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Sample records for noncrystalline xenon-argon clusters

  1. High resolution electron microscopy of Ag-clusters in crystalline and non-crystalline morphologies grown inside superfluid helium nanodroplets

    SciTech Connect

    Volk, Alexander; Thaler, Philipp; Koch, Markus; Ernst, Wolfgang E.; Fisslthaler, Evelin; Grogger, Werner

    2013-06-07

    We present a first investigation of structural properties of Ag clusters with a diameter of up to 5.5 nm grown inside superfluid helium nanodroplets (He{sub N}) and deposited on an amorphous C surface. With high resolution transmission electron microscope images we are able to show that in addition to the crystalline face centered cubic (fcc) structure, noncrystalline icosahedral (Ih), and decahedral (Dh) morphologies are grown. Relative abundances (56% fcc, 31% Dh, and 13% Ih) as well as the size distribution of each morphology (mean diameters d{sub fcc}=2.62(5) nm, d{sub Dh}=3.34(7) nm, and d{sub Ih}=3.93(2) nm) do not reflect the situation expected from pure energetic considerations, where small Ihs should be followed by medium sized Dhs and large fccs. Instead, kinetic factors seem to play an important role in the formation of these structures, as it appears to be the case for clusters formed by inert gas aggregation. Considering the low temperatures (0.37 K) and extremely high cooling rates, we discuss basic ideas that might lead to a qualitative picture of the cluster formation process inside He{sub N}.

  2. High resolution electron microscopy of Ag-clusters in crystalline and non-crystalline morphologies grown inside superfluid helium nanodroplets.

    PubMed

    Volk, Alexander; Thaler, Philipp; Koch, Markus; Fisslthaler, Evelin; Grogger, Werner; Ernst, Wolfgang E

    2013-06-01

    We present a first investigation of structural properties of Ag clusters with a diameter of up to 5.5 nm grown inside superfluid helium nanodroplets (He(N)) and deposited on an amorphous C surface. With high resolution transmission electron microscope images we are able to show that in addition to the crystalline face centered cubic (fcc) structure, noncrystalline icosahedral (Ih), and decahedral (Dh) morphologies are grown. Relative abundances (56% fcc, 31% Dh, and 13% Ih) as well as the size distribution of each morphology (mean diameters d(fcc)=2.62(5) nm, d(Dh)=3.34(7) nm, and d(Ih)=3.93(2) nm) do not reflect the situation expected from pure energetic considerations, where small Ihs should be followed by medium sized Dhs and large fccs. Instead, kinetic factors seem to play an important role in the formation of these structures, as it appears to be the case for clusters formed by inert gas aggregation. Considering the low temperatures (0.37 K) and extremely high cooling rates, we discuss basic ideas that might lead to a qualitative picture of the cluster formation process inside He(N). PMID:23758376

  3. Nanoglasses: a new kind of noncrystalline materials

    PubMed Central

    2013-01-01

    Summary Nanoglasses are a new class of noncrystalline solids. They differ from today’s glasses due to their microstructure that resembles the microstructure of polycrystals. They consist of regions with a melt-quenched glassy structure connected by interfacial regions, the structure of which is characterized (in comparison to the corresponding melt-quenched glass) by (1) a reduced (up to about 10%) density, (2) a reduced (up to about 20%) number of nearest-neighbor atoms and (3) a different electronic structure. Due to their new kind of atomic and electronic structure, the properties of nanoglasses may be modified by (1) controlling the size of the glassy regions (i.e., the volume fraction of the interfacial regions) and/or (2) by varying their chemical composition. Nanoglasses exhibit new properties, e.g., a Fe90Sc10 nanoglass is (at 300 K) a strong ferromagnet whereas the corresponding melt-quenched glass is paramagnetic. Moreover, nanoglasses were noted to be more ductile, more biocompatible, and catalytically more active than the corresponding melt-quenched glasses. Hence, this new class of noncrystalline materials may open the way to technologies utilizing the new properties. PMID:24062978

  4. Study of a splat cooled Cu-Zr-noncrystalline phase.

    NASA Technical Reports Server (NTRS)

    Revcolevschi, A.; Grant, N. J.

    1972-01-01

    By rapid quenching from the melt, using the splat forming gun technique, a noncrystalline phase has been obtained in a Cu-Zr alloy containing 60 at. % Cu. Upon heating, rapid crystallization of the samples takes place at 477 C with a heat release of about 700 cal per mol. The variation of the electrical resistivity of the samples with temperature confirms the transformation. Very high resolution electron microscopy studies of the structural changes of the samples upon heating are presented and show the gradual crystallization of the amorphous structure.

  5. Rapid Mobilization of Noncrystalline U(IV) Coupled with FeS Oxidation.

    PubMed

    Bi, Yuqiang; Stylo, Malgorzata; Bernier-Latmani, Rizlan; Hayes, Kim F

    2016-02-01

    The reactivity of disordered, noncrystalline U(IV) species remains poorly characterized despite their prevalence in biostimulated sediments. Because of the lack of crystalline structure, noncrystalline U(IV) may be susceptible to oxidative mobilization under oxic conditions. The present study investigated the mechanism and rate of oxidation of biogenic noncrystalline U(IV) by dissolved oxygen (DO) in the presence of mackinawite (FeS). Previously recognized as an effective reductant and oxygen scavenger, nanoparticulate FeS was evaluated for its role in influencing U release in a flow-through system as a function of pH and carbonate concentration. The results demonstrated that noncrystalline U(IV) was more susceptible to oxidation than uraninite (UO2) in the presence of dissolved carbonate. A rapid release of U occurred immediately after FeS addition without exhibiting a temporary inhibition stage, as was observed during the oxidation of UO2, although FeS still kept DO levels low. X-ray photoelectron spectroscopy (XPS) characterized a transient surface Fe(III) species during the initial FeS oxidation, which was likely responsible for oxidizing noncrystalline U(IV) in addition to oxygen. In the absence of carbonate, however, the release of dissolved U was significantly hindered as a result of U adsorption by FeS oxidation products. This study illustrates the strong interactions between iron sulfide and U(IV) species during redox transformation and implies the lability of biogenic noncrystalline U(IV) species in the subsurface environment when subjected to redox cycling events.

  6. Fullerene mixtures enhance the thermal stability of a non-crystalline polymer solar cell blend

    NASA Astrophysics Data System (ADS)

    Lindqvist, Camilla; Bergqvist, Jonas; Bäcke, Olof; Gustafsson, Stefan; Wang, Ergang; Olsson, Eva; Inganäs, Olle; Andersson, Mats R.; Müller, Christian

    2014-04-01

    Printing of polymer:fullerene solar cells at high speed requires annealing at temperatures up to 140 °C. However, bulk-heterojunction blends that comprise a non-crystalline donor polymer often suffer from insufficient thermal stability and hence rapidly coarsen upon annealing above the glass transition temperature of the blend. In addition, micrometer-sized fullerene crystals grow, which are detrimental for the solar cell performance. In this manuscript, we present a strategy to limit fullerene crystallization, which is based on the use of fullerene mixtures of the two most common derivatives, PC61BM and PC71BM, as the acceptor material. Blends of this fullerene mixture and a non-crystalline thiophene-quinoxaline copolymer display considerably enhanced thermal stability and largely retain their photovoltaic performance upon annealing at elevated temperatures as high as 170 °C.

  7. Comparison of non-crystalline silica nanoparticles in IL-1β release from macrophages

    PubMed Central

    2012-01-01

    Background Respirable crystalline silica (silicon dioxide; SiO2, quartz) particles are known to induce chronic inflammation and lung disease upon long-term inhalation, whereas non-crystalline (amorphous) SiO2 particles in the submicrometre range are regarded as less harmful. Several reports have demonstrated that crystalline, but also non-crystalline silica particles induce IL-1β release from macrophages via the NALP3-inflammasome complex (caspase-1, ASC and NALP3) in the presence of lipopolysaccharide (LPS) from bacteria. Our aim was to study the potential of different non-crystalline SiO2 particles from the nano- to submicro-sized range to activate IL-1β responses in LPS-primed RAW264.7 macrophages and primary rat lung macrophages. The role of the NALP3-inflammasome and up-stream mechanisms was further explored in RAW264.7 cells. Results In the present study, we have shown that 6 h exposure to non-crystalline SiO2 particles in nano- (SiNPs, 5–20 nm, 50 nm) and submicro-sizes induced strong IL-1β responses in LPS-primed mouse macrophages (RAW264.7) and primary rat lung macrophages. The primary lung macrophages were more sensitive to Si-exposure than the RAW-macrophages, and responded more strongly. In the lung macrophages, crystalline silica (MinUsil 5) induced IL-1β release more potently than the non-crystalline Si50 and Si500, when adjusted to surface area. This difference was much less pronounced versus fumed SiNPs. The caspase-1 inhibitor zYVAD and RNA silencing of the NALP3 receptor reduced the particle-induced IL-1β release in the RAW264.7 macrophages. Furthermore, inhibitors of phagocytosis, endosomal acidification, and cathepsin B activity reduced the IL-1β responses to the different particles to a similar extent. Conclusions In conclusion, non-crystalline silica particles in the nano- and submicro-size ranges seemed to induce IL-1β release from LPS-primed RAW264.7 macrophages via similar mechanisms as crystalline silica, involving particle

  8. Unfolding the band structure of non-crystalline photonic band gap materials

    PubMed Central

    Tsitrin, Samuel; Williamson, Eric Paul; Amoah, Timothy; Nahal, Geev; Chan, Ho Leung; Florescu, Marian; Man, Weining

    2015-01-01

    Non-crystalline photonic band gap (PBG) materials have received increasing attention, and sizeable PBGs have been reported in quasi-crystalline structures and, more recently, in disordered structures. Band structure calculations for periodic structures produce accurate dispersion relations, which determine group velocities, dispersion, density of states and iso-frequency surfaces, and are used to predict a wide-range of optical phenomena including light propagation, excited-state decay rates, temporal broadening or compression of ultrashort pulses and complex refraction phenomena. However, band calculations for non-periodic structures employ large super-cells of hundreds to thousands building blocks, and provide little useful information other than the PBG central frequency and width. Using stereolithography, we construct cm-scale disordered PBG materials and perform microwave transmission measurements, as well as finite-difference time-domain (FDTD) simulations. The photonic dispersion relations are reconstructed from the measured and simulated phase data. Our results demonstrate the existence of sizeable PBGs in these disordered structures and provide detailed information of the effective band diagrams, dispersion relation, iso-frequency contours, and their angular dependence. Slow light phenomena are also observed in these structures near gap frequencies. This study introduces a powerful tool to investigate photonic properties of non-crystalline structures and provides important effective dispersion information, otherwise difficult to obtain. PMID:26289434

  9. Structure characterization of the non-crystalline complexes of copper salts with native cyclodextrins.

    PubMed

    Velasco, Manuel I; Krapacher, Claudio R; de Rossi, Rita H; Rossi, Laura I

    2016-06-28

    The characterization of non-crystalline complexes is particularly difficult when techniques like X-ray diffraction or NMR cannot be used. We propose a simple procedure to characterize the physicochemical properties of amorphous new coordination compounds between cyclodextrins (CD) and Cu(2+) salts, by means of the integration of the information provided by several techniques including elemental analysis, flame atomic absorption, TGA, UV-Vis diffuse reflectance, colorimetry, FT-IR and EPR. On the basis of these procedures, we suggest geometrical and structural approximations resulting in an octahedral or distorted octahedral geometry with diverse positions for the metallic centre. According to the EPR spectrum, only one of the complexes may have rhombic symmetry. We also analyzed enthalpy-entropy compensation and the isokinetic effect. In addition, general trends in thermal stability, spectroscopic properties and inclusion in the cavity were analysed. This complete characterization methodology becomes essential for their future application as catalysts. PMID:27272478

  10. A general protocol for determining the structures of molecularly ordered but noncrystalline silicate frameworks.

    PubMed

    Brouwer, Darren H; Cadars, Sylvian; Eckert, Juergen; Liu, Zheng; Terasaki, Osamu; Chmelka, Bradley F

    2013-04-17

    A general protocol is demonstrated for determining the structures of molecularly ordered but noncrystalline solids, which combines constraints provided by X-ray diffraction (XRD), one- and two-dimensional solid-state nuclear magnetic resonance (NMR) spectroscopy, and first-principles quantum chemical calculations. The approach is used to determine the structure(s) of a surfactant-directed layered silicate with short-range order in two dimensions but without long-range periodicity in three-dimensions (3D). The absence of long-range 3D molecular order and corresponding indexable XRD reflections precludes determination of a space group for this layered silicate. Nevertheless, by combining structural constraints obtained from solid-state (29)Si NMR analyses, including the types and relative populations of distinct (29)Si sites, their respective (29)Si-O-(29)Si connectivities and separation distances, with unit cell parameters (though not space group symmetry) provided by XRD, a comprehensive search of candidate framework structures leads to the identification of a small number of candidate structures that are each compatible with all of the experimental data. Subsequent refinement of the candidate structures using density functional theory calculations allows their evaluation and identification of "best" framework representations, based on their respective lattice energies and quantitative comparisons between experimental and calculated (29)Si isotropic chemical shifts and (2)J((29)Si-O-(29)Si) scalar couplings. The comprehensive analysis identifies three closely related and topologically equivalent framework configurations that are in close agreement with all experimental and theoretical structural constraints. The subtle differences among such similar structural models embody the complexity of the actual framework(s), which likely contain coexisting or subtle distributions of structural order that are intrinsic to the material. PMID:23560776

  11. Vapor-deposited non-crystalline phase vs ordinary glasses and supercooled liquids: Subtle thermodynamic and kinetic differences

    SciTech Connect

    Bhattacharya, Deepanjan; Sadtchenko, Vlad

    2015-04-28

    Vapor deposition of molecules on a substrate often results in glassy materials of high kinetic stability and low enthalpy. The extraordinary properties of such glasses are attributed to high rates of surface diffusion during sample deposition, which makes it possible for constituents to find a configuration of much lower energy on a typical laboratory time scale. However, the exact nature of the resulting phase and the mechanism of its formation are not completely understood. Using fast scanning calorimetry technique, we show that out-of-equilibrium relaxation kinetics and possibly the enthalpy of vapor-deposited films of toluene and ethylbenzene, archetypical fragile glass formers, are distinct from those of ordinary supercooled phase even when the deposition takes place at temperatures above the ordinary glass softening transition temperatures. These observations along with the absolute enthalpy dependences on deposition temperatures support the conjecture that the vapor-deposition may result in formation of non-crystalline phase of unique structural, thermodynamic, and kinetic properties.

  12. Segmental Mobility in the Non-crystalline Regions of Semicrystalline Polymers and its Implications on Melting.

    PubMed

    Rastogi, Sanjay; Yao, Yefeng; Lippits, Dirk R; Höhne, Günther W H; Graf, Robert; Spiess, Hans Wolfgang; Lemstra, Piet J

    2009-05-19

    Detailed knowledge on chain mobility in polymers is of fundamental interest in order to understand their mechanical properties. As a specific example, the melting behavior of semicrystalline polyethylene can be studied by thermal analysis and NMR spectroscopy. In ultra high molecular weight polyethylene (UHMW-PE) crystallised via different routes, i.e., directly during polymerisation, from solution, or from the melt, and melted under different protocols, different melting processes involving detachment of stems from the crystals and cluster melting can be distinguished. Melting by the consecutive detachment of chain stems from the crystal substrate ultimately results in a melt state where chain dynamics for entanglement formation are much more restricted. PMID:21706665

  13. Cluster packed structures in bulk metallic glasses created from BCC derivative compounds

    NASA Astrophysics Data System (ADS)

    Takeuchi, A.; Yubuta, K.; Inoue, A.

    2009-01-01

    Molecular dynamics simulations based on plastic crystal model were performed for the Fe69.0Nb10.3B20.7 and Zr57.1Ni28.6Al14.3 alloys to investigate their forming ability and features of the noncrystalline structures. The Fe69.0Nb10.3B20.7 and Zr57.1Ni28.6Al14.3 alloys were created from C6Cr23 and Ti4Ni2O structures, respectively, by assuming the presence of hypothetical clusters in the crystalline structures under a treatment that the clusters and glue atoms are regarded as the components. The analysis with total pair-distribution function, g(r), revealed that these alloys have high tendencies to form noncrystalline structures while their partial g(r) profiles for pairs among components showed the presence of medium range order. Cluster packed structures from bcc derivative compounds cause high forming ability of noncrystalline structure and the medium range order in the noncrystalline structure.

  14. Cryogenic coherent x-ray diffraction imaging for biological non-crystalline particles using the KOTOBUKI-1 diffraction apparatus at SACLA

    NASA Astrophysics Data System (ADS)

    Oroguchi, Tomotaka; Sekiguchi, Yuki; Kobayashi, Amane; Masaki, Yu; Fukuda, Asahi; Hashimoto, Saki; Nakasako, Masayoshi; Ichikawa, Yuichi; Kurumizaka, Hitoshi; Shimizu, Mitsuhiro; Inui, Yayoi; Matsunaga, Sachihiro; Kato, Takayuki; Namba, Keiichi; Yamaguchi, Keiichi; Kuwata, Kazuo; Kameda, Hiroshi; Fukui, Naoya; Kawata, Yasushi; Kameshima, Takashi; Takayama, Yuki; Yonekura, Koji; Yamamoto, Masaki

    2015-09-01

    We have developed an experimental apparatus named KOTOBUKI-1 for use in the coherent x-ray diffraction imaging experiments of frozen-hydrated non-crystalline particles at cryogenic temperature. The apparatus allows us to collect diffraction data for frozen-hydrated specimens at 66 K and provides an experimental environment to easily transfer frozen-hydrated specimens from liquid nitrogen storage to the specimen stage for x-ray exposure. Since 2012, the apparatus has been used in the single-shot diffraction data collection of non-crystalline biological cells and cellular components with dimensions from micrometer to submicrometer using x-ray free electron lasers at SACLA. Here we report on the performance of the KOTOBUKI-1 diffraction apparatus and some structure analyses of biological cells and cellular components. Based on the present results, we also discuss the future developments of diffraction apparatus for more efficient data collection.

  15. Validity of the second Fick's law for modeling ion-exchange diffusion in non-crystalline viscoelastic media (glasses)

    NASA Astrophysics Data System (ADS)

    Tagantsev, D. K.; Ivanenko, D. V.

    2016-04-01

    It is shown that, in general case, the diffusion equation (or the second Fick's law) does not provide an adequate description of ion-exchange transport phenomena in viscoelastic media, including glassy or any other non-crystalline media. In this connection the general phenomenological model of ion-exchange diffusion in viscoelastic media has been developed. A theoretical analysis of the model shows that, in the case of a linear dependence of medium density on the concentration of diffusing ions, the necessary and sufficient condition of the absolute validity of the diffusion equation in viscoelastic media is Φ ≫ 1, where Φ = τD/τR is the dimensionless value (or criterion of similarity), with τD = L2/D being the characteristic time of diffusion and τR = η/G being the characteristic time of stress relaxation, where L, D, η, and G are the characteristic length of diffusion, the diffusivity, the viscosity, and the shear modulus, respectively. The value of 1/Φ characterizes the accuracy which is provided if the second Fick's law is used in the simulation of ion-exchange diffusion in viscoelastic media. We have demonstrated the applicability of this criterion experimentally. Our experimental studies on ion-exchange diffusion in an oxide glass (typical viscoelastic media) have shown that under the condition the Φ > 105 the experimental concentration profiles are close to those predicted by the second Fick's law to within an accuracy of 1%.

  16. Impact of heat treatment on the physical properties of noncrystalline multisolute systems concentrated in frozen aqueous solutions.

    PubMed

    Izutsu, Ken-ichi; Yomota, Chikako; Kawanishi, Toru

    2011-12-01

    The purpose of this study was to elucidate the effect of heat treatment on the miscibility of multiple concentrated solutes that mimic biopharmaceutical formulations in frozen solutions. The first heating thermal analysis of frozen solutions containing either a low-molecular-weight saccharide (e.g., sucrose, trehalose, and glucose) or a polymer (e.g., polyvinylpyrrolidone and dextran) and their mixtures from -70°C showed a single transition at glass transition temperature of maximally freeze-concentrated solution (T(g) ') that indicated mixing of the freeze-concentrated multiple solutes. The heat treatment of single-solute and various polymer-rich mixture frozen solutions at temperatures far above their T(g) ' induced additional ice crystallization that shifted the transitions upward in the following scan. Contrarily, the heat treatment of frozen disaccharide-rich solutions induced two-step heat flow changes (T(g) ' splitting) that suggested separation of the solutes into multiple concentrated noncrystalline phases, different in the solute compositions. The extent of the T(g) ' splitting depended on the heat treatment temperature and time. Two-step glass transition was observed in some sucrose and dextran mixture solids, lyophilized after the heat treatment. Increasing mobility of solute molecules during the heat treatment should allow spatial reordering of some concentrated solute mixtures into thermodynamically favorable multiple phases.

  17. [Research on the mineral phase and component of non-crystalline and nano-crystalline corrosion products on bronzes unearthed from Shang Tomb in Xingan].

    PubMed

    Cheng, Xiao-lin; Pan, Lu

    2012-05-01

    The patinas on bronzes in Shang Tomb of Xingan were powdery, pale green, which were more like "bronze disease", but the mineral composition of patinas was not paratacamite or atacamite. Micro X-ray diffraction (XRD) and high performance transmission electroscope (HTEM) showed that the patinas were mainly composed of non-crystalline and nano-crystalline SnO2, and the size of nano-crystalline particle was in the range of 4-5.7 nm; Moreover, the energy-dispersive X-ray spectrometry showed that element tin is the primary ingredient of the sample, as well as little copper, silicon, lead and iron were detected. By studying the crystal lattice stripe image of the nanometer SnO2, it was deduced that the chemical formula of nano-crystalline SnO2 did not include other elements; The Raman spectrum of the sample showed that there were not any characteristic peaks of SnO2, the spectrum was more like non-crystalline SnO2, and the weak and broad peak of 973 cm(-1) indicated that the sample may contain silicate grains, It was inferred that little of copper, silicon, lead and iron should exist in the form of non-crystalline silicate particles.

  18. Fingerprinting analysis of non-crystalline pharmaceutical compounds using high energy X-rays and the total scattering pair distribution function

    NASA Astrophysics Data System (ADS)

    Davis, Timur D.

    2011-12-01

    In the development of new medicinal products, poor oral bioavailability, due to the low solubilities of many active pharmaceutical ingredients (APIs), is increasingly a barrier for treatments to be administered using tablet or capsule formulations and one of the main challenges facing the pharmaceutical industry. Non-crystalline phases such as the amorphous and nanostructured states can confer increased solubility to a drug, and therefore, have recently garnered a lot of interest from pharmaceutical researchers. However, little is known about local ordering in non-crystalline pharmaceuticals due to the lack of reliable experimental probes, hindering the clinical application of these compounds. The powerful tools of crystallography begin to lose their potency for structures on the nanoscale; conventional X-ray powder diffraction (XRPD) patterns become broad and featureless in these cases and are not useful for differentiating between different local molecular packing arrangements. In this thesis, we introduce the use of high energy X-rays coupled with total scattering pair distribution function (TSPDF) and fingerprinting analysis to investigate the local structures of non-crystalline pharmaceutical compounds. The high energy X-rays allow us to experimentally collect diffuse scattering intensities, which contain information about a sample's local ordering, in addition to the Bragg scattering available in conventional XRPD experiments, while the TSPDF allows us to view the intra- and inter-molecular correlations in real space. The goal of this study was to address some fundamental problems involving fingerprinting non-crystalline APIs using TSPDF in order to lay the groundwork for the proper use of the technique by the pharmaceutical community. We achieved this by developing the methodology as well as the exploring the scientific implications. On the methodology side, we introduced PDFGetX3, a new software program for calculating TSPDFs that simplifies the procedure

  19. A new class of intermediate phases in non-crystalline films based on a confluent double percolation mechanism

    NASA Astrophysics Data System (ADS)

    Lucovsky, Gerald; Phillips, James C.

    2007-11-01

    Recent research results have suggested that double percolation processes play a significant role in the formation of intermediate phases (IPs) in non-crystalline thin films. One class of IP windows, involving competitive double percolation, occurs in binary AsxSe1-x and GexSe1-x alloys and in the pseudo-binary AsxGexSe1-2x alloy. This IP window occurs over an 8-12% composition range. Transitions that define the IP window in the Ge-Se alloys involve a competition between the elimination of compliant local bonding dimer groups, e.g. Ge-Se-Se-Ge, at the expense of an increasing fraction of rigid local bonding monomer groups, e.g. Ge-Se-Ge. Compliant monomer group bonding defines the first window transition for an average number of bonding constraints/atom, nc = 3; the second transition from rigid to stressed rigid occurs when the compliant monomer concentration drops below a concentration for percolation. A second class of IPs with significantly narrower composition windows, ~1 to at most 3%, is proposed to explain experimentally determined IPs in chalcogenide alloys with halogen dopants; e.g. a-Ge0.25Se0.77-xIx, where the IP window width is ~1%. We suggest that this narrow window is determined by a confluent coherent double percolation process that includes (i) broken bond-bending constraints that minimize local bond strain, and (ii) a percolation pathway based on a second and complementary local bonding group. However, this second class of IPs is not supported by theory and modeling as yet, and as such our designation of this class of IPs must be regarded as more speculative. On the other had, it is significant that at least two other alloy systems, Ge2Se2Te5 and pseudo-ternary Hf, Zr and Ti Si oxynitrides, display narrow regimes where bond constraint counting indicates local strain suppression, and where a second and larger bonding arrangement is present at the percolation limit.

  20. TAKASAGO-6 apparatus for cryogenic coherent X-ray diffraction imaging of biological non-crystalline particles using X-ray free electron laser at SACLA.

    PubMed

    Kobayashi, Amane; Sekiguchi, Yuki; Takayama, Yuki; Oroguchi, Tomotaka; Shirahama, Keiya; Torizuka, Yasufumi; Manoda, Masahiro; Nakasako, Masayoshi; Yamamoto, Masaki

    2016-05-01

    Coherent X-ray diffraction imaging (CXDI) is a technique for structure analyses of non-crystalline particles with dimensions ranging from micrometer to sub-micrometer. We have developed a diffraction apparatus named TAKASAGO-6 for use in single-shot CXDI experiments of frozen-hydrated non-crystalline biological particles at cryogenic temperature with X-ray free electron laser pulses provided at a repetition rate of 30 Hz from the SPring-8 Angstrom Compact free-electron LAser. Specimen particles are flash-cooled after being dispersed on thin membranes supported by specially designed disks. The apparatus is equipped with a high-speed translation stage with a cryogenic pot for raster-scanning of the disks at a speed higher than 25 μm/33 ms. In addition, we use devices assisting the easy transfer of cooled specimens from liquid-nitrogen storages to the cryogenic pot. In the current experimental procedure, more than 20 000 diffraction patterns can be collected within 1 h. Here we report the key components and performance of the diffraction apparatus. Based on the efficiency of the diffraction data collection and the structure analyses of metal particles, biological cells, and cellular organelles, we discuss the future application of this diffraction apparatus for structure analyses of biological specimens. PMID:27250394

  1. TAKASAGO-6 apparatus for cryogenic coherent X-ray diffraction imaging of biological non-crystalline particles using X-ray free electron laser at SACLA

    NASA Astrophysics Data System (ADS)

    Kobayashi, Amane; Sekiguchi, Yuki; Takayama, Yuki; Oroguchi, Tomotaka; Shirahama, Keiya; Torizuka, Yasufumi; Manoda, Masahiro; Nakasako, Masayoshi; Yamamoto, Masaki

    2016-05-01

    Coherent X-ray diffraction imaging (CXDI) is a technique for structure analyses of non-crystalline particles with dimensions ranging from micrometer to sub-micrometer. We have developed a diffraction apparatus named TAKASAGO-6 for use in single-shot CXDI experiments of frozen-hydrated non-crystalline biological particles at cryogenic temperature with X-ray free electron laser pulses provided at a repetition rate of 30 Hz from the SPring-8 Angstrom Compact free-electron LAser. Specimen particles are flash-cooled after being dispersed on thin membranes supported by specially designed disks. The apparatus is equipped with a high-speed translation stage with a cryogenic pot for raster-scanning of the disks at a speed higher than 25 μm/33 ms. In addition, we use devices assisting the easy transfer of cooled specimens from liquid-nitrogen storages to the cryogenic pot. In the current experimental procedure, more than 20 000 diffraction patterns can be collected within 1 h. Here we report the key components and performance of the diffraction apparatus. Based on the efficiency of the diffraction data collection and the structure analyses of metal particles, biological cells, and cellular organelles, we discuss the future application of this diffraction apparatus for structure analyses of biological specimens.

  2. Resolution and measurement of heteronuclear dipolar couplings of a noncrystalline protein immobilized in a biological supramolecular assembly by proton-detected MAS solid-state NMR spectroscopy

    NASA Astrophysics Data System (ADS)

    Park, Sang Ho; Yang, Chen; Opella, Stanley J.; Mueller, Leonard J.

    2013-12-01

    Two-dimensional 15N chemical shift/1H chemical shift and three-dimensional 1H-15N dipolar coupling/15N chemical shift/1H chemical shift MAS solid-state NMR correlation spectra of the filamentous bacteriophage Pf1 major coat protein show single-site resolution in noncrystalline, intact-phage preparations. The high sensitivity and resolution result from 1H detection at 600 MHz under 50 kHz magic angle spinning using ∼0.5 mg of perdeuterated and uniformly 15N-labeled protein in which the exchangeable amide sites are partially or completely back-exchanged (reprotonated). Notably, the heteronuclear 1H-15N dipolar coupling frequency dimension is shown to select among 15N resonances, which will be useful in structural studies of larger proteins where the resonances exhibit a high degree of overlap in multidimensional chemical shift correlation spectra.

  3. Compound mouse mutants of bZIP transcription factors Mafg and Mafk reveal a regulatory network of non-crystallin genes associated with cataract.

    PubMed

    Agrawal, Smriti A; Anand, Deepti; Siddam, Archana D; Kakrana, Atul; Dash, Soma; Scheiblin, David A; Dang, Christine A; Terrell, Anne M; Waters, Stephanie M; Singh, Abhyudai; Motohashi, Hozumi; Yamamoto, Masayuki; Lachke, Salil A

    2015-07-01

    Although majority of the genes linked to early-onset cataract exhibit lens fiber cell-enriched expression, our understanding of gene regulation in these cells is limited to function of just eight transcription factors and largely in the context of crystallins. We report on small Maf transcription factors Mafg and Mafk as regulators of several non-crystallin human cataract-associated genes in fiber cells and establish their significance to this disease. We applied a bioinformatics tool for cataract gene discovery iSyTE to identify Mafg and its co-regulators in the lens, and generated various null-allelic combinations of Mafg:Mafk mouse mutants for phenotypic and molecular analysis. By age 4 months, Mafg-/-:Mafk+/- mutants exhibit lens defects that progressively develop into cataract. High-resolution phenotypic characterization of Mafg-/-:Mafk+/- mouse lens reveals severely disorganized fiber cells, while microarray-based expression profiling identifies 97 differentially regulated genes (DRGs). Integrative analysis of Mafg-/-:Mafk+/- lens-DRGs with (1) binding motifs and genomic targets of small Mafs and their regulatory partners, (2) iSyTE lens expression data, and (3) interactions between DRGs in the String database, unravel a detailed small Maf regulatory network in the lens, several nodes of which are linked to cataract. This approach identifies 36 high-priority candidates from the original 97 DRGs. Significantly, 8/36 (22%) DRGs are associated with cataracts in human (GSTO1, MGST1, SC4MOL, UCHL1) or mouse (Aldh3a1, Crygf, Hspb1, Pcbd1), suggesting a multifactorial etiology that includes oxidative stress and misregulation of sterol synthesis. These data identify Mafg and Mafk as new cataract-associated candidates and define their function in regulating largely non-crystallin genes linked to human cataract. PMID:25896808

  4. A fresh look at dense hydrogen under pressure. IV. Two structural models on the road from paired to monatomic hydrogen, via a possible non-crystalline phase.

    PubMed

    Labet, Vanessa; Hoffmann, Roald; Ashcroft, N W

    2012-02-21

    In this paper, we examine the transition from a molecular to monatomic solid in hydrogen over a wide pressure range. This is achieved by setting up two models in which a single parameter δ allows the evolution from a molecular structure to a monatomic one of high coordination. Both models are based on a cubic Bravais lattice with eight atoms in the unit cell; one belongs to space group Pa3, the other to space group R3m. In Pa3 one moves from effective 1-coordination, a molecule, to a simple cubic 6-coordinated structure but through a very special point (the golden mean is involved) of 7-coordination. In R3m, the evolution is from 1 to 4 and then to 3 to 6-coordinate. If one studies the enthalpy as a function of pressure as these two structures evolve (δ increases), one sees the expected stabilization of minima with increased coordination (moving from 1 to 6 to 7 in the Pa3 structure, for instance). Interestingly, at some specific pressures, there are in both structures relatively large regions of phase space where the enthalpy remains roughly the same. Although the structures studied are always higher in enthalpy than the computationally best structures for solid hydrogen - those emerging from the Pickard and Needs or McMahon and Ceperley numerical laboratories - this result is suggestive of the possibility of a microscopically non-crystalline or "soft" phase of hydrogen at elevated pressures, one in which there is a substantial range of roughly equi-enthalpic geometries available to the system. A scaling argument for potential dynamic stabilization of such a phase is presented.

  5. Symbolic clustering

    SciTech Connect

    Reinke, R.E.

    1991-01-01

    Clustering is the problem of finding a good organization for data. Because there are many kinds of clustering problems, and because there are many possible clusterings for any data set, clustering programs use knowledge and assumptions about individual problems to make clustering tractable. Cluster-analysis techniques allow knowledge to be expressed in the choice of a pairwise distance measure and in the choice of clustering algorithm. Conceptual clustering adds knowledge and preferences about cluster descriptions. In this study the author describes symbolic clustering, which adds representation choice to the set of ways a data analyst can use problem-specific knowledge. He develops an informal model for symbolic clustering, and uses it to suggest where and how knowledge can be expressed in clustering. A language for creating symbolic clusters, based on the model, was developed and tested on three real clustering problems. The study concludes with a discussion of the implications of the model and the results for clustering in general.

  6. CLUSTER CHEMISTRY

    SciTech Connect

    Muetterties, Earl L.

    1980-05-01

    Metal cluster chemistry is one of the most rapidly developing areas of inorganic and organometallic chemistry. Prior to 1960 only a few metal clusters were well characterized. However, shortly after the early development of boron cluster chemistry, the field of metal cluster chemistry began to grow at a very rapid rate and a structural and a qualitative theoretical understanding of clusters came quickly. Analyzed here is the chemistry and the general significance of clusters with particular emphasis on the cluster research within my group. The importance of coordinately unsaturated, very reactive metal clusters is the major subject of discussion.

  7. Cluster headache

    MedlinePlus

    Histamine headache; Headache - histamine; Migrainous neuralgia; Headache - cluster; Horton's headache; Vascular headache - cluster ... be related to the body's sudden release of histamine (chemical in the body released during an allergic ...

  8. Meaningful Clusters

    SciTech Connect

    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.

  9. Abell Clusters

    NASA Astrophysics Data System (ADS)

    Katgert, P.; Murdin, P.

    2000-11-01

    Abell clusters are the most conspicuous groupings of galaxies identified by George Abell on the plates of the first photographic survey made with the SCHMIDT TELESCOPE at Mount Palomar in the 1950s. Sometimes, the term Abell clusters is used as a synonym of nearby, optically selected galaxy clusters....

  10. O-vacancies in (i) nano-crystalline HfO2 and (i) non-crystalline SiO2 and Si3N4 studied by X-ray absorption spectroscopy.

    PubMed

    Lucovsky, Gerald; Miotti, Leonardo; Bastos, Karen Paz

    2012-06-01

    Performance and reliability in semiconductor devices are limited by electronically active defects, primarily O-atom and N-atom vacancies. Synchrotron X-ray spectroscopy results, interpreted in the context of two-electron multiplet theories, have been used to analyze conduction band edge, and O-vacancy defect states in nano-crystalline transition metal oxides, e.g., HfO2, and the noncrystalline dielectrics, SiO2, Si3N4 and Si-oxynitride alloys. Two-electron multiplet theory been used to develop a high-spin state equivalent d2 model for O-vacancy allowed transitions and negative ion states as detected by X-ray absorption spectroscopy in the O K pre-edge regime. Comparisons between theory and experiment have used Tanabe-Sugano energy level diagrams for determining the symmetries and relative energies of intra-d-state transitions for an equivalent d2 ground state occupancy. Trap-assisted-tunneling, Poole-Frenkel hopping transport, and the negative bias temperature instability have been explained in terms of injection and/or trapping into O-atom and N-atom vacancy sites, and applied to gate dielectric, and metal-insulator-metal structures.

  11. Data Clustering

    NASA Astrophysics Data System (ADS)

    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

  12. Quintuplet Cluster

    NASA Technical Reports Server (NTRS)

    1999-01-01

    Penetrating 25,000 light-years of obscuring dust and myriad stars, NASA's Hubble Space Telescope has provided the clearest view yet of one of the largest young clusters of stars inside our Milky Way galaxy, located less than 100 light-years from the very center of the Galaxy. Having the equivalent mass greater than 10,000 stars like our sun, the monster cluster is ten times larger than typical young star clusters scattered throughout our Milky Way. It is destined to be ripped apart in just a few million years by gravitational tidal forces in the galaxy's core. But in its brief lifetime it shines more brightly than any other star cluster in the Galaxy. Quintuplet Cluster is 4 million years old. It has stars on the verge of blowing up as supernovae. It is the home of the brightest star seen in the galaxy, called the Pistol star. This image was taken in infrared light by Hubble's NICMOS camera in September 1997. The false colors correspond to infrared wavelengths. The galactic center stars are white, the red stars are enshrouded in dust or behind dust, and the blue stars are foreground stars between us and the Milky Way's center. The cluster is hidden from direct view behind black dust clouds in the constellation Sagittarius. If the cluster could be seen from earth it would appear to the naked eye as a 3rd magnitude star, 1/6th of a full moon's diameter apart.

  13. Galaxy Clusters

    NASA Astrophysics Data System (ADS)

    Miller, Christopher J. Miller

    2012-03-01

    There are many examples of clustering in astronomy. Stars in our own galaxy are often seen as being gravitationally bound into tight globular or open clusters. The Solar System's Trojan asteroids cluster at the gravitational Langrangian in front of Jupiter’s orbit. On the largest of scales, we find gravitationally bound clusters of galaxies, the Virgo cluster (in the constellation of Virgo at a distance of ˜50 million light years) being a prime nearby example. The Virgo cluster subtends an angle of nearly 8◦ on the sky and is known to contain over a thousand member galaxies. Galaxy clusters play an important role in our understanding of theUniverse. Clusters exist at peaks in the three-dimensional large-scale matter density field. Their sky (2D) locations are easy to detect in astronomical imaging data and their mean galaxy redshifts (redshift is related to the third spatial dimension: distance) are often better (spectroscopically) and cheaper (photometrically) when compared with the entire galaxy population in large sky surveys. Photometric redshift (z) [Photometric techniques use the broad band filter magnitudes of a galaxy to estimate the redshift. Spectroscopic techniques use the galaxy spectra and emission/absorption line features to measure the redshift] determinations of galaxies within clusters are accurate to better than delta_z = 0.05 [7] and when studied as a cluster population, the central galaxies form a line in color-magnitude space (called the the E/S0 ridgeline and visible in Figure 16.3) that contains galaxies with similar stellar populations [15]. The shape of this E/S0 ridgeline enables astronomers to measure the cluster redshift to within delta_z = 0.01 [23]. The most accurate cluster redshift determinations come from spectroscopy of the member galaxies, where only a fraction of the members need to be spectroscopically observed [25,42] to get an accurate redshift to the whole system. If light traces mass in the Universe, then the locations

  14. Occupational Clusters.

    ERIC Educational Resources Information Center

    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…

  15. Cluster generator

    DOEpatents

    Donchev, Todor I.; Petrov, Ivan G.

    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.

  16. The role of fcc tetrahedral subunits in the phase behavior of medium sized Lennard-Jones clusters.

    PubMed

    Saika-Voivod, Ivan; Poon, Louis; Bowles, Richard K

    2010-08-21

    The free energy of a 600-atom Lennard-Jones cluster is calculated as a function of surface and bulk crystallinity in order to study the structural transformations that occur in the core of medium sized clusters. Within the order parameter range studied, we find the existence of two free energy minima at temperatures near freezing. One minimum, at low values of both bulk and surface order, belongs to the liquid phase. The second minimum exhibits a highly ordered core with a disordered surface and is related to structures containing a single fcc-tetrahedral subunit, with an edge length of seven atoms (l=7), located in the particle core. At lower temperatures, a third minimum appears at intermediate values of the bulk order parameter which is shown to be related to the formation of multiple l=6 tetrahedra in the core of the cluster. We also use molecular dynamics simulations to follow a series of nucleation events and find that the clusters freeze to structures containing l=5, 6, 7, and 8 sized tetrahedra as well as those containing no tetrahedral units. The structural correlations between bulk and surface order with the size of the tetrahedral units in the cluster core are examined. Finally, the relationships between the formation of fcc tetrahedral subunits in the core, the phase behavior of medium sized clusters and the nucleation of noncrystalline global structures such as icosahedra and decahedra are discussed.

  17. Cluster headache

    PubMed Central

    2010-01-01

    Introduction The revised International Headache Society (IHS) criteria for cluster headache are: attacks of severe or very severe, strictly unilateral pain, which is orbital, supraorbital, or temporal pain, lasting 15 to 180 minutes and occurring from once every other day to eight times daily. Methods and outcomes We conducted a systematic review and aimed to answer the following clinical questions: What are the effects of interventions to abort cluster headache? What are the effects of interventions to prevent cluster headache? We searched: Medline, Embase, The Cochrane Library, and other important databases up to June 2009 (Clinical Evidence reviews are updated periodically; please check our website for the most up-to-date version of this review). We included harms alerts from relevant organisations, such as the US Food and Drug Administration (FDA) and the UK Medicines and Healthcare products Regulatory Agency (MHRA). Results We found 23 systematic reviews, RCTs, or observational studies that met our inclusion criteria. We performed a GRADE evaluation of the quality of evidence for interventions. Conclusions In this systematic review, we present information relating to the effectiveness and safety of the following interventions: baclofen (oral); botulinum toxin (intramuscular); capsaicin (intranasal); chlorpromazine; civamide (intranasal); clonidine (transdermal); corticosteroids; ergotamine and dihydroergotamine (oral or intranasal); gabapentin (oral); greater occipital nerve injections (betamethasone plus xylocaine); high-dose and high-flow-rate oxygen; hyperbaric oxygen; leuprolide; lidocaine (intranasal); lithium (oral); melatonin; methysergide (oral); octreotide (subcutaneous); pizotifen (oral); sodium valproate (oral); sumatriptan (oral, subcutaneous, and intranasal); topiramate (oral); tricyclic antidepressants (TCAs); verapamil; and zolmitriptan (oral and intranasal). PMID:21718584

  18. Titanium embedded cage structure formation in Al(n)Ti+ clusters and their interaction with Ar.

    PubMed

    Torres, M B; Vega, A; Aguilera-Granja, F; Balbás, L C

    2014-05-01

    Recently, Ar physisorption was used as a structural probe for the location of the Ti dopant atom in aluminium cluster cations, Al(n)Ti(+) [Lang et al., J. Am. Soc. Mass Spectrom. 22, 1508 (2011)]. As an experiment result, the lack of Ar complexes for n > nc determines the cluster size for which the Ti atom is located inside of an Al cage. To elucidate the decisive factors for the formation of endohedrally Al(n)Ti(+), experimentalists proposed detailed computational studies as indispensable. In this work, we investigated, using the density functional theory, the structural and electronic properties of singly titanium doped cationic clusters, Al(n)Ti(+) (n = 16-21) as well as the adsorption of an Ar atom on them. The first endohedral doped cluster, with Ti encapsulated in a fcc-like cage skeleton, appears at nc = 21, which is the critical number consistent with the exohedral-endohedral transition experimentally observed. At this critical size the non-crystalline icosahedral growth pattern, related to the pure aluminium clusters, with the Ti atom in the surface, changes into a endohedral fcc-like pattern. The map of structural isomers, relative energy differences, second energy differences, and structural parameters were determined and analyzed. Moreover, we show the critical size depends on the net charge of the cluster, being different for the cationic clusters (nc = 21) and their neutral counterparts (nc = 20). For the Al(n)Ti(+) · Ar complexes, and for n < 21, the preferred Ar adsorption site is on top of the exohedral Ti atom, with adsorption energy in very good agreement with the experimental value. Instead, for n = 21, the Ar adsorption occurs on the top an Al atom with very low absorption energy. For all sizes the geometry of the Al(n)Ti(+) clusters keeps unaltered in the Ar-cluster complexes. This fact indicates that Ar adsorption does not influence the cluster structure, providing support to the experimental technique used. For nc = 21, the smallest size of

  19. Titanium embedded cage structure formation in AlnTi+ clusters and their interaction with Ar

    NASA Astrophysics Data System (ADS)

    Torres, M. B.; Vega, A.; Aguilera-Granja, F.; Balbás, L. C.

    2014-05-01

    Recently, Ar physisorption was used as a structural probe for the location of the Ti dopant atom in aluminium cluster cations, AlnTi+ [Lang et al., J. Am. Soc. Mass Spectrom. 22, 1508 (2011)]. As an experiment result, the lack of Ar complexes for n > nc determines the cluster size for which the Ti atom is located inside of an Al cage. To elucidate the decisive factors for the formation of endohedrally AlnTi+, experimentalists proposed detailed computational studies as indispensable. In this work, we investigated, using the density functional theory, the structural and electronic properties of singly titanium doped cationic clusters, AlnTi+ (n = 16-21) as well as the adsorption of an Ar atom on them. The first endohedral doped cluster, with Ti encapsulated in a fcc-like cage skeleton, appears at nc = 21, which is the critical number consistent with the exohedral-endohedral transition experimentally observed. At this critical size the non-crystalline icosahedral growth pattern, related to the pure aluminium clusters, with the Ti atom in the surface, changes into a endohedral fcc-like pattern. The map of structural isomers, relative energy differences, second energy differences, and structural parameters were determined and analyzed. Moreover, we show the critical size depends on the net charge of the cluster, being different for the cationic clusters (nc = 21) and their neutral counterparts (nc = 20). For the {Al_nTi^+ {\\cdot} Ar} complexes, and for n < 21, the preferred Ar adsorption site is on top of the exohedral Ti atom, with adsorption energy in very good agreement with the experimental value. Instead, for n = 21, the Ar adsorption occurs on the top an Al atom with very low absorption energy. For all sizes the geometry of the AlnTi+ clusters keeps unaltered in the Ar-cluster complexes. This fact indicates that Ar adsorption does not influence the cluster structure, providing support to the experimental technique used. For nc = 21, the smallest size of

  20. Titanium embedded cage structure formation in Al{sub n}Ti{sup +} clusters and their interaction with Ar

    SciTech Connect

    Torres, M. B.; Vega, A.; Balbás, L. C.; Aguilera-Granja, F.

    2014-05-07

    Recently, Ar physisorption was used as a structural probe for the location of the Ti dopant atom in aluminium cluster cations, Al{sub n}Ti{sup +} [Lang et al., J. Am. Soc. Mass Spectrom. 22, 1508 (2011)]. As an experiment result, the lack of Ar complexes for n > n{sub c} determines the cluster size for which the Ti atom is located inside of an Al cage. To elucidate the decisive factors for the formation of endohedrally Al{sub n}Ti{sup +}, experimentalists proposed detailed computational studies as indispensable. In this work, we investigated, using the density functional theory, the structural and electronic properties of singly titanium doped cationic clusters, Al{sub n}Ti{sup +} (n = 16–21) as well as the adsorption of an Ar atom on them. The first endohedral doped cluster, with Ti encapsulated in a fcc-like cage skeleton, appears at n{sub c} = 21, which is the critical number consistent with the exohedral-endohedral transition experimentally observed. At this critical size the non-crystalline icosahedral growth pattern, related to the pure aluminium clusters, with the Ti atom in the surface, changes into a endohedral fcc-like pattern. The map of structural isomers, relative energy differences, second energy differences, and structural parameters were determined and analyzed. Moreover, we show the critical size depends on the net charge of the cluster, being different for the cationic clusters (n{sub c} = 21) and their neutral counterparts (n{sub c} = 20). For the Al {sub n} Ti {sup +} · Ar complexes, and for n < 21, the preferred Ar adsorption site is on top of the exohedral Ti atom, with adsorption energy in very good agreement with the experimental value. Instead, for n = 21, the Ar adsorption occurs on the top an Al atom with very low absorption energy. For all sizes the geometry of the Al{sub n}Ti{sup +} clusters keeps unaltered in the Ar-cluster complexes. This fact indicates that Ar adsorption does not influence the cluster structure, providing support

  1. PREFACE: Nuclear Cluster Conference; Cluster'07

    NASA Astrophysics Data System (ADS)

    Freer, Martin

    2008-05-01

    The Cluster Conference is a long-running conference series dating back to the 1960's, the first being initiated by Wildermuth in Bochum, Germany, in 1969. The most recent meeting was held in Nara, Japan, in 2003, and in 2007 the 9th Cluster Conference was held in Stratford-upon-Avon, UK. As the name suggests the town of Stratford lies upon the River Avon, and shortly before the conference, due to unprecedented rainfall in the area (approximately 10 cm within half a day), lay in the River Avon! Stratford is the birthplace of the `Bard of Avon' William Shakespeare, and this formed an intriguing conference backdrop. The meeting was attended by some 90 delegates and the programme contained 65 70 oral presentations, and was opened by a historical perspective presented by Professor Brink (Oxford) and closed by Professor Horiuchi (RCNP) with an overview of the conference and future perspectives. In between, the conference covered aspects of clustering in exotic nuclei (both neutron and proton-rich), molecular structures in which valence neutrons are exchanged between cluster cores, condensates in nuclei, neutron-clusters, superheavy nuclei, clusters in nuclear astrophysical processes and exotic cluster decays such as 2p and ternary cluster decay. The field of nuclear clustering has become strongly influenced by the physics of radioactive beam facilities (reflected in the programme), and by the excitement that clustering may have an important impact on the structure of nuclei at the neutron drip-line. It was clear that since Nara the field had progressed substantially and that new themes had emerged and others had crystallized. Two particular topics resonated strongly condensates and nuclear molecules. These topics are thus likely to be central in the next cluster conference which will be held in 2011 in the Hungarian city of Debrechen. Martin Freer Participants and Cluster'07

  2. Survey on granularity clustering.

    PubMed

    Ding, Shifei; Du, Mingjing; Zhu, Hong

    2015-12-01

    With the rapid development of uncertain artificial intelligent and the arrival of big data era, conventional clustering analysis and granular computing fail to satisfy the requirements of intelligent information processing in this new case. There is the essential relationship between granular computing and clustering analysis, so some researchers try to combine granular computing with clustering analysis. In the idea of granularity, the researchers expand the researches in clustering analysis and look for the best clustering results with the help of the basic theories and methods of granular computing. Granularity clustering method which is proposed and studied has attracted more and more attention. This paper firstly summarizes the background of granularity clustering and the intrinsic connection between granular computing and clustering analysis, and then mainly reviews the research status and various methods of granularity clustering. Finally, we analyze existing problem and propose further research.

  3. Cluster automorphism groups of cluster algebras with coefficients

    NASA Astrophysics Data System (ADS)

    Chang, Wen; Zhu, Bin

    2016-10-01

    We study the cluster automorphism group of a skew-symmetric cluster algebra with geometric coefficients. For this, we introduce the notion of gluing free cluster algebra, and show that under a weak condition the cluster automorphism group of a gluing free cluster algebra is a subgroup of the cluster automorphism group of its principal part cluster algebra (i.e. the corresponding cluster algebra without coefficients). We show that several classes of cluster algebras with coefficients are gluing free, for example, cluster algebras with principal coefficients, cluster algebras with universal geometric coefficients, and cluster algebras from surfaces (except a 4-gon) with coefficients from boundaries. Moreover, except four kinds of surfaces, the cluster automorphism group of a cluster algebra from a surface with coefficients from boundaries is isomorphic to the cluster automorphism group of its principal part cluster algebra; for a cluster algebra with principal coefficients, its cluster automorphism group is isomorphic to the automorphism group of its initial quiver.

  4. Mid-gap phenomena in chalcogenide glasses and barrier-cluster-heating model

    SciTech Connect

    Banik, Ivan Kubliha, Marián; Lukovičová, Jozefa; Pavlendová, Gabriela

    2015-12-07

    The physical mechanism of photoluminescence spectrum formation of chalcogenide glasses (CHG) belongs to the important unsolved problems in physics of non-crystalline materials. Photoluminescence is an important means of the electron spectrum investigation. PL spectrum in CHG is produced mostly in the middle of the band gap, and its profile is normal - Gaussian. Several features of PL spectra in CHG is still a great mystery. The aim of the paper is to make reader acquainted with the new insight into the problem. In this article we also deal with the issue of clarifying the nature of mid-gap absorption. From the experiments it is known that after excitation of the glass As{sub 2}S{sub 3} (or As{sub 2}Se{sub 3}) with primary radiation from Urbach-tail region the glass will be able to absorb the photons of low energy (IR) radiation from mid-gap region of spectra. This low photon absorption without action of the primary excitation radiation of the higher photon energy is impossible. Mid-gap absorption yields boost in the photoluminescence. The paper gives the reader the new insights into some, until now, unexplained effects and contexts in chalcogenide glasses from the position of barrier-cluster-heating model.

  5. Mid-gap phenomena in chalcogenide glasses and barrier-cluster-heating model

    NASA Astrophysics Data System (ADS)

    Banik, Ivan; Kubliha, Marián; Lukovičová, Jozefa; Pavlendová, Gabriela

    2015-12-01

    The physical mechanism of photoluminescence spectrum formation of chalcogenide glasses (CHG) belongs to the important unsolved problems in physics of non-crystalline materials. Photoluminescence is an important means of the electron spectrum investigation. PL spectrum in CHG is produced mostly in the middle of the band gap, and its profile is normal - Gaussian. Several features of PL spectra in CHG is still a great mystery. The aim of the paper is to make reader acquainted with the new insight into the problem. In this article we also deal with the issue of clarifying the nature of mid-gap absorption. From the experiments it is known that after excitation of the glass As2S3 (or As2Se3) with primary radiation from Urbach-tail region the glass will be able to absorb the photons of low energy (IR) radiation from mid-gap region of spectra. This low photon absorption without action of the primary excitation radiation of the higher photon energy is impossible. Mid-gap absorption yields boost in the photoluminescence. The paper gives the reader the new insights into some, until now, unexplained effects and contexts in chalcogenide glasses from the position of barrier-cluster-heating model.

  6. Matlab Cluster Ensemble Toolbox

    SciTech Connect

    Sapio, Vincent De; Kegelmeyer, Philip

    2009-04-27

    This is a Matlab toolbox for investigating the application of cluster ensembles to data classification, with the objective of improving the accuracy and/or speed of clustering. The toolbox divides the cluster ensemble problem into four areas, providing functionality for each. These include, (1) synthetic data generation, (2) clustering to generate individual data partitions and similarity matrices, (3) consensus function generation and final clustering to generate ensemble data partitioning, and (4) implementation of accuracy metrics. With regard to data generation, Gaussian data of arbitrary dimension can be generated. The kcenters algorithm can then be used to generate individual data partitions by either, (a) subsampling the data and clustering each subsample, or by (b) randomly initializing the algorithm and generating a clustering for each initialization. In either case an overall similarity matrix can be computed using a consensus function operating on the individual similarity matrices. A final clustering can be performed and performance metrics are provided for evaluation purposes.

  7. Star cluster dynamics.

    PubMed

    Vesperini, Enrico

    2010-02-28

    Dynamical evolution plays a key role in shaping the current properties of star clusters and star cluster systems. A detailed understanding of the effects of evolutionary processes is essential to be able to disentangle the properties that result from dynamical evolution from those imprinted at the time of cluster formation. In this review, I focus my attention on globular clusters, and review the main physical ingredients driving their early and long-term evolution, describe the possible evolutionary routes and show how cluster structure and stellar content are affected by dynamical evolution.

  8. A new clustering strategy

    NASA Astrophysics Data System (ADS)

    Feng, Jian-xin; Tang, Jia-fu; Wang, Guang-xing

    2007-04-01

    On the basis of the analysis of clustering algorithm that had been proposed for MANET, a novel clustering strategy was proposed in this paper. With the trust defined by statistical hypothesis in probability theory and the cluster head selected by node trust and node mobility, this strategy can realize the function of the malicious nodes detection which was neglected by other clustering algorithms and overcome the deficiency of being incapable of implementing the relative mobility metric of corresponding nodes in the MOBIC algorithm caused by the fact that the receiving power of two consecutive HELLO packet cannot be measured. It's an effective solution to cluster MANET securely.

  9. Unconventional methods for clustering

    NASA Astrophysics Data System (ADS)

    Kotyrba, Martin

    2016-06-01

    Cluster analysis or clustering is a task of grouping a set of objects in such a way that objects in the same group (called a cluster) are more similar (in some sense or another) to each other than to those in other groups (clusters). It is the main task of exploratory data mining and a common technique for statistical data analysis used in many fields, including machine learning, pattern recognition, image analysis, information retrieval, and bioinformatics. The topic of this paper is one of the modern methods of clustering namely SOM (Self Organising Map). The paper describes the theory needed to understand the principle of clustering and descriptions of algorithm used with clustering in our experiments.

  10. Information-based clustering

    PubMed Central

    Slonim, Noam; Atwal, Gurinder Singh; Tkačik, Gašper; Bialek, William

    2005-01-01

    In an age of increasingly large data sets, investigators in many different disciplines have turned to clustering as a tool for data analysis and exploration. Existing clustering methods, however, typically depend on several nontrivial assumptions about the structure of data. Here, we reformulate the clustering problem from an information theoretic perspective that avoids many of these assumptions. In particular, our formulation obviates the need for defining a cluster “prototype,” does not require an a priori similarity metric, is invariant to changes in the representation of the data, and naturally captures nonlinear relations. We apply this approach to different domains and find that it consistently produces clusters that are more coherent than those extracted by existing algorithms. Finally, our approach provides a way of clustering based on collective notions of similarity rather than the traditional pairwise measures. PMID:16352721

  11. Convex Discriminative Multitask Clustering.

    PubMed

    Zhang, Xiao-Lei

    2015-01-01

    Multitask clustering tries to improve the clustering performance of multiple tasks simultaneously by taking their relationship into account. Most existing multitask clustering algorithms fall into the type of generative clustering, and none are formulated as convex optimization problems. In this paper, we propose two convex Discriminative Multitask Clustering (DMTC) objectives to address the problems. The first one aims to learn a shared feature representation, which can be seen as a technical combination of the convex multitask feature learning and the convex Multiclass Maximum Margin Clustering (M3C). The second one aims to learn the task relationship, which can be seen as a combination of the convex multitask relationship learning and M3C. The objectives of the two algorithms are solved in a uniform procedure by the efficient cutting-plane algorithm and further unified in the Bayesian framework. Experimental results on a toy problem and two benchmark data sets demonstrate the effectiveness of the proposed algorithms. PMID:26353206

  12. Clusters of galaxies

    NASA Astrophysics Data System (ADS)

    Vikhlinin, A. A.; Kravtsov, A. V.; Markevich, M. L.; Sunyaev, R. A.; Churazov, E. M.

    2014-04-01

    Galaxy clusters are formed via nonlinear growth of primordial density fluctuations and are the most massive gravitationally bound objects in the present Universe. Their number density at different epochs and their properties depend strongly on the properties of dark matter and dark energy, making clusters a powerful tool for observational cosmology. Observations of the hot gas filling the gravitational potential well of a cluster allows studying gasdynamic and plasma effects and the effect of supermassive black holes on the heating and cooling of gas on cluster scales. The work of Yakov Borisovich Zeldovich has had a profound impact on virtually all cosmological and astrophysical studies of galaxy clusters, introducing concepts such as the Harrison-Zeldovich spectrum, the Zeldovich approximation, baryon acoustic peaks, and the Sunyaev-Zeldovich effect. Here, we review the most basic properties of clusters and their role in modern astrophysics and cosmology.

  13. Mini-clusters

    NASA Technical Reports Server (NTRS)

    Chinellato, J. A.; Dobrigkeit, C.; Bellandifilho, J.; Lattes, C. M. G.; Menon, M. J.; Navia, C. E.; Pamilaju, A.; Sawayanagi, K.; Shibuya, E. H.; Turtelli, A., Jr.

    1985-01-01

    Experimental results of mini-clusters observed in Chacaltaya emulsion chamber no.19 are summarized. The study was made on 54 single core shower upper and 91 shower clusters of E(gamma) 10 TeV from 30 families which are visible energy greater than 80 TeV and penetrate through both upper and lower detectors of the two-story chamber. The association of hadrons in mini-cluster is made clear from their penetrative nature and microscopic observation of shower continuation in lower chamber. Small P sub t (gamma) of hadrons in mini-clusters remained in puzzle.

  14. Reactions of intermetallic clusters

    NASA Astrophysics Data System (ADS)

    Farley, R. W.; Castleman, A. W., Jr.

    1990-02-01

    Reaction of bismuth-alkali clusters with closed-shell HX acids provides insight into the structures, formation, and stabilities of these intermetallic species. HC1 and HI are observed to quantitatively strip BixNay and BixKy, respectively, of their alkali component, leaving bare bismuth clusters as the only bismuth-containing species detected. Product bismuth clusters exhibit the same distribution observed when pure bismuth is evaporated in the source. Though evaporated simultaneously from the same crucible, this suggests alkali atoms condense onto existing bismuth clusters and have negligible effect on their formation and consequent distribution. The indistinguishibility of reacted and pure bismuth cluster distributions further argues against the simple replacement of alkali atoms with hydrogen in these reactions. This is considered further evidence that the alkali atoms are external to the stable bismuth Zintl anionic structures. Reactivities of BixNay clusters with HC1 are estimated to lie between 3×10-13 for Bi4Na, to greater than 4×10-11 for clusters possessing large numbers of alkali atoms. Bare bismuth clusters are observed in separate experiments to react significantly more slowly with rates of 1-9×10-14 and exhibit little variation of reactivity with size. The bismuth clusters may thus be considered a relatively inert substrate upon which the alkali overlayer reacts.

  15. Management of cluster headache.

    PubMed

    Tfelt-Hansen, Peer C; Jensen, Rigmor H

    2012-07-01

    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 and prophylactic treatment. In ECH and CCH the attacks can be treated with oxygen (12 L/min) or subcutaneous sumatriptan 6 mg. For both oxygen and sumatriptan there are two randomized, placebo-controlled trials demonstrating efficacy. In both ECH and CCH, verapamil is the prophylactic drug of choice. Verapamil 360 mg/day was found to be superior to placebo in one clinical trial. In clinical practice, daily doses of 480-720 mg are mostly used. Thus, the dose of verapamil used in cluster headache treatment may be double the dose used in cardiology, and with the higher doses the PR interval should be checked with an ECG. At the start of a cluster, transitional preventive treatment such as corticosteroids or greater occipital nerve blockade can be given. In CCH and in long-standing clusters of ECH, lithium, methysergide, topiramate, valproic acid and ergotamine tartrate can be used as add-on prophylactic treatment. In drug-resistant CCH, neuromodulation with either occipital nerve stimulation or deep brain stimulation of the hypothalamus is an alternative treatment strategy

  16. The youngest globular clusters

    NASA Astrophysics Data System (ADS)

    Beck, Sara

    2015-11-01

    It is likely that all stars are born in clusters, but most clusters are not bound and disperse. None of the many protoclusters in our Galaxy are likely to develop into long-lived bound clusters. The super star clusters (SSCs) seen in starburst galaxies are more massive and compact and have better chances of survival. The birth and early development of SSCs takes place deep in molecular clouds, and during this crucial stage the embedded clusters are invisible to optical or UV observations but are studied via the radio-infrared supernebulae (RISN) they excite. We review observations of embedded clusters and identify RISN within 10 Mpc whose exciting clusters have ≈ 106 M⊙ or more in volumes of a few pc3 and which are likely to not only survive as bound clusters, but to evolve into objects as massive and compact as Galactic globulars. These clusters are distinguished by very high star formation efficiency η, at least a factor of 10 higher than the few percent seen in the Galaxy, probably due to the violent disturbances their host galaxies have undergone. We review recent observations of the kinematics of the ionized gas in RISN showing outflows through low-density channels in the ambient molecular cloud; this may protect the cloud from feedback by the embedded H II region.

  17. Clustering versus non-clustering phase synchronizations

    SciTech Connect

    Liu, Shuai; Zhan, Meng

    2014-03-15

    Clustering phase synchronization (CPS) is a common scenario to the global phase synchronization of coupled dynamical systems. In this work, a novel scenario, the non-clustering phase synchronization (NPS), is reported. It is found that coupled systems do not transit to the global synchronization until a certain sufficiently large coupling is attained, and there is no clustering prior to the global synchronization. To reveal the relationship between CPS and NPS, we further analyze the noise effect on coupled phase oscillators and find that the coupled oscillator system can change from CPS to NPS with the increase of noise intensity or system disorder. These findings are expected to shed light on the mechanism of various intriguing self-organized behaviors in coupled systems.

  18. A nonparametric clustering technique which estimates the number of clusters

    NASA Technical Reports Server (NTRS)

    Ramey, D. B.

    1983-01-01

    In applications of cluster analysis, one usually needs to determine the number of clusters, K, and the assignment of observations to each cluster. A clustering technique based on recursive application of a multivariate test of bimodality which automatically estimates both K and the cluster assignments is presented.

  19. Mixed-Initiative Clustering

    ERIC Educational Resources Information Center

    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…

  20. Cluster Interest Inventory.

    ERIC Educational Resources Information Center

    Herzog, Douglas

    The Cluster Interest Inventory is designed to familiarize students with representative occupations in 13 career clusters: (1) agribusiness and natural resources, (2) business marketing, and office occupations, (3) communications and media, (4) consumer and homemaker, (5) fine arts and humanities, (6) health, (7) manufacturing and processing, (8)…

  1. Matlab Cluster Ensemble Toolbox

    2009-04-27

    This is a Matlab toolbox for investigating the application of cluster ensembles to data classification, with the objective of improving the accuracy and/or speed of clustering. The toolbox divides the cluster ensemble problem into four areas, providing functionality for each. These include, (1) synthetic data generation, (2) clustering to generate individual data partitions and similarity matrices, (3) consensus function generation and final clustering to generate ensemble data partitioning, and (4) implementation of accuracy metrics. Withmore » regard to data generation, Gaussian data of arbitrary dimension can be generated. The kcenters algorithm can then be used to generate individual data partitions by either, (a) subsampling the data and clustering each subsample, or by (b) randomly initializing the algorithm and generating a clustering for each initialization. In either case an overall similarity matrix can be computed using a consensus function operating on the individual similarity matrices. A final clustering can be performed and performance metrics are provided for evaluation purposes.« less

  2. [Cluster headache differential diagnosis].

    PubMed

    Guégan-Massardier, Evelyne; Laubier, Cécile

    2015-11-01

    Cluster headache is characterized by disabling stereotyped headache. Early diagnosis allows appropriate treatment, unfortunately diagnostic errors are frequent. The main differential diagnoses are other primary or essential headaches. Migraine, more frequent and whose diagnosis is carried by excess, trigeminal neuralgia or other trigemino-autonomic cephalgia. Vascular or tumoral underlying condition can mimic cluster headache, neck and brain imaging is recommended, ideally MRI.

  3. Blue emitting undecaplatinum clusters

    NASA Astrophysics Data System (ADS)

    Chakraborty, Indranath; Bhuin, Radha Gobinda; Bhat, Shridevi; Pradeep, T.

    2014-07-01

    A blue luminescent 11-atom platinum cluster showing step-like optical features and the absence of plasmon absorption was synthesized. The cluster was purified using high performance liquid chromatography (HPLC). Electrospray ionization (ESI) and matrix assisted laser desorption ionization (MALDI) mass spectrometry (MS) suggest a composition, Pt11(BBS)8, which was confirmed by a range of other experimental tools. The cluster is highly stable and compatible with many organic solvents.A blue luminescent 11-atom platinum cluster showing step-like optical features and the absence of plasmon absorption was synthesized. The cluster was purified using high performance liquid chromatography (HPLC). Electrospray ionization (ESI) and matrix assisted laser desorption ionization (MALDI) mass spectrometry (MS) suggest a composition, Pt11(BBS)8, which was confirmed by a range of other experimental tools. The cluster is highly stable and compatible with many organic solvents. Electronic supplementary information (ESI) available: Details of experimental procedures, instrumentation, chromatogram of the crude cluster; SEM/EDAX, DLS, PXRD, TEM, FT-IR, and XPS of the isolated Pt11 cluster; UV/Vis, MALDI MS and SEM/EDAX of isolated 2 and 3; and 195Pt NMR of the K2PtCl6 standard. See DOI: 10.1039/c4nr02778g

  4. Muster: Massively Scalable Clustering

    2010-05-20

    Muster is a framework for scalable cluster analysis. It includes implementations of classic K-Medoids partitioning algorithms, as well as infrastructure for making these algorithms run scalably on very large systems. In particular, Muster contains algorithms such as CAPEK (described in reference 1) that are capable of clustering highly distributed data sets in-place on a hundred thousand or more processes.

  5. Illinois' Career Cluster Model

    ERIC Educational Resources Information Center

    Jankowski, Natasha A.; Kirby, Catherine L.; Bragg, Debra D.; Taylor, Jason L.; Oertle, Kathleen M.

    2009-01-01

    This booklet provides information to multiple stakeholders on the implementation of career clusters in Illinois. The booklet is an extension of the previous edition titled "An Introduction to Illinois CTE Programs of Study" (2008), and provides a resource for partners to understand Illinois' Career Cluster Model as its own adaptation of the…

  6. Brightest Cluster Galaxy Identification

    NASA Astrophysics Data System (ADS)

    Leisman, Luke; Haarsma, D. B.; Sebald, D. A.; ACCEPT Team

    2011-01-01

    Brightest cluster galaxies (BCGs) play an important role in several fields of astronomical research. The literature includes many different methods and criteria for identifying the BCG in the cluster, such as choosing the brightest galaxy, the galaxy nearest the X-ray peak, or the galaxy with the most extended profile. Here we examine a sample of 75 clusters from the Archive of Chandra Cluster Entropy Profile Tables (ACCEPT) and the Sloan Digital Sky Survey (SDSS), measuring masked magnitudes and profiles for BCG candidates in each cluster. We first identified galaxies by hand; in 15% of clusters at least one team member selected a different galaxy than the others.We also applied 6 other identification methods to the ACCEPT sample; in 30% of clusters at least one of these methods selected a different galaxy than the other methods. We then developed an algorithm that weighs brightness, profile, and proximity to the X-ray peak and centroid. This algorithm incorporates the advantages of by-hand identification (weighing multiple properties) and automated selection (repeatable and consistent). The BCG population chosen by the algorithm is more uniform in its properties than populations selected by other methods, particularly in the relation between absolute magnitude (a proxy for galaxy mass) and average gas temperature (a proxy for cluster mass). This work supported by a Barry M. Goldwater Scholarship and a Sid Jansma Summer Research Fellowship.

  7. Marketing Occupations. Cluster Guide.

    ERIC Educational Resources Information Center

    Oregon State Dept. of Education, Salem.

    This cluster guide, which is designed to show teachers what specific knowledge and skills qualify high school students for entry-level employment (or postsecondary training) in marketing occupations, is organized into three sections: (1) cluster organization and implementation, (2) instructional emphasis areas, and (3) assessment. The first…

  8. Probability and Cancer Clusters

    ERIC Educational Resources Information Center

    Hamilton-Keene, Rachael; Lenard, Christoper T.; Mills, Terry M.

    2009-01-01

    Recently there have been several news items about possible cancer clusters in the Australian media. The term "cancer cluster" is used when an unusually large number of people in one geographic area, often a workplace, are diagnosed with cancer in a short space of time. In this paper the authors explore this important health issue using probability…

  9. Cosmology with galaxy clusters

    NASA Astrophysics Data System (ADS)

    Sartoris, Barbara

    2015-08-01

    Clusters of galaxies are powerful probes to constrain parameters that describe the cosmological models and to distinguish among different models. Since, the evolution of the cluster mass function and large-scale clustering contain the informations about the linear growth rate of perturbations and the expansion history of the Universe, clusters have played an important role in establishing the current cosmological paradigm. It is crucial to know how to determine the cluster mass from observational quantities when using clusters as cosmological tools. For this, numerical simulations are helpful to define and study robust cluster mass proxies that have minimal and well understood scatter across the mass and redshift ranges of interest. Additionally, the bias in cluster mass determination can be constrained via observations of the strong and weak lensing effect, X-ray emission, the Sunyaev- Zel’dovic effect, and the dynamics of galaxies.A major advantage of X-ray surveys is that the observable-mass relation is tight. Moreover, clusters can be easily identified in X-ray as continuous, extended sources. As of today, interesting cosmological constraints have been obtained from relatively small cluster samples (~102), X-ray selected by the ROSAT satellite over a wide redshift range (0clusters, the ROSAT All-Sky Survey.The next generation of X-ray telescopes will enhance the statistics of detected clusters and enlarge their redshift coverage. In particular, eROSITA will produce a catalog of >105 clusters with photometric redshifts from multi-band optical surveys (e.g. PanSTARRS, DES, and LSST). This will vastly improve upon current cosmological constraints, especially by the synergy with other cluster surveys that

  10. Cool Cluster Correctly Correlated

    SciTech Connect

    Varganov, Sergey Aleksandrovich

    2005-01-01

    Atomic clusters are unique objects, which occupy an intermediate position between atoms and condensed matter systems. For a long time it was thought that physical and chemical properties of atomic dusters monotonically change with increasing size of the cluster from a single atom to a condensed matter system. However, recently it has become clear that many properties of atomic clusters can change drastically with the size of the clusters. Because physical and chemical properties of clusters can be adjusted simply by changing the cluster's size, different applications of atomic clusters were proposed. One example is the catalytic activity of clusters of specific sizes in different chemical reactions. Another example is a potential application of atomic clusters in microelectronics, where their band gaps can be adjusted by simply changing cluster sizes. In recent years significant advances in experimental techniques allow one to synthesize and study atomic clusters of specified sizes. However, the interpretation of the results is often difficult. The theoretical methods are frequently used to help in interpretation of complex experimental data. Most of the theoretical approaches have been based on empirical or semiempirical methods. These methods allow one to study large and small dusters using the same approximations. However, since empirical and semiempirical methods rely on simple models with many parameters, it is often difficult to estimate the quantitative and even qualitative accuracy of the results. On the other hand, because of significant advances in quantum chemical methods and computer capabilities, it is now possible to do high quality ab-initio calculations not only on systems of few atoms but on clusters of practical interest as well. In addition to accurate results for specific clusters, such methods can be used for benchmarking of different empirical and semiempirical approaches. The atomic clusters studied in this work contain from a few atoms to

  11. Document clustering methods, document cluster label disambiguation methods, document clustering apparatuses, and articles of manufacture

    DOEpatents

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

    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.

  12. Studies in clustering theory

    NASA Astrophysics Data System (ADS)

    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.

  13. Extending Beowulf Clusters

    USGS Publications Warehouse

    Steinwand, Daniel R.; Maddox, Brian; Beckmann, Tim; Hamer, George

    2003-01-01

    Beowulf clusters can provide a cost-effective way to compute numerical models and process large amounts of remote sensing image data. Usually a Beowulf cluster is designed to accomplish a specific set of processing goals, and processing is very efficient when the problem remains inside the constraints of the original design. There are cases, however, when one might wish to compute a problem that is beyond the capacity of the local Beowulf system. In these cases, spreading the problem to multiple clusters or to other machines on the network may provide a cost-effective solution.

  14. Partially supervised speaker clustering.

    PubMed

    Tang, Hao; Chu, Stephen Mingyu; Hasegawa-Johnson, Mark; Huang, Thomas S

    2012-05-01

    Content-based multimedia indexing, retrieval, and processing as well as multimedia databases demand the structuring of the media content (image, audio, video, text, etc.), one significant goal being to associate the identity of the content to the individual segments of the signals. In this paper, we specifically address the problem of speaker clustering, the task of assigning every speech utterance in an audio stream to its speaker. We offer a complete treatment to the idea of partially supervised speaker clustering, which refers to the use of our prior knowledge of speakers in general to assist the unsupervised speaker clustering process. By means of an independent training data set, we encode the prior knowledge at the various stages of the speaker clustering pipeline via 1) learning a speaker-discriminative acoustic feature transformation, 2) learning a universal speaker prior model, and 3) learning a discriminative speaker subspace, or equivalently, a speaker-discriminative distance metric. We study the directional scattering property of the Gaussian mixture model (GMM) mean supervector representation of utterances in the high-dimensional space, and advocate exploiting this property by using the cosine distance metric instead of the euclidean distance metric for speaker clustering in the GMM mean supervector space. We propose to perform discriminant analysis based on the cosine distance metric, which leads to a novel distance metric learning algorithm—linear spherical discriminant analysis (LSDA). We show that the proposed LSDA formulation can be systematically solved within the elegant graph embedding general dimensionality reduction framework. Our speaker clustering experiments on the GALE database clearly indicate that 1) our speaker clustering methods based on the GMM mean supervector representation and vector-based distance metrics outperform traditional speaker clustering methods based on the “bag of acoustic features” representation and statistical

  15. H-cluster stars

    NASA Astrophysics Data System (ADS)

    Lai, X. Y.; Gao, C. Y.; Xu, R. X.

    2013-06-01

    The study of dense matter at ultrahigh density has a very long history, which is meaningful for us to understand not only cosmic events in extreme circumstances but also fundamental laws of physics. It is well known that the state of cold matter at supranuclear density depends on the non-perturbative nature of quantum chromodynamics (QCD) and is essential for modelling pulsars. A so-called H-cluster matter is proposed in this paper as the nature of dense matter in reality. In compact stars at only a few nuclear densities but low temperature, quarks could be interacting strongly with each other there. That might render quarks grouped in clusters, although the hypothetical quark clusters in cold dense matter have not been confirmed due to the lack of both theoretical and experimental evidence. Motivated by recent lattice QCD simulations of the H-dibaryons (with structure uuddss), we therefore consider here a possible kind of quark clusters, H-clusters, that could emerge inside compact stars during their initial cooling as the dominant components inside (the degree of freedom could then be H-clusters there). Taking into account the in-medium stiffening effect, we find that at baryon densities of compact stars H-cluster matter could be more stable than nuclear matter. We also find that for the H-cluster matter with lattice structure, the equation of state could be so stiff that it would seem to be `superluminal' in the most dense region. However, the real sound speed for H-cluster matter is in fact difficult to calculate, so at this stage we do not put constraints on our model from the usual requirement of causality. We study the stars composed of H-clusters, i.e. H-cluster stars, and derive the dependence of their maximum mass on the in-medium stiffening effect, showing that the maximum mass could be well above 2 M⊙ as observed and that the resultant mass-radius relation fits the measurement of the rapid burster under reasonable parameters. Besides a general

  16. Combining cluster number counts and galaxy clustering

    NASA Astrophysics Data System (ADS)

    Lacasa, Fabien; Rosenfeld, Rogerio

    2016-08-01

    The abundance of clusters and the clustering of galaxies are two of the important cosmological probes for current and future large scale surveys of galaxies, such as the Dark Energy Survey. In order to combine them one has to account for the fact that they are not independent quantities, since they probe the same density field. It is important to develop a good understanding of their correlation in order to extract parameter constraints. We present a detailed modelling of the joint covariance matrix between cluster number counts and the galaxy angular power spectrum. We employ the framework of the halo model complemented by a Halo Occupation Distribution model (HOD). We demonstrate the importance of accounting for non-Gaussianity to produce accurate covariance predictions. Indeed, we show that the non-Gaussian covariance becomes dominant at small scales, low redshifts or high cluster masses. We discuss in particular the case of the super-sample covariance (SSC), including the effects of galaxy shot-noise, halo second order bias and non-local bias. We demonstrate that the SSC obeys mathematical inequalities and positivity. Using the joint covariance matrix and a Fisher matrix methodology, we examine the prospects of combining these two probes to constrain cosmological and HOD parameters. We find that the combination indeed results in noticeably better constraints, with improvements of order 20% on cosmological parameters compared to the best single probe, and even greater improvement on HOD parameters, with reduction of error bars by a factor 1.4-4.8. This happens in particular because the cross-covariance introduces a synergy between the probes on small scales. We conclude that accounting for non-Gaussian effects is required for the joint analysis of these observables in galaxy surveys.

  17. Statistical properties of convex clustering

    PubMed Central

    Tan, Kean Ming; Witten, Daniela

    2016-01-01

    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 some traditional clustering methods in simulation studies.

  18. [Treatment of cluster headache].

    PubMed

    Fabre, N

    2005-07-01

    Remarkable therapeutic improvements have come forward recently for trigemino-autonomic cephalalgias. Attack treatment in cluster headache is based on sumatriptan and oxygen. Non-vasoconstrictive treatments are opening a new post-triptan era but are not yet applicable. Prophylactic treatment of cluster headache is based on verapamil and lithium. The efficacy of anti-epileptic drugs in cluster headache remains to be demonstrated. Surgical treatment aimed at the parasympathetic pathways and at the trigeminal nerve demonstrates a high rate of recurrence and adverse events and questions about the relevance of a "peripheral" target in cluster headache. The efficacy of continuous hypothalamic stimulation in patients with intractable headache constitutes a breakthrough, but must be demonstrated at a larger scale and the benefice/risk ratio must be carefully evaluated. Indomethacin still remains the gold standard in paroxysmal hemicrania treatment. Until recently SUNCT was considered an intractable condition. However there are some reports of complete relief with lamotrigine, topiramate and gabapentin.

  19. Mantis BT Cluster Support

    SciTech Connect

    Riot, V.

    2009-06-05

    The software is a modidication to the Mantis BT V1.5 open source application provided by the mantis BT group to support cluster web servers. It also provides various cosmetic modifications used a LLNL.

  20. Spotlight on Cluster

    NASA Astrophysics Data System (ADS)

    1994-09-01

    For the first and only time during the development and construction of Cluster, all four satellites will be together in the space testing facilities of IABG in Munich. On this unique occasion, ESA invites you, and in particular the visual media, to a joint ESA/Industry briefing on the Cluster project at 10h30 on Tuesday, 11 October at IABG, Einsteinstrasse 20, OTTOBRUNN (Germany). After the meeting, ESA and Industry representatives as well as mission specialists will be available for interviews. A detailed agenda is enclosed. If you intend to participate please return the attached registration form by fax (33.1) 42.73.76.90 to ESA Public Relations Division. CLUSTER BRIEFING Tuesday 11 October 1994 - IABG (Munich) Agenda 09h30 Welcome and first photo opportunity 10h30-10h35 Welcome by IABG Director 10h35-10h40 Introduction by Kurt-Johann Gluitz, Dornier, Vice-President Satellite Systems 10h40-10h55 The ESA science programme by Roger Bonnet, Director of the ESA Science programme 10h55-11h10 The mission overview by Rudi Schmidt, ESA, Cluster Project Scientist 11h10-11h20 The Cluster project by John Credland, ESA Cluster Project Manager 11h20-11h30 Cluster and the European Industry by Gunther Lehn, Dornier Cluster Project Manager 11h30-12h00 Question and answer session 12h00-14h00 Interviews and buffet lunch 13h00-14h00 Second photo opportunity 14h00 End

  1. Wild Duck Cluster

    NASA Technical Reports Server (NTRS)

    2005-01-01

    On April 7, 2005, the Deep Impact spacecraft's Impactor Target Sensor camera recorded this image of M11, the Wild Duck cluster, a galactic open cluster located 6 thousand light years away. The camera is located on the impactor spacecraft, which will image comet Tempel 1 beginning 22 hours before impact until about 2 seconds before impact. Impact with comet Tempel 1 is planned for July 4, 2005.

  2. Cluster functional renormalization group

    NASA Astrophysics Data System (ADS)

    Reuther, Johannes; Thomale, Ronny

    2014-01-01

    Functional renormalization group (FRG) has become a diverse and powerful tool to derive effective low-energy scattering vertices of interacting many-body systems. Starting from a free expansion point of the action, the flow of the RG parameter Λ allows us to trace the evolution of the effective one- and two-particle vertices towards low energies by taking into account the vertex corrections between all parquet channels in an unbiased fashion. In this work, we generalize the expansion point at which the diagrammatic resummation procedure is initiated from a free UV limit to a cluster product state. We formulate a cluster FRG scheme where the noninteracting building blocks (i.e., decoupled spin clusters) are treated exactly, and the intercluster couplings are addressed via RG. As a benchmark study, we apply our cluster FRG scheme to the spin-1/2 bilayer Heisenberg model (BHM) on a square lattice where the neighboring sites in the two layers form the individual two-site clusters. Comparing with existing numerical evidence for the BHM, we obtain reasonable findings for the spin susceptibility, the spin-triplet excitation energy, and quasiparticle weight even in coupling regimes close to antiferromagnetic order. The concept of cluster FRG promises applications to a large class of interacting electron systems.

  3. Behavioral Clustering of School Children.

    ERIC Educational Resources Information Center

    Huberty, Carl J.; And Others

    This article illustrates how a cluster analysis can be conducted, validated, and interpreted. Data normed for a behavioral assessment instrument with 14 scales on a nationally representative sample of U.S. school children were utilized. The discussion explores the similarity index, cluster method, cluster typology, cluster validity, cluster…

  4. ROTATING GLOBULAR CLUSTERS

    SciTech Connect

    Bianchini, P.; Varri, A. L.; Bertin, G.; Zocchi, A.

    2013-07-20

    Internal rotation is thought to play a major role in the dynamics of some globular clusters. However, in only a few cases has internal rotation been studied by the quantitative application of realistic and physically justified global models. Here, we present a dynamical analysis of the photometry and three-dimensional kinematics of {omega} Cen, 47 Tuc, and M15, by means of a recently introduced family of self-consistent axisymmetric rotating models. The three clusters, characterized by different relaxation conditions, show evidence of differential rotation and deviations from sphericity. The combination of line-of-sight velocities and proper motions allows us to determine their internal dynamics, predict their morphology, and estimate their dynamical distance. The well-relaxed cluster 47 Tuc is interpreted very well by our model; internal rotation is found to explain the observed morphology. For M15, we provide a global model in good agreement with the data, including the central behavior of the rotation profile and the shape of the ellipticity profile. For the partially relaxed cluster {omega} Cen, the selected model reproduces the complex three-dimensional kinematics; in particular, the observed anisotropy profile, characterized by a transition from isotropy to weakly radial anisotropy and then to tangential anisotropy in the outer parts. The discrepancy found for the steep central gradient in the observed line-of-sight velocity dispersion profile and for the ellipticity profile is ascribed to the condition of only partial relaxation of this cluster and the interplay between rotation and radial anisotropy.

  5. Clustering in bubbly liquids

    NASA Astrophysics Data System (ADS)

    Figueroa, Bernardo; Zenit, Roberto

    2004-11-01

    We are conducting experiments to determine the amount of clustering that occurs when small gas bubbles ascend in clean water. In particular, we are interested in flows for which the liquid motion around the bubbles can be described, with a certain degree of accuracy, using potential flow theory. This model is applicable for the case of bubbly liquids in which the Reynolds number is large and the Weber number is small. To clearly observe the formation of bubble clusters we propose the use of a Hele-Shaw-type channel. In this thin channel the bubbles cannot overlap in the depth direction, therefore the identification of bubble clusters cannot be misinterpreted. Direct video image analysis is performed to calculate the velocity and size of the bubbles, as well as the formation of clusters. Although the walls do affect the motion of the bubbles, the clustering phenomena does occur and has the same qualitative behavior as in fully three-dimensional flows. A series of preliminary measurements are presented. A brief discussion of our plans to perform PIV measurements to obtain the liquid velocity fields is also presented.

  6. Supervised clustering of genes

    PubMed Central

    Dettling, Marcel; Bühlmann, Peter

    2002-01-01

    Background We focus on microarray data where experiments monitor gene expression in different tissues and where each experiment is equipped with an additional response variable such as a cancer type. Although the number of measured genes is in the thousands, it is assumed that only a few marker components of gene subsets determine the type of a tissue. Here we present a new method for finding such groups of genes by directly incorporating the response variables into the grouping process, yielding a supervised clustering algorithm for genes. Results An empirical study on eight publicly available microarray datasets shows that our algorithm identifies gene clusters with excellent predictive potential, often superior to classification with state-of-the-art methods based on single genes. Permutation tests and bootstrapping provide evidence that the output is reasonably stable and more than a noise artifact. Conclusions In contrast to other methods such as hierarchical clustering, our algorithm identifies several gene clusters whose expression levels clearly distinguish the different tissue types. The identification of such gene clusters is potentially useful for medical diagnostics and may at the same time reveal insights into functional genomics. PMID:12537558

  7. Multiferroic rhodium clusters.

    PubMed

    Ma, Lei; Moro, Ramiro; Bowlan, John; de Heer, Walt A; Kirilyuk, Andrei

    2014-10-10

    Simultaneous magnetic and electric deflection measurements of rhodium clusters (Rh(N), 6 ≤ N ≤ 40) reveal ferromagnetism and ferroelectricity at low temperatures, while neither property exists in the bulk metal. Temperature-independent magnetic moments (up to 1 μ(B) per atom) are observed, and superparamagnetic blocking temperatures up to 20 K. Ferroelectric dipole moments on the order of 1D with transition temperatures up to 30 K are observed. Ferromagnetism and ferroelectricity coexist in rhodium clusters in the measured size range, with size-dependent variations in the transition temperatures that tend to be anticorrelated in the range n = 6-25. Both effects diminish with size and essentially vanish at N = 40. The ferroelectric properties suggest a Jahn-Teller ground state. These experiments represent the first example of multiferroic behavior in pure metal clusters. PMID:25375737

  8. Health Occupations Cluster.

    ERIC Educational Resources Information Center

    Walraven, Catherine; And Others

    These instructional materials consist of a series of curriculum worksheets that cover tasks to be mastered by students in health occupations cluster programs. Covered in the curriculum worksheets are diagnostic procedures; observing/recording/reporting/planning; safety; nutrition/elimination; hygiene/personal care/comfort;…

  9. Nuclear Cluster Physics

    SciTech Connect

    Kamimura, Masayasu

    2011-05-06

    Predictive power of theory needs good models and accurate calculation methods to solve the Schroedinger equations of the systems concerned. We present some examples of successful predictions based on the nuclear cluster models of light nuclei and hypernuclei and on the calculation methods that have been developed by Kyushu group.

  10. Clustering in Bubble Suspensions

    NASA Astrophysics Data System (ADS)

    Zenit, Roberto

    2000-11-01

    A monidisperse bubble suspension is studied experimentally for the limit in which the Weber number is small and the Reynolds number is large. For this regime the suspension can be modeled using potential flow theory to describe the dynamics of the interstitial fluid. Complete theoretical descriptions have been composed (Spelt and Sangani, 1998) to model the behavior of these suspensions. Bubble clustering is a natural instability that arises from the potential flow considerations, in which bubbles tend to align in horizontal rafts as they move upwards. The appearance of bubble clusters was recently corroborated experimentally by Zenit et al. (2000), who found that although clusters did appear, their strength was not as strong as the predictions. Experiments involving gravity driven shear flows are used to explain the nature of the clustering observed in these type of flows. Balances of the bubble phase pressure (in terms of a calculated diffusion coefficient) and the Maxwell pressure (from the potential flow description) are presented to predict the stability of the bubble suspension. The predictions are compared with experimental results.

  11. Infrared Coronet Cluster

    NASA Technical Reports Server (NTRS)

    2007-01-01

    While perhaps not quite as well known as its star formation cousin of Orion, the Corona Australis region (containing, at its heart, the Coronet cluster) is one of the nearest and most active regions of ongoing star formation. The Spitzer image shows young stars plus diffuse emission from dust.

  12. Health Occupations Cluster Guide.

    ERIC Educational Resources Information Center

    Oregon State Dept. of Education, Salem.

    Intended to assist the vocational teacher in designing and implementing a cluster program in health occupations, this guide suggests ideas for teaching the specific knowledge and skills that qualify students for entry-level employment in the health occupations field. The knowledge and skills are applicable to 12 occupations: dental assistant;…

  13. FUEL ROD CLUSTERS

    DOEpatents

    Schultz, A.B.

    1959-08-01

    A cluster of nuclear fuel rods and a tubular casing therefor through which a coolant flows in heat-exchange contact with the fuel rods is described. The fuel rcds are held in the casing by virtue of the compressive force exerted between longitudinal ribs of the fuel rcds and internal ribs of the casing or the internal surfaces thereof.

  14. Buckets, Clusters and Dienst

    NASA Technical Reports Server (NTRS)

    Nelson, Michael L.; Maly, Kurt; Shen, Stewart N. T.

    1997-01-01

    In this paper we describe NCSTRL+, a unified, canonical digital library for scientific and technical information (STI). NCSTRL+ is based on the Networked Computer Science Technical Report Library (NCSTRL), a World Wide Web (WWW) accessible digital library (DL) that provides access to over 80 university departments and laboratories. NCSTRL+ implements two new technologies: cluster functionality and publishing "buckets." We have extended the Dienst protocol, the protocol underlying NCSTRL, to provide the ability to "cluster" independent collections into a logically centralized digital library based upon subject category classification, type of organization, and genres of material. The concept of "buckets" provides a mechanism for publishing and managing logically linked entities with multiple data formats. The NCSTRL+ prototype DL contains the holdings of NCSTRL and the NASA Technical Report Server (NTRS). The prototype demonstrates the feasibility of publishing into a multi-cluster DL, searching across clusters, and storing and presenting buckets of information. We show that the overhead for these additional capabilities is minimal to both the author and the user when compared to the equivalent process within NCSTRL.

  15. Detecting alternative graph clusterings.

    PubMed

    Mandala, Supreet; Kumara, Soundar; Yao, Tao

    2012-07-01

    The problem of graph clustering or community detection has enjoyed a lot of attention in complex networks literature. A quality function, modularity, quantifies the strength of clustering and on maximization yields sensible partitions. However, in most real world networks, there are an exponentially large number of near-optimal partitions with some being very different from each other. Therefore, picking an optimal clustering among the alternatives does not provide complete information about network topology. To tackle this problem, we propose a graph perturbation scheme which can be used to identify an ensemble of near-optimal and diverse clusterings. We establish analytical properties of modularity function under the perturbation which ensures diversity. Our approach is algorithm independent and therefore can leverage any of the existing modularity maximizing algorithms. We numerically show that our methodology can systematically identify very different partitions on several existing data sets. The knowledge of diverse partitions sheds more light into the topological organization and helps gain a more complete understanding of the underlying complex network.

  16. Construction Cluster Skills Standards.

    ERIC Educational Resources Information Center

    DePaul Univ., Chicago, IL. Built Environment Partnership.

    Twelve construction cluster skill standards and associated benchmarks were developed as part of a federally funded school-to-work initiative that included the following parties: the Chicago Public Schools; City Colleges of Chicago; and business, labor, and community organizations. The standards, which include core academic, generic workplace…

  17. PVM Support for Clusters

    NASA Technical Reports Server (NTRS)

    Springer, P.

    2000-01-01

    The latest version of PVM (3.4.3) now contains support for a PC cluster running Linux, also known as a Beowulf system. A PVM user of a computer outside the Beowulf system can add the Beowulf as a single machine.

  18. Curriculum Guide Construction Cluster.

    ERIC Educational Resources Information Center

    Kline, Ken

    As part of a model construction cluster curriculum development project, this guide was developed and implemented in the Beaverton (Oregon) School District. The curriculum guide contains 16 units covering the following topics: introduction to construction jobs; safety and first aid; blueprint readings; basic mathematics; site work; framing; roofing…

  19. PDMS embedded Ag clusters: Coalescence and cluster-matrix interaction

    NASA Astrophysics Data System (ADS)

    Roese, S.; Engemann, D.; Hoffmann, S.; Latussek, K.; Sternemann, C.; Hövel, H.

    2016-05-01

    Polydimethylsiloxane (PDMS) has proven to be a suitable embedding medium for silver clusters to prevent aggregation. In order to investigate the influence of the PDMS on the electronic and local atomic structure of the clusters the measurement of x-ray absorption near edge structure (XANES) spectra for different coverages of silver clusters in PDMS and calculations of corresponding XANES spectra have been performed. The coalescence process and the cluster-PDMS interaction were investigated with XANES.

  20. Femtosecond dynamics of cluster expansion

    NASA Astrophysics Data System (ADS)

    Gao, Xiaohui; Wang, Xiaoming; Shim, Bonggu; Arefiev, Alexey; Tushentsov, Mikhail; Breizman, Boris; Downer, Mike

    2010-03-01

    Noble gas clusters irradiated by intense ultrafast laser expand quickly and become typical plasma in picosecond time scale. During the expansion, the clustered plasma demonstrates unique optical properties such as strong absorption and positive contribution to the refractive index. Here we studied cluster expansion dynamics by fs-time-resolved refractive index and absorption measurements in cluster gas jets after ionization and heating by an intense pump pulse. The refractive index measured by frequency domain interferometry (FDI) shows the transient positive peak of refractive index due to clustered plasma. By separating it from the negative contribution of the monomer plasma, we are able to determine the cluster fraction. The absorption measured by a delayed probe shows the contribution from clusters of various sizes. The plasma resonances in the cluster explain the enhancement of the absorption in our isothermal expanding cluster model. The cluster size distribution can be determined. A complete understanding of the femtosecond dynamics of cluster expansion is essential in the accurate interpretation and control of laser-cluster experiments such as phase-matched harmonic generation in cluster medium.

  1. The Rotation of Galaxy Clusters

    NASA Astrophysics Data System (ADS)

    Tovmassian, H. M.

    2015-09-01

    The method for detection of the galaxy cluster rotation based on the study of distribution of member galaxies with velocities lower and higher than the cluster mean velocity over the cluster image is proposed. The search for rotation is made for flat clusters with a/b > 1.8 and BMI type clusters which are expected to be rotating. For comparison there were studied also round clusters and clusters of NBMI type, the second by brightness galaxy, which does not differ significantly from the cluster cD galaxy. Seventeen out of studied 65 clusters are found to be rotating. It was found that the detection rate is sufficiently high for flat clusters, over 60%, and clusters of BMI type with dominant cD galaxy, ≈ 35% . The obtained results show that clusters were formed from the huge primordial gas clouds and preserved the rotation of the primordial clouds, unless they did not experience mergings with other clusters and groups of galaxies, as a result of which the rotation was prevented.

  2. Choosing the Number of Clusters in K-Means Clustering

    ERIC Educational Resources Information Center

    Steinley, Douglas; Brusco, Michael J.

    2011-01-01

    Steinley (2007) provided a lower bound for the sum-of-squares error criterion function used in K-means clustering. In this article, on the basis of the lower bound, the authors propose a method to distinguish between 1 cluster (i.e., a single distribution) versus more than 1 cluster. Additionally, conditional on indicating there are multiple…

  3. Nuclear Cluster Aspects in Astrophysics

    SciTech Connect

    Kubono, Shigeru

    2010-03-01

    The role of nuclear clustering is discussed for nucleosynthesis in stellar evolution with Cluster Nucleosynthesis Diagram (CND) proposed before. Special emphasis is placed on alpha-induced stellar reactions together with molecular states for O and C burning.

  4. Animation of the Phoenix Cluster

    NASA Video Gallery

    This animation shows how large numbers of stars form in the Phoenix Cluster. It begins by showing several galaxies in the cluster and hot gas (in red). This hot gas contains more normal matter than...

  5. Observations of Distant Clusters

    NASA Technical Reports Server (NTRS)

    Donahue, Megan

    2004-01-01

    The is the proceedings and papers supported by the LTSA grant: Homer, D. J.\\& Donahue, M. 2003, in "The Emergence of Cosmic Structure": 13'h Astrophysics Conference Proceedings, Vol. 666,3 1 1-3 14, (AIP). Baumgartner, W. H., Loewenstein, M., Horner, D. J., Mushotzky, R. F. 2003, HEAD- AAS, 35.3503. Homer, D. J. , Donahue, M., Voit G. M. 2003, HEAD-AAS, 35.1309. Nowak, M. A., Smith, B., Donahue, M., Stocke, J. 2003, HEAD-AAS, 35.1316. Scott, D., Borys, C., Chapman, S. C., Donahue, M., Fahlman, G. G., Halpem, M. Newbury, P. 2002, AAS, 128.01. Jones, L. R. et al. 2002, A new era in cosmology, ASP Conference Proceedings, Vol. 283, p. 223 Donahue, M., Daly, R. A., Homer, D. J. 2003, ApJ, 584, 643, Constraints on the Cluster Environments and Hotspot magnetic field strengths for radio sources 3280 and 3254. Donahue, M., et al. 2003, ApJ, 598, 190. The mass, baryonic fraction, and x-ray temperature of the luminous, high-redshift cluster of galaxies MS045 1.6-0305 Perlman, E. S. et al. 2002, ApJS, 140, 256. Smith, B. J., Nowak, M., Donahue, M., Stocke, J. 2003, AJ, 126, 1763. Chandra Observations of the Interacting NGC44 10 Group of Galaxies. Postman, M., Lauer, T. R., Oegerle, W., Donahue, M. 2002, ApJ, 579, 93. The KPNO/deep-range cluster survey I. The catalog and space density of intermediate-redshift clusters. Molnar, S. M., Hughes, J. P., Donahue, M., Joy, M. 2002, ApJ, 573, L91, Chandra Observations of Unresolved X-Ray Sources around Two Clusters of Galaxies. Donahue, M., Mack, J., 2002 NewAR, 46, 155, HST NIcmos and WFPC2 observations of molecular hydrogen and dust around cooling flows. Koekemoer, A. M. et al. 2002 NewAR, 46, 149, Interactions between the A2597 central radio source and dense gas host galaxy. Donahue, M. et al. 2002 ApJ, 569,689, Distant cluster hunting II.

  6. Massive star clusters in galaxies.

    PubMed

    Harris, William E

    2010-02-28

    The ensemble of all star clusters in a galaxy constitutes its star cluster system. In this review, the focus of the discussion is on the ability of star clusters, particularly the systems of old massive globular clusters (GCs), to mark the early evolutionary history of galaxies. I review current themes and key findings in GC research, and highlight some of the outstanding questions that are emerging from recent work.

  7. The Assembly of Galaxy Clusters

    SciTech Connect

    Berrier, Joel C.; Stewart, Kyle R.; Bullock, James S.; Purcell, Chris W.; Barton, Elizabeth J.; Wechsler, Risa H.

    2008-05-16

    We study the formation of fifty-three galaxy cluster-size dark matter halos (M = 10{sup 14.0-14.76} M{sub {circle_dot}}) formed within a pair of cosmological {Lambda}CDM N-body simulations, and track the accretion histories of cluster subhalos with masses large enough to host {approx} 0.1L{sub *} galaxies. By associating subhalos with cluster galaxies, we find the majority of galaxies in clusters experience no 'pre-processing' in the group environment prior to their accretion into the cluster. On average, {approx} 70% of cluster galaxies fall into the cluster potential directly from the field, with no luminous companions in their host halos at the time of accretion; and less than {approx} 12% are accreted as members of groups with five or more galaxies. Moreover, we find that cluster galaxies are significantly less likely to have experienced a merger in the recent past ({approx}< 6 Gyr) than a field halo of the same mass. These results suggest that local, cluster processes like ram-pressure stripping, galaxy harassment, or strangulation play the dominant role in explaining the difference between cluster and field populations at a fixed stellar mass; and that pre-evolution or past merging in the group environment is of secondary importance for setting cluster galaxy properties for most clusters. The accretion times for z = 0 cluster members are quite extended, with {approx} 20% incorporated into the cluster halo more than 7 Gyr ago and {approx} 20% within the last 2 Gyr. By comparing the observed morphological fractions in cluster and field populations, we estimate an approximate time-scale for late-type to early-type transformation within the cluster environment to be {approx} 6 Gyr.

  8. [Cluster analysis in biomedical researches].

    PubMed

    Akopov, A S; Moskovtsev, A A; Dolenko, S A; Savina, G D

    2013-01-01

    Cluster analysis is one of the most popular methods for the analysis of multi-parameter data. The cluster analysis reveals the internal structure of the data, group the separate observations on the degree of their similarity. The review provides a definition of the basic concepts of cluster analysis, and discusses the most popular clustering algorithms: k-means, hierarchical algorithms, Kohonen networks algorithms. Examples are the use of these algorithms in biomedical research. PMID:24640781

  9. The Orion nebula star cluster

    NASA Technical Reports Server (NTRS)

    Panek, R. J.

    1982-01-01

    Photography through filters which suppress nebular light reveal a clustering of faint red stars centered on the Trapezium, this evidences a distinct cluster within the larger OB1 association. Stars within about 20 ft of trapezium comprise the Orion Nebula star cluster are considered. Topics discussed re: (1) extinction by dust grains; (2) photometric peculiarities; (3) spectroscopic peculiarities; (4) young variables; (5) the distribution and motion of gas within the cluster.

  10. Derivatized gold clusters and antibody-gold cluster conjugates

    DOEpatents

    Hainfeld, J.F.; Furuya, F.R.

    1994-11-01

    Antibody- or antibody fragment-gold cluster conjugates are shown wherein the conjugate size can be as small as 5.0 nm. Methods and reagents are disclosed in which antibodies, Fab' or F(ab')[sub 2] fragments are covalently bound to a stable cluster of gold atoms. The gold clusters may contain 6, 8, 9, 11, 13, 55 or 67 gold atoms in their inner core. The clusters may also contain radioactive gold. The antibody-cluster conjugates are useful in electron microscopy applications as well as in clinical applications that include imaging, diagnosis and therapy. 7 figs.

  11. Derivatized gold clusters and antibody-gold cluster conjugates

    DOEpatents

    Hainfeld, James F.; Furuya, Frederic R.

    1994-11-01

    Antibody- or antibody fragment-gold cluster conjugates are shown wherein the conjugate size can be as small as 5.0 nm. Methods and reagents are disclosed in which antibodies, Fab' or F(ab').sub.2 fragments thereof are covalently bound to a stable cluster of gold atoms. The gold clusters may contain 6, 8, 9, 11, 13, 55 or 67 gold atoms in their inner core. The clusters may also contain radioactive gold. The antibody-cluster conjugates are useful in electron microscopy applications as well as in clinical applications that include imaging, diagnosis and therapy.

  12. Adaptive Clustering of Hypermedia Documents.

    ERIC Educational Resources Information Center

    Johnson, Andrew; Fotouhi, Farshad

    1996-01-01

    Discussion of hypermedia systems focuses on a comparison of two types of adaptive algorithm (genetic algorithm and neural network) in clustering hypermedia documents. These clusters allow the user to index into the nodes to find needed information more quickly, since clustering is "personalized" based on the user's paths rather than representing…

  13. Connecting Remote Clusters with ATM

    SciTech Connect

    Hu, T.C.; Wyckoff, P.S.

    1998-10-01

    Sandia's entry into utilizing clusters of networked workstations is called Computational Plant or CPlant for short. The design of CPlant uses Ethernet to boot the individual nodes, Myrinet to communicate within a node cluster, and ATM to connect between remote clusters. This SAND document covers the work done to enable the use of ATM on the CPlant nodes in the Fall of 1997.

  14. Toward Parallel Document Clustering

    SciTech Connect

    Mogill, Jace A.; Haglin, David J.

    2011-09-01

    A key challenge to automated clustering of documents in large text corpora is the high cost of comparing documents in a multimillion dimensional document space. The Anchors Hierarchy is a fast data structure and algorithm for localizing data based on a triangle inequality obeying distance metric, the algorithm strives to minimize the number of distance calculations needed to cluster the documents into “anchors” around reference documents called “pivots”. We extend the original algorithm to increase the amount of available parallelism and consider two implementations: a complex data structure which affords efficient searching, and a simple data structure which requires repeated sorting. The sorting implementation is integrated with a text corpora “Bag of Words” program and initial performance results of end-to-end a document processing workflow are reported.

  15. Binaries in globular clusters

    NASA Technical Reports Server (NTRS)

    Hut, Piet; Mcmillan, Steve; Goodman, Jeremy; Mateo, Mario; Phinney, E. S.; Pryor, Carlton; Richer, Harvey B.; Verbunt, Frank; Weinberg, Martin

    1992-01-01

    Recent observations have shown that globular clusters contain a substantial number of binaries most of which are believed to be primordial. We discuss different successful optical search techniques, based on radial-velocity variables, photometric variables, and the positions of stars in the color-magnitude diagram. In addition, we review searches in other wavelengths, which have turned up low-mass X-ray binaries and more recently a variety of radio pulsars. On the theoretical side, we give an overview of the different physical mechanisms through which individual binaries evolve. We discuss the various simulation techniques which recently have been employed to study the effects of a primordial binary population, and the fascinating interplay between stellar evolution and stellar dynamics which drives globular-cluster evolution.

  16. Clusterization in Ternary Fission

    NASA Astrophysics Data System (ADS)

    Kamanin, D. V.; Pyatkov, Y. V.

    This lecture notes are devoted to the new kind of ternary decay of low excited heavy nuclei called by us "collinear cluster tri-partition" (CCT) due to the features of the effect observed, namely, decay partners fly away almost collinearly and at least one of them has magic nucleon composition. At the early stage of our work the process of "true ternary fission" (fission of the nucleus into three fragments of comparable masses) was considered to be undiscovered for low excited heavy nuclei. Another possible prototype—three body cluster radioactivity—was also unknown. The most close to the CCT phenomenon, at least cinematically, stands so called "polar emission", but only very light ions (up to isotopes of Be) were observed so far.

  17. Gravitational clustering: an overview

    NASA Astrophysics Data System (ADS)

    Labini, Francesco Sylos

    2008-01-01

    We discuss the differences and analogies of gravitational clustering in finite and infinite systems. The process of collective, or violent, relaxation leading to the formation of quasi-stationary states is one of the distinguished features in the dynamics of self-gravitating systems. This occurs, in different conditions, both in a finite than in an infinite system, the latter embedded in a static or in an expanding background. We then discuss, by considering some simple and paradigmatic examples, the problems related to the definition of a mean-field approach to gravitational clustering, focusing on role of discrete fluctuations. The effect of these fluctuations is a basic issue to be clarified to establish the range of scales and times in which a collision-less approximation may describe the evolution of a self-gravitating system and for the theoretical modeling of the non-linear phase.

  18. Hydrated hydride anion clusters

    NASA Astrophysics Data System (ADS)

    Lee, Han Myoung; Kim, Dongwook; Singh, N. Jiten; Kołaski, Maciej; Kim, Kwang S.

    2007-10-01

    On the basis of density functional theory (DFT) and high level ab initio theory, we report the structures, binding energies, thermodynamic quantities, IR spectra, and electronic properties of the hydride anion hydrated by up to six water molecules. Ground state DFT molecular dynamics simulations (based on the Born-Oppenheimer potential surface) show that as the temperature increases, the surface-bound hydride anion changes to the internally bound structure. Car-Parrinello molecular dynamics simulations are also carried out for the spectral analysis of the monohydrated hydride. Excited-state ab initio molecular dynamics simulations show that the photoinduced charge-transfer-to-solvent phenomena are accompanied by the formation of the excess electron-water clusters and the detachment of the H radical from the clusters. The dynamics of the detachment process of a hydrogen radical upon the excitation is discussed.

  19. Tailoring and Scaling Energetic Aluminum Clusters into Cluster Assembled Materials

    NASA Astrophysics Data System (ADS)

    Smith, Jordan Cesar

    As matter decreases in size the importance of a single atom increases exponentially. The properties of clusters, molecules with less than 100 atoms, will change drastically with the addition or removal of a single atom. Clusters have been shown to have properties that mimic other elements and properties that are completely unique. Cluster assemblies could enable the tailoring of precise properties in materials, providing cheap replacements for expensive elements, or novel materials for new applications. Aluminum clusters show great potential use in many applications including energy and catalysis. This work is focused on gaining a better understanding of how geometry and electronic structure affect aluminum cluster reactivity and how useful clusters might be successfully assembled into materials. The effects of doping aluminum cluster ions with boron atoms are reported and show that the addition of a single boron atom usually stabilizes the cluster while adding more boron atoms results in a breaking of symmetry and destabilization. A new analytical technique, matrix isolation cavity ring-down spectroscopy (MICRDS) was developed to help bridge the gap between gas phase cluster studies and condensed phase cluster materials. Molecules are trapped in an inert matrix and studied using cavity ring-down spectroscopy. MICRDS has the potential to also combine clusters into small stable units that would maintain their advantageous gas phase properties.

  20. Properties of the Brightest Cluster Galaxy and Its Host Cluster

    NASA Astrophysics Data System (ADS)

    Katayama, Haruyoshi; Hayashida, Kiyoshi; Takahara, Fumio; Fujita, Yutaka

    2003-03-01

    We investigate the relation between the properties of brightest cluster galaxies (BCGs) and those of their host clusters. To quantify the properties of cluster hot gas, we employ the parameter Z of the fundamental plane of X-ray clusters. It is found that the offset of the BCG from the peak of cluster X-ray emission is larger for smaller Z clusters. The parameter Z (not the redshift z), which depends mainly on virial density ρvir, is considered to represent the formation epoch of a cluster. We thus consider that the offset of the BCG is correlated with the dynamical equilibrium state of its host cluster. On the contrary, no significant correlation is found between the absolute optical magnitude of the BCG and the parameter Z. If the extreme brightness of the BCG is acquired mainly in the course of cluster evolution by environmental effect, BCGs are expected to be brighter in large Z clusters. Our result is not consistent with this simplified view. On the contrary, it is possible that the extreme brightness of the BCG is likely to be determined in the early history of cluster collapse.

  1. Basic cluster compression algorithm

    NASA Technical Reports Server (NTRS)

    Hilbert, E. E.; Lee, J.

    1980-01-01

    Feature extraction and data compression of LANDSAT data is accomplished by BCCA program which reduces costs associated with transmitting, storing, distributing, and interpreting multispectral image data. Algorithm uses spatially local clustering to extract features from image data to describe spectral characteristics of data set. Approach requires only simple repetitive computations, and parallel processing can be used for very high data rates. Program is written in FORTRAN IV for batch execution and has been implemented on SEL 32/55.

  2. Cosmology, Clusters and Calorimeters

    NASA Technical Reports Server (NTRS)

    Figueroa-Feliciano, Enectali

    2005-01-01

    I will review the current state of Cosmology with Clusters and discuss the application of microcalorimeter arrays to this field. With the launch of Astro-E2 this summer and a slew of new missions being developed, microcalorimeters are the next big thing in x-ray astronomy. I will cover the basics and not-so-basic concepts of microcalorimeter designs and look at the future to see where this technology will go.

  3. Astrophysics of galaxy clusters

    NASA Astrophysics Data System (ADS)

    Ettori, Stefano

    2016-07-01

    As the nodes of the cosmic web, clusters of galaxies trace the large-scale distribution of matter in the Universe. They are thus privileged sites in which to investigate the complex physics of structure formation. However, the complete story of how these structures grow, and how they dissipate the gravitational and non-thermal components of their energy budget over cosmic time, is still beyond our grasp. Most of the baryons gravitationally bound to the cluster's halo is in the form of a diffuse, hot, metal-enriched plasma that radiates primarily in the X-ray band. X-ray observations of the evolving cluster population provide a unique opportunity to address such fundamental open questions as: How do hot diffuse baryons accrete and dynamically evolve in dark matter potentials? How and when was the energy that we observe in the ICM generated and distributed? Where and when are heavy elements produced and how are they circulated? We will present the ongoing activities to define the strategy on how an X-ray observatory with large collecting area and an unprecedented combination of high spectral and angular resolution, such as Athena, can address these questions.

  4. Cluster headache after orbital exenteration.

    PubMed

    Evers, S; Sörös, P; Brilla, R; Gerding, H; Husstedt, I W

    1997-10-01

    A 37-year-old man developed an ipsilateral headache which fulfilled the criteria for cluster headache after orbital extenteration because of a traumatic lesion of the bulb. The headache could be treated successfully by drugs usually applied in the therapy of cluster headache. Six similar cases of cluster headache after orbital exenteration could be identified in the literature suggesting that the eye itself is not necessarily part of the pathogenesis of cluster headache. We hypothesize that orbital exenteration can cause cluster headache by lesions of sympathetic structures. Possibly, these mechanisms are similar to those of sympathetic reflex dystrophy (Sudeck-Leriche syndrome) causing pain of the limbs. PMID:9350391

  5. Cluster AAR Campaign Summary Plots

    NASA Astrophysics Data System (ADS)

    Fazakerley, A. N.; Walsh, A. P.; Garza, K. J.; Christopher, I.; Sadeghi, S.; Lindqvist, P.; Mihaljcic, B.; Forsyth, C.; Pickett, J. S.; Marklund, G. T.; Lucek, E. A.; Dandouras, I. S.

    2010-12-01

    Since late 2008 the Cluster spacecraft have been making the first four-point measurements of the Auroral Acceleration Region, opening up an exciting new opportunity for the auroral science, Cluster and wider magnetospheric physics communities. In order to stimulate auroral research with Cluster and aid in event selection, we have produced a set of summary plots for those Cluster perigee passes best suited for addressing open questions in auroral physics. The plots incorporate data from WBD, FGM, EFW, PEACE and CIS and are available from the Cluster PEACE website.

  6. Stormy weather in galaxy clusters

    PubMed

    Burns

    1998-04-17

    Recent x-ray, optical, and radio observations coupled with particle and gas dynamics numerical simulations reveal an unexpectedly complex environment within clusters of galaxies, driven by ongoing accretion of matter from large-scale supercluster filaments. Mergers between clusters and continuous infall of dark matter and baryons from the cluster periphery produce long-lived "stormy weather" within the gaseous cluster atmosphere-shocks, turbulence, and winds of more than 1000 kilometers per second. This weather may be responsible for shaping a rich variety of extended radio sources, which in turn act as "barometers" and "anemometers" of cluster weather.

  7. Cluster energetics: Models and data

    NASA Astrophysics Data System (ADS)

    Ford, Ian; Vehkamäki, Hanna; Knott, Michael

    2000-08-01

    A wealth of information about the energies of clusters of several tens of molecules has been obtained recently through the analysis of nucleation rate data using the nucleation theorems. We describe here studies of n-pentanol and dibutylphthalate clusters, and using multicomponent nucleation theorems, we present data for binary clusters of water and ethanol, and n- and i-octane. We then attempt a synthesis of alkane cluster information obtained to date, and find that the cluster excess energies show a rough proportionality to the molecular size raised to the 2/3 power.

  8. Stormy weather in galaxy clusters

    PubMed

    Burns

    1998-04-17

    Recent x-ray, optical, and radio observations coupled with particle and gas dynamics numerical simulations reveal an unexpectedly complex environment within clusters of galaxies, driven by ongoing accretion of matter from large-scale supercluster filaments. Mergers between clusters and continuous infall of dark matter and baryons from the cluster periphery produce long-lived "stormy weather" within the gaseous cluster atmosphere-shocks, turbulence, and winds of more than 1000 kilometers per second. This weather may be responsible for shaping a rich variety of extended radio sources, which in turn act as "barometers" and "anemometers" of cluster weather. PMID:9545210

  9. Stellar Snowflake Cluster

    NASA Technical Reports Server (NTRS)

    2005-01-01

    [figure removed for brevity, see original site] Figure 1 Stellar Snowflake Cluster Combined Image [figure removed for brevity, see original site] Figure 2 Infrared Array CameraFigure 3 Multiband Imaging Photometer

    Newborn stars, hidden behind thick dust, are revealed in this image of a section of the Christmas Tree cluster from NASA's Spitzer Space Telescope, created in joint effort between Spitzer's infrared array camera and multiband imaging photometer instruments.

    The newly revealed infant stars appear as pink and red specks toward the center of the combined image (fig. 1). The stars appear to have formed in regularly spaced intervals along linear structures in a configuration that resembles the spokes of a wheel or the pattern of a snowflake. Hence, astronomers have nicknamed this the 'Snowflake' cluster.

    Star-forming clouds like this one are dynamic and evolving structures. Since the stars trace the straight line pattern of spokes of a wheel, scientists believe that these are newborn stars, or 'protostars.' At a mere 100,000 years old, these infant structures have yet to 'crawl' away from their location of birth. Over time, the natural drifting motions of each star will break this order, and the snowflake design will be no more.

    While most of the visible-light stars that give the Christmas Tree cluster its name and triangular shape do not shine brightly in Spitzer's infrared eyes, all of the stars forming from this dusty cloud are considered part of the cluster.

    Like a dusty cosmic finger pointing up to the newborn clusters, Spitzer also illuminates the optically dark and dense Cone nebula, the tip of which can be seen towards the bottom left corner of each image.

    This combined image shows the presence of organic molecules mixed with dust as wisps of green, which have been illuminated by nearby star formation. The larger yellowish dots neighboring the baby red stars in the Snowflake Cluster are massive stellar infants forming

  10. Color segmentation using MDL clustering

    NASA Astrophysics Data System (ADS)

    Wallace, Richard S.; Suenaga, Yasuhito

    1991-02-01

    This paper describes a procedure for segmentation of color face images. A cluster analysis algorithm uses a subsample of the input image color pixels to detect clusters in color space. The clustering program consists of two parts. The first part searches for a hierarchical clustering using the NIHC algorithm. The second part searches the resultant cluster tree for a level clustering having minimum description length (MDL). One of the primary advantages of the MDL paradigm is that it enables writing robust vision algorithms that do not depend on user-specified threshold parameters or other " magic numbers. " This technical note describes an application of minimal length encoding in the analysis of digitized human face images at the NTT Human Interface Laboratories. We use MDL clustering to segment color images of human faces. For color segmentation we search for clusters in color space. Using only a subsample of points from the original face image our clustering program detects color clusters corresponding to the hair skin and background regions in the image. Then a maximum likelyhood classifier assigns the remaining pixels to each class. The clustering program tends to group small facial features such as the nostrils mouth and eyes together but they can be separated from the larger classes through connected components analysis.

  11. Scale free processes in stellar cluster formation

    NASA Astrophysics Data System (ADS)

    Bastian, Nate

    2015-08-01

    I will review what is known about stellar cluster formation, focussing on scale free processes, such as how lower mass open clusters related to their giant cousins, the young massive clusters, and potentially globular cluster as well.

  12. Convex Clustering: An Attractive Alternative to Hierarchical Clustering

    PubMed Central

    Chen, Gary K.; Chi, Eric C.; Ranola, John Michael O.; Lange, Kenneth

    2015-01-01

    The primary goal in cluster analysis is to discover natural groupings of objects. The field of cluster analysis is crowded with diverse methods that make special assumptions about data and address different scientific aims. Despite its shortcomings in accuracy, hierarchical clustering is the dominant clustering method in bioinformatics. Biologists find the trees constructed by hierarchical clustering visually appealing and in tune with their evolutionary perspective. Hierarchical clustering operates on multiple scales simultaneously. This is essential, for instance, in transcriptome data, where one may be interested in making qualitative inferences about how lower-order relationships like gene modules lead to higher-order relationships like pathways or biological processes. The recently developed method of convex clustering preserves the visual appeal of hierarchical clustering while ameliorating its propensity to make false inferences in the presence of outliers and noise. The solution paths generated by convex clustering reveal relationships between clusters that are hidden by static methods such as k-means clustering. The current paper derives and tests a novel proximal distance algorithm for minimizing the objective function of convex clustering. The algorithm separates parameters, accommodates missing data, and supports prior information on relationships. Our program CONVEXCLUSTER incorporating the algorithm is implemented on ATI and nVidia graphics processing units (GPUs) for maximal speed. Several biological examples illustrate the strengths of convex clustering and the ability of the proximal distance algorithm to handle high-dimensional problems. CONVEXCLUSTER can be freely downloaded from the UCLA Human Genetics web site at http://www.genetics.ucla.edu/software/ PMID:25965340

  13. Measuring Cluster Relaxedness

    SciTech Connect

    Moreland, Blythe; /Michigan U. /SLAC

    2012-08-24

    When is a dark matter halo 'relaxed'? In our efforts to understand the structure of the universe, dark matter simulations have provided essential grounds for theoretical predictions. These simulations provide a wealth of ways of parameterizing and measuring the features of astronomical objects. It is these measurements on which we base comparisons of our world and our attempts to re-create it. One of the essential questions dark matter simulations help address is how dark matter halos evolve. How does one characterize different states of that evolution? The focus of this project is identifying cluster relaxedness and how it relates to the internal structure of the halo. A dark matter simulation consists of an N-body simulation which takes an initial set of positions and velocities of the dark matter particles and evolves them under the influence of gravity [6]. Though scientists have so far not been able to detect dark matter particles, the information from these simulations is still valuable especially given the relationship between dark matter halos and galaxy clusters. Galaxies sit within dark matter halos and recent evidence points to filaments of dark matter forming the framework on which galaxy clusters grow [7]. A dark matter halo is a collapsed group of gravitationally bound dark matter particles. Subsets of bound particles form subhalos or substructures. The dark matter simulation is carried out over time - with decreasing redshift (z) or increasing scale factor (a = 1/1+z ). (Thus, z = 0 or a = 1.0 is present-day.) The merger history of a halo can be represented pictorally by a merger tree. A major merger event occurs when a structure joins the main halo with the mass ratio between it and the main halo being above a certain threshold. These events mark important points in the halo's evolution. And it is at these events that one hopes, and perhaps is more likely, to relate measures of relaxedness to this mass accretion. Cluster relaxedness is not a well

  14. Are Earthquake Magnitudes Clustered?

    SciTech Connect

    Davidsen, Joern; Green, Adam

    2011-03-11

    The question of earthquake predictability is a long-standing and important challenge. Recent results [Phys. Rev. Lett. 98, 098501 (2007); ibid.100, 038501 (2008)] have suggested that earthquake magnitudes are clustered, thus indicating that they are not independent in contrast to what is typically assumed. Here, we present evidence that the observed magnitude correlations are to a large extent, if not entirely, an artifact due to the incompleteness of earthquake catalogs and the well-known modified Omori law. The latter leads to variations in the frequency-magnitude distribution if the distribution is constrained to those earthquakes that are close in space and time to the directly following event.

  15. The galactic globular cluster system

    NASA Technical Reports Server (NTRS)

    Djorgovski, S.; Meylan, G.

    1994-01-01

    We explore correlations between various properties of Galactic globular clusters, using a database on 143 objects. Our goal is identify correlations and trends which can be used to test and constrain theoretical models of cluster formation and evolution. We use a set of 13 cluster parameters, 9 of which are independently measured. Several arguments suggest that the number of clusters still missing in the obscured regions of the Galaxy is of the order of 10, and thus the selection effects are probably not severe for our sample. Known clusters follow a power-law density distribution with a slope approximately -3.5 to -4, and an apparent core with a core radius approximately 1 kpc. Clusters show a large dynamical range in many of their properties, more so for the core parameters (which are presumably more affected by dynamical evolution) than for the half-light parameters. There are no good correlations with luminosity, although more luminous clusters tend to be more concentrated. When data are binned in luminosity, several trends emerge: more luminous clusters tend to have smaller and denser cores. We interpret this as a differential survival effect, with more massive clusters surviving longer and reaching more evolved dynamical states. Cluster core parameters and concentrations also correlate with the position in the Galaxy, with clusters closer to the Galactic center or plane being more concentrated and having smaller and denser cores. These trends are more pronounced for the fainter (less massive) clusters. This is in agreement with a picture where tidal shocks form disk or bulge passages accelerate dynamical evolution of clusters. Cluster metallicities do not correlate with any other parameter, including luminosity and velocity dispersion; the only detectable trend is with the position in the Galaxy, probably reflecting Zinn's disk-halo dichotomy. This suggests that globular clusters were not self-enriched systems. Velocity dispersions show excellent correlations

  16. Query Results Clustering by Extending SPARQL with CLUSTER BY

    NASA Astrophysics Data System (ADS)

    Ławrynowicz, Agnieszka

    The task of dynamic clustering of the search results proved to be useful in the Web context, where the user often does not know the granularity of the search results in advance. The goal of this paper is to provide a declarative way for invoking dynamic clustering of the results of queries submitted over Semantic Web data. To achieve this goal the paper proposes an approach that extends SPARQL by clustering abilities. The approach introduces a new statement, CLUSTER BY, into the SPARQL grammar and proposes semantics for such extension.

  17. Properties of The Brightest Cluster Galaxy and Its Host Cluster

    NASA Astrophysics Data System (ADS)

    Katayama, H.; Hayashida, K.; Takahara, F.

    2001-09-01

    We investigate the relation between the brightest cluster galaxy (BCG) and its host cluster. A BCG is a bright and massive elliptical galaxy in a cluster of galaxies. The luminosity of a BCG is 10 times larger than that of normal field galaxy and the mass of a BCG is about 1013Msolar which corresponds to that of galaxy group. In order to explain the origin of BCGs, the following three models are proposed: (1) star formation from cooling flow. In this model, intracluster gas gradually condenses at the center of the cluster and forms the BCG. (2) ``Galactic cannibalism'' or the accretion of smaller galaxies. In this model, dynamical friction accounts for the formation of the BCG. These two models predict the BCG evolves with the evolution of cluster. (3) Galaxy merging in the early history of the formation of the cluster. In this model, the property of BCGs is determined no later than cluster collapse. In any model, the formation of BCGs is related to the collapse and formation of its host cluster. The relation between the BCG and its host cluster was studied by Edge (1991). Edge (1991) found that the optical luminosity of the BCG is positively correlated with the X-ray luminosity and temperature of its host cluster. Edge (1991) concludes that these correlations indicate that the BCG responds to the overall cluster properties. In order to investigate the other relation between the BCG and its host cluster, we analyzed ROSAT archival data and compared the displacement between the X-ray peak and the BCG with the Z parameter of the fundamental relation found by Fujita and Takahara (1999). It is found that the displacement is larger with decreasing Z. Furthermore, the large Z clusters tend to have a regular X-ray profile, which implies a relaxed system. The fundamental parameter Z depends mainly on the virial density ρvir, and is considered to be related to the formation epoch of the cluster, i.e., large Z clusters are old clusters and small Z clusters are young

  18. Cluster synchronization in oscillatory networks

    NASA Astrophysics Data System (ADS)

    Belykh, Vladimir N.; Osipov, Grigory V.; Petrov, Valentin S.; Suykens, Johan A. K.; Vandewalle, Joos

    2008-09-01

    Synchronous behavior in networks of coupled oscillators is a commonly observed phenomenon attracting a growing interest in physics, biology, communication, and other fields of science and technology. Besides global synchronization, one can also observe splitting of the full network into several clusters of mutually synchronized oscillators. In this paper, we study the conditions for such cluster partitioning into ensembles for the case of identical chaotic systems. We focus mainly on the existence and the stability of unique unconditional clusters whose rise does not depend on the origin of the other clusters. Also, conditional clusters in arrays of globally nonsymmetrically coupled identical chaotic oscillators are investigated. The design problem of organizing clusters into a given configuration is discussed.

  19. Rough Clustering for Cancer Datasets

    NASA Astrophysics Data System (ADS)

    Herawan, Tutut

    Cancer is becoming a leading cause of death among people in the whole world. It is confirmed that the early detection and accurate diagnosis of this disease can ensure a long survival of the patients. Expert systems and machine learning techniques are gaining popularity in this field because of the effective classification and high diagnostic capability. This paper presents the application of rough set theory for clustering two cancer datasets. These datasets are taken from UCI ML repository. The method is based on MDA technique proposed by [11]. To select a clustering attribute, the maximal degree of the rough attributes dependencies in categorical-valued information systems is used. Further, we use a divide-and-conquer method to partition/cluster the objects. The results show that MDA technique can be used to cluster to the data. Further, we present clusters visualization using two dimensional plot. The plot results provide user friendly navigation to understand the cluster obtained.

  20. Decaying neutrinos in galaxy clusters

    NASA Technical Reports Server (NTRS)

    Melott, Adrian L.; Splinter, Randall J.; Persic, Massimo; Salucci, Paolo

    1994-01-01

    Davidsen et al. (1991) have argued that the failure to detect UV photons from the dark matter (DM) in cluster A665 excludes the decaying neutrino hypothesis. Sciama et al. (1993) argued that because of high central concentration the DM in that cluster must be baryonic. We study the DM profile in clusters of galaxies simulated using the Harrison-Zel'dovich spectrum of density fluctuations, and an amplitude previously derived from numerical simulations (Melott 1984b; Anninos et al. 1991) and in agreement with microwave background fluctuations (Smoot et al. 1992). We find that with this amplitude normalization cluster neutrino DM densities are comparable to observed cluster DM values. We conclude that given this normalization, the cluster DM should be at least largely composed of neutrinos. The constraint of Davidsen et al. can be somewhat weakened by the presence of baryonic DM; but it cannot be eliminated given our assumptions.

  1. Mass Determinations of Star Clusters

    NASA Astrophysics Data System (ADS)

    Meylan, Georges

    Mass determinations are difficult to obtain and still frequently characterised by deceptively large uncertainties. We review below the various mass estimators used for star clusters of all ages and luminosities. We highlight a few recent results related to (i) very massive old star clusters, (ii) the differences and similarities between star clusters and cores of dwarf elliptical galaxies, and (iii) the possible strong biases on mass determination induced by tidal effects.

  2. The SMART CLUSTER METHOD - adaptive earthquake cluster analysis and declustering

    NASA Astrophysics Data System (ADS)

    Schaefer, Andreas; Daniell, James; Wenzel, Friedemann

    2016-04-01

    Earthquake declustering is an essential part of almost any statistical analysis of spatial and temporal properties of seismic activity with usual applications comprising of probabilistic seismic hazard assessments (PSHAs) and earthquake prediction methods. The nature of earthquake clusters and subsequent declustering of earthquake catalogues plays a crucial role in determining the magnitude-dependent earthquake return period and its respective spatial variation. Various methods have been developed to address this issue from other researchers. These have differing ranges of complexity ranging from rather simple statistical window methods to complex epidemic models. This study introduces the smart cluster method (SCM), a new methodology to identify earthquake clusters, which uses an adaptive point process for spatio-temporal identification. Hereby, an adaptive search algorithm for data point clusters is adopted. It uses the earthquake density in the spatio-temporal neighbourhood of each event to adjust the search properties. The identified clusters are subsequently analysed to determine directional anisotropy, focussing on a strong correlation along the rupture plane and adjusts its search space with respect to directional properties. In the case of rapid subsequent ruptures like the 1992 Landers sequence or the 2010/2011 Darfield-Christchurch events, an adaptive classification procedure is applied to disassemble subsequent ruptures which may have been grouped into an individual cluster using near-field searches, support vector machines and temporal splitting. The steering parameters of the search behaviour are linked to local earthquake properties like magnitude of completeness, earthquake density and Gutenberg-Richter parameters. The method is capable of identifying and classifying earthquake clusters in space and time. It is tested and validated using earthquake data from California and New Zealand. As a result of the cluster identification process, each event in

  3. Brightest Cluster Galaxies and Core Gas Density in REXCESS Clusters

    NASA Astrophysics Data System (ADS)

    Haarsma, Deborah B.; Leisman, Luke; Donahue, Megan; Bruch, Seth; Böhringer, Hans; Croston, Judith H.; Pratt, Gabriel W.; Voit, G. Mark; Arnaud, Monique; Pierini, Daniele

    2010-04-01

    We investigate the relationship between brightest cluster galaxies (BCGs) and their host clusters using a sample of nearby galaxy clusters from the Representative XMM-Newton Cluster Structure Survey. The sample was imaged with the Southern Observatory for Astrophysical Research in R band to investigate the mass of the old stellar population. Using a metric radius of 12 h -1 kpc, we found that the BCG luminosity depends weakly on overall cluster mass as L BCG vprop M 0.18±0.07 cl, consistent with previous work. We found that 90% of the BCGs are located within 0.035 r 500 of the peak of the X-ray emission, including all of the cool core (CC) clusters. We also found an unexpected correlation between the BCG metric luminosity and the core gas density for non-cool-core (non-CC) clusters, following a power law of ne vprop L 2.7±0.4 BCG (where ne is measured at 0.008 r 500). The correlation is not easily explained by star formation (which is weak in non-CC clusters) or overall cluster mass (which is not correlated with core gas density). The trend persists even when the BCG is not located near the peak of the X-ray emission, so proximity is not necessary. We suggest that, for non-CC clusters, this correlation implies that the same process that sets the central entropy of the cluster gas also determines the central stellar density of the BCG, and that this underlying physical process is likely to be mergers.

  4. Independent variables in foam clusters

    NASA Astrophysics Data System (ADS)

    Fortes, M. A.; Teixeira, P. I. C.

    2001-11-01

    We find, by counting the degrees of freedom of two-dimensional bubble clusters (finite or periodic) of given topology and bubble areas, that the Plateau laws determine a unique configuration of a finite free cluster, but allow an infinite number of configurations of a periodic cluster. Each of these configurations is associated with a particular strain (stress) state of the cluster; there is in general one unstrained configuration, which corresponds to the minimum of the (surface) energy. Configurations of given topology that satisfy Plateau's laws may only exist in certain ranges of bubble area ratios and/or strains.

  5. Digging Deep in Pandora's Cluster

    NASA Astrophysics Data System (ADS)

    Blakeslee, John P.; Alamo-Martinez, Karla; Toloba, Elisa; Barro, Guillermo; Peng, Eric W.

    2015-01-01

    Abell 2744, the first and nearest (z=0.31) of the Hubble Frontier Fields, is extraordinarily rich in the number and variety of galaxies it contains. Nicknamed "Pandora's Cluster," it exhibits multiple peaks in the dark matter, X-ray, and galaxy density distributions, suggesting an ongoing collision of several massive clusters. The exceptional depth of the Hubble Frontier Field imaging now makes it possible to throw open Pandora's cluster and peer deep inside. To do this, we first model and remove the stellar light of the cluster galaxies; underneath we find not only distant background galaxies, but (like the Hope that lay at the bottom of Pandora's box) a large population of globular star clusters and compact cluster members within Abell 2744 itself. Our earlier work on the massive lensing cluster Abell 1689 (Alamo-Martinez et al. 2013) revealed the largest known population of globular clusters, with a spatial profile intermediate between the galaxy light and the dark matter. Abell 2744 is similarly massive, but far less regular in its density distribution; we examine what implications this has for the copious globular clusters coursing through its multiple cores.

  6. Active matter clusters at interfaces.

    NASA Astrophysics Data System (ADS)

    Copenhagen, Katherine; Gopinathan, Ajay

    2016-03-01

    Collective and directed motility or swarming is an emergent phenomenon displayed by many self-organized assemblies of active biological matter such as clusters of embryonic cells during tissue development, cancerous cells during tumor formation and metastasis, colonies of bacteria in a biofilm, or even flocks of birds and schools of fish at the macro-scale. Such clusters typically encounter very heterogeneous environments. What happens when a cluster encounters an interface between two different environments has implications for its function and fate. Here we study this problem by using a mathematical model of a cluster that treats it as a single cohesive unit that moves in two dimensions by exerting a force/torque per unit area whose magnitude depends on the nature of the local environment. We find that low speed (overdamped) clusters encountering an interface with a moderate difference in properties can lead to refraction or even total internal reflection of the cluster. For large speeds (underdamped), where inertia dominates, the clusters show more complex behaviors crossing the interface multiple times and deviating from the predictable refraction and reflection for the low velocity clusters. We then present an extreme limit of the model in the absence of rotational damping where clusters can become stuck spiraling along the interface or move in large circular trajectories after leaving the interface. Our results show a wide range of behaviors that occur when collectively moving active biological matter moves across interfaces and these insights can be used to control motion by patterning environments.

  7. Teaching In a Cluster College

    ERIC Educational Resources Information Center

    Lawler, Nancy

    1977-01-01

    Report on the advantages and disadvantages of the interdisciplinary cluster system at Oakton Community College (Illinois) after five years. Reviews effects on students, faculty, administrators, and curriculum. (RT)

  8. Adaptive cluster detection

    NASA Astrophysics Data System (ADS)

    Friedenberg, David

    2010-10-01

    the rate of falsely detected active regions. Additionally we examine the more general field of clustering and develop a framework for clustering algorithms based around diffusion maps. Diffusion maps can be used to project high-dimensional data into a lower dimensional space while preserving much of the structure in the data. We demonstrate how diffusion maps can be used to solve clustering problems and examine the influence of tuning parameters on the results. We introduce two novel methods, the self-tuning diffusion map which replaces the global scaling parameter in the typical diffusion map framework with a local scaling parameter and an algorithm for automatically selecting tuning parameters based on a cross-validation style score called prediction strength. The methods are tested on several example datasets.

  9. Analyzing geographic clustered response

    SciTech Connect

    Merrill, D.W.; Selvin, S.; Mohr, M.S.

    1991-08-01

    In the study of geographic disease clusters, an alternative to traditional methods based on rates is to analyze case locations on a transformed map in which population density is everywhere equal. Although the analyst's task is thereby simplified, the specification of the density equalizing map projection (DEMP) itself is not simple and continues to be the subject of considerable research. Here a new DEMP algorithm is described, which avoids some of the difficulties of earlier approaches. The new algorithm (a) avoids illegal overlapping of transformed polygons; (b) finds the unique solution that minimizes map distortion; (c) provides constant magnification over each map polygon; (d) defines a continuous transformation over the entire map domain; (e) defines an inverse transformation; (f) can accept optional constraints such as fixed boundaries; and (g) can use commercially supported minimization software. Work is continuing to improve computing efficiency and improve the algorithm. 21 refs., 15 figs., 2 tabs.

  10. Clustered engine study

    NASA Technical Reports Server (NTRS)

    Shepard, Kyle; Sager, Paul; Kusunoki, Sid; Porter, John; Campion, AL; Mouritzan, Gunnar; Glunt, George; Vegter, George; Koontz, Rob

    1993-01-01

    Several topics are presented in viewgraph form which together encompass the preliminary assessment of nuclear thermal rocket engine clustering. The study objectives, schedule, flow, and groundrules are covered. This is followed by the NASA groundrules mission and our interpretation of the associated operational scenario. The NASA reference vehicle is illustrated, then the four propulsion system options are examined. Each propulsion system's preliminary design, fluid systems, operating characteristics, thrust structure, dimensions, and mass properties are detailed as well as the associated key propulsion system/vehicle interfaces. A brief series of systems analysis is also covered including: thrust vector control requirements, engine out possibilities, propulsion system failure modes, surviving system requirements, and technology requirements. An assessment of vehicle/propulsion system impacts due to the lessons learned are presented.

  11. Ionized cluster beam deposition

    NASA Astrophysics Data System (ADS)

    Kirkpatrick, A. R.

    1983-11-01

    Ionized Cluster Beam (ICB) deposition, a new technique originated by Takagi of Kyoto University in Japan, offers a number of unique capabilities for thin film metallization as well as for deposition of active semiconductor materials. ICB allows average energy per deposited atom to be controlled and involves impact kinetics which result in high diffusion energies of atoms on the growth surface. To a greater degree than in other techniques, ICB involves quantitative process parameters which can be utilized to strongly control the characteristics of films being deposited. In the ICB deposition process, material to be deposited is vaporized into a vacuum chamber from a confinement crucible at high temperature. Crucible nozzle configuration and operating temperature are such that emerging vapor undergoes supercondensation following adiabatic expansion through the nozzle.

  12. Ionized cluster beam deposition

    NASA Technical Reports Server (NTRS)

    Kirkpatrick, A. R.

    1983-01-01

    Ionized Cluster Beam (ICB) deposition, a new technique originated by Takagi of Kyoto University in Japan, offers a number of unique capabilities for thin film metallization as well as for deposition of active semiconductor materials. ICB allows average energy per deposited atom to be controlled and involves impact kinetics which result in high diffusion energies of atoms on the growth surface. To a greater degree than in other techniques, ICB involves quantitative process parameters which can be utilized to strongly control the characteristics of films being deposited. In the ICB deposition process, material to be deposited is vaporized into a vacuum chamber from a confinement crucible at high temperature. Crucible nozzle configuration and operating temperature are such that emerging vapor undergoes supercondensation following adiabatic expansion through the nozzle.

  13. Cross-Clustering: A Partial Clustering Algorithm with Automatic Estimation of the Number of Clusters

    PubMed Central

    Tellaroli, Paola; Bazzi, Marco; Donato, Michele; Brazzale, Alessandra R.; Drăghici, Sorin

    2016-01-01

    Four of the most common limitations of the many available clustering methods are: i) the lack of a proper strategy to deal with outliers; ii) the need for a good a priori estimate of the number of clusters to obtain reasonable results; iii) the lack of a method able to detect when partitioning of a specific data set is not appropriate; and iv) the dependence of the result on the initialization. Here we propose Cross-clustering (CC), a partial clustering algorithm that overcomes these four limitations by combining the principles of two well established hierarchical clustering algorithms: Ward’s minimum variance and Complete-linkage. We validated CC by comparing it with a number of existing clustering methods, including Ward’s and Complete-linkage. We show on both simulated and real datasets, that CC performs better than the other methods in terms of: the identification of the correct number of clusters, the identification of outliers, and the determination of real cluster memberships. We used CC to cluster samples in order to identify disease subtypes, and on gene profiles, in order to determine groups of genes with the same behavior. Results obtained on a non-biological dataset show that the method is general enough to be successfully used in such diverse applications. The algorithm has been implemented in the statistical language R and is freely available from the CRAN contributed packages repository. PMID:27015427

  14. Steroid hormones in cluster headaches.

    PubMed

    Stillman, Mark

    2006-04-01

    For decades, glucocorticoid therapy has been a well-recognized abortive treatment for cluster headaches. However, the role of steroid hormones, including both glucocorticoids and sex steroids, in the pathophysiology and therapy of cluster headaches has been a topic of much debate and speculation. Current research now points to the importance of cortisol and testosterone in the pathogenesis of cluster headaches, and they appear to be linked mechanistically to another hormone, melatonin. Melatonin, unlike cortisol or testosterone, is not a product of the hypothalamic pituitary axis but of the retinohypothalamic pineal axis, and is the major biomarker of circadian rhythms. The regulation of steroids and melatonin in the pathogenesis of cluster headaches in turn depends on the sympathetic nervous system. Accumulated evidence suggests sympathetic dysfunction--embodied in the Horner sign so commonly seen in the cluster headache--as a necessary ingredient in the inception of the cluster headache. Sympathetic dysfunction now is thought to be associated with the hypercortisolism, hypotestosteronism, and lower-than-normal melatonin levels in the active cluster patient. Future research may hold the key to a fuller explanation of the complex interaction of hormonal systems in the cluster headache.

  15. Hot subdwarfs in globular clusters

    SciTech Connect

    Drukier, G.A.; Fahlman, G.G.; Richter, H.B. )

    1989-07-01

    Spectra of faint blue stars in the globular clusters M71 and M4 are presented. The spectra suggest that they are hot subdwarfs. Arguments in favor of membership in their respective clusters and comments regarding their evolutionary status are given. 18 refs.

  16. Antibody-gold cluster conjugates

    DOEpatents

    Hainfeld, J.F.

    1988-06-28

    Antibody- or antibody fragment-gold cluster conjugates are shown wherein the conjugate size can be about 5.0 nm. Methods and reagents are disclosed in which antibodies or Fab' fragments thereof are covalently bound to a stable cluster of gold atoms. 2 figs.

  17. Two generalizations of Kohonen clustering

    NASA Technical Reports Server (NTRS)

    Bezdek, James C.; Pal, Nikhil R.; Tsao, Eric C. K.

    1993-01-01

    The relationship between the sequential hard c-means (SHCM), learning vector quantization (LVQ), and fuzzy c-means (FCM) clustering algorithms is discussed. LVQ and SHCM suffer from several major problems. For example, they depend heavily on initialization. If the initial values of the cluster centers are outside the convex hull of the input data, such algorithms, even if they terminate, may not produce meaningful results in terms of prototypes for cluster representation. This is due in part to the fact that they update only the winning prototype for every input vector. The impact and interaction of these two families with Kohonen's self-organizing feature mapping (SOFM), which is not a clustering method, but which often leads ideas to clustering algorithms is discussed. Then two generalizations of LVQ that are explicitly designed as clustering algorithms are presented; these algorithms are referred to as generalized LVQ = GLVQ; and fuzzy LVQ = FLVQ. Learning rules are derived to optimize an objective function whose goal is to produce 'good clusters'. GLVQ/FLVQ (may) update every node in the clustering net for each input vector. Neither GLVQ nor FLVQ depends upon a choice for the update neighborhood or learning rate distribution - these are taken care of automatically. Segmentation of a gray tone image is used as a typical application of these algorithms to illustrate the performance of GLVQ/FLVQ.

  18. Active matter clusters at interfaces

    NASA Astrophysics Data System (ADS)

    Copenhagen, Katherine; Gopinathan, Ajay

    Collective and directed motility or swarming is an emergent phenomenon displayed by many self-organized assemblies of active biological matter such as clusters of embryonic cells during tissue development and flocks of birds. Such clusters typically encounter very heterogeneous environments. What happens when a cluster encounters an interface between two different environments has implications for its function and fate. Here we study this problem by using a mathematical model of a cluster that treats it as a single cohesive unit whose movement depends on the nature of the local environment. We find that low speed clusters which exert forces but no active torques, encountering an interface with a moderate difference in properties can lead to refraction or even total internal reflection of the cluster. For large speeds and clusters with active torques, they show more complex behaviors crossing the interface multiple times, becoming trapped at the interface and deviating from the predictable refraction and reflection of the low velocity clusters. Our results show a wide range of behaviors that occur when collectively moving active biological matter moves across interfaces and these insights can be used to control motion by patterning environments.

  19. Protonated water clusters in TPC's

    NASA Astrophysics Data System (ADS)

    Kaya, Yunus; Kalkan, Yalçın; Veenhof, Rob

    2016-07-01

    Water vapour is added to the ALICE TPC gas to enhance its stability. These polar molecules create large protonated water clusters around a H+ core. In this context, the reactions H3O+(H2 O) n - 1 +H2 O →H3O+(H2O)n (n=1-9) were studied in the gas phase. Structures for these clusters are suggested and the most stable structures for each cluster size are shown. The thermodynamic parameters Δ Hn-1,n0, Δ Gn-1,n0, Δ Sn-1,n0 and equilibrium constants K n - 1 , n for the reaction were calculated to determine the size of the water clusters. The results are close to experimental data found in the literature. Protonated water clusters at stp have a size of 6-9 which corresponds to a mass of 127.1 - 181.2 g / mole.

  20. SACS: Spitzer Archival Cluster Survey

    NASA Astrophysics Data System (ADS)

    Stern, Daniel

    Emerging from the cosmic web, galaxy clusters are the most massive gravitationally bound structures in the universe. Thought to have begun their assembly at z > 2, clusters provide insights into the growth of large-scale structure as well as the physics that drives galaxy evolution. Understanding how and when the most massive galaxies assemble their stellar mass, stop forming stars, and acquire their observed morphologies in these environments remain outstanding questions. The redshift range 1.3 < z < 2 is a key epoch in this respect: elliptical galaxies start to become the dominant population in cluster cores, and star formation in spiral galaxies is being quenched. Until recently, however, this redshift range was essentially unreachable with available instrumentation, with clusters at these redshifts exceedingly challenging to identify from either ground-based optical/nearinfrared imaging or from X-ray surveys. Mid-infrared (MIR) imaging with the IRAC camera on board of the Spitzer Space Telescope has changed the landscape. High-redshift clusters are easily identified in the MIR due to a combination of the unique colors of distant galaxies and a negative k-correction in the 3-5 μm range which makes such galaxies bright. Even 90-sec observations with Spitzer/IRAC, a depth which essentially all extragalactic observations in the archive achieve, is sufficient to robustly detect overdensities of L* galaxies out to z~2. Here we request funding to embark on a ambitious scientific program, the “SACS: Spitzer Archival Cluster Survey”, a comprehensive search for the most distant galaxy clusters in all Spitzer/IRAC extragalactic pointings available in the archive. With the SACS we aim to discover ~2000 of 1.3 < z < 2.5 clusters, thus provide the ultimate catalog for high-redshift MIR selected clusters: a lasting legacy for Spitzer. The study we propose will increase by more than a factor of 10 the number of high-redshift clusters discovered by all previous surveys

  1. Decaying neutrinos in galaxy clusters

    NASA Technical Reports Server (NTRS)

    Melott, Adrian L.; Splinter, Randall J.; Persic, Massimo; Salucci, Paolo

    1993-01-01

    The DM profile in clusters of galaxies was studied and simulated using the Harrison-Zel'dovich spectrum of density fluctuations, and an amplitude previously derived from numerical simulations and in agreement with microwave background fluctuations. Neutrino DM densities, with this amplitude normalization cluster, are comparable to observed cluster DM values. It was concluded that given this normalization, the cluster DM should be al least largely composed of neutrinos. The constraint of Davidson et al., who argued that the failure to detect uv photons from the dark matter (DM) in cluster A665 excludes the decaying neutrino hypothesis, could be somewhat weakened by the presence of baryonic DM; but it cannot be eliminated given our assumptions.

  2. Single System Image Cluster Management

    2004-02-13

    Cluster computing has quickly proven itself to be a capable workhorse for a wide variety of production computing tasks; however, setting up and maintaining a cluster still requires significantly more effort than administrating just a single machine. As computing hardware descreases in price and cluster sizes grow, it is becoming increasingly important to manage clusters cleverly so that a system administration effort can "scale" as well. To ease the task of mananging many machines, administratorsmore » often deploy an environment that is homogeneous across all nodes of a cluster, and maintain a snapshot of the filesystem as a 'master image'. However due to operational, behavioral, and physical constraints, many nodes often require numerous deviations from the master image in order to operate as desired.« less

  3. Magnetic anisotropy in single clusters

    NASA Astrophysics Data System (ADS)

    Jamet, Matthieu; Wernsdorfer, Wolfgang; Thirion, Christophe; Dupuis, Véronique; Mélinon, Patrice; Pérez, Alain; Mailly, Dominique

    2004-01-01

    The magnetic measurements on single cobalt and iron nanoclusters containing almost 1000 atoms are presented. Particles are directly buried within the superconducting film of a micro-SQUID (superconducting quantum interference device) which leads to the required sensitivity. The angular dependence of the switching field in three dimensions turns out to be in good agreement with a uniform rotation of cluster magnetization. The Stoner and Wohlfarth model yields therefore an estimation of magnetic anisotropy in a single cluster. In particular, uniaxial, biaxial, and cubic contributions can be separated. Results are interpreted on the basis of a simple atomic model in which clusters are assimilated to “giant spins.” We present an extension of the Néel model to clusters in order to estimate surface anisotropy. In the case of cobalt, this last contribution dominates and numerical simulations allow us to get the morphology of the investigated clusters.

  4. Information Clustering Based on Fuzzy Multisets.

    ERIC Educational Resources Information Center

    Miyamoto, Sadaaki

    2003-01-01

    Proposes a fuzzy multiset model for information clustering with application to information retrieval on the World Wide Web. Highlights include search engines; term clustering; document clustering; algorithms for calculating cluster centers; theoretical properties concerning clustering algorithms; and examples to show how the algorithms work.…

  5. A Linear Algebra Measure of Cluster Quality.

    ERIC Educational Resources Information Center

    Mather, Laura A.

    2000-01-01

    Discussion of models for information retrieval focuses on an application of linear algebra to text clustering, namely, a metric for measuring cluster quality based on the theory that cluster quality is proportional to the number of terms that are disjoint across the clusters. Explains term-document matrices and clustering algorithms. (Author/LRW)

  6. Luminescent iron clusters in solution

    NASA Astrophysics Data System (ADS)

    Goswami, Nirmal; Baksi, Ananya; Giri, Anupam; Xavier, Paulrajpillai Lourdu; Basu, Gautam; Pradeep, Thalappil; Pal, Samir Kumar

    2014-01-01

    Metal clusters, composed of a few atoms at the core, exhibit unique properties and have potential applications. Although atomically precise clusters of noble metals have been synthesized, analogous systems of reactive metals, such as iron, have not been realized in solution due to high reactivity. Here we report the synthesis and characterization of novel iron clusters in the hemoglobin matrix that are highly luminescent (quantum yield 10% at 565 nm). The super-paramagnetic iron clusters, after successful ligand exchange from protein and phase transfer from water to chloroform using tri-octylphosphineoxide (TOPO), were detected as [Fe10(TOPO)3(H2O)3]+, [Fe13(TOPO)2(H2O)]+ and [Fe8(TOPO)(H2O)2]+ by mass spectrometry. This study lays the groundwork for exploiting unique properties of soluble iron clusters.Metal clusters, composed of a few atoms at the core, exhibit unique properties and have potential applications. Although atomically precise clusters of noble metals have been synthesized, analogous systems of reactive metals, such as iron, have not been realized in solution due to high reactivity. Here we report the synthesis and characterization of novel iron clusters in the hemoglobin matrix that are highly luminescent (quantum yield 10% at 565 nm). The super-paramagnetic iron clusters, after successful ligand exchange from protein and phase transfer from water to chloroform using tri-octylphosphineoxide (TOPO), were detected as [Fe10(TOPO)3(H2O)3]+, [Fe13(TOPO)2(H2O)]+ and [Fe8(TOPO)(H2O)2]+ by mass spectrometry. This study lays the groundwork for exploiting unique properties of soluble iron clusters. Electronic supplementary information (ESI) available. See DOI: 10.1039/c3nr05784d

  7. Evolution of brightest cluster galaxies in X-ray clusters

    NASA Astrophysics Data System (ADS)

    Brough, S.; Collins, C. A.; Burke, D. J.; Mann, R. G.; Lynam, P. D.

    2002-01-01

    A recent paper presents the analysis of the K-band Hubble diagram of 76 brightest cluster galaxies (BCGs) in X-ray clusters and shows that the properties of BCGs depend on the X-ray luminosity (LX) of their host clusters. Unfortunately, the low numbers of nearby clusters in this sample makes it difficult to constrain evolutionary trends. In this letter we extend the Hubble diagram of Burke, Collins & Mann to a total of 155 clusters using new data on 79 BCGs at z<=0.1 from the 2MASS extended source catalogue. We show that the major division between BCGs in high- and low-LX clusters disappears at z<=0.1, with BCGs having similar absolute magnitudes independent of the X-ray luminosity of their host clusters. At larger redshifts, the K-band light of BCGs in high-LX systems is consistent with little or no merging back to z~0.8, whereas BCGs in the low-LX systems have a different evolutionary history, with many increasing their mass by a factor >=4 since z~=1. This provides direct evidence of hierarchical merging in a galaxy population.

  8. Plug cluster module demonstration

    NASA Technical Reports Server (NTRS)

    Rousar, D. C.

    1978-01-01

    The low pressure, film cooled rocket engine design concept developed during two previous ALRC programs was re-evaluated for application as a module for a plug cluster engine capable of performing space shuttle OTV missions. The nominal engine mixture ratio was 5.5 and the engine life requirements were 1200 thermal cycles and 10 hours total operating life. The program consisted of pretest analysis; engine tests, performed using residual components; and posttest analysis. The pretest analysis indicated that operation of the operation of the film cooled engine at O/F = 5.5 was feasible. During the engine tests, steady state wall temperature and performance measurement were obtained over a range of film cooling flow rates, and the durability of the engine was demonstrated by firing the test engine 1220 times at a nominal performance ranging from 430 - 432 seconds. The performance of the test engine was limited by film coolant sleeve damage which had occurred during previous testing. The post-test analyses indicated that the nominal performance level can be increased to 436 seconds.

  9. Dust cluster explosion

    SciTech Connect

    Saxena, Vikrant; Avinash, K.; Sen, A.

    2012-09-15

    A model for the dust cluster explosion where micron/sub-micron sized particles are accelerated at the expense of plasma thermal energy, in the afterglow phase of a complex plasma discharge is proposed. The model is tested by molecular dynamics simulations of dust particles in a confining potential. The nature of the explosion (caused by switching off the discharge) and the concomitant dust acceleration is found to depend critically on the pressure of the background neutral gas. At low gas pressure, the explosion is due to unshielded Coulomb repulsion between dust particles and yields maximum acceleration, while in the high pressure regime it is due to shielded Yukawa repulsion and yields much feebler acceleration. These results are in agreement with experimental findings. Our simulations also confirm a recently proposed electrostatic (ES) isothermal scaling relation, P{sub E}{proportional_to}V{sub d}{sup -2} (where P{sub E} is the ES pressure of the dust particles and V{sub d} is the confining volume).

  10. Novae in globular clusters

    SciTech Connect

    Kato, Mariko; Hachisu, Izumi; Henze, Martin

    2013-12-10

    We present the first light-curve analysis of Population II novae that appeared in M31 globular clusters. Our light-curve models, based on the optically thick wind theory, reproduce well both the X-ray turn-on and turnoff times with the white dwarf (WD) mass of about 1.2 M {sub ☉} for M31N 2007-06b in Bol 111 and about 1.37 M {sub ☉} for M31N 2010-10f in Bol 126. The transient supersoft X-ray source CXO J004345 in Bol 194 is highly likely a nova remnant of 1.2-1.3 M {sub ☉} WD. These WD masses are quite consistent with the temperatures deduced from X-ray spectra. We also present the dependence of nova light curves on the metallicity in the range from [Fe/H] = 0.4 to –2.7. Whereas strong optically thick winds are accelerated in Galactic disk novae owing to a large Fe opacity peak, only weak winds occur in Population II novae with low Fe abundance. Thus, nova light curves are systematically slow in low Fe environment. For an extremely low Fe abundance normal nova outbursts may not occur unless the WD is very massive. We encourage V or y filter observation rather than R as well as high cadence X-ray monitorings to open quantitative studies of extragalactic novae.

  11. Clusterization and quadrupole deformation in nuclei

    SciTech Connect

    Cseh, J.; Algora, A.; Antonenko, N. V.; Jolos, R. V.; Scheid, W.; Darai, J.; Hess, P. O.

    2006-04-26

    We study the interrelation of the clusterization and quadrupole deformation of atomic nuclei, by applying cluster models. Both the energetic stability and the exclusion principle is investigated. Special attention is paid to the relative orientations of deformed clusters.

  12. Cluster-assembled metallic glasses

    NASA Astrophysics Data System (ADS)

    Kartouzian, Aras

    2013-07-01

    A bottom-up approach to nanofabricate metallic glasses from metal clusters as building blocks is presented. Considering metallic glasses as a subclass of cluster-assembled materials, the relation between the two lively fields of metal clusters and metallic glasses is pointed out. Deposition of selected clusters or collections of them, generated by state-of-the-art cluster beam sources, could lead to the production of a well-defined amorphous material. In contrast to rapidly quenched glasses where only the composition of the glass can be controlled, in cluster-assembled glasses, one can precisely control the structural building blocks. Comparing properties of glasses with similar compositions but differing in building blocks and therefore different in structure will facilitate the study of structure-property correlation in metallic glasses. This bottom-up method provides a novel alternative path to the synthesis of glassy alloys and will contribute to improving fundamental understanding in the field of metallic glasses. It may even permit the production of glassy materials for alloys that cannot be quenched rapidly enough to circumvent crystallization. Additionally, gaining deeper insight into the parameters governing the structure-property relation in metallic glasses can have a great impact on understanding and design of other cluster-assembled materials.

  13. Cluster-assembled metallic glasses.

    PubMed

    Kartouzian, Aras

    2013-07-30

    A bottom-up approach to nanofabricate metallic glasses from metal clusters as building blocks is presented. Considering metallic glasses as a subclass of cluster-assembled materials, the relation between the two lively fields of metal clusters and metallic glasses is pointed out. Deposition of selected clusters or collections of them, generated by state-of-the-art cluster beam sources, could lead to the production of a well-defined amorphous material. In contrast to rapidly quenched glasses where only the composition of the glass can be controlled, in cluster-assembled glasses, one can precisely control the structural building blocks. Comparing properties of glasses with similar compositions but differing in building blocks and therefore different in structure will facilitate the study of structure-property correlation in metallic glasses. This bottom-up method provides a novel alternative path to the synthesis of glassy alloys and will contribute to improving fundamental understanding in the field of metallic glasses. It may even permit the production of glassy materials for alloys that cannot be quenched rapidly enough to circumvent crystallization. Additionally, gaining deeper insight into the parameters governing the structure-property relation in metallic glasses can have a great impact on understanding and design of other cluster-assembled materials.

  14. Galactic Globular Cluster Relative Ages

    NASA Astrophysics Data System (ADS)

    De Angeli, Francesca; Piotto, Giampaolo; Cassisi, Santi; Busso, Giorgia; Recio-Blanco, Alejandra; Salaris, Maurizio; Aparicio, Antonio; Rosenberg, Alfred

    2005-07-01

    We present accurate relative ages for a sample of 55 Galactic globular clusters. The ages have been obtained by measuring the difference between the horizontal branch and the turnoff in two internally photometrically homogeneous databases. The mutual consistency of the two data sets has been assessed by comparing the ages of 16 globular clusters in common between the two databases. We have also investigated the consistency of our relative age determination within the recent stellar model framework. All clusters with [Fe/H]<-1.7 are found to be old and coeval, with the possible exception of two objects, which are marginally younger. The age dispersion for the metal-poor clusters is 0.6 Gyr (rms), consistent with a null age dispersion. Intermediate-metallicity clusters (-1.7<[Fe/H]<-0.8) are on average 1.5 Gyr younger than the metal-poor ones, with an age dispersion of 1.0 Gyr (rms) and a total age range of ~3 Gyr. About 15% of the intermediate-metallicity clusters are coeval with the oldest clusters. All the clusters with [Fe/H]>-0.8 are ~1 Gyr younger than the most metal-poor ones, with a relatively small age dispersion, although the metal-rich sample is still too small to allow firmer conclusions. There is no correlation of the cluster age with the galactocentric distance. We briefly discuss the implication of these observational results for the formation history of the Galaxy. Based on observations 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, and on observations made at the European Southern Observatory, La Silla, Chile, and with the Isaac Newton Group Telescopes.

  15. THE EXTENDED VIRGO CLUSTER CATALOG

    SciTech Connect

    Kim, Suk; Rey, Soo-Chang; Lee, Youngdae; Chung, Jiwon; Pak, Mina; Yi, Wonhyeong; Lee, Woong; Jerjen, Helmut; Lisker, Thorsten; Sung, Eon-Chang

    2015-01-01

    We present a new catalog of galaxies in the wider region of the Virgo cluster, based on the Sloan Digital Sky Survey (SDSS) Data Release 7. The Extended Virgo Cluster Catalog (EVCC) covers an area of 725 deg{sup 2} or 60.1 Mpc{sup 2}. It is 5.2 times larger than the footprint of the classical Virgo Cluster Catalog (VCC) and reaches out to 3.5 times the virial radius of the Virgo cluster. We selected 1324 spectroscopically targeted galaxies with radial velocities less than 3000 km s{sup –1}. In addition, 265 galaxies that have been overlooked in the SDSS spectroscopic survey but have available redshifts in the NASA Extragalactic Database are also included. Our selection process secured a total of 1589 galaxies, 676 of which are not included in the VCC. The certain and possible cluster members are defined by means of redshift comparison with a cluster infall model. We employed two independent and complementary galaxy classification schemes: the traditional morphological classification based on the visual inspection of optical images and a characterization of galaxies from their spectroscopic features. SDSS u, g, r, i, and z passband photometry of all EVCC galaxies was performed using Source Extractor. We compare the EVCC galaxies with the VCC in terms of morphology, spatial distribution, and luminosity function. The EVCC defines a comprehensive galaxy sample covering a wider range in galaxy density that is significantly different from the inner region of the Virgo cluster. It will be the foundation for forthcoming galaxy evolution studies in the extended Virgo cluster region, complementing ongoing and planned Virgo cluster surveys at various wavelengths.

  16. Systolic architecture for heirarchical clustering

    SciTech Connect

    Ku, L.C.

    1984-01-01

    Several hierarchical clustering methods (including single-linkage complete-linkage, centroid, and absolute overlap methods) are reviewed. The absolute overlap clustering method is selected for the design of systolic architecture mainly due to its simplicity. Two versions of systolic architectures for the absolute overlap hierarchical clustering algorithm are proposed: one-dimensional version that leads to the development of a two dimensional version which fully takes advantage of the underlying data structure of the problems. The two dimensional systolic architecture can achieve a time complexity of O(m + n) in comparison with the conventional computer implementation of a time complexity of O(m/sup 2*/n).

  17. Exploring Web Search Results Clustering

    NASA Astrophysics Data System (ADS)

    Wang, Xiaoxia; Bramer, Max

    As the number of documents on the web has proliferated, the low precision of conventional web search engines and the flat ranked search results presentation make it difficult for users to locate specific information of interest. Grouping web search results into a hierarchy of topics provides an alternative to the flat ranked list and facilitates searching and browsing. In this paper, we present a brief survey of previous work on web search results clustering and existing commercial search engines using this technique, discuss two key issues of web search results clustering: cluster summarisation and evaluation and propose some directions for future research.

  18. Neurostimulation for chronic cluster headache

    PubMed Central

    Kaube, Holger

    2012-01-01

    Neurostimulation techniques for the treatment of primary headache syndromes, particularly of chronic cluster headache, have received much interest in recent years. Occipital nerve stimulation (ONS) has yielded favourable clinical results and, despite the limited numbers of published cases, is becoming a routine treatment for refractory chronic cluster headache in specialized centres. Meanwhile, other promising techniques such as spinal cord stimulation (SCS) or sphenopalate ganglion stimulation have emerged. In this article the current state of clinical research for neurostimulation techniques for chronic cluster headache is reviewed. PMID:22590481

  19. Cluster Model of the Nucleus

    NASA Astrophysics Data System (ADS)

    Horiuchi, Hisashi; Ikeda, Kiyomi

    The following sections are included: * INTRODUCTION * CLUSTER STRUCTURE OF NUCLEI * Typical Clustering States * Molecule-like Structure of Nuclei and the Threshold-energy Rule * Microscopic Cluster Model * Characteristic Points of the Structure Study by the Microscopic Cluster Model * Several Subjects Related to the Study of the Cluster Structure * Connection with the Neighbouring Fields in Nuclear Physics * MANY-CENTER MODEL AND ROTATIONAL STATES * Brink Model * Relation of the Brink Model Wave Function with the Shell Model Wave Function * Molecular Orbital Method * Projection of Parity and Angular Momentum * DESCRIPTION OF THE INTER-CLUSTER RELATIVE MOTION BY THE GENERATOR COORDINATE METHOD * Griffin-Hill-Wheeler Equation * GCM Kernel of Two-spinless-cluster System * DESCRIPTION OF THE INTER-CLUSTER RELATIVE MOTION BY THE RESONATING GROUP METHOD * Formulation * Equivalence of RGM and GCM * Calculation of RGM Kernels by using GCM Kernels * Calculation of Direct Potential * IMPOSITION OF THE SCATTERING BOUNDARY CONDITION * Brief Survey of the Calculational Methods of the Scattering Matrix in RGM and GCM * Wave Functions in the Outside Region and Matrix Elements in the Interaction Region * R-matrix Type Method * Variational Method * CLUSTER MODEL SPACE - RGM NORM KERNEL AND PAULI-FORBIDDEN STATES * Orthonormal Basis Wave Functions of the System and the Eigenvalue Problem of the Norm Kernel * Explicit Solution of the Eigenvalue Problem of the RGM Norm Kernel * Relation between Cluster Model States with Shell Model States * Almost Forbidden States * ORTHOGONALITY CONDITION MODEL * Inner Oscillation of the Inter-cluster Relative Wave Function * Formulation of the OCM * FEW EXAMPLES OF THE MICROSCOPIC CLUSTER MODEL STUDY * α+16O Model for 20Ne * α+12C Model for 16O * 3α Model for 12C * ACKNOWLEDGEMENTS * APPENDIX I SEPARATION OF THE CENTER-OF-MASS COORDINATE IN THE CASE OF THE HARMONIC OSCILLATOR SHELL MODEL * APPENDIX II ANTISYMMETRIZER, LAPLACE EXPANSION OF

  20. AMOEBA clustering revisited. [cluster analysis, classification, and image display program

    NASA Technical Reports Server (NTRS)

    Bryant, Jack

    1990-01-01

    A description of the clustering, classification, and image display program AMOEBA is presented. Using a difficult high resolution aircraft-acquired MSS image, the steps the program takes in forming clusters are traced. A number of new features are described here for the first time. Usage of the program is discussed. The theoretical foundation (the underlying mathematical model) is briefly presented. The program can handle images of any size and dimensionality.

  1. Brightest cluster galaxies in the extended GMRT radio halo cluster sample. Radio properties and cluster dynamics

    NASA Astrophysics Data System (ADS)

    Kale, R.; Venturi, T.; Cassano, R.; Giacintucci, S.; Bardelli, S.; Dallacasa, D.; Zucca, E.

    2015-09-01

    Aims: First-ranked galaxies in clusters, usually referred to as brightest cluster galaxies (BCGs), show exceptional properties over the whole electromagnetic spectrum. They are the most massive elliptical galaxies and show the highest probability to be radio loud. Moreover, their special location at the centres of galaxy clusters raises the question of the role of the environment in shaping their radio properties. In the attempt to separate the effect of the galaxy mass and of the environment on their statistical radio properties, we investigate the possible dependence of the occurrence of radio loudness and of the fractional radio luminosity function on the dynamical state of the hosting cluster. Methods: We studied the radio properties of the BCGs in the Extended GMRT Radio Halo Survey (EGRHS), which consists of 65 clusters in the redshift range 0.2-0.4, with X-ray luminosity LX ≥ 5 × 1044 erg s-1, and quantitative information on their dynamical state from high-quality Chandra imaging. We obtained a statistical sample of 59 BCGs, which we divided into two classes, depending on whether the dynamical state of the host cluster was merging (M) or relaxed (R). Results: Of the 59 BCGs, 28 are radio loud and 31 are radio quiet. The radio-loud sources are favourably located in relaxed clusters (71%), while the reverse is true for the radio-quiet BCGs, which are mostly located in merging systems (81%). The fractional radio luminosity function for the BCGs in merging and relaxed clusters is different, and it is considerably higher for BCGs in relaxed clusters, where the total fraction of radio loudness reaches almost 90%, to be compared to the ~30% in merging clusters. For relaxed clusters, we found a positive correlation between the radio power of the BCGs and the strength of the cool core, consistent with previous studies on local samples. Conclusions: Our study suggests that the radio loudness of the BCGs strongly depends on the cluster dynamics; their fraction is

  2. A Clustering Graph Generator

    SciTech Connect

    Winlaw, Manda; De Sterck, Hans; Sanders, Geoffrey

    2015-10-26

    In very simple terms a network can be de ned as a collection of points joined together by lines. Thus, networks can be used to represent connections between entities in a wide variety of elds including engi- neering, science, medicine, and sociology. Many large real-world networks share a surprising number of properties, leading to a strong interest in model development research and techniques for building synthetic networks have been developed, that capture these similarities and replicate real-world graphs. Modeling these real-world networks serves two purposes. First, building models that mimic the patterns and prop- erties of real networks helps to understand the implications of these patterns and helps determine which patterns are important. If we develop a generative process to synthesize real networks we can also examine which growth processes are plausible and which are not. Secondly, high-quality, large-scale network data is often not available, because of economic, legal, technological, or other obstacles [7]. Thus, there are many instances where the systems of interest cannot be represented by a single exemplar network. As one example, consider the eld of cybersecurity, where systems require testing across diverse threat scenarios and validation across diverse network structures. In these cases, where there is no single exemplar network, the systems must instead be modeled as a collection of networks in which the variation among them may be just as important as their common features. By developing processes to build synthetic models, so-called graph generators, we can build synthetic networks that capture both the essential features of a system and realistic variability. Then we can use such synthetic graphs to perform tasks such as simulations, analysis, and decision making. We can also use synthetic graphs to performance test graph analysis algorithms, including clustering algorithms and anomaly detection algorithms.

  3. Cluster Randomized Controlled Trial

    PubMed Central

    Young, John; Chapman, Katie; Nixon, Jane; Patel, Anita; Holloway, Ivana; Mellish, Kirste; Anwar, Shamaila; Breen, Rachel; Knapp, Martin; Murray, Jenni; Farrin, Amanda

    2015-01-01

    Background and Purpose— We developed a new postdischarge system of care comprising a structured assessment covering longer-term problems experienced by patients with stroke and their carers, linked to evidence-based treatment algorithms and reference guides (the longer-term stroke care system of care) to address the poor longer-term recovery experienced by many patients with stroke. Methods— A pragmatic, multicentre, cluster randomized controlled trial of this system of care. Eligible patients referred to community-based Stroke Care Coordinators were randomized to receive the new system of care or usual practice. The primary outcome was improved patient psychological well-being (General Health Questionnaire-12) at 6 months; secondary outcomes included functional outcomes for patients, carer outcomes, and cost-effectiveness. Follow-up was through self-completed postal questionnaires at 6 and 12 months. Results— Thirty-two stroke services were randomized (29 participated); 800 patients (399 control; 401 intervention) and 208 carers (100 control; 108 intervention) were recruited. In intention to treat analysis, the adjusted difference in patient General Health Questionnaire-12 mean scores at 6 months was −0.6 points (95% confidence interval, −1.8 to 0.7; P=0.394) indicating no evidence of statistically significant difference between the groups. Costs of Stroke Care Coordinator inputs, total health and social care costs, and quality-adjusted life year gains at 6 months, 12 months, and over the year were similar between the groups. Conclusions— This robust trial demonstrated no benefit in clinical or cost-effectiveness outcomes associated with the new system of care compared with usual Stroke Care Coordinator practice. Clinical Trial Registration— URL: http://www.controlled-trials.com. Unique identifier: ISRCTN 67932305. PMID:26152298

  4. Distant Massive Clusters and Cosmology

    NASA Technical Reports Server (NTRS)

    Donahue, Megan

    1999-01-01

    We present a status report of our X-ray study and analysis of a complete sample of distant (z=0.5-0.8), X-ray luminous clusters of galaxies. We have obtained ASCA and ROSAT observations of the five brightest Extended Medium Sensitivity (EMSS) clusters with z > 0.5. We have constructed an observed temperature function for these clusters, and measured iron abundances for all of these clusters. We have developed an analytic expression for the behavior of the mass-temperature relation in a low-density universe. We use this mass-temperature relation together with a Press-Schechter-based model to derive the expected temperature function for different values of Omega-M. We combine this analysis with the observed temperature functions at redshifts from 0 - 0.8 to derive maximum likelihood estimates for the value of Omega-M. We report preliminary results of this analysis.

  5. Architecture of Eph receptor clusters

    SciTech Connect

    Himanen, Juha P.; Yermekbayeva, Laila; Janes, Peter W.; Walker, John R.; Xu, Kai; Atapattu, Lakmali; Rajashankar, Kanagalaghatta R.; Mensinga, Anneloes; Lackmann, Martin; Nikolov, Dimitar B.; Dhe-Paganon, Sirano

    2010-10-04

    Eph receptor tyrosine kinases and their ephrin ligands regulate cell navigation during normal and oncogenic development. Signaling of Ephs is initiated in a multistep process leading to the assembly of higher-order signaling clusters that set off bidirectional signaling in interacting cells. However, the structural and mechanistic details of this assembly remained undefined. Here we present high-resolution structures of the complete EphA2 ectodomain and complexes with ephrin-A1 and A5 as the base unit of an Eph cluster. The structures reveal an elongated architecture with novel Eph/Eph interactions, both within and outside of the Eph ligand-binding domain, that suggest the molecular mechanism underlying Eph/ephrin clustering. Structure-function analysis, by using site-directed mutagenesis and cell-based signaling assays, confirms the importance of the identified oligomerization interfaces for Eph clustering.

  6. Clustering of financial time series

    NASA Astrophysics Data System (ADS)

    D'Urso, Pierpaolo; Cappelli, Carmela; Di Lallo, Dario; Massari, Riccardo

    2013-05-01

    This paper addresses the topic of classifying financial time series in a fuzzy framework proposing two fuzzy clustering models both based on GARCH models. In general clustering of financial time series, due to their peculiar features, needs the definition of suitable distance measures. At this aim, the first fuzzy clustering model exploits the autoregressive representation of GARCH models and employs, in the framework of a partitioning around medoids algorithm, the classical autoregressive metric. The second fuzzy clustering model, also based on partitioning around medoids algorithm, uses the Caiado distance, a Mahalanobis-like distance, based on estimated GARCH parameters and covariances that takes into account the information about the volatility structure of time series. In order to illustrate the merits of the proposed fuzzy approaches an application to the problem of classifying 29 time series of Euro exchange rates against international currencies is presented and discussed, also comparing the fuzzy models with their crisp version.

  7. Cluster randomization and political philosophy.

    PubMed

    Chwang, Eric

    2012-11-01

    In this paper, I will argue that, while the ethical issues raised by cluster randomization can be challenging, they are not new. My thesis divides neatly into two parts. In the first, easier part I argue that many of the ethical challenges posed by cluster randomized human subjects research are clearly present in other types of human subjects research, and so are not novel. In the second, more difficult part I discuss the thorniest ethical challenge for cluster randomized research--cases where consent is genuinely impractical to obtain. I argue that once again these cases require no new analytic insight; instead, we should look to political philosophy for guidance. In other words, the most serious ethical problem that arises in cluster randomized research also arises in political philosophy.

  8. Infrared spectroscopy of ionic clusters

    SciTech Connect

    Price, J.M. . Dept. of Chemistry Lawrence Berkeley Lab., CA )

    1990-11-01

    This thesis describes new experiments wherein the infrared vibrational predissociation spectra of a number of mass-selected ionic cluster systems have been obtained and analyzed in the 2600 to 4000 cm{sup {minus}1} region. The species studied include: the hydrated hydronium ions, H{sub 3}O{sup +} (H{sub 2}O){sub 3 {minus}10}, ammoniated ammonium ions, NH{sub 4}{sup +}(NH{sub 3}){sub 1 {minus}10} and cluster ions involving both water and ammonia around an ammonium ion core, (mixed clusters) NH{sub 4}{sup +}(NH{sub 3}){sub n}(H{sub 2}O){sub m} (n+m=4). In each case, the spectra reveal well resolved structures that can be assigned to transitions arising from the vibrational motions of both the ion core of the clusters and the surrounding neutral solvent molecules. 154 refs., 19 figs., 8 tabs.

  9. Re-shaping colloidal clusters

    NASA Astrophysics Data System (ADS)

    Kraft, Daniela

    2015-03-01

    Controlling the geometry and yield of anisotropic colloidal particles remains a challenge for hierarchical self-assembly. I will discuss a synthetic strategy for fabricating colloidal clusters by creating order in randomly aggregated polymer spheres using surface tension and geometrical constraints. The technique can be extended to a variety of charge-stabilized polymer spheres and offers control over the cluster size distribution. VENI grant from The Netherlands Organization for Scientific Research (NWO).

  10. Binary Stars in Globular Clusters

    NASA Astrophysics Data System (ADS)

    Mateo, M.; Murdin, P.

    2000-11-01

    Globular clusters have long been known to be among the richest stellar groupings within our Galaxy, but for many years they were believed to be largely devoid of the most minimal stellar group: binary stars (see BINARY STARS: OVERVIEW). For many years, the only evidence that any binaries existed in these clusters came from the presence of BLUE STRAGGLERS—stars that appear to be significantly you...

  11. Collective thermoregulation in bee clusters.

    PubMed

    Ocko, Samuel A; Mahadevan, L

    2014-02-01

    Swarming is an essential part of honeybee behaviour, wherein thousands of bees cling onto each other to form a dense cluster that may be exposed to the environment for several days. This cluster has the ability to maintain its core temperature actively without a central controller. We suggest that the swarm cluster is akin to an active porous structure whose functional requirement is to adjust to outside conditions by varying its porosity to control its core temperature. Using a continuum model that takes the form of a set of advection-diffusion equations for heat transfer in a mobile porous medium, we show that the equalization of an effective 'behavioural pressure', which propagates information about the ambient temperature through variations in density, leads to effective thermoregulation. Our model extends and generalizes previous models by focusing the question of mechanism on the form and role of the behavioural pressure, and allows us to explain the vertical asymmetry of the cluster (as a consequence of buoyancy-driven flows), the ability of the cluster to overpack at low ambient temperatures without breaking up at high ambient temperatures, and the relative insensitivity to large variations in the ambient temperature. Our theory also makes testable hypotheses for the response of the cluster to external temperature inhomogeneities and suggests strategies for biomimetic thermoregulation. PMID:24335563

  12. Understanding Galaxy Cluster MKW10

    NASA Astrophysics Data System (ADS)

    Sanders, Tim; Henry, Swain; Coble, Kimberly A.; Rosenberg, Jessica L.; Koopmann, Rebecca A.

    2015-01-01

    As part of the Undergraduate ALFALFA Team (UAT), we are studying the galaxy cluster MKW 10 (RA = 175.454, Dec = 10.306, z ~ 0.02), a poor cluster with a compact core in which tidal interactions have occurred. This cluster has been observed in HI and Hα. We used SDSS and NED to search for optical counterparts. By comparing data at multiple wavelengths, we hope to understand the structure, environment, and star formation history of this cluster. Following the techniques of others involved in the groups project and using the program TOPCAT to manipulate the data, we explored both the spatial and velocity distributions to determine cluster membership. We have determined that this cluster consists of 11 galaxies, mostly spiral in shape. Chicago State University is new the UAT and we began our work after taking part in the winter workshop at Arecibo.This work was supported by: Undergraduate ALFALFA Team NSF Grant AST-1211005 and the Illinois Space Grant Consortium.

  13. Multi-focus cluster labeling.

    PubMed

    Eikvil, Line; Jenssen, Tor-Kristian; Holden, Marit

    2015-06-01

    Document collections resulting from searches in the biomedical literature, for instance, in PubMed, are often so large that some organization of the returned information is necessary. Clustering is an efficient tool for organizing search results. To help the user to decide how to continue the search for relevant documents, the content of each cluster can be characterized by a set of representative keywords or cluster labels. As different users may have different interests, it can be desirable with solutions that make it possible to produce labels from a selection of different topical categories. We therefore introduce the concept of multi-focus cluster labeling to give users the possibility to get an overview of the contents through labels from multiple viewpoints. The concept for multi-focus cluster labeling has been established and has been demonstrated on three different document collections. We illustrate that multi-focus visualizations can give an overview of clusters along axes that general labels are not able to convey. The approach is generic and should be applicable to any biomedical (or other) domain with any selection of foci where appropriate focus vocabularies can be established. A user evaluation also indicates that such a multi-focus concept is useful.

  14. The formation of star clusters

    NASA Astrophysics Data System (ADS)

    Whitmore, Bradley C.

    The ability of HST to resolve objects ten times smaller than possible from the ground has re-juvenated the study of young star clusters. A recurrent morphological theme found in nearby resolved systems is the observation of young (typically 1-10 Myr), massive (103 - 104 Msolar), compact (ρ≍105 Msolar pc-3) clusters which have evacuated the gas and dust from a spherical region around themselves. New stars are being triggered into formation along the edges of the envelopes, with pillars (similar to the Eagle Nebula) of molecular gas streaming away from the regions of star formation. The prototype for these objects is 30 Doradus. Another major theme has been the discovery of large numbers of young (typically 1-500 Myr), massive (103 - 108 Msolar), compact star clusters in merging, starbursting, and even some barred and spiral galaxies. The brightest of these clusters have all the attributes expected of protoglobular clusters, hence allowing us to study the formation of globular clusters in the local universe rather than trying to ascertain how they formed ≍14 Gyr ago. The prototype is the Antennae Galaxy.

  15. AMIC@: All MIcroarray Clusterings @ once.

    PubMed

    Geraci, Filippo; Pellegrini, Marco; Renda, M Elena

    2008-07-01

    The AMIC@ Web Server offers a light-weight multi-method clustering engine for microarray gene-expression data. AMIC@ is a highly interactive tool that stresses user-friendliness and robustness by adopting AJAX technology, thus allowing an effective interleaved execution of different clustering algorithms and inspection of results. Among the salient features AMIC@ offers, there are: (i) automatic file format detection, (ii) suggestions on the number of clusters using a variant of the stability-based method of Tibshirani et al. (iii) intuitive visual inspection of the data via heatmaps and (iv) measurements of the clustering quality using cluster homogeneity. Large data sets can be processed efficiently by selecting algorithms (such as FPF-SB and k-Boost), specifically designed for this purpose. In case of very large data sets, the user can opt for a batch-mode use of the system by means of the Clustering wizard that runs all algorithms at once and delivers the results via email. AMIC@ is freely available and open to all users with no login requirement at the following URL http://bioalgo.iit.cnr.it/amica.

  16. Collective thermoregulation in bee clusters.

    PubMed

    Ocko, Samuel A; Mahadevan, L

    2014-02-01

    Swarming is an essential part of honeybee behaviour, wherein thousands of bees cling onto each other to form a dense cluster that may be exposed to the environment for several days. This cluster has the ability to maintain its core temperature actively without a central controller. We suggest that the swarm cluster is akin to an active porous structure whose functional requirement is to adjust to outside conditions by varying its porosity to control its core temperature. Using a continuum model that takes the form of a set of advection-diffusion equations for heat transfer in a mobile porous medium, we show that the equalization of an effective 'behavioural pressure', which propagates information about the ambient temperature through variations in density, leads to effective thermoregulation. Our model extends and generalizes previous models by focusing the question of mechanism on the form and role of the behavioural pressure, and allows us to explain the vertical asymmetry of the cluster (as a consequence of buoyancy-driven flows), the ability of the cluster to overpack at low ambient temperatures without breaking up at high ambient temperatures, and the relative insensitivity to large variations in the ambient temperature. Our theory also makes testable hypotheses for the response of the cluster to external temperature inhomogeneities and suggests strategies for biomimetic thermoregulation.

  17. Electrodynamic properties of fractal clusters

    NASA Astrophysics Data System (ADS)

    Maksimenko, V. V.; Zagaynov, V. A.; Agranovski, I. E.

    2014-07-01

    An influence of interference on a character of light interaction both with individual fractal cluster (FC) consisting of nanoparticles and with agglomerates of such clusters is investigated. Using methods of the multiple scattering theory, effective dielectric permeability of a micron-size FC composed of non-absorbing nanoparticles is calculated. The cluster could be characterized by a set of effective dielectric permeabilities. Their number coincides with the number of particles, where space arrangement in the cluster is correlated. If the fractal dimension is less than some critical value and frequency corresponds to the frequency of the visible spectrum, then the absolute value of effective dielectric permeability becomes very large. This results in strong renormalization (decrease) of the incident radiation wavelength inside the cluster. The renormalized photons are cycled or trapped inside the system of multi-scaled cavities inside the cluster. A lifetime of a photon localized inside an agglomerate of FCs is a macroscopic value allowing to observe the stimulated emission of the localized light. The latter opens up a possibility for creation of lasers without inverse population of energy levels. Moreover, this allows to reconsider problems of optical cloaking of macroscopic objects. One more feature of fractal structures is a possibility of unimpeded propagation of light when any resistance associated with scattering disappears.

  18. Cancer clusters: findings vs feelings.

    PubMed

    Robinson, David

    2002-11-01

    The issue of cancer clusters, which has been in the spotlight recently, is plagued by a wide disparity between public perceptions and scientific findings. Movies like Erin Brockovich have led the public to think that industrial pollution in the environment is causing local "cancer clusters" where cancer cases are more prevalent due to cancer-causing chemicals. There are many scientifically documented instances in which chemical exposure has caused cancer in humans, but the evidence for purely environmental exposures causing cancer is sparse. The clusters that scientists have been able to attribute successfully to a particular cause have been occupational (such as workers in a factory developing a particular type of cancer from daily exposure to a specific chemical), linked to a particular medicine, or linked to behaviors such as smoking or sunbathing. There is some indication that chemicals dissolved in drinking water may elevate the risk of gastrointestinal and bladder/urinary tract cancers and that living next to a smelter or other "point source" of air pollution may elevate risk of lung cancer. The many efforts that have been made to demonstrate links between other types of cancer and environmental contamination have not conclusively identified such links. Several challenges bedevil any cancer cluster investigation and can result in ambiguous or misleading conclusions. This report discusses the potential cancer clusters in Toms River, New Jersey and Long Island, New York, because they contain many elements typical of cancer cluster investigations and have received considerable media attention. PMID:12817212

  19. Collective thermoregulation in bee clusters

    PubMed Central

    Ocko, Samuel A.; Mahadevan, L.

    2014-01-01

    Swarming is an essential part of honeybee behaviour, wherein thousands of bees cling onto each other to form a dense cluster that may be exposed to the environment for several days. This cluster has the ability to maintain its core temperature actively without a central controller. We suggest that the swarm cluster is akin to an active porous structure whose functional requirement is to adjust to outside conditions by varying its porosity to control its core temperature. Using a continuum model that takes the form of a set of advection–diffusion equations for heat transfer in a mobile porous medium, we show that the equalization of an effective ‘behavioural pressure’, which propagates information about the ambient temperature through variations in density, leads to effective thermoregulation. Our model extends and generalizes previous models by focusing the question of mechanism on the form and role of the behavioural pressure, and allows us to explain the vertical asymmetry of the cluster (as a consequence of buoyancy-driven flows), the ability of the cluster to overpack at low ambient temperatures without breaking up at high ambient temperatures, and the relative insensitivity to large variations in the ambient temperature. Our theory also makes testable hypotheses for the response of the cluster to external temperature inhomogeneities and suggests strategies for biomimetic thermoregulation. PMID:24335563

  20. Autophagy selectivity through receptor clustering

    NASA Astrophysics Data System (ADS)

    Rutenberg, Andrew; Brown, Aidan

    Substrate selectivity in autophagy requires an all-or-none cellular response. We focus on peroxisomes, for which autophagy receptor proteins NBR1 and p62 are well characterized. Using computational models, we explore the hypothesis that physical clustering of autophagy receptor proteins on the peroxisome surface provides an appropriate all-or-none response. We find that larger peroxisomes nucleate NBR1 clusters first, and lose them due to competitive coarsening last, resulting in significant size-selectivity. We then consider a secondary hypothesis that p62 inhibits NBR1 cluster formation. We find that p62 inhibition enhances size-selectivity enough that, even if there is no change of the pexophagy rate, the volume of remaining peroxisomes can significantly decrease. We find that enhanced ubiquitin levels suppress size-selectivity, and that this effect is more pronounced for individual peroxisomes. Sufficient ubiquitin allows receptor clusters to form on even the smallest peroxisomes. We conclude that NBR1 cluster formation provides a viable physical mechanism for all-or-none substrate selectivity in pexophagy. We predict that cluster formation is associated with significant size-selectivity. Now at Simon Fraser University.

  1. Identification of Urban Leprosy Clusters

    PubMed Central

    Paschoal, José Antonio Armani; Paschoal, Vania Del'Arco; Nardi, Susilene Maria Tonelli; Rosa, Patrícia Sammarco; Ismael, Manuela Gallo y Sanches; Sichieri, Eduvaldo Paulo

    2013-01-01

    Overpopulation of urban areas results from constant migrations that cause disordered urban growth, constituting clusters defined as sets of people or activities concentrated in relatively small physical spaces that often involve precarious conditions. Aim. Using residential grouping, the aim was to identify possible clusters of individuals in São José do Rio Preto, Sao Paulo, Brazil, who have or have had leprosy. Methods. A population-based, descriptive, ecological study using the MapInfo and CrimeStat techniques, geoprocessing, and space-time analysis evaluated the location of 425 people treated for leprosy between 1998 and 2010. Clusters were defined as concentrations of at least 8 people with leprosy; a distance of up to 300 meters between residences was adopted. Additionally, the year of starting treatment and the clinical forms of the disease were analyzed. Results. Ninety-eight (23.1%) of 425 geocoded cases were located within one of ten clusters identified in this study, and 129 cases (30.3%) were in the region of a second-order cluster, an area considered of high risk for the disease. Conclusion. This study identified ten clusters of leprosy cases in the city and identified an area of high risk for the appearance of new cases of the disease. PMID:24288467

  2. Identification of urban leprosy clusters.

    PubMed

    Paschoal, José Antonio Armani; Paschoal, Vania Del'Arco; Nardi, Susilene Maria Tonelli; Rosa, Patrícia Sammarco; Ismael, Manuela Gallo y Sanches; Sichieri, Eduvaldo Paulo

    2013-01-01

    Overpopulation of urban areas results from constant migrations that cause disordered urban growth, constituting clusters defined as sets of people or activities concentrated in relatively small physical spaces that often involve precarious conditions. Aim. Using residential grouping, the aim was to identify possible clusters of individuals in São José do Rio Preto, Sao Paulo, Brazil, who have or have had leprosy. Methods. A population-based, descriptive, ecological study using the MapInfo and CrimeStat techniques, geoprocessing, and space-time analysis evaluated the location of 425 people treated for leprosy between 1998 and 2010. Clusters were defined as concentrations of at least 8 people with leprosy; a distance of up to 300 meters between residences was adopted. Additionally, the year of starting treatment and the clinical forms of the disease were analyzed. Results. Ninety-eight (23.1%) of 425 geocoded cases were located within one of ten clusters identified in this study, and 129 cases (30.3%) were in the region of a second-order cluster, an area considered of high risk for the disease. Conclusion. This study identified ten clusters of leprosy cases in the city and identified an area of high risk for the appearance of new cases of the disease.

  3. Spectroscopy of the Perseus Cluster

    NASA Technical Reports Server (NTRS)

    Jones, Christine; Mushotzky, Richard F. (Technical Monitor)

    2004-01-01

    We present preliminary results of a XMM-Newton 50 ks observation of the Perseus Cluster that provides an unprecedented view of the central 0.5 Mpc region. The projected gas temperature declines smoothly by a factor of 2 from a maximum value of approx. 7 keV in the outer regions to just above 3 keV at the cluster center. Over this same range, the heavy-element abundance rises slowly from 0.4 to 0.5 solar as the radius decreases from 14 ft. to 5 ft., and then it rises to a peak of almost 0.7 solar at 1&farcm;25 before declining to 0.4 at the center. Th global east-west asymmetry of the gas temperature and surface brightness distributions, approximately aligned with the chain of bright galaxies, suggests an ongoing merger, although the modest degree of the observed asymmetry certainly excludes a major merger interpretation. The chain of galaxies probably traces the filament along which accretion started some time ago and is continuing at the present time. A cold and dense (low-entropy) cluster core like Perseus is probably well "protected" against the penetration of the gas of infalling groups and poor clusters, whereas in non-cooling core clusters such as Coma and A1367, infalling subclusters can penetrate deeply into the core region. In Perseus, gas associated with infalling groups may be stripped completely at the outskirts of the main cluster and only compression waves (shocks) may reach the central regions. We argue, and show supporting simulations, that the passage of such a wave(s) can qualitatively explain the overall horseshoe shaped appearance of the gas temperature map (the hot horseshoe surrounds the colder, low-entropy core) as well as other features of the Perseus Cluster core. These simulations also show that as compression waves traverse the cluster core, they can induce oscillatory motion of the cluster gas that can generate multiple sharp "edges" on opposite sides of the central galaxy. Gas motions induced by mergers may be a natural way to explain

  4. Nonlocalized clustering: a new concept in nuclear cluster structure physics.

    PubMed

    Zhou, Bo; Funaki, Y; Horiuchi, H; Ren, Zhongzhou; Röpke, G; Schuck, P; Tohsaki, A; Xu, Chang; Yamada, T

    2013-06-28

    We investigate the α+^{16}O cluster structure in the inversion-doublet band (Kπ=0(1)±}) states of 20Ne with an angular-momentum-projected version of the Tohsaki-Horiuchi-Schuck-Röpke (THSR) wave function, which was successful "in its original form" for the description of, e.g., the famous Hoyle state. In contrast with the traditional view on clusters as localized objects, especially in inversion doublets, we find that these single THSR wave functions, which are based on the concept of nonlocalized clustering, can well describe the Kπ=0(1)- band and the Kπ=0(1)+ band. For instance, they have 99.98% and 99.87% squared overlaps for 1- and 3- states (99.29%, 98.79%, and 97.75% for 0+, 2+, and 4+ states), respectively, with the corresponding exact solution of the α+16O resonating group method. These astounding results shed a completely new light on the physics of low energy nuclear cluster states in nuclei: The clusters are nonlocalized and move around in the whole nuclear volume, only avoiding mutual overlap due to the Pauli blocking effect.

  5. Cluster Wideband Data Products in the Cluster Active Archive

    NASA Astrophysics Data System (ADS)

    Pickett, J. S.; Seeberger, J. M.; Christopher, I. W.; Santolík, O.; Sigsbee, K. M.

    Cluster Wideband Data (WBD) plasma wave receivers are mounted on all four of the Cluster spacecraft providing approximately 4-7% orbit coverage since mission operations began in February 2001. Data obtained by the WBD instruments are downlinked in real time to various Deep Space Network (DSN) and Panska Ves (PV) ground stations. The strengths of the WBD instruments lie in their high time and frequency resolution data, which allow analysis of the wave fine structure in order to more accurately investigate the linear and nonlinear nature of the waves, and in their use in carrying out Very Long Baseline Interferometry (VLBI) investigations to locate and characterize remote wave sources and their characteristics. The WBD team has already archived at the Cluster Active Archive (CAA) the documentation, software and data plots required for carrying on an independent scientific investigation. A document on interpretation issues has also been archived to help ensure that signals which are not naturally in the plasma are not misinterpreted. The WBD team also plans to archive digital, calibrated data files for the entire mission in cdf format at NASA's CDAWeb and submit these files for conversion to the Cluster standard cef format and archiving at the CAA. In order to ensure that the calibration of the WBD data has been done properly, WBD has taken part in Cluster cross calibration activities with the other wave instruments with regard to wave amplitudes in the time and frequency domains and with the PEACE instruments with regard to low density measurements.

  6. Growth of atmospheric clusters involving cluster-cluster collisions: comparison of different growth rate methods

    NASA Astrophysics Data System (ADS)

    Kontkanen, Jenni; Olenius, Tinja; Lehtipalo, Katrianne; Vehkamäki, Hanna; Kulmala, Markku; Lehtinen, Kari E. J.

    2016-05-01

    We simulated the time evolution of atmospheric cluster concentrations in a one-component system where not only do clusters grow by condensation of monomers, but cluster-cluster collisions also significantly contribute to the growth of the clusters. Our aim was to investigate the consistency of the growth rates of sub-3 nm clusters determined with different methods and the validity of the common approach to use them to estimate particle formation rates. We compared the growth rate corresponding to particle fluxes (FGR), the growth rate derived from the appearance times of clusters (AGR), and the growth rate calculated based on irreversible vapor condensation (CGR). We found that the relation between the different growth rates depends strongly on the external conditions and the properties of the model substance. The difference between the different growth rates was typically highest at the smallest, sub-2 nm sizes. FGR was generally lower than AGR and CGR; at the smallest sizes the difference was often very large, while at sizes larger than 2 nm the growth rates were closer to each other. AGR and CGR were in most cases close to each other at all sizes. The difference between the growth rates was generally lower in conditions where cluster concentrations were high, and evaporation and other losses were thus less significant. Furthermore, our results show that the conventional method used to determine particle formation rates from growth rates may give estimates far from the true values. Thus, care must be taken not only in how the growth rate is determined but also in how it is applied.

  7. Career Clusters. Trends and Issues Alert.

    ERIC Educational Resources Information Center

    Wonacott, Michael E.

    Many states and local districts use career clusters as a means of broadening the focus of secondary education, particularly career and technical education, as preparation for both further education and work. One continuing trend in career clusters is sheer variety. Cluster frameworks vary in the number, nomenclature, and organization of clusters.…

  8. Bayesian Decision Theoretical Framework for Clustering

    ERIC Educational Resources Information Center

    Chen, Mo

    2011-01-01

    In this thesis, we establish a novel probabilistic framework for the data clustering problem from the perspective of Bayesian decision theory. The Bayesian decision theory view justifies the important questions: what is a cluster and what a clustering algorithm should optimize. We prove that the spectral clustering (to be specific, the…

  9. Cluster galaxy evolution with the Las Campanas Distant Cluster Survey

    NASA Astrophysics Data System (ADS)

    Nelson, Amy Elizabeth

    Understanding the formation and evolution of galaxies is a principal goal of modern cosmology. In this thesis, we place constraints on galaxy evolution models using the largest sample of high redshift clusters to date. Our sample consists of 63 clusters at 0.3 ≲ z ≲ 0.9 drawn from the Las Campanas Distant Cluster Survey (LCDCS). This survey differs from traditional optical surveys in that we detect clusters as regions of excess surface brightness relative to the background sky rather than selecting overdensities of resolved galaxies. Therefore, not only does this sample result in a significant increase in the number of known clusters at these redshifts, but because our cluster identification criteria is independent of those utilized in previous surveys, this catalog provides an independent, well-defined sample with which to compare the results of more traditional surveys. In this work, we take a two-pronged approach to studying galaxy evolution. First, we examine the luminosity and color evolution of the bright cluster galaxies as a class. Specifically, we measure the evolution of: (1) M*I , the characteristic luminosity of cluster galaxies, (2) the location of the red envelope in V--I and I--K', and (3) the fraction of blue galaxies (i.e. the Butcher-Oemler effect; Butcher & Oemler 1984). Our data suggest that luminous early type galaxies (or the progenitors of current day early type galaxies) form the bulk of their stellar populations at high redshifts ( ≲ 5) and that many of these galaxies, if not all, experience a short term episode of star formation at lower redshifts (1.5 < z < 2). Second, we narrow the focus and study a single type of cluster galaxy, the brightest cluster galaxy (BCG). We constrain the amount of luminosity and color evolution of BCGs, particularly in the context of recent claims in the literature of significant mass accretion since z ˜ 1 (Aragon-Salamanca 1998; Burke, Collins, & Mann 2000). Consistent with previous results (Burke

  10. A Nonparametric Bayesian Model for Nested Clustering.

    PubMed

    Lee, Juhee; Müller, Peter; Zhu, Yitan; Ji, Yuan

    2016-01-01

    We propose a nonparametric Bayesian model for clustering where clusters of experimental units are determined by a shared pattern of clustering another set of experimental units. The proposed model is motivated by the analysis of protein activation data, where we cluster proteins such that all proteins in one cluster give rise to the same clustering of patients. That is, we define clusters of proteins by the way that patients group with respect to the corresponding protein activations. This is in contrast to (almost) all currently available models that use shared parameters in the sampling model to define clusters. This includes in particular model based clustering, Dirichlet process mixtures, product partition models, and more. We show results for two typical biostatistical inference problems that give rise to clustering. PMID:26519174

  11. Quantum Monte Carlo methods and lithium cluster properties. [Atomic clusters

    SciTech Connect

    Owen, R.K.

    1990-12-01

    Properties of small lithium clusters with sizes ranging from n = 1 to 5 atoms were investigated using quantum Monte Carlo (QMC) methods. Cluster geometries were found from complete active space self consistent field (CASSCF) calculations. A detailed development of the QMC method leading to the variational QMC (V-QMC) and diffusion QMC (D-QMC) methods is shown. The many-body aspect of electron correlation is introduced into the QMC importance sampling electron-electron correlation functions by using density dependent parameters, and are shown to increase the amount of correlation energy obtained in V-QMC calculations. A detailed analysis of D-QMC time-step bias is made and is found to be at least linear with respect to the time-step. The D-QMC calculations determined the lithium cluster ionization potentials to be 0.1982(14) (0.1981), 0.1895(9) (0.1874(4)), 0.1530(34) (0.1599(73)), 0.1664(37) (0.1724(110)), 0.1613(43) (0.1675(110)) Hartrees for lithium clusters n = 1 through 5, respectively; in good agreement with experimental results shown in the brackets. Also, the binding energies per atom was computed to be 0.0177(8) (0.0203(12)), 0.0188(10) (0.0220(21)), 0.0247(8) (0.0310(12)), 0.0253(8) (0.0351(8)) Hartrees for lithium clusters n = 2 through 5, respectively. The lithium cluster one-electron density is shown to have charge concentrations corresponding to nonnuclear attractors. The overall shape of the electronic charge density also bears a remarkable similarity with the anisotropic harmonic oscillator model shape for the given number of valence electrons.

  12. 3D simulation of the Cluster-Cluster Aggregation model

    NASA Astrophysics Data System (ADS)

    Li, Chao; Xiong, Hailing

    2014-12-01

    We write a program to implement the Cluster-Cluster Aggregation (CCA) model with java programming language. By using the simulation program, the fractal aggregation growth process can be displayed dynamically in the form of a three-dimensional (3D) figure. Meanwhile, the related kinetics data of aggregation simulation can be also recorded dynamically. Compared to the traditional programs, the program has better real-time performance and is more helpful to observe the fractal growth process, which contributes to the scientific study in fractal aggregation. Besides, because of adopting java programming language, the program has very good cross-platform performance.

  13. Large scale cluster computing workshop

    SciTech Connect

    Dane Skow; Alan Silverman

    2002-12-23

    Recent revolutions in computer hardware and software technologies have paved the way for the large-scale deployment of clusters of commodity computers to address problems heretofore the domain of tightly coupled SMP processors. Near term projects within High Energy Physics and other computing communities will deploy clusters of scale 1000s of processors and be used by 100s to 1000s of independent users. This will expand the reach in both dimensions by an order of magnitude from the current successful production facilities. The goals of this workshop were: (1) to determine what tools exist which can scale up to the cluster sizes foreseen for the next generation of HENP experiments (several thousand nodes) and by implication to identify areas where some investment of money or effort is likely to be needed. (2) To compare and record experimences gained with such tools. (3) To produce a practical guide to all stages of planning, installing, building and operating a large computing cluster in HENP. (4) To identify and connect groups with similar interest within HENP and the larger clustering community.

  14. IRAC imaging of GOGREEN clusters

    NASA Astrophysics Data System (ADS)

    McGee, Sean; Balogh, Michael; Cooper, Michael; Gilbank, David; Lidman, Chris; Muzzin, Adam; Old, Lyndsay; Rudnick, Greg; Wilson, Gillian; Yee, Howard

    2016-08-01

    We propose deep IRAC imaging of three galaxy clusters drawn from the GOGREEN survey of 21 galaxy clusters in the redshift range 1 < z < 1.5. This imaging will enable the accurate measurement of unprecedentedly low stellar masses at this redshift, leveraging our deep spectroscopy. This will give a first look at environmental effects on galaxy evolution at a time when galaxies are growing in a fundamentally different way from today. With this data, we will perform accurate SED modeling in order to classify galaxies as passive or star-forming and measure stellar masses, as well as compute cluster membership using accurate photometric redshifts. These data will be augmented by approved VLT, Subaru, Magellan and CFHT imaging and by an ongoing Gemini Large Programme, with which we are obtaining deep spectroscopy of > 1000 member and > 600 field galaxies. With these data and our own lower-redshift descendant data, we will measure 1) the evolution of the quenched fraction and its dependence on distance from the cluster center and 2) the relation between stellar and halo mass and its evolution. This will provide unique constraints to our in-house theoretical models at an epoch where there are currently almost none available. The imaging that we propose will ensure all 21 GOGREEN clusters have deep IRAC data, ensuring the lasting legacy of this benchmark sample.

  15. Dynamic of Faceted Colloidal Clusters

    NASA Astrophysics Data System (ADS)

    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.

  16. Learning regularized LDA by clustering.

    PubMed

    Pang, Yanwei; Wang, Shuang; Yuan, Yuan

    2014-12-01

    As a supervised dimensionality reduction technique, linear discriminant analysis has a serious overfitting problem when the number of training samples per class is small. The main reason is that the between- and within-class scatter matrices computed from the limited number of training samples deviate greatly from the underlying ones. To overcome the problem without increasing the number of training samples, we propose making use of the structure of the given training data to regularize the between- and within-class scatter matrices by between- and within-cluster scatter matrices, respectively, and simultaneously. The within- and between-cluster matrices are computed from unsupervised clustered data. The within-cluster scatter matrix contributes to encoding the possible variations in intraclasses and the between-cluster scatter matrix is useful for separating extra classes. The contributions are inversely proportional to the number of training samples per class. The advantages of the proposed method become more remarkable as the number of training samples per class decreases. Experimental results on the AR and Feret face databases demonstrate the effectiveness of the proposed method.

  17. Seven poor clusters of galaxies

    NASA Astrophysics Data System (ADS)

    Beers, T. C.; Geller, M. J.; Huchra, J. P.; Latham, D. W.; Davis, R. J.

    1984-08-01

    The authors have measured 83 new redshifts for galaxies in the region of seven of the poor clusters of galaxies identified by Morgan, Kayser, and White and Albert, White, and Morgan. For three systems (MKW 1s, AWM 1, and AWM 7) complete redshift samples were obtained for galaxies brighter than mB(0) = 15.7 within 1° of the D or cD galaxy. The authors estimate masses for the clusters by applying both the virial theorem and the projected mass method. For the two clusters with the highest X-ray luminosities, the line-of-sight velocity dispersions are ≡700 km s-1, and mass-to-light ratios M/LB(0) ⪆ 400 M_sun;/L_sun;. For the five other clusters the velocity dispersions are ⪉370 km s-1, and four of the five have mass-to-light ratios ⪉250 M_sun;/L_sun;. The D or cD galaxy in each poor cluster is at the kinematic center of the system.

  18. Amphoteric Aqueous Hafnium Cluster Chemistry.

    PubMed

    Goberna-Ferrón, Sara; Park, Deok-Hie; Amador, Jenn M; Keszler, Douglas A; Nyman, May

    2016-05-17

    Selective dissolution of hafnium-peroxo-sulfate films in aqueous tetramethylammonium hydroxide enables extreme UV lithographic patterning of sub-10 nm HfO2 structures. Hafnium speciation under these basic conditions (pH>10), however, is unknown, as studies of hafnium aqueous chemistry have been limited to acid. Here, we report synthesis, crystal growth, and structural characterization of the first polynuclear hydroxo hafnium cluster isolated from base, [TMA]6 [Hf6 (μ-O2 )6 (μ-OH)6 (OH)12 ]⋅38 H2 O. The solution behavior of the cluster, including supramolecular assembly via hydrogen bonding is detailed via small-angle X-ray scattering (SAXS) and electrospray ionization mass spectrometry (ESI-MS). The study opens a new chapter in the aqueous chemistry of hafnium, exemplifying the concept of amphoteric clusters and informing a critical process in single-digit-nm lithography.

  19. Featured Image: A Double Cluster

    NASA Astrophysics Data System (ADS)

    Kohler, Susanna

    2015-11-01

    This is a color composite image from Hubble of the very young star cluster Westerlund 2, seen near the center of the image (click for the full view!). The image was produced using visible-light data from the Advanced Camera for Surveys and near-infrared data from the Wide Field Camera 3. A recently-published study, led by Peter Zeidler (Center for Astronomy at Heidelberg University), reports the results of a high-resolution multi-band survey of the Westerlund 2 region with Hubble. In their detailed analysis of the cluster, the authors cataloged over 17,000 objects in six different filters! They find that the cluster actually consists of two separate clumps that were born at the same time but have different stellar densities. For more information and the original image, see the paper here:CitationPeter Zeidler et al 2015 AJ 150 78. doi:10.1088/0004-6256/150/3/78

  20. Cluster assembly of hierarchical nanostructures

    SciTech Connect

    Siegel, R.W.

    1992-02-01

    In the past few years, atom clusters with diameters in the range of 2--20 nm of a variety of materials, including both metals and ceramics, have been synthesized by evaporation and condensation in high-purity gases and subsequently consolidated in situ under ultrahigh vacuum conditions to create nanophase materials. These new utlrafine-grained materials have properties that are often significantly different and considerably improved relative to those of their coarser-grained counterparts owing to both their small grain-size scale and the large percentage of their atoms in grain boundary environments. Since their properties can be engineered during the synthesis and processing steps, cluster-assembled materials appear to have significant potential for the introduction of a hierarchy of both structure and properties. Some of the recent research on nanophase materials related to properties and scale are reviewed and some of the possibilities for synthesizing hierarchical nanostructures via cluster assembly are considered.

  1. Fine structure of cluster decays

    SciTech Connect

    Dumitrescu, O.

    1994-03-01

    Within the one level {ital R}-matrix approach, expressions are derived for the hindrance factors of cluster radioactive decays in which {ital y} {ital the} {ital shell} {ital model} {ital with} {ital effective} {ital residual} {ital interactions} [{ital e}.{ital g}.,{ital thelar} in the Michigan State University version for nearly spherical nuclei, or the enlarged superfluid model (ESM) recently proposed for deformed nuclei]. The exterior wave functions are calculated from a cluster-nucleus double-folding model potential obtained with the M3Y interaction. As examples of the cluster decay fine structure we analyzed the particular cases of {alpha} decay of {sup 241}Am and {sup 243}Cm, {sup 14}C decay of {sup 223}Ra, and {sup 34}Si decay of {sup 243}Cm. Good agreement with the experimental data is obtained.

  2. Au20: A Tetrahedral Cluster

    SciTech Connect

    Li, Jun; Li, Xi; Zhai, Hua Jin; Wang, Lai S.

    2003-02-07

    Photoelectron spectroscopy revealed that a 20 atom gold cluster has an extremely large energy gap, which is even greater than that of C60, and an electron affinity comparable with that of C60. This observation suggests that the Au20 cluster must be extremely stable and chemically inert. Using relativistic density functional calculations, we found that Au20 possesses a remarkable tetrahedral structure, which is a fragment of the bulk face-centered cubic lattice of gold with a small structural relaxation. Au20 is thus a true cluster molecule, while at the same time it is exactly part of the bulk, but with very different properties. The tetrahedral Au20 may possess interesting catalytic properties and may be synthesized in bulk quantity or assembled on non-interacting surfaces.

  3. Percolation technique for galaxy clustering

    NASA Technical Reports Server (NTRS)

    Klypin, Anatoly; Shandarin, Sergei F.

    1993-01-01

    We study percolation in mass and galaxy distributions obtained in 3D simulations of the CDM, C + HDM, and the power law (n = -1) models in the Omega = 1 universe. Percolation statistics is used here as a quantitative measure of the degree to which a mass or galaxy distribution is of a filamentary or cellular type. The very fast code used calculates the statistics of clusters along with the direct detection of percolation. We found that the two parameters mu(infinity), characterizing the size of the largest cluster, and mu-squared, characterizing the weighted mean size of all clusters excluding the largest one, are extremely useful for evaluating the percolation threshold. An advantage of using these parameters is their low sensitivity to boundary effects. We show that both the CDM and the C + HDM models are extremely filamentary both in mass and galaxy distribution. The percolation thresholds for the mass distributions are determined.

  4. Ariane-5 and Cluster update

    NASA Astrophysics Data System (ADS)

    1996-06-01

    The Enquiry Board started work on 13 June and will report by mid-July. The Launch Qualification Committee resumed its activities on 14 June. The ESA Director General and the CNES Chairman will have to rule on the Enquiry Board's recommendations and the Launch Qualification Committee's requirements. The ESA Executive will then be able to determine - with CNES - the technical and programmatic implications for the Ariane-5 development programme. The Enquiry Board's findings and recommendations and their implications will be made known to the press soon afterwards. The Ariane Launcher Programme Board (the ESA delegate body that supervises the programme) will meet on 12 August, when the ESA Executive will present the programmatic implications. On the payload side, the Cluster Science Working Team (SWT) met on 17 and 18 June to assess the situation after the loss of the Cluster mission and to explore ways in which its scientific objectives could be revived. The SWT proposed the following approach: a. integration of the Cluster structural model with flight spare subsystems (the Phoenix project) together with a rebuild of three spacecraft identical to the originals. This scenario offers alternative options: a1. integration and testing of the Cluster spare (Phoenix), storage and launch at a later date together with the three rebuilt satellites, and a2. integration and reflight of Phoenix as soon as possible and production and launch of the three rebuilt satellites at a later date. The SWT stressed that the case for an early launch of Phoenix was largely dependent on whether the follow-on programme was also approved. A further option would call for: b. use of the Cluster spare (Phoenix) as outlined above, augmented by three new "mini" satellites funded and produced by ESA Member States that would carry subsets of the Cluster instrumentation. This mission would thus fly one main spacecraft and three "companion" spacecraft, as described in an early proposal for Cluster. On 21

  5. Binary Systems Within Star Clusters

    NASA Astrophysics Data System (ADS)

    Paunzen, Ernst; Stütz, Christian; Baumann, Bernhard

    2012-04-01

    WEBDA (http://www.univie.ac.at/webda) is a site devoted to observational data of stellar clusters in the Milky Way and the Small Magellanic Cloud. It is intended to provide a reliable presentation of the available data and knowledge about these objects. The success of WEBDA is documented by its worldwide usage and the related acknowledgements in the literature: more than 650 refereed publications within the last twelve years acknowledged its use. It collects all published data for stars in open clusters that may be useful either to determine membership, or to study the stellar content and properties of the clusters. The database content includes astrometric data in the form of coordinates, rectangular positions, and proper motions, photometric data in the major systems in which star clusters have been observed, but also spectroscopic data like spectral classification, radial velocities, and rotational velocities. It also contains miscellaneous types of supplementary data like membership probabilities, orbital elements of spectroscopic binaries, and periods for different kinds of variable stars as well as an extensive bibliography. Several powerful tools help to plot, query and extract the data, which can be directly retrieved via http. At the time of writing, about four million individual measurements have been included in the database. The Star Clusters Young & Old Newsletter (SCYON), a bi-monthly newsletter devoted to star cluster research with about 600 subscribers, is hosted in parallel with the database. We present the current and upcoming new interface and tools, which are needed to visualize and analyze the increasing amount of data from all-sky surveys, and deeper investigations of binary systems, low mass dwarfs, as well as planet-hosting stars.

  6. Magnetochirality in hierarchical magnetoplasmonic clusters

    NASA Astrophysics Data System (ADS)

    Yannopapas, Vassilios

    2015-09-01

    We show theoretically that finite hierarchical assemblies of clusters consisting magnetic (magnetite) and plasmonic (gold) nanoparticles show dramatically increased values of the magnetochiral dichroism compared to those measured in conventional materials exhibiting this phenomenon (liquid molecular systems, anisotropic crystals and chiral ferromagnets). These values are attributed to the strong interaction of the magnetite nanoparticles within the clusters as well as by the excitation of surface-plasmons in the gold nanoparticles. Along with the magnetochiral dichroism, in the studied hierarchical magnetoplasmonic designs, magneto-optical phenomena such as magnetic dichroism and Faraday rotation are also enhanced relative to the case of purely magnetic nanostructures.

  7. The IMF of Globular Clusters

    NASA Astrophysics Data System (ADS)

    De Marchi, G.; Paresce, F.

    1999-12-01

    Accurate luminosity functions (LF) for a dozen globular clusters have now been measured at or just beyond their half-light radius using HST. They span almost the entire cluster main sequence below 0.75 MO. All these clusters exhibit LF that rise continuously from an absolute I magnitude MI 6 to a peak at MI 8.5-9 and then drop with increasing MI. Transformation of the LF into mass functions (MF) by means of the most recent mass luminosity relations that are consistent with all presently available data on the physical properties of low mass, low metallicity stars shows that all the LF observed so far can be obtained from MF having the shape of a log-normal distribution with characteristic mass mc=0.33 +/- 0.03 MO and standard deviation sigma =1.81 +/- 0.19. In particular, the LF of the four clusters in the sample that extend well beyond the peak luminosity down to close to the Hydrogen burning limit (NGC6341, NGC6397, NGC6752, and NGC6809) can only be reproduced by such distributions and not by a single power-law in the 0.1 - 0.6 MO range. After correction for the effects of mass segregation, the variation of the ratio of the number of higher to lower mass stars with cluster mass or any simple orbital parameter or the expected time to disruption recently computed for these clusters shows no statistically significant trend over a range of this last parameter of more than a factor of 100. We conclude that the global MF of these clusters have not been measurably modified by evaporation and tidal interactions with the Galaxy and, thus, should reflect the initial distribution of stellar masses. Since the log-normal function that we find is also very similar to the one obtained independently for much younger clusters and to the form expected theoretically, the implication seems to be unavoidable that it represents the true stellar IMF for this type of stars in this mass range.

  8. Messier's nebulae and star clusters.

    NASA Astrophysics Data System (ADS)

    Jones, K. G.

    Charles Messier's Catalogue of nebulae and star clusters, published in 1784, marked the start of a new era of deep sky astronomy. Today, this tradition of observing galaxies and clusters is kept alive by serious amateur astronomers who study the objects of the deep sky. Nearly all the objects are visible in a small telescope. The author has revised his definitive version of Messier's Catalogue. His own observations and drawings, together with maps and diagrams, make this a valuable introduction to deep sky observing. Historical and astrophysical notes bring the science of these nebulae right up to date.

  9. Galaxy Cluster Smashes Distance Record

    NASA Astrophysics Data System (ADS)

    2009-10-01

    he most distant galaxy cluster yet has been discovered by combining data from NASA's Chandra X-ray Observatory and optical and infrared telescopes. The cluster is located about 10.2 billion light years away, and is observed as it was when the Universe was only about a quarter of its present age. The galaxy cluster, known as JKCS041, beats the previous record holder by about a billion light years. Galaxy clusters are the largest gravitationally bound objects in the Universe. Finding such a large structure at this very early epoch can reveal important information about how the Universe evolved at this crucial stage. JKCS041 is found at the cusp of when scientists think galaxy clusters can exist in the early Universe based on how long it should take for them to assemble. Therefore, studying its characteristics - such as composition, mass, and temperature - will reveal more about how the Universe took shape. "This object is close to the distance limit expected for a galaxy cluster," said Stefano Andreon of the National Institute for Astrophysics (INAF) in Milan, Italy. "We don't think gravity can work fast enough to make galaxy clusters much earlier." Distant galaxy clusters are often detected first with optical and infrared observations that reveal their component galaxies dominated by old, red stars. JKCS041 was originally detected in 2006 in a survey from the United Kingdom Infrared Telescope (UKIRT). The distance to the cluster was then determined from optical and infrared observations from UKIRT, the Canada-France-Hawaii telescope in Hawaii and NASA's Spitzer Space Telescope. Infrared observations are important because the optical light from the galaxies at large distances is shifted into infrared wavelengths because of the expansion of the universe. The Chandra data were the final - but crucial - piece of evidence as they showed that JKCS041 was, indeed, a genuine galaxy cluster. The extended X-ray emission seen by Chandra shows that hot gas has been detected

  10. Collaborative Clustering for Sensor Networks

    NASA Technical Reports Server (NTRS)

    Wagstaff. Loro :/; Green Jillian; Lane, Terran

    2011-01-01

    Traditionally, nodes in a sensor network simply collect data and then pass it on to a centralized node that archives, distributes, and possibly analyzes the data. However, analysis at the individual nodes could enable faster detection of anomalies or other interesting events, as well as faster responses such as sending out alerts or increasing the data collection rate. There is an additional opportunity for increased performance if individual nodes can communicate directly with their neighbors. Previously, a method was developed by which machine learning classification algorithms could collaborate to achieve high performance autonomously (without requiring human intervention). This method worked for supervised learning algorithms, in which labeled data is used to train models. The learners collaborated by exchanging labels describing the data. The new advance enables clustering algorithms, which do not use labeled data, to also collaborate. This is achieved by defining a new language for collaboration that uses pair-wise constraints to encode useful information for other learners. These constraints specify that two items must, or cannot, be placed into the same cluster. Previous work has shown that clustering with these constraints (in isolation) already improves performance. In the problem formulation, each learner resides at a different node in the sensor network and makes observations (collects data) independently of the other learners. Each learner clusters its data and then selects a pair of items about which it is uncertain and uses them to query its neighbors. The resulting feedback (a must and cannot constraint from each neighbor) is combined by the learner into a consensus constraint, and it then reclusters its data while incorporating the new constraint. A strategy was also proposed for cleaning the resulting constraint sets, which may contain conflicting constraints; this improves performance significantly. This approach has been applied to collaborative

  11. Cluster compression algorithm: A joint clustering/data compression concept

    NASA Technical Reports Server (NTRS)

    Hilbert, E. E.

    1977-01-01

    The Cluster Compression Algorithm (CCA), which was developed to reduce costs associated with transmitting, storing, distributing, and interpreting LANDSAT multispectral image data is described. The CCA is a preprocessing algorithm that uses feature extraction and data compression to more efficiently represent the information in the image data. The format of the preprocessed data enables simply a look-up table decoding and direct use of the extracted features to reduce user computation for either image reconstruction, or computer interpretation of the image data. Basically, the CCA uses spatially local clustering to extract features from the image data to describe spectral characteristics of the data set. In addition, the features may be used to form a sequence of scalar numbers that define each picture element in terms of the cluster features. This sequence, called the feature map, is then efficiently represented by using source encoding concepts. Various forms of the CCA are defined and experimental results are presented to show trade-offs and characteristics of the various implementations. Examples are provided that demonstrate the application of the cluster compression concept to multi-spectral images from LANDSAT and other sources.

  12. Clusters galore: insights about environmental clusters from probability theory.

    PubMed

    Neutra, R; Swan, S; Mack, T

    1992-12-15

    The posterior probability of a causal explanation given that an environmental cancer cluster is statistically significant depends on the prior probability of an environmentally caused cluster, the sensitivity of the statistical test and its specificity. The prior probability is low, because it is rare to have enough carcinogen in the general environment to cause a relative risk of cancer high enough to achieve statistical significance in a small geographic area. The sensitivity and specificity are not great. The likelihood that a census tract escapes statistically significant elevations in all 80 types of cancer can be calculated. Many of the thousands of census tracts will, by chance alone, have at least one type of cancer whose elevation is statistically significant. Actual observation from a large cancer registry confirms this probabilistic prediction. Applying the principles of Bayes' Theorem would suggest that most statistically significant environmental cancer clusters are not due to environmental carcinogens. One would have to investigate hundreds of environmental cancer clusters to find one with a true environmental cause.

  13. Chaos theory perspective for industry clusters development

    NASA Astrophysics Data System (ADS)

    Yu, Haiying; Jiang, Minghui; Li, Chengzhang

    2016-03-01

    Industry clusters have outperformed in economic development in most developing countries. The contributions of industrial clusters have been recognized as promotion of regional business and the alleviation of economic and social costs. It is no doubt globalization is rendering clusters in accelerating the competitiveness of economic activities. In accordance, many ideas and concepts involve in illustrating evolution tendency, stimulating the clusters development, meanwhile, avoiding industrial clusters recession. The term chaos theory is introduced to explain inherent relationship of features within industry clusters. A preferred life cycle approach is proposed for industrial cluster recessive theory analysis. Lyapunov exponents and Wolf model are presented for chaotic identification and examination. A case study of Tianjin, China has verified the model effectiveness. The investigations indicate that the approaches outperform in explaining chaos properties in industrial clusters, which demonstrates industrial clusters evolution, solves empirical issues and generates corresponding strategies.

  14. Star formation and substructure in galaxy clusters

    SciTech Connect

    Cohen, Seth A.; Hickox, Ryan C.; Wegner, Gary A.; Einasto, Maret; Vennik, Jaan

    2014-03-10

    We investigate the relationship between star formation (SF) and substructure in a sample of 107 nearby galaxy clusters using data from the Sloan Digital Sky Survey. Several past studies of individual galaxy clusters have suggested that cluster mergers enhance cluster SF, while others find no such relationship. The SF fraction in multi-component clusters (0.228 ± 0.007) is higher than that in single-component clusters (0.175 ± 0.016) for galaxies with M{sub r}{sup 0.1}<−20.5. In both single- and multi-component clusters, the fraction of star-forming galaxies increases with clustercentric distance and decreases with local galaxy number density, and multi-component clusters show a higher SF fraction than single-component clusters at almost all clustercentric distances and local densities. Comparing the SF fraction in individual clusters to several statistical measures of substructure, we find weak, but in most cases significant at greater than 2σ, correlations between substructure and SF fraction. These results could indicate that cluster mergers may cause weak but significant SF enhancement in clusters, or unrelaxed clusters exhibit slightly stronger SF due to their less evolved states relative to relaxed clusters.

  15. An Improved Cluster Richness Estimator

    SciTech Connect

    Rozo, Eduardo; Rykoff, Eli S.; Koester, Benjamin P.; McKay, Timothy; Hao, Jiangang; Evrard, August; Wechsler, Risa H.; Hansen, Sarah; Sheldon, Erin; Johnston, David; Becker, Matthew R.; Annis, James T.; Bleem, Lindsey; Scranton, Ryan; /Pittsburgh U.

    2009-08-03

    Minimizing the scatter between cluster mass and accessible observables is an important goal for cluster cosmology. In this work, we introduce a new matched filter richness estimator, and test its performance using the maxBCG cluster catalog. Our new estimator significantly reduces the variance in the L{sub X}-richness relation, from {sigma}{sub lnL{sub X}}{sup 2} = (0.86 {+-} 0.02){sup 2} to {sigma}{sub lnL{sub X}}{sup 2} = (0.69 {+-} 0.02){sup 2}. Relative to the maxBCG richness estimate, it also removes the strong redshift dependence of the richness scaling relations, and is significantly more robust to photometric and redshift errors. These improvements are largely due to our more sophisticated treatment of galaxy color data. We also demonstrate the scatter in the L{sub X}-richness relation depends on the aperture used to estimate cluster richness, and introduce a novel approach for optimizing said aperture which can be easily generalized to other mass tracers.

  16. Cluster Grouping Coast to Coast.

    ERIC Educational Resources Information Center

    Schuler, Patricia A.

    This paper discusses the results of a survey that investigated how 69 school districts associated with the National Research Center on the Gifted and Talented were implementing cluster grouping to meet the intellectual, social, and emotional needs of gifted students. Results from the survey indicate: (1) the majority of school districts did not…

  17. Cluster Inter-Spacecraft Communications

    NASA Technical Reports Server (NTRS)

    Cox, Brian

    2008-01-01

    A document describes a radio communication system being developed for exchanging data and sharing data-processing capabilities among spacecraft flying in formation. The system would establish a high-speed, low-latency, deterministic loop communication path connecting all the spacecraft in a cluster. The system would be a wireless version of a ring bus that complies with the Institute of Electrical and Electronics Engineers (IEEE) standard 1393 (which pertains to a spaceborne fiber-optic data bus enhancement to the IEEE standard developed at NASA's Jet Propulsion Laboratory). Every spacecraft in the cluster would be equipped with a ring-bus radio transceiver. The identity of a spacecraft would be established upon connection into the ring bus, and the spacecraft could be at any location in the ring communication sequence. In the event of failure of a spacecraft, the ring bus would reconfigure itself, bypassing a failed spacecraft. Similarly, the ring bus would reconfigure itself to accommodate a spacecraft newly added to the cluster or newly enabled or re-enabled. Thus, the ring bus would be scalable and robust. Reliability could be increased by launching, into the cluster, spare spacecraft to be activated in the event of failure of other spacecraft.

  18. A Model for Word Clustering.

    ERIC Educational Resources Information Center

    Thom, James A.; Zobel, Justin

    1992-01-01

    Discusses models for the distribution of words in text and proposes a new model based on clustering that can be used to estimate the probability that a document contains a particular word as well as the number of distinct words in a document. Zipf's law and the Poisson approximation are also discussed. (18 references) (LRW)

  19. Exotic shapes and exotic clusterization

    SciTech Connect

    Cseh, J.; Darai, J.; Algora, A.

    2011-10-28

    The interrelation of the largely elongated nuclear shapes and clusterization is discussed by applying semimicroscopic methods. {sup 36}Ar is considered as a specific example, where recent experimental heavy-ion scattering data seem to justify the theoretical predictions on the hyperdeformed states. Alpha-emitting reactions are also suggested for its population.

  20. Cluster Analysis of Adolescent Blogs

    ERIC Educational Resources Information Center

    Liu, Eric Zhi-Feng; Lin, Chun-Hung; Chen, Feng-Yi; Peng, Ping-Chuan

    2012-01-01

    Emerging web applications and networking systems such as blogs have become popular, and they offer unique opportunities and environments for learners, especially for adolescent learners. This study attempts to explore the writing styles and genres used by adolescents in their blogs by employing content, factor, and cluster analyses. Factor…

  1. Competency Index. [Health Technology Cluster.

    ERIC Educational Resources Information Center

    Ohio State Univ., Columbus. Center on Education and Training for Employment.

    This competency index lists the competencies included in the 62 units of the Tech Prep Competency Profiles within the Health Technologies Cluster. The unit topics are as follows: employability skills; professionalism; teamwork; computer literacy; documentation; infection control and risk management; medical terminology; anatomy, physiology, and…

  2. Thermodynamics of confined gallium clusters

    NASA Astrophysics Data System (ADS)

    Chandrachud, Prachi

    2015-11-01

    We report the results of ab initio molecular dynamics simulations of Ga13 and Ga17 clusters confined inside carbon nanotubes with different diameters. The cluster-tube interaction is simulated by the Lennard-Jones (LJ) potential. We discuss the geometries, the nature of the bonding and the thermodynamics under confinement. The geometries as well as the isomer spectra of both the clusters are significantly affected. The degree of confinement decides the dimensionality of the clusters. We observe that a number of low-energy isomers appear under moderate confinement while some isomers seen in the free space disappear. Our finite-temperature simulations bring out interesting aspects, namely that the heat capacity curve is flat, even though the ground state is symmetric. Such a flat nature indicates that the phase change is continuous. This effect is due to the restricted phase space available to the system. These observations are supported by the mean square displacement of individual atoms, which are significantly smaller than in free space. The nature of the bonding is found to be approximately jellium-like. Finally we note the relevance of the work to the problem of single file diffusion for the case of the highest confinement.

  3. Construction Cluster Volume 5 [Electrical].

    ERIC Educational Resources Information Center

    Pennsylvania State Dept. of Justice, Harrisburg. Bureau of Correction.

    The document is the fifth of a series, to be integrated with a G.E.D. program, containing instructional materials for the construction cluster. The volume focuses on electrical work and consists of 20 instructional units which require a month of study: (1) safety precautions and first aid for electrical workers; (2) planning a simple installation;…

  4. Clusters, Innovation and Tertiary Education

    ERIC Educational Resources Information Center

    Madgett, Paul; Belanger, Charles H.; Mount, Joan

    2005-01-01

    The purpose of this paper is to investigate the integration between research findings produced at the University and Community College levels and local SMEs (small and medium enterprises) as it impacts regional innovation systems and in particular the prospect of cluster formation. The paper explores certain factors that have been identified in…

  5. Insulin resistance: regression and clustering.

    PubMed

    Yoon, Sangho; Assimes, Themistocles L; Quertermous, Thomas; Hsiao, Chin-Fu; Chuang, Lee-Ming; Hwu, Chii-Min; Rajaratnam, Bala; Olshen, Richard A

    2014-01-01

    In this paper we try to define insulin resistance (IR) precisely for a group of Chinese women. Our definition deliberately does not depend upon body mass index (BMI) or age, although in other studies, with particular random effects models quite different from models used here, BMI accounts for a large part of the variability in IR. We accomplish our goal through application of Gauss mixture vector quantization (GMVQ), a technique for clustering that was developed for application to lossy data compression. Defining data come from measurements that play major roles in medical practice. A precise statement of what the data are is in Section 1. Their family structures are described in detail. They concern levels of lipids and the results of an oral glucose tolerance test (OGTT). We apply GMVQ to residuals obtained from regressions of outcomes of an OGTT and lipids on functions of age and BMI that are inferred from the data. A bootstrap procedure developed for our family data supplemented by insights from other approaches leads us to believe that two clusters are appropriate for defining IR precisely. One cluster consists of women who are IR, and the other of women who seem not to be. Genes and other features are used to predict cluster membership. We argue that prediction with "main effects" is not satisfactory, but prediction that includes interactions may be. PMID:24887437

  6. Construction Cluster Volume III [Plumbing].

    ERIC Educational Resources Information Center

    Pennsylvania State Dept. of Justice, Harrisburg. Bureau of Correction.

    The document is the third of a series, to be integrated with a G.E.D. program, containing instructional materials at the basic skills level for the construction cluster. The volume focuses on plumbing and consists of 20 instructional units which require a month of study. The units include: (1) importance of plumbing; (2) pipe and tubing…

  7. Clustering at Oakton: Some Observations.

    ERIC Educational Resources Information Center

    Jordan, Richard L.

    This paper reviews the student-centered cluster college concept of organization employed at Oakton Community College (Illinois) and compares this approach to traditional organization by academic department or division. The advantages offered by the division structure include intradisciplinary interchange among teachers, coordinated budget…

  8. Boron Clusters Come of Age

    ERIC Educational Resources Information Center

    Grimes, Russell N.

    2004-01-01

    Boron is the only element other than carbon that can build molecules of unlimited size by covalently boding to itself, a property known as catenation. In contrast to the chains and rings favored by carbon, boron arguably adopts a cluster motif that is reflected in the various forms of the pure element and in the huge area of polyhedral borane…

  9. CLOC: Cluster Luminosity Order-Statistic Code

    NASA Astrophysics Data System (ADS)

    Da Silva, Robert L.; Krumholz, Mark R.; Fumagalli, Michele; Fall, S. Michael

    2016-02-01

    CLOC computes cluster order statistics, i.e. the luminosity distribution of the Nth most luminous cluster in a population. It is flexible and requires few assumptions, allowing for parametrized variations in the initial cluster mass function and its upper and lower cutoffs, variations in the cluster age distribution, stellar evolution and dust extinction, as well as observational uncertainties in both the properties of star clusters and their underlying host galaxies. It uses Markov chain Monte Carlo methods to search parameter space to find best-fitting values for the parameters describing cluster formation and disruption, and to obtain rigorous confidence intervals on the inferred values.

  10. Adsorption of polar molecules on krypton clusters.

    PubMed

    Rosso, A; Pokapanich, W; Ohrwall, G; Svensson, S; Björneholm, O; Tchaplyguine, M

    2007-08-28

    The formation process of binary clusters has been studied using synchrotron based core level photoelectron spectroscopy. Free neutral krypton clusters have been produced by adiabatic expansion and doped with chloromethane molecules using the pickup technique. The comparison between the integrated intensities, linewidths, and level shifts of the cluster features of pure krypton and of chloromethane-krypton clusters has been used to obtain information about the cluster geometry. We have shown that most of the chloromethane molecules remain on the surface of the clusters.

  11. Stability of a deposited liquid cluster

    SciTech Connect

    Kashtanov, P. V.; Hippler, R.; Smirnov, B. M.; Bhattacharyya, S. R.

    2010-03-15

    The fragmentation of silver liquid clusters deposited onto a silicon surface is observed after heating the clusters to 1073 K and subsequent annealing with the exposition time 3 min. This contradicts macroscopic models of a liquid drop deposited on a surface if we use critical parameters of bulk silver. Some versions are analyzed that are based on cluster properties and may explain the phenomenon of cluster fragmentation. An experiment is suggested for clarifying the nature of the cluster fragmentation phenomenon and cluster critical phenomena.

  12. SUPERMODEL ANALYSIS OF GALAXY CLUSTERS

    SciTech Connect

    Fusco-Femiano, R.; Cavaliere, A.; Lapi, A.

    2009-11-01

    We present the analysis of the X-ray brightness and temperature profiles for six clusters belonging to both the Cool Core (CC) and Non Cool Core (NCC) classes, in terms of the Supermodel (SM) developed by Cavaliere et al. Based on the gravitational wells set by the dark matter (DM) halos, the SM straightforwardly expresses the equilibrium of the intracluster plasma (ICP) modulated by the entropy deposited at the boundary by standing shocks from gravitational accretion, and injected at the center by outgoing blast waves from mergers or from outbursts of active galactic nuclei. The cluster set analyzed here highlights not only how simply the SM represents the main dichotomy CC versus NCC clusters in terms of a few ICP parameters governing the radial entropy run, but also how accurately it fits even complex brightness and temperature profiles. For CC clusters like A2199 and A2597, the SM with a low level of central entropy straightforwardly yields the characteristic peaked profile of the temperature marked by a decline toward the center, without requiring currently strong radiative cooling and high mass deposition rates. NCC clusters like A1656 require instead a central entropy floor of a substantial level, and some like A2256 and even more A644 feature structured temperature profiles that also call for a definite floor extension; in such conditions the SM accurately fits the observations, and suggests that in these clusters the ICP has been just remolded by a merger event, in the way of a remnant cool core. The SM also predicts that DM halos with high concentration should correlate with flatter entropy profiles and steeper brightness in the outskirts; this is indeed the case with A1689, for which from X-rays we find concentration values c approx 10, the hallmark of an early halo formation. Thus, we show the SM to constitute a fast tool not only to provide wide libraries of accurate fits to X-ray temperature and density profiles, but also to retrieve from the ICP

  13. Ionization of Water Clusters is Mediated by Exciton Energy Transfer from Argon Clusters

    SciTech Connect

    Golan, Amir; Ahmed, Musahid

    2012-01-25

    The exciton energy deposited in an argon cluster, (Arn ,< n=20>) using VUV radiation is transferred to softly ionize doped water clusters, ((H2O)n, n=1-9) leading to the formation of non-fragmented clusters. Following the initial excitation, electronic energy is channeled to ionize the doped water cluster while evaporating the Ar shell, allowing identification of fragmented and complete water cluster ions. Examination of the photoionization efficiency curve shows that cluster evaporation from excitons located above 12.6 eV are not enough to cool the energized water cluster ion, and leads to their dissociation to (H2O)n-2H+ (protonated) clusters.

  14. Dynamically Evolving Models of Clusters

    NASA Astrophysics Data System (ADS)

    Bode, Paul W.; Berrington, Robert C.; Cohn, Haldan N.; Lugger, Phyllis M.

    1993-12-01

    An N-body method, with up to N=10(5) particles, is used to simulate the dynamical evolution of clusters of galaxies. Each galaxy is represented as an extended structure containing many particles, and the gravitational potential arises from the particles alone. The clusters initially contain 50 or 100 galaxies with masses distributed according to a Schechter function. Mass is apportioned between the galaxies and a smoothly distributed common group halo, or intra-cluster background. The fraction of the total cluster mass initially in this background is varied from 50% to 90%. The models begin in a virialized state. We will be presenting a videotape which contains animations of a number of these models. The animations show important physical processes, such as stripping, merging, and dynamical friction, as they take place, thus allowing one to observe the interplay of these processes in the global evolution of the system. When the galaxies have substantial dark halos (background mass fraction <=75%) a large, centrally located merger remnant is created. The galaxy number density profile around this dominant member becomes cusped, approaching an isothermal distribution. At the same time, the number of multiple nuclei increases. Comparing the 50-galaxy models to MKW/AWM clusters, the values of Delta M12 and the peculiar velocities of the first-ranked galaxies are best fit by a mix of model ages in the range 8--11 Gyr. The growth in luminosity of the first-ranked galaxy during this amount of time is consistent only with weak cannibalism.

  15. Participation in the Cluster Magnetometer Consortium for the Cluster Mission

    NASA Technical Reports Server (NTRS)

    Kivelson, Margaret

    1997-01-01

    Prof. M. G. Kivelson (UCLA) and Dr. R. C. Elphic (LANL) are Co-investigators on the Cluster Magnetometer Consortium (CMC) that provided the fluxgate magnetometers and associated mission support for the Cluster Mission. The CMC designated UCLA as the site with primary responsibility for the inter-calibration of data from the four spacecraft and the production of fully corrected data critical to achieving the mission objectives. UCLA was also charged with distributing magnetometer data to the U.S. Co-investigators. UCLA also supported the Technical Management Team, which was responsible for the detailed design of the instrument and its interface. In this final progress report we detail the progress made by the UCLA team in achieving the mission objectives.

  16. Effective cluster interactions from cluster-variation formalism. I

    NASA Astrophysics Data System (ADS)

    Asta, M.; Wolverton, C.; de Fontaine, D.; Dreyssé, H.

    1991-09-01

    States of (partial) order in binary-alloy systems are described by means of expansions in a complete set of orthogonal cluster functions. The expectation value of the energy of such systems can then be expressed as a bilinear form in multisite correlation variables and effective cluster interactions (ECI's), as originally proposed by Sanchez, Ducastelle, and Gratias [Physica A 128, 334 (1984)]. It is shown that ECI's are defined as interchange energies averaged over all atomic configurations with a fixed concentration or over all configurations and concentrations, depending on the orthogonal expansion considered. The former averaging process leads to concentration-dependent ECI's, the latter to concentration-independent ECI's. From their formal definitions, certain relations will be shown to hold between the interactions derived in the two averaging schemes in the thermodynamic limit. In particular, an interesting convergence criterion is established for the concentration-dependent ECI's.

  17. Cluster Ions and Atmospheric Processes

    NASA Astrophysics Data System (ADS)

    D'Auria, R.; Turco, R. P.

    We investigate the properties and possible roles of naturally occurring ions under at- mospheric conditions. Among other things, the formation of stable charged molecular clusters represents the initial stages of aerosol nucleation [e.g., Keesee and Castle- man, 1982], while the conversion of vapor to aggregates is the first step in certain atmospheric phase transitions [e.g. Hamill and Turco, 2000]. We analyze the stability and size distributions of common ionic clusters by solving the differential equations describing their growth and loss. The necessary reaction rate coefficients are deter- mined using kinetic and thermodynamic data. The latter are derived from direct labo- ratory measurements of equilibrium constants, from the classical charged liquid drop model applied to large aggregates (i.e., the Thomson model [Thomson, 1906]), and from quantum mechanical calculations of the thermodynamic potentials associated with the cluster structures. This approach allows us to characterize molecular clusters across the entire size range from true molecular species to larger aggregates exhibiting macroscopic behavior [D'Auria, 2001]. Cluster systems discussed in this talk include the proton hydrates (PHs) and nitrate-water and nitrate-nitric acid series [D'Auria and Turco, 2001]. These ions have frequently been detected in the stratosphere and tropo- sphere [e.g., Arnold et al., 1977; Viggiano and Arnold, 1981]. We show how the pro- posed hybrid cluster model can be extended to a wide range of ion systems, including non-proton hydrates (NPHs), mixed-ligand clusters such as nitrate-water-nitric acid and sulfate-sulfuric acid-water, as well as more exotic species containing ammonia, pyridine and other organic compounds found on ions [e.g., Eisele, 1988; Tanner and Eisele, 1991]. References: Arnold, F., D. Krankowsky and K. H. Marien, First mass spectrometric measurements of posi- tive ions in the stratosphere, Nature, 267, 30-32, 1977. D'Auria, R., A study of ionic

  18. Spatial clustering with Density-Ordered tree

    NASA Astrophysics Data System (ADS)

    Cheng, Qing; Lu, Xin; Liu, Zhong; Huang, Jincai; Cheng, Guangquan

    2016-10-01

    Clustering has emerged as an active research direction for knowledge discovery in spatial databases. Most spatial clustering methods become ineffective when inappropriate parameters are given or when datasets of diverse shapes and densities are provided. To address this issue, we propose a novel clustering method, called SCDOT (Spatial Clustering with Density-Ordered Tree). By projecting a dataset to a Density-Ordered Tree, SCDOT partitions the data into several relatively small sub-clusters with a box-plot method. A heuristic method is proposed to find the genuine clusters by repeatedly merging sub-clusters and an iteration strategy is utilized to automatically determine input parameters. Moreover, we also provide an innovative way to identify cluster center and noise. Extensive experiments on both synthetic and real-world datasets demonstrate the superior performance of SCDOT over the baseline methods.

  19. Active constrained clustering by examining spectral Eigenvectors

    NASA Technical Reports Server (NTRS)

    Wagstaff, Kiri L.; desJardins, Marie; Xu, Qianjun

    2005-01-01

    This work focuses on the active selection of pairwise constraints for spectral clustering. We develop and analyze a technique for Active Constrained Clustering by Examining Spectral eigenvectorS (ACCESS) derived from a similarity matrix.

  20. OBSERVED SCALING RELATIONS FOR STRONG LENSING CLUSTERS: CONSEQUENCES FOR COSMOLOGY AND CLUSTER ASSEMBLY

    SciTech Connect

    Comerford, Julia M.; Moustakas, Leonidas A.; Natarajan, Priyamvada

    2010-05-20

    Scaling relations of observed galaxy cluster properties are useful tools for constraining cosmological parameters as well as cluster formation histories. One of the key cosmological parameters, {sigma}{sub 8}, is constrained using observed clusters of galaxies, although current estimates of {sigma}{sub 8} from the scaling relations of dynamically relaxed galaxy clusters are limited by the large scatter in the observed cluster mass-temperature (M-T) relation. With a sample of eight strong lensing clusters at 0.3 < z < 0.8, we find that the observed cluster concentration-mass relation can be used to reduce the M-T scatter by a factor of 6. Typically only relaxed clusters are used to estimate {sigma}{sub 8}, but combining the cluster concentration-mass relation with the M-T relation enables the inclusion of unrelaxed clusters as well. Thus, the resultant gains in the accuracy of {sigma}{sub 8} measurements from clusters are twofold: the errors on {sigma}{sub 8} are reduced and the cluster sample size is increased. Therefore, the statistics on {sigma}{sub 8} determination from clusters are greatly improved by the inclusion of unrelaxed clusters. Exploring cluster scaling relations further, we find that the correlation between brightest cluster galaxy (BCG) luminosity and cluster mass offers insight into the assembly histories of clusters. We find preliminary evidence for a steeper BCG luminosity-cluster mass relation for strong lensing clusters than the general cluster population, hinting that strong lensing clusters may have had more active merging histories.

  1. MCS Large Cluster Systems Software Toolkit

    SciTech Connect

    Evard, Remy; Navarro, John-Paul; Nurmi, Daniel

    2002-11-01

    This package contains a number of systems utilities for managing a set of computers joined in a "cluster". The utilities assist a team of systems administrators in managing the cluster by automating routine tasks, centralizing information, and monitoring individual computers within the cluster. Included in the toolkit are scripts used to boot a computer from a floppy, a program to turn on and off the power to a system, and a system for using a database to organize cluster information.

  2. Cluster Dynamics in a Circulating Fluidized Bed

    SciTech Connect

    Guenther, C.P.; Breault, R.W.

    2006-11-01

    A common hydrodynamic feature in industrial scale circulating fluidized beds is the presence of clusters. The continuous formation and destruction of clusters strongly influences particle hold-up, pressure drop, heat transfer at the wall, and mixing. In this paper fiber optic data is analyzed using discrete wavelet analysis to characterize the dynamic behavior of clusters. Five radial positions at three different axial locations under five different operating were analyzed using discrete wavelets. Results are summarized with respect to cluster size and frequency.

  3. Multitask spectral clustering by exploring intertask correlation.

    PubMed

    Yang, Yang; Ma, Zhigang; Yang, Yi; Nie, Feiping; Shen, Heng Tao

    2015-05-01

    Clustering, as one of the most classical research problems in pattern recognition and data mining, has been widely explored and applied to various applications. Due to the rapid evolution of data on the Web, more emerging challenges have been posed on traditional clustering techniques: 1) correlations among related clustering tasks and/or within individual task are not well captured; 2) the problem of clustering out-of-sample data is seldom considered; and 3) the discriminative property of cluster label matrix is not well explored. In this paper, we propose a novel clustering model, namely multitask spectral clustering (MTSC), to cope with the above challenges. Specifically, two types of correlations are well considered: 1) intertask clustering correlation, which refers the relations among different clustering tasks and 2) intratask learning correlation, which enables the processes of learning cluster labels and learning mapping function to reinforce each other. We incorporate a novel l2,p -norm regularizer to control the coherence of all the tasks based on an assumption that related tasks should share a common low-dimensional representation. Moreover, for each individual task, an explicit mapping function is simultaneously learnt for predicting cluster labels by mapping features to the cluster label matrix. Meanwhile, we show that the learning process can naturally incorporate discriminative information to further improve clustering performance. We explore and discuss the relationships between our proposed model and several representative clustering techniques, including spectral clustering, k -means and discriminative k -means. Extensive experiments on various real-world datasets illustrate the advantage of the proposed MTSC model compared to state-of-the-art clustering approaches. PMID:25252288

  4. Multitask spectral clustering by exploring intertask correlation.

    PubMed

    Yang, Yang; Ma, Zhigang; Yang, Yi; Nie, Feiping; Shen, Heng Tao

    2015-05-01

    Clustering, as one of the most classical research problems in pattern recognition and data mining, has been widely explored and applied to various applications. Due to the rapid evolution of data on the Web, more emerging challenges have been posed on traditional clustering techniques: 1) correlations among related clustering tasks and/or within individual task are not well captured; 2) the problem of clustering out-of-sample data is seldom considered; and 3) the discriminative property of cluster label matrix is not well explored. In this paper, we propose a novel clustering model, namely multitask spectral clustering (MTSC), to cope with the above challenges. Specifically, two types of correlations are well considered: 1) intertask clustering correlation, which refers the relations among different clustering tasks and 2) intratask learning correlation, which enables the processes of learning cluster labels and learning mapping function to reinforce each other. We incorporate a novel l2,p -norm regularizer to control the coherence of all the tasks based on an assumption that related tasks should share a common low-dimensional representation. Moreover, for each individual task, an explicit mapping function is simultaneously learnt for predicting cluster labels by mapping features to the cluster label matrix. Meanwhile, we show that the learning process can naturally incorporate discriminative information to further improve clustering performance. We explore and discuss the relationships between our proposed model and several representative clustering techniques, including spectral clustering, k -means and discriminative k -means. Extensive experiments on various real-world datasets illustrate the advantage of the proposed MTSC model compared to state-of-the-art clustering approaches.

  5. Structural Trends of Small Silicon Clusters

    NASA Astrophysics Data System (ADS)

    Ho, K. M.; Pan, B. C.; Wacker, J. G.; Wang, C. Z.; Turner, D. E.; Deaven, D.

    1997-03-01

    We have performed a systematic search for the low energy structures of silicon clusters in the range from Si_10 to Si_20 using a recently developed genetic algorithm. Our results revealed the structural motif for the elongated clusters observed in mobility experiments. We also observe the beginning of another competing family for clusters larger than Si_17.

  6. Using Enrichment Clusters for Performance Based Identification.

    ERIC Educational Resources Information Center

    Renzulli, Joseph S.

    2000-01-01

    This article describes an enrichment cluster approach designed to create highly challenging learning opportunities that allow high potential students to identify themselves. The enrichment clusters focus students' attention on authentic learning applied to real-life problems. Guidelines for enrichment clusters are discussed, along with the teacher…

  7. The Design of Cluster Randomized Crossover Trials

    ERIC Educational Resources Information Center

    Rietbergen, Charlotte; Moerbeek, Mirjam

    2011-01-01

    The inefficiency induced by between-cluster variation in cluster randomized (CR) trials can be reduced by implementing a crossover (CO) design. In a simple CO trial, each subject receives each treatment in random order. A powerful characteristic of this design is that each subject serves as its own control. In a CR CO trial, clusters of subjects…

  8. Interdisciplinary Education in a Cluster College.

    ERIC Educational Resources Information Center

    Butzek, James C.; Carr, Gene

    This paper provides a brief overview of Oakton Community College's (OCC) cluster organization, which is believed to foster offering of true interdisciplinary education. OCC is organized into four learning clusters, each of 30 full-time and 40 part-time faculty, 1,500 students, and headed by a dean. Each cluster is semi-autonomous; authority is…

  9. Career Clusters Implementation in the States

    ERIC Educational Resources Information Center

    Reese, Susan

    2008-01-01

    The majority of states in the U.S. have embraced the career clusters concept. But they face challenges in implementing and expanding the system. This article discusses career cluster initiatives and the challenges they face. The career cluster model has the potential to help meet a number of challenges--from integrating academic and technical…

  10. Precursors to Onset Clusters in Acquisition

    ERIC Educational Resources Information Center

    Gierut, Judith A.; O'Connor, Kathleen M.

    2002-01-01

    Two lawful relationships involving word-initial onset clusters have been advanced in the acquisition literature; namely, that clusters imply affricates, and that liquid clusters imply a liquid distinction. This study evaluated and extended the validity of these implicational laws in a population of 110 children (aged 3;0 to 8;6) with functional…

  11. Evaluating Models for Partially Clustered Designs

    ERIC Educational Resources Information Center

    Baldwin, Scott A.; Bauer, Daniel J.; Stice, Eric; Rohde, Paul

    2011-01-01

    Partially clustered designs, where clustering occurs in some conditions and not others, are common in psychology, particularly in prevention and intervention trials. This article reports results from a simulation comparing 5 approaches to analyzing partially clustered data, including Type I errors, parameter bias, efficiency, and power. Results…

  12. Cluster Analytic Identification of Autistic Preschoolers.

    ERIC Educational Resources Information Center

    Rescorla, Leslie

    1988-01-01

    Cluster analysis on factor analytic symptom profiles obtained from the Achenbach Child Behavior Checklist for 204 three- to five-year-old boys including 79 autistic and autistic-like children identified an autistic group as soon as three clusters were formed. This autistic cluster was later subdivided according to presence/absence of anxiety and…

  13. Tuning Properties in Silver Clusters.

    PubMed

    Joshi, Chakra P; Bootharaju, Megalamane S; Bakr, Osman M

    2015-08-01

    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. PMID:26267198

  14. Cluster approach to dilute magnetism

    NASA Astrophysics Data System (ADS)

    Holvorcem, Paulo R. C.; Osório, Roberto

    1988-10-01

    A cluster algebra is developed for the definition of independent correlation functions in the cluster-variation method (CVM) for the spin-1 Ising model. A scheme is then introduced for the study of site-dilute spin- {1}/{2} Ising models by means of the CVM. The procedure regards the site-dilute spin- {1}/{2} model as the spin-1 model with additional constraints due to dilution. The Desjardins-Steinsvoll algortihm is used for the transformation of the CVM equations into a set of differential equations for the independent correlation functions with the inverse temperature as parameter. The evolution of the correlation functions with temperature and the behavior of response functions such as the specific heat and the susceptability are then obtained for any degree of dilution. As an introduction to this scheme, its detailed application is presented here for the simple case of the pair approximation.

  15. Surface decorated platinum carbonyl clusters

    NASA Astrophysics Data System (ADS)

    Ciabatti, Iacopo; Femoni, Cristina; Iapalucci, Maria Carmela; Longoni, Giuliano; Zacchini, Stefano; Zarra, Salvatore

    2012-06-01

    Four molecular Pt-carbonyl clusters decorated by Cd-Br fragments, i.e., [Pt13(CO)12{Cd5(μ-Br)5Br2(dmf)3}2]2- (1), [Pt19(CO)17{Cd5(μ-Br)5Br3(Me2CO)2}{Cd5(μ-Br)5Br(Me2CO)4}]2- (2), [H2Pt26(CO)20(CdBr)12]8- (3) and [H4Pt26(CO)20(CdBr)12(PtBr)x]6- (4) (x = 0-2), have been obtained from the reactions between [Pt3n(CO)6n]2- (n = 2-6) and CdBr2.H2O in dmf at 120 °C. The structures of these molecular clusters with diameters of 1.5-2 nm have been determined by X-ray crystallography. Both 1 and 2 are composed of icosahedral or bis-icosahedral Pt-CO cores decorated on the surface by Cd-Br motifs, whereas 3 and 4 display a cubic close packed Pt26Cd12 metal frame decorated by CO and Br ligands. An oversimplified and unifying approach to interpret the electron count of these surface decorated platinum carbonyl clusters is suggested, and extended to other low-valent organometallic clusters and Au-thiolate nanoclusters.Four molecular Pt-carbonyl clusters decorated by Cd-Br fragments, i.e., [Pt13(CO)12{Cd5(μ-Br)5Br2(dmf)3}2]2- (1), [Pt19(CO)17{Cd5(μ-Br)5Br3(Me2CO)2}{Cd5(μ-Br)5Br(Me2CO)4}]2- (2), [H2Pt26(CO)20(CdBr)12]8- (3) and [H4Pt26(CO)20(CdBr)12(PtBr)x]6- (4) (x = 0-2), have been obtained from the reactions between [Pt3n(CO)6n]2- (n = 2-6) and CdBr2.H2O in dmf at 120 °C. The structures of these molecular clusters with diameters of 1.5-2 nm have been determined by X-ray crystallography. Both 1 and 2 are composed of icosahedral or bis-icosahedral Pt-CO cores decorated on the surface by Cd-Br motifs, whereas 3 and 4 display a cubic close packed Pt26Cd12 metal frame decorated by CO and Br ligands. An oversimplified and unifying approach to interpret the electron count of these surface decorated platinum carbonyl clusters is suggested, and extended to other low-valent organometallic clusters and Au-thiolate nanoclusters. CCDC 867747 and 867748. For crystallographic data in CIF or other electronic format see DOI: 10.1039/c2nr30400g

  16. Caltrans on a Beowulf Cluster

    NASA Astrophysics Data System (ADS)

    Meyer, William; Casper, Thomas

    2001-10-01

    We have begun to explore using a cluster of Linux computers for parallel applications. Initially utilized as a network of workstations (NOW), these computers were used to calculate the inversion matrix for the tangential viewing Xpt camera diagnostic on DIII-D. The workstations are configured as a Beowulf cluster on a private 100MB network and administered from a master node connected to the LLNL labnet at 10MB. Each host is a dual processor Intel Pentium machine with 1GB of RAM. Commercial FORTRAN compilers have been acquired that support MP to take advantage of the dual processors. MPI and PVM have been installed for inter-host message passing. We will report on the progress of building a parallel version of the transport code Caltrans using both MP and MPI.

  17. Progress on the Cluster Mission

    NASA Technical Reports Server (NTRS)

    Kivelson, Margaret; Khurana, Krishan; Acuna, Mario (Technical Monitor)

    2002-01-01

    Prof M. G. Kivelson and Dr. K. K. Khurana (UCLA (University of California, Los Angeles)) are co-investigators on the Cluster Magnetometer Consortium (CMC) that provided the fluxgate magnetometers and associated mission support for the Cluster Mission. The CMC designated UCLA as the site with primary responsibility for the inter-calibration of data from the four spacecraft and the production of fully corrected data critical to achieving the mission objectives. UCLA will also participate in the analysis and interpretation of the data. The UCLA group here reports its excellent progress in developing fully intra-calibrated data for large portions of the mission and an excellent start in developing inter-calibrated data for selected time intervals, especially extended intervals in August, 2001 on which a workshop held at ESTEC in March, 2002 focused. In addition, some scientific investigations were initiated and results were reported at meetings.

  18. Observer's Guide to Star Clusters

    NASA Astrophysics Data System (ADS)

    Inglis, Mike

    Star clusters are among the most intriguing, amazing, and beautiful objects in the night sky. They can be young or old, large or small, bright or faint, and so on. But what is important, as they relate to this guide, is that seen in a telescope (or binoculars, or even the naked eye), they can be glorious, with a dazzling array of colors, brightnesses, and even shapes with arcs and streams, wisps of nebulosity, and dark dust lanes, making them literally breathtaking.

  19. Clustering in a quark gas

    SciTech Connect

    Welke, G.M.; Heiss, W.D.

    1986-04-01

    In an infinite one-dimensional quark gas it is shown that a static color force, which increases at large distance, leads to a density fluctuation in the ground state. A self-consistent mean field can only be found for an effectively attractive quark-quark interaction that increases less than linearly at large distances. For a fixed coupling constant, the clustering disappears at high quark density.

  20. [Cluster headache and brain imagery].

    PubMed

    Giraud, Pierric; Demarquay, Geneviève

    2015-11-01

    Cluster headache is defined on clinical international criteria developed by International Headache Society (IHS, 2013). The realization of a brain MRI with arterial angio-MRI is required according to the French recommendations (Donnet et al., 2014) based on recent the literature. Numerous causes or diseases can mimic typical or atypical AVF (Edvardsson, 2014). Identification of these causes allows an appropriate treatment in addition with symptomatic treatment. PMID:26585270

  1. Luminosity function for galaxy clusters

    NASA Astrophysics Data System (ADS)

    Bajan, K.; Biernacka, M.; Flin, P.; Godłowski, W.; Panko, E.; Popiela, J.

    2016-10-01

    We constructed and studied the luminosity function of 6188 galaxyclusters. This was performed by counting brightness of galaxiesbelonging to clusters in the PF catalogue, taking galaxy data fromMRSS. Our result shows that the investigated structures arecharacterized by a luminosity function different from that ofoptical galaxies and radiogalaxies (Machalski & Godłowski2000). The implications of this result for theoriesof galaxy formation are briefly discussed.

  2. Customer Behavior Clustering Using SVM

    NASA Astrophysics Data System (ADS)

    Yang, Zhongying; Su, Xiaolong

    In order to supply better service for network customers, deeply analyzing customers' behavior is required. This paper extracts three features from customers' network behavior which is divided into different categories, such as browsing news, downloading shared resources and real-time communications etc. Support vector machine is used to perform clustering, thanks to its fast and valid executing, especially in the situation of small datasets. Using the analysis results, we can make our applications and services more personalized and easier to be used.

  3. cluster-lensing: Tools for calculating properties and weak lensing profiles of galaxy clusters

    NASA Astrophysics Data System (ADS)

    Ford, Jes

    2016-05-01

    The cluster-lensing package calculates properties and weak lensing profiles of galaxy clusters. Implemented in Python, it includes cluster mass-richness and mass-concentration scaling relations, and NFW halo profiles for weak lensing shear, the differential surface mass density ΔΣ(r), and for magnification, Σ(r). Optionally the calculation will include the effects of cluster miscentering offsets.

  4. Applications of cluster analysis to the creation of perfectionism profiles: a comparison of two clustering approaches

    PubMed Central

    Bolin, Jocelyn H.; Edwards, Julianne M.; Finch, W. Holmes; Cassady, Jerrell C.

    2014-01-01

    Although traditional clustering methods (e.g., K-means) have been shown to be useful in the social sciences it is often difficult for such methods to handle situations where clusters in the population overlap or are ambiguous. Fuzzy clustering, a method already recognized in many disciplines, provides a more flexible alternative to these traditional clustering methods. Fuzzy clustering differs from other traditional clustering methods in that it allows for a case to belong to multiple clusters simultaneously. Unfortunately, fuzzy clustering techniques remain relatively unused in the social and behavioral sciences. The purpose of this paper is to introduce fuzzy clustering to these audiences who are currently relatively unfamiliar with the technique. In order to demonstrate the advantages associated with this method, cluster solutions of a common perfectionism measure were created using both fuzzy clustering and K-means clustering, and the results compared. Results of these analyses reveal that different cluster solutions are found by the two methods, and the similarity between the different clustering solutions depends on the amount of cluster overlap allowed for in fuzzy clustering. PMID:24795683

  5. A Test for Cluster Bias: Detecting Violations of Measurement Invariance across Clusters in Multilevel Data

    ERIC Educational Resources Information Center

    Jak, Suzanne; Oort, Frans J.; Dolan, Conor V.

    2013-01-01

    We present a test for cluster bias, which can be used to detect violations of measurement invariance across clusters in 2-level data. We show how measurement invariance assumptions across clusters imply measurement invariance across levels in a 2-level factor model. Cluster bias is investigated by testing whether the within-level factor loadings…

  6. The Earth Observation Technology Cluster

    NASA Astrophysics Data System (ADS)

    Aplin, P.; Boyd, D. S.; Danson, F. M.; Donoghue, D. N. M.; Ferrier, G.; Galiatsatos, N.; Marsh, A.; Pope, A.; Ramirez, F. A.; Tate, N. J.

    2012-07-01

    The Earth Observation Technology Cluster is a knowledge exchange initiative, promoting development, understanding and communication about innovative technology used in remote sensing of the terrestrial or land surface. This initiative provides an opportunity for presentation of novel developments from, and cross-fertilisation of ideas between, the many and diverse members of the terrestrial remote sensing community. The Earth Observation Technology Cluster involves a range of knowledge exchange activities, including organisation of technical events, delivery of educational materials, publication of scientific findings and development of a coherent terrestrial EO community. The initiative as a whole covers the full range of remote sensing operation, from new platform and sensor development, through image retrieval and analysis, to data applications and environmental modelling. However, certain topical and strategic themes have been selected for detailed investigation: (1) Unpiloted Aerial Vehicles, (2) Terrestrial Laser Scanning, (3) Field-Based Fourier Transform Infra-Red Spectroscopy, (4) Hypertemporal Image Analysis, and (5) Circumpolar and Cryospheric Application. This paper presents general activities and achievements of the Earth Observation Technology Cluster, and reviews state-of-the-art developments in the five specific thematic areas.

  7. Pair extended coupled cluster doubles

    SciTech Connect

    Henderson, Thomas M.; Scuseria, Gustavo E.; Bulik, Ireneusz W.

    2015-06-07

    The accurate and efficient description of strongly correlated systems remains an important challenge for computational methods. Doubly occupied configuration interaction (DOCI), in which all electrons are paired and no correlations which break these pairs are permitted, can in many cases provide an accurate account of strong correlations, albeit at combinatorial computational cost. Recently, there has been significant interest in a method we refer to as pair coupled cluster doubles (pCCD), a variant of coupled cluster doubles in which the electrons are paired. This is simply because pCCD provides energies nearly identical to those of DOCI, but at mean-field computational cost (disregarding the cost of the two-electron integral transformation). Here, we introduce the more complete pair extended coupled cluster doubles (pECCD) approach which, like pCCD, has mean-field cost and reproduces DOCI energetically. We show that unlike pCCD, pECCD also reproduces the DOCI wave function with high accuracy. Moreover, pECCD yields sensible albeit inexact results even for attractive interactions where pCCD breaks down.

  8. Extinction in young massive clusters

    NASA Astrophysics Data System (ADS)

    De Marchi, Guido; Panagia, Nino

    2016-01-01

    Up to ages of ~100 Myr, massive clusters are still swamped in large amounts of gas and dust, causing considerable and uneven levels of extinction. At the same time, large grains (ices?) produced by type II supernovae profoundly alter the interstellar medium (ISM), thus resulting in extinction properties very different from those of the diffuse ISM. To obtain physically meaningful parameters of stars (luminosities, effective temperatures, masses, ages, etc.) we must understand and measure the local extinction law. We have developed a powerful method to unambiguously determine the extinction law everywhere across a cluster field, using multi-band photometry of red giant stars belonging to the red clump (RC) and are applying it to young massive clusters in the Local Group. In the Large Magellanic Cloud, with about 20 RC stars per arcmin2, for each field we can easily derive an accurate extinction curve over the entire wavelength range of the photometry. As an example, we present the extinction law of the Tarantula nebula (30 Dor) based on thousands of stars observed as part of the Hubble Tarantula Treasury Project. We discuss how the incautious adoption of the Milky Way extinction law in the analysis of massive star forming regions may lead to serious underestimates of the fluxes and of the star formation rates by factors of 2 or more.

  9. A GMBCG Galaxy Cluster Catalog of 55,424 Rich Clusters from SDSS DR7

    SciTech Connect

    Hao, Jiangang; McKay, Timothy A.; Koester, Benjamin P.; Rykoff, Eli S.; Rozo, Eduardo; Annis, James; Wechsler, Risa H.; Evrard, August; Siegel, Seth R.; Becker, Matthew; Busha, Michael; Gerdes, David; Johnston, David E.; Sheldon, Erin; /Brookhaven

    2011-08-22

    We present a large catalog of optically selected galaxy clusters from the application of a new Gaussian Mixture Brightest Cluster Galaxy (GMBCG) algorithm to SDSS Data Release 7 data. The algorithm detects clusters by identifying the red sequence plus Brightest Cluster Galaxy (BCG) feature, which is unique for galaxy clusters and does not exist among field galaxies. Red sequence clustering in color space is detected using an Error Corrected Gaussian Mixture Model. We run GMBCG on 8240 square degrees of photometric data from SDSS DR7 to assemble the largest ever optical galaxy cluster catalog, consisting of over 55,000 rich clusters across the redshift range from 0.1 < z < 0.55. We present Monte Carlo tests of completeness and purity and perform cross-matching with X-ray clusters and with the maxBCG sample at low redshift. These tests indicate high completeness and purity across the full redshift range for clusters with 15 or more members.

  10. A GMBCG galaxy cluster catalog of 55,880 rich clusters from SDSS DR7

    SciTech Connect

    Hao, Jiangang; McKay, Timothy A.; Koester, Benjamin P.; Rykoff, Eli S.; Rozo, Eduardo; Annis, James; Wechsler, Risa H.; Evrard, August; Siegel, Seth R.; Becker, Matthew; Busha, Michael; /Fermilab /Michigan U. /Chicago U., Astron. Astrophys. Ctr. /UC, Santa Barbara /KICP, Chicago /KIPAC, Menlo Park /SLAC /Caltech /Brookhaven

    2010-08-01

    We present a large catalog of optically selected galaxy clusters from the application of a new Gaussian Mixture Brightest Cluster Galaxy (GMBCG) algorithm to SDSS Data Release 7 data. The algorithm detects clusters by identifying the red sequence plus Brightest Cluster Galaxy (BCG) feature, which is unique for galaxy clusters and does not exist among field galaxies. Red sequence clustering in color space is detected using an Error Corrected Gaussian Mixture Model. We run GMBCG on 8240 square degrees of photometric data from SDSS DR7 to assemble the largest ever optical galaxy cluster catalog, consisting of over 55,000 rich clusters across the redshift range from 0.1 < z < 0.55. We present Monte Carlo tests of completeness and purity and perform cross-matching with X-ray clusters and with the maxBCG sample at low redshift. These tests indicate high completeness and purity across the full redshift range for clusters with 15 or more members.

  11. Symmetry Based Automatic Evolution of Clusters: A New Approach to Data Clustering

    PubMed Central

    Vijendra, Singh; Laxman, Sahoo

    2015-01-01

    We present a multiobjective genetic clustering approach, in which data points are assigned to clusters based on new line symmetry distance. The proposed algorithm is called multiobjective line symmetry based genetic clustering (MOLGC). Two objective functions, first the Davies-Bouldin (DB) index and second the line symmetry distance based objective functions, are used. The proposed algorithm evolves near-optimal clustering solutions using multiple clustering criteria, without a priori knowledge of the actual number of clusters. The multiple randomized K dimensional (Kd) trees based nearest neighbor search is used to reduce the complexity of finding the closest symmetric points. Experimental results based on several artificial and real data sets show that proposed clustering algorithm can obtain optimal clustering solutions in terms of different cluster quality measures in comparison to existing SBKM and MOCK clustering algorithms. PMID:26339233

  12. Dynamic Clustering in Suspension of Motile Bacteria

    NASA Astrophysics Data System (ADS)

    Zhang, Hepeng; Chen, Xiao; Yang, Xiang; Yang, Mingcheng

    2015-03-01

    Bacteria suspension exhibits a wide range of collective phenomena arising from interactions between individual cells. Here we investigate dynamic clusters of motile bacteria near an air-liquid interface. Cell in a cluster orient its flagella perpendicular to the interface and generate attractive radial fluid flow that leads to cluster formation. Rotating cell also creates tangential forces on neighbors that sets clusters into counter-clockwise rotation. We construct a numerical model of self-propelled particles that interact via pair-wise forces extracted from hydrodynamic calculations; such a model reproduces many properties of observed cluster dynamics.

  13. Atomic scale dynamics of ultrasmall germanium clusters

    PubMed Central

    Bals, S.; Van Aert, S.; Romero, C.P.; Lauwaet, K.; Van Bael, M.J.; Schoeters, B.; Partoens, B.; Yücelen, E.; Lievens, P.; Van Tendeloo, G.

    2012-01-01

    Starting from the gas phase, small clusters can be produced and deposited with huge flexibility with regard to composition, materials choice and cluster size. Despite many advances in experimental characterization, a detailed morphology of such clusters is still lacking. Here we present an atomic scale observation as well as the dynamical behaviour of ultrasmall germanium clusters. Using quantitative scanning transmission electron microscopy in combination with ab initio calculations, we are able to characterize the transition between different equilibrium geometries of a germanium cluster consisting of less than 25 atoms. Seven-membered rings, trigonal prisms and some smaller subunits are identified as possible building blocks that stabilize the structure. PMID:22692540

  14. Atomic scale dynamics of ultrasmall germanium clusters.

    PubMed

    Bals, S; Van Aert, S; Romero, C P; Lauwaet, K; Van Bael, M J; Schoeters, B; Partoens, B; Yücelen, E; Lievens, P; Van Tendeloo, G

    2012-06-12

    Starting from the gas phase, small clusters can be produced and deposited with huge flexibility with regard to composition, materials choice and cluster size. Despite many advances in experimental characterization, a detailed morphology of such clusters is still lacking. Here we present an atomic scale observation as well as the dynamical behaviour of ultrasmall germanium clusters. Using quantitative scanning transmission electron microscopy in combination with ab initio calculations, we are able to characterize the transition between different equilibrium geometries of a germanium cluster consisting of less than 25 atoms. Seven-membered rings, trigonal prisms and some smaller subunits are identified as possible building blocks that stabilize the structure.

  15. Ultraviolet colors of old LMC clusters

    NASA Technical Reports Server (NTRS)

    Cowley, A. P.; Hartwick, F. D. A.

    1992-01-01

    New ultraviolet spectra for five red LMC globular clusters have been obtained with IUE. These have been supplemented with archival spectra for eleven old LMC clusters. These data strengthen and extend the UV-color versus age relation for clusters older than about 10 exp 9 yr, but do not offer much precision in age determination, presumably because the ultraviolet colors of the oldest clusters depend strongly on the horizontal-branch morphology. Comparison of LMC data with UV colors for the brightest M31 clusters suggests their ages might be only a few gigayears.

  16. Efficient clustering aggregation based on data fragments.

    PubMed

    Wu, Ou; Hu, Weiming; Maybank, Stephen J; Zhu, Mingliang; Li, Bing

    2012-06-01

    Clustering aggregation, known as clustering ensembles, has emerged as a powerful technique for combining different clustering results to obtain a single better clustering. Existing clustering aggregation algorithms are applied directly to data points, in what is referred to as the point-based approach. The algorithms are inefficient if the number of data points is large. We define an efficient approach for clustering aggregation based on data fragments. In this fragment-based approach, a data fragment is any subset of the data that is not split by any of the clustering results. To establish the theoretical bases of the proposed approach, we prove that clustering aggregation can be performed directly on data fragments under two widely used goodness measures for clustering aggregation taken from the literature. Three new clustering aggregation algorithms are described. The experimental results obtained using several public data sets show that the new algorithms have lower computational complexity than three well-known existing point-based clustering aggregation algorithms (Agglomerative, Furthest, and LocalSearch); nevertheless, the new algorithms do not sacrifice the accuracy. PMID:22334025

  17. XMM Newton Observations of Toothbrush Cluster

    NASA Astrophysics Data System (ADS)

    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.

  18. Directional clustering in highest energy cosmic rays

    SciTech Connect

    Goldberg, Haim; Weiler, Thomas J.

    2001-09-01

    An unexpected degree of small-scale clustering is observed in highest-energy cosmic ray events. Some directional clustering can be expected due to purely statistical fluctuations for sources distributed randomly in the sky. This creates a background for events originating in clustered sources. We derive analytic formulas to estimate the probability of random cluster configurations, and use these formulas to study the strong potential of the HiRes, Auger, Telescope Array and EUSO-OWL-AirWatch facilities for deciding whether any observed clustering is most likely due to nonrandom sources. For a detailed comparison to data, our analytical approach cannot compete with Monte Carlo simulations, including experimental systematics. However, our derived formulas do offer two advantages: (i) easy assessment of the significance of any observed clustering, and most importantly, (ii) an explicit dependence of cluster probabilities on the chosen angular bin size.

  19. Cluster size diversity, percolation, and complex systems.

    PubMed

    Tsang, I R; Tsang, I J

    1999-09-01

    Diversity of cluster size has been used as a measurement of complexity in several systems that generate a statistical distribution of clusters. Using Monte Carlo simulations, we present a statistical analysis of the cluster size diversity and the number of clusters generated on randomly occupied lattices for the Euclidean dimensions 1 to 6. A tuning effect for diversity of cluster size and critical probabilities associated with the maximum diversity and the maximum number of clusters are reported. The probability of maximum diversity is related to the percolation threshold and several scaling relations between the variables measured are reported. The statistics of cluster size diversity has important consequences in the statistical description of the Universe as a complex system. PMID:11970070

  20. Hesitant fuzzy agglomerative hierarchical clustering algorithms

    NASA Astrophysics Data System (ADS)

    Zhang, Xiaolu; Xu, Zeshui

    2015-02-01

    Recently, hesitant fuzzy sets (HFSs) have been studied by many researchers as a powerful tool to describe and deal with uncertain data, but relatively, very few studies focus on the clustering analysis of HFSs. In this paper, we propose a novel hesitant fuzzy agglomerative hierarchical clustering algorithm for HFSs. The algorithm considers each of the given HFSs as a unique cluster in the first stage, and then compares each pair of the HFSs by utilising the weighted Hamming distance or the weighted Euclidean distance. The two clusters with smaller distance are jointed. The procedure is then repeated time and again until the desirable number of clusters is achieved. Moreover, we extend the algorithm to cluster the interval-valued hesitant fuzzy sets, and finally illustrate the effectiveness of our clustering algorithms by experimental results.

  1. UNCLOAKING GLOBULAR CLUSTERS IN THE INNER GALAXY

    SciTech Connect

    Alonso-Garcia, Javier; Catelan, Marcio; Minniti, Dante; Mateo, Mario; Sen, Bodhisattva; Banerjee, Moulinath; Von Braun, Kaspar E-mail: mcatelan@astro.puc.cl E-mail: mmateo@umich.edu E-mail: moulib@umich.edu

    2012-03-15

    Extensive photometric studies of the globular clusters located toward the center of the Milky Way have been historically neglected. The presence of patchy differential reddening in front of these clusters has proven to be a significant obstacle to their detailed study. We present here a well defined and reasonably homogeneous photometric database for 25 of the brightest Galactic globular clusters located in the direction of the inner Galaxy. These data were obtained in the B, V, and I bands using the Magellan 6.5 m Telescope and the Hubble Space Telescope. A new technique is extensively used in this paper to map the differential reddening in the individual cluster fields, and to produce cleaner, dereddened color-magnitude diagrams for all the clusters in the database. Subsequent papers will detail the astrophysical analysis of the cluster populations, and the properties of the obscuring material along the clusters' lines of sight.

  2. Countdown for the Cluster quartet

    NASA Astrophysics Data System (ADS)

    2000-07-01

    Following the successful completion of the Cluster II Flight Readiness Review on 23 June, final launch preparations are progressing smoothly and combined operations with the Soyuz-Fregat launch vehicle are now under way. The dual launches, each involving two Cluster spacecraft built under the prime contractorship of Astrium (former Dornier Satellitensysteme GmbH, Germany), are currently scheduled for 15 July with a launch window opening at 14:40 CEST, 12:40 GMT and lasting 6 minutes, and 9 August from Baikonur Space Centre in Kazakhstan. A number of press events have been organised in various countries to coincide with both launches. The main press centre for the first launch will be located at ESA's European Space Operations Centre (ESOC) at Darmstadt in Germany. Local press centres are also being set up in the other ESA establishments: ESRIN (Italy), ESTEC (The Netherlands), and VILSPA (Spain). See attachment for more detailed information and reply form to register at the various sites. Details of the second launch press event, which will be held in London (UK), will be available at a later date. Cluster II Competition Attracts Record Entries. A highlight of the first launch event at ESOC will be the announcement of the overall winner of ESA's "Name the Cluster quartet" competition and the chosen names of the four Cluster II satellites. Last February, members of the public in all of ESA's 15 member states were asked to suggest the most suitable names for the Cluster II spacecraft. The satellites are currently known as flight models (FM) 5, 6, 7 and 8. Competitors were asked to propose a set of four names (places, people, or things from history, mythology, or fiction, but not living persons) and explain in a few sentences the reasons for their choice. After sifting through more than 5,000 entries from all over Europe and debating at length the merits of the various suggestions, the multinational jury eventually produced a list of 15 national prize winners - one

  3. Star Cluster Buzzing With Pulsars

    NASA Astrophysics Data System (ADS)

    2005-01-01

    A dense globular star cluster near the center of our Milky Way Galaxy holds a buzzing beehive of rapidly-spinning millisecond pulsars, according to astronomers who discovered 21 new pulsars in the cluster using the National Science Foundation's 100-meter Robert C. Byrd Green Bank Telescope (GBT) in West Virginia. The cluster, called Terzan 5, now holds the record for pulsars, with 24, including three known before the GBT observations. Pulsar Diagram Pulsar Diagram: Click on image for more detail. "We hit the jackpot when we looked at this cluster," said Scott Ransom, an astronomer at the National Radio Astronomy Observatory in Charlottesville, VA. "Not only does this cluster have a lot of pulsars -- and we still expect to find more in it -- but the pulsars in it are very interesting. They include at least 13 in binary systems, two of which are eclipsing, and the four fastest-rotating pulsars known in any globular cluster, with the fastest two rotating nearly 600 times per second, roughly as fast as a household blender," Ransom added. Ransom and his colleagues reported their findings to the American Astronomical Society's meeting in San Diego, CA, and in the online journal Science Express. The star cluster's numerous pulsars are expected to yield a bonanza of new information about not only the pulsars themselves, but also about the dense stellar environment in which they reside and probably even about nuclear physics, according to the scientists. For example, preliminary measurements indicate that two of the pulsars are more massive than some theoretical models would allow. "All these exotic pulsars will keep us busy for years to come," said Jason Hessels, a Ph.D student at McGill University in Montreal. Globular clusters are dense agglomerations of up to millions of stars, all of which formed at about the same time. Pulsars are spinning, superdense neutron stars that whirl "lighthouse beams" of radio waves or light around as they spin. A neutron star is what is

  4. DISTANT CLUSTER OF GALAXIES [left

    NASA Technical Reports Server (NTRS)

    2002-01-01

    One of the deepest images to date of the universe, taken with NASA's Hubble Space Telescope (HST), reveals thousands of faint galaxies at the detection limit of present day telescopes. Peering across a large volume of the observable cosmos, Hubble resolves thousands of galaxies from five to twelve billion light-years away. The light from these remote objects has taken billions of years to cross the expanding universe, making these distant galaxies fossil evidence' of events that happened when the universe was one-third its present age. A fraction of the galaxies in this image belong to a cluster located nine billion light-years away. Though the field of view (at the cluster's distance) is only two million light-years across, it contains a multitude of fragmentary objects. (By comparison, the two million light-years between our Milky Way galaxy and its nearest large companion galaxy, in the constellation Andromeda, is essentially empty space!) Very few of the cluster's members are recognizable as normal spiral galaxies (like our Milky Way), although some elongated members might be edge-on disks. Among this zoo of odd galaxies are ``tadpole-like'' objects, disturbed and apparently merging systems dubbed 'train-wrecks,' and a multitude of faint, tiny shards and fragments, dwarf galaxies or possibly an unknown population of objects. However, the cluster also contains red galaxies that resemble mature examples of today's elliptical galaxies. Their red color comes from older stars that must have formed shortly after the Big Bang. The image is the full field view of the Wide Field and Planetary Camera-2. The picture was taken in intervals between May 11 and June 15, 1994 and required an 18-hour long exposure, over 32 orbits of HST, to reveal objects down to 29th magnitude. [bottom right] A close up view of the peculiar radio galaxy 3C324 used to locate the cluster. The galaxy is nine billion light-years away as measured by its spectral redshift (z=1.2), and located in the

  5. Hot outflows in galaxy clusters

    NASA Astrophysics Data System (ADS)

    Kirkpatrick, C. C.; McNamara, B. R.

    2015-10-01

    The gas-phase metallicity distribution has been analysed for the hot atmospheres of 29 galaxy clusters using Chandra X-ray Observatory observations. All host brightest cluster galaxies (BCGs) with X-ray cavity systems produced by radio AGN. We find high elemental abundances projected preferentially along the cavities of 16 clusters. The metal-rich plasma was apparently lifted out of the BCGs with the rising X-ray cavities (bubbles) to altitudes between twenty and several hundred kiloparsecs. A relationship between the maximum projected altitude of the uplifted gas (the `iron radius') and jet power is found with the form R_Fe ∝ P_jet^{0.45}. The estimated outflow rates are typically tens of solar masses per year but exceed 100 M⊙ yr- 1 in the most powerful AGN. The outflow rates are 10-20 per cent of the cooling rates, and thus alone are unable to offset a cooling inflow. Nevertheless, hot outflows effectively redistribute the cooling gas and may play a significant role at regulating star formation and AGN activity in BCGs and presumably in giant elliptical galaxies. The metallicity distribution overall can be complex, perhaps due to metal-rich gas returning in circulation flows or being blown around in the hot atmospheres. Roughly 15 per cent of the work done by the cavities is expended lifting the metal-enriched gas, implying their nuclear black holes have increased in mass by at least ˜107-109 M⊙. Finally, we show that hot outflows can account for the broad, gas-phase metallicity distribution compared to the stellar light profiles of BCGs, and we consider a possible connection between hot outflows and cold molecular gas flows discovered in recent Atacama Large Millimeter Array observations.

  6. Sound oscillation of dropwise cluster

    NASA Astrophysics Data System (ADS)

    Shavlov, A. V.; Dzhumandzhi, V. A.; Romanyuk, S. N.

    2012-06-01

    There was registered sound oscillation of a dropwise cluster formed over the warmed-up water surface. We have calculated the electrical charge of drops on the basis of experimental data on ion-sound oscillation. It was demonstrated that the charge is proportional to surface area of the drops and does not depend on intensity of their evaporation (condensation) in the range of 60-100 °C. The charge of drops reaches 102-103 units of elementary charge and coincides on magnitude order with the literary value of a charge calculated by another method.

  7. Pinwheels in the Quintuplet cluster.

    PubMed

    Tuthill, Peter; Monnier, John; Tanner, Angelle; Figer, Donald; Ghez, Andrea; Danchi, William

    2006-08-18

    The five enigmatic cocoon stars, after which the Quintuplet cluster was christened, have puzzled astronomers since their discovery. Their extraordinary cool, featureless thermal spectra have been attributed to various stellar types from young to highly evolved, whereas their absolute luminosities place them among the supergiants. We present diffraction-limited images from the Keck 1 telescope that resolve this debate with the identification of rotating spiral plumes characteristic of colliding-wind binary "pinwheel" nebulae. Such elegant spiral structures, found around high-luminosity Wolf-Rayet stars, have recently been implicated in the behavior of supernovae light curves in the radio and optical. PMID:16917053

  8. Multi-viewpoint clustering analysis

    NASA Technical Reports Server (NTRS)

    Mehrotra, Mala; Wild, Chris

    1993-01-01

    In this paper, we address the feasibility of partitioning rule-based systems into a number of meaningful units to enhance the comprehensibility, maintainability and reliability of expert systems software. Preliminary results have shown that no single structuring principle or abstraction hierarchy is sufficient to understand complex knowledge bases. We therefore propose the Multi View Point - Clustering Analysis (MVP-CA) methodology to provide multiple views of the same expert system. We present the results of using this approach to partition a deployed knowledge-based system that navigates the Space Shuttle's entry. We also discuss the impact of this approach on verification and validation of knowledge-based systems.

  9. Cluster identification based on correlations

    NASA Astrophysics Data System (ADS)

    Schulman, L. S.

    2012-04-01

    The problem addressed is the identification of cooperating agents based on correlations created as a result of the joint action of these and other agents. A systematic method for using correlations beyond second moments is developed. The technique is applied to a didactic example, the identification of alphabet letters based on correlations among the pixels used in an image of the letter. As in this example, agents can belong to more than one cluster. Moreover, the identification scheme does not require that the patterns be known ahead of time.

  10. STAR cluster-finder ASIC

    SciTech Connect

    Botlo, M.; LeVine, M.J.; Scheetz, R.A.

    1997-12-31

    The STAR experiment reads out a TPC and an SVT (silicon vertex tracker), both of which require in-line pedestal subtraction, compression of ADC values from 10-bit to 8-bit, and location of time sequences representing responses to charged-particle tracks. The STAR cluster finder ASIC responds to all of these needs. Pedestal subtraction and compression are performed using lookup tables in attached RAM. We describe its design and implementation, as well as testing methodology and results of tests performed on foundry prototypes.

  11. On Charged Insulated Metallic Clusters

    NASA Astrophysics Data System (ADS)

    Dietrich, K.; Garny, M.; Pomorski, K.

    We determine the wavefunctions and eigen-values of electrons bound to a positively charged mesoscopic metallic cluster covered by an insulating surface layer. The radius of the metal core and the thickness of the insulating surface layer are of the order of a couple of Ångström. We study in particular the electromagnetic decay of externally located electrons into unoccupied internally located states which exhibits a resonance behaviour. This resonance structure has the consequence that the lifetime of the "mesoscopic atoms" may vary by up to 6 orders of magnitude depending on the values of the parameters (from sec to years).

  12. Effects of cluster location and cluster distribution on performance on the traveling salesman problem.

    PubMed

    MacGregor, James N

    2015-10-01

    Research on human performance in solving traveling salesman problems typically uses point sets as stimuli, and most models have proposed a processing stage at which stimulus dots are clustered. However, few empirical studies have investigated the effects of clustering on performance. In one recent study, researchers compared the effects of clustered, random, and regular stimuli, and concluded that clustering facilitates performance (Dry, Preiss, & Wagemans, 2012). Another study suggested that these results may have been influenced by the location rather than the degree of clustering (MacGregor, 2013). Two experiments are reported that mark an attempt to disentangle these factors. The first experiment tested several combinations of degree of clustering and cluster location, and revealed mixed evidence that clustering influences performance. In a second experiment, both factors were varied independently, showing that they interact. The results are discussed in terms of the importance of clustering effects, in particular, and perceptual factors, in general, during performance of the traveling salesman problem.

  13. Star Clusters in the Magellanic Clouds-1: Parameterisation and Classification of 1072 Clusters in the LMC

    NASA Astrophysics Data System (ADS)

    Nayak, P. K.; Subramaniam, A.; Choudhury, S.; Indu, G.; Sagar, Ram

    2016-08-01

    We have introduced a semi-automated quantitative method to estimate the age and reddening of 1072 star clusters in the Large Magellanic Cloud (LMC) using the Optical Gravitational Lensing Experiment (OGLE) III survey data. This study brings out 308 newly parameterised clusters. In a first of its kind, the LMC clusters are classified into groups based on richness/mass as very poor, poor, moderate and rich clusters, similar to the classification scheme of open clusters in the Galaxy. A major cluster formation episode is found to happen at 125±25 Myr in the inner LMC. The bar region of the LMC appears prominently in the age range 60 - 250 Myr and is found to have a relatively higher concentration of poor and moderate clusters. The eastern and the western ends of the bar are found to form clusters initially, which later propagates to the central part. We demonstrate that there is a significant difference in the distribution of clusters as a function of mass, using a movie based on the propagation (in space and time) of cluster formation in various groups. The importance of including the low mass clusters in the cluster formation history is demonstrated. The catalog with parameters, classification, and cleaned and isochrone fitted CMDs of 1072 clusters, which are available as online material, can be further used to understand the hierarchical formation of clusters in selected regions of the LMC.

  14. ClusterViz: A Cytoscape APP for Cluster Analysis of Biological Network.

    PubMed

    Wang, Jianxin; Zhong, Jiancheng; Chen, Gang; Li, Min; Wu, Fang-xiang; Pan, Yi

    2015-01-01

    Cluster analysis of biological networks is one of the most important approaches for identifying functional modules and predicting protein functions. Furthermore, visualization of clustering results is crucial to uncover the structure of biological networks. In this paper, ClusterViz, an APP of Cytoscape 3 for cluster analysis and visualization, has been developed. In order to reduce complexity and enable extendibility for ClusterViz, we designed the architecture of ClusterViz based on the framework of Open Services Gateway Initiative. According to the architecture, the implementation of ClusterViz is partitioned into three modules including interface of ClusterViz, clustering algorithms and visualization and export. ClusterViz fascinates the comparison of the results of different algorithms to do further related analysis. Three commonly used clustering algorithms, FAG-EC, EAGLE and MCODE, are included in the current version. Due to adopting the abstract interface of algorithms in module of the clustering algorithms, more clustering algorithms can be included for the future use. To illustrate usability of ClusterViz, we provided three examples with detailed steps from the important scientific articles, which show that our tool has helped several research teams do their research work on the mechanism of the biological networks. PMID:26357321

  15. Avoiding common pitfalls when clustering biological data.

    PubMed

    Ronan, Tom; Qi, Zhijie; Naegle, Kristen M

    2016-01-01

    Clustering is an unsupervised learning method, which groups data points based on similarity, and is used to reveal the underlying structure of data. This computational approach is essential to understanding and visualizing the complex data that are acquired in high-throughput multidimensional biological experiments. Clustering enables researchers to make biological inferences for further experiments. Although a powerful technique, inappropriate application can lead biological researchers to waste resources and time in experimental follow-up. We review common pitfalls identified from the published molecular biology literature and present methods to avoid them. Commonly encountered pitfalls relate to the high-dimensional nature of biological data from high-throughput experiments, the failure to consider more than one clustering method for a given problem, and the difficulty in determining whether clustering has produced meaningful results. We present concrete examples of problems and solutions (clustering results) in the form of toy problems and real biological data for these issues. We also discuss ensemble clustering as an easy-to-implement method that enables the exploration of multiple clustering solutions and improves robustness of clustering solutions. Increased awareness of common clustering pitfalls will help researchers avoid overinterpreting or misinterpreting the results and missing valuable insights when clustering biological data. PMID:27303057

  16. Biological cluster evaluation for gene function prediction.

    PubMed

    Klie, Sebastian; Nikoloski, Zoran; Selbig, Joachim

    2014-06-01

    Recent advances in high-throughput omics techniques render it possible to decode the function of genes by using the "guilt-by-association" principle on biologically meaningful clusters of gene expression data. However, the existing frameworks for biological evaluation of gene clusters are hindered by two bottleneck issues: (1) the choice for the number of clusters, and (2) the external measures which do not take in consideration the structure of the analyzed data and the ontology of the existing biological knowledge. Here, we address the identified bottlenecks by developing a novel framework that allows not only for biological evaluation of gene expression clusters based on existing structured knowledge, but also for prediction of putative gene functions. The proposed framework facilitates propagation of statistical significance at each of the following steps: (1) estimating the number of clusters, (2) evaluating the clusters in terms of novel external structural measures, (3) selecting an optimal clustering algorithm, and (4) predicting gene functions. The framework also includes a method for evaluation of gene clusters based on the structure of the employed ontology. Moreover, our method for obtaining a probabilistic range for the number of clusters is demonstrated valid on synthetic data and available gene expression profiles from Saccharomyces cerevisiae. Finally, we propose a network-based approach for gene function prediction which relies on the clustering of optimal score and the employed ontology. Our approach effectively predicts gene function on the Saccharomyces cerevisiae data set and is also employed to obtain putative gene functions for an Arabidopsis thaliana data set.

  17. Young Massive Clusters in the Galactic Center

    NASA Astrophysics Data System (ADS)

    Figer, D. F.

    2004-12-01

    The three young clusters in the Galactic Center represent the closest examples of massive starbursts and they define the upper mass limit of the Galactic cluster mass functions. In this review, I describe the characteristics and content of the Arches, Quintuplet, and Central clusters. They each are more massive than any other cluster in the Galaxy, and the Arches cluster, in particular, has a mass and age that make it ideal for studies of massive stellar evolution and dense stellar systems. A preliminary measurement indicates that the initial mass function in the Galactic center is top-heavy, suggesting an environmental effect that has otherwise been absent in similar observations for Galactic clusters. Given the relatively more evolved nature of the Quintuplet and Central clusters, these clusters contain stars in a wide range of evolutionary states, including Luminous Blue Variables and Wolf-Rayet stars. The Quintuplet cluster provides a particularly interesting view of the most massive stars that are known, the Pistol Star and FMM362. An analysis of the mass spectrum in the Arches cluster suggests an upper mass cutoff of ˜150-200 M⊙.

  18. Cluster analysis of multiple planetary flow regimes

    NASA Technical Reports Server (NTRS)

    Mo, Kingtse; Ghil, Michael

    1987-01-01

    A modified cluster analysis method was developed to identify spatial patterns of planetary flow regimes, and to study transitions between them. This method was applied first to a simple deterministic model and second to Northern Hemisphere (NH) 500 mb data. The dynamical model is governed by the fully-nonlinear, equivalent-barotropic vorticity equation on the sphere. Clusters of point in the model's phase space are associated with either a few persistent or with many transient events. Two stationary clusters have patterns similar to unstable stationary model solutions, zonal, or blocked. Transient clusters of wave trains serve as way stations between the stationary ones. For the NH data, cluster analysis was performed in the subspace of the first seven empirical orthogonal functions (EOFs). Stationary clusters are found in the low-frequency band of more than 10 days, and transient clusters in the bandpass frequency window between 2.5 and 6 days. In the low-frequency band three pairs of clusters determine, respectively, EOFs 1, 2, and 3. They exhibit well-known regional features, such as blocking, the Pacific/North American (PNA) pattern and wave trains. Both model and low-pass data show strong bimodality. Clusters in the bandpass window show wave-train patterns in the two jet exit regions. They are related, as in the model, to transitions between stationary clusters.

  19. Photometric Properties of Galaxies in Poor Clusters

    NASA Astrophysics Data System (ADS)

    Sharma, M.; Prabhu, T.

    We study several statistical properties of galaxies in four poor clusters of galaxies using optical photometry. We select these poor clusters as luminous, extended X-ray sources identified with poor galaxy systems in the EMSS catalogue of clusters of galaxies. The clusters are at moderate redshifts (0.08Cluster. The fraction of blue galaxies is similar to those of low-redshift richness 0 clusters and higher than those of richer clusters at similar redshifts. The luminosity functions (LFs) of the individual clusters are not significantly different from each other. Using these, we construct composite LFs in B, V , and R bands (to MV=-18). The faint-end of these LFs are flat, like the V-band LF of other (e.g., MKW/AWM) poor clusters, but steeper than the field LF in the R-band. In terms of the statistical properties of their member galaxies, poor clusters appear to be lower-mass extensions of their rich counterparts.

  20. Inflammatory breast cancer clusters: A hypothesis

    PubMed Central

    Levine, Paul H; Hashmi, Salman; Minaei, Ashley A; Veneroso, Carmela

    2014-01-01

    Cancer clusters have long been a focus of interest because of the possibility of identifying etiologic agents. Only on rare occasions, however, have such cluster investigations been successful. One major difficulty in cluster investigations, particularly in the area of breast cancer, is the long latent period. There have been a number of publications providing a discouraging picture regarding cancer cluster investigations. The possibility of learning from a cluster investigation, however, is greatly increased if the cancer involved is relatively rare and if it has a short latent period. Inflammatory breast cancer (IBC) fits these criteria and is worth pursuing because of the strong evidence that environmental factors play a major role. In this report we describe our experience with several clusters and the lessons learned which are now being utilized to improve investigation of future IBC clusters. The first IBC cluster that we evaluated was in 2000, when we were asked to investigate an apparent cluster of IBC in Castro Valley, California where three women in an office setting of 24 people were diagnosed with IBC in a ten month period from May 1999 to March 2000. Our investigation of this striking cluster did not yield a specific trigger for this cluster but it did indicate that the women involved all had at least two IBC risk factors that may well have made them susceptible to getting IBC. We are now investigating another apparent cluster in Texas and are aware of several others requiring careful consideration. We see a need for a consistent protocol for the evaluation of IBC clusters focusing on the laboratory investigation of environmental triggers, primarily infectious agents and chemical carcinogens. PMID:25114867

  1. THE SIZE SCALE OF STAR CLUSTERS

    SciTech Connect

    Madrid, Juan P.; Hurley, Jarrod R.; Sippel, Anna C.

    2012-09-10

    Direct N-body simulations of star clusters in a realistic Milky-Way-like potential are carried out using the code NBODY6. Based on these simulations, a new relationship between scale size and galactocentric distance is derived: the scale size of star clusters is proportional to the hyperbolic tangent of the galactocentric distance. The half-mass radius of star clusters increases systematically with galactocentric distance but levels off when star clusters orbit the galaxy beyond {approx}40 kpc. These simulations show that the half-mass radius of individual star clusters varies significantly as they evolve over a Hubble time, more so for clusters with shorter relaxation times, and remains constant through several relaxation times only in certain situations when expansion driven by the internal dynamics of the star cluster and the influence of the host galaxy tidal field balance each other. Indeed, the radius of a star cluster evolving within the inner 20 kpc of a realistic galactic gravitational potential is severely truncated by tidal interactions and does not remain constant over a Hubble time. Furthermore, the half-mass radius of star clusters measured with present-day observations bears no memory of the original cluster size. Stellar evolution and tidal stripping are the two competing physical mechanisms that determine the present-day size of globular clusters. These simulations also show that extended star clusters can form at large galactocentric distances while remaining fully bound to the host galaxy. There is thus no need to invoke accretion from an external galaxy to explain the presence of extended clusters at large galactocentric distances in a Milky-Way-type galaxy.

  2. Studying Dark Energy with Galaxy Cluster Surveys

    NASA Astrophysics Data System (ADS)

    Mohr, J.; Majumdar, S.

    2003-05-01

    Galaxy cluster surveys provide a powerful means of studying the amount and nature of the dark energy. Cluster surveys are complementary to studies using supernova distance estimates, because the cosmological parameter degeneracies are quite different. The redshift distribution of detected clusters in a deep, large solid angle survey is very sensitive to the dark energy equation of state, but robust constraints require mass--observable relations that connect cluster halo mass to observables such as the X-ray luminosity, Sunyaev-Zel'dovich effect distortion, galaxy light or weak lensing shear. Observed regularity in the cluster population and the application of multiple, independent mass estimators provide evidence that these scaling relations exist in the local and intermediate redshift universe. Large cluster surveys contain enough information to study the dark energy and solve for these scaling relations and their evolution with redshift. This self--calibrating nature of galaxy cluster surveys provides a level of robustness that is extremely attractive. Cosmological constraints from a survey can be improved by including more than just the redshift distribution. Limited followup of as few as 1% of the surveyed clusters to make detailed mass measurements improves the cosmological constraints. Including constraints on the mass function at each redshift provides additional power in solving for the evolution of the mass--observable relation. An analysis of the clustering of the surveyed clusters provides additional cosmological discriminating power. There are several planned or proposed cluster surveys that will take place over the next decade. Observational challenges include estimating cluster redshifts and understanding the survey completeness. These challenges vary with wavelength regime, suggesting that multiwavelength surveys provide the most promising avenue for precise galaxy cluster studies of the dark energy. This work is supported in part by the NASA Long

  3. Cubic potential models for cluster radioactivity

    NASA Astrophysics Data System (ADS)

    Shanmugam, G.

    1999-09-01

    Cluster radioactivity is a process by which nuclei equal and heavier than the a-particleis emitted spontaneously. The clusters usually emitted in this process are the a-particle, carbon, oxygen, neon, magnesium, silicon etc. When the mass of the cluster becomes comparable with the mass of the daughter, symmetric fission takes place. Thus the cluster radioactivity is an intermediate process between the well known a-decay and the spontaneous fission. In earlier years such cluster radioactivity was found mostly in actinide nuclei like radium, uranium etc. Very recently it has been predicted that such decays are possible in a new region around 114Ba. There has been an exciting experimental detection of the emission of 12C from 114Ba leading to 102Sn, which is attracting a lot of attention recently. To study the phenomenon of cluster radioactivity there are various theoretical models in vogue. The existing models generally fall under two categories: the unified fission model (UFM) and the preformed cluster model (PCM). The physics of the UFM and the PCM are completely different. The UFM considers cluster radioactivity simply as a barrier penetration phenomenon in between the fission and the a-decay without worrying about the cluster being or not being preformed in the parent nucleus. In the PCM clusters are assumed to be preborn in a parent nucleus before they could penetrate the potential barrier with a given Q-value. The basic assumption of the UFM is that heavy clusters as well as the a-particle have equal probability of being preformed. In PCM, clusters of different sizes have different probabilities of their being preformed in the parent nucleus. We have developed three fission models during the last decade using the cubic potential for the pre-scission region. The use of these models in the study of cluster radioactivity in both the actinide and barium regions will be discussed in this talk in comparison with the other existing theories.

  4. Vapor and Condensed Phase Clusters

    NASA Astrophysics Data System (ADS)

    Kathmann, Shawn

    2015-03-01

    Given the difficulty of directly observing clustering mechanisms underlying nucleation, classical and ab initio statistical mechanics provide crucial insight into the thermodynamics and kinetics of these processes. Recent experiments have shown nucleation can emit (e.g., crystalloluminescence) and be induced (e.g., IR lasers) by electromagnetic radiation. This opens up the possibility of using luminescence as an exquisite probe of the nucleation mechanism in addition to doing the reverse process by imposing external electromagnetic fields to activate specific modes of nucleation. The inclusion of electronic degrees of freedom as well as excited electronic states lies beyond classical theory. In addition, the osmotic coefficients of sub- and supersaturated aqueous electrolytes may provide quantitative insights into salt cluster distribution functions and free energies of crystal formation. Here we outline the chemical physics relevant to these findings and their consequences on how we understand and model nucleation to control and exploit the synthesis of matter. This work is sponsored by the U.S. DOE, Office of Basic Energy Sciences, Division of Chemical Science, Geosciences, and Biosciences. Pacific Northwest National Laboratory is a multiprogram national laboratory operated for DOE by Battelle.

  5. Understanding of multimetallic cluster growth

    PubMed Central

    Mitzinger, Stefan; Broeckaert, Lies; Massa, Werner; Weigend, Florian; Dehnen, Stefanie

    2016-01-01

    The elucidation of formation mechanisms is mandatory for understanding and planning of synthetic routes. For (bio-)organic and organometallic compounds, this has long been realized even for very complicated molecules, whereas the formation of ligand-free inorganic molecules has widely remained a black box to date. This is due to poor structural relationships between reactants and products and the lack of structurally related intermediates—due to the comparably high coordination flexibility of involved atoms. Here we report on investigations of the stepwise formation of multimetallic clusters, based on a series of crystal structures and complementary quantum-chemical studies of (Ge2As2)2−, (Ge7As2)2−, [Ta@Ge6As4]3−, [Ta@Ge8As4]3− and [Ta@Ge8As6]3−. The study makes use of efficient quantum-chemical tools, enabling the first detailed screening of the energy hypersurface along the formation of ligand-free inorganic species for a semi-quantitative picture. The results can be generalized for an entire family of multimetallic clusters. PMID:26805602

  6. Understanding of multimetallic cluster growth.

    PubMed

    Mitzinger, Stefan; Broeckaert, Lies; Massa, Werner; Weigend, Florian; Dehnen, Stefanie

    2016-01-25

    The elucidation of formation mechanisms is mandatory for understanding and planning of synthetic routes. For (bio-)organic and organometallic compounds, this has long been realized even for very complicated molecules, whereas the formation of ligand-free inorganic molecules has widely remained a black box to date. This is due to poor structural relationships between reactants and products and the lack of structurally related intermediates--due to the comparably high coordination flexibility of involved atoms. Here we report on investigations of the stepwise formation of multimetallic clusters, based on a series of crystal structures and complementary quantum-chemical studies of (Ge2As2)(2-), (Ge7As2)(2-), [Ta@Ge6As4](3-), [Ta@Ge8As4](3-) and [Ta@Ge8As6](3-). The study makes use of efficient quantum-chemical tools, enabling the first detailed screening of the energy hypersurface along the formation of ligand-free inorganic species for a semi-quantitative picture. The results can be generalized for an entire family of multimetallic clusters.

  7. Overlapping clusters for distributed computation.

    SciTech Connect

    Mirrokni, Vahab; Andersen, Reid; Gleich, David F.

    2010-11-01

    Scalable, distributed algorithms must address communication problems. We investigate overlapping clusters, or vertex partitions that intersect, for graph computations. This setup stores more of the graph than required but then affords the ease of implementation of vertex partitioned algorithms. Our hope is that this technique allows us to reduce communication in a computation on a distributed graph. The motivation above draws on recent work in communication avoiding algorithms. Mohiyuddin et al. (SC09) design a matrix-powers kernel that gives rise to an overlapping partition. Fritzsche et al. (CSC2009) develop an overlapping clustering for a Schwarz method. Both techniques extend an initial partitioning with overlap. Our procedure generates overlap directly. Indeed, Schwarz methods are commonly used to capitalize on overlap. Elsewhere, overlapping communities (Ahn et al, Nature 2009; Mishra et al. WAW2007) are now a popular model of structure in social networks. These have long been studied in statistics (Cole and Wishart, CompJ 1970). We present two types of results: (i) an estimated swapping probability {rho}{infinity}; and (ii) the communication volume of a parallel PageRank solution (link-following {alpha} = 0.85) using an additive Schwarz method. The volume ratio is the amount of extra storage for the overlap (2 means we store the graph twice). Below, as the ratio increases, the swapping probability and PageRank communication volume decreases.

  8. Deconstructing the Antlia cluster core

    NASA Astrophysics Data System (ADS)

    Caso, J. P.; Richtler, T.

    2015-12-01

    Context. The present literature does not give a satisfactory answer to the question about the nature of the "Antlia galaxy cluster". Aims: The radial velocities of galaxies found in the region around the giant ellipticals NGC 3258/3268 range from about 1000 km s-1 to 4000 km s-1. We characterise this region and its possible kinematical and population substructure. Methods: We have obtained VLT-VIMOS multi-object spectra of the galaxy population in the inner part of the Antlia cluster and measure radial velocities for 45 potential members. We supplement our galaxy sample with literature data, ending up with 105 galaxy velocities. Results: We find a large radial velocity dispersion for the entire sample as reported in previous papers. However, we find three groups at about 1900 km s-1, 2800 km s-1, and 3700 km s-1, which we interpret as differences in the recession velocities rather than peculiar velocities. Conclusions: The high radial velocity dispersion of galaxies in the Antlia region reflects a considerable extension along the line of sight. Appendix A is available in electronic form at http://www.aanda.org

  9. Countdown for the Cluster quartet

    NASA Astrophysics Data System (ADS)

    2000-07-01

    Following the successful completion of the Cluster II Flight Readiness Review on 23 June, final launch preparations are progressing smoothly and combined operations with the Soyuz-Fregat launch vehicle are now under way. The dual launches, each involving two Cluster spacecraft built under the prime contractorship of Astrium (former Dornier Satellitensysteme GmbH, Germany), are currently scheduled for 15 July with a launch window opening at 14:40 CEST, 12:40 GMT and lasting 6 minutes, and 9 August from Baikonur Space Centre in Kazakhstan. A number of press events have been organised in various countries to coincide with both launches. The main press centre for the first launch will be located at ESA's European Space Operations Centre (ESOC) at Darmstadt in Germany. Local press centres are also being set up in the other ESA establishments: ESRIN (Italy), ESTEC (The Netherlands), and VILSPA (Spain). See attachment for more detailed information and reply form to register at the various sites. Details of the second launch press event, which will be held in London (UK), will be available at a later date. Cluster II Competition Attracts Record Entries. A highlight of the first launch event at ESOC will be the announcement of the overall winner of ESA's "Name the Cluster quartet" competition and the chosen names of the four Cluster II satellites. Last February, members of the public in all of ESA's 15 member states were asked to suggest the most suitable names for the Cluster II spacecraft. The satellites are currently known as flight models (FM) 5, 6, 7 and 8. Competitors were asked to propose a set of four names (places, people, or things from history, mythology, or fiction, but not living persons) and explain in a few sentences the reasons for their choice. After sifting through more than 5,000 entries from all over Europe and debating at length the merits of the various suggestions, the multinational jury eventually produced a list of 15 national prize winners - one

  10. Critical exponents from cluster coefficients

    NASA Astrophysics Data System (ADS)

    Rotman, Z.; Eisenberg, E.

    2009-09-01

    For a large class of repulsive interaction models, the Mayer cluster integrals can be transformed into a tridiagonal real symmetric matrix Rmn , whose elements converge to two constants. This allows for an effective extrapolation of the equation of state for these models. Due to a nearby (nonphysical) singularity on the negative real z axis, standard methods (e.g., Padé approximants based on the cluster integrals expansion) fail to capture the behavior of these models near the ordering transition, and, in particular, do not detect the critical point. A recent work [E. Eisenberg and A. Baram, Proc. Natl. Acad. Sci. U.S.A. 104, 5755 (2007)] has shown that the critical exponents σ and σ' , characterizing the singularity of the density as a function of the activity, can be exactly calculated if the decay of the R matrix elements to their asymptotic constant follows a 1/n2 law. Here we employ renormalization group (RG) arguments to extend this result and analyze cases for which the asymptotic approach of the R matrix elements toward their limiting value is of a more general form. The relevant asymptotic correction terms (in RG sense) are identified, and we then present a corrected exact formula for the critical exponents. We identify the limits of usage of the formula and demonstrate one physical model, which is beyond its range of validity. The formula is validated numerically and then applied to analyze a number of concrete physical models.

  11. Challenges in nonlinear gravitational clustering

    NASA Astrophysics Data System (ADS)

    Padmanabhan, Thanu

    2006-04-01

    This article addresses some issues related to the statistical description of gravitating systems in an expanding backgrounds. In particular, I describe (a) how the nonlinear mode-mode coupling transfers power from one scale to another in the Fourier space if the initial power spectrum is sharply peaked at a given scale and (b) what are the asymptotic characteristics of gravitational clustering that are independent of the initial conditions. The analysis uses a new approach based on an integro-differential equation for the evolution of the gravitational potential in the Fourier space. I show how this equation allows one to understand several aspects of nonlinear gravitational clustering and provides insight in to the transfer of power from one scale to another through nonlinear mode coupling. Numerical simulations as well as analytic work shows that power transfer leads to a universal power spectrum at late times, somewhat reminiscent of the existence of Kolmogorov spectrum in fluid turbulence. To cite this article: T. Padmanabhan, C. R. Physique 7 (2006).

  12. Galaxy clustering on large scales.

    PubMed

    Efstathiou, G

    1993-06-01

    I describe some recent observations of large-scale structure in the galaxy distribution. The best constraints come from two-dimensional galaxy surveys and studies of angular correlation functions. Results from galaxy redshift surveys are much less precise but are consistent with the angular correlations, provided the distortions in mapping between real-space and redshift-space are relatively weak. The galaxy two-point correlation function, rich-cluster two-point correlation function, and galaxy-cluster cross-correlation function are all well described on large scales ( greater, similar 20h-1 Mpc, where the Hubble constant, H0 = 100h km.s-1.Mpc; 1 pc = 3.09 x 10(16) m) by the power spectrum of an initially scale-invariant, adiabatic, cold-dark-matter Universe with Gamma = Omegah approximately 0.2. I discuss how this fits in with the Cosmic Background Explorer (COBE) satellite detection of large-scale anisotropies in the microwave background radiation and other measures of large-scale structure in the Universe.

  13. Gene expression data clustering using a multiobjective symmetry based clustering technique.

    PubMed

    Saha, Sriparna; Ekbal, Asif; Gupta, Kshitija; Bandyopadhyay, Sanghamitra

    2013-11-01

    The invention of microarrays has rapidly changed the state of biological and biomedical research. Clustering algorithms play an important role in clustering microarray data sets where identifying groups of co-expressed genes are a very difficult task. Here we have posed the problem of clustering the microarray data as a multiobjective clustering problem. A new symmetry based fuzzy clustering technique is developed to solve this problem. The effectiveness of the proposed technique is demonstrated on five publicly available benchmark data sets. Results are compared with some widely used microarray clustering techniques. Statistical and biological significance tests have also been carried out. PMID:24209942

  14. The nearby Abell clusters. III. Luminosity functions for eight rich clusters

    SciTech Connect

    Oegerle, W.R.; Hoessel, J.G. Washburn Observatory, Madison, WI )

    1989-11-01

    Red photographic data on eight rich Abell clusters are combined with previous results on four other Abell clusters to study the luminosity functions of the clusters. The results produce a mean value of the characteristic galaxy magnitude (M asterisk) that is consistent with previous results. No relation is found between the magnitude of the first-ranked cluster galaxy and M asterisk, suggesting that the value of M asterisk is not changed by dynamical evolution. The faint ends of the luminosity functions for many of the clusters are quite flat, validating the nonuniversality in the parametrization of Schechter (1976) functions for rich clusters of galaxies. 40 refs.

  15. The environments of poor clusters of galaxies

    NASA Astrophysics Data System (ADS)

    Bliton, Mark Alan

    Poor clusters of galaxies are fundamental cosmological structures, but have received relatively little attention compared to rich, Abell clusters. In order to fully understand galaxy clustering, we must examine galaxy associations of all masses and richness levels. We have therefore undertaken an X-ray, optical, and radio investigation of the environments of poor clusters, in order to understand how their galaxies, radio sources, and intracluster media influence and interact with one another. To examine the global properties of poor clusters as observed in these three wavelength regimes, we have utilized three major sky surveys: the ROSAT All-Sky Survey, the Digitized Sky Survey, and the NRAO VLA Sky Survey. For the purposes of this study, we construct a complete, volume-limited sample of 306 poor clusters in the redshift range 0.01--0.03. We compute the X-ray luminosity function (XLF) of poor clusters and compare to XLFs of nearby, rich, Abell clusters. We also compute the bivariate radio luminosity function (BRLF), which is the fraction of radio-loud galaxies of a given optical magnitude. Higher richness clusters produce increased AGN activity in M* galaxies. We find that only clusters with an elliptical as their dominant galaxy possess an ICM. This implies that the presence of a dominant elliptical at the center of a poor cluster is more closely linked to the presence of an ICM than the overall morphological mix of the cluster galaxies. We also find a strong anti-correlation between richness and the fraction of starburst radio galaxies in poor clusters. There may be two factors which contribute to this anti-correlation. For richer clusters, the ICM density may be sufficiently strong that it can strip gas from starforming galaxies, thereby reducing the level of star formation in richer systems. Conversely, the poorest clusters contain higher galaxy compactness, which results in smaller nearest-neighbor distances between galaxies. These smaller galaxy separations

  16. Globular Clusters and Spur Clusters in NGC 4921, the Brightest Spiral Galaxy in the Coma Cluster

    NASA Astrophysics Data System (ADS)

    Lee, Myung Gyoon; Jang, In Sung

    2016-03-01

    We resolve a significant fraction of globular clusters (GCs) in NGC 4921, the brightest spiral galaxy in the Coma cluster. We also find a number of extended bright star clusters (star complexes) in the spur region of the arms. The latter are much brighter and bluer than those in the normal star-forming region, being as massive as 3 × 105 M⊙. The color distribution of the GCs in this galaxy is found to be bimodal. The turnover magnitudes of the luminosity functions of the blue (metal-poor) GCs (0.70 < (V - I) ≤ 1.05) in the halo are estimated V(max) = 27.11 ± 0.09 mag and I(max) = 26.21 ± 0.11 mag. We obtain similar values for NGC 4923, a companion S0 galaxy, and two Coma cD galaxies (NGC 4874 and NGC 4889). The mean value for the turnover magnitudes of these four galaxies is I(max) = 26.25 ± 0.03 mag. Adopting MI (max) = -8.56 ± 0.09 mag for the metal-poor GCs, we determine the mean distance to the four Coma galaxies to be 91 ± 4 Mpc. Combining this with the Coma radial velocity, we derive a value of the Hubble constant, H0 = 77.9 ± 3.6 km s-1 Mpc-1. We estimate the GC specific frequency of NGC 4921 to be SN = 1.29 ± 0.25, close to the values for early-type galaxies. This indicates that NGC 4921 is in the transition phase to S0s.

  17. X ray studies of the Hyades cluster

    NASA Technical Reports Server (NTRS)

    Stern, Robert A.

    1993-01-01

    The Hyades cluster occupies a unique position in both the history of astronomy and at the frontiers of contemporary astronomical research. At a distance of only 45 pc, the Hyades is the nearest star cluster in the Galaxy which is localized in the sky: the UMa cluster, which is closer, but much sparser, essentially surrounds the Solar neighborhood. The Hyades is the prototype cluster for distance determination using the 'moving-cluster' method, and thus serves to define the zero-age main sequence from which the cosmic distance scale is essentially bootstrapped. The Hyades age (0.6-0.7 Gyr), nearly 8 times younger than the Sun, guarantees the Hyades critical importance to studies of stellar evolution. The results of a complete survey of the Hyades cluster using the ROSAT All Sky Survey (RASS) are reported.

  18. Nature of multiple-nucleus cluster galaxies

    SciTech Connect

    Merritt, D.

    1984-05-01

    In models for the evolution of galaxy clusters which include dynamical friction with the dark binding matter, the distribution of galaxies becomes more concentrated to the cluster center with time. In a cluster like Coma, this evolution could increase by a factor of approximately 3 the probability of finding a galaxy very close to the cluster center, without decreasing the typical velocity of such a galaxy significantly below the cluster mean. Such an enhancement is roughly what is needed to explain the large number of first-ranked cluster galaxies which are observed to have extra ''nuclei''; it is also consistent with the high velocities typically measured for these ''nuclei.'' Unlike the cannibalism model, this model predicts that the majority of multiple-nucleus systems are transient phenomena, and not galaxies in the process of merging.

  19. A Review of Subsequence Time Series Clustering

    PubMed Central

    Teh, Ying Wah

    2014-01-01

    Clustering of subsequence time series remains an open issue in time series clustering. Subsequence time series clustering is used in different fields, such as e-commerce, outlier detection, speech recognition, biological systems, DNA recognition, and text mining. One of the useful fields in the domain of subsequence time series clustering is pattern recognition. To improve this field, a sequence of time series data is used. This paper reviews some definitions and backgrounds related to subsequence time series clustering. The categorization of the literature reviews is divided into three groups: preproof, interproof, and postproof period. Moreover, various state-of-the-art approaches in performing subsequence time series clustering are discussed under each of the following categories. The strengths and weaknesses of the employed methods are evaluated as potential issues for future studies. PMID:25140332

  20. Coordination-Cluster-Based Molecular Magnetic Refrigerants.

    PubMed

    Zhang, Shaowei; Cheng, Peng

    2016-08-01

    Coordination polymers serving as molecular magnetic refrigerants have been attracting great interest. In particular, coordination cluster compounds that demonstrate their apparent advantages on cryogenic magnetic refrigerants have attracted more attention in the last five years. Herein, we mainly focus on depicting aspects of syntheses, structures, and magnetothermal properties of coordination clusters that serve as magnetic refrigerants on account of the magnetocaloric effect. The documented molecular magnetic refrigerants are classified into two primary categories according to the types of metal centers, namely, homo- and heterometallic clusters. Every section is further divided into several subgroups based on the metal nuclearity and their dimensionalities, including discrete molecular clusters and those with extended structures constructed from molecular clusters. The objective is to present a rough overview of recent progress in coordination-cluster-based molecular magnetic refrigerants and provide a tutorial for researchers who are interested in the field. PMID:27381662

  1. GRAPE-6 Simulations of Dense Star Clusters

    NASA Astrophysics Data System (ADS)

    Slavin, Shawn D.; Maxwell, J. E.; Cohn, H. N.; Lugger, P. M.

    2007-12-01

    We report on recent results from a long-term program of N-body simulations of dense star cluster evolution which is being done with GRAPE-6 systems at Indiana University and Purdue University Calumet. We have been simulating cases of star cluster evolution with a particular focus on the dynamical evolution of hard binary populations of varying size. Initial models with a range of mass spectra, both with and without primordial binary populations, are being investigated to points well beyond core collapse. Our goal is to better understand the evoultion of compact binary populations in collapsed-core globular clusters. Observations of collapsed-core clusters with HST and Chandra have revealed populations of hard, X-ray binaries well outside the cluster core. Our work is focused on understanding the diffusion of these dynamically hardened binaries to regions in the cluster halo and the robustness of this process in models with mass spectra versus single-mass models.

  2. The Evolving Shape of Galaxy Clusters

    NASA Astrophysics Data System (ADS)

    Just, Dennis W.; Yee, H. K. C.; Muzzin, Adam; Wilson, Gillian; Gilbank, David G.; Gladders, Michael

    2016-10-01

    We present the first measurement of the evolution of the apparent projected shape of galaxy clusters from 0.2<~ z<~2. We measure the ellipticities (ɛcl) of homogeneously selected galaxy clusters over this wide redshift range. We confirm the predictions of N-body simulations that clusters are more elongated at higher redshift, finding the mean projected ellipticity changes linearly from 0.36+/-0.01 to 0.25+/-0.01 over that range. The fraction of relaxed clusters (defined as having ɛ cl <0.2) is 9+5-3% at z~1.8, steadily increasing to 42+7-6% by z~0.3. Because more spherical clusters have a higher degree of virialization, our result shows significant evolution in the degree of cluster virialization over cosmic time.

  3. Globular Clusters in the Galactic Bulge

    NASA Astrophysics Data System (ADS)

    Bica, E.; Ortolani, S.; Barbuy, B.

    2016-06-01

    A view of the Galactic bulge by means of their globular clusters is fundamental for a deep understanding of its formation and evolution. Connections between the globular cluster and field star properties in terms of kinematics, orbits, chemical abundances, and ages should shed light on different stellar population components. Based on spatial distribution and metallicity, we define a probable best list of bulge clusters, containing 43 entries. Future work on newly discovered objects, mostly from the VVV survey, is suggested. These candidates might alleviate the issue of missing clusters on the far side of the bulge. We discuss the reddening law affecting the cluster distances towards the centre of the Galaxy, and conclude that the most suitable total-to-selective absorption value appears to be R V=3.2, in agreement with recent analyses. An update of elemental abundances for bulge clusters is provided.

  4. A review of subsequence time series clustering.

    PubMed

    Zolhavarieh, Seyedjamal; Aghabozorgi, Saeed; Teh, Ying Wah

    2014-01-01

    Clustering of subsequence time series remains an open issue in time series clustering. Subsequence time series clustering is used in different fields, such as e-commerce, outlier detection, speech recognition, biological systems, DNA recognition, and text mining. One of the useful fields in the domain of subsequence time series clustering is pattern recognition. To improve this field, a sequence of time series data is used. This paper reviews some definitions and backgrounds related to subsequence time series clustering. The categorization of the literature reviews is divided into three groups: preproof, interproof, and postproof period. Moreover, various state-of-the-art approaches in performing subsequence time series clustering are discussed under each of the following categories. The strengths and weaknesses of the employed methods are evaluated as potential issues for future studies.

  5. The rate of gravitational galaxy clustering

    NASA Astrophysics Data System (ADS)

    Saslaw, William C.

    1992-06-01

    The rate of gravitational galaxy clustering is considered within the framework of the simple but fundamental case when the initial distribution of galaxy positions is close to Poisson and most of the matter is closely associated with the galaxies. Simple gravitational clustering in an expanding universe is found to evolve along an adiabat of the equation of state which includes gravitational interactions. The faster the universe expands relative to its gravitational clustering time scale, the better this adiabatic approximation becomes. This generalizes the well-known result that a homogeneous unclustered perfect gas in an expanding universe evolves along an adiabat of the perfect gas equation of state. The evolving clustering is characterized. There is a critical value of 0.8604 at which clustering dominates the equation of state and the specific heat at constant volume becomes negative. Subsequent growth of clustering slows appreciably. Numerical N-body experiments are consistent with these properties.

  6. A review of subsequence time series clustering.

    PubMed

    Zolhavarieh, Seyedjamal; Aghabozorgi, Saeed; Teh, Ying Wah

    2014-01-01

    Clustering of subsequence time series remains an open issue in time series clustering. Subsequence time series clustering is used in different fields, such as e-commerce, outlier detection, speech recognition, biological systems, DNA recognition, and text mining. One of the useful fields in the domain of subsequence time series clustering is pattern recognition. To improve this field, a sequence of time series data is used. This paper reviews some definitions and backgrounds related to subsequence time series clustering. The categorization of the literature reviews is divided into three groups: preproof, interproof, and postproof period. Moreover, various state-of-the-art approaches in performing subsequence time series clustering are discussed under each of the following categories. The strengths and weaknesses of the employed methods are evaluated as potential issues for future studies. PMID:25140332

  7. Clustering of Variables for Mixed Data

    NASA Astrophysics Data System (ADS)

    Saracco, J.; Chavent, M.

    2016-05-01

    This chapter presents clustering of variables which aim is to lump together strongly related variables. The proposed approach works on a mixed data set, i.e. on a data set which contains numerical variables and categorical variables. Two algorithms of clustering of variables are described: a hierarchical clustering and a k-means type clustering. A brief description of PCAmix method (that is a principal component analysis for mixed data) is provided, since the calculus of the synthetic variables summarizing the obtained clusters of variables is based on this multivariate method. Finally, the R packages ClustOfVar and PCAmixdata are illustrated on real mixed data. The PCAmix and ClustOfVar approaches are first used for dimension reduction (step 1) before applying in step 2 a standard clustering method to obtain groups of individuals.

  8. The self-enrichment of globular clusters

    SciTech Connect

    Morgan, S.; Lake, G.

    1989-04-01

    It is shown that protoglobular clusters of primordial gas can confine the supernovae needed to enrich themselves. The required protocluster cloud masses and structural parameters are the same as those currently observed for the clusters. Two causal scenarios for star formation are examined to calculate the initial enrichment of primordial clouds. In the 'Christmas tree' scheme, the maximum final (Fe/H) is about 0.1. Since the time scale for formation and evolution of massive stars at the center of a cluster is nearly an order of magnitude less than the collapse time of the cluster, every globular cluster may have to survive a supernova detonation. If this is the case, the minimum mass of a globular cluster is about 10 to the 4.6th solar mass. 24 refs.

  9. Discriminative clustering via extreme learning machine.

    PubMed

    Huang, Gao; Liu, Tianchi; Yang, Yan; Lin, Zhiping; Song, Shiji; Wu, Cheng

    2015-10-01

    Discriminative clustering is an unsupervised learning framework which introduces the discriminative learning rule of supervised classification into clustering. The underlying assumption is that a good partition (clustering) of the data should yield high discrimination, namely, the partitioned data can be easily classified by some classification algorithms. In this paper, we propose three discriminative clustering approaches based on Extreme Learning Machine (ELM). The first algorithm iteratively trains weighted ELM (W-ELM) classifier to gradually maximize the data discrimination. The second and third methods are both built on Fisher's Linear Discriminant Analysis (LDA); but one approach adopts alternative optimization, while the other leverages kernel k-means. We show that the proposed algorithms can be easily implemented, and yield competitive clustering accuracy on real world data sets compared to state-of-the-art clustering methods. PMID:26143036

  10. Chemical Abundances of Giants in Globular Clusters

    NASA Astrophysics Data System (ADS)

    Gratton, Raffaele G.; Bragaglia, Angela; Carretta, Eugenio; D'Orazi, Valentina; Lucatello, Sara

    A large fraction of stars form in clusters. According to a widespread paradigma, stellar clusters are prototypes of single stellar populations. According to this concept, they formed on a very short time scale, and all their stars share the same chemical composition. Recently it has been understood that massive stellar clusters (the globular clusters) rather host various stellar populations, characterized by different chemical composition: these stellar populations have also slightly different ages, stars of the second generations being formed from the ejecta of part of those of an earlier one. Furthermore, it is becoming clear that the efficiency of the process is quite low: many more stars formed within this process than currently present in the clusters. This implies that a significant, perhaps even dominant fraction of the ancient population of galaxies formed within the episodes that lead to formation the globular clusters.

  11. The young SMC cluster NGC 330

    NASA Technical Reports Server (NTRS)

    Carney, B. W.; Janes, K. A.; Flower, P. J.

    1985-01-01

    A color-magnitude diagram has been obtained for the young SMC cluster NGC 330. The diagram shows a well-defined main sequence, a group of blue supergiants, a group of red supergiants between B-V = 1.2 m and 1.6 m about one magnitude fainter, and an empty Hertzsprung gap. The surrounding field is a composite of a very gold population resembling galactic globular clusters and a very young population. DDO and infrared photometry strongly suggest that the cluster is metal-poor, but a definitive measure could not be made because of calibration difficulties. The cluster's age is estimated at 12 million years, with the surrounding field about 50 percent older. The cluster will prove very useful in testing stellar evolution models for young, metal-poor stars if the cluster's metallicity can be established via high-resolution spectroscopy.

  12. Structure of small clusters of parahydrogen molecules

    SciTech Connect

    Guardiola, Rafael; Navarro, Jesus

    2006-08-15

    The ground state energies and the one-body densities of parahydrogen clusters have been systematically calculated by the diffusion Monte Carlo technique in steps of one molecule from 3 to 50 molecules. These calculations show that parahydrogen clusters exhibit a clear geometrical order which excludes any liquidlike structure. A definite confirmation of the magic size for the cluster with 13 molecules is also obtained.

  13. Cluster Dynamics Largely Shapes Protoplanetary Disk Sizes

    NASA Astrophysics Data System (ADS)

    Vincke, Kirsten; Pfalzner, Susanne

    2016-09-01

    To what degree the cluster environment influences the sizes of protoplanetary disks surrounding young stars is still an open question. This is particularly true for the short-lived clusters typical for the solar neighborhood, in which the stellar density and therefore the influence of the cluster environment change considerably over the first 10 Myr. In previous studies, the effect of the gas on the cluster dynamics has often been neglected this is remedied here. Using the code NBody6++, we study the stellar dynamics in different developmental phases—embedded, expulsion, and expansion—including the gas, and quantify the effect of fly-bys on the disk size. We concentrate on massive clusters (M cl ≥ 103-6 ∗ 104 M Sun), which are representative for clusters like the Orion Nebula Cluster (ONC) or NGC 6611. We find that not only the stellar density but also the duration of the embedded phase matters. The densest clusters react fastest to the gas expulsion and drop quickly in density, here 98% of relevant encounters happen before gas expulsion. By contrast, disks in sparser clusters are initially less affected, but because these clusters expand more slowly, 13% of disks are truncated after gas expulsion. For ONC-like clusters, we find that disks larger than 500 au are usually affected by the environment, which corresponds to the observation that 200 au-sized disks are common. For NGC 6611-like clusters, disk sizes are cut-down on average to roughly 100 au. A testable hypothesis would be that the disks in the center of NGC 6611 should be on average ≈20 au and therefore considerably smaller than those in the ONC.

  14. Close binary stars in globular clusters

    NASA Technical Reports Server (NTRS)

    Margon, Bruce

    1991-01-01

    Although close binary stars are thought theoretically to play a major role in globular cluster dynamics, virtually no non-degenerate close binaries are known in clusters. We review the status of observations in this area, and report on two new programs which are finally yielding candidate systems suitable for further study. One of the objects, a close eclipsing system in omega Cen, is also a big straggler, thus finally proving firm evidence that globular cluster blue stragglers really are binary stars.

  15. Microarray gene cluster identification and annotation through cluster ensemble and EM-based informative textual summarization.

    PubMed

    Hu, Xiaohua; Park, E K; Zhang, Xiaodan

    2009-09-01

    Generating high-quality gene clusters and identifying the underlying biological mechanism of the gene clusters are the important goals of clustering gene expression analysis. To get high-quality cluster results, most of the current approaches rely on choosing the best cluster algorithm, in which the design biases and assumptions meet the underlying distribution of the dataset. There are two issues for this approach: 1) usually, the underlying data distribution of the gene expression datasets is unknown and 2) there are so many clustering algorithms available and it is very challenging to choose the proper one. To provide a textual summary of the gene clusters, the most explored approach is the extractive approach that essentially builds upon techniques borrowed from the information retrieval, in which the objective is to provide terms to be used for query expansion, and not to act as a stand-alone summary for the entire document sets. Another drawback is that the clustering quality and cluster interpretation are treated as two isolated research problems and are studied separately. In this paper, we design and develop a unified system Gene Expression Miner to address these challenging issues in a principled and general manner by integrating cluster ensemble, text clustering, and multidocument summarization and provide an environment for comprehensive gene expression data analysis. We present a novel cluster ensemble approach to generate high-quality gene cluster. In our text summarization module, given a gene cluster, our expectation-maximization based algorithm can automatically identify subtopics and extract most probable terms for each topic. Then, the extracted top k topical terms from each subtopic are combined to form the biological explanation of each gene cluster. Experimental results demonstrate that our system can obtain high-quality clusters and provide informative key terms for the gene clusters.

  16. GALAXY CLUSTERS AT HIGH REDSHIFT AND EVOLUTION OF BRIGHTEST CLUSTER GALAXIES

    SciTech Connect

    Wen, Z. L.; Han, J. L.

    2011-06-10

    Identification of high-redshift clusters is important for studies of cosmology and cluster evolution. Using photometric redshifts of galaxies, we identify 631 clusters from the Canada-France-Hawaii Telescope (CFHT) wide field, 202 clusters from the CFHT deep field, 187 clusters from the Cosmic Evolution Survey (COSMOS) field, and 737 clusters from the Spitzer Wide-area InfraRed Extragalactic Survey (SWIRE) field. The redshifts of these clusters are in the range 0.1 {approx}< z {approx}< 1.6. Merging these cluster samples gives 1644 clusters in the four survey fields, of which 1088 are newly identified and more than half are from the large SWIRE field. Among 228 clusters of z {>=} 1, 191 clusters are newly identified, and most of them from the SWIRE field. With this large sample of high-redshift clusters, we study the color evolution of the brightest cluster galaxies (BCGs). The r' - z' and r{sup +} - m{sub 3.6{mu}m} colors of the BCGs are consistent with a stellar population synthesis model in which the BCGs are formed at redshift z{sub f} {>=} 2 and evolved passively. The g' - z' and B - m{sub 3.6{mu}m} colors of the BCGs at redshifts z > 0.8 are systematically bluer than the passive evolution model for galaxies formed at z{sub f} {approx} 2, indicating star formation in high-redshift BCGs.

  17. The 3XMM/SDSS Stripe 82 Galaxy Cluster Survey. I. Cluster catalogue and discovery of two merging cluster candidates

    NASA Astrophysics Data System (ADS)

    Takey, A.; Durret, F.; Mahmoud, E.; Ali, G. B.

    2016-10-01

    We present a galaxy cluster survey based on XMM-Newton observations that are located in Stripe 82 of the Sloan Digital Sky Survey (SDSS). The survey covers an area of 11.25 deg2. The X-ray cluster candidates were selected as serendipitously extended detected sources from the third XMM-Newton serendipitous source catalogue (3XMM-DR5). A cross-correlation of the candidate list that comprises 94 objects with recently published X-ray and optically selected cluster catalogues provided optical confirmations and redshift estimates for about half of the candidate sample. We present a catalogue of X-ray cluster candidates previously known in X-ray and/or optical bands from the matched catalogues or NED. The catalogue consists of 54 systems with redshift measurements in the range of 0.05-1.19 with a median of 0.36. Of these, 45 clusters have spectroscopic confirmations as stated in the matched catalogues. We spectroscopically confirmed another 6 clusters from the available spectroscopic redshifts in the SDSS-DR12. The cluster catalogue includes 17 newly X-ray discovered clusters, while the remainder were detected in previous XMM-Newton and/or ROSAT cluster surveys. Based on the available redshifts and fluxes given in the 3XMM-DR5 catalogue, we estimated the X-ray luminosities and masses for the cluster sample. We also present the list of the remaining X-ray cluster candidates (40 objects) that have no redshift information yet in the literature. Of these candidates, 25 sources are considered as distant cluster candidates beyond a redshift of 0.6. We also searched for galaxy cluster mergers in our cluster sample and found two strong candidates for newly discovered cluster mergers at redshifts of 0.11 and 0.26. The X-ray and optical properties of these systems are presented. Tables A.1, C.1, and C.2 are also 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/594/A32

  18. Photometric Properties of Poor Cluster Galaxies

    NASA Astrophysics Data System (ADS)

    Sharma, M.; Prabhu, T. P.

    2002-12-01

    We study several statistical properties of galaxies in four poor clusters of galaxies using multi-color optical photometry obtained at the Vainu Bappu Telescope, India. The clusters, selected from the EMSS Catalog, are at moderate redshifts (0.08 < z < 0.25), of equivalent Abell richness R=0, and appear to be dynamically young. The early-type galaxy populations are clearly evolved, as traced by the tightness of the color-magnitude relations and the accordance of the latter with those of the Virgo cluster. The blue galaxy fractions are similar to those of R=0 clusters and higher than those of richer clusters at similar redshifts. The composite luminosity functions (LFs) in B, V, and R bands are flat at the faint end, similar to the V-band LF derived by Yamagata & Maehara for other (MKW/AWM) poor clusters but steeper than the R-band field LF derived by Lin et al. In terms of the statistical properties of their member galaxies, poor clusters appear to be lower-mass extensions of their rich counterparts. The brightest galaxies of three of these poor clusters appear to be luminous ellipticals with no incontrovertible signatures of a halo. It is likely that they were formed from multiple mergers early in the history of the clusters.

  19. Complementary ensemble clustering of biomedical data.

    PubMed

    Fodeh, Samah Jamal; Brandt, Cynthia; Luong, Thai Binh; Haddad, Ali; Schultz, Martin; Murphy, Terrence; Krauthammer, Michael

    2013-06-01

    The rapidly growing availability of electronic biomedical data has increased the need for innovative data mining methods. Clustering in particular has been an active area of research in many different application areas, with existing clustering algorithms mostly focusing on one modality or representation of the data. Complementary ensemble clustering (CEC) is a recently introduced framework in which Kmeans is applied to a weighted, linear combination of the coassociation matrices obtained from separate ensemble clustering of different data modalities. The strength of CEC is its extraction of information from multiple aspects of the data when forming the final clusters. This study assesses the utility of CEC in biomedical data, which often have multiple data modalities, e.g., text and images, by applying CEC to two distinct biomedical datasets (PubMed images and radiology reports) that each have two modalities. Referent to five different clustering approaches based on the Kmeans algorithm, CEC exhibited equal or better performance in the metrics of micro-averaged precision and Normalized Mutual Information across both datasets. The reference methods included clustering of single modalities as well as ensemble clustering of separate and merged data modalities. Our experimental results suggest that CEC is equivalent or more efficient than comparable Kmeans based clustering methods using either single or merged data modalities.

  20. Observing dynamical friction in galaxy clusters

    NASA Astrophysics Data System (ADS)

    Adhikari, Susmita; Dalal, Neal; Clampitt, Joseph

    2016-07-01

    We present a novel method to detect the effects of dynamical friction in observed galaxy clusters. Following accretion into clusters, massive satellite galaxies will backsplash to systematically smaller radii than less massive satellites, an effect that may be detected by stacking the number density profiles of galaxies around clusters. We show that this effect may be understood using a simple toy model which reproduces the trends with halo properties observed in simulations. We search for this effect using SDSS redMaPPer clusters with richness 10 < λ < 20, and find that bright (Mi < ‑21.5) satellites have smaller splashback radii than fainter (Mi > ‑20) satellites at 99% confidence.

  1. A New Elliptical Grid Clustering Method

    NASA Astrophysics Data System (ADS)

    Guansheng, Zheng

    A new base on grid clustering method is presented in this paper. This new method first does unsupervised learning on the high dimensions data. This paper proposed a grid-based approach to clustering. It maps the data onto a multi-dimensional space and applies a linear transformation to the feature space instead of to the objects themselves and then approach a grid-clustering method. Unlike the conventional methods, it uses a multidimensional hyper-eclipse grid cell. Some case studies and ideas how to use the algorithms are described. The experimental results show that EGC can discover abnormity shapes of clusters.

  2. INTERRUPTED STELLAR ENCOUNTERS IN STAR CLUSTERS

    SciTech Connect

    Geller, Aaron M.; Leigh, Nathan W. C. E-mail: nleigh@amnh.org

    2015-07-20

    Strong encounters between single stars and binaries play a pivotal role in the evolution of star clusters. Such encounters can also dramatically modify the orbital parameters of binaries, exchange partners in and out of binaries, and are a primary contributor to the rate of physical stellar collisions in star clusters. Often, these encounters are studied under the approximation that they happen quickly enough and within a small enough volume to be considered isolated from the rest of the cluster. In this paper, we study the validity of this assumption through the analysis of a large grid of single–binary and binary–binary scattering experiments. For each encounter we evaluate the encounter duration, and compare this with the expected time until another single or binary star will join the encounter. We find that for lower-mass clusters, similar to typical open clusters in our Galaxy, the percent of encounters that will be “interrupted” by an interloping star or binary may be 20%–40% (or higher) in the core, though for typical globular clusters we expect ≲1% of encounters to be interrupted. Thus, the assumption that strong encounters occur in relative isolation breaks down for certain clusters. Instead, many strong encounters develop into more complex “mini-clusters,” which must be accounted for in studying, for example, the internal dynamics of star clusters, and the physical stellar collision rate.

  3. Laser-driven Acceleration in Clustered Plasmas

    SciTech Connect

    Gao, X.; Wang, X.; Shim, B.; Downer, M. C.

    2009-01-22

    We propose a new approach to avoid dephasing limitation of laser wakefield acceleration by manipulating the group velocity of the driving pulse using clustered plasmas. We demonstrated the control of phase velocity in clustered plasmas by third harmonic generation and frequency domain interferometry experiments. The results agree with a numerical model. Based on this model, the group velocity of the driving pulse in clustered plasmas was calculated and the result shows the group velocity can approach the speed of light c in clustered plasmas.

  4. NEO-FFI personality clusters in trichotillomania.

    PubMed

    Keuthen, Nancy J; Tung, Esther S; Tung, Matthew G; Curley, Erin E; Flessner, Christopher A

    2016-05-30

    The purpose of this study was to determine whether personality prototypes exist among hair pullers and if these groups differ in hair pulling (HP) characteristics, clinical correlates, and quality of life. 164 adult hair pullers completed the NEO-Five Factor Inventory (NEO-FFI; Costa and McCrae, 1992) and self-report measures of HP severity, HP style, affective state, and quality of life. A latent class cluster analysis using NEO-FFI scores was performed to separate participants into clusters. Bonferroni-corrected t-tests were used to compare clusters on HP, affective, and quality of life variables. Multiple regression was used to determine which variables significantly predicted quality of life. Two distinct personality prototypes were identified. Cluster 1 (n=96) had higher neuroticism and lower extraversion, agreeableness, and conscientiousness when compared to cluster 2 (n=68). No significant differences in demographics were reported for the two personality clusters. The clusters differed on extent of focused HP, severity of depression, anxiety, and stress, as well as quality of life. Those in cluster 1 endorsed greater depression, anxiety, and stress, and worse quality of life. Additionally, only depression and cluster membership (based on NEO scores) significantly predicted quality of life. PMID:27016621

  5. An algorithm for spatial heirarchy clustering

    NASA Technical Reports Server (NTRS)

    Dejesusparada, N. (Principal Investigator); Velasco, F. R. D.

    1981-01-01

    A method for utilizing both spectral and spatial redundancy in compacting and preclassifying images is presented. In multispectral satellite images, a high correlation exists between neighboring image points which tend to occupy dense and restricted regions of the feature space. The image is divided into windows of the same size where the clustering is made. The classes obtained in several neighboring windows are clustered, and then again successively clustered until only one region corresponding to the whole image is obtained. By employing this algorithm only a few points are considered in each clustering, thus reducing computational effort. The method is illustrated as applied to LANDSAT images.

  6. The life and death of star clusters

    NASA Astrophysics Data System (ADS)

    Whitmore, B. C.

    It is generally believed that most stars are born in groups and clusters, rather than in the field. In recent years it has been demonstrated that merging galaxies produce large numbers of young massive star clusters, sometimes called super star clusters. Understanding what triggers the formation of these young massive clusters provides important information about the formation of stars in general. In recent years it has also become apparent that most clusters do not survive more than ~ 10 Myr (i.e., "infant mortality"). Hence, it is just as important to understand the disruption of star clusters as it is to to understand their formation if we want to understand the demographics of both star clusters and field stars. This talk will first discuss what triggers star cluster formation in merging galaxies (primarily in the Antennae galaxies) and will then outline a general framework designed to empirically fit observations of both star clusters and field stars in a wide variety of galaxies from mergers to quiescent spirals.

  7. Extragalactic Globular Clusters: Tracers of Galaxy Evolution

    NASA Astrophysics Data System (ADS)

    Bassino, Lilia P.

    2008-09-01

    The study of globular cluster systems provides clues about different topics related to galaxy evolution. In the past years we have been investigating the globular cluster systems of galaxies in the Fornax and Antlia clusters, particularly those associated to the cluster-dominant galaxies. We present here the main results related to these systems. All of them have bimodal color distributions, even those around low-luminosity galaxies, that correspond to the metal-poor (``blue'') and metal-rich (``red'') globular cluster subpopulations. The radial and azimuthal projected areal distributions of the globular clusters are also analyzed. Total globular cluster populations are estimated through the luminosity functions. We stress on the properties of the globular cluster systems that allow us to trace possible interaction processes between the galaxies, like tidal stripping of globular clusters. The observational material consists of CCD images obtained with the wide-field MOSAIC Imager of the CTIO 4-m telescope (La Serena, Chile), and the FORS1 camera at the VLT ``Antu'' 8-m telescope (Cerro Paranal, Chile).

  8. Some properties of ion and cluster plasma

    SciTech Connect

    Gudzenko, L.I.; Derzhiev, V.I.; Yakovlenko, S.I.

    1982-11-01

    The aggregate of problems connected with the physics of ion and cluster plasma is qualitatively considered. Such a plasma can exist when a dense gas is ionized by a hard ionizer. The conditions for the formation of an ion plasma and the difference between its characteristics and those of an ordinary electron plasma are discussed; a solvated-ion model and the distribution of the clusters with respect to the number of solvated molecules are considered. The recombination rate of the positively and negatively charged clusters is roughly estimated. The parameters of a ball-lightning plasma are estimated on the basis of the cluster model.

  9. Water cluster fragmentation probed by pickup experiments.

    PubMed

    Huang, Chuanfu; Kresin, Vitaly V; Pysanenko, Andriy; Fárník, Michal

    2016-09-14

    Electron ionization is a common tool for the mass spectrometry of atomic and molecular clusters. Any cluster can be ionized efficiently by sufficiently energetic electrons, but concomitant fragmentation can seriously obstruct the goal of size-resolved detection. We present a new general method to assess the original neutral population of the cluster beam. Clusters undergo a sticking collision with a molecule from a crossed beam, and the velocities of neat and doped cluster ion peaks are measured and compared. By making use of longitudinal momentum conservation, one can reconstruct the sizes of the neutral precursors. Here this method is applied to H2O and D2O clusters in the detected ion size range of 3-10. It is found that water clusters do fragment significantly upon electron impact: the deduced neutral precursor size is ∼3-5 times larger than the observed cluster ions. This conclusion agrees with beam size characterization by another experimental technique: photoionization after Na-doping. Abundant post-ionization fragmentation of water clusters must therefore be an important factor in the interpretation of experimental data; interestingly, there is at present no detailed microscopic understanding of the underlying fragmentation dynamics. PMID:27634257

  10. Some new indexes of cluster validity.

    PubMed

    Bezdek, J C; Pal, N R

    1998-01-01

    We review two clustering algorithms (hard c-means and single linkage) and three indexes of crisp cluster validity (Hubert's statistics, the Davies-Bouldin index, and Dunn's index). We illustrate two deficiencies of Dunn's index which make it overly sensitive to noisy clusters and propose several generalizations of it that are not as brittle to outliers in the clusters. Our numerical examples show that the standard measure of interset distance (the minimum distance between points in a pair of sets) is the worst (least reliable) measure upon which to base cluster validation indexes when the clusters are expected to form volumetric clouds. Experimental results also suggest that intercluster separation plays a more important role in cluster validation than cluster diameter. Our simulations show that while Dunn's original index has operational flaws, the concept it embodies provides a rich paradigm for validation of partitions that have cloud-like clusters. Five of our generalized Dunn's indexes provide the best validation results for the simulations presented.

  11. Semantic Clustering of Search Engine Results.

    PubMed

    Soliman, Sara Saad; El-Sayed, Maged F; Hassan, Yasser F

    2015-01-01

    This paper presents a novel approach for search engine results clustering that relies on the semantics of the retrieved documents rather than the terms in those documents. The proposed approach takes into consideration both lexical and semantics similarities among documents and applies activation spreading technique in order to generate semantically meaningful clusters. This approach allows documents that are semantically similar to be clustered together rather than clustering documents based on similar terms. A prototype is implemented and several experiments are conducted to test the prospered solution. The result of the experiment confirmed that the proposed solution achieves remarkable results in terms of precision.

  12. Water cluster fragmentation probed by pickup experiments

    NASA Astrophysics Data System (ADS)

    Huang, Chuanfu; Kresin, Vitaly V.; Pysanenko, Andriy; Fárník, Michal

    2016-09-01

    Electron ionization is a common tool for the mass spectrometry of atomic and molecular clusters. Any cluster can be ionized efficiently by sufficiently energetic electrons, but concomitant fragmentation can seriously obstruct the goal of size-resolved detection. We present a new general method to assess the original neutral population of the cluster beam. Clusters undergo a sticking collision with a molecule from a crossed beam, and the velocities of neat and doped cluster ion peaks are measured and compared. By making use of longitudinal momentum conservation, one can reconstruct the sizes of the neutral precursors. Here this method is applied to H2O and D2O clusters in the detected ion size range of 3-10. It is found that water clusters do fragment significantly upon electron impact: the deduced neutral precursor size is ˜3-5 times larger than the observed cluster ions. This conclusion agrees with beam size characterization by another experimental technique: photoionization after Na-doping. Abundant post-ionization fragmentation of water clusters must therefore be an important factor in the interpretation of experimental data; interestingly, there is at present no detailed microscopic understanding of the underlying fragmentation dynamics.

  13. MCS Large Cluster Systems Software Toolkit

    2002-11-01

    This package contains a number of systems utilities for managing a set of computers joined in a "cluster". The utilities assist a team of systems administrators in managing the cluster by automating routine tasks, centralizing information, and monitoring individual computers within the cluster. Included in the toolkit are scripts used to boot a computer from a floppy, a program to turn on and off the power to a system, and a system for using amore » database to organize cluster information.« less

  14. A periodic probabilistic photonic cluster state generator

    NASA Astrophysics Data System (ADS)

    Fanto, Michael L.; Smith, A. Matthew; Alsing, Paul M.; Tison, Christopher C.; Preble, Stefan F.; Lott, Gordon E.; Osman, Joseph M.; Szep, Attila; Kim, Richard S.

    2014-10-01

    The research detailed in this paper describes a Periodic Cluster State Generator (PCSG) consisting of a monolithic integrated waveguide device that employs four wave mixing, an array of probabilistic photon guns, single mode sequential entanglers and an array of controllable entangling gates between modes to create arbitrary cluster states. Utilizing the PCSG one is able to produce a cluster state with nearest neighbor entanglement in the form of a linear or square lattice. Cluster state resources of this type have been proven to be able to perform universal quantum computation.

  15. Multiphoton ionization of large water clusters.

    PubMed

    Apicella, B; Li, X; Passaro, M; Spinelli, N; Wang, X

    2014-05-28

    Water clusters are multimers of water molecules held together by hydrogen bonds. In the present work, multiphoton ionization in the UV range coupled with time of flight mass spectrometry has been applied to water clusters with up to 160 molecules in order to obtain information on the electronic states of clusters of different sizes up to dimensions that can approximate the bulk phase. The dependence of ion intensities of water clusters and their metastable fragments produced by laser ionization at 355 nm on laser power density indicates a (3+1)-photon resonance-enhanced multiphoton ionization process. It also explains the large increase of ionization efficiency at 355 nm compared to that at 266 nm. Indeed, it was found, by applying both nanosecond and picosecond laser ionization with the two different UV wavelengths, that no water cluster sequences after n = 9 could be observed at 266 nm, whereas water clusters up to m/z 2000 Th in reflectron mode and m/z 3000 Th in linear mode were detected at 355 nm. The agreement between our findings on clusters of water, especially true in the range with n > 10, and reported data for liquid water supports the hypothesis that clusters above a critical dimension can approximate the liquid phase. It should thus be possible to study clusters just above 10 water molecules, for getting information on the bulk phase structure.

  16. Stability of Helium Clusters during Displacement Cascades

    SciTech Connect

    Yang, Li; Zu, Xiaotao T.; Xiao, H. Y.; Gao, Fei; Heinisch, Howard L.; Kurtz, Richard J.; Wang, Zhiguo; Liu, K. Z.

    2007-02-01

    The interaction of displacement cascades with helium-vacancy clusters is investigated using molecular dynamics simulations. The He-vacancy clusters initially consist of 20 vacancies with a Helium-to-vacancy ratio ranging from 0.2 to 3. The primary knock-on atom (PKA) energy, Ep, varies from 2 keV to 10 keV, and the PKA direction is chosen such that a displacement cascade is able to directly interact with a helium-vacancy cluster. The simulation results show that the effect of displacement cascades on a helium-vacancy cluster strongly depends on both the helium-to-vacancy ratio and the PKA energy. For the same PKA energy, the size of helium-vacancy clusters increases with the He/V ratio, but for the same ratio, the cluster size changes more significantly with increasing PKA energy. It has been observed that the He-vacancy clusters can be dissolved when the He/V ratio less than 1, but they are able to re-nucleate during the thermal spike phase, forming small He-V nuclei. When the He/V ratio is larger than 1, the He-V clusters can absorb a number of vacancies produced by displacement cascades, forming larger He-V clusters. These results are discussed in terms of PKA energy, helium-to-vacancy ratio, number of vacancies produced by cascades, and mobility of helium atoms.

  17. Shape parameters of Galactic open clusters

    NASA Astrophysics Data System (ADS)

    Kharchenko, N. V.; Berczik, P.; Petrov, M. I.; Piskunov, A. E.; Röser, S.; Schilbach, E.; Scholz, R.-D.

    2009-03-01

    Context: Ellipticities have been determined for only a few tens of open clusters. Aims: We derive the observed and modelled shape parameters (apparent ellipticity and orientation of the ellipse) of 650 Galactic open clusters identified in the ASCC-2.5 catalogue. Methods: We compute the observed shape parameters of Galactic open clusters with a multi-component analysis. For the vast majority of clusters, these parameters are determined for the first time. High resolution (“star by star”) N-body simulations are carried out with a specially developed φGRAPE code providing models of clusters of different initial masses, Galactocentric distances, and rotation velocities. Results: By comparing models and observations for about 150 clusters, we find that the ellipticities of observed clusters are too low (0.2 vs. 0.3), and take a first step in identifying the main reason for this discrepancy. After ≈50 Myr, the models predict that clusters exhibit an oblate shape with an axis ratio of 1.65{:}1.35{:}1, and a major axis tilt by an angle of qXY ≈ 30° with respect to the Galactocentric radius due to the differential rotation of the Galaxy. Conclusions: Unbiased estimates of cluster shape parameters require reliable membership determination in large cluster areas out to 2-3 tidal radii, where the density of cluster stars is considerably lower than the background. Although dynamically bound stars beyond the tidal radius contribute insignificantly to the cluster mass, knowledge of their distribution is essential for a correct determination of cluster shape parameters. In contrast, a restricted mass range of cluster stars does not play such a dramatic role, although deep surveys allow us to identify more cluster members and, therefore, to increase the accuracy of the observed shape parameters. The determined shape parameters for 650 clusters are listed in a table that is available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or

  18. Multiphoton ionization of large water clusters

    SciTech Connect

    Apicella, B.; Li, X.; Passaro, M.; Spinelli, N.; Wang, X.

    2014-05-28

    Water clusters are multimers of water molecules held together by hydrogen bonds. In the present work, multiphoton ionization in the UV range coupled with time of flight mass spectrometry has been applied to water clusters with up to 160 molecules in order to obtain information on the electronic states of clusters of different sizes up to dimensions that can approximate the bulk phase. The dependence of ion intensities of water clusters and their metastable fragments produced by laser ionization at 355 nm on laser power density indicates a (3+1)-photon resonance-enhanced multiphoton ionization process. It also explains the large increase of ionization efficiency at 355 nm compared to that at 266 nm. Indeed, it was found, by applying both nanosecond and picosecond laser ionization with the two different UV wavelengths, that no water cluster sequences after n = 9 could be observed at 266 nm, whereas water clusters up to m/z 2000 Th in reflectron mode and m/z 3000 Th in linear mode were detected at 355 nm. The agreement between our findings on clusters of water, especially true in the range with n > 10, and reported data for liquid water supports the hypothesis that clusters above a critical dimension can approximate the liquid phase. It should thus be possible to study clusters just above 10 water molecules, for getting information on the bulk phase structure.

  19. Transcapillary Trafficking of Clustered Circulating Tumor Cells

    NASA Astrophysics Data System (ADS)

    Storey, Brian; Au, Sam; Chen, Yeng-Long; Sarioglu, Fatih; Javaid, Sarah; Haber, Daniel; Maheswaran, Shyamala; Stott, Shannon; Toner, Mehmet

    2015-11-01

    Aggregates of circulating tumor cells (CTC-clusters) are known to be more metastatic than equal numbers of singlet circulating tumor cells. Yet the mechanisms responsible for CTC-cluster dissemination and tumor seeding are still largely unknown. Without direct experimental evidence, it was assumed that because of their size, CTC-clusters would occlude and rupture capillaries. In this work, we have challenged this assumption by investigating the transit of CTC-clusters through microfluidic capillary constrictions under physiological pressures. Remarkably, cancer cell aggregates containing 2-20 cells were observed to successfully traverse constrictions 5-10 microns with over 90% efficiency. Clusters rapidly and reversibly reorganized into chain-like geometries to pass through constrictions in single file. This observation was verified by computational simulation of clusters modeled with physiological cell-cell interaction energies. Hydrodynamic analysis suggested that CTC-clusters were able to pass narrow constrictions by acting as individual cells in series, not as cohesive units. Upon exiting constrictions, clusters remained viable, proliferative and rapidly returned to `typical' cluster morphologies.

  20. Massive Stars in the Quintuplet Cluster

    NASA Astrophysics Data System (ADS)

    Figer, Donald F.; McLean, Ian S.; Morris, Mark

    1999-03-01

    We present near-infrared photometry and K-band spectra of newly identified massive stars in the Quintuplet cluster, one of the three massive clusters projected within 50 pc of the Galactic center. We find that the cluster contains a variety of massive stars, including more unambiguously identified Wolf-Rayet stars than any cluster in the Galaxy, and over a dozen stars in earlier stages of evolution, i.e., luminous blue variables (LBVs), Ofpe/WN9, and OB supergiants. One newly identified star is the second luminous blue variable in the cluster, after the ``Pistol star.'' Although we are unable to provide certain spectral classifications for the five enigmatic Quintuplet-proper members, we tentatively propose that they are extremely dusty versions of the WC stars found elsewhere in the cluster and similar to the dozen or so known examples in the Galaxy. Although the cluster parameters are uncertain because of photometric errors and uncertainties in stellar models, i.e., extrapolating initial masses and estimating ionizing fluxes, we have the following conclusions. Given the evolutionary stages of the identified stars, the cluster appears to be about 4+/-1 Myr old, assuming coeval formation. The total mass in observed stars is ~103 Msolar, and the implied mass is ~104 Msolar, assuming a lower mass cutoff of 1 Msolar and a Salpeter initial mass function. The implied mass density in stars is greater than or similar to a few thousand Msolar pc-3. The newly identified stars increase the estimated ionizing flux from this cluster by about an order of magnitude with respect to earlier estimates, to 1050.9 photons s-1, or roughly what is required to ionize the nearby ``Sickle'' H II region (G0.18-0.04). The total luminosity from the massive cluster stars is ~107.5 Lsolar, enough to account for the heating of the nearby molecular cloud, M0.20-0.033. We propose a picture that integrates most of the major features in this part of the sky, excepting the nonthermal filaments. We

  1. Self consistency grouping: a stringent clustering method

    PubMed Central

    2012-01-01

    Background Numerous types of clustering like single linkage and K-means have been widely studied and applied to a variety of scientific problems. However, the existing methods are not readily applicable for the problems that demand high stringency. Methods Our method, self consistency grouping, i.e. SCG, yields clusters whose members are closer in rank to each other than to any member outside the cluster. We do not define a distance metric; we use the best known distance metric and presume that it measures the correct distance. SCG does not impose any restriction on the size or the number of the clusters that it finds. The boundaries of clusters are determined by the inconsistencies in the ranks. In addition to the direct implementation that finds the complete structure of the (sub)clusters we implemented two faster versions. The fastest version is guaranteed to find only the clusters that are not subclusters of any other clusters and the other version yields the same output as the direct implementation but does so more efficiently. Results Our tests have demonstrated that SCG yields very few false positives. This was accomplished by introducing errors in the distance measurement. Clustering of protein domain representatives by structural similarity showed that SCG could recover homologous groups with high precision. Conclusions SCG has potential for finding biological relationships under stringent conditions. PMID:23320864

  2. Electronic and magnetothermal properties of ferromagnetic clusters

    NASA Astrophysics Data System (ADS)

    Mahendran, Manickam

    2005-06-01

    The electronic structures and the magnetothermal properties of nickel clusters have been investigated. Their effective magnetic moments and specific heat capacities have been calculated assuming that the clusters undergo superparamagnetic relaxation. The average magnetic moments are computed adopting Friedel's model of ferromagnetic clusters. The surface effect and the cluster size effect on the thermodynamic properties of these clusters have been analysed based on the mean field theory approximation. The specific heat capacity of Ni clusters for N=300, where N is the number of atoms in the cluster, shows the peak value at T=550 K and exhibits a steady increase with N. The effective potentials and energy eigen values of the clusters as a function of the number of atoms and radius of the cluster have also been calculated self-consistently using the local density approximation (LDA) of the density functional theory (DFT); this has been performed within the framework of the spherical jellium background model (SJBM). The results of this study have been compared with the Stern-Gerlach experimental data and other theoretical results already reported in literature

  3. Black holes in young stellar clusters

    SciTech Connect

    Goswami, Sanghamitra; Kiel, Paul; Rasio, Frederic A.

    2014-02-01

    We present theoretical models for stellar black hole (BH) properties in young, massive star clusters. Using a Monte Carlo code for stellar dynamics, we model realistic star clusters with N ≅ 5 × 10{sup 5} stars and significant binary fractions (up to 50%) with self-consistent treatments of stellar dynamics and stellar evolution. We compute the formation rates and characteristic properties of single and binary BHs for various representative ages, cluster parameters, and metallicities. Because of dynamical interactions and supernova (SN) kicks, more single BHs end up retained in clusters compared to BHs in binaries. We also find that the ejection of BHs from a cluster is a strong function of initial density. In low-density clusters (where dynamical effects are negligible), it is mainly SN kicks that eject BHs from the cluster, whereas in high-density clusters (initial central density ρ {sub c}(0) ∼ 10{sup 5} M {sub ☉} pc{sup –3} in our models) the BH ejection rate is enhanced significantly by dynamics. Dynamical interactions of binary systems in dense clusters also modify the orbital period and eccentricity distributions while increasing the probability of a BH having a more massive companion.

  4. Properties of Massive Stars in VVV Clusters

    NASA Astrophysics Data System (ADS)

    Hervé, A.; Martins, F.; Chené, A.-N.; Bouret, J.-C.; Borrissova, J.

    2015-12-01

    The evolution of massive stars is only partly understood. Observational constraints can be obtained from the study of massive stars located in young massive clusters. The ESO Public Survey VISTA Variables in the Via Lactea (VVV) discovered several new clusters hosting massive stars (Borrissova et al. [1]). We derive the stellar parameters of all targets as well as surface abundances for a subset of them. For the cluster with the largest number of objects, we establish firmly that the WN and WC stars were initially more massive than the O stars still present in the cluster.

  5. Uranyl peroxide closed clusters containing topological squares

    SciTech Connect

    Unruh, Daniel K.; Burtner, Alicia; Pressprich, Laura; Sigmon, Ginger E.; Burns, Peter C

    2010-01-01

    Four self-assembling clusters of uranyl peroxide polyhedra have been formed in alkaline aqueous solutions and structurally characterized. These clusters consist of 28, 30, 36 and 44 uranyl polyhedra and exhibit complex new topologies. Each has a structure that contains topological squares, pentagons and hexagons. Analysis of possible topologies within boundary constraints indicates a tendency for adoption of higher symmetry topologies in these cases. Small angle X-ray scattering data demonstrated that crystals of one of these clusters can be dissolved in ultrapure water and that the clusters remain intact for at least several days.

  6. Dynamic clustering in suspension of motile bacteria

    NASA Astrophysics Data System (ADS)

    Chen, Xiao; Yang, Xiang; Yang, Mingcheng; Zhang, H. P.

    2015-09-01

    Bacteria suspension exhibits a wide range of collective phenomena, arising from interactions between individual cells. Here we show Serratia marcescens cells near an air-liquid interface spontaneously aggregate into dynamic clusters through surface-mediated hydrodynamic interactions. These long-lived clusters translate randomly and rotate in the counterclockwise direction; they continuously evolve, merge with others and split into smaller ones. Measurements indicate that long-ranged hydrodynamic interactions have strong influences on cluster properties. Bacterial clusters change material and fluid transport near the interface and hence may have environmental and biological consequences.

  7. Clustering of High Throughput Gene Expression Data

    PubMed Central

    Pirim, Harun; Ekşioğlu, Burak; Perkins, Andy; Yüceer, Çetin

    2012-01-01

    High throughput biological data need to be processed, analyzed, and interpreted to address problems in life sciences. Bioinformatics, computational biology, and systems biology deal with biological problems using computational methods. Clustering is one of the methods used to gain insight into biological processes, particularly at the genomics level. Clearly, clustering can be used in many areas of biological data analysis. However, this paper presents a review of the current clustering algorithms designed especially for analyzing gene expression data. It is also intended to introduce one of the main problems in bioinformatics - clustering gene expression data - to the operations research community. PMID:23144527

  8. Giant Star Clusters Near Galactic Core

    NASA Technical Reports Server (NTRS)

    2001-01-01

    A video sequence of still images goes deep into the Milky Way galaxy to the Arches Cluster. Hubble, penetrating through dust and clouds, peers into the core where two giant clusters shine more brightly than any other clusters in the galaxy. Footage shows the following still images: (1) wide view of Sagittarius constellation; (2) the Palomar Observatory's 2 micron all-sky survey; and (3) an image of the Arches Cluster taken with the Hubble Space Telescope NICMOS instrument. Dr. Don Figer of the Space Telescope Science Institute discusses the significance of the observations and relates his first reaction to the images.

  9. Design of a PACS cluster controller

    NASA Astrophysics Data System (ADS)

    Taira, Ricky K.; Wong, Albert W. K.; Stewart, Brent K.; Huang, H. K.

    1992-07-01

    Our PACS design consists of clusters of computerized devices. At the center of each cluster is an intelligent machine termed a cluster controller. A cluster controller performs the following tasks: (1) receives images from capture computers, (2) extracts descriptive text information describing the received studies, (3) updates a network-accessible database management system, (4) determines the destination workstations to forward the newly generated studies, (5) automatically retrieves necessary comparison images from a distributed optical archive, (6) automatically corrects the orientation of computed radiography images, (7) archives new studies onto optical disk, (8) deletes images stored on remote capture computers upon successful image archival, and (9) services archive retrieval requests from remote workstations and other cluster controllers. The cluster controller is the only class of PACS computers that must communicate with all other types of PACS nodes (acquisition, other cluster controllers, radiologist''s workstation, referring physician''s workstation, printing stations, and database servers). This paper presents details of the logical partitioning of computers into clusters and the central role of the cluster controller machines in image acquisition, image routing, optical archive management, and system reliability.

  10. A fuzzy ontological knowledge document clustering methodology.

    PubMed

    Trappey, Amy J C; Trappey, Charles V; Hsu, Fu-Chiang; Hsiao, David W

    2009-06-01

    This correspondence presents a novel hierarchical clustering approach for knowledge document self-organization, particularly for patent analysis. Current keyword-based methodologies for document content management tend to be inconsistent and ineffective when partial meanings of the technical content are used for cluster analysis. Thus, a new methodology to automatically interpret and cluster knowledge documents using an ontology schema is presented. Moreover, a fuzzy logic control approach is used to match suitable document cluster(s) for given patents based on their derived ontological semantic webs. Finally, three case studies are used to test the approach. The first test case analyzed and clustered 100 patents for chemical and mechanical polishing retrieved from the World Intellectual Property Organization (WIPO). The second test case analyzed and clustered 100 patent news articles retrieved from online Web sites. The third case analyzed and clustered 100 patents for radio-frequency identification retrieved from WIPO. The results show that the fuzzy ontology-based document clustering approach outperforms the K-means approach in precision, recall, F-measure, and Shannon's entropy.

  11. Semantic Clustering of Search Engine Results

    PubMed Central

    Soliman, Sara Saad; El-Sayed, Maged F.; Hassan, Yasser F.

    2015-01-01

    This paper presents a novel approach for search engine results clustering that relies on the semantics of the retrieved documents rather than the terms in those documents. The proposed approach takes into consideration both lexical and semantics similarities among documents and applies activation spreading technique in order to generate semantically meaningful clusters. This approach allows documents that are semantically similar to be clustered together rather than clustering documents based on similar terms. A prototype is implemented and several experiments are conducted to test the prospered solution. The result of the experiment confirmed that the proposed solution achieves remarkable results in terms of precision. PMID:26933673

  12. Estimating the number of clusters via system evolution for cluster analysis of gene expression data.

    PubMed

    Wang, Kaijun; Zheng, Jie; Zhang, Junying; Dong, Jiyang

    2009-09-01

    The estimation of the number of clusters (NC) is one of crucial problems in the cluster analysis of gene expression data. Most approaches available give their answers without the intuitive information about separable degrees between clusters. However, this information is useful for understanding cluster structures. To provide this information, we propose system evolution (SE) method to estimate NC based on partitioning around medoids (PAM) clustering algorithm. SE analyzes cluster structures of a dataset from the viewpoint of a pseudothermodynamics system. The system will go to its stable equilibrium state, at which the optimal NC is found, via its partitioning process and merging process. The experimental results on simulated and real gene expression data demonstrate that the SE works well on the data with well-separated clusters and the one with slightly overlapping clusters. PMID:19527960

  13. Generalized quantum kinetic expansion: Time scale separation between intra-cluster and inter-cluster kinetics

    SciTech Connect

    Tang, Zhoufei; Gong, Zhihao; Wu, Jianlan

    2015-09-14

    For a general two-cluster network, a new methodology of the cluster-based generalized quantum kinetic expansion (GQKE) is developed in the matrix formalism under two initial conditions: the local cluster equilibrium and system-bath factorized states. For each initial condition, the site population evolution follows exactly a distinct closed equation, where all the four terms involved are systematically expanded over inter-cluster couplings. For the system-bath factorized initial state, the numerical investigation of the two models, a biased (2, 1)-site system and an unbiased (2, 2)-site system, verifies the reliability of the GQKE and the relevance of higher-order corrections. The time-integrated site-to-site rates and the time evolution of site population reveal the time scale separation between intra-cluster and inter-cluster kinetics. The population evolution of aggregated clusters can be quantitatively described by the approximate cluster Markovian kinetics.

  14. Hydrogen clusters in clathrate hydrate.

    PubMed

    Mao, Wendy L; Mao, Ho-Kwang; Goncharov, Alexander F; Struzhkin, Viktor V; Guo, Quanzhong; Hu, Jingzhu; Shu, Jinfu; Hemley, Russell J; Somayazulu, Maddury; Zhao, Yusheng

    2002-09-27

    High-pressure Raman, infrared, x-ray, and neutron studies show that H2 and H2O mixtures crystallize into the sII clathrate structure with an approximate H2/H2O molar ratio of 1:2. The clathrate cages are multiply occupied, with a cluster of two H2 molecules in the small cage and four in the large cage. Substantial softening and splitting of hydrogen vibrons indicate increased intermolecular interactions. The quenched clathrate is stable up to 145 kelvin at ambient pressure. Retention of hydrogen at such high temperatures could help its condensation in planetary nebulae and may play a key role in the evolution of icy bodies. PMID:12351785

  15. Boron clusters in luminescent materials.

    PubMed

    Mukherjee, Sanjoy; Thilagar, Pakkirisamy

    2016-01-21

    In recent times, luminescent materials with tunable emission properties have found applications in almost all aspects of modern material sciences. Any discussion on the recent developments in luminescent materials would be incomplete if one does not account for the versatile photophysical features of boron containing compounds. Apart from triarylboranes and tetra-coordinate borate dyes, luminescent materials consisting of boron clusters have also found immense interest in recent times. Recent studies have unveiled the opportunities hidden within boranes, carboranes and metalloboranes, etc. as active constituents of luminescent materials. From simple illustrations of luminescence, to advanced applications in LASERs, OLEDs and bioimaging, etc., the unique features of such compounds and their promising versatility have already been established. In this review, recent revelations about the excellent photophysical properties of such materials are discussed. PMID:26574714

  16. Statistical thermodynamics of clustered populations.

    PubMed

    Matsoukas, Themis

    2014-08-01

    We present a thermodynamic theory for a generic population of M individuals distributed into N groups (clusters). We construct the ensemble of all distributions with fixed M and N, introduce a selection functional that embodies the physics that governs the population, and obtain the distribution that emerges in the scaling limit as the most probable among all distributions consistent with the given physics. We develop the thermodynamics of the ensemble and establish a rigorous mapping to regular thermodynamics. We treat the emergence of a so-called giant component as a formal phase transition and show that the criteria for its emergence are entirely analogous to the equilibrium conditions in molecular systems. We demonstrate the theory by an analytic model and confirm the predictions by Monte Carlo simulation.

  17. Behaviour during a cluster headache.

    PubMed

    Blau, J N

    1993-09-18

    Because cluster headache is short-lasting and tends to occur during the early morning hours, physicians rarely witness an attack. Accurate diagnosis is important because effective treatments are available. The diagnosis is made from the history of temporal pattern, reddening and tearing of the affected eye, and ipsilateral nasal congestion. An additional diagnostic aid is to invite patients to demonstrate how they respond to attacks. The pain, one of the worst known, causes extreme restlessness. 50 patients showed how they walk around, sit (or kneel) and rock, and clutch the affected side of the head. Diagnostic value apart, the patient will often be relieved to learn that bizarre behavioural responses are not a mark of insanity.

  18. An immersed field cluster klystron

    SciTech Connect

    Palmer, R.B.; Herrmannsfeldt, W.B.; Eppley, K.R.

    1989-08-01

    Future linear colliders have a need for high power, high frequency, and short-pulse radio frequency sources. The proposed ''cluster klystron'' should give over 1 GW of 12 GHz radio frequency power, can employ direct current or a long high-voltage pulse, but can be gated to give pulses down to a few tens of nanoseconds. The device consists of 42 parallel 100 A channels. Each channel is fed from an individual magnetron-type gun employing a common 50 kV mod-anode. The beams are accelerated to 400 kV in common dc accelerating gaps and fed into the 42 separate klystron channels. Focusing of all channels is achieved by a single overall 4 kG magnetic field. Simulations of expected performance suggest that the efficiency could be above 70%. 10 refs., 6 figs., 5 tabs.

  19. Nanophase materials assembled from clusters

    SciTech Connect

    Siegel, R.W.

    1992-02-01

    The preparation of metal and ceramic atom clusters by means of the gas-condensation method, followed by their in situ collection and consolidation under high-vacuum conditions, has recently led to the synthesis of a new class of ultrafine-grained materials. These nanophase materials, with typical average grain sizes of 5 to 50 nm and, hence, a large fraction of their atoms in interfaces, exhibit properties that are often considerably improved relative to those of conventional materials. Furthermore, their synthesis and processing characteristics should enable the design of new materials with unique properties. Some examples are ductile ceramics that can be formed and sintered to full density at low temperatures without the need for binding or sintering aids, and metals with dramatically increased strength. The synthesis of these materials is briefly described along with what is presently known of their structure and properties. Their future impact on materials science and technology is also considered.

  20. Boron clusters in luminescent materials.

    PubMed

    Mukherjee, Sanjoy; Thilagar, Pakkirisamy

    2016-01-21

    In recent times, luminescent materials with tunable emission properties have found applications in almost all aspects of modern material sciences. Any discussion on the recent developments in luminescent materials would be incomplete if one does not account for the versatile photophysical features of boron containing compounds. Apart from triarylboranes and tetra-coordinate borate dyes, luminescent materials consisting of boron clusters have also found immense interest in recent times. Recent studies have unveiled the opportunities hidden within boranes, carboranes and metalloboranes, etc. as active constituents of luminescent materials. From simple illustrations of luminescence, to advanced applications in LASERs, OLEDs and bioimaging, etc., the unique features of such compounds and their promising versatility have already been established. In this review, recent revelations about the excellent photophysical properties of such materials are discussed.

  1. Growth mechanism of hydrogen clusters

    SciTech Connect

    Nickel, N.H.; Anderson, G.B.; Johnson, N.M.; Walker, J.

    1997-07-01

    It is demonstrated that the exposure of polycrystalline silicon (poly-Si) to monatomic hydrogen results in the formation of H clusters. These H stabilized platelets appear in the near-surface region (100 nm) and are predominantly oriented along {l_brace}111{r_brace} crystallographic planes. Platelet concentrations of {approx}5 x 10{sup 15}, 1.5 x 10{sup 16} -cm{sup {minus}3}, and 2.4 x 10{sup 17} cm{sup {minus}3} were observed in nominally undoped poly-Si, phosphorous doped poly-Si (P = 10{sup 17} cm{sup {minus}3}), and phosphorous doped single crystal silicon (P > 3 x 10{sup 18} cm{sup {minus}3}), respectively. Results obtained on doped c-Si demonstrate that platelet generation occurs only at Fermi-level positions of E{sub C} - E{sub F} < 0.4 eV.

  2. Scientific Cluster Deployment and Recovery - Using puppet to simplify cluster management

    NASA Astrophysics Data System (ADS)

    Hendrix, Val; Benjamin, Doug; Yao, Yushu

    2012-12-01

    Deployment, maintenance and recovery of a scientific cluster, which has complex, specialized services, can be a time consuming task requiring the assistance of Linux system administrators, network engineers as well as domain experts. Universities and small institutions that have a part-time FTE with limited time for and knowledge of the administration of such clusters can be strained by such maintenance tasks. This current work is the result of an effort to maintain a data analysis cluster (DAC) with minimal effort by a local system administrator. The realized benefit is the scientist, who is the local system administrator, is able to focus on the data analysis instead of the intricacies of managing a cluster. Our work provides a cluster deployment and recovery process (CDRP) based on the puppet configuration engine allowing a part-time FTE to easily deploy and recover entire clusters with minimal effort. Puppet is a configuration management system (CMS) used widely in computing centers for the automatic management of resources. Domain experts use Puppet's declarative language to define reusable modules for service configuration and deployment. Our CDRP has three actors: domain experts, a cluster designer and a cluster manager. The domain experts first write the puppet modules for the cluster services. A cluster designer would then define a cluster. This includes the creation of cluster roles, mapping the services to those roles and determining the relationships between the services. Finally, a cluster manager would acquire the resources (machines, networking), enter the cluster input parameters (hostnames, IP addresses) and automatically generate deployment scripts used by puppet to configure it to act as a designated role. In the event of a machine failure, the originally generated deployment scripts along with puppet can be used to easily reconfigure a new machine. The cluster definition produced in our CDRP is an integral part of automating cluster deployment

  3. Caloric curve of star clusters.

    PubMed

    Casetti, Lapo; Nardini, Cesare

    2012-06-01

    Self-gravitating systems, such as globular clusters or elliptical galaxies, are the prototypes of many-body systems with long-range interactions, and should be the natural arena in which to test theoretical predictions on the statistical behavior of long-range-interacting systems. Systems of classical self-gravitating particles can be studied with the standard tools of equilibrium statistical mechanics, provided the potential is regularized at small length scales and the system is confined in a box. The confinement condition looks rather unphysical in general, so that it is natural to ask whether what we learn with these studies is relevant to real self-gravitating systems. In order to provide an answer to this question, we consider a basic, simple, yet effective model of globular clusters: the King model. This model describes a self-consistently confined system, without the need of any external box, but the stationary state is a nonthermal one. In particular, we consider the King model with a short-distance cutoff on the interactions, and we discuss how such a cutoff affects the caloric curve, i.e., the relation between temperature and energy. We find that the cutoff stabilizes a low-energy phase, which is absent in the King model without cutoff; the caloric curve of the model with cutoff turns out to be very similar to that of previously studied confined and regularized models, but for the absence of a high-energy gaslike phase. We briefly discuss the possible phenomenological as well as theoretical implications of these results. PMID:23005049

  4. Caloric curve of star clusters.

    PubMed

    Casetti, Lapo; Nardini, Cesare

    2012-06-01

    Self-gravitating systems, such as globular clusters or elliptical galaxies, are the prototypes of many-body systems with long-range interactions, and should be the natural arena in which to test theoretical predictions on the statistical behavior of long-range-interacting systems. Systems of classical self-gravitating particles can be studied with the standard tools of equilibrium statistical mechanics, provided the potential is regularized at small length scales and the system is confined in a box. The confinement condition looks rather unphysical in general, so that it is natural to ask whether what we learn with these studies is relevant to real self-gravitating systems. In order to provide an answer to this question, we consider a basic, simple, yet effective model of globular clusters: the King model. This model describes a self-consistently confined system, without the need of any external box, but the stationary state is a nonthermal one. In particular, we consider the King model with a short-distance cutoff on the interactions, and we discuss how such a cutoff affects the caloric curve, i.e., the relation between temperature and energy. We find that the cutoff stabilizes a low-energy phase, which is absent in the King model without cutoff; the caloric curve of the model with cutoff turns out to be very similar to that of previously studied confined and regularized models, but for the absence of a high-energy gaslike phase. We briefly discuss the possible phenomenological as well as theoretical implications of these results.

  5. 2009 Clusters, Nanocrystals & Nanostructures GRC

    SciTech Connect

    Lai-Sheng Wang

    2009-07-19

    For over thirty years, this Gordon Conference has been the premiere meeting for the field of cluster science, which studies the phenomena that arise when matter becomes small. During its history, participants have witnessed the discovery and development of many novel materials, including C60, carbon nanotubes, semiconductor and metal nanocrystals, and nanowires. In addition to addressing fundamental scientific questions related to these materials, the meeting has always included a discussion of their potential applications. Consequently, this conference has played a critical role in the birth and growth of nanoscience and engineering. The goal of the 2009 Gordon Conference is to continue the forward-looking tradition of this meeting and discuss the most recent advances in the field of clusters, nanocrystals, and nanostructures. As in past meetings, this will include new topics that broaden the field. In particular, a special emphasis will be placed on nanomaterials related to the efficient use, generation, or conversion of energy. For example, we anticipate presentations related to batteries, catalysts, photovoltaics, and thermoelectrics. In addition, we expect to address the controversy surrounding carrier multiplication with a session in which recent results addressing this phenomenon will be discussed and debated. The atmosphere of the conference, which emphasizes the presentation of unpublished results and lengthy discussion periods, ensures that attendees will enjoy a valuable and stimulating experience. Because only a limited number of participants are allowed to attend this conference, and oversubscription is anticipated, we encourage all interested researchers from academia, industry, and government institutions to apply as early as possible. An invitation is not required. We also encourage all attendees to submit their latest results for presentation at the poster sessions. We anticipate that several posters will be selected for 'hot topic' oral

  6. THE STRUCTURE OF 2MASS GALAXY CLUSTERS

    SciTech Connect

    Blackburne, Jeffrey A.; Kochanek, Christopher S.

    2012-01-01

    We use a sample of galaxies from the Two Micron All Sky Survey Extended Source Catalog to refine a matched filter method of finding galaxy clusters that takes into account each galaxy's position, magnitude, and redshift if available. The matched filter postulates a radial density profile, luminosity function, and line-of-sight velocity distribution for cluster galaxies. We use this method to search for clusters in the galaxy catalog, which is complete to an extinction-corrected K-band magnitude of 13.25 and has spectroscopic redshifts for roughly 40% of the galaxies, including nearly all brighter than K = 11.25. We then use a stacking analysis to determine the average luminosity function, radial distribution, and velocity distribution of cluster galaxies in several richness classes, and use the results to update the parameters of the matched filter before repeating the cluster search. We also investigate the correlations between a cluster's richness and its velocity dispersion and core radius using these relations to refine priors that are applied during the cluster search process. After the second cluster search iteration, we repeat the stacking analysis. We find a cluster galaxy luminosity function that fits a Schechter form, with parameters M{sub K*} - 5log h = -23.64 {+-} 0.04 and {alpha} = -1.07 {+-} 0.03. We can achieve a slightly better fit to our luminosity function by adding a Gaussian component on the bright end to represent the brightest cluster galaxy population. The radial number density profile of galaxies closely matches a projected Navarro-Frenk-White profile at intermediate radii, with deviations at small radii due to well-known cluster centering issues and outside the virial radius due to correlated structure. The velocity distributions are Gaussian in shape, with velocity dispersions that correlate strongly with richness.

  7. Persistence drives gene clustering in bacterial genomes

    PubMed Central

    Fang, Gang; Rocha, Eduardo PC; Danchin, Antoine

    2008-01-01

    Background Gene clustering plays an important role in the organization of the bacterial chromosome and several mechanisms have been proposed to explain its extent. However, the controversies raised about the validity of each of these mechanisms remind us that the cause of this gene organization remains an open question. Models proposed to explain clustering did not take into account the function of the gene products nor the likely presence or absence of a given gene in a genome. However, genomes harbor two very different categories of genes: those genes present in a majority of organisms – persistent genes – and those present in very few organisms – rare genes. Results We show that two classes of genes are significantly clustered in bacterial genomes: the highly persistent and the rare genes. The clustering of rare genes is readily explained by the selfish operon theory. Yet, genes persistently present in bacterial genomes are also clustered and we try to understand why. We propose a model accounting specifically for such clustering, and show that indispensability in a genome with frequent gene deletion and insertion leads to the transient clustering of these genes. The model describes how clusters are created via the gene flux that continuously introduces new genes while deleting others. We then test if known selective processes, such as co-transcription, physical interaction or functional neighborhood, account for the stabilization of these clusters. Conclusion We show that the strong selective pressure acting on the function of persistent genes, in a permanent state of flux of genes in bacterial genomes, maintaining their size fairly constant, that drives persistent genes clustering. A further selective stabilization process might contribute to maintaining the clustering. PMID:18179692

  8. Cooling Flow Spectra in Ginga Galaxy Clusters

    NASA Technical Reports Server (NTRS)

    White, Raymond E., III

    1997-01-01

    The primary focus of this research project has been a joint analysis of Ginga LAC and Einstein SSS X-ray spectra of the hot gas in galaxy clusters with cooling flows is reported. We studied four clusters (A496, A1795, A2142 & A2199) and found their central temperatures to be cooler than in the exterior, which is expected from their having cooling flows. More interestingly, we found central metal abundance enhancements in two of the clusters, A496 and A2142. We have been assessing whether the abundance gradients (or lack thereof) in intracluster gas is correlated with galaxy morphological gradients in the host clusters. In rich, dense galaxy clusters, elliptical and SO galaxies are generally found in the cluster cores, while spiral galaxies are found in the outskirts. If the metals observed in clusters came from proto-ellipticals and proto-S0s blowing winds, then the metal distribution in intracluster gas may still reflect the distribution of their former host galaxies. In a research project which was inspired by the success of the Ginga LAC/Einstein SSS work, we analyzed X-ray spectra from the HEAO-A2 MED and the Einstein SSS to look for temperature gradients in cluster gas. The HEAO-A2 MED was also a non-imaging detector with a large field of view compared to the SSS, so we used the differing fields of view of the two instruments to extract spatial information. We found some evidence of cool gas in the outskirts of clusters, which may indicate that the nominally isothermal mass density distributions in these clusters are steepening in the outer parts of these clusters.

  9. Study of bright globular clusters and Ultra-Compact Dwarf galaxies in the Antlia cluster.

    NASA Astrophysics Data System (ADS)

    Caso, J. P.; Bassino, L. P.; Richtler, T.; Smith Castelli, A. V.; Faifer, F. R.; Calderón, J. P.

    A sample of confirmed Ultra-Compact Dwarf galaxies and globular clusters around the giant galaxy NGC 3268 in the Antlia cluster is presented, including their Washington photometry. For the Antlia objects discovered so far, the reliability of a common origin with the globular clusters of the galaxies NGC 3258 and NGC 3268 is analyzed.

  10. cluster-lensing: a new Python package for galaxy clusters & lensing

    NASA Astrophysics Data System (ADS)

    Ford, Jes

    2016-03-01

    Short demo and links to a newly released pure Python package called cluster- lensing. This package contains tools to calculate galaxy cluster halo properties and weak lensing shear and magnification profiles. The model can easily include the effects of possible cluster miscentering offsets, which would otherwise lead to biased mass or concentration estimates.

  11. Reinvestigating the clusters Koposov 1 and 2

    SciTech Connect

    Paust, Nathaniel; Wilson, Danielle; Van Belle, Gerard

    2014-07-01

    We investigate the fundamental parameters of age, distance, and mass function slope for the poorly studied clusters Koposov 1 and Koposov 2. These clusters were discovered recently and tentatively classified as globular clusters. Using the Large Monolithic Imager on Lowell Observatory's Discovery Channel Telescope, we present photometry extending to V = 25, three to four magnitudes below the main sequence turnoffs for the clusters. We find the clusters have tidal radii of 15 pc and 10.7 pc and distances of 34.9 kpc and 33.3 kpc for Koposov 1 and Koposov 2, respectively. Studying the stellar content of the clusters, we use completeness-corrected star counts to reveal extremely faint total magnitudes of 2.01 and 0.03 in V, and steep Salpeter-like present-day mass functions. Finally, we show that the spatial positions of the clusters agree well with the position of the Sagittarius stream and conclude that these two objects are open clusters removed from the Sagittarius galaxy.

  12. Star clusters as simple stellar populations.

    PubMed

    Bruzual A, Gustavo

    2010-02-28

    In this paper, I review to what extent we can understand the photometric properties of star clusters, and of low-mass, unresolved galaxies, in terms of population-synthesis models designed to describe 'simple stellar populations' (SSPs), i.e. groups of stars born at the same time, in the same volume of space and from a gas cloud of homogeneous chemical composition. The photometric properties predicted by these models do not readily match the observations of most star clusters, unless we properly take into account the expected variation in the number of stars occupying sparsely populated evolutionary stages, owing to stochastic fluctuations in the stellar initial mass function. In this case, population-synthesis models reproduce remarkably well the full ranges of observed integrated colours and absolute magnitudes of star clusters of various ages and metallicities. The disagreement between the model predictions and observations of cluster colours and magnitudes may indicate problems with or deficiencies in the modelling, and does not necessarily tell us that star clusters do not behave like SSPs. Matching the photometric properties of star clusters using SSP models is a necessary (but not sufficient) condition for clusters to be considered SSPs. Composite models, characterized by complex star-formation histories, also match the observed cluster colours.

  13. Geometrical parameters of a water dropwise cluster

    SciTech Connect

    Shavlov, A. V. Dzumandzi, V. A.

    2012-02-15

    A dropwise cluster is obtained over the surface of water heated to 65-100 Degree-Sign C. The pair correlation function of drops in the cluster is constructed. The temperature dependences of the spacing between the drops, their diameter, and the altitude of their levitation over the water surface are measured.

  14. Exemplar-Based Clustering via Simulated Annealing

    ERIC Educational Resources Information Center

    Brusco, Michael J.; Kohn, Hans-Friedrich

    2009-01-01

    Several authors have touted the p-median model as a plausible alternative to within-cluster sums of squares (i.e., K-means) partitioning. Purported advantages of the p-median model include the provision of "exemplars" as cluster centers, robustness with respect to outliers, and the accommodation of a diverse range of similarity data. We developed…

  15. Palladium clusters deposited on the heterogeneous substrates

    NASA Astrophysics Data System (ADS)

    Wang, Kun; Liu, Juanfang; Chen, Qinghua

    2016-07-01

    To improve the performance of the Pd composite membrane prepared by the cold spraying technology, it is extremely essential to give insights into the deposition process of the cluster and the heterogeneous deposition of the big Pd cluster at the different incident velocities on the atomic level. The deposition behavior, morphologies, energetic and interfacial configuration were examined by the molecular dynamic simulation and characterized by the cluster flattening ratio, the substrate maximum local temperature, the atom-embedded layer number and the surface-alloy formation. According to the morphology evolution, three deposition stages and the corresponding structural and energy evolution were clearly identified. The cluster deformation and penetrating depth increased with the enhancement of the incident velocity, but the increase degree also depended on the substrate hardness. The interfacial interaction between the cluster and the substrate can be improved by the higher substrate local temperature. Furthermore, it is found that the surface alloys were formed by exchanging sites between the cluster and substrate atoms, and the cluster atoms rearranged following as the substrate lattice arrangement from bottom to up in the deposition course. The ability and scope of the structural reconstruction are largely determined by both the size and incident energy of the impacted cluster.

  16. Adaptive-clustering optical neural net.

    PubMed

    Casasent, D P; Barnard, E

    1990-06-10

    Pattern recognition techniques (for clustering and linear discriminant function selection) are combined with neural net methods (that provide an automated method to combine linear discriminant functions into piecewise linear discriminant surfaces). The resulting adaptive-clustering neural net is suitable for optical implementation and has certain desirable properties in comparison with other neural nets. Simulation results are provided.

  17. 5 CFR 9701.211 - Occupational clusters.

    Code of Federal Regulations, 2011 CFR

    2011-01-01

    ... 5 Administrative Personnel 3 2011-01-01 2011-01-01 false Occupational clusters. 9701.211 Section... RESOURCES MANAGEMENT SYSTEM Classification Classification Structure § 9701.211 Occupational clusters. For the purpose of classifying positions, DHS may, after coordination with OPM, establish...

  18. 5 CFR 9701.211 - Occupational clusters.

    Code of Federal Regulations, 2012 CFR

    2012-01-01

    ... 5 Administrative Personnel 3 2012-01-01 2012-01-01 false Occupational clusters. 9701.211 Section... RESOURCES MANAGEMENT SYSTEM Classification Classification Structure § 9701.211 Occupational clusters. For the purpose of classifying positions, DHS may, after coordination with OPM, establish...

  19. The X-ray cluster Abell 744

    NASA Technical Reports Server (NTRS)

    Kurtz, M. J.; Huchra, J. P.; Beers, T. C.; Geller, M. J.; Gioia, I. M.

    1985-01-01

    X-ray and optical observations of the cluster of galaxies Abell 744 are presented. The X-ray flux (assuming H(0) = 100 km/s per Mpc) is about 9 x 10 to the 42nd erg/s. The X-ray source is extended, but shows no other structure. Photographic photometry (in Kron-Cousins R), calibrated by deep CCD frames, is presented for all galaxies brighter than 19th magnitude within 0.75 Mpc of the cluster center. The luminosity function is normal, and the isopleths show little evidence of substructure near the cluster center. The cluster has a dominant central galaxy, which is classified as a normal brightest-cluster elliptical on the basis of its luminosity profile. New redshifts were obtained for 26 galaxies in the vicinity of the cluster center; 20 appear to be cluster members. The spatial distribution of redshifts is peculiar; the dispersion within the 150 kpc core radius is much greater than outside. Abell 744 is similar to the nearby cluster Abell 1060.

  20. The Articulatory Target for Final -s Clusters.

    ERIC Educational Resources Information Center

    Temperley, Mary S.

    1983-01-01

    The pronunciation of final -s clusters is not uniformly treated by dictionaries, phoneticians, and writers of ESL texts. Four reasons for treating the pairs of clusters as homophonous in ESL instruction are: linguistic observation, linguistic patterning, linguistic history, and linguistic and pedagogical simplicity. This explicit treatment may…

  1. Investigations of Galaxy Clusters Using Gravitational Lensing

    SciTech Connect

    Wiesner, Matthew P.

    2014-08-01

    In this dissertation, we discuss the properties of galaxy clusters that have been determined using strong and weak gravitational lensing. A galaxy cluster is a collection of galaxies that are bound together by the force of gravity, while gravitational lensing is the bending of light by gravity. Strong lensing is the formation of arcs or rings of light surrounding clusters and weak lensing is a change in the apparent shapes of many galaxies. In this work we examine the properties of several samples of galaxy clusters using gravitational lensing. In Chapter 1 we introduce astrophysical theory of galaxy clusters and gravitational lensing. In Chapter 2 we examine evidence from our data that galaxy clusters are more concentrated than cosmology would predict. In Chapter 3 we investigate whether our assumptions about the number of galaxies in our clusters was valid by examining new data. In Chapter 4 we describe a determination of a relationship between mass and number of galaxies in a cluster at higher redshift than has been found before. In Chapter 5 we describe a model of the mass distribution in one of the ten lensing systems discovered by our group at Fermilab. Finally in Chapter 6 we summarize our conclusions.

  2. Effect Sizes in Cluster-Randomized Designs

    ERIC Educational Resources Information Center

    Hedges, Larry V.

    2007-01-01

    Multisite research designs involving cluster randomization are becoming increasingly important in educational and behavioral research. Researchers would like to compute effect size indexes based on the standardized mean difference to compare the results of cluster-randomized studies (and corresponding quasi-experiments) with other studies and to…

  3. Grid Computing Environment using a Beowulf Cluster

    NASA Astrophysics Data System (ADS)

    Alanis, Fransisco; Mahmood, Akhtar

    2003-10-01

    Custom-made Beowulf clusters using PCs are currently replacing expensive supercomputers to carry out complex scientific computations. At the University of Texas - Pan American, we built a 8 Gflops Beowulf Cluster for doing HEP research using RedHat Linux 7.3 and the LAM-MPI middleware. We will describe how we built and configured our Cluster, which we have named the Sphinx Beowulf Cluster. We will describe the results of our cluster benchmark studies and the run-time plots of several parallel application codes that were compiled in C on the cluster using the LAM-XMPI graphics user environment. We will demonstrate a "simple" prototype grid environment, where we will submit and run parallel jobs remotely across multiple cluster nodes over the internet from the presentation room at Texas Tech. University. The Sphinx Beowulf Cluster will be used for monte-carlo grid test-bed studies for the LHC-ATLAS high energy physics experiment. Grid is a new IT concept for the next generation of the "Super Internet" for high-performance computing. The Grid will allow scientist worldwide to view and analyze huge amounts of data flowing from the large-scale experiments in High Energy Physics. The Grid is expected to bring together geographically and organizationally dispersed computational resources, such as CPUs, storage systems, communication systems, and data sources.

  4. Argon clusters embedded in helium nanodroplets.

    PubMed

    da Silva, Filipe Ferreira; Bartl, Peter; Denifl, Stephan; Echt, Olof; Märk, Tilmann D; Scheier, Paul

    2009-11-14

    Electron impact ionization of argon clusters embedded in helium droplets is investigated. Superior mass resolution makes it possible to distinguish between nominally isobaric cluster ions. An abundance maximum for ArHe(12)(+) is unambiguously confirmed; the spectra also prove the formation of Ar(2)He(n)(+) complexes that had been claimed to fragment into pure Ar(2)(+). Distributions of larger argon cluster ions containing up to 60 atoms closely resemble distributions observed upon electron impact or photoionization of bare argon clusters; caging and evaporative cooling provided by the helium matrix do not suffice to quench fragmentation of the nascent argon cluster ions. Intriguing abundance anomalies are observed in distributions of argon cluster ions that contain water, nitrogen or oxygen impurities. The strong abundance of Ar(55)H(2)O(+), Ar(54)O(2)(+) and Ar(54)N(2)(+) contrasts with the virtual absence of slightly larger cluster ions containing the corresponding impurities. The features are probably related to enhanced cluster ion stability upon closure of the second icosahedral shell but the difference in magic numbers (54 versus 55) and the well-known reactivity of charged argon-nitrogen complexes suggest structural differences. PMID:19851558

  5. Transportation Cluster Volume 4 [Driver Training].

    ERIC Educational Resources Information Center

    Pennsylvania State Dept. of Justice, Harrisburg. Bureau of Correction.

    The document is one of seven volumes of instructional materials developed around a cluster of Transportation Industries. Primarily technical in focus, they are designed to be used in a cluster-concept program and to integrate with a regular General Education Development (G.E.D.) program so that students may attain an employable skill level and a…

  6. Searching for the missing baryons in clusters

    PubMed Central

    Rasheed, Bilhuda; Bahcall, Neta; Bode, Paul

    2011-01-01

    Observations of clusters of galaxies suggest that they contain fewer baryons (gas plus stars) than the cosmic baryon fraction. This “missing baryon” puzzle is especially surprising for the most massive clusters, which are expected to be representative of the cosmic matter content of the universe (baryons and dark matter). Here we show that the baryons may not actually be missing from clusters, but rather are extended to larger radii than typically observed. The baryon deficiency is typically observed in the central regions of clusters (∼0.5 the virial radius). However, the observed gas-density profile is significantly shallower than the mass-density profile, implying that the gas is more extended than the mass and that the gas fraction increases with radius. We use the observed density profiles of gas and mass in clusters to extrapolate the measured baryon fraction as a function of radius and as a function of cluster mass. We find that the baryon fraction reaches the cosmic value near the virial radius for all groups and clusters above . This suggests that the baryons are not missing, they are simply located in cluster outskirts. Heating processes (such as shock-heating of the intracluster gas, supernovae, and Active Galactic Nuclei feedback) likely contribute to this expanded distribution. Upcoming observations should be able to detect these baryons. PMID:21321229

  7. Semi-Supervised Kernel Mean Shift Clustering.

    PubMed

    Anand, Saket; Mittal, Sushil; Tuzel, Oncel; Meer, Peter

    2014-06-01

    Mean shift clustering is a powerful nonparametric technique that does not require prior knowledge of the number of clusters and does not constrain the shape of the clusters. However, being completely unsupervised, its performance suffers when the original distance metric fails to capture the underlying cluster structure. Despite recent advances in semi-supervised clustering methods, there has been little effort towards incorporating supervision into mean shift. We propose a semi-supervised framework for kernel mean shift clustering (SKMS) that uses only pairwise constraints to guide the clustering procedure. The points are first mapped to a high-dimensional kernel space where the constraints are imposed by a linear transformation of the mapped points. This is achieved by modifying the initial kernel matrix by minimizing a log det divergence-based objective function. We show the advantages of SKMS by evaluating its performance on various synthetic and real datasets while comparing with state-of-the-art semi-supervised clustering algorithms. PMID:26353281

  8. Probing Massive Star Cluster Formation with ALMA

    NASA Astrophysics Data System (ADS)

    Johnson, Kelsey

    2015-08-01

    Observationally constraining the physical conditions that give rise to massive star clusters has been a long-standing challenge. Now with the ALMA Observatory coming on-line, we can finally begin to probe the birth environments of massive clusters in a variety of galaxies with sufficient angular resolution. In this talk I will give an overview of ALMA observations of galaxies in which candidate proto-super star cluster molecular clouds have been identified. These new data probe the physical conditions that give rise to super star clusters, providing information on their densities, pressures, and temperatures. In particular, the observations indicate that these clouds may be subject to external pressures of P/k > 108 K cm-3, which is consistent with the prevalence of optically observed adolescent super star clusters in interacting galaxy systems and other high pressure environments. ALMA observations also enable an assessement of the molecular cloud chemical abundances in the regions surrounding super star clusters. Molecular clouds associated with existing super star clusters are strongly correlated with HCO+ emission, but appear to have relatively low ratio of CO/HCO+ emission compared to other clouds, indicating that the super star clusters are impacting the molecular abundances in their vicinity.

  9. STELLAR ENCOUNTER RATE IN GALACTIC GLOBULAR CLUSTERS

    SciTech Connect

    Bahramian, Arash; Heinke, Craig O.; Sivakoff, Gregory R.; Gladstone, Jeanette C.

    2013-04-01

    The high stellar densities in the cores of globular clusters cause significant stellar interactions. These stellar interactions can produce close binary mass-transferring systems involving compact objects and their progeny, such as X-ray binaries and radio millisecond pulsars. Comparing the numbers of these systems and interaction rates in different clusters drives our understanding of how cluster parameters affect the production of close binaries. In this paper we estimate stellar encounter rates ({Gamma}) for 124 Galactic globular clusters based on observational data as opposed to the methods previously employed, which assumed 'King-model' profiles for all clusters. By deprojecting cluster surface brightness profiles to estimate luminosity density profiles, we treat 'King-model' and 'core-collapsed' clusters in the same way. In addition, we use Monte Carlo simulations to investigate the effects of uncertainties in various observational parameters (distance, reddening, surface brightness) on {Gamma}, producing the first catalog of globular cluster stellar encounter rates with estimated errors. Comparing our results with published observations of likely products of stellar interactions (numbers of X-ray binaries, numbers of radio millisecond pulsars, and {gamma}-ray luminosity) we find both clear correlations and some differences with published results.

  10. Business Clusters: Building on Local Strengths.

    ERIC Educational Resources Information Center

    Baldwin, Fred D.

    2001-01-01

    The Northwest Pennsylvania Industrial Resource Center's "wood cluster initiative" illustrates the benefits of rural business clusters. The initiative is turning a loose grouping of timber and forest-product firms into a competitive system by providing technical assistance, helping businesses plan and conduct job training programs, facilitating…

  11. Constrained Multi-View Video Face Clustering.

    PubMed

    Cao, Xiaochun; Zhang, Changqing; Zhou, Chengju; Fu, Huazhu; Foroosh, Hassan

    2015-11-01

    In this paper, we focus on face clustering in videos. To promote the performance of video clustering by multiple intrinsic cues, i.e., pairwise constraints and multiple views, we propose a constrained multi-view video face clustering method under a unified graph-based model. First, unlike most existing video face clustering methods which only employ these constraints in the clustering step, we strengthen the pairwise constraints through the whole video face clustering framework, both in sparse subspace representation and spectral clustering. In the constrained sparse subspace representation, the sparse representation is forced to explore unknown relationships. In the constrained spectral clustering, the constraints are used to guide for learning more reasonable new representations. Second, our method considers both the video face pairwise constraints as well as the multi-view consistence simultaneously. In particular, the graph regularization enforces the pairwise constraints to be respected and the co-regularization penalizes the disagreement among different graphs of multiple views. Experiments on three real-world video benchmark data sets demonstrate the significant improvements of our method over the state-of-the-art methods. PMID:26259245

  12. Giant light enhancement in atomic clusters

    SciTech Connect

    Gadomsky, O. N. Gadomskaya, I. V.; Altunin, K. K.

    2009-07-15

    We show that the polarizing effect of the atoms in an atomic cluster can lead to full compensation of the radiative damping of excited atomic states, a change in the sign of the dispersion of the atomic polarizability, and giant light enhancement by the atomic cluster.

  13. V-TECS Career Cluster Frameworks.

    ERIC Educational Resources Information Center

    Vocational Technical Education Consortium of States, Decatur, GA.

    This document includes 16 vocational-technical crosswalk wheels relating the 14 Vocational Technical Education Consortium of States (V-TECS) Career Families to the 16 Career Clusters developed by the U.S. Department of Education. The career clusters are based on the common academic, workplace, and technical knowledge and skills that cut across all…

  14. Transportation Cluster Volume 3 [Small Power Sources].

    ERIC Educational Resources Information Center

    Pennsylvania State Dept. of Justice, Harrisburg. Bureau of Correction.

    The document is one of seven volumes of instructional materials developed around a cluster of Transportation Industries. Primarily technical in focus, they are designed to be used in a cluster-concept program and to integrate with a regular General Education Development (G.E.D.) program so that students may attain an employable skill level and a…

  15. Record-breaking ancient galaxy clusters

    NASA Astrophysics Data System (ADS)

    2003-12-01

    A tale of two record-breaking clusters hi-res Size hi-res: 768 kb Credits: for RDCS1252: NASA, ESA, J.Blakeslee (Johns Hopkins Univ.), M.Postman (Space Telescope Science Inst.) and P.Rosati, Chris Lidman & Ricardo Demarco (European Southern Observ.) for TNJ1338: NASA, ESA, G.Miley (Leiden Observ.) and R.Overzier (Leiden Obs) A tale of two record-breaking clusters Looking back in time to when the universe was in its formative youth, the Advanced Camera for Surveys (ACS) aboard the NASA/ESA Hubble Space Telescope captured these revealing images of two galaxy clusters. The image at left, which is made with an additional infrared exposure taken with the European Southern Observatory’s Very Large Telescope, shows mature galaxies in a massive cluster that existed when the cosmos was 5000 million years old. The cluster, called RDCS1252.9-2927, is as massive as ‘300 trillion’ suns and is the most massive known cluster for its epoch. The image reveals the core of the cluster and is part of a much larger mosaic of the entire cluster. Dominating the core are a pair of large, reddish elliptical galaxies [near centre of image]. Their red colour indicates an older population of stars. Most of the stars are at least 1000 million years old. The two galaxies appear to be interacting and may eventually merge to form a larger galaxy that is comparable to the brightest galaxies seen in present-day clusters. The red galaxies surrounding the central pair are also cluster members. The cluster probably contains many thousands of galaxies, but only about 50 can be seen in this image. The full mosaic (heic0313d) reveals several hundred cluster members. Many of the other galaxies in the image, including several of the blue galaxies, are foreground or background galaxies. The colour-composite image was assembled from two observations (through i and z filters) taken between May and June 2002 by the ACS Wide Field Camera, and one image with the ISAAC instrument on the VLT taken in 2002

  16. The Swift AGN and Cluster Survey

    NASA Astrophysics Data System (ADS)

    Danae Griffin, Rhiannon; Dai, Xinyu; Kochanek, Christopher S.; Bregman, Joel N.; Nugent, Jenna

    2016-01-01

    The Swift active galactic nucleus (AGN) and Cluster Survey (SACS) uses 125 deg^2 of Swift X-ray Telescope serendipitous fields with variable depths surrounding X-ray bursts to provide a medium depth (4 × 10^-15 erg cm^-2 s^-1) and area survey filling the gap between deep, narrow Chandra/XMM-Newton surveys and wide, shallow ROSAT surveys. Here, we present the first two papers in a series of publications for SACS. In the first paper, we introduce our method and catalog of 22,563 point sources and 442 extended sources. We examine the number counts of the AGN and galaxy cluster populations. SACS provides excellent constraints on the AGN number counts at the bright end with negligible uncertainties due to cosmic variance, and these constraints are consistent with previous measurements. The depth and areal coverage of SACS is well suited for galaxy cluster surveys outside the local universe, reaching z ˜ 1 for massive clusters. In the second paper, we use Sloan Digital Sky Survey (SDSS) DR8 data to study the 203 extended SACS sources that are located within the SDSS footprint. We search for galaxy over-densities in 3-D space using SDSS galaxies and their photometric redshifts near the Swift galaxy cluster candidates. We find 103 Swift clusters with a > 3σ over-density. The remaining targets are potentially located at higher redshifts and require deeper optical follow-up observations for confirmations as galaxy clusters. We present a series of cluster properties including the redshift, BCG magnitude, BCG-to-X-ray center offset, optical richness, X-ray luminosity and red sequences. We compare the observed redshift distribution of the sample with a theoretical model, and find that our sample is complete for z ≤ 0.3 and 80% complete for z ≤ 0.4, consistent with the survey depth of SDSS. We also match our SDSS confirmed Swift clusters to existing cluster catalogs, and find 42, 2 and 1 matches in optical, X-ray and SZ catalogs, respectively, so the majority of these

  17. Electrochemical Potential Derived from Atomic Cluster Structures.

    PubMed

    Du, Jinglian; Xiao, Debao; Wen, Bin; Melnik, Roderick; Kawazoe, Yoshiyuki

    2016-02-01

    Based on the atomic cluster structures and free electron approximation model, it is revealed that the electrochemical potential (ECP) for the system of interest is proportional to the reciprocal of atomic cluster radius squared, i.e., φ = k·(1/r(2)). Applied to elemental crystals, the correlation between atomic cluster radii and the ECP that we have predicted agrees well with the previously reported results. In addition, some other physicochemical properties associated with the ECP have also been found relevant to the atomic cluster radii of materials. Thus, the atomic cluster radii can be perceived as an effective characteristic parameter to measure the ECP and related properties of materials. Our results provide a better understanding of ECP directly from the atomic structures perspective. PMID:26801811

  18. On the clustering of multidimensional pictorial data

    NASA Technical Reports Server (NTRS)

    Bryant, J. D. (Principal Investigator)

    1979-01-01

    Obvious approaches to reducing the cost (in computer resources) of applying current clustering techniques to the problem of remote sensing are discussed. The use of spatial information in finding fields and in classifying mixture pixels is examined, and the AMOEBA clustering program is described. Internally, a pattern recognition program, from without, AMOEBA appears to be an unsupervised clustering program. It is fast and automatic. No choices (such as arbitrary thresholds to set split/combine sequences) need be made. The problem of finding the number of clusters is solved automatically. At the conclusion of the program, all points in the scene are classified; however, a provision is included for a reject classification of some points which, within the theoretical framework, cannot rationally be assigned to any cluster.

  19. Clusters in neutron-rich light nuclei

    NASA Astrophysics Data System (ADS)

    Jelavić Malenica, D.; Milin, M.; Di Pietro, A.; Figuera, P.; Lattuada, M.; Miljanić, D.; Musumarra, A.; Pellegriti, M. G.; Prepolec, L.; Scuderi, V.; Skukan, N.; Soić, N.; Torresi, D.; Uroić, M.

    2016-05-01

    Due to their high selectivity, transfer and sequential decay reactions are powerful tools for studies of both single particle (nucleon) and cluster states in light nuclei. Their use is particularly simple for investigations of α-particle clustering (because α-particle has Jπ=0+, which simplifies spin and parity assignments to observed cluster states), but they are also easily applicable to other types of clustering. Recent results on clustering in neutron-rich isotopes of beryllium, boron and carbon obtained measuring the 10B+10B reactions (at 50 and 72 MeV) are presented. The highly efficient and segmented detector systems used, built from 4 Double Sided Silicon Strip Detectors (DSSSD) allowed detection of double and multiple coincidences and, in that way, studies of states populated in transfer reactions, as well as their sequential decay.

  20. Fission and dipole resonances in metal clusters

    SciTech Connect

    Martin, T. P.; Billas, I. M. L.; Branz, W.; Heinebrodt, M.; Tast, F.; Malinowski, N.

    1997-06-20

    It is not obvious that metal clusters should behave like atomic nuclei--but they do. Of course the energy and distance scales are quite different. But aside from this, the properties of these two forms of condensed matter are amazingly similar. The shell model developed by nuclear physicists describes very nicely the electronic properties of alkali metal clusters. The giant dipole resonances in the excitation spectra of nuclei have their analogue in the plasmon resonances of metal clusters. Finally, the droplet model describing the fission of unstable nuclei can be successively applied to the fragmentation of highly charged metal clusters. The similarity between clusters and nuclei is not accidental. Both systems consist of fermions moving, nearly freely, in a confined space.

  1. Web document clustering using hyperlink structures

    SciTech Connect

    He, Xiaofeng; Zha, Hongyuan; Ding, Chris H.Q; Simon, Horst D.

    2001-05-07

    With the exponential growth of information on the World Wide Web there is great demand for developing efficient and effective methods for organizing and retrieving the information available. Document clustering plays an important role in information retrieval and taxonomy management for the World Wide Web and remains an interesting and challenging problem in the field of web computing. In this paper we consider document clustering methods exploring textual information hyperlink structure and co-citation relations. In particular we apply the normalized cut clustering method developed in computer vision to the task of hyperdocument clustering. We also explore some theoretical connections of the normalized-cut method to K-means method. We then experiment with normalized-cut method in the context of clustering query result sets for web search engines.

  2. Inhomogeneous high harmonic generation in krypton clusters.

    PubMed

    Ruf, H; Handschin, C; Cireasa, R; Thiré, N; Ferré, A; Petit, S; Descamps, D; Mével, E; Constant, E; Blanchet, V; Fabre, B; Mairesse, Y

    2013-02-22

    High order harmonic generation from clusters is a controversial topic: conflicting theories exist, with different explanations for similar experimental observations. From an experimental point of view, separating the contributions from monomers and clusters is challenging. By performing a spectrally and spatially resolved study in a controlled mixture of clusters and monomers, we are able to isolate a region of the spectrum where the emission purely originates from clusters. Surprisingly, the emission from clusters is depolarized, which is the signature of statistical inhomogeneous emission from a low-density source. The harmonic response to laser ellipticity shows that this generation is produced by a new recollisional mechanism, which opens the way to future theoretical studies.

  3. Clustering high dimensional data using RIA

    SciTech Connect

    Aziz, Nazrina

    2015-05-15

    Clustering may simply represent a convenient method for organizing a large data set so that it can easily be understood and information can efficiently be retrieved. However, identifying cluster in high dimensionality data sets is a difficult task because of the curse of dimensionality. Another challenge in clustering is some traditional functions cannot capture the pattern dissimilarity among objects. In this article, we used an alternative dissimilarity measurement called Robust Influence Angle (RIA) in the partitioning method. RIA is developed using eigenstructure of the covariance matrix and robust principal component score. We notice that, it can obtain cluster easily and hence avoid the curse of dimensionality. It is also manage to cluster large data sets with mixed numeric and categorical value.

  4. Swarm Intelligence in Text Document Clustering

    SciTech Connect

    Cui, Xiaohui; Potok, Thomas E

    2008-01-01

    Social animals or insects in nature often exhibit a form of emergent collective behavior. The research field that attempts to design algorithms or distributed problem-solving devices inspired by the collective behavior of social insect colonies is called Swarm Intelligence. Compared to the traditional algorithms, the swarm algorithms are usually flexible, robust, decentralized and self-organized. These characters make the swarm algorithms suitable for solving complex problems, such as document collection clustering. The major challenge of today's information society is being overwhelmed with information on any topic they are searching for. Fast and high-quality document clustering algorithms play an important role in helping users to effectively navigate, summarize, and organize the overwhelmed information. In this chapter, we introduce three nature inspired swarm intelligence clustering approaches for document clustering analysis. These clustering algorithms use stochastic and heuristic principles discovered from observing bird flocks, fish schools and ant food forage.

  5. Electrochemical Potential Derived from Atomic Cluster Structures.

    PubMed

    Du, Jinglian; Xiao, Debao; Wen, Bin; Melnik, Roderick; Kawazoe, Yoshiyuki

    2016-02-01

    Based on the atomic cluster structures and free electron approximation model, it is revealed that the electrochemical potential (ECP) for the system of interest is proportional to the reciprocal of atomic cluster radius squared, i.e., φ = k·(1/r(2)). Applied to elemental crystals, the correlation between atomic cluster radii and the ECP that we have predicted agrees well with the previously reported results. In addition, some other physicochemical properties associated with the ECP have also been found relevant to the atomic cluster radii of materials. Thus, the atomic cluster radii can be perceived as an effective characteristic parameter to measure the ECP and related properties of materials. Our results provide a better understanding of ECP directly from the atomic structures perspective.

  6. IP Profiling via Service Cluster Membership Vectors

    SciTech Connect

    Bartoletti, A

    2009-02-23

    This study investigates the feasibility of establishing and maintaining a system of compact IP behavioral profiles as a robust means of computer anomaly definition and detection. These profiles are based upon the degree to which a system's (IP's) network traffic is distributed among stable characteristic clusters derived of the aggregate session traffic generated by each of the major network services. In short, an IP's profile represents its degree of membership in these derived service clusters. The goal is to quantify and rank behaviors that are outside of the statistical norm for the services in question, or present significant deviation from profile for individual client IPs. Herein, we establish stable clusters for accessible features of common session traffic, migrate these clusters over time, define IP behavior profiles with respect to these clusters, migrate individual IP profiles over time, and demonstrate the detection of IP behavioral changes in terms of deviation from profile.

  7. Dynamic multifactor clustering of financial networks.

    PubMed

    Ross, Gordon J

    2014-02-01

    We investigate the tendency for financial instruments to form clusters when there are multiple factors influencing the correlation structure. Specifically, we consider a stock portfolio which contains companies from different industrial sectors, located in several different countries. Both sector membership and geography combine to create a complex clustering structure where companies seem to first be divided based on sector, with geographical subclusters emerging within each industrial sector. We argue that standard techniques for detecting overlapping clusters and communities are not able to capture this type of structure and show how robust regression techniques can instead be used to remove the influence of both sector and geography from the correlation matrix separately. Our analysis reveals that prior to the 2008 financial crisis, companies did not tend to form clusters based on geography. This changed immediately following the crisis, with geography becoming a more important determinant of clustering structure. PMID:25353536

  8. Dynamic multifactor clustering of financial networks

    NASA Astrophysics Data System (ADS)

    Ross, Gordon J.

    2014-02-01

    We investigate the tendency for financial instruments to form clusters when there are multiple factors influencing the correlation structure. Specifically, we consider a stock portfolio which contains companies from different industrial sectors, located in several different countries. Both sector membership and geography combine to create a complex clustering structure where companies seem to first be divided based on sector, with geographical subclusters emerging within each industrial sector. We argue that standard techniques for detecting overlapping clusters and communities are not able to capture this type of structure and show how robust regression techniques can instead be used to remove the influence of both sector and geography from the correlation matrix separately. Our analysis reveals that prior to the 2008 financial crisis, companies did not tend to form clusters based on geography. This changed immediately following the crisis, with geography becoming a more important determinant of clustering structure.

  9. Self-Assembled Plasmonic Nanoparticle Clusters

    NASA Astrophysics Data System (ADS)

    Fan, Jonathan A.; Wu, Chihhui; Bao, Kui; Bao, Jiming; Bardhan, Rizia; Halas, Naomi J.; Manoharan, Vinothan N.; Nordlander, Peter; Shvets, Gennady; Capasso, Federico

    2010-05-01

    The self-assembly of colloids is an alternative to top-down processing that enables the fabrication of nanostructures. We show that self-assembled clusters of metal-dielectric spheres are the basis for nanophotonic structures. By tailoring the number and position of spheres in close-packed clusters, plasmon modes exhibiting strong magnetic and Fano-like resonances emerge. The use of identical spheres simplifies cluster assembly and facilitates the fabrication of highly symmetric structures. Dielectric spacers are used to tailor the interparticle spacing in these clusters to be approximately 2 nanometers. These types of chemically synthesized nanoparticle clusters can be generalized to other two- and three-dimensional structures and can serve as building blocks for new metamaterials.

  10. Cluster outskirts and the missing baryons

    NASA Astrophysics Data System (ADS)

    Eckert, D.

    2016-06-01

    Galaxy clusters are located at the crossroads of intergalactic filaments and are still forming through the continuous merging and accretion of smaller structures from the surrounding cosmic web. Deep, wide-field X-ray studies of the outskirts of the most massive clusters bring us valuable insight into the processes leading to the growth of cosmic structures. In addition, cluster outskirts are privileged sites to search for the missing baryons, which are thought to reside within the filaments of the cosmic web. I will present the XMM cluster outskirts project, a VLP that aims at mapping the outskirts of 13 nearby clusters. Based on the results obtained with this program, I will then explore ideas to exploit the capabilities of XMM during the next decade.

  11. Block Coloplyer Nanoreactors for Inorganic Cluster Synthesis

    NASA Astrophysics Data System (ADS)

    Cohen, Robert E.

    1997-03-01

    We have generalized our work on the spatial confinement of inorganic clusters in block copolymers to a nanoreactor scheme for cluster synthesis. Using this new methodology, a wide range of inorganic clusters can be synthesized from a single block copolymer starting material. Metals are selectively sequestered into domains of the heterogeneous block copolymer morphology, either from aqueous solutions of suitably chosen salts or via vapor permeation of organometallic compounds. Once "loaded", these metal-containing domains serve as localized reaction sites for cluster synthesis. The metal-sequestering sites are rejuvenated, rendering the nanoreactors capable of being reloaded with more of the same metal, or another, for further cluster synthesis. Magnetic and optical properties of free-standing block copolymer films containing various types of nanoclusters will be discussed.

  12. Photometric analysis of Collinder Cluster 223

    NASA Astrophysics Data System (ADS)

    Duplancic Videla, M. F.; Molina, S.; González, J. F.

    We present photometric observations of the open-cluster Collinder 223 (RA= 10h 30m 38s , dec =-60° 06' 39'' ), obtained from observation with the HSH telescope in CASLEO. This cluster has not been studied extensively, there is only one photoelectric photometric UBV study, done by Clariá and Lapasset (1991). A later study, done by Tadross (2004), reanalyzed the data, however, no other photometric measurements have been carried out until present. We observed seven fields in the cluster which were chosen prioritizing the zones of major stellar concentration. We obtained color-magnitude diagrams of the cluster, reaching stars two magnitudes weaker than those previously obtained by Clariá and Lapasset. The cluster sequence shows well in accordance with the isochrone corresponding to the age of 3.5 10E7 yr.

  13. Void coalescence within periodic clusters of particles

    NASA Astrophysics Data System (ADS)

    Thomson, C. I. A.; Worswick, M. J.; Pilkey, A. K.; Lloyd, D. J.

    2003-01-01

    The effect of particle clustering on void damage rates in a ductile material under triaxial loading conditions is examined using three-dimensional finite element analysis. An infinite material containing a regular distribution of clustered particles is modelled using a unit cell approach. Three discrete particles are introduced into each unit cell while a secondary population of small particles within the surrounding matrix is represented using the Gurson-Tvergaard-Needleman (GTN) constitutive equations. Deformation strain states characteristic of sheet metal forming are considered; that is, deep drawing, plane strain and biaxial stretching. Uniaxial tensile stress states with varying levels of superimposed hydrostatic tension are also examined. The orientation of a particle cluster with respect to the direction of major principal loading is shown to significantly influence failure strains. Coalescence of voids within a first-order particle cluster (consisting of three particles) is a stable event while collapse of inter-cluster ligaments leads to imminent material collapse through void-sheeting.

  14. Bipartite graph partitioning and data clustering

    SciTech Connect

    Zha, Hongyuan; He, Xiaofeng; Ding, Chris; Gu, Ming; Simon, Horst D.

    2001-05-07

    Many data types arising from data mining applications can be modeled as bipartite graphs, examples include terms and documents in a text corpus, customers and purchasing items in market basket analysis and reviewers and movies in a movie recommender system. In this paper, the authors propose a new data clustering method based on partitioning the underlying biopartite graph. The partition is constructed by minimizing a normalized sum of edge weights between unmatched pairs of vertices of the bipartite graph. They show that an approximate solution to the minimization problem can be obtained by computing a partial singular value decomposition (SVD) of the associated edge weight matrix of the bipartite graph. They point out the connection of their clustering algorithm to correspondence analysis used in multivariate analysis. They also briefly discuss the issue of assigning data objects to multiple clusters. In the experimental results, they apply their clustering algorithm to the problem of document clustering to illustrate its effectiveness and efficiency.

  15. Ages of globular clusters and helium diffusion

    NASA Technical Reports Server (NTRS)

    Chaboyer, Brian; Sarajedini, Ata; Demarque, Pierre

    1992-01-01

    Evolutionary tracks have been calculated with alpha-enhanced compositions which cover the entire globular cluster metallicity range and have constructed isochrones which include the effects of microscopic diffusion of helium. The turnoff magnitudes from the isochrones were combined with the theoretical RR Lyrae magnitudes from Lee to determine the ages of 32 Galactic globular clusters using the magnitude difference between the turnoff and horizontal branch. It is found that including the effects of helium diffusion has a negligible effect on the derived ages of globular clusters. Regardless of the inclusion of helium diffusion, a significant age spread of 5 Gyr among the globular clusters is found. The oldest globular clusters studied here are 17 +/- 2 Gyr old.

  16. Life without Fe-S clusters.

    PubMed

    Rocha, Agostinho G; Dancis, Andrew

    2016-03-01

    Fe-S clusters are critically important cofactors implicated in numerous cellular processes, including respiration, amino acid biosynthesis, cofactor biosynthesis, tRNA modification, DNA repair and regulation of gene expression. In the accompanying manuscript, Tanaka et al. show that reengineering of the isoprenoid biosynthetic pathway in E. coli (to bypass the usage of essential Fe-S cluster proteins by inserting the mevalonate pathway) can offset the indispensability of the Fe-S cluster biosynthetic systems. They show that the resulting Δisc Δsuf double mutants supplemented with mevalonate can grow slowly without detectable Fe-S cluster proteins. This result is astounding and raises interesting questions about what is essential and what is dispensable in the compendium of Fe-S cluster protein functions in this cell. PMID:26560645

  17. Classical and quantum physics of hydrogen clusters.

    PubMed

    Mezzacapo, Fabio; Boninsegni, Massimo

    2009-04-22

    We present results of a comprehensive theoretical investigation of the low temperature (T) properties of clusters of para-hydrogen (p-H(2)), both pristine as well as doped with isotopic impurities (i.e., ortho-deuterium, o-D(2)). We study clusters comprising up to N = 40 molecules, by means of quantum simulations based on the continuous-space Worm algorithm. Pristine p-H(2) clusters are liquid-like and superfluid in the [Formula: see text] limit. The superfluid signal is uniform throughout these clusters; it is underlain by long cycles of permutation of molecules. Clusters with more than 22 molecules display solid-like, essentially classical behavior at temperatures down to T∼1 K; some of them are seen to turn liquid-like at sufficiently low T (quantum melting).

  18. Radio maps for the REXCESS cluster sample

    NASA Astrophysics Data System (ADS)

    Heidenreich, Susanne

    2011-07-01

    We present fluxes and radio maps for the REXCESS cluster sample. The REXCESS sample consists of 33 local (z<0.2) clusters drawn from the flux-limited REFLEX catalogue. It is the first time where this sample is completely mapped in the 610 MHz band. We chose this unique sample in order to fully sample the cluster luminosity function, unbiased from x-ray luminosities and cluster dynamical state. The data for these maps were collected by using the GMRT in Pune, India. After mapping the individual sources and determining the fluxes, the maps will be investigated to examine the different types of radio outburst and there influence on cluster heating. Additionally it will give information about the injection of energy by larger scale central radio emission.

  19. Image clustering using fuzzy graph theory

    NASA Astrophysics Data System (ADS)

    Jafarkhani, Hamid; Tarokh, Vahid

    1999-12-01

    We propose an image clustering algorithm which uses fuzzy graph theory. First, we define a fuzzy graph and the concept of connectivity for a fuzzy graph. Then, based on our definition of connectivity we propose an algorithm which finds connected subgraphs of the original fuzzy graph. Each connected subgraph can be considered as a cluster. As an application of our algorithm, we consider a database of images. We calculate a similarity measure between any paris of images in the database and generate the corresponding fuzzy graph. The, we find the subgraphs of the resulting fuzzy graph using our algorithm. Each subgraph corresponds to a cluster. We apply our image clustering algorithm to the key frames of news programs to find the anchorperson clusters. Simulation results show that our algorithm is successful to find most of anchorperson frames from the database.

  20. Spiral Galaxies in MKW/AWM Clusters

    NASA Astrophysics Data System (ADS)

    Williams, Barbara A.

    1997-03-01

    Observations have been made of the neutral hydrogen content of more than 170 galaxies within MKW 4, MKW 7, MKW 8, MKW 9, MKW 11, AWM 1, AWM 3, AWM 4, and AWM 5. This sample of nine clusters is representative of the general class of poor clusters identified by MKW and AWM in that they all contain D-- or cD--like dominant galaxies at their dynamical centers. We examine the neutral hydrogen (HI) content of the spiral members in these systems as a function of the local and global properties of the cluster, i.e., galaxy density, x-ray intra cluster gas pressure, x-ray and optical luminosities, and compare our findings with the HI properties of similar galaxies in rich clusters and loose groups of galaxies.

  1. Worldwide clustering of the corruption perception

    NASA Astrophysics Data System (ADS)

    Paulus, Michal; Kristoufek, Ladislav

    2015-06-01

    We inspect a possible clustering structure of the corruption perception among 134 countries. Using the average linkage clustering, we uncover a well-defined hierarchy in the relationships among countries. Four main clusters are identified and they suggest that countries worldwide can be quite well separated according to their perception of corruption. Moreover, we find a strong connection between corruption levels and a stage of development inside the clusters. The ranking of countries according to their corruption perfectly copies the ranking according to the economic performance measured by the gross domestic product per capita of the member states. To the best of our knowledge, this study is the first one to present an application of hierarchical and clustering methods to the specific case of corruption.

  2. Dynamical evolution of globular-cluster systems in clusters of galaxies

    SciTech Connect

    Muzzio, J.C.

    1987-04-01

    The dynamical processes that affect globular-cluster systems in clusters of galaxies are analyzed. Two-body and impulsive approximations are utilized to study dynamical friction, drag force, tidal stripping, tidal radii, globular-cluster swapping, tidal accretion, and galactic cannibalism. The evolution of galaxies and the collision of galaxies are simulated numerically; the steps involved in the simulation are described. The simulated data are compared with observations. Consideration is given to the number of galaxies, halo extension, location of the galaxies, distribution of the missing mass, nonequilibrium initial conditions, mass dependence, massive central galaxies, globular-cluster distribution, and lost globular clusters. 116 references.

  3. Constraining the Evolution of Poor Clusters

    NASA Astrophysics Data System (ADS)

    Broming, Emma J.; Fuse, C. R.

    2012-01-01

    There currently exists no method by which to quantify the evolutionary state of poor clusters (PCs). Research by Broming & Fuse (2010) demonstrated that the evolution of Hickson compact groups (HCGs) are constrained by the correlation between the X-ray luminosities of point sources and diffuse gas. The current investigation adopts an analogous approach to understanding PCs. Plionis et al. (2009) proposed a theory to define the evolution of poor clusters. The theory asserts that cannibalism of galaxies causes a cluster to become more spherical, develop increased velocity dispersion and increased X-ray temperature and gas luminosity. Data used to quantify the evolution of the poor clusters were compiled across multiple wavelengths. The sample includes 162 objects from the WBL catalogue (White et al. 1999), 30 poor clusters in the Chandra X-ray Observatory archive, and 15 Abell poor clusters observed with BAX (Sadat et al. 2004). Preliminary results indicate that the cluster velocity dispersion and X-ray gas and point source luminosities can be used to highlight a weak correlation. An evolutionary trend was observed for multiple correlations detailed herein. The current study is a continuation of the work by Broming & Fuse examining point sources and their properties to determine the evolutionary stage of compact groups, poor clusters, and their proposed remnants, isolated ellipticals and fossil groups. Preliminary data suggests that compact groups and their high-mass counterpart, poor clusters, evolve along tracks identified in the X-ray gas - X-ray point source relation. While compact groups likely evolve into isolated elliptical galaxies, fossil groups display properties that suggest they are the remains of fully coalesced poor clusters.

  4. STAR CLUSTERS IN PSEUDOBULGES OF SPIRAL GALAXIES

    SciTech Connect

    Di Nino, Daiana; Trenti, Michele; Stiavelli, Massimo; Carollo, C. Marcella; Scarlata, Claudia; Wyse, Rosemary F. G.

    2009-11-15

    We present a study of the properties of the star-cluster systems around pseudobulges of late-type spiral galaxies using a sample of 11 galaxies with distances from 17 Mpc to 37 Mpc. Star clusters are identified from multiband Hubble Space Telescope ACS and WFPC2 imaging data by combining detections in three bands (F435W and F814W with ACS and F606W with WFPC2). The photometric data are then compared to population synthesis models to infer the masses and ages of the star clusters. Photometric errors and completeness are estimated by means of artificial source Monte Carlo simulations. Dust extinction is estimated by considering F160W NICMOS observations of the central regions of the galaxies, augmenting our wavelength coverage. In all galaxies we identify star clusters with a wide range of ages, from young (age {approx}< 8 Myr) blue clusters, with typical mass of 10{sup 3} M {sub sun} to older (age >100-250 Myr), more massive, red clusters. Some of the latter might likely evolve into objects similar to the Milky Way's globular clusters. We compute the specific frequencies for the older clusters with respect to the galaxy and bulge luminosities. Specific frequencies relative to the galaxy light appear consistent with the globular cluster specific frequencies of early-type spirals. We compare the specific frequencies relative to the bulge light with the globular cluster specific frequencies of dwarf galaxies, which have a surface brightness profile that is similar to that of the pseudobulges in our sample. The specific frequencies we derive for our sample galaxies are higher than those of the dwarf galaxies, supporting an evolutionary scenario in which some of the dwarf galaxies might be the remnants of harassed late-type spiral galaxies that hosted a pseudobulge.

  5. Dynamically allocated virtual clustering management system

    NASA Astrophysics Data System (ADS)

    Marcus, Kelvin; Cannata, Jess

    2013-05-01

    The U.S Army Research Laboratory (ARL) has built a "Wireless Emulation Lab" to support research in wireless mobile networks. In our current experimentation environment, our researchers need the capability to run clusters of heterogeneous nodes to model emulated wireless tactical networks where each node could contain a different operating system, application set, and physical hardware. To complicate matters, most experiments require the researcher to have root privileges. Our previous solution of using a single shared cluster of statically deployed virtual machines did not sufficiently separate each user's experiment due to undesirable network crosstalk, thus only one experiment could be run at a time. In addition, the cluster did not make efficient use of our servers and physical networks. To address these concerns, we created the Dynamically Allocated Virtual Clustering management system (DAVC). This system leverages existing open-source software to create private clusters of nodes that are either virtual or physical machines. These clusters can be utilized for software development, experimentation, and integration with existing hardware and software. The system uses the Grid Engine job scheduler to efficiently allocate virtual machines to idle systems and networks. The system deploys stateless nodes via network booting. The system uses 802.1Q Virtual LANs (VLANs) to prevent experimentation crosstalk and to allow for complex, private networks eliminating the need to map each virtual machine to a specific switch port. The system monitors the health of the clusters and the underlying physical servers and it maintains cluster usage statistics for historical trends. Users can start private clusters of heterogeneous nodes with root privileges for the duration of the experiment. Users also control when to shutdown their clusters.

  6. ChaMP Serendipitous Galaxy Cluster Survey

    SciTech Connect

    Barkhouse, Wayne A.; Green, P.J.; Vikhlinin, A.; Kim, D.-W.; Perley, D.; Cameron, R.; Silverman, J.; Mossman, A.; Burenin, R.; Jannuzi, B.T.; Kim, M.; Smith, M.G.; Smith, R.C.; Tananbaum, H.; Wilkes, B.J.; /Harvard-Smithsonian Ctr. Astrophys. /UC, Berkeley, Astron. Dept. /SLAC /Garching, Max Planck Inst., MPE /Moscow, Space Res. Inst. /NOAO, Tucson /Cerro-Tololo InterAmerican Obs.

    2006-04-03

    We present a survey of serendipitous extended X-ray sources and optical cluster candidates from the Chandra Multi-wavelength Project (ChaMP). Our main goal is to make an unbiased comparison of X-ray and optical cluster detection methods. In 130 archival Chandra pointings covering 13 square degrees, we use a wavelet decomposition technique to detect 55 extended sources, of which 6 are nearby single galaxies. Our X-ray cluster catalog reaches a typical flux limit of about {approx} 10{sup -14} erg s{sup -1} cm{sup -2}, with a median cluster core radius of 21''. For 56 of the 130 X-ray fields, we use the ChaMP's deep NOAO/4m MOSAIC g', r', and i' imaging to independently detect cluster candidates using a Voronoi tessellation and percolation (VTP) method. Red-sequence filtering decreases the galaxy fore/background contamination and provides photometric redshifts to z {approx} 0.7. From the overlapping 6.1 square degree X-ray/optical imaging, we find 115 optical clusters (of which 11% are in the X-ray catalog) and 28 X-ray clusters (of which 46% are in the optical VTP catalog). The median redshift of the 13 X-ray/optical clusters is 0.41, and their median X-ray luminosity (0.5-2 keV) is L{sub X} = (2.65 {+-} 0.19) x 10{sup 43} ergs s{sup -1}. The clusters in our sample that are only detected in our optical data are poorer on average ({approx} 4{sigma}) than the X-ray/optically matched clusters, which may partially explain the difference in the detection fractions.

  7. ASteCA: Automated Stellar Cluster Analysis

    NASA Astrophysics Data System (ADS)

    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.

  8. The 3-Dimensional Structure of Galaxy Clusters

    NASA Astrophysics Data System (ADS)

    King, Lindsay

    NASA's Hubble Space Telescope Multi-Cycle Treasury Program CLASH (PI Postman) has provided the community with the most detailed views ever of the central regions of massive galaxy clusters. These galaxy clusters have also been observed with NASA's Chandra X-Ray Observatory, with the ground-based Subaru telescope, and with other ground- and space-based facilities, resulting in unprecedented multi-wavelength data sets of the most massive bound structures in the universe. Fitting 3-Dimensional mass models is crucial to understanding how mass is distributed in individual clusters, investigating the properties of dark matter, and testing our cosmological model. With the exquisite data available, the time is now ideal to undertake this analysis. We propose to use algorithms that we have developed and obtain mass models for the clusters from the CLASH sample. The project would use archival gravitational lensing data, X-ray data of the cluster's hot gas and additional constraints from Sunyaev-Zel'dovich (SZ) data. Specifically, we would model the 23 clusters for which both HST and Subaru data (or in one case WFI data) are publicly available, since the exquisite imaging of HST in the clusters' central regions is beautifully augmented by the wide field coverage of Subaru imaging. If the true 3-D shapes of clusters are not properly accounted for when analysing data, this can lead to inaccuracies in the mass density profiles of individual clusters - up to 50% bias in mass for the most highly triaxial systems. Our proposed project represents an independent analysis of the CLASH sample, complementary to that of the CLASH team, probing the triaxial shapes and orientations of the cluster dark matter halos and hot gas. Our findings will be relevant to the analysis of data from future missions such as JWST and Euclid, and also to ground-based surveys to be made with telescopes such as LSST.

  9. Clusters of classical water models

    NASA Astrophysics Data System (ADS)

    Kiss, Péter T.; Baranyai, András

    2009-11-01

    The properties of clusters can be used as tests of models constructed for molecular simulation of water. We searched for configurations with minimal energies for a small number of molecules. We identified topologically different structures close to the absolute energy minimum of the system by calculating overlap integrals and enumerating hydrogen bonds. Starting from the dimer, we found increasing number of topologically different, low-energy arrangements for the trimer(3), the tetramer(6), the pentamer(6), and the hexamer(9). We studied simple models with polarizable point dipole. These were the BSV model [J. Brodholt et al., Mol. Phys. 86, 149 (1995)], the DC model [L. X. Dang and T. M. Chang, J. Chem. Phys. 106, 8149 (1997)], and the GCP model [P. Paricaud et al., J. Chem. Phys. 122, 244511 (2005)]. As an alternative the SWM4-DP and the SWM4-NDP charge-on-spring models [G. Lamoureux et al., Chem. Phys. Lett. 418, 245 (2006)] were also investigated. To study the impact of polarizability restricted to the plane of the molecule we carried out calculations for the SPC-FQ and TIP4P-FQ models, too [S. W. Rick et al., J. Chem. Phys. 101, 6141 (1994)]. In addition to them, justified by their widespread use even for near critical or surface behavior calculations, we identified clusters for five nonpolarizable models of ambient water, SPC/E [H. J. C. Berendsen et al., J. Phys. Chem. 91, 6269 (1987)], TIP4P [W. L. Jorgensen et al., J. Chem. Phys. 79, 926 (1983)], TIP4P-EW [H. W. Horn et al., J. Chem. Phys. 120, 9665 (2004)], and TIP4P/2005 [J. L. F. Abascal and C. Vega, J. Chem. Phys. 123, 234505 (2005)]. The fifth was a five-site model named TIP5P [M. W. Mahoney and W. L. Jorgensen, J. Chem. Phys. 112, 8910 (2000)]. To see the impact of the vibrations we studied the flexible SPC model. [K. Toukan and A. Rahman, Phys. Rev. B 31, 2643 (1985)]. We evaluated the results comparing them with experimental data and quantum chemical calculations. The position of the negative

  10. Monitoring the Orion Nebula Cluster

    NASA Astrophysics Data System (ADS)

    Reipurth, Bo

    The VYSOS (Variable Young Stars Optical Survey) project has at its disposal five small telescopes: a 5-inch and a 20-inch robotic optical imaging telescope in Hawaii funded by the NSF, and a 6-inch robotic optical imaging telescope, a 32-inch robotic infrared imaging telescope, and a 60-inch optical spectroscopic telescope in Chile, funded and operated from Germany. Through an agreement between the leaders of the two sites (B. Reipurth and R. Chini), it has been decided to devote a significant fraction of time on these facilities to a large Key Project, conducting a massive monitoring survey of the Orion Nebula Cluster. The vast data streams are being reduced through automated customized pipelines. The applicant seeks funding to employ a postdoc and an undergraduate assistant to work at the University of Hawaii and collaborate on the analysis of the data. Virtually all young stars are variable, with a wide range of amplitudes and characteristic timescales. This is mainly due to accretion shocks as material from circumstellar disks fall onto the stars along magnetic funnel flows, but also giant star spots, magnetic flares, occultations by orbiting dust condensations, and eclipses by companions can modulate the light from the nascent star. It is increasingly recognized that the rather static view of pre-main sequence evolution that has prevailed for many years is misleading, and that time-dependent phenomena may hold the key to an understanding of the way young stars grow and their circumstellar environments evolve. The VYSOS project is designed to bring sophisticated modern techniques to bear on the long neglected problem of variability in young solar type stars. To interpret the observations they will be compared to sophisticated MHD models of circumstellar disks around young stars. The Orion Nebula Cluster is the nearest rich region of star formation, and numerous, albeit heterogeneous, studies exist of the cluster members. The present study will provide the first

  11. Basic research in crystalline and noncrystalline ceramic systems. Annual report, August 1, 1979-October 31, 1980

    SciTech Connect

    Sempolinski, D. R.; Kingery, W. D.; Tuller, H. L.; Diear, J. M.; Dudney, N. J.; Coble, R. L.; French, R.; Cheng, K. W.; Giraldez, E.; Henriksen, A. F.; Kijima, K.; Gattuso, T. R.; Dolhert, L.; Gambino, J.; Yager, T. A.; Chiang, Y. M.; Tajima, Y.; Dynys, J. M.; Cannon, Jr., R. M.; Kuo-Wen, Tsui; Hong, W.; Handwerker, C. A.; Schneibel, J. H.; Zelinski, B.

    1980-01-01

    The Basic Research Programs in Ceramics supports a significant fraction of the research effort and graduate student training in ceramics at M.I.T. The importance of basic research programs in ceramics processing and properties is becoming widely recognized as the critical role of improved ceramic materials for energy systems is acknowledged. The needs identified in the 1977 series of workshops on DOE programs in energy-related materials research and by the ongoing efforts of the DOE Council on Materials Science are being translated into the basic and applied research necessary to fulfill the established objectives in the effort to solve the nation's energy problems. Present indications are that ceramics in numerous applications will be critical in meeting national energy requirements.

  12. The Mechanical Properties of Energetically Deposited Non-Crystalline Carbon Thin Films

    DOE PAGESBeta

    Kracica, M.; Kocer, C.; Lau, D.; Partridge, J. G.; Haberl, Bianca; Bradby, Jodie E.; Mckenzie, Prof David R; McCulloch, Dougal G.

    2015-11-05

    The mechanical behaviour of carbon films prepared with a variety of densities and microstructures was investigated using nanoindentation. Deposition energies between 25 and 600 eV and temperatures in the range 25-600 °C were used. Films prepared at low temperatures and moderate energy were amorphous with a high density. Finite element methods were used to model the stress fields, reproduce the indentation behaviour and evaluate elastic properties. Young s moduli up to 670 GPa and a low Poisson s ratio of ~ 0.17 were found, comparable to polycrystalline cubic boron nitride, one of the hardest materials known. Films with the samemore » density did not always show the same behaviour, emphasising the role of microstructure in determining mechanical response. Extended graphite- like regions within the films grown at high energy and high temperature observed in transmission electron microscopy caused plastic deformation and failure to recover after a complete indentation cycle. At low deposition energies, the graphite-like regions were smaller in size causing plastic deformation but with complete recovery after indentation.« less

  13. The Mechanical Properties of Energetically Deposited Non-Crystalline Carbon Thin Films

    SciTech Connect

    Kracica, M.; Kocer, C.; Lau, D.; Partridge, J. G.; Haberl, Bianca; Bradby, Jodie E.; Mckenzie, Prof David R; McCulloch, Dougal G.

    2015-11-05

    The mechanical behaviour of carbon films prepared with a variety of densities and microstructures was investigated using nanoindentation. Deposition energies between 25 and 600 eV and temperatures in the range 25-600 °C were used. Films prepared at low temperatures and moderate energy were amorphous with a high density. Finite element methods were used to model the stress fields, reproduce the indentation behaviour and evaluate elastic properties. Young s moduli up to 670 GPa and a low Poisson s ratio of ~ 0.17 were found, comparable to polycrystalline cubic boron nitride, one of the hardest materials known. Films with the same density did not always show the same behaviour, emphasising the role of microstructure in determining mechanical response. Extended graphite- like regions within the films grown at high energy and high temperature observed in transmission electron microscopy caused plastic deformation and failure to recover after a complete indentation cycle. At low deposition energies, the graphite-like regions were smaller in size causing plastic deformation but with complete recovery after indentation.

  14. Diagnosis Applications of Non-Crystalline Diffraction of Collagen Fibres: Breast Cancer and Skin Diseases

    NASA Astrophysics Data System (ADS)

    Costa, M.; Benseny-Cases, N.; Cócera, M.; Teixeira, C. V.; Alsina, M.; Cladera, J.; López, O.; Fernández, M.; Sabés, M.

    In previous chapters, the basis of SAXS for the study of biological systems like proteins in solution have been presented. The SAXS patterns of proteins in solution present, in general, broad dependences with the scattering vector, and the interpretation requires a huge component of modelling. In this chapter and in the following one, it is shown how SAXS technique can be used to study biological systems that are partially crystalline and with a large crystalline cells. This is done by analysing the diffraction obtained from these systems at small angles. In this chapter, a new approach to the application of small-angle X-ray scattering (SAXS) for diagnosis using the diffraction pattern of collagen is presented. This chapter shows the development of a new strategy in the preventive diagnosis of breast cancer following changes on collagen from breast connective tissue. SAXS profiles are related to different features in cutaneous preparations and to the supra-molecular arrangement of skin layers (stratum corneum, epidermis and dermis), in order to introduce objective values on the diagnosis of different skin pathologies. Working parameters (size, thickness) and methods (freezing, paraffin embedment) have been established. The results suggest that collagen diffraction patterns could be used as diagnostic indicators; especially for breast cancer and preliminary results obtained with skin collagen are promising too.

  15. EDITORIAL: Cluster issue on microplasmas

    NASA Astrophysics Data System (ADS)

    Chao, Chih C.; Liao, Jiunn-Der; Chang, Juu-En

    2008-10-01

    Ever since the first Workshop on Microplasmas, held in Japan in 2003, plasma scientists and engineers worldwide have been meeting approximately every 18 months to exchange and discuss the results of scientific research and technical applications of this unique type of plasma. Microplasmas are generally described as stable plasmas confined to spatial dimensions below about 1 mm that can be operated at pressures up to and exceeding atmospheric pressure. By their nature, this presents a wide range of opportunities and many advantages in practical applications, just a few examples being low energy consumption, small size, flexibility of use and ease of assembly into a user-friendly package. Nevertheless, there still remain several unanswered basic science questions and a largely untapped potential for environmental, biomedical and industrial applications. The fourth International Workshop on Microplasmas, held during 28-31 October 2007 in Tainan, Taiwan, continued the trend of previous Workshops with an orientation towards industrial and environmental applications. Many high-quality papers on microplasmas and microdischarges were presented and selected full papers were submitted to Journal of Physics D: Applied Physics for assessment by the editors and reviewers in accordance with the usual standards of quality and novelty. This Cluster Issue contains twelve accepted papers, covering four categories: fundamentals and basics, and environmental, biomedical and industrial applications. Fundamentals and basics includes coverage of the physics and microstructure of electrode discharge (Yu A Lebedev et al), the characteristics of low current discharge (Z Lj Petrović et al), plasma ignition (R Gesche et al), novel optical diagnostics (Schulz-von der Gathen et al), plasma generation and micronozzle flow (T Takahashi et al) and the relation between RF-power and atomic oxygen density distribution (N Knake et al). Environmental applications are represented by vapour

  16. Influence of reactive gas admixture on transition metal cluster nucleation in a gas aggregation cluster source

    NASA Astrophysics Data System (ADS)

    Peter, Tilo; Polonskyi, Oleksandr; Gojdka, Björn; Mohammad Ahadi, Amir; Strunskus, Thomas; Zaporojtchenko, Vladimir; Biederman, Hynek; Faupel, Franz

    2012-12-01

    We quantitatively assessed the influence of reactive gases on the formation processes of transition metal clusters in a gas aggregation cluster source. A cluster source based on a 2 in. magnetron is used to study the production rate of titanium and cobalt clusters. Argon served as working gas for the DC magnetron discharge, and a small amount of reactive gas (oxygen and nitrogen) is added to promote reactive cluster formation. We found that the cluster production rate depends strongly on the reactive gas concentration for very small amounts of reactive gas (less than 0.1% of total working gas), and no cluster formation takes place in the absence of reactive species. The influence of discharge power, reactive gas concentration, and working gas pressure are investigated using a quartz micro balance in a time resolved manner. The strong influence of reactive gas is explained by a more efficient formation of nucleation seeds for metal-oxide or nitride than for pure metal.

  17. THE MASSIVE DISTANT CLUSTERS OF WISE SURVEY: THE FIRST DISTANT GALAXY CLUSTER DISCOVERED BY WISE

    SciTech Connect

    Gettings, Daniel P.; Gonzalez, Anthony H.; Mancone, Conor; Stanford, S. Adam; Eisenhardt, Peter R. M.; Stern, Daniel; Brodwin, Mark; Zeimann, Gregory R.; Masci, Frank J.; Papovich, Casey; Tanaka, Ichi; Wright, Edward L.

    2012-11-01

    We present spectroscopic confirmation of a z = 0.99 galaxy cluster discovered using data from the Wide-field Infrared Survey Explorer (WISE). This is the first z {approx} 1 cluster candidate from the Massive Distant Clusters of WISE Survey to be confirmed. It was selected as an overdensity of probable z {approx}> 1 sources using a combination of WISE and Sloan Digital Sky Survey DR8 photometric catalogs. Deeper follow-up imaging data from Subaru and WIYN reveal the cluster to be a rich system of galaxies, and multi-object spectroscopic observations from Keck confirm five cluster members at z = 0.99. The detection and confirmation of this cluster represents a first step toward constructing a uniformly selected sample of distant, high-mass galaxy clusters over the full extragalactic sky using WISE data.

  18. Chirality in thiolate-protected gold clusters.

    PubMed

    Knoppe, Stefan; Bürgi, Thomas

    2014-04-15

    Over recent years, research on thiolate-protected gold clusters Au(m)(SR)n has gained significant interest. Milestones were the successful determination of a series of crystal structures (Au102(SR)44, Au25(SR)18, Au38(SR)24, Au36(SR)24, and Au28(SR)20). For Au102(SR)44, Au38(SR)24, and Au28(SR)20, intrinsic chirality was found. Strong Cotton effects (circular dichroism, CD) of gold clusters protected by chiral ligands have been reported a long time ago, indicating the transfer of chiral information from the ligand into the cluster core. Our lab has done extensive studies on chiral thiolate-protected gold clusters, including those protected with chiral ligands. We demonstrated that vibrational circular dichroism can serve as a useful tool for the determination of conformation of the ligand on the surface of the cluster. The first reports on crystal structures of Au102(SR)44 and Au38(SR)24 revealed the intrinsic chirality of these clusters. Their chirality mainly arises from the arrangement of the ligands on the surface of the cluster cores. As achiral ligands are used to stabilize the clusters, racemic mixtures are obtained. However, the separation of the enantiomers by HPLC was demonstrated which enabled the measurement of their CD spectra. Thermally induced inversion allows determination of the activation parameters for their racemization. The inversion demonstrates that the gold-thiolate interface is anything but fixed; in contrast, it is rather flexible. This result is of fundamental interest and needs to be considered in future applications. A second line of our research is the selective introduction of chiral, bidentate ligands into the ligand layer of intrinsically chiral gold clusters. The ligand exchange reaction is highly diastereoselective. The bidentate ligand connects two of the protecting units on the cluster surface and thus effectively stabilizes the cluster against thermally induced inversion. A minor (but significant) influence of chiral ligands to

  19. Formation and Assembly of Massive Star Clusters

    NASA Astrophysics Data System (ADS)

    McMillan, Stephen

    The formation of stars and star clusters is a major unresolved problem in astrophysics. It is central to modeling stellar populations and understanding galaxy luminosity distributions in cosmological models. Young massive clusters are major components of starburst galaxies, while globular clusters are cornerstones of the cosmic distance scale and represent vital laboratories for studies of stellar dynamics and stellar evolution. Yet how these clusters form and how rapidly and efficiently they expel their natal gas remain unclear, as do the consequences of this gas expulsion for cluster structure and survival. Also unclear is how the properties of low-mass clusters, which form from small-scale instabilities in galactic disks and inform much of our understanding of cluster formation and star-formation efficiency, differ from those of more massive clusters, which probably formed in starburst events driven by fast accretion at high redshift, or colliding gas flows in merging galaxies. Modeling cluster formation requires simulating many simultaneous physical processes, placing stringent demands on both software and hardware. Simulations of galaxies evolving in cosmological contexts usually lack the numerical resolution to simulate star formation in detail. They do not include detailed treatments of important physical effects such as magnetic fields, radiation pressure, ionization, and supernova feedback. Simulations of smaller clusters include these effects, but fall far short of the mass of even single young globular clusters. With major advances in computing power and software, we can now directly address this problem. We propose to model the formation of massive star clusters by integrating the FLASH adaptive mesh refinement magnetohydrodynamics (MHD) code into the Astrophysical Multi-purpose Software Environment (AMUSE) framework, to work with existing stellar-dynamical and stellar evolution modules in AMUSE. All software will be freely distributed on-line, allowing

  20. Kinematics of AWM and MKW Poor Clusters

    NASA Astrophysics Data System (ADS)

    Koranyi, Daniel M.; Geller, Margaret J.

    2002-01-01

    We have measured 1365 redshifts to a limiting magnitude of R~15.5 in 15 AWM/MKW clusters and have collected another 203 from the literature in MKW 4s, MKW 2, and MKW 2s. In AWM 7 we have extended the redshift sample to R~18 in the cluster center. We have identified 704 cluster members in 17 clusters; 201 are newly identified. We summarize the kinematics and distributions of the cluster galaxies and provide an initial discussion of substructure, mass and luminosity segregation, spectral segregation, velocity-dispersion profiles, and the relation of the central galaxy to global cluster properties. We compute optical mass estimates, which we compare with X-ray mass determinations from the literature. The clusters are in a variety of dynamical states, reflected in the three classes of behavior of the velocity-dispersion profile in the core: rising, falling, or flat/ambiguous. The velocity dispersion of the emission-line galaxy population significantly exceeds that of the absorption-line galaxies in almost all of the clusters, and the presence of emission-line galaxies at small projected radii suggests continuing infall of galaxies onto the clusters. The presence of a cD galaxy does not constrain the global cluster properties; these clusters are similar to other poor clusters that contain no cD. We use the similarity of the velocity-dispersion profiles at small radii and the cD-like galaxies' internal velocity dispersions to argue that cD formation is a local phenomenon. Our sample establishes an empirical observational baseline of poor clusters for comparison with simulations of similar systems. Observations reported in this paper were obtained at the Multiple Mirror Telescope Observatory, a facility operated jointly by the University of Arizona and the Smithsonian Institution; at the Whipple Observatory, a facility operated jointly by the Smithsonian Astrophysical Observatory and Harvard University; and at the WIYN Observatory, a joint facility of the University of

  1. The Swift AGN and Cluster Survey. II. Cluster Confirmation with SDSS Data

    NASA Astrophysics Data System (ADS)

    Griffin, Rhiannon D.; Dai, Xinyu; Kochanek, Christopher S.; Bregman, Joel N.

    2016-01-01

    We study 203 (of 442) Swift AGN and Cluster Survey extended X-ray sources located in the SDSS DR8 footprint to search for galaxy over-densities in three-dimensional space using SDSS galaxy photometric redshifts and positions near the Swift cluster candidates. We find 104 Swift clusters with a >3σ galaxy over-density. The remaining targets are potentially located at higher redshifts and require deeper optical follow-up observations for confirmation as galaxy clusters. We present a series of cluster properties including the redshift, brightest cluster galaxy (BCG) magnitude, BCG-to-X-ray center offset, optical richness, and X-ray luminosity. We also detect red sequences in ˜85% of the 104 confirmed clusters. The X-ray luminosity and optical richness for the SDSS confirmed Swift clusters are correlated and follow previously established relations. The distribution of the separations between the X-ray centroids and the most likely BCG is also consistent with expectation. We compare the observed redshift distribution of the sample with a theoretical model, and find that our sample is complete for z ≲ 0.3 and is still 80% complete up to z ≃ 0.4, consistent with the SDSS survey depth. These analysis results suggest that our Swift cluster selection algorithm has yielded a statistically well-defined cluster sample for further study of cluster evolution and cosmology. We also match our SDSS confirmed Swift clusters to existing cluster catalogs, and find 42, 23, and 1 matches in optical, X-ray, and Sunyaev-Zel’dovich catalogs, respectively, and so the majority of these clusters are new detections.

  2. Formation of [4Fe-4S] clusters in the mitochondrial iron-sulfur cluster assembly machinery.

    PubMed

    Brancaccio, Diego; Gallo, Angelo; Mikolajczyk, Maciej; Zovo, Kairit; Palumaa, Peep; Novellino, Ettore; Piccioli, Mario; Ciofi-Baffoni, Simone; Banci, Lucia

    2014-11-19

    The generation of [4Fe-4S] clusters in mitochondria critically depends, in both yeast and human cells, on two A-type ISC proteins (in mammals named ISCA1 and ISCA2), which perform a nonredundant functional role forming in vivo a heterocomplex. The molecular function of ISCA1 and ISCA2 proteins, i.e., how these proteins help in generating [4Fe-4S] clusters, is still unknown. In this work we have structurally characterized the Fe/S cluster binding properties of human ISCA2 and investigated in vitro whether and how a [4Fe-4S] cluster is assembled when human ISCA1 and ISCA2 interact with the physiological [2Fe-2S](2+) cluster-donor human GRX5. We found that (i) ISCA2 binds either [2Fe-2S] or [4Fe-4S] cluster in a dimeric state, and (ii) two molecules of [2Fe-2S](2+) GRX5 donate their cluster to a heterodimeric ISCA1/ISCA2 complex. This complex acts as an "assembler" of [4Fe-4S] clusters; i.e., the two GRX5-donated [2Fe-2S](2+) clusters generate a [4Fe-4S](2+) cluster. The formation of the same [4Fe-4S](2+) cluster-bound heterodimeric species is also observed by having first one [2Fe-2S](2+) cluster transferred from GRX5 to each individual ISCA1 and ISCA2 proteins to form [2Fe-2S](2+) ISCA2 and [2Fe-2S](2+) ISCA1, and then mixing them together. These findings imply that such heterodimeric complex is the functional unit in mitochondria receiving [2Fe-2S] clusters from hGRX5 and assembling [4Fe-4S] clusters before their transfer to the final target apo proteins.

  3. Bregman Clustering for Separable Instances

    NASA Astrophysics Data System (ADS)

    Ackermann, Marcel R.; Blömer, Johannes

    The Bregman k-median problem is defined as follows. Given a Bregman divergence D φ and a finite set P subseteq { R}^d of size n, our goal is to find a set C of size k such that the sum of errors cost(P,C) = ∑ p ∈ P min c ∈ C D φ (p,c) is minimized. The Bregman k-median problem plays an important role in many applications, e.g., information theory, statistics, text classification, and speech processing. We study a generalization of the kmeans++ seeding of Arthur and Vassilvitskii (SODA '07). We prove for an almost arbitrary Bregman divergence that if the input set consists of k well separated clusters, then with probability 2^{-{O}(k)} this seeding step alone finds an {O}(1)-approximate solution. Thereby, we generalize an earlier result of Ostrovsky et al. (FOCS '06) from the case of the Euclidean k-means problem to the Bregman k-median problem. Additionally, this result leads to a constant factor approximation algorithm for the Bregman k-median problem using at most 2^{{O}(k)}n arithmetic operations, including evaluations of Bregman divergence D φ .

  4. Networking Options for Beowulf Clusters

    NASA Astrophysics Data System (ADS)

    Sterling, Thomas L.

    2000-03-01

    Beowulf-class PC clusters have emerged as an important type of high end computing system providing unprecedented price-performance advantage and configuration flexibility. Derived from mass market commodity off-the-shelf hardware and software components, Beowulf systems are being implemented across the country and around the world for a wide array of applications and with diverse structures and scale. Critical to the success and effectiveness of Beowulfs has been the availability of low cost, moderate bandwidth local area networks (LAN) to provide communications channels between PC nodes. From the early days with 10 Mbps Ethernet, system area networking (SAN) has evolved dramatically providing a number of choices of technology and protocol with, in some cases, more than 1 Gbps per channel peak bandwidth. Beowulf systems have been implemented with many of these and in a number of different configurations and topologies. Fast Ethernet, Gigabit Ethernet, Giganet, Myranet, SCI as well as a number of switch nodes are in use. Systems exceeding a thousand processors either have been or are being assembled and commercial vendors are now marketing Beowulf-class systems as turn-key computers. The technology is advancing so rapidly that information even a year old is largely out of date. This presentation will provide an up to date description of the current state-of-the-art in system area networks for Beowulf-class computing and give examples of existing or planned systems employing these technologies.

  5. Scalable rendering on PC clusters

    SciTech Connect

    WYLIE,BRIAN N.; LEWIS,VASILY; SHIRLEY,DAVID NOYES; PAVLAKOS,CONSTANTINE

    2000-04-25

    This case study presents initial results from research targeted at the development of cost-effective scalable visualization and rendering technologies. The implementations of two 3D graphics libraries based on the popular sort-last and sort-middle parallel rendering techniques are discussed. An important goal of these implementations is to provide scalable rendering capability for extremely large datasets (>> 5 million polygons). Applications can use these libraries for either run-time visualization, by linking to an existing parallel simulation, or for traditional post-processing by linking to an interactive display program. The use of parallel, hardware-accelerated rendering on commodity hardware is leveraged to achieve high performance. Current performance results show that, using current hardware (a small 16-node cluster), they can utilize up to 85% of the aggregate graphics performance and achieve rendering rates in excess of 20 million polygons/second using OpenGL{reg_sign} with lighting, Gouraud shading, and individually specified triangles (not t-stripped).

  6. Rheology of clustering protein solutions.

    PubMed

    Dharmaraj, Vishnu L; Godfrin, P Douglas; Liu, Yun; Hudson, Steven D

    2016-07-01

    High viscosity is a major challenge with protein therapeutics at extremely high concentrations. To overcome this obstacle, it is essential to understand the relationship between the concentration of a protein solution and its viscosity as a function of shear rate and temperature. Here, lysozyme is a model charged globular protein having both short-ranged attraction (SA) and long-ranged repulsion (LR) that promote the formation of dynamic clusters at high concentrations. We report viscosity measurements from a micro-capillary rheometer (using only several microliters of solution) over a wide range of lysozyme solution concentrations, shear rates, and temperatures. Solution structural relaxation dynamics are also probed by dynamic light scattering (DLS). As a result of lysozyme's SALR interactions, the viscosity increased dramatically across all shear rates with increasing concentration and decreasing temperature. While most of the solutions exhibited Newtonian behavior, shear thinning was exhibited at the highest concentration (480 g/l) and lowest temperatures at shear rates above approximately 10(4 )s(-1). The onset shear rate for thinning and a structural relaxation rate estimated from a slow-mode measured by DLS are compared. These measurements provide insights into the properties of protein solutions and their microscopic structural origins. PMID:27478524

  7. Giant Planets in Open Clusters

    NASA Astrophysics Data System (ADS)

    Quinn, S. N.; White, R. J.; Latham, D. W.

    2015-10-01

    Two decades after the discovery of 51 Peg b, more than 200 hot Jupiters have now been confirmed, but the details of their inward migration remain uncertain. While it is widely accepted that short period giant planets could not have formed in situ, several different mechanisms (e.g., Type II migration, planet-planet scattering, Kozai-Lidov cycles) may contribute to shrinking planetary orbits, and the relative importance of each is not well-constrained. Migration through the gas disk is expected to preserve circular, coplanar orbits and must occur quickly (within ˜ 10 Myr), whereas multi-body processes should initially excite eccentricities and inclinations and may take hundreds of millions of years. Subsequent evolution of the system (e.g., orbital circularization and inclination damping via tidal interaction with the host star) may obscure these differences, so observing hot Jupiters soon after migration occurs can constrain the importance of each mechanism. Fortunately, the well-characterized stars in young and adolescent open clusters (with known ages and compositions) provide natural laboratories for such studies, and recent surveys have begun to take advantage of this opportunity. We present a review of the discoveries in this emerging realm of exoplanet science, discuss the constraints they provide for giant planet formation and migration, and reflect on the future direction of the field.

  8. Community detection by fuzzy clustering

    NASA Astrophysics Data System (ADS)

    Sun, Peng Gang

    2015-02-01

    How to measure the similarity between nodes is of great importance for fuzzy clustering when we use the approach to uncover communities in complex networks. In this paper, we first measure the similarity between nodes in a network based on edge centralities and model the network as a fuzzy relation. Then, two fuzzy transitive rules (Rule I and Rule II) are applied on the relation respectively, by which the similarity information can be transferred from one node to another in the network until the relation reaches a stable state. By choosing different thresholds, our method finally can partition the network into several non-overlapping subgroups. We compare our method with some state of the art methods on the LFR benchmark and real-world networks. We find that our method based on Rule I can correctly identify communities when the similarity between nodes of same groups is greater than that of different groups, while it is just opposite to Rule II. Our method achieves better results than the state of the art methods when the pre-planted communities of the random networks are vaguer.

  9. Ages of Extragalactic Intermediate-Age Star Clusters

    NASA Technical Reports Server (NTRS)

    Flower, P. J.

    1983-01-01

    A dating technique for faint, distant star clusters observable in the local group of galaxies with the space telescope is discussed. Color-magnitude diagrams of Magellanic Cloud clusters are mentioned along with the metallicity of star clusters.

  10. From designer clusters to synthetic crystalline nanoassemblies.

    PubMed

    Castleman, A Welford; Khanna, Shiv N; Sen, Ayusman; Reber, Arthur C; Qian, Meichun; Davis, Kevin M; Peppernick, Samuel J; Ugrinov, Angel; Merritt, Mark D

    2007-09-01

    Clusters have the potential to serve as building blocks of materials, enabling the tailoring of materials with novel electronic or magnetic properties. Historically, there has been a disconnect between magic clusters found in the gas phase and the synthetic assembly of cluster materials. We approach this challenge through a proposed protocol that combines gas-phase investigations to examine feasible units, theoretical investigations of energetic compositional diagrams and geometrical shapes to identify potential motifs, and synthetic chemical approaches to identify and characterize cluster assemblies in the solid state. Through this approach, we established As7(3-) as a potential stable species via gas-phase molecular beam experiments consistent with its known existence in molecular crystals with As to K ratios of 7:3. Our protocol also suggests another variant of this material. We report the synthesis of a cluster compound, As7K1.5(crypt222-K)1.5, composed of a lattice of As7 clusters stabilized by charge donation from cryptated K atoms and bound by sharing K atoms. The bond dimensions of this supercluster assembled material deduced by X-ray analysis are found to be in excellent agreement with the theoretical calculations. The new compound has a significantly larger band gap than the hitherto known solid. Thus, our approach allows the tuning of the electronic properties of solid cluster assemblies.

  11. Gas Density Discontinuities in Merging Clusters

    NASA Technical Reports Server (NTRS)

    Mushotzky, Richard (Technical Monitor); Markevitch, Maxim

    2005-01-01

    Chandra has discovered a new phenomenon in galaxy clusters, the sharp gas density edges. Depending on the sign of the temperature jump across the edge, these features may either be bow shocks or cold fronts. While bow shocks obviously are driven by merging sub-clusters, what causes cold fronts is not entirely clear, as they are observed both in mergers and in relaxed clusters. The purpose of the XMM study of A3376, an interesting cluster with density edges, is to understand the origin of cold fronts and to look for possible shocks. The XMM data for A3376 have been mostly analyzed (the X-ray edge turned out to be a cold front). Preliminary results have been shown at a conference and a paper is in preparation. We also have Chandra data for this cluster, and are comparing and combining the two datasets. In the course of analyzing the X-ray data for this cluster as well as several others, it has become apparent that we need the help of hydrodynamic simulations to study the precise mechanism by which cold fronts are formed, the main goal of the present project. A postdoc (Yago Ascasibar) is currently running SPH simulations of an idealized sub- cluster merger. These advanced simulations are nearing completion and two papers with their results are in preparation.

  12. Comparing simulated and experimental molecular cluster distributions.

    PubMed

    Olenius, Tinja; Schobesberger, Siegfried; Kupiainen-Määttä, Oona; Franchin, Alessandro; Junninen, Heikki; Ortega, Ismael K; Kurtén, Theo; Loukonen, Ville; Worsnop, Douglas R; Kulmala, Markku; Vehkamäki, Hanna

    2013-01-01

    Formation of secondary atmospheric aerosol particles starts with gas phase molecules forming small molecular clusters. High-resolution mass spectrometry enables the detection and chemical characterization of electrically charged clusters from the molecular scale upward, whereas the experimental detection of electrically neutral clusters, especially as a chemical composition measurement, down to 1 nm in diameter and beyond still remains challenging. In this work we simulated a set of both electrically neutral and charged small molecular clusters, consisting of sulfuric acid and ammonia molecules, with a dynamic collision and evaporation model. Collision frequencies between the clusters were calculated according to classical kinetics, and evaporation rates were derived from first principles quantum chemical calculations with no fitting parameters. We found a good agreement between the modeled steady-state concentrations of negative cluster ions and experimental results measured with the state-of-the-art Atmospheric Pressure interface Time-Of-Flight mass spectrometer (APi-TOF) in the CLOUD chamber experiments at CERN. The model can be used to interpret experimental results and give information on neutral clusters that cannot be directly measured.

  13. Gamma-ray Emission from Globular Clusters

    NASA Astrophysics Data System (ADS)

    Tam, Pak-Hin T.; Hui, Chung Y.; Kong, Albert K. H.

    2016-03-01

    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.

  14. Packing transition in alkali metallic clusters

    NASA Astrophysics Data System (ADS)

    Kawai, R.; Sung, Ming Wen; Weare, John H.

    1996-03-01

    Small metallic clusters form a local geometric configuration quite different from the bulk crystals. As the cluster size increases, several transitions in the local coordination take place before the bulk structure appears. These transitions involve change in the nature of chemical bonds. We have systematically investigated the structural transition of various alkali metal clusters including binary compounds using an ab initio molecular dynamics simulation. Among them, Li clusters exhibit unusual transition in their packing pattern. Small lithium clusters (N <= 21) form open structures based on a ``solvation shell''.(M. Sung, R. Kawai, and J. Weare, Phys. Rev. Lett. 73) (1994) 3552., which is quite different from other alkali metal clusters. The bonding of these small clusters is partially ionic. Above N=25, a close-packed structure is established. However, the local configuration still differ from that of the bulk crystal. As the size further increases, the ionic nature decreases and the system reaches another close-packed structure based on the Mackay icosahedron, which is similar to the bulk crystal structure.

  15. The Origin of the Brightest Cluster Galaxies

    NASA Astrophysics Data System (ADS)

    Dubinski, John

    1998-07-01

    Most clusters and groups of galaxies contain a giant elliptical galaxy in their centers that far outshines and outweighs normal ellipticals. The origin of these brightest cluster galaxies is intimately related to the collapse and formation of the cluster. Using an N-body simulation of a cluster of galaxies in a hierarchical cosmological model, we show that galaxy merging naturally produces a massive central galaxy with surface brightness and velocity dispersion profiles similar to those of observed BCGs. To enhance the resolution of the simulation, 100 dark halos at z = 2 are replaced with self-consistent disk + bulge + halo galaxy models following a Tully-Fisher relation using 100,000 particles for the 20 largest galaxies and 10,000 particles for the remaining ones. This technique allows us to analyze the stellar and dark-matter components independently. The central galaxy forms through the merger of several massive galaxies along a filament early in the cluster's history. Galactic cannibalism of smaller galaxies through dynamical friction over a Hubble time only accounts for a small fraction of the accreted mass. The galaxy is a flattened, triaxial object whose long axis aligns with the primordial filament and the long axis of the cluster galaxy distribution, agreeing with observed trends for galaxy cluster alignment.

  16. Correcting an analysis of variance for clustering.

    PubMed

    Hedges, Larry V; Rhoads, Christopher H

    2011-02-01

    A great deal of educational and social data arises from cluster sampling designs where clusters involve schools, classrooms, or communities. A mistake that is sometimes encountered in the analysis of such data is to ignore the effect of clustering and analyse the data as if it were based on a simple random sample. This typically leads to an overstatement of the precision of results and too liberal conclusions about precision and statistical significance of mean differences. This paper gives simple corrections to the test statistics that would be computed in an analysis of variance if clustering were (incorrectly) ignored. The corrections are multiplicative factors depending on the total sample size, the cluster size, and the intraclass correlation structure. For example, the corrected F statistic has Fisher's F distribution with reduced degrees of freedom. The corrected statistic reduces to the F statistic computed by ignoring clustering when the intraclass correlations are zero. It reduces to the F statistic computed using cluster means when the intraclass correlations are unity, and it is in between otherwise. A similar adjustment to the usual statistic for testing a linear contrast among group means is described.

  17. On Ion Clusters in the Interstellar Gas

    NASA Technical Reports Server (NTRS)

    Donn, Bertram

    1960-01-01

    In a recent paper V.I. Krassovsky (1958) predicts the occurrence of clusters of large numbers of atoms and molecules around ions in the interstellar gas. He then proposes a number of physicochemical processes that would be considerably enhanced by the high particle density in such clusters. In particular, he suggests that absorption by negative ions formed in the clusters would account for the interstellar extinction without any necessity for the presence of grains. Because of the important consequences that ion clusters could have, it is necessary to examine their occurrence more fully. This note re-examines the formation of ion clusters in space and shows that even ion-molecule pairs are essentially non-existent. Ion clusters have been considered by Bloom and Margenau (1952) from the same point of view as that used by Krassovsky, whose basic reference (Joffe and Semenov 1933) unfortunately is not available. A different approach has been used by Eyring, Hirschfelder, and Taylor (1936) following the methods of chemical equilibrium. Both the references cited here enable one to conclude that clustering is negligible. Therefore, the treatment of Eyring et al. is more appropriate than the method of Bloom and Margenau, which depends on the statistical equilibrium of an atmosphere in a force field.

  18. Computer aided detection system for clustered microcalcifications

    PubMed Central

    Ge, Jun; Hadjiiski, Lubomir M.; Sahiner, Berkman; Wei, Jun; Helvie, Mark A.; Zhou, Chuan; Chan, Heang-Ping

    2009-01-01

    We have developed a computer-aided detection (CAD) system to detect clustered microcalcification automatically on full-field digital mammograms (FFDMs) and a CAD system for screen-film mammograms (SFMs). The two systems used the same computer vision algorithms but their false positive (FP) classifiers were trained separately with sample images of each modality. In this study, we compared the performance of the CAD systems for detection of clustered microcalcifications on pairs of FFDM and SFM obtained from the same patient. For case-based performance evaluation, the FFDM CAD system achieved detection sensitivities of 70%, 80%, and 90% at an average FP cluster rate of 0.07, 0.16, and 0.63 per image, compared with an average FP cluster rate of 0.15, 0.38, and 2.02 per image for the SFM CAD system. The difference was statistically significant with the alternative free-response receiver operating characteristic (AFROC) analysis. When evaluated on data sets negative for microcalcification clusters, the average FP cluster rates of the FFDM CAD system were 0.04, 0.11, and 0.33 per image at detection sensitivity level of 70%, 80%, and 90%, compared with an average FP cluster rate of 0.08, 0.14, and 0.50 per image for the SFM CAD system. When evaluated for malignant cases only, the difference of the performance of the two CAD systems was not statistically significant with AFROC analysis. PMID:17264365

  19. Convalescing Cluster Configuration Using a Superlative Framework

    PubMed Central

    Sabitha, R.; Karthik, S.

    2015-01-01

    Competent data mining methods are vital to discover knowledge from databases which are built as a result of enormous growth of data. Various techniques of data mining are applied to obtain knowledge from these databases. Data clustering is one such descriptive data mining technique which guides in partitioning data objects into disjoint segments. K-means algorithm is a versatile algorithm among the various approaches used in data clustering. The algorithm and its diverse adaptation methods suffer certain problems in their performance. To overcome these issues a superlative algorithm has been proposed in this paper to perform data clustering. The specific feature of the proposed algorithm is discretizing the dataset, thereby improving the accuracy of clustering, and also adopting the binary search initialization method to generate cluster centroids. The generated centroids are fed as input to K-means approach which iteratively segments the data objects into respective clusters. The clustered results are measured for accuracy and validity. Experiments conducted by testing the approach on datasets from the UC Irvine Machine Learning Repository evidently show that the accuracy and validity measure is higher than the other two approaches, namely, simple K-means and Binary Search method. Thus, the proposed approach proves that discretization process will improve the efficacy of descriptive data mining tasks. PMID:26543895

  20. Comparing simulated and experimental molecular cluster distributions.

    PubMed

    Olenius, Tinja; Schobesberger, Siegfried; Kupiainen-Määttä, Oona; Franchin, Alessandro; Junninen, Heikki; Ortega, Ismael K; Kurtén, Theo; Loukonen, Ville; Worsnop, Douglas R; Kulmala, Markku; Vehkamäki, Hanna

    2013-01-01

    Formation of secondary atmospheric aerosol particles starts with gas phase molecules forming small molecular clusters. High-resolution mass spectrometry enables the detection and chemical characterization of electrically charged clusters from the molecular scale upward, whereas the experimental detection of electrically neutral clusters, especially as a chemical composition measurement, down to 1 nm in diameter and beyond still remains challenging. In this work we simulated a set of both electrically neutral and charged small molecular clusters, consisting of sulfuric acid and ammonia molecules, with a dynamic collision and evaporation model. Collision frequencies between the clusters were calculated according to classical kinetics, and evaporation rates were derived from first principles quantum chemical calculations with no fitting parameters. We found a good agreement between the modeled steady-state concentrations of negative cluster ions and experimental results measured with the state-of-the-art Atmospheric Pressure interface Time-Of-Flight mass spectrometer (APi-TOF) in the CLOUD chamber experiments at CERN. The model can be used to interpret experimental results and give information on neutral clusters that cannot be directly measured. PMID:24600997