WorldWideScience

Sample records for metallic clusters estudio

  1. [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.

  2. Metal interactions with boron clusters

    International Nuclear Information System (INIS)

    Grimes, R.N.

    1982-01-01

    This book presents information on the following topics: the structural and bonding features of metallaboranes and metallacarboranes; transition-metal derivatives of nido-boranes and some related species; interactions of metal groups with the octahydrotriborate (1-) anion, B 3 H 8 ; metallaboron cage compounds of the main group metals; closo-carborane-metal complexes containing metal-carbon and metal-boron omega-bonds; electrochemistry of metallaboron cage compounds; and boron clusters with transition metal-hydrogen bonds

  3. Size selected metal clusters

    Indian Academy of Sciences (India)

    Soft Landing and Fragmentation of Small Clusters Deposited in Noble-Gas Films. Harbich, W.; Fedrigo, S.; Buttet, J. Phys. Rev. B 1998, 58, 7428 ... When gold is not noble: Nanoscale gold catalysts. Sanchez A, Abbet S, Heiz U J. Phys. Chem. A. 1999, 103, 9573.

  4. Fission of Polyanionic Metal Clusters

    Science.gov (United States)

    König, S.; Jankowski, A.; Marx, G.; Schweikhard, L.; Wolfram, M.

    2018-04-01

    Size-selected dianionic lead clusters Pbn2 -, n =34 - 56 , are stored in a Penning trap and studied with respect to their decay products upon photoexcitation. Contrary to the decay of other dianionic metal clusters, these lead clusters show a variety of decay channels. The mass spectra of the fragments are compared to the corresponding spectra of the monoanionic precursors. This comparison leads to the conclusion that, in the cluster size region below about n =48 , the fission reaction Pbn2 -→Pbn-10 -+Pb10- is the major decay process. Its disappearance at larger cluster sizes may be an indication of a nonmetal to metal transition. Recently, the pair of Pb10- and Pbn-10 - were observed as pronounced fragments in electron-attachment studies [S. König et al., Int. J. Mass Spectrom. 421, 129 (2017), 10.1016/j.ijms.2017.06.009]. The present findings suggest that this combination is the fingerprint of the decay of doubly charged lead clusters. With this assumption, the dianion clusters have been traced down to Pb212 -, whereas the smallest size for the direct observation was as high as n =28 .

  5. Extragalactic globular clusters. I. The metallicity calibration

    International Nuclear Information System (INIS)

    Brodie, J.P.; Huchra, J.P.

    1990-01-01

    The ability of absorption-line strength indices, measured from integrated globular cluster spectra, to predict mean cluster metallicity is explored. Statistical criteria, are used to identify the six best indices out of about 20 measured in a large sample of Galactic and M31 cluster spectra. Linear relations between index and metallicity have been derived along with new calibrations of infrared colors (V - K, J - K, and CO) versus Fe/H. Estimates of metallicity from the six spectroscopic index-metallicity relations have been combined in three different ways to identify the most efficient estimator and the minimum bias estimator of Fe/H - the weighted mean. This provides an estimate of Fe/H accurate to about 15 percent. 37 refs

  6. Microwave Heating of Metal Power Clusters

    Science.gov (United States)

    Rybakov, K. I.; Semenov, V. E.; Volkovskaya, I. I.

    2018-01-01

    The results of simulating the rapid microwave heating of spherical clusters of metal particles to the melting point are reported. In the simulation, the cluster is subjected to a plane electromagnetic wave. The cluster size is comparable to the wavelength; the perturbations of the field inside the cluster are accounted for within an effective medium approximation. It is shown that the time of heating in vacuum to the melting point does not exceed 1 s when the electric field strength in the incident wave is about 2 kV/cm at a frequency of 24 GHz or 5 kV/cm at a frequency of 2.45 GHz. The obtained results demonstrate feasibility of using rapid microwave heating for the spheroidization of metal particles with an objective to produce high-quality powders for additive manufacturing technologies.

  7. (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.

  8. Magic structures of binary metallic clusters

    Science.gov (United States)

    Ferrando, Riccardo

    2005-03-01

    The structure of binary metallic clusters is investigated by a variety of computational tools, ranging from genetic and basin-hopping global optimization algorithms, to molecular dynamics, and to density-functional calculations. Three different binary systems are investigated: Ag-Cu, Ag-Ni, and Ag-Pd. A new family of magic cluster structures is found. These clusters have the common feature of presenting a perfect core-shell chemical arrangement (with an outer Ag shell of monoatomic thickness) and of being polyicosahedra, that is being made of interpenetrating icosahedra of 13 atoms. Core-shell polyicosahedra are of special stability, which originates from the interplay of different factors. First of all, polyicosahedra are very compact structures, so that they maximize the number of nearest-neighbor bonds for a given size. However, in single-element clusters, these bonds are not optimal, since inner bonds are strongly compressed and surface bonds are expanded. This is the contrary of what is required from the bond order -bond length correlation in metals, which favors contracted surface bonds. In binary clusters, the situation is different. Substituting the inner atoms of a single-element polyicosahedron with different atoms of smaller size, the bonds can relax close to their optimal distance. This leads naturally to the appearance of core-shell polyicosahedra. In Ag-Cu, Ag-Ni and Ag-Pd the formation of these structures is reinforced by the tendency of Ag atoms to surface segregation. A similar mechanism of structural relaxation, originating from the interplay of cluster geometry and bond order - bond length correlation, is also the cause of the destabilization of icosahedral structures in pure Pt and Au clusters . In these clusters, the compressed inner atoms of the icosahedra can relax because of the formation of rosette structures at vertices in the outer layer.

  9. The structure of small metal clusters

    Science.gov (United States)

    Bauschlicher, C. W., Jr.; Pettersson, L. G. M.

    1986-01-01

    One metal atom surrounded by its 12 nearest neighbors is considered for both D(3d) (face-centered cubic-like) and D(3h) (hexagonal close-packed-like) geometries. For Al and Be, the neutral cluster and the positive and negative ions are considered for idealized (all bonds equal) and distorted geometries. The D(3d) geometry is found to be the lowest for Be13, while the D(3h) geometry is lower for Al13. This is the reverse of what is expected based upon the bulk metal structures, Be(hcp) and Al(fcc). Al13 is found to have only small distortions, while Be13 shows large distortions for both the D(3d) and D(3h) geometries. The ions have geometries which are similar to those found for the neutral systems. Both all-electron and effective core potential calculations were carried out on the X13 clusters; the agreement is very good.

  10. Metallicity Spreads in M31 Globular Clusters

    Science.gov (United States)

    Bridges, Terry

    2003-07-01

    Our recent deep HST photometry of the M31 halo globular cluster {GC} Mayall II, also called G1, has revealed a red-giant branch with a clear spread that we attribute to an intrinsic metallicity dispersion of at least 0.4 dex in [Fe/H]. The only other GC exhibiting such a metallicity dispersion is Omega Centauri, the brightest and most massive Galactic GC, whose range in [Fe/H] is about 0.5 dex. These observations are obviously linked to the fact that both G1 and Omega Cen are bright and massive GC, with potential wells deep enough to keep part of their gas, which might have been recycled, producing a metallicity scatter among cluster stars. These observations dramatically challenge the notion of chemical homogeneity as a defining characteristic of GCs. It is critically important to find out how common this phenomenon is and how it can constrain scenarios/models of GC formation. The obvious targets are other bright and massive GCs, which exist in M31 but not in our Galaxy where Omega Cen is an isolated giant. We propose to acquire, with ACS/HRC, deep imaging of 3 of the brightest M31 GCs for which we have observed velocity dispersion values similar to those observed in G1 and Omega Cen. A sample of GCs with chemical abundance dispersions will provide essential information about their formation mechanism. This would represent a major step for the studies of the origin and evolution of stellar populations.

  11. 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...... calculations to predict the structure of Pd clusters in UiO-66. The cluster sizes examined are far larger than those in any previous modeling studies of metal clusters in MOFs and allow us to test the hypothesis that the physically separated cavities in UiO-66 could stabilize isolated Pd clusters. Our...

  12. LCAO-Xα calculations of transition metal clusters

    International Nuclear Information System (INIS)

    Seifert, G.; Eschrig, H.

    1985-01-01

    The electronic structure of some transition metal clusters (V 6 , Cr 6 , Cu 6 , Ag 6 ) is studied by an approximate LCAO-Xα scheme. Energy level spectra are discussed with respect to other theoretical investigations. The density-of-states curves are represented and compared with those from band-structure calculations. The correlation between binding energies of clusters and the corresponding cohesive energies of the bulk material is shown. Furthermore, the binding energies in copper clusters versus cluster size are discussed. Finally, some experimental results according beams of copper clusters and ESR studies of matrix isolated copper clusters are explained briefly. (author)

  13. 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.

  14. Oxide-supported metal clusters: models for heterogeneous catalysts

    International Nuclear Information System (INIS)

    Santra, A K; Goodman, D W

    2003-01-01

    Understanding the size-dependent electronic, structural and chemical properties of metal clusters on oxide supports is an important aspect of heterogeneous catalysis. Recently model oxide-supported metal catalysts have been prepared by vapour deposition of catalytically relevant metals onto ultra-thin oxide films grown on a refractory metal substrate. Reactivity and spectroscopic/microscopic studies have shown that these ultra-thin oxide films are excellent models for the corresponding bulk oxides, yet are sufficiently electrically conductive for use with various modern surface probes including scanning tunnelling microscopy (STM). Measurements on metal clusters have revealed a metal to nonmetal transition as well as changes in the crystal and electronic structures (including lattice parameters, band width, band splitting and core-level binding energy shifts) as a function of cluster size. Size-dependent catalytic reactivity studies have been carried out for several important reactions, and time-dependent catalytic deactivation has been shown to arise from sintering of metal particles under elevated gas pressures and/or reactor temperatures. In situ STM methodologies have been developed to follow the growth and sintering kinetics on a cluster-by-cluster basis. Although several critical issues have been addressed by several groups worldwide, much more remains to be done. This article highlights some of these accomplishments and summarizes the challenges that lie ahead. (topical review)

  15. 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.

  16. Oxygen Reduction Reaction Catalyzed by Noble Metal Clusters

    Directory of Open Access Journals (Sweden)

    Zhenghua Tang

    2018-02-01

    Full Text Available Highly-efficient catalysts for the oxygen reduction reaction (ORR have been extensively investigated for the development of proton exchange membrane fuel cells (PEMFCs. The state-of-the-art Pt/C catalysts suffer from high price, limited accessibility of Pt, sluggish reaction kinetics, as well as undesirable long-term durability. Engineering ultra-small noble metal clusters with high surface-to-volume ratios and robust stabilities for ORR represents a new avenue. After a simple introduction regarding the significance of ORR and the recent development of noble metal clusters, the general ORR mechanism in both acidic and basic media is firstly discussed. Subsequently, we will summarize the recent efforts employing Pt, Au, Ag, Pd and Ru clusters, as well as the alloyed bi-metallic clusters for acquiring highly efficient catalysts to enhance both the activity and stability of ORR. Molecular noble metal clusters with definitive composition to reveal the relevant ORR mechanism will be particularly highlighted. Finally, the current challenges, the future outlook, as well as the perspectives in this booming field will be proposed, featuring the great opportunities and potentials to engineering noble metal clusters as highly-efficient and durable cathodic catalysts for fuel cell applications.

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

    International Nuclear Information System (INIS)

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

    2016-01-01

    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 3 nm 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. - Highlights: • Field evaporation of metallic glasses is heterogeneous on a scale of up to 3 nm. • Amount of clustered evaporation depends on ion species and temperature. • Length scales of clustered evaporation and correlative evaporation are similar.

  18. Effect of Graphene with Nanopores on Metal Clusters

    Energy Technology Data Exchange (ETDEWEB)

    Zhou, Hu; Chen, Xianlang; Wang, Lei; Zhong, Xing; Zhuang, Guilin; Li, Xiaonian; Mei, Donghai; Wang, Jianguo

    2015-10-07

    Porous graphene, which is a novel type of defective graphene, shows excellent potential as a support material for metal clusters. In this work, the stability and electronic structures of metal clusters (Pd, Ir, Rh) supported on pristine graphene and graphene with different sizes of nanopore were investigated by first-principle density functional theory (DFT) calculations. Thereafter, CO adsorption and oxidation reaction on the Pd-graphene system were chosen to evaluate its catalytic performance. Graphene with nanopore can strongly stabilize the metal clusters and cause a substantial downshift of the d-band center of the metal clusters, thus decreasing CO adsorption. All binding energies, d-band centers, and adsorption energies show a linear change with the size of the nanopore: a bigger size of nanopore corresponds to a stronger metal clusters bond to the graphene, lower downshift of the d-band center, and weaker CO adsorption. By using a suitable size nanopore, supported Pd clusters on the graphene will have similar CO and O2 adsorption ability, thus leading to superior CO tolerance. The DFT calculated reaction energy barriers show that graphene with nanopore is a superior catalyst for CO oxidation reaction. These properties can play an important role in instructing graphene-supported metal catalyst preparation to prevent the diffusion or agglomeration of metal clusters and enhance catalytic performance. This work was supported by National Basic Research Program of China (973Program) (2013CB733501), the National Natural Science Foundation of China (NSFC-21176221, 21136001, 21101137, 21306169, and 91334013). D. Mei acknowledges the support from the US Department of Energy, Office of Science, Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences & Biosciences. Pacific Northwest National Laboratory (PNNL) is a multiprogram national laboratory operated for DOE by Battelle. Computing time was granted by the grand challenge of computational

  19. Metal nanostructures: from clusters to nanocatalysis and sensors

    Science.gov (United States)

    Smirnov, B. M.

    2017-12-01

    The properties of metal clusters and nanostructures composed of them are reviewed. Various existing methods for the generation of intense beams of metal clusters and their subsequent conversion into nanostructures are compared. Processes of the flow of a buffer gas with active molecules through a nanostructure are analyzed as a basis of using nanostructures for catalytic applications. The propagation of an electric signal through a nanostructure is studied by analogy with a macroscopic metal. An analysis is given of how a nanostructure changes its resistance as active molecules attach to its surface and are converted into negative ions. These negative ions induce the formation of positively charged vacancies inside the metal conductor and attract the vacancies to together change the resistance of the metal nanostructure. The physical basis is considered for using metal clusters and nanostructures composed of them to create new materials in the form of a porous metal film on the surface of an object. The fundamentals of nanocatalysis are reviewed. Semiconductor conductometric sensors consisting of bound nanoscale grains or fibers acting as a conductor are compared with metal sensors conducting via a percolation cluster, a fractal fiber, or a bunch of interwoven nanofibers formed in superfluid helium. It is shown that sensors on the basis of metal nanostructures are characterized by a higher sensitivity than semiconductor ones, but are not selective. Measurements using metal sensors involve two stages, one of which measures to high precision the attachment rate of active molecules to the sensor conductor, and in the other one the surface of metal nanostructures is cleaned from the attached molecules using a gas discharge plasma (in particular, capillary discharge) with a subsequent chromatography analysis for products of cleaning.

  20. Self-assembled metal clusters on an alumina nanomesh

    International Nuclear Information System (INIS)

    Buchsbaum, A.

    2012-01-01

    Template mediated growth of metals has attracted much interest due to the remarkable magnetic and catalytic properties of clusters in the nanometer range and provides the opportunity to grow clusters with narrow size distributions. When the Ni3Al(111) surface is exposed to oxygen at elevated temperature a thin oxide film with a well-defined structure and uniform thickness grows and covers the alloy surface completely. The structure of the alumina film has been solved mainly by the help of scanning tunneling microscopy (STM) combined with density functional theory (DFT) calculations. The structure of the approx. 0.5 nm thick oxide film has sixfold symmetry and exhibits holes with a diameter of approx. 400 pm reaching down to the metal substrate at the corners of the (Sqrt(67) x Sqrt(67))R12.2° unit cell. The side length of the unit cell is 4.1 nm. The driving force for the formation of the oxide nanomesh is the reduction of the metal/oxide interface energy by the formation of energetically favorable Al-Ni bonds at the interface. Due to better wetting of metal on metal surfaces than on oxide surfaces, metal atoms prefer to bind to the substrate in the hole, not to the oxide. Therefore the oxide forms a template with a hexagonal 4.1 nm lattice for the growth of well-ordered metal clusters. Nevertheless, the growth of most metal clusters on top of the corner holes is not straightforward. Fe and Co atoms cannot jump into the corner holes due to a barrier for diffusion and nucleate at their second favorable adsorption site. However, Pd atoms trapped in these corner holes reduce the barrier for diffusion and create metallic nucleation sites where Fe as well as Co clusters can nucleate and form a well-ordered hexagonal arrangement on the oxide nanomesh. We have studied these Fe and Co clusters and applied different methods like STM and surface x-ray diffraction (SXRD) to determine the morphology and crystallography of the clusters. For Fe we found cluster growth with

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

    Science.gov (United States)

    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.

  2. The effect of alkylating agents on model supported metal clusters

    Energy Technology Data Exchange (ETDEWEB)

    Erdem-Senatalar, A.; Blackmond, D.G.; Wender, I. (Pittsburgh Univ., PA (USA). Dept. of Chemical and Petroleum Engineering); Oukaci, R. (CERHYD, Algiers (Algeria))

    1988-01-01

    Interactions between model supported metal clusters and alkylating agents were studied in an effort to understand a novel chemical trapping technique developed for identifying species adsorbed on catalyst surfaces. It was found that these interactions are more complex than had previously been suggested. Studies were completed using deuterium-labeled dimethyl sulfate (DMS), (CH{sub 3}){sub 2}SO{sub 4}, as a trapping agent to interact with the supported metal cluster ethylidyne tricobalt enneacarbonyl. Results showed that oxygenated products formed during the trapping reaction contained {minus}OCD{sub 3} groups from the DMS, indicating that the interaction was not a simple alkylation. 18 refs., 1 fig., 3 tabs.

  3. Theoretical studies of the electronic structure of small metal clusters

    Science.gov (United States)

    Jordan, K. D.

    1982-01-01

    Theoretical studies of the electronic structure of metal clusters, in particular clusters of Group IIA and IIB atoms were conducted. Early in the project it became clear that electron correlation involving d orbitals plays a more important role in the binding of these clusters than had been previously anticipated. This necessitated that computer codes for calculating two electron integrals and for constructing the resulting CI Hamiltonions be replaced with newer, more efficient procedures. Program modification, interfacing and testing were performed. Results of both plans are reported.

  4. Structural evolution, growth and stability of metal titanium clusters

    Science.gov (United States)

    Chauke, Hasani; Phaahla, Tshegofatso; Ngoepe, Phuti; Catlow, Richard

    The transition metals clusters such as titanium have received a significant attention due to their excellent physical and chemical properties and great technological application in many fields. A survey of small Ti clusters was performed using interatomic potentials and computational methods based on density functional theory; and the knowledge led master code with a genetic algorithm to generate the lowest energy geometries of Tin (n = 2-32) clusters. The all electron spin-unpolarized generalized gradient approximation is used to determine the ground state structures, binding energy and electronic properties. The structural evolution of titanium clusters, which favors the icosahedron structure growth pattern is observed. The energy for the ground state configurations is found to increase monotonically with the clusters size. Their relative stability results predict clusters with 5 and 7 as more stable. The energy difference for clusters n >=24 is very small, suggesting that the larger clusters could be stable at moderate temperatures. In addition to the magic numbers that are often reported i.e. Ti7 and Ti13; clusters 5, 9, 14, 17 and 26 have extra stability.

  5. Magnetic anisotropy of deposited transition metal clusters

    Science.gov (United States)

    Bornemann, S.; Minár, J.; Staunton, J. B.; Honolka, J.; Enders, A.; Kern, K.; Ebert, H.

    2007-12-01

    We present results of magnetic torque calculations using the fully relativistic spin-polarized Korringa-Kohn-Rostoker approach applied to small Co and Fe clusters deposited on the Pt(111) surface. From the magnetic torque one can derive amongst others the magnetic anisotropy energy (MAE). It was found that this approach is numerically much more stable and also computationally less demanding than using the magnetic force theorem that allows to calculate the MAE directly. Although structural relaxation effects were not included our results correspond reasonably well to recent experimental data.

  6. 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.

  7. STAR CLUSTERS IN M31. II. OLD CLUSTER METALLICITIES AND AGES FROM HECTOSPEC DATA

    International Nuclear Information System (INIS)

    Caldwell, Nelson; Schiavon, Ricardo; Morrison, Heather; Harding, Paul; Rose, James A.

    2011-01-01

    We present new high signal-to-noise spectroscopic data on the M31 globular cluster (GC) system, obtained with the Hectospec multifiber spectrograph on the 6.5 m MMT. More than 300 clusters have been observed at a resolution of 5 A and with a median S/N of 75 per A, providing velocities with a median uncertainty of 6 km s -1 . The primary focus of this paper is the determination of mean cluster metallicities, ages, and reddenings. Metallicities were estimated using a calibration of Lick indices with [Fe/H] provided by Galactic GCs. These match well the metallicities of 24 M31 clusters determined from Hubble Space Telescope color-magnitude diagrams, the differences having an rms of 0.2 dex. The metallicity distribution is not generally bimodal, in strong distinction with the bimodal Galactic globular distribution. Rather, the M31 distribution shows a broad peak, centered at [Fe/H] = -1, possibly with minor peaks at [Fe/H] = -1.4, -0.7, and -0.2, suggesting that the cluster systems of M31 and the Milky Way had different formation histories. Ages for clusters with [Fe/H] > - 1 were determined using the automatic stellar population analysis program EZ A ges. We find no evidence for massive clusters in M31 with intermediate ages, those between 2 and 6 Gyr. Moreover, we find that the mean ages of the old GCs are remarkably constant over about a decade in metallicity (-0.95∼< [Fe/H] ∼<0.0).

  8. 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. Copyright © 2015 Elsevier B.V. All rights reserved.

  9. 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

  10. Two-phonon states in alkali-metal clusters

    International Nuclear Information System (INIS)

    Abada, A.; Vautherin, D.

    1992-12-01

    Two phonon-states of alkali-metal clusters (treated as jellium spheres) are calculated by using a method based on a perturbative construction of periodic orbits of the time-dependent mean-field equations. Collective vibrations with various multipolarities in charged Na 21 + are considered. (author) 26 refs.; 2 figs.; 3 tabs

  11. The metallicity of the open cluster Tombaugh 2

    Science.gov (United States)

    Villanova, S.; Randich, S.; Geisler, D.; Carraro, G.; Costa, E.

    2010-01-01

    Context. Open clusters are excellent tracers of the structure, kinematics, and chemical evolution of the disk and a wealth of information can be derived from the spectra of their constituent stars. Aims: We investigate the nature of the chemical composition of the outer disk open cluster Tombaugh 2. This has been suggested to be a member of the GASS/Mon substructure, and a recent study by Frinchaboy et al. (2008) suggested that this was a unique open cluster in possessing an intrinsic metal abundance dispersion. We aim to investigate such claims. Methods: High resolution VLT+GIRAFFE spectra in the optical are obtained and analyzed for a number of stars in the Tombaugh 2 field, together with independent UBVIC photometry. Radial velocities and position in the color-magnitude diagram are used to assess cluster membership. The spectra, together with input atmospheric parameters and model atmospheres, are used to determine detailed chemical abundances for a variety of elements in 13 members with good spectra. Results: We find the mean metallicity to be [Fe/H] = -0.31 ± 0.02 with no evidence for an intrinsic abundance dispersion, in contrary to the recent results of Frinchaboy et al. (2008, MNRAS, 391, 39). We find Ca and Ba to be slightly enhanced, while Ni and Sc are solar. The r-process element Eu was found to be enhanced, giving an average [Eu/Ba] = +0.17. The Li abundance decreases with Teff on the upper giant branch and maintains a low level for red clump stars. The mean metallicity we derive agrees well with that expected from the radial abundance gradient in the disk for a cluster at its Galactocentric distance. Conclusions: Tombaugh 2 is found to have abundances as expected from its Galactocentric distance and no evidence for any intrinsic metallicity dispersion. The surprising result found by Frinchaboy et al. (2008), which is the presence of two distinct abundance groups within the cluster, implying either a completely unique open cluster with an intrinsic

  12. 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 selec...... capability in formation of supported size-selected metal nanoparticles with controllable coverage for various practical applications.......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...

  13. Molecular metal clusters synthetized by a radiolytic process

    International Nuclear Information System (INIS)

    Remita, H.; Derai, R.; Delcourt, M.O.

    1991-01-01

    The radiolytic reduction of metal ions in alcohols has been achieved under CO atmosphere. Under such conditions, metal reduction, ligation and aggregation processes compete, leading to metal complexes and molecular clusters. These products are interesting for catalytic purposes. We report here the radiolytic synthesis of compounds of Fe, Ru, Os, Co, Ir, Rh, Pt, Cu, Ag, and of some intermetallic compounds. These synthesis are carried out under very mild temperature and pressure conditions (i.e., room temperature and at most I atmosphere of CO). Factors favoring a high nuclearity are the concentration, the high atomic number, a weak ligand/metal ratio. It is shown that chloride ions are inhibitors of complete reduction [fr

  14. Distribution of interatomic distances in large metallic clusters

    International Nuclear Information System (INIS)

    Glossman, M.D.; Iniguez, M.P.; Alonso, J.A.

    1992-01-01

    Spherically averaged pseudopotential (SAPS) calculations have been done for Mg n clusters, with n up to 250 within the framework of density functional theory. The electronic structure is computed resorting to the Thomas-Fermi-Dirac-Weizsaecker (TFDW) approximation for the kinetic energy. The equilibrium geometries have been obtained by minimizing the total cluster energy with respect to the atomic positions using the steepest-descent method. The ground state geometries obtained in this way are formed by spherical atomic shells, the number of them increasing with cluster size, up to a number of four for the biggest sizes considered here. An analysis of the distribution of the interatomic distances shows that the more internal is the shell, the more contracted are the interatomic distances. This effect diminishes progressively with increasing cluster size. For the purpose of comparison, similar calculations have been done with Cs n clusters in the same size range, allowing us to reproduce previous results obtained using a more elaborated density functional technique (Kohn-Sham method). The inhomogeneous contraction of interatomic distances then appears as a general fact for simple metallic clusters and not only for alkaline ones. (orig.)

  15. Manipulating Light with Transition Metal Clusters, Organic Dyes, and Metal Organic Frameworks

    Energy Technology Data Exchange (ETDEWEB)

    Ogut, Serdar [Univ. of Illinois, Chicago, IL (United States)

    2017-09-11

    The primary goals of our research program is to develop and apply state-of-the-art first-principles methods to predict electronic and optical properties of three systems of significant scientific and technological interest: transition metal clusters, organic dyes, and metal-organic frameworks. These systems offer great opportunities to manipulate light for a wide ranging list of energy-related scientific problems and applications. During this grant period, we focused our investigations on the development, implementation, and benchmarking of many-body Green’s function methods (GW approximation and the Bethe-Salpeter equation) to examine excited-state properties of transition metal/transition-metal-oxide clusters and organic molecules that comprise the building blocks of dyes and metal-organic frameworks.

  16. Metallicities of young massive clusters in NGC 5236 (M83)

    Science.gov (United States)

    Hernandez, Svea; Larsen, Søren; Trager, Scott; Kaper, Lex; Groot, Paul

    2018-01-01

    We present integrated-light (IL) spectra of eight young massive clusters (YMCs) in the metal-rich spiral galaxy NGC 5236 (M83). The observations were taken with the X-Shooter spectrograph on the ESO Very Large Telescope. Through the use of theoretical isochrones and synthetic IL spectra, we derive metallicities and study the radial metallicity gradient observed through these young populations. For the inner regions of the galaxy, we observe a relatively shallow metallicity gradient of -0.37 ± 0.29 dex R_{25}^{-1}, agreeing with chemical evolution models with an absence of infall material and a relatively low mass-loss due to winds in the inner parts of the disc. We estimate a central metallicity of [Z] = +0.17 ± 0.12 dex, finding excellent agreement with that obtained via other methods (e.g. blue supergiants and J band). We infer a metallicity of 12+log(O/H) = 8.75 ± 0.08 dex at R/R25 = 0.4, which fits the stellar mass-metallicity relation compilation of blue supergiants and IL studies.

  17. Oxygen Reduction Reaction Catalyzed by Noble Metal Clusters

    OpenAIRE

    Zhenghua Tang; Wen Wu; Kai Wang

    2018-01-01

    Highly-efficient catalysts for the oxygen reduction reaction (ORR) have been extensively investigated for the development of proton exchange membrane fuel cells (PEMFCs). The state-of-the-art Pt/C catalysts suffer from high price, limited accessibility of Pt, sluggish reaction kinetics, as well as undesirable long-term durability. Engineering ultra-small noble metal clusters with high surface-to-volume ratios and robust stabilities for ORR represents a new avenue. After a simple introduction ...

  18. Synthesis and Properties of Metal Clusters in Polymeric Matrices

    Science.gov (United States)

    Kay, E.

    1986-06-01

    A one-step plasma deposition process is described which allows the uniform dispersion of small metal clusters throughout a thin film polymer matrix. Plasma parameters and plasma gas phase diagnostics relevant to the control of film composition and structure are discussed. Chemical and structural analytical techniques such as I.R. absorption spectroscopy, E.S.C.A., Auger electron spectroscopy, X-ray fluorescence, X-ray and electron diffraction and microscopy are used to characterize the cluster containing films. Changes in cluster size and shape as a function of volume fraction and as a result of post deposition annealing are described. Optical and electrical properties are presented below and above the onset of percolation and are evaluated in terms of contemporary effective medium theories.

  19. Synthesis and characterization of metal sulfide clusters for toxicological studies.

    Science.gov (United States)

    Bowles, L C; Bell, Russell A; Ernste, Michael J; Kramer, James R; Manolopoulos, Helen; Ogden, Nancy

    2002-04-01

    Zinc sulfide clusters were synthesized and characterized at low micromolar concentrations to assess the effect of metal-sulfide ligands on metal toxicity to aquatic organisms in oxic environments. Recommended preparation times are greater than 2 h initial reaction of equimolar sodium sulfide and zinc nitrate, followed by oxic aeration for 3 d. Ionic strength, pH, and anoxic stabilization time were found to be relatively unimportant in controlling the final yield. Adsorptive losses of zinc sulfide (ZnS) clusters to surfaces, however, were significant for a variety of vessel materials and membrane filters. Ionic strength and pH were found to be important factors controlling the extent of adsorptive losses with minimal loss for pHs greater than 9 and for soft waters. The Ag(I), Cu(II), and Hg(II) as metal sulfides completely suppress the analysis of sulfide, whereas Pb(II), Mn(II), and Co(II) partially suppress the analysis of sulfide by the methylene blue technique. Ultraviolet and fluorescence spectra are shown for synthesized ZnS clusters.

  20. FURTHER DEFINITION OF THE MASS-METALLICITY RELATION IN GLOBULAR CLUSTER SYSTEMS AROUND BRIGHTEST CLUSTER GALAXIES

    International Nuclear Information System (INIS)

    Cockcroft, Robert; Harris, William E.; Wehner, Elizabeth M. H.; Whitmore, Bradley C.; Rothberg, Barry

    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 combined data sets show a mean trend for the metal-poor subpopulation that corresponds to a scaling of heavy-element abundance with cluster mass Z ∼ M 0.30±0.05 . No trend is seen for the metal-rich subpopulation which has a scaling relation that is consistent with zero. We also find that the scaling exponent is independent of the GCS specific frequency and host galaxy luminosity, except perhaps for dwarf galaxies. We present new photometry in (g',i') obtained with Gemini/GMOS for the GC populations around the southern giant ellipticals NGC 5193 and IC 4329. Both galaxies have rich cluster populations which show up as normal, bimodal sequences in the color-magnitude diagram. We test the observed MMRs and argue that they are statistically real, and not an artifact caused by the method we used. We also argue against asymmetric contamination causing the observed MMR as our mean results are no different from other contamination-free studies. Finally, we compare our method to the standard bimodal fitting method (KMM or RMIX) and find our results are consistent. Interpretation of these results is consistent with recent models for GC formation in which the MMR is determined by GC self-enrichment during their brief formation period.

  1. 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.)

  2. An age difference of two billion years between a metal-rich and a metal-poor globular cluster.

    Science.gov (United States)

    Hansen, B M S; Kalirai, J S; Anderson, J; Dotter, A; Richer, H B; Rich, R M; Shara, M M; Fahlman, G G; Hurley, J R; King, I R; Reitzel, D; Stetson, P B

    2013-08-01

    Globular clusters trace the formation history of the spheroidal components of our Galaxy and other galaxies, which represent the bulk of star formation over the history of the Universe. The clusters exhibit a range of metallicities (abundances of elements heavier than helium), with metal-poor clusters dominating the stellar halo of the Galaxy, and higher-metallicity clusters found within the inner Galaxy, associated with the stellar bulge, or the thick disk. Age differences between these clusters can indicate the sequence in which the components of the Galaxy formed, and in particular which clusters were formed outside the Galaxy and were later engulfed along with their original host galaxies, and which were formed within it. Here we report an absolute age of 9.9 ± 0.7 billion years (at 95 per cent confidence) for the metal-rich globular cluster 47 Tucanae, determined by modelling the properties of the cluster's white-dwarf cooling sequence. This is about two billion years younger than has been inferred for the metal-poor cluster NGC 6397 from the same models, and provides quantitative evidence that metal-rich clusters like 47 Tucanae formed later than metal-poor halo clusters like NGC 6397.

  3. 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.

  4. Open Cluster Metallicity Scale and the Metallicity Gradient in the Galaxy

    Science.gov (United States)

    Pylskaya, O.; Wiebe, D.

    We analyse the available data on the open cluster metallicity and compare them with those from Lynga (1987) and Gratton (2000). On the base of linear fitting, we find relations between the published studies of the open cluster metallicity (where data on several objects are available) with [Fe/H] data compiled by Lynga (1987) and calculated by Twarog et al. (1997). This allowed to build a quasi-homogeneous metallicity scale for 140 open clusters, more than in any other similar study before (Pylskaya & Wiebe 1993). These data coupled with the distance scale by Barkhatova & Pylskaya (1983) are used to investigate gradients of the Galactic disc chemical composition. Our unified metallicity scales are consistent with the presence of the metallicity gradient in the Galaxy of order of -0.1 dex kpc-1, somewhat steeper that found in other studies. The vertical gradient is less pronounced. The upper envelope on the Z-[Fe/H] diagram has a slope of -0.32 dex kpc-1 for the Lynga-based scale and even steeper slope of -0.48 dex kpc-1 for the scale based on Twarog et al. data. These results are discussed in the context of the Galaxy chemical evolution and the processes that drive the gradient formation. This work is part of the OCL investigations based on the Supplements to Alter-Ruprecht open cluster catalogue (CSCA) that are being prepared in the Urals State University since 1988 (Pylskaya 1997). DW work is supported by the RFBR grants 99-02-16037 and 01-02-06080.

  5. Sulphur in the metal poor globular cluster NGC 6397

    Science.gov (United States)

    Koch, A.; Caffau, E.

    2011-10-01

    Sulphur (S) is a non-refractory α-element that is not locked into dust grains in the interstellar medium. Thus no correction to the measured, interstellar sulphur abundance is needed and it can be readily compared to the S content in stellar photospheres. Here we present the first measurement of sulphur in the metal poor globular cluster (GC) NGC 6397, as detected in a MIKE/Magellan high signal-to-noise, high-resolution spectrum of one red giant star. While abundance ratios of sulphur are available for a larger number of Galactic stars down to an [Fe/H] of ~ -3.5 dex, no measurements in globular clusters more metal poor than -1.5 dex have been reported so far. We find aNLTE, 3-D abundance ratio of [S/Fe] = +0.52 ± 0.20 (stat.) ± 0.08 (sys.), based on theS I, Multiplet 1 line at 9212.8 Å. This value is consistent with a Galactic halo plateau as typical of other α-elements in GCs and field stars, but we cannot rule out its membership with a second branch of increasing [S/Fe] with decreasing [Fe/H], claimed in the literature, which leads to a large scatter at metallicities around - 2 dex. The [S/Mg] and [S/Ca] ratios in this star are compatible with a Solar value to within the (large) uncertainties. Despite the very large scatter in these ratios across Galactic stars between literature samples, this indicates that sulphur traces the chemical imprints of the other α-elements in metal poor GCs. Combined with its moderate sodium abundance ([S/Na]NLTE = 0.48), the [S/Fe] ratio in this GC extends a global, positive S-Na correlation that is not seen in field stars and might indicate that proton-capture reactions contributed to the production of sulphur in the (metal poor) early GC environments. This paper includes data gathered with the 6.5 m Magellan Telescopes located at Las Campanas Observatory, Chile.

  6. 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...... functional theory (DFT) calculations with a genetic algorithm (GA) to reliably predict the structure of the adsorbed clusters. This approach allows comparison of hundreds of adsorbed configurations for each cluster. From the investigation of Au8, Pd8, and Au4Pd4 we find that the organic part of the MOF...... 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...

  7. Clusters agrícolas: un estado del arte para los estudios de competitividad en el campo

    Directory of Open Access Journals (Sweden)

    Lina Tapia

    2015-12-01

    Full Text Available En el siguiente trabajo se revisó cómo se ha abordado el fenómeno del cluster en la agricultura debido a que el encadenamiento entre eslabones de la producción y los modelos de gestión de sistemas agrícolas son cada vez más importantes para el equilibrio de mercado de los productos agroalimentarios, principalmente en un entorno que impulsa el crecimiento acelerado en la demanda de alimentos, bienes industriales y biocombustibles. Para tal propósito se discutió la relación entre agricultura, desarrollo rural, cadenas agroalimentarias y clusters agrícolas. Luego se seleccionaron trabajos de investigación internacionales y latinoamericanos que se ocuparon de caracterizar, medir o diseñar estos sistemas, con el fin de identificar variables, tipos de enfoques, métodos de estudio y principales aportes a la mejora de su productividad y competitividad. Al final, se encontró que los estudios de caso ad hoc han sido los métodos más aplicados, seguidos de los análisis multivariados y las tablas inputs-outputs. Además, se pudo ver que el enfoque cuantitativo a través de la simulación matemática, apenas comienza a incluirse en el problema de diseño de clusters agrícolas y que la preocupación por este tema en Latinoamérica también es reciente.

  8. 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.

  9. Chiral structures and tunable magnetic moments in 3d transition metal doped Pt6 clusters

    International Nuclear Information System (INIS)

    Zhang Xiu-Rong; Yang Xing; Ding Xun-Lei

    2012-01-01

    The structural, electronic, and magnetic properties of transition metal doped platinum clusters MPt 6 (M=Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, and Zn) are systematically studied by using the relativistic all-electron density functional theory with the generalized gradient approximation. Most of the doped clusters show larger binding energies than the pure Pt 7 cluster, which indicates that the doping of the transition metal atom can stabilize the pure platinum cluster. The results of the highest occupied molecular orbital (HOMO)—lowest unoccupied molecular orbital (LUMO) gaps suggest that the doped clusters can have higher chemical activities than the pure Pt 7 cluster. The magnetism calculations demonstrate that the variation range of the magnetic moments of the MPt 6 clusters is from 0 μ B to 7 μ B , revealing that the MPt 6 clusters have potential utility in designing new spintronic nanomaterials with tunable magnetic properties

  10. Supported Dendrimer-Encapsulated Metal Clusters: Toward Heterogenizing Homogeneous Catalysts.

    Science.gov (United States)

    Ye, Rong; Zhukhovitskiy, Aleksandr V; Deraedt, Christophe V; Toste, F Dean; Somorjai, Gabor A

    2017-08-15

    Recyclable catalysts, especially those that display selective reactivity, are vital for the development of sustainable chemical processes. Among available catalyst platforms, heterogeneous catalysts are particularly well-disposed toward separation from the reaction mixture via filtration methods, which renders them readily recyclable. Furthermore, heterogeneous catalysts offer numerous handles-some without homogeneous analogues-for performance and selectivity optimization. These handles include nanoparticle size, pore profile of porous supports, surface ligands and interface with oxide supports, and flow rate through a solid catalyst bed. Despite these available handles, however, conventional heterogeneous catalysts are themselves often structurally heterogeneous compared to homogeneous catalysts, which complicates efforts to optimize and expand the scope of their reactivity and selectivity. Ongoing efforts in our laboratories are aimed to address the above challenge by heterogenizing homogeneous catalysts, which can be defined as the modification of homogeneous catalysts to render them in a separable (solid) phase from the starting materials and products. Specifically, we grow the small nanoclusters in dendrimers, a class of uniform polymers with the connectivity of fractal trees and generally radial symmetry. Thanks to their dense multivalency, shape persistence, and structural uniformity, dendrimers have proven to be versatile scaffolds for the synthesis and stabilization of small nanoclusters. Then these dendrimer-encapsulated metal clusters (DEMCs) are adsorbed onto mesoporous silica. Through this method, we have achieved selective transformations that had been challenging to accomplish in a heterogeneous setting, e.g., π-bond activation and aldol reactions. Extensive investigation into the catalytic systems under reaction conditions allowed us to correlate the structural features (e.g., oxidation states) of the catalysts and their activity. Moreover, we have

  11. 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 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.

  12. vbyCaHbeta CCD Photometry of Clusters. VI. The Metal-Deficient Open Cluster NGC 2420

    OpenAIRE

    Anthony-Twarog, Barbara J.; Tanner, Delora; Cracraft, Misty; Twarog, Bruce A.

    2005-01-01

    CCD photometry on the intermediate-band vbyCaHbeta system is presented for the metal-deficient open cluster, NGC 2420. Restricting the data to probable single members of the cluster using the CMD and the photometric indices alone generates a sample of 106 stars at the cluster turnoff. The average E(b-y) = 0.03 +/- 0.003 (s.e.m.) or E(B-V) = 0.050 +/- 0.004 (s.e.m.), where the errors refer to internal errors alone. With this reddening, [Fe/H] is derived from both m1 and hk, using b-y and Hbeta...

  13. 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...... moments in small clusters compared to bulk as being due to melting of surface spins....

  14. Estudio metalúrgico de causas de falla del puente pescadero

    Directory of Open Access Journals (Sweden)

    Héctor Delgado

    1998-01-01

    Full Text Available Se trata de un puente en arco de una sola luz de 120 m, el cual colapsó después de 10 años de servicio. Con base en elementos estructurales extraídos del puente de falla, se realizó un estudio fractográfico, mecáni co y químico, con el fin de establecer las posibles causas de fallas del puente desde el punto de vista metalúrgico. En nudos de unión de pendolón-arco se observan fracturas por fatiga en uniones soldadas en varios sitios, lo cual es evidenciado por una apariencia de fractura suave de crecimiento estable de grietas combinada con una zona de apariencia fibrosa de fractura súbita final de colapso del puente. Dado que el colapso del puente es precedido por la generación de grietas en uniones soldadas, se considera importante examinar la combinación de las propiedades de resistencia y tenacidad con el fin de estudiar tanto la capacidad de soporte de carga como de la tolerancia de defectos de las uniones soldadas.

  15. Self-Assembly of Silver Metal Clusters of Small Atomicity on Cyclic Peptide Nanotubes.

    Science.gov (United States)

    Cuerva, Miguel; García-Fandiño, Rebeca; Vázquez-Vázquez, Carlos; López-Quintela, M Arturo; Montenegro, Javier; Granja, Juan R

    2015-11-24

    Subnanometric noble metal clusters, composed by only a few atoms, behave like molecular entities and display magnetic, luminescent and catalytic activities. However, noncovalent interactions of molecular metal clusters, lacking of any ligand or surfactant, have not been seen at work. Theoretically attractive and experimentally discernible, van der Waals forces and noncovalent interactions at the metal/organic interfaces will be crucial to understand and develop the next generation of hybrid nanomaterials. Here, we present experimental and theoretical evidence of noncovalent interactions between subnanometric metal (0) silver clusters and aromatic rings and their application in the preparation of 1D self-assembled hybrid architectures with ditopic peptide nanotubes. Atomic force microscopy, fluorescence experiments, circular dichroism and computational simulations verified the occurrence of these interactions in the clean and mild formation of a novel peptide nanotube and metal cluster hybrid material. The findings reported here confirmed the sensitivity of silver metal clusters of small atomicity toward noncovalent interactions, a concept that could find multiple applications in nanotechnology. We conclude that induced supramolecular forces are optimal candidates for the precise spatial positioning and properties modulation of molecular metal clusters. The reported results herein outline and generalize the possibilities that noncovalent interactions will have in this emerging field.

  16. Comparison between XAS, AWAXS and DAFS applied to nanometer scale supported metallic clusters. Pt.1; monometallic clusters

    International Nuclear Information System (INIS)

    Bazin, D.C.; Sayers, D.A.

    1993-01-01

    The structural information found using three techniques related to synchrotron radiation are compared. XAS (X-ray Absorption Spectroscopy), AWAXS (Anomalous Wide Angle X-ray Scattering) and DAFS (Diffraction Anomalous Fine Structure) are applied to nanometer scale metallic clusters. (author)

  17. Estudio experimental de la movilidad de metales pesados en sedimentos de la cuenca del Jequetepeque, Perú

    OpenAIRE

    Isern Roselló, Regina; Martínez Planas, María del Mar

    2011-01-01

    Este proyecto tiene como objetivos determinar la concentración de metales en sedimentos procedentes de actividades mineras en la cuenca del río Jequetepeque así como su movilidad. Estos estudios son necesarios para el análisis de suelos contaminados ya que definen la capacidad tóxica de los sedimentos y, por tanto, su impacto en el medio ambiente. Para poder conocer el comportamiento de los metales estudiados (Zn, Cu, Al, Fe, Cd, Hg, Cr, Pb, As, Ni), se analizan los sedimentos de 5 zonas d...

  18. An efficient laser vaporization source for chemically modified metal clusters characterized by thermodynamics and kinetics

    Science.gov (United States)

    Masubuchi, Tsugunosuke; Eckhard, Jan F.; Lange, Kathrin; Visser, Bradley; Tschurl, Martin; Heiz, Ulrich

    2018-02-01

    A laser vaporization cluster source that has a room for cluster aggregation and a reactor volume, each equipped with a pulsed valve, is presented for the efficient gas-phase production of chemically modified metal clusters. The performance of the cluster source is evaluated through the production of Ta and Ta oxide cluster cations, TaxOy+ (y ≥ 0). It is demonstrated that the cluster source produces TaxOy+ over a wide mass range, the metal-to-oxygen ratio of which can easily be controlled by changing the pulse duration that influences the amount of reactant O2 introduced into the cluster source. Reaction kinetic modeling shows that the generation of the oxides takes place under thermalized conditions at less than 300 K, whereas metal cluster cores are presumably created with excess heat. These characteristics are also advantageous to yield "reaction intermediates" of interest via reactions between clusters and reactive molecules in the cluster source, which may subsequently be mass selected for their reactivity measurements.

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

    International Nuclear Information System (INIS)

    Barborini, E; Bertolini, G; Repetto, P; Leccardi, M; Vinati, S; Corbelli, G; Milani, P

    2010-01-01

    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.

  20. Mass spectrometric probes of metal cluster distributions and metastable ion decay

    International Nuclear Information System (INIS)

    Parks, E.K.; Liu, K.; Cole, S.K.; Riley, S.J.

    1988-01-01

    The study of metal clusters has provided both an opportunity and a challenge to the application of mass spectrometry. These days the most often-used technique for cluster generation - laser vaporization - leads to extensive distributions of cluster sizes, from one to perhaps thousands of atoms, and most studies reported to date use excimer laser ionization and time-of-flight mass spectrometry for cluster detection. Our apparatus is a simple one-stage TOF design employing Wiley-McLauren spatial focusing and a one-meter drift tube. In a second apparatus employing a pulsed valve in the cluster source, we see asymmetric broadening of niobium cluster mass peaks under multiphoton ionization conditions, indicating metastable decay of parent cluster ions. Other studies of niobium clusters have shown no such asymmetric peaks. 2 figs

  1. 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.

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

    Indian Academy of Sciences (India)

    . 1000 atoms) easily, thereby allowing us to study the evolution of van der Waals coefficients with the size of the clusters. For details of the ETF method and its application to study alkali–metal cluster, we refer the reader to [9,10,27–29]. In the.

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

    Indian Academy of Sciences (India)

    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, ...

  4. Theoretical Studies of Catalysis on Supported Metal Clusters

    National Research Council Canada - National Science Library

    Metiu, Horia

    2005-01-01

    ... catalytic chemistry than large ones. In addition they used advanced quantum chemistry method to test whether density functional theory is capable of providing accurate results for adsorption of oxygen, hydrogen, and propene on gold clusters...

  5. Magnetism in clusters of 4d transition metals

    International Nuclear Information System (INIS)

    Salcido A, F.; Villasenor G, P.; Dorantes D, J.

    1999-01-01

    The magnetic properties of ruthenium (Ru N ), rhodium (Rh N ) and palladium (Pd N ) clusters are determined as function of the cluster size N (N=4, 6, 13 and 19). For N=4 and 6 we take the tetrahedral and pentagonal pyramid geometric structures respectively. For N=13 and 19 we consider fcc-like structures. We use a tight binding Hamiltonian for s, p and d electrons in the unrestricted Hartree-Fock approximation. For the considered cluster, we obtain magnetic moments non-vanishing local, with the exception of Rh 4 . Ru N and Rh N present a maximum in the average magnetic moment when the size of the cluster is N=13 and in all the elements we found that the average magnetic moment decreases strongly at N=19. As expected, the local magnetic moments at the atoms of the surface of the cluster are larger than those at inner atoms, except for Ru 19 . We find strong oscillations of the magnetic moment as function of N an are less important in the Pd N clusters. (Author)

  6. Tracing the Chemical Evolution of Metal-rich Galactic Bulge Globular Clusters

    Science.gov (United States)

    Munoz Gonzalez, Cesar; Saviane, Ivo; Geisler, Doug; Villanova, Sandro

    2018-01-01

    We present in this poster the metallicity characterization of the four metal rich Bulge Galactic Gobular Clusters, which have controversial metallicities. We analyzed our high-resolution spectra (using UVES-580nm and GIRAFFE-HR13 setups) for a large sample of RGB/AGB targets in each cluster in order to measure their metallicity and prove or discard the iron spread hypothesis. We have also characterized chemically stars with potentially different iron content by measuring light (O, Na, Mg, Al), alpha (Si, Ca, Ti), iron–peak (V, Cr, Ni, Mn) and s and r process (Y, Zr, Ba, Eu) elements. We have identified possible channels responsible for the chemical heterogeneity of the cluster populations, like AGB or massive fast-rotating stars contamination, or SN explosion. Also, we have analyzed the origin and evolution of these bulge GCs and their connection with the bulge itself.

  7. 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

  8. Binding of noble metal clusters with rare gas atoms: theoretical investigation.

    Science.gov (United States)

    Jamshidi, Zahra; Far, Maryam Fakhraei; Maghari, Ali

    2012-12-27

    Binding of noble metal clusters (M(n), M = Cu, Ag, and Au; n = 2-4) with rare gas atoms (Rg = Kr, Xe, and Rn) has been investigated at the density functional (CAM-B3LYP) and ab initio (MP2) levels of theory. The calculation shows significant affinity of neutral metal clusters for interaction with rare gas atoms. The binding energies indicate that gold clusters have the highest and silver clusters have the lowest affinity for interaction with rare gas atoms, and for the same metal clusters, there is a continuous increase in E(b) from Kr to Rn. The M-Rg bonding mechanism have been interpreted by means of the quantum theory of atoms in molecules (QTAIM), natural bond orbital (NBO), and energy decomposition analysis (EDA). According to these theories, the M-Rg bonds are found to be partially electrostatic and partially covalent. EDA results identify that these bonds have less than 40% covalent character and more than 60% electrostatic, and also NBO calculations predict the amount of charge transfer from the lone pair of rare gas to σ* and n*orbitals of metal clusters.

  9. Suppression of globular cluster formation in metal-poor gas clouds by Lyman α radiation feedback

    Science.gov (United States)

    Abe, Makito; Yajima, Hidenobu

    2018-03-01

    We study the impact of Ly α radiation feedback on globular cluster (GC) formation. In this Letter, we analytically derive the relation between star formation efficiency (SFE) and metallicity in spherical clouds with the Ly α radiation feedback. Our models show that the SFE becomes small as the metallicity decreases. In metal-poor gas clouds, Ly α photons are trapped for a long time and exert strong radiation force to the gas, resulting in the suppression of star formation. We find that bound star clusters (SFE ≳ 0.5) form only for the metallicity higher than ˜ 10- 2.5 Z⊙ in the case with the initial cloud mass 105 M⊙ and the radius 5 pc. Our models successfully reproduce the lower bound of observed metallicity of GCs. Thus, we suggest that the Ly α radiation feedback can be essential in understanding the formation of GCs.

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

    International Nuclear Information System (INIS)

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

    2014-01-01

    Theoretical studies on the structure, stability, and magnetic properties of icosahedral TM 13 (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 TM 13 clusters, Co 13 is absorbed relatively more strongly on pristine and defective graphene as compared to Fe 13 and Ni 13 clusters. The adsorbed clusters show reduced magnetic moment compared to the free clusters

  11. LITHIUM ABUNDANCES OF THE SUPER-METAL-RICH OPEN CLUSTER NGC 6253

    Energy Technology Data Exchange (ETDEWEB)

    Cummings, Jeffrey D. [Departamento de Astronomia, Universidad de Concepcion 160-C Casilla, Concepcion (Chile); Deliyannis, Constantine P.; Maderak, Ryan M. [Department of Astronomy, Indiana University Bloomington, IN 47405-7105 (United States); Anthony-Twarog, Barbara; Twarog, Bruce, E-mail: jcummings@astro-udec.cl, E-mail: con@astro.indiana.edu, E-mail: maderak@astro.indiana.edu, E-mail: bjat@ku.edu, E-mail: btwarog@ku.edu [Department of Physics and Astronomy, University of Kansas Lawrence, KS 66045-7582 (United States)

    2012-11-01

    High-resolution CTIO 4 m/HYDRA spectroscopy of the super-metal-rich open cluster NGC 6253 ([Fe/H] = +0.43 {+-} 0.01) has been used to study the stellar lithium (Li) abundances near the cluster's turnoff. NGC 6253 greatly expands the range of [Fe/H] for clusters that have a Li abundance analysis. This is important for studying the complicated effects of, and potential correlations with, stellar Fe abundance on surface Li abundance. Comparisons to the younger and less-metal-rich Hyades and to the similarly aged but solar-metallicity M67 show that NGC 6253's Li abundances are qualitatively consistent with the prediction, from Standard Stellar Evolution Theory, that higher-metallicity stars have a greater Li depletion. Comparison with M67 provides evidence that the more-metal-rich NGC 6253 had a higher initial Li, which is consistent with expectations from models of Galactic Li production. NGC 6253 is also compared to the intermediate-aged NGC 3680, NGC 752, and IC 4651 open clusters. Comparison of the Li-gap positions in all six clusters shows that (1) the gap's position in T{sub eff} is independent of metallicity, but (2) higher-metallicity clusters have their gaps in higher-mass stars. In addition, the Li gap's position is shown not to evolve with age, which provides an important constraint for the non-standard depletion mechanisms that may create the Li gap.

  12. 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...

  13. Computer simulations of small semiconductor and metal clusters

    International Nuclear Information System (INIS)

    Andreoni, W.

    1991-01-01

    A brief survey is presented of recent simulations of small clusters, made with both ab-initio and classical approaches, with particular emphasis on the application of the Car-Parrinello method. The discussion mainly focusses on the structural properties of a variety of materials and on the effects of temperature. (orig.)

  14. Metal oxide/polyaniline nanocomposites: Cluster size and ...

    Indian Academy of Sciences (India)

    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 ...

  15. 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

    Formation of polymer films with size-selected silver and copper nanoparticles (NPs) is studied. Polymers are prepared by spin coating while NPs are fabricated and deposited utilizing a magnetron sputtering cluster apparatus. The particle embedding into the films is provided by thermal annealing...... 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....... Combining electron beam lithography, cluster beam deposition and thermal annealing allows to form ordered arrays of metal NPs on polymer films. Plasticity and flexibility of polymer host and specific properties added by coinage metal NPs open a way for different applications of such composite materials...

  16. 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.

  17. CO adsorption on transition metal clusters: Trends from density functional theory

    Science.gov (United States)

    Zeinalipour-Yazdi, Constantinos D.; Cooksy, Andrew L.; Efstathiou, Angelos M.

    2008-05-01

    This work reports for the first time the trends for carbon monoxide (CO) chemisorption on transition metal clusters present in supported metal catalysts. In particular, the energetic, structural and infrared adsorption characteristics of linearly (atop) CO adsorbed on transition metal nano-clusters of less than 10 Å in size were explored. Spin-unrestricted density functional theory (DFT) calculations were employed to explore the trends of CO adsorption energy (AM-CO) and C-O vibrational frequency (νCO) for clusters composed of Ni, Cu, Ru, Rh, Pd, Ag, Ir, Pt and Au. The effects of the transition metal electronic structure onto the adsorption energy of CO and the vibrational stretching frequency of C-O, and how these chemical parameters can be correlated to the catalytic activity of transition supported metal catalysts that involve the adsorption, surface diffusion, and C-O bond dissociation elementary steps in heterogeneous catalytic surface reactions, are discussed. Our findings show that an increase of the electronic d-shell occupancy and the principal quantum number (n) in transition metals causes an increase in the vibrational stretching frequency of the C-O bond. This trend is inconsistent with the classical Blyholder model for the metal-carbonyl bond.

  18. Kinetic Consequences of Chemisorbed Oxygen Atoms during Methane Oxidation on Group VIII Metal Clusters

    OpenAIRE

    Chin, Ya Huei

    2011-01-01

    Molecular insights and the kinetic relevance of reaction elementary steps for methane activation on Group VIII metal and oxide clusters are established based on kinetic, isotopic, and theoretical assessments. These fundamental understandings enable accurate prediction of complex rate dependencies and cluster size effects during methane conversion reactions in catalytic partial oxidation, reforming, and combustion processes.Kinetics of methane reactions with oxygen are described by several reg...

  19. BVRI CCD photometry of the metal-poor globular cluster M68 (NGC 4590)

    International Nuclear Information System (INIS)

    Alcaino, G.; Liller, W.; Alvarado, F.; Wenderoth, E.

    1990-01-01

    BVRI photometry of the low metallicity globular cluster M68 (NGC 4590) was obtained with a CCD camera and the 2.2-m ESO telescope. The resulting BV color-magnitude diagrams are compared with the observations of McClure et al. (1987). The observations are also compared with theoretical isochrones, yielding a cluster age of 13 Gyr with a likely external uncertainty of 2 or 3 Gyr. 25 refs

  20. Quintuple super bonding between the superatoms of metallic clusters.

    Science.gov (United States)

    Wang, Haiyan; Cheng, Longjiu

    2017-09-14

    The synthesis of a stable compound with Cr-Cr quintuple bonding (σ, 2π, 2δ) opened the door to a new field of chemistry (T. Nguyen, A. D. Sutton, M. Brynda, J. C. Fettinger, G. J. Long and P. P. Power, Science, 2005, 310, 844). Looking back to the mass experiments on sodium clusters (W. D. Knight, K. Clemenger, W. A. de Heer, W. A. Saunders, M. Y. Chou and M. L. Cohen, Phys. Rev. Lett., 1984, 52, 2141), this work tells some new stories about the experimentally viewed magic numbers 26e and 30e. By unbiased global search, the 26e Li 20 Mg 3 cluster has a perfect double-icosahedral motif with a large HOMO-LUMO energy gap (1.44 eV). We theoretically found that each icosahedron is an independent superatom and molecule-like electronic shell-closure is achieved via quintuple super bonding between two superatoms: [8e](1D2S) 5 -(1D2S) 5 [8e]. Similar quintuple bonding also exists in the 30e double-icosahedral Li 18 Mg 3 Al 2 cluster: [8e](1D2S) 7 -(1D2S) 7 [8e]. The 26e/30e quintuple bonding was verified by the beautiful analogies in molecular orbital diagrams and chemical bonding patterns with V 2 /Re 2 molecules. Such a quintuple super bonding makes a bridge between the jellium model and chemical bonding, which further expands the community of chemical bonds.

  1. Metal oxide/polyaniline nanocomposites: Cluster size and ...

    Indian Academy of Sciences (India)

    Wintec

    report preliminary results on the magnetic properties of self standing sheets prepared using γ-Fe2O3 and. NiFe2O4 nanoparticles and conducting polymers. Keywords. Metal oxide/polyaniline nanocomposites; structural properties; magnetic properties. 1. Introduction. The diverse properties of magnetic nanoparticle systems.

  2. A study of rotating globular clusters. The case of the old, metal-poor globular cluster NGC 4372

    Science.gov (United States)

    Kacharov, N.; Bianchini, P.; Koch, A.; Frank, M. J.; Martin, N. F.; van de Ven, G.; Puzia, T. H.; McDonald, I.; Johnson, C. I.; Zijlstra, A. A.

    2014-07-01

    Context. NGC 4372 is a poorly studied old, very metal-poor globular cluster (GC) located in the inner Milky Way halo. Aims: We present the first in-depth study of the kinematic properties and derive the structural parameters of NGC 4372 based on the fit of a Plummer profile and a rotating, physical model. We explore the link between internal rotation to different cluster properties and together with similar studies of more GCs, we put these in the context of globular cluster formation and evolution. Methods: We present radial velocities for 131 cluster member stars measured from high-resolution FLAMES/GIRAFFE observations. Their membership to the GC is additionally confirmed from precise metallicity estimates. We build a velocity dispersion profile and a systemic rotation curve using this kinematic data set. Additionally, we obtain an elliptical number density profile of NGC 4372 based on optical images using a Markov chain Monte Carlo fitting algorithm. From this, we derive the cluster's half-light radius and ellipticity as rh = 3.44' ± 0.04' and ɛ = 0.08 ± 0.01. Finally, we give a physical interpretation of the observed morphological and kinematic properties of this GC by fitting an axisymmetric, differentially rotating, dynamical model. Results: Our results show that NGC 4372 has an unusually high ratio of rotation amplitude to velocity dispersion (1.2 vs. 4.5 km s-1) for its metallicity. This puts it in line, however, with two other exceptional, very metal-poor GCs: M 15 and NGC 4590. We also find a mild flattening of NGC 4372 in the direction of its rotation. Given its old age, this suggests that the flattening is indeed caused by the systemic rotation rather than tidal interactions with the Galaxy. Additionally, we estimate the dynamical mass of the GC Mdyn = 2.0 ± 0.5 × 105M⊙ based on the dynamical model, which constrains the mass-to-light ratio of NGC 4372 between 1.4 and 2.3 M⊙/L⊙, representative of an old, purely stellar population. Based on

  3. Graphene nucleation and growth on the transition metal surfaces: the role of pentagon, metal step and magic carbon clusters

    Science.gov (United States)

    Gao, Junfeng; Zhao, Jijun; Ding, Feng

    2012-02-01

    The nucleation behavior of graphene on transition metal surfaces, either on a terrace or near a step edge, is systematically explored using density functional theory calculations. The supported carbon clusters, CN (N=1˜24), on the Ni(111) surface are carefully optimized [1,2]. A structural transformation from a C chain to a sp^2 C network at C12 and the most stable structures of sp^2 graphene islands contain one to three pentagons. In agreement with experimental observations, our calculations show that graphene nucleation near a metal step edge is superior to that on a terrace. Besides, ground state structures of supported CN (N = 16˜26), clusters on four selected transition metal surfaces: (Rh(111), Ru(0001), Ni(111) and Cu(111)) are explored [3]. A core-shell structured of C21 stands out as a magic cluster, which is one of the dominating carbon precursors in graphene CVD growth and has been observed in experimental STM images. The energy barrier of two C21 clusters' coalescence is computed to illustrate their influence on the kinetics of graphene CVD growth at different temperatures. [4pt] [1] J. Gao, et al,. J. Am. Chem. Soc. 133, 5009 (2011). [0pt] [2] J. Gao, et al., J. Phys. Chem. C 115, 17695 (2011). [0pt] [3] Q. Yuan, et al., J. Am. Chem. Soc. (accepted).

  4. Proofs of cluster formation and transitions in liquid metals and alloys

    International Nuclear Information System (INIS)

    Filippov, E.S.

    1985-01-01

    Calculational and experimental proofs are presented indicating to existence of clusters in liquid metals and alloys. Systems of liquid alloys both on the base of ferrous metals and non-ferrous metals (Fe-C, Ni-C, Co-C, Fe-Ni, Ni-Mo, Co-Cr, Co-V as well as In-Sn, Bi-Sn, Si-Ge and others) are studied experimentally. It is shown that the general feature of the systems studied is sensitivity of a volume to change in structure, to replacement fcc structure on bcc or to initiation-dissociation of intermetallic compounds AxBy. It is shown that both in pure liquid metals and in their.alloys there are clusters as ordered aggregate of atoms

  5. Atomic structures and covalent-to-metallic transition of lead clusters Pbn (n=2-22)

    International Nuclear Information System (INIS)

    Wang Baolin; Zhao Jijun; Chen Xiaoshuang; Shi Daning; Wang Guanghou

    2005-01-01

    The lowest-energy structures and electronic properties of the lead clusters are studied by density-functional-theory calculations with Becke-Lee-Yang-Parr gradient correction. The lowest-energy structures of Pb n (n=2-22) clusters are determined from a number of structural isomers, which are generated from empirical genetic algorithm simulations. The competition between atom-centered compact structures and layered stacking structures leads to the alternative appearance of the two types of structures as global minimum. The size evolution of geometric and electronic properties from covalent bonding towards bulk metallic behavior in Pb clusters is discussed

  6. 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

    about the structure and properties of glissile clusters of self-interstitial atoms that are formed directly in the cascade volume. It has been found that such clusters consist of sets of crowdions and are highly mobile in the crowdion direction. Very recently, one-dimensional glide of similar character...... 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...

  7. 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.

  8. Gas phase infrared photodissociation spectroscopy of mass-selected ionic clusters: metal oxides and microhydrated anions

    OpenAIRE

    Wende, T.

    2012-01-01

    The central goal of the present thesis is the structural characterization of metal oxide clusters in the framework of the Dedicated Research Center “Structure, Dynamics and Reactivity of Transition Metal Oxide Aggregates” (SFB 546), funded by the German Research Foundation. The SFB 546 aimed at developing a detailed understanding of the relationships between structure and reactivity in catalytic systems. A second goal of this thesis is the characterization of the solvation behavior of anions ...

  9. The most metal-poor Galactic globular cluster: the first spectroscopic observations of ESO280-SC06

    Science.gov (United States)

    Simpson, Jeffrey D.

    2018-04-01

    We present the first spectroscopic observations of the very metal-poor Milky Way globular cluster ESO280-SC06. Using spectra acquired with the 2dF/AAOmega spectrograph on the Anglo-Australian Telescope, we have identified 13 members of the cluster, and estimate from their infrared calcium triplet lines that the cluster has a metallicity of [Fe/H]={-2.48}^{+0.06}_{-0.11}. This would make it the most metal-poor globular cluster known in the Milky Way. This result was verified with comparisons to three other metal-poor globular clusters that had been observed and analyzed in the same manner. We also present new photometry of the cluster from EFOSC2 and SkyMapper and confirm that the cluster is located 22.9 ± 2.1 kpc from the Sun and 15.2 ± 2.1 kpc from the Galactic centre, and has a radial velocity of 92.5 + 2.4-1.6 km s-1. These new data finds the cluster to have a radius about half that previously estimated, and we find that the cluster has a dynamical mass of the cluster of (12 ± 2) × 103 M⊙. Unfortunately, we lack reliable proper motions to fully characterize its orbit about the Galaxy. Intriguingly, the photometry suggests that the cluster lacks a well-populated horizontal branch, something that has not been observed in a cluster so ancient or metal-poor.

  10. 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.

  11. The uniformity and time-invariance of the intra-cluster metal distribution in galaxy clusters from the IllustrisTNG simulations

    Science.gov (United States)

    Vogelsberger, Mark; Marinacci, Federico; Torrey, Paul; Genel, Shy; Springel, Volker; Weinberger, Rainer; Pakmor, Rüdiger; Hernquist, Lars; Naiman, Jill; Pillepich, Annalisa; Nelson, Dylan

    2018-02-01

    The distribution of metals in the intra-cluster medium (ICM) encodes important information about the enrichment history and formation of galaxy clusters. Here, we explore the metal content of clusters in IllustrisTNG - a new suite of galaxy formation simulations building on the Illustris project. Our cluster sample contains 20 objects in TNG100 - a ˜(100 Mpc)3 volume simulation with 2 × 18203 resolution elements, and 370 objects in TNG300 - a ˜(300 Mpc)3 volume simulation with 2 × 25003 resolution elements. The z = 0 metallicity profiles agree with observations, and the enrichment history is consistent with observational data going beyond z ˜ 1, showing nearly no metallicity evolution. The abundance profiles vary only minimally within the cluster samples, especially in the outskirts with a relative scatter of ˜ 15 per cent. The average metallicity profile flattens towards the centre, where we find a logarithmic slope of -0.1 compared to -0.5 in the outskirts. Cool core clusters have more centrally peaked metallicity profiles (˜0.8 solar) compared to non-cool core systems (˜0.5 solar), similar to observational trends. Si/Fe and O/Fe radial profiles follow positive gradients. The outer abundance profiles do not evolve below z ˜ 2, whereas the inner profiles flatten towards z = 0. More than ˜ 80 per cent of the metals in the ICM have been accreted from the proto-cluster environment, which has been enriched to ˜0.1 solar already at z ˜ 2. We conclude that the intra-cluster metal distribution is uniform among our cluster sample, nearly time-invariant in the outskirts for more than 10 Gyr, and forms through a universal enrichment history.

  12. Old Metal-rich Globular Cluster Populations: Peak Color and Peak Metallicity Trends with Mass of Host Spheroids

    OpenAIRE

    Kravtsov, Valery V.

    2007-01-01

    We address the problem of the factors contributing to a peak color trend of old metal-rich globular cluster (MRGC) populations with mass of their hosts, early-type galaxies and spheroidal subsystems of spiral ones (spheroids). The color-mass trend is often converted to a metallicity-mass trend under the assumption that age effects are small or negligible. While direct estimates of the ages of MRGC populations neither can rule out nor reliably support the populations' age trend, key data on ti...

  13. Magic pairs and structural transitions in binary metallic clusters.

    Science.gov (United States)

    Cune, Liviu-Cristian

    2012-06-04

    Structures and binding energies for bimetallic clusters consisting of a large variety of atomic species are obtained for all atomic sizes N≤40 and all concentrations, using an interatomic potential derived within a quasi-classical description. It is found that increasing the difference between the two types of atoms leads to a gradual disappearance of the well-known homo-atomic geometric magic numbers and the appearance of magic pairs corresponding to the number of atoms of each atomic species in binary nanostructures with higher stability. This change is accompanied by structural transitions and ground-state↔isomer inversions, induced by changes in composition or concentration. There is a clear tendency towards phase separation, the core-shell radial segregation being predominant (energetically favored) in this model. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  14. NEAR-IR PHOTOMETRIC PROPERTIES OF HB, MSTO, AND SGB FOR METAL POOR GALACTIC GLOBULAR CLUSTERS

    Directory of Open Access Journals (Sweden)

    J.-W. Kim

    2007-03-01

    Full Text Available We report photometric features of the HB, MSTO, and SGB for a set of metal-poor Galactic globular clusters on the near-IR CMDs. The magnitude and color of the MSTO and SGB are measured on the fiducial normal points of the CMDs by applying a polynomial fit. The near-IR luminosity functions of horizontal branch stars in the classical second parameter pair M3 and M13 indicate that HB stars in M13 are dominated by hot stars that are rotatively faint in the infrared, whereas HB stars in M3 are brighter than those in M13. The luminosity functions of HB stars in the observed bulge clusters, except for NGC 6717, show a trend that the fainter hot HB stars are dominated in the relatively metal-poor clusters while the relatively metal-rich clusters contain the brighter HB stars. It is suggestive that NGC 6717 would be an extreme example of the second-parameter phenomenon for the bulge globular clusters.

  15. Metal Cluster Models for Heterogeneous Catalysis: A Matrix-Isolation Perspective.

    Science.gov (United States)

    Hübner, Olaf; Himmel, Hans-Jörg

    2018-02-19

    Metal cluster models are of high relevance for establishing new mechanistic concepts for heterogeneous catalysis. The high reactivity and particular selectivity of metal clusters is caused by the wealth of low-lying electronically excited states that are often thermally populated. Thereby the metal clusters are flexible with regard to their electronic structure and can adjust their states to be appropriate for the reaction with a particular substrate. The matrix isolation technique is ideally suited for studying excited state reactivity. The low matrix temperatures (generally 4-40 K) of the noble gas matrix host guarantee that all clusters are in their electronic ground-state (with only a very few exceptions). Electronically excited states can then be selectively populated and their reactivity probed. Unfortunately, a systematic research in this direction has not been made up to date. The purpose of this review is to provide the grounds for a directed approach to understand cluster reactivity through matrix-isolation studies combined with quantum chemical calculations. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  16. Infrared studies of astronomically relevant metallic clusters and their interactions with simple molecules

    NARCIS (Netherlands)

    Kiawi, D.M.

    2016-01-01

    The work presented in this thesis aims at: a) providing fundamental knowledge on the interactions of simple ligands with metal clusters relevant to astronomical and (bio-) catalytical processes, b) providing a benchmark that can be used to test current and future DFT methods developed to study these

  17. Metal-halide systems: From molecular clusters to liquid-state structure

    Directory of Open Access Journals (Sweden)

    Mario P. Tosi

    2015-03-01

    Full Text Available I present a short review of the relationship between quantum-mechanical calculations on small molecular clusters of some metal-ion halides and studies of the microscopic structure in the condensed liquid phases of these compounds. The review is dedicated to the memory of Professor Vincenzo Grasso.

  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. 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 FeTi 5 O 4 (O i Pr) 4 (OMc) 10 (OMc = methacrylate), Zn 2 Ti 4 O 4 (O i Pr) 2 (OMc) 10 , Cd 4 Ti 2 O 2 (OAc) 2 (OMc) 10 (HO i Pr) 2 , [Ca 2 Ti 4 O 4 (OAc) 2 (OMc) 10 ] n , and [Sr 2 Ti 4 O 4 (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 Ti 6 O 4 (OR) 8 (OOCR') 8 . The Ca and Sr derivatives consist of chains of condensed clusters.

  20. 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

  1. 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.

  2. Medium-induced change of the optical response of metal clusters in rare-gas matrices

    Science.gov (United States)

    Xuan, Fengyuan; Guet, Claude

    2017-10-01

    Interaction with the surrounding medium modifies the optical response of embedded metal clusters. For clusters from about ten to a few hundreds of silver atoms, embedded in rare-gas matrices, we study the environment effect within the matrix random phase approximation with exact exchange (RPAE) quantum approach, which has proved successful for free silver clusters. The polarizable surrounding medium screens the residual two-body RPAE interaction, adds a polarization term to the one-body potential, and shifts the vacuum energy of the active delocalized valence electrons. Within this model, we calculate the dipole oscillator strength distribution for Ag clusters embedded in helium droplets, neon, argon, krypton, and xenon matrices. The main contribution to the dipole surface plasmon red shift originates from the rare-gas polarization screening of the two-body interaction. The large size limit of the dipole surface plasmon agrees well with the classical prediction.

  3. New semiconducting silicides assembled from transition-metal-encapsulating Si clusters

    Energy Technology Data Exchange (ETDEWEB)

    Uchida, Noriyuki, E-mail: nori-uchida@aist.go.jp [Nanodevice Innovation Research Center, National Institute of Advanced Industrial Science and Technology (AIST), 1-1-1 Higashi, Tsukuba 305-8562 (Japan); Miyazaki, Takehide [Nanosystem Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), 1-1-1 Umezono, Tsukuba 305-8568 (Japan); Matsushita, Yusuke; Sameshima, Kenichiro; Kanayama, Toshihiko [Nanodevice Innovation Research Center, National Institute of Advanced Industrial Science and Technology (AIST), 1-1-1 Higashi, Tsukuba 305-8562 (Japan); Institute of Applied Physics, University of Tsukuba, Tennoudai, Tsukuba 305-8573 (Japan)

    2011-10-03

    We synthesized amorphous films composed of transition-metal-encapsulating Si clusters (MSi{sub n}: M = Zr, Nb, Mo and W) by deposition of hydrogenated MSi{sub n}H{sub x} clusters onto solid substrates followed by annealing at 400-500 deg. C for dehydrogenation. The MSi{sub n} (n = 7-20) cluster films are amorphous semiconductors with an optical gap > 0.4 eV and have larger electron and hole mobility than that of the hydrogenated amorphous Si (a-Si:H) film. In these films, while Si atoms form amorphous networks similar to those in a-Si:H films, the thermal stability is enhanced and the electronic disorder is reduced by the use of MSi{sub n} clusters as the unit structures. Structure modeling by ab initio calculations for MSi{sub n} films suggests that the encapsulated M atom works as a terminator of dangling bonds of the Si network.

  4. Probing the Adsorption of Carbon Monoxide on Transition Metal Clusters Using IR Action Spectroscopy

    Science.gov (United States)

    Lapoutre, Vivike J. F.; Oomens, Jos; Bakker, Joost M.

    2012-06-01

    The discovery of enhanced catalytic activity of small gold clusters has led to a great interest in size-dependent catalytic properties of metal clusters. To obtain a better understanding of the catalytic mechanisms it is essential to know the structures of these clusters and the nature of their interaction with reactant molecules. We have studied the structure of gas-phase niobium clusters with a carbon monoxide adsorbed using IR action spectroscopy. We present size-selective IR spectra obtained via IR multiple photon spectroscopy monitoring either photodetachment or photodissociation depending on the charge state. The combination of these spectra with DFT calculations allows for the structural determination of the adsorption product. M. Haruta et al., Journal of Catalysis 115 301-309 (1989). M. Haertelt et al., The Journal of Physical Chemistry Letters 2 1720-1724 (2011)

  5. 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.

  6. 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.

  7. Magnetic moments and metallic behavior of two-dimensional Ni clusters

    International Nuclear Information System (INIS)

    Rodriguez L, J.L.; Aguilera G, F.; Vega, A.

    1998-01-01

    We have calculated the average magnetic moments per atom μ - of two-dimensional nickel clusters (Ni N ) with different geometrical shapes and two different sizes (N=7 and 19). The spin-polarized electronic structure has been calculated with a self-consistent tight-binding method considering the 3d, 4s and 4p valence electrons. We discuss the dependence of the s, p, and d contribution of the magnetic moment on the geometrical shape and the average coordination number. We also study the nonmetal-metal transition of the two-dimensional clusters using Kubo's criterion. (Author)

  8. Cluster-based bulk metallic glass formation in Fe-Si-B-Nb alloy systems

    Energy Technology Data Exchange (ETDEWEB)

    Zhu, C L; Wang, Q; Li, F W; Li, Y H; Wang, Y M; Dong, C [State Key Laboratory of Materials Modification, Dalian University of Technology (DUT), Dalian 116024 (China); Zhang, W; Inoue, A, E-mail: dong@dlut.edu.c [Institute for Materials Research (IMR), Tohoku University, Katahira 2-1-1, Aoba-Ku, Sendai 980-8577 (Japan)

    2009-01-01

    Bulk metallic glass formations have been explored in Fe-B-Si-Nb alloy system using the so-called atomic cluster line approach in combination with minor alloying guideline. The atomic cluster line refers to a straight line linking binary cluster to the third element in a ternary system. The basic ternary compositions in Fe-B-Si system are determined by the inetersection points of two cluster lines, namely Fe-B cluster to Si and Fe-Si cluster to B, and then further alloyed with 3-5 at. % Nb for enhancing glass forming abilities. BMG rods with a diameter of 3 mm are formed under the case of minor Nb alloying the basic intersecting compositions of Fe{sub 8}B{sub 3}-Si with Fe{sub 12}Si-B and Fe{sub 8}B{sub 2}-Si with Fe{sub 9}Si-B. The BMGs also exhibit high Vickers hardness (H{sub v}) of 1130-1164 and high Young's modulous (E) of 170-180 GPa

  9. The Correlations between the Intrinsic Colors and Spectroscopic Metallicities of M31 Globular Clusters

    OpenAIRE

    Fan, Zhou; Ma, Jun; Zhou, Xu; Jiang, Zhaoji

    2010-01-01

    We present the correlations between the spectroscopic metallicities and ninety-three different intrinsic colors of M31 globular clusters, including seventy-eight BATC colors and fifteen SDSS and near infrared ugrizK colors. The BATC colors were derived from the archival images of thirteen filters (from c to p), which were taken by Beijing-Arizona-Taiwan-Connecticut (BATC) Multicolor Sky Survey with a 60/90 cm f/3 Schmidt telescope. The spectroscopic metallicities adopted in our work were from...

  10. 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.

  11. 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

  12. Electronic relaxation dynamics of a metal atom deposited on argon cluster

    International Nuclear Information System (INIS)

    Awali, Slim

    2014-01-01

    This thesis is a study on the interaction between electronically excited atomic states and a non-reactive environment. We have theoretically and experimentally studied situations where a metal atom (Ba or K) is placed in a finite size environment (argon cluster). The presence of the medium affects the electronic levels of the atom. On the other side, the excitation of the atom induces a relaxation dynamics of the electronic energy through the deformation of the cluster. The experimental part of this work focuses on two aspects: the spectroscopy and the dynamics. In both cases a first laser electronically excites the metal atom and the second ionizes the excited system. The observable is the photoelectron spectrum recorded after photoionization and possibly information on the photoion which are also produced. This pump/probe technique, with also two lasers, provide the ultrafast dynamic when the lasers pulses used are of ultrashort (60 fs). The use of nanosecond lasers leads to resonance spectroscopic measurement, unresolved temporally, which give information on the position of the energy levels of the studied system. From a theoretical point-of-view, the excited states of M-Ar n were calculated at the ab initio level, using large core pseudo-potential to limit the active electrons of the metal to valence electrons. The study of alkali metals (potassium) is especially well adapted to this method since only one electron is active. The ab-initio calculation and a Monte-Carlo simulation where coupled to optimize the geometry of the KAr n (n = 1-10) cluster when K is in the ground state of the neutral and the ion, or excited in the 4p or 5s state. Calculations were also conducted in collaboration with B. Gervais (CIMAP, Caen) on KAr n clusters having several tens of argon atoms. Absorption spectra were also calculated. From an experimental point-of-view, we were able to characterize the excited states of potassium and barium perturbed by the clusters. In both cases a

  13. Interaction of Model Inhibitor Compounds with Minimalist Cluster Representations of Hydroxyl Terminated Metal Oxide Surfaces

    Directory of Open Access Journals (Sweden)

    Christopher D. Taylor

    2018-01-01

    Full Text Available The computational modeling of corrosion inhibitors at the level of molecular interactions has been pursued for decades, and recent developments are allowing increasingly realistic models to be developed for inhibitor–inhibitor, inhibitor–solvent and inhibitor–metal interactions. At the same time, there remains a need for simplistic models to be used for the purpose of screening molecules for proposed inhibitor performance. Herein, we apply a reductionist model for metal surfaces consisting of a metal cation with hydroxide ligands and use quantum chemical modeling to approximate the free energy of adsorption for several imidazoline class candidate corrosion inhibitors. The approximation is made using the binding energy and the partition coefficient. As in some previous work, we consider different methods for incorporating solvent and reference systems for the partition coefficient. We compare the findings from this short study with some previous theoretical work on similar systems. The binding energies for the inhibitors to the metal hydroxide clusters are found to be intermediate to the binding energies calculated in other work for bare metal vs. metal oxide surfaces. The method is applied to copper, iron, aluminum and nickel metal systems.

  14. THE SLUGGS SURVEY: NGC 3115, A CRITICAL TEST CASE FOR METALLICITY BIMODALITY IN GLOBULAR CLUSTER SYSTEMS

    Energy Technology Data Exchange (ETDEWEB)

    Brodie, Jean P.; Conroy, Charlie; Arnold, Jacob A.; Romanowsky, Aaron J. [University of California Observatories and Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064 (United States); Usher, Christopher; Forbes, Duncan A. [Centre for Astrophysics and Supercomputing, Swinburne University, Hawthorn, VIC 3122 (Australia); Strader, Jay, E-mail: brodie@ucolick.org [Department of Physics and Astronomy, Michigan State University, East Lansing, MI 48824 (United States)

    2012-11-10

    Due to its proximity (9 Mpc) and the strongly bimodal color distribution of its spectroscopically well-sampled globular cluster (GC) system, the early-type galaxy NGC 3115 provides one of the best available tests of whether the color bimodality widely observed in GC systems generally reflects a true metallicity bimodality. Color bimodality has alternatively been attributed to a strongly nonlinear color-metallicity relation reflecting the influence of hot horizontal-branch stars. Here, we couple Subaru Suprime-Cam gi photometry with Keck/DEIMOS spectroscopy to accurately measure GC colors and a CaT index that measures the Ca II triplet. We find the NGC 3115 GC system to be unambiguously bimodal in both color and the CaT index. Using simple stellar population models, we show that the CaT index is essentially unaffected by variations in horizontal-branch morphology over the range of metallicities relevant to GC systems (and is thus a robust indicator of metallicity) and confirm bimodality in the metallicity distribution. We assess the existing evidence for and against multiple metallicity subpopulations in early- and late-type galaxies and conclude that metallicity bi/multimodality is common. We briefly discuss how this fundamental characteristic links directly to the star formation and assembly histories of galaxies.

  15. Ab initio GW quasiparticle calculation of small alkali-metal clusters

    CERN Document Server

    Ishii, S; Louie, S G; Ohno, K

    2001-01-01

    Quasiparticle energies of small alkali-metal clusters are evaluated from first principles by means of the GW approximation with the generalized plasmon-pole model. An all-electron mixed-basis approach, in which wave function is represented as a linear combination of both plane waves and atomic orbitals, is adopted in the calculation. Obtained quasiparticle energies (ionization potential and electron affinity) are in good agreement with experimental data.

  16. The Next Generation Virgo Cluster Survey (NGVS). XXVI. The Issues of Photometric Age and Metallicity Estimates for Globular Clusters

    Energy Technology Data Exchange (ETDEWEB)

    Powalka, Mathieu; Lançon, Ariane; Duc, Pierre-Alain [Observatoire Astronomique de Strasbourg, Université de Strasbourg, CNRS, UMR 7550, 11 rue de l’Université, F-67000 Strasbourg (France); Puzia, Thomas H.; Muñoz, Roberto P.; Zhang, Hongxin [Institute of Astrophysics, Pontificia Universidad Católica de Chile, 7820436 Macul, Santiago (Chile); Peng, Eric W. [Department of Astronomy, Peking University, Beijing 100871 (China); Liu, Chengze [Center for Astronomy and Astrophysics, Department of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240 (China); Blakeslee, John P.; Côté, Patrick; Ferrarese, Laura; Roediger, Joel; Gwyn, S. D. J. [National Research Council of Canada, Herzberg Astronomy and Astrophysics Program, Victoria, BC V9E 2E7 (Canada); Sánchez-Janssen, Rúben [UK Astronomy Technology Centre, Royal Observatory Edinburgh, Blackford Hill, Edinburgh EH9 3HJ (United Kingdom); Durrell, Patrick R. [Department of Physics and Astronomy, Youngstown State University, Youngstown, OH (United States); Cuillandre, Jean-Charles [AIM Paris Saclay, CNRS/INSU, CEA/Irfu,Université Paris Diderot, Orme des Merisiers, F-91191 Gif sur Yvette cedex (France); Guhathakurta, Puragra [UCO/Lick Observatory, University of California, Santa Cruz, 1156 High Street, Santa Cruz, CA 95064 (United States); Hudelot, Patrick, E-mail: mathieu.powalka@astro.unistra.fr [Institut d’Astrophysique de Paris, UMR 7095 CNRS and UPMC, 98bis Bd Arago, F-75014 Paris (France); and others

    2017-08-01

    Large samples of globular clusters (GC) with precise multi-wavelength photometry are becoming increasingly available and can be used to constrain the formation history of galaxies. We present the results of an analysis of Milky Way (MW) and Virgo core GCs based on 5 optical-near-infrared colors and 10 synthetic stellar population models. For the MW GCs, the models tend to agree on photometric ages and metallicities, with values similar to those obtained with previous studies. When used with Virgo core GCs, for which photometry is provided by the Next Generation Virgo cluster Survey (NGVS), the same models generically return younger ages. This is a consequence of the systematic differences observed between the locus occupied by Virgo core GCs and models in panchromatic color space. Only extreme fine-tuning of the adjustable parameters available to us can make the majority of the best-fit ages old. Although we cannot exclude that the formation history of the Virgo core may lead to more conspicuous populations of relatively young GCs than in other environments, we emphasize that the intrinsic properties of the Virgo GCs are likely to differ systematically from those assumed in the models. Thus, the large wavelength coverage and photometric quality of modern GC samples, such as those used here, is not by itself sufficient to better constrain the GC formation histories. Models matching the environment-dependent characteristics of GCs in multi-dimensional color space are needed to improve the situation.

  17. Laser-induced cluster-ions from thin foils of metals and semiconductors

    International Nuclear Information System (INIS)

    Fuerstenau, N.; Hillenkamp, F.

    1981-01-01

    Interaction of focused, very high-energy pulses of UV laser light of some 10 8 W cm -2 with thin foils of metals and semiconductors induces solid-gas phase-transitions and ionization of microvolumes of the target material. Mass-spectrometric analysis of the microplasma reveals singly ionized cluster-ions as final products of the interaction processes. Cluster-ion distributions are measured and compared with those obtained in thermal evaporation, high-frequency spark and SIMS experiments. The distributions are shown to be characteristic of the investigated material. While some of their features can be understood in terms of theories of cluster stability, other qualities, also observed in SIMS and evaporation experiments, are thought to be due to the partially non-equilibrium character of the solid-gas phase-transition. Furthermore, estimations concerning parameters of the laser-induced microplasma can be drawn from the distributions. (orig.)

  18. Giant metal sputtering yields induced by 20-5000 keV/atom gold clusters

    International Nuclear Information System (INIS)

    Andersen, H.H.; Brunelle, A.; Della-Negra, S.; Depauw, J.; Jacquet, D.; Le Beyec, Y.

    1997-01-01

    Very large non-linear effects have been found in cluster-induced metal sputtering over a broad projectile energy interval for the first time. Recently available cluster beams from tandem accelerators have allowed sputtering yield measurements to be made with Au 1 to Au 5 from 20 keV/atom to 5 MeV/atom. The cluster-sputtering yield maxima were found at the same total energy but not at the same energy/atom as expected. For Au 5 a yield as high as 3000 was reached at 150 keV/atom while the Au 1 yield was only 55 at the same velocity. The Sigmund-Claussen thermal spike theory, which fits published data at low energy, cannot reproduce our extended new data set. (author)

  19. ANISOTROPIC METAL-ENRICHED OUTFLOWS DRIVEN BY ACTIVE GALACTIC NUCLEI IN CLUSTERS OF GALAXIES

    International Nuclear Information System (INIS)

    Kirkpatrick, C. C.; McNamara, B. R.; Cavagnolo, K. W.

    2011-01-01

    We present an analysis of the spatial distribution of metal-rich gas in 10 galaxy clusters using deep observations from the Chandra X-ray Observatory. The brightest cluster galaxies (BCGs) have experienced recent active galactic nucleus 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 BCG 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 0.42 jet , with a scatter of only 0.5 dex. The heavy elements are transported beyond the extent of the inner cavities in all clusters, suggesting that 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 substantially exceed 10 9 M sun .

  20. Immersion of low-energy deposited metal clusters into poly(methyl methacrylate)

    Science.gov (United States)

    Popok, V. N.; Hanif, M.; Ceynowa, F. A.; Fojan, P.

    2017-10-01

    Immersion of size-selected metal clusters deposited on thin poly(methyl methacrylate) (PMMA) films is studied. Clusters are produced by magnetron sputtering and soft-landed on the polymer substrates. It is found that thermal annealing at temperatures above the polymer glass transition point facilitates embedment of the deposited nanoparticles (NPs) into PMMA. The immersion degree can be controlled by the annealing time. Together with the control of cluster coverage by tuning the deposition time, the described approach represents an efficient method for the formation of thin polymer composite layers with embedded size-selected metal NPs. In the case of silver, the composite films demonstrate excellent plasmonic properties. However, the thermal annealing is found to quench the plasmon resonance of copper NPs. It is suggested that oxidation under elevated temperatures is the most probable mechanism destroying the plasmonic properties of the copper NPs. A simple treatment method by ozone is proposed to form an oxide shell around the metal core, thus, protecting the core against environmental factors causing degradation of the plasmonic properties.

  1. A High-precision Trigonometric Parallax to an Ancient Metal-poor Globular Cluster

    Science.gov (United States)

    Brown, T. M.; Casertano, S.; Strader, J.; Riess, A.; VandenBerg, D. A.; Soderblom, D. R.; Kalirai, J.; Salinas, R.

    2018-03-01

    Using the Wide Field Camera 3 (WFC3) on the Hubble Space Telescope (HST), we have obtained a direct trigonometric parallax for the nearest metal-poor globular cluster, NGC 6397. Although trigonometric parallaxes have been previously measured for many nearby open clusters, this is the first parallax for an ancient metal-poor population—one that is used as a fundamental template in many stellar population studies. This high-precision measurement was enabled by the HST/WFC3 spatial-scanning mode, providing hundreds of astrometric measurements for dozens of stars in the cluster and also for Galactic field stars along the same sightline. We find a parallax of 0.418 ± 0.013 ± 0.018 mas (statistical, systematic), corresponding to a true distance modulus of 11.89 ± 0.07 ± 0.09 mag (2.39 ± 0.07 ± 0.10 kpc). The V luminosity at the stellar main-sequence turnoff implies an absolute cluster age of 13.4 ± 0.7 ± 1.2 Gyr. Based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. These observations are associated with programs GO-13817, GO-14336, and GO-14773.

  2. Atmospheric parameters and metallicities for 2191 stars in the globular cluster M4

    International Nuclear Information System (INIS)

    Malavolta, Luca; Piotto, Giampaolo; Nascimbeni, Valerio; Sneden, Christopher; Milone, Antonino P.; Bedin, Luigi R.

    2014-01-01

    We report new metallicities for stars of Galactic globular cluster M4 using the largest number of stars ever observed at high spectral resolution in any cluster. We analyzed 7250 spectra for 2771 cluster stars gathered with the Very Large Telescope (VLT) FLAMES+GIRAFFE spectrograph at VLT. These medium-resolution spectra cover a small wavelength range, and often have very low signal-to-noise ratios. We approached this data set by reconsidering the whole method of abundance analysis of large stellar samples from beginning to end. We developed a new algorithm that automatically determines the atmospheric parameters of a star. Nearly all of the data preparation steps for spectroscopic analyses are processed on the syntheses, not the observed spectra. For 322 red giant branch (RGB) stars with V ≤ 14.7, we obtain a nearly constant metallicity, ([Fe/H]) = –1.07 (σ = 0.02). No difference in the metallicity at the level of 0.01 dex is observed between the two RGB sequences identified by Monelli et al. For 1869 subgiant and main-sequence stars with V > 14.7, we obtain ([Fe/H]) = –1.16 (σ = 0.09) after fixing the microturbulent velocity. These values are consistent with previous studies that have performed detailed analyses of brighter RGB stars at higher spectroscopic resolution and wavelength coverage. It is not clear if the small mean metallicity difference between brighter and fainter M4 members is real or is the result of the low signal-to-noise characteristics of the fainter stars. The strength of our approach is shown by recovering a metallicity close to a single value for more than 2000 stars, using a data set that is non-optimal for atmospheric analyses. This technique is particularly suitable for noisy data taken in difficult observing conditions

  3. Atmospheric parameters and metallicities for 2191 stars in the globular cluster M4

    Energy Technology Data Exchange (ETDEWEB)

    Malavolta, Luca; Piotto, Giampaolo; Nascimbeni, Valerio [Dipartimento di Fisica e Astronomia, Vicolo dell' Osservatorio 3, I-35122 Padova (Italy); Sneden, Christopher [Department of Astronomy and McDonald Observatory, The University of Texas, Austin, TX 78712 (United States); Milone, Antonino P. [Research School of Astronomy and Astrophysics, The Australian National University, Cotter Road, Weston, ACT 2611 (Australia); Bedin, Luigi R., E-mail: luca.malavolta@unipd.it, E-mail: giampaolo.piotto@unipd.it, E-mail: valerio.nascimbeni@unipd.it, E-mail: luigi.bedin@oapd.inaf.it, E-mail: chris@verdi.as.utexas.edu, E-mail: milone@mso.anu.edu.au [INAF-Osservatorio Astronomico di Padova, Vicolo dell' Osservatorio 5, I-35122 Padova (Italy)

    2014-02-01

    We report new metallicities for stars of Galactic globular cluster M4 using the largest number of stars ever observed at high spectral resolution in any cluster. We analyzed 7250 spectra for 2771 cluster stars gathered with the Very Large Telescope (VLT) FLAMES+GIRAFFE spectrograph at VLT. These medium-resolution spectra cover a small wavelength range, and often have very low signal-to-noise ratios. We approached this data set by reconsidering the whole method of abundance analysis of large stellar samples from beginning to end. We developed a new algorithm that automatically determines the atmospheric parameters of a star. Nearly all of the data preparation steps for spectroscopic analyses are processed on the syntheses, not the observed spectra. For 322 red giant branch (RGB) stars with V ≤ 14.7, we obtain a nearly constant metallicity, ([Fe/H]) = –1.07 (σ = 0.02). No difference in the metallicity at the level of 0.01 dex is observed between the two RGB sequences identified by Monelli et al. For 1869 subgiant and main-sequence stars with V > 14.7, we obtain ([Fe/H]) = –1.16 (σ = 0.09) after fixing the microturbulent velocity. These values are consistent with previous studies that have performed detailed analyses of brighter RGB stars at higher spectroscopic resolution and wavelength coverage. It is not clear if the small mean metallicity difference between brighter and fainter M4 members is real or is the result of the low signal-to-noise characteristics of the fainter stars. The strength of our approach is shown by recovering a metallicity close to a single value for more than 2000 stars, using a data set that is non-optimal for atmospheric analyses. This technique is particularly suitable for noisy data taken in difficult observing conditions.

  4. Membership and lithium in the old, metal-poor open cluster Berkeley 32

    Science.gov (United States)

    Randich, S.; Pace, G.; Pastori, L.; Bragaglia, A.

    2009-03-01

    Context: Measurements of lithium (Li) abundances in open clusters provide a unique tool for following the evolution of this element with age, metallicity, and stellar mass. In spite of the plethora of Li data already available, the behavior of Li in solar-type stars has so far been poorly understood. Aims: Using FLAMES/Giraffe on the VLT, we obtained spectra of 157 candidate members of the old, metal-poor cluster Berkeley 32, to determine membership and to study the Li behavior of confirmed members. Methods: Radial velocities were measured, allowing us to derive both the cluster velocity and membership information for the sample stars. The Li abundances were obtained from the equivalent width of the Li i 670.8 nm feature, using curves of growth. Results: We obtained an average radial velocity of 105.2 ± 0.86 km s-1, and 53% of the stars have a radial velocity consistent with membership. The Li - T_eff distribution of unevolved members matches the upper envelope of M 67, as well as that of the slightly older and more metal-rich NGC 188. No major dispersion in Li is detected. When considering the Li distribution as a function of mass, however, Be 32 members with solar-like temperature are less massive and less Li-depleted than their counterparts in the other clusters. The mean Li of stars in the temperature interval 5750 ≤ T_eff ≤ 6050 K is log n(Li) = 2.47±0.16, less than a factor of two below the average Li of the 600 Myr old Hyades, and slightly above the average of intermediate age (1-2 Gyr) clusters, the upper envelope of M 67, and NGC 188. This value is comparable to or slightly higher than the plateau of Pop. ii stars. The similarity of the average Li abundance of clusters of different age and metallicity, along with its closeness to the halo dwarf plateau, is very intriguing and suggests that, whatever the initial Li abundance and the Li depletion histories, old stars converge to almost the same final Li abundance. Based on observations collected at ESO

  5. Stable structures and potential energy surface of the metallic clusters: Ni, Cu, Ag, Au, Pd, and Pt

    Science.gov (United States)

    Wu, Xia; Sun, Yan

    2017-06-01

    Metallic clusters have been widely studied due to their special electrical, optical, and catalytic properties. The many-body Gupta potential is applied to describe the interatomic interaction of Ni, Cu, Ag, Au, Pd, and Pt clusters, and their global minimal structures within 100 atoms are optimized using dynamic lattice searching (DLS) method. The configurational distribution of global minima is analyzed, and the geometrical difference among these clusters is demonstrated. Results show that the dominant motif of Ni and Cu clusters is the icosahedron, and in Ag and Au clusters the number of decahedra is slightly larger than that of the icosahedra. However, more face-centered cubic (fcc), stacking fault fcc, and amorphous structures are formed in Au clusters than in Ag clusters. Furthermore, the main motif of Pd and Pt clusters is the decahedron. In particular, Ni98 adopts a Leary tetrahedral motif, and Pt54 is a central vacant icosahedron. The difference related to the potential parameters of these metallic clusters is further investigated by energy analysis. Moreover, the potential energy surfaces (PES) of 38-atom metallic clusters is characterized in terms of conformational analysis. It was found that the sequence of the number of local minima on the PES from large to low is Ni, Cu, Ag, Pt, Pd, and Au.

  6. 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.

  7. 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.

  8. Spectra of globular clusters in the Sombrero galaxy: evidence for spectroscopic metallicity bimodality

    Science.gov (United States)

    Alves-Brito, Alan; Hau, George K. T.; Forbes, Duncan A.; Spitler, Lee R.; Strader, Jay; Brodie, Jean P.; Rhode, Katherine L.

    2011-11-01

    We present a large sample of over 200 integrated-light spectra of confirmed globular clusters (GCs) associated with the Sombrero (M104) galaxy taken with the Deep Imaging Multi-Object Spectrograph (DEIMOS) instrument on the Keck telescope. A significant fraction of the spectra have signal-to-noise ratio levels high enough to allow measurements of GC metallicities using the method of Brodie & Huchra. We find a distribution of spectroscopic metallicities in the range -2.2 < [Fe/H] < +0.1 that is bimodal, with peaks at [Fe/H]˜-1.4 and -0.6. Thus, the GC system of the Sombrero galaxy, like a few other galaxies now studied in detail, reveals a bimodal spectroscopic metallicity distribution supporting the long-held belief that colour bimodality reflects two metallicity subpopulations. This further suggests that the transformation from optical colour to metallicity for old stellar populations, such as GCs, is not strongly non-linear. We also explore the radial and magnitude distribution with metallicity for GC subpopulations but small number statistics prevent any clear trends in these distributions. Based on observations obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California and the National Aeronautics and Space Administration.

  9. METALLICITY EFFECT ON LOW-MASS X-RAY BINARY FORMATION IN GLOBULAR CLUSTERS

    Energy Technology Data Exchange (ETDEWEB)

    Kim, D.-W.; Fabbiano, G.; Fragos, T. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Ivanova, N.; Sivakoff, G. R. [Department of Physics, University of Alberta, Edmonton, AB (Canada); Jordan, A. [Departamento de Astronomia y Astrofisica, Pontificia Universidad Catolica de Chile, Santiago (Chile); Voss, R. [Department of Astrophysics/IMAPP, Radboud University, Nijmegen (Netherlands)

    2013-02-10

    We present comprehensive observational results of the metallicity effect on the fraction of globular clusters (GCs) that contain low-mass X-ray binaries (LMXB), by utilizing all available data obtained with Chandra for LMXBs and Hubble Space Telescope Advanced Camera for Surveys (ACS) for GCs. Our primary sample consists of old elliptical galaxies selected from the ACS Virgo and Fornax surveys. To improve statistics at both the lowest and highest X-ray luminosity, we also use previously reported results from other galaxies. It is well known that the fraction of GCs hosting LMXBs is considerably higher in red, metal-rich, GCs than in blue, metal-poor GCs. In this paper, we test whether this metallicity effect is X-ray luminosity-dependent and find that the effect holds uniformly in a wide luminosity range. This result is statistically significant (at {>=}3{sigma}) in LMXBs with luminosities in the range L {sub X} = 2 Multiplication-Sign 10{sup 37} to 5 Multiplication-Sign 10{sup 38} erg s{sup -1}, where the ratio of GC-LMXB fractions in metal-rich to metal-poor GCs is R = 3.4 {+-} 0.5. A similar ratio is also found at lower (down to 10{sup 36} erg s{sup -1}) and higher luminosities (up to the ULX regime), but with less significance ({approx}2{sigma} confidence). Because different types of LMXBs dominate in different luminosities, our finding requires a new explanation for the metallicity effect in dynamically-formed LMXBs. We confirm that the metallicity effect is not affected by other factors such as stellar age, GC mass, stellar encounter rate, and galacto-centric distance.

  10. SOLAR-LIKE OSCILLATIONS IN A METAL-POOR GLOBULAR CLUSTER WITH THE HUBBLE SPACE TELESCOPE

    International Nuclear Information System (INIS)

    Stello, Dennis; Gilliland, Ronald L.

    2009-01-01

    We present analyses of variability in the red giant stars in the metal-poor globular cluster NGC 6397, based on data obtained with the Hubble Space Telescope. We use a nonstandard data reduction approach to turn a 23 day observing run originally aimed at imaging the white dwarf population, into time-series photometry of the cluster's highly saturated red giant stars. With this technique we obtain noise levels in the final power spectra down to 50 parts per million, which allows us to search for low-amplitude solar-like oscillations. We compare the observed excess power seen in the power spectra with estimates of the typical frequency range, frequency spacing, and amplitude from scaling the solar oscillations. We see evidence that the detected variability is consistent with solar-like oscillations in at least one and perhaps up to four stars. With metallicities 2 orders of magnitude lower than those of the Sun, these stars present so far the best evidence of solar-like oscillations in such a low-metallicity environment.

  11. Metallicity effect on stellar granulation detected from oscillating red giants in open clusters

    Science.gov (United States)

    Corsaro, E.; Mathur, S.; García, R. A.; Gaulme, P.; Pinsonneault, M.; Stassun, K.; Stello, D.; Tayar, J.; Trampedach, R.; Jiang, C.; Nitschelm, C.; Salabert, D.

    2017-08-01

    Context. The effect of metallicity on the granulation activity in stars, and hence on the convective motions in general, is still poorly understood. Available spectroscopic parameters from the updated APOGEE-Kepler catalog, coupled with high-precision photometric observations from NASA's Kepler mission spanning more than four years of observation, make oscillating red giant stars in open clusters crucial testbeds. Aims: We aim to determine the role of metallicity on the stellar granulation activity by discriminating its effect from that of different stellar properties such as surface gravity, mass, and temperature. We analyze 60 known red giant stars belonging to the open clusters NGC 6791, NGC 6819, and NGC 6811, spanning a metallicity range from [Fe/H] ≃ - 0.09 to 0.32. The parameters describing the granulation activity of these stars and their frequency of maximum oscillation power, νmax, are studied while taking into account different masses, metallicities, and stellar evolutionary stages. We derive new scaling relations for the granulation activity, re-calibrate existing ones, and identify the best scaling relations from the available set of observations. Methods: We adopted the Bayesian code Diamonds for the analysis of the background signal in the Fourier spectra of the stars. We performed a Bayesian parameter estimation and model comparison to test the different model hypotheses proposed in this work and in the literature. Results: Metallicity causes a statistically significant change in the amplitude of the granulation activity, with a dependency stronger than that induced by both stellar mass and surface gravity. We also find that the metallicity has a significant impact on the corresponding time scales of the phenomenon. The effect of metallicity on the time scale is stronger than that of mass. Conclusions: A higher metallicity increases the amplitude of granulation and meso-granulation signals and slows down their characteristic time scales toward

  12. Chemical study of the metal-rich globular cluster NGC 5927

    Science.gov (United States)

    Mura-Guzmán, A.; Villanova, S.; Muñoz, C.; Tang, B.

    2018-03-01

    Globular clusters (GCs) are natural laboratories where stellar and chemical evolution can be studied in detail. In addition, their chemical patterns and kinematics can tell us to which Galactic structure (disc, bulge, halo or extragalactic) the cluster belongs to. NGC 5927 is one of most metal-rich GCs in the Galaxy and its kinematics links it to the thick disc. We present abundance analysis based on high-resolution spectra of seven giant stars. The data were obtained using Fibre Large Array Multi Element Spectrograph/Ultraviolet Echelle Spectrograph (UVES) spectrograph mounted on UT2 telescope of the European Southern Observatory. The principal objective of this work is to perform a wide and detailed chemical abundance analysis of the cluster and look for possible Multiple Populations (MPs). We determined stellar parameters and measured 22 elements corresponding to light (Na, Al), alpha (O, Mg, Si, Ca, Ti), iron-peak (Sc, V, Cr, Mn, Fe, Co, Ni, Cu, Zn), and heavy elements (Y, Zr, Ba, Ce, Nd, Eu). We found a mean iron content of [Fe/H] = -0.47 ± 0.02 (error on the mean). We confirm the existence of MPs in this GC with an O-Na anti-correlation, and moderate spread in Al abundances. We estimate a mean [α/Fe] = 0.25 ± 0.08. Iron-peak elements show no significant spread. The [Ba/Eu] ratios indicate a predominant contribution from SNeII for the formation of the cluster.

  13. Carbon and nitrogen abundances in giant stars of the metal-poor globular cluster M92

    International Nuclear Information System (INIS)

    Carbon, D.F.; Langer, G.E.; Butler, D.; Kraft, R.P.; Suntzeff, N.B.; Kemper, E.; Trefzger, C.F.; Romanishin, W.

    1982-01-01

    Zinn in 1973 and 1977 and Norris and Zinn in 1977 showed that in M92 and several other metal-poor globular clusters the G bands (mostly due to CH) in the spectra of asymptotic giant branch (AGB) stars are systematically weaker than those found in the less highly evolved subgiant branch (SGB) stars. If carbon is depleted in the atmospheres of evolved stars because material at the base of the envelope, processed through the CN cycle, has been mixed with the material above, then the atmospheric nitrogen abundance should be correspondingly increased. In this paper we test the hypothesis that C and N abundances in M92 giants are negatively correlated as the evolutionary state becomes more advanced. We find that this simple hypothesis is not adequate to describe the complex behavior of C and N in the cluster giants

  14. Atmospheric Parameters and Metallicities for 2191 Stars in the Globular Cluster M4

    Science.gov (United States)

    Malavolta, Luca; Sneden, Christopher; Piotto, Giampaolo; Milone, Antonino P.; Bedin, Luigi R.; Nascimbeni, Valerio

    2014-02-01

    We report new metallicities for stars of Galactic globular cluster M4 using the largest number of stars ever observed at high spectral resolution in any cluster. We analyzed 7250 spectra for 2771 cluster stars gathered with the Very Large Telescope (VLT) FLAMES+GIRAFFE spectrograph at VLT. These medium-resolution spectra cover a small wavelength range, and often have very low signal-to-noise ratios. We approached this data set by reconsidering the whole method of abundance analysis of large stellar samples from beginning to end. We developed a new algorithm that automatically determines the atmospheric parameters of a star. Nearly all of the data preparation steps for spectroscopic analyses are processed on the syntheses, not the observed spectra. For 322 red giant branch (RGB) stars with V 14.7, we obtain lang[Fe/H]rang = -1.16 (σ = 0.09) after fixing the microturbulent velocity. These values are consistent with previous studies that have performed detailed analyses of brighter RGB stars at higher spectroscopic resolution and wavelength coverage. It is not clear if the small mean metallicity difference between brighter and fainter M4 members is real or is the result of the low signal-to-noise characteristics of the fainter stars. The strength of our approach is shown by recovering a metallicity close to a single value for more than 2000 stars, using a data set that is non-optimal for atmospheric analyses. This technique is particularly suitable for noisy data taken in difficult observing conditions.

  15. CHEMICAL ABUNDANCES IN NGC 5053: A VERY METAL-POOR AND DYNAMICALLY COMPLEX GLOBULAR CLUSTER

    Energy Technology Data Exchange (ETDEWEB)

    Boberg, Owen M.; Friel, Eileen D.; Vesperini, Enrico [Astronomy Department, Indiana University, Bloomington, IN 47405 (United States)

    2015-05-10

    NGC 5053 provides a rich environment to test our understanding of the complex evolution of globular clusters (GCs). Recent studies have found that this cluster has interesting morphological features beyond the typical spherical distribution of GCs, suggesting that external tidal effects have played an important role in its evolution and current properties. Additionally, simulations have shown that NGC 5053 could be a likely candidate to belong to the Sagittarius dwarf galaxy (Sgr dSph) stream. Using the Wisconsin–Indiana–Yale–NOAO–Hydra multi-object spectrograph, we have collected high quality (signal-to-noise ratio ∼ 75–90), medium-resolution spectra for red giant branch stars in NGC 5053. Using these spectra we have measured the Fe, Ca, Ti, Ni, Ba, Na, and O abundances in the cluster. We measure an average cluster [Fe/H] abundance of −2.45 with a standard deviation of 0.04 dex, making NGC 5053 one of the most metal-poor GCs in the Milky Way (MW). The [Ca/Fe], [Ti/Fe], and [Ba/Fe] we measure are consistent with the abundances of MW halo stars at a similar metallicity, with alpha-enhanced ratios and slightly depleted [Ba/Fe]. The Na and O abundances show the Na–O anti-correlation found in most GCs. From our abundance analysis it appears that NGC 5053 is at least chemically similar to other GCs found in the MW. This does not, however, rule out NGC 5053 being associated with the Sgr dSph stream.

  16. Chemical Abundances in NGC 5053: A Very Metal-poor and Dynamically Complex Globular Cluster

    Science.gov (United States)

    Boberg, Owen M.; Friel, Eileen D.; Vesperini, Enrico

    2015-05-01

    NGC 5053 provides a rich environment to test our understanding of the complex evolution of globular clusters (GCs). Recent studies have found that this cluster has interesting morphological features beyond the typical spherical distribution of GCs, suggesting that external tidal effects have played an important role in its evolution and current properties. Additionally, simulations have shown that NGC 5053 could be a likely candidate to belong to the Sagittarius dwarf galaxy (Sgr dSph) stream. Using the Wisconsin-Indiana-Yale-NOAO-Hydra multi-object spectrograph, we have collected high quality (signal-to-noise ratio ˜ 75-90), medium-resolution spectra for red giant branch stars in NGC 5053. Using these spectra we have measured the Fe, Ca, Ti, Ni, Ba, Na, and O abundances in the cluster. We measure an average cluster [Fe/H] abundance of -2.45 with a standard deviation of 0.04 dex, making NGC 5053 one of the most metal-poor GCs in the Milky Way (MW). The [Ca/Fe], [Ti/Fe], and [Ba/Fe] we measure are consistent with the abundances of MW halo stars at a similar metallicity, with alpha-enhanced ratios and slightly depleted [Ba/Fe]. The Na and O abundances show the Na-O anti-correlation found in most GCs. From our abundance analysis it appears that NGC 5053 is at least chemically similar to other GCs found in the MW. This does not, however, rule out NGC 5053 being associated with the Sgr dSph stream.

  17. Spectra of matrix isolated metal atoms and clusters. [In rare gases

    Energy Technology Data Exchange (ETDEWEB)

    Meyer, B.

    1977-09-30

    The matrix isolation spectra of all of the 40 presently known atomic metal species show strong matrix effects. The transition energies are increased, and the bands are broad and exhibit splitting of sublevels which are degenerate in the gas phase. Several models have been proposed for splitting of levels, but basic effects are not yet understood, and spectra cannot be predicted, yet it is possible to correlate gas phase and matrix in many of the systems. Selective production of diatomics and clusters via thermal and optical annealing of atomic species can be monitored by optical spectra, but yields spectroscopically complex systems which, however, especially in the case of transition metals, can be used as precursors in novel chemical reactions. A combination of absorption, emission, ir, Raman, ESR, and other methods is now quickly yielding data which will help correlate the increasing wealth of existing data. 55 references, 6 figures.

  18. 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.

    2016-01-01

    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.

  19. clusters

    Indian Academy of Sciences (India)

    2017-09-27

    Sep 27, 2017 ... while CuCoNO, Co3NO, Cu3CoNO, Cu2Co3NO, Cu3Co3NO and Cu6CoNO clusters display stronger chemical stability. Magnetic and electronic properties are also discussed. The magnetic moment is affected by charge transfer and the spd hybridization. Keywords. CumConNO (m + n = 2–7) clusters; ...

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

    International Nuclear Information System (INIS)

    Gazak, J. Zachary; Kudritzki, Rolf; Bresolin, Fabio; Davies, Ben; Bastian, Nate; Bergemann, Maria; Plez, Bertrand; Evans, Chris; Patrick, Lee; Schinnerer, Eva

    2014-01-01

    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.

  1. Electronic structures and water reactivity of mixed metal sulfide cluster anions.

    Science.gov (United States)

    Saha, Arjun; Raghavachari, Krishnan

    2014-08-21

    The electronic structures and chemical reactivity of the mixed metal sulfide cluster anion (MoWS4(-)) have been investigated with density functional theory. Our study reveals the presence of two almost isoenergetic structural isomers, both containing two bridging sulfur atoms in a quartet state. However, the arrangement of the terminal sulfur atoms is different in the two isomers. In one isomer, the two metals are in the same oxidation state (each attached to one terminal S). In the second isomer, the two metals are in different oxidation states (with W in the higher oxidation state attached to both terminal S). The reactivity of water with the two lowest energy isomers has also been studied, with an emphasis on pathways leading to H2 release. The reactive behavior of the two isomers is different though the overall barriers in both systems are small. The origin of the differences are analyzed and discussed. The reaction pathways and barriers are compared with the corresponding behavior of monometallic sulfides (Mo2S4(-) and W2S4(-)) as well as mixed metal oxides (MoWO4(-)).

  2. Structural properties of transition-metal clusters via force-biased Monte Carlo and ab initio calculations: A comparative study

    Science.gov (United States)

    Limbu, Dil K.; Atta-Fynn, Raymond; Drabold, David A.; Elliott, Stephen R.; Biswas, Parthapratim

    2017-11-01

    We present a force-biased Monte Carlo (FMC) method for structural modeling of the transition-metal clusters of Fe, Ni, and Cu with sizes of 13, 30, and 55 atoms. By employing the Finnis-Sinclair potential for Fe and the Sutton-Chen potential for Ni and Cu, the total energy of the clusters is minimized using the local gradient of the potentials in Monte Carlo simulations. The structural configurations of the clusters, obtained from the biased Monte Carlo approach, are analyzed and compared with the same configurations from the Cambridge Cluster Database (CCD) upon relaxation of the clusters using the first-principles density-functional code nwchem. The results show that the total-energy value and the structure of the FMC clusters are essentially identical to the corresponding value and the structure of the CCD clusters. A comparison of the nwchem-relax FMC and CCD structures is presented by computing the pair-correlation function, the bond-angle distribution, the coordination number of the first-coordination shell, and the Steinhardt bond-orientational order parameter, which provide information about the two- and three-body correlation functions, the local bonding environment of the atoms, and the geometry of the clusters. An atom-by-atom comparison of the FMC and CCD clusters is also provided by superposing one set of clusters onto another, and the electronic properties of the clusters are addressed by computing the density of electronic states.

  3. 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

  4. Depth profiling of metal overlayers on organic substrates with cluster SIMS.

    Science.gov (United States)

    Shen, Kan; Mao, Dan; Garrison, Barbara J; Wucher, Andreas; Winograd, Nicholas

    2013-11-05

    Molecular depth profiling of organic thin films by erosion with energetic cluster ion beams is a unique aspect of secondary ion mass spectrometry (SIMS) experiments. Although depth profiles of complex multilayer organic structures can be acquired with little damage accumulation and with depth resolution of gold layer of 1.4 to 3.5 nm deposited either on top of or sandwiched within a cholesterol thin film matrix which is several hundred nanometers thick. For these systems, the results show that by erosion with a 40 keV C60(+) beam, reliable depth profiles can always be acquired as indicated by the presence of a steady state molecular ion signal. During the erosion process, however, gold atoms from the gold overlayer are implanted into the cholesterol matrix beneath it, resulting in a reduced sputter yield, an increase in the amount of cholesterol fragmentation and an increase in the thickness of the cluster ion-induced altered layer. The results also show that the effects of the metal film on the organic substrate are independent of the gold film thickness once the film thickness exceeds 1.4 nm. In general, this model study provides mechanistic insight into the depth profiling of heterogeneous thin film structures and offers a possible path for improving the quality of the depth profiles by employing low energy atomic ion sputtering in the region of the metal layer.

  5. Open cluster Dolidze 25: Stellar parameters and the metallicity in the Galactic anticentre

    Science.gov (United States)

    Negueruela, I.; Simón-Díaz, S.; Lorenzo, J.; Castro, N.; Herrero, A.

    2015-12-01

    Context. The young open cluster Dolidze 25, in the direction of the Galactic anticentre, has been attributed a very low metallicity, with typical abundances between -0.5 and -0.7 dex below solar. Aims: We intend to derive accurate cluster parameters and accurate stellar abundances for some of its members. Methods: We have obtained a large sample of intermediate- and high-resolution spectra for stars in and around Dolidze 25. We used the fastwind code to generate stellar atmosphere models to fit the observed spectra. We derive stellar parameters for a large number of OB stars in the area, and abundances of oxygen and silicon for a number of stars with spectral types around B0. Results: We measure low abundances in stars of Dolidze 25. For the three stars with spectral types around B0, we find 0.3 dex (Si) and 0.5 dex (O) below the values typical in the solar neighbourhood. These values, even though not as low as those given previously, confirm Dolidze 25 and the surrounding H ii region Sh2-284 as the most metal-poor star-forming environment known in the Milky Way. We derive a distance 4.5 ± 0.3 kpc to the cluster (rG ≈ 12.3 kpc). The cluster cannot be older than ~3 Myr, and likely is not much younger. One star in its immediate vicinity, sharing the same distance, has Si and O abundances at most 0.15 dex below solar. Conclusions: The low abundances measured in Dolidze 25 are compatible with currently accepted values for the slope of the Galactic metallicity gradient, if we take into account that variations of at least ±0.15 dex are observed at a given radius. The area traditionally identified as Dolidze 25 is only a small part of a much larger star-forming region that comprises the whole dust shell associated with Sh2-284 and very likely several other smaller H ii regions in its vicinity. Based on observations made with the Nordic Optical Telescope, the Mercator Telescope, and the telescopes of the Isaac Newton Group.

  6. Homochiral coordination polymers with helixes and metal clusters based on lactate derivatives

    Energy Technology Data Exchange (ETDEWEB)

    Xu, Zhong-Xuan, E-mail: xuzhongxuan4201@163.com [Department of Chemistry, Zunyi Normal College, Zunyi, Guizhou 563002 (China); Ma, Yu-Lu [School of Chemical Science and Technology, Yunnan University, Kunming 650091 (China); Lv, Guo-ling [Department of Chemistry, Zunyi Normal College, Zunyi, Guizhou 563002 (China)

    2017-05-15

    Utilizing the lactic acid derivatives (R)-4-(1-carboxyethoxy)benzoic acid (denoted: (R)-H{sub 2}CBA) and (S)-4-(1-carboxyethoxy)benzoic acid (denoted: (S)-H{sub 2}CBA)as chiral linkers to self-assemble with 4, 4′-bipyridine (denoted: BIP) and Cd(II) ions, a couple of three-dimensional homochiral coordination polymers, namely [Cd{sub 3}((R)-CBA){sub 3} (BIP){sub 2}(H{sub 2}O)]·xGuest (1-D) and [Cd{sub 3}((S)-CBA){sub 3}(BIP){sub 2}(H{sub 2}O)]·xGuest (1-L), have been synthesized under solvothermal reaction condition. Single crystal X-ray diffraction analysis reveals the two complexes contain single helical chains based on enantiopure ligands and cadmium clusters. Moreover, some physical characteristics such as PXRD, thermal stability, solid-state circular dichroism (CD) and luminescent were also investigated. - Graphical abstract: Utilizing enantiomeric lactic acid derivatives (R)-H{sub 2}CBA and (S)-H{sub 2}CBA to assemble with Cd{sup 2+} ions and ancillary BIP ligands, a couple of 3D homochiral coordination polymers with metal clusters and helical chains have been prepared by hydrothermal reaction. - Highlights: • Chiral lactic acid derivative. • Enantiomeric coordination polymer. • Helical chain. • Trinuclear cadmium cluster.

  7. THE ROLE OF THERMOHALINE MIXING IN INTERMEDIATE- AND LOW-METALLICITY GLOBULAR CLUSTERS

    Energy Technology Data Exchange (ETDEWEB)

    Angelou, George C.; Stancliffe, Richard J.; Church, Ross P.; Lattanzio, John C. [Monash Centre for Astrophysics, School of Mathematical Sciences, Monash University, Melbourne, VIC 3800 (Australia); Smith, Graeme H., E-mail: George.Angelou@monash.edu [Department of Astronomy and Astrophysics, University of California Observatories/Lick Observatory, UC Santa Cruz, 1156 High Street, Santa Cruz, CA 95064 (United States)

    2012-04-20

    It is now widely accepted that globular cluster red giant branch (RGB) 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 imprints 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 RGBs 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 some primary nitrogen (higher C+N+O than stars in M3). In the metal-poor regime only NGC 5466 can be tentatively explained by thermohaline mixing operating in multiple populations. We find thermohaline mixing unable to model the depletion of [C/Fe] with magnitude in M92 and M15. It appears as if extra mixing is occurring before the luminosity function bump in these clusters. To reconcile the data with the models would require first dredge-up to be deeper than found in extant models.

  8. XMM-Newton survey of the low-metallicity open cluster NGC 2516

    Science.gov (United States)

    Sciortino, S.; Micela, G.; Damiani, F.; Flaccomio, E.; Briggs, K.; Denby, M.; Pye, J.; Grosso, N.; Read, A. M.; Gondoin, P.; Jeffries, R. D.

    2001-01-01

    We present the first results of an XMM-Newton EPIC survey of NGC 2516, a southern low-metallicity open cluster with an age close to the Pleiades. The attained limiting sensitivity is of ~ 2.4 10-15 erg s-1 cm-2 in the 0.1-4.0 keV bandpass. This has been achieved by summing the data of the MOS and PN cameras of two distinct observations for a total exposure time of ~ 33 ks and by analyzing the summed data set with the wavelet detection algorithm developed at Osservatorio Astronomico di Palermo (OAPA) that has yielded over 200 X-ray detections. Using data just from a single exposure or from a single camera would have reduced by a factor 2-4 our limiting sensitivity and would have resulted in 25-40% less X-ray detections. To date, 129 detections have as counterparts one or more of the 540 photometrically selected cluster members in the surveyed region, for a total of 147 likely detected members, with unique identification in 112 cases. We derive the X-ray luminosity functions (XLF) of NGC 2516 members of different spectral types and compare them with those of the more metal rich, approximately coeval Pleiades cluster, finding the NGC 2516 photometrically selected dG and dK stars less luminous than the Pleiades. The XLFs of the NGC 2516 and of the Pleiades dM stars are indistinguishable. We compare the XMM-Newton results with those recently obtained with Chandra.

  9. cluster

    Indian Academy of Sciences (India)

    has been investigated electrochemically in positive and negative microenvironments, both in solution and in film. Charge nature around the active centre ... in plants, bacteria and also in mammals. This cluster is also an important constituent of a ..... selection of non-cysteine amino acid in the active centre of Rieske proteins.

  10. 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

  11. 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

  12. 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.

  13. Ferromagnetism and suppression of metallic clusters in Fe implanted ZnO -- a phenomenon related to defects?

    Energy Technology Data Exchange (ETDEWEB)

    Arenholz, Elke; Zhou, S.; Potzger, K.; Talut, G.; Reuther, H.; Kuepper, K.; Grenzer, J.; Xu, Q.; Mucklich, A.; Helm, M.; Fassbender, J.; Arenholz, E.

    2008-03-12

    We investigated ZnO(0001) single crystals annealed in high vacuum with respect to their magnetic properties and cluster formation tendency after implant-doping with Fe. While metallic Fe cluster formation is suppressed, no evidence for the relevance of the Fe magnetic moment to the observed ferromagnetism was found. The latter along with the cluster suppression is discussed with respect to defects in the ZnO host matrix, since the crystalline quality of the substrates was lowered due to the preparation as observed by x-ray diffraction.

  14. Liquid-liquid phase separation and cluster formation at deposition of metals under inhomogeneous magnetic field

    Science.gov (United States)

    Gorobets, O. Yu; Gorobets, Yu I.; Rospotniuk, V. P.; Grebinaha, V. I.; Kyba, A. A.

    2017-10-01

    The formation and dynamic of expansion and deformation of the liquid-liquid interface of an electrolyte at deposition of metals at the surface of the magnetized steel ball is considered in this paper. The electrochemical processes were investigated in an external magnetic field directed at an arbitrary angle to the force of gravity. These processes are accompanied by the formation of effectively paramagnetic clusters of electrochemical products - magnions. Tyndall effect was used for detection of the presence of magnions near the magnetized steel electrode in a solution. The shape of the interface separating the regions with different concentration of magnions, i.e. different magnetic susceptibilities, was described theoretically based on the equation of hydrostatic equilibrium which takes into account magnetic, hydrostatic and osmotic pressures.

  15. Assessment of Heavy Metal Pollution in Macrophytes, Water and Sediment of a Tropical Wetland System Using Hierarchical Cluster Analysis Technique

    OpenAIRE

    , N. Kumar J.I.; , M. Das; , R. Mukherji; , R.N. Kumar

    2011-01-01

    Heavy metal pollution in aquatic ecosystems is becoming a global phenomenon because these metals are indestructible and most of them have toxic effects on living organisms. Most of the fresh water bodies all over the world are getting contaminated thus declining their suitability. Therefore, monitoring and assessment of such freshwater systems has become an environmental concern. This study aims to elucidate the useful role of the cluster analysis to assess the relationship and interdependenc...

  16. 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 ad...

  17. Unusual structures and reactivity of mixed metal cluster complexes containing the palladium/platinum tri-t-butylphosphine grouping.

    Science.gov (United States)

    Adams, Richard D; Captain, Burjor

    2009-03-17

    Polynuclear metal carbonyl complexes have a range of applications in chemical research: for example, they can serve as surface models to probe features of heterogeneous catalysis and can perform novel transformations of organic molecules in solutions. Mixed metal complexes can demonstrate bimetallic cooperativity and synergism and can also serve as precursors to multimetallic heterogeneous catalysts that have superior activities and selectivities. This Account describes the results of our recent comprehensive study of the chemistry of mixed metal cluster complexes containing the sterically encumbered M(PBu(t)(3)), M = Pd or Pt, group. This grouping readily adds to the metal-metal bonds of metal carbonyl cluster complexes and modifies their reactivity. We have prepared new, highly electronically unsaturated mixed metal complexes that exhibit unusually high reactivity toward hydrogen. The platinum atom of the Pt(PBu(t)(3)) grouping can bond to as many as five metal atoms, and it can interconvert, sometimes rapidly, between the different bonding modes. The large steric effects of the PBu(t)(3) ligand allowed us to prepare highly unsaturated, stable, mixed-metal complexes, and these complexes react with hydrogen, sometimes reversibly, under very mild conditions to yield polyhydride complexes. Strong evidence suggests that the Pt(PBu(t)(3)) group can also activate metal-hydrogen bonds in other complexes. In the future, we expect that researchers will prepare a greater variety of mixed metal complexes containing the Pd/Pt(PBu(t)(3)) group or other similar bulky groups, and that some of these complexes will exhibit even more unusual chemistry than what we have observed so far.

  18. Super-solar Metallicity Stars in the Galactic Center Nuclear Star Cluster: Unusual Sc, V, and Y Abundances

    Science.gov (United States)

    Do, Tuan; Kerzendorf, Wolfgang; Konopacky, Quinn; Marcinik, Joseph M.; Ghez, Andrea; Lu, Jessica R.; Morris, Mark R.

    2018-03-01

    We present adaptive-optics assisted near-infrared high-spectral-resolution observations of late-type giants in the nuclear star cluster of the Milky Way. The metallicity and elemental abundance measurements of these stars offer us an opportunity to understand the formation and evolution of the nuclear star cluster. In addition, their proximity to the supermassive black hole (∼0.5 pc) offers a unique probe of the star formation and chemical enrichment in this extreme environment. We observed two stars identified by medium spectral-resolution observations as potentially having very high metallicities. We use spectral-template fitting with the PHOENIX grid and Bayesian inference to simultaneously constrain the overall metallicity, [M/H], alpha-element abundance [α/Fe], effective temperature, and surface gravity of these stars. We find that one of the stars has very high metallicity ([M/H] > 0.6) and the other is slightly above solar metallicity. Both Galactic center stars have lines from scandium (Sc), vanadium (V), and yttrium (Y) that are much stronger than allowed by the PHOENIX grid. We find, using the spectral synthesis code Spectroscopy Made Easy, that [Sc/Fe] may be an order of magnitude above solar. For comparison, we also observed an empirical calibrator in NGC 6791, the highest metallicity cluster known ([M/H] ∼ 0.4). Most lines are well matched between the calibrator and the Galactic center stars, except for Sc, V, and Y, which confirms that their abundances must be anomalously high in these stars. These unusual abundances, which may be a unique signature of nuclear star clusters, offer an opportunity to test models of chemical enrichment in this region.

  19. 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

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

    International Nuclear Information System (INIS)

    Zhang, Yang

    2013-01-01

    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 x M 3-x N rate at C 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 13 C NMR spectroscopic studies demonstrated exceptional NMR behaviors that resulted from switching the second metal inside of the mixed metal nitride cluster Ho x M 3-x N from Sc to Lu and further to Y. The LnSc 2 N rate at C 80 (Ln= Ce, Pr, Nd, Tb, Dy, Ho, Lu) MMNCFs were characterized by 13 C and 45 Sc NMR study respectively. According to Bleaney's theory and Reilley method, the separation of δ PC and δ con from δ para was achieved by the primary 13 C and 45 Sc NMR analysis of LnSc 2 N rate at C 80 (I). The

  1. Comparison between XAS, AWAXS and DAFS applied to nanometer scale supported metallic clusters. Pt.2; bimetallic clusters

    International Nuclear Information System (INIS)

    Bazin, D.; Sayers, D.

    1993-01-01

    The structural information obtained using three techniques related to synchrotron radiation are compared. XAS (X-ray Absorption Spectroscopy), AWAXS (Anomalous Wide Angle X-ray Scattering) and DAFS (Diffraction Anomalous Fine Structure) are applied to the study of nanometer scale bimetallic clusters. (author)

  2. 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

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

    International Nuclear Information System (INIS)

    Balasubramanian, Krishnan

    2009-01-01

    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 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 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 2 back to Au and H 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 3 , Nb 2 + etc., have been confirmed experimentally by Prof. Lombardi and coworkers using resonance Raman spectroscopy. We have also been studying larger complexes critical to the environmental management of high

  4. Structures, Interconversions, and Spectroscopy of Iron Carbonyl Clusters with an Interstitial Carbide: Localized Metal Center Reduction by Overall Cluster Oxidation.

    Science.gov (United States)

    Kuppuswamy, Subramaniam; Wofford, Joshua D; Joseph, Chris; Xie, Zhu-Lin; Ali, Azim K; Lynch, Vincent M; Lindahl, Paul A; Rose, Michael J

    2017-05-15

    The syntheses, interconversions, and spectroscopic properties of a set of iron carbonyl clusters containing an interstitial carbide are reported. This includes the low temperature X-ray structures of the six-iron clusters (Y) 2 [Fe 6 (μ 6 -C)(μ 2 -CO) 4 (CO) 12 ] (1a-c; where Y = NMe 4 , NEt 4 , PPh 4 ); the five-iron cluster [Fe 5 (μ 5 -C)(CO) 15 ] (3); and the novel formulation of the five-iron cluster (NMe 4 ) 2 [Fe 5 (μ 5 -C)(μ 2 -CO)(CO) 13 ] (4). Also included in this set is the novel charge-neutral cluster, [Fe 6 (μ 6 -C)(CO) 18 ] (2), for which we were unable to obtain a crystallographic structure. As synthetic proof for the identity of 2, we performed a closed loop of interconversions within a family of crystallographically defined species (1, 3, and 4): [Fe 6 ] 2- → [Fe 6 ] 0 → [Fe 5 ] 0 → [Fe 5 ] 2- → [Fe 6 ] 2- . The structural, spectroscopic, and electronic properties of this "missing link" cluster 2 were investigated by IR, Raman, XPS, and Mössbauer spectroscopies-as well as by DFT calculations. A single ν CO feature (1965 cm -1 ) in the IR spectrum of 2, as well as a prominent Raman feature (ν symm = 1550 cm -1 ), are consistent with the presence of terminal carbonyls and a {(μ 6 -C)Fe 6 } arrangement of iron centers around the central carbide. The XPS of 2 exhibits a higher energy Fe 2p 3/2 feature (707.4 eV) as compared to that of 1 (705.5 eV), consistent with the two-electron oxidation induced by treatment of 1 with two equivalents of [Fc](PF 6 ) under CO atmosphere (for the two added CO ligands). DFT calculations indicate two axial and four equatorial Fe sites in 1, all of which have the same or similar oxidation states, for example, two Fe(0) and four Fe(+0.5). These assignments are supported by Mössbauer spectra for 1, which exhibit two closely spaced quadrupole doublets with δ = 0.076 and 0.064 mm s -1 . The high-field Mössbauer spectrum of 2 (4.2 K) exhibits three prominent quadrupole doublets with δ = -0.18, -0.11, and

  5. 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.

  6. THE MASS-METALLICITY RELATION OF GLOBULAR CLUSTERS IN THE CONTEXT OF NONLINEAR COLOR-METALLICTY RELATIONS

    International Nuclear Information System (INIS)

    Blakeslee, John P.; Cantiello, Michele; Peng, Eric W.

    2010-01-01

    Two recent empirical developments in the study of extragalactic globular cluster (GC) populations are the color-magnitude relation of the blue GCs (the 'blue tilt') and the nonlinearity of the dependence of optical GC colors on metallicity. The color-magnitude relation, interpreted as a mass-metallicity relation, is thought to be a consequence of self-enrichment. Nonlinear color-metallicity relations have been shown to produce bimodal color distributions from unimodal metallicity distributions. We simulate GC populations including both a mass-metallicity scaling relation and nonlinear color-metallicity relations motivated by theory and observations. Depending on the assumed range of metallicities and the width of the GC luminosity function (GCLF), we find that the simulated populations can have bimodal color distributions with a 'blue tilt' similar to observations, even though the metallicity distribution appears unimodal. The models that produce these features have the relatively high mean GC metallicities and nearly equal blue and red peaks characteristic of giant elliptical galaxies. The blue tilt is less apparent in the models with metallicities typical of dwarf ellipticals; the narrower GCLF in these galaxies has an even bigger effect in reducing the significance of their color-magnitude slopes. We critically examine the evidence for nonlinearity versus bimodal metallicities as explanations for the characteristic double-peaked color histograms of giant ellipticals and conclude that the question remains open. We discuss the prospects for further theoretical and observational progress in constraining the models presented here and for uncovering the true metallicity distributions of extragalactic GC systems.

  7. Emission processes of molecule-metal cluster ions from self-assembled monolayers of octanethiols on gold and silver

    International Nuclear Information System (INIS)

    Arezki, B.; Delcorte, A.; Bertrand, P.

    2004-01-01

    In this contribution, we focus on the emission processes of molecule-metal cluster ions from self-assembled monolayers (SAMs) of octanethiols CH 3 (CH 2 ) 7 SH on gold and silver. To improve our understanding of these complex phenomena, mass spectra and kinetic energy distributions (KEDs) of these two systems have been measured and compared using time-of-flight-SIMS under 15 keV Ga + bombardment. First, the spectra obtained from SAMs/Ag exhibit positive (M-H) m Ag m+1 + and negative (M-H) m Ag m-1 - cluster ions that are generally more intense than the (M-H) m Au n - observed for SAMs/Au. This trend is attributed to the electronegativity difference between S and these two metals resulting in a more ionic Ag-S bond. Second, our results show that, like for the SAM/Au system already investigated, unimolecular dissociation of Ag-thiolate clusters in the acceleration section of the spectrometer is an important formation mechanism. The fraction of the (M-H) m Ag n +,- aggregates formed in the vacuum via this process is even significantly higher than that of the (M-H) m Au n - cluster ions. This suggests that the cluster ions ejected from SAMs/Ag are less stable than those ejected from SAMs/Au. It is also observed that the high energy parts of the KEDs are steeper than for gold, which is probably due to the same phenomenon

  8. Nature of the interaction between rare gas atoms and transition metal doped silicon clusters: the role of shielding effects.

    Science.gov (United States)

    Ngan, Vu Thi; Janssens, Ewald; Claes, Pieterjan; Fielicke, André; Nguyen, Minh Tho; Lievens, Peter

    2015-07-21

    Mass spectrometry experiments show an exceptionally weak bonding between Si7Mn(+) and rare gas atoms as compared to other exohedrally transition metal (TM) doped silicon clusters and other SinMn(+) (n = 5-10) sizes. The Si7Mn(+) cluster does not form Ar complexes and the observed fraction of Xe complexes is low. The interaction of two cluster series, SinMn(+) (n = 6-10) and Si7TM(+) (TM = Cr, Mn, Cu, and Zn), with Ar and Xe is investigated by density functional theory calculations. The cluster-rare gas binding is for all clusters, except Si7Mn(+) and Si7Zn(+), predominantly driven by short-range interaction between the TM dopant and the rare gas atoms. A high s-character electron density on the metal atoms in Si7Mn(+) and Si7Zn(+) shields the polarization toward the rare gas atoms and thereby hinders formation of short-range complexes. Overall, both Ar and Xe complexes are similar except that the larger polarizability of Xe leads to larger binding energies.

  9. Structural properties of transition metal-Sin (n=14-16) atomic clusters

    International Nuclear Information System (INIS)

    Radny, M.W.; Kumar, V.; Kawazoe, Y.

    2003-01-01

    Full text: Structure has a central role in cluster science and is a prerequisite for elucidating many of the properties of clusters. As a consequence, much experimental and theoretical effort has been expended in order to characterize cluster structures. In this paper we demonstrate that the most energetically stable M-Si n clusters (n = 12, 14, 15, and 16) for Group IV elements are conformally limited to the so-called Frank-Kasper (FK) 14, 15 and 16 structures. By exploring the FK configuration space we have also found that the rearrangement of a M-Si FK-type cluster - by attachment of additional Si atoms - transforms the cluster to another FK-type cluster. The latter shows the preferential growth mode for the M-Si n clusters and indicates on the strong magic behaviour of the FK cluster topologies

  10. Noble metal alloy clusters in the gas phase derived from protein templates: unusual recognition of palladium by gold

    Science.gov (United States)

    Baksi, Ananya; Pradeep, T.

    2013-11-01

    Matrix assisted laser desorption ionization of a mixture of gold and palladium adducts of the protein lysozyme (Lyz) produces naked alloy clusters of the type Au24Pd+ in the gas phase. While a lysozyme-Au adduct forms Au18+, Au25+, Au38+ and Au102+ ions in the gas phase, lysozyme-Pd alone does not form any analogous cluster. Addition of various transition metal ions (Ag+, Pt2+, Pd2+, Cu2+, Fe2+, Ni2+ and Cr3+) in the adducts contributes to drastic changes in the mass spectrum, but only palladium forms alloys in the gas phase. Besides alloy formation, palladium enhances the formation of specific single component clusters such as Au38+. While other metal ions like Cu2+ help forming Au25+ selectively, Fe2+ catalyzes the formation of Au25+ over all other clusters. Gas phase cluster formation occurs from protein adducts where Au is in the 1+ state while Pd is in the 2+ state. The creation of alloys in the gas phase is not affected whether a physical mixture of Au and Pd adducts or a Au and Pd co-adduct is used as the precursor. The formation of Au cores and AuPd alloy cores of the kind comparable to monolayer protected clusters implies that naked clusters themselves may be nucleated in solution.Matrix assisted laser desorption ionization of a mixture of gold and palladium adducts of the protein lysozyme (Lyz) produces naked alloy clusters of the type Au24Pd+ in the gas phase. While a lysozyme-Au adduct forms Au18+, Au25+, Au38+ and Au102+ ions in the gas phase, lysozyme-Pd alone does not form any analogous cluster. Addition of various transition metal ions (Ag+, Pt2+, Pd2+, Cu2+, Fe2+, Ni2+ and Cr3+) in the adducts contributes to drastic changes in the mass spectrum, but only palladium forms alloys in the gas phase. Besides alloy formation, palladium enhances the formation of specific single component clusters such as Au38+. While other metal ions like Cu2+ help forming Au25+ selectively, Fe2+ catalyzes the formation of Au25+ over all other clusters. Gas phase cluster

  11. Spatially resolved stochastic cluster dynamics for radiation damage evolution in nanostructured metals

    International Nuclear Information System (INIS)

    Dunn, Aaron Y.; Capolungo, Laurent; Martinez, Enrique; Cherkaoui, Mohammed

    2013-01-01

    A spatially resolved stochastic cluster dynamics (SRSCD) model is introduced to describe radiation-induced defect evolution in metals. The stochastic nature of the method allows SRSCD to model more chemical species and more mobile defects than rate theory methods without loss of computational efficiency, while reaching larger timescales and simulating larger volumes than object-oriented kinetic Monte Carlo (OKMC) methods. To comprehend the capabilities of the method and access new understanding of defect evolution, SRSCD is used in three scenarios. In the first, the results of Frenkel pair implantation are found to match those of rate theory in both spatially homogeneous and spatially resolved media. Next, to study spatial resolution effects and correspondence to OKMC, the results of 20 keV cascade implantation into copper is simulated and an acceptable match with OKMC is found. Finally the method is used to study the problem of helium desorption in thin iron foils. The model is compared with available experimental measures and is found to be in good agreement. The ability of SRSCD to include many mobile species of defects allows a detailed analysis of the mechanisms of helium release from the free surface of the iron foils. As a result new dominant mechanisms of helium release are discussed as well as their operating regimes

  12. Detailed chemical abundances in NGC 5824: another metal-poor globular cluster with internal heavy element abundance variations

    Science.gov (United States)

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

    2016-01-01

    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 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 anticorrelated with [Na/Fe] and [Al/Fe]. There is no evidence for internal dispersion among the other α- or Fe-group abundance ratios. 25 of the 26 stars exhibit a n-capture enrichment pattern dominated by r-process nucleosynthesis ( = +0.11 ± 0.12; = -0.66 ± 0.05). Only one star shows evidence of substantial s-process enhancement ([Ba/Fe] = +0.56 ± 0.12; [Ba/Eu] = +0.38 ± 0.14), but this star does not exhibit other characteristics associated with s-process enhancement via mass transfer from a binary companion. The Pb and other heavy elements produced by the s-process suggest a time-scale of no more than a few hundred Myr for star formation and chemical enrichment, like the complex globular clusters M2, M22, and NGC 5286.

  13. [Ti8Zr2O12(COO)16] Cluster: An Ideal Inorganic Building Unit for Photoactive Metal-Organic Frameworks.

    Science.gov (United States)

    Yuan, Shuai; Qin, Jun-Sheng; Xu, Hai-Qun; Su, Jie; Rossi, Daniel; Chen, Yuanping; Zhang, Liangliang; Lollar, Christina; Wang, Qi; Jiang, Hai-Long; Son, Dong Hee; Xu, Hongyi; Huang, Zhehao; Zou, Xiaodong; Zhou, Hong-Cai

    2018-01-24

    Metal-organic frameworks (MOFs) based on Ti-oxo clusters (Ti-MOFs) represent a naturally self-assembled superlattice of TiO 2 nanoparticles separated by designable organic linkers as antenna chromophores, epitomizing a promising platform for solar energy conversion. However, despite the vast, diverse, and well-developed Ti-cluster chemistry, only a scarce number of Ti-MOFs have been documented. The synthetic conditions of most Ti-based clusters are incompatible with those required for MOF crystallization, which has severely limited the development of Ti-MOFs. This challenge has been met herein by the discovery of the [Ti 8 Zr 2 O 12 (COO) 16 ] cluster as a nearly ideal building unit for photoactive MOFs. A family of isoreticular photoactive MOFs were assembled, and their orbital alignments were fine-tuned by rational functionalization of organic linkers under computational guidance. These MOFs demonstrate high porosity, excellent chemical stability, tunable photoresponse, and good activity toward photocatalytic hydrogen evolution reactions. The discovery of the [Ti 8 Zr 2 O 12 (COO) 16 ] cluster and the facile construction of photoactive MOFs from this cluster shall pave the way for the development of future Ti-MOF-based photocatalysts.

  14. Design and Formation of a Large, Tetrahedral, Metal-ligand Cluster Using 1,1'-Binaphthyl Ligands

    Energy Technology Data Exchange (ETDEWEB)

    Biros, Shannon M.; Yeh, Robert M.; Raymond, Kenneth N.

    2008-03-13

    Many chemists have been fascinated with the development of discrete supramolecular structures that encapsulate guest molecules. These structures can be assembled through covalent or hydrogen bonds, electrostatic or metal-ligand interactions. These host structures have provided valuable insight into the forces involved in small molecule recognition. Our work has focused on the design and study of metal-ligand clusters of varying sizes. The naphthalene [M{sub 4}L{sub 6}]{sup 12-} cluster 1, shown in Figure 1, has demonstrated diastereoselective guest binding and chiral induction properties as well as the ability to catalyze reactions carried out inside the cavity in an enzyme-like manner. However, the size of the cavity (ca. 300-500 {angstrom}{sup 3}) has often limited the scope of substrates for these transformations.

  15. On the Chemical Abundances of Miras in Clusters: V1 in the Metal-rich Globular NGC 5927

    Science.gov (United States)

    D’Orazi, V.; Magurno, D.; Bono, G.; Matsunaga, N.; Braga, V. F.; Elgueta, S. S.; Fukue, K.; Hamano, S.; Inno, L.; Kobayashi, N.; Kondo, S.; Monelli, M.; Nonino, M.; Przybilla, N.; Sameshima, H.; Saviane, I.; Taniguchi, D.; Thevenin, F.; Urbaneja-Perez, M.; Watase, A.; Arai, A.; Bergemann, M.; Buonanno, R.; Dall’Ora, M.; Da Silva, R.; Fabrizio, M.; Ferraro, I.; Fiorentino, G.; Francois, P.; Gilmozzi, R.; Iannicola, G.; Ikeda, Y.; Jian, M.; Kawakita, H.; Kudritzki, R. P.; Lemasle, B.; Marengo, M.; Marinoni, S.; Martínez-Vázquez, C. E.; Minniti, D.; Neeley, J.; Otsubo, S.; Prieto, J. L.; Proxauf, B.; Romaniello, M.; Sanna, N.; Sneden, C.; Takenaka, K.; Tsujimoto, T.; Valenti, E.; Yasui, C.; Yoshikawa, T.; Zoccali, M.

    2018-03-01

    We present the first spectroscopic abundance determination of iron, α-elements (Si, Ca, and Ti), and sodium for the Mira variable V1 in the metal-rich globular cluster NGC 5927. We use high-resolution (R ∼ 28,000), high signal-to-noise ratio (∼200) spectra collected with WINERED, a near-infrared (NIR) spectrograph covering simultaneously the wavelength range 0.91–1.35 μm. The effective temperature and the surface gravity at the pulsation phase of the spectroscopic observation were estimated using both optical (V) and NIR time-series photometric data. We found that the Mira is metal-rich ([Fe/H] = ‑0.55 ± 0.15) and moderately α-enhanced ([α/Fe] = 0.15 ± 0.01, σ = 0.2). These values agree quite well with the mean cluster abundances based on high-resolution optical spectra of several cluster red giants available in the literature ([Fe/H] = ‑ 0.47 ± 0.06, [α/Fe] = + 0.24 ± 0.05). We also found a Na abundance of +0.35 ± 0.20 that is higher than the mean cluster abundance based on optical spectra (+0.18 ± 0.13). However, the lack of similar spectra for cluster red giants and that of corrections for departures from local thermodynamical equilibrium prevents us from establishing whether the difference is intrinsic or connected with multiple populations. These findings indicate a strong similarity between optical and NIR metallicity scales in spite of the difference in the experimental equipment, data analysis, and in the adopted spectroscopic diagnostics. Based on spectra collected with the WINERED spectrograph available as a visitor instrument at the ESO New Technology Telescope (NTT), La Silla, Chile (ESO Proposal: 098.D-0878(A), PI: G. Bono).

  16. DERIVING METALLICITIES FROM THE INTEGRATED SPECTRA OF EXTRAGALACTIC GLOBULAR CLUSTERS USING THE NEAR-INFRARED CALCIUM TRIPLET

    International Nuclear Information System (INIS)

    Foster, Caroline; Forbes, Duncan A.; Proctor, Robert N.; Spitler, Lee R.; Strader, Jay; Brodie, Jean P.

    2010-01-01

    The Ca II 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 system are (1) the CaT may be affected by a population of hot blue stars, (2) the CaT may saturate earlier than predicted by the models, and/or (3) color may not trace metallicity linearly. Until these possibilities are understood, the use of the CaT as a metallicity indicator for the integrated spectra of extragalactic GCs will remain problematic.

  17. 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

    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...

  18. Magnetism in clusters of 4d transition metals; Magnetismo en cumulos de metales de transicion 4d

    Energy Technology Data Exchange (ETDEWEB)

    Salcido A, F.; Villasenor G, P.; Dorantes D, J. [Instituto de Fisica. Manuel Sandoval Vallarta. Universidad Autonoma de San Luis Potosi. Alvaro Obregon 64, 78000 San Luis Potosi (Mexico)

    1999-07-01

    The magnetic properties of ruthenium (Ru{sub N}), rhodium (Rh{sub N}) and palladium (Pd{sub N}) clusters are determined as function of the cluster size N (N=4, 6, 13 and 19). For N=4 and 6 we take the tetrahedral and pentagonal pyramid geometric structures respectively. For N=13 and 19 we consider fcc-like structures. We use a tight binding Hamiltonian for s, p and d electrons in the unrestricted Hartree-Fock approximation. For the considered cluster, we obtain magnetic moments non-vanishing local, with the exception of Rh{sub 4}. Ru{sub N} and Rh{sub N} present a maximum in the average magnetic moment when the size of the cluster is N=13 and in all the elements we found that the average magnetic moment decreases strongly at N=19. As expected, the local magnetic moments at the atoms of the surface of the cluster are larger than those at inner atoms, except for Ru{sub 19}. We find strong oscillations of the magnetic moment as function of N an are less important in the Pd{sub N} clusters. (Author)

  19. Mass-spectrometric study of ion clustering in alkali-metal hydroxide vapor: cluster-ion energy and structural characteristics

    International Nuclear Information System (INIS)

    Kudin, L.S.; Butman, M.F.; Krasnov, K.S.

    1986-01-01

    Various positive and negative ions have been recorded in the equilibrium vapors from alkali-metal hydroxides: M/sup +/-/, OH - , O - , MO - , MOH - , and X/sup +/-/ (MOH)/sub n/, where X = M/sup +/-/, OH - , n = 1-6. The equilibrium constants have been measured for X/sup +/-/(MOH)/sub n/ = x/sup +/-/ + nMOH(k), n = 1-3, and the enthalpies of reaction have been determined, from which the enthalpies of formation and dissociation energies of X/sup +/-/ (MOH)/sub n/ have been calculated. The relative stabilities of the ions in the series from Na to Cs are examined

  20. 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

  1. Deposition of metallic clusters on a metallic surface at zero initial kinetic energy: Evidence for implantation and site exchanges

    Science.gov (United States)

    Nacer, B.; Massobrio, C.; Félix, C.

    1997-10-01

    We have investigated the deposition at zero impact kinetic energy of the Ag atom and clusters (Ag7,Ag19) on the (100) and (111) surfaces of Pd by molecular-dynamics simulations performed within the embedded-atom-method scheme. Our results elucidate the role played by the adsorption energy in determining the final morphology of the cluster/substrate system when ideal nondestructive deposition conditions are implemented. While implantation of the atom is not observed, we find a finite probability of site Ag-Pd exchanges in the case of clusters. Deposition-assisted mixing occurring at the topmost surface layer appears to be correlated to the size of the cluster and the orientation of the substrate, being higher for Ag7/Pd(100) and lower for Ag19/Pd(111). Total-energy calculations, combined with an analysis of the atomic motion, indicate that the structural transformation accompanying the deposition of the cluster provides the needed activation energy to induce the observed Ag-Pd atomic exchanges.

  2. Detailed Abundances for the Old Population near the Galactic Center. I. Metallicity Distribution of the Nuclear Star Cluster

    Science.gov (United States)

    Rich, R. M.; Ryde, N.; Thorsbro, B.; Fritz, T. K.; Schultheis, M.; Origlia, L.; Jönsson, H.

    2017-12-01

    We report the first high spectral resolution study of 17 M giants kinematically confirmed to lie within a few parsecs of the Galactic center, using R˜ {{24,000}} spectroscopy from Keck/NIRSPEC and a new line list for the infrared K band. We consider their luminosities and kinematics, which classify these stars as members of the older stellar population and the central cluster. We find a median metallicity of = -0.16 and a large spread from approximately -0.3 to +0.3 (quartiles). We find that the highest metallicities are [{Fe}/{{H}}]distribution strongly resemble those of the Galactic bulge rather than the disk or halo; in our small sample we find no statistical evidence for a dependence of velocity dispersion on metallicity.

  3. THE OPEN CLUSTER CHEMICAL ANALYSIS AND MAPPING SURVEY: LOCAL GALACTIC METALLICITY GRADIENT WITH APOGEE USING SDSS DR10

    Energy Technology Data Exchange (ETDEWEB)

    Frinchaboy, Peter M.; Thompson, Benjamin; Jackson, Kelly M., E-mail: p.frinchaboy@tcu.edu, E-mail: b.a.thompson1@tcu.edu, E-mail: Kelly.Jackson@utdallas.edu [Department of Physics and Astronomy, Texas Christian University, TCU Box 298840, Fort Worth, TX 76129 (United States); and others

    2013-11-01

    The Open Cluster Chemical Analysis and Mapping (OCCAM) survey aims to produce a comprehensive, uniform, infrared-based data set for hundreds of open clusters, and constrain key Galactic dynamical and chemical parameters from this sample. This first contribution from the OCCAM survey presents analysis of 141 members stars in 28 open clusters with high-resolution metallicities derived from a large uniform sample collected as part of the Sloan Digital Sky Survey III/Apache Point Observatory Galactic Evolution Experiment. This sample includes the first high-resolution metallicity measurements for 22 open clusters. With this largest ever uniformly observed sample of open cluster stars we investigate the Galactic disk gradients of both [M/H] and [α/M]. We find basically no gradient in [α/M] across 7.9 kpc ≤ R {sub GC} ≤ 14.5 kpc, but [M/H] does show a gradient for R {sub GC} < 10 kpc and a significant flattening beyond R {sub GC} = 10 kpc. In particular, whereas fitting a single linear trend yields an [M/H] gradient of –0.09 ± 0.03 dex kpc{sup –1}—similar to previously measure gradients inside 13 kpc—by independently fitting inside and outside 10 kpc separately we find a significantly steeper gradient near the Sun (7.9 ≤ R {sub GC} ≤ 10) than previously found (–0.20 ± 0.08 dex kpc{sup –1}) and a nearly flat trend beyond 10 kpc (–0.02 ± 0.09 dex kpc{sup –1})

  4. Habilidades metalingüísticas, operaciones metacognitivas y su relación con los niveles de competencia en lectura y escritura: un estudio exploratorio

    Directory of Open Access Journals (Sweden)

    Rita Flórez Romero

    2005-01-01

    Full Text Available El propósito de este estudio fue explorar las habilidades metalingüísticas, las operaciones metacognitivas y su relación con las competencias en lectura y escritura. Para evaluar las habilidades metalingüísticas se construyó un instrumento basado en la propuesta de van Kleeck (1995, relacionada con la arbitrariedad del lenguaje y el lenguaje como sistema. Para evaluar las operaciones metacognitivas se diseñaron dos pruebas, una para metacognición en lectura y otra para escritura. Para evaluar las competencias en lectura y escritura se aplicaron los instrumentos del proyecto de Evaluación Censal de Competencias Básicas en Lenguaje diseñados por la Secretaría de Educación del Distrito y por la Universidad Nacional. En el análisis de datos se utilizaron estadísticos descriptivos, como medidas de tendencia central y distribución en caso de las variables continuas y distribuciones de frecuencia y tablas de contingencia en el caso de las variables nominales

  5. Habilidades metalingüísticas, operaciones metacognitivas y su relación con los niveles de competencia en lectura y escritura: un estudio exploratorio

    Directory of Open Access Journals (Sweden)

    Rita Flórez Romero

    2005-06-01

    Full Text Available El propósito de este estudio fue explorar las habilidades metalingüísticas, las operaciones metacognitivas y su relación con las competencias en lectura y escritura. Para evaluar las habilidades metalingüísticas se construyó un instrumento basado en la propuesta de van Kleeck (1995, relacionada con la arbitrariedad del lenguaje y el lenguaje como sistema. Para evaluar las operaciones metacognitivas se diseñaron dos pruebas, una para metacognición en lectura y otra para escritura. Para evaluar las competencias en lectura y escritura se aplicaron los instrumentos del proyecto de Evaluación Censal de Competencias Básicas en Lenguaje diseñados por la Secretaría de Educación del Distrito y por la Universidad Nacional. En el análisis de datos se utilizaron estadísticos descriptivos, como medidas de tendencia central y distribución en caso de las variables continuas y distribuciones de frecuencia y tablas de contingencia en el caso de las variables nominales.

  6. Habilidades metalingüísticas, operaciones metacognitivas y su relación con los niveles de competencia en lectura y escritura: un estudio exploratorio

    Directory of Open Access Journals (Sweden)

    Flórez Romero Rita

    2005-06-01

    Full Text Available El propósito de este estudio fue explorar las habilidades metalingüísticas, las operaciones metacognitivas y su relación con las competencias en lectura y escritura. Para evaluar las habilidades metalingüísticas se construyó un instrumento basado en la propuesta de van Kleeck (1995, relacionada con la arbitrariedad del lenguaje y  el lenguaje como sistema. Para evaluar las operaciones metacognitivas se diseñaron dos pruebas, una para metacognición en lectura y otra para escritura. Para evaluar las competencias en lectura y escritura se aplicaron los instrumentos del proyecto de Evaluación Censal de Competencias Básicas en Lenguaje diseñados por la Secretaría de Educación del Distrito y por la Universidad Nacional. En el análisis de datos se utilizaron estadísticos descriptivos, como medidas de tendencia central y distribución en caso de las variables continuas y distribuciones de frecuencia y tablas de contingencia en el caso de las variables nominales.

  7. Study of radiation portal monitor and its application to metal recycling industry; Estudio de un sistema de deteccion tipo portico para su aplicacion en la industria del metal

    Energy Technology Data Exchange (ETDEWEB)

    Pujol, L.; Lara-Calleja, S.; Suarez-Navarro, M. J.; Gonzalez-Gonzalez, J. A.

    2009-07-01

    The industry of the iron and the steel in one of the most important sectors in Spain for its economic development. the recycling of metallic materials as well as the import of metallic scrap is very significant. Several reports on accidental dispersion or smelting of radioactive sources in metal recycling industries confirm the possibility that radioactive material might be mixed with scrap. In consequence, this type of accident shows the necessity of a rigorous and specific radiation control of the sector. The control of these materials with radioactive content can be carried out with radiation portal monitors installed at the entrance of these industries. The detection of radioactive materials presents special features as the continuous background acquisition or the minimisation of the relatively large number of innocent/nuisance detections. In the present work, we study a radiation portal monitor, the FHT-1388-T Thermo-Eberline. This is one of the usual radiation portal systems installed at the entrance of the metal recycling industry. Se study the characteristics and parameters of this portal monitor to optimise its use. furthermore, we propose some rapid tests for radiation portal systems in metal recycling industry. (Author) 16 refs.

  8. [Electronic and structural properties of individual nanometer-size supported metallic clusters

    International Nuclear Information System (INIS)

    Reifenberger, R.

    1993-01-01

    This report summarizes the work performed under contract DOE-FCO2-84ER45162. During the past ten years, our study of electron emission from laser-illuminated field emission tips has taken on a broader scope by addressing problems of direct interest to those concerned with the unique physical and chemical properties of nanometer-size clusters. The work performed has demonstrated that much needed data can be obtained on individual nanometer-size clusters supported on a wide-variety of different substrates. The work was performed in collaboration with R.P. Andres in the School of Chemical Engineering at Purdue University. The Multiple Expansion Cluster Source developed by Andres and his students was essential for producing the nanometer-size clusters studied. The following report features a discussion of these results. This report provides a motivation for studying the properties of nanometer-size clusters and summarizes the results obtained

  9. [Electronic and structural properties of individual nanometer-size supported metallic clusters]. Final performance report

    Energy Technology Data Exchange (ETDEWEB)

    Reifenberger, R.

    1993-09-01

    This report summarizes the work performed under contract DOE-FCO2-84ER45162. During the past ten years, our study of electron emission from laser-illuminated field emission tips has taken on a broader scope by addressing problems of direct interest to those concerned with the unique physical and chemical properties of nanometer-size clusters. The work performed has demonstrated that much needed data can be obtained on individual nanometer-size clusters supported on a wide-variety of different substrates. The work was performed in collaboration with R.P. Andres in the School of Chemical Engineering at Purdue University. The Multiple Expansion Cluster Source developed by Andres and his students was essential for producing the nanometer-size clusters studied. The following report features a discussion of these results. This report provides a motivation for studying the properties of nanometer-size clusters and summarizes the results obtained.

  10. 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.

  11. Insights into magnetic interactions in a monodisperse Gd{sub 12}Fe{sub 14} metal cluster

    Energy Technology Data Exchange (ETDEWEB)

    Zheng, Xiu-Ying; Zhang, Hui; Liu, Pengxin; Du, Ming-Hao; Han, Ying-Zi; Wei, Rong-Jia; Kong, Xiang-Jian; Long, La-Sheng; Zheng, Lan-Sun [Collaborative Innovation Center of Chemistry for Energy Materials, State Key Lab. of Physical Chemistry of Solid Surface and Dept. of Chemistry, College of Chemistry and Chemical Engineering, Xiamen Univ. (China); Wang, Zhenxing; Ouyang, Zhong-Wen [Wuhan National High Magnetic Field Center and School of Physics, Huazhong University of Science and Technology, Wuhan (China); Zhuang, Gui-Lin [College of Chemcal Engineering, Zhejiang University of Technology, Hangzhou (China)

    2017-09-11

    The largest Ln-Fe metal cluster [Gd{sub 12}Fe{sub 14}(μ{sub 3}-OH){sub 12}(μ{sub 4}-OH){sub 6}(μ{sub 4}-O){sub 12}(TEOA){sub 6}(CH{sub 3}COO){sub 16}(H{sub 2} O){sub 8}].(CH{sub 3}COO){sub 2}(CH{sub 3}CN){sub 2}.(H{sub 2}O){sub 20} (1) and the core-shell monodisperse metal cluster of 1 a rate at SiO{sub 2} (1 a=[Gd{sub 12}Fe{sub 14}(μ{sub 3}-OH){sub 12}(μ{sub 4}-OH){sub 6}(μ{sub 4}-O){sub 12}(TEOA){sub 6}(CH{sub 3}COO){sub 16} (H{sub 2}O){sub 8}]{sup 2+}) were prepared. Experimental and theoretical studies on the magnetic properties of 1 and 1 a rate at SiO{sub 2} reveal that encapsulation of one cluster into one silica nanosphere not only effectively decreases intermolecular magnetic interactions but also significantly increases the zero-field splitting effect of the outer layer Fe{sup 3+} ions. (copyright 2017 Wiley-VCH Verlag GmbH and Co. KGaA, Weinheim)

  12. Metal Substitution in Keggin-Type Tridecameric Aluminum-Oxo-Hydroxy Clusters.

    Science.gov (United States)

    Parker, Wallace O'Neil; Millini, Roberto; Kiricsi, Imre

    1997-02-12

    The species resulting from a typical preparation for metal-substituted hybrids of the Keggin tridecamer, Al 13 or [AlO 4 Al 12 (OH) 24 (OH 2 ) 12 ] 7+ , were examined by performing 27 Al NMR on the solutions during aging and by studying the precipitated sulfate salts via solid state 27 Al NMR and powder X-ray diffraction (XRD). Aqueous mixtures (0.25 mol L -1 ) of AlCl 3 and another metal ion (M), in a 12:1 mole ratio (Al:M), where M = Fe 3+ , Zn 2+ , Ga 3+ , In 3+ , Sn 2+ , La 3+ , and Bi 3+ , were subjected to forced hydrolysis by addition of NaOH (1.0 mol L -1 ) until OH/(Al + M) = 2.25, and the kinetics of Al 13 formation and disappearance with aging at 80 °C was monitored by 27 Al NMR spectroscopy. Al 13 units polymerize on aging with an apparent rate constant (k) of 4.8(8) × 10 -2 h -1 to form a species referred to as AlP 2 . Only the solutions containing Ga 3+ and Sn 2+ exhibited faster Al 13 conversion rates. GaAl 12 forms quickly at 80 °C (k = 0.54 h -1 ) and is more stable than AlP 2 . Sn 2+ apparently promotes AlP 2 formation (k = 0.38 h -1 ). XRD and solid state NMR reveal that only the Ga hybrid can be prepared by this method. No hybrid formation was evidenced using M = Mg 2+ , Fe 3+ , Co 2+ , Ni 2+ , Cu 2+ , Zn 2+ , In 3+ , La 3+ , or Ce 3+ at 25 °C or M = Co 2+ or La 3+ under reflux conditions. Isostructural (cubic symmetry) single crystals were obtained for the sulfate salts of Al 13 and GaAl 12 . Single-crystal XRD analysis of these two polyoxocations provides the first rigorous comparison between them and shows they have very similar structures. The main crystallographic data for Al 13 and GaAl 12 are as follows:  Na[AlO 4 Al 12 (OH) 24 (H 2 O) 12 ](SO 4 ) 4 ·10H 2 O, cubic, F4̄3m, a = 17.856(2) Å, Z = 4; Na[GaO 4 Al 12 (OH) 24 (H 2 O) 12 ](SO 4 ) 4 ·10H 2 O, cubic, F4̄3m, a = 17.869(3) Å, Z = 4. Thus, the greater thermal stability of GaAl 12 cannot be rationalized in terms of the overall geometric considerations, as suggested by

  13. Health risk assessment of heavy metals in soils and vegetables from wastewater irrigated area, Beijing-Tianjin city cluster, China.

    Science.gov (United States)

    Wang, Yanchun; Qiao, Min; Liu, Yunxia; Zhu, Yongguan

    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.

  14. Quantum molecular dynamics: Numerical methods and physical study of the structure, thermodynamics, stability and fragmentation of sodium metallic clusters

    International Nuclear Information System (INIS)

    Blaise, Philippe

    1998-01-01

    The aim of this thesis is to study metallic sodium clusters by numerical simulation. We have developed two ab initio molecular dynamics programs within the formalism of density functional theory. The first is based on the semi-classical extended Thomas-Fermi approach. We use a real-space grid and a Car-Parrinello-like scheme. The computational cost is O(N), and we have built a pseudopotential that speeds up the calculations. By neglecting quantum shell effects, we are able to study a very large set of clusters. We show that sodium cluster energies fit well a liquid drop formula, by adjusting a few parameters. We have investigated breathing modes, surface oscillations and the net charge density. We have shown that the surface energy varies strongly with temperature, and that clusters have a lower melting point than bulk material. We have calculated fission barriers by a constraint method. The second program is based on the quantum Kohn-Sham approach. We use a real-space grid, and combine a generalized Broyden scheme for assuring self-consistency with an iterative Davidson-Lanczos algorithm for solving the Eigen-problem. The cost of the method is much higher. First of all, we have calculated some stable structures for small clusters and their energetics. We obtained very good agreement with previous works. Then, we have investigated highly charged cluster dynamics. We have identified a chaotic fission process. For high fissility systems, we observe a multi-fragmentation dynamics and we find preferential emission of monomers on a characteristic time scale less than a pico-second. This has been simulated for the first time, with the help of our adaptive grid method which follows each fragment as they move apart during the fragmentation. (author)

  15. Clustering of nucleosides in the presence of alkali metals: Biologically relevant quartets of guanosine, deoxyguanosine and uridine observed by ESI-MS/MS.

    Science.gov (United States)

    Aggerholm, Tenna; Nanita, Sergio C; Koch, Kim J; Cooks, R Graham

    2003-01-01

    Electrospray ionization (ESI) mass spectra of nucleosides, recorded in the presence of alkali metals, display alkali metal ion-bound quartets and other clusters that may have implications for understanding non-covalent interactions in DNA and RNA. The tetramers of guanosine and deoxyguanosine and also their metaclusters (clusters of clusters), cationized by alkali metals, were observed as unusually abundant magic number clusters. The observation of these species in the gas phase parallels previous condensed-phase studies, which show that guanine derivatives can form quartets and metaclusters of quartets in solution in the presence of metal cations. This parallel behavior and also internal evidence suggest that bonding in the guanosine tetramers involves the bases rather than the sugar units. The nucleobases thymine and uracil are known to form magic number pentameric adducts with K+, Cs+ and NH4+ in the gas phase. In sharp contrast, we now show that the nucleosides uridine and deoxythymidine do not form the pentameric clusters characteristic of the corresponding bases. More subtle effects of the sugars are evident in the fact that adenosine and cytidine form numerous higher order clusters with alkali metals, whereas deoxyadenosine and deoxycytidine show no clustering. It is suggested that hydrogen bonding between the bases in the tetramers of dG and rG are the dominant interactions in the clusters, hence changing the ribose group to deoxyribose (and vice versa) generally has little effect. However, the additional hydroxyl group of RNA nucleosides enhances the non-selective formation of higher-order aggregates for adenosine and cytidine and results in the lack of highly stable magic number clusters. Some clusters are the result of aggregation in the course of ionization (ESI) whereas others appear to be intrinsic to the solution being examined. Copyright 2003 John Wiley & Sons, Ltd.

  16. 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. (c) 2004 American Institute of Physics

  17. The Metal-poor non-Sagittarius (?) Globular Cluster NGC 5053: Orbit and Mg, Al, and Si Abundances

    Science.gov (United States)

    Tang, Baitian; Fernández-Trincado, J. G.; Geisler, Doug; Zamora, Olga; Mészáros, Szabolcs; Masseron, Thomas; Cohen, Roger E.; García-Hernández, D. A.; Dell’Agli, Flavia; Beers, Timothy C.; Schiavon, Ricardo P.; Sohn, Sangmo Tony; Hasselquist, Sten; Robin, Annie C.; Shetrone, Matthew; Majewski, Steven R.; Villanova, Sandro; Schiappacasse Ulloa, Jose; Lane, Richard R.; Minnti, Dante; Roman-Lopes, Alexandre; Almeida, Andres; Moreno, E.

    2018-03-01

    Metal-poor globular clusters (GCs) exhibit intriguing Al–Mg anti-correlations and possible Si–Al correlations, which are important clues to decipher the multiple-population phenomenon. NGC 5053 is one of the most metal-poor GCs in the nearby universe and has been suggested to be associated with the Sagittarius (Sgr) dwarf galaxy, due to its similarity in location and radial velocity with one of the Sgr arms. In this work, we simulate the orbit of NGC 5053, and argue against a physical connection between Sgr and NGC 5053. On the other hand, the Mg, Al, and Si spectral lines, which are difficult to detect in the optical spectra of NGC 5053 stars, have been detected in the near-infrared APOGEE spectra. We use three different sets of stellar parameters and codes to derive the Mg, Al, and Si abundances. Regardless of which method is adopted, we see a large Al variation, and a substantial Si spread. Along with NGC 5053, metal-poor GCs exhibit different Mg, Al, and Si variations. Moreover, NGC 5053 has the lowest cluster mass among the GCs that have been identified to exhibit an observable Si spread until now.

  18. 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.

  19. Phase transition temperatures of 405-725 K in superfluid ultra-dense hydrogen clusters on metal surfaces

    Energy Technology Data Exchange (ETDEWEB)

    Holmlid, Leif, E-mail: holmlid@chem.gu.se [Atmospheric Science, Department of Chemistry, University of Gothenburg, SE-412 96 Göteborg (Sweden); Kotzias, Bernhard [Airbus DS, Department Mechanical Engineering, D28199 Bremen (Germany)

    2016-04-15

    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 H{sub 2N}(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 H{sub 4}(0) and H{sub 3}(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 H{sub 2N}(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.

  20. Coulomb frustration of the multiphoton ionization of metallic clusters under intense EUV FEL evidenced by ion spectrometry

    International Nuclear Information System (INIS)

    Mazza, T; Devetta, M; Milani, P; Motomura, K; Liu, X-J; Fukuzawa, H; Yamada, A; Nagaya, K; Iwayama, H; Sugishima, A; Mizoguchi, Y; Saito, N; Coreno, M; Nagasono, M; Tono, K; Togashi, T; Kimura, H; Okunishi, M; Fennel, Th; Senba, Y

    2015-01-01

    Free electron laser light sources delivering high intensity pulses of short wavelength radiation are opening novel possibilities for the investigation of matter at the nanoscale and for the discovery and understanding of new physical processes occurring at the exotic transient states they make accessible. Strong ionization of atomic constituents of a nano-sized sample is a representative example of such processes and the understanding of ionization dynamics is crucial for a realistic description of the experiments. We report here on multiple ionization experiments on free clusters of titanium, a high cohesive energy metal. The time of flight ion spectra reveal a saturation of the cluster ionization at ∼10 16 photons per pulse per cm 2 . Our results also show a clear lack of any explosion process, opposite to what is observed for a rare-gas cluster under similar conditions. A simple and generalized multi-step ionization model including Coulomb frustration of the photoemission process effectively reproduces with a good agreement the main features of the experimental observation and points to an interpretation of the data involving a substantial energy deposition into the cluster through electronic system heating upon scattering events within photoemission. (paper)

  1. 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.

  2. High performance organic photovoltaics with plasmonic-coupled metal nanoparticle clusters.

    Science.gov (United States)

    Park, Hyung Il; Lee, Seunghoon; Lee, Ju Min; Nam, Soo Ah; Jeon, Taewoo; Han, Sang Woo; Kim, Sang Ouk

    2014-10-28

    Performance enhancement of organic photovoltaics using plasmonic nanoparticles has been limited without interparticle plasmon coupling. We demonstrate high performance organic photovoltaics employing gold nanoparticle clusters with controlled morphology as a plasmonic component. Near-field coupling at the interparticle gaps of nanoparticle clusters gives rise to strong enhancement in localized electromagnetic field, which led to the significant improvement of exciton generation and dissociation in the active layer of organic solar cells. A power conversion efficiency of 9.48% is attained by employing gold nanoparticle clusters at the bottom of the organic active layer. This is one of the highest efficiency values reported thus far for the single active layer organic photovoltaics.

  3. 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...... with the results derived from the ab initio all-electron simulations of cluster electronic and ionic structure based on the density functional theory as well as on the post Hartree-Fock perturbation theory on many-electron correlation interaction. The comparison performed demonstrates the great role of cluster...

  4. Estudio de la extracción de metales del rechazo de la desalación

    OpenAIRE

    Rocasalbas Noguera, Xavier

    2008-01-01

    Este proyecto se enmarca en una de las líneas de investigación de proyecto SOSTAQUA, "Desarrollos Tecnológicos para el Ciclo Urbano del Agua Auto sostenible". El agua de mar, así como las salmueras contienen una gran cantidad de metales diluidos, la recuperación de los cuales, ligada a las instalaciones de desalación por ósmosis inversa, podría contribuir a la rentabilización de las mismas y a reducir ligeramente el impacto creado. En esta memoria se realiza una identificaci...

  5. 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.

  6. HST NIC3 Photometry of Metal-Rich Globular Clusters Palomar 6, Liller 1, and 47 Tuc (NGC 104

    Directory of Open Access Journals (Sweden)

    Jae-Woo Lee

    2004-09-01

    Full Text Available We present HST NIC3 photometry of metal-rich globular clusters Palomar 6, Liller 1 and 47 Tuc (NGC 104. We discuss the interstellar reddening law for the HST NICMOS F110W/F160W photometric system which depends on the temperature of the source. The distance moduli and interstellar reddening values for Palomar 6 and Liller 1 are estimated by comparing the magnitudes and colors of RHB stars in the clusters with those of 47 Tuc. We obtain (m-M0 = 14.48 mag and E(B-V = 1.34 mag for Palomar 6 and (m-M0 = 15.17 mag and E(B-V = 2.50 mag for Liller 1.

  7. Quantum size correction to the work function and centroid of excess charge in positively ionized simple metal clusters

    International Nuclear Information System (INIS)

    Payami, M.

    2004-01-01

    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 clusters with different r s values (2≤ r s ≥ 7). For this purpose, firstly we have calculated the self-consistent Kohn-Sham energies of neutral and singly-ionized clusters with sizes 2≤ N ≥100 in the framework of local spin-density approximation and stabilized jellium model as well as simple jellium model 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

  8. Simulation of resonance hyper-Rayleigh scattering of molecules and metal clusters using a time-dependent density functional theory approach.

    Science.gov (United States)

    Hu, Zhongwei; Autschbach, Jochen; Jensen, Lasse

    2014-09-28

    Resonance hyper-Rayleigh scattering (HRS) of molecules and metal clusters have been simulated based on a time-dependent density functional theory approach. The resonance first-order hyperpolarizability (β) is obtained by implementing damped quadratic response theory using the (2n + 1) rule. To test this implementation, the prototypical dipolar molecule para-nitroaniline (p-NA) and the octupolar molecule crystal violet are used as benchmark systems. Moreover, small silver clusters Ag 8 and Ag 20 are tested with a focus on determining the two-photon resonant enhancement arising from the strong metal transition. Our results show that, on a per atom basis, the small silver clusters possess two-photon enhanced HRS comparable to that of larger nanoparticles. This finding indicates the potential interest of using small metal clusters for designing new nonlinear optical materials.

  9. Combining in situ transmission electron microscopy irradiation experiments with cluster dynamics modeling to study nanoscale defect agglomeration in structural metals

    International Nuclear Information System (INIS)

    Xu Donghua; Wirth, Brian D.; Li Meimei; Kirk, Marquis A.

    2012-01-01

    We present a combinatorial approach that integrates state-of-the-art transmission electron microscopy (TEM) in situ irradiation experiments and high-performance computing techniques to study irradiation defect dynamics in metals. Here, we have studied the evolution of visible defect clusters in nanometer-thick molybdenum foils under 1 MeV krypton ion irradiation at 80 °C through both cluster dynamics modeling and in situ TEM experiments. The experimental details are reported elsewhere; we focus here on the details of model construction and comparing the model with the experiments. The model incorporates continuous production of point defects and/or small clusters, and the accompanying interactions, which include clustering, recombination and loss to the surfaces that result from the diffusion of the mobile defects. To account for the strong surface effect in thin TEM foils, the model includes one-dimensional spatial dependence along the foil depth, and explicitly treats the surfaces as black sinks. The rich amount of data (cluster number density and size distribution at a variety of foil thickness, irradiation dose and dose rate) offered by the advanced in situ experiments has allowed close comparisons with computer modeling and permitted significant validation and optimization of the model in terms of both physical model construct (damage production mode, identities of mobile defects) and parameterization (diffusivities of mobile defects). The optimized model exhibits good qualitative and quantitative agreement with the in situ TEM experiments. The combinatorial approach is expected to bring a unique opportunity for the study of radiation damage in structural materials.

  10. 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.

  11. Mono-, di-, and trimetallic methacrylate-substituted metal oxide clusters derived from hafnium butoxide

    International Nuclear Information System (INIS)

    Gross, Silvia; Kickelbick, Guido; Puchberger, Michael; Schubert, Ulrich

    2003-01-01

    The methacrylate-substituted clusters Hf 4 O 2 (OMc) 12 , Hf 6 O 4 (OH) 4 (OMc) 12 (BuOH), Ti 4 Hf 4 O 6 (OBu) 4 (OMc) 16 , andTi 2 Zr 5 HfO 6 (OMc) 20 (OMc = methacrylate) were prepared by reacting Hf(OBu) 4 , or Hf(OBu) 4 /Ti(OBu) 4 and Hf(OBu) 4 /Zr(OBu) 4 /Ti(OBu) 4 mixtures, respectively, with methacrylic acid. All clusters were characterized by x-ray structure analyses and are basically isostructural, although not in each case isomorphous, with the corresponding oxozirconium clusters. Low-temperature NMR studies revealed that the methacrylate ligands of Hf 4 O 2 (OMc) 12 are highly dynamic even at - 80 o C. Refs. 10 (author)

  12. 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.)

  13. New insights into the origin and evolution of the old, metal-rich open cluster NGC 6791

    Science.gov (United States)

    Martinez-Medina, Luis A.; Gieles, Mark; Pichardo, Barbara; Peimbert, Antonio

    2018-02-01

    NGC 6791 is one of the most studied open clusters, it is massive (˜5000 M⊙), located at the solar circle, old (˜8 Gyr) and yet the most metal-rich cluster ([Fe/H] ≃ 0.4) known in the Milky Way. By performing an orbital analysis within a Galactic model including spiral arms and a bar, we found that it is plausible that NGC 6791 formed in the inner thin disc or in the bulge, and later displaced by radial migration to its current orbit. We apply different tools to simulate NGC 6791, including direct N-body summation in time-varying potentials, to test its survivability when going through different Galactic environments. In order to survive the 8-Gyr journey moving on a migrating orbit, NGC 6791 must have been more massive, M0 ≥ 5 × 104 M⊙, when formed. We find independent confirmation of this initial mass in the stellar mass function, which is observed to be flat; this can only be explained if the average tidal field strength experienced by the cluster is stronger than what it is at its current orbit. Therefore, the birth place and journeys of NGC 6791 are imprinted in its chemical composition, in its mass-loss and in its flat stellar mass function, supporting its origin in the inner thin disc or in the bulge.

  14. 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

  15. 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...

  16. Non-Linear Optically Active Metal Clusters in Nanoscaled Systems Including Self-Assembled Organic Films

    DEFF Research Database (Denmark)

    Balzer, Frank; Jett, S. D.; Rubahn, Horst-Günter

    2000-01-01

    are initially monitored in ultrahigh vacuum by comparison of calculated with measured polarization-dependent extinction spectra. We find that at low surface temperatures (150 K) the cluster growth is very similar to growth directly on insulating substrates. With increasing surface temperature the size...

  17. Alternatives for recovering metals from spent catalysts for hydrotreating of heavy hydrocarbons: a case study; Alternativas para la recuperacion de metales a partir de catalizadores gastados del hidrotratamiento de hidrocarburos pesados: un caso de estudio

    Energy Technology Data Exchange (ETDEWEB)

    Alonso, Fernando; Ramirez, Sergio; Ancheyta, Jorge; Mavil, Martha [Instituto Mexicano del Petroleo, Mexico, D.F. (Mexico)]. E-mail: jancheyt@imp.mx

    2008-05-15

    The increasing production of spent hydrotreating catalysts used for processing heavy hydrocarbons and the problems related to their disposal are described in this work. These catalysts contain important amounts of heavy metals such as molybdenum (Mo), nickel (Ni), cobalt (Co) and vanadium (V), which can be recovered and hence an economical benefit may be obtained. The results of experimental tests for alkaline leaching (NaOH) to recover V and Mo, and the effect of operating conditions on metal recovery are also presented. The results show that, in general, the highest recovery of Mo is obtained at pH 8.5 and leaching time of 12 hours, while in the case of V, the highest recovery is observed at pH 9.0 and 8 hours. In both cases, the leaching solution contained 10 wt % alkaline. Based on the experimental information and data from a commercial plant, a preliminary economy study was developed, in which the expected economical benefits of metals recovery from spent catalysts used for hydrotreating heavy hydrocarbon are estimated. [Spanish] En el presente trabajo se describe la problematica de la creciente produccion de catalizadores gastados de los procesos de hidrotratamiento de hidrocarburos pesados. Estos catalizadores contienen cantidades importantes de metales pesados como molibdeno (Mo), niquel (Ni), cobalto (Co) y vanadio (V), que son susceptibles de recuperarse y obtener con ello un beneficio economico. Tambien se presentan resultados de pruebas experimentales de lixiviacion alcalina (NaOH) para la recuperacion de V y Mo, y el efecto de las variables de operacion sobre la recuperacion de metales. En general, se encontro que las mejores recuperaciones de Mo fueron a pH de 8.5 y 12 h, mientras que para el V fueron a pH de 9.0 y 8 h, ambos a una concentracion del agente lixiviante de 10% en peso. Con base en la informacion experimental obtenida y datos de una planta industrial se presenta un estudio economico preliminar, en el que se estiman los beneficios

  18. 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

    Science.gov (United States)

    Carrera, R.; Casamiquela, L.; Ospina, N.; Balaguer-Núñez, L.; Jordi, C.; Monteagudo, L.

    2015-06-01

    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 Å) 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 ⟨Vr⟩ = 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 ± 0.14 and -0.15 ± 0.18 for NGC 559 and NGC 7245, respectively. Berkeley 23 has low metallicity, [ Fe/H ] = -0.42 ± 0.13, which is similar to other open clusters in the outskirts of the Galactic disc. In contrast, we derived high metallicity ([ Fe/H ] = +0.43 ± 0.15) for NGC 6603, which places this system among the most metal-rich known open clusters. To our knowledge, this is the first determination of radial velocities and metallicities from spectroscopy for these clusters, except NGC 6603, for which radial velocities had been previously determined. We have also analysed ten stars in the line of sight to King 1. Because of the large dispersion obtained in both radial velocity and metallicity, we cannot be sure that we have sampled true cluster members. Based on observations made with the 2.5 m Isaac Newton Telescope operated on the island of La Palma by the Isaac Newton Group in the Spanish Observatorio del Roque de los Muchachos of the

  19. Minería de datos con técnica cluster, caso de estudio: estudiantes de Universidad Estatal Península de Santa Elena.

    Directory of Open Access Journals (Sweden)

    Mariuxi De La Cruz

    2015-10-01

    Full Text Available Este trabajo fue realizado para la Universidad Estatal Península de Santa Elena, muestra el proceso de minería de datos aplicando la técnica cluster o conglomerado, con herramientas de software libre como: PostgreSQL, apropiada para el almacenamiento de los datos y R para el análisis estadístico y la generación de los algoritmos que implica la técnica. El análisis cluster fue implementado en datos sociales, económicos y académicos de los estudiantes inscritos en la Facultad de Sistemas y Telecomunicaciones de esta institución de educación superior. El proceso es detallado en tres secciones, la primera donde se describe los conceptos  asociados a minería de datos, técnica cluster y las herramientas tecnológicas utilizadas para explotación de información. En la segunda sección  se describe el proceso de aplicación la técnica cluster con el método particional y con el método jerárquico. En la sección tres se muestra los conglomerados obtenidos al aplicar la técnica en el grupo de datos. Finalmente se presentan las conclusiones y recomendaciones de este trabajo.

  20. Comparison of the periodic slab approach with the finite cluster description of metal-organic interfaces at the example of PTCDA on Ag(110).

    Science.gov (United States)

    Banerjee, Jaita; Behnle, Stefan; Galbraith, Martin C E; Settels, Volker; Engels, Bernd; Tonner, Ralf; Fink, Reinhold F

    2018-02-05

    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 32-290 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, all clusters with four layers of silver atoms and sufficient lateral extension reproduce the adsorbate structure within 0.04 Å with respect to the slab-supercell structure and provide adsorption energies of ( -4.45± 0.08 eV) consistent with the slab result of -4.47 eV. Thus, metal-organic adsorbate systems can be realistically represented by properly defined cluster models. © 2018 Wiley Periodicals, Inc. © 2018 Wiley Periodicals, Inc.

  1. Structural, electronic and magnetic properties of 3d metal trioxide clusters-doped monolayer graphene: A first-principles study

    Energy Technology Data Exchange (ETDEWEB)

    Rafique, Muhammad [School of Energy Science and Engineering, Harbin Institute of Technology, 92 West Dazhi Street, Harbin 150001 (China); M.U.E.T, S.Z.A.B, Campus Khairpur Mir' s, Sindh (Pakistan); Shuai, Yong, E-mail: shuaiyong1978@gmail.com [School of Energy Science and Engineering, Harbin Institute of Technology, 92 West Dazhi Street, Harbin 150001 (China); Tan, He-Ping; Hassan, Muhammad [School of Energy Science and Engineering, Harbin Institute of Technology, 92 West Dazhi Street, Harbin 150001 (China)

    2017-03-31

    Highlights: • First-principles calculations are performed for TMO{sub 3} cluster-doped and TM atoms adsorbed at three O atoms-doped graphene. • Significant magnetic coupling behavior is observed between TM atoms and neighboring C and O atoms for both cases. • The direction of charge transfer is always from monolayer graphene to TMO{sub 3} clusters incorporated into graphene. • TiO{sub 3} and VO{sub 3} doped structures display dilute magnetic semiconductor behavior. • Five different orbitals (d{sub xy}, d{sub yz}, d{sub z}{sup 2}, d{sub xz} and d{sub x}{sup 2}{sub -y}{sup 2}) of 3d TM atoms give rise to magnetic moments for both cases. - Abstract: 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 TMO{sub 3} halogen clusters. In this paper we used two approaches for 3d metal trioxide clusters (i) TMO{sub 3} 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 TMO{sub 3} doped graphene layer, the bond length between C−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 TiO{sub 3} and VO{sub 3} substitution, system exhibits semiconductor properties. Interestingly, TiO{sub 3}-substituted system shows dilute magnetic semiconductor behavior with 2.00 μ{sub B} magnetic moment. On the other hand, the substitution of CoO{sub 3}, CrO{sub 3}, FeO{sub 3} and MnO{sub 3} induced 1.015 μ{sub B}, 2

  2. 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.

  3. Molecular dynamics simulations with electronic stopping can reproduce experimental sputtering yields of metals impacted by large cluster ions

    Science.gov (United States)

    Tian, Jiting; Zhou, Wei; Feng, Qijie; Zheng, Jian

    2018-03-01

    An unsolved problem in research of sputtering from metals induced by energetic large cluster ions is that molecular dynamics (MD) simulations often produce sputtering yields much higher than experimental results. Different from the previous simulations considering only elastic atomic interactions (nuclear stopping), here we incorporate inelastic electrons-atoms interactions (electronic stopping, ES) into MD simulations using a friction model. In this way we have simulated continuous 45° impacts of 10-20 keV C60 on a Ag(111) surface, and found that the calculated sputtering yields can be very close to the experimental results when the model parameter is appropriately assigned. Conversely, when we ignore the effect of ES, the yields are much higher, just like the previous studies. We further expand our research to the sputtering of Au induced by continuous keV C60 or Ar100 bombardments, and obtain quite similar results. Our study indicates that the gap between the experimental and the simulated sputtering yields is probably induced by the ignorance of ES in the simulations, and that a careful treatment of this issue is important for simulations of cluster-ion-induced sputtering, especially for those aiming to compare with experiments.

  4. VizieR Online Data Catalog: Ages and metallicities for M31 star clusters (Fan+, 2016)

    Science.gov (United States)

    Fan, Z.; de Grijs, R.; Chen, B.; Jiang, L.; Bian, F.; Li, Z.

    2017-05-01

    We have selected 22 confirmed M31 globular clusters from Peacock et al. 2010 (Cat. J/MNRAS/402/803). Spectroscopic observations were carried out with the 6.5m MMT/Red Channel Spectrograph from 2010 October 31 to 2010 November 2 and on 2011 November 4. The telescope is located on Mt. Hopkins in Arizona (USA) at an altitude of 2581m. The exposure times used ranged from 480-1800s, depending on the cluster brightness. The median seeing was ~0.98'' and we adopted a slit aperture of 0.75''*180''. The CCD's size is 450*1032 pixels2. It is characterized by a gain of 1.3e- ADU-1, with a readout noise of 3.5e-. A grating with 600l/mm with a blaze 1st/4800 was used. The spectral resolution was R=960 for a slit of 1'' and a central wavelength of 4701Å; the dispersion was 1.63Å/pixel. (7 data files).

  5. The emergence of nonbulk properties in supported metal clusters: negative thermal expansion and atomic disorder in Pt nanoclusters supported on gamma-Al2O3.

    Science.gov (United States)

    Sanchez, Sergio I; Menard, Laurent D; Bram, Ariella; Kang, Joo H; Small, Matthew W; Nuzzo, Ralph G; Frenkel, Anatoly I

    2009-05-27

    The structural dynamics-cluster size and adsorbate-dependent thermal behaviors of the metal-metal (M-M) bond distances and interatomic order-of Pt nanoclusters supported on a gamma-Al(2)O(3) are described. Data from scanning transmission electron microscopy (STEM) and X-ray absorption spectroscopy (XAS) studies reveal that these materials possess a dramatically nonbulklike nature. Under an inert atmosphere small, subnanometer Pt/gamma-Al(2)O(3) clusters exhibit marked relaxations of the M-M bond distances, negative thermal expansion (NTE) with an average linear thermal expansion coefficient alpha = (-2.4 +/- 0.4) x 10(-5) K(-1), large static disorder and dynamical bond (interatomic) disorder that is poorly modeled within the constraints of classical theory. The data further demonstrate a significant temperature-dependence to the electronic structure of the Pt clusters, thereby suggesting the necessity of an active model to describe the cluster/support interactions mediating the cluster's dynamical structure. The quantitative dependences of these nonbulklike behaviors on cluster size (0.9 to 2.9 nm), ambient atmosphere (He, 4% H(2) in He or 20% O(2) in He) and support identity (gamma-Al(2)O(3) or carbon black) are systematically investigated. We show that the nonbulk structural, electronic and dynamical perturbations are most dramatically evidenced for the smallest clusters. The adsorption of hydrogen on the clusters leads to an increase of the Pt-Pt bondlengths (due to a lifting of the surface relaxation) and significant attenuation of the disorder present in the system. Oxidation of these same clusters has the opposite effect, leading to an increase in Pt-Pt bond strain and subsequent enhancement in nonbulklike thermal properties. The structural and electronic properties of Pt nanoclusters supported on carbon black contrast markedly with those of the Pt/gamma-Al(2)O(3) samples in that neither NTE nor comparable levels of atomic disorder are observed. The Pt

  6. Extending the Compositional Range of Nanocasting in the Oxozirconium Cluster-based Metal-Organic Framework NU-1000 – A Comparative Structural Analysis

    Energy Technology Data Exchange (ETDEWEB)

    Zhao, Wenyang; Wang, Zhao; Malonzo, Camille D.; Webber, Thomas E.; Platero-Prats, Ana E.; Sotomayor, Francisco; Vermeulen, Nicolaas; Wang, Timothy C.; Hupp, Joseph T.; Farha, Omar K.; Penn, R. Lee; Chapman, Karena W.; Thommes, Matthias; Stein, Andreas

    2018-02-01

    The process of nanocasting in metal-organic frameworks (MOFs) is a versatile approach to modify these porous materials by introducing supporting scaffolds. The nanocast scaffolds can stabilize metal-oxo clusters in MOFs at high temperatures and modulate their chemical environments. Here we demonstrate a range of nanocasting approaches in the MOF NU-1000, which contains hexanuclear oxozirconium clusters (denoted as Zr6 clusters) that are suitable for modification with other metals. We developed methods for introducing SiO2, TiO2, polymeric, and carbon scaffolds into the NU-1000 structure. The responses of NU-1000 towards different scaffold precursors were studied, including the effects on morphology, precursor distribution, and porosity after nanocasting. Upon removal of organic linkers in the MOF by calcination/pyrolysis at 500 °C or above, the Zr6 clusters remained accessible and maintained their Lewis acidity in SiO2 nanocast samples, whereas additional treatment was necessary for Zr6 clusters to become accessible in carbon nanocast samples. Aggregation of Zr6 clusters was largely prevented with SiO2 or carbon scaffolds even after thermal treatment at 500 °C or above. In the case of titania nanocasting, NU- 1000 crystals underwent a pseudomorphic transformation, in which Zr6 clusters reacted with titania to form small oxaggregates of a Zr/Ti mixed oxide with a local structure resembling that of ZrTi2O6. The ability to maintain high densities of discrete Lewis acidic Zr6 clusters on SiO2 or carbon supports at high temperatures provides a starting point for designing new thermally stable catalysts.

  7. Effects of spin-orbit coupling on the spin structure of deposited transition-metal clusters

    Science.gov (United States)

    Mankovsky, S.; Bornemann, S.; Minár, J.; Polesya, S.; Ebert, H.; Staunton, J. B.; Lichtenstein, A. I.

    2009-07-01

    The influence of the spin-orbit coupling on the magnetic structure of deposited transition-metal nanostructures has been studied by fully relativistic electronic-structure calculations. The interplay of exchange coupling and magnetic anisotropy was monitored by studying the corresponding magnetic torque calculated within ab initio and model approaches. We find that a spin-orbit-induced Dzyaloshinski-Moriya interaction has a profound effect on the spin structure of such complex magnetic systems and that in combination with magnetic anisotropies and isotropic exchange this can result in peculiar magnetic properties.

  8. 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)

  9. 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.

  10. 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 TiO 2 . In these structures, isolated Pt atoms, Pt iso , remain stable through various conditions, and spectroscopic evidence suggests Pt iso species exist in homogeneous local environments. Comparing Pt iso to ∼1 nm preoxidized (Pt ox ) and prereduced (Pt metal ) Pt clusters on TiO 2 , we identify unique spectroscopic signatures of CO bound to each site and find CO adsorption energy is ordered: Pt iso ≪ Pt metal atoms bonded to TiO 2 and that Pt iso exhibits optimal reactivity because every atom is exposed for catalysis and forms an interfacial site with TiO 2 . This approach should be generally useful for studying the behavior of supported precious metal atoms.

  11. Estudio de Factibilidad de Técnicas Vibroacústicas en la Detección de Discontinuidades en Metales. (Parte I. // Vibroacoustical techniques in metals discontinuity detection (part I.

    Directory of Open Access Journals (Sweden)

    F. de la Torre. Silva

    1999-07-01

    Full Text Available En este trabajo se presenta un estudio de factibilidad para la detección de discontinuidades en metales a partir de la aplicación detécnicas de ensayo vibroacústicas mediante la excitación sinusoidal e impulsiva. El análisis simultáneo que puede ser realizado a laseñal de entrada y de salida de un elemento metálico, reportaría una descripción del sistema en cuanto a sus propiedades dinámicasfundamentales, como lo son el caso de la Función Respuesta de Frecuencias y la Respuesta Impulsiva. Además, el uso de la Funciónde Correlación Cruzada, permitiría cuantificar el tiempo de propagación de la señal entre la entrada y la salida, para variaciones dediscontinuidades. El empleo de un Instrumento Virtual, sería la herramienta para la realización del análisis de señales. Se plantea unmodelo físico matemático teórico a partir del empleo del Método de los Elementos Finitos, implementado por el software MSC/PAL,el cual permitirá corroborar los resultados brindados por el diseño experimental, así como, estudiar dinámicamente el sistema objetode análisis.Palabras claves: factibilidad, fractura, vibroacústica, diagnóstico.__________________________________________________________________AbstractIn this work is presented a feasibility study for the discontinuities detection in metals as of the application of trial techniques vibraacoustic through the excitement sinusoidal and impulsive. The simultaneous analysis that it can be accomplished to the entry sign andof exit of a metallic element, would report a description of the system concerning their/its fundamental dynamic properties, as are thecase of the function frequencies response and impulsive response. Furthermore, the use of the correlation function crusade, wouldpermit quantify the spread time of the sign between the entry and the exit, for discontinuity variations. The employment of a virtualinstrument, would be the tool for the accomplishment of the signs analysis

  12. Estudio de inclusiones fluidas de las mineralizaciones epitermales de Ag.Baritina.metales de base de Hiendelaencina y de Baritina de Atienza (Sistema Central Español

    Directory of Open Access Journals (Sweden)

    Oyarzun, R.

    1991-08-01

    Full Text Available Fluid inclusion studies on quartz and barite samples from the Hiendelaencina Ag-base metals epithermal deposit (late Hercynian suggest that this mineralization was formed during four hydrothermal stages. Ore stage I was characterized by aqueous-carbonic fluids from which pyrite and arsenopyrite were precipitated. The interaction between probably magmatic-derived fluids (aqueous solutions; Th = 320 – 200º C, 12 eq. wt. % NaCl and meteoric waters (of lower temperature and salinity caused a generalized decrease in both, T and salinity (from 12 eq. wt. % NaCl to 3 eq. wt. % NaCl, thus probably inducing the precipitation of Cu and Zn minerals (ore stage 11. Ore stage 111 (silver stage was characterized by the interaction between fluids of low temperature and contrasted salinities (Th = 100 – 150º C; 3 eq. wt. % NaCl to 18-22 eq. wt. % NaCl. A final and «barren stage » (stage IV resulted in the precipitation of a late generation of quartz and barite.Estudios de inclusiones fluidas en muestras de cuarzo y baritina del yacimiento epitermal argentífero de Hiendelaencina sugieren que esta mineralización se formó a lo largo de cuatro episodios hidrotermales. El estadio mineral I estuvo caracterizado por la presencia de fluidos acuoso-carbónicos que precipitaron pirita y arsenopirita. La interacción entre fluidos de probable origen magmático (soluciones acuosas; Th = 320 – 200º C, 12 % eq. NaCl y fluidos de origen meteórico (de menor temperatura y salinidad causó un decrecimiento generalizado en T y salinidad (desde 12 % eq. NaCl a 3 % eq. NaCl, lo cual probablemente indujo la precipitación de minerales de Cu y Zn (estadio mineral 11. El estadio mineral 111 (estadio argentífero se caracterizó por la interacción entre fluidos de baja temperatura pero de salinidades contrastadas (Th = 100 – 150º C; 3 % eq. NaCl a 18-22 % eq. NaCl. Un estadio final y estéril (estadio mineral IV originó la precipitación de

  13. Metallic oxide nano-clusters synthesis by ion implantation in high purity Fe10Cr alloy

    International Nuclear Information System (INIS)

    Zheng, Ce

    2015-01-01

    ODS (Oxide Dispersed Strengthened) steels, which are reinforced with metal dispersions of nano-oxides (based on Y, Ti and O elements), are promising materials for future nuclear reactors. The detailed understanding of the mechanisms involved in the precipitation of these nano-oxides would improve manufacturing and mechanical properties of these ODS steels, with a strong economic impact for their industrialization. To experimentally study these mechanisms, an analytical approach by ion implantation is used, to control various parameters of synthesis of these precipitates as the temperature and concentration. This study demonstrated the feasibility of this method and concerned the behaviour of alloys models (based on aluminium oxide) under thermal annealing. High purity Fe-10Cr alloys were implanted with Al and O ions at room temperature. Transmission electron microscopy observations showed that the nano-oxides appear in the Fe-10Cr matrix upon ion implantation at room temperature without subsequent annealing. The mobility of implanted elements is caused by the defects created during ion implantation, allowing the nucleation of these nanoparticles, of a few nm in diameter. These nanoparticles are composed of aluminium and oxygen, and also chromium. The high-resolution experiments show that their crystallographic structure is that of a non-equilibrium compound of aluminium oxide (cubic γ-Al 2 O 3 type). The heat treatment performed after implantation induces the growth of the nano-sized oxides, and a phase change that tends to balance to the equilibrium structure (hexagonal α-Al 2 O 3 type). These results on model alloys are fully applicable to industrial materials: indeed ion implantation reproduces the conditions of milling and heat treatments are at equivalent temperatures to those of thermo-mechanical treatments. A mechanism involving the precipitation of nano-oxide dispersed in ODS alloys is proposed in this manuscript based on the obtained experimental results

  14. The Gaia-ESO Survey: the present-day radial metallicity distribution of the Galactic disc probed by pre-main-sequence clusters

    Science.gov (United States)

    Spina, L.; Randich, S.; Magrini, L.; Jeffries, R. D.; Friel, E. D.; Sacco, G. G.; Pancino, E.; Bonito, R.; Bravi, L.; Franciosini, E.; Klutsch, A.; Montes, D.; Gilmore, G.; Vallenari, A.; Bensby, T.; Bragaglia, A.; Flaccomio, E.; Koposov, S. E.; Korn, A. J.; Lanzafame, A. C.; Smiljanic, R.; Bayo, A.; Carraro, G.; Casey, A. R.; Costado, M. T.; Damiani, F.; Donati, P.; Frasca, A.; Hourihane, A.; Jofré, P.; Lewis, J.; Lind, K.; Monaco, L.; Morbidelli, L.; Prisinzano, L.; Sousa, S. G.; Worley, C. C.; Zaggia, S.

    2017-05-01

    Context. The radial metallicity distribution in the Galactic thin disc represents a crucial constraint for modelling disc formation and evolution. Open star clusters allow us to derive both the radial metallicity distribution and its evolution over time. Aims: In this paper we perform the first investigation of the present-day radial metallicity distribution based on [Fe/H] determinations in late type members of pre-main-sequence clusters. Because of their youth, these clusters are therefore essential for tracing the current interstellar medium metallicity. Methods: We used the products of the Gaia-ESO Survey analysis of 12 young regions (age ages is not easily explained by the models. Our results reveal a complex interplay of several processes (e.g. star formation activity, initial mass function, supernova yields, gas flows) that controlled the recent evolution of the Milky Way. Based on observations made with the ESO/VLT, at Paranal Observatory, under program 188.B-3002 (The Gaia-ESO Public Spectroscopic Survey).Full Table 1 is 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/601/A70

  15. TEORIA DEL FUNCIONAL DE LA DENSIDAD APLICADA AL ESTUDIO DE LA ADSORCIÓN Y DISOCIACIÓN DE HIDRÓGENO MOLECULAR SOBRE PEQUEÑOS CLUSTERS DE MOLIBDENO

    Directory of Open Access Journals (Sweden)

    Samanta M. Carrión

    2011-01-01

    Full Text Available Este trabajo presenta un estudio basado en la Teoría del Funcional de la Densidad, de la adsorción y disociación de hidrógeno molecular sobre pequeños clusters de molibdeno, desde un dímero a un hexámero. Para el mismo se utilizó el funcional de intercambio de Becke y el funcional de correlación de Lee, Yang y Parr, tal como está implementado en el programa ADF. Las funciones base utilizadas son de calidad triple zeta con funciones de polarización. Todas las estructuras fueron optimizadas para distintas multiplicidades de espín hasta encontrar la mínima energía. Se determinaron distancias interatómicas, energías de adsorción y barreras energéticas de los sistemas más estables de la serie MonH2 (n=2-6. Los resultados muestran que las estructuras más estables de los agregados son las que poseen un estado de espín singlete. Se obtuvieron barreras energéticas en todos los casos.

  16. Comparison of single-use and reusable metal laryngoscope blades for orotracheal intubation during rapid sequence induction of anesthesia: a multicenter cluster randomized study.

    Science.gov (United States)

    Amour, Julien; Le Manach, Yannick Le; Borel, Marie; Lenfant, François; Nicolas-Robin, Armelle; Carillion, Aude; Ripart, Jacques; Riou, Bruno; Langeron, Olivier

    2010-02-01

    Single-use metal laryngoscope blades are cheaper and carry a lower risk of infection than reusable metal blades. The authors compared single-use and reusable metal blades during rapid sequence induction of anesthesia in a multicenter cluster randomized trial. One thousand seventy-two adult patients undergoing general anesthesia under emergency conditions and requiring rapid sequence induction were randomly assigned on a weekly basis to either single-use or reusable metal blades (cluster randomization). After induction, a 60-s period was allowed to complete intubation. In the case of failed intubation, a second attempt was performed using the opposite type of blade. The primary endpoint was the rate of failed intubation, and the secondary endpoints were the incidence of complications (oxygen desaturation, lung aspiration, and/or oropharynx trauma) and the Cormack and Lehane score. Both groups were similar in their main characteristics, including the risk factors for difficult intubation. The rate of failed intubation was significantly decreased with single-use metal blades at the first attempt compared with reusable blades (2.8 vs. 5.4%, P < 0.05). In addition, the proportion of grades III and IV in Cormack and Lehane score were also significantly decreased with single-use metal blades (6 vs. 10%, P < 0.05). The global complication rate did not reach statistical significance, although the same trend was noted (6.8% vs. 11.5%, P = not significant). An investigator survey and a measure of illumination pointed that illumination might have been responsible for this result. The single-use metal blade was more efficient than a reusable metal blade in rapid sequence induction of anesthesia.

  17. Estudio EPIFARM

    Directory of Open Access Journals (Sweden)

    Martín Morales A

    2010-12-01

    Full Text Available INTRODUCCIÓN Los farmacéuticos comunitarios pueden ser un importante primer punto de contacto con los pacientes con disfunción eréctil (DE, pero hasta la fecha no hay ningún estudio sobre las características de los hombres que acuden a un farmacéutico solicitando consejo o tratamiento para la DE. OBJETIVO Caracterizar los perfiles de los hombres que solicitan tratamiento para la DE en la farmacia, con o sin receta de inhibidores de la fosfodiesterasa tipo 5 (iPDE5. MÉTODOS Entre septiembre y noviembre de 2008 se realizó un estudio observacional, transversal y multicéntrico en farmacias comunitarias de España. De aquellos hombres que solicitaban consejo o tratamiento para la DE, cada investigador reclutó un paciente que tenía receta médica de iPDE5 y otro que acudía sin receta médica. Los farmacéuticos del estudio completaron un cuestionario de datos demográficos, clínicos y conductuales del paciente, incluido el Cuestionario de salud sexual para varones (Sexual Health Inventory for Men. VARIABLES PRINCIPALES Características demográficas y respuestas a los cuestionarios. RESULTADOS 574 farmacéuticos seleccionaron a 1.147 pacientes, de los cuales 1.113 fueron incluidos en el análisis. No se observaron diferencias estadísticas entre los grupos en cuanto al peso, la hipertensión, la diabetes mellitus, la hipercolesterolemia, la dislipidemia, la depresión o el estrés. Tampoco se observaron diferencias estadísticas respecto a la gravedad de la DE (p = 0,7892 ni a la proporción de hombres sin DE en cada grupo (p = 0,5755. En ambos grupos, los pacientes habían presentado síntomas de DE durante una media de veintiséis meses antes de la primera consulta a un profesional sanitario. Para el 60,2% de los pacientes incluidos en el grupo sin receta, la visita a la farmacia fue la primera ocasión en la que habían hablado de su DE con un profesional sanitario, y el 50% de aquellos que habían hablado previamente de la DE lo hab

  18. Electronic structure and geometries of small compound metal clusters: Progress report, August 1, 1988--July 31, 1989

    International Nuclear Information System (INIS)

    Jena, P.; Rao, B.K.; Khanna, S.N.

    1989-04-01

    Our research during this reporting period has focused on the following two aspects of cluster research. Electronic structure and stability of charged clusters and studies of evolution of magnetic properties with increasing cluster size. Following is a summary of our results

  19. Density functional investigation of mercury and arsenic adsorption on nitrogen doped graphene decorated with palladium clusters: A promising heavy metal sensing material in farmland

    Energy Technology Data Exchange (ETDEWEB)

    Zhao, Chunjiang, E-mail: zhaocj_nercita@163.com [National Engineering Research Center for Information Technology in Agriculture, Beijing 100097 (China); Beijing Research Center for Information Technology in Agriculture, Beijing Academy of Agriculture and Forestry Sciences, Beijing 100097 (China); Key Laboratory for Information Technologies in Agriculture, Ministry of Agriculture, Beijing100097 (China); Wu, Huarui, E-mail: wuhrnercita@163.com [National Engineering Research Center for Information Technology in Agriculture, Beijing 100097 (China); Beijing Research Center for Information Technology in Agriculture, Beijing Academy of Agriculture and Forestry Sciences, Beijing 100097 (China); Key Laboratory for Information Technologies in Agriculture, Ministry of Agriculture, Beijing100097 (China)

    2017-03-31

    Highlights: • PNG can be acted as micro-sensor for monitoring heavy metal in agriculture. • The most favorable adsorption site of Pd atom or cluster on PNG is the vacancy site. • The Pd atom or cluster enhance the reactivity of PNG toward Hg and AsH{sub 3} adsorption. • The efficiency of a sorbent can be tuned by tailoring the ε{sub d} of adsorbed metals. - Abstract: Density functional theory calculations are carried out to study the adsorption of mercury and arsenic on Pd{sub n} (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 AsH{sub 3} adsorption on PNG. The adsorption ability of Hg on Pd{sub n} decorated PNG is found to be related to the d-band center (ε{sub d}) of the Pd{sub n}, in which the closer ε{sub d} of Pd{sub n} to the Fermi level, the higher adsorption strength for Hg on Pd{sub n} decorated PNG. Moreover, the charge transfer between Pd{sub n} and arsenic may constitute arsenic adsorption on Pd{sub n} decorated PNG. Further design of highly efficient carbon based sorbents for heavy metals removal should be focused on tailoring ε{sub d} of adsorbed metals.

  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

    International Nuclear Information System (INIS)

    Zhao, Chunjiang; Wu, Huarui

    2017-01-01

    Highlights: • PNG can be acted as micro-sensor for monitoring heavy metal in agriculture. • The most favorable adsorption site of Pd atom or cluster on PNG is the vacancy site. • The Pd atom or cluster enhance the reactivity of PNG toward Hg and AsH 3 adsorption. • The efficiency of a sorbent can be tuned by tailoring the ε d of adsorbed metals. - Abstract: Density functional theory calculations are carried out to study the adsorption of mercury and arsenic on Pd n (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 AsH 3 adsorption on PNG. The adsorption ability of Hg on Pd n decorated PNG is found to be related to the d-band center (ε d ) of the Pd n , in which the closer ε d of Pd n to the Fermi level, the higher adsorption strength for Hg on Pd n decorated PNG. Moreover, the charge transfer between Pd n and arsenic may constitute arsenic adsorption on Pd n decorated PNG. Further design of highly efficient carbon based sorbents for heavy metals removal should be focused on tailoring ε d of adsorbed metals.

  1. 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.

  2. Coupling of Acoustic Cavitation with Dem-Based Particle Solvers for Modeling De-agglomeration of Particle Clusters in Liquid Metals

    Science.gov (United States)

    Manoylov, Anton; Lebon, Bruno; Djambazov, Georgi; Pericleous, Koulis

    2017-11-01

    The aerospace and automotive industries are seeking advanced materials with low weight yet high strength and durability. Aluminum and magnesium-based metal matrix composites with ceramic micro- and nano-reinforcements promise the desirable properties. However, larger surface-area-to-volume ratio in micro- and especially nanoparticles gives rise to van der Waals and adhesion forces that cause the particles to agglomerate in clusters. Such clusters lead to adverse effects on final properties, no longer acting as dislocation anchors but instead becoming defects. Also, agglomeration causes the particle distribution to become uneven, leading to inconsistent properties. To break up clusters, ultrasonic processing may be used via an immersed sonotrode, or alternatively via electromagnetic vibration. This paper combines a fundamental study of acoustic cavitation in liquid aluminum with a study of the interaction forces causing particles to agglomerate, as well as mechanisms of cluster breakup. A non-linear acoustic cavitation model utilizing pressure waves produced by an immersed horn is presented, and then applied to cavitation in liquid aluminum. Physical quantities related to fluid flow and quantities specific to the cavitation solver are passed to a discrete element method particles model. The coupled system is then used for a detailed study of clusters' breakup by cavitation.

  3. 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. Copyright © 2015. Published by Elsevier Inc.

  4. 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

  5. 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. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  6. 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.

  7. Electronic transmission through a metallic cluster attached to an adsorbed nanowire: creation of a nanoscale electronic on/off switch

    Science.gov (United States)

    Pouthier, V.; Girardet, C.

    2002-06-01

    The electron transport in a nanowire formed by an infinite atomic chain containing an extended cluster of the same atomic species is studied. From the single-electron Schrodinger equation, a decimation procedure is introduced to reduce the influence of the cluster to a point defect with renormalized self-energy and coupling parameters. The behavior of the transmittance of the electron in the nanowire through the attached cluster is discussed for various sizes and shapes of the cluster. Special emphasis is devoted to a small, single row cluster which displays specific resonances and anti-resonances. We show that such a nanostructure can be used to accomplish one of the fundamental operations of electronic devices at the nanoscale, namely to switch the electronic current.

  8. Magnetic properties of 3d-transition-metal alloy clusters: (FexCr1-x)n

    International Nuclear Information System (INIS)

    Vega, A.; Dorantes-Davila, J.; Pastor, G.M.; Balbas, L.C.

    1991-01-01

    We present results for the magnetic properties of (Fe x Cr 1-x ) n alloy clusters obtained by using a tight-binding Hubbard Hamiltonian in the unrestricted Hartree-Fock approximation. The dependence of the average magnetic moment, local magnetic moments, magnetic order, and cohesive energy on the size and composition of the cluster were determined. In agreement with surface calculations, we find that the average magnetic moment of the alloy is larger than that of the cluster of one element. For n=15 a transition from ferromagnetic to antiferromagnetic order is obtained for x≅0.4-0.53. We discuss the importance of the overlap interaction in the spin polarized charge distribution of the alloy (e.g., charge transfer, local magnetic moments). The characteristic properties of the mixed clusters are also discussed by comparison with available results for homogeneous clusters. (orig.)

  9. Magnetic properties of 3d-transition-metal alloy clusters: (Fe sub x Cr sub 1-x ) sub n

    Energy Technology Data Exchange (ETDEWEB)

    Vega, A.; Dorantes-Davila, J.; Pastor, G.M.; Balbas, L.C. (Valladolid Univ. (Spain). Dept. de Fisica Teorica)

    1991-01-01

    We present results for the magnetic properties of (Fe{sub x}Cr{sub 1-x}){sub n} alloy clusters obtained by using a tight-binding Hubbard Hamiltonian in the unrestricted Hartree-Fock approximation. The dependence of the average magnetic moment, local magnetic moments, magnetic order, and cohesive energy on the size and composition of the cluster were determined. In agreement with surface calculations, we find that the average magnetic moment of the alloy is larger than that of the cluster of one element. For n=15 a transition from ferromagnetic to antiferromagnetic order is obtained for x{approx equal}0.4-0.53. We discuss the importance of the overlap interaction in the spin polarized charge distribution of the alloy (e.g., charge transfer, local magnetic moments). The characteristic properties of the mixed clusters are also discussed by comparison with available results for homogeneous clusters. (orig.).

  10. Microporous Hexanuclear Ln(III) Cluster-Based Metal-Organic Frameworks: Color Tunability for Barcode Application and Selective Removal of Methylene Blue.

    Science.gov (United States)

    Gao, Ming-Liang; Wang, Wen-Jing; Liu, Lin; Han, Zheng-Bo; Wei, Na; Cao, Xiao-Man; Yuan, Da-Qiang

    2017-01-03

    Two hexanuclear Ln(III) cluster-based metal-organic frameworks (MOFs) (Ln = Tb or Eu) and a series of isomorphic bimetallic Ln(III)-MOFs have been synthesized by changing the ratio of Tb(III) and Eu(III) under solvothermal conditions. The excellent linear color tunability (from green to red) makes them suitable for barcode application. In addition, the anionic Ln(III)-MOFs exhibit superior uptake capacity toward methylene blue (MB + ) by an ion-exchange process, and its reversible adsorption performance makes 1 suitable for removal of organic dye MB + . The as-prepared anionic hexanuclear Ln(III) cluster-based MOFs can serve as a multifunctional material for an optical and environmental area.

  11. Quasi-2D XY magnetic properties and slow relaxation in a body centered metal organic network of [Co4] clusters.

    Science.gov (United States)

    Mahata, Partha; Natarajan, Srinivasan; Panissod, Pierre; Drillon, Marc

    2009-07-29

    Octahedral Co(2+) centers have been connected by mu(3)-OH and mu(2)-OH(2) units forming [Co(4)] clusters which are linked by pyrazine forming a two-dimensional network. The two-dimensional layers are bridged by oxybisbenzoate (OBA) ligands giving rise to a three-dimensional structure. The [Co(4)] clusters bond with the pyrazine and the OBA results in a body-centered arrangement of the clusters, which has been observed for the first time. Magnetic studies reveal a noncollinear frustrated spin structure of the bitriangular cluster, resulting in a net magnetic moment of 1.4 microB per cluster. For T > 32 K, the correlation length of the cluster moments shows a stretched-exponential temperature dependence typical of a Berezinskii-Kosterlitz-Thouless model, which points to a quasi-2D XY behavior. At lower temperature and down to 14 K, the compound behaves as a soft ferromagnet and a slow relaxation is observed, with an energy barrier of ca. 500 K. Then, on further cooling, a hysteretic behavior takes place with a coercive field that reaches 5 T at 4 K. The slow relaxation is assigned to the creation/annihilation of vortex-antivortex pairs, which are the elementary excitations of a 2D XY spin system.

  12. Archaeological analogous and industrials for deep storage: study of the archaeological metallic piece; Analogos arqueologicos e industriales para almacenamientos profundos: estudio de piezas arqueologicas metalicas

    Energy Technology Data Exchange (ETDEWEB)

    Criado Portal, A. J.; Martinez Garcia, J. A.; Calabres Molina, R.; Garcia abajo, A.; Penco Valenzuela, F.; Lecanda Esteban, J. A.; Garcia Bartual, M.; Jimenez Gonzalez, J. M.; Bravo Munoz, E.; Rodriguez Lobo, L. M.; Fernandez Cascos, T.; Fernandes Cordero, O.; Montero Ruiz, I.

    2000-07-01

    The aim of present research is to obtain information about archaeological analogous of iron and steel, useful for the model of deep geological repository (AGP). The analogous examined have remained buried between 1400 and 2400 years, in very assorted geochemical environments. The extraction of the archaeological pieces has been accomplished according to normalised protocols, trying to carry to the laboratory so the piece as its burial environment, avoiding all possible pollution. Trying to the archaeological analogous could provide valuable information to the AGP model, the study has been directed to related the physical-chemical characteristics of the terrain respect to the deterioration of the archaeological metallic piece. The geology of the surrounding terrain to the archaeological deposit, the geomorphological study of the terrain and data from the analysis of ground: pH, wetness, porosity, organic matter contents, bacteria presence, sulphates, carbonates, chlorides, etc., have allowed to explain the physical-chemical phenomena suffered by the archaeological iron and steel pieces. Also, an exhaustive study of the archaeological piece has been accomplished, concerning the microstructure of the corrosion layer and of the not deteriorated metallic rest. Obtained information concerns different items, such as corrosion velocity and formations of oxide layers, diffusion of chemical elements from the corrosion layer to the metal and viceversa, and structural changes in oxide layers and in the metallic remains by structural ageing. Obtained data have allowed to develop a mathematical model for calculation of corrosion velocity in buried iron and steels, based on physical-chemical variables of grounds, chemical composition and thermomechanical treatment given to the metal during its manufacture. (Author)

  13. Estudio preliminar de la fauna en el morro de basuras de Moravia y presencia de metales pesados en artrópodos y roedores

    Directory of Open Access Journals (Sweden)

    Rolando Barahona

    2010-04-01

    Full Text Available Preliminary study of the fauna in the Morro de Moravia open dump and presence of heavy metals in arthropods and rodents.Characterization of the species present in a given locality by means of biological inventories provides information about diversity, even ifit is done in disturbed environments such as open dumps, which are considered a threat for health due to the accumulation of heavy metalsthat are well known for their negative effects on human health and the environment. Objectives. To carry out a preliminary characterizationof arthropods and non-flying small mammals in the Morro de Moravia open dump, and to determine the heavy metal contents in animaltissue samples. Materials and Methods. Arthropods were collected with pitfall traps and manually. Rodents were captured with Shermantraps. The heavy metal analysis was carried out with atomic spectroscopy. Results. A total of 9 orders, 51 families and 75 morphospeciesof insects, 5 families of spiders, two syrphid and a millipede species were identified; Mus musculus was the only small mammal speciesidentified. Heavy metal analysis showed various concentrations mainly of Pb and Cd. The highest content of Pb (45.05 mg/kg was foundin samples of M. musculus and the highest Cd content (10.31 mg/kg was found in spiders of the family Gasteracantha. Conclusions. TheMorro de Moravia open dump provides conditions that allow the establishment of an arthropod community with various diets and niches.The transference of heavy metals from the residue matrix towards higher levels of the trophic chain was corroborated.

  14. The role of electron localization in the atomic structure of transition-metal 13-atom clusters: the example of Co13, Rh13, and Hf13.

    Science.gov (United States)

    Piotrowski, Maurício J; Piquini, Paulo; Cândido, Ladir; Da Silva, Juarez L F

    2011-10-14

    The crystalline structure of transition-metals (TM) has been widely known for several decades, however, our knowledge on the atomic structure of TM clusters is still far from satisfactory, which compromises an atomistic understanding of the reactivity of TM clusters. For example, almost all density functional theory (DFT) calculations for TM clusters have been based on local (local density approximation--LDA) and semilocal (generalized gradient approximation--GGA) exchange-correlation functionals, however, it is well known that plain DFT fails to correct the self-interaction error, which affects the properties of several systems. To improve our basic understanding of the atomic and electronic properties of TM clusters, we report a DFT study within two nonlocal functionals, namely, the hybrid HSE (Heyd, Scuseria, and Ernzerhof) and GGA+U functionals, of the structural and electronic properties of the Co(13), Rh(13), and Hf(13) clusters. For Co(13) and Rh(13), we found that improved exchange-correlation functionals decrease the stability of open structures such as the hexagonal bilayer (HBL) and double simple-cubic (DSC) compared with the compact icosahedron (ICO) structure, however, DFT-GGA, DFT-GGA+U, and DFT-HSE yield very similar results for Hf(13). Thus, our results suggest that the DSC structure obtained by several plain DFT calculations for Rh(13) can be improved by the use of improved functionals. Using the sd hybridization analysis, we found that a strong hybridization favors compact structures, and hence, a correct description of the sd hybridization is crucial for the relative energy stability. For example, the sd hybridization decreases for HBL and DSC and increases for ICO in the case of Co(13) and Rh(13), while for Hf(13), the sd hybridization decreases for all configurations, and hence, it does not affect the relative stability among open and compact configurations.

  15. THE OPTICAL COLORS OF GIANT ELLIPTICAL GALAXIES AND THEIR METAL-RICH GLOBULAR CLUSTERS INDICATE A BOTTOM-HEAVY INITIAL MASS FUNCTION

    International Nuclear Information System (INIS)

    Goudfrooij, Paul; Diederik Kruijssen, J. M.

    2013-01-01

    We report a systematic and statistically significant offset between the optical (g – z or B – I) colors of seven massive elliptical galaxies and the mean colors of their associated massive metal-rich globular clusters (GCs) in the sense that the parent galaxies are redder by ∼0.12-0.20 mag at a given galactocentric distance. However, spectroscopic indices in the blue indicate that the luminosity-weighted ages and metallicities of such galaxies are equal to that of their averaged massive metal-rich GCs at a given galactocentric distance, to within small uncertainties. The observed color differences between the red GC systems and their parent galaxies cannot be explained by the presence of multiple stellar generations in massive metal-rich GCs, as the impact of the latter to the populations' integrated g – z or B – I colors is found to be negligible. However, we show that this paradox can be explained if the stellar initial mass function (IMF) in these massive elliptical galaxies was significantly steeper at subsolar masses than canonical IMFs derived from star counts in the solar neighborhood, with the GC colors having become bluer due to dynamical evolution, causing a significant flattening of the stellar MF of the average surviving GC.

  16. THE COLOR-MAGNITUDE RELATION FOR METAL-POOR GLOBULAR CLUSTERS IN M87: CONFIRMATION FROM DEEP HST/ACS IMAGING

    International Nuclear Information System (INIS)

    Peng, Eric W.; Jordan, Andres; Blakeslee, John P.; Cote, Patrick; Ferrarese, Laura; Mieske, Steffen; 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 versus V-I color-magnitude diagram (γ I = -0.024 ± 0.006) 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 ∼ 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 the mean for all GCs). These results indicate that there is a mass scale at which the correlation begins, and is consistent with a scenario where self-enrichment drives a mass-metallicity relationship. We show that previously measured half-light radii of M87 GCs from best-fit PSF-convolved King models are consistent with the more accurate measurements in this study, and we also explain how the color-magnitude relation for metal-poor GCs is real and cannot be an artifact of the photometry. We fit Gaussian and evolved Schechter functions to the luminosity distribution of GCs across all colors, as well as divided into blue and red subpopulations, finding that the blue GCs have a brighter mean luminosity and a narrower distribution than the red GCs. Finally, we present a catalog of astrometry and photometry for 2250 M87 GCs.

  17. All-metal aromatic clusters M4(2-) (M = B, Al, and Ga). Are π-electrons distortive or not?

    Science.gov (United States)

    Poater, Jordi; Feixas, Ferran; Bickelhaupt, F Matthias; Solà, Miquel

    2011-12-14

    The π-electrons in benzene, the quintessential aromatic molecule, were previously shown to be distortive, i.e., they prefer localized double bonds alternating with single bonds. It is the σ-electrons that force the double bonds to delocalize, leading to a regular, D(6h) geometry. Herein, we computationally investigate the double-bond localizing or delocalizing propensities of σ- and π-electrons in the archetypal all-metal aromatic cluster Al(4)(2-) and its second- and fourth-period analogs B(4)(2-) and Ga(4)(2-), using Kohn-Sham molecular orbital (MO) theory at BP86/TZ2P in combination with quantitative bond energy decomposition analyses (EDA). We compare the three all-metal aromatic clusters with the structurally related organic species C(4)H(4)(2+), C(4)H(4), and C(4)H(4)(2-). Our analyses reveal that the π-electrons in the group-13 M(4)(2-) molecules have a weak preference for localizing the double bonds. Instead, the σ-electrons enforce the regular D(4h) equilibrium geometry with delocalized double bonds.

  18. Preparation of gold-containing binary metal clusters by co-deposition-precipitation method and for hydrogenation of chloronitrobenzene

    OpenAIRE

    Ya-Ting Tsu; Yu-Wen Chen

    2017-01-01

    Nano-gold catalyst has been reported to have high activity and selectivity for liquid phase hydrogenation reaction. In this study, gold-containing bimetals were loaded on TiO2. For bimetallic catalysts, gold and different metals were prepared by the deposition-precipitation method, and then used NaBH4 to reduce metal cations. The catalysts were characterized by X-ray diffraction, transmission electron microscopy, high resolution transmission electron microscopy, and X-ray photoelectron spectr...

  19. Diffusion of two-dimensional epitaxial clusters on metal (100) surfaces: Facile versus nucleation-mediated behavior and their merging for larger sizes

    Science.gov (United States)

    Lai, King C.; Liu, Da-Jiang; Evans, James W.

    2017-12-01

    For diffusion of two-dimensional homoepitaxial clusters of N atoms on metal (100) surfaces mediated by edge atom hopping, macroscale continuum theory suggests that the diffusion coefficient scales like DN˜ N-β with β =3 /2 . However, we find quite different and diverse behavior in multiple size regimes. These include: (i) facile diffusion for small sizes N mediated diffusion with small β moderate sizes 9 ≤N ≤O (102) ; the same also applies for N =Np+3 , Np+ 4 , ... (iii) facile diffusion but with large β >2 for N =Np+1 and Np+2 also for moderate sizes 9 ≤N ≤O (102) ; (iv) merging of the above distinct branches and subsequent anomalous scaling with 1 ≲β moderate size regime where we show that diffusivity cycles quasiperiodically from the slowest branch for Np+3 (not Np) to the fastest branch for Np+1 . Behavior is quantified by kinetic Monte Carlo simulation of an appropriate stochastic lattice-gas model. However, precise analysis must account for a strong enhancement of diffusivity for short time increments due to back correlation in the cluster motion. Further understanding of this enhancement, of anomalous size scaling behavior, and of the merging of various branches, is facilitated by combinatorial analysis of the number of the ground-state and low-lying excited state cluster configurations, and also of kink populations.

  20. Estudio comparativo in vitro del comportamiento de las cerámicas de recubrimiento según el núcleo:óxido de circonio y metal.

    OpenAIRE

    Agustín Panadero, Rubén

    2012-01-01

    Introducción: La creencia de que la prótesis fija sin metal va a modificar el espectro restaurador tradicional siempre ha encontrado un obstáculo: la naturaleza intrínsecamente quebradiza de la cerámica dental. A principios de los años noventa, con el objetivo de subsanar esta complicación, apareció la circona (óxido de circonio), que actuando como material de núcleo de la restauración dotaba a ésta de gran resistencia. La complicación técnica que se observa en las restauraciones ...

  1. Estudio de la unión adhesiva de caucho a metal desde el enfoque de la formulación del caucho y del adhesivo

    OpenAIRE

    Lasprilla Botero, Juliana

    2012-01-01

    El caucho es un material muy utilizado para el aislamiento de la vibración, la reducción del impacto de choques, o el sellado de los sólidos contra los líquidos y gases. En muchos casos, para estas aplicaciones, es necesario adherirlo de una manera confiable a un metal. Para lograr esta unión existen dos procedimientos, uno involucrando mecanismos de entrecruzamiento (vulcanización), y otro empleando un adhesivo no vulcanizado. Generalmente se utilizan ambos, añadiendo en la formulación del c...

  2. Diffusion of two-dimensional epitaxial clusters on metal (100) surfaces: Facile versus nucleation-mediated behavior and their merging for larger sizes

    International Nuclear Information System (INIS)

    Lai, King C.; Liu, Da-Jiang; Evans, James W.

    2017-01-01

    For diffusion of two-dimensional homoepitaxial clusters of N atoms on metal(100) surfaces mediated by edge atom hopping, macroscale continuum theory suggests that the diffusion coefficient scales like DN ~ N -β with β = 3/2. However, we find quite different and diverse behavior in multiple size regimes. These include: (i) facile diffusion for small sizes N < 9; (ii) slow nucleation-mediated diffusion with small β < 1 for “perfect” sizes N = N p = L 2 or L(L+1), for L = 3, 4,… having unique ground state shapes, for moderate sizes 9 ≤ N ≤ O(10 2 ); the same also applies for N = N p +3, N p + 4,… (iii) facile diffusion but with large β > 2 for N = Np + 1 and N p + 2 also for moderate sizes 9 ≤ N ≤ O(10 2 ); (iv) merging of the above distinct branches and subsequent anomalous scaling with 1 ≲ β < 3/2, reflecting the quasi-facetted structure of clusters, for larger N = O(10 2 ) to N = O(10 3 ); and (v) classic scaling with β = 3/2 for very large N = O(103) and above. The specified size ranges apply for typical model parameters. We focus on the moderate size regime where show that diffusivity cycles quasi-periodically from the slowest branch for N p + 3 (not Np) to the fastest branch for Np + 1. Behavior is quantified by Kinetic Monte Carlo simulation of an appropriate stochastic lattice-gas model. However, precise analysis must account for a strong enhancement of diffusivity for short time increments due to back-correlation in the cluster motion. Further understanding of this enhancement, of anomalous size scaling behavior, and of the merging of various branches, is facilitated by combinatorial analysis of the number of the ground state and low-lying excited state cluster configurations, and also of kink populations.

  3. Structural variability in transition metal oxide clusters: gas phase vibrational spectroscopy of V3O6-8+

    NARCIS (Netherlands)

    Asmis, K. R.; Wende, T.; Brummer, M.; Gause, O.; Santambrogio, G.; Stanca-Kaposta, E. C.; Dobler, J.; Niedziela, A.; Sauer, J.

    2012-01-01

    We present gas phase vibrational spectra of the trinuclear vanadium oxide cations V3O6+[middle dot]He1-4{,} V3O7+[middle dot]Ar0{,}1{,} and V3O8+[middle dot]Ar0{,}2 between 350 and 1200 cm-1. Cluster structures are assigned based on a comparison of the experimental and simulated IR spectra. The

  4. The origin and orbit of the old, metal-rich, open cluster NGC 6791. Insights from kinematics

    Czech Academy of Sciences Publication Activity Database

    Jílková, L.; Carraro, G.; Jungwiert, Bruno; Minchev, I.

    2012-01-01

    Roč. 541, April (2012), A64/1-A64/11 ISSN 0004-6361 R&D Projects: GA MŠk(CZ) LC06014; GA ČR GD205/08/H005 Institutional research plan: CEZ:AV0Z10030501 Keywords : galaxy * kinematics and dynamics * open clusters and associations Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics Impact factor: 5.084, year: 2012

  5. Discusión de las aproximaciones utilizadas en el estudio de la recombinación dielectrónica de los metales en envolturas estelares

    Science.gov (United States)

    Cruzado, A.; di Rocco, H. O.; Ringuelet, A.

    Se calcularon nuevos parámetros atómicos del MgI reemplazando los niveles de energía teóricos por los observados. Con ellos se calculó nuevamente el flujo originado en la Recombinación Dielectrónica (RD) del MgII y se comparó con resultados anteriores. Se evaluó también la posible influencia de diferentes fuentes de opacidad, en el flujo originado en la RD de los metales en atmósferas extendidas de estrellas tempranas. En particular, se calculó la profundidad óptica de las líneas de MgI para diferentes condiciones físicas del medio.

  6. Study of effects of metallic prostheses in radiotherapy treatments in prostate cancer; Estudio de los efectos de las protesis metalicas en tratamientos radioterapicos en irradiacion pelvica

    Energy Technology Data Exchange (ETDEWEB)

    Cabrera, P.; Mateos, J. C.; Herrador, M.; Ortiz, M. J.

    2006-07-01

    In this work it is described the problems related to the radiotherapy treatments of patients with prostate cancer and hip implants Analyze the effects of metallic prostheses in radiotherapy treatments and present the methods to overcome the problems that arise in these situations. Our patients are student in a TAC Philips with a range of Hounsfield number of-1000 to 4000. The planning and measurement of CT numbers are done in a RTP ADAC Pinnacle that have a maximum of 32767 CT units. The metallic implants more frequently used, titanium, stainless steel and cobalt-chromium-molybdenum, generate CT numbers from 2000 to 3000, and cause saturation effects. This problem may be solved with modern scanners that use the extended CT range. It is an algorithm that expand the usual range by a factor of 10. An alternative solution to this problem can be used if the prostheses are able to scan to select the window parameters that allow an automatic region of interest (roi) definition that match to the dimensions of the implants. Finally it is assigned the electronic/physical densities to the created roi's. The clinical dosimetry of patients with prostheses have been done defining the usual regions of interests (target volume and risk organs) in first place. Finally the prostheses are outlined using the window parameters previously measured and assigned the electronic or physical densities. The attenuation of the implant may then be calculated accurately. The presence of implants in the treatment fields originate artifacts in the TAC images of patients and underdosage of target volume that range between 12% and 30% in function of material an energy used. It is necessary the application of methods that correct the dose behind the implant, if it is not possible to prevent the incidence of the treatment beams over the prostheses. (Author)

  7. Electronic transmission through a set of metallic clusters randomly attached to an adsorbed nanowire: Localization-delocalization transition

    Science.gov (United States)

    Pouthier, V.; Girardet, C.

    2002-09-01

    The electron transmission through a monatomic nanowire containing N attached quasiperiodically distributed nanoclusters is studied within the ballistic model. A decimation procedure is performed to renormalize the self-energy of the nanowire sites connected to the clusters and to transform the nanodevice into an effective disordered one-dimensional chain. The transmittance is determined using the transfer matrix formalism. It allows us to express each elementary reflection/transmission process per cluster in terms of a single parameter which accounts for the self-energy renormalization. It is shown that cluster antiresonances are responsible for the occurrence of a localization-delocalization transition which discriminates between insulating and conducting regimes for the electron transport. These results are interpreted in a general way on the basis of the scaling theory which involves the random phase approximation to characterize the behavior of the probability distribution connected to the transmittance. However, the scaling theory fails for particular values of the electron energy leading to singularities in the average transmittance called tips and dips. These singularities are related to the reminiscence of quantum interferences which the disorder is not sufficient to break.

  8. Copper Sensing Function of Drosophila Metal-Responsive Transcription Factor-1 Is Mediated By a Tetranuclear Cu(I) Cluster

    Energy Technology Data Exchange (ETDEWEB)

    Chen, X.; Hua, H.; Balamurugan, K.; Kong, X.; Zhang, L.; George, G.N.; Georgiev, O.; Schaffner, W.; Giedroc, D.P.

    2009-05-12

    Drosophila melanogaster MTF-1 (dMTF-1) is a copper-responsive transcriptional activator that mediates resistance to Cu, as well as Zn and Cd. Here, we characterize a novel cysteine-rich domain which is crucial for sensing excess intracellular copper by dMTF-1. Transgenic flies expressing mutant dMTF-1 containing alanine substitutions of two, four or six cysteine residues within the sequence {sup 547}CNCTNCKCDQTKSCHGGDC{sup 565} are significantly or completely impaired in their ability to protect flies from copper toxicity and fail to up-regulate MtnA (metallothionein) expression in response to excess Cu. In contrast, these flies exhibit wild-type survival in response to copper deprivation thus revealing that the cysteine cluster domain is required only for sensing Cu load by dMTF-1. Parallel studies show that the isolated cysteine cluster domain is required to protect a copper-sensitive S. cerevisiae ace1 strain from copper toxicity. Cu(I) ligation by a Cys-rich domain peptide fragment drives the cooperative assembly of a polydentate [Cu{sub 4}-S{sub 6}] cage structure, characterized by a core of trigonally S{sub 3} coordinated Cu(I) ions bound by bridging thiolate ligands. While reminiscent of Cu{sub 4}-L{sub 6} (L = ligand) tetranuclear clusters in copper regulatory transcription factors of yeast, the absence of significant sequence homology is consistent with convergent evolution of a sensing strategy particularly well suited for Cu(I).

  9. Adsorption of CO and H2 on Transition Metal Clusters : insights from Vibrational Spectroscopy and Density Functional Theory

    NARCIS (Netherlands)

    Swart, I.

    2008-01-01

    Adsorption of hydrogen (H2) and carbon monoxide (CO) molecules on transition metals is of paramount importance for several (catalytic) processes. These include the purification of H2 streams and the Fischer-Tropsch reaction, in which a mixture of H2 and CO is converted to synthetic fuels. As a

  10. Mononuclear Clusterfullerene Single-Molecule Magnet Containing Strained Fused-Pentagons Stabilized by a Nearly Linear Metal Cyanide Cluster

    DEFF Research Database (Denmark)

    Liu, Fupin; Wang, Song; Gao, Cong Li

    2017-01-01

    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 properti...... (SMM)....

  11. Study of the heavy metals speciation in the atmospheric suspended particles in Sevilla (Spain); Estudio de la especiacion de metales pesados en la materia particulada atmosferica de la ciudad de Sevilla

    Energy Technology Data Exchange (ETDEWEB)

    Ternero Rodriguez, M.; Sequeiros Madueno, L.; Jimenez Sanchez, C.; Barragan de la Rosa, J.; Bello Lopez, M.; Fernandez Espinosa, A.J.; Perez Bernal, J.L. [Facultad de Quimica, Universidad de Sevilla (Spain)

    1997-06-01

    This work develops analytical methods for the heavy metals speciation in the atmospheric suspended particles. In base to these methods, we study the atmospheric contamination of the city of Seville, determining the metals Al, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Cd and Pb. We also study the effects of metallic species in the alteration processes on rocks material, in base to the SO{sub 2}/SO{sub 4}{sup {minus}{minus}}. The project develops in two years: in the first, we develop the methods of chemistry speciation based on the extraction with different reagents and the methods of physical speciation based on the particle size distribution with cascade impactors. Also, we develop the methodology for the environmental simulation of alteration processes, in base to the heterogeneous catalysis, by metallic ions, of the SO{sub 2} on the surface of the stone. In the second year we apply the methods of speciation to the study of the contamination by heavy metals in the city of Seville. This part divides in two phases: a first of the preliminary study in the city in order to identify the different polluting focuses, and a secondary of study of the contamination produced by punctual sources, in the more polluted points of the city. On the other hand, the study of the alteration processes of rock materials has centred on materials employees in monuments of the city and on application of the catalyzers found in the particulate matter of the true environment of the materials. (Author)

  12. Preparation of gold-containing binary metal clusters by co-deposition-precipitation method and for hydrogenation of chloronitrobenzene

    Directory of Open Access Journals (Sweden)

    Ya-Ting Tsu

    2017-06-01

    Full Text Available Nano-gold catalyst has been reported to have high activity and selectivity for liquid phase hydrogenation reaction. In this study, gold-containing bimetals were loaded on TiO2. For bimetallic catalysts, gold and different metals were prepared by the deposition-precipitation method, and then used NaBH4 to reduce metal cations. The catalysts were characterized by X-ray diffraction, transmission electron microscopy, high resolution transmission electron microscopy, and X-ray photoelectron spectroscopy. The catalytic properties of these catalysts were tested by hydrogenation of p-chloronitrobenzene (p-CNB in a batch reactor at 1.1 MPa H2 pressure, 373 K and 500 rpm. Cu, Ag, Ru, and Pd formed nano-alloy with Au. In addition, Cu–Au, Ag–Au, and Ru–Au alloy had Cu-, Ag-, and Ru-enriched surface, respectively. Instead, Pd–Au alloy had Pd-enriched surface. There are two kinds of alloy effects: (1 geometric effects, i.e., the surface-enriched metal would change the distance of Au–Au atoms that is required for facilitating the hydrogenation of chloronitrobenzene; and (2 electronic effects, which involve charge transfer between the metals. The activity decreased in the following order: PdAu/TiO2 > Au/TiO2 > NiAu/TiO2 > AgAu/TiO2 > RuAu/TiO2 > CuAu/TiO2. Comparing with other metals, adding Pd in Au showed a higher activity. Adding palladium could reduce gold-valence state, and increased active sites for reaction.

  13. Estudio de las publicaciones periódicas españolas de tecnología e ingeniería mecánica y metalúrgica

    Directory of Open Access Journals (Sweden)

    García del Toro, M. A.

    1998-03-01

    Full Text Available The present article studies the Spanish journals of mechanical and metallurgical technology and engineering, as a first approach to the current state of the main vehicles of diffusion of research in these areas of knowledge in Spain. Their formal features have been analyzed, the types of articles, the origin of contributions, etc. The sources for the analysis of the journals have been the ICYT data base and the original journals. The result is a classification of the Spanish journals of mechanical and metallurgical technology and engineering.

    En el presente artículo se ha realizado un estudio de las revistas españolas de tecnología e ingeniería mecánica y metalúrgica, con el objetivo de poder efectuar una primera aproximación al estado actual de los principales órganos de difusión de los avances de la investigación de este grupo de áreas de conocimiento en España. Para ello se ha analizado la presentación de las mismas, los tipos de artículos más frecuentes, la procedencia de las contribuciones, etc. Los instrumentos básicos para el análisis de las revistas han sido la base de datos ICYT y las propias revistas. Como resultado se ofrece una clasificación de las revistas españolas de tecnología e ingeniería mecánica y metalúrgica.

  14. Theoretical perspective on structural, electronic and magnetic properties of 3d metal tetraoxide clusters embedded into single and di-vacancy graphene

    Energy Technology Data Exchange (ETDEWEB)

    Rafique, Muhammad [School of Energy Science and Engineering, Harbin Institute of Technology, 92 West Dazhi Street, Harbin 150001 (China); Mehran University of Engineering and Technology, S.Z.A.B, Campus Khairpur Mir' s, Sindh (Pakistan); Shuai, Yong, E-mail: shuaiyong@hit.edu.cn [School of Energy Science and Engineering, Harbin Institute of Technology, 92 West Dazhi Street, Harbin 150001 (China); Tan, He-Ping; Muhammad, Hassan [School of Energy Science and Engineering, Harbin Institute of Technology, 92 West Dazhi Street, Harbin 150001 (China)

    2017-06-30

    Highlights: • First-principles calculations are performed for TMO{sub 4} cluster-doped SV and DV monolayer graphene structures. • Ferromagnetism coupling behavior between TM atoms and neighboring C and O atoms was observed for all structural models. • The direction of charge transfer is always from graphene layer to TMO{sub 4} clusters. • CrO{sub 4} and MnO{sub 4} doped SV graphene systems display dilute magnetic semiconductor (DMS) behavior in their spin down channel. • CoO{sub 4}, CrO{sub 4}, FeO{sub 4} and MnO{sub 4} doped DV graphene systems exhibit DMS behavior in their spin up channel. - Abstract: Structural, electronic and magnetic properties of 3d transition metal tetraoxide TMO{sub 4} superhalogen clusters doped single vacancy (SV) and divacancy (DV) monolayer graphene have been studied using first-principles calculations. We found that in both cases of TMO{sub 4} cluster substitution, all the impurity atoms are tightly bonded with graphene, having significant formation energy and large charge transfer occurs from graphene to TMO{sub 4} clusters. CrO{sub 4} and MnO{sub 4} substituted SV graphene structures exhibit dilute magnetic semiconductor behavior in their spin down channel with 2.15 μ{sub B} and 3.51 μ{sub B} magnetic moment, respectively. However, CoO{sub 4}, FeO{sub 4}, TiO{sub 4} and NiO{sub 4} substitution into SV graphene, leads to Fermi level shifting to conduction band, thereby causing the Dirac cone to move into valence band and a band gap appears at high symmetric K-point. Interestingly, CoO{sub 4}, CrO{sub 4}, FeO{sub 4} and MnO{sub 4} substituted DV graphene structures exhibit dilute magnetic semiconductor behavior in their spin up channel with 1.74 μ{sub B}, 3.27 μ{sub B}, 3.09 μ{sub B} and 1.99 μ{sub B} magnetic moment, respectively. Detailed analysis of density of states (DOS) plots show that d orbitals of 3d TM atoms should be responsible for inducing magnetic moments in graphene. We believe that our results are

  15. Measurement of electrochemical noise for the study of corrosion processes of metallic alloys; Medida de ruido electroquimico para el estudio de rocesoso de corrosion de aleaciones metalicas

    Energy Technology Data Exchange (ETDEWEB)

    Sanchez-Amaya, J. M.; Bethencourt, M.; Gonzalez-Rovira, L.; Botana, F. J.

    2009-07-01

    Electrochemical noise (EN) is a technique that allows the estimation of both the rate and the corrosion mechanism of different metallic alloys by means of the measurement and the analysis of the fluctuations of current and voltage. Its main advantage against other electrochemical techniques is that during the measurement process, the corrosive systems under study are not instrumentally disturbed, and therefore, the systems are kept at their natural corrosion potential. Two steps are necessary to use this technique: measurement and analysis of the EN signals. In this paper, the most important concepts related only to the measurement of EN are revised. The parameters most employed in the literature to analyse the EN signals will be described in another paper. In the present article, the experimental devices normally used to measure EN signals are firstly analysed. Subsequently, the most important properties of the EN signals are studied. Finally, the external sources of instrumental noise that can affect to the EN signals are described. (Author) 65 refs.

  16. Estudios de cuantificación de metales en el proceso fermentativo de un vino y de su complejación con ligandos naturales

    Directory of Open Access Journals (Sweden)

    C. Santamaría

    2006-05-01

    Full Text Available Wine samples fermented up to a maximum of 345 days have been monitored, and concentrations of Zn, Cu, Mn and Fe have been measured by inductively coupled plasma atomic emission spectroscopy (ICP-AES. Results show a decrease throughout the fermentation time for Cu and Fe concentrations while Zn and Mn concentrations remained stable for the same period of time. Electrochemical techniques were used to perform complexation studies from pH 4 buffered solutions (pH of the wine containing a model ligand, catechin, to prove the applicability of differential pulse anodic stripping voltammetry (DPASV technique to study samples conditioned at the above mentioned pH. The stoichiometry found for the catechin:metal complexes was 1:1 both for Zn and Cu. The electrochemical behaviour of a diluted wine sample subjected to identical experimental conditions as those applied to the model ligand solutions, suggested that the majority of the natural ligands present in wine, able to complex Zn and Cu, have a very similar structure to that of catechin.

  17. Longitudinal cutting of pure and doped carbon nanotubes to form graphitic nanoribbons using metal clusters as nanoscalpels.

    Science.gov (United States)

    Elías, Ana Laura; Botello-Méndez, Andrés R; Meneses-Rodríguez, David; Jehová González, Viviana; Ramírez-González, Daniel; Ci, Lijie; Muñoz-Sandoval, Emilio; Ajayan, Pulickel M; Terrones, Humberto; Terrones, Mauricio

    2010-02-10

    We report the use of transition metal nanoparticles (Ni or Co) to longitudinally cut open multiwalled carbon nanotubes in order to create graphitic nanoribbons. The process consists of catalytic hydrogenation of carbon, in which the metal particles cut sp(2) hybridized carbon atoms along nanotubes that results in the liberation of hydrocarbon species. Observations reveal the presence of unzipped nanotubes that were cut by the nanoparticles. We also report the presence of partially open carbon nanotubes, which have been predicted to have novel magnetoresistance properties.(1) The nanoribbons produced are typically 15-40 nm wide and 100-500 nm long. This method offers an alternative approach for making graphene nanoribbons, compared to the chemical methods reported recently in the literature.

  18. Excitations in clusters

    International Nuclear Information System (INIS)

    Bertsch, G.F.

    2001-01-01

    Statistical reaction theory is an important tool for understanding dynamic processes in clusters as well as for extracting information about theirs energetics. The author reviews the statistical reaction theory and establishes formulas concerning cluster evaporation rates, electron emission and radiative cooling. The author recalls a number of useful formulas for describing the electromagnetic properties of small particles, generalizes them and applies them in the case of alkali metal clusters and of silver clusters. The author ends discussing carbon structures, going from small clusters and molecules to fullerenes and nano-tubes. (A.C.)

  19. LA TECNOLOGÍA DE LA INFORMACIÓN COMO FACTOR COMPETITIVO: UN ESTUDIO EN EL APL COSECHA METAL-MECÁNICO SANTA ROSA/HORIZONTINA, RS, BRASIL

    Directory of Open Access Journals (Sweden)

    Graniel, Gilmar J.

    2011-06-01

    Full Text Available El presente artículo aborda la utilización de la Tecnología de la Información (TI como factor competitivo en un Arreglo Productivo Local (APL Cosecha Metal-Mecánica en el estado de Río Grande del Sur, Brasil y tiene como objetivo buscar la comprensión de como el uso de la TI contribuye al aumento de la competitividad. Para alcanzar este objetivo, fue realizada una investigación en las empresas que componen el APL. Los resultados de la investigación indicaron que las empresas perciben la importancia del uso de la TI, pero que, en la práctica, su utilización es limitada, sobre todo tratándose de la planificación de la TI. Otro de los resultados que se encontró es que las empresas, aunque formen parte del APL, aún no colaboran entre sí, ya sea a través del cambio de informaciones, o a través de Sistemas de Información. Las principales recomendaciones ante estos resultados es que las empresas traten de actuar activamente para el fortalecimiento del APL. En lo que se refiere al uso de la TI se hace necesaria la planificación y la inversión en la adquisición de sistemas integrados para la mejor gerencia de las informaciones, lo cual contribuirá al aumento de la competitividad de las empresas que pertenecen al arreglo.

  20. Thermodynamics of Small Alkali Metal Halide Cluster Ions: Comparison of Classical Molecular Simulations with Experiment and Quantum Chemistry

    Energy Technology Data Exchange (ETDEWEB)

    Vlcek, Lukas [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Uhlik, Filip [Charles Univ., Prague (Czech Republic); Moucka, Filip [Purkinje Univ. (Czech Republic); Nezbeda, Ivo [Purkinje Univ. (Czech Republic); Academy of Sciences of the Czech Republic (ASCR), Prague (Czech Republic); Chialvo, Ariel A. [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)

    2015-12-16

    We evaluate the ability of selected classical molecular models to describe the thermodynamic and structural aspects of gas-phase hydration of alkali 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 non-polarizable 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.

  1. Cluster and Principal Components Analyses on the Contents of (Total and Sorbed Trace Metals in Fresh Marine Sediments from the Southwest of the Gulf of Mexico

    Directory of Open Access Journals (Sweden)

    De Lorenz-Santos Fernando Jesús

    2013-10-01

    Full Text Available The amounts of total and sorbed Al, Ba, Cr, Fe, Mn, Ni, and V present in three sediment cores from the South of the Gulf of Mexico (N1, N2, and N3 were determined. Of the three samples studied herein (N1. N2, and N3, one of them (N2 is associated to a natural “chapopotera”. ICP/MS analyses show that total concentrations of Al, Fe, Mn, Ba, Cr, Ni, Pb, and V for N1 and N3 were found to be ca. 4.2, 2.3, 206.5, 165, 91, 72, 14 and 97 mg kg-1, and ca. 5.2 (Al2O3, 4, 401.50, 269, 89, 62, 18, and 118 mg kg-1 for N2. As evidenced by the correla- tion matrices, there is a positive association among metals distribution, except for the case of Mn, regardless of the sediment core. Nevertheless, Cluster and Principal Components Analyses denote variability in metal-spatial distribu- tion, signature variability in the composition of the water column. Magnitude values for the enrichment factor (EF relative to background values found in the Southern Gulf of Mexico (bulk seawater for Al, Fe, Mn, Ba, Cr, Ni, Pb, and V were estimated. The outcome of this work show distinctive EF values, ran- ging from moderate to high EF values, regardless of the core source.

  2. Evolution of the Stellar Mass–Metallicity Relation. I. Galaxies in the z ∼ 0.4 Cluster Cl0024

    Science.gov (United States)

    Leethochawalit, Nicha; Kirby, Evan N.; Moran, Sean M.; Ellis, Richard S.; Treu, Tommaso

    2018-03-01

    We present the stellar mass–stellar metallicity relationship (MZR) in the galaxy cluster Cl0024+1654 at z ∼ 0.4 using full-spectrum stellar population synthesis modeling of individual quiescent galaxies. The lower limit of our stellar mass range is M * = 109.7 M ⊙, the lowest galaxy mass at which individual stellar metallicity has been measured beyond the local universe. We report a detection of an evolution of the stellar MZR with observed redshift at 0.037 ± 0.007 dex per Gyr, consistent with the predictions from hydrodynamical simulations. Additionally, we find that the evolution of the stellar MZR with observed redshift can be explained by an evolution of the stellar MZR with the formation time of galaxies, i.e., when the single stellar population (SSP)-equivalent ages of galaxies are taken into account. This behavior is consistent with stars forming out of gas that also has an MZR with a normalization that decreases with redshift. Lastly, we find that over the observed mass range, the MZR can be described by a linear function with a shallow slope ([{Fe}/{{H}}]\\propto (0.16+/- 0.03){log}{M}* ). The slope suggests that galaxy feedback, in terms of mass-loading factor, might be mass-independent over the observed mass and redshift range.

  3. A cluster of pediatric metallic mercury exposure cases treated with meso-2,3-dimercaptosuccinic acid (DMSA)

    OpenAIRE

    Forman, J; Moline, J; Cernichiari, E; Sayegh, S; Torres, J C; Landrigan, M M; Hudson, J; Adel, H N; Landrigan, P J

    2000-01-01

    Nine children and their mother were exposed to vapors of metallic mercury. The source of the exposure appears to have been a 6-oz vial of mercury taken from a neighbor's home. The neighbor reportedly operated a business preparing mercury-filled amulets for practitioners of the Afro-Caribbean religion Santeria. At diagnosis, urinary mercury levels in the children ranged from 61 to 1,213 microg/g creatinine, with a geometric mean of 214.3 microg/m creatinine. All of the children were asymptomat...

  4. Structure and bonding in clusters

    International Nuclear Information System (INIS)

    Kumar, V.

    1991-10-01

    We review here the recent progress made in the understanding of the electronic and atomic structure of small clusters of s-p bonded materials using the density functional molecular dynamics technique within the local density approximation. Starting with a brief description of the method, results are presented for alkali metal clusters, clusters of divalent metals such as Mg and Be which show a transition from van der Waals or weak chemical bonding to metallic behaviour as the cluster size grows and clusters of Al, Sn and Sb. In the case of semiconductors, we discuss results for Si, Ge and GaAs clusters. Clusters of other materials such as P, C, S, and Se are also briefly discussed. From these and other available results we suggest the possibility of unique structures for the magic clusters. (author). 69 refs, 7 figs, 1 tab

  5. Assessment of heavy metal contamination in water and sediments of Trepça and Sitnica rivers, Kosovo, using pollution indicators and multivariate cluster analysis.

    Science.gov (United States)

    Ferati, Flora; Kerolli-Mustafa, Mihone; Kraja-Ylli, Arjana

    2015-06-01

    The concentrations of As, Cd, Cr, Co, Cu, Ni, Pb, and Zn in water and sediment samples from Trepça and Sitnica rivers were determined to assess the level of contamination. Six water and sediment samples were collected during the period from April to July 2014. Most of the water samples was found within the European and Kosovo permissible limits. The highest concentration of As, Cd, Pb, and Zn originates primarily from anthropogenic sources such discharge of industrial water from mining flotation and from the mine waste eroded from the river banks. Sediment contamination assessment was carried out using the pollution indicators such as contamination factor (CF), degree of contamination (Cd), modified degree of contamination (mCd), pollution load index (PLI), and geo-accumulation index (Igeo). The CF values for the investigated metals indicated a high contaminated nature of sediments, while the Cd values indicated a very high contamination degree of sediments. The mCd values indicate a high degree of contamination of Sitnica river sediment to ultrahigh degree of contamination of Trepça river sediment. The PLI values ranged from 1.89 to 14.1 which indicate that the heavy metal concentration levels in all investigated sites exceeded the background values and sediment quality guidelines. The average values of Igeo revealed the following ranking of intensity of heavy metal contamination of the Trepça and Sitnica river sediments: Cd > As > Pb > Zn > Cu > Co > Cr > Ni. Cluster analysis suggests that As, Cd, Cr, Co, Cu, Ni, Pb, and Zn are derived from anthropogenic sources, particularly discharges from mining flotation and erosion form waste from a zinc mine plant. In order to protect the sediments from further contamination, the designing of a monitoring network and reducing the anthropogenic discharges are suggested.

  6. A cluster of pediatric metallic mercury exposure cases treated with meso-2,3-dimercaptosuccinic acid (DMSA)

    Science.gov (United States)

    Forman, J; Moline, J; Cernichiari, E; Sayegh, S; Torres, J C; Landrigan, M M; Hudson, J; Adel, H N; Landrigan, P J

    2000-06-01

    Nine children and their mother were exposed to vapors of metallic mercury. The source of the exposure appears to have been a 6-oz vial of mercury taken from a neighbor's home. The neighbor reportedly operated a business preparing mercury-filled amulets for practitioners of the Afro-Caribbean religion Santeria. At diagnosis, urinary mercury levels in the children ranged from 61 to 1,213 microg/g creatinine, with a geometric mean of 214.3 microg/m creatinine. All of the children were asymptomatic. To prevent development of neurotoxicity, we treated the children with oral meso-2,3-dimercaptosuccinic acid (DMSA). During chelation, the geometric mean urine level rose initially by 268% to 573.2 microg mercury/g creatinine (pmercury level had fallen to 102.1 microg/g creatinine, which was 17.8% of the geometric mean level observed during treatment (poral chelation with DMSA produced a significant mercury diuresis in these children. We observed no adverse side effects of treatment. DMSA appears to be an effective and safe chelating agent for treatment of pediatric overexposure to metallic mercury.

  7. DFT based study of transition metal nano-clusters for electrochemical NH3 production

    DEFF Research Database (Denmark)

    Howalt, Jakob Geelmuyden; Bligaard, Thomas; Rossmeisl, Jan

    2013-01-01

    Theoretical studies of the possibility of producing ammonia electrochemically at ambient temperature and pressure without direct N2 dissociation are presented. Density functional theory calculations were used in combination with the computational standard hydrogen electrode to calculate the free ...... for electrochemical ammonia production. The competing hydrogen evolution reaction has also been analyzed for comparison.......Theoretical studies of the possibility of producing ammonia electrochemically at ambient temperature and pressure without direct N2 dissociation are presented. Density functional theory calculations were used in combination with the computational standard hydrogen electrode to calculate the free...... energy profile for the reduction of N2 admolecules and N adatoms on transition metal nanoclusters in contact with an acidic electrolyte. The work has established linear scaling relations for the dissociative reaction intermediates NH, NH2, and NH3. In addition, linear scaling relations...

  8. Van der Waals potentials between metal clusters and helium atoms obtained with density functional theory and linear response methods

    International Nuclear Information System (INIS)

    Liebrecht, M.

    2014-01-01

    The importance of van der Waals interactions in many diverse research fields such as, e. g., polymer science, nano--materials, structural biology, surface science and condensed matter physics created a high demand for efficient and accurate methods that can describe van der Waals interactions from first principles. These methods should be able to deal with large and complex systems to predict functions and properties of materials that are technologically and biologically relevant. Van der Waals interactions arise due to quantum mechanical correlation effects and finding appropriate models an numerical techniques to describe this type of interaction is still an ongoing challenge in electronic structure and condensed matter theory. This thesis introduces a new variational approach to obtain intermolecular interaction potentials between clusters and helium atoms by means of density functional theory and linear response methods. It scales almost linearly with the number of electrons and can therefore be applied to much larger systems than standard quantum chemistry techniques. The main focus of this work is the development of an ab-initio method to account for London dispersion forces, which are purely attractive and dominate the interaction of non--polar atoms and molecules at large distances. (author) [de

  9. Cluster Implantation and Deposition Apparatus

    DEFF Research Database (Denmark)

    Hanif, Muhammad; Popok, Vladimir

    2015-01-01

    In the current report, a design and capabilities of a cluster implantation and deposition apparatus (CIDA) involving two different cluster sources are described. The clusters produced from gas precursors (Ar, N etc.) by PuCluS-2 can be used to study cluster ion implantation in order to develop...... contributions to the theory of cluster stopping in matter as well as for practical applications requiring ultra-shallow implantation and modification of surfaces on the nanoscale. Metal clusters from the magnetron cluster source are of interest for the production of optical sensors to detect specific biological...

  10. X-ray fluorescence spectrometry used to assess the dispersion of metals within mining environments; Aplicacion de la tecnica de espectrometria de fluorescencia de rayos-X en el estudio de la dispersion de metales en areas mineras

    Energy Technology Data Exchange (ETDEWEB)

    Margui, E.; Gonzalez-Fernandez, O.; Hidalgo, M.; Pardini, G.; Queralt, I.

    2011-07-01

    One critical factor for success in characterizing metals polluting mining environments so as to be able to eliminate them and subsequently recover these areas depends upon a speedy and correct response in the analysis of samples. Rapid, simultaneous, multi-element analysis can be undertaken using X-ray fluorescence spectrometry, a versatile, non-destructive analytical technique commonly employed to identify both major and minor elements in samples related to environmental studies. An additional advantage of this technique is the possibility of conducting the analysis directly on solid samples, which is extremely convenient when dealing with environmental samples that are difficult to dissolve, such as soils, sediments and mining wastes. Moreover, in recent years the development of spectrometers equipped with digital-signal processors combined with enlarged X-ray production, using better designs for excitation-detection, has contributed to an improvement in instrumental sensitivity, thus allowing us to detect important polluting elements such as Cd and Pb at trace levels. In this paper the authors describe, on the basis of their own experience, some interesting applications of XRF spectrometry for the analysis of several types of environmental samples related to the study of the dispersion of metals within mining environments: (A) analysis of mining wastes, soils and sediments; (B) analysis of samples of vegetation used as bio indicators or related to phyto remediation studies; and (C) analysis of water samples related to mining operations. (Author) 26 refs.

  11. Internationalization of companies in industrial clusters: a study of medical, dental and hospital supply industries in Ribeirão Preto - SP Internacionalización de empresas en clusters industriales: un estudio aplicado en el polo médico-hospitalar-odontológico de Ribeirão Preto - SP Internacionalização de empresas em clusters industriais: um estudo aplicado no polo médico-hospitalar-odontológioco de Ribeirão Preto - SP

    Directory of Open Access Journals (Sweden)

    Gustavo Barbieri Lima

    2011-03-01

    Full Text Available A trend, both national and international, has been identified in academic research, as well as in business and government. Micro, small and medium sized companies have sought to organize strategic networks of inter-organizational cooperation to be more competitive in their markets or even ensure survival in face of fierce competition arising from globalization. This research investigated relations of the internationalization process that allow these companies to cooperate in industrial clusters and local productive arrangements as opposed to penetration of individual companies in international markets. The method of case study was used to carry out this research. Results show that these companies are very much in favor of the internationalization process, and that this center may now be characterized as an exporter. Inter-organizational cooperation was cited by SEBRAE-SP as extremely important not only for survival of companies monitored, but also for their entry into international markets and increased exportsUna tendencia, tanto en el ámbito nacional como en el internacional, ha sido evidente en investigaciones académicas, como también en los medios empresariales y gubernamentales: la de empresas, especialmente micro, pequeñas y medianas, que buscan organizarse en redes estratégicas de cooperación ínter organizacionales, para mantenerse competitivas en los mercados donde actúan o, precisamente, para asegurar su sobrevivencia delante de la instigada competición proveniente del proceso denominado globalización de mercados. El objetivo general del presente estudio es investigar las interconexiones del proceso de internacionalización que les permite a las micro y pequeñas empresas cooperar en clusters industriales o arreglos productivos locales, en contrapunto a la inserción individual de las empresas en los mercados internacionales. Se utilizó el método de estudio de caso para la realización de la presente investigación. Como

  12. Pair natural orbital and canonical coupled cluster reaction enthalpies involving light to heavy alkali and alkaline earth metals: the importance of sub-valence correlation

    KAUST Repository

    Minenkov, Yury

    2017-03-07

    In this work, we tested canonical and domain based pair natural orbital coupled cluster methods (CCSD(T) and DLPNO-CCSD(T), respectively) for a set of 32 ligand exchange and association/dissociation reaction enthalpies involving ionic complexes of Li, Be, Na, Mg, Ca, Sr, Ba and Pb(ii). Two strategies were investigated: in the former, only valence electrons were included in the correlation treatment, giving rise to the computationally very efficient FC (frozen core) approach; in the latter, all non-ECP electrons were included in the correlation treatment, giving rise to the AE (all electron) approach. Apart from reactions involving Li and Be, the FC approach resulted in non-homogeneous performance. The FC approach leads to very small errors (<2 kcal mol-1) for some reactions of Na, Mg, Ca, Sr, Ba and Pb, while for a few reactions of Ca and Ba deviations up to 40 kcal mol-1 have been obtained. Large errors are both due to artificial mixing of the core (sub-valence) orbitals of metals and the valence orbitals of oxygen and halogens in the molecular orbitals treated as core, and due to neglecting core-core and core-valence correlation effects. These large errors are reduced to a few kcal mol-1 if the AE approach is used or the sub-valence orbitals of metals are included in the correlation treatment. On the technical side, the CCSD(T) and DLPNO-CCSD(T) results differ by a fraction of kcal mol-1, indicating the latter method as the perfect choice when the CPU efficiency is essential. For completely black-box applications, as requested in catalysis or thermochemical calculations, we recommend the DLPNO-CCSD(T) method with all electrons that are not covered by effective core potentials included in the correlation treatment and correlation-consistent polarized core valence basis sets of cc-pwCVQZ(-PP) quality.

  13. Sequential chemical extraction of heavy metals in a study of the chemical alteration of mine tailings at Ticapampa (Huaraz, Peru); Extraccion quimica secuencial de metales pesados en el estudio de alteracion quimica de relaves de mina en Ticapampa (Huaraz, Peru)

    Energy Technology Data Exchange (ETDEWEB)

    Jara Facundo, M. A.

    2011-07-01

    The upper reaches of the Rio Santa (Huaraz, Peru) are highly affected by the mining activities of generally small and very small mining companies located in two specific areas, Cordillera Blanca, and Cordillera Negra, with the largest mining claims located in the districts of Recuay and Ticapampa. To assess the mobility and bioavailability of heavy metals in the abandoned tailings pond belonging to the Alianza mining company in the district of Ticapampa, and to identify the fractions to which they are associated we applied a sequential chemical extraction. The results were compared with studies into their mineralogical characterization, a quantitative chemical analysis and a determination of potential acidity and potential neutralization by the ABA (acid-base accounting) method applied to samples of tailings. The sequential extraction procedure confirmed the mode of general alteration observed in the area through mineralogical studies: a relatively easy mobility of Pb, and Cd, and considerable immobility with regard to Ag, Cr and Co, as well as an intermediate mobility of Cu, Zn, and As. Significant cadmium and lead contents found in the most mobile fractions of the tailings may represent an environmental threat, bearing in mind the toxic nature of these elements. Despite the low mobility of arsenic, the total quantities of this element are so high that the waters of the Rio Santa are being affected. (Author) 22 refs.

  14. Semiconductor color-center structure and excitation spectra: Equation-of-motion coupled-cluster description of vacancy and transition-metal defect photoluminescence

    Science.gov (United States)

    Lutz, Jesse J.; Duan, Xiaofeng F.; Burggraf, Larry W.

    2018-03-01

    Valence excitation spectra are computed for deep-center silicon-vacancy defects in 3C, 4H, and 6H silicon carbide (SiC), and comparisons are made with literature photoluminescence measurements. Optimizations of nuclear geometries surrounding the defect centers are performed within a Gaussian basis-set framework using many-body perturbation theory or density functional theory (DFT) methods, with computational expenses minimized by a QM/MM technique called SIMOMM. Vertical excitation energies are subsequently obtained by applying excitation-energy, electron-attached, and ionized equation-of-motion coupled-cluster (EOMCC) methods, where appropriate, as well as time-dependent (TD) DFT, to small models including only a few atoms adjacent to the defect center. We consider the relative quality of various EOMCC and TD-DFT methods for (i) energy-ordering potential ground states differing incrementally in charge and multiplicity, (ii) accurately reproducing experimentally measured photoluminescence peaks, and (iii) energy-ordering defects of different types occurring within a given polytype. The extensibility of this approach to transition-metal defects is also tested by applying it to silicon-substituted chromium defects in SiC and comparing with measurements. It is demonstrated that, when used in conjunction with SIMOMM-optimized geometries, EOMCC-based methods can provide a reliable prediction of the ground-state charge and multiplicity, while also giving a quantitative description of the photoluminescence spectra, accurate to within 0.1 eV of measurement for all cases considered.

  15. Co2 and Co3 Mixed Cluster Secondary Building Unit Approach toward a Three-Dimensional Metal-Organic Framework with Permanent Porosity

    Directory of Open Access Journals (Sweden)

    Meng-Yao Chao

    2018-03-01

    Full Text Available Large and permanent porosity is the primary concern when designing metal-organic frameworks (MOFs for specific applications, such as catalysis and drug delivery. In this article, we report a MOF Co11(BTB6(NO34(DEF2(H2O14 (1, H3BTB = 1,3,5-tris(4-carboxyphenylbenzene; DEF = N,N-diethylformamide via a mixed cluster secondary building unit (SBU approach. MOF 1 is sustained by a rare combination of a linear trinuclear Co3 and two types of dinuclear Co2 SBUs in a 1:2:2 ratio. These SBUs are bridged by BTB ligands to yield a three-dimensional (3D non-interpenetrated MOF as a result of the less effective packing due to the geometrically contrasting SBUs. The guest-free framework of 1 has an estimated density of 0.469 g cm−3 and exhibits a potential solvent accessible void of 69.6% of the total cell volume. The activated sample of 1 exhibits an estimated Brunauer-Emmett-Teller (BET surface area of 155 m2 g−1 and is capable of CO2 uptake of 58.61 cm3 g−1 (2.63 mmol g−1, 11.6 wt % at standard temperature and pressure in a reversible manner at 195 K, showcasing its permanent porosity.

  16. Metal-Ion Induced In Situ Ligand Oxidation for Self-Assembled Clusters: from Bis(5-(2-pyridine-2-yl)-1,2,4-triazole-3-yl)methane to Alcohol or Ketone.

    Science.gov (United States)

    Lin, Wei-Quan; Peng, Yuan-Yuan; Tong, Lang; Jia, Jian-Hua; Liu, Jun-Liang; Chen, Yan-Cong; Chen, Wen-Bin; Tong, Ming-Liang

    2017-09-05

    Hydrothermal reactions of metal nitrates and ligand bis(5-(pyridine-2-yl)-1,2,4-triazol-3-yl)methane (H 2 L 1 ) gave three cluster compounds, {Cr 2 }, {Zn 12 } and {Fe 8 }. Notably, methylene group of H 2 L 1 was in situ oxidized either to hydroxymethylated (L 2 -O) 3- in the metallo-ring {Zn 12 } or to a rigid carbonylated (L 3 =O) 2- in the screw-type {Fe 8 }. In light of comparative experimental results, NO 3 - was deduced to be of a catalytic role in the ligand oxidation. Metal ion could be regarded as an "induced" tool for clusters generation in self-assembly process. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  17. ESTUDIOS SEROEPIDEMIOLÓGICOS

    OpenAIRE

    Neus Cardeñosa Marín

    2009-01-01

    Los estudios seroepidemiológicos permiten estudiar la distribución de las enfermedades de manera indirecta, mediante la detección sérica de marcadores de infección y de inmunidad. Estos estudios son aplicables en investigaciones en salud pública, investigaciones destinadas a determinar la prevalencia o incidencia de ciertas infecciones en particular, para evaluar programas de control e inmunización y para evaluar antecedentes históricos cuando un nuevo microorganismo es descubierto. En ...

  18. Transition and post-transition metal ions in borate glasses: Borate ligand speciation, cluster formation, and their effect on glass transition and mechanical properties.

    Science.gov (United States)

    Möncke, D; Kamitsos, E I; Palles, D; Limbach, R; Winterstein-Beckmann, A; Honma, T; Yao, Z; Rouxel, T; Wondraczek, L

    2016-09-28

    A series of transition and post-transition metal ion (Mn, Cu, Zn, Pb, Bi) binary borate glasses was studied with special consideration of the cations impact on the borate structure, the cations cross-linking capacity, and more generally, structure-property correlations. Infrared (IR) and Raman spectroscopies were used for the structural characterization. These complementary techniques are sensitive to the short-range order as in the differentiation of tetrahedral and trigonal borate units or regarding the number of non-bridging oxygen ions per unit. Moreover, vibrational spectroscopy is also sensitive to the intermediate-range order and to the presence of superstructural units, such as rings and chains, or the combination of rings. In order to clarify band assignments for the various borate entities, examples are given from pure vitreous B 2 O 3 to meta-, pyro-, ortho-, and even overmodified borate glass compositions. For binary metaborate glasses, the impact of the modifier cation on the borate speciation is shown. High field strength cations such as Zn 2+ enhance the disproportionation of metaborate to polyborate and pyroborate units. Pb 2+ and Bi 3+ induce cluster formation, resulting in PbO n - and BiO n -pseudophases. Both lead and bismuth borate glasses show also a tendency to stabilize very large superstructural units in the form of diborate polyanions. Far-IR spectra reflect on the bonding states of modifier cations in glasses. The frequency of the measured cation-site vibration band was used to obtain the average force constant for the metal-oxygen bonding, F M-O . A linear correlation between glass transition temperature (T g ) and F M-O was shown for the metaborate glass series. The mechanical properties of the glasses also correlate with the force constant F M-O , though for cations of similar force constant the fraction of tetrahedral borate units (N 4 ) strongly affects the thermal and mechanical properties. For paramagnetic Cu- and Mn-borate glasses

  19. de estudios observacionales

    Directory of Open Access Journals (Sweden)

    Erik von Elm

    2008-01-01

    un documento de explicación y elaboración al que puede accederse libremente en los sitios web de PLoS Medicine, Annals of Internal Medicine y Epidemiology. Esperamos que la declaración STROBE contribuya a mejorar la calidad de la publicación de los estudios observacionales.

  20. ESTUDIOS SEROEPIDEMIOLÓGICOS

    Directory of Open Access Journals (Sweden)

    Neus Cardeñosa Marín

    2009-01-01

    y la evaluación de los programas de vacunaciones. Para la buena calidad de los estudios seroepidemiológicos es importante que la muestra de sueros utilizada sea representativa de la población total que queramos estudiar, y se debe tener en cuenta que la prueba serológica a utilizar debe tener una elevada sensibilidad.

  1. Resumen estudios sobre tabaquismo

    OpenAIRE

    Gónzalez, M.M. (M.)

    2009-01-01

    Este documento se realizó para publicar en la página Web de la Gerencia de Atención primaria del Área III. Este documento es una recopilación de estudios sobre tabaquismo. Gerencia de Atención Primaria Área III

  2. Extending DFT-based genetic algorithms by atom-to-place re-assignment via perturbation theory: a systematic and unbiased approach to structures of mixed-metallic clusters.

    Science.gov (United States)

    Weigend, Florian

    2014-10-07

    Energy surfaces of metal clusters usually show a large variety of local minima. For homo-metallic species the energetically lowest can be found reliably with genetic algorithms, in combination with density functional theory without system-specific parameters. For mixed-metallic clusters this is much more difficult, as for a given arrangement of nuclei one has to find additionally the best of many possibilities of assigning different metal types to the individual positions. In the framework of electronic structure methods this second issue is treatable at comparably low cost at least for elements with similar atomic number by means of first-order perturbation theory, as shown previously [F. Weigend, C. Schrodt, and R. Ahlrichs, J. Chem. Phys. 121, 10380 (2004)]. In the present contribution the extension of a genetic algorithm with the re-assignment of atom types to atom sites is proposed and tested for the search of the global minima of PtHf12 and [LaPb7Bi7](4-). For both cases the (putative) global minimum is reliably found with the extended technique, which is not the case for the "pure" genetic algorithm.

  3. Extending DFT-based genetic algorithms by atom-to-place re-assignment via perturbation theory: A systematic and unbiased approach to structures of mixed-metallic clusters

    Energy Technology Data Exchange (ETDEWEB)

    Weigend, Florian, E-mail: florian.weigend@kit.edu [Institut für Physikalische Chemie, Abteilung für Theoretische Chemie, Karlsruher Institut für Technologie, Fritz-Haber-Weg 2, 76131 Karlsruhe, Germany and Institut für Nanotechnologie, Karlsruher Institut für Technologie, Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen (Germany)

    2014-10-07

    Energy surfaces of metal clusters usually show a large variety of local minima. For homo-metallic species the energetically lowest can be found reliably with genetic algorithms, in combination with density functional theory without system-specific parameters. For mixed-metallic clusters this is much more difficult, as for a given arrangement of nuclei one has to find additionally the best of many possibilities of assigning different metal types to the individual positions. In the framework of electronic structure methods this second issue is treatable at comparably low cost at least for elements with similar atomic number by means of first-order perturbation theory, as shown previously [F. Weigend, C. Schrodt, and R. Ahlrichs, J. Chem. Phys. 121, 10380 (2004)]. In the present contribution the extension of a genetic algorithm with the re-assignment of atom types to atom sites is proposed and tested for the search of the global minima of PtHf{sub 12} and [LaPb{sub 7}Bi{sub 7}]{sup 4−}. For both cases the (putative) global minimum is reliably found with the extended technique, which is not the case for the “pure” genetic algorithm.

  4. Cluster headache

    Science.gov (United States)

    Histamine headache; Headache - histamine; Migrainous neuralgia; Headache - cluster; Horton's headache; Vascular headache - cluster ... Doctors do not know exactly what causes cluster headaches. They ... (chemical in the body released during an allergic response) or ...

  5. Design and capabilities of an experimental setup based on magnetron sputtering for formation and deposition of size-selected metal clusters on ultra-clean surfaces

    DEFF Research Database (Denmark)

    Hartmann, Hannes; Popok, Vladimir; Barke, Ingo

    2012-01-01

    The design and performance of an experimental setup utilizing a magnetron sputtering source for production of beams of ionized size-selected clusters for deposition in ultra-high vacuum is described. For the case of copper cluster formation the influence of different source parameters is studied...

  6. Particle coagulation in molten metal based on three-dimensional analysis of cluster by x-ray micro-computer tomography (CT)

    International Nuclear Information System (INIS)

    Li, Tao; Shimasaki, Shin-ichi; Taniguchi, Shoji; Narita, Shunsuke; Uesugi, Kentaro

    2013-01-01

    Particle coagulation plays a key role in steel refining process to remove inclusions. Many research works focus on the behaviors of particle coagulation. To reveal its mechanism water model experiments have been performed by some researchers including the authors' group. In this paper, experiments of particle coagulation were carried out with molten Al including SiC particles in a mechanically agitated crucible with two baffles. Particle coagulation and formation of clusters were observed on the microscopy images of as-polished samples. Three-dimensional (3D) analysis of the clusters in solidified Al was implemented by X-ray micro CT available at SPring-8. The methods to distinguish clusters on two-dimensional (2D) cross-sectional images were discussed, which were established in the previous works by the present authors' group. The characteristics of the 3D SiC clusters and their 2D cross-sections were analyzed. The statistical ranges of the parameters for 2D clusters were used as criterions to distinguish the clusters on 2D microscopy images from the as-polished samples. The kinetics of SiC particle coagulation was studied by the measured cluster number density and size using our program to distinguish cluster in 2D cross-sectional images according to 3D information (DC-2D-3D). The calculated and experimental results of the SiC particle coagulation in molten Al agree well with each other. (author)

  7. Estenosis traqueal: Estudio preliminar

    OpenAIRE

    Rafael Pinilla González; Asbel Vicente de la Cruz

    2000-01-01

    Se realizó un estudio retrospectivo y descriptivo con la utilización de los expedientes clínicos de 5 pacientes con estenosis traqueal, mayoritariamente como consecuencia de intubación prolongada, y en el que se tuvo en cuenta aspectos relacionados con el diagnóstico, el tratamiento y las complicaciones. Existió un predominio del sexo femenino y edad media de 44,6 años. La intubación prolongada de origen diverso fue la causa de la estenosis en 4 de los 5 pacientes y en 1 fue posterior a la re...

  8. Multireference Equation of Motion Coupled Cluster study of atomic excitation spectra of first-row transition metal atoms Cr, Mn, Fe and Co

    Czech Academy of Sciences Publication Activity Database

    Liu, Z.; Demel, Ondřej; Nooijen, M.

    2015-01-01

    Roč. 311, SI (2015), s. 54-63 ISSN 0022-2852 Institutional support: RVO:61388955 Keywords : multireference * coupled cluster * electronic excited states Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 1.593, year: 2015

  9. EXAFS investigations on nanocomposites composed of surface-modified zirconium and zirconium/titanium mixed metal oxo-clusters and organic polymers

    International Nuclear Information System (INIS)

    Kickelbick, G.; Moraru, B.; Trimmel, G.; Schubert, U.; Feth, M.P.; Bertagnolli, H.

    2002-01-01

    The surface-modified oxometallate clusters Zr 6 (OH) 4 O 4 (OMc) 12 , Ti 4 Zr 4 O 6 (OBu) 4 (OMc) 16 , and Ti 2 Zr 4 O 4 (OBu) 2 (OMc) 14 (OMc methacrylate) as well as their nanocomposites with polystyrene, poly(methacrylic acid) and poly(methyl methacrylate) were investigated by EXAFS. Studies on the nanocomposites revealed that the structure of the cluster core is retained in the hybrid materials. (author)

  10. un estudio comparativo

    Directory of Open Access Journals (Sweden)

    Federico Varona

    2007-01-01

    Full Text Available La comunicación efectiva es uno de los mayores retos que tienen hoy las organizaciones y empresas tanto a nivel nacional como internacional (global. Este artículo presenta los resultados de la investigación realizada por un equipo internacional de investigadores interesados en descubrir y comparar las conductas comunicativas o estilos de comunicación de los empleados finlandeses y mexicanos cuando interactúan con sus superiores. Para ello presentamos: primero, un breve marco teórico del estudio; segundo, la metodología; tercero, los resultados del análisis estadístico comparativo entre los empleados de Finlandia y México; cuarto, las conclusiones generales y su explicación cultural; y quinto, las implicaciones teóricas y prácticas de este estudio con respecto a las competencias comunicativas necesarias para la comunicación efectiva entre empleados y superiores tanto en organizaciones nacionales como internacionales (globales.

  11. Cluster Headache

    Science.gov (United States)

    ... re at risk of cluster headache. A family history. Having a parent or sibling who has had cluster headache might ... of Nondiscrimination Advertising Mayo Clinic is a not-for-profit organization ...

  12. NONLINEAR COLOR-METALLICITY RELATIONS OF GLOBULAR CLUSTERS. II. A TEST ON THE NONLINEARITY SCENARIO FOR COLOR BIMODALITY USING THE u-BAND COLORS: THE CASE OF M87 (NGC 4486)

    International Nuclear Information System (INIS)

    Yoon, Suk-Jin; Lee, Sang-Yoon; Kim, Hak-Sub; Cho, Jaeil; Chung, Chul; Sohn, Sangmo T.; Blakeslee, John P.

    2011-01-01

    The optical color distributions of globular clusters (GCs) in most large elliptical galaxies are bimodal. Based on the assumed linear relationship between GC colors and their metallicities, the bimodality has been taken as evidence of two GC subsystems with different metallicities in each galaxy and has led to a number of theories in the context of galaxy formation. More recent observations and modeling of GCs, however, suggests that the color-metallicity relations (CMRs) are inflected, and thus colors likely trace metallicities in a nonlinear manner. The nonlinearity could produce bimodal color distributions from a broad underlying metallicity spread, even if it is unimodal. Despite the far-reaching implications, whether CMRs are nonlinear and whether the nonlinearity indeed causes the color bimodality are still open questions. Given that the spectroscopic refinement of CMRs is still very challenging, we here propose a new photometric technique to probe the possible nonlinear nature of CMRs. In essence, a color distribution of GCs is a 'projected' distribution of their metallicities. Since the form of CMRs hinges on which color is used, the shape of color distributions varies depending significantly on the colors. Among other optical colors, the u-band related colors (e.g., u – g and u – z) are theoretically predicted to exhibit significantly less inflected CMRs than other preferred CMRs (e.g., for g – z). As a case study, we performed the Hubble Space Telescope (HST)/WFPC2 archival u-band photometry for the M87 (NGC 4486) GC system with confirmed color bimodality. We show that the u-band color distributions are significantly different from that of g – z and consistent with our model predictions. With more u-band measurements, this method will support or rule out the nonlinear CMR scenario for the origin of GC color bimodality with high confidence. The HST/WFC3 observations in F336W for nearby large elliptical galaxies are highly anticipated in this regard.

  13. Meaningful Clusters

    Energy Technology Data Exchange (ETDEWEB)

    Sanfilippo, Antonio P.; Calapristi, Augustin J.; Crow, Vernon L.; Hetzler, Elizabeth G.; Turner, Alan E.

    2004-05-26

    We present an approach to the disambiguation of cluster labels that capitalizes on the notion of semantic similarity to assign WordNet senses to cluster labels. The approach provides interesting insights on how document clustering can provide the basis for developing a novel approach to word sense disambiguation.

  14. Relative Ages of Globular Clusters

    Science.gov (United States)

    Puzia, Thomas H.

    Ages of extragalactic globular clusters can provide valuable insights into the formation and evolution of galaxies. In this contribution the photometric methods of age dating old globular cluster systems are summarised. The spectroscopic approach is reviewed with an emphasis of the fight choice of age diagnostics. We present a new method of quantifying the relatively best age-sensitive spectroscopic index given the quality of a data set and a certain theoretical stellar synthesis model. The relatively best diagnostic plot is constructed from the set of Lick indices and used to age date globular clusters in several early-type galaxies which are part of a large spectroscopic survey of extragalactic globular cluster systems. We find that, independently of host galaxy, metal-poor ([Fe/H] old (t > 8 Gyr) and coeval. Metal-rich clusters show a wide range of ages from ˜ 15 down to a few Gyr.

  15. DE AGUA. ESTUDIO PRELIMINAR

    Directory of Open Access Journals (Sweden)

    Esther E. Pellizzari

    2015-01-01

    Full Text Available El objetivo del presente estudio fue investigar la resistencia al arsénico en cultivos puros de Pseudomonas aeruginosa , aislada de aguas subterráneas de Presidencia Roque Sáenz Peña, provincia de Chaco y evaluar la posibilidad de su uso para la remoción de este contaminante presente en las aguas subterráneas. Las cepas fueron inmovilizadas en piedra natural y se cu ltivaron en caldo de sales y 1 mgAs/L . Se observó la resistencia al arsénico y la formación de biofilm , logrando la interacción entre la s células, roca y arsénico . L a remoción de arsénico se evaluó durante 3 meses y el porcentaje de eliminación de arsénico al final del experimento fue 60%.

  16. Optical properties of cluster plasma

    Energy Technology Data Exchange (ETDEWEB)

    Kishimoto, Yasuaki; Tajima, Toshiki [Japan Atomic Energy Research Inst., Neyagawa, Osaka (Japan). Kansai Research Establishment; Downer, M.C.

    1998-03-01

    It is shown that unlike a gas plasma or an electron plasma in a metal, an ionized clustered material (`cluster plasma`) permits propagation below the plasma cut-off of electromagnetic (EM) waves whose phase velocity is close to but below the speed of light. This results from the excitation of a plasma oscillation mode (and/or polarization mode) through the cluster surface which does not exist in usual gaseous plasma. The existence of this new optical mode, cluster mode, is confirmed via numerical simulation. (author)

  17. EXAFS investigations on nanocomposites composed of surface-modified zirconium and zirconium/titanium mixed metal oxo-clusters and organic polymers

    CERN Document Server

    Kickelbick, G; Trimmel, G; Schubert, U; Feth, M P; Bertagnolli, H

    2002-01-01

    The surface-modified oxometallate clusters Zr sub 6 (OH) sub 4 O sub 4 (OMc) sub 1 sub 2 , Ti sub 4 Zr sub 4 O sub 6 (OBu) sub 4 (OMc) sub 1 sub 6 , and Ti sub 2 Zr sub 4 O sub 4 (OBu) sub 2 (OMc) sub 1 sub 4 (OMc methacrylate) as well as their nanocomposites with polystyrene, poly(methacrylic acid) and poly(methyl methacrylate) were investigated by EXAFS. Studies on the nanocomposites revealed that the structure of the cluster core is retained in the hybrid materials. (author)

  18. Interaction of intense laser fields with metal clusters. Energy absorpion by scattering processes; Wechselwirkung von intensiven Laserfeldern mit Metallclustern. Energieabsorption durch Streuprozesse

    Energy Technology Data Exchange (ETDEWEB)

    Koehn, Joerg

    2010-02-23

    The present thesis aims at the theoretical description of laser-cluster interactions by means of semiclassical simulations, using small sodium clusters as model systems. In particular, the dynamics of ionization and electron emission is analyzed. To this end a model has been developed, which takes the density- and temperature dependence of electron-electron scattering cross sections within the nanoplasma into account. Furthermore the possibility of resonant excitation with few-cycle-pulses and control of the electron emission by means of the carrier-envelope-phase is investigated. (orig.)

  19. Thermal Methane Activation by a Binary V-Nb Transition-Metal Oxide Cluster Cation: A Further Example for the Crucial Role of Oxygen-Centered Radicals

    Czech Academy of Sciences Publication Activity Database

    Wang, Z. C.; Liu, J. W.; Schlangen, M.; Weiske, T.; Schröder, Detlef; Sauer, J.; Schwarz, H.

    2013-01-01

    Roč. 19, č. 35 (2013), s. 11496-11501 ISSN 0947-6539 Institutional support: RVO:61388963 Keywords : binary oxide cluster * density functional calculations * mass spectrometry * methane activation * radical ions Subject RIV: CC - Organic Chemistry Impact factor: 5.696, year: 2013

  20. Data Clustering

    Science.gov (United States)

    Wagstaff, Kiri L.

    2012-03-01

    On obtaining a new data set, the researcher is immediately faced with the challenge of obtaining a high-level understanding from the observations. What does a typical item look like? What are the dominant trends? How many distinct groups are included in the data set, and how is each one characterized? Which observable values are common, and which rarely occur? Which items stand out as anomalies or outliers from the rest of the data? This challenge is exacerbated by the steady growth in data set size [11] as new instruments push into new frontiers of parameter space, via improvements in temporal, spatial, and spectral resolution, or by the desire to "fuse" observations from different modalities and instruments into a larger-picture understanding of the same underlying phenomenon. Data clustering algorithms provide a variety of solutions for this task. They can generate summaries, locate outliers, compress data, identify dense or sparse regions of feature space, and build data models. It is useful to note up front that "clusters" in this context refer to groups of items within some descriptive feature space, not (necessarily) to "galaxy clusters" which are dense regions in physical space. The goal of this chapter is to survey a variety of data clustering methods, with an eye toward their applicability to astronomical data analysis. In addition to improving the individual researcher’s understanding of a given data set, clustering has led directly to scientific advances, such as the discovery of new subclasses of stars [14] and gamma-ray bursts (GRBs) [38]. All clustering algorithms seek to identify groups within a data set that reflect some observed, quantifiable structure. Clustering is traditionally an unsupervised approach to data analysis, in the sense that it operates without any direct guidance about which items should be assigned to which clusters. There has been a recent trend in the clustering literature toward supporting semisupervised or constrained

  1. Estudio de los metales contenidos en aire, agua y sedimentos en un área urbana - rural con influencia industrial ubicada en la Zona Metropolitana de Puebla, México

    OpenAIRE

    Morales García, Sandra Soledad

    2015-01-01

    Por la importancia que tienen los metales y metaloides en el ambiente es propicio conocer su composición y dilucidar sobre las fuentes naturales o antropogénicas que los generan. Esta investigación permitio determinar la concentración de metales y As en aire, agua y sedimentos dentro de un ambiente urbano-rural con influencia industrial en la Zona Metropolitana de la Ciudad de Puebla (region centro-oeste de México). El objetivo del trabajo fue establecer estadísticamente asociaciones entre lo...

  2. Thermodynamic prediction of glass formation tendency, cluster-in-jellium model for metallic glasses, ab initio tight-binding calculations, and new density functional theory development for systems with strong electron correlation

    Energy Technology Data Exchange (ETDEWEB)

    Yao, Yongxin [Iowa State Univ., Ames, IA (United States)

    2009-01-01

    Solidification of liquid is a very rich and complicated field, although there is always a famous homogeneous nucleation theory in a standard physics or materials science text book. Depending on the material and processing condition, liquid may solidify to single crystalline, polycrystalline with different texture, quasi-crystalline, amorphous solid or glass (Glass is a kind of amorphous solid in general, which has short-range and medium-range order). Traditional oxide glass may easily be formed since the covalent directional bonded network is apt to be disturbed. In other words, the energy landcape of the oxide glass is so complicated that system need extremely long time to explore the whole configuration space. On the other hand, metallic liquid usually crystalize upon cooling because of the metallic bonding nature. However, Klement et.al., (1960) reported that Au-Si liquid underwent an amorphous or “glassy” phase transformation with rapid quenching. In recent two decades, bulk metallic glasses have also been found in several multicomponent alloys[Inoue et al., (2002)]. Both thermodynamic factors (e.g., free energy of various competitive phase, interfacial free energy, free energy of local clusters, etc.) and kinetic factors (e.g., long range mass transport, local atomic position rearrangement, etc.) play important roles in the metallic glass formation process. Metallic glass is fundamentally different from nanocrystalline alloys. Metallic glasses have to undergo a nucleation process upon heating in order to crystallize. Thus the short-range and medium-range order of metallic glasses have to be completely different from crystal. Hence a method to calculate the energetics of different local clusters in the undercooled liquid or glasses become important to set up a statistic model to describe metalllic glass formation. Scattering techniques like x-ray and neutron have widely been used to study the structues of metallic glasses. Meanwhile, computer simulation

  3. Concordia. Un estudio comparativo

    Directory of Open Access Journals (Sweden)

    Graciela Mingo de Bevilacqua

    2006-01-01

    Full Text Available Este estudio comparativo buscó develar las heterogeneidades de la pobreza urbana que enmarcan la vida de las familias pobres de dos aglomerados de la Provincia de Entre Ríos: Paraná y Concordia. Se partió del concepto de pobreza como fenómeno heterogéneo, no sólo por su magnitud e intensidad, sino también por su configuración, condicionada por el entorno urbano y las estructuras económico-sociales. En la última década del siglo XX y en los primeros años del actual siglo XXI, la pobreza se fue acentuando; tuvieron lugar en la Argentina las transformaciones estructurales que, sin duda, profundizaron las desigualdades sociales. Ellas se pueden sintetizar en: reforma del estado, privatizaciones y reforma laboral, procesos recesivos y terciarización de la economía. Las perspectivas de descripción y análisis metodológico se encuadran en el estilo de complementariedad, en pos de una aproximación más profunda a la reproducción de la pobreza y las estrategias de los hogares pobres.

  4. Three-atom clusters

    International Nuclear Information System (INIS)

    Pen'kov, F.M.

    1998-01-01

    The Born-Oppenheimer approximation is used to obtain an equation for the effective interaction in three atoms bound by a single electron. For low binding energies in an 'electron + atom' pair, long-range forces arise between the atoms, leading to bound states when the size of the three-atom cluster is a few tens of angstrom. A system made of alkali-metal atoms is considered as an example

  5. Dense Fe cluster-assembled films by energetic cluster deposition

    International Nuclear Information System (INIS)

    Peng, D.L.; Yamada, H.; Hihara, T.; Uchida, T.; Sumiyama, K.

    2004-01-01

    High-density Fe cluster-assembled films were produced at room temperature by an energetic cluster deposition. Though cluster-assemblies are usually sooty and porous, the present Fe cluster-assembled films are lustrous and dense, revealing a soft magnetic behavior. Size-monodispersed Fe clusters with the mean cluster size d=9 nm were synthesized using a plasma-gas-condensation technique. Ionized clusters are accelerated electrically and deposited onto the substrate together with neutral clusters from the same cluster source. Packing fraction and saturation magnetic flux density increase rapidly and magnetic coercivity decreases remarkably with increasing acceleration voltage. The Fe cluster-assembled film obtained at the acceleration voltage of -20 kV has a packing fraction of 0.86±0.03, saturation magnetic flux density of 1.78±0.05 Wb/m 2 , and coercivity value smaller than 80 A/m. The resistivity at room temperature is ten times larger than that of bulk Fe metal

  6. Identification of mixed-valence metal clusters in drier solutions for alkyd-based paints by electrospray ionization mass spectrometry (ESI-MS)

    NARCIS (Netherlands)

    Micciche, F.; Straten, van M.; Ming, W.; Oostveen, E.A.; Haveren, van J.; Linde, van der R.; Reedijk, J.

    2005-01-01

    The oxidative drying of alkyd paints has many similarities with the way lipids are oxidized in biological systems. Metal salts based on Co, Fe and Mn are added to accelerate the oxidative drying of conventional alkyd paints. Although the mechanism by which alkyd paints dry has been the subject of

  7. Complex trend of magnetic order in Fe clusters on 4d transition-metal surfaces. I. Experimental evidence and Monte Carlo simulations

    Czech Academy of Sciences Publication Activity Database

    Sessi, V.; Otte, F.; Krotzky, S.; Tieg, C.; Wasniowska, M.; Ferriani, P.; Heinze, S.; Honolka, Jan; Kern, K.

    2014-01-01

    Roč. 89, č. 20 (2014), "205425-1"-"205425-6" ISSN 1098-0121 Institutional support: RVO:68378271 Keywords : iron atoms on 4d metal surfaces * surface magnetism * complex spin order * indirect exchange interactions Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 3.736, year: 2014

  8. Investigating cluster formation in adsorption of CO2, CH4, and Ar in zeolites and metal organic frameworks at subcritical temperatures

    NARCIS (Netherlands)

    Krishna, R.; van Baten, J.M.

    2010-01-01

    The critical temperatures, T-c, of CO2, CH4, and Ar are 304 K, 191 K, and 151 K, respectively. This paper highlights some unusual characteristics of adsorption and diffusion of these molecules in microporous structures such as zeolites and metal organic frameworks at temperatures T < T-c. Published

  9. Clusters of atoms and molecules theory, experiment, and clusters of atoms

    CERN Document Server

    1994-01-01

    Clusters of Atoms and Molecules is devoted to theoretical concepts and experimental techniques important in the rapidly expanding field of cluster science. Cluster properties are dicussed for clusteres composed of alkali metals, semiconductors, transition metals, carbon, oxides and halides of alkali metals, rare gases, and neutral molecules. The book is composed of several well-integrated treatments all prepared by experts. Each contribution starts out as simple as possible and ends with the latest results so that the book can serve as a text for a course, an introduction into the field, or as a reference book for the expert.

  10. MEXCODE* CASO DE ESTUDIO

    Directory of Open Access Journals (Sweden)

    Gabriel Arturo García Gómez

    2000-01-01

    Full Text Available El caso plantea la reactivación de un proyecto que se presentó en el año 1995 como alternativa para el desarrollo del centro del Valle y mejora de la eficiencia en el manejo del comercio exterior de la Cuenca Pacífica. El proyecto se revivió a raíz de la necesidad de la compañía patrocinadora de mejorar sus flujos de caja proyectados y la reciente autorización para su funcionamiento. El proyecto es el popularmente denominado “Puerto Seco” de la ciudad de Guadalajara de Buga, internamente nombrado Mexcode. Los estudios iniciales estaban encaminados a que el proyecto fuera manejado por el municipio de Buga, sin embargo, posteriormente se vio la necesidad de buscar que pasara a manos de la empresa privada. El municipio, después de analizar las propuestas de varios inversionistas de la región en las cuales se evaluaba la ubicación dentro de la zona de los predios de sus empresas, su área, proximidad a la línea férrea y a la doble calzada Buga-Tuluá (sitio de paso del 80% de la carga de importación y exportación por Buenaventura y evaluar aspectos relativos a su trayectoria empresarial y compromiso con el desarrollo de la región, decidió otorgarle el proyecto al Grupo Empresarial Agri-Supplies S.A.

  11. Weighted Clustering

    DEFF Research Database (Denmark)

    Ackerman, Margareta; Ben-David, Shai; Branzei, Simina

    2012-01-01

    the partitional and hierarchical settings, characterizing the conditions under which algorithms react to weights. Extending a recent framework for clustering algorithm selection, we propose intuitive properties that would allow users to choose between clustering algorithms in the weighted setting and classify...

  12. Cluster editing

    DEFF Research Database (Denmark)

    Böcker, S.; Baumbach, Jan

    2013-01-01

    . The problem has been the inspiration for numerous algorithms in bioinformatics, aiming at clustering entities such as genes, proteins, phenotypes, or patients. In this paper, we review exact and heuristic methods that have been proposed for the Cluster Editing problem, and also applications...

  13. Properties of the open cluster system

    International Nuclear Information System (INIS)

    Janes, K.A.; Tilley, C.; Lynga, G.

    1988-01-01

    A system of weights corresponding to the precision of open cluster data is described. Using these weights, some properties of open clusters can be studied more accurately than was possible earlier. It is clear that there are three types of objects: unbound clusters, bound clusters in the thin disk, and older bound clusters. Galactic gradients of metallicity, longevity, and linear diameter are studied. Distributions at right angles to the galactic plane are discussed in the light of the different cluster types. The clumping of clusters in complexes is studied. An estimate of the selection effects influencing the present material of open cluster data is made in order to evaluate the role played by open clusters in the history of the galactic disk. 58 references

  14. XMM Newton Observations of Toothbrush Cluster

    Science.gov (United States)

    Kara, Sinancan; Nihal Ercan, Enise; De Plaa, Jelle; Mernier, Francois

    2016-07-01

    Galaxy clusters are the largest gravitationally-bound objects in the universe. The member galaxies are embedded in a hot X-ray emitting Intra-Cluster Medium (ICM) that has been enriched over time with metals produced by supernovae. In this presentation we show new results from XMM-Newton regarding the merging cluster 1RXSJ0603.3+4213. This cluster, also known as the Toothbrush cluster, shows a large toothbrush-shaped radio relic associated with a merger shock North of the cluster core. We show the distribution and the abundances of the metals in this merging cluster in relation to the merger shock. The results are derived from spatially resolved X-ray spectra from the EPIC instrument aboard XMM-Newton.

  15. Estenosis traqueal: Estudio preliminar

    Directory of Open Access Journals (Sweden)

    Rafael Pinilla González

    2000-12-01

    Full Text Available Se realizó un estudio retrospectivo y descriptivo con la utilización de los expedientes clínicos de 5 pacientes con estenosis traqueal, mayoritariamente como consecuencia de intubación prolongada, y en el que se tuvo en cuenta aspectos relacionados con el diagnóstico, el tratamiento y las complicaciones. Existió un predominio del sexo femenino y edad media de 44,6 años. La intubación prolongada de origen diverso fue la causa de la estenosis en 4 de los 5 pacientes y en 1 fue posterior a la reparación de lesión traqueal yatrógena. La instalación de la estenosis tuvo lugar entre 8 días y 3 meses. La tomografía lineal en 3 pacientes y en 2 la radiografía simple de tráquea anteroposterior y lateral verificaron el diagnóstico. La endoscopia traqueobronquial preoperatoria fue de utilidad en la caracterización de la estenosis. En todos los pacientes se realizó tratamiento quirúrgico al resecar el área estenótica con posterior anastomosis terminoterminal y fijación del cuello en flexión durante 8 días como promedio. Dos pacientes mostraron granulomas en el nivel de la línea de sutura, los cuales fueron tratados por vacuolización con láser. No se reportó mortalidad en la muestra estudiadaA retrospective and descriptive study was conducted by using the medical histories of 5 patients with tracheal stenosis, mostly as a result of prolongued intubation. Aspects connected with the diagnosis, treatment and complications were taken into account. It was observed a predominance of females and an average age of 44.6. Prolongued intubation of different origin was the cause of stenosis in 4 of the 5 patients, whereas in the other it occurred after the reparation of the tracheal and athrogenous lesion. The installation of stenosis took place between 8 days and 3 months. Lineal tomography in 3 patients and anteroposterior and lateral simple X-ray of the trachea in 2 confirmed the diagnosis. Preoperative tracheobronchial endoscopy was

  16. Constraints on the Distance Moduli, Helium and Metal Abundances, and Ages of Globular Clusters from their RR Lyrae and Non-variable Horizontal-branch Stars. I. M3, M15, and M92

    Science.gov (United States)

    VandenBerg, Don A.; Denissenkov, P. A.; Catelan, Márcio

    2016-08-01

    Up-to-date isochrones, zero-age horizontal-branch (ZAHB) loci, and evolutionary tracks for core He-burning stars are applied to the color-magnitude diagrams of M3, M15, and M92, focusing in particular on their RR Lyrae populations. Periods for the ab- and c-type variables are calculated using the latest theoretical calibrations of {log} {P}{ab} and {log} {P}c as a function of luminosity, mass, effective temperature ({T}{{eff}}), and metallicity. Our models are generally able to reproduce the measured periods to well within the uncertainties implied by the stellar properties on which pulsation periods depend, as well as the mean periods and cluster-to-cluster differences in and , on the assumption of well-supported values of E(B-V), {(m-M)}V, and [Fe/H]. While many of RR Lyrae in M3 lie close to the same ZAHB that fits the faintest horizontal-branch (HB) stars at bluer or redder colors, the M92 variables are all significantly evolved stars from ZAHB locations on the blue side of the instability strip. M15 appears to contain a similar population of HB stars as M92, along with additional helium-enhanced populations not present in the latter which comprise most of its RR Lyrae stars. The large number of variables in M15 and the similarity of the observed values of and in M15 and M92 can be explained by HB models that allow for variations in Y. Similar ages (˜12.5 Gyr) are found for all three clusters, making them significantly younger than the field halo subgiant HD 140283. Our analysis suggests a preference for stellar models that take diffusive processes into account.

  17. Clustering Dycom

    KAUST Repository

    Minku, Leandro L.

    2017-10-06

    Background: Software Effort Estimation (SEE) can be formulated as an online learning problem, where new projects are completed over time and may become available for training. In this scenario, a Cross-Company (CC) SEE approach called Dycom can drastically reduce the number of Within-Company (WC) projects needed for training, saving the high cost of collecting such training projects. However, Dycom relies on splitting CC projects into different subsets in order to create its CC models. Such splitting can have a significant impact on Dycom\\'s predictive performance. Aims: This paper investigates whether clustering methods can be used to help finding good CC splits for Dycom. Method: Dycom is extended to use clustering methods for creating the CC subsets. Three different clustering methods are investigated, namely Hierarchical Clustering, K-Means, and Expectation-Maximisation. Clustering Dycom is compared against the original Dycom with CC subsets of different sizes, based on four SEE databases. A baseline WC model is also included in the analysis. Results: Clustering Dycom with K-Means can potentially help to split the CC projects, managing to achieve similar or better predictive performance than Dycom. However, K-Means still requires the number of CC subsets to be pre-defined, and a poor choice can negatively affect predictive performance. EM enables Dycom to automatically set the number of CC subsets while still maintaining or improving predictive performance with respect to the baseline WC model. Clustering Dycom with Hierarchical Clustering did not offer significant advantage in terms of predictive performance. Conclusion: Clustering methods can be an effective way to automatically generate Dycom\\'s CC subsets.

  18. Clustering analysis

    International Nuclear Information System (INIS)

    Romli

    1997-01-01

    Cluster analysis is the name of group of multivariate techniques whose principal purpose is to distinguish similar entities from the characteristics they process.To study this analysis, there are several algorithms that can be used. Therefore, this topic focuses to discuss the algorithms, such as, similarity measures, and hierarchical clustering which includes single linkage, complete linkage and average linkage method. also, non-hierarchical clustering method, which is popular name K -mean method ' will be discussed. Finally, this paper will be described the advantages and disadvantages of every methods

  19. Cluster analysis

    CERN Document Server

    Everitt, Brian S; Leese, Morven; Stahl, Daniel

    2011-01-01

    Cluster analysis comprises a range of methods for classifying multivariate data into subgroups. By organizing multivariate data into such subgroups, clustering can help reveal the characteristics of any structure or patterns present. These techniques have proven useful in a wide range of areas such as medicine, psychology, market research and bioinformatics.This fifth edition of the highly successful Cluster Analysis includes coverage of the latest developments in the field and a new chapter dealing with finite mixture models for structured data.Real life examples are used throughout to demons

  20. Estudio de organismos acuáticos macrobentónicos como indicadores de la contaminación por metales pesados en ríos de la Huasteca Potosina

    OpenAIRE

    CYNTHIA WONG ARGUELLES

    2009-01-01

    La importancia de utilizar organismos acuáticos macrobentónicos como indicadores de la contaminación es la de evaluar de manera directa el impacto biológico de los metales traza (Cu, Pb, Cd y Zn). El análisis en organismos acuáticos ha sido utilizado como un complemento para el muestreo tradicional, utilizando los organismos acuáticos como biomonitores u organismos centinelas. El biomonitoreo pretende buscar la relación entre la concentración del contaminante en el organismo y en su ambiente...

  1. Occupational Clusters.

    Science.gov (United States)

    Pottawattamie County School System, Council Bluffs, IA.

    The 15 occupational clusters (transportation, fine arts and humanities, communications and media, personal service occupations, construction, hospitality and recreation, health occupations, marine science occupations, consumer and homemaking-related occupations, agribusiness and natural resources, environment, public service, business and office…

  2. Cancer Clusters

    Science.gov (United States)

    ... Peer Review and Funding Outcomes Step 4: Award Negotiation & Issuance Manage Your Award Grants Management Contacts Monitoring ... potentially hazardous working conditions, including suspected cancer clusters. Employees, authorized employee representatives, and employers can request these ...

  3. Cluster generator

    Science.gov (United States)

    Donchev, Todor I [Urbana, IL; Petrov, Ivan G [Champaign, IL

    2011-05-31

    Described herein is an apparatus and a method for producing atom clusters based on a gas discharge within a hollow cathode. The hollow cathode includes one or more walls. The one or more walls define a sputtering chamber within the hollow cathode and include a material to be sputtered. A hollow anode is positioned at an end of the sputtering chamber, and atom clusters are formed when a gas discharge is generated between the hollow anode and the hollow cathode.

  4. Estudio hidrogeoquímico del lago ácido de Cueva de la Mora (IPB, Huelva): controles sobre la concentración de metales y modelo de estratificación

    OpenAIRE

    Diez Ercilla, Marta

    2016-01-01

    298 p. Cueva de la Mora forma parte del conjunto de lagos ácidos de mina de la Faja Pirítica Ibérica formadostras el abandono de la minería. El cese de las actividades de bombeo de agua, indispensables durante lavida útil de esta mina, provocó la recuperación de nivel freático y la inundación de la corta. Este procesooriginó un lago ácido meromíctico caracterizado por un elevado contenido en sulfato y en hierro,productos de la oxidación de la pirita, junto con otros metales y metaloides.A ...

  5. Singular electrostatic energy of nanoparticle clusters

    Science.gov (United States)

    Qin, Jian; Krapf, Nathan W.; Witten, Thomas A.

    2016-02-01

    The binding of clusters of metal nanoparticles is partly electrostatic. We address difficulties in calculating the electrostatic energy when high charging energies limit the total charge to a single quantum, entailing unequal potentials on the particles. We show that the energy at small separation h has a singular logarithmic dependence on h . We derive a general form for this energy in terms of the singular capacitance of two spheres in near contact c (h ) , together with nonsingular geometric features of the cluster. Using this form, we determine the energies of various clusters, finding that more compact clusters are more stable. These energies are proposed to be significant for metal-semiconductor binary nanoparticle lattices found experimentally. We sketch how these effects should dictate the relative abundances of metal nanoparticle clusters in nonpolar solvents.

  6. Bussines Clusters

    Directory of Open Access Journals (Sweden)

    Sarmiza Pencea

    2010-10-01

    Full Text Available Clusters are complex economic structures in which similar companies, their up-stream and down-stream business partners, universities, research institutes, educational units, various service providers, diverse private and public institutions concentrate geografically, striving to get economies of agglomeration and scale, to capitalize on the resulting spill over effects, to cut costs, to better harness resources, to exchange information and experience, to improve quality, innovation, skills and productivity. By somehow unexpectedly combining competition and cooperation, they form a new, sophisticated stage in the evolution of production structures in quest of higher efficiency. This paper forays into the world of clusters and clusterization, which seem to increasingly capture the interest of businesses, scholars and policy makers. It looks at what clusters are, how they arise, what are their specific features, what benefits and challenges they can generate for companies and for the regions in which they locate and if and how they should be fostered by industrial policy interventions. The conclusion is that clusters can be very important development triggers and therefore they should be encouraged and nurtured by adequate policy measures. They should not only be used as a regular policy tool, but be placed at the very center of the development strategies of emerging economies.

  7. Electric-field-modulated exchange coupling within and between magnetic clusters on metal surfaces: Mn dimers on Cu(1 1 1)

    International Nuclear Information System (INIS)

    Juárez-Reyes, L; Pastor, G M; Stepanyuk, V S

    2014-01-01

    The effects of external electric fields (EFs) on the magnetic state and substrate-mediated magnetic coupling between Mn dimers on Cu(1 1 1) have been studied using a first-principles theoretical method. The calculations show that a change in the ground-state magnetic order, from antiferromagnetic (AF) to ferromagnetic (FM), can be induced within an isolated Mn 2 on Cu(1 1 1) by applying a moderately strong EF of about 1 V Å −1 . The magnetic exchange coupling between pairs of dimers displays Ruderman–Kittel–Kasuya–Yosida-like oscillations as a function of the interdimer distance, which depend significantly on the magnetic order within the dimers (FM or AF) and on their relative orientation on the surface. Moreover, it is observed that applying EFs allows modulation of the exchange coupling within and between the clusters as a function of the intercluster distance. At short distances, AF order within the dimers is favoured even in the presence of EFs, while for large distances the EF can induce a FM order. EFs pointing outwards and inwards with respect to the surface favour parallel and antiparallel magnetic alignment between the dimers, resspectively. The dependence of the substrate-mediated interaction on the magnetic state of Mn 2 is qualitatively interpreted in terms of the differences in the scattering of spin-polarized surface electrons. (paper)

  8. Habilidades metalingüísticas, operaciones metacognitivas y su relación con los niveles de competencia en lectura y escritura: un estudio exploratorio Metalinguistic skills, metacognitive operations and their relationship with the different levels of reading and writing competence: an explorative study

    Directory of Open Access Journals (Sweden)

    Rita Flórez Romero

    2005-06-01

    Full Text Available El propósito de este estudio fue explorar las habilidades metalingüísticas, las operaciones metacognitivas y su relación con las competencias en lectura y escritura. Para evaluar las habilidades metalingüísticas se construyó un instrumento basado en la propuesta de van Kleeck (1995, relacionada con la arbitrariedad del lenguaje y el lenguaje como sistema. Para evaluar las operaciones metacognitivas se diseñaron dos pruebas, una para metacognición en lectura y otra para escritura. Para evaluar las competencias en lectura y escritura se aplicaron los instrumentos del proyecto de Evaluación Censal de Competencias Básicas en Lenguaje diseñados por la Secretaría de Educación del Distrito y por la Universidad Nacional. En el análisis de datos se utilizaron estadísticos descriptivos, como medidas de tendencia central y distribución en caso de las variables continuas y distribuciones de frecuencia y tablas de contingencia en el caso de las variables nominales.The authors of this study endeavour to explore the metalinguistic skills, the metacognitive operations and their relationship with the reading and writing competence. For the evaluation of metalinguistic skills an instrument was developed based on van Kleeck’s (1995 proposal, regarding the subjectivity of language and language as a system. Two specimens were designed for the evaluation of metacognitive operations, one for reading and another one for writing metacognition. For the evaluation of reading and writing competence the project instruments for the Census Evaluation of Basic Language Competence, designed by the District Secretary of Education and by the National University, was applied. In the data evaluation descriptive statistics were applied, as a measure of core tendency in the case of continuous variables, and frequency distributions and tables of contiguity in the case of nominal variables.

  9. Thermodynamic basis for cluster kinetics

    DEFF Research Database (Denmark)

    Hu, Lina; Bian, Xiufang; Qin, Xubo

    2006-01-01

    Due to the inaccessibility of the supercooled region of marginal metallic glasses (MMGs) within the experimental time window, we study the cluster kinetics above the liquidus temperature, Tl, to acquire information on the fragility of the MMG systems. Thermodynamic basis for the stability...

  10. Crystallization of organically templated phosphomolybdate cluster ...

    Indian Academy of Sciences (India)

    cluster based solids were isolated in the presence of en (ethylenediamine) by controlling pH of the reaction medium. The lower-valent cluster invariably requires the presence of a suitable metal cation for further sta- bilization. A detailed investigation of the system was carried out where three different weak acids viz. oxalic.

  11. Pressure-induced superconductivity in the semiconducting metal-cluster compounds Ga(Ta,Nb) sub 4 (Se,S) sub 8

    CERN Document Server

    Ni Bing Fa

    2002-01-01

    The effect of pressure on the electronic and structural properties of GaNb sub 4 Se sub 8 , GaNb sub 4 S sub 8 and GaTa sub 4 Se sub 8 has been investigated. Measurements of the magnetic susceptibility and electrical resistance at ambient pressure showed anomalies at low temperatures (GaNb sub 4 Se sub 8 and GaNb sub 4 S sub 8 : 35 K; GaTa sub 4 Se sub 8 : 55 K). These are suggested to be related to a structural distortion of a lower symmetry which results in a change of the population of spin states. The analysis of the temperature dependence of the electrical resistance as a function of increasing pressure shows a transition from semiconducting to metallic behavior in GaNb sub 4 Se sub 8 (p>22.5 GPa) and in GaTa sub 4 Se sub 8 (p>13 GPa) but not in GaNb sub 4 S sub 8 up to p=31 GPa. This has been explained to be due to stronger localized Nb(4d)-states (larger energy gap) than in GaNb sub 4 Se sub 8 and Ta(5d)-states in GaTa sub 4 Se sub 8. Most interesting is the observation of a pressure-induced supercondu...

  12. Robust Fe3Mo3C Supported IrMn Clusters as Highly Efficient Bifunctional Air Electrode for Metal-Air Battery.

    Science.gov (United States)

    Cui, Zhiming; Li, Yutao; Fu, Gengtao; Li, Xiang; Goodenough, John B

    2017-10-01

    Catalysts at the air cathode for oxygen reduction and evolution reactions are central to the stability of rechargeable metal-air batteries, an issue that is gaining increasing interest in recent years. Herein, a highly durable and efficient carbide-based bifunctional catalyst consisting of iron-molybdenum carbide (Fe 3 Mo 3 C) and IrMn nanoalloys is demonstratred. This carbide is chemically stable in alkaline media and over the potential range of an air cathode. More importantly, Fe 3 Mo 3 C is very active for oxygen reduction reaction (ORR) in alkaline media. Fe 3 Mo 3 C supported IrMn as a bifunictional catalysts exhibits superior catalytic performance than the state of the art ORR catalyst (Pt/C) and the oxygen evolution reaction catalyst (Ir/C). IrMn/Fe 3 Mo 3 C enables Zn-air batteries to achieve long-term cycling performance over 200 h with high efficiency. The extraordinarily high performance of IrMn/Fe 3 Mo 3 C bifunictional catalyst provides a very promising alternative to the conventional Pt/C and Ir/C catalyst for an air cathode in alkaline electrolyte. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  13. DNA-Protected Silver Clusters for Nanophotonics

    Directory of Open Access Journals (Sweden)

    Elisabeth Gwinn

    2015-02-01

    Full Text Available DNA-protected silver clusters (AgN-DNA possess unique fluorescence properties that depend on the specific DNA template that stabilizes the cluster. They exhibit peak emission wavelengths that range across the visible and near-IR spectrum. This wide color palette, combined with low toxicity, high fluorescence quantum yields of some clusters, low synthesis costs, small cluster sizes and compatibility with DNA are enabling many applications that employ AgN-DNA. Here we review what is known about the underlying composition and structure of AgN-DNA, and how these relate to the optical properties of these fascinating, hybrid biomolecule-metal cluster nanomaterials. We place AgN-DNA in the general context of ligand-stabilized metal clusters and compare their properties to those of other noble metal clusters stabilized by small molecule ligands. The methods used to isolate pure AgN-DNA for analysis of composition and for studies of solution and single-emitter optical properties are discussed. We give a brief overview of structurally sensitive chiroptical studies, both theoretical and experimental, and review experiments on bringing silver clusters of distinct size and color into nanoscale DNA assemblies. Progress towards using DNA scaffolds to assemble multi-cluster arrays is also reviewed.

  14. Photoionization Spectroscopy of Clusters

    Science.gov (United States)

    Dao, Phan Danh

    Studies of the electronic energies in van der Waals molecules (sometimes referred to as clusters or complexes) help one unravel the microscopic details of the condensed state. Furthermore, they provide the connection between gas-phase and condensed-phase sciences. To achieve this goal, we undertake (1) the spectroscopic studies of van der Waals complexes; (2) the determination of the ionization energies of van der Waals complexes, as well as of mixed alkali metal clusters (e.g., K(,n)O); and (3) the studies of processes that occur upon and after the ionization of van der Waals molecules (namely, dissociation and intracluster reactions). A brief discussion of the non-equilibrium synthesis of weakly bound molecules is given. The operation and performance of the pulsed supersonic jet are described along with some theoretical considerations. The characteristic features of the technique of laser ionization are presented with emphasis on its performance as a spectroscopic tool. Resonance two-photon ionization and time-of-flight mass spectrometry provide us with the tool to measure the perturbed electronic excited state of van der Waals complexes. In these studies, the chromophore species is an aromatic molecule having a single ring (phenylacetylene and para-xylene); and the "solvent" species are rare gas atoms, as well as a variey of molecules. In the case of chromophore-rare gas complexes, the S(,1) excited state is red-shifted, with respect to the nascent chromophore, and the magnitude of the shift shows a definite dependence on the atomic polarizability. Other salient trends of the measured spectral shifts are also discussed. In the measurement of complex ionization energies, the use of two tunable UV lasers is required. With p-xylene(.)Ar(,n) complexes (n = 1-6), these energies vary almost linearly with the number of atoms. Also discussed in the text are the effects of ionization in a weak DC field. A simple hydrogenic model of field-ionization is experimentally

  15. Fuzzy Clustering

    DEFF Research Database (Denmark)

    Berks, G.; Keyserlingk, Diedrich Graf von; Jantzen, Jan

    2000-01-01

    and clustering are the basic concerns in medicine. Classification depends on definitions of the classes and their required degree of participant of the elements in the cases' symptoms. In medicine imprecise conditions are the rule and therefore fuzzy methods are much more suitable than crisp ones. Fuzzy c...

  16. Cluster Matters

    DEFF Research Database (Denmark)

    Gulati, Mukesh; Lund-Thomsen, Peter; Suresh, Sangeetha

    2018-01-01

    In this chapter, we investigate corporate social responsibility (CSR) in industrial clusters in the Indian context. We use the definition of CSR as given in the Indian Ministry of Corporate Affairs’ National Voluntary Guidelines (NVGs) for Business Responsibility: ‘the commitment of an enterprise...

  17. Inorganic-organic hybrid materials with different dimensions constructed from copper-fluconazole metal-organic units and Keggin polyanion clusters.

    Science.gov (United States)

    Li, Shun-Li; Lan, Ya-Qian; Ma, Jian-Fang; Yang, Jin; Liu, Jie; Fu, Yao-Mei; Su, Zhong-Min

    2008-04-21

    Inorganic-organic hybrid materials based on Keggin polyoxometalate building blocks combined with Cu(II)/Cu(I) and flexible fluconazole ligand [1-(2,4-difluorophenyl)-1,1-bis[(1H-1,2,4-triazol-1-yl)methyl]methanol] (Hfcz) have been obtained by hydrothermal methods, namely, [Cu(II)(2)(Hfcz)(4)(SiW(12)O(40))].3H(2)O (1), [Cu(II)(4)(fcz)(4)(H(2)O)(4)(SiMo(12)O(40))].6H(2)O (2), [Cu(II)(2)(fcz)(2)][Cu(II)(4)(fcz)(4)(SiW(12)O(40))][Cu(II)(2)(fcz)(2)(H(2)O)(2)(SiW(12)O(40))].6H(2)O (3), (Et(3)NH)(2)[Cu(I)(2)(Hfcz)(2)(SiW(12)O(40))].2H(2)O (4), (Et(3)NH)(2)[Cu(I)(2)(Hfcz)(2)(SiW(12)O(40))].H(2)O (5) and [Cu(I)(4)(Hfcz)(4)(SiMo(12)O(40))] (6). Their structures have been determined by single-crystal X-ray diffraction analyses, and the compounds are further characterized by elemental analyses, IR spectra and thermogravimetric (TG) analyses. In 1, Cu(II) cations are bridged by fluconazole ligands to form a 3D lvt coordination polymeric network, which is connected by (SiW(12)O(40))(4-) anions to form a complicated 3D (4,6)-connected framework with the topology of (4(2).6(4))(4(6).6(7).8(2))(2). In 2, two fcz(-) anions chelate two Cu(2+) cations to form a [Cu(fcz)](2)(2+) dimer, which is bridged by (SiW(12)O(40))(4-) polyanions to generate a 2D (4,4) grid. Compound 3 is formed by three types of co-crystallizing subunits including a dimer [Cu(fcz)](2)(2+), a dumbbell molecule [Cu(4)(fcz)(4)(SiW(12)O(40))] and an infinite chain {[Cu(2)(fcz)(2)(H(2)O)(2)(SiW(12)O(40))](2-)}(infinity). In compounds 4 and 5, Hfcz ligands link Cu(+) cations to generate 1D coordination polymeric units, and (SiW(12)O(40))(4-) polyanions connect these metal-organic units to form two types of (6(3)) sheets which are topological isomerism. In compound 6, (SiMo(12)O(40))(4-) polyanions fixed in Cu(I)-Hfcz square rings are further extended into a 2D sheet via linking Cu(I) atoms of different rings. By carefully inspection of the structures of 1-6, it is believed that various transition-metal organic units

  18. Modern aspects on tri-and tetranuclear cluster complexes supported ...

    Indian Academy of Sciences (India)

    http://www.ias.ac.in/article/fulltext/jcsc/112/03/0209-0213. Keywords. Heterometallic cluster complexes; hydroformylation catalysts; topomerization process; diastereomers; isomerization process. Abstract. This report on small cluster complexes with metal-metal bonds in the field of coordination chemistry documents results in ...

  19. Linked supramolecular building blocks for enhanced cluster formation

    DEFF Research Database (Denmark)

    McLellan, Ross; Palacios, Maria A.; Beavers, Christine M.

    2015-01-01

    the complex assembly process. The ability to covalently link calix[4]arenes at the methylene bridge provides significantly improved control over the introduction of different metal centres to resulting cluster motifs. Clusters assembled from bis-calix[4]-arenes and transition metal ions or 3d-4 f combinations...

  20. Cluster forcing

    DEFF Research Database (Denmark)

    Christensen, Thomas Budde

    , Portugal and New Zealand have adopted the concept. Public sector interventions that aim to support cluster development in industries most often focus upon economic policy goals such as enhanced employment and improved productivity, but rarely emphasise broader societal policy goals relating to e.......g. sustainability or quality of life. The purpose of this paper is to explore how and to what extent public sector interventions that aim at forcing cluster development in industries can support sustainable development as defined in the Brundtland tradition and more recently elaborated in such concepts as eco...... in 2000 by the Welsh Automotive Task Force under the Welsh Assembly Government. The Accelerate programme takes basically different two directions: The first one, which was the first to be launched, is concerned with the upgrading of existing supply chains in the automotive industry in Wales. The programme...

  1. Regional Innovation Clusters

    Data.gov (United States)

    Small Business Administration — The Regional Innovation Clusters serve a diverse group of sectors and geographies. Three of the initial pilot clusters, termed Advanced Defense Technology clusters,...

  2. Estudios de visitantes a museos

    Directory of Open Access Journals (Sweden)

    Keilyn Rodríguez Sánchez

    2011-01-01

    Full Text Available Este artículo ofrece un estudio bibliográfico en torno a las investigaciones sobre la relación entre la museografía y sus visitantes. El objetivo central de este documento consiste en elaborar una clasificación de esos estudios en programas de investigación de manera que sirva de punto de partida para la construcción de una pedagogía del Museo. Para este fin, se utiliza la propuesta de Schulman, sobre tipificación de estudios en programas de investigación y, al respecto, se plantean cuatro tipos: investigaciones centradas en lo museográfico, investigaciones centradas en el comportamiento museal, investigaciones centradas en la interacción dispositivo-visitantes y las investigaciones centradas en la evaluación museográfica. Se concluye que los resultados de investigación de estos programas, junto con el conocimiento de las técnicas de diseño y a la teoría educativa, serían la base central de un planteamiento sobre pedagogía museológica.

  3. Modeling the formation of globular cluster systems in the Virgo cluster

    International Nuclear Information System (INIS)

    Li, Hui; Gnedin, Oleg Y.

    2014-01-01

    The mass distribution and chemical composition of globular cluster (GC) systems preserve fossil record of the early stages of galaxy formation. The observed distribution of GC colors within massive early-type galaxies in the ACS Virgo Cluster Survey (ACSVCS) reveals a multi-modal shape, which likely corresponds to a multi-modal metallicity distribution. We present a simple model for the formation and disruption of GCs that aims to match the ACSVCS data. This model tests the hypothesis that GCs are formed during major mergers of gas-rich galaxies and inherit the metallicity of their hosts. To trace merger events, we use halo merger trees extracted from a large cosmological N-body simulation. We select 20 halos in the mass range of 2 × 10 12 to 7 × 10 13 M ☉ and match them to 19 Virgo galaxies with K-band luminosity between 3 × 10 10 and 3 × 10 11 L ☉ . To set the [Fe/H] abundances, we use an empirical galaxy mass-metallicity relation. We find that a minimal merger ratio of 1:3 best matches the observed cluster metallicity distribution. A characteristic bimodal shape appears because metal-rich GCs are produced by late mergers between massive halos, while metal-poor GCs are produced by collective merger activities of less massive hosts at early times. The model outcome is robust to alternative prescriptions for cluster formation rate throughout cosmic time, but a gradual evolution of the mass-metallicity relation with redshift appears to be necessary to match the observed cluster metallicities. We also affirm the age-metallicity relation, predicted by an earlier model, in which metal-rich clusters are systematically several billion younger than their metal-poor counterparts.

  4. Cluster Ion Implantation in Graphite and Diamond

    DEFF Research Database (Denmark)

    Popok, Vladimir

    2014-01-01

    Cluster ion beam technique is a versatile tool which can be used for controllable formation of nanosize objects as well as modification and processing of surfaces and shallow layers on an atomic scale. The current paper present an overview and analysis of data obtained on a few sets of graphite...... and diamond samples implanted by keV-energy size-selected cobalt and argon clusters. One of the emphases is put on pinning of metal clusters on graphite with a possibility of following selective etching of graphene layers. The other topic of concern is related to the development of scaling law for cluster...

  5. Subnanometer to nanometer transition metal CO oxidation catalysts

    Energy Technology Data Exchange (ETDEWEB)

    Vajda, Stefan; Fortunelli, Alessandro; Yasumatsu, Hisato

    2017-12-26

    The present invention provides a catalyst defined in part by a conductive substrate; a film overlaying a surface of the substrate; and a plurality of metal clusters supported by the layer, wherein each cluster comprises between 8 and 11 atoms. Further provided is a catalyst defined in part by a conductive substrate; a layer overlaying a surface of the substrate; and a plurality of metal clusters supported by the layer, wherein each cluster comprises at least two metals.

  6. Silver clusters from nozzle expansions

    International Nuclear Information System (INIS)

    Hagena, O.F.

    1990-01-01

    This note reports on the first successful experiments to generate silver clusters (N≤100) in supersonic nozzle flows. A mixture of argon/silver-vapor was used expanding from a conical nozzle (0.35 mm, 10deg full cone angle, 17 mm long conical section). Source temperature and total pressure ranged up to 2200 K/300 kPa, and silver partial pressure up to 25 kPa. The data confirm the scaling laws developed to compare clustering of metals with that of rare gases. (orig.)

  7. Asteroseismic inferences on red giants in open clusters NGC 6791, NGC 6819, and NGC 6811 using Kepler

    DEFF Research Database (Denmark)

    Hekker, S.; Basu, S.; Stello, D.

    2011-01-01

    and metallicity contribute to the observed difference in locations in the H-R diagram of the old metal-rich cluster NGC 6791 and the middle-aged solar-metallicity cluster NGC 6819. For the young cluster NGC 6811, the explanation of the position of the stars in the H-R diagram challenges the assumption of solar...

  8. La reflexión metalingüística de los alumnos de 4º de ESO, 2º de Bachillerato y 3º de Grado en Estudios Hispánicos que implica la alteración del orden oracional / The metalinguistic reflection of students in 4th grade Secondary School, 2nd of Bachillerato and 3rd year Degree in Hispanic Studies that involve the change of the sentence order

    OpenAIRE

    Raquel Badía Iborra

    2014-01-01

    Resumen: Este artículo presenta los datos de una investigación en la que se pretende estudiar cómo los alumnos de 4º de ESO, 2º de Bachillerato y 3º de Grado en Estudios Hispánicos realizan reflexiones metalingüísticas al verse obligados a explicar las diferencias de significado pragmático que implica la alteración del orden oracional (SVO) en español. Todos estos datos son extraídos a través de una prueba escrita realizada a dos parejas de alumnos de cada curso, un cuestionario en el que deb...

  9. Los muertos del Floreanismo (Estudios)

    OpenAIRE

    Ayala Mora, Enrique

    2008-01-01

    El artículo analiza el crimen político durante las primeras décadas de vida de la República del Ecuador. Específicamente centra su estudio en el período dominado por la figura de Juan José Flores, primer presidente del Ecuador. La inestabilidad política, la precariedad de las alianzas entre las élites regionales, la crisis económica generada por las guerras de independencia, las conspiraciones y la violencia que caracterizaron al período de surgimiento de las repúblicas andinas hicieron del c...

  10. Esclavizada en los Estudios Poscoloniales

    Directory of Open Access Journals (Sweden)

    Nellys Montenegro De la Hoz

    2014-01-01

    Full Text Available Este ensayo va a centrarse en el análisis de las formas de resis - tencia e identidad esclavizada presentes en Changó, el gran putas de Manuel Zapata Olivella, a través del análisis de los discur - sos hegemónicos y subalternos que hacían parte del sistema de poder, y la intervención de las teorías o estudios poscoloniales que cuestionan dichas perspectivas para redefinir las diferencias de las identidades contradictorias y desarrollar de esta manera literaturas deslindadas de las estructuras ideológicas y hegemónicas.

  11. Fusion and fission of atomic clusters: recent advances

    DEFF Research Database (Denmark)

    Obolensky, Oleg I.; Solov'yov, Ilia; Solov'yov, Andrey V.

    2005-01-01

    developed an effective scheme of adding new atoms to stable cluster geometries of larger clusters in an efficient way. We apply this algorithm to finding geometries of metal and noble gas clusters. For the fission process the analysis of the potential energy landscape calculated on the ab initio level...... of theory allowed us to obtain very detailed information on energetics and pathways of the different fission channels for the Na^2+_10 clusters....

  12. Study of the leaching of heavy metals from waste water sludge and incinerator's ash, using coupled thermostated columns and DTPA as complex agent; Estudio de la extraccion de metales pesados de lodos y cenizas de aguas residuales usando columnas termostatizadas acopladas y DTPA como agente complejante

    Energy Technology Data Exchange (ETDEWEB)

    Vite T, J.; Vite T, M.; Guerrero D, J.; Carreno de Leon, M.C. [Departamento de Estudios del Ambiente, Instituto Nacional de Investigaciones Nucleares, A.P. 18-1027, 11801 Mexico D.F. (Mexico)

    2000-07-01

    We studied the metallic composition from waste water sludge and incinerators ashes of an incinerator located in Toluca, Mexico, the qualitative studies were made using the Activation Analysis technique, and fluorescence X-ray techniques. The quantitative analysis of heavy metals in the wastes were made using Inductively coupled plasma atomic emission spectrometry (Icp-Aes). For leaching the samples, we used four coupled thermostated columns, each one had a p H of 2,5, 7 and 10. The flux of the air was of 1600 cc/min. The temperature was maintain constant in 60 Centigrade using a thermostated system. For this study we used 100 g of wastes mixed with mineral acid or sodium hydroxide to reach p H 2,5,7 and 10. We added a reducing and tensoactive agents and finally DTPA as complex agent. With this method, we obtain a better leaching efficiency using a complex agent. However the high DTPA cost, make this process expansive that is why we recommend to work with another classes of complex agents, that be cheaper to leach metals of different chemistry matrix. (Author)

  13. Novel Metal Clusters for Imaging Applications

    KAUST Repository

    Alsaiari, Shahad K.

    2014-05-01

    During the past few years, gold nanoparticles (AuNPs) have received considerable attention in many fields due to their optical properties, photothermal effect and biocompatibility. AuNPs, particularly AuNCs and AuNRs, exhibit great potential in diagnostics and imaging. In the present study, AuNCs were used to selectively image and quantify intracellular antioxidants. It was reported by Chen et al. that the strong fluorescence of AuNCs is quenched by highly reactive oxygen species (hROS). Most of applications depend on fluorescence quenching, however, for our project we designed turn-on fluorescent sensors using AuNCs that sense antioxidants. In the presence of antioxidants, AuNCs fluorescence switch on, while in the absence of antioxidants their fluorescence immediately turn off due to hROS effect. AuNRs were also used for cellular imaging in which AuNRs were conjugated to Cy3-labelled molecular beacon (MB) DNA. Next, the previous complex was loaded in two different strains of magnetotactic bacteria (MTB). MTB were used as a targeted delivery vehicle in which magnetosomes direct the movement of bacteria. The DNA sequence was specific to a certain sequence in mitochondria. The exposure of MTB to an alternating magnetic field (AMF) leads to the increase of temperature inside the bacteria, which destruct the cell wall, and hence, bacterial payload is released. When MD-DNA hybrid with the target sequence, AuNR and Cy3 separate from each other, the fluorescence of the Cy3 is restored.

  14. Near infrared photometry of globular clusters

    International Nuclear Information System (INIS)

    Evans, T.L.; Menzies, J.W.

    1977-01-01

    Photographic photometry on the V, Isub(K) system has been obtained for giant stars in the metal-rich globular clusters NGC 5927, 6171, 6352, 6356, 6388, 6522, 6528, 6712 and 6723. Colour-magnitude diagrams are presented. These data, with earlier observations of NGC 104 (47 Tuc), yield new parameters to describe the giant branch. These are the colour of the red variables, represented by their mean colour (V - Isub(K)) 0 or by the colour (V - Isub(K))sub(BO) of the bluest red variable on the giant branch of a cluster, and ΔV' which is the magnitude difference between the horizontal branch and the highest point on the giant branch. The latter is independent of reddening, since the giant branch of the most metal-rich clusters passes through a maximum in the V, V - Isub(K) plane. These parameters are correlated with the metal content, deduced from integrated photometry: the red variables are redder and the giant branch fainter the higher the metal content. Comparison with theoretical evolutionary tracks suggests that the range in metal content of these clusters is at most a factor of 10, the most metal-rich clusters possibly approaching the solar value. The cluster giant branches and those of open clusters, groups and field stars of the old disk population are compared. The assumption that all the globular clusters have an absolute magnitude on the horizontal branch of Msub(v) = + 0.9, as found recently for 47 Tuc, gives good agreement between the magnitudes of giant stars in the most metal rich of the globular clusters and those of field stars deduced from statistical parallaxes and moving group parallaxes. The values of the parameters ΔV' and (V - Isub(k))sub(BO) also approach those in the moving groups. The globular clusters have a longer horizontal branch, however, and the subgiants are bluer even when the values of ) 7Fe/H{ appear to be the same. (author). )

  15. Comparative study of formation and stabilization of Gold and Silver Clusters and Nanoparticles in Mordenites

    NARCIS (Netherlands)

    Bogdanchikova, N.; Tuzovskaya, I.; Pestryakov, A.; Susarrey Arce, A.

    2011-01-01

    Supporting silver and gold on mordenites by ion-exchange method with further reduction with H2 leads to formation of neutral and charged metal clusters inside zeolite channels as well as metal nanoparticles on external surface of mordenite. A portion of the cluster states of the metals and stability

  16. Heavy hitters via cluster-preserving clustering

    DEFF Research Database (Denmark)

    Larsen, Kasper Green; Nelson, Jelani; Nguyen, Huy L.

    2016-01-01

    , providing correctness whp. In fact, a simpler version of our algorithm for p = 1 in the strict turnstile model answers queries even faster than the "dyadic trick" by roughly a log n factor, dominating it in all regards. Our main innovation is an efficient reduction from the heavy hitters to a clustering...... problem in which each heavy hitter is encoded as some form of noisy spectral cluster in a much bigger graph, and the goal is to identify every cluster. Since every heavy hitter must be found, correctness requires that every cluster be found. We thus need a "cluster-preserving clustering" algorithm......, that partitions the graph into clusters with the promise of not destroying any original cluster. To do this we first apply standard spectral graph partitioning, and then we use some novel combinatorial techniques to modify the cuts obtained so as to make sure that the original clusters are sufficiently preserved...

  17. Cluster plasma and its dispersion relation

    International Nuclear Information System (INIS)

    Tajima, T.; Downer, M.C.; Kishimoto, Y.

    1998-01-01

    It is shown that unlike a gas plasma or an electron plasma in a metal, an ionized cluster material (open-quotes cluster plasmaclose quotes) permits propagation below the plasma cut-off of electromagnetic (EM) waves whose phase velocity is close to but below the speed of light. Its unique properties allow a variety of applications, including direct acceleration of particles with its EM fields and the phase matching of waves of high harmonic generation (HHG)

  18. Dynamic of Faceted Colloidal Clusters

    Science.gov (United States)

    Sindoro, Melinda; Jee, Ah-Young; Yu, Changqian; Granick, Steve

    2014-03-01

    We study the emulsion induced clustering of faceted metal organic frameworks (MOFs) and their dynamics. Our approach to anisotropic building block is through the rational synthesis of water stable and highly uniform MOFs. This generates colloidal-sized MOFs of defined polyhedral shape with tunable size in micrometer range that are suitable for in situ imaging. The 3D clusters formations are promoted by hydrophilic MOFs particles confined in aqueous droplets of binary water-lutidine mixture at transition temperature. Below this temperature, the water droplet decreases in volume due to one phase mixing with lutidine which forces the N-mers of faceted particles to aggregate in close contact. We compare the faceted clusters formed to those made of spherical particles in term of the building block sphericity. Other focus of our study involves the dynamic of the clusters. We found that, unlike spherical clusters, these faceted N-mers are highly stable on large scale of temperature due to their dominant capillary force on their facet-to-facet contact.

  19. Brightest Cluster Galaxies in REXCESS Clusters

    Science.gov (United States)

    Haarsma, Deborah B.; Leisman, L.; Bruch, S.; Donahue, M.

    2009-01-01

    Most galaxy clusters contain a Brightest Cluster Galaxy (BCG) which is larger than the other cluster ellipticals and has a more extended profile. In the hierarchical model, the BCG forms through many galaxy mergers in the crowded center of the cluster, and thus its properties give insight into the assembly of the cluster as a whole. In this project, we are working with the Representative XMM-Newton Cluster Structure Survey (REXCESS) team (Boehringer et al 2007) to study BCGs in 33 X-ray luminous galaxy clusters, 0.055 < z < 0.183. We are imaging the BCGs in R band at the Southern Observatory for Astrophysical Research (SOAR) in Chile. In this poster, we discuss our methods and give preliminary measurements of the BCG magnitudes, morphology, and stellar mass. We compare these BCG properties with the properties of their host clusters, particularly of the X-ray emitting gas.

  20. Partitional clustering algorithms

    CERN Document Server

    2015-01-01

    This book summarizes the state-of-the-art in partitional clustering. Clustering, the unsupervised classification of patterns into groups, is one of the most important tasks in exploratory data analysis. Primary goals of clustering include gaining insight into, classifying, and compressing data. Clustering has a long and rich history that spans a variety of scientific disciplines including anthropology, biology, medicine, psychology, statistics, mathematics, engineering, and computer science. As a result, numerous clustering algorithms have been proposed since the early 1950s. Among these algorithms, partitional (nonhierarchical) ones have found many applications, especially in engineering and computer science. This book provides coverage of consensus clustering, constrained clustering, large scale and/or high dimensional clustering, cluster validity, cluster visualization, and applications of clustering. Examines clustering as it applies to large and/or high-dimensional data sets commonly encountered in reali...

  1. Atomic bonding between metal and graphene

    KAUST Repository

    Wang, Hongtao

    2013-03-07

    To understand structural and chemical properties of metal-graphene composites, it is crucial to unveil the chemical bonding along the interface. We provide direct experimental evidence of atomic bonding between typical metal nano structures and graphene, agreeing well with density functional theory studies. Single Cr atoms are located in the valleys of a zigzag edge, and few-atom ensembles preferentially form atomic chains by self-assembly. Low migration barriers lead to rich dynamics of metal atoms and clusters under electron irradiation. We demonstrate no electron-instigated interaction between Cr clusters and pristine graphene, though Cr has been reported to be highly reactive to graphene. The metal-mediated etching is a dynamic effect between metal clusters and pre-existing defects. The resolved atomic configurations of typical nano metal structures on graphene offer insight into modeling and simulations on properties of metal-decorated graphene for both catalysis and future carbon-based electronics. © 2013 American Chemical Society.

  2. Estudio de la fertilidad y de los metales pesados en suelos de agroecosistemas tropicales de una zona transfronteriza de la República Dominicana-Haití Fertility and heavy metal contents of soils in the tropical agroecosys­tems of the Dominican Republic-Haiti frontier zone

    Directory of Open Access Journals (Sweden)

    J. Pastor

    2010-01-01

    Full Text Available Se exponen los datos referidos a la cuanti­ficación de la fertilidad, MO. y metales pe­sados en la capa superficial de los suelos de 30 agroecosistemas tropicales en tres tipos de bosques (nublado, latifoliado y seco, co­rrespondientes a un territorio de marcada pobreza (suroeste de la República Domini­cana-Haití. El desarrollo de una agricultura sostenible en la zona requiere evaluar la fer­tilidad de los suelos; problema fundamental debido al cambio que sufren sus caracterís­ticas físicas y químicas cuando se talan y queman los bosques y luego se cultivan. La información respecto a los suelos del territo­rio es prácticamente nula, por lo que este trabajo constituye una aportación, especial­mente para la cuenca hidrográfica transfron­teriza del río Pedernales. Los agroecosistemas estudiados se en­cuentran mayoritariamente comprendidos entre los 1200 m de altitud y el nivel del mar y constituyen las fuentes esenciales pa­ra la alimentación humana y animal: pastos y cultivos de habichuela, maíz, sorgo, café, plátano-guineo, frutales y tubérculos.This paper reports fertility, organic matter and heavy metal data obtained in topsoil samples from 30 tropical agroecosystems in three types of forest (rain, latifoliated and dry in an area of extreme poverty (SE Do­minican Republic-Haiti. For sustainable ag­ricultural practice in this zone, soil fertility needs to be first assessed since this factor has been severely compromised by changes in the physical and chemical properties of the soil induced by the felling and burning of trees to make way for crops. Information on the soils of the region is practically null. This study focuses mainly on the transfrontier basin of the Pedernales River. The agroecosystems examined occur from an altitude of 1200 m to sea level and are the main food sources for human and animal consumption: bean, corn, sorghum, coffee, Guinea banana, fruit trees and tu­bers.

  3. Diversity among galaxy clusters

    International Nuclear Information System (INIS)

    Struble, M.F.; Rood, H.J.

    1988-01-01

    The classification of galaxy clusters is discussed. Consideration is given to the classification scheme of Abell (1950's), Zwicky (1950's), Morgan, Matthews, and Schmidt (1964), and Morgan-Bautz (1970). Galaxies can be classified based on morphology, chemical composition, spatial distribution, and motion. The correlation between a galaxy's environment and morphology is examined. The classification scheme of Rood-Sastry (1971), which is based on clusters's morphology and galaxy population, is described. The six types of clusters they define include: (1) a cD-cluster dominated by a single large galaxy, (2) a cluster dominated by a binary, (3) a core-halo cluster, (4) a cluster dominated by several bright galaxies, (5) a cluster appearing flattened, and (6) an irregularly shaped cluster. Attention is also given to the evolution of cluster structures, which is related to initial density and cluster motion

  4. Mass and velocity distributions of low energy cluster beams

    Energy Technology Data Exchange (ETDEWEB)

    Compagnini, Giuseppe [Dipartimento di Scienze Chimiche Universita di Catania and MATIS-INFM, Viale A. Doria 6 Catania 95125 (Italy)]. E-mail: gcompagnini@unict.it; D' Urso, Luisa [Dipartimento di Scienze Chimiche Universita di Catania and MATIS-INFM, Viale A. Doria 6 Catania 95125 (Italy); Puglisi, Orazio [Dipartimento di Scienze Chimiche Universita di Catania and MATIS-INFM, Viale A. Doria 6 Catania 95125 (Italy)

    2006-07-15

    We have recently generated several low energy cluster beams by using a laser vaporization source and a pulsed He stream. This has been done both for covalent (silicon and carbon) and metallic (gold) materials. In this work we present a simple procedure to carefully measure the speed and speed distribution of the obtained clusters with the help of an orthogonal time of flight mass spectrometer. Results show average speed values in the range 700-1000 m/s with a mild variation by changing the gas backing pressure and the cluster mass inside each cluster train. Detailed speed distributions for each cluster's mass will be given.

  5. Clustering of correlated networks

    OpenAIRE

    Dorogovtsev, S. N.

    2003-01-01

    We obtain the clustering coefficient, the degree-dependent local clustering, and the mean clustering of networks with arbitrary correlations between the degrees of the nearest-neighbor vertices. The resulting formulas allow one to determine the nature of the clustering of a network.

  6. Cluster knockout reactions

    Indian Academy of Sciences (India)

    2014-04-07

    Apr 7, 2014 ... Cluster knockout reactions are expected to reveal the amount of clustering (such as that of , d and even of heavier clusters such as 12C, 16O etc.) in the target nucleus. In simple terms, incident medium high-energy nuclear projectile interacts strongly with the cluster (present in the target nucleus) as if it ...

  7. What Makes Clusters Decline?

    DEFF Research Database (Denmark)

    Østergaard, Christian Richter; Park, Eun Kyung

    2015-01-01

    Most studies on regional clusters focus on identifying factors and processes that make clusters grow. However, sometimes technologies and market conditions suddenly shift, and clusters decline. This paper analyses the process of decline of the wireless communication cluster in Denmark. The longit...

  8. XMM-Newton Observations of the Toothbrush and Sausage Clusters

    Science.gov (United States)

    Kara, S.; Mernier, F.; Ezer, C.; Akamatsu, H.; Ercan, E.

    2017-10-01

    Galaxy clusters are the largest gravitationally-bound objects in the universe. The member galaxies are embedded in a hot X-ray emitting Intra Cluster Medium (ICM) that has been enriched with metals produced by supernovae over the last billion years. Here we report new results from XMM-Newton archival observations of the merging clusters 1RXSJ0603.3+4213 and CIZA J2242.8+5301. These two clusters, also known as the Toothbrush and Sausage clusters, respectively, show a large radio relic associated with a merger shock North of their respective core. We show the distribution of the metal abundances with respect to the merger structures in these two clusters. The results are derived from spatially resolved X-ray spectra from the EPIC instrument on board XMM-Newton.

  9. Atomic and electronic structure of clusters from car-Parrinello method

    International Nuclear Information System (INIS)

    Kumar, V.

    1994-06-01

    With the development of ab-initio molecular dynamics method, it has now become possible to study the static and dynamical properties of clusters containing up to a few tens of atoms. Here I present a review of the method within the framework of the density functional theory and pseudopotential approach to represent the electron-ion interaction and discuss some of its applications to clusters. Particular attention is focussed on the structure and bonding properties of clusters as a function of their size. Applications to clusters of alkali metals and Al, non-metal - metal transition in divalent metal clusters, molecular clusters of carbon and Sb are discussed in detail. Some results are also presented on mixed clusters. (author). 121 refs, 24 ifigs

  10. Tuning Properties in Silver Clusters

    KAUST Repository

    Joshi, Chakra Prasad

    2015-07-09

    The properties of Ag nanoclusters are not as well understood as those of their more precious Au cousins. However, a recent surge in the exploration of strategies to tune the physicochemical characteristics of Ag clusters addresses this imbalance, leading to new insights into their optical, luminescence, crystal habit, metal-core, ligand-shell and environmental properties. In this Perspective, we provide an overview of the latest strategies along with a brief introduction of the theoretical framework necessary to understand the properties of silver nanoclusters and the basis for their tuning. The advances in cluster research and the future prospects presented in this Perspective will eventually guide the next large systematic study of nanoclusters, resulting in a single collection of data similar to the periodic table of elements.

  11. Clustering in analytical chemistry.

    Science.gov (United States)

    Drab, Klaudia; Daszykowski, Michal

    2014-01-01

    Data clustering plays an important role in the exploratory analysis of analytical data, and the use of clustering methods has been acknowledged in different fields of science. In this paper, principles of data clustering are presented with a direct focus on clustering of analytical data. The role of the clustering process in the analytical workflow is underlined, and its potential impact on the analytical workflow is emphasized.

  12. Study and characterization of noble metal deposits on similar rusty surfaces to those of the reactor U-1 type BWR of nuclear power station of Laguna Verde; Estudio y caracterizacion de depositos de metales nobles sobre superficies oxidadas similares a las del reactor de la Central de Laguna Verde (CNLV) U1 del tipo BWR

    Energy Technology Data Exchange (ETDEWEB)

    Flores S, V. H.

    2011-07-01

    In the present investigation work, were determined the parameters to simulate the conditions of internal oxidation reactor circulation pipes of the nuclear power plant of Laguna Verde in Veracruz. We used 304l stainless steel cylinders with two faces prepared with abrasive paper of No. 600, with the finality to obtain similar surface to the internal circulation piping nuclear reactor. Oxides was formed within an autoclave (Autoclave MEX-02 unit B), which is a device that simulates the working conditions of the nuclear reactor, but without radiation generated by the fission reaction within the reactor. The oxidation conditions were a temperature of 280 C and pressure of 8 MPa, similar conditions to the reactor operating in nuclear power plant of Laguna Verde in Veracruz, Mexico (BWR conditions), with an average conductivity of 4.58 ms / cm and 2352 ppb oxygen to simulate normal water chemistry NWC. Were obtained deposits of noble metal oxides formed on 304l stainless steel samples, in a 250 ml autoclave at a temperature range of 180 to 200 C. The elements that were used to deposit platinum-rhodium (Pt-Rh) with aqueous Na{sub 2}Pt (OH){sub 6} and Na{sub 3}Rh (NO{sub 2}){sub 6}, Silver (Ag) with an aqueous solution of AgNO{sub 3}, zirconium (Zr) with aqueous Zr O (NO{sub 3}) and ZrO{sub 2}, and zinc (Zn) in aqueous solution of Zn (NO{sub 3}){sub 2} under conditions of normal water chemistry. Also there was the oxidation of 304l stainless steel specimens in normal water chemistry with a solution of Zinc (Zn) (NWC + Zn). Oxidation of the specimens in water chemistry with a solution of zinc (Zn + NWC) was prepared in two ways: within the MEX-02 autoclave unit A in a solution of zinc and a flask at constant temperature in zinc solution. The oxides formed and deposits were characterized by scanning electron microscopy, energy dispersive X-ray analysis, elemental field analysis and X-ray diffraction. By other hand was evaluated the electrochemical behavior of the oxides

  13. Metal-metal-hofteproteser

    DEFF Research Database (Denmark)

    Ulrich, Michael; Overgaard, Søren; Penny, Jeannette

    2014-01-01

    In Denmark 4,456 metal-on-metal (MoM) hip prostheses have been implanted. Evidence demonstrates that some patients develope adverse biological reactions causing failures of MoM hip arthroplasty. Some reactions might be systemic. Failure rates are associated with the type and the design of the Mo...

  14. Multiply-negatively charged aluminium clusters and fullerenes

    Energy Technology Data Exchange (ETDEWEB)

    Walsh, Noelle

    2008-07-15

    Multiply negatively charged aluminium clusters and fullerenes were generated in a Penning trap using the 'electron-bath' technique. Aluminium monoanions were generated using a laser vaporisation source. After this, two-, three- and four-times negatively charged aluminium clusters were generated for the first time. This research marks the first observation of tetra-anionic metal clusters in the gas phase. Additionally, doubly-negatively charged fullerenes were generated. The smallest fullerene dianion observed contained 70 atoms. (orig.)

  15. Metallated metal-organic frameworks

    Energy Technology Data Exchange (ETDEWEB)

    Bury, Wojciech; Farha, Omar K.; Hupp, Joseph T.; Mondloch, Joseph E.

    2017-02-07

    Porous metal-organic frameworks (MOFs) and metallated porous MOFs are provided. Also provided are methods of metallating porous MOFs using atomic layer deposition and methods of using the metallated MOFs as catalysts and in remediation applications.

  16. Metallated metal-organic frameworks

    Energy Technology Data Exchange (ETDEWEB)

    Bury, Wojciech; Farha, Omar K.; Hupp, Joseph T.; Mondloch, Joseph E.

    2017-08-22

    Porous metal-organic frameworks (MOFs) and metallated porous MOFs are provided. Also provided are methods of metallating porous MOFs using atomic layer deposition and methods of using the metallated MOFs as catalysts and in remediation applications.

  17. A general method to incorporate metal nanoparticles in zeolites and zeotypes

    DEFF Research Database (Denmark)

    2015-01-01

    Disclosed herein is a method for producing a zeolite, zeolite-like or zeotype structure with selective formation of metal, metal oxide or metal sulphide nanoparticles and/or clusters inside the zeolite, zeolite-like or zeotype structure.......Disclosed herein is a method for producing a zeolite, zeolite-like or zeotype structure with selective formation of metal, metal oxide or metal sulphide nanoparticles and/or clusters inside the zeolite, zeolite-like or zeotype structure....

  18. Management of cluster headache

    DEFF Research Database (Denmark)

    Tfelt-Hansen, Peer C; Jensen, Rigmor H

    2012-01-01

    The prevalence of cluster headache is 0.1% and cluster headache is often not diagnosed or misdiagnosed as migraine or sinusitis. In cluster headache there is often a considerable diagnostic delay - an average of 7 years in a population-based survey. Cluster headache is characterized by very severe...... or severe orbital or periorbital pain with a duration of 15-180 minutes. The cluster headache attacks are accompanied by characteristic associated unilateral symptoms such as tearing, nasal congestion and/or rhinorrhoea, eyelid oedema, miosis and/or ptosis. In addition, there is a sense of restlessness...... and agitation. Patients may have up to eight attacks per day. Episodic cluster headache (ECH) occurs in clusters of weeks to months duration, whereas chronic cluster headache (CCH) attacks occur for more than 1 year without remissions. Management of cluster headache is divided into acute attack treatment...

  19. Anion photoelectron spectroscopy of germanium and tin clusters containing a transition- or lanthanide-metal atom; MGe(n)- (n = 8-20) and MSn(n)- (n = 15-17) (M = Sc-V, Y-Nb, and Lu-Ta).

    Science.gov (United States)

    Atobe, Junko; Koyasu, Kiichirou; Furuse, Shunsuke; Nakajima, Atsushi

    2012-07-14

    The electronic properties of germanium and tin clusters containing a transition- or lanthanide-metal atom from group 3, 4, or 5, MGe(n) (M = Sc, Ti, V, Y, Zr, Nb, Lu, Hf, and Ta) and MSn(n) (M = Sc, Ti, Y. Zr, and Hf), were investigated by anion photoelectron spectroscopy at 213 nm. In the case of the group 3 elements Sc, Y, and Lu, the threshold energy of electron detachment of MGe(n)(-) exhibits local maxima at n = 10 and 16, while in the case of the group 4 elements Ti, Zr, and Hf, it exhibits a local minimum only at n = 16, associated with the presence of a small bump in the spectrum. A similar behavior is observed for MSn(n)(-) around n = 16, and these electronic characteristics of MGe(n) and MSn(n) are closely related to those of MSi(n). Compared to MSi(n), however, the larger cavity size of a Ge(n) cage allows metal atom encapsulation at a smaller size n. A cooperative effect between the electronic and geometric structures of clusters with a large cavity of Ge(16) or Sn(16) is discussed together with the results of experiments that probe their geometric stability via their reactivity to H(2)O adsorption.

  20. Development status of condensed cluster fusion theory

    International Nuclear Information System (INIS)

    Takahashi, Akito

    2015-01-01

    The condensed cluster fusion theory has been developed since 1989, under the view that dynamic ordering processes of confined transient clusters of D(H)-particles in catalytic surface sites, vacancies and global mesoscopic potential well of metal nanoparticles may induce simultaneous multi-body fusion reactions. One thorough answer is obtained for the condensation motion of clusters under platonic symmetry like 4D(H)/TSC, 6D(H)/RDC and 8D(H)/RDC and their fusion reaction rates. Theoretical analysis for initial dynamic clustering process on/in catalytic sites is still speculative and under searching a technique to combine the electron density functional method and the QM Langevin method. (author)

  1. Detecting Globular Star Cluster Tidal Streams

    Science.gov (United States)

    Powell, William Lee, Jr.; Wilhelm, Ronald; Lauchner, Adam; McWilliam, Andrew

    2006-10-01

    Globular cluster tidal streams are of interest for what they can tell us of the dynamical evolution of the clusters and of our Galaxy. Recent studies have used photometric and statistical subtraction methods to attempt to separate potential streams from the field stars that contaminate the samples. As our primary method we choose instead to use photometry to select blue stars that match the horizontal branch of the clusters. We then make spectroscopic observations of these candidates to determine their metallicities and radial velocities, which further constrains whether the candidate stars really originated in the cluster. Combining these results with the photometric data offers a better picture of the structure of tidal streams, and allows comparison of detected stars to theoretical predictions. We present preliminary photometric and spectroscopic results. Data obtained at McDonald Observatory, Kitt Peak National Observatory, and Las Campanas Observatory.

  2. Globular Cluster Tidal Streams: An Observational Study

    Science.gov (United States)

    Powell, William L.; Lauchner, A.; Wilhelm, R.; McWilliam, A.

    2006-12-01

    Globular cluster tidal streams are of interest for what they can tell us of the dynamical evolution of the clusters and of our Galaxy. Recent studies have used photometric and statistical subtraction methods to attempt to separate potential streams from the field stars that contaminate the samples. We chose instead as our primary method to use photometry to select blue stars that match the horizontal branch of the clusters. We then make spectroscopic observations of these candidates to determine their metallicity and radial velocities. Combining these results with the photometric data offers a better picture of the structure and validity of tidal streams. We present photometric and spectroscopic results for several globular clusters and their surrounding fields. Data were obtained at McDonald Observatory, Kitt Peak, and Las Campanas Observatory. SDSS data were also used. WLP acknowledges the support of a Sigma Xi Grant-In-Aid of research. RW acknowledges the support of a AAS Small Research Grant.

  3. Comprehensive cluster analysis with Transitivity Clustering.

    Science.gov (United States)

    Wittkop, Tobias; Emig, Dorothea; Truss, Anke; Albrecht, Mario; Böcker, Sebastian; Baumbach, Jan

    2011-03-01

    Transitivity Clustering is a method for the partitioning of biological data into groups of similar objects, such as genes, for instance. It provides integrated access to various functions addressing each step of a typical cluster analysis. To facilitate this, Transitivity Clustering is accessible online and offers three user-friendly interfaces: a powerful stand-alone version, a web interface, and a collection of Cytoscape plug-ins. In this paper, we describe three major workflows: (i) protein (super)family detection with Cytoscape, (ii) protein homology detection with incomplete gold standards and (iii) clustering of gene expression data. This protocol guides the user through the most important features of Transitivity Clustering and takes ∼1 h to complete.

  4. Metal-metal-hofteproteser

    DEFF Research Database (Denmark)

    Ulrich, Michael; Overgaard, Søren; Penny, Jeannette

    2014-01-01

    In Denmark 4,456 metal-on-metal (MoM) hip prostheses have been implanted. Evidence demonstrates that some patients develope adverse biological reactions causing failures of MoM hip arthroplasty. Some reactions might be systemic. Failure rates are associated with the type and the design of the Mo......M hip implant. A Danish surveillance programme has been initiated addressing these problems....

  5. The experiment and research on the migration of the heavy metal

    International Nuclear Information System (INIS)

    He Zhijie; Le Renchang; Jia Wenyi; Fang Fang

    2007-01-01

    A device available to observe the heavy metal's migration is designed. We discovered that mixed with α-radioactive source such as U, Th etc., the heavy metal processes the obvious upward migration ability because of α-disintegration. The heavy metals and He nuclei can come into being Cluster. When the specific gravity of Clusters is smaller than that of the air, the Clusters of the heavy metal have the ability of upward migration. (authors)

  6. ASteCA: Automated Stellar Cluster Analysis

    Science.gov (United States)

    Perren, G. I.; Vázquez, R. A.; Piatti, A. E.

    2015-04-01

    We present the Automated Stellar Cluster Analysis package (ASteCA), a suit of tools designed to fully automate the standard tests applied on stellar clusters to determine their basic parameters. The set of functions included in the code make use of positional and photometric data to obtain precise and objective values for a given cluster's center coordinates, radius, luminosity function and integrated color magnitude, as well as characterizing through a statistical estimator its probability of being a true physical cluster rather than a random overdensity of field stars. ASteCA incorporates a Bayesian field star decontamination algorithm capable of assigning membership probabilities using photometric data alone. An isochrone fitting process based on the generation of synthetic clusters from theoretical isochrones and selection of the best fit through a genetic algorithm is also present, which allows ASteCA to provide accurate estimates for a cluster's metallicity, age, extinction and distance values along with its uncertainties. To validate the code we applied it on a large set of over 400 synthetic MASSCLEAN clusters with varying degrees of field star contamination as well as a smaller set of 20 observed Milky Way open clusters (Berkeley 7, Bochum 11, Czernik 26, Czernik 30, Haffner 11, Haffner 19, NGC 133, NGC 2236, NGC 2264, NGC 2324, NGC 2421, NGC 2627, NGC 6231, NGC 6383, NGC 6705, Ruprecht 1, Tombaugh 1, Trumpler 1, Trumpler 5 and Trumpler 14) studied in the literature. The results show that ASteCA is able to recover cluster parameters with an acceptable precision even for those clusters affected by substantial field star contamination. ASteCA is written in Python and is made available as an open source code which can be downloaded ready to be used from its official site.

  7. From collisions to clusters

    DEFF Research Database (Denmark)

    Loukonen, Ville; Bork, Nicolai; Vehkamaki, Hanna

    2014-01-01

    The clustering of sulphuric acid with base molecules is one of the main pathways of new-particle formation in the Earth's atmosphere. First step in the clustering process is likely the formation of a (sulphuric acid)1(base)1(water)n cluster. Here, we present results from direct first-principles m......The clustering of sulphuric acid with base molecules is one of the main pathways of new-particle formation in the Earth's atmosphere. First step in the clustering process is likely the formation of a (sulphuric acid)1(base)1(water)n cluster. Here, we present results from direct first...... bridge. In general, water is able to notably stabilise the formed clusters by allocating a fraction of the released clustering energy....

  8. Loose-cluster approximation

    Indian Academy of Sciences (India)

    First page Back Continue Last page Overview Graphics. Loose-cluster approximation. Continuous curve Our Theory. Dashed curve Our Simulation. Loose cluster approx. not only. captures -the anomalous. qualitative features but is also,. quantitatively, quite accurate. Notes:

  9. Cluster beam injection

    International Nuclear Information System (INIS)

    Bottiglioni, F.; Coutant, J.; Fois, M.

    1977-11-01

    Areas of possible applications of cluster injection are discussed. The deposition inside the plasma of molecules, issued from the dissociation of the injected clusters, has been computed. Some empirical scaling laws for the penetration are given

  10. Cluster beam injection

    International Nuclear Information System (INIS)

    Bottiglioni, F.; Coutant, J.; Fois, M.

    1978-01-01

    Areas of possible applications of cluster injection are discussed. The deposition inside the plasma of molecules, issued from the dissociation of the injected clusters, has been computed. Some empirical scaling laws for the penetration are given

  11. Gamma-ray Emission from Globular Clusters

    Directory of Open Access Journals (Sweden)

    Pak-Hin T. Tam

    2016-03-01

    Full Text Available Over the last few years, the data obtained using the Large Area Telescope (LAT aboard the Fermi Gamma-ray Space Telescope has provided new insights on high-energy processes in globular clusters, particularly those involving compact objects such as MilliSecond Pulsars (MSPs. Gamma-ray emission in the 100 MeV to 10 GeV range has been detected from more than a dozen globular clusters in our galaxy, including 47 Tucanae and Terzan 5. Based on a sample of known gammaray globular clusters, the empirical relations between gamma-ray luminosity and properties of globular clusters such as their stellar encounter rate, metallicity, and possible optical and infrared photon energy densities, have been derived. The measured gamma-ray spectra are generally described by a power law with a cut-off at a few gigaelectronvolts. Together with the detection of pulsed γ-rays from two MSPs in two different globular clusters, such spectral signature lends support to the hypothesis that γ-rays from globular clusters represent collective curvature emission from magnetospheres of MSPs in the clusters. Alternative models, involving Inverse-Compton (IC emission of relativistic electrons that are accelerated close to MSPs or pulsar wind nebula shocks, have also been suggested. Observations at >100 GeV by using Fermi/LAT and atmospheric Cherenkov telescopes such as H.E.S.S.-II, MAGIC-II, VERITAS, and CTA will help to settle some questions unanswered by current data.

  12. New Photometric Data of Old Open Clusters in the Anti-Galactic Center Region

    Science.gov (United States)

    Hasegawa, Takashi; Malasan, Hakim L.; Kawakita, Hideyo; Obayashi, Hitoshi; Kurabayashi, Tsutomu; Nakai, Tatsuji; Hyakkai, Masaaki; Arimoto, Nobuo

    2004-04-01

    We present new photometric data for 14 galactic open clusters taken by the 65cm telescope at Gunma Astronomical Observatory. They were in the anti-galactic center region selected from the Catalog of Open Cluster Data (Lyngå 1987). We estimated the parameters of the clusters, i.e., age, metallicity, distance, and reddening, by fitting Padova isochrones to the color-magnitude diagram. While no clusters were dated to be as old as young globular clusters, 13 clusters out of 14 are older than 1Gyr, ranging up to ˜ 3.6 Gyr. Bearing in mind that out of approximately 500 clusters dated so far, only 40 clusters are older than 1Gyr, our sample is exclusively dominated by old clusters. Four clusters were found away from the metallicity gradient curve and age-metallicity relation so far delineated. Especially, 3 metal-rich clusters in the outer disk (Berkeley 36, Biurakan 11, and Biurakan 13) provide evidence against the picture advocated by Twarog etal. (1997, AJ, 114, 2556) that there is a break in the metallicity distribution at rGC = 10 kpc and that the outer disk is chemically less evolved than in the inner disk.

  13. Cluster Physics with Merging Galaxy Clusters

    Directory of Open Access Journals (Sweden)

    Sandor M. Molnar

    2016-02-01

    Full Text Available Collisions between galaxy clusters provide a unique opportunity to study matter in a parameter space which cannot be explored in our laboratories on Earth. In the standard LCDM model, where the total density is dominated by the cosmological constant ($Lambda$ and the matter density by cold dark matter (CDM, structure formation is hierarchical, and clusters grow mostly by merging.Mergers of two massive clusters are the most energetic events in the universe after the Big Bang,hence they provide a unique laboratory to study cluster physics.The two main mass components in clusters behave differently during collisions:the dark matter is nearly collisionless, responding only to gravity, while the gas is subject to pressure forces and dissipation, and shocks and turbulenceare developed during collisions. In the present contribution we review the different methods used to derive the physical properties of merging clusters. Different physical processes leave their signatures on different wavelengths, thusour review is based on a multifrequency analysis. In principle, the best way to analyze multifrequency observations of merging clustersis to model them using N-body/HYDRO numerical simulations. We discuss the results of such detailed analyses.New high spatial and spectral resolution ground and space based telescopeswill come online in the near future. Motivated by these new opportunities,we briefly discuss methods which will be feasible in the near future in studying merging clusters.

  14. Keck Spectroscopy of Globular Clusters in the Elliptical Galaxy NGC 3610

    OpenAIRE

    Strader, Jay; Brodie, Jean P.; Schweizer, Francois; Larsen, Soeren S.; Seitzer, Patrick

    2002-01-01

    We present moderate-resolution Keck spectra of nine candidate globular clusters in the possible merger-remnant elliptical galaxy NGC 3610. Eight of the objects appear to be bona fide globular clusters of NGC 3610. We find that two of the clusters belong to an old metal-poor population, five to an old metal-rich population, and only one to an intermediate-age metal-rich population. The estimated age of the intermediate-age cluster is 1-5 Gyr, which is in agreement with earlier estimates of the...

  15. Minimalist's linux cluster

    International Nuclear Information System (INIS)

    Choi, Chang-Yeong; Kim, Jeong-Hyun; Kim, Seyong

    2004-01-01

    Using barebone PC components and NIC's, we construct a linux cluster which has 2-dimensional mesh structure. This cluster has smaller footprint, is less expensive, and use less power compared to conventional linux cluster. Here, we report our experience in building such a machine and discuss our current lattice project on the machine

  16. Range-clustering queries

    DEFF Research Database (Denmark)

    Abrahamsen, Mikkel; de Berg, Mark; Buchin, Kevin

    2017-01-01

    an optimal k-clustering for S P ∩ Q. We obtain the following results. • We present a general method to compute a (1 + ϵ)-approximation to a range-clustering query, where ϵ > 0 is a parameter that can be specified as part of the query. Our method applies to a large class of clustering problems, including k...

  17. Cosmology with cluster surveys

    Indian Academy of Sciences (India)

    Surveys of clusters of galaxies provide us with a powerful probe of the density and nature of the dark energy. The red-shift distribution of detected clusters is highly sensitive to the dark energy equation of state parameter . Upcoming Sunyaev–Zel'dovich (SZ) surveys would provide us large yields of clusters to very high ...

  18. Cosmology with cluster surveys

    Indian Academy of Sciences (India)

    Cosmology with cluster surveys. SUBHABRATA MAJUMDAR. CITA, University of Toronto, Toronto, ON, M5S 3H8, Canada. E-mail: subha@cita.utoronto.ca. Abstract. Surveys of clusters of galaxies provide us with a powerful probe of the den- sity and nature of the dark energy. The red-shift distribution of detected clusters is.

  19. Structures of Mn clusters

    Indian Academy of Sciences (India)

    Abstract. The geometries of several Mn clusters in the size range Mn13–Mn23 are studied via the generalized gradient approximation to density functional theory. For the 13- and 19-atom clusters, the icosahedral structures are found to be most stable, while for the 15-atom cluster, the bcc structure is more favoured.

  20. Marketing research cluster analysis

    Directory of Open Access Journals (Sweden)

    Marić Nebojša

    2002-01-01

    Full Text Available One area of applications of cluster analysis in marketing is identification of groups of cities and towns with similar demographic profiles. This paper considers main aspects of cluster analysis by an example of clustering 12 cities with the use of Minitab software.

  1. The Durban Auto Cluster

    DEFF Research Database (Denmark)

    Lorentzen, Jochen; Robbins, Glen; Barnes, Justin

    2004-01-01

    The paper describes the formation of the Durban Auto Cluster in the context of trade liberalization. It argues that the improvement of operational competitiveness of firms in the cluster is prominently due to joint action. It tests this proposition by comparing the gains from cluster activities...

  2. Cosmology with cluster surveys

    Indian Academy of Sciences (India)

    Abstract. Surveys of clusters of galaxies provide us with a powerful probe of the den- sity and nature of the dark energy. The red-shift distribution of detected clusters is highly sensitive to the dark energy equation of state parameter w. Upcoming Sunyaev–. Zel'dovich (SZ) surveys would provide us large yields of clusters to ...

  3. Estudio del etiquetado de los alimentos funcionales

    OpenAIRE

    Delgado González, Patricia

    2016-01-01

    El estudio del etiquetado de los alimentos, fundamentalmente de los alimentos funcionales, se basa en el estudio previo de éstos. Dentro de este grupo podemos encontrarnos distintos componentes como polioles, aminoácidos, ácidos grasos insaturados, fitoesteroles, vitaminas, minerales, bacterias ácido-lácticas, fibra, entre otros. Los probióticos son microorganismos vivos, bacterias acido lácticas saprófitas para nuestro organismo y que nos ayudan a mejorar ciertas funciones como las gastro...

  4. Constraining supernova models using the hot gas in clusters of galaxies

    NARCIS (Netherlands)

    de Plaa, J.; Werner, N.|info:eu-repo/dai/nl/30484778X; Bleeker, J.A.M.|info:eu-repo/dai/nl/071892176; Vink, J.|info:eu-repo/dai/nl/182880559; Kaastra, J.S.|info:eu-repo/dai/nl/070911134; Mendes, M.

    2009-01-01

    Context: The hot X-ray emitting gas in clusters of galaxies is a very large repository of metals produced by supernovae. During the evolution of clusters, billions of supernovae eject their material into this Intra-Cluster Medium (ICM). Aims: We aim to accurately measure the abundances in the ICM of

  5. Patrones arquitectónicos, clusters constructivos homogéneos y variabilidad en el estudio de edificios históricos. Aspectos técnico-formales de la vivienda rural en la provincia de La Rioja (Argentina durante el período republicano

    Directory of Open Access Journals (Sweden)

    Rolón, Guillermo

    2014-12-01

    Full Text Available The paper presents the methodological procedure by which the characteristics of the traditional architecture in rural areas in La Rioja province (Argentina of the Republican Period (from 19>th century until nowadays were analyzed. The comprehensive application of stratigraphic and typological analysis along with multivariate analytical techniques allowed the identification and characterization of the developed architectural patterns. The concept of architectural pattern was used within the methodological design, as an alternative to the building type, in order to consider and evaluate not only the stable aspects (the constructive and homogeneous “cluster” as internal structure of the pattern, but also those variable characteristics that were observed in the construction of the dwellings considered.El artículo presenta el procedimiento metodológico con el cual se analizaron las características de la arquitectura popular del ámbito rural en la provincia de La Rioja (Argentina del período republicano (s. XIX a la actualidad. La aplicación integral de análisis estratigráficos y tipológicos, y el auxilio de técnicas analíticas multivariantes, permitió identificar y caracterizar los patrones arquitectónicos desarrollados. Se utilizó el concepto de patrón arquitectónico en el diseño metodológico, como alternativa al de tipo edilicio, para considerar y evaluar no sólo los aspectos estables (el cluster constructivo homogéneo o estructura interna del patrón, sino también aquellas características variables que se observaron en la edificación de las unidades domésticas consideradas.

  6. BVI photometry of globular clusters in M87

    International Nuclear Information System (INIS)

    Couture, J.; Harris, W.E.; Allwright, J.W.B.

    1990-01-01

    CCD photometry in B, V, and I is presented for a sample of globular clusters in the Virgo central giant elliptical galaxy M87. No detectable gradient of mean cluster color (metallicity) in (B - V) or (V - I) with radial distance is found. The cluster system does, however, display a large dispersion in color at any radius, corresponding to sigma (Fe/H) about 0.6 about a mean metallicity of about -1.1 according to the present color index scale. The difference in mean color between the globular clusters and the underlying halo light of the galaxy itself shows up strongly in all the color indices; virtually no clusters as red as the mean color of the halo stars is found at any radius. 43 refs

  7. THERMAL AND CHEMICAL EVOLUTIONS OF GALAXY CLUSTERS OBSERVED WITH SUZAKU

    Directory of Open Access Journals (Sweden)

    Kosuke Sato

    2013-12-01

    Full Text Available We studied the properties of the intracluster medium (ICM of galaxy clusters to outer regions observed with Suzaku. The observed temperature dropped by about ~30% from the central region to the virial radius of the clusters. The derived entropy profile agreed with the expectation from simulations within r500, while the entropy profile in r > r500 indicated a flatter slope than the simulations. This would suggest that the cluster outskirts were out of hydrostatic equilibrium. As for the metallicity, we studied the metal abundances from O to Fe up to ~0.5 times the virial radius of galaxy groups and clusters. Comparing the results with supernova nucleosynthesis models, the number ratio of type II to Ia supernovae is estimated to be ~3.5. We also calculated not only Fe, but also O and Mg mass-to-light ratios (MLRs with K-band luminosity. The MLRs in the clusters had a similar feature.

  8. Cluster analysis for applications

    CERN Document Server

    Anderberg, Michael R

    1973-01-01

    Cluster Analysis for Applications deals with methods and various applications of cluster analysis. Topics covered range from variables and scales to measures of association among variables and among data units. Conceptual problems in cluster analysis are discussed, along with hierarchical and non-hierarchical clustering methods. The necessary elements of data analysis, statistics, cluster analysis, and computer implementation are integrated vertically to cover the complete path from raw data to a finished analysis.Comprised of 10 chapters, this book begins with an introduction to the subject o

  9. The pulsation mode and period-luminosity relationship of cool variables in globular clusters

    International Nuclear Information System (INIS)

    Whitelock, P.A.

    1986-01-01

    The period-luminosity-temperature relationship for globular cluster red and yellow variables is examined. The results suggest that the higher temperature, more metal-deficient cluster variables pulsate in the fundamental mode, while the lower temperature more metal-rich variables pulsate in the first overtone. On the assumption that this is correct, a relationship between fundamental period and bolometric magnitude is derived for cluster variables with observed periods of between 1 and 300 days. (author)

  10. Clustering high dimensional data

    DEFF Research Database (Denmark)

    Assent, Ira

    2012-01-01

    for clustering are required. Consequently, recent research has focused on developing techniques and clustering algorithms specifically for high-dimensional data. Still, open research issues remain. Clustering is a data mining task devoted to the automatic grouping of data based on mutual similarity. Each cluster......High-dimensional data, i.e., data described by a large number of attributes, pose specific challenges to clustering. The so-called ‘curse of dimensionality’, coined originally to describe the general increase in complexity of various computational problems as dimensionality increases, is known...... that provide different cluster models and different algorithmic approaches for cluster detection. Common to all approaches is the fact that they require some underlying assessment of similarity between data objects. In this article, we provide an overview of the effects of high-dimensional spaces...

  11. Spatial cluster modelling

    CERN Document Server

    Lawson, Andrew B

    2002-01-01

    Research has generated a number of advances in methods for spatial cluster modelling in recent years, particularly in the area of Bayesian cluster modelling. Along with these advances has come an explosion of interest in the potential applications of this work, especially in epidemiology and genome research. In one integrated volume, this book reviews the state-of-the-art in spatial clustering and spatial cluster modelling, bringing together research and applications previously scattered throughout the literature. It begins with an overview of the field, then presents a series of chapters that illuminate the nature and purpose of cluster modelling within different application areas, including astrophysics, epidemiology, ecology, and imaging. The focus then shifts to methods, with discussions on point and object process modelling, perfect sampling of cluster processes, partitioning in space and space-time, spatial and spatio-temporal process modelling, nonparametric methods for clustering, and spatio-temporal ...

  12. Clusters in nuclei

    CERN Document Server

    Following the pioneering discovery of alpha clustering and of molecular resonances, the field of nuclear clustering is today one of those domains of heavy-ion nuclear physics that faces the greatest challenges, yet also contains the greatest opportunities. After many summer schools and workshops, in particular over the last decade, the community of nuclear molecular physicists has decided to collaborate in producing a comprehensive collection of lectures and tutorial reviews covering the field. This third volume follows the successful Lect. Notes Phys. 818 (Vol. 1) and 848 (Vol. 2), and comprises six extensive lectures covering the following topics:  - Gamma Rays and Molecular Structure - Faddeev Equation Approach for Three Cluster Nuclear Reactions - Tomography of the Cluster Structure of Light Nuclei Via Relativistic Dissociation - Clustering Effects Within the Dinuclear Model : From Light to Hyper-heavy Molecules in Dynamical Mean-field Approach - Clusterization in Ternary Fission - Clusters in Light N...

  13. Protein-encapsulated gold cluster aggregates: the case of lysozyme

    Science.gov (United States)

    Baksi, Ananya; Xavier, Paulrajpillai Lourdu; Chaudhari, Kamalesh; Goswami, N.; Pal, S. K.; Pradeep, T.

    2013-02-01

    We report the evolution and confinement of atomically precise and luminescent gold clusters in a small protein, lysozyme (Lyz) using detailed mass spectrometric (MS) and other spectroscopic investigations. A maximum of 12 Au0 species could be bound to a single Lyz molecule irrespective of the molar ratio of Lyz : Au3+ used for cluster growth. The cluster-encapsulated protein also forms aggregates similar to the parent protein. Time dependent studies reveal the emergence of free protein and the redistribution of detached Au atoms, at specific Lyz to Au3+ molar ratios, as a function of incubation time, proposing inter-protein metal ion transfer. The results are in agreement with the studies of inter-protein metal transfer during cluster growth in similar systems. We believe that this study provides new insights into the growth of clusters in smaller proteins.We report the evolution and confinement of atomically precise and luminescent gold clusters in a small protein, lysozyme (Lyz) using detailed mass spectrometric (MS) and other spectroscopic investigations. A maximum of 12 Au0 species could be bound to a single Lyz molecule irrespective of the molar ratio of Lyz : Au3+ used for cluster growth. The cluster-encapsulated protein also forms aggregates similar to the parent protein. Time dependent studies reveal the emergence of free protein and the redistribution of detached Au atoms, at specific Lyz to Au3+ molar ratios, as a function of incubation time, proposing inter-protein metal ion transfer. The results are in agreement with the studies of inter-protein metal transfer during cluster growth in similar systems. We believe that this study provides new insights into the growth of clusters in smaller proteins. Electronic supplementary information (ESI) available. See DOI: 10.1039/c2nr33180b

  14. The Cluster-EAGLE project: global properties of simulated clusters with resolved galaxies

    Science.gov (United States)

    Barnes, David J.; Kay, Scott T.; Bahé, Yannick M.; Dalla Vecchia, Claudio; McCarthy, Ian G.; Schaye, Joop; Bower, Richard G.; Jenkins, Adrian; Thomas, Peter A.; Schaller, Matthieu; Crain, Robert A.; Theuns, Tom; White, Simon D. M.

    2017-10-01

    We introduce the Cluster-EAGLE (c-eagle) simulation project, a set of cosmological hydrodynamical zoom simulations of the formation of 30 galaxy clusters in the mass range of 1014 eagle galaxy formation model, with a gas particle mass of 1.8 × 106 M⊙ and physical softening length of 0.7 kpc. In this paper, we introduce the sample and present the low-redshift global properties of the clusters. We calculate the X-ray properties in a manner consistent with observational techniques, demonstrating the bias and scatter introduced by using estimated masses. We find the total stellar content and black hole masses of the clusters to be in good agreement with the observed relations. However, the clusters are too gas rich, suggesting that the active galactic nucleus (AGN) feedback model is not efficient enough at expelling gas from the high-redshift progenitors of the clusters. The X-ray properties, such as the spectroscopic temperature and the soft-band luminosity, and the Sunyaev-Zel'dovich properties are in reasonable agreement with the observed relations. However, the clusters have too high central temperatures and larger-than-observed entropy cores, which is likely driven by the AGN feedback after the cluster core has formed. The total metal content and its distribution throughout the intracluster medium are a good match to the observations.

  15. Modeling Clustered Data with Very Few Clusters.

    Science.gov (United States)

    McNeish, Daniel; Stapleton, Laura M

    2016-01-01

    Small-sample inference with clustered data has received increased attention recently in the methodological literature, with several simulation studies being presented on the small-sample behavior of many methods. However, nearly all previous studies focus on a single class of methods (e.g., only multilevel models, only corrections to sandwich estimators), and the differential performance of various methods that can be implemented to accommodate clustered data with very few clusters is largely unknown, potentially due to the rigid disciplinary preferences. Furthermore, a majority of these studies focus on scenarios with 15 or more clusters and feature unrealistically simple data-generation models with very few predictors. This article, motivated by an applied educational psychology cluster randomized trial, presents a simulation study that simultaneously addresses the extreme small sample and differential performance (estimation bias, Type I error rates, and relative power) of 12 methods to account for clustered data with a model that features a more realistic number of predictors. The motivating data are then modeled with each method, and results are compared. Results show that generalized estimating equations perform poorly; the choice of Bayesian prior distributions affects performance; and fixed effect models perform quite well. Limitations and implications for applications are also discussed.

  16. CLEAN: CLustering Enrichment ANalysis

    Science.gov (United States)

    Freudenberg, Johannes M; Joshi, Vineet K; Hu, Zhen; Medvedovic, Mario

    2009-01-01

    Background Integration of biological knowledge encoded in various lists of functionally related genes has become one of the most important aspects of analyzing genome-wide functional genomics data. In the context of cluster analysis, functional coherence of clusters established through such analyses have been used to identify biologically meaningful clusters, compare clustering algorithms and identify biological pathways associated with the biological process under investigation. Results We developed a computational framework for analytically and visually integrating knowledge-based functional categories with the cluster analysis of genomics data. The framework is based on the simple, conceptually appealing, and biologically interpretable gene-specific functional coherence score (CLEAN score). The score is derived by correlating the clustering structure as a whole with functional categories of interest. We directly demonstrate that integrating biological knowledge in this way improves the reproducibility of conclusions derived from cluster analysis. The CLEAN score differentiates between the levels of functional coherence for genes within the same cluster based on their membership in enriched functional categories. We show that this aspect results in higher reproducibility across independent datasets and produces more informative genes for distinguishing different sample types than the scores based on the traditional cluster-wide analysis. We also demonstrate the utility of the CLEAN framework in comparing clusterings produced by different algorithms. CLEAN was implemented as an add-on R package and can be downloaded at . The package integrates routines for calculating gene specific functional coherence scores and the open source interactive Java-based viewer Functional TreeView (FTreeView). Conclusion Our results indicate that using the gene-specific functional coherence score improves the reproducibility of the conclusions made about clusters of co

  17. Cluster assembly in nitrogenase.

    Science.gov (United States)

    Sickerman, Nathaniel S; Rettberg, Lee A; Lee, Chi Chung; Hu, Yilin; Ribbe, Markus W

    2017-05-09

    The versatile enzyme system nitrogenase accomplishes the challenging reduction of N 2 and other substrates through the use of two main metalloclusters. For molybdenum nitrogenase, the catalytic component NifDK contains the [Fe 8 S 7 ]-core P-cluster and a [MoFe 7 S 9 C-homocitrate] cofactor called the M-cluster. These chemically unprecedented metalloclusters play a critical role in the reduction of N 2 , and both originate from [Fe 4 S 4 ] clusters produced by the actions of NifS and NifU. Maturation of P-cluster begins with a pair of these [Fe 4 S 4 ] clusters on NifDK called the P*-cluster. An accessory protein NifZ aids in P-cluster fusion, and reductive coupling is facilitated by NifH in a stepwise manner to form P-cluster on each half of NifDK. For M-cluster biosynthesis, two [Fe 4 S 4 ] clusters on NifB are coupled with a carbon atom in a radical-SAM dependent process, and concomitant addition of a 'ninth' sulfur atom generates the [Fe 8 S 9 C]-core L-cluster. On the scaffold protein NifEN, L-cluster is matured to M-cluster by the addition of Mo and homocitrate provided by NifH. Finally, matured M-cluster in NifEN is directly transferred to NifDK, where a conformational change locks the cofactor in place. Mechanistic insights into these fascinating biosynthetic processes are detailed in this chapter. © 2017 The Author(s). Published by Portland Press Limited on behalf of the Biochemical Society.

  18. CHANDRA OBSERVATION OF ABELL 1142: A COOL-CORE CLUSTER LACKING A CENTRAL BRIGHTEST CLUSTER GALAXY?

    Energy Technology Data Exchange (ETDEWEB)

    Su, Yuanyuan; Weeren, Reinout van [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Buote, David A. [Department of Physics and Astronomy, University of California, Irvine, 4129 Frederick Reines Hall, Irvine, CA 92697 (United States); Gastaldello, Fabio, E-mail: yuanyuan.su@cfa.harvard.edu [INAF-IASF-Milano, Via E. Bassini 15, I-20133 Milano (Italy)

    2016-04-10

    Abell 1142 is a low-mass galaxy cluster at low redshift containing two comparable brightest cluster galaxies (BCGs) resembling a scaled-down version of the Coma Cluster. Our Chandra analysis reveals an X-ray emission peak, roughly 100 kpc away from either BCG, which we identify as the cluster center. The emission center manifests itself as a second beta-model surface brightness component distinct from that of the cluster on larger scales. The center is also substantially cooler and more metal-rich than the surrounding intracluster medium (ICM), which makes Abell 1142 appear to be a cool-core cluster. The redshift distribution of its member galaxies indicates that Abell 1142 may contain two subclusters, each of which contain one BCG. The BCGs are merging at a relative velocity of ≈1200 km s{sup −1}. This ongoing merger may have shock-heated the ICM from ≈2 keV to above 3 keV, which would explain the anomalous L{sub X}–T{sub X} scaling relation for this system. This merger may have displaced the metal-enriched “cool core” of either of the subclusters from the BCG. The southern BCG consists of three individual galaxies residing within a radius of 5 kpc in projection. These galaxies should rapidly sink into the subcluster center due to the dynamical friction of a cuspy cold dark matter halo.

  19. THE HST/ACS COMA CLUSTER SURVEY. IV. INTERGALACTIC GLOBULAR CLUSTERS AND THE MASSIVE GLOBULAR CLUSTER SYSTEM AT THE CORE OF THE COMA GALAXY CLUSTER

    International Nuclear Information System (INIS)

    Peng, Eric W.; Ferguson, Henry C.; Goudfrooij, Paul; Hammer, Derek; Lucey, John R.; Marzke, Ronald O.; Puzia, Thomas H.; Carter, David; Balcells, Marc; Bridges, Terry; Chiboucas, Kristin; Del Burgo, Carlos; Graham, Alister W.; Guzman, Rafael; Hudson, Michael J.; Matkovic, Ana

    2011-01-01

    Intracluster stellar populations are a natural result of tidal interactions in galaxy clusters. Measuring these populations is difficult, but important for understanding the assembly of the most massive galaxies. The Coma cluster of galaxies is one of the nearest truly massive galaxy clusters and is host to a correspondingly large system of globular clusters (GCs). We use imaging from the HST/ACS Coma Cluster Survey to present the first definitive detection of a large population of intracluster GCs (IGCs) that fills the Coma cluster core and is not associated with individual galaxies. The GC surface density profile around the central massive elliptical galaxy, NGC 4874, is dominated at large radii by a population of IGCs that extend to the limit of our data (R +4000 -5000 (systematic) IGCs out to this radius, and that they make up ∼70% of the central GC system, making this the largest GC system in the nearby universe. Even including the GC systems of other cluster galaxies, the IGCs still make up ∼30%-45% of the GCs in the cluster core. Observational limits from previous studies of the intracluster light (ICL) suggest that the IGC population has a high specific frequency. If the IGC population has a specific frequency similar to high-S N dwarf galaxies, then the ICL has a mean surface brightness of μ V ∼ 27 mag arcsec -2 and a total stellar mass of roughly 10 12 M sun within the cluster core. The ICL makes up approximately half of the stellar luminosity and one-third of the stellar mass of the central (NGC 4874+ICL) system. The color distribution of the IGC population is bimodal, with blue, metal-poor GCs outnumbering red, metal-rich GCs by a ratio of 4:1. The inner GCs associated with NGC 4874 also have a bimodal distribution in color, but with a redder metal-poor population. The fraction of red IGCs (20%), and the red color of those GCs, implies that IGCs can originate from the halos of relatively massive, L* galaxies, and not solely from the disruption of

  20. Clustering and segregation of small vacancy clusters near tungsten (0 0 1) surface

    Science.gov (United States)

    Duan, Guohua; Li, Xiangyan; Xu, Yichun; Zhang, Yange; Jiang, Yan; Hao, Congyu; Liu, C. S.; Fang, Q. F.; Chen, Jun-Ling; Luo, G.-N.; Wang, Zhiguang

    2018-01-01

    Nanoporous metals have been shown to exhibit radiation-tolerance due to the trapping of the defects by the surface. However, the behavior of vacancy clusters near the surface is not clear which involves the competition between the self-trapping and segregation of small vacancy clusters (Vn) nearby the surface. In this study, we investigated the energetic and kinetic properties of small vacancy clusters near tungsten (0 0 1) surface by combining molecular statics (MS) calculations and object Kinetic Monte Carlo (OKMC) simulations. Results show that vacancies could be clustered with the reduced formation energy and migration energy of the single vacancy around a cluster as the respective energetic and kinetic driving forces. The small cluster has a migration energy barrier comparable to that for the single vacancy; the migration energy barriers for V1-5 and V7 are 1.80, 1.94, 2.17, 2.78, 3.12 and 3.11 eV, respectively. Clusters and become unstable near surface (0 0 1) and tend to dissociate into the surface. At the operation temperature of 1000 K, the single vacancy, V2, 2 V 3 V3 and V4 were observed to segregate to the surface within a time of one hour. Meanwhile, larger clusters survived near the surface, which could serve as nucleating center for voids near the surface. Our results suggest that under a low radiation dose, surface (0 0 1) could act as a sink for small vacancy clusters, alleviating defect accumulation in the material under a low radiation dose. We also obtained several empirical expressions for the vacancy cluster formation energy, binding energy, and trapping radius as a function of the number of vacancies in the cluster.

  1. El creciente campo de los Estudios Sensoriales

    Directory of Open Access Journals (Sweden)

    David Howes

    2014-09-01

    Full Text Available Este ensayo presenta una breve descripción acerca del giro sensorial en la investigación contemporánea, y propone algunas perspectivas de trabajo para futuras investigaciones. Esta labor no pretende ser exhaustiva y, más bien, busca indicar las principales tendencias en este campo. El ensayo, en su primera parte, ofrece una mirada general sobre la aparición y el desarrollo de la historia y la antropología de los sentidos. En la segunda parte, la atención se concentra en cómo el campo de los estudios sensoriales puede ser, de otro lado, conceptualizado como compuesto de cultura visual, cultura auditiva (o estudios del sonido, cultura del olfato, cultura del gusto y cultura del tacto. Se ofrece una explicación acerca de la génesis de estas divisiones. Posteriormente, se presenta una visión general de algunas cuestiones claves en los estudios sensoriales, como la pregunta por el número de los sentidos y la relación entre orden sensorial y orden social. El ensayo concluye con ocho proposiciones para los estudios sensoriales.

  2. El creciente campo de los Estudios Sensoriales

    Directory of Open Access Journals (Sweden)

    David Howes

    2014-08-01

    Full Text Available Este ensayo presenta una breve descripción acerca del giro sensorial en la investigación contemporánea, y propone algunas perspectivas de trabajo para futurasinvestigaciones. Esta labor no pretende ser exhaustiva y, más bien, busca indicar las principales tendencias en este campo. El ensayo, en su primera parte, ofrece una mirada general sobre la aparición y el desarrollo de la historia y la antropología de los sentidos. En la segunda parte, la atención se concentra en cómo el campo de los estudios sensoriales puede ser, de otro lado, conceptualizado como compuesto de cultura visual, cultura auditiva (o estudios del sonido, cultura del olfato, cultura del gusto y cultura del tacto. Se ofrece una explicación acerca de la génesis de estas divisiones. Posteriormente,se presenta una visión general de algunas cuestiones claves en los estudios sensoriales, como la pregunta por el número de los sentidos y la relación entre orden sensorial y orden social. El ensayo concluye con ocho proposiciones para los estudios sensoriales.

  3. Agricultural Clusters in the Netherlands

    NARCIS (Netherlands)

    Schouten, M.A.; Heijman, W.J.M.

    2012-01-01

    Michael Porter was the first to use the term cluster in an economic context. He introduced the term in The Competitive Advantage of Nations (1990). The term cluster is also known as business cluster, industry cluster, competitive cluster or Porterian cluster. This article aims at determining and

  4. Open source clustering software.

    Science.gov (United States)

    de Hoon, M J L; Imoto, S; Nolan, J; Miyano, S

    2004-06-12

    We have implemented k-means clustering, hierarchical clustering and self-organizing maps in a single multipurpose open-source library of C routines, callable from other C and C++ programs. Using this library, we have created an improved version of Michael Eisen's well-known Cluster program for Windows, Mac OS X and Linux/Unix. In addition, we generated a Python and a Perl interface to the C Clustering Library, thereby combining the flexibility of a scripting language with the speed of C. The C Clustering Library and the corresponding Python C extension module Pycluster were released under the Python License, while the Perl module Algorithm::Cluster was released under the Artistic License. The GUI code Cluster 3.0 for Windows, Macintosh and Linux/Unix, as well as the corresponding command-line program, were released under the same license as the original Cluster code. The complete source code is available at http://bonsai.ims.u-tokyo.ac.jp/mdehoon/software/cluster. Alternatively, Algorithm::Cluster can be downloaded from CPAN, while Pycluster is also available as part of the Biopython distribution.

  5. New Discoveries in the Search for Iron-Complex Globular Clusters

    Science.gov (United States)

    Johnson, Christian; Caldwell, Nelson; Rich, R. Michael; Mateo, Mario; Bailey, Jeb; Walker, Matthew G.; M2FS Team

    2018-01-01

    A growing number of Galactic globular clusters have been discovered that possess large intrinsic [Fe/H] and heavy element abundance variations. These "iron-complex" clusters are among the most massive in the Galaxy, and frequently exhibit extended blue horizontal branches and low metallicities. Additionally, a handful of clusters with [Fe/H] > -1 may also have large metallicity spreads (e.g., Terzan 5), but are instead characterized by having bimodal red horizontal brances. We present chemical composition analyses of several potential iron-complex clusters spanning [Fe/H] = -1.8 to -0.8, and discover that horizontal branch morphology alone is insufficient to identify clusters with heavy element abundance variations. However, we find that several of these clusters contain 4-5 chemically distinct populations, and the outer halo cluster NGC 6229 is added to the growing list of iron-complex clusters that may be the remnant cores of former dwarf spheroidal galaxies.

  6. Los Estudios Organizacionales. Un campo de conocimiento comprensivo para el estudio de las organizaciones

    Directory of Open Access Journals (Sweden)

    Diego René Gonzales-Miranda

    2014-09-01

    Full Text Available El presente artículo es un texto introductorio para comprender qué son los Estudios Organizacionales. Además, se realiza una contextualización histórica de los Estudios Organizacionales, para luego discutir sus dimensiones ontológicas, epistemológicas y metodológicas, así como su objeto de estudio y los marcos teóricos que se inscriben en este campo de conocimiento. Asimismo, se destacan su carácter pluridisciplinario y su postura crítica como características propias. El artículo termina con una reflexión en torno a las posibilidades que tienen de ser un complemento para la formación en Administración y la importancia de divulgar este campo de conocimiento comprensivo para el estudio de las organizaciones en América Latina.

  7. Fischer–Tropsch Synthesis at a Low Pressure on Subnanometer Cobalt Oxide Clusters: The Effect of Cluster Size and Support on Activity and Selectivity

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Sungsik; Lee, Byeongdu; Seifert, Sönke; Winans, Randall E.; Vajda, Stefan

    2015-05-21

    In this study, the catalytic activity and changes in the oxidation state during the Fischer Tropsch (FT) reaction was investigated on subnanometer size-selected cobalt clusters deposited on oxide (Al2O3, MgO) and carbon-based (ultrananocrystalline diamond UNCD) supports by temperature programmed reaction (TPRx) combined with in-situ grazing-incidence X-ray absorption characterization (GIXAS). The activity and selectivity of ultrasmall cobalt clusters exhibits a very strong dependence on cluster size and support. The evolution of the oxidation state of metal cluster during the reaction reveals that metal-support interaction plays a key role in the reaction.

  8. Comparison of Intra-cluster and M87 Halo Orphan Globular Clusters in the Virgo Cluster

    Science.gov (United States)

    Louie, Tiffany Kaye; Tuan, Jin Zong; Martellini, Adhara; Guhathakurta, Puragra; Toloba, Elisa; Peng, Eric; Longobardi, Alessia; Lim, Sungsoon

    2018-01-01

    We present a study of “orphan” globular clusters (GCs) — GCs with no identifiable nearby host galaxy — discovered in NGVS, a 104 deg2 CFHT/MegaCam imaging survey. At the distance of the Virgo cluster, GCs are bright enough to make good spectroscopic targets and many are barely resolved in good ground-based seeing. Our orphan GC sample is derived from a subset of NGVS-selected GC candidates that were followed up with Keck/DEIMOS spectroscopy. While our primary spectroscopic targets were candidate GC satellites of Virgo dwarf elliptical and ultra-diffuse galaxies, many objects turned out to be non-satellites based on a radial velocity mismatch with the Virgo galaxy they are projected close to. Using a combination of spectral characteristics (e.g., absorption vs. emission), Gaussian mixture modeling of radial velocity and positions, and extreme deconvolution analysis of ugrizk photometry and image morphology, these non-satellites were classified into: (1) intra-cluster GCs (ICGCs) in the Virgo cluster, (2) GCs in the outer halo of M87, (3) foreground Milky Way stars, and (4) background galaxies. The statistical distinction between ICGCs and M87 halo GCs is based on velocity distributions (mean of 1100 vs. 1300 km/s and dispersions of 700 vs. 400 km/s, respectively) and radial distribution (diffuse vs. centrally concentrated, respectively). We used coaddition to increase the spectral SNR for the two classes of orphan GCs and measured the equivalent widths (EWs) of the Mg b and H-beta absorption lines. These EWs were compared to single stellar population models to obtain mean age and metallicity estimates. The ICGCs and M87 halo GCs have = –0.6+/–0.3 and –0.4+/–0.3 dex, respectively, and mean ages of >~ 5 and >~ 10 Gyr, respectively. This suggests the M87 halo GCs formed in relatively high-mass galaxies that avoided being tidally disrupted by M87 until they were close to the cluster center, while IGCCs formed in relatively low-mass galaxies that were

  9. Polyoxometalate coordinated transition metal complexes as ...

    Indian Academy of Sciences (India)

    Keywords. Heptamolybdate type polyoxometalate cluster anion; transition metal coordination complexes; ... industrial chemistry. This oxidation can be divided into three categories: (i) the cleavage of the C=C bond by using the surface of the metal oxide, e.g., osmium or .... supported cobalt complexes (catalysts 1 and 2) pro-.

  10. Atmospheric trace metal concentrations in Suspended Particulate ...

    African Journals Online (AJOL)

    The correlation matrix analysis showed a strong positive correlation between the kitchen, living room and outdoor sites, suggesting identical sources of the trace metals. Principal component analysis (PCA) identified two fundamental sources of the metals, whichwas further confirmed by the hierarchical cluster analysis.

  11. Interação de átomos leves com clusters de metais de transição

    OpenAIRE

    Cassús, Eduardo Pires; Machado, Sérgio de Paula; Garrido, Francisco M. S; Medeiros, Marta E; Machuca-Herrera, Juan Omar

    2011-01-01

    Density Functional Theory (DFT) calculations on the interactions of small atoms (H, C, O, and S) on first-row transition metal clusters were performed. The results show that the adsorption site may vary between the metal surface and the edge of the cluster. The adsorption energies, adatom-nearest neighbor and adatom-metal plane distances were also determined. Finally, the authors present a discussion about the performance of these metals as anodes on solid oxide fuel cells. The results obtain...

  12. Cluster Management Institutionalization

    DEFF Research Database (Denmark)

    Normann, Leo; Agger Nielsen, Jeppe

    2015-01-01

    This article explores a new management form – cluster management – in Danish public sector day care. Although cluster management has been widely adopted in Danish day care at the municipality level, it has attracted only sparse research attention. We use theoretical insights from Scandinavian...... institutionalism together with a longitudinal case-based inquiry into how cluster management has entered and penetrated the management practices of day care in Denmark. We demonstrate how cluster management became widely adopted in the day care field not only because of its intrinsic properties but also because...... of how it was legitimized as a “ready-to-use” management model. Further, our account reveals how cluster management translated into considerably different local variants as it travelled into specific organizations. However, these processes have not occurred sequentially with cluster management first...

  13. Disentangling Porterian Clusters

    DEFF Research Database (Denmark)

    Jagtfelt, Tue

    This dissertation investigates the contemporary phenomenon of industrial clusters based on the work of Michael E. Porter, the central progenitor and promoter of the cluster notion. The dissertation pursues two central questions: 1) What is a cluster? and 2) How could Porter’s seemingly fuzzy...... to his membership on the Commission on Industrial Competitiveness, and that the cluster notion found in his influential book, Nations, represents a significant shift in his conception of cluster compared with his early conceptions. This shift, it is argued, is a deliberate attempt by Porter to create...... a paradigmatic textbook that follows Kuhn’s blueprint for scientific revolutions by instilling Nations with circular references and thus creating a local linguistic holism conceptualized through an encompassing notion of cluster. The dissertation concludes that the two research questions are philosophically...

  14. Cluster Deposition and Implantation on/in Graphite

    DEFF Research Database (Denmark)

    Popok, Vladimir

    2013-01-01

    Cluster ion beam technique is a versatile tool which can be used for controllable formation of nanosize objects on the surface, modification and processing of surfaces and shallow layers on an atomic scale. In this chapter an overview of research on cluster interaction with graphite is presented....... One of the emphases is put on pinning of metal clusters on graphite with a possibility of following selective etching of graphene layers. The other topic of concern is related to the phenomenon of cluster stopping and the development of scaling law for cluster implantation in graphite. Graphite...... is chosen for surface experiments because it is a good model material; it has an atomically smooth surface that makes it easy to resolve very small deposited clusters or damaged areas. Layered structure of graphite with strong covalent bonds in the graphene sheets and very week van der Waals interactions...

  15. The dynamics of cavity clusters in ultrasonic (vibratory) cavitation erosion

    DEFF Research Database (Denmark)

    Hansson, I.; Mørch, Knud Aage

    1980-01-01

    The erosion of solids caused by cavitating liquids is a result of the concerted collapse of clusters of cavities. In vibratory cavitation equipment the clusters grow and collapse adjacent to a solid surface and are typically of hemispherical or cylindrical form. In the present paper the collapse...... process of these clusters is described and the collapse equations are developed and solved. The theoretical results are compared with results from high-speed photography of the clusters and with the initial stages of cavitation erosion on metal specimens. Experimental and theoretical results show...... the ambient pressure. Therefore the collapse velocity of the individual cavities increases towards the cluster center, which explains that the erosion, being caused by the individual cavities, occurs predominantly in this region. Likewise, the pressure increase at the cluster boundary explains why materials...

  16. Formation and Assembly of Massive Star Clusters

    Science.gov (United States)

    McMillan, Stephen

    open access to state-of- the-art simulation techniques within a modern, modular software environment. We will follow the gravitational collapse of 0.1-10 million-solar mass gas clouds through star formation and coalescence into a star cluster, modeling in detail the coupling of the gas and the newborn stars. We will study the effects of star formation by detecting accreting regions of gas in self-gravitating, turbulent, MHD, FLASH models that we will translate into collisional dynamical systems of stars modeled with an N-body code, coupled together in the AMUSE framework. Our FLASH models will include treatments of radiative transfer from the newly formed stars, including heating and radiative acceleration of the surrounding gas. Specific questions to be addressed are: (1) How efficiently does the gas in a star forming region form stars, how does this depend on mass, metallicity, and other parameters, and what terminates star formation? What observational predictions can be made to constrain our models? (2) How important are different mechanisms for driving turbulence and removing gas from a cluster: accretion, radiative feedback, and mechanical feedback? (3) How does the infant mortality rate of young clusters depend on the initial properties of the parent cloud? (4) What are the characteristic formation timescales of massive star clusters, and what observable imprints does the assembly process leave on their structure at an age of 10-20 Myr, when formation is essentially complete and many clusters can be observed? These studies are directly relevant to NASA missions at many electromagnetic wavelengths, including Chandra, GALEX, Hubble, and Spitzer. Each traces different aspects of cluster formation and evolution: X-rays trace supernovae, ultraviolet traces young stars, visible colors can distinguish between young blue stars and older red stars, and the infrared directly shows young embedded star clusters.

  17. 15th Cluster workshop

    CERN Document Server

    Laakso, Harri; Escoubet, C. Philippe; The Cluster Active Archive : Studying the Earth’s Space Plasma Environment

    2010-01-01

    Since the year 2000 the ESA Cluster mission has been investigating the small-scale structures and processes of the Earth's plasma environment, such as those involved in the interaction between the solar wind and the magnetospheric plasma, in global magnetotail dynamics, in cross-tail currents, and in the formation and dynamics of the neutral line and of plasmoids. This book contains presentations made at the 15th Cluster workshop held in March 2008. It also presents several articles about the Cluster Active Archive and its datasets, a few overview papers on the Cluster mission, and articles reporting on scientific findings on the solar wind, the magnetosheath, the magnetopause and the magnetotail.

  18. How atomic nuclei cluster.

    Science.gov (United States)

    Ebran, J-P; Khan, E; Nikšić, T; Vretenar, D

    2012-07-18

    Nucleonic matter displays a quantum-liquid structure, but in some cases finite nuclei behave like molecules composed of clusters of protons and neutrons. Clustering is a recurrent feature in light nuclei, from beryllium to nickel. Cluster structures are typically observed as excited states close to the corresponding decay threshold; the origin of this phenomenon lies in the effective nuclear interaction, but the detailed mechanism of clustering in nuclei has not yet been fully understood. Here we use the theoretical framework of energy-density functionals, encompassing both cluster and quantum liquid-drop aspects of nuclei, to show that conditions for cluster formation can in part be traced back to the depth of the confining nuclear potential. For the illustrative example of neon-20, we show that the depth of the potential determines the energy spacings between single-nucleon orbitals in deformed nuclei, the localization of the corresponding wavefunctions and, therefore, the degree of nucleonic density clustering. Relativistic functionals, in particular, are characterized by deep single-nucleon potentials. When compared to non-relativistic functionals that yield similar ground-state properties (binding energy, deformation, radii), they predict the occurrence of much more pronounced cluster structures. More generally, clustering is considered as a transitional phenomenon between crystalline and quantum-liquid phases of fermionic systems.

  19. Metal-adeninate vertices for the construction of an exceptionally porous metal-organic framework.

    Science.gov (United States)

    An, Jihyun; Farha, Omar K; Hupp, Joseph T; Pohl, Ehmke; Yeh, Joanne I; Rosi, Nathaniel L

    2012-01-03

    Metal-organic frameworks comprising metal-carboxylate cluster vertices and long, branched organic linkers are the most porous materials known, and therefore have attracted tremendous attention for many applications, including gas storage, separations, catalysis and drug delivery. To increase metal-organic framework porosity, the size and complexity of linkers has increased. Here we present a promising alternative strategy for constructing mesoporous metal-organic frameworks that addresses the size of the vertex rather than the length of the organic linker. This approach uses large metal-biomolecule clusters, in particular zinc-adeninate building units, as vertices to construct bio-MOF-100, an exclusively mesoporous metal-organic framework. Bio-MOF-100 exhibits a high surface area (4,300 m(2) g(-1)), one of the lowest crystal densities (0.302 g cm(-3)) and the largest metal-organic framework pore volume reported to date (4.3 cm(3) g(-1)).

  20. Traveling cluster approximation for uncorrelated amorphous systems

    International Nuclear Information System (INIS)

    Kaplan, T.; Sen, A.K.; Gray, L.J.; Mills, R.

    1985-01-01

    In this paper, the authors apply the TCA concepts to spatially disordered, uncorrelated systems (e.g., fluids or amorphous metals without short-range order). This is the first approximation scheme for amorphous systems that takes cluster effects into account while preserving the Herglotz property for any amount of disorder. They have performed some computer calculations for the pair TCA, for the model case of delta-function potentials on a one-dimensional random chain. These results are compared with exact calculations (which, in principle, taken into account all cluster effects) and with the CPA, which is the single-site TCA. The density of states for the pair TCA clearly shows some improvement over the CPA, and yet, apparently, the pair approximation distorts some of the features of the exact results. They conclude that the effects of large clusters are much more important in an uncorrelated liquid metal than in a substitutional alloy. As a result, the pair TCA, which does quite a nice job for alloys, is not adequate for the liquid. Larger clusters must be treated exactly, and therefore an n-TCA with n > 2 must be used

  1. Chemical Dynamics at Surfaces of Metal Nanomaterials

    Science.gov (United States)

    2014-07-23

    method to determine 3D molecular structures One of the major problems in experimentally studying heterogeneous catalysis is the lack of tools...the determinations of molecular structures and dynamics on the surfaces of metal nanomaterials – the critical component of heterogeneous catalysts...for the determinations of molecular structures on the surfaces of metal nanomaterials. Practical catalysts, e.g. oxide-supported metal clusters, are

  2. Statistical properties of convex clustering

    OpenAIRE

    Tan, Kean Ming; Witten, Daniela

    2015-01-01

    In this manuscript, we study the statistical properties of convex clustering. We establish that convex clustering is closely related to single linkage hierarchical clustering and $k$-means clustering. In addition, we derive the range of the tuning parameter for convex clustering that yields a non-trivial solution. We also provide an unbiased estimator of the degrees of freedom, and provide a finite sample bound for the prediction error for convex clustering. We compare convex clustering to so...

  3. Nonlocalized clustering and evolution of cluster structure in nuclei

    Science.gov (United States)

    Horiuchi, H.

    2017-06-01

    It is shown that the THSR (Tohsaki-Horiuchi-Schuck-Roepke) wave function describe well not only cluster-gas like structures but also ordinary cluster structures with spatial localization of clusters. Based on this fact, the container model has been proposed as a new model of cluster dynamics. For better description of cluster dynamics, extended version of container model has been introduced. The container model of cluster dynamics teaches us how is the evolution of cluster structure which starts from the ground state having shell-model structure to many kinds of cluster states up to the cluster-gas states.

  4. Estudios de competitividad en sistemas urbano - territoriales

    Directory of Open Access Journals (Sweden)

    Esteban Soms García

    2007-05-01

    El Ministerio de Planificación y Cooperación de Chile, ha desarrollado varios estudios relacionados con la competitividad regional, destinados a pronosticar y evaluar los impactos positivos y negativos que podrían derivarse de los recientes Acuerdos de Libre Comercio suscritos por Chile con la Comunidad Europea, Estados Unidos y Corea, más los acuerdos ad portas con los Países de la APEC. En lo referente a competitividad urbana, destacan algunos estudios y proyectos relacionados con el programa gubernamental "Ciudades para el Bicentenario", impulsado el Ministerio de Vivienda y Urbanismo y los Gobiernos Regionales de Antofagasta, Bio Bio, Valparaíso y Santiago.

  5. Estrategia organizacional: una propuesta de estudio

    Directory of Open Access Journals (Sweden)

    Ángela Lucía Noguera Hidalgo

    2014-01-01

    Full Text Available El concepto de estrategia en el contexto de las organizaciones empresariales es uno de los temas que genera gran interés en los asuntos del management. Sin embargo, la proposición de nuevos enfoques no ha aportado significativamente al avance en el estudio de este concepto. El estancamiento se hace evidente, razón por la cual el presente documento esboza una propuesta que reúne algunos de los retos para el estudio de la estrategia. En él se presenta una revisión que deja por sentados los posibles caminos a seguir, los cuales contribuyen a la perdurabilidad de las organizaciones.

  6. Lifting to cluster-tilting objects in higher cluster categories

    OpenAIRE

    Liu, Pin

    2008-01-01

    In this note, we consider the $d$-cluster-tilted algebras, the endomorphism algebras of $d$-cluster-tilting objects in $d$-cluster categories. We show that a tilting module over such an algebra lifts to a $d$-cluster-tilting object in this $d$-cluster category.

  7. H-D exchange in metal carbene complexes: Structure of cluster (μ-H)(μ-OCD3)Os3(CO)9{:C(CD3)NC2H8O}

    Science.gov (United States)

    Savkov, Boris; Maksakov, Vladimir; Kuratieva, Natalia

    2015-10-01

    X-ray and spectroscopic data for the new complex (μ-H)(μ-OCH3)Os3(CO)9{:C(CD3)NC2H8O} (2) obtained in the reaction of the (μ-H)(μ-Cl)Os3(CO)9{:C(CH3)NC2H8O} (1) with NaOCD3 in CD3OD solution are reported. It is shown that cluster 1 has the property of CH-acidity inherent of Fisher type carbenes. This had demonstrated using hydrogen deuterium exchange reaction in the presence of a strong base. Bridging chlorine to metoxide ligand substitution takes place during the reaction. The molecular structure of 2 is compared with known analogues.

  8. New metals

    International Nuclear Information System (INIS)

    Bergqvist, U.

    1983-12-01

    The aim of this report is to estimate the exposure to various metals and metal compounds and discuss the available information of the possible toxic effects of these metals and compounds. In the first section, some metals are defined as those with either a large or a fast increasing exposure to living organisms. The available information on toxicity is discussed in the second section. In the third section interesting metals are defined as compounds having a large exposure and an apparent insufficient knowledge of their possible toxic effects. Comments on each of these metals are also to be found in the third section. (G.B.)

  9. ULTRA-COMPACT DWARFS IN THE COMA CLUSTER

    International Nuclear Information System (INIS)

    Chiboucas, Kristin; Tully, R. Brent; Marzke, R. O.; Phillipps, S.; Price, J.; Peng, Eric W.; Trentham, Neil; Carter, David; Hammer, Derek

    2011-01-01

    We have undertaken a spectroscopic search for ultra-compact dwarf galaxies (UCDs) in the dense core of the dynamically evolved, massive Coma cluster as part of the Hubble Space Telescope/Advanced Camera for Surveys (HST/ACS) Coma Cluster Treasury Survey. UCD candidates were initially chosen based on color, magnitude, degree of resolution within the ACS images, and the known properties of Fornax and Virgo UCDs. Follow-up spectroscopy with Keck/Low-Resolution Imaging Spectrometer confirmed 27 candidates as members of the Coma cluster, a success rate >60% for targeted objects brighter than M R = -12. Another 14 candidates may also prove to be Coma members, but low signal-to-noise spectra prevent definitive conclusions. An investigation of the properties and distribution of the Coma UCDs finds these objects to be very similar to UCDs discovered in other environments. The Coma UCDs tend to be clustered around giant galaxies in the cluster core and have colors/metallicity that correlate with the host galaxy. With properties and a distribution similar to that of the Coma cluster globular cluster population, we find strong support for a star cluster origin for the majority of the Coma UCDs. However, a few UCDs appear to have stellar population or structural properties which differentiate them from the old star cluster populations found in the Coma cluster, perhaps indicating that UCDs may form through multiple formation channels.

  10. Evidence for Primordial Mass Segregation in Globular Clusters

    Science.gov (United States)

    Baumgardt, Holger; De Marchi, Guido; Kroupa, Pavel

    2008-09-01

    We have studied the dissolution of initially mass-segregated and unsegregated star clusters due to two-body relaxation in external tidal fields, using Aarseth's collisional N-body code NBODY4 on GRAPE6 special-purpose computers. When extrapolating results of initially non-mass-segregated models to globular clusters, we obtain a correlation between the time until destruction and the slope of the mass function, in the sense that globular clusters that are closer to dissolution are more strongly depleted in low-mass stars. This correlation fits observed mass functions of most globular clusters. The mass functions of several globular clusters are, however, more strongly depleted in low-mass stars than is suggested by these models. Such strongly depleted mass functions can be explained if globular clusters started initially mass segregated. Primordial mass segregation also explains the correlation between the slope of the stellar mass function and the cluster concentration that was recently discovered by De Marchi and coworkers. In this case, it is possible that all globular clusters started with a mass function similar to that seen in young open clusters in the present-day universe, at least for stars below m = 0.8 M⊙. This argues for a near universality of the mass function for different star formation environments and metallicities in the range -2 < [ Fe/H ] < 0. We finally describe a novel algorithm that can initialize stationary mass-segregated clusters with an arbitrary density profile and amount of mass segregation.

  11. Mixed-Initiative Clustering

    Science.gov (United States)

    Huang, Yifen

    2010-01-01

    Mixed-initiative clustering is a task where a user and a machine work collaboratively to analyze a large set of documents. We hypothesize that a user and a machine can both learn better clustering models through enriched communication and interactive learning from each other. The first contribution or this thesis is providing a framework of…

  12. Securing Personal Network Clusters

    NARCIS (Netherlands)

    Jehangir, A.; Heemstra de Groot, S.M.

    2007-01-01

    A Personal Network is a self-organizing, secure and private network of a user’s devices notwithstanding their geographic location. It aims to utilize pervasive computing to provide users with new and improved services. In this paper we propose a model for securing Personal Network clusters. Clusters

  13. Calixarene-supported clusters

    DEFF Research Database (Denmark)

    Taylor, Stephanie M.; McIntosh, Ruaraidh D.; Piligkos, Stergios

    2012-01-01

    A combination of complementary cluster ligands results in the formation of a new calixarene-supported ferromagnetic [Mn(5)] cage that displays the characteristic bonding modes of each support.......A combination of complementary cluster ligands results in the formation of a new calixarene-supported ferromagnetic [Mn(5)] cage that displays the characteristic bonding modes of each support....

  14. Reflections on cluster policies

    NARCIS (Netherlands)

    Brakman, Steven; van Marrewijk, Charles

    Economic activity tends to cluster. This results in productivity gains. For policy makers this offers an opportunity to formulate and promote policies that foster clustering of economic activity. Paradoxically, although agglomeration rents are often found in empirical research, a rationale for

  15. When Clusters become Networks

    NARCIS (Netherlands)

    S.M.W. Phlippen (Sandra); G.A. van der Knaap (Bert)

    2007-01-01

    textabstractPolicy makers spend large amounts of public resources on the foundation of science parks and other forms of geographically clustered business activities, in order to stimulate regional innovation. Underlying the relation between clusters and innovation is the assumption that co-located

  16. Fuzzy clustering of mechanisms

    Indian Academy of Sciences (India)

    type synthesis phase of mechanical design. To the best of the authors' knowledge, this type of clustering of mechanisms has not been attempted before. Thus, this is the first attempt to cluster the mechanisms based on some quantitative measures. It may help the engineers to carry out type synthesis of the mechanisms.

  17. Neurostimulation in cluster headache

    DEFF Research Database (Denmark)

    Pedersen, Jeppe L; Barloese, Mads; Jensen, Rigmor H

    2013-01-01

    PURPOSE OF REVIEW: Neurostimulation has emerged as a viable treatment for intractable chronic cluster headache. Several therapeutic strategies are being investigated including stimulation of the hypothalamus, occipital nerves and sphenopalatine ganglion. The aim of this review is to provide...... effective strategy must be preferred as first-line therapy for intractable chronic cluster headache....

  18. CSR in Industrial Clusters

    DEFF Research Database (Denmark)

    Lund-Thomsen, Peter; Pillay, Renginee G.

    2012-01-01

    development in the South. At the turn of the millennium the industrial cluster debate expanded as clusters were perceived as a potential source of poverty reduction, while their role in promoting CSR among small and medium-sized enterprises began to take shape from 2006 onwards. At present, there is still...

  19. Cluster knockout reactions

    Indian Academy of Sciences (India)

    2014-04-07

    Apr 7, 2014 ... advancements in the area of (α, 2α) reactions and heavy cluster knockout reactions are discussed. Importance of the finite-range vertex and the final-state interactions are brought out. Keywords. Cluster knockout reactions; FR-DWIA calculations; t-matrix effective interaction. PACS Nos 14.20.Pt; 24.10.

  20. Multilevel functional clustering analysis.

    Science.gov (United States)

    Serban, Nicoleta; Jiang, Huijing

    2012-09-01

    In this article, we investigate clustering methods for multilevel functional data, which consist of repeated random functions observed for a large number of units (e.g., genes) at multiple subunits (e.g., bacteria types). To describe the within- and between variability induced by the hierarchical structure in the data, we take a multilevel functional principal component analysis (MFPCA) approach. We develop and compare a hard clustering method applied to the scores derived from the MFPCA and a soft clustering method using an MFPCA decomposition. In a simulation study, we assess the estimation accuracy of the clustering membership and the cluster patterns under a series of settings: small versus moderate number of time points; various noise levels; and varying number of subunits per unit. We demonstrate the applicability of the clustering analysis to a real data set consisting of expression profiles from genes activated by immunity system cells. Prevalent response patterns are identified by clustering the expression profiles using our multilevel clustering analysis. © 2012, The International Biometric Society.

  1. Cluster Synchronization Algorithms

    NARCIS (Netherlands)

    Xia, Weiguo; Cao, Ming

    2010-01-01

    This paper presents two approaches to achieving cluster synchronization in dynamical multi-agent systems. In contrast to the widely studied synchronization behavior, where all the coupled agents converge to the same value asymptotically, in the cluster synchronization problem studied in this paper,

  2. Fuzzy clustering of mechanisms

    Indian Academy of Sciences (India)

    two clustering techniques, the mechanisms have been classified in the present work and in future, it may be extended to develop an expert system, which can automate type synthesis phase of mechanical design. To the best of the authors' knowledge, this type of clustering of mechanisms has not been attempted before.

  3. Collisions between Globular Clusters

    Science.gov (United States)

    Belloni, D. T.; Rocha-Pinto, H. J.

    2014-10-01

    The study of globular clusters (GC) plays an important role in our understanding of the Universe since these systems are true laboratories for theories of stellar dynamics and evolution. We are interested in studying a globular cluster formed by a collision between two different GC with NBODY6 (Aarseth, 2003). Firstly, in order to understand this code, we analyse how tidal streams form from a globular cluster in a circular orbit (on the disk) around the center of the Milky Way. In the next stage of this work we will study that collision. The stellar escape or capture from globular cluster can be understood with the Restricted Three Body Problem. These stars escape in a chaotic orbit, and in some cases may return (again in a chaotic orbit) to the cluster due to the Galactic potential. In most cases, such stars quickly alter their escape chaotic orbits to orbits that are similar to the parent cluster's orbit. Our results show an agglomeration of stars in a normal direction related to the direction towards the center of the Milky Way, forming thus a stream. We can explain this considering that a circular orbit around the dominant potential is the most likely orbit, since it requires minimum energy. In this coordinate systems, the tidal tails (or streams) rotates around the cluster center with the same mean motion associated to cluster around the Milky Way center.

  4. Detecting clusters of mutations.

    Directory of Open Access Journals (Sweden)

    Tong Zhou

    Full Text Available Positive selection for protein function can lead to multiple mutations within a small stretch of DNA, i.e., to a cluster of mutations. Recently, Wagner proposed a method to detect such mutation clusters. His method, however, did not take into account that residues with high solvent accessibility are inherently more variable than residues with low solvent accessibility. Here, we propose a new algorithm to detect clustered evolution. Our algorithm controls for different substitution probabilities at buried and exposed sites in the tertiary protein structure, and uses random permutations to calculate accurate P values for inferred clusters. We apply the algorithm to genomes of bacteria, fly, and mammals, and find several clusters of mutations in functionally important regions of proteins. Surprisingly, clustered evolution is a relatively rare phenomenon. Only between 2% and 10% of the genes we analyze contain a statistically significant mutation cluster. We also find that not controlling for solvent accessibility leads to an excess of clusters in terminal and solvent-exposed regions of proteins. Our algorithm provides a novel method to identify functionally relevant divergence between groups of species. Moreover, it could also be useful to detect artifacts in automatically assembled genomes.

  5. Alpha clustering in nuclei

    International Nuclear Information System (INIS)

    Hodgson, P.E.

    1990-01-01

    The effects of nucleon clustering in nuclei are described, with reference to both nuclear structure and nuclear reactions, and the advantages of using the cluster formalism to describe a range of phenomena are discussed. It is shown that bound and scattering alpha-particle states can be described in a unified way using an energy-dependent alpha-nucleus potential. (author)

  6. Incidencia de la terminología utilizada en la aplicación de la Teoría de Bandas sobre la presencia de un error conceptual referido a la conductividad eléctrica de los metales. Estudio en dos cursos introductorios de Química en la Universidad

    OpenAIRE

    Pliego, Oscar; Rodríguez, Cristina; Juárez, Stella; Contini, Liliana

    2013-01-01

    En cursos anteriores se detectó que los estudiantes asignaban erróneamente mayores valores de conductividad eléctrica a los metales que poseen mayor número de electrones de valencia con la energía de la comúnmente denominada “Banda de Conducción”. Para superar este desconcepto se propone que en los cursos de Química donde se aborden las propiedades de los metales, a los Orbitales de Banda se los denomine según la terminología de la Teoría de Orbitales Moleculares, a saber: “Orbitales de Banda...

  7. Theoretical study of lithium clusters by electronic stress tensor

    International Nuclear Information System (INIS)

    Ichikawa, Kazuhide; Nozaki, Hiroo; Komazawa, Naoya; Tachibana, Akitomo

    2012-01-01

    We study the electronic structure of small lithium clusters Li n (n = 2 ∼ 8) using the electronic stress tensor. We find that the three eigenvalues of the electronic stress tensor of the Li clusters are negative and degenerate, just like the stress tensor of liquid. This leads us to propose that we may characterize a metallic bond in terms of the electronic stress tensor. Our proposal is that in addition to the negativity of the three eigenvalues of the electronic stress tensor, their degeneracy characterizes some aspects of the metallic nature of chemical bonding. To quantify the degree of degeneracy, we use the differential eigenvalues of the electronic stress tensor. By comparing the Li clusters and hydrocarbon molecules, we show that the sign of the largest eigenvalue and the differential eigenvalues could be useful indices to evaluate the metallicity or covalency of a chemical bond.

  8. Star formation properties of galaxy cluster A1767

    International Nuclear Information System (INIS)

    Yan, Peng-Fei; Li, Feng; Yuan, Qi-Rong

    2015-01-01

    Abell 1767 is a dynamically relaxed, cD cluster of galaxies with a redshift of 0.0703. Among 250 spectroscopically confirmed member galaxies within a projected radius of 2.5r 200 , 243 galaxies (∼ 97%) are spectroscopically covered by the Sloan Digital Sky Survey. Based on this homogeneous spectral sample, the stellar evolutionary synthesis code STARLIGHT is applied to investigate the stellar populations and star formation histories of galaxies in this cluster. The star formation properties of galaxies, such as mean stellar ages, metallicities, stellar masses, and star formation rates, are presented as functions of local galaxy density. A strong environmental effect is found such that massive galaxies in the high-density core region of the cluster tend to have higher metallicities, older mean stellar ages, and lower specific star formation rates (SSFRs), and their recent star formation activities have been remarkably suppressed. In addition, the correlations of the metallicity and SSFR with stellar mass are confirmed. (paper)

  9. Mathematical classification and clustering

    CERN Document Server

    Mirkin, Boris

    1996-01-01

    I am very happy to have this opportunity to present the work of Boris Mirkin, a distinguished Russian scholar in the areas of data analysis and decision making methodologies. The monograph is devoted entirely to clustering, a discipline dispersed through many theoretical and application areas, from mathematical statistics and combina­ torial optimization to biology, sociology and organizational structures. It compiles an immense amount of research done to date, including many original Russian de­ velopments never presented to the international community before (for instance, cluster-by-cluster versions of the K-Means method in Chapter 4 or uniform par­ titioning in Chapter 5). The author's approach, approximation clustering, allows him both to systematize a great part of the discipline and to develop many in­ novative methods in the framework of optimization problems. The optimization methods considered are proved to be meaningful in the contexts of data analysis and clustering. The material presented in ...

  10. Negotiating Cluster Boundaries

    DEFF Research Database (Denmark)

    Giacomin, Valeria

    2017-01-01

    Palm oil was introduced to Malay(si)a as an alternative to natural rubber, inheriting its cluster organizational structure. In the late 1960s, Malaysia became the world’s largest palm oil exporter. Based on archival material from British colonial institutions and agency houses, this paper focuses...... on the governance dynamics that drove institutional change within this cluster during decolonization. The analysis presents three main findings: (i) cluster boundaries are defined by continuous tug-of-war style negotiations between public and private actors; (ii) this interaction produces institutional change...... within the cluster, in the form of cumulative ‘institutional rounds’ – the correction or disruption of existing institutions or the creation of new ones; and (iii) this process leads to a broader inclusion of local actors in the original cluster configuration. The paper challenges the prevalent argument...

  11. Improved Density Functional Tight Binding Potentials for Metalloid Aluminum Clusters

    Science.gov (United States)

    2016-06-01

    approach, using solution chemistry methods to grow small metal clusters with a single monolayer of organic ligand on their surface. These may offer the...These liquids are then used for solution growth of larger clusters, which includes a ligand exchange process with, most commonly, cyclopentadienyl...derived in DFT. For the many body problem of a system consisting of nuclei and electrons, the total energy can be written as [3]: ext ee IIE T E

  12. NGC 7789: An open cluster case study

    Energy Technology Data Exchange (ETDEWEB)

    Overbeek, Jamie C.; Friel, Eileen D.; Pilachowski, Catherine A.; Mészáros, Szabolcs [Indiana University Astronomy Department, Swain West 319, 727 East 3rd Street, Bloomington, IN 47405 (United States); Jacobson, Heather R. [Massachusetts Institute of Technology, Kavli Institute for Astrophysics and Space Research, Cambridge, MA 02139 (United States); Johnson, Christian I., E-mail: joverbee@indiana.edu [Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138 (United States)

    2015-01-01

    We have obtained high-resolution spectra of 32 giants in the open cluster NGC 7789 using the Wisconsin–Indiana–Yale–NOAO Hydra spectrograph. We explore differences in atmospheric parameters and elemental abundances caused by the use of the linelist developed for the Gaia-ESO Survey (GES) compared to one based on Arcturus used in our previous work. [Fe/H] values decrease when using the GES linelist instead of the Arcturus-based linelist; these differences are probably driven by systematically lower (∼−0.1 dex) GES surface gravities. Using the GES linelist we determine abundances for 10 elements—Fe, Mg, Si, Ca, Ti, Na, Ni, Zr, Ba, and La. We find the cluster's average metallicity [Fe/H] = 0.03 ± 0.07 dex, in good agreement with literature values, and a lower [Mg/Fe] abundance than has been reported before for this cluster (0.11 ± 0.05 dex). We also find the neutron-capture element barium to be highly enhanced—[Ba/Fe] = +0.48 ± 0.08—and disparate from cluster measurements of neutron-capture elements La and Zr (−0.08 ± 0.05 and 0.08 ± 0.08, respectively). This is in accordance with recent discoveries of supersolar Ba enhancement in young clusters along with more modest enhancement of other neutron-capture elements formed in similar environments.

  13. Metal lagging

    International Nuclear Information System (INIS)

    Lemercier, Guy.

    1974-01-01

    The metal lagging described is characterized by the fact that it is formed of closed sacks composed of an elastic metal mass, compressed in an outer envelope made of a fine mesh metal fabric. The metal mass is composed of stainless steel wool stuffed into the envelope. This lagging is particularly intended for the thermal protection of the end slab of LMFBR type reactors [fr

  14. The next generation Virgo cluster survey. VIII. The spatial distribution of globular clusters in the Virgo cluster

    Energy Technology Data Exchange (ETDEWEB)

    Durrell, Patrick R.; Accetta, Katharine [Department of Physics and Astronomy, Youngstown State University, Youngstown, OH 44555 (United States); Côté, Patrick; Blakeslee, John P.; Ferrarese, Laura; McConnachie, Alan; Gwyn, Stephen [Herzberg Astronomy and Astrophysics, National Research Council, 5071 West Saanich Road, Victoria, BC V9E 2E7 (Canada); Peng, Eric W.; Zhang, Hongxin [Department of Astronomy, Peking University, Beijing 100871 (China); Mihos, J. Christopher [Department of Astronomy, Case Western Reserve University, Cleveland, OH 44106 (United States); Puzia, Thomas H.; Jordán, Andrés [Institute of Astrophysics, Pontificia Universidad Catolica, Av. Vicu' a Mackenna 4860, Macul 7820436, Santiago (Chile); Lançon, Ariane [Observatoire astronomique de Strasbourg, Université de Strasbourg, CNRS, UMR 7550, 11 rue de l' Université, F-67000 Strasbourg (France); Liu, Chengze [Center for Astronomy and Astrophysics, Department of Physics and Astronomy, Shanghai Jiao Tong University, 800 Dongchuan Road, Shanghai 200240 (China); Cuillandre, Jean-Charles [Canada-France-Hawaii Telescope Corporation, Kamuela, HI 96743 (United States); Boissier, Samuel; Boselli, Alessandro [Aix Marseille Université, CNRS, LAM (Laboratoire d' Astrophysique de Marseille) UMR 7326, F-13388 Marseille (France); Courteau, Stéphane [Department of Physics, Engineering Physics and Astronomy, Queen' s University, Kingston, ON K7L 3N6 (Canada); Duc, Pierre-Alain [AIM Paris Saclay, CNRS/INSU, CEA/Irfu, Université Paris Diderot, Orme des Merisiers, F-91191 Gif sur Yvette cedex (France); Emsellem, Eric [Université de Lyon 1, CRAL, Observatoire de Lyon, 9 av. Charles André, F-69230 Saint-Genis Laval (France); CNRS, UMR 5574, ENS de Lyon (France); and others

    2014-10-20

    We report on a large-scale study of the distribution of globular clusters (GCs) throughout the Virgo cluster, based on photometry from the Next Generation Virgo Cluster Survey (NGVS), a large imaging survey covering Virgo's primary subclusters (Virgo A = M87 and Virgo B = M49) out to their virial radii. Using the g{sub o}{sup ′}, (g' – i') {sub o} color-magnitude diagram of unresolved and marginally resolved sources within the NGVS, we have constructed two-dimensional maps of the (irregular) GC distribution over 100 deg{sup 2} to a depth of g{sub o}{sup ′} = 24. We present the clearest evidence to date showing the difference in concentration between red and blue GCs over the full extent of the cluster, where the red (more metal-rich) GCs are largely located around the massive early-type galaxies in Virgo, while the blue (metal-poor) GCs have a much more extended spatial distribution with significant populations still present beyond 83' (∼215 kpc) along the major axes of both M49 and M87. A comparison of our GC maps to the diffuse light in the outermost regions of M49 and M87 show remarkable agreement in the shape, ellipticity, and boxiness of both luminous systems. We also find evidence for spatial enhancements of GCs surrounding M87 that may be indicative of recent interactions or an ongoing merger history. We compare the GC map to that of the locations of Virgo galaxies and the X-ray intracluster gas, and find generally good agreement between these various baryonic structures. We calculate the Virgo cluster contains a total population of N {sub GC} = 67, 300 ± 14, 400, of which 35% are located in M87 and M49 alone. For the first time, we compute a cluster-wide specific frequency S {sub N,} {sub CL} = 2.8 ± 0.7, after correcting for Virgo's diffuse light. We also find a GC-to-baryonic mass fraction ε {sub b} = 5.7 ± 1.1 × 10{sup –4} and a GC-to-total cluster mass formation efficiency ε {sub t} = 2.9 ± 0.5 × 10{sup –5

  15. Silicone metalization

    Energy Technology Data Exchange (ETDEWEB)

    Maghribi, Mariam N. (Livermore, CA); Krulevitch, Peter (Pleasanton, CA); Hamilton, Julie (Tracy, CA)

    2008-12-09

    A system for providing metal features on silicone comprising providing a silicone layer on a matrix and providing a metal layer on the silicone layer. An electronic apparatus can be produced by the system. The electronic apparatus comprises a silicone body and metal features on the silicone body that provide an electronic device.

  16. Ionized cluster beam technology for material science

    International Nuclear Information System (INIS)

    Takagi, Toshinori

    1997-01-01

    The most suitable kinetic energy range of ionized materials in film formation and epitaxial growth is from a few eV to a few hundreds eV, especially, less than about 100eV, when ions are used as a host. The main roles of ions in film formation are the effects due to their kinetic energy and the electronic charge effects which involve the effect to active film formation and the effect acceleration of chemical reactions. Therefore, it is important to develope the technology to transport large volume of a flux of ionized particles with an extremely low incident energy without any troubles due to the space charge effects and charge up problems on the surface. This is the exact motivation for us to have been developing the Ionized Cluster Beam (ICB) technology since 1972. By ICB technology materials (actually wide varieties of materials such as metal, semiconductor, magnetic material, insulator, organic material, etc.) are vaporized and ejected through a small hole nozzle into a high vacuum, where the vaporized material condenses into clusters with loosely coupled atoms with the sizes about from 100 to a few 1000 atoms (mainly 100-2000 atoms) by supercondensation phenomena due to the adiabatic expansion in this evaporation process through a small hole nozzle. In the ICB technology an atom in each cluster is ionized by irradiated by electron shower, and the ionized clusters are accelerated by electric field onto a substrate. The ionized clusters with neutral clusters impinged onto a substrate are spreaded separately into atoms migrating over the substrate, so that the surface migration energy of the impinged atoms, that is, surface diffusion energy are controlled by an incident energy of a cluster. In this report the theoretical and also experimental results of ICB technology are summarized

  17. Estudios transculturales del burnout: Los estudios transculturales Brasil-España

    Directory of Open Access Journals (Sweden)

    Bernardo Moreno Jiménez

    2003-01-01

    Full Text Available Los estudios transculturales no son un ejercicio secundario y complementario en el estudio de la psicología; un modelo antropológico de la conducta humana obliga a plantear que las variables culturales no son secundarias sino primarias. Por estas razones el estudio del “burnout” o desgaste profesional puede profundizarse mediante la utilización de los métodos transculturales. No es suficiente con la simple comparación de resultados, sino que es necesario buscar instrumentos propios de cada cultura y establecer la comparación no sólo del síndrome de desgaste profesional sino de todos los diferentes elementos del proceso. El trabajo presentado establece las bases teóricas de este planteamiento, y expone, mediante un ejemplo, algunas de las vías posibles para una psicología transcultural del burnout

  18. ESTUDIOS TRANSCULTURALES DEL BURNOUT: LOS ESTUDIOS TRANSCULTURALES BRASIL-ESPAÑA

    Directory of Open Access Journals (Sweden)

    Macarena Gálvez Herrer

    2003-07-01

    Full Text Available Los estudios transculturales no son un ejercicio secundario y complementario en el estudio de la psicología; un modelo antropológico de la conducta humana obliga a plantear que las variables culturales no son secundarias sino primarias. Por estas razones el estudio del “burnout†o desgaste profesional puede profundizarse mediante la utilización de los métodos transculturales. No es suficiente con la simple comparación de resultados, sino que es necesario buscar instrumentos propios de cada cultura y establecer la comparación no sólo del síndrome de desgaste profesional sino de todos los diferentes elementos del proceso. El trabajo presentado establece las bases teóricas de este planteamiento, y expone, mediante un ejemplo, algunas de las vías posibles para una psicología transcultural del burnout.

  19. Document clustering methods, document cluster label disambiguation methods, document clustering apparatuses, and articles of manufacture

    Science.gov (United States)

    Sanfilippo, Antonio [Richland, WA; Calapristi, Augustin J [West Richland, WA; Crow, Vernon L [Richland, WA; Hetzler, Elizabeth G [Kennewick, WA; Turner, Alan E [Kennewick, WA

    2009-12-22

    Document clustering methods, document cluster label disambiguation methods, document clustering apparatuses, and articles of manufacture are described. In one aspect, a document clustering method includes providing a document set comprising a plurality of documents, providing a cluster comprising a subset of the documents of the document set, using a plurality of terms of the documents, providing a cluster label indicative of subject matter content of the documents of the cluster, wherein the cluster label comprises a plurality of word senses, and selecting one of the word senses of the cluster label.

  20. Studies in clustering theory

    Science.gov (United States)

    Stell, George

    In recent years the properties of percolation models have been studied intensively. The purpose of our project was to develop a general theory of percolation and clustering between particles of arbitrary size and shape, with arbitrary correlations between them. The goal of such a theory includes the treatment of continuum percolation as well as a novel treatment of lattice percolation. We made substantial progress toward this goal. The quantities basic to a description of clustering, the mean cluster size, mean number of clusters, etc., were developed. Concise formulas were given for the terms in such series, and proved, at least for sufficiently low densities, that the series are absolutely convergent. These series can now be used to construct Pade approximants that will allow one to probe the percolation transition. A scaled-particle theory of percolation was developed which gives analytic approximants for the mean number of clusters in a large class of two and three dimensional percolation models. Although this quantity is essential in many applications, e.g., explaining colligative properties, and interpreting low-angle light-scattering data, no systematic studies of it have been done before this work. Recently carried out detailed computer simulations show that the mean number of clusters is given to high accuracy by several of there approximations. Extensions of this work will allow calculation of the complete cluster size distribution.