Science.gov

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. Europium-152 depth profile of a stone bridge pillar exposed to the Hiroshima atomic bomb: 152Eu activities for analysis of the neutron spectrum.

    PubMed

    Hasai, H; Iwatani, K; Shizuma, K; Hoshi, M; Yokoro, K; Sawada, S; Kosako, T; Morishima, H

    1987-09-01

    The 152Eu activity depth profile of a granite pillar of the Motoyasu bridge located 132 m from the Hiroshima atomic bomb hypocenter was assessed. The pillars each measured 82 cm in depth, 82 cm in width and 193 cm in height. One of the pillars was bored and 6.8-cm-diameter core samples were removed and cut into 2-cm-thick disks. Two gamma rays of 152Eu, 122 keV and 344 keV, in each disk were measured using a low background, gamma-ray spectrometer, and the activity distribution was determined as a function of depth in the granite. A concentration of stable Eu in the granite was determined by activation analysis. The specific radioactivity of 152Eu and 154Eu at the pillar surface was determined to have been 117 and 24 Bq per mg Eu, respectively, at the time of detonation. The value of 152Eu agrees within 20% of that calculated by Loewe. The depth profile of 152Eu in granite demonstrates a distinct difference from the estimates made only by thermal neutrons. Present data provide valuable information for the analysis of the neutron spectrum of the Hiroshima atomic bomb and its intensity.

  4. Experimental design and analysis of activators regenerated by electron transfer-atom transfer radical polymerization experimental conditions for grafting sodium styrene sulfonate from titanium substrates

    PubMed Central

    Foster, Rami N.; Johansson, Patrik K.; Tom, Nicole R.; Koelsch, Patrick; Castner, David G.

    2015-01-01

    A 24 factorial design was used to optimize the activators regenerated by electron transfer-atom transfer radical polymerization (ARGET-ATRP) grafting of sodium styrene sulfonate (NaSS) films from trichlorosilane/10-undecen-1-yl 2-bromo-2-methylpropionate (ester ClSi) functionalized titanium substrates. The process variables explored were: (1) ATRP initiator surface functionalization reaction time; (2) grafting reaction time; (3) CuBr2 concentration; and (4) reducing agent (vitamin C) concentration. All samples were characterized using x-ray photoelectron spectroscopy (XPS). Two statistical methods were used to analyze the results: (1) analysis of variance with α=0.05, using average Ti XPS atomic percent as the response; and (2) principal component analysis using a peak list compiled from all the XPS composition results. Through this analysis combined with follow-up studies, the following conclusions are reached: (1) ATRP-initiator surface functionalization reaction times have no discernable effect on NaSS film quality; (2) minimum (≤24 h for this system) grafting reaction times should be used on titanium substrates since NaSS film quality decreased and variability increased with increasing reaction times; (3) minimum (≤0.5 mg cm−2 for this system) CuBr2 concentrations should be used to graft thicker NaSS films; and (4) no deleterious effects were detected with increasing vitamin C concentration. PMID:26396463

  5. Activation analysis

    SciTech Connect

    Alfassi, Z.B. . Dept. of Nuclear Engineering)

    1990-01-01

    This volume contains 16 chapters on the application of activation analysis in the fields of life sciences, biological materials, coal and its effluents, environmental samples, archaeology, material science, and forensics. Each chapter is processed separately for the data base.

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

    NASA Astrophysics Data System (ADS)

    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

    2015-02-01

    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.

  7. 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

  8. 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.

  9. Adding two active silver atoms on Au₂₅ nanoparticle.

    PubMed

    Yao, Chuanhao; Chen, Jishi; Li, Man-Bo; Liu, Liren; Yang, Jinlong; Wu, Zhikun

    2015-02-11

    Alloy nanoparticles with atomic monodispersity is of importance for some fundamental research (e.g., the investigation of active sites). However, the controlled preparation of alloy nanoparticles with atomic monodispersity has long been a major challenge. Herein, for the first time a unique method, antigalvanic reduction (AGR), is introduced to synthesize atomically monodisperse Au25Ag2(SC2H4Ph)18 in high yield (89%) within 2 min. Interestingly, the two silver atoms in Au25Ag2(SC2H4Ph)18 do not replace the gold atoms in the precursor particle Au25(SC2H4Ph)18 but collocate on Au25, which was supported by experimental and calculated results. Also, the two silver atoms are active to play roles in stabilizing the alloy nanoparticle, triggering the nanoparticle fluorescence and catalyzing the hydrolysis of 1,3-diphenylprop-2-ynyl acetate. PMID:25580617

  10. Potential Applications of Atom Trap Trace Analysis

    NASA Astrophysics Data System (ADS)

    Du, Xu; Li, Yimin; Lu, Zheng-Tian

    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 (isotope abundance 10-12) atoms in atmospheric krypton samples [1]. This method can be used to analyze many other isotope tracers for a wide range of applications including measuring solar neutrino flux, searching for exotic particles, tracing atmospheric and oceanic currents, archeological and geological dating, monitoring bone-loss rates in the diagnosis and treatment of osteoporosis, monitoring fission products in the environment for nuclear waste management, etc. We will discuss these potential applications at this poster. This work is supported by the U.S. Department of Energy, Nuclear Physics Division (Contract W-31-109-ENG-38). [1] C.Y. Chen et. al., Science 286, 1139 (1999).

  11. Atomic Force Microscopy for Soil Analysis

    NASA Astrophysics Data System (ADS)

    gazze, andrea; doerr, stefan; dudley, ed; hallin, ingrid; matthews, peter; quinn, gerry; van keulen, geertje; francis, lewis

    2016-04-01

    Atomic Force Microscopy (AFM) is a high-resolution surface-sensitive technique, which provides 3-dimensional topographical information and material properties of both stiff and soft samples in their natural environments. Traditionally AFM has been applied to samples with low roughness: hence its use for soil analysis has been very limited so far. Here we report the optimization settings required for a standardization of high-resolution and artefact-free analysis of natural soil with AFM: soil immobilization, AFM probe selection, artefact recognition and minimization. Beyond topography, AFM can be used in a spectroscopic mode to evaluate nanomechanical properties, such as soil viscosity, stiffness, and deformation. In this regards, Bruker PeakForce-Quantitative NanoMechanical (QNM) AFM provides a fast and convenient way to extract physical properties from AFM force curves in real-time to obtain soil nanomechanical properties. Here we show for the first time the ability of AFM to describe the topography of natural soil at nanometre resolution, with observation of micro-components, such as clays, and of nano-structures, possibly of biotic origin, the visualization of which would prove difficult with other instrumentations. Finally, nanomechanical profiling has been applied to different wettability states in soil and the respective physical patterns are discussed.

  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. 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. PMID:25399553

  14. Atomic bomb survivor data: utilization and analysis

    SciTech Connect

    Prentice, R.L.; Thompson, D.J.

    1984-01-01

    There were several motivations for organizing the SIMS Conference reported in this monograph. Risk assessment and its methods have been subjects of several SIMS Conferences in the recent past, and focusing these newer, more powerful methods on the largest human experience of exposure to ionizing radiation seemed an appropriate sequel. There was also the conviction that the data resources of the Radiation Effects Research Foundation (RERF), generated through the mortality and medical follow-up of large samples of the survivors of the atomic bombs dropped on Hiroshima and Nagasaki, were being under utilized, and that a conference and its proceedings would create interest in exploiting this resource. The time seemed ripe for gathering a small group of current RERF scientists, veteran US statisticians and epidemiologists, and others with more recent entry into the field of radiation biology to consider long range plans for maximizing the output of information not only on the long term effects of ionizing radiation on man but on new knowledge of the determinants of health and disease that can be learned by study of the records of this cohort. This seemed particularly appropriate at this time while intensive joint Japanese-US efforts are underway to provide a new, more accurate dosimetry for use in these studies. Finally, there was a hope that an ad hoc forum of this type would provide not only a summary of current statistical and epidemiologic activities at RERF, but a useful critique of their scope and quality.

  15. Atomic-scale phase composition through multivariate statistical analysis of atom probe tomography data.

    PubMed

    Keenan, Michael R; Smentkowski, Vincent S; Ulfig, Robert M; Oltman, Edward; Larson, David J; Kelly, Thomas F

    2011-06-01

    We demonstrate for the first time that multivariate statistical analysis techniques can be applied to atom probe tomography data to estimate the chemical composition of a sample at the full spatial resolution of the atom probe in three dimensions. Whereas the raw atom probe data provide the specific identity of an atom at a precise location, the multivariate results can be interpreted in terms of the probabilities that an atom representing a particular chemical phase is situated there. When aggregated to the size scale of a single atom (∼0.2 nm), atom probe spectral-image datasets are huge and extremely sparse. In fact, the average spectrum will have somewhat less than one total count per spectrum due to imperfect detection efficiency. These conditions, under which the variance in the data is completely dominated by counting noise, test the limits of multivariate analysis, and an extensive discussion of how to extract the chemical information is presented. Efficient numerical approaches to performing principal component analysis (PCA) on these datasets, which may number hundreds of millions of individual spectra, are put forward, and it is shown that PCA can be computed in a few seconds on a typical laptop computer.

  16. Analysis of a magnetically trapped atom clock

    SciTech Connect

    Kadio, D.; Band, Y. B.

    2006-11-15

    We consider optimization of a rubidium atom clock that uses magnetically trapped Bose condensed atoms in a highly elongated trap, and determine the optimal conditions for minimum Allan variance of the clock using microwave Ramsey fringe spectroscopy. Elimination of magnetic field shifts and collisional shifts are considered. The effects of spin-dipolar relaxation are addressed in the optimization of the clock. We find that for the interstate interaction strength equal to or larger than the intrastate interaction strengths, a modulational instability results in phase separation and symmetry breaking of the two-component condensate composed of the ground and excited hyperfine clock levels, and this mechanism limits the clock accuracy.

  17. 78 FR 64414 - Assistance to Foreign Atomic Energy Activities

    Federal Register 2010, 2011, 2012, 2013, 2014

    2013-10-29

    ... concerning Assistance to Foreign Atomic Energy Activities since 1986. (76 FR 55278) The NOPR reflected a need.... ] DATES: DOE will continue to accept written comments on the SNOPR published August 2, 2013 (78 FR 46829... a second opportunity to comment. (78 FR 46829) II. Second Public Meeting A public meeting on...

  18. 76 FR 65634 - Assistance to Foreign Atomic Energy Activities

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-10-24

    ... Proposed Rulemaking (76 FR 55278). FOR FURTHER INFORMATION CONTACT: Richard Goorevich, National Nuclear Security Administration, U.S. Department of Energy, Office of Defense Nuclear Nonproliferation (NA-20... assistance to foreign atomic energy activities (76 FR 55278). This regulation provides that persons...

  19. 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

  20. Determination of hafnium at the 10(-4)% level (relative to zirconium content) using neutron activation analysis, inductively coupled plasma mass spectrometry and inductively coupled plasma atomic emission spectrometry.

    PubMed

    Smolik, Marek; Polkowska-Motrenko, Halina; Hubicki, Zbigniew; Jakóbik-Kolon, Agata; Danko, Bożena

    2014-01-01

    Hafnium at the very low level of 1-8 ppm (in relation to zirconium) was determined in zirconium sulfate solutions (originating from investigations of the separation of ca. 44 ppm Hf from zirconium by means of the ion exchange method) by using three independent methods: inductively coupled plasma mass spectrometry (ICP MS), neutron activation analysis (NAA) and inductively coupled plasma atomic emission spectrometry (ICP-AES). The results of NAA and ICP MS determinations were consistent with each other across the entire investigated range (the RSD of both methods did not exceed 38%). The results of ICP-AES determination were more diverse, particularly at less than 5 ppm Hf (RSD was significantly higher: 29-253%). The ion exchange method exploiting Diphonix(®) resin proved sufficient efficiency in Zr-Hf separation when the initial concentration ratio of the elements ([Zr]0/[Hf]0) ranged from 1200 to ca. 143,000.

  1. Analysis of simulated scanning of atomic-scale silicon surface by atomic force microscopy.

    PubMed

    Lin, Zone-Ching; Liu, Shih-Che

    2008-01-01

    This study constructs a contact-mode atomic force microscopy (AFM) simulation measurement model with constant force mode to simulate and analyze the outline scanning measurement by AFM. The simulation method is that when the probe passes the surface of sample, the action force of the atom of sample received by the atom of the probe can be calculated by using Morse potential. Through calculation, the equivalent force on the cantilever of probe can be acquired. By using the deflection angle equation for the cantilever of probe developed and inferred by this study, the deflection angle of receiving action force can be calculated. On the measurement point, as the deflection angle reaches a fixed deflection angle, the scan height of this simulation model can be acquired. By scanning in the right order, the scan curve of the simulation model can be obtained. By using this simulation measurement model, this study simulates and analyzes the scanning of atomic-scale surface outline. Meanwhile, focusing on the tip radii of different probes, the concept of sensitivity analysis is employed to investigate the effects of the tip radius of probe on the atomic-scale surface outline. As a result, it is found from the simulation on the atomic-scale surface that within the simulation scope of this study, when the tip radius of probe is greater than 12 nm, the effects of single atom on the scan curve of AFM can be better decreased or eliminated.

  2. 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.

  3. Direct analysis of solids by graphite furnace atomic absorption spectrometry using a second surface atomizer

    SciTech Connect

    Rettberg, T.M.; Holcombe, J.A.

    1986-06-01

    The direct graphite furnace atomic absorption spectrometric analysis of solids using the second surface atomizer has been investigated. The atomizer features a gas-cooled Ta insert within the graphite furnace onto which the analyte can be condensed, after which atomization is performed by raising the furnace to a higher temperature and shutting off the coolant gas. The analyses were conducted on standard reference material fly ash, river sediment, and citrus leaves, in addition to filter paper samples. All analyses were conducted without sample pretreatment or use of matrix modifiers. Quantitation was done by using simple aqueous standards. By use of peak heights, the recoveries varied from 81% to 127%, although several determinations were within the certified concentration range. The procedures typically gave low background absorbances and peak shapes that were relatively independent of the original sample matrix.

  4. Predicting activity approach based on new atoms similarity kernel function.

    PubMed

    Abu El-Atta, Ahmed H; Moussa, M I; Hassanien, Aboul Ella

    2015-07-01

    Drug design is a high cost and long term process. To reduce time and costs for drugs discoveries, new techniques are needed. Chemoinformatics field implements the informational techniques and computer science like machine learning and graph theory to discover the chemical compounds properties, such as toxicity or biological activity. This is done through analyzing their molecular structure (molecular graph). To overcome this problem there is an increasing need for algorithms to analyze and classify graph data to predict the activity of molecules. Kernels methods provide a powerful framework which combines machine learning with graph theory techniques. These kernels methods have led to impressive performance results in many several chemoinformatics problems like biological activity prediction. This paper presents a new approach based on kernel functions to solve activity prediction problem for chemical compounds. First we encode all atoms depending on their neighbors then we use these codes to find a relationship between those atoms each other. Then we use relation between different atoms to find similarity between chemical compounds. The proposed approach was compared with many other classification methods and the results show competitive accuracy with these methods.

  5. Atomic-level analysis of membrane-protein structure.

    PubMed

    Hendrickson, Wayne A

    2016-06-01

    Membrane proteins are substantially more challenging than natively soluble proteins as subjects for structural analysis. Thus, membrane proteins are greatly underrepresented in structural databases. Recently, focused consortium efforts and advances in methodology for protein production, crystallographic analysis and cryo-EM analysis have accelerated the pace of atomic-level structure determination of membrane proteins.

  6. Theoretical analysis of a realistic atom-chip quantum gate

    SciTech Connect

    Charron, E.; Cirone, M. A.; Negretti, A.; Schmiedmayer, J.; Calarco, T.

    2006-07-15

    We present a detailed, realistic analysis of the implementation of a proposal for a quantum phase gate based on atomic vibrational states, specializing it to neutral rubidium atoms on atom chips. We show how to create a double-well potential with static currents on the atom chips, using for all relevant parameters values that are achieved with present technology. The potential barrier between the two wells can be modified by varying the currents in order to realize a quantum phase gate for qubit states encoded in the atomic external degree of freedom. The gate performance is analyzed through numerical simulations; the operation time is {approx}10 ms with a performance fidelity above 99.9%. For storage of the state between the operations the qubit state can be transferred efficiently via Raman transitions to two hyperfine states, where its decoherence is strongly inhibited. In addition we discuss the limits imposed by the proximity of the surface to the gate fidelity.

  7. 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.

  8. Analysis of a free oscillation atom interferometer

    SciTech Connect

    Kafle, Rudra P.; Zozulya, Alex A.; Anderson, Dana Z.

    2011-09-15

    We analyze a Bose-Einstein condensate (BEC)-based free oscillation atom Michelson interferometer in a weakly confining harmonic magnetic trap. A BEC at the center of the trap is split into two harmonics by a laser standing wave. The harmonics move in opposite directions with equal speeds and turn back under the influence of the trapping potential at their classical turning points. The harmonics are allowed to pass through each other and a recombination pulse is applied when they overlap at the end of a cycle after they return for the second time. We derive an expression for the contrast of the interferometric fringes and obtain the fundamental limit of performance of the interferometer in the parameter space.

  9. 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.

  10. 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.

  11. Differential mobility spectrometry-mass spectrometry for atomic analysis.

    PubMed

    Sinatra, Francy L; Wu, Tianpeng; Manolakos, Spiros; Wang, Jing; Evans-Nguyen, Theresa G

    2015-02-01

    Analysis and separation of atomic ions within a portable setting are studied in forensic applications of radiological debris analysis. Ion mobility spectrometry (IMS) may be used to show separation of atomic ions, while the related method of differential mobility spectrometry (DMS) has focused on fractionation of primarily molecular components. We set out to investigate DMS as a means for separating atomic ions. We initially derived the differential ion mobility parameter, alpha, from classic empirical IMS data of atomic ions, cesium and potassium, each showing its own distinct form of alpha. These alpha functions were applied to DMS simulations and supported by analytical treatment that suggested a means for a rapid disambiguation of atomic ions using DMS. We validated this hypothesis through the prototype cesium-potassium system investigated experimentally by DMS coupled to mass spectrometry (MS). Such a feature would be advantageous in a field portable instrument for rapid atomic analyses especially in the case of isobaric ions that cannot be distinguished by MS. Herein, we first report this novel method for the derivation of alpha from existing field dependent drift tube ion mobility data. Further, we translate experimental DMS data into alpha parameters by expanding upon existing methods. Refining the alpha parameter in this manner helps convey the interpretation of the alpha parameter particularly for those new to the DMS field.

  12. Atomic basis for therapeutic activation of neuronal potassium channels

    NASA Astrophysics Data System (ADS)

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

    2015-09-01

    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.

  13. 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

  14. 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.

  15. 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.

  16. 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

  17. 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. PMID:27160891

  18. 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.

  19. 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

  20. Multivariate statistical analysis of atom probe tomography data.

    PubMed

    Parish, Chad M; Miller, Michael K

    2010-10-01

    The application of spectrum imaging multivariate statistical analysis methods, specifically principal component analysis (PCA), to atom probe tomography (APT) data has been investigated. The mathematical method of analysis is described and the results for two example datasets are analyzed and presented. The first dataset is from the analysis of a PM 2000 Fe-Cr-Al-Ti steel containing two different ultrafine precipitate populations. PCA properly describes the matrix and precipitate phases in a simple and intuitive manner. A second APT example is from the analysis of an irradiated reactor pressure vessel steel. Fine, nm-scale Cu-enriched precipitates having a core-shell structure were identified and qualitatively described by PCA. Advantages, disadvantages, and future prospects for implementing these data analysis methodologies for APT datasets, particularly with regard to quantitative analysis, are also discussed. PMID:20650566

  1. An atomic layer deposition chamber for in situ x-ray diffraction and scattering analysis

    SciTech Connect

    Geyer, Scott M.; Methaapanon, Rungthiwa; Kim, Woo-Hee; Bent, Stacey F.; Johnson, Richard W.; Van Campen, Douglas G.; Metha, Apurva

    2014-05-15

    The crystal structure of thin films grown by atomic layer deposition (ALD) will determine important performance properties such as conductivity, breakdown voltage, and catalytic activity. We report the design of an atomic layer deposition chamber for in situ x-ray analysis that can be used to monitor changes to the crystal structural during ALD. The application of the chamber is demonstrated for Pt ALD on amorphous SiO{sub 2} and SrTiO{sub 3} (001) using synchrotron-based high resolution x-ray diffraction, grazing incidence x-ray diffraction, and grazing incidence small angle scattering.

  2. 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.

  3. Fast oxygen atom studies related to low Earth orbit activities

    NASA Astrophysics Data System (ADS)

    Caledonia, G. E.; Krech, R. H.; Holtzclaw, K. W.; Sonnenfroh, D.

    1993-06-01

    The technique of laser induced gas breakdown to develop a high flux pulsed source of fast oxygen atoms (v = 5 to 12 km/s) is considered. The technique is also used to produce high velocity beams of N/N2 mixtures and can be extended to produce beams of other species. The fast oxygen atoms are of particular current interest since this is the dominant atmospheric species encountered by spacecraft operating in Low Earth Orbit (LEO). The fast oxygen atom source has proven extremely versatile and is used to study a variety of gas-surface and gas-gas collision phenomena. The fast atom facility has reproducibly provided good comparison with LEO observations. Expanded programs involving material testing and measurement of O atom momentum and energy accommodation coefficients with surfaces are presently underway.

  4. Point-by-point compositional analysis for atom probe tomography.

    PubMed

    Stephenson, Leigh T; Ceguerra, Anna V; Li, Tong; Rojhirunsakool, Tanaporn; Nag, Soumya; Banerjee, Rajarshi; Cairney, Julie M; Ringer, Simon P

    2014-01-01

    This new alternate approach to data processing for analyses that traditionally employed grid-based counting methods is necessary because it removes a user-imposed coordinate system that not only limits an analysis but also may introduce errors. We have modified the widely used "binomial" analysis for APT data by replacing grid-based counting with coordinate-independent nearest neighbour identification, improving the measurements and the statistics obtained, allowing quantitative analysis of smaller datasets, and datasets from non-dilute solid solutions. It also allows better visualisation of compositional fluctuations in the data. Our modifications include:.•using spherical k-atom blocks identified by each detected atom's first k nearest neighbours.•3D data visualisation of block composition and nearest neighbour anisotropy.•using z-statistics to directly compare experimental and expected composition curves. Similar modifications may be made to other grid-based counting analyses (contingency table, Langer-Bar-on-Miller, sinusoidal model) and could be instrumental in developing novel data visualisation options.

  5. Zn or O? An Atomic Level Comparison on Antibacterial Activities of Zinc Oxides.

    PubMed

    Yu, Fen; Fang, Xuan; Jia, Huimin; Liu, Miaoxing; Shi, Xiaotong; Xue, Chaowen; Chen, Tingtao; Wei, Zhipeng; Fang, Fang; Zhu, Hui; Xin, Hongbo; Feng, Jing; Wang, Xiaolei

    2016-06-01

    For the first time, the influence of different types of atoms (Zn and O) on the antibacterial activities of nanosized ZnO was quantitatively evaluated with the aid of a 3D-printing-manufactured evaluation system. Two different outermost atomic layers were manufactured separately by using an ALD (atomic layer deposition) method. Interestingly, we found that each outermost atomic layer exhibited certain differences against gram-positive or gram-negative bacterial species. Zinc atoms as outermost layer (ZnO-Zn) showed a more pronounced antibacterial effect towards gram-negative E. coli (Escherichia coli), whereas oxygen atoms (ZnO-O) showed a stronger antibacterial activity against gram-positive S. aureus (Staphylococcus aureus). A possible antibacterial mechanism has been comprehensively discussed from different perspectives, including Zn(2+) concentrations, oxygen vacancies, photocatalytic activities and the DNA structural characteristics of different bacterial species.

  6. Zn or O? An Atomic Level Comparison on Antibacterial Activities of Zinc Oxides.

    PubMed

    Yu, Fen; Fang, Xuan; Jia, Huimin; Liu, Miaoxing; Shi, Xiaotong; Xue, Chaowen; Chen, Tingtao; Wei, Zhipeng; Fang, Fang; Zhu, Hui; Xin, Hongbo; Feng, Jing; Wang, Xiaolei

    2016-06-01

    For the first time, the influence of different types of atoms (Zn and O) on the antibacterial activities of nanosized ZnO was quantitatively evaluated with the aid of a 3D-printing-manufactured evaluation system. Two different outermost atomic layers were manufactured separately by using an ALD (atomic layer deposition) method. Interestingly, we found that each outermost atomic layer exhibited certain differences against gram-positive or gram-negative bacterial species. Zinc atoms as outermost layer (ZnO-Zn) showed a more pronounced antibacterial effect towards gram-negative E. coli (Escherichia coli), whereas oxygen atoms (ZnO-O) showed a stronger antibacterial activity against gram-positive S. aureus (Staphylococcus aureus). A possible antibacterial mechanism has been comprehensively discussed from different perspectives, including Zn(2+) concentrations, oxygen vacancies, photocatalytic activities and the DNA structural characteristics of different bacterial species. PMID:27124263

  7. 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.

  8. 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).

  9. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

    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.

  11. 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.

  12. Voronoi analysis of the short-range atomic structure in iron and iron-carbon melts

    NASA Astrophysics Data System (ADS)

    Sobolev, Andrey; Mirzoev, Alexander

    2015-08-01

    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.

  13. 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)

  14. Analysis of Polarizability Measurements Made with Atom Interferometry

    NASA Astrophysics Data System (ADS)

    Gregoire, Maxwell; Brooks, Nathan; Trubko, Raisa; Cronin, Alexander

    2016-07-01

    We present revised measurements of the static electric dipole polarizabilities of K, Rb, and Cs based on atom interferometer experiments presented in [Phys. Rev. A 2015, 92, 052513] but now re-analyzed with new calibrations for the magnitude and geometry of the applied electric field gradient. The resulting polarizability values did not change, but the uncertainties were significantly reduced. Then we interpret several measurements of alkali metal atomic polarizabilities in terms of atomic oscillator strengths $f_{ik}$, Einstein coefficients $A_{ik}$, state lifetimes $\\tau_{k}$, transition dipole matrix elements $D_{ik}$, line strengths $S_{ik}$, and van der Waals $C_6$ coefficients. Finally, we combine atom interferometer measurements of polarizabilities with independent measurements of lifetimes and $C_6$ values in order to quantify the residual contribution to polarizability due to all atomic transitions other than the principal $ns$-$np_J$ transitions for alkali metal atoms.

  15. Analysis of Fuel Injection and Atomization of a Hybrid Air-Blast Atomizer.

    NASA Astrophysics Data System (ADS)

    Ma, Peter; Esclape, Lucas; Buschhagen, Timo; Naik, Sameer; Gore, Jay; Lucht, Robert; Ihme, Matthias

    2015-11-01

    Fuel injection and atomization are of direct importance to the design of injector systems in aviation gas turbine engines. Primary and secondary breakup processes have significant influence on the drop-size distribution, fuel deposition, and flame stabilization, thereby directly affecting fuel conversion, combustion stability, and emission formation. The lack of predictive modeling capabilities for the reliable characterization of primary and secondary breakup mechanisms is still one of the main issues in improving injector systems. In this study, an unstructured Volume-of-Fluid method was used in conjunction with a Lagrangian-spray framework to conduct high-fidelity simulations of the breakup and atomization processes in a realistic gas turbine hybrid air blast atomizer. Results for injection with JP-8 aviation fuel are presented and compared to available experimental data. Financial support through the FAA National Jet Fuel Combustion Program is gratefully acknowledged.

  16. Atomic teleportation via cavity QED and position measurements: Efficiency analysis

    NASA Astrophysics Data System (ADS)

    Tumminello, M.; Ciccarello, F.

    2008-07-01

    We have recently presented a novel protocol to teleport an unknown atomic state via cavity QED and position measurements. Here, after a brief review of our scheme, we provide a quantitative study of its efficiency. This is accomplished by an explicit description of the measurement process that allows us to derive the fidelity with respect to the atomic internal state to be teleported.

  17. Analysis of a single-atom dipole trap

    SciTech Connect

    Weber, Markus; Volz, Juergen; Saucke, Karen; Kurtsiefer, Christian; Weinfurter, Harald

    2006-04-15

    We describe a simple experimental technique which allows us to store a single {sup 87}Rb atom in an optical dipole trap. Due to light-induced two-body collisions during the loading stage of the trap the maximum number of captured atoms is locked to one. This collisional blockade effect is confirmed by the observation of photon antibunching in the detected fluorescence light. The spectral properties of single photons emitted by the atom were studied with a narrow-band scanning cavity. We find that the atomic fluorescence spectrum is dominated by the spectral width of the exciting laser light field. In addition we observe a spectral broadening of the atomic fluorescence light due to the Doppler effect. This allows us to determine the mean kinetic energy of the trapped atom corresponding to a temperature of 105 {mu}K. This simple single-atom trap is the key element for the generation of atom-photon entanglement required for future applications in quantum communication and a first loophole-free test of Bell's inequality.

  18. 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.

  19. 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''.

  20. 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.

  1. 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.

  2. Fundamental and Applied Investigations in Atomic Spectrometric Analysis

    NASA Astrophysics Data System (ADS)

    Wu, Min

    Simultaneous laser-excited fluorescence and absorption measurements were performed and the results have revealed that any interference caused by easily ionized elements does not originate from variations in analyte emission (quantum) efficiency. A closely related area, the roles of wet and dry aerosols in the matrix interference are clarified through spatially resolved imaging of the plasma by a charged coupled device camera. To eliminate matrix interference effects practically, various methods have been developed based on the above studies. The use of column pre-concentration with flow injection analysis has been found to provide a simple solution for reducing interference effects and increasing sensitivity of elemental analysis. A novel mini-spray chamber was invented. The new vertical rotary spray chamber combines gravitational, centrifugal, turbulent, and impact droplet segregation mechanisms to achieve a higher efficiency of small-droplet formation in a nebulized sample spray. As a result, it offers also higher sample-transport efficiency, lower memory effects, and improved analytical figures of merit over existing devices. This new device was employed with flow injection analysis to simulate an interface for coupling high performance liquid chromatography (HPLC) to a microwave plasma for chromatographic detection. The detection limits for common metallic elements are in the range of 5-50 mug/mL, and are degraded only twofold when the elements are presented in an organic solvent such as ethanol or methanol. Other sample-introduction schemes have also been investigated to improve sample-introduction technology. The direct coupling of hydride-generation techniques to the helium microwave plasma torch was evaluated for the determination of arsenic, antimony and tin by atomic emission spectrometry. A manually controlled peristaltic pump was modified for computer control and continuous flow injection was evaluated for standard calibration and trace elemental

  3. 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

  4. STEM Imaging of Single Pd Atoms in Activated Carbon Fibers Considered for Hydrogen Storage

    SciTech Connect

    Van Benthem, Klaus; Bonifacio, Cecile S; Contescu, Cristian I; Pennycook, Stephen J; Gallego, Nidia C

    2011-01-01

    Aberration corrected scanning transmission electron microscopy was used to demonstrate the feasibility of imaging individual Pd atoms that are highly dispersed throughout the volume of activated carbon fibers. Simultaneous acquisition of high-angle annular dark-field and bright-field images allows correlation of the location of single Pd atoms with microstructural features of the carbon host material. Sub-Angstrom imaging conditions revealed that 18 wt% of the total Pd content is dispersed as single Pd atoms in three re-occurring local structural arrangements. The identified structural configurations may represent effective storage sites for molecular hydrogen through Kubas complex formation as discussed in detail in the preceding article.

  5. Mechanical force analysis of peptide interactions using atomic force microscopy.

    PubMed

    Nakamura, Chikashi; Takeda, Seiji; Kageshima, Masami; Ito, Miyuki; Sugimoto, Naoki; Sekizawa, Kazuko; Miyake, Jun

    2004-01-01

    Some peptides have previously been reported to bind low molecular weight chemicals. One such peptide with the amino acid sequence His-Ala-Ser-Tyr-Ser was selectively screened from a phage library and bound to a cationic porphyrin, 5,10,15,20-tetrakis(N-methylpyridinium-4-yl)-21H,23H-porphine (TMpyP), with a binding constant of 10(5) M(-1) (J. Kawakami, T. Kitano, and N. Sugimoto, Chemical Communications, 1999, pp. 1765-1766). The proposed binding was due to pi-electron stacking from two aromatic amino acids of histidine and tyrosine. In this study, the weak interactions between TMpyP and the peptide were further investigated by force curve analysis using atomic force microscopy (AFM). The mechanical force required to unbind the peptide-porphyrin complex was measured by vertical movement of the AFM tip. Peptide self-assembled monolayers were formed on both a gold-coated mica substrate and a gold-coated AFM tip. The TMpyPs could bind between the two peptide layers when the peptide-immobilized AFM tip contacted the peptide-immobilized substrate in solution containing TMpyP. In the retracting process a force that ruptured the interaction between TMpyPs and peptides was observed. The unbinding force values correlated to the concentration of TMpyP. A detection limit of 100 ng/mL porphyrin was obtained for the force measurement, and was similar to surface plasmon resonance sensor detection limits. Furthermore, we calculated the product of the observed force and the length of the molecular elongation to determine the work required to unbind the complexes. The obtained values of unbinding work were in a reasonable range compared to the binding energy of porphyrin-peptide.

  6. 78 FR 46829 - Assistance to Foreign Atomic Energy Activities

    Federal Register 2010, 2011, 2012, 2013, 2014

    2013-08-02

    ..., Russia, and Canada having emerged to serve customers in these emerging markets. DOE believes the..., 2011, DOE issued a NOPR to propose the updating of part 810 (76 FR 55278). The NOPR listed destinations... activities subject to part 810. 48 FR 2518 (Feb. 4, 1983); 40 FR 44846 (Sep. 30, 1975); 21 FR 418 (Jan....

  7. 76 FR 55278 - Assistance to Foreign Atomic Energy Activities

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-09-07

    ... thorium mining and milling and nuclear fusion reactors when not used in support of systems involving... activities related to uranium and thorium mining and milling and nuclear fusion reactors, per se, are not...; and (4) Nuclear fusion reactors per se, except for supporting systems involving hydrogen...

  8. 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

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

    PubMed

    Lee, Woojun; Kim, Hyosub; Ahn, Jaewook

    2016-05-01

    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.

  10. 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

    2012-02-01

    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.

  11. Stabilizing a Platinum1 Single-Atom Catalyst on Supported Phosphomolybdic Acid without Compromising Hydrogenation Activity.

    PubMed

    Zhang, Bin; Asakura, Hiroyuki; Zhang, Jia; Zhang, Jiaguang; De, Sudipta; Yan, Ning

    2016-07-11

    In coordination chemistry, catalytically active metal complexes in a zero- or low-valent state often adopt four-coordinate square-planar or tetrahedral geometry. By applying this principle, we have developed a stable Pt1 single-atom catalyst with a high Pt loading (close to 1 wt %) on phosphomolybdic acid(PMA)-modified active carbon. This was achieved by anchoring Pt on the four-fold hollow sites on PMA. Each Pt atom is stabilized by four oxygen atoms in a distorted square-planar geometry, with Pt slightly protruding from the oxygen planar surface. Pt is positively charged, absorbs hydrogen easily, and exhibits excellent performance in the hydrogenation of nitrobenzene and cyclohexanone. It is likely that the system described here can be extended to a number of stable SACs with superior catalytic activities.

  12. An Analysis of the Stationary Operation of Atomic Clocks

    NASA Astrophysics Data System (ADS)

    Fraas, Martin

    2016-09-01

    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.

  13. Charge distributions and effective atomic charges in transition-metal complexes using generalized atomic polar tensors and topological analysis

    SciTech Connect

    Cioslowski, J.; Hay, P.J.; Ritchie, J.P. )

    1990-01-11

    Advantages and shortcomings of three different definitions of the atomic charges, namely, the Mulliken, the generalized atomic polar tensors (GAPT), and the topological ones, are judged by applying them to the results of ab initio calculations on the TiF{sub 4}, Ni(CO){sub 4}, and FeH{sub 6}{sup 4{minus}} molecules. In agreement with previous reports, we find that the Mulliken charges vary widely with the choice of basis sets and therefore their utilization for the analysis of electronic structure of the transition-metal complexes is of little practical importance. On the other hand, both the GAPT and Bader's charges show a remarkable insensitivity to the quality of the basis sets.

  14. Extracting chemical information from plane wave calculations by a 3D 'fuzzy atoms' analysis

    NASA Astrophysics Data System (ADS)

    Bakó, I.; Stirling, A.; Seitsonen, A. P.; Mayer, I.

    2013-03-01

    Bond order and valence indices have been calculated by the method of the three-dimensional 'fuzzy atoms' analysis, using the numerical molecular orbitals obtained from plane wave DFT calculations, i.e., without introducing any external atom-centered functions. Weight functions of both Hirshfeld and Becke types have been applied. The results are rather close to the similar 'fuzzy atoms' ones obtained by using atom-centered basis sets and agree well with the chemical expectations, stressing the power of the genuine chemical concepts.

  15. Atoms in parallel fields: Analysis with diffractive periodic orbits

    NASA Astrophysics Data System (ADS)

    Owen, S. M.; Monteiro, T. S.; Dando, P. A.

    2000-11-01

    We show that fluctuations in the density of states of nonhydrogenic atoms in parallel fields are strongly influenced by diffractive periodic orbits. Unlike typical systems with a diffractive point scatterer, the atomic core of small atoms like lithium and helium is best understood as a combined geometric and diffractive scatterer. Each Gutzwiller (geometric) periodic orbit is paired with a diffractive orbit of the same action. We investigate, particularly, amplitudes for contributions from repetitions, and multiple scattering orbits. We find that periodic orbit repetitions are described by ``hybrid'' orbits, combining both diffractive and geometric core scatters, and that by including all possible permutations we can obtain excellent agreement between the semiclassical model and accurate fully quantal calculations. For high repetitions, we find even one-scatter diffractive contributions become of the same order as those of the geometric periodic orbit for repetition numbers n~ħ-1/2. Although the contribution of individual diffractive orbits is suppressed by O(ħ1/2) relative to the geometric periodic orbits, the proliferation of diffractive orbits with increasing period means that the diffractive effect for the atom can persist in the ħ-->0 limit.

  16. 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.

  17. Atomic and molecular physics and data activities for astrophysics at Oak Ridge National Laboratory

    SciTech Connect

    Jeffery, D.J.; Kristic, P.S.; Liu, W.; Schultz, D.R.; Stancil, P.C.

    1998-04-01

    The atomic astrophysics group at ORNL produces, collects, evaluates, and disseminates atomic and molecular data relevant to astrophysics and actively models various astrophysical environments utilizing this information. With the advent of the World Wide Web, these data are also being placed on-line to facilitate their use by end-users. In this brief report, the group`s recent activities in data production and in modeling are highlighted. For example, the authors describe recent calculations of elastic and transport cross sections relevant to ionospheric and heliospheric studies, charge transfer between metal ions and metal atoms and novel supernova nebular spectra modeling, ion-molecule collision data relevant to planetary atmospheres and comets, and data for early universe modeling.

  18. 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.

  19. 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

  20. 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

  1. Accurate abundance analysis of late-type stars: advances in atomic physics

    NASA Astrophysics Data System (ADS)

    Barklem, Paul S.

    2016-05-01

    The measurement of stellar properties such as chemical compositions, masses and ages, through stellar spectra, is a fundamental problem in astrophysics. Progress in the understanding, calculation and measurement of atomic properties and processes relevant to the high-accuracy analysis of F-, G-, and K-type stellar spectra is reviewed, with particular emphasis on abundance analysis. This includes fundamental atomic data such as energy levels, wavelengths, and transition probabilities, as well as processes of photoionisation, collisional broadening and inelastic collisions. A recurring theme throughout the review is the interplay between theoretical atomic physics, laboratory measurements, and astrophysical modelling, all of which contribute to our understanding of atoms and atomic processes, as well as to modelling stellar spectra.

  2. An analysis of pressure swirl and pure airblast atomization

    NASA Astrophysics Data System (ADS)

    Mao, Chien-Pei; Chuech, S. G.; Przekwas, A. J.

    1990-06-01

    The fundamental aspects of airblast atomization in both the breakup and drop dispersion regimes have been investigated. A high-magnification 4 x 5 camera and a phase/Doppler particle analyzer have been used to evaluate the spray charateristics and atomizer performance. The primary parameters under consideration include liquid film breakup length, spray angle, drop size, and trajectory. A model is presented that is capable of predicting the variations in thickness, trajectory, velocity, and angle of a liquid film as a function of nozzle geometry, operating conditions, fluid properties, and ambient conditions. To provide local drop size spectra, secondary breakup and drop history calculations are also included in the model. An excellent agreement is found between the experimental and predicted breakup length and angle. The predictions of drop size, trajectory, and other parameters are qualitatively correct.

  3. 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).

  4. Atom-probe analysis of cemented carbides and cermets

    NASA Astrophysics Data System (ADS)

    Andrén, H.-O.; Rolander, U.; Lindahl, P.

    1994-03-01

    For many years we have studied the detailed microstructure of cemented carbides (WC-Co and WC-MC-Co) and cermets (TiC-TiN-Mo 2C-Ni/Co and (Ti, W, Ta)(C, N)-(Co, Ni)), using mainly atom-probe field ion microscopy. This paper contains an overview of our experimental methods and results. All investigated materials were found to have a hard-phase skeleton with about half a monolayer of binder metal grain boundary segregation. The binder phase contained metal atoms from hard phases, which dissolve during sintering, but was almost completely free of C and N. Depleted zones existed close to hard phases due to diffusion during cooling after sintering. Cobalt binder phase contains W and Mo but little Ti, nickel binder phase Ti and Mo. The amount of Ti did not vary much with N content in the alloy, whereas the Mo content increased substantially with total N content. Carbide or carbonitride grains in materials containing more than one hard phase formed a core-rim structure. Rims precipitated epitaxially onto cores during sintering, and compositional gradients reflect the sequence of hard-phase dissolution. No diffusion of metal atoms occurred in the hard phases during sintering so the material is far from thermodynamic equilibrium. However, C and N may diffuse so that the system approaches equilibrium with respect to these elements during sintering.

  5. Copper-homoscorpionate complexes as active catalysts for atom transfer radical addition to olefins.

    PubMed

    Muñoz-Molina, José María; Caballero, Ana; Díaz-Requejo, M Mar; Trofimenko, Swiatoslaw; Belderraín, Tomas R; Pérez, Pedro J

    2007-09-17

    Cu(I) complexes containing trispyrazolylborate ligands efficiently catalyze the atom transfer radical addition (ATRA) of polyhalogenated alkanes to various olefins under mild conditions. The catalytic activity is enhanced when bulky and electron donating Tpx ligands are employed. Kinetic data have allowed the proposal of a mechanistic interpretation that includes a Cu(II) pentacoordinated species that regulates the catalytic cycle.

  6. AtomicJ: an open source software for analysis of force curves.

    PubMed

    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. PMID:24985823

  7. 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.

  8. 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.

  9. Catalytic Activity and Stability of Oxides: The Role of Near-Surface Atomic Structures and Compositions.

    PubMed

    Feng, Zhenxing; Hong, Wesley T; Fong, Dillon D; Lee, Yueh-Lin; Yacoby, Yizhak; Morgan, Dane; Shao-Horn, Yang

    2016-05-17

    Electrocatalysts play an important role in catalyzing the kinetics for oxygen reduction and oxygen evolution reactions for many air-based energy storage and conversion devices, such as metal-air batteries and fuel cells. Although noble metals have been extensively used as electrocatalysts, their limited natural abundance and high costs have motivated the search for more cost-effective catalysts. Oxides are suitable candidates since they are relatively inexpensive and have shown reasonably high activity for various electrochemical reactions. However, a lack of fundamental understanding of the reaction mechanisms has been a major hurdle toward improving electrocatalytic activity. Detailed studies of the oxide surface atomic structure and chemistry (e.g., cation migration) can provide much needed insights for the design of highly efficient and stable oxide electrocatalysts. In this Account, we focus on recent advances in characterizing strontium (Sr) cation segregation and enrichment near the surface of Sr-substituted perovskite oxides under different operating conditions (e.g., high temperature, applied potential), as well as their influence on the surface oxygen exchange kinetics at elevated temperatures. We contrast Sr segregation, which is associated with Sr redistribution in the crystal lattice near the surface, with Sr enrichment, which involves Sr redistribution via the formation of secondary phases. The newly developed coherent Bragg rod analysis (COBRA) and energy-modulated differential COBRA are uniquely powerful ways of providing information about surface and interfacial cation segregation at the atomic scale for these thin film electrocatalysts. In situ ambient pressure X-ray photoelectron spectroscopy (APXPS) studies under electrochemical operating conditions give additional insights into cation migration. Direct COBRA and APXPS evidence for surface Sr segregation was found for La1-xSrxCoO3-δ and (La1-ySry)2CoO4±δ/La1-xSrxCoO3-δ oxide thin films, and

  10. Atomic lines in multiwavelength spectral analysis of late-type stars

    NASA Astrophysics Data System (ADS)

    Jones, Hugh

    2015-08-01

    We make a multiwavelength analysis of strong/average atomic features which can be used in late-type dwarfs investigations. Quantative analysis of Na, Mg, Al, K, Ca, Sc, Ti, Mn, Fe across the optical and infrared was carried out. Stellar spectra in these wave regions are governed by different molecular species, so precise data of atomic features help not only to determine the fundamental parameters of cooldwarfs, but specify the accuracy of molecular line lists. We show the number of atomic features which are visible in the wide range of wavelengths and temperature regimes and should be seen in spectra of late type dwarfs. We discuss the accuracy of the atomic feature profiles modelling depending on the synthetic spectra parameters, e.g efffective temperature, gravity, metallicity, etc. and show that deviations whithin the model parameters step are only a few percent. We apply our analysis to the spectra modelling from M to T dwarfs.

  11. Atomic force microscopy analysis of cell volume regulation.

    PubMed

    Spagnoli, Chiara; Beyder, Arthur; Besch, Stephen; Sachs, Frederick

    2008-09-01

    Cells swell in response a hypoosmotic challenge. By converting osmotic pressure to hydrostatic pressure at the cell membrane via van't Hoff's law, and converting that to tension via Laplace's law one predicts that the cell membrane should stretch and become stiff. We tested this prediction using the atomic force microscopy. During osmotic swelling cells did not become stiff and generally became softer. This result contradicts the assumption of the cell membrane as the constraining element in osmotic stress but is consistent with the cytoskeleton acting as a cross-linked gel. Models of the cells' response to osmotic stress must include energy terms for three-dimensional stresses. PMID:18851074

  12. Laser assisted field evaporation of oxides in atom probe analysis.

    PubMed

    Chen, Y M; Ohkubo, T; Hono, K

    2011-05-01

    We have investigated the laser assisted field evaporation phenomena of ZnO, and MgO to explore the feasibility of quantitative three dimensional atom probe analyses of insulating oxides. To assist the field evaporation of these oxides, the usage of short wavelength 343 nm ultraviolet (UV) laser was found to be more effective than 515 nm green laser. We observed field ion microscopy (FIM) image expansion and mass peak shifting when 343 nm laser was irradiated on MgO. This phenomenon can be attributed to the laser induced electron excitation which causes the reduction of the resistivity of the specimen.

  13. 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

  14. 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.

  15. Metal oxide nanoparticle growth on graphene via chemical activation with atomic oxygen.

    PubMed

    Johns, James E; Alaboson, Justice M P; Patwardhan, Sameer; Ryder, Christopher R; Schatz, George C; Hersam, Mark C

    2013-12-01

    Chemically interfacing the inert basal plane of graphene with other materials has limited the development of graphene-based catalysts, composite materials, and devices. Here, we overcome this limitation by chemically activating epitaxial graphene on SiC(0001) using atomic oxygen. Atomic oxygen produces epoxide groups on graphene, which act as reactive nucleation sites for zinc oxide nanoparticle growth using the atomic layer deposition precursor diethyl zinc. In particular, exposure of epoxidized graphene to diethyl zinc abstracts oxygen, creating mobile species that diffuse on the surface to form metal oxide clusters. This mechanism is corroborated with a combination of scanning probe microscopy, Raman spectroscopy, and density functional theory and can likely be generalized to a wide variety of related surface reactions on graphene.

  16. 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.

  17. Using Catalytic Atom Maps to Predict the Catalytic Functions Present in Enzyme Active Sites

    PubMed Central

    Nosrati, Geoffrey R.; Houk, K. N.

    2012-01-01

    Catalytic Atom Maps (CAMs) are minimal models of enzyme active sites. The structures in the Protein Data Bank (PDB) were examined to determine if proteins with CAM-like geometries in their active sites all share the same catalytic function. We combined the CAM-based search protocol with a filter based on the weighted contact number (WCN) of the catalytic residues, a measure of the “crowdedness” of the microenvironment around a protein residue. Using this technique, a CAM based on the Ser-His-Asp catalytic triad of trypsin was able to correctly identify catalytic triads in other enzymes within 0.5 Å RMSD of the Catalytic Atom Map with 96% accuracy. A CAM based on the Cys-Arg-(Asp/Glu) active site residues from the tyrosine phosphatase active site achieved 89% accuracy in identifying this type of catalytic functionality. Both of these Catalytic Atom Maps were able to identify active sites across different fold types. Finally, the PDB was searched to locate proteins with catalytic functionality similar to that present in the active site of orotidine 5′-monophosphate decarboxylase (ODCase), whose mechanism is not known with certainty. A CAM, based on the conserved Lys-Asp-Lys-Asp tetrad in the ODCase active site, was used to search the PDB for enzymes with similar active sites. The ODCase active site has a geometry similar to that of Schiff base-forming Class I aldolases, with lowest aldolase RMSD to the ODCase CAM at 0.48 Å. The similarity between this CAM and the aldolase active site suggests that ODCase has the correct catalytic functionality present in its active site for the generation of a nucleophilic lysine. PMID:22909276

  18. 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.

  19. Atomic torsional modal analysis for high-resolution proteins

    NASA Astrophysics Data System (ADS)

    Tirion, Monique M.; ben-Avraham, Daniel

    2015-03-01

    We introduce a formulation for normal mode analyses of globular proteins that significantly improves on an earlier one-parameter formulation [M. M. Tirion, Phys. Rev. Lett. 77, 1905 (1996), 10.1103/PhysRevLett.77.1905] that characterized the slow modes associated with protein data bank structures. Here we develop that empirical potential function that is minimized at the outset to include two features essential to reproduce the eigenspectra and associated density of states in the 0 to 300 cm-1 frequency range, not merely the slow modes. First, introduction of preferred dihedral-angle configurations via use of torsional stiffness constants eliminates anomalous dispersion characteristics due to insufficiently bound surface side chains and helps fix the spectrum thin tail frequencies (100-300 cm-1 ). Second, we take into account the atomic identities and the distance of separation of all pairwise interactions, improving the spectrum distribution in the 20 to 300 cm-1 range. With these modifications, not only does the spectrum reproduce that of full atomic potentials, but we obtain stable reliable eigenmodes for the slow modes and over a wide range of frequencies.

  20. 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

    2015-12-01

    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

  1. Activation analysis using Cornell TRIGA

    SciTech Connect

    Hossain, Tim Z.

    1994-07-01

    A major use of the Cornell TRIGA is for activation analysis. Over the years many varieties of samples have been analyzed from a number of fields of interest ranging from geology, archaeology and textiles. More recently the analysis has been extended to high technology materials for applications in optical and semiconductor devices. Trace analysis in high purity materials like Si wafers has been the focus in many instances, while in others analysis of major/minor components were the goals. These analysis has been done using the delayed mode. Results from recent measurements in semiconductors and other materials will be presented. In addition the near future capability of using prompt gamma activation analysis using the Cornell cold neutron beam will be discussed. (author)

  2. Entropy and complexity analysis of hydrogenic Rydberg atoms

    NASA Astrophysics Data System (ADS)

    López-Rosa, S.; Toranzo, I. V.; Sánchez-Moreno, P.; Dehesa, J. S.

    2013-05-01

    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 Crámer-Rao, Fisher-Shannon, and López 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.

  3. 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.

  4. 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.

  5. Standardizing Activation Analysis: New Software for Photon Activation Analysis

    SciTech Connect

    Sun, Z. J.; Wells, D.; Green, J.; Segebade, C.

    2011-06-01

    Photon Activation Analysis (PAA) of environmental, archaeological and industrial samples requires extensive data analysis that is susceptible to error. For the purpose of saving time, manpower and minimizing error, a computer program was designed, built and implemented using SQL, Access 2007 and asp.net technology to automate this process. Based on the peak information of the spectrum and assisted by its PAA library, the program automatically identifies elements in the samples and calculates their concentrations and respective uncertainties. The software also could be operated in browser/server mode, which gives the possibility to use it anywhere the internet is accessible. By switching the nuclide library and the related formula behind, the new software can be easily expanded to neutron activation analysis (NAA), charged particle activation analysis (CPAA) or proton-induced X-ray emission (PIXE). Implementation of this would standardize the analysis of nuclear activation data. Results from this software were compared to standard PAA analysis with excellent agreement. With minimum input from the user, the software has proven to be fast, user-friendly and reliable.

  6. 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

  7. 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.

  8. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

    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-xSex 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.

  10. 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.

  11. An effective field theory analysis of Efimov features in heteronuclear mixture of ultracold atomic gases

    NASA Astrophysics Data System (ADS)

    Acharya, Bijaya; Ji, Chen; Platter, Lucas

    2016-05-01

    Recent experimental studies have unveiled Efimov physics in ultracold atomic gases of heteronuclear mixtures. The recombination features of such atomic systems display universal correlations including discrete scaling invariance. We use Effective Field Theory (EFT) to study the Efimov features of the heteronuclear three-atom systems consisting of two identical bosons which interact with each other through a natural scattering length and with the third particle through a large scattering length. We compute the corrections to the universal correlations by perturbative insertions of the interspecies effective range and the intraspecies scattering length. Such an analysis is relevant for mixtures of ultracold atomic gases near the interspecies Feshbach resonance. Supported by the US Department of Energy under Contract No. DE-AC05-00OR22725 and the National Science Foundation under Grant No. PHY-1516077.

  12. 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. PMID:22560564

  13. 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.

  14. 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.

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

    PubMed Central

    Wang, Yang-Gang; Mei, Donghai; Glezakou, Vassiliki-Alexandra; Li, Jun; Rousseau, Roger

    2015-01-01

    Catalysis by gold supported on reducible oxides has been extensively studied, yet issues such as the nature of the catalytic site and the role of the reducible support remain fiercely debated topics. Here we present ab initio molecular dynamics simulations of an unprecedented dynamic single-atom catalytic mechanism for the oxidation of carbon monoxide by ceria-supported gold clusters. The reported dynamic single-atom catalytic mechanism results from the ability of the gold cation to strongly couple with the redox properties of the ceria in a synergistic manner, thereby lowering the energy of redox reactions. The gold cation can break away from the gold nanoparticle to catalyse carbon monoxide oxidation, adjacent to the metal/oxide interface and subsequently reintegrate back into the nanoparticle after the reaction is completed. Our study highlights the importance of the dynamic creation of active sites under reaction conditions and their essential role in catalysis. PMID:25735407

  16. 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

  17. 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

  18. 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

  19. Instantaneous normal mode analysis for intermolecular and intramolecular vibrations of water from atomic point of view

    SciTech Connect

    Chen, Yu-Chun; Tang, Ping-Han; Wu, Ten-Ming

    2013-11-28

    By exploiting the instantaneous normal mode (INM) analysis for models of flexible molecules, we investigate intermolecular and intramolecular vibrations of water from the atomic point of view. With two flexible SPC/E models, our investigations include three aspects about their INM spectra, which are separated into the unstable, intermolecular, bending, and stretching bands. First, the O- and H-atom contributions in the four INM bands are calculated and their stable INM spectra are compared with the power spectra of the atomic velocity autocorrelation functions. The unstable and intermolecular bands of the flexible models are also compared with those of the SPC/E model of rigid molecules. Second, we formulate the inverse participation ratio (IPR) of the INMs, respectively, for the O- and H-atom and molecule. With the IPRs, the numbers of the three species participated in the INMs are estimated so that the localization characters of the INMs in each band are studied. Further, by the ratio of the IPR of the H atom to that of the O atom, we explore the number of involved OH bond per molecule participated in the INMs. Third, by classifying simulated molecules into subensembles according to the geometry of their local environments or their H-bond configurations, we examine the local-structure effects on the bending and stretching INM bands. All of our results are verified to be insensible to the definition of H-bond. Our conclusions about the intermolecular and intramolecular vibrations in water are given.

  20. Instantaneous normal mode analysis for intermolecular and intramolecular vibrations of water from atomic point of view.

    PubMed

    Chen, Yu-Chun; Tang, Ping-Han; Wu, Ten-Ming

    2013-11-28

    By exploiting the instantaneous normal mode (INM) analysis for models of flexible molecules, we investigate intermolecular and intramolecular vibrations of water from the atomic point of view. With two flexible SPC/E models, our investigations include three aspects about their INM spectra, which are separated into the unstable, intermolecular, bending, and stretching bands. First, the O- and H-atom contributions in the four INM bands are calculated and their stable INM spectra are compared with the power spectra of the atomic velocity autocorrelation functions. The unstable and intermolecular bands of the flexible models are also compared with those of the SPC/E model of rigid molecules. Second, we formulate the inverse participation ratio (IPR) of the INMs, respectively, for the O- and H-atom and molecule. With the IPRs, the numbers of the three species participated in the INMs are estimated so that the localization characters of the INMs in each band are studied. Further, by the ratio of the IPR of the H atom to that of the O atom, we explore the number of involved OH bond per molecule participated in the INMs. Third, by classifying simulated molecules into subensembles according to the geometry of their local environments or their H-bond configurations, we examine the local-structure effects on the bending and stretching INM bands. All of our results are verified to be insensible to the definition of H-bond. Our conclusions about the intermolecular and intramolecular vibrations in water are given.

  1. Instantaneous normal mode analysis for intermolecular and intramolecular vibrations of water from atomic point of view

    NASA Astrophysics Data System (ADS)

    Chen, Yu-Chun; Tang, Ping-Han; Wu, Ten-Ming

    2013-11-01

    By exploiting the instantaneous normal mode (INM) analysis for models of flexible molecules, we investigate intermolecular and intramolecular vibrations of water from the atomic point of view. With two flexible SPC/E models, our investigations include three aspects about their INM spectra, which are separated into the unstable, intermolecular, bending, and stretching bands. First, the O- and H-atom contributions in the four INM bands are calculated and their stable INM spectra are compared with the power spectra of the atomic velocity autocorrelation functions. The unstable and intermolecular bands of the flexible models are also compared with those of the SPC/E model of rigid molecules. Second, we formulate the inverse participation ratio (IPR) of the INMs, respectively, for the O- and H-atom and molecule. With the IPRs, the numbers of the three species participated in the INMs are estimated so that the localization characters of the INMs in each band are studied. Further, by the ratio of the IPR of the H atom to that of the O atom, we explore the number of involved OH bond per molecule participated in the INMs. Third, by classifying simulated molecules into subensembles according to the geometry of their local environments or their H-bond configurations, we examine the local-structure effects on the bending and stretching INM bands. All of our results are verified to be insensible to the definition of H-bond. Our conclusions about the intermolecular and intramolecular vibrations in water are given.

  2. HPLC-ICP atomic emission spectrometry in environmental analysis

    SciTech Connect

    Frame, E.M.S.

    1996-10-01

    Trace concentrations of many compounds are difficult to determine directly by traditional chromatographic techniques. Organosilicon compounds, for example, have no chromophoric groups. Size exclusion (SEC) and high performance liquid chromatography (HPLC) can separate high and low molecular weight organosilicon compounds, but routinely employ detectors with insufficient sensitivity for trace concentrations in environmental samples. Elemental analysis methods such as inductively coupled plasma optical emission spectrometry (ICP) provide excellent element sensitivity but no speciation information. Interfacing of a chromatographic method with ICP has been shown to provide quantitative determination of trace compounds while retaining the chemical speciation information. This work will describe the power of the HPLC-ICP combination for trace compounds in environmental samples to identify and determine ppm levels of organometallics.

  3. 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.

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

    DOE PAGES

    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 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

  5. 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

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

    NASA Astrophysics Data System (ADS)

    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.

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

    PubMed

    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

  8. 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.

  9. 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...

  10. 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)

  11. Atomic force microscopy : theory and practice in bacteria morphostructural analysis.

    PubMed

    Braga, P C; Ricci, D

    2001-01-01

    The production of the first "microscope" between the end of the sixteenth and the beginning of the seventeenth century was a true breakthrough in the advance of civilization (1). Without the microscope, the natural, biological, medical, and other sciences would not be what they are today. After the optical microscope, a second breakthrough in the analysis of surface morphology occurred in the 1940s with the development of the scanning electron microscope (SEM). Instead of light (photons) and glass lenses, electrons and electromagnetic lenses (magnetic coils) are used to explore the sample. Optical and scanning (or transmission) electron microscopes are classified as "far field microscopes" because the distance between the sample and the point at which the image is obtained is long in comparison with the wavelengths of the photons or electrons involved. In this case, the image is a diffraction pattern and its resolution is wavelength limited (2, 3): in optical microscopy, resolution is determined by the Nyquist relation to the wavelength of the light used (typically about 1 μm); in a general purpose SEM, it is limited by the properties of the electromagnetic lenses (typically about 50Å) (4).

  12. 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

  13. 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.

  14. 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.

  15. Neutron Activation Analysis: Techniques and Applications

    NASA Astrophysics Data System (ADS)

    MacLellan, Ryan

    2011-04-01

    The role of neutron activation analysis in low-energy low-background experimentsis discussed in terms of comparible methods. Radiochemical neutron activation analysis is introduce. The procedure of instrumental neutron activation analysis is detailed especially with respect to the measurement of trace amounts of natural radioactivity. The determination of reactor neutron spectrum parameters required for neutron activation analysis is also presented.

  16. Neutron Activation Analysis: Techniques and Applications

    SciTech Connect

    MacLellan, Ryan

    2011-04-27

    The role of neutron activation analysis in low-energy low-background experimentsis discussed in terms of comparible methods. Radiochemical neutron activation analysis is introduce. The procedure of instrumental neutron activation analysis is detailed especially with respect to the measurement of trace amounts of natural radioactivity. The determination of reactor neutron spectrum parameters required for neutron activation analysis is also presented.

  17. 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.

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

    NASA Technical Reports Server (NTRS)

    Kallman, T.

    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. This talk describes simple numerical experiments designed to examine some of these issues.

  19. Using catalytic atom maps to predict the catalytic functions present in enzyme active sites.

    PubMed

    Nosrati, Geoffrey R; Houk, K N

    2012-09-18

    Catalytic atom maps (CAMs) are minimal models of enzyme active sites. The structures in the Protein Data Bank (PDB) were examined to determine if proteins with CAM-like geometries in their active sites all share the same catalytic function. We combined the CAM-based search protocol with a filter based on the weighted contact number (WCN) of the catalytic residues, a measure of the "crowdedness" of the microenvironment around a protein residue. Using this technique, a CAM based on the Ser-His-Asp catalytic triad of trypsin was able to correctly identify catalytic triads in other enzymes within 0.5 Å rmsd of the CAM with 96% accuracy. A CAM based on the Cys-Arg-(Asp/Glu) active site residues from the tyrosine phosphatase active site achieved 89% accuracy in identifying this type of catalytic functionality. Both of these CAMs were able to identify active sites across different fold types. Finally, the PDB was searched to locate proteins with catalytic functionality similar to that present in the active site of orotidine 5'-monophosphate decarboxylase (ODCase), whose mechanism is not known with certainty. A CAM, based on the conserved Lys-Asp-Lys-Asp tetrad in the ODCase active site, was used to search the PDB for enzymes with similar active sites. The ODCase active site has a geometry similar to that of Schiff base-forming Class I aldolases, with lowest aldolase rmsd to the ODCase CAM at 0.48 Å. The similarity between this CAM and the aldolase active site suggests that ODCase has the correct catalytic functionality present in its active site for the generation of a nucleophilic lysine. PMID:22909276

  20. 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. PMID:27056544

  1. 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.

  2. Nearside-farside analysis of differential cross sections: Diffraction and rainbow scattering in atom-atom and atom-molecule rotationally inelastic sudden collisions

    NASA Astrophysics Data System (ADS)

    McCabe, P.; Connor, J. N. L.

    1996-02-01

    Nearside-farside (NF) theory, as used to understand nuclear heavy-ion differential cross sections, is applied for the first time to the angular scattering of atom-atom and atom-diatom collisions. A NF decomposition of the partial wave series (PWS) for the scattering amplitude has the following advantages: (a) it is exact, (b) it uses PW scattering matrix elements (quantum or semiclassical) as calculated by standard computer programs, (c) it is easily incorporated into existing computer programs which calculate angular distributions, (d) semiclassical techniques, such as stationary phase or saddle point integration, are not invoked for the PWS, although the semiclassical picture is still evident. A disadvantage of a NF decomposition is that it is not unique. The Fuller and Hatchell NF decompositions are used to analyze the angular scattering of four collision systems whose PWS involve Legendre polynomials: (a) atom-atom He+Ne elastic diffraction scattering, (b) atom-atom H++Ar elastic rainbow scattering, (c) atom rigid-rotator Ne+D2(j=0) →Ne+D2(j) diffraction scattering under sudden conditions so that the infinite-order-sudden (IOS) approximation is valid, (d) atom rigid-rotator He+N2(j=0)→He+N2(j) rotational rainbow IOS scattering. The utility of these two NF decompositions is assessed by comparison with results from the semiclassical complex angular momentum (CAM) representation of the scattering amplitude. This is chosen because it allows an unambiguous separation of the scattering amplitude into nearside and farside subamplitudes under semiclassical conditions. The Fuller NF decomposition, unlike the Hatchell NF decomposition, provides a physically clear explanation of the angular scattering, which always agrees with the semiclassical CAM interpretation (except for scattering angles ≊180°). The Fuller NF decomposition is therefore recommended for applications to atomic and molecular collisions. The NF theory for the decomposition of Legendre polynomials

  3. Residual 152Eu and 60Co activities induced by neutrons from the Hiroshima atomic bomb.

    PubMed

    Shizuma, K; Iwatani, K; Hasai, H; Hoshi, M; Oka, T; Morishima, H

    1993-09-01

    Specific activities of 152Eu:Eu in stone samples exposed to the Hiroshima atomic bomb were determined for 70 samples up to a 1,500-m slant range from the epicenter. The specific activities of 60Co:Co were also determined for six samples near the Hiroshima hypocenter. First, the 152Eu data were investigated to find out the directional dependence of neutron activation. Directional anisotropy was not definite; however, there was an indication that the activation in the west-southwest was lower than in other directions. Second, measured 152Eu and 60Co radioactivity data were compared with activation calculations based on DS86 neutrons. It is clearly shown that the measured data are lower than the calculation near the hypocenter and vice versa at long distances beyond 1,000 m. The calculated-to-measured ratios of 152Eu are 1.6 at the hypocenter, 1.0 at approximately 900 m, and 0.05 at a 1,500-m slant range. Present results indicate that systematic errors exist in the DS86 neutrons concerning the source-term spectrum, neutron transport calculations in air, and/or activation measurements.

  4. 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

  5. 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.

  6. 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.

  7. Field evaporation behaviour in the gamma phase in Ti-Al during analysis in the tomographic atom probe.

    PubMed

    Lefebvre, W; Loiseau, A; Menand, A

    2002-07-01

    A Ti-48 at% Al alloy has been successfully investigated, using atom probe field ion microscopy and transmission electron microscopy. After a specific heat treatment, this alloy has a (alpha2 + gamma) lamellar microstructure. Using the tomographic atom probe (TAP), it has been possible to image the stacking of superlattice planes of gamma and to identify titanium as the highest evaporation field element. In addition, the influence of analysis site on atom probe measurements has been estimated for this phase. A TAP analysis has also made it possible to observe an extremely thin step along a gamma/gamma interface at a near atomic scale.

  8. A cluster expansion model for predicting activation barrier of atomic processes

    SciTech Connect

    Rehman, Tafizur; Jaipal, M.; Chatterjee, Abhijit

    2013-06-15

    We introduce a procedure based on cluster expansion models for predicting the activation barrier of atomic processes encountered while studying the dynamics of a material system using the kinetic Monte Carlo (KMC) method. Starting with an interatomic potential description, a mathematical derivation is presented to show that the local environment dependence of the activation barrier can be captured using cluster interaction models. Next, we develop a systematic procedure for training the cluster interaction model on-the-fly, which involves: (i) obtaining activation barriers for handful local environments using nudged elastic band (NEB) calculations, (ii) identifying the local environment by analyzing the NEB results, and (iii) estimating the cluster interaction model parameters from the activation barrier data. Once a cluster expansion model has been trained, it is used to predict activation barriers without requiring any additional NEB calculations. Numerical studies are performed to validate the cluster expansion model by studying hop processes in Ag/Ag(100). We show that the use of cluster expansion model with KMC enables efficient generation of an accurate process rate catalog.

  9. Al-free active region laser diodes at 894 nm for compact Cesium atomic clocks

    NASA Astrophysics Data System (ADS)

    Von Bandel, N.; Bébé Manga Lobé, J.; Garcia, M.; Larrue, A.; Robert, Y.; Vinet, E.; Lecomte, M.; Drisse, O.; Parillaud, O.; Krakowski, M.

    2015-03-01

    Time-frequency applications are in need of high accuracy and high stability clocks. Compact industrial Cesium atomic clocks optically pumped is a promising area that could satisfy these demands. However, the stability of these clocks relies, among others, on the performances of laser diodes that are used for atomic pumping. This issue has led the III-V Lab to commit to the European Euripides-LAMA project that aims to provide competitive compact optical Cesium clocks for earth applications. This work will provide key experience for further space technology qualification. We are in charge of the design, fabrication and reliability of Distributed-Feedback diodes (DFB) at 894nm (D1 line of Cesium) and 852nm (D2 line). The use of D1 line for pumping will provide simplified clock architecture compared to D2 line pumping thanks to simpler atomic transitions and larger spectral separation between lines in the 894nm case. Also, D1 line pumping overcomes the issue of unpumped "dark states" that occur with D2 line. The modules should provide narrow linewidth (<1MHz), very good reliability in time and, crucially, be insensitive to optical feedback. The development of the 894nm wavelength is grounded on our previous results for 852nm DFB. Thus, we show our first results from Al-free active region with InGaAsP quantum well broad-area lasers (100μm width, with lengths ranging from 2mm to 4mm), for further DFB operation at 894nm. We obtained low internal losses below 2cm-1, the external differential efficiency is 0.49W/A with uncoated facets and a low threshold current density of 190A/cm², for 2mm lasers at 20°C.

  10. US--ITER activation analysis

    SciTech Connect

    Attaya, H.; Gohar, Y.; Smith, D.

    1990-09-01

    Activation analysis has been made for the US ITER design. The radioactivity and the decay heat have been calculated, during operation and after shutdown for the two ITER phases, the Physics Phase and the Technology Phase. The Physics Phase operates about 24 full power days (FPDs) at fusion power level of 1100 MW and the Technology Phase has 860 MW fusion power and operates for about 1360 FPDs. The point-wise gamma sources have been calculated everywhere in the reactor at several times after shutdown of the two phases and are then used to calculate the biological dose everywhere in the reactor. Activation calculations have been made also for ITER divertor. The results are presented for different continuous operation times and for only one pulse. The effect of the pulsed operation on the radioactivity is analyzed. 6 refs., 12 figs., 1 tab.

  11. Prompt-gamma activation analysis

    SciTech Connect

    Lindstrom, R.M.

    1993-01-01

    A permenent, 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 the 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.

  12. X-ray STM: Nanoscale elemental analysis & Observation of atomic track.

    PubMed

    Saito, Akira; Furudate, Y; Kusui, Y; Saito, T; Akai-Kasaya, M; Tanaka, Y; Tamasaku, K; Kohmura, Y; Ishikawa, T; Kuwahara, Y; Aono, M

    2014-11-01

    Scanning tunneling microscopy (STM) combined with brilliant X-rays from synchrotron radiation (SR) can provide various possibilities of original and important applications, such as the elemental analysis on solid surfaces at an atomic scale. The principle of the elemental analysis is based on the inner-shell excitation of an element-specific energy level "under STM observation". A key to obtain an atomic locality is to extract the element-specific modulation of the local tunneling current (not emission that can damage the spatial resolution), which is derived from the inner-shell excitation [1]. On this purpose, we developed a special SR-STM system and smart tip. To surmount a tiny core-excitation efficiency by hard X-rays, we focused two-dimensionally an incident beam having the highest photon density at the SPring-8.After successes in the elemental analyses by SR-STM [1,2] on a semiconductor hetero-interface (Ge on Si) and metal-semiconductor interface (Cu on Ge), we succeeded in obtaining the elemental contrast between Co nano-islands and Au substrate. The results on the metallic substrate suggest the generality of the method and give some important implications on the principle of contrast. For all cases of three samples, the spatial resolution of the analysis was estimated to be ∼1 nm or less, and it is worth noting that the measured surface domains had a deposition thickness of less than one atomic layer (Fig. 1, left and center).jmicro;63/suppl_1/i14-a/DFU045F1F1DFU045F1Fig. 1.(left) Topographic image and (center) beam-induced tip current image of Ge(111)-Cu (-2V, 0.2 nA). (right) X-ray- induced atomic motion tracks on Ge(111) that were newly imaged by the Xray-STM. On the other hand, we found that the "X-ray induced atomic motion" can be observed directly with atomic scale using the SR-STM system effectively under the incident photon density of ∼2 x10(15) photon/sec/mm(2) [3]. SR-STM visualized successfully the track of the atomic motion (Fig. 1, right

  13. Characterizing Oxidation State using Bader Analysis, Maximally Localized Wannier Functions and Atomic Orbitals Projection

    NASA Astrophysics Data System (ADS)

    Reeves, Kyle; Kanai, Yosuke

    2013-03-01

    The concept of oxidation state of atoms in molecules and materials is widely used to predict and understand chemical and physical properties. This concept is perhaps driven more empirically than by any rigorous criteria differentiating one oxidation state from another. Within the oxidation state framework, an integer number of electrons is assigned to the nuclei within a system. In practice, a distribution of electron density makes it difficult to quantify such discrete assignments without some ambiguities. We explore three different charge analysis approaches in density functional theory calculations for addressing the oxidation state of important organometallic molecules [Ru(bpy)3]2+ and [Ru(bpy)3]3+, which are widely used for solar energy conversion applications. Bader charge analysis, Wannier function analysis, and atomic orbital projection are employed in this work. Given the highly-localized nature of the d-electrons of the ruthenium atom, the charge analysis methods are also compared with Hubbard-U correction. We also discuss how the solvation by water molecules influences the oxidation state characterization for these organometallic complexes.

  14. 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.

  15. Metastable atom-activated dissociation mass spectrometry of phosphorylated and sulfonated peptides in negative ion mode.

    PubMed

    Cook, Shannon L; Jackson, Glen P

    2011-06-01

    The dissociation behavior of phosphorylated and sulfonated peptide anions was explored using metastable atom-activated dissociation mass spectrometry (MAD-MS) and collision-induced dissociation (CID). A beam of high kinetic energy helium (He) metastable atoms was exposed to isolated phosphorylated and sulfonated peptides in the 3- and 2- charge states. Unlike CID, where phosphate losses are dominant, the major dissociation channels observed using MAD were C(α) - C peptide backbone cleavages and neutral losses of CO(2), H(2)O, and [CO(2) + H(2)O] from the charge reduced (oxidized) product ion, consistent with an electron detachment dissociation (EDD) mechanism such as Penning ionization. Regardless of charge state or modification, MAD provides ample backbone cleavages with little modification loss, which allows for unambiguous PTM site determination. The relative abundance of certain fragment ions in MAD is also demonstrated to be somewhat sensitive to the number and location of deprotonation sites, with backbone cleavage somewhat favored adjacent to deprotonated sites like aspartic acid residues. MAD provides a complementary dissociation technique to CID, ECD, ETD, and EDD for peptide sequencing and modification identification. MAD offers the unique ability to analyze highly acidic peptides that contain few to no basic amino acids in either negative or positive ion mode.

  16. Review of atomic data needs for active charge-exchange spectroscopy on ITERa)

    NASA Astrophysics Data System (ADS)

    Marchuk, O.; Bertschinger, G.; Biel, W.; Delabie, E.; von Hellermann, M. G.; Jaspers, R.; Reiter, D.

    2008-10-01

    The quantitative exploitation of active beam spectra is largely based on an advanced atomic modeling. Under the ITER operating conditions the penetration depth of a diagnostic beam into the plasma core crucially affects the intensities of spectral lines and hence the uncertainties of derived plasma parameters. A critical review of atomic data and an assessment of its error margins are, therefore, urgently needed. The aim of the present work is to verify the existing beam-stopping and beam-emission data for hydrogen beam in fusion plasmas. The agreement between the ADAS database and the present calculations is found to be within 5% for the beam-stopping data in a H-plasma. The calculation of beam attenuation in the presence of He-ash (4%) and Be ions (2%) demonstrates the agreement between the present data and the ADAS database within 10%. Finally, the maximum deviation of 15% is found only for beam-emission data at the electron density of 1×1012-2×1012cm-3, which is significantly below the ITER density of 1014cm-3.

  17. 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.

  18. Influences of halogen atoms on indole-3-acetonitrile (IAN): Crystal structure and Hirshfeld surfaces analysis

    NASA Astrophysics Data System (ADS)

    Luo, Yang-Hui; Yang, Li-Jing; Han, Guangjun; Liu, Qing-Ling; Wang, Wei; Ling, Yang; Sun, Bai-Wang

    2014-11-01

    Crystal structural investigations and Hirshfeld surface analysis of three halogen atoms (4-Cl, 6-Cl and 4-Br) substituted indole-3-acetonitrile (IAN) were reported in this work. The structures of the present three compounds were characterized by Infrared spectra, Elemental analyses, NMR spectra, differential scanning calorimetry (DSC), thermogravimetric analyses (TGA) and hot stage microscopy (HSM). The Hirshfeld surfaces analysis in terms of crystal structure, intermolecular interactions and π⋯π stacking motifs were performed. We found that the different kinds of halogen atoms and the different substituted positions have a significant effect on the crystal structures, molecular π⋯π stacking motifs, melting points, and the nature of intermolecular interactions for IANs.

  19. Gloss Phenomena and Image Analysis of Atomic Force Microscopy in Molecular and Cell Biology

    PubMed Central

    Zhu, Jie; Sabharwal, Tanya; Guo, Lianhong; Kalyanasundaram, Aruna; Wang, Guodong

    2010-01-01

    Summary Proper sample preparation, scan setup, data collection and image analysis are key factors in successful atomic force microscopy which can avoid gloss phenomena effectively from unreasonable manipulations or instrumental defaults. Fresh cleaved mica and newly treated glass cover were checked firstly as the substrates for all of the sample preparation for atomic force microscopy. Then, crystals contamination from buffer were studied separately or combined with several biologic samples, and the influence of scanner, scan mode and cantilever to data collection were also discussed intensively using molecular and cellular samples. At last, images treatment and analysis with off-line software had been focused on standard and biologic samples, and artificial glosses were highly considered for their high probability in occurring. PMID:19191267

  20. Atomic layer deposition encapsulated activated carbon electrodes for high voltage stable supercapacitors.

    PubMed

    Hong, Kijoo; Cho, Moonkyu; Kim, Sang Ouk

    2015-01-28

    Operating voltage enhancement is an effective route for high energy density supercapacitors. Unfortunately, widely used activated carbon electrode generally suffers from poor electrochemical stability over 2.5 V. Here we present atomic layer deposition (ALD) encapsulation of activated carbons for high voltage stable supercapacitors. Two-nanometer-thick Al2O3 dielectric layers are conformally coated at activated carbon surface by ALD, well-maintaining microporous morphology. Resultant electrodes exhibit excellent stability at 3 V operation with 39% energy density enhancement from 2.5 V operation. Because of the protection of surface functional groups and reduction of electrolyte degradation, 74% of initial voltage was maintained 50 h after full charge, and 88% of capacitance was retained after 5000 cycles at 70 °C accelerated test, which correspond to 31 and 17% improvements from bare activated carbon, respectively. This ALD-based surface modification offers a general method to enhance electrochemical stability of carbon materials for diverse energy and environmental applications.

  1. From single crystal surfaces to single atoms: investigating active sites in electrocatalysis.

    PubMed

    O'Mullane, Anthony P

    2014-04-21

    Electrocatalytic processes will undoubtedly be at the heart of energising future transportation and technology with the added importance of being able to create the necessary fuels required to do so in an environmentally friendly and cost effective manner. For this to be successful two almost mutually exclusive surface properties need to be reconciled, namely producing highly active/reactive surface sites that exhibit long term stability. This article reviews the various approaches which have been undertaken to study the elusive nature of these active sites on metal surfaces which are considered as adatoms or clusters of adatoms with low coordination number. This includes the pioneering studies at extended well defined stepped single crystal surfaces using cyclic voltammetry up to the highly sophisticated in situ electrochemical imaging techniques used to study chemically synthesised nanomaterials. By combining the information attained from single crystal surfaces, individual nanoparticles of defined size and shape, density functional theory calculations and new concepts such as mesoporous multimetallic thin films and single atom electrocatalysts new insights into the design and fabrication of materials with highly active but stable active sites can be achieved. The area of electrocatalysis is therefore not only a fascinating and exciting field in terms of realistic technological and economical benefits but also from the fundamental understanding that can be acquired by studying such an array of interesting materials. PMID:24599277

  2. Nanoelectrodes integrated in atomic force microscopy cantilevers for imaging of in situ enzyme activity.

    PubMed

    Kueng, Angelika; Kranz, Christine; Lugstein, Alois; Bertagnolli, Emmerich; Mizaikoff, Boris

    2005-01-01

    For investigation of laterally resolved information on biological activity, techniques for simultaneously obtaining complementary information correlated in time and space are required. In this context, recent developments in scanning probe microscopy are aimed at information on the sample topography and simultaneously on the physical and chemical properties at the nanometer scale. With the integration of submicro- and nanoelectrodes into atomic force microscopy (AFM) probes using microfabrication techniques, an elegant approach combining scanning electrochemical microscopy with AFM is demonstrated. This instrumentation enables simultaneous imaging of topography and obtainment of laterally resolved electrochemical information in AFM tapping mode. Hence, topographical and electrochemical information on soft surfaces (e.g., biological species) and polymers can be obtained. The functionality of tip-integrated electrodes is demonstrated by simultaneous electrochemical and topographical studies of an enzyme-modified micropattern.

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

    DOE PAGES

    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 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

  4. 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.

  5. 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.

  6. 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.

  7. 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.

  8. Data acquisition and analysis procedures for high-resolution atomic force microscopy in three dimensions.

    PubMed

    Albers, Boris J; Schwendemann, Todd C; Baykara, Mehmet Z; Pilet, Nicolas; Liebmann, Marcus; Altman, Eric I; Schwarz, Udo D

    2009-07-01

    Data acquisition and analysis procedures for noncontact atomic force microscopy that allow the recording of dense three-dimensional (3D) surface force and energy fields with atomic resolution are presented. The main obstacles for producing high-quality 3D force maps are long acquisition times that lead to data sets being distorted by drift, and tip changes. Both problems are reduced but not eliminated by low-temperature operation. The procedures presented here employ an image-by-image data acquisition scheme that cuts measurement times by avoiding repeated recording of redundant information, while allowing post-acquisition drift correction. All steps are detailed with the example of measurements performed on highly oriented pyrolytic graphite in ultrahigh vacuum at a temperature of 6 K. The area covered spans several unit cells laterally and vertically from the attractive region to where no force could be measured. The resulting fine data mesh maps piconewton forces with <7 pm lateral and<2 pm vertical resolution. From this 3D data set, two-dimensional cuts along any plane can be plotted. Cuts in a plane parallel to the sample surface show atomic resolution, while cuts along the surface normal visualize how the attractive atomic force fields extend into vacuum. At the same time, maps of the tip-sample potential energy, the lateral tip-sample forces, and the energy dissipated during cantilever oscillation can be produced with identical resolution.

  9. Single Molecule Characterization of UV-Activated Antibodies on Gold by Atomic Force Microscopy.

    PubMed

    Funari, R; Della Ventura, B; Altucci, C; Offenhäusser, A; Mayer, D; Velotta, R

    2016-08-16

    The interaction between proteins and solid surfaces can influence their conformation and therefore also their activity and affinity. These interactions are highly specific for the respective combination of proteins and solids. Consequently, it is desirable to investigate the conformation of proteins on technical surfaces, ideally at single molecule level, and to correlate the results with their activity. This is in particular true for biosensors where the conformation-dependent target affinity of an immobilized receptor determines the sensitivity of the sensor. Here, we investigate for the first time the immobilization and orientation of antibodies (Abs) photoactivated by a photonic immobilization technique (PIT), which has previously demonstrated to enhance binding capabilities of antibody receptors. The photoactivated immunoglobulins are immobilized on ultrasmooth template stripped gold films and investigated by atomic force microscopy (AFM) at the level of individual molecules. The observed protein orientations are compared with results of nonactivated antibodies adsorbed on similar gold films and mica reference samples. We find that the behavior of Abs is similar for mica and gold when the protein are not treated (physisorption), whereas smaller contact area and larger heights are measured when Abs are treated (PIT). This is explained by assuming that the activated antibodies tend to be more upright compared with nonirradiated ones, thereby providing a better exposure of the binding sites. This finding matches the observed enhancement of Abs binding efficiency when PIT is used to functionalize gold surface of QCM-based biosensors.

  10. Single Molecule Characterization of UV-Activated Antibodies on Gold by Atomic Force Microscopy.

    PubMed

    Funari, R; Della Ventura, B; Altucci, C; Offenhäusser, A; Mayer, D; Velotta, R

    2016-08-16

    The interaction between proteins and solid surfaces can influence their conformation and therefore also their activity and affinity. These interactions are highly specific for the respective combination of proteins and solids. Consequently, it is desirable to investigate the conformation of proteins on technical surfaces, ideally at single molecule level, and to correlate the results with their activity. This is in particular true for biosensors where the conformation-dependent target affinity of an immobilized receptor determines the sensitivity of the sensor. Here, we investigate for the first time the immobilization and orientation of antibodies (Abs) photoactivated by a photonic immobilization technique (PIT), which has previously demonstrated to enhance binding capabilities of antibody receptors. The photoactivated immunoglobulins are immobilized on ultrasmooth template stripped gold films and investigated by atomic force microscopy (AFM) at the level of individual molecules. The observed protein orientations are compared with results of nonactivated antibodies adsorbed on similar gold films and mica reference samples. We find that the behavior of Abs is similar for mica and gold when the protein are not treated (physisorption), whereas smaller contact area and larger heights are measured when Abs are treated (PIT). This is explained by assuming that the activated antibodies tend to be more upright compared with nonirradiated ones, thereby providing a better exposure of the binding sites. This finding matches the observed enhancement of Abs binding efficiency when PIT is used to functionalize gold surface of QCM-based biosensors. PMID:27444884

  11. Quantitative Statistical Analysis of Atomic Scale Structural and Chemical Variations in Complex Oxides Interfaces

    NASA Astrophysics Data System (ADS)

    Yang, Hao

    Grain boundaries (GBs) are known to have far-reaching effects on the electrical and mechanical properties of materials. Understanding the atomic scale mechanisms behind these effects requires an accurate determination of the interplay between GB structure and composition. Based on the analysis of a range of grain boundaries using aberration corrected scanning transmission electron microscopy (STEM), a general structural units model has been derived for the structure of grain boundaries in various dense packing cubic materials including FCC metals, perovskites and fluorites. The similarities in the observed grain boundary structures of these materials originate from related space (and point) group symmetries of the parent structures. The presence of structural variations away from the general structural units model may be caused by frustrations of certain symmetry operations that result from the incorporation of point defects (vacancies and impurities). A clear understanding of the similarity and variation in grain boundary atomic structures will not only provide a means to infer the structure-property relationships in broad classes of materials, but also enables us eventually to effectively manipulate the GB structures to achieve better materials properties. To understand these chemical induced variations, and further quantify exactly how atomic scale variations at the boundary plane extend to the practical mesoscale operating length of the system, statistical analysis has been applied to the aberration corrected STEM Z-contrast images acquired from a series of undoped and doped SrTiO3 GBs. In order to understand the effects of oxygen vacancies incorporation, in-situ characterization of GB atomic structures were performed using the Environmental TEM under the reduced gas and heating environment. This analysis of GB similarity and variation provides insights into the structure-composition relationship in GBs to understand the influence of nonstoichiometry and dopant

  12. 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.

  13. 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.

  14. 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.

  15. 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)

  16. 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.

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

    PubMed

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

    2013-09-01

    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(-8) (detection mode), we expect the ATTA system to reach the design goal sensitivity to ppt concentrations of Kr in Xe in <2 h.

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

    NASA Technical Reports Server (NTRS)

    Kallman, T.

    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. This paper describes simple numerical experiments designed to examine some of these issues. Similar studies have been carried out previously in the context of solar UV lines by Gianetti et al. (2000); Savin & Laming (2002) and in the context of the iron M shell UTA in NGC 3783 by Netzer (2004).

  19. Protein folding at atomic resolution: analysis of autonomously folding supersecondary structure motifs by nuclear magnetic resonance.

    PubMed

    Sborgi, Lorenzo; Verma, Abhinav; Sadqi, Mourad; de Alba, Eva; Muñoz, Victor

    2013-01-01

    The study of protein folding has been conventionally hampered by the assumption that all single-domain proteins fold by an all-or-none process (two-state folding) that makes it impossible to resolve folding mechanisms experimentally. Here we describe an experimental method for the thermodynamic analysis of protein folding at atomic resolution using nuclear magnetic resonance (NMR). The method is specifically developed for the study of small proteins that fold autonomously into basic supersecondary structure motifs, and that do so in the sub-millisecond timescale (folding archetypes). From the NMR experiments we obtain hundreds of atomic unfolding curves that are subsequently analyzed leading to the determination of the characteristic network of folding interactions. The application of this approach to a comprehensive catalog of elementary folding archetypes holds the promise of becoming the first experimental approach capable of unraveling the basic rules connecting protein structure and folding mechanism. PMID:22987355

  20. 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.

  1. Cooperation between adsorbates accounts for the activation of atomic layer deposition reactions.

    PubMed

    Shirazi, Mahdi; Elliott, Simon D

    2015-04-14

    Atomic layer deposition (ALD) is a technique for producing conformal layers of nanometre-scale thickness, used commercially in non-planar electronics and increasingly in other high-tech industries. ALD depends on self-limiting surface chemistry but the mechanistic reasons for this are not understood in detail. Here we demonstrate, by first-principle calculations of growth of HfO2 from Hf(N(CH3)2)4-H2O and HfCl4-H2O and growth of Al2O3 from Al(CH3)3-H2O, that, for all these precursors, co-adsorption plays an important role in ALD. By this we mean that previously-inert adsorbed fragments can become reactive once sufficient numbers of molecules adsorb in their neighbourhood during either precursor pulse. Through the calculated activation energies, this 'cooperative' mechanism is shown to have a profound influence on proton transfer and ligand desorption, which are crucial steps in the ALD cycle. Depletion of reactive species and increasing coordination cause these reactions to self-limit during one precursor pulse, but to be re-activated via the cooperative effect in the next pulse. This explains the self-limiting nature of ALD.

  2. Binding activity of patterned concanavalin A studied by atomic force microscopy

    NASA Astrophysics Data System (ADS)

    Lebed, Kateryna; Pyka-Fosciak, Grazyna; Raczkowska, Joanna; Lekka, Malgorzata; Styczen, Jan

    2005-05-01

    The mode of protein immobilization plays a crucial role in the preparation of protein microarrays used for a wide spectrum of applications in analytical biochemistry. The microcontact printing technique was used to form a protein pattern using concanavalin A (Con A) since Con A belongs to a group of proteins widely used in analytical assays due to their selectivity as regards different kinds of carbohydrates. Atomic force microscopy was used to image surface topography, delivering information about the quality of the protein pattern. The force spectroscopy mode was used to verify the functional activity of deposited proteins via determination of the forces of interaction between Con A and carboxypeptidase Y bearing carbohydrate structure recognized by Con A. The calculated binding force between Con A and CaY was 105 ± 2 pN and it was compared with that measured for Con A deposited directly from the protein solution. The similarity of the value obtained for the interaction force was independent of the mode of protein deposition, thereby verifying that the microcontact printing technique did not influence the carbohydrate binding activity of Con A. The correlation between the surface topography of patterned samples and adhesion maps obtained showed the possible use of AFM for studying the chemical properties of different regions of the micropatterns produced.

  3. Metallic influence on the atomic structure and optical activity of ligand-protected nanoparticles: a comparison between Ag and Au.

    PubMed

    Hidalgo, Francisco; Noguez, Cecilia; Olvera de la Cruz, Monica

    2014-03-21

    Using time-perturbed density functional theory the optical activity of metal-thiolate compounds formed by highly symmetric Ag and Au nanoparticles (NPs) and a methyl-thiol molecule is studied after performing atomic optimizations and electronic calculations upon adsorption. Many different sites and orientations of the adsorbed molecule on icosahedral Ag and Au NPs of 55 atoms are considered. Upon molecular adsorption atomic distortions on Au NPs are induced while not on Ag, which causes higher molecular adsorption energies in Au than in Ag. Structural distortions and the specific molecular adsorption site and orientation result in chiral metal-thiolate NPs. Ag and Au compounds with similar chirality, according to Hausdorff chirality measurements, show different optical activity signatures, where circular dichroism spectra of Au NPs are more intense. These dissimilarities are attributed in part to the differences in the electronic density of states, which are a consequence of relativistic effects and the atomic distortion. It is concluded that the optical activity of Ag and Au compounds is due to different mechanisms, while in Au it is mainly due to the atomic distortion of the metallic NPs induced after molecular adsorption, in Ag it is defined by the adsorption site and molecular orientation with respect to the NP symmetry.

  4. Quantitative analysis of surface atom positions in a thick crystal as determined by a reconstructed exit wave.

    PubMed

    Kawasaki, Tadahiro; Taya, Masaki; Takai, Yoshizo

    2003-01-01

    Atomic structures of an Au (110) 2 x 1 reconstructed surface were analysed quantitatively using an exit wave reconstructed by the three-dimensional Fourier filtering method in high-resolution transmission electron microscopy. To reconstruct the exit wave in a relatively thick crystal, a practical criterion was proposed in the present analysis. In the 'pseudo-exit wave' obtained by the proposed criterion, relaxation of surface atoms was clearly visible in the top three layers. The atoms' displacement was measured to be about 5-20 pm. For quantitative analysis of the atom column positions, image contrast calculations were performed using a structural model of the Au (110) reconstructed surface. Calculations confirmed that the reconstructed pseudo-exit wave could represent the atom column positions directly with an accuracy of several pm, even for a relaxed surface, provided the sample thickness was <7 nm.

  5. 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

  6. 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

  7. {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.

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

    PubMed

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

    2016-05-14

    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. PMID:27109550

  9. Analysis of some integrals arising in the atomic three-electron problem

    NASA Astrophysics Data System (ADS)

    King, Frederick W.

    1991-12-01

    A detailed analysis is presented for the evaluation of atomic integrals of the form Fri1rj2rk3r-223rm31r12 ne-αr1-βr2-γr3dr1 dr2 dr3, which arise in several contexts of the three-electron atomic problem. All convergent integrals with i>=-2, j>=-2, k>=-2, m>=-1, and n>=-1 are examined. These integrals are solved by two distinct procedures. A majority of the integrals can be evaluated by a reduction of the three-electron integrals to integrals arising in the atomic two-electron integral problem. A second approach allows all integrals with the aforementioned indices to be evaluated by the use of Sack's expansion [J. Math. Phys. 5, 245 (1964)] of the interelectronic separation, which leads to a reduction of the above nine-dimensional integrals to a set of three-dimensional integrals. A discussion is given for the numerical evaluation of the three-dimensional integrals that arise.

  10. Nanosystem self-assembly pathways discovered via all-atom multiscale analysis.

    PubMed

    Pankavich, Stephen D; Ortoleva, Peter J

    2012-07-26

    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 time scale 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.

  11. 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.

  12. 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.

  13. 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

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

    NASA Astrophysics Data System (ADS)

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

    2015-02-01

    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.

  15. 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

  16. 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.

  17. The Use of Atomic Force Microscopy for Cytomorphological Analysis of Bacterial Infection Agents.

    PubMed

    Nemova, I S; Falova, O E; Potaturkina-Nesterova, N I

    2016-02-01

    Cytomorphological signs of bacterial infection agents were studied by atomic force microscopy. Analysis of the elastic mechanical characteristics of Staphylococcus spp. from the skin of patients with chronic dermatoses showed lower elasticity of S. aureus cell membrane in comparison with that of transitory flora representatives. Significant differences in characteristics of cell membrane relief and presence of fimA pathogenicity factor were detected in E. coli isolated from the reproductive tract mucosa of clinically healthy women and patients with inflammatory urogenital infections. PMID:26899849

  18. 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…

  19. Enhancement of electrical conductivity and electrochemical activity of hydrogenated amorphous carbon by incorporating boron atoms

    NASA Astrophysics Data System (ADS)

    Naragino, Hiroshi; Yoshinaga, Kohsuke; Nakahara, Akira; Tanaka, Sakuya; Honda, Kensuke

    2013-06-01

    Conductive boron-doped hydrogenated amorphous carbon (B-DLC) thin films were successfully synthesized with RF plasma-enhanced CVD method. By incorporating boron atoms in amorphous carbon, conduction types were changed from n- to p-type, and volume resistivity was decreased from 30.4 (non-doped) to 6.36 × 10-2 Ω cm (B/C = 2.500 atom%). B-DLC film with sp2/(sp2 + sp3) carbons of 75 atom% exhibited high resistance to electrochemically-induced corrosion in strong acid solution. Furthermore, it was clarified that boron atoms in DLC could enhance kinetics of hydrogen evolution during water electrolysis at B-DLC surface. B-DLC is, therefore, a promising electrode material for hydrogen production by increasing the concentration of boron atoms in B-DLC and enhancing the reactivity of H2 evolution.

  20. 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.

  1. 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

  2. High energy halogen atom reactions activated by nuclear transformations. Progress report, February 15, 1980-February 14, 1981

    SciTech Connect

    Not Available

    1981-02-01

    The stereochemistry of high energy /sup 18/F, /sup 34m/Cl, and /sup 76/Br substitution reactions involving enantiomeric molecules in the gas and condensed phase is studied. The gas to condensed state transition in halogen high energy chemistry, involving chlorine, bromine, and iodine activated by the (n,..gamma..) and (I.T.) processes in halomethanes, saturated and unsaturated hydrocarbons is being investigated in more detail. Special attention is given to defining the nature of the enhancement yields in the condensed phase. High energy halogen reactions in liquid and frozen aqueous solutions of organic and biomolecular solutes are studied in an attempt to learn more about these reactions. The applications of high energy chemistry techniques and theory to neutron activation analysis of biological systems are being continued. Special attention is given to developing procedures for trace molecular determinations in biological systems. The applications of hot halogen atoms as indicators of solute-solute interactions in liquid and frozen aqueous solutions of halogenated bases and nucleosides are being developed. Experiments are designed to explain the mechanisms of the radioprotection offered biomolecular solutes trapped within the frozen ice lattice. Reactions of bromine and iodine activated by isomeric transition with halogenated biomolecular solutes in liquid and frozen aqueous solutions are studied. The high energy reactions of iodine with the isomers of pentene have been studied in low pressure gaseous systems employing additives and rare gas moderators and liquid systems. Reactivity of excited complex formation and structural effects of electrophilic iodine attack on the pi-bond systems are studied.

  3. A combined coarse-grained and all-atom simulation of TRPV1 channel gating and heat activation

    PubMed Central

    Qin, Feng

    2015-01-01

    The transient receptor potential (TRP) channels act as key sensors of various chemical and physical stimuli in eukaryotic cells. Despite years of study, the molecular mechanisms of TRP channel activation remain unclear. To elucidate the structural, dynamic, and energetic basis of gating in TRPV1 (a founding member of the TRPV subfamily), we performed coarse-grained modeling and all-atom molecular dynamics (MD) simulation based on the recently solved high resolution structures of the open and closed form of TRPV1. Our coarse-grained normal mode analysis captures two key modes of collective motions involved in the TRPV1 gating transition, featuring a quaternary twist motion of the transmembrane domains (TMDs) relative to the intracellular domains (ICDs). Our transition pathway modeling predicts a sequence of structural movements that propagate from the ICDs to the TMDs via key interface domains (including the membrane proximal domain and the C-terminal domain), leading to sequential opening of the selectivity filter followed by the lower gate in the channel pore (confirmed by modeling conformational changes induced by the activation of ICDs). The above findings of coarse-grained modeling are robust to perturbation by lipids. Finally, our MD simulation of the ICD identifies key residues that contribute differently to the nonpolar energy of the open and closed state, and these residues are predicted to control the temperature sensitivity of TRPV1 gating. These computational predictions offer new insights to the mechanism for heat activation of TRPV1 gating, and will guide our future electrophysiology and mutagenesis studies. PMID:25918362

  4. Efficient CO Oxidation Using Dendrimer-Encapsulated Pt Nanoparticles Activated with <2% Cu Surface Atoms.

    PubMed

    Luo, Long; Zhang, Liang; Duan, Zhiyao; Lapp, Aliya S; Henkelman, Graeme; Crooks, Richard M

    2016-09-27

    In this paper, we show that the onset potential for CO oxidation electrocatalyzed by ∼2 nm dendrimer-encapsulated Pt nanoparticles (Pt DENs) is shifted negative by ∼300 mV in the presence of a small percentage (<2%) of Cu surface atoms. Theory and experiments suggest that the catalytic enhancement arises from a cocatalytic Langmuir-Hinshelwood mechanism in which the small number of Cu atoms selectively adsorb OH, thereby facilitating reaction with CO adsorbed to the dominant Pt surface. Theory suggests that these Cu atoms are present primarily on the (100) facets of the Pt DENs.

  5. Efficient CO Oxidation Using Dendrimer-Encapsulated Pt Nanoparticles Activated with <2% Cu Surface Atoms.

    PubMed

    Luo, Long; Zhang, Liang; Duan, Zhiyao; Lapp, Aliya S; Henkelman, Graeme; Crooks, Richard M

    2016-09-27

    In this paper, we show that the onset potential for CO oxidation electrocatalyzed by ∼2 nm dendrimer-encapsulated Pt nanoparticles (Pt DENs) is shifted negative by ∼300 mV in the presence of a small percentage (<2%) of Cu surface atoms. Theory and experiments suggest that the catalytic enhancement arises from a cocatalytic Langmuir-Hinshelwood mechanism in which the small number of Cu atoms selectively adsorb OH, thereby facilitating reaction with CO adsorbed to the dominant Pt surface. Theory suggests that these Cu atoms are present primarily on the (100) facets of the Pt DENs. PMID:27585091

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

    NASA Astrophysics Data System (ADS)

    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.

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

    PubMed

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

    2013-10-01

    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. PMID:23897739

  8. 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. PMID:27517608

  9. 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.

  10. 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.

  11. 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.

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

    PubMed

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

    2013-10-01

    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.

  13. Potential energy of H2 inside the C116 fullerene dimerization: An atomic analysis

    NASA Astrophysics Data System (ADS)

    EL-Barbary, A. A.

    2016-05-01

    DFT method has proved useful for its ability to provide an atomic analysis of the dimerization of fullerene molecules. Such atomic analysis may provide information that is not available by experimental methods. Here, the structures of possible three isomers of C116 fullerene dimerization obtained from two C58 fullerene cages have been optimized using DFT method at the B3LYP/6-31G(d,p) level of theory. The orientation of C58 fullerene and bond reorganization during the dimerization process have been studied. The transition structures and energy barriers between the three isomers are obtained. The potential energies of the H2 molecule motion along and perpendicular to the axial dimer with possible rotational angles are calculated. Also, the 13C NMR chemical shifts and electron density distribution have been applied to distinguish between the C58 fullerene cages and the three isomers of C116 fullerene dimerization. Our results show that the C116 fullerene dimerization could be considered to be good candidate for hydrogen storage.

  14. Direct analysis of silica by means of solid sampling graphite furnace atomic absorption spectrometry

    NASA Astrophysics Data System (ADS)

    Resano, M.; Mozas, E.; Crespo, C.; Pérez, J.; García-Ruiz, E.; Belarra, M. A.

    2012-05-01

    This paper reports on the use of solid sampling-graphite furnace atomic absorption spectrometry for the direct analysis of synthetic amorphous silica. In particular, determination of hazardous elements such As, Cd, Cr, Cu, Pb and Sb is investigated, as required by regulations of the food industry. The conclusion of the work is that, after proper optimization of the working conditions, paying particular attention to the atomization temperature and the use of proper modifiers (graphite powder, HNO3 or Pd), it is possible to develop suitable procedures that rely on the use of aqueous standard solutions to construct the calibration curves for all the elements investigated. The proposed method shows important benefits for the cost-effective analysis of such difficult samples in routine labs, permitting fast screening of those elements that are very rarely present in this type of sample, but also accurate quantification of those often found, while offering low limits of detection (always below 0.1 mg g- 1) that comply well with legal requirements, and precision levels that are fit for the purpose (approx. 6-9% R.S.D.).

  15. 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.

  16. Lacunarity analysis of atomic configurations: Application to ethanol-water mixtures

    NASA Astrophysics Data System (ADS)

    Gereben, Orsolya

    2015-09-01

    Lacunarity analysis is a scale-dependent method quantifying the translational invariance in patterns. In this work it is used to characterize the distribution of several subsets of atoms in molecular systems. Binary clusters and one-component (ethanol or water) hydrogen-bonded clusters of ethanol-water mixtures with 0 -100 mol % ethanol content were analyzed. Molecular dynamics simulations created the configurations, and all were in good agreement with the respective experimental x-ray diffraction data. Lacunarity analysis revealed that the placement of the one-component clusters at low concentration can be described by a multifractal distribution, especially in the case of ethanol. Most of the cases these clusters are not isolated entities, but form islands in binary clusters.

  17. RF Pulse Signal Integrity Analysis for Nonlinear Ended Microstrip Line Atom-Probe Tomography

    NASA Astrophysics Data System (ADS)

    Zhao, L.; Delamare, A.; Normand, A.; Delaroche, F.; Latry, O.; Vurpillot, F.; Ravelo, B.

    2016-03-01

    A signal integrity (SI) analysis of high voltage rectangular short pulses for the atom- probe system is explored in this paper. The operated RF transient pulse is considered for exciting on material sample inside an ultra-high vacuum (UHV) cryogenic chamber. The ns- duration pulse signal is injected into the cryogenic analysis chamber through the transmitting system mainly constituted by a microstrip interconnect line ended by optical controlled nonlinear load. The whole system frequency characterization is performed based on the S- parameter measurements. As expected, a challenging ultra-short rectangular shape pulse is exhibited by the pulser. Promising experimental results with the improvement of ion mass spectrum is demonstrated with the designed RF pulser.

  18. Lacunarity analysis of atomic configurations: application to ethanol-water mixtures.

    PubMed

    Gereben, Orsolya

    2015-09-01

    Lacunarity analysis is a scale-dependent method quantifying the translational invariance in patterns. In this work it is used to characterize the distribution of several subsets of atoms in molecular systems. Binary clusters and one-component (ethanol or water) hydrogen-bonded clusters of ethanol-water mixtures with 0-100mol% ethanol content were analyzed. Molecular dynamics simulations created the configurations, and all were in good agreement with the respective experimental x-ray diffraction data. Lacunarity analysis revealed that the placement of the one-component clusters at low concentration can be described by a multifractal distribution, especially in the case of ethanol. Most of the cases these clusters are not isolated entities, but form islands in binary clusters.

  19. Magnetically-modulated atomic force microscopy for analysis of soft matter systems.

    PubMed

    Kageshima, Masami

    2012-11-01

    Experimental method of studying viscoelasticity, a common idea to understand properties of microscopic biological soft matter systems, especially single biopolymer chains, using atomic force microscopy (AFM) with magnetically- driven cantilever is surveyed. The experimental setup of applying well-characterized excitation to the cantilever and the analysis method to derive the viscoelasticity of the system under study are briefly introduced. Examples of measuring viscoelasticity of single peptide molecule and single titin molecule are shown. Considering the close relation of viscoelasticity and the time-scale for nonequilibrium dynamics in soft matter, extension of the method to a frequency-resolved analysis is attempted. A result of measuring viscoelasticity spectrum of a single dextran chain is shown. Challenges in further progress of the method are also described. PMID:22039807

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

    PubMed Central

    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. PMID:26085952

  1. Single virus detection by means of atomic force microscopy in combination with advanced image analysis.

    PubMed

    Bocklitz, Thomas; Kämmer, Evelyn; Stöckel, Stephan; Cialla-May, Dana; Weber, Karina; Zell, Roland; Deckert, Volker; Popp, Jürgen

    2014-10-01

    In the present contribution virions of five different virus species, namely Varicella-zoster virus, Porcine teschovirus, Tobacco mosaic virus, Coliphage M13 and Enterobacteria phage PsP3, are investigated using atomic force microscopy (AFM). From the resulting height images quantitative features like maximal height, area and volume of the viruses could be extracted and compared to reference values. Subsequently, these features were accompanied by image moments, which quantify the morphology of the virions. Both types of features could be utilized for an automatic discrimination of the five virus species. The accuracy of this classification model was 96.8%. Thus, a virus detection on a single-particle level using AFM images is possible. Due to the application of advanced image analysis the morphology could be quantified and used for further analysis. Here, an automatic recognition by means of a classification model could be achieved in a reliable and objective manner. PMID:25196422

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

    NASA Astrophysics Data System (ADS)

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

    2015-07-01

    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.

  3. 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.

  4. 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.

  5. 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.

  6. 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

    Musil, Stanislav; Matoušek, Tomáš; Currier, Jenna M; Stýblo, Miroslav; Dědina, Jiří

    2014-10-21

    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).

  7. Optical nanofiber fabrication and analysis towards coupling atoms to superconducting qubits

    NASA Astrophysics Data System (ADS)

    Hoffman, Jonathan

    We describe advancements towards coupling superconducting qubits to neutral atoms. To produce a measurably large coupling, the atoms will need to be on the order of a few micrometers away from the qubit. A consequence of combining superconducting qubits and atoms is addressing their operational constraints, such as the deleterious light effects on superconducting systems and the magnetic field sensitivity of superconducting qubits. Our group proposes the use of optical-nanofiber-based optical dipole traps to confine atoms near the superconductor. Optical nanofibers (ONFs) have high-intensity evanescent waves that require less power than equivalent standard dipole traps. This thesis focuses on the fabrication and analysis of the behavior of ONFs. First we present the construction of the pulling apparatus. We outline the necessary steps for a typical pull, detailing the cleaning and alignment process. Then we examine the quality of the fibers by measuring their transmission and comparing our results to other reported measurements, demonstrating a two-order of magnitude decrease in loss. Next we present the modal evolution in ONFs using simulations and spectrogram analysis. We identify crucial elements to improve the transmission and demonstrate understanding of the modal dynamics during the pull. Then we study higher-order modes (HOMs) with ONFs using the first excited TE01, TM01, and HE21 modes. We demonstrate transmissions greater than 97% for 780 nm light when we launch the first excited LP11 family of modes through fibers with a 350 nm waist. This setup enables us to launch these three modes with high purity at the output, where less than 1% of the light is coupled to the fundamental mode. We then focus on the identification of modes on the ONF waist. First we use Rayleigh scattering to identify the modal content of an ONF. Bulk optics can convert the modes in the ONF, and we observe the controllable conversion of superpositions of modes. Finally, we use an

  8. 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.

  9. 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. PMID:27115043

  10. 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.

  11. 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.

  12. Analysis of active renin heterogeneity.

    PubMed

    Katz, S A; Malvin, R L; Lee, J; Kim, S H; Murray, R D; Opsahl, J A; Abraham, P A

    1991-09-01

    Active renin is a heterogeneous enzyme that can be separated into multiple forms with high-resolution isoelectric focusing. The isoelectric heterogeneity may result from differences in glycosylation between the different forms. In order to determine the relationship between active renin heterogeneity and differences in composition or attachment of oligosaccharides, two separate experiments were performed: (i) Tunicamycin, which interferes with normal glycosylation processing, increased the proportion of relatively basic renin forms secreted into the incubation media by rat renal cortical slices. (ii) Endoglycosidase F, which enzymatically removes carbohydrate from some classes of glycoprotein, similarly increased the proportion of relatively basic forms when incubated with active human recombinant renin. In addition, further studies with inhibitors of human renin activity revealed that the heterogeneous renin forms were similarly inhibited by two separate renin inhibitors. These results are consistent with the hypothesis that renin isoelectric heterogeneity is due in part to differences in carbohydrate moiety attachment and that the heterogeneity of renin does not influence access of direct renin inhibitors to the active site of renin.

  13. Analysis of active renin heterogeneity.

    PubMed

    Katz, S A; Malvin, R L; Lee, J; Kim, S H; Murray, R D; Opsahl, J A; Abraham, P A

    1991-09-01

    Active renin is a heterogeneous enzyme that can be separated into multiple forms with high-resolution isoelectric focusing. The isoelectric heterogeneity may result from differences in glycosylation between the different forms. In order to determine the relationship between active renin heterogeneity and differences in composition or attachment of oligosaccharides, two separate experiments were performed: (i) Tunicamycin, which interferes with normal glycosylation processing, increased the proportion of relatively basic renin forms secreted into the incubation media by rat renal cortical slices. (ii) Endoglycosidase F, which enzymatically removes carbohydrate from some classes of glycoprotein, similarly increased the proportion of relatively basic forms when incubated with active human recombinant renin. In addition, further studies with inhibitors of human renin activity revealed that the heterogeneous renin forms were similarly inhibited by two separate renin inhibitors. These results are consistent with the hypothesis that renin isoelectric heterogeneity is due in part to differences in carbohydrate moiety attachment and that the heterogeneity of renin does not influence access of direct renin inhibitors to the active site of renin. PMID:1908097

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

    DOE PAGES

    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 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

  15. 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.

  16. Neutron activation analysis of a penny

    NASA Astrophysics Data System (ADS)

    Stevens, Richard E.

    2000-04-01

    Neutron activation analysis has been used for many years as an analysis tool and as an educational tool to teach students about nuclear properties. This article presents an exercise in the neutron activation analysis of a penny which, due to the simplicity of the resulting gamma-ray spectra, is appropriate for general physics classes. Students express a great deal of interest both in seeing the reactor in use as well as determining the composition of something that is familiar to them.

  17. 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…

  18. LACBWR primary shield activation analysis

    SciTech Connect

    Nelson, L.L.; Lahti, G.P.; Johnson, W.J.

    1996-11-01

    Nuclear power plants in the US are required to estimate the costs of decommissioning to ensure that adequate funds are accumulated during the useful life of the plant. A major component of the decommissioning cost is the disposal of radioactive material, including material near the reactor created by neutron activation. An accurate assessment of the residual radioactivity in the reactor`s primary shield is necessary to determine this portion of the decommissioning demolition and disposal cost. This paper describes the efforts used to determine the activation levels remaining in the primary shield of the LaCrosse boiling water reactor (LACBWR), owned and operated by Dairyland Power Cooperative.

  19. Conference on Instrumental Activation Analysis: IAA 89

    NASA Astrophysics Data System (ADS)

    Vobecky, M.; Obrusnik, I.

    1989-05-01

    The proceedings contain 40 abstracts of papers all of which have been incorporated in INIS. The papers were centred on the applications of radioanalytical methods, especially on neutron activation analysis, x ray fluorescence analysis, PIXE analysis and tracer techniques in biology, medicine and metallurgy, measuring instruments including microcomputers, and data processing methods.

  20. Influence of the atomic force microscope tip on the multifractal analysis of rough surfaces.

    PubMed

    Klapetek, Petr; Ohlídal, Ivan; Bílek, Jindrich

    2004-12-01

    In this paper, the influence of atomic force microscope tip on the multifractal analysis of rough surfaces is discussed. This analysis is based on two methods, i.e. on the correlation function method and the wavelet transform modulus maxima method. The principles of both methods are briefly described. Both methods are applied to simulated rough surfaces (simulation is performed by the spectral synthesis method). It is shown that the finite dimensions of the microscope tip misrepresent the values of the quantities expressing the multifractal analysis of rough surfaces within both the methods. Thus, it was concretely shown that the influence of the finite dimensions of the microscope tip changed mono-fractal properties of simulated rough surface to multifractal ones. Further, it is shown that a surface reconstruction method developed for removing the negative influence of the microscope tip does not improve the results obtained in a substantial way. The theoretical procedures concerning both the methods, i.e. the correlation function method and the wavelet transform modulus maxima method, are illustrated for the multifractal analysis of randomly rough gallium arsenide surfaces prepared by means of the thermal oxidation of smooth gallium arsenide surfaces and subsequent dissolution of the oxide films. PMID:15556700

  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. Regioselective Dichlorination of a Non-Activated Aliphatic Carbon Atom and Phenolic Bismethylation by a Multifunctional Fungal Flavoenzyme.

    PubMed

    Chankhamjon, Pranatchareeya; Tsunematsu, Yuta; Ishida-Ito, Mie; Sasa, Yuzuka; Meyer, Florian; Boettger-Schmidt, Daniela; Urbansky, Barbara; Menzel, Klaus-Dieter; Scherlach, Kirstin; Watanabe, Kenji; Hertweck, Christian

    2016-09-19

    The regioselective functionalization of non-activated carbon atoms such as aliphatic halogenation is a major synthetic challenge. A novel multifunctional enzyme catalyzing the geminal dichlorination of a methyl group was discovered in Aspergillus oryzae (Koji mold), an important fungus that is widely used for Asian food fermentation. A biosynthetic pathway encoded on two different chromosomes yields mono- and dichlorinated polyketides (diaporthin derivatives), including the cytotoxic dichlorodiaporthin as the main product. Bioinformatic analyses and functional genetics revealed an unprecedented hybrid enzyme (AoiQ) with two functional domains, one for halogenation and one for O-methylation. AoiQ was successfully reconstituted in vivo and in vitro, unequivocally showing that this FADH2 -dependent enzyme is uniquely capable of the stepwise gem-dichlorination of a non-activated carbon atom on a freestanding substrate. Genome mining indicated that related hybrid enzymes are encoded in cryptic gene clusters in numerous ecologically relevant fungi. PMID:27559694

  3. Atomically Precise Growth of Catalytically Active Cobalt Sulfide on Flat Surfaces and within a Metal-Organic Framework via Atomic Layer Deposition.

    PubMed

    Peters, Aaron W; Li, Zhanyong; Farha, Omar K; Hupp, Joseph T

    2015-08-25

    Atomic layer deposition (ALD) has been employed as a new synthetic route to thin films of cobalt sulfide on silicon and fluorine-doped tin oxide platforms. The self-limiting nature of the stepwise synthesis is established through growth rate studies at different pulse times and temperatures. Additionally, characterization of the materials by X-ray diffraction and X-ray photoelectron spectroscopy indicates that the crystalline phase of these films has the composition Co9S8. The nodes of the metal-organic framework (MOF) NU-1000 were then selectively functionalized with cobalt sulfide via ALD in MOFs (AIM). Spectroscopic techniques confirm uniform deposition of cobalt sulfide throughout the crystallites, with no loss in crystallinity or porosity. The resulting material, CoS-AIM, is catalytically active for selective hydrogenation of m-nitrophenol to m-aminophenol, and outperforms the analogous oxide AIM material (CoO-AIM) as well as an amorphous CoSx reference material. These results reveal AIM to be an effective method of incorporating high surface area and catalytically active cobalt sulfide in metal-organic frameworks.

  4. Atomically Precise Growth of Catalytically Active Cobalt Sulfide on Flat Surfaces and within a Metal-Organic Framework via Atomic Layer Deposition.

    PubMed

    Peters, Aaron W; Li, Zhanyong; Farha, Omar K; Hupp, Joseph T

    2015-08-25

    Atomic layer deposition (ALD) has been employed as a new synthetic route to thin films of cobalt sulfide on silicon and fluorine-doped tin oxide platforms. The self-limiting nature of the stepwise synthesis is established through growth rate studies at different pulse times and temperatures. Additionally, characterization of the materials by X-ray diffraction and X-ray photoelectron spectroscopy indicates that the crystalline phase of these films has the composition Co9S8. The nodes of the metal-organic framework (MOF) NU-1000 were then selectively functionalized with cobalt sulfide via ALD in MOFs (AIM). Spectroscopic techniques confirm uniform deposition of cobalt sulfide throughout the crystallites, with no loss in crystallinity or porosity. The resulting material, CoS-AIM, is catalytically active for selective hydrogenation of m-nitrophenol to m-aminophenol, and outperforms the analogous oxide AIM material (CoO-AIM) as well as an amorphous CoSx reference material. These results reveal AIM to be an effective method of incorporating high surface area and catalytically active cobalt sulfide in metal-organic frameworks. PMID:26241521

  5. 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.

  6. New Display-type Analyzer for Three-dimensional Fermi Surface Mapping and Atomic Orbital Analysis

    SciTech Connect

    Takahashi, Nobuaki; Matsuda, Hiroyuki; Shigenai, Shin; Hirama, Yoshiteru; Matsui, Fumihiko; Hamada, Yoji; Nakanishi, Koji; Namba, Hidetoshi; Kitamura, Toshiro; Soejima, Hiroyoshi; Daimon, Hiroshi

    2007-01-19

    We have developed and installed a new Display-type ANAlyzer (DIANA) at Ritsumeikan SR center BL-7. We measured the angle-integrated energy distribution curve of poly-crystal gold and the photoelectron intensity angular distribution (PIAD) of HOPG to estimate the total energy resolution and to check the condition of the analyzer. The total energy resolution ({delta}E/E) is up to 0.78%, which is much higher than the old type. The PIAD of HOPG we obtained was the ring pattern as expected. Therefore, a detailed three-dimensional Fermi surface mapping and an analysis of the atomic orbitals constituting the electron energy bands are possible by combining them with a linearly polarized synchrotron radiation.

  7. 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.

  8. 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.

  9. 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)

  10. 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.

  11. New Display-type Analyzer for Three-dimensional Fermi Surface Mapping and Atomic Orbital Analysis

    NASA Astrophysics Data System (ADS)

    Takahashi, Nobuaki; Matsui, Fumihiko; Matsuda, Hiroyuki; Shigenai, Shin; Hirama, Yoshiteru; Hamada, Yoji; Nakanishi, Koji; Namba, Hidetoshi; Kitamura, Toshiro; Soejima, Hiroyoshi; Daimon, Hiroshi

    2007-01-01

    We have developed and installed a new Display-type ANAlyzer (DIANA) at Ritsumeikan SR center BL-7. We measured the angle-integrated energy distribution curve of poly-crystal gold and the photoelectron intensity angular distribution (PIAD) of HOPG to estimate the total energy resolution and to check the condition of the analyzer. The total energy resolution (ΔE/E) is up to 0.78%, which is much higher than the old type. The PIAD of HOPG we obtained was the ring pattern as expected. Therefore, a detailed three-dimensional Fermi surface mapping and an analysis of the atomic orbitals constituting the electron energy bands are possible by combining them with a linearly polarized synchrotron radiation.

  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. 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.

  14. 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

  15. 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.

  16. 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

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

    SciTech Connect

    Osborne, M.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.

  18. [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. PMID:24611406

  19. [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.

  20. Atomic and molecular data for space astronomy - Needs, analysis, and availability; 21st IAU General Assembly, Buenos Aires, Argentina, July 23-Aug. 1, 1991, Selected Papers

    NASA Technical Reports Server (NTRS)

    Smith, Peter L. (Editor); Wiese, Wolfgang L. (Editor)

    1992-01-01

    The present volume on atomic and molecular spectroscopic data for space astrophysics discusses scientific problems and laboratory data needs associated with the Hubble Space Telescope, atomic data needed for far ultraviolet astronomy with HUT and FUSE and for analysis of EUV and X-ray spectra, and data for observations of interstellar medium with the Hubble Space Telescope. Attention is also given to atomic and molecular data for analysis of IR spectra from ISO and SIRTF, atomic data from the opacity project, sources of atomic spectroscopic data for astrophysics, and summary of current molecular data bases.

  1. 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.

  2. 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

    2015-07-01

    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.

  3. 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)

  4. 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.

  5. Atomic Force Microscopic Analysis of the Effect of Lipid Composition on Liposome Membrane Rigidity.

    PubMed

    Takechi-Haraya, Yuki; Sakai-Kato, Kumiko; Abe, Yasuhiro; Kawanishi, Toru; Okuda, Haruhiro; Goda, Yukihiro

    2016-06-21

    Mechanical rigidity of the liposome membrane is often defined by the membrane bending modulus and is one of the determinants of liposome stability, but the quantitative experimental data are still limited to a few kinds of liposomes. Here, we used atomic force microscopy to investigate the membrane bending moduli of liposomes by immobilizing them on bovine serum albumin-coated glass in aqueous medium. The following lipids were used for liposome preparation: egg yolk phosphatidylcholine, dioleoylphosphatidylcholine, hydrogenated soybean phosphatidylcholine, dipalmitoylphosphatidylcholine, 1,2-dioleoyl-3-trimethylammonium-propane, cholesterol, and N-(carbonylmethoxypoly(ethylene glycol) 2000)-1,2-distearoyl-sn-glycero-3-phosphoethanolamine. By using liposomes of various compositions, we showed that the thermodynamic phase state of the membrane rather than the electric potential or liposome surface modification with poly(ethylene glycol) is the predominant determinant of the bending modulus, which decreased in the following order: solid ordered > liquid ordered > liquid disordered. By using the generalized polarization value of the Laurdan fluorescent probe, we investigated membrane rigidity in terms of membrane fluidity. Atomic force microscopic analysis was superior to the Laurdan method, especially in evaluating the membrane rigidity of liposomes containing hydrogenated soybean phosphatidylcholine and cholesterol. Positively charged liposomes with a large bending modulus were taken up by cells more efficiently than those with a small bending modulus. These findings offer a quantitative method of analyzing the membrane rigidity of nanosized liposomes with different lipid compositions and will contribute to the control of liposome stability and cellular uptake efficiency of liposomal formulations intended for clinical use. PMID:27232007

  6. 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.

  7. Estimating the activation energy of the displacement of Mg atoms in the channels of B25C4Mg1.42 crystals

    NASA Astrophysics Data System (ADS)

    Konovalikhin, S. V.; Ponomarev, V. I.

    2016-10-01

    The activation energy of displacement of Mg atoms through channels of B25C4Mg1.42 crystals is estimated using quantum chemical calculations (DFT (B3LYP potential), RHF, and UHF methods, 3-21G basis set) of the element of the structure modeling the channel and location of Mg atoms in it. The changes in the activation energy at the replacement of Mg atoms by Na and Li atoms were estimated. The greatest decreasing in the activation energy was detected for Li atoms. The obtained results can be regarded as a theoretical background for development of conducting systems based on B25C4Mg1.42 crystals.

  8. 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.

  9. 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

  10. Analysis on surface nanostructures present in hindwing of dragon fly (Sympetrum vulgatum) using atomic force microscopy.

    PubMed

    Selvakumar, Rajendran; Karuppanan, Karthikeyan K; Pezhinkattil, Radhakrishnan

    2012-12-01

    The present study involves the analysis of surface nanostructures and its variation present in the hind wing of dragon fly (Sympetrum vulgatum) using atomic force microscopy (AFM). The hindwing was dissected into 4 parts (D1-D4) and each dissected section was analyzed using AFM in tapping mode at different locations. The AFM analysis revealed the presence of irregular shaped nanostructures on the surface of the wing membrane with size varying between 83.25±1.79 nm to 195.08±10.25 nm. The size and shape of the nanostructure varied from tip (pterostigma) to the costa part. The membrane surface of the wing showed stacked arrangement leading to increase in size of the nanostructure. Such arrangement of the nanostructures has lead to the formation of nanometer sized valleys of different depth and length on the membrane surface giving them ripple wave morphology. The average roughness of the surface nanostructures varied from 18.58±3.12 nm to 24.25±8.33 nm. Surfaces of the wings had positive skewness in D1, D2 and D4 regions and negative skewness in D3 region. These surface nanostructures may contribute asymmetric resistance under mechanical loading during the flight by increasing the bending and torsional resistance of the wing. PMID:22099389

  11. Analysis of long-range bullet entrance holes by atomic absorption spectrophotometry and scanning electron microscopy.

    PubMed

    Ravreby, M

    1982-01-01

    Bullet residue and primer particles were analyzed by scanning electron microscopy with energy dispersive analysis (SEM-EDA) and by flame and flameless atomic absorption spectrophotometry (AAS). The residue and particles were on cloth targets around entrance holes produced by bullets fired at distances of 10 to 200 m. Primer particles and their chemical constituents were almost always detected by SEM-EDA around the holes produced by rifles and pistols fired at long ranges, and in many cases the barium and antimony associated with primer particles were detected by flameless AAS. Particles were also detected by SEM-EDA on the rear of bullets fired into and recovered from wooden blocks. Usually a hole caused by a bullet jacketed with gilding metal could be distinguished from one caused by a bullet jacketed with yellow brass alloy. Paint from bullet tips of military tracers was also detected. Analysis of the various residues around entrance holes provides a means for identifying the type of ammunition used. PMID:7097199

  12. Analysis on surface nanostructures present in hindwing of dragon fly (Sympetrum vulgatum) using atomic force microscopy.

    PubMed

    Selvakumar, Rajendran; Karuppanan, Karthikeyan K; Pezhinkattil, Radhakrishnan

    2012-12-01

    The present study involves the analysis of surface nanostructures and its variation present in the hind wing of dragon fly (Sympetrum vulgatum) using atomic force microscopy (AFM). The hindwing was dissected into 4 parts (D1-D4) and each dissected section was analyzed using AFM in tapping mode at different locations. The AFM analysis revealed the presence of irregular shaped nanostructures on the surface of the wing membrane with size varying between 83.25±1.79 nm to 195.08±10.25 nm. The size and shape of the nanostructure varied from tip (pterostigma) to the costa part. The membrane surface of the wing showed stacked arrangement leading to increase in size of the nanostructure. Such arrangement of the nanostructures has lead to the formation of nanometer sized valleys of different depth and length on the membrane surface giving them ripple wave morphology. The average roughness of the surface nanostructures varied from 18.58±3.12 nm to 24.25±8.33 nm. Surfaces of the wings had positive skewness in D1, D2 and D4 regions and negative skewness in D3 region. These surface nanostructures may contribute asymmetric resistance under mechanical loading during the flight by increasing the bending and torsional resistance of the wing.

  13. 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

  14. 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.

  15. Spectral analysis of irregular roughness artifacts measured by atomic force microscopy and laser scanning microscopy.

    PubMed

    Chen, Yuhang; Luo, Tingting; Ma, Chengfu; Huang, Wenhao; Gao, Sitian

    2014-12-01

    Atomic force microscopy (AFM) and laser scanning microscopy (LSM) measurements on a series of specially designed roughness artifacts were performed and the results characterized by spectral analysis. As demonstrated by comparisons, both AFM and LSM can image the complex structures with high resolution and fidelity. When the surface autocorrelation length increases from 200 to 500 nm, the cumulative power spectral density spectra of the design, AFM and LSM data reach a better agreement with each other. The critical wavelength of AFM characterization is smaller than that of LSM, and the gap between the measured and designed critical wavelengths is reduced with an increase in the surface autocorrelation length. Topography measurements of surfaces with a near zero or negatively skewed height distribution were determined to be accurate. However, obvious discrepancies were found for surfaces with a positive skewness owing to more severe dilations of either the solid tip of the AFM or the laser tip of the LSM. Further surface parameter evaluation and template matching analysis verified that the main distortions in AFM measurements are tip dilations while those in LSM are generally larger and more complex.

  16. 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.

  17. Exposure of GaAs to atomic hydrogen for cleaning prior to NEA photocathode activation

    SciTech Connect

    Sinclair, C.K.; Poelker, B.M.; Price, J.S.

    1998-12-31

    Creating an atomically clean semiconductor surface is an essential step in preparing negative electron affinity (NEA) photoemission cathodes. While bulk GaAs can be satisfactorily cleaned by chemical etching and in situ heat cleaning, many high polarization electron source materials are either much too thin, or have oxides and carbides which are too tightly bound, to be cleaned by these methods. Some polarized source candidate materials may be degraded during the heat cleaning step. It is well established that the exposure of many III-V, II-VI, and elemental semiconductors to atomic hydrogen, typically at elevated temperatures, produces semiconductor surfaces free of contamination. Furthermore, this cleaning, possibly followed by thermal annealing, leaves surfaces which show sharp LEED patterns, indicating good stoichiometry and surface order. Atomic hydrogen cleaning should eliminate the chemical etching step, and might reduce the temperature and/or temperature-time product presently used in forming NEA cathodes. The process is readily adaptable to in situ use in ultrahigh vaccum.

  18. 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.

  19. Analysis of photon-atom entanglement generated by Faraday rotation in a cavity

    SciTech Connect

    Lee, S. K. Y.; Law, C. K.

    2006-05-15

    Faraday rotation based on ac Stark shifts is a mechanism that can entangle the polarization states of photons and atoms. We study the entanglement dynamics inside an optical cavity, and characterize the photon-atom entanglement by using the Schmidt decomposition method. The time dependence of entanglement entropy and the effective Schmidt number are examined. We show that the entanglement can be enhanced by the cavity, and the entanglement entropy can be controlled by the initial fluctuations of atoms and photons.

  20. Ultramicro analysis for copper, cadmium, and zinc in human liver tissue by use of atomic absorption spectrophotometry and the heated graphite tube atomizer.

    PubMed

    Evenson, M A; Anderson, C T

    1975-04-01

    We describe a method of analysis for copper, cadmium, and zinc in a 15-mg (wet weight) sample of human liver by atomic absorption spectrophotometry. The sample is digested with nitric acid (1.0 mol/liter), evaporated, and dilute HNO3 (10 mmol/liter) added. The reconstituted acid mixture is injected into the graphite tube atomizer for analysis of Cu and Cd and aspirated into the air--acetylene flame for measurement of Zn. The absorbance for each metal is suppressed with increasing pH. NaNO3, KNO3, KCl, and NaCl (e.g.) quench the Cd absorbance in acid solutions that contain no protein, but not in the presence of protein. Metal ions added to the predigestion human liver sample at 10 percent and 100 percent of the intrinsic metal concentrations were, respectively, 93 percent and 90 percent accounted for analytically in the case of Cu, 98 percent and 102 percent for Zn, and 101 percent and 93 percent for Cd. Analysis of a National Bureau of Standards' Bovine Liver Standard Reference Material yielded results corresponding to 99 percent (Cu), 112 percent (Zn), and 91 percent (Cd) of the mean expected concentrations of these metals. The between-run coefficient of variation for the bovine liver material was 6 percent for Cu, 9 percent for Zn, and 10 percent for Cd. For 16 histologically normal samples of human liver, the mean values were: Cu, 26; Zn, 293; and Cd, 6.0 nanograms of metal per milligram dry weight, in agreement with values published previously. The method can be easily and reliably applied to small samples of liver obtained by closed-needle biopsy.

  1. Activation of C-Cl by ground-state aluminum atoms: an EPR and DFT investigation.

    PubMed

    Joly, Helen A; Newton, Trevor; Myre, Maxine

    2012-01-01

    The reaction of ground-state Al atoms with dichloromethane (CH(2)Cl(2)) in an adamantane matrix at 77 K yielded two mononuclear Al species. The magnetic parameters, extracted from the axial EPR spectrum of Species A/A' (g(1) = 2.0037, g(2) = g(3) = 2.0030, a(Al,1) = 1307 MHz, a(Al,2) = a(Al,3) = 1273 MHz, a(35Cl) = 34 MHz and a(37Cl) = 28 MHz) were assigned to the Al-atom insertion product, ClCH(2)AlCl. Density functional theory (DFT) calculations of the values of the Al and Cl hyperfine interaction (hfi) of the Cl(1)-Cl(2)gauche conformer were in close agreement with the experimental values of ClCH(2)AlCl. The second species, B/B', had identical magnetic parameters to those of ClCH(2)AlCl with the exception that the Al hfi was 15% smaller. Coordination of a ligand, possessing a lone pair of electrons, to the Al atom of the insertion product, [ClCH(2)AlCl]:X, could cause the a(Al) to decrease by 15%. Alternatively, it is possible that the Cl(1)-Cl(2) anti conformer of ClCH(2)AlCl is also isolated in the matrix. Support for the spectral assignments is given by calculation of the nuclear hfi of [ClCH(2)AlCl]:H(2)O and the Cl(1)-Cl(2) anti conformer of ClCH(2)AlCl using a DFT method. The potential energy hypersurface for an Al atom approaching CH(2)Cl(2), calculated at the B3LYP level, suggests that Al atom abstraction of Cl forming AlCl and CH(2)Cl is favoured in the gas phase. When produced in a matrix, the close proximity of AlCl and CH(2)Cl could account for the formation of ClCH(2)AlCl. EPR evidence was also found for the formation of the CHCl(2) radical. PMID:22086441

  2. 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…

  3. The atomic orbitals of the topological atom.

    PubMed

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

    2013-06-01

    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.

  4. A Theoretical Study of Single-Atom Catalysis of CO Oxidation Using Au Embedded 2D h-BN Monolayer: A CO-Promoted O2 Activation

    PubMed Central

    Mao, Keke; Li, Lei; Zhang, Wenhua; Pei, Yong; Zeng, Xiao Cheng; Wu, Xiaojun; Yang, Jinlong

    2014-01-01

    The CO oxidation behaviors on single Au atom embedded in two-dimensional h-BN monolayer are investigated on the basis of first-principles calculations, quantum Born-Oppenheim molecular dynamic simulations (BOMD) and micro-kinetic analysis. We show that CO oxidation on h-BN monolayer support single gold atom prefers an unreported tri-molecular Eley-Rideal (E-R) reaction, where O2 molecule is activated by two pre-adsorbed CO molecules. The formed OCOAuOCO intermediate dissociates into two CO2 molecules synchronously, which is the rate-limiting step with an energy barrier of 0.47 eV. By using the micro-kinetic analysis, the CO oxidation following the tri-molecular E-R reaction pathway entails much higher reaction rate (1.43 × 105 s−1) than that of bimolecular Langmuir-Hinshelwood (L-H) pathway (4.29 s−1). Further, the quantum BOMD simulation at the temperature of 300 K demonstrates the complete reaction process in real time. PMID:24962006

  5. A theoretical study of single-atom catalysis of CO oxidation using Au embedded 2D h-BN monolayer: a CO-promoted O₂ activation.

    PubMed

    Mao, Keke; Li, Lei; Zhang, Wenhua; Pei, Yong; Zeng, Xiao Cheng; Wu, Xiaojun; Yang, Jinlong

    2014-01-01

    The CO oxidation behaviors on single Au atom embedded in two-dimensional h-BN monolayer are investigated on the basis of first-principles calculations, quantum Born-Oppenheim molecular dynamic simulations (BOMD) and micro-kinetic analysis. We show that CO oxidation on h-BN monolayer support single gold atom prefers an unreported tri-molecular Eley-Rideal (E-R) reaction, where O2 molecule is activated by two pre-adsorbed CO molecules. The formed OCOAuOCO intermediate dissociates into two CO2 molecules synchronously, which is the rate-limiting step with an energy barrier of 0.47 eV. By using the micro-kinetic analysis, the CO oxidation following the tri-molecular E-R reaction pathway entails much higher reaction rate (1.43 × 10(5) s(-1)) than that of bimolecular Langmuir-Hinshelwood (L-H) pathway (4.29 s(-1)). Further, the quantum BOMD simulation at the temperature of 300 K demonstrates the complete reaction process in real time. PMID:24962006

  6. 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…

  7. A method to detect low-level 63Ni activity for estimating fast neutron fluence from the Hiroshima atomic bomb.

    PubMed

    Ito, Y; Shibata, T; Imamura, M; Shibata, S; Nogawa, N; Uwamino, Y; Shizuma, K

    1999-06-01

    The Hiroshima and Nagasaki atomic bombs resulted in the worst reported exposure of radiation to the human body. The data of survivors have provided the basis for the risk estimation for ionizing radiation, and thus are widely used as the basis of radiation safety. In this report we have studied a new method to detect the low-level 63Ni activity in copper samples in order to estimate the fast neutron fluence from the Hiroshima atomic bomb. Only 0.8 x 10(-3) Bq g(-1) of 63Ni is expected to be produced by the atomic bomb in a copper sample with the 63Cu(n, p)63Ni reaction at a distance of 500 m from the hypocenter. Our method has the required level of sensitivity for determination of the fast neutron fluence out to distances of at least 500 m, and perhaps as far as 1,000 m. We have already investigated and collected some bomb-irradiated copper samples for further study.

  8. 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. PMID:24734699

  9. Aberration-corrected STEM for atomic-resolution imaging and analysis.

    PubMed

    Krivanek, O L; Lovejoy, T C; Dellby, N

    2015-09-01

    Aberration-corrected scanning transmission electron microscopes are able to form electron beams smaller than 100 pm, which is about half the size of an average atom. Probing materials with such beams leads to atomic-resolution images, electron energy loss and energy-dispersive X-ray spectra obtained from single atomic columns and even single atoms, and atomic-resolution elemental maps. We review briefly how such electron beams came about, and show examples of applications. We also summarize recent developments that are propelling aberration-corrected scanning transmission electron microscopes in new directions, such as complete control of geometric aberration up to fifth order, and ultra-high-energy resolution EELS that is allowing vibrational spectroscopy to be carried out in the electron microscope.

  10. 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.

  11. 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.

  12. Human hair neutron activation analysis: Analysis on population level, mapping

    NASA Astrophysics Data System (ADS)

    Zhuk, L. I.; Kist, A. A.

    1999-01-01

    Neutron activation analysis is an outstanding analytical method having very wide applications in various fields. Analysis of human hair within last decades mostly based on neutron activation analysis is a very attractive illustration of the application of nuclear analytical techniques. Very interesting question is how the elemental composition differs in different areas or cities. In this connection the present paper gives average data and maps of various localities in the vicinity of drying-out Aral Sea and of various industrial cities in Central Asia.

  13. Practical Issues for Atom Probe Tomography Analysis of III-Nitride Semiconductor Materials.

    PubMed

    Tang, Fengzai; Moody, Michael P; Martin, Tomas L; Bagot, Paul A J; Kappers, Menno J; Oliver, Rachel A

    2015-06-01

    Various practical issues affecting atom probe tomography (APT) analysis of III-nitride semiconductors have been studied as part of an investigation using a c-plane InAlN/GaN heterostructure. Specimen preparation was undertaken using a focused ion beam microscope with a mono-isotopic Ga source. This enabled the unambiguous observation of implantation damage induced by sample preparation. In the reconstructed InAlN layer Ga implantation was demonstrated for the standard "clean-up" voltage (5 kV), but this was significantly reduced by using a lower voltage (e.g., 1 kV). The characteristics of APT data from the desorption maps to the mass spectra and measured chemical compositions were examined within the GaN buffer layer underlying the InAlN layer in both pulsed laser and pulsed voltage modes. The measured Ga content increased monotonically with increasing laser pulse energy and voltage pulse fraction within the examined ranges. The best results were obtained at very low laser energy, with the Ga content close to the expected stoichiometric value for GaN and the associated desorption map showing a clear crystallographic pole structure. PMID:25926083

  14. Atomic emission detection for gas chromatographic analysis of nitrogen-containing herbicides in water.

    PubMed

    Olson, N L; Carrell, R; Cummings, R; Rieck, R; Reimer, S

    1995-01-01

    A gas chromatography-atomic emission detection (GC-AED) system was used to analyze nitrogen-containing herbicides. Two methods of sample preparation were used to demonstrate the system's applicability. Method 1 was U.S. Environmental Protection Agency (EPA) Method 507. Method 2 was a modification of EPA Method 507 using larger sample volumes and smaller extract volumes to yield compound detection levels 30 times lower than detection levels from method 1. Analysis of replicate reagent water spikes with method 1 gave analyte recoveries ranging from 82 to 107%, with standard deviations of recovery of not more than 6.7%. Method 2 gave recoveries ranging from 50 to 112%, with a standard deviation of recovery of not more than 33%. A loss in recovery and precision with method 2 compared with method 1 was attributed to loss of more volatile analytes during extract concentration. Selectivity was demonstrated with solvent spiked with fuel oil and atrazine. Response factors generated with the GC-AED system showed compound-independent elemental linearity for analytes. Relative standard deviations of not more than 5.34% were obtained for 3 elements tested: nitrogen, sulphur, and chlorine. An elemental calibration mixture was prepared to validate traditional methods of quantitation. Samples were analyzed for nitrogen-containing herbicides, which were quantitated with both an analyte calibration and an elemental calibration, and results were compared.

  15. 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.

  16. Analysis of atomic force microscopy data for surface characterization using fuzzy logic

    SciTech Connect

    Al-Mousa, Amjed; Niemann, Darrell L.; Niemann, Devin J.; Gunther, Norman G.; Rahman, Mahmud

    2011-07-15

    In this paper we present a methodology to characterize surface nanostructures of thin films. The methodology identifies and isolates nanostructures using Atomic Force Microscopy (AFM) data and extracts quantitative information, such as their size and shape. The fuzzy logic based methodology relies on a Fuzzy Inference Engine (FIE) to classify the data points as being top, bottom, uphill, or downhill. The resulting data sets are then further processed to extract quantitative information about the nanostructures. In the present work we introduce a mechanism which can consistently distinguish crowded surfaces from those with sparsely distributed structures and present an omni-directional search technique to improve the structural recognition accuracy. In order to demonstrate the effectiveness of our approach we present a case study which uses our approach to quantitatively identify particle sizes of two specimens each with a unique gold nanoparticle size distribution. - Research Highlights: {yields} A Fuzzy logic analysis technique capable of characterizing AFM images of thin films. {yields} The technique is applicable to different surfaces regardless of their densities. {yields} Fuzzy logic technique does not require manual adjustment of the algorithm parameters. {yields} The technique can quantitatively capture differences between surfaces. {yields} This technique yields more realistic structure boundaries compared to other methods.

  17. Analysis of affinities between specific biological ligands using atomic force microscopy.

    PubMed

    Hu, Xiao; Dinu, Cerasela Zoica

    2015-12-21

    In the cell, protein-ligand recognition involves association and dissociation processes controlled by the affinity of the two binding partners and chemical harvesting of adenosine triphosphate energy. Fundamental knowledge of selected recognition events is currently translated in a synthetic environment for biosensors, immunoassays and diagnosis applications, or for pharmaceutical development. However, in order to advance such fields, one needs to determine the lifetime and binding efficiency of the two partners, as well as the complex energy landscape parameters. We employed contact mode atomic force microscopy to evaluate the association and dissociation events between streptavidin protein and its anti-streptavidin antibody ligand currently used for nucleotide array, ELISA, and flow cytometry applications, just to name a few. Using biotin as the control, our analysis helped characterize and differentiate multi- or single bonds of different strengths as well as associated energy landscapes to determine the protein-ligand structural arrangement at nanointerfaces and how these depend on the specificity of the ligand-recognition reaction. Our results suggest that understanding the importance of the rupture forces between a protein and its ligand could serve as the first step to protect on-off switches for biomedical research applications where specificity and selectivity are foremost sought. PMID:26525901

  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. 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.

  20. APPLICATIONS OF LASERS AND OTHER TOPICS: Active spectroscopy of excited iron atoms in an erosion laser plasma

    NASA Astrophysics Data System (ADS)

    Gladkov, S. M.; Koroteev, Nikolai I.; Rychev, M. V.; Fedorov, A. B.

    1987-05-01

    The method of coherent anti-Stokes Raman scattering (CARS) was used to probe the plasma of an optical spark formed on the surface of a steel target. Five strong resonances due to transitions between excited states of Fe I atoms were recorded in the CARS spectrum. A study was made of the kinetics and polarization properties of the scattered anti-Stokes radiation. The CARS method is recommended for the study of the plasma formed as a result of optical breakdown at solid targets because it can provide a universal means for the analysis of the chemical composition of the targets.

  1. Sub-part-per-billion analysis of aqueous lead colloids by ArF laser induced atomic fluorescence.

    PubMed

    Ho, S K; Cheung, N H

    2005-01-01

    Highly sensitive analysis of aqueous lead carbonate colloids was demonstrated by two-pulse laser-induced atomic fluorescence. The first laser pulse at 1064 nm ablated the sample solution to create an expanding plume. The colloids, being heavier, trailed behind and became concentrated. They were then intercepted by an ArF laser pulse that induced prompt atomic fluorescence at 405.8 nm from the lead atoms. The detection limit for lead was 0.24 ppb. Tap water was analyzed, and lead emissions were clearly observed. Time-resolved spectroscopy revealed that the efficient 193-nm excitation of the analytes was more universal than expected. That was confirmed by the successful application of the technique to colloids and alloys other than lead.

  2. 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.

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

    NASA Astrophysics Data System (ADS)

    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

    2015-12-01

    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.

  4. Experimental analysis of pressure controlled atomization process (PCAP) coatings for replacement of hard chromium plating

    SciTech Connect

    Tierney, J.C.; Glovan, R.J.; Witt, S.J.; Verbael, D.J.

    1995-12-31

    A four-phase experimental design was utilized to evaluate the abrasive wear and corrosion protection characteristics of VERSAlloy 50 coatings applied to AISI 4130 steel sheet. The coatings were applied with the Pressure Controlled Atomization Process (PCAP), a new thermal spray process being developed for the United States Air Force to replace hard chromium plating. Phase 1 of the design consisted of an evaluation of deposit profiles that were sprayed at five different standoff distances. Profile measurements yielded standard deviations ({sigma}) of the plume at each of the spray distances. Phase 2 consisted of a completely randomized series of eight spray tests in which the track gap or distance between consecutive spray passes was varied by amounts of 0.5{sigma}, 1{sigma}, 2{sigma}, and 3{sigma}. The sprayed test coupons were then evaluated for corrosion protection, abrasive wear resistance, microhardness, and porosity. Results from Phase 2 were used to determine the best track gap or overlap for Phase 3 and Phase 4 testing. Phase 3 consisted of 22-run central composite design. The test coupons were evaluated the same as in Phase 2. Statistical analysis of Phase 3 data revealed that the optimal system operating parameters produced coatings that would either provide superior corrosion protection or resistance to abrasive wear. Phase 4 consisted of four spray tests to validate the results obtained in Phase 3. Phase 4 test coupons were again evaluated with the same analysis as in Phases 2 and 3. The validation tests indicated that PCAP system operating parameters could be controlled to produce VERSAlloy 50 coatings with superior corrosion protection or resistance to abrasive wear.

  5. 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.

  6. 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.

  7. 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. PMID:24444143

  8. Radioactivity analysis in niobium activation foils

    SciTech Connect

    Mueller, G.E.

    1995-06-01

    The motivation for this study was to measure and analyze the activity of six (6) niobium (Nb) foils (the x-rays from an internal transition in Nb-93m) and apply this information with previously obtained activation foil data. The niobium data was used to determine the epithermal to MeV range for the neutron spectrum and fluence. The foil activation data was re-evaluated in a spectrum analysis code (STAY`SL) to provide new estimates of the exposure at the Los Alamos Spallation Radiation Effect Facility (LASREF). The activity of the niobium foils was measured and analyzed at the University of Missouri-Columbia (UMC) under the direction of Professor William Miller. The spectrum analysis was performed at the University of Missouri-Rolla (UMR) by Professor Gary Mueller.

  9. 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

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

    PubMed

    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

  11. Measurement of residual 152Eu activity induced by atomic bomb neutrons in Nagasaki and the contribution of environmental neutrons to this activity.

    PubMed

    Shizuma, Kiyoshi; Endo, Satoru; Hoshi, Masaharu; Takada, Jun; Ishikawa, Masayori; Iwatani, Kazuo; Hasai, Hiromi; Oka, Takamitsu; Fujita, Shoichiro; Watanabe, Tadaaki; Yamashita, Tomoaki; Imanaka, Tetsuji

    2003-06-01

    Residual 152Eu activities induced by neutrons from the Nagasaki atomic bomb were measured for nine mineral samples located up to 1,061 m in the slant range and one control sample at 2,850 m from the hypocenter. A chemical separation to prepare europium-enriched samples was performed for all samples, and gamma ray measurements were carried out with a low background well-type germanium detector. In this paper, the measured specific activities of 152Eu are compared with activation calculations based on the DS86 neutron fluence and the 93Rev one. The calculated-to-measured ratios are also compared with those of 60Co and 36Cl. The present results indicate that the measurements agree to the calculation within a factor of three as observed in the nuclear tests at Nevada. The activation level of environmental neutrons and the detection limit for 152Eu are also discussed. PMID:13678342

  12. Theoretical Analysis of the Adsorption of Late Transition Metal Atoms on the (001) Surface of Early Transition Metal Carbides

    SciTech Connect

    Rodriguez, J.A.; Gómez, T.; Florez, E.; Illas, F.

    2010-01-28

    The interaction of atoms of Groups 9, 10, and 11 with the (001) surface of TiC, ZrC, VC, and {delta}-MoC has been studied by means of periodic density functional calculations using slab models. The calculated values of the adsorption energy are rather large, especially for Groups 9 and 10 elements (E{sub ads} = 3-6 eV), but without clear trends along the series. Nevertheless, the analysis of the interaction at different sites indicates that the adsorbed atoms will be relatively mobile. Many of the admetals are electronically perturbed upon interaction with the carbide surfaces. Co, Ni, Cu, and Rh adatoms get positively or negatively charged, depending on the nature of the carbide substrate. Ir, Pd, Pt, and Au adatoms are always negatively charged. An analysis of the Bader charges for the most stable sites provides strong evidence that the most negative charge on the adatoms corresponds to the interaction with ZrC, followed by TiC. In the case of VC and {delta}-MoC, the charge on the adsorbed atoms may be slightly positive and of the same order for both carbides. The effect of the underlying carbide is large, with ZrC and TiC being predicted as the supports with the largest effect on the electronic structure of the adsorbed atoms with direct implications for the use of these systems in catalysis.

  13. Standardization and Correction of Artifacts in Atom-Probe Tomographic Analysis of Allende Nanodiamonds

    NASA Astrophysics Data System (ADS)

    Lewis, J. B.; Isheim, D.; Moutanabbir, O.; Floss, C.; Seidman, D. N.

    2015-07-01

    We use complementary atom-probe tomography and secondary ion mass spectrometry to measure the 12C/13C isotopic ratios of meteoritic nanodiamonds and thus determine their origins. We are investigating and quantifying instrumental artifacts.

  14. 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

  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. 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.

  17. 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.

  18. 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.

  19. Which hydrogen atom of toluene protonates PAH molecules in (+)-mode APPI MS analysis?

    PubMed

    Ahmed, Arif; Ghosh, Manik Kumer; Choi, Myung Chul; Choi, Cheol Ho; Kim, Sunghwan

    2013-03-01

    A previous study (Ahmed, A. et al., Anal. Chem. 84, 1146-1151( 2012) reported that toluene used as a solvent was the proton source for polyaromatic hydrocarbon compounds (PAHs) that were subjected to (+)-mode atmospheric-pressure photoionization. In the current study, the exact position of the hydrogen atom in the toluene molecule (either a methyl hydrogen or an aromatic ring hydrogen) involved in the formation of protonated PAH ions was investigated. Experimental analyses of benzene and anisole demonstrated that although the aromatic hydrogen atom of toluene did not contribute to the formation of protonated anthracene, it did contribute to the formation of protonated acridine. Thermochemical data and quantum mechanical calculations showed that the protonation of anthracene by an aromatic ring hydrogen atom of toluene is endothermic, while protonation by a methyl hydrogen atom is exothermic. However, protonation of acridine by either an aromatic ring hydrogen or a methyl hydrogen atom of toluene is exothermic. The different behavior of acridine and anthracene was attributed to differences in gas-phase basicity. It was concluded that both types of hydrogen in toluene can be used for protonation of PAH compounds, but a methyl hydrogen atom is preferred, especially for non-basic compounds.

  20. 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.

  1. Measurement of residual 60Co activity induced by atomic-bomb neutrons in Nagasaki and background contribution by environmental neutrons.

    PubMed

    Shizuma, Kiyoshi; Endo, Satoru; Hoshi, Masaharu; Takada, Jun; Iwatani, Kazuo; Hasai, Hiromi; Oka, Takamitsu; Shimazaki, Tatsuya; Okumura, Yutaka; Fujita, Shoichiro; Watanabe, Tadaaki; Imanaka, Tetsuji

    2002-12-01

    Residual 60Co activity in five steel samples induced by neutrons from the Nagasaki atomic bomb has been measured within about 1000 m from the hypocenter. The chemical separation of cobalt and nickel from steel samples was performed, and cobalt-enriched samples were prepared for all samples. Gamma-ray measurements were carried out with a low-background well-type germanium detector. The gamma-ray spectra for five samples were compared with the spectrum of a control sample to ensure that the observed 60Co was actually induced by A-bomb neutrons. The activation of cobalt by environmental neutrons was also investigated. It has been shown that the present 60Co data are consistent with earlier Hashizume's data. PMID:12674203

  2. Atomic ionization by sterile-to-active neutrino conversion and constraints on dark matter sterile neutrinos with germanium detectors

    NASA Astrophysics Data System (ADS)

    Chen, Jiunn-Wei; Chi, Hsin-Chang; Lin, Shin-Ted; Liu, C.-P.; Singh, Lakhwinder; Wong, Henry T.; Wu, Chih-Liang; Wu, Chih-Pan

    2016-05-01

    The transition magnetic moment of a sterile neutrino can give rise to its conversion to an active neutrino through radiative decay or nonstandard interaction (NSI) with matter. For sterile neutrinos of keV-mass as dark matter candidates, their decay signals are actively searched for in cosmic x-ray spectra. In this work, we consider the NSI that leads to atomic ionization, which can be detected by direct dark matter experiments. It is found that this inelastic scattering process for a nonrelativistic sterile neutrino has a pronounced enhancement in the differential cross section at energy transfer about half of its mass, manifesting experimentally as peaks in the measurable energy spectra. The enhancement effects gradually smear out as the sterile neutrino becomes relativistic. Using data taken with low-threshold low-background germanium detectors, constraints on sterile neutrino mass and its transition magnetic moment are derived and compared with those from astrophysical observations.

  3. Transforming Teacher Education, An Activity Theory Analysis

    ERIC Educational Resources Information Center

    McNicholl, Jane; Blake, Allan

    2013-01-01

    This paper explores the work of teacher education in England and Scotland. It seeks to locate this work within conflicting sociocultural views of professional practice and academic work. Drawing on an activity theory framework that integrates the analysis of these seemingly contradictory discourses with a study of teacher educators' practical…

  4. Computer-automated neutron activation analysis system

    SciTech Connect

    Minor, M.M.; Garcia, S.R.

    1983-01-01

    An automated delayed neutron counting and instrumental neutron activation analysis system has been developed at Los Alamos National Laboratory's Omega West Reactor (OWR) to analyze samples for uranium and 31 additional elements with a maximum throughput of 400 samples per day. 5 references.

  5. 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.

  6. 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

    2014-06-01

    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.

  7. 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.

  8. Quantification of the resist dissolution process: an in situ analysis using high speed atomic force microscopy

    NASA Astrophysics Data System (ADS)

    Santillan, Julius Joseph; Shichiri, Motoharu; Itani, Toshiro

    2016-03-01

    This work focuses on the application of a high speed atomic force microscope (HS-AFM) for the in situ visualization / quantification of the resist dissolution process. This technique, as reported in the past, has provided useful pointers on the formation of resist patterns during dissolution. This paper discusses about an investigation made on the quantification of what we refer to as "dissolution unit size" or the basic units of patterning material dissolution. This was done through the establishment of an originally developed analysis method which extracts the difference between two succeeding temporal states of the material film surface (images) to indicate the amount of change occurring in the material film at a specific span of time. Preliminary experiments with actual patterning materials were done using a positive-tone EUV model resist composed only of polyhydroxystyrene (PHS)-based polymer with a molecular weight of 2,500 and a polydispersity index of 1.2. In the absence of a protecting group, the material was utilized at a 50nm film thickness with post application bake of 90°C/60s. The resulting film is soluble in the alkali-based developer even without exposure. Results have shown that the dissolution components (dissolution unit size) of the PHS-based material are not of fixed size. Instead, it was found that aside from one constantly dissolving unit size, another, much larger dissolution unit size trend also occurs during material dissolution. The presence of this larger dissolution unit size suggests an occurrence of "polymer clustering". Such polymer clustering was not significantly present during the initial stages of dissolution (near the original film surface) but becomes more persistently obvious after the dissolution process reaches a certain film thickness below the initial surface.

  9. 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

  10. 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

    2010-04-01

    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.

  11. 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

    2010-04-01

    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. PMID:20106967

  12. 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.

  13. 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.

  14. 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.

  15. Neutron activation analysis of Etruscan pottery

    SciTech Connect

    Whitehead, J.; Silverman, A.; Ouellet, C.G.; Clark, D.D.; Hossain, T.Z

    1992-07-01

    Neutron activation analysis (NAA) has been widely used in archaeology for compositional analysis of pottery samples taken from sites of archaeological importance. Elemental profiles can determine the place of manufacture. At Cornell, samples from an Etruscan site near Siena, Italy, are being studied. The goal of this study is to compile a trace element concentration profile for a large number of samples. These profiles will be matched with an existing data bank in an attempt to understand the place of origin for these samples. The 500 kW TRIGA reactor at the Ward Laboratory is used to collect NAA data for these samples. Experiments were done to set a procedure for the neutron activation analysis with respect to sample preparation, selection of irradiation container, definition of activation and counting parameters and data reduction. Currently, we are able to analyze some 27 elements in samples of mass 500 mg with a single irradiation of 4 hours and two sequences of counting. Our sensitivity for many of the trace elements is better than 1 ppm by weight under the conditions chosen. In this talk, details of our procedure, including quality assurance as measured by NIST standard reference materials, will be discussed. In addition, preliminary results from data treatment using cluster analysis will be presented. (author)

  16. 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…

  17. Infrared spectra of CH3-MH through methane activation by laser-ablated Sn, Pb, Sb, and Bi atoms.

    PubMed

    Cho, Han-Gook; Andrews, Lester

    2012-08-23

    Methane activation has been carried out by laser-ablated Sn, Pb, Sb, and Bi atoms. All four metals generate the insertion complex (CH(3)-MH), but subsequent H-migration from C to M to form CH(2)-MH(2) and CH-MH(3) complexes is not observed. Our previous and present experimental and computational results indicate that the higher oxidation state complexes become less favored with increasing atomic mass in groups 14 and 15, which is opposite the general trend found for transition metals. The C-H bond insertion evidently occurs during reaction on sample condensation, and the product dissociates on broad-band photolysis afterward. The insertion complex contains a near right angle C-M-H moiety because of high p contribution from the metal center to the C-M and M-H bonds unlike many transition-metal analogues. The computed methylidene structures for these main group metals are not agostic possibly because of the absence of valence d-orbitals.

  18. 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.

  19. Quantum trajectory analysis of the two-mode three-level atom microlaser

    SciTech Connect

    Elsayed, Tarek A.; Aljalal, Abdulaziz

    2011-06-15

    We consider a single-atom laser (microlaser) operating on three-level atoms interacting with a two-mode cavity. The quantum statistical properties of the cavity field at steady state are investigated by the quantum trajectory method which is a Monte Carlo simulation applied to open quantum systems. It is found that a steady-state solution exists even when the detailed balance condition may not be guaranteed. The differences between a single-mode microlaser and a two-mode microlaser are highlighted. The second-order correlation function g{sup (2)}({tau}) of a single mode is studied and special attention is paid to the one-photon trapping state, for which a simple formula is derived for its correlation function. We show the effects of the velocity spread of the atoms used to pump the microlaser cavity on the second-order correlation function, trapping states, and phase transitions of the cavity field.

  20. 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. PMID:25747179

  1. 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.

  2. Free energy landscape of activation in a signaling protein at atomic resolution

    PubMed Central

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

    2015-01-01

    The interconversion between inactive and active protein states, traditionally described by two static structures, is at the heart of signaling. 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 NMR, and discover unexpected features underlying efficient signaling. 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. PMID:26073309

  3. 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.

  4. Laser assisted atom probe analysis of thin film on insulating substrate.

    PubMed

    Kodzuka, M; Ohkubo, T; Hono, K

    2011-05-01

    We demonstrate that the atom probe analyses of metallic thin films on insulating substrates are possible using laser assisted field evaporation. The tips with metallic thin film and insulating substrate (0.6-3 μm in thickness) were prepared by the lift-out and annular ion beam milling techniques on tungsten supports. In spite of the existence of thick insulating layer between the metallic film and the tungsten support, atom probe tomography with practical mass resolution, signal-to-noise ratio and spatial resolution was found to be possible using laser assisted field evaporation. PMID:21172729

  5. Holographic analysis of the microstructure of atomized liquid issuing from centrifugal injectors

    NASA Astrophysics Data System (ADS)

    Weclas, M.

    Holographs of sprays of atomized water issuing from centrifugal injectors have been analyzed, and the results are reported. The atomization spectrum was characterized by the presence of a principal maximum of distribution and distinct local maxima. Those extremum values occurred for the same droplet diameters, independently of the size of the injector and of the supply pressure. The character of the spectrum is independent of the distance from the injector outlet at any cross section of the spray. Most of the droplets are 20 to 60 microns in diameter, and the number of droplets within the 60 to 280 micron interval increases with increasing supply pressure.

  6. 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.

  7. Specific activities of 60Co and 152Eu in samples collected from the Atomic-Bomb Dome in Hiroshima.

    PubMed

    Shizuma, K; Iwatani, K; Hashi, H; Oka, T; Morishima, H; Hoshi, M

    1992-06-01

    Neutron-induced activities 60Co and 152Eu have been measured for samples collected from the Atomic-Bomb Dome locating at 161 m from the hypocenter of the Hiroshima Bomb. Specific activities 60Co/Co and 152Eu/Eu at the time of the detonation have been determined as 10.0 +/- 1.0 Bq mg-1 (steel sample S4) and 80 +/- 9 Bq mg-1 (granite sample G1), respectively. Detailed measurements of 60Co and 152Eu activities for samples collected from various locations of the Dome show almost no directional dependence whether the sample faced to the epicenter or not, nor vertical height dependence between 17 m height and the ground level. In addition, 152Eu was not detected in the sample collected from the basement. It has been shown that the present 60Co activity value, the nearest steel one to the hypocenter, as well as other short distance data are systematically lower than the calculated values based on the neutron fluence of the DS86.

  8. 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

  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. 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

  11. Locating Active-site Hydrogen Atoms in D-Xylose Isomerase: Time-of-Flight Neutron Diffraction.

    SciTech Connect

    Bunick, G J

    2006-01-01

    Time-of-flight neutron diffraction has been used to locate hydrogen atoms that define the ionization states of amino acids in crystals of D-xylose isomerase. This enzyme, from Streptomyces rubiginosus, is one of the largest enzymes studied to date at high resolution (1.8 ) by this method. We have determined the position and orientation of a metal ion-bound water molecule that is located in the active site of the enzyme; this water has been thought to be involved in the isomerization step in which D-xylose is converted to D-xylulose or D-glucose to D-fructose. It is shown to be water (rather than a hydroxyl group) under the conditions of measurement (pH 8.0). Our analyses also reveal that one lysine probably has an -NH2 terminal group (rather than NH3+). The ionization state of each histidine residue was also determined.

  12. 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.

  13. Insights into activation and RNA binding of trp RNA-binding attenuation protein (TRAP) through all-atom simulations.

    PubMed

    Murtola, Teemu; Vattulainen, Ilpo; Falck, Emma

    2008-06-01

    Tryptophan biosynthesis in Bacillus stearothermophilus is regulated by a trp RNA binding attenuation protein (TRAP). It is a ring-shaped 11-mer of identical 74 residue subunits. Tryptophan binding pockets are located between adjacent subunits, and tryptophan binding activates TRAP to bind RNA. Here, we report results from all-atom molecular dynamics simulations of the system, complementing existing extensive experimental studies. We focus on two questions. First, we look at the activation mechanism, of which relatively little is known experimentally. We find that the absence of tryptophan allows larger motions close to the tryptophan binding site, and we see indication of a conformational change in the BC loop. However, complete deactivation seems to occur on much longer time scales than the 40 ns studied here. Second, we study the TRAP-RNA interactions. We look at the relative flexibilities of the different bases in the complex and analyze the hydrogen bonds between the protein and RNA. We also study the role of Lys37, Lys56, and Arg58, which have been experimentally identified as essential for RNA binding. Hydrophobic stacking of Lys37 with the nearby RNA base is confirmed, but we do not see direct hydrogen bonding between RNA and the other two residues, in contrast to the crystal structure. Rather, these residues seem to stabilize the RNA-binding surface, and their positive charge may also play a role in RNA binding. Simulations also indicate that TRAP is able to attract RNA nonspecifically, and the interactions are quantified in more detail using binding energy calculations. The formation of the final binding complex is a very slow process: within the simulation time scale of 40 ns, only two guanine bases become bound (and no others), indicating that the binding initiates at these positions. In general, our results are in good agreement with experimental studies, and provide atomic-scale insights into the processes. PMID:18186477

  14. Analysis of flow development in centrifugal atomization: Part I. Film thickness of a fully spreading melt

    NASA Astrophysics Data System (ADS)

    Zhao, Y. Y.

    2004-09-01

    Centrifugal atomization of metal melts is a cost-effective process for powder production and spray deposition. The properties of the as-produced powder and deposit are determined primarily by the characteristics of the atomized droplets, which in turn are largely dependent on the flow development of the melt on the atomizer. This paper develops a model for analysing the flow development of a fully spreading melt on and off the atomizing cup. The model can be used to calculate the velocity and film thickness of the melt as a function of melt volume flow rate, cup rotation speed, cup radius and cup slope angle, as well as to predict the trajectory of the spray off the cup. The model implies that the disintegration of a fully spreading melt takes place in the region just off the cup edge and the film thickness at the cup edge is a critical factor determining the sizes of the resultant droplets. The film thickness at the cup edge is shown to decrease with decreasing volume flow rate, with increasing cup rotation speed, with increasing cup radius and with decreasing cup slope angle.

  15. Multielement determination of heavy metals in water samples by continuous powder introduction microwave-induced plasma atomic emission spectrometry after preconcentration on activated carbon

    NASA Astrophysics Data System (ADS)

    Jankowski, Krzysztof; Yao, Jun; Kasiura, Krzysztof; Jackowska, Adrianna; Sieradzka, Anna

    2005-03-01

    A novel continuous powder introduction microwave-induced plasma atomic emission spectrometry method (CPI-MIP-AES) has been developed for trace determination of metals in ground and tap water samples after preconcentration on activated carbon. The experimental setup consisted of integrated rectangular cavity TE 101 and vertically positioned plasma torch. The technical arrangement of the sample introduction system has been designed based on the fluidized bed concept. The satisfactory signal stability required for sequential analysis was attained owing to the vertical plasma configuration, as well as the plasma gas flow rate compatibility with sample introduction flow rate. The elements of interest (Cd, Cu, Cr, Fe, Mn, Pb, Zn) were preconcentrated in a batch procedure at pH 8-8.5 after addition of activated carbon and then, after filtering and drying of the activated carbon suspension, introduced to the MIP by the CPI system. An enrichment factor of about 1000-fold for a sample volume of 1 l was obtained. The detection limit values for the proposed method were 17-250 ng l -1. The proposed method was validated by analyzing the certified reference materials: SRW "Warta" Synthetic River Water and BCR CRM 399 major elements in freshwater. The method was successfully applied to the determination of the heavy metals in tap water samples.

  16. 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

  17. 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.

  18. The Use of Contact Mode Atomic Force Microscopy in Aqueous Medium for Structural Analysis of Spinach Photosynthetic Complexes.

    PubMed

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

    2015-10-01

    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.

  19. Atomic data and spectral analysis of carbon, nitrogen, oxygen and silicon ions observed with the International Ultraviolet Explorer

    NASA Technical Reports Server (NTRS)

    Pradhan, Anil K.

    1992-01-01

    According to the plan presented in the original proposal we have now completed most of the atomic calculations involving collision strengths and rate coefficients for electron impact excitation of C II, N III, and O IV ions. These have been reported in the first two publications appended with this report. We have now moved into the applications phase of the project with the new data being used to analyze the International Ultraviolet Explorer (IUE) observations of a variety of objects, as described in the third publication recently submitted (also appended). The analysis and interpretation of archival data will continue well into the next year with several collaborators that the PI and Co-PI are involved with. In addition, the atomic calculations on Si II have been started.

  20. 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.

  1. 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.

  2. 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...

  3. Sampling and analysis of particulate matter by glow discharge atomic emission and mass spectrometries.

    PubMed

    Marcus, R K; Dempster, M A; Gibeau, T E; Reynolds, E M

    1999-08-01

    The direct introduction of particulate matter into glow discharge atomic emission and mass spectrometry sources through a particle beam/momentum separator apparatus is described. Vacuum action through a narrow (0.0625 in. i.d.) stainless steel tube allows the introduction of discrete samples of NIST SRM 1648 urban particulate matter (UPM) and caffeine in powder form. Introduction of "ambient" airborne particulate matter is also possible. Particles passing through the aerodynamic momentum separator impinge on the heated (∼200-250 °C) inner surface of the glow discharge plasma volume and are flash-vaporized. The resultant atoms/molecules are subjected to excitation/ionization collisions within the low-pressure (0.5-5 Torr of He or Ar) plasma, producing characteristic photon emission and/or signature ionic species. In this way, atomic emission and mass spectrometry identification of particle constituents is possible. Basic design aspects of the apparatus are presented, and demonstrations of atomic emission detection of the constituents in the NIST SRM illustrate the general characteristics of the approach. Transient atomic emission signals are captured for the introduction of preweighed, discrete samples, with the integrated areas used to construct analytical response curves. Limits of detection using this relatively simple atomic emission system are on the order of tens of nanograms for sample masses of ∼50 μg. Mass spectrometric monitoring of introduced caffeine particles and a mixture of polycyclic aromatic hydrocarbons (PAHs) illustrates the ability of the glow discharge plasma to produce high-quality, library (electron impact) searchable mass spectra of molecular species while also yielding isotopic identification of elemental components of the UPM. Limits of detection for Fe in the NIST SRM are on the order of 175 ng of material, equivalent to ∼7 ng of analyte Fe. It is believed that the small size, low power consumption, ease of operation, and multimode

  4. Comparative Sensitivity Analysis of Muscle Activation Dynamics.

    PubMed

    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

  5. 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.

  6. 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.

  7. 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.

  8. Methods for atom probe analysis of microgradients in functionally graded cemented carbides.

    PubMed

    Frykholm, R; Jansson, B; Andrén, H-O

    2002-01-01

    Methods to prepare needle-shaped specimens for atom probe field ion microscopy from near surface regions have been developed. The material used was a cemented carbide with a composition gradient towards the surface, but the method is equally applicable for other materials. The preparation technique involves dimple grinding, electropolishing and focused ion beam (FIB) milling. The use of FIB milling allows for specimen preparation of materials which due to the preferential etching of different phases are difficult to electropolish. The technique also allows for preparation of specimens at well defined depth from the sample surface, selection of phase to be analysed, and to sharpen and re-use already analysed specimens. Atom probe analyses of the near surface zone region in a gradient sintered WC-Ti(C,N)-TaC-Co cemented carbide are presented.

  9. Chaotic quantum ratchets and filters with cold atoms in optical lattices: Analysis using Floquet states

    SciTech Connect

    Hur, G.; Creffield, C.E.; Jones, P.H.; Monteiro, T.S.

    2005-07-15

    Recently, cesium atoms in optical lattices subjected to cycles of unequally spaced pulses have been found to show interesting behavior: they represent an experimental demonstration of a Hamiltonian ratchet mechanism, and they show strong variability of the dynamical localization lengths as a function of initial momentum. The behavior differs qualitatively from corresponding atomic systems pulsed with equal periods, which are a textbook implementation of a well-studied quantum chaos paradigm, the quantum {delta}-kicked rotor ({delta}-QKR). We investigate here the properties of the corresponding eigenstates (Floquet states) in the parameter regime of the recent experiments and compare them with those of the eigenstates of the {delta}-QKR at similar kicking strengths. We show that by studying the properties of the Floquet states we can shed light on the form of the observed ratchet current, as well as variations in the dynamical localization length.

  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 an atom laser based on the spatial control of the scattering length

    SciTech Connect

    Carpentier, Alicia V.; Michinel, Humberto; Rodas-Verde, Maria I.; Perez-Garcia, Victor M.

    2006-07-15

    In this paper we analyze atom lasers based on the spatial modulation of the scattering length of a Bose-Einstein condensate. We demonstrate, through numerical simulations and approximate analytical methods, the controllable emission of matter-wave bursts and study the dependence of the process on the spatial shape of the scattering length along the axis of emission. We also study the role of an additional modulation of the scattering length in time.

  12. Interfacial atomic structure analysis at sub-angstrom resolution using aberration-corrected STEM

    NASA Astrophysics Data System (ADS)

    Hsiao, Chien-Nan; Kuo, Shou-Yi; Lai, Fang-I.; Chen, Wei-Chun

    2014-10-01

    The atomic structure of a SiGe/Si epitaxial interface grown via molecular beam epitaxy on a single crystal silicon substrate was investigated using an aberration-corrected scanning transmittance electron microscope equipped with a high-angle annular dark-field detector and an energy-dispersive spectrometer. The accuracy required for compensation of the various residual aberration coefficients to achieve sub-angstrom resolution with the electron optics system was also evaluated. It was found that the interfacial layer was composed of a silicon single crystal, connected coherently to epitaxial SiGe nanolaminates. In addition, the distance between the dumbbell structures of the Si and Ge atoms was approximately 0.136 nm at the SiGe/Si interface in the [110] orientation. The corresponding fast Fourier transform exhibited a sub-angstrom scale point resolution of 0.78 Å. Furthermore, the relative positions of the atoms in the chemical composition line scan signals could be directly interpreted from the corresponding incoherent high-angle annular dark-field image.

  13. 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.

  14. Plutonium and Uranium Atom Ratios and Activity Levels in Cochiti Lake Bottom Sediments Provided by Pueblo de Cochiti

    SciTech Connect

    Gallaher, B.M.; Efurd, D.W.; Rokop, D.J.; Benjamin, T.M.

    1999-05-01

    Historical operations at the Los Alamos National Laboratory have contaminated stream sediments with plutonium and other radionuclides. A small portion of these contaminated sediments has been carried by floods into the Rio Grande drainage system, eventually to be trapped by Cochiti Lake located on Pueblo de Cochiti lands approximately 8 km downstream of the Laboratory. In this study, lake bottom sediment samples provided by the Pueblo de Cochiti were analyzed by thermal ionization mass spectrometry to determine plutonium and uranium activity levels and isotopic atom ratios. This specialized analytical method allows us to take isotopic fingerprints of radionuclides found in the sediment and to determine how much plutonium and uranium came from the Laboratory and how much was deposited by worldwide fallout or is natural. Two distinct types of samples were processed: segments of a continuous vertical core of the entire accumulated sediment sequence and other samples from across the lake bottom at the water/sediment interface. Based on measurement of the {sup 240}Pu/{sup 239}Pu atom ratio, Laboratory-derived plutonium is present in eight of nine samples at the core site. On a depth-weighted basis, approximately one-half of the {sup 239}Pu and {sup 240}Pu came from early operations at the Laboratory; the remaining plutonium came from fallout dispersed by above-ground nuclear tests. In contrast to the core site, the samples from the other locations showed little or no evidence of Laboratory-derived plutonium, with more than 90 percent of the plutonium attributable to fallout. The overall amount of plutonium in all the samples is of the same magnitude as other reservoirs in the region. The net increase in plutonium over upstream reservoirs unaffected by Laboratory activities is a maximum of 0.014 pCi/g or 3.5 times. All of the samples reflect natural uranium compositions. Laboratory-derived uranium is not identifiable, presumably because the sediment contains abundant

  15. Scalable histopathological image analysis via active learning.

    PubMed

    Zhu, Yan; Zhang, Shaoting; Liu, Wei; Metaxas, Dimitris N

    2014-01-01

    Training an effective and scalable system for medical image analysis usually requires a large amount of labeled data, which incurs a tremendous annotation burden for pathologists. Recent progress in active learning can alleviate this issue, leading to a great reduction on the labeling cost without sacrificing the predicting accuracy too much. However, most existing active learning methods disregard the "structured information" that may exist in medical images (e.g., data from individual patients), and make a simplifying assumption that unlabeled data is independently and identically distributed. Both may not be suitable for real-world medical images. In this paper, we propose a novel batch-mode active learning method which explores and leverages such structured information in annotations of medical images to enforce diversity among the selected data, therefore maximizing the information gain. We formulate the active learning problem as an adaptive submodular function maximization problem subject to a partition matroid constraint, and further present an efficient greedy algorithm to achieve a good solution with a theoretically proven bound. We demonstrate the efficacy of our algorithm on thousands of histopathological images of breast microscopic tissues. PMID:25320821

  16. Statistical analysis of atom probe data: detecting the early stages of solute clustering and/or co-segregation.

    PubMed

    Hyde, J M; Cerezo, A; Williams, T J

    2009-04-01

    Statistical analysis of atom probe data has improved dramatically in the last decade and it is now possible to determine the size, the number density and the composition of individual clusters or precipitates such as those formed in reactor pressure vessel (RPV) steels during irradiation. However, the characterisation of the onset of clustering or co-segregation is more difficult and has traditionally focused on the use of composition frequency distributions (for detecting clustering) and contingency tables (for detecting co-segregation). In this work, the authors investigate the possibility of directly examining the neighbourhood of each individual solute atom as a means of identifying the onset of solute clustering and/or co-segregation. The methodology involves comparing the mean observed composition around a particular type of solute with that expected from the overall composition of the material. The methodology has been applied to atom probe data obtained from several irradiated RPV steels. The results show that the new approach is more sensitive to fine scale clustering and co-segregation than that achievable using composition frequency distribution and contingency table analyses.

  17. 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. PMID:23855499

  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. Data analysis and other considerations concerning the study of precipitation in Al-Mg-Si alloys by Atom Probe Tomography.

    PubMed

    Zandbergen, M W; Xu, Q; Cerezo, A; Smith, G D W

    2015-12-01

    Atom Probe Tomography (APT) analysis and hardness measurements were used to characterize the early stages of precipitation in an Al-0.51 at%Mg-0.94 at%Si alloy as reported in the accompanying Acta Materialia paper [1]. The changes in microstructure were investigated after single-stage or multi-stage heat treatments including natural ageing at 298 K (NA), pre-ageing at 353 K (PA), and automotive paint-bake ageing conditions at 453 K (PB). This article provides and a detailed report on the experimental conditions and the data analysis methods used for this investigation. Careful design of experimental conditions and analysis methods was carried out to obtain consistent and reliable results. Detailed data on clustering for prolonged NA and PA treatments have been reported.

  20. 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.

  1. Data analysis and other considerations concerning the study of precipitation in Al–Mg–Si alloys by Atom Probe Tomography

    PubMed Central

    Zandbergen, M.W.; Xu, Q.; Cerezo, A.; Smith, G.D.W.

    2015-01-01

    Atom Probe Tomography (APT) analysis and hardness measurements were used to characterize the early stages of precipitation in an Al–0.51 at%Mg–0.94 at%Si alloy as reported in the accompanying Acta Materialia paper [1]. The changes in microstructure were investigated after single-stage or multi-stage heat treatments including natural ageing at 298 K (NA), pre-ageing at 353 K (PA), and automotive paint-bake ageing conditions at 453 K (PB). This article provides Supporting information and a detailed report on the experimental conditions and the data analysis methods used for this investigation. Careful design of experimental conditions and analysis methods was carried out to obtain consistent and reliable results. Detailed data on clustering for prolonged NA and PA treatments have been reported. PMID:26958619

  2. Electrodermal activity analysis during affective haptic elicitation.

    PubMed

    Greco, Alberto; Valenza, Gaetano; Nardelli, Mimma; Bianchi, Matteo; Lanata, Antonio; Scilingo, Enzo Pasquale

    2015-08-01

    This paper investigates how the autonomic nervous system dynamics, quantified through the analysis of the electrodermal activity (EDA), is modulated according to affective haptic stimuli. Specifically, a haptic display able to convey caress-like stimuli is presented to 32 healthy subjects (16 female). Each stimulus is changed according to six combinations of three velocities and two forces levels of two motors stretching a strip of fabric. Subjects were also asked to score each stimulus in terms of arousal (high/low activation) and valence (pleasant/unpleasant), in agreement with the circumplex model of affect. EDA was processed using a deconvolutive method, separating tonic and phasic components. A statistical analysis was performed in order to identify significant differences in EDA features among force and velocity levels, as well as in their valence and arousal scores. Results show that the simulated caress induced by the haptic display significantly affects the EDA. In detail, the phasic component seems to be inversely related to the valence score. This finding is new and promising, since it can be used, e.g., as an additional cue for haptics design. PMID:26737605

  3. DFT study of Fe-Ni core-shell nanoparticles: Stability, catalytic activity, and interaction with carbon atom for single-walled carbon nanotube growth

    SciTech Connect

    Yang, Zhimin; Wang, Qiang Shan, Xiaoye; Zhu, Hongjun; Li, Wei-qi; Chen, Guang-hui

    2015-02-21

    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.

  4. 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.

  5. Temperature Analysis of an Active Region Core Loop Using AIA and XRT Data

    NASA Astrophysics Data System (ADS)

    Garst, Jennifer W.; Schmelz, J.; Kimble, J.

    2012-05-01

    Data obtained on December 10, 2010 by both the Atmospheric Imaging Assembly (AIA) and the X-Ray Telescope (XRT) are co-aligned and appropriately scaled in order to do a differential emission measure analysis of the combined data. This project uses Hybrid abundances from Fludra & Schmelz and atomic data from the CHIANTI atomic physics database to analyze an active region core loop and report on the multithermal analysis of the combined data set. The loop being analyzed is visible in the 94, 131, 171, 193, 211, 335 Å passbands on AIA; and the Al-thick, Ti-poly, Al-mesh, Al-poly/Ti-poly, C-Poly/Ti-poly, C-poly, Be-thin, Be-med, Al-med, and Al-poly filters on XRT. Solar physics research at the University of Memphis is supported by NSF ATM-0402729 as well as a Hinode subcontract from NASA/SAO.

  6. Analysis of zinc in biological samples by flame atomic absorption spectrometry: use of addition calibration technique.

    PubMed

    Dutra, Rosilene L; Cantos, Geny A; Carasek, Eduardo

    2006-01-01

    The quantification of target analytes in complex matrices requires special calibration approaches to compensate for additional capacity or activity in the matrix samples. The standard addition is one of the most important calibration procedures for quantification of analytes in such matrices. However, this technique requires a great number of reagents and material, and it consumes a considerable amount of time throughout the analysis. In this work, a new calibration procedure to analyze biological samples is proposed. The proposed calibration, called the addition calibration technique, was used for the determination of zinc (Zn) in blood serum and erythrocyte samples. The results obtained were compared with those obtained using conventional calibration techniques (standard addition and standard calibration). The proposed addition calibration was validated by recovery tests using blood samples spiked with Zn. The range of recovery for blood serum and erythrocyte samples were 90-132% and 76-112%, respectively. Statistical studies among results obtained by the addition technique and conventional techniques, using a paired two-tailed Student's t-test and linear regression, demonstrated good agreement among them. PMID:16943611

  7. Theoretic analysis of liquid film movement and its disintegration near the orifice of atomizer

    NASA Astrophysics Data System (ADS)

    Zhou, Meng; Zhuang, Fengchen

    1993-04-01

    The movement of a conic liquid film in a restricted space is studied in this paper. The film is produced by a centrifugal nozzle and impinged on by a high-speed gas stream. Based on the theory of aerodynamics, some theoretical formulas for liquid film movement are established, a criterion of breaking up the moving liquid film is proposed and a formula for calculating the size of droplet formed by disintegration of the liquid film is presented. The calculation results can be used as a reference for atomizer design.

  8. Dimensional and Mechanical Dynamics of Active and Stable Edges in Motile Fibroblasts Investigated by Using Atomic Force Microscopy

    NASA Astrophysics Data System (ADS)

    Rotsch, Christian; Jacobson, Ken; Radmacher, Manfred

    1999-02-01

    The atomic force microscope (AFM) was employed to investigate the extension and retraction dynamics of protruding and stable edges of motile 3T3 fibroblasts in culture. Such dynamics closely paralleled the results of earlier studies employing video microscopy that indicated that the AFM force-mapping technique does not appreciably perturb these dynamics. Force scans permitted height determinations of active and stable edges. Whereas the profiles of active edges are flat with average heights of 0.4-0.8 μ m, stable edges smoothly ascend to 2-3 μ m within about 6 μ m of the edge. In the region of the leading edge, the height fluctuates up to 50% (SD) of the mean value, much more than the stable edge; this fluctuation presumably reflects differences in underlying cytoskeletal activity. In addition, force mapping yields an estimate of the local Young's modulus or modulus of elasticity (E, the cortical stiffness). This stiffness will be related to "cortical tension," can be accurately calculated for the stable edges, and is ≈ 12 kPa in this case. The thinness of the leading edge precludes accurate estimation of the E values, but within 4 μ m of the margin it is considerably smaller than that for stable edges, which have an upper limit of 3-5 kPa. Although blebbing cannot absolutely be ruled out as a mechanism of extension, the data are consistent with an actin polymerization and/or myosin motor mechanism in which the average material properties of the extending margin would be nearly constant to the edge. Because the leading edge is softer than the stable edge, these data also are consistent with the notion that extension preferentially occurs in regions of lower cortical tension.

  9. Selection, follow-up, and analysis in the Atomic Bomb Casualty Commission Study.

    PubMed

    Jablon, S

    1985-05-01

    More is known about ionizing radiation as a cause of human cancer than about any other carcinogen. Most of this knowledge is derived from the studies conducted by the Atomic Bomb Casualty Commission and Radiation Effects Research Foundation on about 100,000 Japanese survivors of the atomic bombing in 1945. The importance of these studies is based on the large size of the exposed population and the fact that individual estimates of radiation dose were possible. These factors and the combined excellence of the centralized vital statistics reporting and population registration systems in Japan have made feasible the continuing longitudinal studies of cancer mortality by site in relation to radiation dose over a span of more than 30 years. Excellent voluntary cooperation by the survivors has enabled the continuation of a biennial physical examination program which has made possible the acquisition of blood for studies of radiation-induced chromosomal aberrations and mutations at the level of specific genes. Similarly, with the cooperation of local universities, hospitals, and physicians, tumor and tissue registries necessary for the study of cancer incidence have been developed. An autopsy pathology program has enabled study of the accuracy of cause of death certification.

  10. 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.

  11. 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.

  12. Analysis of anomalous slip in Ta single crystals using optical, atomic force, and orientation imaging microscopies

    SciTech Connect

    Stoelken, J.S.; King, W.E.; Schwartz, A.J.; Campbell, G.H.; Balooch, M.

    1999-07-01

    High purity Ta single crystals oriented for single slip were deformed in compression at 300K and 77K. The sample deformed at 300K exhibited wavy glide whereas the sample deformed at 77K exhibited anomalous slip. Sharp load drops were recorded in the stress-strain curve of the sample tested at 77K. Previous work attributes such unloading events to either the formation of large deformation twins or to the anomalous slip process itself. Orientation imaging microscopy was applied to probe lattice rotations occurring as a result of deformation in an effort to detect the presence of large deformation twins, none were found. Optical and atomic force microscopies were applied to map the slip traces appearing on the sample surface. Atomic force microscopy revealed that the fine structure within the rather coarse anomalous slip bands is comprised of atomistic scale slip lines organized into packets. These slip packets appear to account for the fine slip traces often observed within anomalous slip bands.

  13. Effective-field-theory analysis of Efimov physics in heteronuclear mixtures of ultracold atomic gases

    NASA Astrophysics Data System (ADS)

    Acharya, Bijaya; Ji, Chen; Platter, Lucas

    2016-09-01

    We use an effective-field-theory framework to analyze the Efimov effect in heteronuclear three-body systems consisting of two species of atoms with a large interspecies scattering length. In the leading-order description of this theory, various three-body observables in heteronuclear mixtures can be universally parametrized by one three-body parameter. We present the next-to-leading corrections, which include the effects of the finite interspecies effective range and the finite intraspecies scattering length, to various three-body observables. We show that only one additional three-body parameter is required to render the theory predictive at this order. By including the effective range and intraspecies scattering length corrections, we derive a set of universal relations that connect the different Efimov features near the interspecies Feshbach resonance. Furthermore, we show that these relations can be interpreted in terms of the running of the three-body counterterms that naturally emerge from proper renormalization. Finally, we make predictions for recombination observables of a number of atomic systems that are of experimental interest.

  14. Nondestructive atomic compositional analysis of BeMgZnO quaternary alloys using ion beam analytical techniques

    NASA Astrophysics Data System (ADS)

    Zolnai, Z.; Toporkov, M.; Volk, J.; Demchenko, D. O.; Okur, S.; Szabó, Z.; Özgür, Ü.; Morkoç, H.; Avrutin, V.; Kótai, E.

    2015-02-01

    The atomic composition with less than 1-2 atom% uncertainty was measured in ternary BeZnO and quaternary BeMgZnO alloys using a combination of nondestructive Rutherford backscattering spectrometry with 1 MeV He+ analyzing ion beam and non-Rutherford elastic backscattering experiments with 2.53 MeV energy protons. An enhancement factor of 60 in the cross-section of Be for protons has been achieved to monitor Be atomic concentrations. Usually the quantitative analysis of BeZnO and BeMgZnO systems is challenging due to difficulties with appropriate experimental tools for the detection of the light Be element with satisfactory accuracy. As it is shown, our applied ion beam technique, supported with the detailed simulation of ion stopping, backscattering, and detection processes allows of quantitative depth profiling and compositional analysis of wurtzite BeZnO/ZnO/sapphire and BeMgZnO/ZnO/sapphire layer structures with low uncertainty for both Be and Mg. In addition, the excitonic bandgaps of the layers were deduced from optical transmittance measurements. To augment the measured compositions and bandgaps of BeO and MgO co-alloyed ZnO layers, hybrid density functional bandgap calculations were performed with varying the Be and Mg contents. The theoretical vs. experimental bandgaps show linear correlation in the entire bandgap range studied from 3.26 eV to 4.62 eV. The analytical method employed should help facilitate bandgap engineering for potential applications, such as solar blind UV photodetectors and heterostructures for UV emitters and intersubband devices.

  15. 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

  16. 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.

  17. A new way towards high-efficiency thermally activated delayed fluorescence devices via external heavy-atom effect

    PubMed Central

    Zhang, Wenzhi; Jin, Jiangjiang; Huang, Zhi; Zhuang, Shaoqing; Wang, Lei

    2016-01-01

    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. PMID:27439967

  18. 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

  19. All-atom normal-mode analysis reveals an RNA-induced allostery in a bacteriophage coat protein

    NASA Astrophysics Data System (ADS)

    Dykeman, Eric C.; Twarock, Reidun

    2010-03-01

    Assembly of the T=3 bacteriophage MS2 is initiated by the binding of a 19 nucleotide RNA stem loop from within the phage genome to a symmetric coat protein dimer. This binding event effects a folding of the FG loop in one of the protein subunits of the dimer and results in the formation of an asymmetric dimer. Since both the symmetric and asymmetric forms of the dimer are needed for the assembly of the protein container, this allosteric switch plays an important role in the life cycle of the phage. We provide here details of an all-atom normal-mode analysis of this allosteric effect. The results suggest that asymmetric contacts between the A -duplex RNA phosphodiester backbone of the stem loop with the EF loop in one coat protein subunit results in an increased dynamic behavior of its FG loop. The four lowest-frequency modes, which encompass motions predominantly on the FG loops, account for over 90% of the increased dynamic behavior due to a localization of the vibrational pattern on a single FG loop. Finally, we show that an analysis of the allosteric effect using an elastic network model fails to predict this localization effect, highlighting the importance of using an all-atom full force field method for this problem.

  20. Analysis of the Essential Nutrient Strontium in Marine Aquariums by Atomic Absorption Spectroscopy: An Undergraduate Analytical Chemistry Laboratory Exercise

    NASA Astrophysics Data System (ADS)

    Gilles de Pelichy, Laurent D.; Adam, Carl; Smith, Eugene T.

    1997-10-01

    An undergraduate atomic absorption spectroscopy (AAS) laboratory experiment is presented involving the analysis of the essential nutrient strontium in a real-life sample, sea water. The quantitative analysis of strontium in sea water is a problem well suited for an undergraduate analytical chemistry laboratory. Sea water contains numerous components which prevent the direct quantitative determination of strontium. Students learn first hand about the role of interferences in analytical measurements, and about the method of standard addition which is used to minimize these effects. This laboratory exercise also introduces undergraduate students to practical problems associated with AAS. We encourage students as a part of this experiment to collect and analyze marine water samples from local pet shops.

  1. 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

  2. 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.

  3. Microscopic Analysis of Current and Mechanical Properties of Nafion® Studied by Atomic Force Microscopy

    PubMed Central

    Hiesgen, Renate; Helmly, Stefan; Galm, Ines; Morawietz, Tobias; Handl, Michael; Friedrich, K. Andreas

    2012-01-01

    The conductivity of fuel cell membranes as well as their mechanical properties at the nanometer scale were characterized using advanced tapping mode atomic force microscopy (AFM) techniques. AFM produces high-resolution images under continuous current flow of the conductive structure at the membrane surface and provides some insight into the bulk conducting network in Nafion membranes. The correlation of conductivity with other mechanical properties, such as adhesion force, deformation and stiffness, were simultaneously measured with the current and provided an indication of subsurface phase separations and phase distribution at the surface of the membrane. The distribution of conductive pores at the surface was identified by the formation of water droplets. A comparison of nanostructure models with high-resolution current images is discussed in detail. PMID:24958429

  4. 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.

  5. 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.

  6. Quantum analysis of atom-ion sympathetic cooling in the presence of micromotion

    NASA Astrophysics Data System (ADS)

    Krych, Michal; Idziaszek, Zbigniew

    2014-05-01

    We investigate the problem of a single ion in a radio-frequency trap and immersed in an ultracold Bose gas either in condensed or non-condensed phase. We develop master equation formalism describing the sympathetic cooling and we determine the cooling rates and final energies of ions. We show that cold atomic reservoir modifies the stability diagram of the ion in the Paul trap creating the regions where the ion is either cooled or heated due to the energy quanta exchanged with the time-dependent potential. Our calculation indicates that micromotion constitutes an important source of heating limiting the final temperature of ions to values higher than 100 μK for parameters of present experiments.

  7. Analysis of atomic and ion debris features of laser-produced Sn and Li plasmas

    SciTech Connect

    Coons, R. W.; Harilal, S. S.; Campos, D.; Hassanein, A.

    2010-09-15

    Tin and lithium plasmas emit efficiently in the in-band region (13.5 nm with 2% bandwidth) necessary for extreme ultraviolet (EUV) lithography. We have made a detailed comparison of the atomic and ionic debris, as well as the emission features of Sn and Li plasmas under identical experimental conditions. Planar slabs of pure Sn and Li were irradiated with 1064 nm, 9 ns neodymium-doped yttrium aluminum garnet laser pulses for producing plasmas. A suite of diagnostics were used to analyze the emission and debris features, including optical emission spectroscopy (OES), a Faraday cup, an EUV pinhole camera, the absolute measurement of EUV conversion efficiency (CE), etc. Our results show that Sn plasmas provide a CE nearly twice that of Li. However, the kinetic energies of Sn ions are considerably higher, though with a lower flux. OES studies have showed that the kinetic energies of neutral species are substantially lower compared to that of the charged particle species.

  8. Atomic structure of "multilayer silicene" grown on Ag(111): Dynamical low energy electron diffraction analysis

    NASA Astrophysics Data System (ADS)

    Kawahara, Kazuaki; Shirasawa, Tetsuroh; Lin, Chun-Liang; Nagao, Ryo; Tsukahara, Noriyuki; Takahashi, Toshio; Arafune, Ryuichi; Kawai, Maki; Takagi, Noriaki

    2016-09-01

    We have investigated the atomic structure of the "multilayer silicene" grown on the Ag(111) single crystal surface by using low energy electron diffraction (LEED) and scanning tunneling microscopy (STM). We measured the intensity of the LEED spot as a function of the incident electron energy (I-V curve) and analyzed the I-V curve using a dynamical LEED theory. We have found that the Si(111)(√{ 3} ×√{ 3})-Ag model well reproduces the I-V curve whereas the models consisting of the honeycomb structure of Si do not. The bias dependence of the STM image of multilayer silicene agrees with that of the Si(111)(√{ 3} ×√{ 3})-Ag reconstructed surface. Consequently, we have concluded that the multilayer silicene grown on Ag(111) is identical to the Si(111)(√{ 3} ×√{ 3})-Ag reconstructed structure.

  9. 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.

  10. 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.

  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. Analysis of physical activities in Taekwondo Pumsae.

    PubMed

    Lee, Sang-Bock; Cha, Eun-Jong; Lee, Tae-Soo

    2008-01-01

    Exercise is very important element for successful aging. Among many sports events, Korea is the suzerain of Taekwondo. When competing (Taekwondo Free Fighting) after learning Poomse as basic movements and inuring them, people compete with movements depending on situation. Among Poomses of Taekwondo, Taegeuk Poomse consists of very basic movements from 1 Jang to 8 Jang and they are for inuring to body. In order to prescribe Taegeuk Jang, which is the basic movement of Taekwondo that Korea is the suzerain, as an exercise for successful aging, it is necessary to analyze physical activity level of each Taegeuk Jang (From 1 Jang through 8 Jang) and suggest the same. Therefore, in this study, I analyzed physical activity level of each Jang of Taegeuk Poomse by attaching Armband made by Body Media Company on brachia and legs below knee of Taekwondo trainees. The result of the analysis of the whole momentum from Taegeuk 1 Jang to 8 Jang is as follows: First, the average absolute value of acceleration variation of vertical direction signal (L-MAD): 5.15. Second, the average absolute value of acceleration variation of horizontal direction signal (T-MAD): 3.44. Finally, the average of calorie consumption per minute (AEE/Min): 5.06 Cal. The obtained result corresponds to proper exercise condition for successful aging and it can be utilized as data for exercise prescription for the young and the old.

  13. 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.

  14. Determination of lead in hair and its segmental analysis by solid sampling electrothermal atomic absorption spectrometry

    NASA Astrophysics Data System (ADS)

    Baysal, Asli; Akman, Suleyman

    2010-04-01

    A rapid and practical solid sampling electrothermal atomic absorption spectrometric method was described for the determination of lead in scalp hair. Hair samples were washed once with acetone; thrice with distilled-deionized water and again once with acetone and dried at 75 °C. Typically 0.05 to 1.0 mg of dried samples were inserted on the platforms of solid sampling autosampler. The effects of pyrolysis temperature, atomization temperature, the amount of sample as well as addition of a modifier (Pd/Mg) and/or auxiliary digesting agents (hydrogen peroxide and nitric acid) and/or a surfactant (Triton X-100) on the recovery of lead were investigated. Hair samples were washed once with acetone; thrice with distilled-deionized water and again once with acetone and dried at 75 °C. Typically 0.05 to 1.0 mg of dried samples were inserted on the platforms of solid sampling autosampler. The limit of detection for lead (3 σ, N = 10) was 0.3 ng/g The addition of modifier, acids, oxidant and surfactant hardly improved the results. Due to the risk of contamination and relatively high blank values, the lead in hair were determined directly without adding any reagent(s). Finally, the method was applied for the segmental determination of lead concentrations in hair of different persons which is important to know when and how much a person was exposed to the analyte. For this purpose, 0.5 cm of pieces were cut along the one or a few close strands and analyzed by solid sampling.

  15. Analysis of retrotransposon activity in plants.

    PubMed

    Defraia, Christopher; Slotkin, R Keith

    2014-01-01

    Retrotransposons are transposable elements that duplicate themselves by converting their transcribed RNA genome into cDNA, which is then integrated back into the genome. Retrotransposons can be divided into two major classes based on their mechanism of transposition and the presence or absence of long terminal repeats (LTRs). In contrast to mammalian genomes, in which non-LTR retrotransposons have proliferated, plant genomes show evolutionary evidence of an explosion in LTR retrotransposon copy number. These retrotransposons can comprise a large fraction of the genome (75 % in maize). Although often viewed as molecular parasites, retrotransposons have been shown to influence neighboring gene expression and play a structural and potential regulatory role in the centromere. To prevent retrotransposon activity, eukaryotic cells have evolved overlapping mechanisms to repress transposition. Plants are an excellent system for studying the mechanisms of LTR retrotransposon inhibition such as DNA methylation and small RNA-mediated degradation of retrotransposon transcripts. However, analysis of these multi-copy, mobile elements is considerably more difficult than analysis of single-copy genes located in stable regions of the genome. In this chapter we outline methods for analyzing the progress of LTR retrotransposons through their replication cycle in plants. We describe a mixture of traditional molecular biology experiments, such as Southern, Northern, and Western blotting, in addition to nontraditional techniques designed to take advantage of the specific mechanism of LTR retrotransposition.

  16. A novel kinase mutation in VEGFR-1 predisposes its αC-helix/activation loop towards allosteric activation: Atomic insights from protein simulation.

    PubMed

    Mokhdomi, Taseem A; Bukhari, Shoiab; Chikan, Naveed Anjum; Amin, Asif; Wafai, Asrar H; Wani, Sajad H; Chowdri, Nisar A; Qadri, Raies A

    2016-08-01

    Vascular endothelial growth factor receptor 1 (VEGFR-1) has been implicated in diverse pathologies, including cancers. Although VEGFR-1 is considered as functionally impaired kinase, its decoy characteristics make it an important regulator of VEGFR-mediated signaling, particularly in tumor angiogenesis. VEGFR-1 conveys signaling via its tyrosine kinase (TK) domain whose activation is regulated by phosphorylation of specific tyrosine residues. Thus dysregulation of VEGFR-1 signaling, as reported in most of the cancers, might be a consequence of altered phosphorylation that could be attributed to genotypic variations in its TK domain. Considering the importance of TK domain of VEGFR-1, we carried out its mutational screening in 84 clinically validated and histopathologically confirmed colorectal cancer patients. By means of direct DNA sequencing and SNP analyses, eight novel variations, including one synonymous, two deletion, one missense and four intronic variations, were reported in the TK domain of VEGFR-1. rs730882263:C>G variation specifically reported in colon cancer, representing a single-atomic change (Sulfur to Oxygen) in the predicted (p.Cys1110Ser) protein, was observed as potentially deleterious variation as assessed by multiple single-nucleotide polymorphism prediction servers. Molecular dynamics simulations of VEGFR-1 Wt and (p.Cys1110Ser) variant models revealed major conformational changes in variant protein presumptuously generating an open conformation thereby exposing the activation domain and consequently increasing the probability of phosphorylation events: a condition frequently reported in cancers. PMID:27049304

  17. Analytic study of the chain dark decomposition reaction of iodides - atomic iodine donors - in the active medium of a pulsed chemical oxygen-iodine laser: 1. Criteria for the development of the branching chain dark decomposition reaction of iodides

    SciTech Connect

    Andreeva, Tamara L; Kuznetsova, S V; Maslov, Aleksandr I; Sorokin, Vadim N

    2009-02-28

    The scheme of chemical processes proceeding in the active medium of a pulsed chemical oxygen-iodine laser (COIL) is analysed. Based on the analysis performed, the complete system of differential equations corresponding to this scheme is replaced by a simplified system of equations describing in dimensionless variables the chain dark decomposition of iodides - atomic iodine donors, in the COIL active medium. The procedure solving this system is described, the basic parameters determining the development of the chain reaction are found and its specific time intervals are determined. The initial stage of the reaction is analysed and criteria for the development of the branching chain decomposition reaction of iodide in the COIL active medium are determined. (active media)

  18. Assessing physical activity intensity by video analysis.

    PubMed

    Silva, P; Santiago, C; Reis, L P; Sousa, A; Mota, J; Welk, G

    2015-05-01

    Assessing physical activity (PA) is a challenging task and many different approaches have been proposed. Direct observation (DO) techniques can objectively code both the behavior and the context in which it occurred, however, they have significant limitations such as the cost and burden associated with collecting and processing data. Therefore, this study evaluated the utility of an automated video analysis system (CAM) designed to record and discriminate the intensity of PA using a subject tracking methodology. The relative utility of the CAM system and DO were compared with criterion data from an objective accelerometry-based device (Actigraph GT3X+). Eight 10 year old children (three girls and five boys) wore the GT3X+ during a standard basketball session. PA was analyzed by two observers using the SOPLAY instrument and by the CAM system. The GT3X+ and the CAM were both set up to collect data at 30 Hz while the DO was performed every two minutes, with 10 s of observation for each gender. The GT3X+ was processed using cut points by Evanson and the outcome measure was the percentage of time spent in different intensities of PA. The CAM data were processed similarly using the same speed thresholds as were used in establishing the Evenson cut-off points (light: <2 mph; walking: 2-4 mph; very active: >4 mph). Similar outcomes were computed from the SOPLAY default analyses. A chi-square test was used to test differences in the percentage of time at the three intensity zones (light, walking and very active). The Yates' correction was used to prevent overestimation of statistical significance for small data. When compared with GT3X+, the CAM had better results than the SOPLAY. The chi-square test yielded the following pairwise comparisons: CAM versus GT3x+ was χ(2) (5) = 24.18, p < .001; SOPLAY2 versus GT3x+ was χ(2) (5) = 144.44, p < .001; SOPLAY1 versus GT3x+ was χ(2) (5) = 119.55, p < .001. The differences were smaller between CAM and GT3x

  19. 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.

  20. Single atom microscopy.

    PubMed

    Zhou, Wu; Oxley, Mark P; Lupini, Andrew R; Krivanek, Ondrej L; Pennycook, Stephen J; Idrobo, Juan-Carlos

    2012-12-01

    We show that aberration-corrected scanning transmission electron microscopy operating at low accelerating voltages is able to analyze, simultaneously and with single atom resolution and sensitivity, the local atomic configuration, chemical identities, and optical response at point defect sites in monolayer graphene. Sequential fast-scan annular dark-field (ADF) imaging provides direct visualization of point defect diffusion within the graphene lattice, with all atoms clearly resolved and identified via quantitative image analysis. Summing multiple ADF frames of stationary defects produce images with minimized statistical noise and reduced distortions of atomic positions. Electron energy-loss spectrum imaging of single atoms allows the delocalization of inelastic scattering to be quantified, and full quantum mechanical calculations are able to describe the delocalization effect with good accuracy. These capabilities open new opportunities to probe the defect structure, defect dynamics, and local optical properties in 2D materials with single atom sensitivity.

  1. Single atom microscopy.

    PubMed

    Zhou, Wu; Oxley, Mark P; Lupini, Andrew R; Krivanek, Ondrej L; Pennycook, Stephen J; Idrobo, Juan-Carlos

    2012-12-01

    We show that aberration-corrected scanning transmission electron microscopy operating at low accelerating voltages is able to analyze, simultaneously and with single atom resolution and sensitivity, the local atomic configuration, chemical identities, and optical response at point defect sites in monolayer graphene. Sequential fast-scan annular dark-field (ADF) imaging provides direct visualization of point defect diffusion within the graphene lattice, with all atoms clearly resolved and identified via quantitative image analysis. Summing multiple ADF frames of stationary defects produce images with minimized statistical noise and reduced distortions of atomic positions. Electron energy-loss spectrum imaging of single atoms allows the delocalization of inelastic scattering to be quantified, and full quantum mechanical calculations are able to describe the delocalization effect with good accuracy. These capabilities open new opportunities to probe the defect structure, defect dynamics, and local optical properties in 2D materials with single atom sensitivity. PMID:23146658

  2. Structure-activity relationships for biodistribution, pharmacokinetics, and excretion of atomically precise nanoclusters in a murine model

    NASA Astrophysics Data System (ADS)

    Wong, O. Andrea; Hansen, Ryan J.; Ni, Thomas W.; Heinecke, Christine L.; Compel, W. Scott; Gustafson, Daniel L.; Ackerson, Christopher J.

    2013-10-01

    The absorption, distribution, metabolism and excretion (ADME) and pharmacokinetic (PK) properties of inorganic nanoparticles with hydrodynamic diameters between 2 and 20 nm are presently unpredictable. It is unclear whether unpredictable in vivo properties and effects arise from a subset of molecules in a nanomaterials preparation, or if the ADME/PK properties are ensemble properties of an entire preparation. Here we characterize the ADME/PK properties of atomically precise preparations of ligand protected gold nanoclusters in a murine model system. We constructed atomistic models and tested in vivo properties for five well defined compounds, based on crystallographically resolved Au25(SR)18 and Au102(SR)44 nanoclusters with different (SR) ligand shells. To rationalize unexpected distribution and excretion properties observed for several clusters in this study and others, we defined a set of atomistic structure-activity relationships (SAR) for nanoparticles, which includes previously investigated parameters such as particle hydrodynamic diameter and net charge, and new parameters such as hydrophobic surface area and surface charge density. Overall we find that small changes in particle formulation can provoke dramatic yet potentially predictable changes in ADME/PK.The absorption, distribution, metabolism and excretion (ADME) and pharmacokinetic (PK) properties of inorganic nanoparticles with hydrodynamic diameters between 2 and 20 nm are presently unpredictable. It is unclear whether unpredictable in vivo properties and effects arise from a subset of molecules in a nanomaterials preparation, or if the ADME/PK properties are ensemble properties of an entire preparation. Here we characterize the ADME/PK properties of atomically precise preparations of ligand protected gold nanoclusters in a murine model system. We constructed atomistic models and tested in vivo properties for five well defined compounds, based on crystallographically resolved Au25(SR)18 and Au102(SR

  3. [Analysis of methylmercury in biological guano by the optimized atomic fluorescence spectrometry coupled with microwave assisted extraction].

    PubMed

    Chen, Qian-Qian; Liu, Xiao-Dong; Sun, Li-Guang; Jiang, Shan; Yan, Hong; Liu, Yi; Luo, Yu-Han; Huang, Jing

    2011-01-01

    The analytical method for the determination of methylmercury in seabird excrements was established using atomic fluorescence spectrometry coupled with microwave-assisted extraction In general, temperature and hydrochloric amount are the most important influencing factors on the extraction of MeHg in the samples, and the present paper optimized these two parameters. The result showed that 120 degrees C and 200 microL 6 mol x L(-1) hydrochloric acid are the best extraction conditions. Under these experimental conditions, the relative standard deviation (RSD) values of reduplicative analyses on standard reference material (human hair powder) and the same seabird excrement sample were 0.74% and 6.61% respectively, and their percent recoveries were over 90%. The combination of microwave-assisted extraction and atomic fluorescence spectrometry has many advantages such as simple operation, high sensitivity, low detection limit and low cost, therefore, it is suitable for rapid separation and analysis of trace methylmercury composition in the biological guanos. Using this method, we analyzed the methylmercury contents in the ancient and fresh seabird droppings taken from Xisha Islands of South China Sea, and the result showed that the Xisha guanos were rich in methylmercury and the large input of seabird guanos will cause serious environmental contamination in the remote island ecosystem of Xisha Islands.

  4. 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.

  5. Activation Likelihood Estimation meta-analysis revisited

    PubMed Central

    Eickhoff, Simon B.; Bzdok, Danilo; Laird, Angela R.; Kurth, Florian; Fox, Peter T.

    2011-01-01

    A widely used technique for coordinate-based meta-analysis of neuroimaging data is activation likelihood estimation (ALE), which determines the convergence of foci reported from different experiments. ALE analysis involves modelling these foci as probability distributions whose width is based on empirical estimates of the spatial uncertainty due to the between-subject and between-template variability of neuroimaging data. ALE results are assessed against a null-distribution of random spatial association between experiments, resulting in random-effects inference. In the present revision of this algorithm, we address two remaining drawbacks of the previous algorithm. First, the assessment of spatial association between experiments was based on a highly time-consuming permutation test, which nevertheless entailed the danger of underestimating the right tail of the null-distribution. In this report, we outline how this previous approach may be replaced by a faster and more precise analytical method. Second, the previously applied correction procedure, i.e. controlling the false discovery rate (FDR), is supplemented by new approaches for correcting the family-wise error rate and the cluster-level significance. The different alternatives for drawing inference on meta-analytic results are evaluated on an exemplary dataset on face perception as well as discussed with respect to their methodological limitations and advantages. In summary, we thus replaced the previous permutation algorithm with a faster and more rigorous analytical solution for the null-distribution and comprehensively address the issue of multiple-comparison corrections. The proposed revision of the ALE-algorithm should provide an improved tool for conducting coordinate-based meta-analyses on functional imaging data. PMID:21963913

  6. An atom trap trace analysis (ATTA) system for measuring ultra-low contamination by krypton in xenon dark matter detectors

    NASA Astrophysics Data System (ADS)

    Yoon, Tae Hyun

    The XENON dark matter experiment aims to detect hypothetical weakly interacting massive particles (WIMPs) scattering off nuclei within its liquid xenon (LXe) target. The trace 85Kr in the xenon target undergoes beta-decay with a 687 keV end point and 10.8 year halflife, which contributes background events and limits the sensitivity of the experiment. In order to achieve the desired sensitivity, the contamination by krypton is reduced to the part per trillion (ppt) level by cryogenic distillation. The conventional methods are not well suited for measuring the krypton contamination at such a low level. In this work, we have developed an atom trap trace analysis (ATTA) device to detect the ultra-low krypton concentration in the xenon target. This project was proposed to the National Science Foundation (NSF) as a Major Research Instrumentation (MRI) development [Aprile and Zelevinsky, 2009] and is funded by NSF and Columbia University. The ATTA method, originally developed at Argonne National Laboratory, uses standard laser cooling and trapping techniques, and counts single trapped atoms. Since the isotopic abundance of 85Kr in nature is 1.5 x 10-11, the 85Kr/Xe level is expected to be ˜10-23, which is beyond the capability of our method. Thus we detect the most abundant (57%) isotope 84Kr, and infer the 85Kr contamination from their known abundances. To avoid contamination by krypton, the setup is tested and optimized with 40 Ar which has a similar cooling wavelength to 84Kr. Two main challenges in this experiment are to obtain a trapping efficiency high enough to detect krypton impurities at the ppt level, and to achieve the resolution to discriminate single atoms. The device is specially designed and adjusted to meet these challenges. After achieving these criteria with argon gas, we precisely characterize the efficiency of the system using Kr-Xe mixtures with known ratios, and find that ˜90 minutes are required to trap one 84Kr atom at the 1-ppt Kr

  7. Visualization and structural analysis of the bacterial magnetic organelle magnetosome using atomic force microscopy.

    PubMed

    Yamamoto, Daisuke; Taoka, Azuma; Uchihashi, Takayuki; Sasaki, Hideaki; Watanabe, Hiroki; Ando, Toshio; Fukumori, Yoshihiro

    2010-05-18

    The unique ability of magnetotactic bacteria to navigate along a geomagnetic field is accomplished with the help of prokaryotic organelles, magnetosomes. The magnetosomes have well-ordered chain-like structures, comprising membrane-enveloped, nano-sized magnetic crystals, and various types of specifically associated proteins. In this study, we applied atomic force microscopy (AFM) to investigate the spatial configuration of isolated magnetosomes from Magnetospirillum magneticum AMB-1 in near-native buffer conditions. AFM observation revealed organic material with a approximately 7-nm thickness surrounding a magnetite crystal. Small globular proteins, identified as magnetosome-associated protein MamA, were distributed on the mica surface around the magnetosome. Immuno-labeling with AFM showed that MamA is located on the magnetosome surface. In vitro experiments showed that MamA proteins interact with each other and form a high molecular mass complex. These findings suggest that magnetosomes are covered with MamA oligomers in near-native environments. Furthermore, nanodissection revealed that magnetosomes are built with heterogeneous structures that comprise the organic layer. This study provides important clues to the supramolecular architecture of the bacterial organelle, the magnetosome, and insight into the function of the proteins localized in the organelle.

  8. 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).

  9. 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)

  10. Analysis of dynamic cantilever behavior in tapping mode atomic force microscopy.

    PubMed

    Deng, Wenqi; Zhang, Guang-Ming; Murphy, Mark F; Lilley, Francis; Harvey, David M; Burton, David R

    2015-10-01

    Tapping mode atomic force microscopy (AFM) provides phase images in addition to height and amplitude images. Although the behavior of tapping mode AFM has been investigated using mathematical modeling, comprehensive understanding of the behavior of tapping mode AFM still poses a significant challenge to the AFM community, involving issues such as the correct interpretation of the phase images. In this paper, the cantilever's dynamic behavior in tapping mode AFM is studied through a three dimensional finite element method. The cantilever's dynamic displacement responses are firstly obtained via simulation under different tip-sample separations, and for different tip-sample interaction forces, such as elastic force, adhesion force, viscosity force, and the van der Waals force, which correspond to the cantilever's action upon various different representative computer-generated test samples. Simulated results show that the dynamic cantilever displacement response can be divided into three zones: a free vibration zone, a transition zone, and a contact vibration zone. Phase trajectory, phase shift, transition time, pseudo stable amplitude, and frequency changes are then analyzed from the dynamic displacement responses that are obtained. Finally, experiments are carried out on a real AFM system to support the findings of the simulations. PMID:26303510

  11. Analysis of Load Rate Dependence of Neuronal Soma Using Atomic Force Microscopy

    NASA Astrophysics Data System (ADS)

    Spedden, Elise; Dokukin, Maxim; Sokolov, Igor; Staii, Cristian

    2014-03-01

    Surfaces of biological cells are covered with a layer of molecules (glycocalyx) and membrane protrusions (microvilli and microridges). This so-called ``brush'' layer plays a distinct role in the measured elastic modulus of cells. We utilize atomic force microscopy (AFM) to study mechanical properties of the soma and brush layer of live rat cortical neurons. The elastic modulus of the soma and brush are measured for cells indented at different AFM probe loading rates, ranging from 1-10 μm/s. The cells were studied at both 37 °C (near-physiological temperature at which microtubules dominate high stiffness regions in the soma) and at 25 °C (reduced temperature state at which actin components dominate high stiffness regions in the soma). If one uses a model with no brush taken into account, the derived elastic modulus shows the rate dependence similar to the one reported previously in the literature. Using the model with brush, we observed no statistically significant rate dependence of the elastic modulus of the soma, whereas the effective brush length demonstrates strong rate dependence. These measurements yield insight into the mechanical reaction of living neurons to externally applied stresses.

  12. Inductive effects on proton affinity of benzene derivatives: analysis using fictitious hydrogen atoms.

    PubMed

    Dumont, Elise; Chaquin, Patrick

    2009-03-26

    Pure inductive effects on the gas-phase basicity of seven benzene derivatives (3- and 4-substitution) are monitored in a continuous way using fictitious hydrogen atoms bearing an adjustable nuclear charge Z*. This approach (H* method) affords three main advantages over existing treatments: such entities are by definition purely inductive (without any underlying assumptions), use of empirical parameters is circumvented, and yet the method has been designed to remain particularly easy to use. We directly establish the linear dependence of proton affinities on inductive effects and, more quantitatively, measure accurate sensitivities rho(I)* analogous to Taft's coefficients. Functional centers exhibit contrasted values, up to a factor of 3, which finds an interpretation within the framework of the HSAB theory. The sensitivities rho(I)* for 3- and 4-substitution are quantified. The associated para/meta rho(I)* ratio ranges from 1.02 to 1.16 according to the functional center. These values, always slightly superior to unity, denote a contribution of pi electrons in the transmission of the inductive effect. This effect, first identified by Exner, is shown to account for ca. 30% of the basicity of benzoic acid, which is taken as an example. PMID:19243120

  13. Status of radiotherapy resources in Africa: an International Atomic Energy Agency analysis.

    PubMed

    Abdel-Wahab, May; Bourque, Jean-Marc; Pynda, Yaroslav; Iżewska, Joanna; Van der Merwe, Debbie; Zubizarreta, Eduardo; Rosenblatt, Eduardo

    2013-04-01

    Radiation therapy is an important component of cancer control programmes. The scarcity of radiation oncology resources in Africa is becoming more severe as cancer incidence increases in the continent. We did a longitudinal assessment of the status of radiation oncology resources in Africa to measure the extent of the problem and the effects of programmes designed to enhance radiation services in the continent. Radiation oncology departments in Africa were surveyed through the Directory of Radiotherapy Centres, and this information was supplemented by that available from International Atomic Energy Agency Regional African and Interregional project reports for 2010. Of 52 African countries included, only 23 are known to have teletherapy. These facilities are concentrated in the southern and northern states of the continent. Brachytherapy resources (high-dose rate or low-dose rate) were only available in 20 of the 52 African countries. Although progress has been made in the establishment of radiation oncology services in some countries, a large need still exists for basic radiation services, and much resource mobilisation is needed for services to keep pace with the burgeoning populations of many countries. PMID:23561748

  14. Analysis of force-deconvolution methods in frequency-modulation atomic force microscopy

    PubMed Central

    Illek, Esther; Giessibl, Franz J

    2012-01-01

    Summary In frequency-modulation atomic force microscopy the direct observable is the frequency shift of an oscillating cantilever in a force field. This frequency shift is not a direct measure of the actual force, and thus, to obtain the force, deconvolution methods are necessary. Two prominent methods proposed by Sader and Jarvis (Sader–Jarvis method) and Giessibl (matrix method) are investigated with respect to the deconvolution quality. Both methods show a nontrivial dependence of the deconvolution quality on the oscillation amplitude. The matrix method exhibits spikelike features originating from a numerical artifact. By interpolation of the data, the spikelike features can be circumvented. The Sader–Jarvis method has a continuous amplitude dependence showing two minima and one maximum, which is an inherent property of the deconvolution algorithm. The optimal deconvolution depends on the ratio of the amplitude and the characteristic decay length of the force for the Sader–Jarvis method. However, the matrix method generally provides the higher deconvolution quality. PMID:22496997

  15. 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

  16. 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)

  17. Optimisation of sample preparation and analysis conditions for atom probe tomography characterisation of low concentration surface species

    NASA Astrophysics Data System (ADS)

    Douglas, J. O.; Bagot, P. A. J.; Johnson, B. C.; Jamieson, D. N.; Moody, M. P.

    2016-08-01

    The practicalities for atom probe tomography (APT) analysis of near-surface chemistry, particularly the distribution of low concentration elements, are presented in detail. Specifically, the challenges of surface analysis using APT are described through the characterisation of near-surface implantation profiles of low concentration phosphorus into single crystal silicon. This material system was chosen to illustrate this surface specific approach as low concentration phosphorus has significant mass spectra overlaps with silicon species and the near surface location requires particular attention to focused ion beam specimen preparation and deposition of various capping layers. Required changes to standard sample preparation procedure are described and the effects of changes in APT analysis parameters are discussed with regards to this specific material system. Implantation profiles of 14 kV phosphorus ions with a predicted peak concentration of 0.2 at .% were successfully analysed using APT using pulsed laser assisted evaporation. It is demonstrated that the most important factor in obtaining the most accurate implantation profile was to ensure all phosphorus mass peaks were as free of background noise as possible, with thermal tails from the Si2+ ions obscuring the P2+ ions being the major overlap in the mass spectrum. The false positive contribution to the phosphorus profiles from hydride species appears minimal at the capping layer/substrate interface. The initial capping layer selection of nickel was successful in allowing the analysis of the majority of the phosphorus profile but nickel and phosphorus mass spectra overlaps prevent optimum quantification of phosphorus at the surface.

  18. Active sites without restraints: high-resolution analysis of metal cofactors.

    PubMed

    Burger, Eva-Maria; Andrade, Susana L A; Einsle, Oliver

    2015-12-01

    For most three-dimensional structures of biological macromolecules, the factual accuracy of atom positions by far exceeds the resolution of the experimental data, although the refinement problem presented by a protein structure is substantially underdetermined. This is achieved through using restraints that precisely define protein geometries and thus reduce the degrees of freedom of the refinement problem. If such information is not available or when unusual geometries or particular ligand states complicate structural analysis, possible pitfalls arise that not only concern the precise definition of spatial arrangements, but also the identification of atom types and bond distances. Prominent examples include CO dehydrogenase, hydrogenase, acetylene hydratase and nitrogenase, all of which employ unique active sites that turned out not to be what they seemed upon first inspection.

  19. 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.

  20. Confirmation of disordered structure of ultrasmall CdSe nanoparticles from X-ray atomic pair distribution function analysis.

    PubMed

    Yang, Xiaohao; Masadeh, Ahmad S; McBride, James R; Božin, Emil S; Rosenthal, Sandra J; Billinge, Simon J L

    2013-06-14

    The atomic pair distribution function (PDF) analysis of X-ray powder diffraction data has been used to study the structure of small and ultra-small CdSe nanoparticles. A method is described that uses a wurtzite and zinc-blende mixed phase model to account for stacking faults in CdSe particles. The mixed-phase model successfully describes the structure of nanoparticles larger than 2 nm yielding a stacking fault density of about 30%. However, for ultrasmall nanoparticles smaller than 2 nm, the models cannot fit the experimental PDF showing that the structure is significantly modified from that of larger particles and the bulk. The observation of a significant change in the average structure at ultra-small size is likely to explain the unusual properties of the ultrasmall particles such as their white light emitting ability.

  1. Investigation of the analysis parameters and background subtraction for high-k materials with atom probe tomography.

    PubMed

    Mutas, S; Klein, C; Gerstl, S S A

    2011-05-01

    In this paper we present depth profiles of a high-k layer consisting of HfO(2) with an embedded sub-nm thick ZrO(2) layer obtained with atom probe tomography (APT). In order to determine suitable measurement parameters for reliable, reproducible, and quantitative analysis, we have investigated the influence of the laser energy and the specimen temperature on the resulting elemental composition. In addition we devise a procedure for local background subtraction both for the composition and the depth scale that is crucial for gaining reproducible results. We find that the composition of the high-k material remains unaffected even for extreme laser energies and base temperatures, while higher laser energies lead to an accumulation of silicon at the upper interface of the high-k layer. Furthermore we show that APT is capable of providing sub-nm depth resolution for high-k materials with high reproducibility, good compositional accuracy, and high measurement yield.

  2. Quantitative evaluation of spinodal decomposition in Fe-Cr by atom probe tomography and radial distribution function analysis.

    PubMed

    Zhou, Jing; Odqvist, Joakim; Thuvander, Mattias; Hedström, Peter

    2013-06-01

    Nanostructure evolution during low temperature aging of three binary Fe-Cr alloys has been investigated by atom probe tomography. A new method based on radial distribution function (RDF) analysis to quantify the composition wavelength and amplitude of spinodal decomposition is proposed. Wavelengths estimated from RDF have a power-law type evolution and are in reasonable agreement with wavelengths estimated using other more conventional methods. The main advantages of the proposed method are the following: (1) Selecting a box size to generate the frequency diagram, which is known to generate bias in the evaluation of amplitude, is avoided. (2) The determination of amplitude is systematic and utilizes the wavelength evaluated first to subsequently evaluate the amplitude. (3) The RDF is capable of representing very subtle decomposition, which is not possible using frequency diagrams, and thus a proposed theoretical treatment of the experimental RDF creates the possibility to determine amplitude at very early stages of spinodal decomposition.

  3. 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.

  4. Rapid recognition and functional analysis of membrane proteins on human cancer cells using atomic force microscopy.

    PubMed

    Li, Mi; Xiao, Xiubin; Liu, Lianqing; Xi, Ning; Wang, Yuechao

    2016-09-01

    Understanding the physicochemical properties of cell surface signalling molecules is important for us to uncover the underlying mechanisms that guide the cellular behaviors. Atomic force microscopy (AFM) has become a powerful tool for detecting the molecular interactions on individual cells with nanometer resolution. In this paper, AFM peak force tapping (PFT) imaging mode was applied to rapidly locate and visually map the CD20 molecules on human lymphoma cells using biochemically sensitive tips. First, avidin-biotin system was used to test the effectiveness of using PFT imaging mode to probe the specific molecular interactions. The adhesion images obtained on avidin-coated mica using biotin-tethered tips obviously showed the recognition spots which corresponded to the avidins in the simultaneously obtained topography images. The experiments confirmed the specificity and reproducibility of the recognition results. Then, the established procedure was applied to visualize the nanoscale organization of CD20s on the surface of human lymphoma Raji cells using rituximab (a monoclonal anti-CD20 antibody)-tethered tips. The experiments showed that the recognition spots in the adhesion images corresponded to the specific CD20-rituximab interactions. The cluster sizes of CD20s on lymphoma Raji cells were quantitatively analyzed from the recognition images. Finally, under the guidance of fluorescence recognition, the established procedure was applied to cancer cells from a clinical lymphoma patient. The results showed that there were significant differences between the adhesion images obtained on cancer cells and on normal cells (red blood cell). The CD20 distributions on ten cancer cells from the patient were quantified according to the adhesion images. The experimental results demonstrate the capability of applying PFT imaging to rapidly investigate the nanoscale biophysical properties of native membrane proteins on the cell surface, which is of potential significance in

  5. 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.

  6. 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.

  7. Simple analysis of total mercury and methylmercury in seafood using heating vaporization atomic absorption spectrometry.

    PubMed

    Yoshimoto, Keisuke; Anh, Hoang Thi Van; Yamamoto, Atsushi; Koriyama, Chihaya; Ishibashi, Yasuhiro; Tabata, Masaaki; Nakano, Atsuhiro; Yamamoto, Megumi

    2016-01-01

    This study aimed to develop a simpler method for determining total mercury (T-Hg) and methylmercury (MeHg) in biological samples by using methyl isobutyl ketone (MIBK) in the degreasing step. The fat in the samples was extracted by MIBK to the upper phase. T-Hg transferred into the water phase. This was followed by the extraction of MeHg from the water phase using HBr, CuCl2 and toluene. The MeHg fraction was reverse-extracted into L-cysteine-sodium acetate solution from toluene. The concentrations of T-Hg and MeHg were determined by heating vaporization atomic absorption spectrometry. Certified reference materials for T-Hg and MeHg in hair and fish were accurately measured using this method. This method was then applied to determine T-Hg and MeHg concentrations in the muscle, liver and gonads of seafood for the risk assessment of MeHg exposure. The mean T-Hg and MeHg concentrations in squid eggs were 0.023 and 0.022 µg/g, and in squid nidamental glands 0.052 and 0.049 µg/g, respectively. The MeHg/T-Hg ratios in the eggs and nidamental glands of squid were 94.4% and 96.5%, respectively. The mean T-Hg and MeHg concentrations in the gonads of sea urchins were 0.043 and 0.001 µg/g, respectively, with a MeHg/T-Hg ratio of 3.5%. We developed an efficient analytical method for T-Hg and MeHg using MIBK in the degreasing step. The new information on MeHg concentration and MeHg/T-Hg ratios in the egg or nidamental glands of squid and gonads of sea urchin will also be useful for risk assessment of mercury in seafood. PMID:27432235

  8. Simple analysis of total mercury and methylmercury in seafood using heating vaporization atomic absorption spectrometry.

    PubMed

    Yoshimoto, Keisuke; Anh, Hoang Thi Van; Yamamoto, Atsushi; Koriyama, Chihaya; Ishibashi, Yasuhiro; Tabata, Masaaki; Nakano, Atsuhiro; Yamamoto, Megumi

    2016-01-01

    This study aimed to develop a simpler method for determining total mercury (T-Hg) and methylmercury (MeHg) in biological samples by using methyl isobutyl ketone (MIBK) in the degreasing step. The fat in the samples was extracted by MIBK to the upper phase. T-Hg transferred into the water phase. This was followed by the extraction of MeHg from the water phase using HBr, CuCl2 and toluene. The MeHg fraction was reverse-extracted into L-cysteine-sodium acetate solution from toluene. The concentrations of T-Hg and MeHg were determined by heating vaporization atomic absorption spectrometry. Certified reference materials for T-Hg and MeHg in hair and fish were accurately measured using this method. This method was then applied to determine T-Hg and MeHg concentrations in the muscle, liver and gonads of seafood for the risk assessment of MeHg exposure. The mean T-Hg and MeHg concentrations in squid eggs were 0.023 and 0.022 µg/g, and in squid nidamental glands 0.052 and 0.049 µg/g, respectively. The MeHg/T-Hg ratios in the eggs and nidamental glands of squid were 94.4% and 96.5%, respectively. The mean T-Hg and MeHg concentrations in the gonads of sea urchins were 0.043 and 0.001 µg/g, respectively, with a MeHg/T-Hg ratio of 3.5%. We developed an efficient analytical method for T-Hg and MeHg using MIBK in the degreasing step. The new information on MeHg concentration and MeHg/T-Hg ratios in the egg or nidamental glands of squid and gonads of sea urchin will also be useful for risk assessment of mercury in seafood.

  9. 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

  10. 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.

  11. Analysis of mitogen-activated protein kinase activity in yeast.

    PubMed

    Elion, Elaine A; Sahoo, Rupam

    2010-01-01

    Mitogen-activated protein (MAP) kinases play central roles in transmitting extracellular and intracellular information in a wide variety of situations in eukaryotic cells. Their activities are perturbed in a large number of diseases, and their activating kinases are currently therapeutic targets in cancer. MAPKs are highly conserved among all eukaryotes. MAPKs were first cloned from the yeast Saccharomyces cerevisiae. Yeast has five MAPKs and one MAPK-like kinase. The mating MAPK Fus3 is the best characterized yeast MAPK. Members of all subfamilies of human MAPKs can functionally substitute S. cerevisiae MAPKs, providing systems to use genetic approaches to study the functions of either yeast or human MAPKs and to identify functionally relevant amino acid residues that enhance or reduce the effects of therapeutically relevant inhibitors and regulatory proteins. Here, we describe an assay to measure Fus3 activity in immune complexes prepared from S. cerevisiae extracts. The assay conditions are applicable to other MAPKs, as well. PMID:20811996

  12. [A genetic algorithm approach to qualitative analysis in inductively coupled plasma-atomic emission spectroscopy].

    PubMed

    Peng, Bin; Liu, Ke-ling; Li, Zhi-min; Wang, Yue-song; Huang, Tu-jiang

    2002-06-01

    Genetic algorithm (GA) is used in automatic qualitative analysis by a sequential inductively coupled plasma spectrometer (ICP-AES) and a computer program is developed in this paper. No any standard samples are needed, and spectroscopic interferences can be eliminated. All elements and their concentration ranges of an unknown sample can be reported. The replication rate Pr, crossover rate Pc, and mutation rate of the genetic algorithm were adjusted to be 0.6, 0.4 and 0 respectively. The analytical results of GA are in good agreement with the reference values. It indicates that, combined with the intensity information, the GA can be applied to spectroscopic qualitative analysis and expected to become an effective method in qualitative analysis in ICP-AES after further work. PMID:12938334

  13. 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.

  14. 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

  15. 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

  16. A pressure gauge based on gas density measurement from analysis of the thermal noise of an atomic force microscope cantilever

    SciTech Connect

    Seo, Dongjin; Ducker, William A.; Paul, Mark R.

    2012-05-15

    We describe a gas-density gauge based on the analysis of the thermally-driven fluctuations of an atomic force microscope (AFM) cantilever. The fluctuations are modeled as a ring-down of a simple harmonic oscillator, which allows fitting of the resonance frequency and damping of the cantilever, which in turn yields the gas density. The pressure is obtained from the density using the known equation of state. In the range 10-220 kPa, the pressure readings from the cantilever gauge deviate by an average of only about 5% from pressure readings on a commercial gauge. The theoretical description we use to determine the pressure from the cantilever motion is based upon the continuum hypothesis, which sets a minimum pressure for our analysis. It is anticipated that the cantilever gauge could be extended to measure lower pressures given a molecular theoretical description. Alternatively, the gauge could be calibrated for use in the non-continuum range. Our measurement technique is similar to previous AFM cantilever measurements, but the analysis produces improved accuracy.

  17. Microchemical analysis of intermetallic alloys using the field-ion microscope atom probe: Progress report, (July 1, 1988--December 31, 1988)

    SciTech Connect

    Brenner, S.S.

    1989-02-01

    During the period July 1, 1988 to December 31, 1988 considerable progress has been made in characterizing the distribution of solute atoms in nickel aluminide. Topics covered by this report are: controlled backpolishing of FIM needles; analysis of grain boundaries in B-doped Al-rich Ni/sub 3/Al; clustering of boron in B-doped, Al-rich Ni/sub 3/Al; segregation of carbon to grain boundaries in Ni/sub 3/ Al; site occupation probability of tantalum in Ni/sub 3/Al; and atom probe analysis of Co/sub 3/Ti. (JL)

  18. 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.

  19. 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)

  20. 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.

  1. Single Cell Analysis of Transcriptional Activation Dynamics

    PubMed Central

    Rafalska-Metcalf, Ilona U.; Powers, Sara Lawrence; Joo, Lucy M.; LeRoy, Gary; Janicki, Susan M.

    2010-01-01

    Background Gene activation is thought to occur through a series of temporally defined regulatory steps. However, this process has not been completely evaluated in single living mammalian cells. Methodology/Principal Findings To investigate the timing and coordination of gene activation events, we tracked the recruitment of GCN5 (histone acetyltransferase), RNA polymerase II, Brd2 and Brd4 (acetyl-lysine binding proteins), in relation to a VP16-transcriptional activator, to a transcription site that can be visualized in single living cells. All accumulated rapidly with the VP16 activator as did the transcribed RNA. RNA was also detected at significantly more transcription sites in cells expressing the VP16-activator compared to a p53-activator. After α-amanitin pre-treatment, the VP16-activator, GCN5, and Brd2 are still recruited to the transcription site but the chromatin does not decondense. Conclusions/Significance This study demonstrates that a strong activator can rapidly overcome the condensed chromatin structure of an inactive transcription site and supercede the expected requirement for regulatory events to proceed in a temporally defined order. Additionally, activator strength determines the number of cells in which transcription is induced as well as the extent of chromatin decondensation. As chromatin decondensation is significantly reduced after α-amanitin pre-treatment, despite the recruitment of transcriptional activation factors, this provides further evidence that transcription drives large-scale chromatin decondensation. PMID:20422051

  2. Infrared-active spin-orbit transitions of halogen atom dopants in solid parahydrogen: The role of trapping site geometry

    NASA Astrophysics Data System (ADS)

    Hinde, Robert J.

    2013-10-01

    We present theoretical calculations of the 2P1/2 ← 2P3/2 spin-orbit transition of Cl dopants embedded as substitutional impurities in solid parahydrogen (pH2) matrices. In the lower-energy 2P3/2 spin-orbit level, the Cl atom's electron density distribution is anisotropic, and slightly distorts the geometry of the atom's trapping site. This distortion leads to a blue shift in the spin-orbit transition energy; the blue shift is enhanced when we account for the large-amplitude zero point motions of the pH2 molecules surrounding the Cl dopant. We also show that the intensity of the transition depends on the geometry of the trapping site. In the gas phase, the 2P1/2 ← 2P3/2 atomic transition is electric dipole forbidden. However, when the Cl atom resides in trapping sites that mimic the hexagonal close packed morphology of pure solid pH2, the transition becomes electric dipole allowed through interaction-induced transition dipole moments. These transition dipole moments originate in the anisotropic electron density distribution of the lower-energy 2P3/2 spin-orbit level.

  3. Intruder Activity Analysis under Unreliable Sensor Networks

    SciTech Connect

    Tae-Sic Yoo; Humberto E. Garcia

    2007-09-01

    This paper addresses the problem of counting intruder activities within a monitored domain by a sensor network. The deployed sensors are unreliable. We characterize imperfect sensors with misdetection and false-alarm probabilities. We model intruder activities with Markov Chains. A set of Hidden Markov Models (HMM) models the imperfect sensors and intruder activities to be monitored. A novel sequential change detection/isolation algorithm is developed to detect and isolate a change from an HMM representing no intruder activity to another HMM representing some intruder activities. Procedures for estimating the entry time and the trace of intruder activities are developed. A domain monitoring example is given to illustrate the presented concepts and computational procedures.

  4. 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. PMID:8083048

  5. 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.

  6. 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.

  7. Atomic force microscopy analysis of human cornea surface after UV (λ=266 nm) laser irradiation

    NASA Astrophysics Data System (ADS)

    Spyratou, E.; Makropoulou, M.; Moutsouris, K.; Bacharis, C.; Serafetinides, A. A.

    2009-07-01

    Efficient cornea reshaping by laser irradiation for correcting refractive errors is still a major issue of interest and study. Although the excimer laser wavelength of 193 nm is generally recognized as successful in ablating corneal tissue for myopia correction, complications in excimer refractive surgery leads to alternative laser sources and methods for efficient cornea treatment. In this work, ablation experiments of human donor cornea flaps were conducted with the 4th harmonic of an Nd:YAG laser, with different laser pulses. AFM analysis was performed for examination of the ablated cornea flap morphology and surface roughness.

  8. 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

  9. Accurate crystal-structure refinement of Ca3Ga2Ge4O14 at 295 and 100 K and analysis of the disorder in the atomic positions

    NASA Astrophysics Data System (ADS)

    Dudka, A. P.; Mill', B. V.

    2013-07-01

    The accurate X-ray diffraction study of a Ca3Ga2Ge4O14 crystal (sp. gr. P321, Z = 1) has been performed using repeated X-ray diffraction data sets collected on a diffractometer equipped with a CCD area detector at 295 and 100 K. The asymmetric disorder in the atomic positions in Ca3Ga2Ge4O14 is described in two alternative ways: with the use of anharmonic atomic displacements (at 295 K R/wR = 0.68/0.60%, 3754 reflections; at 100 K R/wR = 0.90/0.70%, 3632 reflections) and using a split model (SM) (at 295 K R/wR = 0.74/0.67%; at 100 K R/wR = 0.95/0.74%). An analysis of the probability density function that defines the probability of finding an atom at a particular point in space shows that, at 295 K, five of the seven independent atoms in the unit cell are asymmetrically disordered in the vicinity of their sites, whereas only three atoms are disordered at 100 K. At both temperatures the largest disorder is observed at the 3 f site on a twofold axis, which is a prerequisite for the formation of helicoidal chains of atoms along the c axis of the crystal and can serve as a structural basis for multiferroic properties of this family of crystals with magnetic ions.

  10. 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.

  11. 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.

  12. Analysis of layer-by-layer thin-film oxide growth using RHEED and Atomic Force Microscopy

    NASA Astrophysics Data System (ADS)

    Adler, Eli; Sullivan, M. C.; Gutierrez-Llorente, Araceli; Joress, H.; Woll, A.; Brock, J. D.

    2015-03-01

    Reflection high energy electron diffraction (RHEED) is commonly used as an in situ analysis tool for layer-by-layer thin-film growth. Atomic force microscopy is an equally common ex situ tool for analysis of the film surface, providing visual evidence of the surface morphology. During growth, the RHEED intensity oscillates as the film surface changes in roughness. It is often assumed that the maxima of the RHEED oscillations signify a complete layer, however, the oscillations in oxide systems can be misleading. Thus, using only the RHEED maxima is insufficient. X-ray reflectivity can also be used to analyze growth, as the intensity oscillates in phase with the smoothness of the surface. Using x-ray reflectivity to determine the thin film layer deposition, we grew three films where the x-ray and RHEED oscillations were nearly exactly out of phase and halted deposition at different points in the growth. Pre-growth and post-growth AFM images emphasize the fact that the maxima in RHEED are not a justification for determining layer completion. Work conducted at the Cornell High Energy Synchrotron Source (CHESS) supported by NSF Awards DMR-1332208 and DMR-0936384 and the Cornell Center for Materials Research Shared Facilities are supported through DMR-1120296.

  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.; 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 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. 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…

  15. A subfemtotesla multichannel atomic magnetometer.

    PubMed

    Kominis, I K; Kornack, T W; Allred, J C; Romalis, M V

    2003-04-10

    The magnetic field is one of the most fundamental and ubiquitous physical observables, carrying information about all electromagnetic phenomena. For the past 30 years, superconducting quantum interference devices (SQUIDs) operating at 4 K have been unchallenged as ultrahigh-sensitivity magnetic field detectors, with a sensitivity reaching down to 1 fT Hz(-1/2) (1 fT = 10(-15) T). They have enabled, for example, mapping of the magnetic fields produced by the brain, and localization of the underlying electrical activity (magnetoencephalography). Atomic magnetometers, based on detection of Larmor spin precession of optically pumped atoms, have approached similar levels of sensitivity using large measurement volumes, but have much lower sensitivity in the more compact designs required for magnetic imaging applications. Higher sensitivity and spatial resolution combined with non-cryogenic operation of atomic magnetometers would enable new applications, including the possibility of mapping non-invasively the cortical modules in the brain. Here we describe a new spin-exchange relaxation-free (SERF) atomic magnetometer, and demonstrate magnetic field sensitivity of 0.54 fT Hz(-1/2) with a measurement volume of only 0.3 cm3. Theoretical analysis shows that fundamental sensitivity limits of this device are below 0.01 fT Hz(-1/2). We also demonstrate simple multichannel operation of the magnetometer, and localization of magnetic field sources with a resolution of 2 mm.

  16. 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.

  17. Atomic Calligraphy

    NASA Astrophysics Data System (ADS)

    Imboden, Matthias; Pardo, Flavio; Bolle, Cristian; Han, Han; Tareen, Ammar; Chang, Jackson; Christopher, Jason; Corman, Benjamin; Bishop, David

    2013-03-01

    Here we present a MEMS based method to fabricate devices with a small number of atoms. In standard semiconductor fabrication, a large amount of material is deposited, after which etching removes what is not wanted. This technique breaks down for structures that approach the single atom limit, as it is inconceivable to etch away all but one atom. What is needed is a bottom up method with single or near single atom precision. We demonstrate a MEMS device that enables nanometer position controlled deposition of gold atoms. A digitally driven plate is swept as a flux of gold atoms passes through an aperture. Appling voltages on four comb capacitors connected to the central plate by tethers enable nanometer lateral precision in the xy plane over 15x15 sq. microns. Typical MEMS structures have manufacturing resolutions on the order of a micron. Using a FIB it is possible to mill apertures as small as 10 nm in diameter. Assuming a low incident atomic flux, as well as an integrated MEMS based shutter with microsecond response time, it becomes possible to deposit single atoms. Due to their small size and low power consumption, such nano-printers can be mounted directly in a cryogenic system at ultrahigh vacuum to deposit clean quench condensed metallic structures.

  18. 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.

  19. Measurement of chromium VI and chromium III in stainless steel welding fumes with electrom spectroscopy for chemical analysis and neutron activation analysis.

    PubMed

    Lautner, G M; Carver, J C; Konzen, R B

    1978-08-01

    Electron Spectroscopy for Chemical Analysis (ESCA) was explored as a means of studying the oxidation state of chromium in SMAC (coated electrode) stainless steel welding fume collected on Nucleopore filters in the laboratory. Chromuim VI and III (as a percent of the total chromium) obtained from ESCA analysis was applied to results from Neutron Activation Analysis (NAA) to yield an average of 69 microgram chromium VI per sample. Diphenylcarbazide/atomic absorption (DPC/AA) results are reported for samples submitted to an industrial laboratory. Possible chemical species and solubility of chromium VI in stainless steel fumes is discussed in light of analogy between the SMAC process and the manufacturing process for chromates.

  20. 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

  1. 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. PMID:27530710

  2. 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.

  3. 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).

  4. Atomic structure of icosahedral B4C boron carbide from a first principles analysis of NMR spectra.

    PubMed

    Mauri, F; Vast, N; Pickard, C J

    2001-08-20

    Density functional theory is demonstrated to reproduce the 13C and 11B NMR chemical shifts of icosahedral boron carbides with sufficient accuracy to extract previously unresolved structural information from experimental NMR spectra. B4C can be viewed as an arrangement of 3-atom linear chains and 12-atom icosahedra. According to our results, all the chains have a CBC structure. Most of the icosahedra have a B11C structure with the C atom placed in a polar site, and a few percent have a B (12) structure or a B10C2 structure with the two C atoms placed in two antipodal polar sites.

  5. 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

  6. Detailed low-energy electron diffraction analysis of the (4×4) surface structure of C60 on Cu(111): Seven-atom-vacancy reconstruction

    NASA Astrophysics Data System (ADS)

    Xu, Geng; Shi, Xing-Qiang; Zhang, R. Q.; Pai, Woei Wu; Jeng, H. T.; Van Hove, M. A.

    2012-08-01

    A detailed and exhaustive structural analysis by low-energy electron diffraction (LEED) is reported for the C60-induced reconstruction of Cu(111), in the system Cu(111) + (4 × 4)-C60. A wide LEED energy range allows enhanced sensitivity to the crucial C60-metal interface that is buried below the 7-Å-thick molecular layer. The analysis clearly favors a seven-Cu-atom vacancy model (with Pendry R-factor Rp = 0.376) over a one-Cu-atom vacancy model (Rp = 0.608) and over nonreconstructed models (Rp = 0.671 for atop site and Rp = 0.536 for hcp site). The seven-Cu-atom vacancy forms a (4 × 4) lattice of bowl-like holes. In each hole, a C60 molecule can nestle by forming strong bonds (shorter than 2.30 Å) between 15 C atoms of the molecule and 12 Cu atoms of the outermost and second Cu layers.

  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. Atomic-Scale Determination of Active Facets on the MoVTeNb Oxide M1 Phase and Their Intrinsic Catalytic Activity for Ethane Oxidative Dehydrogenation.

    PubMed

    Melzer, Daniel; Xu, Pinghong; Hartmann, Daniela; Zhu, Yuanyuan; Browning, Nigel D; Sanchez-Sanchez, Maricruz; Lercher, Johannes A

    2016-07-25

    Aberration-corrected high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) has been used to image the basal {001} plane of the catalytically relevant M1 phase in MoVTeNb complex oxides. Facets {010}, {120}, and {210} are identified as the most frequent lateral termination planes of the crystals. Combination of STEM with He ion microscopy (HIM) images, Rietveld analysis, and kinetic tests reveals that the activation of ethane is correlated to the availability of facets {001}, {120}, and {210} at the surface of M1 crystals. The lateral facets {120} and {210} expose crystalline positions related to the typical active centers described for propane oxidation. Conversely, the low activity of the facet {010} is attributed to its configuration, consisting of only stable M6 O21 units connected by a single octahedron. Thus, we quantitatively demonstrated that differences in catalytic activity among M1 samples of equal chemical composition depend primarily on the morphology of the particles, which determines the predominant terminating facets. PMID:26990594

  9. 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,…

  10. High speed analysis of agricultural samples using inductively coupled plasma-atomic emission spectroscopy

    NASA Astrophysics Data System (ADS)

    Isaac, R. A.; Johnson, W. C.

    The determination of potassium, phosphorus, calcium, magnesium, zinc and manganese in soil extracts are reported at an analysis rate of 200 samples h -1. A 4 cm 3volume of soil is extracted with a 20 ml solution of 0.025 N H 2SO 4-0.05 N HCl (Mehlich I). The filtered solution is then placed on a Technicon Sampler IV, which is interfaced to an 1CP emission spectrometer. This extract is analyzed for all the nutrients above. In addition to soil extracts, the ICP is used for mineral analyses of feed samples at a sample rate of 120 samples h -1. Several "American Association of Feed Control Officials" check feed samples have been analyzed and the results will be discussed comparing the ICP results with other laboratories participating in the program. The preparation of feed samples involves ashing a 1 g sample at 500°C for 4 h. The ashed sample was then taken up in hot HCl and diluted to 250 ml. Analyses are also performed by ICP on water, heavy metals in sewage sludge, and on other materials. The ICP technique has increased the efficiency of our laboratory to the extent that one technician can do the same work that formerly required four technicians.

  11. Analysis of siliceous materials and coal by atomic absorption spectrophotometry with fusion for sample decomposition.

    PubMed

    Lau, O W; Lam, L; Luk, S F

    2000-04-28

    The oxalic acid-lithium carbonate-lithium tetraborate (1:1:1) fusion agent proposed previously for cement analysis is applied to determine the composition of various siliceous samples including granite, clay, flyash, sand and silica fume. For samples with silica content higher than 70%, the sample size had to be reduced from 0.10 to 0.01 g and a recovery factor was needed in silica determination to account for the precipitation of silica during acid dissolution. Attempt has also been made to determine the major metallic elements in coal by fusion directly without the ashing procedure, and the results obtained were good. Further, the ash content of coal was proposed to be determined by establishing a relation between the ash content and the sum of the concentrations of four major oxides (i.e. the oxides of Si, Al, Fe and Ca), and the proposed method is accurate and is time saving compared with that determined by direct ashing at 800 degrees C.

  12. Atomic resolution strain analysis in highly textured FePt thin films

    NASA Astrophysics Data System (ADS)

    Wicht, S.; Wee, S. H.; Hellwig, O.; Mehta, V.; Jain, S.; Weller, D.; Rellinghaus, B.

    2016-03-01

    In this work, we present a detailed investigation of FePt-substrate interfaces and their influence towards the microstructural and magnetic configurations of the resulting metallic films. Discontinuous FePt films of roughly 15 nm thickness are deposited at 750 °C on MgO, MgAl2O4, SrTiO3, and (La,Sr)(Al,Ta)O3 single-crystalline substrates. All of these films mainly show out-of-plane textured FePt islands; however, fractions of L12 and in-plane oriented crystals are observed for the films on substrates with reduced lattice mismatch. Reduced easy axis coercivities and enhanced hard axis remanence values affirm this observation. Moreover, quantitative high-resolution transmission electron microscope analysis reveals that the reduced lattice mismatch results in a decreased density of dislocations, especially misfit dislocations, at the FePt-substrate interface. To further extend the research, carbon-doped FePt+32%C films are deposited on single-crystalline and sputtered MgO at 750 °C and 650 °C, respectively, to characterize the influence of a segregating media and reduced grain size. A comparison to the pure FePt sample reveals that the presence of seed layer grain boundaries leads to an increased fraction of in-plane oriented material, while the density of misfit dislocations solely depends on the degree of lattice mismatch.

  13. 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.

  14. Carbon Dioxide Activation by Scandium Atoms and Scandium Monoxide Molecules: Formation and Spectroscopic Characterization of ScCO3 and OCScCO3 in Solid Neon.

    PubMed

    Zhang, Qingnan; Qu, Hui; Chen, Mohua; Zhou, Mingfei

    2016-01-28

    The reactions of carbon dioxide with scandium monoxide molecules and scandium atoms are investigated using matrix isolation infrared spectroscopy in solid neon. The species formed are identified by the effects of isotopic substitution on their infrared spectra as well as density functional calculations. The results show that the ground state ScO molecule reacts with carbon dioxide to form the carbonate complex ScCO3 spontaneously on annealing. The ground state Sc atom reacts with two carbon dioxide molecules to give the carbonate carbonyl complex OCScCO3 via the previously reported OScCO insertion intermediate on annealing. The observation of these spontaneous reactions is consistent with theoretical predictions that both the Sc + 2CO2 → OCScCO3 and ScO + CO2 → ScCO3 reactions are thermodynamically exothermic and are kinetically facile, requiring little or no activation energy. PMID:26738558

  15. Carbon Dioxide Activation by Scandium Atoms and Scandium Monoxide Molecules: Formation and Spectroscopic Characterization of ScCO3 and OCScCO3 in Solid Neon.

    PubMed

    Zhang, Qingnan; Qu, Hui; Chen, Mohua; Zhou, Mingfei

    2016-01-28

    The reactions of carbon dioxide with scandium monoxide molecules and scandium atoms are investigated using matrix isolation infrared spectroscopy in solid neon. The species formed are identified by the effects of isotopic substitution on their infrared spectra as well as density functional calculations. The results show that the ground state ScO molecule reacts with carbon dioxide to form the carbonate complex ScCO3 spontaneously on annealing. The ground state Sc atom reacts with two carbon dioxide molecules to give the carbonate carbonyl complex OCScCO3 via the previously reported OScCO insertion intermediate on annealing. The observation of these spontaneous reactions is consistent with theoretical predictions that both the Sc + 2CO2 → OCScCO3 and ScO + CO2 → ScCO3 reactions are thermodynamically exothermic and are kinetically facile, requiring little or no activation energy.

  16. 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

    2015-05-01

    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).

  17. Microwave initiated atomic spectra from select atomic species.

    PubMed

    Anand, Amand; Roberts, James; Croley, Richard; Dahiya, Jai N

    2010-01-01

    Isotopes of gaseous Helium (3He and 4He) were admitted into the vacuum system at various pressures and allowed to stabilize. Quantum states were then energized using a 2.45 GHz magnetron coupled to the gases by loose coupling. A residual gas analyzer Model 100 series manufactured by Stanford Research Systems was used to determine the massof each species. An Ocean Optics Optical Spectrometer model collecting the light via an optic probe was used to obtain the spectra and to characterize the spectroscopic peaks. The data collected from these isotopes represent characteristic spectral emission lines generated due to the transitions among discrete quantum energy levels. The data analysis, especially for atomic spectroscopy, becomes an extremely important tool in developing an understanding of the quantum levels active within each atom. In this paper is presented a summary of the analysis of work that was done on two isotopes of helium. Data using both computational as well as theoretical techniques are presented. Traditional high voltage arc discharge data were taken for the gas species and these are compared with microwave stimulated atomic emissions.

  18. 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…

  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. 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.