs, an amine nitrogen (from the protein N-terminus), and an amide nitrogen (from the peptide backbone). Unlike many small molecule and metallopeptide-based NiN2S2 complexes, S-based oxygenation is not observed in NiSOD. Herein we explore the spectroscopic properties of a series of three NiIIN2S2 complexes (bisamine-ligated (bmmp-dmed)NiII, amine/amide-ligated (NiII(BEAAM)), and bisamide-ligated (NiII(emi))2) with varying amine/amide ligation to determine the origin of the dioxygen stability of NiSOD. Ni L-edge X-ray absorption spectroscopy (XAS) demonstrates that there is a progression in ligand-field strength with (bmmp-dmed)NiII having the weakest ligand field and (NiII(emi)2) having the strongest ligand field. Furthermore, these Ni L-edge XAS studies also show that all three complexes are highly covalent with (NiII(BEEAM)) having the highest degree of metal-ligand covalency of the three compounds studied. S K-edge XAS also shows a high degree of NiS covalency in all three complexes. The electronic structures of the three complexes were probed using both hybrid-DFT and multiconfigurational SORCI calculations. These calculations demonstrate that the nucleophilic Ni(3d)/S()* HOMO of these NiN2S2 complexes progressively decreases in energy as the amide-nitrogens are replaced with amine nitrogens. This decrease in energy of the HOMO deactivates the Ni-center toward O2 reactivity. Thus, the NiS bond is protected from S-based oxygenation explaining the enhanced stability of the NiSOD active-site toward oxygenation by dioxygen.

  10. Dynamic energy absorption characteristics of hollow microlattice structures

    SciTech Connect

    Liu, YL; Schaedler, TA; Chen, X

    2014-10-01

    Hollow microlattice structures are promising candidates for advanced energy absorption and their characteristics under dynamic crushing are explored. The energy absorption can be significantly enhanced by inertial stabilization, shock wave effect and strain rate hardening effect. In this paper we combine theoretical analysis and comprehensive finite element method simulation to decouple the three effects, and then obtain a simple model to predict the overall dynamic effects of hollow microlattice structures. Inertial stabilization originates from the suppression of sudden crushing of the microlattice and its contribution scales with the crushing speed, v. Shock wave effect comes from the discontinuity across the plastic shock wave front during dynamic loading and its contribution scales with e. The strain rate effect increases the effective yield strength upon dynamic deformation and increases the energy absorption density. A mechanism map is established that illustrates the dominance of these three dynamic effects at a range of crushing speeds. Compared with quasi-static loading, the energy absorption capacity a dynamic loading of 250 m/s can be enhanced by an order of magnitude. The study may shed useful insight on designing and optimizing the energy absorption performance of hollow microlattice structures under various dynamic loads. (C) 2014 Elsevier Ltd. All rights reserved.

  11. Depth-selective X-ray absorption spectroscopy by detection of energy-loss Auger electrons

    NASA Astrophysics Data System (ADS)

    Isomura, Noritake; Soejima, Narumasa; Iwasaki, Shiro; Nomoto, Toyokazu; Murai, Takaaki; Kimoto, Yasuji

    2015-11-01

    A unique X-ray absorption spectroscopy (XAS) method is proposed for depth profiling of chemical states in material surfaces. Partial electron yield mode detecting energy-loss Auger electrons, called the inelastic electron yield (IEY) mode, enables a variation in the probe depth. As an example, Si K-edge XAS spectra for a well-defined multilayer sample (Si3N4/SiO2/Si) have been investigated using this method at various kinetic energies. We found that the peaks assigned to the layers from the top layer to the substrate appeared in the spectra in the order of increasing energy loss relative to the Auger electrons. Thus, the probe depth can be changed by the selection of the kinetic energy of the energy loss electrons in IEY-XAS.

  12. Adsorption of dopamine on rutile TiO2 (110): a photoemission and near-edge X-ray absorption fine structure study.

    PubMed

    Jackman, Mark J; Syres, Karen L; Cant, David J H; Hardman, Samantha J O; Thomas, Andrew G

    2014-07-29

    Synchrotron radiation photoelectron spectroscopy and near-edge X-ray absorption fine structure (NEXAFS) techniques have been used to study the adsorption of dopamine on a rutile TiO2 (110) single crystal. Photoemission results suggest that dopamine bonds through the oxygen molecules in a bidentate fashion. From the data, it is ambiguous whether the oxygens bond to the same 5-fold coordinated surface titanium atom or bridges across two, although based on the bonding of pyrocatechol on rutile TiO2 (110), it is likely that the dopamine bridges two titanium atoms. Using the searchlight effect, the carbon K-edge near-edge X-ray absorption fine structure NEXAFS spectra recorded for dopamine on rutile TiO2 (110) show the phenyl ring to be oriented at 78° ± 5° from the surface and twisted 11 ± 10° relative to the (001) direction. PMID:25003716

  13. Sulfur and nitrogen speciation in humic substances by x-ray absorption near-edge structure spectroscopy

    SciTech Connect

    Vairavamurthy, M.A.; Wang, Shenghe; Maletic, D.

    1996-12-31

    Understanding the chemical composition and structure of complex macromolecules in the geosphere, such as humic substances and kerogen, poses a challenging analytical problem. Widely used chromatographic techniques, such as the pyrolysis GC-MS, cause severe changes in structure during preparation and analysis of the sample, and thus, may not give accurate information. An important non-destructive technique that is becoming popular in speciation studies of environmental and geochemical samples is x-ray absorption fine structure spectroscopy. We used the x-ray absorption near-edge structure (XANFS) spectroscopy for examining the speciation of sulfur and nitrogen in humic substances of different origins, including soil and marine sediments. XANES provides information on the characteristics of the functional groups containing these atoms because of its sensitivity to the electronic structure, oxidation state, and the geometry of the neighboring atoms. Organic sulfides, di- and poly-sulfides, sulfonates and organic sulfates are the major forms of sulfur detected in all the humics we examined. The oxidized sulfonate-sulfur dominates the composition of sulfur species in soil humics accounting for more than 60% of the total sulfur. In marine humics, although sulfonates are abundant in near-surface sediments, reduced sulfur species, particularly di-and poly-sulfides, also constitute an important fraction. The nitrogen XANES indicates the dominance of amino and amide groups among nitrogen functionalities, although porphyrinic and pyridinic groups also are present. The significance of these results for the transformations of nitrogen and sulfur in soil and sedimentary systems will be presented.

  14. Edge Functionalization of Graphene and Two-Dimensional Covalent Organic Polymers for Energy Conversion and Storage.

    PubMed

    Xiang, Zhonghua; Dai, Quanbin; Chen, Jian-Feng; Dai, Liming

    2016-08-01

    Edge functionalization by selectively attaching chemical moieties at the edge of graphene sheets with minimal damage of the carbon basal plane can impart solubility, film-forming capability, and electrocatalytic activity, while largely retaining the physicochemical properties of the pristine graphene. The resultant edge-functionalized graphene materials (EFGs) are attractive for various potential applications. Here, a focused, concise review on the synthesis of EFGs is presented, along with their 2D covalent organic polymer (2D COP) analogues, as energy materials. The versatility of edge-functionalization is revealed for producing tailor-made graphene and COP materials for efficient energy conversion and storage. PMID:27038041

  15. Heat exchange model in absorption chamber of water-direct-absorption-typed laser energy meter

    NASA Astrophysics Data System (ADS)

    Feng Wei, Ji; Qun Sun, Li; Zhang, Kai; Hu, XiaoYang; Zhou, Shan

    2015-04-01

    The interaction between laser and water flow is very complicated in the absorption chamber of a high energy laser (HEL) energy meter which directly uses water as an absorbing medium. Therefore, the heat exchange model cannot be studied through traditional methods, but it is the most important factor to improve heat exchange efficiency in the absorption chamber. After the exchanges of heat and mass were deeply analyzed, experimental study and numerical fitting were brought out. The original testing data of laser power and water flow temperature at one moment were utilized to calculate those at the next moment, and then the calculated temperature curve was compared with the measured one. If the two curves matched well, the corresponding coefficient was obtained. Meanwhile, numerous experiments were performed to study the effects of laser power, duration, focal spot scale, and water flow rate on heat exchange coefficient. In addition, the relationship between water phase change and heat exchange was analyzed. The heat exchange coefficient was increased by optimizing the construction of the absorption chamber or increasing water flow rate. The results provide the reference for design of water-direct-absorption-typed HEL energy meters, as well as for analysis of the interaction between other similar lasers and water flow.

  16. Cost and sensitivity of restricted active-space calculations of metal L-edge X-ray absorption spectra.

    PubMed

    Pinjari, Rahul V; Delcey, Mickaël G; Guo, Meiyuan; Odelius, Michael; Lundberg, Marcus

    2016-02-15

    The restricted active-space (RAS) approach can accurately simulate metal L-edge X-ray absorption spectra of first-row transition metal complexes without the use of any fitting parameters. These characteristics provide a unique capability to identify unknown chemical species and to analyze their electronic structure. To find the best balance between cost and accuracy, the sensitivity of the simulated spectra with respect to the method variables has been tested for two models, [FeCl6 ](3-) and [Fe(CN)6 ](3-) . For these systems, the reference calculations give deviations, when compared with experiment, of ≤1 eV in peak positions, ≤30% for the relative intensity of major peaks, and ≤50% for minor peaks. When compared with these deviations, the simulated spectra are sensitive to the number of final states, the inclusion of dynamical correlation, and the ionization potential electron affinity shift, in addition to the selection of the active space. The spectra are less sensitive to the quality of the basis set and even a double-ζ basis gives reasonable results. The inclusion of dynamical correlation through second-order perturbation theory can be done efficiently using the state-specific formalism without correlating the core orbitals. Although these observations are not directly transferable to other systems, they can, together with a cost analysis, aid in the design of RAS models and help to extend the use of this powerful approach to a wider range of transition metal systems. PMID:26502979

  17. Restricted active space calculations of L-edge X-ray absorption spectra: From molecular orbitals to multiplet states

    SciTech Connect

    Pinjari, Rahul V.; Delcey, Mickaël G.; Guo, Meiyuan; Lundberg, Marcus; Odelius, Michael

    2014-09-28

    The metal L-edge (2p → 3d) X-ray absorption spectra are affected by a number of different interactions: electron-electron repulsion, spin-orbit coupling, and charge transfer between metal and ligands, which makes the simulation of spectra challenging. The core restricted active space (RAS) method is an accurate and flexible approach that can be used to calculate X-ray spectra of a wide range of medium-sized systems without any symmetry constraints. Here, the applicability of the method is tested in detail by simulating three ferric (3d{sup 5}) model systems with well-known electronic structure, viz., atomic Fe{sup 3+}, high-spin [FeCl{sub 6}]{sup 3−} with ligand donor bonding, and low-spin [Fe(CN){sub 6}]{sup 3−} that also has metal backbonding. For these systems, the performance of the core RAS method, which does not require any system-dependent parameters, is comparable to that of the commonly used semi-empirical charge-transfer multiplet model. It handles orbitally degenerate ground states, accurately describes metal-ligand interactions, and includes both single and multiple excitations. The results are sensitive to the choice of orbitals in the active space and this sensitivity can be used to assign spectral features. A method has also been developed to analyze the calculated X-ray spectra using a chemically intuitive molecular orbital picture.

  18. Derivation of absorption coefficient and reduced scattering coefficient with edge-loss method and comparison with video reflectometry method

    NASA Astrophysics Data System (ADS)

    Yoshida, Kenichiro

    2016-08-01

    We derived the absorption coefficient ( μ a) and the reduced scattering coefficient ( μ s') using the edge-loss method (ELM) and the video reflectometry method (VRM), and compared the results. In a previous study, we developed the ELM to easily evaluate the lateral spread in the skin; the VRM is a conventional method. The ELM measures the translucency index, which is correlated with μ a and μ s'. To obtain a precise estimation of these parameters, we improved the treatment of a white standard and the surface reflection. For both skin phantoms and actual skin, the values for μ a and μ s' that we obtained using the ELM were similar to those obtained using the VRM, when μ a/ μ s' was less than or equal to 0.05 and the diffusion approximation was applicable. Under this condition, the spectral reflectivity is greater than 0.4. In this study, we considered wavelengths longer than 600 nm for Types III and IV of the Fitzpatrick scale. For skin, the repeatability errors of the parameters obtained with the ELM were smaller than those obtained with the VRM; this can be an advantage in field tests.

  19. Determining Orientational Structure of Diamondoid Thiols Attached to Silver Using Near Edge X-ray Absorption Fine Structure Spectroscopy

    SciTech Connect

    Willey, T M; Lee, J I; Fabbri, J D; Wang, D; Nielsen, M; Randel, J C; Schreiner, P R; Fokin, A A; Tkachenko, B A; Fokina, N A; Dahl, J P; Carlson, R K; Terminello, L J; Melosh, N A; van Buuren, T

    2008-10-07

    Near-edge x-ray absorption fine structure spectroscopy (NEXAFS) is a powerful tool for determination of molecular orientation in self-assembled monolayers and other surface-attached molecules. A general framework for using NEXAFS to simultaneously determine molecular tilt and twist of rigid molecules attached to surfaces is presented. This framework is applied to self-assembled monolayers of higher diamondoid, hydrocarbon molecules with cubic-diamond-cage structures. Diamondoid monolayers chemisorbed on metal substrates are known to exhibit interesting electronic and surface properties. This work compares molecular orientation in monolayers prepared on silver substrates using two different thiol positional isomers of [121]tetramantane, and thiols derived from two different pentamantane structural isomers, [1212]pentamantane and [1(2,3)4]pentamantane. The observed differences in monolayer structure demonstrate the utility and limitations of NEXAFS spectroscopy and the framework. The results also demonstrate the ability to control diamondoid assembly, in particular the molecular orientational structure, providing a flexible platform for the modification of surface properties with this exciting new class of nanodiamond materials.

  20. Derivation of absorption coefficient and reduced scattering coefficient with edge-loss method and comparison with video reflectometry method

    NASA Astrophysics Data System (ADS)

    Yoshida, Kenichiro

    2016-07-01

    We derived the absorption coefficient (μ a) and the reduced scattering coefficient (μ s') using the edge-loss method (ELM) and the video reflectometry method (VRM), and compared the results. In a previous study, we developed the ELM to easily evaluate the lateral spread in the skin; the VRM is a conventional method. The ELM measures the translucency index, which is correlated with μ a and μ s'. To obtain a precise estimation of these parameters, we improved the treatment of a white standard and the surface reflection. For both skin phantoms and actual skin, the values for μ a and μ s' that we obtained using the ELM were similar to those obtained using the VRM, when μ a/μ s' was less than or equal to 0.05 and the diffusion approximation was applicable. Under this condition, the spectral reflectivity is greater than 0.4. In this study, we considered wavelengths longer than 600 nm for Types III and IV of the Fitzpatrick scale. For skin, the repeatability errors of the parameters obtained with the ELM were smaller than those obtained with the VRM; this can be an advantage in field tests.

  1. Measurement of mass attenuation coefficients in some Cr, Co and Fe compounds around the absorption edge and the validity of the mixture rule

    NASA Astrophysics Data System (ADS)

    Turgut, U.; Simsek, O.; Büyükkasap, E.

    2007-08-01

    The total mass attenuation coefficients for elements Cr, Co and Fe and compounds CrCl_{2}, CrCl_{3}, Cr_{2}(SO_{4})_{3}K_{2}SO_{4}\\cdot24H_{2}O, CoO, CoCl_{2}, Co(CH_{3}COO)_{2}, FePO_{4}, FeCl_{3}\\cdot6H_{2}O, Fe(SO_{4})_{2}NH_{4}\\cdot12H_{2}O were measured at different energies between 4.508 and 14.142 keV using secondary excitation method. Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Se, Br, Rb, Sr were chosen as secondary exciters. 59.5 keV γ-rays emitted from a ^{241}Am annular source were used to excite a secondary exciter and K_{α}(K-L_{3}, L_{2}) lines emitted by the secondary exciter were counted by a Si(Li) detector with a resolution of 160 eV at 5.9 keV. It was observed that mixture rule method is not a suitable method for determination of the mass attenuation coefficients of compounds, especially at an energy that is near the absorption edge. The obtained values were compared with theoretical values.

  2. New methodological approach for the vanadium K-edge X-ray absorption near-edge structure interpretation: application to the speciation of vanadium in oxide phases from steel slag.

    PubMed

    Chaurand, Perrine; Rose, Jérôme; Briois, Valérie; Salome, Murielle; Proux, Olivier; Nassif, Vivian; Olivi, Luca; Susini, Jean; Hazemann, Jean-Louis; Bottero, Jean-Yves

    2007-05-17

    This paper presents a comparison between several methods dedicated to the interpretation of V K-edge X-ray absorption near-edge structure (XANES) features. V K-edge XANES spectra of several V-bearing standard compounds were measured in an effort to evaluate advantages and limits of each method. The standard compounds include natural minerals and synthetic compounds containing vanadium at various oxidation state (from +3 to +5) and in different symmetry (octahedral, tetrahedral, and square pyramidal). Correlations between normalized pre-edge peak area and its centroid position have been identified as the most reliable method for determining quantitative and accurate redox and symmetry information for vanadium. This methodology has been previously developed for the Fe K edge. It is also well adapted for the V K edge and is less influenced by the standard choice than other methods. This methodology was applied on an "environmental sample," i.e., a well-crystallized leached steel slag containing vanadium as traces. Micro-XANES measurements allowed elucidating the microdistribution of vanadium speciation in leached steel slag. The vanadium exhibits an important evolution from the unaltered to the altered phases. Its oxidation state increases from +3 to +5 together with the decrease of its symmetry (from octahedral to tetrahedral). PMID:17429991

  3. L-edge x-ray absorption fine structure study of growth and morphology of ultrathin nickel films deposited on copper

    SciTech Connect

    Nietubyc, Robert; Foehlisch, Alexander; Glaser, Leif; Lau, Julian Tobias; Martins, Michael; Reif, Matthias; Wurth, Wilfried

    2004-12-15

    We have studied the Ni L edge x-ray absorption fine structure for thin Ni films evaporated on a Cu(001) substrate. The measurements have been carried out for films having coverages ranging from 0.07 monolayers (ML) up to 3.1 ML. The coverage has been calibrated using the ratio of the Ni L{sub 3} to Cu L{sub 3} edge jump heights and independently verified with titration experiments. We have found a clear evolution of the x-ray absorption fine structure at the Ni L{sub 3} edge with coverage. To interpret the measured spectra first-principles calculations have been performed modeling a two-dimensional growth. The calculations reproduced all features observed experimentally. From the comparison between experiment and theory we can conclude that submonolayer films contain a large number of small islands. Deposition of an amount of nickel corresponding to a single layer results in the formation of an almost perfect flat layer. Our studies show that L edge x-ray absorption spectroscopy can provide useful information on thin-film growth and morphology.

  4. Vertical transition energies vs. absorption maxima: illustration with the UV absorption spectrum of ethylene.

    PubMed

    Lasorne, Benjamin; Jornet-Somoza, Joaquim; Meyer, Hans-Dieter; Lauvergnat, David; Robb, Michael A; Gatti, Fabien

    2014-02-01

    We revisit the validity of making a direct comparison between measured absorption maxima and computed vertical transition energies within 0.1 eV to calibrate an excited-state level of theory. This is illustrated on the UV absorption spectrum of ethylene for which the usual experimental values of 7.66 eV (V←N) and 7.11 eV (R(3s)←N) cannot be compared directly to the results of electronic structure calculations for two very different reasons. After validation of our level of theory against experimental data, a new experimental reference of 7.28 eV is suggested for benchmarking the Rydberg state, and the often-cited average transition energy (7.80 eV) is confirmed as a safer estimate for the valence state. PMID:23711543

  5. The iron-site structure of [Fe]-hydrogenase and model systems: an X-ray absorption near edge spectroscopy study†‡

    PubMed Central

    Salomone-Stagni, Marco; Stellato, Francesco; Whaley, C. Matthew; Vogt, Sonja; Morante, Silvia; Shima, Seigo; Rauchfuss, Thomas B.; Meyer-Klaucke, Wolfram

    2012-01-01

    The [Fe]-hydrogenase is an ideal system for studying the electronic properties of the low spin iron site that is common to the catalytic centres of all hydrogenases. Because they have no auxiliary iron-sulfur clusters and possess a cofactor containing a single iron centre, the [Fe]-hydrogenases are well suited for spectroscopic analysis of those factors required for the activation of molecular hydrogen. Specifically, in this study we shed light on the electronic and molecular structure of the iron centre by XAS analysis of [Fe]-hydrogenase from Methanocaldococcus jannashii and five model complexes (Fe(ethanedithiolate)-(CO)2(PMe3)2, [K(18-crown-6)]2[Fe(CN)2(CO)3], K[Fe(CN)(CO)4], K3[Fe(iii)(CN)6], K4[Fe(ii)(CN)6]). The different electron donors have a strong influence on the iron absorption K-edge energy position, which is frequently used to determine the metal oxidation state. Our results demonstrate that the K-edges of Fe(ii) complexes, achieved with low-spin ferrous thiolates, are consistent with a ferrous centre in the [Fe]-hydrogenase from Methanocaldococcus jannashii. The metal geometry also strongly influences the XANES and thus the electronic structure. Using in silico simulation, we were able to reproduce the main features of the XANES spectra and describe the effects of individual donor contributions on the spectra. Thereby, we reveal the essential role of an unusual carbon donor coming from an acyl group of the cofactor in the determination of the electronic structure required for the activity of the enzyme. PMID:20221540

  6. Achieving high energy absorption capacity in cellular bulk metallic glasses

    PubMed Central

    Chen, S. H.; Chan, K. C.; Wu, F. F.; Xia, L.

    2015-01-01

    Cellular bulk metallic glasses (BMGs) have exhibited excellent energy-absorption performance by inheriting superior strength from the parent BMGs. However, how to achieve high energy absorption capacity in cellular BMGs is vital but mysterious. In this work, using step-by-step observations of the deformation evolution of a series of cellular BMGs, the underlying mechanisms for the remarkable energy absorption capacity have been investigated by studying two influencing key factors: the peak stress and the decay of the peak stress during the plastic-flow plateau stages. An analytical model of the peak stress has been proposed, and the predicted results agree well with the experimental data. The decay of the peak stress has been attributed to the geometry change of the macroscopic cells, the formation of shear bands in the middle of the struts, and the “work-softening” nature of BMGs. The influencing factors such as the effect of the strut thickness and the number of unit cells have also been investigated and discussed. Strategies for achieving higher energy absorption capacity in cellular BMGs have been proposed. PMID:25973781

  7. Achieving high energy absorption capacity in cellular bulk metallic glasses

    NASA Astrophysics Data System (ADS)

    Chen, S. H.; Chan, K. C.; Wu, F. F.; Xia, L.

    2015-05-01

    Cellular bulk metallic glasses (BMGs) have exhibited excellent energy-absorption performance by inheriting superior strength from the parent BMGs. However, how to achieve high energy absorption capacity in cellular BMGs is vital but mysterious. In this work, using step-by-step observations of the deformation evolution of a series of cellular BMGs, the underlying mechanisms for the remarkable energy absorption capacity have been investigated by studying two influencing key factors: the peak stress and the decay of the peak stress during the plastic-flow plateau stages. An analytical model of the peak stress has been proposed, and the predicted results agree well with the experimental data. The decay of the peak stress has been attributed to the geometry change of the macroscopic cells, the formation of shear bands in the middle of the struts, and the “work-softening” nature of BMGs. The influencing factors such as the effect of the strut thickness and the number of unit cells have also been investigated and discussed. Strategies for achieving higher energy absorption capacity in cellular BMGs have been proposed.

  8. Quantitative Evaluation of the Carbon Hybridization State by Near Edge X-ray Absorption Fine Structure Spectroscopy.

    PubMed

    Mangolini, Filippo; McClimon, J Brandon; Carpick, Robert W

    2016-03-01

    The characterization of the local bonding configuration of carbon in carbon-based materials is of paramount importance since the properties of such materials strongly depend on the distribution of carbon hybridization states, the local ordering, and the degree of hydrogenation. Carbon 1s near edge X-ray absorption fine structure (NEXAFS) spectroscopy is one of the most powerful techniques for gaining insights into the bonding configuration of near-surface carbon atoms. The common methodology for quantitatively evaluating the carbon hybridization state using C 1s NEXAFS measurements, which is based on the analysis of the sample of interest and of a highly ordered pyrolytic graphite (HOPG) reference sample, was reviewed and critically assessed, noting that inconsistencies are found in the literature in applying this method. A theoretical rationale for the specific experimental conditions to be used for the acquisition of HOPG reference spectra is presented together with the potential sources of uncertainty and errors in the correctly computed fraction of sp(2)-bonded carbon. This provides a specific method for analyzing the distribution of carbon hybridization state using NEXAFS spectroscopy. As an illustrative example, a hydrogenated amorphous carbon film was analyzed using this method and showed good agreement with X-ray photoelectron spectroscopy (which is surface sensitive). Furthermore, the results were consistent with analysis from Raman spectroscopy (which is not surface sensitive), indicating the absence of a structurally different near-surface region in this particular thin film material. The present work can assist surface scientists in the analysis of NEXAFS spectra for the accurate characterization of the structure of carbon-based materials. PMID:26814796

  9. On the edge energy of lipid membranes and the thermodynamic stability of pores

    SciTech Connect

    Pera, H.; Kleijn, J. M.; Leermakers, F. A. M.

    2015-01-21

    To perform its barrier function, the lipid bilayer membrane requires a robust resistance against pore formation. Using a self-consistent field (SCF) theory and a molecularly detailed model for membranes composed of charged or zwitterionic lipids, it is possible to predict structural, mechanical, and thermodynamical parameters for relevant lipid bilayer membranes. We argue that the edge energy in membranes is a function of the spontaneous lipid monolayer curvature, the mean bending modulus, and the membrane thickness. An analytical Helfrich-like model suggests that most bilayers should have a positive edge energy. This means that there is a natural resistance against pore formation. Edge energies evaluated explicitly in a two-gradient SCF model are consistent with this. Remarkably, the edge energy can become negative for phosphatidylglycerol (e.g., dioleoylphosphoglycerol) bilayers at a sufficiently low ionic strength. Such bilayers become unstable against the formation of pores or the formation of lipid disks. In the weakly curved limit, we study the curvature dependence of the edge energy and evaluate the preferred edge curvature and the edge bending modulus. The latter is always positive, and the former increases with increasing ionic strength. These results point to a small window of ionic strengths for which stable pores can form as too low ionic strengths give rise to lipid disks. Higher order curvature terms are necessary to accurately predict relevant pore sizes in bilayers. The electric double layer overlap across a small pore widens the window of ionic strengths for which pores are stable.

  10. The perpendicular electron energy flux driven by magnetic fluctuations in the edge of TEXT-U

    SciTech Connect

    Fiksel, G.; Prager, S.C.; Bengtson, R.D.; Wootton, A.J.

    1995-06-12

    A fast bolometer was used for direct measurements of parallel electron energy flux in the edge of TEXT-U. The fluctuating component of the parallel electron energy flux, combined with a measurement of magnetic fluctuations, provides an upper limit to the perpendicular electron flux. This magnetically driven energy flux cannot account for the observed energy flux.

  11. First principles calculations of the structure and V L-edge X-ray absorption spectra of V2O5 using local pair natural orbital coupled cluster theory and spin-orbit coupled configuration interaction approaches.

    PubMed

    Maganas, Dimitrios; Roemelt, Michael; Hävecker, Michael; Trunschke, Annette; Knop-Gericke, Axel; Schlögl, Robert; Neese, Frank

    2013-05-21

    A detailed study of the electronic and geometric structure of V2O5 and its X-ray spectroscopic properties is presented. Cluster models of increasing size were constructed in order to represent the surface and the bulk environment of V2O5. The models were terminated with hydrogen atoms at the edges or embedded in a Madelung field. The structure and interlayer binding energies were studied with dispersion-corrected local, hybrid and double hybrid density functional theory as well as the local pair natural orbital coupled cluster method (LPNO-CCSD). Convergence of the results with respect to cluster size was achieved by extending the model to up to 20 vanadium centers. The O K-edge and the V L2,3-edge NEXAFS spectra of V2O5 were calculated on the basis of the newly developed Restricted Open shell Configuration Interaction with Singles (DFT-ROCIS) method. In this study the applicability of the method is extended to the field of solid-state catalysis. For the first time excellent agreement between theoretically predicted and experimentally measured vanadium L-edge NEXAFS spectra of V2O5 was achieved. At the same time the agreement between experimental and theoretical oxygen K-edge spectra is also excellent. Importantly, the intensity distribution between the oxygen K-edge and vanadium L-edge spectra is correctly reproduced, thus indicating that the covalency of the metal-ligand bonds is correctly described by the calculations. The origin of the spectral features is discussed in terms of the electronic structure using both quasi-atomic jj coupling and molecular LS coupling schemes. The effects of the bulk environment driven by weak interlayer interactions were also studied, demonstrating that large clusters are important in order to correctly calculate core level absorption spectra in solids. PMID:23575467

  12. Assignment of near-edge x-ray absorption fine structure spectra of metalloporphyrins by means of time-dependent density-functional calculations.

    PubMed

    Schmidt, Norman; Fink, Rainer; Hieringer, Wolfgang

    2010-08-01

    The C 1s and N 1s near-edge x-ray absorption fine structure (NEXAFS) spectra of three prototype tetraphenyl porphyrin (TPP) molecules are discussed in the framework of a combined experimental and theoretical study. We employ time-dependent density-functional theory (TDDFT) to compute the NEXAFS spectra of the open- and closed-shell metalloporphyrins CoTPP and ZnTPP as well as the free-base 2HTPP in realistic nonplanar conformations. Using Becke's well-known half-and-half hybrid functional, the computed core excitation spectra are mostly in good agreement with the experimental data in the low-energy region below the appropriate ionization threshold. To make these calculations feasible, we apply a new, simple scheme based on TDDFT using a modified single-particle input spectrum. This scheme is very easy to implement in standard codes and allows one to compute core excitation spectra at a similar cost as ordinary UV/vis spectra even for larger molecules. We employ these calculations for a detailed assignment of the NEXAFS spectra including subtle shifts in certain peaks of the N 1s spectra, which depend on the central coordination of the TPP ligand. We furthermore assign the observed NEXAFS resonances to the individual molecular subunits of the investigated TPP molecules. PMID:20707545

  13. Assignment of near-edge x-ray absorption fine structure spectra of metalloporphyrins by means of time-dependent density-functional calculations

    NASA Astrophysics Data System (ADS)

    Schmidt, Norman; Fink, Rainer; Hieringer, Wolfgang

    2010-08-01

    The C 1s and N 1s near-edge x-ray absorption fine structure (NEXAFS) spectra of three prototype tetraphenyl porphyrin (TPP) molecules are discussed in the framework of a combined experimental and theoretical study. We employ time-dependent density-functional theory (TDDFT) to compute the NEXAFS spectra of the open- and closed-shell metalloporphyrins CoTPP and ZnTPP as well as the free-base 2HTPP in realistic nonplanar conformations. Using Becke's well-known half-and-half hybrid functional, the computed core excitation spectra are mostly in good agreement with the experimental data in the low-energy region below the appropriate ionization threshold. To make these calculations feasible, we apply a new, simple scheme based on TDDFT using a modified single-particle input spectrum. This scheme is very easy to implement in standard codes and allows one to compute core excitation spectra at a similar cost as ordinary UV/vis spectra even for larger molecules. We employ these calculations for a detailed assignment of the NEXAFS spectra including subtle shifts in certain peaks of the N 1s spectra, which depend on the central coordination of the TPP ligand. We furthermore assign the observed NEXAFS resonances to the individual molecular subunits of the investigated TPP molecules.

  14. Biogeochemical reductive release of soil embedded arsenate around a crater area (Guandu) in northern Taiwan using X-ray absorption near-edge spectroscopy.

    PubMed

    Chiang, Kai-Ying; Chen, Tsan-Yao; Lee, Chih-Hao; Lin, Tsang-Lang; Wang, Ming-Kuang; Jang, Ling-Yun; Lee, Jyh-Fu

    2013-03-01

    This study investigates biogeochemical reductive release of arsenate from beudantite into solution in a crater area in northern Taiwan, using a combination of X-ray absorption near-edge structure (XANES) and atomic absorption spectrometry. Total arsenic (As) concentrations in the soil were more than 200 mg/kg. Over four months of laboratory experiments, less than 0.8% As was released into solution after reduction experiments. The 71% to 83% As was chemically reduced into arsenite (As(III)) and partially weathering into the soluble phase. The kinetic dissolution and re-precipitation of As, Fe, Pb and sulfate in this area of paddy soils merits further study. PMID:23923437

  15. X-ray absorption resonances near L2,3-edges from real-time propagation of the Dirac-Kohn-Sham density matrix.

    PubMed

    Kadek, Marius; Konecny, Lukas; Gao, Bin; Repisky, Michal; Ruud, Kenneth

    2015-09-21

    The solution of the Liouville-von Neumann equation in the relativistic Dirac-Kohn-Sham density matrix formalism is presented and used to calculate X-ray absorption cross sections. Both dynamical relaxation effects and spin-orbit corrections are included, as demonstrated by calculations of the X-ray absorption of SF6 near the sulfur L2,3-edges. We also propose an analysis facilitating the interpretation of spectral transitions from real-time simulations, and a selective perturbation that eliminates nonphysical excitations that are artifacts of the finite basis representation. PMID:26268195

  16. X-ray absorption spectroscopy by full-field X-ray microscopy of a thin graphite flake: Imaging and electronic structure via the carbon K-edge

    PubMed Central

    Hitchock, Adam P; Ke, Xiaoxing; Van Tendeloo, Gustaaf; Ewels, Chris P; Guttmann, Peter

    2012-01-01

    Summary We demonstrate that near-edge X-ray-absorption fine-structure spectra combined with full-field transmission X-ray microscopy can be used to study the electronic structure of graphite flakes consisting of a few graphene layers. The flake was produced by exfoliation using sodium cholate and then isolated by means of density-gradient ultracentrifugation. An image sequence around the carbon K-edge, analyzed by using reference spectra for the in-plane and out-of-plane regions of the sample, is used to map and spectrally characterize the flat and folded regions of the flake. Additional spectral features in both π and σ regions are observed, which may be related to the presence of topological defects. Doping by metal impurities that were present in the original exfoliated graphite is indicated by the presence of a pre-edge signal at 284.2 eV. PMID:23016137

  17. 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.

  18. Simulating Cl K-edge X-ray absorption spectroscopy in MCl62- (M= U, Np, Pu) complexes and UOCl5- using time-dependent density functional theory

    SciTech Connect

    Govind, Niranjan; De Jong, Wibe A.

    2014-02-21

    We report simulations of the X-ray absorption near edge structure (XANES) at the Cl K-edge of actinide hexahalides MCl62- (M = U, Np, Pu) and the UOCl5- complex using linear-response time-dependent density functional theory (LR-TDDFT) extended for core excitations. To the best of our knowledge, these are the first calculations of the Cl K-edge spectra of NpCl62- and PuCl62-. In addition, the spectra are simulated with and without the environmental effects of the host crystal as well as ab initio molecular dynamics (AIMD) to capture the dynamical effects due to atomic motion. The calculated spectra are compared with experimental results, where available and the observed trends are discussed.

  19. Simulating Ru L3-edge X-ray Absorption Spectroscopy with Time-Dependent Density Functional Theory: Model Complexes and Electron Localization in Mixed-Valence Metal Dimers

    SciTech Connect

    Van Kuiken, Benjamin E.; Valiev, Marat; Daifuku, Stephanie L.; Bannan, Caitlin; Strader, Matthew L.; Cho, Hana; Huse, N.; Schoenlein, R. W.; Govind, Niranjan; Khalil, Munira

    2013-05-01

    Ruthenium L2,3-edge X-ray absorption (XA) spectroscopy probes transitions from core 2p orbitals to the 4d levels of the atom and is a powerful tool for interrogating the local electronic and molecular structure around the metal atom. However, a molecular-level interpretation of the Ru L2,3-edge spectral lineshapes is often complicated by spin–orbit coupling (SOC) and multiplet effects. In this study, we develop spin-free time-dependent density functional theory (TDDFT) as a viable and predictive tool to simulate the Ru L3-edge spectra. We successfully simulate and analyze the ground state Ru L3-edge XA spectra of a series of RuII and RuIII complexes: [Ru(NH3)6]2+/3+, [Ru(CN)6]4-/3-, [RuCl6]4-/3-, and the ground (1A1) and photoexcited (3MLCT) transient states of [Ru(bpy)3]2+ and Ru(dcbpy)2(NCS)2 (termed N3). The TDDFT simulations reproduce all the experimentally observed features in Ru L3-edge XA spectra. The advantage of using TDDFT to assign complicated Ru L3-edge spectra is illustrated by its ability to identify ligand specific charge transfer features in complex molecules. We conclude that the B3LYP functional is the most reliable functional for accurately predicting the location of charge transfer features in these spectra. Experimental and simulated Ru L3-edge XA spectra are presented for the transition metal mixed-valence dimers [(NC)5MII-CN-RuIII(NH3)5]- (where M = Fe or Ru) dissolved in water. We explore the spectral signatures of electron delocalization in Ru L3-edge XA spectroscopy and our simulations reveal that the inclusion of explicit solvent molecules is crucial for reproducing the experimentally determined valencies, highlighting the importance of the role of the solvent in transition metal charge transfer chemistry.

  20. Limitations and design considerations for donor–acceptor systems in luminescent solar concentrators: the effect of coupling-induced red-edge absorption

    NASA Astrophysics Data System (ADS)

    MacQueen, Rowan W.; Tayebjee, Murad J. Y.; Webb, James E. A.; Falber, Alexander; Thordarson, Pall; Schmidt, Timothy W.

    2016-06-01

    Luminescent solar concentrators (LSCs) use luminescence and waveguiding to concentrate photons within thin dielectric slabs for use in photovoltaic, lighting, and photobioreactor applications. Donor–acceptor systems of organic chromophores are widely used in LSCs to broaden the sunlight absorption range and attempt to reduce loss-inducing reabsorption by the emitting chromophore. We use raytrace simulations across a large parameter space to model the performance of LSCs containing two novel donor–acceptor trimers based on the perylene moiety. We find that under certain conditions, trimers outperform single-dye LSCs as expected. However, at higher concentrations, a slight increase in red-edge absorption by the trimers increases reabsorption and has a deleterious effect on LSC performance. This underscores the large effect that even small changes in the red edge can have, and may discourage the use of donor–acceptor schemes with high interchromophore coupling that promotes red-edge absorption. Finally, we show that for a LSC-PV pair, selecting a PV cell that is well-matched with the LSC emission spectrum has a large effect on the flux gain of the system, and that the systems studied here are well-matched to emerging PV technologies.

  1. Statistical theory of relaxation of high-energy electrons in quantum Hall edge states

    NASA Astrophysics Data System (ADS)

    Lunde, Anders Mathias; Nigg, Simon E.

    2016-07-01

    We investigate theoretically the energy exchange between the electrons of two copropagating, out-of-equilibrium edge states with opposite spin polarization in the integer quantum Hall regime. A quantum dot tunnel coupled to one of the edge states locally injects electrons at high energy. Thereby a narrow peak in the energy distribution is created at high energy above the Fermi level. A second downstream quantum dot performs an energy-resolved measurement of the electronic distribution function. By varying the distance between the two dots, we are able to follow every step of the energy exchange and relaxation between the edge states, even analytically under certain conditions. In the absence of translational invariance along the edge, e.g., due to the presence of disorder, energy can be exchanged by non-momentum-conserving two-particle collisions. For weakly broken translational invariance, we show that the relaxation is described by coupled Fokker-Planck equations. From these we find that relaxation of the injected electrons can be understood statistically as a generalized drift-diffusion process in energy space for which we determine the drift velocity and the dynamical diffusion parameter. Finally, we provide a physically appealing picture in terms of individual edge-state heating as a result of the relaxation of the injected electrons.

  2. Determining neutrino absorption spectra at ultra-high energies

    SciTech Connect

    Scholten, O; Van Vliet, A R E-mail: A.R.van.Vliet@student.rug.nl

    2008-06-15

    A very efficient method for measuring the flux of ultra-high energy (UHE) neutrinos is through the detection of radio waves which are emitted by the particle shower in the lunar regolith. The highest acceptance is reached for radio waves in the frequency band of 100-200 MHz which can be measured with modern radio telescopes. In this work we investigate the sensitivity of this detection method to structures in the UHE neutrino spectrum caused by their absorption on the low energy relic anti-neutrino background through the Z boson resonance. The position of the absorption peak is sensitive to the neutrino mass and the redshift of the source. A new generation of low frequency digital radio telescopes will provide excellent detection capabilities for measuring these radio pulses, thus making our consideration here very timely.

  3. 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.

  4. Prediction of the energy-absorption capability of composite tubes

    NASA Technical Reports Server (NTRS)

    Farley, Gary L.; Jones, Robert M.

    1992-01-01

    A method of predicting the crack-related energy-absorption capability of composite tubes is presented. The method is based upon a phenomenological model of the crushing process exhibited by continuous-fiber-reinforced tubes. A finite element method is used to model the crushing process. The analysis is compared with experiments on Kevlar-epoxy and graphite-epoxy tubes. Reasonable agreement is obtained between the analysis and experiment.

  5. Chemical forms of sulfur in geological and archeological asphaltenes from Middle East, France, and Spain determined by sulfur K- and L-edge X-ray absorption near-edge structure spectroscopy

    NASA Astrophysics Data System (ADS)

    Sarret, Géraldine; Connan, Jacques; Kasrai, Masoud; Bancroft, G. Michael; Charrié-Duhaut, Armelle; Lemoine, Sylvie; Adam, Pierre; Albrecht, Pierre; Eybert-Bérard, Laurent

    1999-11-01

    Asphaltene samples extracted from archeological and geological bitumens from the Middle East, France, and Spain were studied by sulfur K- and L-edge X-ray absorption near-edge structure (XANES) spectroscopy in combination with isotopic analyses (δ 13C and δD). Within each series, the samples were genetically related by their δ 13C values. The gross and elemental composition and the δD values were used to characterize the weathering state of the samples. Sulfur K- and L-edge XANES results show that in all the samples, dibenzothiophenes are the dominant forms of sulfur. In the least oxidized asphaltenes, minor species include disulfides, alkyl and aryl sulfides, and sulfoxides. With increasing alteration the proportion of oxidized sulfur (sulfoxides, sulfones, sulfonates and sulfates) increases, whereas the disulfide and sulfide content decreases. This evolution is observed in all the series, regardless of the origin of the asphaltenes. This work illustrates the advantages of XANES spectroscopy as a selective probe for determining sulfur speciation in natural samples. It also shows that S K- and L-edge XANES spectroscopy are complementary for identifying the oxidized and reduced forms of sulfur, respectively.

  6. Mechanical properties and energy absorption characteristics of a polyurethane foam

    SciTech Connect

    Goods, S.H.; Neuschwanger, C.L.; Henderson, C.; Skala, D.M.

    1997-03-01

    Tension, compression and impact properties of a polyurethane encapsulant foam have been measured as a function of foam density. Significant differences in the behavior of the foam were observed depending on the mode of testing. Over the range of densities examined, both the modulus and the elastic collapse stress of the foam exhibited power-law dependencies with respect to density. The power-law relationship for the modulus was the same for both tension and compression testing and is explained in terms of the elastic compliance of the cellular structure of the foam using a simple geometric model. Euler buckling is used to rationalize the density dependence of the collapse stress. Neither tension nor compression testing yielded realistic measurements of energy absorption (toughness). In the former case, the energy absorption characteristics of the foam were severely limited due to the inherent lack of tensile ductility. In the latter case, the absence of a failure mechanism led to arbitrary measures of energy absorption that were not indicative of true material properties. Only impact testing revealed an intrinsic limitation in the toughness characteristics of the material with respect to foam density. The results suggest that dynamic testing should be used when assessing the shock mitigating qualities of a foam.

  7. Relative edge energy in the stability of transition metal nanoclusters of different motifs.

    PubMed

    Zhao, X J; Xue, X L; Guo, Z X; Li, S F

    2016-07-01

    When a structure is reduced to a nanometer scale, the proportion of the edge atoms increases significantly, which can play a crucial role in determining both their geometric and electronic properties, as demonstrated by the recently established generalized Wulff construction principle [S. F. Li, et al., Phys. Rev. Lett., 2013, 111, 115501]. Consequently, it is of great interest to clarify quantitatively the role of the edge atoms that dominate the motifs of these nanostructures. In principle, establishing an effective method valid for determining the absolute value of the surface energy and particularly the edge energy for a given nanostructure is expected to resolve such a problem. However, hitherto, it is difficult to obtain the absolute edge energy of transition metal clusters, particularly when their sizes approach the nanometer regime. In this paper, taking Ru nanoclusters as a prototypical example, our first-principles calculations introduce the concept of relative edge energy (REE), reflecting the net edge atom effect over the surface (facet) atom effect, which is fairly powerful to quasi-quantitatively estimate the critical size at which the crossover occurs between different configurations of a given motif, such as from an icosahedron to an fcc nanocrystal. By contrast, the bulk effect should be re-considered to rationalize the power of the REE in predicting the relative stability of larger nanostructures between different motifs, such as fcc-like and hcp-like nanocrystals. PMID:27296770

  8. Predicted versus monitored performance of energy-efficiency measures in new commercial buildings from energy edge

    SciTech Connect

    Piette, M.A.; Nordman, B.; deBuen, O.; Diamond, R.

    1993-08-01

    Energy Edge is a research-oriented demonstration program involving 28 new commercial buildings in the Pacific Northwest. This paper discusses the energy savings and cost-effectiveness of energy-efficiency measures for the first 12 buildings evaluated using simulation models calibrated with measured end-use data. Average energy savings per building from the simulated code baseline building was 19%, less than the 30% target. The most important factor for the lower savings is that many of the installed measures differ from the measures specified in the design predictions. Only one of the first 12 buildings met the project objective of reducing energy use by more than 30% at a cost below the target of 56 mills/kWh (in 1991 dollars). Based on results from the first 12 calibrated simulation models, 29 of the 66 energy-efficiency measures, or 44%, met the levelized cost criterion. Despite the lower energy savings from individual measures, the energy-use intensities of the buildings are lower than other regional comparison data for new buildings. The authors review factors that contribute to the uncertainty regarding measured savings and suggest methods to improve future evaluations.

  9. Wavelength and energy dependent absorption of unconventional fuel mixtures

    NASA Astrophysics Data System (ADS)

    Khan, N.; Saleem, Z.; Mirza, A. A.

    2005-11-01

    Economic considerations of laser induced ignition over the normal electrical ignition of direct injected Compressed Natural Gas (CNG) engines has motivated automobile industry to go for extensive research on basic characteristics of leaner unconventional fuel mixtures to evaluate practical possibility of switching over to the emerging technologies. This paper briefly reviews the ongoing research activities on minimum ignition energy and power requirements of natural gas fuels and reports results of present laser air/CNG mixture absorption coefficient study. This study was arranged to determine the thermo-optical characteristics of high air/fuel ratio mixtures using laser techniques. We measured the absorption coefficient using four lasers of multiple wavelengths over a wide range of temperatures and pressures. The absorption coefficient of mixture was found to vary significantly over change of mixture temperature and probe laser wavelengths. The absorption coefficients of air/CNG mixtures were measured using 20 watts CW/pulsed CO2 laser at 10.6μm, Pulsed Nd:Yag laser at 1.06μm, 532 nm (2nd harmonic) and 4 mW CW HeNe laser at 645 nm and 580 nm for temperatures varying from 290 to 1000K using optical transmission loss technique.

  10. High Energy Absorption Top Nozzle For A Nuclaer Fuel Assembly

    DOEpatents

    Sparrow, James A.; Aleshin, Yuriy; Slyeptsov, Aleksey

    2004-05-18

    A high energy absorption top nozzle for a nuclear fuel assembly that employs an elongated upper tubular housing and an elongated lower tubular housing slidable within the upper tubular housing. The upper and lower housings are biased away from each other by a plurality of longitudinally extending springs that are restrained by a longitudinally moveable piston whose upward travel is limited within the upper housing. The energy imparted to the nozzle by a control rod scram is mostly absorbed by the springs and the hydraulic affect of the piston within the nozzle.

  11. Experimental and Theoretical Comparison of the O K-Edge Non-Resonant Inelastic X-ray Scattering and X-ray Absorption Spectra of NaReO4

    SciTech Connect

    Bradley, Joseph A.; Yang, Ping; Batista, Enrique R.; Boland, Kevin S.; Burns, Carol J.; Clark, David L.; Conradson, Steven D.; Kozimor, Stosh A.; Martin, Richard L.; Seidler, Gerald T.; Scott, Brian L.; Shuh, David K.; Tyliszczak, T.; Wilkerson, Marianne P.; Wolfsberg, Laura E.

    2010-09-14

    Accurate X-ray absorption spectra (XAS) of first row atoms, e.g. O, are notoriously difficult to obtain due to the extreme sensitivity of the measurement to surface contamination, self-absorption, and saturation effects. Herein, we describe a comprehensive approach for determining reliable O K-edge XAS data for ReO41- and provide methodology for obtaining trustworthy and quantitative data on non-conducting molecular systems, even in the presence of surface contamination. This involves comparing spectra measured by non-resonant inelastic X-ray scattering (NRIXS), a bulk-sensitive technique that is not prone to X-ray self-absorption and provides exact peak intensities, with XAS spectra obtained by three different detection modes, namely total electron yield (TEY), fluorescence yield (FY), and scanning transmission X-ray microscopy (STXM). For ReO41-, TEY measurements were heavily influenced by surface contamination, while the FY and STXM data agree well with the bulk NRIXS analysis. These spectra all showed two intense pre-edge features indicative of the covalent interaction between the Re 5d and O 2p orbitals. Time dependent density functional theory calculations were used to assign these two peaks as O 1s excitations to the e and t2 molecular orbitals that result from Re 5d and O 2p covalent mixing in Td symmetry. Electronic structure calculations were used to determine the amount of O 2p character (%) in these molecular orbitals. Time-dependent density functional theory (TD-DFT) was also used to calculate the energies and intensities of the pre-edge transitions. Overall, under these experimental conditions, this analysis suggests that NRIXS, STXM, and FY operate cooperatively, providing a sound basis for validation of bulk-like excitation spectra and, in combination with electronic structure calculations, suggest that NaReO4 may serve as a well-defined O K-edge energy and intensity standard for future O K edge XAS studies.

  12. Experimental and Theoretical Comparison of the O K-Edge Nonresonant Inelastic X-ray Scattering and X-ray Absorption Spectra of NaReO[subscript 4

    SciTech Connect

    Bradley, Joseph A.; Yang, Ping; Batista, Enrique R.; Boland, Kevin S.; Burns, Carol J.; Clark, David L.; Conradson, Steven D.; Kozimor, Stosh A.; Martin, Richard L.; Seidler, Gerald T.; Scott, Brian L.; Shuh, David K.; Tyliszczak, Tolek; Wilkerson, Marianne P.; Wolfsberg, Laura E.

    2010-12-07

    Accurate X-ray absorption spectra (XAS) of first row atoms, e.g., O, are notoriously difficult to obtain due to the extreme sensitivity of the measurement to surface contamination, self-absorption, and saturation affects. Herein, we describe a comprehensive approach for determining reliable O K-edge XAS data for ReO{sub 4}{sup 1-} and provide methodology for obtaining trustworthy and quantitative data on nonconducting molecular systems, even in the presence of surface contamination. This involves comparing spectra measured by nonresonant inelastic X-ray scattering (NRIXS), a bulk-sensitive technique that is not prone to X-ray self-absorption and provides exact peak intensities, with XAS spectra obtained by three different detection modes, namely total electron yield (TEY), fluorescence yield (FY), and scanning transmission X-ray microscopy (STXM). For ReO{sub 4}{sup 1-}, TEY measurements were heavily influenced by surface contamination, while the FY and STXM data agree well with the bulk NRIXS analysis. These spectra all showed two intense pre-edge features indicative of the covalent interaction between the Re 5d and O 2p orbitals. Density functional theory calculations were used to assign these two peaks as O 1s excitations to the e and t{sub 2} molecular orbitals that result from Re 5d and O 2p covalent mixing in T{sub d} symmetry. Electronic structure calculations were used to determine the amount of O 2p character (%) in these molecular orbitals. Time dependent-density functional theory (TD-DFT) was also used to calculate the energies and intensities of the pre-edge transitions. Overall, under these experimental conditions, this analysis suggests that NRIXS, STXM, and FY operate cooperatively, providing a sound basis for validation of bulk-like excitation spectra and, in combination with electronic structure calculations, suggest that NaReO{sub 4} may serve as a well-defined O K-edge energy and intensity standard for future O K-edge XAS studies.

  13. Determining photon energy absorption parameters for different soil samples.

    PubMed

    Kucuk, Nil; Tumsavas, Zeynal; Cakir, Merve

    2013-05-01

    The mass attenuation coefficients (μs) for five different soil samples were measured at 661.6, 1173.2 and 1332.5 keV photon energies. The soil samples were separately irradiated with (137)Cs and (60)Co (370 kBq) radioactive point gamma sources. The measurements were made by performing transmission experiments with a 2″ × 2″ NaI(Tl) scintillation detector, which had an energy resolution of 7% at 0.662 MeV for the gamma-rays from the decay of (137)Cs. The effective atomic numbers (Zeff) and the effective electron densities (Neff) were determined experimentally and theoretically using the obtained μs values for the soil samples. Furthermore, the Zeff and Neff values of the soil samples were computed for the total photon interaction cross-sections using theoretical data over a wide energy region ranging from 1 keV to 15 MeV. The experimental values of the soils were found to be in good agreement with the theoretical values. Sandy loam and sandy clay loam soils demonstrated poor photon energy absorption characteristics. However, clay loam and clay soils had good photon energy absorption characteristics. PMID:23179375

  14. Energy Absorption in Chopped Carbon Fiber Compression Molded Composites

    SciTech Connect

    Starbuck, J.M.

    2001-07-20

    In passenger vehicles the ability to absorb energy due to impact and be survivable for the occupant is called the ''crashworthiness'' of the structure. To identify and quantify the energy absorbing mechanisms in candidate automotive composite materials, test methodologies were developed for conducting progressive crush tests on composite plate specimens. The test method development and experimental set-up focused on isolating the damage modes associated with the frond formation that occurs in dynamic testing of composite tubes. Quasi-static progressive crush tests were performed on composite plates manufactured from chopped carbon fiber with an epoxy resin system using compression molding techniques. The carbon fiber was Toray T700 and the epoxy resin was YLA RS-35. The effect of various material and test parameters on energy absorption was evaluated by varying the following parameters during testing: fiber volume fraction, fiber length, fiber tow size, specimen width, profile radius, and profile constraint condition. It was demonstrated during testing that the use of a roller constraint directed the crushing process and the load deflection curves were similar to progressive crushing of tubes. Of all the parameters evaluated, the fiber length appeared to be the most critical material parameter, with shorter fibers having a higher specific energy absorption than longer fibers. The combination of material parameters that yielded the highest energy absorbing material was identified.

  15. Ultra high energy neutrinos: absorption, thermal effects and signatures

    SciTech Connect

    Lunardini, Cecilia; Sabancilar, Eray; Yang, Lili E-mail: Eray.Sabancilar@asu.edu

    2013-08-01

    We study absorption of ultra high energy neutrinos by the cosmic neutrino background, with full inclusion of the effect of the thermal distribution of the background on the resonant annihilation channel. For a hierarchical neutrino mass spectrum (with at least one neutrino with mass below ∼ 10{sup −2} eV), thermal effects are important for ultra high energy neutrino sources at z∼>16. The neutrino transmission probability shows no more than two separate suppression dips since the two lightest mass eigenstates contribute as a single species when thermal effects are included. Results are applied to a number of models of ultra high energy neutrino emission. Suppression effects are strong for sources that extend beyond z ∼ 10, which can be realized for certain top down scenarios, such as superheavy dark matter decays, cosmic strings and cosmic necklaces. For these, a broad suppression valley should affect the neutrino spectrum at least in the energy interval 10{sup 12}−10{sup 13} GeV — which therefore is disfavored for ultra high energy neutrino searches — with only a mild dependence on the neutrino mass spectrum and hierarchy. The observation of absorption effects would indicate a population of sources beyond z ∼ 10, and favor top-down mechanisms; it would also be an interesting probe of the physics of the relic neutrino background in the unexplored redshift interval z ∼ 10–100.

  16. Determining photon energy absorption parameters for different soil samples

    PubMed Central

    Kucuk, Nil; Tumsavas, Zeynal; Cakir, Merve

    2013-01-01

    The mass attenuation coefficients (μs) for five different soil samples were measured at 661.6, 1173.2 and 1332.5 keV photon energies. The soil samples were separately irradiated with 137Cs and 60Co (370 kBq) radioactive point gamma sources. The measurements were made by performing transmission experiments with a 2″ × 2″ NaI(Tl) scintillation detector, which had an energy resolution of 7% at 0.662 MeV for the gamma-rays from the decay of 137Cs. The effective atomic numbers (Zeff) and the effective electron densities (Neff) were determined experimentally and theoretically using the obtained μs values for the soil samples. Furthermore, the Zeff and Neff values of the soil samples were computed for the total photon interaction cross-sections using theoretical data over a wide energy region ranging from 1 keV to 15 MeV. The experimental values of the soils were found to be in good agreement with the theoretical values. Sandy loam and sandy clay loam soils demonstrated poor photon energy absorption characteristics. However, clay loam and clay soils had good photon energy absorption characteristics. PMID:23179375

  17. Reducing radiation dose by application of optimized low-energy x-ray filters to K-edge imaging with a photon counting detector.

    PubMed

    Choi, Yu-Na; Lee, Seungwan; Kim, Hee-Joung

    2016-01-21

    K-edge imaging with photon counting x-ray detectors (PCXDs) can improve image quality compared with conventional energy integrating detectors. However, low-energy x-ray photons below the K-edge absorption energy of a target material do not contribute to image formation in the K-edge imaging and are likely to be completely absorbed by an object. In this study, we applied x-ray filters to the K-edge imaging with a PCXD based on cadmium zinc telluride for reducing radiation dose induced by low-energy x-ray photons. We used aluminum (Al) filters with different thicknesses as the low-energy x-ray filters and implemented the iodine K-edge imaging with an energy bin of 34-48 keV at the tube voltages of 50, 70 and 90 kVp. The effects of the low-energy x-ray filters on the K-edge imaging were investigated with respect to signal-difference-to-noise ratio (SDNR), entrance surface air kerma (ESAK) and figure of merit (FOM). The highest value of SDNR was observed in the K-edge imaging with a 2 mm Al filter, and the SDNR decreased as a function of the filter thicknesses. Compared to the K-edge imaging with a 2 mm Al filter, the ESAK was reduced by 66%, 48% and 39% in the K-edge imaging with a 12 mm Al filter for 50 kVp, 70 kVp and 90 kVp, respectively. The FOM values, which took into account the ESAK and SDNR, were maximized for 8, 6 to 8 and 4 mm Al filters at 50 kVp, 70 kVp and 90 kVp, respectively. We concluded that the use of an optimal low-energy filter thickness, which was determined by maximizing the FOM, could significantly reduce radiation dose while maintaining image quality in the K-edge imaging with the PCXD. PMID:26733235

  18. Reducing radiation dose by application of optimized low-energy x-ray filters to K-edge imaging with a photon counting detector

    NASA Astrophysics Data System (ADS)

    Choi, Yu-Na; Lee, Seungwan; Kim, Hee-Joung

    2016-01-01

    K-edge imaging with photon counting x-ray detectors (PCXDs) can improve image quality compared with conventional energy integrating detectors. However, low-energy x-ray photons below the K-edge absorption energy of a target material do not contribute to image formation in the K-edge imaging and are likely to be completely absorbed by an object. In this study, we applied x-ray filters to the K-edge imaging with a PCXD based on cadmium zinc telluride for reducing radiation dose induced by low-energy x-ray photons. We used aluminum (Al) filters with different thicknesses as the low-energy x-ray filters and implemented the iodine K-edge imaging with an energy bin of 34-48 keV at the tube voltages of 50, 70 and 90 kVp. The effects of the low-energy x-ray filters on the K-edge imaging were investigated with respect to signal-difference-to-noise ratio (SDNR), entrance surface air kerma (ESAK) and figure of merit (FOM). The highest value of SDNR was observed in the K-edge imaging with a 2 mm Al filter, and the SDNR decreased as a function of the filter thicknesses. Compared to the K-edge imaging with a 2 mm Al filter, the ESAK was reduced by 66%, 48% and 39% in the K-edge imaging with a 12 mm Al filter for 50 kVp, 70 kVp and 90 kVp, respectively. The FOM values, which took into account the ESAK and SDNR, were maximized for 8, 6 to 8 and 4 mm Al filters at 50 kVp, 70 kVp and 90 kVp, respectively. We concluded that the use of an optimal low-energy filter thickness, which was determined by maximizing the FOM, could significantly reduce radiation dose while maintaining image quality in the K-edge imaging with the PCXD.

  19. Effects of strain relaxation in Pr0.67Sr0.33MnO3 films probed by polarization dependent X-ray absorption near edge structure

    DOE PAGESBeta

    zhang, Bangmin; Chen, Jingsheng; Venkatesan, T.; Sun, Cheng -Jun; Heald, Steve M.; Chow, Gan Moog; Yang, Ping; Chi, Xiao; Lin, Weinan

    2016-01-28

    In this study, the Mn K edge X-ray absorption near edge structure (XANES) of Pr0.67Sr0.33MnO3 films with different thicknesses on (001) LaAlO3 substrate were measured, and the effects of strain relaxation on film properties were investigated. The films experienced in-plane compressive strain and out-of-plane tensile strain. Strain relaxation evolved with the film thickness. In the polarization dependent XANES measurements, the in-plane (parallel) and out-of-plane (perpendicular) XANES spectrocopies were anisotropic with different absorption energy Er. The resonance energy Er along two directions shifted towards each other with increasing film thickness. Based on the X-ray diffraction results, it was suggested that themore » strain relaxation weakened the difference of the local environment and probability of electronic charge transfer (between Mn 3d and O 2p orbitals) along the in-plane and out-of-plane directions, which was responsible for the change of Er. XANES is a useful tool to probe the electronic structures, of which the effects on magnetic properties with the strain relaxation was also been studied.« less

  20. Bandgap and optical absorption edge of GaAs1-xBix alloys with 0 < x < 17.8%

    NASA Astrophysics Data System (ADS)

    Masnadi-Shirazi, M.; Lewis, R. B.; Bahrami-Yekta, V.; Tiedje, T.; Chicoine, M.; Servati, P.

    2014-12-01

    The compositional dependence of the fundamental bandgap of pseudomorphic GaAs1-xBix layers on GaAs substrates is studied at room temperature by optical transmission and photoluminescence spectroscopies. All GaAs1-xBix films (0 ≤ x ≤ 17.8%) show direct optical bandgaps, which decrease with increasing Bi content, closely following density functional theory predictions. The smallest measured bandgap is 0.52 eV (˜2.4 μm) at 17.8% Bi. Extrapolating a fit to the data, the GaAs1-xBix bandgap is predicted to reach 0 eV at 35% Bi. Below the GaAs1-xBix bandgap, exponential absorption band tails are observed with Urbach energies 3-6 times larger than that of bulk GaAs. The Urbach parameter increases with Bi content up to 5.5% Bi, and remains constant at higher concentrations. The lattice constant and Bi content of GaAs1-xBix layers (0 < x ≤ 19.4%) are studied using high resolution x-ray diffraction and Rutherford backscattering spectroscopy. The relaxed lattice constant of hypothetical zincblende GaBi is estimated to be 6.33 ± 0.05 Å, from extrapolation of the Rutherford backscattering spectrometry and x-ray diffraction data.

  1. Energy absorption in cold inhomogeneous plasmas - The Herlofson paradox.

    NASA Technical Reports Server (NTRS)

    Crawford, F. W.; Harker, K. J.

    1972-01-01

    Confirmation of Barston's (1964) conclusions regarding the underlying mechanism of the Herlofson paradox by examining in detail several analytically tractable cases of delta-function and sinusoidal excitation. The effects of collisions and nonzero electron temperature in determining the steady state fields and dissipation are considered. Energy absorption without dissipation in plasmas is shown to be analogous to that occurring after application of a signal to a network of lossless resonant circuits. This analogy is pursued and is extended to cover Landau damping in a warm homogeneous plasma in which the resonating elements are the electron streams making up the velocity distribution. Some of the practical consequences of resonant absorption are discussed, together with a number of paradoxical plasma phenomena which can also be elucidated by considering a superposition of normal modes rather than a single Fourier component.

  2. Formation of an SEI on a LiMn(2)O(4) Cathode during Room Temperature Charge-Discharge Cycling Studied by Soft X-Ray Absorption Spectroscopy at the Fluorine K-edge

    SciTech Connect

    Chung, K.Y.; Yang, X.; Yoon, W.-S.; Kim, K.-B.; Cho, B.-W.

    2011-11-01

    The solid electrolyte interface (SEI) formation on the surface of LiMn{sub 2}O{sub 4} electrodes during room temperature charge-discharge cycling was studied using soft X-ray absorption spectroscopy at the Fluorine (F) K-edge. LiMn{sub 2}O{sub 4} electrodes without any binder were prepared by electrostatic spray deposition to eliminate the signal originating from the PVDF binder in the F K-edge X-ray absorption spectra. The F K-edge absorption spectra show that the SEI layer forms at a very early stage of cycling. SEI growth takes place during discharge. In addition, LiF formation is accelerated if the discharge step follows a charge step. The F K-edge absorption spectra suggest that the major component of the SEI is LiF.

  3. Dynamic study of sub-micro sized LiFePO4 cathodes by in-situ tender X-ray absorption near edge structure

    NASA Astrophysics Data System (ADS)

    Wang, Dongniu; Wang, Huixin; Yang, Jinli; Zhou, Jigang; Hu, Yongfeng; Xiao, Qunfeng; Fang, Haitao; Sham, Tsun-Kong

    2016-01-01

    Olivine-type phosphates (LiMPO4, M = Fe, Mn, Co) are promising cathode materials for lithium-ion batteries that are generally accepted to follow first order equilibrium phase transformations. Herein, the phase transformation dynamics of sub-micro sized LiFePO4 particles with limited rate capability at a low current density of 0.14 C was investigated. An in-situ X-ray Absorption Near Edge Structure (XANES) measurement was conducted at the Fe and P K-edge for the dynamic studies upon lithiation and delithiation. Fe K-edge XANES spectra demonstrate that not only lithium-rich intermediate phase LixFePO4 (x = 0.6-0.75), but also lithium-poor intermediate phase LiyFePO4 (y = 0.1-0.25) exist during the charge and discharge, respectively. Furthermore, during charge and discharge, a fluctuation of the FePO4 and LiFePO4 fractions obtained by liner combination fitting around the imaginary phase fractions followed Faraday's law and the equilibrium first-order two-phase transformation versus reaction time is present, respectively. The charging and discharging process has a reversible phase transformation dynamics with symmetric structural evolution routes. P K-edge XANES spectra reveal an enrichment of PF6-1 anions at the surface of the electrode during charging.

  4. 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.

  5. Percolative superconductivity in La{sub 2}CuO{sub 4.06} by lattice granularity patterns with scanning micro x-ray absorption near edge structure

    SciTech Connect

    Poccia, Nicola; Chorro, Matthieu; Ricci, Alessandro; Xu, Wei; Marcelli, Augusto; Campi, Gaetano; Bianconi, Antonio

    2014-06-02

    The simplest cuprate superconductor La{sub 2}CuO{sub 4+y} with mobile oxygen interstitials exhibits a clear phase separation. It is known that oxygen interstitials enter into the rocksalt La{sub 2}O{sub 2+y} spacer layers forming oxygen interstitials rich puddles and poor puddles but only recently a bulk multiscale structural phase separation has been observed by using scanning micro X-ray diffraction. Here we get further information on their spatial distribution, using scanning La L{sub 3}-edge micro X-ray absorption near edge structure. Percolating networks of oxygen rich puddles are observed in different micrometer size portions of the crystals. Moreover, the complex surface resistivity shows two jumps associated to the onset of intra-puddle and inter-puddles percolative superconductivity. The similarity of oxygen doped La{sub 2}CuO{sub 4+y}, with the well established phase separation in iron selenide superconductors is also discussed.

  6. Theory and X-ray Absorption Spectroscopy for Aluminum Coordination Complexes – Al K-Edge Studies of Charge and Bonding in (BDI)Al, (BDI)AlR2, and (BDI)AlX2 Complexes.

    PubMed

    Altman, Alison B; Pemmaraju, C D; Camp, Clément; Arnold, John; Minasian, Stefan G; Prendergast, David; Shuh, David K; Tyliszczak, Tolek

    2015-08-19

    Polarized aluminum K-edge X-ray absorption near edge structure (XANES) spectroscopy and first-principles calculations were used to probe electronic structure in a series of (BDI)Al, (BDI)AlX2, and (BDI)AlR2 coordination compounds (X = F, Cl, I; R = H, Me; BDI = 2,6-diisopropylphenyl-β-diketiminate). Spectral interpretations were guided by examination of the calculated transition energies and polarization-dependent oscillator strengths, which agreed well with the XANES spectroscopy measurements. Pre-edge features were assigned to transitions associated with the Al 3p orbitals involved in metal-ligand bonding. Qualitative trends in Al 1s core energy and valence orbital occupation were established through a systematic comparison of excited states derived from Al 3p orbitals with similar symmetries in a molecular orbital framework. These trends suggested that the higher transition energies observed for (BDI)AlX2 systems with more electronegative X(1-) ligands could be ascribed to a decrease in electron density around the aluminum atom, which causes an increase in the attractive potential of the Al nucleus and concomitant increase in the binding energy of the Al 1s core orbitals. For (BDI)Al and (BDI)AlH2 the experimental Al K-edge XANES spectra and spectra calculated using the eXcited electron and Core-Hole (XCH) approach had nearly identical energies for transitions to final state orbitals of similar composition and symmetry. These results implied that the charge distributions about the aluminum atoms in (BDI)Al and (BDI)AlH2 are similar relative to the (BDI)AlX2 and (BDI)AlMe2 compounds, despite having different formal oxidation states of +1 and +3, respectively. However, (BDI)Al was unique in that it exhibited a low-energy feature that was attributed to transitions into a low-lying p-orbital of b1 symmetry that is localized on Al and orthogonal to the (BDI)Al plane. The presence of this low-energy unoccupied molecular orbital on electron-rich (BDI)Al distinguishes

  7. WATER, ENERGY AND LIFE: FRESH VIEWS FROM THE WATER'S EDGE.

    PubMed

    Pollack, G H

    2010-12-01

    Recent observations have shown an unexpected feature of water adjacent to hydrophilic surfaces: the presence of wide interfacial zone that excludes solutes. The exclusion zone is charged, while the water beyond is oppositely charged, yielding a battery-like feature. The battery is powered by absorbed radiant energy. Implications of this energetic feature are discussed. It appears that the presence of this 'exclusion zone' may play an important role in the behavior of aqueous systems. PMID:22977460

  8. Energy analysis of an ammonia-water absorption refrigeration system

    SciTech Connect

    Dincer, I.; Dost, S.

    1996-09-01

    Absorption refrigeration systems (ARSs) are run on heat-operated cycles. In these systems a secondary fluid (i.e., absorbent) is used to absorb the primary fluid (i.e., refrigerant) vaporized in the evaporator. ARSs for industrial and domestic applications have been attracting increasing interest throughout the world. A simple energy analysis technique for ammonia-water refrigeration systems is presented and verified with actual experimental data taken from the literature. Comparison was made in terms of the coefficient of performance, and very good agreement was found.

  9. Studies on mass energy-absorption coefficients and effective atomic energy-absorption cross sections for carbohydrates

    NASA Astrophysics Data System (ADS)

    Ladhaf, Bibifatima M.; Pawar, Pravina P.

    2015-04-01

    We measured here the mass attenuation coefficients (μ/ρ) of carbohydrates, Esculine (C15H16O9), Sucrose (C12H22O11), Sorbitol (C6H14O6), D-Galactose (C6H12O6), Inositol (C6H12O6), D-Xylose (C5H10O5) covering the energy range from 122 keV up to 1330 keV photon energies by using gamma ray transmission method in a narrow beam good geometry set-up. The gamma-rays were detected using NaI(Tl) scintillation detection system with a resolution of 8.2% at 662 keV. The attenuation coefficient data were then used to obtain the total attenuation cross-section (σtot), molar extinction coefficients (ε), mass-energy absorption coefficients (μen/ρ) and effective (average) atomic energy-absorption cross section (σa,en) of the compounds. These values are found to be in good agreement with the theoretical values calculated based on XCOM data.

  10. Mechanism of the CO oxidation reaction on O-precovered Pt(111) surfaces studied with near-edge x-ray absorption fine structure spectroscopy

    SciTech Connect

    Nakai, I.; Kondoh, H.; Amemiya, K.; Nagasaka, M.; Shimada, T.; Yokota, R.; Nambu, A.; Ohta, T.

    2005-04-01

    The mechanism of CO oxidation reaction on oxygen-precovered Pt(111) surfaces has been studied by using time-resolved near-edge x-ray absorption fine structure spectroscopy. The whole reaction process is composed of two distinct paths: (1) a reaction of isolated oxygen atoms with adsorbed CO, and (2) a reaction of island-periphery oxygen atoms after the CO saturation. CO coadsorption plays a role to induce the dynamic change in spatial distribution of O atoms, which switches over the two reaction paths. These mechanisms were confirmed by kinetic Monte Carlo simulations. The effect of coadsorbed water in the reaction mechanism was also examined.

  11. Unraveling the Solid-Liquid-Vapor Phase Transition Dynamics at the Atomic Level with Ultrafast X-Ray Absorption Near-Edge Spectroscopy

    NASA Astrophysics Data System (ADS)

    Dorchies, F.; Lévy, A.; Goyon, C.; Combis, P.; Descamps, D.; Fourment, C.; Harmand, M.; Hulin, S.; Leguay, P. M.; Petit, S.; Peyrusse, O.; Santos, J. J.

    2011-12-01

    X-ray absorption near-edge spectroscopy (XANES) is a powerful probe of electronic and atomic structures in various media, ranging from molecules to condensed matter. We show how ultrafast time resolution opens new possibilities to investigate highly nonequilibrium states of matter including phase transitions. Based on a tabletop laser-plasma ultrafast x-ray source, we have performed a time-resolved (˜3ps) XANES experiment that reveals the evolution of an aluminum foil at the atomic level, when undergoing ultrafast laser heating and ablation. X-ray absorption spectra highlight an ultrafast transition from the crystalline solid to the disordered liquid followed by a progressive transition of the delocalized valence electronic structure (metal) down to localized atomic orbitals (nonmetal—vapor), as the average distance between atoms increases.

  12. Energy-absorption capability and scalability of square cross section composite tube specimens

    NASA Technical Reports Server (NTRS)

    Farley, Gary L.

    1987-01-01

    Static crushing tests were conducted on graphite/epoxy and Kevlar/epoxy square cross section tubes to study the influence of specimen geometry on the energy-absorption capability and scalability of composite materials. The tube inside width-to-wall thickness (W/t) ratio was determined to significantly affect the energy-absorption capability of composite materials. As W/t ratio decreases, the energy-absorption capability increases nonlinearly. The energy-absorption capability of Kevlar epoxy tubes was found to be geometrically scalable, but the energy-absorption capability of graphite/epoxy tubes was not geometrically scalable.

  13. Energy-absorption capability and scalability of square cross section composite tube specimens

    NASA Technical Reports Server (NTRS)

    Farley, Gary L.

    1989-01-01

    Static crushing tests were conducted on graphite/epoxy and Kevlar/epoxy square cross section tubes to study the influence of specimen geometry on the energy-absorption capability and scalability of composite materials. The tube inside width-to-wall thickness (W/t) ratio was determined to significantly affect the energy-absorption capability of composite materials. As W/t ratio decreases, the energy-absorption capability increases nonlinearly. The energy-absorption capability of Kevlar epoxy tubes was found to be geometrically scalable, but the energy-absorption capability of graphite/epoxy tubes was not geometrically scalable.

  14. Computing at the leading edge: Research in the energy sciences

    SciTech Connect

    Mirin, A.A.; Van Dyke, P.T.

    1994-02-01

    The purpose of this publication is to highlight selected scientific challenges that have been undertaken by the DOE Energy Research community. The high quality of the research reflected in these contributions underscores the growing importance both to the Grand Challenge scientific efforts sponsored by DOE and of the related supporting technologies that the National Energy Research Supercomputer Center (NERSC) and other facilities are able to provide. The continued improvement of the computing resources available to DOE scientists is prerequisite to ensuring their future progress in solving the Grand Challenges. Titles of articles included in this publication include: the numerical tokamak project; static and animated molecular views of a tumorigenic chemical bound to DNA; toward a high-performance climate systems model; modeling molecular processes in the environment; lattice Boltzmann models for flow in porous media; parallel algorithms for modeling superconductors; parallel computing at the Superconducting Super Collider Laboratory; the advanced combustion modeling environment; adaptive methodologies for computational fluid dynamics; lattice simulations of quantum chromodynamics; simulating high-intensity charged-particle beams for the design of high-power accelerators; electronic structure and phase stability of random alloys.

  15. Effects of strain relaxation in Pr0.67Sr0.33MnO3 films probed by polarization dependent X-ray absorption near edge structure

    PubMed Central

    Zhang, Bangmin; Chen, Jingsheng; Yang, Ping; Chi, Xiao; Lin, Weinan; Venkatesan, T.; Sun, Cheng-Jun; Heald, Steve M.; Chow, Gan Moog

    2016-01-01

    The Mn K edge X-ray absorption near edge structure (XANES) of Pr0.67Sr0.33MnO3 films with different thicknesses on (001) LaAlO3 substrate was measured, and the effects of strain relaxation on film properties were investigated. The films showed in-plane compressive and out-of-plane tensile strains. Strain relaxation occurred with increasing film thickness, affecting both lattice constant and MnO6 octahedral rotation. In polarization dependent XANES measurements using in-plane (parallel) and out-of-plane (perpendicular) geometries, the different values of absorption resonance energy Er confirmed the film anisotropy. The values of Er along these two directions shifted towards each other with increasing film thickness. Correlating with X-ray diffraction (XRD) results it is suggested that the strain relaxation decreased the local anisotropy and corresponding probability of electronic charge transfer between Mn 3d and O 2p orbitals along the in-plane and out-of-plane directions. The XANES results were used to explain the film-thickness dependent magnetic and transport properties. PMID:26818583

  16. Effects of strain relaxation in Pr0.67Sr0.33MnO3 films probed by polarization dependent X-ray absorption near edge structure.

    PubMed

    Zhang, Bangmin; Chen, Jingsheng; Yang, Ping; Chi, Xiao; Lin, Weinan; Venkatesan, T; Sun, Cheng-Jun; Heald, Steve M; Chow, Gan Moog

    2016-01-01

    The Mn K edge X-ray absorption near edge structure (XANES) of Pr0.67Sr0.33MnO3 films with different thicknesses on (001) LaAlO3 substrate was measured, and the effects of strain relaxation on film properties were investigated. The films showed in-plane compressive and out-of-plane tensile strains. Strain relaxation occurred with increasing film thickness, affecting both lattice constant and MnO6 octahedral rotation. In polarization dependent XANES measurements using in-plane (parallel) and out-of-plane (perpendicular) geometries, the different values of absorption resonance energy Er confirmed the film anisotropy. The values of Er along these two directions shifted towards each other with increasing film thickness. Correlating with X-ray diffraction (XRD) results it is suggested that the strain relaxation decreased the local anisotropy and corresponding probability of electronic charge transfer between Mn 3d and O 2p orbitals along the in-plane and out-of-plane directions. The XANES results were used to explain the film-thickness dependent magnetic and transport properties. PMID:26818583

  17. Energy-Gap Opening in a Bi(110) Nanoribbon Induced by Edge Reconstruction

    NASA Astrophysics Data System (ADS)

    Sun, Jia-Tao; Huang, Han; Wong, Swee Liang; Gao, H.-J.; Feng, Yuan Ping; Wee, Andrew Thye Shen

    2012-12-01

    Scanning tunnelling microscopy and spectroscopy experiments complemented by first-principles calculations have been conducted to study the electronic structure of 4 monolayer Bi(110) nanoribbons on epitaxial graphene on silicon carbide [4H-SiC(0001)]. In contrast with the semimetal property of elemental bismuth, an energy gap of 0.4 eV is measured at the centre of the Bi(110) nanoribbons. Edge reconstructions, which can facilitate the edge strain energy release, are found to be responsible for the band gap opening. The calculated density of states around the Fermi level are decreased quickly to zero from the terrace edge to the middle of a Bi(110) nanoribbon potentially signifying a spatial metal-to-semiconductor transition. This study opens new avenues for room-temperature bismuth nanoribbon-based electronic devices.

  18. Relative edge energy in the stability of transition metal nanoclusters of different motifs

    NASA Astrophysics Data System (ADS)

    Zhao, X. J.; Xue, X. L.; Guo, Z. X.; Li, S. F.

    2016-06-01

    When a structure is reduced to a nanometer scale, the proportion of the lowly-coordinated edge atoms increases significantly, which can play a crucial role in determining both their geometric and electronic properties, as demonstrated by the recently established generalized Wulff construction principle [S. F. Li, et al., Phys. Rev. Lett., 2013, 111, 115501]. Consequently, it is of great interest to clarify quantitatively the role of the edge atoms that dominate the motifs of these nanostructures. In principle, establishing an effective method valid for determining the absolute value of the surface energy and particularly the edge energy for a given nanostructure is expected to resolve such a problem. However, hitherto, it is difficult to obtain the absolute edge energy of transition metal clusters, particularly when their sizes approach the nanometer regime. In this paper, taking Ru nanoclusters as a prototypical example, our first-principles calculations introduce the concept of relative edge energy (REE), reflecting the net edge atom effect over the surface (facet) atom effect, which is fairly powerful to quasi-quantitatively estimate the critical size at which the crossover occurs between different configurations of a given motif, such as from an icosahedron to an fcc nanocrystal. By contrast, the bulk effect should be re-considered to rationalize the power of the REE in predicting the relative stability of larger nanostructures between different motifs, such as fcc-like and hcp-like nanocrystals.When a structure is reduced to a nanometer scale, the proportion of the lowly-coordinated edge atoms increases significantly, which can play a crucial role in determining both their geometric and electronic properties, as demonstrated by the recently established generalized Wulff construction principle [S. F. Li, et al., Phys. Rev. Lett., 2013, 111, 115501]. Consequently, it is of great interest to clarify quantitatively the role of the edge atoms that dominate the

  19. Origin of improved scintillation efficiency in (Lu,Gd){sub 3}(Ga,Al){sub 5}O{sub 12}:Ce multicomponent garnets: An X-ray absorption near edge spectroscopy study

    SciTech Connect

    Wu, Yuntao Luo, Jialiang; Ren, Guohao; Nikl, Martin

    2014-01-01

    In the recent successful improvement of scintillation efficiency in Lu{sub 3}Al{sub 5}O{sub 12}:Ce driven by Ga{sup 3+} and Gd{sup 3+} admixture, the “band-gap engineering” and energy level positioning have been considered the valid strategies so far. This study revealed that this improvement was also associated with the cerium valence instability along with the changes of chemical composition. By utilizing X-ray absorption near edge spectroscopy technique, tuning the Ce{sup 3+}/Ce{sup 4+} ratio by Ga{sup 3+} admixture was evidenced, while it was kept nearly stable with the Gd{sup 3+} admixture. Ce valence instability and Ce{sup 3+}/Ce{sup 4+} ratio in multicomponent garnets can be driven by the energy separation between 4f ground state of Ce{sup 3+} and Fermi level.

  20. Energy absorption characteristics of lightweight structural member by stacking conditions

    NASA Astrophysics Data System (ADS)

    Choi, Juho; Yang, Yongjun; Hwang, Woochae; Pyeon, Seokbeom; Min, Hanki; Yeo, Ingoo; Yang, Inyoung

    2012-04-01

    The recent trend in vehicle design is aimed at improving crash safety and environmental-friendliness. To solve these issues, the needs for lighter vehicle to limit exhaust gas and improve fuel economy has been requested for environmental-friendliness. Automobile design should be made for reduced weight once the safety of vehicle is maintained. In this study, composite structural members were manufactured using carbon fiber reinforced plastic (CFRP) which are representative lightweight structural materials. Carbon fiber has been researched as alternative to metals for lightweight vehicle and better fuel economy. CFRP is an anisotropic material which is the most widely adapted lightweight structural member because of their inherent design flexibility and high specific strength and stiffness. Also, variation of CFRP interface number is important to increase the energy absorption capacity. In this study, one type of circular shaped composite tube was used, combined with reinforcing foam. The stacking condition was selected to investigate the effect of the fiber orientation angle and interface number. The crashworthy behavior of circular composite material tubes subjected to static axial compression under same conditions is reported. The axial static collapse tests were carried out for each section member. The collapse modes and the energy absorption capability of the members were analyzed.

  1. Energy absorption characteristics of lightweight structural member by stacking conditions

    NASA Astrophysics Data System (ADS)

    Choi, Juho; Yang, Yongjun; Hwang, Woochae; Pyeon, Seokbeom; Min, Hanki; Yeo, Ingoo; Yang, Inyoung

    2011-11-01

    The recent trend in vehicle design is aimed at improving crash safety and environmental-friendliness. To solve these issues, the needs for lighter vehicle to limit exhaust gas and improve fuel economy has been requested for environmental-friendliness. Automobile design should be made for reduced weight once the safety of vehicle is maintained. In this study, composite structural members were manufactured using carbon fiber reinforced plastic (CFRP) which are representative lightweight structural materials. Carbon fiber has been researched as alternative to metals for lightweight vehicle and better fuel economy. CFRP is an anisotropic material which is the most widely adapted lightweight structural member because of their inherent design flexibility and high specific strength and stiffness. Also, variation of CFRP interface number is important to increase the energy absorption capacity. In this study, one type of circular shaped composite tube was used, combined with reinforcing foam. The stacking condition was selected to investigate the effect of the fiber orientation angle and interface number. The crashworthy behavior of circular composite material tubes subjected to static axial compression under same conditions is reported. The axial static collapse tests were carried out for each section member. The collapse modes and the energy absorption capability of the members were analyzed.

  2. Energy Absorption Structure of Laser Supported Detonation Wave

    NASA Astrophysics Data System (ADS)

    Wang, Bin; Yamaguchi, Toshikazu; Hatai, Keigo; Komurasaki, Kimiya; Arakawa, Yoshihiro

    2010-05-01

    In Repetitive Pulsed (RP) laser propulsion, when the high energy laser beam is focused in the thruster, Laser Supported Detonation (LSD) wave is generated. This LSD wave converts the laser energy to the enthalpy of the blast wave, which will then apply impulse to the wall of the thruster. Therefore, the energy absorption structure and sustaining condition of LSD wave are important to be understood, which was still not clear though some visualized experiments have been conducted by Ushio et al. before. In this paper, 2-wavelength Mach-Zehnder interferometry is brought to investigate the electron density distribution of LSD area. At the same time, the temperature of the laser induced plasma is measured by an emission spectroscopy experiment, and calculated based on the assumption of local thermal equilibrium. The results show that in LSD, the electron density has a peak (as high as 2×1024[m-3]) behind the shock wave. The irradiated laser can be entirely absorbed before reaching the position of this peak. As a result, a new peak is always generating in front of the old one and this propagating has the same velocity as that of the blast wave. In this way, high heating ratio is sustained right after the shock front. However, as the laser pulse energy becomes lower, the propagating peak cannot catch up with the blast wave anymore, which leads to a termination of the LSD wave. From this study, it is found that for sustaining the LSD wave, a sufficiently thin laser absorption layer is necessary.

  3. Fabrication of multilayer mirrors consisting of oxide and nitride layers for continual use across the K-absorption edge of carbon.

    PubMed

    Ishino, Masahiko; Yoda, Osamu

    2004-03-20

    The development of multilayer mirrors for continual use around the K-absorption edge of carbon (4.4 nm) has been begun. Cobalt oxide (Co3O4), silicon oxide (SiO2), and boron nitride (BN) are found to be suitable for multilayer mirrors on the basis of theoretical calculations for wavelengths around the carbon K-absorption edge region. X-ray reflectivity curves with CuKalpha1 x rays of the fabricated Co3O4/SiO2 multilayers have sharp Bragg peaks, and the layer structures evaluated from transmission electron microscopy (TEM) observations are uniform. On the other hand, the Bragg peaks of Co3O4/BN multilayers split, and aggregated Co3O4 is observed. To improve the Co3O4 layer structure, chromium oxide (Cr2O3) was mixed into Co3O4. The mixed oxide layer structure in the Mix/BN multilayer (Mix = Co3O4 + Cr2O3) is relatively uniform, and the Bragg peaks do not split. PMID:15065714

  4. X-ray Absorption Spectroscopy at the Sulfur K-Edge: A New Tool to Investigate the Biochemical Mechanisms of Neurodegeneration

    PubMed Central

    2012-01-01

    Sulfur containing molecules such as thiols, disulfides, sulfoxides, sulfonic acids, and sulfates may contribute to neurodegenerative processes. However, previous study in this field has been limited by the lack of in situ analytical techniques. This limitation may now be largely overcome following the development of synchrotron radiation X-ray absorption spectroscopy at the sulfur K-edge, which has been validated as a novel tool to investigate and image the speciation of sulfur in situ. In this investigation, we build the foundation required for future application of this technique to study and image the speciation of sulfur in situ within brain tissue. This study has determined the effect of sample preparation and fixation methods on the speciation of sulfur in thin sections of rat brain tissue, determined the speciation of sulfur within specific brain regions (brain stem and cerebellum), and identified sulfur specific markers of peroxidative stress following metal catalyzed reactive oxygen species production. X-ray absorption spectroscopy at the sulfur K-edge is now poised for an exciting new range of applications to study thiol redox, methionine oxidation, and the role of taurine and sulfatides during neurodegeneration. PMID:22860187

  5. Nb K-edge x-ray absorption investigation of the pressure induced amorphization in A-site deficient double perovskite La1/3NbO3.

    PubMed

    Marini, C; Noked, O; Kantor, I; Joseph, B; Mathon, O; Shuker, R; Kennedy, B J; Pascarelli, S; Sterer, E

    2016-02-01

    Nb K-edge x-ray absorption spectroscopy is utilized to investigate the changes in the local structure of the A-site deficient double perovskite La1/3NbO3 which undergoes a pressure induced irreversible amorphization. EXAFS results show that with increasing pressure up to 7.5 GPa, the average Nb-O bond distance decreases in agreement with the expected compression and tilting of the NbO6 octahedra. On the contrary, above 7.5 GPa, the average Nb-O bond distance show a tendency to increase. Significant changes in the Nb K-edge XANES spectrum with evident low energy shift of the pre-peak and the absorption edge is found to happen in La1/3NbO3 above 6.3 GPa. These changes evidence a gradual reduction of the Nb cations from Nb(5+) towards Nb(4+) above 6.3 GPa. Such a valence change accompanied by the elongation of the average Nb-O bond distances in the octahedra, introduces repulsion forces between non-bonding adjacent oxygen anions in the unoccupied A-sites. Above a critical pressure, the Nb reduction mechanism can no longer be sustained by the changing local structure and amorphization occurs, apparently due to the build-up of local strain. EXAFS and XANES results indicate two distinct pressure regimes having different local and electronic response in the La1/3NbO3 system before the occurence of the pressure induced amorphization at  ∼14.5 GPa. PMID:26742465

  6. Nb K-edge x-ray absorption investigation of the pressure induced amorphization in A-site deficient double perovskite La1/3NbO3

    NASA Astrophysics Data System (ADS)

    Marini, C.; Noked, O.; Kantor, I.; Joseph, B.; Mathon, O.; Shuker, R.; Kennedy, B. J.; Pascarelli, S.; Sterer, E.

    2016-02-01

    Nb K-edge x-ray absorption spectroscopy is utilized to investigate the changes in the local structure of the A-site deficient double perovskite La1/3NbO3 which undergoes a pressure induced irreversible amorphization. EXAFS results show that with increasing pressure up to 7.5 GPa, the average Nb-O bond distance decreases in agreement with the expected compression and tilting of the NbO6 octahedra. On the contrary, above 7.5 GPa, the average Nb-O bond distance show a tendency to increase. Significant changes in the Nb K-edge XANES spectrum with evident low energy shift of the pre-peak and the absorption edge is found to happen in La1/3NbO3 above 6.3 GPa. These changes evidence a gradual reduction of the Nb cations from Nb5+ towards Nb4+ above 6.3 GPa. Such a valence change accompanied by the elongation of the average Nb-O bond distances in the octahedra, introduces repulsion forces between non-bonding adjacent oxygen anions in the unoccupied A-sites. Above a critical pressure, the Nb reduction mechanism can no longer be sustained by the changing local structure and amorphization occurs, apparently due to the build-up of local strain. EXAFS and XANES results indicate two distinct pressure regimes having different local and electronic response in the La1/3NbO3 system before the occurence of the pressure induced amorphization at  ˜14.5 GPa.

  7. X-ray absorption near-edge structure (XANES) spectroscopy study of the interaction of silver ions with Staphylococcus aureus, Listeria monocytogenes, and Escherichia coli.

    PubMed

    Bovenkamp, Gudrun Lisa; Zanzen, Ulrike; Krishna, Katla Sai; Hormes, Josef; Prange, Alexander

    2013-10-01

    Silver ions are widely used as antibacterial agents, but the basic molecular mechanism of this effect is still poorly understood. X-ray absorption near-edge structure (XANES) spectroscopy at the Ag LIII, S K, and P K edges reveals the chemical forms of silver in Staphylococcus aureus and Escherichia coli (Ag(+) treated). The Ag LIII-edge XANES spectra of the bacteria are all slightly different and very different from the spectra of silver ions (silver nitrate and silver acetate), which confirms that a reaction occurs. Death or inactivation of bacteria was observed by plate counting and light microscopy. Silver bonding to sulfhydryl groups (Ag-S) in cysteine and Ag-N or Ag-O bonding in histidine, alanine, and DL-aspartic acid was detected by using synthesized silver-amino acids. Significantly lower silver-cysteine content, coupled with higher silver-histidine content, in Gram-positive S. aureus and Listeria monocytogenes cells indicates that the peptidoglycan multilayer could be buffering the biocidal effect of silver on Gram-positive bacteria, at least in part. Bonding of silver to phosphate groups was not detected. Interaction with DNA or proteins can occur through Ag-N bonding. The formation of silver-cysteine can be confirmed for both bacterial cell types, which supports the hypothesis that enzyme-catalyzed reactions and the electron transport chain within the cell are disrupted. PMID:23934494

  8. L-Edge X-ray Absorption Spectroscopy of Dilute Systems Relevant to Metalloproteins Using an X-ray Free-Electron Laser

    PubMed Central

    Mitzner, Rolf; Rehanek, Jens; Kern, Jan; Gul, Sheraz; Hattne, Johan; Taguchi, Taketo; Alonso-Mori, Roberto; Tran, Rosalie; Weniger, Christian; Schröder, Henning; Quevedo, Wilson; Laksmono, Hartawan; Sierra, Raymond G.; Han, Guangye; Lassalle-Kaiser, Benedikt; Koroidov, Sergey; Kubicek, Katharina; Schreck, Simon; Kunnus, Kristjan; Brzhezinskaya, Maria; Firsov, Alexander; Minitti, Michael P.; Turner, Joshua J.; Moeller, Stefan; Sauter, Nicholas K.; Bogan, Michael J.; Nordlund, Dennis; Schlotter, William F.; Messinger, Johannes; Borovik, Andrew; Techert, Simone; de Groot, Frank M. F.; Föhlisch, Alexander; Erko, Alexei; Bergmann, Uwe; Yachandra, Vittal K.; Wernet, Philippe; Yano, Junko

    2013-01-01

    L-edge spectroscopy of 3d transition metals provides important electronic structure information and has been used in many fields. However, the use of this method for studying dilute aqueous systems, such as metalloenzymes, has not been prevalent because of severe radiation damage and the lack of suitable detection systems. Here we present spectra from a dilute Mn aqueous solution using a high-transmission zone-plate spectrometer at the Linac Coherent Light Source (LCLS). The spectrometer has been optimized for discriminating the Mn L-edge signal from the overwhelming O K-edge background that arises from water and protein itself, and the ultrashort LCLS X-ray pulses can outrun X-ray induced damage. We show that the deviations of the partial-fluorescence yield-detected spectra from the true absorption can be well modeled using the state-dependence of the fluorescence yield, and discuss implications for the application of our concept to biological samples. PMID:24466387

  9. Towards atomic resolution in sodium titanate nanotubes using near-edge X-ray-absorption fine-structure spectromicroscopy combined with multichannel multiple-scattering calculations

    PubMed Central

    Krüger, Peter; Lagos, Maureen J; Ke, Xiaoxing; Van Tendeloo, Gustaaf; Ewels, Chris; Umek, Polona; Guttmann, Peter

    2012-01-01

    Summary Recent advances in near-edge X-ray-absorption fine-structure spectroscopy coupled with transmission X-ray microscopy (NEXAFS–TXM) allow large-area mapping investigations of individual nano-objects with spectral resolution up to E/ΔE = 104 and spatial resolution approaching 10 nm. While the state-of-the-art spatial resolution of X-ray microscopy is limited by nanostructuring process constrains of the objective zone plate, we show here that it is possible to overcome this through close coupling with high-level theoretical modelling. Taking the example of isolated bundles of hydrothermally prepared sodium titanate nanotubes ((Na,H)TiNTs) we are able to unravel the complex nanoscale structure from the NEXAFS–TXM data using multichannel multiple-scattering calculations, to the extent of being able to associate specific spectral features in the O K-edge and Ti L-edge with oxygen atoms in distinct sites within the lattice. These can even be distinguished from the contribution of different hydroxyl groups to the electronic structure of the (Na,H)TiNTs. PMID:23213642

  10. Towards atomic resolution in sodium titanate nanotubes using near-edge X-ray-absorption fine-structure spectromicroscopy combined with multichannel multiple-scattering calculations.

    PubMed

    Bittencourt, Carla; Krüger, Peter; Lagos, Maureen J; Ke, Xiaoxing; Van Tendeloo, Gustaaf; Ewels, Chris; Umek, Polona; Guttmann, Peter

    2012-01-01

    Recent advances in near-edge X-ray-absorption fine-structure spectroscopy coupled with transmission X-ray microscopy (NEXAFS-TXM) allow large-area mapping investigations of individual nano-objects with spectral resolution up to E/ΔE = 10(4) and spatial resolution approaching 10 nm. While the state-of-the-art spatial resolution of X-ray microscopy is limited by nanostructuring process constrains of the objective zone plate, we show here that it is possible to overcome this through close coupling with high-level theoretical modelling. Taking the example of isolated bundles of hydrothermally prepared sodium titanate nanotubes ((Na,H)TiNTs) we are able to unravel the complex nanoscale structure from the NEXAFS-TXM data using multichannel multiple-scattering calculations, to the extent of being able to associate specific spectral features in the O K-edge and Ti L-edge with oxygen atoms in distinct sites within the lattice. These can even be distinguished from the contribution of different hydroxyl groups to the electronic structure of the (Na,H)TiNTs. PMID:23213642

  11. A combined DFT and restricted open-shell configuration interaction method including spin-orbit coupling: application to transition metal L-edge X-ray absorption spectroscopy.

    PubMed

    Roemelt, Michael; Maganas, Dimitrios; DeBeer, Serena; Neese, Frank

    2013-05-28

    A novel restricted-open-shell configuration interaction with singles (ROCIS) approach for the calculation of transition metal L-edge X-ray absorption spectra is introduced. In this method, one first calculates the ground state and a number of excited states of the non-relativistic Hamiltonian. By construction, the total spin is a good quantum number in each of these states. For a ground state with total spin S excited states with spin S' = S, S - 1, and S + 1 are constructed. Using Wigner-Eckart algebra, all magnetic sublevels with MS = S,..., -S for each multiplet of spin S are obtained. The spin-orbit operator is represented by a mean-field approximation to the full Breit-Pauli spin-orbit operator and is diagonalized over this N-particle basis. This is equivalent to a quasi-degenerate treatment of the spin-orbit interaction to all orders. Importantly, the excitation space spans all of the molecular multiplets that arise from the atomic Russell-Saunders terms. Hence, the method represents a rigorous first-principles approach to the complicated low-symmetry molecular multiplet problem met in L-edge X-ray absorption spectroscopy. In order to gain computational efficiency, as well as additional accuracy, the excitation space is restricted to single excitations and the configuration interaction matrix is slightly parameterized in order to account for dynamic correlation effects in an average way. To this end, it is advantageous to employ Kohn-Sham rather than Hartree-Fock orbitals thus defining the density functional theory∕ROCIS method. However, the method can also be used in an entirely non-empirical fashion. Only three global empirical parameters are introduced and have been determined here for future application of the method to any system containing any transition metal. The three parameters were carefully calibrated using the L-edge X-ray absorption spectroscopy spectra of a test set of coordination complexes containing first row transition metals. These

  12. A combined DFT and restricted open-shell configuration interaction method including spin-orbit coupling: Application to transition metal L-edge X-ray absorption spectroscopy

    NASA Astrophysics Data System (ADS)

    Roemelt, Michael; Maganas, Dimitrios; DeBeer, Serena; Neese, Frank

    2013-05-01

    A novel restricted-open-shell configuration interaction with singles (ROCIS) approach for the calculation of transition metal L-edge X-ray absorption spectra is introduced. In this method, one first calculates the ground state and a number of excited states of the non-relativistic Hamiltonian. By construction, the total spin is a good quantum number in each of these states. For a ground state with total spin S excited states with spin S' = S, S - 1, and S + 1 are constructed. Using Wigner-Eckart algebra, all magnetic sublevels with MS = S, …, -S for each multiplet of spin S are obtained. The spin-orbit operator is represented by a mean-field approximation to the full Breit-Pauli spin-orbit operator and is diagonalized over this N-particle basis. This is equivalent to a quasi-degenerate treatment of the spin-orbit interaction to all orders. Importantly, the excitation space spans all of the molecular multiplets that arise from the atomic Russell-Saunders terms. Hence, the method represents a rigorous first-principles approach to the complicated low-symmetry molecular multiplet problem met in L-edge X-ray absorption spectroscopy. In order to gain computational efficiency, as well as additional accuracy, the excitation space is restricted to single excitations and the configuration interaction matrix is slightly parameterized in order to account for dynamic correlation effects in an average way. To this end, it is advantageous to employ Kohn-Sham rather than Hartree-Fock orbitals thus defining the density functional theory/ROCIS method. However, the method can also be used in an entirely non-empirical fashion. Only three global empirical parameters are introduced and have been determined here for future application of the method to any system containing any transition metal. The three parameters were carefully calibrated using the L-edge X-ray absorption spectroscopy spectra of a test set of coordination complexes containing first row transition metals. These

  13. Trichroism in energy-loss near-edge structure spectroscopy: Polarization dependence of near-edge fine structures

    SciTech Connect

    Le Bosse, Jean-Claude; Epicier, Thierry; Chermette, Henry

    2007-08-15

    The goal of this paper is to relate the current of inelastically scattered electrons collected in a transmission electron microscope (TEM) to the double differential electron energy-loss cross section. Up to now, this relationship, which depends on the point symmetry around the probed atom site, has been essentially studied in a situation called dichroism. This situation can be encountered when a principal threefold, fourfold, or sixfold rotation axis through the probed atom site exists. The electron energy-loss cross section is then a linear combination of longitudinal and transversal cross sections, and the weights of these components are cos{sup 2} {theta}{sub q} and sin{sup 2} {theta}{sub q}, where {theta}{sub q} is the angle between the scattering wave vector q and the principal rotation axis. The first aim of this paper is to find the dependence on q of the cross section in all other cases, that is to say, when the symmetry around the probed atom site is described with one of the eight low symmetry point groups C{sub 1}, S{sub 2}, C{sub 1h}, C{sub 2}, C{sub 2h}, C{sub 2v}, D{sub 2}, and D{sub 2h}. In these eight cases of low symmetry, three distinct situations called trichroism can be distinguished. In these situations, the cross section is expressed in terms of the cross sections obtained for six, four, or three particular orientations of the scattering wave vector. The second aim of this paper is to provide an expression of the inelastically scattered electron current collected in a TEM for these three situations of trichroism. This current is expressed in terms of experimental parameters, such as the incident beam convergence, the collector acceptance, the electron beam kinetic energy, and the sample orientation. As in the case of dichroism, magic conditions can be found, for which the collected current becomes independent of the single-crystal sample orientation. The case of the C K edge in the nonstoichiometric V{sub 6}C{sub 5} metallic carbide with a

  14. Ge L{sub 3}-edge x-ray absorption near-edge structure study of structural changes accompanying conductivity drift in the amorphous phase of Ge{sub 2}Sb{sub 2}Te{sub 5}

    SciTech Connect

    Mitrofanov, K. V.; Kolobov, A. V. Fons, P.; Wang, X.; Tominaga, J.; Tamenori, Y.; Uruga, T.; Ciocchini, N.; Ielmini, D.

    2014-05-07

    A gradual uncontrollable increase in the resistivity of the amorphous phase of phase-change alloys, such as Ge{sub 2}Sb{sub 2}Te{sub 5}, known as drift, is a serious technological issue for application of phase-change memory. While it has been proposed that drift is related to structural relaxation, no direct structural results have been reported so far. Here, we report the results of Ge L{sub 3}-edge x-ray absorption measurements that suggest that the drift in electrical conductivity is associated with the gradual conversion of tetrahedrally coordinated Ge sites into pyramidal sites, while the system still remains in the amorphous phase. Based on electronic configuration arguments, we propose that during this process, which is governed by the existence of lone-pair electrons, the concentration of free carriers in the system decreases resulting in an increase in resistance despite the structural relaxation towards the crystalline phase.

  15. The dust-scattering component of X-ray extinction: effects on continuum fitting and high-resolution absorption edge structure

    NASA Astrophysics Data System (ADS)

    Corrales, L. R.; García, J.; Wilms, J.; Baganoff, F.

    2016-05-01

    Small angle scattering by dust grains causes a significant contribution to the total interstellar extinction for any X-ray instrument with sub-arcminute resolution (Chandra, Swift, XMM-Newton). However, the dust-scattering component is not included in the current absorption models: phabs, TBabs, and TBnew. We simulate a large number of Chandra spectra to explore the bias in the spectral fit and NH measurements obtained without including extinction from dust scattering. We find that without incorporating dust scattering, the measured NH will be too large by a baseline level of 25 per cent. This effect is modulated by the imaging resolution of the telescope, because some amount of unresolved scattered light will be captured within the aperture used to extract point source information. In high-resolution spectroscopy, dust scattering significantly enhances the total extinction optical depth and the shape of the photoelectric absorption edges. We focus in particular on the Fe-L edge at 0.7 keV, showing that the total extinction template fits well to the high-resolution spectrum of three X-ray binaries from the Chandra archive: GX 9+9, XTE J1817-330, and Cyg X-1. In cases where dust is intrinsic to the source, a covering factor based on the angular extent of the dusty material must be applied to the extinction curve, regardless of angular imaging resolution. This approach will be particularly relevant for dust in quasar absorption line systems and might constrain clump sizes in active galactic nuclei.

  16. Direct nitrogen fixation at the edges of graphene nanoplatelets as efficient electrocatalysts for energy conversion

    NASA Astrophysics Data System (ADS)

    Jeon, In-Yup; Choi, Hyun-Jung; Ju, Myung Jong; Choi, In Taek; Lim, Kimin; Ko, Jaejung; Kim, Hwan Kyu; Kim, Jae Cheon; Lee, Jae-Joon; Shin, Dongbin; Jung, Sun-Min; Seo, Jeong-Min; Kim, Min-Jung; Park, Noejung; Dai, Liming; Baek, Jong-Beom

    2013-07-01

    Nitrogen fixation is essential for the synthesis of many important chemicals (e.g., fertilizers, explosives) and basic building blocks for all forms of life (e.g., nucleotides for DNA and RNA, amino acids for proteins). However, direct nitrogen fixation is challenging as nitrogen (N2) does not easily react with other chemicals. By dry ball-milling graphite with N2, we have discovered a simple, but versatile, scalable and eco-friendly, approach to direct fixation of N2 at the edges of graphene nanoplatelets (GnPs). The mechanochemical cracking of graphitic C-C bonds generated active carbon species that react directly with N2 to form five- and six-membered aromatic rings at the broken edges, leading to solution-processable edge-nitrogenated graphene nanoplatelets (NGnPs) with superb catalytic performance in both dye-sensitized solar cells and fuel cells to replace conventional Pt-based catalysts for energy conversion.

  17. Direct nitrogen fixation at the edges of graphene nanoplatelets as efficient electrocatalysts for energy conversion

    PubMed Central

    Jeon, In-Yup; Choi, Hyun-Jung; Ju, Myung Jong; Choi, In Taek; Lim, Kimin; Ko, Jaejung; Kim, Hwan Kyu; Kim, Jae Cheon; Lee, Jae-Joon; Shin, Dongbin; Jung, Sun-Min; Seo, Jeong-Min; Kim, Min-Jung; Park, Noejung; Dai, Liming; Baek, Jong-Beom

    2013-01-01

    Nitrogen fixation is essential for the synthesis of many important chemicals (e.g., fertilizers, explosives) and basic building blocks for all forms of life (e.g., nucleotides for DNA and RNA, amino acids for proteins). However, direct nitrogen fixation is challenging as nitrogen (N2) does not easily react with other chemicals. By dry ball-milling graphite with N2, we have discovered a simple, but versatile, scalable and eco-friendly, approach to direct fixation of N2 at the edges of graphene nanoplatelets (GnPs). The mechanochemical cracking of graphitic C−C bonds generated active carbon species that react directly with N2 to form five- and six-membered aromatic rings at the broken edges, leading to solution-processable edge-nitrogenated graphene nanoplatelets (NGnPs) with superb catalytic performance in both dye-sensitized solar cells and fuel cells to replace conventional Pt-based catalysts for energy conversion. PMID:23877200

  18. Full-Field Calcium K-Edge X-ray Absorption Near-Edge Structure Spectroscopy on Cortical Bone at the Micron-Scale: Polarization Effects Reveal Mineral Orientation.

    PubMed

    Hesse, Bernhard; Salome, Murielle; Castillo-Michel, Hiram; Cotte, Marine; Fayard, Barbara; Sahle, Christoph J; De Nolf, Wout; Hradilova, Jana; Masic, Admir; Kanngießer, Birgit; Bohner, Marc; Varga, Peter; Raum, Kay; Schrof, Susanne

    2016-04-01

    Here, we show results on X-ray absorption near edge structure spectroscopy in both transmission and X-ray fluorescence full-field mode (FF-XANES) at the calcium K-edge on human bone tissue in healthy and diseased conditions and for different tissue maturation stages. We observe that the dominating spectral differences originating from different tissue regions, which are well pronounced in the white line and postedge structures are associated with polarization effects. These polarization effects dominate the spectral variance and must be well understood and modeled before analyzing the very subtle spectral variations related to the bone tissue variations itself. However, these modulations in the fine structure of the spectra can potentially be of high interest to quantify orientations of the apatite crystals in highly structured tissue matrices such as bone. Due to the extremely short wavelengths of X-rays, FF-XANES overcomes the limited spatial resolution of other optical and spectroscopic techniques exploiting visible light. Since the field of view in FF-XANES is rather large the acquisition times for analyzing the same region are short compared to, for example, X-ray diffraction techniques. Our results on the angular absorption dependence were verified by both site-matched polarized Raman spectroscopy, which has been shown to be sensitive to the orientation of bone building blocks and by mathematical simulations of the angular absorbance dependence. As an outlook we further demonstrate the polarization based assessment of calcium-containing crystal orientation and specification of calcium in a beta-tricalcium phosphate (β-Ca3(PO4)2 scaffold implanted into ovine bone. Regarding the use of XANES to assess chemical properties of Ca in human bone tissue our data suggest that neither the anatomical site (tibia vs jaw) nor pathology (healthy vs necrotic jaw bone tissue) affected the averaged spectral shape of the XANES spectra. PMID:26959687

  19. Temperature dependence and annealing effects of absorption edges for selenium quantum dots formed by ion implantation in silica glass

    SciTech Connect

    Ueda, A.; Wu, M.; Mu, R.

    1998-12-31

    The authors have fabricated Se nanoparticles in silica substrates by ion implantation followed by thermal annealing up to 1000 C, and studied the Se nanoparticle formation by optical absorption spectroscopy, Rutherford backscattering spectrometry, X-ray diffraction, and transmission electron microscopy. The sample with the highest dose (1 {times} 10{sup 17} ions/cm{sup 2}) showed the nanoparticle formation during the ion implantation, while the lower dose samples (1 and 3 {times} 10{sup 16} ions/cm{sup 2}) required thermal treatment to obtain nano-sized particles. The Se nanoparticles in silica were found to be amorphous. After thermal annealing, the particle doses approached the value of bulk after thermal annealing. The temperature dependent absorption spectra were also measured for this system in a temperature range from 15 to 300 K.

  20. Functionalisation of graphene by edge-halogenation and radical addition using polycyclic aromatic hydrocarbon models: edge electron density-binding energy relationship

    NASA Astrophysics Data System (ADS)

    Yadav, Amarjeet; Mishra, P. C.

    2015-04-01

    Structures and properties of functionalised graphene were investigated using several derivatives of some small polycyclic aromatic hydrocarbons (PAHs) taken as finite size models employing unrestricted density functional theory. The functionalisation reactions included fluorination or chlorination of all the edge carbon sites, addition of H, F or Cl atom, OH or OOH group at the different sites and addition of OH or OOH group at the different sites of the edge-halogenated PAHs. σ-inductive effects of fluorine and chlorine in the edge-fluorinated and edge-chlorinated PAHs, respectively, were found to affect electron density and molecular electrostatic potential (MEP) distributions significantly. σ-holes were located at the MEP surfaces along the CH and CCl bonds of the unmodified and edge-chlorinated PAHs, respectively. The H and F atoms and the OH group were found to add to all the carbon sites of PAHs exothermically, while addition of the Cl atom and the OOH group was found to be exothermic at a few carbon sites and endothermic at the other carbon sites. Enhanced electron densities at the edge carbon sites of the PAHs and binding energies of adducts of H and F atoms and the OH group at these sites were found to be linearly correlated.

  1. NOTE: Near surface photon energy spectra outside a 6 MV field edge

    NASA Astrophysics Data System (ADS)

    Edwards, C. R.; Mountford, P. J.

    2004-09-01

    The purpose of this study was to investigate the difference between a 6 MV linear accelerator x-ray energy spectrum outside the field edge near a phantom surface, and the corresponding spectrum on the central axis. The Monte Carlo code MCNP-4A was used to calculate the spectra on the central axis and at 1, 2, 5 and 10 cm from the edge of a 4 × 4 cm2, 10 × 10 cm2 and 15 × 15 cm2 field. Compared to the spectrum on the central axis, the spectra outside the field edge showed two distinct regions: a broad peak below about 0.5 MeV, and a lower amplitude, less rapidly changing region at higher energies from 0.5 to 6 MeV. The lower energy peak was due to scattered photons, and the higher energy component was due mainly to primary photons transmitted through the jaws of the secondary collimator. The potential impact of these spectral differences on critical organ photon dosimetry was determined by calculating the ratio of the sensitivity of a Scanditronix EDD-5 diode and of a LiF:Mg:Ti thermoluminescent dosimeter (TLD) outside the field edge to their respective sensitivity at the calibration position on the central axis. The lower energy peak combined with the non-uniform energy sensitivity of each detector produced up to a two-thirds overestimate of x-ray dose outside the field by the diode, whereas the response ratio of the TLD was about unity. These results indicated that a similar evaluation was required for profile measurements of a dynamic wedged field and measurements in an intensity modulated beam with either type of detector.

  2. Near surface photon energy spectra outside a 6 MV field edge.

    PubMed

    Edwards, C R; Mountford, P J

    2004-09-21

    The purpose of this study was to investigate the difference between a 6 MV linear accelerator x-ray energy spectrum outside the field edge near a phantom surface, and the corresponding spectrum on the central axis. The Monte Carlo code MCNP-4A was used to calculate the spectra on the central axis and at 1, 2, 5 and 10 cm from the edge of a 4 x 4 cm2, 10 x 10 cm2 and 15 x 15 cm2 field. Compared to the spectrum on the central axis, the spectra outside the field edge showed two distinct regions: a broad peak below about 0.5 MeV, and a lower amplitude, less rapidly changing region at higher energies from 0.5 to 6 MeV. The lower energy peak was due to scattered photons, and the higher energy component was due mainly to primary photons transmitted through the jaws of the secondary collimator. The potential impact of these spectral differences on critical organ photon dosimetry was determined by calculating the ratio of the sensitivity of a Scanditronix EDD-5 diode and of a LiF:Mg:Ti thermoluminescent dosimeter (TLD) outside the field edge to their respective sensitivity at the calibration position on the central axis. The lower energy peak combined with the non-uniform energy sensitivity of each detector produced up to a two-thirds overestimate of x-ray dose outside the field by the diode, whereas the response ratio of the TLD was about unity. These results indicated that a similar evaluation was required for profile measurements of a dynamic wedged field and measurements in an intensity modulated beam with either type of detector. PMID:15509076

  3. Novel Technique for Improving the Signal-to-Background Ratio of X-ray Absorption Near-Edge Structure Spectrum in Fluorescence Mode and Its Application to the Chemical State Analysis of Magnesium Doped in GaN

    NASA Astrophysics Data System (ADS)

    Yonemura, Takumi; Iihara, Junji; Saito, Yoshihiro; Ueno, Masaki

    2013-12-01

    A novel measurement technique for an X-ray absorption near-edge structure (XANES) for magnesium (Mg) doped in gallium nitride (GaN) has been developed. XANES spectra from Mg at very low concentrations of 1 ×1018/cm3 doped in GaN have successfully been obtained by optimizing the region of interest (ROI) and by using highly brilliant synchrotron radiation X-rays of SPring-8. The ROI is the limited energy region from an X-ray fluorescence spectrum to elicit signals of particular atoms. Using this new technique, we have investigated the effect of the annealing process for Mg-doped GaN on the XANES spectra. It has been found that the XANES spectra of Mg significantly changed as the annealing temperature increased. This indicates that the local structure around Mg atoms in GaN was modified by the annealing process.

  4. Band-Selective Measurements of Electron Dynamics in VO2 UsingFemtosecond Near-Edge X-Ray Absorption

    SciTech Connect

    Cavalleri, A.; Rini, M.; Chong, H.H.W.; Fourmaux, S.; Glover,T.E.; Heimann, P.A.; Kieffer, J.C.; Schoenlein, R.W.

    2005-07-20

    We report on the first demonstration of femtosecond x-rayabsorption spectroscopy, made uniquely possible by the use of broadlytunable bending-magnet radiation from "laser-sliced" electron buncheswithin a synchrotron storage ri ng. We measure the femtosecond electronicrearrangements that occur during the photoinduced insulator-metal phasetransition in VO2. Symmetry- and element-specific x-ray absorption fromV2p and O1s core levels (near 500 eV) separately measures the fillingdynamics of differently hybridized V3d-O2p electronic bands near theFermi level.

  5. Electro-absorption of silicene and bilayer graphene quantum dots

    NASA Astrophysics Data System (ADS)

    Abdelsalam, Hazem; Talaat, Mohamed H.; Lukyanchuk, Igor; Portnoi, M. E.; Saroka, V. A.

    2016-07-01

    We study numerically the optical properties of low-buckled silicene and AB-stacked bilayer graphene quantum dots subjected to an external electric field, which is normal to their surface. Within the tight-binding model, the optical absorption is calculated for quantum dots, of triangular and hexagonal shapes, with zigzag and armchair edge terminations. We show that in triangular silicene clusters with zigzag edges a rich and widely tunable infrared absorption peak structure originates from transitions involving zero energy states. The edge of absorption in silicene quantum dots undergoes red shift in the external electric field for triangular clusters, whereas blue shift takes place for hexagonal ones. In small clusters of bilayer graphene with zigzag edges the edge of absorption undergoes blue/red shift for triangular/hexagonal geometry. In armchair clusters of silicene blue shift of the absorption edge takes place for both cluster shapes, while red shift is inherent for both shapes of the bilayer graphene quantum dots.

  6. On the importance of nuclear quantum motions in near edge x-ray absorption fine structure (NEXAFS) spectroscopy of molecules

    SciTech Connect

    Schwartz, Craig P.; Uejio, Janel S.; Saykally, Richard J.; Prendergast, David

    2009-02-26

    We report the effects of sampling nuclear quantum motion with path integral molecular dynamics (PIMD) on calculations of the nitrogen K-edge spectra of two isolated organic molecules. S-triazine, a prototypical aromatic molecule occupying primarily its vibrational ground state at room temperature, exhibits substantially improved spectral agreement when nuclear quantum effects are included via PIMD, as compared to the spectra obtained from either a single fixed-nuclei based calculation or from a series of configurations extracted from a classical molecular dynamics trajectory. Nuclear quantum dynamics can accurately explain the intrinsic broadening of certain features. Glycine, the simplest amino acid, is problematic due to large spectral variations associated with multiple energetically accessible conformations at the experimental temperature. This work highlights the sensitivity of NEXAFS to quantum nuclear motions in molecules, and the necessity of accurately sampling such quantum motion when simulating their NEXAFS spectra.

  7. Electronic and chemical state of aluminum from the single- (K) and double-electron excitation (KLII&III, KLI) x-ray absorption near-edge spectra of α-alumina, sodium aluminate, aqueous Al³⁺•(H₂O)₆, and aqueous Al(OH)₄⁻

    SciTech Connect

    Fulton, John L.; Govind, Niranjan; Huthwelker, Thomas; Bylaska, Eric J.; Vjunov, Aleksei; Pin, Sonia; Smurthwaite, Tricia D.

    2015-07-02

    We probe, at high energy resolution, the double electron excitation (KLII&II) x-ray absorption region that lies approximately 115 eV above the main Al K-edge (1566 eV) of α-alumina and sodium aluminate. The two solid standards, α-alumina (octahedral) and sodium aluminate (tetrahedral) are compared to aqueous species that have the same Al coordination symmetries, Al³⁺•6H₂O (octahedral) and Al(OH)₄⁻ (tetrahedral). For the octahedral species, the edge height of the KLII&III-edge is approximately 10% of the main K-edge however the edge height is much weaker (3% of K-edge height) for Al species with tetrahedral symmetry. For the α-alumina and aqueous Al³⁺•6H₂O the KLII&III spectra contain white line features and extended absorption fine structure (EXAFS) that mimics the K-edge spectra. The KLII&III-edge feature interferes with an important region of the extended-XAFS region of the spectra for the K-edge of the crystalline and aqueous standards. The K-edge spectra and K-edge positions are predicted using time-dependent density functional theory (TDDFT). The TDDFT calculations for the K-edge XANES spectra reproduce the observed transitions in the experimental spectra of the four Al species. The KLII&III and KLI onsets and their corresponding chemical shifts for the four standards are estimated using the delta self-consistent field (ΔSCF) method. Research by JLF, NG, EJB, AV, TDS was supported by U.S. Department of Energy’s (DOE), Office of Science, Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences, and Biosciences. NG thanks Amity Andersen for help with the α-Al₂O₃ and tetrahedral sodium aluminate (NaAlO₂) clusters. All the calculations were performed using the Molecular Science Computing Capability at EMSL, a national scientific user facility sponsored by the U.S. Department of Energy’s Office of Biological and Environmental Research and located at

  8. Study of hard disk and slider surfaces using X-ray photoemission electron microscopy and near-edge X-ray absorption fine structure spectroscopy

    SciTech Connect

    Anders, S.; Stammler, T.; Bhatia, C.S.; Fong, W.; Chen, C.Y.; Bogy, D.B.

    1998-04-01

    X-ray Photo Emission Electron Microscopy (X-PEEM) and Near Edge X-ray Absorption Fine Structure (NEXAFS) spectroscopy were applied to study the properties of amorphous hard carbon overcoats on disks and sliders, and the properties of the lubricant. The modification of lubricants after performing thermal desorption studies was measured by NEXAFS, and the results are compared to the thermal desorption data. The study of lubricant degradation in wear tracks is described. Sliders were investigated before and after wear test, and the modification of the slider coating as well as the transfer of lubricant to the slider was studied. The studies show that the lubricant is altered chemically during the wear. Fluorine is removed and carboxyl groups are formed.

  9. Liquid crystal alignment on ion-beam-treated polyimide with a long alkyl side chain: near edge X-ray absorption fine structure spectroscopy analysis.

    PubMed

    Seo, Joo-Hong; Hwang, Soo Won; Song, Dong Han; Shin, Jae Hoon; Yoon, Tae-Hoon; Kim, Jae Chang; Yi, Mi Hye

    2009-02-19

    Liquid crystal alignment on ion-beam-treated polyimides with a long alkyl side chain was investigated using near edge X-ray absorption fine structure (NEXAFS) spectroscopy. The long alkyl side chains and the asymmetric distribution and orientational order of the pi-bonds of the polyimide surface can be determined by analyzing the angular dependent resonance intensities of the NEXAFS measurements. Herein, we demonstrate that the pretilt angle of the LC cell made by our method decreases as more long alkyl side chains are destroyed. Additionally, the tilt direction of the LC molecules can be determined from the asymmetric distribution of pi-bonds of the polyimide created by the ion beam irradiation. PMID:19161281

  10. 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.

  11. Near edge X-ray absorption fine structure spectroscopy as a tool to probe electronic and structural properties of thin organic films and liquids.

    PubMed

    Hähner, Georg

    2006-12-01

    Synchrotron-based spectroscopic techniques have contributed significantly to a better understanding of the properties of materials on the macroscopic and microscopic scale over the last decades. They can be applied to samples from a diversity of fields, including Biology, Life Sciences, Chemistry and Materials. One of these techniques is Near Edge X-Ray Absorption Fine Structure (NEXAFS) spectroscopy, revealing electronic structure and information on the orientation of adsorbed molecules. The present article describes the basics of the technique and the progress it has made over the last three decades, and summarizes some of its more recent developments and applications. This tutorial review article should be accessible for novices to the field from Physics, Chemistry, Biology, Materials, and the Life Sciences, interested in thin organic films and liquid systems. PMID:17225886

  12. Investigation of Pb species in soils, celery and duckweed by synchrotron radiation X-ray absorption near-edge structure spectrometry

    NASA Astrophysics Data System (ADS)

    Luo, Liqiang; Shen, Yating; Liu, Jian; Zeng, Yuan

    2016-08-01

    The Pb species play a key role in its translocation in biogeochemical cycles. Soils, sediments and plants were collected from farmlands around Pb mines, and the Pb species in them was identified by X-ray absorption near-edge structure spectrometry. In soils, Pb5(PO4)3Cl and Pb3(PO4)2 were detected, and in sediments, Pb-fulvic acids (FAs) complex was identified. A Pb complex with FA fragments was also detected in celery samples. We found that (1) different Pb species were present in soils and sediments; (2) the Pb species in celery, which was grown in sediments, was different from the species present in duckweed, which grew in water; and (3) a Pb-FA-like compound was present in celery roots. The newly identified Pb species, the Pb-FA-like compound, may play a key role in Pb tolerance and translocation within plants.

  13. Composition analysis of a polymer electrolyte membrane fuel cell microporous layer using scanning transmission X-ray microscopy and near edge X-ray absorption fine structure analysis

    NASA Astrophysics Data System (ADS)

    George, Michael G.; Wang, Jian; Banerjee, Rupak; Bazylak, Aimy

    2016-03-01

    The novel application of scanning transmission X-ray microscopy (STXM) to the microporous layer (MPL) of a polymer electrolyte membrane fuel cell is investigated. A spatially resolved chemical component distribution map is obtained for the MPL of a commercially available SGL 25 BC sample. This is achieved with near edge X-ray absorption fine structure spectroscopic analysis. Prior to analysis the sample is embedded in non-reactive epoxy and ultra-microtomed to a thickness of 100 nm. Polytetrafluoroethylene (PTFE), carbon particle agglomerates, and supporting epoxy resin distributions are identified and reconstructed for a scanning area of 6 μm × 6 μm. It is observed that the spatial distribution of PTFE is strongly correlated to the carbon particle agglomerations. Additionally, agglomerate structures of PTFE are identified, possibly indicating the presence of a unique mesostructure in the MPL. STXM analysis is presented as a useful technique for the investigation of chemical species distributions in the MPL.

  14. Effect of gas residence time on near-edge X-ray absorption fine structures of hydrogenated amorphous carbon films grown by plasma-enhanced chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Jia, Lingyun; Sugiura, Hirotsugu; Kondo, Hiroki; Takeda, Keigo; Ishikawa, Kenji; Oda, Osamu; Sekine, Makoto; Hiramatsu, Mineo; Hori, Masaru

    2016-04-01

    In hydrogenated amorphous carbon films, deposited using a radical-injection plasma-enhanced chemical vapor deposition system, the chemical bonding structure was analyzed by near-edge X-ray absorption fine-structure spectroscopy. With a change in the residence times of source gases in a reactor, whereby total gas flow rates of H2/CH4 increased from 50 to 400 sccm, sp2-C fractions showed the minimum value at 150 sccm, while H concentration negligibly changed according to the results of secondary ion mass spectroscopy. On the other hand, widths of σ* C-C peaks increased with decreasing gas residence time, which indicates an increase in the fluctuation of bonding structures.

  15. Assessment of chemical species of lead accumulated in tidemarks of human articular cartilage by X-ray absorption near-edge structure analysis

    PubMed Central

    Meirer, Florian; Pemmer, Bernhard; Pepponi, Giancarlo; Zoeger, Norbert; Wobrauschek, Peter; Sprio, Simone; Tampieri, Anna; Goettlicher, Joerg; Steininger, Ralph; Mangold, Stefan; Roschger, Paul; Berzlanovich, Andrea; Hofstaetter, Jochen G.; Streli, Christina

    2011-01-01

    A highly specific accumulation of the toxic element lead was recently measured in the transition zone between non-calcified and calcified normal human articular cartilage. This transition zone, the so-called ‘tidemark’, is considered to be an active calcification front of great clinical importance. However, little is known about the mechanisms of accumulation and the chemical form of Pb in calcified cartilage and bone. Using spatially resolved X-ray absorption near-edge structure analysis (µ-XANES) at the Pb L 3-edge, the chemical state of Pb in the osteochondral region was investigated. The feasibility of the µ-XANES set-up at the SUL-X beamline (ANKA synchrotron light source) was tested and confirmed by comparing XANES spectra of bulk Pb-reference compounds recorded at both the XAS and the SUL-X beamline at ANKA. The µ-XANES set-up was then used to investigate the tidemark region of human bone (two patella samples and one femoral head sample). The spectra recorded at the tidemark and at the trabecular bone were found to be highly correlated with the spectra of synthetic Pb-doped carbonated hydroxyapatite, suggesting that in both of these very different tissues Pb is incorporated into the hydroxyapatite structure. PMID:21335911

  16. Electronic defect states at the LaAlO3/SrTiO3 heterointerface revealed by O K-edge X-ray absorption spectroscopy.

    PubMed

    Palina, Natalia; Annadi, Anil; Asmara, Teguh Citra; Diao, Caozheng; Yu, Xiaojiang; Breese, Mark B H; Venkatesan, T; Ariando; Rusydi, Andrivo

    2016-05-18

    Interfaces of two dissimilar complex oxides exhibit exotic physical properties that are absent in their parent compounds. Of particular interest is insulating LaAlO3 films on an insulating SrTiO3 substrate, where transport measurements have shown a metal-insulator transition as a function of LaAlO3 thickness. Their origin has become the subject of intense research, yet a unifying consensus remains elusive. Here, we report evidence for the electronic reconstruction in both insulating and conducting LaAlO3/SrTiO3 heterointerfaces revealed by O K-edge X-ray absorption spectroscopy. For the insulating samples, the O K-edge XAS spectrum exhibits features characteristic of electronically active point defects identified as noninteger valence states of Ti. For conducting samples, a new shape-resonance at ∼540.5 eV, characteristic of molecular-like oxygen (empty O-2p band), is observed. This implies that the concentration of electronic defects has increased in proportion with LaAlO3 thickness. For larger defect concentrations, the electronic defect states are no longer localized at the Ti orbitals and exhibit pronounced O 2p-O 2p character. Our results demonstrate that, above a critical thickness, the delocalization of O 2p electronic states can be linked to the presence of oxygen vacancies and is responsible for the enhancement of conductivity at the oxide heterointerfaces. PMID:27146607

  17. Three-dimensional Fe speciation of an inclusion cloud within an ultradeep diamond by confocal μ-X-ray absorption near edge structure: evidence for late stage overprint.

    PubMed

    Silversmit, Geert; Vekemans, Bart; Appel, Karen; Schmitz, Sylvia; Schoonjans, Tom; Brenker, Frank E; Kaminsky, Felix; Vincze, Laszlo

    2011-08-15

    A stream of 1-20 μm sized mineral inclusions having the negative crystal shape of its host within an "ultra-deep" diamond from Rio Soriso (Juina area, Mato Grosso State, Brazil) has been studied with confocal μ-X-ray absorption near edge structure (μXANES) at the Fe K and Mn K edges. This technique allows the three-dimensional nondestructive speciation of the Fe and Mn containing minerals within the inclusion cloud. The observed Fe-rich inclusions were identified to be ferropericlase (Fe,Mg)O, hematite and a mixture of these two minerals. Confocal μ-X-ray fluorescence (μXRF) further showed that Ca-rich inclusions were present as well, which are spatially separated from or in close contact with the Fe-rich inclusions. The inclusions are aligned along a plane, which most likely represents a primary growth zone. In the close vicinity of the inclusions, carbon coated planar features are visible. The three-dimensional distribution indicates a likely fluid overprint along an open crack. Our results imply that an imposed negative diamond shape of an inclusion alone does not exclude epigenetic formation or intense late stage overprint. PMID:21707095

  18. 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

  19. Predicting Near Edge X-ray Absorption Spectra with the Spin-Free Exact-Two-Component Hamiltonian and Orthogonality Constrained Density Functional Theory.

    PubMed

    Verma, Prakash; Derricotte, Wallace D; Evangelista, Francesco A

    2016-01-12

    Orthogonality constrained density functional theory (OCDFT) provides near-edge X-ray absorption (NEXAS) spectra of first-row elements within one electronvolt from experimental values. However, with increasing atomic number, scalar relativistic effects become the dominant source of error in a nonrelativistic OCDFT treatment of core-valence excitations. In this work we report a novel implementation of the spin-free exact-two-component (X2C) one-electron treatment of scalar relativistic effects and its combination with a recently developed OCDFT approach to compute a manifold of core-valence excited states. The inclusion of scalar relativistic effects in OCDFT reduces the mean absolute error of second-row elements core-valence excitations from 10.3 to 2.3 eV. For all the excitations considered, the results from X2C calculations are also found to be in excellent agreement with those from low-order spin-free Douglas-Kroll-Hess relativistic Hamiltonians. The X2C-OCDFT NEXAS spectra of three organotitanium complexes (TiCl4, TiCpCl3, TiCp2Cl2) are in very good agreement with unshifted experimental results and show a maximum absolute error of 5-6 eV. In addition, a decomposition of the total transition dipole moment into partial atomic contributions is proposed and applied to analyze the nature of the Ti pre-edge transitions in the three organotitanium complexes. PMID:26584082

  20. X-ray absorption near-edge structure and nuclear magnetic resonance study of the lithium-sulfur battery and its components.

    PubMed

    Patel, Manu U M; Arčon, Iztok; Aquilanti, Giuliana; Stievano, Lorenzo; Mali, Gregor; Dominko, Robert

    2014-04-01

    Understanding the mechanism(s) of polysulfide formation and knowledge about the interactions of sulfur and polysulfides with a host matrix and electrolyte are essential for the development of long-cycle-life lithium-sulfur (Li-S) batteries. To achieve this goal, new analytical tools need to be developed. Herein, sulfur K-edge X-ray absorption near-edge structure (XANES) and (6,7) Li magic-angle spinning (MAS) NMR studies on a Li-S battery and its sulfur components are reported. The characterization of different stoichiometric mixtures of sulfur and lithium compounds (polysulfides), synthesized through a chemical route with all-sulfur-based components in the Li-S battery (sulfur and electrolyte), enables the understanding of changes in the batteries measured in postmortem mode and in operando mode. A detailed XANES analysis is performed on different battery components (cathode composite and separator). The relative amounts of each sulfur compound in the cathode and separator are determined precisely, according to the linear combination fit of the XANES spectra, by using reference compounds. Complementary information about the lithium species within the cathode are obtained by using (7) Li MAS NMR spectroscopy. The setup for the in operando XANES measurements can be viewed as a valuable analytical tool that can aid the understanding of the sulfur environment in Li-S batteries. PMID:24497200

  1. Sulfur species in source rock bitumen before and after hydrous pyrolysis determined by X-ray absorption near-edge structure

    USGS Publications Warehouse

    Bolin, Trudy B.; Birdwell, Justin E.; Lewan, Michael; Hill, Ronald J.; Grayson, Michael B.; Mitra-Kirtley, Sudipa; Bake, Kyle D.; Craddock, Paul R.; Abdallah, Wael; Pomerantz, Andrew E.

    2016-01-01

    The sulfur speciation of source rock bitumen (chloroform-extractable organic matter in sedimentary rocks) was examined using sulfur K-edge X-ray absorption near-edge structure (XANES) spectroscopy for a suite of 11 source rocks from around the world. Sulfur speciation was determined for both the native bitumen in thermally immature rocks and the bitumen produced by thermal maturation of kerogen via hydrous pyrolysis (360 °C for 72 h) and retained within the rock matrix. In this study, the immature bitumens had higher sulfur concentrations than those extracted from samples after hydrous pyrolysis. In addition, dramatic and systematic evolution of the bitumen sulfur moiety distributions following artificial thermal maturation was observed consistently for all samples. Specifically, sulfoxide sulfur (sulfur double bonded to oxygen) is abundant in all immature bitumen samples but decreases substantially following hydrous pyrolysis. The loss in sulfoxide sulfur is associated with a relative increase in the fraction of thiophene sulfur (sulfur bonded to aromatic carbon) to the extent that thiophene is the dominant sulfur form in all post-pyrolysis bitumen samples. This suggests that sulfur moiety distributions might be used for estimating thermal maturity in source rocks based on the character of the extractable organic matter.

  2. Quantum simulation of thermally-driven phase transition and oxygen K-edge x-ray absorption of high-pressure ice

    PubMed Central

    Kang, Dongdong; Dai, Jiayu; Sun, Huayang; Hou, Yong; Yuan, Jianmin

    2013-01-01

    The structure and phase transition of high-pressure ice are of long-standing interest and challenge, and there is still a huge gap between theoretical and experimental understanding. The quantum nature of protons such as delocalization, quantum tunneling and zero-point motion is crucial to the comprehension of the properties of high-pressure ice. Here we investigated the temperature-induced phase transition and oxygen K-edge x-ray absorption spectra of ice VII, VIII and X using ab initio path-integral molecular dynamics simulations. The tremendous difference between experiments and the previous theoretical predictions is closed for the phase diagram of ice below 300 K at pressures up to 110 GPa. Proton tunneling assists the proton-ordered ice VIII to transform into proton-disordered ice VII where only thermal activated proton-transfer cannot occur. The oxygen K edge with its shift is sensitive to the order-disorder transition, and therefore can be applied to diagnose the dynamics of ice structures. PMID:24253589

  3. 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.

  4. Cellular Energy Depletion Resets Whole-Body Energy by Promoting Coactivator Mediated Dietary Fuel Absorption

    PubMed Central

    Chopra, Atul R.; Kommagani, Ramakrishna; Saha, Pradip; Louet, Jean-Francois; Salazar, Christina; Song, Junghun; Jeong, Jaewook; Finegold, Milton; Viollet, Benoit; DeMayo, Franco; Chan, Lawrence; Moore, David D.; O'Malley, Bert W.

    2010-01-01

    Summary All organisms have devised strategies to counteract energy depletion in order to promote fitness for survival. We show here that cellular energy depletion puts into play a surprising strategy that leads to absorption of exogenous fuel for energy repletion. We found that the energy depletion sensing kinase AMPK, binds, phosphorylates, and activates the transcriptional coactivator SRC-2, which in a liver-specific manner, promotes absorption of dietary fat from the gut. Hepatocyte-specific deletion of SRC-2 results in intestinal fat malabsorption and attenuated entry of fat into the blood stream. This defect can be attributed to AMPK and SRC-2 mediated transcriptional regulation of hepatic bile-acid secretion into the gut, as it can be completely rescued by replenishing intestinal BA, or by genetically restoring the levels of hepatic Bile Salt Export Pump (BSEP). Our results position the hepatic AMPK-SRC-2 axis as an energy rheostat which upon cellular energy depletion resets whole-body energy by promoting absorption of dietary fuel. PMID:21195347

  5. Effect of x-ray energy dispersion in digital subtraction imaging at the iodine K-edge--A Monte Carlo study

    SciTech Connect

    Prino, F.; Ceballos, C.; Cabal, A.; Sarnelli, A.; Gambaccini, M.; Ramello, L.

    2008-01-15

    The effect of the energy dispersion of a quasi-monochromatic x-ray beam on the performance of a dual-energy x-ray imaging system is studied by means of Monte Carlo simulations using MCNPX (Monte Carlo N-Particle eXtended) version 2.6.0. In particular, the case of subtraction imaging at the iodine K-edge, suitable for angiographic imaging application, is investigated. The average energies of the two beams bracketing the iodine K-edge are set to the values of 31.2 and 35.6 keV corresponding to the ones obtained with a compact source based on a conventional x-ray tube and a mosaic crystal monochromator. The energy dispersion of the two beams is varied between 0 and 10 keV of full width at half-maximum (FWHM). The signal and signal-to-noise ratio produced in the simulated images by iodine-filled cavities (simulating patient vessels) drilled in a PMMA phantom are studied as a function of the x-ray energy dispersion. The obtained results show that, for the considered energy separation of 4.4 keV, no dramatic deterioration of the image quality is observed with increasing x-ray energy dispersion up to a FWHM of about 2.35 keV. The case of different beam energies is also investigated by means of fast simulations of the phantom absorption.

  6. Experimental and theoretical correlations between vanadium K-edge X-ray absorption and K[Formula: see text] emission spectra.

    PubMed

    Rees, Julian A; Wandzilak, Aleksandra; Maganas, Dimitrios; Wurster, Nicole I C; Hugenbruch, Stefan; Kowalska, Joanna K; Pollock, Christopher J; Lima, Frederico A; Finkelstein, Kenneth D; DeBeer, Serena

    2016-09-01

    A series of vanadium compounds was studied by K-edge X-ray absorption (XAS) and K[Formula: see text] X-ray emission spectroscopies (XES). Qualitative trends within the datasets, as well as comparisons between the XAS and XES data, illustrate the information content of both methods. The complementary nature of the chemical insight highlights the success of this dual-technique approach in characterizing both the structural and electronic properties of vanadium sites. In particular, and in contrast to XAS or extended X-ray absorption fine structure (EXAFS), we demonstrate that valence-to-core XES is capable of differentiating between ligating atoms with the same identity but different bonding character. Finally, density functional theory (DFT) and time-dependent DFT calculations enable a more detailed, quantitative interpretation of the data. We also establish correction factors for the computational protocols through calibration to experiment. These hard X-ray methods can probe vanadium ions in any oxidation or spin state, and can readily be applied to sample environments ranging from solid-phase catalysts to biological samples in frozen solution. Thus, the combined XAS and XES approach, coupled with DFT calculations, provides a robust tool for the study of vanadium atoms in bioinorganic chemistry. PMID:27251139

  7. Neutralization of calcite in mineral aerosols by acidic sullur species collected in China and Japan studied by ca K-edge X-ray absorption near-edge structure.

    PubMed

    Takahashi, Yoshio; Miyoshi, Takuro; Higashi, Masayuki; Kamioka, Hikari; Kanai, Yutaka

    2009-09-01

    Calcium species in mineral aerosols collected simultaneously in Aksu (near the Taklimakan Desert), Qingdao (eastern China), and Tsukuba (Japan) during dust and nondust periods were determined using Ca K-edge X-ray absorption near-edge structure (XANES). From the fitting of XANES spectra, it was found that (i) calcite and gypsum were the main Ca species in the aerosol samples, and (ii) the gypsum fraction versus total Ca minerals [Gyp]/[Ca2+]t increased progressively in the order Aksu < Qingdao < Tsukuba. Surface-sensitive XANES in the conversion electron yield mode (CEY) showed that the gypsum is formed selectively at the surface of mineral aerosols for all the samples except for that taken in Aksu during the dust period. The decrease of the [Gyp]/[Ca2+]t ratio with an increase in particle size showed that the neutralization effect proceeds from the particle surface. For the Aksu sample in the dust period, however, (i) the [Gyp]/[Ca2+]t ratios obtained by XANES measured in the fluorescence (FL; regarded as bulk analysis) and CEY modes were similar and (ii) size dependence was not found, showing that neutralization is not important for the sample because of the large supply of mineral aerosol with little neutralization effect in Aksu. It was also found that the pH of the aerosol and the ratio of (NH4)2SO4 to gypsum were positively and negatively correlated with the Ca (or calcite) content, respectively. The speciation of Ca by XANES revealed the neutralization processes of acidic sulfur species by calcite during the long-range transport of mineral aerosols. PMID:19764213

  8. Over the energy edge: Results from a seven year new commercial buildings research and demonstration project

    SciTech Connect

    Piette, M.A.; Nordman, B.; deBuen, O.; Diamond, R.; Codey, B.

    1994-08-01

    Edge was a research oriented demonstration project that began in 1985. Twenty-eight commercial buildings were designed and constructed to use 30% less electricity than a hypothetical simulated baseline building. Average savings from the 18 buildings evaluated with post-occupancy, ``tuned`` simulation models were less, at 17%. The cost-effectiveness of the energy-efficiency measures at six of the 18 projects met the target cost-of-conserved (CCE) energy of 5.6cent/kWh for the total package of measures. The most important reason energy savings were not as great as predicted is that the actual, installed energy-efficiency measures and building characteristics changed from the design assumptions. The cost effectiveness of the measures would have been greater if the baseline was common practice rather than assumptions based on the regional building code. For example, the Energy Edge small offices use about 30% to 50% less energy than comparable new buildings. Savings also would have been greater if commissioning had been included within the program. Future projects should consider lower-cost ``hands-on`` evaluation techniques that provide direct feedback on measure performance based on functional and diagnostic testing, with annual check-ups to ensure persistence of savings.

  9. High resolution short focal distance Bent Crystal Laue Analyzer for copper K edge x-ray absorption spectroscopy

    SciTech Connect

    Kujala, N. G.; Barrea, R. A.; Karanfil, C.

    2011-06-15

    We have developed a compact short focal distance Bent Crystal Laue Analyzer (BCLA) for Cu speciation studies of biological systems with specific applications to cancer biology. The system provides high energy resolution and high background rejection. The system is composed of an aluminum block serving as a log spiral bender for a 15 micron thick Silicon 111 crystal and a set of soller slits. The energy resolution of the BCLA--about 14 eV at the Cu K{alpha} line-- allows resolution of the Cu K{alpha}{sub 1} and CuK{alpha}{sub 2} lines. The system is easily aligned by using a set of motorized XYZ linear stages. Two operation modes are available: incident energy scans (IES) and emission energy scans (EES). IES allows scanning of the incident energy while the BCLA system is maintained at a preselected fixed position - typically CuK{alpha}{sub 1} line. EES is used when the incident energy is fixed and the analyzer is scanned to provide the peak profile of the emission lines of Cu.

  10. High resolution short focal distance Bent Crystal Laue Analyzer for copper K edge x-ray absorption spectroscopy

    PubMed Central

    Kujala, N. G.; Karanfil, C.; Barrea, R. A.

    2011-01-01

    We have developed a compact short focal distance Bent Crystal Laue Analyzer (BCLA) for Cu speciation studies of biological systems with specific applications to cancer biology. The system provides high energy resolution and high background rejection. The system is composed of an aluminum block serving as a log spiral bender for a 15 micron thick Silicon 111 crystal and a set of soller slits. The energy resolution of the BCLA—about 14 eV at the Cu Kα line— allows resolution of the Cu Kα1 and CuKα2 lines. The system is easily aligned by using a set of motorized XYZ linear stages. Two operation modes are available: incident energy scans (IES) and emission energy scans (EES). IES allows scanning of the incident energy while the BCLA system is maintained at a preselected fixed position—typically CuKα1 line. EES is used when the incident energy is fixed and the analyzer is scanned to provide the peak profile of the emission lines of Cu. PMID:21721673

  11. Optimization of absorption air-conditioning for solar energy applications

    NASA Technical Reports Server (NTRS)

    Perry, E. H.

    1976-01-01

    Improved performance of solar cooling systems using the lithium bromide water absorption cycle is investigated. Included are computer simulations of a solar-cooled house, analyses and measurements of heat transfer rates in absorption system components, and design and fabrication of various system components. A survey of solar collector convection suppression methods is presented.

  12. Teaching about Climate Change and Energy with Online Materials and Workshops from On the Cutting Edge

    NASA Astrophysics Data System (ADS)

    Kirk, K. B.; Manduca, C. A.; Myers, J. D.; Loxsom, F.

    2009-12-01

    Global climate change and energy use are among the most relevant and pressing issues in today’s science curriculum, yet they are also complex topics to teach. The underlying science spans multiple disciplines and is quickly evolving. Moreover, a comprehensive treatment of climate change and energy use must also delve into perspectives not typically addressed in geosciences courses, such as public policy and economics. Thus, faculty attempting to address these timely issues face many challenges. To support faculty in teaching these subjects, the On the Cutting Edge faculty development program has created a series of websites and workshop opportunities to provide faculty with information and resources for teaching about climate and energy. A web-based collection of teaching materials was developed in conjunction with the On the Cutting Edge workshops “Teaching about Energy in Geoscience Courses: Current Research and Pedagogy.” The website is designed to provide faculty with examples, references and ideas for either incorporating energy topics into existing geoscience courses or for designing or refining a course about energy. The website contains a collection of over 30 classroom and lab activities contributed by faculty and covering such diverse topics as renewable energy, energy policy and energy conservation. Course descriptions and syllabi for energy courses address audiences ranging from introductory courses to advanced seminars. Other materials available on the website include a collection of visualizations and animations, a catalog of recommended books, presentations and related references from the teaching energy workshops, and ideas for novel approaches or new topics for teaching about energy in the geosciences. The Teaching Climate Change website hosts large collections of teaching materials spanning many different topics within climate change, climatology and meteorology. Classroom activities highlight diverse pedagogic approaches such as role

  13. Comparison of the magnetic properties of GeMn thin films through Mn L-edge x-ray absorption

    SciTech Connect

    Ahlers, S.; Stone, P.R.; Sircar, N.; Arenholz, E.; Dubon, O. D.; Bougeard, D.

    2009-08-04

    X-ray absorption spectroscopy of epitaxial GeMn thin films reveals an experimentally indistinguishable electronic configuration of Mn atoms incorporated in Ge{sub 1?x}Mn{sub x} nanoclusters and in precipitates of the intermetallic compound Mn{sub 5}Ge{sub 3}, respectively. However, the average magnetic response of thin films containing Ge{sub 1?x}Mn{sub x} nanoclusters is lower than the response of films containing Mn{sub 5}Ge{sub 3} precipitates. This reduced magnetic response of Ge{sub 1?x}Mn{sub x} nanoclusters is explained in terms of a fraction of Mn atoms being magnetically inactive due to antiferromagnetic coupling or the presence of structural disorder. A determination of the role of magnetically inactive Mn atoms in the self-assembly of the thermodynamically metastable Ge{sub 1?x}Mn{sub x} nanoclusters seems to be an essential ingredient for an enhanced control of this promising high Curie temperature magnetic semiconductor.

  14. Impact energy absorption of sandwich plates with crushable core

    SciTech Connect

    Wierzbicki, T.; Fatt, M.H.; Alvarez, A.L.

    1995-12-31

    The objective of this paper is to derive a closed-form solution for deformations, resisting forces, and energy absorption of a metal honeycomb with face plating subjected to localize static and dynamic loads. Two load cases are considered: a quasi-static indentation by a circular punch and dynamic impact by a cylindrical projectile with a velocity in the range of 20 {divided_by} 40 m/sec. The present analysis is building-up on the earlier solution obtained by one of the authors in which the crash resistance of a bare honeycomb was predicted from a known geometry of the cell and material properties. The face plating increases crush resistance of the honeycomb by spreading deformation outside the loading area and invoking considerable membrane action in the plate. Each of the above contributions is quantified and is shown that the resisting force and the radial extent of deformation are increasing functions of punch displacement. The present analytical predictions are compared with measurements taken on seven impact tests on sandwich plates, reported by Goldsmith and Sackman. A correlation of final plate deflections under the projectile was very good for lower impact velocities (less that 6.3% error) and good for higher impact velocities (between 2.08% and 8.9% error). This exceeds the accuracy of a purely numerical solution presented. Three mechanisms limiting the energy absorbed by a sandwich plate are identified: densification of the honeycomb, punch-through shear of the facing plates, and reaching deformation of the outer boundary of the sandwich plate. The present theory provides the necessary background information for optimum designing of sandwich plates against impact loads.

  15. Using Solution- and Solid-State S K-edge X-ray Absorption Spectroscopy with Density Functional Theory to Evaluate M–S Bonding for MS42- (M = Cr, Mo, W) Dianions

    PubMed Central

    Olson, Angela C.; Keith, Jason M.; Batista, Enrique R.; Boland, Kevin S.; Daly, Scott R.; Kozimor, Stosh A.; MacInnes, Molly M.; Martin, Richard L.; Scott, Brian L.

    2014-01-01

    Herein, we have evaluated relative changes in M–S electronic structure and orbital mixing in Group 6 MS42- dianions using solid- and solution-phase S K-edge X-ray absorption spectroscopy (XAS; M = Mo, W), as well as density functional theory (DFT; M = Cr, Mo, W) and time-dependent density functional theory (TDDFT) calculations. To facilitate comparison with solution measurements (conducted in acetonitrile), theoretical models included gas-phase calculations as well as those that incorporated an acetonitrile dielectric, the latter of which provided better agreement with experiment. Two pre-edge features arising from S 1s → e* and t2* electron excitations were observed in the S K-edge XAS spectra and were reasonably assigned as 1A1 → 1T2 transitions. For MoS42-, both solution-phase pre-edge peak intensities were consistent with results from the solid-state spectra. For WS42-, solution- and solid-state pre-edge peak intensities for transitions involving e* were equivalent, while transitions involving the t2* orbitals were less intense in solution. Experimental and computational results have been presented in comparison to recent analyses of MO42- dianions, which allowed M–S and M–O orbital mixing to be evaluated as the principle quantum number (n) for the metal valence d orbitals increased (3d, 4d, 5d). Overall, the M–E (E = O, S) analyses revealed distinct trends in orbital mixing. For example, as the Group 6 triad was descended, e* (π*) orbital mixing remained constant in the M–S bonds, but increased appreciably for M–O interactions. For the t2* orbitals (σ* + π*), mixing decreased slightly for M–S bonding and increased only slightly for the M–O interactions. These results suggested that the metal and ligand valence orbital energies and radial extensions delicately influenced the orbital compositions for isoelectronic ME42- (E = O, S) dianions. PMID:25311904

  16. Using solution- and solid-state S K-edge X-ray absorption spectroscopy with density functional theory to evaluate M-S bonding for MS4(2-) (M = Cr, Mo, W) dianions.

    PubMed

    Olson, Angela C; Keith, Jason M; Batista, Enrique R; Boland, Kevin S; Daly, Scott R; Kozimor, Stosh A; MacInnes, Molly M; Martin, Richard L; Scott, Brian L

    2014-12-14

    Herein, we have evaluated relative changes in M-S electronic structure and orbital mixing in Group 6 MS4(2-) dianions using solid- and solution-phase S K-edge X-ray absorption spectroscopy (XAS; M = Mo, W), as well as density functional theory (DFT; M = Cr, Mo, W) and time-dependent density functional theory (TDDFT) calculations. To facilitate comparison with solution measurements (conducted in acetonitrile), theoretical models included gas-phase calculations as well as those that incorporated an acetonitrile dielectric, the latter of which provided better agreement with experiment. Two pre-edge features arising from S 1s → e* and t electron excitations were observed in the S K-edge XAS spectra and were reasonably assigned as (1)A1 → (1)T2 transitions. For MoS4(2-), both solution-phase pre-edge peak intensities were consistent with results from the solid-state spectra. For WS4(2-), solution- and solid-state pre-edge peak intensities for transitions involving e* were equivalent, while transitions involving the t orbitals were less intense in solution. Experimental and computational results have been presented in comparison to recent analyses of MO4(2-) dianions, which allowed M-S and M-O orbital mixing to be evaluated as the principle quantum number (n) for the metal valence d orbitals increased (3d, 4d, 5d). Overall, the M-E (E = O, S) analyses revealed distinct trends in orbital mixing. For example, as the Group 6 triad was descended, e* (π*) orbital mixing remained constant in the M-S bonds, but increased appreciably for M-O interactions. For the t orbitals (σ* + π*), mixing decreased slightly for M-S bonding and increased only slightly for the M-O interactions. These results suggested that the metal and ligand valence orbital energies and radial extensions delicately influenced the orbital compositions for isoelectronic ME4(2-) (E = O, S) dianions. PMID:25311904

  17. Interaction of vanadium and sulfate in blood cells from the tunicate Ascidia ceratodes: Observations using x-ray absorption edge structure and EPR spectroscopies

    SciTech Connect

    Frank, P.; Hedman, B.; Hodgson, K.O.; Carlson, R.M.K.

    1994-08-17

    Sulfur K-edge X-ray absorption spectroscopy (S-K XAS) and EPR spectroscopy have been used to investigate the inorganic solution chemistry of vanadium, sulfate, and methanesulfonate, with application to blood cells from the tunicate Ascidia ceratodes. Three independent whole blood cell preparations (S85, S86, W87) collected over a period of 18 months were examined. Average blood cell vanadium concentrations were determined to be 0.099, 0.079, and 0.062 M, respectively. All three collections gave sulfur XAS spectra consistent with significant intracellular concentrations of low-valent sulfur, an alkanesulfonic acid, and sulfate. In model studies, the line width of the sulfate K-edge XAS spectrum was found to titrate with both pH and [V(III)]. Application of this finding to A. ceratodes blood cell sulfur XAS spectra provided evidence for direct interactions between endogenous dissolved sulfate and V(III) in two of the three collections. All three collections yielded sulfate XAS edge spectra consistent with low pH. Curve-fitting analysis of the S-K edge XAS spectra for the three whole blood cell collections yielded the ratios of intracellular sulfate:alkane sulfonate:low-valent sulfur to be as follows: S85, 1.0:0.9:0.36;S86, 1.0;0.5;1.5;W87,1.0;0.44:0.24. Comparisons with models indicated that the low-valent blood cell sulfur included various disulfide-like compounds unlike cystine. This all implies a surprisingly rich and variable sulfur biochemistry in these marine organisms. EPR spectroscopy of whole blood cells from one animal from the W87 collection revealed an endogenous VO{sup 2+}-sulfate interaction. Thus both V(III) and VO{sup 2+} can sense an intracellular pool of sulfate, implying the biological colocation of these two metal ions. The variations in blood chemistry observed over time as described herein caution against definitive application of single point experiments.

  18. Near-edge x-ray absorption studies of Na-doped tetracyanoethylene films: A model system for the V(TCNE)x room-temperature molecular magnet

    NASA Astrophysics Data System (ADS)

    Carlegrim, E.; Gao, B.; Kanciurzewska, A.; de Jong, M. P.; Wu, Z.; Luo, Y.; Fahlman, M.

    2008-02-01

    V(TCNE)x , with TCNE=tetracyanoethylene and xtilde 2 , is an organic-based molecular magnet with potential to be used in spintronic devices. With the aim of shedding light on the unoccupied frontier electronic structure of V(TCNE)x we have studied pristine TCNE and sodium-intercalated TCNE by near edge x-ray absorption fine structure (NEXAFS) spectroscopy as well as with theoretical calculations. Sodium-intercalated TCNE was used as a model system of the more complex V(TCNE)x and both experimental and theoretical results of the model compound have been used to interpret the NEXAFS spectra of V(TCNE)x . By comparing the experimental and theoretical C K -edge of pristine TCNE, the contributions from the various carbon species (cyano and vinyl) could be disentangled. Upon fully sodium intercalation, TCNE is n doped with one electron per molecule and the features in the C and N K -edge spectra of pristine TCNE undergo strong modification caused by partially filling the TCNE lowest unoccupied molecular orbital (LUMO). When comparing the C and N K -edge NEXAFS spectra of fully sodium-doped TCNE with V(TCNE)x , the spectra are similar except for broadening of the features which originates from structural disorder of the V(TCNE)x films. The combined results from the model system and V(TCNE)x suggest that the lowest unoccupied molecular orbital with density on the nitrogen atoms in V(TCNE)x has no significant hybridization with vanadium and is similar to the so-called singly occupied molecular orbital of the TCNE anion. This suggests that the LUMO of V(TCNE)x is TCNE- or vanadiumlike, in contrast to the frontier occupied electronic structure where the highest occupied molecular orbital is a hybridization between V(3d) and cyano carbons. The completely different nature of the unoccupied and occupied frontier electronic structure of the material will most likely affect both charge injection and transport properties of a spintronic device featuring V(TCNE)x .

  19. K- and L-edge X-ray absorption spectrum calculations of closed-shell carbon, silicon, germanium, and sulfur compounds using damped four-component density functional response theory.

    PubMed

    Fransson, Thomas; Burdakova, Daria; Norman, Patrick

    2016-05-21

    X-ray absorption spectra of carbon, silicon, germanium, and sulfur compounds have been investigated by means of damped four-component density functional response theory. It is demonstrated that a reliable description of relativistic effects is obtained at both K- and L-edges. Notably, an excellent agreement with experimental results is obtained for L2,3-spectra-with spin-orbit effects well accounted for-also in cases when the experimental intensity ratio deviates from the statistical one of 2 : 1. The theoretical results are consistent with calculations using standard response theory as well as recently reported real-time propagation methods in time-dependent density functional theory, and the virtues of different approaches are discussed. As compared to silane and silicon tetrachloride, an anomalous error in the absolute energy is reported for the L2,3-spectrum of silicon tetrafluoride, amounting to an additional spectral shift of ∼1 eV. This anomaly is also observed for other exchange-correlation functionals, but it is seen neither at other silicon edges nor at the carbon K-edge of fluorine derivatives of ethene. Considering the series of molecules SiH4-XFX with X = 1, 2, 3, 4, a gradual divergence from interpolated experimental ionization potentials is observed at the level of Kohn-Sham density functional theory (DFT), and to a smaller extent with the use of Hartree-Fock. This anomalous error is thus attributed partly to difficulties in correctly emulating the electronic structure effects imposed by the very electronegative fluorines, and partly due to inconsistencies in the spurious electron self-repulsion in DFT. Substitution with one, or possibly two, fluorine atoms is estimated to yield small enough errors to allow for reliable interpretations and predictions of L2,3-spectra of more complex and extended silicon-based systems. PMID:27136720

  20. Photonic simulation of topological superconductor edge state and zero-energy mode at a vortex

    PubMed Central

    Tan, Wei; Chen, Liang; Ji, Xia; Lin, Hai-Qing

    2014-01-01

    Photonic simulations of quantum Hall edge states and topological insulators have inspired considerable interest in recent years. Interestingly, there are theoretical predictions for another type of topological states in topological superconductors, but debates over their experimental observations still remain. Here we investigate the photonic analogue of the px + ipy model of topological superconductor. Two essential characteristics of topological superconductor, particle-hole symmetry and px + ipy pairing potentials, are well emulated in photonic systems. Its topological features are presented by chiral edge state and zero-energy mode at a vortex. This work may fertilize the study of photonic topological states, and open up the possibility for emulating wave behaviors in superconductors. PMID:25488408

  1. 3D printed elastic honeycombs with graded density for tailorable energy absorption

    NASA Astrophysics Data System (ADS)

    Bates, Simon R. G.; Farrow, Ian R.; Trask, Richard S.

    2016-04-01

    This work describes the development and experimental analysis of hyperelastic honeycombs with graded densities, for the purpose of energy absorption. Hexagonal arrays are manufactured from thermoplastic polyurethane (TPU) via fused filament fabrication (FFF) 3D printing and the density graded by varying cell wall thickness though the structures. Manufactured samples are subject to static compression tests and their energy absorbing potential analysed via the formation of energy absorption diagrams. It is shown that by grading the density through the structure, the energy absorption profile of these structures can be manipulated such that a wide range of compression energies can be efficiently absorbed.

  2. Compton-edge-based energy calibration of double-sided silicon strip detectors in Compton camera

    NASA Astrophysics Data System (ADS)

    Seo, Hee; Park, Jin Hyung; Kim, Chan Hyeong; Lee, Ju Hahn; Lee, Chun Sik; Sung Lee, Jae

    2011-05-01

    Accurate energy calibration of double-sided silicon strip detectors (DSSDs) is very important, but challenging for high-energy photons. In the present study, the calibration was improved by considering the Compton edge additionally to the existing low-energy calibration points. The result, indeed, was very encouraging. The energy-calibration errors were dramatically reduced, from, on average, 15.5% and 16.9% to 0.47% and 0.31% for the 356 (133Ba) and 662 keV (137Cs) peaks, respectively. The imaging resolution of a double-scattering-type Compton camera using DSSDs as the scatterer detectors, for a 22Na point-like source, also was improved, by ˜9%.

  3. Tetrahalide Complexes of the [U(NR)(2)]2+ Ion: Synthesis, Theory, and Chlorine K-Edge X-ray Absorption Spectroscopy

    SciTech Connect

    Spencer, Liam P.; Yang, Ping; Minasian, Stefan G.; Jilek, Robert E.; Batista, Enrique R.; Boland, Kevin S.; Boncella, James M.; Conradson, S. D.; Clark, David L.; Hayton, Trevor W.; Kozimor, Stosh A.; Martin, Richard L.; MacInnes, Molly M.; Olson, Angela C.; Scott, Brian L.; Shuh, D. K.; Wilkerson, Marianne P.

    2013-02-13

    Synthetic routes to salts containing uranium bisimido tetrahalide anions [U(NR)(2)X-4](2-) (X = Cl-, Br-) and non-coordinating NEt4+ and PPh4+ countercations are reported. In general, these compounds can be prepared from U(NR)(2)I-2(THF)(x) (x = 2 and R = 'Bu, Ph; x = 3 and R = Me) upon addition of excess halide. In addition to providing stable coordination complexes with Cl-, the [U(NMe)(2)](2 +) cation also reacts with Br- to form stable [NEt4](2)[U(NMe)(2)Br-4] complexes. These materials were used as a platform to compare electronic structure and bonding in [U(NR)(2)](2+) with [UO2](2+). Specifically, Cl K-edge X-ray absorption spectroscopy (XAS) and both ground-state and time-dependent hybrid density functional theory (DFT and TDDFT) were used to probe U-Cl bonding interactions in [PPh4](2)[U((NBu)-Bu-t)(2)Cl-4] and [PPh4](2)[UO2Cl4]. The DFT and XAS results show the total amount of Cl 3p character mixed with the U 5f orbitals was roughly 7-10% per U-Cl bond for both compounds, which shows that moving from oxo to imido has little effect on orbital mixing between the U 5f and equatorial Cl 3p orbitals. The results are presented in the context of recent Cl K-edge XAS and DFT studies on other hexavalent uranium chloride systems with fewer oxo or imido ligands.

  4. Iron L-edge X-ray Absorption Spectroscopy of Oxy-Picket Fence Porphyrin: Experimental Insight into Fe-O2 Bonding

    PubMed Central

    Wilson, Samuel A.; Kroll, Thomas; Decreau, Richard A.; Hocking, Rosalie K.; Lundberg, Marcus; Hedman, Britt; Hodgson, Keith O.; Solomon, Edward I.

    2013-01-01

    The electronic structure of the Fe–O2 center in oxy-hemoglobin and oxy-myoglobin is a long-standing issue in the field of bioinorganic chemistry. Spectroscopic studies have been complicated by the highly delocalized nature of the porphyrin and calculations require interpretation of multi-determinant wavefunctions for a highly covalent metal site. Here, iron L-edge X-ray absorption spectroscopy (XAS), interpreted using a valence bond configuration interaction (VBCI) multiplet model, is applied to directly probe the electronic structure of the iron in the biomimetic Fe–O2 heme complex [Fe(pfp)(1-MeIm)O2] (pfp = meso-tetra(α,α,α,α-o-pivalamidophenyl) porphyrin or TpivPP). This method allows separate estimates of σ-donor, π-donor, and π-acceptor interactions through ligand to metal charge transfer (LMCT) and metal to ligand charge transfer (MLCT) mixing pathways. The L-edge spectrum of [Fe(pfp)(1-MeIm)O2] is further compared to those of [FeII(pfp)(1-MeIm)2], [FeII(pfp)], and [FeIII(tpp)(ImH)2]Cl (tpp = meso-tetraphenylporphyrin) which have FeII S = 0, FeII S = 1 and FeIII S = 1/2 ground states, respectively. These serve as references for the three possible contributions to the ground state of oxy-pfp. The Fe–O2 pfp site is experimentally determined to have both significant σ-donation and a strong π-interaction of the O2 with the iron, with the latter having implications with respect to the spin polarization of the ground state. PMID:23259487

  5. Electron energy-loss near-edge structures of 3d transition metal oxides recorded at high-energy resolution.

    PubMed

    Mitterbauer, C; Kothleitner, G; Grogger, W; Zandbergen, H; Freitag, B; Tiemeijer, P; Hofer, F

    2003-09-01

    Near-edge fine structures of the metal L(2,3) and O K-edges in transition metal-oxides have been studied with a transmission electron microscope equipped with a monochromator and a high-resolution imaging filter. This system enables the recording of EELS spectra with an energy resolution of 0.1eV thus providing new near-edge fine structure details which could not be observed previously by EELS in conventional TEM instruments. EELS-spectra from well-defined oxides like titanium oxide (TiO(2)), vanadium oxide (V(2)O(5)), chromium oxide (Cr(2)O(3)), iron oxide (Fe(2)O(3)), cobalt oxide (CoO) and nickel oxide (NiO) have been measured with the new system. These spectra are compared with EELS data obtained from a conventional microscope and the main spectral features are interpreted. Additionally, the use of monochromised TEMs is discussed in view of the natural line widths of K and L(2,3) edges. PMID:12871809

  6. Symmetry and vibrationally resolved absorption spectra near the N K edges of N{sub 2}O: Experiment and theory

    SciTech Connect

    Ehara, M.; Horikawa, T.; Fukuda, R.; Nakatsuji, H.; Tanaka, T.; Kato, H.; Hoshino, M.; Tanaka, H.; Feifel, R.; Ueda, K.

    2011-06-15

    In this study, angle-resolved energetic-ion yield spectra were measured in the N 1s excitation region of N{sub 2}O. A Franck-Condon analysis based on ab initio two-dimensional potential energy surfaces of the core-excited Rydberg states, which were calculated by the symmetry-adapted cluster-configuration interaction method, reproduced observed vibrational excitations specific to the individual Rydberg states well and enabled quantitative assignments. Geometric changes in the terminal nitrogen N{sub t} 1s and the central nitrogen N{sub c} 1s excited states with respect to the 3p{pi}, 3p{sigma}, and 4s{sigma} transitions were analyzed. The coupling of these valence and Rydbergs states was examined based on the second moment analysis. Irregular Rydberg-state behavior in the N{sub c} 1s{sup -1} 4s{sigma} state was observed.

  7. Impurity-defect emission from undoped Cd1- x Zn x Te single crystals near the fundamental absorption edge

    NASA Astrophysics Data System (ADS)

    Krivobok, V. S.; Denisov, I. A.; Mozhevitina, E. N.; Nikolaev, S. N.; Onishchenko, E. E.; Pruchkina, A. A.; Silina, A. A.; Smirnova, N. A.; Chernopitsskii, M. A.; Shmatov, N. I.

    2016-05-01

    Shallow impurity-defect states in undoped Cd1- x Zn x Te ( x ˜ 3-6%) single crystals have been studied using low-temperature photoluminescence measurements. It has been found that the effect exerted by zinc is mainly reduced to a rigid shift of all the specific features associated with the exciton radiation, which made it possible, with a high (˜0.3 meV) accuracy, to measure the band gap and the zinc concentration in solid solutions. Hydrogen-like donors with the ground-state energy of ˜14 meV and four types of acceptors with average activation energies of 59.3 ± 0.6 meV, 69.6 ± 1.5 meV, 155.8 ± 2.0 meV, and 52.3 ± 0.6 meV have been identified in all the crystals studied. Based on a comparison with the results of the analysis of the impurity background and the data available in the literature on impurity-defect emission in undoped CdTe, the first three acceptors can be assigned to the substitutional impurities NaCd, PTe, and CuCd, respectively. The most shallow acceptor (52.3 ± 0.6 meV) is a complex defect in which there is a nonstandard excited level separated by only 7 meV from the ground level. This level is formed apparently due to the removal of degeneracy, which is characteristic of T D acceptors, by the low-symmetry potential of the complex defect.

  8. Trends in Covalency for d- and f-Element Metallocene Dichlorides Identified Using Chlorine K-Edge X-Ray Absorption Spectroscopy and Time Dependent-Density Functional Theory

    SciTech Connect

    Kozimor, Stosh A.; Yang, Ping; Batista, Enrique R.; Boland, Kevin S.; Burns, Carol J.; Clark, David L.; Conradson, Steven D.; Martin, Richard L.; Wikerson, Marianne P.; Wolfsberg, Laura E.

    2009-09-02

    We describe the use of Cl K-edge X-ray Absorption Spectroscopy (XAS) and both ground state and time-dependent hybrid density functional theory (DFT) to probe electronic structure and determine the degree of orbital mixing in M-Cl bonds for (C5Me5)2MCl2 (M = Ti, 1; Zr, 2; Hf, 3; Th, 4; and U, 5), where we can directly compare a class of structurally similar compounds for d- and f-elements. We report direct experimental evidence for covalency in M-Cl bonding, including actinides, and offer insight into the relative roles of the valence f- and dorbitals in these systems. The Cl K-edge XAS data for the group IV transition metals, 1 – 3, show slight decreases in covalency in M-Cl bonding with increasing principal quantum number, in the order Ti > Zr > Hf. The percent Cl 3p character per M-Cl bond was experimentally determined to be 25, 23, and 22% per M-Cl bond for 1-3, respectively. For actinides, we find a shoulder on the white line for (C5Me5)2ThCl2, 4, and distinct, but weak pre-edge features for 2 (C5Me5)2UCl2, 5. The percent Cl 3p character in Th-Cl bonds in 4 was determined to be 14 %, with high uncertainty, while the U-Cl bonds in 5 contains 9 % Cl 3p character. The magnitudes of both values are approximately half what was observed for the transition metal complexes in this class of bent metallocene dichlorides. Using the hybrid DFT calculations as a guide to interpret the experimental Cl K-edge XAS, these experiments suggest that when evaluating An- Cl bonding, both 5f- and 6d-orbitals should be considered. For (C5Me5)2ThCl2, the calculations and XAS indicate that the 5f- and 6d-orbitals are nearly degenerate and heavily mixed. In contrast, the 5f- and 6d-orbitals in (C5Me5)2UCl2 are no longer degenerate, and fall in two distinct energy groupings. The 5f-orbitals are lowest in energy and split into a 5-over-2 pattern with the high lying U 6d-orbitals split in a 4-over-1 pattern, the latter of which is similar to the dorbital splitting in group IV transition

  9. Convergence of strain energy release rate components for edge-delaminated composite laminates

    NASA Technical Reports Server (NTRS)

    Raju, I. S.; Crews, J. H., Jr.; Aminpour, M. A.

    1987-01-01

    Strain energy release rates for edge delaminated composite laminates were obtained using quasi 3 dimensional finite element analysis. The problem of edge delamination at the -35/90 interfaces of an 8-ply composite laminate subjected to uniform axial strain was studied. The individual components of the strain energy release rates did not show convergence as the delamination tip elements were made smaller. In contrast, the total strain energy release rate converged and remained unchanged as the delamination tip elements were made smaller and agreed with that calculated using a classical laminated plate theory. The studies of the near field solutions for a delamination at an interface between two dissimilar isotropic or orthotropic plates showed that the imaginary part of the singularity is the cause of the nonconvergent behavior of the individual components. To evaluate the accuracy of the results, an 8-ply laminate with the delamination modeled in a thin resin layer, that exists between the -35 and 90 plies, was analyzed. Because the delamination exists in a homogeneous isotropic material, the oscillatory component of the singularity vanishes.

  10. 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.

  11. Electron density compression and oscillating effects on laser energy absorption in overdense plasma targets.

    PubMed

    Ge, Z Y; Zhuo, H B; Yu, W; Yang, X H; Yu, T P; Li, X H; Zou, D B; Ma, Y Y; Yin, Y; Shao, F Q; Peng, X J

    2014-03-01

    An analytical model for energy absorption during the interaction of an ultrashort, ultraintense laser with an overdense plasma is proposed. Both the compression effect of the electron density profile and the oscillation of the electron plasma surface are self-consistently included, which exhibit significant influences on the laser energy absorption. Based on our model, the general scaling law of the compression effect depending on laser strength and initial density is derived, and the temporal variation of the laser absorption due to the boundary oscillating effect is presented. It is found that due to the oscillation of the electron plasma surface, the laser absorption rate will vibrate periodically at ω or 2ω frequency for the p-polarized and s-polarized laser, respectively. The effect of plasma collision on the laser absorption has also been investigated, which shows a considerable rise in absorption with increasing electron-ion collision frequency for both polarizations. PMID:24730955

  12. Constraints on the inner edge of neutron star crusts from relativistic nuclear energy density functionals

    SciTech Connect

    Moustakidis, Ch. C.; Lalazissis, G. A.; Niksic, T.; Vretenar, D.; Ring, P.

    2010-06-15

    The transition density n{sub t} and pressure P{sub t} at the inner edge between the liquid core and the solid crust of a neutron star are analyzed using the thermodynamical method and the framework of relativistic nuclear energy density functionals. Starting from a functional that has been carefully adjusted to experimental binding energies of finite nuclei, and varying the density dependence of the corresponding symmetry energy within the limits determined by isovector properties of finite nuclei, we estimate the constraints on the core-crust transition density and pressure of neutron stars: 0.086 fm{sup -3}<=n{sub t}<0.090 fm{sup -3} and 0.3 MeV fm{sup -3}

  13. An edge-on charge-transfer design for energy-resolved x-ray detection

    NASA Astrophysics Data System (ADS)

    Shi, Zaifeng; Yang, Haoyu; Cong, Wenxiang; Wang, Ge

    2016-06-01

    As an x-ray beam goes through the human body, it will collect important information via interaction with tissues. Since this interaction is energy-sensitive, the state-of-the-art spectral CT technologies provide higher quality images of biological tissues with x-ray energy information (or spectral information). With existing energy-integrating technologies, a large fraction of energy information is ignored in the x-ray detection process. Although the recently proposed photon-counting technology promises to achieve higher image quality at a lower radiation dose, it suffers from limitations in counting rate, performance uniformity, and fabrication cost. In this paper, we focus on an alternative approach to resolve the energy distribution of transmitted x-ray photons. First, we analyze the x-ray attenuation in a silicon substrate and describe a linear approximation model for x-ray detection. Then, we design an edge-on architecture based on the proposed energy-resolving model. In our design, the x-ray-photon-induced charges are transferred sequentially resembling the working process of a CCD camera. Finally, we numerically evaluate the linear approximation of x-ray attenuation and derive the energy distribution of x-ray photons. Our simulation results show that the proposed energy-sensing approach is feasible and has the potential to complement the photon-counting technology.

  14. An edge-on charge-transfer design for energy-resolved x-ray detection.

    PubMed

    Shi, Zaifeng; Yang, Haoyu; Cong, Wenxiang; Wang, Ge

    2016-06-01

    As an x-ray beam goes through the human body, it will collect important information via interaction with tissues. Since this interaction is energy-sensitive, the state-of-the-art spectral CT technologies provide higher quality images of biological tissues with x-ray energy information (or spectral information). With existing energy-integrating technologies, a large fraction of energy information is ignored in the x-ray detection process. Although the recently proposed photon-counting technology promises to achieve higher image quality at a lower radiation dose, it suffers from limitations in counting rate, performance uniformity, and fabrication cost. In this paper, we focus on an alternative approach to resolve the energy distribution of transmitted x-ray photons. First, we analyze the x-ray attenuation in a silicon substrate and describe a linear approximation model for x-ray detection. Then, we design an edge-on architecture based on the proposed energy-resolving model. In our design, the x-ray-photon-induced charges are transferred sequentially resembling the working process of a CCD camera. Finally, we numerically evaluate the linear approximation of x-ray attenuation and derive the energy distribution of x-ray photons. Our simulation results show that the proposed energy-sensing approach is feasible and has the potential to complement the photon-counting technology. PMID:27192190

  15. The energy of the vacuum related to the theory of energy absorption

    NASA Astrophysics Data System (ADS)

    Danilov, A. P.

    2016-07-01

    The primary objective in this article is to investigate a new source of renewable energy, the existence of the vacuum in five environments, and the possibility of absorption of the explosion. The study has also addressed the development of new principles in the motor industry, protection against explosions, new principles of mineral processing and new types of explosives. Also, this study may offer some insight into new approaches in solving problems in thermodynamics, the development of gravity waves, the basis of renewable energy source, and the mechanism of the emergence of gravitational waves.

  16. Electronic structure and optical properties of CdS{sub x}Se{sub 1−x} solid solution nanostructures from X-ray absorption near edge structure, X-ray excited optical luminescence, and density functional theory investigations

    SciTech Connect

    Murphy, M. W.; Yiu, Y. M. Sham, T. K.; Ward, M. J.; Liu, L.; Hu, Y.; Zapien, J. A.; Liu, Yingkai

    2014-11-21

    The electronic structure and optical properties of a series of iso-electronic and iso-structural CdS{sub x}Se{sub 1−x} solid solution nanostructures have been investigated using X-ray absorption near edge structure, extended X-ray absorption fine structure, and X-ray excited optical luminescence at various absorption edges of Cd, S, and Se. It is found that the system exhibits compositions, with variable local structure in-between that of CdS and CdSe accompanied by tunable optical band gap between that of CdS and CdSe. Theoretical calculation using density functional theory has been carried out to elucidate the observations. It is also found that luminescence induced by X-ray excitation shows new optical channels not observed previously with laser excitation. The implications of these observations are discussed.

  17. Effect of particle size and adsorbates on the L{sub 3}, L{sub 2} and L{sub 1} x-ray absorption near edge structure of supported Pt nanoparaticles.

    SciTech Connect

    Lei, Y.; Jelic, J.; Nitsche, L. C.; Meyer, R.; Miller, J.

    2011-04-01

    Pt nano-particles from about 1 to 10 nm have been prepared on silica, alkali-silica, alumina, silica-alumina, carbon and SBA-15 supports. EXAFS spectra of the reduced catalysts in He show a contraction of the Pt-Pt bond distance as particle size is decreased below 3 nm. The bond length decreased as much as 0.13 {angstrom} for 1 nm Pt particles. Adsorption of CO and H{sub 2} lead to a increase in Pt-Pt bond distance to that near Pt foil, e.g., 2.77 {angstrom}. In addition to changes in the Pt bond distance with size, as the particle size decreases below about 5 nm there is a shift in the XANES to higher energy at the L{sub 3} edge, a decrease in intensity near the edge and an increase in intensity beyond the edge. We suggest these features correspond to effects of coordination (the decrease at the edge) and lattice contraction (the increase beyond the edge). At the L{sub 2} edge, there are only small shifts to higher energy at the edge. However, beyond the edge, there are large increases in intensity with decreasing particle size. At the L{sub 1} edge there are no changes in position or shape of the XANES spectra. Adsorption of CO and H{sub 2} also lead to changes in the L{sub 3} and L{sub 2} edges, however, no changes are observed at the L1 edge. Density Functional Theory and XANES calculations show that the trends in the experimental XANES can be explained in terms of the states available near the edge. Both CO and H{sub 2} adsorption result in a depletion of states at the Fermi level but the creation of anti-bonding states above the Fermi level which give rise to intensity increases beyond the edge.

  18. Simulation of energy absorption spectrum in NaI crystal detector for multiple gamma energy using Monte Carlo method

    SciTech Connect

    Wirawan, Rahadi; Waris, Abdul; Djamal, Mitra; Handayani, Gunawan

    2015-04-16

    The spectrum of gamma energy absorption in the NaI crystal (scintillation detector) is the interaction result of gamma photon with NaI crystal, and it’s associated with the photon gamma energy incoming to the detector. Through a simulation approach, we can perform an early observation of gamma energy absorption spectrum in a scintillator crystal detector (NaI) before the experiment conducted. In this paper, we present a simulation model result of gamma energy absorption spectrum for energy 100-700 keV (i.e. 297 keV, 400 keV and 662 keV). This simulation developed based on the concept of photon beam point source distribution and photon cross section interaction with the Monte Carlo method. Our computational code has been successfully predicting the multiple energy peaks absorption spectrum, which derived from multiple photon energy sources.

  19. Aluminum incorporation in Ti{sub 1-x}Al{sub x}N films studied by x-ray absorption near-edge structure

    SciTech Connect

    Gago, R.; Redondo-Cubero, A.; Endrino, J. L.; Jimenez, I.; Shevchenko, N.

    2009-06-01

    The local bonding structure of titanium aluminum nitride (Ti{sub 1-x}Al{sub x}N) films grown by dc magnetron cosputtering with different AlN molar fractions (x) has been studied by x-ray absorption near-edge structure (XANES) recorded in total electron yield mode. Grazing incidence x-ray diffraction (GIXRD) shows the formation of a ternary solid solution with cubic structure (c-Ti{sub 1-x}Al{sub x}N) that shrinks with the incorporation of Al and that, above a solubility limit of xapprox0.7, segregation of w-AlN and c-Ti{sub 1-x}Al{sub x}N phases occurs. The Al incorporation in the cubic structure and lattice shrinkage can also be observed using XANES spectral features. However, contrary to GIXRD, direct evidence of w-AlN formation is not observed, suggesting a dominance and surface enrichment of cubic environments. For x>0.7, XANES shows the formation of Ti-Al bonds, which could be related to the segregation of w-AlN. This study shows the relevance of local-order information to assess the atomic structure of Ti{sub 1-x}Al{sub x}N solutions.

  20. X-ray absorption near-edge structure study on the configuration of Cu 2+ /histidine complexes at different pH values

    NASA Astrophysics Data System (ADS)

    Mei-Juan, Yu; Yu, Wang; Wei, Xu

    2016-04-01

    The local configurations around metal ions in metalloproteins are of great significance for understanding their biological functions. Cu2+/histidine (His) is a typical complex existing in many metalloproteins and plays an important role in lots of physiological functions. The three-dimensional (3D) structural configurations of Cu2+/His complexes at different pH values (2.5, 6.5, and 8.5) are quantitatively determined by x-ray absorption near-edge structure (XANES). Generally Cu2+/His complex keeps an octahedral configuration consisting of oxygen atoms from water molecules and oxygen or nitrogen atoms from histidine molecules coordinated around Cu2+. It is proved in this work that the oxygen atoms from water molecules, when increasing the pH value from acid to basic value, are gradually substituted by the Ocarboxyl, Nam, and Nim from hisitidine molecules. Furthermore, the symmetries of Cu2+/His complexes at pH 6.5 and pH 8.5 are found to be lower than at pH 2.5. Project supported by the National Natural Science Foundation of China (Grant No. 11205186).

  1. Probing the Ordering of Semiconducting Fluorene-Thiophene Copolymer Surfaces on Rubbed Polyimide Substrates by Near-Edge X-ray Absorption Fine Structure

    SciTech Connect

    Pattison,L.; Hexemer, A.; Kramer, E.; Krishnan, S.; Petroff, P.; Fischer, D.

    2006-01-01

    The temperature-dependent alignment of semiconducting liquid crystalline fluorene-thiophene copolymer (F8T2) thin film surfaces was investigated using the near-edge X-ray absorption fine structure (NEXAFS) technique. Partial electron yield spectra were recorded over a range of temperatures in order to observe directly the surface orientation as the polymer is heated and cooled through glass, crystal, and liquid crystal phases. In addition, samples annealed under varying processing conditions and quenched to room temperature were analyzed. The NEXAFS data show that (a) in thin F8T2 films at all temperatures the polymer backbone lies in the plane of the substrate, (b) the fluorene and thiophene rings are rotated randomly about the molecular axis, (c) orientation of the polymer backbone can be controlled using a rubbed polyimide alignment layer as a template for liquid crystal orientation, and (d) under proper annealing conditions there is strong temperature-dependent alignment of the copolymer main-chain axis to the rubbing direction which extends from the polyimide/F8T2 interface all the way to the F8T2 surface. The surface alignment does not disappear after annealing at temperatures {approx}30 K above the bulk nematic to isotropic transition.

  2. In situ X-ray near-edge absorption spectroscopy investigation of the state of charge of all-vanadium redox flow batteries.

    PubMed

    Jia, Chuankun; Liu, Qi; Sun, Cheng-Jun; Yang, Fan; Ren, Yang; Heald, Steve M; Liu, Yadong; Li, Zhe-Fei; Lu, Wenquan; Xie, Jian

    2014-10-22

    Synchrotron-based in situ X-ray near-edge absorption spectroscopy (XANES) has been used to study the valence state evolution of the vanadium ion for both the catholyte and anolyte in all-vanadium redox flow batteries (VRB) under realistic cycling conditions. The results indicate that, when using the widely used charge-discharge profile during the first charge process (charging the VRB cell to 1.65 V under a constant current mode), the vanadium ion valence did not reach V(V) in the catholyte and did not reach V(II) in the anolyte. Consequently, the state of charge (SOC) for the VRB cell was only 82%, far below the desired 100% SOC. Thus, such incompletely charged mix electrolytes results in not only wasting the electrolytes but also decreasing the cell performance in the following cycles. On the basis of our study, we proposed a new charge-discharge profile (first charged at a constant current mode up to 1.65 V and then continuously charged at a constant voltage mode until the capacity was close to the theoretical value) for the first charge process that achieved 100% SOC after the initial charge process. Utilizing this new charge-discharge profile, the theoretical charge capacity and the full utilization of electrolytes has been achieved, thus having a significant impact on the cost reduction of the electrolytes in VRB. PMID:25191695

  3. 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.

  4. Point defects in hexagonal BN, BC{sub 3} and BC{sub x}N compounds studied by x-ray absorption near-edge structure

    SciTech Connect

    Caretti, Ignacio; Jimenez, Ignacio

    2011-07-15

    The generation of point defects in highly oriented pyrolytic boron nitride (HOPBN) after Ar{sup +} ion bombardment in ultrahigh vacuum and subsequent exposure to air was studied by angle-resolved x-ray absorption near edge structure (XANES). The pristine HOPBN showed well-oriented boron nitride (BN) basal planes parallel to the surface, with a negligible amount of defects. Amorphization of the BN structure took place after Ar{sup +} sputtering, as indicated by the broadening of the XANES spectra and significant decrease of the characteristic {pi}* states. Following air exposure, the XANES analysis revealed a spontaneous reorganization of the sample structure. The appearance of four new B1s {pi}* excitonic peaks indicates an oxygen decoration process of the nitrogen vacancies created by ion bombardment. A core-level shift model is presented to support this statement. This model is successfully extended to the case of oxygen substitutional defects in hexagonal BC{sub 3} and BC{sub x}N (0 < x < 4) materials, which can be applied to any B-based sp{sup 2}-bonded honeycomb structure.

  5. Understanding conversion mechanism of NiO anodic materials for Li-ion battery using in situ X-ray absorption near edge structure spectroscopy

    NASA Astrophysics Data System (ADS)

    Jang, Jue-Hyuk; Chae, Byung-Mok; Oh, Hyun-Jung; Lee, Yong-Kul

    2016-02-01

    Nano-scaled NiO particles (nano-NiO) are prepared by a ligand stabilization method and compared with micron-sized NiO particles (micro-NiO) as anodic material of Li-ion battery. The structural and physical properties are characterized by N2 physisorption, transmission electron microscopy, and X-ray diffraction. The nano-NiO shows uniform spheres with an average particle size of 9 nm with high and stable discharge capacity of 637 mAh g-1, while the micro-NiO forms irregularly shaped particles with an average particle size of 750 nm with low capacity of 431 mAh g-1 at 0.5C. In situ X-ray absorption near edge structure (XANES) analysis reveals that the capacity and reversibility of the NiO anode is highly affected by the particle size of the NiO. The micro-NiO exhibits a low capacity with absence of phase transformation upon the discharge/charge cycles. In contrast, the nano-NiO exhibits a high capacity with reversible phase transformation between NiO and Ni metal upon the cycle test.

  6. A setup for synchrotron-radiation-induced total reflection X-ray fluorescence and X-ray absorption near-edge structure recently commissioned at BESSY II BAMline.

    PubMed

    Fittschen, U; Guilherme, A; Böttger, S; Rosenberg, D; Menzel, M; Jansen, W; Busker, M; Gotlib, Z P; Radtke, M; Riesemeier, H; Wobrauschek, P; Streli, C

    2016-05-01

    An automatic sample changer chamber for total reflection X-ray fluorescence (TXRF) and X-ray absorption near-edge structure (XANES) analysis in TXRF geometry was successfully set up at the BAMline at BESSY II. TXRF and TXRF-XANES are valuable tools for elemental determination and speciation, especially where sample amounts are limited (<1 mg) and concentrations are low (ng ml(-1) to µg ml(-1)). TXRF requires a well defined geometry regarding the reflecting surface of a sample carrier and the synchrotron beam. The newly installed chamber allows for reliable sample positioning, remote sample changing and evacuation of the fluorescence beam path. The chamber was successfully used showing accurate determination of elemental amounts in the certified reference material NIST water 1640. Low limits of detection of less than 100 fg absolute (10 pg ml(-1)) for Ni were found. TXRF-XANES on different Re species was applied. An unknown species of Re was found to be Re in the +7 oxidation state. PMID:27140163

  7. Energy absorption capability and crashworthiness of composite material structures: A review

    SciTech Connect

    Carruthers, J.J.; Kettle, A.P.; Robinson, A.M.

    1998-10-01

    The controlled brittle failure of thermosetting fiber-reinforced polymer composites can provide a very efficient energy absorption mechanism. Consequently, the use of these materials in crashworthy vehicle designs has been the subject of considerable interest. In this respect, their more widespread application has been limited by the complexity of their collapse behavior. This article reviews the current level of understanding i this field, including the correlations between failure mode and energy absorption, the principal material, geometric, and physical parameters relevant to crashworthy design and methods of predicting the energy absorption capability of polymer composites. Areas which require further investigation are identified. This review article contains 70 references.

  8. Energy and Exergy Analysis of Vapour Absorption Refrigeration Cycle—A Review

    NASA Astrophysics Data System (ADS)

    Kanabar, Bhaveshkumar Kantilal; Ramani, Bharatkumar Maganbhai

    2016-07-01

    In recent years, an energy crisis and the energy consumption have become global problems which restrict the sustainable growth. In these scenarios the scientific energy recovery and the utilization of various kinds of waste heat become very important. The waste heat can be utilized in many ways and one of the best practices is to use it for vapour absorption refrigeration system. To ensure efficient working of absorption cycle and utilization of optimum heat, exergy is the best tool for analysis. This paper provides the comprehensive picture of research and development of absorption refrigeration technology, practical and theoretical analysis with different arrangements of the cycle.

  9. Energy and Exergy Analysis of Vapour Absorption Refrigeration Cycle—A Review

    NASA Astrophysics Data System (ADS)

    Kanabar, Bhaveshkumar Kantilal; Ramani, Bharatkumar Maganbhai

    2016-02-01

    In recent years, an energy crisis and the energy consumption have become global problems which restrict the sustainable growth. In these scenarios the scientific energy recovery and the utilization of various kinds of waste heat become very important. The waste heat can be utilized in many ways and one of the best practices is to use it for vapour absorption refrigeration system. To ensure efficient working of absorption cycle and utilization of optimum heat, exergy is the best tool for analysis. This paper provides the comprehensive picture of research and development of absorption refrigeration technology, practical and theoretical analysis with different arrangements of the cycle.

  10. Molecular dynamics study of a CNT-buckyball-enabled energy absorption system.

    PubMed

    Chen, Heng; Zhang, Liuyang; Becton, Matthew; Nie, Hong; Chen, Jinbao; Wang, Xianqiao

    2015-07-14

    An energy absorption system (EAS) composed of a carbon nanotube (CNT) with nested buckyballs is put forward for energy dissipation during impact owing to the outstanding mechanical properties of both CNTs and buckyballs. Here we implement a series of molecular dynamics (MD) simulations to investigate the energy absorption capabilities of several different EASs based on a variety of design parameters. For example, the effects of impact energy, the number of nested buckyballs, and of the size of the buckyballs are analyzed to optimize the energy absorption capability of the EASs by tuning the relevant design parameters. Simulation results indicate that the energy absorption capability of the EAS is closely associated with the deformation characteristics of the confined buckyballs. A low impact energy leads to recoverable deformation of the buckyballs and the dissipated energy is mainly converted to thermal energy. However, a high impact energy yields non-recoverable deformation of buckyballs and thus the energy dissipation is dominated by the strain energy of the EAS. The simulation results also reveal that there exists an optimal value of the number of buckyballs for an EAS under a certain impact energy. Larger buckyballs are able to deform to a larger degree yet also need less impact energy to induce plastic deformation, therefore performing with a better overall energy absorption ability. Overall, the EAS in this study shows a remarkably high energy absorption density of 2 kJ g(-1), it is a promising candidate for mitigating impact energy and sheds light on the research of buckyball-filled CNTs for other applications. PMID:26074446

  11. Impact of inward turbulence spreading on energy loss of edge-localized modes

    SciTech Connect

    Ma, C. H.; Xi, P. W.; Xu, X. Q.; Xia, T. Y.; Snyder, P. B.; Kim, S. S.

    2015-05-15

    Nonlinear two-fluid and gyrofluid simulations show that an edge localized modes (ELM) crash has two phases: fast initial crash of ion temperature perturbation on the Alfvén time scale and slow turbulence spreading. The turbulence transport phase is a slow encroachment of electron temperature perturbation due to the ELM event into pedestal region. Because of the inward turbulence spreading effect, the energy loss of an ELM decreases when density pedestal height increases. The Landau resonance yields the different cross phase-shift of ions and electrons. A 3 + 1 gyro-Landau-fluid model is implemented in BOUT++ framework. The gyrofluid simulations show that the kinetic effects have stabilizing effects on the ideal ballooning mode and the energy loss increases with the pedestal height.

  12. Impact of inward turbulence spreading on energy loss of edge-localized modesa)

    DOE PAGESBeta

    Ma, C. H.; Xu, X. Q.; Xi, P. W.; Xia, T. Y.; Snyder, P. B.; Kim, S. S.

    2015-05-18

    Nonlinear two-fluid and gyrofluid simulations show that an edge localized modes(ELM) crash has two phases: fast initial crash of ion temperature perturbation on the Alfvén time scale and slow turbulence spreading. The turbulencetransport phase is a slow encroachment of electron temperature perturbation due to the ELM event into pedestal region. Because of the inward turbulence spreading effect, the energy loss of an ELM decreases when density pedestal height increases. The Landau resonance yields the different cross phase-shift of ions and electrons. A 3 + 1 gyro-Landau-fluid model is implemented in BOUT++ framework. As a result, the gyrofluid simulations show thatmore » the kinetic effects have stabilizing effects on the ideal ballooning mode and the energy loss increases with the pedestal height.« less

  13. Ab initio Bethe-Salpeter calculations of the x-ray absorption spectra of transition metals at the L-shell edges

    NASA Astrophysics Data System (ADS)

    Vinson, J.; Rehr, J. J.

    2012-11-01

    We present ab initio Bethe-Salpeter equation (BSE) calculations of the L2,3 edges of several insulating and metallic compounds containing Ca, V, Fe, Co, Ni, and Cu, spanning a range of 3d-electron occupations. Our approach includes the key ingredients of a unified treatment of both extended states and atomic multiplet effects, i.e., Bloch states, self-consistent crystal potentials, ground-state magnetism, GW self-energy corrections, spin-orbit terms, and Coulomb interactions between the L2 and L3 levels. The method is implemented in the ocean package, which uses plane-wave pseudopotential wave functions as a basis, a projector-augmented-wave construction for the transition matrix elements, and a resolvent formalism for the BSE calculation. The results are in near quantitative agreement with experiment, including both fine structure at the edges and the nonstatistical L3/L2 ratios observed for these systems. Approximations such as time-dependent density-functional theory are shown to be less accurate.

  14. Temperature dependent electronic structure of Pr{sub 0.67}Sr{sub 0.33}MnO{sub 3} film probed by X-ray absorption near edge structure

    SciTech Connect

    Zhang, Bangmin; Sun, Cheng-Jun E-mail: msecgm@nus.edu.sg; Heald, Steve M.; Chen, Jing-Sheng; Moog Chow, Gan E-mail: msecgm@nus.edu.sg; Venkatesan, T.

    2014-05-07

    The Mn K edge X-ray absorption near edge structures (XANES) of Pr{sub 0.67}Sr{sub 0.33}MnO{sub 3} film (100 nm) on (001) LaAlO{sub 3} substrate was measured at different temperatures to probe the MnO{sub 6} octahedron distortion and corresponding electronic structure. The absorption of high temperature paramagnetic-insulator phase differed from that of the low temperature ferromagnetic-metal phase. The temperature-dependent absorption intensity of Mn K edge XANES was correlated with the relaxation of distorted MnO{sub 6} octahedron, which changed the crystal field acting on the Mn site and the related electronic structure and properties. At low temperature, the splitting of Mn majority e{sub g} orbitals decreased and the density of states above the Fermi level increased in the relaxed MnO{sub 6} octahedron, as reflected by a wider separation between two sub-peaks in the pre-edge XANES spectra.

  15. Optical Absorption in Liquid Semiconductors

    NASA Astrophysics Data System (ADS)

    Bell, Florian Gene

    An infrared absorption cell has been developed which is suitable for high temperature liquids which have absorptions in the range .1-10('3) cm('-1). The cell is constructed by clamping a gasket between two flat optical windows. This unique design allows the use of any optical windows chemically compatible with the liquid. The long -wavelength limit of the measurements is therefore limited only by the choice of the optical windows. The thickness of the cell can easily be set during assembly, and can be varied from 50 (mu)m to .5 cm. Measurements of the optical absorption edge were performed on the liquid alloy Se(,1-x)Tl(,x) for x = 0, .001, .002, .003, .005, .007, and .009, from the melting point up to 475(DEGREES)C. The absorption was found to be exponential in the photon energy over the experimental range from 0.3 eV to 1.2 eV. The absorption increased linearly with concentration according to the empirical relation (alpha)(,T)(h(nu)) = (alpha)(,1) + (alpha)(,2)x, and the absorption (alpha)(,1) was interpreted as the absorption in the absence of T1. (alpha)(,1) also agreed with the measured absorption in 100% Se at corresponding temperatures and energies. The excess absorption defined by (DELTA)(alpha) = (alpha)(,T)(h(nu))-(alpha)(,1) was interpreted as the absorption associated with Tl and was found to be thermally activated with an activation energy E(,t) = 0.5 eV. The exponential edge is explained as absorption on atoms immersed in strong electric fields surrounding ions. The strong fields give rise to an absorption tail similar to the Franz-Keldysh effect. A simple calculation is performed which is based on the Dow-Redfield theory of absorption in an electric field with excitonic effects included. The excess absorption at low photon energies is proportional to the square of the concentration of ions, which are proposed to exist in the liquid according to the relation C(,i) (PROPORTIONAL) x(' 1/2)(.)e('-E)t('/kT), which is the origin of the thermal activation

  16. Study on the d state of platinum in Pt/SiO sub 2 and Na/Pt/SiO sub 2 catalysts under C double bond C hydrogenation conditions by X-ray absorption near-edge structure spectroscopy

    SciTech Connect

    Yoshitake, Hideaki; Iwasawa, Yasuhiro )

    1991-09-19

    The change in the d-electron density of platinum during D{sub 2} + CH{sub 2}{double bond}CHX reactions on Pt/SiO{sub 2} and Na/Pt/SiO{sub 2} catalysts and its influence on the catalysis were studied by X-ray absorption near-edge structure (XANES) spectroscopy, kinetics and FT-IR. It was demonstrated from the change of the white lines in XANES spectra at Pt L{sub 2} and L{sub 3} edges that CH{sub 2}{double bond}CHX (X = H, CH{sub 3}, COCH{sub 3}, CF{sub 3}, and CN) is adsorbed on the Pt surface and extracts the electrons of the d state. Hence, the deuterogenation rate is reduced as the value of Hammett's {sigma}{sub P} increases. The linear free energy relationship between the reaction rate and {sigma}{sub P} was observed for the deuterogenation of CH{sub 2}{double bond}CHX. The rate of ethene deuterogenation was promoted by Na{sub 2}O addition. The electron density of unoccupied d states of pt under vacuum decreased by Na{sub 2}O addition, indicating the electron donation from Na{sub 2}O addition. The electron density of unoccupied d states of Pt under vacuum decreased by Na{sub 2}O addition, indicating the electron donation from Na{sub 2}O addition. However, most of these additional electrons were observed to move to ethene under reaction conditions. The acceptor of the electrons was suggested by di-{sigma}-ethene by the shift of {upsilon}(C-H). The kinetic parameters are discussed in relation to the change in the d state of Pt as a function of {sigma}{sub P} and Na quantity.

  17. The absorption process for heating, cooling and energy storage - An historical survey

    NASA Astrophysics Data System (ADS)

    Bjurstrom, H.; Raldow, W.

    1981-03-01

    A historical overview of the absorption process is given and a wide range of applications, from household refrigerators and air conditioners to topping processes in power plants, are surveyed in historical perspective. The production of mechanical energy and open systems are also included. The current development of the absorption process is sketched out and special attention is given to the aspects of thermal energy storage.

  18. The dust energy balance in the edge-on spiral galaxy NGC 4565

    NASA Astrophysics Data System (ADS)

    De Looze, Ilse; Baes, Maarten; Bendo, George J.; Ciesla, Laure; Cortese, Luca; de Geyter, Gert; Groves, Brent; Boquien, Médéric; Boselli, Alessandro; Brondeel, Lena; Cooray, Asantha; Eales, Steve; Fritz, Jacopo; Galliano, Frédéric; Gentile, Gianfranco; Gordon, Karl D.; Hony, Sacha; Law, Ka-Hei; Madden, Suzanne C.; Sauvage, Marc; Smith, Matthew W. L.; Spinoglio, Luigi; Verstappen, Joris

    2012-12-01

    We combine new dust continuum observations of the edge-on spiral galaxy NGC 4565 in all Herschel/Spectral and Photometric Imaging Receiver (250, 350 and 500 μm) wavebands, obtained as part of the Herschel Reference Survey, and a large set of ancillary data (Spitzer, Sloan Digital Sky Survey, Galaxy Evolution Explorer) to analyse its dust energy balance. We fit a radiative transfer model for the stars and dust to the optical maps with the fitting algorithm FITSKIRT. To account for the observed ultraviolet and mid-infrared emission, this initial model was supplemented with both obscured and unobscured star-forming regions. Even though these star-forming complexes provide an additional heating source for the dust, the far-infrared/submillimetre emission long wards of 100 μm is underestimated by a factor of 3-4. This inconsistency in the dust energy budget of NGC 4565 suggests that a sizable fraction (two-thirds) of the total dust reservoir (Md ˜ 2.9 × 108 M⊙) consists of a clumpy distribution with no associated young stellar sources. The distribution of those dense dust clouds would be in such a way that they remain unresolved in current far-infrared/submillimetre observations and hardly contribute to the attenuation at optical wavelengths. More than two-thirds of the dust heating in NGC 4565 is powered by the old stellar population, with localized embedded sources supplying the remaining dust heating in NGC 4565. The results from this detailed dust energy balance study in NGC 4565 are consistent with that of similar analyses of other edge-on spirals.

  19. Second Generation Gold Nanobeacons for Robust K-Edge Imaging with Multi-Energy CT

    PubMed Central

    Schirra, Carsten O.; Senpan, Angana; Roessl, Ewald; Thran, Axel; Stacy, Allen J.; Wu, Lina; Proska, Roland; Pan, Dipanjan

    2012-01-01

    Spectral CT is the newest advancement in CT imaging technology, which enhances traditional CT images with the capability to image and quantify certain elements based on their distinctive K-edge energies. K-edge imaging feature recognizes high accumulations of targeted elements and presents them as colorized voxels against the normal grayscale X-ray background offering promise to overcome the relatively low inherent contrast within soft tissue and distinguish the high attenuation of calcium from contrast enhanced targets. Towards this aim, second generation gold nanobeacons (GNB2), which incorporate at least five times more metal than the previous generation was developed. The particles were synthesized as lipid-encapsulated, vascularly constrained (>120 nm) nanoparticle incorporating tiny gold nanoparticles (2–4 nm) within a polysorbate core. The choice of core material dictated to achieve a higher metal loading. The particles were thoroughly characterized by physicochemical techniques. This study reports one of the earlier examples of spectral CT imaging with gold nanoparticles demonstrating the potential for targeted in vitro and in vivo imaging and eliminates calcium interference with CT. The use of statistical image reconstruction shows high SNR may allow dose reduction and/or faster scan times. PMID:23185109

  20. Edge multi-energy soft x-ray diagnostic in Experimental Advanced Superconducting Tokamak

    NASA Astrophysics Data System (ADS)

    Li, Y. L.; Xu, G. S.; Tritz, K.; Zhu, Y. B.; Wan, B. N.; Lan, H.; Liu, Y. L.; Wei, J.; Zhang, W.; Hu, G. H.; Wang, H. Q.; Duan, Y. M.; Zhao, J. L.; Wang, L.; Liu, S. C.; Ye, Y.; Li, J.; Lin, X.; Li, X. L.

    2015-12-01

    A multi-energy soft x-ray (ME-SXR) diagnostic has been built for electron temperature profile in the edge plasma region in Experimental Advanced Superconducting Tokamak (EAST) after two rounds of campaigns. Originally, five preamplifiers were mounted inside the EAST vacuum vessel chamber attached to five vertically stacked compact diode arrays. A custom mechanical structure was designed to protect the detectors and electronics under constraints of the tangential field of view for plasma edge and the allocation of space. In the next experiment, the mechanical structure was redesigned with a barrel structure to absolutely isolate it from the vacuum vessel. Multiple shielding structures were mounted at the pinhole head to protect the metal foils from lithium coating. The pre-amplifiers were moved to the outside of the vacuum chamber to avoid introducing interference. Twisted copper cooling tube was embedded into the back-shell near the diode to limit the temperature of the preamplifiers and diode arrays during vacuum vessel baking when the temperature reached 150 °C. Electron temperature profiles were reconstructed from ME-SXR measurements using neural networks.

  1. Edge multi-energy soft x-ray diagnostic in Experimental Advanced Superconducting Tokamak.

    PubMed

    Li, Y L; Xu, G S; Tritz, K; Zhu, Y B; Wan, B N; Lan, H; Liu, Y L; Wei, J; Zhang, W; Hu, G H; Wang, H Q; Duan, Y M; Zhao, J L; Wang, L; Liu, S C; Ye, Y; Li, J; Lin, X; Li, X L

    2015-12-01

    A multi-energy soft x-ray (ME-SXR) diagnostic has been built for electron temperature profile in the edge plasma region in Experimental Advanced Superconducting Tokamak (EAST) after two rounds of campaigns. Originally, five preamplifiers were mounted inside the EAST vacuum vessel chamber attached to five vertically stacked compact diode arrays. A custom mechanical structure was designed to protect the detectors and electronics under constraints of the tangential field of view for plasma edge and the allocation of space. In the next experiment, the mechanical structure was redesigned with a barrel structure to absolutely isolate it from the vacuum vessel. Multiple shielding structures were mounted at the pinhole head to protect the metal foils from lithium coating. The pre-amplifiers were moved to the outside of the vacuum chamber to avoid introducing interference. Twisted copper cooling tube was embedded into the back-shell near the diode to limit the temperature of the preamplifiers and diode arrays during vacuum vessel baking when the temperature reached 150 °C. Electron temperature profiles were reconstructed from ME-SXR measurements using neural networks. PMID:26724032

  2. Edge multi-energy soft x-ray diagnostic in Experimental Advanced Superconducting Tokamak

    SciTech Connect

    Li, Y. L.; Xu, G. S.; Wan, B. N.; Lan, H.; Liu, Y. L.; Wei, J.; Zhang, W.; Hu, G. H.; Wang, H. Q.; Duan, Y. M.; Zhao, J. L.; Wang, L.; Liu, S. C.; Ye, Y.; Li, J.; Lin, X.; Li, X. L.; Tritz, K.; Zhu, Y. B.

    2015-12-15

    A multi-energy soft x-ray (ME-SXR) diagnostic has been built for electron temperature profile in the edge plasma region in Experimental Advanced Superconducting Tokamak (EAST) after two rounds of campaigns. Originally, five preamplifiers were mounted inside the EAST vacuum vessel chamber attached to five vertically stacked compact diode arrays. A custom mechanical structure was designed to protect the detectors and electronics under constraints of the tangential field of view for plasma edge and the allocation of space. In the next experiment, the mechanical structure was redesigned with a barrel structure to absolutely isolate it from the vacuum vessel. Multiple shielding structures were mounted at the pinhole head to protect the metal foils from lithium coating. The pre-amplifiers were moved to the outside of the vacuum chamber to avoid introducing interference. Twisted copper cooling tube was embedded into the back-shell near the diode to limit the temperature of the preamplifiers and diode arrays during vacuum vessel baking when the temperature reached 150 °C. Electron temperature profiles were reconstructed from ME-SXR measurements using neural networks.

  3. Energy transfer and energy absorption in photon interactions with matter revisited: A step-by-step illustrated approach

    NASA Astrophysics Data System (ADS)

    Abdel-Rahman, W.; Podgorsak, E. B.

    2010-05-01

    A clear understanding of energy transfer and energy absorption in photon interactions with matter is essential for the understanding of radiation dosimetry and development of new dosimetry techniques. The concepts behind the two quantities have been enunciated many years ago and described in many scientific papers, review articles, and textbooks. Data dealing with energy transfer and energy absorption as well as the associated mass energy transfer coefficient and the mass energy absorption coefficient are readily available in web-based tabular forms. However, tables, even when available in detailed and easy to access form, do not lend themselves to serve as visual aid to promote better understanding of the dosimetric quantities related to energy transfer and energy absorption as well as their relationship to the photon energy and absorber atomic number. This paper uses graphs and illustrations, in addition to well-known mathematical relationships, to guide the reader in a systematic manner through the various stages involved in the derivation of energy absorbed in medium and its associated quantity, the mass energy absorption coefficient, from the mass attenuation coefficient.

  4. Relationship between mechanical-property and energy-absorption trends for composite tubes

    NASA Technical Reports Server (NTRS)

    Farley, Gary L.

    1992-01-01

    U.S. Army helicopters are designed to dissipate prescribed levels of crash impact kinetic energy without compromising the integrity of the fuselage. Because of the complexity of the energy-absorption process it is imperative for designers of energy-absorbing structures to develop an in-depth understanding of how and why composite structures absorb energy. A description of the crushing modes and mechanisms of energy absorption for composite tubes and beams is presented. Three primary crushing modes of composite structures including transverse shearing, lamina bending, and local buckling are described. The experimental data presented show that fiber and matrix mechanical properties and laminate stiffness and strength mechanical properties cannot reliably predict the energy-absorption response of composite tubes.

  5. Synchrotron-based X-ray absorption near-edge spectroscopy imaging for laterally resolved speciation of selenium in fresh roots and leaves of wheat and rice

    PubMed Central

    Wang, Peng; Menzies, Neal W.; Lombi, Enzo; McKenna, Brigid A.; James, Simon; Tang, Caixian; Kopittke, Peter M.

    2015-01-01

    Knowledge of the distribution of selenium (Se) species within plant tissues will assist in understanding the mechanisms of Se uptake and translocation, but in situ analysis of fresh and highly hydrated plant tissues is challenging. Using synchrotron-based fluorescence X-ray absorption near-edge spectroscopy (XANES) imaging to provide laterally resolved data, the speciation of Se in fresh roots and leaves of wheat (Triticum aestivum L.) and rice (Oryza sativa L.) supplied with 1 μM of either selenate or selenite was investigated. For plant roots exposed to selenate, the majority of the Se was efficiently converted to C-Se-C compounds (i.e. methylselenocysteine or selenomethionine) as selenate was transported radially through the root cylinder. Indeed, even in the rhizodermis which is exposed directly to the bulk solution, only 12–31% of the Se was present as uncomplexed selenate. The C-Se-C compounds were probably sequestered within the roots, whilst much of the remaining uncomplexed Se was translocated to the leaves—selenate accounting for 52–56% of the total Se in the leaves. In a similar manner, for plants exposed to selenite, the Se was efficiently converted to C-Se-C compounds within the roots, with only a small proportion of uncomplexed selenite observed within the outer root tissues. This resulted in a substantial decrease in translocation of Se from the roots to leaves of selenite-exposed plants. This study provides important information for understanding the mechanisms responsible for the uptake and subsequent transformation of Se in plants. PMID:26019258

  6. Cu K-edge X-ray Absorption Spectroscopy Reveals Differential Copper Coordimation Within Amyloid-beta Oligomers Compared to Amyloid-beta Monomers

    SciTech Connect

    J Shearer; P Callan; T Tran; V Szalai

    2011-12-31

    The fatal neurodegenerative disorder Alzheimer's disease (AD) has been linked to the formation of soluble neurotoxic oligomers of amyloid-{beta} (A{beta}) peptides. These peptides have high affinities for copper cations. Despite their potential importance in AD neurodegeneration few studies have focused on probing the Cu{sup 2+/1+} coordination environment within A{beta} oligomers. Herein we present a Cu K-edge X-ray absorption spectroscopic study probing the copper-coordination environment within oligomers of A{beta}(42) (sequence: DAEFRHDSGYEVHHQKLVFFAEDVGSNKGAIIGLMVGGVVIA). We find that the Cu{sup 2+} cation is contained within a square planar mixed N/O ligand environment within A{beta}(42) oligomers, which is similar to the copper coordination environment of the monomeric forms of {l_brace}Cu{sup II}A{beta}(40){r_brace} and {l_brace}Cu{sup II}A{beta}(16){r_brace}. Reduction of the Cu{sup 2+} cation within the A{beta}(42) oligomers to Cu{sup 1+} yields a highly dioxygen sensitive copper-species that contains Cu{sup 1+} in a tetrahedral coordination geometry. This can be contrasted with monomers of {l_brace}Cu{sup I}A{beta}(40){r_brace} and {l_brace}Cu{sup I}A{beta}(16){r_brace}, which contain copper in a dioxygen inert linear bis-histidine ligand environment [Shearer and Szalai, J. Am. Chem. Soc., 2008, 130, 17826]. The biological implications of these findings are discussed.

  7. In-operando synchronous time-multiplexed O K-edge x-ray absorption spectromicroscopy of functioning tantalum oxide memristors

    SciTech Connect

    Kumar, Suhas; Graves, Catherine E.; Strachan, John Paul Williams, R. Stanley; Kilcoyne, A. L. David; Tyliszczak, Tolek; Nishi, Yoshio

    2015-07-21

    Memristors are receiving keen interest because of their potential varied applications and promising large-scale information storage capabilities. Tantalum oxide is a memristive material that has shown promise for high-performance nonvolatile computer memory. The microphysics has been elusive because of the small scale and subtle physical changes that accompany conductance switching. In this study, we probed the atomic composition, local chemistry, and electronic structure of functioning tantalum oxide memristors through spatially mapped O K-edge x-ray absorption. We developed a time-multiplexed spectromicroscopy technique to enhance the weak and possibly localized oxide modifications with spatial and spectral resolutions of <30 nm and 70 meV, respectively. During the initial stages of conductance switching of a micrometer sized crosspoint device, the spectral changes were uniform within the spatial resolution of our technique. When the device was further driven with millions of high voltage-pulse cycles, we observed lateral motion and separation of ∼100 nm-scale agglomerates of both oxygen interstitials and vacancies. We also demonstrate a unique capability of this technique by identifying the relaxation behavior in the material during electrical stimuli by identifying electric field driven changes with varying pulse widths. In addition, we show that changes to the material can be localized to a spatial region by modifying its topography or uniformity, as against spatially uniform changes observed here during memristive switching. The goal of this report is to introduce the capability of time-multiplexed x-ray spectromicroscopy in studying weak-signal transitions in inhomogeneous media through the example of the operation and temporal evolution of a memristor.

  8. In-operando synchronous time-multiplexed O K-edge x-ray absorption spectromicroscopy of functioning tantalum oxide memristors

    NASA Astrophysics Data System (ADS)

    Kumar, Suhas; Graves, Catherine E.; Strachan, John Paul; Kilcoyne, A. L. David; Tyliszczak, Tolek; Nishi, Yoshio; Williams, R. Stanley

    2015-07-01

    Memristors are receiving keen interest because of their potential varied applications and promising large-scale information storage capabilities. Tantalum oxide is a memristive material that has shown promise for high-performance nonvolatile computer memory. The microphysics has been elusive because of the small scale and subtle physical changes that accompany conductance switching. In this study, we probed the atomic composition, local chemistry, and electronic structure of functioning tantalum oxide memristors through spatially mapped O K-edge x-ray absorption. We developed a time-multiplexed spectromicroscopy technique to enhance the weak and possibly localized oxide modifications with spatial and spectral resolutions of <30 nm and 70 meV, respectively. During the initial stages of conductance switching of a micrometer sized crosspoint device, the spectral changes were uniform within the spatial resolution of our technique. When the device was further driven with millions of high voltage-pulse cycles, we observed lateral motion and separation of ˜100 nm-scale agglomerates of both oxygen interstitials and vacancies. We also demonstrate a unique capability of this technique by identifying the relaxation behavior in the material during electrical stimuli by identifying electric field driven changes with varying pulse widths. In addition, we show that changes to the material can be localized to a spatial region by modifying its topography or uniformity, as against spatially uniform changes observed here during memristive switching. The goal of this report is to introduce the capability of time-multiplexed x-ray spectromicroscopy in studying weak-signal transitions in inhomogeneous media through the example of the operation and temporal evolution of a memristor.

  9. 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.

  10. 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.

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

    PubMed Central

    Hong, Xinguo; Newville, Matthew; Prakapenka, Vitali B.; Rivers, Mark L.; Sutton, Stephen R.

    2009-01-01

    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° relative to the x-ray beam direction. Demonstration XAFS spectra are reported for rutile-type GeO2 recorded by traditional ambient pressure and high pressure DAC methods, showing similar quality at 440 eV above the absorption edge. Accurate XAFS spectra of GeO2 glass were obtained at high pressure up to 53 GPa, providing important insight into the structural polymorphism of GeO2 glass at high pressure. This method is expected be applicable for in situ XAFS measurements using a diamond anvil cell up to ultrahigh pressures. PMID:19655966

  12. 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.

  13. The perpendicular electron energy flux driven by magnetic fluctuations in the edge of the Texas Experimental Tokamak

    SciTech Connect

    Fiksel, G.; Bengtson, R.D.; Prager, S.C.; Wootton, A.J. |

    1995-12-01

    A fast bolometer was used for direct measurements of parallel electron energy flux in the edge of the Texas Experimental Tokamak (TEXT-U) [K. W. Gentle, Nucl. Technol. Fusion {bold 1}, 479 (1981)]. The fluctuating component of the parallel electron energy flux, combined with a measurement of magnetic fluctuations, provides an upper limit to the perpendicular electron flux. This magnetically driven energy flux cannot account for the observed energy flux. {copyright} {ital 1995} {ital American} {ital Institute} {ital of} {ital Physics}.

  14. Three dimensional mapping of strontium in bone by dual energy K-edge subtraction imaging

    NASA Astrophysics Data System (ADS)

    Cooper, D. M. L.; Chapman, L. D.; Carter, Y.; Wu, Y.; Panahifar, A.; Britz, H. M.; Bewer, B.; Zhouping, W.; Duke, M. J. M.; Doschak, M.

    2012-09-01

    The bones of many terrestrial vertebrates, including humans, are continually altered through an internal process of turnover known as remodeling. This process plays a central role in bone adaptation and disease. The uptake of fluorescent tetracyclines within bone mineral is widely exploited as a means of tracking new tissue formation. While investigation of bone microarchitecture has undergone a dimensional shift from 2D to 3D in recent years, we lack a 3D equivalent to fluorescent labeling. In the current study we demonstrate the ability of synchrotron radiation dual energy K-edge subtraction (KES) imaging to map the 3D distribution of elemental strontium within rat vertebral samples. This approach has great potential for ex vivo analysis of preclinical models and human tissue samples. KES also represents a powerful tool for investigating the pharmokinetics of strontium-based drugs recently approved in many countries around the globe for the treatment of osteoporosis.

  15. Sulfur K-edge X-ray Absorption Spectroscopy and Density Functional Calculations on Mo(IV) and Mo(VI)=O Bis-dithiolenes: Insights into the Mechanism of Oxo Transfer in DMSO Reductase and Related Functional Analogues

    PubMed Central

    Tenderholt, Adam L.; Wang, Jun-Jieh; Szilagyi, Robert K.; Holm, Richard H.; Hodgson, Keith O.; Hedman, Britt; Solomon, Edward I.

    2010-01-01

    Sulfur K-edge X-ray absorption spectroscopy (XAS) and density functional theory (DFT) calculations have been used to determine the electronic structures of two Mo bis-dithiolene complexes, [Mo(OSi)(bdt)2]1− and [MoO(OSi)(bdt)2]1− where OSi = [OSiPh2tBu]1− and bdt = benzene-1,2-dithiolate(2−), that model the Mo(IV) and Mo(VI)=O states of the DMSO reductase family of molybdenum enzymes. These results show that the Mo(IV) complex undergoes metal-based oxidation unlike the Mo(IV) tris-dithiolene complexes, indicating that the dithiolene ligands are behaving innocently. Experimentally-validated calculations have been extended to model the oxo-transfer reaction coordinate using dimethylsulfoxide (DMSO) as a substrate. The reaction proceeds through a transition state (TS1) to an intermediate with DMSO weakly bound, followed by a subsequent transition state (TS2) which is the largest barrier of the reaction. The factors that control the energies of these transition states, the nature of the oxo transfer process, and the role of the dithiolene ligand are discussed. PMID:20499905

  16. Towards elucidating the energy of the first excited singlet state of xanthophyll cycle pigments by X-ray absorption spectroscopy.

    PubMed

    Gruszecki, W I; Stiel, H; Niedzwiedzki, D; Beck, M; Milanowska, J; Lokstein, H; Leupold, D

    2005-06-01

    The first excited singlet state (S(1)) of carotenoids (also termed 2A(g)(-)) plays a key role in photosynthetic excitation energy transfer due to its close proximity to the S(1) (Q(y)) level of chlorophylls. The determination of carotenoid 2A(g)(-) energies by optical techniques is difficult; transitions from the ground state (S(0), 1A(g)(-)) to the 2A(g)(-) state are forbidden ("optically dark") due to parity (g <-- //--> g) as well as pseudo-parity selection rules (- <-- //--> -). Of particular interest are S(1) energies of the so-called xanthophyll-cycle pigments (violaxanthin, antheraxanthin and zeaxanthin) due to their involvement in photoprotection in plants. Previous determinations of S(1) energies of violaxanthin and zeaxanthin by different spectroscopic techniques vary considerably. Here we present an alternative approach towards elucidation of the optically dark states of xanthophylls by near-edge X-ray absorption fine structure spectroscopy (NEXAFS). The indication of at least one pi* energy level (about 0.5 eV below the lowest 1B(u)(+) vibronic sublevel) has been found for zeaxanthin. Present limitations and future improvements of NEXAFS to study optically dark states of carotenoids are discussed. NEXAFS combined with simultaneous optical pumping will further aid the investigation of these otherwise hardly accessible states. PMID:15949988

  17. A Novel Design of Circular Edge Bow-Tie Nano Antenna for Energy Harvesting

    NASA Astrophysics Data System (ADS)

    Haque, Ahasanul; Reza, Ahmed Wasif; Kumar, Narendra

    2015-11-01

    In this study, a novel nano antenna is designed in order to convert the high frequency solar energy, thermal energy or earth re-emitted sun's energy into electricity. The proposed antenna is gold printed on a SiO2 layer, designed as a circular edge bow-tie with a ground plane at the bottom of the substrate. The Lorentz-Drude model is used to analyze the behavior of gold at the infrared band of frequencies. The proposed antenna is designed by 3D-electromagnetic solver, and analyzed for optimization of metal thickness, gap size, and antenna's geometrical length. Simulations are conducted in order to investigate the behavior of the antenna illuminated by the circularly polarized plane wave. The numerical simulations are studied for improving the harvesting E-field of the antenna within 5 THz-40 THz frequency range. The proposed antenna offers multiple resonance frequency and better return loss within the frequency bands of 23.2 THz to 27 THz (bandwidth 3.8 THz) and 31 THz to 35.9 THz (bandwidth 4.9 THz). An output electric field of 0.656 V/µm is simulated at 25.3 THz. The best fitted gap size at the feed point is achieved as 50 nm with the substrate thickness of 1.2 µm.

  18. HERschel Observations of Edge-on Spirals (HEROES). III. Dust energy balance study of IC 2531

    NASA Astrophysics Data System (ADS)

    Mosenkov, Aleksandr V.; Allaert, Flor; Baes, Maarten; Bianchi, Simone; Camps, Peter; De Geyter, Gert; De Looze, Ilse; Fritz, Jacopo; Gentile, Gianfranco; Hughes, Thomas M.; Lewis, Fraser; Verstappen, Joris; Verstocken, Sam; Viaene, Sébastien

    2016-07-01

    We investigate the dust energy balance for the edge-on galaxy IC 2531, one of the seven galaxies in the HEROES sample. We perform a state-of-the-art radiative transfer modelling based, for the first time, on a set of optical and near-infrared galaxy images. We show that by taking into account near-infrared imaging in the modelling significantly improves the constraints on the retrieved parameters of the dust content. We confirm the result from previous studies that including a young stellar population in the modelling is important to explain the observed stellar energy distribution. However, the discrepancy between the observed and modelled thermal emission at far-infrared wavelengths, the so-called dust energy balance problem, is still present: the model underestimates the observed fluxes by a factor of about two. We compare two different dust models, and find that dust parameters, and thus the spectral energy distribution in the infrared domain, are sensitive to the adopted dust model. In general, the THEMIS model reproduces the observed emission in the infrared wavelength domain better than the popular BARE-GR-S model. Our study of IC 2531 is a pilot case for detailed and uniform radiative transfer modelling of the entire HEROES sample, which will shed more light on the strength and origins of the dust energy balance problem. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.The reduced images (as FITS files) are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/592/A71

  19. Ion target impact energy during Type I edge localized modes in JET ITER-like Wall

    NASA Astrophysics Data System (ADS)

    Guillemaut, C.; Jardin, A.; Horacek, J.; Autricque, A.; Arnoux, G.; Boom, J.; Brezinsek, S.; Coenen, J. W.; De La Luna, E.; Devaux, S.; Eich, T.; Giroud, C.; Harting, D.; Kirschner, A.; Lipschultz, B.; Matthews, G. F.; Moulton, D.; O'Mullane, M.; Stamp, M.

    2015-08-01

    The ITER baseline scenario, with 500 MW of DT fusion power and Q = 10, will rely on a Type I ELMy H-mode, with ΔW = 0.7 MJ mitigated edge localized modes (ELMs). Tungsten (W) is the material now decided for the divertor plasma-facing components from the start of plasma operations. W atoms sputtered from divertor targets during ELMs are expected to be the dominant source under the partially detached divertor conditions required for safe ITER operation. W impurity concentration in the plasma core can dramatically degrade its performance and lead to potentially damaging disruptions. Understanding the physics of plasma-wall interaction during ELMs is important and a primary input for this is the energy of incoming ions during an ELM event. In this paper, coupled Infrared thermography and Langmuir Probe (LP) measurements in JET-ITER-Like-Wall unseeded H-mode experiments with ITER relevant ELM energy drop have been used to estimate the impact energy of deuterium ions (D+) on the divertor target. This analysis gives an ion energy of several keV during ELMs, which makes D+ responsible for most of the W sputtering in unseeded H-mode discharges. These LP measurements were possible because of the low electron temperature (Te) during ELMs which allowed saturation of the ion current. Although at first sight surprising, the observation of low Te at the divertor target during ELMs is consistent with the ‘Free-Streaming’ kinetic model which predicts a near-complete transfer of parallel energy from electrons to ions in order to maintain quasi-neutrality of the ELM filaments while they are transported to the divertor targets.

  20. Bio-Inspired Photon Absorption and Energy Transfer for Next Generation Photovoltaic Devices

    NASA Astrophysics Data System (ADS)

    Magsi, Komal

    Nature's solar energy harvesting system, photosynthesis, serves as a model for photon absorption, spectra broadening, and energy transfer. Photosynthesis harvests light far differently than photovoltaic cells. These differences offer both engineering opportunity and scientific challenges since not all of the natural photon absorption mechanisms have been understood. In return, solar cells can be a very sensitive probe for the absorption characteristics of molecules capable of transferring charge to a conductive interface. The objective of this scientific work is the advancement of next generation photovoltaics through the development and application of natural photo-energy transfer processes. Two scientific methods were used in the development and application of enhancing photon absorption and transfer. First, a detailed analysis of photovoltaic front surface fluorescent spectral modification and light scattering by hetero-structure was conducted. Phosphor based spectral down-conversion is a well-known laser technology. The theoretical calculations presented here indicate that parasitic losses and light scattering within the spectral range are large enough to offset any expected gains. The second approach for enhancing photon absorption is based on bio-inspired mechanisms. Key to the utilization of these natural processes is the development of a detailed scientific understanding and the application of these processes to cost effective systems and devices. In this work both aspects are investigated. Dye type solar cells were prepared and tested as a function of Chlorophyll (or Sodium-Copper Chlorophyllin) and accessory dyes. Forster has shown that the fluorescence ratio of Chlorophyll is modified and broadened by separate photon absorption (sensitized absorption) through interaction with nearby accessory pigments. This work used the dye type solar cell as a diagnostic tool by which to investigate photon absorption and photon energy transfer. These experiments shed

  1. United States Department of Energy large commercial absorption chiller development program

    SciTech Connect

    Garland, P.W.; DeVault, R.C.; Zaltash, A.

    1998-11-01

    The US Department of Energy (DOE) is working with partners from the gas cooling industry to improve energy efficiency and US competitiveness by using advanced absorption technologies that eliminate the use of chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs), refrigerants that contribute to ozone depletion and global warming. Absorption cooling uses natural gas as the heat source, which produces much lower NO{sub x} emissions than oil- or coal-generated electricity. Gas-fired chillers also have the advantage of helping reduce peak electrical usage during summer months. To assist industry in developing advanced absorption cooling technologies, DOE sponsors the Large Commercial Chiller Development Program. The goal of the program is to improve chiller cooling efficiency by 30--50% compared with the best currently available absorption systems.

  2. Calculation tool for transported geothermal energy using two-step absorption process

    DOE Data Explorer

    Kyle Gluesenkamp

    2016-02-01

    This spreadsheet allows the user to calculate parameters relevant to techno-economic performance of a two-step absorption process to transport low temperature geothermal heat some distance (1-20 miles) for use in building air conditioning. The parameters included are (1) energy density of aqueous LiBr and LiCl solutions, (2) transportation cost of trucking solution, and (3) equipment cost for the required chillers and cooling towers in the two-step absorption approach. More information is available in the included public report: "A Technical and Economic Analysis of an Innovative Two-Step Absorption System for Utilizing Low-Temperature Geothermal Resources to Condition Commercial Buildings"

  3. High energy X-ray phase and dark-field imaging using a random absorption mask

    NASA Astrophysics Data System (ADS)

    Wang, Hongchang; Kashyap, Yogesh; Cai, Biao; Sawhney, Kawal

    2016-07-01

    High energy X-ray imaging has unique advantage over conventional X-ray imaging, since it enables higher penetration into materials with significantly reduced radiation damage. However, the absorption contrast in high energy region is considerably low due to the reduced X-ray absorption cross section for most materials. Even though the X-ray phase and dark-field imaging techniques can provide substantially increased contrast and complementary information, fabricating dedicated optics for high energies still remain a challenge. To address this issue, we present an alternative X-ray imaging approach to produce transmission, phase and scattering signals at high X-ray energies by using a random absorption mask. Importantly, in addition to the synchrotron radiation source, this approach has been demonstrated for practical imaging application with a laboratory-based microfocus X-ray source. This new imaging method could be potentially useful for studying thick samples or heavy materials for advanced research in materials science.

  4. Effective Atomic Numbers of Lanthanides with Gamma Radiation for Photon Energy Absorption

    NASA Astrophysics Data System (ADS)

    Shantappa, Anil; Hanagodimath, S. M.

    Effective atomic numbers for photon energy absorption, ZPEA,eff have been calculated for photon from 1 keV to 20 MeV for selected oxides of lanthanides, such as Lanthanum oxide, Cerium oxide, Samarium oxide, Europium oxide, Dysprosium oxide, Thulium oxide, Ytterbium oxide. The ZPEA,eff values then compared with ZPI,eff for photon interaction. The ZPEA,eff values have been found to change with energy and composition of selected lanthanides. Oxides of lanthanides are considered as better shielding materials to the exposure of gamma radiation. The values of effective atomic number for photon energy absorption help in the calculation of absorbed dose.

  5. Energy-dependent parameterization of heavy-ion absorption cross sections

    NASA Technical Reports Server (NTRS)

    Townsend, L. W.; Wilson, J. W.

    1986-01-01

    An energy-dependent parameterization of the total absorption (reaction) cross sections for heavy ion (Z equal to or greater than 2) collisions at energies above 25 MeV per nucleon is presented. The formula will be especially useful in heavy-ion transport applications.

  6. Guided-wave approaches to spectrally selective energy absorption

    NASA Technical Reports Server (NTRS)

    Stegeman, G. I.; Burke, J. J.

    1987-01-01

    Results of experiments designed to demonstrate spectrally selective absorption in dielectric waveguides on semiconductor substrates are reported. These experiments were conducted with three waveguides formed by sputtering films of PSK2 glass onto silicon-oxide layers grown on silicon substrates. The three waveguide samples were studied at 633 and 532 nm. The samples differed only in the thickness of the silicon-oxide layer, specifically 256 nm, 506 nm, and 740 nm. Agreement between theoretical predictions and measurements of propagation constants (mode angles) of the six or seven modes supported by these samples was excellent. However, the loss measurements were inconclusive because of high scattering losses in the structures fabricated (in excess of 10 dB/cm). Theoretical calculations indicated that the power distribution among all the modes supported by these structures will reach its steady state value after a propagation length of only 1 mm. Accordingly, the measured loss rates were found to be almost independent of which mode was initially excited. The excellent agreement between theory and experiment leads to the conclusion that low loss waveguides confirm the predicted loss rates.

  7. Crashworthiness of Aluminium Tubes; Part 2: Improvement of Hydroforming Operation to Increase Absorption Energy

    SciTech Connect

    D'Amours, Guillaume; Rahem, Ahmed; Mayer, Robert; Williams, Bruce; Worswick, Michael

    2007-05-17

    The motivation to reduce overall vehicle weight within the automotive sector drives the substitution of lightweight materials such as aluminium alloys for structural components. Such a substitution requires a significant amount of development to manufacture structurally parts such that the energy absorption characteristics are not sacrificed in the event of crash. The effects of the manufacturing processes on the crash performance of automotive structural components must be better understood to ensure improved crashworthiness. This paper presents results of an experimental and numerical investigation of the crash response and energy absorption properties of impacted hydroformed aluminium alloy tubes. Crash experiments on hydroformed tubes were performed using a deceleration sled test at the General Motors Technical Center. Results from axial crush testing showed that an important parameter that influences the energy absorption characteristics during crash was the thickness reduction caused by circumferential expansion of the tube during hydroforming. It was found that that the energy absorption decreased as the corner radius decreased, which results because of increased thinning. Sensitivity studies of end feeding parameters, such as end feed level and profile, were carried out to evaluate their impact on the energy absorption of the aluminium tubes.

  8. The effects of crushing speed on the energy-absorption capability of composite tubes

    NASA Technical Reports Server (NTRS)

    Farley, Gary L.

    1991-01-01

    The energy-absorption capability as a function of crushing speed was determined for Thornel 300-Fiberite 934 (Gr-E) and Kevlar-49-Fiberite 934 (K-E) composite material. Circular cross section tube specimens were crushed at speeds ranging from 0.01 to 12 m/sec. Ply orientations of the tube specimens were (0/ +/- theta)2 and (+/- theta)2 where theta = 15, 45, and 75 deg. Based upon the results of these tests, the energy-absorption capability of Gr-E and K-E was determined to be a function of crushing speed. The magnitude of the effects of crushing speed on energy-absorption capability was determined to be a function of the mechanisms that control the crushing process. The effects of crushing speed on the energy-absorption capability is related to whether the mechanical response of the crushing mechanism that controls the crushing process is a function of strain rate. Energy-absorption capability of Gr-E and K-E tubes ranged between 0 and 35 percent and 20 and 45 percent, respectively, depending upon ply orientation.

  9. 3D finite element simulation of effects of deflection rate on energy absorption for TRIP steel

    NASA Astrophysics Data System (ADS)

    Hayashi, Asuka; Pham, Hang; Iwamoto, Takeshi

    2015-09-01

    Recently, with the requirement of lighter weight and more safety for a design of automobile, energy absorption capability of structural materials has become important. TRIP (Transformation-induced Plasticity) steel is expected to apply to safety members because of excellent energy absorption capability and ductility. Past studies proved that such excellent characteristics in TRIP steel are dominated by strain-induced martensitic transformation (SIMT) during plastic deformation. Because SIMT strongly depends on deformation rate and temperature, an investigation of the effects of deformation rate and temperature on energy absorption in TRIP is essential. Although energy absorption capability of material can be estimated by J-integral experimentally by using pre-cracked specimen, it is difficult to determine volume fraction of martensite and temperature rise during the crack extension. In addition, their effects on J-integral, especially at high deformation rate in experiment might be quite hard. Thus, a computational prediction needs to be performed. In this study, bending deformation behavior of pre-cracked specimen until the onset point of crack extension are predicted by 3D finite element simulation based on the transformation kinetics model proposed by Iwamoto et al. (1998). It is challenged to take effects of temperature, volume fraction of martensite and deformation rate into account. Then, the mechanism for higher energy absorption characteristic will be discussed.

  10. Crashworthiness of Aluminium Tubes; Part 2: Improvement of Hydroforming Operation to Increase Absorption Energy

    NASA Astrophysics Data System (ADS)

    D'Amours, Guillaume; Rahem, Ahmed; Mayer, Robert; Williams, Bruce; Worswick, Michael

    2007-05-01

    The motivation to reduce overall vehicle weight within the automotive sector drives the substitution of lightweight materials such as aluminium alloys for structural components. Such a substitution requires a significant amount of development to manufacture structurally parts such that the energy absorption characteristics are not sacrificed in the event of crash. The effects of the manufacturing processes on the crash performance of automotive structural components must be better understood to ensure improved crashworthiness. This paper presents results of an experimental and numerical investigation of the crash response and energy absorption properties of impacted hydroformed aluminium alloy tubes. Crash experiments on hydroformed tubes were performed using a deceleration sled test at the General Motors Technical Center. Results from axial crush testing showed that an important parameter that influences the energy absorption characteristics during crash was the thickness reduction caused by circumferential expansion of the tube during hydroforming. It was found that that the energy absorption decreased as the corner radius decreased, which results because of increased thinning. Sensitivity studies of end feeding parameters, such as end feed level and profile, were carried out to evaluate their impact on the energy absorption of the aluminium tubes.

  11. Single-photon absorption and dynamic control of the exciton energy in a coupled quantum-dot-cavity system

    SciTech Connect

    Johne, R.; Fiore, A.

    2011-11-15

    We theoretically investigate the dynamic interaction of a quantum dot in a nanocavity with time-symmetric single-photon pulses. The simulations, based on a wave-function approach, reveal that almost perfect single-photon absorption occurs for quantum-dot-cavity systems operating on the edge between strong- and weak-coupling regimes. The computed maximum absorption probability is close to unity for pulses with a typical length comparable to half of the Rabi period. Furthermore, the dynamic control of the quantum-dot energy via electric fields allows the freezing of the light-matter interaction, leaving the quantum dot in its excited state. Shaping of single-photon wave packets by the electric field control is limited by the occurrence of chirping of the single-photon pulse. This understanding of the interaction of single-photon pulses with the quantum-dot-cavity system provides the basis for the development of advanced protocols for quantum-information processing in the solid state.

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

    SciTech Connect

    Willey, T; Willey, T

    2004-03-24

    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

  13. Characterization of functionalized self-assembled monolayers and surface-attached interlocking molecules using near-edge X-ray absorption fine structure spectroscopy

    NASA Astrophysics Data System (ADS)

    Willey, Trevor Michael

    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

  14. Sulfur K-Edge X-Ray Absorption Spectroscopy And Density Functional Theory Calculations on Superoxide Reductase: Role of the Axial Thiolate in Reactivity

    SciTech Connect

    Dey, A.; Jenney, F.E.; Jr.; Adams, M.W.W.; Johnson, M.K.; Hodgson, K.O.; Hedman, B.; Solomon, E.I.

    2009-06-02

    Superoxide reductase (SOR) is a non-heme iron enzyme that reduces superoxide to peroxide at a diffusion-controlled rate. Sulfur K-edge X-ray absorption spectroscopy (XAS) is used to investigate the ground-state electronic structure of the resting high-spin and CN- bound low-spin FeIII forms of the 1Fe SOR from Pyrococcus furiosus. A computational model with constrained imidazole rings (necessary for reproducing spin states), H-bonding interaction to the thiolate (necessary for reproducing Fe-S bond covalency of the high-spin and low-spin forms), and H-bonding to the exchangeable axial ligand (necessary to reproduce the ground state of the low-spin form) was developed and then used to investigate the enzymatic reaction mechanism. Reaction of the resting ferrous site with superoxide and protonation leading to a high-spin FeIII-OOH species and its subsequent protonation resulting in H2O2 release is calculated to be the most energetically favorable reaction pathway. Our results suggest that the thiolate acts as a covalent anionic ligand. Replacing the thiolate with a neutral noncovalent ligand makes protonation very endothermic and greatly raises the reduction potential. The covalent nature of the thiolate weakens the FeIII bond to the proximal oxygen of this hydroperoxo species, which raises its pKa by an additional 5 log units relative to the pKa of a primarily anionic ligand, facilitating its protonation. A comparison with cytochrome P450 indicates that the stronger equatorial ligand field from the porphyrin results in a low-spin FeIII-OOH species that would not be capable of efficient H2O2 release due to a spin-crossing barrier associated with formation of a high-spin 5C FeIII product. Additionally, the presence of the dianionic porphyrin pi ring in cytochrome P450 allows O-O heterolysis, forming an FeIV-oxo porphyrin radical species, which is calculated to be extremely unfavorable for the non-heme SOR ligand environment. Finally, the 5C FeIII site that results

  15. Acid-site characterization of water-oxidized alumina films by near-edge x-ray absorption and soft x-ray photoemission

    SciTech Connect

    O`Hagan, P.J.; Merrill, R.P.; Rhodin, T.N.; Woronick, S.W.; Shinn, N.D.; Woolery, G.L.; Chester, A.W.

    1994-12-01

    Hydroxylated alumina films have been synthesized by water oxidation of single crystal Al(110) surfaces. Thermal dehydroxylation results in anion vacancies which produce an Al(3s) defect state 3.5 eV below the conduction band edge. A maximum in the defect-DOS occurs for oxides heated to 350 to 400C, which is where the materials exhibit maximum Lewis acidity with respect to C{sub 2}H{sub 4}. Adsorbed C{sub 2}H{sub 4} produces thermally active C{sub 2} species which interact covalently with the defect-DOS and nonbonding O(2p) from the top of the valence band. C(1s) binding energies suggest significant charge transfer which is consistent with a carbenium ion. Ni evaporated onto the surface, however, transfers charge directly to Al species and does not interact with O atoms at the defect site. The defect-DOS is regenerated when the C{sub 2} species decomposes or when Ni migrates thermally through the oxide layer.

  16. Thin Film Structure of Tetraceno[2,3-B]thiophene Characterized By Grazing Incidence X-Ray Scattering And Near-Edge X-Ray Absorption Fine Structure Analysis

    SciTech Connect

    Yuan, Q.; Mannsfeld, S.C.B.; Tang, M.L.; Toney, M.F.; Luening, J.; Bao, Z.A.; /Stanford U., Chem. Eng. /SLAC, SSRL

    2009-05-11

    Understanding the structure-property relationship for organic semiconductors is crucial in rational molecular design and organic thin film process control. Charge carrier transport in organic field-effect transistors predominantly occurs in a few semiconductor layers close to the interface in contact with the dielectric layer, and the transport properties depend sensitively on the precise molecular packing. Therefore, a better understanding of the impact of molecular packing and thin film morphology in the first few monolayers above the dielectric layer on charge transport is needed to improve the transistor performance. In this Article, we show that the detailed molecular packing in thin organic semiconductor films can be solved through a combination of grazing incidence X-ray diffraction (GIXD), near-edge X-ray absorption spectra fine structure (NEXAFS) spectroscopy, energy minimization packing calculations, and structure refinement of the diffraction data. We solve the thin film structure for 2 and 20 nm thick films of tetraceno[2,3-b]thiophene and detect only a single phase for these thicknesses. The GIXD yields accurate unit cell dimensions, while the precise molecular arrangement in the unit cell was found from the energy minimization and structure refinement; the NEXAFS yields a consistent molecular tilt. For the 20 nm film, the unit cell is triclinic with a = 5.96 A, b = 7.71 A, c = 15.16 A, alpha = 97.30 degrees, beta = 95.63 degrees, gamma = 90 degrees; there are two molecules per unit cell with herringbone packing (49-59 degree angle) and tilted about 7 degrees from the substrate normal. The thin film structure is significantly different from the bulk single-crystal structure, indicating the importance of characterizing thin film to correlate with thin film device performance. The results are compared to the corresponding data for the chemically similar and widely used pentacene. Possible effects of the observed thin film structure and morphology on

  17. The edges of graphene.

    PubMed

    Zhang, Xiuyun; Xin, John; Ding, Feng

    2013-04-01

    The edge of two dimensional (2D) graphene, as the surface of a three dimensional (3D) crystal, plays a crucial role in the determination of its physical, electronic and chemical properties and thus has been extensively studied recently. In this review, we summarize the recent advances in the study of graphene edges, including edge formation energy, edge reconstruction, method of graphene edge synthesis and the recent progress on metal-passivated graphene edges and the role of edges in graphene CVD growth. We expect this review to provide a guideline for readers to gain a clear picture of graphene edges from several aspects, especially the catalyst-passivated graphene edges and their role in graphene CVD growth. PMID:23420074

  18. The edges of graphene

    NASA Astrophysics Data System (ADS)

    Zhang, Xiuyun; Xin, John; Ding, Feng

    2013-03-01

    The edge of two dimensional (2D) graphene, as the surface of a three dimensional (3D) crystal, plays a crucial role in the determination of its physical, electronic and chemical properties and thus has been extensively studied recently. In this review, we summarize the recent advances in the study of graphene edges, including edge formation energy, edge reconstruction, method of graphene edge synthesis and the recent progress on metal-passivated graphene edges and the role of edges in graphene CVD growth. We expect this review to provide a guideline for readers to gain a clear picture of graphene edges from several aspects, especially the catalyst-passivated graphene edges and their role in graphene CVD growth.

  19. Study of internal energy flows in dipole vortex beams by knife edge test

    NASA Astrophysics Data System (ADS)

    Singh, Brijesh Kumar; Bahl, Monika; Mehta, Dalip Singh; Senthilkumaran, Paramasivam

    2013-04-01

    The rotation of Poynting vector in dipole vortex beam (DVB) during propagation has been experimentally detected in a knife edge test. The dipole vortex beam is generated, when a collimated laser beam is incident on a phase mask, displayed on spatial light modulator (SLM) in reflection mode. The knife edge test reveals dipole configurations through strikingly distinct intensity intrusions in the geometrical shadow region.

  20. TYPES OF SALT MARSH EDGE AND EXPORT OF TROPHIC ENERGY FROM MARSHES TO DEEPER HABITATS

    EPA Science Inventory

    We quantified nekton and estimated trophic export at salt marshes with both erosional and depositional edges at the Goodwin Islands (York River, Virginia, USA). At depositional-edge marshes, we examined trophic flows through quantitative sampling with 1.75 m2 drop rings, and thro...

  1. Compression Behavior and Energy Absorption of Aluminum Alloy AA6061 Tubes with Multiple Holes

    NASA Astrophysics Data System (ADS)

    Simhachalam, Bade; Lakshmana Rao, C.; Srinivas, Krishna

    2014-05-01

    In this article, compression behavior and energy absorption of aluminum alloy AA6061 tubes are investigated both experimentally and numerically. Static and dynamic simulations are done using LS-Dyna Software for AA6061 tubes. True stress-plastic strain curves from the tensile test are used in the static and dynamic simulations of AA6061 tubes. The energy absorption values between experimental compression results and numeral simulation are found to be in good agreement. Dynamic simulations are done with drop velocity of up to 10 m/s to understand the inertia effects on energy absorption. The deformed modes from the numerical simulation are compared between tubes with and without holes in static and dynamic conditions.

  2. Load-limiting landing gear footpad energy absorption system

    NASA Technical Reports Server (NTRS)

    Hansen, Chris; Tsai, Ted

    1994-01-01

    As a precursor to future manned missions to the moon, an inexpensive, unmanned vehicle that could carry small, scientific payloads to the lunar surface was studied by NASA. The vehicle, called the Common Lunar Lander, required extremely optimized structural systems to increase the potential payload mass. A lightweight energy-absorbing system (LAGFEAS), which also acts as a landing load-limiter was designed to help achieve this optimized structure. Since the versatile and easily tailored system is a load-limiter, it allowed for the structure to be designed independently of the ever-changing landing energy predictions. This paper describes the LAGFEAS system and preliminary verification testing performed at NASA's Johnson Space Center for the Common Lunar Lander program.

  3. Energy absorption at high strain rate of glass fiber reinforced mortars

    NASA Astrophysics Data System (ADS)

    Fenu, Luigi; Forni, Daniele; Cadoni, Ezio

    2015-09-01

    In this paper, the dynamic behaviour of cement mortars reinforced with glass fibers was studied. The influence of the addition of glass fibers on energy absorption and tensile strength at high strain-rate was investigated. Static tests in compression, in tension and in bending were first performed. Dynamic tests by means of a Modified Hopkinson Bar were then carried out in order to investigate how glass fibers affected energy absorption and tensile strength at high strain-rate of the fiber reinforced mortar. The Dynamic Increase Factor (DIF) was finally evaluated.

  4. Coupling continuous damage and debris fragmentation for energy absorption prediction by cfrp structures during crushing

    NASA Astrophysics Data System (ADS)

    Espinosa, Christine; Lachaud, Frédéric; Limido, Jérome; Lacome, Jean-Luc; Bisson, Antoine; Charlotte, Miguel

    2015-05-01

    Energy absorption during crushing is evaluated using a thermodynamic based continuum damage model inspired from the Matzenmiller-Lubliner-Taylors model. It was found that for crash-worthiness applications, it is necessary to couple the progressive ruin of the material to a representation of the matter openings and debris generation. Element kill technique (erosion) and/or cohesive elements are efficient but not predictive. A technique switching finite elements into discrete particles at rupture is used to create debris and accumulated mater during the crushing of the structure. Switching criteria are evaluated using the contribution of the different ruin modes in the damage evolution, energy absorption, and reaction force generation.

  5. Modeling of particle and energy transport in the edge plasma of Alcator C-Mod

    NASA Astrophysics Data System (ADS)

    Umansky, M. V.; Krasheninnikov, S. I.; LaBombard, B.; Lipschultz, B.; Terry, J. L.

    1999-07-01

    In the present study recycling and transport in the edge plasma of Alcator C-Mod [I. H. Hutchinson et al., Phys. Plasmas 1, 1511 (1994)] is modeled and analyzed with the multi-fluid code UEDGE [T. D. Rognlien et al., J. Nucl. Mater. 196-198, 347 (1992)]. Matching the experimental plasma density profiles in the scrape-off layer (SOL) requires a spatially dependent effective anomalous diffusion coefficient D⊥ growing rapidly towards the wall. The midplane pressure of neutral gas, Pmid, is a key parameter that reflects the magnitude of anomalous transport of plasma from the core. Recycling of plasma on the main chamber wall appears to be quite significant, especially in the case of high Pmid˜0.3 mTorr when the main wall provides ˜70% of recycling neutrals in the main chamber. In the upper SOL (well above the x point) draining of particles by the poloidal flow is weak and thus the particle balance is predominantly radial. For the radial heat transport it is found that energy flux carried by radial plasma convection and by charge-exchange (CX) neutrals is quite significant in SOL. In the high Pmid case, heat conduction by CX neutrals along with radial heat convection by plasma carries most of the power flux (˜75%) across the last closed flux surface. Even in the low Pmid case, heat conduction by CX neutrals dominates the radial heat flux far out in the SOL.

  6. Higher-order symmetry energy of nuclear matter and the inner edge of neutron star crusts

    NASA Astrophysics Data System (ADS)

    Seif, W. M.; Basu, D. N.

    2014-02-01

    The parabolic approximation to the equation of state of the isospin asymmetric nuclear matter (ANM) is widely used in the literature to make predictions for the nuclear structure and the neutron star properties. Based on the realistic M3Y-Paris and M3Y-Reid nucleon-nucleon interactions, we investigate the effects of the higher-order symmetry energy on the proton fraction in neutron stars and the location of the inner edge of their crusts and their core-crust transition density and pressure, thermodynamically. Analytical expressions for different-order symmetry energy coefficients of ANM are derived using the realistic interactions mentioned above. It is found that the higher-order terms of the symmetry-energy coefficients up to its eighth order (Esym8) contributes substantially to the proton fraction in β-stable neutron star matter at different nuclear matter densities, the core-crust transition density and pressure. Even by considering the symmetry-energy coefficients up to Esym8, we obtain a significant change of about 40% in the transition pressure value from the one based on the exact equation of state. The slope parameters of the symmetry energies for the M3Y-Paris (Reid) interaction, at the saturation density, are L =47.51(50.98), L4=-0.47(-1.43), L6=0.58(0.67), and L8=0.126(0.133) MeV. Using equations of state based on both Paris and Reid effective interactions which provide saturation incompressibility of symmetric nuclear matter in the range of 220≤K0≤270 MeV, we estimate the ranges 0.090≤ρt≤0.095fm-3 and 0.49≤Pt≤0.59MeVfm-3 for the liquid-core-solid-crust transition density and pressure, respectively. The corresponding range of the proton fraction obtained at this ρt range is 0.029≤xp (t)≤0.032.

  7. Sulfur K-Edge X-Ray Absorption Spectroscopy And Density Functional Theory Calculations on Superoxide Reduc Tase: Role of the Axial Thiolate in Reactivity

    SciTech Connect

    Dey, A.; Jenney, F.E., Jr.; Adams, M.W.; Johnson, M.K.; Hodgson, K.O.; Hedman, B.; Solomon, E.I.; /Stanford U., Chem. Dept. /Athens U. /SLAC, SSRL

    2007-10-26

    Superoxide reductase (SOR) is a non-heme iron enzyme that reduces superoxide to peroxide at a diffusion-controlled rate. Sulfur K-edge X-ray absorption spectroscopy (XAS) is used to investigate the ground-state electronic structure of the resting high-spin and CN{sup -} bound low-spin Fe{sup III} forms of the 1Fe SOR from Pyrococcus furiosus. A computational model with constrained imidazole rings (necessary for reproducing spin states), H-bonding interaction to the thiolate (necessary for reproducing Fe-S bond covalency of the high-spin and low-spin forms), and H-bonding to the exchangeable axial ligand (necessary to reproduce the ground state of the low-spin form) was developed and then used to investigate the enzymatic reaction mechanism. Reaction of the resting ferrous site with superoxide and protonation leading to a high-spin Fe{sup III}-OOH species and its subsequent protonation resulting in H2O2 release is calculated to be the most energetically favorable reaction pathway. Our results suggest that the thiolate acts as a covalent anionic ligand. Replacing the thiolate with a neutral noncovalent ligand makes protonation very endothermic and greatly raises the reduction potential. The covalent nature of the thiolate weakens the Fe{sup III} bond to the proximal oxygen of this hydroperoxo species, which raises its pKa by an additional 5 log units relative to the pK{sub a} of a primarily anionic ligand, facilitating its protonation. A comparison with cytochrome P450 indicates that the stronger equatorial ligand field from the porphyrin results in a low-spin Fe{sup III}-OOH species that would not be capable of efficient H2O2 release due to a spin-crossing barrier associated with formation of a high-spin 5C Fe{sup III} product. Additionally, the presence of the dianionic porphyrin {pi} ring in cytochrome P450 allows O-O heterolysis, forming an Fe{sup IV}-oxo porphyrin radical species, which is calculated to be extremely unfavorable for the non-heme SOR ligand

  8. Intestinal triacylglycerol synthesis in fat absorption and systemic energy metabolism.

    PubMed

    Yen, Chi-Liang Eric; Nelson, David W; Yen, Mei-I

    2015-03-01

    The intestine plays a prominent role in the biosynthesis of triacylglycerol (triglyceride; TAG). Digested dietary TAG is repackaged in the intestine to form the hydrophobic core of chylomicrons, which deliver metabolic fuels, essential fatty acids, and other lipid-soluble nutrients to the peripheral tissues. By controlling the flux of dietary fat into the circulation, intestinal TAG synthesis can greatly impact systemic metabolism. Genes encoding many of the enzymes involved in TAG synthesis have been identified. Among TAG synthesis enzymes, acyl-CoA:monoacylglycerol acyltransferase 2 and acyl-CoA:diacylglycerol acyltransferase (DGAT)1 are highly expressed in the intestine. Their physiological functions have been examined in the context of whole organisms using genetically engineered mice and, in the case of DGAT1, specific inhibitors. An emerging theme from recent findings is that limiting the rate of TAG synthesis in the intestine can modulate gut hormone secretion, lipid metabolism, and systemic energy balance. The underlying mechanisms and their implications for humans are yet to be explored. Pharmacological inhibition of TAG hydrolysis in the intestinal lumen has been employed to combat obesity and associated disorders with modest efficacy and unwanted side effects. The therapeutic potential of inhibiting specific enzymes involved in intestinal TAG synthesis warrants further investigation. PMID:25231105

  9. Intestinal triacylglycerol synthesis in fat absorption and systemic energy metabolism

    PubMed Central

    Yen, Chi-Liang Eric; Nelson, David W.; Yen, Mei-I

    2015-01-01

    The intestine plays a prominent role in the biosynthesis of triacylglycerol (triglyceride; TAG). Digested dietary TAG is repackaged in the intestine to form the hydrophobic core of chylomicrons, which deliver metabolic fuels, essential fatty acids, and other lipid-soluble nutrients to the peripheral tissues. By controlling the flux of dietary fat into the circulation, intestinal TAG synthesis can greatly impact systemic metabolism. Genes encoding many of the enzymes involved in TAG synthesis have been identified. Among TAG synthesis enzymes, acyl-CoA:monoacylglycerol acyltransferase 2 and acyl-CoA:diacylglycerol acyltransferase (DGAT)1 are highly expressed in the intestine. Their physiological functions have been examined in the context of whole organisms using genetically engineered mice and, in the case of DGAT1, specific inhibitors. An emerging theme from recent findings is that limiting the rate of TAG synthesis in the intestine can modulate gut hormone secretion, lipid metabolism, and systemic energy balance. The underlying mechanisms and their implications for humans are yet to be explored. Pharmacological inhibition of TAG hydrolysis in the intestinal lumen has been employed to combat obesity and associated disorders with modest efficacy and unwanted side effects. The therapeutic potential of inhibiting specific enzymes involved in intestinal TAG synthesis warrants further investigation. PMID:25231105

  10. Energy Bandgap and Edge States in an Epitaxially Grown Graphene/h-BN Heterostructure.

    PubMed

    Hwang, Beomyong; Hwang, Jeongwoon; Yoon, Jong Keon; Lim, Sungjun; Kim, Sungmin; Lee, Minjun; Kwon, Jeong Hoon; Baek, Hongwoo; Sung, Dongchul; Kim, Gunn; Hong, Suklyun; Ihm, Jisoon; Stroscio, Joseph A; Kuk, Young

    2016-01-01

    Securing a semiconducting bandgap is essential for applying graphene layers in switching devices. Theoretical studies have suggested a created bulk bandgap in a graphene layer by introducing an asymmetry between the A and B sub-lattice sites. A recent transport measurement demonstrated the presence of a bandgap in a graphene layer where the asymmetry was introduced by placing a graphene layer on a hexagonal boron nitride (h-BN) substrate. Similar bandgap has been observed in graphene layers on metal substrates by local probe measurements; however, this phenomenon has not been observed in graphene layers on a near-insulating substrate. Here, we present bulk bandgap-like features in a graphene layer epitaxially grown on an h-BN substrate using scanning tunneling spectroscopy. We observed edge states at zigzag edges, edge resonances at armchair edges, and bandgap-like features in the bulk. PMID:27503427

  11. Energy Bandgap and Edge States in an Epitaxially Grown Graphene/h-BN Heterostructure

    PubMed Central

    Hwang, Beomyong; Hwang, Jeongwoon; Yoon, Jong Keon; Lim, Sungjun; Kim, Sungmin; Lee, Minjun; Kwon, Jeong Hoon; Baek, Hongwoo; Sung, Dongchul; Kim, Gunn; Hong, Suklyun; Ihm, Jisoon; Stroscio, Joseph A.; Kuk, Young

    2016-01-01

    Securing a semiconducting bandgap is essential for applying graphene layers in switching devices. Theoretical studies have suggested a created bulk bandgap in a graphene layer by introducing an asymmetry between the A and B sub-lattice sites. A recent transport measurement demonstrated the presence of a bandgap in a graphene layer where the asymmetry was introduced by placing a graphene layer on a hexagonal boron nitride (h-BN) substrate. Similar bandgap has been observed in graphene layers on metal substrates by local probe measurements; however, this phenomenon has not been observed in graphene layers on a near-insulating substrate. Here, we present bulk bandgap-like features in a graphene layer epitaxially grown on an h-BN substrate using scanning tunneling spectroscopy. We observed edge states at zigzag edges, edge resonances at armchair edges, and bandgap-like features in the bulk. PMID:27503427

  12. Energy Bandgap and Edge States in an Epitaxially Grown Graphene/h-BN Heterostructure

    NASA Astrophysics Data System (ADS)

    Hwang, Beomyong; Hwang, Jeongwoon; Yoon, Jong Keon; Lim, Sungjun; Kim, Sungmin; Lee, Minjun; Kwon, Jeong Hoon; Baek, Hongwoo; Sung, Dongchul; Kim, Gunn; Hong, Suklyun; Ihm, Jisoon; Stroscio, Joseph A.; Kuk, Young

    2016-08-01

    Securing a semiconducting bandgap is essential for applying graphene layers in switching devices. Theoretical studies have suggested a created bulk bandgap in a graphene layer by introducing an asymmetry between the A and B sub-lattice sites. A recent transport measurement demonstrated the presence of a bandgap in a graphene layer where the asymmetry was introduced by placing a graphene layer on a hexagonal boron nitride (h-BN) substrate. Similar bandgap has been observed in graphene layers on metal substrates by local probe measurements; however, this phenomenon has not been observed in graphene layers on a near-insulating substrate. Here, we present bulk bandgap-like features in a graphene layer epitaxially grown on an h-BN substrate using scanning tunneling spectroscopy. We observed edge states at zigzag edges, edge resonances at armchair edges, and bandgap-like features in the bulk.

  13. Energy-absorption capability of composite tubes and beams. Ph.D. Thesis

    NASA Technical Reports Server (NTRS)

    Farley, Gary L.; Jones, Robert M.

    1989-01-01

    In this study the objective was to develop a method of predicting the energy-absorption capability of composite subfloor beam structures. Before it is possible to develop such an analysis capability, an in-depth understanding of the crushing process of composite materials must be achieved. Many variables affect the crushing process of composite structures, such as the constituent materials' mechanical properties, specimen geometry, and crushing speed. A comprehensive experimental evaluation of tube specimens was conducted to develop insight into how composite structural elements crush and what are the controlling mechanisms. In this study the four characteristic crushing modes, transverse shearing, brittle fracturing, lamina bending, and local buckling were identified and the mechanisms that control the crushing process defined. An in-depth understanding was developed of how material properties affect energy-absorption capability. For example, an increase in fiber and matrix stiffness and failure strain can, depending upon the configuration of the tube, increase energy-absorption capability. An analysis to predict the energy-absorption capability of composite tube specimens was developed and verified. Good agreement between experiment and prediction was obtained.

  14. Estimation of neutron energy for first resonance from absorption cross section for thermal neutrons

    NASA Technical Reports Server (NTRS)

    Bogart, Donald

    1951-01-01

    Examination of published data for some 52 isotopes indicates that the neutron energy for which the first resonance occurs is related to the magnitude of the thermal absorption cross section. The empirical relation obtained is in qualitative agreement with the results of a simplified version of the resonance theory of the nucleus of Breit-Wigner.

  15. Observation of the surface 4f state of CePd{sub 7} by means of the resonant-inverse-photoemission study at the Ce 4d absorption edge

    SciTech Connect

    Kanai, K.; Tezuka, Y.; Fujisawa, M.; Harada, Y.; Shin, S.; Schmerber, G.; Kappler, J.P.; Parlebas, J.C.; Kotani, A.

    1997-01-01

    The resonant inverse photoemission study (RIPES) of CePd{sub 7}, has been carried out at the Ce 4d{r_arrow}4f absorption edge. The strong resonant enhancement of the 4f cross section enables us to distinguish two 4f components in the empty electronic state near the Fermi level. The incidence-angle dependence of the RIPES indicates a clear difference between ground-state configurations at the bulk and surface. It is found that the former shows a strongly hybridized 4f state, while the latter shows a localized 4f character. The angle dependence of the RIPES of {alpha}-Ce metal has been also carried out and similar results as those of CePd{sub 7} were obtained. The RIPES at the Ce 4d{r_arrow}4f edge is found to be a powerful method to investigate the surface 4f state. {copyright} {ital 1997} {ital The American Physical Society}

  16. Bandgap and optical absorption edge of GaAs{sub 1−x}Bi{sub x} alloys with 0 < x < 17.8%

    SciTech Connect

    Masnadi-Shirazi, M.; Lewis, R. B.; Bahrami-Yekta, V.; Tiedje, T.; Chicoine, M.; Servati, P.

    2014-12-14

    The compositional dependence of the fundamental bandgap of pseudomorphic GaAs{sub 1−x}Bi{sub x} layers on GaAs substrates is studied at room temperature by optical transmission and photoluminescence spectroscopies. All GaAs{sub 1−x}Bi{sub x} films (0 ≤ x ≤ 17.8%) show direct optical bandgaps, which decrease with increasing Bi content, closely following density functional theory predictions. The smallest measured bandgap is 0.52 eV (∼2.4 μm) at 17.8% Bi. Extrapolating a fit to the data, the GaAs{sub 1−x}Bi{sub x} bandgap is predicted to reach 0 eV at 35% Bi. Below the GaAs{sub 1−x}Bi{sub x} bandgap, exponential absorption band tails are observed with Urbach energies 3–6 times larger than that of bulk GaAs. The Urbach parameter increases with Bi content up to 5.5% Bi, and remains constant at higher concentrations. The lattice constant and Bi content of GaAs{sub 1−x}Bi{sub x} layers (0 < x ≤ 19.4%) are studied using high resolution x-ray diffraction and Rutherford backscattering spectroscopy. The relaxed lattice constant of hypothetical zincblende GaBi is estimated to be 6.33 ± 0.05 Å, from extrapolation of the Rutherford backscattering spectrometry and x-ray diffraction data.

  17. Absorption of Solar Energy in the Atmosphere: Discrepancy Between Model and Observations

    PubMed

    Arking

    1996-08-01

    An atmospheric general circulation model, which assimilates data from daily observations of temperature, humidity, wind, and sea-level air pressure, was compared with a set of observations that combines satellite and ground-based measurements of solar flux. The comparison reveals that the model underestimates by 25 to 30 watts per square meter the amount of solar energy absorbed by Earth's atmosphere. Contrary to some recent reports, clouds have little or no overall effect on atmospheric absorption, a consistent feature of both the observations and the model. Of several variables considered, water vapor appears to be the dominant influence on atmospheric absorption. PMID:8670414

  18. Energy absorption ability of buckyball C720 at low impact speed: a numerical study based on molecular dynamics

    PubMed Central

    2013-01-01

    The dynamic impact response of giant buckyball C720 is investigated by using molecular dynamics simulations. The non-recoverable deformation of C720 makes it an ideal candidate for high-performance energy absorption. Firstly, mechanical behaviors under dynamic impact and low-speed crushing are simulated and modeled, which clarifies the buckling-related energy absorption mechanism. One-dimensional C720 arrays (both vertical and horizontal alignments) are studied at various impact speeds, which show that the energy absorption ability is dominated by the impact energy per buckyball and less sensitive to the number and arrangement direction of buckyballs. Three-dimensional stacking of buckyballs in simple cubic, body-centered cubic, hexagonal, and face-centered cubic forms are investigated. Stacking form with higher occupation density yields higher energy absorption. The present study may shed lights on employing C720 assembly as an advanced energy absorption system against low-speed impacts. PMID:23360618

  19. Fermi level stabilization and band edge energies in Cd{sub x}Zn{sub 1−x}O alloys

    SciTech Connect

    Detert, Douglas M.; Tom, Kyle B.; Dubon, Oscar D.; Battaglia, Corsin; Javey, Ali; Denlinger, Jonathan D.; Lim, Sunnie H. N.; Anders, André; Yu, Kin M.; Walukiewicz, Wladek

    2014-06-21

    We have measured the band edge energies of Cd{sub x}Zn{sub 1−x}O thin films as a function of composition by three independent techniques: we determine the Fermi level stabilization energy by pinning the Fermi level with ion irradiation, measure the binding energy of valence band states and core levels by X-ray photoelectron spectroscopy, and probe shifts in the conduction band and valence band density of states using soft X-ray absorption and emission spectroscopy, respectively. The three techniques find consensus in explaining the origin of compositional trends in the optical-bandgap narrowing upon Cd incorporation in wurtzite ZnO and widening upon Zn incorporation in rocksalt CdO. The conduction band minimum is found to be stationary for both wurtzite and rocksalt alloys, and a significant upward rise of the valence band maximum accounts for the majority of these observed bandgap changes. Given these band alignments, alloy disorder scattering is found to play a negligible role in decreasing the electron mobility for all alloys. These band alignment details, combined with the unique optical and electrical properties of the two phase regimes, make CdZnO alloys attractive candidates for photoelectrochemical water splitting applications.

  20. Mn L{sub 2,3}-edge X-ray absorption spectroscopic studies on charge-discharge mechanism of Li{sub 2}MnO{sub 3}

    SciTech Connect

    Kubobuchi, Kei; Mogi, Masato; Imai, Hideto; Ikeno, Hidekazu; Tanaka, Isao; Mizoguchi, Teruyasu

    2014-02-03

    The redox reaction of Mn in Li{sub 2}MnO{sub 3} was studied by X-ray absorption spectroscopy and ab initio multiplet calculation. Associated with the de-intercalation of Li-ion, small but clear spectral changes were observed in Mn-L{sub 2,3} X-ray absorption near edge structure (XANES). The systematic ab initio multiplet calculations of Mn-L{sub 2,3} XANES revealed that the spectral changes in the experiment could not simply be ascribed to the change of the valency from Mn{sup 4+} to Mn{sup 5+} but can be explained well by the changes of local atomic structures around Mn{sup 4+} due to the Li de-intercalation. Our results suggest that the electronic state of oxygen should change during charging in Li{sub 2}MnO{sub 3}.

  1. Diurnal Variation and Spatial Distribution Effects on Sulfur Speciation in Aerosol Samples as Assessed by X-Ray Absorption Near-Edge Structure (XANES)

    PubMed Central

    Pongpiachan, Siwatt; Thumanu, Kanjana; Na Pattalung, Warangkana; Hirunyatrakul, Phoosak; Kittikoon, Itthipon; Ho, Kin Fai; Cao, Junji

    2012-01-01

    This paper focuses on providing new results relating to the impacts of Diurnal variation, Vertical distribution, and Emission source on sulfur K-edge XANES spectrum of aerosol samples. All aerosol samples used in the diurnal variation experiment were preserved using anoxic preservation stainless cylinders (APSCs) and pressure-controlled glove boxes (PCGBs), which were specially designed to prevent oxidation of the sulfur states in PM10. Further investigation of sulfur K-edge XANES spectra revealed that PM10 samples were dominated by S(VI), even when preserved in anoxic conditions. The “Emission source effect” on the sulfur oxidation state of PM10 was examined by comparing sulfur K-edge XANES spectra collected from various emission sources in southern Thailand, while “Vertical distribution effects” on the sulfur oxidation state of PM10 were made with samples collected from three different altitudes from rooftops of the highest buildings in three major cities in Thailand. The analytical results have demonstrated that neither “Emission source” nor “Vertical distribution” appreciably contribute to the characteristic fingerprint of sulfur K-edge XANES spectrum in PM10. PMID:22988545

  2. Study and Development of near-Infrared Reflective and Absorptive Materials for Energy Saving Application

    NASA Astrophysics Data System (ADS)

    Cui, Yu Xing

    Near-Infrared (NIR) materials find applications in the field of energy saving. Both NIR reflective and absorptive materials can be used as energy saving materials with different working principles. The reflective materials can reflect the NIR light preventing it from being transmitted. Silver thin films are the best option as reflective films based on its reflectivity and cost. On the other hand, NIR absorptive materials can effectively convert the absorbed NIR light from sunlight to heat or electric energy. The first part of this research explored methods of preparing silver thin films that could be processed at low cost. The second part involved the design, synthesis and characterization of nickel coordination polymers as NIR absorptive materials. In part 1, different solution based methods of preparing silver thin films were studied. A silver nanoparticles solution was used to make thin film by a spray-pyrolysis process. Another method involved the surface activation with a fluoro-compound or silver nanoparticles followed by electroless silver plating on different substrates. Both methods could be processed at low cost. The obtained silver films showed NIR reflection of 50˜90% with transmission of 15-28% in the visible region. In part 2, two Nickel coordination polymers were explored. Tetraamino compounds were used as bridging ligands to increase the scope of electronic delocalization and metal-ligand orbital overlap which would reduce the energy gap to the NIR region. As a result, both polymers showed broad NIR absorption with maximum of 835 and 880 nm, respectively. In addition, the polymer showed NIR halochromism. This ground study pointed out both Ni coordination polymers as NIR absorptive materials with NIR halochromism.

  3. Supporting Structure of the LSD Wave in an Energy Absorption Perspective

    NASA Astrophysics Data System (ADS)

    Fukui, Akihiro; Hatai, Keigo; Cho, Shinatora; Komurasaki, Kimiya; Arakawa, Yoshihiro

    2008-04-01

    In Repetitively Pulsed (RP) Laser Propulsion, laser energy irradiated to a vehicle is converted to blast wave enthalpy during the Laser Supported Detonation (LSD) regime. Based on the measured post-LSD electron number density profiles by two-wavelength Mach Zehnder interferometer in a line-focusing optics, electron temperature and absorption coefficient were estimated assuming Local Thermal Equilibrium. A 10J/pulse CO2 laser was used. As a result, laser absorption was found completed in the layer between the shock wave and the electron density peak. Although the LSD-termination timing was not clear from the shock-front/ionization-front separation in the shadowgraph images, there observed drastic changes in the absorption layer thickness from 0.2 mm to 0.5 mm and in the peak heating rate from 12-17×1013 kW/m3 to 5×1013 kW/m3 at the termination.

  4. Universality of high-energy absorption cross sections for black holes

    SciTech Connect

    Decanini, Yves; Esposito-Farese, Gilles; Folacci, Antoine

    2011-02-15

    We consider the absorption problem for a massless scalar field propagating in static and spherically symmetric black holes of arbitrary dimension endowed with a photon sphere. For this wide class of black holes, we show that the fluctuations of the high-energy absorption cross section are totally and very simply described from the properties (dispersion relation and damping) of the waves trapped near the photon sphere and therefore, in the eikonal regime, from the characteristics (orbital period and Lyapunov exponent) of the null unstable geodesics lying on the photon sphere. This is achieved by using Regge pole techniques. They permit us to make an elegant and powerful resummation of the absorption cross section and to extract then all the physical information encoded in the sum over the partial wave contributions. Our analysis induces moreover some consequences concerning Hawking radiation which we briefly report.

  5. Energy absorption buildup factors of human organs and tissues at energies and penetration depths relevant for radiotherapy and diagnostics.

    PubMed

    Manohara, S R; Hanagodimath, S M; Gerward, L

    2011-01-01

    Energy absorption geometric progression (GP) fitting parameters and the corresponding buildup factors have been computed for human organs and tissues, such as adipose tissue, blood (whole), cortical bone, brain (grey/white matter), breast tissue, eye lens, lung tissue, skeletal muscle, ovary, testis, soft tissue, and soft tissue (4-component), for the photon energy range 0.015-15 MeV and for penetration depths up to 40 mfp (mean free path). The chemical composition of human organs and tissues is seen to influence the energy absorption buildup factors. It is also found that the buildup factor of human organs and tissues changes significantly with the change of incident photon energy and effective atomic number, Z(eff). These changes are due to the dominance of different photon interaction processes in different energy regions and different chemical compositions of human organs and tissues. With the proper knowledge of buildup factors of human organs and tissues, energy absorption in the human body can be carefully controlled. The present results will help in estimating safe dose levels for radiotherapy patients and also useful in diagnostics and dosimetry. The tissue-equivalent materials for skeletal muscle, adipose tissue, cortical bone, and lung tissue are also discussed. It is observed that water and MS20 are good tissue equivalent materials for skeletal muscle in the extended energy range. PMID:22089011

  6. Investigation of human teeth with respect to the photon interaction, energy absorption and buildup factor

    NASA Astrophysics Data System (ADS)

    Kurudirek, Murat; Topcuoglu, Sinan

    2011-05-01

    The effective atomic numbers and electron densities of human teeth have been calculated for total photon interaction (Z, Ne) and photon energy absorption (Z, Z Ne) in the energy region 1 keV-20 MeV. Besides, the energy absorption (EABF) and exposure (EBF) buildup factors have been calculated for these samples by using the geometric progression fitting approximation in the energy region 0.015-15 MeV up to 40 mfp (mean free path). Wherever possible the results were compared with experiment. Effective atomic numbers ( Z) of human teeth were calculated using different methods. Discrepancies were noted in Z between the direct and interpolation methods in the low and high energy regions where absorption processes dominate while good agreement was observed in intermediate energy region where Compton scattering dominates. Significant variations up to 22% were observed between Z and Z in the energy region 30-150 keV which is the used energy range in dental cone beam computed tomography (CBCT) X-ray machines. The Zeff values of human teeth were found to relatively vary within 1% if different laser treatments are applied. In this variation, the Er:YAG laser treated samples were found to be less effected than Nd:YAG laser treated ones when compared with control group. Relative differences between EABF and EBF were found to be significantly high in the energy region 60 keV-1 MeV even though they have similar variations with respect to the different parameters viz. photon energy, penetration depth.

  7. Si K Edge Measurements of the ISM with Chandra

    NASA Astrophysics Data System (ADS)

    Schulz, Norbert S.; Corrales, Lia; Canizares, C. R.

    2016-01-01

    The Si K edge structure in X-ray spectra of the diffuse ISM is expected to exhibit substructure related to the fact that most absorption is due to silicates in dust. We surveyed high resolution X-ray spectra of a large number of bright low-mass X-ray binaries with column densities significantly larger than 10^22 cm^2. Using the to date unprecedented spectral resolution of the high energy transmission gratings onboard the Chandra X-ray observatory we find complex substructure in the Si K edge. The highest resolved spectra show two edges, one at the expected value for atomic, one at the value for most silicate compounds with the dominant contribution of the latter. There is specific subtructure from silicate optical depth caused by absorption and scattering. Some is also variable and can be attributed to ionized absorption in the vicinity of the X-ray sources.

  8. Integration of Semiconducting Sulfides for Full-Spectrum Solar Energy Absorption and Efficient Charge Separation.

    PubMed

    Zhuang, Tao-Tao; Liu, Yan; Li, Yi; Zhao, Yuan; Wu, Liang; Jiang, Jun; Yu, Shu-Hong

    2016-05-23

    The full harvest of solar energy by semiconductors requires a material that simultaneously absorbs across the whole solar spectrum and collects photogenerated electrons and holes separately. The stepwise integration of three semiconducting sulfides, namely ZnS, CdS, and Cu2-x S, into a single nanocrystal, led to a unique ternary multi-node sheath ZnS-CdS-Cu2-x S heteronanorod for full-spectrum solar energy absorption. Localized surface plasmon resonance (LSPR) in the nonstoichiometric copper sulfide nanostructures enables effective NIR absorption. More significantly, the construction of pn heterojunctions between Cu2-x S and CdS leads to staggered gaps, as confirmed by first-principles simulations. This band alignment causes effective electron-hole separation in the ternary system and hence enables efficient solar energy conversion. PMID:27062543

  9. Effect of local coordination of Mn on Mn-L2,3 edge electron energy loss spectrum

    NASA Astrophysics Data System (ADS)

    Nishida, Shuji; Kobayashi, Shunsuke; Kumamoto, Akihito; Ikeno, Hidekazu; Mizoguchi, Teruyasu; Tanaka, Isao; Ikuhara, Yuichi; Yamamoto, Takahisa

    2013-08-01

    The effects of the local coordination environment of Mn ions in perovskite manganese oxides on the Mn-L2,3 edge electron energy loss (EEL) spectra was experimentally and theoretically investigated. The Mn-L2,3 edge EEL spectra were observed for various perovskite manganese oxides, including YMnO3, LaMnO3, BaMnO3, SrMnO3, and CaMnO3, in which the Mn ions have different valence states and local coordination. The experiment revealed that the Mn L3/L2 ratio is influenced not only by the valence state but also by the local environment of the Mn ions. Furthermore, compared to the Mn L3/L2 ratios of Mn3+ compounds, the Mn L3/L2 ratios of the Mn4+ compounds are found to be much more sensitive to local distortions. The ab-initio multiplet calculation of the Mn-L2,3 edge EEL spectra revealed that the effects of local coordination on the spectral features are dependent on the local electronic structures of the Mn ions. These findings indicate that the valence state as well as the local environments of the Mn ions can be unraveled by combining experimental and theoretical investigations of Mn-L2,3 edge EEL spectra.

  10. Near-infrared photoluminescence and ligand K-edge x-ray absorption spectroscopies of AnO2Cl42-(An:u, NP, Pu)

    SciTech Connect

    Wilkerson, Marianne P; Berg, John M; Clark, David L; Conradson, Steven D; Hobart, David E; Kozimor, Stosh A; Scott, Brian L

    2008-01-01

    We have used photoluminescence and X-ray absorption spectroscopies to investigate electronic structures and metal-ligand bonding of a series of An02CI/ ' (An = U, Np, Pu) compounds. Specifically, we will discuss time-resolved near-infrared emission spectra of crystalline Cs2U(An)02C14 (An = Np and Pu) both at 23 K and 75 K, as well as chlorine Kedge X-ray absorption spectra ofCs2An02CI4 (An = U, Np).

  11. Si K Edge Structure and Variability in Galactic X-Ray Binaries

    NASA Astrophysics Data System (ADS)

    Schulz, Norbert S.; Corrales, Lia; Canizares, Claude R.

    2016-08-01

    We survey the Si K edge structure in various absorbed Galactic low-mass X-ray binaries (LMXBs) to study states of silicon in the inter- and circum-stellar medium. The bulk of these LMXBs lie toward the Galactic bulge region and all have column densities above 1022 cm‑2. The observations were performed using the Chandra High Energy Transmission Grating Spectrometer. The Si K edge in all sources appears at an energy value of 1844 ± 0.001 eV. The edge exhibits significant substructure that can be described by a near edge absorption feature at 1849 ± 0.002 eV and a far edge absorption feature at 1865 ± 0.002 eV. Both of these absorption features appear variable with equivalent widths up to several mÅ. We can describe the edge structure using several components: multiple edge functions, near edge absorption excesses from silicates in dust form, signatures from X-ray scattering optical depths, and a variable warm absorber from ionized atomic silicon. The measured optical depths of the edges indicate much higher values than expected from atomic silicon cross sections and interstellar medium abundances, and they appear consistent with predictions from silicate X-ray absorption and scattering. A comparison with models also indicates a preference for larger dust grain sizes. In many cases, we identify Si xiii resonance absorption and determine ionization parameters between log ξ = 1.8 and 2.8 and turbulent velocities between 300 and 1000 km s‑1. This places the warm absorber in close vicinity of the X-ray binaries. In some data, we observe a weak edge at 1.840 keV, potentially from a lesser contribution of neutral atomic silicon.

  12. An experimental investigation of energy absorption in TRIP steel under impact three-point bending deformation

    NASA Astrophysics Data System (ADS)

    Pham, Hang; Iwamoto, Takeshi

    2015-09-01

    TRIP (Transformation-induced Plasticity) steel is nowadays in widespread use in the automobile industry because of their favorable mechanical properties such as high strength, excellent formability and toughness because of strain-induced martensitic transformation. Moreover, when TRIP steel is applied to the components of the vehicles, it is expected that huge amount of kinetic energy will be absorbed into both plastic deformation and martensitic transformation during the collision. Basically, bending deformation due to buckling is one of the major crash deformation modes of automobile structures. Thus, an investigation of energy absorption during bending deformation at high impact velocity for TRIP steel is indispensable. Although TRIP steel have particularly attracted the recent interest of the scientific community, just few studies can be found on the energy absorption characteristic of TRIP steel, especially at impact loading condition. In present study, experimental investigations of bending deformation behaviors of TRIP steel are conducted in the three-point bending tests for both smooth and pre-cracked specimen. Then, energy absorption characteristic during plastic deformation and fracture process at high impact velocity in TRIP steel will be discussed.

  13. Strain Rate Effects on the Energy Absorption of Rapidly Manufactured Composite Tubes

    SciTech Connect

    Brighton, Aaron M; Forrest, Mark; Starbuck, J Michael; ERDMAN III, DONALD L; Fox, Bronwyn

    2009-01-01

    Quasi-static and intermediate rate axial crush tests were conducted on tubular specimens of Carbon/Epoxy (Toray T700/G83C) and Glass/Polypropylene (Twintex). The quasi-static tests were conducted at 10 mm/min (1.67x10-4 m/s); five different crush initiators were used. Tests at intermediate rates were performed at speeds of 0.25 m/s, 0.5 m/s, 0.75 m/s 1m/s, 2 m/s and 4 m/s. Quasi-static tests of tubular specimens showed high specific energy absorption (SEA) values with 86 kJ/kg for Carbon/Epoxy specimens. The specific energy absorption of the Glass/Polypropylene specimens was measured to be 29 kJ/kg. Results from the intermediate test rates showed that while a decrease in specific energy absorbed was observed as speeds increased, values did not fall below 55kj/kg for carbon specimens or 35 kJ/kg for the Glass/Polypropylene specimens. When compared with steel and aluminium, specific energy absorption values of 15 kJ/kg and 30 kJ/kg respectively, the benefits of using composite materials in crash structures are apparent.

  14. High energy X-ray phase and dark-field imaging using a random absorption mask

    PubMed Central

    Wang, Hongchang; Kashyap, Yogesh; Cai, Biao; Sawhney, Kawal

    2016-01-01

    High energy X-ray imaging has unique advantage over conventional X-ray imaging, since it enables higher penetration into materials with significantly reduced radiation damage. However, the absorption contrast in high energy region is considerably low due to the reduced X-ray absorption cross section for most materials. Even though the X-ray phase and dark-field imaging techniques can provide substantially increased contrast and complementary information, fabricating dedicated optics for high energies still remain a challenge. To address this issue, we present an alternative X-ray imaging approach to produce transmission, phase and scattering signals at high X-ray energies by using a random absorption mask. Importantly, in addition to the synchrotron radiation source, this approach has been demonstrated for practical imaging application with a laboratory-based microfocus X-ray source. This new imaging method could be potentially useful for studying thick samples or heavy materials for advanced research in materials science. PMID:27466217

  15. High energy X-ray phase and dark-field imaging using a random absorption mask.

    PubMed

    Wang, Hongchang; Kashyap, Yogesh; Cai, Biao; Sawhney, Kawal

    2016-01-01

    High energy X-ray imaging has unique advantage over conventional X-ray imaging, since it enables higher penetration into materials with significantly reduced radiation damage. However, the absorption contrast in high energy region is considerably low due to the reduced X-ray absorption cross section for most materials. Even though the X-ray phase and dark-field imaging techniques can provide substantially increased contrast and complementary information, fabricating dedicated optics for high energies still remain a challenge. To address this issue, we present an alternative X-ray imaging approach to produce transmission, phase and scattering signals at high X-ray energies by using a random absorption mask. Importantly, in addition to the synchrotron radiation source, this approach has been demonstrated for practical imaging application with a laboratory-based microfocus X-ray source. This new imaging method could be potentially useful for studying thick samples or heavy materials for advanced research in materials science. PMID:27466217

  16. Electromagnetic energy, absorption, and Casimir forces: Uniform dielectric media in thermal equilibrium

    SciTech Connect

    Rosa, F. S. S.; Dalvit, D. A. R.; Milonni, P. W.

    2010-03-15

    The derivation of Casimir forces between dielectrics can be simplified by ignoring absorption, calculating energy changes due to displacements of the dielectrics, and only then admitting absorption by allowing permittivities to be complex. As a first step toward a better understanding of this situation we consider in this article the model of a dielectric as a collection of oscillators, each of which is coupled to a reservoir giving rise to damping and Langevin forces on the oscillators and a noise polarization acting as a source of a fluctuating electromagnetic field in the dielectric. The model leads naturally to expressions for the quantized electric and magnetic fields that are consistent with those obtained in approaches that diagonalize the coupled system of oscillators for the dielectric medium, the reservoir, and the electromagnetic field. It also results in a fluctuation-dissipation relation between the noise polarization and the imaginary part of the permittivity; comparison with the Rytov fluctuation-dissipation relation employed in the well-known Lifshitz theory for the van der Waals (or Casimir) force shows that the Lifshitz theory is actually a classical stochastic electrodynamical theory. The approximate classical expression for the energy density in a band of frequencies at which absorption in a dielectric is negligible is shown to be exact as a spectral thermal equilibrium expectation value in quantum electrodynamic theory. Our main result is the derivation of an expression for the QED energy density of a uniform dispersive, absorbing media in thermal equilibrium. The spectral density of the energy is found to have the same form with or without absorption. We also show how the fluctuation-dissipation theorem ensures a detailed balance of energy exchange between the (absorbing) medium, the reservoir, and the electromagnetic field in thermal equilibrium.

  17. Element distribution and iron speciation in mature wheat grains (Triticum aestivum L.) using synchrotron X-ray fluorescence microscopy mapping and X-ray absorption near-edge structure (XANES) imaging.

    PubMed

    De Brier, Niels; Gomand, Sara V; Donner, Erica; Paterson, David; Smolders, Erik; Delcour, Jan A; Lombi, Enzo

    2016-08-01

    Several studies have suggested that the majority of iron (Fe) and zinc (Zn) in wheat grains are associated with phytate, but a nuanced approach to unravel important tissue-level variation in element speciation within the grain is lacking. Here, we present spatially resolved Fe-speciation data obtained directly from different grain tissues using the newly developed synchrotron-based technique of X-ray absorption near-edge spectroscopy imaging, coupling this with high-definition μ-X-ray fluorescence microscopy to map the co-localization of essential elements. In the aleurone, phosphorus (P) is co-localized with Fe and Zn, and X-ray absorption near-edge structure imaging confirmed that Fe is chelated by phytate in this tissue layer. In the crease tissues, Zn is also positively related to P distribution, albeit less so than in the aleurone. Speciation analysis suggests that Fe is bound to nicotianamine rather than phytate in the nucellar projection, and that more complex Fe structures may also be present. In the embryo, high Zn concentrations are present in the root and shoot primordium, co-occurring with sulfur and presumably bound to thiol groups. Overall, Fe is mainly concentrated in the scutellum and co-localized with P. This high resolution imaging and speciation analysis reveals the complexity of the physiological processes responsible for element accumulation and bioaccessibility. PMID:27038325

  18. Surface and in-depth characterization of lithium-ion battery cathodes at different cycle states using confocal micro-X-ray fluorescence-X-ray absorption near edge structure analysis

    NASA Astrophysics Data System (ADS)

    Menzel, Magnus; Schlifke, Annalena; Falk, Mareike; Janek, Jürgen; Fröba, Michael; Fittschen, Ursula Elisabeth Adriane

    2013-07-01

    The cathode material LiNi0.5Mn1.5O4 for lithium-ion batteries has been studied with confocal micro-X-ray fluorescence (CMXRF) combined with X-ray absorption near edge structure (XANES) at the Mn-K edge and the Ni-K edge. This technique allows for a non-destructive, spatially resolved (x, y and z) investigation of the oxidation states of surface areas and to some extent of deeper layers of the electrode. Until now CMXRF-XANES has been applied to a limited number of applications, mainly geo-science. Here, we introduce this technique to material science applications and show its performance to study a part of a working system. A novel mesoporous LiNi0.5Mn1.5O4 material was cycled (charged and discharged) to investigate the effects on the oxidation states at the cathode/electrolyte interface. With this approach the degradation of Mn3 + to Mn4 + only observable at the surface of the electrode could be directly shown. The spatially resolved non-destructive analysis provides knowledge helpful for further understanding of deterioration and the development of high voltage battery materials, because of its nondestructive nature it will be also suitable to monitor processes during battery cycling.

  19. Relic Neutrino Absorption Spectroscopy

    SciTech Connect

    Eberle, b

    2004-01-28

    Resonant annihilation of extremely high-energy cosmic neutrinos on big-bang relic anti-neutrinos (and vice versa) into Z-bosons leads to sizable absorption dips in the neutrino flux to be observed at Earth. The high-energy edges of these dips are fixed, via the resonance energies, by the neutrino masses alone. Their depths are determined by the cosmic neutrino background density, by the cosmological parameters determining the expansion rate of the universe, and by the large redshift history of the cosmic neutrino sources. We investigate the possibility of determining the existence of the cosmic neutrino background within the next decade from a measurement of these absorption dips in the neutrino flux. As a by-product, we study the prospects to infer the absolute neutrino mass scale. We find that, with the presently planned neutrino detectors (ANITA, Auger, EUSO, OWL, RICE, and SalSA) operating in the relevant energy regime above 10{sup 21} eV, relic neutrino absorption spectroscopy becomes a realistic possibility. It requires, however, the existence of extremely powerful neutrino sources, which should be opaque to nucleons and high-energy photons to evade present constraints. Furthermore, the neutrino mass spectrum must be quasi-degenerate to optimize the dip, which implies m{sub {nu}} 0.1 eV for the lightest neutrino. With a second generation of neutrino detectors, these demanding requirements can be relaxed considerably.

  20. Laser-driven hard-x-ray generation based on ultrafast selected energy x-ray absorption spectroscopy measurements of Ni compounds

    SciTech Connect

    Shan Fang; Carter, Josh D.; Ng, Vicky; Guo Ting

    2005-02-01

    Three Ni compounds were studied by ultrafast selected energy x-ray absorption spectroscopy using a laser-driven electron x-ray source with a tungsten target. The measured K edges of these Ni compounds using this self-referencing method were made identical to those measured with synchrotron x-ray sources. This enabled us to determine the absolute peak positions of tungsten L{alpha}{sub 1} and L{alpha}{sub 2} emitted from this source to be within 1 eV of those from the neutral tungsten atoms, which strongly suggested that the x rays were emitted from high energy electrons interacting with tungsten atoms in the solid target. This is the best evidence to date that directly supports the cold atom x-ray generation theory.

  1. Experimental development and control of magnetorheological damper towards smart energy absorption of composite structures

    NASA Astrophysics Data System (ADS)

    Lim, Shen Hin; Prusty, B. Gangadhara; Lee, Ann; Yeoh, Guan Heng

    2013-08-01

    Experimental investigation and efficient control of magnetorheological (MR) damper towards smart energy absorption of composite structures are presented in this paper. The evaluation of an existing MR damper based on the damping force presented in our earlier work is limited by the experiment configuration setup. Using two arms configuration, an experimental test rig is designed to overcome this limitation and enabled the MR damper to be investigated throughout its full velocity range capability. A controller is then developed based on the MR damper investigation to provide automated variable control of induced current with a set crushing force and available data of composite tube crushing force. The controller is assessed numerically and shows that MR damper is controlled to provide consistent crushing force despite oscillation from the composite tube crushing force. This, thus, shows promise of MR damper integration towards smart energy absorption of composite structures.

  2. A review of infrared laser energy absorption and subsequent healing in the cornea

    NASA Astrophysics Data System (ADS)

    Saunders, Latica L.; Johnson, Thomas E.; Neal, Thomas A.

    2004-07-01

    The purpose of this review is to compile information on the optical and healing properties of the cornea when exposed to infrared lasers. Our long-term goal is to optimize the treatment parameters for corneal injuries after exposure to infrared laser systems. The majority of the information currently available in the literature focuses on corneal healing after therapeutic vision correction surgery with LASIK or PRK. Only a limited amount of information is available on corneal healing after injury with an infrared laser system. In this review we will speculate on infrared photon energy absorption in corneal injury and healing to include the role of the tear layer. The aim of this review is to gain a better understanding of infrared energy absorption in the cornea and how it might impact healing.

  3. Determination of RW3-to-water mass-energy absorption coefficient ratio for absolute dosimetry.

    PubMed

    Seet, Katrina Y T; Hanlon, Peta M; Charles, Paul H

    2011-12-01

    The measurement of absorbed dose to water in a solid-phantom may require a conversion factor because it may not be radiologically equivalent to water. One phantom developed for the use of dosimetry is a solid water, RW3 white-polystyrene material by IBA. This has a lower mass-energy absorption coefficient than water due to high bremsstrahlung yield, which affects the accuracy of absolute dosimetry measurements. In this paper, we demonstrate the calculation of mass-energy absorption coefficient ratios, relative to water, from measurements in plastic water and RW3 with an Elekta Synergy linear accelerator (6 and 10 MV photon beams) as well as Monte Carlo modeling in BEAMnrc and DOSXYZnrc. From this, the solid-phantom-to-water correction factor was determined for plastic water and RW3. PMID:21960410

  4. Efficient energy absorption of intense ps-laser pulse into nanowire target

    NASA Astrophysics Data System (ADS)

    Habara, H.; Honda, S.; Katayama, M.; Sakagami, H.; Nagai, K.; Tanaka, K. A.

    2016-06-01

    The interaction between ultra-intense laser light and vertically aligned carbon nanotubes is investigated to demonstrate efficient laser-energy absorption in the ps laser-pulse regime. Results indicate a clear enhancement of the energy conversion from laser to energetic electrons and a simultaneously small plasma expansion on the surface of the target. A two-dimensional plasma particle calculation exhibits a high absorption through laser propagation deep into the nanotube array, even for a dense array whose structure is much smaller than the laser wavelength. The propagation leads to the radial expansion of plasma perpendicular to the nanotubes rather than to the front side. These features may contribute to fast ignition in inertial confinement fusion and laser particle acceleration, both of which require high current and small surface plasma simultaneously.

  5. Solar energy absorption characteristics and the effects of heat on the optical properties of several coatings

    NASA Technical Reports Server (NTRS)

    Lowery, J. R.

    1981-01-01

    The solar energy absorption characteristics of several high temperature coatings were determined and effects of heat on these coatings were evaluated. Included in the investigation were an electroplated alloy of black chrome and vanadium, electroplated black chrome, and chemically colored 316 stainless steel. Each of the coatings possessed good selective solar energy absorption properties at laboratory ambient temperature. Measured at a temperature of 700 K (800 F), the emittances of black chrome, black chrome vanadium, and colored stainless steel were 0.11, 0.61, and 0.15, respectively. Black chrome and black chrome vanadium did not degrade optically in the presence of high heat (811 K (1000 F)). Chemically colored stainless steel showed slight optical degradation when exposed to moderately high heat (616 K (650 F)0, but showed more severe degradation at exposure temperatures beyond this level. Each of the coatings showed good corrosion resistance to a salt spray environment.

  6. Near-coincident K-line and K-edge energies as ionization diagnostics for some high atomic number plasmas

    SciTech Connect

    Pereira, N. R.; Weber, B. V.; Phipps, D. G.; Schumer, J. W.; Seely, J. F.; Carroll, J. J.; Vanhoy, J. R.; Slabkowska, K.; Polasik, M.

    2012-10-15

    For some high atomic number atoms, the energy of the K-edge is tens of eVs higher than the K-line energy of another atom, so that a few eV increase in the line's energy results in a decreasing transmission of the x-ray through a filter of the matching material. The transmission of cold iridium's Asymptotically-Equal-To 63.287 keV K{alpha}{sub 2} line through a lutetium filter is 7% lower when emitted by ionized iridium, consistent with an energy increase of {Delta}{epsilon} Asymptotically-Equal-To 10{+-}1 eV associated with the ionization. Likewise, the transmission of the K{beta}{sub 1} line of ytterbium through a near-coincident K-edge filter changes depending on plasma parameters that should affect the ionization. Systematic exploration of filter-line pairs like these could become a unique tool for diagnostics of suitable high energy density plasmas.

  7. Nonlinear ionization mechanism dependence of energy absorption in diamond under femtosecond laser irradiation

    SciTech Connect

    Wang Cong; Jiang Lan; Li Xin; Wang Feng; Yuan Yanping; Lu Yongfeng

    2013-04-14

    We present first-principles calculations for nonlinear photoionization of diamond induced by the intense femtosecond laser field. A real-time and real-space time-dependent density functional theory with the adiabatic local-density approximation is applied to describe the laser-material interactions in the Kohn-Sham formalism with the self-interaction correction. For a certain laser wavelength, the intensity dependence of energy absorption on multiphoton and/or tunnel ionization mechanisms is investigated, where laser intensity regions vary from 10{sup 12} W/cm{sup 2} to 10{sup 16} W/cm{sup 2}. In addition, the effect of laser wavelength on energy absorption at certain ionization mechanism is discussed when the Keldysh parameter is fixed. Theoretical results show that: (1) at the fixed laser wavelength, the relationship between the energy absorption and laser intensity shows a good fit of E = c{sub M}I{sup N} (N is the number of photons absorbed to free from the valence band) when multiphoton ionization dominates; (2) while when tunnel ionization becomes significant, the relationship coincides with the expression of E = c{sub T}I{sup n} (n < N).

  8. Atomic Resolution Mapping of the Excited-State Electronic Structure of Cu2O with Time-Resolved X-Ray Absorption Spectroscopy

    SciTech Connect

    Hillyard, Patrick B.; Kuchibhatla, Satyanarayana V N T; Glover, T. E.; Hertlein, M. P.; Huse, N.; Nachimuthu, Ponnusamy; Saraf, Laxmikant V.; Thevuthasan, Suntharampillai; Gaffney, Kelly J.

    2009-09-29

    We have used time-resolved soft x-ray spectroscopy to investigate the electronic structure of optically excited cuprous oxide at the O K-edge and the Cu L3-edge. The 400 nm optical excitation shifts the Cu and O absorptions to lower energy, but does not change the integrated x-ray absorption significantly for either edge. The constant integrated x-ray absorption cross-section indicates that that the conduction band and valence band edges have very similar Cu 3d and O 2p orbital contributions. The 2.1 eV optical band gap of Cu2O significantly exceeds the one eV shift in the Cu L3- and O K-edges absorption edges induced by optical excitation, demonstrating the importance of core-hole excitonic effects and valence electron screening in the x-ray absorption process.

  9. Atomic resolution mapping of the excited-state electronic structure of Cu2O with time-resolved x-ray absorption spectroscopy

    SciTech Connect

    Hillyard, P. W.; Kuchibhatla, S. V. N. T.; Glover, T. E.; Hertlein, M. P.; Huse, Nils; Nachimuthu, P.; Saraf, L. V.; Thevuthasan, S.; Gaffney, K. J.

    2010-05-02

    We have used time-resolved soft x-ray spectroscopy to investigate the electronic structure of optically excited cuprous oxide at the O K-edge and the Cu L3-edge. The 400 nm optical excitation shifts the Cu and O absorptions to lower energy, but does not change the integrated x-ray absorption significantly for either edge. The constant integrated x-ray absorption cross-section indicates that the conduction-band and valence-band edges have very similar Cu 3d and O 2p orbital contributions. The 2.1 eV optical band gap of Cu2O significantly exceeds the one eV shift in the Cu L3- and O K-edges absorption edges induced by optical excitation, demonstrating the importance of core-hole excitonic effects and valence electron screening in the x-ray absorption process.

  10. Thermo-Active Behavior of Ethylene-Vinyl Acetate | Multiwall Carbon Nanotube Composites Examined by in Situ near-Edge X-ray Absorption Fine-Structure Spectroscopy

    PubMed Central

    2015-01-01

    NEXAFS spectroscopy was used to investigate the temperature dependence of thermally active ethylene-vinyl acetate | multiwall carbon nanotube (EVA|MWCNT) films. The data shows systematic variations of intensities with increasing temperature. Molecular orbital assignment of interplaying intensities identified the 1s → π*C=C and 1s → π*C=O transitions as the main actors during temperature variation. Furthermore, enhanced near-edge interplay was observed in prestrained composites. Because macroscopic observations confirmed enhanced thermal-mechanical actuation in prestrained composites, our findings suggest that the interplay of C=C and C=O π orbitals may be instrumental to actuation. PMID:24803975

  11. Optical absorption enhancement of CdTe nanostructures by low-energy nitrogen ion bombardment

    NASA Astrophysics Data System (ADS)

    Akbarnejad, E.; Ghoranneviss, M.; Mohajerzadeh, S.; Hantehzadeh, M. R.; Asl Soleimani, E.

    2016-02-01

    In this paper we present the fabrication of cadmium telluride (CdTe) nanostructures by means of RF magnetron sputtering followed by low-energy ion implantation and post-thermal treatment. We have thoroughly studied the structural, optical, and morphological properties of these nanostructures. The effects of nitrogen ion bombardment on the structural parameters of CdTe nanostructures such as crystal size, microstrain, and dislocation density have been examined. From x-ray diffractometer (XRD) analysis it could be deduced that N+ ion fluence and annealing treatment helps to form (3 0 0) orientation in the crystalline structure of cadmium-telluride films. Fluctuations in optical properties like the optical band gap and absorption coefficient as a function of N+ ion fluences have been observed. The annealing of the sample irradiated by a dose of 1018 ions cm-2 has led to great enhancement in the optical absorption over a wide range of wavelengths with a thickness of 250 nm. The enhanced absorption is significantly higher than the observed value in the original CdTe layer with a thickness of 3 μm. Surface properties such as structure, grain size and roughness are noticeably affected by varying the nitrogen fluences. It is speculated that nitrogen bombardment and post-annealing treatment results in a smaller optical band gap, which in turn leads to higher absorption. Nitrogen bombardment is found to be a promising method to increase efficiency of thin film solar cells.

  12. Self operating absorption cooling system using solar energy: Small power experimental plant

    NASA Astrophysics Data System (ADS)

    Velluet, P.; Dehausse, R.

    This study deals with a solar system for refrigeration specially designed for remote areas conditions. So, it must be very simple and reliable, and in addition it must be also mechanically self-operating. The thermodynamic cycle used is an ammonia-water absorption one. It consumes only thermal energy, which is easily and cheaply converted directly from solar radiation. In order to make a self-operating system, an engine is located between the boiler (at high pressure) and the absorber (at low pressure). It expands ammonia vapor and produces mechanical energy to run the solution pump.

  13. Decay heat and anti-neutrino energy spectra in fission fragments from total absorption spectroscopy

    NASA Astrophysics Data System (ADS)

    Rykaczewski, Krzysztof

    2015-10-01

    Decay studies of over forty 238U fission products have been studied using ORNL's Modular Total Absorption Spectrometer. The results are showing increased decay heat values, by 10% to 50%, and the energy spectra of anti-neutrinos shifted towards lower energies. The latter effect is resulting in a reduced number of anti-neutrinos interacting with matter, often by tens of percent per fission product. The results for several studied nuclei will be presented and their impact on decay heat pattern in power reactors and reactor anti-neutrino physics will be discussed.

  14. Photon interaction and energy absorption in glass: A transparent gamma ray shield

    NASA Astrophysics Data System (ADS)

    Manohara, S. R.; Hanagodimath, S. M.; Gerward, L.

    2009-09-01

    The effective atomic number, Zeff, the effective electron density, Ne,eff, and the energy dependence, ED, have been calculated at photon energies from 1 keV to 1 GeV for CaO-SrO-B 2O 3, PbO-B 2O 3, Bi 2O 3-B 2O 3, and PbO-Bi 2O 3-B 2O 3 glasses with potential applications as gamma ray shielding materials. For medium- Z glasses, Zeff is about constant and equal to the mean atomic number in a wide energy range, typically 0.3 < E < 4 MeV, where Compton scattering is the main photon interaction process. In contrast, for high- Z glasses there is no energy region where Compton scattering is truly dominating. Heavy-metal oxide glasses containing PbO and/or Bi 2O 3 are promising gamma ray shielding materials due to their high effective atomic number and strong absorption of gamma rays. They compare well with concrete and other standard shielding materials and have the additional advantage of being transparent to visible light. The single-valued effective atomic number calculated by XMuDat is approximately valid at low energies where photoelectric absorption is dominating.

  15. Multi-energy soft-x-ray technique for impurity transport measurements in the fusion plasma edge

    NASA Astrophysics Data System (ADS)

    Clayton, D. J.; Tritz, K.; Stutman, D.; Finkenthal, M.; Kaye, S. M.; Kumar, D.; LeBlanc, B. P.; Paul, S.; Sabbagh, S. A.

    2012-10-01

    A new diagnostic technique was developed to produce high-resolution impurity transport measurements of the steep-gradient edge of fusion plasmas. Perturbative impurity transport measurements were performed for the first time in the NSTX plasma edge (r/a ˜ 0.6 to the SOL) with short neon gas puffs, and the resulting line and continuum emission was measured with the new edge multi-energy soft-x-ray (ME-SXR) diagnostic. Neon transport is modeled with the radial impurity transport code STRAHL and the resulting x-ray emission is computed using the ADAS atomic database. The radial transport coefficient profiles D(r) and v(r), and the particle flux from the gas puff Φ(t), are the free parameters in this model and are varied to find the best fit to experimental x-ray emissivity measurements, with bolometry used to constrain the impurity source. Initial experiments were successful and results were consistent with previous measurements of core impurity transport and neoclassical transport calculations. New diagnostic tools will be implemented on NSTX-U to further improve these transport measurements.

  16. Simulation studies for operating electron beam ion trap at very low energy for disentangling edge plasma spectra

    SciTech Connect

    Jin Xuelong; Fei Zejie; Xiao Jun; Lu Di; Hutton, Roger; Zou Yaming

    2012-07-15

    Electron beam ion traps (EBITs) are very useful tools for disentanglement studies of atomic processes in plasmas. In order to assist studies on edge plasma spectroscopic diagnostics, a very low energy EBIT, SH-PermEBIT, has been set up at the Shanghai EBIT lab. In this work, simulation studies for factors which hinder an EBIT to operate at very low electron energies were made based on the Tricomp (Field Precision) codes. Longitudinal, transversal, and total kinetic energy distributions were analyzed for all the electron trajectories. Influences from the electron current and electron energy on the energy depression caused by the space charge are discussed. The simulation results show that although the energy depression is most serious along the center of the electron beam, the electrons in the outer part of the beam are more likely to be lost when an EBIT is running at very low energy. Using the simulation results to guide us, we successfully managed to reach the minimum electron beam energy of 60 eV with a beam transmission above 57% for the SH-PermEBIT. Ar and W spectra were measured from the SH-PermEBIT at the apparent electron beam energies (read from the voltage difference between the electron gun cathode and the central drift tube) of 60 eV and 1200 eV, respectively. The spectra are shown in this paper.

  17. Simulation studies for operating electron beam ion trap at very low energy for disentangling edge plasma spectra

    NASA Astrophysics Data System (ADS)

    Jin, Xuelong; Fei, Zejie; Xiao, Jun; Lu, Di; Hutton, Roger; Zou, Yaming

    2012-07-01

    Electron beam ion traps (EBITs) are very useful tools for disentanglement studies of atomic processes in plasmas. In order to assist studies on edge plasma spectroscopic diagnostics, a very low energy EBIT, SH-PermEBIT, has been set up at the Shanghai EBIT lab. In this work, simulation studies for factors which hinder an EBIT to operate at very low electron energies were made based on the Tricomp (Field Precision) codes. Longitudinal, transversal, and total kinetic energy distributions were analyzed for all the electron trajectories. Influences from the electron current and electron energy on the energy depression caused by the space charge are discussed. The simulation results show that although the energy depression is most serious along the center of the electron beam, the electrons in the outer part of the beam are more likely to be lost when an EBIT is running at very low energy. Using the simulation results to guide us, we successfully managed to reach the minimum electron beam energy of 60 eV with a beam transmission above 57% for the SH-PermEBIT. Ar and W spectra were measured from the SH-PermEBIT at the apparent electron beam energies (read from the voltage difference between the electron gun cathode and the central drift tube) of 60 eV and 1200 eV, respectively. The spectra are shown in this paper.

  18. Comparison of quantitative k-edge empirical estimators using an energy-resolved photon-counting detector

    NASA Astrophysics Data System (ADS)

    Zimmerman, Kevin C.; Gilat Schmidt, Taly

    2016-03-01

    Using an energy-resolving photon counting detector, the amount of k-edge material in the x-ray path can be estimated using a process known as material decomposition. However, non-ideal effects within the detector make it difficult to accurately perform this decomposition. This work evaluated the k-edge material decomposition accuracy of two empirical estimators. A neural network estimator and a linearized maximum likelihood estimator with error look-up tables (A-table method) were evaluated through simulations and experiments. Each estimator was trained on system-specific calibration data rather than specific modeling of non-ideal detector effects or the x-ray source spectrum. Projections through a step-wedge calibration phantom consisting of different path lengths through PMMA, aluminum, and a k-edge material was used to train the estimators. The estimators were tested by decomposing data acquired through different path lengths of the basis materials. The estimators had similar performance in the chest phantom simulations with gadolinium. They estimated four of the five densities of gadolinium with less than 2mg/mL bias. The neural networks estimates demonstrated lower bias but higher variance than the A-table estimates in the iodine contrast agent simulations. The neural networks had an experimental variance lower than the CRLB indicating it is a biased estimator. In the experimental study, the k-edge material contribution was estimated with less than 14% bias for the neural network estimator and less than 41% bias for the A-table method.

  19. Edge energy transport barrier and turbulence in the I-mode regime on Alcator C-Moda)

    NASA Astrophysics Data System (ADS)

    Hubbard, A. E.; Whyte, D. G.; Churchill, R. M.; Cziegler, I.; Dominguez, A.; Golfinopoulos, T.; Hughes, J. W.; Rice, J. E.; Bespamyatnov, I.; Greenwald, M. J.; Howard, N.; Lipschultz, B.; Marmar, E. S.; Reinke, M. L.; Rowan, W. L.; Terry, J. L.

    2011-05-01

    We report extended studies of the I-mode regime [Whyte et al., Nucl. Fusion 50, 105005 (2010)] obtained in the Alcator C-Mod tokamak [Marmar et al., Fusion Sci. Technol. 51(3), 3261 (2007)]. This regime, usually accessed with unfavorable ion B × ∇B drift, features an edge thermal transport barrier without a strong particle transport barrier. Steady I-modes have now been obtained with favorable B × ∇B drift, by using specific plasma shapes, as well as with unfavorable drift over a wider range of shapes and plasma parameters. With favorable drift, power thresholds are close to the standard scaling for L-H transitions, while with unfavorable drift they are ˜ 1.5-3 times higher, increasing with Ip. Global energy confinement in both drift configurations is comparable to H-mode scalings, while density profiles and impurity confinement are close to those in L-mode. Transport analysis of the edge region shows a decrease in edge χeff, by typically a factor of 3, between L- and I-mode. The decrease correlates with a drop in mid-frequency fluctuations (f ˜ 50-150 kHz) observed on both density and magnetics diagnostics. Edge fluctuations at higher frequencies often increase above L-mode levels, peaking at f ˜ 250 kHz. This weakly coherent mode is clearest and has narrowest width (Δf/f ˜ 0.45) at low q95 and high Tped, up to 1 keV. The Er well in I-mode is intermediate between L- and H-mode and is dominated by the diamagnetic contribution in the impurity radial force balance, without the Vpol shear typical of H-modes.

  20. Strain energy release rate as a function of temperature and preloading history utilizing the edge delamination fatique test method

    NASA Technical Reports Server (NTRS)

    Zimmerman, Richard S.; Adams, Donald F.

    1989-01-01

    Static laminate and tension-tension fatigue tests of IM7/8551-7 composite materials was performed. The Edge Delamination Test (EDT) was utilized to evaluate the temperature and preloading history effect on the critical strain energy release rate. Static and fatigue testing was performed at room temperature and 180 F (82 C). Three preloading schemes were used to precondition fatigue test specimens prior to performing the normal tension-tension fatigue EDT testing. Computer software was written to perform all fatigue testing while monitoring the dynamic modulus to detect the onset of delamination and record the test information for later retrieval and reduction.

  1. Solar absorption characteristics of several coatings and surface finishes. [for solar energy collectors

    NASA Technical Reports Server (NTRS)

    Lowery, J. R.

    1977-01-01

    Solar absorption characteristics are established for several films potentially favorable for use as receiving surfaces in solar energy collectors. Included in the investigation were chemically produced black films, black electrodeposits, and anodized coatings. It was found that black nickel exhibited the best combination of selective optical properties of any of the coatings studied. A serious drawback to black nickel was its high susceptibility to degradation in the presence of high moisture environments. Electroplated black chrome generally exhibited high solar absorptivities, but the emissivity varied considerably and was also relatively high under some conditions. The black chrome had the greatest moisture resistance of any of the coatings tested. Black oxide coatings on copper and steel substrates showed the best combination of selective optical properties of any of the chemical conversion films studied.

  2. Short Pulse Laser Absorption and Energy Partition at Relativistic Laser Intensities

    SciTech Connect

    Shepherd, R; Chen, H; Ping, Y; Dyer, G; Wilks, S; Chung, H; Kemp, A; Hanson, S; Widmann, K; Fournier, K; Faenov, A; Pikuz, T; Niles, A; Beiersdorfer, P

    2007-02-27

    We have performed experiments at the COMET and Calisto short pulse laser facilities to make the first comprehensive measurements of the laser absorption and energy partition in solid targets heated with an ultrashort laser pulse focused to relativistic laser intensities (>10 10{sup 17} W/cm{sup 2}). The measurements show an exceedingly high absorption for P polarized laser-target interactions above 10{sup 19} W/cm{sup 2}. Additionally, the hot electron population is observed to markedly increase at the same intensity range. An investigation of the relaxation process was initiated u using time sing time-resolved K{sub {alpha}} spectroscopy. Measurements of the time time-resolved K{sub {alpha}} radiation suggest a 10-20 ps relativistic electron relaxation time. However modeling difficulties of these data are apparent and a more detailed investigation on this subject matter is warranted.

  3. High-Energy X-ray Absorption Diagnostics as an Experimental Combustion Technique

    NASA Astrophysics Data System (ADS)

    Dunnmon, Jared; Sobhani, Sadaf; Hinshaw, Waldo; Fahrig, Rebecca; Ihme, Matthias

    2015-11-01

    X-ray diagnostics such as X-ray Computed Tomography (XCT) have recently been utilized for measurement of scalar concentration fields in gas-phase flow phenomena. In this study, we apply high-energy X-ray absorption techniques to visualize a laboratory-scale flame via fluoroscopic measurements by using krypton as a radiodense tracer media. Advantages of X-ray absorption diagnostics in a combustion context, including application to optically inaccessible environments and lack of ambient photon interference, are demonstrated. Analysis methods and metrics for extracting physical insights from these data are presented. The accuracy of the diagnostic is assessed via comparison to known results from canonical flame configurations, and the potential for further applications is discussed. Support from the NDSEG fellowship, Bosch, and NASA are gratefully acknolwedged.

  4. Impact of the pedestal plasma density on dynamics of edge localized mode crashes and energy loss scaling

    SciTech Connect

    Xu, X. Q.; Ma, J. F.; Li, G. Q.

    2014-12-15

    The latest BOUT++ studies show an emerging understanding of dynamics of edge localized mode (ELM) crashes and the consistent collisionality scaling of ELM energy losses with the world multi-tokamak database. A series of BOUT++ simulations are conducted to investigate the scaling characteristics of the ELM energy losses vs collisionality via a density scan. Linear results demonstrate that as the pedestal collisionality decreases, the growth rate of the peeling-ballooning modes decreases for high n but increases for low n (1 < n < 5), therefore the width of the growth rate spectrum γ(n) becomes narrower and the peak growth shifts to lower n. Nonlinear BOUT++ simulations show a two-stage process of ELM crash evolution of (i) initial bursts of pressure blob and void creation and (ii) inward void propagation. The inward void propagation stirs the top of pedestal plasma and yields an increasing ELM size with decreasing collisionality after a series of micro-bursts. The pedestal plasma density plays a major role in determining the ELM energy loss through its effect on the edge bootstrap current and ion diamagnetic stabilization. The critical trend emerges as a transition (1) linearly from ballooning-dominated states at high collisionality to peeling-dominated states at low collisionality with decreasing density and (2) nonlinearly from turbulence spreading dynamics at high collisionality into avalanche-like dynamics at low collisionality.

  5. The effect of film thickness on the optical absorption edge and optical constants of the Cr(III) organic thin films

    NASA Astrophysics Data System (ADS)

    Yakuphanoglu, F.; Sekerci, M.; Balaban, A.

    2005-05-01

    The effect of film thickness on optical properties of the Cr(III) complex having 2-pyridincarbaldehye thiosemicarbazone thin films was investigated. The analyses of the optical absorption data revealed existence of direct and indirect transitions in the optical band gap. The optical constants (refractive index and dielectric constant) of the thin films were determined. The thickness of the films causes important changes in refractive index and real part-imaginary parts of the dielectric constant. The most significant result of the present study is to indicate that thickness of the film can be used to modify in the optical band gaps and optical constant of the thin films.

  6. V oxidation state in Fe-Ti oxides by high-energy resolution fluorescence-detected X-ray absorption spectroscopy

    NASA Astrophysics Data System (ADS)

    Bordage, Amélie; Balan, Etienne; de Villiers, Johan P. R.; Cromarty, Robert; Juhin, Amélie; Carvallo, Claire; Calas, Georges; Sunder Raju, P. V.; Glatzel, Pieter

    2011-06-01

    The oxidation state of vanadium in natural and synthetic Fe-Ti oxides is determined using high-energy resolution fluorescence-detected X-ray absorption spectroscopy (HERFD-XAS). Eleven natural magnetite-bearing samples from a borehole of the Main Magnetite Layer of the Bushveld Complex (South Africa), five synthetic Fe oxide samples, and three natural hematite-bearing samples from Dharwar supergroup (India) are investigated. V K edge spectra were recorded on the ID26 beamline at the European Synchrotron Radiation Facility (Grenoble, France), and the pre-edge features were used to determine the local environment and oxidation state of vanadium. In the case of the magnetite samples (natural and synthetic), we show that vanadium is incorporated in the octahedral site of the spinel structure under two oxidation states: +III and +IV. The variations of the pre-edge area are interpreted as various proportions in V3+ and V4+ (between 9.5 and 16.3% of V4+), V3+ being the main oxidation state. In particular, the variations of the V4+/V3+ ratio along the profile of the Main Magnetite Layer seem to follow the crystallization sequence of the layer. In the case of the hematite samples from India, the pre-edge features indicate that vanadium is substituted to Fe and mainly incorporated as V4+ (between 40 and 72% of V4+). We also demonstrate the potentiality of HERFD-XAS for mineralogical studies, since it can filter out the unwanted fluorescence and give better resolved spectra than conventional XAS.

  7. The A-Dependence of Pion Absorption in the Energy Region of the DELTA(1232) Resonance

    NASA Astrophysics Data System (ADS)

    Rowntree, David Cedric

    1995-01-01

    The absorption of pi^+ at 118, 162, and 239 MeV on ^3He, ^4He, N, and Ar has been studied using the Large Acceptance Detector System (LADS) at the Paul Scherrer Institute in Villigen, Switzerland. LADS has a solid angle coverage of over 98% of 4pi steradians and an energy threshold of less than 20 MeV for protons, making it an almost ideal detector for studying multi-nucleon final states following pion absorption. The total absorption cross sections at the three energies are, in millibarns: ^3He - 24.8 +/- 2.1, 24.2 +/- 3.1, and 8.1 +/- 2.7; ^4He - 49.5 +/- 3.1, 48.0 +/- 3.8, and 21.9 +/- 4.1; N - 181.6 +/- 9.9, 163.4 +/- 10.5, and 107.0 +/- 9.9; Ar - 393.2 +/- 20.6, 366.1 +/- 21.8, and 281.8 +/- 21.1. With the exception of ^3 He, these are the most accurate measurements reported to date. In addition, the breakup into channels with different numbers of energetic final state nucleons has been determined. The average number of nucleons participating in the absorption reaction has been found to increase more slowly with A than previously reported. Differential spectra show clear signatures of small contributions from initial state interactions, and indicate the presence of at least some final state interactions. (Copies available exclusively from MIT Libraries, Rm. 14-0551, Cambridge, MA 02139-4307. Ph. 617-253-5668; Fax 617-253-1690.).

  8. High energy neutrino absorption and its effects on stars in close X-ray binaries

    NASA Technical Reports Server (NTRS)

    Gaisser, T. K.; Stecker, F. W.

    1986-01-01

    The physics and astrophysics of high energy neutrino production and interactions in close X-ray binary systems are studied. These studies were stimulated by recent observations of ultrahigh energy gamma-rays and possibly other ultrahigh energy particles coming from the directions of Cygnus X-3 and other binary systems and possessing the periodicity characteristics of these systems. Systems in which a compact object, such as a neutron star, is a strong source of high energy particles which, in turn, produce photons, neutronos and other secondary particles by interactions in the atmosphere of the companion star were considered. The highest energy neutrinos are absorbed deep in the companion and the associated energy deposition may be large enough to effect its structure or lead to its ultimate disruption. This neutrino heating was evaluated, starting with a detailed numerical calculation of the hadronic cascade induced in the atmosphere of the companion star. For some theoretical models, the resulting energy deposition from neutrino absorption may be so great as to disrupt the companion star over an astronomically small timescale of the order of 10,000 years. Even if the energy deposition is smaller, it may still be high enough to alter the system substantially, perhaps leading to quenching of high energy signals from the source. Given the cosmic ray luminosities required to produce the observed gamma rays from cygnus X-3 and LMX X-4, such a situation may occur in these sources.

  9. Local structure of epitaxial GeTe and Ge2Sb2Te5 films grown on InAs and Si substrates with (100) and (111) orientations: An x-ray absorption near-edge structure study

    NASA Astrophysics Data System (ADS)

    Kolobov, A. V.; Fons, P.; Krbal, M.; Tominaga, J.; Giussani, A.; Perumal, K.; Riechert, H.; Calarco, R.; Uruga, T.

    2015-03-01

    GeTe is an end-point of the GeTe-Sb2Te3 quasibinary alloys often referred to as phase-change memory materials. The polycrystalline nature of the crystalline films used in devices and the concomitant presence of grain boundaries complicate detailed structural studies of the local structure. Recent progress in the epitaxial growth of phase-change materials offers unique possibilities for precise structural investigations. In this work, we report on results of x-ray absorption near-edge structure (XANES) studies of GeTe and Ge2Sb2Te5 epitaxial films grown on Si and InAs substrates with (100) and (111) orientations. The results show a strong dependence of the local structure on the substrate material and especially orientation and are discussed in conjunction with polycrystalline samples and ab-initio XANES simulations.

  10. Absorption spectra of CdSe-ZnS core-shell quantum dots at high photon energies: Experiment and modeling

    NASA Astrophysics Data System (ADS)

    Mukherjee, Amlan; Ghosh, Sandip

    2014-11-01

    Absorption spectra of CdSe-ZnS core-shell quantum dot (QD) ensembles, with average core diameters ranging from 2.6 nm to 7.2 nm have been obtained using both transmission and photoluminescence excitation measurements. In agreement with previous reports, the absorption coefficient at energies ≃1 eV above the effective bandgap increases monotonically as in bulk solids. A simple effective-mass spherical core-shell potential model cannot explain the relatively high absorption at higher energies. The calculated electron and hole radial envelope wavefunctions show asymmetry due to the core-shell structure. It leads to normally symmetry-disallowed transitions acquiring a weak oscillator strength, with their number and strength increasing with energy. A phenomenological model that invokes normally disallowed transitions in general is shown to reproduce the absorption spectrum at higher energies quite well. The oscillator strength scaling factor for such transitions increases with decrease in QD size, consistent with expectations.

  11. Liquid helium cryostat with internal fluorescence detection for x-ray absorption studies in the 2-6 keV energy region

    NASA Astrophysics Data System (ADS)

    McFarlane Holman, Karen L.; Latimer, Matthew J.; Yachandra, Vittal K.

    2004-06-01

    X-ray absorption spectroscopy (XAS) in the intermediate x-ray region (2-6 keV) for dilute biological samples has been limited because of detector/flux limitations and inadequate cryogenic instrumentation. We have designed and constructed a new tailpiece/sample chamber for a commercially available liquid helium cooled cryostat which overcomes difficulties related to low fluorescence signals by using thin window materials and incorporating an internal photodiode detector. With the apparatus, XAS data at the Cl, S, and Ca K edges have been collected on frozen solutions and biological samples at temperatures down to 60 K. A separate chamber has been incorporated for collecting room-temperature spectra of standard compounds (for energy calibration purposes) which prevents contamination of the cryostat chamber and allows the sample to remain undisturbed, both important concerns for studying dilute and radiation-sensitive samples.

  12. Energy distribution measurement of narrow-band ultrashort x-ray beams via K-edge filters subtraction

    SciTech Connect

    Cardarelli, Paolo; Di Domenico, Giovanni; Marziani, Michele; Mucollari, Irena; Pupillo, Gaia; Sisini, Francesco; Taibi, Angelo; Gambaccini, Mauro

    2012-10-01

    The characterization of novel x-ray sources includes the measurement of the photon flux and the energy distribution of the produced beam. The aim of BEATS2 experiment at the SPARC-LAB facility of the INFN National Laboratories of Frascati (Rome, Italy) is to investigate possible medical applications of an x-ray source based on Thomson relativistic back-scattering. This source is expected to produce a pulsed quasi-monochromatic x-ray beam with an instantaneous flux of 10{sup 20} ph/s in pulses 10 ps long and with an average energy of about 20 keV. A direct measurement of energy distribution of this beam is very difficult with traditional detectors because of the extremely high photon flux. In this paper, we present a method for the evaluation of the energy distribution of quasi-monochromatic x-ray beams based on beam filtration with K-edge absorbing foils in the energy range of interest (16-22 keV). The technique was tested measuring the energy distribution of an x-ray beam having a spectrum similar to the expected one (SPARC-LAB Thomson source) by using a tungsten anode x-ray tube properly filtered and powered. The energy distribution obtained has been compared with the one measured with a HPGe detector showing very good agreement.

  13. Electronic structure and optic absorption of phosphorene under strain

    NASA Astrophysics Data System (ADS)

    Duan, Houjian; Yang, Mou; Wang, Ruiqiang

    2016-07-01

    We studied the electronic structure and optic absorption of phosphorene (monolayer of black phosphorus) under strain. Strain was found to be a powerful tool for the band structure engineering. The in-plane strain in armchair or zigzag direction changes the effective mass components along both directions, while the vertical strain only has significant effect on the effective mass in the armchair direction. The band gap is narrowed by compressive in-plane strain and tensile vertical strain. Under certain strain configurations, the gap is closed and the energy band evolves to the semi-Dirac type: the dispersion is linear in the armchair direction and is gapless quadratic in the zigzag direction. The band-edge optic absorption is completely polarized along the armchair direction, and the polarization rate is reduced when the photon energy increases. Strain not only changes the absorption edge (the smallest photon energy for electron transition), but also the absorption polarization.

  14. Evidence for Topological Edge States in a Large Energy Gap near the Step Edges on the Surface of ZrTe5

    NASA Astrophysics Data System (ADS)

    Wu, R.; Ma, J.-Z.; Nie, S.-M.; Zhao, L.-X.; Huang, X.; Yin, J.-X.; Fu, B.-B.; Richard, P.; Chen, G.-F.; Fang, Z.; Dai, X.; Weng, H.-M.; Qian, T.; Ding, H.; Pan, S. H.

    2016-04-01

    Two-dimensional topological insulators with a large bulk band gap are promising for experimental studies of quantum spin Hall effect and for spintronic device applications. Despite considerable theoretical efforts in predicting large-gap two-dimensional topological insulator candidates, none of them have been experimentally demonstrated to have a full gap, which is crucial for quantum spin Hall effect. Here, by combining scanning tunneling microscopy/spectroscopy and angle-resolved photoemission spectroscopy, we reveal that ZrTe5 crystal hosts a large full gap of ˜100 meV on the surface and a nearly constant density of states within the entire gap at the monolayer step edge. These features are well reproduced by our first-principles calculations, which point to the topologically nontrivial nature of the edge states.

  15. Local dynamics and phase transition in quantum paraelectric SrTiO3 studied by Ti K-edge x-ray absorption spectroscopy

    NASA Astrophysics Data System (ADS)

    Anspoks, Andris; Timoshenko, Janis; Purans, Juris; Rocca, Francesco; Trepakov, Vladimir; Dejneka, Alexander; Itoh, Mitsuru

    2016-05-01

    Strontium titanate is a model quantum paraelectric in which, in the region of dominating quantum statistics, the ferroelectric instability is inhibited due to nearly complete compensation of the harmonic contribution into ferroelectric soft mode frequency by the zero- point motion contribution. The enhancement of atomic masses by the substitution of 16 O with 18O decreases the zero-point atomic motion, and low-T ferroelectricity in SrTi18O3 is realized. In this study we report on the local structure of Ti in SrTi16O3 and SrTi18O3 investigated by Extended X-ray Absorption Fine Structure measurements in the temperature range 6 - 300 K.

  16. Theoretical analysis of X-ray magnetic circular dichroism at the Yb L2, 3 absorption edges of YbInCu4 in high magnetic fields around the field-induced valence transition

    NASA Astrophysics Data System (ADS)

    Kotani, A.

    2012-01-01

    High-magnetic-field X-ray absorption spectra (XAS) and its X-ray magnetic circular dichroism (XMCD) at the Yb L2, 3 edges of YbInCu4 are calculated around the field-induced valence transition at about 30 T. The calculations are made by using a new theoretical framework with an extended single impurity Anderson model (SIAM) developed recently by the present author. Two parameters in SIAM, the 4 f level and the hybridization strength, are taken as different values in low- and high-magnetic-field phases of the field-induced valence transition. The calculated results are compared with recent experimental data measured by Matsuda et al. by utilizing a miniature pulsed magnet up to 40 T. The field-dependence of the calculated XMCD spectra is explained in detail on the basis of the field-dependence of the Yb 4 f wavefunctions in the ground state. Some possibilities are discussed on the negative XMCD signal observed experimentally at the L2 edge.

  17. X-ray absorption, glancing-angle reflectivity, and theoretical study of the N K- and Ga M{sub 2,3}-edge spectra in GaN

    SciTech Connect

    Lambrecht, W.R.; Rashkeev, S.N.; Segall, B.; Lawniczak-Jablonska, K.; Suski, T.; Gullikson, E.M.; Underwood, J.H.; Perera, R.C.; Rife, J.C.; Grzegory, I.; Porowski, S.; Wickenden, D.K.

    1997-01-01

    A comprehensive study of the nitrogen K edge and gallium M{sub 2,3} edge in gallium nitride is presented. Results of two different experimental techniques, x-ray absorption by total photocurrent measurements and glancing-angle x-ray reflectivity, are compared with each other. First-principles calculations of the (polarization averaged) dielectric response {epsilon}{sub 2}({omega}) contributions from the relevant core-level to conduction-band transitions and derived spectral functions are used to interpret the data. These calculations are based on the local density approximation (LDA) and use a muffin-tin orbital basis for the band structure and matrix elements. The angular dependence of the x-ray reflectivity is studied and shown to be in good agreement with the theoretical predictions based on Fresnel theory and the magnitude of the calculated x-ray optical response functions. The main peaks in the calculated and measured spectra are compared with those in the relevant partial density of conduction-band states. Assignments are made to particular band transitions and corrections to the LDA are discussed. From the analysis of the N K and Ga M{sub 2,3} edges the latter are found to be essentially constant up to {approximately}10 eV above the conduction-band minimum. The differences in spectral shape found between the various measurements were shown to be a result of polarization dependence. Since the c axis in all the measurements was normal to the sample surface, p-polarized radiation at glancing angles corresponds to {bold E}{parallel}{bold c} while s polarization corresponds to {bold E}{perpendicular}{bold c} at all incident angles. Thus, this polarization dependence is a result of the intrinsic anisotropy of the wurtzite structure. Spectra on powders which provide an average of both polarizations as well as separate measurements of reflectivity with s polarization and p polarization were used. {copyright} {ital 1997} {ital The American Physical Society}

  18. Supporting Structure of the LSD Wave in an Energy Absorption Perspective

    SciTech Connect

    Fukui, Akihiro; Hatai, Keigo; Cho, Shinatora; Arakawa, Yoshihiro; Komurasaki, Kimiya

    2008-04-28

    In Repetitively Pulsed (RP) Laser Propulsion, laser energy irradiated to a vehicle is converted to blast wave enthalpy during the Laser Supported Detonation (LSD) regime. Based on the measured post-LSD electron number density profiles by two-wavelength Mach Zehnder interferometer in a line-focusing optics, electron temperature and absorption coefficient were estimated assuming Local Thermal Equilibrium. A 10J/pulse CO{sub 2} laser was used. As a result, laser absorption was found completed in the layer between the shock wave and the electron density peak. Although the LSD-termination timing was not clear from the shock-front/ionization-front separation in the shadowgraph images, there observed drastic changes in the absorption layer thickness from 0.2 mm to 0.5 mm and in the peak heating rate from 12-17x10{sup 13} kW/m{sup 3} to 5x10{sup 13} kW/m{sup 3} at the termination.

  19. Crash energy absorption of two-segment crash box with holes under frontal load

    NASA Astrophysics Data System (ADS)

    Choiron, Moch. Agus; Sudjito, Hidayati, Nafisah Arina

    2016-03-01

    Crash box is one of the passive safety components which designed as an impact energy absorber during collision. Crash box designs have been developed in order to obtain the optimum crashworthiness performance. Circular cross section was first investigated with one segment design, it rather influenced by its length which is being sensitive to the buckling occurrence. In this study, the two-segment crash box design with additional holes is investigated and deformation behavior and crash energy absorption are observed. The crash box modelling is performed by finite element analysis. The crash test components were impactor, crash box, and fixed rigid base. Impactor and the fixed base material are modelled as a rigid, and crash box material as bilinear isotropic hardening. Crash box length of 100 mm and frontal crash velocity of 16 km/jam are selected. Crash box material of Aluminum Alloy is used. Based on simulation results, it can be shown that holes configuration with 2 holes and ¾ length locations have the largest crash energy absorption. This condition associated with deformation pattern, this crash box model produces axisymmetric mode than other models.

  20. Theoretical modeling of low-energy electronic absorption bands in reduced cobaloximes

    DOE PAGESBeta

    Bhattacharjee, Anirban; Chavarot-Kerlidou, Murielle; Dempsey, Jillian L.; Gray, Harry B.; Fujita, Etsuko; Muckerman, James T.; Fontecave, Marc; Artero, Vincent; Arantes, Guilherme M.; Field, Martin J.

    2014-08-11

    Here, we report that the reduced Co(I) states of cobaloximes are powerful nucleophiles that play an important role in the hydrogen-evolving catalytic activity of these species. In this work we have analyzed the low energy electronic absorption bands of two cobaloxime systems experimentally and using a variety of density functional theory and molecular orbital ab initio quantum chemical approaches. Overall we find a reasonable qualitative understanding of the electronic excitation spectra of these compounds but show that obtaining quantitative results remains a challenging task.