Silicon drift detectors as a tool for time-resolved fluorescence XAFS on low-concentrated samples in catalysis.

PubMed

Kappen, Peter; Tröger, Larc; Materlik, Gerhard; Reckleben, Christian; Hansen, Karsten; Grunwaldt, Jan-Dierk; Clausen, Bjerne S

2002-07-01

A silicon drift detector (SDD) was used for ex situ and time-resolved in situ fluorescence X-ray absorption fine structure (XAFS) on low-concentrated catalyst samples. For a single-element and a seven-element SDD the energy resolution and the peak-to-background ratio were verified at high count rates, sufficient for fluorescence XAFS. An experimental set-up including the seven-element SDD without any cooling and an in situ cell with gas supply and on-line gas analysis was developed. With this set-up the reduction and oxidation of a zeolite supported catalyst containing 0.3 wt% platinum was followed by fluorescence near-edge scans with a time resolution of 10 min each. From ex situ experiments on low-concentrated platinum- and gold-based catalysts fluorescence XAFS scans could be obtained with sufficient statistical quality for a quantitative analysis. Structural information on the gold and platinum particles could be extracted by both the Fourier transforms and the near-edge region of the XAFS spectra. Moreover, it was found that with the seven-element SDD concentrations of the element of interest as low as 100 ppm can be examined by fluorescence XAFS.

X-ray Absorption Fine Structure (XAFS) Studies of Oxide Glasses—A 45-Year Overview

PubMed Central

Zanotto, Edgar Dutra

2018-01-01

X-ray Absorption Fine Structure (XAFS) spectroscopy has been widely used to characterize the short-range order of glassy materials since the theoretical basis was established 45 years ago. Soon after the technique became accessible, mainly due to the existence of Synchrotron laboratories, a wide range of glassy materials was characterized. Silicate glasses have been the most studied because they are easy to prepare, they have commercial value and are similar to natural glasses, but borate, germanate, phosphate, tellurite and other less frequent oxide glasses have also been studied. In this manuscript, we review reported advances in the structural characterization of oxide-based glasses using this technique. A focus is on structural characterization of transition metal ions, especially Ti, Fe, and Ni, and their role in different properties of synthetic oxide-based glasses, as well as their important function in the formation of natural glasses and magmas, and in nucleation and crystallization. We also give some examples of XAFS applications for structural characterization of glasses submitted to high pressure, glasses used to store radioactive waste and medieval glasses. This updated, comprehensive review will likely serve as a useful guide to clarify the details of the short-range structure of oxide glasses. PMID:29382102

XFAS SPECTROSCOPY ANALYSIS OF SELECTED HAP ELEMENTS IN FINE PM DERIVED FROM COAL COMBUSTION: JOURNAL ARTICLE

EPA Science Inventory

NRMRL-RTP-P-646 Shoji, T., Huggins, F.E., Huffman, G.P., Linak*, W.P., and Miller*, C.A. XFAS Spectroscopy Analysis of Selected HAP Elements in Fine PM Derived from Coal Combustion. Energy and Fuels 16 (2): (2002). 11/30/2001 X-ray absorption fine structure (XAFS) spectroscop...

In situ two-dimensional imaging quick-scanning XAFS with pixel array detector.

PubMed

Tanida, Hajime; Yamashige, Hisao; Orikasa, Yuki; Oishi, Masatsugu; Takanashi, Yu; Fujimoto, Takahiro; Sato, Kenji; Takamatsu, Daiko; Murayama, Haruno; Arai, Hajime; Matsubara, Eiichiro; Uchimoto, Yoshiharu; Ogumi, Zempachi

2011-11-01

Quick-scanning X-ray absorption fine structure (XAFS) measurements were performed in transmission mode using a PILATUS 100K pixel array detector (PAD). The method can display a two-dimensional image for a large area of the order of a centimetre with a spatial resolution of 0.2 mm at each energy point in the XAFS spectrum. The time resolution of the quick-scanning method ranged from 10 s to 1 min per spectrum depending on the energy range. The PAD has a wide dynamic range and low noise, so the obtained spectra have a good signal-to-noise ratio.

Ti-doped ZnO Thin Films Prepared at Different Ambient Conditions: Electronic Structures and Magnetic Properties

PubMed Central

Yong, Zhihua; Liu, Tao; Uruga, Tomoya; Tanida, Hajime; Qi, Dongchen; Rusydi, Andrivo; Wee, Andrew T. S.

2010-01-01

We present a comprehensive study on Ti-doped ZnO thin films using X-ray Absorption Fine Structure (XAFS) spectroscopy. Ti K edge XAFS spectra were measured to study the electronic and chemical properties of Ti ions in the thin films grown under different ambient atmospheres. A strong dependence of Ti speciation, composition, and local structures upon the ambient conditions was observed. The XAFS results suggest a major tetrahedral coordination and a 4+ valence state. The sample grown in a mixture of 80% Ar and 20% O2 shows a portion of precipitates with higher coordination. A large distortion was observed by the Ti substitution in the ZnO lattice. Interestingly, the film prepared in 80% Ar, 20% O2 shows the largest saturation magnetic moment of 0.827 ± 0.013 µB/Ti.

Interference between extrinsic and intrinsic losses in x-ray absorption fine structure

NASA Astrophysics Data System (ADS)

Campbell, L.; Hedin, L.; Rehr, J. J.; Bardyszewski, W.

2002-02-01

The interference between extrinsic and intrinsic losses in x-ray absorption fine structure (XAFS) is treated within a Green's-function formalism, without explicit reference to final states. The approach makes use of a quasiboson representation of excitations and perturbation theory in the interaction potential between electrons and quasibosons. These losses lead to an asymmetric broadening of the main quasiparticle peak plus an energy-dependent satellite in the spectral function. The x-ray absorption spectra (XAS) is then given by a convolution of an effective spectral function over a one-electron cross section. It is shown that extrinsic and intrinsic losses tend to cancel near excitation thresholds, and correspondingly, the strength in the main peak increases. At high energies, the theory crosses over to the sudden approximation. These results thus explain the observed weakness of multielectron excitations in XAS. The approach is applied to estimate the many-body corrections to XAFS, beyond the usual mean-free path, using a phasor summation over the spectral function. The asymmetry of the spectral function gives rise to an additional many-body phase shift in the XAFS formula.

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

PubMed

Hong, Xinguo; Newville, Matthew; Prakapenka, Vitali B; Rivers, Mark L; Sutton, Stephen R

2009-07-01

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 degrees 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.

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

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hong, X.; Newville, M.; Prakapenka, V.B.

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 amore » 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.« less

Characterization of local atomic structure in Co/Zn based ZIFs by XAFS

NASA Astrophysics Data System (ADS)

Podkovyrina, Yulia; Butova, Vera; Bulanova, Elena; Budnyk, Andriy; Kremennaya, Maria; Soldatov, Alexander; Lamberti, Carlo

2018-03-01

The local atomic structure in bimetallic Co/Zn zeolitic imidazolate frameworks (ZIFs) was studied using X-ray Absorption Fine Structure (XAFS) spectroscopy and theoretical calculations. The experimental Co K-edge and Zn K-edge XANES (X-ray Absorption Near Edge Structure) spectra of Zn1-xCoxC8H10N4 samples (x = 0.05, 0.25, 0.75) synthesized by microwave synthesis were compared with the data for the ZIF-67 (x=1) and ZIF-8 (x=0). Theoretical XANES spectra for the bimetallic ZIFs were calculated. It was shown that in bimetallic ZIFs the Co and Zn atoms have the similar local environment.

XAFS Debye-Waller Factors Temperature-Dependent Expressions for Fe+2-Porphyrin Complexes

NASA Astrophysics Data System (ADS)

Dimakis, Nicholas; Bunker, Grant

2007-02-01

We present an efficient and accurate method for directly calculating single and multiple scattering X-ray absorption fine structure (XAFS) thermal Debye-Waller factors for Fe+2 -porphiryn complexes. The number of multiple scattering Debye-Waller factors on metal porphyrin centers exceeds the number of available parameters that XAFS experimental data can support during fitting with simulated spectra. Using the Density Functional Theory (DFT) under the hybrid functional of X3LYP, phonon normal mode spectrum properties are used to express the mean square variation of the half-scattering path length for a Fe+2 -porphiryn complex as a function of temperature for the most important single and multiple scattering paths of the complex thus virtually eliminating them from the fitting procedure. Modeled calculations are compared with corresponding values obtained from DFT-built and optimized Fe+2 -porphyrin bis-histidine structure as well as from experimental XAFS spectra previously reported. An excellent agreement between calculated and reference Debye-Waller factors for Fe+2-porphyrins is obtained.

Ab Initio Calculation of XAFS Debye-Waller Factors for Crystalline Materials

NASA Astrophysics Data System (ADS)

Dimakis, Nicholas

2007-02-01

A direct an accurate technique for calculating the thermal X-ray absorption fine structure (XAFS) Debye-Waller factors (DWF) for materials of crystalline structure is presented. Using the Density Functional Theory (DFT) under the hybrid X3LYP functional, a library of MnO spin—optimized clusters are built and their phonon spectrum properties are calculated; these properties in the form of normal mode eigenfrequencies and eigenvectors are in turn used for calculation of the single and multiple scattering XAFS DWF. DWF obtained via this technique are temperature dependent expressions and can be used to substantially reduce the number of fitting parameters when experimental spectra are fitted with a hypothetical structure without any ad hoc assumptions. Due to the high computational demand a hybrid approach of mixing the DFT calculated DWF with the correlated Debye model for inner and outer shells respectively is presented. DFT obtained DWFs are compared with corresponding values from experimental XAFS spectra on manganosite. The cluster size effect and the spin parameter on the DFT calculated DWFs are discussed.

In situ XAFS and micro-XAFS studies on LiNi 0.8Co 0.15Al 0.05O 2 cathode material for lithium-ion batteries

NASA Astrophysics Data System (ADS)

Nonaka, T.; Okuda, C.; Seno, Y.; Nakano, H.; Koumoto, K.; Ukyo, Y.

We have applied in situ X-ray absorption fine structure (XAFS) and in situ micro-XAFS techniques to study LiNi 0.8Co 0.15Al 0.05O 2 cathode materials in Li-ion coin cells that show various levels of capacity fading: fresh cell, cycle tested cell and aging tested cell. The change in the oxidation state and local structure of Ni and Co during charge has been investigated. Ni and Co K-edge X-ray absorption near edge structure (XANES) show that the Ni oxidation state is converted from Ni 3+ to Ni 4+ upon charging, whereas the Co oxidation state hardly changes. Ni K-edge extended X-ray absorption fine structure (EXAFS) reveals that the Jahn-Teller distorted NiO 6 octahedron turns into the symmetric octahedron upon charging, which is consistent with the change in the Ni oxidation state. Ni K-edge micro-XANES show that the oxidation of Ni proceeds homogeneously in a grain of LiNi 0.8Co 0.15Al 0.05O 2 within the special resolution of ∼2 μm, and proceeds independently of the grain size. All the behaviors of Ni and Co observed in these experiments for the fresh cell remain unchanged after the capacity fade is induced by cycle tests or aging tests, which demonstrates the considerable stability of the LiNi 0.8Co 0.15Al 0.05O 2 cathode material.

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

DOE Office of Scientific and Technical Information (OSTI.GOV)

Watanabe, Yoshihide, E-mail: e0827@mosk.tytlabs.co.jp; Nishimura, Yusaku F.; Suzuki, Ryo

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

XAFS Study on Chlorination of Y2O3 in LiCl-KCl-ZrCl4 Melt

NASA Astrophysics Data System (ADS)

Okamoto, Yoshihiro; Yaita, Tsuyoshi; Shiwaku, Hideaki; Suzuki, Shinichi

2008-11-01

The chlorination reaction of Y2O3 with ZrCl4 in LiCl-KCl eutectic melt was investigated by X-ray absorption fine structure (XAFS) technique. The chlorination reaction was observed between 773 K and 823 K as the 1st peak shift of the Fourier transform magnitude function |FT(k3χ(k))|. The peak corresponding to the nearest Y3+-Cl- correlation was observed in the XAFS analysis at 823 K as the result of the chlorination. It was confirmed that the mixture melts after the reaction is almost equivalent to a molten 5% YCl3-(LiCl-KCl eutectic) mixture.

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

DOE Office of Scientific and Technical Information (OSTI.GOV)

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

2015-02-09

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

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

NASA Astrophysics Data System (ADS)

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

2012-06-01

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

Thermally activated decomposition of (Ga,Mn)As thin layer at medium temperature post growth annealing

NASA Astrophysics Data System (ADS)

Melikhov, Y.; Konstantynov, P.; Domagala, J.; Sadowski, J.; Chernyshova, M.; Wojciechowski, T.; Syryanyy, Y.; Demchenko, I. N.

2016-05-01

The redistribution of Mn atoms in Ga1-xMnxAs layer during medium-temperature annealing, 250-450 oC, by Mn K-edge X-ray absorption fine structure (XAFS) recorded at ALBA facility, was studied. For this purpose Ga1-xMnxAs thin layer with x=0.01 was grown on AlAs buffer layer deposited on GaAs(100) substrate by molecular beam epitaxy (MBE) followed by annealing. The examined layer was detached from the substrate using a “lift-off” procedure in order to eliminate elastic scattering in XAFS spectra. Fourier transform analysis of experimentally obtained EXAFS spectra allowed to propose a model which describes a redistribution/diffusion of Mn atoms in the host matrix. Theoretical XANES spectra, simulated using multiple scattering formalism (FEFF code) with the support of density functional theory (WIEN2k code), qualitatively describe the features observed in the experimental fine structure.

Preparation of γ-LiV2O5 from polyoxovanadate cluster Li7[V15O36(CO3)] as a high-performance cathode material and its reaction mechanism revealed by operando XAFS

NASA Astrophysics Data System (ADS)

Wang, Heng; Isobe, Jin; Shimizu, Takeshi; Matsumura, Daiju; Ina, Toshiaki; Yoshikawa, Hirofumi

2017-08-01

γ-phase LiV2O5, which shows superior electrochemical performance as cathode material in Li-ion batteries, was prepared by annealing the polyoxovanadate cluster Li7 [V15O36(CO3)]. The reaction mechanism was studied using operando X-ray absorption fine structure (XAFS), powder X-ray diffraction (PXRD), and X-ray photoelectron spectroscopy (XPS) analyses. The X-ray absorption near edge structure (XANES) and XPS results reveal that γ-LiV2O5 undergoes two-electron redox reaction per V2O5 pyramid unit, resulting in a large reversible capacity of 260 Ah/kg. The extended X-ray absorption fine structure (EXAFS) and PXRD analyses also suggest that the V-V distance slightly increases, due to the reduction of V5+ to V4+ during Li ion intercalation as the material structure is maintained. As a result, γ-LixV2O5 shows highly reversible electrochemical reaction with x = 0.1-1.9.

Outer-sphere Pb(II) adsorbed at specific surface sites on single crystal α-alumina

USGS Publications Warehouse

Bargar, John R.; Towle, Steven N.; Brown, Gordon E.; Parks, George A.

1996-01-01

Solvated Pb(II) ions were found to adsorb as structurally well-defined outer-sphere complexes at specific sites on the α-Al2O3 (0001) single crystal surface, as determined by grazing-incidence X-ray absorption fine structure (GI-XAFS) measurements. The XAFS results suggest that the distance between Pb(II) adions and the alumina surface is approximately 4.2 Å. In contrast, Pb(II) adsorbs as more strongly bound inner-sphere complexes on α-Al2O3 (102). The difference in reactivities of the two alumina surfaces has implications for modeling surface complexation reactions of contaminants in natural environments, catalysis, and compositional sector zoning of oxide crystals.

Uranium XAFS analysis of kidney from rats exposed to uranium

PubMed Central

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

2017-01-01

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

Uranium XAFS analysis of kidney from rats exposed to uranium.

PubMed

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

2017-03-01

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

Experimental and Theoretical Approaches for the Surface Interaction between Copper and Activated Sludge Microorganisms at Molecular Scale

NASA Astrophysics Data System (ADS)

Luo, Hong-Wei; Chen, Jie-Jie; Sheng, Guo-Ping; Su, Ji-Hu; Wei, Shi-Qiang; Yu, Han-Qing

2014-11-01

Interactions between metals and activated sludge microorganisms substantially affect the speciation, immobilization, transport, and bioavailability of trace heavy metals in biological wastewater treatment plants. In this study, the interaction of Cu(II), a typical heavy metal, onto activated sludge microorganisms was studied in-depth using a multi-technique approach. The complexing structure of Cu(II) on microbial surface was revealed by X-ray absorption fine structure (XAFS) and electron paramagnetic resonance (EPR) analysis. EPR spectra indicated that Cu(II) was held in inner-sphere surface complexes of octahedral coordination with tetragonal distortion of axial elongation. XAFS analysis further suggested that the surface complexation between Cu(II) and microbial cells was the distorted inner-sphere coordinated octahedra containing four short equatorial bonds and two elongated axial bonds. To further validate the results obtained from the XAFS and EPR analysis, density functional theory calculations were carried out to explore the structural geometry of the Cu complexes. These results are useful to better understand the speciation, immobilization, transport, and bioavailability of metals in biological wastewater treatment plants.

X-ray absorption spectroscopic studies on gold nanoparticles in mesoporous and microporous materials.

PubMed

Akolekar, Deepak B; Foran, Garry; Bhargava, Suresh K

2004-05-01

Au L(3)-edge X-ray absorption spectroscopic measurements were carried out over a series of mesoporous and microporous materials containing gold nanoparticles to investigate the effects of the host matrix and preparation methods on the properties of gold nanoparticles. The materials of structure type MCM-41, ZSM-5, SAPO-18 and LSX with varying framework composition containing low concentrations of gold nanoparticles were prepared and characterized. In these materials the size of the gold nanoparticles varied in the range approximately 1 to 4 nm. A series of gold nanoparticles within different mesoporous and microporous materials have been investigated using X-ray absorption fine structure (XANES, EXAFS) and other techniques. Information such as atomic distances, bonding and neighbouring environment obtained from XAFS measurements was useful in elucidating the nature and structure of gold nanoparticles on these catalytic materials. The influence of the high-temperature (823, 1113, 1273 K) treatment on gold nanoparticles inside the mesoporous matrix was investigated using the XAFS technique. The XAFS and XANES results confirm various characteristics of gold nanoparticles in these materials suitable for catalysis, fabrication of nanodevices and other applications.

Controlling the intermediate structure of an ionic liquid for f-block element separations

DOE PAGES

Abney, Carter W.; Do, Changwoo; Luo, Huimin; ...

2017-04-19

Recent research has revealed molecular structure beyond the inner coordination sphere is essential in defining the performance of separations processes, but nevertheless remains largely unexplored. Here we apply small angle neutron scattering (SANS) and x-ray absorption fine structure (XAFS) spectroscopy to investigate the structure of an ionic liquid system studied for f-block element separations. SANS data reveal dramatic changes in the ionic liquid microstructure (~150 Å) which we demonstrate can be controlled by judicious selection of counter ion. Mesoscale structural features (> 500 Å) are also observed as a function of metal concentration. XAFS analysis supports formation of extended aggregatemore » structures, similar to those observed in traditional solvent extraction processes, and suggest additional parallels may be drawn from further study. As a result, achieving precise tunability over the intermediate features is an important development in controlling mesoscale structure and realizing advanced new forms of soft matter.« less

Local atomic and electronic structures of epitaxial strained LaCoO3 thin films

NASA Astrophysics Data System (ADS)

Sterbinsky, G. E.; Ryan, P. J.; Kim, J.-W.; Karapetrova, E.; Ma, J. X.; Shi, J.; Woicik, J. C.

2012-01-01

We have examined the atomic and electronic structures of perovskite lanthanum cobaltite (LaCoO3) thin films using Co K-edge x-ray absorption fine structure (XAFS) spectroscopy. Extended XAFS (EXAFS) demonstrates that a large difference between in-plane and out-of-plane Co-O bond lengths results from tetragonal distortion in highly strained films. The structural distortions are strongly coupled to the hybridization between atomic orbitals of the Co and O atoms, as shown by x-ray absorption near edge spectroscopy (XANES). Our results indicate that increased hybridization is not the cause of ferromagnetism in strained LaCoO3 films. Instead, we suggest that the strain-induced distortions of the oxygen octahedra increase the population of eg electrons and concurrently depopulate t2g electrons beyond a stabilization threshold for ferromagnetic order.

SORPTION OF LEAD ON A RUTHENIUM COMPOUND: A MACROSCOPIC AND MICROSCOPIC STUDY

EPA Science Inventory

The objective of this study was to elucidate the sorption mechanism of Pb on the high-affinity ruthenium compound with time at pH 6 employing batch methods and X-ray absorption fine structure (XAFS) and X-ray diffraction (XRD) spectroscopies. For the spectroscopic studies, Pb so...

Capturing local structure modulations of photoexcited BiVO4 by ultrafast transient XAFS.

PubMed

Uemura, Yohei; Kido, Daiki; Koide, Akihiro; Wakisaka, Yuki; Niwa, Yasuhiro; Nozawa, Shunsuke; Ichiyanagi, Kohei; Fukaya, Ryo; Adachi, Shin-Ichi; Katayama, Tetsuo; Togashi, Tadashi; Owada, Shigeki; Yabashi, Makina; Hatada, Keisuke; Iwase, Akihide; Kudo, Akihiko; Takakusagi, Satoru; Yokoyama, Toshihiko; Asakura, Kiyotaka

2017-06-29

Ultrafast excitation of photocatalytically active BiVO 4 was characterized by femto- and picosecond transient X-ray absorption fine structure spectroscopy. An initial photoexcited state (≪500 fs) changed to a metastable state accompanied by a structural change with a time constant of ∼14 ps. The structural change might stabilize holes on oxygen atoms since the interaction between Bi and O increases.

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

NASA Astrophysics Data System (ADS)

Murphy, Michael Wayne

2010-06-01

Various II-VI semiconducting nanomaterials such as ZnO-ZnS nanoribbons (NRs), CdSxSe1-x nanostructures, ZnS:Mn NRs, ZnS:Mn,Eu nanoprsims (NPs), ZnO:Mn nanopowders, and ZnO:Co nanopowders were synthesized for study. These materials were characterized by techniques such as scanning electron microscopy, transmission electron microscopy, element dispersive X-ray spectroscopy, selected area electron diffraction, and X-ray diffraction. The electronic and optical properties of these nanomaterials were studied by X-ray absorption fine structure (XAFS) spectroscopy and X-ray excited optical luminescence (XEOL) techniques, using tuneable soft X-rays from a synchrotron light source. The complementary nature ofthe XAFS and XEOL techniques give site, element and chemical specific measurements which allow a better understanding of the interplay and role of each element in the system. Chemical vapour deposition (CVD) of ZnS powder in a limited oxygen environment resulted in side-by-side biaxial ZnO-ZnS NR heterostructures. The resulting NRs contained distinct wurtzite ZnS and wurtzite ZnO components with widths of 10--100 nm and 20 --500 nm, respectively and a uniform interface region of 5-15 nm. XAFS and XEOL measurements revealed the luminescence of ZnO-ZnS NRs is from the ZnO component. The luminescence of CdSxSe1-x nanostructures is shown to be dependent on the S to Se ratio, with the band-gap emission being tunable between that of pure CdS and CdSe. Excitation of the CdSxSe 1-x nanostructures by X-ray in XEOL has revealed new de-excitation channels which show a defect emission band not seen by laser excitation. CVD of Mn2+ doped ZnS results in nanostructures with luminescence dominated by the yellow Mn2+ emission due to energy transfer from the ZnS host to the Mn dopant sites. The addition of EuCl3 to the reactants in the CVD process results in a change in morphology from NR to NP. Zn1-xMnxO and Zn1-xCOxO nanopowders were prepared by sol-gel methods at dopant concentrations of 0, 1,3, and 10% and annealed at 400, 600 and 800°C in air. XAFS spectra show that low dopant concentrations and low processing temperatures limit the amount of secondary phase formation. The nanopowders did not show roomtemperature ferromagnetism and increased secondary phase formation increases the paramagnetic character of the hysteresis curves at 5°K. Keywords: X-ray absorption fine structures (XAFS), X-ray absorption near-edge structures (XANES), extended X-ray absorption fine structure (EXAFS), X-ray absorption spectroscopy(XAS), X-ray excited optical luminescence (XEOL), time-resolved, II-VI semiconductors, nanostructure, nanomaterial, nanoribbon, nanowire, nanopartic1e, heterostructure, ZnO, ZnS, ZnO-ZnS, CdS, CdSe, CdSSe, ZnO:Mn, ZnO:Co, ZnS:Mn, dilute magnetic semiconductor (DMS), dilute magnetic oxide (DMO), spintronics, magnetism, paramagnetism, ferromagnetism.

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

NASA Technical Reports Server (NTRS)

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

1993-01-01

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

Wet-chemical synthesis of nanoscale iron boride, XAFS analysis and crystallisation to α-FeB.

PubMed

Rades, Steffi; Kornowski, Andreas; Weller, Horst; Albert, Barbara

2011-06-20

The reaction of lithium tetrahydridoborate and iron bromide in high boiling ether as reaction medium produces an ultrafine, pyrophoric and magnetic precipitate. X-ray and electron diffraction proved the product to be amorphous. According to X-ray absorption fine structure spectroscopy (XAFS) the precipitate has FeB structure up to nearly two coordination spheres around an iron absorber atom. Transmission electron microscopy (TEM) confirms the ultrafine powder to be nanoscale. Subsequent annealing at 450 °C causes the atoms to arrange in a more distinct FeB structure, and further thermal treatment to 1050 °C extends the local structure to the α-modification of FeB. Between 1050 °C and 1500 °C α-FeB is transformed into β-FeB. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

The effect of local atomic structure on the optical properties of GeSi self-assembled islands buried in silicon matrix

NASA Astrophysics Data System (ADS)

Demchenko, I. N.; Lawniczak-Jablonska, K.; Kret, S.; Novikov, A. V.; Laval, J.-Y.; Zak, M.; Szczepanska, A.; Yablonskiy, A. N.; Krasilnik, Z. F.

2007-03-01

The local atomic structure of GeSi self-assembled islands buried in a silicon matrix strongly influences the optical properties of such systems. In the present paper this structure was determined by x-ray absorption fine-structure (XAFS) spectroscopy and high resolution transmission electron microscopy (HRTEM) and used to build a schematic description of the band structure model. Quantitative analysis of the extended XAFS (EXAFS) spectrum was performed for three coordination shells around the Ge absorbing atom with multiple scattering taken into account. It was proved that the coordination number of elements in an alloy resulting from EXAFS analysis for all three coordination spheres (i.e. 'mixing degree' parameters) cannot be taken as the concentration of alloy but can be used together with a proper model of the alloy unit cell to calculate a realistic concentration. The fraction of Ge calculated in this way is consistent with HRTEM results. The found model of the unit cell was used to generate a x-ray absorption near edge structure spectrum by ab initio calculations. This approach yielded a spectrum in good agreement with the experimental one. The information gained from XAFS and HRTEM was then used for calculation of the band structure diagram. Results of the calculation are discussed and compared with the experimental photoluminescence spectrum.

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

NASA Astrophysics Data System (ADS)

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

2015-09-01

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

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

PubMed

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

2007-10-01

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

Long- and Short-Range Structure of Ferrimagnetic Iron-Chromium Maghemites.

PubMed

García-Guaderrama, Marco; Montero-Cabrera, María E; Morán, Emilio; Alario-Franco, Miguel A; Fuentes-Cobas, Luis E; Macías-Ríos, Edgar; Esparza-Ponce, Hilda E; Fuentes-Montero, María E

2015-12-07

Maghemite-like materials containing Fe(3+) and Cr(3+) in comparable amounts have been prepared by solution-combustion synthesis. The conditions of synthesis and the magnetic properties are described. These materials are ferrimagnetic and are much more stable than pure iron maghemite since their maghemite-hematite transformation takes place at about ∼ 700 °C instead of ∼ 300 °C, as usually reported. These materials were studied by synchrotron radiation X-ray diffraction (XRD) and by X-ray absorption fine structure (XAFS) of the K-absorption edge of two elements. High-resolution XRD patterns were processed by means of the Rietveld method. Thus, maghemites were studied by XAFS in both Fe and Cr K-edges to clarify the short-range structure of the investigated systems. Pre-edge decomposition and theoretical modeling of X-ray absorption near edge structure transitions were performed. The extended X-ray absorption fine structure (EXAFS) spectra were fitted considering the facts that the central atom of Fe is able to occupy octahedral and tetrahedral sites, each with a weight adjustment, while Cr occupies only octahedral sites. Interatomic distances were determined for x = 1, by fitting simultaneously both Fe and Cr K-edges average EXAFS spectra. The results showed that the cation vacancies tend to follow a regular pattern within the structure of the iron-chromium maghemite (FeCrO3).

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

USGS Publications Warehouse

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

2003-01-01

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

Probing the influence of the center atom coordination structure in iron phthalocyanine multi-walled carbon nanotube-based oxygen reduction reaction catalysts by X-ray absorption fine structure spectroscopy

NASA Astrophysics Data System (ADS)

Peng, Yingxiang; Li, Zhipan; Xia, Dingguo; Zheng, Lirong; Liao, Yi; Li, Kai; Zuo, Xia

2015-09-01

Three different pentacoordinate iron phthalocyanine (FePc) electrocatalysts with an axial ligand (pyridyl group, Py) anchored to multi-walled carbon nanotubes (MWCNTs) are prepared by a microwave method as high performance composite electrocatalysts (FePc-Py/MWCNTs) for the oxygen reduction reaction (ORR). For comparison, tetracoordinate FePc electrocatalysts without an axial ligand anchored to MWCNTs (FePc/MWCNTs) are assembled in the same way. Ultraviolet-visible spectrophotometry (UV-Vis), Raman spectroscopy (RS), and high-resolution transmission electron microscopy (HRTEM) are used to characterize the obtained electrocatalysts. The electrocatalytic activity of the samples is measured by linear sweep voltammetry (LSV), and the onset potential of all of the FePc-Py/MWCNTs electrocatalysts is found to be more positive than that of their FePc/MWCNTs counterparts. X-ray photoelectron spectroscopy (XPS) and X-ray absorption fine structure (XAFS) spectroscopy are employed to elucidate the relationship between molecular structure and electrocatalytic activity. XPS indicates that higher concentrations of Fe3+ and pyridine-type nitrogen play critical roles in determining the electrocatalytic ORR activity of the samples. XAFS spectroscopy reveals that the FePc-Py/MWCNTs electrocatalysts have a coordination geometry around Fe that is closer to the square pyramidal structure, a higher concentration of Fe3+, and a smaller phthalocyanine ring radius compared with those of FePc/MWCNTs.

Speciation of aqueous Ni(II)-carboxylate and Ni(II)-fulvic acid solutions: Combined ATR-FTIR and XAFS analysis

NASA Astrophysics Data System (ADS)

Strathmann, Timothy J.; Myneni, Satish C. B.

2004-09-01

Aqueous solutions containing Ni(II) and a series of structurally related carboxylic acids were analyzed using attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) and Ni K-edge X-ray absorption fine structure spectroscopy (XAFS). XAFS spectra were also collected for solutions containing Ni 2+ and chelating ligands (ethylenediaminetetraacetic acid, nitrilotriacetic acid (NTA)) as well as soil fulvic acid. Limited spectral changes are observed for aqueous Ni(II) complexes with monocarboxylates (formate, acetate) and long-chain polycarboxylates (succinate, tricarballylate), where individual donor groups are separated by multiple bridging methylene groups. These spectral changes indicate weak interactions between Ni(II) and carboxylates, and the trends are similar to some earlier reports for crystalline Ni(II)-acetate solids, for which X-ray crystallography studies have indicated monodentate Ni(II)-carboxylate coordination. Nonetheless, electrostatic or outer-sphere coordination cannot be ruled out for these complexes. However, spectral changes observed for short-chain dicarboxylates (oxalate, malonate) and carboxylates that contain an alcohol donor group adjacent to one of the carboxylate groups (lactate, malate, citrate) demonstrate inner-sphere metal coordination by multiple donor groups. XAFS spectral fits of Ni(II) solutions containing soil fulvic acid are consistent with inner-sphere Ni(II) coordination by one or more carboxylate groups, but spectra are noisy and outer-sphere modes of coordination cannot be ruled out. These molecular studies refine our understanding of the interactions between carboxylates and weakly complexing divalent transition metals, such as Ni(II).

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

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pham, Van-Thai; Fulton, John L.

2016-06-21

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

Chromium immobilization by extra- and intraradical fungal structures of arbuscular mycorrhizal symbioses.

PubMed

Wu, Songlin; Zhang, Xin; Sun, Yuqing; Wu, Zhaoxiang; Li, Tao; Hu, Yajun; Lv, Jitao; Li, Gang; Zhang, Zhensong; Zhang, Jing; Zheng, Lirong; Zhen, Xiangjun; Chen, Baodong

2016-10-05

Arbuscular mycorrhizal (AM) fungi can enhance plant Cr tolerance through immobilizing Cr in mycorrhizal roots. However, the detailed processes and mechanisms are unclear. The present study focused on cellular distribution and speciation of Cr in both extraradical mycelium (ERM) and mycorrhizal roots exposed to Cr(VI) by using field emission scanning electron microscopy equipped with energy dispersive X-ray spectrometer (FE-SEM-EDS), scanning transmission soft X-ray microscopy (STXM) and X-ray absorption fine structure (XAFS) spectroscopy techniques. We found that amounts of particles (possibly extracellular polymeric substances, EPS) were produced on the AM fungal surface upon Cr(VI) stress, which contributed greatly to Cr(VI) reduction and immobilization. With EDS of the surface of AM fungi exposed to various Cr(VI) levels, a positive correlation between Cr and P was revealed, suggesting that phosphate groups might act as counter ions of Cr(III), which was also confirmed by the XAFS analysis. Besides, STXM and XAFS analyses showed that Cr(VI) was reduced to Cr(III) in AM fungal structures (arbuscules, intraradical mycelium, etc.) and cell walls in mycorrhizal roots, and complexed possibly with carboxyl groups or histidine analogues. The present work provided evidence of Cr immobilization on fungal surface and in fungal structures in mycorrhizal roots at a cellular level, and thus unraveled the underlying mechanisms by which AM symbiosis immobilize Cr. Copyright © 2016 Elsevier B.V. All rights reserved.

X-ray absorption spectroscopy and imaging of heterogeneous hydrothermal mixtures using a diamond microreactor cell

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fulton, John L.; Darab, John G.; Hoffmann, Markus M.

2001-04-01

Hydrothermal synthesis is an important route to novel materials. Hydrothermal chemistry is also an important aspect of geochemistry and a variety of waste remediation technologies. There is a significant lack of information about the speciation of inorganic compounds under hydrothermal conditions. For these reasons we describe a high-temperature, high-pressure cell that allows one to acquire both x-ray absorption fine structure (XAFS) spectra and x-ray transmission and absorption images of heterogeneous hydrothermal mixtures. We demonstrate the utility of the method by measuring the Cu(I) speciation in a solution containing both solid and dissolved Cu phases at temperatures up to 325{sup o}C.more » X-ray imaging of the various hydrothermal phases allows micro-XAFS to be collected from different phases within the heterogeneous mixture. The complete structural characterization of a soluble bichloro-cuprous species was determined. In situ XAFS measurements were used to define the oxidation state and the first-shell coordination structure. The Cu--Cl distance was determined to be 2.12 Aa for the CuCl{sub 2}{sup -} species and the complete loss of tightly bound waters of hydration in the first shell was observed. The microreactor cell described here can be used to test thermodynamic models of solubility and redox chemistry of a variety of different hydrothermal mixtures.« less

Growth of Nanoscale Nickel Ferrite on Carbonaceous Matrix- A Novel Method of Turning Harmful Particulates into a Functional Nanocomposite: An XAFS Study

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pattanaik, S.; Huggins, F; Huffman, G

2010-01-01

Particulate matter (PM) emission from residual oil combustion typically consists of carbonaceous material accompanied by inorganic matter notably transition metal sulfates. Often a minor sulfide form is found in the coarse fraction while an oxide form is more common in the fine and ultrafine fractions. A composite comprising of nanoscale nickel ferrite dispersed on carbonaceous matrix has been obtained following liberation of metal sulfates from the fine PM - a novel method of turning harmful particulates into a functional nanocomposite without the need for elaborate preparation using expensive precursors. The nickel ferrite content in the composite varies with the Fe/Nimore » ratio in particulate, fuel type, and combustion condition. Such variation may lead to the composite exhibiting diverse physical behaviors. Detailed structure and cation distribution in dispersed ferrite have been studied using Fe and Ni K-edges XAFS spectroscopy. Peaks are identified in the radial structure function with specific atom pair correlations within the spinel ferrite from which the relative occupancy of the cations in the octahedral and tetrahedral sites can be discerned. The results show that Ni(II) has strong preference for the octahedral site, while Fe(III) prefers both sites which is consistent with that of an inverted spinel ferrite.« less

Growth of nanoscale nickel ferrite on carbonaceous matrix--A novel method of turning harmful particulates into a functional nanocomposite: An XAFS study.

PubMed

Pattanaik, Sidhartha; Huggins, Frank E; Huffman, Gerald P

2010-06-15

Particulate matter (PM) emission from residual oil combustion typically consists of carbonaceous material accompanied by inorganic matter notably transition metal sulfates. Often a minor sulfide form is found in the coarse fraction while an oxide form is more common in the fine and ultrafine fractions. A composite comprising of nanoscale nickel ferrite dispersed on carbonaceous matrix has been obtained following liberation of metal sulfates from the fine PM--a novel method of turning harmful particulates into a functional nanocomposite without the need for elaborate preparation using expensive precursors. The nickel ferrite content in the composite varies with the Fe/Ni ratio in particulate, fuel type, and combustion condition. Such variation may lead to the composite exhibiting diverse physical behaviors. Detailed structure and cation distribution in dispersed ferrite have been studied using Fe and Ni K-edges XAFS spectroscopy. Peaks are identified in the radial structure function with specific atom pair correlations within the spinel ferrite from which the relative occupancy of the cations in the octahedral and tetrahedral sites can be discerned. The results show that Ni(II) has strong preference for the octahedral site, while Fe(III) prefers both sites which is consistent with that of an inverted spinel ferrite. Copyright 2010 Elsevier B.V. All rights reserved.

Influence of depositional environment in fossil teeth: a micro-XRF and XAFS study

NASA Astrophysics Data System (ADS)

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

2014-04-01

The formation of metal-rich phases during the fossilization of vertebrate fossil teeth, recovered from various deposition environments in northern Greece, is studied by means of synchrotron radiation X-ray fluorescence (SR-XRF) as well as Fe and Mn K edge X-ray absorption fine structure (XAFS) spectroscopy. XRF line-scans from the samples' cross-sections revealed different contamination paths for Mn and Fe. The two-dimensional XRF maps illustrate the spatial distribution of P, Ca, Mn and Fe as well as the precipitation of Fe-rich phases in cementum, dentin and dentinal tubules. Goethite, lepidocrocite and ferrihydrite were detected in the samples' cross-section by means of Fe K edge EXAFS spectroscopy. Moreover the Fe and Mn K edge EXAFS revealed the presence of vivianite and birnessite (MnO2) on the external surface of two samples.

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

USGS Publications Warehouse

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

2000-01-01

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

X-Ray Absorption Microspectroscopy with Electrostatic Force Microscopy and its Application to Chemical States Mapping

NASA Astrophysics Data System (ADS)

Ishii, M.; Rigopoulos, N.; Poolton, N. R. J.; Hamilton, B.

2007-02-01

A new technique named X-EFM that measures the x-ray absorption fine structure (XAFS) of nanometer objects was developed. In X-EFM, electrostatic force microscopy (EFM) is used as an x-ray absorption detector, and photoionization induced by x-ray absorption of surface electron trapping sites is detected by EFM. An EFM signal with respect to x-ray photon energy provides the XAFS spectra of the trapping sites. We adopted X-EFM to observe Si oxide thin films. An edge jump shift intrinsic to the X-EFM spectrum was found, and it was explained with a model where an electric field between the trapping site and probe deepens the energy level of the inner-shell. A scanning probe under x-rays with fixed photon energy provided the chemical state mapping on the surface.

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

PubMed

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

2009-02-01

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

Temperature-dependent local structural properties of redox Pt nanoparticles on TiO 2 and ZrO 2 supports

DOE PAGES

Jeong, Eun -Suk; Park, Chang -In; Jin, Zhenlan; ...

2015-01-21

This paper examined the local structural properties of Pt nanoparticles on SiO 2, TiO 2–SiO 2, and ZrO 2–SiO 2 supports to better understand the impact of oxide-support type on the performance of Pt-based catalysts. In situ X-ray absorption fine structure (XAFS) measurements were taken for the Pt L3-edge in a temperature range from 300 to 700 K in He, H 2, and O 2 gas environments. The XAFS measurements demonstrated that Pt atoms were highly dispersed on TiO 2–SiO 2 and ZrO 2–SiO 2 forming pancake-shaped nanoparticles, whereas Pt atoms formed larger particles of hemispherical shapes on SiO 2more » supports. Contrary to the SiO 2 case, the coordination numbers for Pt, Ti, and Zr around Pt atoms on the TiO 2–SiO 2 and ZrO 2–SiO 2 supports were nearly constant from 300 to 700 K under the different gas environments. These results are consistent with the improvements in thermal stability of Pt nanoparticles achieved by incorporating TiO 2 or ZrO 2 on the surface of SiO 2 supports. XAFS analysis further indicated that the enhanced dispersion and stability of Pt were a consequence of the strong metal support interaction via Pt–Ti and Pt–Zr bonds.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ozkendir, Osman Murat, E-mail: ozkendir@gmail.com

Highlights: • Crystal and electronic structure properties of Nd{sub x}Ti{sub 1−x}BO{sub 2+d} structure were investigated. • New crystal structures for Nd–Ti complexes are determined. • Distortions in the crystal structure were observed as a result of Boron shortage. • Prominent change in electronic properties of the samples with the increasing Nd amount. - Abstract: Neodymium substituted TiBO{sub 3} samples were investigated according to their crystal, electric and electronic properties. Studies were conducted by X-ray absorption fine structure spectroscopy (XAFS) technique for the samples with different substitutions in the preparation processes. To achieve better crystal structure results during the study, XRDmore » pattern results were supported by extended-XAFS (EXAFS) analysis. The electronic structure analysis were studied by X-ray absorption near-edge structure spectroscopy (XANES) measurements at the room temperatures. Due to the substituted Nd atoms, prominent changes in crystal structure, new crystal geometries for Nd-Ti complexes, phase transitions in the crystals structure were detected according to the increasing Nd substitutions in the samples. In the entire stages of the substitutions, Nd atoms were observed as governing the whole phenomena due to their dominant characteristics in Ti geometries. Besides, electrical resistivity decay was determined in the materials with the increasing amount of Nd substitution.« less

Site-selective XAFS spectroscopy tuned to surface active sites of Cu/ZnO and Cr/SiO2 catalysts.

PubMed

Izumi, Y; Nagamori, H; Kiyotaki, F; Minato, T

2001-03-01

XAFS (X-ray absorption fine structure) spectra were measured by using the fluorescence spectrometer for the emitted X-ray from sample. The chemical shifts between Cu0 and Cu1 and between CrIII and CrVI were evaluated. Tuning the fluorescence spectrometer to each energy, the Cu0 and CuI site-selective XANES for Cu/ZnO catalyst were measured. The first one was similar to the XANES of Cu metal and the second one was the 5 : 5 average of XANES for CuI sites + Cu metal. The population ratio of copper site of the Cu/ZnO catalyst was found to be Cu metal: Cu2O : CuI atomically dispersed on surface = 70(+/-23) : 22(+/-14) : 8(+/-5). Site-selective XANES for CrIII site of Cr/SiO2 catalyst was also studied.

Infiltration of trace metal ions in the oral mucosa of a rat analyzed using SRXRF, XAFS, and ICP-MS.

PubMed

Imamura, Toshihiro; Kanno, Zuisei; Imai, Haruki; Sugiyama, Tomoko; Wada, Takahiro; Yoshida, Midori; Sakama, Minoru; Ono, Takashi; Honda, Eiichi; Uo, Motohiro

2015-01-01

Although the accumulation and distribution of metals from metallic orthodontic appliances in the oral mucosa have been studied extensively, they remain unclear because their concentration is quite low. In this study, metal specimens (Ni, Ni-Ti, and Co-Cr) were sutured in the unilateral oral mucosa of rats, and the distribution of the eluted elements in the mucosal tissue was estimated using inductively coupled plasma mass spectrometry (ICP-MS) and synchrotron radiation X-ray fluorescence analysis (SR-XRF). While the infiltrations of Ni, Co, and Cr into the oral mucosal connective tissue were observed with SR-XRF, significant increases were only found in Ni from the pure Ni group and Cr from the Co-Cr group. Furthermore, Ni and Co were estimated as hydrated ions while Cr was estimated in oxide form through X-ray absorption fine structure (XAFS) analysis.

XAFS studies of metal-ligand interactions at organic surfaces and in solution

NASA Astrophysics Data System (ADS)

Boyanov, Maxim I.

X-ray absorption fine structure spectroscopy (XAFS) was used as a structural probe to determine the mechanism of metal adsorption to organic surfaces. Two specific systems were investigated, Pb adsorption to heneicosanoic acid Langmuir monolayers (CH3(CH2)19COOH), and Cd adsorption to isolated cell walls of the Bacillus subtilis bacterium. Although the study of these systems is important for quite different reasons, the goal in both is metal binding site speciation and structural characterization of the surface complex. The adsorption of aqueous Cd to B. subtilis was studied as a function of pH by fluorescence mode bulk XAFS. Samples were prepared at six pH values in the range 3.4 to 7.8, and the bacterial functional groups responsible for the adsorption were identified under each condition. Under the experimental Cd and bacterial concentrations, the spectroscopy results indicate that Cd binds predominantly to protonated phosphoryl ligands below pH 4.4, while at higher pH adsorption to carboxyl groups becomes increasingly important. At pH 7.8 we observe the activation of an additional binding site, which we tentatively ascribe to deprotonated phosphoryl ligands. A quantitative Cd speciation diagram for the pH range is presented. Grazing-incidence Pb L3 edge XAFS was used in situ to determine the adsorption complex structure in the Pb-Langmuir monolayer study. The results indicate covalent binding of the Pb cations to the carboxyl headgroups, and the observed Pb-Pb coordination suggests that the metal is adsorbed as a hydrolysis polymer, rather than as individual Pb 2+ ions. The data suggest a bidentate binding mechanism and a one Pb atom to one carboxyl headgroup binding stoichiometry. We discuss how this adsorption model can explain the peculiarities observed with Pb in previous metal-Langmuir monolayer studies. A systematic study of the metal local environment in aqueous solutions was conducted and used in the above analyses. Perchlorate and acetate salt solutions of Cd, Pb, Mn, Cr, and Cu were characterized as standards of hydrated ions and metal-carboxyl complexes. The utility of XAFS in differentiating between the ionic, monodentate, bridging-bidentate, and bidentate metal-carboxyl complexes through C-C multiple scattering effects and XANES features is demonstrated.

Chemical kinetics of Cs species in an alkali-activated municipal solid waste incineration fly ash and pyrophyllite-based system using Cs K-edge in situ X-ray absorption fine structure analysis

NASA Astrophysics Data System (ADS)

Shiota, Kenji; Nakamura, Takafumi; Takaoka, Masaki; Nitta, Kiyofumi; Oshita, Kazuyuki; Fujimori, Takashi; Ina, Toshiaki

2017-05-01

We conducted in situ X-ray absorption fine structure (in situ XAFS) analysis at the Cs K-edge to investigate the chemical kinetics of Cs species during reaction in an alkali-activated municipal solid waste incineration fly ash (MSWIFA) and pyrophyllite-based system. Understanding the kinetics of Cs is essential to the design of appropriate conditions for Cs stabilization. In situ XAFS analysis of four pastes, prepared from NaOHaq, sodium silicate solution, pyrophyllite, and MSWIFA with the addition of CsCl, was conducted in custom-built reaction cells at four curing temperatures (room temperature, 60 °C, 80 °C, 105 °C) for approximately 34 h. The results indicated that the change in Cs species during reaction at room temperature was small, while changes at higher temperatures were faster and more extreme, with the fastest conversion to pollucite occurring at 105 °C. Further analysis using a leaching test and a simple reaction model for Cs species during reaction showed that the pollucite formation rate was dependent on the curing temperature and had a significant negative correlation with Cs leaching. The activation energy of pollucite formation was estimated to be 31.5 kJ/mol. These results revealed that an important change in the chemical state of Cs occurs during reaction in the system.

Cytochrome C in a dry trehalose matrix: structural and dynamical effects probed by x-ray absorption spectroscopy.

PubMed

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

2007-02-15

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

Mode of occurrence of arsenic in feed coal and its derivative fly ash, Black Warrior Basin, Alabama

USGS Publications Warehouse

Zielinski, R.A.; Foster, A.L.; Meeker, G.P.; Brownfield, I.K.

2007-01-01

An arsenic-rich (As = 55 ppm) bituminous feed coal from the Black Warrior Basin, Alabama and its derivative fly ash (As = 230 ppm) were selected for detailed investigation of arsenic residence and chemical forms. Analytical techniques included microbeam analysis, selective extraction, and As K-edge X-ray absorption fine-structure (XAFS) spectroscopy. Most As in the coal is contained in a generation of As-bearing pyrite (FeS2) that formed in response to epigenetic introduction of hydrothermal fluids. XAFS results indicate that approximately 50% of the As in the coal sample occurs as the oxidized As(V) species, possibly the result of incipient oxidation of coal and pyrite prior to our analysis. Combustion of pyrite and host coal produced fly ash in which 95% of As is present as As(V). Selective extraction of the fly ash with a carbonate buffer solution (pH = 10) removed 49% of the As. A different extraction with an HCl-NH2OH mixture, which targets amorphous and poorly crystalline iron oxides, dissolved 79% of the As. XAFS spectroscopy of this highly acidic (pH = 3.0) fly ash indicated that As is associated with some combination of iron oxide, oxyhydroxide, or sulfate. In contrast, a highly alkaline (pH = 12.7) fly ash from Turkey shows most As associated with a phase similar to calcium orthoarsenate (Ca3(AsO4)2). The combined XAFS results indicate that fly ash acidity, which is determined by coal composition and combustion conditions, may serve to predict arsenic speciation in fly ash.

Local Structures Around Co Atoms in Wurtzite ZnO Nano-Composites Probed by Fluorescence XAFS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shi Tongfei; National Synchrotron Radiation Laboratory, University of Science and Technology of China, Hefei 230029; Liu Wenhan

2007-02-02

The local structures around Co ions in the Zn1-xCoxO nano-composites prepared by the sol-gel method have been investigated by fluorescence X-ray absorption fine structure (XAFS) technique. The results indicate that for dilute Co-doped ZnO (x=0.02, 0.05), the Co2+ ions are incorporated into the ZnO lattice, and are located at the position of the substitutional Zn2+ ions. As the Co content increases to 0.10 or higher, only part of the Co ions enter the lattice of the wurtzite and the others exist in the form of a Co3O4 phase whose content increases with the doped Co concentration. In the substitutional Zn0.98Co0.02Omore » sample, the bond length of the first shell RCo-O and the second shell RCo-Zn is smaller than the second shell Zn-Zn distance in ZnO by about 0.01{approx}0.02 A. These results imply that only small local lattice deformation is induced by dilute Co2+ substituting into the Zn2+ sites.« less

XAFS studies of surface structures of TiO{sub 2} nanoparticles and photocatalytic reduction of metal ions.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chen, L. X.; Rajh, T.; Wang, Z.

1997-01-01

To probe the origin of the unique functions of titanium dioxide (TiO{sub 2}) nanoparticles observed in photocatalytic reactions, structures of Ti atom sites in titanium dioxide (TiO{sub 2}) nanoparticles with different sizes were studied by Ti K-edge XAFS (X-ray absorption fine structure). Compared to the bulk TiO{sub 2} structure, a shorter Ti-O distance from surface TiO{sub 2} resulting from Ti-OH bonding was observed. The XAFS spectra also revealed an increasing disorder of the lattice with decreasing sizes of the nanoparticles based on a coordination number decrease for the third-shell O atoms as well as changes in relative intensities of pre-edgemore » peaks A1, A2, and A3. However, the Ti sites largely remain octahedral even in the 30 Angstrom diameter particles. These results imply that the increasing number of surface Ti sites as well as possible corner defects in small nanoparticles may be the main cause of the unique surface chemistry exhibited by nanoparticles of TiO{sub 2}. XAFS was also used in monitoring the photoreduction reaction products of Cu{sup 2+} and Hg{sup 2+} on TiO{sub 2} nanoparticle surfaces, with or without surface adsorbers, alanine (Ala) and thiolactic acid (TLA). Ala dramatically enhanced photoreduction of Cu{sup 2+} on TiO{sub 2} nanoparticle surfaces, whereas thiolactic acid did not affect or even hindered Hg{sup 2+} photoreduction. Although both surface adsorbers chelated with the metal ions in the absence of TiO{sub 2} nanoparticles, this chelation was drastically changed in the Cu-Ala complex but was largely retained in the Hg-TLA complex when TiO{sub 2} was present. This may correlate with the different effects of the adsorbers on the photoreduction of the metal. Our experimental results suggest that a proper balance between the affinities of the adsorber to the metal ions and to the surface Ti atoms of TiO{sub 2} may be one of the keys in selecting a surface adsorber for enhanced photoreduction efficiency.« less

Anomalous structural disorder and distortion in metal-to-insulator-transition Ti{sub 2}O{sub 3}

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hwang, In-Hui; Jin, Zhenlan; Park, Chang-In

2016-01-07

Mott proposed that impurity bands in corundum-symmetry Ti{sub 2}O{sub 3} at high temperatures caused a collapse in the bandgap. However, the origin of the impurity bands has not yet been clarified. We examine the local structural properties of metal-to-insulator-transition Ti{sub 2}O{sub 3} using in-situ x-ray absorption fine structure (XAFS) measurements at the Ti K edge in the temperature range from 288 to 739 K. The Ti{sub 2}O{sub 3} powder is synthesized by using a chemical reaction method. X-ray diffraction (XRD) measurements from Ti{sub 2}O{sub 3} with a Rietveld refinement demonstrate a single-phased R-3c symmetry without additional distortion. Extended-XAFS combined with XRDmore » reveals a zigzag patterned Ti position and an anomalous structural disorder in Ti-Ti pairs, accompanied by a bond length expansion of the Ti-Ti pairs along the c-axis for T > 450 K. The local structural distortion and disorder of the Ti atoms would induce impurity levels in the band gap between the Ti 3d a{sub 1g} and e{sub g}{sup π} bands, resulting in a collapse of the band gap for T > 450 K.« less

Characterization of pentavalent and hexavalent americium complexes in nitric acid using X-ray absorption fine structure spectroscopy and first-principles modeling

DOE PAGES

Riddle, Catherine; Czerwinski, Kenneth; Kim, Eunja; ...

2016-01-18

We studied the speciation of pentavalent and hexavalent americium (Am) complexes in nitric acidicby X-ray absorption fine structure spectroscopy (XAFS), UV-visible spectroscopy, and density functional theory (DFT). Extended x-ray absorption fine structure (EXAFS) and x-ray absorption near edge structure (XANES) results were consistent with the presence of a mixture of AmO 2 + and AmO 2 2+ with only a small amount AmO 2 present. The resulting average bond distances we found were 1.71 Å for Am=O and 2.44 Å for Am-O. All-electron scalar relativistic calculations were also carried out using DFT to predict the equilibrium geometries and properties ofmore » the AmO 2 + and AmO 2 2+ aquo complexes. Calculated bond distances for the Am(VI) complex are in reasonable agreement with EXAFS data and the computed energy gaps between frontier molecular orbitals suggest a slightly higher kinetic stability and chemical hardness of Am(VI) compared to Am(V).« less

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

NASA Astrophysics Data System (ADS)

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

2014-01-01

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

Local structure analysis of diluted magnetic semiconductor Co and Al co-doped ZnO nanoparticles

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hyodo, K.; Morimoto, S.; Yamazaki, T.

2016-02-01

In this study, Co and Al ions co-doped ZnO nanoparticles (Zn(Al, Co)O NPs) were prepared by our original chemical preparation method. The obtained samples prepared by this method, were encapsulated in amorphous SiO{sub 2}. X-ray diffraction (XRD) results showed Zn(Al, Co)O NPs had a single-phase nature with hexagonal wurtzite structure. These particle sizes could be controlled to be approximately 30 nm. We investigate the effect that the increase in the carrier has on the magnetization by doping Al to Co-doped ZnO NPs. The local structures were qualitatively analyzed using X-ray absorption fine structure (XAFS) measurements.

Cesium Speciation in Dust from Municipal Solid Waste and Sewage Sludge Incineration by Synchrotron Radiation Micro-X-ray Analysis.

PubMed

Shiota, Kenji; Takaoka, Masaki; Fujimori, Takashi; Oshita, Kazuyuki; Terada, Yasuko

2015-11-17

The chemical behavior of Cs in waste incineration processes is important to consider when disposing of radionuclide-contaminated waste from the Fukushima Daiichi nuclear power plant accident in Japan. To determine the speciation of Cs, we attempted the direct speciation of trace amounts of stable Cs in the dust from municipal solid waste incineration (MSWI) and sewage sludge incineration (SSI) by micro-X-ray fluorescence (μ-XRF) and micro-X-ray absorption fine structure (μ-XAFS) at the SPring-8 facility. The μ-XRF results revealed that locally produced Cs was present in MSWI and SSI dust within the cluster size range of 2-10 μm. The μ-XAFS analysis confirmed that the speciation of Cs in MSWI dust was similar to that of CsCl, while in SSI dusts it was similar to pollucite. The solubility of Cs was considered to be influenced by the exact Cs species present in incineration residue.

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

DOE Office of Scientific and Technical Information (OSTI.GOV)

Karim, Ayman M.; Al Hasan, Naila M.; Ivanov, Sergei A.

2015-06-11

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

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Zhicheng; Rao, Linfeng; Abney, Carter W.

Adsorbents developed for the recovery of uranium from seawater display poor selectivity over other transition metals present in the ocean, with vanadium particularly problematic. To improve selectivity, an indispensable step is the positive identification of metal binding environments following actual seawater deployment. In this work we apply x-ray absorption fine structure (XAFS) spectroscopy to directly investigate the vanadium binding environment on seawater-deployed polyamidoxime adsorbents. Comparison of the x-ray absorption near edge spectra (XANES) reveal marked similarities to recently a reported non-oxido vanadium (V) structure formed upon binding with cyclic imidedioxime, a byproduct of generating amidoxime functionalities. Density functional theory (DFT)more » calculations provided a series of putative vanadium binding environments for both vanadium (IV) and vanadium (V) oxidation states, and with both amidoxime and cyclic imidedioxime. Fits of the extended XAFS (EXAFS) data confirmed vanadium (V) is bound exclusively by the cyclic imidedioxime moiety in a 1:2 metal:ligand fashion, though a modest structural distortion is also observed compared to crystal structure data and computationally optimized geometries which is attributed to morphology effects from the polymer graft chain and the absence of crystal packing interactions. These results demonstrate that improved selectivity for uranium over vanadium can be achieved by suppressing the formation of cyclic imidedioxime during preparation of polyamidoxime adsorbents for seawater uranium recovery.« less

Fine tuning and orientation control of surface Cu complexes on TiO2(110) premodified with mercapto compounds: the effect of different mercapto group positions.

PubMed

Takakusagi, Satoru; Nojima, Hirotaka; Ariga, Hiroko; Uehara, Hiromitsu; Miyazaki, Kotaro; Chun, Wang-Jae; Iwasawa, Yasuhiro; Asakura, Kiyotaka

2013-09-07

Three-dimensional structures of vacuum-deposited Cu species formed on TiO2(110) surfaces premodified with three mercaptobenzoic acid (MBA) isomers were studied using polarization-dependent total reflection fluorescence X-ray absorption fine structure (PTRF-XAFS). We explored the possibility of fine tuning and orientation control of the surface Cu structures, including their coordination and configuration against the surface, according to the different mercapto group positions of the three MBA isomers (o-, m-, and p-MBA). Almost linear S-Cu-O (lattice O of TiO2) surface compounds were formed on the three MBA-modified TiO2(110) surfaces; however, the orientation of the Cu species on the o- and m-MBA-modified TiO2(110) surfaces (40-45° inclined from the surface normal) was different from that on the p-MBA-modified TiO2(110) surface (60° from the surface normal). This work suggests that the selection of a different MBA isomer for premodification of a single crystal TiO2(110) surface enables fine tuning and orientation control of surface Cu complexes.

Amorphous-amorphous transition in a porous coordination polymer.

PubMed

Ohtsu, Hiroyoshi; Bennett, Thomas D; Kojima, Tatsuhiro; Keen, David A; Niwa, Yasuhiro; Kawano, Masaki

2017-07-04

The amorphous state plays a key role in porous coordination polymer and metal-organic framework phase transitions. We investigate a crystalline-to-amorphous-to-amorphous-to-crystalline (CAAC) phase transition in a Zn based coordination polymer, by X-ray absorption fine structure (XAFS) and X-ray pair distribution function (PDF) analysis. We show that the system shows two distinct amorphous phases upon heating. The first involves a reversible transition to a desolvated form of the original network, followed by an irreversible transition to an intermediate phase which has elongated Zn-I bonds.

XAFS and X-Ray and Electron Microscopy Investigations of Radionuclide Transformations at the Mineral-Microbe Interface

NASA Astrophysics Data System (ADS)

Kemner, Ken; O'Loughlin, Ed; Kelly, Shelly; Ravel, Bruce; Boyanov, Maxim; Sholto-Douglas, Deirdre; Lai, Barry; Cook, Russ; Carpenter, Everett; Harris, Vince; Nealson, Ken

2007-02-01

The microenvironment at and adjacent to surfaces of actively metabolizing cells, whether in a planktonic state or adhered to mineral surfaces, can be significantly different from the bulk environment. Microbial polymers (polysaccharides, DNA, RNA, and proteins), whether attached to or released from the cell, can contribute to the development of steep chemical gradients over very short distances. It is currently difficult to predict the behavior of contaminant radionuclides and metals in such microenvironments, because the chemistry there has been difficult or impossible to define. The behavior of contaminants in such microenvironments can ultimately affect their macroscopic fates. We have successfully performed a series of U LIII edge x-ray absorption fine structure (XAFS) spectroscopy, hard x-ray fluorescence (XRF) microprobe (150 nm resolution), and electron microscopy (EM) measurements on lepidocrocite thin films (˜1 micron thickness) deposited on kapton films that have been inoculated with the dissimilatory metal reducing bacterium Shewanella oneidensis MR-1 and exposed to 0.05 mM uranyl acetate under anoxic conditions. Similarly, we have performed a series of U LIII edge EXAFS measurements on lepidocrocite powders exposed to 0.05 mM uranyl acetate and exopolymeric components harvested from S. oneidensis MR-1 grown under aerobic conditions. These results demonstrate the utility of combining bulk XAFS with x-ray and electron microscopies.

Ferroelectrics under the Synchrotron Light: A Review.

PubMed

Fuentes-Cobas, Luis E; Montero-Cabrera, María E; Pardo, Lorena; Fuentes-Montero, Luis

2015-12-30

Currently, an intensive search for high-performance lead-free ferroelectric materials is taking place. ABO₃ perovskites (A = Ba, Bi, Ca, K and Na; B = Fe, Nb, Ti, and Zr) appear as promising candidates. Understanding the structure-function relationship is mandatory, and, in this field, the roles of long- and short-range crystal orders and interactions are decisive. In this review, recent advances in the global and local characterization of ferroelectric materials by synchrotron light diffraction, scattering and absorption are analyzed. Single- and poly-crystal synchrotron diffraction studies allow high-resolution investigations regarding the long-range average position of ions and subtle global symmetry break-downs. Ferroelectric materials, under the action of electric fields, undergo crystal symmetry, crystallite/domain orientation distribution and strain condition transformations. Methodological aspects of monitoring these processes are discussed. Two-dimensional diffraction clarify larger scale ordering: polycrystal texture is measured from the intensities distribution along the Debye rings. Local order is investigated by diffuse scattering (DS) and X-ray absorption fine structure (XAFS) experiments. DS provides information about thermal, chemical and displacive low-dimensional disorders. XAFS investigation of ferroelectrics reveals local B-cation off-centering and oxidation state. This technique has the advantage of being element-selective. Representative reports of the mentioned studies are described.

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

NASA Astrophysics Data System (ADS)

soni, Namrata; Parsai, Neetu; Mishra, Ashutosh

2016-10-01

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

Tellurium Distribution and Speciation in Contaminated Soils from Abandoned Mine Tailings: Comparison with Selenium.

PubMed

Qin, Hai-Bo; Takeichi, Yasuo; Nitani, Hiroaki; Terada, Yasuko; Takahashi, Yoshio

2017-06-06

The distribution and chemical species of tellurium (Te) in contaminated soil were determined by a combination of microfocused X-ray fluorescence (μ-XRF), X-ray diffraction (μ-XRD), and X-ray absorption fine structure (μ-XAFS) techniques. Results showed that Te was present as a mixture of Te(VI) and Te(IV) species, while selenium (Se) was predominantly present in the form of Se(IV) in the soil contaminated by abandoned mine tailings. In the contaminated soil, Fe(III) hydroxides were the host phases for Se(IV), Te(IV), and Te(VI), but Te(IV) could be also retained by illite. The difference in speciation and solubility of Se and Te in soil can result from different structures of surface complexes for Se and Te onto Fe(III) hydroxides. Furthermore, our results suggest that the retention of Te(IV) in soil could be relatively weaker than that of Te(VI) due to structural incorporation of Te(VI) into Fe(III) hydroxides. These findings are of geochemical and environmental significance for better understanding the solubility, mobility, and bioavailability of Te in the surface environment. To the best of our knowledge, this is the first study reporting the speciation and host phases of Te in field soil by the μ-XRF-XRD-XAFS techniques.

Effect of milling time and annealing temperature on nanoparticles evolution for 13.5% Cr ODS ferritic steel powders by joint application of XAFS and TEM

NASA Astrophysics Data System (ADS)

He, P.; Hoffmann, J.; Möslang, A.

2018-04-01

The characteristics of strengthening nanoparticles have a major influence on the mechanical property and irradiation resistance of oxide dispersion strengthened (ODS) steels. To determine how to control nanoparticles evolution, 0.3% Ti with 0.3% Y2O3 were added in 13.5%Cr pre-alloyed steel powders via different milling and consolidation conditions, then characterized by transmission electron microscopy (TEM) and X-ray absorption fine structure (XAFS) at synchrotron irradiation facility. The dissolution of Y2O3 is greatly dependent on the milling time at fixed milling speeds. After 24 h of milling, only minor amounts of the initially added Y2O3 dissolve into the steel matrix whereas TEM results reveal nearly complete dissolution of Y2O3 in 80-h-milled powder. The annealed powder FT-A800 (at 800 °C for 1 h) exhibits a structure near to the initially added Y2O3. The slightly deviation may be accounted for considerable lattice distortion related to the presence of atomic vacancies or formation of Y-Ti-O nucleus. The annealed powders FT-A1000 and FT-A1100 contain complex mixtures of Y-O/Y-Ti-O oxides, which cannot be fitted by any single thermally stable compounds. The coordination numbers of these first two shells in the annealed powders significantly raise as a function of the annealing temperature, indicating the formation of more ordered Y-O or Y-Ti-O particles. The extended X-ray absorption fine structure (EXAFS) spectrum could not necessarily distinguish the dominant oxide species.

Insights into the Effects of Zinc Doping on Structural Phase Transition of P2-Type Sodium Nickel Manganese Oxide Cathodes for High-Energy Sodium Ion Batteries.

PubMed

Wu, Xuehang; Xu, Gui-Liang; Zhong, Guiming; Gong, Zhengliang; McDonald, Matthew J; Zheng, Shiyao; Fu, Riqiang; Chen, Zonghai; Amine, Khalil; Yang, Yong

2016-08-31

P2-type sodium nickel manganese oxide-based cathode materials with higher energy densities are prime candidates for applications in rechargeable sodium ion batteries. A systematic study combining in situ high energy X-ray diffraction (HEXRD), ex situ X-ray absorption fine spectroscopy (XAFS), transmission electron microscopy (TEM), and solid-state nuclear magnetic resonance (SS-NMR) techniques was carried out to gain a deep insight into the structural evolution of P2-Na0.66Ni0.33-xZnxMn0.67O2 (x = 0, 0.07) during cycling. In situ HEXRD and ex situ TEM measurements indicate that an irreversible phase transition occurs upon sodium insertion-extraction of Na0.66Ni0.33Mn0.67O2. Zinc doping of this system results in a high structural reversibility. XAFS measurements indicate that both materials are almost completely dependent on the Ni(4+)/Ni(3+)/Ni(2+) redox couple to provide charge/discharge capacity. SS-NMR measurements indicate that both reversible and irreversible migration of transition metal ions into the sodium layer occurs in the material at the fully charged state. The irreversible migration of transition metal ions triggers a structural distortion, leading to the observed capacity and voltage fading. Our results allow a new understanding of the importance of improving the stability of transition metal layers.

Detection of trace metallic elements in oral lichenoid contact lesions using SR-XRF, PIXE, and XAFS

PubMed Central

Sugiyama, Tomoko; Uo, Motohiro; Wada, Takahiro; Omagari, Daisuke; Komiyama, Kazuo; Miyazaki, Serika; Numako, Chiya; Noguchi, Tadahide; Jinbu, Yoshinori; Kusama, Mikio; Mori, Yoshiyuki

2015-01-01

Oral lichen planus (OLP) and oral lichenoid contact lesions (OLCL) are chronic inflammatory mucocutaneous reactions with a risk of malignant transformation that alter the epithelium. OLP and OLCL have similar clinical and histopathological features and it is difficult to distinguish one from the other. Metallic restorations are suspected to generate OLCLs. Trace metal analysis of OLCL specimens may facilitate the discrimination of symptoms and identification of causative metallic restorations. The purpose of this study was to assess OLCL tissue samples for the prevalence of metallic elements derived from dental restorations, and to discriminate OLCL from OLP by using synchrotron radiation-excited X-ray fluorescence analysis (SR-XRF), particle-induced X-ray emission (PIXE), and X-ray absorption fine structure (XAFS). Typical elements of dental materials were detected in the OLCL, whereas no obvious element accumulation was detected in OLP and negative control specimens. The origin of the detected metallic elements was presumed to be dental alloys through erosion. Therefore, our findings support the feasibility of providing supporting information to distinguish OLCL from OLP by using elemental analysis. PMID:26085368

Enhancing the stability of copper chromite catalysts for the selective hydrogenation of furfural using ALD overcoating

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Hongbo; Lei, Yu; Kropf, A. Jeremy

2014-08-01

The stability of a gas-phase furfural hydrogenation catalyst (CuCr2O4 center dot CuO) was enhanced by depositing a thin Al2O3 layer using atomic layer deposition (ALD). Based on temperature-programed reduction (TPR) measurements, the reduction temperature of Cu was raised significantly, and the activation energy for furfural reduction was decreased following the ALD treatment. Thinner ALD layers yielded higher furfural hydrogenation activities. X-ray absorption fine structure (XAFS) spectroscopy studies indicated that Cu1+/Cu-0 are the active species for furfural reduction.

Structural properties of ultrafine Ba-hexaferrite nanoparticles

DOE Office of Scientific and Technical Information (OSTI.GOV)

Makovec, Darko, E-mail: Darko.Makovec@ijs.si; Primc, Darinka; Sturm, Saso

2012-12-15

Crystal structure of ultrafine Ba-hexaferrite (BaFe{sub 12}O{sub 19}) nanoparticles was studied using X-ray diffractometry (XRD), high-resolution transmission electron microscopy (HRTEM), energy-dispersive X-ray spectroscopy (EDXS), X-ray absorption fine structure (XAFS), and Moessbauer spectroscopy (MS), to be compared to the structure of larger nanoparticles and the bulk. The nanoparticles were synthesized with hydrothermal treatment of an appropriate suspension of Ba and Fe hydroxides in the presence of a large excess of OH{sup -}. The ultrafine nanoparticles were formed in a discoid shape, {approx}10 nm wide and only {approx}3 nm thick, comparable to the size of the hexagonal unit cell in the c-direction.more » The HRTEM image analysis confirmed the hexaferrite structure, whereas EDXS showed the composition matching the BaFe{sub 12}O{sub 19} formula. XAFS and MS analyses showed considerable disorder of the structure, most probably responsible for the low magnetization. - Graphical abstract: Left: HREM image of an ultrafine Ba-hexaferrite nanoparticle (inset: TEM image of the nanoparticles); Right: the experimental HRTEM image is compared with calculated image and corresponding atomic model. Highlights: Black-Right-Pointing-Pointer Crystal structure of ultrafine Ba-hexaferrite (BaFe{sub 12}O{sub 19}) nanoparticles was compared to the structure of the bulk. Black-Right-Pointing-Pointer Thickness the discoid nanoparticles was comparable to the size of the hexagonal unit cell in the c-direction. Black-Right-Pointing-Pointer Considerable disorder of the nanoparticles' structure is most probably responsible for their low magnetization.« less

X-Ray Absorption Spectroscopy of Fe-Substituted Allophane and Imogolite

NASA Astrophysics Data System (ADS)

Baker, L. L.; Strawn, D. G.; Nickerson, R. D.; McDaniel, P.

2011-12-01

Martian rocks and sediments contain weathering products including clay minerals formed as a result of interaction between rocks and water, and these materials can act as important indicators of past surface conditions on Mars. Weathering of terrestrial volcanic rocks similar to those on Mars produces nano-sized, variably hydrated aluminosilicate and iron oxide minerals, including allophane, imogolite, halloysite, hisingerite, and ferrihydrite. The nanoaluminosilicates can contain isomorphically substituted Fe, which may affect their spectral and physical properties as well as their eventual recrystallization products. Detection and quantification of such minerals in natural environments on Earth is difficult due to their variable chemical composition and lack of long-range crystalline order. Their accurate detection and quantification on Mars requires a better understanding of how composition affects their spectral properties and evolution to more crystalline phases. Aluminosilicate nanoparticles of varying composition were synthesized with isomorphically substituted Fe at Fe:Al ratios of 1:100. Allophanes were synthesized with Al:Si ratios of 2:1, 1:1, and 1:3. The substituted Fe was probed using Fe K-edge X-ray absorption fine structure spectroscopy (XAFS). The XAFS spectrum contains information about the molecular environment surrounding the target atom, and is an ideal technique for studying poorly crystalline materials that are difficult to characterize using bulk methods such as XRD. The near-edge (XANES) and extended (EXAFS) portions of the XAFS spectrum were examined, and allophane backscattering paths were fit using coordinates for a modified nanoball model (1). XANES spectra rule out ferrihydrite in the synthetic samples, suggesting all Fe was incorporated into the aluminosilicate structure. The XAFS results suggest that Fe substituted into the allophane structure is present as Fe(III) in octahedral coordination in a well-ordered sheet. Some Fe substitution in tetrahedral sites occurs in allophane with Al:Si = 2:1, but not in higher-Si compositions. These results support the nanoball model for allophane (1) based on a rolled octahedral sheet and indicate that sheet is well ordered. They do not support proposed models of an incomplete octahedral sheet in high-Si allophanes. Analysis of Fe distribution suggests considerable Fe clustering in the octahedral sheet which increases with sample aging. This clustering could lead to eventual nucleation of a separate Fe (oxyhydr)oxide phase. (1) Creton et al. (2008) J Phys Chem C 112, 358.

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

PubMed

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

2017-02-21

Herein, we revealed that the electrochemical behaviors on the detection of heavy metal ions (HMIs) would largely rely on the exposed facets of SnO 2 nanoparticles. Compared to the high-energy {221} facet, the low-energy {110} facet of SnO 2 possessed better electrochemical performance. The adsorption/desorption tests, density-functional theory (DFT) calculations, and X-ray absorption fine structure (XAFS) studies showed that the lower barrier energy of surface diffusion on {110} facet was critical for the superior electrochemical property, which was favorable for the ions diffusion on the electrode, and further leading the enhanced electrochemical performance. Through the combination of experiments and theoretical calculations, a reliable interpretation of the mechanism for electroanalysis of HMIs with nanomaterials exposed by different crystal facets has been provided. Furthermore, it provides a deep insight into understanding the key factor to improve the electrochemical performance for HMIs detection, so as to design high-performance electrochemical sensors.

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

NASA Astrophysics Data System (ADS)

Wu, Z. Y.

2013-04-01

The 15th International Conference on X-ray Absorption Fine Structure (XAFS15) was held on 22-28 July 2012 in Beijing, P. R. China. About 340 scientists from 34 countries attended this important international event. Main hall Figure 1. Main hall of XAFS15. The rapidly increasing application of XAFS to the study of a large variety of materials and the operation of the new SR source led to the first meeting of XAFS users in 1981 in England. Following that a further 14 International Conferences have been held. Comparing a breakdown of attendees according to their national origin, it is clear that participation is spreading to include attendees from more and more countries every year. The strategy of development in China of science and education is increasing quickly thanks to the large investment in scientific and technological research and infrastructure. There are three Synchrotron Radiation facilities in mainland China, Hefei Light Source (HLS) in the National Natural Science Foundation of China (NSRL), Beijing Synchrotron Radiation Facility (BSRF) in the Institute of High Energy Physics, and Shanghai Synchrotron Radiation Facility (SSRF) in the Shanghai Institute of Applied Physics. More than 10000 users and over 5000 proposals run at these facilities. Among them, many teams from the USA, Japan, German, Italy, Russia, and other countries. More than 3000 manuscript were published in SCI journals, including (incomplete) Science (7), Nature (10), Nature Series (7), PNAS (3), JACS (12), Angew. Chem. Int. Ed. (15), Nano Lett. (2), etc. In XAFS15, the participants contributed 18 plenary invited talks, 16 parallel invited talks, 136 oral presentations, 12 special talks, and 219 poster presentations. Wide communication was promoted in the conference halls, the classical banquet restaurant, and the Great Wall. Parallel hallCommunicationPoster room Figure 2. Parallel hallFigure 3. CommunicationFigure 4. Poster room This volume contains 136 invited and contributed papers, accepted after a rigorous peer review procedure. A group of about 90 outstanding scientists in the field reviewed and suggested revisions of the manuscripts to improve scientific presentation. As a result, we believe the entire volume has reached a high standard. The 19 topics covered are listed as follows: Theory Data analysis New technology and devices of XAFS Applications in Nano science and technology Applications in Life Science Applications in Chemistry Applications in Catalytic Science Applications in Surface and Interface Science Applications in Material Science Applications in Energy and Environmental Science Applications in Magnetic and Related Material Science Applications in Nuclear Science Applications in Disordered Systems Applications in Extreme Conditions Applications for Time-resolved experiments XMCD technology and its applications Advanced methods (e.g., new coherent sources and spectroscopic imaging techniques) XAFS combined with other experimental methods Other related studies We hope this volume will be a useful reference for the ongoing scientific activity in XAFS. We would also like to express our sincere appreciation to the sponsors for their generous support: Chinese Academy of Science, National Natural Science Foundation of China, China Center of Advanced Science and Technology World Laboratory, University of Science and Technology of China, National Synchrotron Radiation Laboratory, Institute of High Energy Physics Chinese Academy of Sciences, and our commercial sponsors (AREVA, Xi'an Action Power Electric Co., Ltd). Finally, we would like to acknowledge the entire local organizing staff (names are given below) and particularly the collaborators and members of the XAS group at the National Natural Science Foundation of China and Institute of High Energy Physics Chinese Academy of Sciences for their efforts to make the XAFS15 conference a success. Ziyu Wu Chair of the Conference and Proceedings Editor Hefei, P. R. China, 28 September 2012 Committees and Staff Chair of the Conference Ziyu Wu International Advisory Committee Adam Hitchcock, Canada Adriano Filipponi, Italy Alain Manceau, France Alexander Soldatov, Russia Andrea Di Cicco, Italy Britt Hedman, USA Bruce Bunker, USA Calogero R. Natoli, Italy Christopher T. Chantler, Australia Frank M. F. De Groot, Netherlands Hiroyuki Oyanagi, Japan Ingolf Lindau, USA J. Mustre de Leon, México James E Penner-Hahn, USA Joaquin Garcia Ruiz, Spain John Evans, UK John J. Rehr, USA Kiyotaka Asakura, Japan Majed Chergui, Switzerland Mark Newton, UK Shiqiang Wei, P. R. China Tsun-Kong Sham, Canada Ziyu Wu, P. R. China International Program Committee Antonio Bianconi, Italy Augusto Marcelli, Italy Emad Flear Aziz, Germany Jinghua Guo, USA Joly Yves, France Masaharu Nomura, Japan Maurizio Benfatto, Italy Pieter Glatzel, France Shiqiang Wei, China Tiandou Hu, China Toshihiko Yokoyama, Japan Way-Faung Pong, Taiwan Xinyi Zhang, China Yi Xie, China Yuying Huang, China Zhonghua Wu, China Ziyu Wu, China Local Organizing Committee Bo He Fengchun Hu Haifeng Zhao Jing Zhang Meijuan Yu Qin Yu Shuo Zhang Wangsheng Chu Wei He Wei Xu Wensheng Yan Xiaomei Gong Xing Chen Yang Zou Yi Xia Zheng Jiang Zhi Xie Zhihu Sun Zhiyun Pan Additional Staff Chengxun Liu

Coordination and structure of Ca(II)-acetate complexes in aqueous solution studied by a combination of Raman and XAFS spectroscopies

NASA Astrophysics Data System (ADS)

Muñoz Noval, Álvaro; Nishio, Daisuke; Kuruma, Takuya; Hayakawa, Shinjiro

2018-06-01

The determination of the structure of Ca(II)-acetate in aqueous solution has been addressed by combining Raman and X-ray absorption fine structure spectroscopies. The pH-dependent speciation of the acetate/Ca(II) system has been studied observing modifications in specific Raman bands of the carboxyl group. The current results evidence the Ca(II)-acetate above acetate pKa forms a bidentate complex and presents a coordination 6, in which the Ca-O shell radius decrease of about 0.1 Å with respect the hydrated Ca2+ with coordination 8. The experimental results show the OCO angle of the carboxyl in the complex is close to 124°, being the OCaO angle about 60°.

Insights into the Effects of Zinc Doping on Structural Phase Transition of P2-Type Sodium Nickel Manganese Oxide Cathodes for High-Energy Sodium Ion Batteries

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wu, Xuehang; Xu, Gui-Liang; Zhong, Guiming

P2-type sodium nickel manganese oxide-based cathode materials with higher energy densities are prime candidates for applications in rechargeable sodium ion batteries. A systematic study combining in situ high energy X-ray diffraction (HEXRD), ex situ Xray absorption fine spectroscopy (XAFS), transmission electron microscopy (TEM), and solid-state nuclear magnetic resonance (SSNMR) techniques was carried out to gain a deep insight into the structural evolution of P2-Na 0.66Ni 0.33-xZn xMn 0.67O 2 (x = 0, 0.07) during cycling. In situ HEXRD and ex situ TEM measurements indicate that an irreversible phase transition occurs upon sodium insertion-extraction of Na 0.66Ni 0.33Mn 0.67O 2. Zincmore » doping of this system results in a high structural reversibility. XAFS measurements indicate that both materials are almost completely dependent on the Ni 4+/Ni 3+/ Ni 2+ redox couple to provide charge/discharge capacity. SS-NMR measurements indicate that both reversible and irreversible migration of transition metal ions into the sodium layer occurs in the material at the fully charged state. The irreversible migration of transition metal ions triggers a structural distortion, leading to the observed capacity and voltage fading. Our results allow a new understanding of the importance of improving the stability of transition metal layers.« less

Sorption of chromium with struvite during phosphorus recovery.

PubMed

Rouff, Ashaki A

2012-11-20

Struvite (MgNH(4)PO(4)·6H(2)O; MAP) precipitation is a viable means of phosphorus (P) recovery from animal and human wastes. The behavior of metal contaminants such as chromium (Cr) during struvite precipitation, however, requires consideration. Here the influence of both Cr concentration and oxidation state on sorption is assessed. The Cr content of struvite precipitated in the presence of 1-100 μM Cr as Cr(III) (22.3-3030.1 mg/kg) was higher than that of solids from Cr(VI) (4.5-5.1 mg/kg) solutions. For 1-20 μM Cr(III) solids, scanning electron microscopy (SEM) revealed etch pit formation on struvite crystal surfaces, indicative of a surface interaction. The formation of an adsorbate was confirmed by X-ray absorption fine structure spectroscopy (XAFS). At initial concentrations ≥20 μM Cr(III), XAFS confirmed the formation of a Cr(OH)(3)·nH(2)O(am) precipitate. Fourier transform infrared (FT-IR) spectroscopy revealed that both Cr(III) and Cr(VI) sorption resulted in distortion of the PO(4)(3-) tetrahedra in the mineral structure. This, combined with SEM results revealed that even at low sorbed concentrations, the Cr impurity can affect the mineral surface and structure. Thus, the initial Cr concentration and oxidation state in wastes targeted for P recovery will dictate the final Cr content, the mechanism of sorption, and impact on the struvite structure.

In situ X-ray absorption fine structure analysis of redox reactions of nickel species with variable particle sizes supported on silica

NASA Astrophysics Data System (ADS)

Yamamoto, Yusaku; Suzuki, Atsushi; Tsutsumi, Naoki; Katagiri, Masaki; Yamashita, Shohei; Niwa, Yasuhiro; Katayama, Misaki; Inada, Yasuhiro

2018-02-01

The chemical states of Ni species were systematically investigated using an in situ XAFS technique for a series of SiO2-supported Ni catalysts with different Ni particle sizes. The Ni particles were refined by varying the Ni loading in the range between 0.10 and 5 wt% and by adding citric acid into the precursor solution. An in situ observation cell for fluorescence-yield XAFS measurements was developed for the dilute Ni catalysts. The chemical state of the supported Ni species converted between Ni(0) and NiO, and no other stable species were formed during the temperature-programmed oxidation and reduction processes. Refinement of the Ni particles resulted in decreasing the oxidation temperature and increasing the reduction temperature. These shifts were explained by the affinity of NiO to SiO2, and more effective stabilization was thus anticipated for flattened small NiO particles with an increased contact area. In addition, the inhomogeneous distribution of small Ni particles observed for dilute catalysts was explained in terms of the precursor solution volume when nuclei of the precursor compound precipitated on SiO2 during the drying process.

Local Structure Analysis and Interface Layer Effect of Phase-Change Recording Material Using Actual Media

NASA Astrophysics Data System (ADS)

Nakai, Tsukasa; Yoshiki, Masahiko; Satoh, Yasuhiro; Ashida, Sumio

2008-07-01

The influences of the interface layer on crystal structure, the local atomic arrangement, and the electronic and chemical structure of a GeBiTe (GBT) phase-change recording material have been investigated using X-ray diffraction (XRD), X-ray absorption fine structure (XAFS), and hard X-ray photoelectron spectroscopy (HX-PES) methods using actual rewritable high-speed HD DVD media without special sample processing. XRD results showed that the crystal structure of laser-crystallized GBT alloy in the actual HD DVD media is the same as that of GeSbTe (GST) alloy, which has a NaCl-type structure. No differences between samples with and without interface layers were found. The lattice constant of GBT is larger than that of GST. Bi increases the lattice constant of GST with respect to the Bi substitution ratio of Sb. According to HX-PES, the DOS of in the recording film amorphous state with an interface layer is closer to that of the crystalline state than the recording film without an interface layer. From XAFS results, clear differences between amorphous (Amo.) and crystalline states (Cry.) were observed. The interatomic distance of amorphous recording material is independent of the existence of an interface layer. On the other hand, the coordination number varied slightly due to the presence of the interface layer. Therefore, the electronic state of the recording layer changes because of the interface layer, although the local structure changes only slightly except for the coordination number. Combining these results, we conclude that the interface layer changes the electronic state of the recording layer and promotes crystallization, but only affects the local structure of the atomic arrangement slightly.

Combined single crystal polarized XAFS and XRD at high pressure: probing the interplay between lattice distortions and electronic order at multiple length scales in high T c cuprates

DOE PAGES

Fabbris, G.; Hücker, M.; Gu, G. D.; ...

2016-07-14

Some of the most exotic material properties derive from electronic states with short correlation length (~10-500 Å), suggesting that the local structural symmetry may play a relevant role in their behavior. In this study, we discuss the combined use of polarized x-ray absorption fine structure and x-ray diffraction at high pressure as a powerful method to tune and probe structural and electronic orders at multiple length scales. Besides addressing some of the technical challenges associated with such experiments, we illustrate this approach with results obtained in the cuprate La 1.875Ba 0.125CuO 4, in which the response of electronic order tomore » pressure can only be understood by probing the structure at the relevant length scales.« less

XAFS studies on a modified Al-Si hypoeutectic alloy

NASA Astrophysics Data System (ADS)

Srirangam, V. S. Prakash; Chattopadhyay, S.; Shibata, T.; Kaduk, J. A.; Miller, J. T.; Segre, C. U.; Shankar, S.

2009-11-01

To understand the role of Sr in doped aluminium-silicon alloys, we have conducted for the first time, Sr- K edge XAFS measurements on Al-3%Si-0.04%Sr. Aluminium-Silicon alloys are widely used in automobile and aerospace applications. Modification of these alloys with addition of trace levels of Sr (200-400 ppm) results in changing the morphology of Si eutectic from "plate" like structure to "fibrous" structure. Several theories have been proposed to understand the mechanism of modification of eutectic phases with Sr addition in these alloys, but there is no conclusive evidence in support of these theories. From our XAFS analysis, we suggest Sr-Si bonds and Sr-Sr correlations may be responsible for the morphological transformation observed in the alloy.

On the removal of hexavalent chromium from a Class F fly ash.

PubMed

Huggins, F E; Rezaee, M; Honaker, R Q; Hower, J C

2016-05-01

Coarse and fine samples of a Class F fly ash obtained from commercial combustion of Illinois bituminous coal have been exposed to two long-term leaching tests designed to simulate conditions in waste impoundments. ICP-AES analysis indicated that the coarse and fine fly ash samples contained 135 and 171mg/kg Cr, respectively. Measurements by XAFS spectroscopy showed that the ash samples originally contained 5 and 8% of the chromium, respectively, in the hexavalent oxidation state, Cr(VI). After exposure to water for more than four months, the percentage of chromium as Cr(VI) in the fly-ash decreased significantly for the coarse and fine fly-ash in both tests. Combining the XAFS data with ICP-AES data on the concentration of chromium in the leachates indicated that, after the nineteen-week-long, more aggressive, kinetic test on the coarse fly ash, approximately 60% of the Cr(VI) had been leached, 20% had been reduced to Cr(III) and retained in the ash, and 20% remained as Cr(VI) in the ash. In contrast, during the six-month-long baseline test, very little Cr was actually leached from either the coarse or the fine fly-ash (<0.1mg/kg); rather, about 66% and 20%, respectively, of the original Cr(VI) in the coarse and fine fly-ash was retained in the ash in that form, while the remainder, 34% and 80%, respectively, was reduced and retained in the ash as Cr(III). The results are interpreted as indicating that Cr(VI) present in Class F fly-ash can be reduced to Cr(III) when in contact with water and that such chemical reduction can compete with physical removal of Cr(VI) from the ash by aqueous leaching. Copyright © 2016 Elsevier Ltd. All rights reserved.

Structural Characterization of Poorly-Crystalline Scorodite, Iron (III)-arsenate Co-precipitates and Uranium Millneutralized Raffinate Solids using X-ray Absorption Fine Structure Spectroscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chen, N.; Jiang, D; Cutler, J

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

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

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chen, N; Jiang, D T; Cutler, J

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

Comparative Analysis of Microbial Communities in Iron-Dominated Flocculent Mats in Deep-Sea Hydrothermal Environments

PubMed Central

Kikuchi, Sakiko; Mitsunobu, Satoshi; Takaki, Yoshihiro; Yamanaka, Toshiro; Toki, Tomohiro; Noguchi, Takuroh; Nakamura, Kentaro; Abe, Mariko; Hirai, Miho; Yamamoto, Masahiro; Uematsu, Katsuyuki; Miyazaki, Junichi; Nunoura, Takuro; Takahashi, Yoshio; Takai, Ken

2016-01-01

ABSTRACT It has been suggested that iron is one of the most important energy sources for photosynthesis-independent microbial ecosystems in the ocean crust. Iron-metabolizing chemolithoautotrophs play a key role as primary producers, but little is known about their distribution and diversity and their ecological role as submarine iron-metabolizing chemolithotrophs, particularly the iron oxidizers. In this study, we investigated the microbial communities in several iron-dominated flocculent mats found in deep-sea hydrothermal fields in the Mariana Volcanic Arc and Trough and the Okinawa Trough by culture-independent molecular techniques and X-ray mineralogical analyses. The abundance and composition of the 16S rRNA gene phylotypes demonstrated the ubiquity of zetaproteobacterial phylotypes in iron-dominated mat communities affected by hydrothermal fluid input. Electron microscopy with energy-dispersive X-ray microanalysis and X-ray absorption fine structure (XAFS) analysis revealed the chemical and mineralogical signatures of biogenic Fe-(oxy)hydroxide species and the potential contribution of Zetaproteobacteria to the in situ generation. These results suggest that putative iron-oxidizing chemolithoautotrophs play a significant ecological role in producing iron-dominated flocculent mats and that they are important for iron and carbon cycles in deep-sea low-temperature hydrothermal environments. IMPORTANCE We report novel aspects of microbiology from iron-dominated flocculent mats in various deep-sea environments. In this study, we examined the relationship between Zetaproteobacteria and iron oxides across several hydrothermally influenced sites in the deep sea. We analyzed iron-dominated mats using culture-independent molecular techniques and X-ray mineralogical analyses. The scanning electron microscopy–energy-dispersive X-ray spectroscopy SEM-EDS analysis and X-ray absorption fine structure (XAFS) analysis revealed chemical and mineralogical signatures of biogenic Fe-(oxy)hydroxide species as well as the potential contribution of the zetaproteobacterial population to the in situ production. These key findings provide important information for understanding the mechanisms of both geomicrobiological iron cycling and the formation of iron-dominated mats in deep-sea hydrothermal fields. PMID:27422841

Binding characteristics of copper and cadmium by cyanobacterium Spirulina platensis.

PubMed

Fang, Linchuan; Zhou, Chen; Cai, Peng; Chen, Wenli; Rong, Xingmin; Dai, Ke; Liang, Wei; Gu, Ji-Dong; Huang, Qiaoyun

2011-06-15

Cyanobacteria are promising biosorbent for heavy metals in bioremediation. Although sequestration of metals by cyanobacteria is known, the actual mechanisms and ligands involved are not very well understood. The binding characteristics of Cu(II) and Cd(II) by the cyanobacterium Spirulina platensis were investigated using a combination of chemical modifications, batch adsorption experiments, Fourier transform infrared (FTIR) spectroscopy and X-ray absorption fine structure (XAFS) spectroscopy. A significant increase in Cu(II) and Cd(II) binding was observed in the range of pH 3.5-5.0. Dramatical decrease in adsorption of Cu(II) and Cd(II) was observed after methanol esterification of the nonliving cells demonstrating that carboxyl functional groups play an important role in the binding of metals by S. platensis. The desorption rate of Cu(II) and Cd(II) from S. platensis surface was 72.7-80.7% and 53.7-58.0% by EDTA and NH(4)NO(3), respectively, indicating that ion exchange and complexation are the dominating mechanisms for Cu(II) and Cd(II) adsorption. XAFS analysis provided further evidence on the inner-sphere complexation of Cu by carboxyl ligands and showed that Cu is complexed by two 5-membered chelate rings on S. platensis surface. Copyright © 2011 Elsevier B.V. All rights reserved.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ackerson, Michael R.; Tailby, Nicholas D.; Watson, E. Bruce

Titanium can be incorporated either tetrahedrally (IVTi) or octahedrally (VITi) in most silicate minerals. Ti K-edge X-ray absorption fine structure (XAFS) spectroscopy enables observation of Ti coordination in minerals and melts. In this study, XAFS is used to determine the coordination of Ti in synthetic and natural garnets. Garnets grown synthetically at eclogite- and granulite-facies conditions can contain several wt% TiO2, most of which is incorporated as VITi. This observation aligns with major element trends in these garnets. In natural garnets grown at lower temperatures and pressures, on the other hand, Ti is observed to occupy both the octahedral andmore » tetrahedral sites in garnet—in some cases Ti is almost entirely fourfold coordinated. Combined with previous research (see Ackerson et al. 2017, this issue) on substitution mechanisms for VITi, the results of this study demonstrate that Ti is incorporated on two crystallographic sites in garnet by at least three primary substitution mechanisms. In both natural and synthetic garnets, there is a discernible increase in VITi content in garnet with increasing temperature and pressure, suggesting a significant role for these two parameters in determining Ti solubility. However, a continuous increase in VITi with increasing grossular content also suggests that the Ca content of the garnet plays a critical role.« less

X-ray Absorption Spectroscopy Investigation of Iodine Capture by Silver-Exchanged Mordenite

DOE Office of Scientific and Technical Information (OSTI.GOV)

Abney, Carter W.; Nan, Yue; Tavlarides, Lawrence L.

Capture of radioactive iodine is a significant consideration during reprocessing of spent nuclear fuel and disposal of legacy wastes. While silver-exchanged mordenite (AgZ) is widely regarded as a benchmark material for assessing iodine adsorption performance, previous research efforts have largely focused on bulk material properties rather than the underpinning molecular interactions that achieve effective iodine capture. As a result, the fundamental understanding necessary to identify and mitigate deactivation pathways for the recycle of AgZ is not available. In this paper, we applied X-ray Absorption Fine Structure (XAFS) spectroscopy to investigate AgZ following activation, adsorption of iodine, regeneration, and recycle, observingmore » no appreciable degradation in performance due to the highly controlled conditions under which the AgZ was maintained. Fits of the extended XAFS (EXAFS) data reveal complete formation of Ag 0 nanoparticles upon treatment with H 2, and confirm the formation of α-AgI within the mordenite channels in addition to surface γ/β-AgI nanoparticles following iodine exposure. Analysis of the nanoparticle size and fractional composition of α-AgI to γ/β-AgI supports ripening of surface nanoparticles as a function of recycle. Finally, this work provides a foundation for future investigation of AgZ deactivation under conditions relevant to spent nuclear fuel reprocessing.« less

X-ray Absorption Spectroscopy Investigation of Iodine Capture by Silver-Exchanged Mordenite

DOE PAGES

Abney, Carter W.; Nan, Yue; Tavlarides, Lawrence L.

2017-03-29

Capture of radioactive iodine is a significant consideration during reprocessing of spent nuclear fuel and disposal of legacy wastes. While silver-exchanged mordenite (AgZ) is widely regarded as a benchmark material for assessing iodine adsorption performance, previous research efforts have largely focused on bulk material properties rather than the underpinning molecular interactions that achieve effective iodine capture. As a result, the fundamental understanding necessary to identify and mitigate deactivation pathways for the recycle of AgZ is not available. In this paper, we applied X-ray Absorption Fine Structure (XAFS) spectroscopy to investigate AgZ following activation, adsorption of iodine, regeneration, and recycle, observingmore » no appreciable degradation in performance due to the highly controlled conditions under which the AgZ was maintained. Fits of the extended XAFS (EXAFS) data reveal complete formation of Ag 0 nanoparticles upon treatment with H 2, and confirm the formation of α-AgI within the mordenite channels in addition to surface γ/β-AgI nanoparticles following iodine exposure. Analysis of the nanoparticle size and fractional composition of α-AgI to γ/β-AgI supports ripening of surface nanoparticles as a function of recycle. Finally, this work provides a foundation for future investigation of AgZ deactivation under conditions relevant to spent nuclear fuel reprocessing.« less

Electrochemical lithium intercalation into Bi2Sr2CaCu2O8+δ

NASA Astrophysics Data System (ADS)

Shimono, Takahiro; Kobayashi, Wataru; Nitani, Hiroaki; Kumai, Reiji; Moritomo, Yutaka

2013-04-01

We have prepared Li-intercalated LixBi2Sr2CaCu2O8+δ (x =0-2.0) samples by using electrochemical method, and performed synchrotron x-ray diffraction, Cu K-edge x-ray absorption fine structure (XAFS), and magnetic susceptibility measurements. With increasing x, a- and c-lattice parameters monotonically increase, which shows lithium intercalation into Bi2Sr2CaCu2O8+δ. Accompanied by the lithium insertion, the valence of Cu ion changes from Cu2+/Cu3+ to Cu1+/Cu2+ to realize charge neutrality. This change of the valence was detected by Cu K-edge XAFS measurement. A clear increase of spectral weight that corresponds to 1s→ 4pπ(3d10L) was observed at around 8982 eV with x. The superconducting (SC) transition temperature TC significantly changes from 74 K for x = 0 to 90 K for x = 0.8, which is attributed to modified density of states by the decrease of hole concentration. A volume fraction of the superconducting phase was 1-2 % for x >= 0.6 implying phase separation where Li-rich non SC phase and Li-poor SC phase coexist. Such a phase separation is universally seen in electrode active materials.

Ferroelectrics under the Synchrotron Light: A Review

PubMed Central

Fuentes-Cobas, Luis E.; Montero-Cabrera, María E.; Pardo, Lorena; Fuentes-Montero, Luis

2015-01-01

Currently, an intensive search for high-performance lead-free ferroelectric materials is taking place. ABO3 perovskites (A = Ba, Bi, Ca, K and Na; B = Fe, Nb, Ti, and Zr) appear as promising candidates. Understanding the structure–function relationship is mandatory, and, in this field, the roles of long- and short-range crystal orders and interactions are decisive. In this review, recent advances in the global and local characterization of ferroelectric materials by synchrotron light diffraction, scattering and absorption are analyzed. Single- and poly-crystal synchrotron diffraction studies allow high-resolution investigations regarding the long-range average position of ions and subtle global symmetry break-downs. Ferroelectric materials, under the action of electric fields, undergo crystal symmetry, crystallite/domain orientation distribution and strain condition transformations. Methodological aspects of monitoring these processes are discussed. Two-dimensional diffraction clarify larger scale ordering: polycrystal texture is measured from the intensities distribution along the Debye rings. Local order is investigated by diffuse scattering (DS) and X-ray absorption fine structure (XAFS) experiments. DS provides information about thermal, chemical and displacive low-dimensional disorders. XAFS investigation of ferroelectrics reveals local B-cation off-centering and oxidation state. This technique has the advantage of being element-selective. Representative reports of the mentioned studies are described. PMID:28787814

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

NASA Astrophysics Data System (ADS)

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

2006-06-01

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

Selective separation of americium from europium using 2,9-bis(triazine)-1,10-phenanthrolines in ionic liquids: a new twist on an old story

DOE Office of Scientific and Technical Information (OSTI.GOV)

Williams, Neil J.; Dehaudt, Jeremy; Bryantsev, Vyacheslav S.

Bis-triazine phenanthrolines have shown great promise for f-block metal separations, attributable to their highly preorganized structure, nitrogen donors, and more enhanced covalent bonding with actinides over lanthanides. However, their limited solubility in traditional solvents remains a technological bottleneck. Here in this paper we report our recent work using a simple 2,9-bis(triazine)-1,10-phenanthroline (Me-BTPhen) dissolved in an ionic liquid (IL), demonstrating the efficacy of IL extraction systems for the selective separation of americium from europium, achieving separation factors in excess of 7500 and selectively removing up to 99% of the americium. Characterization of the coordination environment was performed using a combination ofmore » X-ray absorption fine structure spectroscopy (XAFS) and density functional theory (DFT) calculations.« less

Selective separation of americium from europium using 2,9-bis(triazine)-1,10-phenanthrolines in ionic liquids: a new twist on an old story

DOE PAGES

Williams, Neil J.; Dehaudt, Jeremy; Bryantsev, Vyacheslav S.; ...

2017-02-10

Bis-triazine phenanthrolines have shown great promise for f-block metal separations, attributable to their highly preorganized structure, nitrogen donors, and more enhanced covalent bonding with actinides over lanthanides. However, their limited solubility in traditional solvents remains a technological bottleneck. Here in this paper we report our recent work using a simple 2,9-bis(triazine)-1,10-phenanthroline (Me-BTPhen) dissolved in an ionic liquid (IL), demonstrating the efficacy of IL extraction systems for the selective separation of americium from europium, achieving separation factors in excess of 7500 and selectively removing up to 99% of the americium. Characterization of the coordination environment was performed using a combination ofmore » X-ray absorption fine structure spectroscopy (XAFS) and density functional theory (DFT) calculations.« less

Local atomic structure of Pd and Ag in the SiC containment layer of TRISO fuel particles fissioned to 20% burn-up

NASA Astrophysics Data System (ADS)

Seibert, Rachel L.; Terrani, Kurt A.; Velázquez, Daniel; Hunn, John D.; Baldwin, Charles A.; Montgomery, Fred C.; Terry, Jeff

2018-03-01

The structure and speciation of fission products within the SiC barrier layer of tristructural-isotropic (TRISO) fuel particles irradiated to 19.6% fissions per initial metal atom (FIMA) burnup in the Advanced Test Reactor (ATR) at Idaho National Laboratory (INL) was investigated. As-irradiated fuel particles, as well as those subjected to simulated accident scenarios, were examined. The TRISO particles were characterized using synchrotron X-ray absorption fine-structure spectroscopy (XAFS) at the Materials Research Collaborative Access Team (MRCAT) beamline at the Advanced Photon Source. The TRISO particles were produced at Oak Ridge National Laboratory under the Advanced Gas Reactor Fuel Development and Qualification Program and sent to the ATR for irradiation. XAFS measurements on the palladium and silver K-edges were collected using the MRCAT undulator beamline. Analysis of the Pd edge indicated the formation of palladium silicides of the form PdxSi (2 ≤ x ≤ 3). In contrast, Ag was found to be metallic within the SiC shell safety tested to 1700 °C. To the best of our knowledge, this is the first result demonstrating metallic bonding of silver from fissioned samples. Knowledge of these reaction pathways will allow for better simulations of radionuclide transport in the various coating layers of TRISO fuels for next generation nuclear reactors. They may also suggest different ways to modify TRISO particles to improve their fuel performance and to mitigate potential fission product release under both normal operation and accident conditions.

Local atomic structure of Pd and Ag in the SiC containment layer of TRISO fuel particles fissioned to 20% burn-up

DOE PAGES

Seibert, Rachel L.; Terrani, Kurt A.; Velázquez, Daniel; ...

2018-03-01

The structure and speciation of fission products within the SiC barrier layer of tristructural-isotropic (TRISO) fuel particles irradiated to 19.6% fissions per initial metal atom (FIMA) burnup in the Advanced Test Reactor (ATR) at Idaho National Laboratory (INL) was investigated. As-irradiated fuel particles, as well as those subjected to simulated accident scenarios, were examined. The TRISO particles were characterized using synchrotron X-ray absorption fine-structure spectroscopy (XAFS) at the Materials Research Collaborative Access Team (MRCAT) beamline at the Advanced Photon Source. The TRISO particles were produced at Oak Ridge National Laboratory under the Advanced Gas Reactor Fuel Development and Qualification Programmore » and sent to the ATR for irradiation. XAFS measurements on the palladium and silver K-edges were collected using the MRCAT undulator beamline. Analysis of the Pd edge indicated the formation of palladium silicides of the form Pd xSi (2 ≤ x ≤ 3). In contrast, Ag was found to be metallic within the SiC shell safety tested to 1700 °C. To the best of our knowledge, this is the first result demonstrating metallic bonding of silver from fissioned samples. Knowledge of these reaction pathways will allow for better simulations of radionuclide transport in the various coating layers of TRISO fuels for next generation nuclear reactors. In conclusion, they may also suggest different ways to modify TRISO particles to improve their fuel performance and to mitigate potential fission product release under both normal operation and accident conditions.« less

Tunable metal-insulator transition in Nd{sub 1−x}Y{sub x}NiO{sub 3} (x = 0.3, 0.4) perovskites thin film at near room temperature

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shao, Tao; Qi, Zeming, E-mail: zmqi@ustc.edu.cn; Wang, Yuyin

2015-07-13

Metal-insulator transition (MIT) occurs due to the charge disproportionation and lattice distortions in rare-earth nickelates. Existing studies revealed that the MIT behavior of rare-earth nickelates is fairly sensitive to external stress/pressure, suggesting a viable route for MIT strain engineering. Unlike applying extrinsic strain, the MIT can also be modulated by through rare-earth cation mixing, which can be viewed as intrinsic quantum stress. We choose Nd{sub 1−X}Y{sub X}NiO{sub 3} (x = 0.3, 0.4) perovskites thin films as a prototype system to exhibit the tunable sharp MIT at near room temperature. By adjusting Y concentration, the transition temperature of the thin films can bemore » changed within the range of 340–360 K. X-ray diffraction, X-ray absorption fine structure (XAFS), and in situ infrared spectroscopy are employed to probe the structural and optical property variation affected by composition and temperature. The infrared transmission intensity decreases with temperature across the MIT, indicating a pronounced thermochromic effect. Meanwhile, the XAFS result exhibits that the crystal atomistic structure changes accompanying with the Y atoms incorporation and MIT phase transition. The heavily doped Y atoms result in the pre-edge peak descent and Ni-O bond elongation, suggesting an enhanced charge disproportionation effect and the weakening of hybridization between Ni-3d and O-2p orbits.« less

Local atomic structure of Pd and Ag in the SiC containment layer of TRISO fuel particles fissioned to 20% burn-up

DOE Office of Scientific and Technical Information (OSTI.GOV)

Seibert, Rachel L.; Terrani, Kurt A.; Velázquez, Daniel

The structure and speciation of fission products within the SiC barrier layer of tristructural-isotropic (TRISO) fuel particles irradiated to 19.6% fissions per initial metal atom (FIMA) burnup in the Advanced Test Reactor (ATR) at Idaho National Laboratory (INL) was investigated. As-irradiated fuel particles, as well as those subjected to simulated accident scenarios, were examined. The TRISO particles were characterized using synchrotron X-ray absorption fine-structure spectroscopy (XAFS) at the Materials Research Collaborative Access Team (MRCAT) beamline at the Advanced Photon Source. The TRISO particles were produced at Oak Ridge National Laboratory under the Advanced Gas Reactor Fuel Development and Qualification Programmore » and sent to the ATR for irradiation. XAFS measurements on the palladium and silver K-edges were collected using the MRCAT undulator beamline. Analysis of the Pd edge indicated the formation of palladium silicides of the form Pd xSi (2 ≤ x ≤ 3). In contrast, Ag was found to be metallic within the SiC shell safety tested to 1700 °C. To the best of our knowledge, this is the first result demonstrating metallic bonding of silver from fissioned samples. Knowledge of these reaction pathways will allow for better simulations of radionuclide transport in the various coating layers of TRISO fuels for next generation nuclear reactors. In conclusion, they may also suggest different ways to modify TRISO particles to improve their fuel performance and to mitigate potential fission product release under both normal operation and accident conditions.« less

Size-Controlled Dissolution of Organic-Coated Silver Nanoparticles

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ma, Rui; Levard, Clément; Marinakos, Stella M.

2012-04-02

The solubility of Ag NPs can affect their toxicity and persistence in the environment. We measured the solubility of organic-coated silver nanoparticles (Ag NPs) having particle diameters ranging from 5 to 80 nm that were synthesized using various methods, and with different organic polymer coatings including poly(vinylpyrrolidone) and gum arabic. The size and morphology of Ag NPs were characterized by transmission electron microscopy (TEM). X-ray absorption fine structure (XAFS) spectroscopy and synchrotron-based total X-ray scattering and pair distribution function (PDF) analysis were used to determine the local structure around Ag and evaluate changes in crystal lattice parameters and structure asmore » a function of NP size. Ag NP solubility dispersed in 1 mM NaHCO{sub 3} at pH 8 was found to be well correlated with particle size based on the distribution of measured TEM sizes as predicted by the modified Kelvin equation. Solubility of Ag NPs was not affected by the synthesis method and coating as much as by their size. Based on the modified Kelvin equation, the surface tension of Ag NPs was found to be {approx}1 J/m{sup 2}, which is expected for bulk fcc (face centered cubic) silver. Analysis of XAFS, X-ray scattering, and PDFs confirm that the lattice parameter, {alpha}, of the fcc crystal structure of Ag NPs did not change with particle size for Ag NPs as small as 6 nm, indicating the absence of lattice strain. These results are consistent with the finding that Ag NP solubility can be estimated based on TEM-derived particle size using the modified Kelvin equation for particles in the size range of 5-40 nm in diameter.« less

Uric acid-derived Fe3C-containing mesoporous Fe/N/C composite with high activity for oxygen reduction reaction in alkaline medium

NASA Astrophysics Data System (ADS)

Ma, Jun; Xiao, Dejian; Chen, Chang Li; Luo, Qiaomei; Yu, Yue; Zhou, Junhao; Guo, Changding; Li, Kai; Ma, Jie; Zheng, Lirong; Zuo, Xia

2018-02-01

In this work, a category of Fe3C-containing Fe/N/C mesoporous material has been fabricated by carbonizing the mixture of uric acid, Iron (Ⅲ) chloride anhydrous and carbon support (XC-72) under different pyrolysis temperature. Of all these samples, pyrolysis temperature (800 °C) becomes the most crucial factor in forming Fe3C active sites which synergizes with high content of graphitic N to catalyze oxygen reduction reaction (ORR). X-ray absorption fine structure spectroscopy (XAFS) is used to exhibit that the space structure around Fe atoms in the catalyst. This kind of catalyst possesses comparable ORR properties with commercial 20% Pt/C (onset potential is 0 V vs. Ag/AgCl in 0.1 M KOH), the average transfer electron number is 3.84 reflecting the 4-electron process. Moreover, superior stability and methanol tolerance deserve to be mentioned.

[CuCl(n)](2-n) ion-pair species in 1-ethyl-3-methylimidazolium chloride ionic liquid-water mixtures: ultraviolet-visible, X-ray absorption fine structure, and density functional theory characterization.

PubMed

Li, Guosheng; Camaioni, Donald M; Amonette, James E; Zhang, Z Conrad; Johnson, Timothy J; Fulton, John L

2010-10-07

We studied the coordination environment about Cu(II) in a pure ionic liquid, 1-ethyl-3-methylimidazolium chloride ([EMIM]Cl), and in binary mixtures of this compound with water across the entire range of compositions, using a combination of X-ray absorption fine structure (XAFS), ultraviolet-visible (UV-vis) spectroscopy, and electronic structure calculations. Our results show a series of stages in the ion pairing of the divalent cation, Cu(II), including the contact ion pairing of Cu(2+) with multiple Cl(-) ligands to form various CuCl(n)((2-n)) polyanions, as well as the subsequent solvation and ion pairing of the polychlorometallate anion with the EMIM(+) cation. Ion-pair formation is strongly promoted in [EMIM]Cl by the low dielectric constant and by the extensive breakdown of the water hydrogen-bond network in [EMIM]Cl-water mixtures. The CuCl(4)(2-) species dominates in the [EMIM]Cl solvent, and calculations along with spectroscopy show that its geometry distorts to C(2) symmetry compared to D(2d) in the gas phase. These results are important in understanding catalysis and separation processes involving transition metals in ionic liquid systems.

Cleaning up the Legacy of the Cold War: Plutonium Oxides and the Role of Synchrotron Radiation Research

DOE Office of Scientific and Technical Information (OSTI.GOV)

Clark, David Lewis

2015-01-21

The deceptively simple binary formula of AnO 2 belies an incredibly complex structural nature, and propensity to form mixed-valent, nonstoichiometric phases of composition AnO 2±x. For plutonium, the very formation of PuO 2+x has challenged a long-established dogma, and raised fundamental questions for long-term storage and environmental migration. This presentation covers two aspects of Los Alamos synchrotron radiation studies of plutonium oxides: (1) the structural chemistry of laboratory-prepared AnO 2+x systems (An = U, Pu; 0 ≤ x ≤ 0.25) determined through a combination of x-ray absorption fine structure spectroscopy (XAFS) and x-ray scattering of laboratory prepared samples; and (2)more » the application of synchrotron radiation towards the decontamination and decommissioning of the Rocky Flats Environmental Technology Site. Making the case for particle transport mechanisms as the basis of plutonium and americium mobility, rather than aqueous sorption-desorption processes, established a successful scientific basis for the dominance of physical transport processes by wind and water. The scientific basis was successful because it was in agreement with general theory on insolubility of PuO 2 in oxidation state IV, results of ultrafiltration analyses of field water/sediment samples, XAFS analyses of soil, sediment, and concrete samples, and was also in general agreement with on-site monitoring data. This understanding allowed Site contractors to rapidly move to application of soil erosion and sediment transport models as the means of predicting plutonium and americium transport, which led to design and application of site-wide soil erosion control technology to help control downstream concentrations of plutonium and americium in streamflow.« less

Atomistic Texture of Amorphous Manganese Oxides for Electrochemical Water Splitting Revealed by Ab Initio Calculations Combined with X-ray Spectroscopy.

PubMed

Mattioli, Giuseppe; Zaharieva, Ivelina; Dau, Holger; Guidoni, Leonardo

2015-08-19

Amorphous transition-metal (hydr)oxides are considered as the most promising catalysts that promote the oxidation of water to molecular oxygen, protons, and "energized" electrons, and, in turn, as fundamental parts of "artificial leaves" that can be exploited for large scale generation of chemical fuels (e.g., hydrogen) directly from sunlight. We present here a joint theoretical-experimental investigation of electrodeposited amorphous manganese oxides with different catalytic activities toward water oxidation (MnCats). Combining the information content of X-ray absorption fine structure (XAFS) measurements with the predictive power of ab initio calculations based on density functional theory, we have been able to identify the essential structural and electronic properties of MnCats. We have elucidated (i) the localization and structural connection of Mn(II), Mn(III), and Mn(IV) ions in such amorphous oxides and (ii) the distribution of protons at the MnCat/water interface. Our calculations result in realistic 3D models of the MnCat atomistic texture, formed by the interconnection of small planar Mn-oxo sheets cross-linked through different kinds of defective Mn atoms, isolated or arranged in closed cubane-like units. Essential for the catalytic activity is the presence of undercoordinated Mn(III)O5 units located at the boundary of the amorphous network, where they are ready to act as hole traps that trigger the oxidation of neighboring water molecules when the catalyst is exposed to an external positive potential. The present validation of a sound 3D model of MnCat improves the accuracy of XAFS fits and opens the way for the development of mechanistic schemes of its functioning beyond a speculative level.

Interfacial Cu + promoted surface reactivity: Carbon monoxide oxidation reaction over polycrystalline copper-titania catalysts

DOE PAGES

Senanayake, S. D.; Pappoe, N. A.; Nguyen-Phan, T. -D.; ...

2016-10-01

We have studied the catalytic carbon monoxide (CO) oxidation (CO+0.5O2 → CO2) reaction using a powder catalyst composed of both copper (5wt% loading) and titania (CuOx-TiO2). Our study was focused on revealing the role of Cu, and the interaction between Cu and TiO2, by systematic comparison between two nanocatalysts, CuOx-TiO2 and pure CuOx. We interrogated these catalysts under in situ conditions using X-ray Diffraction (XRD), X-ray Absorption Fine Structure (XAFS) and Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) to probe the structure and electronic properties of the catalyst at all stages of the reaction and simultaneously probe the surface statesmore » or intermediates of this reaction. With the aid of several ex situ characterization techniques including Transmission Electron Microscopy (TEM), the local catalyst morphology and structure was also studied. Our results show that a CuOx-TiO2 system is more active than bulk CuOx for the CO oxidation reaction due to its lower onset temperature and better stability at higher temperatures. Our results also suggests that a surface Cu+ species observed in the CuOx-TiO2 interface are likely to be a key player in the CO oxidation mechanism, while implicating that the stabilization of this species is probably associated with the oxide-oxide interface. Both in situ DRIFTS and XAFS measurements reveal that there is likely to be a Cu(Ti)-O mixed oxide at this interface. We discuss the nature of this Cu(Ti)-O interface and interpret its role on the CO oxidation reaction.« less

Speciation and characterization of arsenic in gold ores and cyanidation tailings using X-ray absorption spectroscopy

USGS Publications Warehouse

Paktunc, D.; Foster, A.; Heald, S.; Laflamme, G.

2004-01-01

The knowledge of mineralogy and molecular structure of As is needed to better understand the stability of As in wastes resulting from processing of gold ores. In this study, optical microscopy, scanning electron microscopy, electron microprobe, X-ray diffraction and X-ray absorption fine structure (XAFS) spectroscopy (including both XANES and EXAFS regimes) were employed to determine the mineralogical composition and local coordination environment of As in gold ores and process tailings from bench-scale tests designed to mimic a common plant practice. Arsenic-bearing minerals identified in the ores and tailings include iron (III) oxyhydroxides, scorodite (FeAsO4??2H2O), ferric arsenates, arseniosiderite (Ca2Fe3 (AsO4)3O2??3H2O), Ca-Fe arsenates, pharmacosiderite (KFe4 (AsO4)3(OH)4??6-7H2O), jarosite (K2Fe6(SO4)4 (OH)12) and arsenopyrite (FeAsS). Iron (III) oxyhydroxides contain variable levels of As from trace to about 22 wt% and Ca up to approximately 9 wt%. Finely ground ore and tailings samples were examined by bulk XAFS and selected mineral grains were analyzed by microfocused XAFS (micro-EXAFS) spectroscopy to reconcile the ambiguities of multiple As sources in the complex bulk EXAFS spectra. XANES spectra indicated that As occurs as As5+in all the samples. Micro-EXAFS spectra of individual iron (III) oxyhydroxide grains with varying As concentrations point to inner-sphere bidentate-binuclear arsenate complexes as the predominant form of As. There are indications for the presence of a second Fe shell corresponding to bidentate-mononuclear arrangement. Iron (III) oxyhydroxides with high As concentrations corresponding to maximum adsorption densities probably occur as nanoparticles. The discovery of Ca atoms around As in iron (III) oxyhydroxides at interatomic distances of 4.14-4.17 A?? and the coordination numbers suggest the formation of arseniosiderite-like nanoclusters by coprecipitation rather than simple adsorption of Ca onto iron (III) oxyhydroxides. Correlation of Ca with As in iron (III) oxyhydroxides as determined by electron microprobe analysis supports the coprecipitate origin for the presence of Ca in iron (III) oxyhydroxides. The samples containing higher abundances of ferric arsenates released higher As concentrations during the cyanidation tests. The presence of highly soluble ferric arsenates and Ca-Fe arsenates, and relatively unstable iron (III) oxyhydroxides with Fe/As molar ratios of less than 4 in the ore and process tailings suggests that not only the tailings in the impoundment will continue to release As, but also there is the potential for mobilization of As from the natural sources such as the unmined ore. ?? 2004 Elsevier Ltd.

Speciation and characterization of arsenic in gold ores and cyanidation tailings using X-ray absorption spectroscopy

NASA Astrophysics Data System (ADS)

Paktunc, Dogan; Foster, Andrea; Heald, Steve; Laflamme, Gilles

2004-03-01

The knowledge of mineralogy and molecular structure of As is needed to better understand the stability of As in wastes resulting from processing of gold ores. In this study, optical microscopy, scanning electron microscopy, electron microprobe, X-ray diffraction and X-ray absorption fine structure (XAFS) spectroscopy (including both XANES and EXAFS regimes) were employed to determine the mineralogical composition and local coordination environment of As in gold ores and process tailings from bench-scale tests designed to mimic a common plant practice. Arsenic-bearing minerals identified in the ores and tailings include iron (III) oxyhydroxides, scorodite (FeAsO 4·2H 2O), ferric arsenates, arseniosiderite (Ca 2Fe 3(AsO 4) 3O 2·3H 2O), Ca-Fe arsenates, pharmacosiderite (KFe 4(AsO 4) 3(OH) 4·6-7H 2O), jarosite (K 2Fe 6(SO 4) 4(OH) 12) and arsenopyrite (FeAsS). Iron (III) oxyhydroxides contain variable levels of As from trace to about 22 wt% and Ca up to approximately 9 wt%. Finely ground ore and tailings samples were examined by bulk XAFS and selected mineral grains were analyzed by microfocused XAFS (micro-EXAFS) spectroscopy to reconcile the ambiguities of multiple As sources in the complex bulk EXAFS spectra. XANES spectra indicated that As occurs as As 5+in all the samples. Micro-EXAFS spectra of individual iron (III) oxyhydroxide grains with varying As concentrations point to inner-sphere bidentate-binuclear arsenate complexes as the predominant form of As. There are indications for the presence of a second Fe shell corresponding to bidentate-mononuclear arrangement. Iron (III) oxyhydroxides with high As concentrations corresponding to maximum adsorption densities probably occur as nanoparticles. The discovery of Ca atoms around As in iron (III) oxyhydroxides at interatomic distances of 4.14-4.17 Å and the coordination numbers suggest the formation of arseniosiderite-like nanoclusters by coprecipitation rather than simple adsorption of Ca onto iron (III) oxyhydroxides. Correlation of Ca with As in iron (III) oxyhydroxides as determined by electron microprobe analysis supports the coprecipitate origin for the presence of Ca in iron (III) oxyhydroxides. The samples containing higher abundances of ferric arsenates released higher As concentrations during the cyanidation tests. The presence of highly soluble ferric arsenates and Ca-Fe arsenates, and relatively unstable iron (III) oxyhydroxides with Fe/As molar ratios of less than 4 in the ore and process tailings suggests that not only the tailings in the impoundment will continue to release As, but also there is the potential for mobilization of As from the natural sources such as the unmined ore.

XAFS imaging of Tsukuba gabbroic rocks: area analysis of chemical composition and local structure.

PubMed

Mizusawa, Mari; Sakurai, Kenji

2004-03-01

Gabbroic rocks were collected at Mount Tsukuba in Japan, and their XAFS images were studied using a projection-type X-ray fluorescence (XRF) microscope, which is a powerful new tool recently developed for extremely rapid imaging. The instrument employs a grazing-incidence arrangement in order that primary X-rays illuminate the whole sample surface, as well as parallel-beam optics and an extremely close geometry in order to detect XRF by a high-performance X-ray CCD system with 1024 x 1024 pixels. The XRF image indicated that black amphibole and white feldspar, both of which are typical mineral textures of the rock, contain iron. The origin has been suggested to be several small yellowish-brown minerals contained there. The XAFS imaging has been carried out by repeating the exposure of XRF images during the energy scan of the primary X-rays. It has been found that the structure is qualitatively close to that of olivine, and the main differences found in both areas can be explained as a difference in iron and magnesium concentration, i.e. the mixed ratio of forsterite (Mg(2)SiO(4)) and fayalite (Fe(2)SiO(4)). The feasibility of the present XAFS imaging method has been demonstrated for realistic inhomogeneous minerals.

Study of distorted octahedral structure in 3d transition metal complexes using XAFS

NASA Astrophysics Data System (ADS)

Gaur, A.; Nitin Nair, N.; Shrivastava, B. D.; Das, B. K.; Chakrabortty, Monideepa; Jha, S. N.; Bhattacharyya, D.

2018-01-01

Distortion in octahedral structure of 3d transition metal complexes (Mn, Fe, Co, Ni, Cu, Zn) has been studied using XAFS showing divergent nature of Cu complex. EXAFS analysis showed elongated metal-oxygen bonds for Cu complex leading to more distorted structure. Derivative XANES spectrum at Cu K-edge exhibits splitting of main edge which is correlated to elongated Cu-O bond length. Using these coordination geometry around metal centers, theoretical XANES spectra have been generated and features observed have been correlated to the corresponding metals p-DOS. It has been shown that distorted octahedral field in Cu complex is responsible for splitting of p-DOS.

XAFS of short-lived reduction products of structural and functional models of the [Fe Fe] hydrogenase H-cluster

NASA Astrophysics Data System (ADS)

Bondin, Mark I.; Borg, Stacey J.; Cheah, Mun-Hon; Best, Stephen P.

2006-11-01

Thiolate-bridged diiron compounds that are related to the active site of the [Fe-Fe] hydrogenase enzyme have been shown to act as electrocatalysts for reduction of protons. The use of XAFS for clarification of the structures of intermediates formed following reduction of related diiron carbonyl compounds is described. These measurements allow the determination of Fe-Fe and Fe-S bond lengths with good reliability and when used in conjunction with the standard bonding models this provides a means of validating the structures proposed for longer-lived ( t>20 s at -50 °C) reaction intermediates.

Comparative Analysis of Microbial Communities in Iron-Dominated Flocculent Mats in Deep-Sea Hydrothermal Environments.

PubMed

Makita, Hiroko; Kikuchi, Sakiko; Mitsunobu, Satoshi; Takaki, Yoshihiro; Yamanaka, Toshiro; Toki, Tomohiro; Noguchi, Takuroh; Nakamura, Kentaro; Abe, Mariko; Hirai, Miho; Yamamoto, Masahiro; Uematsu, Katsuyuki; Miyazaki, Junichi; Nunoura, Takuro; Takahashi, Yoshio; Takai, Ken

2016-10-01

It has been suggested that iron is one of the most important energy sources for photosynthesis-independent microbial ecosystems in the ocean crust. Iron-metabolizing chemolithoautotrophs play a key role as primary producers, but little is known about their distribution and diversity and their ecological role as submarine iron-metabolizing chemolithotrophs, particularly the iron oxidizers. In this study, we investigated the microbial communities in several iron-dominated flocculent mats found in deep-sea hydrothermal fields in the Mariana Volcanic Arc and Trough and the Okinawa Trough by culture-independent molecular techniques and X-ray mineralogical analyses. The abundance and composition of the 16S rRNA gene phylotypes demonstrated the ubiquity of zetaproteobacterial phylotypes in iron-dominated mat communities affected by hydrothermal fluid input. Electron microscopy with energy-dispersive X-ray microanalysis and X-ray absorption fine structure (XAFS) analysis revealed the chemical and mineralogical signatures of biogenic Fe-(oxy)hydroxide species and the potential contribution of Zetaproteobacteria to the in situ generation. These results suggest that putative iron-oxidizing chemolithoautotrophs play a significant ecological role in producing iron-dominated flocculent mats and that they are important for iron and carbon cycles in deep-sea low-temperature hydrothermal environments. We report novel aspects of microbiology from iron-dominated flocculent mats in various deep-sea environments. In this study, we examined the relationship between Zetaproteobacteria and iron oxides across several hydrothermally influenced sites in the deep sea. We analyzed iron-dominated mats using culture-independent molecular techniques and X-ray mineralogical analyses. The scanning electron microscopy-energy-dispersive X-ray spectroscopy SEM-EDS analysis and X-ray absorption fine structure (XAFS) analysis revealed chemical and mineralogical signatures of biogenic Fe-(oxy)hydroxide species as well as the potential contribution of the zetaproteobacterial population to the in situ production. These key findings provide important information for understanding the mechanisms of both geomicrobiological iron cycling and the formation of iron-dominated mats in deep-sea hydrothermal fields. Copyright © 2016, American Society for Microbiology. All Rights Reserved.

Fe local structure in Pt-free nitrogen-modified carbon based electrocatalysts: XAFS study

NASA Astrophysics Data System (ADS)

Witkowska, Agnieszka; Giuli, Gabriele; Renzi, Marco; Marzorati, Stefania; Yiming, Wubulikasimu; Nobili, Francesco; Longhi, Mariangela

2016-05-01

The paper presents a new results on the bonding environment (coordination number and geometry) and on oxidation states of Fe in nitrogen-modified Fe/C composites used as Pt-free catalysts for oxygen reduction in Direct Hydrogen Fuel Cells. Starting from glucose or fructose, two catalysts displaying different electrochemical performance were prepared and studied in the form of pristine powder and thin catalytic layer of electrode by Fe K-edge XAFS spectroscopy. The results show how the Fe local structure varies as a function of different synthesis conditions and how changes in the structural properties of the catalysts are related to fuel cell electrochemical performance increase during a cell activation period.

REX2000 Version 2.5: Improved DATA Handling and Enhanced User-Interface

NASA Astrophysics Data System (ADS)

Taguchi, Takeyoshi

2007-02-01

XAFS analysis can be applied to various fields such as material science, environmental study, biological science, etc. and is widely used for characterization in those fields. In the early days that XAFS technique was started to be used, scientists wrote their own code for XAFS data analysis. As XAFS technique became very popular and XAFS community grew big, a several analysis code or package had been developed and submitted for people to use. The REX2000 is one of those XAFS analysis packages, which is commercially available. Counting up from its predecessor "REX", REX2000 has been used for more than 15 years in XAFS society. From the previous modification in 2003, a major change was made in this year of 2006. For a dynamical study of advanced material, many XAFS DATA were measured (quick XAFS and in-situ XAFS) and hundreds of DATA sets need to be processed. The REX2000's DATA handling is improved to cope with those huge volume DATA at once and report the fitting result as CSV file. Well-established user-interface is enhanced so that user can customize initial values for data analysis and specify the options through graphical interface. Many small changes are made and described in this paper.

A study on adsorption mechanism of organoarsenic compounds on ferrihydrite by XAFS

NASA Astrophysics Data System (ADS)

Tanaka, M.; Takahashi, Y.; Yamaguchi, N.

2013-04-01

Anthropogenic organoarsenic compounds which were used such as agrochemicals, pesticides, and herbicides can have a potential as a source of arsenic pollution in water. In the process, the adsorption of arsenic onto mineral surface in soil may play an important role to affect arsenic distribution in solid-water interface. However, adsorption structures of organoarsenic compounds on the iron-(oxyhydr)oxides are not well known. In this study, extended X-ray absorption fine structure (EXAFS) spectroscopy was employed to know the adsorption structure of methyl- and phenyl-substituted organoarsenic compounds (methylarsonic acid (MMA), dimethylarsinic acid (DMA), phenylarsonic acid (PAA), and diphenylarsinic acid (DPAA) onto ferrihydrite which can be a strong adsorbent of arsenic. EXAFS analysis suggests that the formation of inner-sphere surface complex for all organoarsenic compounds with ferrihydrite regardless of the organic functional groups and the number of substitution. The As-Fe distances are around 3.27 , which suggests both mono-and bi-dentate inner-sphere complexes by DFT calculations. The corresponding coordination numbers (CNs) are less than two, suggesting that coexistence of both structures of inner-sphere complexes.

Assessing the feasibility of low temperature XAFS experiments at Indus-2, India: First results

NASA Astrophysics Data System (ADS)

Ramanan, Nitya; Rajput, Parasmani; Jha, S. N.; Lahiri, Debdutta

2015-05-01

In this work, we report installation of displex cryostat XAFS sample holder at XAFS beamline (BL-09) of Indus-2 synchrotron facility, India and make critical assessment of feasibility of low-temperature XAFS experiments in terms of data quality and reproducibility, temperature range, calibration and attainable resolution. We adopted the Debye Model-based calibration method by measuring XAFS of standard Au foil with known Debye temperature (ΘDebye)Autheory = 165 K. The data is of good quality and reproducible with international data. By fitting Debye Waller Factor (σexpt2 (T)), we deduced (ΘDebye)Auexpt = 163 K which implies calibration within 2 K. Error bars for σexpt2 (T) correspond to temperature uncertainty ΔT ≤ 5 K, which defines the temperature resolution for low temperature XAFS experiments. Thus, from both calibration and resolution points-of-view, this work demonstrates the feasibility of low temperature XAFS experiments at BL-09, Indus-2. Feasibility of extending XAFS experiments to lower temperature and unknown samples is discussed.

Atomic resolution holography.

PubMed

Hayashi, Kouichi

2014-11-01

Atomic resolution holography, such as X-ray fluorescence holography (XFH)[1] and photoelectron holography (PH), has the attention of researcher as an informative local structure analysis, because it provides three dimensional atomic images around specific elements within a range of a few nanometers. It can determine atomic arrangements around a specific element without any prior knowledge of structures. It is considered that the atomic resolution holographic is a third method of structural analysis at the atomic level after X-ray diffraction (XRD) and X-ray absorption fine structure (XAFS). As known by many researchers, XRD and XAFS are established methods that are widespread use in various fields. XRD and XAFS provide information on long-range translational periodicities and very local environments, respectively, whereas the atomic resolution holography gives 3D information on the local order and can visualize surrounding atoms with a large range of coordination shells. We call this feature "3D medium-range local structure observation".In addition to this feature, the atomic resolution holography is very sensitive to the displacement of atoms from their ideal positions, and one can obtain quantitative information about local lattice distortions by analyzing reconstructed atomic images[2] When dopants with different atomic radii from the matrix elements are present, the lattices around the dopants are distorted. However, using the conventional methods of structural analysis, one cannot determine the extent to which the local lattice distortions are preserved from the dopants. XFH is a good tool for solving this problem.Figure 1 shows a recent achievement on a relaxor ferroelectric of Pb(Mg1/3Nb2/3)O3 (PMN) using XFH. The structural studies of relaxor ferroelectrics have been carried out by X-ray or neutron diffractions, which suggested rhombohedral distortions of their lattices. However, their true pictures have not been obtained, yet. The Nb Kα holograms showed four separate Pb images, as shown in Fig.1. Using these images, we could obtain acute and obtuse rhombohedral structures of the crystal unit cells. Moreover, the Pb-Pb correlated images reconstructed from Pb Lα holograms showed a local structure of body center-like 2a0 ×2a0 × 2a0 superlattice, proving a rigid 3D network structural model combining the two kinds of rhombohedrons. This superstructure are believed to play an important role in the relaxor behaviour of PMN at atomic level[3].jmicro;63/suppl_1/i13/DFU047F1F1DFU047F1Fig. 1.3D images of the nearest Pb and O atoms around Nb in Pb(Mg1/3Nb2/3)O3. The cube represents 1/8 of the unit cell. © The Author 2014. Published by Oxford University Press on behalf of The Japanese Society of Microscopy. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.

Effects of Ag addition on FePt L1{sub 0} ordering transition: A direct observation of ordering transition and Ag segregation in FePtAg alloy films

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Lei; Yu, Youxing, E-mail: yuyouxing@buaa.edu.cn; Gao, Tenghua

FePt and (FePt){sub 91.2}Ag{sub 8.8} alloy films were deposited by magnetron sputtering. The average coercivity of (FePt){sub 91.2}Ag{sub 8.8} films reaches 8.51 × 10{sup 5} A/m, which is 0.63 × 10{sup 5} A/m higher than that of the corresponding FePt films. Ag addition effectively promotes the FePt L1{sub 0} ordering transition at a relatively low annealing temperature of 400 °C. The promotion mechanism was investigated by using in situ high-resolution transmission electron microscopy (HRTEM) and ex situ X-ray absorption fine structure (XAFS). The concurrence of ordering transition and Ag segregation in FePtAg alloy films was first observed by using in situ heating HRTEM. The time-resolved evolution revealsmore » more details on the role of Ag addition in FePt low-temperature ordering. Ex situ XAFS results further confirm that Ag replaces Fe sites in the as-deposited films and segregates from FePt-Ag solid solution phase through annealing at elevated temperatures. The segregation of Ag atoms leaves vacancies in the grain. The vacancy formation is believed to accelerate the diffusion of Fe and Pt atoms, which is critical for the L1{sub 0} ordering transition.« less

Arsenic species in weathering mine tailings and biogenic solids at the Lava Cap Mine Superfund Site, Nevada City, CA

PubMed Central

2011-01-01

Background A realistic estimation of the health risk of human exposure to solid-phase arsenic (As) derived from historic mining operations is a major challenge to redevelopment of California's famed "Mother Lode" region. Arsenic, a known carcinogen, occurs in multiple solid forms that vary in bioaccessibility. X-ray absorption fine-structure spectroscopy (XAFS) was used to identify and quantify the forms of As in mine wastes and biogenic solids at the Lava Cap Mine Superfund (LCMS) site, a historic "Mother Lode" gold mine. Principal component analysis (PCA) was used to assess variance within water chemistry, solids chemistry, and XAFS spectral datasets. Linear combination, least-squares fits constrained in part by PCA results were then used to quantify arsenic speciation in XAFS spectra of tailings and biogenic solids. Results The highest dissolved arsenic concentrations were found in Lost Lake porewater and in a groundwater-fed pond in the tailings deposition area. Iron, dissolved oxygen, alkalinity, specific conductivity, and As were the major variables in the water chemistry PCA. Arsenic was, on average, 14 times more concentrated in biologically-produced iron (hydr)oxide than in mine tailings. Phosphorous, manganese, calcium, aluminum, and As were the major variables in the solids chemistry PCA. Linear combination fits to XAFS spectra indicate that arsenopyrite (FeAsS), the dominant form of As in ore material, remains abundant (average: 65%) in minimally-weathered ore samples and water-saturated tailings at the bottom of Lost Lake. However, tailings that underwent drying and wetting cycles contain an average of only 30% arsenopyrite. The predominant products of arsenopyrite weathering were identified by XAFS to be As-bearing Fe (hydr)oxide and arseniosiderite (Ca2Fe(AsO4)3O3•3H2O). Existence of the former species is not in question, but the presence of the latter species was not confirmed by additional measurements, so its identification is less certain. The linear combination, least-squares fits totals of several samples deviate by more than ± 20% from 100%, suggesting that additional phases may be present that were not identified or evaluated in this study. Conclusions Sub- to anoxic conditions minimize dissolution of arsenopyrite at the LCMS site, but may accelerate the dissolution of As-bearing secondary iron phases such as Fe3+-oxyhydroxides and arseniosiderite, if sufficient organic matter is present to spur anaerobic microbial activity. Oxidizing, dry conditions favor the stabilization of secondary phases, while promoting oxidative breakdown of the primary sulfides. The stability of both primary and secondary As phases is likely to be at a minimum under cyclic wet-dry conditions. Biogenic iron (hydr)oxide flocs can sequester significant amounts of arsenic; this property may be useful for treatment of perpetual sources of As such as mine adit water, but the fate of As associated with natural accumulations of floc material needs to be assessed. PMID:21261983

Arsenic species in weathering mine tailings and biogenic solids at the Lava Cap Mine Superfund Site, Nevada City, CA.

PubMed

Foster, Andrea L; Ashley, Roger P; Rytuba, James J

2011-01-24

A realistic estimation of the health risk of human exposure to solid-phase arsenic (As) derived from historic mining operations is a major challenge to redevelopment of California's famed "Mother Lode" region. Arsenic, a known carcinogen, occurs in multiple solid forms that vary in bioaccessibility. X-ray absorption fine-structure spectroscopy (XAFS) was used to identify and quantify the forms of As in mine wastes and biogenic solids at the Lava Cap Mine Superfund (LCMS) site, a historic "Mother Lode" gold mine. Principal component analysis (PCA) was used to assess variance within water chemistry, solids chemistry, and XAFS spectral datasets. Linear combination, least-squares fits constrained in part by PCA results were then used to quantify arsenic speciation in XAFS spectra of tailings and biogenic solids. The highest dissolved arsenic concentrations were found in Lost Lake porewater and in a groundwater-fed pond in the tailings deposition area. Iron, dissolved oxygen, alkalinity, specific conductivity, and As were the major variables in the water chemistry PCA. Arsenic was, on average, 14 times more concentrated in biologically-produced iron (hydr)oxide than in mine tailings. Phosphorous, manganese, calcium, aluminum, and As were the major variables in the solids chemistry PCA. Linear combination fits to XAFS spectra indicate that arsenopyrite (FeAsS), the dominant form of As in ore material, remains abundant (average: 65%) in minimally-weathered ore samples and water-saturated tailings at the bottom of Lost Lake. However, tailings that underwent drying and wetting cycles contain an average of only 30% arsenopyrite. The predominant products of arsenopyrite weathering were identified by XAFS to be As-bearing Fe (hydr)oxide and arseniosiderite (Ca2Fe(AsO4)3O3•3H2O). Existence of the former species is not in question, but the presence of the latter species was not confirmed by additional measurements, so its identification is less certain. The linear combination, least-squares fits totals of several samples deviate by more than ± 20% from 100%, suggesting that additional phases may be present that were not identified or evaluated in this study. Sub- to anoxic conditions minimize dissolution of arsenopyrite at the LCMS site, but may accelerate the dissolution of As-bearing secondary iron phases such as Fe3+-oxyhydroxides and arseniosiderite, if sufficient organic matter is present to spur anaerobic microbial activity. Oxidizing, dry conditions favor the stabilization of secondary phases, while promoting oxidative breakdown of the primary sulfides. The stability of both primary and secondary As phases is likely to be at a minimum under cyclic wet-dry conditions. Biogenic iron (hydr)oxide flocs can sequester significant amounts of arsenic; this property may be useful for treatment of perpetual sources of As such as mine adit water, but the fate of As associated with natural accumulations of floc material needs to be assessed.

Near quantitative agreement of model free DFT- MD predictions with XAFS observations of the hydration structure of highly charged transition metal ions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fulton, John L.; Bylaska, Eric J.; Bogatko, Stuart A.

DFT-MD simulations (PBE96 and PBE0) with MD-XAFS scattering calculations (FEFF9) show near quantitative agreement with new and existing XAFS measurements for a comprehensive series of transition metal ions which interact with their hydration shells via complex mechanisms (high spin, covalency, charge transfer, etc.). This work was supported by the U.S. Department of Energy (DOE), Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences and Biosciences. Pacific Northwest National Laboratory (PNNL) is operated for the U.S. DOE by Battelle. A portion of the research was performed using EMSL, a national scientific user facility sponsored by the U.S. DOE's Office ofmore » Biological and Environmental Research and located at Pacific Northwest National Laboratory.« less

Structure determination from XAFS using high-accuracy measurements of x-ray mass attenuation coefficients of silver, 11 keV-28 keV, and development of an all-energies approach to local dynamical analysis of bond length, revealing variation of effective thermal contributions across the XAFS spectrum.

PubMed

Tantau, L J; Chantler, C T; Bourke, J D; Islam, M T; Payne, A T; Rae, N A; Tran, C Q

2015-07-08

We use the x-ray extended range technique (XERT) to experimentally determine the mass attenuation coefficient of silver in the x-ray energy range 11 kev-28 kev including the silver K absorption edge. The results are accurate to better than 0.1%, permitting critical tests of atomic and solid state theory. This is one of the most accurate demonstrations of cross-platform accuracy in synchrotron studies thus far. We derive the mass absorption coefficients and the imaginary component of the form factor over this range. We apply conventional XAFS analytic techniques, extended to include error propagation and uncertainty, yielding bond lengths accurate to approximately 0.24% and thermal Debye-Waller parameters accurate to 30%. We then introduce the FDMX technique for accurate analysis of such data across the full XAFS spectrum, built on full-potential theory, yielding a bond length accuracy of order 0.1% and the demonstration that a single Debye parameter is inadequate and inconsistent across the XAFS range. Two effective Debye-Waller parameters are determined: a high-energy value based on the highly-correlated motion of bonded atoms (σ(DW) = 0.1413(21) Å), and an uncorrelated bulk value (σ(DW) = 0.1766(9) Å) in good agreement with that derived from (room-temperature) crystallography.

Ion-pairing in aqueous CaCl 2 and RbBr solutions. Simultaneous structural refinement of XAFS and XRD data

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pham, Thai V.; Fulton, John L.

2013-01-22

We present a new methodology involving the simultaneous refinement of both x-ray absorption and x-ray diffraction spectra (X-ray Absorption/Diffraction Structural Refinement,XADSR), to study hydration and ion pair structure of CaCl 2 and RbBr salts in concentrated aqueous solutions. The XADSR analysis includes the XAFS spectra analysis of both the cation and anion as a probe of their short-range structure with an XRD spectral analysis as a probe of the global structural. Together they deliver a comprehensive picture of the cation and anion hydration, the contact ion pair (CIP) structure and the solvent-separated ion pair (SSIP) structure. XADSR analysis of 6.0more » m aqueous CaCl 2 reveals that there are an insignificant number of Ca 2+-Cl- CIP’s, but there are approximately 3.4 SSIP’s separated by about 4.99 Å. In contrast XADSR analysis of aqueous RbBr yields about 0.7 pair CIP at a bond length 3.51 Å. The present work demonstrates a new approach for a direct co-refinement of XRD and XAFS spectra in a simple and reliable fashion, opening new opportunities for analysis in various disordered and crystalline systems. This work was supported by the U.S. Department of Energy (DOE), Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences and Biosciences. Pacific Northwest National Laboratory (PNNL) is operated for the U.S. Department of Energy by Battelle.« less

Microbes make average 2 nanometer diameter crystalline UO2 particles.

NASA Astrophysics Data System (ADS)

Suzuki, Y.; Kelly, S. D.; Kemner, K. M.; Banfield, J. F.

2001-12-01

It is well known that phylogenetically diverse groups of microorganisms are capable of catalyzing the reduction of highly soluble U(VI) to highly insoluble U(IV), which rapidly precipitates as uraninite (UO2). Because biological uraninite is highly insoluble, microbial uranyl reduction is being intensively studied as the basis for a cost-effective in-situ bioremediation strategy. Previous studies have described UO2 biomineralization products as amorphous or poorly crystalline. The objective of this study is to characterize the nanocrystalline uraninite in detail in order to determine the particle size, crystallinity, and size-related structural characteristics, and to examine the implications of these for reoxidation and transport. In this study, we obtained U-contaminated sediment and water from an inactive U mine and incubated them anaerobically with nutrients to stimulate reductive precipitation of UO2 by indigenous anaerobic bacteria, mainly Gram-positive spore-forming Desulfosporosinus and Clostridium spp. as revealed by RNA-based phylogenetic analysis. Desulfosporosinus sp. was isolated from the sediment and UO2 was precipitated by this isolate from a simple solution that contains only U and electron donors. We characterized UO2 formed in both of the experiments by high resolution-TEM (HRTEM) and X-ray absorption fine structure analysis (XAFS). The results from HRTEM showed that both the pure and the mixed cultures of microorganisms precipitated around 1.5 - 3 nm crystalline UO2 particles. Some particles as small as around 1 nm could be imaged. Rare particles around 10 nm in diameter were also present. Particles adhere to cells and form colloidal aggregates with low fractal dimension. In some cases, coarsening by oriented attachment on \\{111\\} is evident. Our preliminary results from XAFS for the incubated U-contaminated sample also indicated an average diameter of UO2 of 2 nm. In nanoparticles, the U-U distance obtained by XAFS was 0.373 nm, 0.012 nm smaller than found in the bulk structure of UO2 (0.385 nm). This indicates contraction within the nanoparticles due to tensile surface stress. Microbially formed UO2 is highly reactive, thus will be oxidized quickly as redox conditions change. Our findings support a growing number of studies that indicate that biominerals formed as the result of enzyme-mediated redox reactions are nanoparticulate. Preliminary results suggest that these particles will be readily transported through sandy aquifers, especially when conditions prevent high degrees of flocculation. Thus, despite its low (but size-dependent) solubility, UO2 nanoparticle transport may exert a fundamental control on mobility of U in contaminated environments.

Rational Design of Single Molybdenum Atoms Anchored on N-Doped Carbon for Effective Hydrogen Evolution Reaction.

PubMed

Chen, Wenxing; Pei, Jiajing; He, Chun-Ting; Wan, Jiawei; Ren, Hanlin; Zhu, Youqi; Wang, Yu; Dong, Juncai; Tian, Shubo; Cheong, Weng-Chon; Lu, Siqi; Zheng, Lirong; Zheng, Xusheng; Yan, Wensheng; Zhuang, Zhongbin; Chen, Chen; Peng, Qing; Wang, Dingsheng; Li, Yadong

2017-12-11

The highly efficient electrochemical hydrogen evolution reaction (HER) provides a promising pathway to resolve energy and environment problems. An electrocatalyst was designed with single Mo atoms (Mo-SAs) supported on N-doped carbon having outstanding HER performance. The structure of the catalyst was probed by aberration-corrected scanning transmission electron microscopy (AC-STEM) and X-ray absorption fine structure (XAFS) spectroscopy, indicating the formation of Mo-SAs anchored with one nitrogen atom and two carbon atoms (Mo 1 N 1 C 2 ). Importantly, the Mo 1 N 1 C 2 catalyst displayed much more excellent activity compared with Mo 2 C and MoN, and better stability than commercial Pt/C. Density functional theory (DFT) calculation revealed that the unique structure of Mo 1 N 1 C 2 moiety played a crucial effect to improve the HER performance. This work opens up new opportunities for the preparation and application of highly active and stable Mo-based HER catalysts. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Single-atom Catalysis Using Pt/Graphene Achieved through Atomic Layer Deposition

NASA Astrophysics Data System (ADS)

Sun, Shuhui; Zhang, Gaixia; Gauquelin, Nicolas; Chen, Ning; Zhou, Jigang; Yang, Songlan; Chen, Weifeng; Meng, Xiangbo; Geng, Dongsheng; Banis, Mohammad N.; Li, Ruying; Ye, Siyu; Knights, Shanna; Botton, Gianluigi A.; Sham, Tsun-Kong; Sun, Xueliang

2013-05-01

Platinum-nanoparticle-based catalysts are widely used in many important chemical processes and automobile industries. Downsizing catalyst nanoparticles to single atoms is highly desirable to maximize their use efficiency, however, very challenging. Here we report a practical synthesis for isolated single Pt atoms anchored to graphene nanosheet using the atomic layer deposition (ALD) technique. ALD offers the capability of precise control of catalyst size span from single atom, subnanometer cluster to nanoparticle. The single-atom catalysts exhibit significantly improved catalytic activity (up to 10 times) over that of the state-of-the-art commercial Pt/C catalyst. X-ray absorption fine structure (XAFS) analyses reveal that the low-coordination and partially unoccupied densities of states of 5d orbital of Pt atoms are responsible for the excellent performance. This work is anticipated to form the basis for the exploration of a next generation of highly efficient single-atom catalysts for various applications.

Hydrogen adsorption on two catalysts for the ortho- to parahydrogen conversion: Cr-doped silica and ferric oxide gel.

PubMed

Hartl, Monika; Gillis, Robert Chad; Daemen, Luke; Olds, Daniel P; Page, Katherine; Carlson, Stefan; Cheng, Yongqiang; Hügle, Thomas; Iverson, Erik B; Ramirez-Cuesta, A J; Lee, Yongjoong; Muhrer, Günter

2016-06-29

Molecular hydrogen exists in two spin-rotation coupled states: parahydrogen and orthohydrogen. Due to the variation of energy with rotational level, the occupation of ortho- and parahydrogen states is temperature dependent, with parahydrogen being the dominant species at low temperatures. The equilibrium at 20 K (99.8% parahydrogen) can be reached by natural conversion only after a lengthy process. With the use of a suitable catalyst, this process can be shortened significantly. Two types of commercial catalysts currently being used for ortho- to parahydrogen conversion are: iron(iii) oxide (Fe2O3, IONEX®), and chromium(ii) oxide doped silica catalyst (CrO·SiO2, OXISORB®). We investigate the interaction of ortho- and parahydrogen with the surfaces of these ortho-para conversion catalysts using neutron vibrational spectroscopy. The catalytic surfaces have been characterized using X-ray absorption fine structure (XAFS) and X-ray/neutron pair distribution function measurements.

Single-atom Catalysis Using Pt/Graphene Achieved through Atomic Layer Deposition

PubMed Central

Sun, Shuhui; Zhang, Gaixia; Gauquelin, Nicolas; Chen, Ning; Zhou, Jigang; Yang, Songlan; Chen, Weifeng; Meng, Xiangbo; Geng, Dongsheng; Banis, Mohammad N.; Li, Ruying; Ye, Siyu; Knights, Shanna; Botton, Gianluigi A.; Sham, Tsun-Kong; Sun, Xueliang

2013-01-01

Platinum-nanoparticle-based catalysts are widely used in many important chemical processes and automobile industries. Downsizing catalyst nanoparticles to single atoms is highly desirable to maximize their use efficiency, however, very challenging. Here we report a practical synthesis for isolated single Pt atoms anchored to graphene nanosheet using the atomic layer deposition (ALD) technique. ALD offers the capability of precise control of catalyst size span from single atom, subnanometer cluster to nanoparticle. The single-atom catalysts exhibit significantly improved catalytic activity (up to 10 times) over that of the state-of-the-art commercial Pt/C catalyst. X-ray absorption fine structure (XAFS) analyses reveal that the low-coordination and partially unoccupied densities of states of 5d orbital of Pt atoms are responsible for the excellent performance. This work is anticipated to form the basis for the exploration of a next generation of highly efficient single-atom catalysts for various applications.

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

NASA Astrophysics Data System (ADS)

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

2011-12-01

Marine ferromanganese crusts and nodules ("Fe-Mn crusts") are considered a potential mineral resource due to their accumulation of several economically-important elements at concentrations above mean crustal abundances. They are typically composed of intergrown Fe oxyhydroxide and Mn oxide; thicker (older) crusts can also contain carbonate fluorapatite. We used X-ray absorption fine-structure (XAFS) spectroscopy, a molecular-scale structure probe, to determine the speciation of several elements (Te, Bi, Mo, Zr, Pt) in Fe-Mn crusts. As a first step in analysis of this dataset, we have conducted principal component analysis (PCA) of Te K-edge and Mo K-edge, k3-weighted XAFS spectra. The sample set consisted of 12 homogenized, ground Fe-Mn crust samples from 8 locations in the global ocean. One sample was subjected to a chemical leach to selectively remove Mn oxides and the elements associated with it. The samples in the study set contain 50-205 mg/kg Te (average = 88) and 97-802 mg/kg Mo (average = 567). PCAs of background-subtracted, normalized Te K-edge and Mo K-edge XAFS spectra were performed on a data matrix of 12 rows x 122 columns (rows = samples; columns = Te or Mo fluorescence value at each energy step) and results were visualized without rotation. The number of significant components was assessed by the Malinowski indicator function and ability of the components to reconstruct the features (minus noise) of all sample spectra. Two components were significant by these criteria for both Te and Mo PCAs and described a total of 74 and 75% of the total variance, respectively. Reconstruction of potential model compounds by the principal components derived from PCAs on the sample set ("target transformation") provides a means of ranking models in terms of their utility for subsequent linear-combination, least-squares (LCLS) fits (the next step of data analysis). Synthetic end-member models of Te4+, Te6+, and Mo adsorbed to Fe(III) oxyhydroxide and Mn oxide were tested. Te6+ sorbed to Fe oxyhydroxide and Mo sorbed to Fe oxyhydroxide were identified as the best models for Te and Mo PCAs, respectively. However, in the case of Mo, least-squares fits contradicted these results, indicating that about 80% of Mo in crust samples was associated with Mn oxides. Ultimately it was discovered that the sample from which Mn oxide had been leached was skewing the results in the Mo PCA but not in the Te PCA. When the leached sample was removed and the Mo PCA repeated (n = 11), target transformation indicated that Mo sorbed to Mn oxide was indeed the best model for the set. Our results indicate that Te and Mo are strongly partitioned into different phases in these Fe-Mn crusts, and emphasize the importance of evaluating outliers and their effects on PCA.

The role of yttrium and titanium during the development of ODS ferritic steels obtained through the STARS route: TEM and XAS study

NASA Astrophysics Data System (ADS)

Ordás, Nerea; Gil, Emma; Cintins, Arturs; de Castro, Vanessa; Leguey, Teresa; Iturriza, Iñigo; Purans, Juris; Anspoks, Andris; Kuzmin, Alexei; Kalinko, Alexandr

2018-06-01

Oxide Dispersion Strengthened Ferritic Steels (ODS FS) are candidate materials for structural components in future fusion reactors. Their high strength and creep resistance at elevated temperatures and their good resistance to neutron radiation damage is obtained through extremely fine microstructures containing a high density of nanometric precipitates, generally yttrium and titanium oxides. This work shows transmission electron microscopy (TEM) and extended X-ray absorption fine structure (EXAFS) characterization of Fe-14Cr-2W-0.3Ti-0.24Y ODS FS obtained by the STARS route (Surface Treatment of gas Atomized powder followed by Reactive Synthesis), an alternative method to obtain ODS alloys that avoids the mechanical alloying to introduce Y2O3 powder particles. In this route, FS powders already containing Ti and Y, precursors of the nanometric oxides, are obtained by gas atomization. Then, a metastable Cr- and Fe-rich oxide layer is formed on the surface of the powder particles. During consolidation by HIP at elevated temperatures, and post-HIP heat treatments above the HIP temperature, this oxide layer at Prior Particle Boundaries (PPBs) dissociates, the oxygen diffuses, and Y-Ti-O nano-oxides precipitate in the ferritic matrix. TEM characterization combined with XAFS and XANES analyses have proven to be suitable tools to follow the evolution of the nature of the different oxides present in the material during the whole processing route and select appropriate HIP and post-HIP parameters to promote profuse and fine Y-Ti-O nanometric precipitates.

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

PubMed

Ravel, B; Newville, M

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

XAFS Data Interchange: A single spectrum XAFS data file format

NASA Astrophysics Data System (ADS)

Ravel, B.; Newville, M.

2016-05-01

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

Structure and magnetism in Co/X, Fe/Si, and Fe/(FeSi) multilayers

NASA Astrophysics Data System (ADS)

Franklin, Michael Ray

Previous studies have shown that magnetic behavior in multilayers formed by repeating a bilayer unit comprised of a ferromagnetic layer and a non-magnetic spacer layer can be affected by small structural differences. For example, a macroscopic property such as giant magnetoresistance (GMR) is believed to depend significantly upon interfacial roughness. In this study, several complimentary structural probes were used to carefully characterize the structure of several sputtered multilayer systems-Co/Ag, Co/Cu, Co/Mo, Fe/Si, and Fe//[FeSi/]. X-ray diffraction (XRD) studies were used to examine the long-range structural order of the multilayers perpendicular to the plane of the layers. Transmission electron diffraction (TED) studies were used to probe the long-range order parallel to the layer plane. X-ray Absorption Fine Structure (XAFS) studies were used to determine the average local structural environment of the ferromagnetic atoms. For the Co/X systems, a simple correlation between crystal structure and saturation magnetization is discovered for the Co/Mo system. For the Fe/X systems, direct evidence of an Fe-silicide is found for the /[FeSi/] spacer layer but not for the Si spacer layer. Additionally, differences were observed in the magnetic behavior between the Fe in the nominally pure Fe layer and the Fe contained in the /[FeSi/] spacer layers.

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

DOE Office of Scientific and Technical Information (OSTI.GOV)

Qian, Morris; Li, Hong; Li, Liyu

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

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

NASA Astrophysics Data System (ADS)

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

2013-06-01

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

Zircon solubility and of Zr species in subduction zone fluids

NASA Astrophysics Data System (ADS)

Wilke, M.; Schmidt, C.; Rickers, K.; Pascarelli, S.; Manning, C. E.; Stechern, A.

2009-12-01

The geochemical signature of igneous rocks at convergent plate margins is thought to result from complex melt formation processes involving aqueous solutions derived from dehydration of the subducted slab. In these processes, the depletion of high-field-strength elements (HFSE) may be controlled by the presence of accessory phases such as zircon and rutile, which can strongly fractionate these elements; however, the stability and solubility of these phases depends strongly on the fluid composition, including concentration and stoichiometry of Na-Al silicate components. Here we present new data on the influence of the fluid composition on zircon solubility as well as data on the Zr complexation in these fluids at P&T. Experiments were conducted using a modified hydrothermal diamond-anvil cell (HDAC). Zr contents at P&T were determined using SR-µXRF spectra. Zr K-edge X-ray Absorption Fine Structure (XAFS) spectra were acquired to investigate the Zr complexation in-situ at P&T. A grain of synthetic crystalline zircon was equilibrated with an aqueous fluid containing Na2Si2O5 or Na2Si2O5 + Al2O3 components. XAFS and SR-µXRF spectra were taken at the dispersive beamline ID24 of the ESRF, Grenoble, France. Some additional SR-µXRF spectra were taken at HASYLAB, Hamburg, beamline L. The observed Zr concentrations in fluids containing 7-33 wt% Na2Si2O5 and variable Al contents were between 75 and 720 ppm at 500 to 750°C and ~300 MPa to ~700 MPa. These values match expected solubilities calculated from linear interpolation of the maximum solubility in pure H2O (from the detection limit) and the solubility in the most alkaline high-silica melts reported by Ellison and Hess (1986, CMP, 94, 343). The high Zr solubility in sodium silicate-bearing solutions signifies that aqueous fluids with alkali silicates offer an efficient mechanism for HFSE transport. This can be explained by complexation of HFSE with Si, Na, and perhaps also Al, via formation of polymerized solutes. The XAFS results show clear differences between spectra of Zr in an HCl solution and in H2O-Na2Si2O5 (±Al2O3) aqueous fluid, implying considerable differences in Zr complexation. The latter spectra display similarities to spectra of Zr in Na2Si2O5 glass. This may indicate a similar structural environment for the two examined states, and thus point to Zr in (alumino)-silicate-based polymeric units in the aqueous solutions.

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

NASA Astrophysics Data System (ADS)

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

2017-02-01

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

Reversed nanoscale Kirkendall effect in Au–InAs hybrid nanoparticles

DOE PAGES

Liu, Jing; Amit, Yorai; Li, Yuanyuan; ...

2016-10-10

Metal–semiconductor hybrid nanoparticles (NPs) offer interesting synergistic properties, leading to unique behaviors that have already been exploited in photocatalysis, electrical, and optoelectronic applications. A fundamental aspect in the synthesis of metal–semiconductor hybrid NPs is the possible diffusion of the metal species through the semiconductor lattice. The importance of understanding and controlling the co-diffusion of different constituents is demonstrated in the synthesis of various hollow-structured NPs via the Kirkendall effect. Here, we used a postsynthesis room-temperature reaction between AuCl 3 and InAs nanocrystals (NCs) to form metal–semiconductor core–shell hybrid NPs through the “reversed Kirkendall effect”. In the presented system, the diffusionmore » rate of the inward diffusing species (Au) is faster than that of the outward diffusing species (InAs), which results in the formation of a crystalline metallic Au core surrounded by an amorphous, oxidized InAs shell containing nanoscale voids. We used time-resolved X-ray absorption fine-structure (XAFS) spectroscopy to monitor the diffusion process and found that both the size of the Au core and the extent of the disorder of the InAs shell depend strongly on the Au-to-NC ratio. We have determined, based on multielement fit analysis, that Au diffuses into the NC via the kick-out mechanism, substituting for In host atoms; this compromises the structural stability of the lattice and triggers the formation of In–O bonds. These bonds were used as markers to follow the diffusion process and indicate the extent of degradation of the NC lattice. Time-resolved X-ray diffraction (XRD) was used to measure the changes in the crystal structures of InAs and the nanoscale Au phases. By combining the results of XAFS, XRD, and electron microscopy, we correlated the changes in the local structure around Au, As, and In atoms and the changes in the overall InAs crystal structure. This correlative analysis revealed a co-dependence of different structural consequences when introducing Au into the InAs NCs. As a result this study of diffusion effects in nanocrystals has relevance to powerful concepts in solid-state nanochemistry related to processes of cation exchange, doping reactions, and diffusion mechanisms.« less

Reversed Nanoscale Kirkendall Effect in Au–InAs Hybrid Nanoparticles

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, Jing; Amit, Yorai; Li, Yuanyuan

2016-11-08

Metal–semiconductor hybrid nanoparticles (NPs) offer interesting synergistic properties, leading to unique behaviors that have already been exploited in photocatalysis, electrical, and optoelectronic applications. A fundamental aspect in the synthesis of metal–semiconductor hybrid NPs is the possible diffusion of the metal species through the semiconductor lattice. The importance of understanding and controlling the co-diffusion of different constituents is demonstrated in the synthesis of various hollow-structured NPs via the Kirkendall effect. Here, we used a postsynthesis room-temperature reaction between AuCl 3 and InAs nanocrystals (NCs) to form metal–semiconductor core–shell hybrid NPs through the “reversed Kirkendall effect”. In the presented system, the diffusionmore » rate of the inward diffusing species (Au) is faster than that of the outward diffusing species (InAs), which results in the formation of a crystalline metallic Au core surrounded by an amorphous, oxidized InAs shell containing nanoscale voids. We used time-resolved X-ray absorption fine-structure (XAFS) spectroscopy to monitor the diffusion process and found that both the size of the Au core and the extent of the disorder of the InAs shell depend strongly on the Au-to-NC ratio. We have determined, based on multielement fit analysis, that Au diffuses into the NC via the kick-out mechanism, substituting for In host atoms; this compromises the structural stability of the lattice and triggers the formation of In–O bonds. These bonds were used as markers to follow the diffusion process and indicate the extent of degradation of the NC lattice. Time-resolved X-ray diffraction (XRD) was used to measure the changes in the crystal structures of InAs and the nanoscale Au phases. By combining the results of XAFS, XRD, and electron microscopy, we correlated the changes in the local structure around Au, As, and In atoms and the changes in the overall InAs crystal structure. This correlative analysis revealed a co-dependence of different structural consequences when introducing Au into the InAs NCs. Therefore, this study of diffusion effects in nanocrystals has relevance to powerful concepts in solid-state nanochemistry related to processes of cation exchange, doping reactions, and diffusion mechanisms.« less

A moving target: responding to magnetic and structural disorder in lanthanide- and actinide-based superconductors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bauer, Eric D; Mitchell, Jeremy N; Booth, C H

2009-01-01

The effects of various chemical substitutions and induced lattice disorder in the Ce- and Pu-based 115 superconductors are reviewed, with particular emphasis on results from x-ray absorption fine structure (XAFS) measurements. The competition between spin, charge, and lattice interactions is at the heart of many of the strongly-correlated ground states in materials of current interest, such as in colossal magnetoresistors and high-temperature superconductors. This relationship is particularly strong in the CeTIn{sub 5} and PuTGa{sub 5} series (T = Co, Rh, Ir) of heavy-fermion superconductors. In these systems (figure 1), competition between bulk magnetic and non-magnetic ground states, as well asmore » between superconducting and normal states, are directly related to local properties around the lanthanide or actinide ion, such as the nearest-neighbor bond lengths and the local density of states at the Fermi level. Tiny changes in the latter values can easily tip the balance from one ground state to another. This paper reviews recent work by the authors exploring the relationship between local crystal and electronic structure and ground state magnetic and conducting properties in the Ce- and Pu-based 115 materials.« less

Structure of thallium(III) chloride, bromide, and cyanide complexes in aqueous solution

DOE Office of Scientific and Technical Information (OSTI.GOV)

Blixt, J.; Glaser, J.; Sandstroem, M.

1995-05-10

The structures of the hydrated thallium(III) halide and pseudohalide complexes, [TlX{sub n}(OH{sub 2}){sub m}]{sup (3-d)+}, X = Cl, Br, CN, in aqueous solution have been studied by a combination of X-ray absorption fine structure spectroscopy (XAFS), large-angle X-ray scattering (LAXS), and vibrational spectroscopic (Raman and IR) techniques including far-infrared studies of aqueous solutions and some solid phases with known structures. The vibrational Tl-X frequencies of all complexes are reported, force constants are calculated using normal coordinate analysis, and assignments are given. The structural results are consistent with octahedral six-coordination for the cationic complexes Tl(OH{sub 2}){sub 6}{sup 3$PLU}, TlX(OH{sub 2}){sub 5}{supmore » 2+}, and trans-TlX{sub 2}(OH{sub 2}){sub 4}{sup +}. The coordination geometry changes to trigonal bipyramidal for the neutral TlBr{sub 3}(OH{sub 2}){sub 2} complex and possibly also for TlCl{sub 3}(OH{sub 2}){sub 2}. The TlX{sub 4}{sup -} complexes are all tetrahedral. Higher chloride complexes, TlCl{sub 5}(OH{sub 2}){sup 2-} and TlCl{sub 6}{sup 3-}, are formed and have again octahedral coordination geometry. 65 refs., 7 figs., 5 tabs.« less

Multimodal Study of the Speciations and Activities of Supported Pd Catalysts During the Hydrogenation of Ethylene

DOE PAGES

Zhao, Shen; Li, Yuanyuan; Liu, Deyu; ...

2017-08-07

In this paper we describe a multimodal exploration of the atomic structure and chemical state of silica-supported palladium nanocluster catalysts during the hydrogenation of ethylene in operando conditions that variously transform the metallic phases between hydride and carbide speciations. The work exploits a microreactor that allows combined multiprobe investigations by high-resolution transmission electron microscopy (HR-TEM), X-ray absorption fine structure (XAFS), and microbeam IR (μ-IR) analyses on the catalyst under operando conditions. The work specifically explores the reaction processes that mediate the interconversion of hydride and carbide phases of the Pd clusters in consequence to changes made in the composition ofmore » the gas-phase reactant feeds, their stability against coarsening, the reversibility of structural/compositional transformations, and the role that oligomeric/waxy byproducts (here forming under hydrogen-limited reactant compositions) might play in modifying activity. The results provide new insights into structural features of the chemistry/mechanisms of Pd catalysis during the selective hydrogenation of acetylene in ethylene—a process simplified here in the use of binary ethylene/hydrogen mixtures. Finally, these explorations, performed in operando conditions, provide new understandings of structure–activity relationships for Pd catalysis in regimes that actively transmute important attributes of electronic and atomic structures.« less

Multimodal Study of the Speciations and Activities of Supported Pd Catalysts During the Hydrogenation of Ethylene

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhao, Shen; Li, Yuanyuan; Liu, Deyu

In this paper we describe a multimodal exploration of the atomic structure and chemical state of silica-supported palladium nanocluster catalysts during the hydrogenation of ethylene in operando conditions that variously transform the metallic phases between hydride and carbide speciations. The work exploits a microreactor that allows combined multiprobe investigations by high-resolution transmission electron microscopy (HR-TEM), X-ray absorption fine structure (XAFS), and microbeam IR (μ-IR) analyses on the catalyst under operando conditions. The work specifically explores the reaction processes that mediate the interconversion of hydride and carbide phases of the Pd clusters in consequence to changes made in the composition ofmore » the gas-phase reactant feeds, their stability against coarsening, the reversibility of structural/compositional transformations, and the role that oligomeric/waxy byproducts (here forming under hydrogen-limited reactant compositions) might play in modifying activity. The results provide new insights into structural features of the chemistry/mechanisms of Pd catalysis during the selective hydrogenation of acetylene in ethylene—a process simplified here in the use of binary ethylene/hydrogen mixtures. Finally, these explorations, performed in operando conditions, provide new understandings of structure–activity relationships for Pd catalysis in regimes that actively transmute important attributes of electronic and atomic structures.« less

Distribution of trace elements in selected pulverized coals as a function of particle size and density

USGS Publications Warehouse

Senior, C.L.; Zeng, T.; Che, J.; Ames, M.R.; Sarofim, A.F.; Olmez, I.; Huggins, Frank E.; Shah, N.; Huffman, G.P.; Kolker, A.; Mroczkowski, S.; Palmer, C.; Finkelman, R.

2000-01-01

Trace elements in coal have diverse modes of occurrence that will greatly influence their behavior in many coal utilization processes. Mode of occurrence is important in determining the partitioning during coal cleaning by conventional processes, the susceptibility to oxidation upon exposure to air, as well as the changes in physical properties upon heating. In this study, three complementary methods were used to determine the concentrations and chemical states of trace elements in pulverized samples of four US coals: Pittsburgh, Illinois No. 6, Elkhorn and Hazard, and Wyodak coals. Neutron Activation Analysis (NAA) was used to measure the absolute concentration of elements in the parent coals and in the size- and density-fractionated samples. Chemical leaching and X-ray absorption fine structure (XAFS) spectroscopy were used to provide information on the form of occurrence of an element in the parent coals. The composition differences between size-segregated coal samples of different density mainly reflect the large density difference between minerals, especially pyrite, and the organic portion of the coal. The heavy density fractions are therefore enriched in pyrite and the elements associated with pyrite, as also shown by the leaching and XAFS methods. Nearly all the As is associated with pyrite in the three bituminous coals studied. The sub-bituminous coal has a very low content of pyrite and arsenic; in this coal arsenic appears to be primarily organically associated. Selenium is mainly associated with pyrite in the bituminous coal samples. In two bituminous coal samples, zinc is mostly in the form of ZnS or associated with pyrite, whereas it appears to be associated with other minerals in the other two coals. Zinc is also the only trace element studied that is significantly more concentrated in the smaller (45 to 63 ??m) coal particles.

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

DOE Office of Scientific and Technical Information (OSTI.GOV)

Paktunc, D.

2008-09-30

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

Behavior of cesium in municipal solid waste incineration.

PubMed

Oshita, Kazuyuki; Aoki, Hiroshi; Fukutani, Satoshi; Shiota, Kenji; Fujimori, Takashi; Takaoka, Masaki

2015-05-01

As a result of the Fukushima Daiichi Nuclear Power Plant accident on March 11, 2011 in Japan radioactive nuclides, primarily (134)Cs and (137)Cs were released, contaminating municipal solid waste and sewage sludge in the area. Although stabilizing the waste and reducing its volume is an important issue differing from Chernobyl nuclear power plant accident, secondary emission of radioactive nuclides as a result of any intermediate remediation process is of concern. Unfortunately, there is little research on the behavior of radioactive nuclides during waste treatment. This study focuses on waste incineration in an effort to clarify the behavior of radioactive nuclides, specifically, refuse-derived fuel (RDF) with added (133)Cs (stable nuclide) or (134)Cs (radioactive nuclide) was incinerated in laboratory- and pilot-scale experiments. Next, thermogravimetric (TG) and differential thermal analysis (DTA) of stable Cs compounds, as well as an X-ray absorption fine structure (XAFS) analysis of Cs concentrated in the ashes were performed to validate the behavior and chemical forms of Cs during the combustion. Our results showed that at higher temperatures and at larger equivalence ratios, (133)Cs was distributed to the bottom ash at lower concentration, and the influence of the equivalence ratio was more significant at lower temperatures. (134)Cs behaved in a similar fashion as (133)Cs. We found through TG-DTA and XAFS analysis that a portion of Cs in RDF vaporizes and is transferred to fly ash where it exists as CsCl in the MSW incinerator. We conclude that Cs-contaminated municipal solid wastes could be incinerated at high temperatures resulting in a small amount of fly ash with a high concentration of radioactive Cs, and a bottom ash with low concentrations. Copyright © 2015 Elsevier Ltd. All rights reserved.

Sorption mechanisms of metals to graphene oxide

DOE Office of Scientific and Technical Information (OSTI.GOV)

Showalter, Allison R.; Duster, Thomas A.; Szymanowski, Jennifer E. S.

2016-05-01

Environmental toxic metal contamination remediation and prevention is an ongoing issue. Graphene oxide is highly sorptive for many heavy metals over a wide pH range under different ionic strength conditions. We present x-ray absorption fine structure (XAFS) spectroscopy results investigating the binding environment of Pb(II), Cd(II) and U(VI) ions onto multi-layered graphene oxide (MLGO). Analysis indicates that the dominant sorption mechanism of Pb to MLGO changes as a function of pH, with increasing inner sphere contribution as pH increases. In contrast, the sorption mechanism of Cd to MLGO remains constant under the studied pH range. This adsorption mechanism is anmore » electrostatic attraction between the hydrated Cd+2 ion and the MLGO surface. The U(VI), present as the uranyl ion, changes only subtly as a function of pH and is bound to the surface via an inner sphere bond. Knowledge of the binding mechanism for each metal is necessary to help in optimizing environmental remediation or prevention in filtration systems.« less

Preliminary study on the mode of occurrence of arsenic in high arsenic coals from southwest Guizhou Province

USGS Publications Warehouse

Ding, Z.; Zheng, B.; Zhang, Jiahua; Belkin, H.E.; Finkelman, R.B.; Zhao, F.; Zhou, D.; Zhou, Y.; Chen, C.

1999-01-01

Coal samples from high arsenic coal areas have been analyzed by electron microprobe analyzer (EMPA), scanning electron microscopy with an energy dispersive X-ray analyzer (SEM-EDX), X-ray diffraction analysis (XRD), low temperature ashing (LTA), transmission electron microscopy (TEM), X-ray absorption fine structure (XAFS), instrument neutron activation analysis (INAA) and wet chemical analysis. Although some As-bearing minerals such as pyrite, arsenopyrite, realgar (?), As-bearing sulfate, and As-bearing clays are found in the high arsenic coals, their contents do not account for the abundance of arsenic in the some coals. Analysis of the coal indicates that arsenic exists mainly in the form of As5+ and As3+, combined with compounds in the organic matrix. The occurrence of such exceptionally high arsenic contents in coal and the fact that the arsenic is dominantly organically associated are unique observations. The modes of occurrence of arsenic in high As-coals are discussed.

Roles of Pt and BaO in the Sulfation of Pt/BaO/Al2O3 Lean NOx Trap Materials: Sulfur K-edge XANES and Pt LIII XAFS Studies

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kim, Do Heui; Kwak, Ja Hun; Szanyi, Janos

2008-02-28

The roles of barium oxide and platinum during the sulfation of Pt-BaO/Al2O3 lean NOx trap catalysts were investigated by S K edge XANES (X-ray absorption near-edge spectroscopy) and Pt LIII XAFS (X-ray absorption fine structure). All of the samples studied (Al2O3, BaO/Al2O3, Pt/Al2O3 and Pt-BaO/Al2O3) were pre-sulfated prior to the X-ray absorption measurements. It was found that barium oxide itself has the ability to directly form barium sulfate even in the absence of Pt and gas phase oxygen. In the platinum-containing samples, the presence of Pt-O species plays an important role in the formation of sulfate species. Even if bariummore » and aluminum sites are available for SO2 to form sulfate, for the case of the BaO(8)/Al2O3 sample, where the barium coverage is about 0.26 ML, S XANES spectroscopy results show that barium sulfates are preferentially produced over aluminum sulfates . When oxygen is absent from the gas phase, the sulfation route that involves Pt-O is eliminated after the initially present Pt-O species are completely consumed. In this case, formation of sulfates is suppressed unless barium oxide is also present. Pt LIII XAFS results show that the first coordination sphere around the Pt atoms in the Pt particles is dependent upon the redox nature of the gas mixture used during the sulfation process. Sulfation under reducing environments (e.g. SO2+H2) leads to formation of Pt-S bonds, while oxidizing conditions (e.g. SO2+O2) continue to show the presence of Pt-O bonds. In addition, the former condition was found to give rise to a higher degree of Pt sintering than the latter one. This result explains why samples sulfated under reducing conditions had lower NOx uptakes than those sulfated under oxidizing conditions. Therefore, our results provide needed information for the development of optimum practical operation conditions (e.g. sulfation or desulfation) for lean NOx trap catalysts that minimize deactivation by sulfur.« less

Roles of Pt and BaO in the Sulfation of Pt/BaO/Al2O3 Lean NOx Trap Materials: Sulfur K-edge XANES and Pt Llll XAFS Studies

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kim,D.; Kwak, J.; Szanyi, J.

2008-01-01

The roles of barium oxide and platinum during the sulfation of Pt-BaO/Al2O3 lean NOx trap catalysts were investigated by S K edge XANES (X-ray absorption near-edge spectroscopy) and Pt LIII XAFS (X-ray absorption fine structure). All of the samples studied [Al2O3, BaO(x; x = 8 or 20 wt %)/Al2O3, Pt(2.5 wt %)/Al2O3, and Pt(2 wt %)-BaO(x; x = 8 or 20 wt %)/Al2O3] were pre-sulfated prior to the X-ray absorption measurements. It was found that barium oxide itself has the ability to directly form barium sulfate even in the absence of Pt and gas-phase oxygen. In the platinum-containing samples, themore » presence of Pt-O species plays an important role in the formation of sulfate species. For the case of the BaO(8)/Al2O3 sample, where the barium coverage is about 0.26 ML, both baria and alumina phases are available for sulfation. S XANES results show that barium sulfates are formed preferentially over aluminum sulfates. When oxygen is absent from the gas phase, the sulfation route that involves Pt-O is eliminated after the initially present Pt-O species are completely consumed. In this case, formation of sulfates is suppressed unless barium oxide is also present. Pt LIII XAFS results show that the first coordination sphere around the Pt atoms in the Pt particles is dependent upon the gas mixture used during the sulfation process. Sulfation under reducing environments (e.g., SO2/H2) leads to formation of Pt-S bonds, while oxidizing conditions (e.g., SO2/O2) continue to show the presence of Pt-O bonds. In addition, a reducing environment was found to cause Pt sintering in greater extent than an oxidizing one. This result explains why samples sulfated under reducing conditions had lower NOx uptakes than those sulfated under oxidizing conditions. Therefore, our results provide needed information for the development of optimum practical operation conditions (e.g., sulfation or desulfation) for lean NOx trap catalysts that minimize deactivation by sulfur.« less

Sorption behavior of the Pt(II) complex anion on manganese dioxide (δ-MnO2): a model reaction to elucidate the mechanism by which Pt is concentrated into a marine ferromanganese crust

NASA Astrophysics Data System (ADS)

Maeno, Mamiko Yamashita; Ohashi, Hironori; Yonezu, Kotaro; Miyazaki, Akane; Okaue, Yoshihiro; Watanabe, Koichiro; Ishida, Tamao; Tokunaga, Makoto; Yokoyama, Takushi

2016-02-01

It is difficult to directly investigate the chemical state of Pt in marine ferromanganese crusts (a mixture of hydrous iron(III) oxide and manganese dioxide (δ-MnO2)) because it is present at extremely low concentration levels. This paper attempts to elucidate the mechanism by which Pt is concentrated into marine ferromanganese crust from the Earth's continental crust through ocean water. In this investigation, the sorption behavior of the Pt(II) complex ions on the surface of the δ-MnO2 that is a host of Pt was examined as a model reaction. The δ-MnO2 sorbing Pt was characterized by X-ray photoelectron spectroscopy (XPS) and X-ray absorption fine structure (XAFS) to determine the chemical state of the Pt. Hydrolytic Pt(II) complex ions were specifically sorbed above pH 6 by the formation of a Mn-O-Pt bond. XPS spectra and XANES spectra for δ-MnO2 sorbing Pt showed that the sorbed Pt(II) was oxidized to Pt(IV) on δ-MnO2. The extended X-ray absorption fine structure (EXAFS) analysis showed that the coordination structure of Pt sorbed on δ-MnO2 is almost the same as that of the [Pt(OH)6]2- complex ion used as a standard. Therefore, the mechanism for the concentration of Pt in marine ferromanganese crust may be an oxidative substitution (penetration of Pt(IV) into structure of δ-MnO2) by a reduction-oxidation reaction between Pt(II) in [PtCl4-n(OH)n]2- and Mn(IV) in δ-MnO2 through a Mn-O-Pt bond.

Chrysocolla Redefined as Spertiniite

NASA Astrophysics Data System (ADS)

Farges, François; Benzerara, Karim; Brown, Gordon E.

2007-02-01

XAFS and μ-XAFS spectra were collected at the Cu K-edge for seven chrysocolla samples (Peru, USA, and Congo). The results suggest that that the local structure around Cu is similar to that in Cu(OH)2 (spertiniite). Cu-L3 STXM imaging and spectroscopy confirm that the chrysocolla samples examined here consist of mesoscopic Cu(II)-rich domains surrounded by Si-rich domains (in agreement with results from infra-red spectroscopy). Hence, we suggest that chrysocolla, which is generally considered to be orthorhombic with composition (Cu,Al)2H2Si2O5(OH)4ṡnH2O, is in actually a mesoscopic assemblage composed dominantly of spertiniite (Cu(OH)2), water and amorphous silica (SiO2).

MAX: Multiplatform Applications for XAFS

NASA Astrophysics Data System (ADS)

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

2009-11-01

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

XAFS and Protein Crystallography Beamline BL38B1 at SPring-8

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tanida, Hajime; Miura, Keiko; Takeshita, Kunikazu

2004-05-12

The SPring-8 bending magnet beamline BL38B1 is designed for R and D of optics, detectors, experiments for XAFS and protein X-ray crystallography (PX). This beamline has a multi-purpose hutch for two experimental stations of XAFS and PX, and removable optical benches used for R and D of detectors and instruments. The design and the performance of the beamline are presented.

Probing Active Species in the Nanoscale by Combining XAFS and TEM in Operando Conditions

NASA Astrophysics Data System (ADS)

Frenkel, Anatoly

Understanding mechanisms of work in nanoscale systems is often hindered by their inherent complexity and by our inability to identify and characterize their ``active'' sites. In the size range of 1-5nm, they feature a variety of structural motifs, sizes, shapes, compositions, degrees of crystalline order as well as multiple temporal scales. An additional challenge is that only a fraction of them are actors in the catalytic performance, while majority are spectators. Significant progress in developing such tools for studying nanomaterials can be achieved only when active species can be reliably isolated from spectators, and their role in mechanism of work is understood. In our approach the activity of nanomaterial is measured concurrently with other characteristics, obtained by advanced scattering, spectroscopy and imaging methods. In this talk I will demonstrate the application of a microreactor, compatible with electron microscopy and X-ray Absorption Fine Structure spectroscopy probes, for this purpose. I will illustrate its application by our observation of reaction-driven restructuring of Pt catalysts in the size range from single atoms to 3nm in diameter during catalytic hydrogenation of ethylene. We acknowledge support of DOE BES Grant No. DE-FG02- 03ER15476.

Dry Reforming of Ethane and Butane with CO 2 over PtNi/CeO 2 Bimetallic Catalysts

DOE PAGES

Yan, Binhang; Yang, Xiaofang; Yao, Siyu; ...

2016-09-21

Dry reforming is a potential process to convert CO 2 and light alkanes into syngas (H 2 and CO), which can be subsequently transformed to chemicals and fuels. Here in this work, PtNi bimetallic catalysts have been investigated for dry reforming of ethane and butane using both model surfaces and supported powder catalysts. The PtNi bimetallic catalyst shows an improvement in both activity and stability as compared to the corresponding monometallic catalysts. The formation of PtNi alloy and the partial reduction of Ce 4+ to Ce 3+ under reaction conditions are demonstrated by in-situ Ambient Pressure X-ray Photoemission Spectroscopy (AP-XPS),more » X-ray Diffraction (XRD) and X-ray Absorption Fine Structure (XAFS) measurements. A Pt-rich bimetallic surface is revealed by Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) following CO adsorption. Combined in-situ experimental results and Density Functional Theory (DFT) calculations suggest that the Pt-rich PtNi bimetallic surface structure would weaken the binding of surface oxygenates/carbon species and reduce the activation energy for C-C bond scission, leading to an enhanced dry reforming activity.« less

Dry Reforming of Ethane and Butane with CO 2 over PtNi/CeO 2 Bimetallic Catalysts

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yan, Binhang; Yang, Xiaofang; Yao, Siyu

Dry reforming is a potential process to convert CO 2 and light alkanes into syngas (H 2 and CO), which can be subsequently transformed to chemicals and fuels. Here in this work, PtNi bimetallic catalysts have been investigated for dry reforming of ethane and butane using both model surfaces and supported powder catalysts. The PtNi bimetallic catalyst shows an improvement in both activity and stability as compared to the corresponding monometallic catalysts. The formation of PtNi alloy and the partial reduction of Ce 4+ to Ce 3+ under reaction conditions are demonstrated by in-situ Ambient Pressure X-ray Photoemission Spectroscopy (AP-XPS),more » X-ray Diffraction (XRD) and X-ray Absorption Fine Structure (XAFS) measurements. A Pt-rich bimetallic surface is revealed by Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) following CO adsorption. Combined in-situ experimental results and Density Functional Theory (DFT) calculations suggest that the Pt-rich PtNi bimetallic surface structure would weaken the binding of surface oxygenates/carbon species and reduce the activation energy for C-C bond scission, leading to an enhanced dry reforming activity.« less

Structural study of the ammonium octafluoroneptunate, [NH 4] 4NpF 8

DOE PAGES

Poineau, Frederic; Silva, Chinthaka M.; Yeamans, Charles B.; ...

2016-04-21

The [NH 4] 4NpF 8 salt was prepared from the solid-state reaction of NpO 2 with NH 4HF 2 and characterized by powder X-ray diffraction and X-ray absorption fine structure spectroscopy. The diffraction results confirm the compound to be isostructural to [NH 4] 4UF 8 with the following lattice parameter (a = 13.054(4) Å, b = 6.681(2) Å, c = 13.676(5) Å, ß = 121.14 Å). For the first time, a Neptunium fluoride complex has been characterized by XAFS spectroscopy. The energy position of the white line and inflection of the XANES spectra of [NH 4] 4NpF 8 are consistentmore » with the presence of Np(IV). Adjustment of the EXAFS spectra indicates that the coordination number (7.4±1.5) and the average Np-F distance (2.26(1) Å) are consistent with the presence of the NpF8 dodecahedron. The average Np-F distance is ~0.02 Å shorter than the U-F distance in [NH 4] 4UF 8 and is a result of the actinide contraction.« less

The role of ion exchange in the passivation of In(Zn)P nanocrystals with ZnS

PubMed Central

Cho, Deok-Yong; Xi, Lifei; Boothroyd, Chris; Kardynal, Beata; Lam, Yeng Ming

2016-01-01

We have investigated the chemical state of In(Zn)P/ZnS core/shell nanocrystals (NCs) for color conversion applications using hard X-ray absorption spectroscopy (XAS) and photoluminescence excitation (PLE). Analyses of the edge energies as well as the X-ray absorption fine structure (XAFS) reveal that the Zn2+ ions from ZnS remain in the shell while the S2− ions penetrate into the core at an early stage of the ZnS deposition. It is further demonstrated that for short growth times, the ZnS shell coverage on the core was incomplete, whereas the coverage improved gradually as the shell deposition time increased. Together with evidence from PLE spectra, where there is a strong indication of the presence of P vacancies, this suggests that the core-shell interface in the In(Zn)P/ZnS NCs are subject to substantial atomic exchanges and detailed models for the shell structure beyond simple layer coverage are needed. This substantial atomic exchange is very likely to be the reason for the improved photoluminescence behavior of the core-shell particles compare to In(Zn)P-only NCs as S can passivate the NCs surfaces. PMID:26972936

Decoupling the Lattice Distortion and Charge Doping Effects on the Phase Transition Behavior of VO2 by Titanium (Ti4+) Doping

PubMed Central

Wu, Yanfei; Fan, Lele; Liu, Qinghua; Chen, Shi; Huang, Weifeng; Chen, Feihu; Liao, Guangming; Zou, Chongwen; Wu, Ziyu

2015-01-01

The mechanism for regulating the critical temperature (TC) of metal-insulator transition (MIT) in ions-doped VO2 systems is still a matter of debate, in particular, the unclear roles of lattice distortion and charge doping effects. To rule out the charge doping effect on the regulation of TC, we investigated Ti4+-doped VO2 (TixV1-xO2) system. It was observed that the TC of TixV1-xO2 samples first slightly decreased and then increased with increasing Ti concentration. X-ray absorption fine structure (XAFS) spectroscopy was used to explore the electronic states and local lattice structures around both Ti and V atoms in TixV1-xO2 samples. Our results revealed the local structure evolution from the initial anatase to the rutile-like structure around the Ti dopants. Furthermore, the host monoclinic VO2 lattice, specifically, the VO6 octahedra would be subtly distorted by Ti doping. The distortion of VO6 octahedra and the variation of TC showed almost the similar trend, confirming the direct effect of local structural perturbations on the phase transition behavior. By comparing other ion-doping systems, we point out that the charge doping is more effective than the lattice distortion in modulating the MIT behavior of VO2 materials. PMID:25950809

Ultra-small plutonium oxide nanocrystals: an innovative material in plutonium science.

PubMed

Hudry, Damien; Apostolidis, Christos; Walter, Olaf; Janssen, Arne; Manara, Dario; Griveau, Jean-Christophe; Colineau, Eric; Vitova, Tonya; Prüssmann, Tim; Wang, Di; Kübel, Christian; Meyer, Daniel

2014-08-11

Apart from its technological importance, plutonium (Pu) is also one of the most intriguing elements because of its non-conventional physical properties and fascinating chemistry. Those fundamental aspects are particularly interesting when dealing with the challenging study of plutonium-based nanomaterials. Here we show that ultra-small (3.2±0.9 nm) and highly crystalline plutonium oxide (PuO2 ) nanocrystals (NCs) can be synthesized by the thermal decomposition of plutonyl nitrate ([PuO2 (NO3 )2 ]⋅3 H2 O) in a highly coordinating organic medium. This is the first example reporting on the preparation of significant quantities (several tens of milligrams) of PuO2 NCs, in a controllable and reproducible manner. The structure and magnetic properties of PuO2 NCs have been characterized by a wide variety of techniques (powder X-ray diffraction (PXRD), X-ray absorption fine structure (XAFS), X-ray absorption near edge structure (XANES), TEM, IR, Raman, UV/Vis spectroscopies, and superconducting quantum interference device (SQUID) magnetometry). The current PuO2 NCs constitute an innovative material for the study of challenging problems as diverse as the transport behavior of plutonium in the environment or size and shape effects on the physics of transuranium elements. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

High-temperature XAFS measurement of molten salt systems

NASA Astrophysics Data System (ADS)

Okamoto, Y.; Akabori, M.; Motohashi, H.; Itoh, A.; Ogawa, T.

2002-07-01

A measurement system for high temperature XAFS was developed for investigating the local structure of hygroscopic molten salts like rare earth halides. A solid sample was enclosed in the upper tank of a quartz cell having a sandglass shape under reduced pressure to avoid oxygen and moisture. The measurement was carried out in an electric furnace capable of a highest temperature of 1273 K. After melting, the sample runs down through the melt path with 0.1 mm (or 0.2 mm) thickness to the lower tank. The measurable energy was limited to be above 10 keV due to the absorption of the quartz cell. We confirmed that the measurement of the expensive hygroscopic sample is possible with this system.

Xyloglucan endotransglucosylase/hydrolases (XTHs) are inactivated by binding to glass and cellulosic surfaces, and released in active form by a heat-stable polymer from cauliflower florets.

PubMed

Sharples, Sandra C; Nguyen-Phan, Tu C; Fry, Stephen C

2017-11-01

Xyloglucan endotransglucosylase (XET) activity, which cuts and re-joins hemicellulose chains in the plant cell wall, contributing to wall assembly and growth regulation, is the major activity of XTH proteins. During purification, XTHs often lose XET activity which, however, is restored by treatment with certain cold-water-extractable, heat-stable polymers (CHPs), e.g. from cauliflower florets. It was not known whether the XTH-activating factor (XAF) present in CHPs works by promoting (e.g. allosterically) XET activity or by re-solubilising sequestered XTH proteins. We now show that XTHs in dilute solution bind to diverse surfaces (e.g. glass and cellulose), and that CHPs can re-solubilise the bound enzyme, re-activating it. Cell walls prepared from cauliflower florets, mung bean shoots and Arabidopsis cell-suspension cultures each contained endogenous, tightly bound, inactive XTHs, which were likewise rapidly solubilised (within 0.5h) and thus activated by cauliflower XAF. We present a convenient quantitative assay for XAF acting on the native sequestered XTHs of Arabidopsis cell walls; using this assay, we show that CHPs from all plants tested possess XAF activity. The XAF activity of diverse CHPs does not correlate with their conductivity, showing that this activity is not a simple ionic effect. The XAF action of cauliflower CHPs was augmented by NaCl, although NaCl alone was much less effective than a CHP solution of similar conductivity, confirming that the cauliflower polymers did not simply exert a salt effect. We suggest that XAF is an endogenous regulator of XET action, modulating cell-wall loosening and/or assembly in vivo. Copyright © 2017 The Authors. Published by Elsevier GmbH.. All rights reserved.

A commercial Roundup® formulation induced male germ cell apoptosis by promoting the expression of XAF1 in adult mice.

PubMed

Jiang, Xiao; Zhang, Ning; Yin, Li; Zhang, Wen-Long; Han, Fei; Liu, Wen-Bin; Chen, Hong-Qiang; Cao, Jia; Liu, Jin-Yi

2018-06-14

Roundup® is extensively used for weed control worldwide. Residues of this compound may lead to side effects of the male reproductive system. However, the toxic effects and mechanisms of Roundup® of male germ cells remain unclear. We aimed to investigate the apoptosis-inducing effects of Roundup® on mouse male germ cells and explore the role of a novel tumor suppressor XAF1 (X-linked inhibitor of apoptosis-associated factor 1) involved in this process. We demonstrated that Roundup® can impair spermatogenesis, decrease sperm motility and concentration, and increase the sperm deformity rate in mice. In addition, excessive apoptosis of germ cells accompanied by the overexpression of XAF1 occurred after Roundup® exposure both in vitro and in vivo. Furthermore, the low expression of XIAP (X-linked inhibitor of apoptosis) induced by Roundup® was inversely correlated with XAF1. Moreover, the knockdown of XAF1 attenuated germ cell apoptosis, improved XIAP expression and inhibited the activation of its downstream target proteins, caspase-3 and PARP, after Roundup® exposure. Taken together, our data indicated that XAF1 plays an important role in Roundup®-induced male germ cell apoptosis. The present study suggested that Roundup® exposure has potential negative implications on male reproductive health in mammals. Copyright © 2018. Published by Elsevier B.V.

Structure of selenium incorporated in pyrite and mackinawite as determined by XAFS analyses

NASA Astrophysics Data System (ADS)

Diener, A.; Neumann, T.; Kramar, U.; Schild, D.

2012-05-01

Selenium has a toxic potential leading to diseases by ingestion and a radiotoxic potential as 79Se radionuclide if discharged from a high-level nuclear waste repository in deep geological formations into the biosphere. Selenium is often associated with sulfides, such as pyrite, the most important near-surface iron sulfide and constituent of host rocks and bentonite backfills considered for radioactive waste disposal. This study was aimed at investigating the incorporation of Se2- and Se4+ into pyrite and mackinawite to determine the relevance of iron sulfides to Se retention and the type of structural bonding. The syntheses of pyrite and mackinawite occurred via direct precipitation in batches and also produced coatings on natural pyrite in mixed-flow reactor experiments (MFR) under anoxic conditions at Se concentrations in the solutions of up to 10- 3 mol/L. Mineralogical analyses by SEM and XRD reveal the formation of pyrite and mackinawite phases. The average Se2- uptake in pyrite in batch experiments amounts to 98.6%. In MFR syntheses, it reaches 99.5%, both suggesting a high potential for retention. XAFS results indicate a substitution of sulfur by selenide during instantaneous precipitation in highly supersaturated solutions only. In selenide-doted mackinawite S2- was substituted by Se2-, resulting in a mackinawite-type compound. S- is substituted by Se- in selenide-doted pyrite, yielding a FeSSe compound as a slightly distorted pyrite structure. Under slighter supersaturated conditions, XAFS results indicate an incorporation of Se2- and Se4+ predominantly as Se0. This study shows that a substitution of S by Se in iron sulfides is probable only for highly supersaturated solutions under acidic and anoxic conditions. Under closer equilibrium conditions, Se0 is expected to be the most stable species.

Platinum and palladium incorporation into phosphate/viologen-phosphonates of zirconium and hafnium: synthesis and characterization

NASA Astrophysics Data System (ADS)

Dokoutchaev, Alexandre; Krishnan, Venkatesan V.; Thompson, Mark E.; Balasubramanian, Mahalingam

1998-10-01

We have continued previous efforts to synthesize and characterize a microporous metal phosphate/viologen-phosphonate compound, [(ZrF) 2(PO 4)(O 3PCH 2CH 2-4,4'-bipyridinium-CH 2CH 2PO 3)] ṡF·2H 2O, ZrPO PV. A derivative of this material has been shown to be an efficient catalyst for the production of hydrogen peroxide from hydrogen and oxygen. This paper has two objectives—one is to optimize the synthetic routes leading to the preparation of MPO PV (M=zirconium or hafnium) and the second is to characterize MPO PV and the derivatives formed by Pt or Pd incorporation by transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray powder diffraction (XRD), inductively coupled plasma-mass spectrometry (ICP-MS) and X-ray absorption fine structure analysis (XAFS). Powder XRD data have shown much higher crystallinity in MPO PV samples prepared by hydrothermal methods than those prepared by reflux methods. In the hydrothermal synthesis, the amount of mineralizer (HF) present controlled the crystallite size (as determined from TEM micrographs). The larger the quantity of HF in the bomb, the larger the size of the crystals but the lower the yield of the MPO PV material. Crystal sizes of about 2.5 μm in length and 0.15 μm in diameter have been made with very large quantities of HF as mineralizer (10 times the required stoichiometric amount). Ion exchange of the material by PdCl 42- has resulted in the incorporation of the PdCl 42- ions in place of X - in the material. This has been confirmed by XAFS studies that demonstrate the oxidation state of Pd is 2+ and show four Cl atoms bound to Pd. Upon reduction it has been confirmed (by XAFS) that the palladium exists as metal with oxidation state of zero. Ion exchange by PdCl 42- and PtCl 42- and subsequent reduction of the material suspension by hydrogen result in the formation of separate Pt and Pd colloids in the close vicinity of the crystallites. TEM micrographs show clearly that the Pt metal obtained after reduction forms much smaller particles in comparison to Pd. These exchanged and reduced materials have also been investigated as catalysts for production of hydrogen peroxide in mixed acetone/water medium. The production of hydrogen peroxide is enhanced by increasing amounts of Pd in the catalyst. Hydrogen peroxide yields are the highest for catalysts containing only Pd as opposed to a mixture of Pt and Pd.

Seasonal changes in Fe species and soluble Fe concentration in the atmosphere in the Northwest Pacific region based on the analysis of aerosols collected in Tsukuba, Japan

NASA Astrophysics Data System (ADS)

Takahashi, Y.; Furukawa, T.; Kanai, Y.; Uematsu, M.; Zheng, G.; Marcus, M. A.

2013-08-01

Atmospheric iron (Fe) can be a significant source of nutrition for phytoplankton inhabiting remote oceans, which in turn has a large influence on the Earth's climate. The bioavailability of Fe in aerosols depends mainly on the fraction of soluble Fe (= [FeSol]/[FeTotal], where [FeSol] and [FeTotal] are the atmospheric concentrations of soluble and total Fe, respectively). However, the numerous factors affecting the soluble Fe fraction have not been fully understood. In this study, the Fe species, chemical composition, and soluble Fe concentrations in aerosols collected in Tsukuba, Japan were investigated over a year (nine samples from December 2002 to October 2003) to identify the factors affecting the amount of soluble Fe supplied into the ocean. The soluble Fe concentration in aerosols is correlated with those of sulfate and oxalate originated from anthropogenic sources, suggesting that soluble Fe is mainly derived from anthropogenic sources. Moreover, the soluble Fe concentration is also correlated with the enrichment factors of vanadium and nickel emitted by fossil fuel combustion. These results suggest that the degree of Fe dissolution is influenced by the magnitude of anthropogenic activity, such as fossil fuel combustion. X-ray absorption fine structure (XAFS) spectroscopy was performed in order to identify the Fe species in aerosols. Fitting of XAFS spectra coupled with micro X-ray fluorescence analysis (μ-XRF) showed the main Fe species in aerosols in Tsukuba to be illite, ferrihydrite, hornblende, and Fe(III) sulfate. Moreover, the soluble Fe fraction in each sample measured by leaching experiments is closely correlated with the Fe(III) sulfate fraction determined by the XAFS spectrum fitting, suggesting that Fe(III) sulfate is the main soluble Fe in the ocean. Another possible factor that can control the amount of soluble Fe supplied into the ocean is the total Fe(III) concentration in the atmosphere, which was high in spring due to the high mineral dust concentrations during spring in East Asia. However, this factor does not contribute to the amount of soluble Fe to a larger degree than the effect of Fe speciation, or more strictly speaking the presence of Fe(III) sulfate. Therefore, based on these results, the most significant factor influencing the amount of soluble Fe in the North Pacific region is the concentration of anthropogenic Fe species such as Fe(III) sulfate that can be emitted from megacities in Eastern Asia.

Seasonal changes in Fe species and soluble Fe concentration in the atmosphere in the Northwest Pacific region based on the analysis of aerosols collected in Tsukuba, Japan

NASA Astrophysics Data System (ADS)

Takahashi, Y.; Furukawa, T.; Kanai, Y.; Uematsu, M.; Zheng, G.; Marcus, M. A.

2013-03-01

Atmospheric iron (Fe) can be a significant source of nutrition for phytoplankton inhabiting remote oceans, which in turn has a large influence on the Earth's climate. The bioavailability of Fe in aerosols depends mainly on the fraction of soluble Fe (= [FeSol]/[FeTotal], where [FeSol] and [FeTotal] are the atmospheric concentrations of soluble and total Fe, respectively). However, the numerous factors affecting the soluble Fe fraction have not been fully understood. In this study, the Fe species, chemical composition, and soluble Fe concentrations in aerosols collected in Tsukuba, Japan were investigated over a year (nine samples from December 2002 to October 2003) to identify the factors affecting the amount of soluble Fe supplied into the ocean. The soluble Fe concentration in aerosols is correlated with those of sulfate and oxalate originated from anthropogenic sources, suggesting that soluble Fe is mainly derived from anthropogenic sources. Moreover, the soluble Fe concentration is also correlated with the enrichment factors of vanadium and nickel emitted by fossil fuel combustion. These results suggest that the degree of Fe dissolution is influenced by the magnitude of anthropogenic activity, such as fossil fuel combustion. X-ray absorption fine structure (XAFS) spectroscopy was performed in this study to identify the Fe species in aerosols. The fitting of XAFS spectra coupled with micro X-ray fluorescence analysis (XRF) determined the main Fe species in aerosols in Tsukuba to be illite, ferrihydrite, hornblende, and Fe(III) sulfate. Moreover, the soluble Fe fraction in each sample measured by leaching experiments is closely correlated with the Fe(III) sulfate fraction determined by the XAFS spectrum fitting, suggesting that Fe(III) sulfate is the main soluble Fe in the ocean. Another possible factor that can control the amount of soluble Fe supplied into the ocean is the total Fe(III) concentration in the atmosphere, which was high in spring due to the high mineral dust concentrations during spring in East Asia. However, this factor does not contribute to the amount of soluble Fe to a larger degree than the effect of Fe speciation, or more strictly speaking the presence of Fe(III) sulfate. Therefore, based on these results, the most significant factor influencing the amount of soluble Fe in the North Pacific region is the concentration of anthropogenic Fe species such as Fe(III) sulfate that can be emitted from megacities in Eastern Asia.

Chemical bath deposition of semiconductor thin films & nanostructures in novel microreactors

NASA Astrophysics Data System (ADS)

McPeak, Kevin M.

Chemical bath deposition (CBD) offers a simple and inexpensive route to deposit semiconductor nanostructures and thin films, but lack of fundamental understanding and control of the underlying chemistry has limited its versatility. CBD is traditionally performed in a batch reactor, requiring only a substrate to be immersed in a supersaturated solution of aqueous precursors such as metal salts, complexing agents, and pH buffers. Highlights of CBD include low cost, operation at low temperature and atmospheric pressure, and scalability to large area substrates. In this dissertation, I explore CBD of semiconductor thin films and nanowire arrays in batch and continuous flow microreactors. Microreactors offer many advantages over traditional reactor designs including a reduction in mass transport limitations, precise temperature control and ease of production scale-up by "numbering up". Continuous flow micoreactors offer the unique advantage of providing reaction conditions that are time-invariant but change smoothly as a function of distance down the reaction channel. Growth from a bath whose composition changes along the reactor length results in deposited materials whose properties vary as a function of position on the substrate, essentially creating a combinatorial library. These substrates can be rapidly characterized to identify relationships between growth conditions and material properties or growth mechanisms. I have used CBD in a continuous flow microreactor to deposit ZnO nanowire arrays and CdZnS films whose optoelectronic properties vary as a function of position. The spatially-dependent optoelectronic properties of these materials have been correlated to changes in the composition, structure or growth mechanisms of the materials and ultimately their growth conditions by rigorous spatial characterization. CBD in a continuous flow microreactor, coupled with spatial characterization, provides a new route to understanding the connection between CBD growth conditions and the resulting optoelectronic properties of the film. The high surface-to-volume ratio of a microreactor also lends itself to in situ characterization studies. I demonstrated the first in situ x-ray absorption fine-structure spectroscopy (XAFS) study of CBD. The high sensitivity and ability to characterize liquid, amorphous and crystalline materials simultaneously make in situ XAFS spectroscopy an ideal tool to study the CBD of inorganic nanomaterials.

In situ/operando studies for the production of hydrogen through the water-gas shift on metal oxide catalysts.

PubMed

Rodriguez, José A; Hanson, Jonathan C; Stacchiola, Dario; Senanayake, Sanjaya D

2013-08-07

In this perspective article, we show how a series of in situ techniques {X-ray diffraction (XRD), pair-distribution-function analysis (PDF), X-ray absorption fine structure (XAFS), environmental transmission electron microscopy (ETEM), infrared spectroscopy (IR), ambient-pressure X-ray photoelectron spectroscopy (AP-XPS)} can be combined to perform detailed studies of the structural, electronic and chemical properties of metal oxide catalysts used for the production of hydrogen through the water-gas shift reaction (WGS, CO + H2O → H2 + CO2). Under reaction conditions most WGS catalysts undergo chemical transformations that drastically modify their composition with respect to that obtained during the synthesis process. Experiments of time-resolved in situ XRD, XAFS, and PDF indicate that the active phase of catalysts which combine Cu, Au or Pt with oxides such as ZnO, CeO2, TiO2, CeOx/TiO2 and Fe2O3 essentially involves nanoparticles of the reduced noble metals. The oxide support undergoes partial reduction and is not a simple spectator, facilitating the dissociation of water and in some cases modifying the chemical properties of the supported metal. Therefore, to optimize the performance of these catalysts one must take into consideration the properties of the metal and oxide phases. IR and AP-XPS have been used to study the reaction mechanism for the WGS on metal oxide catalysts. Data of IR spectroscopy indicate that formate species are not necessarily involved in the main reaction path for the water-gas shift on Cu-, Au- and Pt-based catalysts. Thus, a pure redox mechanism or associative mechanisms that involve either carbonate-like (CO3, HCO3) or carboxyl (HOCO) species should be considered. In the last two decades, there have been tremendous advances in our ability to study catalytic materials under reaction conditions and we are moving towards the major goal of fully understanding how the active sites for the production of hydrogen through the WGS actually work.

Uniform Doping in Quantum-Dots-Based Dilute Magnetic Semiconductor.

PubMed

Saha, Avijit; Shetty, Amitha; Pavan, A R; Chattopadhyay, Soma; Shibata, Tomohiro; Viswanatha, Ranjani

2016-07-07

Effective manipulation of magnetic spin within a semiconductor leading to a search for ferromagnets with semiconducting properties has evolved into an important field of dilute magnetic semiconductors (DMS). Although a lot of research is focused on understanding the still controversial origin of magnetism, efforts are also underway to develop new materials with higher magnetic temperatures for spintronics applications. However, so far, efforts toward quantum-dots(QDs)-based DMS materials are plagued with problems of phase separation, leading to nonuniform distribution of dopant ions. In this work, we have developed a strategy to synthesize highly crystalline, single-domain DMS system starting from a small magnetic core and allowing it to diffuse uniformly inside a thick CdS semiconductor matrix and achieve DMS QDs. X-ray absorption fine structure (XAFS) spectroscopy and energy-dispersive X-ray spectroscopy-scanning transmission electron microscopy (STEM-EDX) indicates the homogeneous distribution of magnetic impurities inside the semiconductor QDs leading to superior magnetic property. Further, the versatility of this technique was demonstrated by obtaining ultra large particles (∼60 nm) with uniform doping concentration as well as demonstrating the high quality magnetic response.

Studies of EXAFSSpectra using Copper (II) Schiff Base complexes and Determination of Bond lengths Using Synchrotron Radiation

NASA Astrophysics Data System (ADS)

Mishra, A.; Vibhute, V.; Ninama, S.; Parsai, N.; Jha, S. N.; Sharma, P.

2016-10-01

X-ray absorption fine structure (XAFS) at the K-edge of copper has been studied in some copper (II) complexes with substituted anilines like (2Cl, 4Br, 2NO2, 4NO2 and pure aniline) with o-PDA (orthophenylenediamine) as ligand. The X-ray absorption measurements have been performed at the recently developed BL-8 dispersive EXAFS beam line at 2.5 GeV Indus-2 Synchrotron Source at RRCAT, Indore, India. The data obtained has been processed using EXAFS data analysis program Athena.The graphical method gives the useful information about bond length and also the environment of the absorbing atom. The theoretical bond lengths of the complexes were calculated by using interactive fitting of EXAFS using fast Fourier inverse transformation (IFEFFIT) method. This method is also called as Fourier transform method. The Lytle, Sayers and Stern method and Levy's method have been used for determination of bond lengths experimentally of the studied complexes. The results of both methods have been compared with theoretical IFEFFIT method.

Current status of BL-2B at photon factory

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nambu, Akira, E-mail: akia.nambu.tw@hitachi.com; Ueda, Kazuhiro; Horiba, Koji

A new soft x-ray beamline BL-2B at Photon Factory of High Energy Accelerator Research Organization (KEK-PF) covers energy range from vacuum ultraviolet (30 eV) to soft x-ray (4000 eV). This wide energy range could be achieved by employing two undulators and two monochromators. Two different energy range undulators were installed tandem to a 9-meter straight section of PF storage ring. The 1{sup st} undulator is for VUV (30 eV) to SX (280 eV), while the other one is for SX (280 eV) to HX (4000 eV). It is also necessary to be equipped with two different monochrometors for energy abovemore » and under 2000 eV; grating monochrometor and double crystal monochrometor. One of the main purposes of this bemaline is spectroscopic study of light elements contained in several functional materials. The beamline is designed for photoemission spectroscopy (PES), X-ray absorption fine structure (XAFS) and other types of experiments. The performance of the new beamline is reported and typical examples of its application to material science are demonstrated.« less

Graphene-Immobilized fac-Re(bipy)(CO)3Cl for Syngas Generation from Carbon Dioxide.

PubMed

Zhou, Xin; Micheroni, Daniel; Lin, Zekai; Poon, Christopher; Li, Zhong; Lin, Wenbin

2016-02-17

We report the synthesis of fac-M(4-amino-bipy)(CO)3X (M = Mn and X = Br or M = Re and X = Cl, with bipy = 2,2'-bipyridine), their immobilization on graphene oxide (GrO) via diazonium grafting, and the use of Re-functionalized GrO for electrocatalytic syngas production. Infrared (IR) spectroscopy, X-ray absorption fine structure (XAFS) spectroscopy, and electrocatalysis indicated successful grafting of the Re catalyst onto GrO. Re-functionalized GrO was then deposited onto a glassy carbon electrode (GCE) for CO2 reduction. Investigation of the Re-functionalized GCE for syngas production was performed in a CO2-saturated acetonitrile solution with 3.1 M H2O as the proton source and 0.1 M tetrabutylammonium hexafluorophosphate (TBAPF6) as the supporting electrolyte. Cyclic voltammetry (CV), controlled potential electrolysis (CPE), and gas chromatography (GC) were employed to determine its CO2-to-CO conversion performance. The Re catalyst shows a turnover frequency (TOF) for generating CO up to 4.44 s(-1) with a CO/H2 ratio of 7:5.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Farges, Francois; /Museum Nat. Hist., Paris /Stanford U., Geo. Environ. Sci.; Benzerara, Karim

XAFS and {mu}-XAFS spectra were collected at the Cu K-edge for seven chrysocolla samples (Peru, USA, and Congo). The results suggest that the local structure around Cu is similar to that in Cu(OH){sub 2} (spertiniite). Cu-L{sub 3} STXM imaging and spectroscopy confirm that the chrysocolla samples examined here consist of mesoscopic Cu(II)-rich domains surrounded by Si-rich domains (in agreement with results from infra-red spectroscopy). Hence, we suggest that chrysocolla, which is generally considered to be orthorhombic with composition (Cu,Al){sub 2}H{sub 2}Si{sub 2}O{sub 5}(OH){sub 4} {center_dot} nH{sub 2}O, is in actually a mesoscopic assemblage composed dominantly of spertiniite (Cu(OH){sub 2}), watermore » and amorphous silica (SiO{sub 2}).« less

Uniform 2 nm gold nanoparticles supported on iron oxides as active catalysts for CO oxidation reaction: structure-activity relationship

NASA Astrophysics Data System (ADS)

Guo, Yu; Gu, Dong; Jin, Zhao; Du, Pei-Pei; Si, Rui; Tao, Jing; Xu, Wen-Qian; Huang, Yu-Ying; Senanayake, Sanjaya; Song, Qi-Sheng; Jia, Chun-Jiang; Schüth, Ferdi

2015-03-01

Uniform Au nanoparticles (~2 nm) with narrow size-distribution (standard deviation: 0.5-0.6 nm) supported on both hydroxylated (Fe_OH) and dehydrated iron oxide (Fe_O) have been prepared by either deposition-precipitation (DP) or colloidal-deposition (CD) methods. Different structural and textural characterizations were applied to the dried, calcined and used gold-iron oxide samples. Transmission electron microscopy (TEM) and high-resolution TEM (HRTEM) showed high homogeneity in the supported Au nanoparticles. The ex situ and in situ X-ray absorption fine structure (XAFS) characterization monitored the electronic and short-range local structure of active gold species. The synchrotron-based in situ X-ray diffraction (XRD), together with the corresponding temperature-programmed reduction by hydrogen (H2-TPR), indicated a structural evolution of the iron-oxide supports, correlating to their reducibility. An inverse order of catalytic activity between DP (Au/Fe_OH < Au/Fe_O) and CD (Au/Fe_OH > Au/Fe_O) was observed. Effective gold-support interaction results in a high activity for gold nanoparticles, locally generated by the sintering of dispersed Au atoms on the oxide support in the DP synthesis, while a hydroxylated surface favors the reactivity of externally introduced Au nanoparticles on Fe_OH support for the CD approach. This work reveals why differences in the synthetic protocol translate to differences in the catalytic performance of Au/FeOx catalysts with very similar structural characteristics in CO oxidation.

Uniform 2 nm gold nanoparticles supported on iron oxides as active catalysts for CO oxidation reaction: Structure-activity relationship

DOE PAGES

Guo, Yu; Senanayake, Sanjaya; Gu, Dong; ...

2015-01-12

Uniform Au nanoparticles (~2 nm) with narrow size-distribution (standard deviation: 0.5–0.6 nm) supported on both hydroxylated (Fe_OH) and dehydrated iron oxide (Fe_O) have been prepared by either deposition-precipitation (DP) or colloidal-deposition (CD) methods. Different structural and textural characterizations were applied to the dried, calcined and used gold-iron oxide samples. The transmission electron microscopy (TEM) and high-resolution TEM (HRTEM) described the high homogeneity in the supported Au nanoparticles. The ex-situ and in-situ X-ray absorption fine structure (XAFS) characterization monitored the electronic and short-range local structure of active gold species. The synchrotron-based in-situ X-ray diffraction (XRD), together with the corresponding temperature-programmed reductionmore » by hydrogen (H₂-TPR), indicated a structural evolution of the iron-oxide supports, correlating to their reducibility. An inverse order of catalytic activity between DP (Au/Fe_OH < Au/Fe_O) and CD (Au/Fe_OH > Au/Fe_O) was observed. Effective gold-support interaction results in a high activity for gold nanoparticles, locally generated by the sintering of dispersed Au atoms on the oxide support in the DP synthesis, while a hydroxylated surface favors the reactivity of externally introduced Au nanoparticles on Fe_OH support for the CD approach. This work reveals why differences in the synthetic protocol translate to differences in the catalytic performance of Au/FeO x catalysts with very similar structural characteristics in CO oxidation.« less

Local Structure of Sb in Cretaceous-Tertiary Boundary Clays from Stevns Klint By the XAFS Method

NASA Astrophysics Data System (ADS)

Hongu, H.; Yoshiasa, A.; Tobase, T.; Hiratoko, T.; Isobe, H.; Arima, H.; Sugiyama, K.; Okube, M.

2014-12-01

The Cretaceous-Tertiary (K-T) mass extinctions has been thought to be due to the asteroid impact since Ir anomalies was found by Alvarez et al. (1980) . The boundary clay is also enriched in Cr, Co, Ni, Cu, Zn, As and Sb. Especially concentrations of Sb and As are unusually large. However, the origins and concentration processes of Sb are unknown. In this study, local structure around antimony atoms in K-T boundary clay from Stevns Klint, Denmark, was determined by Sb K-edge XAFS spectroscopy. The XAFS analyses give the information about the chemical state and coordination environment around Sb atoms and help identify of the concentration phase, and also may provide various kinds of information about the asteroid impact and mass extinction. The XAFS measurements were performed at the BL-NW10A beamline at the Photon Factory in KEK, Tsukuba, Japan. The XANES spectra and radial structure function (RSF) showed that Sb in K-T boundary clays is high oxidation state Sb5+ and occupies a SbO6 octahedral site. The Sb-O interatomic distance in K-T clay sample is 2.08(1) A. It is known that Sb5+ is stable form in soil and soil water under an equilibrium situation within the Earth's surface environment. Antimony belongs to group 15 in the periodic table below arsenic, and the chemical behavior of Sb5+ is similar to that of As5+. Because there is a close correlation on co-precipitation between As and Fe (Ebihara and Miura, 1996; Sakai et al., 2007) , it is considered that Sb also correlates closely with Fe compounds (e.g., ferric hydroxides). Abundant ferric hydroxides occur in K-T boundary clays. It is considered that one of the reasons of abnormal high concentrations of Sb and As in K-T boundary clays is a lot of dust from impact ejecta falls with iron ions and deposits on surface of the Earth for a short period of time after the asteroid impact. ReferencesL. W. Alvarez, Science, 208, 1095-1108 (1980) M. Ebihara and T. Miura, Geochimica et Cosmochimica Acta, 60, 5133-5144 (1996) S. Sakai et al., The American Institute of Physics, Conference Proceeding, 882, 274-276 (2007)

Mercury speciation and selenium in toothed-whale muscles

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sakamoto, Mineshi, E-mail: sakamoto@nimd.go.jp; Itai, Takaaki; Yasutake, Akira

2015-11-15

Mercury accumulates at high levels in marine mammal tissues. However, its speciation is poorly understood. The main goal of this investigation was to establish the relationships among mercury species and selenium (Se) concentrations in toothed-whale muscles at different mercury levels. The concentrations of total mercury (T-Hg), methylmercury (MeHg), inorganic mercury (I-Hg) and Se were determined in the muscles of four toothed-whale species: bottlenose dolphins (n=31), Risso's dolphins (n=30), striped dolphins (n=29), and short-finned pilot whales (n=30). In each species, the MeHg concentration increased with increasing T-Hg concentration, tending to reach a plateau. In contrast, the proportion of MeHg in T-Hgmore » decreased from 90–100% to 20–40%. The levels of T-Hg and Se showed strong positive correlations. Se/I-Hg molar ratios rapidly decreased with the increase of I-Hg and reached almost 1 in all species. These results suggested that the demethylated MeHg immediately formed Se/I-Hg equimolar complex of mercury selenide (HgSe) in their muscles. In addition, an X-ray absorption fine structure analysis (XAFS) of a bottlenose dolphin muscle confirmed that the dominant chemical form of the Se/I-Hg equimolar complex was HgSe. HgSe was mainly localized in cells near the endomysium using electron probe microanalysis (EPMA). These results suggested that the demethylated MeHg finally deposits within muscle cells of bottlenose dolphin as an inert HgSe. - Highlights: • T-Hg, MeHg, I-Hg and Se were determined in the muscles of four toothed-whales. • MeHg increased with increasing T-Hg and tended to reach a plateau in all species. • Se/I-Hg molar ratios rapidly decreased with increase of I-Hg and reached almost 1. • XAFS of bottlenose dolphin muscle confirmed that HgSe was dominant chemical form. • EPMA of bottlenose dolphin muscle showed that HgSe deposited in muscle cells.« less

Plutonium-uranium mixed oxide characterization by coupling micro-X-ray diffraction and absorption investigations

NASA Astrophysics Data System (ADS)

Degueldre, C.; Martin, M.; Kuri, G.; Grolimund, D.; Borca, C.

2011-09-01

Plutonium-uranium mixed oxide (MOX) fuels are currently used in nuclear reactors. The potential differences of metal redox state and microstructural developments of the matrix before and after irradiation are commonly analysed by electron probe microanalysis. In this work the structure and next-neighbor atomic environments of Pu and U oxide features within unirradiated homogeneous MOX and irradiated (60 MW d kg -1) MOX samples was analysed by micro-X-ray fluorescence (μ-XRF), micro-X-ray diffraction (μ-XRD) and micro-X-ray absorption fine structure (μ-XAFS) spectroscopy. The grain properties, chemical bonding, valences and stoichiometry of Pu and U are determined from the experimental data gained for the unirradiated as well as for irradiated fuel material examined in the center of the fuel as well as in its peripheral zone (rim). The formation of sub-grains is observed as well as their development from the center to the rim (polygonization). In the irradiated sample Pu remains tetravalent (>95%) and no (<5%) Pu(V) or Pu(VI) can be detected while the fuel could undergo slight oxidation in the rim zone. Any slight potential plutonium oxidation is buffered by the uranium dioxide matrix while locally fuel cladding interaction could also affect the redox of the fuel.

Electronic structure, optical and thermal/concentration quenching properties of Lu{sub 2−2x}Eu{sub 2x}WO{sub 6} (0 ≤ x ≤0.2)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chen, Xiang-Yang; University of Chinese Academy of Science, Beijing 100039; Zhang, Zhi-Jun, E-mail: zhangzhijun@shu.edu.cn

Highlights: • The band gap of Lu{sub 2}WO{sub 6} is calculated to be 3.13 eV using the CASTEP mode. • Valent state and occupation site of Eu are clarified by X-ray absorption fine structure (XAFS) spectra. • The thermal/concentration quenching mechanisms of Eu in Lu{sub 2}WO{sub 6} have been investigated in detail. - Abstract: Density functional theory calculations on monoclinic Lu{sub 2}WO{sub 6} is carried out using the Cambridge Sequential Total Energy Package code. The result indicates that Lu{sub 2}WO{sub 6} is a broad band gap semiconductor with an indirect band gap of 3.13 eV. Eu ions are trivalency and themore » average coordination number is 7.6(5), indicating that the site of Lu is occupied by Eu. The activation energy ΔE is calculated as 0.314 eV. In addiation, the thermal quenching mechnism of Eu-activated Lu{sub 2}WO{sub 6} and the different concentration quenching mechanisms for {sup 5}D{sub 0} and {sup 5}D{sub 1} emissions of Eu ions have been proposed.« less

Effect of Iron(II) on Arsenic Sequestration by δ-MnO 2 : Desorption Studies Using Stirred-Flow Experiments and X-Ray Absorption Fine-Structure Spectroscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

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

2015-10-18

Arsenic (As) mobility in the environment is greatly affected by its oxidation state and the degree to which it is sorbed on metal oxide surfaces. Manganese (Mn) and iron (Fe) oxides are ubiquitous solids in terrestrial systems and have high sorptive capacities for many trace metals, including As. Although numerous studies have studied the effects of As adsorption and desorption onto Fe and Mn oxides individually, the fate of As within mixed systems representative of natural environments has not been resolved. In this research, As(III) was initially reacted with a poorly crystalline phyllomanganate (δ-MnO 2) in the presence of Fe(II)more » prior to desorption. This initial reaction resulted in the sorption of both As(III) and As(V) on mixed Fe/Mn-oxides surfaces. A desorption study was carried out using two environmentally significant ions, phosphate (PO 4 3–) and calcium (Ca 2+). Both a stirred-flow technique and X-ray absorption fine-structure spectroscopy (XAFS) analysis were used to investigate As desorption behavior. Results showed that when As(III)/Fe(II) = 1:1 in the initial reaction, only As(V) was desorbed, agreeing with a previous study showing that As(III) is not associated with the Fe/Mn-oxides. When As(III)/Fe(II) = 1:10 in the initial reaction, both As(III) and As(V) can be desorbed from the Fe/Mn-oxide surface, and more As(III) is desorbed than As(V). Neither of the desorbents used in this study completely removed As(III) or As(V) from the Fe/Mn-oxides surface. However, the As desorption fraction decreases with increasing Fe(II) concentration in the initial reactions.« less

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

PubMed

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

2015-11-17

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

The use of XAFS to determine the nature of interaction of iron and molybdenum metal salts within PS-b-P2VP micelles.

PubMed

Riskin, Alexander; Beale, Andrew M; Boyen, Hans-Gerhard; Vantomme, André; Hardy, An; Van Bael, Marlies K

2013-02-07

The poly(styrene)-block-poly(2-vinylpyridine) (PS-b-P2VP) micelle route is a well established method for the preparation of bimetallic nanoparticles used for the catalysis of carbon nanotubes and other applications like ultrahigh density storage devices, yet to date no information is available concerning the internal structure of the P2VP-metal salt complex. For the first time, XAFS measurements were performed on micelles loaded with either iron(III) chloride or molybdenum(V) chloride and a combination of both. Analysis of the data revealed that iron is tetrahedrally coordinated within the core, whereas molybdenum is octahedrally coordinated in the pure loaded micelles and trigonally coordinated in the mixed micelles. For the bimetallic samples, analysis of the Fe and Mo K-edge data revealed the existence of an interaction between iron and molybdenum. This approach to obtain detailed structural information during the preparation of these catalyst samples will allow for a deeper understanding of the effects of structure on the function of catalysts used for CNT growth i.e. to explain differences in yield as well as potentially providing a deeper understanding of the CNT growth mechanism itself.

Characterization of magnetic and dielectric properties of Bi(1-x)Gd(x)FeO3 nanoparticles by local structure analyses.

PubMed

Yanoh, Takuya; Kurokawa, Akinobu; Takeuchi, Hiromasa; Yano, Shinya; Onuma, Kazuki; Kondo, Takaya; Miike, Kazunari; Miyasaka, Toshiki; Mibu, Ko; Ichiyanagi, Yuko

2014-03-01

Bi(1-x)Gd(x)FeO3 (0 < or = x < or = 1.0) nanoparticles were synthesized by a wet chemical method. The annealing temperatures were controlled to obtain single-phase Bi(1-x)Gd(x)FeO3 nanoparticles. The crystal diameters decreased as the number of doped Gd ions increased. The crystal structure changed, as the number of Gd ions increased, from rhombohedral to orthorhombic perovskite, at x = 0.2. The behavior of the magnetization curves observed at various values of x (x = 0.05, 0.1, 0.15) of the rhombohedral structure suggested that the canted antiferromagnetism and remanent magnetization (M(r)) drastically increased, compared with those at x = 0 (BiFeO3). It is suggested that the spin-canting angle of the Fe ions increased with the increase in the number of Gd ions. The dielectric properties at x = 0.1 showed that the dielectric loss (tan delta) was improved, compared with that at x = 0 (BiFeO3), by approximately 90%, while the real part of the dielectric constant epsilon' was reduced by approximately 15%. The reason is that the doping impurities restrained the reduction in the leakage current. It was found, from the X-ray absorption fine structure (XAFS) spectra, that Gd ions were doped accurately and that the symmetry of the B site was improved. The Mössbauer analysis suggested the existence of magnetic cycloid spiral ordering.

New XAFS Facility for In-Situ Measurements at Beamline C at HASYLAB

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rickers, K.; Drube, W.; Schulte-Schrepping, H.

2007-02-02

A XAFS-experiment allowing for in-situ experiments has been set up at DORIS bending magnet beamline C. For that purpose, a new double-crystal, UHV-compatible monochromator with fast scanning capability was designed. This fixed-exit monochromator uses two crystal sets on a common central rotation axis driven by an ex-vacuo goniometer. Bragg angles range from 5 deg. to 55.5 deg. resulting in a total energy range 2.3 - 43.4 keV using Si(111)/(311) crystal sets. Crystal pairs can be remotely selected by translating the vacuum chamber. Energy encoding is performed using an optical encoder system. The standard XAFS sample environment is set-up in vacuomore » and can be adapted for special sample environments. For in-situ experiments, the beamline is equipped with twelve gas lines. An exhaust line allows toxic/reactive gases to be handled. As an initial performance test of the instrument, Ti, Cr, Fe and Cu XAFS and Ce K-shell QEXAFS measurements were performed.« less

Photocatalytic reduction of heavy metal ions on derivatized titanium dioxide nano-particle surface studied by XAFS

NASA Astrophysics Data System (ADS)

Chen, Lin X.; Rajh, Tijana; Mićić, Olga Wang, Zhiyu; Tiede, David M.; Thurnauer, Marion

1997-12-01

Photoreduction of heavy metal ions, Cu 2- and Hg 2+, on TiO 2 nano-particle surfaces, has been investigated by XAFS measurements. The effects of TiO 2 surface modification reagents on the reaction efficiency have been studied. We observed a significant reaction efficiency enhancement when amino acid alanine was added to a mixture of 0.01 M Cu 2+ and TiO 2 nano-particles. Fifty percent of the adsorbed Cu 2+ has been reduced to Cu 0 after 1-h illumination with a UV-enhanced xenon lamp. Photoreduction of Hg 2+ on TiO 2 colloid surfaces was also investigated without and with thiolactic acid (TLA). In this case, the photoreduction efficiency for Hg 2+ was lowered. Structures of metal ion surroundings in various complexes as well as their role in photoreduction of metal ions are discussed.

Direct comparison of XAFS spectroscopy and sequential extraction for arsenic speciation in coal

USGS Publications Warehouse

Huggins, Frank E.; Huffman, G.P.; Kolker, A.; Mroczkowski, S.; Palmer, C.A.; Finkelman, R.B.

2000-01-01

The speciation of arsenic in an Ohio bituminous coal and a North Dakota lignite has been examined by the complementary methods of arsenic XAFS spectroscopy and sequential extraction by aqueous solutions of ammonium acetate, HCl, HF, and HNO3. In order to facilitate a more direct comparison of the two methods, the arsenic XAFS spectra were obtained from aliquots of the coal prepared after each stage of the leaching procedure. For the aliquots, approximately linear correlations (r2 > 0.98 for the Ohio coal, > 0.90 for the ND lignite) were observed between the height of the edge-step in the XAFS analysis and the concentration of arsenic measured by instrumental neutron activation analysis. Results from the leaching sequence indicate that there are two major arsenic forms present in both coals; one is removed by leaching with HCl and the other by HNO3. Whereas the XAFS spectral signatures of the arsenic leached by HCl are compatible with arsenate for both coals, the arsenic leached by HNO3 is identified as arsenic associated with pyrite for the Ohio coal and as an As3+ species for the North Dakota lignite. Minor arsenate forms persist in both coals after the final leaching with nitric acid. The arsenate forms extracted in HCl are believed to be oxidation products derived from the other major arsenic forms upon exposure of the pulverized coals to air.

Atomic Scale Structure-Chemistry Relationships at Oxide Catalyst Surfaces and Interfaces

NASA Astrophysics Data System (ADS)

McBriarty, Martin E.

Oxide catalysts are integral to chemical production, fuel refining, and the removal of environmental pollutants. However, the atomic-scale phenomena which lead to the useful reactive properties of catalyst materials are not sufficiently understood. In this work, the tools of surface and interface science and electronic structure theory are applied to investigate the structure and chemical properties of catalytically active particles and ultrathin films supported on oxide single crystals. These studies focus on structure-property relationships in vanadium oxide, tungsten oxide, and mixed V-W oxides on the surfaces of alpha-Al2O3 and alpha-Fe2O 3 (0001)-oriented single crystal substrates, two materials with nearly identical crystal structures but drastically different chemical properties. In situ synchrotron X-ray standing wave (XSW) measurements are sensitive to changes in the atomic-scale geometry of single crystal model catalyst surfaces through chemical reaction cycles, while X-ray photoelectron spectroscopy (XPS) reveals corresponding chemical changes. Experimental results agree with theoretical calculations of surface structures, allowing for detailed electronic structure investigations and predictions of surface chemical phenomena. The surface configurations and oxidation states of V and W are found to depend on the coverage of each, and reversible structural shifts accompany chemical state changes through reduction-oxidation cycles. Substrate-dependent effects suggest how the choice of oxide support material may affect catalytic behavior. Additionally, the structure and chemistry of W deposited on alpha-Fe 2O3 nanopowders is studied using X-ray absorption fine structure (XAFS) measurements in an attempt to bridge single crystal surface studies with real catalysts. These investigations of catalytically active material surfaces can inform the rational design of new catalysts for more efficient and sustainable chemistry.

Tracking the Chemical Transformations at the Brønsted Acid Site upon Water-Induced Deprotonation in a Zeolite Pore

DOE Office of Scientific and Technical Information (OSTI.GOV)

Vjunov, Aleksei; Wang, Meng; Govind, Niranjan

We report the structural changes induced by Brønsted acidic site deprotonation in a zeolite with MFI structure as a function of temperature up to 430°C using in situ Al K-edge X-ray absorption fine structure spectroscopy (XAFS). At ambient conditions, the protons are present as hydrated hydronium ions (H3O+(H2O)n) that are ion-paired to the anionic, Al tetrahedral (T) site. At elevated temperatures, loss of water molecules hydrating the hydronium ions leads to an unstable free hydronium ion that disso-ciates to form the hydroxylated T-site. The formation of this (-O3)-Al-(OH-) species leads to the elongation of one of the four Al-O bondsmore » and causes significant distortion of the tetrahedral symmetry about the Al atom. This distortion leads to the appearance of new pre-edge features in the Al K-edge X-ray absorption near edge structure (XANES) spectra. The pre-edge peak assignment is confirmed by time-dependent density functional theory calculation of the XANES spectrum. The XANES spectra are also sensitive to solutes or solvent that are in proximity to the T-site. A second structural transition occurs at about the same temperature, namely the conversion of a minor fraction of extra-framework octahedral Al present in the sample at ambient conditions to a tetrahedral species through the de-coordination of H2O-ligands. Both IR spectroscopy and thermogravimetric analysis (TGA) are further used to confirm the overall chemical transformation of the T-site.« less

XAFS STUDIES OF NICKEL AND SULFUR SPECIATION IN RESIDENTIAL OIL FLY-ASH PARTICULATE MATTERS (ROFA PM)

EPA Science Inventory

XAFS spectroscopy has been employed to evaluate the effect of fuel compositions and combustion conditions on the amount, form, and distribution of sulfur and nickel in size-fractionated ROFA PM. Analysis of S K-edge XANES establish that sulfate is abundant in all PM. However, dep...

Manganese speciation in Diplodon chilensis patagonicus shells: a XANES study

NASA Astrophysics Data System (ADS)

Soldati, A. L.; Vicente-Vilas, V.; Goettlicher, J.; Jacob, D. E.

2009-04-01

In addition to other types of climate archives, biogenic skeletons of a variety of different organisms (i.e. shells of bivalves, skeletal hard parts of corals or sponges) are increasingly used for high-resolution climate reconstructions. Bivalves are particularly suited for such analyses because they are geographically broadly distributed and have been shown to record climate and environmental information reliably and over long time intervals. Variation of environmental parameters such as food supply, substratum type, salinity, illumination, temperature, concentration of dissolved oxygen or oxygen/carbon dioxide ratio, among others, may affect growth pattern, shell structure, mineralogy, isotopic fractionation and chemistry. Thus, shell features, minor and trace element composition patterns and isotopic signals may serve as an archive of environmental history. In turn, palaeoclimatic parameters such as ambient temperature, precipitation gradients, seawater salinity and primary production can be reconstructed from the shells by means of sclerochronological and geochemical methods. However, the distribution of minor and trace elements in the biominerals is not only influenced by the environment or vital effects, but also by intrinsic biomineralisation parameters like the carbonate polymorphism and the mineral habit (Soldati et al., 2008a). Generally, it is assumed that the X2+ ions are replacing the Ca2+ ion in the calcium carbonate (CaCO3) structure, but newest findings show that amorphous (or disordered) phases may play a role in hosting some of the elements use as proxies (Meibom et al., 2008; and Finch and Allison, 2007). In this work we focused on the freshwater clam Diplodon chilensis patagonicus, a widely distributed inhabitant of lakes and rivers in southern South America. Thanks to its long life span and seasonal growth Diplodon mussels exhibit excellent characteristics to construct an accurate chronological archive, with time windows of up to around a century, resolving the environmental signal annually and even seasonally (Soldati et al., 2008b). High resolution trace elemental analysis by LA-ICPMS and EPMA in the shells show that elements like Mg and Mn are related to the seasonal pattern and can be enriched along the organic-rich annual shell growth lines. Thus, these elements could possibly be bound organically instead of occupying a defined site in the crystal lattice of the calcium carbonate phase. LA-ICP-MS results show that Mn concentrations in these Diplodon shells range between 1000-300 g/g and 100-10 g/g and that the areas of enrichment are in the micrometer range. Raman and XRD measurements at high spatial resolution failed in recognizing whether the Mn is in carbonate solid solution or not. Therefore, speciation techniques like X-ray absorption fine structure (XAFS) spectroscopy with a high lateral resolution are required to address this question. Prior to XAFS spectroscopy the samples were mapped with the intensity of the Mn Kα fluorescence emission line in order to locate the Mn rich areas of interest. Because of the Mn concentrations in the sub % range the XAFS spectra at the positions of interest have been recorded in fluorescence mode using a 7 element Si(Li) detector. This study focuses on the near edge (XANES: X-ray absorption near edge structure) part of the spectra. For data evaluation, XANES spectra of reference substances were additionally measured in order to get first hints to Mn valence and bonding. As standards were used Mn and Mn rich carbonates, Mn oxides with Mn in different oxidation states, and Mn in organic compounds (Mn-porphyrin and Mn-acetate). The XAFS measurements have been carried out at the SUL-X beamline of the synchrotron radiation source ANKA of the Forschungszentrum Karlsruhe. Data evaluation is ongoing. References MEIBOM, A., CUIF, J.P., HOULBREQUE, F., MOSTEFAOUI, S., DAUPHIN, Y., MEIBOM; K.L. & DUNBAR, R. (2008). Compositional variations at ultra-structure length scales in coral skeleton. Geochimica et Cosmochimica Acta 72: 1555-1569. FINCH, A.A. & ALLISON, N. (2007). Coordination of Sr and Mg in calcite and aragonite. Mineralogical Magazine 71: 539-552. SOLDATI A.L., JACOB D.E., WEHRMEISTER, U. & HOFMEISTER, W. (2008a). Structural characterization and chemical composition of aragonite and vaterite in freshwater cultured pearls. Mineralogical Magazine 72: 577-590. SOLDATI A.L., JACOB D., SCHÖNE B.R., BIANCHI M.M. & HAJDUK A. (2008b). Seasonal periodicity of growth and composition in valves of Diplodon chilensis patagonicus (D'Orbigny, 1835). Journal of Molluscan Studies, doi:10.1093/mollus/eyn044.

Enhanced sequestration of Cr(VI) by nanoscale zero-valent iron supported on layered double hydroxide by batch and XAFS study.

PubMed

Sheng, Guodong; Hu, Jun; Li, Hui; Li, Jiaxing; Huang, Yuying

2016-04-01

Herein, the reduction of nanoscale zero-valent iron (NZVI) and adsorption of layered double hydroxides (LDH) to sequester Cr(VI) were well combined by the immobilization of NZVI onto LDH surface (NZVI/LDH). The characterization results revealed that LDH decreased NZVI aggregation and thus increased Cr(VI) sequestration. The batch results indicated that Cr(VI) sequestration by NZVI/LDH was higher than that of NZVI, and superior to the sum of reduction and adsorption. The LDH with good anion exchange property allowed the adsorption of Cr(VI), facilitating interfacial reaction by increasing the local concentration of Cr(VI) in the NZVI vicinity. X-ray absorption near edge structure (XANES) results indicated that Cr(VI) was almost completely reduced to Cr(III) by NZVI/LDH, but Cr(VI) was partly reduced to Cr(III) by NZVI with a trace of Cr(VI) adsorbed on corrosion products. The coordination environment of Cr from extended X-ray absorption fine structure (EXAFS) analysis revealed that LDH could be a good scavenger for the insoluble products produced during reaction. So, the insoluble products on NZVI could be reduced, and its reactivity could be maintained. These results demonstrated that NZVI/LDH exhibits multiple functionalities relevant to the remediation of Cr(VI)-contaminated sites. Copyright © 2016 Elsevier Ltd. All rights reserved.

X-ray absorption fine structure of artificial antigens for cadmium

NASA Astrophysics Data System (ADS)

Lu, Liang; Liu, Aiping; Chen, Fusheng; Wang, Xiaohong

2011-11-01

Immunoassay technology as a quick and large-scale screening method to detect metal ions in foods and environmental samples has rapidly been developed due to several advantages over conventional instrument-intensive methods. Unlike biomacromolecule, metal ions are haptens without immunogenicity, so successful preparation of artificial antigens is the first critical step for establishing immunoassay methods for them. In the current paper, cadmium ions were conjugated to BSA and OVA, respectively, using bifunctional chelator, p-SCN-Bn-DTPA. The ultraviolet analysis indicated that the maximum absorption peak of Cd-p-SCN-DTPA-BSA and Cd-p-SCN-DTPA-OVA had a small peak shift and an apparent absorbance increase compared to that of BSA and OVA, and the extents of substitution of ɛ-amino in both conjugates were 51.2% and 58.6%, respectively. In addition, the EXAFS of conjugates implied that Cd 2+ coordinated with N and O atoms of DTPA in artificial antigens, the coordination type and number of Cd-DTPA, Cd-p-SCN-Bn-DTPA-BSA, Cd-p-SCN-Bn-DTPA-OVA were the same. XANES region and geometries of the three compounds were also same. These results implied that the three antigens had the similar local structure and atomic geometry. This was the first time that the XAFS was attempted for the identification of artificial heavy metal ion antigens.

Hydrothermal diamond-anvil cell: Application to studies of geologic fluids

USGS Publications Warehouse

Chou, I.-Ming

2003-01-01

The hydrothermal diamond-anvil cell (HDAC) was designed to simulate the geologic conditions of crustal processes in the presence of water or other fluids. The HDAC has been used to apply external pressure to both synthetic and natural fluid inclusions in quartz to minimize problems caused by stretching or decrepitation of inclusions during microthermometric analysis. When the HDAC is loaded with a fluid sample, it can be considered as a large synthetic fluid inclusion and therefore, can be used to study the PVTX properties as well as phase relations of the sample fluid. Because the HDAC has a wide measurement pressure-temperature range and also allows in-situ optical observations, it has been used to study critical phenomena of various chemical systems, such as the geologically important hydrous silicate melts. It is possible, when the HDAC is combined with synchrotron X-ray sources, to obtain basic information on speciation and structure of metal including rare-earth elements (REE) complexes in hydrothermal solutions as revealed by X-ray absorption fine structure (XAFS) spectra. Recent modifications of the HDAC minimize the loss of intensity of X-rays due to scattering and absorption by the diamonds. These modifications are especially important for studying elements with absorption edges below 10 keV and therefore particularly valuable for our understanding of transport and deposition of first-row transition elements and REE in hydrothermal environments.

K 3 Fe(CN) 6 under External Pressure: Dimerization of CN – Coupled with Electron Transfer to Fe(III)

DOE PAGES

Li, Kuo; Zheng, Haiyan; Wang, Lijuan; ...

2015-09-14

The addition polymerization of charged monomers like C≡C 2– and C≡N– is scarcely seen at ambient conditions but can progress under external pressure with their conductivity significantly enhanced, which expands the research field of polymer science to inorganic salts. Moreover, the reaction pressures of transition metal cyanides like Prussian blue and K 3Fe(CN) 6 are much lower than that of alkali cyanides. To figure out the effect of the transition metal on the reaction, the crystal structure and electronic structure of K 3Fe(CN) 6 under external pressure are investigated by in situ neutron diffraction, in situ X-ray absorption fine structuremore » (XAFS), and neutron pair distribution functions (PDF) up to ~15 GPa. The cyanide anions react following a sequence of approaching–bonding–stabilizing. The Fe(III) brings the cyanides closer which makes the bonding progress at a low pressure (2–4 GPa). At ~8 GPa, an electron transfers from the CN to Fe(III), reduces the charge density on cyanide ions, and stabilizes the reaction product of cyanide. Finally, from this study we can conclude that bringing the monomers closer and reducing their charge density are two effective routes to decrease the reaction pressure, which is important for designing novel pressure induced conductor and excellent electrode materials.« less

Spectroscopic and first-principles calculation studies of the chemical forms of palladium ion in nitric acid solution for development of disposal of high-level radioactive nuclear wastes

NASA Astrophysics Data System (ADS)

Watanabe, Shinta; Sato, Toshikazu; Yoshida, Tomoko; Nakaya, Masato; Yoshino, Masahito; Nagasaki, Takanori; Inaba, Yusuke; Takeshita, Kenji; Onoe, Jun

2018-04-01

We have investigated the chemical forms of palladium (Pd) ion in nitric acid solution, using XAFS/UV-vis spectroscopic and first-principles methods in order to develop the disposal of high-level radioactive nuclear liquid wastes (HLLW: radioactive metal ions in 2 M nitric acid solution). The results of theoretical calculations and XAFS/UV-vis spectroscopy indicate that Pd is a divalent ion and forms a square-planar complex structure coordinated with four nitrate ions, [Pd(NO3)4]2-, in nitric acid solution. This complex structure is also thermodynamically predicted to be most stable among complexes [Pd(H2O)x(NO3)4-x]x-2 (x = 0-4). Since the overall feature of UV-vis spectra of the Pd complex was independent of nitric acid concentration in the range 1-6 M, the structure of the Pd complex remains unchanged in this range. Furthermore, we examined the influence of γ-ray radiation on the [Pd(NO3)4]2- complex, using UV-vis spectroscopy, and found that UV-vis spectra seemed not to be changed even after 1.0 MGy irradiation. This implies that the Pd complex structure will be still stable in actual HLLW. These findings obtained above are useful information to develop the vitrification processes for disposal of HLLW.

2D XAFS-XEOL Spectroscopy - Some recent developments

NASA Astrophysics Data System (ADS)

Ward, M. J.; Smith, J. G.; Regier, T. Z.; Sham, T. K.

2013-03-01

The use of optical photons to measure the modulation of the absorption coefficient upon X-ray excitation, or optical XAFS, is of particular interest for application to the study of light emitting semiconducting nanomaterials due to the additional information that may be gained. The potential for site-selectivity, elemental and excitation energy specific luminescence decay channels, and surface vs. bulk effects all make the use of X-ray excited optical luminescence (XEOL) desirable as a detection method. Previous experiments have made use of a monochromator to select the optical emission wavelength used to monitor optical XAFS. This method of detection suffers from the primary limitation of only being able to monitor the optical response at one emission wavelength. By combining the high resolution soft X-ray Spherical Grating Monochromator beam-line at the Canadian Light Source with an Ocean Optics QE 65000 fast CCD spectrophotometer and custom integration software we have developed a technique for collecting 2D XAFS-XEOL spectra, in which the excitation energy is scanned and a XEOL spectra is collected for every energy value. Herein we report the development of this technique and its capabilities using the study of the luminescence emitted from single crystal zinc oxide as an example.

Synchrotron X-ray spectroscopic investigations of an Nb-bearing silicate melt in contact with an aqueous fluid

NASA Astrophysics Data System (ADS)

Mayanovic, R. A.; Anderson, A. J.; Bassett, W. A.; Chou, I.

2006-05-01

Understanding the structural properties of trace elements in hydrous silicate melts in contact with a hydrothermal fluid is fundamentally important for a better assessment of the role of such elements in silicate melts being subjected to hydrothermal processes. We describe the use of synchrotron x-ray microprobe techniques and the modified hydrothermal diamond-anvil cell for in-situ spectroscopic analysis of individual phases of a silicate-melt/fluid system. Synchrotron X-ray fluorescence (XRF) and Nb K-edge X-ray absorption fine structure (XAFS) measurements were made on sectors ID20 and ID13 at the Advanced Photon Source, at the Argonne National Laboratory, on a Nb-bearing granitic glass in H2O and separately in a 1 M Na2CO3 aqueous solution at temperatures ranging from 25 to 880 °C and at up to 700 MPa of pressure. Individual phases of the Nb-glass/fluid system (at low temperatures) or the hydrous-silicate-melt/fluid system (at elevated temperatures) were probed using an X-ray beam focused to a diameter of 5 μm at the location of the sample. XRF analysis shows that the Nb partitions selectively from the hydrous silicate melt into the aqueous fluid at high temperatures in the Nb-glass/Na2CO3/H2O system but not so in the Nb-glass/H2O system. Analysis of XAFS spectra measured from the hydrous silicate melt phase of the Nb-glass/H2O sample in the 450 to 700 °C range shows that the first shell contains six oxygen atoms at a distance of ~1.98 Å. Our results suggest that reorganization of the silicate structure surrounding Nb occurs in the melt when compared to that of the starting glass. The X-ray absorption near edge structure (XANES) spectra show a pre-edge peak feature located at ~18995 eV that exhibits sharpening and becomes more intensified in the 450 to 700 °C range. Fitting of the Nb K-edge XANES spectra measured from the melt is accomplished using FEFF8.28 and an atomic model NbSi4O6-4(Na, K). The model is based on the structure of fresnoite (Ba2TiSi2O8), in which an NbO6 octahedron unit is substituted for the TiO5 unit, four Na and four K atoms are placed alternately on nearby Ba atom sites, and four Si atoms are arranged in a single plane intersecting the NbO6 unit. The results from fitting indicate that the local structure of Nb in the silicate melt is altered from its local structure in the quenched glass before heating and in the glass after heating in the diamond anvil cell. The importance of in situ analysis of melts and hydrothermal fluids at various temperatures and pressures is discussed in the context of our study.

XAFS investigation of polyamidoxime-bound uranyl contests the paradigm from small molecule studies

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mayes, Richard T.; Piechowicz, Marek; Lin, Zekai

In this study, limited resource availability and population growth have motivated interest in harvesting valuable metals from unconventional reserves, but developing selective adsorbents for this task requires structural knowledge of metal binding environments. Amidoxime polymers have been identified as the most promising platform for large-scale extraction of uranium from seawater. However, despite more than 30 years of research, the uranyl coordination environment on these adsorbents has not been positively identified. We report the first XAFS investigation of polyamidoxime-bound uranyl, with EXAFS fits suggesting a cooperative chelating model, rather than the tridentate or η 2 motifs proposed by small molecule andmore » computational studies. Samples exposed to environmental seawater also display a feature consistent with a μ 2-oxo-bridged transition metal in the uranyl coordination sphere, suggesting in situ formation of a specific binding site or mineralization of uranium on the polymer surface. These unexpected findings challenge several long-held assumptions and have significant implications for development of polymer adsorbents with high selectivity.« less

XAFS investigation of polyamidoxime-bound uranyl contests the paradigm from small molecule studies

DOE PAGES

Mayes, Richard T.; Piechowicz, Marek; Lin, Zekai; ...

2015-11-12

In this study, limited resource availability and population growth have motivated interest in harvesting valuable metals from unconventional reserves, but developing selective adsorbents for this task requires structural knowledge of metal binding environments. Amidoxime polymers have been identified as the most promising platform for large-scale extraction of uranium from seawater. However, despite more than 30 years of research, the uranyl coordination environment on these adsorbents has not been positively identified. We report the first XAFS investigation of polyamidoxime-bound uranyl, with EXAFS fits suggesting a cooperative chelating model, rather than the tridentate or η 2 motifs proposed by small molecule andmore » computational studies. Samples exposed to environmental seawater also display a feature consistent with a μ 2-oxo-bridged transition metal in the uranyl coordination sphere, suggesting in situ formation of a specific binding site or mineralization of uranium on the polymer surface. These unexpected findings challenge several long-held assumptions and have significant implications for development of polymer adsorbents with high selectivity.« less

Photocatalytic reduction of heavy metal ions on derivatized titanium dioxide nano-particle surface studied by XAFS.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chen, L. X.; Rajh, T.; Micic, O.

1997-01-01

Photoreduction of heavy metal ions, Cu{sup 2-} and Hg{sup 2+}, on TiO{sup 2} nano-particle surfaces, has been investigated by XAFS measurements. The effects of TiO{sup 2} surface modification reagents on the reaction efficiency have been studied. We observed a significant reaction efficiency enhancement when amino acid alanine was added to a mixture of 0.01 M Cu{sup 2+} and TiO{sup 2} nano-particles. Fifty percent of the adsorbed Cu{sup 2+} has been reduced to Cu{sup 0} after 1-h illumination with a UV-enhanced xenon lamp. Photoreduction of Hg{sup 2+} on TiO{sup 2} colloid surfaces was also investigated without and with thiolactic acid (TLA).more » In this case, the photoreduction efficiency for Hg{sup 2+} was lowered. Structures of metal ion surroundings in various complexes as well as their role in photoreduction of metal ions are discussed.« less

Identification of different coordination geometries by XAFS in copper(II) complexes with trimesic acid

NASA Astrophysics Data System (ADS)

Gaur, A.; Klysubun, W.; Soni, Balram; Shrivastava, B. D.; Prasad, J.; Srivastava, K.

2016-10-01

X-ray absorption spectroscopy (XAS) is very useful in revealing the information about geometric and electronic structure of a transition-metal absorber and thus commonly used for determination of metal-ligand coordination. But XAFS analysis becomes difficult if differently coordinated metal centers are present in a system. In the present investigation, existence of distinct coordination geometries around metal centres have been studied by XAFS in a series of trimesic acid Cu(II) complexes. The complexes studied are: Cu3(tma)2(im)6 8H2O (1), Cu3(tma)2(mim)6 17H2O (2), Cu3(tma)2(tmen)3 8.5H2O (3), Cu3(tma) (pmd)3 6H2O (ClO4)3 (4) and Cu3(tma)2 3H2O (5). These complexes have not only Cu metal centres with different coordination but in complexes 1-3, there are multiple coordination geometries present around Cu centres. Using XANES spectra, different coordination geometries present in these complexes have been identified. The variation observed in the pre-edge features and edge features have been correlated with the distortion of the specific coordination environment around Cu centres in the complexes. XANES spectra have been calculated for the distinct metal centres present in the complexes by employing ab-initio calculations. These individual spectra have been used to resolve the spectral contribution of the Cu centres to the particular XANES features exhibited by the experimental spectra of the multinuclear complexes. Also, the variation in the 4p density of states have been calculated for the different Cu centres and then correlated with the features originated from corresponding coordination of Cu. Thus, these spectral features have been successfully utilized to detect the presence of the discrete metal centres in a system. The inferences about the coordination geometry have been supported by EXAFS analysis which has been used to determine the structural parameters for these complexes.

Speciation and Release Kinetics of Cadmium in an Alkaline Paddy Soil Under Various Flooding Periods and Draining Conditions

DOE Office of Scientific and Technical Information (OSTI.GOV)

S Khaokaew; R Chaney; G Landrot

2011-12-31

This study determined Cd speciation and release kinetics in a Cd-Zn cocontaminated alkaline paddy soil, under various flooding periods and draining conditions, by employing synchrotron-based techniques, and a stirred-flow kinetic method. Results revealed that varying flooding periods and draining conditions affected Cd speciation and its release kinetics. Linear least-squares fitting (LLSF) of bulk X-ray absorption fine structure (XAFS) spectra of the air-dried, and the 1 day-flooded soil samples, showed that at least 50% of Cd was bound to humic acid. Cadmium carbonates were found as the major species at most flooding periods, while a small amount of cadmium sulfide wasmore » found after the soils were flooded for longer periods. Under all flooding and draining conditions, at least 14 mg/kg Cd was desorbed from the soil after a 2-hour desorption experiment. The results obtained by micro X-ray fluorescence ({mu}-XRF) spectroscopy showed that Cd was less associated with Zn than Ca, in most soil samples. Therefore, it is more likely that Cd and Ca will be present in the same mineral phases rather than Cd and Zn, although the source of these two latter elements may originate from the same surrounding Zn mines in the Mae Sot district.« less

Mode of occurrence of chromium in four US coals

USGS Publications Warehouse

Huggins, Frank E.; Shah, N.; Huffman, G.P.; Kolker, A.; Crowley, S.; Palmer, C.A.; Finkelman, R.B.

2000-01-01

The mode of occurrence of chromium in three US bituminous coals and one US subbituminous has been examined using both X-ray absorption fine structure (XAFS) spectroscopy and a selective leaching protocol supplemented by scanning electron microscopy (SEM) and electron microprobe measurements. A synthesis of results from both methods indicates that chromium occurs principally in two forms in the bituminous coals: the major occurrence of chromium is associated with the macerals and is not readily leached by any reagent, whereas a second, lesser occurrence, which is leachable in hydrofluoric acid (HF), is associated with the clay mineral, illite. The former occurrence is believed to be a small particle oxyhydroxide phase (CrO(OH)). One coal also contained a small fraction (<5%) of the chromium in the form of a chromian magnetite, and the leaching protocol indicated the possibility of a similar small fraction of chromium in sulfide form in all three coals. There was little agreement between the two techniques on the mode of occurrence of chromium in the subbituminous coal; however, only a limited number of subbituminous coals have been analyzed by either technique. The chromium in all four coals was trivalent as no evidence was found for the Cr6+ oxidation state in any coal.

Molecular binding mechanisms of aqueous cadmium and lead to siderophores, bacteria and mineral surfaces

NASA Astrophysics Data System (ADS)

Mishra, Bhoopesh

Recent studies have shown that diverse groups of bacteria adsorb metals to similar extents and uptake can be modeled using a universal adsorption model. In this study, XAFS has been used to resolve whether binding sites determined for single species systems are responsible for adsorption in more complex natural bacterial assemblages. Results obtained from a series of XAFS experiments on pure Gram positive and Gram negative bacterial strains and consortia of bacteria as a function of pH and Cd loading suggests that every bacterial strain has a complex physiology and they are all slightly different from each other. Nevertheless from the metal adsorption chemistry point of view, the main difference between them lies in the site ratio of three fundamental sites only - carboxyl, phosphoryl and sulfide. Two completely different consortia of bacteria (obtained from natural river water, and soil system with severe organic contamination) were successfully modeled in the pH range 3.4--7.8 using the EXAFS models developed for single species systems. Results thus obtained can potentially have very high impact on the modeling of the complex bacterial systems in realistic geological settings, leading to further refinement and development of robust remediation strategies for metal contamination at macroscopic level. In another study, solution speciation of Pb and Cd with DFO-B has been examined using a combination of techniques (ICP, TOC, thermodynamic modeling and XAFS). Results indicate that Pb does not complex with DFO-B at all until about pH 3.5, but forms a totally caged structure at pH 7.5. At intermediate pH conditions, mixture of species (one and two hydroxamate groups complexed) is formed. Cd on the other hand, does not complex until pH 5, forms intermediate complexes at pH 8 and is totally chelated at pH 9. Further studies were conducted for Pb sorption to mineral surface kaolinite with and without DFO-B. In the absence of DFO-B, results suggest outer sphere and inner sphere sorption of Pb on kaolinite surface at acidic and circumneutral pH conditions respectively. In the presence of DFO-B, bulk sorption studies indicated that Pb sorption is enhanced in the presence of DFO-B around pH 6 and inhibited above pH 6.5. This was confirmed by x-ray fluorescence measurements. Extended XAFS study clearly indicated unwrapping of DFO-B molecule at the surface. Our study has unambiguously recognized it as a "Type A" ternary complex ("Type A" complex means surface-metal-ligand type of interaction). Taken together, bulk adsorption measurements and XAFS experiments represent a powerful approach for determining and modeling metal speciation and adsorption.

Detection of Remarkably Low Isotopic Ratio of Iron in Anthropogenic Aerosols and Evaluation of its Contribution to the Surface Ocean

NASA Astrophysics Data System (ADS)

Kurisu, M.; Iizuka, T.; Sakata, K.; Uematsu, M.; Takahashi, Y.

2015-12-01

It has been reported that phytoplankton growth in the High Nutrient-Low Chlorophyll (HNLC) regions is limited by dissolved iron (DFe) concentration (e.g., Martin and Fitzwater, 1988). Aerosol is known as one of the dominant sources of DFe to the ocean and classified into two origins such as anthropogenic and natural. A series of recent studies showed that Fe in anthropogenic aerosols is more soluble than that in natural aerosols (Takahashi et al., 2013) and has lower isotopic ratio (Mead et al., 2013). However, the difference between Fe isotopic ratio　(δ56Fe: [(56Fe/54Fe)sample/(56Fe/54Fe)IRMM-14]-1) of two origins reported in Mead et al. (2013) is not so large compared with the standard deviation. Therefore, the aim of this study is to determine Fe species and δ56Fe in anthropogenic aerosols more accurately and to evaluate its contribution to the ocean surface. Iron species were determined by X-ray absorption fine structure (XAFS) analysis, while δ56Fe in size-fractionated aerosols were measured by MC-ICP-MS (NEPTUNE Plus) after chemical separation using anion exchange resin. Dominant Fe species in the samples were, ferrihydrite, hematite, and biotite. It was also revealed that coarse particles contained a larger amount of biotite and that fine particles contained a larger amount of hematite, which suggested that anthropogenic aerosols were emitted during combustion processes. In addition, results of Fe isotopic ratio analysis suggested that δ56Fe of coarse particles were around +0.25‰, whereas that of fine particles were -0.5 ˜ -2‰, which was lower than the δ56Fe in anthropogenic aerosol by Mead et al. (2013). The size-fractionated sampling made it possible to determine the δ56Fe in anthropogenic aerosol. Soluble component in fine particles extracted by simulated rain water also showed much lower δ56Fe (δ56Fe = -3.9±0.12‰), suggesting that anthropogenic Fe has much lower isotopic ratio. The remarkably low δ56Fe may be caused by the anthropogenic combustion process. The δ56Fe in anthropogenic aerosols measured here is important to model the budget of iron in the surface ocean.

Relationship between elemental distribution in soil and human impact in Majuro Atoll

NASA Astrophysics Data System (ADS)

Ito, L.; Takahashi, Y.; Yoneda, M.; Omori, T.; Yamazaki, K.; Yoshida, H.; Tamenori, Y.; Suga, H.; Yamaguchi, T.

2015-12-01

Majuro Atoll is one of islands of the Marshall Islands, located in the central Pacific Ocean. Reef-building corals and biological remains such as foraminifera have formed the islands under the influence of sea-level changes in the Holocene. Since the altitude of the general coral reef island tends to be very low, it is believed that the islands are vulnerable to natural disasters and climate change. However, people have lived in the Majuro Atoll in Marshall Islands for more than 2000 years. Reef islands in the same atoll are often considered to have same tendencies in the developing process; however, (i) there are possibilities that each geography produces different condition in habitat and (ii) human activities have changed the original nature in the island. In this study, we focus on the changes of physico-chemical conditions of soil depending on the depth according to time series variation in three islands in Majuro Atoll. Dating of each depth was conducted by radiocarbon (14C) measurement for foraminifera using accelerator mass spectrometry (AMS) and Bayesian age-depth Models. X-ray fluorescence (XRF) and ICP-MS analyses were employed to measure major and trace elements at different depth, respectively. Among them, phosphorus (P) is considered to play an important role in soil development; therefore X-ray absorption fine structure (XAFS) analysis was also conducted to examine the chemical form of P. Scanning electron microscope (SEM) was used to examine the elemental distribution in the soil particles, while X-ray computed tomography (CT) was used to calculate the rate of porosity of foraminifera at each depth. Concentrations of Fe, Mn, and P decrease with depth and vice versa for Mg. As a result of the μ-XAFS analysis, P in the soil exists as organic phosphorus and apatite. Phosphorous detected from the upper layer was found to distribute heterogeneously in the particles, which was observed as punctate pattern by the SEM observation. The ICP-MS results showed that Zn concentration was high in the upper layers which are likely affected by human activities. In this presentation, we discuss (i) the relationship between the pedological development and human impact and (ii) the elements that can be used as an indicator of human activities.

Enrichment mechanisms of tellurium in ferromanganese crusts

NASA Astrophysics Data System (ADS)

Sakaguchi, A.; Sugiyama, T.; Usui, A.; Takahashi, Y.

2012-04-01

Marine ferromanganese crusts (FMCs) consist of iron (Fe) hydroxides and manganese (Mn) oxides with various minor and trace elements. Especially for tellurium (Te), which is recognized as one of the rare metals, it has been reported that this element is concentrated about 105 times in FMCs compared with earth's crust, and the host phase might be Fe (oxy)hydroxide (Hein et al., 2003). Actually, in our previous study, the high concentration of Te in very surface layers of FMCs was found from the top to halfway down of a seamount in the Pacific Ocean. However, the concentration of Te in surface layers through the seamount showed good correlation with that of Mn instead of Fe. In this study, we attempted to clarify the enrichment mechanism of Te in FMCs with some methods including X-ray absorption fine structure (XAFS) technique for synthesised /natural samples. Seventeen FMC samples were collected from the Takuyo-Daigo seamount, from 950 m (summit) to 3000 m in water depth, with hyper-dolphin (remotely operated vehicle) equipped with live video camera and manipulators. The growth rates of all FMC samples were estimated to be about 3 mm/Ma. Very surface layer (less than 1 mm) of all FMC was analyzed with XRD and XAFS to confirm the mineral composition and speciation of Te. Furthermore, to serve as an aid to clarify the adsorption mechanism of Te on FMCs, distribution coefficients (Kd) and oxidation states were determined through the adsorption experiments of Te(IV) and Te(VI) on ferrihydrite and δ-MnO2. In all the experiments, pH and ionic strength were adjusted to pH 7.5 and 0.7 M, respectively. The oxidation state of Te in water phase was determined with HPLC-ICP-MS. As for the analysis of oxidation and adsorption states on the solid phase, XAFS was employed. The major mineral composition of Fe and Mn had no significant variation through the water depth of Takuyo-Daigo seamount. The oxidation state of Te in all samples showed hexavalent, and there was no significant difference of adsorption state independent of the DO, salinity and temperature in water. It has been reported that Te exists as tetravalent and hexavalent in sea water of the Pacific Ocean (Nozaki, 1996). Thus, it can be said that the Te in sea water is oxidised and incorporated into FMCs. As a result of the adsorption experiments in laboratory, the Kd of Te on ferrihydrite was larger than that of δ-MnO2, and Te(IV) was adsorbed to a larger degree than Te(VI) on both minerals. The adsorption experiments of Te(IV) on δ-MnO2 showed that the solid phase has only hexavalent Te, although the water phase has both tetra and hexavalent species of Te. Te(IV) on ferrihydrite was not oxidized to Te(VI). From these results, it can be suggested that Te(IV) was oxidized by δ-MnO2 and would be adsorbed onto ferrihydrite. Actually, the results of double-cell adsorption experiments support this hypothesis. The detail of our results and discussion will be given in the presentation.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yang, Ying; Lee, Sungsik; Brown, Dennis E.

Ultrafine manganese oxide-decorated carbon nanofibers (MnOn-CNF) as a new type of electrode materials are facilely fabricated by direct conversion of Mn, Zn-trimesic acid (H3BTC) metal organic framework fibers (Mn-ZnBTC). The construction and evolution of Mn-ZnBTC precursors are investigated by SEM and in situ high-energy XRD. The manganese oxides are highly dispersed onto the porous carbon nanofibers formed simultaneously, verified by TEM, X-ray absorption fine structure (XAFS), Raman, ICP-AES and N2 adsorption techniques. As expected, the resulting MnOn-CNF composites are highly stable, and can be cycled up to 5000 times with a high capacitance retention ratio of 98% in electrochemical capacitormore » measurements. They show a high capacitance of up to 179 F g–1 per mass of the composite electrode, and a remarkable capacitance of up to 18290 F g–1 per active mass of the manganese(IV) oxide, significantly exceeding the theoretical specific capacitance of manganese(IV) oxide (1370 F g–1). The maximum energy density is up to 19.7 Wh kg–1 at the current density of 0.25 A g–1, even orders higher than those of reported electric double-layer capacitors and pseudocapacitors. The excellent capacitive performance can be ascribed to the joint effect of easy accessibility, high porosity, tight contact and superior conductivity integrated in final MnOn-CNF composites.« less

Effect of weak magnetic field on arsenate and arsenite removal from water by zerovalent iron: an XAFS investigation.

PubMed

Sun, Yuankui; Guan, Xiaohong; Wang, Jianmin; Meng, Xiaoguang; Xu, Chunhua; Zhou, Gongming

2014-06-17

In this study, a weak magnetic field (WMF), superimposed with a permanent magnet, was utilized to improve ZVI corrosion and thereby enhance As(V)/As(III) removal by ZVI at pHini 3.0-9.0. The experiment with real arsenic-bearing groundwater revealed that WMF could greatly improve arsenic removal by ZVI even in the presence of various cations and anions. The WMF-induced improvement in As(V)/As(III) removal by ZVI should be primarily associated with accelerated ZVI corrosion, as evidenced by the pH variation, Fe(2+) release, and the formation of corrosion products as characterized with X-ray absorption fine structure spectroscopy. The arsenic species analysis in solution/solid phases at pHini 3.0 revealed that As(III) oxidation to As(V) in aqueous phase preceded its subsequent sequestration by the newly formed iron (hydr)oxides. However, both As(V) adsorption following As(III) oxidation to As(V) in solution and As(III) adsorption preceding its conversion to As(V) in solid phase were observed at pHini 5.0-9.0. The application of WMF accelerated the transformation of As(III) to As(V) in both aqueous and solid phases at pHini 5.0-9.0 and enhanced the oxidation of As(III) to As(V) in solution at pHini 3.0.

Covalent heterogenization of discrete bis(8-quinolinolato)dioxomolybdenum(VI) and dioxotungsten(VI) complexes by a metal-template/metal-exchange method: Cyclooctene epoxidation catalysts with enhanced performances

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yang, Ying; Chattopadhyay, Soma; Shibata, Tomohiro

A metal-template/metal-exchange method was used to imprint covalently attached bis(8- quinolinolato)dioxomolybdenum(VI) and dioxotungsten(VI) complexes onto large surface-area, mesoporous SBA-15 silica to obtain discrete MoO2 VIT and WO2 VIT catalysts bearing different metal loadings, respectively. Homogeneous counterparts, MoO2 VIN and WO2 VIN, as well as randomly ligandgrafted heterogeneous analogues, MoO2 VIG and WO2 VIG, were also prepared for comparison. X-ray absorption fine structure (XAFS), pair distribution function (PDF) and UV–vis data demonstrate that MoO2 VIT and WO2 VIT adopt a more solution-like bis(8-quinolinol) coordination environment than MoO2 VIG and WO2 VIG, respectively. Correspondingly, the templated MoVI and WVI catalysts show superiormore » performances to their randomly grafted counterparts and neat analogues in the epoxidation of cyclooctene. It is found that the representative MoO2 VIT-10% catalyst can be recycled up to five times without significant loss of reactivity, and heterogeneity test confirms the high stability of MoO2 VIT-10% catalyst against leaching of active species into solution. The homogeneity of the discrete bis(8-quinolinol) metal spheres templated on SBA-15 should be responsible for the superior performances.« less

A comprehensive study of catalytic, morphological and electronic properties of ligand-protected gold nanoclusters using XPS, STM, XAFS, and TPD techniques

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wu, Qiyuan; Cen, Jiajie; Zhao, Yue

Ultra-small gold nanoclusters were synthesized via a ligand exchange method and deposited onto different TiO2 supports to study their properties. STM imaging revealed that the as-synthesized gold nanoclusters had 2-D morphology consisting of monolayers of gold atoms. In conclusion, subsequent XPS, XAFS, and CO oxidation TPD results indicated that heat treatments of gold clusters at different temperatures significantly altered their electronic and catalytic properties due to ligand deprotection and cluster agglomeration.

A comprehensive study of catalytic, morphological and electronic properties of ligand-protected gold nanoclusters using XPS, STM, XAFS, and TPD techniques

DOE PAGES

Wu, Qiyuan; Cen, Jiajie; Zhao, Yue; ...

2017-12-08

Ultra-small gold nanoclusters were synthesized via a ligand exchange method and deposited onto different TiO2 supports to study their properties. STM imaging revealed that the as-synthesized gold nanoclusters had 2-D morphology consisting of monolayers of gold atoms. In conclusion, subsequent XPS, XAFS, and CO oxidation TPD results indicated that heat treatments of gold clusters at different temperatures significantly altered their electronic and catalytic properties due to ligand deprotection and cluster agglomeration.

XAFS measurements on zinc chloride aqueous solutions from ambient to supercritical conditions using the diamond anvil cell

USGS Publications Warehouse

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

1999-01-01

The structure and bonding properties of metal complexes in subcritical and supercritical fluids are still largely unknown. Conventional high pressure and temperature cell designs impose considerable limitations on the pressure, temperature, and concentration of metal salts required for measurements on solutions under supercritical conditions. In this study, we demonstrate the first application of the diamond anvil cell, specially designed for x-ray absorption studies of first-row transition metal ions in supercritical fluids. Zn K-edge XAFS spectra were measured from aqueous solutions of 1-2m ZnCl2 and up to 6m NaCl, at temperatures ranging from 25-660 ??C and pressures up to 800 MPa. Our results indicate that the ZnCl42- complex is predominant in the 1m ZnCl2/6m NaCl solution, while ZnCl2(H2O)2 is similarly predominant in the 2m ZnCl2 solution, at all temperatures and pressures. The Zn-Cl bond length of both types of chlorozinc(II) complexes was found to decrease at a rate of about 0.01 A??/100 ??C.

Crystal Structure, Electric Polarization and Heat Capacity Measurements on Small R-Ion Multiferroic Hexagonal RMnO3

NASA Astrophysics Data System (ADS)

Yu, Tian; Gao, Peng; Wu, Tao; Tyson, Trevor; Lalancette, Roger

2013-03-01

Crystal structure, electric polarization and heat capacity measurements on the hexagonal multiferroic RMnO3 reveal that small R ion (Lu and lower cation size) systems are ferroelectric and possess the same space-group as YMnO3. Combined local and long range structural measurements were conducted by XAFS, PDF and single crystal and powder XRD methods. The influence of the Mn-O and R-O distribution on the electric polarization is discussed. Point charge estimates of the electrical polarization are given for comparison with the YMnO3 system. This work is supported by DOE Grant DE-FG02-07ER46402.

Structural study of Cu(II) complexes with benzo[b]furancarboxylic acids

NASA Astrophysics Data System (ADS)

Kalinowska, Diana; Klepka, Marcin T.; Wolska, Anna; Drzewiecka-Antonik, Aleksandra; Ostrowska, Kinga; Struga, Marta

2017-11-01

Four Cu(II) complexes with 2- and 3-benzo[b]furancarboxylic acids have been synthesized and characterized using combination of two spectroscopic techniques. These techniques were: (i) FTIR and (ii) XAFS. FTIR analysis confirmed that complexes were formed and gave insight into identification of possible coordinating groups to the metallic center. XANES analysis indicated that the oxidation state of Cu is +2. EXAFS analysis allowed to identify that the first coordination sphere is formed by 4-5 oxygen atoms with the Cu-O distances around 2 Å. Combining these techniques it was possible to structurally describe novel Cu(II) complexes with benzo[b]furancarboxylic acids.

XAFS study of copper(II) complexes with square planar and square pyramidal coordination geometries

NASA Astrophysics Data System (ADS)

Gaur, A.; Klysubun, W.; Nitin Nair, N.; Shrivastava, B. D.; Prasad, J.; Srivastava, K.

2016-08-01

X-ray absorption fine structure of six Cu(II) complexes, Cu2(Clna)4 2H2O (1), Cu2(ac)4 2H2O (2), Cu2(phac)4 (pyz) (3), Cu2(bpy)2(na)2 H2O (ClO4) (4), Cu2(teen)4(OH)2(ClO4)2 (5) and Cu2(tmen)4(OH)2(ClO4)2 (6) (where ac, phac, pyz, bpy, na, teen, tmen = acetate, phenyl acetate, pyrazole, bipyridine, nicotinic acid, tetraethyethylenediamine, tetramethylethylenediamine, respectively), which were supposed to have square pyramidal and square planar coordination geometries have been investigated. The differences observed in the X-ray absorption near edge structure (XANES) features of the standard compounds having four, five and six coordination geometry points towards presence of square planar and square pyramidal geometry around Cu centre in the studied complexes. The presence of intense pre-edge feature in the spectra of four complexes, 1-4, indicates square pyramidal coordination. Another important XANES feature, present in complexes 5 and 6, is prominent shoulder in the rising part of edge whose intensity decreases in the presence of axial ligands and thus indicates four coordination in these complexes. Ab initio calculations were carried out for square planar and square pyramidal Cu centres to observe the variation of 4p density of states in the presence and absence of axial ligands. To determine the number and distance of scattering atoms around Cu centre in the complexes, EXAFS analysis has been done using the paths obtained from Cu(II) oxide model and an axial Cu-O path from model of a square pyramidal complex. The results obtained from EXAFS analysis have been reported which confirmed the inference drawn from XANES features. Thus, it has been shown that these paths from model of a standard compound can be used to determine the structural parameters for complexes having unknown structure.

Effects of the microbial siderophore DFO-B on Pb and Cd speciation in aqueous solution.

PubMed

Mishra, Bhoopesh; Haack, Elizabeth A; Maurice, Patricia A; Bunker, Bruce A

2009-01-01

This study investigates the complexation environments of aqueous Pb and Cd in the presence of the trihydroxamate microbial siderophore, desferrioxamine-B (DFO-B) as a function of pH. Complexation of aqueous Pb and Cd with DFO-B was predicted using equilibrium speciation calculation. Synchrotron-based X-ray absorption fine structure (XAFS) spectroscopy at Pb L(III) edge and Cd K edge was used to characterize Pb and Cd-DFO-B complexes at pH values predicted to best represent each of the metal-siderophore complexes. Pb was not found to be complexed measurably by DFO-B at pH 3.0, but was complexed by all three hydroxamate groups to form a totally "caged" hexadentate structure at pH 7.5-9.0. At the intermediate pH value (pH 4.8), a mixture of Pb-DFOB complexes involving binding of the metal through one and two hydroxamate groups was observed. Cd, on the other hand, remained as hydrated Cd2+ at pH 5.0, occurred as a mixture of Cd-DFOB and inorganic species at pH 8.0, and was bound by three hydroxamate groups from DFO-B at pH 9.0. Overall, the solution species observed with EXAFS were consistent with those predicted thermodynamically. However, Pb speciation at higher pH values differed from that predicted and suggests that published constants underestimate the binding constant for complexation of Pb with all three hydroxamate groups of the DFO-B ligand. This molecular-level understanding of metal-siderophore solution coordination provides physical evidence for complexes of Pb and Cd with DFO-B, and is an important first step toward understanding processes at the microbial- and/or mineral-water interface in the presence of siderophores.

Unraveling sorption of lead in aqueous solutions by chemically modified biochar derived from coconut fiber: A microscopic and spectroscopic investigation.

PubMed

Wu, Weidong; Li, Jianhong; Lan, Tian; Müller, Karin; Niazi, Nabeel Khan; Chen, Xin; Xu, Song; Zheng, Lirong; Chu, Yingchao; Li, Jianwu; Yuan, Guodong; Wang, Hailong

2017-01-15

In this study, we examined the efficacy of nine different types of coconut-fiber derived biochars (CFBs), prepared at different temperatures and chemically modified with ammonia, hydrogen peroxide and nitric acid, to remove lead (Pb 2+ ) from aqueous solutions. Langmuir-q m values of the biochars pyrolyzed at 300°C and modified with ammonia and nitric acid increased from 49.5 to 105.5 and 85.2mgg -1 , respectively, compared to control (unmodified), whereas hydrogen peroxide treatment had no effect. The maximum amount of Pb adsorbed on biochars was in the order of CFB-700>MCFB-300-NH 3 ·H 2 O>CFB-500>MCFB-300-HNO 3 >CFB-300. X-ray absorption fine structure (XAFS) spectroscopy results revealed that Pb-montmorillonite, Pb(C 2 H 3 O 2 ) 2 , PbSO 4 , Pb-Al 2 O 3 and Pb 3 (PO 4 ) 2 were the five most important Pb species observed in Pb-loaded biochars, and as such, favoring Pb immobilization in aqueous solutions. Overall, the sorption capacity of CFBs pyrolyzed at 300°C substantially increased for Pb 2+ with ammonia and nitric acid modification. However, these chemical modifications did not improve the sorption of Pb on CFBs pyrolyzed at temperatures ≥500°C, thereby highlighting a temperature dependent response of chemically modified biochars to Pb sorption in this study. Copyright © 2016 Elsevier B.V. All rights reserved.

Nitrite reduction by biogenic hydroxycarbonate green rusts: evidence for hydroxy-nitrite green rust formation as an intermediate reaction product.

PubMed

Guerbois, Delphine; Ona-Nguema, Georges; Morin, Guillaume; Abdelmoula, Mustapha; Laverman, Anniet M; Mouchel, Jean-Marie; Barthelemy, Kevin; Maillot, Fabien; Brest, Jessica

2014-04-15

The present study investigates for the first time the reduction of nitrite by biogenic hydroxycarbonate green rusts, bio-GR(CO3), produced from the bioreduction of ferric oxyhydroxycarbonate (Fohc), a poorly crystalline solid phase, and of lepidocrocite, a well-crystallized Fe(III)-oxyhydroxide mineral. Results show a fast Fe(II) production from Fohc, which leads to the precipitation of bio-GR(CO3) particles that were roughly 2-fold smaller (2.3 ± 0.4 μm) than those obtained from the bioreduction of lepidocrocite (5.0 ± 0.4 μm). The study reveals that both bio-GR(CO3) are capable of reducing nitrite ions into gaseous nitrogen species such as NO, N2O, or N2 without ammonium production at neutral initial pH and that nitrite reduction proceeded to a larger extent with smaller particles than with larger ones. On the basis of the identification of intermediates and end-reaction products using X-ray diffraction and X-ray absorption fine structure (XAFS) spectroscopy at the Fe K-edge, our study shows the formation of hydroxy-nitrite green rust, GR(NO2), a new type of green rust 1, and suggests that the reduction of nitrite by biogenic GR(CO3) involves both external and internal reaction sites and that such a mechanism could explain the higher reactivity of green rust with respect to nitrite, compared to other mineral substrates possessing only external reactive sites.

Annealing-temperature-dependent voltage-sign reversal in all-oxide spin Seebeck devices using RuO2

NASA Astrophysics Data System (ADS)

Kirihara, Akihiro; Ishida, Masahiko; Yuge, Ryota; Ihara, Kazuki; Iwasaki, Yuma; Sawada, Ryohto; Someya, Hiroko; Iguchi, Ryo; Uchida, Ken-ichi; Saitoh, Eiji; Yorozu, Shinichi

2018-04-01

Thermoelectric converters based on the spin Seebeck effect (SSE) have attracted great attention due to their potential to offer novel applications such as energy harvesting and heat-flow sensing. For converting a SSE-induced spin current into an electric current, a transition metal film such as Pt, which exhibits large inverse spin-Hall effect (ISHE), has been typically used. In this work, we show an all-oxide SSE device using ruthenium oxide (RuO2) as a conductive film. We found that both the sign and magnitude of the SSE-induced ISHE voltage V appearing in the RuO2 film changes depending on the post annealing temperature, and that the magnitude can become larger than that of a standard SSE device using Pt. The similar sign change was also observed in Hall-resistance measurements of the RuO2 films. X-ray absorption fine structure (XAFS) spectra of as-deposited and annealed RuO2 revealed that the annealing process substantially improved the long-range crystalline order in RuO2. This suggests that change in the crystalline order may modify the dominant ISHE mechanism or electronic states in RuO2, leading to the sign reversal of V as well as the Hall coefficient. Our result demonstrates that RuO2 is an interesting material not only as a practical ISHE film but also as a testbed to study physics of spin-to-charge converters that depend on their crystalline order.

Gallium(III) adsorption on carbonates and oxides: X-ray absorption fine structure spectroscopy study and surface complexation modeling.

PubMed

Pokrovsky, O S; Pokrovski, G S; Schott, J

2004-11-15

Adsorption of Ga on calcite, magnesite, amorphous silica, and manganese oxide as a function of pH and gallium concentration in solution was studied using a batch adsorption technique. Adsorbed complexes of Ga on calcite, magnesite, and delta-MnO2 were further characterized using XAFS spectroscopy. At high surface loadings from supersaturated solutions, Ga is likely to form a polymeric network at the surface (edge- and corner-sharing octahedra). At low surface loadings, Ga presents as isolated octahedra, probably attached to the Me-O sites on the surface, and coordinated by water molecules and hydroxide groups at 1.90-1.94 A. At pH>6, Ga therefore changes its coordination from 4 to 6 when adsorbing from solution (Ga(OH)(-)4(aq)) onto metal surface sites (MeOGa(OH)n(H2O)2-n(5-n), Me = Ca, Mg, or Mn, and n=1 and 2 for carbonate minerals and MnO2, respectively). Because the EXAFS is not capable of seeing hydrogen atoms, the protonation of surface complexes was determined by fitting the experimental pH-dependent Ga adsorption edge. A surface complexation model which assumes the constant capacitance of the electric double layer (CCM) and postulates the formation of positively charged, neutral and negatively charged surface complexes for carbonates, manganese oxide and silica, respectively, was used to describe the dependence of adsorption equilibria on aqueous solution composition in a wide range of pH and Ga concentration.

Oxygen Fugacity of Mare Basalts and the Lunar Mantle Application of a New Microscale Oxybarometer Based on the Valence State of Vanadium

NASA Technical Reports Server (NTRS)

Shearer, C. K.; Karner, J.; Papike, J. J.; Sutton, S. R.

2004-01-01

The ability to estimate oxygen fugacities for mare basalts and to extend these observations to the lunar mantle is limited using bulk analysis techniques based on buffering assemblages or the valence state of iron. These limitations are due to reequilibration of mineral assemblages at subsolidus conditions, deviations of mineral compositions from thermodynamic ideality, size requirements, and the limits of the iron valence at very low fO2. Still, these approaches have been helpful and indicate that mare basalts crystallized at fO2 between the iron-w stite buffer (IW) and the ilmenite breakdown reaction (ilmenite = rutile + iron). It has also been inferred from these estimates that the lunar mantle is also highly reduced lying at conditions below IW. Generally, these data cannot be used to determine if the mare basalts become increasingly reduced during transport from their mantle source and eruption at the lunar surface and if there are differences in fO2 among mare basalts or mantle sources. One promising approach to determining the fO2 of mare basalts is using the mean valence of vanadium (2+, 3+, 4+, 5+) determined on spots of a few micrometers in diameter using synchrotron x-ray absorption fine structure (XAFS) spectroscopy. The average valence state of V in basaltic glasses is a function of fO2, temperature, V coordination, and melt composition. Here, we report the initial results of this approach applied to lunar pyroclastic glasses.

Mercury speciation and selenium in toothed-whale muscles.

PubMed

Sakamoto, Mineshi; Itai, Takaaki; Yasutake, Akira; Iwasaki, Toshihide; Yasunaga, Genta; Fujise, Yoshihiro; Nakamura, Masaaki; Murata, Katsuyuki; Chan, Hing Man; Domingo, José L; Marumoto, Masumi

2015-11-01

Mercury accumulates at high levels in marine mammal tissues. However, its speciation is poorly understood. The main goal of this investigation was to establish the relationships among mercury species and selenium (Se) concentrations in toothed-whale muscles at different mercury levels. The concentrations of total mercury (T-Hg), methylmercury (MeHg), inorganic mercury (I-Hg) and Se were determined in the muscles of four toothed-whale species: bottlenose dolphins (n=31), Risso's dolphins (n=30), striped dolphins (n=29), and short-finned pilot whales (n=30). In each species, the MeHg concentration increased with increasing T-Hg concentration, tending to reach a plateau. In contrast, the proportion of MeHg in T-Hg decreased from 90-100% to 20-40%. The levels of T-Hg and Se showed strong positive correlations. Se/I-Hg molar ratios rapidly decreased with the increase of I-Hg and reached almost 1 in all species. These results suggested that the demethylated MeHg immediately formed Se/I-Hg equimolar complex of mercury selenide (HgSe) in their muscles. In addition, an X-ray absorption fine structure analysis (XAFS) of a bottlenose dolphin muscle confirmed that the dominant chemical form of the Se/I-Hg equimolar complex was HgSe. HgSe was mainly localized in cells near the endomysium using electron probe microanalysis (EPMA). These results suggested that the demethylated MeHg finally deposits within muscle cells of bottlenose dolphin as an inert HgSe. Copyright © 2015 Elsevier Inc. All rights reserved.

A study of the origin of large magnetic field coupled electric polarization in HoAl(BO3)4

NASA Astrophysics Data System (ADS)

Yu, Tian; Zhang, Han; Tyson, Trevor; Chen, Zhiqiang; Abeykoon, Milinda; Nelson, Christie; Bezmaternykh, Leonard

2015-03-01

The multiferroic system RAl(BO3)4 is known to exhibit a strong coupling of magnetic field to the electrical polarization. Recently a giant magnetoelectric effect was found in HoAl3(BO3)4 system. This phenomenon is considered quite interesting because the value discovered is significantly higher than reported values of linear magnetoelectric or even multiferroic compounds. We are conducting detailed structural measurements to understand the coupling. We are exploring the local and long range structure in these systems using x-ray PDF, XAFS and single crystal diffraction measurement between 10 K and 400 K. Structural parameters including lattice parameters and ADPs are being determined over the full temperature range. This work is supported by DOE Grant DE-FG02-07ER46402.

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

NASA Astrophysics Data System (ADS)

Klementiev, K.; Chernikov, R.

2016-05-01

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

The structure of Yb3+ aquo ion and chloro complexes in aqueous solutions at up to 500 °C and 270 MPa

USGS Publications Warehouse

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

2002-01-01

We report here on X-ray absorption fine structure (XAFS) measurements used to determine the structure of the Yb3+ ion in aqueous solutions over a range of temperatures from 25 to 500 °C and pressures up to 270 MPa. Fluorescence Yb L3-edge spectra were collected separately from nitrate (0.006m Yb/0.16m HNO3) and chloride (0.006 m YbCl3/0.017 m HCl) aqueous solutions within a hydrothermal diamond anvil cell. The Yb−O distance of the Yb3+aquo ion in the nitrate solution exhibits a uniform reduction at a rate of 0.02 Å/100 °C, whereas the number of oxygens decreases from 8.3 ± 0.6 to 4.8 ± 0.7, in going from 25 to 500 °C. No evidence for nitrate complexes was found from measurements made on this solution. The Yb3+ is found to persist as an aquo ion up to 150 °C in the chloride aqueous solution. In the 300−500 °C range, chloro complexes are found to occur in the solution, most likely of the type Yb(H2O)δ-nCln+3-n (δ ≈ 7). The Yb−Cl distance of the chloro ytterbium(III) complexes is found to decrease uniformly at a rate of about 0.02 Å/100 °C, whereas the number of chlorines increases from 0.5 ± 0.3 to 1.8 ± 0.2 in the 300−500 °C temperature range. Conversely, the Yb−O distance undergoes a lower uniform reduction at a rate of 0.007 Å/100 °C, whereas the number of oxygens decreases from 8.3 ± 0.5 to 5.1 ± 0.3 in going from 25 to 500 °C in the same solution.

Mechanisms of interfacial reactivity in near surface and extreme environments

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chen, Ying; Balaska, Eric; Weare, John

The local water structure surrounding ions in aqueous solutions greatly affects their chemical properties such as reaction rates, ion association, and proton and electron transport. These properties result in the behavior of ions in natural aqueous environments. For example ore transport is facilitated by chloride ion pair formation and the reaction of ions in an interface is strongly dependent on the dehydration of the ion hydration shell. We are developing the use of high-­resolution XAFS observations and 1st principles based MD-­XAFS analysis (spectra simulated using 1st principle methods with no adjustable parameters, AIMD) to interpret the solution properties of stronglymore » interacting aqueous solutes under arbitrary pressure and temperature conditions. In the 1st principle MD-­XAFS method density functional theory (DFT) based MD simulations(Car and Parrinello, 1985) are used to generate a large ensemble of structural snap shots of the hydration region. These are then used to generate scattering intensities. I emphasize three points about this novel approach to analyzing XAFS data. 1st: As illustrated in Figure 1, the level of agreement between the calculated and observed intensities is considerably higher than has been obtained by any XAFS analysis to date (note 2nd shell region, R> 2 Å). 2nd: This result was obtained from a parameter free simulation with no fitting of the interaction potentials to any data. This supports the use of these methods for more difficult environments and more complex solutes (polyions). 3rd: New information about the shell structure (Figure 1) is now available because of this more detailed agreement. We note also that both multiple scattering and second shell features are well represented in the analysis. As far as we know this is the 1st analysis of second shell structure and multiple scattering. Excellent agreement has been obtained for most of the third row metal ions: Ca 2+, Zn 2+, Cu 2+, Ni 2+, Co 2+, Mn 2+, Fe 3+, Cr 3+. Calculations on these systems are demanding because of their open electronic shells, and high ionic charge. Principal Investigator: Professor John Weare (University of California, San Diego) The prediction of the interactions of geochemical fluids with minerals, nanoparticles, and colloids under extreme near surface conditions of temperature (T) and pressure (P) is a grand challenge research need in geosciences (U.S. DOE 2007, Basic Research Needs for Geosciences: Facilitating the 21st Energy Systems.). To evaluate the impact of these processes on energy production and management strategies it is necessary to have a high level of understanding of the interaction between complex natural fluids and mineral formations. This program emphasizes 1st principle parameter free simulations of complex chemical processes in solutions, in the mineral phase, and in the interfaces between these phases The development of new computational tools (with emphasis on oxide materials and reaction dynamics) tailored to treat wide range of conditions and time scales experienced in such geochemical applications is has been developed. Because of the sensitivity of the interaction in these systems to electronic structure and local bonding environments, and of the need to describe bond breaking/formation, our simulations are based on interactions calculated at the electronic structure level (ab-initio molecular dynamics, AIMD). The progress in the computational aspects of program may be summarized in terms of the following themes (objectives); Development of efficient parameter free dynamical simulation technology based on 1st principles force and energy calculations especially adapted for geochemical applications (e.g., mineral, interfaces and aqueous solutions) (continuing program); Calculation of the dynamics of water structure of in the surface-water interface of transition metal oxides and oxihydroxides; and Development of improved (beyond DFT+GGA) electronic structure calculations for minerals and the interface region that more accurately calculate electron correlation, spin density, and localization. The focus of the program is also on the iron oxide and oxihydroxide minerals and Fe 2+(aq)/Fe 3+(cr) oxidation in the mineral solution interface region. These methods included the development of model Hamilitonian methods that can be solved to near convergence for single site models (DMFT) and many-body perturbation methods (MP2, GW); Development of time decomposition methods to extend time scales of molecular dynamics (MD) simulations and support the use of high complexity electronic structure calculations (MP2, CCSD(T)) of forces for use in dynamical simulations where very high chemical accuracy is required (microsolvated reactions in absorbed surface layers); and The development of a new linear scaling finite element solver for eigenvalue problem that supports solution of quantum problems with unusual potential and boundary values. Application progress of the above new simulation technology to problems of geochemical interests includes; The prediction of metal oxide surface structure and the reduction/oxidation of Fe 3+(cr)/Fe 2+ (aq) in metal oxide (hematite, goethite)/solution interfaces. Result: water interacts strongly with the 001 Hematite surface; interaction of water with the 100 goethite is weak; The study of ion solvation and the composition of ion hydration shells under extreme conditions (focus on Fe 3+/2+, Al 3+ and Mg 2+ and their hydroxide speciation). Result: Ion association in water solutions can be calculated from 1st principle methods. Efficient sampling of the free energy requires more development; The continued development of new high resolution analysis of XAFS scattering of disordered systems (particularly Al, Mg) and of XANES calculations for aqueous ions. Result: EXAFS spectra can be calculated to high accuracy with DFT level dynamic simulations; The exploration of electron localization and electron transport in metal oxides (highly correlated materials). Result: Proper description of electron localization requires levels of calculation beyond DFT; and Localization of electrons in DFT type Hamiltonians was studied. Result: For very Dirac high exchange new solutions (New unphysical bifrucations) to the eigenvalue problem are found. The program was highly collaborative involving faculty and students in mathematics, physics and computer science departments as well as coworkers at the Pacific Northwest National Laboratories (PNNL). The students in this program had the opportunity to develop skills in the development of methods, the implementation of method on high performance parallel computers and the application of these methods to problem in geochemical science. Much of the software that was developed was incorporated in the NWchem software package maintained by PNNL.« less

A Comparative XAFS Study of Gold-thiolate Nanoparticles and Nanoclusters

NASA Astrophysics Data System (ADS)

Chevrier, D. M.; Chatt, A.; Sham, T. K.; Zhang, P.

2013-04-01

Tiopronin-capped gold nanoparticles and gold nanoclusters of sizes 3.0 and 1.5 nm, respectively, were investigated with XAFS at the gold L3-edge. The specific EXAFS fitting procedure is discussed for obtaining reliable fit parameters for each system. The difficulties and challenges faced when analysing EXAFS data for gold nanoparticles and nanoclusters are also mentioned. Fitting results for gold nanoparticles reveal a small amount of surface Au-thiolate interactions with a large Au-Au metal core. For gold nanoclusters, only a one-shell fit was obtainable. Instead of Au-Au metal core, long-range interactions are expected for gold nanoclusters. Tiopronin-capped gold nanoclusters are proposed to be polymeric in nature, which helps explain the observed red luminescence.

Thermal decomposition of ammonium hexachloroosmate.

PubMed

Asanova, T I; Kantor, I; Asanov, I P; Korenev, S V; Yusenko, K V

2016-12-07

Structural changes of (NH 4 ) 2 [OsCl 6 ] occurring during thermal decomposition in a reduction atmosphere have been studied in situ using combined energy-dispersive X-ray absorption spectroscopy (ED-XAFS) and powder X-ray diffraction (PXRD). According to PXRD, (NH 4 ) 2 [OsCl 6 ] transforms directly to metallic Os without the formation of any crystalline intermediates but through a plateau where no reactions occur. XANES and EXAFS data by means of Multivariate Curve Resolution (MCR) analysis show that thermal decomposition occurs with the formation of an amorphous intermediate {OsCl 4 } x with a possible polymeric structure. Being revealed for the first time the intermediate was subjected to determine the local atomic structure around osmium. The thermal decomposition of hexachloroosmate is much more complex and occurs within a minimum two-step process, which has never been observed before.

New strategies for submicron characterization the carbon binding of reactive minerals in long-term contrasting fertilized soils: implications for soil carbon storage

NASA Astrophysics Data System (ADS)

Xiao, Jian; He, Xinhua; Hao, Jialong; Zhou, Ying; Zheng, Lirong; Ran, Wei; Shen, Qirong; Yu, Guanghui

2016-06-01

Mineral binding is a major mechanism for soil carbon (C) stabilization. However, the submicron information about the in situ mechanisms of different fertilization practices affecting organo-mineral complexes and associated C preservation remains unclear. Here, we applied nano-scale secondary ion mass spectrometry (NanoSIMS), X-ray photoelectron spectroscopy (XPS), and X-ray absorption fine structure spectroscopy (XAFS) to examine differentiating effects of inorganic versus organic fertilization on interactions between highly reactive minerals and soil C preservation. To examine such interactions, soils and their extracted colloids were collected during a 24-year long-term fertilization period (1990-2014) (no fertilization, control; chemical nitrogen (N), phosphorus (P), and potassium (K) fertilization, NPK; and NPK plus swine manure fertilization, NPKM). The results for different fertilization conditions showed a ranked soil organic matter concentration with NPKM > NPK > control. Meanwhile, oxalate-extracted Al (Alo), Fe (Feo), short-range ordered Al (Alxps), Fe (Fexps), and dissolved organic carbon (DOC) ranked with NPKM > control > NPK, but the ratios of DOC / Alxps and DOC / Fexps ranked with NPKM > NPK > control. Compared with the NPK treatment, the NPKM treatment enhanced the C-binding loadings of Al and Fe minerals in soil colloids at the submicron scale. Furthermore, a greater concentration of highly reactive Al and Fe minerals was presented under NPKM than under NPK. Together, these submicron-scale findings suggest that both the reactive mineral species and their associations with C are differentially affected by 24-year long-term inorganic and organic fertilization.

Synthesis and Characterization of the Actinium Aquo Ion

PubMed Central

2017-01-01

Metal aquo ions occupy central roles in all equilibria that define metal complexation in natural environments. These complexes are used to establish thermodynamic metrics (i.e., stability constants) for predicting metal binding, which are essential for defining critical parameters associated with aqueous speciation, metal chelation, in vivo transport, and so on. As such, establishing the fundamental chemistry of the actinium(III) aquo ion (Ac-aquo ion, Ac(H2O)x3+) is critical for current efforts to develop 225Ac [t1/2 = 10.0(1) d] as a targeted anticancer therapeutic agent. However, given the limited amount of actinium available for study and its high radioactivity, many aspects of actinium chemistry remain poorly defined. We overcame these challenges using the longer-lived 227Ac [t1/2 = 21.772(3) y] isotope and report the first characterization of this fundamentally important Ac-aquo coordination complex. Our X-ray absorption fine structure study revealed 10.9 ± 0.5 water molecules directly coordinated to the AcIII cation with an Ac–OH2O distance of 2.63(1) Å. This experimentally determined distance was consistent with molecular dynamics density functional theory results that showed (over the course of 8 ps) that AcIII was coordinated by 9 water molecules with Ac–OH2O distances ranging from 2.61 to 2.76 Å. The data is presented in the context of other actinide(III) and lanthanide(III) aquo ions characterized by XAFS and highlights the uniqueness of the large AcIII coordination numbers and long Ac–OH2O bond distances. PMID:28386595

Advantages of MgAlOx over gamma-Al2O3 as a support material for potassium-based high temperature lean NOx traps

DOE Office of Scientific and Technical Information (OSTI.GOV)

Luo, Jinyong; Gao, Feng; Karim, Ayman M.

MgAlOx mixed oxides were employed as supports for potassium-based lean NOx traps (LNTs) targeted for high temperature applications. Effects of support compositions, K/Pt loadings, thermal aging and catalyst regeneration on NOx storage capacity were systematically investigated. The catalysts were characterized by XRD, NOx-TPD, TEM, STEM-HAADF and in-situ XAFS. The results indicate that MgAlOx mixed oxides have significant advantages over conventional gamma-Al2O3-supports for LNT catalysts, in terms of high temperature NOx trapping capacity and thermal stability. First, as a basic support, MgAlOx stabilizes stored nitrates (in the form of KNO3) to much higher temperatures than mildly acidic gamma-Al2O3. Second, MgAlOx minimizesmore » Pt sintering during thermal aging, which is not possible for gamma-Al2O3 supports. Notably, combined XRD, in-situ XAFS and STEM-HAADF results indicate that Pt species in the thermally aged Pt/MgAlOx samples are finely dispersed in the oxide matrix as isolated atoms. This strong metal-support interaction stabilizes Pt and minimizes the extent of sintering. However, such strong interactions result in Pt oxidation via coordination with the support so that NO oxidation activity can be adversely affected after aging which, in turn, decreases NOx trapping ability for these catalysts. Interestingly, a high-temperature reduction treatment regenerates essentially full NOx trapping performance. In fact, regenerated Pt/K/MgAlOx catalyst exhibits much better NOx trapping performance than fresh Pt/K/Al2O3 LNTs over the entire temperature range investigated here. In addition to thermal aging, Pt/K loading effects were systemically studied over the fresh samples. The results indicate that NOx trapping is kinetically limited at low temperatures, while thermodynamically limited at high temperatures. A simple conceptual model was developed to explain the Pt and K loading effects on NOx storage. An optimized K loading, which allows balancing between the stability of nitrates and exposed Pt surface, gives the best NOx trapping capability.« less

Is It Homogeneous or Heterogeneous Catalysis Derived from [RhCp*Cl2]2? In Operando-XAFS, Kinetic and Crucial Kinetic Poisoning Evidence for Subnanometer Rh4 Cluster-Based Benzene Hydrogenation Catalysis

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bayram, Ercan; Linehan, John C.; Fulton, John L.

2011-11-23

Determining the true, kinetically dominant catalytically active species, in the classic benzene hydrogenation system pioneered by Maitlis and co-workers 34 years ago starting with [RhCp*Cl2]2 (Cp* = [{eta}5-C5(CH3)5]), has proven to be one of the most challenging case studies in the quest to distinguish single-metal-based 'homogeneous' from polymetallic, 'heterogeneous' catalysis. The reason, this study will show, is the previous failure to use the proper combination of (i) operando spectroscopy to determine the dominant form(s) of the precatalyst's mass under catalysis (i.e., operating) conditions, plus then and crucially also (ii) the previous lack of the necessary kinetic studies, catalysis being amore » 'wholly kinetic phenomenon' as J. Halpern long ago noted. An important contribution from this study will be to reveal the power of quantitiative kinetic poisoning experiments for distinguishing single-metal, or in this case subnanometer Rh4 cluster-based catalysis from larger, polymetallic Rh(0)n nanoparticle catalysis, at least under favorable conditions. The combined operando-XAFS (X-ray absorption fine structure) spectroscopy and kinetic evidences provide a compelling case for Rh4-based, with average stoichiometry 'Rh4Cp*2.4Cl4Hc', benzene hydrogenation catalysis in 2-propanol with added Et3N and at 100 C and 50 atm initial H2 pressure. The results also reveal, however, that if even ca. 1.4% of the total soluble Rh(0)n had formed nanoparticles, then those Rh(0)n nanoparticles would have been able to account for all the observed benzene hydrogenation catalytic rate (using commercial, ca. 2 nm, polyethyleneglycol-dodecylether hydrosol stabilized Rh(0)n nanoparticles as a model system). The results 'especially the poisoning methodology developed and employed' are of significant, broader interest since determining the nature of the true catalyst continues to be a central, often vexing issue in any and all catalytic reactions. The results are also of fundamental interest in that they add to a growing body of evidence indicating that certain, appropriately ligated, coordinatively unsaturated, subnanometer M4 transition-metal clusters can be relatively robust catalysts. Also demonstrated herein is that Rh4 clusters are poisoned by Hg(0), demonstrating for the first time that the classic Hg(0) poisoning test of 'homogeneous' vs 'heterogeneous'catalysts cannot distinguish Rh4-based subnanometer catalysts from Rh(0)n nanoparticle catalysts, at least for the present examples of these two specific, Rh-based catalysts.« less

The Co(II), Ni(II) and Cu(II) complexes with herbicide 2,4-dichlorophenoxyacetic acid - Synthesis and structural studies

NASA Astrophysics Data System (ADS)

Drzewiecka-Antonik, Aleksandra; Ferenc, Wiesława; Wolska, Anna; Klepka, Marcin T.; Cristóvão, Beata; Sarzyński, Jan; Rejmak, Paweł; Osypiuk, Dariusz

2017-01-01

The Co(II), Ni(II) and Cu(II) complexes with herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) were synthesized and structurally characterized. The geometry of metal-ligand interaction was refined using XAFS and DFT studies. The Co(2,4-D)2·6H2O and Ni(2,4-D)2·4H2O complexes have octahedral geometry with two carboxylate groups of 2,4-D anions and four water molecules in the coordination sphere. The square planar geometry around metal cations formed by the carboxylate groups from two monodentate ligands and two water molecules, is observed for Cu(2,4-D)2·4H2O complex. In the recrystallized Ni(II) complex dinuclear 'Chinese lantern' structures with bridging carboxylate groups of 2,4-D were observed.

Iron biomineralization of brain tissue and neurodegenerative disorders

NASA Astrophysics Data System (ADS)

Mikhaylova (Mikhailova), Albina

The brain is an organ with a high concentration of iron in specific areas, particularly in the globus pallidus, the substantia nigra, and the red nucleus. In certain pathological states, such as iron overload disease and neurodegenerative disorders, a disturbed iron metabolism can lead to increased accumulation of iron not only in these areas, but also in the brain regions that are typically low in iron content. Recent studies of the physical and magnetic properties of metalloproteins, and in particular the discovery of biogenic magnetite in human brain tissue, have raised new questions about the role of biogenic iron formations in living organisms. Further investigations revealed the presence of magnetite-like crystalline structures in human ferritin, and indicated that released ferritin iron might act as promoter of oxidative damage to tissue, therefore contributing to pathogenesis of neurodegenerative disorders such as Alzheimer's, Parkinson's and Huntington's diseases. The purpose of this work was to examine the elemental composition and structure of iron deposits in normal brain tissue as well as tissue affected by neurodegenerative disorders. Employing the methods of X-ray microfocus fluorescence mapping, X-ray Absorption Near Edge Structure (XANES), X-ray Absorption Fine Structure spectroscopy (XAFS), and light and electron microscopic examinations allows one to obtain qualitative as well as quantitative data with respect to the cellular distribution and chemical state of iron at levels not detected previously. The described tissue preparation technique allows not only satisfactory XAS iron elemental imaging in situ but also multimodal examination with light and electron microscopes of the same samples. The developed protocol has assured consistent and reproducible results on relatively large sections of flat-embedded tissue. The resulting tissue samples were adequate for XAS examination as well as sufficiently well-preserved for future microscopy studies. The continued development of this technique should lead to major advances in mapping iron anomalies and the related chemical and structural information directly to cells and tissue structures in human brain tissue. At present this is done primarily by iron staining methods and any information on the relationship between iron distribution and cellular structures obtained this way is limited. Iron staining also offers no information on the specific compounds of iron that are present. This can be vitally important as the form of iron [including its oxidation state] in the human body can determine whether it plays a detrimental or beneficial role in neurophysiological processes.

Chemical processes for the extreme enrichment of tellurium into marine ferromanganese oxides

NASA Astrophysics Data System (ADS)

Kashiwabara, Teruhiko; Oishi, Yasuko; Sakaguchi, Aya; Sugiyama, Toshiki; Usui, Akira; Takahashi, Yoshio

2014-04-01

Tellurium, an element of growing economic importance, is extremely enriched in marine ferromanganese oxides. We investigated the mechanism of this enrichment using a combination of spectroscopic analysis and adsorption/coprecipitation experiments. X-ray Absorption Near-Edge Structure (XANES) analysis showed that in adsorption/coprecipitation systems, Te(IV) was oxidized on δ-MnO2 and not oxidized on ferrihydrite. Extended X-ray Absorption Fine Structure (EXAFS) analysis showed that both Te(IV) and Te(VI) were adsorbed on the surface of δ-MnO2 and ferrihydrite via formation of inner-sphere complexes. In addition, Te(VI) can be structurally incorporated into the linkage of Fe octahedra through a coprecipitation process because of its molecular geometry that is similar to the Fe octahedron. The largest distribution coefficient obtained in the adsorption/coprecipitation experiments was for the Te(VI)/ferrihydrite coprecipitation system, and it was comparable to those calculated from the distribution between natural ferromanganese oxides and seawater. Our XAFS and micro-focused X-ray fluorescence (μ-XRF) mapping of natural ferromanganese oxides showed that Te was structurally incorporated as Te(VI) in Fe (oxyhydr)oxide phases. We conclude that the main process for the enrichment of Te in ferromanganese oxides is structural incorporation of Te(VI) into Fe (oxyhydr)oxide phases through coprecipitation. This mechanism can explain the unique degree of enrichment of Te compared with other oxyanions, which are mainly enriched via adsorption on the surface of the solid structures. In particular, the great contrast in the distributions of Te and Se is caused by their oxidized species: (i) the similar geometry of the Te(VI) molecule to Fe octahedron, and (ii) quite soluble nature of Se(VI). Coexisting Mn oxide phases may promote structural incorporation of Te(VI) by oxidation of Te(IV), although the surface oxidation itself may not work as the critical enrichment process as in the case of some cations. This enrichment mechanism also means that ferromanganese oxides mainly scavenge dominant Te(VI) species from seawater and do not affect its species distribution in seawater, as described in a previous model. The variation in Te abundances and the correlation of Te concentration with the growth rate of natural ferromanganese oxides are consistent with the coprecipitation mechanism.

Speciation analysis of I-127,129 in the crop field soil contaminated by the Fukushima Dai-ichi nuclear power plant accident with newly developed chemical separation techniques

NASA Astrophysics Data System (ADS)

Honda, Maki; Matsuzaki, Hiroyuki; Saito, Takumi; Nagai, Hisao

2014-05-01

In previous study, we investigated the depth profile of the accident derived I-129 and downward migration speed in soils of near-field of Fukushima Dai-ichi Nuclear Power Plant, including crop fields and man-made fields. I-129 in soil was measured by AMS and stable iodine (I-127) was measured by ICP-MS at MALT (Micro Analysis Laboratory, Tandem accelerator), The University of Tokyo. It was found that I-129 was concentrated near surface but distributed deeper compared with Cs-137. It was also found that I-129 seems to move downward more quickly than Cs-137. To investigate the adsorption mechanism and the elemental process of migration of the accident derived I-129 in soil, it is important to know what kind of component the I-129 combines with. Recent studies on the X-ray absorption fine structure (XAFS), especially near edge structure (XANES), reported that the stable iodine (I-127) in soil existed as an organic component. However, it had not yet been proved that it was also the case with the accident derived I-129 because it had been incorporated in the soil system only recently and the abundance of I-129 in soil was more than 8 orders of magnitude smaller than sub-ppm level stable iodine (I-127). In this study a progressive sequential extraction method including the dialysis and the dynamic headspace method was newly developed to obtain only the iodine sticking to the soil organic component. The stable iodine can be quantified by direct analysis of the fraction and I-129 can be quantified by AMS method of the fraction added with carrier. The fraction of the organic component for I-127 and I-129 can be evaluated respectively by comparing with the other fraction and/or with the total concentration obtained by the bulk analysis (e.g. by the pyrohydrolysis).

Synthesis and Characterization of the Actinium Aquo Ion

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ferrier, Maryline G.; Stein, Benjamin W.; Batista, Enrique R.

Metal aquo ions occupy central roles in all equilibria that define metal complexation in natural environments. These complexes are used to establish thermodynamic metrics (i.e., stability constants) for predicting metal binding, which are essential for defining critical parameters associated with aqueous speciation, metal chelation, in vivo transport, and so on. As such, establishing the fundamental chemistry of the actinium(III) aquo ion (Ac-aquo ion, Ac(H 2O) x 3+) is critical for current efforts to develop 225Ac [t 1/2 = 10.0(1) d] as a targeted anticancer therapeutic agent. However, given the limited amount of actinium available for study and its high radioactivity,more » many aspects of actinium chemistry remain poorly defined. We overcame these challenges using the longer-lived 227Ac [t 1/2 = 21.772(3) y] isotope and report the first characterization of this fundamentally important Ac-aquo coordination complex. Our X-ray absorption fine structure study revealed 10.9 ± 0.5 water molecules directly coordinated to the Ac III cation with an Ac–O H2O distance of 2.63(1) Å. This experimentally determined distance was consistent with molecular dynamics density functional theory results that showed (over the course of 8 ps) that Ac III was coordinated by 9 water molecules with Ac–O H2O distances ranging from 2.61 to 2.76 Å. Lastly, the data is presented in the context of other actinide(III) and lanthanide(III) aquo ions characterized by XAFS and highlights the uniqueness of the large Ac III coordination numbers and long Ac–O H2O bond distances.« less

Multiscale Speciation of U and Pu at Chernobyl, Hanford, Los Alamos, McGuire AFB, Mayak, and Rocky Flats.

PubMed

Batuk, Olga N; Conradson, Steven D; Aleksandrova, Olga N; Boukhalfa, Hakim; Burakov, Boris E; Clark, David L; Czerwinski, Ken R; Felmy, Andrew R; Lezama-Pacheco, Juan S; Kalmykov, Stepan N; Moore, Dean A; Myasoedov, Boris F; Reed, Donald T; Reilly, Dallas D; Roback, Robert C; Vlasova, Irina E; Webb, Samuel M; Wilkerson, Marianne P

2015-06-02

The speciation of U and Pu in soil and concrete from Rocky Flats and in particles from soils from Chernobyl, Hanford, Los Alamos, and McGuire Air Force Base and bottom sediments from Mayak was determined by a combination of X-ray absorption fine structure (XAFS) spectroscopy and X-ray fluorescence (XRF) element maps. These experiments identify four types of speciation that sometimes may and other times do not exhibit an association with the source terms and histories of these samples: relatively well ordered PuO2+x and UO2+x that had equilibrated with O2 and H2O under both ambient conditions and in fires or explosions; instances of small, isolated particles of U as UO2+x, U3O8, and U(VI) species coexisting in close proximity after decades in the environment; alteration phases of uranyl with other elements including ones that would not have come from soils; and mononuclear Pu-O species and novel PuO2+x-type compounds incorporating additional elements that may have occurred because the Pu was exposed to extreme chemical conditions such as acidic solutions released directly into soil or concrete. Our results therefore directly demonstrate instances of novel complexity in the Å and μm-scale chemical speciation and reactivity of U and Pu in their initial formation and after environmental exposure as well as occasions of unexpected behavior in the reaction pathways over short geological but significant sociological times. They also show that incorporating the actual disposal and site conditions and resultant novel materials such as those reported here may be necessary to develop the most accurate predictive models for Pu and U in the environment.

Synthesis and detection the oxidization of Co cores of Co@SiO2 core-shell nanoparticles by in situ XRD and EXAFS.

PubMed

Zhang, Kunhao; Zhao, Ziyan; Wu, Zhonghua; Zhou, Ying

2015-01-01

In this paper, the Co@SiO2 core-shell nanoparticles were prepared by the sol-gel method. The oxidization of Co core nanoparticles was studied by the synchrotron radiation-based techniques including in situ X-ray diffraction (XRD) and X-ray absorption fine structure (XAFS) up to 800°C in air and N2 protection conditions, respectively. It was found that the oxidization of Co cores is undergoing three steps regardless of being in air or in N2 protection condition. In the first step ranging from room temperature to 200°C, the Co cores were dominated by Co(0) state as well as small amount of Co(2+) ions. When temperature was above 300°C, the interface between Co cores and SiO2 shells was gradually oxidized into Co(2+), and the CoO layer was observed. As the temperature increasing to 800°C, the Co cores were oxidized to Co3O4 or Co3O4/CoO. Nevertheless, the oxidization kinetics of Co cores is different for the Co@SiO2 in air and N2 gas conditions. Generally, the O2 in the air could get through the SiO2 shells easily onto the Co core surface and induce the oxidization of the Co cores due to the mesoporous nature of the SiO2 shells. However, in N2 gas condition, the O atoms can only be from the SiO2 shells, so the diffusion effect of O atoms in the interface between Co core and SiO2 shell plays a key role.

Synthesis and Characterization of the Actinium Aquo Ion

DOE PAGES

Ferrier, Maryline G.; Stein, Benjamin W.; Batista, Enrique R.; ...

2017-02-01

Metal aquo ions occupy central roles in all equilibria that define metal complexation in natural environments. These complexes are used to establish thermodynamic metrics (i.e., stability constants) for predicting metal binding, which are essential for defining critical parameters associated with aqueous speciation, metal chelation, in vivo transport, and so on. As such, establishing the fundamental chemistry of the actinium(III) aquo ion (Ac-aquo ion, Ac(H 2O) x 3+) is critical for current efforts to develop 225Ac [t 1/2 = 10.0(1) d] as a targeted anticancer therapeutic agent. However, given the limited amount of actinium available for study and its high radioactivity,more » many aspects of actinium chemistry remain poorly defined. We overcame these challenges using the longer-lived 227Ac [t 1/2 = 21.772(3) y] isotope and report the first characterization of this fundamentally important Ac-aquo coordination complex. Our X-ray absorption fine structure study revealed 10.9 ± 0.5 water molecules directly coordinated to the Ac III cation with an Ac–O H2O distance of 2.63(1) Å. This experimentally determined distance was consistent with molecular dynamics density functional theory results that showed (over the course of 8 ps) that Ac III was coordinated by 9 water molecules with Ac–O H2O distances ranging from 2.61 to 2.76 Å. Lastly, the data is presented in the context of other actinide(III) and lanthanide(III) aquo ions characterized by XAFS and highlights the uniqueness of the large Ac III coordination numbers and long Ac–O H2O bond distances.« less

Oxygen fugacity of mare basalts and the lunar mantle application of a new microscale oxybarometer based on the valence state of vanadium

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shearer, C.K.; Karner, J.; Papike, J.J.

2004-05-25

Using the valence state of vanadium on a microscale in lunar volcanic glasses we have developed another approach to estimating the oxygen fugacity of mare basalts. The ability to estimate oxygen fugacities for mare basalts and to extend these observations to the lunar mantle is limited using bulk analysis techniques based on buffering assemblages or the valence state of iron. These limitations are due to reequilibration of mineral assemblages at subsolidus conditions, deviations of mineral compositions from thermodynamic ideality, size requirements, and the limits of the iron valence at very low fO{sub 2}. Still, these approaches have been helpful andmore » indicate that mare basalts crystallized at fO{sub 2} between the iron-wuestite buffer (IW) and the ilmenite breakdown reaction (ilmenite = rutile + iron). It has also been inferred from these estimates that the lunar mantle is also highly reduced lying at conditions below IW. Generally, these data cannot be used to determine if the mare basalts become increasingly reduced during transport from their mantle source and eruption at the lunar surface and if there are differences in fO{sub 2} among mare basalts or mantle sources. One promising approach to determining the fO2 of mare basalts is using the mean valence of vanadium (2+, 3+, 4+, 5+) determined on spots of a few micrometers in diameter using synchrotron x-ray absorption fine structure (XAFS) spectroscopy. The average valence state of V in basaltic glasses is a function of fO{sub 2}, temperature, V coordination, and melt composition. Here, we report the initial results of this approach applied to lunar pyroclastic glasses.« less

u d b \\xAF b \\xAF tetraquark resonances with lattice QCD potentials and the Born-Oppenheimer approximation

NASA Astrophysics Data System (ADS)

Bicudo, Pedro; Cardoso, Marco; Peters, Antje; Pflaumer, Martin; Wagner, Marc

2017-09-01

We study tetraquark resonances with lattice QCD potentials computed for a static b ¯b ¯ pair in the presence of two lighter quarks u d , the Born-Oppenheimer approximation and the emergent wave method. As a proof of concept we focus on the system with isospin I =0 , but consider different relative angular momenta l of the heavy quarks b ¯b ¯. For l =0 a bound state has already been predicted with quantum numbers I (JP)=0 (1+). Exploring various angular momenta we now compute the phase shifts and search for S and T matrix poles in the second Riemann sheet. We predict a tetraquark resonance for l =1 , decaying into two B mesons, with quantum numbers I (JP)=0 (1-) , mass m =10 57 6-4+4 MeV and decay width Γ =11 2-103+90 MeV .

Spatially resolved XRF, XAFS, XRD, STXM and IR investigation of a natural U-rich clay

NASA Astrophysics Data System (ADS)

Denecke, M. A.; Michel, P.; Schäfer, T.; Huber, F.; Rickers, K.; Rothe, J.; Dardenne, K.; Brendebach, B.; Vitova, T.; Elie, M.

2009-11-01

Combined spatially resolved hard X-ray μ-XRF and μ-XAFS studies using an X-ray beam with micrometer dimensions at the INE-Beamline for actinide research at ANKA and Beamline L at HASYLAB with those from scanning transmission soft X-ray microscopy (STXM) and synchrotron-based Fourier transform infrared microspectroscopy (μ-FTIR) recorded with beam spots in the nanometer range are used to study a U-rich clay originating from Autunian shales in the Permian Lodève Basin (France). This argillaceous formation is a natural U deposit associated with organic matter (bitumen). Results allow us to differentiate between possible mechanisms leading to U enrichment: likely U immobilization via reaction with organic material associated with clay mineral. Such investigations support development of reliable assessment of the long term radiological safety for proposed nuclear waste disposal sites.

Strategies and limitations for fluorescence detection of XAFS at high flux beamlines

DOE PAGES

Heald, Steve M.

2015-02-17

The issue of detecting the XAFS signal from dilute samples is discussed in detail with the aim of making best use of high flux beamlines that provide up to 10 13 photons -1. Various detection methods are compared, including filters with slits, solid state detectors, crystal analyzers and combinations of these. These comparisons rely on simulations that use experimentally determined parameters. It is found that inelastic scattering places a fundamental limit on detection, and that it is important to take proper account of the polarization dependence of the signals. The combination of a filter–slit system with a solid state detectormore » is a promising approach. With an optimized system good performance can be obtained even if the total count rate is limited to 10 7 Hz. Detection schemes with better energy resolution can help at the largest dilutions if their collection efficiency and count rate limits can be improved.« less

Strategies and limitations for fluorescence detection of XAFS at high flux beamlines

PubMed Central

Heald, Steve M.

2015-01-01

The issue of detecting the XAFS signal from dilute samples is discussed in detail with the aim of making best use of high flux beamlines that provide up to 1013 photons s−1. Various detection methods are compared, including filters with slits, solid state detectors, crystal analyzers and combinations of these. These comparisons rely on simulations that use experimentally determined parameters. It is found that inelastic scattering places a fundamental limit on detection, and that it is important to take proper account of the polarization dependence of the signals. The combination of a filter–slit system with a solid state detector is a promising approach. With an optimized system good performance can be obtained even if the total count rate is limited to 107 Hz. Detection schemes with better energy resolution can help at the largest dilutions if their collection efficiency and count rate limits can be improved. PMID:25723945

Particle size effect of redox reactions for Co species supported on silica

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chotiwan, Siwaruk; Tomiga, Hiroki; Katagiri, Masaki

Conversions of chemical states during redox reactions of two silica-supported Co catalysts, which were prepared by the impregnation method, were evaluated by using an in situ XAFS technique. The addition of citric acid into the precursor solution led to the formation on silica of more homogeneous and smaller Co particles, with an average diameter of 4 nm. The supported Co{sub 3}O{sub 4} species were reduced to metallic Co via the divalent CoO species during a temperature-programmed reduction process. The reduced Co species were quantitatively oxidized with a temperature-programmed oxidation process. The higher observed reduction temperature of the smaller CoO particlesmore » and the lower observed oxidation temperature of the smaller metallic Co particles were induced by the higher dispersion of the Co oxide species, which apparently led to a stronger interaction with supporting silica. The redox temperature between CoO and Co{sub 3}O{sub 4} was found to be independent of the particle size. - Graphical abstract: Chemical state conversions of SiO{sub 2}-supported Co species and the particle size effect have been analyzed by means of in situ XAFS technique. The small CoO particles have endurance against the reduction and exist in a wide temperature range. Display Omitted - Highlights: • The conversions of the chemical state of supported Co species during redox reaction are evaluated. • In operando XAFS technique were applied to measure redox properties of small Co particles. • A small particle size affects to the redox temperatures of cobalt catalysts.« less

Iron-oxide Aerogel and Xerogel Catalyst Formulations: Characterization by 57Fe Mössbauer and XAFS Spectroscopies

DOE Office of Scientific and Technical Information (OSTI.GOV)

Huggins, F.; Bali, S; Huffman, G

2010-01-01

Iron in various iron-oxide aerogel and xerogel catalyst formulations ({ge}85% Fe{sub 2}O{sub 3}; {le}10% K, Co, Cu, or Pd) developed for possible use in Fischer-Tropsch synthesis (FTS) or the water-gas-shift (WGS) reaction has been examined by {sup 57}Fe Moessbauer spectroscopy. The seventeen samples consisted of both as-prepared and calcined aerogels and xerogels and their products after use as catalysts for FTS or the WGS reaction. Complementary XAFS spectra were obtained on the occurrence of the secondary elements in some of the same materials. A broad, slightly asymmetric, two-peak Moessbauer spectrum was obtained from the different as-prepared and calcined catalyst formulationsmore » in the majority of cases. Such spectra could only be satisfactorily fit with three quadrupole doublet components, but no systematic trends in the isomer shift and quadrupole splitting parameters and area ratios of the individual components could be discerned that reflected variations in the composition or preparation of the aerogel or xerogel materials. However, significant reductions were noted in the Moessbauer effective thickness (recoilless absorption effect per unit mass of iron) parameter, {chi}{sub eff}/g, determined at room temperature, for aerogels and xerogels compared to bulk iron oxides, reflecting the openness and lack of rigidity of the aerogel and xerogel structures. Moessbauer measurements for two aerogels over the range from 15 to 292 K confirmed the greatly diminished nature of this parameter at room temperature. Major increases in the effective thickness parameter were observed when the open structure of the aerogel or xerogel collapsed during calcination resulting in the formation of iron oxides (hematite, spinel ferrite). Similar structural changes were indicated by increases in this parameter after use of iron-oxide aerogels as catalysts for FTS or the WGS reaction, during which the iron-oxide aerogel was converted to a mixture of nonstoichiometric magnetite and the Haegg carbide, {chi}-Fe{sub 5}C{sub 2}, or nonstoichiometric magnetite, respectively.« less

Acoustic fine structure may encode biologically relevant information for zebra finches.

PubMed

Prior, Nora H; Smith, Edward; Lawson, Shelby; Ball, Gregory F; Dooling, Robert J

2018-04-18

The ability to discriminate changes in the fine structure of complex sounds is well developed in birds. However, the precise limit of this discrimination ability and how it is used in the context of natural communication remains unclear. Here we describe natural variability in acoustic fine structure of male and female zebra finch calls. Results from psychoacoustic experiments demonstrate that zebra finches are able to discriminate extremely small differences in fine structure, which are on the order of the variation in acoustic fine structure that is present in their vocal signals. Results from signal analysis methods also suggest that acoustic fine structure may carry information that distinguishes between biologically relevant categories including sex, call type and individual identity. Combined, our results are consistent with the hypothesis that zebra finches can encode biologically relevant information within the fine structure of their calls. This study provides a foundation for our understanding of how acoustic fine structure may be involved in animal communication.

Ampelopsin-induced reactive oxygen species enhance the apoptosis of colon cancer cells by activating endoplasmic reticulum stress-mediated AMPK/MAPK/XAF1 signaling

PubMed Central

Park, Ga Bin; Jeong, Jee-Yeong; Kim, Daejin

2017-01-01

Ampelopsin (Amp) is bioactive natural product and exerts anti-cancer effects against several cancer types. The present study investigated the anti-colon cancer activity of Amp and explored its mechanism of action. The treatment of colon cancer cells with Amp resulted in the dose- and time-dependent induction of apoptosis via the activation of endoplasmic reticulum (ER) stress, 5′ adenosine monophosphate-activated protein kinase (AMPK), and c-Jun N-terminal protein kinase (JNK)/p38 mitogen-activated protein kinases (MAPKs). Salubrinal, an ER stress inhibitor, prevented the upregulation of ER stress-associated proteins, including phosphorylated protein kinase RNA-like ER kinase, phosphorylated eukaryotic translation initiation factor 2α, glucose-regulated protein 78, and CCAAT/enhancer-binding protein homologous protein, as well as suppressing AMPK activation and the MAPK signaling pathway. Knockdown of AMPK by RNA interference failed to block ER stress. Additionally, SP600125 (a JNK inhibitor) and SB203580 (a p38-MAPK inhibitor) effectively inhibited apoptosis and attenuated the expression of X-linked IAP-associated factor 1 (XAF1) and apoptotic Bcl-2 family proteins (BCL2 antagonist/killer 1 and BCL2-associated X protein) in Amp-treated colon cancer cells. Furthermore, reactive oxygen species (ROS)-mediated ER stress/AMPK apoptotic signaling pathway in Amp-treated colon cancer cells were markedly inhibited by treatment with N-acetyl-L-cysteine, a ROS scavenger. These results demonstrate that treatment with Amp induces the apoptotic death of colon cancer cells through ER stress-initiated AMPK/MAPK/XAF1 signaling. These results also provide experimental information for developing Amp as therapeutic drug against colon cancer. PMID:29250183

On the formation and structure of rare-earth element complexes in aqueous solutions under hydrothermal conditions with new data on gadolinium aqua and chloro complexes

USGS Publications Warehouse

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

2007-01-01

Synchrotron X-ray spectroscopy experiments were made on the Gd(III) aqua and chloro complexes in low pH aqueous solutions at temperatures ranging from 25 to 500????C and at pressures up to 480??MPa using a hydrothermal diamond anvil cell. Analysis of fluorescence Gd L3-edge X-ray absorption fine structure (XAFS) spectra measured from a 0.006m Gd/0.16m HNO3 aqueous solution at temperatures up to 500????C and at pressures up to 260??MPa shows that the Gd-O distance of the Gd3+ aqua ion decreases steadily at a rate of ??? 0.007??A??/100????C whereas the number of coordinated H2O molecules decreases from 9.0 ?? 0.5 to 7.0 ?? 0.4. The loss of water molecules in the Gd3+ aqua ion inner hydration shell over this temperature range (a 22% reduction) is smaller than exhibited by the Yb3+ aqua ion (42% reduction) indicating that the former is significantly more stable than the later. We conjecture that the anomalous enrichment of Gd reported from measurement of REE concentrations in ocean waters may be attributed to the enhanced stability of the Gd3+ aqua ion relative to other REEs. Gd L3-edge XAFS measurements of 0.006m and 0.1m GdCl3 aqueous solutions at temperatures up to 500????C and pressures up to 480??MPa reveal that the onset of significant Gd3+-Cl- association occurs around 300????C. Partially-hydrated stepwise inner-sphere complexes most likely of the type Gd(H2O)??-nCln+3-n occur in the chloride solutions at higher temperatures, where ?? ??? 8 at 300????C decreasing slightly to an intermediate value between 7 and 8 upon approaching 500????C. This is the first direct evidence for the occurrence of partially-hydrated REE Gd (this study) and Yb [Mayanovic, R.A., Jayanetti, S., Anderson, A.J., Bassett, W.A., Chou, I-M., 2002a. The structure of Yb3+ aquo ion and chloro complexes in aqueous solutions at up to 500 ??C and 270 MPa. J. Phys. Chem. A 106, 6591-6599.] chloro complexes in hydrothermal solutions. The number of chlorides (n) of the partially-hydrated Gd(III) chloro complexes increases steadily with temperature from 0.4 ?? 0.2 to 1.7 ?? 0.3 in the 0.006m chloride solution and from 0.9 ?? 0.7 to 1.8 ?? 0.7 in the 0.1m GdCl3 aqueous solution in the 300-500????C range. Conversely, the number of H2O ligands of Gd(H2O)??-nCln+3-n complexes decreases steadily from 8.9 ?? 0.4 to 5.8 ?? 0.7 in the 0.006m GdCl3 aqueous solution and from 9.0 ?? 0.5 to 5.3 ?? 1.0 in the 0.1m GdCl3 aqueous solution at temperatures from 25 to 500????C. Analysis of our results shows that the chloride ions partially displace the inner-shell water molecules during Gd(III) complex formation under hydrothermal conditions. The Gd-OH2 bond of the partially-hydrated Gd(III) chloro complexes exhibits slightly smaller rates of length contraction (??? 0.005??A??/100????C) for both solutions. The structural aspects of chloride speciation of Gd(III) as measured from this study and of Yb(III) as measured from our previous experiments are consistent with the solubility of these and other REE in deep-sea hydrothermal fluids. ?? 2006 Elsevier B.V. All rights reserved.

In-situ XAFS study for calcination process of Cr catalyst supported on γ-Al2O3 and SiO2

NASA Astrophysics Data System (ADS)

Watanabe, T.; Ikeda, K.; Katayama, M.; Inada, Y.

2016-05-01

The catalytic performance is largely affected by the oxidation state of supported Cr species, and its control changes the activity of Cr catalysts and the selectivity of products. In this study, the calcination process of the supported Cr catalysts on γ-Al2O3 and SiO2 was investigated by in-situ XAFS spectroscopy. The hydrate species was first supported by the impregnation method and was converted to CrO3 via Cr2O3 during the calcination process on both supporting materials. It was found that the temperature to complete the oxidation from Cr2O3 to CrO3 on SiO2 was higher than that on γ-Al2O3. The similarity of the interatomic distance between the surface oxygen atoms of the intermediate Cr2O3 species to that of SiO2 contributes to the stabilization of Cr2O3 on SiO2 during the calcination process.

Same-View Nano-XAFS/STEM-EDS Imagings of Pt Chemical Species in Pt/C Cathode Catalyst Layers of a Polymer Electrolyte Fuel Cell.

PubMed

Takao, Shinobu; Sekizawa, Oki; Samjeské, Gabor; Nagamatsu, Shin-ichi; Kaneko, Takuma; Yamamoto, Takashi; Higashi, Kotaro; Nagasawa, Kensaku; Uruga, Tomoya; Iwasawa, Yasuhiro

2015-06-04

We have made the first success in the same-view imagings of 2D nano-XAFS and TEM/STEM-EDS under a humid N2 atmosphere for Pt/C cathode catalyst layers in membrane electrode assemblies (MEAs) of polymer electrolyte fuel cells (PEFCs) with Nafion membrane to examine the degradation of Pt/C cathodes by anode gas exchange cycles (start-up/shut-down simulations of PEFC vehicles). The same-view imaging under the humid N2 atmosphere provided unprecedented spatial information on the distribution of Pt nanoparticles and oxidation states in the Pt/C cathode catalyst layer as well as Nafion ionomer-filled nanoholes of carbon support in the wet MEA, which evidence the origin of the formation of Pt oxidation species and isolated Pt nanoparticles in the nanohole areas of the cathode layer with different Pt/ionomer ratios, relevant to the degradation of PEFC catalysts.

M553 sphere forming experiment: Pure nickel specimen evaluation

NASA Technical Reports Server (NTRS)

Johnson, P. C.; Peters, E. T.

1973-01-01

A region or cap of very fine two-dimensional surface growth structure was observed at the top of three of the six pure nickel flight specimens. Such two-dimensional surface growth structures have been observed both on the ground-based specimens and on other surface areas of the flight specimens. However, the fine structures observed on the three flight samples are at least an order of magnitude finer than those previously observed, and resemble similar localized, fine, two-dimensional surface structures observed in both ground and flight specimens for the nickel alloys. The two-dimensional growth areas consist primarily of fine equiaxed grains, specimen SL-2.6, fine dendrites, specimen SL-2.5, or a core of fine equiaxed grains surrounded by a ring of fine dendrites, specimen SL-1.9.

Simple hydrothermal synthesis of metal oxides coupled nanocomposites: Structural, optical, magnetic and photocatalytic studies

NASA Astrophysics Data System (ADS)

Ganeshraja, Ayyakannu Sundaram; Clara, Antoni Samy; Rajkumar, Kanniah; Wang, Yanjie; Wang, Yu; Wang, Junhu; Anbalagan, Krishnamoorthy

2015-10-01

The present article is focused on recent developments toward the preparation of room temperature ferromagnetic nanocomposites using better photocatalytic performance. These nanocomposites were successfully prepared by a simple hydrothermal method and their molecular formulas were confirmed as Ti0.90Sn0.10O2 (S1), 0.2CuO-Ti0.73Sn0.06Cu0.21O2-δ (S2), and Ti0.82Sn0.09Fe0.09O2-δ (S3). The ICP, XRD, DRS, FTIR, Raman, XAFS, XPS, EPR, SEM-EDX, HRSEM, HRTEM, photoluminescence and vibrating sample magnetometric measurements were employed to characterize the phase structures, morphologies, optical and magnetic properties of the photocatalysts. The local structures of Sn4+ and Fe3+ were confirmed by 119Sn and 57Fe Mössbauer analysis. The photocatalytic activities of the samples were evaluated by the degradation of methyl orange in water under visible light irradiation. Among the samples, tin doped TiO2 (S1) showed the best photocatalytic performance and stability.

XAFS and XEOL of tetramesityldigermene - An electronic structure study of a heavy group 14 ethylene analogue

NASA Astrophysics Data System (ADS)

Ward, Matthew J.; Rupar, Paul A.; Murphy, Michael W.; Yiu, Yun-Mui; Baines, Kim M.; Sham, Tsun-Kong

2013-04-01

Digermene, the germanium analogue of ethylene, has a multiple bonding motif that differs greatly from that of alkenes and exhibits no pure σ or π type bonds. The electronic structure of digermenes is difficult to study experimentally due to their reactivity, and is computationally challenging because of their shallow potential energy surfaces. Using X-ray absorption near edge structures at both the germanium K and L edges we have been able to directly probe the unoccupied electronic states, or the lowest unoccupied molecular orbital (LUMO), and LUMO+ etc. in the Ge=Ge bond of tetramesityldigermene. We have demonstrated that the LUMO, LUMO+, etc. are composed of hybrid Ge 4s and 4p orbitals. Additionally, our data suggest that the LUMO exhibits relatively more Ge 4s character, whereas the LUMO+ and LUMO+2 exhibit relatively more Ge 4p character. An X-ray excited optical luminescence study of Ge2Mes4 revealed one broad optical emission band at 620 nm, which is significantly red shifted compared to the known energy gap of this molecular germanium compound.

Local structure of Iridium organometallic catalysts covalently bonded to carbon nanotubes.

NASA Astrophysics Data System (ADS)

Blasco, J.; Cuartero, V.; Subías, G.; Jiménez, M. V.; Pérez-Torrente, J. J.; Oro, L. A.; Blanco, M.; Álvarez, P.; Blanco, C.; Menéndez, R.

2016-05-01

Hybrid catalysts based on Iridium N-heterocyclic carbenes anchored to carbon nanotubes (CNT) have been studied by XAFS spectroscopy. Oxidation of CNT yields a large amount of functional groups, mainly hydroxyl groups at the walls and carboxylic groups at the tips, defects and edges. Different kinds of esterification reactions were performed to functionalize oxidized CNT with imidazolium salts. Then, the resulting products were reacted with an Ir organometallic compound to form hybrid catalysts efficient in hydrogen transfer processes. XANES spectroscopy agree with the presence of Ir(I) in these catalysts and the EXAFS spectra detected differences in the local structure of Ir atoms between the initial Ir organometallic compound and the Ir complexes anchored to the CNT. Our results confirm that the halide atom, present in the Ir precursor, was replaced by oxygen from -OH groups at the CNT wall in the first coordination shell of Ir. The lability of this group accounts for the good recyclability and the good efficiency shown by these hybrid catalysts.

Set-up of an XAFS beamline for measurements between 2.4-8 keV at DORIS III

DOE Office of Scientific and Technical Information (OSTI.GOV)

Welter, Edmund

2010-06-23

In this paper results from the commissioning phase and from first user experiments of a new EXAFS beamline at the DORIS III storage ring are presented. The bending magnet EXAFS beamline A1 underwent a complete rebuild and now covers the energy range 2.4-8 keV. A Ni-coated toroidal mirror, placed in a 2:1 focusing position and a plane mirror with one Ni coated stripe and one uncoated (SiO{sub 2}) stripe are used for effective higher harmonics suppression and focusing. The UHV-compatible fixed-exit Double Crystal Monochromator (DCM) is equipped with two Si(111) crystal pairs. The second crystal of one of the twomore » crystal pairs is tilted by 90 deg. around the surface normal to shift the position of glitches. It allows Bragg angles between 5 deg. and 55.5 deg. and continuous scans in quick-EXAFS mode. Test measurements during the commissioning phase proved the excellent performance of the monochromator and a high quality of the XAFS spectra over the entire working range.« less

Photoluminescence and positron annihilation studies on Mg-doped nitrogen-polarity semipolar (101xAF1xAF) GaN heteroepitaxial layers grown by metalorganic vapor phase epitaxy

NASA Astrophysics Data System (ADS)

Onuma, T.; Uedono, A.; Asamizu, H.; Sato, H.; Kaeding, J. F.; Iza, M.; DenBaars, S. P.; Nakamura, S.; Chichibu, S. F.

2010-03-01

The influences of enhanced stacking fault (SF) formation, which is peculiar to nitrogen-(N-) polarity growth and lattice-mismatched semipolar heteroepitaxy, on the electrical properties of (101¯1¯) Mg-doped GaN (GaN:Mg) epilayers were investigated. Although the residual donor concentration was higher than (0001) GaN because of N-polar growth, comparatively low Mg doping (3×1019 cm-3) gave a hole concentration approximately 1.5×1018 cm-3, which was an order of magnitude higher than (0001) GaN:Mg. As the acceptor ionization energy estimated from low temperature photoluminescence was quite similar for (101¯1¯) and (0001) GaN:Mg, the high Mg activation seems to result with the aid of high density SFs. Because the Doppler broadening S parameter for the positron annihilation measurement, which reflects the concentration or size of negatively charged cation vacancies, of (101¯1¯) GaN:Mg was smaller than (0001) case, (101¯1¯) orientation is well suited to Mg-doping.

Fine structure of heliumlike ions and determination of the fine structure constant.

PubMed

Pachucki, Krzysztof; Yerokhin, Vladimir A

2010-02-19

We report a calculation of the fine-structure splitting in light heliumlike atoms, which accounts for all quantum electrodynamical effects up to order alpha{5} Ry. For the helium atom, we resolve the previously reported disagreement between theory and experiment and determine the fine-structure constant with an accuracy of 31 ppb. The calculational results are extensively checked by comparison with the experimental data for different nuclear charges and by evaluation of the hydrogenic limit of individual corrections.

Transformation of nanosilver in oxidized and reduced soils

NASA Astrophysics Data System (ADS)

Hashimoto, Y.; Mitsunobu, S.; Yamaguchi, N.

2013-12-01

A recent development in the manufacturing of consumer products has been the incorporation of nano-sized (< 100 nm) particles. Because of their antimicrobial properties, Ag nanoparticles (NPs) have been used in many purposes including medical devices, foodstorage containers, soaps and sanitizers, wound dressings, and fabrics. Textiles enhanced with AgNPs (e.g., socks) may leach Ag(I) and nanoparticles as they are washed. These nanoparticles are either deposited directly to land or gradually washed away in household wastewater. The AgNPs, similar to Ag(I), will partition to sludge in a wastewater treatment plant, and the sewage sludge may be applied as a land amendment to agricultural fields and urban landscapes. As a consequence, the concentration of Ag in soils can increase gradually for a long period of Ag-containing sludge. Because of their antimicrobial properties, the presence of Ag in the soil adversely affects soil's biologically-mediated functions such as nutrient cycling. In many of previous studies, however, it was not clear if toxicity was caused by the AgNPs themselves or Ag ions released as the result of oxidation and dissolution. Also, mobility and fate of Ag in the environment remain little known. To understand toxicological properties and fate of Ag in soils, chemical speciation of Ag is the critical information. The objective of this study was to determine chemical speciation of Ag derived from AgNP (Ago) and Ag chemicals (AgNO3) in oxidized and reduced soils. We employed X-ray absorption fine structure (XAFS) spectroscopy to identify Ag species and probable hosting phases in soils, and the study was focused on how the soil redox condition transforms AgNP into Ag(I) and vice versa. A soil incubation study was conducted using a volcanic ash soil amended with AgNO3 and AgNPs up to the levels of 1000 mg kg-1 soil. The soil water content was adjusted to the levels of field capacity (oxidized) and saturated (reduced) condition. After 30 days of incubation at 25 C, the soils were collected and analyzed for Ag by sequential extraction and Ag K-edge XAFS spectroscopy. To find probable Ag species in the soils, linear combination fitting was performed on Ag EXAFS data of soils using known reference Ag chemicals and sorption phases. According to the EXAFS analysis, AgNO3 did not exist and was transformed into humus and phyllosilicate-associated phases in the oxidized soil. In the reduced soils, AgNO3 was completely transformed into other compounds including Ago and Ag associated with soil colloids (phyllosilicate and gibbsite). The redox potential of this soil remained oxic levels (457 mV) due to extremely high Ag+ concentration, and the redox condition was not low enough to form sulfide Ag species. About 90% of AgNPs remained persistent in the oxidized soil. In contrast, AgNPs was transformed mainly into Ag2S in the reduced soil. Our study found that AgNPs remained persistent in oxidized soils but can be transformed into sulfide-associated forms in reduced soils.

Orenia metallireducens sp. nov. strain Z6, a Novel Metal-reducing [member of the Phylum] Firmicute from the Deep Subsurface

DOE PAGES

Dong, Yiran; Sanford, Robert A.; Boyanov, Maxim I.; ...

2016-08-26

A novel halophilic and metal-reducing bacterium, Orenia metallireducens strain Z6, was isolated from briny groundwater extracted from a 2.02 km-deep borehole in the Illinois Basin, IL. This organism shared 96% 16S rRNA gene similarity with Orenia marismortui but demonstrated physiological properties previously unknown for this genus. In addition to exhibiting a fermentative metabolism typical of the genus Orenia, strain Z6 reduces various metal oxides [Fe(III), Mn(IV), Co(III), and Cr(VI)], using H 2 as the electron donor. Strain Z6 actively reduced ferrihydrite over broad ranges of pH (6 to 9.6), salinity (0.4 to 3.5 M NaCl), and temperature (20 to 60°C).more » At pH 6.5, strain Z6 also reduced more crystalline iron oxides, such as lepidocrocite (γ-FeOOH), goethite (α-FeOOH), and hematite (α-Fe 2O 3). Analysis of X-ray absorption fine structure (XAFS) following Fe(III) reduction by strain Z6 revealed spectra from ferrous secondary mineral phases consistent with the precipitation of vivianite [Fe 3(PO 4) 2] and siderite (FeCO 3). The draft genome assembled for strain Z6 is 3.47 Mb in size and contains 3,269 protein-coding genes. Unlike the well-understood iron-reducing Shewanella and Geobacter species, this organism lacks the c-type cytochromes for typical Fe(III) reduction. Strain Z6 represents the first bacterial species in the genus Orenia (order Halanaerobiales) reported to reduce ferric iron minerals and other metal oxides. This microbe expands both the phylogenetic and physiological scopes of iron-reducing microorganisms known to inhabit the deep subsurface and suggests new mechanisms for microbial iron reduction. In conclusion, these distinctions from other Orenia spp. support the designation of strain Z6 as a new species, Orenia metallireducens sp. nov.« less

Effect of thermal maturity on remobilization of molybdenum in black shales

NASA Astrophysics Data System (ADS)

Ardakani, Omid H.; Chappaz, Anthony; Sanei, Hamed; Mayer, Bernhard

2016-09-01

Molybdenum (Mo) concentrations in sedimentary records have been widely used as a method to assess paleo-redox conditions prevailing in the ancient oceans. However, the potential effects of post-depositional processes, such as thermal maturity and burial diagenesis, on Mo concentrations in organic-rich shales have not been addressed, compromising its use as a redox proxy. This study investigates the distribution and speciation of Mo at various thermal maturities in the Upper Ordovician Utica Shale from southern Quebec, Canada. Samples display maturities ranging from the peak oil window (VRo ∼ 1%) to the dry gas zone (VRo ∼ 2%). While our data show a significant correlation between total organic carbon (TOC) and Mo (R2 = 0.40, n = 28, P < 0.0003) at lower thermal maturity, this correlation gradually deteriorates with increasing thermal maturity. Intervals within the thermally overmature section of the Utica Shale that contain elevated Mo levels (20-81 ppm) show petrographic and sulfur isotopic evidence of thermochemical sulfate reduction (TSR) along with formation of recrystallized pyrite. X-ray Absorption Fine Structure spectroscopy (XAFS) was used to determine Mo speciation in samples from intervals with elevated Mo contents (>30 ppm). Our results show the presence of two Mo species: molybdenite Mo(IV)S2 (39 ± 5%) and Mo(VI)-Organic Matter (61 ± 5%). This new evidence suggests that at higher thermal maturities, TSR causes sulfate reduction coupled with oxidation of organic matter (OM). This process is associated with H2S generation and pyrite formation and recrystallization. This in turn leads to the remobilization of Mo and co-precipitation of molybdenite with TSR-derived carbonates in the porous intervals. This could lead to alteration of the initial sedimentary signature of Mo in the affected intervals, hence challenging its use as a paleo-redox proxy in overmature black shales.

A new generation of x-ray spectrometry UHV instruments at the SR facilities BESSY II, ELETTRA and SOLEIL

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lubeck, J., E-mail: janin.lubeck@ptb.de; Fliegauf, R.; Holfelder, I.

A novel type of ultra-high vacuum instrument for X-ray reflectometry and spectrometry-related techniques for nanoanalytics by means of synchrotron radiation (SR) has been constructed and commissioned at BESSY II. This versa-tile instrument was developed by the PTB, Germany’s national metrology institute, and includes a 9-axis manipulator that allows for an independent alignment of the samples with respect to all degrees of freedom. In addition, it integrates a rotational and translational movement of several photodiodes as well as a translational movement of a beam-geometry-defining aperture system. Thus, the new instrument enables various analytical techniques based on energy dispersive X-ray detectors suchmore » as reference-free X-Ray Fluorescence (XRF) analysis, total-reflection XRF, grazing-incidence XRF, in addition to optional X-Ray Reflectometry (XRR) measurements or polarization-dependent X-ray absorption fine structure analyses (XAFS). Samples having a size of up to (100 × 100) mm{sup 2}; can be analyzed with respect to their mass deposition, elemental, spatial or species composition. Surface contamination, nanolayer composition and thickness, depth pro-file of matrix elements or implants, nanoparticles or buried interfaces as well as molecular orientation of bonds can be accessed. Three technology transfer projects of adapted instruments have enhanced X-Ray Spectrometry (XRS) research activities within Europe at the synchrotron radiation facilities ELETTRA (IAEA) and SOLEIL (CEA/LNE-LNHB) as well as at the X-ray innovation laboratory BLiX (TU Berlin) where different laboratory sources are used. Here, smaller chamber requirements led PTB in cooperation with TU Berlin to develop a modified instrument equipped with a 7-axis manipulator: reduced freedom in the choice of experimental geometry modifications (absence of out-of-SR-plane and reference-free XRS options) has been compensated by encoder-enhanced angular accuracy for GIXRF and XRR.« less

Fine-scale structure in the far-infrared Milky-Way

NASA Technical Reports Server (NTRS)

Waller, William H.; Wall, William F.; Reach, William T.; Varosi, Frank; Ebert, Rick; Laughlin, Gaylin; Boulanger, Francois

1995-01-01

This final report summarizes the work performed and which falls into five broad categories: (1) generation of a new data product (mosaics of the far-infrared emission in the Milky Way); (2) acquisition of associated data products at other wavelengths; (3) spatial filtering of the far-infrared mosaics and resulting images of the FIR fine-scale structure; (4) evaluation of the spatially filtered data; (5) characterization of the FIR fine-scale structure in terms of its spatial statistics; and (6) identification of interstellar counterparts to the FIR fine-scale structure.

Effects of interaural time differences in fine structure and envelope on lateral discrimination in electric hearing.

PubMed

Majdak, Piotr; Laback, Bernhard; Baumgartner, Wolf-Dieter

2006-10-01

Bilateral cochlear implant (CI) listeners currently use stimulation strategies which encode interaural time differences (ITD) in the temporal envelope but which do not transmit ITD in the fine structure, due to the constant phase in the electric pulse train. To determine the utility of encoding ITD in the fine structure, ITD-based lateralization was investigated with four CI listeners and four normal hearing (NH) subjects listening to a simulation of electric stimulation. Lateralization discrimination was tested at different pulse rates for various combinations of independently controlled fine structure ITD and envelope ITD. Results for electric hearing show that the fine structure ITD had the strongest impact on lateralization at lower pulse rates, with significant effects for pulse rates up to 800 pulses per second. At higher pulse rates, lateralization discrimination depended solely on the envelope ITD. The data suggest that bilateral CI listeners benefit from transmitting fine structure ITD at lower pulse rates. However, there were strong interindividual differences: the better performing CI listeners performed comparably to the NH listeners.

[The role of temporal fine structure in tone recognition and music perception].

PubMed

Zhou, Q; Gu, X; Liu, B

2017-11-07

The sound signal can be decomposed into temporal envelope and temporal fine structure information. The temporal envelope information is crucial for speech perception in quiet environment, and the temporal fine structure information plays an important role in speech perception in noise, Mandarin tone recognition and music perception, especially the pitch and melody perception.

Willis Lamb, Jr., the Hydrogen Atom, and the Lamb Shift

Science.gov Websites

1955, Lamb won the Nobel Prize in Physics for his discoveries concerning "the fine structure of , May 7 - September 30, 1979 Fine Structure of the Hydrogen Atom, Part I; Part II; Part III; Part IV ; Part V; Part VI (from Physical Review 1950-1953) Microwave Technique for Determining the Fine Structure

GEMMs shine a light on resistance to androgen deprivation therapy for prostate cancer

PubMed Central

Karantanos, Theodoros; Thompson, Timothy C.

2013-01-01

Summary Androgen deprivation therapy (ADT) for advanced prostate cancer inexorably leads to resistance, and clinically useful biomarkers are lacking. The value of genetically engineered mice for co-clinical studies is clearly demonstrated in a recent publication that reveals XAF1, XIAP, and SRD5A1 as novel predictive biomarkers and therapeutic targets for ADT resistance. PMID:23845440

Measurement of the inclusive t t xAF production cross section in p p xAF collisions at √{s }=1.96 TeV and determination of the top quark pole mass

NASA Astrophysics Data System (ADS)

Abazov, V. M.; Abbott, B.; Acharya, B. S.; Adams, M.; Adams, T.; Agnew, J. P.; Alexeev, G. D.; Alkhazov, G.; Alton, A.; Askew, A.; Atkins, S.; Augsten, K.; Aushev, Y.; Avila, C.; Badaud, F.; Bagby, L.; Baldin, B.; Bandurin, D. V.; Banerjee, S.; Barberis, E.; Baringer, P.; Bartlett, J. F.; Bassler, U.; Bazterra, V.; Bean, A.; Begalli, M.; Bellantoni, L.; Beri, S. B.; Bernardi, G.; Bernhard, R.; Bertram, I.; Besançon, M.; Beuselinck, R.; Bhat, P. C.; Bhatia, S.; Bhatnagar, V.; Blazey, G.; Blessing, S.; Bloom, K.; Boehnlein, A.; Boline, D.; Boos, E. E.; Borissov, G.; Borysova, M.; Brandt, A.; Brandt, O.; Brock, R.; Bross, A.; Brown, D.; Bu, X. B.; Buehler, M.; Buescher, V.; Bunichev, V.; Burdin, S.; Buszello, C. P.; Camacho-Pérez, E.; Casey, B. C. K.; Castilla-Valdez, H.; Caughron, S.; Chakrabarti, S.; Chan, K. M.; Chandra, A.; Chapon, E.; Chen, G.; Cho, S. W.; Choi, S.; Choudhary, B.; Cihangir, S.; Claes, D.; Clutter, J.; Cooke, M.; Cooper, W. E.; Corcoran, M.; Couderc, F.; Cousinou, M.-C.; Cuth, J.; Cutts, D.; Das, A.; Davies, G.; de Jong, S. J.; De La Cruz-Burelo, E.; Déliot, F.; Demina, R.; Denisov, D.; Denisov, S. P.; Desai, S.; Deterre, C.; DeVaughan, K.; Diehl, H. T.; Diesburg, M.; Ding, P. F.; Dominguez, A.; Dubey, A.; Dudko, L. V.; Duperrin, A.; Dutt, S.; Eads, M.; Edmunds, D.; Ellison, J.; Elvira, V. D.; Enari, Y.; Evans, H.; Evdokimov, A.; Evdokimov, V. N.; Fauré, A.; Feng, L.; Ferbel, T.; Fiedler, F.; Filthaut, F.; Fisher, W.; Fisk, H. E.; Fortner, M.; Fox, H.; Franc, J.; Fuess, S.; Garbincius, P. H.; Garcia-Bellido, A.; García-González, J. A.; Gavrilov, V.; Geng, W.; Gerber, C. E.; Gershtein, Y.; Ginther, G.; Gogota, O.; Golovanov, G.; Grannis, P. D.; Greder, S.; Greenlee, H.; Grenier, G.; Gris, Ph.; Grivaz, J.-F.; Grohsjean, A.; Grünendahl, S.; Grünewald, M. W.; Guillemin, T.; Gutierrez, G.; Gutierrez, P.; Haley, J.; Han, L.; Harder, K.; Harel, A.; Hauptman, J. M.; Hays, J.; Head, T.; Hebbeker, T.; Hedin, D.; Hegab, H.; Heinson, A. P.; Heintz, U.; Hensel, C.; Heredia-De La Cruz, I.; Herner, K.; Hesketh, G.; Hildreth, M. D.; Hirosky, R.; Hoang, T.; Hobbs, J. D.; Hoeneisen, B.; Hogan, J.; Hohlfeld, M.; Holzbauer, J. L.; Howley, I.; Hubacek, Z.; Hynek, V.; Iashvili, I.; Ilchenko, Y.; Illingworth, R.; Ito, A. S.; Jabeen, S.; Jaffré, M.; Jayasinghe, A.; Jeong, M. S.; Jesik, R.; Jiang, P.; Johns, K.; Johnson, E.; Johnson, M.; Jonckheere, A.; Jonsson, P.; Joshi, J.; Jung, A. W.; Juste, A.; Kajfasz, E.; Karmanov, D.; Katsanos, I.; Kaur, M.; Kehoe, R.; Kermiche, S.; Khalatyan, N.; Khanov, A.; Kharchilava, A.; Kharzheev, Y. N.; Kiselevich, I.; Kohli, J. M.; Kozelov, A. V.; Kraus, J.; Kumar, A.; Kupco, A.; Kurča, T.; Kuzmin, V. A.; Lammers, S.; Lebrun, P.; Lee, H. S.; Lee, S. W.; Lee, W. M.; Lei, X.; Lellouch, J.; Li, D.; Li, H.; Li, L.; Li, Q. Z.; Lim, J. K.; Lincoln, D.; Linnemann, J.; Lipaev, V. V.; Lipton, R.; Liu, H.; Liu, Y.; Lobodenko, A.; Lokajicek, M.; Lopes de Sa, R.; Luna-Garcia, R.; Lyon, A. L.; Maciel, A. K. A.; Madar, R.; Magaña-Villalba, R.; Malik, S.; Malyshev, V. L.; Mansour, J.; Martínez-Ortega, J.; McCarthy, R.; McGivern, C. L.; Meijer, M. M.; Melnitchouk, A.; Menezes, D.; Mercadante, P. G.; Merkin, M.; Meyer, A.; Meyer, J.; Miconi, F.; Mondal, N. K.; Mulhearn, M.; Nagy, E.; Narain, M.; Nayyar, R.; Neal, H. A.; Negret, J. P.; Neustroev, P.; Nguyen, H. T.; Nunnemann, T.; Orduna, J.; Osman, N.; Osta, J.; Pal, A.; Parashar, N.; Parihar, V.; Park, S. K.; Partridge, R.; Parua, N.; Patwa, A.; Penning, B.; Perfilov, M.; Peters, Y.; Petridis, K.; Petrillo, G.; Pétroff, P.; Pleier, M.-A.; Podstavkov, V. M.; Popov, A. V.; Prewitt, M.; Price, D.; Prokopenko, N.; Qian, J.; Quadt, A.; Quinn, B.; Ratoff, P. N.; Razumov, I.; Ripp-Baudot, I.; Rizatdinova, F.; Rominsky, M.; Ross, A.; Royon, C.; Rubinov, P.; Ruchti, R.; Sajot, G.; Sánchez-Hernández, A.; Sanders, M. P.; Santos, A. S.; Savage, G.; Savitskyi, M.; Sawyer, L.; Scanlon, T.; Schamberger, R. D.; Scheglov, Y.; Schellman, H.; Schott, M.; Schwanenberger, C.; Schwienhorst, R.; Sekaric, J.; Severini, H.; Shabalina, E.; Shary, V.; Shaw, S.; Shchukin, A. A.; Simak, V.; Skubic, P.; Slattery, P.; Smirnov, D.; Snow, G. R.; Snow, J.; Snyder, S.; Söldner-Rembold, S.; Sonnenschein, L.; Soustruznik, K.; Stark, J.; Stoyanova, D. A.; Strauss, M.; Suter, L.; Svoisky, P.; Titov, M.; Tokmenin, V. V.; Tsai, Y.-T.; Tsybychev, D.; Tuchming, B.; Tully, C.; Uvarov, L.; Uvarov, S.; Uzunyan, S.; Van Kooten, R.; van Leeuwen, W. M.; Varelas, N.; Varnes, E. W.; Vasilyev, I. A.; Verkheev, A. Y.; Vertogradov, L. S.; Verzocchi, M.; Vesterinen, M.; Vilanova, D.; Vokac, P.; Wahl, H. D.; Wang, M. H. L. S.; Warchol, J.; Watts, G.; Wayne, M.; Weichert, J.; Welty-Rieger, L.; Williams, M. R. J.; Wilson, G. W.; Wobisch, M.; Wood, D. R.; Wyatt, T. R.; Xie, Y.; Yamada, R.; Yang, S.; Yasuda, T.; Yatsunenko, Y. A.; Ye, W.; Ye, Z.; Yin, H.; Yip, K.; Youn, S. W.; Yu, J. M.; Zennamo, J.; Zhao, T. G.; Zhou, B.; Zhu, J.; Zielinski, M.; Zieminska, D.; Zivkovic, L.; D0 Collaboration

2016-11-01

The inclusive cross section of top quark-antiquark pairs produced in p p ¯ collisions at √{s }=1.96 TeV is measured in the lepton+jets and dilepton decay channels. The data sample corresponds to 9.7 fb-1 of integrated luminosity recorded with the D0 detector during Run II of the Fermilab Tevatron Collider. Employing multivariate analysis techniques we measure the cross section in the two decay channels and we perform a combined cross section measurement. For a top quark mass of 172.5 GeV, we measure a combined inclusive top quark-antiquark pair production cross section of σt t ¯=7.26 ±0.13 (stat )-0.50+0.57(syst ) pb which is consistent with standard model predictions. We also perform a likelihood fit to the measured and predicted top quark mass dependence of the inclusive cross section, which yields a measurement of the pole mass of the top quark. The extracted value is mt=172.8 ±1.1 (theo )-3.1+3.3(exp ) GeV .

Core–Shell to Doped Quantum Dots: Evolution of the Local Environment Using XAFS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Saha, Avijit; Chattopadhyay, Soma; Shibata, Tomohiro

2016-09-30

Internal structure study at an atomic level is a challenging task with far reaching consequences to its material properties, specifically in the field of transition metal doping in quantum dots. Diffusion of transition metal ions in and out of quantum dots forming magnetic clusters has been a major bottleneck in this class of materials. Diffusion of the magnetic ions from the core into the nonmagnetic shell in a core/shell heterostructure architecture to attain uniform doping has been recently introduced and yet to be understood. In this work, we have studied the local structure variation of Fe as a function ofmore » CdS matrix thickness and annealing time during the overcoating of Fe 3O 4 core with CdS using X-ray absorption spectroscopy. The data reveals that Fe 3O 4 core initially forms a core/shell structure with CdS followed by alloying at the interface eventually completely diffusing all the way through the CdS matrix to form homogeneously Fe-doped CdS QDs with excellent control over size and size distribution. Study of Fe K-edge shows a complete change of Fe local environment from Fe–O to FeS.« less

Statistical Fine Structure in the Inhomogeneously Broadened Electronic Origin of Pentacene in p-Terphenyl.

DTIC Science & Technology

1988-01-29

Electronic Origin of Pentacene in p-Terphenyl by T. P. Carter, M. Manavi, and W. E. Moerner Prepared for Publication inDTIC Journal of Chemical Physics...Classification) Statistical Fine Structure in the Inhomogeneously Broadened Electronic Origin of Pentacene in p-Terphenyl 12. PERSONAL AUTHOR(S) T. P...of pentacene in p-terphenyl using laser FM spectroscopy. Statistical fine structure is time-independent structure on the inhomogeneous line caused by

Statistical Fine Structure of Inhomogeneously Broadened Absorption Lines.

DTIC Science & Technology

1987-07-31

inhomogeneously broadened optical absorption of pentacene n p-terphenyl at liquid helium temperatures... SFS is the actual frequency- ependent, time...statistical fine structure (SFS) in the inhomogeneously broadened optical absorption of pentacene in p-terphenyl at liquid helium temperatures. SFS is the...quite difficult . -2- We have observed for the first time statistical fine structure in the inhomogeneously broadened optical absorption of pentacene

Atomic Fine-Structure Diagnostic and Cooling Transitions for Far Infrared and Submillimeter Observations

NASA Astrophysics Data System (ADS)

Balance, Connor

Some of the strongest emission lines observed from a variety of astronomical sources originate from transitions between fine-structure levels in the ground term of neutral atoms and lowly-charged ions. These fine-structure levels are populated due to collisions with -, H+, H, He, and/or H2 depending on the temperature and ionization fraction of e the environment. As fine-structure excitation measurements are rare, modeling applications depend on theoretically determined rate coefficients. However, for many ions electron collision studies have not been performed for a decade or more, while over that time period the theoretical/computational methodology has significantly advanced. For heavy-particle collisions, very few systems have been studied. As a result, most models rely on estimates or on low-quality collisional data for fine-structure excitation. To significantly advance the state of fine-structure data for astrophysical models, we propose a collaborative effort in electron collisions, heavy-particle collisions, and quantum chemistry. Using the R-matrix method, fine-structure excitation due to electron collisions will be investigated for C, O, Ne^+, Ne^2+, Ar^+, Ar^2+, Fe, Fe^+, and Fe^2+. Fine-structure excitation due to heavy-particle collisions will be studied with a fully quantum molecular-orbital approach using potential energy surfaces computed with a multireference configuration-interaction method. The systems to be studied include: C/H^+, C/H2, O/H^+, O/H2, Ne^+/H, Ne^+/H2, Ne^2+/H, Ne^2+/H2, Fe/H^+, Fe^+/H, and Fe^2+/H. 2D rigid-rotor surfaces will be constructed for H2 collisions, internuclear distance dependent spin-orbit coupling will be computed in some cases, and all rate coefficients will be obtained for the temperature range 10-2000 K. The availability the proposed fine-structure excitation data will lead to deeper examination and understanding of the properties of many astrophysical environments, including young stellar objects, protoplanetary disks, planetary nebulae, photodissociation regions, active galactic nuclei, and x-ray dominated regions, hence elevating the scientific return from current (SOFIA, Spitzer, Herschel, HST) and upcoming (JWST) NASA IR/Submm astrophysics missions, as well as from ground-based telescopes.

Formation and nitrile hydrogenation performance of Ru nanoparticles on a K-doped Al2O3 surface.

PubMed

Muratsugu, Satoshi; Kityakarn, Sutasinee; Wang, Fei; Ishiguro, Nozomu; Kamachi, Takashi; Yoshizawa, Kazunari; Sekizawa, Oki; Uruga, Tomoya; Tada, Mizuki

2015-10-14

Decarbonylation-promoted Ru nanoparticle formation from Ru3(CO)12 on a basic K-doped Al2O3 surface was investigated by in situ FT-IR and in situ XAFS. Supported Ru3(CO)12 clusters on K-doped Al2O3 were converted stepwise to Ru nanoparticles, which catalyzed the selective hydrogenation of nitriles to the corresponding primary amines via initial decarbonylation, the nucleation of the Ru cluster core, and the growth of metallic Ru nanoparticles on the surface. As a result, small Ru nanoparticles, with an average diameter of less than 2 nm, were formed on the support and acted as efficient catalysts for nitrile hydrogenation at 343 K under hydrogen at atmospheric pressure. The structure and catalytic performance of Ru catalysts depended strongly on the type of oxide support, and the K-doped Al2O3 support acted as a good oxide for the selective nitrile hydrogenation without basic additives like ammonia. The activation of nitriles on the modelled Ru catalyst was also investigated by DFT calculations, and the adsorption structure of a nitrene-like intermediate, which was favourable for high primary amine selectivity, was the most stable structure on Ru compared with other intermediate structures.

Determination of the fine structure constant using helium fine structure.

PubMed

Smiciklas, Marc; Shiner, David

2010-09-17

We measure 31,908,131.25(30) kHz for the 2(3)}P J=0 to 2 fine structure interval in helium. The difference between this and theory to order mα7 (20 Hz numerical uncertainty) implies 0.22(30) kHz for uncalculated terms. The measurement is performed by using atomic beam and electro-optic laser techniques. Various checks include a 3He 2{3}S hyperfine measurement. We can obtain an independent value for the fine structure constant α with a 5 ppb experimental uncertainty. However, dominant mα8 terms (potentially 1.2 kHz) limit the overall uncertainty to a less competitive 20 ppb in α.

g-Factor of heavy ions: a new access to the fine structure constant.

PubMed

Shabaev, V M; Glazov, D A; Oreshkina, N S; Volotka, A V; Plunien, G; Kluge, H-J; Quint, W

2006-06-30

A possibility for a determination of the fine structure constant in experiments on the bound-electron g-factor is examined. It is found that studying a specific difference of the g-factors of B- and H-like ions of the same spinless isotope in the Pb region to the currently accessible experimental accuracy of 7 x 10(-10) would lead to a determination of the fine structure constant to an accuracy which is better than that of the currently accepted value. Further improvements of the experimental and theoretical accuracy could provide a value of the fine structure constant which is several times more precise than the currently accepted one.

Ultrafast exciton fine structure relaxation dynamics in lead chalcogenide nanocrystals.

PubMed

Johnson, Justin C; Gerth, Kathrine A; Song, Qing; Murphy, James E; Nozik, Arthur J; Scholes, Gregory D

2008-05-01

The rates of fine structure relaxation in PbS, PbSe, and PbTe nanocrystals were measured on a femtosecond time scale as a function of temperature with no applied magnetic field by cross-polarized transient grating spectroscopy (CPTG) and circularly polarized pump-probe spectroscopy. The relaxation rates among exciton fine structure states follow trends with nanocrystal composition and size that are consistent with the expected influence of material dependent spin-orbit coupling, confinement enhanced electron-hole exchange interaction, and splitting between L valleys that are degenerate in the bulk. The size dependence of the fine structure relaxation rate is considerably different from what is observed for small CdSe nanocrystals, which appears to result from the unique material properties of the highly confined lead chalcogenide quantum dots. Modeling and qualitative considerations lead to conclusions about the fine structure of the lowest exciton absorption band, which has a potentially significant bearing on photophysical processes that make these materials attractive for practical purposes.

Polygamy and an absence of fine-scale structure in Dendroctonus ponderosae (Hopk.) (Coleoptera: Curcilionidae) confirmed using molecular markers

PubMed Central

Janes, J K; Roe, A D; Rice, A V; Gorrell, J C; Coltman, D W; Langor, D W; Sperling, F A H

2016-01-01

An understanding of mating systems and fine-scale spatial genetic structure is required to effectively manage forest pest species such as Dendroctonus ponderosae (mountain pine beetle). Here we used genome-wide single-nucleotide polymorphisms to assess the fine-scale genetic structure and mating system of D. ponderosae collected from a single stand in Alberta, Canada. Fine-scale spatial genetic structure was absent within the stand and the majority of genetic variation was best explained at the individual level. Relatedness estimates support previous reports of pre-emergence mating. Parentage assignment tests indicate that a polygamous mating system better explains the relationships among individuals within a gallery than the previously reported female monogamous/male polygynous system. Furthermore, there is some evidence to suggest that females may exploit the galleries of other females, at least under epidemic conditions. Our results suggest that current management models are likely to be effective across large geographic areas based on the absence of fine-scale genetic structure. PMID:26286666

Connecting traces of galaxy evolution: the missing core mass-morphological fine structure relation

NASA Astrophysics Data System (ADS)

Bonfini, P.; Bitsakis, T.; Zezas, A.; Duc, P.-A.; Iodice, E.; González-Martín, O.; Bruzual, G.; González Sanoja, A. J.

2018-01-01

Deep exposure imaging of early-type galaxies (ETGs) are revealing the second-order complexity of these objects, which have been long considered uniform, dispersion-supported spheroidals. `Fine structure' features (e.g. ripples, plumes, tidal tails, rings) as well as depleted stellar cores (i.e. central light deficits) characterize a number of massive ETG galaxies, and can be interpreted as the result of galaxy-galaxy interactions. We discuss how the time-scale for the evolution of cores and fine structures are comparable, and hence it is expected that they develop in parallel after the major interaction event which shaped the ETG. Using archival data, we compare the `depleted stellar mass' (i.e. the mass missing from the depleted stellar core) against the prominence of the fine structure features, and observe that they correlate inversely. This result confirms our expectation that, while the supermassive black hole (SMBH) binary (constituted by the SMBHs of the merger progenitors) excavates the core via three-body interactions, the gravitational potential of the newborn galaxy relaxes, and the fine structures fade below detection levels. We expect the inverse correlation to hold at least within the first Gyr from the merger which created the SMBH binary; after then, the fine structure evolves independently.

Nanoclusters of α-Fe naturally formed in twinned martensite after martensitic transformation

NASA Astrophysics Data System (ADS)

Liu, X.; Ping, D. H.; Xiang, H. P.; Lu, X.; Shen, J.

2018-05-01

Various Fe-C binary alloys with the carbon content from 0.05 to 2.0 (wt. %) have been prepared and water-quenched at austenitizing temperatures. The fine structure of the twinned martensite in the quenched samples has been investigated by means of transmission electron microscopy (TEM) in order to understand the initial products during the formation of the martensite structure. In the twinned structure (body-centered-cubic {112}⟨111⟩-type twin), TEM dark field observations have revealed that both matrix and twinned crystal regions are fully composed of ultra-fine particles (α-Fe nano-crystallites). The particles tend to have the same preferred direction (or texture) in the twinned martensite and the size is almost the same (1-2 nm). The ultra-fine particle structure has been commonly observed regardless of the carbon content; however, such a fine particle structure has been observed only in the martensite with the twinning structure. After in-situ TEM heating, recrystallization occurred and the fine particles merged into larger α-Fe grains; at the same time, the twinned relationship also disappeared.

Iron and Arsenic Speciation During As(III) Oxidation by Manganese Oxides in the Presence of Fe(II): Molecular-Level Characterization Using XAFS, Mössbauer, and TEM Analysis

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wu, Yun; Kukkadapu, Ravi K.; Livi, Kenneth J. T.

The redox state and speciation of metalloid arsenic (As) determine its toxicity and mobility. Knowledge of biogeochemical processes influencing the As redox state is therefore important to understand and predict its environmental behavior. Many previous studies examined As(III) oxidation by various Mn-oxides, but little is known the environmental influences (e.g. co-existing ions) on such process. In this study, we investigated the mechanisms of As(III) oxidation by a poorly crystalline hexagonal birnessite (δ-MnO2) in the presence of Fe(II) using X-ray absorption spectroscopy (XAS), Mössbauer spectroscopy and transmission electron microscopy (TEM) coupled with energy-dispersive X-ray spectroscopy (EDS). As K-edge X-ray absorption nearmore » edge spectroscopy (XANES) analysis revealed that, at low Fe(II) concentration (100 μM), As(V) was the predominant As species on the solid phase, while at higher Fe(II) concentration (200-1000 μM), both As(III) and As(V) were sorbed on the solid phase. As K-edge extended X-ray absorption fine structure spectroscopy (EXAFS) analysis showed an increasing As-Mn/Fe distance over time, indicating As prefers to bind with the newly formed Fe(III)-(hydr)oxides. As adsorbed on Fe(III)-(hydr)oxides as a bidentate binuclear corner-sharing complex. Both Mössbauer and TEM-EDS investigations demonstrated that the oxidized Fe(III) products formed during Fe(II) oxidation by δ-MnO2 were predominantly ferrihydrite, goethite, and ferric arsenate like compounds. However, Fe EXAFS analysis also suggested the formation of a small amount of lepidocrocite. The Mn K-edge XANES data indicated that As(III) and Fe(II) oxidation occurs as a two electron transfer with δ-MnO2 and the observed Mn(III) is due to conproportionation of surface sorbed Mn(II) with Mn(IV) in δ-MnO2 structure. This study reveals that the mechanisms of As(III) oxidation by δ-MnO2 in the presence of Fe(II) are very complex, involving many simultaneous reactions, and the formation of Fe(III)-(hydr)oxides plays a very important role in reducing As mobility.« less

GeoSoilEnviroCARS: A National User Facility for Synchrotron Radiation Research

NASA Astrophysics Data System (ADS)

Rivers, M. L.; Sutton, S. R.

2002-12-01

GeoSoilEnviroCARS (GSECARS) is a national user facility for frontier research in the earth sciences using synchrotron radiation at the Advanced Photon Source, Argonne National Laboratory. GSECARS provides earth scientists with access to the high-brilliance hard x-rays from this third-generation synchrotron light source. Both an undulator and a bending magnet beamline are available. All principal synchrotron-based analytical techniques in demand by earth scientists are being brought to bear on earth science problems: (1) high-pressure/high-temperature crystallography and spectroscopy using the diamond anvil cell; (2) high-pressure/high-temperature crystallography using the large-volume press; (3) powder, single crystal and interface diffraction; (4) inelastic x-ray scattering; (5) x-ray absorption fine structure (XAFS) spectroscopy; (6) x-ray fluorescence microprobe analysis; and (7) microtomography. The major instrumentation includes 250 and 1000 MN multianvil presses, a double-sided laser heating system, a large general-purpose 5-circle diffractometer, a focused microprobe, and a Raman laboratory. A proposal-based system for beamtime allocation, open to all earth scientists, has been in place since Fall, 1998. Since then, over 450 beamtime proposals have been received and more than 320 outside users have conducted experiments at GSECARS. The research conducted by these investigators has resulted in more than 170 publications. The unique capabilities of the APS and GSECARS have allowed groundbreaking experiments to be conducted. These include: (1) phase transformations in the Mg-Si-O system at mantle conditions; (2) structure of hydrated a-Al2O3 surfaces; (3) alloying properties of silicon in the Earth's core; (4) dynamics of iron-rich melt segregation from silicates during core formation; (5) electronic spin state of FeO at high pressure and temperature; (6) elastic wave velocities of mantle minerals at lower mantle conditions; (7) copper partitioning and speciation in natural hydrothermal fluids; and (8) mechanisms of arsenic sequestration at a Superfund site. The GSECARS mission is to provide a research environment where users receive expert assistance in planning and conducting experiments, and in analyzing data. The facility operation is funded by the NSF EAR Instrumentation and Facilities program and the DOE Geosciences program. Major instrumentation was also provided by the W.M. Keck Foundation. Information and applications for beam time can be found at http://gsecars.org.

Electrochemical reaction mechanisms under various charge-discharge operating conditions for Li1.2Ni0.13Mn0.54Co0.13O2 in a lithium-ion battery

NASA Astrophysics Data System (ADS)

Konishi, Hiroaki; Hirano, Tatsumi; Takamatsu, Daiko; Gunji, Akira; Feng, Xiaoliang; Furutsuki, Sho; Okumura, Takefumi; Terada, Shohei; Tamura, Kazuhisa

2018-06-01

The potential in each state of charge (SOC) during charging of Li1.2Ni0.13Mn0.54Co0.13O2 is higher than that during discharging. In other words, the potential hysteresis occurs between charging and discharging. Furthermore, the potential in each SOC changes according to the charge-discharge operating conditions, indicating that the charge-discharge reaction mechanism is also affected. To clarify the effect of charge-discharge operating conditions on the electrochemical reaction, Li1.2Ni0.13Mn0.54Co0.13O2 was charged and discharged under various charge-discharge operating ranges, and open-circuit potential (OCP), crystal structure, and oxidation states of the transition metals were evaluated by electrochemical measurement, X-ray diffraction (XRD), and X-ray absorption fine structure (XAFS). These results indicate that OCP, lattice parameters, and oxidation states of the transition metals of Li1.2Ni0.13Mn0.54Co0.13O2 in each SOC are not constant. The XRD results indicate that two phases, namely, LiNi0.33Mn0.33Co0.33O2-like and Li2MnO3-like, exist in Li1.2Ni0.13Mn0.54Co0.13O2. For the LiNi0.33Mn0.33Co0.33O2-like phase, the relationship between OCP, lattice parameters, and oxidation states of the transition metals in each SOC is not affected by the charge-discharge operating conditions, indicating that extraction and insertion of lithium ions for the LiNi0.33Mn0.33Co0.33O2-like phase progresses at almost the same potential. Although the extraction and insertion of lithium ions for the Li2MnO3-like phase progresses at almost the same potential in the low-SOC region, the OCP and lattice parameter in each SOC in the high-SOC region are not constant. Therefore, the extraction of lithium ions from the Li2MnO3-like phase in the high-SOC region causes the potential hysteresis of Li1.2Ni0.13Mn0.54Co0.13O2.

An Action-Based Fine-Grained Access Control Mechanism for Structured Documents and Its Application

PubMed Central

Su, Mang; Li, Fenghua; Tang, Zhi; Yu, Yinyan; Zhou, Bo

2014-01-01

This paper presents an action-based fine-grained access control mechanism for structured documents. Firstly, we define a describing model for structured documents and analyze the application scenarios. The describing model could support the permission management on chapters, pages, sections, words, and pictures of structured documents. Secondly, based on the action-based access control (ABAC) model, we propose a fine-grained control protocol for structured documents by introducing temporal state and environmental state. The protocol covering different stages from document creation, to permission specification and usage control are given by using the Z-notation. Finally, we give the implementation of our mechanism and make the comparisons between the existing methods and our mechanism. The result shows that our mechanism could provide the better solution of fine-grained access control for structured documents in complicated networks. Moreover, it is more flexible and practical. PMID:25136651

An action-based fine-grained access control mechanism for structured documents and its application.

PubMed

Su, Mang; Li, Fenghua; Tang, Zhi; Yu, Yinyan; Zhou, Bo

2014-01-01

This paper presents an action-based fine-grained access control mechanism for structured documents. Firstly, we define a describing model for structured documents and analyze the application scenarios. The describing model could support the permission management on chapters, pages, sections, words, and pictures of structured documents. Secondly, based on the action-based access control (ABAC) model, we propose a fine-grained control protocol for structured documents by introducing temporal state and environmental state. The protocol covering different stages from document creation, to permission specification and usage control are given by using the Z-notation. Finally, we give the implementation of our mechanism and make the comparisons between the existing methods and our mechanism. The result shows that our mechanism could provide the better solution of fine-grained access control for structured documents in complicated networks. Moreover, it is more flexible and practical.

InAs Band-Edge Exciton Fine Structure

DTIC Science & Technology

2015-07-29

Chapter 1 InAs Band-Edge Exciton Fine Structure 1.1 Contributions This work was carried out in collaboration with Oscar Sandoval, a summer student at...diffusion,1,2 charg- ing,2,3 and excitonic fine structure.1,3–9 While spectral diffusion and charging are most likely photoinduced effects and thus can be...unavoidable. A complete understanding of the excitonic 1 Distribution A: Public Release energy landscape enables us to determine dephasing rates

Atomic sulfur: Frequency measurement of the J = 0 left arrow 1 fine-structure transition at 56.3 microns by laser magnetic resonance

NASA Technical Reports Server (NTRS)

Brown, John M.; Evenson, Kenneth M.; Zink, Lyndon R.

1994-01-01

The J = 0 left arrow 1 fine-structure transition in atomic sulfur (S I) in its ground (3)P state has been detected in the laboratory by far-infrared laser magnetic resonance. The fine-structure interval has been measured accurately as 5,322,492.9 +/- 2.8 MHz which corresponds to a wavelength of 56.325572 +/- 0.000030 micrometers.

Fine reservoir structure modeling based upon 3D visualized stratigraphic correlation between horizontal wells: methodology and its application

NASA Astrophysics Data System (ADS)

Chenghua, Ou; Chaochun, Li; Siyuan, Huang; Sheng, James J.; Yuan, Xu

2017-12-01

As the platform-based horizontal well production mode has been widely applied in petroleum industry, building a reliable fine reservoir structure model by using horizontal well stratigraphic correlation has become very important. Horizontal wells usually extend between the upper and bottom boundaries of the target formation, with limited penetration points. Using these limited penetration points to conduct well deviation correction means the formation depth information obtained is not accurate, which makes it hard to build a fine structure model. In order to solve this problem, a method of fine reservoir structure modeling, based on 3D visualized stratigraphic correlation among horizontal wells, is proposed. This method can increase the accuracy when estimating the depth of the penetration points, and can also effectively predict the top and bottom interfaces in the horizontal penetrating section. Moreover, this method will greatly increase not only the number of points of depth data available, but also the accuracy of these data, which achieves the goal of building a reliable fine reservoir structure model by using the stratigraphic correlation among horizontal wells. Using this method, four 3D fine structure layer models have been successfully built of a specimen shale gas field with platform-based horizontal well production mode. The shale gas field is located to the east of Sichuan Basin, China; the successful application of the method has proven its feasibility and reliability.

Fine-structure-resolution for Rovibrational Excitation of CN Due to H2

NASA Astrophysics Data System (ADS)

Byrd, Nat; Yang, Benhui H.; Stancil, Phillip C.

2018-06-01

Diatomic molecules can be readily excited in interstellar environments exposed to intense UV radiation, such as the inner rim of a protoplanetary disk. Non-thermal populations of excited rovibrational levels can result, for example, following decay from electronically excited states to the electronic ground state. Competition between radiative decay and collisional processes, mostly due to H2, determine the resulting rovibrational emission spectrum. For CN, and other open-shell molecules, the resulting spectrum will be complicated due to fine-structure splitting of the rotational levels. In some cases, fine-structure resolution has been previously computed for rotational transitions in atom- or diatom-diatom collisional processes. Here we present the first fine-structure resolution for vibrational deexcitation for CN colliding with H2. The collisional cross sections were computed using a 6D potential energy surface with a full close-coupling approach. Fine-structure resolution is obtained by adopting an angular momentum recoupling scheme to transform the scattering matrices to a recoupled basis. Here we present low-energy calculations for the v=1 to 0 transition.This work was supported by NASA Grant NNX16AF09G.

The impact of cochlear fine structure on hearing thresholds and DPOAE levels

NASA Astrophysics Data System (ADS)

Lee, Jungmee; Long, Glenis; Talmadge, Carrick L.

2004-05-01

Although otoacoustic emissions (OAE) are used as clinical and research tools, the correlation between OAE behavioral estimates of hearing status is not large. In normal-hearing individuals, the level of OAEs can vary as much as 30 dB when the frequency is changed less than 5%. These pseudoperiodic variations of OAE level with frequency are known as fine structure. Hearing thresholds measured with high-frequency resolution reveals a similar (up to 15 dB) fine structure. We examine the impact of OAE and threshold fine structures on the prediction of auditory thresholds from OAE levels. Distortion product otoacoustic emissions (DPOAEs) were measured with sweeping primary tones. Psychoacoustic detection thresholds were measured using pure tones, sweep tones, FM tones, and narrow-band noise. Sweep DPOAE and narrow-band threshold estimates provide estimates that are less influenced by cochlear fine structure and should lead to a higher correlation between OAE levels and psychoacoustic thresholds. [Research supported by PSC CUNY, NIDCD, National Institute on Disability and Rehabilitation Research in U.S. Department of Education, and The Ministry of Education in Korea.

GEMMs shine a light on resistance to androgen deprivation therapy for prostate cancer.

PubMed

Karantanos, Theodoros; Thompson, Timothy C

2013-07-08

Androgen deprivation therapy (ADT) for advanced prostate cancer inexorably leads to resistance, and clinically useful biomarkers are lacking. The value of genetically engineered mice for coclinical studies is clearly demonstrated in a recent publication that reveals XAF1, XIAP, and SRD5A1 as novel predictive biomarkers and therapeutic targets for ADT resistance. Copyright © 2013 Elsevier Inc. All rights reserved.

XAFS studies of nickel and sulfur speciation in residual oil fly-ash particulate matters (ROFA PM).

PubMed

Pattanaik, Sidhartha; Huggins, Frank E; Huffman, Gerald P; Linak, William P; Miller, C Andrew

2007-02-15

XAFS spectroscopy has been employed to evaluate the effect of fuel compositions and combustion conditions on the amount, form, and distribution of sulfur and nickel in size-fractionated ROFA PM. Analysis of S K-edge XANES establish that sulfate is abundant in all PM. However, depending upon the combustion conditions, lesser amounts of thiophenic sulfur, metal sulfide, and elemental sulfur may also be observed. Least-squares fitting of Ni K-edge XANES reveals that most of the nickel in PM is present as bioavailable NiSO4.nH2O. The insoluble Ni mainly exists as a minor species, as nickel ferrite in PM2.5 (PM < 2.5 microm) and nickel sulfide, Ni(x)SY(y) in PM2.5+ (PM > 2.5 microm). The Ni K-edge XANES results are in agreement with the EXAFS data. Such detailed speciation of Ni and S in PM is needed for determining their mobility, bioavailability, and reactivity, and hence, their role in PM toxicity. This information is also important for understanding the mechanism of PM formation, developing effective remediation measures, and providing criteria for identification of potential emission sources. Transition metals complexing with sulfur is ubiquitous in nature. Therefore, this information on metal sulfur complex can be critical to a large body of environmental literature.

CONSTRAINTS ON SPATIAL VARIATIONS IN THE FINE-STRUCTURE CONSTANT FROM PLANCK

DOE Office of Scientific and Technical Information (OSTI.GOV)

O'Bryan, Jon; Smidt, Joseph; De Bernardis, Francesco

2015-01-01

We use the cosmic microwave background (CMB) anisotropy data from Planck to constrain the spatial fluctuations of the fine-structure constant α at a redshift of 1100. We use a quadratic estimator to measure the four-point correlation function of the CMB temperature anisotropies and extract the angular power spectrum fine-structure constant spatial variations projected along the line of sight at the last scattering surface. At tens of degree angular scales and above, we constrain the fractional rms fluctuations of the fine-structure constant to be (δα/α){sub rms} < 3.4 × 10{sup –3} at the 68% confidence level. We find no evidence formore » a spatially varying α at a redshift of 10{sup 3}.« less

Spectral structure and stability studies on microstructure-fiber continuum

NASA Astrophysics Data System (ADS)

Gu, Xun; Kimmel, Mark; Zeek, Erik; Shreenath, Aparna P.; Trebino, Rick P.; Windeler, Robert S.

2003-07-01

Although previous direct measurements of the microstructure-fiber continuum have all showed a smooth and stable spectrum, our cross-correlation frequency-resolved optical gating (XFROG) full-intensity-and-phase characterization of the continuum pulse, utilizing sum-frequency-generation with a pre-characterized reference pulse and the angle-dithered-crystal technique, indicates that fine-scale spectral structure exists on a single-shot basis, contrary to previous observations. In particular, deep and fine oscillations are found in the retrieved spectrum, and the retrieved trace contains a "measles" pattern, whereas the measured trace and the independently-measured spectrum are rather smooth. The discrepancy is shown to be the result of unstable single-shot spectral structure. Although the XFROG measurement is not able to directly measure the single-shot fine structure in the trace, the redundancy of information in FROG traces enables the retrieval algorithm to correctly recognize the existence of the spectral fine structure, and restore the structure in the retrieved trace and spectrum. Numerical simulations have supported our hypothesis, and we directly observed the fine spectral structure in single-shot measurements of the continuum spectrum and the structure was seen to be highly unstable, the continuum spectrum appearing smooth only when many shots are averaged. Despite the structure and instability in the continuum spectrum, coherence experiments also reveal that the spectral phase is rather stable, being able to produce well-defined spectral fringes across the entire continuum bandwidth.

Fine structural dependence of ultraviolet reflections in the King Penguin beak horn.

PubMed

Dresp, Birgitta; Langley, Keith

2006-03-01

The visual perception of many birds extends into the near-ultraviolet (UV) spectrum and ultraviolet is used by some to communicate. The beak horn of the King Penguin (Aptenodytes patagonicus) intensely reflects in the ultraviolet and this appears to be implicated in partner choice. In a preliminary study, we recently demonstrated that this ultraviolet reflectance has a structural basis, resulting from crystal-like photonic structures, capable of reflecting in the near-UV. The present study attempted to define the origin of the photonic elements that produce the UV reflectance and to better understand how the UV signal is optimized by their fine structure. Using light and electron microscopic analysis combined with new spectrophotometric data, we describe here in detail the fine structure of the entire King Penguin beak horn in addition to that of its photonic crystals. The data obtained reveal a one-dimensional structural periodicity within this tissue and demonstrate a direct relationship between its fine structure and its function. In addition, they suggest how the photonic structures are produced and how they are stabilized. The measured lattice dimensions of the photonic crystals, together with morphological data on its composition, permit predictions of the wavelength of reflected light. These correlate well with experimentally observed values. The way the UV signal is optimized by the fine structure of the beak tissue is discussed with regard to its putative biological role.

Spin fine structure of optically excited quantum dot molecules

NASA Astrophysics Data System (ADS)

Scheibner, M.; Doty, M. F.; Ponomarev, I. V.; Bracker, A. S.; Stinaff, E. A.; Korenev, V. L.; Reinecke, T. L.; Gammon, D.

2007-06-01

The interaction between spins in coupled quantum dots is revealed in distinct fine structure patterns in the measured optical spectra of InAs/GaAs double quantum dot molecules containing zero, one, or two excess holes. The fine structure is explained well in terms of a uniquely molecular interplay of spin-exchange interactions, Pauli exclusion, and orbital tunneling. This knowledge is critical for converting quantum dot molecule tunneling into a means of optically coupling not just orbitals but also spins.

Congenital amusia: a cognitive disorder limited to resolved harmonics and with no peripheral basis.

PubMed

Cousineau, Marion; Oxenham, Andrew J; Peretz, Isabelle

2015-01-01

Pitch plays a fundamental role in audition, from speech and music perception to auditory scene analysis. Congenital amusia is a neurogenetic disorder that appears to affect primarily pitch and melody perception. Pitch is normally conveyed by the spectro-temporal fine structure of low harmonics, but some pitch information is available in the temporal envelope produced by the interactions of higher harmonics. Using 10 amusic subjects and 10 matched controls, we tested the hypothesis that amusics suffer exclusively from impaired processing of spectro-temporal fine structure. We also tested whether the inability of amusics to process acoustic temporal fine structure extends beyond pitch by measuring sensitivity to interaural time differences, which also rely on temporal fine structure. Further tests were carried out on basic intensity and spectral resolution. As expected, pitch perception based on spectro-temporal fine structure was impaired in amusics; however, no significant deficits were observed in amusics' ability to perceive the pitch conveyed via temporal-envelope cues. Sensitivity to interaural time differences was also not significantly different between the amusic and control groups, ruling out deficits in the peripheral coding of temporal fine structure. Finally, no significant differences in intensity or spectral resolution were found between the amusic and control groups. The results demonstrate a pitch-specific deficit in fine spectro-temporal information processing in amusia that seems unrelated to temporal or spectral coding in the auditory periphery. These results are consistent with the view that there are distinct mechanisms dedicated to processing resolved and unresolved harmonics in the general population, the former being altered in congenital amusia while the latter is spared. Copyright © 2014 Elsevier Ltd. All rights reserved.

[Fine stereo structure for natural organic molecules, a preliminary study. II. Melting point influenced by structure factors].

PubMed

Lu, Y; Zheng, Q; Lu, D; Ma, P; Chen, Y

1995-06-01

Crystal structures of two compounds from Tripterygium wilfordii Hook f. have been determined by X-ray diffraction method. Structure factors influencing melting point of solid state have been analysed. Crystal class (or space group), recrystallization solvent, force between molecules and fine changes of molecular structures will all cause melting point changes of crystal substance.

Laser marking on soda-lime glass by laser-induced backside wet etching with two-beam interference

NASA Astrophysics Data System (ADS)

Nakazumi, Tomoka; Sato, Tadatake; Narazaki, Aiko; Niino, Hiroyuki

2016-09-01

For crack-free marking of glass materials, a beam-scanning laser-induced backside wet etching (LIBWE) process by a beam spot with a fine periodic structure was examined. The fine periodic structure was produced within a beam spot by means of a Mach-Zehnder interferometer incorporated to the optical setup for the beam-scanning LIBWE. A fine structure with a period of 9 µm was observed within the microstructures with a diameter of ca. 40 µm fabricated by a laser shot under double-beam irradiation, and they could be homogeneously fabricated within an area of 800  ×  800 µm. The area filled with the microstructures, including fine periodic structures, could be observed in high contrast under a diffuse, on-axis illumination that was used in commercial QR code readers.

3D WHOLE-PROMINENCE FINE STRUCTURE MODELING

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gunár, Stanislav; Mackay, Duncan H.

2015-04-20

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

Fate of Zinc Oxide Nanoparticles Coated onto Macronutrient Fertilizers in an Alkaline Calcareous Soil

PubMed Central

Milani, Narges; Hettiarachchi, Ganga M.; Kirby, Jason K.; Beak, Douglas G.; Stacey, Samuel P.; McLaughlin, Mike J.

2015-01-01

Zinc oxide (ZnO) nanoparticles may provide a more soluble and plant available source of Zn in Zn fertilizers due to their greater reactivity compared to equivalent micron- or millimetre-sized (bulk) particles. However, the effect of soil on solubility, spatial distribution and speciation of ZnO nanoparticles has not yet been investigated. In this study, we examined the diffusion and solid phase speciation of Zn in an alkaline calcareous soil following application of nanoparticulate and bulk ZnO coated fertilizer products (monoammonium phosphate (MAP) and urea) using laboratory-based x-ray techniques and synchrotron-based μ-x-ray fluorescence (μ–XRF) mapping and absorption fine structure spectroscopy (μ–XAFS). Mapping of the soil-fertilizer reaction zones revealed that most of the applied Zn for all treatments remained on the coated fertilizer granule or close to the point of application after five weeks of incubation in soil. Zinc precipitated mainly as scholzite (CaZn2(PO4)2.2H2O) and zinc ammonium phosphate (Zn(NH4)PO4) species at the surface of MAP granules. These reactions reduced dissolution and diffusion of Zn from the MAP granules. Although Zn remained as zincite (ZnO) at the surface of urea granules, limited diffusion of Zn from ZnO-coated urea granules was also observed for both bulk and nanoparticulate ZnO treatments. This might be due to either the high pH of urea granules, which reduced solubility of Zn, or aggregation (due to high ionic strength) of released ZnO nanoparticles around the granule/point of application. The relative proportion of Zn(OH)2 and ZnCO3 species increased for all Zn treatments with increasing distance from coated MAP and urea granules in the calcareous soil. When coated on macronutrient fertilizers, Zn from ZnO nanoparticles (without surface modifiers) was not more mobile or diffusible compared to bulk forms of ZnO. The results also suggest that risk associated with the presence of ZnO NPs in calcareous soils would be the same as bulk sources of ZnO. PMID:25965385

Impact of zeolite aging in hot liquid water on activity for acid-catalyzed dehydration of alcohols

DOE Office of Scientific and Technical Information (OSTI.GOV)

Vjunov, Aleksei; Derewinski, Miroslaw A.; Fulton, John L.

The catalytic performance of zeolite in aqueous medium depends on a multitude of factors, such as the concentration and distribution of active sites and framework integrity. Al K–edge extended X–ray absorption fine structure and 27Al MAS NMR spectroscopies in combination with DFT calculations are used to determine the distribution of tetrahedral Al sites both qualitatively and quantitatively for both parent and 48 h 160 ºC water treated HBEA catalysts. There is no evidence of Al coordination modification after aging in water. The distribution and concentration of Al T–sites, active centers for the dehydration of cyclohexanol, do not markedly impact themore » catalytic performance in water, because the Brønsted acidic protons are present in the form of hydrated hydronium ions and thus have very similar acid properties. The results suggest that all Brønsted acid sites are equally active in aqueous medium. The decrease of zeolite catalytic performance after water treatment is attributed to the reduced concentration of Brønsted acid sites. Increasing the stability of pore walls and decreasing the rate of Si–O–Si group hydrolysis may result in improved apparent zeolite catalytic performance in aqueous medium. Authors thank B. W. Arey (PNNL) for HIM measurements, T. Huthwelker for support during Al XAFS measurements at the Swiss Light Source (PSI, Switzerland), J. Z. Hu and S. D. Burton (PNNL) for support during NMR experiments. This work was supported by the U. S. Department of Energy (DOE), Office of Science, Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences & Biosciences. MD acknowledges support by the Materials Synthesis and Simulation Across Scales (MS3 Initiative) conducted under Laboratory Directed Research & Development Program at PNNL. HIM imaging and NMR experiments were performed at the Environmental Molecular Sciences Laboratory, a national scientific user facility sponsored by the DOE Office of Science, Office of Biological and Environmental Research, located at Pacific Northwest National Laboratory (PNNL). PNNL is a multiprogram national laboratory operated for the DOE by Battelle Memorial Institute under contract # DE-AC05-76RL0-1830« less

[Ultraviolet spectroscopic study on the fine structures in the solar polar hole].

PubMed

Zhang, Min; Wang, Dong; Liu, Guo-Hong

2014-07-01

Fine structures in the south solar polar coronal hole were observed by N IV line of SOHO/SUMER spectrograph. The scales of the fine structures range spatially range from 1 arcsec to several arcsecs, temporally from 1 min to several minutes, and parts of them are in strip shape along the slit direction. The line-of-sight velocity of them is up to tens of km x s(-1) with red and blue shift intercrossed occasionally, which appear periodically as long as 100 minutes in some regions. Part of the fine structures can be clearly observed at the Ne V III line with higher formation temperature in the same spectral window. The time and location of some fine structures with high velocity in the Ne V III spectrum are almost the same as that in N IV spectrum, but they are extended and diffused in the Ne V III spectrum. Some fine structures have non-Gaussian profiles with the line-of-sight Doppler velocities up to 150 km x s(-1) in the N IV blue/red wings, which is similar with the explosive events in the transition region. In the past, explosive events are small-scale dynamic phenomena often observed in the quiet-sun (QS) region, while their properties in coronal holes (CHs) remain unclear. Here, we find the EE-like events with strong dynamics in the south solar polar coronal hole by N IV line of SOHO/SUMER spectrograph.

Detailed transient heme structures of Mb-CO in solution after CO dissociation: an X-ray transient absorption spectroscopic study.

PubMed

Stickrath, Andrew B; Mara, Michael W; Lockard, Jenny V; Harpham, Michael R; Huang, Jier; Zhang, Xiaoyi; Attenkofer, Klaus; Chen, Lin X

2013-04-25

Although understanding the structural dynamics associated with ligand photodissociation is necessary in order to correlate structure and function in biological systems, few techniques are capable of measuring the ultrafast dynamics of these systems in solution-phase at room temperature. We present here a detailed X-ray transient absorption (XTA) study of the photodissociation of CO-bound myoglobin (Fe(II)CO-Mb) in room-temperature aqueous buffer solution with a time resolution of 80 ps, along with a general procedure for handling biological samples under the harsh experimental conditions that transient X-ray experiments entail. The XTA spectra of (Fe(II)CO-Mb) exhibit significant XANES and XAFS alterations following 527 nm excitation, which remain unchanged for >47 μs. These spectral changes indicate loss of the CO ligand, resulting in a five-coordinate, domed heme, and significant energetic reorganization of the 3d orbitals of the Fe center. With the current experimental setup, each X-ray pulse in the pulse train, separated by ~153 ns, can be separately discriminated, yielding snapshots of the myoglobin evolution over time. These methods can be easily applied to other biological systems, allowing for simultaneous structural and electronic measurements of any biological system with both ultrafast and slow time resolutions, effectively mapping out all of the samples' relevant physiological processes.

Variations in Grain-Scale Sediment Structure in a Gravel-Bed Channel as a Function of Fine Sediment Content and Morphological Location

NASA Astrophysics Data System (ADS)

Voepel, H.; Ahmed, S. I.; Hodge, R. A.; Leyland, J.; Sear, D. A.

2016-12-01

One of the major causes of uncertainty in estimates of bedload transport rates in gravel bed rivers is a lack of understanding of grain-scale sediment structure, and the impact that this structure has on bed stability. Furthermore, grain-scale structure varies throughout a channel and over time in ways that have not been fully quantified. Our research aims to quantify variations in sediment structure caused by two key variables; morphological location within a riffle-pool sequence (reflecting variation in hydraulic conditions), and the fine sediment content of the gravel bed (sand and clay). We report results from a series of flume experiments in which we water-worked a gravel bed with a riffle-pool morphology. The fine sediment content of the bed was incrementally increased over a series of runs from gravel only, to coarse sand, fine sand and two concentrations of clay. After each experimental run intact samples of the bed at different locations were extracted and the internal structure of the bed was measured using non-destructive, micro-focus X-ray computed tomography (CT) imaging. The CT images were processed to measure the properties of individual grains, including volume, center of mass, dimension, and contact points. From these data we were able to quantify the sediment structure through metrics including measurement of grain pivot angles, grain exposure and protrusion, and vertical variation in bed porosity and fine sediment content. Metrics derived from the CT data were verified using data from grain counts and tilt-table measurements on co-located samples. Comparison of the metrics across different morphological locations and fine sediment content demonstrates how these factors affect the bed structure. These results have implications for the development of sediment entrainment models for gravel bed rivers.

Fine Structure of Anomalously Intense Pulses of PSR J0814+7429 Radio Emission in the Decameter Range

NASA Astrophysics Data System (ADS)

Skoryk, A. O.; Ulyanov, O. M.; Zakharenko, V. V.; Shevtsova, A. I.; Vasylieva, I. Y.; Plakhov, M. S.; Kravtsov, I. M.

2017-06-01

Purpose: The fine structure of the anomalously intense pulses of PSR J0814+7429 (B0809+74) has been studied. The pulsar radio emission fine structure is investigated to determine its parameters in the lowest part of spectrum available for groundbased observations. Design/methodology/approach: The scattering measure in the interstellar plasma have been estimated using the spectral and correlation analyses of pulsar data recorded by the UTR-2 radio telescope. Results: Two characteristic time scales of the anomalously intense pulses fine structure of the PSR J0814+7429 radio emission have been found. The strongest pulses of this pulsar in the decameter range can have a duration of about t 2÷3 ms. These pulses are emitted in short series. In some cases, they are emitted over the low-intensity plateau consisting of the “long” subpulse component. Conclusions: The narrowest correlation scale of pulsar J0814+7429 radio emission corresponds to the doubled scattering time constant of the interstellar medium impulse response. Broader scale of the fine structure of its radio emission can be explained by the radiation of a short series of narrow pulses or relatively broad pulses inside this pulsar magnetosphere.

Chimaeric sounds reveal dichotomies in auditory perception

PubMed Central

Smith, Zachary M.; Delgutte, Bertrand; Oxenham, Andrew J.

2008-01-01

By Fourier's theorem1, signals can be decomposed into a sum of sinusoids of different frequencies. This is especially relevant for hearing, because the inner ear performs a form of mechanical Fourier transform by mapping frequencies along the length of the cochlear partition. An alternative signal decomposition, originated by Hilbert2, is to factor a signal into the product of a slowly varying envelope and a rapidly varying fine time structure. Neurons in the auditory brainstem3–6 sensitive to these features have been found in mammalian physiological studies. To investigate the relative perceptual importance of envelope and fine structure, we synthesized stimuli that we call ‘auditory chimaeras’, which have the envelope of one sound and the fine structure of another. Here we show that the envelope is most important for speech reception, and the fine structure is most important for pitch perception and sound localization. When the two features are in conflict, the sound of speech is heard at a location determined by the fine structure, but the words are identified according to the envelope. This finding reveals a possible acoustic basis for the hypothesized ‘what’ and ‘where’ pathways in the auditory cortex7–10. PMID:11882898

The Effect of Quantum-Mechanical Interference on Precise Measurements of the n = 2 Triplet P Fine Structure of Helium

DOE Office of Scientific and Technical Information (OSTI.GOV)

Marsman, A.; Horbatsch, M.; Hessels, E. A., E-mail: hessels@yorku.ca

2015-09-15

For many decades, improvements in both theory and experiment of the fine structure of the n = 2 triplet P levels of helium have allowed for an increasingly precise determination of the fine-structure constant. Recently, it has been observed that quantum-mechanical interference between neighboring resonances can cause significant shifts, even if such neighboring resonances are separated by thousands of natural widths. The shifts depend in detail on the experimental method used for the measurement, as well as the specific experimental parameters employed. Here, we review how these shifts apply for the most precise measurements of the helium 2{sup 3}P fine-structuremore » intervals.« less

Sample-based synthesis of two-scale structures with anisotropy

DOE PAGES

Liu, Xingchen; Shapiro, Vadim

2017-05-19

A vast majority of natural or synthetic materials are characterized by their anisotropic properties, such as stiffness. Such anisotropy is effected by the spatial distribution of the fine-scale structure and/or anisotropy of the constituent phases at a finer scale. In design, proper control of the anisotropy may greatly enhance the efficiency and performance of synthesized structures. In this paper, we propose a sample-based two-scale structure synthesis approach that explicitly controls anisotropic effective material properties of the structure on the coarse scale by orienting sampled material neighborhoods at the fine scale. We first characterize the non-uniform orientations distribution of the samplemore » structure by showing that the principal axes of an orthotropic material may be determined by the eigenvalue decomposition of its effective stiffness tensor. Such effective stiffness tensors can be efficiently estimated based on the two-point correlation functions of the fine-scale structures. Then we synthesize the two-scale structure by rotating fine-scale structures from the sample to follow a given target orientation field. Finally, the effectiveness of the proposed approach is demonstrated through examples in both 2D and 3D.« less

Sample-based synthesis of two-scale structures with anisotropy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, Xingchen; Shapiro, Vadim

A vast majority of natural or synthetic materials are characterized by their anisotropic properties, such as stiffness. Such anisotropy is effected by the spatial distribution of the fine-scale structure and/or anisotropy of the constituent phases at a finer scale. In design, proper control of the anisotropy may greatly enhance the efficiency and performance of synthesized structures. In this paper, we propose a sample-based two-scale structure synthesis approach that explicitly controls anisotropic effective material properties of the structure on the coarse scale by orienting sampled material neighborhoods at the fine scale. We first characterize the non-uniform orientations distribution of the samplemore » structure by showing that the principal axes of an orthotropic material may be determined by the eigenvalue decomposition of its effective stiffness tensor. Such effective stiffness tensors can be efficiently estimated based on the two-point correlation functions of the fine-scale structures. Then we synthesize the two-scale structure by rotating fine-scale structures from the sample to follow a given target orientation field. Finally, the effectiveness of the proposed approach is demonstrated through examples in both 2D and 3D.« less

Coupling fine-scale root and canopy structure using ground-based remote sensing

Treesearch

Brady Hardiman; Christopher Gough; John Butnor; Gil Bohrer; Matteo Detto; Peter Curtis

2017-01-01

Ecosystem physical structure, defined by the quantity and spatial distribution of biomass, influences a range of ecosystem functions. Remote sensing tools permit the non-destructive characterization of canopy and root features, potentially providing opportunities to link above- and belowground structure at fine spatial resolution in...

Formation of fine {gamma} grain structure through fine {alpha}{sub 2}/{gamma} lamellar structure in Ti-rich TiAl alloy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kumagai, T.; Abe, E.; Nakamura, M.

1997-12-31

Microstructural development of an extremely fine {alpha}{sub 2}-Ti{sub 32}Al/{gamma}-TiAl lamellar structure, which was formed by ice water quenching after solution-treatment in a high-temperature {alpha}-Ti phase field for a long period of time, was examined during isothermal treatment. In an as-quenched Ti-48at.%Al alloy, the massively transformed {gamma} ({gamma}{sub m}) and untransformed (meaning massively untransformed) fine {alpha}{sub 2}/{gamma} lamellar regions were observed. Fine {gamma} grains, which were similar to {gamma}{sub m}, were generated both within the fine {alpha}{sub 2}/{gamma} lamellae and at the boundary area between the {gamma}{sub m} and the fine {alpha}{sub 2}/{gamma} lamellar regions by aging at low-temperature (1,173 K)more » for a short time (180s). Further aging (1.8ks) caused the coarsening of these newly generated fine {gamma} grains. On the other hand, the coarsening of the {gamma} grains occurred by a high-temperature (1,323 K) aging treatment even for 180s. Fine {alpha}{sub 2} plates and particles, which were aligned to a particular direction, were observed in the {gamma} grain interiors, indicating that the newly generated {gamma} grains grew at the expense of the fine {alpha}{sub 2}/{gamma} lamellae. It can be considered that the {gamma} grain formation through the fine {alpha}{sub 2}/{gamma} lamellae is closely related to the {alpha}{sub 2}{yields}{gamma} reaction of the {alpha}{sub 2} plates sandwiched by the {gamma} plates, and needs the fast heating rate enough to overcome the {alpha}{sub 2}/{gamma}{yields}{gamma}/{gamma} lamellae reaction.« less

Fine Structure of Trious and Excitons in Single GaAs Quantum Dots

DTIC Science & Technology

2002-08-30

RAPID COMMUNICATIONS PHYSICAL REVIEW B 66, 081310~R! ~2002!Fine structure of trions and excitons in single GaAs quantum dots J. G. Tischler, A. S ...fine structure of single localized excitons and trions. DOI: 10.1103/PhysRevB.66.081310 PACS number~ s !: 78.67.Hc, 73.21.2b, 71.35.2yAlthough the...AUTHOR( S ) 5d. PROJECT NUMBER 5e. TASK NUMBER 5f. WORK UNIT NUMBER 7. PERFORMING ORGANIZATION NAME( S ) AND ADDRESS(ES) Naval Research Laboratory

Noble-transition metal nanoparticle breathing in a reactive gas atmosphere.

PubMed

Petkov, Valeri; Shan, Shiyao; Chupas, Peter; Yin, Jun; Yang, Lefu; Luo, Jin; Zhong, Chuan-Jian

2013-08-21

In situ high-energy X-ray diffraction coupled to atomic pair distribution function analysis is used to obtain fundamental insight into the effect of the reactive gas environment on the atomic-scale structure of metallic particles less than 10 nm in size. To substantiate our recent discovery we investigate a wide range of noble-transition metal nanoparticles and confirm that they expand and contract radially when treated in oxidizing (O2) and reducing (H2) atmospheres, respectively. The results are confirmed by supplementary XAFS experiments. Using computer simulations guided by the experimental diffraction data we quantify the effect in terms of both relative lattice strain and absolute atomic displacements. In particular, we show that the effect leads to a small percent of extra surface strain corresponding to several tenths of Ångström displacements of the atoms at the outmost layer of the particles. The effect then gradually decays to zero within 4 atomic layers inside the particles. We also show that, reminiscent of a breathing type structural transformation, the effect is reproducible and reversible. We argue that because of its significance and widespread occurrence the effect should be taken into account in nanoparticle research.

Monte Carlo Simulations of Electron Energy-Loss Spectra with the Addition of Fine Structure from Density Functional Theory Calculations.

PubMed

Attarian Shandiz, Mohammad; Guinel, Maxime J-F; Ahmadi, Majid; Gauvin, Raynald

2016-02-01

A new approach is presented to introduce the fine structure of core-loss excitations into the electron energy-loss spectra of ionization edges by Monte Carlo simulations based on an optical oscillator model. The optical oscillator strength is refined using the calculated electron energy-loss near-edge structure by density functional theory calculations. This approach can predict the effects of multiple scattering and thickness on the fine structure of ionization edges. In addition, effects of the fitting range for background removal and the integration range under the ionization edge on signal-to-noise ratio are investigated.

Influence of Carbon interstitials to Ti1-xMexN (Me = Zr, Al, Cr) coatings by pulsed laser ablation on wear resistance

NASA Astrophysics Data System (ADS)

Jeon, Seol; Hong, Eunpyo; Kwon, Se-Hun; Lee, Heesoo

2018-06-01

The wear resistance of Ti1-xMexN (Me = Zr, Al, Cr) coatings by the laser carburization process was investigated in terms of local atomic structural changes. The repeated pulsed laser ablation was performed to the Ti1-xMexN coating surfaces after Graphite paste was covered. The friction coefficients of the coating specimens were decreased from ∼0.7 to 0.2, and the formation of cracks and debris was suppressed by implementing the laser ablation process. ToF-SIMS depth profiles showed that the laser carburization helps Carbon penetrate into the coating layer as deep as ∼20 nm below its surface. XPS and XAFS analyses revealed that the improvement of the wear resistance of the coatings was achieved not by formation of TiC or ZrC lattices on the coatings surfaces but by Carbon interstitials to the Ti1-xMexN lattices.

XAFS Study of the Ferro- and Antiferromagnetic Binuclear Copper(II) Complexes of Azomethine Based Tridentate Ligands

NASA Astrophysics Data System (ADS)

Vlasenko, Valery G.; Vasilchenko, Igor S.; Pirog, Irina V.; Shestakova, Tatiana E.; Uraev, Ali I.; Burlov, Anatolii S.; Garnovskii, Alexander D.

2007-02-01

Binuclear copper complexes are known to be models for metalloenzymes containing copper active sites, and some of them are of considerable interest due to their magnetic and charge transfer properties. The reactions of the complex formation of bibasic tridentate heterocyclic imines with copper acetate leads to two types of chelates with mono deprotonated ligands and with totally deprotonated ligands. Cu K-edge EXAFS has been applied to determine the local structure around the metal center in copper(II) azomethine complexes with five tridentate ligands: 1-(salycilideneimino)- or 1-(2-tosylaminobenzilideneimino)-2-amino(oxo, thio)benzimidazoles. It has been found that some of the chelates studied are bridged binuclear copper complexes, and others are mononuclear complexes. The copper-copper interatomic distances in the bridged binuclear copper complexes were found to be 2.85-3.01 Å. Variable temperature magnetic susceptibility data indicate the presence of both ferromagnetic and antiferromagnetic interactions within the dimer, the former is dominating at low temperatures and the latter at high temperatures.

On formation mechanism of Pd-Ir bimetallic nanoparticles through thermal decomposition of [Pd(NH3)4][IrCl6

NASA Astrophysics Data System (ADS)

Asanova, Tatyana I.; Asanov, Igor P.; Kim, Min-Gyu; Gerasimov, Evgeny Yu.; Zadesenets, Andrey V.; Plyusnin, Pavel E.; Korenev, Sergey V.

2013-10-01

The formation mechanism of Pd-Ir nanoparticles during thermal decomposition of double complex salt [Pd(NH3)4][IrCl6] has been studied by in situ X-ray absorption (XAFS) and photoelectron (XPS) spectroscopies. The changes in the structure of the Pd and Ir closest to the surroundings and chemical states of Pd, Ir, Cl, and N atoms were traced in the range from room temperature to 420 °C in inert atmosphere. It was established that the thermal decomposition process is carried out in 5 steps. The Pd-Ir nanoparticles are formed in pyramidal/rounded Pd-rich (10-200 nm) and dendrite Ir-rich (10-50 nm) solid solutions. A d charge depletion at Ir site and a gain at Pd, as well as the intra-atomic charge redistribution between the outer d and s and p electrons of both Ir and Pd in Pd-Ir nanoparticles, were found to occur.

How Ag Nanospheres Are Transformed into AgAu Nanocages

DOE Office of Scientific and Technical Information (OSTI.GOV)

Moreau, Liane M.; Schurman, Charles A.; Kewalramani, Sumit

Bimetallic hollow, porous noble metal nanoparticles are of broad interest for biomedical, optical and catalytic applications. The most straightforward method for preparing such structures involves the reaction between HAuCl4 and well-formed Ag particles, typically spheres, cubes, or triangular prisms, yet the mechanism underlying their formation is poorly understood at the atomic scale. By combining in situ nanoscopic and atomic-scale characterization techniques (XAFS, SAXS, XRF, and electron microscopy) to follow the process, we elucidate a plausible reaction pathway for the conversion of citrate-capped Ag nanospheres to AgAu nanocages; importantly, the hollowing event cannot be explained by the nanoscale Kirkendall effect, normore » by Galvanic exchange alone, two processes that have been previously proposed. We propose a modification of the bulk Galvanic exchange process that takes into account considerations that can only occur with nanoscale particles. This nanoscale Galvanic exchange process explains the novel morphological and chemical changes associated with the typically observed hollowing process.« less

A simulation for gravity fine structure recovery from high-low GRAVSAT SST data

NASA Technical Reports Server (NTRS)

Estes, R. H.; Lancaster, E. R.

1976-01-01

Covariance error analysis techniques were applied to investigate estimation strategies for the high-low SST mission for accurate local recovery of gravitational fine structure, considering the aliasing effects of unsolved for parameters. Surface density blocks of 5 deg x 5 deg and 2 1/2 deg x 2 1/2 deg resolution were utilized to represent the high order geopotential with the drag-free GRAVSAT configured in a nearly circular polar orbit at 250 km. altitude. GEOPAUSE and geosynchronous satellites were considered as high relay spacecraft. It is demonstrated that knowledge of gravitational fine structure can be significantly improved at 5 deg x 5 deg resolution using SST data from a high-low configuration with reasonably accurate orbits for the low GRAVSAT. The gravity fine structure recoverability of the high-low SST mission is compared with the low-low configuration and shown to be superior.

Revisiting place and temporal theories of pitch

PubMed Central

2014-01-01

The nature of pitch and its neural coding have been studied for over a century. A popular debate has revolved around the question of whether pitch is coded via “place” cues in the cochlea, or via timing cues in the auditory nerve. In the most recent incarnation of this debate, the role of temporal fine structure has been emphasized in conveying important pitch and speech information, particularly because the lack of temporal fine structure coding in cochlear implants might explain some of the difficulties faced by cochlear implant users in perceiving music and pitch contours in speech. In addition, some studies have postulated that hearing-impaired listeners may have a specific deficit related to processing temporal fine structure. This article reviews some of the recent literature surrounding the debate, and argues that much of the recent evidence suggesting the importance of temporal fine structure processing can also be accounted for using spectral (place) or temporal-envelope cues. PMID:25364292

Usage of Crushed Concrete Fines in Decorative Concrete

NASA Astrophysics Data System (ADS)

Pilipenko, Anton; Bazhenova, Sofia

2017-10-01

The article is devoted to the questions of usage of crushed concrete fines from concrete scrap for the production of high-quality decorative composite materials based on mixed binder. The main problem in the application of crushed concrete in the manufacture of decorative concrete products is extremely low decorative properties of crushed concrete fines itself, as well as concrete products based on them. However, crushed concrete fines could have a positive impact on the structure of the concrete matrix and could improve the environmental and economic characteristics of the concrete products. Dust fraction of crushed concrete fines contains non-hydrated cement grains, which can be opened in screening process due to the low strength of the contact zone between the hydrated and non-hydrated cement. In addition, the screening process could increase activity of the crushed concrete fines, so it can be used as a fine aggregate and filler for concrete mixes. Previous studies have shown that the effect of the usage of the crushed concrete fines is small and does not allow to obtain concrete products with high strength. However, it is possible to improve the efficiency of the crushed concrete fines as a filler due to the complex of measures prior to mixing. Such measures may include a preliminary mechanochemical activation of the binder (cement binder, iron oxide pigment, silica fume and crushed concrete fines), as well as the usage of polycarboxylate superplasticizers. The development of specific surface area of activated crushed concrete fines ensures strong adhesion between grains of binder and filler during the formation of cement stone matrix. The particle size distribution of the crushed concrete fines could achieve the densest structure of cement stone matrix and improve its resistance to environmental effects. The authors examined the mechanisms of structure of concrete products with crushed concrete fines as a filler. The results of studies of the properties of the crushed concrete fines were provided. It is shown that the admixture of the crushed concrete fines has little effect on the colour characteristics of the decorative concrete products. The preferred options to improve the surfaces of decorative concrete are also proposed.

P-polarized reflectance spectroscopy: A high sensitive real-time monitoring technique to study surface kinetics under steady state epitaxial deposition conditions

NASA Technical Reports Server (NTRS)

Dietz, Nikolaus; Bachmann, Klaus J.

1995-01-01

This paper describes the results of real-time optical monitoring of epitaxial growth processes by p-polarized reflectance spectroscopy (PRS) using a single wavelength application under pulsed chemical beam epitaxy (PCBE) condition. The high surface sensitivity of PRS allows the monitoring of submonolayer precursors coverage on the surface as shown for GaP homoepitaxy and GaP on Si heteroepitaxy as examples. In the case of heteroepitaxy, the growth rate and optical properties are revealed by PRS using interference oscillations as they occur during growth. Super-imposed on these interference oscillations, the PRS signal exhibits a fine structure caused by the periodic alteration of the surface chemistry by the pulsed supply of chemical precursors. This fine structure is modeled under conditions where the surface chemistry cycles between phosphorus supersaturated and phosphorus depleted surfaces. The mathematical model describes the fine structure using a surface layer that increases during the tertiarybutyl phosphine (TBP) supply and decreases during and after the triethylgallium (TEG) pulse, which increases the growing GaP film thickness. The imaginary part of the dielectric function of the surface layer is revealed from the turning points in the fine structure, where the optical response to the first precursor pulse in the cycle sequence changes sign. The amplitude of the fine structure is determined by the surface layer thickness and the complex dielectric functions for the surface layer with the underlying bulk film. Surface kinetic data can be obtained by analyzing the rise and decay transients of the fine structure.

Effect of metal complex formation on the potential of organic aerosols as cloud condensation nuclei

NASA Astrophysics Data System (ADS)

Furukawa, T.; Takahashi, Y.

2010-12-01

Secondary organic aerosols (SOA) play a key role on the solar radiation balance in troposphere, since SOA can act as cloud condensation nuclei (CCN) due to its high hygroscopic nature. Oxalic acid is one of the most dominant components of SOA, which has cooling effects of the earth by acting as CCN. However, it is uncertain whether the oxalic acid can exist as free oxalic acid or metal-oxalate complexes in aerosols, even if there is a largedifference in their solubilities into water. Consequently, XAFS measurement was conducted to demonstrate the presence of metal-oxalate complexes. Size fractionated aerosol samples were collected in Tsukuba (located at northeast about 60 km from Tokyo) using a low-volume Andersen-type air sampler. The sampler had eight stages and a back-up filter. The sampling was conducted during winter and summer in 2002. Calcium oxalate was observed in finer particles in each period from Ca K-edge XANES, and its fractions among total Ca were approximately 20%. Similarly,, Zn oxalate was also detected in finer particles from Zn K-edge XANES and EXAFS. The [Zn-oxalate] / [Zn]total ratio in each period clearly increased with the decrease in the particle diameter. This result revealed that Zn-oxalate was formed in the aqueous phase at particle surfaces or in cloud processing. In other words, Zn-oxalate was abundant at the particle surface, resulting from the increase in the [surface]/[bulk] ratio with decreasing particle size. Based on (i) total concentrations of oxalate, Ca, and Zn determined by ion-chromatography and ICP-AES analyses and (ii) Ca- and Zn- oxalate fractions obtained by XAFS, we determined the fraction of metal-oxalate complexes among total oxalate in aerosols. In winter, Ca- and Zn- oxalate fractions reached about 60% of total oxalate in the ranges of 1.1-2.1 μm and 0.65-1.1 μm, while the value was about 60-80% in the same particle size range in summer. On the other hand, Ca- and Zn- oxalates are highly insoluble, showing that the complexes cannot act as CCN. Therefore, the ability of oxalic acid as CCN is needed to be reconsidered, because most of oxalic acid in aerosols exists as metal-oxalate complexes as shown by XAFS spectroscopy in this study.

Thorium partitioning in Greek industrial bauxite investigated by synchrotron radiation and laser-ablation techniques

NASA Astrophysics Data System (ADS)

Gamaletsos, P.; Godelitsas, A.; Mertzimekis, T. J.; Göttlicher, J.; Steininger, R.; Xanthos, S.; Berndt, J.; Klemme, S.; Kuzmin, A.; Bárdossy, G.

2011-12-01

Typical red-brown (Fe-rich) and high-quality white-grey (Fe-depleted) bauxite samples from active mines of the Parnassos-Ghiona area, central Greece, were investigated. According to XRF and ICP-MS analyses their actinide content, and particularly of Th, is relatively increased. Fe-depleted samples contain up to 62.75 ppm Th corresponding to 220 Bq/kg due to 228Ac ( 232Th-series), whereas Fe-rich samples are less Th-radioactive (up to 58.25 ppm Th, 180 Bq/kg due to 228Ac). Powder-XRD patterns showed that Th-enriched (Fe-depleted) bauxite consists mostly of diaspore (AlOOH polymorph), anatase and rutile (TiO 2 polymorphs). SEM-EDS indicated the presence of Ti-Fe-containing phases (e.g. ilmenite, FeTiO 3), chromite (Cr-spinel) and besides LREE-minerals (mostly bastnäsite/parisite-group) and zircon (ZrSiO 4) hosting a part of the bulk Th. The presence of Th in diaspore and in Ti-containing phases (not detected by SEM-EDS as in the case of REE-minerals and zircon) was investigated, into distinct pisoliths of Fe-depleted bauxite, using μ-XRF and μ-XAFS in the SUL-X beamline of the ANKA Synchrotron facility (KIT, Germany). XAFS spectra of Th salts and Th-containing reference materials were obtained as well. Accordingly it was revealed, for the first time in the literature, that Ti-phases, and particularly anatase, host significant amounts of Th. This novel conclusion was complementary supported by LA-ICP-MS analyses indicated an average of 73 ppm Th in anatase grains together with abundant Nb (3356 ppm), Ta (247 ppm) and U (33 ppm). The Th LIII-edge XAFS spectra as compared to reference materials, give also evidence that Th 4+ may not replace Ti 4+ in distorted [TiO 6] fundamental octahedral units of anatase and ilmenite lattice (CN = 6). The occupation of either extraframework sites of higher coordination (CN = 6.9 or even CN = 7.4), according to EXAFS signals evaluation, or of defected/vacant (**) sites is more probable. This is likely explained by the difficulty of Th 4+ to replace directly Ti 4+ in [6]-coordinated (octahedral) sites due to the large difference in the relevant ionic radii (0.940 and 0.605 Å respectively).

Lack of sex-biased dispersal promotes fine-scale genetic structure in alpine ungulates

Treesearch

Gretchen H. Roffler; Sandra L. Talbot; Gordon Luikart; George K. Sage; Kristy L. Pilgrim; Layne G. Adams; Michael K. Schwartz

2014-01-01

Identifying patterns of fine-scale genetic structure in natural populations can advance understanding of critical ecological processes such as dispersal and gene flow across heterogeneous landscapes. Alpine ungulates generally exhibit high levels of genetic structure due to female philopatry and patchy configuration of mountain habitats. We assessed the spatial scale...

Energy, fine structure, hyperfine structure, and radiative transition rates of the high-lying multi-excited states for B-like neon

NASA Astrophysics Data System (ADS)

Zhang, Chun Mei; Chen, Chao; Sun, Yan; Gou, Bing Cong; Shao, Bin

2015-04-01

The Rayleigh-Ritz variational method with multiconfiguration interaction wave functions is used to obtain the energies of high-lying multi-excited quartet states 1 s 22 s2 pnl and 1 s 22 p 2 nl 4Pe,o ( n ≥ 2) in B-like neon, including the mass polarization and relativistic corrections. The fine structure and hyperfine structure of the excited quartet states for this system are investigated. Configuration structures of the high-lying multi-excited series are further identified by relativistic corrections and fine structure splittings. The transition rates and wavelengths are also calculated. Calculated wavelengths include the quantum electrodynamic effects. The results are compared with other theoretical and experimental data in the literature.

Interferon-gamma enhances radiation-induced cell death via downregulation of Chk1

PubMed Central

Kim, Kwang Seok; Choi, Kyu Jin; Bae, Sangwoo

2012-01-01

Interferon-gamma (IFNγ) is a cytokine with roles in immune responses as well as in tumor control. Interferon is often used in cancer treatment together with other therapies. Here we report a novel approach to enhancement of cancer cell killing by combined treatment of IFNγ with ionizing radiation. We found that IFNγ treatment alone in HeLa cells induced phosphorylation of Chk1 in a time- and dose-dependent manner, and resulted in cell arrest. Moreover IFNγ treatment was correlated with attenuation of Chk1 as the treatment shortened protein half-life of Chk1. As Chk1 is an essential cell cycle regulator for viability after DNA damage, attenuation of Chk1 by IFNγ pre-treatment in HeLa cells resulted in increased cell death following ionizing radiation about 2-folds than ionizing radiation treatment alone whereas IFNγ treatment alone had little effect on cell death. X-linked inhibitor of apoptosis-associated factor 1 (XAF1), an IFN-induced gene, seems to partly regulate IFNγ-induced Chk1 destabilization and radiation sensitivity because transient depletion of XAF1 by siRNA prevented IFNγ-induced Chk1 attenuation and partly protected cells from IFNγ-enhanced radiation cell killing. Therefore the results provide a novel rationale to combine IFNγ pretreatment and DNA-damaging anti-cancer drugs such as ionizing radiation to enhance cancer cell killing. PMID:22825336

Precision measurement of the three 2(3)P(J) helium fine structure intervals.

PubMed

Zelevinsky, T; Farkas, D; Gabrielse, G

2005-11-11

The three 2(3)P fine structure intervals of 4H are measured at an improved accuracy that is sufficient to test two-electron QED theory and to determine the fine structure constant alpha to 14 parts in 10(9). The more accurate determination of alpha, to a precision higher than attained with the quantum Hall and Josephson effects, awaits the reconciliation of two inconsistent theoretical calculations now being compared term by term. A low pressure helium discharge presents experimental uncertainties quite different than for earlier measurements and allows direct measurements of light pressure shifts.

Collisional excitation of CH2 rotational/fine-structure levels by helium

NASA Astrophysics Data System (ADS)

Dagdigian, P. J.; Lique, F.

2018-02-01

Accurate determination of the abundance of CH2 in interstellar media relies on both radiative and collisional rate coefficients. We investigate here the rotational/fine-structure excitation of CH2 induced by collisions with He. We employ a recoupling technique to generate fine-structure-resolved cross-sections and rate coefficients from close coupling spin-free scattering calculations. The calculations are based on a recent, high-accuracy CH2-He potential energy surface computed at the coupled clusters level of theory. The collisional cross-section calculations are performed for all fine-structure transitions among the first 22 and 24 energy levels of ortho- and para-CH2, respectively, and for temperatures up to 300 K. As a first application, we simulate the excitation of CH2 in typical molecular clouds. The excitation temperatures of the CH2 lines are found to be small at typical densities of molecular clouds, showing that the non-local thermodynamic equilibrium approach has to be used to analyse interstellar spectra. We also found that the fine-structure lines connected with the 404 - 313 and 505 - 414 rotational transitions show possible maser emissions so that they can be easily seen in emission. These calculations show that CH2 may have to be detected mainly through absorption spectra.

Fine structure in plasma waves and radiation near the plasma frequency in Earth's foreshock

NASA Technical Reports Server (NTRS)

Cairns, Iver H.

1994-01-01

Novel observations are presented of intrunsic fine structure in the frequency spectrum of electomagnetic (EM) radiation and plasma waves near the electron plasma frequency f(sub p) during a period of unusually high interplanetary magnetic field strength. Measured using the wideband receiver on the International Sun-Earth Explorer (ISEE) 1 spacecraft, fine-structured emissions are observed both in the solar wind and the foreshock, The fine structure is shown to correspond to emissions spaced above f(sub p) near half harmonies of the electon cyclotron frequency f(sub ce), i.e., near f(sub p) + nf(sub ce)/2. These appear to be the first space physics observations of emissions spaced by f(sub ce)/2. Indirect but strong arguments are used to discriminate between EM and electrostatic (ES) signals, to identify whether ISEE 1 is in the solar wind or the foreshock, and to determine the relative frequencies of the emissions and the local f(sub p). The data are consistent with generation of the ES and EM emissions in the foreshock, with subsequent propagation of the EM emissions into the solar wind. It remains possible that some emissions currently identified as ES have significant EM character. The ES and EM emisions often merge into one another with minimal changes in frequency, arguing that their source regions and generation mechanisms are related and imposing significant constraints on theories. The f(sub ce)/2 ES and EM fine structures observed may be intrinsic to the emission mechanisms or to superposition of two series of signals with f(sub ce) spacing that differ in starting frequency by f(sub ce)/2. Present theories for nonlinear wave coupling processes, cyclotron maser emission, and other linear instability processes are all unable to explain multiple EM and/or ES components spaced by approximately f(sub ce)/2 above f(sub p) for f(sub p)/f(sub ce) much greater than 1 and typical for shock beams parameters. Suitable avenues for further theoretical research are identified. Empirically, the observed fine structures appear very similar to those in split bnad and multiple-lane type II solar radio bursts; interpretation of both these type II fine structures in terms of f(sub ce)/2 splitting is suggested, thereby supporting and generalizing a suggestion by Wild (1950). A possible application to continuum radiation is mentioned. The ubiquity of these fine structures in the Earth's f(sub p) radiation and foreshock waves remains unknown. Only the ISEE 1 wideband receiver has sufficient frequency resolution (approximately less than or equal to 100 Hz) to perform a dedicated search. Further study of the ubiquity of these fine structures, of how reliably the splitting corresponds to f(sub ce)/2, and of the other interpretations above is necessary.

High Resolutions Studies of the Structure of the Solar Atmosphere

DTIC Science & Technology

1992-06-30

Pairs in the Solar Wind", submitted to J. Geophys. Res., July 20, 1992. M. Karovska , F. Blundell and S. R. Habbal, "Fine Scale Structure of Active...Regions", manuscript in preparation. M. Karovska , F. Blundell and S. R. Habbal, "Fine Scale Structure of the Solar Limb in a Coronal Hole", manuscript in

Fine-scale genetic structure of whitebark pine (Pinus albicaulis) associations with watershed and growth form

Treesearch

Deborah L. Rogers; Constance I. Millar; Robert D. Westfall

1999-01-01

The fine-scale genetic structure of a subalpine conifer, whitebark pine (Pinus albicaulis Engelm.), was studied at nested geographic levels from watershed to adjacent stems in the eastern Sierra Nevada Range of California. A combination of several characteristics contributed to unpredicted genetic structure in this species. This includes being one of...

Fine- and hyperfine-structure effects in molecular photoionization. I. General theory and direct photoionization.

PubMed

Germann, Matthias; Willitsch, Stefan

2016-07-28

We develop a model for predicting fine- and hyperfine intensities in the direct photoionization of molecules based on the separability of electron and nuclear spin states from vibrational-electronic states. Using spherical tensor algebra, we derive highly symmetrized forms of the squared photoionization dipole matrix elements from which we derive the salient selection and propensity rules for fine- and hyperfine resolved photoionizing transitions. Our theoretical results are validated by the analysis of the fine-structure resolved photoelectron spectrum of O2 reported by Palm and Merkt [Phys. Rev. Lett. 81, 1385 (1998)] and are used for predicting hyperfine populations of molecular ions produced by photoionization.

The contribution of visual information to the perception of speech in noise with and without informative temporal fine structure

PubMed Central

Stacey, Paula C.; Kitterick, Pádraig T.; Morris, Saffron D.; Sumner, Christian J.

2017-01-01

Understanding what is said in demanding listening situations is assisted greatly by looking at the face of a talker. Previous studies have observed that normal-hearing listeners can benefit from this visual information when a talker's voice is presented in background noise. These benefits have also been observed in quiet listening conditions in cochlear-implant users, whose device does not convey the informative temporal fine structure cues in speech, and when normal-hearing individuals listen to speech processed to remove these informative temporal fine structure cues. The current study (1) characterised the benefits of visual information when listening in background noise; and (2) used sine-wave vocoding to compare the size of the visual benefit when speech is presented with or without informative temporal fine structure. The accuracy with which normal-hearing individuals reported words in spoken sentences was assessed across three experiments. The availability of visual information and informative temporal fine structure cues was varied within and across the experiments. The results showed that visual benefit was observed using open- and closed-set tests of speech perception. The size of the benefit increased when informative temporal fine structure cues were removed. This finding suggests that visual information may play an important role in the ability of cochlear-implant users to understand speech in many everyday situations. Models of audio-visual integration were able to account for the additional benefit of visual information when speech was degraded and suggested that auditory and visual information was being integrated in a similar way in all conditions. The modelling results were consistent with the notion that audio-visual benefit is derived from the optimal combination of auditory and visual sensory cues. PMID:27085797

Fine Structure in Helium-like Fluorine by Fast-Beam Laser Spectroscopy

NASA Astrophysics Data System (ADS)

Myers, E. G.; Thompson, J. K.; Silver, J. D.

1998-05-01

With the aim of providing an additional precise test of higher-order corrections to high precision calculations of fine structure in helium and helium-like ions(T. Zhang, Z.-C. Yan and G.W.F. Drake, Phys. Rev. Lett. 77), 1715 (1996)., a measurement of the 2^3P_2,F - 2^3P_1,F' fine structure in ^19F^7+ is in progress. The method involves doppler-tuned laser spectroscopy using a CO2 laser on a foil-stripped fluorine ion beam. We aim to achieve a higher precision, compared to an earlier measurement(E.G. Myers, P. Kuske, H.J. Andrae, I.A. Armour, H.A. Klein, J.D. Silver, and E. Traebert, Phys. Rev. Lett. 47), 87 (1981)., by using laser beams parallel and anti-parallel to the ion beam, to obtain partial cancellation of the doppler shift(J.K. Thompson, D.J.H. Howie and E.G. Myers, Phys. Rev. A 57), 180 (1998).. A calculation of the hyperfine structure, allowing for relativistic, QED and nuclear size effects, will be required to obtain the ``hyperfine-free'' fine structure interval from the measurements.

Doppler-free spectroscopy of the atomic rubidium fine structure using ultrafast spatial coherent control method

NASA Astrophysics Data System (ADS)

Kim, Minhyuk; Kim, Kyungtae; Lee, Woojun; Kim, Hyosub; Ahn, Jaewook

2017-04-01

Spectral programming solutions for the ultrafast spatial coherent control (USCC) method to resolve the fine-structure energy levels of atomic rubidium are reported. In USCC, a pair of counter-propagating ultrashort laser pulses are programmed to make a two-photon excitation pattern specific to particular transition pathways and atom species, thus allowing the involved transitions resolvable in space simultaneously. With a proper spectral phase and amplitude modulation, USCC has been also demonstrated for the systems with many intermediate energy levels. Pushing the limit of system complexity even further, we show here an experimental demonstration of the rubidium fine-structure excitation pattern resolvable by USCC. The spectral programming solution for the given USCC is achieved by combining a double-V-shape spectral phase function and a set of phase steps, where the former distinguishes the fine structure and the latter prevents resonant transitions. The experimental results will be presented along with its application in conjunction with the Doppler-free frequency-comb spectroscopy for rubidium hyperfine structure measurements. Samsung Science and Technology Foundation [SSTFBA1301-12].

Designing, producing, and constructing fine-graded hot mix asphalt on Illinois roadways.

DOT National Transportation Integrated Search

2015-04-01

Fine-graded (F-G) asphalt concrete mixtures are composed of an aggregate structure in which the fine fraction controls the : load-carrying capacity of the mix. Other states have reported benefits in using F-G mixtures, including improved compaction, ...

SESAME: an opportunity for science in the Middle-East

NASA Astrophysics Data System (ADS)

Paolucci, Giorgio

SESAME, the Synchrotron Radiation Laboratory of the Middle East, is becoming reality. As of November 2016, the injector has been commissioned, the storage ring is in an advanced state of installation and it is expected that two beamlines (XAFS/XRF and IR) will start producing scientific results in 2017. The talk will present the status of the facility and will illustrate its scientific objectives. The expected social and cultural impact of the project in the tumultuous Middle East Region will also be highlighted.

Variations in the fine-structure constant constraining gravity theories

NASA Astrophysics Data System (ADS)

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

2016-08-01

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

Fine Structure of Diffuse Scattering Rings in Al-Li-Cu Quasicrystal: A Comparative X-ray and Electron Diffraction Study

NASA Astrophysics Data System (ADS)

Donnadieu, P.; Dénoyer, F.

1996-11-01

A comparative X-ray and electron diffraction study has been performed on Al-Li-Cu icosahedral quasicrystal in order to investigate the diffuse scattering rings revealed by a previous work. Electron diffraction confirms the existence of rings but shows that the rings have a fine structure. The diffuse aspect on the X-ray diffraction patterns is then due to an averaging effect. Recent simulations based on the model of canonical cells related to the icosahedral packing give diffractions patterns in agreement with this fine structure effect. Nous comparons les diagrammes de diffraction des rayon-X et des électrons obtenus sur les mêmes échantillons du quasicristal icosaèdrique Al-Li-Cu. Notre but est d'étudier les anneaux de diffusion diffuse mis en évidence par un travail précédent. Les diagrammes de diffraction électronique confirment la présence des anneaux mais ils montrent aussi que ces anneaux possèdent une structure fine. L'aspect diffus des anneaux révélés par la diffraction des rayons X est dû à un effet de moyenne. Des simulations récentes basées sur la décomposition en cellules canoniques de l'empilement icosaédrique produisent des diagrammes de diffraction en accord avec ces effects de structure fine.

Local Fine Structural Insight into Mechanism of Electrochemical Passivation of Titanium.

PubMed

Wang, Lu; Yu, Hongying; Wang, Ke; Xu, Haisong; Wang, Shaoyang; Sun, Dongbai

2016-07-20

Electrochemically formed passive film on titanium in 1.0 M H2SO4 solution and its thickness, composition, chemical state, and local fine structure are examined by Auger electron spectroscopy (AES), X-ray photoelectron spectroscopy (XPS), and X-ray absorption fine structure. AES analysis reveals that the thickness and composition of oxide film are proportional to the reciprocal of current density in potentiodynamic polarization. XPS depth profiles of the chemical states of titanium exhibit the coexistence of various valences cations in the surface. Quantitative X-ray absorption near edge structure analysis of the local electronic structure of the topmost surface (∼5.0 nm) shows that the ratio of [TiO2]/[Ti2O3] is consistent with that of passivation/dissolution of electrochemical activity. Theoretical calculation and analysis of extended X-ray absorption fine structure spectra at Ti K-edge indicate that both the structures of passivation and dissolution are distorted caused by the appearance of two different sites of Ti-O and Ti-Ti. And the bound water in the topmost surface plays a vital role in structural disorder confirmed by XPS. Overall, the increase of average Ti-O coordination causes the electrochemical passivation, and the dissolution is due to the decrease of average Ti-Ti coordination. The structural variations of passivation in coordination number and interatomic distance are in good agreement with the prediction of point defect model.

Fine- and hyperfine-structure effects in molecular photoionization. I. General theory and direct photoionization

DOE Office of Scientific and Technical Information (OSTI.GOV)

Germann, Matthias; Willitsch, Stefan, E-mail: stefan.willitsch@unibas.ch

2016-07-28

We develop a model for predicting fine- and hyperfine intensities in the direct photoionization of molecules based on the separability of electron and nuclear spin states from vibrational-electronic states. Using spherical tensor algebra, we derive highly symmetrized forms of the squared photoionization dipole matrix elements from which we derive the salient selection and propensity rules for fine- and hyperfine resolved photoionizing transitions. Our theoretical results are validated by the analysis of the fine-structure resolved photoelectron spectrum of O{sub 2} reported by Palm and Merkt [Phys. Rev. Lett. 81, 1385 (1998)] and are used for predicting hyperfine populations of molecular ionsmore » produced by photoionization.« less

Charge distribution and local structure and speciation in the UO 2+x and PuO 2+x binary oxides for x⩽0.25

NASA Astrophysics Data System (ADS)

Conradson, Steven D.; Begg, Bruce D.; Clark, David L.; den Auwer, Christophe; Ding, Mei; Dorhout, Peter K.; Espinosa-Faller, Francisco J.; Gordon, Pamela L.; Haire, Richard G.; Hess, Nancy J.; Hess, Ryan F.; Webster Keogh, D.; Lander, Gerard H.; Manara, Dario; Morales, Luis A.; Neu, Mary P.; Paviet-Hartmann, Patricia; Rebizant, Jean; Rondinella, Vincenzo V.; Runde, Wolfgang; Drew Tait, C.; Kirk Veirs, D.; Villella, Phillip M.; Wastin, Franck

2005-02-01

The local structure and chemical speciation of the mixed valence, fluorite-based oxides UO 2+x (0.00⩽ x⩽0.20) and PuO 2+x/PuO 2+x-y(OH) 2y· zH 2O have been determined by U/Pu L III XAFS spectroscopy. The U spectra indicate (1) that the O atoms are incorporated as oxo groups at short (1.75 Å) U-O distances consistent with U(VI) concomitant with a large range of U displacements that reduce the apparent number of U neighbors and (2) that the UO 2 fraction remains intact implying that these O defects interact to form clusters and give the heterogeneous structure consistent with the diffraction patterns. The PuO 2+x system, which does not show a separate phase at its x=0.25 endpoint, also displays (1) oxo groups at longer 1.9 Å distances consistent with Pu(V+ δ), (2) a multisite Pu-O distribution even when x is close to zero indicative of the formation of stable species with H 2O and its hydrolysis products with O 2-, and (3) a highly disordered, spectroscopically invisible Pu-Pu component. The structure and bonding in AnO 2+x are therefore more complicated than have previously been assumed and show both similarities but also distinct differences among the different elements.

a Measurement of the Fine Structure Constant

NASA Astrophysics Data System (ADS)

Hensley, Joel M.; Wicht, Andreas; Sarajlic, Edina; Chu, Steven

2002-06-01

Using an atom interferometer method, we measure the recoil velocity of cesium due to the coherent scattering of a photon. This measurement is used to obtain a preliminary value of ħ/MCs and the fine structure constant, α, with an uncertainty Δα/α = 7.3 × 10-9.

NASAL FILTERING OF FINE PARTICLES IN CHILDREN VS. ADULTS

EPA Science Inventory

Nasal efficiency for removing fine particles may be affected by developmental changes in nasal structure associated with age. In healthy Caucasian children (age 6-13, n=17) and adults (age 18-28, n=11) we measured the fractional deposition (DF) of fine particles (1 and 2um MMAD)...

Fine Structure of Dark Energy and New Physics

DOE PAGES

Jejjala, Vishnu; Kavic, Michael; Minic, Djordje

2007-01-01

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

Quantum-gravity predictions for the fine-structure constant

NASA Astrophysics Data System (ADS)

Eichhorn, Astrid; Held, Aaron; Wetterich, Christof

2018-07-01

Asymptotically safe quantum fluctuations of gravity can uniquely determine the value of the gauge coupling for a large class of grand unified models. In turn, this makes the electromagnetic fine-structure constant calculable. The balance of gravity and matter fluctuations results in a fixed point for the running of the gauge coupling. It is approached as the momentum scale is lowered in the transplanckian regime, leading to a uniquely predicted value of the gauge coupling at the Planck scale. The precise value of the predicted fine-structure constant depends on the matter content of the grand unified model. It is proportional to the gravitational fluctuation effects for which computational uncertainties remain to be settled.

Excitonic fine-structure splitting in telecom-wavelength InAs/GaAs quantum dots: Statistical distribution and height-dependence

DOE Office of Scientific and Technical Information (OSTI.GOV)

Goldmann, Elias, E-mail: goldmann@itp.uni-bremen.de; Barthel, Stefan; Florian, Matthias

The variation of the excitonic fine-structure splitting is studied for semiconductor quantum dots under the influence of a strain-reducing layer, utilized to shift the emission wavelength of the excitonic transition into the telecom-wavelength regime of 1.3–1.5 μm. By means of a sp{sup 3}s{sup *}-tight-binding model and configuration interaction, we calculate wavelength shifts and fine-structure splittings for various quantum dot geometries. We find the splittings remaining small and even decreasing with strain-reducing layer composition for quantum dots with large height. Combined with an observed increased emission efficiency, the applicability for generation of entanglement photons is persistent.

High-resolution x-ray absorption spectroscopy studies of metal compounds in neurodegenerative brain tissue

NASA Astrophysics Data System (ADS)

Collingwood, J. F.; Mikhaylova, A.; Davidson, M. R.; Batich, C.; Streit, W. J.; Eskin, T.; Terry, J.; Barrea, R.; Underhill, R. S.; Dobson, J.

2005-01-01

Fluorescence mapping and microfocus X-ray absorption spectroscopy are used to detect, locate and identify iron biominerals and other inorganic metal accumulations in neurodegenerative brain tissue at sub-cellular resolution (<5 microns). Recent progress in developing the technique is reviewed. Synchrotron X-rays are used to map tissue sections for metals of interest, and XANES and XAFS are used to characterise anomalous concentrations of the metals in-situ so that they can be correlated with tissue structures and disease pathology. Iron anomalies associated with biogenic magnetite, ferritin and haemoglobin are located and identified in an avian tissue model with a pixel resolution ~5 microns. Subsequent studies include brain tissue sections from transgenic Huntington's mice, and the first high-resolution mapping and identification of iron biominerals in human Alzheimer's and control autopsy brain tissue. Technical developments include use of microfocus diffraction to obtain structural information about biominerals in-situ, and depositing sample location grids by lithography for the location of anomalies by conventional microscopy. The combined techniques provide a breakthrough in the study of both intra- and extra-cellular iron compounds and related metals in tissue. The information to be gained from this approach has implications for future diagnosis and treatment of neurodegeneration, and for our understanding of the mechanisms involved.

Controlled Pyrolysis of Ni-MOF-74 as a Promising Precursor for the Creation of Highly Active Ni Nanocatalysts in Size-Selective Hydrogenation.

PubMed

Nakatsuka, Kazuki; Yoshii, Takeharu; Kuwahara, Yasutaka; Mori, Kohsuke; Yamashita, Hiromi

2018-01-19

Metal organic frameworks (MOFs) are a class of porous organic-inorganic crystalline materials that have attracted much attention as H 2 storage devices and catalytic supports. In this paper, the synthesis of highly-dispersed Ni nanoparticles (NPs) for the hydrogenation of olefins was achieved by employing Ni-MOF-74 as a precursor. Investigations of the structural transformation of Ni species derived from Ni-MOF-74 during heat treatment were conducted. The transformation was monitored in detail by a combination of XRD, in situ XAFS, and XPS measurements. Ni NPs prepared from Ni-MOF-74 were easily reduced by the generation of reducing gases accompanied by the decomposition of Ni-MOF-74 structures during heat treatment at over 300 °C under N 2 flow. Ni-MOF-74-300 exhibited the highest activity for the hydrogenation of 1-octene due to efficient suppression of excess agglomerated Ni species during heat treatment. Moreover, Ni-MOF-74-300 showed not only high activity for the hydrogenation of olefins but also high size-selectivity because of the selective formation of Ni NPs covered by MOFs and the MOF-derived carbonaceous layer. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

A tale of two pectins: Diverse fine structures can result from identical processive PME treatments on similar high DM subtrates

USDA-ARS?s Scientific Manuscript database

The effects of a processive pectin-methylesterase treatment on two different pectins, both possessing a high degree of methylesterification, were investigated. While the starting samples were purportedly very similar in fine structure, and even though the sample-averaged degree of methylesterificati...

Temporal Fine Structure and Applications to Cochlear Implants

ERIC Educational Resources Information Center

Li, Xing

2013-01-01

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

Laser Spectroscopy of the Fine-Structure Splitting in the 2^{3}P_{J} Levels of ^{4}He.

PubMed

Zheng, X; Sun, Y R; Chen, J-J; Jiang, W; Pachucki, K; Hu, S-M

2017-02-10

The fine-structure splitting in the 2^{3}P_{J} (J=0, 1, 2) levels of ^{4}He is of great interest for tests of quantum electrodynamics and for the determination of the fine-structure constant α. The 2^{3}P_{0}-2^{3}P_{2} and 2^{3}P_{1}-2^{3}P_{2} intervals are measured by laser spectroscopy of the ^{3}P_{J}-2^{3}S_{1} transitions at 1083 nm in an atomic beam, and are determined to be 31 908 130.98±0.13  kHz and 2 291 177.56±0.19  kHz, respectively. Compared with calculations, which include terms up to α^{5}Ry, the deviation for the α-sensitive interval 2^{3}P_{0}-2^{3}P_{2} is only 0.22 kHz. It opens the window for further improvement of theoretical predictions and an independent determination of the fine-structure constant α with a precision of 2×10^{-9}.

QUIESCENT PROMINENCES IN THE ERA OF ALMA: SIMULATED OBSERVATIONS USING THE 3D WHOLE-PROMINENCE FINE STRUCTURE MODEL

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gunár, Stanislav; Heinzel, Petr; Mackay, Duncan H.

2016-12-20

We use the detailed 3D whole-prominence fine structure model to produce the first simulated high-resolution ALMA observations of a modeled quiescent solar prominence. The maps of synthetic brightness temperature and optical thickness shown in the present paper are produced using a visualization method for synthesis of the submillimeter/millimeter radio continua. We have obtained the simulated observations of both the prominence at the limb and the filament on the disk at wavelengths covering a broad range that encompasses the full potential of ALMA. We demonstrate here extent to which the small-scale and large-scale prominence and filament structures will be visible inmore » the ALMA observations spanning both the optically thin and thick regimes. We analyze the relationship between the brightness and kinetic temperature of the prominence plasma. We also illustrate the opportunities ALMA will provide for studying the thermal structure of the prominence plasma from the cores of the cool prominence fine structure to the prominence–corona transition region. In addition, we show that detailed 3D modeling of entire prominences with their numerous fine structures will be important for the correct interpretation of future ALMA observations of prominences.« less

Demonstrating the Uneven Importance of Fine-Scale Forest Structure on Snow Distributions using High Resolution Modeling

NASA Astrophysics Data System (ADS)

Broxton, P. D.; Harpold, A. A.; van Leeuwen, W.; Biederman, J. A.

2016-12-01

Quantifying the amount of snow in forested mountainous environments, as well as how it may change due to warming and forest disturbance, is critical given its importance for water supply and ecosystem health. Forest canopies affect snow accumulation and ablation in ways that are difficult to observe and model. Furthermore, fine-scale forest structure can accentuate or diminish the effects of forest-snow interactions. Despite decades of research demonstrating the importance of fine-scale forest structure (e.g. canopy edges and gaps) on snow, we still lack a comprehensive understanding of where and when forest structure has the largest impact on snowpack mass and energy budgets. Here, we use a hyper-resolution (1 meter spatial resolution) mass and energy balance snow model called the Snow Physics and Laser Mapping (SnowPALM) model along with LIDAR-derived forest structure to determine where spatial variability of fine-scale forest structure has the largest influence on large scale mass and energy budgets. SnowPALM was set up and calibrated at sites representing diverse climates in New Mexico, Arizona, and California. Then, we compared simulations at different model resolutions (i.e. 1, 10, and 100 m) to elucidate the effects of including versus not including information about fine scale canopy structure. These experiments were repeated for different prescribed topographies (i.e. flat, 30% slope north, and south-facing) at each site. Higher resolution simulations had more snow at lower canopy cover, with the opposite being true at high canopy cover. Furthermore, there is considerable scatter, indicating that different canopy arrangements can lead to different amounts of snow, even when the overall canopy coverage is the same. This modeling is contributing to the development of a high resolution machine learning algorithm called the Snow Water Artificial Network (SWANN) model to generate predictions of snow distributions over much larger domains, which has implications for improving land surface models that do not currently resolve or parameterize fine-scale canopy structure. In addition, these findings have implications for understanding the potential of different forest management strategies (i.e. thinning) based on local topography and climate to maximize the amount and retention of snow.

Simple preparation of magnetic field-responsive structural colored Janus particles.

PubMed

Teshima, Midori; Seki, Takahiro; Takeoka, Yukikazu

2018-03-08

We established a simple method for preparing Janus particles displaying different structural colors using submicron-sized fine silica particles and magnetic nanoparticles composed of Fe 3 O 4 . A w/o emulsion is prepared by vortex-stirring a mixed aqueous solution of suspended fine silica particles and magnetic nanoparticles and of hexadecane containing an emulsifier. Subsequent drying of the emulsion on a hot plate using a magnetic stirrer provides a polydisperse particle aggregate displaying two different structural colors according to the ratio of the amount of fine silica particles to the amount of magnetic nanoparticles. This polydisperse particle aggregate can be converted into monodisperse particles simply by using a sieve made of stainless steel. In the presence of a magnet, the monodisperse Janus particles can change their orientation and can switch between two different structural colors.

The fine-structure intervals of (N-14)+ by far-infrared laser magnetic resonance

NASA Technical Reports Server (NTRS)

Brown, John M.; Varberg, Thomas D.; Evenson, Kenneth M.; Cooksy, Andrew L.

1994-01-01

The far-infrared laser magnetic resonance spectra associated with both fine-structure transitions in (N-14)+ in its ground P-3 state have been recorded. This is the first laboratory observation of the J = 1 left arrow 0 transition and its frequency has been determined two orders of magnitude more accurately than previously. The remeasurement of the J = 2 left arrow 1 spectrum revealed a small error in the previous laboratory measurements. The fine-structure splittings (free of hyperfine interactions) determined in this work are (delta)E(sub 10) = 1461.13190 (61) GHz, (delta)E(sub 21) = 2459.38006 (37) GHz. Zero-field transition frequencies which include the effects of hyperfine structure have also been calculated. Refined values for the hyperfine constants and the g(sub J) factors have been obtained.

Dynamical Study of Femtosecond-Laser-Ablated Liquid-Aluminum Nanoparticles Using Spatiotemporally Resolved X-Ray-Absorption Fine-Structure Spectroscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Oguri, Katsuya; Okano, Yasuaki; Nishikawa, Tadashi

2007-10-19

We study the temperature evolution of aluminum nanoparticles generated by femtosecond laser ablation with spatiotemporally resolved x-ray-absorption fine-structure spectroscopy. We successfully identify the nanoparticles based on the L-edge absorption fine structure of the ablation plume in combination with the dependence of the edge structure on the irradiation intensity and the expansion velocity of the plume. In particular, we show that the lattice temperature of the nanoparticles is estimated from the L-edge slope, and that its spatial dependence reflects the cooling of the nanoparticles during plume expansion. The results reveal that the emitted nanoparticles travel in a vacuum as a condensedmore » liquid phase with a lattice temperature of about 2500 to 4200 K in the early stage of plume expansion.« less

Adsorption and electron-induced polymerization of methyl methacrylate on Ru(101xAF0)

NASA Astrophysics Data System (ADS)

Hedhili, M. N.; Yakshinskiy, B. V.; Wasielewski, R.; Ciszewski, A.; Madey, T. E.

2008-05-01

The adsorption and electron irradiation of methyl methacrylate (MMA) on a Ru(101¯0) surface have been studied using x-ray photoelectron spectroscopy (XPS), temperature programmed desorption (TPD), and low energy ion scattering. TPD analysis indicates that a monolayer of MMA chemisorbs and dissociates on the Ru(101¯0) surface. The reaction products observed upon heating include H2, CO, CO2, and a small amount of MMA. Physisorbed multilayers of MMA desorb at temperatures around 170K. Electron irradiation of physisorbed MMA at 140K leads to a modification of the MMA film: The XPS spectra show an increase in thermal stability of the film with retention of the MMA structure, and indicate that electron irradiation induces polymerization. An increase in the electron bombardment fluence induces a degradation of the formed polymerized species and leads to the accumulation of carbon on the Ru surface. These results are relevant to the accumulation of carbon on surfaces of Ru films that serve as capping layers on Mo /Si multilayer mirrors used in extreme ultraviolet lithography.

Adaptive root foraging strategies along a boreal-temperate forest gradient.

PubMed

Ostonen, Ivika; Truu, Marika; Helmisaari, Heljä-Sisko; Lukac, Martin; Borken, Werner; Vanguelova, Elena; Godbold, Douglas L; Lõhmus, Krista; Zang, Ulrich; Tedersoo, Leho; Preem, Jens-Konrad; Rosenvald, Katrin; Aosaar, Jürgen; Armolaitis, Kęstutis; Frey, Jane; Kabral, Naima; Kukumägi, Mai; Leppälammi-Kujansuu, Jaana; Lindroos, Antti-Jussi; Merilä, Päivi; Napa, Ülle; Nöjd, Pekka; Parts, Kaarin; Uri, Veiko; Varik, Mats; Truu, Jaak

2017-08-01

The tree root-mycorhizosphere plays a key role in resource uptake, but also in the adaptation of forests to changing environments. The adaptive foraging mechanisms of ectomycorrhizal (EcM) and fine roots of Picea abies, Pinus sylvestris and Betula pendula were evaluated along a gradient from temperate to subarctic boreal forest (38 sites between latitudes 48°N and 69°N) in Europe. Variables describing tree resource uptake structures and processes (absorptive fine root biomass and morphology, nitrogen (N) concentration in absorptive roots, extramatrical mycelium (EMM) biomass, community structure of root-associated EcM fungi, soil and rhizosphere bacteria) were used to analyse relationships between root system functional traits and climate, soil and stand characteristics. Absorptive fine root biomass per stand basal area increased significantly from temperate to boreal forests, coinciding with longer and thinner root tips with higher tissue density, smaller EMM biomass per root length and a shift in soil microbial community structure. The soil carbon (C) : N ratio was found to explain most of the variability in absorptive fine root and EMM biomass, root tissue density, N concentration and rhizosphere bacterial community structure. We suggest a concept of absorptive fine root foraging strategies involving both qualitative and quantitative changes in the root-mycorrhiza-bacteria continuum along climate and soil C : N gradients. © 2017 The Authors. New Phytologist © 2017 New Phytologist Trust.

A preliminary investigation of projectile shape effects in hypervelocity impact of a double-sheet structure

NASA Technical Reports Server (NTRS)

Morrison, R. H.

1972-01-01

Impact tests of a sphere and several cylinders of various masses and fineness ratios, all of aluminum, fired into an aluminum double-sheet structure at velocities near 7 km/sec, show that a cylinder, impacting in the direction of its axis, is considerably more effective as a penetrator than a sphere. Impacts of three cylinders of equal mass, but different fineness ratios, produced holes through the structures' rear sheet, whereas impact of a sphere of the same mass did not. Moreover, it was found that to prevent rear-sheet penetration, the mass of the 1/2-fineness-ratio cylinder had to be reduced by a factor greater than three. Further tests wherein the cylinder diameter was held constant while the cylinder length was systematically reduced showed that a cylinder with a fineness ratio of 0.07 and a mass of only 1/7 that of the sphere was still capable of producing a hole in the rear sheet.

Clonal growth and fine-scale genetic structure in tanoak (Notholithocarpus densiflorus: Fagaceae)

Treesearch

Richard S. Dodd; Wasima Mayer; Alejandro Nettel; Zara Afzal-Rafii

2013-01-01

The combination of sprouting and reproduction by seed can have important consequences on fine-scale spatial distribution of genetic structure (SGS). SGS is an important consideration for species’ restoration because it determines the minimum distance among seed trees to maximize genetic diversity while not prejudicing locally adapted genotypes. Local environmental...

Cation distribution in NiZn-ferrite films via extended x-ray absorption fine structure

NASA Astrophysics Data System (ADS)

Harris, V. G.; Koon, N. C.; Williams, C. M.; Zhang, Q.; Abe, M.; Kirkland, J. P.

1996-04-01

We have applied extended x-ray absorption fine structure (EXAFS) spectroscopy to study the cation distribution in a series of spin-sprayed NiZn-ferrite films. A least-squares fitting of experimental EXAFS data with theoretical, multiple-scattering, EXAFS data allowed the quantitative determination of site distributions for all transition metal cations.

Precision microwave measurement of the 2(3)P(1)-2(3)P(0) interval in atomic helium: a determination of the fine-structure constant.

PubMed

George, M C; Lombardi, L D; Hessels, E A

2001-10-22

The 2(3)P(1)-to- 2(3)P(0) interval in atomic helium is measured using a thermal beam of metastable helium atoms excited to the 2(3)P state using a 1.08-microm diode laser. The 2(3)P(1)-to- 2(3)P(0) transition is driven by 29.6-GHz microwaves in a rectangular waveguide cavity. Our result of 29,616,950.9+/-0.9 kHz is the most precise measurement of helium 2(3)P fine structure. When compared to precise theory for this interval, this measurement leads to a determination of the fine-structure constant of 1/137.0359864(31).

Fine Structure of Reovirus Type 2

PubMed Central

Loh, Philip C.; Hohl, H. R.; Soergel, M.

1965-01-01

Loh, Philip C. (University of Hawaii, Honolulu), H. R. Hohl, and M. Soergel. Fine structure of reovirus type 2. J. Bacteriol. 89:1140–1144. 1965.—The fine structure reovirus type 2 was studied by electron microscopy with the negative-staining method. The virus has a mean diameter of 772 A and shows evidence of icosahedral shape and 5:3:2 symmetry. The particle is composed of a core, an inner layer, and a capsid composed of 92 elongated hollow capsomeres. These capsomeres have mean dimensions of 116 A × 110 A and a central hole 48 A in diameter. In size and architecture, reovirus type 2 is very similar to the other members (reoviruses types 1 and 3) of this group of animal viruses. Images PMID:14276109

Nine Years of Irrigation Cause Vegetation and Fine Root Shifts in a Water-Limited Pine Forest

PubMed Central

Herzog, Claude; Steffen, Jan; Graf Pannatier, Elisabeth; Hajdas, Irka; Brunner, Ivano

2014-01-01

Scots pines (Pinus sylvestris L.) in the inner-Alpine dry valleys of Switzerland have suffered from increased mortality during the past decades, which has been caused by longer and more frequent dry periods. In addition, a proceeding replacement of Scots pines by pubescent oaks (Quercus pubescens Willd.) has been observed. In 2003, an irrigation experiment was performed to track changes by reducing drought pressure on the natural pine forest. After nine years of irrigation, we observed major adaptations in the vegetation and shifts in Scots pine fine root abundance and structure. Irrigation permitted new plant species to assemble and promote canopy closure with a subsequent loss of herb and moss coverage. Fine root dry weight increased under irrigation and fine roots had a tendency to elongate. Structural composition of fine roots remained unaffected by irrigation, expressing preserved proportions of cellulose, lignin and phenolic substances. A shift to a more negative δ13C signal in the fine root C indicates an increased photosynthetic activity in irrigated pine trees. Using radiocarbon (14C) measurement, a reduced mean age of the fine roots in irrigated plots was revealed. The reason for this is either an increase in newly produced fine roots, supported by the increase in fine root biomass, or a reduced lifespan of fine roots which corresponds to an enhanced turnover rate. Overall, the responses belowground to irrigation are less conspicuous than the more rapid adaptations aboveground. Lagged and conservative adaptations of tree roots with decadal lifespans are challenging to detect, hence demanding for long-term surveys. Investigations concerning fine root turnover rate and degradation processes under a changing climate are crucial for a complete understanding of C cycling. PMID:24802642

Editorial

NASA Astrophysics Data System (ADS)

Musilek, L.; Dunn, W. L.

2017-08-01

The selected proceedings of the 13th International Symposium on Radiation Physics (ISRP-13) are presented here across a broad range of important topics including: Fundamental processes in radiation physics, Theoretical investigations, New radiation sources, techniques & detectors, Absorption and fluorescence spectroscopy (XAFS, XANES, XRF Spectroscopy, Raman, Infrared …), Applications of radiation in material science, nano-science & nanotechnology, Applications of radiation in biology & medical science, Applications of radiation in space, earth, energy & environmental sciences, Applications of radiation in cultural heritage & art and Applications of radiation in industry. In total, 48 papers have been accepted for these proceedings.

Construction and Commissioning of BL37XU at SPring-8

DOE Office of Scientific and Technical Information (OSTI.GOV)

Terada, Yasuko; Goto, Shunji; Takimoto, Naoki

2004-05-12

Trace element analysis beamline (BL37XU) at SPring-8 was designed for application to various X-ray fluorescence analyses such as XRF imaging, XAFS, TXRF and XRF holography. The beamline has of two branches, one being a SPring-8 standard undulator-beamline optics branch (Branch A) and the other a high-energy branch (Branch B). In the experimental hutches, several kinds of experimental device are equipped. The end-stations have been opened to public use since November 2002, and various experiments have been carried out.

Fine structure transitions in Fe XIV

NASA Astrophysics Data System (ADS)

Nahar, Sultana N.

2013-07-01

Results are reported for Fe XIV energy levels and transitions obtained from the ab initio relativistic Breit-Pauli R-matrix (BPRM) method. BPRM method developed under the Iron Project is capable of calculating very large number of fine structure energy levels and corresponding transitions. However, unlike in the atomic structure calculations, where levels are identified spectroscopically based on the leading percentage contributions of configurations, BPRM is incapable of such identification of the levels and hence the transitions. The main reason for it is that the percentage contributions can not be determined exactly from the large number of channels in the R-matrix space. The present report describes an identification method that uses considerations of quantum defects of channels, contributions of channel from outer regions, Hund's rule, and angular momenta algebra for addition and completeness of fine structure components. The present calculations are carried out using a close coupling wave function expansion that included 26 core excitations from configurations 2s22p63s2, 2s22p63s3p,2s22p63p2,2s22p63s3d, and 2s22p63p3d. A total of 1002 fine structure levels with n ⩽ 10, l⩽9, and 0.5 ⩽J⩽ 9.5 with even and odd parities and the corresponding 130,520 electric dipole allowed (E1) fine structure transitions, a most complete set for astrophysical modelings of spectral analysis and opacities, is presented. Large number of new energy levels are found and identified. The energies agree very well, mostly in less than 1% with the highest being 1.9%, with the 68 observed fine structure levels. While the high lying levels may have some uncertainty, an overall accuracy of energy levels should be within 10%. BPRM transitions have been benchmarked with the existing most accurate calculated transition probabilities with very good agreement for most cases. Based on the accuracy of the method and comparisons, most of the transitions can be rated with A (⩽10%) to C (⩽30%).

Size structure of marine soft-bottom macrobenthic communities across natural habitat gradients: implications for productivity and ecosystem function.

PubMed

Macdonald, Tara A; Burd, Brenda J; van Roodselaar, Albert

2012-01-01

Size distributions of biotic assemblages are important modifiers of productivity and function in marine sediments. We investigated the distribution of proportional organic biomass among logarithmic size classes (2(-6)J to 2(16)J) in the soft-bottom macrofaunal communities of the Strait of Georgia, Salish Sea on the west coast of Canada. The study examines how size structure is influenced by 3 fundamental habitat descriptors: depth, sediment percent fines, and organic flux (modified by quality). These habitat variables are uncorrelated in this hydrographically diverse area, thus we examine their effects in combination and separately. Cluster analyses and cumulative biomass size spectra reveal clear and significant responses to each separate habitat variable. When combined, habitat factors result in three distinct assemblages: (1) communities with a high proportion of biomass in small organisms, typical of shallow areas (<10 m) with coarse sediments (<10% fines) and low accumulation of organic material (<3.0 gC/m(2)/yr/δ(15)N); (2) communities with high proportion of biomass in the largest organisms found in the Strait, typical of deep, fine sediments with high modified organic flux (>3 g C/m(2)/yr/δ(15)N) from the Fraser River; and (3) communities with biomass dominated by moderately large organisms, but lacking the smallest and largest size classes, typical of deep, fine sediments experiencing low modified organic flux (<3.0 gC/m(2)/yr/δ(15)N). The remaining assemblages had intermediate habitat types and size structures. Sediment percent fines and flux appear to elicit threshold responses in size structure, whereas depth has the most linear influence on community size structure. The ecological implications of size structure in the Strait of Georgia relative to environmental conditions, secondary production and sediment bioturbation are discussed.

Size Structure of Marine Soft-Bottom Macrobenthic Communities across Natural Habitat Gradients: Implications for Productivity and Ecosystem Function

PubMed Central

Macdonald, Tara A.; Burd, Brenda J.; van Roodselaar, Albert

2012-01-01

Size distributions of biotic assemblages are important modifiers of productivity and function in marine sediments. We investigated the distribution of proportional organic biomass among logarithmic size classes (2−6J to 216J) in the soft-bottom macrofaunal communities of the Strait of Georgia, Salish Sea on the west coast of Canada. The study examines how size structure is influenced by 3 fundamental habitat descriptors: depth, sediment percent fines, and organic flux (modified by quality). These habitat variables are uncorrelated in this hydrographically diverse area, thus we examine their effects in combination and separately. Cluster analyses and cumulative biomass size spectra reveal clear and significant responses to each separate habitat variable. When combined, habitat factors result in three distinct assemblages: (1) communities with a high proportion of biomass in small organisms, typical of shallow areas (<10 m) with coarse sediments (<10% fines) and low accumulation of organic material (<3.0 gC/m2/yr/δ15N); (2) communities with high proportion of biomass in the largest organisms found in the Strait, typical of deep, fine sediments with high modified organic flux (>3 g C/m2/yr/δ15N) from the Fraser River; and (3) communities with biomass dominated by moderately large organisms, but lacking the smallest and largest size classes, typical of deep, fine sediments experiencing low modified organic flux (<3.0 gC/m2/yr/δ15N). The remaining assemblages had intermediate habitat types and size structures. Sediment percent fines and flux appear to elicit threshold responses in size structure, whereas depth has the most linear influence on community size structure. The ecological implications of size structure in the Strait of Georgia relative to environmental conditions, secondary production and sediment bioturbation are discussed. PMID:22911694

Effect of diurnal photosynthetic activity on the fine structure of amylopectin from normal and waxy barley starch.

PubMed

Goldstein, Avi; Annor, George; Blennow, Andreas; Bertoft, Eric

2017-09-01

The impact of diurnal photosynthetic activity on the fine structure of the amylopectin fraction of starch synthesized by normal barley (NBS) and waxy barley (WBS), the latter completely devoid of amylose biosynthesis, was determined following the cultivation under normal diurnal or constant light growing conditions. The amylopectin fine structures were analysed by characterizing its unit chain length profiles after enzymatic debranching as well as its φ,β-limit dextrins and its clusters and building blocks after their partial and complete hydrolysis with α-amylase from Bacillus amyloliquefaciens, respectively. Regardless of lighting conditions, no structural effects were found when comparing both the amylopectin side-chain distribution and the internal chain fragments of these amylopectins. However, the diurnally grown NBS and WBS both showed larger amylopectin clusters and these had lower branching density and longer average chain lengths than clusters derived from plants grown under constant light conditions. Amylopectin clusters from diurnally grown plants also consisted of a greater number of building blocks, and shorter inter-block chain lengths compared to clusters derived from plants grown under constant light. Our data demonstrate that the diurnal light regime influences the fine structure of the amylopectin component both in amylose and non-amylose starch granules. Copyright © 2017 Elsevier B.V. All rights reserved.

Studies on the wintertime current structure and T-S fine-structure in the Taiwan Strait

NASA Astrophysics Data System (ADS)

Hu, Jianyu; Fu, Zilang; Wu, Lianxing

1990-12-01

A cruise through the western sea area of the Taiwan Strait was carried out by the R/V Dong Fang Hong in December, 1987. Eight anchored and 10 not anchored stations were set up. Over 25 time-series current observations were made at each station and CTD (Conductivity-temperature-depth) measurements were made at 5 anchored and 10 not anchored stations. Based on the measured data. fine-structures and step-like vertical structures of temperature and salinity were analysed and a tentative wintertime current structure in the Taiwan Strait was described.

Effects of a suppressor tone on distortion product otoacoustic emissions fine structure: why a universal suppressor level is not a practical solution to obtaining single-generator DP-grams.

PubMed

Dhar, Sumitrajit; Shaffer, Lauren A

2004-12-01

The use of a suppressor tone has been proposed as the method of choice in obtaining single-generator distortion product (DP) grams, the speculation being that such DP grams will be more predictive of hearing thresholds. Current distortion product otoacoustic emissions (DPOAE) theory points to the ear canal DPOAE signal being a complex interaction between multiple components. The effectiveness of a suppressor tone is predicted to be dependent entirely on the relative levels of these components. We examine the validity of using a suppressor tone through a detailed examination of the effects of a suppressor on DPOAE fine structure in individual ears. DPOAE fine structure, recorded in 10 normal-hearing individuals with a suppressor tone at 45, 55, and 65 dB SPL, was compared with recordings without a suppressor. Behavioral hearing thresholds were also measured in the same subjects, using 2-dB steps. The effect of the suppressor tone on DPOAE fine structure varied between ears and was dependent on frequency within ears. Correlation between hearing thresholds and DPOAE level measured without a suppressor was similar to previous reports. The effects of the suppressor are explained in the theoretical framework of a model involving multiple DPOAE components. Our results suggest that a suppressor tone can have highly variable effects on fine structure across individuals or even across frequency within one ear, thereby making the use of a suppressor less viable as a clinical tool for obtaining single-generator DP grams.

Time-dependent changes of zinc speciation in four soils contaminated with zincite or sphalerite.

PubMed

Voegelin, Andreas; Jacquat, Olivier; Pfister, Sabina; Barmettler, Kurt; Scheinost, Andreas C; Kretzschmar, Ruben

2011-01-01

The long-term speciation of Zn in contaminated soils is strongly influenced by soil pH, clay, and organic matter content as well as Zn loading. In addition, the type of Zn-bearing contaminant entering the soil may influence the subsequent formation of pedogenic Zn species, but systematic studies on such effects are currently lacking. We therefore conducted a soil incubation study in which four soils, ranging from strongly acidic to calcareous, were spiked with 2000 mg/kg Zn using either ZnO (zincite) or ZnS (sphalerite) as the contamination source. The soils were incubated under aerated conditions in moist state for up to four years. The extractability and speciation of Zn were assessed after one, two, and four years using extractions with 0.01 M CaCl(2) and Zn K-edge X-ray absorption fine structure (XAFS) spectroscopy, respectively. After four years, more than 90% of the added ZnO were dissolved in all soils, with the fastest dissolution occurring in the acidic soils. Contamination with ZnO favored the formation of Zn-bearing layered double hydroxides (LDH), even in acidic soils, and to a lesser degree Zn-phyllosilicates and adsorbed Zn species. This was explained by locally elevated pH and high Zn concentrations around dissolving ZnO particles. Except for the calcareous soil, ZnS dissolved more slowly than ZnO, reaching only 26 to 75% of the added ZnS after four years. ZnS dissolved more slowly in the two acidic soils than in the near-neutral and the calcareous soil. Also, the resulting Zn speciation was markedly different between these two pairs of soils: Whereas Zn bound to hydroxy-interlayered clay minerals (HIM) and octahedrally coordinated Zn sorption complexes prevailed in the two acidic soils, Zn speciation in the neutral and the calcareous soil was dominated by Zn-LDH and tetrahedrally coordinated inner-sphere Zn complexes. Our results show that the type of Zn-bearing contaminant phase can have a significant influence on the formation of pedogenic Zn species in soils. Important factors include the rate of Zn release from the contaminant phases and effects of the contaminant phase on bulk soil properties and on local chemical conditions around weathering contaminant particles.

Advanced Test Reactor National Scientific User Facility (ATR NSUF) Monthly Report November 2014

DOE Office of Scientific and Technical Information (OSTI.GOV)

Soelberg, Renae

2014-11-01

Advanced Test Reactor National Scientific User Facility (ATR NSUF) Monthly Report November 2014 Highlights Rory Kennedy and Sarah Robertson attended the American Nuclear Society Winter Meeting and Nuclear Technology Expo in Anaheim, California, Nov. 10-13. ATR NSUF exhibited at the technology expo where hundreds of meeting participants had an opportunity to learn more about ATR NSUF. Dr. Kennedy briefed the Nuclear Engineering Department Heads Organization (NEDHO) on the workings of the ATR NSUF. • Rory Kennedy, James Cole and Dan Ogden participated in a reactor instrumentation discussion with Jean-Francois Villard and Christopher Destouches of CEA and several members of themore » INL staff. • ATR NSUF received approval from the NE-20 office to start planning the annual Users Meeting. The meeting will be held at INL, June 22-25. • Mike Worley, director of the Office of Innovative Nuclear Research (NE-42), visited INL Nov. 4-5. Milestones Completed • Recommendations for the Summer Rapid Turnaround Experiment awards were submitted to DOE-HQ Nov. 12 (Level 2 milestone due Nov. 30). Major Accomplishments/Activities • The University of California, Santa Barbara 2 experiment was unloaded from the GE-2000 at HFEF. The experiment specimen packs will be removed and shipped to ORNL for PIE. • The Terrani experiment, one of three FY 2014 new awards, was completed utilizing the Advanced Photon Source MRCAT beamline. The experiment investigated the chemical state of Ag and Pd in SiC shell of irradiated TRISO particles via X-ray Absorption Fine Structure (XAFS) spectroscopy. Upcoming Meetings/Events • The ATR NSUF program review meeting will be held Dec. 9-10 at L’Enfant Plaza. In addition to NSUF staff and users, NE-4, NE-5 and NE-7 representatives will attend the meeting. Awarded Research Projects Boise State University Rapid Turnaround Experiments (14-485 and 14-486) Nanoindentation and TEM work on the T91, HT9, HCM12A and 9Cr ODS specimens has been completed at CAES by Boise State PI Janelle Wharry and Cory Dolph. PI Corey Dolph returned in early November to complete their research by performing nanoindentation on unirradiated specimens that will be used as a baseline for their research.« less

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

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fulton, John L.; Govind, Niranjan; Huthwelker, Thomas

2015-07-02

We probe, at high energy resolution, the double electron excitation (KL II&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 KL II&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⁺•6H₂Omore » the KL II&III spectra contain white line features and extended absorption fine structure (EXAFS) that mimics the K-edge spectra. The KL II&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 KL II&III and KL I 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 Pacific Northwest National Laboratory (PNNL). PNNL is a multi-program national laboratory operated for DOE by Battelle under Contract # AC05-76RL01830.« less

Microwave spectroscopy of the 1 s n p P3J fine structure of high Rydberg states in 4He

NASA Astrophysics Data System (ADS)

Deller, A.; Hogan, S. D.

2018-01-01

The 1 s n p P3J fine structure of high Rydberg states in helium has been measured by microwave spectroscopy of single-photon transitions from 1 s n s S31 levels in pulsed supersonic beams. For states with principal quantum numbers in the range from n =34 to 36, the J =0 →2 and J =1 →2 fine structure intervals were both observed. For values of n between 45 and 51 only the larger J =0 →2 interval was resolved. The experimental results are in good agreement with theoretical predictions. Detailed characterization of residual uncanceled electric and magnetic fields in the experimental apparatus and calculations of the Stark and Zeeman structures of the Rydberg states in weak fields were used to quantify systematic contributions to the uncertainties in the measurements.

Gravity Wave Interactions with Fine Structures in the Mesosphere and Lower Thermosphere

NASA Astrophysics Data System (ADS)

Mixa, Tyler; Fritts, David; Bossert, Katrina; Laughman, Brian; Wang, Ling; Lund, Thomas; Kantha, Lakshmi

2017-04-01

An anelastic numerical model is used to probe the influences of fine layering structures on gravity wave propagation in the Mesosphere and Lower Thermosphere (MLT). Recent lidar observations confirm the presence of persistent layered structures in the MLT that have sharp stratification and vertical scales below 1km. Gravity waves propagating through finely layered environments can excite and modulate the evolution of small scale instabilities that redefine the layering structure in these regions. Such layers in turn filter the outgoing wave spectra, promote ducting or reflection, hasten the onset of self-acceleration dynamics, and encourage wave/mean-flow interactions via energy and momentum transport. Using high resolution simulations of a localized gravity wave packet in a deep atmosphere, we identify the relative impacts of various wave and mean flow parameters to improve our understanding of these dynamics and complement recent state-of-the-art observations.

Strained spiral vortex model for turbulent fine structure

NASA Technical Reports Server (NTRS)

Lundgren, T. S.

1982-01-01

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

Photoionization modeling of the LWS fine-structure lines in IR bright galaxies

NASA Technical Reports Server (NTRS)

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

1997-01-01

The long wavelength spectrometer (LWS) fine structure line spectra from infrared luminous galaxies were modeled using stellar evolutionary synthesis models combined with photoionization and photodissociation region models. The calculations were carried out by using the computational code CLOUDY. Starburst and active galactic nuclei models are presented. The effects of dust in the ionized region are examined.

Study of the Role of Vortex Annihilation in the Mechanism of Neutron and X-Ray Production in the Plasma Focus.

DTIC Science & Technology

This paper shows that an understanding of the nature of the x-ray and neutron producing processes in the plasma focus requires a study of the ’fine...structure’ of the plasma focus and that this fine structure study requires diagnostic techniques with spacial resolution down to 50 micrometers and

Titanium dioxide fine structures by RF magnetron sputter method deposited on an electron-beam resist mask

NASA Astrophysics Data System (ADS)

Hashiba, Hideomi; Miyazaki, Yuta; Matsushita, Sachiko

2013-09-01

Titanium dioxide (TiO2) has been draw attention for wide range of applications from photonic crystals for visible light range by its catalytic characteristics to tera-hertz range by its high refractive index. We present an experimental study of fabrication of fine structures of TiO2 with a ZEP electron beam resist mask followed by Ti sputter deposition techniques. A TiO2 thin layer of 150 nm thick was grown on an FTO glass substrate with a fine patterned ZEP resist mask by a conventional RF magnetron sputter method with Ti target. The deposition was carried out with argon-oxygen gases at a pressure of 5.0 x 10 -1 Pa in a chamber. During the deposition, ratio of Ar-O2 gas was kept to the ratio of 2:1 and the deposition ratio was around 0.5 Å/s to ensure enough oxygen to form TiO2 and low temperature to avoid deformation of fine pattern of the ZPU resist mask. Deposited TiO2 layers are white-transparent, amorphous, and those roughnesses are around 7 nm. Fabricated TiO2 PCs have wider TiO2 slabs of 112 nm width leaving periodic 410 x 410 nm2 air gaps. We also studied transformation of TiO2 layers and TiO2 fine structures by baking at 500 °C. XRD measurement for TiO2 shows that the amorphous TiO2 transforms to rutile and anatase forms by the baking while keeping the same profile of the fine structures. Our fabrication method can be one of a promising technique to optic devices on researches and industrial area.

Effective Collision Strengths for Fine-structure Transitions in Si VII

NASA Astrophysics Data System (ADS)

Sossah, A. M.; Tayal, S. S.

2014-05-01

The effective collision strengths for electron-impact excitation of fine-structure transitions in Si VII are calculated as a function of electron temperature in the range 5000-2,000,000 K. The B-spline Breit-Pauli R-matrix method has been used to calculate collision strengths by electron impact. The target wave functions have been obtained using the multi-configuration Hartree-Fock method with term-dependent non-orthogonal orbitals. The 92 fine-structure levels belonging to the 46 LS states of 2s 22p 4, 2s2p 5, 2p 6, 2s 22p 33s, 2s 22p 33p, 2s 22p 33d, and 2s2p 43s configurations are included in our calculations of oscillator strengths and collision strengths. There are 4186 possible fine-structure allowed and forbidden transitions among the 92 levels. The present excitation energies, oscillator strengths, and collision strengths have been compared with previous theoretical results and available experimental data. Generally, a good agreement is found with the 6 LS-state close-coupling approximation results of Butler & Zeippen and the 44 LS-state distorted wave calculation of Bhatia & Landi.

Rotational and fine structure of open-shell molecules in nearly degenerate electronic states

NASA Astrophysics Data System (ADS)

Liu, Jinjun

2018-03-01

An effective Hamiltonian without symmetry restriction has been developed to model the rotational and fine structure of two nearly degenerate electronic states of an open-shell molecule. In addition to the rotational Hamiltonian for an asymmetric top, this spectroscopic model includes the energy separation between the two states due to difference potential and zero-point energy difference, as well as the spin-orbit (SO), Coriolis, and electron spin-molecular rotation (SR) interactions. Hamiltonian matrices are computed using orbitally and fully symmetrized case (a) and case (b) basis sets. Intensity formulae and selection rules for rotational transitions between a pair of nearly degenerate states and a nondegenerate state have also been derived using all four basis sets. It is demonstrated using real examples of free radicals that the fine structure of a single electronic state can be simulated with either a SR tensor or a combination of SO and Coriolis constants. The related molecular constants can be determined precisely only when all interacting levels are simulated simultaneously. The present study suggests that analysis of rotational and fine structure can provide quantitative insights into vibronic interactions and related effects.

Structural Coloration of a Colloidal Amorphous Array is Intensified by Carbon Nanolayers.

PubMed

Takeoka, Yukikazu; Iwata, Masanori; Seki, Takahiro; Nueangnoraj, Khanin; Nishihara, Hirotomo; Yoshioka, Shinya

2018-04-10

In this study, we introduce the possibility of applying a colloidal amorphous array composed of fine silica particles as a structural-color material to invisible information technology. The appearance of a thick filmlike colloidal amorphous array formed from fine silica particles is considerably influenced by incoherent light scattering across the entire visible region. Therefore, regardless of the diameter of the fine silica particles, the thick colloidal amorphous array exhibits a white color to the naked eye. When carbon is uniformly deposited in the colloidal amorphous array by a pressure-pulsed chemical vapor deposition method, incoherent light scattering in the colloidal amorphous array is suppressed. As a result, coherent light scattering due to the short-range order in the colloidal amorphous array becomes conspicuous and the array exhibits a vivid structural color. As structures, such as letters and pictures, can be drawn using this technology, the colloidal amorphous array as a structural-colored material may also be applicable for invisible information technology.

Human brain detects short-time nonlinear predictability in the temporal fine structure of deterministic chaotic sounds

NASA Astrophysics Data System (ADS)

Itoh, Kosuke; Nakada, Tsutomu

2013-04-01

Deterministic nonlinear dynamical processes are ubiquitous in nature. Chaotic sounds generated by such processes may appear irregular and random in waveform, but these sounds are mathematically distinguished from random stochastic sounds in that they contain deterministic short-time predictability in their temporal fine structures. We show that the human brain distinguishes deterministic chaotic sounds from spectrally matched stochastic sounds in neural processing and perception. Deterministic chaotic sounds, even without being attended to, elicited greater cerebral cortical responses than the surrogate control sounds after about 150 ms in latency after sound onset. Listeners also clearly discriminated these sounds in perception. The results support the hypothesis that the human auditory system is sensitive to the subtle short-time predictability embedded in the temporal fine structure of sounds.

The fine structure of human germ layers in vivo: clues to the early differentiation of embryonic stem cells in vitro.

PubMed

Sathananthan, Henry; Selvaraj, Kamala; Clark, Joan

2011-08-01

The fine structure of the three germ layers in human ectopic embryos (stage 7) have been documented by digital light and electron microscopy. The formation of ectoderm, endoderm and mesoderm and notochordal cells, and also the extraembryonic membranes, amnion and yolk sac, are imaged. The germ layers give rise to all the cells and tissues of the human body. Possible clues to the early differentiation of embryonic stem cells (ESC) in vitro were obtained, since these events are more or less mimicked in cultures of ESC derived from the inner cell mass of human blastocysts. The findings are discussed with reference to previous studies on the fine structure of ESC using the same technique. Copyright © 2011. Published by Elsevier Ltd.

21-cm radiation: a new probe of variation in the fine-structure constant.

PubMed

Khatri, Rishi; Wandelt, Benjamin D

2007-03-16

We investigate the effect of variation in the value of the fine-structure constant (alpha) at high redshifts (recombination > z > 30) on the absorption of the cosmic microwave background (CMB) at 21 cm hyperfine transition of the neutral atomic hydrogen. We find that the 21 cm signal is very sensitive to the variations in alpha and it is so far the only probe of the fine-structure constant in this redshift range. A change in the value of alpha by 1% changes the mean brightness temperature decrement of the CMB due to 21 cm absorption by >5% over the redshift range z < 50. There is an effect of similar magnitude on the amplitude of the fluctuations in the brightness temperature. The redshift of maximum absorption also changes by approximately 5%.

Measuring the fine structure constant with Bragg diffraction and Bloch oscillations

NASA Astrophysics Data System (ADS)

Parker, Richard; Yu, Chenghui; Zhong, Weicheng; Estey, Brian; Müller, Holger

2017-04-01

We have demonstrated a new scheme for atom interferometry based on large-momentum-transfer Bragg beam splitters and Bloch oscillations. In this new scheme, we have achieved a resolution of δÎ+/-/Î+/-=0.25ppb in the fine structure constant measurement, which gives over 10 million radians of phase difference between freely evolving matter waves. We have suppressed many systematic effects known in most atom interferometers with Raman beam splitters such as light shift, Zeeman effect shift as well as vibration. We have also simulated multi-atom Bragg diffraction to understand sub-ppb systematic effects, and implemented spatial filtering to further suppress systematic effects. We present our recent progress toward a measurement of the fine structure constant, which will provide a stringent test of the standard model of particle physics.

Transformation of zinc-concentrate in surface and subsurface environments: Implications for assessing zinc mobility/toxicity and choosing an optimal remediation strategy.

PubMed

Kwon, Man Jae; Boyanov, Maxim I; Yang, Jung-Seok; Lee, Seunghak; Hwang, Yun Ho; Lee, Ju Yeon; Mishra, Bhoopesh; Kemner, Kenneth M

2017-07-01

Zinc contamination in near- and sub-surface environments is a serious threat to many ecosystems and to public health. Sufficient understanding of Zn speciation and transport mechanisms is therefore critical to evaluating its risk to the environment and to developing remediation strategies. The geochemical and mineralogical characteristics of contaminated soils in the vicinity of a Zn ore transportation route were thoroughly investigated using a variety of analytical techniques (sequential extraction, XRF, XRD, SEM, and XAFS). Imported Zn-concentrate (ZnS) was deposited in a receiving facility and dispersed over time to the surrounding roadside areas and rice-paddy soils. Subsequent physical and chemical weathering resulted in dispersal into the subsurface. The species identified in the contaminated areas included Zn-sulfide, Zn-carbonate, other O-coordinated Zn-minerals, and Zn species bound to Fe/Mn oxides or clays, as confirmed by XAFS spectroscopy and sequential extraction. The observed transformation from S-coordinated Zn to O-coordinated Zn associated with minerals suggests that this contaminant can change into more soluble and labile forms as a result of weathering. For the purpose of developing a soil washing remediation process, the contaminated samples were extracted with dilute acids. The extraction efficiency increased with the increase of O-coordinated Zn relative to S-coordinated Zn in the sediment. This study demonstrates that improved understanding of Zn speciation in contaminated soils is essential for well-informed decision making regarding metal mobility and toxicity, as well as for choosing an appropriate remediation strategy using soil washing. Copyright © 2017 Elsevier Ltd. All rights reserved.

Toyota beamline (BL33XU) at SPring-8

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nonaka, T., E-mail: nonaka@mosk.tytlabs.co.jp; Dohmae, K.; Hayashi, Y.

2016-07-27

The Toyota beamline (BL33XU) at SPring-8 is an undulator beamline developed to assist in the study of various automotive-related materials. The light source is a tapered in-vacuum undulator that provides a variable energy band width as well as a high brilliance X-ray beam. Two different optical arrangements are available: Optics 1 and Optics 2. Optics 1 is dedicated to time-resolved X-ray absorption spectroscopy (XAFS), and consists of two channel-cut crystal monochromators and four water-cooled flat Si mirrors. The Si(111) and Si(220) monochromator crystals cover an energy range of 4.0–46.0 keV and are driven by high-speed AC servo motors. These monochromators,more » in conjunction with the tapered undulator, enable high-quality XAFS data acquisition with a temporal resolution of 10 ms. Optics 2 is optimized for X-ray diffraction, scattering and imaging and includes a recently installed double crystal monochromator, two water-cooled flat Si mirrors and Kirkpatrick-Baez (KB) focusing mirrors. The monochromator incorporates parallel mounted Si(111) and Si(311) crystals and covers an energy range of 4.5–70 keV. The beamline provides two experimental stations: Exp. Hutch 2 and Exp. Hutch 3. The gas supply system and mass spectrometers installed in Exp. Hutch 2 allow in-operando measurements under various atmospheres. The scanning three-dimensional X-ray diffraction (scanning 3DXRD) microscopy instrumentation developed and installed in Exp. Hutch 3 enables non-destructive orientation and stress mapping of 1 mm-thick steel specimens using a high energy microbeam.« less

Transformation of zinc-concentrate in surface and subsurface environments: Implications for assessing zinc mobility/toxicity and choosing an optimal remediation strategy

DOE PAGES

Kwon, Man Jae; Boyanov, Maxim I.; Yang, Jung -Seok; ...

2017-03-24

Zinc contamination in near- and sub-surface environments is a serious threat to many ecosystems and to public health. Sufficient understanding of Zn speciation and transport mechanisms is therefore critical to evaluating its risk to the environment and to developing remediation strategies. The geochemical and mineralogical characteristics of contaminated soils in the vicinity of a Zn ore transportation route were thoroughly investigated using a variety of analytical techniques (sequential extraction, XRF, XRD, SEM, and XAFS). Imported Zn-concentrate (ZnS) was deposited in a receiving facility and dispersed over time to the surrounding roadside areas and rice-paddy soils. Subsequent physical and chemical weatheringmore » resulted in dispersal into the subsurface. The species identified in the contaminated areas included Zn-sulfide, Zn-carbonate, other O-coordinated Zn-minerals, and Zn species bound to Fe/Mn oxides or clays, as confirmed by XAFS spectroscopy and sequential extraction. The observed transformation from S-coordinated Zn to O-coordinated Zn associated with minerals suggests that this contaminant can change into more soluble and labile forms as a result of weathering. For the purpose of developing a soil washing remediation process, the contaminated samples were extracted with dilute acids. The extraction efficiency increased with the increase of O-coordinated Zn relative to S-coordinated Zn in the sediment. Furthermore, this study demonstrates that improved understanding of Zn speciation in contaminated soils is essential for well-informed decision making regarding metal mobility and toxicity, as well as for choosing an appropriate remediation strategy using soil washing.« less

The use of C-near edge X-ray absorption fine structure spectroscopy for the elaboration of chemistry in lignocellulosics

Treesearch

Lucian A. Lucia; Hiroki Nanko; Alan W. Rudie; Doug G. Mancosky; Sue Wirick

2006-01-01

The research presented elucidates the oxidation chemistry occurring in hydrogen peroxide bleached kraft pulp fibers by employing carbon near edge x-ray absorption fine structure spectroscopy (C-NEXAFS). C-NEXAFS is a soft x-ray technique that selectively interrogates atomic moieties using photoelectrons (Xrays) of variable energies. The X1A beam line at the National...

A New Multibeam Sonar Technique for Evaluating Fine-Scale Fish Behavior Near Hydroelectric Dam Guidance Structures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Johnson, Robert L.; Simmons, Mary Ann; Simmons, Carver S.

2002-03-07

This book chapter describes a Dual-Head Multibeam Sonar (DHMS) system developed by Battelle and deployed at two dam sites on the Snake and Columbia rivers in Washington State to evaluate the fine-scale (

Simple Model with Time-Varying Fine-Structure ``Constant''

NASA Astrophysics Data System (ADS)

Berman, M. S.

2009-10-01

Extending the original version written in colaboration with L.A. Trevisan, we study the generalisation of Dirac's LNH, so that time-variation of the fine-structure constant, due to varying electrical and magnetic permittivities is included along with other variations (cosmological and gravitational ``constants''), etc. We consider the present Universe, and also an inflationary scenario. Rotation of the Universe is a given possibility in this model.

Accuracy of mapping the Earth's gravity field fine structure with a spaceborne gravity gradiometer mission

NASA Technical Reports Server (NTRS)

Kahn, W. D.

1984-01-01

The spaceborne gravity gradiometer is a potential sensor for mapping the fine structure of the Earth's gravity field. Error analyses were performed to investigate the accuracy of the determination of the Earth's gravity field from a gravity field satellite mission. The orbital height of the spacecraft is the dominating parameter as far as gravity field resolution and accuracies are concerned.

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

PubMed Central

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

2016-01-01

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

The impact of mating systems and dispersal on fine-scale genetic structure at maternally, paternally and biparentally inherited markers.

PubMed

Shaw, Robyn E; Banks, Sam C; Peakall, Rod

2018-01-01

For decades, studies have focused on how dispersal and mating systems influence genetic structure across populations or social groups. However, we still lack a thorough understanding of how these processes and their interaction shape spatial genetic patterns over a finer scale (tens-hundreds of metres). Using uniparentally inherited markers may help answer these questions, yet their potential has not been fully explored. Here, we use individual-level simulations to investigate the effects of dispersal and mating system on fine-scale genetic structure at autosomal, mitochondrial and Y chromosome markers. Using genetic spatial autocorrelation analysis, we found that dispersal was the major driver of fine-scale genetic structure across maternally, paternally and biparentally inherited markers. However, when dispersal was restricted (mean distance = 100 m), variation in mating behaviour created strong differences in the comparative level of structure detected at maternally and paternally inherited markers. Promiscuity reduced spatial genetic structure at Y chromosome loci (relative to monogamy), whereas structure increased under polygyny. In contrast, mitochondrial and autosomal markers were robust to differences in the specific mating system, although genetic structure increased across all markers when reproductive success was skewed towards fewer individuals. Comparing males and females at Y chromosome vs. mitochondrial markers, respectively, revealed that some mating systems can generate similar patterns to those expected under sex-biased dispersal. This demonstrates the need for caution when inferring ecological and behavioural processes from genetic results. Comparing patterns between the sexes, across a range of marker types, may help us tease apart the processes shaping fine-scale genetic structure. © 2017 John Wiley & Sons Ltd.

Joint the active source and passive source seismic to research the fine crustal structure of the Lushan area

NASA Astrophysics Data System (ADS)

Chen, Q.; Yu, C.

2017-12-01

On April 20, 2013, Ms7.0 strong earthquake (Lushan earthquake) occurred in Lanshan County Ya'an City, Sichuan Province. It is another earthquake that occurred in the Longmenshan fault zone after the Wenchuan earthquake. However, there is still no conclusive conclusion in relationship between the fine structure of the Lushan area and triggering seismic fault . In this study, the crustal structure, the shallow structure and the hidden faults and the focal mechanism of the Lushan earthquake were analyzed by using the deep seismic reflection profile and the broadband seismic array data. Combined with the surface geological information, the structure and fracture cause of the Lishan earthquake were discussed.We have synthetic analyzed the seismic precursors, fine locating, focal mechanism analysis and time-tomographic imaging of the broadband seismic data before and after the earthquake in Lushan earthquake, and obtained the seismic distribution, the focal mechanism and the crustal fine structure in the Lushan area. And we use these results to detailed interpreted the deep reflection seismic section of the Lushan earthquake zone.The results show that the crust of the Lushan area is characterized by a distinct structure of upper crust with thickness about 14.75km. The nature of the faults is inferred to be thrusting in the region due to the pushing of the crustal material of the Tibetan plateau into the southeast part of the rigid Sichuan basin. The shuangshi-Dachuan fault stretches from the surface to the deep crust at a low angle, and is dominated by thrusting in a form of imbricate structure with small-scale faults nearby. Whereas the Guangyuan-Dayi fault is a positive flower structure with a listric shape, consisting of six branches. Its movement is dominated by thrusting with gentle horizontal slip.

Photoionization of ground and excited levels of P II

NASA Astrophysics Data System (ADS)

Nahar, Sultana N.

2017-01-01

Photoionization cross section (σPI) of P II, (hν + P II → P III + e), from ground and a large number of excited levels are presented. The study includes the resonant structures and the characteristics of the background in photoionization cross sections. The present calculations were carried out in the Breit-Pauli R-matrix (BPRM) method that includes relativistic effects. The autoionizing resonances are delineated with a fine energy mesh to observe the fine structure effects. A singular resonance, formed by the coupling of channels in fine structure but not allowed in LS coupling, is seen at the ionization threshold of photoionization for the ground and many excited levels. The background cross section is seen enhanced compared to smooth decay for the excited levels. Examples are presented to illustrate the enhanced background cross sections at the energies of the core levels, 4P3/2 and 2D3/2, that are allowed for electric dipole transitions by the core ground level 2 P1/2o. In addition strong Seaton or photo-excitation-of-core (PEC) resonances are found in the photoionization of single valence electron excited levels. Calculations used a close coupling wave function expansion that included 18 fine structure levels of core P III from configurations 3s23p, 3s3p2, 3s23d, 3s24s, 3s24p and 3p3. Photoionization cross sections are presented for all 475 fine structure levels of P II found with n ≤ 10 and l ≤ 9. The present results will provide high precision parameters of various applications involving this less studied ion.

Counting individual sulfur atoms in a protein by ultrahighresolution Fourier transform ion cyclotron resonance mass spectrometry: Experimental resolution of isotopic fine structure in proteins

PubMed Central

Shi, Stone D.-H.; Hendrickson, Christopher L.; Marshall, Alan G.

1998-01-01

A typical molecular ion mass spectrum consists of a sum of signals from species of various possible isotopic compositions. Only the monoisotopic peak (e.g., all carbons are 12C; all nitrogens are 14N, etc.) has a unique elemental composition. Every other isotope peak at approximately integer multiples of ∼1 Da higher in nominal mass represents a sum of contributions from isotope combinations differing by a few mDa (e.g., two 13C vs. two 15N vs. one 13C and one 15N vs. 34S, vs. 18O, etc., at ∼2 Da higher in mass than the monoisotopic mass). At sufficiently high mass resolving power, each of these nominal-mass peaks resolves into its isotopic fine structure. Here, we report resolution of the isotopic fine structure of proteins up to 15.8 kDa (isotopic 13C,15N doubly depleted tumor suppressor protein, p16), made possible by electrospray ionization followed by ultrahigh-resolution Fourier transform ion cyclotron resonance mass analysis at 9.4 tesla. Further, a resolving power of m/Δm50% ≈8,000,000 has been achieved on bovine ubiquitin (8.6 kDa). These results represent a 10-fold increase in the highest mass at which isotopic fine structure previously had been observed. Finally, because isotopic fine structure reveals elemental composition directly, it can be used to confirm or determine molecular formula. For p16, for example, we were able to determine (5.1 ± 0.3) the correct number (five) of sulfur atoms solely from the abundance ratio of the resolved 34S peak to the monoisotopic peak. PMID:9751700

Determinants of fish assemblage structure in Northwestern Great Plains streams

USGS Publications Warehouse

Mullen, J.A.; Bramblett, R.G.; Guy, C.S.; Zale, A.V.; Roberts, D.W.

2011-01-01

Prairie streams are known for their harsh and stochastic physical conditions, and the fish assemblages therein have been shown to be temporally variable. We assessed the spatial and temporal variation in fish assemblage structure in five intermittent, adventitious northwestern Great Plains streams representing a gradient of watershed areas. Fish assemblages and abiotic conditions varied more spatially than temporally. The most important variables explaining fish assemblage structure were longitudinal position and the proportion of fine substrates. The proportion of fine substrates increased proceeding upstream, approaching 100% in all five streams, and species richness declined upstream with increasing fine substrates. High levels of fine substrate in the upper reaches appeared to limit the distribution of obligate lithophilic fish species to reaches further downstream. Species richness and substrates were similar among all five streams at the lowermost and uppermost sites. However, in the middle reaches, species richness increased, the amount of fine substrate decreased, and connectivity increased as watershed area increased. Season and some dimensions of habitat (including thalweg depth, absolute distance to the main-stem river, and watershed size) were not essential in explaining the variation in fish assemblages. Fish species richness varied more temporally than overall fish assemblage structure did because common species were consistently abundant across seasons, whereas rare species were sometimes absent or perhaps not detected by sampling. The similarity in our results among five streams varying in watershed size and those from other studies supports the generalization that spatial variation exceeds temporal variation in the fish assemblages of prairie and warmwater streams. Furthermore, given longitudinal position, substrate, and stream size, general predictions regarding fish assemblage structure and function in prairie streams are possible. ?? American Fisheries Society 2011.

Structure of Co-Doped Alq3 thin films investigated by grazing incidence X-ray absorption fine structure and Fourier transform infrared spectroscopy.

PubMed

Lin, Liang; Pang, Zhiyong; Fang, Shaojie; Wang, Fenggong; Song, Shumei; Huang, Yuying; Wei, Xiangjun; Yu, Haisheng; Han, Shenghao

2011-02-10

The structural properties of Co-doped tris(8-hydroxyquinoline)aluminum (Alq(3)) have been studied by grazing incidence X-ray absorption fine structure (GIXAFS) and Fourier transform infrared spectroscopy (FTIR). GIXAFS analysis suggests that there are multivalent Co-Alq(3) complexes and the doped Co atoms tend to locate at the attraction center with respect to N and O atoms and bond with them. The FTIR spectra indicate that the Co atoms interact with the meridional (mer) isomer of Alq(3) rather than forming inorganic compounds.

Spin interactions in InAs quantum dots

NASA Astrophysics Data System (ADS)

Doty, M. F.; Ware, M. E.; Stinaff, E. A.; Scheibner, M.; Bracker, A. S.; Gammon, D.; Ponomarev, I. V.; Reinecke, T. L.; Korenev, V. L.

2006-03-01

Fine structure splittings in optical spectra of self-assembled InAs quantum dots (QDs) generally arise from spin interactions between particles confined in the dots. We present experimental studies of the fine structure that arises from multiple charges confined in a single dot [1] or in molecular orbitals of coupled pairs of dots. To probe the underlying spin interactions we inject particles with a known spin orientation (by using polarized light to perform photoluminescence excitation spectroscopy experiments) or use a magnetic field to orient and/or mix the spin states. We develop a model of the spin interactions that aids in the development of quantum information processing applications based on controllable interactions between spins confined to QDs. [1] Polarized Fine Structure in the Photoluminescence Excitation Spectrum of a Negatively Charged Quantum Dot, Phys. Rev. Lett. 95, 177403 (2005)

Measuring h /mCs and the Fine Structure Constant with Bragg Diffraction and Bloch Oscillations

NASA Astrophysics Data System (ADS)

Parker, Richard

2016-05-01

We have demonstrated a new scheme for atom interferometry based on large-momentum-transfer Bragg beam splitters and Bloch oscillations. In this new scheme, we have achieved a resolution of δα / α =0.25ppb in the fine structure constant measurement, which gives up to 4.4 million radians of phase difference between freely evolving matter waves. We suppress many systematic effects, e.g., Zeeman shifts and effects from Earth's gravity and vibrations, use Bloch oscillations to increase the signal and reduce the diffraction phase, simulate multi-atom Bragg diffraction to understand sub-ppb systematic effects, and implement spatial filtering to further suppress systematic effects. We present our recent progress toward a measurement of the fine structure constant, which will provide a stringent test of the standard model of particle physics.

Porous-electrode preparation method

DOEpatents

Arons, R.M.; Dusek, J.T.

1981-09-17

A porous sintered plaque is provided with a bimodal porosity that is especially well suited for use as an electrode within a molten carbonate fuel cell. The coarse porosity is sufficient for admitting gases into contact with the reaction surfaces while the fine porosity is wetted with and retains molten electrolyte on the reaction sites. The electrode structure is prepared by providing a very fine powder such as nickel oxide and blending the powder with a suitable decomposable binder to form a solid mass. The mass is comminuted into agglomerate size particles substantially larger than the fine oxide particles and formed into a cohesive compact for subsequent sintering. Sintering is carried out at sufficient conditions to bind the agglomerates together into a porous structure having both coarse and fine porosity. Where lithiated nickel oxide cathodes are prepared, the sintering conditions can be moderate enough to retain substantial quantities of lithium within the electrode for adequate conductivity.

Porous electrode preparation method

DOEpatents

Arons, Richard M.; Dusek, Joseph T.

1983-01-01

A porous sintered plaque is provided with a bimodal porosity that is especially well suited for use as an electrode within a molten carbonate fuel cell. The coarse porosity is sufficient for admitting gases into contact with the reaction surfaces while the fine porosity is wetted with and retains molten electrolyte on the reaction sites. The electrode structure is prepared by providing a very fine powder of such as nickel oxide and blending the powder with a suitable decomposable binder to form a solid mass. The mass is comminuted into agglomerate size particles substantially larger than the fine oxide particles and formed into a cohesive compact for subsequent sintering. Sintering is carried out at sufficient conditions to bind the agglomerates together into a porous structure having both coarse and fine porosity. Where lithiated nickel oxide cathodes are prepared, the sintering conditions can be moderate enough to retain substantial quantities of lithium within the electrode for adequate conductivity.

Porous electrode preparation method

DOEpatents

Arons, R.M.; Dusek, J.T.

1983-10-18

A porous sintered plaque is provided with a bimodal porosity that is especially well suited for use as an electrode within a molten carbonate fuel cell. The coarse porosity is sufficient for admitting gases into contact with the reaction surfaces while the fine porosity is wetted with and retains molten electrolyte on the reaction sites. The electrode structure is prepared by providing a very fine powder of such as nickel oxide and blending the powder with a suitable decomposable binder to form a solid mass. The mass is comminuted into agglomerate size particles substantially larger than the fine oxide particles and formed into a cohesive compact for subsequent sintering. Sintering is carried out at sufficient conditions to bind the agglomerates together into a porous structure having both coarse and fine porosity. Where lithiated nickel oxide cathodes are prepared, the sintering conditions can be moderate enough to retain substantial quantities of lithium within the electrode for adequate conductivity. 2 figs.

Optimal Design of Experiments by Combining Coarse and Fine Measurements

NASA Astrophysics Data System (ADS)

Lee, Alpha A.; Brenner, Michael P.; Colwell, Lucy J.

2017-11-01

In many contexts, it is extremely costly to perform enough high-quality experimental measurements to accurately parametrize a predictive quantitative model. However, it is often much easier to carry out large numbers of experiments that indicate whether each sample is above or below a given threshold. Can many such categorical or "coarse" measurements be combined with a much smaller number of high-resolution or "fine" measurements to yield accurate models? Here, we demonstrate an intuitive strategy, inspired by statistical physics, wherein the coarse measurements are used to identify the salient features of the data, while the fine measurements determine the relative importance of these features. A linear model is inferred from the fine measurements, augmented by a quadratic term that captures the correlation structure of the coarse data. We illustrate our strategy by considering the problems of predicting the antimalarial potency and aqueous solubility of small organic molecules from their 2D molecular structure.

High-performance Chinese multiclass traffic sign detection via coarse-to-fine cascade and parallel support vector machine detectors

NASA Astrophysics Data System (ADS)

Chang, Faliang; Liu, Chunsheng

2017-09-01

The high variability of sign colors and shapes in uncontrolled environments has made the detection of traffic signs a challenging problem in computer vision. We propose a traffic sign detection (TSD) method based on coarse-to-fine cascade and parallel support vector machine (SVM) detectors to detect Chinese warning and danger traffic signs. First, a region of interest (ROI) extraction method is proposed to extract ROIs using color contrast features in local regions. The ROI extraction can reduce scanning regions and save detection time. For multiclass TSD, we propose a structure that combines a coarse-to-fine cascaded tree with a parallel structure of histogram of oriented gradients (HOG) + SVM detectors. The cascaded tree is designed to detect different types of traffic signs in a coarse-to-fine process. The parallel HOG + SVM detectors are designed to do fine detection of different types of traffic signs. The experiments demonstrate the proposed TSD method can rapidly detect multiclass traffic signs with different colors and shapes in high accuracy.

Limited Effects of Variable-Retention Harvesting on Fungal Communities Decomposing Fine Roots in Coastal Temperate Rainforests.

PubMed

Philpott, Timothy J; Barker, Jason S; Prescott, Cindy E; Grayston, Sue J

2018-02-01

Fine root litter is the principal source of carbon stored in forest soils and a dominant source of carbon for fungal decomposers. Differences in decomposer capacity between fungal species may be important determinants of fine-root decomposition rates. Variable-retention harvesting (VRH) provides refuge for ectomycorrhizal fungi, but its influence on fine-root decomposers is unknown, as are the effects of functional shifts in these fungal communities on carbon cycling. We compared fungal communities decomposing fine roots (in litter bags) under VRH, clear-cut, and uncut stands at two sites (6 and 13 years postharvest) and two decay stages (43 days and 1 year after burial) in Douglas fir forests in coastal British Columbia, Canada. Fungal species and guilds were identified from decomposed fine roots using high-throughput sequencing. Variable retention had short-term effects on β-diversity; harvest treatment modified the fungal community composition at the 6-year-postharvest site, but not at the 13-year-postharvest site. Ericoid and ectomycorrhizal guilds were not more abundant under VRH, but stand age significantly structured species composition. Guild composition varied by decay stage, with ruderal species later replaced by saprotrophs and ectomycorrhizae. Ectomycorrhizal abundance on decomposing fine roots may partially explain why fine roots typically decompose more slowly than surface litter. Our results indicate that stand age structures fine-root decomposers but that decay stage is more important in structuring the fungal community than shifts caused by harvesting. The rapid postharvest recovery of fungal communities decomposing fine roots suggests resiliency within this community, at least in these young regenerating stands in coastal British Columbia. IMPORTANCE Globally, fine roots are a dominant source of carbon in forest soils, yet the fungi that decompose this material and that drive the sequestration or respiration of this carbon remain largely uncharacterized. Fungi vary in their capacity to decompose plant litter, suggesting that fungal community composition is an important determinant of decomposition rates. Variable-retention harvesting is a forestry practice that modifies fungal communities by providing refuge for ectomycorrhizal fungi. We evaluated the effects of variable retention and clear-cut harvesting on fungal communities decomposing fine roots at two sites (6 and 13 years postharvest), at two decay stages (43 days and 1 year), and in uncut stands in temperate rainforests. Harvesting impacts on fungal community composition were detected only after 6 years after harvest. We suggest that fungal community composition may be an important factor that reduces fine-root decomposition rates relative to those of above-ground plant litter, which has important consequences for forest carbon cycling. Copyright © 2018 American Society for Microbiology.

Atomic oxygen fine-structure splittings with tunable far-infrared spectroscopy

NASA Technical Reports Server (NTRS)

Zink, Lyndon R.; Evenson, Kenneth M.; Matsushima, Fusakazu; Nelis, Thomas; Robinson, Ruth L.

1991-01-01

Fine-structure splittings of atomic oxygen (O-16) in the ground state have been accurately measured using a tunable far-infrared spectrometer. The 3P0-3pl splitting is 2,060,069.09 (10) MHz, and the 3Pl-3P2 splitting is 4,744,777.49 (16) MHz. These frequencies are important for measuring atomic oxygen concentration in earth's atmosphere and the interstellar medium.

Novel visualization studies of lignocellulosic oxidation chemistry by application of C-near edge X-ray absorption fine structure spectroscopy

Treesearch

Douglas G. Mancosky; Lucian A. Lucia; Hiroki Nanko; Sue Wirick; Alan W. Rudie; Robert Braun

2005-01-01

The research presented herein is the first attempt to probe the chemical nature of lignocellulosic samples by the application of carbon near edge X-ray absorption fine structure spectroscopy (C-NEXAFS). C-NEXAFS is a soft X-ray technique that principally provides selective interrogation of discrete atomic moieties using photoelectrons of variable energies. The X1A beam...

A correlational method to concurrently measure envelope and temporal fine structure weights: effects of age, cochlear pathology, and spectral shaping.

PubMed

Fogerty, Daniel; Humes, Larry E

2012-09-01

The speech signal may be divided into spectral frequency-bands, each band containing temporal properties of the envelope and fine structure. This study measured the perceptual weights for the envelope and fine structure in each of three frequency bands for sentence materials in young normal-hearing listeners, older normal-hearing listeners, aided older hearing-impaired listeners, and spectrally matched young normal-hearing listeners. The availability of each acoustic property was independently varied through noisy signal extraction. Thus, the full speech stimulus was presented with noise used to mask six different auditory channels. Perceptual weights were determined by correlating a listener's performance with the signal-to-noise ratio of each acoustic property on a trial-by-trial basis. Results demonstrate that temporal fine structure perceptual weights remain stable across the four listener groups. However, a different weighting typography was observed across the listener groups for envelope cues. Results suggest that spectral shaping used to preserve the audibility of the speech stimulus may alter the allocation of perceptual resources. The relative perceptual weighting of envelope cues may also change with age. Concurrent testing of sentences repeated once on a previous day demonstrated that weighting strategies for all listener groups can change, suggesting an initial stabilization period or susceptibility to auditory training.

Quantitative performance measurements of bent crystal Laue analyzers for X-ray fluorescence spectroscopy.

PubMed

Karanfil, C; Bunker, G; Newville, M; Segre, C U; Chapman, D

2012-05-01

Third-generation synchrotron radiation sources pose difficult challenges for energy-dispersive detectors for XAFS because of their count rate limitations. One solution to this problem is the bent crystal Laue analyzer (BCLA), which removes most of the undesired scatter and fluorescence before it reaches the detector, effectively eliminating detector saturation due to background. In this paper experimental measurements of BCLA performance in conjunction with a 13-element germanium detector, and a quantitative analysis of the signal-to-noise improvement of BCLAs are presented. The performance of BCLAs are compared with filters and slits.

High-resolution observations of active region moss and its dynamics

DOE Office of Scientific and Technical Information (OSTI.GOV)

Morton, R. J.; McLaughlin, J. A., E-mail: richard.morton@northumbria.ac.uk

2014-07-10

The High Resolution Coronal Imager has provided the sharpest view of the EUV corona to date. In this paper, we exploit its impressive resolving power to provide the first analysis of the fine-scale structure of moss in an active region. The data reveal that the moss is made up of a collection of fine threads that have widths with a mean and standard deviation of 440 ± 190 km (FWHM). The brightest moss emission is located at the visible head of the fine-scale structure and the fine structure appears to extend into the lower solar atmosphere. The emission decreases alongmore » the features, implying that the lower sections are most likely dominated by cooler transition region plasma. These threads appear to be the cool, lower legs of the hot loops. In addition, the increased resolution allows for the first direct observation of physical displacements of the moss fine structure in a direction transverse to its central axis. Some of these transverse displacements demonstrate periodic behavior, which we interpret as a signature of kink (Alfvénic) waves. Measurements of the properties of the transverse motions are made and the wave motions have means and standard deviations of 55 ± 37 km for the transverse displacement amplitude, 77 ± 33 s for the period, and 4.7 ± 2.5 km s{sup –1} for the velocity amplitude. The presence of waves in the transition region of hot loops could have important implications for the heating of active regions.« less

Detection of fibrils associated with Rickettsia rickettsii.

PubMed

Todd, W J; Burgdorfer, W; Wray, G P

1983-09-01

The ultrastructural appearance of the "halozone" formed at the interface between the spotted fever agent Rickettsia rickettsii and the cytoplasm of persistently infected cultured vole cells (Microtus pennsylvanicus) was studied by transmission electron microscopy. In sections of epoxy-embedded specimens stained with uranyl acetate and lead citrate, the halozone appeared clear and devoid of ultrastructural features. However, when unembedded preparations of whole infected cells were examined at 1,000 kV, fine structural features were observed within the halozone. These features, associated with the rickettsial outer membrane, were more clearly detectable when the infected cells were extracted with the detergent Triton X-100 before fixation. Under such conditions, long extensions of the rickettsial outer membrane, microfilament-like structures attached to that membrane, and extensive attachments between adjacent rickettsiae were seen. The fine structural features within the rickettsial halozone were also seen at 75 kV when unembedded sections were prepared from polyethylene glycol-embedded specimens. Thus, epoxy-embedding medium obscures the fine structural features within the halozone surrounding the rickettsiae in infected cells.

Detection of fibrils associated with Rickettsia rickettsii.

PubMed Central

Todd, W J; Burgdorfer, W; Wray, G P

1983-01-01

The ultrastructural appearance of the "halozone" formed at the interface between the spotted fever agent Rickettsia rickettsii and the cytoplasm of persistently infected cultured vole cells (Microtus pennsylvanicus) was studied by transmission electron microscopy. In sections of epoxy-embedded specimens stained with uranyl acetate and lead citrate, the halozone appeared clear and devoid of ultrastructural features. However, when unembedded preparations of whole infected cells were examined at 1,000 kV, fine structural features were observed within the halozone. These features, associated with the rickettsial outer membrane, were more clearly detectable when the infected cells were extracted with the detergent Triton X-100 before fixation. Under such conditions, long extensions of the rickettsial outer membrane, microfilament-like structures attached to that membrane, and extensive attachments between adjacent rickettsiae were seen. The fine structural features within the rickettsial halozone were also seen at 75 kV when unembedded sections were prepared from polyethylene glycol-embedded specimens. Thus, epoxy-embedding medium obscures the fine structural features within the halozone surrounding the rickettsiae in infected cells. Images PMID:6411620

Julius Edgar Lilienfeld Prize Talk: Measuring the Electron Magnetic Moment and the Fine Structure Constant

NASA Astrophysics Data System (ADS)

Gabrielse, Gerald

2011-05-01

The electron magnetic moment in Bohr magnetons has been measured to a precision of 3 parts in 1013. This measurement, with quantum electrodynamics (AED) theory, provides the most precise value of the fine structure constant. This measurement, with a value of the fine structure from other measurements, also tests QED and sets a limit on the internal structure of the electron. A one-electron quantum cyclotron is at the heart of the measurement -- an electron suspended in a magnetic field and cooled enough that its lowest cyclotron and spin quantum states can be deduced with quantum nondemolition (QND) measurements. A cylindrical Penning trap cavity inhibits spontaneous emission and feedback methods make the electron excite and sustain its own motion for detection. A new apparatus is being commissioned in pursuit of more precise measurements. Adapted methods are promising for observing a proton spin flip, which should make it possible to compare the antiproton and proton magnetic moments a million times more accurately than is currently possible.

New determination of the fine structure constant from the electron value and QED.

PubMed

Gabrielse, G; Hanneke, D; Kinoshita, T; Nio, M; Odom, B

2006-07-21

Quantum electrodynamics (QED) predicts a relationship between the dimensionless magnetic moment of the electron (g) and the fine structure constant (alpha). A new measurement of g using a one-electron quantum cyclotron, together with a QED calculation involving 891 eighth-order Feynman diagrams, determine alpha(-1)=137.035 999 710 (96) [0.70 ppb]. The uncertainties are 10 times smaller than those of nearest rival methods that include atom-recoil measurements. Comparisons of measured and calculated g test QED most stringently, and set a limit on internal electron structure.

Structural and electrical properties of In-implanted Ge

DOE PAGES

Feng, R.; Kremer, F.; Sprouster, D. J.; ...

2015-10-22

Here, we report on the effects of dopant concentration on the structural and electrical properties of In-implanted Ge. For In concentrations of ≤ 0.2 at. %, extended x-ray absorption fine structure and x-ray absorption near-edge structure measurements demonstrate that all In atoms occupy a substitutional lattice site while metallic In precipitates are apparent in transmission electron micrographs for In concentrations ≥0.6 at. %. Evidence of the formation of In-vacancy complexes deduced from extended x-ray absorption fine structure measurements is complimented by density functional theory simulations. Hall effect measurements of the conductivity, carrier density, and carrier mobility are then correlated withmore » the substitutional In fraction.« less

Adsorption of Fe(II) and U(VI) to carboxyl-functionalized microspheres: The influence of speciation on uranyl reduction studied by titration and XAFS

NASA Astrophysics Data System (ADS)

Boyanov, Maxim I.; O'Loughlin, Edward J.; Roden, Eric E.; Fein, Jeremy B.; Kemner, Kenneth M.

2007-04-01

The chemical reduction of U(VI) by Fe(II) is a potentially important pathway for immobilization of uranium in subsurface environments. Although the presence of surfaces has been shown to catalyze the reaction between Fe(II) and U(VI) aqueous species, the mechanism(s) responsible for the enhanced reactivity remain ambiguous. To gain further insight into the U-Fe redox process at a complexing, non-conducting surface that is relevant to common organic phases in the environment, we studied suspensions containing combinations of 0.1 mM U(VI), 1.0 mM Fe(II), and 4.2 g/L carboxyl-functionalized polystyrene microspheres. Acid-base titrations were used to monitor protolytic reactions, and Fe K-edge and U L-edge X-ray absorption fine structure spectroscopy was used to determine the valence and atomic environment of the adsorbed Fe and U species. In the Fe + surface carboxyl system, a transition from monomeric to oligomeric Fe(II) surface species was observed between pH 7.5 and pH 8.4. In the U + surface carboxyl system, the U(VI) cation was adsorbed as a mononuclear uranyl-carboxyl complex at both pH 7.5 and 8.4. In the ternary U + Fe + surface carboxyl system, U(VI) was not reduced by the solvated or adsorbed Fe(II) at pH 7.5 over a 4-month period, whereas complete and rapid reduction to U(IV) nanoparticles occurred at pH 8.4. The U(IV) product reoxidized rapidly upon exposure to air, but it was stable over a 4-month period under anoxic conditions. Fe atoms were found in the local environment of the reduced U(IV) atoms at a distance of 3.56 Å. The U(IV)-Fe coordination is consistent with an inner-sphere electron transfer mechanism between the redox centers and involvement of Fe(II) atoms in both steps of the reduction from U(VI) to U(IV). The inability of Fe(II) to reduce U(VI) in solution and at pH 7.5 in the U + Fe + carboxyl system is explained by the formation of a transient, "dead-end" U(V)-Fe(III) complex that blocks the U(V) disproportionation pathway after the first electron transfer. The increased reactivity at pH 8.4 relative to pH 7.5 is explained by the reaction of U(VI) with an Fe(II) oligomer, whereby the bonds between Fe atoms facilitate the transfer of a second electron to the hypothetical U(V)-Fe(III) intermediate. We discuss how this mechanism may explain the commonly observed higher efficiency of uranyl reduction by adsorbed or structural Fe(II) relative to aqueous Fe(II).

Rocket observations of electron-density irregularities in the equatorial ionosphere below 200 km

NASA Technical Reports Server (NTRS)

Klaus, D. E.; Smith, L. G.

1978-01-01

Nike Apache rockets carring instrumentation to measure electron density and its fine structure in the equatorial ionosphere were launched from Chilca, Peru in May and June 1975. The fine structure experiment and the data reduction system are described. Results obtained from this system are presented and compared with those obtained by VHF radar and from other rocket studies. A description of the equatorial ionosphere and its features is also presented.

Effective collision strengths for the electron impact excitation of Mg

NASA Astrophysics Data System (ADS)

Hudson, C. E.; Ramsbottom, C. A.; Norrington, P. H.; Scott, M. P.

2008-05-01

Electron impact excitation collision strengths for fine structure transitions of Mg,have been determined by a Breit-Pauli R-matrix calculation. The target states are represented by configuration interaction wavefunctions and consist of the 19 lowest LS states, having configurations 2s^22p^4, 2s2p^5, 2p^6, 2s^22p^33s and 2s^22p^33p. These target states give rise to 37 fine structure levels and 666 possible transitions. The effective collision strengths are calculated by averaging the electron collision strengths over a Maxwellian distribution of electron velocities. Effective collision strengths for transitions between the fine structure levels are given for electron temperatures in the range 10Te(K) = 3.0 - 7.0. Results are compared with the previous R-matrix calculation of Butler & Zeippen (AASS, 1994) and the recent Distorted Wave evaluations of Bhatia, Landi & Eissner (ADNDT, 2006).

Origin of fine structure of the giant dipole resonance in s d -shell nuclei

NASA Astrophysics Data System (ADS)

Fearick, R. W.; Erler, B.; Matsubara, H.; von Neumann-Cosel, P.; Richter, A.; Roth, R.; Tamii, A.

2018-04-01

A set of high-resolution zero-degree inelastic proton scattering data on 24Mg, 28Si, 32S, and 40Ca provides new insight into the long-standing puzzle of the origin of fragmentation of the giant dipole resonance (GDR) in s d -shell nuclei. Understanding is achieved by comparison with random phase approximation calculations for deformed nuclei using for the first time a realistic nucleon-nucleon interaction derived from the Argonne V18 potential with the unitary correlation operator method and supplemented by a phenomenological three-nucleon contact interaction. A wavelet analysis allows one to extract significant scales both in the data and calculations characterizing the fine structure of the GDR. The fair agreement for scales in the range of a few hundred keV supports the surmise that the fine structure arises from ground-state deformation driven by α clustering.

Annealing induced atomic rearrangements on (Ga,In) (N,As) probed by hard X-ray photoelectron spectroscopy and X-ray absorption fine structure.

PubMed

Ishikawa, Fumitaro; Higashi, Kotaro; Fuyuno, Satoshi; Morifuji, Masato; Kondow, Masahiko; Trampert, Achim

2018-04-13

We study the effects of annealing on (Ga 0.64 ,In 0.36 ) (N 0.045 ,As 0.955 ) using hard X-ray photoelectron spectroscopy and X-ray absorption fine structure measurements. We observed surface oxidation and termination of the N-As bond defects caused by the annealing process. Specifically, we observed a characteristic chemical shift towards lower binding energies in the photoelectron spectra related to In. This phenomenon appears to be caused by the atomic arrangement, which produces increased In-N bond configurations within the matrix, as indicated by the X-ray absorption fine structure measurements. The reduction in the binding energies of group-III In, which occurs concomitantly with the atomic rearrangements of the matrix, causes the differences in the electronic properties of the system before and after annealing.

Dynamic Jahn-Teller effect: Calculation of fine structure spectrum, isotope shift and Zeeman behavior at deep center Ni2+ in CdS

NASA Astrophysics Data System (ADS)

Schoepp, Juergen

The internal transition of the deep center Ni2+ in II to IV semiconductor cadmium sulfide is examined with reference to crystal field theory. An algorithm was developed for calculation, in a basis fitted to trigonal symmetry, of fine structure operator matrix which is made of the sum of operators from spin trajectory coupling, trigonal field and electron phonon coupling. The dependence of energy level on the mass was calculated in order to examine the isotropy effect at Ni2+ transition. The mass dependence of phonon energy was estimated in an atomic cluster by using a valence force model from Keating for elastic energy. The Zeeman behavior of Ni2+ transition was examined for magnetic fields; the Zeeman operator was added to the fine structure operator and the resulting matrix was diagonalized. It is noticed that calculations are quantitatively and qualitatively in agreement with experiments.

Fine structure constant and quantized optical transparency of plasmonic nanoarrays.

PubMed

Kravets, V G; Schedin, F; Grigorenko, A N

2012-01-24

Optics is renowned for displaying quantum phenomena. Indeed, studies of emission and absorption lines, the photoelectric effect and blackbody radiation helped to build the foundations of quantum mechanics. Nevertheless, it came as a surprise that the visible transparency of suspended graphene is determined solely by the fine structure constant, as this kind of universality had been previously reserved only for quantized resistance and flux quanta in superconductors. Here we describe a plasmonic system in which relative optical transparency is determined solely by the fine structure constant. The system consists of a regular array of gold nanoparticles fabricated on a thin metallic sublayer. We show that its relative transparency can be quantized in the near-infrared, which we attribute to the quantized contact resistance between the nanoparticles and the metallic sublayer. Our results open new possibilities in the exploration of universal dynamic conductance in plasmonic nanooptics.

Fine Structure of Beta Decay Strength Function and Anisotropy of Isovector Nuclear Dencity Component Oscillations in Deformed Nuclei

NASA Astrophysics Data System (ADS)

Izosimov, I. N.; Solnyshkin, A. A.; Khushvaktov, J. H.; Vaganov, Yu. A.

2018-05-01

The experimental measurement data on the fine structure of beta-decay strength function S β( E) in spherical, transitional, and deformed nuclei are analyzed. Modern high-resolution nuclear spectroscopy methods made it possible to identify the splitting of peaks in S β( E) for deformed nuclei. By analogy with splitting of the peak of E1 giant dipole resonance (GDR) in deformed nuclei, the peaks in S β( E) are split into two components from the axial nuclear deformation. In this report, the fine structure of S β( E) is discussed. Splitting of the peaks connected with the oscillations of neutrons against protons (E1GDR), of proton holes against neutrons (peaks in S β( E) of β+/ EC-decay), and of protons against neutron holes (peaks in S β( E) of β--decay) is discussed.

Band-Edge Exciton Fine Structure and Recombination Dynamics in InP/ZnS Colloidal Nanocrystals.

PubMed

Biadala, Louis; Siebers, Benjamin; Beyazit, Yasin; Tessier, Mickaël D; Dupont, Dorian; Hens, Zeger; Yakovlev, Dmitri R; Bayer, Manfred

2016-03-22

We report on a temperature-, time-, and spectrally resolved study of the photoluminescence of type-I InP/ZnS colloidal nanocrystals with varying core size. By studying the exciton recombination dynamics we assess the exciton fine structure in these systems. In addition to the typical bright-dark doublet, the photoluminescence stems from an upper bright state in spite of its large energy splitting (∼100 meV). This striking observation results from dramatically lengthened thermalization processes among the fine structure levels and points to optical-phonon bottleneck effects in InP/ZnS nanocrystals. Furthermore, our data show that the radiative recombination of the dark exciton scales linearly with the bright-dark energy splitting for CdSe and InP nanocrystals. This finding strongly suggests a universal dangling bonds-assisted recombination of the dark exciton in colloidal nanostructures.

Reconstruction of vessel structures from serial whole slide sections of murine liver samples

NASA Astrophysics Data System (ADS)

Schwier, Michael; Hahn, Horst K.; Dahmen, Uta; Dirsch, Olaf

2013-03-01

Image-based analysis of the vascular structures of murine liver samples is an important tool for scientists to understand liver physiology and morphology. Typical assessment methods are MicroCT, which allows for acquiring images of the whole organ while lacking resolution for fine details, and confocal laser scanning microscopy, which allows detailed insights into fine structures while lacking the broader context. Imaging of histological serial whole slide sections is a recent technology able to fill this gap, since it provides a fine resolution up to the cellular level, but on a whole organ scale. However, whole slide imaging is a modality providing only 2D images. Therefore the challenge is to use stacks of serial sections from which to reconstruct the 3D vessel structures. In this paper we present a semi-automatic procedure to achieve this goal. We employ an automatic method that detects vessel structures based on continuity and shape characteristics. Furthermore it supports the user to perform manual corrections where required. With our methods we were able to successfully extract and reconstruct vessel structures from a stack of 100 and a stack of 397 serial sections of a mouse liver lobe, thus proving the potential of our approach.

Fine-scale genetic structure in populations of the Chagas' disease vector Triatoma infestans (Hemiptera, Reduvidae).

PubMed

Pérez de Rosas, Alicia R; Segura, Elsa L; Fusco, Octavio; Guiñazú, Adolfo L Bareiro; García, Beatriz A

2013-03-01

Fine scale patterns of genetic structure and dispersal in Triatoma infestans populations from Argentina was analysed. A total of 314 insects from 22 domestic and peridomestic sites from the locality of San Martín (Capayán department, Catamarca province) were typed for 10 polymorphic microsatellite loci. The results confirm subdivision of T. infestans populations with restricted dispersal among sampling sites and suggest inbreeding and/or stratification within the different domestic and peridomestic structures. Spatial correlation analysis showed that the scale of structuring is approximately of 400 m, indicating that active dispersal would occur within this distance range. It was detected difference in scale of structuring among sexes, with females dispersing over greater distances than males. This study suggests that insecticide treatment and surveillance should be extended within a radius of 400 m around the infested area, which would help to reduce the probability of reinfestation by covering an area of active dispersal. The inferences made from fine-scale spatial genetic structure analyses of T. infestans populations has demonstrated to be important for community-wide control programs, providing a complementary approach to help improve vector control strategies.

A review of hybrid implicit explicit finite difference time domain method

NASA Astrophysics Data System (ADS)

Chen, Juan

2018-06-01

The finite-difference time-domain (FDTD) method has been extensively used to simulate varieties of electromagnetic interaction problems. However, because of its Courant-Friedrich-Levy (CFL) condition, the maximum time step size of this method is limited by the minimum size of cell used in the computational domain. So the FDTD method is inefficient to simulate the electromagnetic problems which have very fine structures. To deal with this problem, the Hybrid Implicit Explicit (HIE)-FDTD method is developed. The HIE-FDTD method uses the hybrid implicit explicit difference in the direction with fine structures to avoid the confinement of the fine spatial mesh on the time step size. So this method has much higher computational efficiency than the FDTD method, and is extremely useful for the problems which have fine structures in one direction. In this paper, the basic formulations, time stability condition and dispersion error of the HIE-FDTD method are presented. The implementations of several boundary conditions, including the connect boundary, absorbing boundary and periodic boundary are described, then some applications and important developments of this method are provided. The goal of this paper is to provide an historical overview and future prospects of the HIE-FDTD method.

(1,3;1,4)-β-Glucan Biosynthesis by the CSLF6 Enzyme: Position and Flexibility of Catalytic Residues Influence Product Fine Structure.

PubMed

Dimitroff, George; Little, Alan; Lahnstein, Jelle; Schwerdt, Julian G; Srivastava, Vaibhav; Bulone, Vincent; Burton, Rachel A; Fincher, Geoffrey B

2016-04-05

Cellulose synthase-like F6 (CslF6) genes encode polysaccharide synthases responsible for (1,3;1,4)-β-glucan biosynthesis in cereal grains. However, it is not clear how both (1,3)- and (1,4)-linkages are incorporated into a single polysaccharide chain and how the frequency and arrangement of the two linkage types that define the fine structure of the polysaccharide are controlled. Through transient expression in Nicotiana benthamiana leaves, two CSLF6 orthologs from different cereal species were shown to mediate the synthesis of (1,3;1,4)-β-glucans with very different fine structures. Chimeric cDNA constructs with interchanged sections of the barley and sorghum CslF6 genes were developed to identify regions of the synthase enzyme responsible for these differences. A single amino acid residue upstream of the TED motif in the catalytic region was shown to dramatically change the fine structure of the polysaccharide produced. The structural basis of this effect can be rationalized by reference to a homology model of the enzyme and appears to be related to the position and flexibility of the TED motif in the active site of the enzyme. The region and amino acid residue identified provide opportunities to manipulate the solubility of (1,3;1,4)-β-glucan in grains and vegetative tissues of the grasses and, in particular, to enhance the solubility of dietary fibers that are beneficial to human health.

Covellite CuS as a matrix for "invisible" gold: X-ray spectroscopic study of the chemical state of Cu and Au in synthetic minerals

NASA Astrophysics Data System (ADS)

Tagirov, Boris R.; Trigub, Alexander L.; Kvashnina, Kristina O.; Shiryaev, Andrey A.; Chareev, Dmitriy A.; Nickolsky, Maximilian S.; Abramova, Vera D.; Kovalchuk, Elena V.

2016-10-01

Geological processes leading to formation of sulfide ores often result in precipitation of gold-bearing sulfides which can contain high concentrations of this metal in ;invisible; (or ;refractory;) state. Covellite (CuS) is ubiquitous mineral in many types of the ore deposits, and numerous studies of the natural ores show that covellite can contain high concentrations of Au. At the same time, Au-bearing covellite withstands cooling in contrast to other minerals of the Cu-Fe-S system (chalcocite, bornite, chalcopyrite), where Au exsolves at low temperatures. This makes covellite a convenient model system for investigation of the chemical state (local environment and valence) of the ;invisible; Au in copper-sulfide ores (copper-porphyry, epithermal, volcanogenic massive sulfide, SEDEX deposits). Therefore, it is necessary to determine the location of Au in the covellite matrix as it will have important implications for the methods employed by mineral processing industry to extract Au from sulfide ores. Here we investigate the chemical state of Cu and Au in synthetic covellite containing up to 0.3 wt.% of Au in the ;invisible; state. The covellite crystals were synthesized by hydrothermal and salt flux methods. Formation of the chemically bound Au is indicated by strong dependence of the concentration of Au in covellite on the sulfur fugacity in the experimental system (d(log C(Au))/d(log f(S2)) ∼ 0.65). The Au concentration of covellite grows with increasing temperature from 400 to 450 °C, whereas further temperature increase to 500 °C has only minor effect. The synthesized minerals were studied using X-ray absorption fine structure spectroscopy (XAFS) in high energy resolution fluorescence detection (HERFD) mode. Ab initio simulations of Cu K edge XANES spectra show that the Cu oxidation state in two structural positions in covellite (tetrahedral and triangular coordination with S atoms) is identical: the total loss of electronic charge for the 3d shell is ∼0.3 for both positions of Cu. This result is confirmed by theoretical analysis of electron density performed using quantum theory of atoms in molecules (QTAIM). Modeling of the Au L3 edge EXAFS/XANES spectra showed that Au in covellite exists in the form of the isomorphous solid solution formed by substitution for Cu atoms in triangular coordination with the Me-S distance in the first coordination shell increased by 0.18 Å relative to the pure CuS structure. The ;formal; oxidation state of Au in covellite is +1. The Bader partial atomic charge for Au in covellite is lower than the charge of Cu (+0.2 e vs. +0.5 e) indicating that the degree of covalency for the Au-bearing covellite is higher than that of pure CuS. The analysis of electronic density of states shows that this structural position of Au results in strong interactions between hybridized Au s,p,d, S p, and Cu p,d orbitals. Such chemical bonding of Au to S and Cu can result in the formation of Au-bearing solid solution with other minerals in the Cu-Fe-S system.

Inbreeding Avoidance Drives Consistent Variation of Fine-Scale Genetic Structure Caused by Dispersal in the Seasonal Mating System of Brandt’s Voles

PubMed Central

Liu, Xiao Hui; Yue, Ling Fen; Wang, Da Wei; Li, Ning; Cong, Lin

2013-01-01

Inbreeding depression is a major evolutionary and ecological force influencing population dynamics and the evolution of inbreeding-avoidance traits such as mating systems and dispersal. Mating systems and dispersal are fundamental determinants of population genetic structure. Resolving the relationships among genetic structure, seasonal breeding-related mating systems and dispersal will facilitate our understanding of the evolution of inbreeding avoidance. The goals of this study were as follows: (i) to determine whether females actively avoided mating with relatives in a group-living rodent species, Brandt’s voles (Lasiopodomys brandtii), by combined analysis of their mating system, dispersal and genetic structure; and (ii) to analyze the relationships among the variation in fine-genetic structure, inbreeding avoidance, season-dependent mating strategies and individual dispersal. Using both individual- and population-level analyses, we found that the majority of Brandt’s vole groups consisted of close relatives. However, both group-specific FISs, an inbreeding coefficient that expresses the expected percentage rate of homozygosity arising from a given breeding system, and relatedness of mates showed no sign of inbreeding. Using group pedigrees and paternity analysis, we show that the mating system of Brandt’s voles consists of a type of polygyny for males and extra-group polyandry for females, which may decrease inbreeding by increasing the frequency of mating among distantly-related individuals. The consistent variation in within-group relatedness, among-group relatedness and fine-scale genetic structures was mostly due to dispersal, which primarily occurred during the breeding season. Biologically relevant variation in the fine-scale genetic structure suggests that dispersal during the mating season may be a strategy to avoid inbreeding and drive the polygynous and extra-group polyandrous mating system of this species. PMID:23516435

Redefining fine roots improves understanding of belowground contributions to terrestrial biosphere processes

DOE PAGES

McCormack, M. Luke; Dickie, Ian A.; Eissenstat, David M.; ...

2015-03-10

Fine roots acquire essential soil resources and mediate biogeochemical cycling in terrestrial ecosystems. Estimates of carbon and nutrient allocation to build and maintain these structures remain uncertain due to challenges in consistent measurement and interpretation of fine-root systems. We define fine roots as all roots less than or equal to 2 mm in diameter, yet it is now recognized that this approach fails to capture the diversity of form and function observed among fine-root orders. We demonstrate how order-based and functional classification frameworks improve our understanding of dynamic root processes in ecosystems dominated by perennial plants. In these frameworks, finemore » roots are separated into either individual root orders or functionally defined into a shorter-lived absorptive pool and a longer-lived transport fine root pool. Furthermore, using these frameworks, we estimate that fine-root production and turnover represent 22% of terrestrial net primary production globally a ca. 30% reduction from previous estimates assuming a single fine-root pool. In the future we hope to develop tools to rapidly differentiate functional fine-root classes, explicit incorporation of mycorrhizal fungi in fine-root studies, and wider adoption of a two-pool approach to model fine roots provide opportunities to better understand belowground processes in the terrestrial biosphere.« less

Compact cell-centered discretization stencils at fine-coarse block structured grid interfaces

NASA Astrophysics Data System (ADS)

Pletzer, Alexander; Jamroz, Ben; Crockett, Robert; Sides, Scott

2014-03-01

Different strategies for coupling fine-coarse grid patches are explored in the context of the adaptive mesh refinement (AMR) method. We show that applying linear interpolation to fill in the fine grid ghost values can produce a finite volume stencil of comparable accuracy to quadratic interpolation provided the cell volumes are adjusted. The volume of fine cells expands whereas the volume of neighboring coarse cells contracts. The amount by which the cells contract/expand depends on whether the interface is a face, an edge, or a corner. It is shown that quadratic or better interpolation is required when the conductivity is spatially varying, anisotropic, the refinement ratio is other than two, or when the fine-coarse interface is concave.

[The burden of disability in Cameroon].

PubMed

Foti, Calogero; Albensi, Caterina; Giordani, Laura; Azeufack Ngueko, Yannick; Sanou Sobze, Martin; Colizzi, Vittorio

2017-01-01

Rehabilitation services for disabled persons are lacking in countries with limited economic resources. Reliable and objective data are needed to plan for their implementation and to determine the burden of disability in these countries. A descriptive cross-sectional study conducted in June 2013 among people living in Dschang Health District, in the West region of Cameroon, to collect information about socio-demographic aspects of physically disabled subjects and health determinants of disabilities. Data was collected using a standard questionnaire in French. In total, 159 physically disabled subjects were enrolled in the study. Mean age was 36 years [± SD 17.26], 55.9% of subjects were female, and 33.8% had a low educational-level. The most frequently reported disabilities were orthopaedic problems (mainly fractures) [45.8%], infectious diseases [29.1%]), and neurological disabilities (mainly hemiplegia [33.3%], hemiparesis [23.8%], and monoplegia [23.8%]). The main causes of disability were trauma due to traffic accidents (17.8%) and inappropriate medical interventions (14.5%). Disability was related to age and 50% of participants experienced social discrimination. Disabled subjects with low-incomes (from 50.000 to 200.000 XAF) were required to pay for rehabilitative care (XAF 10.000 to 100.000), and up to 83% had appealed for improved quality of Rehabilitation Medicine. Although Law n. 83/013 for the protection of persons with disabilities in Cameroon dates back to 1983, the results of this study show that disabled people, and children in particular, are still marginalized, vulnerable and have little chance of recovery. Therefore, there is a clear need to improve the quality and availability of rehabilitative care services , with programmatic interventions that ensure implementation of existing laws, improve access to rehabilitative services, provide disabled persons with the necessary specialty medical products, and eliminate barriers to their social participation.

A comparative study to evaluate liquid dish washing soap as an alternative to xylene and alcohol in deparaffinization and hematoxylin and eosin staining.

PubMed

Pandey, Pinki; Dixit, Alok; Tanwar, Aparna; Sharma, Anuradha; Mittal, Sanjeev

2014-07-01

Our study presents a new deparaffinizing and hematoxylin and eosin (H and E) staining method that involves the use of easily available, nontoxic and eco-friendly liquid diluted dish washing soap (DWS) by completely eliminating expensive and hazardous xylene and alcohol from deparaffinizing and rehydration prior to staining, staining and from dehydration prior to mounting. The aim was to evaluate and compare the quality of liquid DWS treated xylene and alcohol free (XAF) sections with that of the conventional H and E sections. A total of 100 paraffin embedded tissue blocks from different tissues were included. From each tissue block, one section was stained with conventional H and E (normal sections) and the other with XAF H and E (soapy sections) staining method. Slides were scored using five parameters: Nuclear, cytoplasmic, clarity, uniformity, and crispness of staining. Z-test was used for statistical analysis. Soapy sections scored better for cytoplasmic (90%) and crisp staining (95%) with a statistically significant difference. Whereas for uniformity of staining, normal sections (88%) scored over soapy sections (72%) (Z = 2.82, P < 0.05). For nuclear (90%) and clarity of staining (90%) total scored favored soapy sections, but the difference was not statistically significant. About 84% normal sections stained adequately for diagnosis when compared with 86% in soapy sections (Z = 0.396, P > 0.05). Liquid DWS is a safe and efficient alternative to xylene and alcohol in deparaffinization and routine H and E staining procedure. We are documenting this project that can be used as a model for other histology laboratories.

A comparative study to evaluate liquid dish washing soap as an alternative to xylene and alcohol in deparaffinization and hematoxylin and eosin staining

PubMed Central

Pandey, Pinki; Dixit, Alok; Tanwar, Aparna; Sharma, Anuradha; Mittal, Sanjeev

2014-01-01

Introduction: Our study presents a new deparaffinizing and hematoxylin and eosin (H and E) staining method that involves the use of easily available, nontoxic and eco-friendly liquid diluted dish washing soap (DWS) by completely eliminating expensive and hazardous xylene and alcohol from deparaffinizing and rehydration prior to staining, staining and from dehydration prior to mounting. The aim was to evaluate and compare the quality of liquid DWS treated xylene and alcohol free (XAF) sections with that of the conventional H and E sections. Materials and Methods: A total of 100 paraffin embedded tissue blocks from different tissues were included. From each tissue block, one section was stained with conventional H and E (normal sections) and the other with XAF H and E (soapy sections) staining method. Slides were scored using five parameters: Nuclear, cytoplasmic, clarity, uniformity, and crispness of staining. Z-test was used for statistical analysis. Results: Soapy sections scored better for cytoplasmic (90%) and crisp staining (95%) with a statistically significant difference. Whereas for uniformity of staining, normal sections (88%) scored over soapy sections (72%) (Z = 2.82, P < 0.05). For nuclear (90%) and clarity of staining (90%) total scored favored soapy sections, but the difference was not statistically significant. About 84% normal sections stained adequately for diagnosis when compared with 86% in soapy sections (Z = 0.396, P > 0.05). Conclusion: Liquid DWS is a safe and efficient alternative to xylene and alcohol in deparaffinization and routine H and E staining procedure. We are documenting this project that can be used as a model for other histology laboratories. PMID:25328332

Fine structure of the epicytoplasmic eimerid coccidium Acroeimeria pintoi Lainson & Paperna, 1999, a gut parasite of the lizard Ameiva ameiva in north Brazil.

PubMed

Paperna, L; Lainson, R

1999-12-01

An account is given of the fine structure of Acroeimerio pintoi, an epicytoplasmic coccidium infecting the small intestine of the teiid lizard Ameiva ameiva in north Brazil. The merozoile becomes encircled by outgrowths of the host-cell wall which then merge to form a parasitophorous sack in which the parasite continues to develop when this bulges out above the epithelium surface. The account includes a description of merozoites, young meronts and young and mature macrogamonts. The parasitophorous vacuole has a complex tubular system connected to its junction with the host-cell. The parasites are coated with a droplet-like glycocalyx and covered by a fine filamentous layer.

Quark mass variations of nuclear forces, BBN, and all that

NASA Astrophysics Data System (ADS)

Meissner, Ulf-G.

2014-03-01

In this talk, I discuss the modifications of the nuclear forces due to variations of the light quark masses and of the fine structure constant. This is based on the chiral nuclear effective field theory, that successfully describes a large body of data. The generation of the light elements in the Big Bang Nucleosynthesis provides important constraints on these modifications. In addition, I discuss the role of the anthropic principle in the triple-alpha process that underlies carbon and oxygen generation in hot stars. It appears that a fine-tuning of the quark masses and the fine structure constant within 2 to 3 per cent is required to make life on Earth viable. Supported in part by DFG, HGF and the BMBF.

Rare variation facilitates inferences of fine-scale population structure in humans.

PubMed

O'Connor, Timothy D; Fu, Wenqing; Mychaleckyj, Josyf C; Logsdon, Benjamin; Auer, Paul; Carlson, Christopher S; Leal, Suzanne M; Smith, Joshua D; Rieder, Mark J; Bamshad, Michael J; Nickerson, Deborah A; Akey, Joshua M

2015-03-01

Understanding the genetic structure of human populations has important implications for the design and interpretation of disease mapping studies and reconstructing human evolutionary history. To date, inferences of human population structure have primarily been made with common variants. However, recent large-scale resequencing studies have shown an abundance of rare variation in humans, which may be particularly useful for making inferences of fine-scale population structure. To this end, we used an information theory framework and extensive coalescent simulations to rigorously quantify the informativeness of rare and common variation to detect signatures of fine-scale population structure. We show that rare variation affords unique insights into patterns of recent population structure. Furthermore, to empirically assess our theoretical findings, we analyzed high-coverage exome sequences in 6,515 European and African American individuals. As predicted, rare variants are more informative than common polymorphisms in revealing a distinct cluster of European-American individuals, and subsequent analyses demonstrate that these individuals are likely of Ashkenazi Jewish ancestry. Our results provide new insights into the population structure using rare variation, which will be an important factor to account for in rare variant association studies. © The Author 2014. Published by Oxford University Press on behalf of the Society for Molecular Biology and Evolution.

Rocket experiments for spectral estimation of electron density fine structure in the auroral and equatorial ionosphere and preliminary results

NASA Technical Reports Server (NTRS)

Tomei, B. A.; Smith, L. G.

1986-01-01

Sounding rockets equipped to monitor electron density and its fine structure were launched into the auroral and equatorial ionosphere in 1980 and 1983, respectively. The measurement electronics are based on the Langmuir probe and are described in detail. An approach to the spectral analysis of the density irregularities is addressed and a software algorithm implementing the approach is given. Preliminary results of the analysis are presented.

Re/Os constraint on the time variability of the fine-structure constant.

PubMed

Fujii, Yasunori; Iwamoto, Akira

2003-12-31

We argue that the accuracy by which the isochron parameters of the decay 187Re-->187Os are determined by dating iron meteorites may constrain the possible time dependence of the decay rate and hence of the fine-structure constant alpha, not directly but only in a model-dependent manner. From this point of view, some of the attempts to analyze the Oklo constraint and the results of the quasistellar-object absorption lines are reexamined.

A correlational method to concurrently measure envelope and temporal fine structure weights: Effects of age, cochlear pathology, and spectral shaping1

PubMed Central

Fogerty, Daniel; Humes, Larry E.

2012-01-01

The speech signal may be divided into spectral frequency-bands, each band containing temporal properties of the envelope and fine structure. This study measured the perceptual weights for the envelope and fine structure in each of three frequency bands for sentence materials in young normal-hearing listeners, older normal-hearing listeners, aided older hearing-impaired listeners, and spectrally matched young normal-hearing listeners. The availability of each acoustic property was independently varied through noisy signal extraction. Thus, the full speech stimulus was presented with noise used to mask six different auditory channels. Perceptual weights were determined by correlating a listener’s performance with the signal-to-noise ratio of each acoustic property on a trial-by-trial basis. Results demonstrate that temporal fine structure perceptual weights remain stable across the four listener groups. However, a different weighting typography was observed across the listener groups for envelope cues. Results suggest that spectral shaping used to preserve the audibility of the speech stimulus may alter the allocation of perceptual resources. The relative perceptual weighting of envelope cues may also change with age. Concurrent testing of sentences repeated once on a previous day demonstrated that weighting strategies for all listener groups can change, suggesting an initial stabilization period or susceptibility to auditory training. PMID:22978896

Helium induced fine structure in the electronic spectra of anthracene derivatives doped into superfluid helium nanodroplets

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pentlehner, D.; Slenczka, A., E-mail: alkwin.slenczka@chemie.uni-regensburg.de

2015-01-07

Electronic spectra of organic molecules doped into superfluid helium nanodroplets show characteristic features induced by the helium environment. Besides a solvent induced shift of the electronic transition frequency, in many cases, a spectral fine structure can be resolved for electronic and vibronic transitions which goes beyond the expected feature of a zero phonon line accompanied by a phonon wing as known from matrix isolation spectroscopy. The spectral shape of the zero phonon line and the helium induced phonon wing depends strongly on the dopant species. Phonon wings, for example, are reported ranging from single or multiple sharp transitions to broadmore » (Δν > 100 cm{sup −1}) diffuse signals. Despite the large number of example spectra in the literature, a quantitative understanding of the helium induced fine structure of the zero phonon line and the phonon wing is missing. Our approach is a systematic investigation of related molecular compounds, which may help to shed light on this key feature of microsolvation in superfluid helium droplets. This paper is part of a comparative study of the helium induced fine structure observed in electronic spectra of anthracene derivatives with particular emphasis on a spectrally sharp multiplet splitting at the electronic origin. In addition to previously discussed species, 9-cyanoanthracene and 9-chloroanthracene will be presented in this study for the first time.« less

Fine-scale human genetic structure in Western France.

PubMed

Karakachoff, Matilde; Duforet-Frebourg, Nicolas; Simonet, Floriane; Le Scouarnec, Solena; Pellen, Nadine; Lecointe, Simon; Charpentier, Eric; Gros, Françoise; Cauchi, Stéphane; Froguel, Philippe; Copin, Nane; Le Tourneau, Thierry; Probst, Vincent; Le Marec, Hervé; Molinaro, Sabrina; Balkau, Beverley; Redon, Richard; Schott, Jean-Jacques; Blum, Michael Gb; Dina, Christian

2015-06-01

The difficulties arising from association analysis with rare variants underline the importance of suitable reference population cohorts, which integrate detailed spatial information. We analyzed a sample of 1684 individuals from Western France, who were genotyped at genome-wide level, from two cohorts D.E.S.I.R and CavsGen. We found that fine-scale population structure occurs at the scale of Western France, with distinct admixture proportions for individuals originating from the Brittany Region and the Vendée Department. Genetic differentiation increases with distance at a high rate in these two parts of Northwestern France and linkage disequilibrium is higher in Brittany suggesting a lower effective population size. When looking for genomic regions informative about Breton origin, we found two prominent associated regions that include the lactase region and the HLA complex. For both the lactase and the HLA regions, there is a low differentiation between Bretons and Irish, and this is also found at the genome-wide level. At a more refined scale, and within the Pays de la Loire Region, we also found evidence of fine-scale population structure, although principal component analysis showed that individuals from different departments cannot be confidently discriminated. Because of the evidence for fine-scale genetic structure in Western France, we anticipate that rare and geographically localized variants will be identified in future full-sequence analyses.

Fine structures of azimuthal correlations of two gluons in the glasma

NASA Astrophysics Data System (ADS)

Zhang, Hengying; Zhang, Donghai; Zhao, Yeyin; Xu, Mingmei; Pan, Xue; Wu, Yuanfang

2018-02-01

We investigate the azimuthal correlations of the glasma in p-p collisions at √{sNN}=7 TeV by using the color glass condensate (CGC) formalism. As expected, the azimuthal correlations show two peaks at Δ ϕ =0 and π , which represent collimation production in the CGC. Beyond that, azimuthal correlations show fine structures, i.e., bumps or shoulders between the two peaks, when at least one gluon has small x . The structures are demonstrated to be associated with saturation momentum and likely appear at transverse momentum around 2 Qsp=1.8 GeV /c .

Structural Ceramics Database

National Institute of Standards and Technology Data Gateway

SRD 30 NIST Structural Ceramics Database (Web, free access)   The NIST Structural Ceramics Database (WebSCD) provides evaluated materials property data for a wide range of advanced ceramics known variously as structural ceramics, engineering ceramics, and fine ceramics.

The NaK 1 1,3delta states: theoretical and experimental studies of fine and hyperfine structure of rovibrational levels near the dissociation limit.

PubMed

Wilkins, A D; Morgus, L; Hernandez-Guzman, J; Huennekens, J; Hickman, A P

2005-09-22

Earlier high-resolution spectroscopic studies of the fine and hyperfine structure of rovibrational levels of the 1 3delta state of NaK have been extended to include high lying rovibrational levels with v < or = 59, of which the highest levels lie within approximately 4 cm(-1) of the dissociation limit. A potential curve is determined using the inverted perturbation approximation method that reproduces these levels to an accuracy of approximately 0.026 cm(-1). For the largest values of v, the outer turning points occur near R approximately 12.7 angstroms, which is sufficiently large to permit the estimation of the C6 coefficient for this state. The fine and hyperfine structure of the 1 3delta rovibrational levels has been fit using the matrix diagonalization method that has been applied to other states of NaK, leading to values of the spin-orbit coupling constant A(v) and the Fermi contact constant b(F). New values determined for v < or = 33 are consistent with values determined by a simpler method and reported earlier. The measured fine and hyperfine structure for v in the range 44 < or = v < or = 49 exhibits anomalous behavior whose origin is believed to be the mixing between the 1 3delta and 1 1delta states. The matrix diagonalization method has been extended to treat this interaction, and the results provide an accurate representation of the complicated patterns that arise. The analysis leads to accurate values for A(v) and b(F) for all values of v < or = 49. For higher v (50 < or = v < or = 59), several rovibrational levels have been assigned, but the pattern of fine and hyperfine structure is difficult to interpret. Some of the observed features may arise from effects not included in the current model.

Carbon cycling in fine roots of several mature forests: results using either locally-derived or bomb-derived radiocarbon enrichment

NASA Astrophysics Data System (ADS)

Gaudinski, J. B.; Riley, W. J.; Torn, M. S.; Dawson, T. E.; Trumbore, S. E.; Joslin, J. D.; Majdi, H.; Hanson, P. J.; Swanston, C.

2008-12-01

This work seeks to improve our ability to quantify C cycling rates in fine roots of trees in mature deciduous and coniferous forests. We use two different types of atmospheric 14CO2 enrichment to trace the time elapsed since C in plant tissues was fixed from the atmosphere by photosynthesis. The first uses a local enrichment of 14CO2 which occurred in early summer 1999, at the Oak Ridge Reservation, Tennessee. The second, employed at three different sites, uses the global enrichment in background atmospheric 14CO2 caused by thermonuclear weapons testing (bomb-14C). In both cases we employ a new model (Radix1.0) to track C and 14C fluxes through fine root populations. Radix simulates two live-root populations (the longer-lived one having structural and non-structural C components), two dead-root pools, non-normally distributed root mortality turnover times, a stored C pool, seasonal growth and respiration patterns, a best-fit to measurements approach to estimate model parameters, and Monte Carlo uncertainty analysis. Our results show that: (1) New fine-root growth contains a lot of stored C (~55%) but it is young in age (0.7 y). (2) The effect of stored reserves on estimated ages of fine roots is unlikely to be large in most natural abundance isotope studies. However, models should take stored reserves into account, particularly for pulse labeling studies and fast-cycling roots (< 1 y). (3) Radiocarbon values show a stronger correlation with position on the root branch system than they do with diameter or depth in the soil profile. (4) Live fine root dynamics are well described by a short-lived and a long-lived population, with mean turnover times <1 y and ~12 y, respectively. (5) Dead root decomposition is best modeled with (at least) two pools, with moderate (~2 y) and slow (~10 y) decomposition turnover times. (6) Root respiration has a large effect on fine root biomass and isotopic composition, and should be included in ecosystem C and isotope models. (7) It is important to distinguish structural from non-structural components in the long-lived root pool. Otherwise the 14C signature of root respiration is significantly different than atmospheric. We conclude that realistic quantification of C flows through fine roots requires a model with a level of complexity similar to Radix. Moreover, future root research efforts should seek to sample and sort roots by position on the root branch system rather than by diameter size class and improve estimates of root respiration within fine root populations.

Thermal expansion behavior study of Co nanowire array with in situ x-ray diffraction and x-ray absorption fine structure techniques

NASA Astrophysics Data System (ADS)

Mo, Guang; Cai, Quan; Jiang, Longsheng; Wang, Wei; Zhang, Kunhao; Cheng, Weidong; Xing, Xueqing; Chen, Zhongjun; Wu, Zhonghua

2008-10-01

In situ x-ray diffraction and x-ray absorption fine structure techniques were used to study the structural change of ordered Co nanowire array with temperature. The results show that the Co nanowires are polycrystalline with hexagonal close packed structure without phase change up until 700 °C. A nonlinear thermal expansion behavior has been found and can be well described by a quadratic equation with the first-order thermal expansion coefficient of 4.3×10-6/°C and the second-order thermal expansion coefficient of 5.9×10-9/°C. The mechanism of this nonlinear thermal expansion behavior is discussed.

Ultra-Fine Scale Spatially-Integrated Mapping of Habitat and Occupancy Using Structure-From-Motion.

PubMed

McDowall, Philip; Lynch, Heather J

2017-01-01

Organisms respond to and often simultaneously modify their environment. While these interactions are apparent at the landscape extent, the driving mechanisms often occur at very fine spatial scales. Structure-from-Motion (SfM), a computer vision technique, allows the simultaneous mapping of organisms and fine scale habitat, and will greatly improve our understanding of habitat suitability, ecophysiology, and the bi-directional relationship between geomorphology and habitat use. SfM can be used to create high-resolution (centimeter-scale) three-dimensional (3D) habitat models at low cost. These models can capture the abiotic conditions formed by terrain and simultaneously record the position of individual organisms within that terrain. While coloniality is common in seabird species, we have a poor understanding of the extent to which dense breeding aggregations are driven by fine-scale active aggregation or limited suitable habitat. We demonstrate the use of SfM for fine-scale habitat suitability by reconstructing the locations of nests in a gentoo penguin colony and fitting models that explicitly account for conspecific attraction. The resulting digital elevation models (DEMs) are used as covariates in an inhomogeneous hybrid point process model. We find that gentoo penguin nest site selection is a function of the topography of the landscape, but that nests are far more aggregated than would be expected based on terrain alone, suggesting a strong role of behavioral aggregation in driving coloniality in this species. This integrated mapping of organisms and fine scale habitat will greatly improve our understanding of fine-scale habitat suitability, ecophysiology, and the complex bi-directional relationship between geomorphology and habitat use.

Sedimentation Investigation at Masirah Island, Oman.

DTIC Science & Technology

1983-11-01

source of fine-graine"’ rJ-.e.i _. BAt Is .iA Anchorage t-e botton is gravel and coarse sand. C’. rrents are so swift there, fine meterial will not settle...stable and with the proposed pier (a gravity structure to -3 m MLW) and the new intake groin, it will likely remain stable in the future. The volume of...US-BUILT SALTWATER INTAKE GROIN. This shore-normal gravity structure, which affects adjacent shores in .alythe same manner a groin would, was completed

Physics based calculation of the fine structure constant

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lestone, John Paul

2009-01-01

We assume that the coupling between particles and photons is defined by a surface area and a temperature, and that the square of the temperature is the inverse of the surface area ({Dirac_h}=c= 1). By making assumptions regarding stimulated emission and effects associated with the finite length of a string that forms the particle surface, the fine structure constant is calculated to be {approx}1/137.04. The corresponding calculated fundamental unit of charge is 1.6021 x 10{sup -19} C.

Fine-scale genetic population structure in a mobile marine mammal: inshore bottlenose dolphins in Moreton Bay, Australia.

PubMed

Ansmann, Ina C; Parra, Guido J; Lanyon, Janet M; Seddon, Jennifer M

2012-09-01

Highly mobile marine species in areas with no obvious geographic barriers are expected to show low levels of genetic differentiation. However, small-scale variation in habitat may lead to resource polymorphisms and drive local differentiation by adaptive divergence. Using nuclear microsatellite genotyping at 20 loci, and mitochondrial control region sequencing, we investigated fine-scale population structuring of inshore bottlenose dolphins (Tursiops aduncus) inhabiting a range of habitats in and around Moreton Bay, Australia. Bayesian structure analysis identified two genetic clusters within Moreton Bay, with evidence of admixture between them (F(ST) = 0.05, P = 0.001). There was only weak isolation by distance but one cluster of dolphins was more likely to be found in shallow southern areas and the other in the deeper waters of the central northern bay. In further analysis removing admixed individuals, southern dolphins appeared genetically restricted with lower levels of variation (AR = 3.252, π = 0.003) and high mean relatedness (r = 0.239) between individuals. In contrast, northern dolphins were more diverse (AR = 4.850, π = 0.009) and were mixing with a group of dolphins outside the bay (microsatellite-based STRUCTURE analysis), which appears to have historically been distinct from the bay dolphins (mtDNA Φ(ST) = 0.272, P < 0.001). This study demonstrates the ability of genetic techniques to expose fine-scale patterns of population structure and explore their origins and mechanisms. A complex variety of inter-related factors including local habitat variation, differential resource use, social behaviour and learning, and anthropogenic disturbances are likely to have played a role in driving fine-scale population structure among bottlenose dolphins in Moreton Bay. © 2012 Blackwell Publishing Ltd.

Dispersal, mating events and fine-scale genetic structure in the lesser flat-headed bats.

PubMed

Hua, Panyu; Zhang, Libiao; Guo, Tingting; Flanders, Jon; Zhang, Shuyi

2013-01-01

Population genetic structure has important consequences in evolutionary processes and conservation genetics in animals. Fine-scale population genetic structure depends on the pattern of landscape, the permanent movement of individuals, and the dispersal of their genes during temporary mating events. The lesser flat-headed bat (Tylonycteris pachypus) is a nonmigratory Asian bat species that roosts in small groups within the internodes of bamboo stems and the habitats are fragmented. Our previous parentage analyses revealed considerable extra-group mating in this species. To assess the spatial limits and sex-biased nature of gene flow in the same population, we used 20 microsatellite loci and mtDNA sequencing of the ND2 gene to quantify genetic structure among 54 groups of adult flat-headed bats, at nine localities in South China. AMOVA and F(ST) estimates revealed significant genetic differentiation among localities. Alternatively, the pairwise F(ST) values among roosting groups appeared to be related to the incidence of associated extra-group breeding, suggesting the impact of mating events on fine-scale genetic structure. Global spatial autocorrelation analyses showed positive genetic correlation for up to 3 km, indicating the role of fragmented habitat and the specialized social organization as a barrier in the movement of individuals among bamboo forests. The male-biased dispersal pattern resulted in weaker spatial genetic structure between localities among males than among females, and fine-scale analyses supported that relatedness levels within internodes were higher among females than among males. Finally, only females were more related to their same sex roost mates than to individuals from neighbouring roosts, suggestive of natal philopatry in females.

The final word. OSHA's final ruling offers firm deadlines for infection control.

PubMed

West, K

1992-03-01

Departments that have put off program development while waiting for the final ruling to be published have a lot of work to do. Many departments have been cited and fined by OSHA in the past year for failure to begin infection-control programs or provide hepatitis-B vaccines to personnel. Under the new budget, OSHA was granted permission to up its fine structure sevenfold--thus, a small fine is $7,000, and the highest fine for a single violation is $70,000. Fines can have a greater impact on a department's budget than implementation of the program over time. A key point to remember is that a strong infection-control program will reduce exposure follow-up costs and worker-compensation claims. Infection control is a win-win situation.

The interplay between tissue plasminogen activator domains and fibrin structures in the regulation of fibrinolysis: kinetic and microscopic studies

PubMed Central

Thelwell, Craig; Williams, Stella C.; Silva, Marta M. C. G.; Szabó, László; Kolev, Krasimir

2011-01-01

Regulation of tissue-type plasminogen activator (tPA) depends on fibrin binding and fibrin structure. tPA structure/function relationships were investigated in fibrin formed by high or low thrombin concentrations to produce a fine mesh and small pores, or thick fibers and coarse structure, respectively. Kinetics studies were performed to investigate plasminogen activation and fibrinolysis in the 2 types of fibrin, using wild-type tPA (F-G-K1-K2-P, F and K2 binding), K1K1-tPA (F-G-K1-K1-P, F binding), and delF-tPA (G-K1-K2-P, K2 binding). There was a trend of enzyme potency of tPA > K1K1-tPA > delF-tPA, highlighting the importance of the finger domain in regulating activity, but the differences were less apparent in fine fibrin. Fine fibrin was a better surface for plasminogen activation but more resistant to lysis. Scanning electron and confocal microscopy using orange fluorescent fibrin with green fluorescent protein-labeled tPA variants showed that tPA was strongly associated with agglomerates in coarse but not in fine fibrin. In later lytic stages, delF-tPA-green fluorescent protein diffused more rapidly through fibrin in contrast to full-length tPA, highlighting the importance of finger domain-agglomerate interactions. Thus, the regulation of fibrinolysis depends on the starting nature of fibrin fibers and complex dynamic interaction between tPA and fibrin structures that vary over time. PMID:20966169

Assessing polar bear (Ursus maritimus) population structure in the Hudson Bay region using SNPs.

PubMed

Viengkone, Michelle; Derocher, Andrew Edward; Richardson, Evan Shaun; Malenfant, René Michael; Miller, Joshua Moses; Obbard, Martyn E; Dyck, Markus G; Lunn, Nick J; Sahanatien, Vicki; Davis, Corey S

2016-12-01

Defining subpopulations using genetics has traditionally used data from microsatellite markers to investigate population structure; however, single-nucleotide polymorphisms (SNPs) have emerged as a tool for detection of fine-scale structure. In Hudson Bay, Canada, three polar bear ( Ursus maritimus ) subpopulations (Foxe Basin (FB), Southern Hudson Bay (SH), and Western Hudson Bay (WH)) have been delineated based on mark-recapture studies, radiotelemetry and satellite telemetry, return of marked animals in the subsistence harvest, and population genetics using microsatellites. We used SNPs to detect fine-scale population structure in polar bears from the Hudson Bay region and compared our results to the current designations using 414 individuals genotyped at 2,603 SNPs. Analyses based on discriminant analysis of principal components (DAPC) and STRUCTURE support the presence of four genetic clusters: (i) Western-including individuals sampled in WH, SH (excluding Akimiski Island in James Bay), and southern FB (south of Southampton Island); (ii) Northern-individuals sampled in northern FB (Baffin Island) and Davis Strait (DS) (Labrador coast); (iii) Southeast-individuals from SH (Akimiski Island in James Bay); and (iv) Northeast-individuals from DS (Baffin Island). Population structure differed from microsatellite studies and current management designations demonstrating the value of using SNPs for fine-scale population delineation in polar bears.

Development of a sub-cm high resolution ion Doppler tomography diagnostics for fine structure measurement of guide field reconnection in TS-U

NASA Astrophysics Data System (ADS)

Tanabe, Hiroshi; Koike, Hideya; Hatano, Hironori; Hayashi, Takumi; Cao, Qinghong; Himeno, Shunichi; Kaneda, Taishi; Akimitsu, Moe; Sawada, Asuka; Ono, Yasushi

2017-10-01

A new type of high-throughput/high-resolution 96CH ion Doppler tomography diagnostics has been developed using ``multi-slit'' spectroscopy technique for detailed investigation of fine structure formation during high guide field magnetic reconnection. In the last three years, high field merging experiment in MAST pioneered new frontiers of reconnection heating: formation of highly peaked structure around X-point in high guide field condition (Bt > 0.3 T), outflow dissipation under the influence of better plasma confinement to form high temperature ring structure which aligns with closed flux surface of toroidal plasma, and interaction between ion and electron temperature profile during transport/confinement phase to form triple peak structure (τeiE 4 ms). To investigate more detailed mechanism with in-situ magnetic measurement, the university of Tokyo starts the upgrade of plasma parameters and spatial resolution of optical diagnostics as in MAST. Now, a new type of high-throughput/high-resolution 96CH ion Doppler tomography diagnostics system construction has been completed and it successfully resolved fine structure of ion heating downstream, aligned with closed flux surface formed by reconnected field. This work was supported by JSPS KAKENHI Grant Numbers 15H05750, 15K14279 and 17H04863.

XAFS of human tyrosine hydroxylase

NASA Astrophysics Data System (ADS)

Meyer, W.; Haavik, J.; Winkler, H.; Trautwein, A. X.; Nolting, H.-F.

1995-02-01

Tyrosine hydroxylase (TH) catalyses the rate-limiting step (hydroxylation of tyrosine to form dihydroxyphenylalanine) in the biosynthetic pathway leading to the catecholamines dopamine, noradrenaline and adrenaline. The human enzyme (hTH) is present in four isoforms, generated by splicing of pre-mRNA. The purified apoenzyme (metal free) binds stoichiometric amounts of iron. The incorporation of Fe(II) results in a rapid and up to 40-fold increase of activity [1]. Besides the coordination of the metal centers in native enzyme we studied the purported inhibition of TH by its immediate products. So we analysed Fe-hTH isoform 1 native as well as oxidized with dopamine and Co-hTH isoform 2.

Undecalcified temporal bone morphology: a methodology useful for gross to fine observation and three-dimensional reconstruction.

PubMed

Fujiyoshi, T; Mogi, G; Watanabe, T; Matsushita, F

1992-01-01

Using a novel method of cutting undecalcified temporal bone specimens, quantitative structural analysis in the human and the Japanese monkey was undertaken. One millimeter thick serial slices made from unembedded temporal bones retained fine structure. Therefore, gross to fine observation could be performed systematically at the macroscopic, light, scanning, and transmission electron microscopic levels. The entire temporal bone three-dimensional reconstruction was completed from embedded sections; consequently, the volume of the tubotympanum and air cell system could be calculated. Available methods by embedding, tungsten carbide sectioning, grinding, and microwave irradiation for decalcification were also examined. These morphologic studies suggest that these novel methods offer timesaving advantages over any presently available techniques, and allow for elucidation of temporal bone morphology with only a few specimens.

76 FR 10880 - Initiation of Administrative Review of the Antidumping Duty Order on Wooden Bedroom Furniture...

Federal Register 2010, 2011, 2012, 2013, 2014

2011-02-28

..., including, but not limited to, changes to corporate structure, acquisitions of new companies or facilities... Furniture Co., (PTE) Ltd.* Ever Spring Furniture Company Ltd. Evershine Enterprise Co. Fine Furniture (Shanghai) Ltd.* Fleetwood Fine Furniture LP. Foshan Guanqiu Furniture Co., Ltd.* Fujian Putian Jinggong...

77 FR 12235 - Wooden Bedroom Furniture From the People's Republic of China: Initiation of Administrative Review

Federal Register 2010, 2011, 2012, 2013, 2014

2012-02-29

... have subsequently made changes, including, but not limited to, changes to corporate structure...., (Pte) Ltd.* Ever Spring Furniture Co., Ltd. Evershine Enterprise Co. Fairmont Designs Fine Furniture (Shanghai) Ltd.* Fleetwood Fine Furniture Lp. Foliot Furniture Inc. Foliot Furniture Corporation Foliot...

CFD MODELING OF FINE SCALE FLOW AND TRANSPORT IN THE HOUSTON METROPOLITAN AREA, TEXAS

EPA Science Inventory

Fine scale modeling of flows and air quality in Houston, Texas is being performed; the use of computational fluid dynamics (CFD) modeling is being applied to investigate the influence of morphologic structures on the within-grid transport and dispersion of sources in grid models ...

Heavy precipitation episodes in the Western Mediterranean : Use of a semi-Lagrangian advection model for the fine-scale description of upper-level troughs

NASA Astrophysics Data System (ADS)

Gauthier, N.; Claud, C.; Funatsu, B. M.; Chaboureau, J.-P.; Argence, S.; Lambert, D.; Richard, E.; Hauchecorne, A.; Arbogast, P.; Maynard, K.

2009-09-01

Heavy precipitation events over the Mediterranean Sea are generally associated with upper-level troughs. The mesoscale structures of such troughs are however not well reproduced by the atmospheric analyses due to inappropriate spatial resolution. We propose here to use a semi-Lagrangian advection model called MIMOSA (Modélisation Isentrope du transport Méso-échelle de l'Ozone Stratosphérique par Advection) initially developed to describe stratospheric filaments, to calculate fine-scale Potential Vorticity (PV) fields on isentropic surfaces near the tropopause. After a description of MIMOSA, we will focus on the model-generated PV fields for several high impact weather cases that occurred over the Western Mediterreanean Sea. We will demonstrate the ability of MIMOSA to resolve fine scale structures of upper-level troughs considering the Algiers' flash flood, which occurred on November 2001, and then a heavy precipitation event over southeast France on the 5-6 September 2005. Finally, with a PV inversion method, we will show the impact of the fine scales PV structures as depicted by MIMOSA to improve the numerical simulation of a « hurricane » that hit Italy in September 2006, both in terms of surface pressure and precipitation forecasts.

Unprecedented Fine Structure of a Solar Flare Revealed by the 1.6 m New Solar Telescope

PubMed Central

Jing, Ju; Xu, Yan; Cao, Wenda; Liu, Chang; Gary, Dale; Wang, Haimin

2016-01-01

Solar flares signify the sudden release of magnetic energy and are sources of so called space weather. The fine structures (below 500 km) of flares are rarely observed and are accessible to only a few instruments world-wide. Here we present observation of a solar flare using exceptionally high resolution images from the 1.6 m New Solar Telescope (NST) equipped with high order adaptive optics at Big Bear Solar Observatory (BBSO). The observation reveals the process of the flare in unprecedented detail, including the flare ribbon propagating across the sunspots, coronal rain (made of condensing plasma) streaming down along the post-flare loops, and the chromosphere’s response to the impact of coronal rain, showing fine-scale brightenings at the footpoints of the falling plasma. Taking advantage of the resolving power of the NST, we measure the cross-sectional widths of flare ribbons, post-flare loops and footpoint brighenings, which generally lie in the range of 80–200 km, well below the resolution of most current instruments used for flare studies. Confining the scale of such fine structure provides an essential piece of information in modeling the energy transport mechanism of flares, which is an important issue in solar and plasma physics. PMID:27071459

Infrared fine-structure line diagnostics of shrouded active galactic nuclei

NASA Technical Reports Server (NTRS)

Voit, G. M.

1993-01-01

Far-infrared spectroscopy of celestial objects will improve dramatically in the coming decade, allowing astronomers to use fine-structure line emission to probe photoionized regions obscured in the optical band by thick clouds of dust. The ultraluminous far-IR galaxies revealed by IRAS, quasar-like in luminosity but smothered in molecular gas, probably conceal either immense starbursts or luminous active nuclei. In both scenarios, these objects ought to produce copious infrared fine-structure emission with several lines comparable to H(beta) in luminosity. This paper shows how these lines, if detected, can be used to determine the electron densities and far-IR obscurations of shrouded photoionized regions and to constrain the shape and ionization parameter of the ionizing spectra. The presence of (Ne V) emission in particular will distinguish shrouded AGN's from shrouded starbursts. Since all active galaxies photoionize at least some surrounding material, these diagnostics can also be applied to active galaxies in general and will aid in studying how an active nucleus interacts with the interstellar medium of its host galaxy.

Fine structure of the red luminescence band in undoped GaN

DOE Office of Scientific and Technical Information (OSTI.GOV)

Reshchikov, M. A., E-mail: mreshchi@vcu.edu; Usikov, A.; Saint-Petersburg National Research University of Information Technologies, Mechanics and Optics, 49 Kronverkskiy Ave., 197101 Saint Petersburg

2014-01-20

Many point defects in GaN responsible for broad photoluminescence (PL) bands remain unidentified. Their presence in thick GaN layers grown by hydride vapor phase epitaxy (HVPE) detrimentally affects the material quality and may hinder the use of GaN in high-power electronic devices. One of the main PL bands in HVPE-grown GaN is the red luminescence (RL) band with a maximum at 1.8 eV. We observed the fine structure of this band with a zero-phonon line (ZPL) at 2.36 eV, which may help to identify the related defect. The shift of the ZPL with excitation intensity and the temperature-related transformation of the RLmore » band fine structure indicate that the RL band is caused by transitions from a shallow donor (at low temperature) or from the conduction band (above 50 K) to an unknown deep acceptor having an energy level 1.130 eV above the valence band.« less

Solar Cycle Fine Structure and Surface Rotation from Ca II K-Line Time Series Data

NASA Technical Reports Server (NTRS)

Scargle, Jeff; Keil, Steve; Worden, Pete

2011-01-01

Analysis of three and a half decades of data from the NSO/AFRL/Sac Peak K-line monitoring program yields evidence for four components to the variation: (a) the solar cycle, with considerable fine structure and a quasi-periodicity of 122.4 days; (b) a stochastic process, faster than (a) and largely independent of it, (c) a quasi-periodic signal due to rotational modulation, and of course (d) observational errors (shown to be quite small). Correlation and power spectrum analyses elucidate periodic and aperiodic variation of these chromospheric parameters. Time-frequency analysis is especially useful for extracting information about differential rotation, and in particular elucidates the connection between its behavior and fine structure of the solar cycle on approximately one-year time scales. These results further suggest that similar analyses will be useful at detecting and characterizing differential rotation in stars from stellar light-curves such as those being produced at NASA's Kepler observatory.

Generation and control of polarization-entangled photons from GaAs island quantum dots by an electric field.

PubMed

Ghali, Mohsen; Ohtani, Keita; Ohno, Yuzo; Ohno, Hideo

2012-02-07

Semiconductor quantum dots are potential sources for generating polarization-entangled photons efficiently. The main prerequisite for such generation based on biexciton-exciton cascaded emission is to control the exciton fine-structure splitting. Among various techniques investigated for this purpose, an electric field is a promising means to facilitate the integration into optoelectronic devices. Here we demonstrate the generation of polarization-entangled photons from single GaAs quantum dots by an electric field. In contrast to previous studies, which were limited to In(Ga)As quantum dots, GaAs island quantum dots formed by a thickness fluctuation were used because they exhibit a larger oscillator strength and emit light with a shorter wavelength. A forward voltage was applied to a Schottky diode to control the fine-structure splitting. We observed a decrease and suppression in the fine-structure splitting of the studied single quantum dot with the field, which enabled us to generate polarization-entangled photons with a high fidelity of 0.72 ± 0.05.