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Sample records for activation analysis atomic

  1. Atom trap trace analysis

    SciTech Connect

    Lu, Z.-T.; Bailey, K.; Chen, C.-Y.; Du, X.; Li, Y.-M.; O'Connor, T. P.; Young, L.

    2000-05-25

    A new method of ultrasensitive trace-isotope analysis has been developed based upon the technique of laser manipulation of neutral atoms. It has been used to count individual {sup 85}Kr and {sup 81}Kr atoms present in a natural krypton sample with isotopic abundances in the range of 10{sup {minus}11} and 10{sup {minus}13}, respectively. The atom counts are free of contamination from other isotopes, elements,or molecules. The method is applicable to other trace-isotopes that can be efficiently captured with a magneto-optical trap, and has a broad range of potential applications.

  2. Compartmentalization of trace elements in guinea pig tissues by INAA (instrumental neutron activation analysis) and AAS (atomic absorption spectroscopy)

    SciTech Connect

    Chatt, A.; Holzbecher, J.; Katz, S.A.

    1988-01-01

    Human scalp hair analysis has received considerable attention from a variety of disciplines over the last 20 yr or so. Trace element levels of hair have been used in environmental, epidemiological, forensic, nutritional, predictive, and preventive medicine studies. There still exist confusion, skepticism, and controversy, however, among the experts as well as lay persons in the interpretation of hair trace element data. Much of the criticism stems from the lack of quantitative and reliable data on the ability of hair to accurately reflect dose-response relationships. To better define the significance or hair trace element levels (under the auspices of the International Atomic Energy Agency), the authors have undertaken a controlled set of animal experiments in which trace element levels in hair and other tissues have been measured after a mild state of systemic intoxication by chronic, low-does exposure to cadmium and selenium. Instrumental neutron activation analysis (INAA) and atomic absorption spectroscopy (AAS) methods have been developed for the determination of several elements with a high degree of precision and accuracy.

  3. Quantitative analysis of the temperature dependency in Raman active vibrational modes of molybdenum disulfide atomic layers.

    PubMed

    Najmaei, Sina; Ajayan, Pulickel M; Lou, J

    2013-10-21

    Raman spectroscopy is utilized to quantify the temperature dependency of the vibrational modes in molybdenum disulfide (MoS2) atomic layers. These analyses are essential for understanding the structural properties and phononic behaviors of this two-dimensional (2D) material. We quantitatively analyze the temperature dependent shifts of the Raman peak positions in the temperature range from 300 to 550 K, and find that both planar and out-of-plane characteristic modes are highly sensitive to temperature variations. This temperature dependency is linear and can be fully explained by the first-order temperature coefficient. Using a semi-quantitative model, we evaluate the contributions of the material's thermal expansion and intrinsic temperature effects to this dependency. We reveal that the dominating source of shift in the peak position of planar mode E2g(1) for samples of all thicknesses investigated is the four-phonon process. In addition to the four-phonon process, thermal expansion plays a significant role in the temperature dependency of the out-of-plane mode, A1g. The thickness dependency of the temperature coefficient for MoS2 and a drastic change in behaviors of samples from bi- to single-layered are also demonstrated. We further explore the role of defects in the thermal properties of MoS2 by examining the temperature dependency of Raman modes in CVD-grown samples.

  4. Probing a Device's Active Atoms.

    PubMed

    Studniarek, Michał; Halisdemir, Ufuk; Schleicher, Filip; Taudul, Beata; Urbain, Etienne; Boukari, Samy; Hervé, Marie; Lambert, Charles-Henri; Hamadeh, Abbass; Petit-Watelot, Sebastien; Zill, Olivia; Lacour, Daniel; Joly, Loïc; Scheurer, Fabrice; Schmerber, Guy; Da Costa, Victor; Dixit, Anant; Guitard, Pierre André; Acosta, Manuel; Leduc, Florian; Choueikani, Fadi; Otero, Edwige; Wulfhekel, Wulf; Montaigne, François; Monteblanco, Elmer Nahuel; Arabski, Jacek; Ohresser, Philippe; Beaurepaire, Eric; Weber, Wolfgang; Alouani, Mébarek; Hehn, Michel; Bowen, Martin

    2017-03-13

    Materials science and device studies have, when implemented jointly as "operando" studies, better revealed the causal link between the properties of the device's materials and its operation, with applications ranging from gas sensing to information and energy technologies. Here, as a further step that maximizes this causal link, the paper focuses on the electronic properties of those atoms that drive a device's operation by using it to read out the materials property. It is demonstrated how this method can reveal insight into the operation of a macroscale, industrial-grade microelectronic device on the atomic level. A magnetic tunnel junction's (MTJ's) current, which involves charge transport across different atomic species and interfaces, is measured while these atoms absorb soft X-rays with synchrotron-grade brilliance. X-ray absorption is found to affect magnetotransport when the photon energy and linear polarization are tuned to excite FeO bonds parallel to the MTJ's interfaces. This explicit link between the device's spintronic performance and these FeO bonds, although predicted, challenges conventional wisdom on their detrimental spintronic impact. The technique opens interdisciplinary possibilities to directly probe the role of different atomic species on device operation, and shall considerably simplify the materials science iterations within device research.

  5. GPS Block IIF Atomic Frequency Standard Analysis

    DTIC Science & Technology

    2010-11-01

    Frequency stability of GPS constellation for October 2010 (NGA products). REFERENCES [1] “ Rubidium Atomic Frequency Standard (RAFS) GPS...Block IIR Rubidium Atomic Frequency Standard Life Test,” in Proceedings of the 30 th Annual Precise Time and Time Interval (PTTI) Applications and...42 nd Annual Precise Time and Time Interval (PTTI) Meeting 181 GPS BLOCK IIF ATOMIC FREQUENCY STANDARD ANALYSIS

  6. 76 FR 55278 - Assistance to Foreign Atomic Energy Activities

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-09-07

    ...; ] DEPARTMENT OF ENERGY 10 CFR Part 810 RIN 1994-AA02 Assistance to Foreign Atomic Energy Activities AGENCY.... SUMMARY: DOE proposes to amend its regulation concerning unclassified assistance to foreign atomic energy... territories for which a general authorization for foreign atomic energy activities is available. This...

  7. Atom trap trace analysis of krypton isotopes

    SciTech Connect

    Bailey, K.; Chen, C. Y.; Du, X.; Li, Y. M.; Lu, Z.-T.; O'Connor, T. P.; Young, L.

    1999-11-17

    A new method of ultrasensitive isotope trace analysis has been developed. This method, based on the technique of laser manipulation of neutral atoms, has been used to count individual {sup 85}Kr and {sup 81}Kr atoms present in a natural krypton gas sample with isotopic abundances in the range of 10{sup {minus}11} and 10{sup {minus}13}, respectively. This method is free of contamination from other isotopes and elements and can be applied to several different isotope tracers for a wide range of applications. The demonstrated detection efficiency is 1 x 10{sup {minus}7}. System improvements could increase the efficiency by many orders of magnitude.

  8. Atomic Scale Analysis of the Enhanced Electro- and Photo-Catalytic Activity in High-Index Faceted Porous NiO Nanowires

    PubMed Central

    Shen, Meng; Han, Ali; Wang, Xijun; Ro, Yun Goo; Kargar, Alireza; Lin, Yue; Guo, Hua; Du, Pingwu; Jiang, Jun; Zhang, Jingyu; Dayeh, Shadi A.; Xiang, Bin

    2015-01-01

    Catalysts play a significant role in clean renewable hydrogen fuel generation through water splitting reaction as the surface of most semiconductors proper for water splitting has poor performance for hydrogen gas evolution. The catalytic performance strongly depends on the atomic arrangement at the surface, which necessitates the correlation of the surface structure to the catalytic activity in well-controlled catalyst surfaces. Herein, we report a novel catalytic performance of simple-synthesized porous NiO nanowires (NWs) as catalyst/co-catalyst for the hydrogen evolution reaction (HER). The correlation of catalytic activity and atomic/surface structure is investigated by detailed high resolution transmission electron microscopy (HRTEM) exhibiting a strong dependence of NiO NW photo- and electrocatalytic HER performance on the density of exposed high-index-facet (HIF) atoms, which corroborates with theoretical calculations. Significantly, the optimized porous NiO NWs offer long-term electrocatalytic stability of over one day and 45 times higher photocatalytic hydrogen production compared to commercial NiO nanoparticles. Our results open new perspectives in the search for the development of structurally stable and chemically active semiconductor-based catalysts for cost-effective and efficient hydrogen fuel production at large scale. PMID:25707903

  9. Atom location by electron channeling analysis

    SciTech Connect

    Pennycook, S.J.

    1984-07-01

    For many years the orientation dependence of the characteristic x-ray emission close to a Bragg reflection has been regarded as a hindrance to accurate microanalysis, and a random incident beam direction has always been recommended for accurate composition analysis. However, this orientation dependence can be put to use to extract information on the lattice location of foreign atoms within the crystalline matrix. Here a generalization of the technique is described which is applicable to any crystal structure including monatomic crystals, and can quantitatively determine substitutional fractions of impurities. The technique was referred to as electron channeling analysis, by analogy with the closely related and widely used bulk technique of ion channeling analysis, and was developed for lattice location studies of dopants in semiconductors at high spatial resolution. Only two spectra are required for each channeling analysis, one in each of the channeling conditions described above. If the matrix and dopant x-ray yields vary identically between the two orientations then the dopant necessarily lies within the reflecting matrix planes. If the dopant x-ray yield does not vary the dopant atoms are randomly located with respect to the matrix planes. 10 references, 2 figures.

  10. Analysis of atomic thermospheric nitrogen density

    NASA Technical Reports Server (NTRS)

    Engebretson, M. J.

    1985-01-01

    A NASA grant provided support for a research project at Augsbury College, Minneapolis, Minnesota for the analysis of atomic nitrogen density data obtained by the Neutral Atmospheric Composition Spectrometer (NACS) on board the Dynamics Explorer-2 satellite. Initial funding was for an exploratory study of the feasibility of obtaining ambient densities of N from source densities of NO. Funding was continued under the Dynamics Explorer Guest Investigator Program when initial studies indicated probable success in obtaining such ambient densities. The major scientific focus of the later work was to be to characterize the behavior of N densities at high latitudes.

  11. Flameless Atomic Absorption Spectrophotometric Analysis for Lewisite (L).

    DTIC Science & Technology

    1978-10-01

    method that was developed for detection of Lewisite by analysis for arsenic, using flameless atomic absorption spectroscopy (FAAS). “Flameless atomic ...place in a furnace, and the flame associated with con- ventional atomic absorption spectroscopy is not needed. The procedure that was used is given along...nickel was unnecessary for the Lewisite samples. Table 1. Flameless atomic absorption spectroscopy conditions used for determination of arsenic in

  12. Atom column indexing: atomic resolution image analysis through a matrix representation.

    PubMed

    Sang, Xiahan; Oni, Adedapo A; LeBeau, James M

    2014-12-01

    Here, we report the development of an approach to map atomic resolution images into a convenient matrix representation. Through the combination of two-dimensional Gaussian fitting and the projective standard deviation, atom column locations are projected onto two noncollinear reference lattice vectors that are used to assign each a unique (i, j) matrix index. By doing so, straightforward atomic resolution image analysis becomes possible. Using practical examples, we demonstrate that the matrix representation greatly simplifies categorizing atom columns to different sublattices. This enables a myriad of direct analyses, such as mapping atom column properties and correlating long-range atom column pairs. MATLAB source code can be downloaded from https://github.com/subangstrom/aci.

  13. Approaching the Limit in Atomic Spectrochemical Analysis.

    ERIC Educational Resources Information Center

    Hieftje, Gary M.

    1982-01-01

    To assess the ability of current analytical methods to approach the single-atom detection level, theoretical and experimentally determined detection levels are presented for several chemical elements. A comparison of these methods shows that the most sensitive atomic spectrochemical technique currently available is based on emission from…

  14. Tomographic Atom Probe: New Dimension in Materials Analysis.

    PubMed

    Deconihout; Pareige; Pareige; Blavette; Menand

    1999-01-01

    : Materials science requires the use of increasingly powerful tools in materials analysis. The last 20 years have witnessed the development of a number of analytical techniques. However, among these techniques, only a few allow observation and analysis of materials at the nanometer level. The tomographic atom probe (TAP) is a three-dimensional atom-probe (3-DAP) developed at the University of Rouen. In this instrument, the specimen is field evaporated, atomic layer by atomic layer, and the use of a position-sensing system makes it possible to map out the chemical identity of individual atoms within each field-evaporated layer on a nearly atomic scale. After analysis, the volume of matter removed from the specimen can be reconstructed atom by atom in the three dimensions of real space. The main advantages of the 3-DAP is its single-atom sensitivity and very high spatial resolution. In addition to 3-D visual information on chemical heterogeneity, 3-D images give an accurate measurement of the composition of any feature without any convolution bias. This study first describes the history of the 3-DAP technique. Its main features and the latest developments of the TAP are then detailed. The performance of this instrument is illustrated through two recent applications in materials science. Possible ways to further improve the technique are also discussed.

  15. Toward the Atomic-Level Mass Analysis of Biomolecules by the Scanning Atom Probe.

    PubMed

    Nishikawa, Osamu; Taniguchi, Masahiro

    2016-12-22

    In 1994, a new type of atom probe instrument, named the scanning atom probe (SAP), was proposed. The unique feature of the SAP is the introduction of a small extraction electrode, which scans over a specimen surface and confines the high field, required for field evaporation of surface atoms in a small space, between the specimen and the electrode. Thus, the SAP does not require a sharp specimen tip. This indicates that the SAP can mass analyze the specimens which are difficult to form in a sharp tip, such as organic materials and biomolecules. Clean single wall carbon nanotubes (CNT), made by high-pressure carbon monoxide process are found to be the best substrates for biomolecules. Various amino acids and dipeptide biomolecules were successfully mass analyzed, revealing characteristic clusters formed by strongly bound atoms in the specimens. The mass analysis indicates that SAP analysis of biomolecules is not only qualitative, but also quantitative.

  16. 2. VIEW IN ROOM 111, ATOMIC ABSORPTION BERYLLIUM ANALYSIS LABORATORY. ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    2. VIEW IN ROOM 111, ATOMIC ABSORPTION BERYLLIUM ANALYSIS LABORATORY. AIR FILTERS AND SWIPES ARE DISSOLVED WITH ACIDS AND THE REMAINING RESIDUES ARE SUSPENDED IN NITRIC ACID SOLUTION. THE SOLUTION IS PROCESSED THROUGH THE ATOMIC ABSORPTION SPECTROPHOTOMETER TO DETECT THE PRESENCE AND LEVELS OF BERYLLIUM. - Rocky Flats Plant, Health Physics Laboratory, On Central Avenue between Third & Fourth Streets, Golden, Jefferson County, CO

  17. Atomic hydrogen maser active oscillator cavity and bulb design optimization

    NASA Technical Reports Server (NTRS)

    Peters, H. E.; Washburn, P. J.

    1984-01-01

    The performance characteristics and reliability of the active oscillator atomic hydrogen maser depend upon oscillation parameters which characterize the interaction region of the maser, the resonant cavity and atom storage bulb assembly. With particular attention to use of the cavity frequency switching servo (1) to reduce cavity pulling, it is important to maintain high oscillation level, high atomic beam flux utilization efficiency, small spin exchange parameter and high cavity quality factor. It is also desirable to have a small and rigid cavity and bulb structure and to minimize the cavity temperature sensitivity. Curves for a novel hydrogen maser cavity configuration which is partially loaded with a quartz dielectric cylinder and show the relationships between cavity length, cavity diameter, bulb size, dielectric thickness, cavity quality factor, filling factor and cavity frequency temperature coefficient are presented. The results are discussed in terms of improvement in maser performance resulting from particular design choices.

  18. Active Control of Laser Wavefronts in Atom Interferometers

    NASA Astrophysics Data System (ADS)

    Trimeche, A.; Langlois, M.; Merlet, S.; Pereira Dos Santos, F.

    2017-03-01

    Wavefront aberrations are identified as a major limitation in quantum sensors. They are today the main contribution in the uncertainty budget of the best cold-atom interferometers based on two-photon laser beam splitters and constitute an important limit for their long-term stability, impeding these instruments from reaching their full potential. Moreover, they will also remain a major obstacle in future experiments based on large-momentum beam splitters. In this article, we tackle this issue by using a deformable mirror to control actively the laser wavefronts in atom interferometry. In particular, we demonstrate in an experimental proof of principle the efficient correction of wavefront aberrations in an atomic gravimeter.

  19. Atomic Ordering Enhanced Electrocatalytic Activity of Nanoalloys for Oxygen Reduction Reaction

    SciTech Connect

    Loukrakpam, Rameshwori; Shan, Shiyao; Petkov, Valeri; Yang, Lefu; Luo, Jin; Zhong, Chuan-Jian

    2013-10-01

    For oxygen reduction reaction (ORR) over alloy electrocatalysts, the understanding of how the atomic arrangement of the metal species in the nanocatalysts is responsible for the catalytic enhancement is challenging for achieving better design and tailoring of nanoalloy catalysts. This paper reports results of an investigation of the atomic structures and the electrocatalytic activities of ternary and binary nanoalloys, aiming at revealing a fundamental insight into the unique atomic-scale structure-electrocatalytic activity relationship. PtIrCo catalyst and its binary counterparts (PtCo and PtIr) are chosen as a model system for this study. The effect of thermochemical treatment temperature on the atomic-scale structure of the catalysts was examined as a useful probe to the structure-activity correlation. The structural characterization of the binary and ternary nanoalloy catalysts was performed by combining surface sensitive techniques such as XPS and 3D atomic ordering sensitive techniques such as high-energy X-ray diffraction (HE-XRD) coupled to atomic pair distribution function (PDF) analysis (HE-XRD/PDFs) and computer simulations. The results show that the thermal treatment temperature tunes the nanoalloy’s atomic and chemical ordering in a different way depending on the chemical composition, leading to differences in the nanoalloy’s mass and specific activities. A unique structural tunability of the atomic ordering in a platinum-iridium-cobalt nanoalloy has been revealed for enhancing greatly the electrocatalytic activity toward oxygen reduction reaction, which has significant implication for rational design and nanoengineering of advanced catalysts for electrochemical energy conversion and storage.

  20. Atom probe tomography analysis of WC powder.

    PubMed

    Weidow, Jonathan

    2013-09-01

    A tantalum doped tungsten carbide powder, (W,Ta)C, was prepared with the purpose to maximise the amount of Ta in the hexagonal mixed crystal carbide. Atom probe tomography (APT) was considered to be the best technique to quantitatively measure the amount of Ta within this carbide. As the carbide powder consisted in the form of very small particles (<1 μm), a method to produce APT specimens of such a powder was developed. The powder was at first embedded in copper and a FIB-SEM workstation was used to make an in-situ lift-out from a selected powder particle. The powder particle was then deposited on a post made from a WC-Co based cemented carbide specimen. With the use of a laser assisted atom probe, it was shown that the method is working and the Ta content of the (W,Ta)C could be measured quantitatively.

  1. Synchronization of active atomic clocks via quantum and classical channels

    NASA Astrophysics Data System (ADS)

    Roth, Alexander; Hammerer, Klemens

    2016-10-01

    Superradiant lasers based on atomic ensembles exhibiting ultranarrow optical transitions can emit light of unprecedented spectral purity and may serve as active atomic clocks. We consider two frequency-detuned active atomic clocks, which are coupled in a cascaded setup, i.e., as master and slave lasers, and study the synchronization of the slave to the master clock. In a setup where both atomic ensembles are coupled to a common cavity mode, such synchronization phenomena have been predicted by Xu et al. [M. Xu, D. A. Tieri, E. C. Fine, J. K. Thompson, and M. J. Holland, Phys. Rev. Lett. 113, 154101 (2014)., 10.1103/PhysRevLett.113.154101] and experimentally observed by Weiner et al. (J. M. Weiner et al., arXiv:1503.06464). Here we demonstrate that synchronization still occurs in cascaded setups but exhibits distinctly different phase diagrams. We study the characteristics of synchronization in comparison to the case of coupling through a common cavity. We also consider synchronization through a classical channel where light of the master laser is measured phase sensitively and the slave laser is injection locked by feedback and compare to the results achievable by coupling through quantum channels.

  2. Removal of Biologically Active Organic Contaminants using Atomic Oxygen

    NASA Technical Reports Server (NTRS)

    Banks, Bruce A. (Inventor); Banks, Michael A. (Inventor); Banks, Eric B. (Inventor)

    2003-01-01

    Biomedical devices that are to come into contact with living tissue, such as prosthetic and other implants for the human body and the containers used to store and transport them, are together cleaned of non-living, but biologically active organic materials, including endotoxins such as lipopolysaccharides, and assembled into a hermetically sealed package without recontamination. This is achieved by cleaning both the device and package components together in an apparatus, which includes a hermetically sealed chamber, in which they are contacted with atomic oxygen which biocleans them, by oxidizing the biologically active organic materials. The apparatus also includes means for manipulating the device and container and hermetically sealing the cleaned device into the cleaned container to form the package. A calibrated witness coupon visually indicates whether or not the device and container have received enough exposure to the atomic oxygen to have removed the organic materials from their surfaces. Gamma radiation is then used to sterilize the device in the sealed container.

  3. Atomic-Based-Combined-Cycle Analysis

    NASA Technical Reports Server (NTRS)

    Han, Samuel S.

    1999-01-01

    Atomic-based-combined-cycle (ABCC) engine combines an air-breathing ramjet engine with an atomic reactor to increase the mission-averaged specific impulse and thereby increasing the dry-mass ratio. ABCC engine is similar to RBCC engine except that energy needed for the propulsive power is derived from nuclear reaction rather than chemical combustion used in the RBCC engine. The potential performance improvement of an ABCC engine over a RBCC engine comes from two factors. Firstly, the energy density of nuclear reaction is several order of magnitudes higher than the chemical combustion. Secondly, hydrogen can produce much higher nozzle exit velocity because of its small molecular weight. A one-dimensional, transient numerical model was used to analyze a generic RBCC engine and it is used as a baseline to evaluate an imaginary ABCC engine performance. A nuclear reactor is treated as a black box energy source that replaces the role of the primary rocket and the chemical combustion chamber in a RBCC engine. The performance of a generic ABCC engine along a flight path (q0 =10 (exp 3) lbf per square ft) shows that the mission averaged-specific impulse is about twice larger than RBCC engine and the dry mass-ratio is about 50% larger. Results of the present ABCC engine performance are based on the assumptions that the flow passage of working fluids is identical to that of RBCC engine and that a nuclear reactor is treated as an energy black box. Preliminary heat transfer calculation shows that the rate of heat transfer to the working fluids is within the limit of turbulent convective heat transfer regimes. The flow passage of realistic ABCC engine must be known for a better prediction of ABCC engine performance. Also, critical heat transfer calculations must be performed for the ejector mode and ramjet mode operations. This is possible only when the details of a reactor configuration are available.

  4. Atomic-Based-Combined-Cycle Analysis

    NASA Technical Reports Server (NTRS)

    Han, Sam; Bai, Don; Schmidt, George

    2000-01-01

    Atomic-based-combined-cycle (ABCC) engine combines an air-breathing ramjet engine with an atomic reactor to increase the mission-averaged specific impulse and thereby increasing the dry-mass ratio. ABCC engine is similar to RBCC engine except that energy needed for the propulsive power is derived from nuclear reaction rather than chemical combustion used in the RBCC engine. The potential performance improvement of an ABCC engine over a RBCC engine comes from two factors. Firstly, the energy density of nuclear reaction is several order of magnitudes higher than the chemical combustion. Secondly, hydrogen can produce much higher nozzle exit velocity because of its small molecular weight. A one-dimensional, transient numerical model was used to analyze a generic scramjet engine and it is used as a baseline to evaluate an imaginary ABCC engine performance. A nuclear reactor is treated as a black box energy source that replaces the role of the primary rocket and the chemical combustion chamber in a RBCC engine. Hydrogen is heated by the reactor and accelerated to produce high-speed ejection velocity. The ejection velocity up 10,000 m/sec is theoretically possible because of high energy density from the reactor and large gas constant of the hydrogen. Oxygen contained in the entrained air reacts with hydrogen and produces propulsive power for ejector mode operation. To provide enough thrust for initial acceleration, relatively large amount of hydrogen must be pumped through the reactor. Amount of oxygen contained in the entrained air may not be sufficient to burn all hydrogen and consequently combustion could occur at the end of exit nozzle. It is assumed that this combustion process is constant-pressure combustion at 1.0 atmospheric pressure and thus not affects the nozzle exit condition.

  5. Atomic Beam Laser Spectrometer for In-field Isotopic Analysis

    SciTech Connect

    Castro, Alonso

    2016-06-22

    This is a powerpoint presentation for the DTRA quarterly program review that goes into detail about the atomic beam laser spectrometer for in-field isotopic analysis. The project goals are the following: analysis of post-detonation debris, determination of U and Pu isotopic composition, and fieldable prototype: < 2ft3, < 1000W.

  6. A near atomic structure of the active human apoptosome.

    PubMed

    Cheng, Tat Cheung; Hong, Chuan; Akey, Ildikó V; Yuan, Shujun; Akey, Christopher W

    2016-10-04

    In response to cell death signals, an active apoptosome is assembled from Apaf-1 and procaspase-9 (pc-9). Here we report a near atomic structure of the active human apoptosome determined by cryo-electron microscopy. The resulting model gives insights into cytochrome c binding, nucleotide exchange and conformational changes that drive assembly. During activation an acentric disk is formed on the central hub of the apoptosome. This disk contains four Apaf-1/pc-9 CARD pairs arranged in a shallow spiral with the fourth pc-9 CARD at lower occupancy. On average, Apaf-1 CARDs recruit 3 to 5 pc-9 molecules to the apoptosome and one catalytic domain may be parked on the hub, when an odd number of zymogens are bound. This suggests a stoichiometry of one or at most, two pc-9 dimers per active apoptosome. Thus, our structure provides a molecular framework to understand the role of the apoptosome in programmed cell death and disease.

  7. Catalytically active single-atom niobium in graphitic layers

    NASA Astrophysics Data System (ADS)

    Zhang, Xuefeng; Guo, Junjie; Guan, Pengfei; Liu, Chunjing; Huang, Hao; Xue, Fanghong; Dong, Xinglong; Pennycook, Stephen J.; Chisholm, Matthew F.

    2013-05-01

    Carbides of groups IV through VI (Ti, V and Cr groups) have long been proposed as substitutes for noble metal-based electrocatalysts in polymer electrolyte fuel cells. However, their catalytic activity has been extremely limited because of the low density and stability of catalytically active sites. Here we report the excellent performance of a niobium-carbon structure for catalysing the cathodic oxygen reduction reaction. A large number of single niobium atoms and ultra small clusters trapped in graphitic layers are directly identified using state-of-the-art aberration-corrected scanning transmission electron microscopy. This structure not only enhances the overall conductivity for accelerating the exchange of ions and electrons, but it suppresses the chemical/thermal coarsening of the active particles. Experimental results coupled with theory calculations reveal that the single niobium atoms incorporated within the graphitic layers produce a redistribution of d-band electrons and become surprisingly active for O2 adsorption and dissociation, and also exhibit high stability.

  8. STATISTICAL ANALYSIS OF THE HEAVY NEUTRAL ATOMS MEASURED BY IBEX

    SciTech Connect

    Park, Jeewoo; Kucharek, Harald; Möbius, Eberhard; Galli, André; Livadiotis, George; Fuselier, Steve A.; McComas, David J.

    2015-10-15

    We investigate the directional distribution of heavy neutral atoms in the heliosphere by using heavy neutral maps generated with the IBEX-Lo instrument over three years from 2009 to 2011. The interstellar neutral (ISN) O and Ne gas flow was found in the first-year heavy neutral map at 601 keV and its flow direction and temperature were studied. However, due to the low counting statistics, researchers have not treated the full sky maps in detail. The main goal of this study is to evaluate the statistical significance of each pixel in the heavy neutral maps to get a better understanding of the directional distribution of heavy neutral atoms in the heliosphere. Here, we examine three statistical analysis methods: the signal-to-noise filter, the confidence limit method, and the cluster analysis method. These methods allow us to exclude background from areas where the heavy neutral signal is statistically significant. These methods also allow the consistent detection of heavy neutral atom structures. The main emission feature expands toward lower longitude and higher latitude from the observational peak of the ISN O and Ne gas flow. We call this emission the extended tail. It may be an imprint of the secondary oxygen atoms generated by charge exchange between ISN hydrogen atoms and oxygen ions in the outer heliosheath.

  9. Statistical Analysis of the Heavy Neutral Atoms Measured by IBEX

    NASA Astrophysics Data System (ADS)

    Park, Jeewoo; Kucharek, Harald; Möbius, Eberhard; Galli, André; Livadiotis, George; Fuselier, Steve A.; McComas, David J.

    2015-10-01

    We investigate the directional distribution of heavy neutral atoms in the heliosphere by using heavy neutral maps generated with the IBEX-Lo instrument over three years from 2009 to 2011. The interstellar neutral (ISN) O&Ne gas flow was found in the first-year heavy neutral map at 601 keV and its flow direction and temperature were studied. However, due to the low counting statistics, researchers have not treated the full sky maps in detail. The main goal of this study is to evaluate the statistical significance of each pixel in the heavy neutral maps to get a better understanding of the directional distribution of heavy neutral atoms in the heliosphere. Here, we examine three statistical analysis methods: the signal-to-noise filter, the confidence limit method, and the cluster analysis method. These methods allow us to exclude background from areas where the heavy neutral signal is statistically significant. These methods also allow the consistent detection of heavy neutral atom structures. The main emission feature expands toward lower longitude and higher latitude from the observational peak of the ISN O&Ne gas flow. We call this emission the extended tail. It may be an imprint of the secondary oxygen atoms generated by charge exchange between ISN hydrogen atoms and oxygen ions in the outer heliosheath.

  10. Atomic basis for therapeutic activation of neuronal potassium channels

    PubMed Central

    Kim, Robin Y.; Yau, Michael C.; Galpin, Jason D.; Seebohm, Guiscard; Ahern, Christopher A.; Pless, Stephan A.; Kurata, Harley T.

    2015-01-01

    Retigabine is a recently approved anticonvulsant that acts by potentiating neuronal M-current generated by KCNQ2–5 channels, interacting with a conserved Trp residue in the channel pore domain. Using unnatural amino-acid mutagenesis, we subtly altered the properties of this Trp to reveal specific chemical interactions required for retigabine action. Introduction of a non-natural isosteric H-bond-deficient Trp analogue abolishes channel potentiation, indicating that retigabine effects rely strongly on formation of a H-bond with the conserved pore Trp. Supporting this model, substitution with fluorinated Trp analogues, with increased H-bonding propensity, strengthens retigabine potency. In addition, potency of numerous retigabine analogues correlates with the negative electrostatic surface potential of a carbonyl/carbamate oxygen atom present in most KCNQ activators. These findings functionally pinpoint an atomic-scale interaction essential for effects of retigabine and provide stringent constraints that may guide rational improvement of the emerging drug class of KCNQ channel activators. PMID:26333338

  11. Atom depth analysis delineates mechanisms of protein intermolecular interactions

    SciTech Connect

    Alocci, Davide; Bernini, Andrea; Niccolai, Neri

    2013-07-12

    Highlights: •3D atom depth analysis is proposed to identify different layers in protein structures. •Amino acid contents for each layers have been analyzed for a large protein dataset. •Charged amino acids in the most external layer are present at very different extents. •Atom depth indexes of K residues reflect their side chains flexibility. •Mobile surface charges can be responsible for long range protein–protein recognition. -- Abstract: The systematic analysis of amino acid distribution, performed inside a large set of resolved protein structures, sheds light on possible mechanisms driving non random protein–protein approaches. Protein Data Bank entries have been selected using as filters a series of restrictions ensuring that the shape of protein surface is not modified by interactions with large or small ligands. 3D atom depth has been evaluated for all the atoms of the 2,410 selected structures. The amino acid relative population in each of the structural layers formed by grouping atoms on the basis of their calculated depths, has been evaluated. We have identified seven structural layers, the inner ones reproducing the core of proteins and the outer one incorporating their most protruding moieties. Quantitative analysis of amino acid contents of structural layers identified, as expected, different behaviors. Atoms of Q, R, K, N, D residues are increasingly more abundant in going from core to surfaces. An opposite trend is observed for V, I, L, A, C, and G. An intermediate behavior is exhibited by P, S, T, M, W, H, F and Y. The outer structural layer hosts predominantly E and K residues whose charged moieties, protruding from outer regions of the protein surface, reorient free from steric hindrances, determining specific electrodynamics maps. This feature may represent a protein signature for long distance effects, driving the formation of encounter complexes and the eventual short distance approaches that are required for protein

  12. Structural dynamics and activity of nanocatalysts inside fuel cells by in operando atomic pair distribution studies

    NASA Astrophysics Data System (ADS)

    Petkov, Valeri; Prasai, Binay; Shan, Shiyao; Ren, Yang; Wu, Jinfang; Cronk, Hannah; Luo, Jin; Zhong, Chuan-Jian

    2016-05-01

    Here we present the results from a study aimed at clarifying the relationship between the atomic structure and activity of nanocatalysts for chemical reactions driving fuel cells, such as the oxygen reduction reaction (ORR). In particular, using in operando high-energy X-ray diffraction (HE-XRD) we tracked the evolution of the atomic structure and activity of noble metal-transition metal (NM-TM) nanocatalysts for ORR as they function at the cathode of a fully operational proton exchange membrane fuel cell (PEMFC). Experimental HE-XRD data were analysed in terms of atomic pair distribution functions (PDFs) and compared to the current output of the PEMFC, which was also recorded during the experiments. The comparison revealed that under actual operating conditions, NM-TM nanocatalysts can undergo structural changes that differ significantly in both length-scale and dynamics and so can suffer losses in their ORR activity that differ significantly in both character and magnitude. Therefore we argue that strategies for reducing ORR activity losses should implement steps for achieving control not only over the length but also over the time-scale of the structural changes of NM-TM NPs that indeed occur during PEMFC operation. Moreover, we demonstrate how such a control can be achieved and thereby the performance of PEMFCs improved considerably. Last but not least, we argue that the unique capabilities of in operando HE-XRD coupled to atomic PDF analysis to characterize active nanocatalysts inside operating fuel cells both in a time-resolved manner and with atomic level resolution, i.e. in 4D, can serve well the ongoing search for nanocatalysts that deliver more with less platinum.Here we present the results from a study aimed at clarifying the relationship between the atomic structure and activity of nanocatalysts for chemical reactions driving fuel cells, such as the oxygen reduction reaction (ORR). In particular, using in operando high-energy X-ray diffraction (HE

  13. Structural dynamics and activity of nanocatalysts inside fuel cells by in operando atomic pair distribution studies.

    PubMed

    Petkov, Valeri; Prasai, Binay; Shan, Shiyao; Ren, Yang; Wu, Jinfang; Cronk, Hannah; Luo, Jin; Zhong, Chuan-Jian

    2016-05-19

    Here we present the results from a study aimed at clarifying the relationship between the atomic structure and activity of nanocatalysts for chemical reactions driving fuel cells, such as the oxygen reduction reaction (ORR). In particular, using in operando high-energy X-ray diffraction (HE-XRD) we tracked the evolution of the atomic structure and activity of noble metal-transition metal (NM-TM) nanocatalysts for ORR as they function at the cathode of a fully operational proton exchange membrane fuel cell (PEMFC). Experimental HE-XRD data were analysed in terms of atomic pair distribution functions (PDFs) and compared to the current output of the PEMFC, which was also recorded during the experiments. The comparison revealed that under actual operating conditions, NM-TM nanocatalysts can undergo structural changes that differ significantly in both length-scale and dynamics and so can suffer losses in their ORR activity that differ significantly in both character and magnitude. Therefore we argue that strategies for reducing ORR activity losses should implement steps for achieving control not only over the length but also over the time-scale of the structural changes of NM-TM NPs that indeed occur during PEMFC operation. Moreover, we demonstrate how such a control can be achieved and thereby the performance of PEMFCs improved considerably. Last but not least, we argue that the unique capabilities of in operando HE-XRD coupled to atomic PDF analysis to characterize active nanocatalysts inside operating fuel cells both in a time-resolved manner and with atomic level resolution, i.e. in 4D, can serve well the ongoing search for nanocatalysts that deliver more with less platinum.

  14. Determination of palladium, platinum and rhodium in used automobile catalysts and active pharmaceutical ingredients using high-resolution continuum source graphite furnace atomic absorption spectrometry and direct solid sample analysis

    NASA Astrophysics Data System (ADS)

    Resano, Martín; Flórez, María del Rosario; Queralt, Ignasi; Marguí, Eva

    2015-03-01

    This work investigates the potential of high-resolution continuum source graphite furnace atomic absorption spectrometry for the direct determination of Pd, Pt and Rh in two samples of very different nature. While analysis of active pharmaceutical ingredients is straightforward and it is feasible to minimize matrix effects, to the point that calibration can be carried out against aqueous standard solutions, the analysis of used automobile catalysts is more challenging requiring the addition of a chemical modifier (NH4F·HF) to help in releasing the analytes, a more vigorous temperature program and the use of a solid standard (CRM ERM®-EB504) for calibration. However, in both cases it was possible to obtain accurate results and precision values typically better than 10% RSD in a fast and simple way, while only two determinations are needed for the three analytes, since Pt and Rh can be simultaneously monitored in both types of samples. Overall, the methods proposed seem suited for the determination of these analytes in such types of samples, offering a greener and faster alternative that circumvents the traditional problems associated with sample digestion, requiring a small amount of sample only (0.05 mg per replicate for catalysts, and a few milligrams for the pharmaceuticals) and providing sufficient sensitivity to easily comply with regulations. The LODs achieved were 6.5 μg g- 1 (Pd), 8.3 μg g- 1 (Pt) and 9.3 μg g- 1 (Rh) for catalysts, which decreased to 0.08 μg g- 1 (Pd), 0.15 μg g- 1 (Pt) and 0.10 μg g- 1 (Rh) for pharmaceuticals.

  15. Comparison of the quantitative analysis performance between pulsed voltage atom probe and pulsed laser atom probe.

    PubMed

    Takahashi, J; Kawakami, K; Raabe, D

    2017-01-31

    The difference in quantitative analysis performance between the voltage-mode and laser-mode of a local electrode atom probe (LEAP3000X HR) was investigated using a Fe-Cu binary model alloy. Solute copper atoms in ferritic iron preferentially field evaporate because of their significantly lower evaporation field than the matrix iron, and thus, the apparent concentration of solute copper tends to be lower than the actual concentration. However, in voltage-mode, the apparent concentration was higher than the actual concentration at 40K or less due to a detection loss of matrix iron, and the concentration decreased with increasing specimen temperature due to the preferential evaporation of solute copper. On the other hand, in laser-mode, the apparent concentration never exceeded the actual concentration, even at lower temperatures (20K), and this mode showed better quantitative performance over a wide range of specimen temperatures. These results indicate that the pulsed laser atom probe prevents both detection loss and preferential evaporation under a wide range of measurement conditions.

  16. A near atomic structure of the active human apoptosome

    PubMed Central

    Cheng, Tat Cheung; Hong, Chuan; Akey, Ildikó V; Yuan, Shujun; Akey, Christopher W

    2016-01-01

    In response to cell death signals, an active apoptosome is assembled from Apaf-1 and procaspase-9 (pc-9). Here we report a near atomic structure of the active human apoptosome determined by cryo-electron microscopy. The resulting model gives insights into cytochrome c binding, nucleotide exchange and conformational changes that drive assembly. During activation an acentric disk is formed on the central hub of the apoptosome. This disk contains four Apaf-1/pc-9 CARD pairs arranged in a shallow spiral with the fourth pc-9 CARD at lower occupancy. On average, Apaf-1 CARDs recruit 3 to 5 pc-9 molecules to the apoptosome and one catalytic domain may be parked on the hub, when an odd number of zymogens are bound. This suggests a stoichiometry of one or at most, two pc-9 dimers per active apoptosome. Thus, our structure provides a molecular framework to understand the role of the apoptosome in programmed cell death and disease. DOI: http://dx.doi.org/10.7554/eLife.17755.001 PMID:27697150

  17. On the mechanism of silicon activation by halogen atoms.

    PubMed

    Soria, Federico A; Patrito, Eduardo M; Paredes-Olivera, Patricia

    2011-03-15

    Despite the widespread use of chlorinated silicon as the starting point for further functionalization reactions, the high reactivity of this surface toward a simple polar molecule such as ammonia still remains unclear. We therefore undertook a comprehensive investigation of the factors that govern the reactivity of halogenated silicon surfaces. The reaction of NH3 was investigated comparatively on the Cl-Si(100)-2 × 1, Br-Si(100)-2 × 1, H-Si(100)-2 × 1, and Si(100)-2 × 1 surfaces using density functional theory. The halogenated surfaces show considerable activation with respect to the hydrogenated surface. The reaction on the halogenated surfaces proceeds via the formation of a stable datively bonded complex in which a silicon atom is pentacoordinated. The activation of the halogenated Si(100)-2 × 1 surfaces toward ammonia arises from the large redistribution of charge in the transition state that precedes the breakage of the Si-X bond and the formation of the Si-NH2 bond. This transition state has an ionic nature of the form Si-NH3(+)X(-). Steric effects also play an important role in surface reactivity, making brominated surfaces less reactive than chlorinated surfaces. The overall activation-energy barriers on the Cl-Si(100)-2 × 1 and Br-Si(100)-2 × 1 surfaces are 12.3 and 19.9 kcal/mol, respectively, whereas on the hydrogenated Si(100)-2 × 1 surface the energy barrier is 38.3 kcal/mol. The reaction of ammonia on the chlorinated surface is even more activated than on the bare Si(100)-2 × 1 surface, for which the activation barrier is 21.3 kcal/mol. Coadsorption effects in partially aminated surfaces and in the presence of reaction products increase activation-energy barriers and have a blocking effect for further reactions of NH3.

  18. Encapsulation method for atom probe tomography analysis of nanoparticles.

    PubMed

    Larson, D J; Giddings, A D; Wu, Y; Verheijen, M A; Prosa, T J; Roozeboom, F; Rice, K P; Kessels, W M M; Geiser, B P; Kelly, T F

    2015-12-01

    Open-space nanomaterials are a widespread class of technologically important materials that are generally incompatible with analysis by atom probe tomography (APT) due to issues with specimen preparation, field evaporation and data reconstruction. The feasibility of encapsulating such non-compact matter in a matrix to enable APT measurements is investigated using nanoparticles as an example. Simulations of field evaporation of a void, and the resulting artifacts in ion trajectory, underpin the requirement that no voids remain after encapsulation. The approach is demonstrated by encapsulating Pt nanoparticles in an ZnO:Al matrix created by atomic layer deposition, a growth technique which offers very high surface coverage and conformality. APT measurements of the Pt nanoparticles are correlated with transmission electron microscopy images and numerical simulations in order to evaluate the accuracy of the APT reconstruction.

  19. Atom-by-Atom Analysis of Semiconductor Nanowires with Parts Per Million Sensitivity.

    PubMed

    Koelling, S; Li, A; Cavalli, A; Assali, S; Car, D; Gazibegovic, S; Bakkers, E P A M; Koenraad, P M

    2017-02-08

    The functionality of semiconductor devices is determined by the incorporation of dopants at concentrations down to the parts per million (ppm) level and below. Optimization of intentional and unintentional impurity doping relies on methods to detect and map the level of impurities. Detecting such low concentrations of impurities in nanostructures is however challenging to date as on the one hand methods used for macroscopic samples cannot be applied due to the inherent small volumes or faceted surfaces and on the other hand conventional microscopic analysis techniques are not sufficiently sensitive. Here, we show that we can detect and map impurities at the ppm level in semiconductor nanowires using atom probe tomography. We develop a method applicable to a wide variety of nanowires relevant for electronic and optical devices. We expect that it will contribute significantly to the further optimization of the synthesis of nanowires, nanostructures and devices based on these structures.

  20. Study of proper conditions for quantitative atom-probe analysis

    NASA Astrophysics Data System (ADS)

    Rolander, Ulf; Andrén, Hans-Olof

    1994-03-01

    Atom-probe microanalysis is a truly quantitative method only if certain requirements are fulfilled. Field evaporation must only happen when the detector system is active; ions must travel from specimen to detector without being obstructed; and ions must be detected with the same probability regardless of mass and energy. Designs and methods to achieve these requirements are presented in the paper, such as a controlled high-voltage pulser, a detector with good and variable multi-hit resolution, ion optical alignment procedures, and a method to statistically correct for pile-up in the detector.

  1. Analysis of cement by atomic absorption spectrophotometry and volumetric method.

    PubMed

    Choi, K K; Lam, L; Luk, S F

    1994-01-01

    A new method to determine the composition of cement raw mix and cement is devised. The sample was fused with a mixture of sodium carbonate and lithium tetraborate (3:1) at 925 degrees C for 10 min. The fusion cake was dissolved in hydrochloric acid. The concentration of analyte in solution was either determined by atomic absorption spectrophotometry or titrimetry. The proposed method is quick and the analysis for interested oxides (SiO(2), Al(2)O(3), Fe(2)O(3), and CaO) can be completed within 1 hr. The accuracy and precision are comparable to that of X-ray fluorescence spectrometry.

  2. Reactivity and Catalytic Activity of Hydrogen Atom Chemisorbed Silver Clusters.

    PubMed

    Manzoor, Dar; Pal, Sourav

    2015-06-18

    Metal clusters of silver have attracted recent interest of researchers as a result of their potential in different catalytic applications and low cost. However, due to the completely filled d orbital and very high first ionization potential of the silver atom, the silver-based catalysts interact very weakly with the reacting molecules. In the current work, density functional theory calculations were carried out to investigate the effect of hydrogen atom chemisorption on the reactivity and catalytic properties of inert silver clusters. Our results affirm that the hydrogen atom chemisorption leads to enhancement in the binding energy of the adsorbed O2 molecule on the inert silver clusters. The increase in the binding energy is also characterized by the decrease in the Ag-O and increase in the O-O bond lengths in the case of the AgnH silver clusters. Pertinent to the increase in the O-O bond length, a significant red shift in the O-O stretching frequency is also noted in the case of the AgnH silver clusters. Moreover, the hydrogen atom chemisorbed silver clusters show low reaction barriers and high heat of formation of the final products for the environmentally important CO oxidation reaction as compared to the parent catalytically inactive clusters. The obtained results were compared with those of the corresponding gold and hydrogen atom chemisorbed gold clusters obtained at the same level of theory. It is expected the current computational study will provide key insights for future advances in the design of efficient nanosilver-based catalysts through the adsorption of a small atom or a ligand.

  3. Progress on Atom Trap Trace Analysis of 41Ca

    NASA Astrophysics Data System (ADS)

    Li, Yimin; Bailey, Kevin; Du, Xu; Lu, Zheng-Tian; O'Connor, Thomas; Young, Linda

    2000-06-01

    A new method of ultrasensitive trace-isotope analysis, based on the techniques of laser cooling and trapping, has recently been used to detect the rare 81Kr atoms in atmospheric krypton samples [1]. We are working on applying this method to another important tracer - 41Ca, which has a half-life of 1.0 x 105 years and a natural isotope abundance of about 10-15. As a tracer, 41Ca is ideal for dating bones as old as a few hundred thousand years. This is an important era of human development, but too old for radiocarbon dating. It is also a useful medical tracer that can be applied to monitor bone-loss rates in the diagnosis and treatment of osteoporosis. We are setting up a MOT-system for the efficient trapping and counting of 41Ca atoms. The details of the system and experimental results will be presented at this poster. This work is supported by the U.S. Department of Energy, Nuclear Physics Division; L.Young is supported by the Office of Basic Energy Sciences, Division of Chemical Sciences (Contract W-31-109-ENG-38). [1] C.Y. Chen et. al., Science 286, 1139 (1999).

  4. Exceptional oxidation activity with size-controlled supported gold clusters of low atomicity

    NASA Astrophysics Data System (ADS)

    Corma, Avelino; Concepción, Patricia; Boronat, Mercedes; Sabater, Maria J.; Navas, Javier; Yacaman, Miguel José; Larios, Eduardo; Posadas, Alvaro; López-Quintela, M. Arturo; Buceta, David; Mendoza, Ernest; Guilera, Gemma; Mayoral, Alvaro

    2013-09-01

    The catalytic activity of gold depends on particle size, with the reactivity increasing as the particle diameter decreases. However, investigations into behaviour in the subnanometre regime (where gold exists as small clusters of a few atoms) began only recently with advances in synthesis and characterization techniques. Here we report an easy method to prepare isolated gold atoms supported on functionalized carbon nanotubes and their performance in the oxidation of thiophenol with O2. We show that single gold atoms are not active, but they aggregate under reaction conditions into gold clusters of low atomicity that exhibit a catalytic activity comparable to that of sulfhydryl oxidase enzymes. When clusters grow into larger nanoparticles, catalyst activity drops to zero. Theoretical calculations show that gold clusters are able to activate thiophenol and O2 simultaneously, and larger nanoparticles are passivated by strongly adsorbed thiolates. The combination of both reactants activation and facile product desorption makes gold clusters excellent catalysts.

  5. Light pulse analysis with a multi-state atom interferometer

    SciTech Connect

    Herrera, I.; Lombardi, P.; Schäfer, F.; Petrovic, J.; Cataliotti, F. S.

    2014-12-04

    We present a controllable multi-state cold-atom interferometer that is easy-to-use and fully merged on an atom chip. We demonstrate its applications as a sensor of the fields whose interactions with atoms are state-dependent.

  6. A Superradiant Raman Laser as a Hybrid Active/Passive Atomic Sensor

    NASA Astrophysics Data System (ADS)

    Bohnet, Justin; Weiner, Joshua; Cox, Kevin; Chen, Zilong; Thompson, James

    2013-05-01

    We have realized an atomic sensor that combines active, wideband sensing with passive measurement periods using dynamic control of a cold-atom, superradiant Raman laser. In a superradiant laser, collective emission of the atomic ensemble maps the quantum phase stored in the atoms onto the detected cavity field. We discuss the fundamental precision of the superradiant mapping and show theoretically that the precision of the non-demolition measurement is only a factor of two worse than the standard quantum limit on phase estimation for a coherent spin state. Using the superradiant readout, we experimentally demonstrate a repeated, non-demolition conditional Ramsey sequence that has the potential to combine the benefit of a high-bandwidth active frequency reference with a high-accuracy passive device. We also present an experimental realization of a superradiant Raman laser operated as a hybrid active/passive atomic magnetometer.

  7. Voronoi analysis of the short–range atomic structure in iron and iron–carbon melts

    SciTech Connect

    Sobolev, Andrey; Mirzoev, Alexander

    2015-08-17

    In this work, we simulated the atomic structure of liquid iron and iron–carbon alloys by means of ab initio molecular dynamics. Voronoi analysis was used to highlight changes in the close environments of Fe atoms as carbon concentration in the melt increases. We have found, that even high concentrations of carbon do not affect short–range atomic order of iron atoms — it remains effectively the same as in pure iron melts.

  8. Solution and slurry sampling electrothermal atomic absorption spectrometry for the analysis of high purity quartz

    NASA Astrophysics Data System (ADS)

    Hauptkorn, Susanne; Krivan, Viliam

    1996-07-01

    A slurry sampling electrothermal atomic absorption spectrometry (ETAAS) method for the determination of Al, Cr, Cu, Fe, K, Li, Mg, Mn and Na at trace and ultratrace level in high purity quartz samples has been developed. The influence of atomization temperature, internal gas flow during atomization and carbide modification of the graphite tube on the background absorption has been studied. Simple quantification via calibration curves, recorded with aqueous standards, is possible for all elements except Al. The performance and the accuracy of the slurry sampling technique are compared to those of the analysis of hydrofluoric acid digests. With both methods, the blanks could be substantially reduced by minimization of sample handling. Because of essentially higher applicable sample portions, the solution technique provides lower limits of detection for all elements excluding Al, Na and K. For the slurry sampling technique, the achievable limits of detection are in the range of 2 (Mg) to 500 (Fe) ng g -1 and for the solution technique, they are between 0.4 (Mg) and 500 (Al) ng g -1. Thus, both developed methods are well suited for ultratrace analysis of high purity quartz for microelectronic applications. The results obtained by these two ETAAS techniques are compared with those of independent methods including neutron activation analysis.

  9. Activation energies of metal atomization and nitrate and sulfate decomposition in concentrated matrices (10 -1 M).

    NASA Astrophysics Data System (ADS)

    Le Bihan, A.; Le Garrec, H.; Cabon, J. Y.; Guern, Y.

    1998-08-01

    This paper reports on activation energies measured during copper and manganese atomization in a graphite furnace in the presence of large amounts of nitrate and sulfate matrices. It also deals with activation energies corresponding to the decomposition of these matrices and to the atomization of their metal, i.e. Na, Ca or Mg. These results were obtained from Arrhenius-type calculations carried out on specific and non-specific absorbance values. Atomization was achieved under a very high gas flow which allowed us to get to the source function. Some of the calculated energies were compared to reaction energies deduced from tables of thermodynamic data.

  10. Quantitative structure-activity relationship study using refractotopological state atom index on some neonicotinoid insecticides.

    PubMed

    Debnath, Bikash; Gayen, Shovanlal; Basu, Anindya; Ghosh, Balaram; Srikanth, Kolluru; Jha, Tarun

    2004-12-01

    Importance of atom-level topological descriptors like electrotopological state atom (E-state) index in QSAR study is increasing. These descriptors help to relate structure and activity at atomic/fragmental level. In view of the earlier success of E-state index on some azidopyridinyl neonicotinoid insecticides, a relatively new atom-level topological descriptor; refractotopological state atom (R-state) index was used in this work. This was used to identify the important atoms/fragments related to dispersive/van der Waals interactions of neonicotinoids with the nicotinic acetylcholine receptor (nAChR). This study showed the structural requirements for the mammal alpha(4)beta(2) and Drosophila nAChR agonistic activity. It also revealed that substituted imine, nitromethylene at X-position were selective to the insecticidal activity. Azido substitution at pyridine ring of neonicotinoids disfavored the binding with the receptors. This study confirmed the validity of the R-state index as a new tool for quantitative structure-activity relationships. It has the ability to find out the required structural features as well as to predict the activity of the neonicotinoids.

  11. Operando atomic structure and active sites of TiO2(110)-supported gold nanoparticles during carbon monoxide oxidation.

    PubMed

    Saint-Lager, Marie-Claire; Laoufi, Issam; Bailly, Aude

    2013-01-01

    It is well known that gold nanoparticles supported on TiO2 act as a catalyst for CO oxidation, even below room temperature. Despite extensive studies, the origin of this catalytic activity remains under debate. Indeed, when the particle size decreases, many changes may occur; thus modifying the nanoparticles' electronic properties and consequently their catalytic performances. Thanks to a state-of-the-art home-developed setup, model catalysts can be prepared in ultra-high vacuum and their morphology then studied in operando conditions by Grazing Incidence Small Angle X-ray Scattering, as well as their atomic structure by Grazing Incidence X-ray Diffraction as a function of their catalytic activity. We previously reported on the existence of a catalytic activity maximum observed for three-dimensional gold nanoparticles with a diameter of 2-3 nm and a height of 6-7 atomic planes. In the present work we correlate this size dependence of the catalytic activity to the nanoparticles' atomic structure. We show that even when their size decreases below the optimum diameter, the gold nanoparticles keep the face-centered cubic structure characteristic of bulk gold. Nevertheless, for these smallest nanoparticles, the lattice parameter presents anisotropic strains with a larger contraction in the direction perpendicular to the surface. Moreover a careful analysis of the atomic-scale morphology around the catalytic activity maximum tends to evidence the role of sites with a specific geometry at the interface between the nanoparticles and the substrate. This argues for models where atoms at the interface periphery act as catalytically active sites for carbon monoxide oxidation.

  12. Applications of Atom Trap Trace Analysis in the Earth Sciences

    NASA Astrophysics Data System (ADS)

    Lu, Z.-T.; Jiang, W.; Bailey, K.; Mueller, P.; O'Connor, T. P.

    2013-05-01

    With the successful development of the Atom Trap Trace Analysis (ATTA) method, radiokrypton dating has become available for the first time to the Earth science community at large. This novel tool is enabling new research opportunities and improved understanding in the Earth sciences, with implications in studying climate change and in water resource management. Examples of applications of ATTA in the Earth sciences are: (1) ATTA measurements of 81Kr in the Nubian Aquifer of Africa, the Great Artesian Basin of Australia, and the Guarani Aquifer of South America have transformed our understanding of the long-term behavior of these large aquifer systems. 81Kr dating with more extensive sampling will be carried out on major aquifer systems around the world. (2) A systematic survey of 39Ar throughout the oceans, particularly when combined with 14C data, will fill major gaps in our knowledge of deep ocean circulation and mixing, and will allow more accurate predictions of oceanic sequestration of atmospheric CO2. (3) The feasibility and accuracy of 81Kr dating of old ice has been tested with the well-dated stratigraphy of Taylor Glacier in Antarctica. For more information, search for ``TANGR2012''. This work is supported by DOE, Office of Nuclear Physics, under contract DE-AC02-06CH11357.

  13. Applications of Atom Trap Trace Analysis in the Earth Sciences

    NASA Astrophysics Data System (ADS)

    Lu, Z.-T.; Jiang, W.; Bailey, K.; Mueller, P.; O'Connor, T. P.

    2013-04-01

    With the successful development of the Atom Trap Trace Analysis (ATTA) method, radiokrypton dating has become available for the first time to the Earth science community at large. This novel tool is enabling new research opportunities and improved understanding in the Earth sciences, with implications in studying climate change and in water resource management. Examples of applications of ATTA in the Earth sciences are: (1) ATTA measurements of ^81Kr in the Nubian Aquifer of Africa, the Great Artesian Basin of Australia, and the Guarani Aquifer of South America have transformed our understanding of the long-term behavior of these large aquifer systems. ^81Kr dating with more extensive sampling will be carried out on major aquifer systems around the world. (2) A systematic survey of ^39Ar throughout the oceans, particularly when combined with ^14C data, will fill major gaps in our knowledge of deep ocean circulation and mixing, and will allow more accurate predictions of oceanic sequestration of atmospheric CO2. (3) The feasibility and accuracy of ^81Kr dating of old ice has been tested with the well-dated stratigraphy of Taylor Glacier in Antarctica. For more information, search for ``TANGR2012''.

  14. Towards Corrected and Completed Atomic Site Occupancy Analysis of Superalloys Using Atom Probe Tomography Techniques

    DTIC Science & Technology

    2012-08-17

    Ag and Cu alloy (b) the missing atoms of the rectified reconstruction with...Mg- Cu alloy before lattice rectification (left) and after lattice rectification (right). (b) Partial RDFs before and after rectification Radial...and Next Steps: Rectify -Si -Sb A B Ag Cu + Restored Ag and Cu Detected Ag and Cu Ag Cu 30 x 30 x 120 nm Completed Reconstruc on A

  15. Analysis of the physical atomic forces between noble gas atoms, alkali ions and halogen ions

    NASA Technical Reports Server (NTRS)

    Wilson, J. W.; Heinbockel, J. H.; Outlaw, R. A.

    1986-01-01

    The physical forces between atoms and molecules are important in a number of processes of practical importance, including line broadening in radiative processes, gas and crystal properties, adhesion, and thin films. The components of the physical forces between noble gas atoms, alkali ions, and halogen ions are analyzed and a data base for the dispersion forces is developed from the literature based on evaluations with the harmonic oscillator dispersion model for higher order coefficients. The Zener model of the repulsive core is used in the context of the recent asymptotic wave functions of Handler and Smith; and an effective ionization potential within the Handler and Smith wave functions is defined to analyze the two body potential data of Waldman and Gordon, the alkali-halide molecular data, and the noble gas crystal and salt crystal data. A satisfactory global fit to this molecular and crystal data is then reproduced by the model to within several percent. Surface potentials are evaluated for noble gas atoms on noble gas and salt crystal surfaces with surface tension neglected. Within this context, the noble gas surface potentials on noble gas and salt crystals are considered to be accurate to within several percent.

  16. Stability analysis for bad cavity lasers using inhomogeneously broadened spin-1/2 atoms as a gain medium

    NASA Astrophysics Data System (ADS)

    Kazakov, G. A.; Schumm, T.

    2017-02-01

    Bad cavity lasers are experiencing renewed interest in the context of active optical frequency standards, due to their enhanced robustness against fluctuations of the laser cavity. The gain medium would consist of narrow-linewidth atoms, either trapped inside the cavity or intersecting the cavity mode dynamically. A series of effects like the atoms finite velocity distribution, atomic interactions, or interactions of realistic multilevel atoms with auxiliary or stray fields can lead to an inhomogeneous broadening of the atomic gain profile. This causes the emergence of unstable regimes of laser operation, characterized by complex temporal patterns of the field amplitude. We study the steady-state solutions and their stability for the metrology-relevant case of a bad cavity laser with spin-1/2 atoms, such as 171Yb, interacting with an external magnetic field. For the stability analysis, we present an efficient method, which can be applied to a broad class of single-mode bad cavity lasers with inhomogeneously broadened multilevel atoms acting as a gain medium.

  17. Analysis of size correlations for microdroplets produced by ultrasonic atomization.

    PubMed

    Dalmoro, Annalisa; Barba, Anna Angela; d'Amore, Matteo

    2013-01-01

    Microencapsulation techniques are widely applied in the field of pharmaceutical production to control drugs release in time and in physiological environments. Ultrasonic-assisted atomization is a new technique to produce microencapsulated systems by a mechanical approach. Interest in this technique is due to the advantages evidenceable (low level of mechanical stress in materials, reduced energy request, reduced apparatuses size) when comparing it to more conventional techniques. In this paper, the groundwork of atomization is introduced, the role of relevant parameters in ultrasonic atomization mechanism is discussed, and correlations to predict droplets size starting from process parameters and material properties are presented and tested.

  18. Analysis of Size Correlations for Microdroplets Produced by Ultrasonic Atomization

    PubMed Central

    Barba, Anna Angela; d'Amore, Matteo

    2013-01-01

    Microencapsulation techniques are widely applied in the field of pharmaceutical production to control drugs release in time and in physiological environments. Ultrasonic-assisted atomization is a new technique to produce microencapsulated systems by a mechanical approach. Interest in this technique is due to the advantages evidenceable (low level of mechanical stress in materials, reduced energy request, reduced apparatuses size) when comparing it to more conventional techniques. In this paper, the groundwork of atomization is introduced, the role of relevant parameters in ultrasonic atomization mechanism is discussed, and correlations to predict droplets size starting from process parameters and material properties are presented and tested. PMID:24501580

  19. AN ACTIVE NITROGEN PLASMA ATOM RESERVOIR FOR LASER-INDUCED IONIZATION SPECTROMETRY

    DTIC Science & Technology

    1988-01-01

    An active nitrogen plasma was generat-J using a laboratory - constructed Beenakker type microwave cavity. 2 5 The microwave power oscillator (Micro...exhausting of ozone. Microarc Atomizer A laboratory -constructed microarc atomizer was positioned at the rear of the Beenakker cavity in direct line with the...the regions of interest, the laser- induced ionization signal was monitored. A laboratory -constructed etalon system of very low finesse was used to

  20. Origin of the catalytic activity of face-centered-cubic ruthenium nanoparticles determined from an atomic-scale structure.

    PubMed

    Kumara, L S R; Sakata, Osami; Kohara, Shinji; Yang, Anli; Song, Chulho; Kusada, Kohei; Kobayashi, Hirokazu; Kitagawa, Hiroshi

    2016-11-09

    The 3-dimensional (3D) atomic-scale structure of newly discovered face-centered cubic (fcc) and conventional hexagonal close packed (hcp) type ruthenium (Ru) nanoparticles (NPs) of 2.2 to 5.4 nm diameter were studied using X-ray pair distribution function (PDF) analysis and reverse Monte Carlo (RMC) modeling. Atomic PDF based high-energy X-ray diffraction measurements show highly diffuse X-ray diffraction patterns for fcc- and hcp-type Ru NPs. We here report the atomic-scale structure of Ru NPs in terms of the total structure factor and Fourier-transformed PDF. It is found that the respective NPs have substantial structural disorder over short- to medium-range order atomic distances from the PDF analysis. The first-nearest-neighbor peak analyses show a significant size dependence for the fcc-type Ru NPs demonstrating the increase in the peak height due to an increase in the number density as a function of particle size. The bond angle and coordination number (CN) distribution for the RMC-simulated fcc- and hcp-type Ru NP models indicated inherited structural features from their bulk counterparts. The CN analysis of the whole NP and surface of each RMC model of Ru NPs show the low activation energy packing sites on the fcc-type Ru NP surface atoms. Finally, our newly defined order parameters for RMC simulated Ru NP models suggested that the enhancement of the CO oxidation activity of fcc-type NPs was due to a decrease in the close packing ordering that resulted from the increased NP size. These structural findings could be positively supported for synthesized low-cost and high performance nano-sized catalysts and have potential application in fuel-cell systems and organic synthesis.

  1. Neutron activation analysis system

    DOEpatents

    Taylor, M.C.; Rhodes, J.R.

    1973-12-25

    A neutron activation analysis system for monitoring a generally fluid media, such as slurries, solutions, and fluidized powders, including two separate conduit loops for circulating fluid samples within the range of radiation sources and detectors is described. Associated with the first loop is a neutron source that emits s high flux of slow and thermal neutrons. The second loop employs a fast neutron source, the flux from which is substantially free of thermal neutrons. Adjacent to both loops are gamma counters for spectrographic determination of the fluid constituents. Other gsmma sources and detectors are arranged across a portion of each loop for deterMining the fluid density. (Official Gazette)

  2. Application of atomic Hirshfeld surface analysis to intermetallic systems: is Mn in cubic CeMnNi4 a thermoelectric rattler atom?

    PubMed

    Jørgensen, Mads R V; Skovsen, Iben; Clausen, Henrik F; Mi, Jian-Li; Christensen, Mogens; Nishibori, Eiji; Spackman, Mark A; Iversen, Bo B

    2012-02-06

    The Mn atom in the cubic polymorph of CeMnNi(4) appears to be located in an oversized cage-like structure, and anomalously large atomic displacement parameters (ADPs) for the Mn atom indicate that it is a potential "rattler" atom. Here, multitemperature synchrotron powder X-ray diffraction data measured between 110 and 900 K are used to estimate ADPs for the Mn "guest" atom and the "host" structure atoms in cubic CeMnNi(4). The ADPs are subsequently fitted with Debye and Einstein models, giving Θ(D) = 301(2) K for the "host" structure and Θ(E) = 165(2) K for the Mn atom. This is higher than typical Einstein temperatures for rattlers in thermoelectric skutterudites and clathrates (Θ(E) = 50-80 K), indicating that the Mn atom in cubic CeMnNi(4) is more strongly bonded. In order to probe the chemical interactions of the potential Mn rattler atom, atomic Hirshfeld surface (AHS) analysis is carried out and compared with AHS analysis of well-established guest atom rattlers in archetypical skutterudites, MCoSb(3). Surprisingly, the skutterudite rattlers have more deformed AHSs than the Mn atom in cubic CeMnNi(4). This is related to the highly ionic nature of the skutterudite rattlers, which is not taken into account in the neutral spherical atom approach of the AHS. Additionally, visualization of void spaces in the two materials using the procrystal electron density shows that while the Mn atom is tightly fitting in the CeMnNi(4) structure then the La atom in the skutterudite is truly situated in an oversized cage of the host structure. Overall, we conclude that the Mn atom in cubic CeMnNi(4) cannot be coined a rattler.

  3. 78 FR 46829 - Assistance to Foreign Atomic Energy Activities

    Federal Register 2010, 2011, 2012, 2013, 2014

    2013-08-02

    ... Supporting Commercial Power Reactors 3. ``Deemed Exports'' and ``Deemed Re-Exports'' 4. Technology Transfers... Hoc Utility Group (a number of companies that operate 56 nuclear reactors at 35 sites), offered... research''; Assistance for certain mining and milling activities, and certain fusion reactors because...

  4. Three-dimensional rearrangement of single atoms using actively controlled optical microtraps.

    PubMed

    Lee, Woojun; Kim, Hyosub; Ahn, Jaewook

    2016-05-02

    We propose and demonstrate three-dimensional rearrangements of single atoms. In experiments performed with single 87Rb atoms in optical microtraps actively controlled by a spatial light modulator, we demonstrate various dynamic rearrangements of up to N = 9 atoms including rotation, 2D vacancy filling, guiding, compactification, and 3D shuffling. With the capability of a phase-only Fourier mask to generate arbitrary shapes of the holographic microtraps, it was possible to place single atoms at arbitrary geometries of a few μm size and even continuously reconfigure them by conveying each atom. For this purpose, we loaded a series of computer-generated phase masks in the full frame rate of 60 Hz of the spatial light modulator, so the animation of phase mask transformed the holographic microtraps in real time, driving each atom along the assigned trajectory. Possible applications of this method of transformation of single atoms include preparation of scalable quantum platforms for quantum computation, quantum simulation, and quantum many-body physics.

  5. An Analysis of the Stationary Operation of Atomic Clocks

    NASA Astrophysics Data System (ADS)

    Fraas, Martin

    2016-12-01

    We develop an abstract model of atomic clocks that fully describes the dynamics of repeated synchronization between a classical oscillator and a quantum reference. We prove existence of a stationary state of the model and study its dependence on the control scheme, the interrogation time and the stability of the oscillator. For unbiased atomic clocks, we derive a fundamental bound on atomic clocks long time stability for a given local oscillator noise. In particular, we show that for a local oscillator noise with integrated frequency variance scaling as {T^α} for short times T, the optimal clock time variance scales as {F^{-(α +1)/(α +2)}} with respect to the quantum Fisher information, F, associated to the quantum reference. In an attempt to prove the bounds without the unbiasedness assumption, we derive a new Cramer-Rao type inequality.

  6. Atoms for peace. An analysis after thirty years

    SciTech Connect

    Pilat, J.F.; Pendley, R.E.; Ebinger, C.K.

    1985-01-01

    Thirty years ago, President Eisenhower's Atoms for Peace proposal to the U.N. provided the basis for development of nuclear cooperation, trade, and nonproliferation policy in the noncommunist world. Ever since its inception, however, the policy has sparked widespread debate, and it remains controversial today. Exploring the past, present, and future significance of Atoms for Peace, the contributors to this volume analyze the future role of the U.S. in international affairs, the nature of controls over nuclear cooperation and trade, the scope and limitations of international cooperation in nuclear energy and nonproliferation matters, and the prospects for multinational and international institutional measures to achieve these ends.

  7. Stable isolated metal atoms as active sites for photocatalytic hydrogen evolution.

    PubMed

    Xing, Jun; Chen, Jian Fu; Li, Yu Hang; Yuan, Wen Tao; Zhou, Ying; Zheng, Li Rong; Wang, Hai Feng; Hu, P; Wang, Yun; Zhao, Hui Jun; Wang, Yong; Yang, Hua Gui

    2014-02-17

    The process of using solar energy to split water to produce hydrogen assisted by an inorganic semiconductor is crucial for solving our energy crisis and environmental problems in the future. However, most semiconductor photocatalysts would not exhibit excellent photocatalytic activity without loading suitable co-catalysts. Generally, the noble metals have been widely applied as co-catalysts, but always agglomerate during the loading process or photocatalytic reaction. Therefore, the utilization efficiency of the noble co-catalysts is still very low on a per metal atom basis if no obvious size effect exists, because heterogeneous catalytic reactions occur on the surface active atoms. Here, for the first time, we have synthesized isolated metal atoms (Pt, Pd, Rh, or Ru) stably by anchoring on TiO2 , a model photocatalystic system, by a facile one-step method. The isolated metal atom based photocatalysts show excellent stability for H2 evolution and can lead to a 6-13-fold increase in photocatalytic activity over the metal clusters loaded on TiO2 by the traditional method. Furthermore, the configurations of isolated atoms as well as the originality of their unusual stability were analyzed by a collaborative work from both experiments and theoretical calculations.

  8. New Active Optical Technique Developed for Measuring Low-Earth-Orbit Atomic Oxygen Erosion of Polymers

    NASA Technical Reports Server (NTRS)

    Banks, Bruce A.; deGroh, Kim K.; Demko, Rikako

    2003-01-01

    Polymers such as polyimide Kapton (DuPont) and Teflon FEP (DuPont, fluorinated ethylene propylene) are commonly used spacecraft materials because of desirable properties such as flexibility, low density, and in the case of FEP, a low solar absorptance and high thermal emittance. Polymers on the exterior of spacecraft in the low-Earth-orbit (LEO) environment are exposed to energetic atomic oxygen. Atomic oxygen reaction with polymers causes erosion, which is a threat to spacecraft performance and durability. It is, therefore, important to understand the atomic oxygen erosion yield E (the volume loss per incident oxygen atom) of polymers being considered in spacecraft design. The most common technique for determining E is a passive technique based on mass-loss measurements of samples exposed to LEO atomic oxygen during a space flight experiment. There are certain disadvantages to this technique. First, because it is passive, data are not obtained until after the flight is completed. Also, obtaining the preflight and postflight mass measurements is complicated by the fact that many polymers absorb water and, therefore, the mass change due to water absorption can affect the E data. This is particularly true for experiments that receive low atomic oxygen exposures or for samples that have a very low E. An active atomic oxygen erosion technique based on optical measurements has been developed that has certain advantages over the mass-loss technique. This in situ technique can simultaneously provide the erosion yield data on orbit and the atomic oxygen exposure fluence, which is needed for erosion yield determination. In the optical technique, either sunlight or artificial light can be used to measure the erosion of semitransparent or opaque polymers as a result of atomic oxygen attack. The technique is simple and adaptable to a rather wide range of polymers, providing that they have a sufficiently high optical absorption coefficient. If one covers a photodiode with a

  9. Local atomic structure modulations activate metal oxide as electrocatalyst for hydrogen evolution in acidic water

    PubMed Central

    Li, Yu Hang; Liu, Peng Fei; Pan, Lin Feng; Wang, Hai Feng; Yang, Zhen Zhong; Zheng, Li Rong; Hu, P.; Zhao, Hui Jun; Gu, Lin; Yang, Hua Gui

    2015-01-01

    Modifications of local structure at atomic level could precisely and effectively tune the capacity of materials, enabling enhancement in the catalytic activity. Here we modulate the local atomic structure of a classical but inert transition metal oxide, tungsten trioxide, to be an efficient electrocatalyst for hydrogen evolution in acidic water, which has shown promise as an alternative to platinum. Structural analyses and theoretical calculations together indicate that the origin of the enhanced activity could be attributed to the tailored electronic structure by means of the local atomic structure modulations. We anticipate that suitable structure modulations might be applied on other transition metal oxides to meet the optimal thermodynamic and kinetic requirements, which may pave the way to unlock the potential of other promising candidates as cost-effective electrocatalysts for hydrogen evolution in industry. PMID:26286479

  10. Local atomic structure modulations activate metal oxide as electrocatalyst for hydrogen evolution in acidic water

    NASA Astrophysics Data System (ADS)

    Li, Yu Hang; Liu, Peng Fei; Pan, Lin Feng; Wang, Hai Feng; Yang, Zhen Zhong; Zheng, Li Rong; Hu, P.; Zhao, Hui Jun; Gu, Lin; Yang, Hua Gui

    2015-08-01

    Modifications of local structure at atomic level could precisely and effectively tune the capacity of materials, enabling enhancement in the catalytic activity. Here we modulate the local atomic structure of a classical but inert transition metal oxide, tungsten trioxide, to be an efficient electrocatalyst for hydrogen evolution in acidic water, which has shown promise as an alternative to platinum. Structural analyses and theoretical calculations together indicate that the origin of the enhanced activity could be attributed to the tailored electronic structure by means of the local atomic structure modulations. We anticipate that suitable structure modulations might be applied on other transition metal oxides to meet the optimal thermodynamic and kinetic requirements, which may pave the way to unlock the potential of other promising candidates as cost-effective electrocatalysts for hydrogen evolution in industry.

  11. Local atomic structure modulations activate metal oxide as electrocatalyst for hydrogen evolution in acidic water.

    PubMed

    Li, Yu Hang; Liu, Peng Fei; Pan, Lin Feng; Wang, Hai Feng; Yang, Zhen Zhong; Zheng, Li Rong; Hu, P; Zhao, Hui Jun; Gu, Lin; Yang, Hua Gui

    2015-08-19

    Modifications of local structure at atomic level could precisely and effectively tune the capacity of materials, enabling enhancement in the catalytic activity. Here we modulate the local atomic structure of a classical but inert transition metal oxide, tungsten trioxide, to be an efficient electrocatalyst for hydrogen evolution in acidic water, which has shown promise as an alternative to platinum. Structural analyses and theoretical calculations together indicate that the origin of the enhanced activity could be attributed to the tailored electronic structure by means of the local atomic structure modulations. We anticipate that suitable structure modulations might be applied on other transition metal oxides to meet the optimal thermodynamic and kinetic requirements, which may pave the way to unlock the potential of other promising candidates as cost-effective electrocatalysts for hydrogen evolution in industry.

  12. Behavior of Na atoms in the lunar exosphere during activity of meteor showers

    NASA Astrophysics Data System (ADS)

    Berezhnoy, A. A.; Churyumov, K. I.; Shevchenko, V. V.; Buchachenko, A. A.; Baransky, O. R.; Churyumova, T. K.; Kleshchenok, V. V.; Kozlova, E. A.; Ponomarenko, V. O.; Stolyarov, A. V.; Tvorun, O. V.

    2011-12-01

    The chemical composition of gas-phase species released to the lunar exosphere during meteoroid impacts has been analyzed. Majority of impact-produced metal-containing molecules are destroyed by the solar photons because typical photolysis lifetimes are shorter than ballistic flight times. Energies of metal atoms produced via photolysis of its monoxides are estimated. The column density of impact-produced Na atoms in the exosphere during activity of main meteor shower and quiet periods are estimated. In searching for impact-produced Na atoms in the lunar exosphere, it is better to perform spectral observations during activity of the main meteor showers at altitudes of about 1000-2000 km, lunar eclipses, and during passages of the Moon through the Earth's magnetosphere.

  13. MoS2 atomic layers with artificial active edge sites as transparent counter electrodes for improved performance of dye-sensitized solar cells.

    PubMed

    Zhang, Jing; Najmaei, Sina; Lin, Hong; Lou, Jun

    2014-05-21

    A novel MoS2 transparent counter electrode for dye-sensitized solar cells is reported. In order to enhance the catalytic activity of the electrode, active edge sites are created artificially by patterning holes on MoS2 atomic layers. Electrochemical analysis shows that the electrochemical activity is significantly improved after the patterning of holes. The photon-to-electron efficiency of the dye-sensitized solar cells based on MoS2 atomic layer counter electrodes is increased remarkably from 2% to 5.8% after the hole patterning.

  14. Quantitative analysis of immobilized metalloenzymes by atomic absorption spectroscopy.

    PubMed

    Opwis, Klaus; Knittel, Dierk; Schollmeyer, Eckhard

    2004-12-01

    A new, sensitive assay for the quantitative determination of immobilized metal containing enzymes has been developed using atomic absorption spectroscopy (AAS). In contrast with conventionally used indirect methods the described quantitative AAS assay for metalloenzymes allows more exact analyses, because the carrier material with the enzyme is investigated directly. As an example, the validity and reliability of the method was examined by fixing the iron-containing enzyme catalase on cotton fabrics using different immobilization techniques. Sample preparation was carried out by dissolving the loaded fabrics in sulfuric acid before oxidising the residues with hydrogen peroxide. The iron concentrations were determined by flame atomic absorption spectrometry after calibration of the spectrometer with solutions of the free enzyme at different concentrations.

  15. AtomicJ: An open source software for analysis of force curves

    NASA Astrophysics Data System (ADS)

    Hermanowicz, Paweł; Sarna, Michał; Burda, Kvetoslava; Gabryś, Halina

    2014-06-01

    We present an open source Java application for analysis of force curves and images recorded with the Atomic Force Microscope. AtomicJ supports a wide range of contact mechanics models and implements procedures that reduce the influence of deviations from the contact model. It generates maps of mechanical properties, including maps of Young's modulus, adhesion force, and sample height. It can also calculate stacks, which reveal how sample's response to deformation changes with indentation depth. AtomicJ analyzes force curves concurrently on multiple threads, which allows for high speed of analysis. It runs on all popular operating systems, including Windows, Linux, and Macintosh.

  16. Atomic absorption background of Ba in EXAFS analysis of BaFe(12)O(19) nanoparticles.

    PubMed

    Padeznik Gomilšek, Jana; Kodre, Alojz; Arčon, Iztok; de Panfilis, Simone; Makovec, Darko

    2011-07-01

    The approximate barium X-ray atomic absorption in the energy region of L-edges is reconstructed from the absorption spectrum of an aqueous solution of BaCl(2). The result is corroborated by comparison with pure atomic absorption spectra of neighbour elements Xe and Cs. The application of the atomic absorption signal as a proper EXAFS background is demonstrated and discussed in the analysis of Ba hexaferrite nanoparticles with a very weak structural signal. The essential gain is found in the decrease of uncertainty intervals of structural parameters and their correlations. A simple analytical model of the absorption background for the practical EXAFS analysis is demonstrated.

  17. AtomicJ: An open source software for analysis of force curves

    SciTech Connect

    Hermanowicz, Paweł Gabryś, Halina; Sarna, Michał; Burda, Kvetoslava

    2014-06-15

    We present an open source Java application for analysis of force curves and images recorded with the Atomic Force Microscope. AtomicJ supports a wide range of contact mechanics models and implements procedures that reduce the influence of deviations from the contact model. It generates maps of mechanical properties, including maps of Young's modulus, adhesion force, and sample height. It can also calculate stacks, which reveal how sample's response to deformation changes with indentation depth. AtomicJ analyzes force curves concurrently on multiple threads, which allows for high speed of analysis. It runs on all popular operating systems, including Windows, Linux, and Macintosh.

  18. Sampling and analysis plan for the former Atomic Energy Commission bus lot property

    SciTech Connect

    Nielson, R.R.

    1998-07-01

    This sampling and analysis plan (SAP) presents the rationale and strategy for the sampling and analysis activities proposed in support of an initial investigation of the former Atomic Energy Commission (AEC) bus lot property currently owned by Battelle Memorial Institute. The purpose of the proposed sampling and analysis activity is to investigate the potential for contamination above established action levels. The SAP will provide defensible data of sufficient quality and quantity to support recommendations of whether any further action within the study area is warranted. To assist in preparing sampling plans and reports, the Washington State Department of Ecology (Ecology) has published Guidance on Sampling and Data Analysis Methods. To specifically address sampling plans for petroleum-contaminated sites, Ecology has also published Guidance for Remediation of Petroleum Contaminated Sites. Both documents were used as guidance in preparing this plan. In 1992, a soil sample was taken within the current study area as part of a project to remove two underground storage tanks (USTs) at Battelle`s Sixth Street Warehouse Petroleum Dispensing Station (Section 1.3). The results showed that the sample contained elevated levels of total petroleum hydrocarbons (TPH) in the heavy distillate range. This current study was initiated in part as a result of that discovery. The following topics are considered: the historical background of the site, current site conditions, previous investigations performed at the site, an evaluation based on the available data, and the contaminants of potential concern (COPC).

  19. Atom Probe Analysis of Ex Situ Gas-Charged Stable Hydrides.

    PubMed

    Haley, Daniel; Bagot, Paul A J; Moody, Michael P

    2017-01-30

    In this work, we report on the atom probe tomography analysis of two metallic hydrides formed by pressurized charging using an ex situ hydrogen charging cell, in the pressure range of 200-500 kPa (2-5 bar). Specifically we report on the deuterium charging of Pd/Rh and V systems. Using this ex situ system, we demonstrate the successful loading and subsequent atom probe analysis of deuterium within a Pd/Rh alloy, and demonstrate that deuterium is likely present within the oxide-metal interface of a native oxide formed on vanadium. Through these experiments, we demonstrate the feasibility of ex situ hydrogen analysis for hydrides via atom probe tomography, and thus a practical route to three-dimensional imaging of hydrogen in hydrides at the atomic scale.

  20. Catalytic activity of Pd-doped Cu nanoparticles for hydrogenation as a single-atom-alloy catalyst.

    PubMed

    Cao, Xinrui; Fu, Qiang; Luo, Yi

    2014-05-14

    The single atom alloy of extended surfaces is known to provide remarkably enhanced catalytic performance toward heterogeneous hydrogenation. Here we demonstrate from first principles calculations that this approach can be extended to nanostructures, such as bimetallic nanoparticles. The catalytic properties of the single-Pd-doped Cu55 nanoparticles have been systemically examined for H2 dissociation as well as H atom adsorption and diffusion, following the concept of single atom alloy. It is found that doping a single Pd atom at the edge site of the Cu55 shell can considerably reduce the activation energy of H2 dissociation, while the single Pd atom doped at the top site or in the inner layers is much less effective. The H atom adsorption on Cu55 is slightly stronger than that on the Cu(111) surface; however, a larger nanoparticle that contains 147 atoms could effectively recover the weak binding of the H atoms. We have also investigated the H atom diffusion on the 55-atom nanoparticle and found that spillover of the produced H atoms could be a feasible process due to the low diffusion barriers. Our results have demonstrated that facile H2 dissociation and weak H atom adsorption could be combined at the nanoscale. Moreover, the effects of doping one more Pd atom on the H2 dissociation and H atom adsorption have also been investigated. We have found that both the doping Pd atoms in the most stable configuration could independently exhibit their catalytic activity, behaving as two single-atom-alloy catalysts.

  1. Active and passive sensing of collective atomic coherence in a superradiant laser

    NASA Astrophysics Data System (ADS)

    Bohnet, Justin G.; Chen, Zilong; Weiner, Joshua M.; Cox, Kevin C.; Thompson, James K.

    2013-07-01

    We study the nondemolition mapping of collective quantum coherence onto a cavity light field in a superradiant, cold-atom 87Rb Raman laser. We show theoretically that the fundamental precision of the mapping is near the standard quantum limit on phase estimation for a coherent spin state, Δϕ=1/N, where N is the number of atoms. The associated characteristic measurement time scale τW∝1/N is collectively enhanced. The nondemolition nature of the measurement is characterized by only 0.5 photon recoils deposited per atom due to optical repumping in a time τW. We experimentally realize conditional Ramsey spectroscopy in our superradiant Raman laser, compare the results to the predicted precision, and study the mapping in the presence of decoherence, far from the steady-state conditions previously considered. Finally, we demonstrate a hybrid mode of operation in which the laser is repeatedly toggled between active and passive sensing.

  2. Analysis of glycolipids by fast atom bombardment mass spectrometry.

    PubMed

    Bosch, M P; Parra, J L; Manresa, M A; Ventura, F; Rivera, J

    1989-12-01

    The positive and negative ion fast atom bombardment (FAB) mass spectra of four glycolipids obtained from microbial cultures are reported. The spectra of the glycolipids in the positive ion mode are characterized by abundant [M + Na]+, [M + Na + matrix]+ and [M + 2Na - H]+ species. In negative FAB conditions the molecules yield [M - H]-. Our understanding of the FAB behaviour of glycolipids in both positive and negative modes has been considerably aided in the structure elucidation, without any derivatization or degradation reaction of the compounds studied. The technique allows unambiguous molecular weight determination of low-microgram amounts of these glycolipids purified from biological sources and provides useful fragmentation information.

  3. Bohr model and dimensional scaling analysis of atoms and molecules

    NASA Astrophysics Data System (ADS)

    Urtekin, Kerim

    It is generally believed that the old quantum theory, as presented by Niels Bohr in 1913, fails when applied to many-electron systems, such as molecules, and nonhydrogenic atoms. It is the central theme of this dissertation to display with examples and applications the implementation of a simple and successful extension of Bohr's planetary model of the hydrogenic atom, which has recently been developed by an atomic and molecular theory group from Texas A&M University. This "extended" Bohr model, which can be derived from quantum mechanics using the well-known dimentional scaling technique is used to yield potential energy curves of H2 and several more complicated molecules, such as LiH, Li2, BeH, He2 and H3, with accuracies strikingly comparable to those obtained from the more lengthy and rigorous "ab initio" computations, and the added advantage that it provides a rather insightful and pictorial description of how electrons behave to form chemical bonds, a theme not central to "ab initio" quantum chemistry. Further investigation directed to CH, and the four-atom system H4 (with both linear and square configurations), via the interpolated Bohr model, and the constrained Bohr model (with an effective potential), respectively, is reported. The extended model is also used to calculate correlation energies. The model is readily applicable to the study of molecular species in the presence of strong magnetic fields, as is the case in the vicinities of white dwarfs and neutron stars. We find that magnetic field increases the binding energy and decreases the bond length. Finally, an elaborative review of doubly coupled quantum dots for a derivation of the electron exchange energy, a straightforward application of Heitler-London method of quantum molecular chemistry, concludes the dissertation. The highlights of the research are (1) a bridging together of the pre- and post quantum mechanical descriptions of the chemical bond (Bohr-Sommerfeld vs. Heisenberg-Schrodinger), and

  4. Passive microrheology of soft materials with atomic force microscopy: A wavelet-based spectral analysis

    SciTech Connect

    Martinez-Torres, C.; Streppa, L.; Arneodo, A.; Argoul, F.; Argoul, P.

    2016-01-18

    Compared to active microrheology where a known force or modulation is periodically imposed to a soft material, passive microrheology relies on the spectral analysis of the spontaneous motion of tracers inherent or external to the material. Passive microrheology studies of soft or living materials with atomic force microscopy (AFM) cantilever tips are rather rare because, in the spectral densities, the rheological response of the materials is hardly distinguishable from other sources of random or periodic perturbations. To circumvent this difficulty, we propose here a wavelet-based decomposition of AFM cantilever tip fluctuations and we show that when applying this multi-scale method to soft polymer layers and to living myoblasts, the structural damping exponents of these soft materials can be retrieved.

  5. High energy halogen atom reactions activated by nuclear transformations. Progress report, February 15, 1979-February 14, 1980

    SciTech Connect

    Rack, E.P.

    1980-02-01

    The program consists of six interrelated areas: (1) Reactions of iodine with alkenes and alkynes activated by radiative neutron capture and isomeric transition in low pressure gaseous systems employing additives and rare gas moderators, high pressure, and liquid systems. Special attention was given to the reactivity of excited complex formation and structural effects of electrophilic iodine attack on various pi-bond systems. (2) The gas-to-condensed phase transition in halogen high energy chemistry. Current interest involves the study of caging effects of an ice lattice on recombination reactions involving neutron-irradiated frozen aqueous solutions of halogenated organic and biochemical solutes in order to learn more about kinetic energy effects, halogen size, solute molecule size, steric effects and hydrogen bonding within an ice lattice cage. (3) Systematics of halogen hot atom reactions. The reactions of /sup 80m/Br, /sup 80/Br, /sup 82m/Br + /sup 82/Br, /sup 82/Br, /sup 82/Br, /sup 128/I, /sup 130/I, and /sup 130m/I + /sup 130/I activated by radiative neutron capture or isomeric transition in hydrocarbons and halo-substituted alkanes in low pressure and high pressure gaseous systems employing additives and rare gas moderators are currently being studied. (4) Mathematical and computer simulation studies of caging events within an ice lattice are being investigated. (5) At Brookhaven National Laboratory, cyclotron-produced chlorine and fluorine hot atoms substitution reactions with molecules possessing a single chiral center are under investigation to determine the role of hot atom kinetic energy, halogen atom, enantioner structure, steric effects and phase on the extent of substitution by retention of configuration or by Walden inversion. (6) The applications of high energy techniques and concepts to neutron activation analysis for trace element determinations in biological systems was continued.

  6. The mystery of gold's chemical activity: local bonding, morphology and reactivity of atomic oxygen.

    PubMed

    Baker, Thomas A; Liu, Xiaoying; Friend, Cynthia M

    2011-01-07

    Recently, gold has been intensely studied as a catalyst for key synthetic reactions. Gold is an attractive catalyst because, surprisingly, it is highly active and very selective for partial oxidation processes suggesting promise for energy-efficient "green" chemistry. The underlying origin of the high activity of Au is a controversial subject since metallic gold is commonly thought to be inert. Herein, we establish that one origin of the high activity for gold catalysis is the extremely reactive nature of atomic oxygen bound in 3-fold coordination sites on metallic gold. This is the predominant form of O at low concentrations on the surface, which is a strong indication that it is most relevant to catalytic conditions. Atomic oxygen bound to metallic Au in 3-fold sites has high activity for CO oxidation, oxidation of olefins, and oxidative transformations of alcohols and amines. Among the factors identified as important in Au-O interaction are the morphology of the surface, the local binding site of oxygen, and the degree of order of the oxygen overlayer. In this Perspective, we present an overview of both theory and experiments that identify the reactive forms of O and their associated charge density distributions and bond strengths. We also analyze and model the release of Au atoms induced by O binding to the surface. This rough surface also has the potential for O(2) dissociation, which is a critical step if Au is to be activated catalytically. We further show the strong parallels between product distributions and reactivity for O-covered Au at low pressure (ultrahigh vacuum) and for nanoporous Au catalysts operating at atmospheric pressure as evidence that atomic O is the active species under working catalytic conditions when metallic Au is present. We briefly discuss the possible contributions of oxidants that may contain intact O-O bonds and of the Au-metal oxide support interface in Au catalysis. Finally, the challenges and future directions for fully

  7. Evaluation of a carbon-rod atomizer for routine determination of trace metals by atomic-absorption spectroscopy applications to analysis of lubricating oil and crude oil.

    PubMed

    Hall, G; Bratzel, M P; Chakrabarti, C L

    1973-08-01

    A carbon-rod atomizer (CRA) fitted with a 'mini-Massmann' carbon rod was evaluated for routine analysis of petroleum and petroleum products for trace metal content by atomic-absorption spectroscopy. Aspects investigated included sensitivity, detection limit, effect of solvent type, and interferences. The results of analysis of oil samples with this technique were compared with those obtained by other techniques. Metals studied were silver, copper, iron, nickel, and lead. Sensitivity and detection limit values obtained with the CRA were similar to those obtained with the carbon-filament atomizer. Strong 'solvent effects' were observed as well as interference by cations. On the basis of this study, design changes for the CRA are suggested, with the object of minimizing 'solvent effects' and interferences, increasing the atomization efficiency, and increasing the residence time of the atomic vapour in the optical path of the instrumental system.

  8. Catalytic activity of bimetallic catalysts highly sensitive to the atomic composition and phase structure at the nanoscale.

    PubMed

    Shan, Shiyao; Petkov, Valeri; Prasai, Binay; Wu, Jinfang; Joseph, Pharrah; Skeete, Zakiya; Kim, Eunjoo; Mott, Derrick; Malis, Oana; Luo, Jin; Zhong, Chuan-Jian

    2015-12-07

    The ability to determine the atomic arrangement in nanoalloy catalysts and reveal the detailed structural features responsible for the catalytically active sites is essential for understanding the correlation between the atomic structure and catalytic properties, enabling the preparation of efficient nanoalloy catalysts by design. Herein we describe a study of CO oxidation over PdCu nanoalloy catalysts focusing on gaining insights into the correlation between the atomic structures and catalytic activity of nanoalloys. PdCu nanoalloys of different bimetallic compositions are synthesized as a model system and are activated by a controlled thermochemical treatment for assessing their catalytic activity. The results show that the catalytic synergy of Pd and Cu species evolves with both the bimetallic nanoalloy composition and temperature of the thermochemical treatment reaching a maximum at a Pd : Cu ratio close to 50 : 50. The nanoalloys are characterized structurally by ex situ and in situ synchrotron X-ray diffraction, including atomic pair distribution function analysis. The structural data show that, depending on the bimetallic composition and treatment temperature, PdCu nanoalloys adopt two different structure types. One features a chemically ordered, body centered cubic (B2) type alloy consisting of two interpenetrating simple cubic lattices, each occupied with Pd or Cu species alone, and the other structure type features a chemically disordered, face-centered cubic (fcc) type of alloy wherein Pd and Cu species are intermixed at random. The catalytic activity for CO oxidation is strongly influenced by the structural features. In particular, it is revealed that the prevalence of chemical disorder in nanoalloys with a Pd : Cu ratio close to 50 : 50 makes them superior catalysts for CO oxidation in comparison with the same nanoalloys of other bimetallic compositions. However, the catalytic synergy can be diminished if the Pd50Cu50 nanoalloys undergo

  9. Fast atom bombardment mass spectrometry and its application to the analysis of some peptides and proteins.

    PubMed

    Hemling, M E

    1987-02-01

    The techniques of fast atom bombardment mass spectrometry has overtaken (but not entirely replaced) field desorption mass spectrometry as the method of choice for the analysis of nonvolatile, thermally labile polar compounds. The ease with which information may be obtained on a wide variety of molecules is a result of the relative simplicity of the technique. A brief history of bioorganic mass spectrometry leading to the development of fast atom bombardment is presented, as well as a description of the method and ancillary techniques. Selected examples of its application to peptide and protein structural problems attest to the power and utility of fast atom bombardment mass spectrometry.

  10. Entropy and complexity analysis of hydrogenic Rydberg atoms

    SciTech Connect

    Lopez-Rosa, S.; Toranzo, I. V.; Dehesa, J. S.; Sanchez-Moreno, P.

    2013-05-15

    The internal disorder of hydrogenic Rydberg atoms as contained in their position and momentum probability densities is examined by means of the following information-theoretic spreading quantities: the radial and logarithmic expectation values, the Shannon entropy, and the Fisher information. As well, the complexity measures of Cramer-Rao, Fisher-Shannon, and Lopez Ruiz-Mancini-Calvet types are investigated in both reciprocal spaces. The leading term of these quantities is rigorously calculated by use of the asymptotic properties of the concomitant entropic functionals of the Laguerre and Gegenbauer orthogonal polynomials which control the wavefunctions of the Rydberg states in both position and momentum spaces. The associated generalized Heisenberg-like, logarithmic and entropic uncertainty relations are also given. Finally, application to linear (l= 0), circular (l=n- 1), and quasicircular (l=n- 2) states is explicitly done.

  11. Containment venting analysis for the Peach Bottom Atomic Power Station

    SciTech Connect

    Hanson, D.J.; Blackman, H.S.; Nelson, W.R.; Wright, R.E.; Leonard, M.T.; DiSalvo, R.

    1986-12-01

    The extent to which containment venting is an effective means of preventing or mitigating the consequences of overpressurization during severe accidents was evaluated for the Peach Bottom Atomic Power Station Units 2 and 3 (boiling water reactors with Mark I containments). Detailed analyses were conducted on operator performance, equipment performance, and the physical phenomenology for three severe accident sequences currently identified as being important contributors to risk. The results indicate that containment venting can be effective in reducing risk for several classes of severe accidents but, based on procedures in draft form and equipment in place at the time of the analyses, has limited potential for further reducing the risk for severe accidents currently identified as being important contributors to the risk for Peach Bottom.

  12. Graphite furnace atomic absorption elemental analysis of ecstasy tablets.

    PubMed

    French, Holly E; Went, Michael J; Gibson, Stuart J

    2013-09-10

    Six metals (copper, magnesium, barium, nickel, chromium and lead) were determined in two separate batches of seized ecstasy tablets by graphite furnace atomic absorption spectroscopy (GFAAS) following digestion with nitric acid and hydrogen peroxide. Large intra-batch variations were found as expected for tablets produced in clandestine laboratories. For example, nickel in batch 1 was present in the range 0.47-13.1 parts per million (ppm) and in batch 2 in the range 0.35-9.06 ppm. Although batch 1 had significantly higher 3,4-methylenedioxy-N-methamphetamine (MDMA) content than batch 2, barium was the only element which discriminated between the two ecstasy seizures (batch 1: 0.19-0.66 ppm, batch 2: 3.77-5.47 ppm).

  13. Molecular mimicry of substrate oxygen atoms by water molecules in the beta-amylase active site.

    PubMed

    Pujadas, G; Palau, J

    2001-08-01

    Soybean beta-amylase (EC 3.2.1.2) has been crystallized both free and complexed with a variety of ligands. Four water molecules in the free-enzyme catalytic cleft form a multihydrogen-bond network with eight strategic residues involved in enzyme-ligand hydrogen bonds. We show here that the positions of these four water molecules are coincident with the positions of four potential oxygen atoms of the ligands within the complex. Some of these waters are displaced from the active site when the ligands bind to the enzyme. How many are displaced depends on the shape of the ligand. This means that when one of the four positions is not occupied by a ligand oxygen atom, the corresponding water remains. We studied the functional/structural role of these four waters and conclude that their presence means that the conformation of the eight side chains is fixed in all situations (free or complexed enzyme) and preserved from unwanted or forbidden conformational changes that could hamper the catalytic mechanism. The water structure at the active pocket of beta-amylase is therefore essential for providing the ligand recognition process with plasticity. It does not affect the protein active-site geometry and preserves the overall hydrogen-bonding network, irrespective of which ligand is bound to the enzyme. We also investigated whether other enzymes showed a similar role for water. Finally, we discuss the potential use of these results for predicting whether water molecules can mimic ligand atoms in the active center.

  14. Atomic structure of the apoptosome: mechanism of cytochrome c- and dATP-mediated activation of Apaf-1

    PubMed Central

    Zhou, Mengying; Li, Yini; Hu, Qi; Bai, Xiao-chen; Huang, Weiyun; Yan, Chuangye; Scheres, Sjors H.W.; Shi, Yigong

    2015-01-01

    The apoptotic protease-activating factor 1 (Apaf-1) controls the onset of many known forms of intrinsic apoptosis in mammals. Apaf-1 exists in normal cells as an autoinhibited monomer. Upon binding to cytochrome c and dATP, Apaf-1 oligomerizes into a heptameric complex known as the apoptosome, which recruits and activates cell-killing caspases. Here we present an atomic structure of an intact mammalian apoptosome at 3.8 Å resolution, determined by single-particle, cryo-electron microscopy (cryo-EM). Structural analysis, together with structure-guided biochemical characterization, uncovered how cytochrome c releases the autoinhibition of Apaf-1 through specific interactions with the WD40 repeats. Structural comparison with autoinhibited Apaf-1 revealed how dATP binding triggers a set of conformational changes that results in the formation of the apoptosome. Together, these results constitute the molecular mechanism of cytochrome c- and dATP-mediated activation of Apaf-1. PMID:26543158

  15. Atomic structure of the apoptosome: mechanism of cytochrome c- and dATP-mediated activation of Apaf-1.

    PubMed

    Zhou, Mengying; Li, Yini; Hu, Qi; Bai, Xiao-Chen; Huang, Weiyun; Yan, Chuangye; Scheres, Sjors H W; Shi, Yigong

    2015-11-15

    The apoptotic protease-activating factor 1 (Apaf-1) controls the onset of many known forms of intrinsic apoptosis in mammals. Apaf-1 exists in normal cells as an autoinhibited monomer. Upon binding to cytochrome c and dATP, Apaf-1 oligomerizes into a heptameric complex known as the apoptosome, which recruits and activates cell-killing caspases. Here we present an atomic structure of an intact mammalian apoptosome at 3.8 Å resolution, determined by single-particle, cryo-electron microscopy (cryo-EM). Structural analysis, together with structure-guided biochemical characterization, uncovered how cytochrome c releases the autoinhibition of Apaf-1 through specific interactions with the WD40 repeats. Structural comparison with autoinhibited Apaf-1 revealed how dATP binding triggers a set of conformational changes that results in the formation of the apoptosome. Together, these results constitute the molecular mechanism of cytochrome c- and dATP-mediated activation of Apaf-1.

  16. Research Update: Spatially resolved mapping of electronic structure on atomic level by multivariate statistical analysis

    SciTech Connect

    Belianinov, Alex; Panchapakesan, G.; Lin, Wenzhi; Sales, Brian C.; Sefat, Athena Safa; Jesse, Stephen; Pan, Minghu; Kalinin, Sergei V.

    2014-12-02

    Atomic level spatial variability of electronic structure in Fe-based superconductor FeTe0.55Se0.45 (Tc = 15 K) is explored using current-imaging tunneling-spectroscopy. Multivariate statistical analysis of the data differentiates regions of dissimilar electronic behavior that can be identified with the segregation of chalcogen atoms, as well as boundaries between terminations and near neighbor interactions. Subsequent clustering analysis allows identification of the spatial localization of these dissimilar regions. Similar statistical analysis of modeled calculated density of states of chemically inhomogeneous FeTe1 x Sex structures further confirms that the two types of chalcogens, i.e., Te and Se, can be identified by their electronic signature and differentiated by their local chemical environment. This approach allows detailed chemical discrimination of the scanning tunneling microscopy data including separation of atomic identities, proximity, and local configuration effects and can be universally applicable to chemically and electronically inhomogeneous surfaces.

  17. Catalytic activity of bimetallic catalysts highly sensitive to the atomic composition and phase structure at the nanoscale

    NASA Astrophysics Data System (ADS)

    Shan, Shiyao; Petkov, Valeri; Prasai, Binay; Wu, Jinfang; Joseph, Pharrah; Skeete, Zakiya; Kim, Eunjoo; Mott, Derrick; Malis, Oana; Luo, Jin; Zhong, Chuan-Jian

    2015-11-01

    The ability to determine the atomic arrangement in nanoalloy catalysts and reveal the detailed structural features responsible for the catalytically active sites is essential for understanding the correlation between the atomic structure and catalytic properties, enabling the preparation of efficient nanoalloy catalysts by design. Herein we describe a study of CO oxidation over PdCu nanoalloy catalysts focusing on gaining insights into the correlation between the atomic structures and catalytic activity of nanoalloys. PdCu nanoalloys of different bimetallic compositions are synthesized as a model system and are activated by a controlled thermochemical treatment for assessing their catalytic activity. The results show that the catalytic synergy of Pd and Cu species evolves with both the bimetallic nanoalloy composition and temperature of the thermochemical treatment reaching a maximum at a Pd : Cu ratio close to 50 : 50. The nanoalloys are characterized structurally by ex situ and in situ synchrotron X-ray diffraction, including atomic pair distribution function analysis. The structural data show that, depending on the bimetallic composition and treatment temperature, PdCu nanoalloys adopt two different structure types. One features a chemically ordered, body centered cubic (B2) type alloy consisting of two interpenetrating simple cubic lattices, each occupied with Pd or Cu species alone, and the other structure type features a chemically disordered, face-centered cubic (fcc) type of alloy wherein Pd and Cu species are intermixed at random. The catalytic activity for CO oxidation is strongly influenced by the structural features. In particular, it is revealed that the prevalence of chemical disorder in nanoalloys with a Pd : Cu ratio close to 50 : 50 makes them superior catalysts for CO oxidation in comparison with the same nanoalloys of other bimetallic compositions. However, the catalytic synergy can be diminished if the Pd50Cu50 nanoalloys undergo phase

  18. Progress in Visualizing Atomic Size Effects with DFT-Chemical Pressure Analysis: From Isolated Atoms to Trends in AB5 Intermetallics.

    PubMed

    Berns, Veronica M; Engelkemier, Joshua; Guo, Yiming; Kilduff, Brandon J; Fredrickson, Daniel C

    2014-08-12

    The notion of atomic size poses an important challenge to chemical theory: empirical evidence has long established that atoms have spatial requirements, which are summarized in tables of covalent, ionic, metallic, and van der Waals radii. Considerations based on these radii play a central role in the design and interpretation of experiments, but few methods are available to directly support arguments based on atomic size using electronic structure methods. Recently, we described an approach to elucidating atomic size effects using theoretical calculations: the DFT-Chemical Pressure analysis, which visualizes the local pressures arising in crystal structures from the interactions of atomic size and electronic effects. Using this approach, a variety of structural phenomena in intermetallic phases have already been understood in terms that provide guidance to new synthetic experiments. However, the applicability of the DFT-CP method to the broad range of the structures encountered in the solid state is limited by two issues: (1) the difficulty of interpreting the intense pressure features that appear in atomic core regions and (2) the need to divide space among pairs of interacting atoms in a meaningful way. In this article, we describe general solutions to these issues. In addressing the first issue, we explore the CP analysis of a test case in which no core pressures would be expected to arise: isolated atoms in large boxes. Our calculations reveal that intense core pressures do indeed arise in these virtually pressure-less model systems and allow us to trace the issue to the shifts in the voxel positions relative to atomic centers upon expanding and contracting the unit cell. A compensatory grid unwarping procedure is introduced to remedy this artifact. The second issue revolves around the difficulty of interpreting the pressure map in terms of interatomic interactions in a way that respects the size differences of the atoms and avoids artificial geometrical

  19. Recent Data Generation Activities at the Atomic and Molecular Data Unit of the IAEA

    SciTech Connect

    Clark, R.E.H.; Humbert, D.

    2005-05-27

    The main data generation mechanism of the Atomic and Molecular (A+M) Data Unit of the IAEA is the Co-ordinated Research Project (CRP). The International Fusion Research Council Subcommittee on Atomic and Molecular Data for Fusion recommends topics for new CRPs to be initiated by the A+M Unit. A typical CRP has a lifetime of three to five years. At the start of the CRP a Research Co-ordination Meeting (RCM) is held with the purpose of formulating a detailed work plan. At later RCMs progress on these work plans is reported and the studies debated and expanded. At the conclusion of the CRP the results are compiled in a volume of the journal Atomic and Plasma-Material Interaction Data for Fusion. Numerical results are also added to the electronic database as appropriate. Normally the Unit has three to four active CRPs, and also holds Technical Meetings and invites individual Consultants to IAEA Headquarters, Vienna for specific tasks. Such activities can result in providing advice on a particular topic, on data for a particular process, or a new capability to be made widely available. Recently, consultants to the Unit have provided extensive additions to the Unit databases, as well as interfaces to run several calculational tools through the Internet. Specific examples will be presented.

  20. Single Pd atoms in activated carbon fibers and their contribution to hydrogen storage

    SciTech Connect

    Contescu, Cristian I; van Benthem, Klaus; Li, Sa; Bonifacio, Cecile S; Pennycook, Stephen J; Jena, Puru; Gallego, Nidia C

    2011-01-01

    Palladium-modified activated carbon fibers (Pd-ACF) were synthesized by meltspinning, carbonization and activation of an isotropic pitch carbon precursor premixed with an organometallic Pd compound. The hydrogen uptake at 25 oC and 20 bar on Pd- ACF exceeded the expected capacity based solely on Pd hydride formation and hydrogen physisorption on the microporous carbon support. Aberration-corrected scanning transmission electron microscopy (STEM) with sub- ngstrom spatial resolution provided unambiguous identification of isolated Pd atoms occurring in the carbon matrix that coexist with larger Pd particles. First principles calculations revealed that each single Pd atom can form Kubas-type complexes by binding up to three H2 molecules in the pressure range of adsorption measurements. Based on Pd atom concentration determined from STEM images, the contribution of various mechanisms to the excess hydrogen uptake measured experimentally was evaluated. With consideration of Kubas binding as a viable mechanism (along with hydride formation and physisorption to carbon support) the role of hydrogen spillover in this system may be smaller than previously thought.

  1. The International Atomic Energy Agency's activities in radiation medicine and cancer: promoting global health through diplomacy.

    PubMed

    Deatsch-Kratochvil, Amanda N; Pascual, Thomas Neil; Kesner, Adam; Rosenblatt, Eduardo; Chhem, Rethy K

    2013-02-01

    Global health has been an issue of seemingly low political importance in comparison with issues that have direct bearing on countries' national security. Recently, health has experienced a "political revolution" or a rise in political importance. Today, we face substantial global health challenges, from the spread of infectious disease, gaps in basic maternal and child health care, to the globalization of cancer. A recent estimate states that the "overall lifetime risk of developing cancer (both sexes) is expected to rise from more than one in three to one in two by 2015." These issues pose significant threats to international health security. To successfully combat these grave challenges, the international community must embrace and engage in global health diplomacy, defined by scholars Thomas Novotny and Vicanne Adams as a political activity aimed at improving global health, while at the same time maintaining and strengthening international relations. The IAEA (International Atomic Energy Agency) is an international organization with a unique mandate to "accelerate and enlarge the contribution of atomic energy to peace, health, and prosperity throughout the world." This article discusses global health diplomacy, reviews the IAEA's program activities in human health by focusing on radiation medicine and cancer, and the peaceful applications of atomic energy within the context of global health diplomacy.

  2. Weak-light solitons and their active control in a parity-time-symmetric atomic system

    NASA Astrophysics Data System (ADS)

    Hang, Chao; Huang, Guoxiang

    2015-04-01

    We propose a realistic physical scheme to produce one-dimensional and two-dimensional weak-light solitons in an atomic system with PT symmetry. The system we suggest is a cold three-level atomic gas with two species and is driven by control and probe laser fields. We show that by the interference of two Raman resonances a highly adjustable probe-field refractive index with PT symmetry in one and two dimensions can be realized. We further show that it is possible to produce various light solitons when the weak nonlinearity of the probe field is taken into account. Due to the resonant character of the system, the light solitons obtained in one and two dimensions have extremely low light power (at the level of nanowatts). In addition, we demonstrate that the stability of these light solitons can be actively controlled via PT phase transition of the system.

  3. Noise reduction in differential phase extraction of dual atom interferometers using an active servo loop

    NASA Astrophysics Data System (ADS)

    Chiow, Sheng-wey; Williams, Jason; Yu, Nan

    2016-01-01

    Differential measurements using simultaneous atom interferometers provide unprecedented precision and stability for explorations on the scientific frontiers. Phase extraction between two atom interferometers, however, imposes additional limitations on the overall instrument performance due to nonlinear multiparameter fit and associated reduced data rate and sensitivity. We propose an active differential phase extraction method, which is self-calibratable and yields the theoretical performance of differential measurement for uncorrelated errors, and demonstrate the scheme on a transportable gravity gradiometer. The gravity gradient sensitivity of the instrument is improved by a factor of 3 with the implementation of the technique, which is in consistent with independently measured detection noise. We also demonstrate the accuracy and applicability of the scheme with 33-kg test masses, and achieve 1 E uncertainty after 4000 s.

  4. Nano Scale Mechanical Analysis of Biomaterials Using Atomic Force Microscopy

    NASA Astrophysics Data System (ADS)

    Dutta, Diganta

    The atomic force microscope (AFM) is a probe-based microscope that uses nanoscale and structural imaging where high resolution is desired. AFM has also been used in mechanical, electrical, and thermal engineering applications. This unique technique provides vital local material properties like the modulus of elasticity, hardness, surface potential, Hamaker constant, and the surface charge density from force versus displacement curve. Therefore, AFM was used to measure both the diameter and mechanical properties of the collagen nanostraws in human costal cartilage. Human costal cartilage forms a bridge between the sternum and bony ribs. The chest wall of some humans is deformed due to defective costal cartilage. However, costal cartilage is less studied compared to load bearing cartilage. Results show that there is a difference between chemical fixation and non-chemical fixation treatments. Our findings imply that the patients' chest wall is mechanically weak and protein deposition is abnormal. This may impact the nanostraws' ability to facilitate fluid flow between the ribs and the sternum. At present, AFM is the only tool for imaging cells' ultra-structure at the nanometer scale because cells are not homogeneous. The first layer of the cell is called the cell membrane, and the layer under it is made of the cytoskeleton. Cancerous cells are different from normal cells in term of cell growth, mechanical properties, and ultra-structure. Here, force is measured with very high sensitivity and this is accomplished with highly sensitive probes such as a nano-probe. We performed experiments to determine ultra-structural differences that emerge when such cancerous cells are subject to treatments such as with drugs and electric pulses. Jurkat cells are cancerous cells. These cells were pulsed at different conditions. Pulsed and non-pulsed Jurkat cell ultra-structures were investigated at the nano meter scale using AFM. Jurkat cell mechanical properties were measured under

  5. Identification of Conserved Moieties in Metabolic Networks by Graph Theoretical Analysis of Atom Transition Networks

    PubMed Central

    Haraldsdóttir, Hulda S.; Fleming, Ronan M. T.

    2016-01-01

    Conserved moieties are groups of atoms that remain intact in all reactions of a metabolic network. Identification of conserved moieties gives insight into the structure and function of metabolic networks and facilitates metabolic modelling. All moiety conservation relations can be represented as nonnegative integer vectors in the left null space of the stoichiometric matrix corresponding to a biochemical network. Algorithms exist to compute such vectors based only on reaction stoichiometry but their computational complexity has limited their application to relatively small metabolic networks. Moreover, the vectors returned by existing algorithms do not, in general, represent conservation of a specific moiety with a defined atomic structure. Here, we show that identification of conserved moieties requires data on reaction atom mappings in addition to stoichiometry. We present a novel method to identify conserved moieties in metabolic networks by graph theoretical analysis of their underlying atom transition networks. Our method returns the exact group of atoms belonging to each conserved moiety as well as the corresponding vector in the left null space of the stoichiometric matrix. It can be implemented as a pipeline of polynomial time algorithms. Our implementation completes in under five minutes on a metabolic network with more than 4,000 mass balanced reactions. The scalability of the method enables extension of existing applications for moiety conservation relations to genome-scale metabolic networks. We also give examples of new applications made possible by elucidating the atomic structure of conserved moieties. PMID:27870845

  6. High purity polyimide analysis by solid sampling graphite furnace atomic absorption spectrometry

    NASA Astrophysics Data System (ADS)

    Santos, Rafael F.; Carvalho, Gabriel S.; Duarte, Fabio A.; Bolzan, Rodrigo C.; Flores, Erico M. M.

    2017-03-01

    In this work, Cr, Cu, Mn, Na and Ni were determined in high purity polyimides (99.5%) by solid sampling graphite furnace atomic absorption spectrometry (SS-GFAAS) using Zeeman effect background correction system with variable magnetic field, making possible the simultaneous measurement at high or low sensitivity. The following analytical parameters were evaluated: pyrolysis and atomization temperatures, feasibility of calibration with aqueous solution, linear calibration range, sample mass range and the use of chemical modifier. Calibration with aqueous standard solutions was feasible for all analytes. No under or overestimated results were observed and up to 10 mg sample could be introduced on the platform for the determination of Cr, Cu, Mn, Na and Ni. The relative standard deviation ranged from 3 to 20%. The limits of detection (LODs) achieved using the high sensitivity mode were as low as 7.0, 2.5, 1.7, 17 and 0.12 ng g- 1 for Cr, Cu, Mn, Na and Ni, respectively. No addition of chemical modifier was necessary, except for Mn determination where Pd was required. The accuracy was evaluated by analyte spike and by comparison of the results with those obtained by inductively coupled plasma optical emission spectrometry and inductively coupled plasma mass spectrometry after microwave-assisted digestion in a single reaction chamber system and also by neutron activation analysis. No difference among the results obtained by SS-GFAAS and those obtained by alternative analytical methods using independent techniques. SS-GFAAS method showed some advantages, such as the determination of metallic contaminants in high purity polyimides with practically no sample preparation, very low LODs, calibration with aqueous standards and determination in a wide range of concentration.

  7. International Atomic Energy Agency intercomparison of ion beam analysis software

    NASA Astrophysics Data System (ADS)

    Barradas, N. P.; Arstila, K.; Battistig, G.; Bianconi, M.; Dytlewski, N.; Jeynes, C.; Kótai, E.; Lulli, G.; Mayer, M.; Rauhala, E.; Szilágyi, E.; Thompson, M.

    2007-09-01

    Ion beam analysis (IBA) includes a group of techniques for the determination of elemental concentration depth profiles of thin film materials. Often the final results rely on simulations, fits and calculations, made by dedicated codes written for specific techniques. Here we evaluate numerical codes dedicated to the analysis of Rutherford backscattering spectrometry, non-Rutherford elastic backscattering spectrometry, elastic recoil detection analysis and non-resonant nuclear reaction analysis data. Several software packages have been presented and made available to the community. New codes regularly appear, and old codes continue to be used and occasionally updated and expanded. However, those codes have to date not been validated, or even compared to each other. Consequently, IBA practitioners use codes whose validity, correctness and accuracy have never been validated beyond the authors' efforts. In this work, we present the results of an IBA software intercomparison exercise, where seven different packages participated. These were DEPTH, GISA, DataFurnace (NDF), RBX, RUMP, SIMNRA (all analytical codes) and MCERD (a Monte Carlo code). In a first step, a series of simulations were defined, testing different capabilities of the codes, for fixed conditions. In a second step, a set of real experimental data were analysed. The main conclusion is that the codes perform well within the limits of their design, and that the largest differences in the results obtained are due to differences in the fundamental databases used (stopping power and scattering cross section). In particular, spectra can be calculated including Rutherford cross sections with screening, energy resolution convolutions including energy straggling, and pileup effects, with agreement between the codes available at the 0.1% level. This same agreement is also available for the non-RBS techniques. This agreement is not limited to calculation of spectra from particular structures with predetermined

  8. Analysis of Radiation Damage in Light Water Reactors: Comparison of Cluster Analysis Methods for the Analysis of Atom Probe Data.

    PubMed

    Hyde, Jonathan M; DaCosta, Gérald; Hatzoglou, Constantinos; Weekes, Hannah; Radiguet, Bertrand; Styman, Paul D; Vurpillot, Francois; Pareige, Cristelle; Etienne, Auriane; Bonny, Giovanni; Castin, Nicolas; Malerba, Lorenzo; Pareige, Philippe

    2017-01-30

    Irradiation of reactor pressure vessel (RPV) steels causes the formation of nanoscale microstructural features (termed radiation damage), which affect the mechanical properties of the vessel. A key tool for characterizing these nanoscale features is atom probe tomography (APT), due to its high spatial resolution and the ability to identify different chemical species in three dimensions. Microstructural observations using APT can underpin development of a mechanistic understanding of defect formation. However, with atom probe analyses there are currently multiple methods for analyzing the data. This can result in inconsistencies between results obtained from different researchers and unnecessary scatter when combining data from multiple sources. This makes interpretation of results more complex and calibration of radiation damage models challenging. In this work simulations of a range of different microstructures are used to directly compare different cluster analysis algorithms and identify their strengths and weaknesses.

  9. Single-molecule imaging of DNA polymerase I (Klenow fragment) activity by atomic force microscopy

    NASA Astrophysics Data System (ADS)

    Chao, J.; Zhang, P.; Wang, Q.; Wu, N.; Zhang, F.; Hu, J.; Fan, C. H.; Li, B.

    2016-03-01

    We report a DNA origami-facilitated single-molecule platform that exploits atomic force microscopy to study DNA replication. We imaged several functional activities of the Klenow fragment of E. coli DNA polymerase I (KF) including binding, moving, and dissociation from the template DNA. Upon completion of these actions, a double-stranded DNA molecule was formed. Furthermore, the direction of KF activities was captured and then confirmed by shifting the KF binding sites on the template DNA.We report a DNA origami-facilitated single-molecule platform that exploits atomic force microscopy to study DNA replication. We imaged several functional activities of the Klenow fragment of E. coli DNA polymerase I (KF) including binding, moving, and dissociation from the template DNA. Upon completion of these actions, a double-stranded DNA molecule was formed. Furthermore, the direction of KF activities was captured and then confirmed by shifting the KF binding sites on the template DNA. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr06544e

  10. Matrix-Assisted Plasma Atomization Emission Spectrometry for Surface Sampling Elemental Analysis

    PubMed Central

    Yuan, Xin; Zhan, Xuefang; Li, Xuemei; Zhao, Zhongjun; Duan, Yixiang

    2016-01-01

    An innovative technology has been developed involving a simple and sensitive optical spectrometric method termed matrix-assisted plasma atomization emission spectrometry (MAPAES) for surface sampling elemental analysis using a piece of filter paper (FP) for sample introduction. MAPAES was carried out by direct interaction of the plasma tail plume with the matrix surface. The FP absorbs energy from the plasma source and releases combustion heating to the analytes originally present on its surface, thus to promote the atomization and excitation process. The matrix-assisted plasma atomization excitation phenomenon was observed for multiple elements. The FP matrix served as the partial energy producer and also the sample substrate to adsorb sample solution. Qualitative and quantitative determinations of metal ions were achieved by atomic emission measurements for elements Ba, Cu, Eu, In, Mn, Ni, Rh and Y. The detection limits were down to pg level with linear correlation coefficients better than 0.99. The proposed MAPAES provides a new way for atomic spectrometry which offers advantages of fast analysis speed, little sample consumption, less sample pretreatment, small size, and cost-effective. PMID:26762972

  11. Dynamic formation of single-atom catalytic active sites on ceria-supported gold nanoparticles

    DOE PAGES

    Wang, Yanggang; Mei, Donghai; Glezakou, Vassiliki Alexandra; ...

    2015-03-04

    Ab initio Molecular Dynamics simulations and static Density Functional Theory calculations have been performed to investigate the reaction mechanism of CO oxidation on Au/CeO2 catalyst. It is found that under reaction condition CO adsorption significantly labializes the surface atoms of the Au cluster and leads to the formation of isolated Au+-CO species that resides on the support in the vicinity of the Au particle. In this context, we identified a dynamic single-atom catalytic mechanism at the interfacial area for CO oxidation on Au/CeO2 catalyst, which is a lower energy pathway than that of CO oxidation at the interface with themore » metal particle. This results from the ability of the single atom site to strongly couple with the redox properties of the support in a synergistic manner thereby lowering the barrier for redox reactions. We find that the single Au+ ion, which only exists under reaction conditions, breaks away from the Au cluster to catalyze CO oxidation and returns to the Au cluster after the catalytic cycle is completed. Generally, our study highlights the importance of the dynamic creation of active sites under reaction conditions and their essential role in a catalytic process.« less

  12. Dynamic formation of single-atom catalytic active sites on ceria-supported gold nanoparticles

    SciTech Connect

    Wang, Yanggang; Mei, Donghai; Glezakou, Vassiliki Alexandra; Li, Jun; Rousseau, Roger J.

    2015-03-04

    Ab initio Molecular Dynamics simulations and static Density Functional Theory calculations have been performed to investigate the reaction mechanism of CO oxidation on Au/CeO2 catalyst. It is found that under reaction condition CO adsorption significantly labializes the surface atoms of the Au cluster and leads to the formation of isolated Au+-CO species that resides on the support in the vicinity of the Au particle. In this context, we identified a dynamic single-atom catalytic mechanism at the interfacial area for CO oxidation on Au/CeO2 catalyst, which is a lower energy pathway than that of CO oxidation at the interface with the metal particle. This results from the ability of the single atom site to strongly couple with the redox properties of the support in a synergistic manner thereby lowering the barrier for redox reactions. We find that the single Au+ ion, which only exists under reaction conditions, breaks away from the Au cluster to catalyze CO oxidation and returns to the Au cluster after the catalytic cycle is completed. Generally, our study highlights the importance of the dynamic creation of active sites under reaction conditions and their essential role in a catalytic process.

  13. Ultrafast dynamics in atomic clusters: Analysis and control

    PubMed Central

    Bonačić-Koutecký, Vlasta; Mitrić, Roland; Werner, Ute; Wöste, Ludger; Berry, R. Stephen

    2006-01-01

    We present a study of dynamics and ultrafast observables in the frame of pump–probe negative-to-neutral-to-positive ion (NeNePo) spectroscopy illustrated by the examples of bimetallic trimers Ag2Au−/Ag2Au/Ag2Au+ and silver oxides Ag3O2−/Ag3O2/Ag3O2+ in the context of cluster reactivity. First principle multistate adiabatic dynamics allows us to determine time scales of different ultrafast processes and conditions under which these processes can be experimentally observed. Furthermore, we present a strategy for optimal pump–dump control in complex systems based on the ab initio Wigner distribution approach and apply it to tailor laser fields for selective control of the isomerization process in Na3F2. The shapes of pulses can be assigned to underlying processes, and therefore control can be used as a tool for analysis. PMID:16740664

  14. Circuit Board Analysis for Lead by Atomic Absorption Spectroscopy in a Course for Nonscience Majors

    ERIC Educational Resources Information Center

    Weidenhammer, Jeffrey D.

    2007-01-01

    A circuit board analysis of the atomic absorption spectroscopy, which is used to measure lead content in a course for nonscience majors, is being presented. The experiment can also be used to explain the potential environmental hazards of unsafe disposal of various used electronic equipments.

  15. COMPREHENSIVE ANALYSIS OF BIOLOGICALLY RELEVANT ARSENICALS BY PH-SELECTIVE HYDRIDE GENERATION-ATOMIC ABSORPTION SPECTROMETRY

    EPA Science Inventory


    A method based on pH-selective generation and separation of arsines is commonly used for analysis of inorganic, methylated, and dimethylated trivalent and pentavalent arsenicals by hydride generation-atomic absorption spectrometry (HG-AAS). We have optimized this method to pe...

  16. Atomic and Molecular Structure in Chemical Education: A Critical Analysis from Various Perspectives of Science Education.

    ERIC Educational Resources Information Center

    Tsaparlis, Georgios

    1997-01-01

    Provides a critical analysis of the role that atomic theory plays in the science curriculum from elementary through secondary school. Examines structural concepts from the perspective of the theory of meaningful learning, information processing theory, and the alternative conceptions movement. Contains 54 references. (DDR)

  17. The FTS atomic spectrum tool (FAST) for rapid analysis of line spectra

    NASA Astrophysics Data System (ADS)

    Ruffoni, M. P.

    2013-07-01

    The FTS Atomic Spectrum Tool (FAST) is an interactive graphical program designed to simplify the analysis of atomic emission line spectra obtained from Fourier transform spectrometers. Calculated, predicted and/or known experimental line parameters are loaded alongside experimentally observed spectral line profiles for easy comparison between new experimental data and existing results. Many such line profiles, which could span numerous spectra, may be viewed simultaneously to help the user detect problems from line blending or self-absorption. Once the user has determined that their experimental line profile fits are good, a key feature of FAST is the ability to calculate atomic branching fractions, transition probabilities, and oscillator strengths-and their uncertainties-which is not provided by existing analysis packages. Program SummaryProgram title: FAST: The FTS Atomic Spectrum Tool Catalogue identifier: AEOW_v1_0 Program summary URL: http://cpc.cs.qub.ac.uk/summaries/AEOW_v1_0.html Program obtainable from: CPC Program Library, Queen's University, Belfast, N. Ireland Licensing provisions: GNU General Public License version 3 No. of lines in distributed program, including test data, etc.: 293058 No. of bytes in distributed program, including test data, etc.: 13809509 Distribution format: tar.gz Programming language: C++. Computer: Intel x86-based systems. Operating system: Linux/Unix/Windows. RAM: 8 MB minimum. About 50-200 MB for a typical analysis. Classification: 2.2, 2.3, 21.2. Nature of problem: Visualisation of atomic line spectra including the comparison of theoretical line parameters with experimental atomic line profiles. Accurate intensity calibration of experimental spectra, and the determination of observed relative line intensities that are needed for calculating atomic branching fractions and oscillator strengths. Solution method: FAST is centred around a graphical interface, where a user may view sets of experimental line profiles and compare

  18. Neutron activation analysis for antimetabolites. [in food samples

    NASA Technical Reports Server (NTRS)

    1973-01-01

    Determination of metal ion contaminants in food samples is studied. A weighed quantity of each sample was digested in a concentrated mixture of nitric, hydrochloric and perchloric acids to affect complete solution of the food products. The samples were diluted with water and the pH adjusted according to the specific analysis performed. The samples were analyzed by neutron activation analysis, polarography, and atomic absorption spectrophotometry. The solid food samples were also analyzed by neutron activation analysis for increased sensitivity and lower levels of detectability. The results are presented in tabular form.

  19. Note: A three-dimension active vibration isolator for precision atom gravimeters

    SciTech Connect

    Zhou, Min-Kang; Xiong, Xin; Chen, Le-Le; Cui, Jia-Feng; Duan, Xiao-Chun; Hu, Zhong-Kun

    2015-04-15

    An ultra-low frequency active vibration isolator, simultaneously suppressing three-dimensional vibration noise, is demonstrated experimentally. The equivalent natural period of the isolator is 100 s and 12 s for the vertical and horizontal direction, respectively. The vibration noise in the vertical direction is about 50 times reduced during 0.2 and 2 Hz, and 5 times reduced in the other two orthogonal directions in the same frequency range. This isolator is designed for atom gravimeters, especially suitable for the gravimeter whose sensitivity is limited by vibration couplings.

  20. Ethanol Electro-Oxidation on Ternary Platinum–Rhodium–Tin Nanocatalysts: Insights in the Atomic 3D Structure of the Active Catalytic Phase

    SciTech Connect

    Erini, Nina; Loukrakpam, Rameshwori; Petkov, Valeri; Baranova, Elena A.; Yang, Ruizhi; Teschner, Detre; Huang, Yunhui; Brankovic, Stanko R.; Strasser, Peter

    2014-04-25

    Novel insights in the synthesis–structure–catalytic activity relationships of nanostructured trimetallic Pt–Rh–Sn electrocatalysts for the electrocatalytic oxidation of ethanol are reported. In particular, we identify a novel single-phase Rh-doped Pt–Sn Niggliite mineral phase as the source of catalytically active sites for ethanol oxidation; we discuss its morphology, composition, chemical surface state, and the detailed 3D atomic arrangement using high-energy (HE-XRD), atomic pair distribution function (PDF) analysis, and X-ray photoelectron spectroscopy (XPS). The intrinsic ethanol oxidation activity of the active Niggliite phase exceeded those of earlier reports, lending support to the notion that the atomic-scale neighborhood of Pt, Rh, and Sn is conducive to the emergence of active surface catalytic sites under reaction conditions. In situ mechanistic Fourier transform infrared (in situ FTIR) analysis confirms an active 12 electron oxidation reaction channel to CO2 at electrode potentials as low as 450 mV/RHE, demonstrating the favorable efficiency of the PtRhSn Niggliite phase for C–C bond splitting.

  1. Diagrammatic analysis of multiphoton processes in a ladder-type three-level atomic system

    SciTech Connect

    Noh, Heung-Ryoul; Moon, Han Seb

    2011-11-15

    We present a diagrammatic method for complete characterization of multiphoton processes in three-level atomic systems. By considering the interaction routes of the coupling and probe photons for a ladder-type, three-level, noncycling (or cycling) atomic system, we are able to completely discriminate between the pure one-photon and the pure two-photon resonance effects, and the effect of their combination in electromagnetically induced transparency (EIT) using our diagrammatic method. We show that the proposed diagrammatic method is very useful for the analysis of multiphoton processes in ladder-type EIT.

  2. Adjoint design sensitivity analysis of reduced atomic systems using generalized Langevin equation for lattice structures

    SciTech Connect

    Kim, Min-Geun; Jang, Hong-Lae; Cho, Seonho

    2013-05-01

    An efficient adjoint design sensitivity analysis method is developed for reduced atomic systems. A reduced atomic system and the adjoint system are constructed in a locally confined region, utilizing generalized Langevin equation (GLE) for periodic lattice structures. Due to the translational symmetry of lattice structures, the size of time history kernel function that accounts for the boundary effects of the reduced atomic systems could be reduced to a single atom’s degrees of freedom. For the problems of highly nonlinear design variables, the finite difference method is impractical for its inefficiency and inaccuracy. However, the adjoint method is very efficient regardless of the number of design variables since one additional time integration is required for the adjoint GLE. Through numerical examples, the derived adjoint sensitivity turns out to be accurate and efficient through the comparison with finite difference sensitivity.

  3. Preparation and Analysis of Atom Probe Tips by Xenon Focused Ion Beam Milling.

    PubMed

    Estivill, Robert; Audoit, Guillaume; Barnes, Jean-Paul; Grenier, Adeline; Blavette, Didier

    2016-06-01

    The damage and ion distribution induced in Si by an inductively coupled plasma Xe focused ion beam was investigated by atom probe tomography. By using predefined patterns it was possible to prepare the atom probe tips with a sub 50 nm end radius in the ion beam microscope. The atom probe reconstruction shows good agreement with simulated implantation profiles and interplanar distances extracted from spatial distribution maps. The elemental profiles of O and C indicate co-implantation during the milling process. The presence of small disc-shaped Xe clusters are also found in the three-dimensional reconstruction. These are attributed to the presence of Xe nanocrystals or bubbles that open during the evaporation process. The expected accumulated dose points to a loss of >95% of the Xe during analysis, which escapes undetected.

  4. Design criteria for molecular mimics of fragments of the β-turn. 1. Cα atom analysis

    NASA Astrophysics Data System (ADS)

    Garland, S. L.; Dean, P. M.

    1999-09-01

    Peptides represent an extensive class of biologically active molecules. They may be used as leads in the development of novel therapeutic agents provided the pharmacophoric information present within them can be translated into non-peptide analogs that lack the peptide backbone and are stable to proteolysis. This is the rationale for peptidomimetic drug design. Frequently, the β-turn has been implicated as a conformation important for biological recognition of peptides. Empirical evidence from known peptidomimetics, coupled with a theoretical model of peptide binding and the observation that glycine and proline residues are common within the β-turn, has suggested the design of molecules to mimic placement of between two and four of the side-chains. The moderate number of different β-turn conformations, combined with the combinatoric nature of side-chain selection complicates the procedure. In this paper, cluster analysis has been used to classify the arrangement of C_α atoms about the various fragments of the β-turn. Recombination of the observed patterns provides a general model for the β-turn which may be used as an effective screen for potential peptidomimetic scaffolds in chemical databases.

  5. Interaction of interstitial atoms and configurational contribution to their thermodynamic activity in V, Nb, and Ta

    NASA Astrophysics Data System (ADS)

    Blanter, M. S.; Dmitriev, V. V.; Mogutnov, B. M.; Ruban, A. V.

    2017-02-01

    The pairwise interaction energies of O-O and N-N in bcc metals of group VB, which were calculated earlier using first-principles methods, have been employed to analyze the effect of the interatomic interactions on the configurational contribution to the thermodynamic activity. The strong effect of interstitial- interstitial interaction has been shown. The configurational contribution grows in the row (Nb-N) → (V-N) → (Ta-N) → (Nb-O) → (V-O) → (Ta-O), which is caused by a weakening of the mutual attraction of interstitial atoms in these solid solutions. The strong repulsion that characterizes the majority of coordination shells only weakly affects the thermodynamic activity. The character of the temperature dependence of the configurational contribution is defined by the strength of the mutual attraction of the interstitial atoms, i.e., upon strong attraction, the contribution increases with increasing temperature (Nb-N, V-N, Ta-N, and Nb-O) and, upon weak attraction, it decreases (V-O and Ta-O).

  6. Exploring the optical contrast effect in strong atomic lines for exoplanets transiting active stars

    NASA Astrophysics Data System (ADS)

    Cauley, Paul W.; Redfield, Seth

    2017-01-01

    Transmission spectroscopy is a powerful tool for detecting and characterizing planetary atmospheres. Non-photospheric features on the stellar disk, however, can contaminate the planetary signal: during transit the observed spectrum is weighted towards the features not currently being occulted by the planet. This contrast effect can mimic absorption in the planetary atmosphere for strong atomic lines such as Na I, Ca II, and the hydrogen Balmer lines. While the contrast effect is negligible for quiet stars, contributions to the transmission signal from active stellar surfaces can produce ~1% changes in the line core. It is therefore critical that these contrast signals be differentiated from true absorption features in the planetary atmosphere. Here we present our work on simulating the contrast effect for an active stellar surface. We discuss the particular case of HD 189733 b, a well-studied hot Jupiter orbiting an active K-dwarf, due to the plethora of atomic absorption signals reported in its atmosphere.Specifically, we focus on Hα to address recent suggestions that the measured in-transit signals are a result of stellar activity. In the contrast model we include center-to-limb variations and calculate limb darkening parameters as a function of wavelength across the line of interest. The model includes contributions to the spectrum from spots, faculae and plages, filaments, and the bare stellar photosphere. Stellar rotation is also included. We find that it is very difficult to reproduce the measured in-transit Hα signals for reasonable active region parameters. In addition, it is difficult to create an in-transit contrast signature that lasts for the duration of the transit unless the planet is crossing an active latitudinal belt and is always obscuring active regions. This suggests that the Hα measurements arise predominantly in the planetary atmosphere. However, the contrast effect likely contributes to these signals. Furthermore, our results could be

  7. Identifying the Atomic-Level Effects of Metal Composition on the Structure and Catalytic Activity of Peptide-Templated Materials.

    PubMed

    Merrill, Nicholas A; McKee, Erik M; Merino, Kyle C; Drummy, Lawrence F; Lee, Sungsik; Reinhart, Benjamin; Ren, Yang; Frenkel, Anatoly I; Naik, Rajesh R; Bedford, Nicholas M; Knecht, Marc R

    2015-12-22

    Bioinspired approaches for the formation of metallic nanomaterials have been extensively employed for a diverse range of applications including diagnostics and catalysis. These materials can often be used under sustainable conditions; however, it is challenging to control the material size, morphology, and composition simultaneously. Here we have employed the R5 peptide, which forms a 3D scaffold to direct the size and linear shape of bimetallic PdAu nanomaterials for catalysis. The materials were prepared at varying Pd:Au ratios to probe optimal compositions to achieve maximal catalytic efficiency. These materials were extensively characterized at the atomic level using transmission electron microscopy, extended X-ray absorption fine structure spectroscopy, and atomic pair distribution function analysis derived from high-energy X-ray diffraction patterns to provide highly resolved structural information. The results confirmed PdAu alloy formation, but also demonstrated that significant surface structural disorder was present. The catalytic activity of the materials was studied for olefin hydrogenation, which demonstrated enhanced reactivity from the bimetallic structures. These results present a pathway to the bioinspired production of multimetallic materials with enhanced properties, which can be assessed via a suite of characterization methods to fully ascertain structure/function relationships.

  8. An x ray scatter approach for non-destructive chemical analysis of low atomic numbered elements

    NASA Technical Reports Server (NTRS)

    Ross, H. Richard

    1993-01-01

    A non-destructive x-ray scatter (XRS) approach has been developed, along with a rapid atomic scatter algorithm for the detection and analysis of low atomic-numbered elements in solids, powders, and liquids. The present method of energy dispersive x-ray fluorescence spectroscopy (EDXRF) makes the analysis of light elements (i.e., less than sodium; less than 11) extremely difficult. Detection and measurement become progressively worse as atomic numbers become smaller, due to a competing process called 'Auger Emission', which reduces fluorescent intensity, coupled with the high mass absorption coefficients exhibited by low energy x-rays, the detection and determination of low atomic-numbered elements by x-ray spectrometry is limited. However, an indirect approach based on the intensity ratio of Compton and Rayleigh scattered has been used to define light element components in alloys, plastics and other materials. This XRS technique provides qualitative and quantitative information about the overall constituents of a variety of samples.

  9. Activators generated by electron transfer for atom transfer radical polymerization of styrene in the presence of mesoporous silica nanoparticles

    SciTech Connect

    Khezri, Khezrollah; Roghani-Mamaqani, Hossein

    2014-11-15

    Graphical abstract: Effect of mesoporous silica nanoparticles (MCM-41) on the activator generated by electron transfer for atom transfer radical polymerization (AGET ATRP) is investigated. Decrement of conversion and number average molecular weight and also increment of polydispersity index (PDI) values are three main results of addition of MCM-41 nanoparticles. Incorporation of MCM-41 nanoparticles in the polystyrene matrix can clearly increase thermal stability and decrease glass transition temperature of the nanocomposites. - Highlights: • Spherical morphology, hexagonal structure, and high surface area with regular pore diameters of the synthesized MCM-41 nanoparticles are examined. • AGET ATRP of styrene in the presence of MCM-41 nanoparticles is performed. • Effect of MCM-41 nanoparticles addition on the polymerization rate, conversion and molecular weights of the products are discussed. • Improvement in thermal stability of the nanocomposites and decreasing T{sub g} values was also observed by incorporation of MCM-41 nanoparticles. - Abstract: Activator generated by electron transfer for atom transfer radical polymerization was employed to synthesize well-defined mesoporous silica nanoparticles/polystyrene composites. Inherent features of spherical mesoporous silica nanoparticles were evaluated by nitrogen adsorption/desorption isotherm, X-ray diffraction and scanning electron microscopy analysis techniques. Conversion and molecular weight evaluations were carried out using gas and size exclusion chromatography respectively. By the addition of only 3 wt% mesoporous silica nanoparticles, conversion decreases from 81 to 58%. Similarly, number average molecular weight decreases from 17,116 to 12,798 g mol{sup −1}. However, polydispersity index (PDI) values increases from 1.24 to 1.58. A peak around 4.1–4.2 ppm at proton nuclear magnetic resonance spectroscopy results clearly confirms the living nature of the polymerization. Thermogravimetric

  10. Antitumor activity of 3,4-ethylenedioxythiophene derivatives and quantitative structure-activity relationship analysis

    NASA Astrophysics Data System (ADS)

    Jukić, Marijana; Rastija, Vesna; Opačak-Bernardi, Teuta; Stolić, Ivana; Krstulović, Luka; Bajić, Miroslav; Glavaš-Obrovac, Ljubica

    2017-04-01

    The aim of this study was to evaluate nine newly synthesized amidine derivatives of 3,4- ethylenedioxythiophene (3,4-EDOT) for their cytotoxic activity against a panel of human cancer cell lines and to perform a quantitative structure-activity relationship (QSAR) analysis for the antitumor activity of a total of 27 3,4-ethylenedioxythiophene derivatives. Induction of apoptosis was investigated on the selected compounds, along with delivery options for the optimization of activity. The best obtained QSAR models include the following group of descriptors: BCUT, WHIM, 2D autocorrelations, 3D-MoRSE, GETAWAY descriptors, 2D frequency fingerprint and information indices. Obtained QSAR models should be relieved in elucidation of important physicochemical and structural requirements for this biological activity. Highly potent molecules have a symmetrical arrangement of substituents along the x axis, high frequency of distance between N and O atoms at topological distance 9, as well as between C and N atoms at topological distance 10, and more C atoms located at topological distances 6 and 3. Based on the conclusion given in the QSAR analysis, a new compound with possible great activity was proposed.

  11. Lattice and strain analysis of atomic resolution Z-contrast images based on template matching.

    PubMed

    Zuo, Jian-Min; Shah, Amish B; Kim, Honggyu; Meng, Yifei; Gao, Wenpei; Rouviére, Jean-Luc

    2014-01-01

    A real space approach is developed based on template matching for quantitative lattice analysis using atomic resolution Z-contrast images. The method, called TeMA, uses the template of an atomic column, or a group of atomic columns, to transform the image into a lattice of correlation peaks. This is helped by using a local intensity adjusted correlation and by the design of templates. Lattice analysis is performed on the correlation peaks. A reference lattice is used to correct for scan noise and scan distortions in the recorded images. Using these methods, we demonstrate that a precision of few picometers is achievable in lattice measurement using aberration corrected Z-contrast images. For application, we apply the methods to strain analysis of a molecular beam epitaxy (MBE) grown LaMnO₃ and SrMnO₃ superlattice. The results show alternating epitaxial strain inside the superlattice and its variations across interfaces at the spatial resolution of a single perovskite unit cell. Our methods are general, model free and provide high spatial resolution for lattice analysis.

  12. Characterization of Tyrosine Nitration and Cysteine Nitrosylation Modifications by Metastable Atom-Activation Dissociation Mass Spectrometry

    NASA Astrophysics Data System (ADS)

    Cook, Shannon L.; Jackson, Glen P.

    2011-02-01

    The fragmentation behavior of nitrated and S-nitrosylated peptides were studied using collision induced dissociation (CID) and metastable atom-activated dissociation mass spectrometry (MAD-MS). Various charge states, such as 1+, 2+, 3+, 2-, of modified and unmodified peptides were exposed to a beam of high kinetic energy helium (He) metastable atoms resulting in extensive backbone fragmentation with significant retention of the post-translation modifications (PTMs). Whereas the high electron affinity of the nitrotyrosine moiety quenches radical chemistry and fragmentation in electron capture dissociation (ECD) and electron transfer dissociation (ETD), MAD does produce numerous backbone cleavages in the vicinity of the modification. Fragment ions of nitrosylated cysteine modifications typically exhibit more abundant neutral losses than nitrated tyrosine modifications because of the extremely labile nature of the nitrosylated cysteine residues. However, compared with CID, MAD produced between 66% and 86% more fragment ions, which preserved the labile -NO modification. MAD was also able to differentiate I/L residues in the modified peptides. MAD is able to induce radical ion chemistry even in the presence of strong radical traps and therefore offers unique advantages to ECD, ETD, and CID for determination of PTMs such as nitrated and S-nitrosylated peptides.

  13. Use of flameless atomic absorption spectroscopy in immune cytolysis for nonradioactive determination of killer cell activity.

    PubMed

    Borella, P; Bargellini, A; Salvioli, S; Cossarizza, A

    1996-02-01

    We describe here a novel method to evaluate natural killer (NK) cytolytic activity by use of flameless atomic absorption spectroscopy (GF-AAS). This technique may be adopted for use in laboratories equipped with electrothermal atomic absorption spectrometers. Nonradioactive Cr as Na2CrO4 was used to label target cells (K562), and cell lysis was evaluated by measuring Cr released after 4 h of incubation with the effectors. We selected 520 micrograms/L as the optimal dose for labeling targets, between 12 and 20 h as the optimal incubation time, and 10(4) cells as the optimal target size. Advantages of this method include: (a) exclusion of radioactive tracer, with no risk for workers; (b) limited costs; (c) high sensitivity and reproducibility; (d) possibility to store samples; and (e) better control of Cr used for labeling cells due to well-determined, fixed Cr concentrations in the range of nontoxic and linear cellular uptake. Comparison with data obtained by conventional 51Cr labeling of targets killed by the same effectors was excellent, yielding comparable results and corroborating the method.

  14. Atom probe tomography of reactor pressure vessel steels: an analysis of data integrity.

    PubMed

    Hyde, J M; Burke, M G; Gault, B; Saxey, D Wf; Styman, P; Wilford, K B; Williams, T J

    2011-05-01

    In this work, the importance of optimising experimental conditions for the analysis of reactor pressure vessel (RPV) steels using atom probe tomography is explored. The quality of the resultant atom probe data is assessed in terms of detection efficiency, noise levels and mass resolution. It is demonstrated that artefacts can exist even when experimental conditions have been optimised. In particular, it is shown that surface diffusion of some minority species, including P and Si, to major poles prior to field evaporation can be an issue. The effects were most noticeable during laser pulsing. The impact of surface migration on the characterisation of dislocations and grain boundaries is assessed. The importance of selecting appropriate regions of the reconstructed data for subsequent re-analysis is emphasised.

  15. Understanding amyloid aggregation by statistical analysis of atomic force microscopy images

    NASA Astrophysics Data System (ADS)

    Adamcik, Jozef; Jung, Jin-Mi; Flakowski, Jérôme; de Los Rios, Paolo; Dietler, Giovanni; Mezzenga, Raffaele

    2010-06-01

    The aggregation of proteins is central to many aspects of daily life, including food processing, blood coagulation, eye cataract formation disease and prion-related neurodegenerative infections. However, the physical mechanisms responsible for amyloidosis-the irreversible fibril formation of various proteins that is linked to disorders such as Alzheimer's, Creutzfeldt-Jakob and Huntington's diseases-have not yet been fully elucidated. Here, we show that different stages of amyloid aggregation can be examined by performing a statistical polymer physics analysis of single-molecule atomic force microscopy images of heat-denatured β-lactoglobulin fibrils. The atomic force microscopy analysis, supported by theoretical arguments, reveals that the fibrils have a multistranded helical shape with twisted ribbon-like structures. Our results also indicate a possible general model for amyloid fibril assembly and illustrate the potential of this approach for investigating fibrillar systems.

  16. Acting Atoms.

    ERIC Educational Resources Information Center

    Farin, Susan Archie

    1997-01-01

    Describes a fun game in which students act as electrons, protons, and neutrons. This activity is designed to help students develop a concrete understanding of the abstract concept of atomic structure. (DKM)

  17. Sensitivity Analysis Applied to Atomic Data Used for X-ray Spectrum Synthesis

    NASA Technical Reports Server (NTRS)

    Kallman, Tim

    2006-01-01

    A great deal of work has been devoted to the accumulation of accurate quantities describing atomic processes for use in analysis of astrophysical spectra. But in many situations of interest the interpretation of a quantity which is observed, such as a line flux, depends on the results of a modeling- or spectrum synthesis code. The results of such a code depends in turn 011 many atomic rates or cross sections, and the sensitivity of the observable quantity on the various rates and cross sections may be non-linear and if so cannot easily be derived analytically. In such cases the most practical approach to understanding the sensitivity of observables to atomic cross sections is to perform numerical experiments, by calculating models with various rates perturbed by random (but known) factors. In addition, it is useful to compare the results of such experiments with some sample observations, in order to focus attention on the rates which are of the greatest relevance to real observations. In this paper I will present some attempts to carry out this program, focussing on two sample datasets taken with the Chandra HETG. I will discuss the sensitivity of synthetic spectra to atomic data affecting ionization balance, temperature, and line opacity or emissivity, and discuss the implications for the ultimate goal of inferring astrophysical parameters.

  18. Sensitivity Analysis Applied to Atomic Data Used for X-ray Spectrum Synthesis

    NASA Technical Reports Server (NTRS)

    Kallman, Tim

    2006-01-01

    A great deal of work has been devoted to the accumulation of accurate quantities describing atomic processes for use in analysis of astrophysical spectra. But in many situations of interest the interpretation of a quantity which is observed, such as a line flux, depends on the results of a modeling- or spectrum synthesis code. The results of such a code depends in turn on many atomic rates or cross sections, and the sensitivity of the observable quantity on the various rates and cross sections may be non-linear and if so cannot easily be derived analytically. In such cases the most practical approach to understanding the sensitivity of observables to atomic cross sections is to perform numerical experiments, by calculating models with various rates perturbed by random (but known) factors. In addition, it is useful to compare the results of such experiments with some sample observations, in order to focus attention on the rates which are of the greatest relevance to real observations. In this paper I will present some attempts to carry out this program, focussing on two sample datasets taken with the Chandra HETG. I will discuss the sensitivity of synthetic spectra to atomic data affecting ionization balance, temperature, and line opacity or emissivity, and discuss the implications for the ultimate goal of inferring astrophysical parameters.

  19. Ultrasound-assisted emulsification of cosmetic samples prior to elemental analysis by different atomic spectrometric techniques.

    PubMed

    Lavilla, I; Cabaleiro, N; Costas, M; de la Calle, I; Bendicho, C

    2009-11-15

    In this work, ultrasound-assisted emulsification with a probe system is proposed as a rapid and simple sample treatment for atomic spectrometric determinations (Electrothermal Atomic Absorption Spectrometry, Inductively Coupled Plasma Optical Emission Spectrometry, Flame Atomic Absorption Spectrometry and Cold Vapour Atomic Absorption Spectrometry) of trace elements (As, Cd, Cr, Cu, Hg, Mg, Mn, Ni, Sr and Zn) in cosmetic samples such as shampoos, gel (hair gel), crèmes (body milk, hair conditioner) and oil (body oil). The type of dispersion medium, the sample mass-to-dispersion medium volume ratio, as well as the parameters related to the ultrasound-assisted emulsification (sonication amplitude and treatment time) were exhaustively studied. Only 1 min of ultrasonic shaking and a dispersion medium containing 0.5% (w/v) of SDS+3% (v/v) of HNO(3) or HCl allows obtaining a stable emulsion at least for 3 months. Thermal programs, nebulization of emulsions, speed of pumps and concentration of reagents used in cold vapour generation were optimized. Calibration using aqueous standards was feasible in all cases. Calibration by the standard addition method and recovery studies was also applied for validation. Microwave-assisted digestion and Inductively Coupled Plasma Mass Spectrometry were used for comparison purposes. Relative standard deviations from analysis of five independent emulsions were less than 9% in all cases.

  20. Research Update: Spatially resolved mapping of electronic structure on atomic level by multivariate statistical analysis

    DOE PAGES

    Belianinov, Alex; Panchapakesan, G.; Lin, Wenzhi; ...

    2014-12-02

    Atomic level spatial variability of electronic structure in Fe-based superconductor FeTe0.55Se0.45 (Tc = 15 K) is explored using current-imaging tunneling-spectroscopy. Multivariate statistical analysis of the data differentiates regions of dissimilar electronic behavior that can be identified with the segregation of chalcogen atoms, as well as boundaries between terminations and near neighbor interactions. Subsequent clustering analysis allows identification of the spatial localization of these dissimilar regions. Similar statistical analysis of modeled calculated density of states of chemically inhomogeneous FeTe1 x Sex structures further confirms that the two types of chalcogens, i.e., Te and Se, can be identified by their electronic signaturemore » and differentiated by their local chemical environment. This approach allows detailed chemical discrimination of the scanning tunneling microscopy data including separation of atomic identities, proximity, and local configuration effects and can be universally applicable to chemically and electronically inhomogeneous surfaces.« less

  1. Research Update: Spatially resolved mapping of electronic structure on atomic level by multivariate statistical analysis

    SciTech Connect

    Belianinov, Alex Ganesh, Panchapakesan; Lin, Wenzhi; Jesse, Stephen; Pan, Minghu; Kalinin, Sergei V.; Sales, Brian C.; Sefat, Athena S.

    2014-12-01

    Atomic level spatial variability of electronic structure in Fe-based superconductor FeTe{sub 0.55}Se{sub 0.45} (T{sub c} = 15 K) is explored using current-imaging tunneling-spectroscopy. Multivariate statistical analysis of the data differentiates regions of dissimilar electronic behavior that can be identified with the segregation of chalcogen atoms, as well as boundaries between terminations and near neighbor interactions. Subsequent clustering analysis allows identification of the spatial localization of these dissimilar regions. Similar statistical analysis of modeled calculated density of states of chemically inhomogeneous FeTe{sub 1−x}Se{sub x} structures further confirms that the two types of chalcogens, i.e., Te and Se, can be identified by their electronic signature and differentiated by their local chemical environment. This approach allows detailed chemical discrimination of the scanning tunneling microscopy data including separation of atomic identities, proximity, and local configuration effects and can be universally applicable to chemically and electronically inhomogeneous surfaces.

  2. Microencapsulation effectiveness of small active molecules in biopolymer by ultrasonic atomization technique.

    PubMed

    Cascone, Sara; Lamberti, Gaetano; Titomanlio, Giuseppe; Barba, Anna Angela; d'Amore, Matteo

    2012-12-01

    A method to produce biopolymeric (alginate) microparticles by ultrasonic assisted atomization, previously developed, has been applied to the production of microparticles loaded with a small active molecule (theophylline). Fine loaded alginate droplets have been cross-linked with divalent ions to produce microparticles. Once produced, the particles have been separated by centrifugation or filtration and then they have been dried. Drug release has been evaluated by dissolution tests, dissolving the dried particles in acidic solution at pH 1 for a given time and then at pH 7 to simulate the stomach and intestinal environment, respectively. The encapsulation efficiency and the drug loading have been investigated and the operating conditions have been changed to clarify the role of the transport phenomena on the overall process. To increase the drug loading, shorter separation time and better network's structure were identified as the key operating parameters to allow the process to gain interest from a practical point of view.

  3. Aldose reductase inhibitors for diabetic complications: Receptor induced atom-based 3D-QSAR analysis, synthesis and biological evaluation.

    PubMed

    Vyas, Bhawna; Singh, Manjinder; Kaur, Maninder; Bahia, Malkeet Singh; Jaggi, Amteshwar Singh; Silakari, Om; Singh, Baldev

    2015-06-01

    Herein, atom-based 3D-QSAR analysis was performed using receptor-guided alignment of 46 flavonoid inhibitors of aldose reductase (ALR2) enzyme. 3D-QSAR models were generated in PHASE programme, and the best model corresponding to PLS factor four (QSAR4), was selected based on different statistical parameters (i.e., Rtrain(2), 0.96; Qtest(2) 0.81; SD, 0.26). The contour plots of different structural properties generated from the selected model were utilized for the designing of five new congener molecules. These designed molecules were duly synthesized, and evaluated for their in vitro ALR2 inhibitory activity that resulted in the micromolar (IC50<22μM) activity of all molecules. Thus, the newly designed molecules having ALR inhibitory potential could be employed for the management of diabetic complications.

  4. Note: Artificial neural networks for the automated analysis of force map data in atomic force microscopy

    SciTech Connect

    Braunsmann, Christoph; Schäffer, Tilman E.

    2014-05-15

    Force curves recorded with the atomic force microscope on structured samples often show an irregular force versus indentation behavior. An analysis of such curves using standard contact models (e.g., the Sneddon model) would generate inaccurate Young's moduli. A critical inspection of the force curve shape is therefore necessary for estimating the reliability of the generated Young's modulus. We used a trained artificial neural network to automatically recognize curves of “good” and of “bad” quality. This is especially useful for improving the analysis of force maps that consist of a large number of force curves.

  5. Opacity and atomic analysis of double pulse laser ablated Li plasma

    NASA Astrophysics Data System (ADS)

    Sivakumaran, V.; Joshi, H. C.; Kumar, Ajai

    2014-09-01

    Opacity effects for neutral and ionic emission lines of lithium have been investigated by Atomic Data Analysis Structure (ADAS). Line ratios and opacity corrected photon emissivity coefficients are calculated over a wide range of electron temperatures and densities. The experimentally measured temporal evolution of the line profiles of the over dense Li plasma formed in the double pulse laser ablation experiment have been explained using the ADAS analysis and the plasma parameters of the plasma plume under consideration have been estimated. These results could be projected as a diagnostic tool to estimate plasma parameters of an over dense lithium plasma.

  6. A correlational analysis of the effects of changing environmental conditions on the NR atomic hydrogen maser

    NASA Technical Reports Server (NTRS)

    Dragonette, Richard A.; Suter, Joseph J.

    1992-01-01

    An extensive statistical analysis has been undertaken to determine if a correlation exists between changes in an NR atomic hydrogen maser's frequency offset and changes in environmental conditions. Correlation analyses have been performed comparing barometric pressure, humidity, and temperature with maser frequency offset as a function of time for periods ranging from 5.5 to 17 days. Semipartial correlation coefficients as large as -0.9 have been found between barometric pressure and maser frequency offset. Correlation between maser frequency offset and humidity was small compared to barometric pressure and unpredictable. Analysis of temperature data indicates that in the most current design, temperature does not significantly affect maser frequency offset.

  7. The role of atomic excited states of Au on N2O capture and activation: a multireference second-order perturbation theory study.

    PubMed

    Olvera-Neria, Oscar; Bertin, Virineya; Poulain, Enrique

    2010-12-28

    Nitrous oxide (N(2)O) is an intermediate compound formed during catalysis occurring in automobile exhaust pipes. Atomic Au in its ground state is unable to react with N(2)O, however, several Au excited states are bound to N(2)O, but not all of these states are able to activate N(2)O bonds. In this work, N(2)O capture and activation by a single Au atom are studied considering Au in the ground and excited states with multiplicities = 2, 4 and 6. The Au + N(2)O reactions are studied at multireference second-order perturbation level of theory using C(s) symmetry. The AuN(2)O ((4)A', (4)A'', (6)A' and (6)A'') adducts are spontaneously created from Au excited states. From these complexes, only the (4)A', (6)A' and (6)A'' states exhibit N(2)O activation reaction paths yielding N(2,) NO and O atoms as end products when N(2)O approaches Au excited states side-on. Cations both ground and excited states, capture N(2)O although only the Au(+) ((5)A') + N(2)O ((1)Σ(+)) → NAuNO(+) ((5)A') reaction (for the end-on and side-on approaches) shows N(2)O activation with N-N bond breaking. In the case of Au anions, the ground state and most of the excited states capture N(2)O and activation takes place according to Au(-) ((3)A', (5)A', (5)A'') + N(2)O ((1)Σ(+)) → AuO(-) ((3)A', (5)A', (5)A'') + N(2)(g) for the N(2)O end-on approach by the oxygen atom. The reaction paths show a metal-gas dative covalent bonding character. Mulliken charge population analysis obtained for the active states shows that the binding is done through charge donation and retro-donation between the metal and the N(2)O molecule.

  8. The role of atomic excited states of Au on N2O capture and activation: A multireference second-order perturbation theory study

    NASA Astrophysics Data System (ADS)

    Olvera-Neria, Oscar; Bertin, Virineya; Poulain, Enrique

    2010-12-01

    Nitrous oxide (N2O) is an intermediate compound formed during catalysis occurring in automobile exhaust pipes. Atomic Au in its ground state is unable to react with N2O, however, several Au excited states are bound to N2O, but not all of these states are able to activate N2O bonds. In this work, N2O capture and activation by a single Au atom are studied considering Au in the ground and excited states with multiplicities = 2, 4 and 6. The Au + N2O reactions are studied at multireference second-order perturbation level of theory using Cs symmetry. The AuN2O (4A', 4A'', 6A' and 6A'') adducts are spontaneously created from Au excited states. From these complexes, only the 4A', 6A' and 6A'' states exhibit N2O activation reaction paths yielding N2, NO and O atoms as end products when N2O approaches Au excited states side-on. Cations both ground and excited states, capture N2O although only the Au+ (5A') + N2O (1Σ+) → NAuNO+ (5A') reaction (for the end-on and side-on approaches) shows N2O activation with N-N bond breaking. In the case of Au anions, the ground state and most of the excited states capture N2O and activation takes place according to Au- (3A', 5A', 5A'') + N2O (1Σ+) → AuO- (3A', 5A', 5A'') + N2(g) for the N2O end-on approach by the oxygen atom. The reaction paths show a metal-gas dative covalent bonding character. Mulliken charge population analysis obtained for the active states shows that the binding is done through charge donation and retro-donation between the metal and the N2O molecule.

  9. Analysis of lithium in deep basalt groundwaters using graphite furnace atomic absorption spectrophotometry

    SciTech Connect

    Dill, J.A.; Marcy, A.D.

    1986-05-01

    Lithium is under consideration for use as a reactive (sorptive) tracer in experiments designed to provide information regarding natural attenuation processes in a basalt-groundwater environment. In support of these activities, background lithium concentrations in samples obtained from a variety of test horizons have been determined using graphite furnace atomic absorption spectrophotometry. Significant interference was observed in these determinations and was found to be due to the presence of silicate in the samples. It was found that these problems could be circumvented through the use of alkaline silicate or synthetic groundwater matrix modifiers. This matrix effect was examined in some detail. Results obtained using the graphite furnace were compared to results obtained using inductively coupled plasma atomic emission spectroscopy.

  10. [Application of atomic emission spectroscopy analysis in the atmospheric pressure plasma polishing process study].

    PubMed

    Wang, Bo; Zhang, Ju-Fan; Dong, Shen

    2008-07-01

    The atmospheric pressure plasma polishing (APPP) is a novel precision machining technology. It performs the atom scale material removal based on low temperature plasma chemical reactions. As the machining process is chemical in nature, it avoids the surface/subsurface defects usually formed in conventional mechanical machining processes. APPP firstly introduces a capacitance coupled radio frequency (RF) plasma torch to generate reactive plasma and excite chemical reactions further. The removal process is a complicated integrating action which tends to be affected by many factors, such as the gas ratio, the RF power and so on. Therefore, to improve the machining quality, all the aspects should be considered and studied, to establish the foundation for further model building and theoretical analysis. The atomic emission spectroscopy analysis was used to study the process characteristics. A commercial micro spectrometer was used to collect the spectrograms under different parameters, by comparing which the influence of the RF power and gas ratio was initially studied. The analysis results indicate that an increase in RF power results in a higher removal rate within a certain range. The gas ratio doesn't show obvious influence on the removal rate and surface roughness in initial experiments, but the element compositions detected by X-ray photoelectron spectroscopy technology on the machined surfaces under different ratios really indicate distinct difference. Then the theoretical analysis revealed the corresponding electron transition orbits of the excited reactive fluorine atoms, which is necessary for further mechanism research and apparatus improvement. Then the initial process optimization was made based on the analysis results, by which the Ra 0.6 nm surface roughness and 32 mm3 x min(-1) removal rate were achieved on silicon wafers.

  11. Design and analysis of control system for VCSEL of atomic interference magnetometer

    NASA Astrophysics Data System (ADS)

    Zhang, Xiao-nan; Sun, Xiao-jie; Kou, Jun; Yang, Feng; Li, Jie; Ren, Zhang; Wei, Zong-kang

    2016-11-01

    Magnetic field detection is an important means of deep space environment exploration. Benefit from simple structure and low power consumption, atomic interference magnetometer become one of the most potential detector payloads. Vertical Cavity Surface Emitting Laser (VCSEL) is usually used as a light source in atomic interference magnetometer and its frequency stability directly affects the stability and sensitivity of magnetometer. In this paper, closed-loop control strategy of VCSEL was designed and analysis, the controller parameters were selected and the feedback error algorithm was optimized as well. According to the results of experiments that were performed on the hardware-in-the-loop simulation platform, the designed closed-loop control system is reasonable and it is able to effectively improve the laser frequency stability during the actual work of the magnetometer.

  12. Analysis of 2015 Meteorological Data from the Bettis Atomic Power Laboratory

    SciTech Connect

    Aluzzi, F. J.

    2016-02-19

    The Bettis Atomic Power Laboratory (Bettis) in West Miffin, PA is required to estimate the effects of hypothetical emissions of radiological material from its facility by the U.S. Environmental Protection Agency (EPA). An atmospheric dispersion model known as CAP88, which was developed and approved by the EPA for such purposes, is used by Bettis to meet this requirement. CAP88 calculations over a given time period are based on statistical data on the meteorological conditions for that period. The Bettis facility has an on-site meteorological tower which takes atmospheric measurements at a frequency ideal for EPA regulatory model input. However, an independent analysis and processing of the meteorological data from the site tower is required to derive a data set appropriate for use in the CAP88 model. The National Atmospheric Release Advisory Center (NARAC) was contracted by the Bettis Atomic Power Laboratory to process the on-site meteorological data for the calendar year 2015.

  13. An atom trap trace analysis system for measuring krypton contamination in xenon dark matter detectors

    SciTech Connect

    Aprile, E.; Yoon, T.; Loose, A.; Goetzke, L. W.; Zelevinsky, T.

    2013-09-15

    We have developed an atom trap trace analysis (ATTA) system to measure Kr in Xe at the part per trillion (ppt) level, a prerequisite for the sensitivity achievable with liquid xenon dark matter detectors beyond the current generation. Since Ar and Kr have similar laser cooling wavelengths, the apparatus has been tested with Ar to avoid contamination prior to measuring Xe samples. A radio-frequency plasma discharge generates a beam of metastable atoms which is optically collimated, slowed, and trapped using standard magneto-optical techniques. Based on the measured overall system efficiency of 1.2 × 10{sup −8} (detection mode), we expect the ATTA system to reach the design goal sensitivity to ppt concentrations of Kr in Xe in <2 h.

  14. Revisiting the Dielectric Constant Effect on the Nucleophile and Leaving Group of Prototypical Backside Sn2 Reactions: a Reaction Force and Atomic Contribution Analysis.

    PubMed

    Pedraza-González, Laura Milena; Galindo, Johan Fabian; Gonzalez, Ronald; Reyes, Andrés

    2016-10-09

    The solvent effect on the nucleophile and leaving group atoms of the prototypical F(-) + CH3Cl → CH3F + Cl(-) backside bimolecular nucleophilic substitution reaction (SN2) is analyzed employing the reaction force and the atomic contributions methods on the intrinsic reaction coordinate (IRC). Solvent effects were accounted for using the polarizable continuum solvent model. Calculations were performed employing eleven dielectric constants, ε, ranging from 1.0 to 78.5, to cover a wide spectrum of solvents. The reaction force data reveals that the solvent mainly influences the region of the IRC preceding the energy barrier, where the structural rearrangement to reach the transition state occurs. A detailed analysis of the atomic role in the reaction as a function of ε reveals that the nucleophile and the carbon atom are the ones that contribute the most to the energy barrier. In addition, we investigated the effect of the choice of nucleophile and leaving group on the ΔE0 and ΔE(↕) of Y(-) + CH3X → YCH3 + X(-) (X,Y= F, Cl, Br, I) in aqueous solution. Our analysis allowed us to find relationships between the atomic contributions to the activation energy and leaving group ability and nucleophilicity.

  15. Synthesis of nanoporous activated iridium oxide films by anodized aluminum oxide templated atomic layer deposition.

    SciTech Connect

    Comstock, D. J.; Christensen, S. T.; Elam, J. W.; Pellin, M. J.; Hersam, M. C.

    2010-08-01

    Iridium oxide (IrOx) has been widely studied due to its applications in electrochromic devices, pH sensing, and neural stimulation. Previous work has demonstrated that both Ir and IrOx films with porous morphologies prepared by sputtering exhibit significantly enhanced charge storage capacities. However, sputtering provides only limited control over film porosity. In this work, we demonstrate an alternative scheme for synthesizing nanoporous Ir and activated IrOx films (AIROFs). This scheme utilizes atomic layer deposition to deposit a thin conformal Ir film within a nanoporous anodized aluminum oxide template. The Ir film is then activated by potential cycling in 0.1 M H{sub 2}SO{sub 4} to form a nanoporous AIROF. The morphologies and electrochemical properties of the films are characterized by scanning electron microscopy and cyclic voltammetry, respectively. The resulting nanoporous AIROFs exhibit a nanoporous morphology and enhanced cathodal charge storage capacities as large as 311 mC/cm{sup 2}.

  16. A Near-Atomic Structure of the Dark Apoptosome Provides Insight into Assembly and Activation.

    PubMed

    Cheng, Tat Cheung; Akey, Ildikó V; Yuan, Shujun; Yu, Zhiheng; Ludtke, Steven J; Akey, Christopher W

    2017-01-03

    In Drosophila, the Apaf-1-related killer (Dark) forms an apoptosome that activates procaspases. To investigate function, we have determined a near-atomic structure of Dark double rings using cryo-electron microscopy. We then built a nearly complete model of the apoptosome that includes 7- and 8-blade β-propellers. We find that the preference for dATP during Dark assembly may be governed by Ser325, which is in close proximity to the 2' carbon of the deoxyribose ring. Interestingly, β-propellers in V-shaped domains of the Dark apoptosome are more widely separated, relative to these features in the Apaf-1 apoptosome. This wider spacing may be responsible for the lack of cytochrome c binding to β-propellers in the Dark apoptosome. Our structure also highlights the roles of two loss-of-function mutations that may block Dark assembly. Finally, the improved model provides a framework to understand apical procaspase activation in the intrinsic cell death pathway.

  17. Determination of nickel in active pharmaceutical ingredients by electrothermal atomic absorption spectrometry.

    PubMed

    Bubnič, Zoran; Urleb, Uroš; Kreft, Katjuša; Veber, Marjan

    2010-03-01

    An electrothermal atomic absorption spectrometric procedure for the determination of nickel in active pharmaceutical ingredients was developed. Since the recoveries of nickel by the direct dissolution of samples in diluted nitric acid were low and caused errors in the determination of Ni in pharmaceutical samples, different approaches for sample pre-treatment were examined. It was found that the microwave digestion was the most suitable way for sample preparation. Various combinations of digestion agents and different microwave conditions were tested. The combination of nitric acid and hydrogen peroxide was found to be the most appropriate. The validity of the method was evaluated by recovery studies of spiked samples and by the comparison of the results obtained by inductively coupled plasma mass spectrometry (ICP-MS). The recovery ranged from 87.5 to 104.0% and a good agreement was achieved between both methods. The detection limit and the limit of quantification were 0.6 and 2.1 µg g-1 respectively. The precision of the method was confirmed by the determination of Ni in the spiked samples and was below 4%, expressed in terms of a relative standard deviation. The method was applied to the determination of nickel in production samples of active pharmaceutical ingredients and intermediates.

  18. Prompt-Gamma Activation Analysis.

    PubMed

    Lindstrom, Richard M

    1993-01-01

    A permanent, full-time instrument for prompt-gamma activation analysis is nearing completion as part of the Cold Neutron Research Facility (CNRF). The design of the analytical system has been optimized for high gamma detection efficiency and low background, particularly for hydrogen. Because of the purity of the neutron beam, shielding requirements are modest and the scatter-capture background is low. As a result of a compact sample-detector geometry, the sensitivity (counting rate per gram of analyte) is a factor of four better than the existing Maryland-NIST thermal-neutron instrument at this reactor. Hydrogen backgrounds of a few micrograms have already been achieved, which promises to be of value in numerous applications where quantitative nondestructive analysis of small quantities of hydrogen in materials is necessary.

  19. First dating of groundwater with Atom Trap Trace Analysis of 39Ar - technique

    NASA Astrophysics Data System (ADS)

    Ritterbusch, Florian; Ebser, Sven; Welte, Joachim; Reichel, Thomas; Kersting, Arne; Purtschert, Roland; Aeschbach-Hertig, Werner; Oberthaler, Markus K.

    2013-04-01

    The importance of 39Ar as a dating tracer for the time range between 50 and 1000 years has clearly been identified [1]. So far, it has been routinely accessible only by Low-Level-Counting (LLC) in the underground laboratory in Bern requiring a sample size of several tons of water and a measuring time of several weeks [2]. Here we report on the first dating results with 39Ar using an atom optical technique known as Atom Trap Trace Analysis (ATTA). This method has been developed for rare krypton isotopes in the past decade and is now available for routine analysis [3]. However, the applicability of ATTA to 39Ar has only been demonstrated in a proof of principle experiment [4]. We will discuss the essential experimental improvements that were necessary for bringing this method to the level of dating real samples. Our apparatus achieves an atmospheric 39Ar-count-rate of 4.1(3) atoms/h, which corresponds to an 18-fold improvement over the reported results in [4]. Based on that, we dated a groundwater sample of the upper Rhine Graben to 360(68) years within one day of measurement. Further samples of the investigated aquifer system are dated similarly in order to obtain the age information for a comprehensive hydrological study. The apparatus has the potential to measure 39Ar-concentrations on small samples down to less than 1 ccSTP of Argon, corresponding to about 100 ml of air, 2.5 l of water or 1 kg of ice. This opens up the way for a broader application of 39Ar as a tracer e.g. in oceanography or glaciology, where the sample sizes are typically limited to 10 l of water or 1 kg of ice respectively. [1] Loosli, H. H. (1983), A dating method with 39Ar, Earth and Planetary Science Letters, 63, 51-62. [2] P. Collon, W. Kutschera, and Z.-T. Lu. Tracing noble gas radionuclides in the environment. Annual Review of Nuclear and Particle Science, 54(1): 39-67, 2004. [3] W. Jiang et al., An atom counter for measuring 81Kr and 85Kr in environmental samples. Geochimica et

  20. Determination of atomic oxygen fluence using spectrophotometric analysis of infrared transparent witness coupons for long duration exposure tests

    NASA Technical Reports Server (NTRS)

    Podojil, Gregg M.; Jaworske, Donald A.

    1993-01-01

    Atomic oxygen degradation is one of several major threats to the durability of spaceborne systems in low Earth orbit. Ground-based simulations are conducted to learn how to minimize the adverse effects of atomic oxygen exposure. Assessing the fluence of atomic oxygen in test chambers such as a plasma asher over long periods of time is necessary for accurate determination of atomic oxygen exposure. Currently, an atomic oxygen susceptible organic material such as Kapton is placed next to samples as a witness coupon and its mass loss is monitored and used to determine the effective atomic oxygen fluence. However, degradation of the Kapton witness coupons occurs so rapidly in plasma ashers that for any long term test many witness coupons must be used sequentially in order to keep track of the fluence. This necessitates opening vacuum to substitute fresh coupons. A passive dosimetry technique was sought to monitor atomic oxygen exposure over longer periods without the need to open the plasma asher to the atmosphere. This paper investigates the use of spectrophotometric analysis of durable IR transparent witness coupons to measure atomic oxygen exposure for longer duration testing. The method considered would be conductive to making in situ measurements of atomic oxygen fluence.

  1. {sup 39}Ar Detection at the 10{sup -16} Isotopic Abundance Level with Atom Trap Trace Analysis

    SciTech Connect

    Jiang, W.; Williams, W.; Bailey, K.; O'Connor, T. P.; Mueller, P.; Davis, A. M.; Hu, S.-M.; Sun, Y. R.; Lu, Z.-T.; Purtschert, R.; Sturchio, N. C.

    2011-03-11

    Atom trap trace analysis, a laser-based atom counting method, has been applied to analyze atmospheric {sup 39}Ar (half-life=269 yr), a cosmogenic isotope with an isotopic abundance of 8x10{sup -16}. In addition to the superior selectivity demonstrated in this work, the counting rate and efficiency of atom trap trace analysis have been improved by 2 orders of magnitude over prior results. The significant applications of this new analytical capability lie in radioisotope dating of ice and water samples and in the development of dark matter detectors.

  2. Quantum-mechanical theory including angular momenta analysis of atom-atom collisions in a laser field

    NASA Technical Reports Server (NTRS)

    Devries, P. L.; George, T. F.

    1978-01-01

    The problem of two atoms colliding in the presence of an intense radiation field, such as that of a laser, is investigated. The radiation field, which couples states of different electronic symmetry, is described by the number state representation while the electronic degrees of freedom (plus spin-orbit interaction) are discussed in terms of a diabatic representation. The total angular momentum of the field-free system and the angular momentum transferred by absorption (or emission) of a photon are explicitly considered in the derivation of the coupled scattering equations. A model calculation is discussed for the Xe + F collision system.

  3. Nanosystem Self-Assembly Pathways Discovered via All-Atom Multiscale Analysis

    PubMed Central

    Pankavich, Stephen D.; Ortoleva, Peter J.

    2012-01-01

    We consider the self-assembly of composite structures from a group of nanocomponents, each consisting of particles within an N-atom system. Self-assembly pathways and rates for nanocomposites are derived via a multiscale analysis of the classical Liouville equation. From a reduced statistical framework, rigorous stochastic equations for population levels of beginning, intermediate, and final aggregates are also derived. It is shown that the definition of an assembly type is a self-consistency criterion that must strike a balance between precision and the need for population levels to be slowly varying relative to the timescale of atomic motion. The deductive multiscale approach is complemented by a qualitative notion of multicomponent association and the ensemble of exact atomic-level configurations consistent with them. In processes such as viral self-assembly from proteins and RNA or DNA, there are many possible intermediates so that it is usually difficult to predict the most efficient assembly pathway. However, in the current study rates of assembly of each possible intermediate can be predicted. This avoids the need, as in a phenomenological approach, for recalibration with each new application. The method accounts for the feedback across scales in space and time that is fundamental to nanosystem self-assembly. The theory has applications to bionanostructures, geomaterials, engineered composites, and nanocapsule therapeutic delivery systems. PMID:22372746

  4. Atomically monodisperse nickel nanoclusters as highly active electrocatalysts for water oxidation

    NASA Astrophysics Data System (ADS)

    Joya, Khurram S.; Sinatra, Lutfan; Abdulhalim, Lina G.; Joshi, Chakra P.; Hedhili, M. N.; Bakr, Osman M.; Hussain, Irshad

    2016-05-01

    Achieving water splitting at low overpotential with high oxygen evolution efficiency and stability is important for realizing solar to chemical energy conversion devices. Herein we report the synthesis, characterization and electrochemical evaluation of highly active nickel nanoclusters (Ni NCs) for water oxidation at low overpotential. These atomically precise and monodisperse Ni NCs are characterized by using UV-visible absorption spectroscopy, single crystal X-ray diffraction and mass spectrometry. The molecular formulae of these Ni NCs are found to be Ni4(PET)8 and Ni6(PET)12 and are highly active electrocatalysts for oxygen evolution without any pre-conditioning. Ni4(PET)8 are slightly better catalysts than Ni6(PET)12 which initiate oxygen evolution at an amazingly low overpotential of ~1.51 V (vs. RHE; η ~ 280 mV). The peak oxygen evolution current density (J) of ~150 mA cm-2 at 2.0 V (vs. RHE) with a Tafel slope of 38 mV dec-1 is observed using Ni4(PET)8. These results are comparable to the state-of-the-art RuO2 electrocatalyst, which is highly expensive and rare compared to Ni-based materials. Sustained oxygen generation for several hours with an applied current density of 20 mA cm-2 demonstrates the long-term stability and activity of these Ni NCs towards electrocatalytic water oxidation. This unique approach provides a facile method to prepare cost-effective, nanoscale and highly efficient electrocatalysts for water oxidation.Achieving water splitting at low overpotential with high oxygen evolution efficiency and stability is important for realizing solar to chemical energy conversion devices. Herein we report the synthesis, characterization and electrochemical evaluation of highly active nickel nanoclusters (Ni NCs) for water oxidation at low overpotential. These atomically precise and monodisperse Ni NCs are characterized by using UV-visible absorption spectroscopy, single crystal X-ray diffraction and mass spectrometry. The molecular formulae of these

  5. Integrated atomic force microscopy techniques for analysis of biomaterials: Study of membrane proteins

    NASA Astrophysics Data System (ADS)

    Connelly, Laura S.

    Atomic Force Microscopy (AFM) is the prominent techniques for structural studies of biological materials in physiological relevant fluidic environments. AFM has been used to resolve the three-dimensional (3D) surface structure of cells, membranes, and proteins structures. Ion channels, formed by membrane proteins, are the key structures that control the activity of all living systems. This dissertation focuses on the structural evaluation of membrane proteins through atomic force microscopy. In Part I, AFM is utilized to study one of the most prominent medical issues facing our society, Alzheimer's Disease (AD). AD is a misfolded protein disease characterized by the accumulation of beta-amyloid (Abeta) peptide as senile plaques, progressive neurodegeneration, and memory loss. Recent evidence suggests that AD pathology is linked to the destabilization of cellular ionic homeostasis mediated by toxic channel structures composed of Abeta peptides. Selectively engineered sequences of Abeta were examined by AFM to elucidate the substructures and thus activity Abeta channels. Key residues were evaluated with the intent better understand the exact nature by which these pores conduct electrical and molecular signals, which could aid in identifying potential therapeutic targets for the prevention/treatment of AD. Additionally, AFM was used to analyze brain derived Abeta and newly developed pharmacological agents to study membranes and Abeta. Part II, presents a novel technology that incorporates electrophysiology into the AFM interface, enabling simultaneous imaging and complementary conductance measurements. The activity of ion channels is studied by various techniques, including patch clamp, free standing lipid bilayers, droplet interface bilayers, and supported lipid bilayers. However, direct correlation with channel structures has remained a challenge. The integrated atomic force microscopy system presented offers a solution to this challenge. The functionality of the

  6. Full quantum mechanical analysis of atomic three-grating Mach–Zehnder interferometry

    SciTech Connect

    Sanz, A.S.; Davidović, M.; Božić, M.

    2015-02-15

    Atomic three-grating Mach–Zehnder interferometry constitutes an important tool to probe fundamental aspects of the quantum theory. There is, however, a remarkable gap in the literature between the oversimplified models and robust numerical simulations considered to describe the corresponding experiments. Consequently, the former usually lead to paradoxical scenarios, such as the wave–particle dual behavior of atoms, while the latter make difficult the data analysis in simple terms. Here these issues are tackled by means of a simple grating working model consisting of evenly-spaced Gaussian slits. As is shown, this model suffices to explore and explain such experiments both analytically and numerically, giving a good account of the full atomic journey inside the interferometer, and hence contributing to make less mystic the physics involved. More specifically, it provides a clear and unambiguous picture of the wavefront splitting that takes place inside the interferometer, illustrating how the momentum along each emerging diffraction order is well defined even though the wave function itself still displays a rather complex shape. To this end, the local transverse momentum is also introduced in this context as a reliable analytical tool. The splitting, apart from being a key issue to understand atomic Mach–Zehnder interferometry, also demonstrates at a fundamental level how wave and particle aspects are always present in the experiment, without incurring in any contradiction or interpretive paradox. On the other hand, at a practical level, the generality and versatility of the model and methodology presented, makes them suitable to attack analogous problems in a simple manner after a convenient tuning. - Highlights: • A simple model is proposed to analyze experiments based on atomic Mach–Zehnder interferometry. • The model can be easily handled both analytically and computationally. • A theoretical analysis based on the combination of the position and

  7. Learning about Modes in Atomic Force Microscopy by Means of Hands-On Activities Based on a Simple Apparatus

    ERIC Educational Resources Information Center

    Phuapaiboon, Unchada; Panijpan, Bhinyo; Osotchan, Tanakorn

    2009-01-01

    This study was conducted to examine the results of using a low-cost hands-on setup in combination with accompanying activities to promote understanding of the contact mode of atomic force microscopy (AFM). This contact mode setup enabled learners to study how AFM works by hand scanning using probing cantilevers with different characteristics on…

  8. Catalytic activation of OKO zeolite with intersecting pores of 10- and 12-membered rings using atomic layer deposition of aluminium.

    PubMed

    Verheyen, E; Pulinthanathu Sree, S; Thomas, K; Dendooven, J; De Prins, M; Vanbutsele, G; Breynaert, E; Gilson, J-P; Kirschhock, C E A; Detavernier, C; Martens, J A

    2014-05-07

    Tetrahedral framework aluminium was introduced in all-silica zeolite -COK-14 using Atomic Layer Deposition (ALD) involving alternating exposure to trimethylaluminium and water vapour. The modification causes permanent conversion of the originally interrupted framework of -COK-14 to a fully connected OKO type framework, and generates catalytic activity in the acid catalysed hydrocarbon conversion reaction.

  9. Error analysis for momentum conservation in Atomic-Continuum Coupled Model

    NASA Astrophysics Data System (ADS)

    Yang, Yantao; Cui, Junzhi; Han, Tiansi

    2016-08-01

    Atomic-Continuum Coupled Model (ACCM) is a multiscale computation model proposed by Xiang et al. (in IOP conference series materials science and engineering, 2010), which is used to study and simulate dynamics and thermal-mechanical coupling behavior of crystal materials, especially metallic crystals. In this paper, we construct a set of interpolation basis functions for the common BCC and FCC lattices, respectively, implementing the computation of ACCM. Based on this interpolation approximation, we give a rigorous mathematical analysis of the error of momentum conservation equation introduced by ACCM, and derive a sequence of inequalities that bound the error. Numerical experiment is carried out to verify our result.

  10. Thermodynamic analysis of liquid bridge for fixed volume in atomic force microscope

    NASA Astrophysics Data System (ADS)

    Wei, Zheng; He, MengFu; Zhao, WenBin; Li, Yang

    2013-10-01

    In ambient condition, capillary forces are the major contributors to the adhesive forces between the tip of an atomic force microscope (AFM) and the sample. In general, capillary forces are thought to be related to water film thickness, contact time and relative humidity and so on. In this paper, an original analysis regarding the liquid bridge, based on the surface and interface thermodynamic theory, is proposed. The cases covered in the study include the capillary forces and temperature of liquid bridge for quickly drawn liquid bridge, and for nonvolatile liquid bridge. The study results show that variation in temperature may occur in the liquid bridge when it is stretched.

  11. Energy landscape investigation by wavelet transform analysis of atomic force spectroscopy data in a biorecognition experiment.

    PubMed

    Bizzarri, Anna Rita

    2016-01-01

    Force fluctuations recorded in an atomic force spectroscopy experiment, during the approach of a tip functionalized with biotin towards a substrate charged with avidin, have been analyzed by a wavelet transform. The observation of strong transient changes only when a specific biorecognition process between the partners takes place suggests a drastic modulation of the force fluctuations when biomolecules recognize each other. Such an analysis allows to investigate the peculiar features of a biorecognition process. These results are discussed in connection with the possible role of energy minima explored by biomolecules during the biorecognition process.

  12. Antimalarial activity of molecules interfering with Plasmodium falciparum phospholipid metabolism. Structure-activity relationship analysis.

    PubMed

    Calas, M; Cordina, G; Bompart, J; Ben Bari, M; Jei, T; Ancelin, M L; Vial, H

    1997-10-24

    A series of 80 compounds, primary, secondary, and tertiary amines and quaternary ammonium and bisammonium salts, most of them synthesized as potential choline or ethanolamine analogs, were tested against the in vitro growth of Plasmodium falciparum, the human malaria parasite. They were active over the 10(-3)-10(-8) M concentration range. A structure-activity relationship study was carried out using autocorrelation vectors as structural descriptors, and multidimensional analysis. Principal component analysis, ascending hierarchical classification, and stepwise discriminant analysis showed that both the size and shape of the molecule were essential for antimalarial potency, making the lipophilicity and electronegativity distribution in the molecular space essential. Using the autocorrelogram describing the molecular shape and the electronegativity distribution on the molecular graph, 98% of the molecules were correctly classified either as poorly active or active with only three explanatory variables. The most active compounds were quaternary ammoniums salts whose nitrogen atom had only one long lipophilic chain of 11 or 12 methylene groups (E5, E6, E10, E13, E20, E21, E22, E23, F4, F8), or the bisammoniums whose polar heads were linked by linear alkyl chains of 10 to 12 carbon atoms (G4, G23). The hydroxyethyl group of choline was not very beneficial, whereas the charge and substitutions of nitrogen (aimed at increasing lipophilicity) were essential for optimal interactions. A crude topographic model of the ligand (choline) binding site was thus drawn up.

  13. Time autocorrelation function analysis of master equation and its application to atomic clusters.

    PubMed

    Zhang, Chi; Berry, R Stephen

    2005-09-01

    We derive the energy fluctuation Delta(2)E, and the time autocorrelation kappa(tau) and its Fourier transformation--the fluctuation spectra S(omega)--of the master-equation transition matrix. The contribution from each eigenmode of the transition matrix to these fluctuation quantities reveals the relevant importance of the individual mode in the relaxation processes. The time scales associated with these relaxation processes are determined by the corresponding eigenvalues. Unlike traditional time evolution analysis, the autocorrelation function and fluctuation spectra analysis does not involve an arbitrary initial population. It is also more suitable for analyzing the underlying dynamic, kinetic behavior near the equilibrium and the behavior of the long-time-scale rare events. We utilize our technique to analyze the solid-liquid phase coexistence of the 13-atom Morse cluster and the fcc-to-icosahedral structure transition of the 38-atom Lennard-Jones cluster. For the processes studied, the fluctuation spectra from the master equation simplify the analysis of the transition matrix, and the important relaxation modes are easily extracted.

  14. C-C Bond Activation and Coupling of Propene Induced by la Atom

    NASA Astrophysics Data System (ADS)

    Hewage, Dilrukshi; Tao, Hong; Silva, Ruchira; Kumari, Sudesh; Yang, Dong-Sheng

    2013-06-01

    A series of La(C_nH_m) complexes with n ≤ 6 and m ≤ 12 were produced by the reactions between propene and La in a supersonic molecular beam source. Their formation and structures were investigated using mass-analyzed threshold ionization (MATI) spectroscopy in combination with theoretical calculations. Previously, we identified the formation of La(C_3H_4) and H-La(C_3H_5) through dehydrogenation and metal insertion mechanisms. In this work, we will discuss the formation of La(CH_2) and La(C_4H_6) by La induced C-C bond activation and coupling. La(CH_2) is formed by the C-C bond breakage and 1,2-hydride shift of propene and is a Schrock-type carbene complex. This complex is then coupled with the C=C bond of a second propene molecule to form La(C_4H_6) by removing two hydrogen atoms. The resultant La(C_4H_6) complex was idetified in two low-energy isomeric forms: one was a metallacycle (isomer A) and the other was lanthanum trimethylenemethane (isomer B). Both La(C_4H_6) isomers are in a doublet ground state, with isomer A in C_s point group and isomer B in C_3_v. Adiabatic ionization energies and several vibrational frequencies of the two complexes were obtained from the sharp MATI spectra.

  15. Active site of bimetallic heterogeneous catalyst by atomic resolution aberration-corrected STEM

    NASA Astrophysics Data System (ADS)

    Hsiao, Chien-Nan; Lin, Chun-Ting

    2015-11-01

    The localized defect of Au-Pd bimetallic heterogeneous nanoparticles catalyst was investigated using HRTEM and aberration-corrected HRSTEM. The phase plates were calculated from the aberration coefficients of the measured probe tableau for various outer tilt angle of the optical axis and the accuracy required for the compensation of the various residual aberration coefficients in order to achieve sub-angstrom resolution with the electron optics system was evaluated up to the fifth order aberrations. It is found that the interplanar spacing of the Au-Pd nanoparticle (1 1 1) planes observed along the [1 1 0] zone axis was approximately 0.24 nm measured by HRTEM. In addition, the HRSTEM HAADF image demonstrated that the twin boundaries on the surfaces of heterogeneous nanoparticles catalysts at atomic scale. These defects might be introduced during the growth to alleviate the internal stress caused by the 4.6% lattice mismatch of Au-Pd bimetallic system. Current research could be applied to the study of active sites in nanocatalysts.

  16. Atom-transfer cyclization with CuSO4/KBH4: a formal "activators generated by electron transfer" process also applicable to atom-transfer polymerization.

    PubMed

    Clark, Andrew J; Collis, Alana E C; Fox, David J; Halliwell, Lauren L; James, Natalie; O'Reilly, Rachel K; Parekh, Hemal; Ross, Andrew; Sellars, Andrew B; Willcock, Helen; Wilson, Paul

    2012-08-17

    The 4-exo and 5-exo-trig atom-transfer cyclizations of 1, 8a-e, 9, 12, and 13 can be mediated with as little as 0.05 mol % of Cu(TPMA)SO(4)·5H(2)O in the presence of 2.5 mol % of borohydride salts in 10 min at room temperature in air. This formal "activators generated by electron transfer" (AGET) procedure utilizes a cheap and oxidatively stable copper source (CuSO(4)·5H(2)O) and can be carried out in environmentally benign solvents (EtOH). It is possible to alter the product distribution in the 5-endo radical-polar crossover reactions of 10a,b and 11 by tailoring the amount of borohydride. Cyclization onto alkynes 14 and 15 is also possible in only 20 min. Controlled radical polymerization of styrene, with increased rates over conventional atom-transfer radical polymerization (ATRP), can be carried out in a controlled fashion (Mn, PDI) using either CuBr or CuSO(4)·5H(2)O and Bu(4)NBH(4).

  17. An atomic orbital-based formulation of the complete active space self-consistent field method on graphical processing units

    SciTech Connect

    Hohenstein, Edward G.; Luehr, Nathan; Ufimtsev, Ivan S.; Martínez, Todd J.

    2015-06-14

    Despite its importance, state-of-the-art algorithms for performing complete active space self-consistent field (CASSCF) computations have lagged far behind those for single reference methods. We develop an algorithm for the CASSCF orbital optimization that uses sparsity in the atomic orbital (AO) basis set to increase the applicability of CASSCF. Our implementation of this algorithm uses graphical processing units (GPUs) and has allowed us to perform CASSCF computations on molecular systems containing more than one thousand atoms. Additionally, we have implemented analytic gradients of the CASSCF energy; the gradients also benefit from GPU acceleration as well as sparsity in the AO basis.

  18. The Cold War legacy of regulatory risk analysis: The Atomic Energy Commission and radiation safety

    NASA Astrophysics Data System (ADS)

    Boland, Joseph B.

    From its inception in 1946 the Atomic Energy Commission pioneered the use of risk analysis as a mode of regulatory rationality and political rhetoric, yet historical treatments of risk analysis nearly always overlook the important role it played in the administration of atomic energy during the early Cold War. How this absence from history has been achieved and why it characterizes most historical accounts are the subjects of Chapter II. From there, this study goes on to develop the thesis that the advent of the atomic bomb was a world-shattering event that forced the Truman administration to choose between two novel alternatives: (1) movement towards global governance based initially on cooperative control of atomic energy or (2) unsparing pursuit of nuclear superiority. I refer to these as nuclear internationalism and nuclear nationalism, respectively. Each defined a social risk hierarchy. With the triumph of nuclear nationalism, nuclear annihilation was designated the greatest risk and a strong nuclear defense the primary means of prevention. The AEC's mission in the 1950s consisted of the rapid development of a nuclear arsenal, continual improvements in weapons technologies, and the promotion of nuclear power. The agency developed a risk-based regulatory framework through its dominant position within the National Committee on Radiation Protection. It embraced a technocratic model of risk analysis whose articulation and application it controlled, largely in secret. It used this to undergird a public rhetoric of reassurance and risk minimization. In practice, safety officials adjusted exposure levels within often wide parameters and with considerable fluidity in order to prevent safety concerns from interfering with operations. Secrecy, the political climate of the time, and a lack of accountability enabled the agency to meld technical assessments with social value judgments in a manner reflective of nuclear nationalism's risk hierarchy. In the late fifties

  19. Phases and Interfaces from Real Space Atomically Resolved Data: Physics-Based Deep Data Image Analysis.

    PubMed

    Vasudevan, Rama K; Ziatdinov, Maxim; Jesse, Stephen; Kalinin, Sergei V

    2016-09-14

    Advances in electron and scanning probe microscopies have led to a wealth of atomically resolved structural and electronic data, often with ∼1-10 pm precision. However, knowledge generation from such data requires the development of a physics-based robust framework to link the observed structures to macroscopic chemical and physical descriptors, including single phase regions, order parameter fields, interfaces, and structural and topological defects. Here, we develop an approach based on a synergy of sliding window Fourier transform to capture the local analog of traditional structure factors combined with blind linear unmixing of the resultant 4D data set. This deep data analysis is ideally matched to the underlying physics of the problem and allows reconstruction of the a priori unknown structure factors of individual components and their spatial localization. We demonstrate the principles of this approach using a synthetic data set and further apply it for extracting chemical and physically relevant information from electron and scanning tunneling microscopy data. This method promises to dramatically speed up crystallographic analysis in atomically resolved data, paving the road toward automatic local structure-property determinations in crystalline and quasi-ordered systems, as well as systems with competing structural and electronic order parameters.

  20. Semiclassical analysis of long-wavelength multiphoton processes: The Rydberg atom

    SciTech Connect

    Vela-Arevalo, Luz V.; Fox, Ronald F.

    2004-06-01

    We study the problem of multiphoton processes for intense, long-wavelength irradiation of atomic and molecular electrons. An exact, nonperturbative approach is applied to the standard vector potential coupling Hamiltonian for a three-dimensional hydrogenlike atom in a microwave field treated semiclassically. Multiphoton probability exchange is calculated in both the velocity and the length gauges, by applying the Goeppert-Mayer gauge transformation. The expansion of the time-dependent solution in terms of Floquet states delineates the mechanism of multiphoton transitions. A detailed analysis of the Floquet states and quasienergies as functions of the field parameters allows us to describe the relation between avoided quasienergy crossings and multiphoton probability exchange. We formulate analytical expressions for the variation of quasienergies and Floquet states with respect to the field parameters, and demonstrate that avoided quasienergy crossings are accompanied by dramatic changes in the Floquet states. Analysis of the Floquet states, for small values of the field strength, yields selection rules for the avoided quasienergy crossings. In the case of strong fields, the simultaneous choice of frequency and strength of the field producing an avoided crossing results in improved ionization probability.

  1. Classical and quantum analysis of quasiresonance in grazing atom-surface collisions

    SciTech Connect

    Ruiz, Antonia; Palao, Jose P.; Heller, Eric J.

    2009-05-15

    Quasiresonance is a general effect that may arise from the coupling between approximately resonant degrees of freedom in a system perturbed by some transient interaction. In a process induced by a slowly switching on and off of the coupling interaction, quasiresonance is characterized by the existence of significant ranges of initial states in the perturbed system over which some very specific and efficient transfer of energy between the approximately resonant degrees of freedom occurs. This work presents a classical and quantum analysis of quasiresonant processes in grazing incident angle atom-surface collisions. The momentum transfer between the normal components to an index direction is investigated. For fast atoms with grazing angle of incidence there is an interval of azimuthal angles around the index directions, the quasiresonance region, in which the energy transfer can be very efficient. This effect is reflected in quantum diffraction patterns with large nonspecular peaks, associated with the parallel to the surface and normal to the index direction momentum component. We demonstrate the essentially classical underlying mechanism for the persistence of a pattern of diffraction peak intensities for incidence close to an index direction. The analysis also shows that the size of the quasiresonance region is approximately equal to the spectral width of the diffraction pattern.

  2. Bonding analysis of planar hypercoordinate atoms via the generalized BLW-LOL.

    PubMed

    Bomble, Laetitia; Steinmann, Stephan N; Perez-Peralta, Nancy; Merino, Gabriel; Corminboeuf, Clemence

    2013-10-05

    The multicenter bonding pattern of the intriguing hexa-, hepta-, and octacoordinate boron wheel series (e.g., CB62-, CB7-, B82-, and SiB8 as well as the experimentally detected CB7- isomer) is revised using the block-localized wave function analyzed by the localized orbital locator (BLW-LOL). The more general implementation of BLW combined with the LOL scalar field is not restricted to the analysis of the out-of-plane π-system but can also provide an intuitive picture of the σ-radial delocalization and of the role of the central atom. The results confirm the presence of a π-ring current pattern similar to that of benzene. In addition, the LOLπ isosurfaces along with the maximum intensity in the ΔLOL profiles located above and below the ring suggest that the central atom plays a minor role in the π-delocalized bonding pattern. Finally, the analysis of the σ-framework in these boron wheels is in line with a moderated inner cyclic rather than disk-type delocalization.

  3. Phases and interfaces from real space atomically resolved data: Physics-based deep data image analysis

    SciTech Connect

    Vasudevan, Rama K.; Ziatdinov, Maxim; Jesse, Stephen; Kalinin, Sergei V.

    2016-08-12

    Advances in electron and scanning probe microscopies have led to a wealth of atomically resolved structural and electronic data, often with ~1–10 pm precision. However, knowledge generation from such data requires the development of a physics-based robust framework to link the observed structures to macroscopic chemical and physical descriptors, including single phase regions, order parameter fields, interfaces, and structural and topological defects. Here, we develop an approach based on a synergy of sliding window Fourier transform to capture the local analog of traditional structure factors combined with blind linear unmixing of the resultant 4D data set. This deep data analysis is ideally matched to the underlying physics of the problem and allows reconstruction of the a priori unknown structure factors of individual components and their spatial localization. We demonstrate the principles of this approach using a synthetic data set and further apply it for extracting chemical and physically relevant information from electron and scanning tunneling microscopy data. Furthermore, this method promises to dramatically speed up crystallographic analysis in atomically resolved data, paving the road toward automatic local structure–property determinations in crystalline and quasi-ordered systems, as well as systems with competing structural and electronic order parameters.

  4. Microwave-enhanced cold vapor generation for speciation analysis of mercury by atomic fluorescence spectrometry.

    PubMed

    Wu, Li; Long, Zhou; Liu, Liwei; Zhou, Qin; Lee, Yong-Ill; Zheng, Chengbin

    2012-05-30

    A new and simple cold vapor generation technique utilizing microwave irradiation coupled with atomic fluorescence spectrometry is developed for the speciation analysis of mercury in biological and geological samples. In the presence of formic acid, inorganic mercury (Hg(2+)) and total mercury (both Hg(2+) and methylmercury (MeHg)) can be converted to mercury cold vapor (Hg(0)) by microwave irradiation without and with H(2)O(2), respectively. The cold vapor was subsequently released from the liquid phase and rapidly transported to an atomic fluorescence spectrometer for the mercury detection. Optimum conditions for vapor generation as well as interferences from concomitant ions were carefully investigated. The conventionally required evaporation of the remnants of acid or oxidants was avoided because no significant interferences from these substances were observed, and thus analyte loss and potential contamination were minimized. A limit of detection of 0.005 ng mL(-1) for total mercury or inorganic mercury was obtained. A precision of less than 3% (RSD) at 2 μg L(-1) of mercury species was typical. The accuracy of the method was validated by determination of mercury in geological and biological certified reference materials. The speciation analysis of Hg(2+) and MeHg was achieved by controlling the conditions of microwave-enhanced cold vapor generation and validated via determination of Certified Reference Materials DORM-2, DORM-3 and a real river water sample.

  5. Speciation Analysis of Arsenic by Selective Hydride Generation-Cryotrapping-Atomic Fluorescence Spectrometry with Flame-in-Gas-Shield Atomizer: Achieving Extremely Low Detection Limits with Inexpensive Instrumentation

    PubMed Central

    2015-01-01

    This work describes the method of a selective hydride generation-cryotrapping (HG-CT) coupled to an extremely sensitive but simple in-house assembled and designed atomic fluorescence spectrometry (AFS) instrument for determination of toxicologically important As species. Here, an advanced flame-in-gas-shield atomizer (FIGS) was interfaced to HG-CT and its performance was compared to a standard miniature diffusion flame (MDF) atomizer. A significant improvement both in sensitivity and baseline noise was found that was reflected in improved (4 times) limits of detection (LODs). The yielded LODs with the FIGS atomizer were 0.44, 0.74, 0.15, 0.17 and 0.67 ng L–1 for arsenite, total inorganic, mono-, dimethylated As and trimethylarsine oxide, respectively. Moreover, the sensitivities with FIGS and MDF were equal for all As species, allowing for the possibility of single species standardization with arsenate standard for accurate quantification of all other As species. The accuracy of HG-CT-AFS with FIGS was verified by speciation analysis in two samples of bottled drinking water and certified reference materials, NRC CASS-5 (nearshore seawater) and SLRS-5 (river water) that contain traces of methylated As species. As speciation was in agreement with results previously reported and sums of all quantified species corresponded with the certified total As. The feasibility of HG-CT-AFS with FIGS was also demonstrated by the speciation analysis in microsamples of exfoliated bladder epithelial cells isolated from human urine. The results for the sums of trivalent and pentavalent As species corresponded well with the reference results obtained by HG-CT-ICPMS (inductively coupled plasma mass spectrometry). PMID:25300934

  6. The stereochemistry and dynamics of the introduction of hydrogen atoms onto FeMo-co, the active site of nitrogenase.

    PubMed

    Dance, Ian

    2013-11-18

    The catalyzed hydrogenations effected at the active site FeMo-co of nitrogenase have been proposed to involve serial supply of the required multiple protons along a proton wire terminating at sulfur atom S3B of FeMo-co. In conjunction with serial electron transfer to FeMo-co, these protons become H atoms, and then are able to migrate from S3B to other Fe and S atoms of FeMo-co, and to transfer to bound substrate and intermediates. This general model, which can account for all reactions of nitrogenase, involves a preparatory stage in which each incoming H atom is required to move from the proton delivery side of S3B to the opposite migration side of S3B. This report examines the mechanism of this reconfiguration of S3B-H, finding four stable configurations in which S3B-H has pyramidal-trigonal coordination, with one elongated Fe-S3B interaction. The transition states and energies for reconfiguration are described. Pseudotetrahedral four coordination and planar-trigonal coordination for S3B-H are less stable than pyramidal-trigonal coordination. Results are presented for FeMo-co with one, two, three, and four H atoms (the E1H1, E2H2, E3H3, and E4H4 Thorneley-Lowe stages), and the general principles are defined, for application in the various chemical mechanisms of nitrogenase.

  7. Automation of preparation of nonmetallic samples for analysis by atomic absorption and inductively coupled plasma spectrometry

    NASA Technical Reports Server (NTRS)

    Wittmann, A.; Willay, G.

    1986-01-01

    For a rapid preparation of solutions intended for analysis by inductively coupled plasma emission spectrometry or atomic absorption spectrometry, an automatic device called Plasmasol was developed. This apparatus used the property of nonwettability of glassy C to fuse the sample in an appropriate flux. The sample-flux mixture is placed in a composite crucible, then heated at high temperature, swirled until full dissolution is achieved, and then poured into a water-filled beaker. After acid addition, dissolution of the melt, and filling to the mark, the solution is ready for analysis. The analytical results obtained, either for oxide samples or for prereduced iron ores show that the solutions prepared with this device are undistinguished from those obtained by manual dissolutions done by acid digestion or by high temperature fusion. Preparation reproducibility and analytical tests illustrate the performance of Plasmasol.

  8. Analysis of scattering mechanisms in zinc oxide films grown by the atomic layer deposition technique

    SciTech Connect

    Krajewski, Tomasz A. Dybko, Krzysztof; Luka, Grzegorz; Wachnicki, Lukasz; Kopalko, Krzysztof; Paszkowicz, Wojciech; Guziewicz, Elzbieta

    2015-07-21

    In this work, the analysis of the temperature-dependent electrical conductivity of highly crystalline zinc oxide (ZnO) thin films obtained by the Atomic Layer Deposition (ALD) method is performed. It is deduced that the most important scattering mechanisms are: scattering by ionized defects (at low temperatures) as well as by phonons (mainly optical ones) at higher temperatures. Nevertheless, the role of grain boundaries in the carrier mobility limitation ought to be included as well. These conclusions are based on theoretical analysis and temperature-dependent Hall mobility measurements. The presented results prove that existing models can explain the mobility behavior in the ALD-ZnO films, being helpful for understanding their transport properties, which are strongly related both to the crystalline quality of deposited ZnO material and defects in its lattice.

  9. Analysis of containment venting at the Peach Bottom Atomic Power Station

    SciTech Connect

    Hanson, D.J.; Blackman, H.S.; Nelson, W.R.; Wright, R.E.; Leonard, M.T.; DiSalvo, R.

    1986-10-24

    An analysis of the extent to which containment venting would be effective in preventing or mitigating the consequences of severe accidents has been completed for the Peach Bottom Atomic Power Station, Units 2 and 3 (BWR-4s with Mark I containments). The analysis indicates that the effectiveness of venting in preventing containment overpressurization highly depends on the sequence of the severe accident. Containment venting can be effective for several classes of sequences, including transients with failure of long-term decay heat removal and loss-of-coolant accidents with breaks inside the containment. However, based on draft procedures and equipment in place at the time of the evaluation, containment venting has limited potential for further reducing the risk associated with three severe accident sequences currently identified as important risk contributors at Peach Bottom. Means of improving the potential for risk reduction is identified, but their influence on risk is not analyzed.

  10. The Use of Atomic Force Microscopy for 3D Analysis of Nucleic Acid Hybridization on Microarrays.

    PubMed

    Dubrovin, E V; Presnova, G V; Rubtsova, M Yu; Egorov, A M; Grigorenko, V G; Yaminsky, I V

    2015-01-01

    Oligonucleotide microarrays are considered today to be one of the most efficient methods of gene diagnostics. The capability of atomic force microscopy (AFM) to characterize the three-dimensional morphology of single molecules on a surface allows one to use it as an effective tool for the 3D analysis of a microarray for the detection of nucleic acids. The high resolution of AFM offers ways to decrease the detection threshold of target DNA and increase the signal-to-noise ratio. In this work, we suggest an approach to the evaluation of the results of hybridization of gold nanoparticle-labeled nucleic acids on silicon microarrays based on an AFM analysis of the surface both in air and in liquid which takes into account of their three-dimensional structure. We suggest a quantitative measure of the hybridization results which is based on the fraction of the surface area occupied by the nanoparticles.

  11. Seismic margin review of the Maine Yankee Atomic Power Station: Fragility analysis

    SciTech Connect

    Ravindra, M. K.; Hardy, G. S.; Hashimoto, P. S.; Griffin, M. J.

    1987-03-01

    This Fragility Analysis is the third of three volumes for the Seismic Margin Review of the Maine Yankee Atomic Power Station. Volume 1 is the Summary Report of the first trial seismic margin review. Volume 2, Systems Analysis, documents the results of the systems screening for the review. The three volumes are part of the Seismic Margins Program initiated in 1984 by the Nuclear Regulatory Commission (NRC) to quantify seismic margins at nuclear power plants. The overall objectives of the trial review are to assess the seismic margins of a particular pressurized water reactor, and to test the adequacy of this review approach, quantification techniques, and guidelines for performing the review. Results from the trial review will be used to revise the seismic margin methodology and guidelines so that the NRC and industry can readily apply them to assess the inherent quantitative seismic capacity of nuclear power plants.

  12. Atomic force microscopy and scanning electron microscopy analysis of daily disposable limbal ring contact lenses

    PubMed Central

    Lorenz, Kathrine Osborn; Kakkassery, Joseph; Boree, Danielle; Pinto, David

    2014-01-01

    Background Limbal ring (also known as ‘circle’) contact lenses are becoming increasingly popular, especially in Asian markets because of their eye-enhancing effects. The pigment particles that give the eye-enhancing effects of these lenses can be found on the front or back surface of the contact lens or ‘enclosed’ within the lens matrix. The purpose of this research was to evaluate the pigment location and surface roughness of seven types of ‘circle’ contact lenses. Methods Scanning electron microscopic (SEM) analysis was performed using a variable pressure Hitachi S3400N instrument to discern the placement of lens pigments. Atomic force microscopy (Dimension Icon AFM from Bruker Nano) was used to determine the surface roughness of the pigmented regions of the contact lenses. Atomic force microscopic analysis was performed in fluid phase under contact mode using a Sharp Nitride Lever probe (SNL-10) with a spring constant of 0.06 N/m. Root mean square (RMS) roughness values were analysed using a generalised linear mixed model with a log-normal distribution. Least square means and their corresponding 95% confidence intervals were estimated for each brand, location and pigment combination. Results SEM cross-sectional images at 500× and 2,000× magnification showed pigment on the surface of six of the seven lens types tested. The mean depth of pigment for 1-DAY ACUVUE DEFINE (1DAD) lenses was 8.1 μm below the surface of the lens, while the remaining lens types tested had pigment particles on the front or back surface. Results of the atomic force microscopic analysis indicated that 1DAD lenses had significantly lower root mean square roughness values in the pigmented area of the lens than the other lens types tested. Conclusions SEM and AFM analysis revealed pigment on the surface of the lens for all types tested with the exception of 1DAD. Further research is required to determine if the difference in pigment location influences on-eye performance. PMID

  13. Analysis of Adhesive Characteristics of Asphalt Based on Atomic Force Microscopy and Molecular Dynamics Simulation.

    PubMed

    Xu, Meng; Yi, Junyan; Feng, Decheng; Huang, Yudong; Wang, Dongsheng

    2016-05-18

    Asphalt binder is a very important building material in infrastructure construction; it is commonly mixed with mineral aggregate and used to produce asphalt concrete. Owing to the large differences in physical and chemical properties between asphalt and aggregate, adhesive bonds play an important role in determining the performance of asphalt concrete. Although many types of adhesive bonding mechanisms have been proposed to explain the interaction forces between asphalt binder and mineral aggregate, few have been confirmed and characterized. In comparison with chemical interactions, physical adsorption has been considered to play a more important role in adhesive bonding between asphalt and mineral aggregate. In this study, the silicon tip of an atomic force microscope was used to represent silicate minerals in aggregate, and a nanoscale analysis of the characteristics of adhesive bonding between asphalt binder and the silicon tip was conducted via an atomic force microscopy (AFM) test and molecular dynamics (MD) simulations. The results of the measurements and simulations could help in better understanding of the bonding and debonding procedures in asphalt-aggregate mixtures during hot mixing and under traffic loading. MD simulations on a single molecule of a component of asphalt and monocrystalline silicon demonstrate that molecules with a higher atomic density and planar structure, such as three types of asphaltene molecules, can provide greater adhesive strength. However, regarding the real components of asphalt binder, both the MD simulations and AFM test indicate that the colloidal structural behavior of asphalt also has a large influence on the adhesion behavior between asphalt and silicon. A schematic model of the interaction between asphalt and silicon is presented, which can explain the effect of aging on the adhesion behavior of asphalt.

  14. Analysis of 2011 Meteorological Data from the Knolls Atomic Power Laboratory and Kesselring Site Operations Facilities

    SciTech Connect

    Aluzzi, F J

    2012-02-27

    Both the Knolls Atomic Power Laboratory (KAPL) in Schenectady, NY and the Kesselring Site Operations (KSO) facility near Ballston Spa, NY are required to estimate the effects of hypothetical emissions of radiological material from their respective facilities by the US Environmental Protection Agency (EPA), which regulates these facilities. An atmospheric dispersion model known as CAP88, which was developed and approved by the EPA for such purposes, is used by KAPL and KSO to meet this requirement. CAP88 calculations over a given time period are based on statistical data on the meteorological conditions for that period. Both KAPL and KSO have on-site meteorological towers which take atmospheric measurements at a frequency ideal for EPA regulatory model input. However, an independent analysis and processing of the meteorological data from each tower is required to derive a data set appropriate for use in the CAP88 model. The National Atmospheric Release Advisory Center (NARAC) was contracted by KAPL to process the on-site data for the calendar year 2011. The purpose of this document is to: (1) summarize the procedures used in the preparation/analysis of the 2011 meteorological data; and (2) document adherence of these procedures to the guidance set forth in 'Meteorological Monitoring Guidance for Regulatory Modeling Applications', EPA document - EPA-454/R-99-005 (EPA-454). This document outlines the steps in analyzing and processing meteorological data from the Knolls Atomic Power Laboratory and Kesselring Site Operations facilities into a format that is compatible with the steady state dispersion model CAP88. This process is based on guidance from the EPA regarding the preparation of meteorological data for use in regulatory dispersion models. The analysis steps outlined in this document can be easily adapted to process data sets covering time period other than one year. The procedures will need to be modified should the guidance in EPA-454 be updated or revised.

  15. Cluster protein structures using recurrence quantification analysis on coordinates of alpha-carbon atoms of proteins

    NASA Astrophysics Data System (ADS)

    Zhou, Yu; Yu, Zu-Guo; Anh, Vo

    2007-08-01

    The 3-dimensional coordinates of alpha-carbon atoms of proteins are used to distinguish the protein structural classes based on recurrence quantification analysis (RQA). We consider two independent variables from RQA of coordinates of alpha-carbon atoms, %determ1 and %determ2, which were defined by Webber et al. [C.L. Webber Jr., A. Giuliani, J.P. Zbilut, A. Colosimo, Proteins Struct. Funct. Genet. 44 (2001) 292]. The variable %determ2 is used to define two new variables, %determ21 and %determ22. Then three variables %determ1, %determ21 and %determ22 are used to construct a 3-dimensional variable space. Each protein is represented by a point in this variable space. The points corresponding to proteins from the α, β, α+β and α/β structural classes position into different areas in this variable space. In order to give a quantitative assessment of our clustering on the selected proteins, Fisher's discriminant algorithm is used. Numerical results indicate that the discriminant accuracies are very high and satisfactory.

  16. Atomic force microscopy analysis of nanoparticles in non-ideal conditions

    PubMed Central

    2011-01-01

    Nanoparticles are often measured using atomic force microscopy or other scanning probe microscopy methods. For isolated nanoparticles on flat substrates, this is a relatively easy task. However, in real situations, we often need to analyze nanoparticles on rough substrates or nanoparticles that are not isolated. In this article, we present a simple model for realistic simulations of nanoparticle deposition and we employ this model for modeling nanoparticles on rough substrates. Different modeling conditions (coverage, relaxation after deposition) and convolution with different tip shapes are used to obtain a wide spectrum of virtual AFM nanoparticle images similar to those known from practice. Statistical parameters of nanoparticles are then analyzed using different data processing algorithms in order to show their systematic errors and to estimate uncertainties for atomic force microscopy analysis of nanoparticles under non-ideal conditions. It is shown that the elimination of user influence on the data processing algorithm is a key step for obtaining accurate results while analyzing nanoparticles measured in non-ideal conditions. PMID:21878120

  17. Kinetic analysis of interaction between N atoms and O-covered Ru(0001)

    SciTech Connect

    Kang, Kai; Kleyn, A. W.; Gleeson, M. A.

    2015-10-28

    Eley-Rideal (ER) reactions involving neutral atoms heavier than hydrogen reacting with adsorbed atoms of similar mass were first observed in recent molecular beam experiments by Zaharia et al. [Phys. Rev. Lett. 113, 053201 (2014)]. Through analysis of two types of measurements, they obtained different estimations for the N–O ER reaction cross section, one of which is unexpectedly high. This was qualitatively accounted for by invoking a secondary effect whereby the presence of N adatoms on the surface acted to “shield” O adatoms from prompt recombinative desorption. We apply a rate equation model that includes two ER processes involving different adsorbed species (N–O{sub ad} and N–N{sub ad}) and an N-adsorption process to the full-beam exposure subset of the experimental data in order to study the reaction kinetics. Values for the individual reaction cross sections are derived. The measured N{sub 2} response can be well described by the model, but it is insufficient to completely describe the NO response. Modeling of different exposures is used to evaluate the qualitative picture presented by Zaharia et al.

  18. Phases and interfaces from real space atomically resolved data: Physics-based deep data image analysis

    DOE PAGES

    Vasudevan, Rama K.; Ziatdinov, Maxim; Jesse, Stephen; ...

    2016-08-12

    Advances in electron and scanning probe microscopies have led to a wealth of atomically resolved structural and electronic data, often with ~1–10 pm precision. However, knowledge generation from such data requires the development of a physics-based robust framework to link the observed structures to macroscopic chemical and physical descriptors, including single phase regions, order parameter fields, interfaces, and structural and topological defects. Here, we develop an approach based on a synergy of sliding window Fourier transform to capture the local analog of traditional structure factors combined with blind linear unmixing of the resultant 4D data set. This deep data analysismore » is ideally matched to the underlying physics of the problem and allows reconstruction of the a priori unknown structure factors of individual components and their spatial localization. We demonstrate the principles of this approach using a synthetic data set and further apply it for extracting chemical and physically relevant information from electron and scanning tunneling microscopy data. Furthermore, this method promises to dramatically speed up crystallographic analysis in atomically resolved data, paving the road toward automatic local structure–property determinations in crystalline and quasi-ordered systems, as well as systems with competing structural and electronic order parameters.« less

  19. A Simplified Digestion Protocol for the Analysis of Hg in Fish by Cold Vapor Atomic Absorption Spectroscopy

    ERIC Educational Resources Information Center

    Kristian, Kathleen E.; Friedbauer, Scott; Kabashi, Donika; Ferencz, Kristen M.; Barajas, Jennifer C.; O'Brien, Kelly

    2015-01-01

    Analysis of mercury in fish is an interesting problem with the potential to motivate students in chemistry laboratory courses. The recommended method for mercury analysis in fish is cold vapor atomic absorption spectroscopy (CVAAS), which requires homogeneous analyte solutions, typically prepared by acid digestion. Previously published digestion…

  20. Stable and solubilized active Au atom clusters for selective epoxidation of cis-cyclooctene with molecular oxygen

    PubMed Central

    Qian, Linping; Wang, Zhen; Beletskiy, Evgeny V.; Liu, Jingyue; dos Santos, Haroldo J.; Li, Tiehu; Rangel, Maria do C.; Kung, Mayfair C.; Kung, Harold H.

    2017-01-01

    The ability of Au catalysts to effect the challenging task of utilizing molecular oxygen for the selective epoxidation of cyclooctene is fascinating. Although supported nanometre-size Au particles are poorly active, here we show that solubilized atomic Au clusters, present in ng ml−1 concentrations and stabilized by ligands derived from the oxidized hydrocarbon products, are active. They can be formed from various Au sources. They generate initiators and propagators to trigger the onset of the auto-oxidation reaction with an apparent turnover frequency of 440 s−1, and continue to generate additional initiators throughout the auto-oxidation cycle without direct participation in the cycle. Spectroscopic characterization suggests that 7–8 atom clusters are effective catalytically. Extension of work based on these understandings leads to the demonstration that these Au clusters are also effective in selective oxidation of cyclohexene, and that solubilized Pt clusters are also capable of generating initiators for cyclooctene epoxidation. PMID:28348389

  1. SOARCA Peach Bottom Atomic Power Station Long-Term Station Blackout Uncertainty Analysis: Knowledge Advancement.

    SciTech Connect

    Gauntt, Randall O.; Mattie, Patrick D.; Bixler, Nathan E.; Ross, Kyle; Cardoni, Jeffrey N; Kalinich, Donald A.; Osborn, Douglas M.; Sallaberry, Cedric Jean-Marie; Ghosh, S. Tina

    2014-02-01

    This paper describes the knowledge advancements from the uncertainty analysis for the State-of- the-Art Reactor Consequence Analyses (SOARCA) unmitigated long-term station blackout accident scenario at the Peach Bottom Atomic Power Station. This work assessed key MELCOR and MELCOR Accident Consequence Code System, Version 2 (MACCS2) modeling uncertainties in an integrated fashion to quantify the relative importance of each uncertain input on potential accident progression, radiological releases, and off-site consequences. This quantitative uncertainty analysis provides measures of the effects on consequences, of each of the selected uncertain parameters both individually and in interaction with other parameters. The results measure the model response (e.g., variance in the output) to uncertainty in the selected input. Investigation into the important uncertain parameters in turn yields insights into important phenomena for accident progression and off-site consequences. This uncertainty analysis confirmed the known importance of some parameters, such as failure rate of the Safety Relief Valve in accident progression modeling and the dry deposition velocity in off-site consequence modeling. The analysis also revealed some new insights, such as dependent effect of cesium chemical form for different accident progressions. (auth)

  2. Development of mixed-waste analysis capability for graphite furnace atomic absorption spectrophotometry

    SciTech Connect

    Bass, D.A.; TenKate, L.B.; Wroblewski, A.

    1995-03-01

    Graphite furnace atomic absorption spectrophotometer (GFAAS) are typically configured with ventilation to capture potentially toxic and corrosive gases emitted from the vaporization of sample aliquots. When radioactive elements are present, additional concerns (such as meeting safety guidelines and ALARA principles) must be addressed. This report describes a modification to a GFAAS that provides additional containment of vaporized sample aliquots. The modification was found to increase containment by a factor of 80, given expected operating conditions. The use of the modification allows more mixed-waste samples to be analyzed, permits higher levels of radioactive samples to be analyzed, or exposes the analyst to less airborne radioactivity. The containment apparatus was attached to a Perkin-Elmer Zeeman 5000 spectrophotometer for analysis of mixed-waste samples; however, it could also be used on other systems and in other applications where greater containment of vaporized material is desired.

  3. Removal of iron interferences by solvent extraction for geochemical analysis by atomic-absorption spectrophotometry

    USGS Publications Warehouse

    Zhou, L.; Chao, T.T.; Sanzolone, R.F.

    1985-01-01

    Iron is a common interferent in the determination of many elements in geochemical samples. Two approaches for its removal have been taken. The first involves removal of iron by extraction with methyl isobutyl ketone (MIBK) from hydrochloric acid medium, leaving the analytes in the aqueous phase. The second consists of reduction of iron(III) to iron(II) by ascorbic acid to minimize its extraction into MIBK, so that the analytes may be isolated by extraction. Elements of interest can then be determined using the aqueous solution or the organic extract, as appropriate. Operating factors such as the concentration of hydrochloric acid, amounts of iron present, number of extractions, the presence or absence of a salting-out agent, and the optimum ratio of ascorbic acid to iron have been determined. These factors have general applications in geochemical analysis by atomic-absorption spectrophotometry. ?? 1985.

  4. Determination of cyanide by a flow injection analysis-atomic absorption spectrometric method.

    PubMed

    López Gómez, A V; Martínez Calatayud, J

    1998-10-01

    A new flow injection analysis (FIA) procedure is proposed for the indirect atomic absorption spectrometric determination of cyanide. The FIA manifold is based on the insertion of the sample into a distilled water carrier, then the sample flows through a solid-phase reactor filled with silver iodide entrapped in polymeric resin beads. The calibration graph is linear over the range 0.2-6.0 mg l-1 of cyanide (correlation coefficient 0.9974), the detection limit is 0.1 mg l-1, the sample throughput is 193 h-1 and the RSD is 0.8%. The method is simple, quick and more selective than other published FIA procedures. The reproducibility obtained by using different solid-phase reactors and solutions is in the range 2.2-3.1% (RSD). The method was applied to the determination of cyanide in commercial samples such as pharmaceutical formulations and industrial electrolytic baths.

  5. Numerical analysis of atomic density distribution in arc driven negative ion sources

    SciTech Connect

    Yamamoto, T. Shibata, T.; Hatayama, A.; Kashiwagi, M.; Hanada, M.; Sawada, K.

    2014-02-15

    The purpose of this study is to calculate atomic (H{sup 0}) density distribution in JAEA 10 ampere negative ion source. A collisional radiative model is developed for the calculation of the H{sup 0} density distribution. The non-equilibrium feature of the electron energy distribution function (EEDF), which mainly determines the H{sup 0} production rate, is included by substituting the EEDF calculated from 3D electron transport analysis. In this paper, the H{sup 0} production rate, the ionization rate, and the density distribution in the source chamber are calculated. In the region where high energy electrons exist, the H{sup 0} production and the ionization are enhanced. The calculated H{sup 0} density distribution without the effect of the H{sup 0} transport is relatively small in the upper region. In the next step, the effect should be taken into account to obtain more realistic H{sup 0} distribution.

  6. Mesoscopic dynamics of fermionic cold atoms - Quantitative analysis of transport coefficients and relaxation times

    NASA Astrophysics Data System (ADS)

    Kikuchi, Yuta; Tsumura, Kyosuke; Kunihiro, Teiji

    2016-05-01

    We give a quantitative analysis of the dynamical properties of fermionic cold atomic gases in normal phase, such as the shear viscosity, heat conductivity, and viscous relaxation times, using the novel microscopic expressions derived by the renormalization group (RG) method, where the Boltzmann equation is faithfully solved to extract the hydrodynamics without recourse to any ansatz. In particular, we examine the quantum statistical effects, temperature dependence, and scattering-length dependence of the transport coefficients and the viscous relaxation times. The numerical calculation shows that the relation τπ = η / P, which is derived in the relaxation-time approximation (RTA) and is used in most of the literature, turns out to be satisfied quite well, while the similar relation for the viscous relaxation time τJ of the heat conductivity is satisfied only approximately with a considerable error.

  7. Multielement analysis of geologic materials by inductively coupled plasma-atomic emission spectroscopy

    SciTech Connect

    Christensen, O.D.; Kroneman, R.L.; Capuano, R.M.

    1980-03-01

    Atomic emission spectroscopy using an inductively coupled plasma (ICP) source permits the rapid acquisition of multielement geochemical data from a wide variety of geologic materials. Rocks or other solid samples are taken into solution with a four acid digestion procedure and introduced directly into the plasma; fluid samples are acidified or analyzed directly. The entire process is computer-controlled, fully-automated, and requires less than five minutes per sample for quantitative determination of 37 elements. The procedures and instrumentation employed at the ESL for multielement ICP analysis of geologic materials are described and these are intended as a guide for evaluating analytic results reported from this laboratory. The quality of geochemical data can be characterized by precision, limits of quantitative determination, and accuracy. Precision values are a measure of the repeatability of analyses. In general, major element and analyses have precision of better than 5% and trace elements of better than 10% of the amount present. (MHR)

  8. Atomic force microscopy analysis of different surface treatments of Ti dental implant surfaces

    NASA Astrophysics Data System (ADS)

    Bathomarco, Ti R. V.; Solorzano, G.; Elias, C. N.; Prioli, R.

    2004-06-01

    The surface of commercial unalloyed titanium, used in dental implants, was analyzed by atomic force microscopy. The morphology, roughness, and surface area of the samples, submitted to mechanically-induced erosion, chemical etching and a combination of both, were compared. The results show that surface treatments strongly influence the dental implant physical and chemical properties. An analysis of the length dependence of the implant surface roughness shows that, for scan sizes larger than 50 μm, the average surface roughness is independent of the scanning length and that the surface treatments lead to average surface roughness in the range of 0.37 up to 0.48 μm. It is shown that the implant surface energy is sensitive to the titanium surface area. As the area increases there is a decrease in the surface contact angle.

  9. Capturing local atomic environment dependence of activation barriers in metals using cluster expansion models

    NASA Astrophysics Data System (ADS)

    Kulkarni, Nimish; Chatterjee, Abhijit

    2016-10-01

    It is well known that surface diffusion in metals can proceed via multiple mechanisms, such as hop, exchange and other types of concerted moves. However, the manner in which kinetic rates associated with a mechanism can depend sensitively on local atomic environment is relatively less understood. We describe recent attempts in our research group to capture the atomic environment dependence using the cluster expansion model (CEM). In particular, we focus on hop and exchange moves at the (001) surface in homoepitaxy, and show that while CEM can work remarkably well in most cases, it can sometimes provide inaccurate predictions for concerted moves.

  10. Atomic research

    NASA Technical Reports Server (NTRS)

    Hadaway, James B.; Connatser, Robert; Cothren, Bobby; Johnson, R. B.

    1993-01-01

    Work performed by the University of Alabama in Huntsville's (UAH) Center for Applied Optics (CAO) entitled Atomic Research is documented. Atomic oxygen (AO) effects on materials have long been a critical concern in designing spacecraft to withstand exposure to the Low Earth Orbit (LEO) environment. The objective of this research effort was to provide technical expertise in the design of instrumentation and experimental techniques for analyzing materials exposed to atomic oxygen in accelerated testing at NASA/MSFC. Such testing was required to answer fundamental questions concerning Space Station Freedom (SSF) candidate materials and materials exposed to atomic oxygen aboard the Long-Duration Exposure Facility (LDEF). The primary UAH task was to provide technical design, review, and analysis to MSFC in the development of a state-of-the-art 5eV atomic oxygen beam facility required to simulate the RAM-induced low earth orbit (LEO) AO environment. This development was to be accomplished primarily at NASA/MSFC. In support of this task, contamination effects and ultraviolet (UV) simulation testing was also to be carried out using NASA/MSFC facilities. Any materials analysis of LDEF samples was to be accomplished at UAH.

  11. Determination of zinc in serum, blood, and ultrafiltrate fluid from patients on hemofiltration by graphite furnace/atomic absorption spectroscopy or flow injection analysis/atomic absorption spectroscopy.

    PubMed

    de Blas, O J; Rodriguez, R S; Mendez, J H; Tomero, J A; Gomez, B de L; Gonzalez, S V

    1994-01-01

    Two methods were optimized for the determination of zinc in samples of blood, serum, and ultrafiltrate fluid from patients with chronic renal impairment undergoing hemofiltration. In the first procedure, after acid digestion of the samples, Zn in blood and serum is determined by a system coupled to flow injection analysis and atomic absorption spectroscopy. The method is rapid, automated, simple, needs small amounts of sample, and has acceptable analytical characteristics. The analytical characteristics obtained were as follows: determination range of method, 0.05-2.0 ppm of Zn; precision as coefficient of variation (CV), 5.3%; recovery, 95-105%; and detection limit (DL), 0.02 ppm. The second method is optimized for ultrafiltrate fluid because the sensitivity of the first procedure is not suitable for the levels of Zn (ppb or ng/mL) in these samples. The technique chosen was atomic absorption spectroscopy with electrothermal atomization in a graphite furnace. The analytical characteristics obtained were as follows: determination range of method, 0.3-2.0 ppb Zn; CV, 5.7%; recovery, 93-107%; and DL, 0.12 ppb. The methods were used to determine zinc in samples of blood, serum, and ultrafiltrate fluid from 5 patients with chronic renal impairment undergoing hemofiltration to discover whether there were significant differences in the zinc contents of blood, serum, and ultrafiltrate fluid after the hemofiltration process. An analysis of variance of the experimental data obtained from a randomly selected group of 5 patients showed that zinc concentrations in the ultrafiltrate fluid, venous blood, and venous serum do not vary during hemofiltration (p < 0.05), whereas in arterial blood and serum, the time factor has a significant effect.

  12. Neutron-induced 63Ni activity and microscopic observation of copper samples exposed to the Hiroshima atomic bomb

    NASA Astrophysics Data System (ADS)

    Shizuma, Kiyoshi; Endo, Satoru; Shinozaki, Kenji; Fukushima, Hiroshi

    2013-05-01

    Fast neutron activation data for 63Ni in copper samples exposed to the Hiroshima atomic bomb are important in evaluating neutron doses to the survivors. Up to until now, accelerator mass spectrometry and liquid scintillation counting methods have been applied in 63Ni measurements and data were accumulated within 1500 m from the hypocenter. The slope of the activation curve versus distance shows reasonable agreement with the calculation result, however, data near the hypocenter are scarce. In the present work, two copper samples obtained from the Atomic bomb dome (155 m from the hypocenter) and the Bank of Japan building (392 m) were utilized in 63Ni beta-ray measurement with a Si surface barrier detector. Additionally, microscopic observation of the metal surfaces was performed for the first time. Only upper limit of 63Ni production was obtained for copper sample of the Atomic bomb dome. The result of the 63Ni measurement for Bank of Japan building show reasonable agreement with the AMS measurement and to fast neutron activation calculations based on the Dosimetry System 2002 (DS02) neutrons.

  13. Low-temperature SiON films deposited by plasma-enhanced atomic layer deposition method using activated silicon precursor

    SciTech Connect

    Suh, Sungin; Kim, Jun-Rae; Kim, Seongkyung; Hwang, Cheol Seong; Kim, Hyeong Joon; Ryu, Seung Wook; Cho, Seongjae

    2016-01-15

    It has not been an easy task to deposit SiN at low temperature by conventional plasma-enhanced atomic layer deposition (PE-ALD) since Si organic precursors generally have high activation energy for adsorption of the Si atoms on the Si-N networks. In this work, in order to achieve successful deposition of SiN film at low temperature, the plasma processing steps in the PE-ALD have been modified for easier activation of Si precursors. In this modification, the efficiency of chemisorption of Si precursor has been improved by additional plasma steps after purging of the Si precursor. As the result, the SiN films prepared by the modified PE-ALD processes demonstrated higher purity of Si and N atoms with unwanted impurities such as C and O having below 10 at. % and Si-rich films could be formed consequently. Also, a very high step coverage ratio of 97% was obtained. Furthermore, the process-optimized SiN film showed a permissible charge-trapping capability with a wide memory window of 3.1 V when a capacitor structure was fabricated and measured with an insertion of the SiN film as the charge-trap layer. The modified PE-ALD process using the activated Si precursor would be one of the most practical and promising solutions for SiN deposition with lower thermal budget and higher cost-effectiveness.

  14. Synthetically Tuned Atomic Ordering in PdCu Nanoparticles with Enhanced Catalytic Activity toward Solvent-Free Benzylamine Oxidation.

    PubMed

    Marakatti, Vijaykumar S; Sarma, Saurav Ch; Joseph, Boby; Banerjee, Dipanjan; Peter, Sebastian C

    2017-02-01

    Synthesis of ordered compounds with nano size is of particular interest for tuning the surface properties with enhanced activity and selectivity toward various important industrial catalytic processes. In this work, we synthesized ordered PdCu nanoparticles as highly efficient catalyst for the solvent-free aerobic oxidation of benzylamine. The PdxCu1-x catalysts with different chemical compositions (x = 0, 0.25, 0.4, 0.5, 0.6, 0.75, 1) were prepared by polyol method using NaBH4 as a reducing agent and were well-characterized by X-ray diffraction (XRD), inductively coupled plasma optical emission spectroscopy, X-ray photoelectron spectroscopy, transmission electron microscopy (TEM) energy-dispersive analysis of X-rays, and X-ray absorption fine structure. The effect of different metal concentrations of Pd and Cu on the formation of PdxCu1-x nanoparticles was investigated. The XRD and TEM confirmed the formation of ordered PdCu intermetallic phase with body-centered cubic (BCC) structure for the synthetic composition of Pd/Cu = 1:1. For compositions x = 0, 0.25, 0.75, and 1, PdxCu1-x alloy with face-centered cubic (FCC) structure was observed, whereas mixed phase of BCC and FCC was observed for x = 0.4 and 0.6. The use of strong reducing agent (NaBH4) was essential to synthesize PdCu ordered phase compared to weak reducing agents such as oleylamine and ascorbic acid. The PdCu nanocatalyst with ordered structure (BCC) showed excellent catalytic activity compared to PdxCu1-x alloy nanoparticles with FCC structure. The atomic ordering in the PdCu intermetallic was the driving force for the enhancement in the catalytic activity with high benzylamine conversion of 94.0% and dibenzylimine selectivity of 92.2% compared to its monometallic and alloy counterparts. Moreover, ordered PdCu alloy showed good recyclability and activity toward the oxidation of different amines.

  15. Solidification analysis of a centrifugal atomizer using the Al-32.7wt.% Cu alloy

    SciTech Connect

    Osborne, Matthew G.

    1998-02-23

    A centrifugal atomizer (spinning disk variety) was designed and constructed for the production of spherical metal powders, 100-1,000 microns in diameter in an inert atmosphere. Initial atomization experiments revealed the need for a better understanding of how the liquid metal was atomized and how the liquid droplets solidified. To investigate particle atomization, Ag was atomized in air and the process recorded on high-speed film. To investigate particle solidification, Al-32.7 wt.% Cu was atomized under inert atmosphere and the subsequent particles were examined microscopically to determine solidification structure and rate. This dissertation details the experimental procedures used in producing the Al-Cu eutectic alloy particles, examination of the particle microstructures, and determination of the solidification characteristics (e.g., solidification rate) of various phases. Finally, correlations are proposed between the operation of the centrifugal atomizer and the observed solidification spacings.

  16. 3D Quantification of Low-Coordinate Surface Atom Density: Bridging Catalytic Activity to Concave Facets of Nanocatalysts in Fuel Cells.

    PubMed

    Xia, Ye; Zhong, Xiaoyan; Ke, Xiaoxing; Zhang, Gui-Rong; Cheng, Zhiying; Xu, Bo-Qing

    2016-12-01

    A protocol to quantify the distribution of surface atoms of concave nanocatalysts according to their coordination number is proposed. The 3D surface of an Au@Pd concave nanocube is reconstructed and segmented. The crystallographic coordinates and low-coordinate surface atom densities of the concave facets are determined. The result shows that 32% of the surface atoms are low-coordinated, which may contribute to the high activity.

  17. [The progress in speciation analysis of trace elements by atomic spectrometry].

    PubMed

    Wang, Zeng-Huan; Wang, Xu-Nuo; Ke, Chang-Liang; Lin, Qin

    2013-12-01

    The main purpose of the present work is to review the different non-chromatographic methods for the speciation analysis of trace elements in geological, environmental, biological and medical areas. In this paper, the sample processing methods in speciation analysis were summarized, and the main strategies for non-chromatographic technique were evaluated. The basic principles of the liquid extractions proposed in the published literatures recently and their advantages and disadvantages were discussed, such as conventional solvent extraction, cloud point extraction, single droplet microextraction, and dispersive liquid-liquid microextraction. Solid phase extraction, as a non-chromatographic technique for speciation analysis, can be used in batch or in flow detection, and especially suitable for the online connection to atomic spectrometric detector. The developments and applications of sorbent materials filled in the columns of solid phase extraction were reviewed. The sorbents include chelating resins, nanometer materials, molecular and ion imprinted materials, and bio-sorbents. Other techniques, e. g. hydride generation technique and coprecipitation, were also reviewed together with their main applications.

  18. Activity of N-coordinated multi-metal-atom active site structures for Pt-free oxygen reduction reaction catalysis: Role of *OH ligands

    PubMed Central

    Holby, Edward F.; Taylor, Christopher D.

    2015-01-01

    We report calculated oxygen reduction reaction energy pathways on multi-metal-atom structures that have previously been shown to be thermodynamically favorable. We predict that such sites have the ability to spontaneously cleave the O2 bond and then will proceed to over-bind reaction intermediates. In particular, the *OH bound state has lower energy than the final 2 H2O state at positive potentials. Contrary to traditional surface catalysts, this *OH binding does not poison the multi-metal-atom site but acts as a modifying ligand that will spontaneously form in aqueous environments leading to new active sites that have higher catalytic activities. These *OH bound structures have the highest calculated activity to date. PMID:25788358

  19. Activity of N-coordinated multi-metal-atom active site structures for Pt-free oxygen reduction reaction catalysis: Role of *OH ligands

    DOE PAGES

    Holby, Edward F.; Taylor, Christopher D.

    2015-03-19

    We report calculated oxygen reduction reaction energy pathways on multi-metal-atom structures that have previously been shown to be thermodynamically favorable. We predict that such sites have the ability to spontaneously cleave the O₂ bond and then will proceed to over-bind reaction intermediates. In particular, the *OH bound state has lower energy than the final 2 H₂O state at positive potentials. Contrary to traditional surface catalysts, this *OH binding does not poison the multi-metal-atom site but acts as a modifying ligand that will spontaneously form in aqueous environments leading to new active sites that have higher catalytic activities. These *OH boundmore » structures have the highest calculated activity to date.« less

  20. Activity of N-coordinated multi-metal-atom active site structures for Pt-free oxygen reduction reaction catalysis: Role of *OH ligands

    SciTech Connect

    Holby, Edward F.; Taylor, Christopher D.

    2015-03-19

    We report calculated oxygen reduction reaction energy pathways on multi-metal-atom structures that have previously been shown to be thermodynamically favorable. We predict that such sites have the ability to spontaneously cleave the O₂ bond and then will proceed to over-bind reaction intermediates. In particular, the *OH bound state has lower energy than the final 2 H₂O state at positive potentials. Contrary to traditional surface catalysts, this *OH binding does not poison the multi-metal-atom site but acts as a modifying ligand that will spontaneously form in aqueous environments leading to new active sites that have higher catalytic activities. These *OH bound structures have the highest calculated activity to date.

  1. Activity of N-coordinated multi-metal-atom active site structures for Pt-free oxygen reduction reaction catalysis: Role of *OH ligands

    NASA Astrophysics Data System (ADS)

    Holby, Edward F.; Taylor, Christopher D.

    2015-03-01

    We report calculated oxygen reduction reaction energy pathways on multi-metal-atom structures that have previously been shown to be thermodynamically favorable. We predict that such sites have the ability to spontaneously cleave the O2 bond and then will proceed to over-bind reaction intermediates. In particular, the *OH bound state has lower energy than the final 2 H2O state at positive potentials. Contrary to traditional surface catalysts, this *OH binding does not poison the multi-metal-atom site but acts as a modifying ligand that will spontaneously form in aqueous environments leading to new active sites that have higher catalytic activities. These *OH bound structures have the highest calculated activity to date.

  2. Analysis conditions of an industrial Al-Mg-Si alloy by conventional and 3D atom probes.

    PubMed

    Danoix, F; Miller, M K; Bigot, A

    2001-10-01

    Industrial 6016 Al-Mg-Si(Cu) alloys are presently regarded as attractive candidates for heat treatable sheet materials. Their mechanical properties can be adjusted for a given application by age hardening of the alloys. The resulting microstructural evolution takes place at the nanometer scale, making the atom probe a well suited instrument to study it. Accuracy of atom probe analysis of these aluminium alloys is a key point for the understanding of the fine scale microstructural evolution. It is known to be strongly dependent on the analysis conditions (such as specimen temperature and pulse fraction) which have been widely studied for ID atom probes. The development of the 3D instruments, as well as the increase of the evaporation pulse repetition rate have led to different analysis conditions, in particular evaporation and detection rates. The influence of various experimental parameters on the accuracy of atom probe data, in particular with regard to hydride formation sensitivity, has been reinvestigated. It is shown that hydrogen contamination is strongly dependent on the electric field at the specimen surface, and that high evaporation rates are beneficial. Conversely, detection rate must be limited to smaller than 0.02 atoms/pulse in order to prevent drastic pile-up effect.

  3. Oxide-Nanotrap-Anchored Platinum Nanoparticles with High Activity and Sintering Resistance by Area-Selective Atomic Layer Deposition.

    PubMed

    Liu, Xiao; Zhu, Qianqian; Lang, Yun; Cao, Kun; Chu, Shengqi; Shan, Bin; Chen, Rong

    2017-02-01

    An area-selective atomic layer deposition (AS-ALD) method is described to construct oxide nanotraps to anchor Pt nanoparticles (NPs) on Al2 O3 supports. The as-synthesized catalysts have exhibited outstanding room-temperature CO oxidation activity, with a significantly lowered apparent activation energy (ca. 22.17 kJ mol(-1) ) that is half that of pure Pt catalyst with the same loading. Furthermore, the structure shows excellent sintering resistance with the high catalytic activity retention up to 600 °C calcination. The key feature of the oxide nanotraps lies in its ability to anchor Pt NPs via strong metal-oxide interactions while still leaving active metal facets exposed. Our reported method for forming such oxide structure with nanotraps shows great potential for the simultaneous enhancement of thermal stability and activity of precious metal NPs.

  4. Mini-Column Ion-Exchange Separation and Atomic Absorption Quantitation of Nickel, Cobalt, and Iron: An Undergraduate Quantitative Analysis Experiment.

    ERIC Educational Resources Information Center

    Anderson, James L.; And Others

    1980-01-01

    Presents an undergraduate quantitative analysis experiment, describing an atomic absorption quantitation scheme that is fast, sensitive and comparatively simple relative to other titration experiments. (CS)

  5. The atomic orbitals of the topological atom.

    PubMed

    Ramos-Cordoba, Eloy; Salvador, Pedro; Mayer, István

    2013-06-07

    The effective atomic orbitals have been realized in the framework of Bader's atoms in molecules theory for a general wavefunction. This formalism can be used to retrieve from any type of calculation a proper set of orthonormalized numerical atomic orbitals, with occupation numbers that sum up to the respective Quantum Theory of Atoms in Molecules (QTAIM) atomic populations. Experience shows that only a limited number of effective atomic orbitals exhibit significant occupation numbers. These correspond to atomic hybrids that closely resemble the core and valence shells of the atom. The occupation numbers of the remaining effective orbitals are almost negligible, except for atoms with hypervalent character. In addition, the molecular orbitals of a calculation can be exactly expressed as a linear combination of this orthonormalized set of numerical atomic orbitals, and the Mulliken population analysis carried out on this basis set exactly reproduces the original QTAIM atomic populations of the atoms. Approximate expansion of the molecular orbitals over a much reduced set of orthogonal atomic basis functions can also be accomplished to a very good accuracy with a singular value decomposition procedure.

  6. In Situ Conductance Analysis of Zinc Oxide Nucleation and Coalescence during Atomic Layer Deposition on Metal Oxides and Polymers.

    PubMed

    Sweet, William J; Parsons, Gregory N

    2015-07-07

    Real time in situ conductance is collected continuously during atomic layer deposition (ALD) of zinc oxide films, and trends are used to study ALD nucleation on polypropylene, nylon-6, SiO2, TiO2, and Al2O3 substrates. The detailed conductance change during the ALD cycle is ascribed to changes in surface band bending upon precursor/reactant exposure. Conductive pathways form earlier on the inorganic surfaces than on the polymers, with Al2O3 substrates showing more rapid nucleation than SiO2 or TiO2, consistent with the expected density of nucleation sites (e.g., hydroxyl groups) on these different materials. The measured conductance is ohmic, and both two- and four-electrode configurations show the same data trends. Detailed analysis of conductivity at deposition temperatures between 100 and 175 °C shows faster conductivity decay at higher temperature during the water purge step, ascribed to thermally activated water desorption kinetics. Analysis of real-time conductivity during ALD of other material systems could provide further insight into key aspects of film nucleation and nuclei coalescence.

  7. Atomic resolution structure of prokaryotic phospholipase A2: analysis of internal motion and implication for a catalytic mechanism.

    PubMed

    Matoba, Yasuyuki; Sugiyama, Masanori

    2003-05-15

    We have found a secreted phospholipase A(2) (PLA(2), EC 3.1.1.4) from Streptomyces violaceoruber A-2688, which is the first PLA(2) identified in prokaryote, and determined its tertiary structure by NMR and X-ray analyses. In this study, we collected the X-ray diffraction data of the bacterial PLA(2) at room temperature (297 K) using conventional MoK(alpha) radiation and refined the structure at a 1.05 A resolution. The atomic resolution analysis led us to introduce disordered conformations and hydrogen atoms into a full anisotropic model. The molecular motion, which is expressed as the sum of rigid-body motion and internal motion of protein, is roughly estimated as the thermal motion when the X-ray diffraction data are collected at room temperature. In this study, we applied a TLS (rigid-body motion in terms of translation, libration, and screw motions) model to analyze the rigid-body motion of the bacterial PLA(2) and calculated the internal motion by subtracting the estimate of the rigid-body motion from the observed anisotropic temperature factor. We also subjected the TLS model to estimate the internal motion of the bovine pancreatic PLA(2) using the anisotropic temperature factor deposited in the Protein Data Bank. Both results indicate that the localization of regions exhibiting larger internal motion in the bacterial PLA(2) is almost the same as that in the bovine pancreatic PLA(2), suggesting that although the tertiary structure of the bacterial PLA(2) is strikingly different from that of the bovine pancreatic PLA(2), the internal motion, which is associated with the calcium(II) ion-binding, phospholipid-binding, and allosteric interfacial activation, is commonly observed in both PLA(2)s.

  8. Nonperturbative analysis of the two-level atom: Applications to multiphoton excitation

    SciTech Connect

    Duvall, R.E.; Valeo, E.J.; Oberman, C.R.

    1987-08-01

    Selective excitation in an atomic system subjected to a slowly varying external electromagnetic field is studied using a two-level model. Time evolution of the system is found using an approach which is nonperturbative in the field strength. There is no constraint to small values of the applied field, that is, the field (in appropriate energy units) need not be small compared to the difference in energies of the two levels. Rather, we prey upon the fact that the situation of interest to us is where the frequency of the exciting field is small compared to the frequency associated with the level difference. Transition probabilities and resonance conditions are found which circumscribe both the large and small field limits. In the weak field limit the previous results of high-order perturbation theory are readily recovered. For a monochromatic field the characteristic features of resonance excitation at high harmonic number of the applied field are (a) extremely narrow resonance widths and (b) shifts in resonance positions which are strong functions of field intensity. Because of this sensitivity, we are able to demonstrate that when slow temporal evolution of the field amplitude is taken into account (e.g., due to finite pulse duration) the appropriate mean excitation rate is that due to the uncorrelated contribution of many resonances. The results of this analysis are used to estimate excitation rates in a specific atomic system, Cd/sup 12 +/, which are then compared to multiphoton ionization rates. Our calculations suggest that the ionization rate exceeds the excitation rate by several orders of magnitude. 15 refs., 3 figs.

  9. Quantitative chemical-structure evaluation using atom probe tomography: Short-range order analysis of Fe-Al.

    PubMed

    Marceau, R K W; Ceguerra, A V; Breen, A J; Raabe, D; Ringer, S P

    2015-10-01

    Short-range-order (SRO) has been quantitatively evaluated in an Fe-18Al (at%) alloy using atom probe tomography (APT) data and by calculation of the generalised multicomponent short-range order (GM-SRO) parameters, which have been determined by shell-based analysis of the three-dimensional atomic positions. The accuracy of this method with respect to limited detector efficiency and spatial resolution is tested against simulated D03 ordered data. Whilst there is minimal adverse effect from limited atom probe instrument detector efficiency, the combination of this with imperfect spatial resolution has the effect of making the data appear more randomised. The value of lattice rectification of the experimental APT data prior to GM-SRO analysis is demonstrated through improved information sensitivity.

  10. Intrinsic differences in atomic ordering of calcium (alumino)silicate hydrates in conventional and alkali-activated cements

    SciTech Connect

    White, Claire E.; Daemen, Luke L.; Hartl, Monika; Page, Katharine

    2015-01-15

    The atomic structures of calcium silicate hydrate (C–S–H) and calcium (–sodium) aluminosilicate hydrate (C–(N)–A–S–H) gels, and their presence in conventional and blended cement systems, have been the topic of significant debate over recent decades. Previous investigations have revealed that synthetic C–S–H gel is nanocrystalline and due to the chemical similarities between ordinary Portland cement (OPC)-based systems and low-CO{sub 2} alkali-activated slags, researchers have inferred that the atomic ordering in alkali-activated slag is the same as in OPC–slag cements. Here, X-ray total scattering is used to determine the local bonding environment and nanostructure of C(–A)–S–H gels present in hydrated tricalcium silicate (C{sub 3}S), blended C{sub 3}S–slag and alkali-activated slag, revealing the large intrinsic differences in the extent of nanoscale ordering between C–S–H derived from C{sub 3}S and alkali-activated slag systems, which may have a significant influence on thermodynamic stability, and material properties at higher length scales, including long term durability of alkali-activated cements.

  11. First dating of groundwater with Atom Trap Trace Analysis of 39Ar - application

    NASA Astrophysics Data System (ADS)

    Reichel, Thomas; Kersting, Arne; Ritterbusch, Florian; Ebser, Sven; Bender, Klaus; Purtschert, Roland; Oberthaler, Markus; Aeschbach-Hertig, Werner

    2013-04-01

    Groundwater from the intermediate aquifer layers of the Rhine Graben sediments in the Rhein-Neckar metropolitan region is strongly exploited for the purpose of drinking water supply. Isotope hydrological investigations of the regional groundwater dynamics have been initiated with the ultimate goal of improving the protection of this important water resource. However, these studies are hampered by the fact that the groundwater falls in the age dating gap of classical isotope methods between about 50 and 1000 years of water age, which can only be bridged by the extremely rare isotope 39Ar. Here we report and discuss the first 39Ar groundwater ages obtained by the new analytical method Atom Trap Trace Analysis (ATTA). Groundwater samples from the Upper Rhine Graben aquifers were collected and analysed by established methods for a large range of tracers, including tritium, stable isotopes, noble gases, and 14C. For 39Ar analysis, several tons of water were degassed in the field using a membrane contactor. In the laboratory, a gas-chromatographic system at cryogenic temperatures was used to separate pure argon from the extracted gas. ATTA was then used to isolate and count 39Ar atoms from these samples. In parallel, samples for 39Ar analysis by low-level counting at the University of Bern were taken to enable comparison of the two analytical techniques. The resulting 39Ar groundwater ages in the range of several hundred years are in accordance with the indications obtained from the classical dating tracers. They provide quantitative information on the groundwater travel time for an important, strongly exploited part of the investigated aquifer system, which could not be obtained from the other tracers. These results significantly improve the knowledge of the time scale of groundwater renewal in the aquifer layers of intermediate depth. Furthermore, the combination of the 39Ar age scale with noble gas recharge temperatures and stable isotope data has the potential to

  12. Total body nitrogen analysis. [neutron activation analysis

    NASA Technical Reports Server (NTRS)

    Palmer, H. E.

    1975-01-01

    Studies of two potential in vivo neutron activation methods for determining total and partial body nitrogen in animals and humans are described. A method using the CO-11 in the expired air as a measure of nitrogen content was found to be adequate for small animals such as rats, but inadequate for human measurements due to a slow excretion rate. Studies on the method of measuring the induced N-13 in the body show that with further development, this method should be adequate for measuring muscle mass changes occurring in animals or humans during space flight.

  13. Nanoscale Stoichiometric Analysis of a High-Temperature Superconductor by Atom Probe Tomography.

    PubMed

    Pedrazzini, Stella; London, Andrew J; Gault, Baptiste; Saxey, David; Speller, Susannah; Grovenor, Chris R M; Danaie, Mohsen; Moody, Michael P; Edmondson, Philip D; Bagot, Paul A J

    2017-01-31

    The functional properties of the high-temperature superconductor Y1Ba2Cu3O7-δ (Y-123) are closely correlated to the exact stoichiometry and oxygen content. Exceeding the critical value of 1 oxygen vacancy for every five unit cells (δ>0.2, which translates to a 1.5 at% deviation from the nominal oxygen stoichiometry of Y7.7Ba15.3Cu23O54-δ ) is sufficient to alter the superconducting properties. Stoichiometry at the nanometer scale, particularly of oxygen and other lighter elements, is extremely difficult to quantify in complex functional ceramics by most currently available analytical techniques. The present study is an analysis and optimization of the experimental conditions required to quantify the local nanoscale stoichiometry of single crystal yttrium barium copper oxide (YBCO) samples in three dimensions by atom probe tomography (APT). APT analysis required systematic exploration of a wide range of data acquisition and processing conditions to calibrate the measurements. Laser pulse energy, ion identification, and the choice of range widths were all found to influence composition measurements. The final composition obtained from melt-grown crystals with optimized superconducting properties was Y7.9Ba10.4Cu24.4O57.2.

  14. Simultaneous multielemental analysis of some environmental and biological samples by inductively coupled plasma atomic emission spectrometry

    SciTech Connect

    Hee, S.S.Q.; Boyle, J.R.

    1988-05-15

    The Parr bomb technique is found to be the preferred acid digestion method for multielemental analysis by simultaneous inductively coupled plasma atomic emission spectroscopy (ICP-AES) when compared with microwave and hot plate methods for many environmental and biological specimens, but especially for the latter. One digestion alone often did not produce quantitative results compared with a sequential digestion scheme. The digestions were then refined to be as similar as possible for the various substrates studied. The interference of carbon on As and Se had to be corrected at less than or equal to 3000 ..mu..g of C/mL in the analysis solution, and thus the C content had to be monitored to assess the efficiency of the digestions and to determine if interelemental correction for C presence was required. The C correction was adequate in the range 3000-10,000 ..mu..g of C/ml. The use of modified k values was demonstrated to provide accuracy and had to be used for ICP-AES spectrometers where background corrections were performed first for fixed channels. The results on Cincinnati soils and feces of Cincinnati children showed that Si and Ti were possible tracer elements for soil ingestion by the children.

  15. Thermal denaturation studies of collagen by microthermal analysis and atomic force microscopy.

    PubMed

    Bozec, Laurent; Odlyha, Marianne

    2011-07-06

    The structural properties of collagen have been the subject of numerous studies over past decades, but with the arrival of new technologies, such as the atomic force microscope and related techniques, a new era of research has emerged. Using microthermal analysis, it is now possible to image samples as well as performing localized thermal measurements without damaging or destroying the sample itself. This technique was successfully applied to characterize the thermal response between native collagen fibrils and their denatured form, gelatin. Thermal transitions identified at (150 ± 10)°C and (220 ± 10)°C can be related to the process of gelatinization of the collagen fibrils, whereas at higher temperatures, both the gelatin and collagen samples underwent two-stage transitions with a common initial degradation temperature at (300 ± 10)°C and a secondary degradation temperature of (340 ± 10)°C for the collagen and of (420 ± 10)°C for the gelatin, respectively. The broadening and shift in the secondary degradation temperature was linked to the spread of thermal degradation within the gelatin and collagen fibrils matrix further away from the point of contact between probe and sample. Finally, similar measurements were performed inside a bone resorption lacuna, suggesting that microthermal analysis is a viable technique for investigating the thermomechanical response of collagen for in situ samples that would be, otherwise, too challenging or not possible using bulk techniques.

  16. ATOMIC DIFFUSION AND MIXING IN OLD STARS. III. ANALYSIS OF NGC 6397 STARS UNDER NEW CONSTRAINTS

    SciTech Connect

    Nordlander, T.; Korn, A. J.; Richard, O.; Lind, K.

    2012-07-01

    We have previously reported on chemical abundance trends with evolutionary state in the globular cluster NGC 6397 discovered in analyses of spectra taken with FLAMES at the Very Large Telescope. Here, we reinvestigate the FLAMES-UVES sample of 18 stars, ranging from just above the turnoff point to the red giant branch below the bump. Inspired by new calibrations of the infrared flux method, we adopt a set of hotter temperature scales. Chemical abundances are determined for six elements (Li, Mg, Ca, Ti, Cr, and Fe). Signatures of cluster-internal pollution are identified and corrected for in the analysis of Mg. On the modified temperature scales, evolutionary trends in the abundances of Mg and Fe are found to be significant at the 2{sigma} and 3{sigma} levels, respectively. The detailed evolution of abundances for all six elements agrees with theoretical isochrones, calculated with effects of atomic diffusion and a weak to moderately strong efficiency of turbulent mixing. The age of these models is compatible with the external determination from the white dwarf cooling sequence. We find that the abundance analysis cannot be reconciled with the strong turbulent-mixing efficiency inferred elsewhere for halo field stars. A weak mixing efficiency reproduces observations best, indicating a diffusion-corrected primordial lithium abundance of log {epsilon}(Li) = 2.57 {+-} 0.10. At 1.2{sigma}, this value agrees well with Wilkinson Microwave Anisotropy Probe calibrated big bang nucleosynthesis predictions.

  17. Thermal Denaturation Studies of Collagen by Microthermal Analysis and Atomic Force Microscopy

    PubMed Central

    Bozec, Laurent; Odlyha, Marianne

    2011-01-01

    The structural properties of collagen have been the subject of numerous studies over past decades, but with the arrival of new technologies, such as the atomic force microscope and related techniques, a new era of research has emerged. Using microthermal analysis, it is now possible to image samples as well as performing localized thermal measurements without damaging or destroying the sample itself. This technique was successfully applied to characterize the thermal response between native collagen fibrils and their denatured form, gelatin. Thermal transitions identified at (150 ± 10)°C and (220 ± 10)°C can be related to the process of gelatinization of the collagen fibrils, whereas at higher temperatures, both the gelatin and collagen samples underwent two-stage transitions with a common initial degradation temperature at (300 ± 10)°C and a secondary degradation temperature of (340 ± 10)°C for the collagen and of (420 ± 10)°C for the gelatin, respectively. The broadening and shift in the secondary degradation temperature was linked to the spread of thermal degradation within the gelatin and collagen fibrils matrix further away from the point of contact between probe and sample. Finally, similar measurements were performed inside a bone resorption lacuna, suggesting that microthermal analysis is a viable technique for investigating the thermomechanical response of collagen for in situ samples that would be, otherwise, too challenging or not possible using bulk techniques. PMID:21723833

  18. Structural analysis and classification of human metaphase chromosomes by atomic force microscopy

    NASA Astrophysics Data System (ADS)

    Okamoto, Naoaki; Okada, Takao

    1999-06-01

    We applied atomic force microscopy (AFM) to the analysis and classification of metaphase chromosomes. Human chromosomes were isolated from blood and spread over a glass substrate. We found that air-dried and Giemsa stained chromosomes had a granular surface and the height of approximately 250 nm; however unstained chromosomes had a smooth surface and the height was approximately 100 nm. Giemsa staining caused swelling of the chromosome structure. For the structural analysis, chromosomes were treated with hyaluronidase or a citric acid buffer. The effects of the treatments on chromosomal components, spiral structure and 30-nm solenoid fiber were observed. Each step of G-banding treatments of chromosomes was also visualized by AFM. The trypsin treatment collapsed the chromosomes and subsequent Giemsa staining caused dramatically reswelling of the chromosomes. The height of the G-positive region was approximately 200 nm but the unstained region was approximately 50 nm. The difference in thickness observed was produced by binding of the dye. The AFM image of the banding patterns of treated chromosomes was clearer than the image obtained with an optical microscope. These images made it possible to visualize the karyotyping of chromosomes using AFM. Detection of in situ hybridization using AFM and microdissection of chromosomes using AFM were also investigated.

  19. Deformation analysis of amorphous metals based on atomic elastic stiffness coefficients

    NASA Astrophysics Data System (ADS)

    Yashiro, K.; Nishimura, M.; Tomita, Y.

    2006-06-01

    The elastic limit of a crystal can be evaluated by the positiveness of elastic stiffness coefficients, Bijkl. We had demonstrated that the nucleation of lattice defects such as dislocation and cleavage cracking can be predicted by the atomic Bijkl at each atom point. Amorphous metals and bulk metallic glasses draw intense interest whether the criteria are applicable or not since they are regarded as the ultimate of lattice defects. In the present study, an amorphous Ni-Al binary alloy is made by a usual melt-quench simulation and subjected to tension by means of molecular dynamics simulation. During simulations, the positiveness of atomic Bijkl is discussed for all atoms. Contrary to an Ni-Al crystal, many atoms show negative value even in the initial equilibrium of the amorphous before loading. These unstable atoms turn out to be the non-clustered atom or the outer-shell of the local cluster such as 12(0, 0, 12, 0) icosahedron. On the other hand, the centre atoms of the local clusters show high stability resulting in the positive Bijkl of the whole system. It is also demonstrated that the change in the atomic Bijkl can reveal the collapse and re-configuration of local clusters during the deformation.

  20. Solvatochromism, spectral properties and antimicrobial activities of new azo-azomethine dyes with N2S2O2 donor set of atoms

    NASA Astrophysics Data System (ADS)

    Khanmohammadi, Hamid; Pass, Maryam; Rezaeian, Khatereh; Talei, Gholamreza

    2014-08-01

    Six new azo-azomethine dyes, H2Ln (n = 1-6), with N2S2O2 donor set of atoms have been prepared via condensation reaction of 1,10-diaza-4,7-dithiadecane, I, with substituted azo-coupled salicylaldehyde. The dyes were characterized by IR, UV-Vis and 1H NMR spectroscopic methods as well as elemental analysis. The solvatochromic behavior of the dyes was also probed by studying their UV-Vis spectra in four pure organic solvents of different polarities and a meaningful correlation was observed. Furthermore, all prepared dyes were assayed for their antibacterial and antifungal activities by disc diffusion method. The results indicated that all prepared dyes show good inhibition against Staphylococcus epidermidis and Bacillus cereus and did not show any antibacterial activity against Escherichia coli as compared to standard drugs.

  1. The Journey from Classical to Quantum Thinking: An Analysis of Student Understanding through the Lens of Atomic Spectra

    ERIC Educational Resources Information Center

    Rao, Sandhya Kolla

    2012-01-01

    This dissertation aims to explore how students think about atomic absorption and emission of light in the area of introductory quantum chemistry. In particular, the impact of classical ideas of electron position and energy on student understanding of spectra is studied. The analysis was undertaken to discover how student learning can be…

  2. Analysis of the Alternative Conceptions of Preservice Teachers and High School Students Concerning Atomic Size

    ERIC Educational Resources Information Center

    Eymur, Guluzar; Çetin, Pinar; Geban, Ömer

    2013-01-01

    The purpose of this study was to analyze and compare the alternative conceptions of high school students and preservice teachers on the concept of atomic size. The Atomic Size Diagnostic Instrument was developed; it is composed of eight, two-tier multiple-choice items. The results of the study showed that as a whole 56.2% of preservice teachers…

  3. Chemical analysis of impurity boron atoms in diamond using soft X-ray emission spectroscopy.

    PubMed

    Muramatsu, Yasuji; Iihara, Junji; Takebe, Toshihiko; Denlinger, Jonathan D

    2008-07-01

    To analyze the local structure and/or chemical states of boron atoms in boron-doped diamond, which can be synthesized by the microwave plasma-assisted chemical vapor deposition method (CVD-B-diamond) and the temperature gradient method at high pressure and high temperature (HPT-B-diamond), we measured the soft X-ray emission spectra in the CK and BK regions of B-diamonds using synchrotron radiation at the Advanced Light Source (ALS). X-ray spectral analyses using the fingerprint method and molecular orbital calculations confirm that boron atoms in CVD-B-diamond substitute for carbon atoms in the diamond lattice to form covalent B-C bonds, while boron atoms in HPT-B-diamond react with the impurity nitrogen atoms to form hexagonal boron nitride. This suggests that the high purity diamond without nitrogen impurities is necessary to synthesize p-type B-diamond semiconductors.

  4. Modelization of nanospace interaction involving a ferromagnetic atom: a spin polarization effect study by thermogravimetric analysis.

    PubMed

    Santhanam, K S V; Chen, Xu; Gupta, S

    2014-04-01

    Ab initio studies of ferromagnetic atom interacting with carbon nanotubes have been reported in the literature that predict when the interaction is strong, a higher hybridization with confinement effect will result in spin polarization in the ferromagnetic atom. The spin polarization effect on the thermal oxidation to form its oxide is modeled here for the ferromagnetic atom and its alloy, as the above studies predict the 4s electrons are polarized in the atom. The four models developed here provide a pathway for distinguishing the type of interaction that exists in the real system. The extent of spin polarization in the ferromagnetic atom has been examined by varying the amount of carbon nanotubes in the composites in the thermogravimetric experiments. In this study we report the experimental results on the CoNi alloy which appears to show selective spin polarization. The products of the thermal oxidation has been analyzed by Fourier Transform Infrared Spectroscopy.

  5. Interaction of Rydberg atoms with surfaces. Using surface ionisation as a probe for surface analysis

    NASA Astrophysics Data System (ADS)

    Kohlhoff, Mike W.

    2016-12-01

    The interface of neutral Rydberg atoms in the gas phase with a solid surface is of interest in many fields of modern research. This interface poses a particular challenge for any application in which Rydberg atoms are close to a substrate but also opens up the possibility of studying properties of the surface material itself through the atomic response. In this review the focus is on the process of electron tunneling from the excited state into the substrate that occurs when a Rydberg atom is located in front of a surface at a range of a few hundred nm and is demonstrated with a metallic surface. It is shown how variations in this ionisation mechanism can provide a powerful tool to probe image-charge effects, measure small superficial electric stray or patch fields and how charge transfer from the Rydberg atom can be in resonance with energetically discrete surface states.

  6. Chemical Analysis of Impurity Boron Atoms in Diamond Using Soft X-ray Emission Spectroscopy

    SciTech Connect

    Muramatsu, Yasuji; Iihara, Junji; Takebe, Toshihiko; Denlinger, Jonathan D.

    2008-03-29

    To analyze the local structure and/or chemical states of boron atoms in boron-doped diamond, which can be synthesized by the microwave plasma-assisted chemical vapor deposition method (CVD-B-diamond) and the temperature gradient method at high pressure and high temperature (HPT-B-diamond), we measured the soft X-ray emission spectra in the CK and BK regions of B-diamonds using synchrotron radiation at the Advanced Light Source (ALS). X-ray spectral analyses using the fingerprint method and molecular orbital calculations confirm that boron atoms in CVD-B-diamond substitute for carbon atoms in the diamond lattice to form covalent B-C bonds, while boron atoms in HPT-B-diamond react with the impurity nitrogen atoms to form hexagonal boron nitride. This suggests that the high purity diamond without nitrogen impurities is necessary to synthesize p-type B-diamond semiconductors.

  7. Atomic-scale analysis of plastic deformation in thin-film forms of electronic materials

    NASA Astrophysics Data System (ADS)

    Kolluri, Kedarnath

    Nanometer-scale-thick films of metals and semiconductor heterostructures are used increasingly in modern technologies, from microelectronics to various areas of nanofabrication. Processing of such ultrathin-film materials generates structural defects, including voids and cracks, and may induce structural transformations. Furthermore, the mechanical behavior of these small-volume structures is very different from that of bulk materials. Improvement of the reliability, functionality, and performance of nano-scale devices requires a fundamental understanding of the atomistic mechanisms that govern the thin-film response to mechanical loading in order to establish links between the films' structural evolution and their mechanical behavior. Toward this end, a significant part of this study is focused on the analysis of atomic-scale mechanisms of plastic deformation in freestanding, ultrathin films of face-centered cubic (fcc) copper (Cu) that are subjected to biaxial tensile strain. The analysis is based on large-scale molecular-dynamics simulations. Elementary mechanisms of dislocation nucleation are studied and several problems involving the structural evolution of the thin films due to the glide of and interactions between dislocations are addressed. These problems include void nucleation, martensitic transformation, and the role of stacking faults in facilitating dislocation depletion in ultrathin films and other small-volume structures of fcc metals. Void nucleation is analyzed as a mechanism of strain relaxation in Cu thin films. The glide of multiple dislocations causes shearing of atomic planes and leads to formation of surface pits, while vacancies are generated due to the glide motion of jogged dislocations. Coalescence of vacancy clusters with surface pits leads to formation of voids. In addition, the phase transformation of fcc Cu films to hexagonal-close packed (hcp) ones is studied. The resulting martensite phase nucleates at the film's free surface and

  8. Investigating the role of atomic hydrogen on chloroethene reactions with iron using tafel analysis and electrochemical impedance spectroscopy.

    PubMed

    Wang, Jiankang; Farrell, James

    2003-09-01

    Metallic iron filings are commonly employed as reducing agents in permeable barriers used for remediating groundwater contaminated by chlorinated solvents. Reactions of trichloroethylene (TCE) and tetrachloroethylene (PCE) with zerovalent iron were investigated to determine the role of atomic hydrogen in their reductive dechlorination. Experiments simultaneously measuring dechlorination and iron corrosion rates were performed to determine the fractions of the total current going toward dechlorination and hydrogen evolution. Corrosion rates were determined using Tafel analysis, and dechlorination rates were determined from rates of byproduct generation. Electrochemical impedance spectroscopy (EIS) was used to determine the number of reactions that controlled the observed rates of chlorocarbon disappearance, as well as the role of atomic hydrogen in TCE and PCE reduction. Comparison of iron corrosion rates with those for TCE reaction showed that TCE reduction occurred almost exclusively via atomic hydrogen at low pH values and via atomic hydrogen and direct electron transfer at neutral pH values. In contrast, reduction of PCE occurred primarily via direct electron transfer at both low and neutral pH values. At low pH values and micromolar concentrations, TCE reaction rates were faster than those for PCE due to more rapid reduction of TCE by atomic hydrogen. At neutral pH values and millimolar concentrations, PCE reaction rates were faster than those for TCE. This shift in relative reaction rates was attributed to a decreasing contribution of the atomic hydrogen reaction mechanism with increasing halocarbon concentrations and pH values. The EIS data showed that all the rate limitations for TCE and PCE dechlorination occurred during the transfer of the first two electrons. Results from this study show that differences in relative reaction rates of TCE and PCE with iron are dependent on the significance of the reduction pathway involving atomic hydrogen.

  9. Kinetic-Energy Distribution of D(2p) Atoms from Analysis of the D Lyman-Alpha Line Profile

    NASA Technical Reports Server (NTRS)

    Ciocca, M.; Ajello, Joseph M.; Liu, Xianming; Maki, Justin

    1997-01-01

    The kinetic-energy distribution of D(2p) atoms resulting from electron-impact dissociation of D2 has been measured. A high-resolution vacuum ultraviolet spectrometer was employed for the first measurement of the D Lyman-alpha (D L(alpha)) emission line profiles at 20- and 100-eV excitation energies. Analysis of the deconvoluted line profile of D L(alpha) at 100 eV reveals the existence of a narrow line central peak of 29+/-2 mA full width at half maximum and a broad pedestal wing structure about 190 mA wide. The wings of the line can be used to determine the fast atom distribution. The wings of D L(alpha) arise from dissociative excitation of a series of doubly excited states that cross the Franck-Condon region between 23 and 40 eV. The fast atom distribution at 100-eV electron impact energy spans the energy range from 1 to 10 eV with a peak value near 6 eV. Slow D(2p) atoms characterized by a distribution function with peak energy near 100 meV produce the central peak profile, which is nearly independent of the impact energy. The deconvoluted line profiles of the central peak at 20 eV for dissociative excitation of D2 and H2 are fitted with an analytical function for use in calibration of space flight instrumentation equipped with a D/H absorption cell. The kinetic-energy and line profile results are compared to similar measurements for H2. The absolute cross sections for the line center (slow atoms) and wings (fast atoms) and total emission line profile were measured from threshold to 400 eV. Analytical model coefficients are given for the energy dependence of the measured slow atom cross section.

  10. Atomic force microscopy analysis of synthetic membranes applied in release studies

    NASA Astrophysics Data System (ADS)

    Olejnik, Anna; Nowak, Izabela

    2015-11-01

    Synthetic membranes are commonly used in drug release studies and are applied mostly in quality control. They contain pores through which the drug can be diffused directly into the receptor fluid. Investigation of synthetic membranes permits determination of their structure and characterization of their properties. We suggest that the preliminary characterization of the membranes can be relevant to the interpretation of the release results. The aim of this study was to compare eight synthetic membranes by using atomic force microscopy in order to predict and understand their behavior in the release experiments. The results proved that polytetrafluoroethylene membrane was not suitable for the release study of tetrapeptide due to its hydrophobic nature, thickness and the specific structure with high trapezoid shaped blocks. The additional substructures in pores of mixed cellulose esters and nylon membranes detected by AFM influenced the diffusion rate of the active compound. These findings indicate that the selection of the membrane for the release studies should be performed cautiously by taking into consideration the membrane properties and by analyzing them prior the experiment.

  11. Peak separation method for sub-lattice strain analysis at atomic resolution: Application to InAs/GaSb superlattice.

    PubMed

    Kim, Honggyu; Meng, Yifei; Rouviére, Jean-Luc; Zuo, Jian-Min

    2017-01-01

    We report on a direct measurement of cation and anion sub-lattice strain in an InAs/GaSb type-II strained layer superlattice (T2SLs) using atomic resolution imaging and advanced image processing. Atomic column positions in InAs and GaSb are determined by separating the cation and anion peak intensities. Analysis of the InAs/GaSb T2SLs reveals the compressive strain in the nominal GaSb layer and tensile strain at interfaces between constituent layers, which indicate In incorporation into the nominal GaSb layer and the formation of GaAs like interfaces, respectively. The results are compared with the model-dependent X-ray diffraction measurements in terms of interfacial chemical intermixing and strain. Together, these techniques provide a robust measurement of atomic-scale strain which is vital to determine T2SL properties.

  12. An atomic force microscopy statistical analysis of laser-induced azo-polyimide periodic tridimensional nanogrooves.

    PubMed

    Stoica, Iuliana; Epure, Luiza; Sava, Ion; Damian, Victor; Hurduc, Nicolae

    2013-09-01

    The surface morphology of azo-polyimide films was investigated after 355 nm Nd: YAG laser irradiation with two different incident fluencies. Atomic force microscopy (AFM) was employed to correlate the laser-induced tridimensional nanogrooved surface relief with the incident fluence and the number of irradiation pulses. The height images revealed that the grooves depth increased even tens of times by increasing the incident fluence, using the same numbers of irradiation pulses. For low incident fluence, the films were uniformly patterned till 100 pulses of irradiation. Instead, when using higher fluence, after 15 pulses of irradiation the accuracy of the surface relief definition was reduced. This behavior could be explained by means of two different mechanisms, one that suppose the film photo-fluidization due to the cis-trans isomerization processes of the azo-groups and the second one responsible for the directional mass displacement. The dominant surface direction and parameters like isotropy, periodicity, and period were evaluated from the polar representation for texture analysis, revealing the appearance of ordered and directionated nanostructures for most of the experimental conditions. Also, the graphical studies of the functional volume parameters have evidenced the improvement of the relief structuration during surface nanostructuration. The correlation of these statistical texture parameters with the irradiation characteristics is important in controlling the alignment of either the liquid crystals or the cells/tissues on patterned azo-polyimide surfaces for optoelectronic devices and implantable biomaterials, respectively.

  13. Analysis of 2015 Meteorological Data from the Knolls Atomic Power Laboratory and Kesselring Site Operations Facilities

    SciTech Connect

    Aluzzi, F. J.

    2016-02-19

    Both the Knolls Atomic Power Laboratory (KAPL) in Schenectady, N.Y. and the Kesselring Site Operations (KSO) facility near Ballston Spa, N.Y. are required to estimate the effects of hypothetical emissions of radiological material from their respective facilities by the U.S. Environmental Protection Agency (EPA), which regulates both sites. An atmospheric dispersion model known as CAP88, which was developed and approved by the EPA for such purposes, is used by KAPL and KSO to meet this requirement. CAP88 calculations over a given time period are based on statistical data on the meteorological conditions for that period. Both KAPL and KSO have on-site meteorological towers which take atmospheric measurements at a frequency ideal for EPA regulatory model input. However, an independent analysis and processing of the meteorological data from each tower is required to derive a data set appropriate for use in the CAP88 model. The National Atmospheric Release Advisory Center (NARAC) was contracted to process the meteorological tower data for the 2015 calendar year from both on-site meteorological towers.

  14. Analysis of 2014 Meteorological Data from the Knolls Atomic Power Laboratory and Kesselring Site Operations Facilities

    SciTech Connect

    Aluzzi, Fernando J.

    2015-02-25

    Both the Knolls Atomic Power Laboratory (KAPL) in Schenectady, N.Y. and the Kesselring Site Operations (KSO) facility near Ballston Spa, N.Y. are required to estimate the effects of hypothetical emissions of radiological material from their respective facilities by the U.S. Environmental Protection Agency (EPA), which regulates both sites. An atmospheric dispersion model known as CAP88, which was developed and approved by the EPA for such purposes, is used by KAPL and KSO to meet this requirement. CAP88 calculations over a given time period are based on statistical data on the meteorological conditions for that period. Both KAPL and KSO have on-site meteorological towers which take atmospheric measurements at a frequency ideal for EPA regulatory model input. However, an independent analysis and processing of the meteorological data from each tower is required to derive a data set appropriate for use in the CAP88 model. The National Atmospheric Release Advisory Center (NARAC) was contracted by KAPL to process the on-site data for the calendar year 2014.

  15. Improved preparation of small biological samples for mercury analysis using cold vapor atomic absorption spectroscopy.

    PubMed

    Adair, B M; Cobb, G P

    1999-05-01

    Concentrations of mercury in biological samples collected for environmental studies are often less than 0.1 microgram/g. Low mercury concentrations and small organ sizes in many wildlife species (approximately 0.1 g) increase the difficulty of mercury determination at environmentally relevant concentrations. We have developed a digestion technique to extract mercury from small (0.1 g), biological samples at these relevant concentrations. Mean recoveries (+/- standard error) from validation trials of mercury fortified tissue samples using cold vapor atomic absorption spectroscopy for analysis ranged from 102 +/- 4.3% (2.5 micrograms/L, n = 15) to 108 +/- 1.4% (25 micrograms/L, n = 15). Recoveries of inorganic mercury were 99 +/- 5 (n = 19) for quality assurance samples analyzed during environmental evaluations conducted during a 24 month period. This technique can be used to determine total mercury concentrations of 60 ng Hg/g sample. Samples can be analyzed in standard laboratories in a short time, at minimal cost. The technique is versatile and can be used to determine mercury concentrations in several different matrices, limiting the time and expense of method development and validation.

  16. Determination of firing distance. Lead analysis on the target by atomic absorption spectroscopy (AAS).

    PubMed

    Gagliano-Candela, Roberto; Colucci, Anna P; Napoli, Salvatore

    2008-03-01

    This paper reports a method for the determination of the firing distance. Atomic absorption spectroscopy (AAS) was used to determine the lead (Pb) pattern around bullet holes produced by shots on test targets from the gun. Test shots were made with a Colt 38 Special at 5, 10, 20, 25, 30, 35, 40, 45, 50, 60, 80, and 100 cm target distance. The target was created with sheets of Whatman no. 1 paper on a polystyrene support. The target was subdivided into three carefully cut out rings (1, 2, and 3; with external diameters of 1.4 cm; 5 cm; 10.2 cm, respectively). Each sample was analyzed with graphite furnace AAS. Lead values analysis performed for each ring yielded a linear relation between the firing distance (cm) and the logarithm of lead amounts (microg/cm(2)) in definite target areas (areas 2 + 3): [ln dPb(2+3) = a(0) + a(1)l]; where dPb(2+3) = lead microg/cm(2) of area 2 + 3; a(0) and a(1) are experimentally calculated; l = distance in cm.

  17. Characteristics of receptor- and transducer-coupled activation of the intracellular signalling in sensory neuron revealed by atomic force microscopy

    NASA Astrophysics Data System (ADS)

    Khalisov, M. M.; Penniyaynen, V. A.; Esikova, N. A.; Ankudinov, A. V.; Krylov, B. V.

    2017-01-01

    The mechanical properties of sensory neurons upon activation of intracellular cascade processes by comenic acid binding to a membrane opioid-like receptor (receptor-coupled), as well as a very low (endogenous) concentration of ouabain (transducer-coupled), have been investigated. Using atomic force microscopy, it is established that exposure to ouabain, in contrast to the impact of comenic acid, leads to a hardening of the neuron soma. This suggests that the receptor-coupled signal transmission to the cell genome is carried out through mechanisms that are different from the transducer-coupled signal pathways.

  18. Chitinase activity on amorphous chitin thin films: a quartz crystal microbalance with dissipation monitoring and atomic force microscopy study.

    PubMed

    Wang, Chao; Kittle, Joshua D; Qian, Chen; Roman, Maren; Esker, Alan R

    2013-08-12

    Chitinases are widely distributed in nature and have wide-ranging pharmaceutical and biotechnological applications. This work highlights a real-time and label-free method to assay Chitinase activity via a quartz crystal microbalance with dissipation monitoring (QCM-D) and atomic force microscopy (AFM). The chitin substrate was prepared by spincoating a trimethylsilyl chitin solution onto a silica substrate, followed by regeneration to amorphous chitin (RChi). The QCM-D and AFM results clearly showed that the hydrolysis rate of RChi films increased as Chitinase (from Streptomyces griseus) concentrations increased, and the optimal temperature and pH for Chitinase activity were around 37 °C and 6-8, respectively. The Chitinase showed greater activity on chitin substrates, having a high degree of acetylation, than on chitosan substrates, having a low degree of acetylation.

  19. Quantitative analysis of doped/undoped ZnO nanomaterials using laser assisted atom probe tomography: Influence of the analysis parameters

    SciTech Connect

    Amirifar, Nooshin; Lardé, Rodrigue Talbot, Etienne; Pareige, Philippe; Rigutti, Lorenzo; Mancini, Lorenzo; Houard, Jonathan; Castro, Celia; Sallet, Vincent; Zehani, Emir; Hassani, Said; Sartel, Corine; Ziani, Ahmed; Portier, Xavier

    2015-12-07

    In the last decade, atom probe tomography has become a powerful tool to investigate semiconductor and insulator nanomaterials in microelectronics, spintronics, and optoelectronics. In this paper, we report an investigation of zinc oxide nanostructures using atom probe tomography. We observed that the chemical composition of zinc oxide is strongly dependent on the analysis parameters used for atom probe experiments. It was observed that at high laser pulse energies, the electric field at the specimen surface is strongly dependent on the crystallographic directions. This dependence leads to an inhomogeneous field evaporation of the surface atoms, resulting in unreliable measurements. We show that the laser pulse energy has to be well tuned to obtain reliable quantitative chemical composition measurements of undoped and doped ZnO nanomaterials.

  20. A fuzzy-atom analysis of electron delocalization on hydrogen bonds.

    PubMed

    Guillaumes, L; Salvador, P; Simon, S

    2014-02-13

    The extent of electron delocalization is quantified for set of cyclic complexes exhibiting two or more hydrogen bonds (HBs). In particular, the delocalization index (DI) between the atoms directly involved in the HB, and the ING (a normalized n-center delocalization index) have been evaluated using several fuzzy-atom schemes, namely Becke, Becke-ρ, Hirshfeld, and Hirshfeld-Iterative. The results have been compared with the widely used Quantum Theory of Atoms in Molecules (QTAIM) atomic definition. The DI values are found to correlate very well with geometrical or topological descriptors widely used in the literature to characterize HB systems. Among all fuzzy-atom methods, the ones that can better accommodate the different partial ionic character of the bonds perform particularly well. The best performing fuzzy-atom scheme for both pairwise and n-center electron delocalization is found to be the Becke-ρ method, for which similar results to QTAIM model are obtained with a much reduced computational cost. These results open up a wide range of applications of such electron delocalization descriptors based on fuzzy-atoms for noncovalent interactions in more complex and larger systems.

  1. The enrichment ratio of atomic contacts in crystals, an indicator derived from the Hirshfeld surface analysis.

    PubMed

    Jelsch, Christian; Ejsmont, Krzysztof; Huder, Loïc

    2014-03-01

    The partitioning of space with Hirshfeld surfaces enables the analysis of fingerprint molecular interactions in crystalline environments. This study uses the decomposition of the crystal contact surface between pairs of interacting chemical species to derive an enrichment ratio. This quantity enables the analysis of the propensity of chemical species to form intermolecular interactions with themselves and other species. The enrichment ratio is obtained by comparing the actual contacts in the crystal with those computed as if all types of contacts had the same probability to form. The enrichments and contact tendencies were analyzed in several families of compounds, based on chemical composition and aromatic character. As expected, the polar contacts of the type H⋯N, H⋯O and H⋯S, which are generally hydrogen bonds, show enrichment values larger than unity. O⋯O and N⋯N contacts are impoverished while H⋯H interactions display enrichment ratios which are generally close to unity or slightly lower. In aromatic compounds, C⋯C contacts can display large enrichment ratios due to extensive π⋯π stacking in the crystal packings of heterocyclic compounds. C⋯C contacts are, however, less enriched in pure (C,H) hydrocarbons as π⋯π stacking is not so favourable from the electrostatic point of view compared with heterocycles. C⋯H contacts are favoured in (C,H) aromatics, but these interactions occur less in compounds containing O, N or S as some H atoms are then involved in hydrogen bonds. The study also highlights the fact that hydrogen is a prefered interaction partner for fluorine.

  2. Localization and force analysis at the single virus particle level using atomic force microscopy

    SciTech Connect

    Liu, Chih-Hao; Horng, Jim-Tong; Chang, Jeng-Shian; Hsieh, Chung-Fan; Tseng, You-Chen; Lin, Shiming

    2012-01-06

    Highlights: Black-Right-Pointing-Pointer Localization of single virus particle. Black-Right-Pointing-Pointer Force measurements. Black-Right-Pointing-Pointer Force mapping. -- Abstract: Atomic force microscopy (AFM) is a vital instrument in nanobiotechnology. In this study, we developed a method that enables AFM to simultaneously measure specific unbinding force and map the viral glycoprotein at the single virus particle level. The average diameter of virus particles from AFM images and the specificity between the viral surface antigen and antibody probe were integrated to design a three-stage method that sets the measuring area to a single virus particle before obtaining the force measurements, where the influenza virus was used as the object of measurements. Based on the purposed method and performed analysis, several findings can be derived from the results. The mean unbinding force of a single virus particle can be quantified, and no significant difference exists in this value among virus particles. Furthermore, the repeatability of the proposed method is demonstrated. The force mapping images reveal that the distributions of surface viral antigens recognized by antibody probe were dispersed on the whole surface of individual virus particles under the proposed method and experimental criteria; meanwhile, the binding probabilities are similar among particles. This approach can be easily applied to most AFM systems without specific components or configurations. These results help understand the force-based analysis at the single virus particle level, and therefore, can reinforce the capability of AFM to investigate a specific type of viral surface protein and its distributions.

  3. AtomPy: an open atomic-data curation environment

    NASA Astrophysics Data System (ADS)

    Bautista, Manuel; Mendoza, Claudio; Boswell, Josiah S; Ajoku, Chukwuemeka

    2014-06-01

    We present a cloud-computing environment for atomic data curation, networking among atomic data providers and users, teaching-and-learning, and interfacing with spectral modeling software. The system is based on Google-Drive Sheets, Pandas (Python Data Analysis Library) DataFrames, and IPython Notebooks for open community-driven curation of atomic data for scientific and technological applications. The atomic model for each ionic species is contained in a multi-sheet Google-Drive workbook, where the atomic parameters from all known public sources are progressively stored. Metadata (provenance, community discussion, etc.) accompanying every entry in the database are stored through Notebooks. Education tools on the physics of atomic processes as well as their relevance to plasma and spectral modeling are based on IPython Notebooks that integrate written material, images, videos, and active computer-tool workflows. Data processing workflows and collaborative software developments are encouraged and managed through the GitHub social network. Relevant issues this platform intends to address are: (i) data quality by allowing open access to both data producers and users in order to attain completeness, accuracy, consistency, provenance and currentness; (ii) comparisons of different datasets to facilitate accuracy assessment; (iii) downloading to local data structures (i.e. Pandas DataFrames) for further manipulation and analysis by prospective users; and (iv) data preservation by avoiding the discard of outdated sets.

  4. Preparation of water and ice samples for 39Ar dating by atom trap trace analysis (ATTA)

    NASA Astrophysics Data System (ADS)

    Schwefel, R.; Reichel, T.; Aeschbach-Hertig, W.; Wagenbach, D.

    2012-04-01

    Atom trap trace analysis (ATTA) is a new and promising method to measure very rare noble gas radioisotopes in the environment. The applicability of this method for the dating of very old groundwater with 81Kr has already been demonstrated [1]. Recent developments now show its feasibility also for the analysis of 39Ar [2,3], which is an ideal dating tracer for the age range between 50 and 1000 years. This range is of interest in the fields of hydro(geo)logy, oceanography, and glaciology. We present preparation (gas extraction and Ar separation) methods for groundwater and ice samples for later analysis by the ATTA technique. For groundwater, the sample size is less of a limitation than for applications in oceanography or glaciology. Large samples are furthermore needed to enable a comparison with the classical method of 39Ar detection by low-level counting. Therefore, a system was built that enables gas extraction from several thousand liters of water using membrane contactors. This system provides degassing efficiencies greater than 80 % and has successfully been tested in the field. Gas samples are further processed to separate a pure Ar fraction by a gas-chromatographic method based on Li-LSX zeolite as selective adsorber material at very low temperatures. The gas separation achieved by this system is controlled by a quadrupole mass spectrometer. It has successfully been tested and used on real samples. The separation efficiency was found to be strongly temperature dependent in the range of -118 to -130 °C. Since ATTA should enable the analysis of 39Ar on samples of less than 1 ccSTP of Ar (corresponding to about 100 ml of air, 2.5 l of water or 1 kg of ice), a method to separate Ar from small amounts of gas was developed. Titanium sponge was found to absorb 60 ccSTP of reactive gases per g of the getter material with reasonably high absorption rates at high operating temperatures (~ 800 ° C). Good separation (higher than 92 % Ar content in residual gas) was

  5. Atom-economic catalytic amide synthesis from amines and carboxylic acids activated in situ with acetylenes

    PubMed Central

    Krause, Thilo; Baader, Sabrina; Erb, Benjamin; Gooßen, Lukas J.

    2016-01-01

    Amide bond-forming reactions are of tremendous significance in synthetic chemistry. Methodological research has, in the past, focused on efficiency and selectivity, and these have reached impressive levels. However, the unacceptable amounts of waste produced have led the ACS GCI Roundtable to label ‘amide bond formation avoiding poor atom economy' as the most pressing target for sustainable synthetic method development. In response to this acute demand, we herein disclose an efficient one-pot amide coupling protocol that is based on simple alkynes as coupling reagents: in the presence of a dichloro[(2,6,10-dodecatriene)-1,12-diyl]ruthenium catalyst, carboxylate salts of primary or secondary amines react with acetylene or ethoxyacetylene to vinyl ester intermediates, which undergo aminolysis to give the corresponding amides along only with volatile acetaldehyde or ethyl acetate, respectively. The new amide synthesis is broadly applicable to the synthesis of structurally diverse amides, including dipeptides. PMID:27282773

  6. Macroscopic irreversibility and microscopic paradox: A Constructal law analysis of atoms as open systems

    PubMed Central

    Lucia, Umberto

    2016-01-01

    The relation between macroscopic irreversibility and microscopic reversibility is a present unsolved problem. Constructal law is introduced to develop analytically the Einstein’s, Schrödinger’s, and Gibbs’ considerations on the interaction between particles and thermal radiation (photons). The result leads to consider the atoms and molecules as open systems in continuous interaction with flows of photons from their surroundings. The consequent result is that, in any atomic transition, the energy related to the microscopic irreversibility is negligible, while when a great number of atoms (of the order of Avogadro’s number) is considered, this energy related to irreversibility becomes so large that its order of magnitude must be taken into account. Consequently, macroscopic irreversibility results related to microscopic irreversibility by flows of photons and amount of atoms involved in the processes. PMID:27762333

  7. Macroscopic irreversibility and microscopic paradox: A Constructal law analysis of atoms as open systems

    NASA Astrophysics Data System (ADS)

    Lucia, Umberto

    2016-10-01

    The relation between macroscopic irreversibility and microscopic reversibility is a present unsolved problem. Constructal law is introduced to develop analytically the Einstein’s, Schrödinger’s, and Gibbs’ considerations on the interaction between particles and thermal radiation (photons). The result leads to consider the atoms and molecules as open systems in continuous interaction with flows of photons from their surroundings. The consequent result is that, in any atomic transition, the energy related to the microscopic irreversibility is negligible, while when a great number of atoms (of the order of Avogadro’s number) is considered, this energy related to irreversibility becomes so large that its order of magnitude must be taken into account. Consequently, macroscopic irreversibility results related to microscopic irreversibility by flows of photons and amount of atoms involved in the processes.

  8. Analysis of concentration characteristics in ultrasonic atomization by droplet diameter distribution.

    PubMed

    Yasuda, Keiji; Bando, Yoshiyuki; Yamaguchi, Soyoko; Nakamura, Masaaki; Oda, Akiyoshi; Kawase, Yasuhito

    2005-01-01

    The droplet diameter distribution and concentration characteristics in ultrasonic atomization were experimentally studied. The samples were aqueous solutions of methanol, ethanol and 1-propanol. The diameter distribution of atomized droplets showed the normal distribution, and the median diameter and standard deviation were expressed by means of the ultrasonic condition and the liquid properties. The concentration characteristic in ultrasonic atomization was analyzed by using the model of shell and core to the atomized droplet, where the former and latter consist of solute and solution, respectively. The value, which was surface solute amount in droplet multiplied by the molecular volume, increased with increasing solute molar fraction in bulk liquid and was independent of alcohol kinds. The rate of accompanying liquid and the solute molar fraction in accompanied liquid were estimated from the diameter distribution and the surface solute amount in droplet.

  9. Active control of electromagnetically induced transparency with dual dark mode excitation pathways using MEMS based tri-atomic metamolecules

    NASA Astrophysics Data System (ADS)

    Pitchappa, Prakash; Manjappa, Manukumara; Ho, Chong Pei; Singh, Ranjan; Singh, Navab; Lee, Chengkuo

    2016-11-01

    We report experimental results of the active switching of electromagnetically induced transparency (EIT) analogue by controlling the dark mode excitation pathways in a microelectromechanical system based tri-atomic metamolecule, operating in the terahertz spectral region. The tri-atomic metamolecule consists of two bright cut wire resonators (CWRs) on either side of the dark split ring resonators (SRRs). Each of the CWRs can independently excite the dark inductive-capacitive resonance mode of the SRRs through inductive coupling, and this allows for the dual pathways of dark mode excitation. The CWRs are made movable along the out-of-plane direction and electrically isolated to achieve selective reconfiguration. Hence, by controlling the physical position of these CWRs, the excitation pathways can be actively reconfigured. This enables the strong excitation of EIT analogue at 0.65 THz, only when one of the pathways is made accessible. Moreover, the transparency peak is completely modulated when both pathways are made either inaccessible or equally accessible. The proposed approach of realizing independent control of constituent resonators in a multi-resonator coupled system, enables the realization of efficient slow light devices and tunable high-Q resonators in terahertz spectral region.

  10. Activation of Propane C-H and C-C Bonds by Gas-Phase Pt Atom: A Theoretical Study

    PubMed Central

    Li, Fang-Ming; Yang, Hua-Qing; Ju, Ting-Yong; Li, Xiang-Yuan; Hu, Chang-Wei

    2012-01-01

    The reaction mechanism of the gas-phase Pt atom with C3H8 has been systematically investigated on the singlet and triplet potential energy surfaces at CCSD(T)//BPW91/6-311++G(d, p), Lanl2dz level. Pt atom prefers the attack of primary over secondary C-H bonds in propane. For the Pt + C3H8 reaction, the major and minor reaction channels lead to PtC3H6 + H2 and PtCH2 + C2H6, respectively, whereas the possibility to form products PtC2H4 + CH4 is so small that it can be neglected. The minimal energy reaction pathway for the formation of PtC3H6 + H2, involving one spin inversion, prefers to start at the triplet state and afterward proceed along the singlet state. The optimal C-C bond cleavages are assigned to C-H bond activation as the first step, followed by cleavage of a C-C bond. The C-H insertion intermediates are kinetically favored over the C-C insertion intermediates. From C-C to C-H oxidative insertion, the lowering of activation barrier is mainly caused by the more stabilizing transition state interaction ΔE≠int, which is the actual interaction energy between the deformed reactants in the transition state. PMID:22942766

  11. Innovative bi-fluid atomizer inner flow characterization and outer spray diffusion analysis

    NASA Astrophysics Data System (ADS)

    Elzo, D.; Mazin, C.

    2012-11-01

    We developed an atomizer nozzle equipping a medical device used for airborne disinfection of medical rooms. The diffusion technology of the equipment is based on the spraying of fine liquid droplets of disinfectant into the volume to be treated. The liquid phase is expulsed thanks to an air assist atomizer we designed, which originality comes from the geometry we give to the throat of the micro-venturi, inner part of the atomizer nozzle. The micro-venturi throat is deviated of angle of 4° and will permit a homogeneous diffusion. We computed three dimensional numerical calculations of the inner compressible turbulent air flow through the atomizer we designed and compared the results obtained with the ones computed for a symmetrical atomizer. The modeling was done with the CFD codes STARCCM+ and Fluent, choosing the k-omega turbulent model. The modeling has been validated especially by one dimensional analytical calculations and experimental measurements of the mean axial velocity and mass flow rate circulating through the atomizer. Three dimensional numerical calculations show the vertical deviation of the flow at throat level and swirl effect generated by the deviated inner throat of the micro-venturi. These calculations allowed understanding the nature of the spray observed in experimental conditions, and the advantages to use a deviated micro-venturi throat. Indeed, micro bacteriological tests showed that the quality and the effectiveness of the diffusion are enhanced in comparison to equipments with a symmetrical micro-venturi.

  12. Theoretical analysis of the spectroscopy of atomic Bose-Hubbard systems

    NASA Astrophysics Data System (ADS)

    Inaba, Kensuke; Yamashita, Makoto

    2016-04-01

    We provide a numerical method to calculate comprehensively the microwave and the laser spectra of ultracold bosonic atoms in optical lattices at finite temperatures. Our formulation is built up with the sum rules, up to the second order, derived from the general principle of spectroscopy. The sum rule approach allows us to discuss the physical origins of a spectral peak shift and also a peak broadening. We find that a spectral broadening of superfluid atoms can be determined from number fluctuations of atoms, while that of normal-state atoms is mainly attributed to quantum fluctuations resulting from hopping of atoms. To calculate spectra at finite temperatures, based on the sum rule approach, we provide a two-mode approximation assuming that spectra of the superfluid and normal state atoms can be calculated separately. Our method can properly deal with multipeak structures of spectra resulting from thermal fluctuations and also coexisting of the superfluid and the normal states. By combining the two-mode approximation with a finite temperature Gutzwiller approximation, we calculate spectra at finite temperatures by considering realistic systems, and the calculated spectra show nice agreements with those in experiments.

  13. Comparative analysis of the atomization characteristics of fifteen biodiesel fuel types

    SciTech Connect

    Allen, C.A.W.; Watts, K.C.

    2000-04-01

    Engine results using biofuels have varied considerably in the reported literature. This article addresses two potential sources of this variation, atomization differences and impurities due to lack of quality control during production. Atomization is the first process encountered during the combustion of fuels in a compression ignition engine and is largely determined by the fuel's viscosity and surface tension. Previous work using five experimentally produced methyl ester biodiesel fuels showed that the viscosity and surface tension could be predicted from their fatty acid ester composition, and the atomization characteristics in turn could be predicted from their viscosity and surface tension. This article utilizes the results of that work to give a quantitative comparison of the atomization characteristics of fifteen biodiesel fuel types using the fuel's viscosity and surface tension, predicted directly from the fatty acid composition of the fuels. Except for coconut and rapeseed biodiesel fuels, all of the rest of the 15 biodiesel fuels had similar atomization characteristics. Since the most likely contaminant in the fuel from the processing was residual glycerides, their effect on viscosity and surface tension was studied experimentally and their effect on the atomization characteristics was computed.

  14. Neutron Activation Analysis of Water - A Review

    NASA Technical Reports Server (NTRS)

    Buchanan, John D.

    1971-01-01

    Recent developments in this field are emphasized. After a brief review of basic principles, topics discussed include sources of neutrons, pre-irradiation physical and chemical treatment of samples, neutron capture and gamma-ray analysis, and selected applications. Applications of neutron activation analysis of water have increased rapidly within the last few years and may be expected to increase in the future.

  15. Biosynthetic incorporation of telluromethionine into dihydrofolate reductase and crystallographic analysis of the distribution of tellurium atoms in the protein molecule

    SciTech Connect

    Kunkle, M.G.; Lewinski, K.; Boles, J.O.; Dunlap, R.B.; Odom, J.D.; Lebioda, L.

    1994-12-01

    Recent successes in crystallographic studies of proteins with methionine (Met) residues replaced with SeMet, pioneered by Hendrickson and coworkers, inspired us to replace Met with TeMet in Escherichia coli dihydrofolate reductase (DHFR). E. coli DHFR, which catalyzes the NADPH-dependent reduction of dihydrofolate to tetrahydrofolate, consists of 159 residues, 5 of which are Met. TeMet was incorporated into DHFR using the Met auxotroph, E. coli DL41, carrying the expression vector pWT8 with an IPTG inducible promoter and ampicillin resistance gene. The enzyme was purified by successive chromatography on Q-Sepharose and PHenyl Sepharose resins, yielding milligram quantities of homogeneous enzyme with a specific activity of 40 units/mg. TeMet DHFR exhibits kinetic properties similar to those of wt DHFR. Amino acid analysis indicated 3 authentic Met residues in TeMet DHFR, whereas atomic absorption spectroscopy detected 2 Te per protein molecule. Amino acid sequence analysis results suggested that only authentic Met was present in the first three Met positions (1,16,and 20). Crystals of Te-DHFR were grown in the presence of methotrexate from PEG 4000 and were isomorphous with wt-DHFR crystals grown from ethanol. Difference Fourier maps and restrained least-squares refinement show very little, if any, Te in the first three Met positions: Met{sup 1}, Met{sup 16}, and Met{sup 20}, whereas the occupancy of Te in positions 42 and 92 is 0.64. Apparently, the process of folding, subsequent purification, and crystallization select DHFR molecules with Te in Met{sup 42} and Met{sup 92}. Replacing Met with TeMet provides an internal probe that should facilitate structural and mechanistic studies of proteins.

  16. A study of the formation of magnetically active solid dispersions of phenacetin using atomic and magnetic force microscopy.

    PubMed

    Usmanova, Liana Stanislavovna; Ziganshin, Marat Akhmedovich; Gorbatchuk, Valery Vilenovich; Ziganshina, Sufia Askhatovna; Bizyaev, Dmitry Anatolevich; Bukharaev, Anastas Akhmetovich; Mukhametzyanov, Timur Anvarovich; Gerasimov, Alexander Vladimirovich

    2017-01-01

    A lot of pharmaceutical substances have a poor solubility that limits their absorption and distribution to the targeted sites to elicit the desired action without causing untoward effects on healthy cells or tissues. For such drugs, new modes of delivery have to be developed for efficient and effective delivery of the drug to the target site. Formation of magnetically active solid dispersion of such drugs could be a useful approach to addressing this problem because they combine targeted delivery and good solubility. In this work, the distribution of superparamagnetic nanoparticles in the solid dispersion of polyethylene glycol with average molecular weight 950-1050 g/mol and phenacetin was studied using atomic force and magnetic force microscopy. The distribution of nanoparticles was found to be uniform in studied composites. Magnetically active solid dispersions may find application in the production of the capsulated drug delivery systems with enhanced solubility parameters.

  17. A study of the formation of magnetically active solid dispersions of phenacetin using atomic and magnetic force microscopy

    PubMed Central

    Usmanova, Liana Stanislavovna; Ziganshin, Marat Akhmedovich; Gorbatchuk, Valery Vilenovich; Ziganshina, Sufia Askhatovna; Bizyaev, Dmitry Anatolevich; Bukharaev, Anastas Akhmetovich; Mukhametzyanov, Timur Anvarovich; Gerasimov, Alexander Vladimirovich

    2017-01-01

    A lot of pharmaceutical substances have a poor solubility that limits their absorption and distribution to the targeted sites to elicit the desired action without causing untoward effects on healthy cells or tissues. For such drugs, new modes of delivery have to be developed for efficient and effective delivery of the drug to the target site. Formation of magnetically active solid dispersion of such drugs could be a useful approach to addressing this problem because they combine targeted delivery and good solubility. In this work, the distribution of superparamagnetic nanoparticles in the solid dispersion of polyethylene glycol with average molecular weight 950–1050 g/mol and phenacetin was studied using atomic force and magnetic force microscopy. The distribution of nanoparticles was found to be uniform in studied composites. Magnetically active solid dispersions may find application in the production of the capsulated drug delivery systems with enhanced solubility parameters. PMID:28217547

  18. Cationic Membrane Peptides: Atomic-Level Insight of Structure-Activity Relationships from Solid-State NMR

    PubMed Central

    Su, Yongchao; Li, Shenhui; Hong, Mei

    2012-01-01

    Many membrane-active peptides, such as cationic cell-penetrating peptides (CPPs) and antimicrobial peptides (AMPs), conduct their biological functions by interacting with the cell membrane. The interactions of charged residues with lipids and water facilitate membrane insertion, translocation or disruption of these highly hydrophobic species. In this mini-review we will summarize high-resolution structural and dynamic findings towards the understanding of the structure-activity relationship of lipid membrane-bound CPPs and AMPs, as examples of the current development of solid-state NMR (SSNMR) techniques for studying membrane peptides. We will present the most recent atomic-resolution structure of the guanidinium-phosphate complex, as constrained from experimentally measured site-specific distances. These SSNMR results will be valuable specifically for understanding the intracellular translocation pathway of CPPs and antimicrobial mechanism of AMPs, and more generally broaden our insight into how cationic macromolecules interact with and cross the lipid membrane. PMID:23108593

  19. Weak-light rogue waves, breathers, and their active control in a cold atomic gas via electromagnetically induced transparency

    NASA Astrophysics Data System (ADS)

    Liu, Junyang; Hang, Chao; Huang, Guoxiang

    2016-06-01

    We propose a scheme to demonstrate the existence of optical Peregrine rogue waves and Akhmediev and Kuznetsov-Ma breathers and realize their active control via electromagnetically induced transparency (EIT). The system we suggest is a cold, Λ -type three-level atomic gas interacting with a probe and a control laser fields and working under EIT condition. We show that, based on EIT with an incoherent optical pumping, which can be used to cancel optical absorption, (1+1)-dimensional optical Peregrine rogue waves, Akhmediev breathers, and Kuznetsov-Ma breathers can be generated with very low light power. In addition, we demonstrate that the Akhmediev and Kuznetsov-Ma breathers in (2+1)-dimensions obtained can be actively manipulated by using an external magnetic field. As a result, these breathers can display trajectory deflections and bypass obstacles during propagation.

  20. Characterizing nanoscale changes in the activity of VEGFR-2 on glioma microvascular endothelial cell membranes using atomic force microscopy

    PubMed Central

    Zhou, Dexiang; Zhan, Shengquan; Zhou, Dong; Wang, Peng; Chen, Guangzhong; Qin, Kun; Lin, Xiaofeng

    2017-01-01

    The aim of the current study was to demonstrate the distribution of VEGFR-2 on glioma microvascular endothelial cells on a nanoscale and investigate changes in VEGFR-2 activity following treatment with the VEGFR-2 inhibitor and agonist sorafenib and bradykinin, respectively. Three groups were evaluated in this study: Control glioma microvascular endothelial cells, sorafenib-treated glioma microvascular endothelial cells and bradykinin-treated glioma microvascular endothelial cells. Changes in the activity of VEGFR-2 on the glioma microvascular endothelial cell membranes following treatment with sorafenib and bradykinin were characterized by atomic force microscopy (AFM). Colloidal gold-labeled immune complexes and AFM were used to visualize the distribution of VEGFR-2 on the cell membranes. In the control group, VEGFR-2, which was observed as numerous globular structures, was evenly distributed on the cell surface membranes. The majority of the receptors were active. In the sorafenib group, only a few globular structures were observed on the cell membranes, with a density significantly lower than that in the control group (P<0.01). Furthermore, compared with the control group, fewer of the receptors were active. In the bradykinin group, numerous globular structures were densely distributed on the cell membranes, with a density significantly higher than that in the control group (P<0.01). The distribution and activity of VEGFR-2 on glioma microvascular endothelial cell membranes treated with sorafenib and bradykinin suggested that the activity of VEGFR-2 could be regulated by its inhibitor or agonist. PMID:28352319

  1. Importance of π-stacking interactions in the hydrogen atom transfer reactions from activated phenols to short-lived N-oxyl radicals.

    PubMed

    Mazzonna, Marco; Bietti, Massimo; DiLabio, Gino A; Lanzalunga, Osvaldo; Salamone, Michela

    2014-06-06

    A kinetic study of the hydrogen atom transfer from activated phenols (2,6-dimethyl- and 2,6-di-tert-butyl-4-substituted phenols, 2,2,5,7,8-pentamethylchroman-6-ol, caffeic acid, and (+)-cathechin) to a series of N-oxyl radical (4-substituted phthalimide-N-oxyl radicals (4-X-PINO), 6-substituted benzotriazole-N-oxyl radicals (6-Y-BTNO), 3-quinazolin-4-one-N-oxyl radical (QONO), and 3-benzotriazin-4-one-N-oxyl radical (BONO)), was carried out by laser flash photolysis in CH3CN. A significant effect of the N-oxyl radical structure on the hydrogen transfer rate constants (kH) was observed with kH values that monotonically increase with increasing NO-H bond dissociation energy (BDENO-H) of the N-hydroxylamines. The analysis of the kinetic data coupled to the results of theoretical calculations indicates that these reactions proceed by a hydrogen atom transfer (HAT) mechanism where the N-oxyl radical and the phenolic aromatic rings adopt a π-stacked arrangement. Theoretical calculations also showed pronounced structural effects of the N-oxyl radicals on the charge transfer occurring in the π-stacked conformation. Comparison of the kH values measured in this study with those previously reported for hydrogen atom transfer to the cumylperoxyl radical indicates that 6-CH3-BTNO is the best N-oxyl radical to be used as a model for evaluating the radical scavenging ability of phenolic antioxidants.

  2. Complex signal analysis for wind turbine planetary gearbox fault diagnosis via iterative atomic decomposition thresholding

    NASA Astrophysics Data System (ADS)

    Feng, Zhipeng; Liang, Ming

    2014-09-01

    The vibration signals from complex structures such as wind turbine (WT) planetary gearboxes are intricate. Reliable analysis of such signals is the key to success in fault detection and diagnosis for complex structures. The recently proposed iterative atomic decomposition thresholding (IADT) method has shown to be effective in extracting true constituent components of complicated signals and in suppressing background noise interferences. In this study, such properties of the IADT are exploited to analyze and extract the target signal components from complex signals with a focus on WT planetary gearboxes under constant running conditions. Fault diagnosis for WT planetary gearboxes has been a very important yet challenging issue due to their harsh working conditions and complex structures. Planetary gearbox fault diagnosis relies on detecting the presence of gear characteristic frequencies or monitoring their magnitude changes. However, a planetary gearbox vibration signal is a mixture of multiple complex components due to the unique structure, complex kinetics and background noise. As such, the IADT is applied to enhance the gear characteristic frequencies of interest, and thereby diagnose gear faults. Considering the spectral properties of planetary gearbox vibration signals, we propose to use Fourier dictionary in the IADT so as to match the harmonic waves in frequency domain and pinpoint the gear fault characteristic frequency. To reduce computing time and better target at more relevant signal components, we also suggest a criterion to estimate the number of sparse components to be used by the IADT. The performance of the proposed approach in planetary gearbox fault diagnosis has been evaluated through analyzing the numerically simulated, lab experimental and on-site collected signals. The results show that both localized and distributed gear faults, both the sun and planet gear faults, can be diagnosed successfully.

  3. Atomic Absorption Spectrometry Analysis of Trace Elements in Degenerated Intervertebral Disc Tissue

    PubMed Central

    Kubaszewski, Łukasz; Zioła-Frankowska, Anetta; Frankowski, Marcin; Nowakowski, Andrzej; Czabak-Garbacz, Róża; Kaczmarczyk, Jacek; Gasik, Robert

    2014-01-01

    Background Few studies have investigated trace elements (TE) in human intervertebral disc (IVD) tissue. Trace element presence can have diverse meanings: essential TE show the metabolic modalities of the tissue, while environmentally-related TE indicate pollution and tissue-specific absorption and accumulation. IVD is a highly specific compartment with impaired communication with adjacent bone. Analysis of TE in IVD provides new insights regarding tissue metabolism and IVD communication with other tissues. Material/Methods Thirty intervertebral discs were acquired from 22 patients during surgical treatment for degenerative disease. Atomic absorption spectrometry was used to evaluate the concentrations of Al, Cd, Pb, Cu, Ni, Mo, Mg, and Zn. Results Al, Pb, Cu, Mg, and Zn were detected in all samples. Pb was significantly positively correlated with age, and Ni concentration was weakly correlated with population count in the patient’s place of residence. Only Cu was observed in higher concentrations in IVD compared to in other tissues. Significant positive correlations were observed between the following pairs: Mg/Zn, Mg/Al, Mg/Pb, Zn/Al, Zn/Pb, and Al/Pb. Negative correlations were observed between Mg/Cd, Zn/Cd, Mg/Mo, and Mo/Pb. Conclusions This study is one of few to profile the elements in intervertebral discs in patients with degenerative changes. We report significant differences between trace element concentrations in intervertebral discs compared to in other tissues. Knowledge of the TE accumulation pattern is vital for better understanding intervertebral disc nutrition and metabolism. PMID:25366266

  4. Atomic Layer-by-Layer Deposition of Pt on Pd Nanocubes for Catalysts with Enhanced Activity and Durability toward Oxygen Reduction

    SciTech Connect

    Xie, Shuifen; Choi, Sang; Lu, Ning; Roling, Luke T.; Herron, Jeffrey A.; Zhang, Lei; Park, Jinho; Wang, Jinguo; Kim, Moon J.; Xie, Zhaoxiong; Mavrikakis, Manos; Xia, Younan

    2014-06-11

    An effective strategy for reducing the Pt content while retaining the activity of a Pt-based catalyst is to deposit the Pt atoms as ultrathin skins of only a few atomic layers thick on nanoscale substrates made of another metal. During deposition, however, the Pt atoms often take an island growth mode because of a strong bonding between Pt atoms. Here we report a versatile route to the conformal deposition of Pt as uniform, ultrathin shells on Pd nanocubes in a solution phase. The introduction of the Pt precursor at a relatively slow rate and high temperature allowed the deposited Pt atoms to spread across the entire surface of a Pd nanocube to generate a uniform shell. The thickness of the Pt shell could be controlled from one to six atomic layers by varying the amount of Pt precursor added into the system. Compared to a commercial Pt/C catalyst, the Pd@PnL (n = 1-6) core-shell nanocubes showed enhancements in specific activity and durability toward the oxygen reduction reaction (ORR). Density functional theory (DFT) calculations on model (100) surfaces suggest that the enhancement in specific activity can be attributed to the weakening of OH binding through ligand and strain effects, which, in turn, increases the rate of OH hydrogenation. A volcano-type relationship between the ORR specific activity and the number of Pt atomic layers was derived, in good agreement with the experimental results. Both theoretical and experimental studies indicate that the ORR specific activity was maximized for the catalysts based on Pd@Pt2-3L nanocubes. Because of the reduction in Pt content used and the enhancement in specific activity, the Pd@Pt1L nanocubes showed a Pt mass activity with almost three-fold enhancement relative to the Pt/C catalyst.

  5. Fast atom bombardment mass spectral analysis of three new oxidative products of primaquine

    NASA Astrophysics Data System (ADS)

    Sinha, Sukesh N.; Dua, V. K.

    2004-03-01

    FAB mass spectrum of 5,5-di-[6-methoxy-8-(4'-amino-1'butyl amino)] quinoline (PI) was recorded in three different concentrations to establish the structure of new oxidative products of primaquine and also the effect of matrix on percentage relative abundance of molecular as well as fragment ions which were demonstrated first time. At three concentrations, three different behaviors of matrix, molecular and fragment ions were observed. At higher concentration (>1 nM) molecular ion behaved as a base peak, but due to side reaction with matrix certain extra peak were also obtained. Thus, the higher concentration was interesting to show the side reaction of analyte with m-nitro-benzyl alcohol (NBA) but not for molecular weight determination. At the lowest concentration (<0.6 nM) matrix ion behaved as a base peak in addition to molecular ion. Therefore, this region of concentration is useful for determining the molecular weight of the compound. However, the mass spectra of 0.6-1 nM concentrations were useful for structural elucidation as compared to mass spectra below 0.6 nM and above 1 nM. Thus, fast atom bombardment mass spectrum with NBA as a matrix was recorded in between 0.6 and 1 nM concentrations for the structural elucidation of new compounds. Molecular ions and fragment ions of 5,5-di-[6-methoxy-8-(4'-amino-1' butyl amino)] quinoline (PI), 6-methoxy-5,8-di-[4'amino-1'-methyl butyl amino] quinoline (PII), and 5,5-di-[7-hydroxy-6-methoxy-8(4'-amino-1'-methyl butyl amino)] quinoline (PIII) were identified. The fragment ions were obtained due to ring cleavages, Retero-Diels-Alder reaction (RDA), loss of side chain, proton transfer and substituted groups of the ring. On the basis of the fragmentation schemes and molecular ion peaks the structure of three new compounds PI, PII and PIII were proposed. In vitro studies showed that the compounds PI and PII had four times more gametocytocidal activity than primaquine but the compound 6-methoxy-5,8-di-[4'-amino-1'-methyl

  6. Development of atomic layer deposition-activated microchannel plates for single particle detection at cryogenic temperatures

    SciTech Connect

    Gorelikov, Dmitry Sullivan, Neal; Rouffignac, Philippe de; Li, Huazhi; Narayanamoorthy, Jayasri; Tremsin, Anton S.

    2014-03-15

    Atomic layer deposition (ALD) technology is used to nanoengineer functional films inside the pores of microchannel plate (MCP) electron multipliers, enabling a novel MCP manufacturing technology that substantially improves performance and opens novel applications. The authors have developed custom tools and recipes for the growth of conformal films, with optimized conductance and secondary electron emission inside very long channels (∼6–20 μm diameter and >600 μm length, with tens of millions of channels per single MCP) by ALD. The unique ability to tune the characteristics of these ALD films enables their optimization to applications where time-resolved single particle imaging can be performed in extreme conditions, such as high counting rates at cryogenic temperatures. Adhesion of the conductive and emissive nanofilms to the 20 μm pore MCP glass substrates and their mechanical stability over a very wide range of temperatures (10–700 K) were confirmed experimentally. Resistance of ALD MCPs was reproducible during multiple cool-down cycles with no film degradation observed. Optimizing resistance of novel MCPs for operation at cryogenic temperature should enable high count rate event detection at temperatures below 20 K.

  7. Communication between thiamin cofactors in the Escherichia coli pyruvate dehydrogenase complex E1 component active centers: evidence for a "direct pathway" between the 4'-aminopyrimidine N1' atoms.

    PubMed

    Nemeria, Natalia S; Arjunan, Palaniappa; Chandrasekhar, Krishnamoorthy; Mossad, Madouna; Tittmann, Kai; Furey, William; Jordan, Frank

    2010-04-09

    Kinetic, spectroscopic, and structural analysis tested the hypothesis that a chain of residues connecting the 4'-aminopyrimidine N1' atoms of thiamin diphosphates (ThDPs) in the two active centers of the Escherichia coli pyruvate dehydrogenase complex E1 component provides a signal transduction pathway. Substitution of the three acidic residues (Glu(571), Glu(235), and Glu(237)) and Arg(606) resulted in impaired binding of the second ThDP, once the first active center was filled, suggesting a pathway for communication between the two ThDPs. 1) Steady-state kinetic and fluorescence quenching studies revealed that upon E571A, E235A, E237A, and R606A substitutions, ThDP binding in the second active center was affected. 2) Analysis of the kinetics of thiazolium C2 hydrogen/deuterium exchange of enzyme-bound ThDP suggests half-of-the-sites reactivity for the E1 component, with fast (activated site) and slow exchanging sites (dormant site). The E235A and E571A variants gave no evidence for the slow exchanging site, indicating that only one of two active sites is filled with ThDP. 3) Titration of the E235A and E237A variants with methyl acetylphosphonate monitored by circular dichroism suggested that only half of the active sites were filled with a covalent predecarboxylation intermediate analog. 4) Crystal structures of E235A and E571A in complex with ThDP revealed the structural basis for the spectroscopic and kinetic observations and showed that either substitution affects cofactor binding, despite the fact that Glu(235) makes no direct contact with the cofactor. The role of the conserved Glu(571) residue in both catalysis and cofactor orientation is revealed by the combined results for the first time.

  8. Wear-metal analysis in engine oil by microwave digestion and atomic absorption spectroscopy. Final report, August 1987-January 1988

    SciTech Connect

    Muse, W.T.

    1990-05-01

    Digestion procedures are described for the analysis of wear metals in National Bureau of Standards (NBS) oil samples by a closed vessel microwave digestion system. Samples were analyzed by flame atomic absorption spectroscopy. Recoveries of Al, Fe, Ni, Cu, and Pb in the 300-ppm NBS oil ranged from 98 to 103% with standard deviations from 3 to 14%. This method serves as a relatively quick matrix destruction technique for the quantitation of metals in oil.

  9. Analysis of an Air Conditioning Coolant Solution for Metal Contamination Using Atomic Absorption Spectroscopy: An Undergraduate Instrumental Analysis Exercise Simulating an Industrial Assignment

    ERIC Educational Resources Information Center

    Baird, Michael J.

    2004-01-01

    A real-life analytical assignment is presented to students, who had to examine an air conditioning coolant solution for metal contamination using an atomic absorption spectroscopy (AAS). This hands-on access to a real problem exposed the undergraduate students to the mechanism of AAS, and promoted participation in a simulated industrial activity.

  10. Au-supported Pt-Au mixed atomic monolayer electrocatalyst with ultrahigh specific activity for oxidation of formic acid in acidic solution.

    PubMed

    Huang, Zhao; Liu, Yan; Xie, Fangyun; Fu, Yingchun; He, Yong; Ma, Ming; Xie, Qingji; Yao, Shouzhuo

    2012-12-25

    Au-supported Pt-Au mixed atomic monolayer electrocatalyst was prepared by underpotential deposition of Cu on Au and then redox replacement with noble metal atoms, which shows an ultrahigh Pt-mass (or Pt-area) normalized specific electrocatalytic activity of 102 mA μg(Pt)(-1) (124 mA cm(Pt)(-2)) for oxidation of formic acid in acidic aqueous solution.

  11. Significant change of local atomic configurations at surface of reduced activation Eurofer steels induced by hydrogenation treatments

    NASA Astrophysics Data System (ADS)

    Greculeasa, S. G.; Palade, P.; Schinteie, G.; Kuncser, A.; Stanciu, A.; Lungu, G. A.; Porosnicu, C.; Lungu, C. P.; Kuncser, V.

    2017-04-01

    Reduced-activation steels such as Eurofer alloys are candidates for supporting plasma facing components in tokamak-like nuclear fusion reactors. In order to investigate the impact of hydrogen/deuterium insertion in their crystalline lattice, annealing treatments in hydrogen atmosphere have been applied on Eurofer slabs. The resulting samples have been analyzed with respect to local structure and atomic configuration both before and after successive annealing treatments, by X-ray diffractometry (XRD), scanning electron microscopy and energy dispersive spectroscopy (SEM-EDS), X-ray photoelectron spectroscopy (XPS) and conversion electron Mössbauer spectroscopy (CEMS). The corroborated data point out for a bcc type structure of the non-hydrogenated alloy, with an average alloy composition approaching Fe0.9Cr0.1 along a depth of about 100 nm. EDS elemental maps do not indicate surface inhomogeneities in concentration whereas the Mössbauer spectra prove significant deviations from a homogeneous alloying. The hydrogenation increases the expulsion of the Cr atoms toward the surface layer and decreases their oxidation, with considerable influence on the surface properties of the steel. The hydrogenation treatment is therefore proposed as a potential alternative for a convenient engineering of the surface of different Fe-Cr based alloys.

  12. The application of atomic absorption spectrometry for the determination of residual active pharmaceutical ingredients in cleaning validation samples.

    PubMed

    Bubnič, Zoran; Urleb, Uroš; Kreft, Katjuša; Veber, Marjan

    2011-03-01

    The objective of this work was the development and validation of atomic absorption spectrometric (AAS) methods for the determination of residual active pharmaceutical ingredients (API) in rinse samples for cleaning validation. AAS as an indirect method for the determination of API in rinse samples can be applied when it is in the form of salt with metal ions or when the metal ion is a part of the API's structure. The electrothermal AAS methods (aqueous and ethanol medium) for the determination of magnesium in esomeprazole magnesium and the flame AAS method for the determination of lithium in lithium carbonate in rinse samples were developed. Various combinations of solvents were tested and a combination of 1% aqueous or ethanol solution of nitric acid for esomeprazole magnesium and 0.1% aqueous solution of nitric acid for lithium carbonate were found to be the most suitable. The atomization conditions in the graphite furnace and in the flame were carefully studied to avoid losses of analyte and to achieve suitable sensitivity. The cleaning verification methods were validated with respect to accuracy, precision, linearity, limit of detection, and quantification. In all the cases, the limits of detection were at the microgram level. The methods were successfully applied for the determination of esomeprazole magnesium and lithium carbonate in rinse samples from cleaning procedures.

  13. A theoretical approach to the photochemical activation of matrix isolated aluminum atoms and their reaction with methane

    SciTech Connect

    Pacheco-Blas, M. A.; Novaro, O. A.; Pacheco-Sanchez, J. H.

    2010-11-07

    The photochemical activation of Al atoms in cryogenic matrices to induce their reaction with methane has been experimentally studied before. Here, a theoretical study of the nonadiabatic transition probabilities for the ground ({sup 2}P:3s{sup 2}3p{sup 1}) and the lowest excited states ({sup 2}S:3s{sup 2}4s{sup 1} and {sup 2}D:3s{sup 2}3d{sup 1}) of an aluminum atom interacting with a methane molecule (CH{sub 4}) was carried out through ab initio Hartree-Fock self-consistent field calculations. This was followed by a multiconfigurational study of the correlation energy obtained by extensive variational and perturbational configuration interaction analyses using the CIPSI program. The {sup 2}D state is readily inserted into a C-H bond, this being a prelude to a sequence of avoided crossings with the initially repulsive (to CH{sub 4}) lower lying states {sup 2}P and {sup 2}S. We then use a direct extension of the Landau-Zener theory to obtain transition probabilities at each avoided crossing, allowing the formation of an HAlCH{sub 3} intermediate that eventually leads to the final pair of products H+AlCH{sub 3} and HAl+CH{sub 3}.

  14. A new systematic framework for crystallographic analysis of atom probe data.

    PubMed

    Araullo-Peters, Vicente J; Breen, Andrew; Ceguerra, Anna V; Gault, Baptiste; Ringer, Simon P; Cairney, Julie M

    2015-07-01

    In this article, after a brief introduction to the principles behind atom probe crystallography, we introduce methods for unambiguously determining the presence of crystal planes within atom probe datasets, as well as their characteristics: location; orientation and interplanar spacing. These methods, which we refer to as plane orientation extraction (POE) and local crystallography mapping (LCM) make use of real-space data and allow for systematic analyses. We present here application of POE and LCM to datasets of pure Al, industrial aluminium alloys and doped-silicon. Data was collected both in DC voltage mode and laser-assisted mode (in the latter of which extracting crystallographic information is known to be more difficult due to distortions). The nature of the atomic planes in both datasets was extracted and analysed.

  15. [Studies on organic protective coatings for anti-atomic oxygen effects by spectrum analysis].

    PubMed

    Zhang, Lei

    2004-11-01

    This paper describes organic protective coatings on space material for anti-AO effects and the experiments to assess properties of the coatings. Organic protection was analyzed after exposures to ground state fast atomic (AO) radiation in the atomic oxygen beam facility for ground simulation experiments. The tests results have been analyzed with advanced FTIR, XPS and SEM. The test indicated that epoxy, alkyd and urethane organic coatings were highly reactive to AO with a strong degradation and changed in morphology of the surface layer. It is evident that siloxane coatings have excellent properties for anti-AO effects. The erosion product has SiO2 left on the surface, thus providing protection from further attack by the energetic oxygen atoms.

  16. Analysis of deterministic swapping of photonic and atomic states through single-photon Raman interaction

    NASA Astrophysics Data System (ADS)

    Rosenblum, Serge; Borne, Adrien; Dayan, Barak

    2017-03-01

    The long-standing goal of deterministic quantum interactions between single photons and single atoms was recently realized in various experiments. Among these, an appealing demonstration relied on single-photon Raman interaction (SPRINT) in a three-level atom coupled to a single-mode waveguide. In essence, the interference-based process of SPRINT deterministically swaps the qubits encoded in a single photon and a single atom, without the need for additional control pulses. It can also be harnessed to construct passive entangling quantum gates, and can therefore form the basis for scalable quantum networks in which communication between the nodes is carried out only by single-photon pulses. Here we present an analytical and numerical study of SPRINT, characterizing its limitations and defining parameters for its optimal operation. Specifically, we study the effect of losses, imperfect polarization, and the presence of multiple excited states. In all cases we discuss strategies for restoring the operation of SPRINT.

  17. Efficacy of Light-Activated Sealant on Enamel Demineralization in Orthodontic Patients: An Atomic Force Microscope Evaluation

    PubMed Central

    Shinaishin, Suzi F; Ghobashy, Safaa A; EL-Bialy, Tarek H

    2011-01-01

    Objective: The purpose of this study was to investigate the efficacy of (Pro Seal) sealant in preventing enamel decalcification in-vivo and compare its effect with fluoride varnish and unfilled sealant using atomic force microscopy. Materials and Methods: Eight orthodontic patients who were candidates for extraction of all first premolars for orthodontic treatment were recruited to this study. Thirty two premolars (upper and lower) were randomly divided into four groups (n=8) for each group, 4 maxillary and 4 mandibular); Control (no -treatment); Fluoride varnish, Unfilled sealant (Light Bond) and filled sealant (Pro-Seal). After two months the brackets were debonded and the teeth were extracted and prepared for Atomic force microscopic scanning. Each sample was scanned twice at two different scan areas 50 and 10µm at the buccal cervical third of the crown. Images were recorded with slow scan rate and resolution and the mean roughness height and total surface area were calculated for each scan area. Comparison between groups was performed using one way analysis of variance test with level of significance was set to be 0.05. Results: Pro Seal treated samples show the lowest roughness height and total surface area. Conclusion: Pro Seal was the most effective prophylaxis technique in preventing enamel demineralization during orthodontic treatment. PMID:22207889

  18. Methods for analysis of selected metals in water by atomic absorption

    USGS Publications Warehouse

    Fishman, Marvin J.; Downs, Sanford C.

    1966-01-01

    This manual describes atomic-absorption-spectroscopy methods for determining calcium, copper, lithium, magnesium, manganese, potassium, sodium, strontium and zinc in atmospheric precipitation, fresh waters, and brines. The procedures are intended to be used by water quality laboratories of the Water Resources Division of the U.S. Geological Survey. Detailed procedures, calculations, and methods for the preparation of reagents are given for each element along with data on accuracy, precision, and sensitivity. Other topics discussed briefly are the principle of atomic absorption, instrumentation used, and special analytical techniques.

  19. Efficient first-principles simulation of noncontact atomic force microscopy for structural analysis.

    PubMed

    Chan, T-L; Wang, C Z; Ho, K M; Chelikowsky, James R

    2009-05-01

    We propose an efficient scheme to simulate noncontact atomic force microscopy images by using first-principles self-consistent potential from the sample as input without explicit modeling of the atomic force microscopy tip. Our method is applied to various types of semiconductor surfaces including Si(111)-(7x7), TiO2(110)-(1x1), Ag/Si(111)-(sqrt[3]xsqrt[3])R30 degrees, and Ge/Si(105)-(1x2) surfaces. We obtain good agreement with experimental results and previous theoretical studies, and our method can aid in identifying different structural models for surface reconstruction.

  20. Free energy landscape of activation in a signalling protein at atomic resolution

    NASA Astrophysics Data System (ADS)

    Pontiggia, F.; Pachov, D. V.; Clarkson, M. W.; Villali, J.; Hagan, M. F.; Pande, V. S.; Kern, D.

    2015-06-01

    The interconversion between inactive and active protein states, traditionally described by two static structures, is at the heart of signalling. However, how folded states interconvert is largely unknown due to the inability to experimentally observe transition pathways. Here we explore the free energy landscape of the bacterial response regulator NtrC by combining computation and nuclear magnetic resonance, and discover unexpected features underlying efficient signalling. We find that functional states are defined purely in kinetic and not structural terms. The need of a well-defined conformer, crucial to the active state, is absent in the inactive state, which comprises a heterogeneous collection of conformers. The transition between active and inactive states occurs through multiple pathways, facilitated by a number of nonnative transient hydrogen bonds, thus lowering the transition barrier through both entropic and enthalpic contributions. These findings may represent general features for functional conformational transitions within the folded state.

  1. Updated mortality analysis of radiation workers at Rocketdyne (Atomics International), 1948-2008.

    PubMed

    Boice, John D; Cohen, Sarah S; Mumma, Michael T; Ellis, Elizabeth Dupree; Eckerman, Keith F; Leggett, Richard W; Boecker, Bruce B; Brill, A Bertrand; Henderson, Brian E

    2011-08-01

    Updated analyses of mortality data are presented on 46,970 workers employed 1948-1999 at Rocketdyne (Atomics International). Overall, 5,801 workers were involved in radiation activities, including 2,232 who were monitored for intakes of radionuclides, and 41,169 workers were engaged in rocket testing or other non-radiation activities. The worker population is unique in that lifetime occupational doses from all places of employment were sought, updated and incorporated into the analyses. Further, radiation doses from intakes of 14 different radionuclides were calculated for 16 organs or tissues using biokinetic models of the International Commission on Radiation Protection (ICRP). Because only negligible exposures were received by the 247 workers monitored for radiation activities after 1999, the mean dose from external radiation remained essentially the same at 13.5 mSv (maximum 1 Sv) as reported previously, as did the mean lung dose from external and internal radiation combined at 19.0 mSv (maximum 3.6 Sv). An additional 9 years of follow-up, from December 31,1999 through 2008, increased the person-years of observation for the radiation workers by 21.7% to 196,674 (mean 33.9 years) and the number of cancer deaths by 50% to 684. Analyses included external comparisons with the general population and the computation of standardized mortality ratios (SMRs) and internal comparisons using proportional hazards models and the computation of relative risks (RRs). A low SMR for all causes of death (SMR 0.82; 95% CI 0.78-0.85) continued to indicate that the Rocketdyne radiation workers were healthier than the general population and were less likely to die. The SMRs for all cancers taken together (SMR 0.88; 95% CI 0.81-0.95), lung cancer (SMR 0.87; 95% CI 0.76-1.00) and leukemia other than chronic lymphocytic leukemia (CLL) (SMR 1.04; 95% 0.67-1.53) were not significantly elevated. Cox regression analyses revealed no significant dose-response trends for any cancer. For all

  2. Updated Mortality Analysis of Radiation Workers at Rocketdyne (Atomics International), 1948-2008

    SciTech Connect

    Boice Jr JD, Colen SS, Mumma MT, Ellis ED, Eckerman DF, Leggett RW, Boecker BB, Brill B, Henderson BE

    2011-08-01

    Updated analyses of mortality data are presented on 46,970 workers employed 1948-1999 at Rocketdyne (Atomics International). Overall, 5,801 workers were involved in radiation activities, including 2,232 who were monitored for intakes of radionuclides, and 41,169 workers were engaged in rocket testing or other non-radiation activities. The worker population is unique in that lifetime occupational doses from all places of employment were sought, updated and incorporated into the analyses. Further, radiation doses from intakes of 14 different radionuclides were calculated for 16 organs or tissues using biokinetic models of the International Commission on Radiation Protection (ICRP). Because only negligible exposures were received by the 247 workers monitored for radiation activities after 1999, the mean dose from external radiation remained essentially the same at 13.5 mSv (maximum 1 Sv) as reported previously, as did the mean lung dose from external and internal radiation combined at 19.0 mSv (maximum 3.6 Sv). An additional 9 years of follow-up, from December 31,1999 through 2008, increased the person-years of observation for the radiation workers by 21.7% to 196,674 (mean 33.9 years) and the number of cancer deaths by 50% to 684. Analyses included external comparisons with the general population and the computation of standardized mortality ratios (SMRs) and internal comparisons using proportional hazards models and the computation of relative risks (RRs). A low SMR for all causes of death (SMR 0.82; 95% CI 0.78-0.85) continued to indicate that the Rocketdyne radiation workers were healthier than the general population and were less likely to die. The SMRs for all cancers taken together (SMR 0.88; 95% CI 0.81-0.95), lung cancer (SMR 0.87; 95% CI 0.76-1.00) and leukemia other than chronic lymphocytic leukemia (CLL) (SMR 1.04; 95% 0.67-1.53) were not significantly elevated. Cox regression analyses revealed no significant dose-response trends for any cancer. For all

  3. Calculation of activation energies for hydrogen-atom abstractions by radicals containing carbon triple bonds

    NASA Technical Reports Server (NTRS)

    Brown, R. L.; Laufer, A. H.

    1981-01-01

    Activation energies are calculated by the bond-energy-bond-order (BEBO) and the bond-strength-bond-length (BSBL) methods for the reactions of C2H radicals with H2, CH4, and C2H6 and for the reactions of CN radicals with H2 and CH4. The BSBL technique accurately predicts the activation energies for these reactions while the BEBO method yields energies averaging 9 kcal higher than those observed. A possible reason for the disagreement is considered.

  4. Photocatalytic activity and photocorrosion of atomic layer deposited ZnO ultrathin films for the degradation of methylene blue.

    PubMed

    Cao, Yan-Qiang; Chen, Jun; Zhou, Hang; Zhu, Lin; Li, Xin; Cao, Zheng-Yi; Wu, Di; Li, Ai-Dong

    2015-01-16

    ZnO ultrathin films with varied thicknesses of 7-70 nm were prepared at 200 °C on Si and fused quartz substrates by atomic layer deposition (ALD). The impact of film thickness and annealing temperature on the crystallinity, morphology, optical bandgap, and photocatalytic properties of ZnO in the degradation of methylene blue (MB) dye under UV light irradiation (λ = 365 nm) has been investigated deeply. The as-deposited 28 nm thick ZnO ultrathin film exhibits highest photocatalytic activity, ascribed to the smallest band gap of 3.21 eV and proper thickness. The photocorrosion effect of ALD ZnO ultrathin films during photocatalytic process is observed. The presence of MB significantly accelerates the dissolution of ZnO ultrathin films. The possible photoetching mechanism of ZnO in MB solution is proposed.

  5. Activation of C-H bond in methane by Pd atom from the bonding evolution theory perspective.

    PubMed

    Nizovtsev, Anton S

    2013-08-15

    We report detailed study focused on the electron density redistribution during the simple oxidative addition reaction being the crucial stage of various catalytic processes. The bonding evolution theory based on the electron localization function and Thom's catastrophe theory shows that activation of methane's C-H bond by Pd atom consist of six elementary steps. The important feature revealed is the pronounced reorganization of Pd's outer core maxima corresponding to N-shell electrons of metal. Electronic rearrangements identified in this model reaction are likely to be the case in the more complex reactions of the same type involving transition metal compounds and, in principle, can be observed by modern ultrafast spectroscopy and diffraction techniques.

  6. Analysis and modification of defective surface aggregates on PCDTBT:PCBM solar cell blends using combined Kelvin probe, conductive and bimodal atomic force microscopy

    PubMed Central

    Noh, Hanaul; Diaz, Alfredo J

    2017-01-01

    Organic photovoltaic systems comprising donor polymers and acceptor fullerene derivatives are attractive for inexpensive energy harvesting. Extensive research on polymer solar cells has provided insight into the factors governing device-level efficiency and stability. However, the detailed investigation of nanoscale structures is still challenging. Here we demonstrate the analysis and modification of unidentified surface aggregates. The aggregates are characterized electrically by Kelvin probe force microscopy and conductive atomic force microscopy (C-AFM), whereby the correlation between local electrical potential and current confirms a defective charge transport. Bimodal AFM modification confirms that the aggregates exist on top of the solar cell structure, and is used to remove them and to reveal the underlying active layer. The systematic analysis of the surface aggregates suggests that the structure consists of PCBM molecules. PMID:28382247

  7. Characterization of gold nanoparticle films: Rutherford backscattering spectroscopy, scanning electron microscopy with image analysis, and atomic force microscopy

    SciTech Connect

    Lansåker, Pia C. Niklasson, Gunnar A.; Granqvist, Claes G.; Hallén, Anders

    2014-10-15

    Gold nanoparticle films are of interest in several branches of science and technology, and accurate sample characterization is needed but technically demanding. We prepared such films by DC magnetron sputtering and recorded their mass thickness by Rutherford backscattering spectroscopy. The geometric thickness d{sub g}—from the substrate to the tops of the nanoparticles—was obtained by scanning electron microscopy (SEM) combined with image analysis as well as by atomic force microscopy (AFM). The various techniques yielded an internally consistent characterization of the films. In particular, very similar results for d{sub g} were obtained by SEM with image analysis and by AFM.

  8. Design of activated serine-containing catalytic triads with atomic level accuracy

    PubMed Central

    Rajagopalan, Sridharan; Wang, Chu; Yu, Kai; Kuzin, Alexandre P.; Richter, Florian; Lew, Scott; Miklos, Aleksandr E.; Matthews, Megan L.; Seetharaman, Jayaraman; Su, Min; Hunt, John. F.; Cravatt, Benjamin F.; Baker, David

    2014-01-01

    A challenge in the computational design of enzymes is that multiple properties must be simultaneously optimized -- substrate-binding, transition state stabilization, and product release -- and this has limited the absolute activity of successful designs. Here, we focus on a single critical property of many enzymes: the nucleophilicity of an active site residue that initiates catalysis. We design proteins with idealized serine-containing catalytic triads, and assess their nucleophilicity directly in native biological systems using activity-based organophosphate probes. Crystal structures of the most successful designs show unprecedented agreement with computational models, including extensive hydrogen bonding networks between the catalytic triad (or quartet) residues, and mutagenesis experiments demonstrate that these networks are critical for serine activation and organophosphate-reactivity. Following optimization by yeast-display, the designs react with organophosphate probes at rates comparable to natural serine hydrolases. Co-crystal structures with diisopropyl fluorophosphate bound to the serine nucleophile suggest the designs could provide the basis for a new class of organophosphate captures agents. PMID:24705591

  9. Fiscal Year 1985 Congressional budget request. Volume 1. Atomic energy defense activities

    SciTech Connect

    Not Available

    1984-02-01

    Contents include: summaries of estimates by appropriation, savings from management initiatives, staffing by subcommittee, staffing appropriation; appropriation language; amounts available for obligation; estimates by major category; program overview; weapons activities; verification and control technology; materials production; defense waste and by-products management; nuclear safeguards and security; security investigations; and naval reactors development.

  10. Rydberg States of rb and cs Atoms on Helium Nanodroplets: a Rydberg-Ritz Analysis

    NASA Astrophysics Data System (ADS)

    Lackner, Florian; Krois, Gunter; Ernst, Wolfgang E.

    2013-06-01

    Rydberg series of Rb and Cs atoms on the surface of helium nanodroplets (He_{N}) have been studied by resonance enhanced multi-photon ionization spectroscopy and laser induced fluorescence spectroscopy. The recorded excitation spectra are analyzed by using a Rydberg-Ritz approach. The dependence of the quantum defects on the principal quantum number within a Rydberg series gives insight into the interaction between the alkali atom's valence electron and the superfluid helium droplet. For higher excited states a screening of the valence electron from the alkali atom core by the helium droplet is observed. For lower states the strength of the screening effect decreases and the quantum defects are found to lie closer to free atom values. In addition, the large spin-orbit (SO) constant of the Cs-He_{N} nP(^{2}Π) states allows a detailed study of the influence of the helium droplet on the SO splitting as function of the principal quantum number. Within the pseudo-diatomic picture the alkali-He_{N} system represents a diatomic molecule. The coupling of the Cs valence electrons spin and the orbital angular momentum with the intermolecular axis, which is defined by the connection between the droplet center and the alkali nucleus, depends on the strength of the atomic SO interaction. While the splitting of the 6^{2}P_{1/2}(^{2}Π_{1/2}) and 6^{2}P_{3/2}(^{2}Π_{3/2}) components has an atom-like character (Hund's case (c) coupling), the SO splitting of higher n states is lower than the atomic value (Hund's case (a) coupling). C. Callegari and W. E. Ernst, Helium Droplets as Nanocryostats for Molecular Spectroscopy - from the Vacuum Ultraviolet to the Microwave Regime, in: Handbook of High-Resolution Spectroscopy, eds. M. Quack and F. Merkt, John Wiley & Sons, Chichester, (2011) F. Lackner, G. Krois, M. Theisen, M. Koch, and W.E. Ernst, Phys. Chem. Chem. Phys., 13, 18781-18788 (2011) F. Lackner, G. Krois, and W.E. Ernst, J. Phys. Chem. Lett., 3, 1404-1408 (2012)

  11. Quantitative analysis of hydrogen in SiO2/SiN/SiO2 stacks using atom probe tomography

    NASA Astrophysics Data System (ADS)

    Kunimune, Yorinobu; Shimada, Yasuhiro; Sakurai, Yusuke; Inoue, Masao; Nishida, Akio; Han, Bin; Tu, Yuan; Takamizawa, Hisashi; Shimizu, Yasuo; Inoue, Koji; Yano, Fumiko; Nagai, Yasuyoshi; Katayama, Toshiharu; Ide, Takashi

    2016-04-01

    We have demonstrated that it is possible to reproducibly quantify hydrogen concentration in the SiN layer of a SiO2/SiN/SiO2 (ONO) stack structure using ultraviolet laser-assisted atom probe tomography (APT). The concentration of hydrogen atoms detected using APT increased gradually during the analysis, which could be explained by the effect of hydrogen adsorption from residual gas in the vacuum chamber onto the specimen surface. The amount of adsorbed hydrogen in the SiN layer was estimated by analyzing another SiN layer with an extremely low hydrogen concentration (<0.2 at. %). Thus, by subtracting the concentration of adsorbed hydrogen, the actual hydrogen concentration in the SiN layer was quantified as approximately 1.0 at. %. This result was consistent with that obtained by elastic recoil detection analysis (ERDA), which confirmed the accuracy of the APT quantification. The present results indicate that APT enables the imaging of the three-dimensional distribution of hydrogen atoms in actual devices at a sub-nanometer scale.

  12. The Use of Contact Mode Atomic Force Microscopy in Aqueous Medium for Structural Analysis of Spinach Photosynthetic Complexes1[OPEN

    PubMed Central

    Phuthong, Witchukorn; Huang, Zubin; Wittkopp, Tyler M.; Sznee, Kinga; Heinnickel, Mark L.; Dekker, Jan P.; Frese, Raoul N.; Prinz, Fritz B.; Grossman, Arthur R.

    2015-01-01

    To investigate the dynamics of photosynthetic pigment-protein complexes in vascular plants at high resolution in an aqueous environment, membrane-protruding oxygen-evolving complexes (OECs) associated with photosystem II (PSII) on spinach (Spinacia oleracea) grana membranes were examined using contact mode atomic force microscopy. This study represents, to our knowledge, the first use of atomic force microscopy to distinguish the putative large extrinsic loop of Photosystem II CP47 reaction center protein (CP47) from the putative oxygen-evolving enhancer proteins 1, 2, and 3 (PsbO, PsbP, and PsbQ) and large extrinsic loop of Photosystem II CP43 reaction center protein (CP43) in the PSII-OEC extrinsic domains of grana membranes under conditions resulting in the disordered arrangement of PSII-OEC particles. Moreover, we observed uncharacterized membrane particles that, based on their physical characteristics and electrophoretic analysis of the polypeptides associated with the grana samples, are hypothesized to be a domain of photosystem I that protrudes from the stromal face of single thylakoid bilayers. Our results are interpreted in the context of the results of others that were obtained using cryo-electron microscopy (and single particle analysis), negative staining and freeze-fracture electron microscopy, as well as previous atomic force microscopy studies. PMID:26220954

  13. All-Atom Molecular-Level Analysis of the Ballistic-Impact-Induced Densification and Devitrification of Fused Silica

    NASA Astrophysics Data System (ADS)

    Grujicic, M.; Snipes, J. S.; Ramaswami, S.; Yavari, R.; Barsoum, R. S.

    2015-08-01

    All-atom molecular-level computations are carried out to infer the dynamic response and material microstructure/topology changes of fused silica subjected to ballistic impact by a hard projectile. The analysis was focused on the investigation of specific aspects of the dynamic response and of the microstructural changes such as the deformation of highly sheared and densified regions and the conversion of amorphous fused silica to SiO2 crystalline allotropic modifications (in particular, α-quartz and stishovite). The microstructural changes in question were determined by carrying out a post-processing atom-coordination procedure. This procedure suggested the formation of stishovite (and perhaps α-quartz) within fused silica during ballistic impact. To rationalize the findings obtained, the all-atom molecular-level computational analysis is complemented by a series of quantum-mechanics density functional theory (DFT) computations. The latter computations enable determination of the relative potential energies of the fused silica, α-quartz, and stishovite under ambient pressure (i.e., under their natural densities) as well as under imposed (as high as 50 GPa) pressures (i.e., under higher densities) and shear strains. In addition, the transition states associated with various fused-silica devitrification processes were identified. The results obtained are found to be in good agreement with their respective experimental counterparts.

  14. Speciation analysis of arsenic in biological matrices by automated hydride generation-cryotrapping-atomic absorption spectrometry with multiple microflame quartz tube atomizer (multiatomizer).

    EPA Science Inventory

    This paper describes an automated system for the oxidation state specific speciation of inorganic and methylated arsenicals by selective hydride generation - cryotrapping- gas chromatography - atomic absorption spectrometry with the multiatomizer. The corresponding arsines are ge...

  15. The Tübingen Model-Atom Database: A Revised Aluminum Model Atom and its Application for the Spectral Analysis of White Dwarfs

    NASA Astrophysics Data System (ADS)

    Löbling, L.

    2017-03-01

    Aluminum (Al) nucleosynthesis takes place during the asymptotic-giant-branch (AGB) phase of stellar evolution. Al abundance determinations in hot white dwarf stars provide constraints to understand this process. Precise abundance measurements require advanced non-local thermodynamic stellar-atmosphere models and reliable atomic data. In the framework of the German Astrophysical Virtual Observatory (GAVO), the Tübingen Model-Atom Database (TMAD) contains ready-to- use model atoms for elements from hydrogen to barium. A revised, elaborated Al model atom has recently been added. We present preliminary stellar-atmosphere models and emergent Al line spectra for the hot white dwarfs G191–B2B and RE 0503–289.

  16. Compositional analysis with atomic column spatial resolution by 5th-order aberration-corrected scanning transmission electron microscopy.

    PubMed

    Hernández-Maldonado, David; Herrera, Miriam; Alonso-González, Pablo; González, Yolanda; González, Luisa; Gazquez, Jaume; Varela, María; Pennycook, Stephen J; Guerrero-Lebrero, María de la Paz; Pizarro, Joaquín; Galindo, Pedro L; Molina, Sergio I

    2011-08-01

    We show in this article that it is possible to obtain elemental compositional maps and profiles with atomic-column resolution across an InxGa1-xAs multilayer structure from 5th-order aberration-corrected high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) images. The compositional profiles obtained from the analysis of HAADF-STEM images describe accurately the distribution of In in the studied multilayer in good agreement with Muraki's segregation model [Muraki, K., Fukatsu, S., Shiraki, Y. & Ito, R. (1992). Surface segregation of In atoms during molecular beam epitaxy and its influence on the energy levels in InGaAs/GaAs quantums wells. Appl Phys Lett 61, 557-559].

  17. Synthesis, reactions and biological activity of some new bis-heterocyclic ring compounds containing sulphur atom

    PubMed Central

    2013-01-01

    Background The derivatives of thieno[2,3-b]thiophene belong to a significant category of heterocyclic compounds, which have shown a wide spectrum of medical and industrial application. Results A new building block with two electrophilic center of thieno[2,3-b]thiophene derivatives 2 has been reported by one-pot reaction of diketone derivative 1 with Br2/AcOH in excellent yield. A variety of heteroaromatics having bis(1H-imidazo[1,2a] benzimidazole), bis(1H-imidazo[1,2-b][1,2,4]triazole)-3-methyl-4-phenylthieno[2,3-b]thiophene derivatives, dioxazolo-, dithiazolo-, and 1H-imidazolo-3-methyl-4-phenylthieno[2,3-b]thiophene derivatives as well pyrrolo, thiazolo -3-methyl-4-phenylthieno[2,3-b]thiophene derivatives have been designed, synthesized, characterized, and evaluated for their biological activity. Compounds 3–9 showed good bioassay result. These new derivatives were evaluated for anti-cancer activity against PC-3 cell lines, in vitro antioxidant potential and β-glucuronidase and α-glucosidase inhibitory activities. Compound 3 (IC50 = 56.26 ± 3.18 μM) showed a potent DPPH radical scavenging antioxidant activity and found to be more active than standard N-acetylcystein (IC50 = 105.9 ± 1.1 μM). Compounds 8a (IC50 = 13.2 ± 0.34 μM) and 8b (IC50 = 14.1 ± 0.28 μM) found as potent inhibitor of α-glucusidase several fold more active than the standard acarbose (IC50 = 841 ± 1.73 μM). Most promising results were obtained in β-glucuronidase enzyme inhibition assay. Compounds 5 (IC50 = 0.13 ± 0.019 μM), 6 (IC50 = 19.9 ± 0.285 μM), 8a (IC50 = 1.2 ± 0.0785 μM) and 9 (IC50 = 0.003 ± 0.09 μM) showed a potent inhibition of β-glucuronidase. Compound 9 was found to be several hundred fold more active than standard D-Saccharic acid 1,4-lactone (IC50 = 45.75 ± 2.16 μM). Conclusions Synthesis, characterization, and in vitro biological activity of a series of

  18. Plasma-enhanced atomic layer deposition of silicon dioxide films using plasma-activated triisopropylsilane as a precursor

    SciTech Connect

    Jeon, Ki-Moon; Shin, Jae-Su; Yun, Ju-Young; Jun Lee, Sang; Kang, Sang-Woo

    2014-05-15

    The plasma-enhanced atomic layer deposition (PEALD) process was developed as a growth technique of SiO{sub 2} thin films using a plasma-activated triisopropylsilane [TIPS, ((iPr){sub 3}SiH)] precursor. TIPS was activated by an argon plasma at the precursor injection stage of the process. Using the activated TIPS, it was possible to control the growth rate per cycle of the deposited films by adjusting the plasma ignition time. The PEALD technique allowed deposition of SiO{sub 2} films at temperatures as low as 50 °C without carbon impurities. In addition, films obtained with plasma ignition times of 3 s and 10 s had similar values of root-mean-square surface roughness. In order to evaluate the suitability of TIPS as a precursor for low-temperature deposition of SiO{sub 2} films, the vapor pressure of TIPS was measured. The thermal stability and the reactivity of the gas-phase TIPS with respect to water vapor were also investigated by analyzing the intensity changes of the C–H and Si–H peaks in the Fourier-transform infrared spectrum of TIPS.

  19. Efficient solar photocatalytic activity of TiO2 coated nano-porous silicon by atomic layer deposition

    NASA Astrophysics Data System (ADS)

    Sampath, Sridhar; Maydannik, Philipp; Ivanova, Tatiana; Shestakova, Marina; Homola, Tomáš; Bryukvin, Anton; Sillanpää, Mika; Nagumothu, Rameshbabu; Alagan, Viswanathan

    2016-09-01

    In the present study, TiO2 coated nano-porous silicon (TiO2/PS) was prepared by atomic layer deposition (ALD) whereas porous silicon was prepared by stain etching method for efficient solar photocatalytic activity. TiO2/PS was characterized by FESEM, AFM, XRD, XPS and DRS UV-vis spectrophotometer. Absorbance spectrum revealed that TiO2/PS absorbs complete solar light with wave length range of 300 nm-800 nm and most importantly, it absorbs stronger visible light than UV light. The reason for efficient solar light absorption of TiO2/PS is that nanostructured TiO2 layer absorbs UV light and nano-porous silicon layer absorbs visible light which is transparent to TiO2 layer. The amount of visible light absorption of TiO2/PS directly increases with increase of silicon etching time. The effect of silicon etching time of TiO2/PS on solar photocatalytic activity was investigated towards methylene blue dye degradation. Layer by layer solar absorption mechanism was used to explain the enhanced photocatalytic activity of TiO2/PS solar absorber. According to this, the photo-generated electrons of porous silicon will be effectively injected into TiO2 via hetero junction interface which leads to efficient charge separation even though porous silicon is not participating in any redox reactions in direct.

  20. Excellent c-Si surface passivation by thermal atomic layer deposited aluminum oxide after industrial firing activation

    NASA Astrophysics Data System (ADS)

    Liao, B.; Stangl, R.; Ma, F.; Mueller, T.; Lin, F.; Aberle, A. G.; Bhatia, C. S.; Hoex, B.

    2013-09-01

    We demonstrate that by using a water (H2O)-based thermal atomic layer deposited (ALD) aluminum oxide (Al2O3) film, excellent surface passivation can be attained on planar low-resistivity silicon wafers. Effective carrier lifetime values of up to 12 ms and surface recombination velocities as low as 0.33 cm s-1 are achieved on float-zone wafers after a post-deposition thermal activation of the Al2O3 passivation layer. This post-deposition activation is achieved using an industrial high-temperature firing process which is commonly used for contact formation of standard screen-printed silicon solar cells. Neither a low-temperature post-deposition anneal nor a silicon nitride capping layer is required in this case. Deposition temperatures in the 100-400 °C range and peak firing temperatures of about 800 °C (set temperature) are investigated. Photoluminescence imaging shows that the surface passivation is laterally uniform. Corona charging and capacitance-voltage measurements reveal that the negative fixed charge density near the AlOx/c-Si interface increases from 1.4 × 1012 to 3.3 × 1012 cm-2 due to firing, while the midgap interface defect density reduces from 3.3 × 1011 to 0.8 × 1011 cm-2 eV-1. This work demonstrates that direct firing activation of thermal ALD Al2O3 is feasible, which could be beneficial for solar cell manufacturing.

  1. Content Analysis in Systems Engineering Acquisition Activities

    DTIC Science & Technology

    2016-04-30

    shape requirements definitions for system upgrade or modification contracts and new baseline contracts. Finally, content analysis training and skill...back to the system designers, this information can then be used to shape requirements definition for system upgrade or modification contracts and new...Activity System Requirements Definition Ensuring the system requirements adequately reflect the stakeholder requirements Negotiating modifications to

  2. Accession Medical Standards Analysis and Research Activity

    DTIC Science & Technology

    2010-01-01

    Chief, Accession Medical Standards Analysis & Research Activity Li Yuanzhang, PhD Senior Statistician Department of Epidemiology David N...ORGANIZATION NAME(S) AND ADDRESS(ES) AMSARA, Department of Epidemiology , Division of Preventive Medicine Walter Reed Army Institute of Research 503... Epidemiology of Injury form the Assessment of Recruit Strength and Motivation study ARMS) and Program

  3. Radio frequency superconducting quantum interference device meta-atoms and metamaterials: Experiment, theory and analysis

    NASA Astrophysics Data System (ADS)

    Zhang, Daimeng

    Metamaterials are 1D, 2D or 3D arrays of artificial atoms. The artificial atoms, called "meta-atoms", can be any component with tailorable electromagnetic properties, such as resonators, LC circuits, nano particles, and so on. By designing the properties of individual meta-atoms and the interaction created by putting them in a lattice, one can create a metamaterial with intriguing properties not found in nature. My Ph. D. work examines the meta-atoms based on radio frequency superconducting quantum interference devices (rf-SQUIDs); their tunability with dc magnetic field, rf magnetic field, and temperature are studied. The rf-SQUIDs are superconducting split ring resonators in which the usual capacitance is supplemented with a Josephson junction, which introduces strong nonlinearity in the rf properties. At relatively low rf magnetic field, a magnetic field tunability of the resonant frequency of up to 80 THz/Gauss by dc magnetic field is observed, and a total frequency tunability of 100% is achieved. The macroscopic quantum superconducting metamaterial also shows manipulative self-induced broadband transparency due to a qualitatively novel nonlinear mechanism that is different from conventional electromagnetically induced transparency (EIT) or its classical analogs. A near complete disappearance of resonant absorption under a range of applied rf flux is observed experimentally and explained theoretically. The transparency comes from the intrinsic bi-stability and can be tuned on/ off easily by altering rf and dc magnetic fields, temperature and history. Hysteretic in situ 100% tunability of transparency paves the way for auto-cloaking metamaterials, intensity dependent filters, and fast-tunable power limiters. An rf-SQUID metamaterial is shown to have qualitatively the same behavior as a single rf-SQUID with regards to dc flux, rf flux and temperature tuning. The two-tone response of self-resonant rf-SQUID meta-atoms and metamaterials is then studied here via

  4. Kinetics of Hydrogen Atom Abstraction from Substrate by an Active Site Thiyl Radical in Ribonucleotide Reductase

    PubMed Central

    2015-01-01

    Ribonucleotide reductases (RNRs) catalyze the conversion of nucleotides to deoxynucleotides in all organisms. Active E. coli class Ia RNR is an α2β2 complex that undergoes reversible, long-range proton-coupled electron transfer (PCET) over a pathway of redox active amino acids (β-Y122 → [β-W48] → β-Y356 → α-Y731 → α-Y730 → α-C439) that spans ∼35 Å. To unmask PCET kinetics from rate-limiting conformational changes, we prepared a photochemical RNR containing a [ReI] photooxidant site-specifically incorporated at position 355 ([Re]-β2), adjacent to PCET pathway residue Y356 in β. [Re]-β2 was further modified by replacing Y356 with 2,3,5-trifluorotyrosine to enable photochemical generation and spectroscopic observation of chemically competent tyrosyl radical(s). Using transient absorption spectroscopy, we compare the kinetics of Y· decay in the presence of substrate and wt-α2, Y731F-α2 ,or C439S-α2, as well as with 3′-[2H]-substrate and wt-α2. We find that only in the presence of wt-α2 and the unlabeled substrate do we observe an enhanced rate of radical decay indicative of forward radical propagation. This observation reveals that cleavage of the 3′-C–H bond of substrate by the transiently formed C439· thiyl radical is rate-limiting in forward PCET through α and has allowed calculation of a lower bound for the rate constant associated with this step of (1.4 ± 0.4) × 104 s–1. Prompting radical propagation with light has enabled observation of PCET events heretofore inaccessible, revealing active site chemistry at the heart of RNR catalysis. PMID:25353063

  5. Second order classical perturbation theory for atom surface scattering: Analysis of asymmetry in the angular distribution

    SciTech Connect

    Zhou, Yun Pollak, Eli; Miret-Artés, Salvador

    2014-01-14

    A second order classical perturbation theory is developed and applied to elastic atom corrugated surface scattering. The resulting theory accounts for experimentally observed asymmetry in the final angular distributions. These include qualitative features, such as reduction of the asymmetry in the intensity of the rainbow peaks with increased incidence energy as well as the asymmetry in the location of the rainbow peaks with respect to the specular scattering angle. The theory is especially applicable to “soft” corrugated potentials. Expressions for the angular distribution are derived for the exponential repulsive and Morse potential models. The theory is implemented numerically to a simplified model of the scattering of an Ar atom from a LiF(100) surface.

  6. Analysis of non-Markovian coupling of a lattice-trapped atom to free space

    NASA Astrophysics Data System (ADS)

    Stewart, Michael; Krinner, Ludwig; Pazmiño, Arturo; Schneble, Dominik

    2017-01-01

    Behavior analogous to that of spontaneous emission in photonic band-gap materials has been predicted for an atom-optical system consisting of an atom confined in a well of a state-dependent optical lattice that is coupled to free space through an internal-state transition [de Vega et al., Phys. Rev. Lett. 101, 260404 (2008), 10.1103/PhysRevLett.101.260404]. Using the Weisskopf-Wigner approach and considering a one-dimensional geometry, we analyze the properties of this system in detail, including the evolution of the lattice-trapped population, the momentum distribution of emitted matter waves, and the detailed structure of an evanescent matter-wave state below the continuum boundary. We compare and contrast our findings for the transition from Markovian to non-Markovian behaviors to those previously obtained for three dimensions.

  7. Surface field analysis of splitting of orbitals of atoms and ions approaching a metal surface.

    NASA Technical Reports Server (NTRS)

    Rao, P. V. S.; Waber, J. T.

    1971-01-01

    The splitting of p- and d-orbitals of an atom or an ion which is caused by the locally varying potential near the surface of a realistic metal has been studied for bcc and fcc substrates. A quasi-ionic model is reasonable at close distance, inasmuch as the electron gas does not completely screen the ionic cores. The arrangement of ion cores near the surface causes the potential to vary in three dimensions. Expressions for energy levels were derived for an unsymmetric group using the quasi-ionic model and techniques used in the treatment of crystal field of nearest neighbors. A number of cases involving ions, as well as atoms in the vicinity of a metal substrate were numerically evaluated.

  8. Depth profiles and bulk analysis of semiconductor materials using ICP mass spectroscopy with electrothermal atomization

    NASA Astrophysics Data System (ADS)

    Faulkner, William; Henderson, William; Rogers, Michael

    1988-10-01

    The purpose of the contract was to build the equipment necessary to show technical feasibility of a Demand Modulated Electrothermal Atomization System. This system was thought to have advantages over current technology as follows: (1) Prevents excessive analyte concentrations in the plasma giving the analyst control over matrix suppression effects. (2) Allows the analyst to control atomization rates and avoid buildup of deposits in the throat of the sample cone opening. (3) Allows the analyst to work in the optimum counting range for isotropic ratio work regardless of concentration variations. (4) Allows the data to be taken over the temperature dimension, thus resolving isobaric interferences as well as improving the signal to noise ratio resulting in improved detection limits across the entire mass range.

  9. Influence of laser power on atom probe tomographic analysis of boron distribution in silicon.

    PubMed

    Tu, Y; Takamizawa, H; Han, B; Shimizu, Y; Inoue, K; Toyama, T; Yano, F; Nishida, A; Nagai, Y

    2017-02-01

    The relationship between the laser power and the three-dimensional distribution of boron (B) in silicon (Si) measured by laser-assisted atom probe tomography (APT) is investigated. The ultraviolet laser employed in this study has a fixed wavelength of 355nm. The measured distributions are almost uniform and homogeneous when using low laser power, while clear B accumulation at the low-index pole of single-crystalline Si and segregation along the grain boundaries in polycrystalline Si are observed when using high laser power (100pJ). These effects are thought to be caused by the surface migration of atoms, which is promoted by high laser power. Therefore, for ensuring a high-fidelity APT measurement of the B distribution in Si, high laser power is not recommended.

  10. Recommended practices for in-space and ground laboratory. Atomic oxygen exposure and analysis

    NASA Technical Reports Server (NTRS)

    Banks, Bruce; Koontz, Steve; Mccargo, Matt; Pippin, Gary; Rutledge, Sharon

    1992-01-01

    A detailed guide to testing materials for atomic oxygen durability in earth orbit environments is presented. The steps covered include sample preparation, including masking of the sample, dehydration, weighing, and handling; effective fluence prediction, including the use of witness samples (notably Kapton); plasma facility and operational considerations, involving such matters as avoidance of silicone contamination, the use of continuous versus incremental ashing, and temperature of operation; and erosion yield measurement, with calculation methods and protective coating performance indices provided.

  11. Analysis of relativistic effects in electron-impact excitation of SP transitions in heavy atoms.

    NASA Astrophysics Data System (ADS)

    Andersen, Nils; Bartschat, Klaus

    2002-05-01

    While elastic electron scattering from heavy atoms is known to be strongly affected by relativistic effects such as Mott scattering, it seems surprising that several sets of recent experimental results for electron-impact excitation of the (6s)^2S_1/2 (6p)^2P_1/2,3/2 transition [1,2] in Cs could be well reproduced by a non-relativistic ``convergent close-coupling'' (CCC) model. It is, therefore, desirable to analyze the sensitivity of currently measured observables to relativistic effects, as well as to develop new prescriptions to enhance the potential for experimental tests of sophisticated collision theories. Using the above transition as an example, we developed a new formulation to describe the collision process and the experimental investigations, based on the concept of ``generalized Stokes parameters'' [3]. [1] V. Karaganov, P.J.O. Teubner, and M.J. Brunger, in Correlations, Polarization, and Ionization in Atomic Systems, AIP (New York, 2000). [2] G. Baum and I. Bray (2002), private communication. [3] N. Andersen and K. Bartschat, Polarization, Alignment, and Orientation in Atomic Collisions, Springer (New York, 2000).

  12. Size Dependence of Atomically Precise Gold Nanoclusters in Chemoselective Hydrogenation and Active Site Structure

    SciTech Connect

    Li, Gao; Jiang, Deen; Kumar, Santosh; Chen, Yuxiang; Jin, Rongchao

    2014-01-01

    We here investigate the catalytic properties of water-soluble Aun(SG)m nanocluster catalysts (H-SG = glutathione) of different sizes, including Au15(SG)13, Au18(SG)14, Au25(SG)18, Au38(SG)24, and captopril-capped Au25(Capt)18 nanoclusters. These Aun(SR)m nanoclusters (-SR represents thiolate generally) are used as homogeneous catalysts (i.e., without supports) in the chemoselective hydrogenation of 4-nitrobenzaldehyde (4-NO2PhCHO) to 4-nitrobenzyl alcohol (4-NO2PhCH2OH) in water with H2 gas (20 bar) as the hydrogen source. These nanocluster catalysts, except Au18(SG)14, remain intact after the catalytic reaction, evidenced by UV-vis spectra which are characteristic of each sized nanoclusters and thus serve as spectroscopic fingerprints . We observe a drastic size-dependence and steric effect of protecting ligands on the gold nanocluster catalysts in the hydrogenation reaction. Density functional theory (DFT) modeling of the 4-nitrobenzaldehyde adsorption shows that both the CHO and NO2 groups are in close interact with the S-Au-S staples on the gold nanocluster surface; the adsorption of the 4-nitrobenzaldehyde molecule on the four different sized Aun(SR)m nanoclusters are moderately strong and similar in strength. The DFT results suggest that the catalytic activity of the Aun(SR)m nanoclusters is primarily determined by the surface area of the Au nanocluster, consistent with the observed trend of the conversion of 4-nitrobenzaldehyde versus the cluster size. Overall, this work offers the molecular insight into the hydrogenation of 4-nitrobenzaldehyde and the catalytically active site structure on gold nanocluster catalysts.

  13. Atomic geometry of GaSb(110): Determination via elastic low-energy electron diffraction intensity analysis

    NASA Astrophysics Data System (ADS)

    Duke, C. B.; Paton, A.; Kahn, A.

    1983-03-01

    Elastic low-energy electron diffraction (ELEED) intensities from GaSb(110) of normally incident electrons with energies 30<=E<=210 eV were measured at T=125 K. Intensity versus incident-energy profiles were recorded for 14 diffracted beams. The surfaces were prepared by a chemical-polish-ion-bombard-anneal cycle. The stoichiometry of the surfaces and reproducibility of the data from one sample to another were verified explicitly. Comparison of these measured intensities with dynamical ELEED intensity calculations indicates that the dimensions of the surface unit cell are identical to those of truncated bulk GaSb, but that the atomic geometry within that cell is reconstructed. The best-fit structure consists of a bond-length-conserving rotation by ω1=(30+/-2)∘ of species in the uppermost atomic layer with the Sb relaxing outward and the Ga inward. No displacements of the second-layer species are indicated by the analysis. The structure resembles those of ZnTe(110) and GaP(110), but is quite distinct from those of GaAs(110), InSb(110), and CdTe(110). This result reveals that ionicity alone is an inadequate index of the surface atomic geometries of compound semiconductors, independent of the definition chosen for the ionicity.

  14. Atom Recombination on Surface

    NASA Astrophysics Data System (ADS)

    Kim, Young Chai

    Upon high speed re-entry of the Space Shuttle Orbiter (SSO) through the earth's atmosphere, oxygen and nitrogen atoms produced in the shock wave in front of the SSO recombine on the surface of the SSO, releasing heat. To minimize the rise of surface temperature due to the reaction, surface material of the SSO should have a low recombination probability, gamma, of atoms impinging on it. To design such material, it is necessary to understand the mechanism of atom recombination. With this in mind, gamma values were measured for recombination of O, N, and H atoms in a diffusion tube reactor between 700 and 1250 K (HT), 300 and 700 K (MT), and at 194 K (LT) on silica. The rate of recombination was first order with respect to the atom concentration from LT to HT. The Arrhenius plots, gamma vs. 1/T, were very complex. All observations are explained by assuming a surface with a small fraction of active sites that irreversibly bind chemisorbed atoms. Everything happens as if the active sites were surrounded by collection zones within which all atoms striking the surface are adsorbed reversibly with an assumed sticking probability of unity. These atoms then diffuse on the surface. Some of them reach the active sites where they can recombine with the chemisorbed atoms. At LT, all atoms striking the surface reach the active sites. As a result of desorption at MT, the collection zones shrink with increasing temperature. At HT, only atoms striking active sites directly from the gas phase lead to recombination. An analytical solution of the diffusion-reaction problem obtained for a model where the active sites are distributed uniformly fits with the experimental data from LT to HT. The two novel features of this work are the identification of the active sites on silica for recombination of H on silica at HT as surface OH groups and the suggestion that another kind of active site is responsible for recombination of O and N atoms at HT as well as for H atoms at LT and MT. Although

  15. Excitation and relaxation of metastable atomic states in an active medium of a repetitively pulsed copper vapour laser

    SciTech Connect

    Bokhan, P A; Zakrevskii, D E; Lavrukhin, M A; Lyabin, N A; Chursin, A D

    2016-02-28

    The influence of a pre-pulse population of copper atom metastable states and their sub-population at a current pulse edge on the copper vapour laser pulse energy is studied under optimal temperature conditions. Experiments have been performed with active elements of a commercial laser having an internal diameter of a discharge channel of 14 and 20 mm. It is found that at a pulse repetition frequency of 12 – 14 kHz, corresponding to a maximal output power, the reduction of the energy due to a residual population of metastable states is by an order of magnitude less than due to their sub-population at a current pulse edge. The modelling based on the experimental results obtained has shown that in the case of an active element with an internal diameter of 14 mm, a decrease in the pulse leading edge from ∼25 ns to 0.6 ns does not reduce the laser pulse energy up to the repetition frequency of ∼50 kHz at an average output power of 70 W m{sup -1} and efficiency of ∼11%. (lasers)

  16. The Software Atom

    NASA Astrophysics Data System (ADS)

    Javanainen, Juha

    2017-03-01

    By putting together an abstract view on quantum mechanics and a quantum-optics picture of the interactions of an atom with light, we develop a corresponding set of C++ classes that set up the numerical analysis of an atom with an arbitrary set of angular-momentum degenerate energy levels, arbitrary light fields, and an applied magnetic field. As an example, we develop and implement perturbation theory to compute the polarizability of an atom in an experimentally relevant situation.

  17. Activity Analysis and Cost Analysis in Medical Schools.

    ERIC Educational Resources Information Center

    Koehler, John E.; Slighton, Robert L.

    There is no unique answer to the question of what an ongoing program costs in medical schools. The estimates of program costs generated by classical methods of cost accounting are unsatisfactory because such accounting cannot deal with the joint production or joint cost problem. Activity analysis models aim at calculating the impact of alternative…

  18. Drug release-modulating mechanism of hydrophilic hydroxypropylmethylcellulose matrix tablets: distribution of atoms and carrier and texture analysis.

    PubMed

    Park, Jun-Bom; Lim, Jisung; Kang, Chin-Yang; Lee, Beom-Jin

    2013-12-01

    Although release profiles of drug from hydrophilic matrices have been well recognized, the visual distribution of hydroxypropylmethylcellulose (HPMC) and atoms inside of internal structures of hydrophilic HPMC matrices has not been characterized. In this paper, drug release mechanism from HPMC matrix tablet was investigated based on the release behaviors of HPMC, physical properties of gelled HPMC tablet and atomic distributions of formulation components using diverse instruments. A matrix tablet consisting of hydroxypropyl methylcellulose (HPMC 6, 4,000 and 100,000 mPa·s), chlorpheniramine maleate (CPM) as a model and fumed silicon dioxide (Aerosil(®) 200) was prepared via direct compression. The distribution of atoms and HPMC imaging were characterized using scanning electron microscope (SEM)/ energy-dispersive X-ray spectroscopy (EDX), and near-infrared (NIR) analysis, respectively as a function of time. A texture analyzer was also used to characterize the thickness and maintenance of gel layer of HPMC matrix tablet. The HPMC matrix tablets showed Higuchi release kinetics with no lag time against the square root of time. High viscosity grades of HPMC gave retarded release rate because of the greater swelling and gel thickness as characterized by texture analyzer. According to the NIR imaging, low-viscosity-grade HPMC (6 mPa·s) quickly leached out onto the surface of the tablet, while the high-viscosity-grade HPMC (4000 mPa·s) formed much thicker gel layer around the tablet and maintained longer via slow erosion, resulting in retarded drug release. The atomic distribution of the drug (chlorine, carbon, oxygen), HPMC (carbon, oxygen) and silicon dioxide (silica, oxygen) and NIR imaging of HPMC corresponded with the dissolution behaviors of drug as a function of time. The use of imaging and texture analyses could be applicable to explain the release- modulating mechanism of hydrophilic HPMC matrix tablets.

  19. Non-thermal hydrogen atoms in the terrestrial upper thermosphere.

    PubMed

    Qin, Jianqi; Waldrop, Lara

    2016-12-06

    Model predictions of the distribution and dynamical transport of hydrogen atoms in the terrestrial atmosphere have long-standing discrepancies with ultraviolet remote sensing measurements, indicating likely deficiencies in conventional theories regarding this crucial atmospheric constituent. Here we report the existence of non-thermal hydrogen atoms that are much hotter than the ambient oxygen atoms in the upper thermosphere. Analysis of satellite measurements indicates that the upper thermospheric hydrogen temperature, more precisely the mean kinetic energy of the atomic hydrogen population, increases significantly with declining solar activity, contrary to contemporary understanding of thermospheric behaviour. The existence of hot hydrogen atoms in the upper thermosphere, which is the key to reconciling model predictions and observations, is likely a consequence of low atomic oxygen density leading to incomplete collisional thermalization of the hydrogen population following its kinetic energization through interactions with hot atomic or ionized constituents in the ionosphere, plasmasphere or magnetosphere.

  20. Non-thermal hydrogen atoms in the terrestrial upper thermosphere

    PubMed Central

    Qin, Jianqi; Waldrop, Lara

    2016-01-01

    Model predictions of the distribution and dynamical transport of hydrogen atoms in the terrestrial atmosphere have long-standing discrepancies with ultraviolet remote sensing measurements, indicating likely deficiencies in conventional theories regarding this crucial atmospheric constituent. Here we report the existence of non-thermal hydrogen atoms that are much hotter than the ambient oxygen atoms in the upper thermosphere. Analysis of satellite measurements indicates that the upper thermospheric hydrogen temperature, more precisely the mean kinetic energy of the atomic hydrogen population, increases significantly with declining solar activity, contrary to contemporary understanding of thermospheric behaviour. The existence of hot hydrogen atoms in the upper thermosphere, which is the key to reconciling model predictions and observations, is likely a consequence of low atomic oxygen density leading to incomplete collisional thermalization of the hydrogen population following its kinetic energization through interactions with hot atomic or ionized constituents in the ionosphere, plasmasphere or magnetosphere. PMID:27922018

  1. Non-thermal hydrogen atoms in the terrestrial upper thermosphere

    NASA Astrophysics Data System (ADS)

    Qin, Jianqi; Waldrop, Lara

    2016-12-01

    Model predictions of the distribution and dynamical transport of hydrogen atoms in the terrestrial atmosphere have long-standing discrepancies with ultraviolet remote sensing measurements, indicating likely deficiencies in conventional theories regarding this crucial atmospheric constituent. Here we report the existence of non-thermal hydrogen atoms that are much hotter than the ambient oxygen atoms in the upper thermosphere. Analysis of satellite measurements indicates that the upper thermospheric hydrogen temperature, more precisely the mean kinetic energy of the atomic hydrogen population, increases significantly with declining solar activity, contrary to contemporary understanding of thermospheric behaviour. The existence of hot hydrogen atoms in the upper thermosphere, which is the key to reconciling model predictions and observations, is likely a consequence of low atomic oxygen density leading to incomplete collisional thermalization of the hydrogen population following its kinetic energization through interactions with hot atomic or ionized constituents in the ionosphere, plasmasphere or magnetosphere.

  2. DFT study of Fe-Ni core-shell nanoparticles: Stability, catalytic activity, and interaction with carbon atom for single-walled carbon nanotube growth

    NASA Astrophysics Data System (ADS)

    Yang, Zhimin; Wang, Qiang; Shan, Xiaoye; Li, Wei-qi; Chen, Guang-hui; Zhu, Hongjun

    2015-02-01

    Metal catalysts play an important role in the nucleation and growth of single-walled carbon nanotubes (SWCNTs). It is essential for probing the nucleation and growth mechanism of SWCNTs to fundamentally understand the properties of the metal catalysts and their interaction with carbon species. In this study, we systematically studied the stability of 13- and 55-atom Fe and Fe-Ni core-shell particles as well as these particles interaction with the carbon atoms using the density functional theory calculations. Icosahedral 13- and 55-atom Fe-Ni core-shell bimetallic particles have higher stability than the corresponding monometallic Fe and Ni particles. Opposite charge transfer (or distribution) in these particles leads to the Fe surface-shell displays a positive charge, while the Ni surface-shell exhibits a negative charge. The opposite charge transfer would induce different chemical activities. Compared with the monometallic Fe and Ni particles, the core-shell bimetallic particles have weaker interaction with C atoms. More importantly, C atoms only prefer staying on the surface of the bimetallic particles. In contrast, C atoms prefer locating into the subsurface of the monometallic particles, which is more likely to form stable metal carbides. The difference of the mono- and bimetallic particles on this issue may result in different nucleation and growth mechanism of SWCNTs. Our findings provide useful insights for the design of bimetallic catalysts and a better understanding nucleation and growth mechanism of SWCNTs.

  3. Calibration of a new experimental chamber for PIXE analysis at the Accelerator Facilities Division of Atomic Energy Centre Dhaka (AECD)

    NASA Astrophysics Data System (ADS)

    Hassan, Md. Taufique; Shariff, Md. Asad; Hossein, Amzad; Abedin, Md. Joynal; Fazlul Hoque, A. K. M.; Chowdhuri, M. S.

    2015-05-01

    A new experimental chamber has been installed at the 3 MV Van de Graaff Accelerator Facilities Division in the Atomic Energy Centre, Dhaka, to perform different Ion Beam Analysis (IBA) techniques. The calibration of this new setup for Particle Induced X-ray Emission (PIXE) technique has been done using a set of thin MicroMatter standards and GUPIX (PIXE spectrum analysis software), which is explicated in this paper. The effective thicknesses of the beryllium window of the X-ray detector and of the different absorbers used were determined. For standardization, the so called instrumental constant H (product of detector solid angle and the correction factor for the setup) as function of X-ray energy were determined and stored inside the GUPIX library for further PIXE analysis.

  4. Structure and analysis of atomic vibrations in clusters of Cu n ( n ≤ 20)

    NASA Astrophysics Data System (ADS)

    Rusina, G. G.; Borisova, S. D.; Chulkov, E. V.

    2013-02-01

    The binding energy, equilibrium geometry, and vibration frequencies of free clusters Cu n (2 ≤ n ≤ 20) are calculated using the potentials of interatomic interactions found using the tight-binding approximation. The nonmonotonic dependence of the clusters' minimum vibration frequency on their sizes and the extreme values for the number of atoms in a cluster n = 4, 6, 13, and 19 is demonstrated. It is noted that this result agrees with the theoretical and experimental data on stable structures of small and medium metallic clusters.

  5. Phase-space analysis for ionization processes in the laser-atom interaction using Gabor transformation

    NASA Astrophysics Data System (ADS)

    Shu, X. F.; Liu, S. B.; Song, H. Y.

    2016-04-01

    In this paper, the ionization processes during laser-atom interaction are investigated in phase-space using Gabor transformation. Based on the time-dependent Schrödinger equation (TDSE), the depletion of the whole system caused by the mask function is taken into consideration in calculating the plasma density. We obtain the momentum distribution via the Gabor transformation of the escaping portions of the time-dependent wave packet at the detector-like points on the interior boundaries from which the kinetic energies carried by the escaping portions are calculated.

  6. Iron analysis in atmospheric water samples by atomic absorption spectroscopy (AAS) in water-methanol.

    PubMed

    Sofikitis, A M; Colin, J L; Desboeufs, K V; Losno, R

    2004-01-01

    To distinguish between Fe(II) and Fe(III) species in atmospheric water samples, we have adapted an analytical procedure based on the formation of a specific complex between Fe(II) and ferrozine (FZ) on a chromatographic column. After elution of Fe(III), the Fe(II) complex is recovered with water-methanol (4:1). The possibility of trace iron measurements in this complex medium by graphite-furnace atomic-absorption spectrometry has been investigated. A simplex optimization routine was required to complete the development of the analytical method.

  7. High-speed imaging optical techniques for shockwave and droplets atomization analysis

    NASA Astrophysics Data System (ADS)

    Slangen, Pierre R.; Lauret, Pierre; Heymes, Frederic; Aprin, Laurent; Lecysyn, Nicolas

    2016-12-01

    Droplets atomization by shockwave can act as a consequence in domino effects on an industrial facility: aggression of a storage tank (projectile from previous event, for example) can cause leakage of hazardous material (toxic and flammable). As the accident goes on, a secondary event can cause blast generation, impacting the droplets and resulting in their atomization. Therefore, exchange surface increase impacts the evaporation rate. This can be an issue in case of dispersion of such a cloud. The experiments conducted in the lab generate a shockwave with an open-ended shock tube to break up liquid droplets. As the expected shockwave speed is about 400 m/s (˜Mach 1.2), the interaction with falling drops is very short. High-speed imaging is performed at about 20,000 fps. The shockwave is measured using both overpressure sensors: particle image velocimetry and pure in line shadowgraphy. The size of fragmented droplets is optically measured by direct shadowgraphy simultaneously in different directions. In these experiments, secondary breakups of a droplet into an important number of smaller droplets from the shockwave-induced flow are shown. The results of the optical characterizations are discussed in terms of shape, velocity, and size.

  8. Cooperative effects and disorder: A scaling analysis of the spectrum of the effective atomic Hamiltonian

    NASA Astrophysics Data System (ADS)

    Bellando, L.; Gero, A.; Akkermans, E.; Kaiser, R.

    2014-12-01

    We study numerically the spectrum of the non-Hermitian effective Hamiltonian that describes the dipolar interaction of a gas of N ≫1 atoms with the radiation field. We analyze the interplay between cooperative effects and disorder for both scalar and vectorial radiation fields. We show that for dense gases, the resonance width distribution follows, both in the scalar and vectorial cases, a power law P (Γ ) ˜Γ-4 /3 that originates from cooperative effects between more than two atoms. This power law is different from the P (Γ ) ˜Γ-1 behavior, which has been considered as a signature of Anderson localization of light in random systems. We show that in dilute clouds, the center of the energy distribution is described by Wigner's semicircle law in the scalar and vectorial cases. For dense gases, this law is replaced in the vectorial case by the Laplace distribution. Finally, we show that in the scalar case the degree of resonance overlap increases as a power law of the system size for dilute gases, but decays exponentially with the system size for dense clouds.

  9. Oxygen atom transfer reactions from Mimoun complexes to sulfides and sulfoxides. A bonding evolution theory analysis.

    PubMed

    González-Navarrete, Patricio; Sensato, Fabricio R; Andrés, Juan; Longo, Elson

    2014-08-07

    In this research, a comprehensive theoretical investigation has been conducted on oxygen atom transfer (OAT) reactions from Mimoun complexes to sulfides and sulfoxides. The joint use of the electron localization function (ELF) and Thom's catastrophe theory (CT) provides a powerful tool to analyze the evolution of chemical events along a reaction pathway. The progress of the reaction has been monitored by structural stability domains from ELF topology while the changes between them are controlled by turning points derived from CT which reveal that the reaction mechanism can be separated in several steps: first, a rupture of the peroxo O1-O2 bond, then a rearrangement of lone pairs of the sulfur atom occurs and subsequently the formation of S-O1 bond. The OAT process involving the oxidation of sulfides and sulfoxides is found to be an asynchronous process where O1-O2 bond breaking and S-O1 bond formation processes do not occur simultaneously. Nucleophilic/electrophilic characters of both dimethyl sulfide and dimethyl sulfoxide, respectively, are sufficiently described by our results, which hold the key to unprecedented insight into the mapping of electrons that compose the bonds while the bonds change.

  10. MISSE 2 PEACE Polymers Experiment Atomic Oxygen Erosion Yield Error Analysis

    NASA Technical Reports Server (NTRS)

    McCarthy, Catherine E.; Banks, Bruce A.; deGroh, Kim, K.

    2010-01-01

    Atomic oxygen erosion of polymers in low Earth orbit (LEO) poses a serious threat to spacecraft performance and durability. To address this, 40 different polymer samples and a sample of pyrolytic graphite, collectively called the PEACE (Polymer Erosion and Contamination Experiment) Polymers, were exposed to the LEO space environment on the exterior of the International Space Station (ISS) for nearly 4 years as part of the Materials International Space Station Experiment 1 & 2 (MISSE 1 & 2). The purpose of the PEACE Polymers experiment was to obtain accurate mass loss measurements in space to combine with ground measurements in order to accurately calculate the atomic oxygen erosion yields of a wide variety of polymeric materials exposed to the LEO space environment for a long period of time. Error calculations were performed in order to determine the accuracy of the mass measurements and therefore of the erosion yield values. The standard deviation, or error, of each factor was incorporated into the fractional uncertainty of the erosion yield for each of three different situations, depending on the post-flight weighing procedure. The resulting error calculations showed the erosion yield values to be very accurate, with an average error of 3.30 percent.

  11. Multi-element analysis of manganese nodules by atomic absorption spectrometry without chemical separation

    USGS Publications Warehouse

    Kane, J.S.; Harnly, J.M.

    1982-01-01

    Five manganese nodules, including the USGS reference nodules A-1 and P-1, were analyzed for Co, Cu, Fe, K, Mg, Mn, Na, Ni and Zn without prior chemical separation by using a simultaneous multi-element atomic absorption spectrometer with an air-cetylene flame. The nodules were prepared in three digestion matrices. One of these solutions was measured using sixteen different combinations of burner height and air/acetylene ratios. Results for A-1 and P-1 are compared to recommended values and results for all nodules are compared to those obtained with an inductively coupled plasma. The elements Co, Cu, Fe, K, Mg, Mn, Na, Ni, and Zn are simultaneously determined with a composite recovery for all elements of 100 ?? 7%, independent of the digestion matrices, heights in the flame, or flame stoichiometries examined. Individual recoveries for Co, K, and Ni are considerably poorer in two digests than this composite figure, however. The optimum individual recoveries of 100 ?? 5% and imprecisions of 1-4%, except for zinc, are obtained when Co, K, Mn, Na and Ni are determined simultaneously in a concentrated digest, and in another analytical sequence, when Cu, Fe, Mg, Mn and Zn are measured simultaneously after dilution. Determination of manganese is equally accurate in the two sequences; its measurement in both assures internal consistency between the two measurement sequences. This approach improves analytical efficiency over that for conventional atomic absorption methods, while minimizing loss of accuracy or precision for individual elements. ?? 1982.

  12. Atomic and molecular analysis highlights the biophysics of unprotonated and protonated retinal in UV and scotopic vision.

    PubMed

    Kubli-Garfias, Carlos; Vázquez-Ramírez, Ricardo; Cabrera-Vivas, Blanca M; Gómez-Reyes, Baldomero; Ramírez, Juan Carlos

    2015-09-26

    During the photoreaction of rhodopsin, retinal isomerizes, rotating the C11[double bond, length as m-dash]C12 π-bond from cis to an all-trans configuration. Unprotonated (UR) or protonated (PR) retinal in the Schiff's base (SB) is related to UV and light vision. Because the UR and PR have important differences in their physicochemical reactivities, we compared the atomic and molecular properties of these molecules using DFT calculations. The C10-C11[double bond, length as m-dash]C12-C13 dihedral angle was rotated from 0° to 180° in 45° steps, giving five conformers, and the following were calculated from them: atomic orbital (AO) contributions to the HOMO and LUMO, atomic charges, bond length, bond order, HOMO, LUMO, hardness, electronegativity, polarizability, electrostatic potential, UV-vis spectra and dipole moment (DM). Similarly, the following were analyzed: the energy profile, hybridization, pyramidalization and the hydrogen-out-of-plane (HOOP) wagging from the H11-C11[double bond, length as m-dash]C12-H12 dihedral angle. In addition, retinal with a water H-bond (HR) in the SB was included for comparison. Interestingly, in the PR, C11 and C12 are totally the LUMO and the HOMO, respectively, and have a large electronegativity difference, which predicts an electron jump in these atoms during photoexcitation. At the same time, the PR showed a longer bond length and lower bond order, with a larger DM, lower HOMO-LUMO gap, lower hardness and higher electronegativity. In addition, the AOs of -45° and -90° conformers changed significantly, from pz to py, during the rotation concomitantly with marked hybridization, smooth pyramidalization and lower HOOP activity. Clearly, the atomic and molecular differences between the UR and PR are overwhelming, including the rotational energy profile and light absorption spectra, which indicates that light absorption of UR and PR is already determined by the retinal characteristics of the SB protonation. The HR

  13. Neutron activation analysis detection limits using {sup 252}Cf sources

    SciTech Connect

    DiPrete, D.P.; Sigg, R.A.

    2000-07-01

    The Savannah River Technology Center (SRTC) developed a neutron activation analysis (NAA) facility several decades ago using low-flux {sup 252}Cf neutron sources. Through this time, the facility has addressed areas of applied interest in managing the Savannah River Site (SRS). Some applications are unique because of the site's operating history and its chemical-processing facilities. Because sensitivity needs for many applications are not severe, they can be accomplished using an {approximately}6-mg {sup 252}Cf NAA facility. The SRTC {sup 252}Cf facility continues to support applied research programs at SRTC as well as other SRS programs for environmental and waste management customers. Samples analyzed by NAA include organic compounds, metal alloys, sediments, site process solutions, and many other materials. Numerous radiochemical analyses also rely on the facility for production of short-lived tracers, yielding by activation of carriers and small-scale isotope production for separation methods testing. These applications are more fully reviewed in Ref. 1. Although the flux [{approximately}2 x 10{sup 7} n/cm{sup 2}{center_dot}s] is low relative to reactor facilities, more than 40 elements can be detected at low and sub-part-per-million levels. Detection limits provided by the facility are adequate for many analytical projects. Other multielement analysis methods, particularly inductively coupled plasma atomic emission and inductively coupled plasma mass spectrometry, can now provide sensitivities on dissolved samples that are often better than those available by NAA using low-flux isotopic sources. Because NAA allows analysis of bulk samples, (a) it is a more cost-effective choice when its sensitivity is adequate than methods that require digestion and (b) it eliminates uncertainties that can be introduced by digestion processes.

  14. Comparison of CID, ETD and metastable atom-activated dissociation (MAD) of doubly and triply charged phosphorylated tau peptides.

    PubMed

    Cook, Shannon L; Zimmermann, Carolyn M; Singer, David; Fedorova, Maria; Hoffmann, Ralf; Jackson, Glen P

    2012-06-01

    The fragmentation behavior of the 2+ and 3+ charge states of eleven different phosphorylated tau peptides was studied using collision-induced dissociation (CID), electron transfer dissociation (ETD) and metastable atom-activated dissociation (MAD). The synthetic peptides studied contain up to two known phosphorylation sites on serine or threonine residues, at least two basic residues, and between four and eight potential sites of phosphorylation. CID produced mainly b-/y-type ions with abundant neutral losses of the phosphorylation modification. ETD produced c-/z-type ions in highest abundance but also showed numerous y-type ions at a frequency about 50% that of the z-type ions. The major peaks observed in the ETD spectra correspond to the charge-reduced product ions and small neutral losses from the charge-reduced peaks. ETD of the 2+ charge state of each peptide generally produced fewer backbone cleavages than the 3+ charge state, consistent with previous reports. Regardless of charge state, MAD achieved more extensive backbone cleavage than CID or ETD, while retaining the modification(s) in most cases. In all but one case, unambiguous modification site determination was achieved with MAD. MAD produced 15-20% better sequence coverage than CID and ETD for both the 2+ and 3+ charge states and very different fragmentation products indicating that the mechanism of fragmentation in MAD is unique and complementary to CID and ETD.

  15. A new way towards high-efficiency thermally activated delayed fluorescence devices via external heavy-atom effect

    NASA Astrophysics Data System (ADS)

    Zhang, Wenzhi; Jin, Jiangjiang; Huang, Zhi; Zhuang, Shaoqing; Wang, Lei

    2016-07-01

    Thermally activated delayed fluorescence (TADF) mechanism is a significant method that enables the harvesting of both triplet and singlet excitons for emission. However, up to now most efforts have been devoted to dealing with the relation between singlet-triplet splitting (ΔEST) and fluorescence efficiency, while the significance of spin-orbit coupling (SOC) is usually ignored. In this contribution, a new method is developed to realize high-efficiency TADF-based devices through simple device-structure optimizations. By inserting an ultrathin external heavy-atom (EHA) perturber layer in a desired manner, it provides useful means of accelerating the T1 → S1 reverse intersystem crossing (RISC) in TADF molecules without affecting the corresponding S1 → T1 process heavily. Furthermore, this strategy also promotes the utilization of host triplets through Förster mechanism during host → guest energy transfer (ET) processes, which helps to get rid of the solely dependence upon Dexter mechanism. Based on this strategy, we have successfully raised the external quantum efficiency (EQE) in 4CzPN-based devices by nearly 38% in comparison to control devices. These findings provide keen insights into the role of EHA played in TADF-based devices, offering valuable guidelines for utilizing certain TADF dyes which possess high radiative transition rate but relatively inefficient RISC.

  16. Activation of Methane and Ethane as Mediated by the Triatomic Anion HNbN(-): Electronic Structure Similarity with a Pt Atom.

    PubMed

    Ma, Jia-Bi; Xu, Lin-Lin; Liu, Qing-Yu; He, Sheng-Gui

    2016-04-11

    Investigations of the intrinsic properties of gas-phase transition metal nitride (TMN) ions represent one approach to gain a fundamental understanding of the active sites of TMN catalysts, the activities and electronic structures of which are known to be comparable to those of noble metal catalysts. Herein, we investigate the structures and reactivities of the triatomic anions HNbN(-) by means of mass spectrometry and photoelectron imaging spectroscopy, in conjunction with density functional theory calculations. The HNbN(-) anions are capable of activating CH4 and C2H6 through oxidative addition, exhibiting similar reactivities to free Pt atoms. The similar electronic structures of HNbN(-) and Pt, especially the active orbitals, are responsible for this resemblance. Compared to the inert NbN(-), the coordination of the H atom in HNbN(-) is indispensable. New insights into how to replace noble metals with TMNs may be derived from this combined experimental/computational study.

  17. Nanostructure and force spectroscopy analysis of human peripheral blood CD4+ T cells using atomic force microscopy.

    PubMed

    Hu, Mingqian; Wang, Jiongkun; Cai, Jiye; Wu, Yangzhe; Wang, Xiaoping

    2008-09-12

    To date, nanoscale imaging of the morphological changes and adhesion force of CD4(+) T cells during in vitro activation remains largely unreported. In this study, we used atomic force microscopy (AFM) to study the morphological changes and specific binding forces in resting and activated human peripheral blood CD4(+) T cells. The AFM images revealed that the volume of activated CD4(+) T cells increased and the ultrastructure of these cells also became complex. Using a functionalized AFM tip, the strength of the specific binding force of the CD4 antigen-antibody interaction was found to be approximately three times that of the unspecific force. The adhesion forces were not randomly distributed over the surface of a single activated CD4(+) T cell, indicated that the CD4 molecules concentrated into nanodomains. The magnitude of the adhesion force of the CD4 antigen-antibody interaction did not change markedly with the activation time. Multiple bonds involved in the CD4 antigen-antibody interaction were measured at different activation times. These results suggest that the adhesion force involved in the CD4 antigen-antibody interaction is highly selective and of high affinity.

  18. Three-phase plasma arc atomic-emission spectrometric analysis of environmental samples using an ultrasonic nebulizer.

    PubMed

    Ghatass, Zekry F; Roston, Gamal D; Mohamed, Moustafa M

    2003-06-01

    Combination of an ultrasonic nebulizer and plasma excitation sources for spectrochemical analysis offers desirable features of low detection limits, high sample throughput, wide dynamic range of operation, acceptable precision and accuracy, and simultaneous quantitative analytical capabilities. Moreover, the ultrasonic nebulizer does not require sample preconcentration. Recently we have developed a three-phase plasma arc (TPPA) for atomic emission spectrochemical analysis. In the present work, to increase the analytical utility of the three-phase plasma system, an ultrasonic nebulizer was used for sample introduction. The effects of the argon gas flow rate, current, excitation temperature have been studied. The analytical calibration curves are obtained for Ca, Cr, Fe, Mg and Mn, and detection limits have been calculated. The present technique is used to determine the concentration of the elements Ca, Cr, Fe, Mg and Mn in airborne samples.

  19. A new approach to mineralization of flaxseed (Linum usitatissimum L.) for trace element analysis by flame atomic absorption spectrometry.

    PubMed

    Oliveira, João P S; Silva, Francisco L F; Monte, Raimundo J G; Matos, Wladiana O; Lopes, Gisele S

    2017-06-01

    A new approach to the analysis of Cu, Fe, Mn and Zn in flaxseed was developed based on infrared-assisted acid digestion. Quantitation by flame atomic absorption spectrometry yields results in agreement with those arising from aggressive total decomposition using conventional microwave-assisted (MW) digestions. A full factorial design in two levels was applied to evaluate the impact of significant variables for all elements to determine optimal experimental conditions. A desirability function revealed these to be: 2.0g sample mass, 8mL of HNO3 and 8min of heating time in the IR system. Precision better than 10% (RSD) was obtained, superior to that of a combined IR-MW approach. Sample preparation based on IR-assisted digestion provides a rapid and inexpensive alternative to other conventional techniques for the analysis of complex samples and is able to accommodate relatively large masses of sample, alleviating potential homogeneity issues as well as enhancing detection power.

  20. From Aβ Filament to Fibril: Molecular Mechanism of Surface-Activated Secondary Nucleation from All-Atom MD Simulations.

    PubMed

    Schwierz, Nadine; Frost, Christina V; Geissler, Phillip L; Zacharias, Martin

    2017-02-02

    Secondary nucleation pathways in which existing amyloid fibrils catalyze the formation of new aggregates and neurotoxic oligomers are of immediate importance for the onset and progression of Alzheimer's disease. Here, we apply extensive all-atom molecular dynamics simulations in explicit water to study surface-activated secondary nucleation pathways at the extended lateral β-sheet surface of a preformed Aβ9-40 filament. Calculation of free-energy profiles allows us to determine binding free energies and conformational intermediates for nucleation complexes consisting of 1-4 Aβ peptides. In addition, we combine the free-energy profiles with position-dependent diffusion profiles to extract complementary kinetic information and macroscopic growth rates. Single monomers bind to the β-sheet surface in a disordered, hydrophobically collapsed conformation, whereas dimers and larger oligomers can retain a cross-β conformation resembling a more ordered fibril structure. The association processes during secondary nucleation follow a dock/lock mechanism consisting of a fast initial encounter phase (docking) and a slow structural rearrangement phase (locking). The major driving forces for surface-activated secondary nucleation are the release of a large number of hydration water molecules and the formation of hydrophobic interface contacts, the latter being in contrast to the elongation process at filament tips, which is dominated by the formation of stable and highly specific interface hydrogen bonds. The calculated binding free energies and the association rates for the attachment of Aβ monomers and oligomers to the extended lateral β-sheet surface of the filament seed are higher compared to those for elongation at the filament tips, indicating that secondary nucleation pathways can become important once a critical concentration of filaments has formed.

  1. Atomic polarizabilities

    SciTech Connect

    Safronova, M. S.; Mitroy, J.; Clark, Charles W.; Kozlov, M. G.

    2015-01-22

    The atomic dipole polarizability governs the first-order response of an atom to an applied electric field. Atomic polarization phenomena impinge upon a number of areas and processes in physics and have been the subject of considerable interest and heightened importance in recent years. In this paper, we will summarize some of the recent applications of atomic polarizability studies. A summary of results for polarizabilities of noble gases, monovalent, and divalent atoms is given. The development of the CI+all-order method that combines configuration interaction and linearized coupled-cluster approaches is discussed.

  2. Shape-selective catalysts for Fischer-Tropsch chemistry : atomic layer deposition of active catalytic metals. Activity report : January 1, 2005 - September 30, 2005.

    SciTech Connect

    Cronauer, D. C.

    2011-04-15

    Argonne National Laboratory is carrying out a research program to create, prepare, and evaluate catalysts to promote Fischer-Tropsch (FT) chemistry - specifically, the reaction of hydrogen with carbon monoxide to form long-chain hydrocarbons. In addition to needing high activity, it is desirable that the catalysts have high selectivity and stability with respect to both mechanical strength and aging properties. The broad goal is to produce diesel fraction components and avoiding excess yields of both light hydrocarbons and heavy waxes. Originally the goal was to prepare shape-selective catalysts that would limit the formation of long-chain products and yet retain the active metal sites in a protected 'cage.' Such catalysts were prepared with silica-containing fractal cages. The activity was essentially the same as that of catalysts without the cages. We are currently awaiting follow-up experiments to determine the attrition strength of these catalysts. A second experimental stage was undertaken to prepare and evaluate active FT catalysts formed by atomic-layer deposition [ALD] of active components on supported membranes and particulate supports. The concept was that of depositing active metals (i.e. ruthenium, iron or cobalt) upon membranes with well defined flow channels of small diameter and length such that the catalytic activity and product molecular weight distribution could be controlled. In order to rapidly evaluate the catalytic membranes, the ALD coating processes were performed in an 'exploratory mode' in which ALD procedures from the literature appropriate for coating flat surfaces were applied to the high surface area membranes. Consequently, the Fe and Ru loadings in the membranes were likely to be smaller than those expected for complete monolayer coverage. In addition, there was likely to be significant variation in the Fe and Ru loading among the membranes due to difficulties in nucleating these materials on the aluminum oxide surfaces. The first

  3. Analysis of a Bose-Einstein Condensate Double-Well Atom Interferometer

    SciTech Connect

    Faust, Douglas K.; Reinhardt, William P.

    2010-12-10

    Motivated by an open theoretical question in Bose-Einstein condensate atom interferometry, we introduce a novel computational method to describe the condensate order parameter in the presence of a central barrier. We are able to follow the full dynamics of the system during the raising of a barrier, from a single macroscopically occupied ground state to a state where imaging shows a split density and, finally, to the observation of a phase-controlled interference pattern. We are able to discriminate between a mean-field and a two-mode state via the Penrose-Onsager criterion. By simulating the first such experiment, where in spite of the observed splitting of the condensate density there is never more than a single macroscopically occupied state, we provide a definitive interpretation of these systems as a novel many-body form of Young's double-slit experiment.

  4. Analysis of a Bose-Einstein condensate double-well atom interferometer.

    PubMed

    Faust, Douglas K; Reinhardt, William P

    2010-12-10

    Motivated by an open theoretical question in Bose-Einstein condensate atom interferometry, we introduce a novel computational method to describe the condensate order parameter in the presence of a central barrier. We are able to follow the full dynamics of the system during the raising of a barrier, from a single macroscopically occupied ground state to a state where imaging shows a split density and, finally, to the observation of a phase-controlled interference pattern. We are able to discriminate between a mean-field and a two-mode state via the Penrose-Onsager criterion. By simulating the first such experiment, where in spite of the observed splitting of the condensate density there is never more than a single macroscopically occupied state, we provide a definitive interpretation of these systems as a novel many-body form of Young's double-slit experiment.

  5. Analysis of a Bose-Einstein Condensate Double-Well Atom Interferometer

    NASA Astrophysics Data System (ADS)

    Faust, Douglas K.; Reinhardt, William P.

    2010-12-01

    Motivated by an open theoretical question in Bose-Einstein condensate atom interferometry, we introduce a novel computational method to describe the condensate order parameter in the presence of a central barrier. We are able to follow the full dynamics of the system during the raising of a barrier, from a single macroscopically occupied ground state to a state where imaging shows a split density and, finally, to the observation of a phase-controlled interference pattern. We are able to discriminate between a mean-field and a two-mode state via the Penrose-Onsager criterion. By simulating the first such experiment, where in spite of the observed splitting of the condensate density there is never more than a single macroscopically occupied state, we provide a definitive interpretation of these systems as a novel many-body form of Young’s double-slit experiment.

  6. Sensitivity analysis of single-layer graphene resonators using atomic finite element method

    SciTech Connect

    Lee, Haw-Long; Hsu, Jung-Chang; Lin, Shu-Yu; Chang, Win-Jin

    2013-09-28

    Atomic finite element simulation is applied to study the natural frequency and sensitivity of a single-layer graphene-based resonator with CCCC, SSSS, CFCF, SFSF, and CFCF boundary conditions using the commercial code ANSYS. The fundamental frequencies of the graphene sheet are compared with the results of the previous finite element study. In addition, the sensitivity of the resonator is compared with the early work based on nonlocal elasticity theory. The results of the comparison are very good in all considered cases. The sensitivities of the resonator with different boundary conditions are obtained, and the order based on the boundary condition is CCCC > SSSS > CFCF > SFSF > CFFF. The highest sensitivity is obtained when the attached mass is located at the center of the resonator. This is useful for the design of a highly sensitive graphene-based mass sensor.

  7. Analysis of the coagulation of human blood cells on diamond surfaces by atomic force microscopy

    NASA Astrophysics Data System (ADS)

    Baranauskas, V.; Fontana, M.; Guo, Zhao Jing; Ceragioli, H. J.; Peterlevitz, A. C.

    2004-11-01

    Atomic force microscopy (AFM) was used to study the morphology and coagulation of human blood cells in contact with solid surfaces. Blood was extracted from the veins of healthy adult donors and the samples were used immediately after extraction, deposited either on borosilicate glass or diamond substrates. Some blood samples were anti-coagulated by adding heparin for single cell AFM imaging. No chemicals were used for attaching or immobilizing the cells. The diamond substrates were produced by chemical vapour deposition (CVD diamond) using a hot-filament CVD system fed with ethanol highly diluted in hydrogen. AFM imaging of isolated cells (anti-coagulated by heparin) was only possible on the glass substrates due to the lack of adherence of the cells to the diamond surface. The coagulation results suggest that blood clotting on diamond produces a less rough surface than blood clotting on glass.

  8. Atom Probe Tomography Analysis of Precipitation during Tempering of a Nanostructured Bainitic Steel

    SciTech Connect

    Caballero, Francesca G.; Miller, Michael K; Garcia-Mateo, C.

    2011-01-01

    Carbon distribution during tempering of a nanostructured bainitic steel was analyzed by atom probe tomography (APT). Three different types of particles are detected on samples tempered at 673 K (400 C) for 30 minutes: lower bainite cementite with a carbon content of {approx}25 at. pct, {var_epsilon}-carbides with a carbon content close to 30 at. pct, and carbon clusters, small features with a carbon content of {approx}14 at. pct indicative of a stage of tempering prior to precipitation of {var_epsilon}-carbide. After tempering at 773 K (500 C) for 30 minutes, the {var_epsilon}-carbide-to-cementite transition was observed. Solute concentration profiles across carbide/ferrite interfaces showed the distribution of substitutional elements in {var_epsilon}-carbide and cementite for all the tempering conditions.

  9. Analysis of containment venting for the Peach Bottom Atomic Power Station

    SciTech Connect

    Hanson, D.J.; Wright, R.E.; Jenkins, J.P.

    1986-09-12

    The effectiveness of containment venting as a means of preventing or mitigating the consequences of severe accidents was evaluated for Peach Bottom Atomic Power Station Units 2 and 3 (BWR-4s with Mark I containments). Results from this evaluation indicate that the effectiveness of venting in preventing containment failure is highly dependent on the severe accident sequence. Containment venting can be effective for several classes of sequences, including loss-of-coolant accidents with breaks in the containment and transients with a failure of containment heat removal. However, based on draft procedures and equipment in place at the time of the evaluation, containment venting has limited potential for further reducing the risk associated with several sequences currently identified as significant contributors to risk. Means of improving the potential for risk reduction were identified, but their influence on risk was not analyzed.

  10. Bulk Analysis of International Atomic Energy Agency Environmental Samples in Support of International Safeguards

    SciTech Connect

    Wogman, Ned A.; Olsen, Khris B.; Farmer, Orville T.

    2008-03-28

    Inspectors for the International Atomic Energy Agency’s (IAEA) Safeguards Program collect environmental samples under traditional safeguards, strengthened safeguards, or additional protocols during facility inspections at declared nuclear facilities throughout the world. Currently, there are 400 facilities under IAEA safeguards in 70 countries. All environmental samples are returned to IAEA’s Clean Laboratory located in Seiberdorf, Austria, where they are screened for gamma-ray emitting isotopes and prepared for distribution to laboratories for additional sampling. After the sample(s) are analyzed, the results are reported to the United States Network of Analytical Laboratories for input into its database. The IAEA reviews the data and incorporates the results into the safeguards evaluation of the state (country).

  11. Atom Probe Tomography Analysis of the Distribution of Rhenium in Nickel Alloys

    SciTech Connect

    Mottura, A.; Warnken, N; Miller, Michael K; Reed, R. C.; Finnis, M.

    2010-01-01

    Atom probe tomography (APT) is used to characterise the distributions of rhenium in a binary Ni-Re alloy and the nickel-based single-crystal CMSX-4 superalloy. A purpose-built algorithm is developed to quantify the size distribution of solute clusters, and applied to the APT datasets to critique the hypothesis that rhenium is prone to the formation of clusters in these systems. No evidence is found to indicate that rhenium forms solute clusters above the level expected from random fluctuations. In CMSX-4, enrichment of Re is detected in the matrix phase close to the matrix/precipitate ({gamma}/{gamma}{prime}) phase boundaries. Phase field modelling indicates that this is due to the migration of the {gamma}/{gamma}{prime} interface during cooling from the temperature of operation. Thus, neither clustering of rhenium nor interface enrichments can be the cause of the enhancement in high temperature mechanical properties conferred by rhenium alloying.

  12. Routine application of the in situ soil analysis technique by the Yankee Atomic Environmental Laboratory

    SciTech Connect

    Murray, J.C.; McCurdy, D.E.; Laurenzo, E.L.

    1989-01-01

    Using a technique developed by the Environmental Measurements Laboratory (EML) for field spectrometry, the Yankee Atomic Environmental Laboratory (YAEL) has routinely performed in situ soil measurements in the vicinity of five nuclear power stations for more than a decade. As a special research endeavor, several locations at the FURNAS Angra 1 site in Brazil having high natural backgrounds were also measured in 1987. The technical basis of the technique, a comparison of soil radionuclide concentrations predicted by the in situ technique to soil radionuclide concentrations predicted by the in situ technique to soil analyses from the same sites, the advantages and disadvantages of the in situ methodology, and the evolution of the portable equipment utilized at YAEL for the field measurements are presented in this paper.

  13. An analytical model accounting for tip shape evolution during atom probe analysis of heterogeneous materials.

    PubMed

    Rolland, N; Larson, D J; Geiser, B P; Duguay, S; Vurpillot, F; Blavette, D

    2015-12-01

    An analytical model describing the field evaporation dynamics of a tip made of a thin layer deposited on a substrate is presented in this paper. The difference in evaporation field between the materials is taken into account in this approach in which the tip shape is modeled at a mesoscopic scale. It was found that the non-existence of sharp edge on the surface is a sufficient condition to derive the morphological evolution during successive evaporation of the layers. This modeling gives an instantaneous and smooth analytical representation of the surface that shows good agreement with finite difference simulations results, and a specific regime of evaporation was highlighted when the substrate is a low evaporation field phase. In addition, the model makes it possible to calculate theoretically the tip analyzed volume, potentially opening up new horizons for atom probe tomographic reconstruction.

  14. The total scattering atomic pair distribution function: New methodology for nanostructure analysis

    NASA Astrophysics Data System (ADS)

    Masadeh, Ahmad

    The conventional xray diffration (XRD) methods probe for the presence of long-range order (periodic structure) which are reflected in the Bragg peaks. Local structural deviations or disorder mainly affect the diffuse scattering intensity. In order to obtain structural information about both long-range order and local structure disorder, a technique that takes in account both Bragg and diffuse scattering need to be employed, such as the atomic pair distribution function (PDF) technique. This work introduces a PDF based methodology to quantitatively investigate nanostructure materials in general. The introduced methodology can be applied to extract quantitatively structural information about structure, crystallinity level, core/shell size, nanoparticle size, and inhomogeneous internal strain in the measured nanoparticles. This method is generally applicable to the characterization of the nano-scale solid, many of which may exhibit complex disorder and strain

  15. Comparative Sensitivity Analysis of Muscle Activation Dynamics

    PubMed Central

    Rockenfeller, Robert; Günther, Michael; Schmitt, Syn; Götz, Thomas

    2015-01-01

    We mathematically compared two models of mammalian striated muscle activation dynamics proposed by Hatze and Zajac. Both models are representative for a broad variety of biomechanical models formulated as ordinary differential equations (ODEs). These models incorporate parameters that directly represent known physiological properties. Other parameters have been introduced to reproduce empirical observations. We used sensitivity analysis to investigate the influence of model parameters on the ODE solutions. In addition, we expanded an existing approach to treating initial conditions as parameters and to calculating second-order sensitivities. Furthermore, we used a global sensitivity analysis approach to include finite ranges of parameter values. Hence, a theoretician striving for model reduction could use the method for identifying particularly low sensitivities to detect superfluous parameters. An experimenter could use it for identifying particularly high sensitivities to improve parameter estimation. Hatze's nonlinear model incorporates some parameters to which activation dynamics is clearly more sensitive than to any parameter in Zajac's linear model. Other than Zajac's model, Hatze's model can, however, reproduce measured shifts in optimal muscle length with varied muscle activity. Accordingly we extracted a specific parameter set for Hatze's model that combines best with a particular muscle force-length relation. PMID:26417379

  16. Neutron activation analysis in archaeological chemistry

    SciTech Connect

    Harbottle, G.

    1987-01-01

    Neutron activation analysis has proven to be a convenient way of performing the chemical analysis of archaeologically-excavated artifacts and materials. It is fast and does not require tedious laboratory operations. It is multielement, sensitive, and can be made nondestructive. Neutron activation analysis in its instrumental form, i.e., involving no chemical separation, is ideally suited to automation and conveniently takes the first step in data flow patterns that are appropriate for many taxonomic and statistical operations. The future will doubtless see improvements in the practice of NAA in general, but in connection with archaeological science the greatest change will be the filling, interchange and widespread use of data banks based on compilations of analytical data. Since provenience-oriented data banks deal with materials (obsidian, ceramics, metals, semiprecious stones, building materials and sculptural media) that participated in trade networks, the analytical data is certain to be of interest to a rather broad group of archaeologists. It is to meet the needs of the whole archaeological community that archaeological chemistry must now turn.

  17. Silane activation by laser-ablated Be atoms: Formation of HBeSiH3 and HBe(μ-H)3Si molecules

    NASA Astrophysics Data System (ADS)

    Zhao, Jie; Yu, Wenjie; Xu, Bing; Huang, Tengfei; Wang, Xuefeng

    2017-03-01

    Laser-ablated beryllium atoms have been reacted with silane molecules during condensation in excess neon and argon at 4 K. Absorptions due to HBeSiH3 and HBe(μ-H)3Si were observed and identified on the basis of isotopic IR spectroscopy, deuterium substitution with SiD4, and quantum chemical frequency calculations. The observed results show excited Be atom (1P1:2s12p1) can insert into Sisbnd H bond spontaneously and the insertion product rearranges to HBe(μ-H)3Si upon photolysis. The electron localization function (ELF) analysis suggests that 3c-2e hydrogen bridge bond (Besbnd Hsbnd Si) was formed by the donation of electrons for Sisbnd H σ bond to the empty p orbital of Be atom for HBe(μ-H)3Si molecule, which shows much difference from Csbnd H bond complexes.

  18. Autoionizing states of atomic boron

    NASA Astrophysics Data System (ADS)

    Argenti, Luca; Moccia, Roberto

    2016-04-01

    We present a B -spline K -matrix method for three-active-electron atoms in the presence of a polarizable core, with which it is possible to compute multichannel single-ionization scattering states with good accuracy. We illustrate the capabilities of the method by computing the parameters of several autoionizing states of the boron atom, with S2e, 2,o2P and D2e symmetry, up to at least the 2 p2(1S) excitation threshold of the B ii parent ion, as well as selected portions of the photoionization cross section from the ground state. Our results exhibit remarkable gauge consistency, they significantly extend the existing sparse record of data for the boron atom, and they are in good agreement with the few experimental and theoretical data available in the literature. These results open the way to extend to three-active-electron systems the spectral analysis of correlated wave packets in terms of accurate scattering states that has already been demonstrated for two-electron atoms in Argenti and Lindroth [Phys. Rev. Lett. 105, 053002 (2010), 10.1103/PhysRevLett.105.053002].

  19. The Atomic Dating Game.

    ERIC Educational Resources Information Center

    Cummo, Evelyn; Matthews, Catherine E.

    2002-01-01

    Presents an activity designed to provide students with opportunities to practice drawing atomic models and discover the logical pairings of whole families on the periodic table. Follows the format of a television game show. (DDR)

  20. Analysis of DOE international environmental management activities

    SciTech Connect

    Ragaini, R.C.

    1995-09-01

    The Department of Energy`s (DOE) Strategic Plan (April 1994) states that DOE`s long-term vision includes world leadership in environmental restoration and waste management activities. The activities of the DOE Office of Environmental Management (EM) can play a key role in DOE`s goals of maintaining U.S. global competitiveness and ensuring the continuation of a world class science and technology community. DOE`s interest in attaining these goals stems partly from its participation in organizations like the Trade Policy Coordinating Committee (TPCC), with its National Environmental Export Promotion Strategy, which seeks to strengthen U.S. competitiveness and the building of public-private partnerships as part of U.S. industrial policy. The International Interactions Field Office task will build a communication network which will facilitate the efficient and effective communication between DOE Headquarters, Field Offices, and contractors. Under this network, Headquarters will provide the Field Offices with information on the Administration`s policies and activities (such as the DOE Strategic Plan), interagency activities, as well as relevant information from other field offices. Lawrence Livermore National Laboratory (LLNL) will, in turn, provide Headquarters with information on various international activities which, when appropriate, will be included in reports to groups like the TPCC and the EM Focus Areas. This task provides for the collection, review, and analysis of information on the more significant international environmental restoration and waste management initiatives and activities which have been used or are being considered at LLNL. Information gathering will focus on efforts and accomplishments in meeting the challenges of providing timely and cost effective cleanup of its environmentally damaged sites and facilities, especially through international technical exchanges and/or the implementation of foreign-development technologies.

  1. Laser based analysis using a passively Q-switched laser employing analysis electronics and a means for detecting atomic optical emission of the laser media

    DOEpatents

    Woodruff, Steven D.; Mcintyre, Dustin L.

    2016-03-29

    A device for Laser based Analysis using a Passively Q-Switched Laser comprising an optical pumping source optically connected to a laser media. The laser media and a Q-switch are positioned between and optically connected to a high reflectivity mirror (HR) and an output coupler (OC) along an optical axis. The output coupler (OC) is optically connected to the output lens along the optical axis. A means for detecting atomic optical emission comprises a filter and a light detector. The optical filter is optically connected to the laser media and the optical detector. A control system is connected to the optical detector and the analysis electronics. The analysis electronics are optically connected to the output lens. The detection of the large scale laser output production triggers the control system to initiate the precise timing and data collection from the detector and analysis.

  2. Spectral and Atomic Physics Analysis of Xenon L-Shell Emission From High Energy Laser Produced Plasmas

    NASA Astrophysics Data System (ADS)

    Thorn, Daniel; Kemp, G. E.; Widmann, K.; Benjamin, R. D.; May, M. J.; Colvin, J. D.; Barrios, M. A.; Fournier, K. B.; Liedahl, D.; Moore, A. S.; Blue, B. E.

    2016-10-01

    The spectrum of the L-shell (n =2) radiation in mid to high-Z ions is useful for probing plasma conditions in the multi-keV temperature range. Xenon in particular with its L-shell radiation centered around 4.5 keV is copiously produced from plasmas with electron temperatures in the 5-10 keV range. We report on a series of time-resolved L-shell Xe spectra measured with the NIF X-ray Spectrometer (NXS) in high-energy long-pulse (>10 ns) laser produced plasmas at the National Ignition Facility. The resolving power of the NXS is sufficiently high (E/ ∂E >100) in the 4-5 keV spectral band that the emission from different charge states is observed. An analysis of the time resolved L-shell spectrum of Xe is presented along with spectral modeling by detailed radiation transport and atomic physics from the SCRAM code and comparison with predictions from HYDRA a radiation-hydrodynamics code with inline atomic-physics from CRETIN. This work was performed under the auspices of the U.S. Department of Energy by LLNL under Contract DE-AC52-07NA27344.

  3. The Journey from Classical to Quantum Thinking: An Analysis of Student Understanding Through the Lens of Atomic Spectra

    NASA Astrophysics Data System (ADS)

    Rao, Sandhya Kolla

    This dissertation aims to explore how students think about atomic absorption and emission of light in the area of introductory quantum chemistry. In particular, the impact of classical ideas of electron position and energy on student understanding of spectra is studied. The analysis was undertaken to discover how student learning can be characterized along different dimensions of competence, and to determine the strength of the correlations between these dimensions. The research in this dissertation study comes from a set of semi-structured clinical interviews after a unit on quantum chemistry using a stratified random sample. Open-ended questions were asked on the topic of atomic spectra to a representative sample (N=65) of students from a large introductory chemistry class. Data was examined using elements of grounded theory. Three dimensions were found, Continuous to Discrete, Interpreting Spectra, and Energy/Force, that explain how student thinking about atomic spectra can be characterized. A fourth dimension, Deterministic to Probabilistic, had been discussed in the research before. Students who exhibited a mastery of discrete energy absorption predominantly were skilled with a difference reasoning, an understanding that the energy values of the spectral lines correlate to differences of energy levels. Students who successfully interpreted spectra did not necessarily have a probabilistic view of electron position, signaling that those two concepts, as least as they were assessed, do not strongly impact each other. Using grounded methods on ten student interviews, four main types of representation use and conceptual understanding in the topic of atomic spectra were discovered: Literal Reasoning, Threshold Reasoning, Exact Difference Reasoning, and Meta-Reasoning. Threshold reasoning was indicative of an influence of classical ideas of energy absorption, while Exact-Difference reasoning consisted of a full appreciation of the all or nothing discrete absorption

  4. Direct quantitative analysis of HCV RNA by atomic force microscopy without labeling or amplification

    PubMed Central

    Jung, Yu Jin; Albrecht, Jeffrey A.; Kwak, Ju-Won; Park, Joon Won

    2012-01-01

    Force-based atomic force microscopy (AFM) was used to detect HCV (hepatitis C virus) RNA directly and to quantitatively analyse it without the need for reverse transcription or amplification. Capture and detection DNA probes were designed. The former was spotted onto a substrate with a conventional microarrayer, and the latter was immobilized on an AFM probe. To control the spacing between the immobilized DNAs on the surface, dendron self-assembly was employed. Force–distance curves showed that the mean force of the specific unbinding events was 32 ± 5 pN, and the hydrodynamic distance of the captured RNA was 30–60 nm. Adhesion force maps were generated with criteria including the mean force value, probability of obtaining the specific curves and hydrodynamic distance. The maps for the samples whose concentrations ranged from 0.76 fM to 6.0 fM showed that cluster number has a linear relationship with RNA concentration, while the difference between the observed number and the calculated one increased at low concentrations. Because the detection limit is expected to be enhanced by a factor of 10 000 when a spot of 1 micron diameter is employed, it is believed that HCV RNA of a few copy numbers can be detected by the use of AFM. PMID:23074195

  5. Analysis of tungsten carbide coatings by UV laser ablation inductively coupled plasma atomic emission spectrometry

    NASA Astrophysics Data System (ADS)

    Kanicky, V.; Otruba, V.; Mermet, J.-M.

    2000-06-01

    Tungsten carbide coatings (thickness 0.1-0.2 mm) containing 8.0, 12.2, 17.2 and 22.9% Co were studied with laser ablation inductively coupled plasma atomic emission spectrometry (LA-ICP-AES). Composition of these plasma sprayed deposits on steel disks was determined using X-ray fluorescence spectrometry and electron microprobe energy/wavelength dispersive X-ray spectrometry. The coatings were ablated by means of a Q-switched Nd:YAG laser at 266 nm (10 Hz, 10 mJ per shot) coupled to an ICP echelle-based spectrometer equipped with a segmented charge-coupled device detector. Non-linear dependences of cobalt lines intensities on the Co percentage were observed both at a single spot ablation and at a sample translation. This behaviour could be attributed to a complex phase composition of the system W-C-Co. However, employing tungsten as internal standard the linear calibration was obtained for studied analytical lines Co II 228.616 nm, Co II 230.786 nm, Co II 236.379 nm and Co II 238.892 nm.

  6. A Comprehensive Opacities/Atomic Database for the Analysis of Astrophysical Spectra and Modeling

    NASA Technical Reports Server (NTRS)

    Pradhan, Anil K. (Principal Investigator)

    1997-01-01

    The main goals of this ADP award have been accomplished. The electronic database TOPBASE, consisting of the large volume of atomic data from the Opacity Project, has been installed and is operative at a NASA site at the Laboratory for High Energy Astrophysics Science Research Center (HEASRC) at the Goddard Space Flight Center. The database will be continually maintained and updated by the PI and collaborators. TOPBASE is publicly accessible from IP: topbase.gsfc.nasa.gov. During the last six months (since the previous progress report), considerable work has been carried out to: (1) put in the new data for low ionization stages of iron: Fe I - V, beginning with Fe II, (2) high-energy photoionization cross sections computed by Dr. Hong Lin Zhang (consultant on the Project) were 'merged' with the current Opacity Project data and input into TOPbase; (3) plans laid out for a further extension of TOPbase to include TIPbase, the database for collisional data to complement the radiative data in TOPbase.

  7. Some aspects of atom probe specimen preparation and analysis of thin film materials.

    PubMed

    Thompson, G B; Miller, M K; Fraser, H L

    2004-07-01

    Some of the factors in the preparation of atom probe specimens of metallic multilayer thin films have been investigated. A series of Ti/Nb multilayer films were sputtered deposited on n-doped Si [001] substrates with either 5 or 0.05Omega cm resistivity. Each wafer was pre-fabricated into a series of 5 microm x 5 microm x approximately 80 microm island posts by photolithography and reactive ion etching. Once the film was grown on the wafer, a Si post was mounted to either a tungsten or stainless steel fine tip needle that was mechanically crimped to a Cu tube for handling. The specimen was then loaded into a Focus Ion Beam instrument where a sacrificial Pt cap was in situ deposited onto the surface of the film and subsequently annularly ion milled into the appropriate geometry. The Pt cap was found to be an effective method in reducing Ga ion damage and implantation into the film during milling. The multilayers deposited on the high resistivity Si exhibited uncontrolled field evaporation which lead to high mass tails in the mass spectra, a reduction in the mass resolution, high background noise, propensity for "flash-failure", and a variation in the apparent layer thickness as the experiment elapsed in time. The multilayers deposited on lower resistivity Si did not suffer from these artifacts.

  8. Re-Analysis of the Dispersed Fluorescence Spectra of the C_3-RARE Gas Atom Complexes

    NASA Astrophysics Data System (ADS)

    Wang, Yi-Jen; Merer, Anthony; Hsu, Yen-Chu

    2015-06-01

    The dispersed fluorescence (DF) spectra of the C_3Ne, C_3Ar, C_3Kr, and C_3Xe complexes near the 0 2^- 0- 000, 0 4^- 0- 000, 0 2^+ 0- 000 and 100-000 bands of the {A}- {X} system of C_3 have been revisited. Some of the DF spectra of the Ne and Ar complexes have been recently obtained with a slightly improved resolution of 6-10 wn. All the DF spectra have been reassigned as emission from van der Waals (vdW) complexes and C_3 fragments. The optically excited C_3-Rg (Rg = rare-gas atom) complexes fluorescence and/or decay down to slightly lower (about 2-30 wn) vibrational levels without changing the internal energy of C_3 and then predissociate via the continua of the nearby vibronic states of C_3. The available dissociation channels depend on the binding energy of the ground electronic state complex. Exceptions have been found at the vdW bands near the 0 4^- 0- 000 band of C_3. The binding energies of the ground electronic states of these four complexes will be discussed. G. Zhang, B.-G. Lin, S.-M. Wen, and Y.-C. Hsu, J. Chem. Phys. 20, 3189(2004) J.-M. Chao, K. S. Tham, G. Zhang, A. J. Merer, Y.-C. Hsu, and W.-P. Hu, J. Chem. Phys. 34, 074313(2011)

  9. Cholesterol oxidase: ultrahigh-resolution crystal structure and multipolar atom model-based analysis.

    PubMed

    Zarychta, Bartosz; Lyubimov, Artem; Ahmed, Maqsood; Munshi, Parthapratim; Guillot, Benoît; Vrielink, Alice; Jelsch, Christian

    2015-04-01

    Examination of protein structure at the subatomic level is required to improve the understanding of enzymatic function. For this purpose, X-ray diffraction data have been collected at 100 K from cholesterol oxidase crystals using synchrotron radiation to an optical resolution of 0.94 Å. After refinement using the spherical atom model, nonmodelled bonding peaks were detected in the Fourier residual electron density on some of the individual bonds. Well defined bond density was observed in the peptide plane after averaging maps on the residues with the lowest thermal motion. The multipolar electron density of the protein-cofactor complex was modelled by transfer of the ELMAM2 charge-density database, and the topology of the intermolecular interactions between the protein and the flavin adenine dinucleotide (FAD) cofactor was subsequently investigated. Taking advantage of the high resolution of the structure, the stereochemistry of main-chain bond lengths and of C=O···H-N hydrogen bonds was analyzed with respect to the different secondary-structure elements.

  10. Atom probe tomography analysis of high dose MA957 at selected irradiation temperatures

    NASA Astrophysics Data System (ADS)

    Bailey, Nathan A.; Stergar, Erich; Toloczko, Mychailo; Hosemann, Peter

    2015-04-01

    Oxide dispersion strengthened (ODS) alloys are meritable structural materials for nuclear reactor systems due to the exemplary resistance to radiation damage and high temperature creep. Summarized in this work are atom probe tomography (APT) investigations on a heat of MA957 that underwent irradiation in the form of in-reactor creep specimens in the Fast Flux Test Facility-Materials Open Test Assembly (FFTF-MOTA) for the Liquid Metal Fast Breeder Reactor (LMFBR) program. The oxide precipitates appear stable under irradiation at elevated temperature over extended periods of time. Nominally, the precipitate chemistry is unchanged by the accumulated dose; although, evidence suggests that ballistic dissolution and reformation processes are occurring at all irradiation temperatures. At 412 °C-109 dpa, chromium enrichments - consistent with the α‧ phase - appear between the oxide precipitates, indicating radiation induced segregation. Grain boundaries, enriched with several elements including nickel and titanium, are observed at all irradiation conditions. At 412 °C-109 dpa, the grain boundaries are also enriched in molecular titanium oxide (TiO).

  11. A New Nitrogenase Mechanism Using a CFe8S9 Model: Does H2 Elimination Activate the Complex to N2 Addition to the Central Carbon Atom?

    PubMed

    McKee, Michael L

    2016-02-11

    A truncated model of the FeMo cofactor is used to explore a new mechanism for the conversion of N2 to NH3 by the nitrogenase enzyme. After four initial protonation/reduction steps, the H4CFe8S9 cluster has two hydrogen atoms attached to sulfur, one hydrogen bridging two iron centers and one hydrogen bonded to carbon. The loss of the CH and FeHFe hydrogens as molecular hydrogen activates the cluster to addition of N2 to the carbon center. This unique step takes place at a nearly planar four-coordinate carbon center and leads to an intermediate with a significantly weakened N-N bond. A hydrogen attached to a sulfur atom is then transferred to the distal nitrogen atom. Additional prontonation/reduction steps are modeled by adding a hydrogen atom to sulfur and locating the transition states for transfer to nitrogen. The first NH3 is lost in a thermal neutral step, while the second step is endothermic. The loss of H2 activates the complex by reducing the barrier for N2 addition by 3.5 kcal/mol. Since this is the most difficult step in the mechanism, reducing the barrier for this step justifies the "extra expense" of H2 production.

  12. Kinetic Energy Distribution of D(2p) Atoms From Analysis of the D Lyman-a Line Profile

    NASA Technical Reports Server (NTRS)

    Ciocca, Marco; Ajello, Joseph M.; Liu, Xianming; Maki, Justin

    1997-01-01

    The absolute cross sections of the line center (slow atoms) and wings (fast atoms) and total emission line profile were measured from threshold to 400 eV. Analytical model coeffiecients are given for the energy dependence of the measured slow atom cross section.

  13. Indirect Determinations of Atomic Radii

    ERIC Educational Resources Information Center

    Walker, Noojin

    1976-01-01

    Describes laboratory activities which relate the mass, volume, density, and radii of atoms through the assumption that the smallest unit of matter is a cubic box containing one atom. From calculations based on macroscopic materials, the author feels that the concept of an atom may be better developed. (CP)

  14. Mesoscale Thermodynamic Analysis of Atomic-Scale Dislocation-Obstacle Interactions Simulated by Molecular Dynamics

    SciTech Connect

    Monet, Giath; Bacon, David J; Osetskiy, Yury N

    2010-01-01

    Given the time and length scales in molecular dynamics (MD) simulations of dislocation-defect interactions, quantitative MD results cannot be used directly in larger scale simulations or compared directly with experiment. A method to extract fundamental quantities from MD simulations is proposed here. The first quantity is a critical stress defined to characterise the obstacle resistance. This mesoscopic parameter, rather than the obstacle 'strength' designed for a point obstacle, is to be used for an obstacle of finite size. At finite temperature, our analyses of MD simulations allow the activation energy to be determined as a function of temperature. The results confirm the proportionality between activation energy and temperature that is frequently observed by experiment. By coupling the data for the activation energy and the critical stress as functions of temperature, we show how the activation energy can be deduced at a given value of the critical stress.

  15. Atom Probe Tomography Analysis of Ag Doping in 2D Layered Material (PbSe)5(Bi2Se3)3.

    PubMed

    Ren, Xiaochen; Singh, Arunima K; Fang, Lei; Kanatzidis, Mercouri G; Tavazza, Francesca; Davydov, Albert V; Lauhon, Lincoln J

    2016-10-12

    Impurity doping in two-dimensional (2D) materials can provide a route to tuning electronic properties, so it is important to be able to determine the distribution of dopant atoms within and between layers. Here we report the tomographic mapping of dopants in layered 2D materials with atomic sensitivity and subnanometer spatial resolution using atom probe tomography (APT). APT analysis shows that Ag dopes both Bi2Se3 and PbSe layers in (PbSe)5(Bi2Se3)3, and correlations in the position of Ag atoms suggest a pairing across neighboring Bi2Se3 and PbSe layers. Density functional theory (DFT) calculations confirm the favorability of substitutional doping for both Pb and Bi and provide insights into the observed spatial correlations in dopant locations.

  16. Combined use of atomic force microscopy, X-ray photoelectron spectroscopy, and secondary ion mass spectrometry for cell surface analysis.

    PubMed

    Dague, Etienne; Delcorte, Arnaud; Latgé, Jean-Paul; Dufrêne, Yves F

    2008-04-01

    Understanding the surface properties of microbial cells is a major challenge of current microbiological research and a key to efficiently exploit them in biotechnology. Here, we used three advanced surface analysis techniques with different sensitivity, probing depth, and lateral resolution, that is, in situ atomic force microscopy, X-ray photoelectron spectroscopy, and secondary ion mass spectrometry, to gain insight into the surface properties of the conidia of the human fungal pathogen Aspergillus fumigatus. We show that the native ultrastructure, surface protein and polysaccharide concentrations, and amino acid composition of three mutants affected in hydrophobin production are markedly different from those of the wild-type, thereby providing novel insight into the cell wall architecture of A. fumigatus. The results demonstrate the power of using multiple complementary techniques for probing microbial cell surfaces.

  17. Atomic Resolution Structure of the Orotidine 5′-Monophosphate Decarboxylase Product Complex Combined with Surface Plasmon Resonance Analysis

    PubMed Central

    Fujihashi, Masahiro; Mito, Kazuya; Pai, Emil F.; Miki, Kunio

    2013-01-01

    Orotidine 5′-monophosphate decarboxylase (ODCase) accelerates the decarboxylation of its substrate by 17 orders of magnitude. One argument brought forward against steric/electrostatic repulsion causing substrate distortion at the carboxylate substituent as part of the catalysis has been the weak binding affinity of the decarboxylated product (UMP). The crystal structure of the UMP complex of ODCase at atomic resolution (1.03 Å) shows steric competition between the product UMP and the side chain of a catalytic lysine residue. Surface plasmon resonance analysis indicates that UMP binds 5 orders of magnitude more tightly to a mutant in which the interfering side chain has been removed than to wild-type ODCase. These results explain the low affinity of UMP and counter a seemingly very strong argument against a contribution of substrate distortion to the catalytic reaction mechanism of ODCase. PMID:23395822

  18. Sensitivity analysis of rectangular atomic force microscope cantilevers immersed in liquids based on the modified couple stress theory.

    PubMed

    Lee, Haw-Long; Chang, Win-Jin

    2016-01-01

    The modified couple stress theory is adopted to study the sensitivity of a rectangular atomic force microscope (AFM) cantilever immersed in acetone, water, carbon tetrachloride (CCl4), and 1-butanol. The theory contains a material length scale parameter and considers the size effect in the analysis. However, this parameter is difficult to obtain via experimental measurements. In this study, a conjugate gradient method for the parameter estimation of the frequency equation is presented. The optimal method provides a quantitative approach for estimating the material length scale parameter based on the modified couple stress theory. The results show that the material length scale parameter of the AFM cantilever immersed in acetone, CCl4, water, and 1-butanol is 0, 25, 116.3, and 471 nm, respectively. In addition, the vibration sensitivities of the AFM cantilever immersed in these liquids are investigated. The results are useful for the design of AFM cantilevers immersed in liquids.

  19. The estimation of the possibilities of synchrotron radiation X-ray fluorescent analysis and atomic specrometry for the bone's elemental composition determination

    NASA Astrophysics Data System (ADS)

    Gonchar, A. M.; Kolmogorov, U. P.; Gladkikh, E. A.; Shuvaeva, O. V.; Beisel, N. F.; Kolosova, N. G.

    2005-05-01

    Possibilities of multielemental highly sensitive techniques of analysis have been studied: synchrotron radiation X-ray fluorescence analysis (SR XFA), and atomic emission spectrometry with inductively bound plasma (ISP) and atomic absorption spectrometry (AAS) with flame (air-acetylene) atomization for assay of element composition of bone tissue with minimal preparation procedure. Results of comparative studies of elemental composition of bone tissue samples from experimental animals with inherited accelerated aging (rats of OXYS strain) using the SR XFA, ISP and AAS techniques are presented. It is shown that there exists in principle a possibility of assay of 22 biologically important essential macro- and trace elements within the range of 1.0-100,000 μg/g with a mean square analysis error of no more them 10-15% when using SR XFA.

  20. Atomic scale analysis of phase formation and diffusion kinetics in Ag/Al multilayer thin films

    NASA Astrophysics Data System (ADS)

    Aboulfadl, Hisham; Gallino, Isabella; Busch, Ralf; Mücklich, Frank

    2016-11-01

    Thin films generally exhibit unusual kinetics leading to chemical reactions far from equilibrium conditions. Binary metallic multilayer thin films with miscible elements show some similar behaviors with respect to interdiffusion and phase formation mechanisms. Interfacial density, lattice defects, internal stresses, layer morphologies and deposition conditions strongly control the mass transport between the individual layers. In the present work, Ag/Al multilayer thin films are used as a simple model system, in which the effects of the sputtering power and the bilayer period thickness on the interdiffusion and film reactions are investigated. Multilayers deposited by DC magnetron sputtering undergo calorimetric and microstructural analyses. In particular, atom probe tomography is extensively used to provide quantitative information on concentration gradients, grain boundary segregations, and reaction mechanisms. The magnitude of interdiffusion was found to be inversely proportional to the period thickness for the films deposited under the same conditions, and was reduced using low sputtering power. Both the local segregation at grain boundaries as well as pronounced non-equilibrium supersaturation effects play crucial roles during the early stages of the film reactions. For multilayers with small periods of 10 nm supersaturation of the Al layers with Ag precedes the polymorphic nucleation and growth of the hcp γ-Ag2Al phase. In larger periods the γ phase formation is triggered at junctions between grain boundaries and layers interfaces, where the pathway to heterogeneous nucleation is local supersaturation. Other Ag-rich phases also form as intermediate phases due to asymmetric diffusion rates of parent phases in the γ phase during annealing.

  1. Direct analysis of reference biofluids by coupled in situ electrodeposition-electrothermal atomic absorption spectrometry

    NASA Astrophysics Data System (ADS)

    Matousek, Jaroslav P.; Powell, Kipton J.

    1999-12-01

    The application of coupled in situ electrodeposition-electrothermal atomic absorption spectrometry (ED-ETAAS) to the determination of Pb in biological standard reference materials is described. In situ electrodeposition at a cell voltage of 3.0 V from 25-μl samples onto electrodeposited Pd is used to quantitatively separate the analyte from blood and urine matrices. With subsequent withdrawal of spent electrolyte, this overcomes the atomisation problems inherent with high salt and organic contents. ED-ETAAS is applied with minimal sample pre-treatment (acidification). The electrolysis process aids decomposition of the organic matrix, and the release of trace elements. Evolution of H 2 at the cathode counters fouling of the Pd modifier surface. The palladium deposit is renewed in situ for each determination. For AMI certified lyophilised blood, diluted 1+3 with 0.1 M HCl (18.1 μg/l Pb), the R.S.D. was 3.0% (peak height; n=5) and the detection limit (3 σ blank; n=5) was 1.5 μg/l. Results for certified blood samples were AMI 72.3±4.3 μg/l (certified 76.2±7.6 μg/l) and Seronorm 34.2±2.0 μg/l (36±4 μg/l). The result for NIST SRM 2670 normal urine acidified to 1% HNO 3 was 8.1±0.6 μg/l (recommended value 10 μg/l).

  2. Silicone hydrogel contact lens surface analysis by atomic force microscopy: shape parameters

    NASA Astrophysics Data System (ADS)

    Giraldez, M. J.; Garcia-Resua, C.; Lira, M.; Sánchez-Sellero, C.; Yebra-Pimentel, E.

    2011-05-01

    Purpose: Average roughness (Ra) is generally used to quantify roughness; however it makes no distinction between spikes and troughs. Shape parameters as kurtosis (Rku) and skewness (Rsk) serve to distinguish between two profiles with the same Ra. They have been reported in many biomedical fields, but they were no applied to contact lenses before. The aim of this study is to analyze surface properties of four silicone hydrogel contact lenses (CL) by Atomic Force Microscopy (AFM) evaluating Ra, Rku and Rsk. Methods: CL used in this study were disposable silicone hydrogel senofilcon A, comfilcon A, balafilcon A and lotrafilcon B. Unworn CL surfaces roughness and topography were measured by AFM (Veeco, multimode-nanoscope V) in tapping modeTM. Ra, Rku and Rsk for 25 and 196 μm2 areas were determined. Results: Surface topography and parameters showed different characteristics depending on the own nature of the contact lens (Ra/Rku/Rsk for 25 and 196 μm2 areas were: senofilcon A 3,33/3,74/0,74 and 3,76/18,16/1,75; comfilcon A: 1,56/31,09/2,93 and 2,76/45,82/3,60; balafilcon A: 2,01/33,62/-2,14 and 2,54/23,36/-1,96; lotrafilcon B: 26,97/4,11/-0,34 and 29,25/2,82/-0,23). In lotrafilcon B, with the highest Ra, Rku showed a lower degree of peakedness of its distribution. Negative Rsk value obtained for balafilcon A showed a clear predominance of valleys in this lens. Conclusions: Kku and Rsk are two statistical parameters useful to analyse CL surfaces, which complete information from Ra. Differences in values distribution and symmetry were observed between CL.

  3. Gunshot residue testing in suicides: Part II: Analysis by inductive coupled plasma-atomic emission spectrometry.

    PubMed

    Molina, D Kimberley; Castorena, Joe L; Martinez, Michael; Garcia, James; DiMaio, Vincent J M

    2007-09-01

    Several different methods can be employed to test for gunshot residue (GSR) on a decedent's hands, including scanning electron microscopy with energy dispersive x-ray (SEM/EDX) and inductive coupled plasma-atomic emission spectrometry (ICP-AES). In part I of this 2-part series, GSR results performed by SEM/EDX in undisputed cases of suicidal handgun wounds were studied. In part II, the same population was studied, deceased persons with undisputed suicidal handgun wounds, but GSR testing was performed using ICP-AES. A total of 102 cases were studied and analyzed for caliber of weapon, proximity of wound, and the results of the GSR testing. This study found that 50% of cases where the deceased was known to have fired a handgun immediately prior to death had positive GSR results by ICP/AES, which did not differ from the results of GSR testing by SEM/EDX. Since only 50% of cases where the person is known to have fired a weapon were positive for GSR by either method, this test should not be relied upon to determine whether someone has discharged a firearm and is not useful as a determining factor of whether or not a wound is self-inflicted or non-self-inflicted. While a positive GSR result may be of use, a negative result is not helpful in the medical examiner setting as a negative result indicates that either a person fired a weapon prior to death or a person did not fire a weapon prior to death.

  4. THE APPLICATION OF SOME HARTREE-FOCK MODEL CALCULATION TO THE ANALYSIS OF ATOMIC AND FREE-ION OPTICAL SPECTRA

    SciTech Connect

    Hayhurst, Thomas Laine

    1980-08-06

    Techniques for applying ab-initio calculations to the is of atomic spectra are investigated, along with the relationship between the semi-empirical and ab-initio forms of Slater-Condon theory. Slater-Condon theory is reviewed with a focus on the essential features that lead to the effective Hamiltonians associated with the semi-empirical form of the theory. Ab-initio spectroscopic parameters are calculated from wavefunctions obtained via self-consistent field methods, while multi-configuration Hamiltonian matrices are constructed and diagonalized with computer codes written by Robert Cowan of Los Alamos Scientific Laboratory. Group theoretical analysis demonstrates that wavefunctions more general than Slater determinants (i.e. wavefunctions with radial correlations between electrons) lead to essentially the same parameterization of effective Hamiltonians. In the spirit of this analysis, a strategy is developed for adjusting ab-initio values of the spectroscopic parameters, reproducing parameters obtained by fitting the corresponding effective Hamiltonian. Secondary parameters are used to "screen" the calculated (primary) spectroscopic parameters, their values determined by least squares. Extrapolations of the secondary parameters determined from analyzed spectra are attempted to correct calculations of atoms and ions without experimental levels. The adjustment strategy and extrapolations are tested on the K I sequence from K{sup 0+} through Fe{sup 7+}, fitting to experimental levels for V{sup 4+}, and Cr{sup 5+}; unobserved levels and spectra are predicted for several members of the sequence. A related problem is also discussed: Energy levels of the Uranium hexahalide complexes, (UX{sub 6}){sup 2-} for X= F, Cl, Br, and I, are fit to an effective Hamiltonian (the f{sup 2} configuration in O{sub h} symmetry) with corrections proposed by Brian Judd.

  5. Analysis of Ligand-Receptor Association and Intermediate Transfer Rates in Multienzyme Nanostructures with All-Atom Brownian Dynamics Simulations.

    PubMed

    Roberts, Christopher C; Chang, Chia-En A

    2016-08-25

    We present the second-generation GeomBD Brownian dynamics software for determining interenzyme intermediate transfer rates and substrate association rates in biomolecular complexes. Substrate and intermediate association rates for a series of enzymes or biomolecules can be compared between the freely diffusing disorganized configuration and various colocalized or complexed arrangements for kinetic investigation of enhanced intermediate transfer. In addition, enzyme engineering techniques, such as synthetic protein conjugation, can be computationally modeled and analyzed to better understand changes in substrate association relative to native enzymes. Tools are provided to determine nonspecific ligand-receptor association residence times, and to visualize common sites of nonspecific association of substrates on receptor surfaces. To demonstrate features of the software, interenzyme intermediate substrate transfer rate constants are calculated and compared for all-atom models of DNA origami scaffold-bound bienzyme systems of glucose oxidase and horseradish peroxidase. Also, a DNA conjugated horseradish peroxidase enzyme was analyzed for its propensity to increase substrate association rates and substrate local residence times relative to the unmodified enzyme. We also demonstrate the rapid determination and visualization of common sites of nonspecific ligand-receptor association by using HIV-1 protease and an inhibitor, XK263. GeomBD2 accelerates simulations by precomputing van der Waals potential energy grids and electrostatic potential grid maps, and has a flexible and extensible support for all-atom and coarse-grained force fields. Simulation software is written in C++ and utilizes modern parallelization techniques for potential grid preparation and Brownian dynamics simulation processes. Analysis scripts, written in the Python scripting language, are provided for quantitative simulation analysis. GeomBD2 is applicable to the fields of biophysics, bioengineering

  6. Three-dimensional analysis of Eu dopant atoms in Ca-α-SiAlON via through-focus HAADF-STEM imaging.

    PubMed

    Saito, Genki; Yamaki, Fuuta; Kunisada, Yuji; Sakaguchi, Norihito; Akiyama, Tomohiro

    2017-01-31

    Three-dimensional (3D) distributional analysis of individual dopant atoms in materials is important to development of optical, electronic, and magnetic materials. In this study, we adopted through-focus high-angle annular dark-field (HAADF) imaging for 3D distributional analysis of Eu dopant atoms in Ca-α-SiAlON phosphors. In this context, the effects of convergence semi-angle and Eu z-position on the HAADF image contrast were investigated. Multi-slice image simulation revealed that the contrast of the dopant site was sensitive to change of the defocus level. When the defocus level matched the depth position of a Eu atom, the contrast intensity was significantly increased. The large convergence semi-angle greatly increased the depth resolution because the electron beam tends spread instead of channeling along the atomic columns. Through-focus HAADF-STEM imaging was used to analyze the Eu atom distribution surrounding 10nm cubes with defocus steps of 0.68nm each. The contrast depth profile recorded with a narrow step width clearly analyzed the possible depth positions of Eu atoms. The radial distribution function obtained for the Eu dopants was analyzed using an atomic distribution model that was based on the assumption of random distribution. The result suggested that the Ca concentration did not affect the Eu distribution. The decreased fraction of neighboring Eu atoms along z-direction might be caused by the enhanced short-range Coulomb-like repulsive forces along the z-direction.

  7. Transition state of a SH3 domain detected with principle component analysis and a charge-neutralized all-atom protein model.

    PubMed

    Mitomo, Daisuke; Nakamura, Hironori K; Ikeda, Kazuyoshi; Yamagishi, Akihiko; Higo, Junichi

    2006-09-01

    The src SH3 domain has been known to be a two-state folder near room temperature. However, in a previous study with an all-atom model simulation near room temperature, the transition state of this protein was not successfully detected on a free-energy profile using two axes: the radius of gyration (R(g)) and native contact reproduction ratio (Q value). In this study, we focused on an atom packing effect to characterize the transition state and tried another analysis to detect it. To explore the atom packing effect more efficiently, we introduced a charge-neutralized all-atom model, where all of the atoms in the protein and water molecules were treated explicitly, but their partial atomic charges were set to zero. Ten molecular dynamics simulations were performed starting from the native structure at 300 K, where the simulation length of each run was 90 ns, and the protein unfolded in all runs. The integrated trajectories (10 x 90 = 900 ns) were analyzed by a principal component analysis (PCA) and showed a clear free-energy barrier between folded- and unfolded-state conformational clusters in a conformational space generated by PCA. There were segments that largely deformed when the conformation passed through the free-energy barrier. These segments correlated well with the structural core regions characterized by large phi-values, and the atom-packing changes correlated with the conformational deformations. Interestingly, using the same simulation data, no significant barrier was found in a free-energy profile using the R(g) and Q values for the coordinate axes. These results suggest that the atom packing effect may be one of the most important determinants of the transition state.

  8. High fidelity simulation and analysis of liquid jet atomization in a gaseous crossflow at intermediate Weber numbers

    NASA Astrophysics Data System (ADS)

    Li, Xiaoyi; Soteriou, Marios C.

    2016-08-01

    Recent advances in numerical methods coupled with the substantial enhancements in computing power and the advent of high performance computing have presented first principle, high fidelity simulation as a viable tool in the prediction and analysis of spray atomization processes. The credibility and potential impact of such simulations, however, has been hampered by the relative absence of detailed validation against experimental evidence. The numerical stability and accuracy challenges arising from the need to simulate the high liquid-gas density ratio across the sharp interfaces encountered in these flows are key reasons for this. In this work we challenge this status quo by presenting a numerical model able to deal with these challenges, employing it in simulations of liquid jet in crossflow atomization and performing extensive validation of its results against a carefully executed experiment with detailed measurements in the atomization region. We then proceed to the detailed analysis of the flow physics. The computational model employs the coupled level set and volume of fluid approach to directly capture the spatiotemporal evolution of the liquid-gas interface and the sharp-interface ghost fluid method to stably handle high liquid-air density ratio. Adaptive mesh refinement and Lagrangian droplet models are shown to be viable options for computational cost reduction. Moreover, high performance computing is leveraged to manage the computational cost. The experiment selected for validation eliminates the impact of inlet liquid and gas turbulence and focuses on the impact of the crossflow aerodynamic forces on the atomization physics. Validation is demonstrated by comparing column surface wavelengths, deformation, breakup locations, column trajectories and droplet sizes, velocities, and mass rates for a range of intermediate Weber numbers. Analysis of the physics is performed in terms of the instability and breakup characteristics and the features of downstream

  9. Activation of extended red emission photoluminescence in carbon solids by exposure to atomic hydrogen and UV radiation

    NASA Technical Reports Server (NTRS)

    Furton, Douglas G.; Witt, Adolf N.

    1993-01-01

    We report on new laboratory results which relate directly to the observation of strongly enhanced extended red emission (ERE) by interstellar dust in H2 photodissociation zones. The ERE has been attributed to photoluminescence by hydrogenated amorphous carbon (HAC). We are demonstrating that exposure to thermally dissociated atomic hydrogen will restore the photoluminescence efficiency of previously annealed HAC. Also, pure amorphous carbon (AC), not previously photoluminescent, can be induced to photoluminesce by exposure to atomic hydrogen. This conversion of AC into HAC is greatly enhanced by the presence of UV irradiation. The presence of dense, warm atomic hydrogen and a strong UV radiation field are characteristic environmental properties of H2 dissociation zones. Our results lend strong support to the HAC photoluminescence explanation for ERE.

  10. Single atom electrochemical and atomic analytics

    NASA Astrophysics Data System (ADS)

    Vasudevan, Rama

    In the past decade, advances in electron and scanning-probe based microscopies have led to a wealth of imaging and spectroscopic data with atomic resolution, yielding substantial insight into local physics and chemistry in a diverse range of systems such as oxide catalysts, multiferroics, manganites, and 2D materials. However, typical analysis of atomically resolved images is limited, despite the fact that image intensities and distortions of the atoms from their idealized positions contain unique information on the physical and chemical properties inherent to the system. Here, we present approaches to data mine atomically resolved images in oxides, specifically in the hole-doped manganite La5/8Ca3/8MnO3, on epitaxial films studied by in-situ scanning tunnelling microscopy (STM). Through application of bias to the STM tip, atomic-scale electrochemistry is demonstrated on the manganite surface. STM images are then further analyzed through a suite of algorithms including 2D autocorrelations, sliding window Fourier transforms, and others, and can be combined with basic thermodynamic modelling to reveal relevant physical and chemical descriptors including segregation energies, existence and strength of atomic-scale diffusion barriers, surface energies and sub-surface chemical species identification. These approaches promise to provide tremendous insights from atomically resolved functional imaging, can provide relevant thermodynamic parameters, and auger well for use with first-principles calculations to yield quantitative atomic-level chemical identification and structure-property relations. This research was sponsored by the Division of Materials Sciences and Engineering, BES, DOE. Research was conducted at the Center for Nanophase Materials Sciences, which also provided support and is a DOE Office of Science User Facility.

  11. Development of rapid slurry methods for flame and direct current plasma emission and graphite furnace atomic absorption analysis of solid animal tissue

    SciTech Connect

    Fietkau, R.

    1986-01-01

    Studies are presented describing developments in the rapid, direct atomic spectrochemical analysis of meat samples by the technique of slurry atomization. The number of elements that can be determined in meat slurry samples has been increased and the concentration range that can be detected extended to included analysis at the part per billion as well as the percent level. Slurry atomization involves the rapid preparation procedure whereby the sample is simple homogenized with deionized distilled water prior to analysis. In this manner, rapid, quantitative analysis of hot dogs (processed meat) for dietary salt (Na, K) was achieved by premixed air-natural gas flame emission spectrometry. Quantitative analysis of mechanically separated meat for residual bone fragments (as Ca) was attained using a simple photometer when the premixed air-acetylene flame was used. The phosphate interference of the Ca emission signal was overcome by placing an insert in the spray chamber which decreased the droplet size of the aerosol reaching the flame. Slight matrix modification in the form of 2% nitric acid was necessary to solubilize the Ca from the bone fragments. Determining elements present at very low concentrations i.e. part per billion levels, in homogenized beef liver was evaluated using graphite furnace atomic absorption and shown to be viable for determinations of Pb, Cd, Cr, and Ni. Qualitative multielement analysis of several types of meat slurries by direct current plasma (DCP) emission spectrometry using both photographic and electronic modes of detection was reported for the first time.

  12. Molecular dynamics simulation and conformational analysis of some catalytically active peptides.

    PubMed

    Honarparvar, Bahareh; Skelton, Adam A

    2015-04-01

    The design of stable and inexpensive artificial enzymes with potent catalytic activity is a growing field in peptide science. The first step in this design process is to understand the key factors that can affect the conformational preference of an enzyme and correlate them with its catalytic activity. In this work, molecular dynamics simulations in explicit water of two catalytically active peptides (peptide 1: Fmoc-Phe1-Phe2-His-CONH2; peptide 2: Fmoc-Phe1-Phe2-Arg-CONH2) were performed at temperatures of 300, 400, and 500 K. Conformational analysis of these peptides using Ramachandran plots identified the secondary structures of the amino acid residues involved (Phe1, Phe2, His, Arg) and confirmed their conformational flexibility in solution. Furthermore, Ramachandran maps revealed the intrinsic preference of the constituent residues of these compounds for a helical conformation. Long-range interaction distances and radius of gyration (R g) values obtained during 20 ns MD simulations confirmed their tendency to form folded conformations. Results showed a decrease in side-chain (Phe1, Phe2, His ring, and Arg) contacts as the temperature was raised from 300 to 400 K and then to 500 K. Finally, the radial distribution functions (RDF) of the water molecules around the nitrogen atoms in the catalytically active His and Arg residues of peptide 1 and peptide 2 revealed that the strongest water-peptide interaction occurred with the arginine nitrogen atoms in peptide 2. Our results highlight differences in the secondary structures of the two peptides that can be explained by the different arrangement of water molecules around the nitrogen atoms of Arg in peptide 2 as compared to the arrangement of water molecules around the nitrogen atoms of His in peptide 1. The results of this work thus provide detailed insight into peptide conformations which can be exploited in the future design of peptide analogs.

  13. Updated mortality analysis of radiation workers at Rocketdyne (Atomics International), 1948-2008

    SciTech Connect

    Boice, John; Cohen, Sarah; Mumma, Michael; Ellis, Elizabeth D; Eckerman, Keith F; Leggett, Richard Wayne; Boecker, Bruce; Brill, Bertrand; Henderson, Brian

    2011-01-01

    Updated analyses of mortality data are presented on 5,801 radiation workers, including 2,232 monitored for radionuclide intakes, and 41,169 non-radiation workers employed 1948-1999 at Rocketdyne (Atomics International). The worker population is unique in that lifetime occupational doses from all places of employment were sought and incorporated into the analyses. Further, radiation doses from intakes of 14 different radionuclides were calculated for 16 organs or tissues using biokinetic models of the International Commission on Radiation Protection (ICRP). The mean dose from external radiation was 13.5 mSv (maximum 1 Sv), and the mean lung dose from external and internal radiation combined was 19.0 mSv (maximum 3.6 Sv). An additional nine years of follow-up, from December 31,1999 through 2008, increased the person-years of observation by 21.7% to 196,674 (mean 33.9 years) and the number of cancer deaths by 50% to 684. Analyses included comparisons with the general population and the computation of standardized mortality ratios (SMRs), and internal comparisons using proportional hazards models. All cancers taken together (SMR 0.88; 95% CI 0.81-0.95), lung cancer (SMR 0.87; 95% CI 0.76-1.00) and leukemia other than chronic lymphocytic leukemia (CLL) (SMR 1.04; 95% 0.67-1.53) were not significantly elevated. Cox regression analyses revealed no significant dose-response trends for any cancer. For all cancers excluding leukemia, the relative risk (RR) at 100 mSv was estimated as 0.98 (95% CI 0.82-1.17) and for all leukemia other than CLL it was 1.06 (95% CI 0.50-2.23). Uranium was the primary radionuclide contributing to internal exposures, but significant increases in lung and kidney disease were not seen. The extended follow-up re-enforces the findings in the previous study in failing to observe a detectable increase in cancer deaths associated with radiation, but strong conclusions still cannot be drawn because of small numbers and relatively low career doses. Larger

  14. Analysis of Indium Tin Oxide Film Using Argon Fluroide (ArF) Laser-Excited Atomic Fluorescence of Ablated Plumes.

    PubMed

    Ho, Sut Kam; Garcia, Dario Machado

    2017-01-01

    A two-pulse laser-excited atomic fluorescence (LEAF) technique at 193 nm wavelength was applied to the analysis of indium tin oxide (ITO) layer on polyethylene terephthalate (PET) film. Fluorescence emissions from analytes were induced from plumes generated by first laser pulse. Using this approach, non-selective LEAF can be accomplished for simultaneous multi-element analysis and it overcomes the handicap of strict requirement for laser excitation wavelength. In this study, experimental conditions including laser fluences, times for gating and time delay between pulses were optimized to reveal high sensitivity with minimal sample destruction and penetration. With weak laser fluences of 100 and 125 mJ/cm(2) for 355 and 193 nm pulses, detection limits were estimated to be 0.10% and 0.43% for Sn and In, respectively. In addition, the relation between fluorescence emissions and number of laser shots was investigated; reproducible results were obtained for Sn and In. It shows the feasibility of depth profiling by this technique. Morphologies of samples were characterized at various laser fluences and number of shots to examine the accurate penetration. Images of craters were also investigated using scanning electron microscopy (SEM). The results demonstrate the imperceptible destructiveness of film after laser shot. With such weak laser fluences and minimal destructiveness, this LEAF technique is suitable for thin-film analysis.

  15. Atomic supersymmetry

    NASA Technical Reports Server (NTRS)

    Kostelecky, V. Alan

    1993-01-01

    Atomic supersymmetry is a quantum-mechanical supersymmetry connecting the properties of different atoms and ions. A short description of some established results in the subject are provided and a few recent developments are discussed including the extension to parabolic coordinates and the calculation of Stark maps using supersymmetry-based models.

  16. Accelerated design and quality control of impact modifiers for plastics through atomic force microscopy (AFM) analysis

    NASA Astrophysics Data System (ADS)

    Moeller, Gunter

    2011-03-01

    Standard polymer resins are often too brittle or do not meet other mechanical property requirements for typical polymer applications. To achieve desired properties it is common to disperse so called ``impact modifiers'', which are spherical latex particles with diameters of much less than one micrometer, into the pure resin. Understanding and control of the entire process from latex particle formation to subsequent dispersion into polymer resins are necessary to accelerate the development of new materials that meet specific application requirements. In this work AFM imaging and nanoindentation techniques in combination with AFM-based spectroscopic techniques were applied to assess latex formation and dispersion. The size and size distribution of the latex particles can be measured based on AFM amplitude modulation images. AFM phase images provide information about the chemical homogeneity of individual particles. Nanoindentation may be used to estimate their elastic and viscoelastic properties. Proprietary creep and nanoscale Dynamic Mechanical Analysis (DMA) tests that we have developed were used to measure these mechanical properties. The small size of dispersed latex inclusions requires local mechanical and spectroscopic analysis techniques with high lateral and spatial resolution. We applied the CRAVE AFM method, developed at NIST, to perform mechanical analysis of individual latex inclusions and compared results with those obtained using nanoscale DMA. NanoIR, developed by Anasys Inc., and principal component confocal Raman were used for spectroscopic analysis and results from both techniques compared.

  17. Analysis of Dicke Narrowing in Wall-Coated and Buffer-Gas-Filled Atomic Storage Cells,

    DTIC Science & Technology

    1986-04-01

    unshifted frequency. For the various reasons outlined the " particle in a box " analysis of motional narrowing in bufferless, wall-coated cells is...buffer gas or a wall, and consequently, one should not need two apparently distinct formalisms, buffer gas and particle in a box , to describe spectral line

  18. Atomic softness-based QSAR study of testosterone

    NASA Astrophysics Data System (ADS)

    Srivastava, H. K.; Pasha, F. A.; Singh, P. P.

    Ionization potential of an atom in a molecule, electron affinity of an atom in a molecule, and quantum chemical descriptor atomic softness values En‡-based quantitative structure-activity relationship (QSAR) study of testosterone derivatives have been done with the help of PM3 calculations on WinMOPAC 7.21 software. The 3D modeling and geometry optimization of all the compounds have been done with the help of PCMODEL software. The biological activities of testosterone derivatives have been taken from literature. The predicted values of biological activity with the help of multiple linear regression (MLR) analysis is very close to observed biological activity. The cross-validation coefficient and correlation coefficient also indicate that the QSAR model is valuable. Regression analysis shows a very good relationship with biological activity and En‡ values. With the help of these values, prediction of the biological activity of any unknown compound is possible.

  19. A multistate analysis of active life expectancy.

    PubMed

    Rogers, A; Rogers, R G; Branch, L G

    1989-01-01

    With today's lower mortality rates, longer expectations of life, and new medical technologies, the nation's health policy focus has shifted from emphasis on individual survival to emphasis on personal health and independent living. Using longitudinal data sets and new methodological techniques, researchers have begun to assess active life expectancies, estimating not only how long a subpopulation can expect to live beyond each age, but what fractions of the expected remaining lifetime will be lived as independent, dependent, or institutionalized. New ideas are addressed, applying recently developed multistate life table methods to Waves One and Two of the Massachusetts Health Care Panel Study. Expectations of active life are presented for those 65 and older who initially are in one of two functional states of well-being. Included are expectations of life, for those, for example, who were independent and remained so, or those who were dependent and became independent. Although public health officials are concerned about the number of elderly who cease being independent, preliminary analysis shows that a significant number of the dependent elderly regain their independence, a situation which needs to be addressed in health care planning.

  20. Neutron activation analysis of some building materials

    NASA Astrophysics Data System (ADS)

    Salagean, M. N.; Pantelica, A. I.; Georgescu, I. I.; Muntean, M. I.

    1999-01-01

    Concentrations of As, Au, Ba, Br, Ca, Ce, Co, Cr, Cs, Eu, Fe, Hf, K, La, Lu, Mo, Na, Nd, Rb, Sb, Sc, Sr, Ta, Tb, Th, U. Yb, W and Zn in seven Romanian building materials were determined by the Instrumental Neutron Activation Analysis (INAA) method using the VVR-S Reactor of NIPNE- Bucharest. Raw matarials used in cement obtaining ≈ 75% of limestone and ≈ 25% of clay, cement samples from three different factories, furnace slag, phosphogypsum, and a type of brick have been analyzed. The brick was compacted from furnace slay, fly coal ash, phosphogypsum, lime and cement. The U, Th and K concentrations determined in the brick are in agreement with the natural radioactivity measurements of226Ra,232Th and40K. These specific activities were found about twice and 1.5 higher than the accepted levels in the case of226Ra and232Th, as well as40K, respectively. By consequence, the investigated brick is considered a radioactive waste. The rather high content of Co, Cr, K, Th, and Zh in the brick is especially due to the slag and fly ash, the main componets. The presence of U, Th and K in slag is mainly correlated with the limestone and dolomite as fluxes in matallurgy.

  1. Active polarimeter optical system laser hazard analysis.

    SciTech Connect

    Augustoni, Arnold L.

    2005-07-01

    A laser hazard analysis was performed for the SNL Active Polarimeter Optical System based on the ANSI Standard Z136.1-2000, American National Standard for Safe Use of Lasers and the ANSI Standard Z136.6-2000, American National Standard for Safe Use of Lasers Outdoors. The Active Polarimeter Optical System (APOS) uses a pulsed, near-infrared, chromium doped lithium strontium aluminum fluoride (Cr:LiSAF) crystal laser in conjunction with a holographic diffuser and lens to illuminate a scene of interest. The APOS is intended for outdoor operations. The system is mounted on a height adjustable platform (6 feet to 40 feet) and sits atop a tripod that points the beam downward. The beam can be pointed from nadir to as much as 60 degrees off of nadir producing an illuminating spot geometry that can vary from circular (at nadir) to elliptical in shape (off of nadir). The JP Innovations crystal Cr:LiSAF laser parameters are presented in section II. The illuminating laser spot size is variable and can be adjusted by adjusting the separation distance between the lens and the holographic diffuser. The system is adjusted while platform is at the lowest level. The laser spot is adjusted for a particular spot size at a particular distance (elevation) from the laser by adjusting the separation distance (d{sub diffuser}) to predetermined values. The downward pointing angle is also adjusted before the platform is raised to the selected operation elevation.

  2. Atomic Oxygen Fluence Monitor

    NASA Technical Reports Server (NTRS)

    Banks, Bruce A.

    2011-01-01

    This innovation enables a means for actively measuring atomic oxygen fluence (accumulated atoms of atomic oxygen per area) that has impinged upon spacecraft surfaces. Telemetered data from the device provides spacecraft designers, researchers, and mission managers with real-time measurement of atomic oxygen fluence, which is useful for prediction of the durability of spacecraft materials and components. The innovation is a compact fluence measuring device that allows in-space measurement and transmittance of measured atomic oxygen fluence as a function of time based on atomic oxygen erosion yields (the erosion yield of a material is the volume of material that is oxidized per incident oxygen atom) of materials that have been measured in low Earth orbit. It has a linear electrical response to atomic oxygen fluence, and is capable of measuring high atomic oxygen fluences (up to >10(exp 22) atoms/sq cm), which are representative of multi-year low-Earth orbital missions (such as the International Space Station). The durability or remaining structural lifetime of solar arrays that consist of polymer blankets on which the solar cells are attached can be predicted if one knows the atomic oxygen fluence that the solar array blanket has been exposed to. In addition, numerous organizations that launch space experiments into low-Earth orbit want to know the accumulated atomic oxygen fluence that their materials or components have been exposed to. The device is based on the erosion yield of pyrolytic graphite. It uses two 12deg inclined wedges of graphite that are over a grit-blasted fused silica window covering a photodiode. As the wedges erode, a greater area of solar illumination reaches the photodiode. A reference photodiode is also used that receives unobstructed solar illumination and is oriented in the same direction as the pyrolytic graphite covered photodiode. The short-circuit current from the photodiodes is measured and either sent to an onboard data logger, or

  3. Atomic Force Microscopy Thermally-Assisted Microsampling with Atmospheric Pressure Temperature Ramped Thermal Desorption/Ionization-Mass Spectrometry Analysis

    DOE PAGES

    Hoffmann, William D.; Kertesz, Vilmos; Srijanto, Bernadeta R.; ...

    2017-02-20

    The use of atomic force microscopy controlled nano-thermal analysis probes for reproducible spatially resolved thermally-assisted sampling of micrometer-sized areas (ca. 11 m 17 m wide 2.4 m deep) from relatively low number average molecular weight (Mn < 3000) polydisperse thin films of poly(2-vinylpyridine) (P2VP) is presented. Following sampling, the nano-thermal analysis probes were moved up from the surface and the probe temperature ramped to liberate the sampled materials into the gas phase for atmospheric pressure chemical ionization and mass spectrometric analysis. Furthermore, the procedure and mechanism for material pickup, the sampling reproducibility and sampling size are discussed and the oligomermore » distribution information available from slow temperature ramps versus ballistic temperature jumps is presented. For the Mn = 970 P2VP, the Mn and polydispersity index determined from the mass spectrometric data were in line with both the label values from the sample supplier and the value calculated from the simple infusion of a solution of polymer into the commercial atmospheric pressure chemical ionization source on this mass spectrometer. With a P2VP sample of higher Mn (Mn = 2070 and 2970), intact oligomers were still observed (as high as m/z 2793 corresponding to the 26-mer), but a significant abundance of thermolysis products were also observed. In addition, the capability for confident identification of the individual oligomers by slowly ramping the probe temperature and collecting data dependent tandem mass spectra was also demonstrated. We also discuss the material type limits to the current sampling and analysis approach as well as possible improvements in nano-thermal analysis probe design to enable smaller area sampling and to enable controlled temperature ramps beyond the present upper limit of about 415°C.« less

  4. Atomic Force Microscopy Thermally-Assisted Microsampling with Atmospheric Pressure Temperature Ramped Thermal Desorption/Ionization-Mass Spectrometry Analysis

    SciTech Connect

    Hoffmann, William D; Kertesz, Vilmos; Srijanto, Bernadeta R; Van Berkel, Gary J

    2017-01-01

    The use of atomic force microscopy controlled nano-thermal analysis probes for reproducible spatially resolved thermally-assisted sampling of micrometer-sized areas (ca. 11 m 17 m wide 2.4 m deep) from relatively low number average molecular weight (Mn < 3000) polydisperse thin films of poly(2-vinylpyridine) (P2VP) is presented. Following sampling, the nano-thermal analysis probes were moved up from the surface and the probe temperature ramped to liberate the sampled materials into the gas phase for atmospheric pressure chemical ionization and mass spectrometric analysis. The procedure and mechanism for material pickup, the sampling reproducibility and sampling size are discussed and the oligomer distribution information available from slow temperature ramps versus ballistic temperature jumps is presented. For the Mn = 970 P2VP, the Mn and polydispersity index determined from the mass spectrometric data were in line with both the label values from the sample supplier and the value calculated from the simple infusion of a solution of polymer into the commercial atmospheric pressure chemical ionization source on this mass spectrometer. With a P2VP sample of higher Mn (Mn = 2070 and 2970), intact oligomers were still observed (as high as m/z 2793 corresponding to the 26-mer), but a significant abundance of thermolysis products were also observed. In addition, the capability for confident identification of the individual oligomers by slowly ramping the probe temperature and collecting data dependent tandem mass spectra was also demonstrated. The material type limits to the current sampling and analysis approach as well as possible improvements in nano-thermal analysis probe design to enable smaller area sampling and to enable controlled temperature ramps beyond the present upper limit of about 415 oC are also discussed.

  5. Determination of aluminum by electrothermal atomic absorption spectroscopy in lubricating oils emulsified in a sequential injection analysis system.

    PubMed

    Burguera, José L; Burguera, Marcela; Antón, Raquel E; Salager, Jean-Louis; Arandia, María A; Rondón, Carlos; Carrero, Pablo; de Peña, Yaneira Petit; Brunetto, Rosario; Gallignani, Máximo

    2005-12-15

    The sequential injection (SIA) technique was applied for the on-line preparation of an "oil in water" microemulsion and for the determination of aluminum in new and used lubricating oils by electrothermal atomic absorption spectrometry (ET AAS) with Zeeman-effect background correction. Respectively, 1.0, 0.5 and 1.0ml of surfactants mixture, sample and co-surfactant (sec-butanol) solutions were sequentially aspirated to a holding coil. The sonication and repetitive change of the flowing direction improved the stability of the different emulsion types (oil in water, water in oil and microemulsion). The emulsified zone was pumped to fill the sampling arm of the spectrometer with a sub-sample of 200mul. Then, 10mul of this sample solution were introduced by means of air displacement in the graphite tube atomizer. This sequence was timed to synchronize with the previous introduction of 15mug of Mg(NO(3))(2) (in a 10mul) by the spectrometer autosampler. The entire SIA system was controlled by a computer, independent of the spectrometer. The furnace program was carried out by employing a heating cycle in four steps: drying (two steps at 110 and 130 degrees C), pyrolisis (at 1500 degrees C), atomization (at 2400 degrees C) and cleaning (at 2400 degrees C). The calibration graph was linear from 7.7 to 120mugAll(-1). The characteristic mass (mo) was 33.2pg/0.0044s and the detection limit was 2.3mugAll(-1). The relative standard (RSD) of the method, evaluated by replicate analyses of different lubricating oil samples varied in all cases between 1.5 and 1.7%, and the recovery values found in the analysis of spiked samples ranged from 97.2 to 100.4%. The agreement between the observed and reference values obtained from two NIST Standard Certified Materials was good. The method was simple and satisfactory for determining aluminum in new and used lubricating oils.

  6. Sequence analysis of the cbb3 oxidases and an atomic model for the Rhodobacter sphaeroides enzyme.

    PubMed

    Sharma, Vivek; Puustinen, Anne; Wikström, Mårten; Laakkonen, Liisa

    2006-05-09

    The cbb3-type oxidases are members of the heme-copper oxidase superfamily, distant by sequence comparisons, but sharing common functional characteristics. To understand the minimal common properties of the superfamily, and to learn about cbb3-type oxidases specifically, we have analyzed a wide set of heme-copper oxidase sequences and built a homology model of the catalytic subunit of the cbb3 oxidase from Rhodobacter sphaeroides. We conclude that with regard to the active site surroundings, the cbb3 oxidases greatly resemble the structurally known oxidases, while major differences are found in three segments: the additional N-terminal stretch of ca. 60 amino acids, the segment following helix 3 to the end of helix 5, and the C-terminus from helix 11 onward. The conserved core contains the active site tyrosine and also an analogue of the K-channel of proton transfer, but centered on a well-conserved histidine in the lower part of helix 7. Modeling the variant parts of the enzyme suggests that two periplasmic loops (between helices 3 and 4 and between helices 11 and 12) could interact with each other as a part of the active site structure and might have an important role in proton pumping. An analogue of the D-channel is not found, but an alternative channel might form around helix 9. A preliminary packing model of the trimeric enzyme is also presented.

  7. Solid sampling in analysis of animal organs by two-jet plasma atomic emission spectrometry

    NASA Astrophysics Data System (ADS)

    Zaksas, Natalia P.; Nevinsky, Georgy A.

    2011-11-01

    A study of high-power two-jet plasma capabilities for the direct multi-elemental analysis of animal organs was undertaken. The experimental conditions chosen allow the direct analysis of different animal organs after drying and grinding to powder (particle size 20-200 μm). It was found that evaporation efficiency of the samples depends on the particle size and thermal stability of tissues and can be improved by reduction of a carrier gas flow. Calibration samples based on graphite powder and a tenfold dilution of powdered samples with buffer (graphite powder containing 15% NaCl) were used. 5-10 mg of the sample was quite enough to get the detection limits of elements at the level of 0.1-10 μg g - 1 . A prior carbonization procedure (not ashing) makes it possible to decrease the detection limits of elements by an order of magnitude. The validation of the techniques was confirmed by the analysis of certified reference materials NIST 8414, BCR 278R and NCS ZC 81001 as well as by using different sample preparation procedures.

  8. Analysis of Short and Long Range Atomic Order in Nanocrystalline Diamonds with Application of Powder Diffractometry

    NASA Technical Reports Server (NTRS)

    Palosz, B.; Grzanka, E.; Stelmakh, S.; Pielaszek, R.; Bismayer, U.; Neuefiend, J.; Weber, H.-P.; Proffen, T.; VonDreele, R.; Palosz, W.; Curreri, Peter A. (Technical Monitor)

    2002-01-01

    Fundamental limitations, with respect to nanocrystalline materials, of the traditional elaboration of powder diffraction data like the Rietveld method are discussed. A tentative method of the analysis of powder diffraction patterns of nanocrystals is introduced which is based on the examination of the variation of lattice parameters calculated from individual Bragg lines (named the "apparent lattice parameter", alp). We examine the application of our methodology using theoretical diffraction patterns computed for models of nanocrystals with a perfect crystal lattice and for grains with a two-phase, core-shell structure. We use the method for the analysis of X-ray and neutron experimental diffraction data of nanocrystalline diamond powders of 4, 6 and 12 nm in diameter. The effects of an internal pressure and strain at the grain surface is discussed. This is based on the dependence of the alp values oil the diffraction vector Q and on the PDF analysis. It is shown, that the experimental results support well the concept of the two-phase structure of nanocrystalline diamond.

  9. Benchmark test of neutron transport calculations: Indium, nickel, gold, europium, and cobalt activation with and without energy moderated fission neutrons by iron simulating the Hiroshima atomic bomb casing

    SciTech Connect

    Iwatani, Kazuo; Shizuma, Kiyoshi; Hasai, Hiromi; Hoshi, Masaharu; Hiraoka, Masayuki; Hayakawa, Norihiko; Oka, Takamitsu

    1994-10-01

    A benchmark test of the Monte Carlo neutron and photon transport code system (MCNP) was performed using a bare- and energy-moderated {sup 252}Cf fission neutron source which was obtained by transmission through 10-cm-thick iron. An iron plate was used to simulate the effect of the Hiroshima atomic bomb casing. This test includes the activation of indium and nickel for fast neutrons and gold, europium, and cobalt for thermal and epithermal neutrons, which were inserted in the moderators. The latter two activations are also to validate {sup 152}Eu and {sup 60}Co activity data obtained from the atomic bomb-exposed specimens collected at Hiroshima and Nagasaki, Japan. The neutron moderators used were Lucite and Nylon 6 and the total thickness of each moderator was 60 cm or 65 cm. Measured activity data (reaction yield) of the neutron-irradiated detectors in these moderators decreased to about 1/1,000th or 1/10,000th, which corresponds to about 1,500 m ground distance from the hypocenter in Hiroshima. For all of the indium, nickel, and gold activity data, the measured and calculated values agreed within 25%, and the corresponding values for europium and cobalt were within 40%. From this study, the MCNP code was found to be accurate enough for the bare- and energy-moderated {sup 252}Cf neutron activation calculations of these elements using moderators containing hydrogen, carbon, nitrogen, and oxygen. 18 refs., 10 figs., 4 tabs.

  10. Benchmark test of neutron transport calculations: indium, nickel, gold, europium, and cobalt activation with and without energy moderated fission neutrons by iron simulating the Hiroshima atomic bomb casing.

    PubMed

    Iwatani, K; Hoshi, M; Shizuma, K; Hiraoka, M; Hayakawa, N; Oka, T; Hasai, H

    1994-10-01

    A benchmark test of the Monte Carlo neutron and photon transport code system (MCNP) was performed using a bare- and energy-moderated 252Cf fission neutron source which was obtained by transmission through 10-cm-thick iron. An iron plate was used to simulate the effect of the Hiroshima atomic bomb casing. This test includes the activation of indium and nickel for fast neutrons and gold, europium, and cobalt for thermal and epithermal neutrons, which were inserted in the moderators. The latter two activations are also to validate 152Eu and 60Co activity data obtained from the atomic bomb-exposed specimens collected at Hiroshima and Nagasaki, Japan. The neutron moderators used were Lucite and Nylon 6 and the total thickness of each moderator was 60 cm or 65 cm. Measured activity data (reaction yield) of the neutron-irradiated detectors in these moderators decreased to about 1/1,000th or 1/10,000th, which corresponds to about 1,500 m ground distance from the hypocenter in Hiroshima. For all of the indium, nickel, and gold activity data, the measured and calculated values agreed within 25%, and the corresponding values for europium and cobalt were within 40%. From this study, the MCNP code was found to be accurate enough for the bare- and energy-moderated 252Cf neutron activation calculations of these elements using moderators containing hydrogen, carbon, nitrogen, and oxygen.

  11. Inverted repeats: computer analysis of microorganism genome and imaging of cruciform structure in DNA by atomic force microscopy

    NASA Astrophysics Data System (ADS)

    Limansky, Alex; Limanskaya, Olga Y.

    2003-04-01

    Inverted repeats may regulate genetic procceses by formation of hairpin secondary structures that block DNA polymerases. Two different DNA conformations may cor-respond to inverted repeats: either a linear double stranded helix or a cruciform struc-ture consisting of two symmetrical hairpins. Theoretical and experimental studies have shown that cruciform structures can exist in negatively supercoiled DNA, cont-rary to relaxed molecules. Cruciform formation depends on many factors, firstly, on temperature and supercoils density. Recently application of the scanning probe mic-roscopy has allowed for significant progress in cruciform structure studies. The goal of present work is computer analysis of inverted repeats in viruses, bac-teria and plasmid DNA (human immunodeficiency virus (HIV), bovine immunode-ficiency virus (BIV), bovine leukemia virus (BLV), mycobacterium tuberculosis (MTB), plasmid pUC8) and direct visualization of the cruciform structure in super-coiled DNA by atomic force microscopy (AFM). The cruciform dimensions were determined. Analysis and modeling of the most thermodynamically stable cruciform formations in viral and bacterial DNA were carried out. The complete genome sequence of HIV, BIV, BLV is ~9000 base pairs (bp), my-cobacterium tuberculosis - over 4000000 bp, pUC8 DNA - 2665 bp. Computer ana-lysis showed that two different isolates of MTB with complete genome contain 45 and 50 inverted repeats; HIV, BIV, BLV and plasmid pUC8 contain only one palin-drome which can form cruciform structure in buffer solution. Cruciform in plasmid pUC8 supercoiled DNA, was directly visualized by atomic force microscopy. Cruciform is seen as clear-cut extrusions on the DNA filaments with the lengths of the arms fully consistent with the size of the hairpins expected from a 26 bp inverted repeat in pUC8 plasmid DNA. Application of the aminomodi-fied mica allowed to obtain stable DNA images. DNA molecules on aminomica are not stretched and their contours are

  12. The energetics of hydrogen atom recombination - Analysis, experiments, and modeling. [in electrothermal propulsion system

    NASA Technical Reports Server (NTRS)

    Filpus, J. W.; Hawley, M. C.

    1984-01-01

    A theoretical investigation of the effect of the microscopic energetics of the recombination reaction on the performance of a microwave-plasma electrothermal propulsion system is described, and the results of the analysis are presented. A series of experiments to test the concept is described and analyzed by comparison with a computer model of the recombination reaction. It is concluded that internal energy considerations are not likely to significantly affect the design of a microwave-plasma electrothermal rocket. The experimental results indicate that the microwave power is far higher than the capacity of the gas to absorb it; the cooling needed to control the energy dominates the experimental results.

  13. Atomic-column scanning transmission electron microscopy analysis of misfit dislocations in GaSb/GaAs quantum dots

    DOE PAGES

    Chisholm, Matthew F.; Fernandez-Delgado, N.; Herrera, M.; ...

    2016-05-17

    The structural quality of GaSb/GaAs quantum dots (QDs) has been analyzed at atomic scale by aberration-corrected high-angle annular dark-field scanning transmission electron microscopy. In particular, we have studied the misfit dislocations that appear because of the high-lattice mismatch in the heterostructure. Our results have shown the formation of Lomer dislocations not only at the interface between the GaSb QDs and the GaAs substrate, but also at the interface with the GaAs capping layer, which is not a frequent observation. The analysis of these dislocations points to the existence of chains of dislocation loops around the QDs. The dislocation core ofmore » the observed defects has been characterized, showing that they are reconstructed Lomer dislocations, which have less distortion at the dislocation core in comparison to unreconstructed ones. As a result, strain measurements using geometric phase analysis show that these dislocations may not fully relax the strain due to the lattice mismatch in the GaSb QDs.« less

  14. Atomic-column scanning transmission electron microscopy analysis of misfit dislocations in GaSb/GaAs quantum dots

    SciTech Connect

    Chisholm, Matthew F.; Fernandez-Delgado, N.; Herrera, M.; Kamarudin, M. A.; Zhuang, Q. D.; Hayne, M.; Molina, S. I.

    2016-05-17

    The structural quality of GaSb/GaAs quantum dots (QDs) has been analyzed at atomic scale by aberration-corrected high-angle annular dark-field scanning transmission electron microscopy. In particular, we have studied the misfit dislocations that appear because of the high-lattice mismatch in the heterostructure. Our results have shown the formation of Lomer dislocations not only at the interface between the GaSb QDs and the GaAs substrate, but also at the interface with the GaAs capping layer, which is not a frequent observation. The analysis of these dislocations points to the existence of chains of dislocation loops around the QDs. The dislocation core of the observed defects has been characterized, showing that they are reconstructed Lomer dislocations, which have less distortion at the dislocation core in comparison to unreconstructed ones. As a result, strain measurements using geometric phase analysis show that these dislocations may not fully relax the strain due to the lattice mismatch in the GaSb QDs.

  15. Thermal and fractal analysis of diclofenac/Gelucire 50/13 microparticles obtained by ultrasound-assisted atomization.

    PubMed

    Cavallari, Cristina; Rodriguez, Lorenzo; Albertini, Beatrice; Passerini, Nadia; Rosetti, Francesca; Fini, Adamo

    2005-05-01

    The study describes the application of a spray-congealing technique, using a new ultrasound-assisted atomizer to prepare microparticles of diclofenac/Gelucire 50/13, with the aim to obtain a formulation of enhanced-release, at 10% w/w drug-to-excipient ratio, without any employ of solvent. Scanning electron microscopy showed that it was possible to obtain almost spherically shaped and non-aggregated microparticles; with good encapsulation efficiency (90% in most size fraction) and with a prevalent particle size in the range 150-350 mum. Image analysis results by SEM and the high fractal dimension value suggested that most particles have actually an ellipsoidal shape and a rather rough contour. Hot stage microscopy, differential scanning calorimetry, and X-ray powder diffractometry analysis were carried out to evaluate the nature of the solid state and the thermal behavior of the microparticles thus prepared. The in vitro tests displayed a significant increase of the diclofenac dissolution rate from ultrasound microparticles, compared with pure drug and with drug/Gelucire 50/13 physical mixtures.

  16. Determination of Plutonium Activity Concentrations and 240Pu/239Pu Atom Ratios in Brown Algae (Fucus distichus) Collected from Amchitka Island, Alaska.

    SciTech Connect

    Hamilton, T F; Brown, T A; Marchetti, A A; Martinelli, R E; Kehl, S R

    2005-05-02

    Plutonium-239 ({sup 239}Pu) and plutonium-240 ({sup 240}Pu) activity concentrations and {sup 240}Pu/{sup 239}Pu atom ratios are reported for Brown Algae (Fucus distichus) collected from the littoral zone of Amchitka Island (Alaska) and at a control site on the Alaskan peninsula. Plutonium isotope measurements were performed in replicate using Accelerator Mass Spectrometry (AMS). The average {sup 240}Pu/{sup 239}Pu atom ratio observed in dried Fucus d. collected from Amchitka Island was 0.227 {+-} 0.007 (n=5) and compares with the expected {sup 240}Pu/{sup 239}Pu atom ratio in integrated worldwide fallout deposition in the Northern Hemisphere of 0.1805 {+-} 0.0057 (Cooper et al., 2000). In general, the characteristically high {sup 240}Pu/{sup 239}Pu content of Fucus d. analyzed in this study appear to indicate the presence of a discernible basin-wide secondary source of plutonium entering the marine environment. Of interest to the study of plutonium source terms within the Pacific basin are reports of elevated {sup 240}Pu/{sup 239}Pu atom ratios in fallout debris from high-yield atmospheric nuclear tests conducted in the Marshall Islands during the 1950s (Diamond et al., 1960), the wide range of {sup 240}Pu/{sup 239}Pu atom ratio values (0.19 to 0.34) observed in sea water, sediments, coral and other environmental media from the North Pacific Ocean (Hirose et al., 1992; Buesseler, 1997) and updated estimates of the relative contributions of close-in and intermediate fallout deposition on oceanic inventories of radionuclidies, especially in the Northern Pacific Ocean (Hamilton, 2004).

  17. Iron-embedded C2N monolayer: a promising low-cost and high-activity single-atom catalyst for CO oxidation.

    PubMed

    He, B L; Shen, J S; Tian, Z X

    2016-09-21

    An Fe-embedded C2N monolayer as a promising single-atom catalyst for CO oxidation by O2 has been investigated based on first-principles calculations. It is found that the single Fe atom can be strongly trapped in the cavity of the C2N monolayer with a large adsorption energy of 4.55 eV and a high diffusion barrier of at least 3.00 eV to leave the cavity, indicating that Fe should exist in the isolated single-atom form. Due to the localized metal 3d orbitals near the Fermi level, the embedded Fe single-atom catalyst has a high chemical activity for the adsorption of CO and O2 molecules. CO oxidation by O2 on the catalyst would proceed via a two-step mechanism. The first step of the CO oxidation reaction has been studied via the Langmuir-Hinshelwood and Eley-Rideal mechanisms with energy barriers of 0.46 and 0.65 eV, respectively. The second step of the CO oxidation reaction follows the Eley-Rideal mechanism with a much smaller energy barrier of 0.24 eV. For both the steps, the CO2 molecules produced are weakly adsorbed on the substrates, suggesting that the proposed catalyst will not be poisoned by the generated CO2. Our results indicate that the Fe-embedded C2N monolayer is a promising single-atom catalyst for CO oxidation by O2 at low temperatures.

  18. Parameter sensitivity analysis of nonlinear piezoelectric probe in tapping mode atomic force microscopy for measurement improvement

    SciTech Connect

    McCarty, Rachael; Nima Mahmoodi, S.

    2014-02-21

    The equations of motion for a piezoelectric microcantilever are derived for a nonlinear contact force. The analytical expressions for natural frequencies and mode shapes are obtained. Then, the method of multiple scales is used to analyze the analytical frequency response of the piezoelectric probe. The effects of nonlinear excitation force on the microcantilever beam's frequency and amplitude are analytically studied. The results show a frequency shift in the response resulting from the force nonlinearities. This frequency shift during contact mode is an important consideration in the modeling of AFM mechanics for generation of more accurate imaging. Also, a sensitivity analysis of the system parameters on the nonlinearity effect is performed. The results of a sensitivity analysis show that it is possible to choose parameters such that the frequency shift minimizes. Certain parameters such as tip radius, microcantilever beam dimensions, and modulus of elasticity have more influence on the nonlinearity of the system than other parameters. By changing only three parameters—tip radius, thickness, and modulus of elasticity of the microbeam—a more than 70% reduction in nonlinearity effect was achieved.

  19. An Analysis of Taiwanese Eighth Graders' Science Achievement, Scientific Epistemological Beliefs and Cognitive Structure Outcomes After Learning Basic Atomic Theory.

    ERIC Educational Resources Information Center

    Tsai, Chin-Chung

    1998-01-01

    Explores the interrelationships between students' general science achievement, scientific epistemological beliefs, and cognitive structure outcomes derived from instruction of basic atomic theory. Contains 19 references. (DDR)

  20. Pharmacophore generation, atom-based 3D-QSAR, HQSAR and activity cliff analyses of benzothiazine and deazaxanthine derivatives as dual A2A antagonists/MAO‑B inhibitors.

    PubMed

    Bhayye, S S; Roy, K; Saha, A

    2016-02-12

    Dual inhibition of A2A and MAO-B is an emerging strategy in neurodegenerative diseases, such as Alzheimer's disease (AD) and Parkinson's disease (PD). In this study, atom-based three-dimensional quantitative structure-activity relationship (3D-QSAR) and hologram quantitative structure-activity relationship (HQSAR) models were generated with benzothiazine and deazaxanthine derivatives. Based on activity against A2A and MAO-B, two statistically significant 3D-QSAR models (r(2) = 0.96, q(2) = 0.76 and r(2) = 0.91, q(2) = 0.63) and HQSAR models (r(2) = 0.93, q(2) = 0.68 and r(2) = 0.97, q(2) = 0.58) were developed. In an activity cliff analysis, structural outliers were identified by calculating the Mahalanobis distance for a pair of compounds with A2A and MAO-B inhibitory activities. The generated 3D-QSAR and HQSAR models, activity cliff analysis, molecular docking and dynamic studies for dual target protein inhibitors provide key structural scaffolds that serve as building blocks in designing drug-like molecules for neurodegenerative diseases.

  1. Activated carbon-modified knotted reactor coupled to electrothermal atomic absorption spectrometry for sensitive determination of arsenic species in medicinal herbs and tea infusions

    NASA Astrophysics Data System (ADS)

    Grijalba, Alexander Castro; Martinis, Estefanía M.; Lascalea, Gustavo E.; Wuilloud, Rodolfo G.

    2015-01-01

    A flow injection system based on a modified polytetrafluoroethylene (PTFE) knotted reactor (KR) was developed for arsenite [As(III)] and arsenate [As(V)] species preconcentration and determination by electrothermal atomic absorption spectrometry (ETAAS). Activated carbon (AC) was immobilized on the inner walls of a PTFE KR by a thermal treatment. A significant increase in analyte retention was obtained with the AC-modified KR (100%) as compared to the regular PTFE KR (25%). The preconcentration method involved the on-line formation of As(III)-ammonium pyrrolidinedithiocarbamate (As-APDC) complex, followed by its adsorption onto the inner walls of the AC-modified KR. After analyte retention, the complex was eluted with acetone directly into the graphite furnace of ETAAS. The parameters affecting the flow injection system were evaluated with a full central composite face centered design with three center points. Under optimum conditions, a preconcentration factor of 200 was obtained with 10 ml of sample. The detection limit was 4 ng L- 1 and the relative standard deviation (RSD) for six replicate measurements at 0.2 μg L- 1 of As were 4.3% and 4.7% for As(III) and As(V), respectively. The developed methodology was highly selective towards As(III), while As(V), monomethylarsonic acid [MMA(V)] and dimethylarsinic [DMA(V)] were not retained in the AC-modified KR. The proposed method was successfully applied for As speciation analysis in infusions originated from medicinal herbs and tea.

  2. Stability of atomic clocks based on entangled atoms.

    PubMed

    André, A; Sørensen, A S; Lukin, M D

    2004-06-11

    We analyze the effect of realistic noise sources for an atomic clock consisting of a local oscillator that is actively locked to a spin-squeezed (entangled) ensemble of N atoms. We show that the use of entangled states can lead to an improvement of the long-term stability of the clock when the measurement is limited by decoherence associated with instability of the local oscillator combined with fluctuations in the atomic ensemble's Bloch vector. Atomic states with a moderate degree of entanglement yield the maximal clock stability, resulting in an improvement that scales as N(1/6) compared to the atomic shot noise level.

  3. Regime Transition in Electromechanical Fluid Atomization and Implications to Analyte Ionization for Mass Spectrometric Analysis

    PubMed Central

    Forbes, Thomas P.; Degertekin, F. Levent; Fedorov, Andrei G.

    2015-01-01

    The physical processes governing the transition from purely mechanical ejection to electromechanical ejection to electrospraying are investigated through complementary scaling analysis and optical visualization. Experimental characterization and visualization are performed with the ultrasonically-driven array of micromachined ultrasonic electrospray (AMUSE) ion source to decouple the electrical and mechanical fields. A new dimensionless parameter, the Fenn number, is introduced to define a transition between the spray regimes, in terms of its dependence on the characteristic Strouhal number for the ejection process. A fundamental relationship between the Fenn and Strouhal numbers is theoretically derived and confirmed experimentally in spraying liquid electrolytes of different ionic strength subjected to a varying magnitude electric field. This relationship and the basic understanding of the charged droplet generation physics have direct implications on the optimal ionization efficiency and mass spectrometric response for different types of analytes. PMID:20729096

  4. Regime transition in electromechanical fluid atomization and implications to analyte ionization for mass spectrometric analysis.

    PubMed

    Forbes, Thomas P; Degertekin, F Levent; Fedorov, Andrei G

    2010-11-01

    The physical processes governing the transition from purely mechanical ejection to electromechanical ejection to electrospraying are investigated through complementary scaling analysis and optical visualization. Experimental characterization and visualization are performed with the ultrasonically-driven array of micromachined ultrasonic electrospray (AMUSE) ion source to decouple the electrical and mechanical fields. A new dimensionless parameter, the Fenn number, is introduced to define a transition between the spray regimes, in terms of its dependence on the characteristic Strouhal number for the ejection process. A fundamental relationship between the Fenn and Strouhal numbers is theoretically derived and confirmed experimentally in spraying liquid electrolytes of different ionic strength subjected to a varying magnitude electric field. This relationship and the basic understanding of the charged droplet generation physics have direct implications on the optimal ionization efficiency and mass spectrometric response for different types of analytes.

  5. Application of principal component analysis in protein unfolding: an all-atom molecular dynamics simulation study.

    PubMed

    Das, Atanu; Mukhopadhyay, Chaitali

    2007-10-28

    We have performed molecular dynamics (MD) simulation of the thermal denaturation of one protein and one peptide-ubiquitin and melittin. To identify the correlation in dynamics among various secondary structural fragments and also the individual contribution of different residues towards thermal unfolding, principal component analysis method was applied in order to give a new insight to protein dynamics by analyzing the contribution of coefficients of principal components. The cross-correlation matrix obtained from MD simulation trajectory provided important information regarding the anisotropy of backbone dynamics that leads to unfolding. Unfolding of ubiquitin was found to be a three-state process, while that of melittin, though smaller and mostly helical, is more complicated.

  6. Determination of Fe Content of Some Food Items by Flame Atomic Absorption Spectroscopy (FAAS): A Guided-Inquiry Learning Experience in Instrumental Analysis Laboratory

    ERIC Educational Resources Information Center

    Fakayode, Sayo O.; King, Angela G.; Yakubu, Mamudu; Mohammed, Abdul K.; Pollard, David A.

    2012-01-01

    This article presents a guided-inquiry (GI) hands-on determination of Fe in food samples including plantains, spinach, lima beans, oatmeal, Frosted Flakes cereal (generic), tilapia fish, and chicken using flame atomic absorption spectroscopy (FAAS). The utility of the GI experiment, which is part of an instrumental analysis laboratory course,…

  7. Superior Photostability and Photocatalytic Activity of ZnO Nanoparticles Coated with Ultrathin TiO2 Layers through Atomic-Layer Deposition.

    PubMed

    Sridharan, Kishore; Jang, Eunyong; Park, Young Min; Park, Tae Joo

    2015-12-21

    Atomic-layer deposition (ALD) is a thin-film growth technology that allows for conformal growth of thin films with atomic-level control over their thickness. Although ALD is successful in the semiconductor manufacturing industry, its feasibility for nanoparticle coating has been less explored. Herein, the ALD coating of TiO2 layers on ZnO nanoparticles by employing a specialized rotary reactor is demonstrated. The photocatalytic activity and photostability of ZnO nanoparticles coated with TiO2 layers by ALD and chemical methods were examined by the photodegradation of Rhodamine B dye under UV irradiation. Even though the photocatalytic activity of the presynthesized ZnO nanoparticles is higher than that of commercial P25 TiO2 nanoparticles, their activity tends to decline due to severe photocorrosion. The chemically synthesized TiO2 coating layer on ZnO resulted in severely declined photoactivity despite the improved photostability. However, ultrathin and conformal ALD TiO2 coatings (≈ 0.75-1.5 nm) on ZnO improved its photostability without degradation of photocatalytic activity. Surprisingly, the photostability is comparable to that of pure TiO2, and the photocatalytic activity to that of pure ZnO.

  8. Graphite filter atomizer in atomic absorption spectrometry

    NASA Astrophysics Data System (ADS)

    Katskov, Dmitri A.

    2007-09-01

    Graphite filter atomizers (GFA) for electrothermal atomic absorption spectrometry (ETAAS) show substantial advantages over commonly employed electrothermal vaporizers and atomizers, tube and platform furnaces, for direct determination of high and medium volatility elements in matrices associated with strong spectral and chemical interferences. Two factors provide lower limits of detection and shorter determination cycles with the GFA: the vaporization area in the GFA is separated from the absorption volume by a porous graphite partition; the sample is distributed over a large surface of a collector in the vaporization area. These factors convert the GFA into an efficient chemical reactor. The research concerning the GFA concept, technique and analytical methodology, carried out mainly in the author's laboratory in Russia and South Africa, is reviewed. Examples of analytical applications of the GFA in AAS for analysis of organic liquids and slurries, bio-samples and food products are given. Future prospects for the GFA are discussed in connection with analyses by fast multi-element AAS.

  9. Eulogy for a neutron activation analysis facility

    SciTech Connect

    Lepel, E.A.

    2000-07-01

    A relatively inexpensive facility for neutron activation analysis (NAA) was developed in the early 1970s at Pacific Northwest National Laboratory (PNNL). With the availability of large {sup 252}Cf sources, a subcritical facility was designed that could contain up to 100 mg of {sup 252}Cf (T{sub 1/2} = 2.645 yr and a spontaneous fission yield of 2.34 x 10{sup 9} n/s{center_dot}mg{sup {minus}1}). The {sup 252}Cf source was surrounded by a hexagonal array of {sup 235}U enriched fuel rods, which provided a 10- to 20-fold multiplication of the neutrons emitted from the {sup 252}Cf source. This assembly was located near the bottom of a 1.52-m-diam x 6.10-m-deep water-filled pool. The Neutron Multiplier Facility (NMF) was operational from November 1977 to April 1998--a period of 20.4 yr. The NMF began operation with {approximately}100 mg of {sup 252}Cf, and because of decay of the {sup 252}Cf, it had decreased to 0.34 mg at the time of shutdown. Decommissioning of the NMF began April 1998 and was completed in October 1999.

  10. Kinetic Atom.

    ERIC Educational Resources Information Center

    Wilson, David B.

    1981-01-01

    Surveys the research of scientists like Joule, Kelvin, Maxwell, Clausius, and Boltzmann as it comments on the basic conceptual issues involved in the development of a more precise kinetic theory and the idea of a kinetic atom. (Author/SK)

  11. Radiochemical neutron activation analysis for certification of ion-implanted phosphorus in silicon.

    PubMed

    Paul, Rick L; Simons, David S; Guthrie, William F; Lu, John

    2003-08-15

    A radiochemical neutron activation analysis procedure has been developed, critically evaluated, and shown to have the necessary sensitivity, chemical specificity, matrix independence, and precision to certify phosphorus at ion implantation levels in silicon. 32P, produced by neutron capture of 31P, is chemically separated from the sample matrix and measured using a beta proportional counter. The method is used here to certify the amount of phosphorus in SRM 2133 (Phosphorus Implant in Silicon Depth Profile Standard) as (9.58 +/- 0.16) x 10(14) atoms x cm(-2). A detailed evaluation of uncertainties is given.

  12. Stereodynamical Origin of Anti-Arrhenius Kinetics: Negative Activation Energy and Roaming for a Four-Atom Reaction.

    PubMed

    Coutinho, Nayara D; Silva, Valter H C; de Oliveira, Heibbe C B; Camargo, Ademir J; Mundim, Kleber C; Aquilanti, Vincenzo

    2015-05-07

    The OH + HBr → H2O + Br reaction, prototypical of halogen-atom liberating processes relevant to mechanisms for atmospheric ozone destruction, attracted frequent attention of experimental chemical kinetics: the nature of the unusual reactivity drop from low to high temperatures eluded a variety of theoretical efforts, ranking this one among the most studied four-atom reactions. Here, inspired by oriented molecular-beams experiments, we develop a first-principles stereodynamical approach. Thermalized sets of trajectories, evolving on a multidimensional potential energy surface quantum mechanically generated on-the-fly, provide a map of most visited regions at each temperature. Visualizations of rearrangements of bonds along trajectories and of the role of specific angles of reactants' mutual approach elucidate the mechanistic change from the low kinetic energy regime (where incident reactants reorient to find the propitious alignment leading to reaction) to high temperature (where speed hinders adjustment of directionality and roaming delays reactivity).

  13. Comparison of two methods for blood lead analysis in cattle: graphite-furnace atomic absorption spectrometry and LeadCare(R) II system.

    PubMed

    Bischoff, Karyn; Gaskill, Cynthia; Erb, Hollis N; Ebel, Joseph G; Hillebrandt, Joseph

    2010-09-01

    The current study compared the LeadCare(R) II test kit system with graphite-furnace atomic absorption spectrometry for blood lead (Pb) analysis in 56 cattle accidentally exposed to Pb in the field. Blood Pb concentrations were determined by LeadCare II within 4 hr of collection and after 72 hr of refrigeration. Blood Pb concentrations were determined by atomic absorption spectrometry, and samples that were coagulated (n = 12) were homogenized before analysis. There was strong rank correlation (R(2) = 0.96) between atomic absorption and LeadCare II (within 4 hr of collection), and a conversion formula was determined for values within the observed range (3-91 mcg/dl, although few had values >40 mcg/dl). Median and mean blood pb concentrations for atomic absorption were 7.7 and 15.9 mcg/dl, respectively; for LeadCare II, medians were 5.2 mcg/dl at 4 hr and 4.9 mcg/dl at 72 hr, and means were 12.4 and 11.7, respectively. LeadCare II results at 4 hr strongly correlated with 72 hr results (R(2) = 0.96), but results at 72 hr were lower (P < 0.01). There was no significant difference between coagulated and uncoagulated samples run by atomic absorption. Although there have been several articles that compared LeadCare with other analytical techniques, all were for the original system, not LeadCare II. The present study indicated that LeadCare II results correlated well with atomic absorption over a wide range of blood Pb concentrations and that refrigerating samples for up to 72 hr before LeadCare II analysis was acceptable for clinical purposes.

  14. A Flexible Method for Production of Stable Atomic Clusters with Variable Size for Chemical and Catalytic Activity Studies

    DTIC Science & Technology

    2011-12-01

    predicted, as it does not correspond to a magic number and the less stable sizes were likely etched away by oxidizing impurities. Both problems appear... oxidizing impurities. Both problems appear solvable for future research. Thus up to date, we were neither able to prove nor to disprove the...specific numbers of atoms of a number of metallic elements. The paper predicts the highest transition temperatures for clusters of zinc and gallium

  15. Phase noise analysis of voltage controlled oscillator used in cesium atomic clock

    NASA Astrophysics Data System (ADS)

    Zhi, Menghui; Tang, Liang; Qiao, Donghai

    2017-03-01

    Coherent population trapping (CPT) cesium frequency standard plays a significant role in precision guidance of missile and global positioning system (GPS). Low noise 4.596 GHz voltage controlled oscillator (VCO) is an indispensable part of microwave signal source in cesium frequency standard. Low-phase noise is also the most important and difficult performance indicator of VCO. Starting from phase noise analysis method proposed by Leeson, the formulas about the relationship between phase noise of output signal of oscillator feedback model and phase fluctuation spectrum of amplifier, phase noise of oscillator are derived in this paper. Finally, the asymptote model of microwave oscillator is proposed based on the formula derivation. The experiment shows that when the reverse bias voltage of variode is 1.8 V, the designed oscillation frequency of VCO is 4.596 GHz, the power is ‑1 dBm and the DC power consumption is 19.6 mW. The tendency of phase noise simulation curve and actual test curve conform to asymptote model. The phase noise in 1 and 10 kHz is, respectively, ‑60.86 and ‑86.58 dBc/Hz. The significance of the paper lies in determining the main factors influencing oscillator phase noise and providing guiding direction for the design of low-phase noise VCO.

  16. Matrix modifiers for feedstuff selenium analysis by graphite furnace atomic absorption spectroscopy

    SciTech Connect

    Brown, T.F.; Zeringue, L.K.

    1988-01-01

    Gallium, Co, Mn, Ni, Cd, Cu, and Zn, dissolved in methanol, were evaluated for efficacy as an alternate volume matrix modifier in Se analysis of forages and concentrates. Gallium, Co, Mn, and Zn were unsuitable as modifiers. Nickel, Cd, Cu, and modifier M (Ni + Cd + Cu) were used to test recovery of Se addition (.025, .050, .100, .200, and .500 ..mu..g) in meat and bone meal, pelleted grain dust, dry milk replacer, whole soybeans, and alfalfa hay. Recovery of Se with Cu, Cd, and M had large and variable SD of means within Se concentrations across feedstuffs and within feedstuff across Se concentrations. Mean percent recoveries of Se with the Ni modifier for the five concentrations over all feedstuffs were 106.4, 102.4, 100.2, 97.5, and 97.4, respectively. Repeated analyses of these same five feedstuffs, plus National Bureau of Standards citrus leaves and corn stalk (recommended Se = .016 ..mu..g/g), gave Se concentration (means ..mu..g/g) of .423, .104, .168, .196, .624, .027, and .015, respectively. Results obtained with Cd, Cu, and M had larger SD than did results obtained with Ni. Nickel nitrate in methanol as an alternate volume matrix modifier for Se provided reliable and sensititive Se analyses for a variety of feedstuffs.

  17. 40 CFR Appendix C to Part 136 - Inductively Coupled Plasma-Atomic Emission Spectrometric Method for Trace Element Analysis of...

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 40 Protection of Environment 22 2010-07-01 2010-07-01 false Inductively Coupled Plasma-Atomic... to Part 136—Inductively Coupled Plasma—Atomic Emission Spectrometric Method for Trace Element... technique. Samples are nebulized and the aerosol that is produced is transported to the plasma torch...

  18. 40 CFR Appendix C to Part 136 - Inductively Coupled Plasma-Atomic Emission Spectrometric Method for Trace Element Analysis of...

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... 40 Protection of Environment 23 2011-07-01 2011-07-01 false Inductively Coupled Plasma-Atomic... to Part 136—Inductively Coupled Plasma—Atomic Emission Spectrometric Method for Trace Element... technique. Samples are nebulized and the aerosol that is produced is transported to the plasma torch...

  19. Determination of Copper by Graphite Furnace Atomic Absorption Spectrophotometry: A Student Exercise in Instrumental Methods of Analysis.

    ERIC Educational Resources Information Center

    Williamson, Mark A.

    1989-01-01

    Discusses a student exercise which requires the optimizing of the charring and atomization temperatures by producing a plot of absorbance versus temperature for each temperature parameter. Notes that although the graphite furnace atomic absorption spectroscopy technique has widespread industrial use, there are no published, structured experiments…

  20. Determination of Calcium in Cereal with Flame Atomic Absorption Spectroscopy: An Experiment for a Quantitative Methods of Analysis Course

    ERIC Educational Resources Information Center

    Bazzi, Ali; Kreuz, Bette; Fischer, Jeffrey

    2004-01-01

    An experiment for determination of calcium in cereal using two-increment standard addition method in conjunction with flame atomic absorption spectroscopy (FAAS) is demonstrated. The experiment is intended to introduce students to the principles of atomic absorption spectroscopy giving them hands on experience using quantitative methods of…

  1. Force field analysis suggests a lowering of diffusion barriers in atomic manipulation due to presence of STM tip.

    PubMed

    Emmrich, Matthias; Schneiderbauer, Maximilian; Huber, Ferdinand; Weymouth, Alfred J; Okabayashi, Norio; Giessibl, Franz J

    2015-04-10

    We study the physics of atomic manipulation of CO on a Cu(111) surface by combined scanning tunneling microscopy and atomic force microscopy at liquid helium temperatures. In atomic manipulation, an adsorbed atom or molecule is arranged on the surface using the interaction of the adsorbate with substrate and tip. While previous experiments are consistent with a linear superposition model of tip and substrate forces, we find that the force threshold depends on the force field of the tip. Here, we use carbon monoxide front atom identification (COFI) to characterize the tip's force field. Tips that show COFI profiles with an attractive center can manipulate CO in any direction while tips with a repulsive center can only manipulate in certain directions. The force thresholds are independent of bias voltage in a range from 1 to 10 mV and independent of temperature in a range of 4.5 to 7.5 K.

  2. Atomic displacement in solids: analysis of the primary event and the collision cascade. Part I: Neutron and positive ion irradiation

    NASA Astrophysics Data System (ADS)

    de Almeida, P.; Räisänen, J.

    2005-05-01

    A modern, mathematical-physics introduction to the analytical problem of atomic displacement in solids which is both technically adequate and relevant to an introductory graduate students' curriculum in radiation damage theory is reported. The problematic of atomic displacement in solids is introduced didactically, deriving first the primary event (that is, the formation of the primary knock-on atom) and then building on that specific set of results in order to extend their basics to secondary, tertiary and higher-order progeny—the collision cascade—for both neutrons and positive ions, namely, their average damage functions, displacement cross-sections and energy spectra. A comparison of atomic displacement in solids under neutron and positive ion irradiation is discussed in terms of the physical concept of concentration of displaced atoms (or displacement dose).

  3. Analysis of tungsten carbide coatings by infrared laser-induced argon spark with inductively coupled plasma atomic emission spectrometry

    NASA Astrophysics Data System (ADS)

    Kanický, V.; Otruba, V.; Mermet, J.-M.

    2000-10-01

    Infrared laser ablation was studied for application to the analysis of plasma-sprayed tungsten carbide/cobalt coatings. The potential of the laser induced argon-spark (LINA-Spark™), as a sample introduction device in inductively coupled plasma atomic emission spectrometry was studied. The use of an IR laser along with defocusing led to laser-induced microplasma-based ablation. The mass ablation rate, represented by the ICP emission intensity per laser beam unit area, exhibited a flat increase in the irradiance range 2-250 GW/cm 2. A low slope (0.5) of this dependence in log-log scale gave evidence of plasma shielding. The steep increase in the measured acoustic signal when focused in front of the sample, i.e. in argon, indicated a breakdown of argon. Consequently, considerably lower ICP emissions were observed within the same range of irradiance. The cobalt/tungsten line intensity ratio in the ICP was practically constant from 1.5 up to at least 250 GW/cm 2. Acceptable precision (R.S.D.<5%) was obtained without internal standardization for irradiance between 2 and 8 GW/cm 2. Optimization of the laser pulse energy, repetition rate, beam focusing and sample displacement during interaction led to the linearization of dependences of signal vs. cobalt percentage, at least up to the highest studied value of 23% Co.

  4. Morphological analysis of the antimicrobial action of nitric oxide on Gram-negative pathogens using atomic force microscopy

    PubMed Central

    Deupree, Susan M.; Schoenfisch, Mark H.

    2013-01-01

    Atomic force microscopy (AFM) was used to study the morphological changes of two Gram-negative pathogens, Pseudomonas aeruginosa and Escherichia coli, after exposure to nitric oxide (NO). The time-dependent effects of NO released from a xerogel coating and the concentration-dependent effects rendered by a small-molecule that releases NO in a bolus were examined and compared. Bacteria exhibited irregular and degraded exteriors. With NO-releasing surfaces, an increase in surface debris and disorganized adhesion patterns were observed compared to controls. Analysis of cell surface topography revealed that increasing membrane roughness correlated with higher doses of NO. At a lower total dose, NO delivered via a bolus resulted in greater membrane roughness than NO released from a surface via a sustained flux. At sub-inhibitory levels, treatment with amoxicillin, an antibiotic known to compromise the integrity of the cell wall, led to morphologies resembling those resulting from NO treatment. Our observations indicate that cell envelope deterioration is a visible consequence of NO-exposure for both Gram-negative species studied. PMID:19250890

  5. Atomization efficiency and photon yield in laser-induced breakdown spectroscopy analysis of single nanoparticles in an optical trap

    NASA Astrophysics Data System (ADS)

    Purohit, Pablo; Fortes, Francisco J.; Laserna, J. Javier

    2017-04-01

    Laser-induced breakdown spectroscopy (LIBS) was employed for investigating the influence of particle size on the dissociation efficiency and the absolute production of photons per mass unit of airborne solid graphite spheres under single-particle regime. Particles of average diameter of 400 nm were probed and compared with 2 μm particles. Samples were first catapulted into aerosol form and then secluded in an optical trap set by a 532 nm laser. Trap stability was quantified before subjecting particles to LIBS analysis. Fine alignment of the different lines comprising the optical catapulting-optical trapping-laser-induced breakdown spectroscopy instrument and tuning of excitation parameters conditioning the LIBS signal such as fluence and acquisition delay are described in detail with the ultimate goal of acquiring clear spectroscopic data on masses as low as 75 fg. The atomization efficiency and the photon yield increase as the particle size becomes smaller. Time-resolved plasma imaging studies were conducted to elucidate the mechanisms leading to particle disintegration and excitation.

  6. Analysis of spin crossover nanochains using parabolic approximation in the framework of atom-phonon coupling model

    NASA Astrophysics Data System (ADS)

    Chiruta, D.; Jureschi, C.-M.; Linares, J.; Nasser, J.; Rotaru, A.

    2015-11-01

    In this paper the atom-phonon coupling model is applied to explain and illustrate the behavior of a linear chain of molecules in the case of spin crossover (SCO) compounds. It is well known that besides the system's cooperativity which influences the hysteretic behavior of SCO complexes, the size of the system also plays a determinant role. The system's properties are analyzed using a parabolic algorithm as a new method proposed herein for the first time in order to take into account the phonon contribution. Based on exact calculations, this method is closer to the reality and more efficient than the mean-field approximation (MFA). In particular, both the parabolic algorithm and the dynamic-matrix method are tested and compared and it is shown from the analysis of the system's behavior that large size can be handled without generating all the system states. We also analyzed the role of degeneracy, and the thermal variation of both the entropy and heat capacity in the ferromagnetic-like coupling case.

  7. [Trace Analysis of Lead in Copper Gluconate by Atomic Absorption Spectrometry after Separation by Co-Precipitation with Bismuth].

    PubMed

    Ito, Michio; Ishiguro, Satoshi; Takahashi, Fumihito; Nomura, Takakazu; Sugimoto, Toshiaki; Nishimura, Tsutomu

    2015-01-01

    In order to determine trace amounts of lead in copper gluconate by atomic absorption spectrometry (AAS), the authors investigated a separation and pre-concentration procedure using a co-precipitation technique with bismuth. After ashing 2.0 g of the sample by means of a dry process, the ash was dissolved in (1→100) nitric acid and 75 μg of bismuth was added. Lead was co-precipitated by using an ammonium solution controlled to pH 9.5-10.5. The precipitate was left at room temperature for over 15 minutes to age, and then washed with a (3→100) ammonium solution three times. The precipitate was dissolved in (1→100) nitric acid and then analyzed by AAS. The quantification limit of this method was 0.5 mg/kg, and the trueness, repeatability and intermediate precision were 99.6%, 4.2% and 4.2% at the spiked concentration of 0.5 mg/kg, and 94.4%, 2.8% and 4.0% at the spiked concentration of 5.0 mg/kg, respectively. Thus, the present method for trace analysis of lead in copper gluconate was validated.

  8. Effects of laser energy and wavelength on the analysis of LiFePO₄ using laser assisted atom probe tomography

    DOE PAGES

    Santhanagopalan, Dhamodaran; Schreiber, Daniel K.; Perea, Daniel E.; ...

    2014-09-21

    The effects of laser wavelength (355 nm and 532 nm) and laser pulse energy on the quantitative analysis of LiFePO₄ by atom probe tomography are considered. A systematic investigation of ultraviolet (UV, 355 nm) and green (532 nm) laser assisted field evaporation has revealed distinctly different behaviors. With the use of a UV laser, the major issue was identified as the preferential loss of oxygen (up to 10 at%) while other elements (Li, Fe and P) were observed to be close to nominal ratios. Lowering the laser energy per pulse to 1 pJ/pulse from 50 pJ/pulse increased the observed oxygenmore » concentration to nearer its correct stoichiometry, which was also well correlated with systematically higher concentrations of ¹⁶O₂⁺ ions. Green laser assisted field evaporation led to the selective loss of Li (33% deficiency) and a relatively minor O deficiency. The loss of Li is likely a result of selective dc evaporation of Li between or after laser pulses. Comparison of the UV and green laser data suggests that the green wavelength energy was absorbed less efficiently than the UV wavelength because of differences in absorption at 355 and 532 nm for LiFePO₄. Plotting of multihit events on Saxey plots also revealed a strong neutral O₂ loss from molecular dissociation, but quantification of this loss was insufficient to account for the observed oxygen deficiency.« less

  9. Direct atomic-level observation and chemical analysis of ZnSe synthesized by in situ high-throughput reactive fiber drawing.

    PubMed

    Hou, Chong; Jia, Xiaoting; Wei, Lei; Stolyarov, Alexander M; Shapira, Ofer; Joannopoulos, John D; Fink, Yoel

    2013-03-13

    We demonstrate a high-throughput method for synthesizing zinc selenide (ZnSe) in situ during fiber drawing. Central to this method is a thermally activated chemical reaction occurring across multiple interfaces between alternately layered elemental zinc- (Zn-) and selenium- (Se-) rich films embedded in a preform and drawn into meters of fiber at a temperature well below the melting temperature of either Zn or ZnSe. By depositing 50 nm thick layers of Zn interleaved between 1 μm thick Se layers, a controlled breakup of the Zn sheet is achieved, thereby enabling a complete and controlled chemical reaction. The thermodynamics and kinetics of this synthesis process are studied using thermogravimetric analysis and differential scanning calorimetry, and the in-fiber compound is analyzed by a multiplicity of materials characterization tools, including transmission electron microscopy, Raman microscopy, energy-dispersive X-ray spectroscopy, and X-ray diffraction, all resulting in unambiguous identification of ZnSe as the compound produced from the reactive fiber draw. Furthermore, we characterize the in-fiber ZnSe/Se97S3 heterojunction to demonstrate the prospect of ZnSe-based fiber optoelectronic devices. The ability to synthesize new compounds during fiber drawing at nanometer scale precision and to characterize them at the atomic-level extends the architecture and materials selection compatible with multimaterial fiber drawing, thus paving the way toward more complex and sophisticated functionality.

  10. SOARCA Peach Bottom Atomic Power Station Long-Term Station Blackout Uncertainty Analysis: Convergence of the Uncertainty Results

    SciTech Connect

    Bixler, Nathan E.; Osborn, Douglas M.; Sallaberry, Cedric Jean-Marie; Eckert-Gallup, Aubrey Celia; Mattie, Patrick D.; Ghosh, S. Tina

    2014-02-01

    This paper describes the convergence of MELCOR Accident Consequence Code System, Version 2 (MACCS2) probabilistic results of offsite consequences for the uncertainty analysis of the State-of-the-Art Reactor Consequence Analyses (SOARCA) unmitigated long-term station blackout scenario at the Peach Bottom Atomic Power Station. The consequence metrics evaluated are individual latent-cancer fatality (LCF) risk and individual early fatality risk. Consequence results are presented as conditional risk (i.e., assuming the accident occurs, risk per event) to individuals of the public as a result of the accident. In order to verify convergence for this uncertainty analysis, as recommended by the Nuclear Regulatory Commission’s Advisory Committee on Reactor Safeguards, a ‘high’ source term from the original population of Monte Carlo runs has been selected to be used for: (1) a study of the distribution of consequence results stemming solely from epistemic uncertainty in the MACCS2 parameters (i.e., separating the effect from the source term uncertainty), and (2) a comparison between Simple Random Sampling (SRS) and Latin Hypercube Sampling (LHS) in order to validate the original results obtained with LHS. Three replicates (each using a different random seed) of size 1,000 each using LHS and another set of three replicates of size 1,000 using SRS are analyzed. The results show that the LCF risk results are well converged with either LHS or SRS sampling. The early fatality risk results are less well converged at radial distances beyond 2 miles, and this is expected due to the sparse data (predominance of “zero” results).

  11. Significance of genomic instability in breast cancer in atomic bomb survivors: analysis of microarray-comparative genomic hybridization

    PubMed Central

    2011-01-01

    Background It has been postulated that ionizing radiation induces breast cancers among atomic bomb (A-bomb) survivors. We have reported a higher incidence of HER2 and C-MYC oncogene amplification in breast cancers from A-bomb survivors. The purpose of this study was to clarify the effect of A-bomb radiation exposure on genomic instability (GIN), which is an important hallmark of carcinogenesis, in archival formalin-fixed paraffin-embedded (FFPE) tissues of breast cancer by using microarray-comparative genomic hybridization (aCGH). Methods Tumor DNA was extracted from FFPE tissues of invasive ductal cancers from 15 survivors who were exposed at 1.5 km or less from the hypocenter and 13 calendar year-matched non-exposed patients followed by aCGH analysis using a high-density oligonucleotide microarray. The total length of copy number aberrations (CNA) was used as an indicator of GIN, and correlation with clinicopathological factors were statistically tested. Results The mean of the derivative log ratio spread (DLRSpread), which estimates the noise by calculating the spread of log ratio differences between consecutive probes for all chromosomes, was 0.54 (range, 0.26 to 1.05). The concordance of results between aCGH and fluorescence in situ hybridization (FISH) for HER2 gene amplification was 88%. The incidence of HER2 amplification and histological grade was significantly higher in the A-bomb survivors than control group (P = 0.04, respectively). The total length of CNA tended to be larger in the A-bomb survivors (P = 0.15). Correlation analysis of CNA and clinicopathological factors revealed that DLRSpread was negatively correlated with that significantly (P = 0.034, r = -0.40). Multivariate analysis with covariance revealed that the exposure to A-bomb was a significant (P = 0.005) independent factor which was associated with larger total length of CNA of breast cancers. Conclusions Thus, archival FFPE tissues from A-bomb survivors are useful for genome-wide a

  12. Atomic force microscopy methods for the analysis of high-LET tracks in CR-39 plastic nuclear track detector

    NASA Astrophysics Data System (ADS)

    Johnson, Carl E., Jr.

    Scope and Method of Study. Proton- and neutron-induced target fragmentation reactions generate short-range (˜1-10 mum), high-linear energy transfer (LET) heavy nuclear recoil (HNR) particles that contribute to total radiation dose deposited in healthy tissue in patients undergoing proton cancer therapy and to astronauts during spaceflight. Conventional detection using CR-39 plastic nuclear track detector (PNTD) that has been chemically etched for analysis by standard visible light microscopy fails because the required bulk etch, B ≈ 40 mum removes short-range tracks. We have developed a method based on Atomic Force Microscopy (AFM) to directly measure HNR particle tracks in CR-39 PNTD. Novel algorithms using least squares ellipse fitting and estimation of fitting in an iterative process were developed to enable the analysis of nuclear tracks in AFM data. In irradiations conducted at the Loma Linda University Medical Center (LLUMC) Proton Therapy Facility and the NASA Space Radiation Laboratory (NSRL) at Brookhaven National Laboratory (BNL), targets of varying composition, including a number of elemental targets of high Z, were exposed in contact with layers of CR-39 PNTD to beams of 60 MeV, 230 MeV, and 1 GeV protons at doses between 2 and 10 Gy. Chemical etching of the CR-39 PNTD was performed under standard conditions (50°C, 6.25 N NaOH) for 2-4 hours (removed layer B = 0.5-1.0 mum). Findings and Conclusions. The use of a short duration chemical etch yielded densities of secondary tracks of 105-10 6 cm-2 using the analysis methods presented in this work for accelerator-based experiments. LET spectra were obtained with good statistics between 200 and 1500 keV/mum and the results were consistent with nonelastic nuclear cross sections. Absorbed dose measurements were also completed for selected detectors, ˜7 x 10-10 Gy ion -1 was measured for 230 MeV protons. Additionally our data are consistent with an isotropic HNR particle production mechanism. The semi

  13. Atom Interferometry

    ScienceCinema

    Mark Kasevich

    2016-07-12

    Atom de Broglie wave interferometry has emerged as a tool capable of addressing a diverse set of questions in gravitational and condensed matter physics, and as an enabling technology for advanced sensors in geodesy and navigation. This talk will review basic principles, then discuss recent applications and future directions. Scientific applications to be discussed include measurement of G (Newton’s constant), tests of the Equivalence Principle and post-Newtonian gravity, and study of the Kosterlitz-Thouless phase transition in layered superfluids. Technology applications include development of precision gryoscopes and gravity gradiometers. The talk will conclude with speculative remarks looking to the future: Can atom interference methods be sued to detect gravity waves? Can non-classical (entangled/squeezed state) atom sources lead to meaningful sensor performance improvements?

  14. Atom Interferometry

    SciTech Connect

    Kasevich, Mark

    2008-05-08

    Atom de Broglie wave interferometry has emerged as a tool capable of addressing a diverse set of questions in gravitational and condensed matter physics, and as an enabling technology for advanced sensors in geodesy and navigation. This talk will review basic principles, then discuss recent applications and future directions. Scientific applications to be discussed include measurement of G (Newton's constant), tests of the Equivalence Principle and post-Newtonian gravity, and study of the Kosterlitz-Thouless phase transition in layered superfluids. Technology applications include development of precision gyroscopes and gravity gradiometers. The talk will conclude with speculative remarks looking to the future: Can atom interference methods be used to detect gravity waves? Can non-classical (entangled/squeezed state) atom sources lead to meaningful sensor performance improvements?

  15. Atom Interferometry

    SciTech Connect

    Mark Kasevich

    2008-05-07

    Atom de Broglie wave interferometry has emerged as a tool capable of addressing a diverse set of questions in gravitational and condensed matter physics, and as an enabling technology for advanced sensors in geodesy and navigation. This talk will review basic principles, then discuss recent applications and future directions. Scientific applications to be discussed include measurement of G (Newton’s constant), tests of the Equivalence Principle and post-Newtonian gravity, and study of the Kosterlitz-Thouless phase transition in layered superfluids. Technology applications include development of precision gryoscopes and gravity gradiometers. The talk will conclude with speculative remarks looking to the future: Can atom interference methods be sued to detect gravity waves? Can non-classical (entangled/squeezed state) atom sources lead to meaningful sensor performance improvements?

  16. Molecular structure matching by simulated annealing. IV. Classification of atom correspondences in sets of dissimilar molecules

    NASA Astrophysics Data System (ADS)

    Papadopoulos, M. C.; Dean, P. M.

    1991-04-01

    A set of 6 molecules, active at the benzodiazepine GABAA site are matched pairwise with one member of the set in turn. Matchings are performed by simulated annealing using null correspondences to reject poorly matched atom positions. Cluster analysis is employed to identify molecular similarities after an optimal molecular superimposition has been discovered. A statistic for the compactness of clustered atom positions is suggested. The introduction of null correspondences causes the clusters of matched atoms to become more compact.

  17. Accelerator Mass Spectrometric (AMS) Measurements of Plutonium Activity Concentrations and 240Pu/239Pu Atom Ratios In Soil Extracts Supplied by the Carlsbad Environmental Monitoring & Research Center

    SciTech Connect

    Hamilton, T F; Brown, T A; Marchetti, A A; Martinelli, R E; Kehl, S R

    2005-02-28

    Plutonium-239 ({sup 239}Pu) and plutonium-239+240 ({sup 239+240}Pu) activities concentrations and {sup 240}Pu/{sup 239}Pu atom ratios are reported for a series of chemically purified soil extracts received from the Carlsbad Environmental Monitoring & Research Center (CEMRC) in New Mexico. Samples were analyzed without further purification at the Lawrence Livermore National Laboratory (LLNL) using accelerator mass spectrometry (AMS). This report also includes a brief description of the AMS system and internal laboratory procedures used to ensure the quality and reliability of the measurement data.

  18. Insight into the general rule for the activation of the X-H bonds (X = C, N, O, S) induced by chemisorbed oxygen atoms.

    PubMed

    Xing, Bin; Wang, Gui-Chang

    2014-02-14

    Density functional theory calculations are presented for adsorption and dissociation of NH3, H2O, CH3OH, H2S and C2H4 on clean and oxygen atom pre-adsorbed metal surfaces (Cu, Ag, Au, Ni, Pd, Pt, Rh, Ru, Os and Ir). The calculation results indicated that the oxygen-promotion effect depends both on the metallic activity and the character of the X-H bond. On the one hand, for a given reaction on a series metals, a good linear correlation was found between the energy barrier difference of X-H bond breaking on clean and oxygen-covered metals and the binding strength of oxygen on metals, namely an oxygen-promotion effect was favorable to the less active metals but unfavorable to the more active metals. On the other hand, for a series of X-H bond breaking reactions on a given metal, it was found that the promotion effect follows the trend of O-H > N-H > C-H, that is, the O-H bond is most promoted by the oxygen atom. The possible reason is the O-H bond forms the strongest hydrogen bond in the transition state among the X-H bonds investigated in this work. Additionally, it was found that the oxygen coverage has little effect on the X-H bond scission.

  19. High-Throughput Analysis of Enzyme Activities

    SciTech Connect

    Lu, Guoxin

    2007-01-01

    High-throughput screening (HTS) techniques have been applied to many research fields nowadays. Robot microarray printing technique and automation microtiter handling technique allows HTS performing in both heterogeneous and homogeneous formats, with minimal sample required for each assay element. In this dissertation, new HTS techniques for enzyme activity analysis were developed. First, patterns of immobilized enzyme on nylon screen were detected by multiplexed capillary system. The imaging resolution is limited by the outer diameter of the capillaries. In order to get finer images, capillaries with smaller outer diameters can be used to form the imaging probe. Application of capillary electrophoresis allows separation of the product from the substrate in the reaction mixture, so that the product doesn't have to have different optical properties with the substrate. UV absorption detection allows almost universal detection for organic molecules. Thus, no modifications of either the substrate or the product molecules are necessary. This technique has the potential to be used in screening of local distribution variations of specific bio-molecules in a tissue or in screening of multiple immobilized catalysts. Another high-throughput screening technique is developed by directly monitoring the light intensity of the immobilized-catalyst surface using a scientific charge-coupled device (CCD). Briefly, the surface of enzyme microarray is focused onto a scientific CCD using an objective lens. By carefully choosing the detection wavelength, generation of product on an enzyme spot can be seen by the CCD. Analyzing the light intensity change over time on an enzyme spot can give information of reaction rate. The same microarray can be used for many times. Thus, high-throughput kinetic studies of hundreds of catalytic reactions are made possible. At last, we studied the fluorescence emission spectra of ADP and obtained the detection limits for ADP under three different

  20. Karyotype Analysis Activity: A Constructivist Learning Design

    ERIC Educational Resources Information Center

    Ahmed, Noveera T.

    2015-01-01

    This classroom activity is based on a constructivist learning design and engages students in physically constructing a karyotype of three mock patients. Students then diagnose the chromosomal aneuploidy based on the karyotype, list the symptoms associated with the disorder, and discuss the implications of the diagnosis. This activity is targeted…

  1. Tried and True: The Romance of the Atoms--Animated Atomic Attractions

    ERIC Educational Resources Information Center

    Hibbitt, Catherine

    2010-01-01

    Since the formation of atomic bonds is active, the authors sought a way of learning through drama or kinetic activity. To achieve this goal, they developed an activity called Romance of the Atoms. The activity requires students to use computer-animation technology to develop short cartoons that explain atomic classification and bonds. This…

  2. Conformational analysis of a quinolonic ribonucleoside with anti-HSV-1 activity

    NASA Astrophysics Data System (ADS)

    Yoneda, Julliane D.; Velloso, Marcia Helena R.; Leal, Kátia Z.; Azeredo, Rodrigo B. de V.; Sugiura, Makiko; Albuquerque, Magaly G.; Santos, Fernanda da C.; Souza, Maria Cecília B. V. de; Cunha, Anna Claudia; Seidl, Peter R.; Alencastro, Ricardo B. de; Ferreira, Vitor F.

    2011-01-01

    The infections caused by the Herpes Simplex Virus are one of the most common sources of diseases in adults and several natural nucleoside analogues are currently used in the treatment of these infections. In vitro tests of a series of quinolonic ribonucleosides derivatives synthesized by part of our group indicated that some of them have antiviral activity against HSV-1. The conformational analysis of bioactive compounds is extremely important in order to better understand their chemical structures and biological activity. In this work, we have carried out a nuclear relaxation NMR study of 6-Me ribonucleoside derivative in order to determine if the syn or anti conformation is preferential. The NMR analysis permits the determination of inter-atomic distances by using techniques which are based on nuclear relaxation and related phenomena. Those techniques are non-selective longitudinal or spin-lattice relaxation rates and NULL pulse sequence, which allow the determination of distances between pairs of hydrogen atoms. The results of NMR studies were compared with those obtained by molecular modeling.

  3. Advanced oxidation using Fe(3)O(4) magnetic nanoparticles and its application in mercury speciation analysis by high performance liquid chromatography-cold vapor generation atomic fluorescence spectrometry.

    PubMed

    Ai, Xi; Wang, Yu; Hou, Xiandeng; Yang, Lu; Zheng, Chengbin; Wu, Li

    2013-06-21

    A novel, green and efficient post-column oxidation method using Fe(3)O(4) magnetic nanoparticles (MNPs) was developed to on-line convert hydride generation/cold vapor generation (HG/CV) inactive species to their active species without microwave/UV irradiation. It was applied to high performance liquid chromatography HG/CV atomic fluorescence spectrometry (HPLC-HG/CV-AFS) to enable sensitive speciation analysis of both HG/CV inactive and active species. Inorganic mercury (Hg(2+)), methylmercury (MeHg), ethylmercury (EtHg) and phenylmercury (PhHg) were selected as model compounds to validate the methodology. Separation of these mercury species was accomplished on a RP-C18 column with a mixture of acetonitrile and water (10 : 90) at pH 6.8 containing 0.12% (m/v) L-cysteine as the mobile phase. In the presence of 0.6% (v/v) H(2)O(2), on-line conversion of the organomercury species eluted from the HPLC column to Hg(2+) was obtained using the advanced oxidation method at pH 2.0. Optimum conditions for the separation, oxidation and cold vapor generation were carefully investigated. The limits of detection (LODs) were 0.7, 1.1, 0.8 and 0.9 μg L(-1) (as Hg) for Hg(2+), MeHg, EtHg and PhHg, respectively, corresponding to 14, 22, 16 and 18 pg absolute detection limits for Hg(2+), MeHg, EtHg and PhHg by using a 20 μL sample loop, which are comparable to or better than those previously reported. National Research Council Canada DORM-2 fish muscle tissue and several real water samples were analyzed to validate the accuracy of the proposed method.

  4. Analysis of the in vivo phosphorylation state of rabbit skeletal muscle glycogen synthase by fast-atom-bombardment mass spectrometry.

    PubMed

    Poulter, L; Ang, S G; Gibson, B W; Williams, D H; Holmes, C F; Caudwell, F B; Pitcher, J; Cohen, P

    1988-08-15

    The in vivo phosphorylation state of glycogen synthase was re-examined by fast-atom-bombardment mass spectrometry and a procedure in which phosphoserine residues are first converted to S-ethylcysteine. In animals injected with the beta-adrenergic antagonist propranolol, the phosphorylation sites in the N-terminal (N) and C-terminal (C) cyanogen bromide peptides were identified as the serine residues at N7, the region C28-C39, C42, C46 and C100. In animals injected with adrenalin, the phosphorylation of N7 increased from 0.6 to 0.8 mol/mol, the region C28-C39 from 0.7 to 1.2 mol/mol and C100 from 0.3 to 0.6 mol/mol. The phosphorylation states of C42 (0.7 mol/mol) and C46 (0.9 mol/mol) were unchanged. In addition, two further serine residues became phosphorylated at positions N10 (0.5 mol/mol) and C87 (0.5 mol/mol), which were not phosphorylated in the absence of adrenalin. Residues N10 and C42 have not been recognized as in vivo sites of phosphorylation previously. The results suggest that N10 is phosphorylated by a novel protein kinase which may be activated by cyclic-AMP-dependent protein kinase. The phosphorylation of C42 is likely to be catalysed by glycogen synthase kinase 3. The protein kinases responsible for phosphorylating N7, the region C28-C39, C46, C87 and C100 in vivo and the molecular mechanisms by which adrenalin inactivates glycogen synthase in vivo are discussed. Residue N3, a major site phosphorylated by casein kinase-I in vitro is not phosphorylated in vivo. This and other evidence indicates that casein kinase-I is not a glycogen synthase kinase in vivo.

  5. Activity Analysis for Cognitive-Perceptual-Motor Dysfunction

    ERIC Educational Resources Information Center

    Llorens, Lela A.

    1973-01-01

    This paper presents a review of several approaches to activity and task analysis for their selection for use in occupational therapy and proposes a neuro-behavioral approach to activity analysis and selection for use in treatment of cognitive-perceptual-motor dysfunction. (Editors/JA)

  6. Overview of MSFC's Applied Fluid Dynamics Analysis Group Activities

    NASA Technical Reports Server (NTRS)

    Garcia, Roberto; Griffin, Lisa; Williams, Robert

    2003-01-01

    TD64, the Applied Fluid Dynamics Analysis Group, is one of several groups with high-fidelity fluids design and analysis expertise in the Space Transportation Directorate at Marshall Space Flight Center (MSFC). TD64 assists personnel working on other programs. The group participates in projects in the following areas: turbomachinery activities, nozzle activities, combustion devices, and the Columbia accident investigation.

  7. Atomic thin titania nanosheet-coupled reduced graphene oxide 2D heterostructures for enhanced photocatalytic activity and fast lithium storage

    NASA Astrophysics Data System (ADS)

    Li, Dong Jun; Huang, Zhegang; Hwang, Tae Hoon; Narayan, Rekha; Choi, Jang Wook; Kim, Sang Ouk

    2016-03-01

    Realizing practical high performance materials and devices using the properties of 2D materials is of key research interest in the materials science field. In particular, building well-defined heterostructures using more than two different 2D components in a rational way is highly desirable. In this paper, a 2D heterostructure consisting of atomic thin titania nanosheets densely grown on reduced graphene oxide surface is successfully prepared through incorporating polymer functionalized graphene oxide into the novel TiO2 nanosheets synthesis scheme. As a result of the synergistic combination of a highly accessible surface area and abundant interface, which can modulate the physicochemical properties, the resultant heterostructure can be used in high efficiency visible light photocatalysis as well as fast energy storage with a long lifecycle. [Figure not available: see fulltext.

  8. Activity Landscape Plotter: A Web-Based Application for the Analysis of Structure-Activity Relationships.

    PubMed

    González-Medina, Mariana; Méndez-Lucio, Oscar; Medina-Franco, José L

    2017-03-27

    Activity landscape modeling is a powerful method for the quantitative analysis of structure-activity relationships. This cheminformatics area is in continuous growth, and several quantitative and visual approaches are constantly being developed. However, these approaches often fall into disuse due to their limited access. Herein, we present Activity Landscape Plotter as the first freely available web-based tool to automatically analyze structure-activity relationships of compound data sets. Based on the concept of activity landscape modeling, the online service performs pairwise structure and activity relationships from an input data set supplied by the user. For visual analysis, Activity Landscape Plotter generates Structure-Activity Similarity and Dual-Activity Difference maps. The user can interactively navigate through the maps and export all the pairwise structure-activity information as comma delimited files. Activity Landscape Plotter is freely accessible at https://unam-shiny-difacquim.shinyapps.io/ActLSmaps /.

  9. Methods of analysis by the U.S. Geological Survey National Water Quality Laboratory; determination of antimony by automated-hydride atomic absorption spectrophotometry

    USGS Publications Warehouse

    Brown, G.E.; McLain, B.J.

    1994-01-01

    The analysis of natural-water samples for antimony by automated-hydride atomic absorption spectrophotometry is described. Samples are prepared for analysis by addition of potassium and hydrochloric acid followed by an autoclave digestion. After the digestion, potassium iodide and sodium borohydride are added automatically. Antimony hydride (stibine) gas is generated, then swept into a heated quartz cell for determination of antimony by atomic absorption spectrophotometry. Precision and accuracy data are presented. Results obtained on standard reference water samples agree with means established by interlaboratory studies. Spike recoveries for actual samples range from 90 to 114 percent. Replicate analyses of water samples of varying matrices give relative standard deviations from 3 to 10 percent.

  10. Overview of MSFC's Applied Fluid Dynamics Analysis Group Activities

    NASA Technical Reports Server (NTRS)

    Garcia, Roberto; Griffin, Lisa; Williams, Robert

    2002-01-01

    This viewgraph report presents an overview of activities and accomplishments of NASA's Marshall Space Flight Center's Applied Fluid Dynamics Analysis Group. Expertise in this group focuses on high-fidelity fluids design and analysis with application to space shuttle propulsion and next generation launch technologies. Topics covered include: computational fluid dynamics research and goals, turbomachinery research and activities, nozzle research and activities, combustion devices, engine systems, MDA development and CFD process improvements.

  11. Surface Acoustic Wave Atomizer and Electrostatic Deposition

    NASA Astrophysics Data System (ADS)

    Yamagata, Yutaka

    A new methodology for fabricating thin film or micro patters of organic/bio material using surface acoustic wave (SAW) atomizer and electrostatic deposition is proposed and characteristics of atomization techniques are discussed in terms of drop size and atomization speed. Various types of SAW atomizer are compared with electrospray and conventional ultrasonic atomizers. It has been proved that SAW atomizers generate drops as small as electrospray and have very fast atomization speed. This technique is applied to fabrication of micro patterns of proteins. According to the result of immunoassay, the specific activity of immunoglobulin was preserved after deposition process.

  12. Surface acoustic wave atomizer and electrostatic deposition.

    PubMed

    Yamagata, Yutaka

    2010-01-01

    A new methodology for fabricating thin film or micro patters of organic/bio material using surface acoustic wave (SAW) atomizer and electrostatic deposition is proposed and characteristics of atomization techniques are discussed in terms of drop size and atomization speed. Various types of SAW atomizer are compared with electrospray and conventional ultrasonic atomizers. It has been proved that SAW atomizers generate drops as small as electrospray and have very fast atomization speed. This technique is applied to fabrication of micro patterns of proteins. According to the result of immunoassay, the specific activity of immunoglobulin was preserved after deposition process.

  13. Neutron Activation Analysis, A Titanium Material Study

    NASA Astrophysics Data System (ADS)

    Dresser, Charles

    2011-04-01

    In order to obtain faster and more accurate measurements of radioactive contaminates within a sample of titanium we expose it to a neutron flux. This flux will activate the stable and quasi stable (those with extremely long half lives) isotopes into resultant daughter cells that are unstable which will result in shorter half lives on the order of minutes to days. We measured the resulting decays in the Germanium Crystal Detector and obtained a complex gamma spectrum. A mathematical model was used to recreate the production of the measured isotopes in the neutron flux and the resultant decays. Using this model we calculated the mass percent of the contaminate isotopes inside our titanium sample. Our mathematical model accounted for two types of neutron activation, fast or thermal activation, since this would determine which contaminate was the source of our signals. By looking at the percent abundances, neutron absorption cross-sections and the resulting mass percents of each contaminate we are able to determine the exact source of our measured signals. Additionally we implemented a unique ratio method to cross check the mathematical model. Our results have verified that for fast neutron activation and thermal neutron activation the method is accurate.

  14. Faculty Activity Analysis in the Universidad Tecnica Del Estado Campuses.

    ERIC Educational Resources Information Center

    Karadima, Oscar

    An analysis of academic activities of college faculty at the eight campuses of Chile's Universidad Tecnica del Estado was conducted. Activities were grouped into seven categories: direct teaching, indirect teaching, research, community services, faculty development, academic administration, and other activities. Following the narrative…

  15. Characterization of the physico-chemical properties of polymeric materials for aerospace flight. [differential thermal and atomic absorption spectroscopic analysis of nickel cadmium batteries

    NASA Technical Reports Server (NTRS)

    Rock, M.

    1981-01-01

    Electrodes and electrolytes of nickel cadmium sealed batteries were analyzed. Different thermal analysis of negative and positive battery electrodes was conducted and the temperature ranges of occurrence of endotherms indicating decomposition of cadmium hydroxide and nickel hydroxide are identified. Atomic absorption spectroscopy was used to analyze electrodes and electrolytes for traces of nickel, cadmium, cobalt, and potassium. Calibration curves and data are given for each sample analyzed. Instrumentation and analytical procedures used for each method are described.

  16. Atoms in Astronomy.

    ERIC Educational Resources Information Center

    Blanchard, Paul A.

    This booklet is part of an American Astronomical Society curriculum project designed to provide teaching materials to teachers of secondary school chemistry, physics, and earth science. A Basic Topics section discusses atomic structure, emphasizing states of matter at high temperature and spectroscopic analysis of light from the stars. A section…

  17. Method for photon activation positron annihilation analysis

    DOEpatents

    Akers, Douglas W.

    2006-06-06

    A non-destructive testing method comprises providing a specimen having at least one positron emitter therein; determining a threshold energy for activating the positron emitter; and determining whether a half-life of the positron emitter is less than a selected half-life. If the half-life of the positron emitter is greater than or equal to the selected half-life, then activating the positron emitter by bombarding the specimen with photons having energies greater than the threshold energy and detecting gamma rays produced by annihilation of positrons in the specimen. If the half-life of the positron emitter is less then the selected half-life, then alternately activating the positron emitter by bombarding the specimen with photons having energies greater then the threshold energy and detecting gamma rays produced by positron annihilation within the specimen.

  18. Structural analysis of a (Pt/Co){sub 3}/IrMn multilayer: Investigation of sub-nanometric layers by tomographic atom probe

    SciTech Connect

    Larde, R.; Lechevallier, L.; Zarefy, A.; Bostel, A.; Juraszek, J; Le Breton, J. M.; Rodmacq, B.; Dieny, B.

    2009-04-15

    The structure of a Ta{sub 3nm}/[(Pt{sub 2nm}/Co{sub 0.4nm}){sub 3}/IrMn{sub 7nm}]{sub 7}/Pt{sub 10nm} multilayer exhibiting perpendicular exchange bias has been investigated by x-ray reflectometry and laser-assisted tomographic atom probe (LATAP). A strong intermixing at the Co/IrMn interface is pointed out by x-ray reflectometry, this interface being more diffuse than the IrMn/Pt interface. A direct observation of this intermixing at the atomic scale is obtained thanks to the LATAP in real space. The three-dimensional reconstructions reveal the atomic planes in the Pt layers and the Pt-Co intermixing in the (Pt/Co){sub 3} multilayer. The analysis of the concentration profiles allows to determine the chemical composition of the Co subnanometric layers; thus providing for the first time an accurate structural characterization of such layers leading to an estimation of their thickness, roughness, atomic concentration and width of their interfaces.

  19. A novel solution procedure for a three-level atom interacting with one-mode cavity field via modified homotopy analysis method

    NASA Astrophysics Data System (ADS)

    Abdel Wahab, N. H.; Salah, Ahmed

    2015-05-01

    In this paper, the interaction of a three-level -configration atom and a one-mode quantized electromagnetic cavity field has been studied. The detuning parameters, the Kerr nonlinearity and the arbitrary form of both the field and intensity-dependent atom-field coupling have been taken into account. The wave function when the atom and the field are initially prepared in the excited state and coherent state, respectively, by using the Schrödinger equation has been given. The analytical approximation solution of this model has been obtained by using the modified homotopy analysis method (MHAM). The homotopy analysis method is mentioned summarily. MHAM can be obtained from the homotopy analysis method (HAM) applied to Laplace, inverse Laplace transform and Pade approximate. MHAM is used to increase the accuracy and accelerate the convergence rate of truncated series solution obtained by the HAM. The time-dependent parameters of the anti-bunching of photons, the amplitude-squared squeezing and the coherent properties have been calculated. The influence of the detuning parameters, Kerr nonlinearity and photon number operator on the temporal behavior of these phenomena have been analyzed. We noticed that the considered system is sensitive to variations in the presence of these parameters.

  20. Microscopic Analysis of Activated Sludge. Training Manual.

    ERIC Educational Resources Information Center

    Office of Water Program Operations (EPA), Cincinnati, OH. National Training and Operational Technology Center.

    This training manual presents material on the use of a compound microscope to analyze microscope communities, present in wastewater treatment processes, for operational control. Course topics include: sampling techniques, sample handling, laboratory analysis, identification of organisms, data interpretation, and use of the compound microscope.…