WorldWideScience

Sample records for supersonic metal cluster

  1. Supersonic Bare Metal Cluster Beams. Technical Progress Report, March 16, 1984 - April 1, 1985

    Science.gov (United States)

    Smalley, R. E.

    1985-01-01

    There have been four major areas of concentration for the study of bare metal cluster beams: neutral cluster, chemical reactivity, cold cluster ion source development (both positive and negative), bare cluster ion ICR (ion cyclotron resonance) development, and photofragmentation studies of bare metal cluster ions.

  2. Supersonic Motions of Galaxies in Clusters

    CERN Document Server

    Faltenbacher, A; Nagai, D; Gottlöber, S; Faltenbacher, Andreas; Kravtsov, Andrey V.; Nagai, Daisuke; Gottloeber, Stefan

    2004-01-01

    We study motions of galaxies in galaxy clusters formed in the concordance LCDM cosmology. We use high-resolution cosmological simulations that follow dynamics of dark matter and gas and include various physical processes critical for galaxy formation: gas cooling, heating and star formation. Analysing motions of galaxies and the properties of intracluster gas in the sample of eight simulated clusters at z=0, we study velocity dispersion profiles of the dark matter, gas, and galaxies. We measure the mean velocity of galaxy motions and gas sound speed as a function of radius and calculate the average Mach number of galaxy motions. The simulations show that galaxies, on average, move supersonically with the average Mach number of ~1.4, approximately independent of the cluster-centric radius. The supersonic motions of galaxies may potentially provide an important source of heating for the intracluster gas by driving weak shocks and via dynamical friction, although these heating processes appear to be inefficient ...

  3. Structure and Chemistry of Atomic Clusters from Supersonic Beams.

    Science.gov (United States)

    Yang, Shi-He.

    A tandem time-of-flight (TOF) apparatus was designed to study the structure and chemistry of cold transition metal cluster ions from supersonic beams. By means of a photodissociation laser fluence dependence technique, binding energies of Nb_{rm x }^{+} (x = 2 - 20), Co_{rm x}^{+ } (x = 4 - 20) and etc. were found to generally increase with cluster size. The desorption energies of Nb_{rm x}N _2^{+} (x = 2 - 17) and Nb_{rm x} CO^{+} (x = 2 - 10) also increase with cluster size with some oscillations similar to the size dependent reactivities of these clusters. Photodetachment studies revealed that electron affinities of copper clusters increase with cluster size with a sharp even/odd alternation. Unlike other noble metals, Ag_{rm x}^ {-} clusters display two competing processes: photodissociation and photodetachment. Relative reactivities of cluster ions of Nb, Co, Ag, and etc. have been measured using a fast flow cluster reactor, displaying a similar function of cluster size to that of the neutrals. In addition, preliminary photoelectron experiments have been performed on Cu_{ rm x}^{-} and Nb _{rm x}^{-}. A magnetic Time-of-flight ultraviolet photoelectron spectrometer (MTOFUPS) has been developed to study electronic structures of cold metal and semiconductor cluster anions prepared in supersonic beams. Application of this spectrometer to carbon clusters with a F_2 laser (7.9 eV) allowed their electron affinities and UPS patterns to be measured,demonstrating a remarkable structural evolution of these clusters: Chains (C_2^{ -}-C_9^{-} ) - Rings (C_{10}^ {-}-C_{29}^ {-}) - Cages (C_{38 }^{-}-C_{84 }^{-}). In particular, the UPS of C_{60}^{-} is in excellent agreement with the CNDO/S calculation, providing a striking spectral evidence for the highly symmetric icosahedral soccer ball structure--Buckminsterfullerene. For comparison, the UPS of Si_ {rm x}^{-} and Ge_{rm x}^{ -} are presented. Unlike carbon clusters which prefer structures of low dimensionality, these

  4. Supersonic Line Broadening within Young and Massive Super Star Clusters

    CERN Document Server

    Tenorio-Tagle, G; Silich, S; Munoz-Tunon, C; Palous, J

    2009-01-01

    The origin of supersonic infrared and radio recombination nebular lines often detected in young and massive superstar clusters are discussed. We suggest that these arise from a collection of repressurizing shocks (RSs), acting effectively to re-establish pressure balance within the cluster volume and from the cluster wind which leads to an even broader although much weaker component. The supersonic lines are here shown to occur in clusters that undergo a bimodal hydrodynamic solution (Tenorio-Tagle et al. 2007), that is within clusters that are above the threshold line in the mechanical luminosity or cluster mass vs the size of the cluster (Silich et al. 2004). The plethora of repressurizing shocks is due to frequent and recurrent thermal instabilities that take place within the matter reinserted by stellar winds and supernovae. We show that the maximum speed of the RSs and of the cluster wind, are both functions of the temperature reached at the stagnation radius. This temperature depends only on the cluster...

  5. Stretchable nanocomposite electrodes with tunable mechanical properties by supersonic cluster beam implantation in elastomers

    Energy Technology Data Exchange (ETDEWEB)

    Borghi, F.; Podestà, A.; Milani, P., E-mail: pmilani@mi.infn.it [CIMAINA and Dipartimento di Fisica, Università degli Studi di Milano, via Celoria 16, 20133 Milano (Italy); Melis, C.; Colombo, L. [Dipartimento di Fisica, Università di Cagliari, Cittadella Universitaria, I-09042 Monserrato (Italy); Ghisleri, C.; Ravagnan, L. [WISE srl, Piazza Duse 2, 20122 Milano (Italy)

    2015-03-23

    We demonstrate the fabrication of gold-polydimethylsiloxane nanocomposite electrodes, by supersonic cluster beam implantation, with tunable Young's modulus depending solely on the amount of metal clusters implanted in the elastomeric matrix. We show both experimentally and by atomistic simulations that the mechanical properties of the nanocomposite can be maintained close to that of the bare elastomer for significant metal volume concentrations. Moreover, the elastic properties of the nanocomposite, as experimentally characterized by nanoindentation and modeled with molecular dynamics simulations, are also well described by the Guth-Gold classical model for nanoparticle-filled rubbers, which depends on the presence, concentration, and aspect ratio of metal nanoparticles, and not on the physical and chemical modification of the polymeric matrix due to the embedding process. The elastic properties of the nanocomposite can therefore be determined and engineered a priori, by controlling only the nanoparticle concentration.

  6. Electrochemical impedance spectroscopy on nanostructured carbon electrodes grown by supersonic cluster beam deposition

    Energy Technology Data Exchange (ETDEWEB)

    Bettini, Luca Giacomo; Bardizza, Giorgio; Podesta, Alessandro; Milani, Paolo; Piseri, Paolo, E-mail: piseri@mi.infn.it [Universita degli Studi di Milano, Dipartimento di Fisica and CIMaINa (Italy)

    2013-02-15

    Nanostructured porous films of carbon with density of about 0.5 g/cm{sup 3} and 200 nm thickness were deposited at room temperature by supersonic cluster beam deposition (SCBD) from carbon clusters formed in the gas phase. Carbon film surface topography, determined by atomic force microscopy, reveals a surface roughness of 16 nm and a granular morphology arising from the low kinetic energy ballistic deposition regime. The material is characterized by a highly disordered carbon structure with predominant sp2 hybridization as evidenced by Raman spectroscopy. The interface properties of nanostructured carbon electrodes were investigated by cyclic voltammetry and electrochemical impedance spectroscopy employing KOH 1 M solution as aqueous electrolyte. An increase of the double layer capacitance is observed when the electrodes are heat treated in air or when a nanostructured nickel layer deposited by SCBD on top of a sputter deposited film of the same metal is employed as a current collector instead of a plain metallic film. This enhancement is consistent with an improved charge injection in the active material and is ascribed to the modification of the electrical contact at the interface between the carbon and the metal current collector. Specific capacitance values up to 120 F/g have been measured for the electrodes with nanostructured metal/carbon interface.

  7. Computer simulation and visualization of supersonic jet for gas cluster equipment

    Science.gov (United States)

    Ieshkin, A.; Ermakov, Y.; Chernysh, V.; Ivanov, I.; Kryukov, I.; Alekseev, K.; Kargin, N.; Insepov, Z.

    2015-09-01

    Supersonic nozzle is a key component of a gas cluster condensation system. We describe a flow visualization system using glow discharge with annular or plane electrodes. The geometric parameters of a supersonic jet under typical conditions used in a gas cluster ion beam accelerator are investigated. As well numerical simulations were performed. Dependence of inlet and ambient pressures and nozzle throat diameter on the shock bottle dimensions is described for different working gases. Influence of condensation rate on shock bottle axial size is discussed.

  8. Computer simulation and visualization of supersonic jet for gas cluster equipment

    Energy Technology Data Exchange (ETDEWEB)

    Ieshkin, A. [Faculty of Physics, Lomonosov Moscow State University, Leninskie Gory, Moscow 119991 (Russian Federation); Ermakov, Y. [Scobeltsyn Nuclear Physics Research Institute, Lomonosov State Moscow University, GSP-1, Leninskiye Gory, Moscow 119991 (Russian Federation); Chernysh, V.; Ivanov, I. [Faculty of Physics, Lomonosov Moscow State University, Leninskie Gory, Moscow 119991 (Russian Federation); Kryukov, I. [Institute for Problems in Mechanics, Russian Academy of Sciences, prosp. Vernadskogo, 101, Block 1, Moscow 119526 (Russian Federation); Alekseev, K.; Kargin, N. [National Research Nuclear University «MEPhI», Kashirskoye shosse 31, Moscow 115409 (Russian Federation); Insepov, Z., E-mail: zinsepov@purdue.edu [Purdue University, 500 Central Drive, West Lafayette, IN (United States); Nazarbayev University Research and Innovation System, Kabanbay Batyr Avenue 53, Astana (Kazakhstan)

    2015-09-21

    Supersonic nozzle is a key component of a gas cluster condensation system. We describe a flow visualization system using glow discharge with annular or plane electrodes. The geometric parameters of a supersonic jet under typical conditions used in a gas cluster ion beam accelerator are investigated. As well numerical simulations were performed. Dependence of inlet and ambient pressures and nozzle throat diameter on the shock bottle dimensions is described for different working gases. Influence of condensation rate on shock bottle axial size is discussed.

  9. Synthesis of photocatalytic TiO2 nano-coatings by supersonic cluster beam deposition

    NARCIS (Netherlands)

    Fraters, B.D.; Cavaliere, E; Mul, G.; Gavioli, L.

    2014-01-01

    In this paper we report on the photocatalytic behavior in gas phase propane oxidation of well-defined TiO2 nanoparticle (NP) coatings prepared via Supersonic Cluster Beam Deposition (SCBD) on Si-wafers and quartz substrates. The temperature dependent crystal phase of the coatings was analyzed by Ram

  10. Polarizability effect in metallic clusters

    Indian Academy of Sciences (India)

    Ş Şentürk; K Harigaya; O Özsoy

    2006-03-01

    Langevin approach implemented in the inelastic cross-sections measured for the low-energy electrons colliding with metallic clusters points out that statical form of the polarizability dominate at energies less than 1.25 eV. The dynamical form comes into play at energies around 1.3 eV. The form of the polarizabilities indicates that polarizability of the metallic clusters is energy-dependent.

  11. Cluster Bose Metals

    OpenAIRE

    Ying, Tao; Dalmonte, Marcello; Angelone, Adriano; Mezzacapo, Fabio; Zoller, Peter; Pupillo, Guido

    2016-01-01

    Quantum phases of matter are usually characterised by broken symmetries. Identifying physical mechanisms and microscopic Hamiltonians that elude this paradigm is one of the key present challenges in many-body physics. Here, we use quantum Monte-Carlo simulations to show that a Bose metal phase, breaking no symmetries, is realized in simple Hubbard models for bosonic particles on a square lattice complemented by soft-shoulder interactions. The Bose metal appears at strong coupling and is separ...

  12. Condensed-Phase Mass Fraction in a Supersonic Molecular Beam Containing Clusters

    Science.gov (United States)

    Knuth, Eldon L.; Toennies, J. Peter

    2008-12-01

    For a supersonic molecular beam containing clusters, a relatively general and simple conservation-of-energy procedure for deducing from time-of-flight measurements the fraction of the beam in the condensed phase is developed. The procedure is applied to measurements for 4He beams formed by expansions which approach the two-phase region either near the critical point or to the liquid side of the critical point. The deduced values of the mass fraction are correlated using a scaling parameter which was used previously for correlating mean values of cluster sizes formed via fragmentation in free-jet expansions of liquid 4He.

  13. Nanomanufacturing of titania interfaces with controlled structural and functional properties by supersonic cluster beam deposition

    Science.gov (United States)

    Podestà, Alessandro; Borghi, Francesca; Indrieri, Marco; Bovio, Simone; Piazzoni, Claudio; Milani, Paolo

    2015-12-01

    Great emphasis is placed on the development of integrated approaches for the synthesis and the characterization of ad hoc nanostructured platforms, to be used as templates with controlled morphology and chemical properties for the investigation of specific phenomena of great relevance in interdisciplinary fields such as biotechnology, medicine, and advanced materials. Here, we discuss the crucial role and the advantages of thin film deposition strategies based on cluster-assembling from supersonic cluster beams. We select cluster-assembled nanostructured titania (ns-TiO2) as a case study to demonstrate that accurate control over morphological parameters can be routinely achieved, and consequently, over several relevant interfacial properties and phenomena, like surface charging in a liquid electrolyte, and proteins and nanoparticles adsorption. In particular, we show that the very good control of nanoscale morphology is obtained by taking advantage of simple scaling laws governing the ballistic deposition regime of low-energy, mass-dispersed clusters with reduced surface mobility.

  14. Nanomanufacturing of titania interfaces with controlled structural and functional properties by supersonic cluster beam deposition

    Energy Technology Data Exchange (ETDEWEB)

    Podestà, Alessandro, E-mail: alessandro.podesta@mi.infn.it, E-mail: pmilani@mi.infn.it; Borghi, Francesca; Indrieri, Marco; Bovio, Simone; Piazzoni, Claudio; Milani, Paolo, E-mail: alessandro.podesta@mi.infn.it, E-mail: pmilani@mi.infn.it [Centro Interdisciplinare Materiali e Interfacce Nanostrutturati (C.I.Ma.I.Na.), Dipartimento di Fisica, Università degli Studi di Milano, via Celoria 16, 20133 Milano (Italy)

    2015-12-21

    Great emphasis is placed on the development of integrated approaches for the synthesis and the characterization of ad hoc nanostructured platforms, to be used as templates with controlled morphology and chemical properties for the investigation of specific phenomena of great relevance in interdisciplinary fields such as biotechnology, medicine, and advanced materials. Here, we discuss the crucial role and the advantages of thin film deposition strategies based on cluster-assembling from supersonic cluster beams. We select cluster-assembled nanostructured titania (ns-TiO{sub 2}) as a case study to demonstrate that accurate control over morphological parameters can be routinely achieved, and consequently, over several relevant interfacial properties and phenomena, like surface charging in a liquid electrolyte, and proteins and nanoparticles adsorption. In particular, we show that the very good control of nanoscale morphology is obtained by taking advantage of simple scaling laws governing the ballistic deposition regime of low-energy, mass-dispersed clusters with reduced surface mobility.

  15. Cluster Effects during High Pressure Supersonic Molecular Beam Injection into Plasma

    Institute of Scientific and Technical Information of China (English)

    YAOLianghua; FENGBeibin; DONGJiafu; LIWenzhong; FENGZhen; HONGWenyu; LIBo

    2001-01-01

    When we speak of clusters, we have in mind entities which have neither the well-defined compositions, geometries, and strong bonds of conventional molecules northe boundary-independent properties of bulk matter. For example, an aggregate of a few atoms held together by Van der Waals forces constitutes a cluster. But clusters need not be weakly bound, several metal atoms bound together also constitute a cluster. Clusters need not be composed of a single kind of chemical entity, either atomic or molecular,

  16. Internal gettering by metal alloy clusters

    Science.gov (United States)

    Buonassisi, Anthony; Heuer, Matthias; Istratov, Andrei A.; Pickett, Matthew D.; Marcus, Mathew A.; Weber, Eicke R.

    2010-07-27

    The present invention relates to the internal gettering of impurities in semiconductors by metal alloy clusters. In particular, intermetallic clusters are formed within silicon, such clusters containing two or more transition metal species. Such clusters have melting temperatures below that of the host material and are shown to be particularly effective in gettering impurities within the silicon and collecting them into isolated, less harmful locations. Novel compositions for some of the metal alloy clusters are also described.

  17. Metallic bonding and cluster structure

    Energy Technology Data Exchange (ETDEWEB)

    Soler, Jose M. [Department of Physics, Lyman Laboratory, Harvard University, Cambridge, Massachusetts 02138 (United States); Departamento de Fisica de la Materia Condensada, Universidad Autonoma de Madrid, E-28049 Madrid, (Spain); Beltran, Marcela R. [Instituto de Investigaciones en Materiales, Universidad Nacional Autonoma de Mexico, Apartado Postal 70-360, Mexico Distrito Federal, 01000 Mexico (Mexico); Michaelian, Karo [Instituto de Fisica, Universidad Nacional Autonoma de Mexico, Apartado Postal 20-364, Mexico Distrito Federal, 01000 Mexico (Mexico); Garzon, Ignacio L. [Departamento de Fisica de la Materia Condensada, Universidad Autonoma de Madrid, E-28049 Madrid, (Spain); Instituto de Fisica, Universidad Nacional Autonoma de Mexico, Apartado Postal 20-364, Mexico Distrito Federal, 01000 Mexico (Mexico); Ordejon, Pablo [Institut de Ciencia de Materials de Barcelona-CSIC, Campus de la U.A.B., 08193 Bellaterra, Barcelona, (Spain); Sanchez-Portal, Daniel [Department of Physics and Materials Research Laboratory, University of Illinois, Urbana, Illinois 61801 (United States); Artacho, Emilio [Departamento de Fisica de la Materia Condensada, Universidad Autonoma de Madrid, E-28049 Madrid, (Spain)

    2000-02-15

    Knowledge of the structure of clusters is essential to predict many of their physical and chemical properties. Using a many-body semiempirical Gupta potential (to perform global minimizations), and first-principles density functional calculations (to confirm the energy ordering of the local minima), we have recently found [Phys. Rev. Lett. 81, 1600 (1998)] that there are many intermediate-size disordered gold nanoclusters with energy near or below the lowest-energy ordered structure. This is especially surprising because we studied ''magic'' cluster sizes, for which very compact-ordered structures exist. Here, we show how the analysis of the local stress can be used to understand the physical origin of this amorphization. We find that the compact ordered structures, which are very stable for pair potentials, are destabilized by the tendency of metallic bonds to contract at the surface, because of the decreased coordination. The amorphization is also favored by the relatively low energy associated to bondlength and coordination disorder in metals. Although these are very general properties of metallic bonding, we find that they are especially important in the case of gold, and we predict some general trends in the tendency of metallic clusters towards amorphous structures. (c) 2000 The American Physical Society.

  18. The influence of nanoscale morphology on the resistivity of cluster-assembled nanostructured metallic thin films

    Energy Technology Data Exchange (ETDEWEB)

    Barborini, E; Bertolini, G; Repetto, P; Leccardi, M; Vinati, S [Tethis srl, via Franco Russoli 3, 20143 Milano (Italy); Corbelli, G; Milani, P, E-mail: emanuele.barborini@tethis-lab.co, E-mail: pmilani@mi.infn.i [CIMAINA and Dipartimento di Fisica, Universita di Milano, via Celoria 16, 20133 Milano (Italy)

    2010-07-15

    We have studied in situ the evolution of the electrical resistivity of Fe, Pd, Nb, W and Mo cluster-assembled films during their growth by supersonic cluster beam deposition. We observed resistivity of cluster-assembled films several orders of magnitude larger than the bulk, as well as an increase in resistivity by increasing the film thickness in contrast to what was observed for atom-assembled metallic films. This suggests that the nanoscale morphological features typical of ballistic films growth, such as the minimal cluster-cluster interconnection and the evolution of surface roughness with thickness, are responsible for the observed behaviour.

  19. Supersonic cluster jet source for debris-free extreme ultraviolet production

    Energy Technology Data Exchange (ETDEWEB)

    Kubiak, G.D.; Bernardez, L.J.

    1997-09-01

    The supersonic cluster jet has been developed and characterized for use as a target medium to produce a clean source of extreme ultraviolet radiation for extreme ultraviolet lithography and other applications. Spectroscopic characterization of the laser plasma emission produced from Xe, O{sub 2} and Kr cluster gas targets has been performed. Xe is the most efficient target gas, exhibiting a conversion efficiency at 13.5 nm of 0.8% into the relevant 2.5% spectral bandwidth. The other target gases are less efficient in the spectral region of interest and, in the case of oxygen, emit {approximately}5 times less off-band radiation. The angular distribution of the Xe plasma emission has also been characterized.

  20. The Clustering of Intergalactic Metals

    CERN Document Server

    Pichon, C; Aracil, B; Petitjean, P; Aubert, D; Bergeron, J; Colombi, S; Pichon, Christophe; Scannapieco, Evan; Aracil, Bastien; Petitjean, Patrick; Aubert, Dominique; Bergeron, Jacqueline; Colombi, Stephane

    2003-01-01

    We measure the spatial clustering of metals in the intergalactic medium from z = 1.7 to 3.0, as traced by 643 CIV and 104 SiIV N >= 10^12 cm^-2 absorption systems in 19 high signal-to-noise (40-80) and high resolution (R = 45000) quasar spectra. The number densities and two-point correlation functions of both these species are largely constant with redshift, suggesting the bulk of metal ejection occurred at z >= 3. However, at z = M_s, and use numerical simulations to derive best-fit values of R_s ~ 2 comoving Mpc and M_s ~ 5x10^11 solar masses at z = 3. This does not exclude that metals could have been produced at higher redshifts in smaller, but equally rare, objects. At the level of detection of this survey, IGM enrichment is likely to be incomplete and inhomogeneous, with a filling factor ~ 10%.

  1. Synthesis of photocatalytic TiO{sub 2} nano-coatings by supersonic cluster beam deposition

    Energy Technology Data Exchange (ETDEWEB)

    Fraters, Bindikt D. [Photo Catalytic Synthesis Group, MESA+ Institute for Nanotechnology, Faculty of Science and Technology, University of Twente, P.O. Box 217, 7500 AE Enschede (Netherlands); Cavaliere, Emanuele [Dipartimento di Matematica e Fisica and Interdisciplinary Laboratories for Advanced Materials Physics (i-Lamp), Università Cattolica del Sacro Cuore, Via dei Musei 41, Brescia 25121 (Italy); Mul, Guido [Photo Catalytic Synthesis Group, MESA+ Institute for Nanotechnology, Faculty of Science and Technology, University of Twente, P.O. Box 217, 7500 AE Enschede (Netherlands); Gavioli, Luca, E-mail: luca.gavioli@unicatt.it [Dipartimento di Matematica e Fisica and Interdisciplinary Laboratories for Advanced Materials Physics (i-Lamp), Università Cattolica del Sacro Cuore, Via dei Musei 41, Brescia 25121 (Italy)

    2014-12-05

    Graphical abstract: - Highlights: • Synthesis of well-defined TiO{sub 2} coatings by supersonic cluster beam deposition. • Morphology is studied for samples annealed at 500, 650 and 800 °C by HR-SEM. • Anatase (500, 650 °C) and Rutile (800 °C) are observed by Raman spectroscopy. • Quartz support improved the coating activity by factor 4–6 compared to Si-wafer. • Silicon is detrimental for photocatalytic activity promoting charge recombination. - Abstract: In this paper we report on the photocatalytic behavior in gas phase propane oxidation of well-defined TiO{sub 2} nanoparticle (NP) coatings prepared via Supersonic Cluster Beam Deposition (SCBD) on Si-wafers and quartz substrates. The temperature dependent crystal phase of the coatings was analyzed by Raman spectroscopy, and the morphology by High Resolution-Scanning Electron Microscopy. SCBD deposition in the presence of oxygen enables the in situ synthesis of TiO{sub 2} layers of amorphous NP at room temperature. Adapting the deposition temperature to 500 °C or 650 °C leads to Anatase crystals of variable size ranges, and layers showing significant porosity. At 800 °C mainly Rutile is formed. Post annealing by wafer heating of the amorphous NP prepared at room temperature results in comparable temperature dependent phases and morphologies. Photocatalytic activity in propane oxidation was dependent on the morphology of the samples: the activity decreases as a function of increasing particle size. The presence of water vapor in the propane feed generally increased the activity of the wafer-heated samples, suggesting OH groups are not profoundly present on SCBD synthesized layers. In addition, a remarkable effect of the substrate (Si or Quartz) was observed: strong interaction between Si and TiO{sub 2} is largely detrimental for photocatalytic activity. The consequences of these findings for the application of SCBD to synthesize samples for fundamental (spectroscopic) study of photocatalysis are

  2. Quantum chemical treatments of metal clusters.

    Science.gov (United States)

    Weigend, Florian; Ahlrichs, Reinhart

    2010-03-28

    This work focuses on finding and rationalizing the building principles of clusters with approximately 300 atoms of different types of metals: main group elements (Al, Sn), alkaline earth metals (Mg), transition metals (Pd) and clusters consisting of two different elements (Ir and Pt). Two tools are inevitable for this purpose: (i) quantum chemical methods that are able to treat a given cluster with both sufficient accuracy and efficiency and (ii) algorithms that are able to systematically scan the (3n-6)-dimensional potential surface of an n-atomic cluster for promising isomers. Currently, the only quantum chemical method that can be applied to metal clusters is density functional theory (DFT). Other methods either do not account for the multi-reference character of metal clusters or are too expensive and thus can be applied only to clusters of very few atoms, which usually is not sufficient for studying the building principles. The accuracy of DFT is not known a priori, but extrapolations to bulk values from calculated series of data show satisfying agreement with experimental data. For scans of the potential surface, simulated annealing techniques or genetic algorithms were used for the smaller clusters (approx. 20-30 atoms), and for the larger clusters considerations were restricted to selected packings and shapes. For the mixed-metallic clusters, perturbation theory turned out to be efficient and successful for finding the most promising distributions of the two atom types at the different sites.

  3. Characteristics of laser supersonic heating method for producing micro metallic particles

    Science.gov (United States)

    Lin, Shih-Lung; Lin, Jehnming

    2005-10-01

    In this article, the authors analyzed the process characteristics of laser supersonic heating method for producing metallic particles and predicted the in-flight tracks and shapes of micro-particles. A pulse Nd-YAG laser was used to heat the carbon steel target placed within an air nozzle. The high-pressure air with supersonic velocity was used to carry out carbon steel particles in the nozzle. The shock wave structures at the nozzle exit were visualized by the shadowgraph method. The carbon steel particles produced by laser supersonic heating method were grabbed and the spraying angles of the particle tracks were visualized. The velocity of the in-flight particles was measured by a photodiode sensor and compared with the numerical result. The solidification of carbon steel particles with diameters of 1-50 μm in compressible flow fields were investigated. The result shows that there is no significant difference in the dimension of solid carbon steel particles produced at shock wave fields under various entrance pressures (3-7 bar) with a constant laser energy radiation.

  4. Nanosized alkali-metal-doped ethoxotitanate clusters.

    Science.gov (United States)

    Chen, Yang; Trzop, Elzbieta; Makal, Anna; Sokolow, Jesse D; Coppens, Philip

    2013-05-06

    The synthesis and crystallographic characterization of alkali-metal-doped ethoxotitanate clusters with 28 and 29 Ti atoms as well as a new dopant-free Ti28 cluster are presented. The light-metal-doped polyoxotitanate clusters in which the alkali-metal atom is the critical structure-determining component are the largest synthesized so far. Calculations show that doping with light alkali atoms narrows the band gap compared with the nondoped crystals but does not introduce additional energy levels within the band gap.

  5. On metallic clusters squeezed in atomic cages

    CERN Document Server

    Apostol, M

    1996-01-01

    The stability of metallic clusters of sodium (Na) in the octahedral cages of Na-doped fullerites Na6C60 and Na11C60 is discussed within a Thomas-Fermi model. It is shown that the tetrahedral Na4-cluster in Na6C60 has an electric charge of cca. +2.7 (in electron charge units), while the body-centered cubic Na9-cluster in Na11C60 is almost electrically neutral.

  6. XMM Observations of Metal Abundances in Galaxy Clusters

    Directory of Open Access Journals (Sweden)

    L. Lovisari

    2011-01-01

    Full Text Available The hot gas that fills the space between galaxies in clusters is rich in metals. Due to their large potential well, galaxy clusters accumulate metals over the whole history of the cluster, and retain important information on cluster formation and evolution.We derive detailed metallicity maps for a sample of 5 clusters, observed with XMM-Newton, to study the distribution of metals in the Intra-Cluster Medium (ICM. We show that even in relaxed clusters the distribution of metals shows many inhomogeneities with several maxima separated by low metallicity regions. We also found a deviation from the expected temperature-metallicity relation.

  7. Flow characteristics and micro-scale metallic particle formation in the laser supersonic heating technique

    Science.gov (United States)

    Lin, Shih-Lung; Lin, Jehnming

    2007-02-01

    The characteristics of the supersonic flow of the laser heating technique for producing micro-scale metallic particles were investigated in this study. A numerical model was established to predict the flow fields and particle trajectories leaving a spray nozzle with shock wave effects. The compressible flow of the shock waves and the trajectories of particles in diameters of 1-20 μm were simulated and compared with the flow visualization. In the experiment, a pulsed Nd-YAG laser was used as heat source on a carbon steel target within the nozzle, and the carbon steel particles were ejected by high-pressure air. The result shows that the shock wave structures were generated at various entrance pressures, and there is a significant increase in the amount of carbon steel particles and the spraying angles by increasing the entrance air pressure.

  8. Infrared absorption imaging of 2D supersonic jet expansions: Free expansion, cluster formation, and shock wave patterns.

    Science.gov (United States)

    Zischang, Julia; Suhm, Martin A

    2013-07-14

    N2O/He gas mixtures are expanded through a 10 × 0.5 mm(2) slit nozzle and imaged by direct absorption vibrational spectroscopy, employing a HgCdTe focal plane array detector after interferometric modulation. N2O cluster formation in the free supersonic expansion is visualized. The expansion structure behind the frontal shock is investigated as a function of background pressure. At high pressures, a sequence of stationary density peaks along a narrow directed flow channel is characterized. The potential of the technique for the elucidation of aggregation mechanisms is emphasized.

  9. Structural evolution and metallicity of lead clusters

    Science.gov (United States)

    Götz, Daniel A.; Shayeghi, Armin; Johnston, Roy L.; Schwerdtfeger, Peter; Schäfer, Rolf

    2016-05-01

    The evolution of the metallic state in lead clusters and its structural implications are subject to ongoing discussions. Here we present molecular beam electric deflection studies of neutral PbN (N = 19-25, 31, 36, 54) clusters. Many of them exhibit dipole moments or anomalies of the polarizability indicating a non-metallic state. In order to resolve their structures, the configurational space is searched using the Pool Birmingham Cluster Genetic algorithm based on density functional theory. Spin-orbit effects on the geometries and dipole moments are taken into account by further relaxing them with two-component density functional theory. Geometries and dielectric properties from quantum chemical calculations are then used to simulate beam deflection profiles. Structures are assigned by the comparison of measured and simulated beam profiles. Energy gaps are calculated using time-dependent density functional theory. They are compared to Kubo gaps, which are an indicator of the metallicity in finite particles. Both, experimental and theoretical data suggest that lead clusters are not metallic up to at least 36 atoms.The evolution of the metallic state in lead clusters and its structural implications are subject to ongoing discussions. Here we present molecular beam electric deflection studies of neutral PbN (N = 19-25, 31, 36, 54) clusters. Many of them exhibit dipole moments or anomalies of the polarizability indicating a non-metallic state. In order to resolve their structures, the configurational space is searched using the Pool Birmingham Cluster Genetic algorithm based on density functional theory. Spin-orbit effects on the geometries and dipole moments are taken into account by further relaxing them with two-component density functional theory. Geometries and dielectric properties from quantum chemical calculations are then used to simulate beam deflection profiles. Structures are assigned by the comparison of measured and simulated beam profiles. Energy gaps

  10. (Electronic structure and reactivities of transition metal clusters)

    Energy Technology Data Exchange (ETDEWEB)

    1992-01-01

    The following are reported: theoretical calculations (configuration interaction, relativistic effective core potentials, polyatomics, CASSCF); proposed theoretical studies (clusters of Cu, Ag, Au, Ni, Pt, Pd, Rh, Ir, Os, Ru; transition metal cluster ions; transition metal carbide clusters; bimetallic mixed transition metal clusters); reactivity studies on transition metal clusters (reactivity with H{sub 2}, C{sub 2}H{sub 4}, hydrocarbons; NO and CO chemisorption on surfaces). Computer facilities and codes to be used, are described. 192 refs, 13 figs.

  11. Pulsed supersonic molecular beam for characterization of chemically active metal-organic complexes at surfaces

    Science.gov (United States)

    Lear, Amanda M.

    Metal-organic coordination networks (MOCNs) at surfaces consist of a complex of organic ligands bound to an atomic metal center. The MOCNs, when chosen appropriately, can form highly-ordered arrays at surfaces. Ultra-high vacuum surface studies allow control of surface composition and provide 2D growth restrictions, which lead to under-coordinated metal centers. These systems provide an opportunity to tailor the chemical function of the metal centers due to the steric restrictions imposed by the surface. Tuning the adsorption/desorption energy at a metal center and developing a cooperative environment for catalysis are the key scientific questions that motivate the construction of a molecular beam surface analysis system. Characterization of the created systems can be performed utilizing a pulsed supersonic molecular beam (PSMB) in unison with a quadrupole mass spectrometer. A PSMB allows for the highly controlled delivery of reactants with well-defined energy to a given platform making it possible to elucidate detailed chemical tuning information. In this thesis, a summary of prior theoretical molecular beam derivations is provided. Design considerations and an overview of the construction procedure for the current molecular beam apparatus, including initial characterization experiments, are presented. By impinging an Ar beam on a Ag(111) surface, the location of the specular angle (˜65°) and rough sample perimeter coordinates were determined. Additionally, surface analysis experiments, mainly Auger Electron Spectroscopy (AES), were performed to investigate the oxidation of epitaxial graphene on the SiC(0001) surface utilizing an oxygen cracking method. The AES experiments are described in detail and highlight the challenges that were faced when several different graphene samples were used for the oxygen adsorption/desorption experiments.

  12. Solidification analysis of micro-scale metallic particles in the laser supersonic heating technique

    Science.gov (United States)

    Lin, Shih-Lung; Lin, Jehnming

    2004-04-01

    In this paper, the authors analysed the solidification phenomenon in the laser supersonic heating technique used for producing metallic particles. A mathematical model was established to predict the velocity, temperature and solidification situation of metallic particles leaving a spray nozzle. The numerical analysis method was used to simulate the flow field structure of shock waves and to proceed with related experiment. In the experiment, a pulsed Nd-YAG laser was used as the heat source on a carbon steel target within the nozzle, and carbon steel particles were ejected by high pressure air. The solidification problem of carbon steel particles with radii of 1-50 µm in the compressible flow field was calculated and compared with experimental results. The result shows that the shock wave flow fields are generated at different entrance pressures (3-7 bar), and there is no significant difference in the radii of carbon steel particles produced by a fixed laser energy; however, in the flow field without the shock wave effect, the cooling effect is less evident in the solidification process.

  13. Electrophobic interaction induced impurity clustering in metals

    Energy Technology Data Exchange (ETDEWEB)

    Zhou, Hong-Bo; Wang, Jin-Long; Jiang, W.; Lu, Guang-Hong; Aguiar, J. A.; Liu, Feng

    2016-10-01

    We introduce the concept of electrophobic interaction, analogous to hydrophobic interaction, for describing the behavior of impurity atoms in a metal, a 'solvent of electrons'. We demonstrate that there exists a form of electrophobic interaction between impurities with closed electron shell structure, which governs their dissolution behavior in a metal. Using He, Be and Ar as examples, we predict by first-principles calculations that the electrophobic interaction drives He, Be or Ar to form a close-packed cluster with a clustering energy that follows a universal power-law scaling with the number of atoms (N) dissolved in a free electron gas, as well as W or Al lattice, as Ec is proportional to (N2/3-N). This new concept unifies the explanation for a series of experimental observations of close-packed inert-gas bubble formation in metals, and significantly advances our fundamental understanding and capacity to predict the solute behavior of impurities in metals, a useful contribution to be considered in future material design of metals for nuclear, metallurgical, and energy applications.

  14. Characterization of cluster/monomer ratio in pulsed supersonic gas jets

    Science.gov (United States)

    Gao, Xiaohui; Shim, Bonggu; Wang, Xiaoming; Downer, Mike

    2008-11-01

    While Rayleigh scatter and interferometry are standard methods for determining average cluster size and total atomic density, respectively, in cluster gas jets, determination of cluster mass fraction has required additional input from gasdynamic simulations. Here we determine cluster mass fraction experimentally with fs-time-resolved measurement of refractive index using frequency domain interferometery (FDI) after ionization and heating by a pump pulse. The essence of this method is that the negative index contribution of monomer plasma appears immediately after ionization by the pump, whereas the positive contribution of clustered plasma becomes significant only after clusters expand to a Mie resonance condition, enabling separation of monomer and cluster densities in the time domain. This method allows us to investigate various influences (nozzle geometry, temperature, etc.) on cluster fraction, which varies widely in nominally identical gas jets, and is a critical parameter in realizing phase-matched harmonic generation at high laser intensity, which would lead to an efficient table-top soft X-ray source.

  15. Probing the bonding of CO to heteronuclear group 4 metal-nickel clusters by photoelectron spectroscopy.

    Science.gov (United States)

    Zou, Jinghan; Xie, Hua; Yuan, Qinqin; Zhang, Jumei; Dai, Dongxu; Fan, Hongjun; Tang, Zichao; Jiang, Ling

    2017-04-12

    A series of heterobinuclear group 4 metal-nickel carbonyls MNi(CO)n(-) (M = Ti, Zr, Hf; n = 3-7) has been generated via a laser vaporization supersonic cluster source and characterized by mass-selected photoelectron velocity-map imaging spectroscopy. Quantum chemical calculations have been carried out to elucidate the geometric and electronic structures and support the spectral assignments. The n = 3 cluster is determined to be capable of simultaneously accommodating three different types of CO bonds (i.e., side-on-bonded, bridging, and terminal modes), resulting in a MNi[η(2)(μ2-C, O)](μ-CO)(CO)(-) structure, which represents the smallest metal carbonyl with the involvement of all the main modes of metal-CO coordination to date. The building block of three bridging CO molecules is favored at n = 4, the structure of which persists up to n = 7. The additional CO ligands are bonded terminally to the metal atoms. The present findings provide important new insight into the structure and bonding mechanisms of CO molecules with heteronuclear transition metals, which would have important implications for understanding chemisorbed CO molecules on alloy surfaces.

  16. On the metallicity of open clusters. III. Homogenised sample

    CERN Document Server

    Netopil, M; Heiter, U; Soubiran, C

    2016-01-01

    Open clusters are known as excellent tools for various topics in Galactic research. For example, they allow accurately tracing the chemical structure of the Galactic disc. However, the metallicity is known only for a rather low percentage of the open cluster population, and these values are based on a variety of methods and data. Therefore, a large and homogeneous sample is highly desirable. In the third part of our series we compile a large sample of homogenised open cluster metallicities using a wide variety of different sources. These data and a sample of Cepheids are used to investigate the radial metallicity gradient, age effects, and to test current models. We used photometric and spectroscopic data to derive cluster metallicities. The different sources were checked and tested for possible offsets and correlations. In total, metallicities for 172 open cluster were derived. We used the spectroscopic data of 100 objects for a study of the radial metallicity distribution and the age-metallicity relation. W...

  17. Deposition of metal Islands, metal clusters and metal containing single molecules on self-assembled monolayers

    NARCIS (Netherlands)

    Speets, Emiel Adrianus

    2005-01-01

    The central topic of this thesis is the deposition of metals on Self-Assembled Monolayers (SAMs). Metals are deposited in the form of submicron scale islands, nanometer scale clusters, and as supramolecular, organometallic coordination cages. Several SAMs on various substrates were prepared and anal

  18. On the metallicity of open clusters. III. Homogenised sample

    Science.gov (United States)

    Netopil, M.; Paunzen, E.; Heiter, U.; Soubiran, C.

    2016-01-01

    Context. Open clusters are known as excellent tools for various topics in Galactic research. For example, they allow accurately tracing the chemical structure of the Galactic disc. However, the metallicity is known only for a rather low percentage of the open cluster population, and these values are based on a variety of methods and data. Therefore, a large and homogeneous sample is highly desirable. Aims: In the third part of our series we compile a large sample of homogenised open cluster metallicities using a wide variety of different sources. These data and a sample of Cepheids are used to investigate the radial metallicity gradient, age effects, and to test current models. Methods: We used photometric and spectroscopic data to derive cluster metallicities. The different sources were checked and tested for possible offsets and correlations. Results: In total, metallicities for 172 open cluster were derived. We used the spectroscopic data of 100 objects for a study of the radial metallicity distribution and the age-metallicity relation. We found a possible increase of metallicity with age, which, if confirmed, would provide observational evidence for radial migration. Although a statistical significance is given, more studies are certainly needed to exclude selection effects, for example. The comparison of open clusters and Cepheids with recent Galactic models agrees well in general. However, the models do not reproduce the flat gradient of the open clusters in the outer disc. Thus, the effect of radial migration is either underestimated in the models, or an additional mechanism is at work. Conclusions: Apart from the Cepheids, open clusters are the best tracers for metallicity over large Galactocentric distances in the Milky Way. For a sound statistical analysis, a sufficiently large and homogeneous sample of cluster metallicities is needed. Our compilation is currently by far the largest and provides the basis for several basic studies such as the statistical

  19. Molecular dynamical simulations of melting behaviors of metal clusters

    Directory of Open Access Journals (Sweden)

    Ilyar Hamid

    2015-04-01

    Full Text Available The melting behaviors of metal clusters are studied in a wide range by molecular dynamics simulations. The calculated results show that there are fluctuations in the heat capacity curves of some metal clusters due to the strong structural competition; For the 13-, 55- and 147-atom clusters, variations of the melting points with atomic number are almost the same; It is found that for different metal clusters the dynamical stabilities of the octahedral structures can be inferred in general by a criterion proposed earlier by F. Baletto et al. [J. Chem. Phys. 116 3856 (2002] for the statically stable structures.

  20. Development of a molecular-dynamics-based cluster-heat-capacity model for study of homogeneous condensation in supersonic water-vapor expansions.

    Science.gov (United States)

    Borner, Arnaud; Li, Zheng; Levin, Deborah A

    2013-02-14

    Supersonic expansions to vacuum produce clusters of sufficiently small size that properties such as heat capacities and latent heat of evaporation cannot be described by bulk vapor thermodynamic values. In this work the Monte-Carlo Canonical-Ensemble (MCCE) method was used to provide potential energies and constant-volume heat capacities for small water clusters. The cluster structures obtained using the well-known simple point charge model were found to agree well with earlier simulations using more rigorous potentials. The MCCE results were used as the starting point for molecular dynamics simulations of the evaporation rate as a function of cluster temperature and size which were found to agree with unimolecular dissociation theory and classical nucleation theory. The heat capacities and latent heat obtained from the MCCE simulations were used in direct-simulation Monte-Carlo of two experiments that measured Rayleigh scattering and terminal dimer mole fraction of supersonic water-jet expansions. Water-cluster temperature and size were found to be influenced by the use of kinetic rather than thermodynamic heat-capacity and latent-heat values as well as the nucleation model.

  1. Inhomogeneous Metal Distribution in the Intra-Cluster Medium

    CERN Document Server

    Lovisari, L; Kapferer, W

    2011-01-01

    The hot gas that fills the space between galaxies in clusters is rich in metals. In their large potential wells, galaxy clusters accumulate metals over the whole cluster history and hence they retain important information on cluster formation and evolution. We use a sample of 5 cool core clusters to study the distribution of metals in the ICM. We investigate whether the X-ray observations yield good estimates for the metal mass and whether the heavy elements abundances are consistent with a certain relative fraction of SN Ia to SNCC. We derive detailed metallicity maps of the clusters from XMM - Newton observations and we use them as a measure for the metal mass in the ICM. We determine radial profiles for several elements and using population synthesis and chemical enrichment models, we study the agreement between the measured abundances and the theoretical yields. We show that even in relaxed clusters the distribution of metals show a lot of inhomogeneities. Using metal maps usually gives a metal mass 10-30...

  2. Structure and Dynamics in Metal-Containing Clusters

    Science.gov (United States)

    2010-03-11

    produced composed of a metal ion bound to one or more molecular "ligands" (e.g., water, nitrogen, acetylene , methanol, etc.). These gas phase...NUMBER OF PAGES metal clusters, metal ions, metal-ligand interactions, solvation 12 16. PRICE CODE 17. SECURITY CLASSIFICATION 18. SECURITY CLASSIFICATION...which confirms the it-complex structure. Vibrational frequencies in the excited state are measured for the metal- acetylene stretch, the C-C stretch, the

  3. Further definition of the mass-metallicity relation in globular cluster systems around brightest cluster galaxies

    NARCIS (Netherlands)

    Cockcroft, R.; Harris, W.E.; Wehner, E.M.; Whitmore, B.C.; Rothberg, B.

    2009-01-01

    We combine the globular cluster (GC) data for 15 brightest cluster galaxies and use this material to trace the mass–metallicity relations (MMRs) in their globular cluster systems (GCSs). This work extends previous studies which correlate the properties of the MMR with those of the host galaxy. Our c

  4. Electronic Structure and Geometries of Small Compound Metal Clusters

    Energy Technology Data Exchange (ETDEWEB)

    NONE

    1999-04-14

    During the tenure of the DOE grant DE-FG05-87EI145316 we have concentrated on equilibrium geometries, stability, and the electronic structure of transition metal-carbon clusters (met-cars), clusters designed to mimic the chemistry of atoms, and reactivity of homo-nuclear metal clusters and ions with various reactant molecules. It is difficult to describe all the research the authors have accomplished as they have published 38 papers. In this report, they outline briefly the salient features of their work on the following topics: (1) Designer Clusters: Building Blocks for a New Class of Solids; (2) Atomic Structure, Stability, and Electronic Properties of Metallo-Carbohedrenes; (3) Reactivity of Metal Clusters with H{sub 2} and NO; and (4) Anomalous Spectroscopy of Li{sub 4} Clusters.

  5. Electronic Structure and Geometries of Small Compound Metal Clusters

    Energy Technology Data Exchange (ETDEWEB)

    NONE

    1999-04-14

    During the tenure of the DOE grant DE-FG05-87EI145316 we have concentrated on equilibrium geometries, stability, and the electronic structure of transition metal-carbon clusters (met-cars), clusters designed to mimic the chemistry of atoms, and reactivity of homo-nuclear metal clusters and ions with various reactant molecules. It is difficult to describe all the research the authors have accomplished as they have published 38 papers. In this report, they outline briefly the salient features of their work on the following topics: (1) Designer Clusters: Building Blocks for a New Class of Solids; (2) Atomic Structure, Stability, and Electronic Properties of Metallo-Carbohedrenes; (3) Reactivity of Metal Clusters with H{sub 2} and NO; and (4) Anomalous Spectroscopy of Li{sub 4} Clusters.

  6. Gas phase metal cluster model systems for heterogeneous catalysis.

    Science.gov (United States)

    Lang, Sandra M; Bernhardt, Thorsten M

    2012-07-14

    Since the advent of intense cluster sources, physical and chemical properties of isolated metal clusters are an active field of research. In particular, gas phase metal clusters represent ideal model systems to gain molecular level insight into the energetics and kinetics of metal-mediated catalytic reactions. Here we summarize experimental reactivity studies as well as investigations of thermal catalytic reaction cycles on small gas phase metal clusters, mostly in relation to the surprising catalytic activity of nanoscale gold particles. A particular emphasis is put on the importance of conceptual insights gained through the study of gas phase model systems. Based on these concepts future perspectives are formulated in terms of variation and optimization of catalytic materials e.g. by utilization of bimetals and metal oxides. Furthermore, the future potential of bio-inspired catalytic material systems are highlighted and technical developments are discussed.

  7. Estimating the Metallicity of Old Star Clusters in M33

    Institute of Scientific and Technical Information of China (English)

    2002-01-01

    Based on the method proposed by Kong et al. And on the multi-color spectrophotometry by Ma et al., we estimate the metallicities of 16 old star clusters in the nearby spiral galaxy M33, ten of which are halo globular clusters. These old clusters are all metal poor, the range of metallicity ([Fe/H]) is from -0.14 to -2.12.In general, our results are consistent with those derived by other methods, such as integrated spectra and photometry, and our study confirms the reliability of the method of Kong et al.

  8. Nanosized metal clusters : Challenges and opportunities

    NARCIS (Netherlands)

    De Hosson, JTM; Palasantzas, G; Vystavel, T; Koch, S

    2004-01-01

    This article presents challenges and opportunities to control the microstructure in nanostructured coatings using a nanocluster source. The cluster size distribution is monodisperse and the kinetic energy of the clusters during deposition can be varied. Interestingly, the clusters are grown in extre

  9. Ionisation Potentials of Metal Carbide Clusters

    Science.gov (United States)

    Dryza, Viktoras; Addicoat, M.; Gascooke, Jason; Buntine, Mark; Metha, Gregory

    2006-03-01

    Photo-Ionisation Efficiency (PIE) experiments have been performed on gas phase niobium and tantalum carbide clusters to determine their ionisation potentials (IPs). For TanCm (n = 3-4, m = 0-4) clusters an oscillatory behaviour is observed such that clusters with an odd number of carbon atoms have higher IPs and clusters with an even number of carbons have lower IPs. Excellent agreement is found with relative IPs calculated using density functional theory for the lowest energy structures, which are consistent with the development of a 2x2x2 face-centred nanocrystal. For the niobium carbide clusters we observe the species Nb4C5 and Nb4C6. Initial calculations suggest that these clusters contain carbon-carbon bonding. Interestingly, the stoichiometry for Nb4C6 is half that of a metcar, M8C12. Preliminary data will also be shown on bimetallic-carbide clusters.

  10. Clusters distributions on charges and dimensions at ion metal sputtering

    CERN Document Server

    Matveev, V I

    2001-01-01

    The theory on the metal sputtering in form of large (with the atoms number N >= 5) neutral and charged clusters under the impact of the ion bombardment is considered. The probability of the cluster emission, consisting of the N atoms, is calculated on the basis of the Einstein model. The charge state of the cluster, consisting of the N atoms, is determined. The obtained formulae agree well with the experimental results. It is noted, that the mass-spectra of the neutral clusters slightly depend on the target temperature, whereas the mass-spectra of the single charge clusters essentially depend on the target temperature

  11. METALS IN THE ICM: WITNESSES OF CLUSTER FORMATION AND EVOLUTION

    Directory of Open Access Journals (Sweden)

    Lorenzo Lovisari

    2013-12-01

    Full Text Available The baryonic composition of galaxy clusters and groups is dominated by a hot, X-ray emitting Intra-Cluster Medium (ICM. The mean metallicity of the ICM has been found to be roughly 0.3 ÷ 0.5 times the solar value, therefore a large fraction of this gas cannot be of purely primordial origin. Indeed, the distribution and amount of metals in the ICM is a direct consequence of the past history of star formation in the cluster galaxies and of the processes responsible for the injection of enriched material into the ICM. We here shortly summarize the current views on the chemical enrichment, focusing on the observational evidence in terms of metallicity measurements in clusters, spatial metallicity distribution and evolution, and expectations from future missions.

  12. Orbital Magnetism and Dynamics in Alkali Metal Clusters

    CERN Document Server

    Nesterenko, V O; De Souza-Cruz, F F; Marinelli, J R

    2000-01-01

    Two remarkable orbital magnetic resonances, M1 scissor mode and M2 twist mode, are predicted in deformed and spherical metal clusters, respectively. We show that these resonances provide a valuable information about many cluster properties (quadrupole deformation, magnetic susceptibility, single-particle spectrum, etc.)

  13. Metal Enrichment Processes in the Intra-Cluster Medium

    CERN Document Server

    Schindler, S; Domainko, W; Mair, M; Van Kampen, E; Kronberger, T; Kimeswenger, S; Ruffert, M; Mangete, O E; Breitschwerdt, D

    2005-01-01

    We present numerical simulations of galaxy clusters which include interaction processes between the galaxies and the intra-cluster gas. The considered interaction processes are galactic winds and ram-pressure stripping, which both transfer metal-enriched interstellar medium into the intra-cluster gas and hence increase its metallicity. We investigate the efficiency and time evolution of the interaction processes by simulated metallicity maps, which are directly comparable to those obtained from X-ray observations. We find that ram-pressure stripping is more efficient than quiet (i.e. non-starburst driven) galactic winds in the redshift interval between 1 and 0. The expelled metals are not mixed immediately with the intra-cluster gas, but inhomogeneities are visible in the metallicity maps. Even stripes of higher metallicity that a single galaxy has left behind can be seen. The spatial distribution of the metals transported by ram-pressure stripping and by galactic winds are very different for massive clusters...

  14. Infrared Multiple Photon Dissociation Spectroscopy Of Metal Cluster-Adducts

    Science.gov (United States)

    Cox, D. M.; Kaldor, A.; Zakin, M. R.

    1987-01-01

    Recent development of the laser vaporization technique combined with mass-selective detection has made possible new studies of the fundamental chemical and physical properties of unsupported transition metal clusters as a function of the number of constituent atoms. A variety of experimental techniques have been developed in our laboratory to measure ionization threshold energies, magnetic moments, and gas phase reactivity of clusters. However, studies have so far been unable to determine the cluster structure or the chemical state of chemisorbed species on gas phase clusters. The application of infrared multiple photon dissociation IRMPD to obtain the IR absorption properties of metal cluster-adsorbate species in a molecular beam is described here. Specifically using a high power, pulsed CO2 laser as the infrared source, the IRMPD spectrum for methanol chemisorbed on small iron clusters is measured as a function of the number of both iron atoms and methanols in the complex for different methanol isotopes. Both the feasibility and potential utility of IRMPD for characterizing metal cluster-adsorbate interactions are demonstrated. The method is generally applicable to any cluster or cluster-adsorbate system dependent only upon the availability of appropriate high power infrared sources.

  15. Thermodynamics of Pore Filling Metal Clusters in Metal Organic Frameworks: Pd in UiO-66

    DEFF Research Database (Denmark)

    Vilhelmsen, Lasse; Sholl, David S.

    2012-01-01

    Metal organic frameworks (MOFs) have experimentally been demonstrated to be capable of supporting isolated transition-metal clusters, but the stability of these clusters with respect to aggregation is unclear. In this letter we use a genetic algorithm together with density functional theory calcu...

  16. Thermodynamics of Pore Filling Metal Clusters in Metal Organic Frameworks: Pd in UiO-66

    DEFF Research Database (Denmark)

    Vilhelmsen, Lasse; Sholl, David S.

    2012-01-01

    Metal organic frameworks (MOFs) have experimentally been demonstrated to be capable of supporting isolated transition-metal clusters, but the stability of these clusters with respect to aggregation is unclear. In this letter we use a genetic algorithm together with density functional theory...

  17. Metallic Softness Influence on Magic Numbers of Clusters

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    The metallic softness parameter αr0 determines the structure of the cluster and governs the rule of magic numbers. Using molecular dynamic method, the stable structures and magic numbers are determined for the clusters consisting of 13 up to 147 atoms in medium range Morse potentials, which is suitable for most of metals. As the number of atoms constituting the cluster increases, the stable structures undergo transition from face-centered (FC) to edge-centered (EC) structures. The magic numbers take ones of FC series before transition and take ones of EC series after that. The transition point from FC to EC structures depends on the value of softness parameter.

  18. Magnetic properties of supported metal atoms and clusters

    Science.gov (United States)

    Martins, Michael; Wurth, Wilfried

    2016-12-01

    Clusters are small systems ranging from a few atoms up to several thousand atoms. They are of high interest in basic research, but also for applications due to their specific electronic, magnetic or chemical properties depending on size and composition. For small clusters, quantum size effects play an important role and specific material properties might be tailored by choosing a special size or composition of the cluster. Here, we review the magnetic properties of adatoms and supported small mass-selected transition-metal clusters in the few-atom limit investigated by x-ray magnetic circular dichroism spectroscopy in the soft x-ray regime. The influence of cluster size, composition, the cluster-surface and intra-cluster interaction on the spin and orbital magnetic moments will be discussed.

  19. Protein-protected luminescent noble metal quantum clusters: an emerging trend in atomic cluster nanoscience

    OpenAIRE

    Paulrajpillai Xavier; Kamalesh Chaudhari; Ananya Baksi; Thalappil Pradeep

    2012-01-01

    Noble metal quantum clusters (NMQCs) are the missing link between isolated noble metal atoms and nanoparticles. NMQCs are sub-nanometer core sized clusters composed of a group of atoms, most often luminescent in the visible region, and possess intriguing photo-physical and chemical properties. A trend is observed in the use of ligands, ranging from phosphines to functional proteins, for the synthesis of NMQCs in the liquid phase. In this review, we briefly overview recent advancements in the ...

  20. Microstructures and Tribological Properties of Fe-Based Amorphous Metallic Coatings Deposited via Supersonic Plasma Spraying

    Science.gov (United States)

    Zhou, Yang-yang; Ma, Guo-zheng; Wang, Hai-dou; Li, Guo-lu; Chen, Shu-ying; Fu, Bin-guo

    2017-08-01

    The effects of the Ar flow rate and spraying power of a supersonic plasma spraying process on the microstructures and amorphous phase contents of Fe48Cr15Mo14C15B6Y2 amorphous coatings were systematically investigated. The tribological properties of the coatings were evaluated in pin-on-disk mode using a sliding tribometer. The results show that the amorphous phase content and microhardness initially increase with the Ar flow rate and then gradually decrease. However, the amorphous phase content and microhardness increase with the power. In particular, the amorphous phase content of the coating reaches 96.78% with a spraying power of 62 kW and a 110 L min-1 Ar flow rate. Tribological testing demonstrates that the coatings exhibit similar steady-state coefficients of friction (0.75-0.82) with a total test time of 20 min and an applied load of 20 N. However, the wear rates vary with the spraying parameters. In particular, the relative wear rate of the coating can be enhanced up to sixfold under optimal spraying conditions, resulting in excellent wear resistance. Detailed analysis of the coating wear surfaces indicates that the dominant wear mechanisms are abrasive and oxidative wear. Moreover, delamination may occur during the wear process.

  1. Simulations of Metal Enrichment in Galaxy Clusters by AGN Outflows

    CERN Document Server

    Moll, R; Domainko, W; Kapferer, W; Mair, M; Van Kampen, E; Kronberger, T; Kimeswenger, S; Ruffert, M

    2006-01-01

    We assess the importance of AGN outflows with respect to the metal enrichment of the intracluster medium (ICM) in galaxy clusters. We use combined N-body and hydrodynamic simulations, along with a semi-numerical galaxy formation and evolution model. Using assumptions based on observations, we attribute outflows of metal-rich gas initiated by AGN activity to a certain fraction of our model galaxies. The gas is added to the model ICM, where the evolution of the metallicity distribution is calculated by the hydrodynamic simulations. For the parameters describing the AGN content of clusters and their outflow properties, we use the observationally most favorable values. We find that AGNs have the potential to contribute significantly to the metal content of the ICM or even explain the complete abundance, which is typically ~0.5 Z_sun in core regions. Furthermore, the metals end up being inhomogeneously distributed, in accordance with observations.

  2. Systems and methods for producing metal clusters; functionalized surfaces; and droplets including solvated metal ions

    Energy Technology Data Exchange (ETDEWEB)

    Cooks, Robert Graham; Li, Anyin; Luo, Qingjie

    2017-08-01

    The invention generally relates to systems and methods for producing metal clusters; functionalized surfaces; and droplets including solvated metal ions. In certain aspects, the invention provides methods that involve providing a metal and a solvent. The methods additionally involve applying voltage to the solvated metal to thereby produce solvent droplets including ions of the metal containing compound, and directing the solvent droplets including the metal ions to a target. In certain embodiments, once at the target, the metal ions can react directly or catalyze reactions.

  3. Systems and methods for producing metal clusters; functionalized surfaces; and droplets including solvated metal ions

    Energy Technology Data Exchange (ETDEWEB)

    Cooks, Robert Graham; Li, Anyin; Luo, Qingjie

    2017-01-24

    The invention generally relates to systems and methods for producing metal clusters; functionalized surfaces; and droplets including solvated metal ions. In certain aspects, the invention provides methods that involve providing a metal and a solvent. The methods additionally involve applying voltage to the solvated metal to thereby produce solvent droplets including ions of the metal containing compound, and directing the solvent droplets including the metal ions to a target. In certain embodiments, once at the target, the metal ions can react directly or catalyze reactions.

  4. Metallicity map of the galaxy cluster A3667

    CERN Document Server

    Lovisari, L; Schindler, S; Ferrari, C

    2009-01-01

    We use XMM-Newton data of the merging cluster Abell 3667 to analyze its metallicity distribution. A detailed abundance map of the central 1.1x1.1 Mpc region indicates that metals are inhomogeneously distributed in the cluster showing a non-uniform and very complex metal pattern. The highest peak in the map corresponds to a cold region, slightly offset South of the X-ray center. This could be interpreted as stripped gas due to a merger between a group moving from NW towards the SE and the main cluster. We note several clumps of high metallicity also in the opposite direction with respect to the X-ray peak. Furthermore we determined abundances for 5 elements (O, Si, S, Ar, Fe) in four different regions of the cluster. Comparisons between these observed abundances and theoretical supernovae yields allow to get constraints on the relative number of SN Ia and II contributing to the enrichment of the intra-cluster medium. To reproduce the observed abundances of the best determined elements (Fe, O and Si) in a regio...

  5. Metal Enrichment and Energetics of Galactic Winds in Galaxy Clusters

    CERN Document Server

    Kapferer, W

    2004-01-01

    We investigate efficiency and time dependence of metal enrichment processes in the Intra-Cluster Medium (ICM). In this presentation we concentrate on the effects of galactic winds. The mass loss rates due to galactic winds are calculated with a special algorithm, which takes into account cosmic rays and magnetic fields. This algorithm is embedded in a combined N-body/hydrodynamic code which calculates the dynamics and evolution of a cluster. We present mass loss rates depending on galaxy properties like type, mass, gas mass fraction and the surrounding ICM. In addition we show metallicity maps as they would be observed with X-ray telescopes.

  6. Tailoring the Properties of Metallic Clusters by Ligand Coatings

    OpenAIRE

    Fresch, Barbara

    2014-01-01

    Tuning the properties of metallic clusters using different protecting ligand shells is an important step toward the application-orientated design of nanoparticles for nano-electronics and catalysis. An attractive property of these materials is the ability to engineer ligand shells composed of different molecules that influence the electronic structure of the system due to their chemical interaction with the metal core. Sometimes properties are not simply additive, and cooperative effects emer...

  7. Theoretical dynamical studies of metal clusters and cluster-ligand systems

    Energy Technology Data Exchange (ETDEWEB)

    Jellinek, J.

    1995-06-01

    In what follows we use the term cluster to designate a cohesive group of like atoms (molecules), i.e., bare ({open_quotes}neet{close_quotes} {open_quotes}naked{close_quotes}) clusters. More generally, the term is also used for organo- and inorganometallic compounds, i.e., ligated clusters. Although the approaches and techniques used by the various disciplines to study metal-ligand interactions are quite different, many of the central subjects and issues are common for them. The common subjects include possible geometric structures and isomeric forms, structural (isomerization) transitions, stability, fluxionality, structure-reactivity correlation (or lack of it), role of coordination, etc. However, the precise interpretation of these issues and the details emphasized by the different disciplines are dictated by the nature of the objects studied and may not, therefore, be identical. For example, questions regarding structures, isomerization transitions, fluxionality or even melting of metal clusters refer to the state and properties of the metal network itself. The same questions, when asked in connection with organo- and inorganometallic compounds, often refer to the arrangements and rearrangements of the ligands attached to a metal framework of a fixed structure. Of course, when required, the state of and changes in the metal framework are considered as well. The fields of metal-containing molecular compounds, surface science, and physics and chemistry of clusters furnish complementary information on a broad variety of metal-ligand systems. A comprehensive understanding of the nature and properties of these systems, as defined by the type and number of metal atoms and ligands involved, can be achieved only through a mutual awareness of and continuing progress in all of these research areas.

  8. Photodissociation Studies of Metal-Containing Clusters and Complexes

    Science.gov (United States)

    Pilgrim, Jeffrey Scott

    1995-01-01

    There have been two major areas of investigation for researchers working with laser ablation in molecular beams. The first area is the study of weakly-bound complexes. These complexes are bound by electrostatic interactions. In the present study the weakly bound interactions of the rare gases with the magnesium ion are investigated with electronic spectroscopy. The second major area is the study of metal and metal-containing clusters. Examples of previous investigations are the alkali metal clusters and the fullerenes. The present investigation is on metal -carbon clusters. The so-called metallo-carbohedrenes and metal-carbon nanocrystals are studied. Resonance enhanced photodissociation spectroscopy is used to obtain electronic excitation spectra of the Mg^+-rare gas species in the ultraviolet region. This investigation is facilitated by a reflectron time-of-flight mass spectrometer. The interaction of the rare gas with the metal ion is attributed to a "solvation" of the atomic ion transition. Simple bonding arguments predict that the excited state is more bound than the ground state for these complexes. This will result in a shift of the complex vibronic origin to lower energy from the atomic ion transition. This is exactly what is observed in the experiment with progressively larger shifts for the heavier rare gases. The electronic excitation spectra allow the vibrational frequencies and anharmonicities for these complexes to be obtained for the excited state. In turn, the excited state bond dissociation energies can be determined. Finally, conservation of energy allows calculation of the ground state bond dissociation energies. In the metal-carbon systems the stability of the metallo-carbohedrene, met-car, stoichiometry is shown to extend into the transition period at least to the iron group. Photodissociation with a 532 nm laser causes a loss of metal atoms for met-cars formed with first row transition metals and a loss of metal-carbon units for met

  9. Nanocomposites Based on Metal and Metal Sulfide Clusters Embedded in Polystyrene

    Directory of Open Access Journals (Sweden)

    Gianfranco Carotenuto

    2011-08-01

    Full Text Available Transition-metal alkane-thiolates (i.e., organic salts with formula Me(SRx, where R is a linear aliphatic hydrocarbon group, –CnH2n+1 undergo a thermolysis reaction at moderately low temperatures (close to 200 °C, which produces metal atoms or metal sulfide species and an organic by-product, disulfide (RSSR or thioether (RSR molecules, respectively. Alkane-thiolates are non-polar chemical compounds that dissolve in most techno-polymers and the resulting solid solutions can be annealed to generate polymer-embedded metal or metal sulfide clusters. Here, the preparation of silver and gold clusters embedded into amorphous polystyrene by thermolysis of a dodecyl-thiolate precursor is described in detail. However, this chemical approach is quite universal and a large variety of polymer-embedded metals or metal sulfides could be similarly prepared.

  10. Clustered field evaporation of metallic glasses in atom probe tomography.

    Science.gov (United States)

    Zemp, J; Gerstl, S S A; Löffler, J F; Schönfeld, B

    2016-03-01

    Field evaporation of metallic glasses is a stochastic process combined with spatially and temporally correlated events, which are referred to as clustered evaporation (CE). This phenomenon is investigated by studying the distance between consecutive detector hits. CE is found to be a strongly localized phenomenon (up to 3nm in range) which also depends on the type of evaporating ions. While a similar effect in crystals is attributed to the evaporation of crystalline layers, CE of metallic glasses presumably has a different - as yet unknown - physical origin. The present work provides new perspectives on quantification methods for atom probe tomography of metallic glasses.

  11. Flexible macrocycles as versatile supports for catalytically active metal clusters

    Energy Technology Data Exchange (ETDEWEB)

    Ryan, JD; Gagnon, KJ; Teat, SJ; McIntosh, RD

    2016-02-12

    Here we present three structurally diverse clusters stabilised by the same macrocyclic polyphenol; t-butylcalix[8]arene. This work demonstrates the range of conformations the flexible ligand is capable of adopting, highlighting its versatility in metal coordination. In addition, a Ti complex displays activity for the ring-opening polymerisation of lactide

  12. Hydride encapsulation by molecular alkali-metal clusters.

    Science.gov (United States)

    Haywood, Joanna; Wheatley, Andrew E H

    2008-07-14

    The sequential treatment of group 12 and 13 Lewis acids with alkali-metal organometallics is well established to yield so-called ''ate' complexes, whereby the Lewis-acid metal undergoes nucleophilic attack to give an anion, at least one group 1 metal acting to counter this charge. However, an alternative, less well recognised, reaction pathway involves the Lewis acid abstracting hydride from the organolithium reagent via a beta-elimination mechanism. It has recently been shown that in the presence of N,N'-bidentate ligands this chemistry can be harnessed to yield a new type of molecular main-group metal cluster in which the abstracted LiH is effectively trapped, with the hydride ion occupying an interstitial site in the cluster core. Discussion focuses on the development of this field, detailing advances in our understanding of the roles of Lewis acid, organolithium, and amine substrates in the syntheses of these compounds. Structure-types are discussed, as are efforts to manipulate cluster geometry and composition as well as hydride-coordination. Embryonic mechanistic studies are reported, as well as attempts to generate hydride-encapsulation clusters under catalytic control.

  13. Age and Metallicities of Cluster Galaxies: A1185 and Coma

    CERN Document Server

    Rakos, K; Odell, A

    2006-01-01

    We present age and metallicities determinations based on narrow band continuum colors for the galaxies in the rich clusters A1185 and Coma. Using a new technique to extract luminosity-weighted age and [Fe/H] values for non-star-forming galaxies, we find that both clusters have two separate populations based on these parameters. One population is old ($\\tau >$ 11 Gyrs) with a distinct mass-metallicity relation. The second population is slightly younger ($\\tau \\approx$ 9 Gyrs) with lower metallicities and lower stellar masses. We find detectable correlations between age and galaxy mass in both populations such that older galaxies are more massive and have higher mean metallicities, confirming previous work with line indices for the same type of galaxies in other clusters (Kelson et al 2006, Thomas et al 2005). Our results imply shorter durations for higher mass galaxies, in contradiction to the predictions of classic galactic wind models. Since we also find a clear mass-metallicity relation for these galaxies, ...

  14. Toward the creation of stable, functionalized metal clusters.

    Science.gov (United States)

    Negishi, Yuichi; Kurashige, Wataru; Niihori, Yoshiki; Nobusada, Katsuyuki

    2013-11-21

    Nanomaterials which exhibit both stability and functionality are currently considered to hold the most promise as components of nanotechnology devices. Thiolate (RS)-protected gold nanoclusters (Aun(SR)m) have attracted significant attention in this regard and, among these, the magic clusters are believed to be the best candidates since they are the most stable. We have investigated the effects of heteroatom doping, protection by selenolate ligands and protection by photoresponsive thiolates on the stability and physical/chemical properties of these clusters. Through such studies, we have attempted to establish methods of modifying magic Aun(SR)m clusters as a means of creating metal clusters that are both robust and functional. This paper summarizes our studies towards this goal and the obtained results.

  15. Cooperative Cluster Metalation and Ligand Migration in Zirconium Metal-Organic Frameworks

    Energy Technology Data Exchange (ETDEWEB)

    Yuan, Shuai; Chen, Ying-Pin; Qin, Junsheng; Lu, Weigang; Wang, Xuan; Zhang, Qiang; Bosch, Mathieu; Liu, Tian-Fu; Lian, Xizhen; Zhou, Hong-Cai

    2015-10-23

    Cooperative cluster metalation and ligand migration were performed on a Zr-MOF, leading to the isolation of unique bimetallic MOFs based on decanuclear Zr6M4 (M=Ni, Co) clusters. The M2+ reacts with the μ3-OH and terminal H2O ligands on an 8-connected [Zr6O4(OH)8(H2O)4] cluster to form a bimetallic [Zr6M4O8(OH)8(H2O)8] cluster. Along with the metalation of Zr6 cluster, ligand migration is observed in which a Zr–carboxylate bond dissociates to form a M–carboxylate bond. Single-crystal to single-crystal transformation is realized so that snapshots for cooperative cluster metalation and ligand migration processes are captured by successive single-crystal X-ray structures. In3+ was metalated into the same Zr-MOF which showed excellent catalytic activity in the acetaldehyde cyclotrimerization reaction. This work not only provides a powerful tool to functionalize Zr-MOFs with other metals, but also structurally elucidates the formation mechanism of the resulting heterometallic MOFs.

  16. Supersonic metal plasma impact on a surface: An optical investigation of the pre-surface region

    Energy Technology Data Exchange (ETDEWEB)

    Fusion Science Group, AFRD; Plasma Applications Group, AFRD; Ni, Pavel A.; Anders, Andre

    2009-12-15

    Aluminum plasma, produced in high vacuum by a pulsed, filtered cathodic arc plasma source, was directed onto a wall where if formed a coating. The accompanying ?optical flare? known from the literature was visually observed, photographed, and spectroscopically investigated with appropriately high temporal (1 ?s) and spatial (100 ?m) resolution. Consistent with other observations using different techniques, it was found that the impact of the fully ionized plasma produces metal neutrals as well as desorbed gases, both of which interact with the incoming plasma. Most effectively are charge exchange collisions between doubly charged aluminum and neutral aluminum, which lead to a reduction of the flow of doubly charged before they reach the wall, and a reduction of neutrals as the move away from the surface. Those plasma-wall interactions are relevant for coating processes as well as for interpreting the plasma properties such as ion charge state distributions.

  17. Cluster Analysis of Metal Concentrations in River Kubanni Zaria, Nigeria

    Directory of Open Access Journals (Sweden)

    A.W. Butu

    2013-08-01

    Full Text Available The cluster analysis was used to assess the degree of association of the metal concentrations in river Kubanni Zaria, Nigeria. The main sources of data for the analysis were the sediment from four distinct locations along the long profile Kubanni River which were analyzed using Instrumental Nitrogen Activities Analysis (INAA techniques. The Nigerian Research Reactor-1(NIRR-1 which is Miniature Nitrogen Source Reactor (MNSR was used to analyze the data. The result of the laboratory analysis was subjected to cluster analysis. The analysis shows a stable clustering system where the metal concentrations in the four different locations were grouped into two main groups with one outlier. The level of concentration of elements that were sampled in the dry months were cluster in group I and those collected in the raining months were in group II. This strongly support that there is temporal variation in the levels of concentration of metal contaminants between wet and dry seasons in river Kubanni and also confirms the fact that the elements that were collected in the wet season are from the same source and those in the dry season are also from common source.

  18. Peripheral collisions of highly charged ions with metal clusters

    Institute of Scientific and Technical Information of China (English)

    Zhang Cheng-Jun; Hu Bi-Tao; Luo Xian-Wen

    2012-01-01

    Within the framework of the dynamical classical over-barrier model,the soft collisions between slow highly charged ions(SHCIs)Ar17+ and the large copper clusters under large impact parameters have been studied in this paper.We present the dominant mechanism of the electron transfer between SHCls and a large metal cluster by computational simulation.The evolution of the occupation of projectile ions,KLχ satellite lines,X-ray yields,Auger electron spectrum and scattering angles are provided.

  19. The lifetime of electronic excitations in metal clusters

    Science.gov (United States)

    Quijada, M.; Díez Muiño, R.; Echenique, P. M.

    2005-05-01

    Density functional theory and the self-energy formalism are used to evaluate the lifetime of electronic excitations in metal clusters of nanometre size. The electronic structure of the cluster is obtained in the jellium model and spherical symmetry is assumed. Two effects that depend on the size of the clusters are discussed: the change in the number of final states to which the excitation can decay, and the modification in the screened interaction between electrons. For clusters with density parameter rs = 4 and diameter a few nanometres, a lifetime value of {\\approx }5 fs is reached for electronic excitations of {\\approx }1 eV. This value is of the same order of magnitude of that obtained in the bulk limit at the same level of approximation. For smaller clusters, a distinct non-monotonic behaviour of the lifetime as a function of the cluster size is found and the lifetime of excitations of {\\approx }1 eV can vary between 4 and 30 fs.

  20. The old, metal-poor, anticentre open cluster Trumpler 5

    CERN Document Server

    Donati, P; Bragaglia, A; Pancino, E; Cantat-Gaudin, T; Carrera, R; Tosi, M

    2014-01-01

    As part of a long term programme, we analyse the evolutionary status and properties of the old and populous open cluster Trumpler 5 (Tr 5), located in the Galactic anticentre direction, almost on the Galactic plane. Tr 5 was observed with WFI@MPG/ESO Telescope using the Bessel $U$, $B$, and $V$ filters. The cluster parameters have been obtained using the synthetic colour-magnitude diagram (CMD) method, i.e. the direct comparison of the observational CMD with a library of synthetic CMDs generated with different stellar evolution sets (Padova, FRANEC, and FST). Age, reddening, and distance are derived through the synthetic CMD method using stellar evolutionary models with subsolar metallicity ($Z=0.004$ or $Z=0.006$). Additional spectroscopic observations with UVES@VLT of three red clump stars of the cluster were used to determine more robustly the chemical properties of the cluster. Our analysis shows that Tr 5 has subsolar metallicity, with [Fe/H]$=-0.403\\pm0.006$ dex (derived from spectroscopy), age between ...

  1. Bonding, aromaticity and reactivity patterns in some all-metal and non-metal clusters

    Indian Academy of Sciences (India)

    S Duley; S Giri; A Chakraborty; P K Chattaraj

    2009-09-01

    Several sandwich-like metal clusters have been studied at the B3LYP/6-311 + G∗ level of theory. Bonding and reactivity have been analysed through various geometrical parameters and conceptual density functional theory based global reactivity descriptors. Aromaticity patterns have been understood in terms of the associated nucleus independent chemical shift values. Possibility of bond-stretch isomerism in some doped clusters is explored. Preferable sites for electrophilic and nucleophilic attacks have been identified using different local reactivity descriptors.

  2. Protein-protected luminescent noble metal quantum clusters: an emerging trend in atomic cluster nanoscience.

    Science.gov (United States)

    Xavier, Paulrajpillai Lourdu; Chaudhari, Kamalesh; Baksi, Ananya; Pradeep, Thalappil

    2012-01-01

    Noble metal quantum clusters (NMQCs) are the missing link between isolated noble metal atoms and nanoparticles. NMQCs are sub-nanometer core sized clusters composed of a group of atoms, most often luminescent in the visible region, and possess intriguing photo-physical and chemical properties. A trend is observed in the use of ligands, ranging from phosphines to functional proteins, for the synthesis of NMQCs in the liquid phase. In this review, we briefly overview recent advancements in the synthesis of protein protected NMQCs with special emphasis on their structural and photo-physical properties. In view of the protein protection, coupled with direct synthesis and easy functionalization, this hybrid QC-protein system is expected to have numerous optical and bioimaging applications in the future, pointers in this direction are visible in the literature.

  3. Protein-protected luminescent noble metal quantum clusters: an emerging trend in atomic cluster nanoscience

    Directory of Open Access Journals (Sweden)

    Paulrajpillai Xavier

    2012-02-01

    Full Text Available Noble metal quantum clusters (NMQCs are the missing link between isolated noble metal atoms and nanoparticles. NMQCs are sub-nanometer core sized clusters composed of a group of atoms, most often luminescent in the visible region, and possess intriguing photo-physical and chemical properties. A trend is observed in the use of ligands, ranging from phosphines to functional proteins, for the synthesis of NMQCs in the liquid phase. In this review, we briefly overview recent advancements in the synthesis of protein protected NMQCs with special emphasis on their structural and photo-physical properties. In view of the protein protection, coupled with direct synthesis and easy functionalization, this hybrid QC-protein system is expected to have numerous optical and bioimaging applications in the future, pointers in this direction are visible in the literature.

  4. Supersonic compressor

    Science.gov (United States)

    Roberts, II, William Byron; Lawlor, Shawn P.; Breidenthal, Robert E.

    2016-04-12

    A supersonic compressor including a rotor to deliver a gas at supersonic conditions to a diffuser. The diffuser includes a plurality of aerodynamic ducts that have converging and diverging portions, for deceleration of gas to subsonic conditions and then for expansion of subsonic gas, to change kinetic energy of the gas to static pressure. The aerodynamic ducts include vortex generating structures for controlling boundary layer, and structures for changing the effective contraction ratio to enable starting even when the aerodynamic ducts are designed for high pressure ratios, and structures for boundary layer control. In an embodiment, aerodynamic ducts are provided having an aspect ratio of in excess of two to one, when viewed in cross-section orthogonal to flow direction at an entrance to the aerodynamic duct.

  5. Metal clusters on supported argon layers; Metallcluster auf dielektrischen Substraten

    Energy Technology Data Exchange (ETDEWEB)

    Faber, Bernhard

    2011-10-21

    The deposition of small sodium clusters on supported Ar(001)-surfaces is simulated. Theoretical description is achieved by a hierarchical model consisting of time-dependent DFT and molecular dynamics. The valence electrons of the sodium atoms are considered by Kohn-Sham-Scheme with self interaction correction. The interaction of argon atoms and sodium ions is described by atom-atom potentials whereas the coupling to the QM electrons is done by local pseudo-potentials. A decisive part of the model is the dynamical polarizability of the rare-gas atoms. The optional metal support is considered by the method of image charges. The influence of the forces caused by image charges and the influence of the number of argon monolayers on structure, optical response and deposition dynamics of Na{sub 6} and Na{sub 8} is investigated. There is very little influence on cluster structure and only a small shift of the cluster perpendicular to the surface. Concerning optical response the position of the Mie plasmon peak stays robust whereas the details of spectral fragmentation react very sensitively to changes. The forces caused by image charges of the metal support play only a little role with the dynamics of deposition while the thickness of the argon surface strongly influences the dissipation. (orig.)

  6. Oligomeric rare-earth metal cluster complexes with endohedral transition metal atoms

    Energy Technology Data Exchange (ETDEWEB)

    Steinberg, Simon; Zimmermann, Sina; Brühmann, Matthias; Meyer, Eva; Rustige, Christian; Wolberg, Marike; Daub, Kathrin; Bell, Thomas; Meyer, Gerd, E-mail: gerd.meyer@uni-koeln.de

    2014-11-15

    Comproportionation reactions of rare-earth metal trihalides (RX{sub 3}) with the respective rare-earth metals (R) and transition metals (T) led to the formation of 22 oligomeric R cluster halides encapsulating T, in 19 cases for the first time. The structures of these compounds were determined by single-crystal X-ray diffraction and are composed of trimers ((T{sub 3}R{sub 11})X{sub 15}-type, P6{sub 3}/m), tetramers ((T{sub 4}R{sub 16})X{sub 28}(R{sub 4}) (P-43m), (T{sub 4}R{sub 16})X{sub 20} (P4{sub 2}/nnm), (T{sub 4}R{sub 16})X{sub 24}(RX{sub 3}){sub 4} (I4{sub 1}/a) and (T{sub 4}R{sub 16})X{sub 23} (C2/m) types of structure) and pentamers ((Ru{sub 5}La{sub 14}){sub 2}Br{sub 39}, Cc) of (TR{sub r}){sub n} (n=2–5) clusters. These oligomers are further enveloped by inner (X{sup i}) as well as outer (X{sup a}) halido ligands, which possess diverse functionalities and interconnect like oligomers through i–i, i–a and/or a–i bridges. The general features of the crystal structures for these new compounds are discussed and compared to literature entries as well as different structure types with oligomeric T centered R clusters. Dimers and tetramers originating from the aggregation of (TR{sub 6}) octahedra via common edges are more frequent than trimers and pentamers, in which the (TR{sub r}) clusters share common faces. - Graphical abstract: Rare earth-metal cluster complexes with endohedral transition metal atoms (TR{sub 6}) may connect via common edges or faces to form dimers, trimers, tetramers and pentamers of which the tetramers are the most prolific. Packing effects and electron counts play an important role. - Highlights: • Rare-earth metal cluster complexes encapsulate transition metal atoms. • Oligomers are built via connection of octahedral clusters via common edges or faces. • Dimers through pentamers with closed structures are known. • Tetramers including a tetrahedron of endohedral atoms are the most prolific.

  7. Ages and metallicities of star clusters: new calibrations and diagnostic diagrams from visible integrated spectra

    CERN Document Server

    Santos, J F C

    2004-01-01

    We present homogeneous scales of ages and metallicities for star clusters from very young objects, through intermediate-age ones up to the oldest known clusters. All the selected clusters have integrated spectra in the visible range, as well as reliable determinations of their ages and metallicities. From these spectra equivalent widths (EWs) of KCaII, Gband(CH) and MgI metallic, and Hdelta, Hgamma and Hbeta Balmer lines have been measured homogeneously. The analysis of these EWs shows that the EW sums of the metallic and Balmer H lines, separately, are good indicators of cluster age for objects younger than 10 Gyr, and that the former is also sensitive to cluster metallicity for ages greater than 10 Gyr. We propose an iterative procedure for estimating cluster ages by employing two new diagnostic diagrams and age calibrations based on the above EW sums. For clusters older than 10 Gyr, we also provide a calibration to derive their overall metal contents.

  8. The electronic structure of free aluminum clusters: metallicity and plasmons.

    Science.gov (United States)

    Andersson, Tomas; Zhang, Chaofan; Tchaplyguine, Maxim; Svensson, Svante; Mårtensson, Nils; Björneholm, Olle

    2012-05-28

    The electronic structure of free aluminum clusters with ∼3-4 nm radius has been investigated using synchrotron radiation-based photoelectron and Auger electron spectroscopy. A beam of free clusters has been produced using a gas-aggregation source. The 2p core level and the valence band have been probed. Photoelectron energy-loss features corresponding to both bulk and surface plasmon excitation following photoionization of the 2p level have been observed, and the excitation energies have been derived. In contrast to some expectations, the loss features have been detected at energies very close to those of the macroscopic solid. The results are discussed from the point of view of metallic properties in nanoparticles with a finite number of constituent atoms.

  9. The electronic structure of free aluminum clusters: Metallicity and plasmons

    Science.gov (United States)

    Andersson, Tomas; Zhang, Chaofan; Tchaplyguine, Maxim; Svensson, Svante; Mârtensson, Nils; Björneholm, Olle

    2012-05-01

    The electronic structure of free aluminum clusters with ˜3-4 nm radius has been investigated using synchrotron radiation-based photoelectron and Auger electron spectroscopy. A beam of free clusters has been produced using a gas-aggregation source. The 2p core level and the valence band have been probed. Photoelectron energy-loss features corresponding to both bulk and surface plasmon excitation following photoionization of the 2p level have been observed, and the excitation energies have been derived. In contrast to some expectations, the loss features have been detected at energies very close to those of the macroscopic solid. The results are discussed from the point of view of metallic properties in nanoparticles with a finite number of constituent atoms.

  10. Large amplitude femtosecond electron dynamics in metal clusters

    CERN Document Server

    Daligault, J

    2003-01-01

    We present a theoretical model that allows us to study linear and non-linear aspects of the femtosecond electron dynamics in metal clusters. The theoretical approach consists in the classical limit of the time-dependent Kohn-Sham equations. The electrons are described by a phase-space distribution function which satisfies a Vlasov-like equation while the ions are treated classically. This allows simulations for clusters containing several hundreds of atoms and extending up to several hundreds of femtoseconds during which the description conserves the fermionic character of the electron distribution. This semi-quantal approach compares very well with the purely quantal treatment. As an application of this approach, we show the prominent role of the electron dynamics during and after the interaction with an intense femtosecond laser pulse.

  11. Mixed-metal chalcogenide tetrahedral clusters with an exo-polyhedral metal fragment.

    Science.gov (United States)

    Yuvaraj, K; Roy, Dipak Kumar; Anju, V P; Mondal, Bijnaneswar; Varghese, Babu; Ghosh, Sundargopal

    2014-12-07

    The reaction of metal carbonyl compounds with group 6 and 8 metallaboranes led us to report the synthesis and structural characterization of several novel mixed-metal chalcogenide tetrahedral clusters. Thermolysis of arachno-[(Cp*RuCO)2B2H6], 1, and [Os3(CO)12] in the presence of 2-methylthiophene yielded [Cp*Ru(CO)2(μ-H){Os3(CO)9}S], 3, and [Cp*Ru(μ-H){Os3(CO)11}], 4. In a similar fashion, the reaction of [(Cp*Mo)2B5H9], 2, with [Ru3(CO)12] and 2-methylthiophene yielded [Cp*Ru(CO)2(μ-H){Ru3(CO)9}S], 5, and conjuncto-[(Cp*Mo)2B5H8(μ-H){Ru3(CO)9}S], 6. Both compounds 3 and 5 can be described as 50-cve (cluster valence electron) mixed-metal chalcogenide clusters, in which a sulfur atom replaces one of the vertices of the tetrahedral core. Compounds 3 and 5 possess a [M3S] tetrahedral core, in which the sulfur is attached to an exo-metal fragment, unique in the [M3S] metal chalcogenide tetrahedral arrangements. All the compounds have been characterized by mass spectrometry, IR, and (1)H, (11)B and (13)C NMR spectroscopy in solution, and the solid state structures were unequivocally established by crystallographic analysis of compounds 3, 5 and 6.

  12. Superatoms and Metal-Semiconductor Motifs for Cluster Materials

    Energy Technology Data Exchange (ETDEWEB)

    Castleman, A. W.

    2013-10-11

    A molecular understanding of catalysis and catalytically active materials is of fundamental importance in designing new substances for applications in energy and fuels. We have performed reactivity studies and ultrafast ionization and coulomb explosion studies on a variety of catalytically-relevant materials, including transition metal oxides of Fe, Co, Ni, Cu, Ti, V, Nb, and Ta. We demonstrate that differences in charge state, geometry, and elemental composition of clusters of such materials determine chemical reactivity and ionization behavior, crucial steps in improving performance of catalysts.

  13. Zintl cluster chemistry in the alkali-metal-gallium systems

    Energy Technology Data Exchange (ETDEWEB)

    Henning, Robert [Iowa State Univ., Ames, IA (United States)

    1998-03-27

    Previous research into the alkali-metal-gallium systems has revealed a large variety of networked gallium deltahedra. The clusters are analogues to borane clusters and follow the same electronic requirements of 2n+2 skeletal electrons for closo-deltahedra. This work has focused on compounds that do not follow the typical electron counting rules. The first isolated gallium cluster was found in Cs8Ga11. The geometry of the Ga117- unit is not deltahedral but can be described as a penta-capped trigonal prism. The reduction of the charge from a closo-Ga1113- to Ga117- is believed to be the driving force of the distortion. The compound is paramagnetic because of an extra electron but incorporation of a halide atom into the structure captures the unpaired electron and forms a diamagnetic compound. A second isolated cluster has been found in Na10Ga10Ni where the tetra-capped trigonal prismatic gallium is centered by nickel. Stabilization of the cluster occurs through Ni-Ga bonding. A simple two-dimensional network occurs in the binary K2Ga3 Octahedra are connected through four waist atoms to form a layered structure with the potassium atoms sitting between the layers. Na30.5Ga60-xAgx is nonstoichiometric and needs only a small amount of silver to form (x ~ 2-6). The structure is composed of three different clusters which are interconnected to form a three-dimensional structure. The RbGa3-xAux system is also nonstoichiometric with a three-dimensional structure composed of Ga8 dodecahedra and four-bonded gallium atoms. Unlike Na30.5Ga60-xAgx, the RbGa3 binary is also stable. The binary is formally a Zintl phase but the ternary is not. Some chemistry in the alkali-metal-indium system also has been explored. A new potassium-indium binary

  14. Structure and Mobility of Metal Clusters in MOFs: Au, Pd, and AuPd Clusters in MOF-74

    DEFF Research Database (Denmark)

    Vilhelmsen, Lasse; Walton, Krista S.; Sholl, David S.

    2012-01-01

    Understanding the adsorption and mobility of metal–organic framework (MOF)-supported metal nanoclusters is critical to the development of these catalytic materials. We present the first theoretical investigation of Au-, Pd-, and AuPd-supported clusters in a MOF, namely MOF-74. We combine density...... is just as important for nanocluster adsorption as open Zn or Mg metal sites. Using the large number of clusters generated by the GA, we developed a systematic method for predicting the mobility of adsorbed clusters. Through the investigation of diffusion paths a relationship between the cluster...

  15. Magnetism of Metals, Alloys and of Clusters of Transition Metal Atoms

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    A condition for local moment formation in metals derived by Stoddart and March (Ann. Phys.NY 1972 64, 174) is first used to discuss the ferromagnetism of body-centred-cubic Fe. A less detailed discussion is also added on Ni and Co. This leads into a treatment of the nonlinear response of such 3d ferromagnets to dilute substitutional impurities. Antiferromagnets responding to local changes in the exchange field caused by such impurities are also studied, Mn in Cr being one such system discussed. The paper concludes with a brief summary of clusters of transition metal atoms, with most attention devoted to Cr and to Mn.

  16. All-metal clusters that mimic the chemistry of halogens.

    Science.gov (United States)

    Zhao, Tianshan; Li, Yawei; Wang, Qian; Jena, Puru

    2013-10-07

    Owing to their s(2)p(5) electronic configuration, halogen atoms are highly electronegative and constitute the anionic components of salts. Whereas clusters that contain no halogen atoms, such as AlH(4), mimic the chemistry of halogens and readily form salts (e.g., Na(+)(AlH(4))(-)), clusters that are solely composed of metal atoms and yet behave in the same manner as a halogen are rare. Because coinage-metal atoms (Cu, Ag, and Au) only have one valence electron in their outermost electronic shell, as in H, we examined the possibility that, on interacting with Al, in particular as AlX(4) (X=Cu, Ag, Au), these metal atoms may exhibit halogen-like properties. By using density functional theory, we show that AlAu(4) not only mimics the chemistry of halogens, but also, with a vertical detachment energy (VDE) of 3.98 eV in its anionic form, is a superhalogen. Similarly, analogous to XHX superhalogens (X=F, Cl, Br), XAuX species with VDEs of 4.65, 4.50, and 4.34 eV in their anionic form, respectively, also form superhalogens. In addition, Au can also form hyperhalogens, a recently discovered species that show electron affinities (EAs) that are even higher than those of their corresponding superhalogen building blocks. For example, the VDEs of M(AlAu(4))(2)(-) (M=Na and K) and anionic (FAuF)Au(FAuF) range from 4.06 to 5.70 eV. Au-based superhalogen anions, such as AlAu(4)(-) and AuF(2)(-), have the additional advantage that they exhibit wider optical absorption ranges than their H-based analogues, AlH(4)(-) and HF(2)(-). Because of the catalytic properties and the biocompatibility of Au, Au-based superhalogens may be multifunctional. However, similar studies that were carried out for Cu and Ag atoms have shown that, unlike AlAu(4), AlX(4) (X=Cu, Ag) clusters are not superhalogens, a property that can be attributed to the large EA of the Au atom. Copyright © 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim.

  17. Monitoring the dissolution process of metals in the gas phase: reactions of nanoscale Al and Ga metal atom clusters and their relationship to similar metalloid clusters.

    Science.gov (United States)

    Burgert, Ralf; Schnöckel, Hansgeorg

    2008-05-14

    Formation and dissolution of metals are two of the oldest technical chemical processes. On the atomic scale, these processes are based on the formation and cleavage of metal-metal bonds. During the past 15 years we have studied intensively the intermediates during the formation process of metals, i.e. the formation of compounds containing many metal-metal bonds between naked metal atoms in the center and ligand-bearing metal atoms at the surface. We have called the clusters metalloid or, more generally, elementoid clusters. Via a retrosynthetic route, the many different Al and Ga metalloid clusters which have been structurally characterized allow us to understand also the dissolution process; i.e. the cleavage of metal-metal (M-M) bonds. However, this process can be detected much more directly by the reaction of single metal atom clusters in the gas phase under high vacuum conditions. A suitable tool to monitor the dissolution process of a metal cluster in the gas phase is FT-ICR (Fourier transform ion cyclotron resonance) mass spectrometry. Snapshots during these cleavage processes are possible because only every 1-10 s is there a contact between a cluster molecule and an oxidizing molecule (e.g. Cl2). This period is long, i.e. the formation of the primary product (a smaller metal atom cluster) is finished before the next collision happens. We have studied three different types of reaction:(1) Step-by-step fragmentation of a structurally known metalloid cluster allows us to understand the bonding principle of these clusters because in every step only the weakest bond is broken.(2) There are three oxidation reactions of an Al13(-) cluster molecule with Cl2, HCl and O2 central to this review. These three reactions represent three different reaction types, (a) an exothermic reaction (Cl2), (b) an endothermic reaction (HCl), and (c) a kinetically limited reaction based on spin conservation rules (O2).(3) Finally, we present the reaction of a metalloid cluster with Cl2

  18. Atomically precise arrays of fluorescent silver clusters: a modular approach for metal cluster photonics on DNA nanostructures.

    Science.gov (United States)

    Copp, Stacy M; Schultz, Danielle E; Swasey, Steven; Gwinn, Elisabeth G

    2015-03-24

    The remarkable precision that DNA scaffolds provide for arraying nanoscale optical elements enables optical phenomena that arise from interactions of metal nanoparticles, dye molecules, and quantum dots placed at nanoscale separations. However, control of ensemble optical properties has been limited by the difficulty of achieving uniform particle sizes and shapes. Ligand-stabilized metal clusters offer a route to atomically precise arrays that combine desirable attributes of both metals and molecules. Exploiting the unique advantages of the cluster regime requires techniques to realize controlled nanoscale placement of select cluster structures. Here we show that atomically monodisperse arrays of fluorescent, DNA-stabilized silver clusters can be realized on a prototypical scaffold, a DNA nanotube, with attachment sites separated by <10 nm. Cluster attachment is mediated by designed DNA linkers that enable isolation of specific clusters prior to assembly on nanotubes and preserve cluster structure and spectral purity after assembly. The modularity of this approach generalizes to silver clusters of diverse sizes and DNA scaffolds of many types. Thus, these silver cluster nano-optical elements, which themselves have colors selected by their particular DNA templating oligomer, bring unique dimensions of control and flexibility to the rapidly expanding field of nano-optics.

  19. Permanent excimer superstructures by supramolecular networking of metal quantum clusters

    Science.gov (United States)

    Santiago-Gonzalez, Beatriz; Monguzzi, Angelo; Azpiroz, Jon Mikel; Prato, Mirko; Erratico, Silvia; Campione, Marcello; Lorenzi, Roberto; Pedrini, Jacopo; Santambrogio, Carlo; Torrente, Yvan; De Angelis, Filippo; Meinardi, Francesco; Brovelli, Sergio

    2016-08-01

    Excimers are evanescent quasi-particles that typically form during collisional intermolecular interactions and exist exclusively for their excited-state lifetime. We exploited the distinctive structure of metal quantum clusters to fabricate permanent excimer-like colloidal superstructures made of ground-state noninteracting gold cores, held together by a network of hydrogen bonds between their capping ligands. This previously unknown aggregation state of matter, studied through spectroscopic experiments and ab initio calculations, conveys the photophysics of excimers into stable nanoparticles, which overcome the intrinsic limitation of excimers in single-particle applications—that is, their nearly zero formation probability in ultra-diluted solutions. In vitro experiments demonstrate the suitability of the superstructures as nonresonant intracellular probes and further reveal their ability to scavenge reactive oxygen species, which enhances their potential as anticytotoxic agents for biomedical applications.

  20. High speed titanium coating by Supersonic Laser Deposition

    OpenAIRE

    LUPOI, ROCCO

    2011-01-01

    PUBLISHED The importance of metal coating technologies drives the continuous improvement of metal deposition techniques for application in a wide range of industrial sectors. This work presents the foundations of a new process technology f or the deposition of t itanium coatings on steel tube substrates using supersonic powder streams and impact site laser heating , known as Supersonic Laser Deposition (SLD). M et...

  1. Homometallic rare-Earth metal phosphinidene clusters: synthesis and reactivity.

    Science.gov (United States)

    Wang, Kai; Luo, Gen; Hong, Jianquan; Zhou, Xigeng; Weng, Linhong; Luo, Yi; Zhang, Lixin

    2014-01-20

    Two new trinuclear μ3 -bridged rare-earth metal phosphinidene complexes, [{L(Ln)(μ-Me)}3 (μ3 -Me)(μ3 -PPh)] (L=[PhC(NC6 H4 iPr2 -2,6)2 ](-) , Ln=Y (2 a), Lu (2 b)), were synthesized through methane elimination of the corresponding carbene precursors with phenylphosphine. Heating a toluene solution of 2 at 120 °C leads to an unprecedented ortho CH bond activation of the PhP ligand to form the bridged phosphinidene/phenyl complexes. Reactions of 2 with ketones, thione, or isothiocyanate show clear phospha-Wittig chemistry, giving the corresponding organic phosphinidenation products and oxide (sulfide) complexes. Reaction of 2 with CS2 leads to the formation of novel trinuclear rare-earth metal thione dianion clusters, for which a possible pathway was determined by DFT calculation. Copyright © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  2. Electroless deposition of metal nanoparticle clusters: Effect of pattern distance

    KAUST Repository

    Gentile, Francesco

    2014-04-03

    Electroless plating is a deposition technique in which metal ions are reduced as atoms on specific patterned sites of a silicon surface to form metal nanoparticles (NPs) aggregates with the desired characteristics. Those NPs, in turn, can be used as constituents of surface enhanced Raman spectroscopy substrates, which are devices where the electromagnetic field and effects thereof are giantly amplified. Here, the electroless formation of nanostructures was studied as a function of the geometry of the substrate. High resolution, electron beam lithography techniques were used to obtain nonperiodic arrays of circular patterns, in which the spacing of patterns was varied over a significant range. In depositing silver atoms in those circuits, the authors found that the characteristics of the aggregates vary with the pattern distance. When the patterns are in close proximity, the interference of different groups of adjacent aggregates cannot be disregarded and the overall growth is reduced. Differently from this, when the patterns are sufficiently distant, the formation of metal clusters of NPs is independent on the spacing of the patterns. For the particular subset of parameters used here, this critical correlation distance is about three times the pattern diameter. These findings were explained within the framework of a diffusion limited aggregation model, which is a simulation method that can decipher the formation of nanoaggregates at an atomic level. In the discussion, the authors showed how this concept can be used to fabricate ordered arrays of silver nanospheres, where the size of those spheres may be regulated on varying the pattern distance, for applications in biosensing and single molecule detection.

  3. Hydrogen mimicking the properties of coinage metal atoms in Cu and Ag monohydride clusters.

    Science.gov (United States)

    Vetter, Karsten; Proch, Sebastian; Ganteför, Gerd F; Behera, Swayamprabha; Jena, Puru

    2013-12-28

    A systematic study of the electronic structure and equilibrium geometries of Cun, Cun-1H, Agn, and Agn-1H; n = 2-5 clusters is carried out using photoelectron spectroscopy (PES) experiments and density functional theory based calculations. Our objective is to see if the substitution of a coinage metal atom by hydrogen would retain the electronic structure of the parent metal cluster since both systems are isoelectronic. For clusters with n ≥ 3, we find that the measured PES and vertical detachment energies (VDEs) (i.e. energies necessary to remove an electron from the anionic Mn(-) (M = Cu, Ag) clusters without changing their geometries) are close to those of Mn-1H(-) clusters, suggesting that substitution of a metal atom with hydrogen does not perturb the electronic structure of the parent cluster anion significantly. Calculated VDEs agree very well with experiment validating the theoretical methods used as well as the geometries of the neutral and anionic clusters.

  4. RHAPSODY-G simulations - II. Baryonic growth and metal enrichment in massive galaxy clusters

    Science.gov (United States)

    Martizzi, Davide; Hahn, Oliver; Wu, Hao-Yi; Evrard, August E.; Teyssier, Romain; Wechsler, Risa H.

    2016-07-01

    We study the evolution of the stellar component and the metallicity of both the intracluster medium and of stars in massive (Mvir ≈ 6 × 1014 M⊙ h-1) simulated galaxy clusters from the RHAPSODY-G suite in detail and compare them to observational results. The simulations were performed with the AMR code RAMSES and include the effect of active galactic nucleus (AGN) feedback at the subgrid level. AGN feedback is required to produce realistic galaxy and cluster properties and plays a role in mixing material in the central regions and regulating star formation in the central galaxy. In both our low- and high-resolution runs with fiducial stellar yields, we find that stellar and ICM metallicities are a factor of 2 lower than in observations. We find that cool core clusters exhibit steeper metallicity gradients than non-cool core clusters, in qualitative agreement with observations. We verify that the ICM metallicities measured in the simulation can be explained by a simple `regulator' model in which the metallicity is set by a balance of stellar yield and gas accretion. It is plausible that a combination of higher resolution and higher metal yield in AMR simulation would allow the metallicity of simulated clusters to match observed values; however, this hypothesis needs to be tested with future simulations. Comparison to recent literature highlights that results concerning the metallicity of clusters and cluster galaxies might depend sensitively on the scheme chosen to solve the hydrodynamics.

  5. Optimum Metallic-Bond Scheme: A Quantitative Analysis of Mass Spectra of Sodium Clusters

    Institute of Scientific and Technical Information of China (English)

    苏长荣; 李家明

    2001-01-01

    Based on the results of the optimum metallic-bond scheme for sodium clusters, we present a quantitative analysis of the detailed features of the mass spectra of sodium clusters. We find that, in the generation of sodium clusters with various abundances, the quasi-steady processes through adding or losing a sodium atom dominate. The quasi-steady processes through adding or losing a sodium dimer are also important to understand the detailed features of mass spectra for small clusters.

  6. Metal clusters and nanoparticles in dielectric matrices: Formation and optical properties

    Science.gov (United States)

    Gladskikh, I. A.; Vartanyan, T. A.

    2016-12-01

    The optical properties of thin dielectric films with metal inclusions and their dependence on thermal and laser annealing are studied experimentally. Metal clusters (Ag, Au, and Cu) in dielectric materials (Al2O3 and SiO2) are obtained by simultaneous vacuum deposition of metal and dielectric on the surface of a corresponding dielectric substrate (sapphire and quartz). It is shown that, depending on the deposited dielectric material, on the weight ratio of deposited metal and dielectric, and on the subsequent thermal treatment, one can obtain different metal structures, from clusters with a small number of atoms to complex dendritic plasmonic structures.

  7. White Dwarfs in the Metal-Rich Open Cluster NGC 6253

    CERN Document Server

    Jeffery, Elizabeth J; Romero, Alejandra; Kepler, S O

    2016-01-01

    We have obtained 53 images with the $g$ filter and 19 images with the $i$ filter, each with 600-second exposures of the super metal rich open cluster NGC 6253 with the Gemini-South telescope to create deep images of the cluster to observe the cluster white dwarfs for the first time. We will analyze the white dwarf luminosity function to measure the cluster's white dwarf age, search for any anomalous features (as has been seen in the similarly metal rich cluster NGC 6791), and constrain the initial-final mass relation at high metallicities. We present an update on these observations and our program to study the formation of white dwarfs in super high metallicity environments.

  8. Composite Hybrid Cluster Built from the Integration of Polyoxometalate and a Metal Halide Cluster: Synthetic Strategy, Structure, and Properties.

    Science.gov (United States)

    Li, Xin-Xiong; Ma, Xiang; Zheng, Wen-Xu; Qi, Yan-Jie; Zheng, Shou-Tian; Yang, Guo-Yu

    2016-09-06

    A step-by-step synthetic strategy, setting up a bridge between the polyoxometalate (POM) and metal halide cluster (MHC) systems, is demonstrated to construct an unprecedented composite hybrid cluster built up from one high-nuclearity cationic MHC [Cu8I6](2+) and eight Anderson-type anionic POMs [HCrMo6O18(OH)6](2-) cross-linked by a tripodal alcohol derivative.

  9. X-ray measured metallicities of the intra-cluster medium: a good measure for the metal mass?

    CERN Document Server

    Kapferer, W; Weratschnig, J; Schindler, S

    2007-01-01

    Aims. We investigate whether X-ray observations map heavy elements in the Intra-Cluster Medium (ICM) well and whether the X-ray observations yield good estimates for the metal mass, with respect to predictions on transport mech- anisms of heavy elements from galaxies into the ICM. We further test the accuracy of simulated metallicity maps. Methods. We extract synthetic X-ray spectra from N-body/hydrodynamic simulations including metal enrichment pro- cesses, which we then analyse with the same methods as are applied to observations. By changing the metal distribution in the simulated galaxy clusters, we investigate the dependence of the overall metallicity as a function of the metal distribution. In addition we investigate the difference of X-ray weighted metal maps produced by simulations and metal maps extracted from artifcial X-ray spectra, which we calculate with SPEX2.0 and analyse with XSPEC12.0. Results. The overall metallicity depends strongly on the distribution of metals within the galaxy cluster. T...

  10. Supersonic Plasma Flow Control Experiments

    Science.gov (United States)

    2005-12-01

    to liquid metals , for example, the conductivities of typical plasma and electrolyte flows are relatively low. Ref. 14 cites the conductivity of...heating is the dominant effect. 15. SUBJECT TERMS Supersonic, plasma , MHD , boundary-layer 16. SECURITY CLASSIFICATION OF: 19a. NAME OF RESPONSIBLE...horns in operation on Mach 5 wind tunnel with a plasma discharge. 31 Figure 17 Front view of a 100 mA DC discharge generated with upstream pointing

  11. Magnetron sputtering cluster apparatus for formation and deposition of size-selected metal nanoparticles

    DEFF Research Database (Denmark)

    Hanif, Muhammad; Popok, Vladimir

    2015-01-01

    The experimental setup utilizing a DC magnetron sputtering source for production of metal clusters, their size (mass) selection and following deposition in high vacuum is described. The source is capable to form clusters of various metals, for example, copper, silver, gold etc. Cluster size...... selection is achieved using an electrostatic quadrupole mass selector. The deposited silver clusters are studied using atomic force microscopy. The height distributions show typical relative standard size deviation of 9-13% for given sizes in the range between 5-23 nm. Thus, the apparatus demonstrates good...

  12. Formation and evolution mechanisms of large-clusters during rapid solidification process of liquid metal Al

    Institute of Scientific and Technical Information of China (English)

    LIU Rangsu; DONG Kejun; LIU Fengxiang; ZHENG Caixing; LIU Hairong; LI Jiyong

    2005-01-01

    A molecular dynamics simulation study has been performed for the formation and evolution characteristics of nano-clusters in a large-scale system consisting of 400000 atoms of liquid metal Al. The center-atom method combined with pair-bond analysis technique and cluster-type index method (CTIM) has been applied here to describe the structural configurations of various basic clusters. It is demonstrated that both the 1551 bond-type and the icosahedral cluster (12 0 12 0) constructed by 1551 bond-types are dominant among all the bond-types and cluster-types, respectively, in the system and play a critical role in the microstructure transitions of liquid metal Al. The nano-clusters (containing up to 150 atoms) are formed by the combination of some middle and small clusters with distinctly different sizes, through mutual competition by unceasing annex and evolution in a seesaw manner (in turn of obtaining and losing),which do not occur as the multi-shell structures accumulated with an atom as the center and the surrounding atoms are arranged according to a certain rule. This is the essential distinction of nano-cluster in liquid metal from those obtained by gaseous deposition, ionic spray methods, and so on. Though the nano-clusters differ from each other in shape and size, all of them possess protruding corners that could become the starting points of various dendrite structures in the solidification processes of liquid metals.

  13. Reactions of metal cluster anions with inorganic and organic molecules in the gas phase.

    Science.gov (United States)

    Zhao, Yan-Xia; Liu, Qing-Yu; Zhang, Mei-Qi; He, Sheng-Gui

    2016-07-28

    The study of gas phase ion-molecule reactions by state-of-the-art mass spectrometric experiments in conjunction with quantum chemistry calculations offers an opportunity to clarify the elementary steps and mechanistic details of bond activation and conversion processes. In the past few decades, a considerable number of publications have been devoted to the ion-molecule reactions of metal clusters, the experimentally and theoretically tractable models for the active phase of condensed phase systems. The focus of this perspective concerns progress on activation and transformation of important inorganic and organic molecules by negatively charged metal clusters. The metal cluster anions cover bare metal clusters as well as ligated systems with oxygen, carbon, and nitrogen, among others. The following important issues have been summarized and discussed: (i) dependence of chemical reactivity and selectivity on cluster structures and sizes, metals and metal oxidation states, odd-even electron numbers, etc. and (ii) effects of doping, ligation, and pre-adsorption on the reactivity of metal clusters toward rather inert molecules.

  14. Bright Stars and Metallicity Spread in the Globular Cluster omega Centauri

    Science.gov (United States)

    Ortolani, Sergio; Covino, Stefano; Carraro, Giovanni

    The globular cluster omega Centauri (NGC~5139) is the most massive and brightest cluster in our Galaxy. It has also a moderately high mass to light ratio (3.6) and an anomalous flattening (0.83) for a globular cluster. This cluster is also very interesting because it is one of a few examples of globular clusters with a measurable spread in the metal abundance (see Da Costa & Willumsen 1981, Norris et al. 1996, and Suntzeff and Kraft 1996 and references therein) and then it offers a unique, big sample of nearby stars having all the same distance and reddening but showing different metallicity (and age ?) effects. A recent paper by Norris et al. (1997) shows also an interesting correlation between kinematics and metal abundance.

  15. Bright Stars and Metallicity Spread in the Globular Cluster Omega Centauri

    CERN Document Server

    Ortolani, S; Carraro, G; Ortolani, Sergio; Covino, Stefano; Carraro, Giovanni

    1998-01-01

    The globular cluster Omega Centauri (NGC 5139) is the most massive and brightest cluster in our Galaxy. It has also a moderately high mass to light ratio (3.6) and an anomalous flattening (0.83) for a globular cluster. This cluster is also very interesting because it is one of a few examples of globular clusters with a measurable spread in the metal abundance (see Da Costa & Willumsen 1981, Norris et al. 1996, and Suntzeff and Kraft 1996 and references therein) and then it offers a unique, big sample of nearby stars having all the same distance and reddening but showing different metallicity (and age ?) effects. A recent paper by Norris et al. (1997) shows also an interesting correlation between kinematics and metal abundance.

  16. VizieR Online Data Catalog: Metallicity estimates of M31 globular clusters (Galleti+, 2009)

    Science.gov (United States)

    Galleti, S.; Bellazzini, M.; Buzzoni, A.; Federici, L.; Fusi Pecci, F.

    2010-04-01

    New empirical relations of [Fe/H] as a function of [MgFe] and Mg2 indices are based on the well-studied galactic globular clusters, complemented with theoretical model predictions for -0.2<=[Fe/H]<=+0.5. Lick indices for M31 clusters from various literature sources (225 clusters) and from new observations by our team (71 clusters) have been transformed into the Trager et al. (2000AJ....119.1645T) system, yielding new metallicity estimates for 245 globular clusters of M31. (3 data files).

  17. Van der Waals coefficients for alkali metal clusters and their size dependence

    Indian Academy of Sciences (India)

    Arup Banerjee; Manoj K Harbola

    2006-02-01

    In this paper we employ the hydrodynamic formulation of time-dependent density functional theory to obtain the van der Waals coefficients 6 and 8 of alkali metal clusters of various sizes including very large clusters. Such calculations become computationally very demanding in the orbital-based Kohn-Sham formalism, but are quite simple in the hydrodynamic approach. We show that for interactions between the clusters of the same sizes, 6 and 8 scale as the sixth and the eighth power of the cluster radius, respectively, and approach their classically predicted values for the large size clusters.

  18. Hard X-ray-induced optical luminescence via biomolecule-directed metal clusters.

    Science.gov (United States)

    Osakada, Yasuko; Pratx, Guillem; Sun, Conroy; Sakamoto, Masanori; Ahmad, Moiz; Volotskova, Olga; Ong, Qunxiang; Teranishi, Toshiharu; Harada, Yoshie; Xing, Lei; Cui, Bianxiao

    2014-04-07

    Here, we demonstrate that biomolecule-directed metal clusters are applicable in the study of hard X-ray excited optical luminescence, promising a new direction in the development of novel X-ray-activated imaging probes.

  19. Near-Infrared Photometry of Globular Clusters Towards the Galactic Bulge: Observations and Photometric Metallicity Indicators

    CERN Document Server

    Cohen, Roger E; Mauro, Francesco; Bonatto, Charles; Geisler, Douglas

    2016-01-01

    We present wide field JHKs photometry of 16 Galactic globular clusters located towards the Galactic bulge, calibrated on the 2MASS photometric system. Differential reddening corrections and statistical field star decontamination are employed for all of these clusters before fitting fiducial sequences to the cluster red giant branches (RGBs). Observed values and uncertainties are reported for several photometric features, including the magnitude of the RGB bump, tip, the horizontal branch (HB) and the slope of the upper RGB. The latest spectroscopically determined chemical abundances are used to build distance- and reddening-independent relations between observed photometric features and cluster metallicity, optimizing the sample size and metallicity baseline of these relations by supplementing our sample with results from the literature. We find that the magnitude different between the HB and the RGB bump can be used to predict metallicities, in terms of both iron abundance [Fe/H] and global metallicity [M/H]...

  20. 25. Steenbock symposium -- Biosynthesis and function of metal clusters for enzymes: Proceedings

    Energy Technology Data Exchange (ETDEWEB)

    NONE

    1997-12-31

    This symposium was held June 10--14, 1997 in Madison, Wisconsin. The purpose of this conference was to provide a multidisciplinary forum for exchange of state-of-the-art information on biochemistry of enzymes that have an affinity for metal clusters. Attention is focused on the following: metal clusters involved in energy conservation and remediation; tungsten, molybdenum, and cobalt-containing enzymes; Fe proteins, and Mo-binding proteins; nickel enzymes; and nitrogenase.

  1. Effect of functionalization of boron nitride flakes by main group metal clusters on their optoelectronic properties

    Science.gov (United States)

    Chakraborty, Debdutta; Chattaraj, Pratim Kumar

    2017-10-01

    The possibility of functionalizing boron nitride flakes (BNFs) with some selected main group metal clusters, viz. OLi4, NLi5, CLi6, BLI7 and Al12Be, has been analyzed with the aid of density functional theory (DFT) based computations. Thermochemical as well as energetic considerations suggest that all the metal clusters interact with the BNF moiety in a favorable fashion. As a result of functionalization, the static (first) hyperpolarizability (β ) values of the metal cluster supported BNF moieties increase quite significantly as compared to that in the case of pristine BNF. Time dependent DFT analysis reveals that the metal clusters can lower the transition energies associated with the dominant electronic transitions quite significantly thereby enabling the metal cluster supported BNF moieties to exhibit significant non-linear optical activity. Moreover, the studied systems demonstrate broad band absorption capability spanning the UV–visible as well as infra-red domains. Energy decomposition analysis reveals that the electrostatic interactions principally stabilize the metal cluster supported BNF moieties.

  2. The Gaia-ESO Survey: Detailed Abundances in the Metal-poor Globular Cluster NGC 4372

    CERN Document Server

    Roman, I San; Geisler, D; Villanova, S; Kacharov, N; Koch, A; Carraro, G; Tautvaišiene, G; Vallenari, A; Alfaro, E J; Bensby, T; Flaccomio, E; Francois, P; Korn, A J; Pancino, E; Recio-Blanco, A; Smiljanic, R; Bergemann, M; Costado, M T; Damiani, F; Heiter, U; Hourihane, A; Jofré, P; Lardo, C; de Laverny, P; Masseron, T; Morbidelli, L; Sbordone, L; Sousa, S G; Worley, C C; Zaggia, S

    2015-01-01

    We present the abundance analysis for a sample of 7 red giant branch stars in the metal-poor globular cluster NGC 4372 based on UVES spectra acquired as part of the Gaia-ESO Survey. This is the first extensive study of this cluster from high resolution spectroscopy. We derive abundances of O, Na, Mg, Al, Si, Ca, Sc, Ti, Fe, Cr, Ni, Y, Ba, and La. We find a metallicity of [Fe/H] = -2.19 $\\pm$ 0.03 and find no evidence for a metallicity spread. This metallicity makes NGC 4372 one of the most metal-poor galactic globular clusters. We also find an {\\alpha}-enhancement typical of halo globular clusters at this metallicity. Significant spreads are observed in the abundances of light elements. In particular we find a Na-O anti-correlation. Abundances of O are relatively high compared with other globular clusters. This could indicate that NGC 4372 was formed in an environment with high O for its metallicity. A Mg-Al spread is also present which spans a range of more than 0.5 dex in Al abundances. Na is correlated wit...

  3. Magnetic behavior of clusters of ferromagnetic transition metals

    DEFF Research Database (Denmark)

    Khanna, S. N.; Linderoth, Søren

    1991-01-01

    The effective magnetic moments of small iron and cobalt clusters have been calculated by assuming that the clusters undergo superparamagnetic relaxation. The effective moments per atom are found to be much below the bulk values, even at low temperatures (100 K). They increase with particle size a...

  4. On supersonic combustion

    Institute of Scientific and Technical Information of China (English)

    袁生学

    1999-01-01

    Some basic concepts and features of supersonic combustion are explained from the view point of macroscopic aerodynamics. Two kinds of interpretations of supersonic combustion are proposed. The difference between supersonic combustion and subsonic combustion is discussed, and the mechanism of supersonic combustion propagation and the limitation of heat addition in supersonic flow are pointed out. The results of the calculation of deflagration in supersonic flow show that the entropy increment and the total pressure loss of the combustion products may decrease with the increase of combustion velocity. It is also demonstrated that the oblique detonation wave angle may not be controlled by the wedge angle under weak underdriven solution conditions and be determined only by combustion velocity. Therefore, the weak underdriven solution may become self-sustaining oblique detonation waves with a constant wave angle.

  5. vbyCaHbeta CCD Photometry of Clusters. VIII. The Super-Metal Rich, Old Open Cluster NGC 6791

    CERN Document Server

    Anthony-Twarog, B J; Mayer, L

    2006-01-01

    CCD photometry on the intermediate-band vbyCaHbeta system is presented for the metal-rich, old open cluster, NGC 6791. Preliminary analysis led to [Fe/H] above +0.4 with an anomalously high reddening and an age below 5 Gyr. A revised calibration between (b-y)_0 and [Fe/H] at a given temperature shows that the traditional color-metallicity relations underestimate the color of the turnoff stars at high metallicity. With the revised relation, the metallicity from hk and the reddening for NGC 6791 become [Fe/H] = +0.45 +/- 0.04 and E(b-y) = 0.113 +/- 0.012 or E(B-V) = 0.155 +/- 0.016. Using the same technique, reanalysis of the photometry for NGC 6253 produces [Fe/H] = +0.58 +/-0.04 and E(b-y) = 0.120 +/- 0.018 or E(B-V) = 0.160 +/- 0.025. The errors quoted include both the internal and external errors. For NGC 6791, the metallicity from m_1 is a factor of two below that from hk, a result that may be coupled to the consistently low metal abundance from DDO photometry of the cluster and the C-deficiency found from...

  6. H2 adsorption on 3d transition metal clusters: a combined infrared and density functional study

    NARCIS (Netherlands)

    Swart, I.; de Groot, F.M.F.; Weckhuysen, B.M.; Gruene, P.; Meijer, G.; Fielicke, A.

    2008-01-01

    The adsorption of H2 on a series of gas-phase transition metal (scandium, vanadium, iron, cobalt, and nickel) clusters containing up to 20 metal atoms is studied using IR-multiple photon dissociation spectroscopy complemented with density functional theory based calculations. Comparison of the exper

  7. Metal cluster structures and properties from Born-Oppenheimer molecular dynamics

    Energy Technology Data Exchange (ETDEWEB)

    Calaminici, Patrizia, E-mail: pcalamin@cinvestav.mx; Köster, Andreas M., E-mail: pcalamin@cinvestav.mx; Vásquez-Pérez, José Manuel, E-mail: pcalamin@cinvestav.mx; Martínez, Gabriel Ulises Gamboa, E-mail: pcalamin@cinvestav.mx [Departamento de Química, CINVESTAV, Av. Instituto Politécnico Nacional 2508, A.P. 14-740, México D.F. 07000 (Mexico)

    2015-01-22

    Density functional theory (DFT) Born-Oppenheimer molecular dynamics (BOMD) simulations of metal clusters are presented. The calculations have been performed with the deMon2k [1] code employing all-electron basis sets and local and non-local functionals. The capability to perform reasonable long (∼ 100 ps) first-principle BOMD simulations in order to explore potential energy landscape of metallic clusters will be presented [2,3]. The evolution of the cluster structures and properties, such as polarizability and heat capacity, with temperature is discussed.

  8. How AGN feedback and metal cooling shape cluster entropy profiles

    CERN Document Server

    Dubois, Yohan; Teyssier, Romain; Slyz, Adrianne

    2011-01-01

    Observed clusters of galaxies essentially come in two flavors: non cool core clusters characterized by an isothermal temperature profile and a central entropy floor, and cool-core clusters where temperature and entropy in the central region are increasing with radius. Using cosmological resimulations of a galaxy cluster, we study the evolution of its intracluster medium (ICM) gas properties, and through them we assess the effect of different (sub-grid) modelling of the physical processes at play, namely gas cooling, star formation, feedback from supernovae and active galactic nuclei (AGN). More specifically we show that AGN feedback plays a major role in the pre-heating of the proto-cluster as it prevents a high concentration of mass from collecting in the center of the future galaxy cluster at early times. However, AGN activity during the cluster's later evolution is also required to regulate the mass flow into its core and prevent runaway star formation in the central galaxy. Whereas the energy deposited by...

  9. Near-infrared photometry of globular clusters towards the Galactic bulge: observations and photometric metallicity indicators

    Science.gov (United States)

    Cohen, Roger E.; Moni Bidin, Christian; Mauro, Francesco; Bonatto, Charles; Geisler, Douglas

    2017-01-01

    We present wide-field JHKS photometry of 16 Galactic globular clusters located towards the Galactic bulge, calibrated on the Two Micron All-Sky Survey photometric system. Differential reddening corrections and statistical field star decontamination are employed for all of these clusters before fitting fiducial sequences to the cluster red giant branches (RGBs). Observed values and uncertainties are reported for several photometric features, including the magnitude of the RGB bump, tip, the horizontal branch (HB) and the slope of the upper RGB. The latest spectroscopically determined chemical abundances are used to build distance- and reddening-independent relations between observed photometric features and cluster metallicity, optimizing the sample size and metallicity baseline of these relations by supplementing our sample with results from the literature. We find that the magnitude difference between the HB and the RGB bump can be used to predict metallicities, in terms of both iron abundance [Fe/H] and global metallicity [M/H], with a precision of better than 0.1 dex in all three near-IR bandpasses for relatively metal-rich ([M/H] ≳ -1) clusters. Meanwhile, both the slope of the upper RGB and the magnitude difference between the RGB tip and bump are useful metallicity indicators over the entire sampled metallicity range (-2 ≲ [M/H] ≲ 0) with a precision of 0.2 dex or better, despite model predictions that the RGB slope may become unreliable at high (near-solar) metallicities. Our results agree with previous calibrations in light of the relevant uncertainties, and we discuss implications for clusters with controversial metallicities as well as directions for further investigation.

  10. Metal enrichment of the intra-cluster medium over a Hubble time for merging and relaxed galaxy clusters

    CERN Document Server

    Kapferer, W; Weratschnig, J; Schindler, S; Domainko, W; Van Kampen, E; Kimeswenger, S; Mair, M; Ruffert, M

    2007-01-01

    We investigate the efficiency of galactic mass loss, triggered by ram-pressure stripping and galactic winds of cluster galaxies, on the chemical enrichment of the intra-cluster medium (ICM). We combine N-body and hydrodynamic simulations with a semi-numerical galaxy formation model. By including simultaneously different enrichment processes, namely ram-pressure stripping and galactic winds, in galaxy-cluster simulations, we are able to reproduce the observed metal distribution in the ICM. We find that the mass loss by galactic winds in the redshift regime z>2 is ~10% to 20% of the total galactic wind mass loss, whereas the mass loss by ram-pressure stripping in the same epoch is up to 5% of the total ram-pressure stripping mass loss over the whole simulation time. In the cluster formation epochs z<2 ram-pressure stripping becomes more dominant than galactic winds. We discuss the non-correlation between the evolution of the mean metallicity of galaxy clusters and the galactic mass losses. For comparison wit...

  11. Nonlinear Color-Metallicity Relations of Globular Clusters. III. On the Discrepancy in Metallicity between Globular Cluster Systems and their Parent Elliptical Galaxies

    CERN Document Server

    Yoon, Suk-Jin; Blakeslee, John P; Peng, Eric W; Sohn, Sangmo T; Cho, Jaeil; Kim, Hak-Sub; Chung, Chul; Kim, Sooyoung; Lee, Young-Wook

    2011-01-01

    One of the conundrums in extragalactic astronomy is the discrepancy in observed metallicity distribution functions (MDFs) between the two prime stellar components of early-type galaxies-globular clusters (GCs) and halo field stars. This is generally taken as evidence of highly decoupled evolutionary histories between GC systems and their parent galaxies. Here we show, however, that new developments in linking the observed GC colors to their intrinsic metallicities suggest nonlinear color-to-metallicity conversions, which translate observed color distributions into strongly-peaked, unimodal MDFs with broad metal-poor tails. Remarkably, the inferred GC MDFs are similar to the MDFs of resolved field stars in nearby elliptical galaxies and those produced by chemical evolution models of galaxies. The GC MDF shape, characterized by a sharp peak with a metal-poor tail, indicates a virtually continuous chemical enrichment with a relatively short timescale. The characteristic shape emerges across three orders of magni...

  12. Mo-Cu metal cluster formation and binding in an orange protein isolated from Desulfovibrio gigas.

    Science.gov (United States)

    Carepo, Marta S P; Pauleta, Sofia R; Wedd, Anthony G; Moura, José J G; Moura, Isabel

    2014-06-01

    The orange protein (ORP) isolated from the sulfate-reducing bacterium Desulfovibrio gigas (11.8 kDa) contains a mixed-metal sulfide cluster of the type [S2MoS2CuS2MoS2](3-) noncovalently bound to the polypeptide chain. The D. gigas ORP was heterologously produced in Escherichia coli in the apo form. Different strategies were used to reconstitute the metal cluster into apo-ORP and obtain insights into the metal cluster synthesis: (1) incorporation of a synthesized inorganic analogue of the native metal cluster and (2) the in situ synthesis of the metal cluster on the addition to apo-ORP of copper chloride and tetrathiomolybdate or tetrathiotungstate. This latter procedure was successful, and the visible spectrum of the Mo-Cu reconstituted ORP is identical to the one reported for the native protein with absorption maxima at 340 and 480 nm. The (1)H-(15)N heteronuclear single quantum coherence spectra of the reconstituted ORP obtained by strategy 2, in contrast to strategy 1, exhibited large changes, which required sequential assignment in order to identify, by chemical shift differences, the residues affected by the incorporation of the cluster, which is stabilized inside the protein by both electrostatic and hydrophobic interactions.

  13. A uniform metal distribution in the intergalactic medium of the Perseus cluster of galaxies

    CERN Document Server

    Werner, Norbert; Simionescu, Aurora; Allen, Steven W

    2013-01-01

    Most of the metals (elements heavier than helium) ever produced by stars in the member galaxies of galaxy clusters currently reside within the hot, X-ray emitting intra-cluster gas. Observations of X-ray line emission from this intergalactic medium have suggested a relatively small cluster-to-cluster scatter outside of the cluster centers and enrichment with iron out to large radii, leading to the idea that the metal enrichment occurred early in the history of the Universe. Models with early enrichment predict a uniform metal distribution at large radii in clusters, while late-time enrichment, favored by some previous studies, is expected to introduce significant spatial variations of the metallicity. To discriminate clearly between these competing models, it is essential to test for potential inhomogeneities by measuring the abundances out to large radii along multiple directions in clusters, which has not hitherto been done. Here we report a remarkably uniform measured iron abundance, as a function of radiu...

  14. Radial velocities and metallicities of red giant stars in the old open cluster NGC 7762

    CERN Document Server

    Carraro, Giovanni; Villanova, Sandro

    2016-01-01

    We present and discuss radial velocity and the very first metallicity measurements for nine evolved stars in the poorly known old open cluster NGC 7762. We isolated eight radial velocity cluster members and one interloper. Radial velocities are in good agreement with previous studies. NGC 7762 turns out to be of solar metallicity within the uncertainties ([Fe/H]=0.04$\\pm$0.12). For this metallicity, the cluster age is 2.5$\\pm$0.2 Gyr, and falls in a age range where only a few old open clusters are known. With respect to previous studies, we find a larger distance, implying the cluster to be located at 900$^{+70}_{-50}$ pc from the Sun. For most of the elements we measure solar-scaled abundance ratios. We searched the literature for open clusters of similar age in the solar vicinity and found that NGC 7762 can be considered a twin of Ruprecht 147, a similar age cluster located at only 300 pc from the Sun. In fact, beside age, also metallicity and abundance ratios are very close to Ruprecht 147 values within th...

  15. Chemical bonding and aromaticity in trinuclear transition-metal halide clusters.

    Science.gov (United States)

    Weck, Philippe F; Sergeeva, Alina P; Kim, Eunja; Boldyrev, Alexander I; Czerwinski, Kenneth R

    2011-02-07

    Trinuclear transition-metal complexes such as Re(3)X(9) (X = Cl, Br, I), with their uniquely featured structure among metal halides, have posed intriguing questions related to multicenter electron delocalization for several decades. Here we report a comprehensive study of the technetium halide clusters [Tc(3)(μ-X)(3)X(6)](0/1-/2-) (X = F, Cl, Br, I), isomorphous with their rhenium congeners, predicted from density functional theory calculations. The chemical bonding and aromaticity in these clusters are analyzed using the recently developed adaptive natural density partitioning method, which indicates that only [Tc(3)X(9)](2-) clusters exhibit aromatic character, stemming from a d-orbital-based π bond delocalized over the three metal centers. We also show that standard methods founded on the nucleus-independent chemical shift concept incorrectly predict the neutral Tc(3)X(9) clusters to be aromatic.

  16. Metallic Clusters: Theoretical Background, Properties and Synthesis in Microemulsions

    Directory of Open Access Journals (Sweden)

    David Buceta

    2014-11-01

    Full Text Available Reducing the size from the bulk material to nanoparticles produces a scaling behavior in physical properties in the later ones, due to the large surface-to-volume fraction. By further size reduction, entering into the subnanometric cluster region, physical properties are largely affected by strong quantum confinement. These quantum size effects (HOMO-LUMO gap, the small size and the specific geometry award subnanometric clusters with totally new and fascinating properties, including cluster photoluminescence, enhanced catalytic activity, etc. In this review, we report an introduction to the physical properties of clusters based on the jellium model; the controlled synthesis by microemulsion methods and the catalytic properties in different areas as heterogeneous catalysis, photocatalysis or electrocatalysis among others.

  17. Age and metallicity of star clusters in the Small Magellanic Cloud from integrated spectroscopy

    CERN Document Server

    Dias, Bruno; Barbuy, Beatriz; Kerber, Leandro; Idiart, Thais

    2010-01-01

    Context: Analysis of ages and metallicities of star clusters in the Magellanic Clouds bring information for studies on the chemical evolution of the Clouds and other dwarf Irregular galaxies. Aims: The aim is to derive ages and metallicities from integrated spectra of 14 star clusters in the Small Magellanic Cloud. We are seeking at identifying, in particular, intermediate/old age star clusters. Methods: Making use of a full spectrum fitting technique, we compared the integrated spectra of the sample clusters to three different sets of single stellar population models, using two fitting codes available in the literature. Results: We derive the ages and metallicities of 9 intermediate/old age clusters, some of them previously unstudied, and 5 young clusters. Conclusions: We point out the interest of the newly identified as intermediate/old age clusters HW1, NGC 152, Lindsay 3, Lindsay 11 and Lindsay 113. We also confirm the old ages of NGC 361, NGC 419, Kron 3, and of the very well-known oldest SMC cluster NGC...

  18. Abundances of metals in five nearby open clusters

    CERN Document Server

    Hui-Bon-Hoa, A

    1998-01-01

    Abundances of Mg, Ca, Sc, Cr, Fe, and Ni are derived for A stars of five nearby open clusters of various ages using high resolution spectroscopy. We point out a correlation between the abundance of Ca and that of Sc, suggesting that the abundance anomalies of these elements arise from the same physical process. Pronounced Am patterns are rather found in the oldest cluster stars whereas younger targets show weaker Am anomalies and atypical patterns for some of them.

  19. Dispersed metal cluster catalysts by design. Synthesis, characterization, structure, and performance

    Energy Technology Data Exchange (ETDEWEB)

    Arslan, Ilke [Pacific Northwest National Lab. (PNNL), Richland, WA (United States); Dixon, David A. [Univ. of Alabama, Tuscaloosa, AL (United States); Gates, Bruce C. [Univ. of California, Davis, CA (United States); Katz, Alexander [Univ. of California, Berkeley, CA (United States)

    2015-09-30

    To understand the class of metal cluster catalysts better and to lay a foundation for the prediction of properties leading to improved catalysts, we have synthesized metal catalysts with well-defined structures and varied the cluster structures and compositions systematically—including the ligands bonded to the metals. These ligands include supports and bulky organics that are being tuned to control both the electron transfer to or from the metal and the accessibility of reactants to influence catalytic properties. We have developed novel syntheses to prepare these well-defined catalysts with atomic-scale control the environment by choice and placement of ligands and applied state-of-the art spectroscopic, microscopic, and computational methods to determine their structures, reactivities, and catalytic properties. The ligands range from nearly flat MgO surfaces to enveloping zeolites to bulky calixarenes to provide controlled coverages of the metal clusters, while also enforcing unprecedented degrees of coordinative unsaturation at the metal site—thereby facilitating bonding and catalysis events at exposed metal atoms. With this wide range of ligand properties and our arsenal of characterization tools, we worked to achieve a deep, fundamental understanding of how to synthesize robust supported and ligand-modified metal clusters with controlled catalytic properties, thereby bridging the gap between active site structure and function in unsupported and supported metal catalysts. We used methods of organometallic and inorganic chemistry combined with surface chemistry for the precise synthesis of metal clusters and nanoparticles, characterizing them at various stages of preparation and under various conditions (including catalytic reaction conditions) and determining their structures and reactivities and how their catalytic properties depend on their compositions and structures. Key characterization methods included IR, NMR, and EXAFS spectroscopies to identify

  20. Generation and characterization of alkali metal clusters in Y-FAU zeolites. An ESR and MAS NMR spectroscopic study

    Science.gov (United States)

    Hannus, István; Béres, Attila; Nagy, János B.; Halász, János; Kiricsi, Imre

    1997-06-01

    Charged and neutral metal clusters of various compositions and sizes can be prepared by controlling the alkali metal content by the decomposition of alkali azides and the composition of the host zeolite by ion-exchange. ESR signals show that electron transfer from alkali metal atoms to alkali metal cations does occur, but in a direction opposite to that predicted by the gas-phase thermochemistry. Alkali metal clusters proved to be very active basic catalytic centers.

  1. Ligand-modified metal clusters for gas separation and purification

    Energy Technology Data Exchange (ETDEWEB)

    Okrut, Alexander; Ouyang, Xiaoying; Runnebaum, Ron; Gates, Bruce C.; Katz, Alexander

    2017-02-21

    Provided is an organic ligand-bound metal surface that selects one gaseous species over another. The species can be closely sized molecular species having less than 1 Angstrom difference in kinetic diameter. In one embodiment, the species comprise carbon monoxide and ethylene. Such organic ligand-bound metal surfaces can be successfully used in gas phase separations or purifications, sensing, and in catalysis.

  2. NGC 1252: a high altitude, metal poor open cluster remnant

    CERN Document Server

    Marcos, R de la Fuente; Bidin, C Moni; Carraro, G; Costa, E

    2013-01-01

    If stars form in clusters but most stars belong to the field, understanding the details of the transition from the former to the latter is imperative to explain the observational properties of the field. Aging open clusters are one of the sources of field stars. The disruption rate of open clusters slows down with age but, as an object gets older, the distinction between the remaining cluster or open cluster remnant (OCR) and the surrounding field becomes less and less obvious. As a result, finding good OCR candidates or confirming the OCR nature of some of the best candidates still remain elusive. One of these objects is NGC 1252, a scattered group of about 20 stars in Horologium. Here we use new wide-field photometry in the UBVI pass-bands, proper motions from the Yale/San Juan SPM 4.0 catalogue, and high resolution spectroscopy concurrently with results from N-body simulations to decypher NGC 1252's enigmatic character. Spectroscopy shows that most of the brightest stars in the studied area are chemically,...

  3. Nanoscale electrodeposition of low-dimensional metal phases and clusters.

    Science.gov (United States)

    Staikov, Georgi

    2016-08-01

    The present status of the problem of electrochemical formation of low-dimensional metal phases is reviewed. The progress in this field achieved in the last two decades is discussed on the basis of experimental results obtained in selected electrochemical systems with well defined single crystal substrates. The influence of crystallographic orientation and surface inhomogeneities of foreign substrates on the mechanism of formation and the atomic structure of two-dimensional (2D) metal phases in the underpotential deposition range is considered. The localized electrodeposition of metal nanoclusters on solid state surfaces applying the STM-tip as a nanoelectrode is demonstrated.

  4. Melting of bcc Transition Metals and Icosahedral Clustering

    Energy Technology Data Exchange (ETDEWEB)

    Ross, M; Boehler, R; Japel, S

    2006-05-26

    In contrast to polyvalent metals, transition metals have low melting slopes(dT/dP) that are due to partially filled d-bands that allow for a lowering of liquid phase energy through s-d electron transfer and the formation of local structures. In the case of bcc transition metals we show the apparent discrepancy of DAC melting measurements with shock melting of Mo can be understood by reexamining the shock data for V and Ta and introducing the presence of an icosahedral short range order (ISRO) melt phase.

  5. Nanoscale electrodeposition of low-dimensional metal phases and clusters

    Science.gov (United States)

    Staikov, Georgi

    2016-07-01

    The present status of the problem of electrochemical formation of low-dimensional metal phases is reviewed. The progress in this field achieved in the last two decades is discussed on the basis of experimental results obtained in selected electrochemical systems with well defined single crystal substrates. The influence of crystallographic orientation and surface inhomogeneities of foreign substrates on the mechanism of formation and the atomic structure of two-dimensional (2D) metal phases in the underpotential deposition range is considered. The localized electrodeposition of metal nanoclusters on solid state surfaces applying the STM-tip as a nanoelectrode is demonstrated.

  6. Energetics of small clusters of group IB metals (Cu, Ag, and Au) adsorbed on graphene

    Science.gov (United States)

    Kaur, Gagandeep; Gupta, Shuchi; Dharamvir, Keya

    2013-06-01

    The 2D structure of graphene maximizes the interaction of adsorbate on the layer. Many experiments have been devised to form stable metallic clusters of different sizes. We study the structure and binding energies of group IB clusters Mn (M=Au, Ag, Cu n=1, 3) adsorbed on graphene using Gupta potential [1] (for M-M interaction) and Lennard-Jones potential [2] (for metal-carbon interaction). The total energy of the system has been obtained by placing each of Mn cluster a certain distance above the graphene sheet at various positions and in various orientations. The minimized energy configurations, for all Mn clusters, lie above the center of a hexagon and parallel to the graphene sheet. Binding energy per atom for Ag and Cu metal clusters are less than those of respective Au indicating the lower stability of Ag/Cu metal-graphene system. Using various energy barriers, we can calculate the energy required to move small cluster from one position of minimum energy to another on graphene.

  7. Formation and properties of metal clusters isolated in helium droplets.

    Science.gov (United States)

    Tiggesbäumker, Josef; Stienkemeier, Frank

    2007-09-14

    The unique conditions forming atomic and molecular complexes and clusters using superfluid helium nanodroplets have opened up an innovative route for studying the physical and chemical properties of matter on the nanoscale. This review summarizes the specific characteristics of the formation of atomic clusters partly generated far from equilibrium in the helium environment. Special emphasis is on the optical response, electronic properties as well as dynamical processes which are mostly affected by the surrounding quantum matrix. Experiments include the optical induced response of isolated cluster systems in helium under quite different excitation conditions ranging from the linear regime up to the violent interaction with a strong laser field leading to Coulomb explosion and the generation of highly charged atomic fragments. The variety of results on the outstanding properties in the quantum size regime highlights the peculiar capabilities of helium nanodroplet isolation spectroscopy.

  8. First-principles studies on graphene-supported transition metal clusters.

    Science.gov (United States)

    Sahoo, Sanjubala; Gruner, Markus E; Khanna, Shiv N; Entel, Peter

    2014-08-21

    Theoretical studies on the structure, stability, and magnetic properties of icosahedral TM13 (TM = Fe, Co, Ni) clusters, deposited on pristine (defect free) and defective graphene sheet as well as graphene flakes, have been carried out within a gradient corrected density functional framework. The defects considered in our study include a carbon vacancy for the graphene sheet and a five-membered and a seven-membered ring structures for graphene flakes (finite graphene chunks). It is observed that the presence of defect in the substrate has a profound influence on the electronic structure and magnetic properties of graphene-transition metal complexes, thereby increasing the binding strength of the TM cluster on to the graphene substrate. Among TM13 clusters, Co13 is absorbed relatively more strongly on pristine and defective graphene as compared to Fe13 and Ni13 clusters. The adsorbed clusters show reduced magnetic moment compared to the free clusters.

  9. Spherical Clusters of Simple Metals: Madelung Energies and Structure.

    Science.gov (United States)

    1986-06-01

    crystalline structures remain lower than those of the optimal structures even at cluster sizes of more than 90 atoms. Also the calculations of the...differ from crystalline structures up to clus- ter sizes of hundreds of atoms. Acknowledgements - The author would like to thank N.W. Ashcroft, J.W

  10. Metal cluster fission: jellium model and Molecular dynamics simulations

    DEFF Research Database (Denmark)

    Lyalin, Andrey G.; Obolensky, Oleg I.; Solov'yov, Ilia;

    2004-01-01

    Fission of doubly charged sodium clusters is studied using the open-shell two-center deformed jellium model approximation and it ab initio molecular dynamic approach accounting for all electrons in the system. Results of calculations of fission reactions Na_10^2+ --> Na_7^+ + Na_3^+ and Na_18^2+ ...

  11. Electron correlations in transition metal-telluride cluster compounds

    NARCIS (Netherlands)

    Palstra, T.T.M.; Steigerwald, M.L.; Ramirez, A.P.; Zaanen, J.

    1994-01-01

    We report the magnetic properties of a new class of materials: Ni9Te6n+ and Co6Te8n+ with n = 0, 1, 2. These cluster compounds, which can be charged by chemical means from neutral to 2 +, provide a unique and novel way to change the Fermi level. For most charge states, we observe quenching of the

  12. Optimum metallic-bond scheme: Theoretical study ofgeometric structures for ground-state sodium clusters

    Institute of Scientific and Technical Information of China (English)

    苏长荣; 李家明

    2002-01-01

    We present an optimum metallic-bond scheme to study the geometric structures of sodium clusters Nan (n≤15) systematically by combining the characteristics of metallic bonds and the first principle molecular dynamics simulation. The scheme provides an optimum way to examine almost all stable structures of sodium clusters and to determine their ground state structures. It is interesting to note that for the larger sodium clusters (13≤n≤15), there are some plane-like substructures on their surfaces, which resemble the fragments of the (110) plane with the highest atomic area density in the bulk bcc sodium crystal. We also propose a possible way to understand the formation of large icosahedral sodium clusters (1500<n<22000).

  13. An Aligned Stream of Low-Metallicity Clusters in the Halo of the Milky Way

    CERN Document Server

    Lee, S J Y Y W

    2002-01-01

    One of the long-standing problems in modern astronomy is the curious division of Galactic globular clusters, the "Oosterhoff dichotomy," according to the properties of their RR Lyrae stars. Here, we find that most of the lowest-metallicity ([Fe/H]<-2.0) clusters, which are essential to an understanding of this phenomenon, display a planar alignment in the outer halo. This alignment, combined with evidence from kinematics and stellar population, indicates a captured origin from a satellite galaxy. We show that, together with the horizontal-branch evolutionary effect, the factor producing the dichotomy could be a small time-gap between the cluster-formation epochs in the Milky Way and the satellite. The results oppose the traditional view that the metal-poorest clusters represent the indigenous and oldest population of the Galaxy.

  14. The old metal-poor open cluster ESO 92-SC05: accreted from a dwarf galaxy?

    CERN Document Server

    ortolani, S; Barbuy, B

    2008-01-01

    The study of old open clusters outside the solar circle can bring constraints on formation scenarios of the outer disk. In particular, accretion of dwarf galaxies has been proposed as a likely mechanism in the area. We use BVI photometry for determining fundamental parameters of the faint open cluster ESO 92-SC05. Colour-Magnitude Diagrams are compared with Padova isochrones, in order to derive age, reddening and distance. We derive a reddening E(B-V)= 0.17, and an old age of $\\sim$6.0 Gyr. It is one of the rare open clusters known to be older than 5 Gyr. A metallicity of Z$\\sim$0.004 or [M/H]$\\sim$-0.7 is found. The rather low metallicity suggests that this cluster might be the result of an accretion episode of a dwarf galaxy.

  15. Comparative study of metal cluster fission in Hartree-Fock and LDA

    CERN Document Server

    Lyalin, A; Greiner, W; Lyalin, Andrey; Solov'yov, Andrey; Greiner, Walter

    2001-01-01

    Fission of doubly charged metal clusters is studied using the open-shell two-center deformed jellium Hartree-Fock model and Local Density Approximation. Results of calculations of the electronic structure and fission barriers for the symmetric and asymmetric channels associated with the following processes Na_{10}^{2+} --> Na_{7}^{+} + Na_{3}^{+}, Na_{18}^{2+} --> Na_{15}^{+} + Na_{3}^{+} and Na_{18}^{2+} --> 2 Na_{9}^{+} are presented. The role of the exact exchange and many-body correlation effects in metal clusters fission is analysed. It is demonstrated that the influence of many-electron correlation effects on the height of the fission barrier is more profound if the barrier arises nearby or beyond the scission point. The importance of cluster deformation effects in the fission process is elucidated with the use of the overlapping-spheroids shape parametrization allowing one an independent variation of deformations in the parent and daughter clusters.

  16. Nonlinear Color--Metallicity Relations of Globular Clusters. VI. On Calcium II Triplet Based Metallicities of Globular Clusters in Early-type Galaxies

    CERN Document Server

    Chung, Chul; Lee, Sang-Yoon; Lee, Young-Wook

    2016-01-01

    The metallicity distribution function of globular clusters (GCs) in galaxies is a key to understanding galactic formation and evolution. The calcium II triplet (CaT) index has recently become a popular metal abundance indicator thanks to its sensitivity to GC metallicity. Here we revisit and assess the reliability of CaT as a metallicity indicator using our new stellar population synthesis simulations based on empirical, high-resolution fluxes. The model shows that the CaT strength of old ($>$ 10 Gyr) GCs is proportional to ${\\rm [Fe/H]}$ below $-0.5$. In the modest metal-rich regime, however, CaT does not increase anymore with ${\\rm [Fe/H]}$ due to the little contribution from coolest red giant stars to the CaT absorption. The nonlinear nature of the color--$CaT$ relation is confirmed by the observations of GCs in nearby early-type galaxies. This indicates that the CaT should be used carefully when deriving metallicities of metal-rich stellar populations. Our results offer an explanation for the observed sha...

  17. METAL DEFICIENCY IN CLUSTER STAR-FORMING GALAXIES AT Z = 2

    Energy Technology Data Exchange (ETDEWEB)

    Valentino, F.; Daddi, E.; Strazzullo, V.; Gobat, R.; Bournaud, F.; Juneau, S.; Zanella, A. [Laboratoire AIM-Paris-Saclay, CEA/DSM-CNRS-Université Paris Diderot, Irfu/Service d’Astrophysique, CEA Saclay, Orme des Merisiers, F-91191 Gif sur Yvette (France); Onodera, M.; Carollo, M. [Institute for Astronomy, ETH Zürich Wolfgang-Pauli-strasse 27, 8093 Zürich (Switzerland); Renzini, A. [INAF-Osservatorio Astronomico di Padova Vicolo dell’Osservatorio 5, I-35122 Padova (Italy); Arimoto, N., E-mail: francesco.valentino@cea.fr [Subaru Telescope, National Astronomical Observatory of Japan 650 North A’ohoku Place, Hilo, HI 96720 (United States)

    2015-03-10

    We investigate the environmental effect on the metal enrichment of star-forming galaxies (SFGs) in the farthest spectroscopically confirmed and X-ray-detected cluster, CL J1449+0856 at z = 1.99. We combined Hubble Space Telescope/WFC3 G141 slitless spectroscopic data, our thirteen-band photometry, and a recent Subaru/Multi-object InfraRed Camera and Spectrograph (MOIRCS) near-infrared spectroscopic follow-up to constrain the physical properties of SFGs in CL J1449+0856 and in a mass-matched field sample. After a conservative removal of active galactic nuclei, stacking individual MOIRCS spectra of 6 (31) sources in the cluster (field) in the mass range 10 ≤ log(M/M{sub ⊙}) ≤ 11, we find a ∼4σ lower [N ii]/Hα ratio in the cluster than in the field. Stacking a subsample of 16 field galaxies with Hβ and [O iii] in the observed range, we measure an [O iii]/Hβ ratio fully compatible with the cluster value. Converting these ratios into metallicities, we find that the cluster SFGs are up to 0.25 dex poorer in metals than their field counterparts, depending on the adopted calibration. The low metallicity in cluster sources is confirmed using alternative indicators. Furthermore, we observe a significantly higher Hα luminosity and equivalent width in the average cluster spectrum than in the field. This is likely due to the enhanced specific star formation rate; even if lower dust reddening and/or an uncertain environmental dependence on the continuum-to-nebular emission differential reddening may play a role. Our findings might be explained by the accretion of pristine gas around galaxies at z = 2 and from cluster-scale reservoirs, possibly connected with a phase of rapid halo mass assembly at z > 2 and of a high galaxy merging rate.

  18. Nonequilibrium electron energy-loss kinetics in metal clusters

    CERN Document Server

    Guillon, C; Fatti, N D; Vallee, F

    2003-01-01

    Ultrafast energy exchanges of a non-Fermi electron gas with the lattice are investigated in silver clusters with sizes ranging from 4 to 26 nm using a femtosecond pump-probe technique. The results yield evidence for a cluster-size-dependent slowing down of the short-time energy losses of the electron gas when it is strongly athermal. A constant rate is eventually reached after a few hundred femtoseconds, consistent with the electron gas internal thermalization kinetics, this behaviour reflecting evolution from an individual to a collective electron-lattice type of coupling. The timescale of this transient regime is reduced in small nanoparticles, in agreement with speeding up of the electron-electron interactions with size reduction. The experimental results are in quantitative agreement with numerical simulations of the electron kinetics.

  19. Evidence for metallicity spreads in three massive M31 globular clusters

    CERN Document Server

    Fuentes-Carrera, Isaura; Sarajedini, Ata; Bridges, Terry; Djorgovski, George; Meylan, Georges

    2008-01-01

    We quantify the intrinsic width of the red giant branches of three massive globular clusters in M31 in a search for metallicity spreads within these objects. We present HST/ACS observations of three massive clusters in M31, G78, G213, and G280. A thorough description of the photometry extraction and calibration is presented. After derivation of the color-magnitude diagrams, we quantify the intrinsic width of the red giant branch of each cluster. This width translates into a metallicity dispersion that indicates a complex star formation history for this type of system. For G78, sigma_[Fe/H]}=0.86 \\pm 0.37; for G213, 0.89 \\pm 0.20; and for G280, 1.03 \\pm 0.26. We find that the metallicity dispersion of the clusters does not scale with mean metallicity. We also find no trend with the cluster mass. We discuss some possible formation scenarios that would explain our results.

  20. Formation of fe cluster superlattice in a metal-organic quantum-box network.

    Science.gov (United States)

    Pivetta, Marina; Pacchioni, Giulia E; Schlickum, Uta; Barth, Johannes V; Brune, Harald

    2013-02-22

    We report on the self-assembly of Fe adatoms on a Cu(111) surface that is patterned by a metal-organic honeycomb network, formed by coordination of dicarbonitrile pentaphenyl molecules with Cu adatoms. Fe atoms landing on the metal surface are mobile and steered by the quantum confinement of the surface state electrons towards the center of the network hexagonal cavities. In cavities hosting more than one Fe, preferential interatomic distances are observed. The adatoms in each hexagon aggregate into a single cluster upon gentle annealing. These clusters are again centered in the cavities and their size is discerned by their distinct apparent heights.

  1. Hami’s Nonferrous Metal Industry Evolves Towards Clusters

    Institute of Scientific and Technical Information of China (English)

    2012-01-01

    <正>In the development of black and nonferrous metals, Hami is characterized by a high starting point, high level, and high efficiency. Large enterprises and large groups are brought in to develop mineral resources. Focusing on large projects, Hami makes great efforts to extend the industry chain, turning resource advantages into industrial advantages.

  2. Fe-B-Y-Nb bulk metallic glasses in relation to clusters

    Institute of Scientific and Technical Information of China (English)

    CHENG Xu; WANG Qing; CHEN WeiRong; DONG Chuang

    2008-01-01

    Bulk metallic glass formations in the Fe-B-Y-Nb quaternary alloy system were in-vestigated by using the cluster line rule in combination with the minor alloying principle. The Fe-B-Y ternary system was selected as the basic system and the intersections of cluster lines were taken as the basic ternary compositions. The basic compositions were further alloyed with minor amounts of Nb. After 3-5 at.% Nb was added, the basic composition Fe68.6B25.7Y5.7, which was developed from the most densely packed cluster Fe8B3, formed 3 mm bulk metallic glasses. These quaternary bulk metallic glasses (Fe68.6B25.7Y5.7)100-xNbx (x=3-5at. %) are expressed approximately with a unified simple composition formula: (Fe8B3)1(Y, Nb)1. The (Fe68.6B25.7Y5.7)97Nb3 bulk metallic glass has the largest glass forming ability with the following characteristic parameters Tg=907 K, Tx=1006 K, Tg/T1=0.644, γ= 0.434, and Iongness t=22 mm. The combination of the cluster line rule and the minor-alloying principle is a promising new route towards the quantitative composition design of multi-component metallic glasses.

  3. Fe-B-Y-Nb bulk metallic glasses in relation to clusters

    Institute of Scientific and Technical Information of China (English)

    2008-01-01

    Bulk metallic glass formations in the Fe-B-Y-Nb quaternary alloy system were in-vestigated by using the cluster line rule in combination with the minor alloying principle. The Fe-B-Y ternary system was selected as the basic system and the intersections of cluster lines were taken as the basic ternary compositions. The basic compositions were further alloyed with minor amounts of Nb. After 3-5 at.% Nb was added,the basic composition Fe68.6B25.7Y5.7,which was developed from the most densely packed cluster Fe8B3,formed 3 mm bulk metallic glasses. These quaternary bulk metallic glasses (Fe68.6B25.7Y5.7)100-xNbx (x=3-5 at.%) are expressed approximately with a unified simple composition formula: (Fe8B3)1(Y,Nb)1. The (Fe68.6B25.7Y5.7)97Nb3 bulk metallic glass has the largest glass forming ability with the following characteristic parameters Tg=907 K,Tx=1006 K,Tg/Tl=0.644,γ=0.434,and longness t=22 mm. The combination of the cluster line rule and the minor-alloying principle is a promising new route towards the quantitative composition design of multi-component metallic glasses.

  4. The N-heterocyclic carbene chemistry of transition-metal carbonyl clusters.

    Science.gov (United States)

    Cabeza, Javier A; García-Álvarez, Pablo

    2011-11-01

    In the last decade, chemists have dedicated many efforts to investigate the coordination chemistry of N-heterocyclic carbenes (NHCs). Although most of that research activity has been devoted to mononuclear complexes, transition-metal carbonyl clusters have not escaped from these investigations. This critical review, which is focussed on the reactivity of NHCs (or their precursors) with transition-metal carbonyl clusters (mostly are of ruthenium and osmium) and on the transformations underwent by the NHC-containing species initially formed in those reactions, shows that the polynuclear character of these metallic compounds or, more precisely, the close proximity of one or more metal atoms to that which is or can be attached to the NHC ligand, is responsible for reactivity patterns that have no parallel in the NHC chemistry of mononuclear complexes (74 references).

  5. Trinuclear Metal Chalcogenide Clusters as Precursors for Superatomic Solids and Cluster Organic Frameworks

    Science.gov (United States)

    Shott, Jessica Lauren

    Inorganic molecular clusters Ni3(mu3-I) 2(mu2-dppm)3 (1), Ni3(mu 3-Te)2(mu2-dppm)3 (2), Ni3(mu3-Se)2(mu2-dppm) 3 (3), Ni3(mu3-S)2(mu 2-dppm)3 (4), Co4(mu3-S) 4(PPri3)4 (5), and Mo3(mu3-S)2(mu2-S)3(PMe 3)6 (6) have been used as building block precursors in the formation of binary superatomic solids with fullerenes (1-6•C 60). These solids are crystallized from solution and charge transfer from the electron-rich molecular cluster precursors to fullerene was confirmed using infrared (IR) spectroscopy. Structural data for these superatomic solids was obtained using single-crystal X-ray diffraction (XRD) experiments and suggests that their assembly is directed by noncovalent interactions. Close-contacts, reminiscent of halogen bonds, between cluster capping ligands and fulleride anions are observed in the solid state. Superconducting quantum interference device (SQUID) magnetometry and two-probe conductivity measurements indicate that compounds 1•C60 and 2•C 60 are paramagnetic and one hundred times more conductive than the constituent cluster precursors. Additionally, derivatives of molecular clusters 5 and 6 have been synthesized and investigated for use as superatomic secondary building units for 2D and 3D cluster organic frameworks. Characterization of these novel building blocks was accomplished using NMR spectroscopy as well as matrix-assisted laser desorption ionization mass spectrometry (MALDI-MS) and XRD analysis.

  6. Heating and ionization of metal clusters in the field of an intense femtosecond laser pulse

    Science.gov (United States)

    Kostenko, O. F.; Andreev, N. E.

    2007-06-01

    Inverse bremsstrahlung heating and thermal electron-impact ionization of a metal cluster are analyzed with account for the spatial structure of the electromagnetic field. It is shown that, for a femtosecond IR radiation pulse with an intensity of ˜1018 W/cm2 and for an iron cluster with an optimum radius of ˜25 nm, the electron temperature is higher than 1 keV. In this case, the L shell of the ions is highly stripped. The X-ray bremsstrahlung yield from clusters with a radius greater than the skin depth is estimated.

  7. Temporal stability of magic-number metal clusters: beyond the shell closing model

    Science.gov (United States)

    Desireddy, Anil; Kumar, Santosh; Guo, Jingshu; Bolan, Michael D.; Griffith, Wendell P.; Bigioni, Terry P.

    2013-02-01

    The anomalous stability of magic-number metal clusters has been associated with closed geometric and electronic shells and the opening of HOMO-LUMO gaps. Despite this enhanced stability, magic-number clusters are known to decay and react in the condensed phase to form other products. Improving our understanding of their decay mechanisms and developing strategies to control or eliminate cluster instability is a priority, to develop a more complete theory of their stability, to avoid studying mixtures of clusters produced by the decay of purified materials, and to enable technology development. Silver clusters are sufficiently reactive to facilitate the study of the ambient temporal stability of magic-number metal clusters and to begin to understand their decay mechanisms. Here, the solution phase stability of a series of silver:glutathione (Ag:SG) clusters was studied as a function of size, pH and chemical environment. Cluster stability was found to be a non-monotonic function of size. Electrophoretic separations showed that the dominant mechanism involved the redistribution of mass toward smaller sizes, where the products were almost exclusively previously known cluster sizes. Optical absorption spectra showed that the smaller clusters evolved toward the two most stable cluster sizes. The net surface charge was found to play an important role in cluster stabilization although charge screening had no effect on stability, contrary to DLVO theory. The decay mechanism was found to involve the loss of Ag+ ions and silver glutathionates. Clusters could be stabilized by the addition of Ag+ ions and destabilized by either the addition of glutathione or the removal of Ag+ ions. Clusters were also found to be most stable in near neutral pH, where they had a net negative surface charge. These results provide new mechanistic insights into the control of post-synthesis stability and chemical decay of magic-number metal clusters, which could be used to develop design principles

  8. DFT study of adsorption of CO2 on palladium cluster doped by transition metal

    Science.gov (United States)

    Saputro, A. G.; Agusta, M. K.; Wungu, T. D. K.; Suprijadi; Rusydi, F.; Dipojono, H. K.

    2016-08-01

    We report on a theoretical study of CO2 adsorption on Pd6-M (M: Ni, Cu, Pt, Rh) cluster using first-principles density functional theory (DFT) calculations. We find that CO2 molecule is adsorbed with a bidendate configuration on Pd7 and on most of Pd6M clusters. The bidendate adsorption configuration is formed due to the filling of the unoccupied n* orbital of CO2 molecule upon its interaction with d-orbitals of the cluster. We find that transition metal doping could modify the adsorption energy, adsorption site and adsorption configuration of CO2 molecule on Pd7 cluster. We also predict that the usage of Pd6M clusters as CO2 hydrogenation catalysts might facilitate the formations of HCOO/COOH.

  9. EFFECT OF SMALL CLUSTER DIFFUSION DURING TWO-DIMENSIONAL THIN FILM GROWTH ON METAL SURFACE

    Institute of Scientific and Technical Information of China (English)

    WU FENG-MIN; LI QIAO-WEN; WU ZI-QIN

    2000-01-01

    The diffusion of small clusters such as dimers and trimers on metal surface and the growth of two-dimensional thin films are studied by Monte Carlo simulation, using realistic growth model and physical parameters. It is found that small cluster diffusion plays an important role in the process of thin film growth at not very low temperature. It affects not only the island density and the size of islands but also the critical value of saturation occurring during growth of thin films. The effect of small cluster diffusion depends on both the size of critical nucleus and the growth temperature.The simulation results also show that the larger the cluster allowed to diffuse, the easier the saturation that takes place,giving rise to the lower critical coverage of saturation occurring. It is suggested that the effect of small cluster diffusion should be included in establishing the growth models of thin films.

  10. Quantum chemical calculation of the equilibrium structures of small metal atom clusters

    Science.gov (United States)

    Kahn, L. R.

    1982-01-01

    Metal atom clusters are studied based on the application of ab initio quantum mechanical approaches. Because these large 'molecular' systems pose special practical computational problems in the application of the quantum mechanical methods, there is a special need to find simplifying techniques that do not compromise the reliability of the calculations. Research is therefore directed towards various aspects of the implementation of the effective core potential technique for the removal of the metal atom core electrons from the calculations.

  11. Energy model for the Zr-based metallic glass alloy melt with clusters

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    An energy model for the melt of bulk metallic glass (BMG) with clusters was estab- lished, the Gibbs free energy and interfacial energy for the Zr-Al-Ni ternary alloy melt with Zr2Ni clusters were calculated, and the effects of the clusters on the Gibbs free energy, interfacial energy and nucleation rate were analyzed. The results showed that the existence of the clusters in the Zr-Al-Ni ternary alloy melt enables the Gibbs free energy to decrease in the composition range where bulk metallic glass forms easily, makes the interfacial energy increase and changes the distribu- tion of the interfacial energy with the alloy composition. Because of the clusters in the melt, the Gibbs free energy of the Zr66Al8Ni26 alloy melt decreases about 0.3-1 kJ/mol and the interfacial energy between the melt and crystal nucleus increases about 0.016 J/m2. The nucleation rate of the undercooled Zr66Al8Ni26 alloy melt de- creases evidently under the influence of the clusters on Gibbs free energy and the interfacial energy, and the maximum of the nucleation rate in the melt with the Zr2Ni clusters is only about 107 mol1s1.

  12. Energy model for the Zr-based metallic glass alloy melt with clusters

    Institute of Scientific and Technical Information of China (English)

    YANG YuanSheng; LI HuiQiang; TONG WenHui

    2007-01-01

    An energy model for the melt of bulk metallic glass (BMG) with clusters was established, the Gibbs free energy and interfacial energy for the Zr-Al-Ni ternary alloy melt with Zr2Ni clusters were calculated, and the effects of the clusters on the Gibbs free energy, interfacial energy and nucleation rate were analyzed. The results showed that the existence of the clusters in the Zr-Al-Ni ternary alloy melt enables the Gibbs free energy to decrease in the composition range where bulk metallic glass forms easily, makes the interfacial energy increase and changes the distribution of the interfacial energy with the alloy composition. Because of the clusters in the melt, the Gibbs free energy of the Zr66Al8Ni26 alloy melt decreases about 0.3-1 kJ/mol and the interfacial energy between the melt and crystal nucleus increases about 0.016 J/m2. The nucleation rate of the undercooled Zr66Al8Ni26 alloy melt decreases evidently under the influence of the clusters on Gibbs free energy and the interfacial energy, and the maximum of the nucleation rate in the melt with the Zr2Ni clusters is only about 107 mol-1·s-1.

  13. Synthesis and catalytic properties of metal clusters encapsulated within small-pore (SOD, GIS, ANA) zeolites.

    Science.gov (United States)

    Goel, Sarika; Wu, Zhijie; Zones, Stacey I; Iglesia, Enrique

    2012-10-24

    The synthesis protocols for encapsulation of metal clusters reported here expand the diversity in catalytic chemistries made possible by the ability of microporous solids to select reactants, transition states, and products on the basis of their molecular size. We report a synthesis strategy for the encapsulation of noble metals and their oxides within SOD (Sodalite, 0.28 nm × 0.28 nm), GIS (Gismondine, 0.45 nm × 0.31 nm), and ANA (Analcime, 0.42 nm × 0.16 nm) zeolites. Encapsulation was achieved via direct hydrothermal synthesis for SOD and GIS using metal precursors stabilized by ammonia or organic amine ligands, which prevent their decomposition or precipitation as colloidal hydroxides at the conditions of hydrothermal synthesis (12), thereby causing precipitation of even ligand-stabilized metal precursors as hydroxides. As a result, encapsulation was achieved by the recrystallization of metal clusters containing GIS into ANA, which retained these metal clusters within voids throughout the GIS-ANA transformation.

  14. Pulse laser-induced generation of cluster codes from metal nanoparticles for immunoassay applications

    Directory of Open Access Journals (Sweden)

    Chia-Yin Chang

    2017-05-01

    Full Text Available In this work, we have developed an assay for the detection of proteins by functionalized nanomaterials coupled with laser-induced desorption/ionization mass spectrometry (LDI-MS by monitoring the generation of metal cluster ions. We achieved selective detection of three proteins [thrombin, vascular endothelial growth factor-A165 (VEGF-A165, and platelet-derived growth factor-BB (PDGF-BB] by modifying nanoparticles (NPs of three different metals (Au, Ag, and Pt with the corresponding aptamer or antibody in one assay. The Au, Ag, and Pt acted as metal bio-codes for the analysis of thrombin, VEGF-A165, and PDGF-BB, respectively, and a microporous cellulose acetate membrane (CAM served as a medium for an in situ separation of target protein-bound and -unbound NPs. The functionalized metal nanoparticles bound to their specific proteins were subjected to LDI-MS on the CAM. The functional nanoparticles/CAM system can function as a signal transducer and amplifier by transforming the protein concentration into an intense metal cluster ion signal during LDI-MS analysis. This system can selectively detect proteins at picomolar concentrations. Most importantly, the system has great potential for the detection of multiple proteins without any pre-concentration, separation, or purification process because LDI-MS coupled with CAM effectively removes all signals except for those from the metal cluster ions.

  15. Pulse laser-induced generation of cluster codes from metal nanoparticles for immunoassay applications

    Science.gov (United States)

    Chang, Chia-Yin; Chu, Han-Wei; Unnikrishnan, Binesh; Peng, Lung-Hsiang; Cang, Jinshun; Hsu, Pang-Hung; Huang, Chih-Ching

    2017-05-01

    In this work, we have developed an assay for the detection of proteins by functionalized nanomaterials coupled with laser-induced desorption/ionization mass spectrometry (LDI-MS) by monitoring the generation of metal cluster ions. We achieved selective detection of three proteins [thrombin, vascular endothelial growth factor-A165 (VEGF-A165), and platelet-derived growth factor-BB (PDGF-BB)] by modifying nanoparticles (NPs) of three different metals (Au, Ag, and Pt) with the corresponding aptamer or antibody in one assay. The Au, Ag, and Pt acted as metal bio-codes for the analysis of thrombin, VEGF-A165, and PDGF-BB, respectively, and a microporous cellulose acetate membrane (CAM) served as a medium for an in situ separation of target protein-bound and -unbound NPs. The functionalized metal nanoparticles bound to their specific proteins were subjected to LDI-MS on the CAM. The functional nanoparticles/CAM system can function as a signal transducer and amplifier by transforming the protein concentration into an intense metal cluster ion signal during LDI-MS analysis. This system can selectively detect proteins at picomolar concentrations. Most importantly, the system has great potential for the detection of multiple proteins without any pre-concentration, separation, or purification process because LDI-MS coupled with CAM effectively removes all signals except for those from the metal cluster ions.

  16. Advanced use of high-performance liquid chromatography for synthesis of controlled metal clusters.

    Science.gov (United States)

    Niihori, Yoshiki; Matsuzaki, Miku; Uchida, Chihiro; Negishi, Yuichi

    2014-07-21

    Because the synthesis of metal clusters with multiple ligand types results in a distribution of ligands, high-resolution separation of each unique cluster from the mixture is required for precise control of the ligand composition. Reverse-phase high-performance liquid chromatography combined with appropriate transitioning of the mobile phase composition is an extremely effective means of separating ligand combinations when working with metal clusters protected by two different types of thiolates. We report herein advanced use of this method. The studies involving Au₂₄Pd(SR₁)₁₈-x(SR₂)x and Au₂₄Pd(SR₁)₁₈-x(SeR₂)x (SR₁, SR₂ = thiolate, SeR₂ = selenolate) revealed the following. (1) In general, an increase in the difference between the polarities of the functional groups incorporated in the two types of ligands improves the separation resolution. A suitable ligand combination for separation can be predicted from the retention times of Au₂₄Pd(SR₁)₁₈ and Au₂₄Pd(SR₂)₁₈, which cause the terminal peaks in a series of peaks. (2) The use of a step-gradient program during the mobile phase substitution results in improved resolution compared to that achievable with the linear gradients applied in prior work. (3) This technique is also useful for the evaluation of the chemical compositions of metal clusters protected by two different types of ligands with similar molecular weights. These findings will provide clear design guidelines for the functionalization of metal clusters via control of the ligand composition, and will also improve our understanding of the high-resolution isolation of metal clusters.

  17. Supersonic unstalled flutter

    Science.gov (United States)

    Adamczyk, J. J.; Goldstein, M. E.; Hartmann, M. J.

    1978-01-01

    Recently two flutter analyses have been developed at NASA Lewis Research Center to predict the onset of supersonic unstalled flutter of a cascade of two-dimensional airfoils. The first of these analyzes the onset of supersonic flutter at low levels of aerodynamic loading (i.e., backpressure), while the second examines the occurrence of supersonic flutter at moderate levels of aerodynamic loading. Both of these analyses are based on the linearized unsteady inviscid equations of gas dynamics to model the flow field surrounding the cascade. The details of the development of the solution to each of these models have been published. The objective of the present paper is to utilize these analyses in a parametric study to show the effects of cascade geometry, inlet Mach number, and backpressure on the onset of single and multi degree of freedom unstalled supersonic flutter. Several of the results from this study are correlated against experimental qualitative observation to validate the models.

  18. Asymmetric partitioning of metals among cluster anions and cations generated via laser ablation of mixed aluminum/Group 6 transition metal targets.

    Science.gov (United States)

    Waller, Sarah E; Mann, Jennifer E; Jarrold, Caroline Chick

    2013-02-28

    While high-power laser ablation of metal alloys indiscriminately produces gas-phase atomic ions in proportion to the abundance of the various metals in the alloy, gas-phase ions produced by moderate-power laser ablation sources coupled with molecular beams are formed by more complicated mechanisms. A mass spectrometric study that directly compares the mass distributions of cluster anions and cations generated from laser ablation of pure aluminum, an aluminum/molybdenum mixed target, and an aluminum/tungsten mixed target is detailed. Mass spectra of anionic species generated from the mixed targets showed that both tungsten and molybdenum were in higher abundance in the negatively charged species than in the target material. Mass spectra of the cationic species showed primarily Al(+) and aluminum oxide and hydroxide cluster cations. No molybdenum- or tungsten-containing cluster cations were definitively assigned. The asymmetric distribution of aluminum and Group 6 transition metals in cation and anion cluster composition is attributed to the low ionization energy of atomic aluminum and aluminum suboxide clusters. In addition, the propensity of both molybdenum and tungsten to form metal oxide cluster anions under the same conditions that favor metallic aluminum cluster anions is attributed to differences in the optical properties of the surface oxide that is present in the metal powders used to prepare the ablation targets. Mechanisms of mixed metal oxide clusters are considered.

  19. The LAMOST spectroscopic survey of star clusters in M31. II. Metallicities, ages and masses

    CERN Document Server

    Bingqiu, Chen; Maosheng, Xiang; Haibo, Yuan; Yang, Huang; Jianrong, Shi; Zhou, Fan; Zhiying, Huo; Chun, Wang; Juanjuan, Ren; Zhijia, Tian; Huawei, Zhang; Gaochao, Liu; Zihuang, Cao; Yong, Zhang; Yonghui, Hou; Yuefei, Wang

    2016-01-01

    We select from Paper I a sample of 306 massive star clusters observed with the Large Sky Area Multi-Object Fibre Spectroscopic Telescope (LAMOST) in the vicinity fields of M31 and M33 and determine their metallicities, ages and masses. Metallicities and ages are estimated by fitting the observed integrated spectra with stellar synthesis population (SSP) models with a pixel-to-pixel spectral fitting technique. Ages for most young clusters are also derived by fitting the multi-band photometric measurements with model spectral energy distributions (SEDs). The estimated cluster ages span a wide range, from several million years to the age of the universe. The numbers of clusters younger and older than 1 Gyr are respectively 46 and 260. With ages and metallicities determined, cluster masses are then estimated by comparing the multi-band photometric measurements with SSP model SEDs. The derived masses range from $\\sim 10^{3}$ to $\\sim 10^7$ $M_{\\odot}$, peaking at $\\sim 10^{4.3}$ and $\\sim 10^{5.7}$ $M_{\\odot}$ for...

  20. Negative ion photoelectron spectroscopic studies of transition metal cluster

    Science.gov (United States)

    Marcy, Timothy Paul

    The studies reported in this thesis were performed using a negative ion photoelectron spectrometer consisting of a cold cathode DC discharge ion source, a flowing afterglow ion-molecule reactor, a magnetic sector mass analyzer, an argon ion laser for photodetachment and a hemispherical electron kinetic energy analyzer and microchannel plate detector for photoelectron spectrum generation. The 476.5 nm (2.601 eV), 488.0 nm (2.540 eV) and 514.5 nm (2.410 eV) negative ion photoelectron spectra of VMn are reported and compared to the previously studied spectra of isoelectronic Cr2.1 The photoelectron spectra are remarkably similar to those of Cr2 in electron affinity and vibrational frequencies. The 488.0 nm photoelectron spectra and electron affinities of Nb n- (n = 1 - 9) are reported with discussion of observed vibrational structure. There are transitions to several electronic states of Nb2 in the reported spectra with overlapping vibrational progressions. The spectra of Nb3, Nb4 and Nb6 show partially resolved vibrational structure in the transitions to the lowest observed electronic state of each cluster. There is a single distinct active vibrational mode in the transition to the ground state of Nb8. Spin-orbit energies of Nb- are also reported. The 488.0 nm negative ion photoelectron spectra of Nb3H(D) are reported and compared to those of Nb3. There is a single vibrational mode active in the spectra of Nb3H(D) which is very similar to the most distinct mode active in the spectrum of Nb3. The 488.0 nm photoelectron spectra of the NbxCyH(D) y- (x = 1, 2, 3, y = 2, 4, 6) dehydrogenated products of the reactions of ethylene with niobium cluster anions are reported. Temperature studies of some of these species give evidence for the presence of multiple isomers of each molecule in the ion beam. The spectra of NbC6H(D) 6 are identical to those obtained from the reactions of benzene with niobium clusters and indicate that benzene is being formed from ethylene in the flow

  1. RHAPSODY-G simulations II - Baryonic growth and metal enrichment in massive galaxy clusters

    CERN Document Server

    Martizzi, Davide; Wu, Hao-Yi; Evrard, August E; Teyssier, Romain; Wechsler, Risa H

    2015-01-01

    We study the evolution of the stellar component and the metallicity of both the intracluster medium and of stars in massive ($M_{\\rm vir}\\approx 6\\times 10^{14}$ M$_{\\odot}$) simulated galaxy clusters from the RHAPSODY-G suite in detail and compare them to observational results. The simulations were performed with the AMR code RAMSES and include the effect of AGN feedback at the sub-grid level. AGN feedback is required to produce realistic galaxy and cluster properties and plays a role in mixing material in the central regions and regulating star formation in the central galaxy. In our low resolution runs with fiducial stellar yields, we find that stellar and ICM metallicities are a factor of two lower than in observations, however they tend to converge to the observed values $\\sim 0.3$ Z$_{\\odot}$ as the resolution is increased. We find that cool core clusters exhibit steeper metallicity gradients than non-cool core clusters, in qualitative agreement with observations. We verify that the ICM metallicities me...

  2. The Metal-rich Globular Cluster NGC6553 Observations with WFPC2, STIS, and NICMOS

    CERN Document Server

    Beaulieu, S F; Elson, R A W; Johnson, R A; Santiago, B; Sigurdsson, S; Tanvir, N R; Beaulieu, Sylvie F.; Gilmore, Gerard; Elson, Rebecca A.W.; Johnson, Rachel A.; Santiago, Basilio; Sigurdsson, Steinn; Tanvir, Nial

    2001-01-01

    We present a HST study of the metal-rich globular cluster NGC6553 using WFPC2, NICMOS and STIS. Our primary motivation is to calibrate the STIS broad-band LP magnitude against $V_{555}$ and $I_{814}$ magnitudes for stars of known metallicity and absolute (visual) magnitude, for application to our study of LMC globular clusters. NGC6553 has been shown in earlier studies to have a very unusual colour-magnitude diagram, so we also use our data to investigate the reddening, distance, luminosity function and structure of this cluster. We deduce a higher metallicity and smaller distance modulus than did some previous studies, but emphasise that very large patchy extinction on small angular scales prohibits accurate determination of the parameters of this cluster. The horizontal branch of NGC6553 in ($V,V-I$) is tilted at an angle close to that of the reddening vector. We show that extinction does not, however, explain the tilt, which is presumably a metallicity effect. The colour-magnitude diagram shows an apparent...

  3. Optical trapping of metal-dielectric nanoparticle clusters near photonic crystal microcavities.

    Science.gov (United States)

    Mejia, Camilo A; Huang, Ningfeng; Povinelli, Michelle L

    2012-09-01

    We predict the formation of optically trapped, metal-dielectric nanoparticle clusters above photonic crystal microcavities. We determine the conditions on particle size and position for a gold particle to be trapped above the microcavity. We then show that strong field redistribution and enhancement near the trapped gold nanoparticle results in secondary trapping sites for a pair of dielectric nanoparticles.

  4. Formation and evolution properties of clusters in liquid metal copper during rapid cooling processes

    Institute of Scientific and Technical Information of China (English)

    YI Xue-hua; LIU Rang-su; TIAN Ze-an; HOU Zhao-yang; LI Xiao-yang; ZHOU Qun-yi

    2008-01-01

    Based on the quantum Sutton-Chen many-body potential, a molecular dynamics simulation was performed to investigate the formation and evolution properties of clusters in liquid Cu with 50 000 atoms. The cluster-type index method(CTIM) was used to describe the complex microstructure transitions. It is demonstrated that the amorphous structures are mainly formed with the three bond-types of 1551, 1541 and 1431 in the system, and the icosahedral cluster (12 0 12 0) and other basic polyhedron clusters of (12 2 8 2), (13 1 10 2), (13 3 6 4), (14 1 10 3), (14 2 8 4) and (14 3 6 5) play a critical and leading role in the transition from liquid to glass. The nano-clusters formed in the system consist of some basic clusters and middle cluster configurations by connecting to each other, and distinguish from those obtained by gaseous deposition and ionic spray. From the results of structural parameter pair distribution function g(r), bond-types and basic cluster-types, it is found that the glass transition temperature Tg for liquid metal Cu is about 673 K at the cooling rate of 1.0×1014 K/s.

  5. Light-Induced In Situ Transformation of Metal Clusters to Metal Nanocrystals for Photocatalysis.

    Science.gov (United States)

    Xiao, Fang-Xing; Zeng, Zhiping; Hsu, Shao-Hui; Hung, Sung-Fu; Chen, Hao Ming; Liu, Bin

    2015-12-30

    In situ transformation of glutathione-capped gold (Aux) clusters to gold (Au) nanocrystals under simulated solar light irradiation was achieved and utilized as a facile synthetic approach to rationally fabricate Aux/Au/TiO2 ternary and Au/TiO2 binary heterostructures. Synergistic interaction of Aux clusters and Au nanocrystals contributes to enhanced visible-light-driven photocatalysis.

  6. Mixed-Metal Oxo Clusters Structurally Derived from Ti6O4(OR)8(OOCR')8.

    Science.gov (United States)

    Artner, Christine; Koyun, Ayse; Czakler, Matthias; Schubert, Ulrich

    2014-10-01

    The mixed-metal oxo clusters FeTi5O4(OiPr)4(OMc)10 (OMc = methacrylate), Zn2Ti4O4(OiPr)2(OMc)10, Cd4Ti2O2(OAc)2(OMc)10(HOiPr)2, [Ca2Ti4O4(OAc)2(OMc)10] n , and [Sr2Ti4O4(OMc)12(HOMc)2] n were obtained from the reaction of titanium alkoxides with the corresponding metal acetates and methacrylic acid. Their structures are derived from Ti clusters with the composition Ti6O4(OR)8(OOCR')8. The Ca and Sr derivatives consist of chains of condensed clusters.

  7. Mixed-Metal Oxo Clusters Structurally Derived from Ti6O4(OR)8(OOCR′)8

    Science.gov (United States)

    Artner, Christine; Koyun, Ayse; Czakler, Matthias; Schubert, Ulrich

    2014-01-01

    The mixed-metal oxo clusters FeTi5O4(OiPr)4(OMc)10 (OMc = methacrylate), Zn2Ti4O4(OiPr)2(OMc)10, Cd4Ti2O2(OAc)2(OMc)10(HOiPr)2, [Ca2Ti4O4(OAc)2(OMc)10]n, and [Sr2Ti4O4(OMc)12(HOMc)2]n were obtained from the reaction of titanium alkoxides with the corresponding metal acetates and methacrylic acid. Their structures are derived from Ti clusters with the composition Ti6O4(OR)8(OOCR′)8. The Ca and Sr derivatives consist of chains of condensed clusters. PMID:25814833

  8. A very deep Chandra view of metals, sloshing and feedback in the Centaurus cluster of galaxies

    CERN Document Server

    Sanders, J S; Taylor, G B; Russell, H R; Blundell, K M; Canning, R E A; Hlavacek-Larrondo, J; Walker, S A; Grimes, C K

    2016-01-01

    We examine deep Chandra X-ray observations of the Centaurus cluster of galaxies, Abell 3526. Applying a gradient magnitude filter reveals a wealth of structure, from filamentary soft emission on 100pc (0.5 arcsec) scales close to the nucleus to features 10s of kpc in size at larger radii. The cluster contains multiple high-metallicity regions with sharp edges. Relative to an azimuthal average, the deviations of metallicity and surface brightness are correlated, and the temperature is inversely correlated, as expected if the larger scale asymmetries in the cluster are dominated by sloshing motions. Around the western cold front are a series of ~7 kpc 'notches', suggestive of Kelvin-Helmholtz instabilities. The cold front width varies from 4 kpc down to close to the electron mean free path. Inside the front are multiple metallicity blobs on scales of 5-10 kpc, which could have been uplifted by AGN activity, also explaining the central metallicity drop and flat inner metallicity profile. Close to the nucleus are...

  9. Processes of conversion of a hot metal particle into aerogel through clusters

    Energy Technology Data Exchange (ETDEWEB)

    Smirnov, B. M., E-mail: bmsmirnov@gmail.com [Russian Academy of Sciences, Joint Institute for High Temperatures (Russian Federation)

    2015-10-15

    Processes are considered for conversion into a fractal structure of a hot metal micron-size particle that is located in a buffer gas or a gas flow and is heated by an external electric or electromagnetic source or by a plasma. The parameter of this heating is the particle temperature, which is the same in the entire particle volume because of its small size and high conductivity. Three processes determine the particle heat balance: particle radiation, evaporation of metal atoms from the particle surface, and heat transport to the surrounding gas due to its thermal conductivity. The particle heat balance is analyzed based on these processes, which are analogous to those for bulk metals with the small particle size, and its high temperature taken into account. Outside the particle, where the gas temperature is lower than on its surface, the formed metal vapor in a buffer gas flow is converted into clusters. Clusters grow as a result of coagulation until they become liquid, and then clusters form fractal aggregates if they are removed form the gas flow. Subsequently, associations of fractal aggregates join into a fractal structure. The rate of this process increases in medium electric fields, and the formed fractal structure has features of aerogels and fractal fibers. As a result of a chain of the above processes, a porous metal film may be manufactured for use as a filter or catalyst for gas flows.

  10. On the metallicity distribution of the peculiar globular cluster M22

    CERN Document Server

    Lee, Jae-Woo

    2016-01-01

    In our previous study, we showed that the peculiar globular cluster (GC) M22 contains two distinct stellar populations, namely the Ca-w and Ca-s groups with different physical properties, having different chemical compositions, spatial distributions and kinematics. We proposed that M22 is most likely formed via a merger of two GCs with heterogeneous metallicities in a dwarf galaxy environment and accreted later to our Galaxy. In their recent study, Mucciarelli et al. claimed that M22 is a normal mono-metallic globular cluster without any perceptible metallicity spread among the two groups of stars, which challenges our results and those of others. We devise new strategies for the local thermodynamic equilibrium (LTE) abundance analysis of red giant branch (RGB) stars in GCs and show there exists a spread in the iron abundance distribution in M22.

  11. Dynamic screening of a localized hole during photoemission from a metal cluster

    CERN Document Server

    Koval, N E; Borisov, A G; Muiño, R Díez

    2012-01-01

    Recent advances in attosecond spectroscopy techniques have fueled the interest in the theoretical description of electronic processes taking place in the subfemtosecond time scale. We here study the coupled dynamic screening of a localized hole and a photoelectron emitted from a metal cluster using a semi-classical model. Electron density dynamics in the cluster is calculated with Time Dependent Density Functional Theory and the motion of the photoemitted electron is described classically. We show that the dynamic screening of the hole by the cluster electrons affects the motion of the photoemitted electron. At the very beginning of the photoemission process, the emitted electron is accelerated by the cluster electrons that pile up to screen the hole. This is a velocity dependent effect that needs to be accounted for when calculating the energy lost by the electron due to inelastic processes.

  12. Mixed clusters from the coexpansion of C2F6 and n2 in a pulsed, supersonic expansion cluster ion source and beam deflection time-of-flight mass spectrometer: A first application

    Science.gov (United States)

    Thompson, Steven D.

    The following topics are discussed: (1) cluster ion genesis; (2) cluster ion detection; (3) Ion source; (4) pulse valve; (5) e-gun; (6) Ion optics; (7) a first order model; and (8) a modified Bakker's model.

  13. Cluster-induced desorption from metal organic surfaces: Structural effects

    Energy Technology Data Exchange (ETDEWEB)

    Delcorte, A., E-mail: arnaud.delcorte@uclouvain.be [Institute of Condensed Matter and Nanosciences, Université catholique de Louvain, 1 Croix du Sud, B-1348 Louvain-la-Neuve (Belgium); Hoecke, E. van; Restrepo, O.A. [Institute of Condensed Matter and Nanosciences, Université catholique de Louvain, 1 Croix du Sud, B-1348 Louvain-la-Neuve (Belgium)

    2013-05-15

    Molecular dynamics (MD) simulations are used to model the 10 keV bombardment of Au-nanoparticle (NP)-covered polymeric samples by Ga, C{sub 60} and Au{sub 400} projectiles, at normal incidence. While the presence of the Au-NPs tends to enhance the organic material emission upon Ga and Au{sub 400} bombardment, as a result of increased projectile stopping, it strongly reduces the organic emission upon C{sub 60} bombardment because of the projectile reflection. Our results show that these trends are valid for kDa polymers (which can be emitted intact) as well as for virtually infinite length chains (which require fragmentation), but that the polymer sputtered mass is consistently >3 times larger in the case of the kDa molecules for all impact points and projectiles. Using a series of samples, it is also shown that embedding the Au-NPs in the organic material leads to completely different results, with, upon C{sub 60} bombardment, the largest sputtered masses observed for impacts above the NPs. For Au{sub 400} bombardment, the burial of the Au-NPs leads to comparatively lower sputtered masses. These new results demonstrate the complexity of the sputtering of nanostructured hybrid materials by cluster projectiles and suggest various artifacts that should complicate the analysis and depth profiling of such materials.

  14. Advanced Electrochemistry of Individual Metal Clusters Electrodeposited Atom by Atom to Nanometer by Nanometer.

    Science.gov (United States)

    Kim, Jiyeon; Dick, Jeffrey E; Bard, Allen J

    2016-11-15

    Metal clusters are very important as building blocks for nanoparticles (NPs) for electrocatalysis and electroanalysis in both fundamental and applied electrochemistry. Attention has been given to understanding of traditional nucleation and growth of metal clusters and to their catalytic activities for various electrochemical applications in energy harvesting as well as analytical sensing. Importantly, understanding the properties of these clusters, primarily the relationship between catalysis and morphology, is required to optimize catalytic function. This has been difficult due to the heterogeneities in the size, shape, and surface properties. Thus, methods that address these issues are necessary to begin understanding the reactivity of individual catalytic centers as opposed to ensemble measurements, where the effect of size and morphology on the catalysis is averaged out in the measurement. This Account introduces our advanced electrochemical approaches to focus on each isolated metal cluster, where we electrochemically fabricated clusters or NPs atom by atom to nanometer by nanometer and explored their electrochemistry for their kinetic and catalytic behavior. Such approaches expand the dimensions of analysis, to include the electrochemistry of (1) a discrete atomic cluster, (2) solely a single NP, or (3) individual NPs in the ensemble sample. Specifically, we studied the electrocatalysis of atomic metal clusters as a nascent electrocatalyst via direct electrodeposition on carbon ultramicroelectrode (C UME) in a femtomolar metal ion precursor. In addition, we developed tunneling ultramicroelectrodes (TUMEs) to study electron transfer (ET) kinetics of a redox probe at a single metal NP electrodeposited on this TUME. Owing to the small dimension of a NP as an active area of a TUME, extremely high mass transfer conditions yielded a remarkably high standard ET rate constant, k(0), of 36 cm/s for outer-sphere ET reaction. Most recently, we advanced nanoscale

  15. Metals on graphene and carbon nanotube surfaces: From mobile atoms to atomtronics to bulk metals to clusters and catalysts

    KAUST Repository

    Sarkar, Santanu C.

    2014-01-14

    In this Perspective, we present an overview of recent fundamental studies on the nature of the interaction between individual metal atoms and metal clusters and the conjugated surfaces of graphene and carbon nanotube with a particular focus on the electronic structure and chemical bonding at the metal-graphene interface. We discuss the relevance of organometallic complexes of graphitic materials to the development of a fundamental understanding of these interactions and their application in atomtronics as atomic interconnects, high mobility organometallic transistor devices, high-frequency electronic devices, organometallic catalysis (hydrogen fuel generation by photocatalytic water splitting, fuel cells, hydrogenation), spintronics, memory devices, and the next generation energy devices. We touch on chemical vapor deposition (CVD) graphene grown on metals, the reactivity of its surface, and its use as a template for asymmetric graphene functionalization chemistry (ultrathin Janus discs). We highlight some of the latest advances in understanding the nature of interactions between metals and graphene surfaces from the standpoint of metal overlayers deposited on graphene and SWNT thin films. Finally, we comment on the major challenges facing the field and the opportunities for technological applications. © 2013 American Chemical Society.

  16. Metal-Organic Frameworks (MOFs) of a Cubic Metal Cluster with Multicentered Mn(I)-Mn(I) Bonds.

    Science.gov (United States)

    Hu, Huan-Cheng; Hu, Han-Shi; Zhao, Bin; Cui, Ping; Cheng, Peng; Li, Jun

    2015-09-28

    MOFs with both multicentered metal-metal bonds and low-oxidation-state (LOS) metal ions have been underexplored hitherto. Here we report the first cubic [Mn(I) 8 ] cluster-based MOF (1) with multicentered Mn(I)-Mn(I) bonds and +1 oxidation state of manganese (Mn(I) or Mn(I)), as is supported by single-crystal structure determination, XPS analyses, and quantum chemical studies. Compound 1 possesses the shortest Mn(I)-Mn(I) bond of 2.372 Å. Theoretical studies with density functional theory (DFT) reveal extensive electron delocalization over the [Mn(I) 8 ] cube. The 48 electrons in the [Mn(I) 8 ] cube fully occupy half of the 3d-based and the lowest 4s-based bonding orbitals, with six electrons lying at the nonbonding 3d-orbitals. This bonding feature renders so-called cubic aromaticity. Magnetic properties measurements show that 1 is an antiferromagnet. This work is expected to inspire further investigation of cubic metal-metal bonding, MOF materials with LOS metals, and metalloaromatic theory.

  17. Controlling optical responses through local dielectric resonance in nanometre metallic clusters

    Institute of Scientific and Technical Information of China (English)

    Chen Liang-Liang; Gu Ying; Wang Li-Jin; Gong Qi-Huang

    2007-01-01

    Optical responses in dilute composites are controlled through the local dielectric resonance of metallic clusters. We consider two located metallic clusters close to each other with admittances ε1 and ε2. Through varying the difference admittance ratio η[= (ε2 - ε0)/(ε1 - ε0)], we find that their optical responses are determined by the local resonance.There is a blueshift of absorption peaks with the increase of η. Simultaneously, it is known that the absorption peaks will be redshifted by enlarging the cluster size. By adjusting the nano-metallic cluster geometry, size and admittances,we can control the positions and intensities of absorption peaks effectively. We have also deduced the effective linear optical responses of three-comPonent composites εe = ε0 (1 + ∑nsn=1 [(γn1 + ηγn2 )/(ε0 (s - sn))]), and the sum rule of cross sections: ∑nsn=1 (γn1 + ηγn2) = Nh1 + Nh2, where Nh1and Nh2 are the numbers of ε1 and ε2 bonds along the electric field, respectively. These results may be beneficial to the study of surface plasmon resonances on a nanometre scale.

  18. Anisotropic Metal-enriched Outflows Driven by AGN in Clusters of Galaxies

    CERN Document Server

    Kirkpatrick, C C; Cavagnolo, K W

    2011-01-01

    We present an analysis of the spatial distribution of metal-rich gas in ten galaxy clusters using deep observations from the Chandra X-ray Observatory. The brightest cluster galaxies have experienced recent AGN activity in the forms of bright radio emission, cavities, and shock fronts embedded in the hot atmospheres. The heavy elements are distributed anisotropically and are aligned with the large-scale radio and cavity axes. They are apparently being transported from the halo of the brightest cluster galaxy into the intracluster medium along large-scale outflows driven by the radio jets. The radial ranges of the metal-enriched outflows are found to scale with jet power as R_Fe ~ P_jet^0.42, with a scatter of only 0.5 dex. The heavy elements are transported beyond the extent of the inner cavities in all clusters, suggesting this is a long lasting effect sustained over multiple generations of outbursts. Black holes in BCGs will likely have difficulty ejecting metal enriched gas beyond 1 Mpc unless their masses...

  19. LOW-METALLICITY YOUNG CLUSTERS IN THE OUTER GALAXY. I. Sh 2-207

    Energy Technology Data Exchange (ETDEWEB)

    Yasui, Chikako [Department of Astronomy, Graduate School of Science, University of Tokyo, Bunkyo-ku, Tokyo 113-0033 (Japan); Kobayashi, Naoto; Izumi, Natsuko [Institute of Astronomy, School of Science, University of Tokyo, 2-21-1 Osawa, Mitaka, Tokyo 181-0015 (Japan); Tokunaga, Alan T. [Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI 96822 (United States); Saito, Masao, E-mail: ck.yasui@astron.s.u-tokyo.ac.jp [Nobeyama Radio Observatory, 462-2 Nobeyama, Minamimaki-mura, Minamisaku-gun, Nagano 384-1305 (Japan)

    2016-03-15

    To study star formation in low-metallicity environments ([M/H] ∼ −1 dex), we obtained deep near-infrared (NIR) images of Sh 2-207 (S207), which is an H ii region in the outer Galaxy with a spectroscopically determined metallicity of [O/H] ≃ −0.8 dex. We identified a young cluster in the western region of S207 with a limiting magnitude of K{sub S} = 19.0 mag (10σ) that corresponds to a mass detection limit of ≲0.1 M{sub ⊙} and enables the comparison of star-forming properties under low metallicity with those of the solar neighborhood. From the fitting of the K-band luminosity function (KLF), the age and distance of the S207 cluster are estimated at 2–3 Myr and ∼4 kpc, respectively. The estimated age is consistent with the suggestion of small extinctions of stars in the cluster (A{sub V} ∼ 3 mag) and the non-detection of molecular clouds. The reasonably good fit between the observed KLF and the model KLF suggests that the underlying initial mass function (IMF) of the cluster down to the detection limit is not significantly different from the typical IMFs in the solar metallicity. From the fraction of stars with NIR excesses, a low disk fraction (<10%) in the cluster with a relatively young age is suggested, as we had previously proposed.

  20. From Metal Cluster to Metal Nanowire: A Topological Analysis of Electron Density and Band Structure Calculation

    Directory of Open Access Journals (Sweden)

    Yu Wang

    2002-01-01

    Full Text Available Abstract:We investigate a theoretical model of molecular metalwire constructed from linear polynuclear metal complexes. In particular we study the linear Crn metal complex and Cr molecular metalwire. The electron density distributions of the model nanowire and the linear Crn metal complexes, with n = 3, 5, and 7, are calculated by employing CRYSTAL98 package with topological analysis. The preliminary results indicate that the bonding types between any two neighboring Cr are all the same, namely the polarized open-shell interaction. The pattern of electron density distribution in metal complexes resembles that of the model Cr nanowire as the number of metal ions increases. The conductivity of the model Cr nanowire is also tested by performing the band structure calculation.

  1. Nanocomposite metal/plasma polymer films prepared by means of gas aggregation cluster source

    Energy Technology Data Exchange (ETDEWEB)

    Polonskyi, O.; Solar, P.; Kylian, O.; Drabik, M.; Artemenko, A.; Kousal, J.; Hanus, J.; Pesicka, J.; Matolinova, I. [Charles University in Prague, Faculty of Mathematics and Physics, V Holesovickach 2, 18000 Prague 8 (Czech Republic); Kolibalova, E. [Tescan, Libusina trida 21, 632 00 Brno (Czech Republic); Slavinska, D. [Charles University in Prague, Faculty of Mathematics and Physics, V Holesovickach 2, 18000 Prague 8 (Czech Republic); Biederman, H., E-mail: bieder@kmf.troja.mff.cuni.cz [Charles University in Prague, Faculty of Mathematics and Physics, V Holesovickach 2, 18000 Prague 8 (Czech Republic)

    2012-04-02

    Nanocomposite metal/plasma polymer films have been prepared by simultaneous plasma polymerization using a mixture of Ar/n-hexane and metal cluster beams. A simple compact cluster gas aggregation source is described and characterized with emphasis on the determination of the amount of charged clusters and their size distribution. It is shown that the fraction of neutral, positively and negatively charged nanoclusters leaving the gas aggregation source is largely influenced by used operational conditions. In addition, it is demonstrated that a large portion of Ag clusters is positively charged, especially when higher currents are used for their production. Deposition of nanocomposite Ag/C:H plasma polymer films is described in detail by means of cluster gas aggregation source. Basic characterization of the films is performed using transmission electron microscopy, ultraviolet-visible and Fourier-transform infrared spectroscopies. It is shown that the morphology, structure and optical properties of such prepared nanocomposites differ significantly from the ones fabricated by means of magnetron sputtering of Ag target in Ar/n-hexane mixture.

  2. The evolution of the Galactic metallicity gradient from high-resolution spectroscopy of open clusters

    CERN Document Server

    Magrini, Laura; Randich, Sofia; Galli, Daniele

    2008-01-01

    Open clusters offer a unique possibility to study the time evolution of the radial metallicity gradients of several elements in our Galaxy, because they span large intervals in age and Galactocentric distance, and both quantities can be more accurately derived than for field stars. We re-address the issue of the Galactic metallicity gradient and its time evolution by comparing the empirical gradients traced by a sample of 45 open clusters with a chemical evolution model of the Galaxy. At variance with previous similar studies, we have collected from the literature only abundances derived from high--resolution spectra. The clusters have distances $7 < RGC<22$ kpc and ages from $\\sim 30$ Myr to 11 Gyr. We also consider the $\\alpha$-elements Si, Ca, Ti, and the iron-peak elements Cr and Ni. The data for iron-peak and $\\alpha$-elements indicate a steep metallicity gradient for R_GC<12$ kpc and a plateau at larger radii. The time evolution of the metallicity distribution is characterized by a uniform incr...

  3. Cluster chemical reactions at mineral–liquid interface in metal leaching by photo-electroactive water-and-gas emulsions

    Science.gov (United States)

    Sekisov, AG

    2017-02-01

    Possibility of cluster (inter-cluster) reactions at the interface of mineral and liquid phases in leaching of metals mainly in dispersed cluster form by photo-electrically activated water-and-gas emulsions is theoretically evaluated. The governing role of active clusters of water and clustered hydrate envelopes generated under dissolution of active oxygen forms is determined. The scope of the study covers possible processes of transformation of clustered gold in mineral substance under direct interaction with the components of the active water-and-gas emulsions.

  4. Stability and mobility of defect clusters and dislocation loops in metals

    DEFF Research Database (Denmark)

    Osetsky, Y.N.; Bacon, D.J.; Serra, A.;

    2000-01-01

    has been observed in the computer simulation of small vacancy loops in alpha-Fe. In the present paper we summarise results obtained by molecular dynamics simulations of defect clusters and small dislocation loops in alpha-Fe(bcc) and Cu(fcc). The structure and stability of vacancy and interstitial...... loops are reviewed, and the dynamics of glissile clusters assessed. The relevance and importance of these results in establishing a better understanding of the observed differences in the damage accumulation behaviour between bcc and fee metals irradiated under cascade damage conditions are pointed out...

  5. Synthesis of DPA dendron encapsulated gold clusters with metal-assembling function

    Directory of Open Access Journals (Sweden)

    Yi Men, Masayoshi Higuchi and Kimihisa Yamamoto

    2006-01-01

    Full Text Available Gold clusters modified with first, second and third generation dendritic polyphenylazomethines (DPA were synthesized by an exchanged reaction of corresponding DPA dendron thiols. Measurements by high performance perfect sizer (HPPS and TEM reveal that their diameters increase with a change in the chain length of the modifying molecules from the first to third generation. These gold clusters with DPA dendrons exhibit coordination quantitatively to metal ions such as Fe3+, Sn2+, etc., because of their imine groups; this then resulted in self-aggregation to form a large sphere.

  6. Globular clusters in the outer Galactic halo: new HST/ACS imaging of 6 globular clusters and the Galactic globular cluster age-metallicity relation

    CERN Document Server

    Dotter, Aaron; Anderson, Jay

    2011-01-01

    Color-magnitude diagrams (CMDs) derived from Hubble Space Telescope (HST) Advanced Camera for Surveys F606W,F814W photometry of 6 globular clusters (GCs) are presented. The six GCs form two loose groupings in Galactocentric distance (Rgc): IC 4499, NGC 6426, and Ruprecht 106 at ~15-20 kpc and NGC 7006, Palomar 15, and Pyxis at ~40 kpc. The CMDs allow the ages to be estimated from the main sequence turnoff in every case. In addition, the age of Palomar 5 (Rgc ~ 18 kpc) is estimated using archival HST Wide Field Planetary Camera 2 V,I photometry. The age analysis reveals the following: IC 4499, Ruprecht 106, and Pyxis are 1-2 Gyr younger than inner halo GCs with similar metallicities; NGC 7006 and Palomar 5 are marginally younger than their inner halo counterparts; NGC 6426 and Palomar 15, the two most metal-poor GCs in the sample, are coeval with all the other metal-poor GCs within the uncertainties. Combined with our previous efforts, the current sample provides strong evidence that the Galactic GC age-metall...

  7. Structurally Well-Defined Sigmoidal Gold Clusters: Probing the Correlation between Metal Atom Arrangement and Chiroptical Response.

    Science.gov (United States)

    He, Xin; Wang, Yuechao; Jiang, Hong; Zhao, Liang

    2016-05-04

    Asymmetric arrangement of metal atoms is crucial for understanding the chirality origin of chiral metal nanoclusters and facilitating the design and development of new chiral catalysts and chiroptical devices. Here, we describe the construction of four asymmetric gold and gold-silver clusters by chirality transfer from diimido ligands. The acquired metal clusters show strong circular dichroism (CD) response with large anisotropy factors of up to 6 × 10(-3), larger than the values of most reported chiral gold nanoclusters. Regardless of the same absolute configuration of the applied three diimido ligands, sigmoidal and reverse-sigmoidal arrangements of gold atoms both can be achieved, which resultantly produce an opposite Cotton effect within a specific absorption range. On the basis of the detailed structural characterization via X-ray crystallography and contrast experiments, the chirality contribution of the imido ligand, the asymmetrically arranged metal cluster, and the chiral arrangement of aromatic rings of phosphine ligands have been qualitatively evaluated. Time-dependent DFT calculations reveal that the chiroptical property of the acquired metal clusters is mainly influenced by the asymmetrically arranged metal atoms. Correlation of asymmetric arrangements of metal atoms in clusters with their chiroptical response provides a viable means of fabricating a designable chiral surface of metal nanoclusters and opens a broader prospect for chiral cluster application.

  8. VizieR Online Data Catalog: On the metallicity of open clusters. II. (Heiter+, 2014)

    Science.gov (United States)

    Heiter, U.; Soubiran, C.; Netopil, M.; Paunzen, E.

    2013-11-01

    In Table 1 we list the basic information for each star and each metallicity determination in the starting sample, which should be sufficient to extract the corresponding atmospheric parameters from the PASTEL catalogue. Table 4 lists the weighted mean metallicities for each OC and each paper, which were computed using the metallicities from the references in Table 1. For the weights we used the inverse square of the individual errors quoted by the authors. Table 4 also gives the ranges of effective temperature (Teff) and surface gravity (logg) of the stars corresponding to each paper. After removing all determinations with Teff outside the range 4400 to 6500K and with logg<2.0, we constructed a list of recommended cluster metallicities, which we call the final high-resolution sample. The weighted mean metallicities for each cluster in the final sample are given in Table 11, and the individual determinations included in the final sample are identified in Table 1 (first column). (3 data files).

  9. Environmental Effects on the Metal Enrichment of Low Mass Galaxies in Nearby Clusters

    CERN Document Server

    Petropoulou, Vasiliki; Iglesias-Paramo, Jorge

    2012-01-01

    In this paper we study the chemical history of low-mass star-forming (SF) galaxies in the local Universe clusters Coma, A1367, A779, and A634. The aim of this work is to search for the imprint of the environment on the chemical evolution of these galaxies. Galaxy chemical evolution is linked to the star formation history (SFH), as well as to the gas interchange with the environment, and low-mass galaxies are well known to be vulnerable systems to environmental processes affecting both these parameters. For our study we have used spectra from the SDSS-III DR8. We have examined the mass-metallicity relation of cluster galaxies finding well defined sequences. The slope of these sequences, for galaxies in low-mass clusters and galaxies at large cluster-centric distances, follows the predictions of recent hydrodynamic models. A flattening of this slope has been observed for galaxies located in the core of the two more massive clusters of the sample, principally in Coma, suggesting that the imprint of the cluster e...

  10. Oxidation induced ionization and reactions of metal carbide clusters (Nb, Zr, V, Ta)

    Science.gov (United States)

    Deng, H. T.; Kerns, K. P.; Bell, R. C.; Castleman, A. W.

    1997-11-01

    Following our recent report of the oxidation induced formation of Ti8C12+ (H.T. Deng, K.P. Kerns, and A.W. Castleman, Jr., J. Chem. Phys. 104 (1996) 4862), the oxidation induced ionization of niobium and zirconium carbide clusters are studied using a triple quadrupole mass spectrometer coupled with a laser induced plasma reaction source. It was found that reactions of both of these neutral carbide clusters with dioxygen leads to formation of carbide ions. The ion product distributions show that zirconium carbide clusters mainly take the form of Met--Car cations, but niobium carbide clusters favor a cubic-like crystalline pattern. Furthermore, reactions of mass-selected NbxCy+ with dioxygen result in a sequential loss of C2 units from NbxCy+, and leads to formation of Nbx+ and NbxC+ depending on y being an even or odd number. However, NbxCy+ shows comparably low reactivity towards nitrous oxide through a single oxygen abstraction mechanism. In comparison with the reaction products of VxCy+ with dioxygen, the complementary information obtained in the present study suggests that the C2 unit is a basic building block for formation of small early transition metal carbide clusters. The oxidation induced ionization mechanisms are also discussed in relation with the stability, ionization potentials, and structures of the clusters.

  11. Electron affinities of d1 transition metal chloride clusters and onset of super halogen behavior

    Science.gov (United States)

    Behera, Swayamprabha; Joseph, Jorly; Jena, Purusottam

    2011-03-01

    Geometry, electronic structure, and electron affinity of d1 transition metal chloride clusters (MCl n , M = Sc,Y, La; n = 1--5) have been calculated using density functional theory. Chlorine atoms are chemically bound in all cases except for MCl 5 . The electron affinities of MCl n (n = 1--3) are small and increase only marginally as a function of n until the valence of the metal atom is consumed. Beyond this, they rise sharply and reach a value of 5.96, 6.03 and 5.90 eV for ScCl 4 , YCl 4 and LaCl 4 , respectively and remain high for n = 5. MCl n , (n = 4,5) clusters, therefore, behave as superhalogens. Results are compared with available experimental data

  12. The 3-Dimensional q-Deformed Harmonic Oscillator and Magic Numbers of Alkali Metal Clusters

    CERN Document Server

    Bonatsos, Dennis; Raychev, P P; Roussev, R P; Terziev, P A; Bonatsos, Dennis

    1999-01-01

    Magic numbers predicted by a 3-dimensional q-deformed harmonic oscillator with Uq(3) > SOq(3) symmetry are compared to experimental data for alkali metal clusters, as well as to theoretical predictions of jellium models, Woods--Saxon and wine bottle potentials, and to the classification scheme using the 3n+l pseudo quantum number. The 3-dimensional q-deformed harmonic oscillator correctly predicts all experimentally observed magic numbers up to 1500 (which is the expected limit of validity for theories based on the filling of electronic shells), thus indicating that Uq(3), which is a nonlinear extension of the U(3) symmetry of the spherical (3-dimensional isotropic) harmonic oscillator, is a good candidate for being the symmetry of systems of alkali metal clusters.

  13. Linear and nonlinear surface spectroscopy of supported size selected metal clusters and organic adsorbates

    Energy Technology Data Exchange (ETDEWEB)

    Thaemer, Martin Georg

    2012-03-08

    The spectroscopic investigation of supported size selected metal clusters over a wide wavelength range plays an important role for understanding their outstanding catalytic properties. The challenge which must be overcome to perform such measurements is the difficult detection of the weak spectroscopic signals from these samples. As a consequence, highly sensitive spectroscopic methods are applied, such as surface Cavity Ringdown Spectroscopy and surface Second Harmonic Generation Spectroscopy. The spectroscopic apparatus developed is shown to have a sensitivity which is high enough to detect sub-monolayer coverages of adsorbates on surfaces. In the measured spectra of small supported silver clusters of the sizes Ag{sub 4}2, Ag{sub 2}1, Ag{sub 9}, and Ag atoms a stepwise transition from particles with purely metallic character to particles with molecule-like properties can be observed within this size range.

  14. Electrospray Ionization Mass Spectrometry: From Cluster Ions to Toxic metal Ions in Biology

    Energy Technology Data Exchange (ETDEWEB)

    Lentz, Nicholas B. [Iowa State Univ., Ames, IA (United States)

    2007-01-01

    This dissertation focused on using electrospray ionization mass spectrometry to study cluster ions and toxic metal ions in biology. In Chapter 2, it was shown that primary, secondary and quarternary amines exhibit different clustering characteristics under identical instrument conditions. Carbon chain length also played a role in cluster ion formation. In Chapters 3 and 4, the effects of solvent types/ratios and various instrumental parameters on cluster ion formation were examined. It was found that instrument interface design also plays a critical role in the cluster ion distribution seen in the mass spectrum. In Chapter 5, ESI-MS was used to investigate toxic metal binding to the [Gln11]-amyloid β-protein fragment (1-16). Pb and Cd bound stronger than Zn, even in the presence of excess Zn. Hg bound weaker than Zn. There are endless options for future work on cluster ions. Any molecule that is poorly ionized in positive ion mode can potentially show an increase in ionization efficiency if an appropriate anion is used to produce a net negative charge. It is possible that drug protein or drug/DNA complexes can also be stabilized by adding counter-ions. This would preserve the solution characteristics of the complex in the gas phase. Once in the gas phase, CID could determine the drug binding location on the biomolecule. There are many research projects regarding toxic metals in biology that have yet to be investigated or even discovered. This is an area of research with an almost endless future because of the changing dynamics of biological systems. What is deemed safe today may show toxic effects in the future. Evolutionary changes in protein structures may render them more susceptible to toxic metal binding. As the understanding of toxicity evolves, so does the demand for new toxic metal research. New instrumentation designs and software make it possible to perform research that could not be done in the past. What was undetectable yesterday will

  15. Supersonic flows over cavities

    Institute of Scientific and Technical Information of China (English)

    Tianwen FANG; Meng DING; Jin ZHOU

    2008-01-01

    The characteristics of supersonic cold flows over cavities were investigated experimentally and numer-ically, and the effects of cavities of different sizes on super-sonic flow field were analyzed. The results indicate that the ratio of length to depth L/D within the range of 5-9 has little relevance to integral structures of cavity flow. The bevel angle of the rear wall does not alter the overall structure of the cavity flow within the range of 30°-60°, but it can exert obvious effect on the evolvement of shear layer and vortexes in cavities.

  16. The response of metal clusters to q- and L-dependent external fields

    Energy Technology Data Exchange (ETDEWEB)

    Serra, Ll.; Garcias, F. (Universidad de las Islas Baleares, Palma de Mallorca (Spain). Dept. de Fisica); Barberan, N.; Barranco, M. (Barcelona Univ. (Spain). Dept. de Estructura y Constituyentes de la Materia); Navarro, J. (Valencia Univ. (Spain). Dept. de Fisica Atomica, Molecular y Nuclear Consejo Superior de Investigaciones Cientificas, Valencia (Spain). Inst. de Fisica Corpuscular); Rubio, A. (Valladolid Univ. (Spain). Dept. de Fisica Teorica, Atomica, Molecular y Nuclear)

    1991-01-01

    We have calculated the static polarizability and mean excitation energy of metal clusters submitted to q-and L-dependent external fields of j{sub L} (qr) Y{sub LO}({Omega}) type. Use has been made of an Extended Random-Phase Approximation which includes exchange and correlation effects within a local model, and of the spherical jellium model to describe the neutralizing positive background. (orig.).

  17. Metal Abundances of Red Clump Stars in Open Clusters I. NGC 6819

    CERN Document Server

    Bragaglia, A; Gratton, R G; Tosi, M P; Bonanno, G; Bruno, P; Cali`, A; Claudi, R; Cosentino, R; Desidera, S; Farisato, G; Rebeschini, M; Scuderi, S

    2001-01-01

    We present an analysis of high dispersion spectra (R~40000) of three red clump stars in the old open cluster NGC 6819. The spectra were obtained with SARG, the high dispersion spectrograph of the Telescopio Nazionale Galileo. The spectra were analyzed using both equivalent widths measured with an automatic procedure, and comparisons with synthetic spectra. NGC 6819 is found to be slightly metal-rich ([Fe/H]= +0.09 +/-0.03, internal error); there are no previous high resolution studies to compare with. Most element-to-element abundance ratios are close to solar; we find a slight excess of Si, and a significant Na overabundance. Our spectra can also be used to derive the interstellar reddening towards the cluster, by comparing the observed colours with those expected from line excitation: we derive E(B-V)=0.14 +/-0.04, in agreement with the most recent estimate for this cluster.

  18. Collective-field-corrected strong field approximation for laser-irradiated metal clusters

    CERN Document Server

    Keil, Th

    2013-01-01

    The strong field approximation (SFA) formulated in terms of so-called "quantum orbits" led to much insight into intense-laser driven ionization dynamics. In plain SFA, the emitted electron is treated as a free electron in the laser field alone. However, with improving experimental techniques and more advanced numerical simulations it becomes more and more obvious that the plain SFA misses interesting effects even on a qualitative level. Examples are holographic side lobes, the low-energy structure, radial patterns in photoelectron spectra at low kinetic energies, and strongly rotated angular distributions. For this reason increasing effort has been recently devoted to Coulomb corrections of the SFA. In the current paper, we follow a similar line but consider ionization of metal clusters. It is known that photoelectrons from clusters can be much more energetic than those emitted from atoms or small molecules, especially if the Mie resonance of the expanding cluster is evoked. We develop a SFA that takes the co...

  19. Formation of the metal and energy-carrier price clusters on the world market of nonferrous metals in the postcrisis period

    Science.gov (United States)

    Bogdanov, S. V.; Shevelev, I. M.; Chernyi, S. A.

    2016-06-01

    The laws of formation of price clusters are revealed upon statistical processing of the data on changing the quotation prices of nonferrous and precious metals, oil, black oil, gasoline, and natural gas in the postcrisis period from January 1, 2009 to November 1, 2013. It is found that the metal prices entering in the price cluster of nonferrous metals most strongly affect the formation of the nonferrous metal price and that the prices of precious metals and energy carriers correct the exchange price of the metal to some extent but do not determine its formation. Equations are derived to calculate the prices. The results of calculation by these equations agree well with the real nonferrous metal prices in the near future.

  20. Magnetic properties of bimetallic clusters composed of Gd and transition metals

    Science.gov (United States)

    Mukherjee, Prajna; Gupta, Bikash C.; Jena, Puru

    2016-02-01

    Gadolinium, a rare earth metal, is ferromagnetic, while Mn, a transition metal atom, is antiferromagnetic in the bulk phase. Clusters of these elements, however, share some common properties; both exhibit ferrimagnetic behavior and maintain magnetic moments close to their free atomic value. Using density functional theory and generalized gradient approximation for exchange and correlation, we have studied the magnetic properties of bimetallic clusters composed of Gd and Mn to see if they show unusual behavior. The coupling between Gd and Mn spins is found to be antiferromagnetic, while that between Mn atoms is ferromagnetic. Moreover, the bonding between Gd and Mn atoms is stronger than that between the Gd atoms or Mn atoms, thus enabling the possibility of creating more stable magnetic particles. A systematic study of the magnetic and binding properties of clusters composed of Gd atom and other transition metal atoms such as V, Sc, Ti, Cr, Fe, and Co is also carried out to probe the effect of 3d-orbital occupation on magnetic coupling.

  1. Molecular heterometallic hydride clusters composed of rare-earth and d-transition metals.

    Science.gov (United States)

    Shima, Takanori; Luo, Yi; Stewart, Timothy; Bau, Robert; McIntyre, Garry J; Mason, Sax A; Hou, Zhaomin

    2011-09-18

    Heteromultimetallic hydride clusters containing both rare-earth and d-transition metals are of interest in terms of both their structure and reactivity. However, such heterometallic complexes have not yet been investigated to a great extent because of difficulties in their synthesis and structural characterization. Here, we report the synthesis, X-ray and neutron diffraction studies, and hydrogen addition and release properties of a family of rare-earth/d-transition-metal heteromultimetallic polyhydride complexes of the core structure type 'Ln(4)MH(n)' (Ln = Y, Dy, Ho; M = Mo, W; n = 9, 11, 13). Monitoring of hydrogen addition to a hydride cluster such as [{(C(5)Me(4)SiMe(3))Y}(4)(μ-H)(9)Mo(C(5)Me(5))] in a single-crystal to single-crystal process by X-ray diffraction has been achieved for the first time. Density functional theory studies reveal that the hydrogen addition process is cooperatively assisted by the Y/Mo heteromultimetallic sites, thus offering unprecedented insight into the hydrogen addition and release process of a metal hydride cluster.

  2. Luminescent sub-nanometer clusters for metal ion sensing: a new direction in nanosensors.

    Science.gov (United States)

    Chakraborty, Indranath; Udayabhaskararao, T; Pradeep, T

    2012-04-15

    We describe the application of a recently discovered family of materials called quantum clusters, which are sub-nanometer particles composed of a few atoms with well-defined molecular formulae, exhibiting intense absorption and emission in the visible region in metal ion sensing, taking Ag(25) as an example. The changes in the optical properties of the cluster, in both absorption and emission upon exposure to various metal ions in aqueous medium are explored. The cluster can detect Hg(2+) down to ppb levels. It can also detect 5d block ions (Pt(2+), Au(3+) and Hg(2+)) down to ppm limits. Hg(2+) interacts with the metal core as well as the functional groups of the capping agents and the interaction is concentration-dependent. To understand the mechanism behind this type of specific interaction, we have used spectroscopic and microscopic techniques such as UV-vis spectroscopy, luminescence spectroscopy, Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM), and X-ray diffraction (XRD). Specific reasons responsible for the interaction of Hg(2+) have been proposed. Copyright © 2011 Elsevier B.V. All rights reserved.

  3. Mono- and Dinuclear Macrocyclic Calcium Complexes as Platforms for Mixed-Metal Complexes and Clusters.

    Science.gov (United States)

    Connolly, Emma A; Leeland, James W; Love, Jason B

    2016-01-19

    Mono- and dinuclear calcium complexes of the Schiff-base macrocycles H4L have been prepared and characterized spectroscopically and crystallographically. In the formation of Ca(THF)2(H2L(1)), Ca2(THF)2(μ-THF)(L(1)), and Ca2(THF)4(L(2)), the ligand framework adopts a bowl-shaped conformation instead of the conventional wedge, Pacman-shaped structure as seen with the anthracenyl-hinged complex Ca2(py)5(L(3)). The mononuclear calcium complex Ca(THF)2(H2L(1)) reacts with various equivalents of LiN(SiMe3)2 to form calcium/alkali metal clusters and dinuclear transition metal complexes when reacted subsequently with transition metal salts. The dinuclear calcium complex Ca2(THF)2(μ-THF)(L(1)), when reacted with various equivalents of NaOH, is shown to act as a platform for the formation of calcium/alkali metal hydroxide clusters, displaying alternate wedged and bowl-shaped conformations.

  4. Infinitesimal Conical Supersonic Flow

    Science.gov (United States)

    Busemann, Adolf

    1947-01-01

    The calculation of infinitesimal conical supersonic flow has been applied first to the simplest examples that have also been calculated in another way. Except for the discovery of a miscalculation in an older report, there was found the expected conformity. The new method of calculation is limited more definitely to the conical case.

  5. Metal-Organic Framework of Lanthanoid Dinuclear Clusters Undergoes Slow Magnetic Relaxation

    Directory of Open Access Journals (Sweden)

    Hikaru Iwami

    2017-01-01

    Full Text Available Lanthanoid metal-organic frameworks (Ln-MOFs can adopt a variety of new structures due to the large coordination numbers of Ln metal ions, and Ln-MOFs are expected to show new luminescence and magnetic properties due to the localized f electrons. In particular, some Ln metal ions, such as Dy(III and Tb(III ions, work as isolated quantum magnets when they have magnetic anisotropy. In this work, using 4,4′,4″-s-triazine-2,4,6-triyl-tribenzoic acid (H3TATB as a ligand, two new Ln-MOFs, [Dy(TATB(DMF2] (1 and [Tb(TATB(DMF2] (2, were obtained. The Ln-MOFs contain Ln dinuclear clusters as secondary building units, and 1 underwent slow magnetic relaxation similar to single-molecule magnets.

  6. Metal-carbon clusters: The origin of the delayed atomic ion

    Science.gov (United States)

    Davis, K. M.; Peppernick, S. J.; Castleman, A. W.

    2006-04-01

    Studies of the emission of electrons from excited metal-carbon cluster systems that include the Met-Car (M8C12, where M is Ti, Zr, and V) also have revealed the evolution of a delayed atomic ion. The source of the delayed atomic ion, which involves the emission of ionized atoms on the microsecond time scale, is the focus of this investigation. By studying the delayed ionization of mixed zirconium and titanium carbon complexes produced in a laser vaporization source coupled to a time-of-flight mass spectrometer, for the first time both the zirconium and titanium delayed atomic ions were observed to be emitted in the same experiment. These studies allowed a determination that the source of the delayed atomic ion is an excited metal dicarbide. A plausible mechanism involving the excitation of a high Rydberg state of the metal dicarbide prior to an excited ion pair separation is proposed.

  7. Orbitals in inorganic chemistry: metal rings and clusters, hydronitrogens, and heterocyles.

    Science.gov (United States)

    Inagaki, Satoshi

    2010-01-01

    A chemical orbital theory is useful in inorganic chemistry. Some applications are described for understanding and designing of inorganic molecules. Among the topics included are: (1) valence electron rules to predict stabilities of three- and four-membered ring metals and for those of regular octahedral M(6) metal clusters solely by counting the number of valence electrons; (2) pentagon stability (stability of five- relative to six-membered rings in some classes of molecules), predicted and applied for understanding and designing saturated molecules of group XV elements; (3) properties of unsaturated hydronitrogens N( m )H( n ) in contrast to those of hydrocarbons C( m )H( n ); (4) unusually short nonbonded distances between metal atoms in cyclic molecules.

  8. Mass and metal ejection efficiency in disk galaxies driven by young stellar clusters of nuclear starburst

    CERN Document Server

    Rodriguez-Gonzalez, A; Raga, A C; Colin, P

    2011-01-01

    We present results from models of galactic winds driven by energy injected by nuclear starbursts. The total energy of the starburst is provided by young central stellar clusters and parts of the galactic interstellar medium are pushed out as part of the galactic wind (in some cases the galactic wind contains an important part of the metals produced in the new generation of stars). We have performed adiabatic and radiative 3D N-Body/Smooth Particle Hydrodynamics simulations of galactic winds using the GADGET-2 code. The numerical models cover a wide range of starburst (from $\\sim10^2$ to $\\sim10^7$ M$_\\odot$) and galactic gas masses (from $\\sim6\\times10^6$ to $\\sim10^{11}$ M$_\\odot$). The concentrated central starburst regions are an efficient engine for producing of the mass and metal loss in galaxies, and also for driving the metal redistribution in the galaxies.

  9. Exchange-correlation interaction and AO-hybridization of alkali-metal atomic clusters.

    Science.gov (United States)

    Liu, Xuan; Ito, Haruhiko; Torikai, Eiko

    2013-09-19

    The structure of alkali-metal atomic clusters is optimized with B3P86 hybrid functional for the highest spin state as well as with B3LYP hybrid functional for the lowest spin state. A dramatic change from plane to solid occurs in the highest spin state when the number of constituent atoms is four. The binding, exchange, and correlation energies are evaluated for both the highest and lowest spin states. Next, we explore the dependence of the exchange and correlation energies on the binding energy. The exchange energy contributes to the formation of the highest spin clusters, whereas the correlation energy contributes to the formation of the lowest spin clusters. The highest spin clusters are most stable when the exchange energy is a minimum. Then, to see why the ferromagnetic bond among spin-aligned identical atoms arises against Pauli exclusion principle, we estimate the mixing ratio of p orbitals in molecular orbitals. The s-p hybridization increases the binding energy in absolute value due to the extensive overlap of molecular orbitals and leads to generation of the highest spin clusters.

  10. Ir Spectroscopy of First-Row Transition Metal Clusters and Their Complexes with Simple Molecules

    Science.gov (United States)

    Kiawi, D. M.; Bakker, J.; Oomens, J.; Buma, W. J.; Waters, L. B. F. M.

    2014-06-01

    Iron is an important element in the formation of solids in space. Spectroscopic observations of interstellar iron shows that its atomic gas-phase abundance is strongly depleted with respect to that of hydrogen. In contrast, sulfur is mostly found in the gas phase in low-density regions of interstellar space, but is highly depleted in regions of star- and planet formation. Furthermore, the dominant source of sulfur in our solar system is solid FeS, as found in primitive meteorites, implying an efficient chemical pathway to convert sulphur or sulphur containing compounds into solid FeS during the (early phases of) the star formation process. We address the evolution of iron and sulfur in space on a molecular level by studying metal nanoclusters and their interaction with ligands using IR action spectroscopy. Clusters are formed through laser ablation of solid precursor materials and brought into a molecular beam environment. Complexes with ligands are obtained by directing the beam through a reaction channel containing low-pressure reactant gas. Mass-selected IR action spectra are recorded by irradiating the clusters using the Free Electron Laser for Infrared eXperiments (FELIX). Experimental spectra are then compared with DFT predictions which enables us to determine the structure of the selected cluster and its binding interactions with ligands. As part of this project, we here present IR action spectra of size-selected Fe clusters and the chemically closely related Co clusters, and their complexes with relevant ligands.

  11. Control of star formation by supersonic turbulence

    CERN Document Server

    MacLow, M M; Low, Mordecai-Mark Mac; Klessen, Ralf S.

    2004-01-01

    Understanding the formation of stars in galaxies is central to much of modern astrophysics. For several decades it has been thought that stellar birth is primarily controlled by the interplay between gravity and magnetostatic support, modulated by ambipolar diffusion. Recently, however, both observational and numerical work has begun to suggest that support by supersonic turbulence rather than magnetic fields controls star formation. In this review we outline a new theory of star formation relying on the control by turbulence. We demonstrate that although supersonic turbulence can provide global support, it nevertheless produces density enhancements that allow local collapse. Inefficient, isolated star formation is a hallmark of turbulent support, while efficient, clustered star formation occurs in its absence. The consequences of this theory are then explored for both local star formation and galactic scale star formation. (Abstract abbreviated)

  12. Subcascade formation and defect cluster size scaling in high-energy collision events in metals

    Science.gov (United States)

    De Backer, A.; Sand, A. E.; Nordlund, K.; Luneville, L.; Simeone, D.; Dudarev, S. L.

    2016-07-01

    It has been recently established that the size of the defects created under ion irradiation follows a scaling law (Sand A. E. et al., EPL, 103 (2013) 46003; Yi X. et al., EPL, 110 (2015) 36001). A critical constraint associated with its application to phenomena occurring over a broad range of irradiation conditions is the limitation on the energy of incident particles. Incident neutrons or ions, with energies exceeding a certain energy threshold, produce a complex hierarchy of collision subcascade events, which impedes the use of the defect cluster size scaling law derived for an individual low-energy cascade. By analyzing the statistics of subcascade sizes and energies, we show that defect clustering above threshold energies can be described by a product of two scaling laws, one for the sizes of subcascades and the other for the sizes of defect clusters formed in subcascades. The statistics of subcascade sizes exhibits a transition at a threshold energy, where the subcascade morphology changes from a single domain below the energy threshold, to several or many sub-domains above the threshold. The number of sub-domains then increases in proportion to the primary knock-on atom energy. The model has been validated against direct molecular-dynamics simulations and applied to W, Fe, Be, Zr and sixteen other metals, enabling the prediction of full statistics of defect cluster sizes with no limitation on the energy of cascade events. We find that populations of defect clusters produced by the fragmented high-energy cascades are dominated by individual Frenkel pairs and relatively small defect clusters, whereas the lower-energy non-fragmented cascades produce a greater proportion of large defect clusters.

  13. Metal enrichment of the intra-cluster medium by thermally and cosmic-ray driven galactic winds

    CERN Document Server

    Kapferer, W; Breitschwerdt, D; Schindler, S; Van Kampen, E; Kimeswenger, S; Domainko, W; Mair, M; Ruffert, M

    2009-01-01

    We investigate the efficiency and time-dependence of thermally and cosmic ray driven galactic winds for the metal enrichment of the intra-cluster medium (ICM) using a new analytical approximation for the mass outflow. The spatial distribution of the metals are studied using radial metallicity profiles and 2D metallicity maps of the model clusters as they would be observed by X-ray telescopes like XMM-Newton. Analytical approximations for the mass loss by galactic winds driven by thermal and cosmic ray pressure are derived from the Bernoulli equation and implemented in combined N-body/hydrodynamic cosmological simulations with a semi-analytical galaxy formation model. Observable quantities like the mean metallicity, metallicity profiles, and 2D metal maps of the model clusters are derived from the simulations. We find that galactic winds alone cannot account for the observed metallicity of the ICM. At redshift $z=0$ the model clusters have metallicities originating from galactic winds which are almost a factor...

  14. An updated survey of globular clusters in M 31. III. A spectroscopic metallicity scale for the Revised Bologna Catalog

    CERN Document Server

    Galleti, S; Buzzoni, A; Federici, L; Pecci, F Fusi

    2009-01-01

    We present a new homogeneous set of metallicity estimates based on Lick indices for 245 old globular clusters of the M31 galaxy comprised in the Revised Bologna Catalog. The metallicity distribution of the M31 globular clusters is briefly discussed and compared with that of the Milky Way. Simple parametric statistics suggests that the [Fe/H] distribution is likely not unimodal. The strong correlation between metallicity and kinematics found in previous studies is confirmed. The most metal-rich GCs tend to be packed at the center of the system and share the galactic rotation as traced by the HI disk. Although the velocity dispersion around the curve increases with decreasing metallicity, also clusters with [Fe/H]<-1.0 display a clear rotational pattern, at odds with their Milky Way counterparts.

  15. Encapsulation of metal clusters within MFI via interzeolite transformations and direct hydrothermal syntheses and catalytic consequences of their confinement.

    Science.gov (United States)

    Goel, Sarika; Zones, Stacey I; Iglesia, Enrique

    2014-10-29

    The encapsulation of metal clusters (Pt, Ru, Rh) within MFI was achieved by exchanging cationic metal precursors into a parent zeolite (BEA, FAU), reducing them with H2 to form metal clusters, and transforming these zeolites into daughter structures of higher framework density (MFI) under hydrothermal conditions. These transformations required MFI seeds or organic templates for FAU parent zeolites, but not for BEA, and occurred with the retention of encapsulated clusters. Clusters uniform in size (1.3-1.7 nm) and exposing clean and accessible surfaces formed in BEA and FAU zeolites; their size remained essentially unchanged upon transformation into MFI. Encapsulation selectivities, determined from the relative hydrogenation rates of small (toluene) and large (alkyl arenes) molecules and defined as the ratio of the surface areas of all the clusters in the sample to that of external clusters, were very high (8.1-40.9) for both parent and daughter zeolites. Encapsulation into MFI via direct hydrothermal syntheses was unsuccessful because metal precursors precipitated prematurely at the pH and temperatures required for MFI synthesis. Delayed introduction of metal precursors and F(-) (instead of OH(-)) as the mineralizing agent in hydrothermal syntheses increased encapsulation selectivities, but they remained lower than those achieved via interzeolite transformations. These interconversions provide a general and robust strategy for encapsulation of metals when precursors can be introduced via exchange into a zeolite that can be transformed into target daughter zeolites with higher framework densities, whether spontaneously or by using seeds or structure-directing agents (SDA).

  16. Globular Cluster Abundances from High-Resolution, Integrated-Light Spectroscopy. II. Expanding the Metallicity Range for Old Clusters and Updated Analysis Techniques

    CERN Document Server

    Colucci, J E; McWilliam, A

    2016-01-01

    We present abundances of globular clusters in the Milky Way and Fornax from integrated light spectra. Our goal is to evaluate the consistency of the integrated light analysis relative to standard abundance analysis for individual stars in those same clusters. This sample includes an updated analysis of 7 clusters from our previous publications and results for 5 new clusters that expand the metallicity range over which our technique has been tested. We find that the [Fe/H] measured from integrated light spectra agrees to $\\sim$0.1 dex for globular clusters with metallicities as high as [Fe/H]=$-0.3$, but the abundances measured for more metal rich clusters may be underestimated. In addition we systematically evaluate the accuracy of abundance ratios, [X/Fe], for Na I, Mg I, Al I, Si I, Ca I, Ti I, Ti II, Sc II, V I, Cr I, Mn I, Co I, Ni I, Cu I, Y II, Zr I, Ba II, La II, Nd II, and Eu II. The elements for which the integrated light analysis gives results that are most similar to analysis of individual stellar ...

  17. Photoelectron Spectroscopy of Transition Metal Hydride Cluster Anions and Their Roles in Hydrogenation Reactions

    Science.gov (United States)

    Zhang, Xinxing; Bowen, Kit

    The interaction between transition metals and hydrogen has been an intriguing research topic for such applications as hydrogen storage and catalysis of hydrogenation and dehydrogenation. Special bonding features between TM and hydrogen are interesting not only because they are scarcely reported but also because they could help to discover and understand the nature of chemical bonding. Very recently, we discovered a PtZnH5- cluster which possessed an unprecedented planar pentagonal coordination between the H5- moiety and Pt, and exhibited special σ-aromaticity. The H5-kernel as a whole can be viewed as a η5-H5 ligand for Pt. As the second example, an H2 molecule was found to act as a ligand in the PdH3-cluster, in which two H atoms form a η2-H2 type of ligation to Pd. These transition metal hydride clusters were considered to be good hydrogen sources for hydrogenation. The reactions between PtHn- and CO2 were investigated. We observed formate in the final product H2Pt(HCO2)- .

  18. Simulating the effect of AGN feedback on the metal enrichment of galaxy clusters

    CERN Document Server

    Fabjan, D; Tornatore, L; Saro, A; Murante, G; Dolag, K

    2009-01-01

    We present a study of the effect of AGN feedback on metal enrichment and thermal properties of the intracluster medium (ICM) in hydrodynamical simulations. The cosmological simulations are performed for a set of clusters using a version of the TreePM-SPH Gadget code that follows chemo-dynamical evolution by accounting for metal enrichment by different stellar populations. Besides runs not including any efficient form of energy feedback, we carry out simulations including: (i) kinetic feedback in the form of galactic winds triggered by supernova explosions; (ii) AGN feedback from gas accretion onto super-massive black holes (BHs); (iii) AGN feedback in which a 'radio mode' is included. We find that AGN feedback is able to quench star formation in the brightest cluster galaxies at z<4 and provides correct temperature profiles in the central regions of galaxy groups. However, its effect is not sufficient to create cool cores in massive clusters. AGN feedback creates a widespread enrichment in the outskirts of...

  19. Transition-Metal Planar Boron Clusters: a New Class of Aromatic Compounds with High Coordination

    Science.gov (United States)

    Wang, Lai-Sheng

    2012-06-01

    Photoelectron spectroscopy in combination with computational studies over the past decade has shown that boron clusters possess planar or quasi-planar structures, in contrast to that of bulk boron, which is dominated by three-dimensional cage-like building blocks. All planar or quasi-planar boron clusters are observed to consist of a monocyclic circumference with one or more interior atoms. The propensity for planarity has been found to be due to both σ and π electron delocalization throughout the molecular plane, giving rise to concepts of σ and π double aromaticity. We have found further that the central boron atoms can be substituted by transition metal atoms to form a new class of aromatic compounds, which consist of a central metal atom and a monocyclic boron ring (M B_n). Eight-, nine-, and ten-membered rings of boron have been observed, giving rise to octa-, ennea-, and deca-coordinated aromatic transition metal compounds [1-3]. References: [1] ``Aromatic Metal-Centered Monocyclic Boron Rings: Co B_9^- and Ru B_9^-" (Constantin Romanescu, Timur R. Galeev, Wei-Li Li, A. I. Boldyrev, and L. S. Wang), Angew. Chem. Int. Ed. {50}, 9334-9337 (2011). [2] ``Transition-Metal-Centered Nine-Membered Boron Rings: M B_9 and M B_9^- (M = Rh, Ir)" (Wei-Li Li, Constantin Romanescu, Timur R. Galeev, Zachary Piazza, A. I. Boldyrev, and L. S. Wang), J. Am. Chem. Soc. {134}, 165-168 (2012). [3] ``Observation of the Highest Coordination Number in Planar Species: Decacoordinated Ta B10^- and Nb B_9^- Anions" (Timur R. Galeev, Constantin Romanescu, Wei-Li Li, L. S. Wang, and A. I. Boldyrev), Angew. Chem. Int. Ed. {51}, 2101-2105 (2012).

  20. Yields of AGB and SAGB models with chemistry of low- and high-metallicity Globular Clusters

    CERN Document Server

    Ventura, P; Carini, R; D'Antona, F

    2013-01-01

    We present yields from stars of mass in the range Mometallicities Z=0.0003 and Z=0.008, thus encompassing the chemistry of low- and high-Z Globular Clusters. The yields are based on full evolutionary computations, following the evolution of the stars from the pre-Main Sequence through the Asymptotic Giant Branch phase, until the external envelope is lost. Independently of metallicity, stars with M<3Mo are dominated by Third Dredge-Up, thus ejecting into their surroundings gas enriched in carbon and nitrogen. Conversely, Hot Bottom Burning is the main responsible for the modification of the surface chemistry of more massive stars, whose mass exceeds 3Mo: their gas shows traces of proton-capture nucleosynthesis. The extent of Hot Bottom Burning turns out to be strongly dependent on metallicity. In this paper we analyze the consequences of this fact. These results can be used to understand the role played by intermediate mass stars in the self-enrichment scenario of globular clusters: the resu...

  1. Unified description of magic numbers of metal clusters in terms of the 3-dimensional q-deformed harmonic oscillator

    CERN Document Server

    Bonatsos, Dennis; Lenis, D; Raychev, P P; Roussev, R P; Terziev, P A

    2000-01-01

    Magic numbers predicted by a 3-dimensional q-deformed harmonic oscillator with Uq(3)>SOq(3) symmetry are compared to experimental data for atomic clusters of alkali metals (Li, Na, K, Rb, Cs), noble metals (Cu, Ag, Au), divalent metals (Zn, Cd), and trivalent metals (Al, In), as well as to theoretical predictions of jellium models, Woods-Saxon and wine bottle potentials, and to the classification scheme using the 3n+l pseudo quantum number. In alkali metal clusters and noble metal clusters the 3-dimensional q-deformed harmonic oscillator correctly predicts all experimentally observed magic numbers up to 1500 (which is the expected limit of validity for theories based on the filling of electronic shells), while in addition it gives satisfactory results for the magic numbers of clusters of divalent metals and trivalent metals, thus indicating that Uq(3), which is a nonlinear extension of the U(3) symmetry of the spherical (3-dimensional isotropic) harmonic oscillator, is a good candidate for being the symmetry ...

  2. Electric dipole polarizability of alkaline-Earth-metal atoms from perturbed relativistic coupled-cluster theory with triples

    CERN Document Server

    Chattopadhyay, S; Angom, D

    2014-01-01

    The perturbed relativistic coupled-cluster (PRCC) theory is applied to calculate the electric dipole polarizabilities of alkaline Earth metal atoms. The Dirac-Coulomb-Breit atomic Hamiltonian is used and we include the triple excitations in the relativistic coupled-cluster (RCC) theory. The theoretical issues related to the triple excitation cluster operators are described in detail and we also provide details on the computational implementation. The PRCC theory results are in good agreement with the experimental and previous theoretical results. We, then, highlight the importance of considering the Breit interaction for alkaline Earth metal atoms.

  3. An updated survey of globular clusters in M 31. III. A spectroscopic metallicity scale for the Revised Bologna Catalog

    Science.gov (United States)

    Galleti, S.; Bellazzini, M.; Buzzoni, A.; Federici, L.; Fusi Pecci, F.

    2009-12-01

    Aims. We present a new homogeneous set of metallicity estimates based on Lick indices for the old globular clusters of the M 31 galaxy. The final aim is to add homogeneous spectroscopic metallicities to as many entries as possible of the Revised Bologna Catalog of M 31 clusters, by reporting Lick index measurements from any source (literature, new observations, etc.) on the same scale. Methods: New empirical relations of [Fe/H] as a function of [MgFe] and Mg2 indices are based on the well-studied galactic globular clusters, complemented with theoretical model predictions for -0.2≤ [Fe/H]≤ +0.5. Lick indices for M 31 clusters from various literature sources (225 clusters) and from new observations by our team (71 clusters) have been transformed into the Trager et al. system, yielding new metallicity estimates for 245 globular clusters of M 31. Results: Our values are in good agreement with recent estimates based on detailed spectral fitting and with those obtained from color magnitude diagrams of clusters imaged with the Hubble Space Telescope. The typical uncertainty on individual estimates is ≃±0.25 dex, as resulted from the comparison with metallicities derived from color magnitude diagrams of individual clusters. Conclusions: The metallicity distribution of M 31 globular cluster is briefly discussed and compared with that of the Milky Way. Simple parametric statistical tests suggest that the distribution is probably not unimodal. The strong correlation between metallicity and kinematics found in previous studies is confirmed. The most metal-rich GCs tend to be packed into the center of the system and to cluster tightly around the galactic rotation curve defined by the HI disk, while the velocity dispersion about the curve increases with decreasing metallicity. However, also the clusters with [Fe/H]<-1.0 display a clear rotation pattern, at odds with their Milky Way counterparts. Based on observations made at La Palma, at the Spanish Observatorio del Roque

  4. A RAVE Investigation on Galactic open Clusters I. Radial velocities and metallicities

    CERN Document Server

    Conrad, C; Kharchenko, N V; Piskunov, A E; Schilbach, E; Röser, S; Boeche, C; Kordopatis, G; Siebert, A; Williams, M; Munari, U; Matijevič, G; Grebel, E K; Zwitter, T; de Jong, R S; Steinmetz, M; Gilmore, G; Seabroke, G; Freeman, K; Navarro, J F; Parker, Q; Reid, W; Watson, F; Gibson, B K; Bienaymé, O; Wyse, R; Bland-Hawthorn, J; Siviero, A

    2013-01-01

    Context. Galactic open clusters (OCs) mainly belong to the young stellar population in the Milky Way disk, but are there groups and complexes of OCs that possibly define an additional level in hierarchical star formation? Current compilations are too incomplete to address this question, especially regarding radial velocities (RVs) and metallicities ($[M/H]$). Aims. Here we provide and discuss newly obtained RV and $[M/H]$ data, which will enable us to reinvestigate potential groupings of open clusters and associations. Methods.We extracted additional RVs and $[M/H]$ from the RAdial Velocity Experiment (RAVE) via a cross-match with the Catalogue of Stars in Open Cluster Areas (CSOCA). For the identified OCs in RAVE we derived RV and $[M/H]$ from a cleaned working sample and compared the results with previous findings. Results. Although our RAVE sample does not show the same accuracy as the entire survey, we were able to derive reliable RV for 110 Galactic open clusters. For 37 OCs we publish RV for the first t...

  5. Encapsulating Metal Clusters and Acid Sites within Small Voids: Synthetic Strategies and Catalytic Consequences

    Science.gov (United States)

    Goel, Sarika

    The selective encapsulation of metal clusters within zeolites can be used to prepare clusters that are uniform in diameter and to protect them against sintering and contact with feed impurities, while concurrently allowing active sites to select reactants based on their molecular size, thus conferring enzyme-like specificity to chemical catalysis. The apertures in small and medium-pore zeolites preclude the use of post-synthetic protocols to encapsulate the relevant metal precursors because cationic or anionic precursors with their charge-balancing double layer and gaseous complexes cannot diffuse through their windows or channels. We have developed general strategies to encapsulate metal clusters within small-pore zeolites by using metal precursors stabilized by ammonia or organic amine ligands, which stabilize metal precursors against their premature precipitation at the high temperature and pH conditions required for the hydrothermal synthesis of the target zeolite structures and favor interactions between metal precursors and incipient aluminosilicate nuclei during the self-assembly of microporous frameworks. When synthesis temperatures were higher than 400 K, available ligands were unable to prevent the premature precipitation of the metal precursors. In such cases, encapsulation was achieved instead via interzeolite transformations after successfully encapsulating metal precursors or clusters via post-synthesis exchange or ligand protection into parent zeolites and subsequently converting them into the target structures while retaining the encapsulated clusters or precursors. Such strategies led to the successful selective encapsulation of a wide range of metal clusters (Pt, Pd, Ru, Rh, Ir, Re, and Ag) within small-pore (SOD (sodalite), LTA (Linde type A (zeolite A)), GIS (gismondine), and ANA (analcime)) and medium-pore (MFI (ZSM-5)) zeolites. These protocols provide novel and diverse mechanism-based strategies for the design of catalysts with protected

  6. Insights into Pre-Enrichment of Star Clusters and Self-Enrichment of Dwarf Galaxies from their Intrinsic Metallicity Dispersions

    CERN Document Server

    Leaman, Ryan

    2012-01-01

    Star clusters are known to have smaller intrinsic metallicity spreads than dwarf galaxies due to their shorter star formation timescales. Here we use individual spectroscopic [Fe/H] measurements of stars in 19 Local Group dwarf galaxies, 13 Galactic open clusters, and 49 globular clusters to show that star cluster and dwarf galaxy linear metallicity distributions are binomial in form, with all objects showing strong correlations between their mean linear metallicity $\\bar{Z}$ and intrinsic spread in metallicity $\\sigma(Z)^{2}$. A plot of $\\sigma(Z)^{2}$ versus $\\bar{Z}$ shows that the correlated relationships are offset for the dwarf galaxies from the star clusters. The common binomial nature of these linear metallicity distributions can be explained with a simple inhomogeneous chemical evolution model (e.g., Oey 2000), where the star cluster and dwarf galaxy behaviour in the $\\sigma(Z)^{2}-\\bar{Z}$ diagram is reproduced in terms of the number of enrichment events, covering fraction, and intrinsic size of the...

  7. "Quantized" Doping of Individual Colloidal Nanocrystals Using Size-Focused Metal Quantum Clusters.

    Science.gov (United States)

    Santiago-González, Beatriz; Monguzzi, Angelo; Pinchetti, Valerio; Casu, Alberto; Prato, Mirko; Lorenzi, Roberto; Campione, Marcello; Chiodini, Norberto; Santambrogio, Carlo; Meinardi, Francesco; Manna, Liberato; Brovelli, Sergio

    2017-06-27

    The insertion of intentional impurities, commonly referred to as doping, into colloidal semiconductor quantum dots (QDs) is a powerful paradigm for tailoring their electronic, optical, and magnetic behaviors beyond what is obtained with size-control and heterostructuring motifs. Advancements in colloidal chemistry have led to nearly atomic precision of the doping level in both lightly and heavily doped QDs. The doping strategies currently available, however, operate at the ensemble level, resulting in a Poisson distribution of impurities across the QD population. To date, the synthesis of monodisperse ensembles of QDs individually doped with an identical number of impurity atoms is still an open challenge, and its achievement would enable the realization of advanced QD devices, such as optically/electrically controlled magnetic memories and intragap state transistors and solar cells, that rely on the precise tuning of the impurity states (i.e., number of unpaired spins, energy and width of impurity levels) within the QD host. The only approach reported to date relies on QD seeding with organometallic precursors that are intrinsically unstable and strongly affected by chemical or environmental degradation, which prevents the concept from reaching its full potential and makes the method unsuitable for aqueous synthesis routes. Here, we overcome these issues by demonstrating a doping strategy that bridges two traditionally orthogonal nanostructured material systems, namely, QDs and metal quantum clusters composed of a "magic number" of atoms held together by stable metal-to-metal bonds. Specifically, we use clusters composed of four copper atoms (Cu4) capped with d-penicillamine to seed the growth of CdS QDs in water at room temperature. The elemental analysis, performed by electrospray ionization mass spectrometry, X-ray fluorescence, and inductively coupled plasma mass spectrometry, side by side with optical spectroscopy and transmission electron microscopy

  8. Beyond organic chemistry: aromaticity in atomic clusters.

    Science.gov (United States)

    Boldyrev, Alexander I; Wang, Lai-Sheng

    2016-04-28

    We describe joint experimental and theoretical studies carried out collaboratively in the authors' labs for understanding the structures and chemical bonding of novel atomic clusters, which exhibit aromaticity. The concept of aromaticity was first discovered to be useful in understanding the square-planar unit of Al4 in a series of MAl4(-) bimetallic clusters that led to discoveries of aromaticity in many metal cluster systems, including transition metals and similar cluster motifs in solid compounds. The concept of aromaticity has been found to be particularly powerful in understanding the stability and bonding in planar boron clusters, many of which have been shown to be analogous to polycyclic aromatic hydrocarbons in their π bonding. Stimulated by the multiple aromaticity in planar boron clusters, a design principle has been proposed for stable metal-cerntered aromatic molecular wheels of the general formula, M@Bn(k-). A series of such borometallic aromatic wheel complexes have been produced in supersonic cluster beams and characterized experimentally and theoretically, including Ta@B10(-) and Nb@B10(-), which exhibit the highest coordination number in two dimensions.

  9. POLYMER COMPOSITE FILMS WITH SIZE-SELECTED METAL NANOPARTICLES FABRICATED BY CLUSTER BEAM TECHNIQUE

    DEFF Research Database (Denmark)

    Ceynowa, F. A.; Chirumamilla, Manohar; Popok, Vladimir

    2017-01-01

    after the deposition. The degree of immersion can be controlled by the annealing temperature and time. Together with control of cluster coverage the described approach represents an efficient method for the synthesis of thin polymer composite layers with either partially or fully embedded metal NPs......, in particular, for the use of phenomenon of localized surface plasmon resonance (LSPR). Unfortunately, it is found that the thermal annealing used in the production process can lead to quenching of plasmonic properties in the case of copper. To solve this problem, it is suggested to treat the samples with ozone...

  10. Thermal Methane Activation by the Metal-Free Cluster Cation [Si2 O4 ](.)

    Science.gov (United States)

    Sun, Xiaoyan; Zhou, Shaodong; Schlangen, Maria; Schwarz, Helmut

    2017-01-31

    The thermal reaction of methane with the metal-free cluster cation [Si2 O4 ](.+) has been examined by using Fourier transform-ion cyclotron resonance (FT-ICR) mass spectrometry. In addition to generating a methyl radical via hydrogen-atom abstraction, [Si2 O4 ](.+) can selectively oxidize methane to formaldehyde. The mechanisms of these rather efficient reactions have been elucidated by high-level quantum-chemical calculations. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  11. Simulation study on the formation and transition properties of cluster structures in liquid metals during rapid cooling processes

    Institute of Scientific and Technical Information of China (English)

    郑采星; 刘让苏; 董科军; 彭平; 刘海蓉; 徐仲榆; 卢小勇

    2002-01-01

    For the first time, a molecular dynamics simulation study has been performed for a liquid metal system consisting of 50000 atoms to deeply investigate the transitions of microstructure configurations dudng the rapid cooling processes. Especially, the cluster-type index method has been adopted to analyze the transforming and evolving processes of clusters and cluster configurations from liquid metal atoms. It has been found that the bigger cluster configurations in the system are formed by means of connecting some small clusters (they are combined by several smaller clusters), and not taken on the multi-shells configuration accumulated with an atom as the center and the surrounding atoms arranged according to some fixed pattern. With the decrease in temperature, the probability of repetitive appearance for clusters increases largely, which reveals that clusters are indeed possessing a certain relative stability and continuity (namely hereditary effect). These results will give us an important enlightenment to understand not only the forming mechanisms and microscopic processes of the short-order sections and disorder sparse sections in amorphous structures but also the freezing processes of liquid metals.``

  12. Destructive Clustering of Metal Nanoparticles in Chalcogenide and Oxide Glassy Matrices.

    Science.gov (United States)

    Shpotyuk, M V; Shpotyuk, O I; Cebulski, J; Kozyukhin, S

    2016-12-01

    The energetic χ-criterion is developed to parameterize difference in the origin of high-order optical non-linearity associated with metallic atoms (Cu, Ag, Au) embedded destructively in oxide- and chalcogenide glasses. Within this approach, it is unambiguously proved that covalent-bonded networks of soft semiconductor chalcogenides exemplified by binary As(Ge)-S(Se) glasses differ essentially from those typical for hard dielectric oxides like vitreous silica by impossibility to accommodate pure agglomerates of metallic nanoparticles. In an excellence according to known experimental data, it is suggested that destructive clustering of nanoparticles is possible in Cu-, Ag-, and Au-ion-implanted dielectric oxide glass media, possessing a strongly negative χ-criterion. Some recent speculations trying to ascribe equally this ability to soft chalcogenide glasses despite an obvious difference in the corresponding bond dissociation energies have been disclosed and criticized as inconclusive.

  13. Constraining stellar population models - I. Age, metallicity, and abundance pattern compilation for Galactic globular clusters

    CERN Document Server

    Roediger, Joel C; Graves, Genevieve; Schiavon, Ricardo

    2013-01-01

    We present an extenstive literature compilation of age, metallicity, and chemical abundance pattern information for the 41 Galactic globular clusters (GGCs) studied by Schiavon et al. (2005). Our compilation constitutes a notable improvement over previous similar work, particularly in terms of chemical abundances. Its primary purpose is to enable detailed evaluations of and refinements to stellar population synthesis models designed to recover the above information for unresolved stellar systems based on their integrated spectra. However, since the Schiavon sample spans a wide range of the known GGC parameter space, our compilation may also benefit investigations related to a variety of astrophysical endeavours, such as the early formation of the Milky Way, the chemical evolution of GGCs, and stellar evolution and nucleosynthesis. For instance, we confirm with our compiled data that the GGC system has a bimodal metallicity distribution and is uniformly enhanced in the alpha-elements. When paired with the ages...

  14. Quantum Mechanics and Electrodynamics Studies of the Optical Properties of Metal Clusters/Nanoparticles

    Science.gov (United States)

    Schatz, George

    2008-03-01

    This talk will describe the use of electrodynamics and quantum mechanics methods to describe the optical properties of silver and gold nanoparticles and other nanostructures. This work has been done in collaboration with several experimental colleagues, including Chad Mirkin, Rick Van Duyne and Teri Odom. Our recent work has focused on the optical properties of metal nanoparticles that are coated with molecules that are detected either through their influence plasmon resonance excitation, or via surface enhanced Raman spectroscopy (SERS). Electrodynamics calculations using either the DDA or FDTD methods provide a quantitative tool for characterizing far field properties, and at a more primitive level estimates of SERS intensities. Quantum mechanics, as developed using time dependent density functional theory, is restricted to small metal clusters, but the same methods of far field spectroscopy and SERS can still be studied.

  15. A new method for measuring metallicities of young super star clusters

    Energy Technology Data Exchange (ETDEWEB)

    Gazak, J. Zachary; Kudritzki, Rolf; Bresolin, Fabio [Institute for Astronomy, University of Hawai' i, 2680 Woodlawn Dr, Honolulu, HI 96822 (United States); Davies, Ben; Bastian, Nate [Astrophysics Research Institute, Liverpool John Moores University, 146 Brownlow Hill, Liverpool L3 5RF (United Kingdom); Bergemann, Maria [Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA (United Kingdom); Plez, Bertrand [Laboratoire Univers et Particules de Montpellier, Université Montpellier 2, CNRS, F-34095 Montpellier (France); Evans, Chris [UK Astronomy Technology Centre, Royal Observatory Edinburgh, Blackford Hill, Edinburgh, EH9 3HJ (United Kingdom); Patrick, Lee [Institute for Astronomy, Royal Observatory Edinburgh, Blackford Hill, Edinburgh, EH9 3HJ (United Kingdom); Schinnerer, Eva [MPI for Astronomy, Konigstuhl 17, D-69117 Heidelberg (Germany)

    2014-06-01

    We demonstrate how the metallicities of young super star clusters (SSC) can be measured using novel spectroscopic techniques in the J-band. The near-infrared flux of SSCs older than ∼6 Myr is dominated by tens to hundreds of red supergiant stars. Our technique is designed to harness the integrated light of that population and produces accurate metallicities for new observations in galaxies above (M83) and below (NGC 6946) solar metallicity. In M83 we find [Z] = +0.28 ± 0.14 dex using a moderate resolution (R ∼ 3500) J-band spectrum and in NGC 6496 we report [Z] = -0.32 ± 0.20 dex from a low resolution spectrum of R ∼ 1800. Recently commissioned low resolution multiplexed spectrographs on the Very Large Telescope (KMOS) and Keck (MOSFIRE) will allow accurate measurements of SSC metallicities across the disks of star-forming galaxies up to distances of 70 Mpc with single night observation campaigns using the method presented in this paper.

  16. Ages and Metallicities of Cluster Galaxies in A779 using Modified Str\\"omgren Photometry

    CERN Document Server

    Sreedhar, Yuvraj Harsha; Rakos, Karl D; Hensler, Gerhard; Zeilinger, Werner W

    2012-01-01

    In the quest for the formation and evolution of galaxy clusters, Rakos and co-workers introduced a spectrophotometric method using the modified Str\\"omgren photometry. But with the considerable debate toward the project's abilities, we re-introduce the system after a thorough testing of repeatability of colors and reproducibility of the ages and metallicities for six common galaxies in the three A779 data sets. A fair agreement has been found between the modified Str\\"omgren and Str\\"omgren filter systems to produce similar colors (with the precision of 0.09 mag in (uz-vz), 0.02 mag in (bz-yz), and 0.03 mag in (vz-vz)), ages and metallicities (with the uncertainty of 0.36 Gyr and 0.04 dex from the PCA and 0.44 Gyr and 0.2 dex using the GALEV models). We infer that the technique is able to relieve the age-metallicity degeneracy by separating the age effects from the metallicity effects, but still unable to completely break. We further extend this paper to re-study the evolution of galaxies in the low mass, dyn...

  17. Dark Matter Halos in Galaxies and Globular Cluster Populations. II: Metallicity and Morphology

    CERN Document Server

    Harris, William; Hudson, Michael

    2015-01-01

    An increasing body of data reveals a one-to-one linear correlation between galaxy halo mass and the total mass in its globular cluster (GC) population, M_{GCS} ~ M_h^{1.03 \\pm 0.03}, valid over 5 orders of magnitude. We explore the nature of this correlation for galaxies of different morphological types, and for the subpopulations of metal-poor (blue) and metal-rich (red) GCs. For the subpopulations of different metallicity we find M_{GCS}(blue) ~ M_h^{0.96 \\pm 0.03} and M_{GCS}(red) ~ M_h^{1.21 \\pm 0.03} with similar scatter. The numerical values of these exponents can be derived from the detailed behavior of the red and blue GC fractions with galaxy mass and provide a self-consistent set of relations. In addition, all morphological types (E, S0, S/Irr) follow the same relation, but with a second-order trend for spiral galaxies to have a slightly higher fraction of metal-rich GCs for a given mass. These results suggest that the amount of gas available for GC formation at high redshift was in nearly direct pr...

  18. Ab Initio Molecular Dynamics of Dimerization and Clustering in Alkali Metal Vapors.

    Science.gov (United States)

    Chaban, Vitaly V; Prezhdo, Oleg V

    2016-06-30

    Alkali metals are known to form dimers, trimers, and tetramers in their vapors. The mechanism and regularities of this phenomenon characterize the chemical behavior of the first group elements. We report ab initio molecular dynamics (AIMD) simulations of the alkali metal vapors and characterize their structural properties, including radial distribution functions and atomic cluster size distributions. AIMD confirms formation of Men, where n ranges from 2 to 4. High pressure sharply favors larger structures, whereas high temperature decreases their fraction. Heavier alkali metals maintain somewhat larger fractions of Me2, Me3, and Me4, relative to isolated atoms. A single atom is the most frequently observed structure in vapors, irrespective of the element and temperature. Due to technical difficulties of working with high temperatures and pressures in experiments, AIMD is the most affordable method of research. It provides valuable understanding of the chemical behavior of Li, Na, K, Rb, and Cs, which can lead to development of new chemical reactions involving these metals.

  19. Globular Cluster Abundances from High-resolution, Integrated-light Spectroscopy. II. Expanding the Metallicity Range for Old Clusters and Updated Analysis Techniques

    Science.gov (United States)

    Colucci, Janet E.; Bernstein, Rebecca A.; McWilliam, Andrew

    2017-01-01

    We present abundances of globular clusters (GCs) in the Milky Way and Fornax from integrated-light (IL) spectra. Our goal is to evaluate the consistency of the IL analysis relative to standard abundance analysis for individual stars in those same clusters. This sample includes an updated analysis of seven clusters from our previous publications and results for five new clusters that expand the metallicity range over which our technique has been tested. We find that the [Fe/H] measured from IL spectra agrees to ∼0.1 dex for GCs with metallicities as high as [Fe/H] = ‑0.3, but the abundances measured for more metal-rich clusters may be underestimated. In addition we systematically evaluate the accuracy of abundance ratios, [X/Fe], for Na i, Mg i, Al i, Si i, Ca i, Ti i, Ti ii, Sc ii, V i, Cr i, Mn i, Co i, Ni i, Cu i, Y ii, Zr i, Ba ii, La ii, Nd ii, and Eu ii. The elements for which the IL analysis gives results that are most similar to analysis of individual stellar spectra are Fe i, Ca i, Si i, Ni i, and Ba ii. The elements that show the greatest differences include Mg i and Zr i. Some elements show good agreement only over a limited range in metallicity. More stellar abundance data in these clusters would enable more complete evaluation of the IL results for other important elements. This paper includes data gathered with the 6.5 m Magellan Telescopes located at Las Campanas Observatory, Chile.

  20. Relaxation processes in optically excites metal clusters; Relaxationsprozesse in optisch angeregten Metallclustern

    Energy Technology Data Exchange (ETDEWEB)

    Stanzel, J.

    2007-08-10

    The present work is concerned with the dynamics of optically excited metal clusters in the gas phase. Small mass-selected gold and tungsten cluster anions (Au{sup -}{sub n}, n=5-8, 14, 20 and W{sup -}{sub n}, n=3-14) are studied using femtosecond time-resolved photoelectron spectroscopy. Depending on the electronic structure in the valence region as well as on the optical excitation energy fundamentally different relaxation processes are observed. In small gold cluster anions excited with 1.56 eV an isolated electronically excited state is populated. The time-dependent measurements are strongly sizedependent and open insights into photoinduced geometry changes of the nuclear framework. Oscillatory vibrational wavepacket motion in Au{sup -}{sub 5}, an extremely longlived ({tau} >90 ns) electronically excited state in Au{sup -}{sub 6} as well as photoinduced melting in Au{sup -}{sub 7} and Au{sup -}{sub 8} is monitored in real time. By increasing the OPTICAL excitation energy to 3.12 eV a completely different scenario is observed. A multitude of electronically excited states can be reached upon optical excitation and as a consequence electronic relaxation processes that take place on a time scale of 1 ps are dominating. This is shown for Au{sup -}{sub 7}, Au{sup -}{sub 14} and Au{sup -}{sub 20}. Compared to gold clusters, tungsten clusters are characterized by a significantly higher electronic density of states in the valence region. Therefore electronic relaxation processes are much more likely and take place on a significantly faster time scale. The fast electronic relaxation processes are distinguished from pure vibrational relaxation. It is shown that already in the four atomic tungsten cluster W{sup -}{sub 4} electronic relaxation processes take place on a time scale of 30 fs. In all investigated tungsten cluster anions (W{sup -}{sub n}, n=3-14) an equilibrium between electronic and vibrational system is reached within around 1 ps after optical excitation which

  1. Investigation into the reactivity of unsupported and supported Ag7 and Ag8 clusters with toxic metal ions.

    Science.gov (United States)

    Bootharaju, M S; Pradeep, T

    2011-07-05

    We report the chemical interactions of unsupported and alumina-supported Ag(7) and Ag(8) clusters protected with MSA (mercaptosuccinic acid) with heavy metal ions Hg(II), Cd(II), and Pb(II) in water at different concentrations. The investigation was carried out to determine the feasibility of this interesting new class of materials called quantum clusters for water purification. These systems were studied using various spectroscopic and microscopic techniques such as ultraviolet-visible spectroscopy, Fourier transform infrared spectroscopy, X-ray diffraction, dynamic light scattering, zeta potential measurements, scanning electron microscopy, transmission electron microscopy, Raman spectroscopy, and photoluminescence spectroscopy and in detail by X-ray photoelectron spectroscopy. We observed that the metal ions interact with both the silver atoms of the clusters and the functional groups of the capping agent (MSA). The mercuric ions were reduced to metallic mercury by both supported and unsupported clusters, due to the feasibility of the redox reaction, whereas no reduction was observed for Cd(II) and Pb(II). As a result of the interaction, the luminescence of the cluster is lost which can be used to sense Hg(II). At lower concentrations, the metal ions were chemically bonded to the carboxylate groups of MSA. Absence of reduction of Hg(II) at lower concentration is due to the chemical affinity of the ligands and the lower silver content per cluster compared to the number of carboxylate groups. © 2011 American Chemical Society

  2. Simultaneous Forecast for Three Speciations of Heavy Metal Elements Using Fuzzy Cluster-Artificial Neural Network

    Institute of Scientific and Technical Information of China (English)

    ZHAO Tian-qi; MENG Fan-yu; WANG Hong-yan; GAO Yan

    2012-01-01

    Abstract The three speciations(water extract,adsorption and organic speciations) of Cu,Zn,Fe and Mn in geo-chemical samples were determined by fuzzy cluster-artificial neural network(FC-ANN) method coupled with atomic absorption spectrometry.A back-propagation artificial neural network with one input node and three export nodes was constructed,which could forecaste three speciations of heavy metals simultaneously.In the learning sample set,the three speciations of each element were allowed to change in a wide concentration range and the accuracy of the analysis was apparently increased via the learning sample set optimized with the help of the fuzzy cluster analysis.The average relative errors of the three speciations of Cu,Zn,Fe or Mn from 100 geo-chemical samples were less than 5%.The relative standard deviations of the three speciations of each of four heavy metals were 0.008%-4.43%.

  3. Ultrathin magnesia films as support for molecules and metal clusters: Tuning reactivity by thickness and composition

    Energy Technology Data Exchange (ETDEWEB)

    Vaida, Mihai E.; Bernhardt, Thorsten M. [Institute of Surface Chemistry and Catalysis, University of Ulm (Germany); Barth, Clemens [CINAM-CNRS, Marseille (France); Esch, Friedrich; Heiz, Ueli [Department of Chemistry, Technical University of Munich, Garching (Germany); Landman, Uzi [School of Physics, Georgia Institute of Technology, Atlanta, Georgia (United States)

    2010-05-15

    Ultrathin metal oxide films have attracted considerable interest in recent years as versatile substrate for the design of nanocatalytic model systems. In particular, it has been proposed theoretically and confirmed experimentally that the electronic structure of adsorbates can be influenced by the layer thickness and the stoichiometry, i.e., the type and number of defects, of the oxide film. This has important consequences on the chemical reactivity of the oxide surface itself and of oxide supported metal clusters. It also opens new possibilities to influence and to control chemical reactions occurring at the surface of these systems. The present feature focuses on very recent experiments that illustrate the effects of a proper adjustment of layer thickness and composition of ultrathin MgO(100) films on chemical transformations. On the magnesia surface itself, the photodissociation dynamics of methyl iodide molecules is investigated via femtosecond-laser pump-probe mass spectrometry. Furthermore, the catalytic oxidation of carbon monoxide at mass-selected Au{sub 20} clusters deposited on magnesia is explored through temperature programmed reaction measurements. In the latter case, detailed first principles calculations are able to correlate the experimentally observed reactivity with structural dimensionality changes that are induced by the changing thickness and composition of the magnesia support. (Abstract Copyright [2010], Wiley Periodicals, Inc.)

  4. The two metallicity groups of the globular cluster M22: a chemical perspective

    CERN Document Server

    Marino, A F; Kraft, R P; Wallerstein, G; Norris, J E; Da Costa, G; Milone, A P; Ivans, I I; Gonzalez, G; Fulbright, J P; Hilker, M; Piotto, G; Zoccali, M; Stetson, P B

    2011-01-01

    We present a detailed chemical composition analysis of 35 red giant stars in the globular cluster M22. High resolution spectra for this study were obtained at five observatories, and analyzed in a uniform manner. We have determined abundances of representative light proton-capture, alpha, Fe-peak and neutron-capture element groups. Our aim is to better understand the peculiar chemical enrichment history of this cluster, in which two stellar groups are characterized by a different content in iron, neutron capture elements Y, Zr and Ba, and alpha element Ca. The principal results of this study are: (i) substantial star-to-star metallicity scatter (-2.0<[Fe/H]<-1.6); (ii) enhancement of s-process/r-process neutron-capture abundance ratios in a fraction of giants, positively correlated with metallicity; (iii) sharp separation between the s-process rich and s-process poor groups by [La/Eu] ratio; (iv) possible increase of [Cu/Fe] ratios with increasing [Fe/H], suggesting that this element also has a signific...

  5. Dynamics of alkyl chains in monolayer protected metal clusters and their superlattices

    Energy Technology Data Exchange (ETDEWEB)

    Mukhopadhyay, R [Solid State Physics Division, BARC, Mumbai 400085 (India); Mitra, S [Solid State Physics Division, BARC, Mumbai 400085 (India); Johnson, M [Institute Lau-Langevin, BP156, F-38042, Grenoble, Cedex 9 (France); Pradeep, T [Department of Chemistry and SAIF, IITm, Chennai 600 036 (India)

    2007-12-15

    Alkyl chains dynamics in monolayer protected metal cluster (MPC) systems of gold and silver have been studied by the quasielastic neutron scattering (QENS) technique. Isolated MPCs investigated are 6, 12 and 18 carbon n-alkyl chain thiolate protected 4 nm diameter gold clusters while the superlattices are their silver analogues. Evolution of dynamics with temperature is found to be very different in the isolated clusters and their superlattices. While continuous evolution of the dynamics of the monolayer was observed in isolated MPCs, it is abrupt in superlattice systems and occurs at a temperature consistent with the superlattice melting detected in calorimetry measurements. A model where the chain undergoes uniaxial rotational diffusion with additional body axis fluctuation was found to describe the data consistently. For the superlattice systems, the chains are found to be held by strong inter-chain interactions below the superlattice melting. The data from the planar silver thiolate systems show similar behavior like the superlattice systems, consistent with the calorimetric data.

  6. Searching for variable stars in the cores of five metal rich globular clusters using EMCCD observations

    CERN Document Server

    Skottfelt, Jesper; Jaimes, R Figuera; Jørgensen, U G; Kains, N; Ferro, A Arellano; Alsubai, K A; Bozza, V; Novati, S Calchi; Ciceri, S; DAgo, G; Dominik, M; Galianni, P; Gu, S -H; Harpsøe, K B W; Haugbølle, T; Hinse, T C; Hundertmark, M; Juncher, D; Korhonen, H; Liebig, C; Mancini, L; Popovas, A; Rabus, M; Rahvar, S; Scarpetta, G; Schmidt, R W; Snodgrass, C; Southworth, J; Starkey, D; Street, R A; Surdej, J; Wang, X -B; Wertz, O

    2014-01-01

    In this paper, we present the analysis of time-series observations from 2013 and 2014 of five metal rich ([Fe/H] $>$ -1) globular clusters: NGC~6388, NGC~6441, NGC~6528, NGC~6638, and NGC~6652. The data have been used to perform a census of the variable stars in the central parts of these clusters. The observations were made with the electron multiplying CCD (EMCCD) camera at the Danish 1.54m Telescope at La Silla, Chile, and they were analysed using difference image analysis (DIA) to obtain high-precision light curves of the variable stars. It was possible to identify and classify all of the previously known or suspected variable stars in the central regions of the five clusters. Furthermore, we were able to identify, and in most cases classify 48, 49, 7, 8, and 2 previously unknown variables in NGC~6388, NGC~6441, NGC~6528, NGC~6638, and NGC~6652, respectively. Especially interesting is the case of NGC~6441, for which the variable star population of about 150 stars has been thoroughly examined by previous s...

  7. Membership, binarity and metallicity of red giants in the southern open cluster NGC 2354

    Science.gov (United States)

    Clariá, J. J.; Mermilliod, J.-C.; Piatti, A. E.

    1999-01-01

    We present new Coravel radial-velocity observations and photoelectric photometry in the UBV, DDO and Washington systems for a sample of red giant candidates in the field of the intermediate-age open cluster NGC 2354. Photometric membership probabilities show very good agreement with those obtained from Coravel radial velocities. The analysis of the photometric and kinematical data allow us to confirm cluster membership for 9 red giants, one of them being a spectroscopic binary, while 4 confirmed spectroscopic binaries appear to be probable members. We have also discovered 4 spectroscopic binaries not belonging to the cluster. A mean radial velocity of (33.40 +/- 0.27) km s(-1) and a mean reddening E(B-V) = 0.13 +/- 0.03 were derived for the cluster giants. NGC 2354 has a mean ultraviolet excess B)> = -0.03 +/- 0.01, relative to the field K giants, and a mean new cyanogen anomaly Delta CN = -0.035 +/- 0.007, both implying [Fe/H] ~ -0.3. The moderately metal-poor character of NGC 2354 is confirmed using five different metal abundance indicators of the Washington system. The cluster giant branch is formed by a well defined clump of 7 stars and 4 stars with high membership probabilities seem to define an ascending giant branch. The whole red giant locus cannot be reproduced by any theoretical track. Based on observations collected with the Danish\\protect\\linebreak 1.54-m telescope at the European Southern Observatory, La Silla (Chile); at Complejo Astronómico El Leoncito, which is operated under agreement between the Consejo Nacional de Investigaciones Científicas y Técnicas de la República Argentina and the National Universities of La Plata, Córdoba, and San Juan, Argentina, and at Cerro Tololo Inter-American Observatory, National Optical Astronomy Observatories, operated by the Association of Universities for Research in Astronomy, Inc., under contract with the National Science Foundation.

  8. Continuous supersonic plasma wind tunnel

    DEFF Research Database (Denmark)

    Andersen, S.A.; Jensen, Vagn Orla; Nielsen, P.

    1968-01-01

    The B field configuration of a Q-device has been modified into a magnetic Laval nozzle. Continuous supersonic plasma flow is observed with M≈3......The B field configuration of a Q-device has been modified into a magnetic Laval nozzle. Continuous supersonic plasma flow is observed with M≈3...

  9. Continuous supersonic plasma wind tunnel

    DEFF Research Database (Denmark)

    Andersen, S.A.; Jensen, Vagn Orla; Nielsen, P.

    1969-01-01

    The normal magnetic field configuration of a Q device has been modified to obtain a 'magnetic Laval nozzle'. Continuous supersonic plasma 'winds' are obtained with Mach numbers ~3. The magnetic nozzle appears well suited for the study of the interaction of supersonic plasma 'winds' with either...

  10. MODIFICATION OF TRANSITION METAL CATIONS TO POLYMER- STABILIZED PLATINUM COLLOIDAL CLUSTERS IN ENANTIOSELECTIVE HYDROGENATION OF METHYL PYRUVATE

    Institute of Scientific and Technical Information of China (English)

    Xiao-ping Yan; Bao-lin He; Jie Zhang; Han-fan Liu

    2005-01-01

    Modification of transition metal cations to polymer-stabilized Pt colloidal clusters modified with cinchonidine was studied in enantioselective hydrogenation of methyl pyruvate. Compared to the enantiomeric excess (e.e.) value (71.4%)obtained without the presence of metal cations, obvious e.e. enhancement (up to 82.5%) was resulted from the addition of Zn2+ but with a certain decrease in activity. The reaction parameters in the presence of Zn2+ were also studied. It was found that the Pt colloidal catalysts in the presence of metal cations performed very differently from that in the absence of metal cations.

  11. Supersonic Cloud Collision-II

    CERN Document Server

    Anathpindika, S

    2009-01-01

    In this, second paper of the sequel of two papers, we present five SPH simulations of fast head-on cloud collisions and study the evolution of the ram pressure confined gas slab. Anathpindika (2008) (hereafter paper I) considered highly supersonic cloud collisions and examined the effect of bending and shearing instabilities on the shocked gas slab. The post-collision shock here, as in paper I, is also modelled by a simple barotropic equation of state (EOS). However, a much stiffer EOS is used to model the shock resulting from a low velocity cloud collision. We explore the parameter space by varying the pre-collision velocity and the impact parameter. We observe that pressure confined gas slabs become Jeans unstable if the sound crossing time, $t_{cr}$, is much larger than the freefall time, $t_{ff}$, of putative clumps condensing out of them. Self gravitating clumps may spawn multiple/larger $N$-body star clusters. We also suggest that warmer gas slabs are unlikely to fragment and may end up as diffuse gas c...

  12. The Edge supersonic transport

    Science.gov (United States)

    Agosta, Roxana; Bilbija, Dushan; Deutsch, Marc; Gallant, David; Rose, Don; Shreve, Gene; Smario, David; Suffredini, Brian

    1992-01-01

    As intercontinental business and tourism volumes continue their rapid expansion, the need to reduce travel times becomes increasingly acute. The Edge Supersonic Transport Aircraft is designed to meet this demand by the year 2015. With a maximum range of 5750 nm, a payload of 294 passengers and a cruising speed of M = 2.4, The Edge will cut current international flight durations in half, while maintaining competitive first class, business class, and economy class comfort levels. Moreover, this transport will render a minimal impact upon the environment, and will meet all Federal Aviation Administration Part 36, Stage III noise requirements. The cornerstone of The Edge's superior flight performance is its aerodynamically efficient, dual-configuration design incorporating variable-geometry wingtips. This arrangement combines the benefits of a high aspect ratio wing at takeoff and low cruising speeds with the high performance of an arrow-wing in supersonic cruise. And while the structural weight concerns relating to swinging wingtips are substantial, The Edge looks to ever-advancing material technologies to further increase its viability. Heeding well the lessons of the past, The Edge design holds economic feasibility as its primary focus. Therefore, in addition to its inherently superior aerodynamic performance, The Edge uses a lightweight, largely windowless configuration, relying on a synthetic vision system for outside viewing by both pilot and passengers. Additionally, a fly-by-light flight control system is incorporated to address aircraft supersonic cruise instability. The Edge will be produced at an estimated volume of 400 aircraft and will be offered to airlines in 2015 at $167 million per transport (1992 dollars).

  13. Investigation of dispersion and clustering in bubbles of ion implanted potassium in refractory metals

    Energy Technology Data Exchange (ETDEWEB)

    Kim, K.

    1989-01-01

    Potassium is a well known dopant for refractory metals. Being insoluble and of large atomic size it forms stable trapping sites for mobile defects at high temperature in the form of fine bubbles. Because of its insolubility it is difficult to introduce potassium into refractory metals, such as in lamp filaments. Ion implantation offers an excellent research tool as it permits the injection of insoluble element into the surface layer. This method was used to produce a uniform dispersion of potassium at a very fine level into tungsten and rhenium. Clustering and bubble formation were studied as a function of annealing time (up to 20 hours) and temperature (up to 2300 C). The methods of investigation were transmission electron microscopy and microchemical analysis. Orientation relationships between host metal and potassium precipitates inside bubbles were analyzed from superimposed electron diffraction patterns. In tungsten, the orientation relationship and the morphology of the bubbles are identical to those published for powder-metallurgically doped material. The bubbles are trapping sites for grain boundaries and dislocations as explained by the Zener drag-force model.

  14. Metal Clustering and Solvation in Hydrothermal Steam: FT-MS, IRMPD, and Quantum Chemical Studies.

    Science.gov (United States)

    Lemke, K.

    2016-12-01

    FT-mass spectrometry in combination with wave tunable IRMPD spectroscopy can be used to probe the speciation of metals in aqueous media [1], and, in particular, shed light on clustering and solvation processes that occur in low-density aqueous fluids close to and on the Earth's surface [2]. In order to probe the structure of the solvation envelope around geochemicially important molecular ions, we have begun to survey a range of representative metal clusters of the form [Mn(ClO4)2n-1]+(H2O)m, (M=Mn, Ni, Cu, Co, Zn) using a combination of SWIFT mass isolation and wave tunable IR techniques. Ion cluster experiments have been conducted on a modified FT-ICR mass spectrometer coupled to a Nd:YAG pumped OPO/OPA laser; for example, ESI FT-MS of dilute (0.5 mM) aqueous Ni(ClO4)2 yields ion signals at m/z 452 (m=2), 470 (m=3), 488 (m=4) and 506 (m=5) due to clusters of the form [Ni2(ClO4)3]+(H2O)m with up to 5 waters, and larger trinuclear clusters at m/z 726, i.e. [Ni3(ClO4)5]+(H2O)3 and m/z 744, i.e.[Ni3(ClO4)5]+(H2O)4. Following mass isolation and IRMPD of Ni2(ClO4)3]+(H2O)4 at m/z 488, there is clear spectroscopic evidence for strongly red-shifted water OH stretching modes because of hydrogen bonding. Assignment of individual IR bands in Ni2(ClO4)3]+(H2O)4 was achieved by using a swarm based optimization algorithm and anharmonic DFT and MP2 calculations. Infrared spectral assignment could be made by assuming that two H2O molecules bind to each Ni center in two structurally distinct but isoenergetic Ni2(ClO4)3]+(H2O)4 clusters. In the case of Ni2(ClO4)3]+(H2O)4, the two lowest energy structures predicted by theory have all 4 water molecules bound into the first solvation shell, in other words, the strongly red-shifted OH stretching bands below 3590 cm-1 are due to asym. and sym. OH stretching modes of water moleculess directly bound to nickel and perchlorate O. These new FT-MS and IRMPD data together with results from IR spectral simulations of [Nin(ClO4)2n-1]+(H2O

  15. High-rate production of functional nanostructured films and devices by coupling flame spray pyrolysis with supersonic expansion.

    Science.gov (United States)

    Wegner, K; Vinati, S; Piseri, P; Antonini, A; Zelioli, A; Barborini, E; Ducati, C; Milani, P

    2012-05-11

    The fabrication of functional thin films and devices by direct deposition of nanoparticles from the gas phase is a promising approach enabling, for instance, the integration of complex analytical and sensing capabilities on microfabricated platforms. Aerosol-based techniques ensure large-scale nanoparticle production and they are potentially suited for this goal. However, they are not adequate in terms of fine control over the lateral resolution of the coatings, mild processing conditions (avoiding high temperature and aggressive chemicals), low contamination and compatibility with microfabrication processes. Here we report the high-rate and efficient production of functional nanostructured films by nanoparticle assembling obtained by the combination of flame spray pyrolysis and supersonic expansion. Our approach merges the advantages of flame spray pyrolysis for bulk nanopowders such as process stability and wide material library availability with those of supersonic cluster beam deposition in terms of lateral resolution and of direct integration of nanomaterials on devices. We efficiently produced nanostructured films and devices (such as gas sensors) using metal oxide, pure noble metal and oxide-supported noble metal nanoparticles.

  16. Reducing Capsule Based on Electron Programming: Versatile Synthesizer for Size-Controlled Ultra-Small Metal Clusters.

    Science.gov (United States)

    Kambe, Tetsuya; Imaoka, Takane; Yamamoto, Kimihisa

    2016-11-07

    Controlled reducing capsules with a specific number of reducing electrons were achieved by appropriately placed BH3 units in the dendritic polyphenylazomethines (DPAs). Using the 1:1 coordination fashion on their basic branches with radius affinity gradient, the 4th generation DPA (DPAG4) possessing four BH3 units in the central positions was prepared as a template synthesizer for size-controlled ultra-small metal clusters. This was well-demonstrated by reduction of Ag, Pt, and other metal ions resulting in monodispersed ultra-small clusters.

  17. Metallicities and radial velocities of two stellar clusters located in the outer regions of the Small Magellanic Cloud

    Science.gov (United States)

    Gramajo, L. V.; Parisi, M. C.; Clariá, J. J.; Geisler, D.; Vásquez, S.; Da Costa, G.; Grebel, E. K.

    2016-08-01

    We studied near-infrared spectra of red giant stars in two Small Magellanic Cloud (SMC) clusters. We used the Caii lines to measure radial velocities as well as the equivalent widths of these lines to determine metallicity. The two studied clusters (L32 and L38) are projected on the outer regions of the SMC so they are particularly interesting to examine the possible existence of a change of sign in the metallicity gradient in the outer regions, as suggested by a recent study.

  18. Hypersensitive dual-function luminescence switching of a silver-chalcogenolate cluster-based metal-organic framework

    Science.gov (United States)

    Huang, Ren-Wu; Wei, Yong-Sheng; Dong, Xi-Yan; Wu, Xiao-Hui; Du, Chen-Xia; Zang, Shuang-Quan; Mak, Thomas C. W.

    2017-07-01

    Silver(I) chalcogenide/chalcogenolate clusters are promising photofunctional materials for sensing, optoelectronics and solar energy harvesting applications. However, their instability and poor room-temperature luminescent quantum yields have hampered more extensive study. Here, we graft such clusters to adaptable bridging ligands, enabling their interconnection and the formation of rigid metal-organic frameworks. By controlling the spatial separation and orientation of the clusters, they then exhibit enhanced stability (over one year) and quantum yield (12.1%). Ultrafast dual-function fluorescence switching (volatile organic compounds. Single-crystal X-ray diffraction of the inclusion materials, obtained by single-crystal-to-single-crystal transformation, enables precise determination of the position of the small molecules within the framework, elucidating the switching mechanism. The work enriches the cluster-based metal-organic framework portfolio, bridges the gap between silver chalcogenide/chalcogenolate clusters and metal-organic frameworks, and provides a foundation for further development of functional silver-cluster-based materials.

  19. Ionic versus metallic bonding in AlnNam and AlnMgm (m ≤ 3, n + m ≤ 15) clusters

    Science.gov (United States)

    Grover, Cameron J.; Reber, Arthur C.; Khanna, Shiv N.

    2017-06-01

    First principles electronic structure studies on the ground state geometries, stability, and the electronic structure of AlnNam and AlnMgm (m ≤ 3, n + m ≤ 15) clusters have been carried out to examine the nature of bonding between Na or Mg and Al. Identifying whether the bonding is ionic or metallic in bulk materials is typically straightforward; however, in small clusters where quantum confinement is important, the nature of bonding may become unclear. We have performed a critical analysis of the bonding in these bimetallic clusters using charge analysis, electrical dipole moments, hybridization of the atomic orbitals, the Laplacian of the charge density at the bond critical points, and the change in the bonding energy between neutral and anionic forms of the cluster. For NanAlm clusters, we find that the Na binding is primarily ionic, while the bonding in AlnMgm is primarily metallic. We find that the Mulliken population of the 3p orbital of Na and Mg can provide a rapid assessment of the nature of bonding. We also find that the Hirshfeld charge and dipole moments are effective indicators, when placed in context. We found that the Laplacian of the charge density at the bond critical points can be misleading in identifying whether the bonding is ionic or metallic in small clusters.

  20. Assessment of PM10 and heavy metals concentration in a Ceramic Cluster (NE Spain)

    Science.gov (United States)

    Belen Vicente, Ana; Pardo, Francisco; Sanfeliu, Teofilo; Bech, Joan

    2013-04-01

    Environmental pollution control is one of the most important goals in pollution risk assessment today. The aim of this study is conducting a retrospective view of the evolution of particulate matter (PM10) and heavy metals (As, Cd, Ni and Pb) at different localities in the Spanish cluster ceramic in the period between January 2007 and December 2011. The study area is in the province of Castellón. This province is a strategical area in the framework of European Union Pollution control. Approximately 80% of European ceramic tiles and ceramic frits manufacturers are concentrated in two areas, forming the so-called "Ceramics Clusters"; one is in Modena (Italy) and the other in Castellón (Spain). In this kind of areas, there are a lot of pollutants from this industry that represent an important contribution to soil contamination so it is necessary to control the air quality in them. These atmospheric particles are deposited in the ground through both dry and wet deposition. Soil is a major sink for heavy metals released into the environment. The level of pollution of soils by heavy metals depends on the retention capacity of the soil, especially on physical-chemical properties (mineralogy, grain size, organic matter) affecting soil particle surfaces and also on the chemical properties of the metal. The most direct consequences on the ground of air pollutants are acidification, salinization and the pollutions that can cause heavy metals as components of suspended particulate matter. For this purpose the levels of PM10 in ambient air and the corresponding annual and weekly trend were calculated. The results of the study show that the PM10 and heavy metals concentrations are below the limit values recommended by European Union Legislation for the protection of human health and ecosystems in the study period. There is an important reduction of them from 2009 in all control stations due to the economic crisis. References Moral, R., Gilkes, R.J., Jordán, M.M., 2005

  1. Mixing in Supersonic Turbulence

    CERN Document Server

    Pan, Liubin

    2010-01-01

    In many astrophysical environments, mixing of heavy elements occurs in the presence of a supersonic turbulent velocity field. Here we carry out the first systematic numerical study of such passive scalar mixing in isothermal supersonic turbulence. Our simulations show that the ratio of the scalar mixing timescale, $\\tau_{\\rm c}$, to the flow dynamical time, $\\tau_{\\rm dyn}$ (defined as the flow driving scale divided by the rms velocity), increases with the Mach number, $M$, for $M \\lsim3$, and becomes essentially constant for $M \\gsim3.$ This trend suggests that compressible modes are less efficient in enhancing mixing than solenoidal modes. However, since the majority of kinetic energy is contained in solenoidal modes at all Mach numbers, the overall change in $\\tau_{\\rm c}/\\tau_{\\rm dyn}$ is less than 20\\% over the range $1 \\lsim M \\lsim 6$. At all Mach numbers, if pollutants are injected at around the flow driving scale, $\\tau_{\\rm c}$ is close to $\\tau_{\\rm dyn}.$ This suggests that scalar mixing is drive...

  2. Formation of transition metal cluster adducts on the surface of single-walled carbon nanotubes: HRTEM studies

    KAUST Repository

    Kalinina, Irina V.

    2014-01-01

    We report the formation of chromium clusters on the outer walls of single-walled carbon nanotubes (SWNTs). The clusters were obtained by reacting purified SWNTs with chromium hexacarbonyl in dibutyl ether at 100°C. The functionalized SWNTs were characterized by thermogravimetic analysis, XPS, and high-resolution TEM. The curvature of the SWNTs and the high mobility of the chromium moieties on graphitic surfaces allow the growth of the metal clusters and we propose a mechanism for their formation. © 2014 Taylor and Francis Group, LLC.

  3. UB CCD photometry of the old, metal rich, open clusters NGC 6791, NGC 6819 and NGC 7142

    CERN Document Server

    Carraro, G; Bertone, E; Buson, L

    2013-01-01

    We report on a UV-oriented imaging survey in the fields of the old, metal-rich open clusters, NGC 6791, NGC 6819 and NGC 7142. These three clusters represent both very near and ideal stellar aggregates to match the distinctive properties of the evolved stellar populations, as in elliptical galaxies and bulges of spirals. The CMD of the three clusters is analyzed in detail, with special emphasis to the hot stellar component. We report, in this regard, one new extreme horizontal-branch star candidate in NGC 6791. For NGC 6819 and 7142, the stellar luminosity function points to a looser radial distribution of faint lower Main Sequence stars, either as a consequence of cluster dynamical interaction with the Galaxy or as an effect of an increasing fraction of binary stars toward the cluster core, as actually observed in NGC 6791 too.

  4. Deformed Harmonic Oscillators for Metal Clusters and Balian-Bloch Theory

    CERN Document Server

    Bonatsos, D; Raychev, P P; Terziev, P A; Bonatsos, Dennis

    2003-01-01

    The predictions for the shell structure of metal clusters of the three-dimensional q-deformed harmonic oscillator (3D q-HO), utilizing techniques of quantum groups and having the symmetry Uq(3)$\\supset$SOq(3), are compared to the restrictions imposed by the periodic orbit theory of Balian and Bloch, of electrons moving in a spherical cavity. It is shown that agreement between the predictions of the two models is established through the introduction of an additional term to the Hamiltonian of the 3D q-HO, which does not influence the predictions for supershells. This term preserves the Uq(3)$\\supset$SOq(3) symmetry, while in addition it can be derived through a variational procedure, analogous to the one leading from the usual harmonic oscillator to the Morse oscillator by introducing the concept of the Variable Frequency Oscillator (VFO).

  5. Formation of Two-dimensional Metal-water Framework Containing (H2O)2O Cluster

    Institute of Scientific and Technical Information of China (English)

    SUN,Ya-Guang; DING,Fu; GU,Xiao-Fu; ZHANG,Wan-Zhong; WEI,De-Zhou; GAO,En-Jun

    2008-01-01

    [Cd(phen)2(male)(H2O)]·9.5H2O (1) has been synthesized by the reaction of Cd(NO3)2 with phen and male (phen= 1,10-phenanthroline, H2male=maleic acid) in a mixture solvent of ethanol and distilled water. The complex was characterized by elemental analysis, infrared spectrum and thermal gravimetric analyses. The crystal structure was determined by X-ray single-crystal diffraction. In 1, a novel 1D water chain containing water (H2O)20 cluster was formed. Further hydrogen bonding interaction between the water chain and [Cd(phen)2(male)(H2O)] constructs a unique metal-water 2D framework.

  6. Rapid structural mapping of ternary metallic alloy systems using the combinatorial approach and cluster analysis.

    Science.gov (United States)

    Long, C J; Hattrick-Simpers, J; Murakami, M; Srivastava, R C; Takeuchi, I; Karen, V L; Li, X

    2007-07-01

    We are developing a procedure for the quick identification of structural phases in thin film composition spread experiments which map large fractions of compositional phase diagrams of ternary metallic alloy systems. An in-house scanning x-ray microdiffractometer is used to obtain x-ray spectra from 273 different compositions on a single composition spread library. A cluster analysis software is then used to sort the spectra into groups in order to rapidly discover the distribution of phases on the ternary diagram. The most representative pattern of each group is then compared to a database of known structures to identify known phases. Using this method, the arduous analysis and classification of hundreds of spectra is reduced to a much shorter analysis of only a few spectra.

  7. Alkali metal-cationized serine clusters studied by sonic spray ionization tandem mass spectrometry.

    Science.gov (United States)

    Nanita, Sergio C; Sokol, Ewa; Cooks, R Graham

    2007-05-01

    Serine solutions containing salts of alkali metals yield magic number clusters of the type (Ser(4)+C)(+), (Ser(8)+C)(+), (Ser(12)+C)(+), and (Ser(17)+2C)(+2) (where C = Li(+), Na(+), K(+), Rb(+), or Cs(+)), in relative abundances which are strongly dependent on the cation size. Strong selectivity for homochirality is involved in the formation of serine tetramers cationized by K(+), Rb(+), and Cs(+). This is also the case for the octamers cationized by the smaller alkalis but there is a strong preference for heterochirality in the octamers cationized by the larger alkali cations. Tandem mass spectrometry shows that the octamers and dodecamers cationized by K(+), Rb(+), and Cs(+) dissociate mainly by the loss of Ser(4) units, suggesting that the neutral tetramers are the stable building blocks of the observed larger aggregates, (Ser(8)+C)(+) and (Ser(12)+C)(+). Remarkably, although the Ser(4) units are formed with a strong preference for homochirality, they aggregate further regardless of their handedness and, therefore, with a preference for the nominally racemic 4D:4L structure and an overall strong heterochiral preference. The octamers cationized by K(+), Rb(+), or Cs(+) therefore represent a new type of cluster ion that is homochiral in its internal subunits, which then assemble in a random fashion to form octamers. We tentatively interpret the homochirality of these tetramers as a consequence of assembly of the serine molecules around a central metal ion. The data provide additional evidence that the neutral serine octamer is homochiral and is readily cationized by smaller ions.

  8. Evolution of long-lived globular cluster stars. II. Sodium abundance variations on the asymptotic giant branch as a function of globular cluster age and metallicity

    CERN Document Server

    Charbonnel, C

    2016-01-01

    Long-lived stars in GCs exhibit chemical peculiarities with respect to their halo counterparts. In particular, Na-enriched stars are identified as belonging to a 2d stellar population born from cluster material contaminated by the H-burning ashes of a 1st stellar population. Their presence and numbers in different locations of the CMDs provide important constraints on the self-enrichment scenarios. In particular, the ratio of Na-poor to Na-rich stars on the AGB has recently been found to vary strongly from cluster to cluster, while it is relatively constant on the RGB. We investigate the impact of both age and metallicity on the theoretical Na spread along the AGB within the framework of the fast rotating massive stars scenario for GC self-enrichment. (tb continued)

  9. WIYN Open Cluster Study. LXXII. A uvbyCaHβ CCD Analysis of the Metal-deficient Open Cluster NGC 2506

    Science.gov (United States)

    Anthony-Twarog, Barbara J.; Deliyannis, Constantine P.; Twarog, Bruce A.

    2016-12-01

    Precision uvbyCaHβ photometry of the metal-deficient, old open cluster NGC 2506 is presented. The survey covers an area of 20\\prime × 20\\prime and extends to V˜ 18 for b - y and Hβ and to V˜ 17.0 for c 1 and hk. For V brighter than 16.0, photometric scatter among the indices leads to the recovery of six known variables within the cluster core and five new variables in the outer 5\\prime of the survey field. Proper motions, radial velocities, and precise multicolor indices are used to isolate a highly probable sample of cluster members from the very rich color-magnitude diagram. From 257 highly probable members at the cluster turnoff, we derive a reddening estimate of E(b-y)=0.042+/- 0.001 (E(B-V)=0.058+/- 0.001), where the errors refer to the internal standard errors of the mean. [Fe/H] is derived from the A/F dwarf members using both m 1 and hk, leading to [Fe/H] = -0.296 ± 0.011 (sem) and -0.317 ± 0.004 (sem), respectively. The weighted average, heavily dominated by hk, is [Fe/H] = -0.316 ± 0.033. Based on red giant members, we place an upper limit of ±0.010 on the variation in the reddening across the face of the cluster. We also identify two dozen potential red giant cluster members outside the cluster core. Victoria-Regina isochrones on the Strömgren system produce an excellent match to the cluster for an apparent modulus of (m-M)=12.75+/- 0.1 and an age of 1.85 ± 0.05 Gyr.

  10. The Role of Thermohaline Mixing in Intermediate- and Low-Metallicity Globular Clusters

    CERN Document Server

    Angelou, George C; Church, Ross P; Lattanzio, John C; Smith, Graeme H

    2012-01-01

    It is now widely accepted that globular cluster red giant branch stars owe their strange abundance patterns to a combination of pollution from progenitor stars and in situ extra mixing. In this hybrid theory a first generation of stars imprint abundance patterns into the gas from which a second generation forms. The hybrid theory suggests that extra mixing is operating in both populations and we use the variation of [C/Fe] with luminosity to examine how efficient this mixing is. We investigate the observed red giant branches of M3, M13, M92, M15 and NGC 5466 as a means to test a theory of thermohaline mixing. The second parameter pair M3 and M13 are of intermediate metallicity and our models are able to account for the evolution of carbon along the RGB in both clusters. Although, in order to fit the most carbon-depleted main-sequence stars in M13 we require a model whose initial [C/Fe] abundance leads to a carbon abundance lower than is observed. Furthermore our results suggest that stars in M13 formed with s...

  11. The horizontal branch luminosity vs metallicity in M31 globular clusters

    CERN Document Server

    Federici, Luciana; Bellazzini, Michele; Pecci, Flavio Fusi; Galleti, Silvia; Perina, Sibilla

    2012-01-01

    Thanks to the outstanding capabilites of the HST, our current knowledge about the M31 globular clusters (GCs) is similar to our knowledge of the Milky Way GCs in the 1960s-1970s, which set the basis for studying the halo and galaxy formation using these objects as tracers, and established their importance in defining the cosmic distance scale. We intend to derive a new calibration of the M_V(HB)-[Fe/H] relation by exploiting the large photometric database of old GCs in M31 in the HST archive. We collected the BVI data for 48 old GCs in M31 and analysed them by applying the same methods and procedures to all objects. We obtained a set of homogeneous colour-magnitude diagrams (CMDs) that were best-fitted with the fiducial CMD ridge lines of selected Milky Way template GCs. Reddening, metallicity, Horizontal Branch (HB) luminosity and distance were determined self-consistently for each cluster. There are three main results of this study: i) the relation M_V(HB)=(0.25+/-0.02)[Fe/H]+(0.89+/-0.03), which is obtaine...

  12. C-H Bond Activation by Early Transition Metal Carbide Cluster Anion MoC3 (-).

    Science.gov (United States)

    Li, Zi-Yu; Hu, Lianrui; Liu, Qing-Yu; Ning, Chuan-Gang; Chen, Hui; He, Sheng-Gui; Yao, Jiannian

    2015-12-01

    Although early transition metal (ETM) carbides can activate CH bonds in condensed-phase systems, the electronic-level mechanism is unclear. Atomic clusters are ideal model systems for understanding the mechanisms of bond activation. For the first time, CH activation of a simple alkane (ethane) by an ETM carbide cluster anion (MoC3 (-) ) under thermal-collision conditions has been identified by using high-resolution mass spectrometry, photoelectron imaging spectroscopy, and high-level quantum chemical calculations. Dehydrogenation and ethene elimination were observed in the reaction of MoC3 (-) with C2 H6 . The CH activation follows a mechanism of oxidative addition that is much more favorable in the carbon-stabilized low-spin ground electronic state than in the high-spin excited state. The reaction efficiency between the MoC3 (-) anion and C2 H6 is low (0.23±0.05) %. A comparison between the anionic and a highly efficient cationic reaction system (Pt(+) +C2 H6 ) was made. It turned out that the potential-energy surfaces for the entrance channels of the anionic and cationic reaction systems can be very different. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  13. Correlation clusters in the accumulation of metals in human scalp hair: effects of age, community of residence, and abundances of metals in air and water supplies.

    Science.gov (United States)

    Moon, J; Davison, A J; Smith, T J; Fadl, S

    1988-06-15

    Scalp hair samples taken from 122 children and 27 adults from three native Indian villages in northern Alberta, Canada were analyzed for 32 metals, in an attempt to trace industrial pollution into the human population. One of the villages has been exposed since 1967 to increased levels of several metals due to its proximity to the world's first two oil sands petroleum extraction plants (Suncor and Syncrude), which release large amounts of metals into the environment. Metal-enriched particulates are emitted at a rate of 547-780 kg h-1 for Suncor, and 713-1067 kg h-1 for Syncrude. To test the hypothesis that hair content reflected accumulation of environmental metals, water and aerometric samples were collected and analyzed for their metal content. These analyses demonstrated that elevated levels of nine metals in hair from children in one of the control villages (Garden River) are (with the exception of Al) correlated with increased levels of metals in water and air. Moreover, increased levels of Cu, but lowest levels of all other metals were found in hair and environmental samples from one control village (Fort Chipewyan). Correlation matrices for metals in the hair samples revealed three sets of highly intercorrelated metals ('correlation clusters'): (i) Pb/Cd; (ii) Al/V/Fe; (iii) Ca/Mg/Sr/Ba. These groups of metals were significantly intercorrelated (r greater than 0.6, p less than 0.001) in the total population, and in both children and adults, or both males and females, as well as when the population was compared according to community of residence. The robustness of the clusters is particularly noteworthy in view of large differences in the proportions and absolute amounts of the various metals in hair from children in the three villages. Plots of metal levels in hair as a function of age of subject reveal a dramatic decrease in concentrations of Al, V, and Fe during the first years of life. The high levels of Al and V in hair from very young children may

  14. Metal-cluster-sensitized solar cells. A new class of thiolated gold sensitizers delivering efficiency greater than 2%.

    Science.gov (United States)

    Chen, Yong-Siou; Choi, Hyunbong; Kamat, Prashant V

    2013-06-19

    A new class of metal-cluster sensitizers has been explored for designing high-efficiency solar cells. Thiol-protected gold clusters which exhibit molecular-like properties have been found to inject electrons into TiO2 nanostructures under visible excitation. Mesoscopic TiO2 films modified with gold clusters deliver stable photocurrent of 3.96 mA/cm(2) with power conversion efficiencies of 2.3% under AM 1.5 illumination. The overall absorption features and cell performance of metal-cluster-sensitized solar cells (MCSCs) are comparable to those of CdS quantum-dot-based solar cells (QDSCs). The relatively high open-circuit voltage of 832 mV and fill factor of 0.7 for MCSCs as compared to QDSCs show the viability of these new sensitizers as alternatives to semiconductor QDs and sensitizing dyes in the next generation of solar cells. The superior performance of MCSCs discussed in this maiden study lays the foundation to explore other metal clusters with broader visible absorption.

  15. A new family of Ln₇ clusters with an ideal D(3h) metal-centered trigonal prismatic geometry, and SMM and photoluminescence behaviors.

    Science.gov (United States)

    Mazarakioti, Eleni C; Poole, Katye M; Cunha-Silva, Luis; Christou, George; Stamatatos, Theocharis C

    2014-08-14

    The first use of the flexible Schiff base ligand N-salicylidene-2-aminocyclohexanol in metal cluster chemistry has afforded a new family of Ln7 clusters with ideal D(3h) point group symmetry and metal-centered trigonal prismatic topology; solid-state and solution studies revealed SMM and photoluminescence behaviors.

  16. Star Formation in the First Galaxies - II: Clustered Star Formation and the Influence of Metal Line Cooling

    CERN Document Server

    Safranek-Shrader, Chalence; Bromm, Volker

    2013-01-01

    Population III stars are believed to have been more massive than typical stars today and to have formed in relative isolation. The thermodynamic impact of metals is expected to induce a transition leading to clustered, low-mass Population II star formation. In this work, we present results from three cosmological simulations, only differing in gas metallicity, that focus on the impact of metal fine-structure line cooling on the formation of stellar clusters in a high-redshift atomic cooling halo. Introduction of sink particles allows us to follow the process of gas hydrodynamics and accretion onto cluster stars for 4 Myr corresponding to multiple local free-fall times. At metallicities at least 10^-3 Zsun, gas is able to reach the CMB temperature floor and fragment pervasively resulting in a stellar cluster of size ~1 pc and total mass ~1000 Msun. The masses of individual sink particles vary, but are typically ~100 Msun, consistent with the Jeans mass when gas cools to the CMB temperature, though some solar m...

  17. Nonlocal Coulomb interactions and metal-insulator transition in Ti2O3: a cluster LDA+DMFT approach.

    NARCIS (Netherlands)

    Poteryaev, A.I.; Lichtenstein, A.I.; Kotliar, G.

    2004-01-01

    We present an ab initio quantum theory of the metal-insulator transition in Ti2O3. The recently developed cluster LDA+DMFT scheme is applied to describe the many-body features of this compound. The conventional single site DMFT cannot reproduce a low temperature insulating phase for any reasonable

  18. Independent control of metal cluster and ceramic particle characteristics during one-step synthesis of Pt/TiO2

    DEFF Research Database (Denmark)

    Schulz, H.; Madler, L.; Strobel, R.

    2005-01-01

    Rapid quenching during flame spray synthesis of Pt/TiO2 (0-10 Wt% Pt) is demonstrated as a versatile method for independent control of support (TiO2) and noble metal (Pt)cluster characteristics. Titania grain size, morphology, crystal phase structure, and crystal size were analyzed by nitrogen...

  19. Mass loss on the red giant branch: the value and metallicity dependence of Reimers' {\\eta} in globular clusters

    CERN Document Server

    McDonald, Iain

    2015-01-01

    The impact of metallicity on the mass-loss rate from red giant branch (RGB) stars is studied through its effect on the parameters of horizontal branch (HB) stars. The scaling factors from Reimers (1975) and Schroder & Cuntz (2005) are determined for 56 well-studied Galactic globular clusters (GCs). The median values among clusters are, respectively, {\\eta}_R = 0.477 +/- 0.070 (+0.050/-0.062) and {\\eta}_SC = 0.172 +/- 0.024 (+0.018/-0.023) (standard deviation and systematic uncertainties, respectively). Mass-loss mechanisms on the RGB have very little metallicity dependence: over a factor of 200 in iron abundance, {\\eta} varies by <~30 per cent, within the current systematic uncertainties on cluster ages and evolution models. Since {\\eta} incorporates cluster age, the low standard deviation of {\\eta} among clusters (~14 per cent) suggests that age can almost entirely account for the "second parameter problem". The remaining spread in {\\eta} correlates with cluster mass and density, suggesting helium enr...

  20. UB CCD PHOTOMETRY OF THE OLD, METAL-RICH, OPEN CLUSTERS NGC 6791, NGC 6819, AND NGC 7142

    Energy Technology Data Exchange (ETDEWEB)

    Carraro, G. [European Southern Observatory, Alonso de Cordova 3107, Casilla 19001, Santiago 19 (Chile); Buzzoni, A. [INAF-Osservatorio Astronomico di Bologna, Via Ranzani 1, I-40127 Bologna (Italy); Bertone, E. [INAOE-Instituto Nacional de Astrofísica Optica y Electrónica, Calle L.E. Erro 1, 72840 Tonantzintla, Puebla (Mexico); Buson, L., E-mail: gcarraro@eso.org, E-mail: alberto.buzzoni@oabo.inaf.it, E-mail: ebertone@inaoep.mx, E-mail: lucio.buson@oapd.inaf.it [INAF-Osservatorio Astronomico di Padova, Vicolo Osservatorio 5, I-35122 Padova (Italy)

    2013-11-01

    We report on a UV-oriented imaging survey in the fields of the old, metal-rich open clusters NGC 6791, NGC 6819, and NGC 7142. With their super-solar metallicity and ages ∼> 3-8 Gyr, these three clusters represent both very near and ideal stellar aggregates to match the distinctive properties of the evolved stellar populations, as in elliptical galaxies and bulges of spirals. Following a first discussion of NGC 6791 observations in an accompanying paper, here we complete our analysis, also presenting for NGC 6819 and NGC 7142 the first-ever U CCD photometry. The color-magnitude diagram of the three clusters is analyzed in detail, with special emphasis on the hot stellar component. We report, in this regard, one new extreme horizontal-branch star candidate in NGC 6791. For NGC 6819 and 7142, the stellar luminosity function clearly points to a looser radial distribution of faint lower main sequence stars, either as a consequence of cluster dynamical interaction with the Galaxy or as an effect of an increasing fraction of binary stars toward the cluster core, as also observed in NGC 6791. Compared to a reference theoretical model for the Galaxy disk, the analysis of the stellar field along the line of sight of each cluster indicates that a more centrally concentrated thick disk, on a scale length shorter than ∼2.8 kpc, might better reconcile the lower observed fraction of bright field stars and their white-dwarf progeny.

  1. UB CCD Photometry of the Old, Metal-rich, Open Clusters NGC 6791, NGC 6819, and NGC 7142

    Science.gov (United States)

    Carraro, G.; Buzzoni, A.; Bertone, E.; Buson, L.

    2013-11-01

    We report on a UV-oriented imaging survey in the fields of the old, metal-rich open clusters NGC 6791, NGC 6819, and NGC 7142. With their super-solar metallicity and ages >~ 3-8 Gyr, these three clusters represent both very near and ideal stellar aggregates to match the distinctive properties of the evolved stellar populations, as in elliptical galaxies and bulges of spirals. Following a first discussion of NGC 6791 observations in an accompanying paper, here we complete our analysis, also presenting for NGC 6819 and NGC 7142 the first-ever U CCD photometry. The color-magnitude diagram of the three clusters is analyzed in detail, with special emphasis on the hot stellar component. We report, in this regard, one new extreme horizontal-branch star candidate in NGC 6791. For NGC 6819 and 7142, the stellar luminosity function clearly points to a looser radial distribution of faint lower main sequence stars, either as a consequence of cluster dynamical interaction with the Galaxy or as an effect of an increasing fraction of binary stars toward the cluster core, as also observed in NGC 6791. Compared to a reference theoretical model for the Galaxy disk, the analysis of the stellar field along the line of sight of each cluster indicates that a more centrally concentrated thick disk, on a scale length shorter than ~2.8 kpc, might better reconcile the lower observed fraction of bright field stars and their white-dwarf progeny.

  2. A wide-field photometric survey for extratidal tails around five metal-poor globular clusters in the Galactic halo

    CERN Document Server

    Chun, Sang-Hyun; Sohn, Sangmo T; Park, Jang-Hyun; Han, Wonyong; Kim, Ho-Il; Lee, Young-Wook; Lee, Myung Gyoon; Lee, Sang-Gak; Sohn, Young-Jong

    2009-01-01

    Wide-field deep gri images obtained with the Megacam of the Canada-France-Hawaii Telescope (CFHT) are used to investigate the spatial configuration of stars around five metal-poor globular cluster M15, M30, M53, NGC 5053, and NGC 5466, in a field-of-view ~3 degree. Applying a mask filtering algorithm to the color-magnitude diagrams of the observed stars, we sorted cluster's member star candidates that are used to examine the characteristics of the spatial stellar distribution surrounding the target clusters. The smoothed surface density maps and the overlaid isodensity contours indicate that all of the five metal-poor globular clusters exhibit strong evidence of extratidal overdensity features over their tidal radii, in the form of extended tidal tails around the clusters. The orientations of the observed extratidal features show signatures of tidal tails tracing the clusters' orbits, inferred from their proper motions, and effects of dynamical interactions with the Galaxy. Our findings include detections of ...

  3. CCD Photometry of the Globular Cluster Omega Centauri; 1, Metallicity of RR Lyrae Stars from Caby Photometry

    CERN Document Server

    Rey, S C; Joo, J M; Walker, A; Baird, S A; Rey, Soo-Chang; Lee, Young-Wook; Joo, Jong-Myung; Walker, Alistair; Baird, Scott

    2000-01-01

    We present new measurements of the metallicity of 131 RR Lyrae stars in the globular cluster Omega Centauri, using the hk index of the Caby photometric system. The hk method has distinct advantages over Delta-S and other techniques in determining the metallicity of RR Lyrae stars, and has allowed us to obtain the most complete and homogeneous metallicity data to date for the RR Lyrae stars in this cluster. For RR Lyrae stars in common with the Delta-S observations of Butler et al. (1978) and Gratton et al. (1986), we have found that our metallicities, [Fe/H](hk), deviate systematically from their Delta-S metallicity, while our [Fe/H](hk) for well observed field RRab stars are consistent with previous spectroscopic measurements. We conclude that this is due to the larger errors associated with the previous Delta-S observations for this cluster. The Mv(RR) - [Fe/H] and period-shift - [Fe/H] relations obtained from our new data are consistent with the evolutionary models predicted by Lee (1991), confirming that ...

  4. Type Ia and II supernovae contributions to the metal enrichment in intra-cluster medium observed with Suzaku

    CERN Document Server

    Sato, Kosuke; Matsushita, Kyoko; Ishisaki, Yoshitaka; Yamasaki, Noriko Y; Ishida, Manabu; Ohashi, Takaya

    2007-01-01

    We studied the properties of the intra-cluster medium (ICM) in two clusters of galaxies (AWM 7 and Abell 1060) and two groups (HCG 62 and NGC 507) with the X-ray Observatory Suzaku. Based on spatially resolved energy spectra, we measured for the first time precise cumulative ICM metal masses within 0.1 and ~0.3 r_{180}. Comparing our results with supernova nucleosynthesis models, the number ratio of type II (SNe II) to type Ia (SNe Ia) is estimated to be ~3.5, assuming the metal mass in the ICM is represented by the sum of products synthesized in SNe Ia and SNe II. Normalized by the K-band luminosities of present galaxies, and including the metals in stars, the integrated number of past SNe II explosions is estimated to be close to or somewhat higher than the star formation rate determined from Hubble Deep Field observations.

  5. Supersonic induction plasma jet modeling

    Energy Technology Data Exchange (ETDEWEB)

    Selezneva, S.E. E-mail: svetlana2@hermes.usherbS_Selezneva2@hermes.usherb; Boulos, M.I

    2001-06-01

    Numerical simulations have been applied to study the argon plasma flow downstream of the induction plasma torch. It is shown that by means of the convergent-divergent nozzle adjustment and chamber pressure reduction, a supersonic plasma jet can be obtained. We investigate the supersonic and a more traditional subsonic plasma jets impinging onto a normal substrate. Comparing to the subsonic jet, the supersonic one is narrower and much faster. Near-substrate velocity and temperature boundary layers are thinner, so the heat flux near the stagnation point is higher in the supersonic jet. The supersonic plasma jet is characterized by the electron overpopulation and the domination of the recombination over the dissociation, resulting into the heating of the electron gas. Because of these processes, the supersonic induction plasma permits to separate spatially different functions (dissociation and ionization, transport and deposition) and to optimize each of them. The considered configuration can be advantageous in some industrial applications, such as plasma-assisted chemical vapor deposition of diamond and polymer-like films and in plasma spraying of nanoscaled powders.

  6. Metal nitride cluster as a template to tune the electronic and magnetic properties of rare-earth metal containing endohedral fullerenes

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Yang

    2013-10-16

    Rare-earth metal containing endohedral fullerenes have attracted much attention due to the feasibility of encaging metal atom, atoms or cluster inside of carbon cages. By switching the metal atom or cluster entrapped inside of the carbon cage the physical and chemical properties of the fullerene compounds can be tuned. The understanding of magnetic and electrochemical properties of endohedral fullerenes plays an essential role in fundamental scientific researches and potential applications in materials science. In this thesis, synthesizing novel rare-earth metal containing endohedral fullerene structures, studying the properties of these isolated endohedral fullerenes and the strategies of tuning the electronic and magnetic properties of endohedral fullerenes were introduced. The DC-arc discharging synthesis of different lanthanide metal-based (Ho, Ce and Pr) mixed metal nitride clusterfullerenes was achieved. Those rare-earth metal containing endohedral fullerenes were isolated by multi-step HPLC. The isolated samples were characterized by spectroscopic techniques included UV-vis-NIR, FTIR, Raman, LDI-TOF mass spectrometry, NMR and electrochemistry. The Ho-based mixed metal nitride clusterfullerenes Ho{sub x}M{sub 3-x}N rate at C{sub 80} (M= Sc, Lu, Y; x=1, 2) were synthesized by ''reactive gas atmosphere'' method or ''selective organic solid'' route. The isolated samples were characterized by LDI-TOF mass spectrometry, UV-vis-NIR, FTIR, Raman and NMR spectroscopy. The {sup 13}C NMR spectroscopic studies demonstrated exceptional NMR behaviors that resulted from switching the second metal inside of the mixed metal nitride cluster Ho{sub x}M{sub 3-x}N from Sc to Lu and further to Y. The LnSc{sub 2}N rate at C{sub 80} (Ln= Ce, Pr, Nd, Tb, Dy, Ho, Lu) MMNCFs were characterized by {sup 13}C and {sup 45}Sc NMR study respectively. According to Bleaney's theory and Reilley method, the separation of δ{sup PC} and δ{sup con

  7. Selective electrodesorption based atomic layer deposition (SEBALD): a novel electrochemical route to deposit metal clusters on Ag(111).

    Science.gov (United States)

    Innocenti, M; Bellandi, S; Lastraioli, E; Loglio, F; Foresti, M L

    2011-09-20

    The possibility of synergic effects of some metals on the catalytic activity of silver led us to study the way to perform controlled deposition on silver. In fact, many metals of technological interest such as Co, Ni, and Fe cannot be deposited at underpotential on silver, and any attempt to control the deposition at overpotential, even at potentials slightly negative of the Nernst value, did not allow an effective control. However, due to the favorable energy gain involved in the formation of the corresponding sulfides, these metals can be deposited at underpotential on sulfur covered silver. The deposition is surface limited and the successive electrodesorption of sulfur leaves confined clusters of metals. The method can also be used to obtain metal clusters of different size. In fact, the alternate underpotential deposition of elements that form a compound is the basis of the electrochemical atomic layer epitaxy (ECALE), and the reiteration of the basic cycle allows us to obtain sulfide deposits whose thickness increases with the number of cycles. Therefore, the successive selective desorption of sulfur leaves increasing amounts of metals.

  8. Detailed Chemical Abundances in NGC 5824: Another Metal-Poor Globular Cluster with Internal Heavy Element Abundance Variations

    CERN Document Server

    Roederer, Ian U; Bailey, John I; Spencer, Meghin; Crane, Jeffrey D; Shectman, Stephen A

    2015-01-01

    We present radial velocities, stellar parameters, and detailed abundances of 39 elements derived from high-resolution spectroscopic observations of red giant stars in the luminous, metal-poor globular cluster NGC 5824. We observe 26 stars in NGC 5824 using the Michigan/Magellan Fiber System (M2FS) and two stars using the Magellan Inamori Kyocera Echelle (MIKE) spectrograph. We derive a mean metallicity of [Fe/H]=-1.94+/-0.02 (statistical) +/-0.10 (systematic). The metallicity dispersion of this sample of stars, 0.08 dex, is in agreement with previous work and does not exceed the expected observational errors. Previous work suggested an internal metallicity spread only when fainter samples of stars were considered, so we cannot exclude the possibility of an intrinsic metallicity dispersion in NGC 5824. The M2FS spectra reveal a large internal dispersion in [Mg/Fe], 0.28 dex, which is found in a few other luminous, metal-poor clusters. [Mg/Fe] is correlated with [O/Fe] and anti-correlated with [Na/Fe] and [Al/F...

  9. Electrochemical lithium intercalation chemistry of condensed molybdenum metal cluster oxide: LiMo4O6

    Science.gov (United States)

    Lim, Sung-Chul; Chae, Munseok S.; Heo, Jongwook W.; Hong, Seung-Tae

    2017-10-01

    The electrochemical lithium-ion intercalation properties of molybdenum metal-cluster oxide LixMo4O6 (0.33 ≤ x ≤ 1.0) in an organic electrolyte of 1.0 M LiPF6 in ethylene carbonate/dimethyl carbonate (1:2 v/v) were characterized for the first time. Li0.66Mo4O6 (tetragonal, P4/mbm, a = 9.5914(3) Å, c = 2.8798(1) Å, V = 264.927(15) Å3, Z = 2) was prepared via ion-exchange of indium and lithium ions from InMo4O6 (tetragonal, P4/mbm, a = 9.66610(4) Å, c = 2.86507(2) Å, V = 267.694(2) Å3, Z = 2), which was first synthesized from a stoichiometric mixture of In, Mo, and MoO3 via a solid-state reaction for 11 h at 1100 °C. Then, Li0.33Mo4O6 was obtained via electrochemical charge of the electrode at 3.4 V vs. Li. The electrochemical lithium-ion insertion into Li0.33Mo4O6 occurs stepwise: three separate peaks were observed in the cyclic voltammogram and three quasi-plateaus in the galvanostatic profile, indicating a complicated intercalation mechanism. However, examination of the structural evolution of LixMo4O6 during the electrochemical cycle indicated a reversible reaction over the measured voltage range (2.0-3.2 V) and x range (0.33 ≤ x ≤ 1.00). Despite the excellent electrochemical reversibility, LixMo4O6 showed poor rate performance with a low capacity of 36.3 mAh g-1 at a rate of 0.05 C. Nonetheless, this work demonstrates a new structural class of lithium cathode materials with condensed metal clusters and 1D tunnels, and provides a host material candidate for multivalent-ion batteries.

  10. A study into the role of surface capping on energy transfer in metal cluster-semiconductor nanocomposites

    Science.gov (United States)

    Bain, Dipankar; Paramanik, Bipattaran; Sadhu, Suparna; Patra, Amitava

    2015-12-01

    Metal cluster-semiconductor nanocomposite materials remain a frontier area of research for the development of optoelectronic, photovoltaic and light harvesting devices because metal nanoclusters and semiconductor QDs are promising candidates for photon harvesting. Here, we have designed well defined metal cluster-semiconductor nanostructures using different surface capped negatively charged Au25 nanoclusters (Au NCs) and positively charged cysteamine capped CdTe quantum dots using electrostatic interactions. The main focus of this article is to address the impact of surface capping agents on the photophysical properties of Au cluster-CdTe QD hybrid nanocomposites. Steady state and time resolved spectroscopic studies reveal that photoluminescence quenching, radiative and nonradiative rate, and energy transfer between Au nanoclusters and CdTe QDs have been influenced by the nature of the capping agent. We have calculated the energy transfer related parameters such as the overlap integral, distance between donor and acceptor, Förster distance, efficiency of energy transfer and rate of energy transfer from CdTe QDs to three different Au NCs. Photoluminescence quenching varies from 73% to 43% when changing the capping agents from bovine serum albumin (BSA) to glutathione (GSH). The efficiency of the energy transfer from CdTe QDs to BSA-capped Au NCs is found to be 83%, for Cys-capped Au NCs it was 46% and for GSH-capped Au NCs it was 35%. The efficiency depends on the number of Au clusters attached per QD. This reveals that the nature of capping ligands plays a crucial role in the energy transfer phenomena from CdTe QDs to Au NCs. Interesting findings reveal that the efficient energy transfer in metal cluster-semiconductor nanocomposites may open up new possibilities in designing artificial light harvesting systems for future applications.Metal cluster-semiconductor nanocomposite materials remain a frontier area of research for the development of optoelectronic

  11. Novel linear transition metal clusters of a heptadentate bis-beta-diketone ligand.

    Science.gov (United States)

    Aromí, Guillem; Gamez, Patrick; Krzystek, J; Kooijman, Huub; Spek, Anthony L; MacLean, Elizabeth J; Teat, Simon J; Nowell, Harriott

    2007-04-02

    The synthesis and the structure of the new potentially heptadentate ligand 1,3-bis-(3-oxo-3-(2-hydroxyphenyl)-propionyl)-2-methoxybenzene (H5L) is described. The reaction in pyridine or DMF of this ligand with various M(AcO)2 salts (M = NiII, CoII, MnII) leads to very different products depending on the metal. Thus, the dinuclear complexes [M2(H3L)2(py)4] (M = NiII, 1; CoII, 2) or the linear zigzag tetranuclear clusters [Mn4(H2L)2(AcO)2(py)5] (3) and [Mn4(H2L)2(AcO)2(dmf)4] (4) have been synthesized and characterized crystallographically. Slow oxidation of complex 3 leads to the formation of the novel mixed-valence linear complex [Mn3(HL)2(py)6] (5), displaying an unprecedented asymmetric MnIIIMnIIIMnII topology. The coordination geometry of complexes 1 to 5 has been analyzed and discussed by means of continuous shape measures. Magnetic measurements of 3 and 5 demonstrate that the metals within these complexes weakly interact magnetically with coupling constants of J1 = -1.13 cm-1 and J2 = -0.43 cm-1 (S = 0) for complex 3 and J1 = -5.4 cm-1 and J2 = -0.4 cm-1 (S = 5/2) for complex 5 (using the H = -Sigma2JijSiSj convention). These results are consistent with X-band EPR measurements on these compounds.

  12. First-principles simulation of light propagation and exciton dynamics in metal cluster nanostructures

    Science.gov (United States)

    Lisinetskaya, Polina G.; Röhr, Merle I. S.; Mitrić, Roland

    2016-06-01

    We present a theoretical approach for the simulation of the electric field and exciton propagation in ordered arrays constructed of molecular-sized noble metal clusters bound to organic polymer templates. In order to describe the electronic coupling between individual constituents of the nanostructure we use the ab initio parameterized transition charge method which is more accurate than the usual dipole-dipole coupling. The electronic population dynamics in the nanostructure under an external laser pulse excitation is simulated by numerical integration of the time-dependent Schrödinger equation employing the fully coupled Hamiltonian. The solution of the TDSE gives rise to time-dependent partial point charges for each subunit of the nanostructure, and the spatio-temporal electric field distribution is evaluated by means of classical electrodynamics methods. The time-dependent partial charges are determined based on the stationary partial and transition charges obtained in the framework of the TDDFT. In order to treat large plasmonic nanostructures constructed of many constituents, the approximate self-consistent iterative approach presented in (Lisinetskaya and Mitrić in Phys Rev B 89:035433, 2014) is modified to include the transition-charge-based interaction. The developed methods are used to study the optical response and exciton dynamics of Ag3+ and porphyrin-Ag4 dimers. Subsequently, the spatio-temporal electric field distribution in a ring constructed of ten porphyrin-Ag4 subunits under the action of circularly polarized laser pulse is simulated. The presented methodology provides a theoretical basis for the investigation of coupled light-exciton propagation in nanoarchitectures built from molecular size metal nanoclusters in which quantum confinement effects are important.

  13. A study into the role of surface capping on energy transfer in metal cluster-semiconductor nanocomposites.

    Science.gov (United States)

    Bain, Dipankar; Paramanik, Bipattaran; Sadhu, Suparna; Patra, Amitava

    2015-12-28

    Metal cluster-semiconductor nanocomposite materials remain a frontier area of research for the development of optoelectronic, photovoltaic and light harvesting devices because metal nanoclusters and semiconductor QDs are promising candidates for photon harvesting. Here, we have designed well defined metal cluster-semiconductor nanostructures using different surface capped negatively charged Au25 nanoclusters (Au NCs) and positively charged cysteamine capped CdTe quantum dots using electrostatic interactions. The main focus of this article is to address the impact of surface capping agents on the photophysical properties of Au cluster-CdTe QD hybrid nanocomposites. Steady state and time resolved spectroscopic studies reveal that photoluminescence quenching, radiative and nonradiative rate, and energy transfer between Au nanoclusters and CdTe QDs have been influenced by the nature of the capping agent. We have calculated the energy transfer related parameters such as the overlap integral, distance between donor and acceptor, Förster distance, efficiency of energy transfer and rate of energy transfer from CdTe QDs to three different Au NCs. Photoluminescence quenching varies from 73% to 43% when changing the capping agents from bovine serum albumin (BSA) to glutathione (GSH). The efficiency of the energy transfer from CdTe QDs to BSA-capped Au NCs is found to be 83%, for Cys-capped Au NCs it was 46% and for GSH-capped Au NCs it was 35%. The efficiency depends on the number of Au clusters attached per QD. This reveals that the nature of capping ligands plays a crucial role in the energy transfer phenomena from CdTe QDs to Au NCs. Interesting findings reveal that the efficient energy transfer in metal cluster-semiconductor nanocomposites may open up new possibilities in designing artificial light harvesting systems for future applications.

  14. Electronic Structure of Transition Metal Clusters, Actinide Complexes and Their Reactivities

    Energy Technology Data Exchange (ETDEWEB)

    Krishnan Balasubramanian

    2009-07-18

    methods with all-electron Douglas-Kroll relativistic methods. We have the capabilities for computing full CI extrapolations including spin-orbit effects and several one-electron properties and electron density maps including spin-orbit effects. We are continuously collaborating with several experimental groups around the country and at National Labs to carry out computational studies on the DOE-BES funded projects. The past work in the last 3 years was primarily motivated and driven by the concurrent or recent experimental studies on these systems. We were thus significantly benefited by coordinating our computational efforts with experimental studies. The interaction between theory and experiment has resulted in some unique and exciting opportunities. For example, for the very first time ever, the upper spin-orbit component of a heavy trimer such as Au{sub 3} was experimentally observed as a result of our accurate computational study on the upper electronic states of gold trimer. Likewise for the first time AuH{sub 2} could be observed and interpreted clearly due to our computed potential energy surfaces that revealed the existence of a large barrier to convert the isolated AuH{sub 2} back to Au and H{sub 2}. We have also worked on yet to be observed systems and have made predictions for future experiments. We have computed the spectroscopic and thermodynamic properties of transition metal carbides transition metal clusters and compared our electronic states to the anion photodetachment spectra of Lai Sheng Wang. Prof Mike Morse and coworkers(funded also by DOE-BES) and Prof Stimle and coworkers(also funded by DOE-BES) are working on the spectroscopic properties of transition metal carbides and nitrides. Our predictions on the excited states of transition metal clusters such as Hf{sub 3}, Nb{sub 2}{sup +} etc., have been confirmed experimentally by Prof. Lombardi and coworkers using resonance Raman spectroscopy. We have also been studying larger complexes critical to the

  15. WIYN Open Cluster Study. LXXII. A uvbyCa Hbeta CCD Analysis of the Metal-Deficient Open Cluster, NGC 2506

    CERN Document Server

    Anthony-Twarog, B J; Twarog, B A

    2016-01-01

    Precision uvbyCa Hbeta photometry of the metal-deficient, old open cluster, NGC 2506, is presented. The survey covers an area 20 by 20 arcminutes, and extends to V~18 for b-y and Hbeta and to V~17.0 for c_1 and hk. For V < 16.0, photometric scatter among the indices leads to the recovery of 6 known variables within the cluster core and 5 new variables in the outer 5 arcmin of the survey field. Proper motions, radial velocities, and precise multicolor indices are used to isolate a highly probable sample of cluster members from the very rich color-magnitude diagram (CMD). From 257 highly probable members at the cluster turnoff, we derive a reddening estimate of E(b-y) = 0.042 +/- 0.001 (E(B-V) = 0.058 +/- 0.001), where the errors refer to the internal standard errors of the mean. [Fe/H] is derived from the A/F dwarf members using both m_1 and hk, leading to [Fe/H] = -0.296 +/- 0.011 (sem) and -0.317 +/- 0.004 (sem), respectively. The weighted average, heavily dominated by hk, is [Fe/H] = -0.316 +/- 0.033. Ba...

  16. Laser ablation source for formation and deposition of size-selected metal clusters.

    Science.gov (United States)

    Vucković, S; Svanqvist, M; Popok, V N

    2008-07-01

    This work describes construction of a source and optimisation of its parameters for production of cluster ion beams using material ablation by the second harmonic of a Nd:YAG laser (532 nm). The influence of different source parameters such as carrier gas pressure, laser power, delay time between gas, and laser pulses as well as nozzle configuration on the cluster formation are studied. For the current experiments the laser ablation cluster source was optimized for production of Con+ cluster ions. Clusters with n up to 150 atoms are registered by a time-of-flight mass spectrometer. Deposition of size-selected Co50+ clusters with kinetic energies in the interval of 250-4850 eV/cluster on highly ordered pyrolytic graphite is studied. At the highest impact energies the clusters are implanted. Craters and well-like structures can be seen by scanning tunneling microscopy at impact spots. A decrease in cluster kinetic energy leads to formation of bumplike structures which probably represent damaged graphite areas with incorporated Co atoms. Further decrease in the cluster impact energy to the level of 450-250 eV/cluster creates condition for so-called cluster pinning when the cluster constituents are intact but the energy transferred to the graphite is still enough to produce radiation defects to which the cluster is bound.

  17. New projectiles: multicharged metal clusters and biopolymers; De nouveaux projectiles, les agregats metalliques et les biopolymeres multicharges

    Energy Technology Data Exchange (ETDEWEB)

    Della-Negra, S.; Gardes, D.; Le Beyec, Y.; Waast, B.

    1991-12-31

    Metal clusters and molecules are the one mean to realize simultaneous impacts of several atoms on a reduced surface({approx}100A). The interaction characteristics is the non-linearity of energy deposition; the perturbation that the cluster produces, is above than the sum of the perturbation induced by its components, taken separately. The purpose of ORION project is to accelerate these new projectiles at ORSAY Tandem. The considered mass range is from 100 Daltons to 100 000 Daltons and energy range from MeV to GeV.

  18. Tesseract supersonic business transport

    Science.gov (United States)

    Reshotko, Eli; Garbinski, Gary; Fellenstein, James; Botting, Mary; Hooper, Joan; Ryan, Michael; Struk, Peter; Taggart, Ben; Taillon, Maggie; Warzynski, Gary

    1992-01-01

    This year, the senior level Aerospace Design class at Case Western Reserve University developed a conceptual design of a supersonic business transport. Due to the growing trade between Asia and the United States, a transpacific range was chosen for the aircraft. A Mach number of 2.2 was chosen, too, because it provides reasonable block times and allows the use of a large range of materials without a need for active cooling. A payload of 2,500 lbs. was assumed corresponding to a complement of nine passengers and crew, plus some light cargo. With these general requirements set, the class was broken down into three groups. The aerodynamics of the aircraft were the responsibility of the first group. The second developed the propulsion system. The efforts of both the aerodynamics and propulsion groups were monitored and reviewed for weight considerations and structural feasibility by the third group. Integration of the design required considerable interaction between the groups in the final stages. The fuselage length of the final conceptual design was 107.0 ft, while the diameter of the fuselage was 7.6 ft. The delta wing design consisted of an aspect ratio of 1.9 with a wing span of 47.75 ft and mid-chord length of 61.0 ft. A SNECMA MCV 99 variable-cycle engine design was chosen for this aircraft.

  19. Tesseract: Supersonic business transport

    Science.gov (United States)

    Reshotko, Eli; Garbinski, Gary

    1992-01-01

    This year, the senior level Aerospace Design class at Case Western Reserve University developed a conceptual design of a supersonic business transport. Due to the growing trade between Asia and the United States, a transpacific range has been chosen for the aircraft. A Mach number of 2.2 was chosen too because it provides reasonable block times and allows the use of a large range of materials without a need for active cooling. A payload of 2500 lbs. has been assumed corresponding to a complement of nine (passengers and crew) plus some light cargo. With these general requirements set, the class was broken down into three groups. The aerodynamics of the aircraft were the responsibility of the first group. The second developed the propulsion system. The efforts of both the aerodynamics and propulsion groups were monitored and reviewed for weight considerations and structural feasibility by the third group. Integration of the design required considerable interaction between the groups in the final stages. The fuselage length of the final conceptual design was 107.0 ft. while the diameter of the fuselage was 7.6 ft. The delta wing design consisted of an aspect ratio of 1.9 with a wing span of 47.75 ft and midcord length of 61.0 ft. A SNEMCA MCV 99 variable-cycle engine design was chosen for this aircraft.

  20. Variable stars in metal-rich globular clusters. IV. Long-period variables in NGC 6496

    Energy Technology Data Exchange (ETDEWEB)

    Abbas, Mohamad A. [Astronomisches Rechen-Institut, Zentrum für Astronomie der Universität Heidelberg, Mönchhofstr. 12-14, D-69120 Heidelberg (Germany); Layden, Andrew C.; Guldenschuh, Katherine A. [Physics and Astronomy Department, Bowling Green State University, Bowling Green, OH 43403 (United States); Reichart, D. E.; Ivarsen, K. M.; Haislip, J. B.; Nysewander, M. C.; LaCluyze, A. P. [Department of Physics and Astronomy, University of North Carolina, Chapel Hill, NC 27599 (United States); Welch, Douglas L., E-mail: mabbas@ari.uni-heidelberg.de, E-mail: laydena@bgsu.edu [Department of Physics and Astronomy, McMaster University, Hamilton, Ontario, L8 S 4M1 (Canada)

    2015-02-01

    We present VI-band photometry for stars in the metal-rich globular cluster NGC 6496. Our time-series data were cadenced to search for long-period variables (LPVs) over a span of nearly two years, and our variability search yielded the discovery of 13 new variable stars, of which 6 are LPVs, 2 are suspected LPVs, and 5 are short-period eclipsing binaries. An additional star was found in the ASAS database, and we clarify its type and period. We argue that all of the eclipsing binaries are field stars, while five to six of the LPVs are members of NGC 6496. We compare the period–luminosity distribution of these LPVs with those of LPVs in the Large Magellanic Cloud and 47 Tucanae, and with theoretical pulsation models. We also present a VI color–magnitude diagram, display the evolutionary states of the variables, and match isochrones to determine a reddening of E(B−V)= 0.21±0.02 mag and apparent distance modulus of 15.60±0.15 mag.

  1. Sputtering simulations of organic overlayers on metal substrates by monoatomic and clusters projectiles

    Energy Technology Data Exchange (ETDEWEB)

    Postawa, Z

    2004-06-15

    This paper reviews our recent work on computer simulations of monoatomic and cluster bombardment of metal and organic surfaces. The investigated surfaces are irradiated with keV monoatomic (C, Ar, Ga) and polyatomic (C{sub 60}) projectiles that are recognized as valuable sources for desorption of high mass particles in secondary ion and neutral mass spectrometry (SIMS/SNMS) experiments. The analysis of the results reveals that the C{sub 60} ion beam enables to perform chemical imaging with higher sensitivity, better depth resolution, and lower contamination than monoatomic projectiles with similar kinetic energy. For monoatomic projectiles, the development of a linear collision cascade is the predominant mechanism responsible for the ejection of particles. In contrast, strongly nonlinear, collective processes occur during C{sub 60} bombardment. These nonlinear processes lead to the enhanced removal of material and the formation of a macroscopic crater. This paper presents theoretical insight into possible mechanisms responsible for the observed behavior with the emphasis on the phenomena important to the SIMS/SNMS community.

  2. Supergalactic winds driven by multiple superstar clusters

    CERN Document Server

    Tenorio-Tagle, G; Muñoz-Tunón, C

    2003-01-01

    We present two dimensional hydrodynamic calculations of free expanding supergalactic winds, taking into consideration strong radiative cooling. Our main premise is that supergalactic winds are powered by collections of superstar clusters. Every individual superstar cluster is a source of a high metallicity radiative supersonic outflow (paper I, 2003, ApJ, 590, 791). The interaction of winds from neighboring knots of star formation is shown to lead to a collection of stationary oblique shocks and crossing shocks, able to structure the general outflow into a network of dense and cold, kpc long filaments that originate near the base of the outflow. The shocks also lead to extended regions of diffuse soft X-ray emission and furthermore, to channel the outflow with a high degree of collimation into the intergalactic medium.

  3. Size of the fragment for crystal cluster SCF-X/sub /-SW calculations of alkaline earth metal oxides

    Energy Technology Data Exchange (ETDEWEB)

    Lobach, V.A.; Sobolev, A.B.; Shul' gin, B.V.

    Calculation of (A/sub x/B/sub y/) (x=1, 13; y=6, 14) clusters, corresponding to ideal crystals of alkaline earth metal oxides (AEMO) MgO, CaO, SrO by means of molecular cluster (MC) and crystal cluster (CC) SCF-X/sub /-SW method is carried out. MC method is not suitable for description of ideal AEMO electron structure due to long-range Coulomb interaction and potential cluster effect. Even in CC method at x < 13 and y < 14 (A/sub x/B/sub y/) cluster nonstoichiometry is inhibitory to the obtaining of satisfactory agreement with the experimental optical and X-ray spectra. (A13B14) and (B13A14) clusters satisfactorily reproduce partial composition of valence band (VB) and conduction band (CB), VB and CB widths, a fine structure of oxygen K-emission spectra in MgO and also experimental distribution of electron density. Sphere radii variation effect on the value of intersphere region error with muffin-tin averaging is considered.

  4. Computer simulation structure and vibrations of small metal cluster on the Cu (111) surface

    Science.gov (United States)

    Borisova, Svetlana D.; Rusina, Galina G.

    2015-10-01

    Vibrational properties of the small tetrahedral cluster of Co on the Cu (111) surface are studied by using tight-binding second moment approximation interatomic interaction potentials. It was shown that interaction of the clusters with substrate leads to arising of frustrated translation and frustrated rotation in-plane polarized vibrational modes localized on the cluster atoms. The Co4 cluster on the surface the high frequency modes remain strongly localized and mixed with the nearest neighbor atoms vibrations.

  5. Computer simulation structure and vibrations of small metal cluster on the Cu (111) surface

    Energy Technology Data Exchange (ETDEWEB)

    Borisova, Svetlana D., E-mail: svbor@ispms.tsc.ru; Rusina, Galina G., E-mail: rusina@ispms.tsc.ru [Institute of Strength Physics and Materials Science SB RAS, Tomsk, 634055 (Russian Federation); National Research Tomsk State University, Tomsk 634050 (Russian Federation)

    2015-10-27

    Vibrational properties of the small tetrahedral cluster of Co on the Cu (111) surface are studied by using tight-binding second moment approximation interatomic interaction potentials. It was shown that interaction of the clusters with substrate leads to arising of frustrated translation and frustrated rotation in-plane polarized vibrational modes localized on the cluster atoms. The Co{sub 4} cluster on the surface the high frequency modes remain strongly localized and mixed with the nearest neighbor atoms vibrations.

  6. Supersonic Dislocation Bursts in Silicon

    Science.gov (United States)

    Hahn, E. N.; Zhao, S.; Bringa, E. M.; Meyers, M. A.

    2016-06-01

    Dislocations are the primary agents of permanent deformation in crystalline solids. Since the theoretical prediction of supersonic dislocations over half a century ago, there is a dearth of experimental evidence supporting their existence. Here we use non-equilibrium molecular dynamics simulations of shocked silicon to reveal transient supersonic partial dislocation motion at approximately 15 km/s, faster than any previous in-silico observation. Homogeneous dislocation nucleation occurs near the shock front and supersonic dislocation motion lasts just fractions of picoseconds before the dislocations catch the shock front and decelerate back to the elastic wave speed. Applying a modified analytical equation for dislocation evolution we successfully predict a dislocation density of 1.5 × 1012 cm-2 within the shocked volume, in agreement with the present simulations and realistic in regards to prior and on-going recovery experiments in silicon.

  7. Structure and property of metal melt Ⅲ—Relationship between kinematic viscosity and size of atomic clusters

    Institute of Scientific and Technical Information of China (English)

    POPEL; P; S; KONSTANTINOVA; N; Yu

    2010-01-01

    The method of crucible rotating oscillation damping was employed to measure the kinematic viscosity of aluminum melt,and the curve of viscosity v versus temperature T from 935 to 1383 K was obtained.Besides,based on the calculation model of the evolution behavior of atomic clusters in liquid structure,the curve of atomic clusters size d versus temperature was obtained,and the calculated results are in good agreement with the experimental values.By analyzing experimental data,it was found that both the viscosity and the size of atomic clusters of aluminum melt are monodrome functions of temperature,and the relation between v(T) and d(T) is a linear function,i.e.,v = v 0 + K·d(T).This relation indirectly verifies the calculation model of the structural information of metal melt,which is of great significance for studying the relation between melt microstructure and macro-physical properties.

  8. Structure and magnetic exchange in heterometallic 3d-3d transition metal triethanolamine clusters.

    Science.gov (United States)

    Langley, Stuart K; Chilton, Nicholas F; Moubaraki, Boujemaa; Murray, Keith S

    2012-01-21

    Synthetic methods are described that have resulted in the formation of seven heterometallic complexes, all of which contain partially deprotonated forms of the ligand triethanolamine (teaH(3)). These compounds are [Mn(III)(4)Co(III)(2)Co(II)(2)O(2)(teaH(2))(2)(teaH)(0.82)(dea)(3.18)(O(2)CMe)(2)(OMe)(2)](BF(4))(2)(O(2)CMe)(2)·3.18MeOH·H(2)O (1), [Mn(II)(2)Mn(III)(2)Co(III)(2)(teaH)(4)(OMe)(2)(acac)(4)](NO(3))(2)·2MeOH (2), [Mn(III)(2)Ni(II)(4)(teaH)(4)(O(2)CMe)(6)]·2MeCN (3), [Mn(III)(2)Co(II)(2)(teaH)(2)(sal)(2)(acac)(2)(MeOH)(2)]·2MeOH (4), [Mn(II)(2)Fe(III)(2)(teaH)(2)(paa)(4)](NO(3))(2)·2MeOH·CH(2)Cl(2) (5), [Mn(II)Mn(III)(2)Co(III)(2)O(teaH)(2)(dea)(Iso)(OMe)(F)(2)(Phen)(2)](BF(4))(NO(3))·3MeOH (6) and [Mn(II)(2)Mn(III)Co(III)(2)(OH)(teaH)(3)(teaH(2))(acac)(3)](NO(3))(2)·3CH(2)Cl(2) (7). All of the compounds contain manganese, combined with 3d transition metal ions such as Fe, Co and Ni. The crystal structures are described and examples of 'rods', tetranuclear 'butterfly' and 'triangular' Mn(3) cluster motifs, flanked in some cases by diamagnetic cobalt(III) centres, are presented. Detailed DC and AC magnetic susceptibility and magnetization studies, combined with spin Hamiltonian analysis, have yielded J values and identified the spin ground states. In most cases, the energies of the low-lying excited states have also been obtained. The features of note include the 'inverse butterfly' spin arrangement in 2, 4 and 5. A S = 5/2 ground state occurs, for the first time, in the Mn(III)(2)Mn(II) triangular moiety within 6, the many other reported [Mn(3)O](6+) examples having S = ½ or 3/2 ground states. Compound 7 provides the first example of a Mn(II)(2)Mn(III) triangle, here within a pentanuclear Mn(3)Co(2) cluster.

  9. Properties of Supersonic Evershed Downflows

    Science.gov (United States)

    Pozuelo, S. Esteban; Bellot Rubio, L. R.; de la Cruz Rodríguez, J.

    2016-12-01

    We study supersonic Evershed downflows in a sunspot penumbra by means of high spatial resolution spectropolarimetric data acquired in the Fe i 617.3 nm line with the CRISP instrument at the Swedish 1 m Solar Telescope. Physical observables, such as Dopplergrams calculated from line bisectors and Stokes V zero-crossing wavelengths, and Stokes V maps in the far red-wing, are used to find regions where supersonic Evershed downflows may exist. We retrieve the line-of-sight velocity and the magnetic field vector in these regions using two-component inversions of the observed Stokes profiles with the help of the SIR code. We follow these regions during their lifetime to study their temporal behavior. Finally, we carry out a statistical analysis of the detected supersonic downflows to characterize their physical properties. Supersonic downflows are contained in compact patches moving outward, which are located in the mid- and outer penumbra. They are observed as bright, roundish structures at the outer end of penumbral filaments that resemble penumbral grains. The patches may undergo fragmentations and mergings during their lifetime; some of them are recurrent. Supersonic downflows are associated with strong and rather vertical magnetic fields with a reversed polarity compared to that of the sunspot. Our results suggest that downflows returning back to the solar surface with supersonic velocities are abruptly stopped in dense deep layers and produce a shock. Consequently, this shock enhances the temperature and is detected as a bright grain in the continuum filtergrams, which could explain the existence of outward-moving grains in the mid- and outer penumbra.

  10. High Metallicity of the X-Ray Gas up to the Virial Radius of a Binary Cluster of Galaxies: Evidence of Galactic Superwinds at High-Redshift

    CERN Document Server

    Fujita, Yutaka; Hayashida, Kiyoshi; Takizawa, Motokazu; Matsumoto, Hironori; Okabe, Nobuhiro; Reiprich, Thomas H

    2007-01-01

    We present the analysis of a Suzaku observation of the link region between the galaxy clusters A399 and A401. We obtain the metallicity of the intracluster medium (ICM) up to the cluster virial radii for the first time. We determine the metallicity where the viral radii of the two clusters cross each other (~2 Mpc away from their centers) and find that it is comparable to that in their inner regions (~0.2 Z_sun). It is unlikely that the uniformity of metallicity up to the virial radii is due to mixing caused by a cluster collision. Since ram-pressure is too small to strip interstellar medium of galaxies around the virial radius of a cluster, the fairly high metallicity we found there indicates that the metals in the ICM are not transported from member galaxies by ram-pressure stripping. Instead, the uniformity suggests that the proto-cluster region was extensively polluted with metals by extremely powerful outflows (superwinds) from galaxies before the clusters formed. We also search for the oxygen emission f...

  11. Using Predefined M3(μ3-O) Clusters as Building Blocks for an Isostructural Series of Metal-Organic Frameworks.

    Science.gov (United States)

    Peng, Li; Asgari, Mehrdad; Mieville, Pascal; Schouwink, Pascal; Bulut, Safak; Sun, Daniel T; Zhou, Zhongrui; Pattison, Philip; van Beek, Wouter; Queen, Wendy L

    2017-07-19

    Metal-organic frameworks (MOFs) have attracted much attention in the past decade owing to their unprecedented internal surface areas, tunable topologies, designable surfaces, and various potential applications. One bottleneck in the field regarding MOF synthesis is controlling the metal-containing secondary building unit (SBU) incorporated into the structure. In this work we report the synthesis and characterization of five trimeric [M3(μ3-O)(CH3CO2)6](x) clusters (where M = Fe(3+), Cr(3+), Fe(3+)/Cr(3+), Fe(3+)/Co(2+), or Fe(3+)/Ni(2+) and x = +1 or 0). The monocarboxylate capping ligand, acetate in this case, readily undergoes exchange with several difunctional counterparts, including 1,4-benzenedicarboxylic acid (H2-BDC) and biphenyl-4,4'-dicarboxylic acid (H2-BPDC), for the formation of an isostructural series of MOFs, several of which are newly reported (for M = Fe(3+)/Cr(3+), Fe(3+)/Co(2+), and Fe(3+)/Ni(2+)) and show excellent CO2 adsorption properties. In this report, a host of techniques including NMR, ICP, and ESI-MS are used to probe the ligand exchange process and composition of the SBUs, and XAS is used to monitor the Fe(3+) and Cr(3+) environment throughout the reactions, giving strong evidence that the clusters stay intact throughout the MOF synthesis. This work reveals that predefined SBUs is an effective means to create metal-substituted analogues of known frameworks. Further, CO adsorption and in situ IR are used to probe accessibility of the metals after solvent removal. We show for the first time that the incorporation of the neutral clusters, containing weaker Lewis acids like Ni(2+) and Co(2+), can promote the formation of open metal sites in the MOF frameworks, structural features known to enhance the binding energy of small guest molecules like CO2.

  12. Low-temperature electronic transport in one-dimensional hybrid systems: Metal cluster embedded carbon nanotubes

    Science.gov (United States)

    Soldano, Caterina

    The investigation of the electronic and magnetotransport properties at low temperature in individual MWNT with embedded clusters are here presented. The majority of studies of transport in MWNT reported in literature has been carried out on arc-discharge grown tubes, generally considered "clean" and defect-free. In this project, individual MWNT grown in alumina template are used; these tubes are highly disordered compared for example to arc-discharge ones, conditions that dramatically will impact the charge transport. As-fabricated devices are in general highly resistive. A large decrease in the value of the device resistance can be achieved through a controlled and fast high-bias sweep method (HBT) across the sample. Scanning electron microscopy analysis shows that this method induces a metal (platinum) decoration of the MWNT surface as a consequence of the large amount of Joule heating developed during the sweep. Temperature dependence study (5wires. DFT calculations show that the enhancement in conductance can be explained in term of enhanced density of states around the Fermi energy due to presence of platinum on the wall. Magneto-transport measurements carried out up to a value of magnetic field up to |5|T show a clear dependence from the energy (i.e. applied bias). A nearly symmetric and monotonically increasing positive magneto-conductance is observed in the range of the applied field, confirming the presence of weak localization in the system. A small but distinct Rashba spin-orbit scattering effect in the magneto-conductance in the low-field regime (|B|<.5T) is found and attributed to the surface decoration. Electronic and magnetotransport measurements independently confirm the 1D nature of the transport in the system. "Zero-field" measurements were performed on magnetic cluster-embedded MWNT-based devices (FM-MWNT). Temperature dependence of the conductance reveals a Luttinger liquid type of behavior in the range of investigated temperatures but no

  13. SMC west halo: a slice of the galaxy that is being tidally stripped?. Star clusters trace age and metallicity gradients

    Science.gov (United States)

    Dias, B.; Kerber, L.; Barbuy, B.; Bica, E.; Ortolani, S.

    2016-06-01

    Context. The evolution and structure of the Magellanic Clouds is currently under debate. The classical scenario in which both the Large and Small Magellanic Clouds (LMC, SMC) are orbiting the Milky Way has been challenged by an alternative in which the LMC and SMC are in their first close passage to our Galaxy. The clouds are close enough to us to allow spatially resolved observation of their stars, and detailed studies of stellar populations in the galaxies are expected to be able to constrain the proposed scenarios. In particular, the west halo (WH) of the SMC was recently characterized with radial trends in age and metallicity that indicate tidal disruption. Aims: We intend to increase the sample of star clusters in the west halo of the SMC with homogeneous age, metallicity, and distance derivations to allow a better determination of age and metallicity gradients in this region. Positions are compared with the orbital plane of the SMC from models. Methods: Comparisons of observed and synthetic V(B-V) colour-magnitude diagrams were used to derive age, metallicity, distance, and reddening for star clusters in the SMC west halo. Observations were carried out using the 4.1 m SOAR telescope. Photometric completeness was determined through artificial star tests, and the members were selected by statistical comparison with a control field. Results: We derived an age of 1.23 ± 0.07 Gyr and [Fe/H] = -0.87 ± 0.07 for the reference cluster NGC 152, compatible with literature parameters. Age and metallicity gradients are confirmed in the WH: 2.6 ± 0.6 Gyr/° and -0.19 ± 0.09 dex/°, respectively. The age-metallicity relation for the WH has a low dispersion in metallicity and is compatible with a burst model of chemical enrichment. All WH clusters seem to follow the same stellar distribution predicted by dynamical models, with the exception of AM-3, which should belong to the counter-bridge. Brück 6 is the youngest cluster in our sample. It is only 130 ± 40 Myr old and

  14. Discovery of a Metal-Poor Field Giant with a Globular Cluster Second-Generation Abundance Pattern

    CERN Document Server

    Fernandez-Trincado, J G; Moreno, E; Schiavon, R P; Peréz, A E García; Vieira, K; Cunha, K; Zamora, O; Sneden, C; Carrera, R; Johnson, J A; Shetrone, M; Zasowski, G; García-Hernándes, D A; Majewski, S R; Reylé, C; Blanco-Cuaresma, S; Martinez-Medina, L A; Pérez-Villegas, A; Valenzuela, O; Pichardo, B; Meza, A; Mészáros, Sz; Sobeck, J; Geisler, D; Anders, F; Schultheis, M; Tang, B; Roman-Lopes, A; Mennickent, R E; Pan, K; Nitschelm, C; Allard, F

    2016-01-01

    We report on the direct detection from observations obtained with the APOGEE survey of a metal-poor ([Fe/H]$=-1.3$) field giant star in the Milky Way, with an extreme Mg-Al abundance ([Mg/Fe]$=$-0.31; [Al/Fe]$=$1.49) seen only among the secondary population of globular clusters. This star, 2M16011638-1201525 found using SDSSIII/APOGEE data also shows particularly atypical light-element patterns not seen among Galactic disk field stars, indicating that it could have been born in a globular cluster. We explore several explanations, in particular studying the orbit of the star to check the probability of it being related to known globular clusters. With the use of a Monte Carlo scheme, we performed simple orbital integrations assuming the estimated distance of 2M16011638-1201525 and the available six-dimensional phase-space coordinates of 63 globular clusters, looking for close encounters in the past with a minimum distance approach within the tidal radius for each cluster. We found a very low probability that 2...

  15. Thermochemistry and Dynamics of Reactive Species: Nitrogen-rich Compounds, Metals and SiC Clusters in Free and Solvated Environment

    Science.gov (United States)

    2005-10-31

    of Reactive Species : Nitrogen-rich F49620-02-1-0371 Compounds, Metals and SiC clusters in Free and Solvated Environments Sb. GRANT NUMBER 5c. PROGRAM...F49620-02-1-0371 Thermochemistry and Dynamics of Reactive Species : Nitrogen-rich Compounds, Metals, and SiC clusters in Free and Solvated Environments...research program remain the same as before: obtaining fundamental thermochemical and dynamical data on reactive species Status of Effort This report

  16. Comparison of the periodic slab approach with the finite cluster ansatz for metal-organic interfaces at the example of PTCDA on Ag(110)

    CERN Document Server

    Banerjee, Jaita; Galbraith, Martin C E; Mack, Hans-Georg; Settels, Volker; Engels, Bernd; Tonner, Ralf; Fink, Reinhold F

    2016-01-01

    We present a comparative study of metal-organic interface properties obtained from dispersion corrected density functional theory calculations based on two different approaches: the periodic slab supercell technique and cluster models with 18 to 290 Ag atoms. Fermi smearing and fixing of cluster borders are required to make the cluster calculation feasible and realistic. The considered adsorption structure and energy of a PTCDA molecule on the Ag(110) surface is not well reproduced with clusters containing only two metallic layers. However, clusters with four layers of silver atoms and sufficient lateral extension reproduce the adsorbate structure within 0.02 \\AA\\ and adsorption energies within 10\\% of the slab result. A consideration of the computational effort shows that the cluster approach is a competitive alternative to methods using periodic boundary conditions and of particular interest for research at surface defects and other systems that do not show periodic symmetry.

  17. Properties of Supersonic Evershed Downflows

    CERN Document Server

    Pozuelo, Sara Esteban; Rodriguez, Jaime de la Cruz

    2016-01-01

    We study supersonic Evershed downflows in a sunspot penumbra by means of high spatial resolution spectropolarimetric data acquired in the Fe I 617.3 nm line with the CRISP instrument at the Swedish 1-m Solar Telescope. Physical observables, such as Dopplergrams calculated from line bisectors and Stokes V zero-crossing wavelengths, and Stokes V maps in the far red wing, are used to find regions where supersonic Evershed downflows may exist. We retrieve the LOS velocity and the magnetic field vector in these regions using two-component inversions of the observed Stokes profiles with the help of the SIR code. We follow these regions during their lifetime to study their temporal behavior. Finally, we carry out a statistical analysis of the detected supersonic downflows to characterize their physical properties. Supersonic downflows are contained in compact patches moving outward, which are located in the mid and outer penumbra. They are observed as bright, roundish structures at the outer end of penumbral filamen...

  18. The Evolution of the Intracluster Medium Metallicity in Sunyaev-Zel'dovich-Selected Galaxy Clusters at 0 < z < 1.5

    CERN Document Server

    McDonald, M; de Haan, T; Miller, E D; Benson, B A; Bleem, L E; Brodwin, M; Carlstrom, J E; Chiu, I; Forman, W R; Hlavacek-Larrondo, J; Garmire, G P; Gupta, N; Mohr, J J; Reichardt, C L; Saro, A; Stalder, B; Stark, A A; Vieira, J D

    2016-01-01

    We present the results of an X-ray spectral analysis of 153 galaxy clusters observed with the Chandra, XMM-Newton, and Suzaku space telescopes. These clusters, which span 0 = 0.23 +/- 0.01 Zsun and a scatter of 0.08 +/- 0.01 Zsun. These results imply that >60% of the metals in the ICM were already in place at z=1 (at 95% confidence), consistent with the picture of an early (z>1) enrichment. We find, in agreement with previous works, a significantly higher mean value for the metallicity in the centers of cool core clusters versus non-cool core clusters. We find weak evidence for evolution in the central metallicity of cool core clusters (dZ/dz = -0.21 +/- 0.11 Zsun), which is sufficient to account for this enhanced central metallicity over the past ~10 Gyr. We find no evidence for metallicity evolution outside of the core (dZ/dz = -0.03 +/- 0.06 Zsun), and no significant difference in the core-excised metallicity between cool core and non-cool core clusters. This suggests that strong radio-mode AGN feedback d...

  19. Covalent Metal-Metal-Bonded Mn4 Tetrahedron Inscribed within a Four-Coordinate Manganese Cubane Cluster, As Evidenced by Unexpected Temperature-Independent Diamagnetism.

    Science.gov (United States)

    Vaddypally, Shivaiah; Jovinelli, Daniel J; McKendry, Ian G; Zdilla, Michael J

    2017-04-03

    The electronic structures of the manganese(IV) cubane cluster Mn(μ3-N(t)Bu)4(N(t)Bu)4 (1) and its one-electron-oxidized analogue, the 3:1 Mn(IV)/Mn(V) cluster [Mn(μ3-N(t)Bu)4(N(t)Bu)4](+)[PF6](-) (1(+)[PF6]), are described. The S = 0 spin quantum number of 1 is explained by a diamagnetic electronic structure where all metal-based d electrons are paired in Mn-Mn bonding orbitals. Temperature- and power-dependent studies of the S = (1)/2 electron paramagnetic resonance signal of 1(+) are consistent with an electronic structure described as a delocalized one-electron radical.

  20. Oxidation of nanostructured Ti films produced by low energy cluster beam deposition: An X-ray Photoelectron Spectroscopy characterization

    Energy Technology Data Exchange (ETDEWEB)

    Simone, Monica de, E-mail: desimone@tasc.infm.it [CNR-IOM Laboratorio TASC, Area Science Park Basovizza, 34149 Trieste (Italy); Snidero, Elena [CNR-IOM Laboratorio TASC, Area Science Park Basovizza, 34149 Trieste (Italy); Coreno, Marcello [CNR-IMIP, c/o Laboratorio TASC Area Science Park Basovizza, 34149 Trieste (Italy); Sincrotrone Trieste ScpA, Area Science Park Basovizza, 34149 Trieste (Italy); Bongiorno, Gero [Fondazione Filarete, v.le Ortles 22/4, 20139 Milano (Italy); Giorgetti, Luca [Istituto Europeo di Oncologia, Dip. di Oncologia Sperimentale, Via Adamello 16, 20139, Milano (Italy); Amati, Matteo [Sincrotrone Trieste ScpA, Area Science Park Basovizza, 34149 Trieste (Italy); Cepek, Cinzia [CNR-IOM Laboratorio TASC, Area Science Park Basovizza, 34149 Trieste (Italy)

    2012-05-01

    We used in-situ X-ray Photoelectron Spectroscopy (XPS) to study the oxidation process of a cluster-assembled metallic titanium film exposed to molecular oxygen at room temperature. The nanostructured film has been grown on a Si(111) substrate, in ultra high vacuum conditions, by coupling a supersonic cluster beam deposition system with an XPS experimental chamber. Our results show that upon in-situ oxygen exposure Ti{sup 3+} is the first oxidation state observed, followed by Ti{sup 4+}, whereas Ti{sup 2+} is practically absent during the whole process. Our results compare well with the existing literature on Ti films produced using other techniques.

  1. Hartree-Fock Cluster Study of Interstitial Transition Metals in Silicon

    NARCIS (Netherlands)

    Broer, R.; Aissing, G.; Nieuwpoort, W.C.; Feiner, L.F.

    1986-01-01

    Results are presented of a Hartree-Fock cluster study of interstitial Ti, V, Cr, and Mn impurities in silicon. A Si10 cluster models the nearest Si atoms around a tetrahedral interstitial site in crystalline Si. The dangling bonds of the Si atoms are saturated by hydrogens. The effect of the Si core

  2. Hartree-Fock Cluster Study of Interstitial Transition Metals in Silicon

    NARCIS (Netherlands)

    Broer, R.; Aissing, G.; Nieuwpoort, W.C.; Feiner, L.F.

    Results are presented of a Hartree-Fock cluster study of interstitial Ti, V, Cr, and Mn impurities in silicon. A Si10 cluster models the nearest Si atoms around a tetrahedral interstitial site in crystalline Si. The dangling bonds of the Si atoms are saturated by hydrogens. The effect of the Si core

  3. Molecular dynamics simulations of the structural and dynamic properties of graphite-supported bimetallic transition metal clusters

    Science.gov (United States)

    Sankaranarayanan, Subramanian K. R. S.; Bhethanabotla, Venkat R.; Joseph, Babu

    2005-11-01

    Molecular dynamics simulations were carried out for Pd-Pt , Pd-Rh , and Pd-Cu nanoclusters supported on a static graphite substrate using the quantum Sutton-Chen potential for the metal-metal interactions. The graphite substrate was represented as layers of fixed carbons sites and modeled with the Lennard-Jones potential model. Metal-graphite interaction potentials obtained by fitting experimental cohesive energies were utilized. Monte Carlo simulations employing the bond order simulation model were used to generate initial configurations. The melting temperatures for bimetallic nanoclusters of varying composition were estimated based on variations in thermodynamic properties such as potential energy and heat capacity. Melting transition temperatures were found to decrease with increasing Cu (for Pd-Cu ) and Pd (for Pd-Pt and Pd-Rh ) concentrations and are at least 100to200K higher than those of the same-sized free clusters. Density distributions perpendicular to the surface and components of the velocity autocorrelation functions in the plane of the surface indicate that one of the metals in the bimetallic nanoclusters wets the graphite surface more, and that this weak graphite substrate is able to structure the melted fluid in the first few monolayers. The wetting characteristics are dictated by the delicate balance between metal-metal and metal-graphite interactions. Components of velocity-autocorrelation functions characterizing diffusion of constituent atoms in these bimetallics suggest greater out-of-plane movement, which increases with Cu (for Pd-Cu ) and Pd (for Pd-Rh and Pd-Pt ) concentrations. Deformation parameters showed that the core (Pd in Pd-Cu , Rh in Pd-Rh and Pt in Pd-Pt ) atoms diffuse out and the surface-segregated (Cu in Pd-Cu , Pd in Pd-Rh and Pd-Pt ) atoms diffuse into the nanoclusters upon melting. Near linear dependence of melting temperature on composition was found for unsupported clusters in our recent work, which results from the

  4. Structure investigation of metal ions clustering in dehydrated gel using x-ray anomalous dispersion effect

    CERN Document Server

    Soejima, Y; Sugiyama, M; Annaka, M; Nakamura, A; Hiramatsu, N; Hara, K

    2003-01-01

    The structure of copper ion clusters in dehydrated N-isopropylacrylamide/sodium acrylate (NIPA/SA) gel has been studied by means of small angle X-ray scattering (SAXS) method. In order to distinguish the intensity scattered by Cu ions, the X-ray anomalous dispersion effect around the Cu K absorption edge has been coupled with SAXS. It is found that the dispersion effect dependent on the incident X-ray energy is remarkable only at the momentum transfer q = 0.031 A sup - sup 1 , where a SAXS peak is observed. The results indicate that copper ions form clusters in the dehydrated gel, and that the mean size of clusters is the same as that of SA clusters produced by microphase separation. It is therefore naturally presumed that copper ions are adsorbed into the SA molecules. On the basis of the presumption, a mechanism is proposed for microphase-separation and clustering of Cu ions.

  5. Deriving Metallicities From the Integrated Spectra of Extragalactic Globular Clusters Using the Near-Infrared Calcium Triplet

    CERN Document Server

    Foster, Caroline; Proctor, Robert N; Strader, Jay; Brodie, Jean P; Spitler, Lee R

    2010-01-01

    The Ca triplet (CaT) feature in the near-infrared has been employed as a metallicity indicator for individual stars as well as integrated light of Galactic globular clusters (GCs) and galaxies with varying degrees of success, and sometimes puzzling results. Using the DEIMOS multi-object spectrograph on Keck we obtain a sample of 144 integrated light spectra of GCs around the brightest group galaxy NGC 1407 to test whether the CaT index can be used as a metallicity indicator for extragalactic GCs. Different sets of single stellar population models make different predictions for the behavior of the CaT as a function of metallicity. In this work, the metallicities of the GCs around NGC 1407 are obtained from CaT index values using an empirical conversion. The measured CaT/metallicity distributions show unexpected features, the most remarkable being that the brightest red and blue GCs have similar CaT values despite their large difference in mean color. Suggested explanations for this behavior in the NGC 1407 GC ...

  6. Health risk assessment of heavy metals in soils and vegetables from wastewater irrigated area, Beijing-Tianjin city cluster, China

    Institute of Scientific and Technical Information of China (English)

    Yanchun Wang; Min Qiao; Yunxia Liu; Yongguan Zhu

    2012-01-01

    The possible health risks of heavy metals contamination to local population through food chain were evaluated in Beijing and Tianjin city cluster,China,where have a long history of sewage irrigation.The transfer factors (TF) for heavy metals from soil to vegetables for six elements including Cu,Zn,Pb,Cr,As and Cd were calculated and the pollution load indexes (PLI) were also assessed.Results indicate that only Cd exceeded the maximum acceptable limit in these sites.So far,the heavy metal concentrations in soils and vegetables were all below the permissible limits set by the Ministry of Environmental Protection of China and World Health Organization.The transfer factors of six heavy metals showed the trend as Cd > Zn > Cu > Pb > As > Cr,which were dependent on the vegetable species.The estimated dietary intakes of Cu,Zn,Pb,Cr,As and Cd were far below the tolerable limits and the target hazard quotient (THQ) values were less than 1,which suggested that the health risks of heavy metals exposure through consuming vegetables were generally assumed to be safe.

  7. Hydrogen storage on metal oxide model clusters using density-functional methods and reliable van der Waals corrections.

    Science.gov (United States)

    Gebhardt, Julian; Viñes, Francesc; Bleiziffer, Patrick; Hieringer, Wolfgang; Görling, Andreas

    2014-03-21

    We investigate the capability of low-coordinated sites on small model clusters to act as active centers for hydrogen storage. A set of small magic clusters with the formula (XY)6 (X = Mg, Ba, Be, Zn, Cd, Na, Li, B and Y = O, Se, S, F, I, N) and a "drumlike" hexagonal shape showing a low coordination number of three was screened. Oxide clusters turned out to be the most promising candidates for hydrogen storage. For these ionic compounds we explored the suitability of different van der Waals (vdW) corrections to density-functional calculations by comparing the respective H2 physisorption profile to highly accurate CCSD(T) (Coupled Cluster Singles Doubles with perturbative Triples) calculations. The Grimme D3 vdW correction in combination with the Perdew-Burke-Ernzerhof exchange-correlation functional was found to be the best approach compared to CCSD(T) hydrogen physisorption profiles and is, therefore, suited to study these and other light metal oxide systems. H2 adsorption on sites of oxide model clusters is found to meet the adsorption energy criteria for H2 storage, with bond strengths ranging from 0.15 to 0.21 eV. Energy profiles and estimates of kinetic constants for the H2 splitting reaction reveal that H2 is likely to be adsorbed molecularly on sites of (MgO)6, (BaO)6, and (BeO)6 clusters, suggesting a rapid H2 uptake/release at operating temperatures and moderate pressures. The small mass of beryllium and magnesium makes such systems appealing for meeting the gravimetric criterion for H2 storage.

  8. Real-time study of the adiabatic energy loss in an atomic collision with a metal cluster.

    Science.gov (United States)

    Baer, Roi; Siam, Nidal

    2004-10-01

    Gas-phase hydrogen atoms are accelerated towards metallic surfaces in their vicinity. As it approaches the surface, the velocity of an atom increases and this motion excites the metallic electrons, causing energy loss to the atom. This dissipative dynamics is frequently described as atomic motion under friction, where the friction coefficient is obtained from ab initio calculations assuming a weak interaction and slow atom. This paper tests the aforementioned approach by comparing to a real-time Ehrenfest molecular dynamics simulation of such a process. The electrons are treated realistically using standard approximations to time-dependent density functional theory. We find indeed that the electronic excitations produce a friction-like force on the atom. However, the friction coefficient strongly depends on the direction of the motion of the atom: it is large when the atom is moving towards the cluster and much smaller when the atom is moving away. It is concluded that a revision of the model for energy dissipation at metallic surfaces, at least for clusters, may be necessary.

  9. The red giant branches of Galactic globular clusters in the [(V-I)o,Mv] plane metallicity indices and morphology

    CERN Document Server

    Saviane, I; Piotto, G; Aparicio, A; Saviane, Ivo; Rosenberg, Alfred; Piotto, Giampaolo; Aparicio, Antonio

    2000-01-01

    The purpose of this study is to carry out a thorough investigation of the changes in morphology of the red giant branch (RGB) of Galactic globular clusters (GGC) as a function of metallicity, in the V,I bands. To this aim, two key points are developed in the course of the analysis. (a) Using our photometric V,I database for Galactic globular clusters (the largest homogeneous data sample to date; Rosenberg et al. 1999) we measure a complete set of metallicity indices, based on the morphology and position of the red-giant branch. In particular, we provide here the first calibration of the S, DV_(1.1) and DV_(1.4) indices in the (V-I,V) plane. We show that our indices are internally consistent, and we calibrate each index in terms of metallicity, both on the Zinn & West (1984) and the Carretta & Gratton (1997) scales. Our new calibrations of the (V-I)o,g, DV_(1.2), (V-I)_(-3.0) and (V-I)_(-3.5) indices are consistent with existing relations. (b) Using a grid of selected RGB fiducial points, we define a f...

  10. Dodecanuclear 3d/4f-metal clusters with a 'Star of David' topology: single-molecule magnetism and magnetocaloric properties.

    Science.gov (United States)

    Alexandropoulos, Dimitris I; Cunha-Silva, Luís; Lorusso, Giulia; Evangelisti, Marco; Tang, Jinkui; Stamatatos, Theocharis C

    2016-01-28

    A family of interwoven molecular inorganic knots, shaped like the 'Star of David', was prepared by the employment of naphthalene-2,3-diol in 3d/4f-metal cluster chemistry; the isoskeletal dodecanuclear compounds exhibit slow relaxation of the magnetization and magnetocaloric properties, depending on the metal ion.

  11. A New View of the Super Star Clusters in the Low-Metallicity Galaxy SBS 0335-052

    CERN Document Server

    Reines, Amy E; Hunt, Leslie K

    2008-01-01

    We present a study of the individual super star clusters (SSCs) in the low-metallicity galaxy SBS 0335-052 using new near-infrared and archival optical Hubble Space Telescope observations. The physical properties of the SSCs are derived from fitting model spectral energy distributions (SEDs) to the optical photometry, as well as from the H_alpha and Pa_alpha nebular emission. Among the clusters, we find a significant age spread that is correlated with position in the galaxy, suggesting successive cluster formation occurred in SBS 0335-052 triggered by a large-scale disturbance traveling through the galaxy at a speed of ~35 km/s. The SSCs exhibit I-band (~0.8 um) and near-IR (~1.6-2.1 um) excesses with respect to model SEDs fit to the optical data. We hypothesize that the I-band excess is dominated by a photoluminescent process known as Extended Red Emission; however, this mechanism cannot account for the excesses observed at longer near-IR wavelengths. From the cluster SEDs and colors, we find that the primar...

  12. High rate deposition system for metal-cluster/SiO x C y H z -polymer nanocomposite thin films

    Science.gov (United States)

    Peter, T.; Rehders, S.; Schürmann, U.; Strunskus, T.; Zaporojtchenko, V.; Faupel, F.

    2013-06-01

    A system for deposition of nanocomposite materials consisting of a SiO x C y H z -polymer matrix and Ag nanoclusters is presented. Ag nanoclusters with sizes between 2 and 20 nm are produced in a gas aggregation cluster source and are deposited through a focused beam at a high rate. This cluster source is presented in detail and the characteristics of the produced nanoclusters are shown. Simultaneously, a SiO x C y H z -polymer matrix is grown from the precursor hexamethyldisiloxane in an RF plasma. The beam of clusters is deposited into the growing polymer, forming the composite material. This process allows the rapid deposition of composite material with varying metal nanocluster concentrations and properties. Since the cluster generation is separated from the matrix growth, the properties of both can be controlled independently. In this study, we present two types of nanocomposite samples, in the first the Ag nanoclusters are homogeneously distributed in the matrix, in the second type the Ag nanoclusters form a layer which is covered by the matrix. These samples are investigated using transmission electron micrography to determine the morphology. Furthermore, the optical properties are probed using optical transmission spectroscopy and the plasmonic resonance behavior is discussed.

  13. Metal-cluster-decorated TiO2 nanotube arrays: a composite heterostructure toward versatile photocatalytic and photoelectrochemical applications.

    Science.gov (United States)

    Xiao, Fang-Xing; Hung, Sung-Fu; Miao, Jianwei; Wang, Hsin-Yi; Yang, Hongbin; Liu, Bin

    2015-02-04

    Recent years have witnessed increasing interest in the solution-phase synthesis of atomically precise thiolate-protected gold clusters (Aux ); nonetheless, research on the photocatalytic properties of Aux -semiconductor nanocomposites is still in its infancy. In this work, recently developed glutathione-capped gold clusters and highly ordered nanoporous layer-covered TiO2 nanotube arrays (NP-TNTAs) are employed as nanobuilding blocks for the construction of a well-defined Aux /NP-TNTA heterostructure via a facile electrostatic self-assembly strategy. Versatile photocatalytic performances of the Aux /NP-TNTA heterostructure which acts as a model catalyst, including photocatalytic oxidation of organic pollutant, photocatalytic reduction of aromatic nitro compounds and photoelectrochemical (PEC) water splitting under simulated solar light irradiation, are systematically exploited. It is found that synergistic interaction stemming from monodisperse coverage of Aux clusters on NP-TNTAs in combination with hierarchical nanostructure of NP-TNTAs reinforce light absorption of Aux /NP-TNTA heterostructure especially within visible region, hence contributing to the significantly enhanced photocatalytic and PEC water splitting performances. Moreover, photocatalytic and PEC mechanisms over Aux /NP-TNTA heterostructure are elucidated and corresponding reaction models were presented. It is anticipated that this work could boost new insight for photocatalytic properties of metal-cluster-sensitized semiconductor nanocomposites. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  14. A theoretical analysis of bi-metallic (Cu–Agn = 1 − 7 nano alloy clusters invoking DFT based descriptors

    Directory of Open Access Journals (Sweden)

    Ranjan Prabhat

    2015-12-01

    Full Text Available Due to its large scale applications in the real field, the study of bi-metallic nano-alloy clusters is an active field of research. Though a number of experimental reports are available in this domain, a deep theoretical insight is yet to receive. Among several nano-clusters, the compound formed between Cu–Ag has gained a large importance due to its remarkable optical property. Density Functional Theory (DFT is one of the most popular approaches of quantum mechanics to study the electronic properties of materials. Conceptually, DFT based descriptors have turned to be indispensable tools for analyzing and correlating the experimental properties of compounds. In this venture, we have analyzed the experimental properties of the (Cu–Agn = 1 − 7 nano-alloy clusters invoking DFT methodology. A nice correlation has been found between optical properties of the aforesaid nano-clusters with our evaluated theoretical descriptors. The similar agreement between experimental bond length and computed data is also reflected in this analysis. Beside these, the effect of even-odd alternation behavior of nano compounds on the HOMO-LUMO gap is very important in our computation. It is probably the first attempt to establish such type of correlation.

  15. Phase transition temperatures of 405-725 K in superfluid ultra-dense hydrogen clusters on metal surfaces

    Science.gov (United States)

    Holmlid, Leif; Kotzias, Bernhard

    2016-04-01

    Ultra-dense hydrogen H(0) with its typical H-H bond distance of 2.3 pm is superfluid at room temperature as expected for quantum fluids. It also shows a Meissner effect at room temperature, which indicates that a transition point to a non-superfluid state should exist above room temperature. This transition point is given by a disappearance of the superfluid long-chain clusters H2N(0). This transition point is now measured for several metal carrier surfaces at 405 - 725 K, using both ultra-dense protium p(0) and deuterium D(0). Clusters of ordinary Rydberg matter H(l) as well as small symmetric clusters H4(0) and H3(0) (which do not give a superfluid or superconductive phase) all still exist on the surface at high temperature. This shows directly that desorption or diffusion processes do not remove the long superfluid H2N(0) clusters. The two ultra-dense forms p(0) and D(0) have different transition temperatures under otherwise identical conditions. The transition point for p(0) is higher in temperature, which is unexpected.

  16. Galaxy Clusters with Chandra

    CERN Document Server

    Forman, W; Markevitch, M L; Vikhlinin, A A; Churazov, E

    2002-01-01

    We discuss Chandra results related to 1) cluster mergers and cold fronts and 2) interactions between relativistic plasma and hot cluster atmospheres. We describe the properties of cold fronts using NGC1404 in the Fornax cluster and A3667 as examples. We discuss multiple surface brightness discontinuities in the cooling flow cluster ZW3146. We review the supersonic merger underway in CL0657. Finally, we summarize the interaction between plasma bubbles produced by AGN and hot gas using M87 and NGC507 as examples.

  17. Switching Plasmons: Gold Nanorod-Copper Chalcogenide Core-Shell Nanoparticle Clusters with Selectable Metal/Semiconductor NIR Plasmon Resonances.

    Science.gov (United States)

    Muhammed, Madathumpady Abubaker Habeeb; Döblinger, Markus; Rodríguez-Fernández, Jessica

    2015-09-16

    Exerting control over the near-infrared (NIR) plasmonic response of nanosized metals and semiconductors can facilitate access to unexplored phenomena and applications. Here we combine electrostatic self-assembly and Cd(2+)/Cu(+) cation exchange to obtain an anisotropic core-shell nanoparticle cluster (NPC) whose optical properties stem from two dissimilar plasmonic materials: a gold nanorod (AuNR) core and a copper selenide (Cu(2-x)Se, x ≥ 0) supraparticle shell. The spectral response of the AuNR@Cu2Se NPCs is governed by the transverse and longitudinal plasmon bands (LPB) of the anisotropic metallic core, since the Cu2Se shell is nonplasmonic. Under aerobic conditions the shell undergoes vacancy doping (x > 0), leading to the plasmon-rich NIR spectrum of the AuNR@Cu(2-x)Se NPCs. For low vacancy doping levels the NIR optical properties of the dually plasmonic NPCs are determined by the LPBs of the semiconductor shell (along its major longitudinal axis) and of the metal core. Conversely, for high vacancy doping levels their NIR optical response is dominated by the two most intense plasmon modes from the shell: the transverse (along the shortest transversal axis) and longitudinal (along the major longitudinal axis) modes. The optical properties of the NPCs can be reversibly switched back to a purely metallic plasmonic character upon reversible conversion of AuNR@Cu(2-x)Se into AuNR@Cu2Se. Such well-defined nanosized colloidal assemblies feature the unique ability of holding an all-metallic, a metallic/semiconductor, or an all-semiconductor plasmonic response in the NIR. Therefore, they can serve as an ideal platform to evaluate the crosstalk between plasmonic metals and plasmonic semiconductors at the nanoscale. Furthermore, their versatility to display plasmon modes in the first, second, or both NIR windows is particularly advantageous for bioapplications, especially considering their strong absorbing and near-field enhancing properties.

  18. Quantum size correction to the work function and the centroid of excess charge in positively ionized simple metal clusters

    Directory of Open Access Journals (Sweden)

    M. Payami

    2003-12-01

    Full Text Available  In this work, we have shown the important role of the finite-size correction to the work function in predicting the correct position of the centroid of excess charge in positively charged simple metal clusters with different values . For this purpose, firstly we have calculated the self-consistent Kohn-Sham energies of neutral and singly-ionized clusters with sizes in the framework of local spin-density approximation and stabilized jellium model (SJM as well as simple jellium model (JM with rigid jellium. Secondly, we have fitted our results to the asymptotic ionization formulas both with and without the size correction to the work function. The results of fittings show that the formula containing the size correction predict a correct position of the centroid inside the jellium while the other predicts a false position, outside the jellium sphere.

  19. Electronic spectroscopy and electronic structure of the smallest metal clusters: the diatomic 3D transition metal aluminides

    Science.gov (United States)

    Behm, Jane M.; Morse, Michael D.

    1994-06-01

    A systematic study of the electronic spectroscopy, electronic structure, and chemical bonding has been initiated for the 3d series of diatomic transition metal aluminides. This report provides a review of the progress to date, with specific emphasis on AlCa, AlV, AlCr, AlMn, AlCo, AlNi, AlCu, and AlZn.

  20. ROLE OF C AND P SITES ON THE CHEMICAL ACTIVITY OF METAL CARBIDE AND PHOSPHIDES: FROM CLUSTERS TO SINGLE-CRYSTAL SURFACES

    Energy Technology Data Exchange (ETDEWEB)

    RODRIGUEZ,J.A.; VINES, F.; LIU, P.; ILLAS, F.

    2007-07-01

    Transition metal carbides and phosphides have shown tremendous potential as highly active catalysts. At a microscopic level, it is not well understood how these new catalysts work. Their high activity is usually attributed to ligand or/and ensemble effects. Here, we review recent studies that examine the chemical activity of metal carbide and phosphides as a function of size, from clusters to extended surfaces, and metal/carbon or metal/phosphorous ratio. These studies reveal that the C and P sites in these compounds cannot be considered as simple spectators. They moderate the reactivity of the metal centers and provide bonding sites for adsorbates.

  1. Validation and Verification the Expanded Table for Transition Metal Carbonyl and Main Group Element Cluster Series which obey the 18-Electron and 8-Electron (octet Rules respectively

    Directory of Open Access Journals (Sweden)

    Enos Masheija Kiremire

    2014-12-01

    Full Text Available The transition metal carbonyl clusters and Main group element clusters belong to natural series based on the number theory. The number series of the cluster series have been generated using the empirical formula k = ½ (E-V where k represents the linkages or bonds that glue together the cluster elements which obey the eighteen electron rule or the octet rule and E is related to the sum of eighteen electrons or the eight electrons and V is the sum of the valence electrons. An expanded cluster table been constructed to accommodate the analysis of medium to relatively large clusters of high nuclearity. Using the knowledge of k-value and the cluster table it is possible for a given cluster formula to be categorized into its type of series and its geometry deduced. This is relatively easy for simple to medium clusters. It is hoped that this simple approach to be adapted to categorize and deduce structures of clusters with high nuclearity. This approach to clusters using number theory will complement the existing clusters theories such as Wade-Mingos rules1-7, Jemmismno rules8-9 and topology rules10.

  2. Insights into the chemical composition of the metal-poor Milky Way halo globular cluster NGC 6426

    Science.gov (United States)

    Hanke, M.; Koch, A.; Hansen, C. J.; McWilliam, A.

    2017-03-01

    We present our detailed spectroscopic analysis of the chemical composition of four red giant stars in the halo globular cluster NGC 6426. We obtained high-resolution spectra using the Magellan2/MIKE spectrograph, from which we derived equivalent widths and subsequently computed abundances of 24 species of 22 chemical elements. For the purpose of measuring equivalent widths, we developed a new semi-automated tool, called EWCODE. We report a mean Fe content of [Fe/H] =-2.34 ± 0.05 dex (stat.) in accordance with previous studies. At a mean α-abundance of [(Mg, Si, Ca)/3 Fe] = 0.39 ± 0.03 dex, NGC 6426 falls on the trend drawn by the Milky Way halo and other globular clusters at comparably low metallicities. The distribution of the lighter α-elements as well as the enhanced ratio [Zn/Fe] = 0.39 dex could originate from hypernova enrichment of the pre-cluster medium. We find tentative evidence for a spread in the elements Mg, Si, and Zn, indicating an enrichment scenario, where ejecta of evolved massive stars of a slightly older population have polluted a newly born younger one. The heavy element abundances in this cluster fit well into the picture of metal-poor globular clusters, which in that respect appear to be remarkably homogeneous. The pattern of the neutron-capture elements heavier than Zn points toward an enrichment history governed by the r-process with little, if any, sign of s-process contributions. This finding is supported by the striking similarity of our program stars to the metal-poor field star HD 108317. This paper includes data gathered with the 6.5-m Magellan Telescopes located at Las Campanas Observatory, Chile.Equivalent widths and full Table 2 are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/599/A97

  3. Quantum-chemical Calculations of the Adsorption of CO on the Metal Oxide Clusters

    National Research Council Canada - National Science Library

    E.A. Koblova; A.Yu. Ustinov; O.L. Shcheka

    2016-01-01

    The geometric, energetic, spectral and electronic properties of the most stable clusters of the aluminum, nickel and copper oxides with the adsorbed CO molecule have been studied using Density Functional Theory...

  4. Mode conversion of Mie plasmons at the surface of metallic atomic clusters

    Science.gov (United States)

    El-Khawaldeh, A.; Kull, H.-J.

    2017-04-01

    The dynamics of the Mie plasmon is described in the framework of the self-consistent quantum Vlasov theory by a reduced single-state model. The single-state model is validated by many-electron calculations for Na clusters. In this framework, collisionless damping of the Mie plasmon can be investigated for a wide range of cluster parameters by linear perturbation theory. The characteristic scaling of the damping rate with the inverse cluster radius is demonstrated. The basic damping mechanism of the Mie plasmon can be explained by a conversion of surface modes into volume modes due to the scattering by the self-consistent potential of the electron-electron interaction at the cluster boundary.

  5. Reactions of Laser Ablated Metal Plasma with Molecular Alcohol Beams: Dependence of the Produced Cluster Ion Species on the Beam Condition

    Institute of Scientific and Technical Information of China (English)

    NIU Dong-Mei; LI Hai-Yang; ZHANG Shu-Dong

    2006-01-01

    The gas phase reactions of metal plasma with alcohol clusters were studied by time of flight mass spectrometry(TOFMS) using laser ablation-molecular beam (LAMB) method. The significant dependence of the product cluster ions on the molecular beam conditions was observed. When the plasma acted on the low density parts of the pulsed molecular beam, the metal-alcohol complexes M+An (M=Cu, Al, Mg, Ni and A=C2H5OH, CH3OH) were the dominant products, and the sizes of product ion clusters were smaller. While the plasma acted on the high density part of the beam, however, the main products turned to be protonated alcohol clusters H+An and, as the reactions of plasma with methanol were concerned, the protonated water-methanol complexes H3O+(CH3OH)n with a larger size(n≤ 12 for ethanol and n≤24 for methanol). Similarly, as the pressure of the carrier helium gas was varied from1 × 105 to 5 × 105 Pa, the main products were changed from M+An to H+An and the sizes of the clusters also increased. The changes in the product clusters were attributed to the different formation mechanism of the output ions,that is, the M+An ions came from the reaction of metal ion with alcohol clusters, while H+An mainly from collisional reaction of electron with alcohol clusters.

  6. Quantum Monte Carlo study of one-dimensional transition metal organometallic cluster systems and their suitability as spin filters

    CERN Document Server

    Horváthová, L; Mitas, L; Štich, I

    2014-01-01

    We present calculations of electronic and magnetic structures of vanadium-benzene multidecker clusters V$_{n}$Bz$_{n+1}$ ($n$ = 1 - 3) using advanced quantum Monte Carlo methods. These and related systems have been identified as prospective spin filters in spintronic applications, assuming that their ground states are half-metallic ferromagnets. Although we find that magnetic properties of these multideckers are consistent with ferromagnetic coupling, their electronic structures do not appear to be half-metallic as previously assumed. In fact, they are ferromagnetic insulators with large and broadly similar $\\uparrow$-/$\\downarrow$-spin gaps. This makes the potential of these and related materials as spin filtering devices very limited, unless they are further modified or functionalized.

  7. Combination of lacunary polyoxometalates and high-nuclear transition metal clusters under hydrothermal conditions: IX. a series of novel polyoxotungstates sandwiched by octa-copper clusters.

    Science.gov (United States)

    Zhao, Jun-Wei; Wang, Chun-Mei; Zhang, Jie; Zheng, Shou-Tian; Yang, Guo-Yu

    2008-01-01

    The reaction of CuCl(2).2 H2O with trivacant Keggin polyoxoanions K8Na2[A-alpha-GeW9O34].25 H2O or K10[A-alpha-SiW9O34].25 H2O in the presence of 1,2-diaminopropane (dap), ethylenediamine (en) or 2,2'-bipyridine (2,2'-bpy) under hydrothermal conditions afforded five novel hybrid inorganic-organic octa-Cu sandwiched polyoxotungstates (POTs): H4[CuII8(dap)4(H2O)2(B-alpha-GeW9O34)2].13 H2O (1), (H2en)2[CuII8-(en)4(H2O)2(B-alpha-GeW9O34)2].5 H2O(2), (H2en)2[CuII8(en)4(H2O)2(B-alpha-SiW9-O34)2].8 H2O (3), [CuII(H2O)2]H2[CuII8-(en)4(H2O)2(B-alpha-SiW9O34)2] (4), and [CuII2(H2O)2(2,2'-bpy)2]{[CuII(bdyl)]2-[CuII8(2,2'-bpy)4(H2O)2(B-alpha-GeW9-O34)2]}.4 H2O (bdyl=2,2'-bipyridinyl)(5). Additionally, CuCl(2).2 H2O reacts with the mixture of GeO2, Na2WO(4).2 H2O, H2SiW12O(40).2 H2O in the presence of 2,2'-bpy and 4,4'-bpy under hydrothermal conditions leading to another novel mixed-valent octa-Cu sandwiched POT hybrid: [CuI(2,2'-bpy)(4,4'-bpy)]2[{CuI2(2,2'-bpy)2(4,4'-bpy)]2[CuI2CuII6(2,2'-bpy)2(4,4'-bpy)2(B-alpha-GeW9O34)2}].2 H2O (6). 1, 2, and 3 are discrete dimers constructed from two trivacant Keggin [B-alpha-XW9O34]10- (X=GeIV/SiIV) fragments and an octa-Cu cluster whereas 4 displays the 3D (3,6)-connected nets with (4.6(2))(4(2).6(4).8(7).10(2)) topology, which are built by octa-Cu sandwiched polyoxometalate building blocks through copper cation bridges. 5 is a novel 2D layer based on octa-Cu sandwiched POT clusters and [CuII2(bdyl)] units. Interestingly, the rollover metalation of 2,2'-bpy is firstly observed in the system containing the copper complex under hydrothermal conditions. 6 is a discrete mixed-valent octa-Cu sandwiched POT supported by two CuI-complexes [CuI2-(2,2'-bpy)2(4,4'-bpy)]2+ through 4,4'-bpy bridges, which constructs a novel dodeca-copper cluster. Notably, the octa-Cu cluster in 6 is mixed-valent and is different from those in 1-5. To our knowledge, 1-6 represent a rare family of POTs incorporating novel octa-nuclear transition-metal clusters in

  8. The Evolution of the Intracluster Medium Metallicity in Sunyaev Zel’dovich-selected Galaxy Clusters at 0 > z > 1.5

    Science.gov (United States)

    McDonald, M.; Bulbul, E.; de Haan, T.; Miller, E. D.; Benson, B. A.; Bleem, L. E.; Brodwin, M.; Carlstrom, J. E.; Chiu, I.; Forman, W. R.; Hlavacek-Larrondo, J.; Garmire, G. P.; Gupta, N.; Mohr, J. J.; Reichardt, C. L.; Saro, A.; Stalder, B.; Stark, A. A.; Vieira, J. D.

    2016-08-01

    We present the results of an X-ray spectral analysis of 153 galaxy clusters observed with the Chandra, XMM-Newton, and Suzaku space telescopes. These clusters, which span 0 =0.23+/- 0.01 Z ⊙ and a scatter of σ Z = 0.08 ± 0.01 Z ⊙. These results imply that the emission-weighted metallicity has not changed by more than 40% since z = 1 (at 95% confidence), consistent with the picture of an early (z > 1) enrichment. We find, in agreement with previous works, a significantly higher mean value for the metallicity in the centers of cool core clusters versus non-cool core clusters. We find weak evidence for evolution in the central metallicity of cool core clusters (dZ/dz = -0.21 ± 0.11 Z ⊙), which is sufficient to account for this enhanced central metallicity over the past ˜10 Gyr. We find no evidence for metallicity evolution outside of the core (dZ/dz = -0.03 ± 0.06 Z ⊙), and no significant difference in the core-excised metallicity between cool core and non-cool core clusters. This suggests that strong radio-mode active galactic nucleus feedback does not significantly alter the distribution of metals at r\\gt 0.15{R}500. Given the limitations of current-generation X-ray telescopes in constraining the ICM metallicity at z > 1, significant improvements on this work will likely require next-generation X-ray missions.

  9. Supersonic Chordwise Bending Flutter in Cascades

    Science.gov (United States)

    1975-05-31

    such a flutter boundary can be made by utilizing the trend lines predicted from a supersonic analysis based on supersonic cascade theory (Appendix I...bonding agent was injected via hypodermic needles after the blade tabs were properly inserted, The integrity and repeatability of the mounting of the indi...in conjunction with NASTRAN predictions and supersonic cascade aerodynamic computa- tions. Comparisons between theory and experiment are discussed. DD

  10. The Herschel Virgo Cluster Survey. IX. Dust-to-gas mass ratio and metallicity gradients in four Virgo spiral galaxies

    CERN Document Server

    Magrini, Laura; Corbelli, Edvige; Cortese, Luca; Hunt, Leslie; Smith, Matthew; Vlahakis, Catherine; Davies, Jonathan; Bendo, George J; Baes, Maarten; Boselli, Alessandro; Clemens, Marcel; Casasola, Viviana; De Looze, Ilse; Fritz, Jacopo; Giovanardi, Carlo; Grossi, Marco; Hughes, Thomas; Madden, Suzanne; Pappalardo, Ciro; Pohlen, Michael; Alighieri, Sperello di Serego; Verstappen, Joris

    2011-01-01

    Using Herschel data from the Open Time Key Project the Herschel Virgo Cluster Survey (HeViCS), we investigated the relationship between the metallicity gradients expressed by metal abundances in the gas phase as traced by the chemical composition of HII regions, and in the solid phase, as traced by the dust-to-gas mass ratio. We derived the radial gradient of the dust-to-gas mass ratio for all galaxies observed by HeViCS whose metallicity gradients are available in the literature. They are all late type Sbc galaxies, namely NGC4254, NGC4303, NGC4321, and NGC4501. We examined different dependencies on metallicity of the CO-to-H$_2$ conversion factor (\\xco), used to transform the $^{12}$CO observations into the amount of molecular hydrogen. We found that in these galaxies the dust-to-gas mass ratio radial profile is extremely sensitive to choice of the \\xco\\ value, since the molecular gas is the dominant component in the inner parts. We found that for three galaxies of our sample, namely NGC4254, NGC4321, and N...

  11. Clear evidence for the presence of second-generation asymptotic giant branch stars in metal-poor Galactic globular clusters

    CERN Document Server

    Garcia-Hernandez, D A; Monelli, M; Cassisi, S; Stetson, P B; Zamora, O; Shetrone, M; Lucatello, S

    2015-01-01

    Galactic globular clusters (GCs) are known to host multiple stellar populations: a first generation with a chemical pattern typical of halo field stars and a second generation (SG) enriched in Na and Al and depleted in O and Mg. Both stellar generations are found at different evolutionary stages (e.g., the main-sequence turnoff, the subgiant branch, and the red giant branch). The non detection of SG asymptotic giant branch (AGB) stars in several metal-poor ([Fe/H] < -1) GCs suggests that not all SG stars ascend the AGB phase, and that failed AGB stars may be very common in metal-poor GCs. This observation represents a serious problem for stellar evolution and GC formation/evolution theories. We report fourteen SG-AGB stars in four metal-poor GCs (M 13, M 5, M 3, and M 2) with different observational properties: horizontal branch (HB) morphology, metallicity, and age. By combining the H-band Al abundances obtained by the APOGEE survey with ground-based optical photometry, we identify SG Al-rich AGB stars in...

  12. Supersonic flow imaging via nanoparticles

    Institute of Scientific and Technical Information of China (English)

    2009-01-01

    Due to influence of compressibility,shock wave,instabilities,and turbulence on supersonic flows, current flow visualization and imaging techniques encounter some problems in high spatiotemporal resolution and high signal-to-noise ratio(SNR)measurements.Therefore,nanoparticle based planar laser scattering method(NPLS)is developed here.The nanoparticles are used as tracer,and pulse planar laser is used as light source in NPLS;by recording images of particles in flow field with CCD, high spatiotemporal resolution supersonic flow imaging is realized.The flow-following ability of nanoparticles in supersonic flows is studied according to multiphase flow theory and calibrating experiment of oblique shock wave.The laser scattering characteristics of nanoparticles are analyzed with light scattering theory.The results of theoretical and experimental studies show that the dynamic behavior and light scattering characteristics of nanoparticles highly enhance the spatiotemporal resolution and SNR of NPLS,with which the flow field involving shock wave,expansion,Mach disk,boundary layer,sliding-line,and mixing layer can be imaged clearly at high spatiotemporal resolution.

  13. THE X-RAY LUMINOSITY FUNCTION OF LOW MASS X-RAY BINARIES IN EARLY-TYPE GALAXIES, THEIR METAL-RICH, AND METAL-POOR GLOBULAR CLUSTERS

    Energy Technology Data Exchange (ETDEWEB)

    Peacock, Mark B.; Zepf, Stephen E., E-mail: mpeacock@msu.edu [Department of Physics and Astronomy, Michigan State University, East Lansing, MI 48824 (United States)

    2016-02-10

    We present the X-ray luminosity function (XLF) of low-mass X-ray binaries (LMXBs) in the globular clusters (GCs) and fields of seven early-type galaxies. These galaxies are selected to have both deep Chandra observations, which allow their LMXB populations to be observed to X-ray luminosities of 10{sup 37}–10{sup 38} erg s{sup −1}, and Hubble Space Telescope optical mosaics that enable the X-ray sources to be separated into field LMXBs, GC LMXBs, and contaminating background and foreground sources. We find that at all luminosities the number of field LMXBs per stellar mass is similar in these galaxies. This suggests that the field LMXB populations in these galaxies are not effected by the GC specific frequency, and that properties such as binary fraction and the stellar initial mass function are either similar across the sample or change in a way that does not affect the number of LMXBs. We compare the XLF of the field LMXBs to that of the GC LMXBs and find that they are significantly different with a p-value of 3 × 10{sup −6} (equivalent to 4.7σ for a normal distribution). The difference is such that the XLF of the GC LMXBs is flatter than that of the field LMXBs, with the GCs hosting relatively more bright sources and fewer faint sources. A comparison of the XLF of the metal-rich and metal-poor GCs hints that the metal-poor clusters may have more bright LMXBs, but the difference is not statistically significant.

  14. Surface plasmons in quantum-sized noble-metal clusters: TDDFT quantum calculations and the classical picture of charge oscillations.

    Science.gov (United States)

    Weissker, Hans-Christian; López-Lozano, Xóchitl

    2015-11-14

    The localized surface-plasmon resonance of metal nanoparticles corresponds to a classical charge oscillation of the quasi-free conduction electrons. In the case of noble-metal nanoparticles, interband transitions from the d electrons influence the spectra strongly. In addition, the inhomogeneity of the nanoparticles at the atomistic level becomes important for small sizes. Using the time-evolution formulation of time-dependent density-functional theory, we show that in spherical 147-atom silver clusters, the localized surface-plasmon resonance corresponds indeed to a collective charge oscillation resembling the schematic picture, while the dynamics in a comparable gold cluster shows multiple modes which correspond to the spectra without strong resonance. Short nanorods show the same difference between Au and Ag. However, nanorods of high aspect ratio develop a silver-like charge oscillation. Monatomic silver chains behave similarly to the nanorods and show a clear transverse charge oscillation mode. The role of the d electrons in the screening of the localized surface-plasmon resonance is demonstrated.

  15. Stability and structure of metal clusters - Be(13) and Be(55)

    Science.gov (United States)

    Pettersson, Lars G. M.; Bauschlicher, Charles W., Jr.

    1986-01-01

    Face-centered cubic (fcc) and hexagonally close-packed (hcp) structures are compared for Be(13) and Be(55) clusters. Both Be(13) and Be(55) prefer the fcc structure over the bulk hcp structure, but the energy difference per atom decreases for Be(55) relative to Be(13). The binding energy per atom, 1.3 eV for Be(55) and 0.8-0.9 eV for Be(13), reflects the greater total number of bonds in the larger cluster rather than a difference in bonding. The energies per bond are much more similar, in the range of 0.30-0.34 eV for both clusters. The size of the p-basis set used influences both stability and ionization potentials strongly.

  16. Mass distribution of cluster ions produced from laser ablation of metal-composite-oxides Y-M-Cu-O (M = Ba, Sr, Ca, Mg)

    Energy Technology Data Exchange (ETDEWEB)

    Liu Zhaoyang; Wang Chunru; Huang Rongbin; Zheng Lansun [Xiamen Univ. (China). Dept. of Chem.

    1995-09-01

    Laser ablation of YMCuO metal-composite-oxides (M = Ba, Sr, Ca, Mg) in high vacuum produced cluster ions with various sizes and compositions. Mass spectra of the cluster ions were recorded by a home-built time-of-flight (TOF) mass spectrometer and the mass distributions were analyzed by a statistical model. For YBa{sub 2}Cu{sub 3}O{sub 7-x} (YBCO) high-Tc superconducting samples, six series of cluster ions were observed. Replacement of barium in the metal-composite-oxide sample with other alkaline earth metal, such as strontium, calcium, or magnesium, not only removed the superconductivity, but also changed the compositions and distributions of the laser generated cluster ions. For instance, copper was only found in the compositions of cluster ions generated from YBCO sample. From comparison of the experimental results, interactions among components of the metal-composite-oxides and the function of alkaline earth metal in superconducting material were discussed. (orig.) 19 refs.

  17. Density functional study of structural and catalytic properties of free and supported metal nano cluster; Dichtefunktionalstudie der strukturellen und katalytischen Eigenschaften freier und getraegerter Metallnanocluster

    Energy Technology Data Exchange (ETDEWEB)

    Huber, B.

    2007-04-11

    The structural and catalytic properties of metal clusters were determined in the framework of density functional theory. The first part of this work investigates the electronic and geometrical structure of sodium clusters with up to 309 atoms. The ground-state structures of the clusters are determined and the corresponding electronic density of states is compared to experimental photoelectron spectras. The excellent agreement to the experimental results indicates that the correct growth motive of the sodium clusters was found. Small clusters from Na{sup -}{sub 20} to Na{sup -}{sub 42} prefer pentagonal and icosahedral structures with anti-Mackay overlayers, while clusters larger than Na{sup -}{sub 50} prefer icosahedral structures with Mackay overlayers. Clusters between the closed-shell Mackay Clusters often exhibit a twist deformation with respect to the regular Mackay positions. The second part of this work investigates the catalytic properties of free and supported palladium clusters. For both cases the oxidation of small Pd{sub N} clusters (N {<=} 9) was studied. It turned out that MgO supported Pd-clusters dissociate oxygen with a significant lower reaction energy than free clusters or supported systems with particles consisting of several thousands of atoms. The reaction with oxygen transforms the non-crystalline Pd-clusters into crystalline Pd{sub x}O{sub y} nano-oxide clusters that are in epitaxy with the underlying support. Simulations of the CO oxidation on the Pd{sub x}O{sub y} cluster predict a low-temperature reaction mechanism. By calculating the electronic density of states and CO stretch frequencies, different ways of verifying the results experimentally are discussed. (orig.)

  18. On the applicability of deformed jellium model to the description of metal clusters

    DEFF Research Database (Denmark)

    Lyalin, Andrey G.; Matveentsev, Anton; Solov'yov, Ilia;

    2003-01-01

    This work is devoted to the elucidation the applicability of jellium model to the description of alkali cluster properties on the basis of comparison the jellium model results with those derived from experiment and within ab initio theoretical framework. On the basis of the Hartree-Fock and local......-density approximation deformed jellium model we have calculated the binding energies per atom, ionization potentials, deformation parameters and the optimized values of the Wigner-Seitz radii for neutral and singly charged sodium clusters with the number of atoms $N0$. These characteristics are compared...

  19. Mononuclear Clusterfullerene Single‐Molecule Magnet Containing Strained Fused‐Pentagons Stabilized by a Nearly Linear Metal Cyanide Cluster

    Science.gov (United States)

    Liu, Fupin; Wang, Song; Gao, Cong‐Li; Deng, Qingming; Zhu, Xianjun; Kostanyan, Aram; Westerström, Rasmus; Jin, Fei

    2017-01-01

    Abstract Fused‐pentagons results in an increase of local steric strain according to the isolated pentagon rule (IPR), and for all reported non‐IPR clusterfullerenes multiple (two or three) metals are required to stabilize the strained fused‐pentagons, making it difficult to access the single‐atom properties. Herein, we report the syntheses and isolations of novel non‐IPR mononuclear clusterfullerenes MNC@C76 (M=Tb, Y), in which one pair of strained fused‐pentagon is stabilized by a mononuclear cluster. The molecular structures of MNC@C76 (M=Tb, Y) were determined unambiguously by single‐crystal X‐ray diffraction, featuring a non‐IPR C 2v(19138)‐C76 cage entrapping a nearly linear MNC cluster, which is remarkably different from the triangular MNC cluster within the reported analogous clusterfullerenes based on IPR‐obeying C82 cages. The TbNC@C76 molecule is found to be a field‐induced single‐molecule magnet (SMM). PMID:28079303

  20. High-resolution abundance analysis of red giants in the metal-poor bulge globular cluster HP~1

    CERN Document Server

    Barbuy, B; Vemado, A; Ernandes, H; Ortolani, S; Saviane, I; Bica, E; Minniti, D; Dias, B; Momany, Y; Hill, V; Zoccali, M; Siqueira-Mello, C

    2016-01-01

    The globular cluster HP~1 is projected at only 3.33 degrees from the Galactic center. Together with its distance, this makes it one of the most central globular clusters in the Milky Way. It has a blue horizontal branch (BHB) and a metallicity of [Fe/H]~-1.0. This means that it probably is one of the oldest objects in the Galaxy. Abundance ratios can reveal the nucleosynthesis pattern of the first stars as well as the early chemical enrichment and early formation of stellar populations. High-resolution spectra obtained for six stars were analyzed to derive the abundances of the light elements C, N, O, Na, and Al, the alpha-elements Mg, Si, Ca, and Ti, and the heavy elements Sr, Y , Zr, Ba, La, and Eu.} High-resolution spectra of six red giants that are confirmed members of the bulge globular cluster HP~1 were obtained with the 8m VLT UT2-Kueyen telescope with the UVES spectrograph in FLAMES-UVES configuration. The spectroscopic parameter derivation was based on the excitation and ionization equilibrium of FeI...

  1. Graphene-supported small transition-metal clusters: A density functional theory investigation within van der Waals corrections

    Science.gov (United States)

    Rêgo, Celso R. C.; Tereshchuk, Polina; Oliveira, Luiz N.; Da Silva, Juarez L. F.

    2017-06-01

    Transition-metal nanoparticles adsorbed on graphene are of great interest due to the unique catalytic and magnetic properties resulting from nanoparticles-graphene interactions. Comparison between the physical properties of such systems and those of the same nanoparticles in the gas phase is especially important. Here we report a systematic density functional investigation of the structural, energetic, and magnetic properties of small Nin, Pdn, and Ptn clusters, comprising from n =1 to 6 atoms, in the gas phase and adsorbed on a graphene monolayer. Our results show that the Ni adatom binds to the graphene hollow site, with -1.47 -meV adsorption energy, while Pd and Pt prefer the bridge sites, with -1.14 - and -1.62 -meV adsorption energies, respectively. This difference is determined by a competition between quantum and classical forces. Ni2 and Pt2 dimers bind perpendicularly on hollow and bridge sites, respectively, while Pd2 lies parallel to the graphene sheet, with each adatom on a bridge site. For larger TMn (TM = Ni , Pd , Pt ; n =3 -6 ) clusters, either two or three atoms bind to bridge graphene sites. In almost all cases the adsorbed clusters retain their gas-phase structures. The exceptions are Ni5 and Pt4, which acquire more compact structures with effective coordination number 12 and 19 % larger than in the gas phase, respectively. As the number of atoms grows, the cluster binds more weakly to the graphene, while its binding energy mounts up. Van der Waals corrections to the plain density functional theory (DFT) total energy raise the adsorption energy, but leave the cluster structure unchanged, in the gas phase or upon adsorption. Bader charge analysis shows that adsorption causes minor charge redistribution: the TM atoms bound to C atoms become positively charged, while the remaining metal atoms acquire negative charge. We have derived an approximate analytical expression for the local densities of states for the d orbitals of Ni , Pd , and Pt adatoms

  2. Formation of Fe Cluster Superlattice in a Metal-Organic Quantum-Box Network

    OpenAIRE

    Pivetta, Marina; Pacchioni, Giulia E.; Schlickum, Uta; Barth, Johannes V.; Brune, Harald

    2013-01-01

    We report on the self-assembly of Fe adatoms on a Cu(111) surface that is patterned by a metal-organic honeycomb network, formed by coordination of dicarbonitrile pentaphenyl molecules with Cu adatoms. Fe atoms landing on the metal surface are mobile and steered by the quantum confinement of the surface state electrons towards the center of the network hexagonal cavities. In cavities hosting more than one Fe, preferential interatomic distances are observed. The adatoms in each hexagon aggrega...

  3. Suzaku and XMM-Newton Observations of the Fornax cluster: Temperature and Metallicity Distribution

    CERN Document Server

    Murakami, Hideyoshi; Matsushita, Kyoko; Nagino, Ryo; Sato, Takuya; Sato, Kosuke; Kawaharada, Madoka; Nakazawa, Kazuhiro; Ohashi, Takaya; Takei, Yoh

    2011-01-01

    Suzaku observed a central region and five offset regions within 0.2 r180 in the Fornax cluster, a nearby poor cluster, and XMM-Newton mapped the cluster with 15 pointings out to 0.3 r180. The distributions of O, Mg, Si, S, and Fe in the intracluster medium (ICM) were studied with Suzaku, and those of Fe and temperature were studied with XMM. The temperature of the ICM gradually decreases with radius from 1.3 keV at 0.04 r180 to 1 keV at 0.2-0.3 r180. If the new solar abundances of Lodders et al. (2003) and a single-temperature plasma model are adopted, O, Mg, Si, S, and Fe show similar abundances: 0.4-0.6 solar within 0.02-0.2 r180. This Fe abundance is similar to those at 0.1-0.2 r180 in rich clusters and other groups of galaxies. At 0.2-0.3 r180, the Fe abundance becomes 0.2-0.3 solar. A two-temperature plasma model yields ICM abundances that are higher by a factor of 1.2-1.5, but gives similar abundance ratios among O, Mg, Si, S, and Fe. The northern region has a lower ICM temperature and higher brightness...

  4. Investigation of Catalytic Finite-Size-Effects of Platinum Metal Clusters

    DEFF Research Database (Denmark)

    Li, Lin; Larsen, Ask Hjorth; Romero, Nichols A.

    2012-01-01

    In this paper, we use density functional theory (DFT) calculations on highly parallel computing resources to study size-dependent changes in the chemical and electronic properties of platinum (Pt) for a number of fixed freestanding clusters ranging from 13 to 1415 atoms, or 0.7–3.5 nm in diameter...

  5. Electron Correlations on a Mesoscopic Scale : Magnetic Properties of Transition Metal Telluride Cluster Compounds

    NARCIS (Netherlands)

    Palstra, T.T.M.; Steigerwald, M.L.; Ramirez, A.P.; Kwon, Y.-U.; Stuczynski, S.M.; Schneemeyer, L.F.; Waszczak, J.V.; Zaanen, J.

    1993-01-01

    We report the magnetic properties of a new class of materials: Ni9Te6n+ and Co6Te8n+ with n=0,1,2. These cluster compounds, which can be charged by chemical means from neutral to 2+, provide a unique and novel way to change the Fermi level. For most charge states we observe quenching of the spin and

  6. Stabilization of Metal Ensembles at Room Temperature: Palladium Clusters in Zeolites.

    NARCIS (Netherlands)

    Koningsberger, D.C.; Möller, K.; Bein, T.

    1989-01-01

    Palladium clusters of low nuclearity have been prepared in the cavities of X zeolites via ion exchange with Pd(NH,),Cl,, oxidative dehydration, and subsequent reduction of the dry Pd(I1) zeolites with hydrogen at 295 and 425 K. Detailed EXAFS analysis of Pd K-edge data shows that the average first-s

  7. Chemical Bonding of Transition-Metal Co13 Clusters with Graphene.

    Science.gov (United States)

    Alonso-Lanza, Tomás; Ayuela, Andrés; Aguilera-Granja, Faustino

    2015-12-01

    We carried out density functional calculations to study the adsorption of Co13 clusters on graphene. Several free isomers were deposited at different positions with respect to the hexagonal lattice nodes, allowing us to study even the hcp 2d isomer, which was recently obtained as the most stable one. Surprisingly, the Co13 clusters attached to graphene prefer icosahedron-like structures in which the low-lying isomer is much distorted; in such structures, they are linked with more bonds than those reported in previous works. For any isomer, the most stable position binds to graphene by the Co atoms that can lose electrons. We find that the charge transfer between graphene and the clusters is small enough to conclude that the Co-graphene binding is not ionic-like but chemical. Besides, the same order of stability among the different isomers on doped graphene is kept. These findings could also be of interest for magnetic clusters on graphenic nanostructures such as ribbons and nanotubes.

  8. Collision induced fragmentation dynamics of small metallic clusters; Dynamique de fragmentation induite par collision de petits agregats metalliques

    Energy Technology Data Exchange (ETDEWEB)

    Picard, Y

    1999-04-15

    The goal of this work is the complete analysis of the fragmentation of alkali clusters (Na{sub n}{sup +} (n < 10), NaK{sup +} and K{sub 2}{sup +}) induced by collision with light atomic (He) or molecular (H{sub 2}) targets. The main point is to study how the energy is transmitted to the cluster during the collision and how this energy is shared among the various degrees of freedom of the system and leads to its fragmentation. Two types of interactions govern the collision induced dissociation processes: on one hand, the electronic mechanisms where the target perturbs the electronic cloud and brings the molecule into a dissociative state, and on the other hand, the impulsive mechanisms where the momentum transferred to the atomic cores leads to the rotational-vibrational dissociation of the molecule. The experimental procedure is based on the measurement of the velocity vectors of the outgoing fragments detected in coincidence. This allows to reconstruct the full kinematics of the fragmentation and to separate and characterize for the first time the two types of interactions. The two basic mechanisms of collision induced dissociation are then clearly resolved for the diatomic molecule Na{sub 2}{sup +}. For the heteronuclear molecular ion NaK{sup +}, it is shown that the dissociation process is due to a combination of electronic and impulsive mechanisms in some of the dissociation pathways. The extension to the study of metallic clusters Na{sub n}{sup +} (n < 10) fragmentation shows the role and the relative importance of the electronic and impulsive mechanisms and their evolution with the cluster size. The complete analysis of Na{sub 3}{sup +} multi-fragmentation is also presented. (author)

  9. FRACTAL PATTERN GROWTH OF METAL ATOM CLUSTERS IN ION IMPLANTED POLYMERS

    Institute of Scientific and Technical Information of China (English)

    ZHANG TONG-HE; WU YU-GUANG; SANG HAI-BO; ZHOU GU

    2001-01-01

    The fractal and multi-fractal patterns of metal atoms are observed in the surface layer and cross section of a metal ion implanted polymer using TEM and SEM for the first time. The surface structure in the metal ion implanted polyethylene terephthalane (PET) is the random fractal. Certain average quantities of the random geometric patterns contain self-similarity. Some growth origins appeared in the fractal pattern which has a dimension of 1.67. The network structure of the fractal patterns is formed in cross section, having a fractal dimension of 1.87. So it can be seen that the fractal pattern is three-dimensional space fractal. We also find the collision cascade fractal in the cross section of implanted nylon, which is similar to the collision cascade pattern in transverse view calculated by the TRIM computer program. Finally, the mechanism for the formation and growth of the fractal patterns during ion implantation is discussed.

  10. Luminescent quantum clusters of gold in bulk by albumin-induced core etching of nanoparticles: metal ion sensing, metal-enhanced luminescence, and biolabeling.

    Science.gov (United States)

    Habeeb Muhammed, Madathumpady Abubaker; Verma, Pramod Kumar; Pal, Samir Kumar; Retnakumari, Archana; Koyakutty, Manzoor; Nair, Shantikumar; Pradeep, Thalappil

    2010-09-03

    The synthesis of a luminescent quantum cluster (QC) of gold with a quantum yield of approximately 4 % is reported. It was synthesized in gram quantities by the core etching of mercaptosuccinic acid protected gold nanoparticles by bovine serum albumin (BSA), abbreviated as Au(QC)@BSA. The cluster was characterized and a core of Au(38) was assigned tentatively from mass spectrometric analysis. Luminescence of the QC is exploited as a "turn-off" sensor for Cu(2+) ions and a "turn-on" sensor for glutathione detection. Metal-enhanced luminescence (MEL) of this QC in the presence of silver nanoparticles is demonstrated and a ninefold maximum enhancement is seen. This is the first report of the observation of MEL from QCs. Folic acid conjugated Au(QC)@BSA was found to be internalized to a significant extent by oral carcinoma KB cells through folic acid mediated endocytosis. The inherent luminescence of the internalized Au(QC)@BSA was used in cell imaging.

  11. Reaction of niobium and tantalum neutral clusters with low pressure, unsaturated hydrocarbons in a pickup cell: From dehydrogenation to Met-Car formation

    Science.gov (United States)

    He, S.-G.; Xie, Y.; Dong, F.; Bernstein, E. R.

    2006-10-01

    Neutral niobium and tantalum clusters (Nbn and Tan) are generated by laser ablation and supersonic expansion into a vacuum and are reacted in a pickup cell with various low pressure (˜1mTorr) unsaturated hydrocarbons (acetylene, ethylene, propylene, 1-butene, 1,3-butadiene, benzene, and toluene) under nearly single collision conditions. The bare metal clusters and their reaction products are ionized by a 193nm laser and detected by a time of flight mass spectrometer. Partially and fully dehydrogenated products are observed for small (n⩽m) and large (n⩾m) neutral metal clusters, respectively, with m ranging from 2 to 5 depending on the particular hydrocarbon. In addition to primary, single collision products, sequential addition products that are usually fully dehydrogenated are also observed. With toluene used as the reactant gas, carbon loss products are observed, among which Nb8C12 and Ta8C12 are particularly abundant, indicating that the Met-Car molecule M8C12 can be formed from the neutral metal cluster upon two collisions with toluene molecules. The dehydrogenation results for low pressure reactions are compared with those available from previous studies employing flow tube (high pressure) reactors. Low pressure and high pressure cluster ion reactions are also compared with the present neutral metal cluster reactions. Reactions of unsaturated hydrocarbons and metal surfaces are discussed in terms of the present neutral cluster results.

  12. Structural, electronic and magnetic properties of 3d metal trioxide clusters-doped monolayer graphene: A first-principles study

    Science.gov (United States)

    Rafique, Muhammad; Shuai, Yong; Tan, He-Ping; Hassan, Muhammad

    2017-03-01

    We present first-principles density-functional calculations for the structural, electronic and magnetic properties of monolayer graphene doped with 3d (Ti, V, Cr, Fe, Co, Mn and Ni) metal trioxide TMO3 halogen clusters. In this paper we used two approaches for 3d metal trioxide clusters (i) TMO3 halogen cluster was embedded in monolayer graphene substituting four carbon (C) atoms (ii) three C atoms were substituted by three oxygen (O) atoms in one graphene ring and TM atom was adsorbed at the hollow site of O atoms substituted graphene ring. All the impurities were tightly bonded in the graphene ring. In first case of TMO3 doped graphene layer, the bond length between Csbnd O atom was reduced and bond length between TM-O atom was increased. In case of Cr, Fe, Co and Ni atoms substitution in between the O atoms, leads to Fermi level shifting to conduction band thereby causing the Dirac cone to move into valence band, however a band gap appears at high symmetric K-point. In case of TiO3 and VO3 substitution, system exhibits semiconductor properties. Interestingly, TiO3-substituted system shows dilute magnetic semiconductor behavior with 2.00 μB magnetic moment. On the other hand, the substitution of CoO3, CrO3, FeO3 and MnO3 induced 1.015 μB, 2.347 μB, 2.084 μB and 3.584 μB magnetic moment, respectively. In second case of O atoms doped in graphene and TM atoms adsorbed at the hollow site, the O atom bulges out of graphene plane and bond length between TM-O atom is increased. After TM atoms adsorption at the O substituted graphene ring the Fermi level (EF) shifts into conduction band. In case of Cr and Ni adsorption, system displays indirect band gap semiconductor properties with 0.0 μB magnetic moment. Co adsorption exhibits dilute magnetic semiconductor behavior producing 0.916 μB magnetic moment. Fe, Mn, Ti and V adsorption introduces band gap at high symmetric K-point also inducing 1.54 μB, 0.9909 μB, 1.912 μB, and 0.98 μB magnetic moments, respectively

  13. Detonation in supersonic radial outflow

    KAUST Repository

    Kasimov, Aslan R.

    2014-11-07

    We report on the structure and dynamics of gaseous detonation stabilized in a supersonic flow emanating radially from a central source. The steady-state solutions are computed and their range of existence is investigated. Two-dimensional simulations are carried out in order to explore the stability of the steady-state solutions. It is found that both collapsing and expanding two-dimensional cellular detonations exist. The latter can be stabilized by putting several rigid obstacles in the flow downstream of the steady-state sonic locus. The problem of initiation of standing detonation stabilized in the radial flow is also investigated numerically. © 2014 Cambridge University Press.

  14. Cluster-cluster clustering

    Science.gov (United States)

    Barnes, J.; Dekel, A.; Efstathiou, G.; Frenk, C. S.

    1985-01-01

    The cluster correlation function xi sub c(r) is compared with the particle correlation function, xi(r) in cosmological N-body simulations with a wide range of initial conditions. The experiments include scale-free initial conditions, pancake models with a coherence length in the initial density field, and hybrid models. Three N-body techniques and two cluster-finding algorithms are used. In scale-free models with white noise initial conditions, xi sub c and xi are essentially identical. In scale-free models with more power on large scales, it is found that the amplitude of xi sub c increases with cluster richness; in this case the clusters give a biased estimate of the particle correlations. In the pancake and hybrid models (with n = 0 or 1), xi sub c is steeper than xi, but the cluster correlation length exceeds that of the points by less than a factor of 2, independent of cluster richness. Thus the high amplitude of xi sub c found in studies of rich clusters of galaxies is inconsistent with white noise and pancake models and may indicate a primordial fluctuation spectrum with substantial power on large scales.

  15. Cluster-cluster clustering

    Energy Technology Data Exchange (ETDEWEB)

    Barnes, J.; Dekel, A.; Efstathiou, G.; Frenk, C.S.

    1985-08-01

    The cluster correlation function xi sub c(r) is compared with the particle correlation function, xi(r) in cosmological N-body simulations with a wide range of initial conditions. The experiments include scale-free initial conditions, pancake models with a coherence length in the initial density field, and hybrid models. Three N-body techniques and two cluster-finding algorithms are used. In scale-free models with white noise initial conditions, xi sub c and xi are essentially identical. In scale-free models with more power on large scales, it is found that the amplitude of xi sub c increases with cluster richness; in this case the clusters give a biased estimate of the particle correlations. In the pancake and hybrid models (with n = 0 or 1), xi sub c is steeper than xi, but the cluster correlation length exceeds that of the points by less than a factor of 2, independent of cluster richness. Thus the high amplitude of xi sub c found in studies of rich clusters of galaxies is inconsistent with white noise and pancake models and may indicate a primordial fluctuation spectrum with substantial power on large scales. 30 references.

  16. Mass and metal ejection efficiency in disk galaxies driven by young stellar clusters of nuclear starburst

    Directory of Open Access Journals (Sweden)

    A. Rodríguez-González

    2011-01-01

    Full Text Available Presentamos las eficiencias de pérdida de masa y metales obtenidas de modelos numéricos de vientos galácticos empujados por la energía depositada en brotes de formación estelar nucleares. Los brotes de formación estelar contienen cúmulos estelares jóvenes los cuales inyectan la energía suficiente para empujar parte del medio interestelar fuera de las galaxias. En algunos casos los vientos galácticos contienen una importante parte de los metales producidos por las nuevas generaciones estelares. Para estudiar las eficiencias de pérdida de masa y metales hemos desarrollado simulaciones numéricas 3D N-Cuerpos/Smooth Particle Hydrodynamics de vientos galácticos para los casos: adiabáticos y con pérdidas radiativas. Los modelos numéricos cubren una amplio intervalo de masas de los brotes de formación estelar (de ∼ 10 2 a ∼ 10 7 M ⊙ y de masas en las galaxias anfitrionas (de ∼ 6 × 10 6 a ∼ 10 11 M ⊙. Las regiones de formación estelar concentradas en el centro del potencial son una maquinaria importante para la pérdida y redistribución de mas a y metales en este tipo de galaxias.

  17. Star formation efficiency as a function of metallicity: from star clusters to galaxies

    CERN Document Server

    Dib, Sami; Mohanty, Subhanjoy; Braine, Jonathan

    2011-01-01

    We explore how the star formation efficiency in a protocluster clump is regulated by metallicity dependent stellar winds from the newly formed OB stars (Mstar > 5 Msol). The model describes the co-evolution of the mass function of gravitationally bound cores and of the IMF in a protocluster clump. Dense cores are generated uniformly in time at different locations in the clump, and contract over lifetimes that are a few times their free fall times. The cores collapse to form stars that power strong stellar winds whose cumulative kinetic energy evacuates the gas from the clump and quenches further core and star formation. This sets the final star formation efficiency, SFEf. Models are run with various metallicities in the range Z/Zsol=[0.1,2]. We find that the SFEf decreases strongly with increasing metallicity. The SFEf-metallicity relation is well described by a decaying exponential whose exact parameters depend weakly on the value of the core formation efficiency. We find that there is almost no dependence o...

  18. Radial Distribution Of ISM Gas-phase Metallicity In CLASH Clusters at z~0.35: A New Outlook On Environmental Impact On Galaxy Evolution

    CERN Document Server

    Gupta, Anshu; Tran, Kim-Vy H; Martizzi, Davide; Taylor, Philip; Kewley, Lisa J

    2016-01-01

    We present the first observation of cluster-scale radial metallicity gradients from star-forming galaxies. We use the DEIMOS spectrograph on the Keck II telescope to observe two CLASH clusters at z~0.35: MACS1115+0129 and RXJ1532+3021. Based on our measured interstellar medium (ISM) properties of star-forming galaxies out to a radius of 2.5 Mpc from the cluster centre, we find that the galaxy metallicity decreases as a function of projected cluster-centric distance (-0.15+/-0.08 dex/Mpc}) in MACS1115+01. On the mass-metallicity relation (MZR), star-forming galaxies in MACS1115+01 are offset to higher metallicity (~0.2 dex) than the local SDSS galaxies at a fixed mass range. In contrast, the MZR of RXJ1532+30 is consistent with the local comparison sample. RXJ1532+30 exhibits a bimodal radial metallicity distribution, with one branch showing a similar negative gradient as MACS1115+01 (-0.14+/-0.05 dex/Mpc) and the other branch showing a positive radial gradient. The positive gradient branch in RXJ1532+30 is li...

  19. Real-time monitoring of abnormal conditions based on Fuzzy Kohonen clustering network in gas metal arc welding

    Institute of Scientific and Technical Information of China (English)

    GAO Jinqiang; WU Chuansong; HU Jiakun

    2007-01-01

    A real-time monitoring system based on through-the-arc sensing is developed for detecting abnormal conditions in gas metal arc welding. The transient signals of welding voltage and current during the welding process are sampled and processed by statistical analysis methods. It is found that three statistical parameters (the standard deviation,variance, and kurtosis of welding current) show obvious variations during the step disturbance, which is intentionally introduced into the T-joint test pieces by cutting a gap in the vertical plane. A Fuzzy Kohonen clustering network (FKCN) is put forward to monitor the abnormal conditions in real-time. Ten robotic welding experiments are conducted to verify the real-time monitoring system. It is found that the correct identification rate is above 90%.

  20. Cell-free synthesis of the H-cluster: a model for the in vitro assembly of metalloprotein metal centers.

    Science.gov (United States)

    Kuchenreuther, Jon M; Shiigi, Stacey A; Swartz, James R

    2014-01-01

    Many organometallic cofactors are highly complex and require multiple accessory proteins for both their assembly and transfer to a target protein. A cell-free system in which the biosynthetic pathway for a prosthetic group has been fully or even partially reconstructed enables investigations of the reaction sequence as well as the cofactor itself. As a model for the in vitro assembly of protein-bound metal centers, we describe a procedure for the cell-free synthesis of the H-cluster in the context of producing purified and active [FeFe] hydrogenase samples for spectroscopic studies. In general terms, this in vitro system is a combination of non-purified accessory proteins, exogenous substrates, and purified hydrogenase apoprotein. We also describe methods for making the required components used in the cell-free system. Specifically, these procedures include anaerobic expression of heterologous metalloproteins in Escherichia coli, anaerobic cell lysate production, and anaerobic metalloprotein purification using Strep-Tactin(®) chromatography.

  1. Cluster Chemistry

    Institute of Scientific and Technical Information of China (English)

    2011-01-01

    @@ Cansisting of eight scientists from the State Key Laboratory of Physical Chemistry of Solid Surfaces and Xiamen University, this creative research group is devoted to the research of cluster chemistry and creation of nanomaterials.After three-year hard work, the group scored a series of encouraging progresses in synthesis of clusters with special structures, including novel fullerenes, fullerene-like metal cluster compounds as well as other related nanomaterials, and their properties study.

  2. A Possible Solution for the M/L-[Fe/H] Relation of Globular Clusters in M31: A metallicity and density dependent top-heavy IMF

    CERN Document Server

    Zonoozi, Akram Hasani; Kroupa, Pavel

    2016-01-01

    The observed mass-to-light ($M/L$) ratios of a large sample of GCs in M31 show an inverse trend with metallicity compared to what is expected from Simple Stellar Population (SSP) models with an invariant canonical stellar IMF, in the sense that the observed $M/L$ ratios decrease with increasing metallicity. We show that incorporating the effect of dynamical evolution the SSP models with a canonical IMF can not explain the decreasing $M/L$ ratios with increasing metallicity for the M31 GCs. The recently derived top-heavy IMF as a function of metallicity and embedded cluster density is proposed to explain the lower than expected $M/L$ ratios of metal-rich GCs. We find that the SSP models with a top-heavy IMF, retaining a metallicity- and cluster mass- dependent fraction of the remnants within the clusters, and taking standard dynamical evolution into account can successfully explain the observed $M/L-[Fe/H]$ relation of M31 GCs. Thus we propose that the kinematical data of GCs can be used to constrain the top-h...

  3. Adsorption Behavior of CH2 and CH3 on Metal Clusters Cun (n=1-6)

    Institute of Scientific and Technical Information of China (English)

    Xi-hui Cheng; Ming-xing Jin; Zhan Hu; Fei-fei Hu; Da-jun Ding

    2008-01-01

    Using density functional theory with generalized gradient approximation and hybrid functional, we studied the properties of energy, charge population, and vibration of CH2 and CH3 adsorbed on Cun (n=1-6)clusters. The results show that the DFT calculation with the hybrid functional matches the experimental results better in both cases. The calculation results indicate that the adsorption of CH2 is stronger than that of CH3. During adsorption, the charges transfer from Cu to CH2 or CH3. The obtained vibrational frequencies for different modes of CH2 and CH3 adsorbed on Cun agree well with the experimental results for the adsorption on Cu(111) surface.

  4. Metal Enhanced Fluorescence on Super-Hydrophobic Clusters of Gold Nanoparticles

    KAUST Repository

    Battista, Edmondo

    2016-12-15

    We used optical lithography, electroless deposition and deep reactive ion etching techniques to realize arrays of super-hydrophobic gold nanoparticles arranged in a hierarchical structure. At the micro-scale, silicon-micro pillars in the chip permit to manipulate and concentrate biological solutions, at the nano-scale, gold nanoparticles enable metal enhanced fluorescence (MEF) effects, whereby fluorescence signal of fluorophores in close proximity to a rough metal surface is amplified by orders of magnitude. Here, we demonstrated the device in the analysis of fluorescein derived gold-binding peptides (GBP-FITC). While super-hydrophobic schemes and MEF effects have been heretofore used in isolation, their integration in a platform may advance the current state of fluorescence-based sensing technology in medical diagnostics and biotechnology. This scheme may be employed in protein microarrays where the increased sensitivity of the device may enable the early detection of cancer biomarkers or other proteins of biomedical interest.

  5. Evolution of Cluster Red-Sequence Galaxies from redshift 0.8 to 0.4: ages, metallicities and morphologies

    CERN Document Server

    Sánchez-Blazquez, P; Noll, S; Poggianti, B M; Moustakas, J; Milvang-Jensen, B; Halliday, C; Aragón-Salamanca, A; Saglia, R P; Desai, V; De Lucia, G; Clowe, D I; Pellò, R; Rudnick, G; Simard, L; White, S D M; Zaritsky, D

    2009-01-01

    We present a comprehensive analysis of the stellar population properties (age, metallicity and the alpha-element enhancement [E/Fe]) and morphologies of red-sequence galaxies in 24 clusters and groups from z~0.75 to z~0.45. The dataset, consisting of 215 spectra drawn from the ESO Distant Cluster Survey, constitutes the largest spectroscopic sample at these redshifts for which such an analysis has been conducted. Analysis reveals that the evolution of the stellar population properties of red-sequence galaxies depend on their mass: while the properties of most massive are well described by passive evolution and high-redshift formation, the less massive galaxies require a more extended star formation history. We show that these scenarios reproduce the index-sigma relations as well as the galaxy colours. The two main results of this work are (1) the evolution of the line-strength indices for the red-sequence galaxies can be reproduced if 40% of the galaxies with sigma < 175 km/s entered the red-sequence betwe...

  6. Thermodynamics of small alkali metal halide cluster ions: comparison of classical molecular simulations with experiment and quantum chemistry.

    Science.gov (United States)

    Vlcek, Lukas; Uhlik, Filip; Moucka, Filip; Nezbeda, Ivo; Chialvo, Ariel A

    2015-01-22

    We evaluate the ability of selected classical molecular models to describe the thermodynamic and structural aspects of gas-phase hydration of alkali metal halide ions and the formation of small water clusters. To understand the effect of many-body interactions (polarization) and charge penetration effects on the accuracy of a force field, we perform Monte Carlo simulations with three rigid water models using different functional forms to account for these effects: (i) point charge nonpolarizable SPC/E, (ii) Drude point charge polarizable SWM4-DP, and (iii) Drude Gaussian charge polarizable BK3. Model predictions are compared with experimental Gibbs free energies and enthalpies of ion hydration, and with microscopic structural properties obtained from quantum DFT calculations. We find that all three models provide comparable predictions for pure water clusters and cation hydration but differ significantly in their description of anion hydration. None of the investigated classical force fields can consistently and quantitatively reproduce the experimental gas-phase hydration thermodynamics. The outcome of this study highlights the relation between the functional form that describes the effective intermolecular interactions and the accuracy of the resulting ion hydration properties.

  7. Radial velocities and metallicities from infrared Ca II triplet spectroscopy of open clusters II. Berkeley 23, King 1, NGC 559, NGC 6603 and NGC 7245

    CERN Document Server

    Carrera, R; Ospina, N; Balaguer-Nuñez, L; Jordi, C; Monteagudo, L

    2015-01-01

    Context: Open clusters are key to studying the formation and evolution of the Galactic disc. However, there is a deficiency of radial velocity and chemical abundance determinations for open clusters in the literature. Aims: We intend to increase the number of determinations of radial velocities and metallicities from spectroscopy for open clusters. Methods: We acquired medium-resolution spectra (R~8000) in the infrared region Ca II triplet lines (~8500 AA) for several stars in five open clusters with the long-slit IDS spectrograph on the 2.5~m Isaac Newton Telescope (Roque de los Muchachos Observatory, Spain). Radial velocities were obtained by cross-correlation fitting techniques. The relationships available in the literature between the strength of infrared Ca II lines and metallicity were also used to derive the metallicity for each cluster. Results: We obtain = 48.6+/-3.4, -58.4+/-6.8, 26.0+/-4.3 and -65.3+/-3.2 km s-1 for Berkeley 23, NGC 559, NGC 6603 and NGC 7245, respectively. We found [Fe/H] =-0.25+...

  8. Effects of carbonyl bond, metal cluster dissociation, and evaporation rates on predictions of nanotube production in high-pressure carbon monoxide

    Science.gov (United States)

    Scott, Carl D.; Smalley, Richard E.

    2003-01-01

    The high-pressure carbon monoxide (HiPco) process for producing single-wall carbon nanotubes (SWNTs) uses iron pentacarbonyl as the source of iron for catalyzing the Boudouard reaction. Attempts using nickel tetracarbonyl led to no production of SWNTs. This paper discusses simulations at a constant condition of 1300 K and 30 atm in which the chemical rate equations are solved for different reaction schemes. A lumped cluster model is developed to limit the number of species in the models, yet it includes fairly large clusters. Reaction rate coefficients in these schemes are based on bond energies of iron and nickel species and on estimates of chemical rates for formation of SWNTs. SWNT growth is measured by the conformation of CO2. It is shown that the production of CO2 is significantly greater for FeCO because of its lower bond energy as compared with that of NiCO. It is also shown that the dissociation and evaporation rates of atoms from small metal clusters have a significant effect on CO2 production. A high rate of evaporation leads to a smaller number of metal clusters available to catalyze the Boudouard reaction. This suggests that if CO reacts with metal clusters and removes atoms from them by forming MeCO, this has the effect of enhancing the evaporation rate and reducing SWNT production. The study also investigates some other reactions in the model that have a less dramatic influence.

  9. Selective deposition of Pt onto supported metal clusters for fuel cell electrocatalysts

    Science.gov (United States)

    Jeon, Tae-Yeol; Pinna, Nicola; Yoo, Sung Jong; Ahn, Docheon; Choi, Sun Hee; Willinger, Marc-Georg; Cho, Yong-Hun; Lee, Kug-Seung; Park, Hee-Young; Yu, Seung-Ho; Sung, Yung-Eun

    2012-09-01

    We report a new method for deposition of Pt on a metal core to develop real electrocatalysts with significantly reduced amounts of expensive Pt as well as enhanced activity for oxygen reduction reaction. Ru and Pd have different crystal structures and modify the electronic structure of Pt to a different extent (shifts in d-band center). They were chosen as core materials to examine whether hydroquinone dissolved in ethanol can be used to deposit additional Pt atoms onto preformed core nanoparticles, and whether the modified d-character of Pt on different host metals can result in the enhanced ORR activity. The physicochemical characteristics of Pd-Pt and Ru-Pt core-shell nanoparticles are investigated. The core-shell structure was identified through a combination of experimental methods, employing electron microscopy, electrochemical measurements, and synchrotron X-ray measurements such as powder X-ray diffraction, X-ray absorption fine structure, and X-ray photoelectron spectroscopy. The hydroquinone reduction method proved to be an excellent route for the epitaxial growth of a Pt shell on the metal cores, leading to enhanced ORR activities.We report a new method for deposition of Pt on a metal core to develop real electrocatalysts with significantly reduced amounts of expensive Pt as well as enhanced activity for oxygen reduction reaction. Ru and Pd have different crystal structures and modify the electronic structure of Pt to a different extent (shifts in d-band center). They were chosen as core materials to examine whether hydroquinone dissolved in ethanol can be used to deposit additional Pt atoms onto preformed core nanoparticles, and whether the modified d-character of Pt on different host metals can result in the enhanced ORR activity. The physicochemical characteristics of Pd-Pt and Ru-Pt core-shell nanoparticles are investigated. The core-shell structure was identified through a combination of experimental methods, employing electron microscopy

  10. Structure and nature of the metal-support interface. Characterization of iridium clusters on magnesium oxide by extended X-ray absorption fine structure spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Van Zon, F.B.M.; Koningsberger, D.C. (Univ. of Utrecht (Netherlands)); Maloney, S.D.; Gates, B.C. (Univ. of Delaware, Newark, DE (United States))

    1993-11-03

    X-ray absorption spectroscopy was used to characterize the metal-support interface in catalysts consisting of very small Ir clusters of nearly uniform nuclearity on the surface of MgO powder. [Ir[sub 4](CO)[sub 12

  11. A porous metal-organic framework based on Zn6O2 clusters: chemical stability, gas adsorption properties and solvatochromic behavior.

    Science.gov (United States)

    Cui, Jiehu; Li, Yizhi; Guo, Zijian; Zheng, Hegen

    2013-01-21

    A highly connected 3D metal-organic framework with tfz-d topology based on Zn(6)O(2) clusters and flexible carboxylate ligands has been synthesized. The obtained Zn-MOF shows solvatochromic behavior for fluorescence sensing of small molecules, gas adsorption properties and exceptional chemical stability and might have applications for separation and detection purposes.

  12. Pdf prediction of supersonic hydrogen flames

    Science.gov (United States)

    Eifler, P.; Kollmann, W.

    1993-01-01

    A hybrid method for the prediction of supersonic turbulent flows with combustion is developed consisting of a second order closure for the velocity field and a multi-scalar pdf method for the local thermodynamic state. It is shown that for non-premixed flames and chemical equilibrium mixture fraction, the logarithm of the (dimensionless) density, internal energy per unit mass and the divergence of the velocity have several advantages over other sets of scalars. The closure model is applied to a supersonic non-premixed flame burning hydrogen with air supplied by a supersonic coflow and the results are compared with a limited set of experimental data.

  13. Star formation in the first galaxies - III. Formation, evolution, and characteristics of the first metal-enriched stellar cluster

    Science.gov (United States)

    Safranek-Shrader, Chalence; Montgomery, Michael H.; Milosavljević, Miloš; Bromm, Volker

    2016-01-01

    We simulate the formation of a low-metallicity (10-2 Z⊙) stellar cluster at redshift z ˜ 14. Beginning with cosmological initial conditions, the simulation utilizes adaptive mesh refinement and sink particles to follow the collapse and evolution of gas past the opacity limit for fragmentation, thus resolving the formation of individual protostellar cores. A time- and location-dependent protostellar radiation field, which heats the gas by absorption on dust, is computed by integration of protostellar evolutionary tracks. The simulation also includes a robust non-equilibrium chemical network that self-consistently treats gas thermodynamics and dust-gas coupling. The system is evolved for 18 kyr after the first protostellar source has formed. In this time span, 30 sink particles representing protostellar cores form with a total mass of 81 M⊙. Their masses range from ˜0.1 to 14.4 M⊙ with a median mass ˜0.5-1 M⊙. Massive protostars grow by competitive accretion while lower mass protostars are stunted in growth by close encounters and many-body ejections. In the regime explored here, the characteristic mass scale is determined by the cosmic microwave background temperature floor and the onset of efficient dust-gas coupling. It seems unlikely that host galaxies of the first bursts of metal-enriched star formation will be detectable with the James Webb Space Telescope or other next-generation infrared observatories. Instead, the most promising access route to the dawn of cosmic star formation may lie in the scrutiny of metal-poor, ancient stellar populations in the Galactic neighbourhood. The observable targets corresponding to the system simulated here are ultra-faint dwarf satellite galaxies such as Boötes II and Willman I.

  14. Basis set convergence on static electric dipole polarizability calculations of alkali-metal clusters

    Energy Technology Data Exchange (ETDEWEB)

    Souza, Fabio A. L. de; Jorge, Francisco E., E-mail: jorge@cce.ufes.br [Departamento de Fisica, Universidade Federal do Espirito Santo, 29060-900 Vitoria-ES (Brazil)

    2013-07-15

    A hierarchical sequence of all-electron segmented contracted basis sets of double, triple and quadruple zeta valence qualities plus polarization functions augmented with diffuse functions for the atoms from H to Ar was constructed. A systematic study of basis sets required to obtain reliable and accurate values of static dipole polarizabilities of lithium and sodium clusters (n = 2, 4, 6 and 8) at their optimized equilibrium geometries is reported. Three methods are examined: Hartree-Fock (HF), second-order Moeller-Plesset perturbation theory (MP2), and density functional theory (DFT). By direct calculations or by fitting the directly calculated values through one extrapolation scheme, estimates of the HF, MP2 and DFT complete basis set limits were obtained. Comparison with experimental and theoretical data reported previously in the literature is done (author)

  15. CURiuos Variables Experiment (CURVE): Variable Stars in the metal-poor Globular Cluster M56

    CERN Document Server

    Pietrukowicz, P; Kedzierski, P; Zloczewski, K; Wisniewski, M; Mularczyk, K

    2008-01-01

    We have surveyed a 6.5' x 6.5' field centered on the globular cluster M56 (NGC 6779) in search for variable stars. We have detected seven variables, among which two objects are new identifications. One of the new variables is an RR Lyrae star, the third such star in M56. Comparison of the new observations and old photometric data for an RV Tauri variable V6 indicates a likely period change in the star. Its slow and negative rate of -0.005+/-0.003 d/yr would disagree with post-AGB evolution, however this could be a result of blue-loop evolution and/or random fluctuations of the period.

  16. A DNA-Encapsulated and Fluorescent Ag 10 6+ Cluster with a Distinct Metal-Like Core

    Energy Technology Data Exchange (ETDEWEB)

    Petty, Jeffrey T.; Ganguly, Mainak; Rankine, Ian J.; Chevrier, Daniel M.; Zhang, Peng (Dalhousie U.); (Furman)

    2017-06-29

    Silver cluster–DNA complexes are optical chromophores, and pairs of these conjugates can be toggled from fluorescently dim to bright states using DNA hybridization. This paper highlights spectral and structural differences for a specific cluster pair. We have previously characterized a cluster with low emission and violet absorption that forms a compact structure with single-stranded oligonucleotides. We now consider its counterpart with blue absorption and strong green emission. This cluster develops with a single-stranded/duplex DNA construct and is favored by low silver concentrations with ≲8 Ag+:DNA, an oxygen atmosphere, and neutral pH. The resulting cluster displays key signatures of a molecular metal with well-defined absorption/emission bands at 490/550 nm, and with a fluorescence quantum yield of 15% and lifetime of 2.4 ns. The molecular cluster conjugates with the larger DNA host because it chromatographically elutes with the DNA and it exhibits circular dichroism. The silver cluster is identified as Ag106+ using two modes of mass spectrometry and elemental analysis. Our key finding is that it adopts a low-dimensional shape, as determined from a Ag K-edge extended X-ray absorption fine structure analysis. The Ag0 in this oxidized cluster segregates from the Ag+ via a sparse number of metal-like bonds and a denser network of silver–DNA bonds. This structure contrasts with the compact, octahedral-like shape of the violet counterpart to the blue cluster, which is also a Ag106+ species. We consider that the blue- and violet-absorbing clusters may be isomers with shapes that are controlled by the secondary structures of their DNA templates.

  17. MASS AND METAL EJECTION EFFICIENCY IN DISK GALAXIES DRIVEN BY YOUNG STELLAR CLUSTERS OF NUCLEAR STARBURST

    Directory of Open Access Journals (Sweden)

    A. Rodríguez-González

    2011-01-01

    Full Text Available Presentamos las eficiencias de pérdida de masa obtenidas de modelos numéricos de vientos galácticos empujados por la energía depositada en brotes de formación estelar nucleares. Los brotes de formación estelar contienen cúmulos estelares jóvenes los cuales inyectan la energía suficiente para empujar parte del medio interestelar fuera de las galaxias. En algunos casos los vientos galácticos contienen una importante parte de los metales producidos por las nuevas generaciones estelares. Para estudiar las eficiencias de pérdida de masa hemos desarrollado simulaciones numéricas 3D "N-Body/Smooth Particle Hydrodynamics" de vientos galácticos para el caso con pérdidas radiativas. Los modelos numéricos cubren una amplio intervalo de masas en los brotes de formación estelar (de -102 a -107 M¿ y de masas en las galaxias anfitrionas (de -6×106 a -1011 M¿. Las regiones de formación estelar concentradas en el centro del potencial, son una maquinaria importante para la pérdida y redistribución de masa y metales en este tipo de galaxias.

  18. MetalPredator: a web server to predict iron-sulfur cluster binding proteomes.

    Science.gov (United States)

    Valasatava, Yana; Rosato, Antonio; Banci, Lucia; Andreini, Claudia

    2016-09-15

    The prediction of the iron-sulfur proteome is highly desirable for biomedical and biological research but a freely available tool to predict iron-sulfur proteins has not been developed yet. We developed a web server to predict iron-sulfur proteins from protein sequence(s). This tool, called MetalPredator, is able to process complete proteomes rapidly with high recall and precision. The web server is freely available at: http://metalweb.cerm.unifi.it/tools/metalpredator/ andreini@cerm.unifi.it Supplementary data are available at Bioinformatics online. © The Author 2016. Published by Oxford University Press. All rights reserved. For Permissions, please e-mail: journals.permissions@oup.com.

  19. [Dynamic study of small metallic clusters]; Estudio Dinamico de Pequenos Agregados Metalicos

    Energy Technology Data Exchange (ETDEWEB)

    Lopez, M.J. [Valladolid Univ. (Spain). Dept. de Fisica Teorica; Jellinek, J. [Argonne National Lab., IL (United States)

    1995-12-31

    We present a brief introduction to computer simulation techniques (particularly to classical molecular dynamics) and their application to the study of the thermodynamic properties of a material system. The basic concepts are illustrated in the study of structural and energetic properties such as the liquid-solid transition and the fragmentation of small clusters of nickel. [Espanol] Presentamos una breve introducci{acute o}n de las t{acute e}cnicas de simulaci{acute o}n por ordenador (en particular de la Din{acute a}mica Molecular cl{acute a}sica) y de su aplicaci{acute o}n al estudio de las propiedades termodin{acute a}micas de un sistema material. Los conceptos b{acute a}sicos se ilustran en el estudio de las propieades estructurales y energ{acute e}ticas, as{acute i} como de la transici{acute o}n de fase s{acute o}lido-l{acute i}quido y de las fragmentaciones de peque{tilde n}os agregados de n{acute i}quel.

  20. Formation of anomalous globular clusters with metallicity spreads: A unified picture

    CERN Document Server

    Bekki, Kenji

    2016-01-01

    Recent observations have revealed that at least 8 globular clusters (GCs) in the Galaxy show internal abundance spreads in [Fe/H]. We investigate the origin of these `anomalous' GCs using numerical simulations of GCs in the dwarfs orbiting around the Galaxy and chemical evolution model of dwarfs hosting the GCs. The principal results are as follows. GCs formed in a host dwarf galaxy with a total mass of ~ 10^10 M_sun can merge to form a single nuclear GC before the host is completely destroyed by the Galaxy, if they are massive (> 3*10^5 M_sun) and if they are formed in the inner region (R<400 pc). The GC merger remnants can capture field stars during its spiral-in to nuclear regions. If two GCs are formed from star formation events separated by ~300 Myr in their host dwarf, then the new GC formed from GC merging can have [Fe/H] spread of 0.2 dex and [Ba/Fe] spread of 0.3 dex. GCs formed from GC merging can show variety of internal abundance spreads depending on the details of their hosts' chemical evoluti...

  1. Molecular metal sulfide cluster model for substrate binding to oil-refinery hydrodesulfurization catalysts.

    Science.gov (United States)

    Herbst, Konrad; Monari, Magda; Brorson, Michael

    2002-03-25

    Reaction between [(eta5-Cp')3Mo3S4]+ and [Ni(1,5-cod)2] (Cp' = methylcyclopentadienyl; 1,5-cod = 1,5-cyclooctadiene) in THF at ambient temperature yielded a coordinatively unsaturated cubane-like cluster cation, [(eta5-Cp')3Mo3S4Ni]+. The ligand sphere at the Ni atom could be saturated by coordinating dimethyl sulfide, diethyl sulfide, di(tert-butyl) sulfide, tetrahydrothiophene, thiochroman-4-ol, 1,4-dithiane, pyridine, quinoline, or 4,4'-bipyridine. The products structurally model a mode of substrate coordination on proposed binding sites of heterogeneous MoNi sulfide hydrotreating catalysts. No stable coordination compounds could be isolated for thiophene derivatives. X-ray crystal structures are reported for the ligand-bridged dicluster compounds [[(eta5-Cp')3Mo3S4Ni]2(mu-C4H4S2)][pts]2 (C4H8S2 = 1,4-dithiane) and [[(eta5-Cp')3Mo3S4Ni]2(mu-bipy)][pts]2 (bipy = 4,4'-bipyridine).

  2. Metal oxide/polyaniline nanocomposites: Cluster size and composition dependent structural and magnetic properties

    Indian Academy of Sciences (India)

    Raksha Sharma; Rakesh Malik; Subhalakshmi Lamba; S Annapoorni

    2008-06-01

    Nanocomposites of iron oxide with conducting polymer in the form of powders of varying compositions have been studied to understand the effects of particle size, cluster size and magnetic inter-particle interactions. The sizes of the nanoparticles were estimated to be ∼ 10–20 nm from the X-ray diffraction (XRD) and the transmission electron micrographs (TEM). XRD shows a single crystalline phase for the -Fe2O3. The presence of conducting polymer was confirmed through Fourier transform infrared (FTIR) spectroscopy. The amount of polymer present in the composite, the transition temperature of iron oxide and the thermal stability of polymer was determined through thermogravimetric and differential thermal analysis (TGA–DTA). The room temperature magnetic hysteresis measurements show reduction in saturation magnetization with increasing polymer concentrations. A low value of coercivity was observed for low polymer composites. On increasing the polymer concentration, the coercivity and remanence become negligible indicating a superparamagnetic phase at room temperature. Beyond a certain composition, the system shows paramagnetic behaviour which is also confirmed through zero field cooled–field cooled (ZFC–FC) measurements. We also report preliminary results on the magnetic properties of self standing sheets prepared using -Fe2O3 and NiFe2O4 nanoparticles and conducting polymers.

  3. Experiments on free and impinging supersonic microjets

    Energy Technology Data Exchange (ETDEWEB)

    Phalnikar, K.A.; Kumar, R.; Alvi, F.S. [Florida A and M University and Florida State University, Department of Mechanical Engineering, Tallahassee, FL (United States)

    2008-05-15

    The fluid dynamics of microflows has recently commanded considerable attention because of their potential applications. Until now, with a few exceptions, most of the studies have been limited to low speed flows. This experimental study examines supersonic microjets of 100-1,000 {mu}m in size with exit velocities in the range of 300-500 m/s. Such microjets are presently being used to actively control larger supersonic impinging jets, which occur in STOVL (short takeoff and vertical landing) aircraft, cavity flows, and flow separation. Flow properties of free as well as impinging supersonic microjets have been experimentally investigated over a range of geometric and flow parameters. The flowfield is visualized using a micro-schlieren system with a high magnification. These schlieren images clearly show the characteristic shock cell structure typically observed in larger supersonic jets. Quantitative measurements of the jet decay and spreading rates as well as shock cell spacing are obtained using micro-pitot probe surveys. In general, the mean flow features of free microjets are similar to larger supersonic jets operating at higher Reynolds numbers. However, some differences are also observed, most likely due to pronounced viscous effects associated with jets at these small scales. Limited studies of impinging microjets were also conducted. They reveal that, similar to the behavior of free microjets, the flow structure of impinging microjets strongly resembles that of larger supersonic impinging jets. (orig.)

  4. Experiments on free and impinging supersonic microjets

    Science.gov (United States)

    Phalnikar, K. A.; Kumar, R.; Alvi, F. S.

    2008-05-01

    The fluid dynamics of microflows has recently commanded considerable attention because of their potential applications. Until now, with a few exceptions, most of the studies have been limited to low speed flows. This experimental study examines supersonic microjets of 100-1,000 μm in size with exit velocities in the range of 300-500 m/s. Such microjets are presently being used to actively control larger supersonic impinging jets, which occur in STOVL (short takeoff and vertical landing) aircraft, cavity flows, and flow separation. Flow properties of free as well as impinging supersonic microjets have been experimentally investigated over a range of geometric and flow parameters. The flowfield is visualized using a micro-schlieren system with a high magnification. These schlieren images clearly show the characteristic shock cell structure typically observed in larger supersonic jets. Quantitative measurements of the jet decay and spreading rates as well as shock cell spacing are obtained using micro-pitot probe surveys. In general, the mean flow features of free microjets are similar to larger supersonic jets operating at higher Reynolds numbers. However, some differences are also observed, most likely due to pronounced viscous effects associated with jets at these small scales. Limited studies of impinging microjets were also conducted. They reveal that, similar to the behavior of free microjets, the flow structure of impinging microjets strongly resembles that of larger supersonic impinging jets.

  5. Discovery of a Metal-poor Field Giant with a Globular Cluster Second-generation Abundance Pattern

    Science.gov (United States)

    Fernández-Trincado, J. G.; Robin, A. C.; Moreno, E.; Schiavon, R. P.; García Pérez, A. E.; Vieira, K.; Cunha, K.; Zamora, O.; Sneden, C.; Souto, Diogo; Carrera, R.; Johnson, J. A.; Shetrone, M.; Zasowski, G.; García-Hernández, D. A.; Majewski, S. R.; Reylé, C.; Blanco-Cuaresma, S.; Martinez-Medina, L. A.; Pérez-Villegas, A.; Valenzuela, O.; Pichardo, B.; Meza, A.; Mészáros, Sz.; Sobeck, J.; Geisler, D.; Anders, F.; Schultheis, M.; Tang, B.; Roman-Lopes, A.; Mennickent, R. E.; Pan, K.; Nitschelm, C.; Allard, F.

    2016-12-01

    We report on the detection, from observations obtained with the Apache Point Observatory Galactic Evolution Experiment spectroscopic survey, of a metal-poor ([Fe/H] = -1.3 dex) field giant star with an extreme Mg-Al abundance ratio ([Mg/Fe] = -0.31 dex; [Al/Fe] = 1.49 dex). Such low Mg/Al ratios are seen only among the second-generation population of globular clusters (GCs) and are not present among Galactic disk field stars. The light-element abundances of this star, 2M16011638-1201525, suggest that it could have been born in a GC. We explore several origin scenarios, studying the orbit of the star in particular to check the probability of its being kinematically related to known GCs. We performed simple orbital integrations assuming the estimated distance of 2M16011638-1201525 and the available six-dimensional phase-space coordinates of 63 GCs, looking for close encounters in the past with a minimum distance approach within the tidal radius of each cluster. We found a very low probability that 2M16011638-1201525 was ejected from most GCs; however, we note that the best progenitor candidate to host this star is GC ω Centauri (NGC 5139). Our dynamical investigation demonstrates that 2M16011638-1201525 reaches a distance | {Z}\\max | \\lt 3 {kpc} from the Galactic plane and minimum and maximum approaches to the Galactic center of R min < 0.62 kpc and R max < 7.26 kpc in an eccentric (e ˜ 0.53) and retrograde orbit. Since the extreme chemical anomaly of 2M16011638-1201525 has also been observed in halo field stars, this object could also be considered a halo contaminant, likely to have been ejected into the Milky Way disk from the halo. We conclude that 2M16011638-20152 is also kinematically consistent with the disk but chemically consistent with halo field stars.

  6. High resolution CCD spectra of stars in globular clusters. Part 2: Metals and CNO in M71

    Science.gov (United States)

    Leep, E. M.; Oke, J. B.; Wallerstein, G.

    1986-01-01

    Palomar coude CCD spectra of resolution 0.3 and 0.6 has been used to redetermine abundances in five stars of the relatively metal rich globular cluster M71. The (Fe/H) value is restricted to the limits of -0.6 to -1.0. The largest source of uncertainty is a systematic difference in f-values between those derived via the Holweger-Muller (1974) solar model and the Bell et al. (1976) solar model. If we use absolute f-values measured by the Oxford group (Blackwell et al. 1982) we find Fe/H to lie in the range of -0.6 to -0.75, i.e., as given by using the Bell et al. solar model. The relative abundances of the light elements, i.e., Na through Ca and probably including Ti show an average excess relative to iron of 0.4 dex. The effect of this difference on metal indices derived from broad- and narrow- band photometry is discussed. For three stars we find O/H = -0.6 using absolute f-values. For CN an analysis of individual rotational lines of the 2-0 band of the red system yields lines in the (C/H,N/H) plane that are consistent with either an original C/Fe = N/Fe = 0 or a modest increase in N relative to C due to CN burning and mixing. A search for C-13N was not successful and an uncertain lower limit of C-12/C-13 near 10 was obtained.

  7. High-resolution CCD spectra of stars in globular clusters. II - Metals and CNO in M71

    Science.gov (United States)

    Leep, E. Myckky; Wallerstein, George; Oke, J. B.

    1987-01-01

    Palomar coude CCD spectra of resolution 0.3 and 0.6 has been used to redetermine abundances in five stars of the relatively metal rich globular cluster M71. The (Fe/H) value is restricted to the limits of -0.6 to -1.0. The largest source of uncertainty is a systematic difference in f-values between those derived via the Holweger-Muller (1974) solar model and the Bell et al. (1976) solar model. If we use absolute f-values measured by the Oxford group (Blackwell et al. 1982) we find Fe/H to lie in the range of -0.6 to -0.75, i.e., as given by using the Bell et al. solar model. The relative abundances of the light elements, i.e., Na through Ca and probably including Ti show an average excess relative to iron of 0.4-dex. The effect of this difference on metal indices derived from broad- and narrow- band photometry is discussed. For three stars we find O/H = -0.6 using absolute f-values. For CN an analysis of individual rotational lines of the 2-0 band of the red system yields lines in the (C/H, N/H) plane that are consistent with either an original C/Fe = N/Fe = 0 or a modest increase in N relative to C due to CN burning and mixing. A search for C-13N was not successful and an uncertain lower limit of C-12/C-13 near 10 was obtained.

  8. The Integrated Calcium II Triplet as a Metallicity Indicator: Comparisons with High Resolution [Fe/H] in M31 Globular Clusters

    CERN Document Server

    Sakari, Charli M

    2015-01-01

    Medium resolution (R=4,000 to 9,000) spectra of the near infrared Ca II lines (at 8498, 8542, and 8662 A) in M31 globular cluster integrated light spectra are presented. In individual stars the Ca II triplet (CaT) traces stellar metallicity; this paper compares integrated CaT strengths to well determined, high precision [Fe/H] values from high resolution integrated light spectra. The target globular clusters cover a wide range in metallicity (from [Fe/H] = -2.1 to -0.2). While most are older than 10 Gyr, some may be of intermediate age (2-6 Gyr). A handful (3-6) have detailed abundances (e.g. low [Ca/Fe]) that indicate they may have been accreted from dwarf galaxies. Using various measurements and definitions of CaT strength, it is confirmed that for GCs with [Fe/H] < -0.4 and older than 2 Gyr the integrated CaT traces cluster [Fe/H] to within about 0.2 dex, independent of age. CaT lines in metal rich GCs are very sensitive to nearby atomic lines (and TiO molecular lines in the most metal rich GCs), largel...

  9. Structure and Nature of the Metal-Support Interface: Characterization of Iridium Clusters on Magnesium Oxide by Extended X-Ray Absorption Fine Structure Spectroscopy.

    OpenAIRE

    Koningsberger, D.C.; Zon, F.B.M. van; Maloney, S.D.; Gates, B. C.

    1993-01-01

    X-ray absorption spectroscopy was used to characterize the metal-support interface in catalysts consisting of very small Ir clusters of nearly uniform nuclearity on the surface of MgO powder. [Ir4(CO)12] on MgO was converted in high yield into [HIr4(CO)11]- and separately into [Ir6(CO)15l2-. Extended X-ray absorption fine structure (EXAFS) data are consistent with the hypothesis that each cluster retained its nuclearity upon decarbonylation. The average Ir-Ir coordination in Ir,/MgO is 2.6 ne...

  10. Evolutionary models for metal-poor low-mass stars lower main sequence of globular clusters and halo field stars

    CERN Document Server

    Baraffe, I; Allard, F; Hauschildt, P H; Baraffe, Isabelle; Chabrier, Gilles; Allard, France; Hauschildt, Peter

    1997-01-01

    We have performed evolutionary calculations of very-low-mass stars from 0.08 to 0.8 $\\msol$ for different metallicites from [M/H]= -2.0 to -1.0 and we have tabulated the mechanical, thermal and photometric characteristics of these models. The calculations include the most recent interior physics and improved non-grey atmosphere models. The models reproduce the entire main sequences of the globular clusters observed with the Hubble Space Telescope over the afore-mentioned range of metallicity. Comparisons are made in the WFPC2 Flight system including the F555, F606 and F814 filters, and in the standard Johnson-Cousins system. We examine the effects of different physical parameters, mixing-length, $\\alpha$-enriched elements, helium fraction, as well as the accuracy of the photometric transformations of the HST data into standard systems. We derive mass-effective temperature and mass-magnitude relationships and we compare the results with the ones obtained with different grey-like approximations. These latter ar...

  11. Synthesis and Structure of 1D Na6 Cluster Chain with Short Na-Na Distance: Organic like Aromaticity in Inorganic Metal Cluster

    CERN Document Server

    Khatua, S; Chattaraj, P K; Roy, D R; Bhattacharjee*, Manish; Chattaraj*, Pratim K.; Khatua, Snehadrinarayan; Roy, Debesh R.

    2006-01-01

    A unique 1D chain of sodium cluster containing (Na6) rings stabilized by a molybdenum containing metalloligand has been synthesized and characterized. DFT calculations show striking resemblance in their aromatic behaviour with the corresponding hydrocarbon analogues

  12. The effect of metal cluster deposition route on structure and photocatalytic activity of mono- and bimetallic nanoparticles supported on TiO2 by radiolytic method

    Science.gov (United States)

    Klein, Marek; Nadolna, Joanna; Gołąbiewska, Anna; Mazierski, Paweł; Klimczuk, Tomasz; Remita, Hynd; Zaleska-Medynska, Adriana

    2016-08-01

    TiO2 (P25) was modified with small and relatively monodisperse mono- and bimetallic clusters (Ag, Pd, Pt, Ag/Pd, Ag/Pt and Pd/Pt) induced by radiolysis to improve its photocatalytic activity. The as-prepared samples were characterized by X-ray fluorescence spectrometry (XRF), photoluminescence spectrometry (PL), diffuse reflectance spectroscopy (DRS), X-ray powder diffractometry (XRD), scanning transition electron microscopy (STEM) and BET surface area analysis. The effect of metal type (mono- and bimetallic modification) as well as deposition method (simultaneous or subsequent deposition of two metals) on the photocatalytic activity in toluene removal in gas phase under UV-vis irradiation (light-emitting diodes- LEDs) and phenol degradation in liquid phase under visible light irradiation (λ > 420 nm) were investigated. The highest photoactivity under Vis light was observed for TiO2 co-loaded with platinum (0.1%) and palladium (0.1%) clusters. Simultaneous addition of metal precursors results in formation of larger metal nanoparticles (15-30 nm) on TiO2 surface and enhances the Vis-induced activity of Ag/Pd-TiO2 up to four times, while the subsequent metal ions addition results in formation of metal particle size ranging from 4 to 20 nm. Subsequent addition of metal precursors results in formation of BNPs (bimetallic nanoparticle) composites showing higher stability in four cycles of toluene degradation under UV-vis. Obtained results indicated that direct electron transfer from the BNPs to the conduction band of the semiconductor is responsible for visible light photoactivity, whereas superoxide radicals (such as O2rad- and rad OOH) are responsible for pollutants degradation over metal-TiO2 composites.

  13. The Color-Magnitude Relation for Metal-Poor Globular Clusters in M87: Confirmation From Deep HST/ACS Imaging

    CERN Document Server

    Peng, Eric W; Blakeslee, John P; Mieske, Steffen; Cote, Patrick; Ferrarese, Laura; Harris, William E; Madrid, Juan P; Meurer, Gerhardt R

    2009-01-01

    Metal-poor globular clusters (GCs) are our local link to the earliest epochs of star formation and galaxy building. Studies of extragalactic GC systems using deep, high-quality imaging have revealed a small but significant slope to the color-magnitude relation for metal-poor GCs in a number of galaxies. We present a study of the M87 GC system using deep, archival HST/ACS imaging with the F606W and F814W filters, in which we find a significant color-magnitude relation for the metal-poor GCs. The slope of this relation in the I vs. V-I color-magnitude diagram ($\\gamma_I=-0.024\\pm0.006$) is perfectly consistent with expectations based on previously published results using data from the ACS Virgo Cluster Survey. The relation is driven by the most luminous GCs, those with $M_I<-10$, and its significance is largest when fitting metal-poor GCs brighter than $M_I=-7.8$, a luminosity which is ~1 mag fainter than our fitted Gaussian mean for the luminosity function (LF) of blue, metal-poor GCs (~0.8 mag fainter than...

  14. Spectroscopic Study of Globular Clusters in the Halo of M31 with Xinglong 2.16m Telescope II: Dynamics, Metallicity and Age

    CERN Document Server

    Fan, Zhou; Li, Jin-Zeng; Zhou, Xu; Ma, Jun; Zhao, Yong-Heng

    2012-01-01

    (Abridged) We performed the spectroscopic observations of 11 confirmed GCs in M31 with the Xinglong 2.16m telescope and we mainly focus on the fits method and the metallicity gradient for the M31 GC sample. We analyzed and discussed more about the dynamics, metallicity and age, and their distributions as well as the relationships between these parameters. Eight more confirmed GCs in the halo of M31 were observed, most of which lack the spectroscopic information before. These star clusters are located far from the galactic center at a projected radius of ~14 to ~117 kpc. The Lick absorption-line indices and the radial velocities have been measured and ages, metallicities [Fe/H] and alpha-element [alpha/Fe] have also been fitted by comparing the observed spectral feature indices and Thomas et al.SSP model. Our results show that most of the star clusters of our sample are older than 10 Gyr except B290 ~5.5 Gyr, and most of them are metal-poor with the metallicity [Fe/H]25 kpc may not exist with a slope of -0.005...

  15. Catalyst Architecture for Stable Single Atom Dispersion Enables Site-Specific Spectroscopic and Reactivity Measurements of CO Adsorbed to Pt Atoms, Oxidized Pt Clusters, and Metallic Pt Clusters on TiO2.

    Science.gov (United States)

    DeRita, Leo; Dai, Sheng; Lopez-Zepeda, Kimberly; Pham, Nicholas; Graham, George W; Pan, Xiaoqing; Christopher, Phillip

    2017-10-11

    Oxide-supported precious metal nanoparticles are widely used industrial catalysts. Due to expense and rarity, developing synthetic protocols that reduce precious metal nanoparticle size and stabilize dispersed species is essential. Supported atomically dispersed, single precious metal atoms represent the most efficient metal utilization geometry, although debate regarding the catalytic activity of supported single precious atom species has arisen from difficulty in synthesizing homogeneous and stable single atom dispersions, and a lack of site-specific characterization approaches. We propose a catalyst architecture and characterization approach to overcome these limitations, by depositing ∼1 precious metal atom per support particle and characterizing structures by correlating scanning transmission electron microscopy imaging and CO probe molecule infrared spectroscopy. This is demonstrated for Pt supported on anatase TiO2. In these structures, isolated Pt atoms, Ptiso, remain stable through various conditions, and spectroscopic evidence suggests Ptiso species exist in homogeneous local environments. Comparing Ptiso to ∼1 nm preoxidized (Ptox) and prereduced (Ptmetal) Pt clusters on TiO2, we identify unique spectroscopic signatures of CO bound to each site and find CO adsorption energy is ordered: Ptiso ≪ Ptmetal atoms bonded to TiO2 and that Ptiso exhibits optimal reactivity because every atom is exposed for catalysis and forms an interfacial site with TiO2. This approach should be generally useful for studying the behavior of supported precious metal atoms.

  16. Design project: LONGBOW supersonic interceptor

    Science.gov (United States)

    Stoney, Robert; Baker, Matt; Capstaff, Joseph G.; Dishman, Robert; Fick, Gregory; Frick, Stephen N.; Kelly, Mark

    1993-01-01

    A recent white paper entitled 'From the Sea' has spotlighted the need for Naval Aviation to provide overland support to joint operations. The base for this support, the Aircraft Carrier (CVN), will frequently be unable to operate within close range of the battleground because of littoral land-based air and subsurface threats. A high speed, long range, carrier capable aircraft would allow the CVN to provide timely support to distant battleground operations. Such an aircraft, operating as a Deck-Launched Interceptor (DLI), would also be an excellent counter to Next Generation Russian Naval Aviation (NGRNA) threats consisting of supersonic bombers, such as the Backfire, equipped with the next generation of high-speed, long-range missiles. Additionally, it would serve as an excellent high speed Reconnaissance airplane, capable of providing Battle Force commanders with timely, accurate pre-mission targeting information and post-mission Bomb Damage Assessment (BDA). Recent advances in computational hypersonic airflow modeling has produced a method of defining aircraft shapes that fit a conical shock flow model to maximize the efficiency of the vehicle. This 'Waverider' concept provides one means of achieving long ranges at high speeds. A Request for Proposal (RFP) was issued by Professor Conrad Newberry that contained design requirements for an aircraft to accomplish the above stated missions, utilizing Waverider technology.

  17. On highly focused supersonic microjets

    CERN Document Server

    Tagawa, Yoshiyuki; Willem, Claas; Peters, Ivo R; van der Meer, Deveraj; Sun, Chao; Prosperetti, Andrea; Lohse, Detlef

    2011-01-01

    By focusing a laser pulse in a liquid-filled glass-microcapillary open at one end, a small mass of liquid is instantaneously vapourised. This leads to a shock wave which travels towards the concave free surface where it generates a high-speed microjet. The initial shape of the meniscus plays a dominant role in the process. The velocity of the jet can reach supersonic speeds up to 850\\,m/s while maintaining a very sharp geometry. The entire evolution of the jet is observed by high-speed recordings of up to $10^6\\,$fps. A parametric study of the jet velocity as a function of the contact angle of the liquid-glass interface, the energy absorbed by the liquid, the diameter of the capillary tube, and the distance between the laser focus and the free surface is performed, and the results are rationalised. The method could be used for needle-free injection of vaccines or drugs.

  18. Structure Characterization of Supported Metal Clusters%负载金属催化剂的结构性能表征

    Institute of Scientific and Technical Information of China (English)

    吴霞

    2012-01-01

    The paper reviewed some structure characterization methods(H2-TPR,TEM,XRD etc),which can be used to study the metal dispersion,surface structure and electronstate of supported metal clusters.%综述了H2-TPR,TEM,XRD等物化方法在负载型金属催化剂的结构性能(包括金属分散度、表面结构、电子状态)方面的应用,为更好地认识和使用负载型金属催化剂提供了可靠的依据。

  19. Metal-metal and metal-ligand bonding at a QTAIM catastrophe: a combined experimental and theoretical charge density study on the alkylidyne cluster Fe3(μ-H)(μ-COMe)(CO)10.

    Science.gov (United States)

    Farrugia, Louis J; Senn, Hans Martin

    2010-12-30

    The charge density in the tri-iron methoxymethylidyne cluster Fe(3)(μ-H)(μ-COMe)(CO)(10) (1) has been studied experimentally at 100 K and by DFT calculations on the isolated molecule using the Quantum Theory of Atoms in Molecules (QTAIM). The COMe ligand acts as a nearly symmetric bridge toward two of the Fe atoms (Fe-C = 1.8554(4), 1.8608(4) Å) but with a much longer interaction to the third Fe atom, Fe-C = 2.6762(4) Å. Complex 1 provides a classic example where topological QTAIM catastrophes render an exact structure description ambiguous. While all experimental and theoretical studies agree in finding no direct metal-metal interaction for the doubly bridged Fe-Fe vector, the chemical bonding between the Fe(CO)(4) unit and the Fe(2)(μ-H)(μ-COMe)(CO)(6) moiety in terms of conventional QTAIM descriptors is much less clear. Bond paths implying direct Fe-Fe interactions and a weak interaction between the COMe ligand and the Fe(CO)(4) center are observed, depending on the experimental or theoretical density model examined. Theoretical studies using the Electron Localizability Indicator (ELI-D) suggest the metal-metal bonding is more significant, while the delocalization indices imply that both Fe-Fe bonding and Fe···C(alkylidyne) bonding are equally important. The source functions at various interfragment reference points are similar and highly delocalized. The potential-energy surface (PES) for the migration of the alkylidyne group from a μ(2) to a semi-μ(3) coordination mode has been explored by DFT calculations on 1 and the model complexes M(3)(μ-H)(μ-CH)(CO)(10) (M = Fe, 2; Ru, 3; and Os, 4). These calculations confirm a semi-μ(3) bridging mode for the alkylidyne ligand as the minimum-energy geometry for compounds 2-4 and demonstrate that, for 1, both Fe-Fe and Fe···C(alkylidyne) interactions are important in the cluster bonding. The PES between μ(2) and semi-μ(3) alkylidyne coordination for 1 is extremely soft, and the interconversion between

  20. Time-resolved analysis of strong-field induced plasmon oscillations in metal clusters by spectral interferometry with few-cycle laser fields

    CERN Document Server

    Köhn, Jörg

    2010-01-01

    We propose a scheme for ultrafast real-time imaging of laser-induced collective electron oscillations (Mie plasmons) in gas phase metal clusters by interferometrically stable scanning of two intense few-cycle optical laser pulses. The feasibility of our nonlinear spectral interferometry method with experimentally accessible observables is tested in a theoretical case study on simple-metal clusters (Na$_{147}$). The results show that the plasmon period and lifetime as well as the phase and relative amplitude of the collective electron motion can be extracted with sub-fs resolution. The access to nonlinear response effects, as the demonstrated increase of the plasmon lifetime with laser intensity due to ionization-induced contraction of the electron cloud, opens up vast opportunities for interrogating ultrafast many-particle dynamics in nanosystems under strong laser fields with unprecedented resolution.

  1. Silent and Efficient Supersonic Bi-Directional Flying Wing Project

    Data.gov (United States)

    National Aeronautics and Space Administration — We propose a Phase I study for a novel concept of a supersonic bi-directional (SBiDir) flying wing (FW) that has the potential to revolutionize supersonic flight...

  2. Highly porous and robust ionic MOFs with nia topology constructed by connecting an octahedral ligand and a trigonal prismatic metal cluster.

    Science.gov (United States)

    Jia, Jiangtao; Sun, Fuxing; Borjigin, Tsolmon; Ren, Hao; Zhang, Tingting; Bian, Zheng; Gao, Lianxun; Zhu, Guangshan

    2012-06-18

    Two non-interpenetrated and isomorphous MOFs with nia topology, cationic JUC-101 and anionic JUC-102, are synthesized by connecting a trigonal prismatic metal cluster with an octahedral organic ligand. JUC-101 obtains a BET surface area of 3742 m(2) g(-1) and can absorb 4.18 wt% of H2 at 30 atm and 77 K, while JUC-102 can absorb cationic dye molecules and release them under the triggering of ions.

  3. The Distances to Open Clusters from Main-Sequence Fitting. V. Extension of Color Calibration and Test using Cool and Metal-Rich Stars in NGC 6791

    CERN Document Server

    An, Deokkeun; Pinsonneault, Marc H; Lee, Jae-Woo

    2015-01-01

    We extend our effort to calibrate stellar isochrones in the Johnson-Cousins ($BVI_C$) and the 2MASS ($JHK_s$) filter systems based on observations of well-studied open clusters. Using cool main-sequence (MS) stars in Praesepe, we define empirical corrections to the Lejeune et al. color-effective temperature ($T_{\\rm eff}$) relations down to $T_{\\rm eff} \\sim 3600$ K, complementing our previous work based on the Hyades and the Pleiades. We apply empirically corrected isochrones to existing optical and near-infrared photometry of cool ($T_{\\rm eff} \\leq 5500$ K) and metal-rich ([Fe/H]$=+0.37$) MS stars in NGC 6791. The current methodology relies on an assumption that color-$T_{\\rm eff}$ corrections are independent of metallicity, but we find that estimates of color-excess and distance from color-magnitude diagrams with different color indices converge on each other at the precisely known metallicity of the cluster. Along with a satisfactory agreement with eclipsing binary data in the cluster, we view the improv...

  4. Four-shell polyoxometalates featuring high-nuclearity Ln{sub 26} clusters. Structural transformations of nanoclusters into frameworks triggered by transition-metal ions

    Energy Technology Data Exchange (ETDEWEB)

    Li, Zhong; Li, Xin-Xiong; Yang, Tao; Cai, Zhen-Wen; Zheng, Shou-Tian [State Key Laboratory of Photocatalysis on Energy and Environment, College of Chemistry, Fuzhou University, Fujian (China)

    2017-03-01

    A series of polyoxometalates (POMs) that incorporate the highest-nuclearity Ln clusters that have been observed in such structures to date (Ln{sub 26}, Ln=La and Ce) are described, which exhibit giant multishell configurations (Ln is contained in W{sub 6} is contained in Ln{sub 26} is contained in W{sub 100}). Their structures are remarkably different from known giant POMs that feature multiple Ln ions. In particular, the incorporated Ln-O clusters with a nuclearity of 26 are significantly larger than known high-nuclearity (≤10) Ln-O clusters in POM chemistry. Furthermore, they also contain the largest number of La and Ce centers for any POM reported to date and represent a new kind of rare giant POMs with more than 100 W atoms. Interestingly, the La{sub 26}-containing POM can undergo a single-crystal to single-crystal structural transformation in the presence of various transition-metal ions, such as Cu{sup 2+}, Co{sup 2+}, and Ni{sup 2+}, from an inorganic molecular nanocluster into an inorganic-organic hybrid extended framework that is built from POM building blocks with even higher-nuclearity La{sub 28} clusters bridged by transition-metal complexes. (copyright 2017 Wiley-VCH Verlag GmbH and Co. KGaA, Weinheim)

  5. Supersonic combustion engine testbed, heat lightning

    Science.gov (United States)

    Hoying, D.; Kelble, C.; Langenbahn, A.; Stahl, M.; Tincher, M.; Walsh, M.; Wisler, S.

    1990-01-01

    The design of a supersonic combustion engine testbed (SCET) aircraft is presented. The hypersonic waverider will utilize both supersonic combustion ramjet (SCRAMjet) and turbofan-ramjet engines. The waverider concept, system integration, electrical power, weight analysis, cockpit, landing skids, and configuration modeling are addressed in the configuration considerations. The subsonic, supersonic and hypersonic aerodynamics are presented along with the aerodynamic stability and landing analysis of the aircraft. The propulsion design considerations include: engine selection, turbofan ramjet inlets, SCRAMjet inlets and the SCRAMjet diffuser. The cooling requirements and system are covered along with the topics of materials and the hydrogen fuel tanks and insulation system. A cost analysis is presented and the appendices include: information about the subsonic wind tunnel test, shock expansion calculations, and an aerodynamic heat flux program.

  6. Simulating Supersonic Turbulence in Galaxy Outflows

    CERN Document Server

    Scannapieco, Evan

    2010-01-01

    We present three-dimensional, adaptive mesh simulations of dwarf galaxy out- flows driven by supersonic turbulence. Here we develop a subgrid model to track not only the thermal and bulk velocities of the gas, but also its turbulent velocities and length scales. This allows us to deposit energy from supernovae directly into supersonic turbulence, which acts on scales much larger than a particle mean free path, but much smaller than resolved large-scale flows. Unlike previous approaches, we are able to simulate a starbursting galaxy modeled after NGC 1569, with realistic radiative cooling throughout the simulation. Pockets of hot, diffuse gas around individual OB associations sweep up thick shells of material that persist for long times due to the cooling instability. The overlapping of high-pressure, rarefied regions leads to a collective central outflow that escapes the galaxy by eating away at the exterior gas through turbulent mixing, rather than gathering it into a thin, unstable shell. Supersonic, turbul...

  7. Supersonic Flutter of Laminated Curved Panels

    Directory of Open Access Journals (Sweden)

    M. Ganapathi

    1995-04-01

    Full Text Available Supersonic flutter analysis of laminated composite curved panels is investigated using doubly-curved, quadrilateral, shear flexible, shell element based on field-consistency approach. The formulation includes transverse shear deformation, in-plane and rotary inertias. The aerodynamic force is evaluated using two-dimensional static aerodynamic approximation for high supersonic flow. Initially, the model developed here is verified for the flutter analysis of flat plates. Numerical results are presented for isotropic, orthotropic and laminated anisotropic curved panels. A detailed parametric study is carried out to observe the effects of aspect and thickness ratios, number of layers, lamination scheme, and boundary conditions on flutter boundary.

  8. Supersonic gas shell for puff pinch experiments

    Science.gov (United States)

    Smith, R. S., III; Doggett, W. O.; Roth, I.; Stallings, C.

    1982-09-01

    An easy-to-fabricate, conical, annular supersonic nozzle has been developed for use in high-power, puff gas z-pinch experiments. A fast responding conical pressure probe has also been developed as an accurate supersonic gas flow diagnostic for evaluating the transient gas jet formed by the nozzle. Density profile measurements show that the magnitude and radial position of the gas annulus are fairly constant with distance from the nozzle, but the gas density in the center of the annulus increases with distance from the nozzle.

  9. Proximity gettering of C3H5 carbon cluster ion-implanted silicon wafers for CMOS image sensors: Gettering effects of transition metal, oxygen, and hydrogen impurities

    Science.gov (United States)

    Kurita, Kazunari; Kadono, Takeshi; Okuyama, Ryousuke; Hirose, Ryo; Onaka-Masada, Ayumi; Koga, Yoshihiro; Okuda, Hidehiko

    2016-12-01

    A new technique is described for manufacturing silicon wafers with the highest capability yet reported for gettering transition metallic, oxygen, and hydrogen impurities in CMOS image sensor fabrication. It is demonstrated that this technique can implant wafers simultaneously with carbon and hydrogen elements that form the projection range by using hydrocarbon compounds. Furthermore, these wafers can getter oxygen impurities out-diffused from the silicon substrate to the carbon cluster ion projection range during heat treatment. Therefore, they can reduce the formation of transition metals and oxygen-related defects in the device active regions and improve electrical performance characteristics, such as dark current and image lag characteristics. The new technique enables the formation of high-gettering-capability sinks for transition metals, oxygen, and hydrogen impurities under device active regions of CMOS image sensors. The wafers formed by this technique have the potential to significantly reduce dark current in advanced CMOS image sensors.

  10. Comparative study of energy of particles ejected from coulomb explosion of rare gas and metallic clusters irradiated by intense femtosecond laser field

    Science.gov (United States)

    Boucerredj, N.; Beggas, K.

    2016-10-01

    We present our study of high intensity femtosecond laser field interaction with large cluster of Kr and Na (contained 2.103 to 2.107 atoms). When laser intensity is above a critical value, it blows off all of electrons from the cluster and forms a non neutral ion cloud. The irradiation of these clusters by the intense laser field leads to highly excitation energy which can be the source of energetic electrons, electronic emission, highly charge, energetic ions and fragmentation process. During the Coulomb explosion of the resulting highly ionized, high temperature nanoplasma, ions acquire again their energy. It is shown that ultra fast ions are produced. The goal of our study is to investigate in detail a comparative study of the expansion and explosion then the ion energy of metallic and rare gas clusters irradiated by an intense femtosecond laser field. We have found that ions have a kinetic energy up to 105 eV and the Coulomb pressure is little than the hydrodynamic pressure. The Coulomb explosion of a cluster may provide a new high energy ion source.

  11. Barrierless growth of precursor-free, ultrafast laser-fragmented noble metal nanoparticles by colloidal atom clusters - A kinetic in situ study.

    Science.gov (United States)

    Jendrzej, Sandra; Gökce, Bilal; Amendola, Vincenzo; Barcikowski, Stephan

    2016-02-01

    Unintended post-synthesis growth of noble metal colloids caused by excess amounts of reactants or highly reactive atom clusters represents a fundamental problem in colloidal chemistry, affecting product stability or purity. Hence, quantified kinetics could allow defining nanoparticle size determination in dependence of the time. Here, we investigate in situ the growth kinetics of ps pulsed laser-fragmented platinum nanoparticles in presence of naked atom clusters in water without any influence of reducing agents or surfactants. The nanoparticle growth is investigated for platinum covering a time scale of minutes to 50days after nanoparticle generation, it is also supplemented by results obtained from gold and palladium. Since a minimum atom cluster concentration is exceeded, a significant growth is determined by time resolved UV/Vis spectroscopy, analytical disc centrifugation, zeta potential measurement and transmission electron microscopy. We suggest a decrease of atom cluster concentration over time, since nanoparticles grow at the expense of atom clusters. The growth mechanism during early phase (<1day) of laser-synthesized colloid is kinetically modeled by rapid barrierless coalescence. The prolonged slow nanoparticle growth is kinetically modeled by a combination of coalescence and Lifshitz-Slyozov-Wagner kinetic for Ostwald ripening, validated experimentally by the temperature dependence of Pt nanoparticle size and growth quenching by Iodide anions.

  12. Stellar lifetime and ultraviolet properties of the old metal-rich Galactic open cluster NGC6791: a pathway to understand the UV upturn of elliptical galaxies

    CERN Document Server

    Buzzoni, Alberto; Carraro, Giovanni; Buson, Lucio

    2012-01-01

    The evolutionary properties of the old metal-rich Galactic open cluster NGC6791 are assessed, based on deep UB photometry and 2Mass JK data. For 4739 stars in the cluster, bolometric luminosity and effective temperature have been derived from theoretical (U-B) and (J-K) color fitting. The derived H-R diagram has been matched with the UVBLUE grid of synthetic stellar spectra to obtain the integrated SED of the system, together with a full set UV (Fanelli) and optical (Lick) narrow-band indices. The cluster appears to be a fairly good proxy of standard elliptical galaxies, although with significantly bluer infrared colors, a shallower 4000A Balmer break, and a lower Mg2 index. The confirmed presence of a dozen hot stars, along their EHB evolution, leads the cluster SED to consistently match the properties of the most active UV-upturn galaxies, with 1.7+/-0.4% of the total bolometric luminosity emitted shortward of 2500A. The cluster Helium abundance results Y=0.30 +/-0.04, while the Post-MS implied stellar life...

  13. A quantum Monte Carlo study on electron correlation in all-metal aromatic clusters MAl4(-) (M = Li, Na, K, Rb, Cu, Ag and Au).

    Science.gov (United States)

    Brito, Bráulio Gabriel A; Hai, G-Q; Teixeira Rabelo, J N; Cândido, Ladir

    2014-05-14

    Using fixed-node diffusion quantum Monte Carlo (FN-DMC) simulation we investigate the electron correlation in all-metal aromatic clusters MAl4(-) (with M = Li, Na, K, Rb, Cu, Ag and Au). The electron detachment energies and electron affinities of the clusters are obtained. The vertical electron detachment energies obtained from the FN-DMC calculations are in very good agreement with the available experimental results. Calculations are also performed within the Hartree-Fock approximation, density-functional theory (DFT), and the couple-cluster (CCSD(T)) method. From the obtained results, we analyse the impact of the electron correlation effects in these bimetallic clusters and find that the correlation of the valence electrons contributes significantly to the detachment energies and electron affinities, varying between 20% and 50% of their total values. Furthermore, we discuss the electron correlation effects on the stability of the clusters as well as the accuracy of the DFT and CCSD(T) calculations in the present systems.

  14. The effect of metal cluster deposition route on structure and photocatalytic activity of mono- and bimetallic nanoparticles supported on TiO{sub 2} by radiolytic method

    Energy Technology Data Exchange (ETDEWEB)

    Klein, Marek [Department of Chemical Technology, Faculty of Chemistry, Gdansk University of Technology, 80-233 Gdansk (Poland); Institute of Fluid-Flow Machinery, Polish Academy of Sciences, 80-231 Gdansk (Poland); Nadolna, Joanna, E-mail: joanna.nadolna@ug.edu.pl [Department of Chemical Technology, Faculty of Chemistry, Gdansk University of Technology, 80-233 Gdansk (Poland); Department of Environmental Technology, University of Gdansk, 80-308 Gdansk (Poland); Gołąbiewska, Anna [Department of Chemical Technology, Faculty of Chemistry, Gdansk University of Technology, 80-233 Gdansk (Poland); Mazierski, Paweł [Department of Environmental Technology, University of Gdansk, 80-308 Gdansk (Poland); Klimczuk, Tomasz [Department of Solid State Physics, Faculty of Applied Physics and Mathematics, Gdansk University of Technology, 80-233 Gdansk (Poland); Remita, Hynd [Laboratoire de Chimie Physique, CNRS-UMR 8000, Université Paris-Sud, Université Paris-Saclay, 91405 Orsay (France); CNRS, Laboratoire de Chimie Physique, UMR 8000, 91405 Orsay (France); Zaleska-Medynska, Adriana [Department of Chemical Technology, Faculty of Chemistry, Gdansk University of Technology, 80-233 Gdansk (Poland); Department of Environmental Technology, University of Gdansk, 80-308 Gdansk (Poland)

    2016-08-15

    Highlights: • Pd-Pt decorated TiO{sub 2} shows the highest activity under visible light among all. • Concurrent addition of metal precursors results in rise of BNPs size and Vis-activity. • Subsequent addition of metal precursors enhances UV–vis stability of modified TiO{sub 2}. • Superoxide radicals are responsible for pollutants degradation over BNPs-TiO{sub 2}. - Abstract: TiO{sub 2} (P25) was modified with small and relatively monodisperse mono- and bimetallic clusters (Ag, Pd, Pt, Ag/Pd, Ag/Pt and Pd/Pt) induced by radiolysis to improve its photocatalytic activity. The as-prepared samples were characterized by X-ray fluorescence spectrometry (XRF), photoluminescence spectrometry (PL), diffuse reflectance spectroscopy (DRS), X-ray powder diffractometry (XRD), scanning transition electron microscopy (STEM) and BET surface area analysis. The effect of metal type (mono- and bimetallic modification) as well as deposition method (simultaneous or subsequent deposition of two metals) on the photocatalytic activity in toluene removal in gas phase under UV–vis irradiation (light-emitting diodes- LEDs) and phenol degradation in liquid phase under visible light irradiation (λ > 420 nm) were investigated. The highest photoactivity under Vis light was observed for TiO{sub 2} co-loaded with platinum (0.1%) and palladium (0.1%) clusters. Simultaneous addition of metal precursors results in formation of larger metal nanoparticles (15–30 nm) on TiO{sub 2} surface and enhances the Vis-induced activity of Ag/Pd-TiO{sub 2} up to four times, while the subsequent metal ions addition results in formation of metal particle size ranging from 4 to 20 nm. Subsequent addition of metal precursors results in formation of BNPs (bimetallic nanoparticle) composites showing higher stability in four cycles of toluene degradation under UV–vis. Obtained results indicated that direct electron transfer from the BNPs to the conduction band of the semiconductor is responsible for

  15. STELLAR LIFETIME AND ULTRAVIOLET PROPERTIES OF THE OLD METAL-RICH GALACTIC OPEN CLUSTER NGC 6791: A PATHWAY TO UNDERSTAND THE ULTRAVIOLET UPTURN OF ELLIPTICAL GALAXIES

    Energy Technology Data Exchange (ETDEWEB)

    Buzzoni, Alberto [INAF-Osservatorio Astronomico di Bologna, Via Ranzani 1, 40127 Bologna (Italy); Bertone, Emanuele [INAOE-Instituto Nacional de Astrofisica Optica y Electronica, Luis Enrique Erro 1, 72840 Tonantzintla, Puebla (Mexico); Carraro, Giovanni [ESO-European Southern Observatory, Alonso de Cordova 3107, Casilla 19001, Santiago 19 (Chile); Buson, Lucio, E-mail: alberto.buzzoni@oabo.inaf.it [INAF-Osservatorio Astronomico di Padova, Vicolo Osservatorio 5, 35122 Padova (Italy)

    2012-04-10

    The evolutionary properties of the old metal-rich Galactic open cluster NGC 6791 are assessed based on deep UB photometry and Two Micron All Sky Survey JK data. For the 4739 stars in the cluster, bolometric luminosity and effective temperature have been derived from theoretical (U - B) and (J - K) color fitting. The derived H-R diagram has been matched with the UVBLUE grid of synthetic stellar spectra to obtain the integrated spectral energy distribution (SED) of the system, together with a full set of UV (Fanelli) and optical (Lick) narrowband indices. The total bolometric magnitude of NGC 6791 is M{sup bol}{sub 6791} = -6.29, with a color (B - V){sub 6791} = 0.97. The cluster appears to be a fairly good proxy of standard elliptical galaxies, although with significantly bluer infrared colors, a shallower 4000 A Balmer break, and a lower Mg{sub 2} index. The confirmed presence of a dozen hot stars along their extreme horizontal-branch evolution leads the cluster SED to consistently match the properties of the most active UV-upturn galaxies, with 1.7% {+-} 0.4% of the total bolometric luminosity emitted shortward of 2500 Angstrom-Sign . The cluster helium abundance results in Y{sub 6791} = 0.30 {+-} 0.04, while the post-main-sequence (PMS) implied stellar lifetime from star number counts fairly agrees with the theoretical expectations from both the PADOVA and BASTI stellar tracks. A PMS fuel consumption of 0.43 {+-} 0.01 M{sub Sun} is found for NGC 6791 stars, in close agreement with the estimated mass of cluster He-rich white dwarfs. Such a tight figure may lead one to suspect that a fraction of the cluster stellar population does not actually reach the minimum mass required to effectively ignite He in the stellar core.

  16. Stellar Lifetime and Ultraviolet Properties of the Old Metal-rich Galactic Open Cluster NGC 6791: A Pathway to Understand the Ultraviolet Upturn of Elliptical Galaxies

    Science.gov (United States)

    Buzzoni, Alberto; Bertone, Emanuele; Carraro, Giovanni; Buson, Lucio

    2012-04-01

    The evolutionary properties of the old metal-rich Galactic open cluster NGC 6791 are assessed based on deep UB photometry and Two Micron All Sky Survey JK data. For the 4739 stars in the cluster, bolometric luminosity and effective temperature have been derived from theoretical (U - B) and (J - K) color fitting. The derived H-R diagram has been matched with the UVBLUE grid of synthetic stellar spectra to obtain the integrated spectral energy distribution (SED) of the system, together with a full set of UV (Fanelli) and optical (Lick) narrowband indices. The total bolometric magnitude of NGC 6791 is M bol 6791 = -6.29, with a color (B - V)6791 = 0.97. The cluster appears to be a fairly good proxy of standard elliptical galaxies, although with significantly bluer infrared colors, a shallower 4000 Å Balmer break, and a lower Mg2 index. The confirmed presence of a dozen hot stars along their extreme horizontal-branch evolution leads the cluster SED to consistently match the properties of the most active UV-upturn galaxies, with 1.7% ± 0.4% of the total bolometric luminosity emitted shortward of 2500 Å. The cluster helium abundance results in Y 6791 = 0.30 ± 0.04, while the post-main-sequence (PMS) implied stellar lifetime from star number counts fairly agrees with the theoretical expectations from both the PADOVA and BASTI stellar tracks. A PMS fuel consumption of 0.43 ± 0.01 M ⊙ is found for NGC 6791 stars, in close agreement with the estimated mass of cluster He-rich white dwarfs. Such a tight figure may lead one to suspect that a fraction of the cluster stellar population does not actually reach the minimum mass required to effectively ignite He in the stellar core. Based on observations carried out at the Italian Telescopio Nazionale Galileo, operated by INAF at the Roque de los Muchachos Observatory (La Palma, Spain).

  17. A complete guide on the influence of metal clusters in the Diels-Alder regioselectivity of I(h)-C80 endohedral metallofullerenes.

    Science.gov (United States)

    Garcia-Borràs, Marc; Osuna, Sílvia; Luis, Josep M; Swart, Marcel; Solà, Miquel

    2013-10-25

    The chemical functionalization of endohedral metallofullerenes (EMFs) has aroused considerable interest due to the possibility of synthesizing new species with potential applications in materials science and medicine. Experimental and theoretical studies on the reactivity of endohedral metallofullerenes are scarce. To improve our understanding of the endohedral metallofullerene reactivity, we have systematically studied with DFT methods the Diels-Alder cycloaddition between s-cis-1,3-butadiene and practically all X@I(h)-C80 EMFs synthesized to date: X=Sc3N, Lu3N, Y3N, La2, Y3, Sc3C2, Sc4C2, Sc3CH, Sc3NC, Sc4O2 and Sc4O3. We have studied both the thermodynamic and kinetic regioselectivity, taking into account the free rotation of the metallic cluster inside the fullerene. This systematic study has been made possible through the use of the frozen cage model (FCM), a computationally cheap approach to accurately predicting the exohedral regioselectivity of cycloaddition reactions in EMFs. Our results show that the EMFs are less reactive than the hollow I(h)-C80 cage. Except for the Y3 cluster, the additions occur predominantly at the [5,6] bond. In many cases, however, a mixture of the two possible regioisomers is predicted. In general, [6,6] addition is favored in EMFs that have a larger charge transfer from the metal cluster to the cage or a voluminous metal cluster inside. The present guide represents the first complete and exhaustive investigation of the reactivity of I(h)-C80-based EMFs.

  18. Electron ionization LC-MS with supersonic molecular beams--the new concept, benefits and applications.

    Science.gov (United States)

    Seemann, Boaz; Alon, Tal; Tsizin, Svetlana; Fialkov, Alexander B; Amirav, Aviv

    2015-11-01

    A new type of electron ionization LC-MS with supersonic molecular beams (EI-LC-MS with SMB) is described. This system and its operational methods are based on pneumatic spray formation of the LC liquid flow in a heated spray vaporization chamber, full sample thermal vaporization and subsequent electron ionization of vibrationally cold molecules in supersonic molecular beams. The vaporized sample compounds are transferred into a supersonic nozzle via a flow restrictor capillary. Consequently, while the pneumatic spray is formed and vaporized at above atmospheric pressure the supersonic nozzle backing pressure is about 0.15 Bar for the formation of supersonic molecular beams with vibrationally cold sample molecules without cluster formation with the solvent vapor. The sample compounds are ionized in a fly-though EI ion source as vibrationally cold molecules in the SMB, resulting in 'Cold EI' (EI of vibrationally cold molecules) mass spectra that exhibit the standard EI fragments combined with enhanced molecular ions. We evaluated the EI-LC-MS with SMB system and demonstrated its effectiveness in NIST library sample identification which is complemented with the availability of enhanced molecular ions. The EI-LC-MS with SMB system is characterized by linear response of five orders of magnitude and uniform compound independent response including for non-polar compounds. This feature improves sample quantitation that can be approximated without compound specific calibration. Cold EI, like EI, is free from ion suppression and/or enhancement effects (that plague ESI and/or APCI) which facilitate faster LC separation because full separation is not essential. The absence of ion suppression effects enables the exploration of fast flow injection MS-MS as an alternative to lengthy LC-MS analysis. These features are demonstrated in a few examples, and the analysis of the main ingredients of Cannabis on a few Cannabis flower extracts is demonstrated. Finally, the advantages of

  19. Supersonic Injection of Aerated Liquid Jet

    Science.gov (United States)

    Choudhari, Abhijit; Sallam, Khaled

    2016-11-01

    A computational study of the exit flow of an aerated two-dimensional jet from an under-expanded supersonic nozzle is presented. The liquid sheet is operating within the annular flow regime and the study is motivated by the application of supersonic nozzles in air-breathing propulsion systems, e.g. scramjet engines, ramjet engines and afterburners. The simulation was conducted using VOF model and SST k- ω turbulence model. The test conditions included: jet exit of 1 mm and mass flow rate of 1.8 kg/s. The results show that air reaches transonic condition at the injector exit due to the Fanno flow effects in the injector passage. The aerated liquid jet is alternately expanded by Prandtl-Meyer expansion fan and compressed by oblique shock waves due to the difference between the back (chamber) pressure and the flow pressure. The process then repeats itself and shock (Mach) diamonds are formed at downstream of injector exit similar to those typical of exhaust plumes of propulsion system. The present results, however, indicate that the flow field of supersonic aerated liquid jet is different from supersonic gas jets due to the effects of water evaporation from the liquid sheet. The contours of the Mach number, static pressure of both cases are compared to the theory of gas dynamics.

  20. Conditions for supersonic bent Marshak waves

    CERN Document Server

    Xu, Qiang; Li, Jing; Dan, Jia-kun; Wang, Kun-lun; Zhou, Shao-tong

    2014-01-01

    Supersonic radiation diffusion approximation is a useful way to study the radiation transportation. Considering the bent Marshak wave theory in 2-dimensions, and an invariable source temperature, we get the supersonic radiation diffusion conditions which are about the Mach number $M>8(1+\\sqrt{\\ep})/3$, and the optical depth $\\tau>1$. A large Mach number requires a high temperature, while a large optical depth requires a low temperature. Only when the source temperature is in a proper region these conditions can be satisfied. Assuming the material opacity and the specific internal energy depend on the temperature and the density as a form of power law, for a given density, these conditions correspond to a region about source temperature and the length of the sample. This supersonic diffusion region involves both lower and upper limit of source temperature, while that in 1-dimension only gives a lower limit. Taking $\\rm SiO_2$ and the Au for example, we show the supersonic region numerically.

  1. Dielectric barrier discharge source for supersonic beams

    Energy Technology Data Exchange (ETDEWEB)

    Luria, K.; Lavie, N.; Even, U. [Sackler School of Chemistry, Tel Aviv University, Tel Aviv 69978 (Israel)

    2009-10-15

    We present a new excitation source for pulsed supersonic beams. The excitation is based on dielectric barrier discharge in the beam. It produces cold beams of metastable atoms, dissociated neutral atoms from molecular precursors, and both positive and negative ions with high efficiency and reliability.

  2. Numerical and experimental investigations on supersonic ejectors

    Energy Technology Data Exchange (ETDEWEB)

    Bartosiewicz, Y.; Aidoun, Z. [CETC-Varennes, Natural Resources Canada (Canada); Desevaux, P. [CREST-UMR 6000, Belfort (France); Mercadier, Y. [Sherbrooke Univ. (Canada). THERMAUS

    2005-02-01

    Supersonic ejectors are widely used in a range of applications such as aerospace, propulsion and refrigeration. The primary interest of this study is to set up a reliable hydrodynamics model of a supersonic ejector, which may be extended to refrigeration applications. The first part of this work evaluated the performance of six well-known turbulence models for the study of supersonic ejectors. The validation concentrated on the shock location, shock strength and the average pressure recovery prediction. Axial pressure measurements with a capillary probe performed previously [Int. J. Turbo Jet Engines 19 (2002) 71; Conference Proc., 10th Int. Symp. Flow Visualization, Kyoto, Japan, 2002], were compared with numerical simulations while laser tomography pictures were used to evaluate the non-mixing length. The capillary probe has been included in the numerical model and the non-mixing length has been numerically evaluated by including an additional transport equation for a passive scalar, which acted as an ideal colorant in the flow. At this point, the results show that the k-omega-sst model agrees best with experiments. In the second part, the tested model was used to reproduce the different operation modes of a supersonic ejector, ranging from on-design point to off-design. In this respect, CFD turned out to be an efficient diagnosis tool of ejector analysis (mixing, flow separation), for design, and performance optimization (optimum entrainment and recompression ratios). (Author)

  3. Influence of clusters in melt on the subsequent glass-formation and crystallization of Fe-Si-B metallic glasses

    Institute of Scientific and Technical Information of China (English)

    Shaoxiong Zhou; Bangshao Dong; Rui Xiang; Guangqiang Zhang; Jingyu Qin; Xiufang Bian

    2015-01-01

    The liquid structure of seven representative Fe–Si–B alloys has been investigated by ab initio molecular dynamics simulation focusing on the role of clusters in terms of glass-forming ability (GFA) and crystallization. It is demonstrated that the type of primary phase precipitated from amorphous state under heat treatment is determined by the relative fraction and role of various clusters in melt. The alloy melt shows higher stability and resultantly larger GFA when there is no dominant cluster or several clusters coexist, which explains the different GFAs and crystallization processes at various ratios of Si and B in the Fe–Si–B system. The close correlation among clusters, crystalline phase and GFA is also studied.

  4. Influence of clusters in melt on the subsequent glass-formation and crystallization of Fe–Si–B metallic glasses

    Directory of Open Access Journals (Sweden)

    Shaoxiong Zhou

    2015-04-01

    Full Text Available The liquid structure of seven representative Fe–Si–B alloys has been investigated by ab initio molecular dynamics simulation focusing on the role of clusters in terms of glass-forming ability (GFA and crystallization. It is demonstrated that the type of primary phase precipitated from amorphous state under heat treatment is determined by the relative fraction and role of various clusters in melt. The alloy melt shows higher stability and resultantly larger GFA when there is no dominant cluster or several clusters coexist, which explains the different GFAs and crystallization processes at various ratios of Si and B in the Fe–Si–B system. The close correlation among clusters, crystalline phase and GFA is also studied.

  5. An Automated DAKOTA and VULCAN-CFD Framework with Application to Supersonic Facility Nozzle Flowpath Optimization

    Science.gov (United States)

    Axdahl, Erik L.

    2015-01-01

    Removing human interaction from design processes by using automation may lead to gains in both productivity and design precision. This memorandum describes efforts to incorporate high fidelity numerical analysis tools into an automated framework and applying that framework to applications of practical interest. The purpose of this effort was to integrate VULCAN-CFD into an automated, DAKOTA-enabled framework with a proof-of-concept application being the optimization of supersonic test facility nozzles. It was shown that the optimization framework could be deployed on a high performance computing cluster with the flow of information handled effectively to guide the optimization process. Furthermore, the application of the framework to supersonic test facility nozzle flowpath design and optimization was demonstrated using multiple optimization algorithms.

  6. Structure and property of metal melt Ⅱ—Evolution of atomic clusters in the not high temperature range above liquidus

    Institute of Scientific and Technical Information of China (English)

    2010-01-01

    Based on the theory of micro-inhomogeneity of liquid metal,a calculation model is established for the quantitative description of the structural information of metal melts.Only by thermophysical property parameters and basic structural parameters of solid metal,can this model produce the main information of melt structure,including the relative concentration of active atoms,size of atomic clusters and number of short-range order atoms.Based on this model,the main structural information of Al and Ni melts in the not high range above the liquidus is calculated,with results in good agreement with experimental values.Besides,analyzed is the influence of superheating temperature and atomic number on the melt structural information of the first (IA) and second main group (IIA) elements.With temperature increasing,melt structural information regularly changes for both IA and IIA elements.With the atomic number increasing,melt structural information of IA elements changes regularly,for the crystal structures of the IA elements are all of bcc lattice type.However,no notable regular change of melt structural information for IIA elements has been found,mainly because the lattice type of IIA elements is of hcp-fcc-bcc transition.The present work presents an effective way for better understanding metal melt structure and for forecasting the change of the physical property of metal melts.

  7. Metalloid Aluminum Clusters with Fluorine

    Science.gov (United States)

    2016-12-01

    molecular-scale metalloid clusters as a way to achieve very rapid rates of metal combustion. These clusters contain a mixture of low-valence metals...using molecular-scale metalloid clusters as a way to achieve very rapid rates of metal combustion. These clusters contain a mixture of low- valence...25 Table 2. Calculated binding energy, HOMO/LUMO gap and Fermi energy

  8. Tracking Rh Atoms in Zeolite HY: First Steps of Metal Cluster Formation and Influence of Metal Nuclearity on Catalysis of Ethylene Hydrogenation and Ethylene Dimerization

    Energy Technology Data Exchange (ETDEWEB)

    Yang, Dong; Xu, Pinghong; Browning, Nigel D.; Gates, Bruce C.

    2016-07-07

    The initial steps of rhodium cluster formation from zeolite-supported mononuclear Rh(C2H4)2 complexes in H2 at 373 K and 1 bar were investigated by infrared and extended X-ray absorption fine structure spectroscopies and scanning transmission electron microscopy (STEM). The data show that ethylene ligands on the rhodium react with H2 to give supported rhodium hydrides and trigger the formation of rhodium clusters. STEM provided the first images of the smallest rhodium clusters (Rh2) and their further conversion into larger clusters. The samples were investigated in a plug-flow reactor as catalysts for the conversion of ethylene + H2 in a molar ratio of 4:1 at 1 bar and 298 K, with the results showing how the changes in catalyst structure affect the activity and selectivity; the rhodium clusters are more active for hydrogenation of ethylene than the single-site complexes, which are more selective for dimerization of ethylene to give butenes

  9. Supersonic Particle Deposition (Cold Spray)

    Science.gov (United States)

    2006-01-26

    Dr. William DeRosset Modeling/ Simulation (410) 306-0816 Victor Cha pagne Phillip Ley an Dr. Dennis Helfritch Dr. Andrew Davis athew cCarry Dr. illia...H-60 Transmission System Powertrain All gearbox housings fabricated from Mg alloys Number of H-60 helicopters in service: Army: 1100 Navy: 350...severe degradation in service • Most corrosion occurs at mating pads, supports, and mounting lugs where dissimilar metal is in contact with Mg

  10. Deuterium cluster jet produced at moderate backing pressures

    Institute of Scientific and Technical Information of China (English)

    Hongbin Wang; Tianshu Wen; Yingling He; Chunye Jiao; Shuanggen Zhang; Xiangxian Wang; Fangfang Ge; Hongjie Liu; Guoquan Ni; Xiangdong Yang; Yuqiu Gu; Xianlun Wen; Weimin Zhou; Guangchang Wang

    2006-01-01

    @@ A deuterium cluster jet produced in the supersonic expansion into vacuum of deuterium gas at liquid nitrogen temperature and moderate backing pressures are studied by Rayleigh scattering techniques. The experimental results show that deuterium clusters can be created at moderate gas backing pressures ranging from 8 to 23 bar, and a maximum average cluster size of 350 atoms per cluster is estimated. The temporal evolution of the cluster jet generated at the backing pressure of 20 bar demonstrates a two-plateau structure. The possible mechanism responsible for this structure is discussed. The former plateau with higher average atom and cluster densities is more suitable for the general laser-cluster interaction experiments.

  11. Laser Desorption Supersonic Jet Spectroscopy of Hydrated Tyrosine

    Science.gov (United States)

    Oba, Hikari; Shimozono, Yoko; Ishiuchi, Shun-Ichi; Fujii, Masaaki; Carcabal, Pierre

    2013-06-01

    The structure of tyrosine (tyr) consists of amino-acid chain and phenol, and it has roughly two possible binding sites for water, amino-acid site and phenolic OH site. Investigating how water molecule binds to tyr will give fundamental information for hydrations of peptide and protein. Resonance enhanced multi photon ionization (REMPI) spectrum of tyr-water 1:1 cluster has already been reported by de Vries and co-workers, however, no analysis on the hydrated structures has been reported. In the REMPI spectrum, two clusters of bands are observed; one appears at ˜35600 cm^{-1} energy region which is the almost same with 0-0 transitions of tyr monomer, and another is observed at ˜300 cm^{-1} lower than the former. Based on the electronic transition energy of phenylalanine and the hydrated clusters, the former is expected to be derived from a structure that water binds to amino acid site. On the other hand, it is plausibly predicted that the latter originates from a structure that water binds to phenolic OH group, because the electronic transition of mono hydrated phenol is ˜300 cm^{-1} red-shifted from the monomer. We applied IR dip spectroscopy which can measure conformer selective IR spectra to the tyr-(H_{2}O)_{1} clusters by using laser desorption supersonic jet technique to confirm the assignments. Especially in the phenolic OH bound isomer, it was found that the intra molecular hydrogen bond within amino-acid chain, which is far from the water molecule and cannot interact directly with each other, is strengthened by the hydration. A. Abio-Riziq et al., J. Phys. Chem. A, 115, 6077 (2011). Y. Shimozono, et al., Phys. Chem. Chem. Phys., (2013) DOI: 10.1039/c3cp43573c. T. Ebata et al., Phys. Chem. Chem. Phys., 8, 4783 (2006). T. Watanabe et al., J. Chem. Phys., 105, 408 (1996).

  12. The Origin of the Efficient, Thermal Chemisorption of Methane by the Heteronuclear Metal-Oxide Cluster [Al2 TaO5 ]().

    Science.gov (United States)

    Zhou, Shaodong; Li, Jilai; Schlangen, Maria; Schwarz, Helmut

    2016-11-14

    The thermal gas-phase reactions of the closed-shell metal-oxide cluster [Al2 TaO5 ](+) with methane have been explored by using FT-ICR mass spectrometry complemented by high-level quantum chemical calculations. Mechanistic aspects have been addressed to reveal the origins of the efficient addition process which results in activating the C-H bond of methane. The [Al2 TaO5 ](+) /CH4 couple has been compared with several other systems reported previously, and the electronic origins of their rather distinct performances are discussed. © 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  13. The Effect of Reflector with Sound-Absorbing Material on Supersonic Jet Noise

    Institute of Scientific and Technical Information of China (English)

    Y.-H. KWEON; M. TSUCHIDA; Y. MIYAZATO; T. AOKI; H.-D. KIM; T. SETOGUCHI

    2005-01-01

    This paper describes an experimental work to investigate the effect of a reflector on supersonic jet noise radiated from a convergent-divergent nozzle with a design Mach number 2.0. In the present study, a metal reflector and reflectors made of three different sound-absorbing materials (grass wool and polyurethane foam) were employed,and the reflector size was varied. Acoustic measurement is carried out to obtain the acoustic characteristics such as frequency, amplitude of screech tone and overall sound pressure level (OASPL). A high-quality schlieren optical system is used to visualize the detailed structure of supersonic jet. The results obtained show that the acoustic characteristics of supersonic jet noise are strongly dependent upon the jet pressure ratio and the reflector size. It is also found that the reflector with sound-absorbing material reduces the screech tone amplitude by about 5-13dB and the overall sound pressure levels by about 2-5dB, compared with those of the metal reflector.

  14. Cluster expansion reactions of group 6 and 8 metallaboranes using transition metal carbonyl compounds of groups 7-9.

    Science.gov (United States)

    Geetharani, K; Bose, Shubhankar Kumar; Sahoo, Satyanarayan; Varghese, Babu; Mobin, Shaikh M; Ghosh, Sundargopal

    2011-06-20

    The reinvestigation of an early synthesis of heterometallic cubane-type clusters has led to the isolation of a number of new clusters which have been characterized by spectroscopic and crystallographic techniques. The thermolysis of [(Cp*Mo)(2)B(4)H(4)E(2)] (1: E = S; 2: E = Se; Cp* = η(5)-C(5)Me(5)) in presence of [Fe(2)(CO)(9)] yielded cubane-type clusters [(Cp*Mo)(2)(μ(3)-E)(2)B(2)H(μ-H){Fe(CO)(2)}(2)Fe(CO)(3)], 4 and 5 (4: E = S; 5: E = Se) together with fused clusters [(Cp*Mo)(2)B(4)H(4)E(2)Fe(CO)(2)Fe(CO)(3)] (8: E = S; 9: E = Se). In a similar fashion, reaction of [(Cp*RuCO)(2)B(2)H(6)], 3, with [Fe(2)(CO)(9)] yielded [(Cp*Ru)(2)(μ(3)-CO)(2)B(2)H(μ-H){Fe(CO)(2)}(2)Fe(CO)(3)], 6, and an incomplete cubane cluster [(μ(3)-BH)(3)(Cp*Ru)(2){Fe(CO)(3)}(2)], 7. Clusters 4-6 can be described as heterometallic cubane clusters containing a Fe(CO)(3) moiety exo-bonded to the cubane, while 7 has an incomplete cubane [Ru(2)Fe(2)B(3)] core. The geometry of both compounds 8 and 9 consist of a bicapped octahedron [Mo(2)Fe(2)B(3)E] and a trigonal bipyramidal [Mo(2)B(2)E] core, fused through a common three vertex [Mo(2)B] triangular face. In addition, thermolysis of 3 with [Mn(2)(CO)(10)] permits the isolation of arachno-[(Cp*RuCO)(2)B(3)H(7)], 10. Cluster 10 constitutes a diruthenaborane analogue of 8-sep pentaborane(11) and has a structural isomeric relationship to 1,2-[{Cp*Ru}(2)(CO)(2)B(3)H(7)].

  15. Hydride mobility in trinuclear sulfido clusters with the core [Rh3(μ-H)(μ3-S)2]: molecular models for hydrogen migration on metal sulfide hydrotreating catalysts.

    Science.gov (United States)

    Jiménez, M Victoria; Lahoz, Fernando J; Lukešová, Lenka; Miranda, José R; Modrego, Francisco J; Nguyen, Duc H; Oro, Luis A; Pérez-Torrente, Jesús J

    2011-07-11

    The treatment of [{Rh(μ-SH){P(OPh)(3)}(2)}(2)] with [{M(μ-Cl)(diolef)}(2)] (diolef=diolefin) in the presence of NEt(3) affords the hydrido-sulfido clusters [Rh(3)(μ-H)(μ(3)-S)(2)(diolef){P(OPh)(3)}(4)] (diolef=1,5-cyclooctadiene (cod) for 1, 2,5-norbornadiene (nbd) for 2, and tetrafluorobenzo[5,6]bicyclo[2.2.2]octa-2,5,7-triene (tfb) for 3) and [Rh(2)Ir(μ-H)(μ(3)-S)(2)(cod){P(OPh)(3)}(4)] (4). Cluster 1 can be also obtained by treating [{Rh(μ-SH){P(OPh)(3)}(2)}(2)] with [{Rh(μ-OMe)(cod)}(2)], although the main product of the reaction with [{Ir(μ-OMe)(cod)}(2)] was [RhIr(2)(μ-H)(μ(3)-S)(2)(cod)(2){P(OPh)(3)}(2)] (5). The molecular structures of clusters 1 and 4 have been determined by X-ray diffraction methods. The deprotonation of a hydrosulfido ligand in [{Rh(μ-SH)(CO)(PPh(3))}(2)] by [M(acac)(diolef)] (acac=acetylacetonate) results in the formation of hydrido-sulfido clusters [Rh(3)(μ-H)(μ(3)-S)(2)(CO)(2) (diolef)(PPh(3))(2)] (diolef=cod for 6, nbd for 7) and [Rh(2)Ir(μ-H)(μ(3)-S)(2)(CO)(2)(cod)(PPh(3))(2)] (8). Clusters 1-3 and 5 exist in solution as two interconverting isomers with the bridging hydride ligand at different edges. Cluster 8 exists as three isomers that arise from the disposition of the PPh(3) ligands in the cluster (cis and trans) and the location of the hydride ligand. The dynamic behaviour of clusters with bulky triphenylphosphite ligands, which involves hydrogen migration from rhodium to sulfur with a switch from hydride to proton character, is significant to understand hydrogen diffusion on the surface of metal sulfide hydrotreating catalysts.

  16. Minimally Intrusive and Nonintrusive Supersonic Injectors for LANTR and RBCC/Scramjet Propulsion Systems

    Science.gov (United States)

    Buggele, Alvin E.; Gallagher, John R.

    2002-10-01

    A family of supersonic injectors for use on spaceplanes, rockets and missiles and the like is disclosed and claimed. Each injector maintains a specific constant (uniform) Mach number along its length when used while being minimally intrusive at significantly higher injectant pressure than combuster freestream total pressure. Each injector is substantially non-intrusive when it is not being used. The injectors may be used individually or in a group. Different orientations of the injectors in a group promotes greater penetration and mixing of fuel or oxidizer into a supersonic combustor. The injectors can be made from single piece of Aluminum, investment cast metal, or ceramic or they can be made from starboard and port blocks strapped together to accurately control the throat area. Each injector includes an elongated body having an opening which in cross section is an hour glass (venturi shaped) and the opening diverges in width and depth from the bow section to the stem section of the opening.

  17. Analysis of heterogeneous water vapor uptake by metal iodide cluster ions via differential mobility analysis-mass spectrometry

    Energy Technology Data Exchange (ETDEWEB)

    Oberreit, Derek [Department of Mechanical Engineering, University of Minnesota, Minneapolis, Minnesota 55455 (United States); Fluid Measurement Technologies, Inc., Saint Paul, Minnesota 55110 (United States); Rawat, Vivek K.; Larriba-Andaluz, Carlos; Ouyang, Hui; McMurry, Peter H.; Hogan, Christopher J., E-mail: hogan108@umn.edu [Department of Mechanical Engineering, University of Minnesota, Minneapolis, Minnesota 55455 (United States)

    2015-09-14

    The sorption of vapor molecules onto pre-existing nanometer sized clusters is of importance in understanding particle formation and growth in gas phase environments and devising gas phase separation schemes. Here, we apply a differential mobility analyzer-mass spectrometer based approach to observe directly the sorption of vapor molecules onto iodide cluster ions of the form (MI){sub x}M{sup +} (x = 1-13, M = Na, K, Rb, or Cs) in air at 300 K and with water saturation ratios in the 0.01-0.64 range. The extent of vapor sorption is quantified in measurements by the shift in collision cross section (CCS) for each ion. We find that CCS measurements are sensitive enough to detect the transient binding of several vapor molecules to clusters, which shift CCSs by only several percent. At the same time, for the highest saturation ratios examined, we observed CCS shifts of up to 45%. For x < 4, cesium, rubidium, and potassium iodide cluster ions are found to uptake water to a similar extent, while sodium iodide clusters uptake less water. For x ≥ 4, sodium iodide cluster ions uptake proportionally more water vapor than rubidium and potassium iodide cluster ions, while cesium iodide ions exhibit less uptake. Measured CCS shifts are compared to predictions based upon a Kelvin-Thomson-Raoult (KTR) model as well as a Langmuir adsorption model. We find that the Langmuir adsorption model can be fit well to measurements. Meanwhile, KTR predictions deviate from measurements, which suggests that the earliest stages of vapor uptake by nanometer scale species are not well described by the KTR model.

  18. Supersonic Turbulent Boundary Layer: DNS and RANS

    Institute of Scientific and Technical Information of China (English)

    XU Jing-Lei; MA Hui-Yang

    2007-01-01

    We assess the performance of a few turbulence models for Reynolds averaged Navier-Stokes (RANS) simulation of supersonic boundary layers, compared to the direct numerical simulations (DNS) of supersonic flat-plate turbulent boundary layers, carried out by Gao et al. [Chin. Phys. Lett. 22 (2005) 1709] and Huang et al. [Sci.Chin. 48 (2005) 614], as well as some available experimental data. The assessment is made for two test cases, with incoming Mach numbers and Reynolds numbers M = 2.25, Re = 365, 000/in, and M = 4.5, Re - 1.7 × 107/m,respectively. It is found that in the first case the prediction of RANS models agrees well with the DNS and the experimental data, while for the second case the agreement of the DNS models with experiment is less satisfactory.The compressibility effect on the RANS models is discussed.

  19. Turbulent Shear Layers in Supersonic Flow

    CERN Document Server

    Smits, Alexander J

    2006-01-01

    A good understanding of turbulent compressible flows is essential to the design and operation of high-speed vehicles. Such flows occur, for example, in the external flow over the surfaces of supersonic aircraft, and in the internal flow through the engines. Our ability to predict the aerodynamic lift, drag, propulsion and maneuverability of high-speed vehicles is crucially dependent on our knowledge of turbulent shear layers, and our understanding of their behavior in the presence of shock waves and regions of changing pressure. Turbulent Shear Layers in Supersonic Flow provides a comprehensive introduction to the field, and helps provide a basis for future work in this area. Wherever possible we use the available experimental work, and the results from numerical simulations to illustrate and develop a physical understanding of turbulent compressible flows.

  20. Study of active cooling for supersonic transports

    Science.gov (United States)

    Brewer, G. D.; Morris, R. E.

    1975-01-01

    The potential benefits of using the fuel heat sink of hydrogen fueled supersonic transports for cooling large portions of the aircraft wing and fuselage are examined. The heat transfer would be accomplished by using an intermediate fluid such as an ethylene glycol-water solution. Some of the advantages of the system are: (1) reduced costs by using aluminum in place of titanium, (2) reduced cabin heat loads, and (3) more favorable environmental conditions for the aircraft systems. A liquid hydrogen fueled, Mach 2.7 supersonic transport aircraft design was used for the reference uncooled vehicle. The cooled aircraft designs were analyzed to determine their heat sink capability, the extent and location of feasible cooled surfaces, and the coolant passage size and spacing.

  1. Size-specific interaction of alkali metal ions in the solvation of M+-benzene clusters by Ar atoms.

    Science.gov (United States)

    Huarte-Larrañaga, F; Aguilar, A; Lucas, J M; Albertí, M

    2007-08-23

    The size-specific influence of the M+ alkali ion (M = Li, Na, K, Rb, and Cs) in the solvation process of the M+-benzene clusters by Ar atoms is investigated by means of molecular dynamic simulations. To fully understand the behavior observed in M+-bz-Ar(n) clusters, solvation is also studied in clusters containing either M+ or benzene only. The potential energy surfaces employed are based on a semiempirical bond-atom decomposition, which has been developed previously by some of the authors. The outcome of the dynamics is analyzed by employing radial distribution functions, studying the evolution of the distances between the Ar atoms and the alkali ion M+ or the benzene molecule for all M+-bz-Ar(n) clusters. For all members, in the M+-bz series, the benzene molecule (bz) is found to remain strongly bound to M+ even in the presence of solvent atoms. The radial distribution functions for the heavier clusters (K+-bz, Rb+-bz, and Cs+-bz), are found to be different than for the lighter (Na+-bz and Li+-bz) ones.

  2. Conceptual Design of a Supersonic Jet Engine

    OpenAIRE

    Kareliusson, Joakim; Nordqvist, Melker

    2014-01-01

    This thesis is a response to the request for proposal issued by a joint collaboration between the AIAA Foundation and ASME/IGTI as a student competition to design a new turbofan engine intended for a conceptual supersonic business jet expected to enter service in 2025. Due to the increasing competition in the aircraft industry and the more stringent environmental legislations the new engine is expected to provide a lower fuel burn than the current engine intended for the aircraft to increase ...

  3. Chemically reacting supersonic flow calculation using an assumed PDF model

    Science.gov (United States)

    Farshchi, M.

    1990-01-01

    This work is motivated by the need to develop accurate models for chemically reacting compressible turbulent flow fields that are present in a typical supersonic combustion ramjet (SCRAMJET) engine. In this paper the development of a new assumed probability density function (PDF) reaction model for supersonic turbulent diffusion flames and its implementation into an efficient Navier-Stokes solver are discussed. The application of this model to a supersonic hydrogen-air flame will be considered.

  4. Research of low boom and low drag supersonic aircraft design

    OpenAIRE

    Feng Xiaoqiang; Li Zhanke; Song Bifeng

    2014-01-01

    Sonic boom reduction will be an issue of utmost importance in future supersonic transport, due to strong regulations on acoustic nuisance. The paper describes a new multi-objective optimization method for supersonic aircraft design. The method is developed by coupling Seebass–George–Darden (SGD) inverse design method and multi-objective genetic algorithm. Based on the method, different codes are developed. Using a computational architecture, a conceptual supersonic aircraft design environment...

  5. Atomic collisions in suprafluid helium-nanodroplets: timescales for metal-cluster formation derived from He-density functional theory.

    Science.gov (United States)

    Hauser, Andreas W; Volk, Alexander; Thaler, Philipp; Ernst, Wolfgang E

    2015-04-28

    Collision times for the coinage metal atoms Cu, Ag and Au in He-droplets are derived from helium density functional theory and molecular dynamics simulations. The strength of the attractive interaction between the metal atoms turns out to be less important than the mass of the propagating metal atoms. Even for small droplets consisting of a few thousand helium atoms, the collision times are shortest for Cu, followed by Ag and Au, despite the higher binding energy of Au2 compared to Cu2.

  6. Supersonic and subsonic measurements of mesospheric ionization.

    Science.gov (United States)

    Hale, L. C.; Nickell, L. C.; Kennedy, B.; Powell, T. A.

    1972-01-01

    An Arcas rocket-parachute system was used at night to compare supersonic and subsonic ionization measurements below 75 km. A hemispherical nose-tip probe was used on ascent and a parachute-borne blunt probe on descent to measure polar conductivities, which were due entirely to positive and negative ions. The velocity of the supersonic probe was Mach 2.5 at 50 km and 1.75 at 70 km; the blunt probe was subsonic below 71 km. Between 65 and 75 km the ratio of negative to positive conductivities (and thus of mobilities) determined by the blunt probe was about 1.2, and it approached 1 below this altitude range. The ratio obtained by the nose-tip probe varied from 1.5 at 75 km to .6 at 65 km, thus indicating a rapid variation of the effects of the shock wave on the sampled ions. The absolute values of positive conductivity measured subsonically and supersonically were essentially identical from 60 to 75 km, indicating that the sampled ions were unchanged by the shock. However, below 60 km the shock apparently 'broke up' the positive ions, as indicated by higher measured conductivities.

  7. Supersonic Jet Excitation using Flapping Injection

    CERN Document Server

    Hafsteinsson, Haukur; Andersson, Niklas; Cuppoletti, Daniel; Gutmark, Ephraim; Prisell, Erik

    2013-01-01

    Supersonic jet noise reduction is important for high speed military aircraft. Lower acoustic levels would reduce structural fatigue leading to longer lifetime of the jet aircraft. It is not solely structural aspects which are of importance, health issues of the pilot and the airfield per- sonnel are also very important, as high acoustic levels may result in severe hearing damage. It remains a major challenge to reduce the overall noise levels of the aircraft, where the supersonic exhaust is the main noise source for near ground operation. Fluidic injection into the supersonic jet at the nozzle exhaust has been shown as a promising method for noise reduction. It has been shown to speed up the mix- ing process of the main jet, hence reducing the kinetic energy level of the jet and the power of the total acoustic radiation. Furthermore, the interaction mechanism between the fluidic injection and the shock structure in the jet exhaust plays a crucial role in the total noise radia- tion. In this study, LES is used...

  8. Supersonic Gas-Liquid Cleaning System

    Science.gov (United States)

    Kinney, Frank

    1996-01-01

    The Supersonic Gas-Liquid Cleaning System Research Project consisted mainly of a feasibility study, including theoretical and engineering analysis, of a proof-of-concept prototype of this particular cleaning system developed by NASA-KSC. The cleaning system utilizes gas-liquid supersonic nozzles to generate high impingement velocities at the surface of the device to be cleaned. The cleaning fluid being accelerated to these high velocities may consist of any solvent or liquid, including water. Compressed air or any inert gas is used to provide the conveying medium for the liquid, as well as substantially reduce the total amount of liquid needed to perform adequate surface cleaning and cleanliness verification. This type of aqueous cleaning system is considered to be an excellent way of conducting cleaning and cleanliness verification operations as replacements for the use of CFC 113 which must be discontinued by 1995. To utilize this particular cleaning system in various cleaning applications for both the Space Program and the commercial market, it is essential that the cleaning system, especially the supersonic nozzle, be characterized for such applications. This characterization consisted of performing theoretical and engineering analysis, identifying desirable modifications/extensions to the basic concept, evaluating effects of variations in operating parameters, and optimizing hardware design for specific applications.

  9. a Chirped Pulse Fourier Transform Microwave Cp-Ftmw Spectrometer with Laser Ablation Source to Search for Actinide-Containing Molecules and Noble Metal Clusters

    Science.gov (United States)

    Marshall, Frank E.; Gillcrist, David Joseph; Persinger, Thomas D.; Moon, Nicole; Grubbs, G. S., II

    2016-06-01

    Microwave spectroscopic techniques have traditionally been part of the foundation of molecular structure and this conference. Instrumental developments by Brooks Pate and sourcing developments by Steve Cooke on these instruments have allowed for the dawning of a new era in modern microwave spectroscopic techniques. With these advances and the growth of powerful computational approaches, microwave spectroscopists can now search for molecules and/or cluster systems of actinide and noble metal-containing species with increasing certainty in molecular assignment even with the difficulties presented with spin-orbit coupling and relativistic effects. Spectrometer and ablation design will be presented along with any preliminary results on actinide-containing molecules or noble metal clusters or interactions. G. G. Brown, B. C. Dian, K. O. Douglass, S. M. Geyer, S. T. Shipman, B. H. Pate, Rev. Sci. Instrum. 79 (2008) 053103-1 - 053103-13 G. S. Grubbs II, C. T. Dewberry, K. C. Etchison, K. E. Kerr, S. A. Cooke, Rev. Sci. Instrum. 78 (2007) 096106-1 - 096106-3

  10. The Old, Super-Metal-Rich Open Cluster, NGC 6791 - Elemental Abundances in Turn-off Stars from Keck/HIRES Spectra

    CERN Document Server

    Boesgaard, Ann Merchant; Deliyannis, Constantine P

    2014-01-01

    The study of star clusters has advanced our understanding of stellar evolution, Galactic chemical evolution and nucleosynthesis. Here we investigate the composition of turn-off stars in the intriguing open cluster, NGC 6791, which is old, but super-metal-rich with high-resolution (46,000) Keck/HIRES spectra. We find [Fe/H] = +0.30 +/-0.02 from measurements of some 40 unblended, unsaturated lines of both Fe I and Fe II in eight turn-off stars. Our O abundances come from the O I triplet near 7774 A and we do a differential analysis relative to the Sun from our Lunar spectrum also obtained with Keck/HIRES. The O results are corrected for small nLTE effects. We find consistent ratios of [O/Fe]n with a mean of $-$0.06 +/-0.02. This continues the trend of decreasing [O/Fe] with increasing [Fe/H] found in field stars that are also both old and metal-rich. The small range in our oxygen abundances is consistent with a single population of stars. Our results for the alpha elements [Mg/Fe], [Si/Fe], [Ca/Fe], and [Ti/Fe]...

  11. Skin Friction and Pressure Measurements in Supersonic Inlets Project

    Data.gov (United States)

    National Aeronautics and Space Administration — Supersonic propulsion systems include internal ducts, and therefore, the flow often includes shock waves, shear layers, vortices, and separated flows. Passive flow...

  12. Quantum size correction to the work function and the centroid of excess charge in positively ionized simple metal clusters

    National Research Council Canada - National Science Library

    M. Payami

    2003-01-01

    In this work, we have shown the important role of the finite-size correction to the work function in predicting the correct position of the centroid of excess charge in positively charged simple metal...

  13. ZFIRE: Galaxy Cluster Kinematics, H$\\alpha$ Star Formation Rates, and Gas-Phase Metallicities of XMM-LSS J02182-05102 at z=1.6233

    CERN Document Server

    Tran, Kim-Vy H; Yuan, Tiantian; Kacprzak, Glenn G; Glazebrook, Karl; Kewley, Lisa J; Momcheva, Ivelina; Papovich, Casey J; Quadri, Ryan; Rudnick, Greg; Saintonge, Amélie; Spitler, Lee R; Straatman, Caroline; Tomczak, Adam

    2015-01-01

    We spectroscopically survey the galaxy cluster XMM-LSS J02182-05102 (hereafter IRC 0218) using LRIS (optical) and MOSFIRE (near-infrared) on Keck I as part of the ZFIRE survey. IRC 0218 has a narrow redshift range of $1.612cluster redshift and velocity dispersion are $z_{\\rm cl}=1.6233\\pm0.0003$ and $\\sigma_{\\rm cl}=254\\pm50$ km s$^{-1}$. We reach NIR line sensitivities of $\\sim0.3\\times10^{-17}$ erg s$^{-1}$ cm$^{-2}$ that, combined with multi-wavelength photometry, provide extinction-corrected H$\\alpha$ star formation rates (SFR), gas phase metallicities from [NII]/H$\\alpha$, and stellar masses. We measure an integrated H$\\alpha$ SFR of $\\sim325{\\rm M}_{\\odot}$ yr$^{-1}$ (26 members; R$_{\\rm proj}<2$ Mpc) and show that the elevated star formation in the cluster core (R$_{\\rm proj}<0.25$ Mpc) is driven by the concentration of star-forming members, but the average SFR per H$\\alpha$-detected galaxy is half th...

  14. A new quantum chemical approach to the magnetic properties of oligonuclear transition-metal complexes: application to a model for the tetranuclear manganese cluster of photosystem II.

    Science.gov (United States)

    Pantazis, Dimitrios A; Orio, Maylis; Petrenko, Taras; Zein, Samir; Bill, Eckhard; Lubitz, Wolfgang; Messinger, Johannes; Neese, Frank

    2009-01-01

    The reliable correlation of structural features and magnetic or spectroscopic properties of oligonuclear transition-metal complexes is a critical requirement both for research into innovative magnetic materials and for elucidating the structure and function of many metalloenzymes. We have developed a novel method that for the first time enables the extraction of hyperfine coupling constants (HFCs) from broken-symmetry density functional theory (BS-DFT) calculations on clusters. Using the geometry-optimized tetranuclear manganese complex [Mn(4)O(6)(bpy)(6)](4+/3+) as a model, we first examine in detail the calculation of exchange coupling constants J through the BS-DFT approach. Complications arising from the indeterminacy of experimentally fitted J constants are identified and analyzed. It is found that only the energy levels derived from Hamiltonian diagonalization are a physically meaningful basis for comparing theory and experiment. Subsequently, the proposed theoretical scheme is applied to the calculation of (55)Mn HFCs of the Mn(III,IV,IV,IV) state of the complex, which is similar to the S(2) state of the oxygen-evolving complex (OEC) in photosystem II of oxygenic photosynthesis. The new approach performs reliably and accurately, and yields calculated HFCs that can be directly compared with experimental data. Finally, we carefully examine the dependence of HFC on the J value and draw attention to the sensitivity of the calculated values to the exchange coupling parameters. The proposed strategy extends naturally to hetero-oligonuclear clusters of arbitrary shape and nuclearity, and hence is of general validity and usefulness in the study of magnetic metal clusters. The successful application of the new approach presented here is a first step in the effort to establish correlations between the available spectroscopic information and the structural features of complex metalloenzymes like OEC.

  15. Argon Nanoclusters with Fivefold Symmetry in Supersonic Gas Jets and Superfluid Helium

    Science.gov (United States)

    Danylchenko, O. G.; Boltnev, R. E.; Khmelenko, V. V.; Kiryukhin, V.; Konotop, O. P.; Lee, D. M.; Krainyukova, N. V.

    2017-04-01

    In this study argon nanoclusters (800 to ˜ 6500 atoms) formed in supersonic gas jets are compared to the nanoclusters stabilized in superfluid helium. High-energy electron and X-ray diffraction methods are utilized. Both techniques allow investigation of isolated clusters. It is shown that the theoretical prediction of the so-called multiply twinned particles with fivefold symmetry, such as icosahedra (ico) and decahedra (dec) is valid in the investigated cluster size interval. Around the point of the expected ico-to-dec size-dependent transformation at a cluster size of ˜ 2000 atoms, hexagonal ico and the statistical distribution of structures with a tendency for dec to replace ico are observed. Kinetic reasons, as well as temperature-related effects, could be responsible for the latter observations.

  16. Searching for variable stars in the cores of five metal-rich globular clusters using EMCCD observations

    DEFF Research Database (Denmark)

    Skottfelt, Jesper; Bramich, D. M.; Jaimes, R. Figuera;

    2015-01-01

    of NGC~6441, for which the variable star population of about 150 stars has been thoroughly examined by previous studies, including a Hubble Space Telescope study. In this paper we are able to present 49 new variable stars for this cluster, of which one (possibly two) are RR Lyrae stars, two are W...

  17. Accelerated growth from amorphous clusters to metallic nanoparticles observed in electrochemical deposition of platinum within nanopores of porous silicon

    NARCIS (Netherlands)

    Munoz-Noval, Alvaro; Fukami, Kazuhiro; Koyama, Akira; Gallach, Dario; Hermida-Merino, Daniel; Portale, Giuseppe; Kitada, Atsushi; Murase, Kuniaki; Abe, Takeshi; Hayakawa, Shinjiro; Sakka, Tetsuo

    2016-01-01

    This study examined the formation of amorphous platinum (Pt) clusters in nanopores of porous silicon at an initial stage of pore filling. The time dependency of the chemical state and local structure of Pt in the nanoporous silicon were characterized by X-ray absorption fine structure spectroscopy (

  18. On the Critical Effect of the Metal (Mo vs. W) on the [3+2] Cycloaddition Reaction of M3 S4 Clusters with Alkynes: Insights from Experiment and Theory.

    Science.gov (United States)

    Bustelo, Emilio; Gushchin, Artem L; Fernández-Trujillo, M Jesús; Basallote, Manuel G; Algarra, Andrés G

    2015-10-12

    Whereas the cluster [Mo3 S4 (acac)3 (py)3 ](+) ([1](+) , acac=acetylacetonate, py=pyridine) reacts with a variety of alkynes, the cluster [W3 S4 (acac)3 (py)3 ](+) ([2](+) ) remains unaffected under the same conditions. The reactions of cluster [1](+) show polyphasic kinetics, and in all cases clusters bearing a bridging dithiolene moiety are formed in the first step through the concerted [3+2] cycloaddition between the C≡C atoms of the alkyne and a Mo(μ-S)2 moiety of the cluster. A computational study has been conducted to analyze the effect of the metal on these concerted [3+2] cycloaddition reactions. The calculations suggest that the reactions of cluster [2](+) with alkynes feature ΔG(≠) values only slightly larger than its molybdenum analogue, however, the differences in the reaction free energies between both metal clusters and the same alkyne reach up to approximately 10 kcal mol(-1) , therefore indicating that the differences in the reactivity are essentially thermodynamic. The activation strain model (ASM) has been used to get more insights into the critical effect of the metal center in these cycloadditions, and the results reveal that the change in reactivity is entirely explained on the basis of the differences in the interaction energies Eint between the cluster and the alkyne. Further decomposition of the Eint values through the localized molecular orbital-energy decomposition analysis (LMO-EDA) indicates that substitution of the Mo atoms in cluster [1](+) by W induces changes in the electronic structure of the cluster that result in weaker intra- and inter-fragment orbital interactions.

  19. Generation of intense plasma jets and microparticle beams by an arc in a supersonic vortex

    Science.gov (United States)

    Winterberg, F.

    1990-04-01

    Temperatures up to 50000 have been reached in water vortex stabilized Gerdien arcs. In arcs confined within the cores of supersonic hydrogen vortices much higher temperatures should be possible. Furthermore if these arcs are thermally insulated by a strong magnetic field temperatures up to a 106 K may be attainable. At these temperatures and in passing through a Laval nozzle the arc plasma can reach jet velocities of 100km/sec. If small quantities of heavy elements are entrained by this high velocity plasma jet these heavy elements are carried along reaching the same speed and upon condensation can form beams of clusters and microparticles.

  20. Density functional investigation of mercury and arsenic adsorption on nitrogen doped graphene decorated with palladium clusters: A promising heavy metal sensing material in farmland

    Science.gov (United States)

    Zhao, Chunjiang; Wu, Huarui

    2017-03-01

    Density functional theory calculations are carried out to study the adsorption of mercury and arsenic on Pdn (n = 1-6) supported on pyridine-like nitrogen doped graphene (PNG). Owing to the promising sensitivity in trace amounts of atoms or molecules, PNG can be acted as micro-sensor for sensing heavy metals in agriculture soils. Through the analyses of structural and electronic properties of pristine PNG and Pd atom decorated PNG, we find that the most favorable adsorption site for Pd atom is the vacancy site. The analyses of structural and electronic properties reveal that the Pd atom or clusters can enhance the reactivity for Hg and AsH3 adsorption on PNG. The adsorption ability of Hg on Pdn decorated PNG is found to be related to the d-band center (εd) of the Pdn, in which the closer εd of Pdn to the Fermi level, the higher adsorption strength for Hg on Pdn decorated PNG. Moreover, the charge transfer between Pdn and arsenic may constitute arsenic adsorption on Pdn decorated PNG. Further design of highly efficient carbon based sorbents for heavy metals removal should be focused on tailoring εd of adsorbed metals.